Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session K1: Poster Session II (2-5:00pm): Education; SPS/Undergrad Research; Metals; Magnetism; Instrumentation and Measurements; Chemical Physics; Artificially Structured Materials; Surfaces, Interfaces and Thin Films; AMO Physics; Quantum Information; Bio Physics |
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Room: Exhibit Hall A |
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K1.00001: PHYSICS EDUCATION |
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K1.00002: Stokes analysis of an optical system Georgi Georgiev, Thomas Slavkovsky As a transfer from research to teaching we are using stokes analysis to represent changes in the vectors for polarization of light as acted upon by the matrices of optical elements in undergraduate physics lab. The goal is to integrate students' knowledge for matrix analysis with an experimental determination of the changes in the polarization of light. This method allows students to learn how to design an optical system by using mathematical analysis, a skill necessary for future scientists or engineers in the fields of optics. We have tested and implemented the lab. The results are that it is well accepted by the students, but is very involved computationally, and needs to be shortened. The Stokes analysis needs to be introduces earlier in the curriculum in order to make the students comfortable with the formalism. [Preview Abstract] |
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K1.00003: The Doppler Effect in Sound Waves, Light Waves, and Quantum Waves Alan M. Kadin In undergraduate modern physics courses, special relativity and quantum mechanics are generally introduced as a series of sharp breaks from classical physics. An alternative approach is suggested, focusing on the Doppler effect, closely related to changes in reference frames. In the classical acoustic Doppler effect with a source or observer moving with speed u, the frequency f shifts while the wavelength $\lambda $ must remain fixed for classical transformations. Hence the phase velocity v$_{ph}$=f$\lambda $ must also shift. In the optical Doppler effect, f also shifts for u approaching c, but this must be accompanied by a corresponding shift in $\lambda $ (from the Lorentz transformation) in order to maintain v$_{ph}$=c constant. The Doppler effect is usually not considered for quantum waves, but this clearly requires a non-classical shift in the de Broglie wavelength $\lambda $=h/mv even for u$<<$c. This shift is fully explained by the Lorentz transformation if one takes f =mc$^{2}$/h, as was shown by de Broglie in his original 1924 paper. This is a dispersive wave with v$_{ph}$=c$^{2}$/v, but a group velocity v$_{g}$=v, as required for a consistent physical interpretation. This emphasizes the relativistic basis of quantum waves. [Preview Abstract] |
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K1.00004: Kinematic analysis of the Cretaceous Era dinosaur footprints near the Paluxy River, Texas: Predation event or not? Scott Lee Motivation is enhanced by challenging students with interesting and open-ended questions. In this talk, a methodology for studying the locomotion of extinct animals based on their footprint trackways is developed and applied to a possible predation event recorded in Cretaceous Era deposits.\footnote{J.O. Farlow, ``Lower Cretaceous Dinosaur Tracks, Paluxy River Valley, Texas,'' South Central Geological Society of America, Baylor University, 1987.} Students usually love learning about dinosaurs, an unexpected treat in a physics class. This example can be used in the classroom to help build critical thinking skills as the students decide whether the evidence supports a predation scenario or not. [Preview Abstract] |
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K1.00005: Locomotion speeds of various dinosaurs Mary Dougherty, Scott Lee Most students have a passing curiosity about dinosaurs. Piquing this interest is an excellent tool to engage students. A methodology for estimating the locomotion speed of an animal based upon their footprint tracks is developed. Using this technique, an analysis of the locomotion speeds of various dinosaurs is performed. The tracks studied include 28 theropods (meat-eating dinosaurs), 23 sauropods (the ``long-necked'' herbivores), 28 non-armored, non-sauropod herbivores and 10 armored, non-sauropod herbivores. The theropods show the fastest locomotion speed as well as the greatest variety of speeds while the armored dinosaurs are the slowest. [Preview Abstract] |
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K1.00006: Avogadro: Free, Open Source, Cross-Platform Computer Program for Building Molecules and Visualizing Structure Marcus Hanwell, Geoffrey Hutchison The Avogadro project is a free, open source approach to building chemical structures. It has integrated analysis, and three-dimensional visualization capabilities. Avogadro also uses external packages to perform quantum structure calculations. The work presented here illustrates a novel approach to working with the results of quantum calculations by visualizing possible molecular orbitals and allowing the user to select orbitals of interest. The Avogadro program allows the user to prepare new jobs for various quantum codes such as GAMESS-US, Q-Chem, Gaussian and Molpro. Due to the plugin based nature of the Avogadro project many specialized options can be added, such as raytracing the electronic structure of the molecule to produce high quality output, building carbon nanotube structures, or designing solid-state structures. Avogadro is already being used by educators and researchers. Due to the free and open source nature of the project, it can be readily downloaded and used by all students in and out of the classroom. It can also be tailored to particular institutions and/or courses. [Preview Abstract] |
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K1.00007: Gaps and Tails: The restricted N-body problem in colliding galaxies and the asteriod belt Anna Pancoast, Shea Garrison-Kimmel, Peter Love We report simulations of the restricted n-body problem performed in the class Computational Physics at Haverford College. We simulated gravitational interactions in a large system in which nearly all of the particles, such as asteroids or stars, are assumed to have no effect on the trajectories of other particles. We begin by simulating the emergence of Kirkwood Gaps in the asteroid belt. We then modify the code to include the extensive initial conditions necessary to model the parabolic collision of two galaxies. We explored both direct and retrograde passages between the galaxies, reproducing the results of the 1972 paper by Toomre and Toomre, specifically the formation of galactic bridges and tails. [Preview Abstract] |
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K1.00008: Understanding Statistical Mechanics and Biophysics Using Excel Peter Nelson A new approach to teaching statistical mechanics and biophysics is presented using the classic two-box system from statistical mechanics as an example. This approach makes advanced physics concepts accessible to a broad audience including undergraduates with no calculus background. Students develop a simple Excel spreadsheet that implements a kinetic Monte Carlo (kMC) simulation algorithm ``from scratch''. The students discover for themselves the properties of the system by analyzing the simulation output in a directed, activity-based exercise. By changing the number and initial distribution of the particles, students see how the system approaches equilibrium and how system variability changes with system size. A finite difference solution is also implemented in Excel, and students compare its predictions with the kMC results. This approach is quite different from using ``canned'' computer demonstrations, as students design, implement and debug the simulation themselves -- ensuring that they understand the model system intimately. [Preview Abstract] |
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K1.00009: Computational Physics Undergraduate Research Experience (A case Study) Homeyra Sadaghiani, Alex Samll There is a growing trend of inclusion of more research programs into undergraduate education. In spite of that, the assessment of undergraduate-research experience in physics is limited. This presentation describes a ten weeks undergraduate summer research experience in computational physics in the field of biophysics for two upper division physics students at Cal Poly Pomona. The analysis of Pre/post test data suggests more gains on research methodologies and skills than actual physical concepts underling the research project. We also discuss student attitude change measured by survey and interviews. [Preview Abstract] |
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K1.00010: Scientific Inquiry: A Problem-Based Approach for Improving Teaching and Learning Peter Sheldon, Peggy Schimmoeller, Tatiana Toteva We describe a research project that had two goals: (1) to design and develop a content specific science inquiry institute to improve teachers' instructional practices in the sciences and thus students' achievement in science; and (2) to investigate students' perception of scientists as a measure of their attitude toward science, and to see whether an inquiry science curriculum can improve attitudes. We report that certain stereotypical images of scientists are prevalent among students. Teacher participants increased content knowledge and familiarity with using inquiry and hands-on methods in the classroom. [Preview Abstract] |
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K1.00011: To Click or Not to Click Nina Abramzon, Homeyra Sadaghiani A comparison of clickers v. flashcards in a controlled setting was done to test a) whether clickers show an improvement over flashcards in students learning the following concepts: i) Coulomb's force law and ii) magnetic fields caused by currents, and b) if students using clickers are more open towards conceptual questions and the peer instruction method compared to students using flashcards. Two classes taught concurrently by the same instructor were taught identically, except that in one class the collection of answers to concept questions was done using clickers, and in the other using flashcards. To test which students learned the concepts better, a few multiple choice questions from a standard exam used in physics education were included in the final exam of both classes, and the performance of the two classes was compared. In addition, a questionnaire was given to each class to evaluate students' opinions about the benefits of lectures including conceptual TPS questions and the use of related conceptual questions on exams. The results of the survey were compared between the two classes. The experimental design and results of the study will be presented. [Preview Abstract] |
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K1.00012: SOCIETY OF PHYSICS STUDENTS AND UNDERGRADUATE RESEARCH |
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K1.00013: Flexible Solution-Processed TiO2-Based Memory Barbara Dunlap, Nadine Gergel-Hackett, Behrang Hamadani, John Suehle, Christina Hacker, David Gundlach, Curt Richter We have fabricated flexible titanium dioxide memory devices using a room temperature spin-on titanium dioxide (TiO2) sol gel technique. These devices show a non-volatile memory behavior with on/off ratios up to 10,000:1 and can be switched between low and high current states by applying an adequate bias (less than 10 V). Once switched, the state can be read by applying a small bias (0.5 V). The device can then be set back to the previous current state by applying a bias that is equal in magnitude but opposite in polarity to the initial bias. Devices maintain on/off ratios greater than four orders of magnitude when flexed 4,000 times, still switch after being flexed 8,000 times, and hold their set state for longer than 1x10\^{}6 seconds. The advantages of our devices include that they are low power, rewritable, nonvolatile, lightweight, physically flexible, and they have a simple, inexpensive, two-terminal, room temperature processed device design. [Preview Abstract] |
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K1.00014: Hydrogen storage media through nanostructured polymeric materials Scott Kirklin, Brian Dorney, Shengwen Yuan, Peter Zapol, Luping Yu, Di-Jia Liu On-board hydrogen storage is critical to future transportation technologies such as H2-powered fuel cell vehicles. Reported here is our current effort in developing nanostructured polymeric materials as the non-dissociative hydrogen adsorbents for the transportation application. Various porous polymers were prepared. The discussion will be focused on the surface structural characterization using BET approach and hydrogen adsorption capacities and physical properties using a Sieverts type isotherm measurement. Details on improving the accuracy of measurement as well as data analysis will also be reported. [Preview Abstract] |
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K1.00015: Polymer Electrolyte Membrane Fuel Cell with Vertically Aligned Carbon Nanotube Electrode Ann Call, Gabriel Goenaga, Junbing Yang, Di-Jia Liu Carbon nanotubes (CNTs) have been considered a promising material for various applications. Electro-catalyst support for polymer electrolyte membrane fuel cells (PEMFCs) is one of them. There have been a number of reports on CNT based membrane electrode assembly (MEA) in PEMFC, but CNTs in these electrodes are oriented randomly and the advantages associated with the structural properties of CNTs were not fully utilized. We report here our progress in fabricating and evaluating MEA made of catalyst decorated, vertically aligned carbon nanotube (ACNT) layers. For comparison, a commercial MEA prepared through the ink-based process was also tested under similar conditions. Improved performance was observed for ACNT-based MEA, particularly at high current region, suggesting enhancement in mass transport and improved water management. [Preview Abstract] |
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K1.00016: Measuring and Using the dn/dc of HPC Polymer and Microgel Solutions Krista Freeman, Kiril Streletzky The specific refractive index increment (dn/dc), the change in index of refraction with concentration, is essential for static light scattering (SLS) experiments on polymer solutions. With a reliable value for dn/dc, SLS yields basic polymer properties such as radius of gyration, molecular weight, and second virial coefficient. This study focuses on determining dn/dc values of hydroxypropylcellulose (HPC) polymer and microgel solutions and practically applying these values in SLS. Using a differential refractometer, HPC solutions were analyzed at a range of concentrations, molecular weights, wavelengths, temperatures, and filtration protocols. It was determined that dn/dc of HPC polymer is independent of temperature in good solvents, slightly dependent on molecular weight, inversely proportional to wavelength squared, and sensitive to polymer solution's filtration protocol. HPC microgel testing produced dn/dc values one order of magnitude larger than those of HPC polymer solutions and did not support the expected wavelength dependence. These findings were analyzed and used to obtain a molecular weight, radius of gyration, and second virial coefficient for HPC polymer and microgel solutions. [Preview Abstract] |
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K1.00017: Measuring Insulation in Walls Using a Thermocouple to Measure Temperature Differences Beth Parks, Clayton Brown It would be useful to develop tools to measure building insulation non-invasively and inexpensively. The temperature difference between the surface of an exterior wall and the center of the room is a sensitive measure of the amount of insulation in the wall. We describe measurements using a thermocouple to determine the insulation in a mock house. [Preview Abstract] |
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K1.00018: Lasing in Superconducting Qubits Alyssa Wilson, Roberto Ramos Qubits are superconducting circuits that have exhibit many interesting quantum properties similar to those displayed by atoms. One such behavior is lasing, as manifested in a resonator coupled to a qubit. I will review experiments in which lasing was exhibited in charge qubits and three-Josephson-junction flux qubits. I will also examine the similarities between these systems and compare these to properties of the Josephson phase qubit. In this presentation, I will discuss the feasibility of demonstrating this phenomenon in the phase qubit. [Preview Abstract] |
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K1.00019: Evaluation and Redesign of Introductory Undergraduate Physics Series for Use with USB Devices Leah Parsons, Gary Bedrosian The introductory physics laboratory series at many colleges suffer from several problems, including a large time commitment, inflexibility of lab set-ups, and lack of accommodation of multiple learning styles.~It is difficult in a conventional lab set-up, in which students follow a carefully specified series of steps, to be able to generalize findings to more than one specific case.~In this project, we propose changes that will allow students to form the labs to their own learning styles to better study the phenomena of interest as well as to address the other issues. To test our ideas, we have reduced the current introductory physics labs at Allegheny College to their basic principles in order to apply them to a new, more flexible, lab paradigm.~Using a USB device designed by Rensselaer Polytechnic Institute, labs that reflect the core concepts of introductory physics will be able to be performed in a more agreeable environment: the student's own home, at a time of their choice, with use of a personal computer and simple additional materials. This project will present the method of lab design as well as proposed testing of lab effectiveness. [Preview Abstract] |
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K1.00020: Measuring Proper Motion of Barnard's Star Katrina Wiechmann, Tom Michalik Stars of the night sky are generally considered to be fixed points, not changing noticeably over generations of observations. While most stars seem to appear in the same place year after year, some change location noticeably, the best example being Barnard's Star. Barnard's star is closer to Earth than any other star except Proxima Centauri. It also appears to move across the sky faster than any other star. This change in apparent location is caused by the movements of our Solar System and the motion of the star in question, and is known as proper motion. Using the astrometric capabilities of the MIRA software along with precise positional information for reference stars from the Tycho satellite star catalogue, the position of Barnard's star is computed relative to the reference stars. We calibrate a series of images of Barnard's Star taken in the Randolph College Observatory between 2001 and 2008 in order to independently determine the coordinates of Barnard's Star, revealing how these change over time. By measuring changes in the celestial coordinates, Right Ascension and Declination, we determine the proper motion of Barnard's star and compare this measurement to the accepted value of 10.25'' per year. [Preview Abstract] |
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K1.00021: Sync-map Description of Coupled Oscillators Gilad Barlev, Edward Ott, Michelle Girvan The Kuramoto model describes the tendency of coupled oscillators to synchronize when the coupling strength is above a critical value. Through Monte Carlo simulations, we study the behavior of a variation on the discrete-time Kuramoto model and verify certain properties of the model, namely the critical coupling value and the rate of relaxation towards synchronization. We then apply the model to non-directed networks with community structure to investigate synchronization within communities. Further, we propose a method for the discovery of community structure within networks based on observations of the time-averaged degree of synchronism between pairs of oscillators within our system. [Preview Abstract] |
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K1.00022: Partial Molar Volume of Helium Dissolved in Hydrogen Madeline Smith, M.S. Pettersen We have determined the partial molar volume $v ^{\prime}$ of helium dissolved in hydrogen, by analyzing existing data on the concentrations of the liquid and the coexisting vapor phase at high pressures. The partial molar volume can be found from the chemical potential of the helium in solution ($v ^{\prime} =\partial \mu_2 / \partial p |_{T,X_2}$, where $\mu_2$ is the chemical potential of the helium in solution, and $X_2$ its concentration), and the chemical potential can be determined from pressure and the concentration of the vapor phase, after applying virial corrections. Both $v ^{\prime}$ and the virial terms lead to corrections to Henry's law. Over the range studied (0-50 bar and 15.5-29 K), we find that the partial molar volume of helium is equal to the molar volume of pure hydrogen, within a few percent. The results are relevant to recent experiment on the wetting of cesium by helium/hydrogen solutions, and may also have astrophysical applications. [Preview Abstract] |
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K1.00023: Harmonic and Intermodulation Distortion in a Superconducting Microwave Resonator Bradley Dober, Stephen Remillard Experiments on the response of a thin film high temperature superconducting resonator to microwave stimulus have revealed a measurable amount of nonlinearity characterized by both second and third order distortion, as well as current dependant surface impedance. The power law dependence of the surface impedance was determined for both its real and imaginary parts. The 3rd order intermodulation distortion (IMD) was measured in the same regime and found to have a somewhat weaker than cubic power law dependence on source power, P. However, due to the nonlinearity, the power that is actually introduced into the resonator, also depends on P, and when this is accounted for, it is found that the IMD power depends on the cube of the power inside the resonator. 2nd and 3rd order harmonic emission is also generated by this resonator, providing evidence of time reversal symmetry breaking nonlinearity. The currents associated with 2nd and 3rd order harmonic generation were found to exist in different locations on the microstrip resonator. [Preview Abstract] |
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K1.00024: The Depletion Layer: A mystery of Science Satoko Asahi, Simon Kohnstamm, Adele Poynor Hydrophobic surfaces are those that resist contact with water. When water and a hydrophobic surface are forced into contact with each other complicated interactions ensue. Previous research predicts a layer of low density water exists at the interface between the water and hydrophobic surface which is known as depletion layer. We investigated the interaction between bulk water and a hydrophobic surface using Surface Plasmon Resonance (SPR). Using Self Assembling Monolayers (SAM) on gold foil, we created hydrophobic and hydrophilic surfaces and tested them in order to observe the effect on the depletion layer. [Preview Abstract] |
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K1.00025: The Design and Construction of a Surface Plasmon Resonance Imaging Apparatus for the Study of Patched Hydrophobic and Hydrophilic Surfaces in Water Christopher Whiting, Adele Poynor Proteins have hydrophobic and hydrophilic areas which, by studying how water behaves near hydrophobic and hydrophilic regions, helps to understand protein structures and interactions. We modified our existing surface plasmon resonance (SPR) system to create a surface plasmon resonance imaging setup. SPR imaging allows us to study differences in how water interacts with hydrophobic and hydrophilic regions in real time. [Preview Abstract] |
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K1.00026: Computational Electromagnetics Post Processing Using `MD-Grape' Board Brandon Momeyer, Gary Bedrosian The goal of Computational Electromagnetism (CEM) is to write and use computer codes to solve complex problems involving electric and magnetic fields. In CEM one can follow a three-step process: The first step is pre-processing, which involves building and generating a matrix equation from the electric and magnetic field properties. The second step is the solution to the matrix equation, which is solving for the unknown variable in the matrix equation. The final step is post-processing, which is to prepare numerical calculations from the results of the matrix and to create three-dimensional displays. The main focus in this study will be on the final step of the process. We are investigating whether a hardware accelerator board that was designed from problems in molecular dynamics and astrophysics, called MD{\_}GRAPE, can be adapted to accelerate the numerical computations required for CEM post-processing. Several computer codes have already been developed that go through these steps, it is our goal to accelerate them using MD{\_}GRAPE. We present results for post-processing 3D magnetic fields computed numerically using the finite element method (FEM). [Preview Abstract] |
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K1.00027: Computational Electromagnetics: Adaptation of the MD{\_}GRAPE Accelerator Board Adam Simbeck, Gary Bedrosian Computational Electromagnetics (CEM) uses numerical methods to calculate interactions between electromagnetic fields and objects of interest. To speed up the CEM process, is it possible to adapt an accelerator chip that was designed for other applications? We are researching the use of such a device, the MD{\_}GRAPE, for a CEM application based on the Finite Element Method (FEM). The MD{\_}GRAPE was designed to accelerate the numerical analysis of any problem involving interparticle forces, such as molecular dynamics, plasma physics, and hydrodynamics, but must be modified for the purposes of CEM. We present our progress in using the MD-GRAPE for the numerical generation of the FEM matrix equation for 3D magnetostatic fields, as a first step toward accelerating the full analysis process. [Preview Abstract] |
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K1.00028: Impact of barrier height distribution on tunneling conductance and extracted barrier parameters Dustin Belyea, Casey Miller The net tunneling conductance of metal-insulator-metal tunnel junctions is modeled using a distribution of barrier heights consistent with distributions typical of state-of-the-art junctions. Fitting numerically generated conductance data that include height distributions with tunneling models that assume a single-height barrier allows us to determine the effective barrier height and width associated with a more realistic tunnel junction. Moderate distributions cause the net conductance to resemble that of a perfect barrier that is shorter, and slightly wider than the mean barrier. [Preview Abstract] |
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K1.00029: ABSTRACT WITHDRAWN |
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K1.00030: Experimental study of plasma sheath conformation to rectangular depression Andrew Magyar, T.E. Sheridan We will characterize the plasma sheath above a rectangular depression in an otherwise flat, horizontal electrode in the Dusty ONU experimenT (DONUT) using micrometer-sized plastic spheres floating inside the sheath. Center-of-mass frequencies for two-particle clusters excited by Brownian motion will be analyzed in the plane parallel to the electrode to determine to ellipticity of the equipotentials above the depression, i.e., the conformation of the sheath to the depression, as a function of the aspect ratio of the depression. The particle charge can be found from the breathing mode frequency allowing an estimate of the Debye length and vertical electric field, and a measurement of the vertical resonance frequency gives the electric field gradient. [Preview Abstract] |
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K1.00031: Synthesis of Nanosized Silicon Powders and Characterization of Their Electrical Properties Wai Sze Cheung, Ingo Pluemel, Hartmut Wiggers The use of nanosized silicon powders in nanoelectronics and photovoltaics opens the path for new technologies while reducing production costs of existing devices like solar cells. However, the electrical properties of such systems are not yet fully understood. In this research, nanosized silicon powders with varying particle size and dopant concentration were synthesized in a low pressure reactor. The current-voltage relationship of the powders was then characterized by the means of cyclic voltammetry while applying a uniaxial pressure. It has been observed that the resistance of nanosized silicon powders increased over time after applying a force ranging from 10kN to 80kN. Cyclic voltammetry was used to track the non-linear change in resistance during the compression. [Preview Abstract] |
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K1.00032: Electron Paramagnetic Resonance Spectroscopic Studies of Cyanide-Bridged Fe/Os and Fe/Ru Clusters Katlyn Meier, Tanya Nocera, R. Abood, M. Chen, M. Hilfiger, D. Petasis, C. Achim, K. Dunbar The pentanuclear, cyanide-bridged metal clusters with the general formula {\{}[M(tmphen)2]3[M'(CN)6]2{\}} (tmphen = 3, 4, 7, 8-tetramethyl-1, 10-phenanthroline) have a core with trigonal bipyramidal geometry with equatorial [M(tmphen)2(CN)2] and axial [M'(CN)6] ions and contain M-CN-M' or M-NC-M' units, depending on the relative preference of the M and M' ions for the C or N terminus of the cyanide bridge. Spin-crossover behavior has been observed in these clusters and has motivated the current study. A series of Electron Paramagnetic Resonance (EPR) spectra of solid samples of the complexes with M/M'=Fe/Os and Fe/Ru were obtained between the temperatures of 2K and 300K. EPR spectra were also collected for samples dissolved in MeCN and MeOH. The EPR signals observed from Os (III) ions in the Fe/Os cluster and the signals from the Fe/Ru cluster indicating changes in oxidation and spin states of the metal ions as a function of temperature will be presented. [Preview Abstract] |
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K1.00033: METALS |
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K1.00034: Low energy positron sticking on surfaces -- comparison of experiment and calculations S. Mukherjee, K. Shastry, N. G. Fazleev, A. H. Weiss Recent measurements have provided evidence that low energy positrons incident upon a metal surface can make a single step transition from an unbound scattering state to an image potential bound state resulting in the creation of an electron-hole pair.~~~Because the transition into the surface state results in the release of an additional $\sim $3 eV of energy as compared to a transition into a bulk state, the direct transition from scattering state to surface state can result in the creation of secondary electrons even at beam kinetic energies below the energy threshold necessary to generate secondary electrons in scattering processes in which the positron final state is a bulk state. In this poster we present a comparison of the experimental results with model calculations from which the rate of the direct process is estimated and the implications of these measurements in the understanding of quantum-sticking of positrons to surfaces are considered. [Preview Abstract] |
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K1.00035: The Surface Dynamics of the Initial Oxidation Behavior of CuNi Alloys Steve Ziemack, Li Sun, Judith Yang, Jeff Eastman, Guangwen Zhou As an extension of our previous work on the initial oxidation stages of pure Cu and CuAu alloy, we are currently visualizing the oxidation of CuNi alloys by in-situ ultra high vacuum transmission electron microscope (UHV-TEM) and X-ray diffraction. We investigated systematically a range of CuNi (001) compositions, including 2,8,15 and 24 at\%Ni at P (O2) =5x10-4 torr and T=500-700$^{\circ}$C. The initial oxidation behavior is similar to that of Cu (001) AND CuAu (001), where oxide islands rapidly nucleate, grow and coalesce. However, remarkable differences exist: 1) a second rapid nucleation of compact and dense oxide islands occurred and 2) polycrystalline oxides formed, where only cube-on-cube epitaxial Cu2O islands nucleated on Cu (001) and CuAu (001) for all temperature and pressures studied. The surface segregation behavior of Cu and Ni may explain these surprising results. [Preview Abstract] |
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K1.00036: Creation and Characterization of Gold Coated Slides with a Home Built Deposition Chamber Nate Rieders, Adele Poynor I discuss the creation of gold slides as part of a physics senior thesis at Allegheny College. The device used for making the gold slides was constructed as part of this project. Gold wire was placed in an evacuated chamber along with an array of glass slides. The gold wire is heated and evaporated onto the glass slides, leaving a thin deposition layer. The gold slides are created for the study of hydrophobic materials using surface plasmon resonance (SPR). The use of SPR as the experimental method requires the thickness of the gold layer to be precisely determined. Thus, the thickness of the gold slides is characterized using scanning tunneling microscopy. [Preview Abstract] |
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K1.00037: Surface Layer Availability Approach to Systems with Solid-Fluid Surfaces Robert Cammarata Although the dividing surface method as devised by Gibbs can be used to completely describe the surfaces of fluid systems, in the case of fluid-solid interfaces with a finite size crystal the approach is generally restricted to systems where the solid is a single phase material. This is a result of the fact that the surface chemical potential of the solid component is not well-defined. As a result, Gibbs chose a dividing surface location where the surface excess amount of that component is zero so that the corresponding surface chemical potential was never needed. However this approach cannot be extended to systems containing multicomponent solids. It is proposed that for such systems a surface availability function, analogous to the thermodynamic availability function used in engineering thermodynamics, can be employed. It will be shown that such an approach can be used without the need of a particular dividing surface location, and that more generally the dividing surface construction can be dispensed with in favor of a finite volume surface layer. It is shown that by using this surface layer formulation a variety of problems, including surface adsorption and nucleation during solidification, can be rigorously treated for multicomponent systems. [Preview Abstract] |
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K1.00038: Dielectric function trajectory of ultrathin gold films Xuefeng Wang, David Nolte There have been attempts to study the complex refractive index $\tilde {n}_g $ of gold films by ellipsometry, but the measurements become unreliable when the average film thickness is below several nanometers, presumably because of optical anisotropy of the thin film. Here, we apply interferometric picometrology to measure $\tilde {n}_g $ by analyzing the Fourier-domain anisotropic diffraction of a normal-incidence scanning Gaussian laser beam reflected by a stripe-patterned gold film. The $\tilde {n}_g $ and dielectric constant $\varepsilon _g $ of the gold film were measured for thicknesses ranging continuously from 0.1 nm to 10 nm at a wavelength of 488 nm. Three distinct regimes of the $\varepsilon _g $ trajectory on the complex plane were observed as the gold thickness increased. The first regime (gold thickness: 0.1 nm $\sim $ 0.7 nm) reveals an evolution from sparse clusters to dense clusters. The real part of $\varepsilon _g $ changes from 2.3 to 7.0 and the imaginary part changes from 0 to 0.7. The Maxwell-Garnett equation is applied for this regime by treating the film as an effective medium consisting of air and gold clusters. The second regime (0.7 nm$\sim $ 2 nm) is a linear curve of $\varepsilon _g $ suggesting a transition from isolated clusters into a continuous thin film. The third regime (2 nm $\sim $ 10 nm) shows a circular trajectory of $\varepsilon _g $ moving towards the bulk value, which can be interpreted by the Drude equation. [Preview Abstract] |
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K1.00039: The Variational Calculation for Small Cylindrical Metallic Cluster Chin-Sheng Wu We use the Hohenberg-Kohn principle to calculate the density of the surface electronic charge around small cylindrical metallic cluster. The surface potential is varied in order to get the minimum total energy, which is the summation of electro-static energy and exchange-correlation energy. We use the local approximation for the inhomogeneous dielectric function around the surface. Therefore this surface charge can be applied to find dielectric constant, which is a function of the electron density. The dielectric constants are calculated on the cylindrical surface for various metal densities. [Preview Abstract] |
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K1.00040: A Green Hydrothermal Synthesis for Iron-Doped, Carbon-Coated Tellurium Nanostructures and an Analysis of the Effects of the Molecular Weight and Ratio of Poly(vinylpyrrolidone) on Nanostructure Morphology T. Mulliger, S. Mishra, S. Guha A poly(vinylpyrrolidone) (PVP)-assisted hydrothermal process was used to synthesize tellurium nanostructures, as well as carbon-coated tellurium nanostructures (Te@C) in the presence of glucose as a carbon source. The thickness of ultra-thin tellurium nanostructures in the presence of PVP was found to depend upon the molecular weight of the polymer, as well as the ratio of polymer to tellurium source (Na2TeO3) used as starting materials. Structures ranging from 3-15nm were synthesized using four different molecular weights of PVP polymer (10,000; 29,000; 40,000; and 55,000) as well as different ratios of polymer to sodium tellurite, and their difference are compared. Varying the reaction time of the carbon-coating hydrothermal process yielded carbon-shell thickness ranging 20-60nm. As-prepared Te@C nanostructures were decorated with iron nanoparticles through an ultrasonication process at 0C under a flow of argon. Hollow carbon nanostructures were also synthesized through a mild chemical treatment process at room temperature. Samples were extensively characterized through transmission electron microscopy (TEM), scanning electron microscopy and energy dispersive x-ray analysis (SEM/EDAX), ultraviolet visible, and PL. [Preview Abstract] |
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K1.00041: Polymer Assisted Core-shell Ag-C nanoparticles Synthesis via Green hydrothermal Technique James Williams, Sanjay Mishra Core-Shell Ag-C nanoparticles were synthesized in the presence of glucose through a one-pot green hydrothermal wet chemical process. An aqueous solution of glucose and Ag nitrate was hydrothermally treated to produce porous carbonaceous shell over silver core nanoparticles. The growth of carbon shells was regulated by either of the polymers (poly) vinyl pyrrolidone (PVP) or poly vinyl alcohol (PVA). The two polymers were compared to take a measure of different tunable sizes of cores, and shells. The effects of hydrothermal temperature, time, and concentration of reagents on the final formation of nanostructures were studied using UV-vis extinction spectra, transmission electron microscope, and Raman spectroscopy. The polymer molecules were found to be incorporated into carbonaceous shell. The resulting opacity of the shell was found to be hydrothermal time and temperature dependent. The shell structure was found to be more uniform with PVP than PVA. Furthermore, the polymer concentration was found to influence size and shape of the core-silver particles as well. The core-shelled nanoparticles have surfaces with organic groups capable of assembling with different reagents that could be useful in drug-delivery, optical nanodevices or biochemistry. [Preview Abstract] |
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K1.00042: Growth Mechanism Study of Carbon Nanospheres Synthesized using Green Hydrothermal Technique M. Doorley, S.R. Mishra, M. Laradji, S.K. Karna, R. Gupta, K. Ghosh An attempt is made to understand the growth kinetics of carbon nanospheres (CNS) synthesized using a green technique. An aqueous solution of glucose, was hydrothermally treated to produce porous CNS with homogeneous size distribution, smooth surfaces, and high porosity. The growth kinetics of CNS was studied by evaluating TEM images as a function of hydrothermal reaction time and temperatures. CNSs with tight size distribution in the range of 100-200nm were successfully synthesized. Raman spectra revealed the presence of short-ordered graphitic nanostructures in an amorphous carbon matrix. FTIR spectroscopy confirms the carbonization of glucose and shows the presence of surface hydroxyl groups on CNSs. BET surface area analysis show that the equivalent pore volume is about 50 percent for all nanoparticles. Based on various experimental observations it is proposed that the growth of CNSs is dictated by a reaction-controlled mechanism where long chain glucose-based oligomers bond to the CNS surface. The narrow size distribution and highly hydrophilic surface of these amorphous CNS makes them potential candidates for biomedical applications. [Preview Abstract] |
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K1.00043: Polymer assisted synthesis of FeNi nanoparticles S.K. Karna, S.R. Mishra, I. Dubenko, N. Ali, E. Gunapala, K. Marasinghe FeNi nanoparticles (NP) in the size range of 50 to 250 nm were synthesized via wet chemical method. The precursor, sulfate salts of iron and nickel were reduced in alkaline media and in the presence of either polymers PEG (200-20,000 MW) or PVP(10,000 to 55,000 MW). The synthesis process was studied to understand the role of polymers in the growth of NP. TEM and XRD studies show formation of highly crystalline and well dispersed FeNi NP in polymer matrix. A decrease in particle size with an increase in PVP MW and increase in particle size with increase in PEG MW was observed. Furthermore, increase in PVP concentration leads to increase in particle size while increase in PEG concentration did not affect the particle size. Low temperature ZFC magnetization studied show decrease in saturation magnetization value with the increase in polymer MW. It is concluded that the polymer mediated growth of FeNi NP involved 1) the formation of coordinative bonds between polymer and metal ions, 2) polymer-promoted nucleation, which produce small FeNi nanoparticles, and 3) steric shielding of the FeNi nanoparticles surfaces through chemical bonding to polymer which inhibited particle-particle contact and, thus the agglomeration of NP. [Preview Abstract] |
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K1.00044: Adiabatic Electron-Phonon Coupling in the A15 Compounds V3Si, V3Ge and V3Co Olivier Delaire, M. Lucas, J. Munoz, M. Kresch, B. Fultz The phonon density of states (DOS) of the A15 compounds V3Si, V3Ge, and V3Co was measured as function of temperature between 10K and 1273K with inelastic neutron scattering. The temperature dependence of the phonon DOS strongly departs from the predictions of the quasiharmonic model in the superconducting compounds V3Si and V3Ge, but behaves more normally in the non-superconducting V3Co. Using first-principles electronic structure calculations, the observed anomalies are related to the details of the band structure in these compounds. It is shown that sharp features in proximity to the Fermi level lead to anomalous phonons through a sensitivity to thermal disorder, or adiabatic electron-phonon coupling. In the case of V3Si and V3Ge, a sharp peak in the electronic DOS leads to a stiffening of the phonons with increasing temperature. These results are compared to recent measurements of the phonon DOS and its temperature dependence in the B20 compounds Fe(1-x)Co(x)-Si. [Preview Abstract] |
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K1.00045: Impurity Studies in CeCoIn$_{5}$ Abebe Kebede, Terell Dial Systematic alloy studies of CeTlIn$_{5}$ (T = Co, Rh, Ir,) reveal the stability of superconductivity in a wide range of composition; and in some cases it coexists with a magnetically ordered phase. We extended these studies to include (R, Ce)(Co, M)In$_{5}$ are ( R= Pr and M= Fe, Mn). Our preliminary measurements indicate that the samples are single phase, and they exhibiting a wide range of transport and magnetic properties. In this communication we present the results of our resistivity and magnetic susceptibility measurements. [Preview Abstract] |
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K1.00046: The 0.7 anomalous conductance D. Schmeltzer, A. Kuklov At low electronic densities and finite temperatures the method of one dimensional Bosonization is not applicable. We introduce the $zero$ $modes$ method to incorporate Fermi Dirac Statistics. We compute the conductance at finite temperatures in the presence of long range $Coulomb$ and biased $umklapp$ interactions. We show that the $0.7$ conductance anomaly appears at low densities when the Fermi energy and the temperature are of the same order of magnitude. [Preview Abstract] |
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K1.00047: Quantum critical fluctuations in the itinerant antiferromagnet Nb$_{12}$O$_{29}$ Jinguang Cheng, Jianshi Zhou, John Goodenough, Haidong Zhou Monoclinic Nb$_{12}$O$_{29}$ is a metallic antiferromagnet with T$_{N} \approx $12 K. [1] We have studied critical behaviors near T$_{N}$ by measuring the resistivity ($\rho )$, specific heat (C$_{p})$, and thermoelectric power (S). As T$_{N}$ is approached from T$_{N}^{+}$, critical behaviors used in ferromagnetic metals, d$\rho $/dT = (a$^{+}$/$\alpha )\vert $t$\vert ^{-\alpha }$+ b$^{+ }$+ c$^{+}$t and C$_{p }$= (A$^{+}$/$\alpha )\vert $t$\vert ^{-\alpha }$+ B$^{+}$ + C$^{+}$t provide the best description for d$\rho $/dT and C$_{p}$, respectively. We found an identical $\alpha \quad \approx $ 0.2(2) in both d$\rho $/dT and C$_{p}$, as predicted by Fisher and Langer in a ferromagnetic metal. [2] These observations indicate strong critical scattering of conduction electrons by short-range spin fluctuations near T$_{N}$. In addition, the S is strongly enhanced at low temperatures. The temperature dependence of S above T$_{N}$ follows closely the formula S/T $\propto \quad -$lnT, which suggests that quantum critical fluctuations [3] plays a role in enhancing the thermoelectric power on top of the classic critical fluctuations. \\[0pt] [1] R. J. Cava, \textit{et al}., Phys. Rev. B \textbf{44}, 6973 (1991).\\[0pt] [2] M. E. Fisher and J. S. Langer, Phys. Rev. Lett. \textbf{20}, 665 (1968).\\[0pt] [3] I. Paul and G. Kotliar, Phys. Rev. B \textbf{64}, 184414 (2001). [Preview Abstract] |
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K1.00048: The Superconducting Phase Diagram of V3Si0.98X0.02, X=Ni, Mn, Co, Fe, Cu M.D. Almeida, C.P. Opeil, J.C. Lashley, J.L. Smith We report on the results of AC Resistivity measurements of V$_{3}$Si$_{0.98}$X$_{0.02}$ in the presence of a magnetic field, where the dopants include Ni, Fe, Mn, Co, and Cu. From this we see a clear shift in the superconducting critical temperature of the materials in response to increasing in field strength. Additionally, dilatometry measurements provide information on the thermal expansion coefficients of these materials. [Preview Abstract] |
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K1.00049: Electrical transport and thermodynamic properties of $\gamma-Mo_4O_{11}$ Ariana de Campos, M.S. da Luz, B.D. White, J.J. Neumeier Low-dimensional systems have attracted a lot of attention during the last two decades because of their unusual chemical and physical properties [1]. $\gamma-Mo_4O_{11}$ is one such system exhibiting strong structural anisotropy, which is reflected in the electronic structure. This gives rise to uncommon features such as low-dimensional transport, metal– insulator and metal$-$metal transitions, and periodic lattice distortions and charge density waves (CDW) [2]. In this work the properties of $\gamma-Mo_4O_{11}$ single crystals are revisited. The single crystals were grown using a temperature- gradient flux method [3]. Electrical resistance as a function of temperature was determined with the Logan-Montgomery methods [4, 5] and was compared with reported measurements. We will report results of heat capacity and high-resolution thermal expansion measurements as well. [1] M.A.Valbuena, et al. Appl. Surf. Sci., 254, 40 (2007). [2] C. Schlenker, et al. Philos. Mag. B, 52, 643 (1985). [3] W. H. McCarroll and M. Greenblatt, J. Solid State Chem. 54, 282 (1984). [4] H. C. Montgomery, J. Appl. Phys. 42, 2971 (1971). [5] B. F. Logan, S. O. Rice, and R. F. Wick, J. Appl. Phys. 42, 2975 (1971). This material is based upon work supported by the Brazilian Agency CNPq (Grant No. 201439/2007-7), the NSF (Grant No. DMR- 0504769) and U.S. DOE Office of Basic Energy Sciences (Grant No. DE-FG-06ER46269). [Preview Abstract] |
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K1.00050: DFT Calculation of the Electronic Properties and EEL Spectrum of NiSi$_{2}$ Roberto N\'u\~nez-Gonz\'alez, Armando Reyes-Serrato, Donald H. Galvan, Alvaro Posada-Amarillas In this work we present theoretical band structure, total and projected density of states (DOS), dielectric function and electron energy-loss spectrum (EELS) of NiSi$_{2}$. The calculations were carried out using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method, within the Density Functional Theory (DFT) with the Local Density Approximation (LDA). Our theoretical EELS results are in excellent agreement with recent experimental findings, indicating that the main peak corresponds to a plasmon. Additional peaks in our calculations are identified as interband transitions (at 2.67 eV, 4.77 eV and 6.1 eV) associated to transitions between Ni d to Si p states, and low magnitude plasmons (at 1.3 eV and 4.02 eV). [Preview Abstract] |
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K1.00051: Using Image Processing Techniques for Cluster Analysis, and Droplet Formation in Phase Separating Fluids Gregory Smith, Ana Oprisan, John Hegseth, Sorinel Oprisan, Carole Lecoutre, Yves Garrabos, Daniel Beysens A series of experiments were performed using the Alice II apparatus in microgravity to study phase separation near critical temperature. Using image analysis techniques, we were able to obtain quantitative~information regarding the morphology of gas-liquid interface near~critical point of pure SF6 fluid in microgravity. Growth laws for liquid and gas clusters were extracted based on image segmentation~both with thresholding and k-means clustering. By measuring the image~features we analyzed the formation of spherical droplets during late~stage of phase separation for a series of full view images. The growth~of a wetting layer around the border of the cell containing the fluid was also investigated using image processing techniques. [Preview Abstract] |
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K1.00052: Insights on copper coordination and reactivity of endonuclease EcoRI by ESR spectroscopy and modeling Ming Ji The cleavage of DNA by restriction endonuclease EcoRI is catalyzed by metal ions such as Mg$^{2+}$. However, Cu$^{2+}$ does not catalyze the cleavage of DNA by EcoRI. In order to understand the functional difference between Cu$^{2+}$ and Mg$^{2+}$, coordination of Cu$^{2+}$ in the EcoRI--DNA complex was clarified by ESR and MD simulation. There are two Cu$^{2+}$ components in the specific EcoRI-DNA complex. Each component has one N atom from histidine imidazole and one oxygen atom from the phosphate backbone of DNA coordinate to Cu$^{2+}$ based on the ESR experimental results. MD simulation further confirmed that the N$\delta $ atom of His114 imidazole and one oxygen atom from the phosphate backbone of DNA coordinate to Cu$^{2+}$. Difference in the coordination of Cu$^{2+}$ and Mg$^{2+}$ explains their different functional behaviors. [Preview Abstract] |
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K1.00053: Twist Defect in an Imprinted Cholesteric Elastomer Paola Castro-Garay, Juan Adrian Reyes, Adalberto Corella-Madue\~no We have found that a chiral twist defect inserted in a cholesteric elastomer gives rise to circularly polarized localized modes of both handedness. This defect enhances the resonance mode amplitude whose handedness is opposite to the cholesteric helix for high cross-linked density. Complementarily, for low cross-linked density, the circular polarization opposite to helix cholesteric of the elastomer is decoupled with the defect mode so that the resonance mode disappears . Finally, the resonance mode of the circularly polarization of the same handedness to elastomer helix is maintained either, for high or low cross-linked density. [Preview Abstract] |
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K1.00054: Meso-scale Harmonic Analysis of Homogenous Dislocation Nucleation. Asad Hasan, Craig Maloney Under sufficiently high loads dislocations will be nucleated in perfect crystals. A typical scenario is the nano-indentation of a defect-free metal. An outstanding issue is the prediction of where and under what loads nucleation will occur. Many criteria have been put forward which address this question, some in terms of the local stress field, others in terms of the local tangent stiffness of the material. More recently it has been questioned whether a local criterion can be used at all [1]. We address the locality of the nucleation process via analysis of molecular dynamics simulations in terms of the vibrational eigenmodes of the mesoscale regions of the crystal for various model systems. [1] R.E. Miller and D. Rodney, J. Mech. Phy. Solids 56(4) 1203-1223, 2008. [Preview Abstract] |
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K1.00055: MAGNETISM: OXIDES AND NANOSTRUCTURES |
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K1.00056: The origin of the double-triangle hysteresis loops in ErFeO$_3$ near the low temperature erbium ordering transition L.T. Tsymbal, Ya. B. Bazaliy, G.N. Kakazei Magnetic properties of an orthoferrite ErFeO$_3$ are determined by the iron and the rare-earth magnetic ions. Interactions between magnetic sub-systems of ErFeO$_3$ lead to a sequence of orientation phase transitions observed in this material. In this work hysteresis loops in single crystal ErFeO$_3$ samples were studied below the spin-rotation transition region, $T < 80$ K. Above and around the compensation point $T_{\rm comp} = 46$ K the hysteresis loops are rectangular, with the coercive force diverging at $T_{comp}$. As the temperature is lowered towards the erbium ordering transition $T_{N2} = 4.1$ K, the shape of the loops experiences a dramatic change. At 20 K the loops develop triangular ``tails.'' At 10 K the triangles become prominent while the central rectangular part near $H = 0$ collapses. A double-loop hysteresis pattern with two triangular loops emerges. We explain this behavior by a domain wall motion reversal mechanism with negligible pinning of the walls in the sample. The transition from the rectangular to the double-triangle loops is due to the competition between the energy barrier of wall nucleation and the demagnetization energy gain achieved by placing the wall inside the sample. Our model explains well the correlation of the loop's shapes and sizes with the total magnetization of ErFeO$_3$. [Preview Abstract] |
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K1.00057: Impact of transition metal buffer layers on Magnetite thin film growth and properties Priyanga Jayathilaka, Daryl Williams, Chris Bauer, Dustin Belyea, Casey Miller Magnetite thin films were grown on MgO single crystals with 3nm buffer layers of Fe, Cr, Mo, and Nb. An in situ masking system allowed the deposition of the individual buffer layers on separate substrates, followed by the simultaneous growth of 100nm thick magnetite films on all substrates via reactive sputtering. We are thus able to demonstrate the impact of the resulting lattice strain on the magnetite films' structure, and temperature dependent resistivity and magnetization. [Preview Abstract] |
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K1.00058: Origin of multiferroicity in hexagonal Y$_{1-x}$Dy$_{x}$MnO$_{3}$ A.K. Singh, S.D. Kaushik, V. Siruguri, S. Patnaik Multiferroic materials, that offer the possibility of manipulating an ordered electric state by applying magnetic field, have attracted considerable attention in the recent past. Here we report a detailed analysis of structural, magnetic and dielectric properties of polycrystalline samples of Y$_{1-x}$Dy$_{x}$MnO$_{3}$ (0 $\le $ x $\le $ 0.2). These materials belong to space group $P6_{3}$\textit{cm }with hexagonal crystal structure and were synthesized by solid state reaction method. We have carried out extensive zero field and in-field neutron diffraction, and dielectric measurements. Our study provides evidence for change in the lattice parameters, buckling of Y (Dy) layers, Mn-O-Mn bond angles and tilting of MnO$_{5}$ pollyhedra as a function of temperature and magnetic field. We also study the magnetoelectric coupling in YMnO$_{3}$ as well as doped samples by in-field dielectric measurements. A distinct anomaly near N\'{e}el temperature is observed in these measurements that vary with the application of magnetic field. In essence, we develop a model to understand the magnetoelectric coupling of these antiferromagnetic multiferroics with their field dependent magnetic structure. [Preview Abstract] |
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K1.00059: Anomalous magnetic transition in multiferroic BiMnO$_{3}$ under high pressure Chih Chieh Chou, S. Taran, J.L. Her, C.P. Sun, C.L. Huang, H. Sakurai, A.A. Belik, E. Takayama-Muromachi, H.D. Yang The magnetic-field-dependent dc magnetization and the pressure-dependent ($p_{max} \quad \sim $ 16 kbar) ac susceptibilities $\chi _{p}(T)$ on both powder and bulk multiferroic BiMnO$_{3}$ samples, synthesized in different batches under high pressure, are reported. The ferromagnetic (FM) transition ($T_{C }\sim $ 100 K) increases with higher magnetic field. The magnetic hysteresis shows the behavior as a soft ferromagnet. Ac susceptibility data indicate the following phenomena. (I) The FM peak (peak I) and its temperature ($T_{C})$ decrease simultaneously with increasing pressure. (II) Above a certain pressure (9 -11 kbar), another peak (peak II) appears at ($T_{p} \quad _{\sim }$93 K). (III) Peak II also decreases with increasing pressure. (IV) Both these peaks persist over some intermediate pressure range (9--13 kbar). (V) Peak I disappears with further application of pressure; however, the second peak survives until present pressure limit ($p_{max} \quad \sim $ 16 kbar). These features are considered to originate from the complex interplay of the magnetic and orbital structure of BiMnO$_{3}$ being affected by pressure. [Preview Abstract] |
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K1.00060: Magnetic frustration and spin glass behaviour in layered lithium oxide, LiNi$_{0.65}$Co$_{0.25}$Mn$_{0.10}$O$_{2}$. Magnus Wikberg, Peter Svedlindh, Mohammed Dahbi, Ismael Saadoune, Torbjorn Gustafsson, Kristina Edstrom Samples of Li$_{x}$Ni$_{0.65}$Co$_{0.25}$Mn$_{0.10}$O$_{2}$ with different amount of Li (x) have been investigated with ac and dc SQUID magnetometry, X-ray diffraction as well as with neutron scattering. The Li$_{x}$Ni$_{0.65}$Co$_{0.25}$Mn$_{0.10}$O$_{2}$ exhibit a rhombohedral structure (space-group $R\bar {3}m)$ with non-magnetic Li$^{+}$ layers alternating with transition metal (TM) slabs with edge-sharing oxygen octahedras. The nickel slabs contain several intralayer interactions of both antiferromagnetic (AFM), ferromagnetic (FM) type, e.g. 90$^{o}$ Ni$^{2+}$-O-Mn$^{4+}$ and 90$^{o}$ Ni$^{3+}$-O-Ni$^{3+}$, respectively. Also, the presence of Ni$^{2+}$ in the Li-plane further induces AFM and FM couplings due to 180$^{o}$ superexchange interactions between Ni$^{2+}$ in the Li-plane and TM- ions present in the slabs. The resulting magnetic structure shows no evidence of long range order due to a high degree of spin frustration, thus yielding magnetic properties reminiscent of a spin glass. [Preview Abstract] |
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K1.00061: Spin and charge orderings in single layered cobaltate La$_{2-x}$Ca$_{x}$CoO$_{4}$ (0.3$ Kazumasa Horigane, Haruhiro Hiraka, Toru Uchida, Kazuyoshi Yamada, Jun Akimitsu Neutron scattering experiments were performed on single crystals of layered cobalt-oxides La$_{2-x}$Ca$_{x}$CoO$_{4}$ (LCCO) to characterize the charge and spin orders in a wide hole-doping range of 0.3$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $x$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $0.8. For a commensurate value of x=0.5 in (H,0,L) plane, two types of superlattice reflections concomitantly appear at low temperature; one corresponds to a checkerboard charge ordered pattern of Co$^{2+}$/Co$^{3+}$ ions and the other is magnetic in origin. Further, the latter magnetic-superlattice peaks show two types of symmetry in the reflections, suggesting antiferromagnetic-stacking (AF-S) and ferromagnetic-stacking (F-S) patterns of spins along the c direction. From the hole-doping dependence, the in-plane correlation lengths of both charge and spin orders are found to give a maximum at x=0.5. These features are the same with those of x=0.5 in La$_{1-x}$Sr$_{1+x}$MnO$_{4}$ (LSMO), a typical checkerboard and spin ordered compound. [Preview Abstract] |
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K1.00062: Electronegativity and Valence Electron Spectrum of Room Temperature Ferromagnets O. Paul Isikaku-Ironkwe Materials that exhibit room temperature ferromagnetism (RTFM) are of interest in the fabrication of spintronic devices. RTFM has been observed in semiconductors, oxides and other non-magnetic materials and nanocrystals. There is yet no consensus on the origin of RTFM or how to predict the next RTFM. Here we study the electronegativity and valence electron count of known RTFMs as a step to understanding this fascinating family of materials. Understanding the process of RTFM may aid the search for \textbf{room temperature superconductivity }(RTS) --- a similar phenomenon. [Preview Abstract] |
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K1.00063: Molecular nanomagnets for information technologies Marco Affronte I have recently reviewed challenges, achievents and perspectives in the field of molecular magnets in a review article in J. of Mat. Ch. DOI: 10.1039/b809251f (2008) focusing on quantum information. Molecular magnets are indeed quantum objects, with well-defined spin states at low temperature. The challenge is to obtain scalable quantum hardware with long coherence time. A paradimatic case is that of AF rings in which an extra spin was introduced to have a S=1/2 as ground state (Phys. Rev. Lett. 94, 190501 (2005) and use excited states as a resource for implementing two-qubit gates (Phys. Rev. Lett. 94, 190501 (2005), Phys. Rev. B 76, 024408 (2007). The mechanism of decoherence can be studied in details by considering hyperfine interactions with finite number of nuclear spins(Physical Review B 77, 054428 (2008). Cr7Ni are stable in solution, can be functionalized to be grafted on surface (Inor. Chem. 46, 4968-4978 (2007) or to be linked each other by forming supramolecular complexes (Angew. Chem Int. Ed. 44, 6496 (2005) and Nature Nanotechnology 2008) with tuneable entanglement of spin states. [Preview Abstract] |
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K1.00064: Correlation effects on the properties of small cobalt clusters Yvette Hancock, Mari Ij\"as Demands for higher-density magnetic storage media and smaller memory devices require atomic-scale magnetic components with stable magnetic properties. One such candidate for this application is a small transition metal cluster. The magnetic properties of transition metal clusters are very sensitive to the geometry of the cluster, the local atomic and structural environments, and to the system size. In this work, the GGA + U DFT approach is used for the first time to study the system properties of small cobalt clusters consisting of 2 to 5 atoms. Previous studies using DFT and tight-binding approaches have been found to overestimate the binding energies, dissociation energies and vibrational frequencies of the clusters against their known experimental values. By including a Hubbard U correction between 2 -- 3 eV, the DFT method can then be fitted to reproduce the experimental results, thereby improving upon previous theoretical descriptions of these systems. The effect of U on the calculated magnetic and structural properties of the clusters is also discussed. [Preview Abstract] |
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K1.00065: Temperature and size dependence of electron magnetic resonance spectra of Ni nanoparticles chemically dispersed in silica Vivek Singh, Mohindar Seehra The temperature dependence (5K to 300K) of the electron magnetic resonance (EMR) lines observed at 9.28 GHz in Ni:SiO$_{2}$ (15:85) nanocomposites with mean diameter D of the Ni nanoparticles (NPs) of D=3.8, 11.7, 15 and 21 nm are reported. The sizes of the Ni NPs were determined by TEM and XRD, with SiO$_{2}$ being in the amorphous state. The procedures for the synthesis of the samples along with their DC and AC magnetization behavior were reported recently [1]. In EMR, three resonance lines are observed: (i) Line 1 with linewidth $\Delta $H $\simeq $ 50 Oe and g $\simeq $ 2, and Curie-like variation of the line-intensity, with $\Delta $H and g being temperature and size-independent; (ii) Line 2 with $\Delta $H $\simeq $ 950 Oe and g $\simeq $ 2.2 for D=3.8nm at 300K with both $\Delta $H and g increasing with decreasing T and $\Delta $H size-dependent; and (iii) weak line 3 with g $\sim $ 4 at 300K, with g also increasing with decreasing T. We argue that the line 1 is due to dangling bonds in SiO$_{2}$ as a similar line with $\Delta $H $\simeq $ 9 Oe is also observed in SiO$_{2}$ without Ni doping. Lines 2 and 3 are attributed to majority Ni NPs and large Ni clusters respectively whose anisotropy is both size and temperature-dependent [2], leading to the observed $\Delta $H and g values of the lines. \\[0pt] [1]. Singh, Seehra and Bonevich, J. Appl. Phys. \underline {103}, 070524 (2008) and ibid (in press). \\[0pt] [2]. R. S. de Biasi and T. C. Devezas, J. Appl. Phys. \underline {49}, 2466 (1978). [Preview Abstract] |
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K1.00066: Synthesis and Characterization of Gd and Nd Nanoparticles Dulce G. Romero, Pei-Chun Ho, Saeed Attar Due to the reduced dimensionality, nano-sized materials have physical properties significantly different from the bulk material, such as, superparamagnetic behavior, enhanced magnetization, and self-organization [1-3]. Nano-sized materials have great potential for technical applications, for example, magnetic information storage, imaging, medical devices, and magnetic refrigeration. In this report, we will present the growth and filtration of rare-earth Gd and Nd nanoparticles by the inverse micelle technique [4]. The results of the characterization of these clusters by X- ray diffraction, scanning electron microscope, and energy-dispersive x-ray spectroscopy will be presented. [1] D.C. Douglass, et al. Phys. Rev. B. 47, 19 (1993). [2] J.P. Chen, et al. Phys. Rev. B. 51, 11527 (1995). [3] C. Petit, et al. Advanced Materials. 10, 259 (1998). [4] X.M. Lin, et al. Langmuir. 14, 7140 (1998). [Preview Abstract] |
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K1.00067: Development of ferromagnetism in Pd nanoparticles with reduction in size Mohindar Seehra, James Rall, J. Liu, C. Roberts Bulk fcc Pd is a paramagnet just missing the Stoner criterion for ferromagnetism (N(E$_{F})$I $>$ 1) [1]. Several groups have reported weak ferromagnetism in 2-4 nm Pd nanoparticles (NPs) [2]. We report systematic development of weak ferromagnetism in Pd NPs with reduction in size. Magnetic measurements (M vs. T) are compared for bulk Pd with those of size D $\approx $ 50nm, 7nm, and 6nm. The samples of size D = 7 nm and 6 nm were prepared by an aqueous seed-mediated growth and characterized by TEM and x-ray diffraction with the latter showing expansion of the lattice with decrease in size. Compared with the low-field magnetic susceptibility $\chi $ of bulk Pd, $\chi $ for the 7 and 6 nm NPs are enhanced by an order of magnitude. For the 50 nm NPs, $\chi $ follows nearly the Curie law. The hysteresis loops (M vs. H) for the 7 and 6 nm NPs shows a decrease in coercivity and remanence from 2K to 300K suggesting T$_{C} \quad >$ 300K. Origin of this ferromagnetism in terms of surface magnetism and lattice expansion is discussed. [1] W. Gerhardt et al, Phys. Rev. B \underline {24}, 6744 (1981); [2] T. Shinohara et al, Phys. Rev. B \underline {91}, 197201 (2003); Jeon et al, J. Appl. Phys. \underline {103}, 09413 (2008); Litran et al, Phys. Rev. B \underline {73}, 054404 (2006). [Preview Abstract] |
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K1.00068: M\"{o}ssbauer and magnetic studies of (Ni$_{0.6-x}$Co$_{x})$Zn$_{0.4}$Fe$_{2}$O$_{4 }$nanoparticles J.C. Ho, M.M. El-tabey, H.H. Hamdeh, R. Asmatulu, S.H. Wu, Y.Y. Chen Mixed-ferrites (Ni$_{0.6-x}$Co$_{x})$Zn$_{0.4}$Fe$_{2}$O$_{4}$ with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 were synthesized by co-precipitation of Ni-, Co-, Zn- and Fe-sulfates. Structural characterization of the approximately 10-nm particles was made by x-ray powder diffraction. Through M\"{o}ssbauer spectroscopic measurements, the composition- and temperature-dependence of magnetic blocking temperature and anisotropic constant were obtained. SQUID data yielded corroborative results, in addition to magnetization and saturation values. [Preview Abstract] |
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K1.00069: Effect of Anisotropy in Two-dimensional Dimer model of magnetic ferrofluids Abdalla Obeidat, Wesam Al-Sharo The magnetization and the Initial susceptibility have been calculated using statistical mechanics for two-dimensional structured dilute ferro-fluid taking the effect of the magnetic anisotropy and inter-particle interaction. We assumed the assembly consists of N/2 non-interacting systems. Each system is composed of 2 interacting single domain fine magnetic spherical particles. We referred to this model as a Dimer-model. We found that when the easy axis is fixed with respect to the external magnetic field, the ordering temperature depend on the anisotropy constant K in both parallel and perpendicular cases. [Preview Abstract] |
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K1.00070: Magnetic Nanoparticle Arrays prepared via Coaxial Electrospinning Nikhil Sharma, Hassnain Jaffari, Ismat Shah, Darrin Pochan One dimensional nanoparticle (1D NP) arrays display strong anisotropy in their physical properties making them interesting from a fundamental as well as applications perspective. 1D arrays of Fe$_{3}$O$_{4}$ nanoparticles have been constructed by encapsulating magnetite nanoparticles within Poly(ethylene oxide) nanofibers, by a modified solution spinning process. Electrospinning is a facile process for creating 1D nanostructures and a simple modification to the process renders a coaxial delivery mechanism that facilitates the construction of nanoparticle arrays. These hybrid 1D nanomaterials were structurally characterized by electron microscopy and the magnetic characteristics of these fiber encapsulated particle arrays were studied using vibrating sample magnetometry. Anisotropic magnetic behavior along different orthogonal axes (parallel and perpendicular) was observed even at room temperature with an appreciable increase in coercivity in the perpendicular configuration. Experimental work is underway to use these particle arrays as precursor materials for the creation of magnetite nanorods. [Preview Abstract] |
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K1.00071: Initiating magnetization switching in computational Fe nanopillars via local heating Sam Thompson, Greg Brown, Mark Novotny, Per Rikvold The use of high-coercivity materials in recording media assists in extending the areal information density by allowing smaller, more closely spaced bits. To achieve densities greater than one terabit per square inch, however, the necessary coercivity of the particles challenges the maximum applied field that can be attained by the write head. One proposed technique to overcome this dilemma is heat-assisted magnetization reversal (HAMR), in which a locally applied heat pulse lowers the coercivity, allowing the applied field to initiate switching. To model this, we employ micromagnetic simulations of iron nanopillars with thermal fluctuations that depend spatially and temporally on a solution of the heat equation corresponding to an initial heat pulse applied to the end of the pillar. For the case of an applied magnetic field parallel to the easy axis, the magnetization-switching behavior is explored as a function of total heat input and applied-field magnitude. [Preview Abstract] |
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K1.00072: Fabrication of magnetic trilayer stripes using interference lithography Meng Zhu, James Macarthur, Robert McMichael Both theoretical (PRB, 74, 024424, 2006) and experimental (APL, 90, 232504, 2007) studies of a single layer magnetic film edge have shown that the edge-mode of magnetization precession detected by ferromagnetic resonance (FMR) is an effective tool to probe magnetic properties of thin film edges. To extend the measurement technique to realistic devices such as spin-valves or tunnel junctions, magnetic multilayer stripes have to be fabricated. Here, we present the fabrication of Py/Cu/Co magnetic trilayer stripes by interference lithography. A resist stack consisting of positive photoresist 1805 and WIDE-B anti-reflective coating (ARC) is exposed by a blue laser at 405nm using Lloyd's mirror interferometer. Optimal soft-baking temperature of ARC results in an undercut during the development of the photoresist. This undercut facilitates the lift-off process after the evaporation of Py/Cu/Co trilayer. A uniform array of trilayer stripes with a period of $\sim $620nm was obtained. This work has been supported in part by the NIST-CNST/UMD-NanoCenter Cooperative Agreement and NIST CNST-NSF REU {\#}DMR-0754115. [Preview Abstract] |
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K1.00073: Enhanced magneto-optical effect in two-dimensional spin photonic crystals JinBae Kim, WonChang Nam, Nishad Deshpande, XingRi Jin, MinSoo Seo, Sung-Jae Lee, YoungPak Lee, JooYull Rhee, Kiwon Kim Patterned arrays of magnetic nanostructures have become one of the key issues in recent years because of their potential application to the information technology which utilizes optical and magnetic storage devices. In this study, we have successfully fabricated two-dimensional patterned arrays of Co by using the photolithography and the wet-etching process. The magnetic anisotropy, the magnetic domain structures, and the magnetization reversal process are investigated by means of magnetic-force microscopy and magneto-optical Kerr effect. The in-plane magnetization reversal process could be understood through a detailed investigation the field-dependent magnetic domain structures. The magneto-optical response is measured for both reflected and diffracted beams, and compared with the results of micromagnetic simulation. [Preview Abstract] |
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K1.00074: Fabrication and characterization of rectangular thin film planar loops for transformer applications Gregory A. Topasna, Daniela M. Topasna, Frank R. Powell This study focuses on optimizing the configuration and performance of a thin film planar loop that is flux linked to a short straight wire. Our calculations for the mutual inductance show its dependence on the geometry of the planar loop as well as on its location relative to the wire. We have fabricated and characterized various geometries and compared the data to the solutions predicted by our model. These results are used in designing the next generation of devices which will incorporate magnetic nanoparticles. [Preview Abstract] |
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K1.00075: MAGNETISM: DYNAMICS AND TRANSPORT |
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K1.00076: Laser-induced orbital and spin excitations in ferromagnets: Insights from a two-level system Guoping Zhang, Yihua Bai A recent element-specific and time-resolved measurement in Fe/Gd multilayers showed the laser-induced orbital and spin excitations proceed in unison and the spin-orbit ratio is held constant during the demagnetization. Here a two-level model shows that these orbital and spin excitations originate from state population and state interference effect. For an addressed state, spin and orbital dynamics are solely from the state interference, where the spin and orbital momenta oscillate with the laser frequency and match the dipole moment exactly, an unambiguous test case for time-resolved magneto-optical Kerr effect. For an undressed state, the inference effect introduces a rapid beating in orbital momentum, which is observed in the first-principles calculation in fcc Ni. The state population change leads to a constant spin-orbit ratio, which explains the linear dependence between spin and orbital momentum changes within 2 ps upon the arrival of pump pulse in ferromagnetic iron. [Preview Abstract] |
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K1.00077: Origin of light-induced precession of magnetization in ferromagnetic (Ga,Mn)As Eva Rozkotova, Petr Nemec, Daniel Sprinzl, Nada Tesarova, Petr Maly, Vit Novak, Kamil Olejnik, Jan Zemen, Miroslav Cukr, Tomas Jungwirth, Joerg Wunderlich The impact of femtosecond laser pulse leads to the precession of magnetization in (Ga,Mn)As, which can be detected by the time- resolved Kerr rotation (KR) technique. Even though this phenomenon is known for several years [1], the exact physical mechanism inducing the precession is still not clear [2,3]. We show, by a detailed comparison of the KR experimental results and the microscopic calculations of the magnetic anisotropy, that the precession is a consequence of the anisotropy field modification due to the laser pulse-induced change of hole concentration and lattice temperature. [1] A. Oiwa, H. Takechi, H. Munekata, J. Supercond. 18, 9 (2005).[2] Y. Hashimoto, S. Kobayashi, H. Munekata, PRL 100, 067202 (2008).[3] E. Rozkotova, P. Nemec, P. Horodyska, D. Sprinzl, F. Trojanek, P. Maly, V. Novak, K. Olejnik, M. Cukr, T. Jungwirth, Appl. Phys. Lett 92, 122507 (2008). [Preview Abstract] |
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K1.00078: Longitudinal Field $\mu $SR Study of Spin Dynamics and Onset of Magnetic Correlations in LiY$_{1-x}$Ho$_{x}$F$_{4}$ with 0.002$\le \quad x\le $ 0.10 R.C. Johnson, K. Chen, M.J. Graf The Ho$^{3+}$ ions in LiY$_{1-x}$Ho$_{x}$F$_{4}$ exhibit a crossover from single ion to spin glass behavior with increasing $x$. We have studied the longitudinal field depolarization rate for samples with 0.002 $\le \quad x \quad \le $ 0.10 over the temperature range 50 mK $\le \quad x \quad \le $ 50 K and for magnetic fields up to 0.1 T. For low concentrations, we find a peak in the temperature-dependent depolarization, as often observed in 1/$T_{1}$ NMR measurements on single molecule magnets (SMM); at high concentrations the depolarization rate increases monotonically with decreasing temperature. These results suggest that the difference in behavior of SMMs systems as seen in NMR and $\mu $SR measurements may be due to differences in the strength of the interactions between the magnetic clusters. [Preview Abstract] |
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K1.00079: A $^{51}$V NMR Investigation of the Quasi-1D Antiferromagnet BaCo$_{2}$V$_{2}$O$_{8 }$: Is there a New ordered Phase? T. Besara, L.L. Lumata, K.-Y. Choi, A.P. Reyes, P.L. Kuhns, N.S. Dalal, J.S. Brooks, H.D. Zhou, C.R. Wiebe We report on detailed $^{51}$V ( I=7/2) NMR spectral and spin-lattice relaxation time (T$_{1})$ measurements on the quasi-1D antiferromagnet BaCo$_{2}$V$_{2}$O$_{8}$. Our major focus was on probing the possible existence of the new ordered state in its field-induced phase above the critical field H$_{c}$=3.9T. This phase is believed to be of the incommensurate type, and thus quite amenable to investigation by NMR line shape and T$_{1}$ measurements. T$_{1}$ data were obtained using a spin-echo pulse sequence. Measurements were done on a single crystal, with the field parallel to the easy axis (c-axis). Details of the lineshape and T$_{1}$ analysis in terms of the evolution of the anticipated new phase will be presented. [Preview Abstract] |
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K1.00080: NMR and Spin Relaxation in Systems with Magnetic Nanoparticles: Effects of Size and Molecular Motion Natalia Noginova, Tracee Weaver, Alexandr Andreyev, Vadim A. Atsarkin To better understand the specifics of nuclear magnetic resonance and spin relaxation in systems with magnetic nanoparticles and test the limits of the outer sphere model for the diffusion related relaxation, iron oxide nanoparticle suspensions were studied in the dependence of the particle size, and for different degree of molecular motion. For the liquid suspensions with relatively small particles or clusters, spin relaxation rates well correspond to the theory, which predict maximum and decrease of the longitudinal rate and increase in the transverse rate with the increase in the effective radius, R. For the larger particle size $>$ 20 nm, as well as in cases of strong aggregation or slowdown of molecular motion, the relaxation rates are significantly lower than theoretical predictions. We discussed the results and frames of the fast-motion and fast-diffusion approximations. [Preview Abstract] |
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K1.00081: Magnetic properties of MnCr${}_{2}$O${}_{4}$ investigated by NMR Dong Young Yoon, Soonchil Lee, Yoon Seok Oh, Kee Hoon Kim We investigated the magnetic properties of spinel MnCr${}_{2}$O${}_4$ by nuclear magnetic resonance (NMR) and superconducting quantum interference device (SQUID). The magnetization vs. temperature curves under zero field cooling and field cooling show the ferrimagneic spiral structure below 20 K and the collinear ferrimagnet from 40 K to 20 K. The magnetization vs. time curve show the spin-glass-like behavior below 9 K. The canting angles of Mn and Cr spins at liquid He temperature are determined by NMR to be $50\,^{\circ}$ and $110\,^{\circ}$, respectively.In the ferrimagnetic spiral state, the nuclear spin-spin relaxation rate steeply increases with increasing temperature above 12 K, which expected to come from the fast fluctuation of electron spins. The NMR shows that the volume of the ferrimagnetic spiral domain decreases faster than the local magnetization as temperature increases. Furthermore, the domain volume shows the differences between cooling and warming processes. We depict that the ferrimagnetic spiral is embedded in the collinear ferrimagnet matrix. [Preview Abstract] |
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K1.00082: Direct Observation of Orbital Reorientation in MnV$_{2}$O$_{4}$ by NMR Jeong Hyun Shim, Euna Jo, Jooseop Lee, Soonchil Lee, Takehito Suzuki, Takuro Katsufuji The effect of magnetostriction on the orbital states in MnV$_{2} $O$_{4}$ was investigated by rotating the direction of magnetic field. The microscopic evidence of the orbital reorientation process, induced by the rotation, was found from the variation of V$^{3+}$ NMR spectrum. Despite the magnetic field is rotated from z axis to y axis, NMR spectrum of $0\,^{\circ}$ is almost identical to that of $90\,^{\circ}$, which reveals the reorientation of the orbital states of V$^{3+}$ ions following deformation of lattice. It was also observed that the reorientation process takes place suddenly when the magnetic field made $45\,^{\circ}$ with respect to the z axis. Such a sudden behavior implies that the orbital-lattice coupling is much stronger than the spin-orbital coupling in MnV$_{2}$O$_{4} $. [Preview Abstract] |
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K1.00083: In-plane and out-of-plane ferromagnetic resonance investigations of epitaxial CrO$_{2}$ (110) Hwachol Lee, Krishna Chetry, Claudia Mewes, Arunava Gupta, Tim Mewes We report on in-plane and out-of-plane ferromagnetic resonance experiments to determine the magnetization damping in epitaxial CrO$_{2}$(110) thin films. The films were grown on TiO$_{2}$ (110) substrates using chemical vapor deposition (CVD) with a CrO$_{3}$ precursor [1]. Ferromagnetic resonance experiments as a function of the in-plane angle confirm a uniaxial in-plane anisotropy with the easy axis along the c-axis. To determine the effective damping constant in the films we carried out frequency dependent FMR measurements with the field aligned parallel to the in-plane easy axis of the film and along the film normal. Both measurements show a weak dependence of the linewidth on the microwave frequency once the sample is fully saturated. The effective damping constant as determined by the frequency dependent measurements is very small. Over the experimentally accessible frequency range (4-60 GHz) the dominant contribution to the ferromagnetic resonance linewidth is therefore extrinsic in nature. References: [1]: X. W. Li, A. Gupta, and G. Xiao, Appl. Phys. Lett. \textbf{75}, 713 (1999). [Preview Abstract] |
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K1.00084: Broadband Ferromagnetic Resonance Using Coplanar Waveguides Adam Reed, I.H. Lee, Y. Obukhov, D. Pelekhov, P. Hammel Many schemes to exploit the spin of the electron involve microscale or nanoscale ferromagnets. Ferromagnetic resonance (FMR) is a powerful probe of the magnetic properties of magnetic materials. For many applications multi-frequency operation is desirable; however, conventional FMR operates at a fixed frequency. We present a broadband FMR detection scheme based on coplanar wave guides. Increasing the sensitivity of the FMR experiment will permit the study of micron and nano-sized ferromagnets, such as ferromagnetic nanowires.\footnote{S. Pignard, \textit{et al.}, ``Ferromagnetic Resonance in Submicron Metallic Wires,'' \textbf{IEEE Transactions on Magnetics}, Vol. 36, No. 5, pp. 3482 -- 3484, September 2000.} Understanding nanomagnetic structures is significant not only to fundamental physics, but for potential applications such as high density magnetic storage. [Preview Abstract] |
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K1.00085: Excitations in the chiral spin liquid Darrell Schroeter Recently, a spin-Hamiltonian was presented [Schroeter et al, Phys. Rev. Lett. \textbf{99}, 097202 (2007)] for which the chiral spin liquid is the exact ground state. This poster will present a numerical study of the excitations of the model, including results obtained by exact diagonalization of the model on 16 and 25-site lattices. [Preview Abstract] |
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K1.00086: Electrical and Optical Characterization of Spin Transfer Torques Joshua Emerick, S.C. Parks, K. Li, A. Hauser, J. E. Thompson, J. Ciraldo, J. Lucy, F. Y. Yang, E. Johnston-Halperin The spin-transfer torque (STT) phenomenon is a direct outgrowth of giant magnetoresistance (GMR) in the regime of high current density. Investigations of this phenomenon have contributed to improved understanding of fundamental processes and revealed the potential for technological innovation. To further this exploration, we have constructed an instrument that simultaneously measures microwave electrical response and magnetization in an external magnetic field of up to 1 T. The microwave probe is sensitive at frequencies up to 30 GHz and the magneto-optical Kerr effect (MOKE) magnetometer is configured to measure the magnetization of the active region during operation (resolution of $\sim $ 100 $\mu $m). We present the experimental configuration of this instrument and calibration data from prototype samples. The ability to directly measure layer orientation for active devices provides a powerful tool for the investigation of STT. [Preview Abstract] |
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K1.00087: Pure Spin Current Injection through Superconductive/Normal Metal Ohmic Interface Kohei Ohnishi, Takashi Kimura, YoshiChika Otani In past few years, spin-dependent transport properties in nano- structured systems have drawn considerable attention owing to potential applications in spintronics. Spin transport has so far been investigated both experimentally and theoretically much more intensively in normal- or semi-conductors than in superconductors. However recent theoretical studies on the spin transport in superconductor predict the intriguing phenomena such as the non-linearity and the control of superconductivity that may lead to functional superconductive spintronic devices. Therefore, it is urgent to elucidate experimentally the spin transports in superconductor. Here, we investigate the influence of pure spin currents on superconductivity in a lateral structure consisting of superconductive Nb, normal metal Cu and ferromagnetic Ni-Fe wires. Using nonlocal spin injection technique, we found that pure spin current injection into the superconductive Nb wire induces the voltage drop along the wire. This can be understood as conversion from the spin current to the supercurrent via the quasi-particle current. [Preview Abstract] |
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K1.00088: Spin-dependent conductance switching in organic molecular junctions Yun-Wen Chen, Luis A. Agapito, Hai-Ping Cheng We use density-functional theory to calculate the electronic transport through single molecules attached to capped (5,5) carbon nanotubes (CNTs) as leads. We observed a strong variation in the electrical conductance with respect to the spin-state of the junction. The singlet state exhibits high conductance whereas the triplet low. The deformation of the CNTs' cap structure, upon covalent adsorption of the phenyl rings, triggers the spin dependence in the organic junctions. Two different $\pi$-conjugated phenylene-vinylene-containing molecules were tested, yielding similar behavior. [Preview Abstract] |
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K1.00089: Giant positive magnetoresistance in Co@CoO nanoparticle array Hui Xing, Wenjie Kong, Chaehyun Kim, Shouheng Sun, Zhuan Xu, Hao Zeng The spin-dependent charge transport has been extensively studied due to its technological applications in information industry. Of particular interests are magnetic granular systems consisting of magnetic grains embedded in a nonmagnetic matrix, which typically exhibits negative granular MR. Interestingly, anomalous positive MR in granular systems has been reported in different materials [1]. Possible origins that can account for the positive MR include: ordinary MR caused by the curving of the carrier trajectories in the magnetic field6, shrinkage of the wave functions of localized electronic states due to the external field7, and suppression of hopping paths due to the Zeeman splitting of the localized state8. Here we present magnetotransport studies in self-assembled Co@CoO nanoparticle arrays which provide model granular systems. Efros Shklovskii variable range hopping to Mott variable range hopping crossover occurs at around 25K. Giant positive MR with its saturation field increasing with increasing temperature is observed, and is well explained by the Zeeman splitting of the localized states that suppresses the spin dependent hopping paths in the presence of magnetic field. \\[3pt] [1] K. A. Matveev et al., ``Theory of hopping magnetoresistance induced by Zeeman splitting,'' Physical Review B \textbf{52} (7), 5289 (1995). [Preview Abstract] |
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K1.00090: ABSTRACT WITHDRAWN |
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K1.00091: Measurements of the Contact Resistance Between GaMnAs and Different Metals Noah Opondo, Grant Riley, Robert Tolley, Tyler Brest, Xinyu Liu, Jacek Furdyna, Khalid Eid We have measured the contact resistance between the ferromagnetic semiconductor GaMnAs and each of the metals silver, aluminum, cupper, and gold. We employed the linear-contact-array geometry$^{[1]}$ for measuring the contact resistance for a range of temperature from 10 K to 300 K. Our samples were made using photolithography, wet etching, and metal deposition. Even though there is a depletion zone between the heavily doped p-type semiconductor GaMnAs and the metals, yet the very high carrier concentration in GaMnAs causes the contact resistance to be quite small and ohmic. We will also discuss the possible mechanisms of conduction at the interface. Determining the contact resistance of GaMnAs is important for spin injection experiments. This work is supported by the Research Corporation for Science Advancement \newline [1] R.E. Williams, Gallium Arsenide Processing Techniques, Second Edition (Artech House, Norwood, MA, 1990) [Preview Abstract] |
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K1.00092: Vortex-core reversal by rotating currents Thomas Kamionka, Michael Martens, Markus Bolte, Guido Meier, Benjamin Krueger, Kang Wei Chou, Tolek Tyliszczak, Michael Curcic, Bartel Van Waeyenberge, Hermann Stoll The investigation of the interaction between a spin-polarized current and the magnetization of a ferromagnet is of great interest. One concept for data storage is to use the current- induced switching of the vortex-core polarization, i.e. the out- of-plane component of the magnetization in the center of a micronsized permalloy element. It has been shown both theoretically [1] and experimentally [2] that the polarization can be switched selectively by resonant field excitation. We carried out time-resolved scanning transmission X-ray microscopy while exciting the vortex core with rotating currents of varying frequency, amplitude and rotation sense. We observed vortex core switching, and by analyzing the gyration phase with respect to the exciting current we derive whether the Oersted-field or the spin torque mainly contributes to the excitation and causes the switching process. [1] S. K. Kim et al., Appl. Phys. Lett. \textbf{92}, 022509 (2008). [2] M. Curcic et al., Phys. Rev. Lett. \textbf{101}, 197204 (2008). [Preview Abstract] |
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K1.00093: Antivortex-core switching as write process in random access memories Andre Drews, Toru Matsuyama, Lars Bocklage, Markus Bolte, Guido Meier, Benjamin Krueger, Stellan Bohlens Magnetic vortices observed in ferromagnetic thin films have received a great deal of interest in recent years. The topological counterpart of a vortex, the antivortex, has not been investigated as intensively so far. Like vortices, magnetic antivortices gyrate when excited by alternating fields or spin-polarized currents. When excited by alternating currents and fields simultaneously, the superposition of the forces leads to an enhancement or suppression of the gyration amplitude, depending on the orientation of the in-plane magnetization, i.e., the c-value of the antivortex, and the antivortex-core polarization p. Thus the c-p-dependent amplitude variation of antivortex core gyration can lead to antivortex-core switching and thus to write binary data. Reading out of the data can be done by detecting the amplitude of gyration, e.g. by inductive loops. A logical zero (one) is represented by a small (large) gyration amplitude, i.e., suppression (enhancement) of the gyration. Due to the c-p-dependence of the excitation amplitude, an ensuing toggle switching is impossible. This technique allows bringing the antivortex into a distinct binary state without the need of a reading process before writing the bits. [Preview Abstract] |
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K1.00094: MAGNETISM: GENERAL AND THEORY |
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K1.00095: Local hyperfine field systematic of sp impurities on (001) and (111) Ni Surfaces Marcus Tovar Costa, Alexandre de Oliveira A self-consistent calculation of the local magnetic moments and the hyperfine fields is performed, considering a systematic of n-\textit{sp}, (n=4,5) impurities on (001)Ni and (111)Ni surfaces and sub-layers. A simple model is adopted which is, in principle, an extension on that of Daniel and Friedel. The behavior obtained for the hyperfine fields for each one of the series namely above is drastically different from that obtained for the bulk. The calculations of the electronic structure of the systems are based on a full multi-orbital tight-binding model and using the Green function formalism. The effect of next-neighbor perturbation on the magnetic properties, due to the lost of translational invariance introduced by the impurity, is taken into account in the present picture. The theoretical results are in agreement with known experimental data. [Preview Abstract] |
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K1.00096: Long-range behavior of exchange bias in CoFe/FeMn-based multilayers Nam Dao, Wei Chen, Kevin West, David Kirkwood, Jiwei Lu, Stuart Wolf CoFe/FeMn-interface-based multilayers were grown in magnetic field and at room temperature. The exchange bias field $H_{\mathrm{EB}}$ depends strongly on the order of depositions and is much higher for CoFe/FeMn than FeMn/CoFe bilayers. By combining the two bilayer structures into symmetric CoFe/FeMn ($t_{\mathrm{FeMn}}$)/CoFe trilayers, $H_{\mathrm{EB}}$ is enhanced for both the top and bottom CoFe layers. Enhancements of exchange bias are also observed by reducing the FeMn thickness $t_{\mathrm{FeMn}}$ of the trilayers. These results evidence the propagation of exchange bias between the two CoFe/FeMn and FeMn/CoFe interfaces mediated by the FeMn antiferromagnetic order. Furthermore, the exchange bias is even considerably increased when a thin Al or Mg layer is inserted into the CoFe/FeMn interface (i.e., CoFe/Al/FeMn or CoFe/Mg/FeMn) and persists for the insertion layer thicknesses of up to about 1.5 nm. These results strongly indicate that exchange bias is not a pure interfacial phenomenon, but mainly governed by possible long-range couplings such as dipole-dipole and RKKY between the antiferromagnetic uncompensated spins and the ferromagnetic layer. [Preview Abstract] |
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K1.00097: Direct Measurement of the Bose-Einstein Condensation Universality Class in NiCl$_{2}$-4SC(NH$_{2})_{2}$ at Ultralow Temperatures Liang Yin, J.S. Xia, N.S. Sullivan, V.S. Zapf, A. Paduan-Filho In this work, we demonstrate field-induced Bose-Einstein condensation (BEC) in the organic compound NiCl$_{2}$-4SC(NH$_{2})_{2}$ using ac susceptibility measurements down to 1 mK. The Ni S=1 spins exhibit 3D XY antiferromagnetism between a lower critical field H$_{c1} \quad \sim $ 2 T and a upper critical field H$_{c2} \quad \sim $ 12 T. The results show a power-law temperature dependence of the phase transition line H$_{c1}$(T) -- H$_{c1}$(0) = aT$^{\alpha }$ with $\alpha $ = 1.47$\pm $ 0.10 and H$_{c1}$(0) = 2.053 T, consistent with the 3D BEC universality class. Near H$_{c2}$, a kink was found in the phase boundary at approximately 150 mK. [Preview Abstract] |
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K1.00098: Magnetization Plateau of Classical Ising Model on Shastry-Sutherland Lattice Ming-Che Chang, Min-Fong Yang Magnetization of the classical antiferromagnetic Ising model on the Shastry-Sutherland lattice is investigated using the tensor renormalization group approach. We find a single magnetization plateau at 1/3 of the saturation value and investigate its dependence on temperature and frustration. The spin configuration of this plateau has also been determined. [Preview Abstract] |
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K1.00099: Phase transitions in site diluted systems of Ising dipoles Juan J. Alonso, Julio F. Fernandez By Monte Carlo simulations, we study dilute systems of Ising
magnetic dipoles on simple cubic lattices.
Dipoles are restricted to point along the $z$ axis and are
randomly placed in a fraction $x$ of the $L^3$ sites of the lattice.
For $x_c < x\le1$ where $x_c \simeq 0.6$ we find a thermally
driven second order transition between a paramagnetic
and a dipolar antiferromagnetic (AF) phase at a temperature
$T_o$ which can be fitted by
$k_B T_o/ \varepsilon_d \simeq 4.3 (x-x_c)^{0.6}$,
where $\varepsilon_d$ is a nearest neighbor dipole-dipole
interaction energy.
We explore whether an equilibrium spin glass phase exists for $x
< x_c$.
To this end, we study the spin glass overlap parameter $q$
between equilibrium configurations which we obtain
from tempered Monte Carlo simulations for systems of $N$ dipoles
in the range $40 \le N \le 500$.
For $x < x_c$ we find no AF phase transition. However, we
observe rather large AF
correlation lengths at low temperatures for $0.2 |
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K1.00100: Ab-Initio Study of Magnetic Properties of M-doped (M = Cr or V) ZnGeN$_2$ J. Rufinus The current interest in the emerging field of semiconductor spintronics is mostly focused on transition metal-doped binary materials. Recently, however, the explorations of transition metal-doped ternary semiconductors have intensified, due to some experimental confirmations of high Curie temperature in chalcopyrite compounds. In ternary materials, there are possibilities of having ferromagnetic or antiferromagnetic configurations, depending on which metal site was substituted by the dopant. A donor (i.e. releasing electrons) will be produced when a metal atom substitutes a lower valent site, while an acceptor (i.e. releasing holes) will be produced when a metal atom substitutes a higher valent site. Only holes are expected to lead to ferromagnetism. A density functional theory within generalized gradient approximation study was performed on M-doped (M = Cr or V) ternary material ZnGeN$_2$. The objective of this study is to determine whether substitutional transition metal in a group II (Zn) site and in a group IV (Ge) site will be ferromagnetic or antiferromagnetic. Our results show that both Cr- and V-doped ZnGeN$_2$ to be ferromagnetic, independent of the substitution sites. Additionally, formation of half-metallic ferromagnetism is possible in this type of material. [Preview Abstract] |
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K1.00101: Spin-glass transition of magnetic dipoles with random anisotropy axes Julio F. Fernandez, Juan J. Alonso We study partially occupied lattice systems of classical magnetic dipoles which point along randomly oriented axes. Only dipolar interactions are taken into account. From Tempered Monte Carlo simulations, we obtain equilibrium results for $xL^3$ dipoles, randomly located on $L^3$ simple cubic lattice sites, for $L=4, 6,8$ and $12$, with an $x (=0.35,0.5$ and $1)$ fraction of occupied sites. The numerical evidence we obtain supports the existence of an equilibrium spin glass phase below a transition temperature $T_o$, given by $k_BT_o= (0.9\pm 0.1)x\varepsilon_d $, where $\varepsilon_d$ is a nearest neighbor dipole-dipole interaction energy. The spin glass overlap parameter $q$ is statistically distributed, and its mean square deviation follows the rule, $\langle \delta q^2\rangle \simeq 0.25 \langle\mid q \mid \rangle^2 T/x$ in the spin-glass phase. [Preview Abstract] |
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K1.00102: A Finite Temperature First-Principles Model for Spin Fluctuations Yi Wang, ShunLi Shang, Long-Qing Chen, Zi-Kui Liu In the past decades, the steady increasing in both computer power and the efficiency of computational methods has made it realistic the accurate first-principles calculations of material properties at finite temperature. The current frontier is how to extend the first-principles approach when it becomes important of the role of the internal degrees of freedom, which is beyond the spatial degrees of freedom of a material. One of important examples is the interplay between magnetic and lattice fluctuations at finite temperature. Solution of this enigma can reveal the microscopic origin of the novel properties of many materials. Hereby we propose a general framework to calculate the Helmholtz energy for system with spin fluctuations. The theory has been applied for EuTiO3. The energetics includes 256 spin configurations, of a 2x2x2 supercell, which are reduced to 14 not equivalent ones. We find a Schottky anomaly in the specific heat at T = 5.8 K which is matching closely to the Neel Temperature of 5.5 K for EuTiO3. [Preview Abstract] |
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K1.00103: Study of the magnetic structures of the atacamite and botallackite forms of Cu$_{2}$(OH)$_{3}$Cl in terms of first principles DFT calculations Jinhee Kang, Changhoon Lee, Mike H. Whangbo The atacamite and botallackite forms of Cu$_{2}$Cl(OH)$_{3}$ are made up of edge- and corner-sharing Cu(OH)$_{4}$Cl$_{2}$ octahedra. Each polymorph consists of two slightly different types of Cu(OH)$_{4}$Cl$_{2}$ octahedra, with their Cu x$^{2}$-y$^{2}$ magnetic orbitals contained in the Cu(OH)$_{4}$ square planes. Atacamite and botallackite are different in the way the Cu(OH)$_{4}$ square planes are connected, but their magnetic properties of atacamite and botallackite are quite similar. To explain these observations, the crystal structures of the two polymorphs were optimized by first principles DFT calculations. We then evaluated the spin exchange interactions of the two polymorphs using the optimized structures on the basis of DFT calculations. To a first approximation, both polymorphs were found to be described by a uniform 1D antiferromagetic chain model with spin frustration arising from the next-nearest-neighbor interactions. Implications of these observations were explored. [Preview Abstract] |
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K1.00104: Electromagnetic response of the planar metamaterial consisting of cut-wire pair and continuous wire Vu Dinh Lam, Nguyen Thanh Tung, JinWoo Park, SeongJae Lee, YoungPak Lee The left-handed materials (LHMs) attract more and more attention in recent years because of their intriguing physical properties and applications. Recently, a simple structure, the so-called cut-wire pair (CWP) was proposed and successfully used as the magnetic component in fabricating the LHMs. The simple geometry of CWPs means that such structures can be scaled down to the nanometer dimension much more easily than those based on the conventional split-ring resonator structures. In addition, the main advantages of the CWP structure comparing to the other structures is its ability to produce a strong magnetic resonance for the normal-to-plane propagation with only one CWP layer. In this report, we present the influence of lattice constants on the electromagnetic properties of CWP structures in the microwave frequency regime. In addition, we also discussed on how the lattice constants affect the LH behavior of combined structure consisting of CWP and continuous wire. A good agreement between the measurement and the numerical simulation is achieved. [Preview Abstract] |
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K1.00105: Magneto-optical imaging of magnetic domain pattern produced by intense femtosecond laser pulse irradiation Jaivarhan Sinha, Shyam Mohan, S.S. Banerjee, S. Kahaly, G. Ravindra Kumar An important and intriguing area of research is laser plasma generated giant magnetic field pulses. Interaction of ultrashort high intensity laser pulses with matter involves several mechanisms for generating ultrastrong magnetic fields. By irradiating a magnetic recordable tape constituting of $\gamma $-Fe$_{2}$O$_{3}$ particles with an intense p-polarized femtosecond laser pulses ($\sim $ 10$^{16}$ W cm$^{-2}$, 100fs), we have found complex magnetic field patterns stored in the tape. We image the local magnetic field distribution around the irradiated region [1] using the high sensitivity magneto-optical imaging technique. We understand the complex magnetic domains patterns recoded on the tape in terms of interesting instabilities [1] generated in the plasma produced during the irradiation of the tape with intense laser pulses. \\[0pt] [1] Jaivardhan Sinha, Shyam Mohan, S. S Banerjee, S. Kahaly, G. Ravindra Kumar, Phys. Rev. E \textbf{77}, 046118(2008). \textit{*satyajit@iitk.ac.in} [Preview Abstract] |
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K1.00106: INSTRUMENTATION AND MEASUREMENT SCIENCE |
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K1.00107: Low Temperature Conducting Probe Microscopy of Carbon Nanotubes Ivan Borzenets, Henok Mebrahtu, Ulas Coskun, Mathew Prior, Gleb Finkelstein In order to measure local electrical properties of nano-devices at liquid He temperatures, we have built an atomic force microscope. The instrument is outfitted with a conducting tip, which allows us to acquire both topography and electrical signals at the same time. The AFM has a scan window of up to 10 microns at low temperature and allows one to translate the sample laterally by up to a millimeter. To find a specific device within this range, the samples structure has to be specially optimized by addition of the ``search pattern''. The electrically conducting tip of the AFM allows us to make a variety of measurements such as: gating and tunneling, and to apply a mechanical force to the sample. [Preview Abstract] |
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K1.00108: Fabrication Of Nickel-tipped Cantilevers for Magnetic Resonance Force Microscopy Steven Hickman, E.W. Moore, S. Lee, S.R. Garner, J.C. Ong, S. Kuehn, J.A. Marohn Magnetic resonance force microscopy (MRFM) is a technique that may one day allow us to acquire magnetic resonance images of single molecules. To date we have demonstrated that MRFM can achieve a sensitivity of $\sim $10$^5$ proton spins, using a custom-fabricated silicon cantilever with a 9 micron diameter magnet tip. By making improved magnetic tips and mitigating surface dissipation, it may be possible to achieve single-proton sensitivity. Achieving the attonewton force sensitivity necessary to image single proton spins requires custom-fabricating cantilevers with extreme dimensions. In MRFM the force exerted on the cantilever, per spin, is proportional to the field gradient from the cantilever's magnetic tip. Achieving single proton sensitivity therefore also requires dramatically reducing magnet size. We have developed an electron-beam-lithography(EBL) process for batch fabricating nanoscale tip magnets on ultrasensitive silicon cantilevers. Research by our group has shown that surface induced dissipation is a major source of noise, which can be minimized by fabricating the magnets overhanging the end of the cantilever. We will present 50-600 nm wide nickel overhanging magnets fabricated by EBL and isotropic plasma etching. With our designed cantilever, we expect a sensitivity of better than 10$^3$ protons. [Preview Abstract] |
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K1.00109: Controlling and measuring substrate stiffness for cell motility studies Lindsay Runyan, Peter Hoffmann, Karen Beningo Cell motility and differentiation is generally considered to be controlled by mostly chemical cues. However, recent evidence has shown that mechanical cues may be just as important. Here, we present a study to create patterned substrates that allow to test the hypothesis that cells prefer substrates of certain mechanical moduli and will migrate towards these substrates. In this context, we present a discussion of optimal methods to measure substrate moduli at the local level and compare different methods with respect to ease of implementation, data interpretation and reliability. [Preview Abstract] |
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K1.00110: Measuring the energy landscape of complex bonds using AFM Essa Mayyas, Peter Hoffmann, Lindsay Runyan We measured rupture force of a complex bond of two interacting proteins with atomic force microscopy. Proteins of interest were active and latent Matrix metalloproteinases (MMPs), type 2 and 9, and their tissue inhibitors TIMP1 and TIMP2. Measurements show that the rupture force depends on the pulling speed; it ranges from 30 pN to 150 pN at pulling speeds 30nm/s to 48000nm/s. Analyzing data using an extended theory enabled us to understand the mechanism of MMP-TIMP interaction; we determined all physical parameters that form the landscape energy of the interaction, in addition to the life time of the bond and its length. Moreover, we used the pulling experiment to study the interaction of TIMP2 with the receptor MT1-MMP on the surface of living cells. [Preview Abstract] |
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K1.00111: Scanning tunneling microscope-cathodoluminescence (STM-CL) imaging of the GaAs/AlGaAs (110) cross-section: evaluation of spatial resolution and imaging area shift Kentaro Watanabe, Yoshiaki Nakamura, Shigeyuki Kuboya, Ryuji Katayama, Kentaro Onabe, Masakazu Ichikawa We studied local optical properties of AlGaAs/GaAs multilayer structures by scanning tunneling microscope cathodoluminescence (STM-CL) spectroscopy, where low-energy ($\sim $100 eV) electrons field-emitted from STM tips were used as bright excitation sources. The STM-CL measurements were performed at the (110) cross-sectional surface of the AlGaAs/GaAs multilayer structure. We found that the field-emitted electron beam (FEEB) diameter mainly determined the spatial resolution of this system in STM-CL spectroscopy by evaluating some contributors: the thermalization length and the diffusion length of generated hot electrons. We also clarified that the shift of the STM-CL measurement position from the STM tip position was caused by the FEEB angled from the surface normal. [Preview Abstract] |
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K1.00112: Twisted Pair Cryogenic Low Pass Filters Woon Song, Mushtaq Rehman, Sang-Wan Ryu, Yonuk Chong For precise electronic-transport measurement at low temperatures, low pass filters are usually required to block external interference. However, since filters designed for the RF often don't work at microwave frequencies, separate low pass filters such as copper powder filter have been used widely, even though the copper powder filter is bulky for many applications. We fabricated a low pass filter consisting of twisted pair of manganin wires wrapped in a copper tape, which can be made compact. We measured its microwave transmission characteristics with various filter parameters such as length, insulation thickness and twisted turns per unit length and compared the result with copper powder filter. The constructed filter with length of one meter showed a high attenuation (more than 60 dB at 1 GHz) with cutoff frequency of about 8 MHz. This result is in good agreement with the theoretical model, which assumes the cable as a resistive transmission line. [Preview Abstract] |
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K1.00113: Data Encoding on Continuous Wave THZ Signals for Sensing Ke Su, Zhiwei Liu, Lothar Moller, John F. Federici The intrinsic advantages of potentially ultra-high bandwidth, unrestricted frequency bands, and relative secure channels lead to a steadily increasing interest in THz communications. Other than for communication purposes, data modulation on THz signals could find application in sensing. When imprinting code sequences on pulse trains, ranging information from far distance scattering objects can be obtained to define selective measurement intervals. This technique is known from M-sequence radar where digital beam modulation enhances the system's unambiguous range. In this paper we describe a method for encoding continuous wave THz radiation via rapid, voltage controlled phase modulation. An electro-optic phase modulator is used to directly modulate the THz wave through a 2$\pi $ phase shift. While data rates in the MB/s range are demonstrated, the method should be capable of data transmission rates in the hundreds of MB/s range. Applications of the data modulation to sensing applications will be discussed. [Preview Abstract] |
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K1.00114: Metal embedded Fiber Brag Grating Sensors Chooda Khanal, Garman Vargas, Kantesh Balani, Anup Keshri, Carmen Barbosa, Arvind Agarwal, Roberto Panepucci A novel method of embedding optical fibers and optical fiber sensors, inside metallic structures will be discussed. We specifically report results for embedding fiber bragg grating sensors in an aluminum coating onto a steel plate. Characterization of an embedded FBG sensor and its effects on the sensor operation are also presented. Temperature sensitivity and the strain sensitivity will be discussed. The novel high throughput deposition method show the potential of embedding optical sensors onto metallic structures which make it suitable for many engineering applications in biomedical, civil, mechanical and aeronautical, among other fields. [Preview Abstract] |
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K1.00115: Image contrast dependence on the field emitter in near field emission scanning electron microscopy Olivier Scholder, Taryl Kirk, Lorenzo De Pietro, Thomas Baehler, Urs Ramsperger, Danilo Pescia In conventional scanning electron microscopy (SEM) the lateral resolution is limited by the electron beam diameter impinging on the specimen surface. Near field emission scanning electron microscopy (NFESEM) provides a simple means of overcoming this limit; however the most suitable field emitter remains to be determined. NFESEM has been used in this work to investigate the W (110) surface with single crystal Tungsten tips of (310), (111), and (100)-orientations. The topographic images generated from both the electron intensity variations and the field emission current indicate higher resolution capabilities with decreasing tip work function than with polycrystalline Tungsten tips. The confinement of the electron beam transcends the resolution limitations of the geometrical models, which are determined by the minimum beam width. Moreover the electron intensity images show more detail with higher resolution than field emission current imaging. This implies that the electron yield is more sensitive to additional parameters, which may be the local work function, specimen curvature, primary beam energy, and detector sensitivity. [Preview Abstract] |
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K1.00116: Quantitative analysis of scanning force microscopy data using harmonic models Thomas Henze, Klaus Schroeter, Albrecht Petzold, Thomas Thurn-Albrecht The separate identification of dissipative and elastic force contributions in Atomic Force Microscopy (AFM) is discussed. We show that within a harmonic approximation the interaction of the AFM tip with the sample surface can be described by average interaction parameters, namely an effective elastic tip-sample interaction $k_{ts}$ and an effective dissipation $\alpha_{ts}$, which can be extracted in a simple way from measured data. The method is applied to force spectroscopy curves on hard and soft polymeric model surfaces. The approach enables a thorough discussion of the influence of experimental parameters on the measured data. In imaging a clear identification of phases in systems with hard-soft contrast as for instance in semicrystalline polymers is made possible. [Preview Abstract] |
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K1.00117: A nanoscopic study of degradation of optical recording media Kwonjae Yoo, H.R. Kang, K.J. Kim, B.C. Woo, D.A. Ha, N.H. Lee, Wan S. Yun, M.Y. Yun The life expectancy of optical recording media usually depends on loss of physical property, that is, optical elements in digital recording unit cells eventually will be disappeared by physical and chemical degradation. Nevertheless, the study of information loss in the element by natural degradation is not so many, which need a practical~and scientific investigation in detail. Here we present the results of the life expectancy of archiving DVDs and their optical and atomic force microscopy studies on the recording unit cells by employing accelerated aging tool. Our results showed that archiving DVDs, which have double reflective layers, indicate the acceptable life expectancy over one hundred years. Additional optical, Surface Kelvin probe microscopy (SKPM) and electrostatic force microscopy (EFM) measurements clearly reveal the degradation of dye layer depending on accelerated aging time. The correlation between those physical quantities and PI errors might lead a key factor for the development of new life expectancy estimation method of optical recording media. [Preview Abstract] |
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K1.00118: In-situ TEM observation on STM tunneling gap Suhyun Kim, Yasumasa Tanishiro, Kunio Takayanagi Transmission Electron Microscope and Scanning Tunneling Microscope in an ultra high vacuum environment (UHV-TEM-STM) have been combined to simultaneously perform both high resolution TEM and atomically resolved STM experiments. This system was constructed for in-situ investigation of physical property of impurity atoms embedded below semiconductor surface. To image TEM and STM at the same time, crucial requirement is that, the STM image must be acquired under the electron beam irradiation. As a preliminary test, we used HOPG (Highly Oriented Pyrolytic Graphite) sample and tungsten tip as schematically shown in Fig 1(a). Fig 1(b) shows an atomic resolution STM image of HOPG obtained with 300mV sample bias and 3nA tunneling current even in the condition of the electron beam irradiation on the tip. TEM image can be simultaneously acquired by performing In-situ TEM observation on STM tunneling gap formed between the tip and a thin sample. Fig 1(a) Geometry of STM observation on STM tunneling gap Fig 1(b) STM image of HOPG obtained with 300mV sample bias and 3nA tunneling current [Preview Abstract] |
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K1.00119: Micromechanical devices for magnetization measurements at high magnetic fields and low temperatures J. Paster, K. Ninios, H.B. Chan, L. Balicas We constructed micromechanical faraday balance magnetometers for measuring the absolute value of the magnetization of very small samples ($\sim $ 1 ugram) at high magnetic fields and a wide range of temperatures. The magnetometers consist of a movable polysilicon plate (500 by 500 micrometers) suspended by four springs above a fixed electrode. When small samples of the magnetic material are placed at the center of the movable plate, the magnetic field gradient creates a force on the sample that changes the capacitance between the plate and electrode. The absolute magnetization of the sample can be determined provided that the magnetic field gradient is known. Springs with different shapes are designed to minimize the response to magnetic torque. Experimental results will be compared to numerical simulation. [Preview Abstract] |
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K1.00120: X-ray Young's double slit experiment and other aspects of kinoform X-ray prism arrays A.F. Isakovic, K. Evans-Lutterodt, A. Stein, J.B. Warren, S. Narayanan, A.R. Sandy Numerical design and large aspect ratio nanofabrication techniques [1] were employed to produce kinoform prisms and lenses for the purpose of focusing, deflecting and characterizing hard X-ray synchrotron radiation. Purely refractive lenses are hampered by the effects of absorbtion, which limits the numerical aperture of the lens and hence the optic resolution. Kinoform lenses allow one to circumvent these limitations, with the trade-off of an energy bandwidth for the optic. Purely refractive prisms have similar limitations due to absorption, and consequently we choose to fabricate kinoform prisms and study their properties experimentally and theoretically. In particular we analyze theoretically the extent to which the kinoform prism can be modeled by a simple prism, and the effect of nanofabrication precision on the prism performance. The focus of the nanofabrication efforts is in balancing out patterning of a large area and a deep anisotropic etch. Experimental characterization is performed at APS 8-ID beamline. We observed, controlled and measured interference fringes, in analogy with the Young's double slit experiment. [1] A. F. Isakovic \textit{et al.}, JVST-A \textbf{26}, 1182 (2008) and J. Synchr. Rad. \textbf{16}. [Preview Abstract] |
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K1.00121: Characterization and Modeling of Off-Specular Neutron Scattering for Analysis of Two Dimensional Ordered Structures Christopher Metting, Robert Briber, Paul Kienzle, Brian Maranville, Julie Borchers, Joe Dura, Chuck Majkrzak Work is currently being done to expand neutron reflectometry to the off-specular regime for the characterization of thin films with two-dimensional, ordered in-plane structures. The combination of in-plane information obtained from off-specular analysis with the depth-profile that is routinely determined from reflectivity data can produce a detailed description of both the structure and magnetic characteristics of these films. The University of Maryland along with the NIST Center for Neutron Research (NCNR) are developing modeling and fitting software which can easily be integrated into existing reflectivity analysis package such as \textit{Reflpak},\footnote{http://www.ncnr.nist.gov/reflpak/} and will expand the general accessibility of off-specular neutron reflectometry. In this presentation, we show aspects of the current \textit{Python}\footnote{http://www.python.org/} software including in-plane feature representation, model calculations using the Born Approximation, and fits. Also, applications of the modeling capabilities to data from a patterned Au film will be presented. [Preview Abstract] |
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K1.00122: X-rays and Magnetism $–$ A Perfect Match Hendrik Ohldag, Elke Arenholz, Yves Acremann, Andreas Scholl, Joachim St\"{o}hr Today's fundamental and applied magnetism research is particularly focused on magnetic materials that are suitable as magnetic sensors, spin valves, spin transistors or magnetic media consisting of complex magnetic multilayer structures. Investigations in this area are concerned with the origin of magnetic coupling, spin transport across interfaces, magnetic properties of magnetic oxides and complex magnetic multilayers. Dichroism x-ray absorption spectroscopy (XAS) using synchrotron radiation represents a unique tool to understand complex nanomagnetic samples. The power of XAS is that it provides a possibility to address individual magnetic properties of different elements in a sample and a way to distinguish between different magnetic order like AF and FM order at the same time. It can furthermore be used to study the magnetism of buried interfaces, diluted magnetic systems like FM semiconductors or other exotic new magnets. The pulsed nature of the synchrotron as x-ray source allows for studying the time dependent behavior of a sample with a temporal resolution of a few tens of picoseconds. Dichroism soft x-ray absorption spectroscopy can furthermore be used to obtain spatially resolved information with less than 50nm lateral resolution in a modern full field or scanning x-ray microscopes. [Preview Abstract] |
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K1.00123: Characterization of the Throughout of Short Fiber-Optic Arrays as a Function of the Angle of Incidence Julia Blackburn An instrument was constructed to measure the light distribution at the back of a thin fiber-optic array as a function of the angle of incidence and the location at which the incoming 633 nm light strikes a fiber. The f-number of the incoming light is 10 and the diameter of the focal spot is 8 microns. The input optics are mounted on a rail that rotates in such a manner that the focal location remains fixed. Images of the light distribution at the back of the array are recorded using a 12-bit 2.5 megapixel camera. Data recorded using commercial face plates is presented. [Preview Abstract] |
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K1.00124: Nano-scale Spin State in Invar Alloy Fe-36at\%Ni Peng Zhao, P. Chris Hammel, Ji-Cheng Zhao We use high-resolution ferromagnetic resonance force microscopy (FMRFM) to image the nano-scale spin structure of an Invar alloy (Fe-36at\%Ni) to test the well-known two-spin-state hypothesis proposed by Weiss. Weiss proposed that the two-spin- state model could explain the Invar effect; but to our knowledge this has have not been experimentally confirmed. With nano-scale spatial resolution of FMRFM, we intend to experimentally examine the existence or absence of such states in the Fe-36at\%Ni Invar alloy. [Preview Abstract] |
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K1.00125: CHEMICAL PHYSICS |
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K1.00126: Salt-induced overcharging, charge inversion and reentrant condensation in polyelectrolyte solutions Pai-Yi Hsiao The behavior of highly-charged polyelectrolytes (PE) in multivalent salt solutions is investigated by computer simulations. By studying the charge distribution function around a chain, we show that PE is charge-overcompensated near its surface by condensed multivalent counterions when salt concentration is high. Nonetheless, the effective chain charge, computed by the ratio of the electrophoretic mobility to the diffusive mobility, can be positive or negative, depending sensitively on the ion size. This finding violates our intuitive thinking that an overcharging on the surface of a charged macromolecule leads inevitably the sign inversion of its effective charge. Moreover, the reentrant condensation of PE is studied by calculating the mean distance between chains. Chain aggregation happens only when salt concentration is intermediate and the ion size is comparable to the monomer size. The results demonstrate the importance of ion excluded volume and suggest a disconnection of the salt-induced segregation of PE chains at high salt concentrations with charge inversion. [Preview Abstract] |
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K1.00127: Free energy landscapes of short polyproline peptides in vacuo and solvated environments Mahmoud Moradi, Christopher Roland, Volodymyr Babin, Celeste Sagui Polyproline peptides are known to occur in two different conformations, including right-handed PPI and left-handed PPII. Depending on the solvated environment and the peptide length, either PPI or PPII is favored. Specifically, we calculated the free energy landscapes of short polyproline peptides (length 6, 9, 13-mers) in vacuo, in implicit water, and in the solvents hexane and propanol as a function of the radius of gyration and handedness. To calculate the free energies, the recently developed Adaptively Biased Molecular Dynamics (ABMD) method, which belongs to the general category of umbrella sampling methods with a time-dependent potential, was used. [Preview Abstract] |
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K1.00128: In situ sum-frequency generation spectroscopy of ethylene-glycol and poly-N-isopropylacrylamide films Volker Kurz, Patrick Koelsch Ethylene-glycol(EG)-based self-assembled monolayers (SAMs) are often used as a model systems for thin liquid films. Temperature series in heavy water were measured using a unique sample cell developed for in situ sum-frequency generation (SFG) spectroscopy experiments. Results obtained from model EG-SAMs with different lengths and terminating groups in various ionic solutions showed temperature-dependent changes in the molecular order. Films of poly-N-isopropylacrylamide(pNIPAM) were also characterized by in situ SFG spectroscopy in the CH, OH, OD and amide spectral regions under different polarization combinations. These systems have many applications as thermo-responsive polymers due to their ability to change solubility in water at the biologically relevant temperature of 32\r{ }C. This so-called lower critical solution temperature (LCST) phase transition was characterized in depth, allowing for the identification of the molecular groups involved in this process. [Preview Abstract] |
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K1.00129: The Effects of Multiwalled Carbon Nanotube Doped Poly(Ethyl Methacrylate) on Optical Field Induced Nematic Liquid Crystal Reorientation Matthew Kerr, David Statman We have been investigating photoinduced gliding of the easy axis at the nematic liquid crystal/polymer interface. Gliding of the easy axis on polyethyl methacrylate (PEMA) surfaces has been observed when magnetic or electric fields are applied to the bulk liquid crystal. We have studied similar gliding when the surface is coated with a carbon nanotube/PEMA composite. Our experiments utilize polarimetry techniques and cross-polarized microscopy. The results of photoinduced gliding experiments on PEMA surfaces doped with multiwalled carbon nanotubes will be presented. [Preview Abstract] |
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K1.00130: Mapping hydration dynamics and coupled water-protein fluctuations around a protein surface Luyuan Zhang, Lijuan Wang, Ya-Ting Kao, Weihong Qiu, Yi Yang, Oghaghare Okobiah, Dongping Zhong Elucidation of the molecular mechanism of water-protein interactions is critical to understanding many fundamental aspects of protein science, such as protein folding and misfolding and enzyme catalysis. We recently carried out a global mapping of protein-surface hydration dynamics around a globular $\alpha $-helical protein apomyoglobin. The intrinsic optical probe tryptophan was employed to scan the protein surface one at a time by site-specific mutagenesis. With femtosecond resolution, we mapped out the dynamics of water-protein interactions with more than 20 mutants and for two states, native and molten globular. A robust bimodal distribution of time scales was observed, representing two types of water motions: local relaxation and protein-coupled fluctuations. The time scales show a strong correlation with the local protein structural rigidity and chemical identity. We also resolved two distinct contributions to the overall Stokes-shifts from the two time scales. These results are significant to understanding the role of hydration water on protein structural stability, dynamics and function. [Preview Abstract] |
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K1.00131: Structural Properties of Water Nano-pockets Encapsulated in Polymerized Reverse Micelles Jacob Urquidi, Jose L. Banuelos, Nancy Levinger Reverse micelles, that is, small surfactant coated droplets of polar solvent, can form in a range of systems of varying surfactant and polar solvent. SANS has been used to characterize the shape, size and polydispersity of these reverse micelle systems which are macroscopically clear but nanoscopically heterogeneous. Particular sensor applications have been developed using a reverse micellar starting material to create a sample that is macroscopically a robust solid with encapsulated nanoscopic pockets of fluid. This poster will discuss the nanopockets of the fluid phase (water in this case) within the matrix as investigated by small angle X-ray scattering (SAXS) and neutron scattering techniques. The SAXS technique was used to investigate the polydispersity, shape, and distribution of the nanopockets of fluid. Neutron scattering was used to lend insight into the nature of the water encapsulated within these micelles by looking at the position, width, and height of the First Sharp Diffraction Peak (FSDP) to probe the physical perturbations that the water is subject to. [Preview Abstract] |
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K1.00132: Quantized ionic conductance in nanopores Michael Zwolak, Johan Lagerqvist, Massimiliano Di Ventra We study ion transport through nanopores via molecular dynamics calculations. Due to the confined geometry and large local field of a single ion, the nanoscale atomic configurations of species influence the ionic conductance. In particular, hydration layers that form around ions in aqueous solution create a series of energy barriers to ion transport. As an ion enters the pore, these hydration layers have to be partially broken due to steric restrictions of the pore. The breaking of the layers proceeds in a highly nonlinear, step-like fashion, giving rise to a strong nonlinear dependence of the electrostatic energy barrier on the pore diameter and therefore also a step-like conductance. We discuss this effect as well as the conditions under which it may be experimentally observed. [Preview Abstract] |
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K1.00133: Base sequence dependence and backbone-induced effects on charge transport through DNA Yong Joe, Sun Lee, Eric Hedin We investigate quantum mechanical electron transmission along the long axis of the DNA molecule using a tight-binding model. Specifically, we use two different DNA models to study the charge transfer efficiency of synthetic ds-DNA. First, the generic form of a simple one-conduction channel model, called the fishbone model, is used. The sugar-phosphate backbone and the coupling amplitude between each site of the base and the backbone are incorporated into an energy-dependent on-site potential in the main DNA site. Here, individual sites represent a base-pair formed by either AT (TA) or GC (CG) pairs coupled via hydrogen bonds. Second, we employ a two-dimensional three-chain model where the backbone on-site energy, the coupling amplitude between the bases and the backbone, and a possible hopping of charge carriers between the successive backbone sites are used as key parameters. The overall transmission and the current-voltage characteristics are calculated to determine the influence of mismatch (impurity) effects in the DNA sequence. Finally, we discuss the transmission gap as a function of coupling between the bases and between the bases and the backbone. *One of the authors (E.R.H) is partially supported by a grant from the Center for Energy Research, Education, and Service (CERES) at Ball State University. [Preview Abstract] |
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K1.00134: Lanthanide Metal-Organic Framework Materials Ping-Yen Hsieh, Mark A. Green, Robert M. Briber A series of lanthanide metal-organic framework materials (MOF) with variable organic linkages including benzene-dicarboxylic acid (BDC); 1,3,5-benzene-tricarboxylic acid (BTC); and 1,3,5-tris(4-carboxyphenyl)benzene (BTB) have been synthesized. The low density and high porosity of MOFs make them candidates molecular sieve or hydrogen storage materials. The crystal structures have been determined using a combination of single crystal X-ray diffractometer and synchrotron powder X-ray diffraction work. Holmium with the BDC ligand material (Ho-BDC) crystallizes in a monoclinic C2/c space group, with lattice parameters of a = 17.06 {\AA}, b = 10.67 {\AA}, c = 10.57 {\AA}, b = 96.12$^{\circ}$. The crystal structure of Ho-BTC is in tetragonal P 41 2 2 space group and Ho-BTB is in a triclinic P-1 space group. A comprehensive examination of Ho-MOF with different ligands by x-ray and thermogravimetric analysis shows that there is a stable nanoporous structure for dehydrated Ho-BTC up to 250$^{\circ}$C. The same phenomenon is not observed in the Ho-BDC and Ho-BTB materials. The collapsed structure with BDC and BTB indicates the stability of dehydrated samples is strongly related to the interactions between the metal and the organic linkers. [Preview Abstract] |
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K1.00135: Ultrafast Spectroscopy of Single-Stranded Adenine Oligomers Charlene Su, Chris Middleton, Bern Kohler The excited-state dynamics of single-stranded homo-oligomers containing a variable number of adenine bases have been studied by femtosecond transient absorption technique within the ground state absorption band. The bleach recovery signals show that all the adenine oligomers decay with a long-lived component of a hundred picosecond in addition to a short-lived component, which is also observed in the adenine mononucleotide, 2'-deoxyadenosine 5'-monophophate. The latter component is attributed to vibrationally cooling to the electronic ground state and the former one is associated with intrastrand excimer formation between stacking bases. It is found that the amplitude of long-lived component increases with the elongation the of adenine oligomers in comparison to the short-lived one. Excimer yields estimated on the basis of relative amplitude show that adenine oligomers have higher excimer formation in longer strands, indicating a greater degree of base stacking. [Preview Abstract] |
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K1.00136: Homogeneous bubble nucleation in liquids: a molecular dynamics study Zun-Jing Wang, Chantal Valeriani, Daan Frenkel We have studied homogenous bubble nucleation in a Lennard-Jones fluid by performing Molecular Dynamics simulation coupled with Forward-Flux Sampling (MD-FFS). The MD-FFS estimate of bubble-nucleation rate is higher than predicted on the basis of Classical Nucleation Theory (CNT). Although this discrepancy is consistent with earlier findings, our simulations show that bubble nuclei are compact rather than ramified as had been suggested by Shen and Debenedetti (J. Chem. Phys. 1999, 111:3581). We find bubble nucleation starts with local spots much hotter than superheated environment, and the local temperature correlates strongly with subsequent bubble formation - this mechanism is not taken into account in CNT. [Preview Abstract] |
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K1.00137: Investigation into the Mpemba Effect: Variation in the Freezing Time of Water Dependent on Initial Temperature and Purity Ingrid Thvedt, Martha Roseberry, Susan Lehman The observation that hot water sometimes appears to freeze more quickly than cold water, known as the Mpemba effect, has generated vigorous debate. Prior research [1] into the Mpemba effect has resulted in conflicting results, due to a variety of observation techniques, multiple definitions of freezing, and different water treatments. To clarify the previous results, we have tested multiple types of water and improved the sample monitoring. During cooling and freezing, each 50 g water sample is continually monitored by three thermistors at different depths. Samples of tap, distilled, and nanopure water were heated, heated and cooled, or boiled before being frozen. We monitor the time to reach freezing, the duration of freezing, and the total time to reach -7$^{o}$C. We observe the Mpemba effect most consistently in the length of the freezing transition in tap water. Observations of temperature variation during freezing will also be presented. [1] See the review by M. Jeng, Am.J.Phys. \textbf{74} 514 (2006). [Preview Abstract] |
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K1.00138: Clockwork Rotation and Rotation Transduction in 2D crystals of Janus amphiphilic colloidal spheres Shan Jiang, Stephen Anthony, Steve Granick Colloidal spheres with one side hydrophilic and the other side hydrophobic can self-assemble into clusters owing to amphiphilicity. When the particle concentration is high enough, 2D crystals with hexagonal translational order and additional orientational order will form. By using the Fourier Transform and particle tracking techniques, the position and the rotation of each single particle can be tracked. Long-range clockwork rotation behaviors were observed for the particles inside the clusters. In other words, when one particle rotates by Brownian motion, the particle next to it is impelled to counter-rotate. This transduction extends for a distance up to half a dozen particles. [Preview Abstract] |
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K1.00139: Modeling Chemical Reactions on Metal Oxide Surfaces Haitao Liu, Michael Falcetta, Kenneth Jordan Photocatalytic conversion of carbon dioxide to methanol has been observed at titanium dioxide interfaces, but the detailed mechanisms are unknown. Computer simulations can prove valuable in elucidating the mechanisms and aid in improving the efficiency. Two major computational strategies for treating such systems are slab and cluster models. The present work uses both periodic slab and embedded cluster models to elucidate the important factors in developing an embedding scheme that properly treats the system and allows the treatment of excited electronic states. Ground state adsorption energies are calculated for a variety of basis sets, cluster sizes, electronic structure methods and embedding schemes to demonstrate convergence with respect to all of these variables. Detailed comparisons of the electrostatic potential obtained from periodic and embedded cluster models are presented to clarify the importance of various effects in the embedding scheme. [Preview Abstract] |
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K1.00140: Spontaneous spreading of particle monolayers from unstable Pickering emulsions Hsin-Ling Cheng, Sachin Velankar Partially-wettable particles can adsorb at liquid/liquid interfaces and give stable Pickering emulsions. However, if there are insufficient particles, then the emulsion is unstable. In such an unstable emulsion, we document a remarkable phenomenon, viz. coalescence of an oil/water/particle Pickering emulsion contained in a vial induces a particle film to climb up the walls of the vial. While this has been noted previously with nanoparticles, we show that such film-climbing is highly general and can be induced by a variety of particle types, particle sizes ranging from a few nm to a few microns, and different emulsion types. Many of the features of film growth described previously with nm-sized particles are found to remain true even with the far larger particles studied here. Binks et al., Langmuir, 22, 4100, 2006, have postulated that the particle films that climb up the walls of a vial are actually comprised of one oil layer and one water layer, with particles adsorbed at the interface between them. We confirmed this ``sandwich'' structure experimentally and also show that such interfacially-adsorbed particles can easily exert the very modest surface pressure necessary to sustain the weight of the film. Finally, while some climbing films are tightly-packed particle monolayers, tight packing is not essential; even sparsely-populated monolayers can display film climbing. [Preview Abstract] |
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K1.00141: Kinetics and Cross-Stream Migration of Polymer Solutions in Nanoscale Channel Undergoing Shear Flow Jaime A. Millan, Sidy Danioko, Mohamed Laradji Polymer solutions confined to nanoscale slit pores are investigated in detail via generalized dissipative particle dynamics. We focus both on Poiseuille and planar Couette flows. In both cases, we investigated the effect of Schmidt number through the modification of both random and dissipative forces. The trend of the cross-stream migration of the polymer chains depends strongly on the value Schmidt number of the solution. In particular, we found a migration towards the walls for relatively low Schmidt number. However, polymer migration toward the channel centerline is observed for relatively high Schmidt number, in agreement with experimental observations and simulations based on other numerical approaches. The polymer chains kinetics is characterized by tumbling with well-defined characteristic time scale that decreases with increasing shear rate. The power spectra of both polymer stretch and tilt are in agreement with recent experiments. [Preview Abstract] |
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K1.00142: Synthesis, characterization and optical properties of magnesium hydroxide micro-/nanostructures Latha Kumari, Wenzhi Li, Charles H. Vannoy, Roger M. Leblanc, Dezhi Wang Magnesium hydroxide (Mg(OH)$_{2})$ crystals of various shapes and sizes (micron to nano) were synthesized by single step hydrothermal route at different reaction conditions. The as-prepared hexagonal (Mg(OH)$_{2})$ particles were converted to cubic MgO by calcination at 450$^{o}$C. The Mg(OH)$_{2}$ and MgO nanostructures showed optical band gaps of 5.7 and 3.43 eV, respectively. Broad band photoluminescence emission spectra were observed in the vicinity of UV and visible region. Mg(OH)$_{2}$ and MgO nanostructures with wide optical band gap and short-wavelength luminescence emission can be used as a luminescent material for photonic applications. [Preview Abstract] |
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K1.00143: Fabrication of zinc oxide microstructures and their properties Latha Kumari, Wenzhi Li, Charles H. Vannoy, Roger M. Leblanc, Dezhi Wang The bitter-melon-like and prism-like zinc oxide (ZnO) microstructures have been synthesized by hydrothermal route. Besides these microstructures, the ZnO material also consists of spherical nanoparticles with narrow size distribution. The as-synthesized ZnO material depicts hexagonal crystal structure. An optical band gap of 2.95 eV is determined from the UV-vis absorption band edge. The prism-like ZnO microstructure shows an ultraviolet near-band-edge emission at about 3.27 eV (380 nm) at room temperature which can be assigned to the radiative annihilation of excitons. The wide-band gap oxide materials like ZnO with short-wavelength PL emission can find application in light emitting devices. [Preview Abstract] |
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K1.00144: Size dependent thermalization time of Ag nanoparticles and the surface density profile Catalina Lopez-Bastidas It is well known that the lack of d-electron screening in the s-electron spill-out region at the surface of Ag nanoparticles increases the electron-electron interaction in this region compared to the bulk. Therefore when comparing the electron-electron interaction contribution to the thermalization time of Ag nanoparticles of varying radius, smaller particles thermalize faster due to the increased surface to bulk ratio. One aspect which has not been addressed is the effect of the spatial distribution of charge at the surface of the nanoparticle. In this work it is shown that the size dependence of the thermalization time is very sensitive to the surface density profile. The electron thermalization time of conduction electrons in Ag nanoparticles as a function of the radius is calculated. The sensitivity of the scattering rate to the spatial distribution of charge at the surface of the nanostructure is analyzed using several model surface profiles. The change in surface charge distribution via charging or coating of the nanospheres is shown to be a tool for control and probing of the ultra-fast electron-electron dynamics in metallic nanoparticles. [Preview Abstract] |
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K1.00145: A General Route to Inorganic Nanoparticles Using a Condensed Electron Beam Marissa Caldwell, Shaul Aloni, Jeffrey Urban, Delia Milliron, H.-S. Philip Wong Inorganic nanoparticles are of interest to study the size dependence of various material properties. However, current colloidal synthetic routes are limited in the scope of accessible inorganic materials. Here we present a facile route to inorganic nanoparticles of a wide range of material compositions and sizes. Using the beam from an electron microscope, 2 -- 100nm particles were formed from micron sized pieces of a wide range of materials including: semiconductors, metals, insulators. Using this route, we have produced nanoparticles of over 25 different compositions. Each material demonstrated an energetic threshold barrier to particle formation. To help elucidate the formation mechanism, we collected cathodoluminescence spectra which, when correlated with known temperature-dependent bandgap data, showed a large increase in temperature due to the e-beam-to-material interaction. The temperature rise dependence on the e-beam current and acceleration voltage was studied. We conclude that the temperature rise is large enough to compare with vaporization energies and is a plausible mechanism for the production of nanocrystals. [Preview Abstract] |
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K1.00146: Can isolated Au nanoclusters catalyze CO oxidation? P.-S. Lin, A.-L. Chin, C.-P. Chang, F.-K. Men It has been more than twenty years since the discovery of oxide-layer supported Au nanoclusters ($<$5 nm) capable of catalyzing CO oxidation. This discovery has attracted a lot of attention owing to possible practical applications as well as a model system for understanding nanoscale catalysis. One mechanism that has been proposed to explain this observation is that the process takes place entirely on Au nanoclusters. Since most experiments performed on this topic have been done in complicated environments, it would be difficult to fully justify/dismiss the validity of a particular mechanism. We have chosen a clean and inert support, highly oriented pyrolytic graphite, to grow Au nanoclusters via molecular beam epitaxy under ultrahigh vacuum conditions. We measured the change in CO$_{2}$ partial pressure after leaking high-purity CO and O$_{2}$ gases into the vacuum chamber with and without the presence of Au nanoclusters. To perform a systematic investigation, we also prepared Au nanoclusters of different densities and sizes. With the presence of Au nanoclusters we could not find any discernible increase in the CO$_{2}$ partial pressure, thus rules out the possibility that Au nanoclusters would take a full credit in catalyzing CO oxidation. [Preview Abstract] |
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K1.00147: Chemical Synthesis and Characterization of Self-Assembled Nanoparticles Prepared in the Presence of Citrate Ions Karl Unruh, Thomas Ekiert Iron(II) ions in aqueous solutions containing various concentrations of citrate ions have been reduced to metallic Fe using sodium borohydrate. In comparison to the 10-20 nm diameter Fe particles formed in the absence of citrate, the presence of citrate results in the formation of 100--200 nm spherical (or in some cases cubical) particles self-assembled from much smaller Fe nanoparticles. Structural, chemical, and magnetic measurements indicate that for appropriate citrate/Fe ratios, air stable powders that exhibit a room temperature saturation magnetization of nearly 200 emu/g and a coercivity less than 100 Oe -- even without deoxygenating the reaction solution or an explicit surface passivation step -- can be obtained. Thermal treatments at temperatures between 350 and 450 \r{ }C result in the sintering of the Fe nanoparticles within the larger aggregates while heat treatments at higher temperatures result in the sintering of the aggregates themselves into a continuous porous matrix. [Preview Abstract] |
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K1.00148: Brownian Motion of an Ellipsoid in Correlated Fluids Shaoqing Zhang, Wu-Pei Su To account for the correlation in the fluctuation force due to the surrounding media, we analytically study the diffusive behavior of an anisotropic Brownian particle by introducing an exponentially correlated colored noise in the rotational motion. The crossover from anisotropic to isotropic diffusion slows down, and the increase in the translational diffusion coefficient induced by an external force is enhanced. These results are of great interest in the research on biological physics and soft matters. [Preview Abstract] |
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K1.00149: Enantiospecific Interaction of Histidine with Planes of Single Crystalline alpha Quartz Danish Faruqui, Paul J. Sides, Vladimir V. Pushkarev, Andrew J. Gellman Chiral chemistry profoundly affects living organisms because they are homochiral environments. The origin of life itself trace to enantiospecific interactions. Chiral purity is an important scientific and technological goal. Adsorption of chiral compounds on `powdered' quartz is sometimes enantioselective. Here we offer positive evidence of diastereomeric, chiral recognition at the interface between `single crystal' alpha quartz and aqueous histidine and verification of the effect for three principal chiral crystallographic orientations of quartz. Characterizing the electrostatic environment, the zeta potential of (0001) L-quartz decreased by approximately 40 mV$\pm $5 as R-histidine was added incrementally to a concentration of 400 u molar; the zeta potential of the same L-quartz sample, however, decreased by only 20 mV$\pm $ 5 in an otherwise identical experiment with L-histidine Results of all diasteriomeric and control experiments on each plane were consistent, The zeta-potential provides evidence that adsorption on quartz is enantiospecific; is influenced by the chirality of quartz but not necessarily by the crystallographic orientation of the surface. [Preview Abstract] |
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K1.00150: Electronic Structure of Ti substituted hydroxyapatite: TiHap Shuxia Yin, Donald Ellis Hydroxyapatite (Hap), with the chemical formula Ca$_{10}$(PO$_{4}$)$_{6}$(OH)$_{2}$, is the main mineral constituent of mammal tooth enamel and bone and has become an important biomaterial with medical applications. Hap also attracts increasing interest for use in environmental adsorbents and catalysts due to its porous nature and highly active ion-exchange character. Ti-modified Hap (TiHap) has been proved to possess high affinity to organic molecules and bacteria as well as high photocatalytic activity for their oxidative decomposition. The concentration of Ti$^{4+}$ is a key factor controlling TiHap crystallinity and catalytic efficiency. Here we studied the sorption mechanism of Ti$^{4+}$ on Hap using Density Functional Theory within periodic slab models. Ti$^{4+}$ or (Ti(OH)$_{2}$)$^{2+}$, as the most likely ion exchange species with Ca$^{2+}$, were first considered in bulk Hap. A second charge compensated model considered includes both surface Ca ion vacancies and substitutional Ti$^{4+}$. To obtain insight of the energetic stability and microscopic crystal structure of TiHap, Ti substitution on different Ca sites and distributions at different atomic ratios are investigated in both bulk and surface models. [Preview Abstract] |
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K1.00151: Time-Dependent Density Functional Theory Applied for Pulse Laser Shot: Criterion of the Numerical Stability Yoshiyuki Miyamoto, Hong Zhang In this talk, applications of TDDFT [1] for irradiation of pulse laser to materials and subsequent structural change are shown. Contrary to the pioneering works [2-3], we present a way of judging numerical stability which can be confirmed by the energy conservation rule. The conserved quantity is the DFT total energy plus kinetic energy of ions minus work done by the pulse shot [4], which can simply be demonstrated with use of adiabatic exchange-correlation functional and time-varying electric field generated by a time-varying fictitious charge. As an example, structural change on graphite surface induced by pulse laser shot is demonstrated with use of 10-layer AB- stacked slab model. After irradiating laser shot with wavelength of 800 nm, pulse width of 50 fs, and a power about 90 mJ/cm$^2$ per pulse, the top graphene monolayer spontaneously leaves while other layers remain. \\[0pt] [1] E. Runge and E. K. U. Gross, Phys. Rev. Lett, {\bf 52}, 997 (1984).\\[0pt] [2] K. Yabana and G. F. Bertsch, Phys. Rev. B{\bf 54}, 4484 (1996)\\[0pt] [3] A. Castro et al., Eur. Phys. J. D{\bf 28}, 211 (2004).\\[0pt] [4] Y. Miyamoto and H. Zhang, Phys. Rev. B{\bf 77},165123 (2008). [Preview Abstract] |
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K1.00152: Enhanced Surface Plasmon Resonance. Weiqiang Mu, Joon Jang, Maxim Sukharev, Donald Buchholz, Robert Chang, John Ketterson We have studied the surface plasmon resonances in thin silver films sandwiched between silica. This is the so-called Sarid geometry which supports a (short-range) symmetric and a (long-range) anti symmetric mode. The coupling is achieved diffractively via an approximately sinusoidal surface etched in the underlying silica prior to deposition of a 20nm Ag film and a 400nm silica capping layer; the modulation amplitudes were 10, 30 and 50nm. FDTD simulations of the transmission (T) and reflection (R) coefficients show that for perpendicular incidence strong coupling occurs to the two plasmon modes along with a much weaker electromagnetic Woods anomaly. We will present data on both T and R showing evidence of coupling to the antisymmetric and symmetric Sarid modes as well as observations of waveguiding effects in the silica capping layer. Data will be compared with FDTD calculations for corresponding film parameters. [Preview Abstract] |
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K1.00153: Changing What Science Is and How It's Done Robert Jones Knowledge is of an approximate character. Our formalisms abstract and simplify. Each formalism is an idealization, often times approximating in its own DIFFERENT ways, each offering somewhat different coverage of the domain. Having MULTIPLE overlaping theories of a knowledge domain is then better than having just one theory (R. Jones, APS Gen. Meeting, March 2008 and refs. therein). In the future each field will possess multiple theories of its domain and scientific work and engineering will be performed based on the ensemble predictions of ALL of these. This idea can be considered an extension of Bohr's notion of complementarity, ``...different experimental arrangements...described by different physical concepts...together and only together exhaust the definable information we can obtain about the object.'' Although finding the ``correct'' or ``most probable'' theory has been the goal of scientific investigation in the past we now know that the pluralistic science that I am describing here is more successful (Peter Cheeseman in The Mathematics of Generalization, D. H. Wolpert, Ed, 1995, pg. 315 and Michael Weisberg, J. of Philosophy, 2007, pg. 646). This is not postmodernism. Theories are accepted based upon experimental evidence not human opinion. Over the years I have tried to keep with this new pluralism in both my fusion energy and artificial intelligence work. [Preview Abstract] |
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K1.00154: The Role of the Element Rhodium in the hyperbolic law of the Periodic Table of Elements Albert Khazan The method of equilateral hyperboles assumes that their tops should be certain with high accuracy by means of Lagrange's theorem. On this basis the scaling factor for transition from the coordinate system usual to mathematicians to that which is to be used in chemistry is calculated. Such an approach has allowed calculating parameters of the last element. The calculation can be checked by means of the first sequel from the hyperbolic law, proceeding only from the atomic mass of the element Rhodium. As it has appeared, the direct and adjacent hyperboles are crossed in a point with the coordinates 205.811; 0.5, which abscissa makes a half of the last element's atomic mass (the deviation is about 0.01{\%}). The real axes of the hyperboles coincide with the tangents and normals, and the scaling factor differs from the first calculation as 0.001{\%}. However these insignificant divergences are so small to the most important conclusion that the validity of the Hyperbolic Law, as calculation on Rhodium our data consists of (Progr. Physics, 2007, v.1, 38; v.2, 83; v.2, 104; 2008, v.3, 56). [Preview Abstract] |
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K1.00155: Coordination of Swarmed Unmanned Ground Vehicles using Self Organization Mapping with Generic Algorithm Shekhar Pradhan The methodologies for path planning for individual UGVs have been well studied and modeled. The Simultaneous Localization and Mapping (SLAM) is an example of such study. However, there is no reliable method of communication among swarmed UGVs. The author along with other collaborators, Dr. Wei Cao of NASA Research Center and Dr. James Burghart of Cleveland State University, proposes a Master-slave approach for the coordinated management of UGVs using Neural Networks. SOM is used to work with GA to update the patterns of UGVs for coordination among themselves and with ground station(s). One (or more) UGV with advanced computational power and virtual link to other ground stations serves as the Master. SOM and GA reside on the Master as well as ground stations. All other UGVs behave as slaves. The individual UGVs conducts its own or grouped path planning. Using Matlab,, the prototype version of SOM and GA for swamed UGVs was simulated and tested with an advanced multi-UGV system. The author will present the results followed by the outlook for the future work. [Preview Abstract] |
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K1.00156: Effects of Aggregation on the Electronic Properties of Polythiophene and its Oligomers Kelly Zewe, Linda Peteanu, Wynee Lee Polythiophene is a commonly used component of organic electronics and solar cells. Polythiophene chains are readily aggregated under the processing conditions used to form thin films for applications in devices. This aggregation can drastically alter the charge transfer and optical properties of the material. In order to better understand these effects, oligomers of polythiophene were studied. Because oligomers have shorter, well-defined chain lengths and are free of defects, the effects of aggregation on their electronic properties are easier to interpret than those of the polymer systems and are more readily modeled using electronic structure theory. Bulk and single-molecule fluorescence methods are used to explore the emission properties as a function of aggregate size, precipitating solvent, and monomer properties and to correlate these to the polymer properties. Stark spectroscopy is used to measure the change in charge separation and in excited-state delocalization caused by aggregation and the consequent increase in chain-chain contacts. [Preview Abstract] |
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K1.00157: Adsorption on Nanotubes With Repulsive First Neighbors Alain Phares, David Grumbine, Francis Wunderlich We consider adsorption on nanotube lattices with zigzag triangular geometry. In Langmuir, Vol.\ 24, pp.\ 11722-11727 (2008), we studied such adsorptions with first- and second-neighbor interactions and attractive first-neighbors. The nanotube energy phase diagram is independent of $M$, the number of atoms in the nanotube circumference, and holds for infinite $M$, reproducing the infinite width limit of a triangular terrace [Langmuir, Vol. 24, pp. 124-134 (2008)]. Here, we consider repulsive first-neighbors. The phase characteristics, \{$\theta_0$, $\theta$, $\beta$\}, are the coverage, and the numbers per site of first and second neighbors, respectively. Particle-hole symmetry holds for all nanotube diameters and the energy phase diagram is $M$ dependent. In the infinite-$M$ limit, the non-trivial phases with their complements are: \{1/4, 0, 0\}, or ($2 \times 2$), and \{3/4, 3/2, 3/2\}; \{1/3, 1/3, 0\}, or ($3 \times 1$), and \{2/3, 4/3, 1\}; \{1/3, 0, 1\}, or ($\sqrt{3} \times \sqrt{3}$) R30$^\circ$, and \{2/3, 1, 2\}; and \{1/2, 1/2, 1/2\}, which is its own complement. This infinite-$M$ limit should be the same as the infinite width limit of a triangular terrace. We found that we had missed the \{2/3, 4/3, 1\}-phase in Langmuir, Vol.\ 23, pp.\ 1928-1936 (2007). [Preview Abstract] |
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K1.00158: Fast algorithms for classical X$->$0 diffusion-reaction processes Fabrice Thalmann, Nam-Kyung Lee The Doi formalism [J.Phys.A 9, p1465, 1976] treats a reaction-diffusion process as a quantum many-body problem. We use this second quantized formulation as a starting point to derive a numerical scheme for simulating X$->$0 reaction-diffusion processes, following a well-established time discretization procedure. In the case of a reaction zone localized in the configuration space, this formulation provides also a systematic way of designing an optimized, multiple time step algorithm, spending most of the computation time to sample the configurations where the reaction is likely to occur. [Preview Abstract] |
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K1.00159: Luminescence of nanoparticles in solvent environment near its phase transitions Andrey Antipov, Matthew Bell, Mesut Yasar, Vladimir Mitin, Aleksandr Verevkin We demonstrate phenomenon of colloidal CdSe and CdSe/ZnS nanoparticles (NPs) photoluminescence (PL) sensitivity to the phase state of solvent environment. New dramatic PL features in close vicinity of the solvent phase transitions are observed, such as pronounced singularities in PL peak energy, PL line width, and PL lifetime vs. temperature. For instance, a singularity in the PL peak energy with amplitude of up to ~25 meV is observed at around the freezing point of water ~273 K for water-solved CdSe/ZnS NPs. We observe similar singularities in the vicinity of the freezing point for core and core/shell NPs solved in both water and toluene. We also observe a singularity in the vicinity of the glass/solid state transition for NPs solved toluene. Such features are not observed in dry samples. We associate an origin of such singularities with non-monotonic behavior of Kapitza resistance between NPs and their environment during temperature-induced phase transitions in solvent: the escape rate of acoustical phonons from NPs is dramatically modified by the changes in acoustical mismatching. [Preview Abstract] |
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K1.00160: Vibrational spectroscopic study of newly developed self-forming lipids and nanovesicles. Rajan Bista, Reinhard Bruch We present the first experimental study of self-forming synthetic nanovesicles, trademarked as QuSomes{\texttrademark}, using vibrational spectroscopic techniques namely near-infrared (NIR) and laser tweezers Raman spectroscopy. Raman spectra of these new artificial nanovesicles suspended in Phosphate Buffered Saline (PBS) have been obtained by using an inverted confocal laser-tweezers-Raman-microscopy system in the spectral range of 3100 to 500 cm$^{-1}$. This spectrometer works with an 80 mW diode-pumped solid-state laser, operating at a wavelength of 785 nm in the TEM$_{00}$ mode. The laser is used both for optical trapping and Raman excitation. Similarly, NIR absorption spectra of these novel nanovesicles have been recorded in the spectral range of 9000-4800 cm$^{-1}$ by using a new miniaturized micro-mirror spectrometer based on micro-optical-electro-mechanical systems (MOEMS) technology. In this work, we have found that the most prominent bands in the studied spectral region of Raman spectra are dominated by vibrational modes arising from C-C and CH$_{2}$ bonds. Similarly, NIR spectra are primarily assigned as first and second overtone of C-H stretching mode and second overtone of C=O stretching mode. These spectroscopic techniques have proven to be an excellent tool to establish the fingerprint region revealing the molecular structure and conformation of QuSomes{\texttrademark} nanoparticles. [Preview Abstract] |
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K1.00161: Effects of Aggregation on the Properties of Individual Conjugated Oligomers and Polymers Probed by Fluorescence Microscopy Gizelle Sherwood, Linda Peteanu, Jurjen Wildeman The recent upsurge in use of conjugated polymers in photovoltaic devices and in displays drives the need for understanding how morphology affects important functional features such as emission and charge migration. Due to the inherent complexity of polymers, a parallel effort to `build-up' understanding of their features \textit{via} a detailed study of important electronic and photo-physical properties of oligomer aggregates is needed. These exhibit remarkably uniform spectral properties that defy analysis via standard exciton coupling models. Fluorescence microscopy is used to probe both variations in vibronic structure and emission lifetime between individual aggregates and trends in these properties as a function of aggregate size. [Preview Abstract] |
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K1.00162: ARTIFICIALLY STRUCTURED MATERIALS |
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K1.00163: Template assisted synthesis and optical properties of gold nanoparticles. Petru Fodor, Vincenzo LaSalvia A hybrid nanofabrication method (interference lithography + self assembly) was explored for the fabrication of arrays of gold nanoparticles. To ensure the uniformity of the nanoparticles, a template assisted synthesis was used in which the gold is electrodeposited in the pores of anodized aluminum membranes. The spacing between the pores and their ordering is controlled in the first fabrication step of the template in which laser lithography and metal deposition are used to produce aluminum films with controlled strain profiles. The diameter of the pores produced after anodizing the aluminum film in acidic solution determines the diameter of the gold particles, while their aspect ratio is controlled through the deposition time. Optical absorbance spectroscopy is used to evaluate the ability to tune the nanoparticles plasmon resonance spectra through control over their size and aspect ratio. [Preview Abstract] |
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K1.00164: Structural and Electrical Study of ZnO Nanowires Grown on Silicon and Titanium Substrates Edward Likovich, Eric Petersen, Venkatesh Narayanamurti We studied the VLS (vapor-liquid-solid) growth of ZnO nanowires on catalytically patterned Silicon and Titanium foil substrates. We provide evidence for VLS growth from the formation of a eutectic liquid between Au catalyst particles and the Si or Ti substrate. In order to further understand conduction in nanowires, we present preliminary data from electrical measurements on wires grown on each substrate and provide a comparison. We show that the use of metal foil substrates exhibits promise for future nanowire applications in large-area light emitters, collectors, and thermoelectrics. [Preview Abstract] |
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K1.00165: Electronic properties of boron nano-ribbons: - DFT study Sumit Saxena, Trevor A. Tyson Electronic properties of boron nano-ribbons have been studied using density functional techniques employing ultra-soft pseudo-potentials. Spin restricted calculations were performed for boron nano-ribbons constructed from stable boron sheet$^{1}$ structures. Different stable edge configurations of nano-ribbons were observed. Band structure analysis was performed and Density of states was calculated to determine the electronic phase of these nano-ribbons. Comparisons with the carbon systems will be made. This work is supported in part by NSF DMR-051219. \\[3pt] [1] H. Tang and S. Ismail-Beigi, Phys. Rev. Lett. \textbf{99}, 115501 (2007). [Preview Abstract] |
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K1.00166: Fundamentals of magneto-optics of single Rashba spintronic quantum dots Manvir Kushwaha We report on the theoretical investigation of the effect of the Rashba-type spin-orbit interaction (SOI) on the Fock-Darwin energy spectrum in the parabolically confined quantum dots in the presence of a perpendicular [to the original two-dimensional electron gas (2DEG)] magnetic field. The study is based on the formal (analytical) results without resorting to any numerical simulation. We observe that the SOI modifies drastically the optical, thermodynamic, as well as magneto-optical properties of the (narrow-gap InAs) quantum dots. We discuss the dependence of the Fock-Darwin spectrum, Fermi energy, optical transitions, and magnetization on all the important parameters involved in the theory such as, for example, the orbital quantum number, the magnetic field, the confinement potential, and the Rashba parameter that characterizes the strength of the SOI. The illustrative examples include the results both with and without the SOI, for the sake of comparison. One of the most important observation is that the Rashba SOI causes the band mixing and band shifting in the quantum dots and the Fock-Darwin energy spectrum becomes richer but complex. This complexity seems to arise due to an intricate interplay between the SOI and the Zeeman energy. [Preview Abstract] |
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K1.00167: Quantum Wire Fano Resonance in an Electric Field V. Vargiamidis, V. Fessatidis, N.J.M. Horing Electronic transport through a straight parabolically confined quantum wire with an attractive impurity and a transverse electric field is investigated via the Feshbach coupled-channel theory. The impurity is modeled by a $\delta$-function potential in the propagation direction while it is Gaussian in the transverse direction. In the presence of an impurity, the transmission probability of the wire may exhibit resonances of the Fano type (which is the result of the interference between background transmission and transmission via a quasibound state created in the impurity). It is shown here that increasing the field strength from zero causes displacement of the confining potential, thereby inducing a ``shifting'' of the impurity across the channel and therefore influencing the resonance structure. As the center of the confining potential approaches the center of the impurity, the coupling of the (first) propagating state with the quasibound state of the second channel gradually decreases, resulting in a decrease of the resonance width. For a particular value of the field strength the resonance width shrinks to zero and the Fano profile collapses. The resonance energy is also examined as a function of the electric field strength. [Preview Abstract] |
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K1.00168: Fabrication and Electrical Characterization of Zinc Oxide Nanowires Daqing Zhang, Chun-Hong Lee, Chris Berven, Vanvilai Katkanant One dimensional semiconducting zinc oxide (ZnO) nanowires have drawn attractive attentions in the past years. The unique electrical, optical, and piezoelectric properties of ZnO nanowires make them broaden applications ranging from light emitting diode and lasers, solar cells, photodetectors, electron transporters and transistors, to piezoelectric generators. In our research, two-terminal current-voltage (I-V) measurements were conducted to determine the electrical conductivity alternation of the ZnO nanowires under laser irradiation, and various gaseous surroundings. The I-V curves at the temperature ranged from 150 to 300 K were recorded in vacuum. The Arrhenius plot shows perfect linear relation between I and 1/T. The donor lever of the semiconducting nanowire is about 326 meV. We observed that the current increased 50{\%} with laser on in comparison to that with it off; it raised by a factor of four under ambient reductive gas CO. In addition, the I-V behaviors were found to be reversible with those various environments. Further studies on the possible nano- devices such as optical switches and chemical sensors are undergoing. [Preview Abstract] |
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K1.00169: Elementary process of electromigration investigated by novel spectroscopic approach to electrical break junctions Akinori Umeno, Kazuhiko Hirakawa We have investigated electromigration process at gold nanojunctions by introducing a novel spectroscopic analysis. Gold nanojunctions were broken into nanogaps by passing large current, which was controlled by monitoring the evolution of junction conductance. We observed that, for the junctions as small as few tens of atoms, the junction conductance showed successive drops by one quantum (e2/h), corresponding to one-by-one removal of gold atoms, only when the junction voltage exceeded certain critical values. The histogram of the observed critical voltages showed a clear peak, Vp, and eVp was found to agree with the activation energy for surface diffusion of gold atoms. The result indicates that the elementary process of electromigration in such small junctions is the self-diffusion of metal atoms driven by microscopic kinetic energy transfer from a single conduction electron to a single metal atom. Technological implications of this new finding are also discussed in terms of reproducible formation of nanogap electrodes for single molecular junctions and also failure-tolerant interconnections for VLSIs. [Preview Abstract] |
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K1.00170: Band structure of core-shell semiconductor nanowires Mats-Erik Pistol, Craig Pryor We present band structures of strained core-shell nanowires composed of zincblende III-V (binary) semiconductors. We consider all combinations of AlN, GaN, InN, and all combinations of AlP, GaP, AlAs, GaAs, InP, InAs, AlSb, GaSb, and InSb. We compute the ${\Gamma}$- and X-conduction band minima as well as the valence band maximum, all as functions of the core and shell radii. The calculations were performed using continuum elasticity theory for the strain, eight-band strain-dependent {\boldmath $k\cdot p$} theory for the $\Gamma$-point energies, and single band approximation for the X-point conduction minima. We identify structures with type-I, type-II and type-III band alignment, as well as systems in which one material becomes metallic due to a negative band-gap. We identify structures that may support exciton crystals with and without photoexcitation. We have also computed the effective masses, from which the confinement energy may be estimated. All the results [Pistol and Pryor, Phys. Rev. B 78, 115319] are available in graphical and tabular form at www.semiconductor.physics.uiowa.edu [Preview Abstract] |
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K1.00171: Analysis of electron transport through quantum dots using the Hidden Markov Model (HMM) Matthew House, Hong Wen Jiang The number of electrons present on a quantum dot defined in a two-dimensional electron gas in a semiconductor heterostructure can be observed using a nearby quantum point contact (QPC), but counting the number of electrons present in the dot does not directly reveal the presence of multiple allowed states that contain the same number of electrons; i.e. different orbital or spin states. Two or more states with the same number of electrons may have different rates of transition to other, directly observable states. In this case they may be indirectly distinguishable, by analysis of the statistics of a time series of data. We present a new approach to analysis of QPC data based on the Hidden Markov Model (HMM). HMM theory provides a mathematical framework for optimally estimating the rates of transition between a system with various states, which may include states that cannot be directly distinguished from one another by observation (they are ``hidden''). Statistical tests can be applied to determine if the hypothesis of a ``hidden'' state is justified by the data. The application of the HMM framework to the quantum dot analysis problem and preliminary results of the application of this approach to electron transport data is presented. [Preview Abstract] |
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K1.00172: Si$_{0.7}$Ge$_{0.3}$ Nanorings Mediated By Ag Nanodots: Structural Evolution and Enhanced Photoluminescence Properties Chih Ho, Cheng-Ying Chen, Jr-Hau He Currently nanorings (NRs) are attractive because there is a great deal of interest in nanostructures from theoretical, experimental, and device perspectives. The feasible NR fabrication is demanded in the field of electronic and optoelectronic devices at the nanoscale. In the present study, the growth of high-density Si$_{0.7}$Ge$_{0.3}$ NRs has been achieved on ultrathin Ag films on Si$_{0.7}$Ge$_{0.3}$ substrate. In situ ultrahigh-vacuum transmission electron microscopy revealed that the formation of nanorings involves a mechanism mediated by Ag NDs and evaporation of Ag-Si-Ge eutectic liquid at high temperature. Si$_{0.7}$Ge$_{0.3}$ NRs exhibit the enhanced PL intensity over Si$_{0.7}$Ge$_{0.3}$ thin film due to quantum size effects. The luminescence efficiency as a function of the size of Si$_{0.7}$Ge$_{0.3}$ NRs has been investigated. Power-dependent PL demonstrates that the NR mediated by Ag NDs is type-I band alignment. The process promising the availability of type-I Si$_{1-x}$Ge$_{x}$ NRs can serve as a useful platform for the fundamental understanding and future practical applications of NRs. [Preview Abstract] |
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K1.00173: Experimental demonstration of reflection minimization at 2D photonic crystal interfaces via antireflection structures Teun-Teun Kim, Sun-Goo Lee, Myeong-Woo Kim, Jae-Eun Kim, Hae Yong Park We experimentally confirm that the antireflection structures effectively minimize the unnecessary reflections of self-collimated microwave beams in a two-dimensional square lattice photonic crystal composed of alumina rods. The optimized design parameters for the antireflection structures are obtained from the one-dimensional antireflection coating theory and the finite-difference time-domain simulations. Measurements of the transmittance through the photonic crystal samples with and without the antireflection coating structures agree well with the simulation results. Measured results show that the photonic crystal with an antireflection coating structure yields transmittance of more than 80{\%} of the incident power near the self-collimation frequency, which is more improved transmittance with wider band compared to the case without the antireflection coating structure. [Preview Abstract] |
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K1.00174: Localized and Resonant elastic sagittal modes in one-dimensional phononic crystals L. Castro-Arce, F. Ramos-Mendieta By incorporating a defect Zn layer in an Epoxi/Sn one-dimensional phononic crystal we found transmission peaks associated to localized longitudinal and transverse elastic states. The same localized modes of orthogonal polarizations are excited by incident longitudinal or transverse waves; thus, the transmission spectrum of localized vibrations does not depend on the polarization of the incident wave. The phenomenon can be explained on basis of mode conversion. In addition, resonant modes with frequencies lying inside a bulk band were also found. It is interesting that as function of both the size of the phononic sample and the angle of incidence, the polarization of the transmission resonant peaks change; for example, for a sample of seven cells with the defect at the center, the mode can change from quasitransverse to quasilongitudinal when the angle of incidence changes from 30 to 40 degrees. The variation of polarization is also independent of the polarization of the incident wave. [Preview Abstract] |
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K1.00175: Transport Properties of Nanoscale Materials by First-principles Calculations Hiroshi Mizuseki, Rodion V. Belosludov, S.-U. Lee, Yoshiyuki Kawazoe Molecular devices are potential candidates for the next step towards nanoelectronic technology. Our group has covered a wide range of nanoscale wires, which have potential application in molecular electronics using first-principles calculations and nonequilibrium Green's function formalism [1]. Our target materials are supramolecular enamel wires (covered wires) [2], connection between organic molecules and metal electrodes, self-assembled nanowires on silicon surface [3], porphyrin [4], phthalocyanine, metallocene [5], fused-ring thiophene molecules, length dependence of conductance in alkanedithiols and so on. Namely, we have investigated a relationship of the energy levels of delocalized frontier orbitals (HOMO and LUMO) and Fermi level of metal electrodes and estimate the electronic transport properties through atomic and molecular wires using Green's function approach. References [1] http://www-lab.imr.edu/$\sim $mizuseki/nanowire.html [2] R. V. Belosludov, A. A. Farajian, H. Baba, H. Mizuseki, and Y. Kawazoe, Jpn. J. Appl. Phys., \textbf{44}, 2823 (2005). [3] R. V. Belosludov, A. A. Farajian, H. Mizuseki, K. Miki, and Y. Kawazoe, Phys. Rev. B, \textbf{75}, 113411 (2007). [4] S.-U. Lee, R. V. Belosludov, H. Mizuseki, and Y. Kawazoe, Small \textbf{4} (2008) 962. [5] S.-U Lee, R. V. Belosludov, H. Mizuseki, and Y. Kawazoe, J. Phys. Chem. C. \textbf{111} (2007) 15397. [Preview Abstract] |
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K1.00176: Thermoelectrical and Structural Properties of Sintered LaCoO$_{3}$ Ceramics A. Cortes, W. Lopera, P. Prieto Electrical and thermal transport properties of LaCoO$_{3}$ in bulk are reported in the temperature range from 10 to 390 K. The crystalline structure of the samples was determined by x-ray diffractometry (XRD). XRD measurements indicated that the formation of LaCoO$_{3}$ was completed, and it was verified that a pure phase with rhombohedral crystalline structure was obtained. The results of the thermoelectric measurements show that the Seebeck coefficient ($S)$ initially grow with the increasing of temperature up to a maximum value around of 650 $\mu $V/K at 230 K. After this temperature $S$ decrease slowly up to a value of 520 $\mu $V/K, at room temperature. The polycrystalline LaCoO$_{3}$ samples show thermal conductivity around 0.4 W$/$mK at room temperature, that is a lower value than the reported for single crystal samples of this material. Electrical resistivity measurements show typical semiconducting behavior, with a large value of resistivity, close to 2.6 $\Omega $cm. Finally the thermoelectric figure of merit have a maximum value of 0.09, at room temperature, that is comparable to previous reported values for this material. [Preview Abstract] |
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K1.00177: Accurate thermopower measurement of quasi-one dimensional nanomaterials Yi-Bin Gao, Ye Wang, Jun-Yi Wang, Lian-Mao Peng, Sheng-Yong Xu To measure the accurate thermopower (Seebeck coefficient) of a nanomaterial is of importance for developing low-dimensional thermoelectrics and energy-conversion devices. We have built up sample stages with copper bulks and 25 micron-diameter gold wires, and assembled multi-walled carbon nanotubes (MWCNT) and individual nanowires onto these stages using in situ nano-probe manipulation in a scanning electron microscope. We can establish a temperature difference as high as 80K between two ends of a nanomaterial sample with this kind of stage, thus obtain a measurement accuracy of 2{\%}-5{\%}. For MWCNT bundles, we have observed a trend that, when the number of individual tubes in a bundle varies from several millions to around a thousand, the thermopower almost remains as a constant value around 10 microvolt per Kelvin. But when the tube number in the bundle is further reduced to less than a hundred, the thermopower increases steeply to a value near 20 microvolt per Kelvin. The result is attributed to the effect of surface adsorption of oxygen on the thermopower of the bundle. [Preview Abstract] |
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K1.00178: Phonon Thermal Conductivity of Si/Ge Nanostructures Shang-Fen Ren, Wei Cheng Phonon thermal conductivities of various Si/Ge nanostructures (NSs), including nanocrystals, nanowires, nanovacancies, and Si/Ge nanocomposites, are investigated with three different models: macroscopic approximation, semi-microscopic model that calculates the heat capacity of NCs with a microscopic Valance-Force-Field Model (VFFM), and a full microscopic description of phonon thermal conduction that calculate both heat capacity and phonon group velocity by the VFFM. The results are compared, and the advantages and limitations of each of the models are discussed. It is shown that with full microscopic description, phonon thermal conductivity in Si/Ge nanostructures might be quite different from those obtained with the macroscopic description, mainly depending on the roughness of the interfaces and the size of the nanostructures. This further indicates that it is critically important to investigate phonon thermal conductivities in nanostructures with microscopic models when the roughness is important to consider and the size of the nanostructures is small. [Preview Abstract] |
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K1.00179: High Pressure Structural and Electrical Transport Properties of the Ca$_{3}$Co$_{4}$O$_{9 }$System T. Wu, T.A. Tyson, Z. Chen, Q. Jie, Q. Li, J.J. Tu High pressure and temperature dependent resistivity measurements were conducted on the Ca$_{3}$Co$_{4}$O$_{9}$ system to understand the influence of internal pressure by doping on the properties of these materials. To directly probe the effect of pressure on the structure, x-ray diffraction measurements under pressure were also conduct with diamond anvil cells at ambient temperature. The results are compared with ambient pressure chemically materials. The influence of the atomic structure on the thermoelectric properties will be discussed. [Preview Abstract] |
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K1.00180: Magnetism in ZnO Chanyong Hwang, W. Kim, Jisang Hong, H.J. Kim, Y.P. Lee DMS has drawn a lot of attention for the possible use in spintornics. Ferromagnetic order showed up after the doping the oxide such as ZnO with transition metals. The origin of this ferromagnetic order is still controversial. Especially addition of Cu as a dopant material for ferromagnetic order raises the question on the role of transition metal dopant for the existence of ferromagnetic order. We have used high energy electron beam to build the Zn vacancy. SQUID and MCD results will be presented for the existence of long range ferromagnetic order. First principles calculation also supports our model for the origin of this ferromagnetism. [Preview Abstract] |
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K1.00181: Fabrication of Si nanowires on Si (100) using a scanning probe tip Joshua Smith, Robert Davis, Ying Yi Dang, Gary Fedder, Jim Bain, David Ricketts Reliable fabrication on the nanoscale is becoming increasingly important. The co-author team is investigating a nanolithography technique for the deposition of nanoscale features entitled ``Tip-directed, field-emission assisted nanomanufacturing'' (TFAN). The TFAN process involves the adsorption of a layer of silicon-containing gas, such as disilane, to a substrate and the selective patterning of the surface with field-emitted electrons from a scanning probe tip. The electrons crack the Si containing molecules, which results in the deposition of Si on the substrate. The adsorption of the Si-containing molecules to the substrate surface is critical to the success of this approach. The investigation involves the determination of the coverage, sticking coefficient, and time constant of disilane on the Si(100) surface using temperature programmed desorption and scanning tunneling microscopy. [Preview Abstract] |
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K1.00182: Excitation energy dependence of fluorescence intermittency in CdSe/ZnS core-shell nanocrystals Robert Mohr, Thomas Emmons, Catherine Crouch We report measurements of the excitation energy dependence of the fluorescence intermittency of single CdSe/ZnS core/shell nanocrystals (NCs) using two different excitation energies. The lower excitation energy, at 532 nm, corresponds to excitation 270 meV above the band gap. The higher energy, at 405 nm, corresponds to excitation 1.0 eV above the bandgap. At each excitation energy, 77 individual NCs were measured for 1500 s. The off-times from each individual NC follow a power-law distribution with the same exponent regardless of excitation energy. The on-times follow a truncated power law distribution with an exponent that is independent of energy, but the distribution of truncation times obtained from the individual NCs at the higher energy is peaked at shorter values than the distribution obtained with the lower excitation energy. [Preview Abstract] |
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K1.00183: Polarization-independent extraordinary optical transmission in one-dimensional metallic gratings Yuehui Lu, MinHyung Cho, YoungPak Lee, JooYull Rhee Extraordinary optical transmission (EOT) is a unique effect that light is transmitted with an efficiency greater than unity when it is normalized to the area of grooves or holes. In this work, the EOT of both transverse-electric (TE) and transverse-magnetic (TM) polarizations was investigated for sub-wavelength metallic gratings by the rigorous coupled-wave analysis, implemented as the Airy-like internal reflection series. Generally, the EOT is achievable for TM polarization due to the excitation of coupled surface plasmon polaritons (SPPs), whereas the SPP-produced EOT for TE polarized light is impossible because of the absence of SPPs for this polarization. However, the TE-polarized EOT produced by cavity modes is available. In this work, the polarization-independent EOT is exhibited in the pure metallic gratings with broad slits without need for a specific dielectric filler in the grooves. The design proposed in this work simplifies the realization of gratings that possess the polarization-independent EOT. [Preview Abstract] |
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K1.00184: On Static and Dynamic Properties of Solitons in Molecular Chains Irina Bariakhtar The cross section for scattering of x rays by solitons is calculated for the solitons corresponding to the formation of kinks in quasi-one-dimensional systems, e.g. molecular chains. Obtained is the temperature dependence of the soliton density, the shape of the particle density distribution in the soliton, based on the study of the x-ray scattering cross section by solitons, and other static and dynamic properties of the solitons in quasi-one-dimensional systems. [Preview Abstract] |
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K1.00185: SPP resonance and transmission enhancement of 1D slit array on aluminum film at microwave regime Myeong-Woo Kim, Teun-Teun Kim, Jae-Eun Kim, Hae Yong Park In this presentation, we show the transmission enhancement through periodic slit arrays on a metallic film experimentally measured in the microwave regime. Enhanced transmission peaks and sharp transmission dips are clearly observed near the surface plasmon polariton(SPP) resonance frequencies calculated theoretically. The measured transmittance spectra exhibit considerable dependence on the geometrical properties of slits such as slit width, slit periodicity and metallic film thickness. Transmission peaks and dips are originated from the coupling between the incident light and SPPs which are caused by the slit array which acts like a grating coupler. Obtained results are theoretically explained by solving the Maxwell's equations and the diffraction theory with appropriate boundary conditions, which are in excellent agreement with those calculated by the finite-difference time-domain method. [Preview Abstract] |
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K1.00186: Photoresponse in large area multi-walled carbon nanotube/ polymer nanocomposite films Paul Stokes, Jianhua Zou, Lei Zhai, Qun Huo , Saiful I. Khondaker Recently, photoresponse of CNTs (both in visible and near infared (NIR) regime) have generated considerable debate in terms of whether the photoresponse is (i) due to photon induced charge carrier (excitonic), (ii) due to heating of the CNT network (bolometric), or (iii) caused by photodesorption of oxygen molecules at the surface of the CNT. In addition, the role of the metal electrode -- CNT contact's effect on the photoresponse has also been debated. Here, we will present near IR photoresponse study of large area multi-walled carbon nanotube/poly(3-hexylthiophene)-b-polystyrene polymer (MWNT/P3HT-b-PS) nanocomposite films for different loading ratio of MWNT in polymer matrix. We show that, compared to pure MWNT film, there is a large enhancement of photocurrent in MWNT/polymer composite film. The photocurrent strongly depends on the position of the laser spot with maximum response occurring at the metal -- film interface. The time constant for the photoresponse is slow and varies between 0.6 and 1.2 seconds. We explain the photoresponse of the composite film by Schottky barrier modulation at the metal -- film interface and discuss reasons for the slow time response. [Preview Abstract] |
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K1.00187: Enhanced 1540 nm emission from ZnO:Er nanorod arrays via Ag island films Jiang-Wei Lo, Chin-An Lin, Jr-Hau He Self-assembled nanorod arrays (NRAs) heterostructures that consist of a single-crystalline Er-doped ZnO NRAs grown on Ag nanodot films have been synthesized by a chemical method and proposed as one of the promising optoelectronic materials since the Er intra-4f shell transition leads to 1540 nm emission for optical communication. The enhancement of 1540-nm emission of Er-doped ZnO NRAs via enhanced deep level emission of ZnO host resulted from local field enhancement effects of Ag nanodot films, and subsequent energy transfer to Er$^{3+}$ has been demonstrated. The microstructural analysis, electronic structure analysis, and photoluminescence characterizations have been performed to clarify the mechanism of enhanced 1540 nm emission. This paves the way to electrical pumping in a nano-system that forms NRAs of high-quality optical cavity. [Preview Abstract] |
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K1.00188: Influence of Negative-Bias Voltage on Mechanical Properties of Quaternary Ti(Nb)C(N) Coatings M.E. Gomez, J.C. Caicedo, C. Amaya, G.A. Mendoza, J. Alvarado-Rivera, J. Munoz-Saldana, P. Prieto Mechanical properties of quaternary Ti-Nb-C-N films via r.f magnetron sputtering process were studied by nanoindentation. The r.f. bias voltage was systematically varied from 0, -50, -100 V, keeping all other growth parameters fixed. Active vibration modes were analyzed by using Fourier transformed infrared spectroscopy (FTIR), where bands associated to Ti-N, Nb-C-N and Ti-C-N bonds, and to Ti-Nb-C-N stretching vibrations were found. Nanoindentation results reaching the elastic-plastic behavior of the Ti-Nb-C-N films indicate that both hardness and elastic modulus increase from 22 to 30 GPa and from 220 to 306 GPa, respectively. Thus, increasing the bias-voltage from 0 to -100V a clear improvement of hardness and elastic modulus were obtained. [Preview Abstract] |
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K1.00189: Electrical and Optical characterization of GaN$_{x}$As$_{1-x}$ fabricated using Ion Implantation and Pulsed Laser Melting Taeseok Kim, Michael J. Aziz, Venkatesh Narayanamurti, Kirstin Alberi, Oscar D. Dubon We present a systematic investigation of the band structure of GaN$_{x}$As$_{1-x}$ alloys synthesized using nitrogen ion implantation followed by pulsed laser melting and rapid thermal annealing. The evolution of the nitrogen concentration-depth profile is consistent with liquid-phase diffusion, solute trapping at the rapidly moving solidification front, and surface evaporation. The reduction of the Schottky barrier height at nitrogen composition up to $x$ = 0.016 is studied by ballistic electron emission microscopy (BEEM) and determined quantitatively using second voltage derivative (SD) BEEM spectra. This composition effect on the barrier height is consistent with the bandgap narrowing measured on the same samples by photomodulated reflectance and is also consistent with the band anti-crossing model for the splitting of the conduction band in GaN$_{x}$As$_{1-x}$ alloys. Lithographically patterned GaN$_{x}$As$_{1-x}$ dots are imaged by BEEM. Analysis of BEEM spectra from the locally confined dots indicates an alloying-induced decrease in the Schottky barrier height of four times the thermal energy at room temperature. [Preview Abstract] |
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K1.00190: SURFACES, INTERFACES AND THIN FILMS |
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K1.00191: Ab-initio study of the O covered Cu(100), Cu(110), and Cu(111) surfaces W.B. Maddox, N.G. Fazleev The study of adsorption of oxygen on transition metal surface is important for the understanding of oxidation, heterogeneous catalysis, and metal corrosion. The structures formed on transition metal surfaces vary from simple adlayers of chemisorbed oxygen to oxygen diffusion into the sub-surface region and the formation of oxides. In this work we present an ab-initio investigation of stability and associated physical and electronic properties of different adsorption phases of oxygen on Cu(100), Cu(110) and Cu(111) as well as of the clean Cu surfaces using density functional theory in the generalized gradient approximation and a four-layer slab to model the ideal Cu surfaces. In particular, we fully optimize the geometry of the surfaces with adsorbed oxygen and study the electronic structure, the changes in electron work function, surface energy, and interlayer spacings as a function of oxygen coverage. Furthermore, we study the chemistry of the metal-adsorbate bonding. Results and analysis are also presented for the Cu20 (100) surface. We compare our results to both experimental data and other theoretical models. [Preview Abstract] |
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K1.00192: Adsorption and Dissociation of Water on the (0001) Surface of DHCP Americium Pratik Dholabhai, Asok Ray Ab initio total energy calculations within the framework of density functional theory have been performed for water molecule adsorption on the (0001) surface of double hexagonal closed packed americium. Subsequent partial dissociation (OH+H) and complete dissociation (H+O+H) of the water molecule have been examined. The completely dissociated configuration exhibits the strongest binding with the surface followed by partially dissociated species, with all molecular H2O configurations showing weak physisorption. The change in work functions and net magnetic moments before and after adsorption will be presented for all the cases studied. The adsorbate-substrate interactions will be elaborated using the difference charge density distributions and the local density of states. The effects of adsorption on Am 5f electron localization-delocalization in the vicinity of the Fermi level will be discussed. [Preview Abstract] |
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K1.00193: Hydrogen adsorption on the (020) surface of $\alpha $-Pu -- A computational Study Asok Ray, Md Islam We have studied the hydrogen adsorption on (020) surface of $\alpha $-Pu and the effect of surface relaxation on chemisorption using relativistic full-potential augmented plane wave with local orbital basis method. The surface is modeled with four-layer slab consisting of 32 atoms with layer by layer anti-ferromagnetic arrangements. We have investigated the adsorption properties for four different adsorption sites, namely the top, the hollow, the short bridge and the long bridge sites. All the computations are carried out both at scalar relativistic level where spin-orbit interaction is ignored and where it is included, to study the effect of SO interaction on the adsorption properties. The effect of relaxation is also studied by calculating adsorption properties both on the relaxed and the non-relaxed surfaces. Our studies show that the short bridge is the most favorable site for hydrogen adsorption with chemisorption energy of 2.75 eV. Our study also shows that the spin-orbit coupling and the surface relaxation have very little impact on adsorption. [Preview Abstract] |
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K1.00194: Ab initio Calculation of optical properties of II-VI semiconductor surfaces R.A. Vazquez-Nava, Norberto Arzate, B.S. Mendoza In this work we present some {\it ab initio} calculations of reflectance anisotropy spectra (RAS) of VI-II semiconductor surfaces having different surface reconstructions. We use an $ab$ $initio$ pseudopotential formalism in the framework of the density functional theory and within the local density approximation (DFT-LDA). We study the (001) polar surface of cadmium telluride (CdTe) and zinc telluride ZnTe with differents reconstructions. Also we obtain RAS using a microscopic formulation based on a semi-empirical tight binding (SETB) approach which includes spin-orbit (SO) interactions [1]. We show RAS of each surface reconstruction and compare both theoretical results with experimental results [2]. We find a good agreement between experimental and theoretical spectra. \\[3pt] [1] R.A. V\'azquez-Nava, B.S. Mendoza and C. Castillo, Phys. Rev. B {\bf 70}, 165306 (2004). \\[0pt] [2] R. E. Balderas-Navarro, K. Hingerl, W. Hilber, D. Stifter, A. Bonanni and H. Sitter, J. Vac. Sci. Technol. B {\bf 18}, 2224 (2000). [Preview Abstract] |
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K1.00195: Structure, composition and optical band gap of TiO$_{2}$ films prepared by d.c. magnetron sputtering M.E. Gomez, A. Arias, E. Camps, L. Escobar-Alarcon, F. Espinoza, J. Munoz-Saldana, G.A. Mendoza, G. Zambrano Titanium dioxide (TiO$_{2})$ thin films have been grown on silicon (001) substrate by d.c. magnetron sputtering. in an gas mixture at different Ar/O$_{2}$ ratio flow and at two different substrate temperatures (400 and 550 $^{\circ}$C). Samples were characterized by X-ray diffraction, XRD, Raman spectroscopy, Scanning Electron Microscopy (SEM), Fourier Transformed Infrared Spectroscopy (FTIR) and UV-Vis analysis. Results showed that we obtained TiO$_{2}$-Anatase phase for the 90/10 of Ar/O$_{2}$ ratio in the gas mixture and at substrate temperature of 400 $^{\circ}$C. The anatase phase proportion in the films decreases by increasing the oxygen concentration in the Ar/O$_{2}$ gas mixture. Optical band gap of 2.9 and 2.7 eV was calculated from UV-Vis spectra for sample grown at 90/10 and 80/20 of Ar/O$_{2}$ ratio, respectively. [Preview Abstract] |
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K1.00196: Growth and characterization of EuO thin films Tom Brenner, M. Eblen-Zayas Eu-rich EuO is a ferromagnetic semiconductor that exhibits an insulator-metal transition associated with the onset of ferromagnetism and a colossal magnetoresistance response. In addition, the material is of interest for its possible use in spintronics. The materials properties are extremely sensitive to the stoichiometry of films. We will compare the properties of these films as a function of growth parameters, and discuss the stability of these films over time. In addition, we will present work comparing the properties of EuO thin films grown via reactive evaporation of Eu in the presence of an oxygen partial pressure with EuO films grown by Eu deposition followed by oxidation. [Preview Abstract] |
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K1.00197: Evolution of size distribution of Cobalt Silicide islands on (5x2) reconstructed Au/Si(111) surfaces Hung-Chih Kan, Ti-Li Lin, An-Li Chin, Fu-Kwo Men We report our preliminary result on the observation of the evolution of Cobalt silicide islands on (5x2) reconstructed Au/Si(111) surfaces during high temperature annealing with snap-shot scanning tunneling microscopy (STM). At room temperature, we deposited Co on (5x2) reconstructed Au/Si(111) surfaces in an ultra-high vacuum (UHV) enviroment. We then annealed the surface at temperatures around 500 \r{ }C, and first observed the formation of cobalt silicide islands on the terraces and across the steps. Subsequent annealing causes the islands to evolve: the islands across the step continued to grow while those on the terraces eventually disappeared. The ripening process clearly favors the islands cross the steps. We developed our own image processing algorithm to segment the STM images scanned from the surface into individual islands and terraces. With that we analyze and compare the statistical trend of the evolution of the islands across the steps and that of those on the terraces. [Preview Abstract] |
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K1.00198: Atomistic Modeling of the Grain Boundary in Silicon Hiroshi Mizuseki, Ryoji Sahara, Yoshiyuki Kawazoe By combining empirical potential approach with first-principles calculations, we investigate the atomic and electronic structures of grain boundary in silicon to estimate the deleterious effect on photovoltaic properties. Optimized geometries of several boundary structures are obtained by using a Tersoff potential. Moreover, the electronic structures of boundary have been examined using the density-functional theory with the plane-wave pseudopotential method. Calculations show that the electronic properties depend strongly on the atomistic structures, their properties are corresponding to efficiency of photovoltaic cell. This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) [Preview Abstract] |
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K1.00199: First principles study of Cu on Zn(0001): Resolution of the ($\sqrt{3}\times\sqrt{3}$)-R30$^{\circ}$ -- Cu/ZnO(0001) surface phase Katawut Chuasiripattana, Oliver Warschkow, Bernard Delley, Cathy Stampfl The Cu/ZnO system is a well known catalyst for methanol synthesis as well as hydrogen production from methanol by the reverse water gas-shift reaction. Despite many years of effort to clarify the characterization and the synergetic mechanisms between Cu and ZnO, there still exists considerable controversy such as the active phase of this combination catalyst. Recently, a ($\sqrt{3}\times\sqrt{3}$)-R30$^{\circ}$ phase has been reported on the Cu/ZnO(0001) surface (Dulub {\it et. al.}, Topics in Catalysis, {\bf 36}, 65 (2005)). This reconstruction appears in the LEED pattern after annealing the pre-deposited Cu-clusters on the ZnO(0001) surface at 350 $^{\circ}$C in a 10$^{-6}$ mbar O$_2$ environment for 10 minutes. In this work, we perform first-principles total- energy calculations within the framework of {\it ab initio} atomistic thermodynamics to investigate the atomic geometry and relative stability of this structure. We have extensively surveyed many possible atomic geometries, from which we are able to we propose the atomic structure of this ($\sqrt{3}\times\sqrt{3}$)-R30$^ {\circ}$ phase. To provide an overall understanding of this system, we also construct a two-dimensional phase diagram as a function of the Cu and O chemical potential, thus displaying the most stable surface structures. [Preview Abstract] |
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K1.00200: Halomethane Adsorption on Graphite and Silica surfaces C. Lamsal, G. Leuty, Jonathan Nehring, Mesfin Tsige Owing to their simple nature and number of practical applications, the adsorption of halomethanes onto various substrates has been a topic of study in materials science for a number of years. While a number of studies have reported on the surface characteristics of halomethane adsorption on simple, neutral substrates such as graphite, less well understood in general is the behavior of similar adsorbates on other, possibly widely different substrates. How the choice of substrate affects the manner in which these compounds are adsorbed as well as the effects of the substrate on the structure of the adsorbate more than a monolayer thick is less understood. In this presentation, we report the results of a recent molecular dynamics study comparing the structure and dynamics of systems composed separately of three tetra substituted halomethanes - $CF_4$, $CF_3Cl$, and $CF_3Br$ - adsorbed onto two different substrates - graphite and silica ($\alpha$-quartz) - along a range of temperatures to examine how these systems evolve and change according to the characteristics of the substrate surface. [Preview Abstract] |
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K1.00201: Structure analysis and Physical property of Multiferroic LuFe$_{2}$O$_{4}$ Thin films Minhwa Jung, Sangyoun Park, Yoonhee Jeong Multi-ferroic materials have stimulated considerable interest because of technical applications in modern electronic devices such as memory elements and switch devices. LuFe$_{2}$O$_{4}$ was reported to have both ferrimagnetism and charge-ordering-induced ferroelectricity with the charge and spin frustrations. Since the material must be grown in thin film form before one would utilize the physical phenomena in practical applications, we have attempted to grow thin films of LuFe$_{2}$O$_{4}$. We have successfully obtained LuFe$_{2}$O$_{4}$ thin films on sapphire (0001) substrates by the PLD method. Through XRD and PPMS measurements, their structure and magnetic property were characterized. In pole figure result, it showed 6 fold symmetry and there was a 30 degree rotation between the in-plane film and substrate direction. As for magnetic properties, we ascertained that the critical temperature was near 250K and it was identical to that of the bulk system. [Preview Abstract] |
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K1.00202: Optical and structural analysis of In$_{1-x}$Ga$_{x}$N alloys grown by HPCVD Goksel Durkaya, Max Buegler, Enno Malguth, Will Fenwick, Ian Ferguson, Nikolaus Dietz The In$_{1-x}$Ga$_{x}$N ternary alloy system has potential for development of high efficiency solar energy conversion and advanced optoelectronic device applications. Ga$_{1-x}$In$_{x}$N/In$_{1-x}$Ga$_{x}$N hetero-structures of various compositions can be engineered to the responsive from UV to IR wavelength regime, so that devices based on such heterostructures can cover the whole visible spectrum. However, the growth of such ternary In$_{1-x}$Ga$_{x}$N alloys is challenging. This contribution focuses on the structural and optical characterization of In$_{1-x}$Ga$_{x}$N layers and heterostructures grown by `high-pressure chemical vapor deposition (HPCVD), a growth technique that enables the stabilization of indium-rich In$_{1-x}$Ga$_{x}$N alloys at elevated temperatures using 15 to 20 bar nitrogen overpressure. We will present the structural analysis of In$_{1-x}$Ga$_{x}$N layers studied by Raman spectroscopy (RS), X-Ray Diffraction (XRD) and atomic force microscopy (AFM). The effects of composition and growth conditions on the layer surface topography and growth modes are studied by AFM. [Preview Abstract] |
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K1.00203: Two Different Types of Single Crystal Morphologies of the $\gamma $-Phase and Their Conversion in Isotactic Polypropylene Yan Cao, Ryan Van Horn, Chi-Chun Tsai, Matthew Graham, Kwuang-Un Jeong, Claudio De Rosa, Bernard Lotz, Stephen Z.D. Cheng In the past, the crystallographic relationship between the $\gamma $-phase and the $\alpha $-phase in isotactic polypropylene was extensively studied via oligomers of iPP. We attempt to investigate how the crystal morphological changes take place in the $\gamma $-phase using high molecular weight iPP-co-polyethylene samples. Due to the specific epitaxial growth of the $\gamma $-phase on the elongated $\alpha $-phase single crystals, two different morphologies were identified via transmission electron and atomic force microscopies. The first $\gamma $-phase crystal morphology is needle-like. Selective area electron diffraction results showed that their [$\overline 1 10$] or [110] zone axis was parallel to the thin film normal. The growth of this type of epitaxial $\gamma $-phase crystal was due to the stem direction in the initial $\alpha $-phase single crystal being parallel to the thin film normal. The second $\gamma $-phase crystal morphology was flat lamellae. This requires that the initial $\alpha $-phase single crystal had to have a stem orientation tilted away from the thin film normal. Therefore, the sufficient and necessary condition for the $\gamma $-phase morphological conversion from the needle-like crystal to the flat crystal is the change of the stem orientation direction of the initial $\alpha $-phase single crystals. [Preview Abstract] |
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K1.00204: Reactive properties of chemically modified Pd(100) surface revealed by Kinetic Monte Carlo simulations Dominic Alfonso The interaction of H$_{2}$ and CO with sulfur-covered Pd(100) surface represents a prototype model for understanding the various reasons for the poisoning of palladium by sulfur compounds. The use of Kinetic Monte Carlo method to investigate this system was explored. A Kinetic Monte Carlo code was developed and used to monitor the hosts of competing elementary steps associated with the adsorption, diffusion and desorption of H$_{2}$ and CO on the metal surface. The input parameters such as rate of reactions and lateral interactions were obtained from density functional theory calculations within the generalized gradient approximation. We demonstrate that Kinetic Monte Carlo simulation is a powerful tool for elucidating the microscopic details of the behavior of H$_{2}$ and CO on the poisoned surface. [Preview Abstract] |
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K1.00205: Adsorption of Dimethyl Disulfide (DMDS)~on a Metallic Quantum Well System Levan Tskipuri, Sylvie Rangan, Robert Bartynski We have studied the bonding of the thiol molecule dimethyldisulfide (SCH$_{3})_{2}$ on ultrathin Cu films that exhibit metallic quantum well (MQW) states using inverse photoemission (IPE), reflection-absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD). This thiol is similar to more complex organic molecule that exhibits the self-assembled properties on metal surfaces. After a room temperature exposure of the Cu surface to the thiol molecule at a dose of $\sim $ 2.5 L, a c(2 x 2) low energy electron diffraction (LEED) pattern confirmed that the adsorbate forms an ordered overlayer. A large sulfur signal is observed in Auger electron spectroscopy (AES) and the C-H stretch mode was observed in IR with a frequency of 2915 cm$^{-1}$ confirming molecular adsorption. Changes in the IPE spectrum upon adsorption are dominated by suppression of the substrate-related features, although some weak adsorbate-induced peaks are also observed. Both experimental and theoretical evidence indicates that electronic orbitals involved in molecule-surface bonding are in the same energy range as the MQW states of the substrate and the possible influence of MQW states on molecular adsorption and self-assembly of the thiol molecule will be discussed. [Preview Abstract] |
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K1.00206: Surface-state Emission of Si(111)-(7x7) Induced by Scanning Tunneling Microscopy Hiroshi Imada, Masashi Ohta, Naoki Yamamoto The luminescence measurement method we employ which utilizes a phenomenon called scanning tunneling microscope light emission (STM-LE) enables us to investigate surface structures with atomic resolution. However, STM-LE has not been well established, because the involved physics leaves many problems to be solved. In the present work, we studied STM-LE from Si(111)-7x7 surface to elucidate the nature of STM-LE of semiconductor surfac. All the experiments were performed in an UHV-STM. Ag-covered Mo tips were used. Photon mapping and spectral measurement were performed. Emission spectra of Si(111)-7x7 at both bias polarities show very similar shape and behavior. The peaks are at 1.4eV, 2.3eV and around 1.8eV and do not shift with applied voltage. Since the position of the peak around 1.8eV shifts with tip shape but those of the 1.4eV and 2.3eV do not, the 1.4eV and 2.3eV peaks are intrinsic to Si(111)-7x7 surface. Whole emission mechanism includes excitation of localized surface plasmon (LSP), excitation and decay (light emission) of surface electron and enhancement of the light. The photon maps show so high spatial resolution that individual adatoms can be clearly recognized. [Preview Abstract] |
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K1.00207: Confined states in metallic thin films analyzed with a one-dimensional-pseudo-potential approach Dah-An Luh, Cheng-Maw Cheng, Ku-Ding Tsuei, Jian-Ming Tang An approach based on a one-dimensional pseudo-potential (1DPP) is proposed to analyze the confined states in metallic thin films. The potential of a thin-film system near the Fermi level is approximated with a pseudo-potential that is constructed with periodic potentials in the substrate and the film and with an image potential in the vacuum. The confined states are obtained by solving the Schr\"{o}dinger equation. The result from applying the 1DPP approach to analyze the bound states in Ag/Au(111) thin films will be presented. [Preview Abstract] |
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K1.00208: ABSTRACT WITHDRAWN |
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K1.00209: A First Principles Study of the Adsorption and Dissociation of CO$_{2}$ on the $\delta $-Pu (111) Surface~ Raymond Atta-Fynn, Asok Ray \textit{Ab initio} calculations within the framework of density functional theory have been used to study the adsorption of molecular CO$_{2}$ and the corresponding partially dissociated (CO+O) and completely dissociated (C+O+O) products on the $\delta $-Pu (111) surface. The completely dissociated C+O+O configurations exhibit the strongest binding with the surface (5.85 eV), followed by partially dissociated products CO+O (4.34 eV), with molecular CO$_{2}$ adsorption having the lowest binding energies (2.98 eV). For all initial vertically upright orientations the CO$_{2}$ molecule is physisorbed and its geometry and orientation does not change. For all initial flat lying orientations chemisorption occurs, with the final state corresponding to a bent CO$_{2}$ molecule with bond angles of 118$^{o}$-130$^{o}$ except one case where spontaneous partial dissociation from the atop site occurs. The interactions of the CO$_{2}$ and CO with the Pu surface have been analyzed using the energy density of states and difference charge density distributions. [Preview Abstract] |
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K1.00210: delta zeta: Improvement of the reproducibility of zeta potential measurements by transformation Danish Faruqui, Paul J. Sides, Andrew J. Gellman When measuring the zeta potential of planar substrates as a function of pH, the results sometimes varied day by day even for the same sample treated exactly the same way. The shapes of the titration curves, however, were consistent despite apparent offsets. When data acquired on fused silica were transformed by subtracting the zeta potential measured at the initial condition from each subsequent measurement, however, data from many experiments fell on the same curve with a much reduced variance. Examination of the fundamental relationship between charge density and the zeta potential, derived from the Gouy Chapman theory of the electrical double layer, revealed that subtraction of the initial datum from each subsequent point amounted to cancellation of the total number of ionizable sites from the measurement. The transformed data reflected only chemical information such as equilibrium constants and activities. The principle assumptions are that the number of ionizable sites are fixed during a given experiment and the zeta potential magnitude is 100 mV or higher. Model expressions were verified for different mineral surfaces in range of aqueous solutions. [Preview Abstract] |
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K1.00211: Operando Positron Annihilation Gamma Spectrometer (OPAGS) S. Satyal, K. Shastry, S. Mukherjee, A.H. Weiss Surface properties measured under UHV conditions cannot be extended to surfaces interacting with gases under realistic pressures due to surface reconstruction and other strong perturbations of the surface. Surface probing techniques require UHV conditions to perform efficiently and avoid data loss due to scattering of outgoing particles. This poster describes the design of an Operando Positron Annihilation Gamma Spectrometer (OPAGS) currently under construction at the University of Texas at Arlington. The new system will be capable of obtaining surface and defect specific chemical and charge state information from surfaces under realistic pressures. Differential pumping will be used to maintain the sample in a gas environment while the rest of the beam is under UHV. Elemental content of the surface interacting with the gas environment will be determined from the Doppler broadened gamma spectra. This system will also include a time of flight (TOF) Auger spectrometer which correlates with the results of the Doppler measurements at lower pressures. By employing the unique capabilities of OPAGS together with those of the TOF PAES spectroscopy the charge transfer mechanisms at the surface in catalytic systems can be understood. [Preview Abstract] |
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K1.00212: Temperature Programmed Desorption Study of Dodecanethiol Self-Assembled Monolayers on Ag Simona Rieman, Nicholas Clark, Jennifer Walters, Daniel Field, Heike Geisler, Carl Ventrice The desorption kinetics of dodecanethiol self-assembled monolayers grown on Ag films has been studied using temperature programmed desorption. The self-assembled monolayers have been grown either in solution or by vapor deposition in UHV. The direct detection of dodecanethiol by the residual gas analyzer gives a complex spectrum due to multiple cracking fragments that are produced during the ionization of the molecule. The temperature programmed desorption measurements indicate that desorption of the self-assembled monolayer occurs in a two-stage process: dissociation of the alkane chain followed by desorption of the sulfur from the surface. Alkane chain fragments other than methane are observed to desorb over a range of $\sim $150$^{\circ}$C to $\sim $220$^{\circ}$C. Methane desorption starts at $\sim $100 ûC and persists to $\sim $350$^{\circ}$C. In addition, the desoption of sulfur is observed starting at $\sim $220$^{\circ}$C. [Preview Abstract] |
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K1.00213: Terpyridine Monolayer FETs as models for charge transport Xialing Chen, Aaron Crandall, Marcus Hanwell, Geoffrey Hutchison With the rising interest in organic electronic materials, an understanding of electronic transport, and the effects of defects on electronic transport, will be an important step towards a useful understanding of these materials. To this end, 2,2':6',2'' terpyridine will be used to make metal complexes which can act as organic semiconductors. Controlled variation of metals and ligands in these systems will make electronic defects in the system without substantive effect on the morphology of the film. Surface chemistry and self assembly can be used to form highly ordered monolayers on various substrates. AFM, FET mobility and bulk electrochemistry measurements are used to characterize these systems. Finally, experimental measurements will be compared with simulations of these systems, and the two will be used to better predict the behaviors of organic semiconductors in general. [Preview Abstract] |
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K1.00214: Ordered Layers of Co Clusters On Boron-Nitride Template Layers Axel Enders, Jae-Sung Kim , Geoffrey Rojas, Xumin Chen, Jian Zhang, Jan Honolka, Ralph Skomski The synthesis of highly ordered monolayers of metallic nanoclusters by a buffer-layer assisted growth (BLAG) route is introduced and investigated. The focus is on clusters of Co deposited onto mechanically stable, periodically corrugated boron-nitride layers by repeated BLAG cycles. The approach combines the advantages of well-established preparation methods for surface-supported clusters, namely the versatility of cluster deposition from the gas phase and the positional accuracy of the directed growth on template surfaces. The particle coverage and geometry are obtained from scanning tunneling microscopy experiments and analyzed with analytic models and by Monte-Carlo simulations. The model shows that the approach to full coverage is critically slowed down by attractive interparticle interaction, which results in the coalescence and growth of some of the clusters. The method represents a generic approach to fabricate ordered layers of clusters of virtually any metal. [Preview Abstract] |
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K1.00215: A Theoretical Study of the Graphite Surface Patterns Da Gao A quantitative understanding of surface patterns of graphite and other materials might has applications in nanostructure fabrication and surfaces engineering. For example, the controlled nanostructures growth is essential for the nanofabrication, which has already established its potential in industry. In this study, the Kinetic Monte Carlo (KMC) method has been employed to model and simulate the graphite crystal growth and surface patterns with our own developed software. In addition, we compared our theoretical results with the experimental observations. The good agreement between our simulations and the experiments not only provides insights and feasible mechanisms for controlling nanostructures growth in a more desirable pattern but also establishes that KMC is a promising method for such studies. [Preview Abstract] |
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K1.00216: Temperature and Interlayer Control of Schottky Barrier Height Yang Li, Wei Long, Raymond Tung The control of the magnitude of the Schottky barrier height (SBH) has been a much needed capability for advanced devices and design. Recent experimental and theoretical work has established the importance of controlling the interface structure in tuning the SBH. In our recent work, the temperature of the substrate and the effective temperature of the metal flux were individually and systematically varied to study their effects on the formation of the Schottky barrier. Electrical measurements, by variable temperature I-V and C-V method, of Au/Si and Ag/Si diodes fabricated on n- and p-type $<$100$>$ and $<$111$>$ substrates showed a significant dependence on fabrication conditions of the Schottky barrier. Lower deposition temperature led to more uniform contact between metal and semiconductor, which then led to higher SBH on n-type Si, with the expected, opposite dependence observed on p-type Si. In our present work, Silicon surfaces terminated with different types of stable closed-shell configurations are used to systematically study the influence of the interlayer on tuning the SBH. Electrical results and results obtained from surface chemical analysis and microscopic techniques are presented with special attention paid to the possible electrical inhomogeneity in the systems. [Preview Abstract] |
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K1.00217: Quantifying Polarization at Peptide-Gold Interfaces Due to Mirror Charges Kshitij Jha, Hendrik Heinz The contribution of attractive polarization effects~to interfacial interactions between even gold {\{}111{\}} and {\{}100{\}} surfaces with~water, a neutral~peptide (A3: AYSSGAPPMPPF), and a charged peptide (FlgNa$_{3}$: DYKDDDDK with Na counter-ions) in aqueous solution is quantified as part of an investigation to understand binding and specific interactions between peptides and metal nanoparticles. We apply the simple concept of mirror charges (additional Coulomb energy) a posteriori to molecular dynamics trajectories for different locations of the mirror plane, using the Consistent Valence Force Field (CVFF) extended with accurate LJ parameters for fcc metals.~The values of polarization energy show a relative trend A3 $<$ Flg-Na$_{3}<$ H$_{2}$O, and they are lower on {\{}111{\}} surfaces compared to {\{}100{\}} surfaces. On average, polarization energies amount to $\sim $140 mJ/m$^{2}$ when the image plane is located at the jellium edge and decrease to $\sim $5 mJ/m$^{2}$ when the image plane is located at the metal surface plane. Experiment and theory suggest a location close to the jellium edge, possibly inwards to the metal surface plane. Though absolute values are thus high, up to 2 kcal/mol per amino acid, they are $<$10{\%} of the experimental value of 1400 mJ/m$^{2 }$for gold-water interfacial tensions and $<$10{\%} compared to the strongest adsorbing amino acids ($>$20 kcal/mol). [Preview Abstract] |
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K1.00218: ATOMIC, MOLECULAR AND OPTICAL (AMO) PHYSICS |
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K1.00219: Ground state of the hydrogen negative ion Boyan Obreshkov Based on recently developed variational many-body Schr\"{o}dinger equation for electrons with Coulomb interactions [1], we provide first numerical results for the ground state electron structure of the hydrogen negative ion. It is shown that Fermi-Teller promotion effect together with non-adiabatic screening effects due to the Pauli's exclusion principle are responsible for the weak binding of the anion. The calculated ionization potential $J=-1/2 - 2 \lambda + \langle 1/r_{12} \rangle$ of the hydrogen negative ion is compared with the experiment, where $\lambda$ is the mean binding energy per one electron in the ground state.\\[0pt] [1] B.~D.~Obreshkov , Phys.~Rev.~A {\bf 78}, 032503 (2008). [Preview Abstract] |
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K1.00220: Electric Field-enhanced Intermolecular Bonding: an Ab Initio Density Functional Investigation Rajeev Pathak Effects of external electric field on some otherwise weakly bound molecular complexes are investigated within the density functional theory. The complexes are comprised of polar and non-polar molecules, which otherwise interact via van der Waals bond, or through a weak hydrogen bond. Applied field distorts the geometry and forces the molecules to come closer to each other leading to a remarkable enhancement in the bonding between the otherwise weakly bonded atoms. We investigate this phenomenon with the density functional theory applied two prototype systems in external electric field, viz. acetylene + water and carbon-dioxide + water systems where the applied field strengthens the bonding, considerably so in the latter case. [Preview Abstract] |
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K1.00221: Charge Exchange in Slow Collisions of O+ with He L.B. Zhao, D.C. Joseph, B.C. Saha, H.P. Lebermann, P. Funke, R.J. Buenker A comparative study is reported for the charge transfer in collisions of O$^+$ with He using the fully quantal and semiclassical molecular-orbital close-coupling (MOCC) approaches in the adiabatic representation. The electron capture processes O$^+$($^4$S$^o$, $^2$D$^o$, $^2$P$^o$) + He $\to$ O($^3$P) + He$^+$ are recalculated. The semiclassical MOCC approach was examined by a detailed comparision of cross sections and transition probabilities from both the fully quantal and semiclassical MOCC approaches. The discrepancies reported previously between the semiclassical and the quantal MOCC cross sections may be attributed due to the insufficient step-size resolution of the semiclassical calculations. Our results are also compared with the experimental cross sections and found good agreements. This work is supported by NSF, CREST program (Grant\#0630370). [Preview Abstract] |
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K1.00222: K-Shell Ionization of Neutral Targets by Electron Impact A.K.F. Haque, M.S.I. Sarker, M.A.R. Patoary, M. Shahjahan, M.I. Hossain, M.A. Uddin, A.K. Basak, B.C. Saha The electron impact K-shell ionization cross sections (EIKICS) are needed in diverse fields, such as plasma-, radiation-, astro-physics. For plasma modeling the demand of EIKICS is enormous; this can only be fulfilled by simple analytical or semi-classical models that can generate efficiently accurate results over broad ranges of projectile energies and target species. We modified the Deutsch-Mark [1] model by incorporating ionic and relativistic corrections and applied to evaluate K-shell ionization cross sections for 30 atomic targets, 1$<$Z$<$92 for 1$<$E$<$2 GeV with very encouraging results as compared to available experimental findings. Work is supported by NSF, CREST project.\\[0pt] [1] H. Deutsch, P. Scheier, K. Becker, T. D. Mark, Int. J of Mass Spectrom, 233, 13 (2004). [Preview Abstract] |
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K1.00223: Gold cluster beyond hollow cage: Double-shell Au$_{58}$ Chuan-ding Dong, Xin-gao Gong Gold clusters were found to have planar and hollow cage-like structures due to the strong relativistic effect. By using first principles calculation, we take Au$_{58}$ as an example to demonstrate that gold cluster can show shell structure. Au$_{58} $ reaches its highest stability with an optimal inner core of $10$ atoms. Particularly, a double-shell structure with a hollow inner shell shows remarkable robustness. It is significant to consider this shell structure as a descendant of the hollow cage structures found previously, such as tetrahedral Au$_{16}$, icosahedral Au$_{32}$, tubular Au$_{50}$ and so on, for this implies a possible evolution from planar, to cage, to shells and finally to the compact structure as the number of atoms in the cluster increasing. [Preview Abstract] |
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K1.00224: An Investigation of Methanol Transitions at Cold Temperatures through Collisional Cooling Kelly Salb, Daniel Willey The detection of molecular transitions in the interstellar medium (ISM) has long been of interest to astrophysicists. If molecules and their interactions can be understood, then scientists may better understand the workings of space such as star formation. Methanol, CH3OH, has long been detected by astrophysicists in the ISM as an important constituent with a rich spectrum as a result of its asymmetry and that its low-energy torsional vibrations of the methyl group against the OH top can be excited under interstellar conditions. We investigate collisions of methanol with helium, a prominent constituent of the ISM, at temperatures between 5-30K through spectroscopy to better understand the interaction in the ISM. [Preview Abstract] |
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K1.00225: Non-Linear Interactions in Pump-Probe Optical Phenomena Verne Jacobs Reduced density matrix descriptions are developed for pump-probe optical phenomena in atomic systems, taking into account atomic collisions as environmental phenomena. Time-domain (equation-of-motion) and frequency-domain (resolvent- operator) formulations are developed in a unified manner. In a semiclassical perturbative treatment of the electromagnetic interaction, compact Liouville-space operator expressions are derived for the linear and the general (n'th order) non-linear electromagnetic-response tensors. These expressions are valid for coherent atomic excitations and for the full tetradic-matrix form of the collision operator in the Markov approximation. [Preview Abstract] |
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K1.00226: Efficient and Selective Photon Detection using Amplification Without Inversion. Kevin Mertes, Michael Di Rosa We describe ongoing theoretical and experimental research at Los Alamos National Laboratory of a new technology for photon detection that exploits quantum processes to attain an unrivaled combination of high quantum efficiency and sharp spectral discrimination. The amplification without inversion (AWI) scheme we are exploring consists of a $\Lambda $ system found in the excited states of $^{202}$Hg. The $6^3P_0 \Rightarrow \left| 1 \right\rangle $ and $6^3P_2 \Rightarrow \left| 2 \right\rangle $ states form the lower 2 levels of the $\Lambda $ system, and $7^3S_1 \Rightarrow \left| 3 \right\rangle $ forms the upper level. By incoherently pumping Hg vapor into $\left| 3 \right\rangle $ while simultaneously driving $\left| 3 \right\rangle \leftrightarrow \left| 2 \right\rangle $, approximately 50{\%} of the population will reside in $\left| 1 \right\rangle $. Under these conditions, the system is radiating along $\left| 3 \right\rangle \to \left| 1 \right\rangle $ with an emission spectrum with a narrow dark line centered precisely on the $\left| 3 \right\rangle \to \left| 1 \right\rangle $ resonance. A faint light signal that is resonant with the $\left| 3 \right\rangle \to \left| 2 \right\rangle $ transition that enters the system would precipitate a coherent pulse of photons. This gain occurs from the coherent redistribution of population through level $\left| 3 \right\rangle $. The expected spectral width for gain is a narrow 20 MHz. Due to spontaneous-emission quenching the noise added from this scheme should be significantly less than ordinary laser amplifiers. [Preview Abstract] |
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K1.00227: Improved test of the standard model of elementary particles with atomic parity violation Kyle Beloy, Sergey Porsev, Andrei Derevianko Atomic parity violation places powerful constraints on new physics beyond the Standard Model (SM) of elementary particles. The measurements are interpreted in terms of the nuclear weak charge, quantifying the strength of the electroweak coupling between atomic electrons and quarks of the nucleus. We report the most accurate to-date determination of this coupling strength by combining previous measurements by the Boulder group with our high-precision calculations in cesium atom. Our result is in a perfect agreement with the prediction of the SM. In combination with the results of high-energy collider experiments, our work confirms the predicted energy dependence (or ``running'') of the electroweak interaction over an energy range spanning four orders of magnitude (from $\sim 10$ MeV to $\sim 100$ GeV) and places new limits on the masses of extra $Z$ bosons ($Z^\prime$). Our raised bound on the $Z^\prime$ masses carves out a lower-energy part of the discovery reach of the Large Hadron Collider. At the same time, a major goal of the LHC is to find evidence for supersymmetry (SUSY), one of the basic, yet experimentally unproven, concepts of particle physics. Our result is consistent with the R-parity conserving SUSY with relatively light (sub-TeV) superpartners. This raises additional hopes of discovering SUSY at the LHC. [Preview Abstract] |
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K1.00228: Micromagic clock: microwave clock based on atoms in an engineered optical lattice Kyle Beloy, Andrei Derevianko, Vladimir Dzuba, Victor Flambaum We propose a new class of atomic microwave clocks based on the hyperfine transitions in the ground state of aluminum or gallium atoms trapped in optical lattices. For these elements {\em magic} wavelengths exist at which both levels of the hyperfine doublet are shifted at the same rate by the lattice laser field, cancelling its effect on the clock transition. This work represents an elegant piece of theoretical physics containing a challenge to the experimentalist to realize a new frequency standard based on these proposed clocks. [Preview Abstract] |
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K1.00229: Electron Precession in Atonic Mechanics Alfred Phillips, Jr. With Atonic Mechanics we have been able to accurately calculate the measured values of the NIST He I and He II energy levels. Our model requires much less mathematical tedium than does the Schrodinger method but with equal accuracy. We made the conjecture that the angular momentum for excited electrons is (n + delta n) h-bar. We had hypothesized that the delta n was a fractal. We have subsequently found a more conventional quantum mechanical explanation for delta n. We model the delta n by assuming that the excited electron undergoes precession with a quantum number, l, having values of 1, 2, 3, . . . We will discuss the precession model. We expect that our model may be used in calculating the spectra of more complex atoms, lithium onward, that have been formidable mathematically using the Schrodinger theory. [Preview Abstract] |
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K1.00230: COLD GAS |
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K1.00231: Faraday patterns in interference experiments with one dimensional gases of ultracold atoms Susanne Pielawa, Vladimir Gritsev, Eugene Demler We analyze a quantum analogue of the Faraday instability in one dimensional ultracold gases. Temporal periodic modulation of the interaction strength parametrically excites collective modes and gives rise to standing wave patterns in interference experiments. We discuss both bosonic and fermionic systems and demonstrate that such experiments can be used to probe spin charge separation. [Preview Abstract] |
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K1.00232: Phase Separation in Bose-Superfluid Fermi Mixtures B. Ramachandhran, S.G. Bhongale, H. Pu We study the phase diagram of 3-dimensional mixtures of BEC and a two-component superfluid fermi gas, referred to as Bose-Superfluid fermi mixtures, at zero and finite temperature. At zero temperature, we identify regimes at equilibrium in which the mixture exists either as a pure superfluid phase coexisting with a mixed phase or as a single homogenous phase. We identify critical boson densities at which phase separation occurs for different values of the fermi-fermi interaction strength. As a potential application of this phase separation phenomenon, we consider BEC to be in a realistic cigar-shaped double-well trap acting as a probe of the superfluid state. We show that the critical boson densities obtained from the phase diagram can be used to map the spatial density profile of the bosons using Local Density Approximation (LDA) in the trap setting. We show a methodology to robustly detect the ``local'' value of the superfluid Gap parameter by observing the boson density profile in the trap. We also explore the more challenging problem of phase separation in these mixtures at finite temperature. We show that, under proper conditions, this spatial phase separation phenomenon occurring in the presence of the BEC probe can be used to potentially detect the onset temperature of the BCS superfluidity. [Preview Abstract] |
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K1.00233: Fermionic quantum gases with tunable interactions in optical lattices Ulrich Schneider, Lucia Hackerm\"uller, Thorsten Best, Sebastian Will, Simon Braun, Maria Moreno Cardoner, Belen Paredes, Immanuel Bloch Fermionic atoms in optical lattices can serve as a model system for condensed matter physics, as they present an implementation of the Hubbard hamiltonian with high experimental control of the relevant parameters. In our system we sympathetically cool $^{87}$Rb and $^{40}$K in an optically plugged quadrupole trap and an optical dipole trap. After evaporation, a balanced spin mixture of 40K atoms is loaded into a blue detuned optical lattice where the interactions can be changed via a Feshbach resonance. We present experimental and theoretical studies of the behaviour of fermionic atoms for both attractive and repulsive interactions. For repulsive interactions we show a transition from compressible, metallic states to Mott-insulating and finally band insulating states. On the attractive side we investigate an anomalous expansion when the interaction is strongly attractive and study the dynamics of atoms and repulsively and attractively bound pairs. [Preview Abstract] |
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K1.00234: Interacting Mixtures of Bosons and Fermions in Optical Lattices Sebastian Will, Thorsten Best, Simon Braun, Ulrich Schneider, Lucia Hackerm\"uller, Immanuel Bloch Mixtures of ultracold atomic quantum gases in optical lattices form novel quantum many-body systems offering unique controllability. In particular, degenerate Bose-Fermi mixtures have only recently come into experimental reach and are the topic of fruitful theoretical investigation. Among the most prominent predictions are the formation of charge-density waves, polaron-like quasi-particles and even supersolid ordering. We have prepared a mixture of bosonic ${}^{87}$Rb and fermionic ${}^{40}$K in a 3D optical lattice potential and investigated its properties depending on the interspecies interaction. We found a marked shift in the superfluid to Mott-insulator transition and were able to fully explain our findings in terms of an effective Bose-Hubbard model, employing renormalized Hubbard parameters. In recent measurements of the absolute intra- and interspecies interaction energies on individual lattice sites, we were able to further elucidate the effects of interaction in the optical lattice – a thorough understanding of which may be an important step on the way towards complex quantum many-body states. [Preview Abstract] |
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K1.00235: Spin-imbalance of ultracold Fermions in quasi-1D Ann Sophie C. Rittner, Yean-an Liao, Wenhui Li, Tobias Paprotta, Randall G. Hulet After the success of BCS theory, more exotic forms of superfluidity have generated large interest in the condensed matter and cold atoms community. One prominent example is the elusive Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, a polarized superfluid that is predicted to occur when superconductors are subjected to a strong magnetic field. At present, there is only indirect experimental evidence of FFLO in the heavy fermion superconductor CeCoIn5. An alternate route to directly observe this phase is provided by ultracold spin-polarized Fermi gases. 3D polarized Fermi gases exhibit two distinct low temperature phases, an unpolarized superfluid and a polarized normal phase, which phase separate in an optical trap \footnote{Partridge et al., Science 311, 503 (2006)}. There is no experimental evidence for the FFLO phase in a 3D system, but it is predicted to occupy a larger region of the phase diagram in a quasi-1D system. We have implemented a 2D optical lattice in order to explore the phase diagram of a quasi-1D polarized Fermi gas. [Preview Abstract] |
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K1.00236: Wavepacket Dynamics in Energy Space of a Chaotic Trimeric Bose-Hubbard System Moritz Hiller, Tsampikos Kottos, Theo Geisel We study the energy redistribution of interacting bosons in a ring-shaped quantum trimer as the coupling strength between neighboring sites of the corresponding Bose-Hubbard Hamiltonian undergoes a sudden change $\delta k$. In the framework of (ultra-)cold atoms on optical lattices this perturbation corresponds to a modulation of the trapping potential height. Our analysis is based on a three-fold approach combining linear response theory calculations as well as semiclassical and random matrix theory considerations. The $\delta k$-borders of applicability of each of these methods are identified by direct comparison with the exact quantum mechanical results. We find that while the variance of the evolving quantum distribution shows a remarkable quantum-classical correspondence (QCC) for all $\delta k$-values, other moments exhibit this QCC only in the non-perturbative $\delta k$-regime. [Preview Abstract] |
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K1.00237: A quantum gas microscope for the simulation of condensed matter systems Waseem Bakr, Jonathon Gillen, Amy Peng, Simon Foelling, Markus Greiner Ultracold atoms in optical lattices provide an exciting new opportunity to study condensed matter physics. These systems allow for the implementation of idealized theoretical models with high fidelity. Compared to typical real crystals, the lattice spacings of the optical potential are increased by at least three orders of magnitude, bringing optical single site addressability within reach. Imaging atoms on single lattice sites will allow direct detection of quantum states such as the Mott insulator and antiferromagnetic states. We present our implementation of a quantum gas microscope to experimentally realize high resolution imaging and spatial addressability of a rubidium atom ensemble loaded into an optical lattice. Very good optical access to the atoms combined with solid immersion-like geometry is expected to provide an imaging resolution of about 0.5 microns. We realize a long lived two-dimensional quantum gas inside a novel opto-magnetic surface trap using an evanescent wave potential. To create the lattice potential we developed a projection approach using holographic phase masks. We have loaded a quantum gas into the lattice potential and are working on resolving single atoms on the lattice sites. [Preview Abstract] |
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K1.00238: Quantum nucleation and macroscopic quantum tunneling in cold-atom boson-fermion mixtures Dmitry Solenov, Dmitry Mozyrsky We present the results on kinetics of phase separation transition in boson-fermion cold atom mixtures. The parameters at which the transition is governed by quantum nucleation mechanism are identified. We demonstrate that for low fermion-boson mass ratio the density dependence of quantum nucleation transition rate is experimentally observable. The crossover to macroscopic quantum tunneling regime is analyzed. Based on a microscopic description of interacting cold atom boson-fermion mixtures we derive an effective action for the critical droplet and obtain an asymptotic expression for the nucleation rate in the vicinity of the phase transition and near the spinodal instability of the mixed phase. We show that dissipation due to excitations in fermion subsystem play a dominant role close to the transition point. [Preview Abstract] |
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K1.00239: QUANTUM INFORMATION, CONCEPTS, AND COMPUTATION |
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K1.00240: ABSTRACT WITHDRAWN |
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K1.00241: Quantum manipulation of low-frequency fluctuators with a superconducting resonator Lin Tian, Kurt Jacobs Spurious two-level systems (fluctuators) in superconducting devices have demonstrated long coherence time and can be considered as qubits instead of sources of decoherence. Coherent coupling between two-level system (TLS) and superconducting phase qubit has been observed in experiments. Here, we show that universal quantum logic gates on the TLS qubits can be implemented via the coupling between the TLSs and a superconducting microwave resonator in a cavity QED setup. By adjusting the driving on the resonator mode, parameters of individual TLS can be controlled to realize single qubit gates. Meanwhile, effective coupling can be generated between TLSs via their simultaneous coupling to the resonator mode. We present concrete designs for the gate operations and our numerically simulation shows that high fidelity can be achieved for the gate operations in the presence of resonator decay even at decay rates of a few megahertz. The nonlocal nature of the resonator mode also makes the TLSs intrinsically scalable for testing quantum algorithms. [Preview Abstract] |
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K1.00242: Higher Energy Levels in Qubit Networks Zechariah Thrailkill, Joseph Lambert, Roberto Ramos Josephson junctions can be capacitively coupled together to form qubit networks capable of carrying out quantum logic operations. In order to fully utilize these systems, the influence of energy levels higher than the ground and first excited states in the qubits must be examined. We have analyzed such networks with three, four, and more qubits biased to both anharmonic and harmonic regimes. As the qubits become harmonic, the higher energy levels will interact more strongly with the computational basis. Allowing the system to pass through these higher energy levels can allow quantum state transfers where, in the anharmonic regime, it would not occur. We will discuss the impact these higher energy levels have on the natural state evolution of the systems, quantum information transfer, and state manipulation using a time independent, or adiabatically changing Hamiltonian. [Preview Abstract] |
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K1.00243: Quantum hacking: Experimental demonstration of time-shift attack against practical quantum-key-distribution systems Yi Zhao, Chi-Hang F. Fung, Bing Qi, Christine Chen, Hoi-Kwong Lo Quantum key distribution (QKD) systems can send signals over more than 100 km standard optical fiber and are widely believed to be secure. Here, we show experimentally for the first time a technologically feasible attack, namely the time-shift attack, against a commercial QKD system. Our result shows that, contrary to popular belief, an eavesdropper, Eve, has a non-negligible probability ($\sim$4\%) to break the security of the system. Eve's success is due to the well-known detection efficiency loophole in the experimental testing of Bell inequalities. Therefore, the detection efficiency loophole plays a key role not only in fundamental physics, but also in technological applications such as QKD. Our work is published in [1]. \\[4pt] [1] Y. Zhao, C.-H. F. Fung, B. Qi, C. Chen, and H.-K. Lo, Phys. Rev. A, 78:042333 (2008). [Preview Abstract] |
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K1.00244: Density functional theory and quantum computation Frank Gaitan, Franco Nori We demonstrate the applicability of ground-state and time-dependent density functional theory to quantum computing systems by proving the Hohenberg-Kohn and Runge-Gross theorems for a fermion system representing $N$ qubits. Time-dependent density functional theory is used to determine the minimum energy gap $\Delta (N)$ arising from application of the quantum adiabatic evolution algorithm to the NP-Complete problem MAXCUT. As density functional theory has been used to treat quantum systems with as many as 650 interacting degrees of freedom, this raises the realistic prospect of evaluating the gap $\Delta (N)$ for systems with $N\alt 650$ qubits. [Preview Abstract] |
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K1.00245: Efficient local implementation of bipartite nonlocal unitaries Li Yu, Robert Griffiths, Scott Cohen By definition, nonlocal unitaries cannot be implemented locally. However, if spatially separated parties share nonlocal resources (i.e., entanglement), they may be able to implement a nonlocal unitary by performing only local operations and sharing classical information. We provide protocols for doing so, which generalize previously published methods and in many cases allow tasks to be accomplished with fewer nonlocal resources than is required when using teleportation. We also discuss our insight into how and why entanglement allows such a task to be accomplished, an insight which arises from a diagrammatic approach allowing one to picture the processing of quantum information. [Preview Abstract] |
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K1.00246: Electronic and Magnetic Properties of B$_{5}$CX (X=V, Cr, Mn, Fe, Ni, and Co): a Theoretical Study Dayne Shields, Wai-Ning Mei, Jing Lu, Peter A. Dowben We used on-site correlation corrected density functional theory to investigate the structure and magnetic properties of the recently synthesized B$_{5}$CX-Co and many other substitutions. We found that the Co and Ni molecules were non-magnetic. Other than that: Cr had both stable ferro- and antiferromagnetic structures. The V, Mn, and Fe molecules are not stable, we have to treat them as infinitely long chain molecules. [Preview Abstract] |
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K1.00247: Scattering in Quantum Lattice Gases Andrew O'Hara, Peter Love Quantum Lattice Gas Automata (QLGA) are of interest for their use in simulating quantum mechanics on both classical and quantum computers. QLGAs are an extension of classical Lattice Gas Automata where the constraint of unitary evolution is added. In the late 1990s, David A. Meyer as well as Bruce Boghosian and Washington Taylor produced similar models of QLGAs. We start by presenting a unified version of these models and study them from the point of view of the physics of wave-packet scattering. We show that the Meyer and Boghosian-Taylor models are actually the same basic model with slightly different parameterizations and limits. We then implement these models computationally using the Python programming language and show that QLGAs are able to replicate the analytic results of quantum mechanics (for example reflected and transmitted amplitudes for step potentials and the Klein paradox). [Preview Abstract] |
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K1.00248: Novel approach to the dynamics of a dissipative two-state system Peter P. Orth, Adilet Imambekov, Karyn Le Hur A two-state system in contact with a harmonic oscillator bath is frequently used to describe the process of decoherence in physical systems, such as a spin in a solid-state environment or a qubit coupled to external and uncontrolled degrees of freedom. The problem in general cannot be solved exactly, and several approximative methods have been devised such as Bloch-Redfield master equations, which are limited to weak-coupling, or the Non-Interacting Blip Approximation (NIBA), that neglects the system's backaction onto the bath. We study the dissipative two-state dynamics in a novel way, rephrasing the problem as that of (non-)unitary time evolution of a quantum state vector exposed to a random Gaussian perturbation Hamiltonian. Our formalism goes beyond the NIBA and is particularly well suited to study the case of time-dependent system parameters. We compare it to common approaches such as the (extended)-NIBA, or stochastic wave-function methods. Furthermore, we investigate dissipative Landau-Zener tunneling in the so-called scaling limit. [Preview Abstract] |
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K1.00249: Classical Derivation of Fermion Operators and Correlations Robert Close A second-order wave equation is derived for an ideal elastic solid. The Klein-Gordon equation is a special case of this equation in which the mass term replaces the nonlinear rotation and convection terms. The second-order wave equation is factored to yield a first order bispinor equation. This equation is similar to the Dirac equation. The corresponding Lagrangian is constructed in terms of bispinors. The quantity conjugate to angular velocity is the quantum mechanical angular momentum. The quantity conjugate to velocity includes the quantum mechanical wave momentum and also the momentum of the medium. Along a given axis there are two independent solutions corresponding to forward- and backward-propagating waves. Since these independent states are separated by 180 degrees, their bispinor wave functions transform under rotation with spin one-half. Potentials are derived from consideration of wave interference. Parity is conserved. The conventional Dirac parity operator is incorrect because it represents a 180 degree rotation rather than inversion of velocity space. Correlations between classical bispinor wave functions are identical to the quantum correlations. [Preview Abstract] |
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K1.00250: Modeling and Simulation of Fault Tolerant Quantum-dot Cellular Automata Devices Benjamin Padgett, Gabriel Anduwan, Michael Kuntzman, Ioan Sturzu, Mahfuza Khatun We present a theoretical study of fault tolerant properties in Quantum-dot Cellular Automata (QCA) Devices. The study consists of modeling and simulation of various possible manufacturing, fabrication and operational defects. We will present specifically the effects of temperature and manufacturing defects at the cell level and array level of various QCA devices. Results of simple devices such as quantum wire, logical gates, inverter, cross-over and XOR will be presented. The cell defects would include displaced dots and missing dots. A Hubbard-type Hamiltonian and the Inter-cellular Hartree approximation have been used for modeling the QCA devices. Various techniques such as normal, uniform and random distributions have been used for defect simulations. In order to show the operational limit of a device, defect parameters have been defined and calculated. Results show fault tolerance of a device is strongly dependent on the temperature as well as on the manufacturing defects. [Preview Abstract] |
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K1.00251: Fault-Tolerant Characteristics of Quantum-dot Cellular Automata Devices Mahfuza Khatun, Gabriel Anduwan, Ioan Sturzu The operational behavior of the Quantum-dot Cellular Automata (QCA) devices has been investigated regarding both dot displacement and temperature effects. Each of the breakdown characteristics displayed unique features for every particular QCA device. We have found that the characteristic features of the basic logic QCA devices are inherited by the higher or complicated QCA devices, such as the full adder. It was observed that the presence of a crossover of QCA lines in a full adder design was a major factor for the breakdown. Thus, a proposed full adder QCA device without a crossover was seen to improve the successful operation of a full adder. [Preview Abstract] |
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K1.00252: Extraction of correlated 2-photons with near unity efficiency Alexander Ling, Jun Chen, Jingyun Fan, Alan Migdall We report a source of 2-photons that can be extracted with near unit efficiency. The reduced mode area of solid-core microstructure fibers lets a light pulse induce significant nonlinear optical interaction inside a short fiber, making it easy to generate 2-photon entanglement. However, the photon extraction efficiency is low due to the small core size ($d\sim $1 $\mu $m) that requires high numerical aperture (NA) lenses to couple light in and out of the fiber. Tapering the core at the fiber end to 10 $\mu $m allows the use of anti-reflection-coated lenses of smaller NA, to achieve a single-photon extraction efficiency of \textit{$\eta $}$_{f}$ = 96{\%}. Using a pair of volume holographic gratings for selecting any wavelength of interest increased our spectral transmittance for that wavelength to \textit{$\eta $}$_{g}$ = (98{\%})$^{2}$, enabling a near unit efficiency in extracting a single photon from the fiber source: \textit{$\eta $}$_{f}$\textit{$\eta $}$_{g}$ = 92.2{\%}. The final 2-photon detection efficiency of 10{\%} includes the efficiencies of single-photon detection modules ($\sim $ 70{\%} each) and single-mode fiber collection ($\sim $ 50{\%} per channel). At an average pump power of $P$ = 50 $\mu $W and a laser repetition rate of $R$ = 76 MHz, we detect 50 photon pairs s$^{-1}$ with $g^{(2)}$(0) = 0.0055 and a coincidence-to-accidental ratio of 900:1. Higher pair rates at the same $g^{(2)}$ level can be achieved by increasing $R. $With better photon detection, this source may enable loophole-free Bell tests. [Preview Abstract] |
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K1.00253: Negativity for spin one anisotropic Heisenberg clusters in magnetic field Armen Kocharian, Nerses Ananikyan, Lev Ananikyan, Vahagn Abgaryan The quantum and thermal phase transitions are studied for spin s=1 in anisotropic (ferromagnetic and antiferromagnetic) XXZ and Heisenberg small clusters with longitudinal crystalline and magnetic fields. We investigate the concept of entanglement. The grand canonical ensemble of Heisenberg clusters is also used for exact analytical and numerical calculations of thermal properties and negativity as a function of magnetic and anisotropic fields. We study the negativity, magnetic phase transitions and crossovers in small clusters of various topologies driven by exchange interaction, external field and temperature. The negativity effect as a function of temperature and magnetic field is studied for both ferromagnetic and antiferromagnetic cases. The thermal behavior of negativity can capture the important properties in single molecule magnets, the dynamic magnetization and these our results can be useful for interpretation of the phase diagram in molecular nanomagnets and nanometer-sized magnetic particles. [Preview Abstract] |
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K1.00254: Cavity -Quantum Dot interactions and mode coupling in a nanocavity Vijay Kasisomayajula, Onofrio Russo We describe an approach for realizing effective manipulation of single electron state level transitions for quantum dots mediated by a nano-cavity. The two quantum dots interact with the cavity for the two dot system in the coulomb blockade energy region. Because of the zero dimensional structure of the quantum dots, the system can be implemented to be a characteristic entity for an efficient generator of single photons. This process is emphatically more selective in the coulomb/spin blockade region, where also, the system efficiency of the single photon event is most likely more probable. Whereas, it is clear that the photon efficiency is small, the cavity quantum electrodynamics (CQED) nature suggests an enhancement in the electron energy state being occupied by the second quantum dot. This is more likely with very strong coupling of the quantum dots to the cavity with cavity quality factors larger than perhaps 10$^{5}$. Quality factors in excess of 10$^{5 }$have been demonstrated experimentally$^{1}$. 1. K. Srinivasan, M. Borselli, T. J. Johnson, P. E. Barclay, O. Painter, A. Stintz, and S. Krishna, Appl. Phys. Lett. \textbf{86}, 151106 (2005). [ISI] [Preview Abstract] |
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K1.00255: Linear, Rotational and Vibrational KInetic Energies Must Be Included in Mass-Energy Calculations Stewart Brekke All bodies have no motion, have linear, rotational and/or vibrational motion, singly or in some combination. Curvilinear motion is linear motion influenced by an external force field. The total energy of a body therefore must include the linear rotational and vibrational kinetic energies if present besides just the mass-energy conversion which may reconcile experimental data with theory even though these extra energies may be very small in comparison. If k is a force constant, x is the amplitude of vibration and omega is the angular speed, the formula for E zero is as follows.\[E_0= m_0c^2 + 1/2m_0v^2 + 1/2I\omega^2 + 1/2kx_{0}^{2}\] [Preview Abstract] |
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K1.00256: Consciousness Can Change the Output Signals of a Solar Cell and the Photoelectric Conversion Equation of Slow Mass Wave Dayong Cao The experiment's results show that human consciousness can change output signals such as V$_{oc}$ (open-circuit voltage) and I$_{sc}$ (short circuit current) of a solar cell placed some distance from a participant. For the first time, a consciousness signal is able to be recorded through the experiment conducted in Oct 2002. The order and rhythm of the changing wave pattern of V$_{oc}$ is related to the action of consciousness. The order and rhythm of slow brain signal of ERP and EEG are related to the cognized objects. Consciousness is independent and self-determined while brain signal is passive and driven. Consciousness is spiritual and Intelligence while brain signal is physical, corporality and mechanic. So consciousness is different from the brain signal. And consciousness effection is different from physical effection of light. Because consciousness can choose the object which it acts on. The light have a pairt of mass wave of low frequency and energy wave of high frequency. In photoelectric conversion process, We only use the energy wave to get the $\eta$ (photoelectric transformation efficiency) which is little. If being used a pairt of wave, we will get a larger $\eta$. The photoelectric conversion equation of slow mass wave are being put forward. [Preview Abstract] |
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K1.00257: Quantum Quasi-Paradoxes and Quantum Sorites Paradoxes Florentin Smarandache There can be generated many paradoxes or quasi-paradoxes that may occur from the combination of quantum and non-quantum worlds in physics. Even the passage from the micro-cosmos to the macro-cosmos, and reciprocally, can generate unsolved questions or counter-intuitive ideas. We define a quasi-paradox as a statement which has a \textit{prima facie} self-contradictory support or an explicit contradiction, but which is not completely proven as a paradox. We present herein four elementary quantum quasi-paradoxes and their corresponding quantum Sorites paradoxes, which form a class of quantum quasi-paradoxes. [Preview Abstract] |
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K1.00258: BIOLOGICAL PHYSICS |
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K1.00259: Nonmonotonic Behavior of Nonnative Contacts in Small Proteins: An Exact Study on a Square Lattice Chong Chen, Purushottam Gujrati Nonnative contacts are defined as contacts absent in the native state, and can be used to study the process of folding. They are expected to increase with temperature or energy. By \textit{exactly} \textit{generating} all possible conformations on a square lattice, we have investigated nonnative contacts for proteins in the standard HP model and its modified versions introduced by our group$^{ [1]}$. This enables us to carry out exact calculation for the nonnative contact density $n_c (e)$as a function of the energy density $e$ as well as its canonical average $\bar {n}_c (T)$as a function of temperature of $T $from which we construct $\overline n _c (\overline e )$to compare with $n_c (e)$. The sequence dependence of $n_c (e)$and $\bar {n}_c (T)$ are also investigated. Some new understandings of the role for nonnative contacts play in the protein folding process, as will be discussed during the talk. 1) The density $n_c (e)$ is always monotonically increasing in the standard model. This need not be true for all kinds of interactions. 2) The density $\bar {n}_c (T)$ is usually monotonically increasing. A few violations can be seen. 3) The protein property is sequence dependent, as expected. Reference [1] P. D. Gujrati, B. Lambeth, Jr., A . Corsi, and E. Askanazi, arXiv: 0708.3739 (2007). [Preview Abstract] |
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K1.00260: Photoreceptor rearrangement and vision restoration in eyes with outer retinopathy: Quantitative assessment by fractal analysis Delia Cabrera DeBuc, Robert Tchitnga The differentiation between normal and abnormal photoreceptor rearrangement before and after treatments may improve understanding on the sequence of events involved in the visual field defects. In this study, we evaluated a fractal analysis approach to quantify photoreceptor rearrangement and vision restoration. We analyzed Optical Coherence Tomography (OCT) data from an individual with outer retinopathy before and after treatment. The outer nuclear layer (ONL) was delineated from the rest of the retinal structure by using a custom-built segmentation algorithm. We then determined the fractal box dimension of the ONL's outline using the box counting method. Thickness and reflectance of the ONL were also calculated. Our results showed that the ONL's fractal dimension, thickness and relative reflectivity decreased after treatment. These early results showed that ONL's fractal dimension could be used as an index of photoreceptor rearrangement, which might lead to a more effective approach to therapy and improved diagnosis. [Preview Abstract] |
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K1.00261: Statistical Characterization of a 1D Random Potential Problem-- with applications in score statistics of MS-based peptide sequencing Gelio Alves, Yi-Kuo Yu We provide a complete thermodynamic solution of a 1D hopping model in the presence of a random potential by obtaining the density of states. Since the partition function is related to the density of states by a Laplace transform, the density of states determines completely the thermodynamic behavior of the system. We have also shown that the transfer matrix technique, or the so-called dynamic programming, used to obtain the density of states in the 1D hopping model may be generalized to tackle a long-standing problem in statistical significance assessment for one of the most important {\em proteomic} tasks - - peptide sequencing using tandem mass spectrometry data. [Preview Abstract] |
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K1.00262: ABSTRACT WITHDRAWN |
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K1.00263: Single Molecule Study on Incorporation Efficiency of DPO4 and Klenow Fragment to BPDE Adduct Lu Song, Yin Yeh, Rod Balhorn, Monique Cosman DNA synthesis involving high fidelity A-family polymerases such as Klenow fragment is blocked by DNA adducts, while Y-family DNA polymerases such as Dpo4 can bypass the DNA adducts to resume DNA synthesis. So understanding the functional relationship between A-family and Y-family DNA polymerases in DNA replication and the mechanism of bypassing DNA adducts is of great help to explain the cause of mutagenesis. We introduce a flow cell on modified surface to study the incorporation efficiency of Dpo4 and Klenow fragments to benzo[a]pyrene-diol-epoxide (BPDE) adduct at single molecule level. Specifically, we anchor the labeled DNA onto the modified surface with adduct site open for nucleotide incorporation and flow the polymerases and labeled nucleotides into flow cell. With Total Internal Reflection Fluorescence Microscopy (TIRFM) we identify the incorporation of the nucleotides onto the anchored DNA template by identifying the co-localization of the template position and that of the labeled nucleotide. We further quantify the signal densities of the images obtained from the two different polymerases, thus examining whether incorporation reactions have been executed and quantifying the incorporation efficiency of the polymerases. We can also identify, on the specific adduct site, which nucleotide, if any, is incorporated by each of the two polymerases. [Preview Abstract] |
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K1.00264: Mechanical Properties of Type IV Pili in \textit{P. Aeruginosa} Shun Lu, Ahmed Touhami, Edie Scheurwater, Hanjeong Harvey, Lori Burrows, John Dutcher Type IV pili (Tfp) are thin flexible protein filaments that extend from the cell membrane of bacteria such as \textit{Pseudomonas aeruginosa} and \textit{Neisseria gonorrhoeae}. The mechanical properties of Tfp are of great importance since they allow bacteria to interact with and colonize various surfaces. In the present study, we have used atomic force microscopy (AFM) for both imaging and pulling on Tfp from \textit{P. aeruginosa} (PAO1) and from its PilA, PilT, and FliC mutants. A single pilus filament was mechanically stretched and the resulting force-extension profiles were fitted using the worm-like-chain (WLC) model. The statistical distributions obtained for contour length, persistence length, and number of pili per bacteria pole, were used to evaluate the mechanical properties of a single pilus and the biogenesis functions of different proteins (PilA, PilT) involved in its assembly and disassembly. Importantly, the persistence length value of $\sim $ 1 $\mu $m measured in the present study, which is consistent with the curvature of the pili observed in our AFM images, is significantly lower than the value of 5 $\mu $m reported earlier by Skerker \textit{et al.} (1). Our results shed new light on the role of mechanical forces that mediate bacteria-surface interactions and biofilm formation. 1- J.M. Skerker and H.C. Berg, Proc. Natl. Acad. Sci. USA, 98, 6901-6904 (2001). [Preview Abstract] |
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K1.00265: Inhibition of Oncogenic functionality of STAT3 Protein by Membrane Anchoring Baoxu Liu, Steven Fletcher, Patrick Gunning, Claudiu Gradinaru Signal Transducer and Activator of Transcription 3 (STAT3) protein plays an important role in oncogenic processes. A novel molecular therapeutic approach to inhibit the oncogenic functionality of STAT3 is to design a prenylated small peptide sequence which could sequester STAT3 to the plasma membrane. We have also developed a novel fluorescein derivative label (F-NAc), which is much more photostable compared to the popular fluorescein label FITC. Remarkably, the new dye shows fluorescent properties that are invariant over a wide pH range, which is advantageous for our application. We have shown that F-NAc is suitable for single-molecule measurements and its properties are not affected by ligation to biomolecules. The membrane localization via high-affinity prenylated small-molecule binding agents is studied by encapsulating FNAc-labeled STAT3 and inhibitors within a liposome model cell system. The dynamics of the interaction between the protein and the prenylated ligands is investigated at single molecule level. The efficiency and stability of the STAT3 anchoring in lipid membranes are addressed via quantitative confocal imaging and single-molecule spectroscopy using a custom-built multiparameter fluorescence microscope. [Preview Abstract] |
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K1.00266: Towards real-time 3D Tracking of Structural Transitions in Adenylate Kinase by Thermal Noise Imaging Arnd Pralle, Vijay Rana, Yunshiang Hsu Proteins in contrast to macroscopic machines are subject to thermal fluctuations in shape which provide both opportunities and challenges. They have to be flexible enough to support turn-over rates up to hundreds per second, yet stable enough to maintain their three-dimensional structure over hours and days. As result of thermal excitation they fluctuate between structural conformations. We measured thermally excited structural fluctuations in the Adenylate Kinase using a site-specifically attached nanoparticle and a laser trap based position sensing scheme. This 'Thermal Noise Imaging' (TNI) can provide real-time tracking of 3D structural transitions. TNI uses scattering of laser light to locate a nanoparticle with {\AA}ngstr{\o}m spatial and microsecond temporal resolution. We present details of the technique and a comparison of thermally excited structure fluctuations with functional transitions. [Preview Abstract] |
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K1.00267: Single molecule study of ClpP enzymatic activity Amir Mazouchi, Angela Yu, Walid Houry, Claudiu Gradinaru Elementary processes that form the basis of biological activities pass through a number of short-lived intermediate states while progressing from initial state to final state. Single-molecule techniques, unlike ensemble averaging measurements, are often able to resolve these transient states. ClpP, a known target of antibacterial drugs like acydepsipeptides (ADEPs), is a classical representative of serine proteases, enzymes that cleave peptide bonds in proteins. We performed single-molecule fluorescence measurements including burst spectroscopy and fluorescence correlation spectroscopy (FCS) to address unknown aspects of this degradation process. Our study reveals important molecular details of protein degradation, such as the enzyme-substrate binding rate, the lifetime distribution of the conjugated state and the probability of substrate cleavage upon conjugation. [Preview Abstract] |
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K1.00268: The effect of macromolecular crowding on reaction rates: a computational and theoretical study Jun Soo Kim, Arun Yethiraj The effect of macromolecular crowding on the rates of association reactions are investigated using theory and computer simulations. Reactants and crowding agents are both hard spheres, and when two reactants collide they form product with a reaction probability, $p_{rxn}$. A value of $p_{rxn} < 1$ crudely mimics the fact that proteins must be oriented properly in order for an association reaction to occur. The simulations show that the dependence of the reaction rate on the volume fraction of crowding agents varies with the reaction probability. For reaction probabilities close to unity where most of encounters between reactants lead to a reaction, the reaction rate always decreases as the volume fraction of crowding agents is increased due to the reduced diffusion coefficient of reactants. On the other hand, for very small reaction probabilities where in most of encounters the reaction does not occur, the reaction rate increases with the volume fraction of crowding agents, in this case, due to the increase probability of a re-collision. The Smoluchowski theory is in quantitative agreement with simulations for the reaction rate constant and allows the quantitative analysis of both effects separately. [Preview Abstract] |
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K1.00269: Polymer translocation induced by bad solvent Christopher Lorscher, Aniket Bhattacharya, Tapio Ala-Nissila We report Langevin dynamics simulation studies of a translocating homopolymer through a nano pore induced by different existing solvent conditions at the \textit{cis} and \textit{trans} compartments of the pore. Specifically, we study the mean first passage time $\langle \tau \rangle $ as a function of the chain length $N$ and determine the scaling exponent $\langle \tau \rangle \sim N^\alpha $. We also look at the mean force experienced by the chain and its conformations as a function of the translocated segments. Our studies also reveal detail picture of the translocation process which may provide insights relevant for the entry of a DNA into a host cell. [Preview Abstract] |
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K1.00270: Statistical test of a null hypothesis: Taser{\textregistered} shocks have {\it not} caused or contributed to subsequent in-custody deaths Marjorie Lundquist Since 1999 over 425 in-custody deaths have occurred in the USA after law enforcement officers (LEOs) used an M26 or X26 Taser{\textregistered}, causing Amnesty International and the ACLU to call for a moratorium on Taser use until its physiological effects on people have been better studied. A person's {\it Taser dose} is defined as the total duration (in seconds) of all Taser shocks received by that person during a given incident. Utilizing the concept of {\it Taser dose} for these deaths, TASER International's claim of Taser safety can be treated as a null hypothesis and its validity scientifically tested. Such a test using chi-square as the test statistic is presented. It shows that the null hypothesis should be {\bf rejected}; {\it i.e.}, model M26 and X26 Tasers{\textregistered} are capable of producing lethal effects {\bf non-electrically} and so {\bf have} played a causal or contributory role in a great many of the in-custody deaths following their use. This implies that the Taser{\textregistered} is a {\bf lethal} weapon, and that LEOs have {\bf not} been adequately trained in its {\bf safe} use! [Preview Abstract] |
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K1.00271: Computing Transitions in Macromolecular Systems: Dynamic Importance Sampling Juan Perilla, Oliver Beckstein, Anu Nagarajan, Thomas Woolf Understanding and predicting conformational change in macromolecules is central to linking structure and function. Performing straight-forward all-atom molecular dynamics would, in principle, enable sampling of conformational changes. However, the time-scale for functionally important transitions, exceeds the usual MD timescales by several orders of magnitude. Thus to sample on longer time-scales requires the development of biased molecular dynamic methods, where the bias can be applied and corrected for at the end. In our approach, called 'Dynamic Importance Sampling' we generate a series of independent trajectories that are conditioned on starting and ending in defined conformations. Trajectories are generated using two different algorithms: one that uses an adaptive soft-racheting scheme, based on stochastic trajectories and, the other uses information from the set of normal modes. Both algorithms do not require a previous knowledge on the reaction coordinate, furthermore using this framework we are also able to introduce a generalized reaction coordinate in order to guide the transitions for virtually any system. The algorithms, which require no initial pathway, are capable of rapidly determining multiple pathways between known states. The associated probability scores allow us to rank order the most likely pathways. [Preview Abstract] |
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K1.00272: The Origin of Power Law Distributions in Protein Synthesis Jeffrey Barker, Chuck Yeung, Xiao-lun Wu, Emily Chapman-McQuiston A genetically identical bacteria population will show heterogeneous gene expression due to the stochastic nature of the protein production mechanism. Therefore, the probability distribution of the resulting protein(s) can be used to gain information about these underlying processes. The experiments of Chapman-McQuistion et. al. show that under certain circumstances the protein probability distribution has a power law form $p(n) \sim n^{-\alpha}$ at small $n$. Our simulations and analysis find, in agreement with work by Friedlander and Brenner, that a linear protein production rate will produce a power law distribution with the exponent depending on the amplitude of the production rate. We also find that a protein distribution generated by rare occurrences of large bursts will produce a distribution of the form $p(n) \sim 1/n$. [Preview Abstract] |
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K1.00273: Toward a Detailed Description of the Thermally Induced Dynamics of the Core Promoter Boian Alexandrov, Vladimir Gelev, Kim Rasmussen, Alan Bishop, Anny Usheva Experimental data suggest that a spontaneous dsDNA strand separation at the transcriptional start site (TSS) is likely to be a requirement for transcription initiation in several promoters. We present molecular dynamic simulations of DNA to analyze the strand separation (bubble) dynamics of 80 bp long promoter DNA sequences. We suggest that three dynamic quantities: bubble probability, bubble lifetime, and average strand separation, together represent an adequate characterization of the bubble formation at TSS's of eight mammalian gene promoters. The TSS is distinguished by large, frequent, and \textit{long-lived} transient openings in the double helix. In support of these results are our experimental transcription data demonstrating that an artificial DNA template, viz., a bubble-template of 5 bp mismatch at the TSS, is transcribed bi-directionally by human RNA polymerase alone in \textit{the absence} of any other transcription factors. [Preview Abstract] |
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K1.00274: In Silico Docking of Ligands to Drug Oxidation Enzymes Cytochrome P450 3A4 and Cytochrome P450 1A2. David Smith, Jonathan Guglielmon, Marsch Glenn, Guengerich F. Peter Cytochrome P450 3A4 (CYP3A4) and Cytochrome P450 1A2 (CYP1A2) oxidize most drugs in humans. Protein modeling toolkits from OpenEye Scientific Software were used to examine the interaction of drug substrates with CYP3A4 and CYP1A2. Conformers and partial atomic charges were generated for each drug molecule. User-defined volumes were defined around CYP3A4 and CYP1A2 active sites. Ligands were docked assuming protein and substrates as rigid bodies. To assess rigid docking accuracy, x-ray diffraction coordinates of CYP3A4-erythromycin and CYP3A4-metyrapone complexes were obtained. Rigid re-docking of erythromycin and metyrapone into CYP3A4 yielded poses similar to the crystal structures. Rigid docking revealed two other energetically-favorable CYP3A4-metyrapone poses. The best poses were obtained by using all the Open Eye scoring functions. Optimization of protein-ligand interactions within 5-10 Angstroms of the docked ligand was then performed using the Merck Molecular Force Field in which the protein was assumed to be flexible and the ligand to be rigid. Nearby protein residues pulled slightly closer to the substrate, reducing the volume of the active site. [Preview Abstract] |
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K1.00275: Examination of mathematical models for voltage attenuation in dendritic trees of geniculate neurons Keegan Hines, William Guido An examination of Rall's model of Electrotonic Compactness in neuronal dentritic trees was conducted. The principal power of this model is a prediction for dendritic morphology as it is related to voltage attenuation and efficient transmission of electrical signals. In particular, this study tested the validity of Rall's ``3/2 power rule'' with precision and accuracy not previously sought. Cells were imaged using fluorescent tagging and multi-photon confocal microscopy in order to render three dimensional images of cells \textit{in vivo}. Dendritic diameters and lengths were measured on either side of junction points and these values were compared to Rall's prediction. Cells of varying ages were measured in order to simultaneously investigate whether deviations from Rall's model increased or decreased with brain development. Cells of age P8 tend to adhere closely to Rall's predictions while mature cells ($\sim $P30) show morphologies which would lead to inefficient signal flow. These data coincide well with previous studies which indicate that as cells grow, membranes mature and acquire ion channels which lead to non-linear conductances across the membrane. This is a possible explanation for why, from a purely morphological standpoint, cells grow into a less electrically efficient formation. [Preview Abstract] |
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K1.00276: The Interaction of Photon Beams with the DNA Molecules: Genomic Medical Physics V. Alexander Stefan I propose a novel method for the modification of the corrupted human DNA\footnote{J.D. Watson and F. H. C. Crick, \textbf{Nature}, 171, 737-738 (1953).} code that causes particular genetic disease. The method is based on the nonlinear interaction between the DNA molecule and the ``modulation photons'' generated in beat wave driven free electron laser, BW-FEL.\footnote{V. Alexander Stefan. \textbf{Beat Wave Driven Free Electron Laser} (S-U-Press, 2002, La Jolla, CA)[cf. V. Stefan, et al., \textbf{Bull.~Am. Phys. Soc.} 32, No. 9, 1713 (1987)]} The BW-FEL frequency is given by $\nu $\textbf{$\sim $}$\gamma ^{2}$n$\Omega _{e }$(\textbf{$\gamma $} is the free electron beam relativistic factor, n is the harmonic number of the electron Bernstein plasma mode, and $\Omega _{e}$ is the electron cyclotron frequency). The meV ``carrier photons'' are focused on the area of the brain, the source-center of a genetic disease. For the BW-FEL parameters: the free electron beam guiding d.c. magnetic field \textbf{$\sim$} 1kG, \textbf{$\gamma \sim $}10$^{3}$, and n=10, the keV ``modulation photons'' are generated, which are easily focused on the nucleotides. By modulating the frequency of the BW-FEL, the parametric resonance with the different DNA (sub-DNA) eigen molecular oscillation-modes are achieved, leading to the ``knock-on'' of the unwanted (corrupted) nucleotides. [Preview Abstract] |
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K1.00277: A kinetics study of the activation energy for the desorption of water from guanosine Megan Schwenker Smith, Scott Lee The interactions of the nucleic acids with their water of hydration are of fundamental importance but are still poorly characterized. As an initial effort, we have studied the nucleoside guanosine (rG), composed of the ribose sugar and the guanine base, which is a component of RNA. We have measured the interactions of the water of primary hydration with rG via thermogravimetric measurements and differential thermal analysis by studying the kinetics of the dehydration process. These data yield the activation energy for the desorption of the water of primary hydration from rG. [Preview Abstract] |
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K1.00278: Novel techniques for study of the nucleosome core particle ionic atmosphere and its role in electrostatically-driven DNA packing Kurt Andresen The nucleosome core particle (NCP) is the primary mechanism for DNA compaction. While the wrapping of the DNA around the histone core is thought to be at least partially sequence-dependent, the packing of the nucleosome cores is believed to be almost entirely electrostatic in nature. Using novel techniques to probe the ionic atmosphere, we hope to elucidate details of this compaction and provide a quantitative description of the positive and negative ions that surround the nucleosome. Results of these experiments will be presented. This work should have implications for nucleosome compaction, chromatin remodeling, and more generally electrostatics of highly charged biomolecules. [Preview Abstract] |
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K1.00279: Hill Parameters and Heterogeneity of alpha-Naphthoflavone Binding to Human Cytochrome P450 3A4 by Fluorescence Spectroscopic Analysis Benjamin Carlson, Glenn Marsch, Martha Martin, F. Peter Guengerich Human cytochrome P450 3A4 (CYP 3A4) is an alpha-helical
membrane-bound
protein that metabolizes approximately 50{\%} of all drugs. The
interaction
between CYP450 3A4 and alpha-naphthoflavone (ANF) was
characterized using
fluorescence methods. ANF quenched fluorescence from tryptophan
residues in
CYP 3A4, and CYP 3A4 quenched bound ANF. The ANF emission energy was
unchanged upon binding to CYP 3A4, implying that enzyme-bound 3A4 is
completely quenched. Fluorescence difference spectra were fit to
the Hill
equation by varying the parameters $K_{d}$ and $n$. For quenching
of tryptophan
fluorescence by ANF, no significant sigmoidal behavior was
observed with
$n$=1, and the spectral dissociation constant revealed a strong
ANF-CYP 3A4
interaction with $K_{d}$=27n$M$. Modest cooperativity and very
tight binding was
observed in the quenching of ANF by CYP 3A4, with n=1.4 and
$K_{d}$= 4.9n$M$.
Fluorescence polarization anisotropy $<$r$>$ decreased at low
ANF/CYP 3A4
molar ratios; then $ |
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K1.00280: Residue mobility and energy profiles of an HIV-1 protease (1DIFA) chain by a coarse-grained Monte Carlo simulation Ras Pandey, Barry Farmer HIV-1 protease (1DIFA), an enzyme consists of two polypeptides, 99 amino acids each. Aspartic acid residue (Asp$^{25})$ forms the active catalytic site. Specificities of residues are captured via an interaction matrix (residue-residue, residue-solvent) of the Lennard-Jones potential. Simulations are performed for a range of interaction strength ($f)$ with the solvent-residue interaction describing the quality of the solvent. Snapshots of the protein show considerable changes in the conformation of the protein on varying the interaction. From the mobility and energy profiles of the residues, it is possible to identify the active (and not so active) segments of the protein and consequently their role in proteolysis. Contrary to interaction thermodynamics, the hydrophobic residues possess higher configurational energy and lower mobility while the electrostatic and polar residues are more mobile despite their lower interaction energy. [Preview Abstract] |
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K1.00281: Interaction of Human Cytochrome P450 3A4 with Hydrophobicity Probe Nile Red Shows Heterogeneous, Strong Binding Jennifer Hansen, F. Guengerich, Martha Martin, Glenn Marsch Human cytochrome P450 3A4 (CYP 3A4) binds an unusually wide variety of substrates, and metabolizes about 50{\%} of all drugs. Steady-state fluorescence spectra were acquired for complexes of CYP 3A4 and the fluorescence probe Nile Red. Difference fluorescence spectra and Hill plots were generated, and Hill coefficients were determined. The fluorescence from multiple Nile Red bound states was observed, with all bound states having higher emission energies than the fluorescence from free Nile Red. Nile Red was titrated into 150n$M$ CYP 3A4, and fluorescence difference spectra showed the quenching of CYP 3A4 tryptophan fluorescence by Nile Red. CYP 3A4 was also added to Nile Red, and changes in the Nile Red fluorescence spectra were monitored. The dissociation constant showed tight binding, with $K_{d}$ = 44n$M$. Good fits to the Hill plots were obtained with $n$ = 1, suggesting non-cooperative binding. This study revealed strong, heterogeneous, non-cooperative binding of Nile Red to CYP 3A4. [Preview Abstract] |
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K1.00282: Investigation on mineralization behaviour of Type I collagen and noncollageneous extracellular matrix protein immobilized on polymer thin film Xiaolan Ba, Ariella Kristal, Elaine DiMisi, Miriam Rafailovich The effects of the components of extracellular matrix on the bone formation and the kinetics of crystal growth of calcium phosphate have remained unknown. Here we reported a method to investigate the role of Type I collagen and the interactions with other ECM proteins such as fibronectin and elastin during biomineralization process. The early stage of mineralization was characterized by atomic force microscopy (AFM) and shear modulation force microscopy (SMFM). The late stage of mineralization was investigated by scanning electron microscopy (SEM), grazing incident x-ray diffraction (GIXD). The results showed the calcium phosphate biomineralization only occurred when the collagen interacted with fibronectin or elastin. [Preview Abstract] |
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K1.00283: Effects of cholesterol and unsaturated DOPC lipid on chain packing of saturated gel-phase DPPC bilayers John Nagle, Thalia Mills, Juyang Huang, Gerald Feigenson Wide angle x-ray scattering (WAXS) from oriented lipid multilayers was used to study the effect of adding cholesterol (Chol) or DOPC to gel-phase DPPC bilayers. Small quantities ($X<$0.10 mole fraction) of both molecules disrupt the tight packing of tilted chains of pure gel-phase DPPC, forming a more disordered, untilted phase. The addition of larger quantities of DOPC causes the sample to phase-separate into a gel phase, characterized by a narrow WAXS peak, and liquid disordered phase, characterized by wide, diffuse WAXS scattering. In contrast, two WAXS peaks indicative of two coexisting phases were not observed in Chol/DPPC mixtures ($X_{Chol}$ = 0.07 to 0.40). Instead, Chol caused a gradual increase in the width of the WAXS peak, consistent with a gradual change from a more gel-like to a more liquid-like state rather than passing through a region of two phase coexistence. Our WAXS data include a huge amount of information. A new method of analysis suggests that WAXS data may provide definitive results relating to the disagreements between previously published phase diagrams for Chol/DPPC. [Preview Abstract] |
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K1.00284: Motional Coherence in Fluid Phospholipid Membranes Maikel Rheinstadter, Jhuma Das, Elijah Flenner, Beate Br\"uning, Tilo Seydel, Ioan Kosztin Modern experimental and computational techniques give access to collective molecular properties and raise the fundamental question of coherence in biology. While incoherent systems are systems wherein each particle is a separate, localized entity interacting with others through collisions and other energy exchanges, in a coherent regime particles lose their individual identity. Even in simple models, a biological system must be considered as an array of units interacting through coherent reactions. Coherence must therefore possibly be considered as a fundamental property of biomolecular systems. By employing high energy-resolution neutron backscattering, combined with in-situ diffraction, we have investigated slow molecular motions on nanosecond time scales in the fluid phase of phospholipid model membrane of DMPC [1]. A cooperative structural relaxation process was observed. Combined with results from a 0.1 microsecond long all atom molecular dynamics simulation, we found that correlated dynamics in lipid membranes occurs over several lipid distances, spanning a time interval from pico- to nanoseconds. [1] Rheinstadter et al., accepted for Phys. Rev. Lett., http://arXiv.org/abs/0809.3040. [Preview Abstract] |
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K1.00285: Coarse-grain Modeling of Lipid Membrane Adsorption on Nanopatterned Surfaces Matthew Hoopes, Marjorie Longo, Roland Faller Substrate interactions with adsorbed membranes modify the intrinsic mechanics of supported lipid bilayers. Coarse-graining of the membrane lipids and surface allow for the larger system size necessary for membrane shape studies. Supported lipid bilayers (SLB) continue to be an important means of measuring the thermodynamic and mechanical properties of phospholipid membranes, which are the basis of compartmentalization in living cells. Understanding SLB systems with respect to their substrates enhances the understanding of the measurements taken thereon and promotes design of new substrates to expand the usefulness of these systems. We present data for the interaction of coarse-grained lipid membranes with nanopatterned surfaces, showing the effect of the balance between bending energy and adsorption energy on membrane topology. [Preview Abstract] |
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K1.00286: The Effect of Titanium Dioxide Nanoparticles on Keratinocyte Cell (KC) and Squamous Cell Carcinoma (SCC-13) Chienhsiu Lin, Marcia Simon, Vladimir Jurukovski, Wilson Lee, Miriam Rafailovich We have studied the effects of TiO$_{2}$ nanoparticles on cell keratinocyte and SCC (Squamous Cell Carcinoma) cells. We found that the concentration of particles required to adversely affect the cells was many times higher for keratinocyte than SCC cells. Confocal microscope shows that the particles in keratinocyte culture are sequestered in membranes between the cell colonies. The particles penetrated into the cells in the case of the SCC cells. TEM images revealed very few particles in the keratinocyte, many more particles were observed sequestered in vacuole of the SCC cells. These results indicate that the keratinocyte layer behaves very different from the fibroblast layers which are much more sensate to TiO$_{2}$ nanoparticle damage and may suggest a protection mechanism of the dermal tissue. The effect of UV exposure in the presence of DNA was also investigated. We found that adsorbed proteins, as well as grafted polymer provided a measure of protection against free radical formation. The effects of low level UV exposure when the particles are near in-vitro cell culture will be presented. [Preview Abstract] |
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K1.00287: Theoretical Description of Microtubule Dynamics in Fission Yeast During Interphase Yung-Chin Oei, Andrea Jim\'enez-Dalmaroni, Andrej Vilfan, Thomas Duke Fission yeast (S. pombe) is a unicellular organism with a characteristic cylindrical shape. Cell growth during interphase is strongly influenced by microtubule self-organization - a process that has been experimentally well characterised. The microtubules are organized in 3 to 4 bundles, called ``interphase microtubule assemblies'' (IMAs). Each IMA is composed of several microtubules, arranged with their dynamic ``plus'' ends facing the cell tips and their ``minus'' ends overlapping at the cell middle. Although the main protein factors involved in interphase microtubule organization have been identified, an understanding of how their collective interaction with microtubules leads to the organization and structures observed in vivo is lacking. We present a physical model of microtubule dynamics that aims to provide a quantitative description of the self-organization process. First, we solve equations for the microtubule length distribution in steady-state, taking into account the way that a limited tubulin pool affects the nucleation, growth and shrinkage of microtubules. Then we incorporate passive and active crosslinkers (the bundling factor Ase1 and molecular motor Klp2) and investigate the formation of IMA structures. Analytical results are complemented by a 3D stochastic simulation. [Preview Abstract] |
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K1.00288: The Effect of Electric and Magnetic Fields on Protein Self-Organization and Osteoblast Biomineralization Xiaolan Ba, Lara Fourman, Sanchita Singal, Yizhi Meng, Miriam Rafailovich The induction of bone formation to an intentional orientation is a potentially viable clinical treatment for bone regeneration. Among the many chemical and physical factors, electric and magnetic fields are an essential way to regulate the behavior of cells and matrix fibers. The aims of this study are to investigate the effects of electric and magnetic fields on protein self-organization and osteoblast biomineralization on polymer surfaces in vitro. To this end, we use atomic force microscopy (AFM) to characterize the morphology of protein fiber and ECM by cells. The mechanical property of protein fibers was investigated by shear modulation force microscopy (SMFM). The late-stage of mineralization was characterized by scanning electron microscopy (SEM) and grazing incident x-ray diffraction (GIXD). The primary data indicated that the magnetic field could enhance the biomineralization of osteoblast. [Preview Abstract] |
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K1.00289: Elastic properties of vimentin networks Yi-Chia Lin, Amy C. Rowat, Harald Herrmann, Chase C. Broedersz, Frederick C. MacKintosh, Eleanor A. Millman, David A. Weitz We measure the mechanical properties of in vitro networks of the intermediate filament protein vimentin by rheometry. Vimentin networks are highly elastic even for small volume fractions of protein and exhibit dramatic stiffening with strain. We find that divalent ions such as Ca2+ and Mg2+ act as effective cross-linkers in the vimentin network. The observed linear and nonlinear elastic responses at intermediate strains can be explained quantitatively by affinely stretching the entropic fluctuations of single semiflexible filaments; at high strains, enthalpic stretching of the individual filaments contributes to the observed nonlinear response. [Preview Abstract] |
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K1.00290: \textit{In Vitro} Migration of Human Dermal Fibroblasts on the Electrospun Fibrous Scaffold Ying Liu, Dilip Gersasppe, Alicia Franco, Sarajane Gross, Elias Goodman, Richard Clark, Miriam Rafailovich Cell migration has become the focus of much research due to its importance through out cell life. We hypothesized that the aligned scaffold obtained from electrospinning would enhance the rate of cell migration and ultimately the rate of new tissue ingrowth. An \textit{in vitro} en- masse assay was used to study the effects of fiber diameter and alignment on the cell migration. It was found that, while the cells were spreading out on the fibers with diameter of 200nm, nearly all the cells were oriented along the fibers for the 1 and 8 micron scaffolds. In addition to fiber diameter, orientation is another crucial parameter which can determine cell migration. Cell migration rates and persistence increased on the aligned PMMA fibers compared to the random fibers. The role of focal adhesions during cell migration was detected by staining the Vinculin after 6 and 24h of cell culture time. The computational model was used to stimulate cell migration on the aligned scaffold, and it was turned out that various cellular parameter were integrated to accomplish the specific cell locomotion pattern on the aligned scaffold. [Preview Abstract] |
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K1.00291: Nanoscale Mechanics of Type I Collagen H. Harper, E. Cropper, A. Bulger, U. Choksi, T.J. Koob, S. Pandit, W.G. Matthews Collagen is the most abundant protein in the body by mass. Type I collagen fibrils provide mechanical strength and cellular housing within tissues exhibiting a broad range of mechanical properties. This diversity in the mechanics of tissues with similar underlying components warrants detailed study of the process by which structure and mechanics develop. While collagen mechanics have been studied at the tissue level for decades, surprising little is known about collagen mechanics at the fibril and molecular level. Presented herein is a multi-scale experimental and computational investigation of collagen I mechanics, bridging the single molecule and fibril hierarchal forms. The mechanics of single collagen molecules are explored using AFM and force spectroscopy. Moreover, atomistic molecular-dynamics simulations are performed to provide structural information not accessible to the experimental system. Fibrils then are grown from molecular collagen, and the mechanics of these fibrils are investigated using AFM. Based upon the single molecule and fibril results, a coarse-grain computational model is being developed. The outcomes include a better understanding of how the mechanics of filamentous self-organizing systems are derived and how their hierarchical forms are established. [Preview Abstract] |
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K1.00292: Self-assembly of FKE8 peptides using CHARMM Abdelillah Ouazzani, Abdelkader Kara, Aniket Bhattacharya We investigate the molecular self-assembly of FKE8 peptides (with a sequence FKFEFKFE) using CHARMM. Previous studies$^{1,2}$ of the FKE8 peptides have shown helical ribbon structures during the formation of $\beta$-sheets. In order to understand this supra-molecular structure,first we investigate the stable configuration of two FKE8 molecules as a function of the orientation of the long axis of the molecules. We find that stable configuration of these two molecules (based on energy minimization) occurs when the long axes of the two molecules are orientated at an angle $\simeq 51.5^0$ with respect to each other. This angle may be relevant to understand the pitch of the helical structure. Next we study the self-assembly of several FKE8 molecules starting with an initial configuration where two successive FKE8 molecules are oriented at an angle $\simeq 51.5^0$ with respect to each other. \\ $^1$ W. Hwang, D. Marini, R.~D. Kamm, and S. Zhang, J. Chem. Phys. {\bf 118}, 389 (2003).\\ $^2$ S. Vauthey, S. Santoso, H. Gong, N. Watson, and S. Zhang, Proc. Natl. Acad. Sci. U.S.A. {\bf 99}, 5355 (2002).\\ [Preview Abstract] |
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K1.00293: Simulation of Peptide Binding to Silica and Silica Mineralization F.S. Emami, H. Heinz, R.J. Berry, V. Varshney, B.L. Farmer, R.R. Naik, S.V. Patwardhan, C.C. Perry The purpose of this study is to identify the nature of the interaction of peptides with silica surfaces and their effect on mineralization. Classical force fields (CVFF, PCFF) have been extended for silica aiming at the computation of surface properties in quantitative agreement with experiment, taking explicitly into account water molecules, pH, and surface coverage with peptides. We focus on the interaction of five short peptides (pep1, pep4, 82-4, H4, R5) identified by biopanning with regular and amorphous silica surfaces (Q3 and Q2) to understand the relation between peptide sequence and affinity to the surface. Results of the atomistic molecular dynamics simulation indicate adsorption energies, binding constants and conformational changes upon adsorption. The comparison of NMR chemical shifts in solution and on the surface in computation and experiment further aids in understanding the mechanism of binding. [Preview Abstract] |
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K1.00294: NMR Studies in Macromolecular Solutions Anand Yethiraj, Suliman Barhoum We use diffusion nmr to characterize the dynamics of multi-component macromolecular solutions. Diffusion coefficients of all components are obtained simultaneously. We also present a scheme to extract the diffusion coefficients associated with transient aggregates in solution. Applications and limitations of this scheme are discussed. [Preview Abstract] |
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K1.00295: Surface imprinting of proteins: from mechanism to application Yantian Wang, Steffen Mueller, Jonathan Sokolov, Kalle Levon, Basil Rigas, Miriam Rafailovich Protein adsorption properties on different surfaces have been of great interest due to their importance in biomedical applications. In this study, adsorption of proteins on gold, thiol self-assembled monolayer (SAM), and molecularly imprinted thiol SAM was studied. Alkaline phosphatase (AP), an enzyme that can catalyze p-nitrophenyl phosphate and produce a yellow end product which has light absorbance at 405nm, was co-adsorbed with 11-mercapto-1-undecanol to fabricate the imprinted surface. Different washing methods were used to remove AP and create re-adsorption sites. The adsorption amount of AP before and after washing was measured by spectrophotometer after enzyme reaction. Re-adsorption of AP onto the three surfaces was compared and showed that the imprinted surface re-bound the protein molecules at the template site. Potentiometric response of the three substrates to AP was measured at different pH, the charge effect on the potential response was studied. The selective binding of the template proteins made it a useful technique as a protein sensor. [Preview Abstract] |
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K1.00296: Single Molecule Optical Signal Comparison of Fluorescent Molecules and Raman Active Nanoprobes Edward Allgeyer, Adam Pongan, Gary Craig, Michael Mason In recent years various enhancement techniques have been used to greatly improve the effective cross section of all flavors of raman spectroscopy. Further, coupling specific probe molecules to metal nanoparticles allows for a nanoprobe with an enhanced effective raman cross section making raman probes a viable technique for imaging and spectroscopy in biological and material systems. However, it has been claimed that intensity variations of raman nanoprobes are to large for raman nanoprobes to be useful. Here we report on a study of intensity variations of novel raman active nanoprobes and contrast this with intensity variations of typical single molecule fluorescent probes. In both cases an intensity distribution is built from the single molecule level. [Preview Abstract] |
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K1.00297: Atomic Force Microscope Investigations of Biofilm-Forming Bacterial Cells Treated with Gas Discharge Plasmas Kurt Vandervoort, Andrew Renshaw, Nina Abramzon, Graciela Brelles-Marino We present investigations of biofilm-forming bacteria before and after treatment from gas discharge plasmas. Gas discharge plasmas represent a way to inactivate bacteria under conditions where conventional disinfection methods are often ineffective. These conditions involve bacteria in biofilm communities, where cooperative interactions between cells make organisms less susceptible to standard killing methods. \textit{Chromobacterium violaceum} were imaged before and after plasma treatment using an atomic force microscope (AFM). After 5 min. plasma treatment, 90{\%} of cells were inactivated, that is, transformed to non-culturable cells. Results for cell surface morphology and micromechanical properties for plasma treatments lasting from 5 to 60 minutes were obtained and will be presented. [Preview Abstract] |
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K1.00298: Electrostatic perturbation in neurons and endothelial cells under stress using Atomic Force Microscopy-assisted Electrostatic Nanolithography Victoria Nedashkivska, Sergei Lyuksyutov, Lois-May Bezuidenhout, Cornelis Van der Schyf The~morphological and membrane properties of neuronal and vascular endothelial cells need to be studied to reveal their possible role in neurodegeneration after injury. Atomic Force Microscopy Electrostatic Nanolithography (AFMEN) offers an opportunity to measure cellular perturbations during stress conditions. AFMEN is based on electrostatic manipulations of macromolecules and biological tissues at a nanoscale level which generates electric fields of the order of magnitude 10$^{8}$-10$^{9}$ V m$^{-1}$ and studies membrane changes in \textit{in vitro} cell culture systems. Two cell culture systems were selected based on their ability to represent neurons on the one hand, and vascular epithelial cells differentiated to model the blood-brain barrier, on the other. The imaging was completed for cells in wet (natural) and also in dry conditions. Changes in membrane behavior will be compared between stressed cells and controls that have not undergone exposure to pathologic conditions. [Preview Abstract] |
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K1.00299: Ballistics and Biophysics of Fatal Lesion in Thorax Saami J. Shaibani The examination of body-related factors does not always provide the level of insight required to resolve the mechanism of death for major chest injury. Indeed, many autopsy findings are limited when environmental information is either not available at all or is incomplete. Such was the case when a gunshot wound was inflicted upon a standing adult male whose torso was rotated by a forward pitch and a rightward yaw. Highly accurate values for these angles were derived by a process independent from any standard medical approach, along with precise measurements for various anatomical landmarks, so that a meticulous analysis could be performed to determine all plausible bullet trajectories. A combination of physics and medicine then allowed only one viable set of conditions to be identified. The interdisciplinary nature of the research described here was responsible for its success; without such a collaborative study, a full understanding of the relevant issues could not have emerged. Physics-based techniques can also be of benefit in many other applications when the appropriate protocol is defined properly and then implemented correctly. [Preview Abstract] |
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K1.00300: How are static magnetic fields detected biologically? Leonard Finegold There is overwhelming evidence that life, from bacteria to birds to bats, detects magnetic fields, using the fields for orientation or navigation. Indeed there are recent reports (based on Google Earth imagery) that cattle and deer align themselves with the earth's magnetic field. [1]. The development of frog and insect eggs are changed by high magnetic fields, probably through known physical mechanisms. However, the mechanisms for eukaryotic navigation and alignment are not clear. Persuasive published models will be discussed. Evidence, that static magnetic fields might produce therapeutic effects, will be updated [2]. \\[4pt] [1] S. Begall, \textit{et al., Proc Natl Acad Sci USA,} 105:13451 (2008). \\[0pt] [2] L. Finegold and B.L. Flamm, \textit{BMJ}, 332:4~(2006). [Preview Abstract] |
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K1.00301: Raman Spectroscopy Study of Prostatic Adenocarcinoma Bulk Tissues S. Devpura, H. Dai, J.S. Thakur, R. Naik, A. Cao, A. Pandya, G.W. Auner, F. Sarkar, W. Sakr, V. Naik Prostate cancer is one of the most common types of cancer among men. The mortality rate for this disease can be dramatically reduced if it can be diagnosed in its early stages. Raman spectroscopy is one of the optical techniques which can provide fingerprints of a disease in terms of its molecular composition which changes due to the onset of disease. The aim of this project is to investigate the differences in the Raman spectra to identify benign epithelium (BE), prostatic intraepithelial neoplasia (PIN) and adenocarcinoma of various Gleason grades in archived bulk tissues embedded in paraffin wax. For each tissue, two adjacent tissue sections were cut and dewaxed, where one of the sections was stained using haematoxylin and eosin for histological examination and the other unstained adjacent section was used for Raman spectroscopic studies. We have collected Raman spectra from 10 prostatic adenocarcinoma dewaxed tissue sections using Raman microscope (785 nm excitation laser). The data were analyzed using statistical methods of principal component analysis and discriminant function analysis to classify the tissue regions. The results indicate that Raman Spectroscopy can differentiate between BE, PIN and Cancer regions. [Preview Abstract] |
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K1.00302: Biophysical modeling of mismatch repair proteins Freddie Salsbury Mismatch repair proteins play a vital role in the bology of cancer due to their dual functions as repair proteins and as sensors of DNA damage. Computational modeling of mismatch repair proteins in conjunction with biological experimentation has demonstrated the role of long-range communication in the functions of these proteins. Furthermore, different conformations have been shown to be associated with different cellular functions, and these differences are being exploited in drug discovery. The latest results in this modeling will be presented. [Preview Abstract] |
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K1.00303: \textit{In vivo} determination of the structure of oligomers of a G protein-coupled receptor Sasmita Rath, Valerica Raicu Resonance Energy Transfer (RET) is a process of nonradiative energy transfer between a donor and an acceptor molecule, which is widely used for studies of protein-protein interactions in living cells. Here we report on the results of a spectrally-resolved two-photon microscopy study of image pixel-level RET in yeast cells (\textit{S. cerevisiae}) expressing a G-protein-coupled receptor called Sterile 2 $\alpha $ factor protein (Ste2P). The number of pixels showing RET were plotted against the RET efficiency to obtain distributions of RET efficiency in the cells. These distributions were simulated with models for plausible geometries and sizes of protein complexes (V. Raicu, 2007, \textit{J. Biol. Phys.} \textbf{33:}109--127). From all the models tested we found that a parallelogram-shaped tetramer is the most likely structure for the Ste2p oligomers. [Preview Abstract] |
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