Bulletin of the American Physical Society
11th Annual Meeting of the Northwest Section of APS
Volume 54, Number 6
Thursday–Saturday, May 14–16, 2009; Vancouver, BC, Canada
Session C1: Poster Session |
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Room: TRIUMF Main Floor |
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C1.00001: What Gravity Is. Some Recent Considerations Vic Christianto, Florentin Smarandache It is well-known, that when it comes to discussions among physicists concerning the meaning and nature of gravitation, the room temperature can be so hot. Therefore, for the sake of clarity, it seems worth that all choices were put on a table, and we consider each choice's features and problems. The present article describes a nonexhaustive list of such gravitation theories for the purpose of inviting further and more clear discussions. [Preview Abstract] |
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C1.00002: Predictions on Higher-Order Statistics with Weak Gravitational Lensing Sanaz Vafaei Weak gravitational lensing by large-scale structure is now routinely measured at the two-points statistics level. When using the second order statistics only, weak gravitational lensing enables us to set cosmological constraints on the combination of the amplitude of the matter power spectrum and the matter density parameter. The existing degeneracy between the two parameters can be broken by third-order statistics measurements, namely the skewness statistic. Since this effect is weak, we must invest in an optimal survey design for the future surveys to detect and better measure the skewness. We demonstrate the power of including the third-order statistics in weak lensing analysis. We present the promising predictions for the measurement of the third-order statistics on the complete CFHTLS wide survey, based on an extensive set of cosmological ray-tracing lensing simulations with realistic noise estimates. We also investigate the type of survey that is optimal to detect the higher-order cosmic shear statistics. [Preview Abstract] |
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C1.00003: The Effect of \textit{Trans} Unsaturation on Molecular Organization in a Phospholipid Membrane Smita Soni, Jenniffer Runyan, Garrison Brich, Jesse Ward, Stephanie Sen, Scott Feller, Stephen Wassall The ingestion of \textit{trans} fatty acids (TFA) formed during the partial hydrogenation of vegetable oils has been linked to a detrimental impact on health by an, as yet, unknown mechanism. We synthesized deuterated analogs of 1-elaidoyl-2-stearoylphosphatidylcholine ($t$18:1-18:0PC) that contains a single ``unnatural'' \textit{trans} double bond and 1-oleoyl-2-stearoylphosphatidylcholine ($c$18:1-18:0PC) that contains a single ``natural'' \textit{cis} double bond. Solid state $^{2}$H NMR spectra for model membranes prepared from these phospholipids reveal a higher chain melting temperature for the \textit{trans} isomer, indicating tighter molecular packing in the gel state. In the liquid crystalline, however, the difference between the \textit{trans} and \textit{cis }isomers is subtle. Order as probed by the perdeuterated [$^{2}$H$_{31}$]18:0 \textit{sn}-2 chain, and corroborated by molecular dynamics (MD) simulation, coincides within $<$5{\%}. [Preview Abstract] |
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C1.00004: New Photoelectron/Photoion Spectrometer: New Look at the Adiabatic Ionization Potential of Acetic Acid Piotr W. Forysinski, Philipp Zielke, David Luckhaus, Ruth Signorell We report the setup of a new photoion/photoelectron spectrometer for the investigation of the interaction of extreme ultraviolet (EUV) light (wavelength $\ge $ 70nm) with molecules, clusters and aerosol particles. We perform pulsed field ionization zero kinetic energy electron (PFI-ZEKE) spectroscopic studies of the acetic acid monomer (AA) as a stepping stone on the way to larger systems. We measure the adiabatic ionization potential of AA at higher resolution than previously reported, ending a 40 year debate regarding its true position. The newly established value for the ionization potential is thus 85912 $\pm $ 5 cm$^{-1}$. We resolve torsional hot bands adjacent to the 0 - 0 transition, explaining the shift in previously reported values. These hot band frequencies allow us to calculate the torsional barrier in the cation, which is nearly double of that in the ground state. The value of 316 $\pm $ 10 cm$^{-1 }$for the torsional barrier suggests a significant shortening of the C-C bond in the molecular cation. Furthermore, we also observe the CCO deformation mode of the cation at 357 $\pm $ 5 cm$^{-1}$ above the adiabatic ionization potential. [Preview Abstract] |
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C1.00005: Exploring the Detection Limit of Nanohole Array Sensors Donna Hohertz, Karen Kavanagh Light incident on an opaque metallic film perforated by a periodic array of nanoholes demonstrates ``extraordinary optical transmission'' (EOT), where certain frequencies of light pass through the sub-wavelength sized holes. This behavior has been attributed to resonance interactions between incident photons and surface plasmon polaritons [1]. Arrays of various periodicities have been milled in 100nm gold films on glass substrates using focused ion beam. Surface plasmon resonance peaks have been recorded using a spectrometer. Peak shape and position is a function of the array geometry and dielectric environment. EOT's sensitivity to the dielectric environment suggests it may be used to detect chemical/biological events occurring at an array surface [2, 3]. We seek to understand how small of an event may be measured with such arrays. With this knowledge, we will attempt to fabricate a quick and efficient sensor for antibody detection and characterization. References 1 Ebbesen, NATURE, 391 (6668): 667-669 FEB 12 1998 2 Brolo, LANGMUIR, 20 (12): 4813-4815 JUN 8 2004 3 Gordon, ACC. OF CHEM. RES., 41 (8): 1049-1057 AUG 2008 [Preview Abstract] |
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C1.00006: Grating Ti:Sa laser: Rydberg \& auto-ionizing state spectroscopy Andrea Teigelhoefer, Pierre Bricault, Jens Lassen, Walter Neu, Klaus Wendt TRIUMF's Isotope Separator and Accelerator facility (ISAC) provides intense radioactive isotope beams (RIB) for nuclear and particle physics experiments. Resonant laser ionization is well suited as an on-line ion source for RIB production due to its efficiency and element selectivity. TRIUMF's Laser Ion Source (TRI LIS) uses BRF tuned Ti:Sa lasers with GHz linewidth and 10kHz rep. rate. Continuous wavelength scanning of these lasers is involved. A grating tuned Ti:Sa laser was built to allow for high resolution continuous wavelength scans (10nm/h) thus allowing for systematic studies of high lying atomic energy levels and the development of efficient RIS schemes. This grating tuned Ti:Sa laser system will be presented. [Preview Abstract] |
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C1.00007: Analysis of Self-Terminated Pressure-Driven Quantum Point Contacts with Ultrafast Optical Pulses Fatemeh Soltani, Alex Wlasenko, Geoff Steeves A self-terminated electrochemical method was used to fabricate atomic-scale contacts between two Au electrodes in a microfluidic channel. The conductance of the contacts varies in a stepwise fashion. The mechanism works by a pressure-driven flow parallel with a pair of Au electrodes with a 100 $\mu$m gap in an electrolyte of HCl. Without applied flow, dendrite growth and dense branching morphology were typically observed at the cathode. The addition of applied pressure-driven flow resulted in a densely packed gold structure that filled the channel. The electrochemical fabrication approach introduces large variance in the formation and location of individual junctions. Understanding and controlling this process will enable the precise positioning of reproducible geometries into nano-electronic devices. To investigate the high speed behaviour of a QPC, it can be integrated with a transmission line structure patterned on a photoconductive GaAs substrate. The nonlinear conductance of the QPC (due to the finite density of states of the conductors) can be examined and compared with recent theoretical studies. Samples are fabricated in situ using an electrochemical procedure to produce QPCs along the transmission line structure. This method may provide insight into Terahertz Optoelectronic devices and ultrafast communication systems. [Preview Abstract] |
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C1.00008: Silicon Nanoparticle Mass by Milliken Oil Drop Experiment Austin Stafford, Alan Craig Silicon nanoparticles created through electrochemical etching have been found to have five unique sizes by using a transmission electron microscope (TEM). By creating an apparatus similar to the Millikan experiment an alternative method has been designed to confirm the TEM results. The particles will be suspended between two capacitor plates to allow balancing of the gravitational and electric forces as a means to calculate the mass to charge ratio. This poster will detail the designs for the experimental apparatus. [Preview Abstract] |
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C1.00009: Preparation and Optical Properties of Metallodielectric Core-Shell-Corona Particles Thomas Preston, Ruth Signorell The preparation of metallodielectric core-shell-corona particles is described and their optical properties are analyzed using the discrete dipole approximation. These particles consist of a spherical gold core coated with a thin dielectric layer and an outer gold layer (the corona). We demonstrate that stable dispersions of these particles possess plasmon modes in the near-infrared that can be tuned in a controlled fashion, while particle diameters can be kept below 100 nm. [Preview Abstract] |
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C1.00010: Deep levels due to hydrogen in ZnO single crystals Narendra Parmar, Marc Weber, Kelvin Lynn Hydrogen impurities and oxygen vacancies are involved in the $\sim $0.7 eV shift of the optical absorption edge of ZnO. Deuterium causes a smaller shift. Titanium metal is used to bind hydrogen as it diffuses out of ZnO. Positron annihilation spectroscopy coupled with other techniques point to the presence of oxygen vacancies. Removing hydrogen followed by annealing in oxygen reduces the carrier concentration. [Preview Abstract] |
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C1.00011: Influence of annealing on ZnO films grown by flow modulation epitaxy Heh Huang, Simon Watkins We have previously reported the growth of the wide bandgap semiconductor ZnO by the growth technique of flow modulation epitaxy (FME), a variation of metalorganic vapor phase epitaxy, in which the wafer is alternately exposed to diethylzinc and nitrous oxide. In this work we report on the effect of annealing ZnO samples under air at temperatures up to 1100\r{ }C. Evidence of significant mass transport following annealing is apparent in X-ray diffraction (XRD) and atomic force microscope (AFM) measurements. XRD data show that the as-grown ZnO films are highly c-axis (0001) oriented, since only ZnO (0002) and (0004) peaks can be seen. The annealing procedure has significantly improved the crystalline quality of ZnO films as evidenced by an order of magnitude increase in intensity and a significant narrowing of $\omega $-scan linewidths. AFM scans show that the surface morphology has been significantly flattened after annealing, while the grain size increased with the annealing temperature from 0.4 $\mu $m to great than 1 $\mu $m. In addition, atomic terraces became evident at higher annealing temperatures. [Preview Abstract] |
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C1.00012: New Technique to Make Biprism for Electron Holography Azadeh Akhtari-Zavareh, Karen L. Kavanagh, Rodney A. Herring Electron holography is based on the formation of interference patterns using a coherent electron source. In most TEM imaging modes the final recorded image is a spatial distribution of intensity and all of the phase information is lost. Like optical holography to make a hologram at least two waves, the reference wave and the object one are needed. A biprism is a narrow wire put in the path of the electron beam with an applied electric field. The beam is split into two coherent beams one of them passing through the sample. There are different techniques for making a biprism. The first method still commonly used today is a silica filament covered with a Au or Pt layer. Since a smaller biprism diameter results in wider phase information, efforts have been aimed at reducing the glass filament diameters. We have found that glass biprisms are prone to contamination, subsequent charging, and fracture in the TEM. We are therefore working on making biprisms using alternative approaches including focussed Ga ion beam milling and by microfabrication techniques. We have patterned a set of wires with different diameters on a silicon nitride wafar by e-beam litography followed by evaporation of Cr/Pt. Their properties will be compared to the conventional metal coated glass and ones make via the FIB. [Preview Abstract] |
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C1.00013: Electrochemical Zinc Oxide Nanowires Grown in the Presence of a Lithium Donor Ion Benjamin Wutzke, Bjoern Seipel We report on the electrolytic growth of zinc oxide in the presence of lithium or potassium donor ions. It is observed that a lithium ion donor precedes a morphological increase in wire diameter by $\sim$300 percent (potassium 100 nanometers to lithium at 300 nanometers, Fig. 1,3). Novel structures were found in trials of ZnO grown in the presence of both lithium and potassium with identical cell parameters and dopant electrolyte concentrations (Fig. 10). Deposition currents indicate divergent growth kinetics in the assemblage of ZnO structures in the presence of lithium or potassium and that this divergence relies upon the addition of a copper electrolyte. [Preview Abstract] |
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C1.00014: Student Understanding and Enjoyment in Introductory Physics Allison Shaffer, Brian Pyper Recent research in physics education has shown that a student's perception of enjoyment may have a large influence on what they understand. When they have a favorable attitude to what and how they can learn new concepts they generally also have strong reasoning ability and conceptual understanding. Our research was conducted through the administration of three diagnostic tests (EBAPS, Lawson, CSEM/FCI) at BYUI over the last several semesters and shows what we think are some interesting correlations. [Preview Abstract] |
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C1.00015: Examining gender differences on FCI performance in algebra and calculus based physics courses Kimberley Kreutzer, Andrew Boudreaux The Force Concept Inventory (FCI) has been widely used to asses student understanding of Newtonian principles. Studies have shown a marked difference in the performance of men and women on both pre- and post-tests [1,2] and also indicate that experiential based instruction may lead to a reduction in this gender gap [1,3]. This poster presents FCI data collected at Western Washington University. Initial analysis of gender differences are consistent with those reported nationally. We also discuss factors that may contribute to the differences in performance and propose instructional strategies that are designed to address the gender gap. \\[4pt] [1] M. Lorenzo, et. al., ``Reducing the gender gap in the physics classroom,'' AJP 74(2), 118-122 (2006) \\[0pt] [2] J. Docktor and K. Heller, ``Gender Differences in Both Force Concept Inventory and Introductory Physics Performance,'' \textit{Proceedings at the 2008 PERC} \\[0pt] [3] S. Pollack, \textit{et. al.}, ``Reducing the gender gap in the physics classroom: How sufficient is interactive engagement?'' \textit{PRST-PER} \textbf{3} (2007) [Preview Abstract] |
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C1.00016: Examining student multi-step reasoning ability Frances DeRook, Zack Pope, Andrew Boudreaux Experienced instructors recognize that students often struggle with multi-step reasoning. At Western Washington University, we have been investigating the nature of these difficulties in the calculus-based introductory course. The research grew out of a study on student understanding of fluid dynamics. While many students were proficient in applying isolated principles such as the Bernoulli effect and pressure-depth relationship, the majority had difficulty integrating these concepts to reach a correct response. Many had difficulty combining factors that acted either as enhancing or competing effects on fluid pressure. We developed curriculum to address student difficulties and observed improvements in student ability to apply reasoning to subsequent fluids problems. We also wished to know whether students could transfer multi-step reasoning to new contexts. In particular, we examined student ability to resolve two competing factors, vector magnitude and direction, in electrostatics. In this poster we describe specific difficulties with multi-step reasoning and present results from the transfer experiment. [Preview Abstract] |
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C1.00017: Meta-cognitive student reflections Britt Barquist, Jim Stewart We have recently concluded a project testing the effectiveness of a weekly assignment designed to encourage awareness and improvement of meta-cognitive skills. The project is based on the idea that successful problem solvers implement a meta-cognitive process in which they identify the specific concept they are struggling with, and then identify what they understand, what they don't understand, and what they need to know in order to resolve their problem. The assignment required the students to write an email assessing the level of completion of a weekly workbook assignment and to examine in detail their experiences regarding a specific topic they struggled with. The assignment guidelines were designed to coach them through this meta-cognitive process. We responded to most emails with advice for next week's assignment. Our data follow 12 students through a quarter consisting of 11 email assignments which were scored using a rubric based on the assignment guidelines. We found no correlation between rubric scores and final grades. We do have anecdotal evidence that the assignment was beneficial. [Preview Abstract] |
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C1.00018: Probing Nucleosynthesis in Novae: $^{22}$Na(p,$\gamma$)$^{23}$Mg A.L. Sallaska, D.W. Storm, A. Garcia, T.A.D. Brown, K.A. Snover, C. Wrede, K. Deryckx, C. Ruiz, D.F. Ottewell, D.A. Hutcheon, C. Vockenhuber, J.A. Caggiano, L. Buchmann Orbiting gamma ray telescopes have yet to observe the elusive $^{22}$Na isotope. More sensitive observatories are planned, and present uncertainties in the dominant destructive reaction, $^{22}$Na(p,$\gamma$), suggest new measurements in the proton energy range of 150 to 300 keV are needed to clarify the predictions of the amount of $^{22}$Na expected in a nova explosion. In particular, a state in $^{23}$Mg reported by Jenkins et al. [1] implies a possible resonance at E$_p$ = 198 keV, which could be significant. We are in the process of measuring the $^{22}$Na(p,$\gamma$) reaction rate directly by using protons from the UW tandem on a specially designed beamline, which includes rastering and cold vacuum protection of the $^{22}$Na implanted targets, fabricated at TRIUMF. Utilizing two 100$\%$ Ge detectors with anticoincidence shields to reduce cosmic backgrounds, measurements have been performed on known resonances of $^{22}$Na, as well as on the proposed new resonance. Preliminary results will be presented, which indicate the dominant contribution to the reaction rate in the region of interest to novae is not the new resonance at E$_p$ = 198 keV and is, instead, the resonance at E$_p$ = 214 keV.\\[0pt] [1] Jenkins $\it{et}$ $\it{al}$., PRL $\bf{92}$ (2004) 031101 [Preview Abstract] |
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C1.00019: Investigating the $^{23}$Mg(p,$\gamma )^{24}$Al Reaction at Astrophysically Relevant Energies with DRAGON Scott Foubister The DRAGON (Detector of Recoils and Gammas Of Nuclear Reactions) collaboration at TRIUMF is currently pursuing the first direct measurement of the strength of the most influential resonance (predicted to be at E$_{cm}$ = 473$\pm $3 keV) in the $^{23}$Mg(p,$\gamma )^{24}$Al reaction. This is a challenging experiment due to high beam contamination and very low expected yield. It is made possible thanks to the availability of the most intense accelerated $^{23}$Mg beam in the world and the world-class beam suppression {\&} particle identification capabilities of the DRAGON recoil mass spectrometer. Two beta monitors use plastic scintillators to measure the amount of radioactive $^{23}$Mg present in a beam contaminated with between 1:1 and 500:1 stable $^{23}$Na. Time-of-flight (TOF) detectors in combination with an ionization chamber are used to count the number of $^{24}$Al ``recoils''. In the first phase of this experiment, an upper limit of the resonance strength was calculated that indicates resonance strength much lower than the value predicted by nuclear shell-model estimates. [Preview Abstract] |
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C1.00020: FFAGs and Cyclotrons with Reverse Bends Michael Craddock, Yi-Nong Rao This paper describes tracking studies of radial-sector FFAGs and cyclotrons with reverse bends using the cyclotron equilibrium orbit code CYCLOPS. The results for FFAGs confirm those obtained with lumped-element codes, and suggest that cyclotron codes will prove to be important tools for evaluating the measured fields of FFAG magnets. The results for radial-sector cyclotrons show that the use of negative valley fields would allow vertical focusing to be maintained, and hence allow intense cw beams to be accelerated, to energies as high as 10 GeV. [Preview Abstract] |
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C1.00021: On nonlocal, causal quantum field theory, applied to tachyonic neutrinos Marek Radzikowski Presented is a framework for viewing nonlocal behaviour in the context of quantum field theory, while maintaining a consistent semblance of causality. The framework is comprised of a model for a Klein-Gordon quantum field theory of tachyons on Minkowski spacetime, without exponentially growing modes, and yet with a sensible notion of causality. (The latter may be expressed as a ``no antitelephones'' or ``chronology protection'' property.) A criterion for the two-point function of the model, known as the ``microlocal spectral condition'', is found to be satisfied, suggesting a straightforward inclusion of the free QFT within a renormalizable interacting theory involving other particles (regular or tachyonic). Parity breaking is satisfied for the Dirac version at the free QFT level, suggesting an electroweak interaction involving only V coupling, assuming the tachyonic neutrino hypothesis of Chodos, Hauser and Kostelecky. Lorentz symmetry is necessarily spontaneously broken, requiring the notion of a ``tachyon'' frame, first developed by Ciborowski and Rembielinski. Such a ``tachyon frame'', viewed as respecting the principles of relativity, may be of use in describing other candidate nonlocal phenomena, e.g., as seen in quantum entanglement experiments. [Preview Abstract] |
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C1.00022: Improving the One Dimensional Schr\"{o}dinger Equation Bradley Schorer, Stephen Bricher, Joelle Murray The simple harmonic oscillator (SHO) model is a useful approach for approximating energies close to the ground state in a one dimensional hydrogen atom. According to empirical evidence, the actual potential results in an asymmetric equilibrium point and exhibits and exhibits asymptotic behavior at large distances from the nucleus. This creates a problem in the SHO model, as it does not possess such characteristics, and as a result, has energy values that do not match do not agree with the known energy levels very well. We propose a new one dimensional potential that more accurately fits the empirical data than the SHO model. We test our model by comparing the Schr\"{o}dinger equation's energy states to accepted energy levels of the hydrogen atom. Possible other uses for this model include the description of energy levels of atoms other than the hydrogen atom. [Preview Abstract] |
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C1.00023: Improved Noise in high impedance samples using differential voltage Michael Holten, M.S. Crosser We report initial efforts to develop a high-impedance, lock-in amplifier-based technique for investigating the surface density of states of semiconducting polymers. An inverting signal adder is used to combine the signal from a lock-in amplifier and a slowly ramping bias from a function generator. This combined signal is then sent to the sample through an insulating surface. Operational amplifiers are used to buffer the voltage signal across the sample despite the high impedance of the sample. Potential applications for this technique will be discussed. [Preview Abstract] |
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C1.00024: Fifty Years of the Tangherlini Transformations -- an Alternative Version of Special Relativity Dmitri Rabounski, Gregory Malykin In 1958, Frank Robert Tangherlini, the US physicist, suggested an original procedure of synchronizations of clocks at two distant inertial frames, which differs from Einstein's method (Tangherlini F.R., PhD thesis, Stanford Univ., 1958; Malykin G.B. Prog. Phys., 2009, v.1, L9, v.2, L14). Einstein's method uses light signals, while Tangherlini's method uses faster-than-light signals, e.g. phase light spots produced by a rotating laser (Malykin G.B. Phys. Usp., 2004, v.47(7), 739) or even super-light speed tachyons. As a result, Tangherlini has obtained the so-called Tangherlini transformations from one inertial frame to another, different from the Lorentz transformations. In particular, the Tangherlini transformations allow an anisotropy of the velocity of light observed in a moving inertial frame, and they give a proper explanations to all known interference experiments of Special Relativity. We emphasize the Tangherlini transformations due to the possibility of a weak anisotropy of the velocity of light as claimed by the Grenoble group (Navia C.E. et al., Prog. Phys., 2007, v.1, 53), and the anisotropy of the Cosmic Microwave Background. [Preview Abstract] |
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C1.00025: Control of DNA replication by anomalous reaction-diffusion kinetics Michel Gauthier, John Bechhoefer DNA replication requires two distinct processes: the initiation of pre-licensed replication origins and the propagation of replication forks away from the fired origins. Experiments indicate that these origins are triggered over the whole genome at a rate $I(t)$ (the number of initiations per unreplicated length per time) that increases throughout most of the synthesis (S) phase, before rapidly decreasing to zero at the end of the replication process. We propose a simple model for the control of DNA replication in which the rate of initiation of replication origins is controlled by the interaction with a population of rate-limiting proteins. We find the time set by reaction-diffusion kinetics for such proteins to find, bind to, and trigger a potential origin. Analyzing data from \emph{Xenopus} frog embryos, we find that the initiation rate is reaction limited until nearly the end of replication, when it becomes diffusion limited. Initiation of origins and hence $I(t)$ is suppressed when the diffusion-limited search time dominates. We find that, in order to fit the experimental data, the interaction between DNA and the rate-limiting protein must be subdiffusive. [Preview Abstract] |
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C1.00026: Label-free Electrochemical Impedance Detection of C-reactive Protein Allison Whited, K..V. Singh, Raj Solanki C-reactive protein, CRP, is a marker present in human serum indicating inflammation and infection. By measuring the amount present in serum, it is possible to monitor the effectiveness of a treatment or roughly gauge the risk of heart disease. Using a double antibody capture system immobilized on an interdigitated electrode array, a label-free device was developed to detect the presence of CRP present in buffer solution and various concentrations of human serum. Electrochemical impedance spectroscopy was used to measure the end point data of the binding signal as the assay was exposed to varying amounts of CRP in the presence of a constant concentration of anti-CRP. The sensor is able to achieve linear detection in both buffer solution and human serum spiked with CRP in the range of 1ng/ml to 1ug/ml. The sensor developed can be integrated into a portable microfluidic device. [Preview Abstract] |
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C1.00027: Application of laser tweezers to passive microrheology of collagen solutions Marjan Shayegan, Nancy R. Forde Rheology is the field that can describe both viscous and elastic properties of a material in response to applied force or deformation. Passive microrheology (PMR) is a technique in which motion of a particle arising from thermal fluctuations is measured on nanometer length scales. One experimental approach to PMR uses optical tweezers, which trap and probe $\mu $m-sized particles, located within the material, at a high bandwidth. In this study, viscoelastic properties of solutions of collagen are characterized. To do this, we have probed the power spectral density of fluctuations of 1-$\mu $m-diameter microspheres optically trapped in acidic solutions of varying concentration of collagen type I (0, 0.5, and 1 mg/ml). The results show evidence that the behaviour of the solutions becomes increasingly non-Newtonian at high protein concentration. We attribute this to the presence of the viscoelastic polymer. This introduces frequency dependence to the complex modulus of the solution which is used to characterize the elasticity and viscosity of these systems. [Preview Abstract] |
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C1.00028: Force detection technique for molecular experiments in living cells using gradient optical traps Arnau Farre, Carol Lopez-Quesada, Josep Mas, Estela Martin-Badosa, Mario Montes-Usategui The powerful results in the molecular and cellular domain that are currently obtained using optical tweezers are leading to an increasing interest in this biophysical tool. This technique uses a highly focused laser beam to noninvasively trap and manipulate microscopic particles. Moreover, once calibrated, it can be used to accurately measure the forces and positions involved in many different molecular processes. Our research interest revolves around the study of the mechanics of cytoplasmic streaming in tobacco cells. Unfortunately, standard force detection techniques are not suitable for experiments in living cells. Golgi apparatuses that need to be used as handles to interact with motor proteins propelling them along the cytoskeletal filaments are not spherical, and the cytoplasm is an optically nonhomogeneous medium. In that case, the experiment does not meet the requirements for current force calibration methods, so forces cannot be accurately measured. Here, we show a new force detection technique for gradient optical traps based on the measurement of the change in momentum of the photons of a trapping beam. This method allows the study of molecular processes in living samples, and the use of beams and particles with arbitrary shapes. [Preview Abstract] |
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C1.00029: Detection of superparamagnetic nanoparticles using magnetoencephalography Teresa Cheung, Karen Kavanagh, Sarmita Majumder, Urs Ribary, Alexander Moiseev When bound to a biomarker, iron oxide nanoparticles have found applications in medicine because they are non-toxic and detectable using SQUID magnetometers in opaque tissue. In a liquid carrier, these particles are superparamagnetic with moments that randomly rotate due to thermal fluctuations. We have utilized a 151-channel magnetoencephalography (MEG) device to measure the net magnetic fluctuations from a 0.5 ml sample of Fe3O4 in a colloidal suspension spatially, temporally and as a function of temperature. TEM measurements suggest the sample particles are 10 to 50 nm in size. The sample was placed in an MEG and magnetic noise data was collected. The presence of these particles caused an increase in noise that was detectable in the frequency domain but was difficult to detect in the time domain. Temperature dependence exhibited a 1/T relationship with measured power. Spatial contour maps of the frequency data showed a distinct peak near the location of the sample. We hope to utilize our results towards creation of a model to localize these nanoparticles in vivo. [Preview Abstract] |
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C1.00030: Sources of Aerosol Sulphate in the Arctic Atmosphere Rempillo Ofelia, Ann-Lise Norman, A. Michelle Seguin Sulphate aerosols play a key role in the earth's radiation balance via direct and indirect aerosol effect. One of the major sources of biogenic sulphate aerosols in the Arctic atmosphere is Dimethyl Sulphide, a compound released by phytoplankton. Change in the Arctic Climate could potentially alter the amount of DMS derived sulphate released into the atmosphere and thus affect climate radiative forcing. The formation of sulphate from the oxidation of Dimethyl Sulphide (DMS) could provide a biological climate feedback in the event of a warming episode. The feedback mechanism, however, is highly uncertain. Measurements of atmospheric DMS, and its major oxidation products were obtained during the Fall 2007 and Fall 2008 cruise in the Canadian Arctic. Preliminary results from these measurements are presented along with external conditions that may affect these. Isotope analysis is used to determine sources of aerosol sulphate and apportion the amount derived from DMS. This we hope will shed light on the mechanism of DMS oxidation in the atmosphere and the factors that affect it, and ascertain the effects of DMS in the changing Arctic climate. [Preview Abstract] |
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C1.00031: A 2h-nmr Study Of Popc/sterol Membranes: Some Exciting Anomalies Mehran Shaghaghi, Martin Zuckermann, Jenifer Thewalt In a recent article [1], Y-W Hsueh et al showed that the 2H-NMR order parameter, M1, of 1-[2H31]palmitoyl, 2-oleoyl, sn-glycero-3-phosphocholine (POPC)/ergosterol multi-bilayers at 25oC increased linearly as a function of ergosterol concentration to 25 mol{\%}, but did not increase further when more ergosterol was added. By contrast, M1 for POPC/cholesterol bilayers increases linearly to at least 50{\%} sterol. The structural difference between cholesterol and ergosterol is that ergosterol has an additional double bond in its fused ring (C7-8) and a trans double bond (C22-23) plus a methyl group (at C24) in its alkyl chain. We study which of these structural changes is responsible for the observed saturation of the order parameter in POPC/ergosterol bilayers. In [1] it was shown that the M1 of POPC/7-dehydrocholesterol (7-DHC) multilayers behaves similarly to that of POPC/cholesterol, increasing linearly with [7-DHC]. 7-DHC has an ergosterol fused ring structure but a cholesterol alkyl tail. To explore this phenomenon, we determined the sterol concentration dependence of POPC containing two different sterols with structural similarities with respect to the before studied sterols. Other sterols are also being investigated in order to understand the sensitivity of POPC/sterol membranes to the sterol's alkyl tail structure. [1] Y-W Hsueh et al., (2007) Biophys. J. 92:1606-1615. [Preview Abstract] |
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C1.00032: Photoluminescence of GaAsBi alloys with emission wavelength up to 1.5 $\mu$m Xianfeng Lu, Daniel Beaton, Tom Tiedje, Yong Zhang GaAsBi alloy has recently attracted much attention due to its wide range of bandgap accessible by incorporation of a small amount of bismuth. However Bi incorporation into GaAs requires anomalous growth conditions due to the strong tendency for Bi surface segregation under usual GaAs growth conditions. These anomalous growth conditions raise the question as to whether the electronic properties of the bismide alloys are adequate for device applications. To address this question we measured the room temperature photoluminescence (PL) of GaAsBi layers as a function of Bi concentration in the 0.4{\%} - 10.6{\%} range. At the maximum Bi concentration (10.6{\%}) the PL emission peaks at 1500 nm. The PL intensity is found to increase with Bi concentration up to 4.5{\%}, and then decrease at higher concentrations. The composition dependence of the PL emission wavelength is in good agreement with theoretical calculations of the bandgap from density functional theory. In addition, there is a logarithmic increase in the PL peak energy at high excitation intensity. These effects are attributed to the existence of localized states near the top of the valence band. [Preview Abstract] |
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C1.00033: Schroedinger's Wave Structure of Matter (WSM) Milo Wolff The puzzling electron is due to the belief that it is a discrete particle. Einstein deduced this structure impossible since Nature does not match the discrete particle. Clifford (1876) rejected discrete matter and suggested structures in `space'. Schroedinger, (1937) also eliminated discrete particles writing: What we observe as material bodies and forces are nothing but shapes and variations in the structure of space. Particles are just schaumkommen (appearances). He rejected wave-particle duality. Schroedinger's concept was developed by Milo Wolff and Geoff Haselhurst (http://www.SpaceAndMotion.com) using the Scalar Wave Equation to find spherical wave solutions in a 3D quantum space. This WSM is the origin of all the Natural Laws; thus it contains all the electron's properties including the Schroedinger Equation. The origin of Newton's Law F=ma is no longer a puzzle; it is shown to originate from Mach's principle of inertia (1883) that depends on the space medium. Carver Mead (1999) applied the WSM to design Intel micro-chips correcting errors of Maxwell's magnetic Equations. Applications of the WSM describe matter at molecular dimensions: alloys, catalysts, the mechanisms of biology and medicine, molecular computers and memories. See http://www.amazon.com/Schro at Amazon.com. [Preview Abstract] |
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C1.00034: Analysis of electrodeposited Fe GaAs (110) interfaces using Atom Probe Tomography Sarmita Majumder, Chao Liu, Gianmarco Spiga, Savanna Shaw, Clive Jones, Prosa Ty, Peter Clifton, Tom Kelly, Karen Kavanagh Spin-polarized electron injection at magnetic-metal semiconductor interfaces have been demonstrated for epitaxial Fe-GaAs (100).[1, 2] fabricated via ultra-high vacuum deposition techniques, MBE. We fabricated similar epitaxial Fe-GaAs interfaces by electrodeposition using aqueous electrolyte solutions.[3] The structural abruptness of this electrodeposited interface have been investigated by cross-sectional transmission electron microscopy [4, 5] and by high resolution x-ray diffraction. Spin transport is being investigated. This report concerns our further investigations of the purity and compositional abruptness of these interfaces by Atom Probe Tomography (APT). The potential capability of APT is the atom by atom mapping of the atomic composition and location of each atom in a nanowire--like volume of material including the interface. Preliminary results confirm that electrodeposited Fe-GaAs is atomically abrupt with undetectable levels of impurities including S, C, or O. We expect spin transport at these interfaces to be equally efficient as those prepared in vacuum. [1] Lebeau, \textit{et al} \textit{APL} 93, 121909 (2008). [2] S. A. Crooker, \textit{et al} \textit{Sci.} 309 (2005) 2191\textbf{.} [3] Z. L. Bao, K. L. Kavanagh, \textit{J. Appl. Phys.} (2005) [4] Z.L. Bao, \textit{et al, J. Electrochem. Soc.} 155 (2008) H841. [5] S. Majumder, A. Arrott, K. L. Kavanagh, \textit{J. Appl. Phys. }(2009) [Preview Abstract] |
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C1.00035: Viscosity and drag measurements in quasi-two-dimensional fluid flows Edward Titmus, Paul W. Fontana Many fluid flows in nature and the laboratory exhibit quasi-two-dimensional (Q2D) dynamics. Accurate measurements of viscosity and surface friction in Q2D flows are critical for comparing experiments with theoretical and numerical models, but have proven elusive. We demonstrate precise, independent measurements of both quantities in a Q2D experiment using soap films. The measurements are being used to test the theoretical linear stability threshold in 2D vortex arrays. [Preview Abstract] |
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