Bulletin of the American Physical Society
2014 Annual Meeting of the Mid-Atlantic Section of the APS
Volume 59, Number 9
Friday–Sunday, October 3–5, 2014; University Park, Pennsylvania
Session F1: Poster Session |
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Chair: Stephane Coutu, Pennsylvania State University Room: Days Inn Atrium |
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F1.00001: Partial Trace of Hypergraph States Daniel Upchurch Hypergraph states are generalizations of graph states, which are known resources for models of quantum computation and error correction. We have shown that partial tracing over single qubit subsystems of hypergraph states results in the equal mixture of smaller hypergraph states, that is, of their density matrices. We have also described all possible hypergraphs that could share the same reduced density matrices that are smaller by one qubit. Comparing reduced density matrices of different quantum systems can show if they share entanglement properties. [Preview Abstract] |
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F1.00002: Experimental Approach for Circuit Analysis Frank Malatino, Matthew Widjaja, Jason Shulman For complex circuits, implementation of Kirchoff's Laws can be tedious and time consuming. Here, we present an alternative procedure, which is based on a methodology designed to control complex networks. It is an experimental, rather than analytical, approach to analyzing circuits. From this, one can generate equations that describe the behavior of a circuit. These are the same equations that would be obtained through more traditional means. [Preview Abstract] |
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F1.00003: Discrete Symmetries of Symmetric Hypergraph States Chase Yetter Hypergraph states are a generalization of graph states, which have proven to be useful in quantum error correction and are resource states for quantum computation. Quantum entanglement is at the heart of quantum information; an important related study is that of local unitary symmetries. In this project, I have studied discrete symmetries of symmetric hypergraph states (that is, hypergraph states that are invariant under permutation of qubits). Using computer aided searches and visualization on the Bloch sphere, we have found a number of families of states with particular symmetries. [Preview Abstract] |
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F1.00004: Ultra-light carbon nanotube sponge as an efficient electromagnetic shielding material in the GHz range Maria Crespo, Maria Gonz\'alez Gonz\'alez, Lakshmy Pulickal Rajukumar, Ana Laura Elias, Juan Baselga, Mauricio Terrones, Javier Pozuelo A CVD-synthesized CNT flexible sponge, with density lower than 0.02 g cm$^{-3}$, has been found to serve as high performance EMI shielding material without the aid of any polymer infiltration or impregnation. Due to its extreme lightweight, the specific SE of the CNT-sponge was found to be as high as 1100 dB cm$^{3}$ g$^{-1}$, having a total SE above 20 dB in the whole 1--18 GHz range, and being able to shield by absorption. The material is the best of our knowledge this specific SE value appears to be the highest reported hitherto. Improved EM absorbers should fulfill the synergic requirements of being low reflective and highly absorptive. In our CNT-sponges this condition is not satisfied because, although their net absorption ability is strongly remarkable, their high electrical conductivity favors the wave to be reflected at the input interface. Therefore, this sponge material would have a great potential for microwave-frequency applications that need negligible reflection and great absorption when combined in a multilayered structure that could prevent the wave to be reflected at the input interface. [Preview Abstract] |
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F1.00005: Capacitance of the Parallel Plate Capacitor Filled with Multiple Dielectric Slabs and its Electricity Analysis Seha Choi, Richard Kyung In recent years, the development of the hybrid microelectronics technology in electrical and energy engineering has been arising in many technological fields. In this research, we showed the influence of the multiple dielectric slabs inserted in one capacitor on the electric field distribution in the capacitor system. We considered two cases: one case in which multiple dielectric slabs are perpendicular to electric field lines, and the other case in which the slabs are parallel to electric field lines. In this paper, capacitance of the parallel-plate capacitor filled with multiple dielectric slabs perpendicular to the electric field lines was compared to capacitance of the capacitor filled with multiple dielectric slabs parallel to the electric field lines to evaluate its efficiency. Patterns of the capacitances were found, and the electric field between the plates was calculated based on the capacitance. Also, to validate its efficiency and effectiveness, coding techniques were employed to find the equivalent capacitance. [Preview Abstract] |
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F1.00006: Interface behavior in La$_{\mathrm{1-x}}$Sr$_{\mathrm{x}}$FeO$_{3-\delta}$ /Nb:SrTiO$_{3}$ perovskite oxide heterostructures Caroline (Lige) Zhang, Mark Scafetta, Steven May We report the interfacial transport behavior in La$_{\mathrm{1-x}}$Sr$_{\mathrm{x}}$FeO$_{3-\delta}$ /Nb:SrTiO$_{\mathrm{3}}$ perovskite oxide heterostructures. Strained epitaxial films were deposited on SrTiO$_{3}$ and Nb:SrTiO$_{3}$ substrates using oxide molecular beam epitaxy. Oxygen concentration was controlled by heating and re-annealing in a tube furnace with a mixture of O$_{2}$ and O$_{3}$. Temperature dependent current-voltage (I-V) characteristics were measured from the junctions. From these I-V data, ideality factors for the heterojunctions were obtained. The ideality factors are found to be much larger than 1, indicating transport differs substantially compared to conventional semiconductor heterostructures. [Preview Abstract] |
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F1.00007: Energetic of formation of molecular hydrogen on graphene using Eley-Rideal (ER) and Langmuir-Hinshelwood mechanisms Majid Karimi, Sean Morgan, Justin Petucci, Carl LeBlond, Razi Hassan, Gianfranco Vidali The second generation AIREBO potential for hydrocarbons is modified to accurately reproduce features of the chemical interactions and reaction of H atoms on graphene surface. The adapted potential reproduces many features of the adsorption potential of hydrogen on graphene in close agreement with the corresponding data from DFT. The modified potential is employed to study formation of H2 on graphene using ER and LH processes. This study will be carried out using classical molecular dynamics (LAMMPS) and nudged elastic band (NEB) for the calculation of barriers. Partition of the internal energy of the nascent H2 molecule into translational, vibrational, rotational, and graphene phonons will be studied and compared with the first-principles data. [Preview Abstract] |
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F1.00008: Shapiro Delay of Pulsar J1640$+$2224 Natasha L. McMann, Joris Verbiest Pulsar J1640$+$2224 is a binary millisecond pulsar with a white dwarf companion and is being used in pulsar timing arrays being used in experiments to detect gravitational waves. A previous study of the system's Shapiro Delay by L\"{o}hmer et al, 2005 constrained the companion mass to m2 $=$0.15$+$0.08 -0.05 Msolar which would imply an unprecedentedly low pulsar mass. We improved their result by analyzing pulsar timing data from four different radio telescopes: the Effelsberg 100m radio telescope in Germany, the Westerbork Synthesis Radio Telescope in the Netherlands, the Nan\c{c}ay radio telescope in France, and the Lovell radio telescope at Jodrell Bank in the United Kingdom. Our study constrains the companion mass to m2$=$0.28$+$0.35 -0.03 Msolar and the pulsar mass to m1$=$1.51$+$3.30 -0.22 Msolar. The relatively wide orbit in which this pulsar resides (period $\sim$ 6 months) complicates this analysis as it introduces covariances with the Earth's motion. Continued monitoring should therefore allow further improvements to this mass measurement. [Preview Abstract] |
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F1.00009: The Formation and Assembly of Star Clusters Mark Giovinazzi, Stephen McMillan We perform multiple simulations of the early evolution of young star clusters. Astronomers recognize that all stars form in clusters and that over time, the resulting group will dissolve; the life cycle of such a process is contingent upon the initial conditions of the fractal clusters. The first question is how much time is necessary for a given assemblage of stars to reach an effective equilibrium. The second physical effect we study is the degree of mass segregation in the final star cluster. As the system evolves, we observe that heavier stars sink towards the center of the cluster. In both investigations, we modify the following parameters and analyze the effects they have on the resulting time scale for stabilization of the cluster: the number of stars, the fractal dimension of our cluster, the scaling of the initial velocities, and the initial mass distribution of our stars. Each simulation is performed for numerous random realizations of the system and all calculations are continued until the cluster reaches dynamical equilibrium. We find that while neither the number of stars in the system nor the fractal dimension have significant effects on the time to reach equilibrium, the decrease in initial velocities causes the cluster to reach equilibrium faster. [Preview Abstract] |
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F1.00010: Finding the Lowest Mass Exoplanet with Improved Radial Velocimetry Sharon Xuesong Wang, Jason Wright Radial velocimetry detects the star's radial velocity (RV) variations caused by the gravitational pull of the planets orbiting around the star. Surveys using radial velocimetry have been extremely successful in detecting extra-solar planets (exoplanets) and measuring their masses in the counts of hundreds, including many interesting low-mass and likely rocky planets such as Kepler-78b, the first exoplanet known to have radius and mass very close to Earth's. However, the current precision of radial velocimetry ($\sim$0.5-1 m/s) is limiting our ability to detect exoplanets with even lower masses or rocky planets further out in the orbit, especially the ones that are potentially habitable. We have identified several contributing factors to RV systematic errors through our study, including the annual jitter caused by the earth's atmospheric absorption, which creates an systematic signal at $>$ 1m/s level. Through our pilot study, we have successfully removed part of this systematics and improved the RV precision of Keck HIRES, the leading 10-meter telescope and instrument for exoplanet discoveries. Our study will enable the discoveries of more low mass exoplanets through RV surveys or follow-up program on planet candidates discovered via NASA's Kepler mission. [Preview Abstract] |
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F1.00011: Classifying Dwarf Galaxies as Satellites Brean Prefontaine By studying the properties of galaxies in both voids and walls, we can learn how galaxy formation is influenced by environment. We focus on the properties of dwarf galaxies, which are more sensitive to environmental effects than massive galaxies. Being a void or wall galaxy can tell us about the large-scale environment around a dwarf galaxy. However, the small-scale environment of a dwarf galaxy can be explored through whether or not the dwarf galaxy is a satellite to a larger galaxy. I used the spatial distribution of brighter galaxies in SDSS to classify each dwarf galaxy as being a satellite galaxy with a single host, within a group of galaxies, or isolated. To look for a possible host around the dwarf galaxy, the dwarf galaxy had to be within the calculated virial radius of at least one of the nearby galaxies. All of the qualifying larger galaxies were treated as possible hosts for the dwarf galaxies. We found that roughly 82 percent of all void dwarf galaxies are isolated, 14 percent have a single host, and 4 percent have multiple possible hosts and most likely lie within a dense region. In contrast, only 70 percent of wall dwarf galaxies are isolated, 20 percent have a single host, and 10 percent have multiple possible hosts and most likely lie within a dense region. [Preview Abstract] |
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F1.00012: Exploring HETDEX Pilot Survey Lyman-alpha Emitters with Spectral Energy Distribution Fitting Alex Hagen, Robin Ciardullo, Caryl Gronwall, Joanna Bridge, Gregory Zeimann We use photometry spanning from the rest-frame UV to the rest-frame NIR to fit the individual spectral energy distributions (SEDs) of 67 bright Ly-alpha emitting galaxies (LAEs) discovered in the HETDEX Pilot Survey. We find that bright LAEs in the redshift range 1.9 $<$ z $<$ 3.5 are quite heterogeneous. Our LAE masses span more than three orders of magnitude and are distributed in a manner that suggests that the objects are drawn in an almost uniform manner from the underlying galaxy mass function. This diversity is also reflect in the LAEs' dust content: while most of our objects are dust poor, some of the more massive LAEs are dust-rich, with differential extinctions as large as E(B-V) $\sim$ 1.2. We find no significant correlation between half-light radius and stellar mass but we show that the Ly-alpha escape fraction does depend on mass, with low-mass systems being more efficient Ly-alpha emitters. Finally, we present evidence which suggests that there is an upper limit to the mass-specific star formation rates of Ly-alpha emitting galaxies. [Preview Abstract] |
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F1.00013: Searching for Protostars using MYStIX Gregory Romine, Eric Feigelson The MYStIX data set synthesizes photometric data in the Xray, nearIR, and farIR for 20 star forming regions in the nearby galaxy with rich OBdominated clusters. Data are obtained from NASA's Chandra Xray Observatory, the UKIRT telescope in Hawaii, and NASA's Spitzer Space Telescope. This project attempts to utilize the MYStIX data sets and ESA's Herschel mission farIR cloud maps to find protostellar candidates within dense cloud cores of the star forming regions. Within the data set are stars with strong infrared excesses indicative of dusty protoplanetary disks at the Class I stage of protostellar evolution. In addition, Xray sources with very high extinction are present that may represent enshrouded protostars. The study will describe the selection process for candidate protostars, reducing contamination from extraneous Galactic and extragalactic objects. Candidates are then compared to known protostars in the regions, and we provide an atlas and catalog of the resulting candidate protostars. [Preview Abstract] |
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F1.00014: Physical and Morphological Properties of [O II] Emitting Galaxies in the HETDEX Pilot Survey Joanna Bridge, Caryl Gronwall, Robin Ciardullo, Alex Hagen, Greg Zeimann The Hobby-Eberly Dark Energy Experiment pilot survey identified 284 [O II] 3727 emitting galaxies in a 169 square-arcminute field of sky in the redshift range 0 \textless\ z \textless\ 0.57. This line flux limited sample provides a bridge between studies in the local universe and higher-redshift [O II] surveys. We present an analysis of the star formation rates (SFRs) of these galaxies as a function of stellar mass as determined via spectral energy distribution fitting. The [O II] emitters fall on the ``main sequence'' of star-forming galaxies with SFR decreasing at lower masses and redshifts. However, the slope of our relation is flatter than that found for most other samples, a result of the metallicity dependence of the [O II] star formation rate indicator. The mass specific SFR is higher for lower mass objects, supporting the idea that massive galaxies formed more quickly and efficiently than their lower mass counterparts. This is confirmed by the fact that the equivalent widths of the [O II] emission lines trend smaller with larger stellar mass. Examination of the morphologies of the [O II] emitters reveals that their star formation is not a result of mergers, and the galaxies' half-light radii do not indicate evolution of physical sizes. [Preview Abstract] |
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F1.00015: First Results from the Swift/UVOT Near-Ultraviolet Survey of the SMC Lea Hagen, Mike Siegel, Caryl Gronwall, Erik Hoversten, Stefan Immler The Swift Ultraviolet/Optical Telescope (UVOT) has recently completed the first wide-field multi-color NUV survey of the Small Magellanic Cloud. The resulting images, the product of nearly two complete days of imaging, covers nearly four square degrees and includes over 250,000 NUV sources. We present early analysis of this outstanding data set, looking at the recent star formation history of the SMC, the distribution of young stellar populations over the face of the SMC, the location of rare stellar types such as Post-Asymptotic Giant Branch stars, and the SMC dust extinction law. [Preview Abstract] |
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F1.00016: R-mode frequencies for slowly rotating neutron stars with realistic equations of state Ashikuzzaman Idrisy, Benjamin Owen, David Jones The frequency of r-mode oscillations of rotating neutron stars is of interest when carrying out gravitational wave and electromagnetic observations. The r-mode frequency in the slow rotation limit of Newtonian stars is well known, but will be subject to various corrections. We make simple estimates of the importance of several sorts of correction, and conclude that relativistic corrections are likely to be the most important. For this reason we extend the formalism of Lockitch et al. [1], who consider relativistic polytropes, to the case of realistic equations of state. The perturbation equations resulting from this formulation are solved using a spectral method. We find that for stars with realistic equations of state, the r-mode frequency ranges from 1.39$\Omega $ to 1.56$\Omega $ (where $\Omega $ is the rotation rate of the star), when the relativistic compactness parameter M/R is varied over the astrophysically-motivated interval from 0.11 to 0.31. The results presented here are relevant to the design of gravitational wave and electromagnetic r-mode searches, and will help in constraining the compactness parameter following a successful r-mode detection, which is itself related to the high density equation of state. [Preview Abstract] |
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F1.00017: Characteristics of a 2-D Magneto-Optical-Trap Christiane Ebongue, Eric Magnan, Pablo Solano, Jeffrey Grover, Luis Orozco The 2D Magneto-Optical-Trap (MOT) produces a cold collimated Rubidium ($^{87}$Rb) atomic beam in a compact set up. The 2D MOT is in a stainless steel vacuum system, and requires a gradient of magnetic field as well as two different laser frequencies, one for cooling through a cycling transition and one for re-pumping atoms that fall into the wrong state. The vacuum system has four vacuum windows to allow retroflection of the cooling beams, a dispenser that generates a vapor of Rb atoms. The lowest pressure attained is about 10$^{-10}$ mbar. We have produced the quadrupole field using first small permanent rare earth magnets, and then coils. Finally, the red-detuned cooling beam has a frequency offset a few MHz from transition frequency of $^{87}$Rb, 5 $^{2}$S$_{1/2}$ F$=$2 $\to$ 5 $^{2}$P$_{3/2}$ F$=$3) with a circular polarization. The optics arrangement is compact using fiber optics. We present here advances and results of the 2D MOT. [Preview Abstract] |
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F1.00018: Construction of Zeeman Slower and Ultra High Vacuum for Use in Laser Cooling and Trapping Joshua Halbfoerster, Nicholas Hitcho, John Huckans Laser cooling and trapping involves slowing vaporized rubium-87 ($^{87}$Rb) atoms in a vacuum using red-detuned laser light to observe atomic behavior in a microkelvin environment. $^{87}$Rb atoms are first vaporized in a 135$^{\circ}$ oven, sent through a collimating apparatus down a Zeeman slower toward a counterpropagating laser beam that slows them down to millikelvin temperatures. Subsequent techniques further cool the atoms to microkelvin temperatures. A Zeeman slower consists of a one-meter solenoid of precisely wound copper wire, creating a spatially-varying magnetic field that compensates for the spatially-changing Doppler shift of the $^{87}$Rb ground state transition due to the fact that the atoms are decelerating relative to the counterpropagating leaser beam. Our experiment occurs in an ultra-high vacuum (UHV) environment ($\le $ 10$^{-7}$ Pa). We achieve this level of vacuum using tools and methods such as sonication, baking, turbomolecular, ion and titanium sublimation pumps. [Preview Abstract] |
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F1.00019: Tuning and Locking a Diode Laser for a Magneto-Optical Trap Matthew Gift, Rachel Livingston, Ju Xin, John Huckans The purpose of a magneto-optical trap (MOT) is to use the atomic structure of rubidium-87 to manipulate a sample into an ultra-cold atom cloud in a vacuum sealed environment via a laser array. The extended cavity diode lasers used in this experiment must be tuned using an absorption spectroscopy system which utilizes the Doppler effect of light through a rubidium cell as the extended cavity of the diode laser is scanned across the rubidium absorption peaks with a piezo stack. The laser is then locked with a lock-in amplifier to ensure the frequency remains stable. When the lasers are locked they will be ready for use in the creation of a MOT. The light will be red-detuned so as to excite atoms moving towards each beam. When an atom absorbs the photon it will lose momentum along the photon's axis of motion, then spontaneously emit a photon of the observed frequency in a random direction. The isotropic nature of the emitted photons creates a randomly-directed recoil momentum in the affected atoms and reduces the average energy of the sample as a whole. With the orthogonal laser set-up and in conjunction with an anti-Helmholtz magnetic field this will create a point where the least energetic atoms will form an ultra-cold cloud with a temperature on the order of 200 microkelvins. [Preview Abstract] |
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F1.00020: Rotationally inelastic collisions of He and Ar with NaK: Theory and Experiment T.J. Price, K. Richter, J. Jones, C. Faust, A.P. Hickman, J. Huennekens, R.F. Malenda, A.J. Ross, P. Crozet Rotationally inelastic collisions of NaK ($A\,^1\Sigma^+$) molecules with He and Ar have been studied. At Lehigh, we use a pump-probe scheme (the probe is scanned over transitions to the $3\,^1\Pi$ state) with either polarization labeling (PL) or laser-induced fluorescence (LIF) spectroscopy. At Lyon, one-laser excitation is used with Fourier Transform (FT) fluorescence spectroscopy. In both cases, the pump laser excites a particular ro-vibrational level $A\,^1\Sigma^+$($v, J$). We observe strong direct lines corresponding to transitions from the ($v, J$) level pumped, and weak satellite lines corresponding to transitions from collisionally-populated levels ($v,J^{\prime} = J + \Delta J$). The ratios of satellite to direct line intensities in LIF and PL yield information about population and orientation transfer. A strong propensity for $\Delta J =$ even transitions is observed for both He and Ar perturbers. In the FT fluorescence experiment we also observe $v$ changing collisions. Theoretical calculations are also underway for collisions in both the $A\,^1\Sigma^+$ and $X\,^1\Sigma^+$ states. For He-NaK we have calculated potential surfaces using GAMESS and carried out coupled channel scattering calculations of transfer of population, orientation, and alignment. [Preview Abstract] |
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F1.00021: Biophysical Aspects of Blood Flow in the Cardiac Valve Ayoung Cho, Soon Sung Hong, Matthew Seh Blood flow through cardiac valve occurs by the pressure gradient in the cardiovascular system. Assuming the incompressibility of the blood in the cardiovascular system, this paper applied a numerical method to find the blood flow rate and biofluid parameters in the mitral valve. Also biomechanical analysis was performed on a disk-type prosthetic mitral valve in heart. For the purpose of computational and mathematical modeling, the valve was assumed to be immersed in fluid and symmetric about the midline plane. Incompressible laminar steady flow with constant viscosity was assumed. The flow is considered during the greater part of systole when the valve is fully open. Stress, displacement distributions are computed at every grid point. And two-dimensional velocity profiles across anterior mitral valve are presented. In this study, computational and numerical method were attempted to analyze the mitral valve quantitatively by using finite element analysis. A finite element model of the mitral valve showed that the maximum pressure occurs at the early diastolic period. Also, high velocity flow through the mitral valve was observed due to pressure buildup during initial filling. [Preview Abstract] |
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F1.00022: Analysis of the Biophysical Factors Affecting Cardiovascular Disease Sheamin Khyeam, Richard Kyung The object of this research is to find the biomechanical effects of aortic valve stenosis on the heart disease using biophysical and computational analysis. Observations are carried out for significant factors, such as blood pressure changes, aortic valve area changes, and possible correlations with blood velocity and other fluid dynamic-related properties. The Gorlin equation is expressed as a formula that directly links cardiovascular and geometric properties central to our purpose of establishing a malicious link between pressure and aortic valve stenosis. Based on Bernoulli's principle, Gorlin Equation differs only in that it is an application of the principle to cardiovascular analysis and combines cardiovascular properties to determine heart valve area. To determine the area of the aortic valve, hemodynamic parameters are set: heart rate is set at 80 beats/minute, systolic ejection period at 0.33 seconds, cardiac output at 6400 mL/minute, and the ``standard Gorlin constant'' at 44.3. Additionally, computer program MATLAB is used to support and help with the calculation of results respectively. [Preview Abstract] |
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F1.00023: Dynamics of the Blowfly Photoreceptor-LMC Synapse Christopher Boughter, Rob de Ruyter The blowfly visual information pathway is a well-studied system, from the initial absorption of a photon by a photoreceptor to the corresponding reaction by the fly. One particularly interesting component of this pathway is the communication between photoreceptors and large monopolar cells (LMCs). Photoreceptors transmit information to an LMC through the release of vesicles containing histamine. The dynamics of vesicle release is usually modeled as an inhomogeneous Poisson process with a rate driven by the presynaptic voltage. Preliminary experimental evidence suggests that this release may have a more complex temporal structure consistent with a population of driven oscillators. To determine the validity of this model, in-vivo measurements were made on both photoreceptor cells and LMCs. The response of these cells to high frequency light pulses was recorded in an attempt to entrain the putative oscillators. In the LMC we observe transient oscillatory behavior after cessation of stimulation at 125 Hz. This behavior is not observed in the photoreceptors, and there is some published evidence that postsynaptic mechanisms are not responsible for these oscillations. These observations are consistent with our hypothesis, but future work is needed to determine the validity of the idea. [Preview Abstract] |
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F1.00024: Microstructural Analysis of Porcine Skull Bone Subjected to Impact Loading Allison Ranslow, Kimberly Thompson, Sikhanda Satapathy, Raul Radovitsky, Reuben Kraft Fracture and damage of the skull remains one of the largest and most detrimental injuries in combat. Although skull fracture is a common injury, its mechanics are still unknown due to bone's complex structure, which spans the molecular level and macroscopic dimensions. Using finite element analysis of the microscopic architecture allows for a controlled evaluation of stress wave interactions, micro-crack growth, propagation and coalescence. To gain a better understanding of the microstructure and the mechanics of bone fracture under impact loading, thirty finite element models of small sections of a porcine skull were created. MicroCT scans of the skull were used to generate three-dimensional surface geometry meshes of various locations throughout the skull, from which volume meshes were developed. All samples were analyzed using finite element simulations, subjected to quasi-static compression. The output models allowed for a detailed understanding of the failure mechanics of the skull. Upon completion of the simulations, we found that although each sample was initially provided with the same material parameters, under stress, the structures behave very differently due to varying levels of porosity, causing the material response to change drastically with load. [Preview Abstract] |
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F1.00025: A Computational Analysis of Bone Formation in the Cranial Vault Chanyoung Lee, Joan T. Richtsmeier, Reuben H. Kraft Bones of the cranial vault are formed by the differentiation of mesenchymal cells in osteoblast cells on a surface that surrounds the brain, eventually forming mineralized bone. Signaling pathways causative for the cell differentiation start from some actions of extracellular proteins driven by information from genes. We assume that the interaction of cells and extracellular molecules which are associated with cell differentiation can be modeled using Turing's reaction-diffusion model, which is a mathematical model for pattern formation controlled by two interacting molecules (activator and inhibitor). In this study we hypothesize that regions of high concentration of an activator develop into primary centers of ossification, the earliest bone. In addition to the Turing model, we use another diffusion model dealing with a morphogen associated with bone growth. These mathematical models were solved using the finite element method. The computational domain and model parameters are determined using a large collection of experimental animal models. The results show that the five ossification centers that form in our model occur at the same position as those identified in experimental data. As bones grow from these ossification centers, sutures form between the bones. [Preview Abstract] |
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F1.00026: Cell fate Affected by Carbon Nanotubes during C17.2 Neural Stem Cell Differentiation Massooma Pirbhai, Sabrina Jedlicka, Slava V. Rotkin Delivery of materials, such as drug compounds or imaging agents for treatment or diagnosis of disease still presents a biomedical challenge. Nanotechnological advances have presented biomedicine with a number of agents that possess the appropriate size and chemistry to pass the blood brain barrier. Functionalized carbon nanotubes are one such agent. Functionalized carbon nanotubes, shown to penetrate the blood brain barrier can potentially aid in drug and gene delivery to the central nervous system. In addition, carbon nanotubes have already been applied in several areas of nerve tissue engineering to probe and augment cell behavior, to label and track subcellular components, and to study the growth and organization of neural networks. Although the production of engineered carbon nanotubes has escalated in recent years, knowledge of cellular changes associated with exposure to these materials remains unclear. In this study, we employed multipotent C17.2 neural stem cells to probe how individual single-wall carbon nanotubes functionalized with synthetic ssDNA or RNA affect cellular processes of adhesion, proliferation, and differentiation. The research has shown that while toxicity might not be an issue at low concentration of the carbon nanotubes, irregular behavior is nonetheless observed in terms of the fate of cells after differentiation and is worth considering when developing strategies to deliver components to the central nervous system. [Preview Abstract] |
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F1.00027: Simulation of the Effects of Flanking Sequences on Polyglutamine Aggregation Jason Haaga, Siddique Khan, James Gunton Huntington's disease is one of a set of nine progressive neurodegenerative diseases caused by the expansion of CAG sequence repeats. This results in affected proteins with abnormally long polyglutamine (polyQ) tracts, which beyond a pathological threshold length form toxic aggregates.~Recent experimental studies suggest the sequences flanking the polyQ tract have a profound impact on the aggregation rates and morphologies. The 17 residues N terminus to the polyQ insert in the huntingtin protein (Htt) have been shown to accelerate aggregation, particularly the formation of insoluble fibrils.~The proline-rich C terminal region has been demonstrated to slow the rate of aggregation.~We propose a coarse-grain model of the polyQ tract, with and without its N and C terminal regions, and utilize Brownian dynamics simulation to examine the kinetics of aggregation. [Preview Abstract] |
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F1.00028: Finite Element Modeling of Impact and Injury to the Lower Extremity Rebecca Fielding, Reuben Kraft, Andrzej Przekwas, X.G. Tan An underbody blast (UBB) is the detonation an explosive device under a military vehicle. Such incidents can lead to severe injuries in the lower extremities. Research has been conducted at a variety of anatomical levels to better understand the mechanisms that lead to injury in the lower extremity. A finite element model of the lower leg was validated against experimental data for vertical loading at 5 m/s. This model was used as a basis for full leg simulations and preliminary fracture modeling. In UBB events, the foot and ankle, particularly the understudied calcaneus, may sustain significant damage. A cadaveric calcaneus was scanned to a resolution of 55 microns using an industrial microCT scanner. This data was used to generate a 2D finite element mesh of the calcaneus that included marrow, trabecular bone, and cortical bone. Loading conditions for the calcaneus were based on results of the lower leg simulations. The calcaneus model was used for exploratory investigations into the effect of trabecular structure and material interaction on patterns of stress propagation and potential fracture paths. As research continues, the aim is to develop model accuracy and resolution at micro- and macroscale levels for a thorough understanding of injury mechanisms. [Preview Abstract] |
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F1.00029: Steady-state fluorescence anisotropy and lifetime measurements of fluorophores and fluorescent-dye-loaded microspheres Jacob A. Cole, Sam V. Migirditch, Tyler W. Foley, Brooke C. Hester We perform steady-state fluorescence anisotropy and lifetime measurements via illumination of fluorophores with a continuous intensity beam of light. In steady-state fluorescence anisotropy, fluorophore molecules are excited when the polarization of the incoming excitation light is parallel to the excitation axis of the fluorophore. Following a delay known as the fluorophore lifetime $\tau $ a molecule will return to its rest state by emitting photons polarized along the instantaneous orientation of the molecule. The steady-state anisotropy r is defined as the average change in orientation of the sample weighted by the average intensity of each polarization axis. Experimental results are used to determine the anisotropy r and the lifetime $\tau $ of the samples: freely diffusing rhodamine as well as yellow-green fluorescent-dye-loaded microspheres with sizes ranging from 0.51 $\mu$m to 6.2 $\mu$m. Experimental outcomes confirm that the custom-made steady-state fluorescence anisotropy optical system and analysis software are properly engineered and optimized. These outcomes include the fluorescence lifetime $\tau $ for each fluorophore type, the fluorescence lifetime $\tau $ for each fluorescent bead size, and the anisotropy r at various temperatures. [Preview Abstract] |
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F1.00030: A Fluorometrical Study of the Impact of Gold Nanoparticles on the Fluidity DMPC Liposomes Lance Edwards, Dillon Badman, Fatima Edwards, Qi Lu Liposomes are model membrane systems composed of phospholipid bilayers that are the major constituent of cellular membranes. In this study, we aim to understand how nanoparticles affect the integrity of cell membranes by examining the interactions between liposomes and gold nanoparticles (AuNPs). The liposomes were prepared by sonicating 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) in PBS partitioned with Laurdan (6-lauroyl, 1-2-dimethylamino naphthalene), a hydrophobic fluorescent dye. AuNPs in four different sizes (5, 10, 20 and 30 nm) at various concentrations were introduced to extruded or non-extruded liposomes. The extrusion process allowed for a size uniformity of the liposomes below 100 nm in diameter, confirmed with an IX-71 fluorescence microscope. The emission spectra of Laudan-labeled liposomes upon AuNP interactions were collected with a K2 spectrofluorometer. The emission peaks at 440 and 490 nm were then used to derive the generalized polarization (GP) functions, which reveal the change of fluidity in the lipid bilayers induced by AuNPs. These changes may lead to new insights on how AuNPs may be used to control the metabolic pathways of lipid membranes in the process of cancer cell adhesion. [Preview Abstract] |
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F1.00031: Reinforced composite based modeling of axonal injury - A physics based approach Harsha Garimella, Reuben Kraft Sports related concussion/brain injury is a major health problem in the United States that is particularly common in contact sports like American football, hockey etc. Despite the significance and growing concerns about the potential long terms consequences of concussion, its biomechanical mechanisms are not fully understood. Since 1970s computational modeling proved to be an efficient tool for biomechanical modeling of human brain. Computational modeling coupled with recent advancements in brain imaging technology would provide us with a robust method in developing accurate constitutive models for computational analysis. This paper presents a physics based finite element modeling of human brain with axonal fibers using the concept of embedded finite element method and composite based modeling. Axonal strains, which play a major role in neurotrauma, can be obtained with much less complexity using this method. This model will be further developed to include the physics areas like diffusion (spread of disease), electomagnetism(EEG) etc. [Preview Abstract] |
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F1.00032: A simulation study of a polypeptide model of a hydrogel Songul Kutlu, Siddique Khan, Jason Haaga, James Gunton Hydogels are water insoluble, cross linked polymers that are capable of swelling substantially in aqueous conditions. The crosslinked nature of a hydrogel makes it strong mechanically. Hydrogels has many applications such as in drug delivery, tissue engineering, contact lenses and wound dressing. The preparation of hydrogels through molecular self-assembly gives microscopic information about the material properties. Some of the hydrogels are environmentally responsive to pH and temperature. MAX1 is a chemically synthesized responsive hydrogel which is the chain of valine and lysine aminoacids flanking a tetrapeptide VDPPT. Therefore, the general structure of MAX1 is: VKVKVKVK-VDPPTKVKVKVKV-NH2. In this poster we present preliminary Monte Carlo simulation results which shows that the structure of a single MAX1 peptide is a random coil shape. We will also present preliminary Monte Carlo dimer simulation results for the MAX1 peptide chains in order to study the conformational variations at dimer level. In addition, we also propose a coarse-grained model that we will use to study the self-assembly of these polypeptide chains, in order to understand the formation of hydrogels. [Preview Abstract] |
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F1.00033: Enhanced Imaging of Dental Structure Using MRI Physics Julia Kim, Nayeoun Kim, Bosul Lee Magnetic Resonance Imaging is a common medical imaging technique that uses magnetism and computers to determine the anatomy and physiology of intended subjects in multiple areas. The technique is prevalently used in medical and dental diagnosis. In this paper, human tooth and jaw image data are first transmitted into a spatial frequency (k-space) domain through the Fourier Transformation and physical coordinate transformations. This study compares the resolution of an original MRI image with image obtained using filtered data of a human tooth and jaw. The main purpose of this research is to develop a better algorithm that would enhance the quality of the final MRI image, decrease the amount of time required to produce it, and generate the image with less ringing artifact. [Preview Abstract] |
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F1.00034: Analysis of Alzheimer's Disease Using Computational Neuroimaging Soo Hwan Park, Sheamin Khyeam, Ha Young Kyung As Alzheimer's is becoming more common in our population, it is important to develop adequate medical technology that will help physicians better examine patients with Alzheimer's disease. Alzheimer's disease is a progressive neurodegenerative disorder characterized by the gradual onset of other disease such as dementia. Neuroimaging is widely studied for the purpose of removing the causes of dementia syndrome, such as brain tumors and cerebrovascular disease. Structural imaging based on magnetic resonance is an integral part of the clinical assessment of patients with suspected Alzheimer dementia. In this paper, MRI image of the brain affected with Alzheimer's disease was used to determine the frequency domain, which can be used to reconstruct the image by mathematical and computational transformations. Since the frequency data of the brain with Alzheimer's disease produced through the MRI process is in a large magnitude, not all of the data is necessary in producing the required image. [Preview Abstract] |
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F1.00035: Reconfigurable Tunable Hyperbolic Metamaterial Thomas Gresock, Bradley Yost, David Lahneman, Vera Smolyaninova, Igor Smolyaninov Hyperbolic metamaterials are artificially created materials that have unique properties for light transmitted in different polarization directions. For one polarization direction the material will behave as a metal, while for the other polarization direction the material behaves like a dielectric. This behavior allows hyperbolic metamaterials to manipulate light on the sub microscopic level, which has applications that range from cloaking to creating a perfect lens. We used a cobalt based ferrofluid in an applied magnetic field to attempt to recreate the effects of hyperbolic metamaterials. Ferrofluids selfassemble in nanocolumns in applied magnetic field. By measuring the polarization dependence of the light in the visible and infrared spectrum, we demonstrate that the ferrofluid exhibits hyperbolic metamaterial behavior. This study found a novel polarization property of the ferrofluid, which blocks the light polarized in one direction for a very narrow range of polarization angles. These novel properties have potential applications in efficient chemical and biological sensing. Supported by NSF Grant DMR-1104676 [Preview Abstract] |
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F1.00036: Computational studies of the boron carbide structure Sanxi Yao Boron carbide is a structure that exhibits a broad composition range, implying a degree of intrinsic substitutional disorder. While the observed symmetry is rhombohedral, the enthalpy minimizing structure has lower, monoclinic, symmetry. We apply compressive sensing to fit a pair interaction model to a database of structural energies. Utilizing histogram methods to analyze Monte Carlo simulations of this model, we investigate the symmetry-restoring phase transition that explains the observed rhombohedral symmetry at high temperatures. [Preview Abstract] |
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F1.00037: Growth pattern and emergence of bulk-like structures in Aluminum Hydride (AlH$_{3})$ nanoclusters Georgia Montone, Anil Kandalam, William Sawyer Complex aluminum hydrides, because of their light weight and being hydrogen-rich, have attracted considerable attention as a potential hydrogen storage materials and propellants. In this poster, we will present our computational results exploring the structural evolution and stabilities of neutral and anionic (AlH$_{3})_{\mathrm{n}}$ (n $=$ 2-8) nanoclusters. Using density functional theory based calculations of neutral (AlH$_{3})_{\mathrm{n}}$ (n$=$2-8) clusters, we identified a new prototype, based on the unit cell of $\gamma $-AlH$_{3}$, that forms a template for the growth pattern of higher alanes, n \textgreater 6. Structures containing hexa-coordinated Al atoms dominate this growth pattern. These findings contradict previous studies which predict ring or polymer-like chain structures for AlH$_{3}$ nanoclusters. For anionic (AlH$_{3})_{\mathrm{n}}$ clusters, the preference for structures containing hexa-coordinated Al atoms was observed for clusters n \textgreater 4. The stabilities of these clusters against fragmentation will also be presented and discussed. [Preview Abstract] |
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F1.00038: The Role of Donor Acceptor Pairs (DAP) and Influence of Gallium Nitride Co-Doping on Excitation Efficiency Natalie Hernandez, Brandon Mitchell, Yasafumi Fujiwara, Dongwha Lee Europium doped Gallium Nitride (GaN:Eu) has been identified as a candidate for the active layer in nitride-based light emitting diodes. In order to understand and improve the critical excitation energy transfer from the excited GaN host to the Eu ion, we performed an extensive study of a wide variety of GaN:Eu and GaN:Eu,Mg samples, which were grown under various growth and temperature conditions. In these studies, we focused on the different incorporation sites of the Eu ions and the role of intensionally doped and unintentional defects on the optical properties and excitation efficiencies. We found that Eu centers for which the ions is close to a donor acceptor pair exhibit the most efficient luminescence. We further discovered temperature and sample dependent structural changes of some defect complexes and studied their influence on the excitation efficiency. [Preview Abstract] |
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F1.00039: Photon statistics of quantum dot resonance fluorescence Disheng Chen, Gary Lander, Cabot Zabriskie, Edward Flagg We study the blinking behavior of a self-assembled InAs quantum dot in a planar cavity formed by AlGaAs/GaAs distributed Bragg reflectors. The quantum dot is resonantly excited through the waveguide mode of the sample while being simultaneously illuminated by a second laser with photon energy above the GaAs band gap. We characterize the fluorescence blinking behavior as a function of the above-band laser power via second-order correlation measurements and extract the local intrinsic charge density. [Preview Abstract] |
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F1.00040: Prediction of New Crystal Structures of Bi-Sb Compounds using Minima Hopping Structural Search Method Sobhit Singh, Irais Valencia-Jaime, Andres Garcia-Castro, Aldo Romero In the last few years, semi-conducting alloy Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$ has emerged as a potential candidate for topological insulators [1]. In this work, we present systematic study of the low-enthalpy phases of Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$ alloys at zero pressure by using the ab-initio minima hopping structural prediction method [2]. Even though, Bi and Sb crystallize in the same 166 space group, our calculations indicate that the Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$ alloys can have several other thermodynamically stable crystal structures. Additionally to the configurations on the convex hull, we also find a large number of metastable structures which are dynamically and elastically stable. Band structure calculations of the stable phases reveal the presence of strong spin-orbit interaction leading to the Rashba spin splitting of the bands which is of great interest for spintronics applications. \\[4pt] [1] J. C. Y. Teo, L. Fu and C. L. Kane; Phys. Rev. B 78, 045426 (2008)\\[0pt] [2] S. Goedecker; J. Chem. Phys. 133, 224104 (2004) [Preview Abstract] |
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F1.00041: Construction of a dual-filament 3D printer M. Craig, G. Tcherniatinsky, J. Obiefule, R. Edelman, R.D. Diehl 3D printers are a new form of technology that can create 3-dimensional solid objects from a digital file. My project is to design and construct a new 3D printer that prints using two different plastics, ABS plastic and PLA plastic, in two different colors. The plastic material is heated and squeezed through the extruder of the printer and is than deposited onto a heated plate in layers to create a 3-dimensional object. My objective is to print models of C-60 molecules as a conceptual tool for our research group. To do this, the new printer will use a dual extruder that can print multicolored plastic objects. This new printer's exterior was completely laser cut out of acrylic while the inside of the printer itself was created using our old 3D printer. [Preview Abstract] |
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F1.00042: Bidimensional hybrid materials based graphene oxide Cynthia Guerrero-Bermea, Selene Sepulveda-Guzman, Rodolfo Cruz-Silva, Mauricio Terrones Two-dimensional materials (2D) have historically been studied, due to the large number of unusual physical phenomena that occur when the charge and heat transport are limited to a plane. Some materials with properties dominated by two-dimensional structure are derived from carbon, transition metal chalcogenides (TMS), and other hexagonal materials, exhibiting great electronics phenomena and a high-temperature superconductivity. In this work exfoliation of graphite and MoS2 by intercalation and chemical techniques have been achieved, including the characterization of the resulting materials by SEM and TEM, having good exfoliation to few-layer. The microstructure was also studied by using UV-Vis spectroscopy, FTIR spectroscopy and XRD. In order to produce hybrid functional materials besides of 2D materials with good quality, and for applications in nanoelectronic devices, a casting method was used to produce a paper based of graphene oxide and molybdenum disuilfide. The resultant paper has excellent flexibility, and apparently has a good charge transport. Characterization by SEM, XRD, FTIR, and DSC were achieved. [Preview Abstract] |
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F1.00043: Three dimensional Porous Architectures from Carbon Nanomaterials Based Hydrogels Archi Dasgupta, Bunshi Fugetsu, LakshmyPullickel Rajkumar, N\'estor Perea-L\'opez, Ana Laura El\'Ias, Mauricio Terrones Carbon nanotube (CNT) and graphene oxide (GO) based macroscopic solids with a light weight, high porosity and large surface area are of great importance for applications such as in energy, as electrodes in batteries, in medicine, as scaffolds for tissue regeneration and in environment for absorption and filtration materials. However, establishing 3-Dimensional interconnected Carbon nanomaterial structures with controlled porosity and functionality is still in its infancy. Here we report reproducible and inexpensive methods to obtain macroscopic 3D solids consisting of CNT and graphene oxide, with or without polymers as backbones. The hydrogels are formed by simply mixing graphene oxide dispersed in water, carbon nanotubes and polymers. The hydrogels are then subjected to freeze-drying that results in ultralight, macroporous and stable solid. The porosity of the 3D solid can be controlled by the freezing protocol. When using a thermal gradient during freezing (unidirectional freezing), homogenous pore alignment within the solid is achieved. Field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA) are employed for characterizing the materials. Processing of similar solids with nitrogen-doped CNTs and functionalized CNTs will also be presented. [Preview Abstract] |
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F1.00044: Structural and Electrical Properties of Electron-doped CaMnO3 Thin Films Zoey Warecki, Cacie Hart, Grace Yong, Prakash Sharma, Chris Stumpf, David Schaefer, Rajeswari Kolagani Perovskite metal oxides are a class of materials that are predicted to play as big a role in future electronic technologies as silicon does in today's semiconductor based electronic technologies. Research in thin films of manganites in the past has largely been focused on the hole-doped compositions that exhibit the phenomenon of colossal magnetoresistance. We are currently investigating the properties of thin films of electron-doped calcium manganese oxide. We use the technique of pulsed laser deposition to grow these thin films. The films are grown epitaxially on LaAlO$_3$ substrates, whose lattice parameters are larger than that of CaMnO$_3$, thus causing the films to be under tensile stress. By decreasing the film thickness we can increase the tensile strain. We have studied structural and electrical properties of CaMnO$_3$ films under tensile strain, by means of X-ray diffraction and temperature dependent resistivity measurements. Our results suggest that tensile strain causes CaMnO$_3$ to be more susceptible to the formation of oxygen vacancies, thus reducing electrical resistivity. [Preview Abstract] |
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F1.00045: Adsorption of gases on graphene Sidi Maiga, Tabia Muhammad, Alozie Pat-Ekeji, Bibiana Valdes, Silvina Gatica We have studied the adsorption of several gases (Ar, Kr, Xe, NO) on graphene. We run Monte Carlo simulations to characterize the equilibrium properties of the monolayer film adsorbated on graphene. We were able to construct the phase diagrams of Ar and Kr showing commensurate and incommensurate 2D-solid phases. By analyzing the adsorption isotherms and structure functions of the films, we obtain the L-V, L-S and V-S coexistence lines. We also compared the Langmuir-model isotherms to the results of the Monte Carlo simulations, finding strong disagreement even at low coverage. A modified Langmuir model is proposed and tested. [Preview Abstract] |
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F1.00046: Mode Coupling for Primordial Nonlocal Non-Gaussianity Bekir Baytas, Aruna Kesavan, Elliot Nelson, Sohyun Park, Sarah Shandera The purpose of this study is to build the statistical formalism of a nonlocal functional of a Gaussian random field and to identify the relationship between non-Gaussian statistics in a large volume (the entire universe beyond our Hubble volume) and the statistics measured in a smaller subvolume (the observable universe). We set the rules and the constraints on the coefficients of the each nonlocal contribution term, which are derived under the known behavior of power spectrum and bispectrum, to generate the possible subset of cubic terms which can reproduce the quadratic terms under the long-short wavelength split. Under this split, one can write the possible shift to the power spectrum and the bispectrum in the subvolume from the subleading orders in the quadratic terms which are sensitive to up to quadratic powers of the long mode. [Preview Abstract] |
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F1.00047: When you dance, you dance with the universe Kielan Wilcomb, James Overduin As she spins, a dancer's hands are acted on by non-inertial forces such as the centrifugal and Coriolis force. After briefly summarizing the standard treatment of these forces, we ask whether the dancer would still experience them if, instead, she stood still while the rest of the universe spun around her. Within Newtonian physics, the answer is no, since the dancer is in an inertial frame. Within Einstein's general relativity, however, theoretical calculations show that a rotating mass distribution of cosmological dimensions pulls the inertial frame of an observer around with it, by a process known as frame dragging. The existence of frame dragging has recently been experimentally confirmed using gyroscopes in orbit around the spinning Earth. If the extrapolation to cosmology is valid, as we argue here, then a dancer experiences the same forces, whether or not she spins clockwise or the universe spins counter-clockwise around her. Her arms are, in a real sense, pulled out and around by the stars. The facts we present are not new, but they imply a radical reinterpretation of non-inertial motion on the conceptual level, one that we argue deserves to be brought into the standard undergraduate physics curriculum. [Preview Abstract] |
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F1.00048: Higher moments of primordial non-Gaussianity and constraints from X-ray clusters Saroj Adhikari, Sarah Shandera, Neal Dalal We perform cosmological N-body simulations of dark matter structure formation using non-Gaussian initial conditions, with two different scaling of higher order moments (skewness, kurtosis etc). The scalings determine the relative strength of the total non-Gaussianity for a given value of skewness. We show that a current analytic prescription to compute the non-Gaussian mass function (number density of dark matter halos as a function of the halo mass) can describe the simulation results, after some calibration, in a useful parameter space when the strength of non-Gaussianity is small. We use our simulation results to produce semi-analytic fitting functions for the non-Gaussian mass function relative to the Gaussian mass function. These mass function results have already been used to generate constraints on the primordial non-Gaussianity parameter $f_{\rm NL}$ using X-ray cluster measurements. The constraints are consistent with Gaussian initial conditions, and demonstrate the potential of cluster mass function in constraining primordial non-Gaussianity. [Preview Abstract] |
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F1.00049: Non-Gaussianities from Long Wavelength Modes Anne-Sylvie Deutsch, B\'eatrice Bonga, Suddhasattwa Brahma, Sarah Shandera We consider a two field model; a light inflaton $\phi$ coupled to a heavy field in the hidden sector $\sigma$ which has a cubic self-interaction. At low energies, the heavy field can be integrated out to get an effective description of the theory. With this effective Lagrangian, we derive correlation functions such as the powerspectrum and the bispectrum to look at non-Gaussianities. However, we only have access to a portion of the universe, and some very long wavelength modes ($\lambda > H$, nearly constant across our Hubble volume) can be unobservable to us, but still affect the correlation functions and generate non-Gaussianities in CMB data. We therefore derive the adjusted form for the observed correlation functions. It allows us to study with more accuracy the origin of the non-Gaussianities. This may have direct implications for renormalisation in cosmology, and affect the constraints that the detection of non-Gaussianities can have on inflation models. [Preview Abstract] |
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F1.00050: Mining the Sky for Very High Energy Gamma Rays Harris Bernstein, John Pretz, Miguel Mostafa Gamma rays with energies above 100 GeV are detected by the High Altitude Water Cherenkov (HAWC) Observatory. The HAWC Observatory is an array of 300 water Cherenkov detectors. Each detector has four photomultiplier tubes (PMTs) that are used to pinpoint the incoming directions of large air showers originating from the interaction of gamma rays with the Earth's atmosphere. We analyze the impact of parameters that affect the reconstruction of the arrival directions. We vary the calibration parameters and the number of the PMTs used in the reconstruction. We also examine the impact of timing and signal noise. Results show that large changes to the calibrations do not impact significantly the distribution of arrival directions, while changes in the reconstruction parameters may inhibit our ability to identify point sources of very high energy gamma rays. We discuss the results in detail and their implications for further research. [Preview Abstract] |
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F1.00051: Neutron detection using far ultraviolet radiation from noble-gas excimers Jacob C. McComb, Eric Miller, Christopher M. Lavelle, Alan K. Thompson, Michael A. Coplan, Robert E. Vest, Mohamad I. Al-Sheikhly, Charles W. Clark When triggered in a noble gas medium at atmospheric pressure, neutron-absorption reactions such as $^3$He($n,tp$) [1] and $^{10}$B($n,\alpha$)$^7$Li [2] can generate tens of thousands of far ultraviolet photons per neutron absorbed. In some cases, up to 30\% of the $\sim$ MeV nuclear reaction energy is channeled into far ultraviolet emission. The far ultraviolet photons are produced by noble-gas excimer radiation, to which the noble gas medium is transparent, facilitating efficient optical detection. We report progress in the development of the Neutron Observatory, an absolute neutron detector stationed at the fundamental physics beamline at the NIST Center for Neutron Research. Our reaction initiators consist of arrays of thin films of $^{10}$B [2] and boron-coated vitreous carbon foams [3].\\[4pt] [1] P. P. Hughes, \textit{ et al., Appl. Phys. Lett.} \textbf{97}, 234105 (2010)\\[0pt] [2] J. C. McComb, \textit{ et al., J. Appl. Phys. } \textbf{115}, 144504 (2014)\\[0pt] [3] C. M. Lavelle, \textit{ et al., Nuc. Inst. Meth. A} \textbf{729}, 346 (2013) [Preview Abstract] |
(Author Not Attending)
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F1.00052: Investigation of Voltage Configuration and Radial Dependence of Transmission Curves in PTOLEMY Hadar Lazar, J. Suerfu, C. Gentile, C. Tully Princeton Tritium Observatory for Light, Early-Universe, Massive-Neutrino Yield (PTOLEMY) aims to directly detect relic neutrinos. This is achieved by measuring the energies of electrons produced from neutrino capture by tritium, which would lie just above the endpoint of tritium beta decay. The Magnetic Adiabatic Collimation combined with an Electrostatic filter (MAC-E filter) is a spectrometer that allows for the transmission and detection of these high-energy signal electrons while filtering the background beta electrons. Characterizing the process by which the MAC-E filter utilizes electric and magnetic fields helps determine the desired properties of the filter's configuration. The electric field is generated by nine electrode rings of adjustable voltages. A mathematical method incorporating the superposition principle is used as a guide to estimate the voltages that achieve the most favorable transmission curve. Once these values are determined, the different cut-off potentials of electrons due to magnetic field expansion are calculated. By manipulating the voltages on the electron source, the transmission curve for different source radii can be aligned. This overall process approaches the accuracy that the MAC-E filter demands in order to limit the flux of electrons on the calorimeter to those with energies that could indicate a relic neutrino signal. [Preview Abstract] |
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F1.00053: Searching for $D^0 \rightarrow K^- \pi^+ \eta^0$ in Belle Data Yasiel Cabrera, David Cinabro, Sudeshna Ganguly We describe the reconstruction of the CP- decay mode $D^0\rightarrow K^-\pi^+ \eta^0 $in the Belle I data set. Using a set of simulated signal and a generic simulated sample equal in size to the Belle I data set, we reconstructed 826 events from an initial sample of 18,900 simulated events for an efficiency of 4.4\%. We studied backgrounds in the generic simulated sample, and checked in the real data. We found, in agreement with the simulations, no obvious signal in the Belle I data indicating that further work has to go into suppressing the background. [Preview Abstract] |
(Author Not Attending)
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F1.00054: Optimization of Preliminary Data Analysis for PINGU Daria Pankova The IceCube Neutrino Observatory (INO), a 1 km$^3$-sized detector at the South Pole, collects Cherenkov light from neutrino interactions in the ice. The light is detected by Photomultiplier tubes (PMT), which are contained inside the Digital Optical Modules (DOM) along with an FPGA board with an ARM CPU meant to process and analyze the incoming signal. The analysis includes the Wavedeform routine, which uses a Non-Negative Least Squares algorithm to unfold the signal into a series of separate pulses. The Precision IceCube Next Generation Upgrade (PINGU) is a proposed low energy infill extension to the INO, which will require the deployment of many additional DOMs. The new DOMs can be optimized by running a routine like Wavedefom on the FPGA fabric or CPU. Because the output of Wavedeform is much more compact than the original waveforms, the amount of data transmitted from the DOM would be greatly reduced. As it is, Wavedeform is a complicated procedure that depends on several libraries and requires a lot of processor power to run. It needs to be optimized or substituted by a faster algorithm. The performance of other algorithms for identification of single photoelectron pulses (SPE) is evaluated and the received parameters of SPE pulses are compared to those by Wavedeform. [Preview Abstract] |
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F1.00055: Characterizing Hardware Requirements for the Digital Optical Modules of PINGU, Using Current Experience from IceCube Feifei Huang The Precision IceCube Next Generation Upgrade (PINGU) is a proposed low energy extension to the IceCube Neutrino Observatory, with the primary scientific goal of determining the neutrino mass hierarchy. Neutrinos interacting in the ice will produce secondary charged particles which emit Cherenkov radiation, which is then detected by photomultiplier tubes within the Digital Optical Modules (DOMs) of IceCube. We will present results of our investigations related to the redesign of the IceCube DOMs for deployment in PINGU. First, we investigated the dynamic range of the DOMs by characterizing the signal in the current IceCube data. Second, we studied the impact of two hardware design parameters, the DOM-to-DOM timing difference and the ADC sampling rate, on zenith and neutrino energy resolutions. Thirdly, we investigated the optimal DOM buffer length for PINGU by using the most energetic IceCube neutrino events. These studies will also be used in re-designing the DOMs for the high energy extension of IceCube which has the goal of improving the understanding of the recently discovered astrophysical neutrinos. [Preview Abstract] |
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F1.00056: A Quality-of-Fit Indicator for Reconstructions of Neutrino Interactions in the IceCube-PINGU Detector Justin Lanfranchi PINGU, a proposed low-energy infill of the IceCube detector, will trigger due to hundreds of thousands of atmospheric neutrinos per year with energies above 3 GeV. PINGU will consist of an array of digital optical modules (DOMs) that detect cherenkov radiation from charged secondaries due to neutrino interactions in the ice beneath the South Pole. PINGU's primary scientific goal of resolving the neutrino mass hierarchy (NMH) relies upon accurately reconstructing neutrino-nucleon interactions (events) from data recorded by the DOMs. We reconstruct events using MultiNest which seeks to find the event vertex, energy, and direction most likely to have produced the DOMs' data. This usually performs well, as assessed using simulated events to verify that reconstructed vertices, energies, and directions are close to their true values. However, there remain inaccurately-reconstructed events that degrade our ability to resolve NMH. We expect our sensitivity to NMH will improve by introducing a quality-of-fit (QoF) indicator, currently under development, that correlates with the accuracy of reconstructions using information from the event's data, MultiNest's fitting process, and the reconstructed parameters. We will present the development status of the QoF indicator in our poster. [Preview Abstract] |
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F1.00057: Reduction of Radiation Damage in Lead-Glass by Thermal Annealing Fernando Torales - Acosta, Bogdan Wojtsekhowski The elastic electric form factor (GEp) experiment at Jefferson Lab aims to measure properties that directly relate to the charge and current distributions of the proton. Electrons from the experiment are detected by an electromagnetic (EM) calorimeter based on lead-glass blocks (ECal). Due to its density and transparency, lead-glass is a good material to be used calorimeters. The material, however, suffers from radiation damage and a loss of transparency during operation. The transparency can be recovered through thermal annealing, but the timescale and affect of temperature on the annealing process in lead-glass need further investigation before implementation in future GEp experiments. A transparency measurement was conducted by shining a low power laser through a block of damaged lead-glass as the block is heated and its transmission monitored. Additionally, blocks of lead-glass were placed in an oven as temperature-time profiles as well as the reduction factor of damage were recorded. From these temperature profiles, we were able to obtain an expression for the characteristic annealing time as a function of temperature modeled after the electrical conductivity of glass. [Preview Abstract] |
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F1.00058: Tourist or Traveler: Student Attitudes Toward the Study of Physics - A Survey of High School Physics Students and its Implications in the Classroom A. Tabor-Morris, T. Briles, H. Nolan When students take physics in high school they do so for a variety of reasons, including, in some cases, its usefulness toward their future career goals. Students may engage in different learning strategies toward physics problem solving, for example, desiring step-by-step directions or committing to creating a mental map. Physics education research in the past indicates that the creation of a mental map can generate a sense of learning stability for students studying physics, especially due to of the complexity of this learning and its use of multiple intellectual abilities including verbal, graphical, pictorial and mathematical skills. Yet not all students appear to feel compelled to use mental mapping. An analogy is made here that indicates that some students appear to take on attitudes more aligned with visiting tourist observers, while other students seem to want to ``go native'' or even ``move in.'' A survey of 133 high school physics students was taken which included both students who indicated taking physics because of an interest in future science careers and those who did not. Results of these groups are compared and possible implications in the physics classroom are suggested. [Preview Abstract] |
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F1.00059: Comparison among Three Charge Models for Dust Grain Transport in an Abrupt Inhomogeneity Jeffrey Walker, Mark Koepke, Michael Zimmerman, William Farrell, Vladimir Demidov The trajectory of a dust grain, radius $a$, is modeled semi-analytically for an abrupt inhomogeneity, and it is shown that the guiding center drift is sensitive to grain charging rate. For an abrupt inhomogeneity, two neighboring regions are characterized by two respective sets of plasma parameters and corresponding in-situ equilibrium charge states. The grain charges or discharges with each gyro-excursion between regions at a characteristic charging time $\tau_{ch}$. We assess grain transport due to guiding center drift for the Orbit Motion Limited, Patacchini-Hutchinson electron current, and Gatti-Kortshagen ion current charging models for a given set of plasma parameters. The three models yield different guiding center drift magnitudes, demonstrating that charge models can be in principle be discriminated under certain conditions. Neutral drag force, or Epstein drag, is included in our analysis, and it is assumed that the perpendicular dust grain velocity is small with respect to the thermal speed of neutrals. The application of these theoretical results to dust confinement and model validation in the Auburn Magnetized Dusty Plasma Experiment is assessed through theory and simulation. [Preview Abstract] |
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F1.00060: Development of the Spacecraft Environmental Anomalies Expert System (SEAES) at NASA Dhanesh Krishnarao, Yihua Zheng, Marlo Maddox, Tyler Schiewe We develop and implement a post-anomaly analysis and monitoring tool for NASA satellite operators to understand causes for specific spacecraft anomalies and specify thresholds for future watches and warnings. A hazard quotient showing the ratio of instantaneous to mission averaged likelihood of an anomaly is available for four space weather hazards at geosynchronous orbit (GEO): surface charging, internal charging, single-event effects (SEE) from solar energetic particle events (SEP), and total dose to solar arrays. We use the algorithms and rules developed by O'Brien (2009) as a guideline and make modifications to improve accuracy and account for more recent satellite data. In conjunction with the Community Coordinated Modeling Center (CCMC) at NASA Goddard Space Flight Center (GSFC), we will provide hazard quotients in the Space Environment Automated Alerts \& Anomaly Analysis Assistant (SEA$^5$), a comprehensive analysis and dissemination system currently under development. In the future, we plan to expand the system to other orbits such as those in Low Earth Orbit (LEO), Middle Earth Orbit (MEO), High Earth Orbit (HEO) and those in the interplanetary space. [Preview Abstract] |
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F1.00061: Analysis of Ion Temperatures During a Geomagnetic Storm Tessa Maynard, Amy Keesee The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite was launched in the Earth's magnetosphere in 2000 with the Medium Energy Neutral Atom (MENA) instrument attached. MENA is an energetic neutral atom (ENA) imager. ENA data can be used to determine ion energy spectra from which a temperature can be calculated. By doing such, images of ion temperature can be produced with spatial and temporal resolution. The data and images collected by MENA during geomagnetic storms are being analyzed. The data analysis will result in in graphs mapping the ion temperature in relation to time and position. This will improve our understanding of ion heating during storms. Geomagnetic storms can be powerful and dangerous, knocking out power grids and satellites. Looking at the storm data will give us a better understanding of the dynamic relationship between the Earth's magnetosphere and the geomagnetic storms. [Preview Abstract] |
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F1.00062: Algebraic Geometry of Tree Tensor Network States Shahrzad Jamshidi, Jason Morton Tree tensor networks have been used to model the ground states of Hamiltonians in condensed matter physics and quantum chemistry. Exactly which quantum states can be represented by a tree tensor network with a given topology and given restrictions on the parameter tensors? When the restrictions are algebraic, the set of states is a projective algebraic variety. We describe those varieties, using techniques originally developed for phylogenetics. [Preview Abstract] |
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F1.00063: Prediction and Mechanical Characterization of the Al-P compounds by ab-initio Minima Hopping O. Palvic, I. Valencia-Jaime, A.C. Garcia-Castro, A.H. Romero The III-V group compound semiconductors, including GaAs and InP, have led to large technological advances [1]. Of these, AlP has the largest direct band gap (3.56 eV) and is arguably the least understood [2]. Here, we present a study of the AlP phase-diagram by means of first principle minima hopping calculations [3]. We were able to reproduce the previously obtained structure for AlP (cubic, F-43m). Also reported here are a large number of metastable structures and the mechanical properties as a function of the P content. We discuss alternative path for synthesis to stabilize metastable structures. Our results are relevant also for ternary alloys such as AlInP, AlAsP, and AlPSb. Such compounds have applications in quantum wells [4], solar cells [5], and optical equipment [6]. Our research is the initial step for the ternary characterization.\\[4pt] [1] New Supercomputers use GaAs Technology. Mechanical Engineering 116.8(1994):10 \newline [2] I. Vurgaftman, J of App Phys 89(11),5828(2001) \newline [3] S. Goedecker, The J of chem phys 120,9911(2004) \newline [4] Ishitani et al. J of App Phys 80.8 (1996):4592. \newline [5] I.A. Morozov, A.S Gudovskikh. Semiconductors 48.4,459-64(2014) \newline [6] Shimomura, H; Anan, T; Sugou, S. Seventh International Conference on Indium Phosphide and Related Materials,1995,ISBN 9780780321472,801-804 [Preview Abstract] |
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F1.00064: An off axis OH center in ZnO studied by IR spectroscopy Philip Weiser, Ellen Farmer, Michael Stavola, W. Beall Fowler Experiments on H in ZnO have revealed several donor species. Two major H vibrational modes were found at 3326 and 3611 cm$^{-1}$ and assigned to H donors. The IR line at 3611 cm$^{-1}$ has been associated with an isolated H donor in a bond-centered configuration. The line at 3326 cm-1 has been suggested to be due to H in an antibonding configuration in the vicinity of another defect (a Ca impurity is one such possibility). The band at 3326 cm$^{-1}$ has a distinctive dependence on temperature. At low temperature, the 3326 cm$^{-1}$ band appears to consist of three overlapping components. As the temperature is increased, the relative intensities of the components change and additional sidebands appear. This behavior is reminiscent of our previous findings for an OD-Li center in MgO. In this case, the D atom was found to be displaced off axis and added a hindered-rotation structure to the O-D vibrational band. IR absorption experiments and theory are being used to investigate the possible off-axis motion of the 3326 cm$^{-1}$ center in ZnO. [Preview Abstract] |
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F1.00065: Development and Characterization of Dynamic Light Scattering Instrumentation to Determine Nanoparticle Size T.J. Sebastian, J. Harding, T. Volpe, J.R. Simpson, M. Schulze, S.M. Lev Dynamic Light Scattering (DLS) provides a high-throughput and accurate measurement of particle sizes for monodisperse (MD) spherical nanoparticles (NPs). We report on the development and characterization of homebuilt DLS instrumentation to measure the size of MD NPs of gold, polystyrene, and ZnO. HeNe and Argon-ion laser comprise the excitation sources for the scattering experiment. We have evaluated an avalanche photo-diode detector for the acquisition of scattered light. Time averaging and time-autocorrelation electronic signal detection and analysis provides a measure of the translation diffusion coefficient, which for MD and spherical particles allows for the determination of the NP radius. We have tested our apparatus using commercially-produced gold NPs in the range of 10 nm to 200 nm and synthesized ZnO NPs. DLS measurements were compared to those obtained by Atomic Force Microscopy (AFM). After size characterization, the ZnO NPs will be employed in ongoing toxicity studies. [Preview Abstract] |
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F1.00066: OH centers and the conductivity of hydrogen-doped In$_{2}$O$_{3}$ single crystals Weikai Yin, Kirby Smithe, Philip Weiser, Michael Stavola, Beall Fowler Mechanisms for the n-type conductivity of In$_{2}$O$_{3}$ have been controversial. Recent experiments suggest that O vacancies are the cause of conductivity.\footnote{S. Lee and D.C. Paine, Appl. Phys. Lett. \textbf{102}, 052101 (2013).} However, other recent experiments find that the H-doping of thin films gives rise to shallow donors.\footnote{T. Koida \textit{et al.}, Jpn. J. Appl. Phys. \textbf{46}, L685 (2007).} Theory also finds that interstitial H and H at an O vacancy are shallow donors in In$_{2}$O$_{3}$.\footnote{S. Limpijumnong \textit{et al.}, Phys. Rev. B \textbf{80}, 193202 (2009).} We have performed a series of IR absorption experiments to determine the properties of OH and OD centers in In$_{2}$O$_{3}$ single crystals. Annealing In$_{2}$O$_{3}$ samples in H$_{2}$ or D$_{2}$ at temperatures near 450$^{\circ}$C (30 min) produces an n-type layer $\approx $0.05 mm thick with an n-type doping of 2x10$^{19}$ cm$^{-3}$. The resulting free-carrier absorption is correlated with an OH center with a vibrational frequency of 3306 cm$^{-3}$ that we associate with interstitial H.\footnote{M. Stavola, J. Appl. Phys., to be published.} [Preview Abstract] |
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F1.00067: Osmotic Pressure of E.coli in Suspension Wenxin Huang The non-equilibrium statistical mechanics of active particles have raised considerable interest over the recent years. Here, we investigate the thermodynamic properties (i.e. osmotic pressure and effective temperature) by dielectrophoresis (DEP) and the single particle behaviors by tracking E. coli's movements (i.e. mean-square-displacement and diffusivity) in order to characterize the motion activities of E. coli. [Preview Abstract] |
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F1.00068: Density of Surface States in the Region of the Energy Gap for a-Si/Ge Using a Two Parameter Hamiltonian Eliezer Richmond To rigorously investigate the contribution of surfaces to the density of electronic states of a-Si/Ge and the effect of the topology on the density of surface states (DOSS), a surface for amorphous homopolar tetrahedral solids has been defined.\footnote{http://www.tandfonline.com/eprint/dZXIzBKDCsZVENFurTZs/full} The effects on the DOSS in the region of the energy gap are investigated using a two parameter Hamiltonian. We address the effects of ring structure, nearest neighbor dangling bonds, multiple dangling bonds per surface atom, and back bonds on the DOSS. In particular, the results here predict a shift of 0.12 eV of the bulk p-like peak at the top of the valence band to higher energies due to the DOSS. Additionally, surface contributions in the lower portion of the conduction band (CB) give rise to a hump in the lower portion of the CB density of states. Lastly, a gap state is found 0.6 eV below the CB edge. These conclusions will be compared to experimental results and are found to be in surprisingly good agreement. [Preview Abstract] |
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F1.00069: Infrared absorption studies of OH centers in the metal-insulator-transition oxide VO2 Ying Qin, Weikai Yin, Michael Stavola, W. Beall Fowler, Lynn Boatner VO$_2$ is an unusual solid-state material that undergoes a metal insulator transition at approximately 68 $^{\circ}$C that accompanies a structural transition from monoclinic to rutile. The introduction of hydrogen into VO2 has been found to suppress the monoclinic insulating phase, providing a means to tune the metal-insulator-transition temperature. Single crystals of VO2 have been grown recently at the Oak Ridge National Laboratory. We have introduced hydrogen and deuterium into VO$_2$ single crystals for study by low temperature IR spectroscopy. OH and OD vibrational lines (4.2K) have been found at 3289 and 2446 cm$^{-1}$ that provide information about the structure of the OH (and OD) center in VO$_2$. The vibrational frequencies are similar to those found for OH and OD modes in other oxides with the rutile structure, for example SnO$_2$ and TiO$_2$. The frequency ratio, r $= \omega $H/$\omega $D, is r $=$ 1.345, consistent with H (and D) being bonded to a light element like oxygen. Furthermore, our experiments determine the polarization of the OH vibrational mode and the thermal stability of H centers in VO$_2$. Supported by NSF Grant DMR-1160756. [Preview Abstract] |
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F1.00070: Rotational Dynamics in Ionic Liquids Chris Rumble, Mark Maroncelli Our group has been investigating rotational dynamics of small molecule solutes in ionic liquids (ILs, a class of salts which are molten below 100 $^{\circ}$C) using experimental methods and molecular dynamics (MD) simulations. The strong self-association between IL molecules due to Coulombic attractions results in slow dynamics and structural heterogeneity, which reveal themselves in rotations through large angle jump motion, distributed dynamics, and deviations from predictions made using hydrodynamic theory. To explore the effects of solute size and charge distribution on rotations in ILs, we have performed fluorescence anisotropy and NMR T1 relaxation experiments on a series of charged and uncharged solutes of differing sizes in an IL and 1-propanol, as a comparison to a simple glass forming liquid. In conjunction, MD simulations of each solute were performed using our group's coarse-grained IL model to model the dynamics we observe in experiment. The poster will include a discussion of our experimental and simulation results with comparison to hydrodynamic predictions and comments on the similarity of rotational dynamics in ILs and other systems such as glasses and polymer melts. [Preview Abstract] |
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F1.00071: Lithium-Silicon crystal structure prediction by minima hopping method I. Valencia-Jaime, R. Sarmiento-P\'erez, S. Botti, M.A.L. Marques, A.H. Romero A throughput structural prediction of the lowest energy configurations for Li-Si alloys is presented by means of the Minima Hopping Method [1]. A convex hull is reported and compared with previous calculations and experimental structures. Unit cells with at most sixteen atoms were considered. In particular, we have found eight crystal structures lying on the convex hull. We reproduce the Li5Si2 (R-3m), as foreseen in previous theoretical calculations [2]. Additionally, we predict the thermal and elastic stability of Li3Si2 (C12/m1), Li2Si (C12/m1), Li9Si4 (C12/m1), Li3Si (P12/m1), Li7Si2 (P-3m1), Li4Si (I4/m), Li5Si (P-3m1) and Li6Si (R-3m), structures that have not been previously reported. The potential-composition curve based on those structures is also calculated and compared with previous calculations and experimental measurements.\\[4pt] [1] S. Goedecker, The Journal of chemical physics 120, 9911 (2004). \newline [2] W. W. Tipton, et. al, Physical Review B 87, 184114 (2013) [Preview Abstract] |
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F1.00072: Structural and Magnetic Properties of Oxygen-Deficient Perovskites (Sr,Ca)FeOx and Sr(Fe,Co)Ox J.R. Pollichemi, M.E. Evans, I.A. Leahy, W. Vogel, J.P. Carlo A wide variety of compounds crystallize into perovskite-related structures, making them versatile laboratories for a variety of inquiries and applications. Oxygen-deficient perovskites, in particular, have attracted interest for use in fuel cells and related applications due to high oxygen mobility. We have studied oxygen-deficient perovskites based on SrFeO$_x$ using x-ray diffraction and Mossbauer spectroscopy. While SrFeO$_x$ exhibits cubic Pm-3m symmetry, CaFeOx has a more distorted structure (orthorhombic Pnma), with gradual reduction in lattice symmetry in doped (Sr,Ca) intermediaries. SrFeO$_x$ exhibits magnetic order below 50K, while CaFeO$_x$ is ordered (with a possible paramagnetic volume fraction) at 300K. Oxygen contents x of the air-annealed samples ranged from 2.3 to 2.65; interestingly, synthesis under 1 atm of flowing O$_2$ did not result in a significant change in oxygen content. Somewhat different behavior is observed for the B-site doped series Sr(Fe,Co)O$_x$. In this case, cubic symmetry is maintained down to 10\% Fe composition, with a sudden reduction thereafter. While the structure of air-annealed SrCoO$_x$ is consistent with orthorhombic symmetry, it is not consistent with previously reported results; the reason for this discrepancy remains unknown. [Preview Abstract] |
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F1.00073: Anomalous Aharonov-Bohm Oscillations in Bi$_{2}$Te$_{3}$ Nanotubes with disorders Renzhong Du, Yuewei Yin, Sining Dong, Wenqing Dai, Weiwei Zhao, DukSoo Kim, Shih-Ying Yu, Jian Wang, Xiaoguang Li, Suzanne Mohney, Srinivas Tadigadapa, Nitin Samarth, Chaoxing Liu, Jainendra Jain, Moses Chan, Qi Li Topological insulator Bi$_{2}$Te$_{3}$ nanotubes have been synthesized and their magnetotransport properties have been studied on single nanotubes. The conductance of the nanotube can be characterized by Mott's variable range hopping model in a wide temperature range, indicating the system is in a strong disorder regime. Magnetoresistance oscillations with h/e period from the nanotube outer surface were observed, suggesting the presence of surface states due to anomalous Aharonov-Bohm effect. The results show for the first time that the topological surface states are robust against strong disorders. [Preview Abstract] |
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F1.00074: Enabling Comparability in Back-Scattered TERS instrumentation via Lithographic Test Structures Erin Wood, Angela Hight-Walker Tip-enhanced Raman spectroscopy promises unprecedented spatial resolution and selectivity; however this burgeoning technique is not yet truly robust. Tip size, shape and composition as well as variations in instrumental setup may cause deviation in the resultant spectra, even with the same sample. In order to account for these problems and enable comparability between different instruments, we propose to use a 3-D lithographically-printed, strained silicon standard which will act as both a calibration as well as a benchmark test for instrument robustness. This proposed test structure also will allow for further development and enhancement quantification of TERS instrumentation. Current progress on TERS mapping of the 3-D sample allows us to resolve individual SiGe@Si lines with widths of 32 nm. We also present methodology to allow for robust TERS-active probes using gold as the plasmonic enhancing materials. [Preview Abstract] |
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F1.00075: Determination of Colloidal Osmotic Equation of State by Dielectrophoresis Jacob Mazza, Hao Huang, H. Daniel Ou-Yang Osmotic equation of state [P(N,T)] of a colloidal suspension, where P is the osmotic pressure, N the particle number density and T the absolute temperature, describes both the mechanical properties and phase behavior of a colloidal suspension. As an alternative to the conventional sedimentation or scattering approaches to determine P(N,T), we propose a new approach by dielectrophoresis (DEP). Spatial distributions of the density of fluorescent nanoparticles in a DEP field -- imaged by confocal microscopy -- can be used to determine the DEP force field at low particle concentration, at which the inter-particle interactions are negligible. Using the known force field and Einstein's osmotic equilibrium equation, we calculate P(N,T) from the particle density profiles of interacting, charge-stabilized polystyrene latex particles under different salt concentrations. [Preview Abstract] |
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F1.00076: Coarsening Dynamics of Actively Rotating Binary Liquids Syeda Sabrina, Kyle J.M. Bishop Active matter comprised of many self-driven units ($e.g.$ colloidal swimmers) exhibit emergent behaviors such as clustering and swarming depending on the nature of local energy input and the interactions between individual units. A recent \underline {study} showed that binary mixtures of actively rotating particles phase separate by spinodal decomposition. Other more exotic types of coarsening dynamics are anticipated in this nonequilibrium system. Here we develop a continuum model of phase separation in actively rotating binary liquids and investigate the role of active rotation, frictional damping and viscous coupling on the system's macroscopic dynamics. The model combines the convective Cahn-Hilliard equation and the Stokes equation with active rotation governing local composition and velocity field respectively. Besides reproducing previous results under \textit{weak} \textit{rotation} ($Pe<1)$, our model predicts a rich phase behavior of the system in different dynamical regimes such as drag dominant ($\beta \gg 1)$ and viscous hydrodynamic ($\beta \ll 1)$ regimes. Numerical results along with scaling arguments elucidate diverse behaviors under both \textit{weak} and \textit{strong} \textit{rotation }($Pe>1)$ as well as emergence of \textit{active doublets}. [Preview Abstract] |
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F1.00077: New results from experimental studies of single-crystal quantum structures of spin-triplet superconductor Sr$_{2}$RuO$_{4}$ Xinxin Cai, Brain Zakrzewski, Shaun Mills, Yiqun Ying, Zongli Wang, Libin Wen, Shun Wang, David Fobes, Tijiang Liu, Zhiqiang Mao, Ying Liu Sr$_{2}$RuO$_{4}$, the only layered perovskite that becomes superconducting without the presence of Cu, was predicted to be an odd-parity, spin-triplet (possibly chiral p-wave) superconductor shortly after the discovery of its superconductivity. This prediction was supported by intensive work in the past two decades. Our experimental studies of Sr$_{2}$RuO$_{4}$ aim at detecting novel topological objects predicted for this superconducting material, including chiral edge currents, domains and domain walls, half-quantum vortices, and others. We established a process to prepare single-crystal quantum structures of Sr$_{2}$RuO$_{4}$ starting from mechanically exfoliated thin flakes. We identified Ru-free flakes of Sr$_{2}$RuO$_{4}$ showing enhanced superconductivity and demonstrated the link between the local enhancement of $T_{\mathrm{c}}$ and the presence of edge dislocations due to symmetry lowering. We fabricated mesoscopic superconducting rings of Sr$_{2}$RuO$_{4}$ and carried out Little-Parks resistance oscillation measurements, finding anomalously large resistance oscillations of full-flux period. With the application of an in-plane field and a large measurement current, the emergence of a second set of resistance oscillations was observed that suggested the existence of half-flux L-P resistance oscillations. Further experimental issues need to be clarified before the half-flux L-P resistance oscillations are fully established. [Preview Abstract] |
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F1.00078: First-principles study of monolayer and bilayer TaSe$_2$ Mack Adrian Dela Cruz, Jia-An Yan Two-dimensional atomic crystals of transition metal dichalcogenides (such as MoS$_2$, TaSe$_2$, etc.) are currently attracting growing attention due to the broad variety of electronic properties presented in these systems. Here we present a first-principles study of the structural, electronic and vibrational properties of monolayer and bilayer TaSe$_2$, which is a charge-density wave material in the bulk form. The structure of monolayer TaSe$_2$ is determined by performing a series of total energy calculations. For bilayer TaSe$_2$, various stackings of monolayer TaSe$_2$ with the hexagonal (2H) and the trigonal (1T) phases, will be considered. Calculated electronic and phonon properties of the energetically favorable states will be compared with the available experimental data. [Preview Abstract] |
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F1.00079: Morphology-Dependent Properties of Semiconducting SnS Nanomaterials and Evidence for a Structural Distortion at the Nanoscale Adam J. Biacchi, Raymond E. Schaak, Angela R. Hight Walker The synthesis of semiconducting nanomaterials with controlled size, structure, and morphology using solution-based methods has emerged as an active field of research due to their excellent properties. Tin(II) sulfide is a intermediate band gap semiconductor that has received markedly less attention than other related compounds despite its non-toxic and earth-abundant constituent elements, as well as its comparably low cost and favorable electronic properties. Here we present a novel route for the solution synthesis of 2D SnS nanosheets as well as monodisperse 0D colloidal SnS nanocubes and spherical nanopolyhedra. The sheets are $\sim$ 270 nm squares with an orthorhombic crystal structure matching that of bulk $\alpha $-SnS. The cubes and spherical polyhedra are $\sim$ 10 nm, below the exciton Bohr radius of SnS, allowing them to act as ``quantum dots.'' An inability to reconcile incongruences in the diffraction patterns of the 0D nanocrystals with the 2D nanosheets leads us to propose that these SnS quantum dots crystallize in a distorted pseudotetragonal structure, which is confirmed by detailed crystallographic characterization and modeling. We interrogate the optoelectronic and photocatalytic properties of these materials to display that they are size-, shape-, and structure-dependent. [Preview Abstract] |
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F1.00080: The effects of initial pH and cobalt concentration on cobalt-doped maghemite Brian Ruane, Rama Balasubramanian We investigate the effect of varying cobalt (Co) concentrations and initial pH on the growth of Co-doped iron oxide nanoparticles used for carbon nanotube growth. Co-doped nanoparticles were grown using a coprecipitation method in an acidic medium. Crystallite size was estimated using x-ray diffraction and supported with atomic force microscopy. The size of the nanoparticles decreased when cobalt concentrations increased for the unadjusted pH (9.1 nm to 6.5 nm) and the 0.5 pH solutions (10.4 nm to 7.7 nm) but increased for the 1.0 pH solutions (7.9 nm to 9.6 nm). Understanding how the conditions of the coprecipitation reaction affect particle size will allow us to tailor nanoparticles for use as catalysts in carbon nanotube synthesis. [Preview Abstract] |
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F1.00081: Introduction to the Neutrosophic Statistical Mechanics Florentin Smarandache Neutrosophic Statistical Mechanics is the theory in which, using the neutrosophic statistical behavior of the constituent particles of a macroscopic system, are predicted the approximate properties of this macroscopic system. Neutrosophic Statistics means statistical analysis of population or sample that has indeterminate (imprecise, ambiguous, vague, incomplete, unknown) data. For example, the population or sample size might not be exactly determinate because of some individuals that partially belong to the population or sample, and partially they do not belong, or individuals whose appurtenance is completely unknown. Also, there are population or sample individuals whose data could be indeterminate. (Depending on the type of indeterminacy one can define various types of neutrosophic statistics.) The neutrosophic value of the average energy of one system, for a given period of time, is close to the neutrosophic average instantaneous value of this energy over a large number of systems. Therefore, in principle if one knows the neutrosophic energy levels of its components, one obtains the approximate thermodynamic properties of the system. [Preview Abstract] |
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F1.00082: Phase Transitions in a Model of Y-Shaped Molecules Donovan Ruth, Raul Toral, Danielle Holz, James Gunton Increasing attention in statistical mechanics is being given to non-spherical molecules, such as polypeptide chains and protein molecules. One example is provided by immunoglobulin, which has a ``Y'' shape. In this work, we determine the phase diagram of ``Y''-shaped molecules on a triangular lattice through Monte Carlo Grand Canonical ensemble simulation, using histogram reweighting and multicanonical sampling. We show that this system is a member of the Ising universality class through finite size scaling techniques. The molecules interact via the distal tips with the nearest neighbor distal ends of other molecules; There are no center to center interactions, center to tip, or molecule to lattice interactions included in this particular study. For low temperatures, multicanonical sampling was implemented to induce faster phase transitions in the simulation. Studying several system sizes, finite size scaling was used to determine the two phase coexistence curve, bulk critical temperature, and critical chemical potential. [Preview Abstract] |
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F1.00083: Combining Etching with Laser Ablation to Form Hierarchical Structures in Silicon, Aluminum, and Titanium Abbie Ganas, Nahum Alba, Kurt Kolasinski Combining nanoscale with mesoscale features across macroscopic substrates can lead to functional materials. Self-limiting electrochemical etching is well known for making nanostructures.\footnote{K. W. Kolasinski, J. W. Gogola and W. B. Barclay, J. Phys. Chem. C \textbf{116}, 21472--21481 (2012).} Chemical etching is capable of making geometrically well-defined structures spanning from the nanoscale to the macroscale.\footnote{M. E. Dudley and K. W. Kolasinski, J. Electrochem. Soc. \textbf{155}, H164-H171 (2008).}$^,$\footnote{D. Mills and K. W. Kolasinski, J. Phys. D: Appl. Phys. \textbf{38}, 632-636 (2005).} Both require control over the initiation sites to make hierarchical structures with features ranging over several orders of magnitude. Laser ablation with a nanosecond pulsed Nd:YAG laser produces texture in the form of regular arrays of pillars (with a $\approx $period of several micrometers) or ripples (with a period $\approx $wavelength of light). These substrates are etched electrochemically or chemically to produce combinations of properties such as low reflectivity (black Si, black Ti, black Al) with quantum confinement induced visible photoluminescence; or membranes composed of micrometer sized pores, the walls of which contain high surface area nanoporous material. Methods and mechanisms of hierarchical structure formation will be discussed. [Preview Abstract] |
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F1.00084: Finding Sterile Neutrinos from Nuclear Reactors Jared Haughton A neutrino is a subatomic particle with no electrical charge that only interacts with other particles through the weak force and gravitational force. Neutrinos are produced in nuclear reactions, such as those in nuclear reactors and the sun. Furthermore, neutrinos come in three distinct ``flavors'' -- electron, muon, and tau neutrinos. Neutrinos have been found to oscillate between their different flavor states. Due to differences in the expected number of neutrinos from nuclear reactions and the actual observed count, there is speculation that there is at least one more flavor of neutrino that has not been observed yet. This ``sterile'' neutrino would not interact via the weak force, and thus would be functionally invisible. This project, PROSPECT, is focused around searching for these sterile neutrinos, using a nuclear reactor as a source. I have calibrated a prototype of a segmented plastic scintillator, which will use light to distinguish between neutrino interactions and other types of interactions in the prototype. The final detector may use this technology to provide evidence of some undetectable ``sterile'' neutrino. [Preview Abstract] |
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F1.00085: Automated temperature measurement in an optical tweezers system Alexander Mandarino, Samuel V. Migirditch, Tyler W. Foley, Brooke Hester An optical tweezers system uses highly focused laser radiation in order to confine small particles and typically are used to study biological systems or materials. The measurement of the trap stiffness can be completed through various calibration techniques. Many calibration methods require an accurate knowledge of particle size, fluid viscosity, and temperature. We present an automated method for high-frequency power spectral analysis of thermal motion position data to find the temperature of the particle in the optical trap. The implementation of this method of temperature measurement allows for a more accurate determination of trap stiffness in the automation program. [Preview Abstract] |
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F1.00086: A Comprehensive Analysis of GRB X-ray Afterglows with Deep Chandra Follow-up: Implications for Off-Axis Jets David Burrows, Bin-bin Zhang, Hendrik Van Eerten, Geoffrey Ryan, Andrew MacFadyen, Judith Racusin, Eleanora Troja We present a sample of 27 GRBs with detailed Swift light curves supplemented by late time Chandra observations. By fitting to empirical mathematical functions, we find a higher fraction of jet-break candidates (56{\%}) than previous studies using Swift-only samples and different analysis techniques (12{\%}). To answer the missing jet-break problem in general, we further develop a numerical simulation-based model which can be directly fit to the data using Monte Carlo methods. Our numerical model takes into account all the factors that can shape a jet break: (i) lateral expansion (ii) edge effects and (iii) off-axis effects. Comparing to the empirical function fit, our results provide improved fits to the light curves and better constraints on physical parameters. More importantly, our results suggest that off-axis effects are important and must be included in interpretations of GRB jet breaks. [Preview Abstract] |
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F1.00087: Novel 3-dimensional nanocomposite of covalently interconnected multiwalled carbon nanotubes using Silicon as an atomic welder Lakshmy Pulickal Rajukumar, Manuel Belmonte, Benito Roman, John Slimak, Ana Laura El\'Ias, Eduardo Cruz-Silva, Nestor Perea-L\'opez, Aaron Morelos-G\'omez, Humberto Terrones, Pilar Miranzo, Mauricio Terrones There is a growing interest in synthesizing three-dimensional (3-D) carbon nanotube structures with multi-functional characteristics. Here, we report the fabrication of a novel composite material consisting of 3-D interconnected multi-walled carbon nanotubes (MWNTs) with Silicon Carbide (SiC). The material was synthesized by a two-step process involving the chemical coating of MWNTs with Silicon oxide, followed by Spark Plasma Sintering (SPS). SPS enables the use of high temperatures and pressures that result in carbothermal reduction of silica and densification of the material into a 3-D composite block. Covalent interconnections of MWNTs are facilitated by a carbon diffusion process resulting in SiC formation during SPS. The presence of SiC in the sintered composite has been confirmed through Raman spectroscopy, which shows the characteristic peak close to 800 cm$^{-1}$ and also EFTEM maps. XRD, SEM, EDX and HRTEM have also been used to characterize the produced material. Interestingly, a high thermal conductivity value (16.72 W/mK) and a 3-D variable range hopping (VRH) electron hopping was observed in the sintered composite. [Preview Abstract] |
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F1.00088: Renyi Entropies and Generating Invariants of Local Conjugation Jacob Turner, Jason Morton We invesitigate the invariant ring of density matrices acted upon by conjugation of a tensor product of Unitary Groups. This is often called Local Conjugation. We find a minimal, algebraically independent set of generators for this ring and see that they are closely related to the Renyi Entropies. [Preview Abstract] |
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F1.00089: Development of a Syringe-Pump for use in Disposable PSA-Tape Microfluidic Chips Alain M. Schremmer Disposable, 12\^{I}1/4m-thick microfluidic chips were designed and constructed for use in fluorescence microscopy. A syringe pump was also designed and created in order to drive discreet amounts of fluid through microfluidic channels with the highest amount of control. Procedures and images of the setup can be found in the Appendix of this paper to allow further experimentation and improvement. Chip designs were significantly improved although not perfected due to occasional leakage during use. There is vast potential for use of these procedures in future experiments due to the ability to tweak aspects of the setup to accommodate a wide variety of projects including terbium gel formation, neuron cell observation, and CNT behavior in aqueous solution. [Preview Abstract] |
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