Bulletin of the American Physical Society
16th Annual Meeting of the Northwest Section of the APS
Volume 60, Number 6
Thursday–Saturday, May 14–16, 2015; Pullman, Washington
Session C1: Poster Session |
Hide Abstracts |
Chair: James Imamura, University of Oregon Room: Smith Center for Undergraduate Education (CUE) 2nd Floor Lobby |
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C1.00001: The Knobs that Dial Up a Galaxy Guy Worthey There are hundreds of billions of stars in a typical galaxy, seemingly organized and orderly. Yet, eons ago, those stars were billows of primordial hydrogen and helium gas, fresh from the foundry of the expanding young universe. Connecting the dots between then and now is a fascinating frontier in modern astrophysics. I report here on efforts to analyze the spectrum of a galaxy to discover what truly drives it. We track (1) when stars condense out of gas during the assembly of the galaxy, (2) how newly created elements from the nucleosynthetic furnaces of stars are distributed and then reincorporated in subsequent generations of stars, (3) the elemental signatures of different flavors of enrichment, such as different types of supernova explosions, (4) the rules about how stars lose mass back to space during their lifetime, and (5) at formation time, the number of stars born at each stellar mass. One might notice that almost all of these items are keying in on the component stars, and that is the paradigm shift this research is ushering in. It is time to learn about stars by studying galaxies, not the other way around. [Preview Abstract] |
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C1.00002: Effects of Radiative Cooling on Nonaxisymmetric Instabilities in Self-Gravitating Disks James Imamura, William Dumas, Kathryn Hadley, Erik Keever, Rebecka Tumblin We study the effects radiative cooling has on fragmentation in massive disks. We consider systems studied earlier without cooling by Hadley {\it et al}. (2015). Hadley {\it et al}. looked at disks dominated by shear-driven instabilities (P modes), gravity-driven instabilities (J modes), and modes intermediate between P and J modes (I modes). We include radiation using a cooling function defined so that the local cooling time scale $\tau$ is constant in the disk. Cooling does not qualitatively alter the early development of disk modes for cooling times on the order or longer than the modal growth rates. It can change outcomes of nonlinear simulations by modifying the disk before instability can grow. This may change the type of mode which dominates the evolution. This is important as we find that fragmentation is most likely in disks dominated by J modes. Disks dominated by I and P modes we study, do not fragment even for strong cooling. This is at odds with current fragmentation criteria which say that disks fragment when the Toomre Q-parameter $<$ 1.6-1.7, somewhere in the disk, and $\tau$ is shorter than the local disk rotation period. In our disks, Q is always $<$ 1.6 somewhere and we consider efficient cooling. The type of mode excited must play a role in disk fragmentation. [Preview Abstract] |
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C1.00003: Particle Transport in 1D Lattices with Weakly Coupled Overlap Impurities Evan Johnson, Brandon Peden, Seth Rittenhouse We examine the transport properties of short molecular wires containing an atomic orbital overlap impurity that is weakly coupled to two electron reservoirs by two methods, a single-particle scattering model and a quantum master equation many-body approach. The two approaches agree qualitatively on the predicted electronic current. For certain parameter regimes, the current is dramatically changed due to the presence of an interference minimum in the transmission coefficient. This minimum manifests itself in the steady-state solutions to the quantum master equation as a dark state which is decoupled from the electronic reservoirs. In both cases, the effects are due to long-range hopping from the overlap impurity. We conclude that each model sufficiently captures the underlying physics of the system and that the interference behavior in the single particle transmission coefficient is well described by a quantum master equation with long-range system reservoir coupling. [Preview Abstract] |
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C1.00004: Quantum-state tomography of single-photon entangled states E. Burch, C. Henelsmith, W. Larson, M. Beck We have performed quantum-state tomography of several different single-photon entangled states, that is, states in which a single photon is shared between two possible paths. We do this by projecting the states corresponding to the two paths onto a tomographically complete set of states (within the one-photon subspace) using interference. We simultaneously verify that our states exist in a single-photon subspace by measuring the degree of second-order coherence, $g^{\left( 2 \right)}\left( 0 \right)$. We are able to create high purity, path-entangled states. The measured states are found to have fidelities of larger than 0.95 when compared to the states that we had intended to prepare. [Preview Abstract] |
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C1.00005: One-dimensional Fermi gas with a single impurity in a harmonic trap: Perturbative description of the upper branch Seyed Ebrahim Gharashi, X.Y. Yin, Yangqian Yan, D. Blume The transition from ``few to many'' has recently been probed experimentally in an ultracold harmonically confined one-dimensional lithium gas, in which a single impurity atom interacts with a background gas consisting of one, two, or more identical fermions [A. N. Wenz {\em{et al.}}, Science {\bf{342}}, 457 (2013)]. For repulsive interactions between the background or majority atoms and the impurity, the interaction energy for relatively moderate system sizes was analyzed and found to converge toward the corresponding expression for an infinitely large Fermi gas. Motivated by these experimental results, we apply perturbative techniques to determine the interaction energy for weak and strong coupling strengths and derive approximate descriptions for the interaction energy for repulsive interactions with varying strength between the impurity and the majority atoms and any number of majority atoms. [Preview Abstract] |
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C1.00006: Energy spectrum and spin structure of harmonically trapped one-dimensional atoms with spin-orbit coupling Qingze Guan, Doerte Blume Ultracold atomic gases provide a novel platform with which to study spin-orbit coupling, a mechanism that plays a central role in the nuclear shell model, atomic fine structure and two-dimensional electron gases. We introduce a theoretical framework that allows for the efficient determination of the energy spectrum and spin structure of harmonically trapped atoms with zero-range interactions subject to an equal mixture of Rashba and Dresselhaus spin-orbit coupling created through Raman coupling of atomic hyperfine states. The spin structure of bosonic and fermonic two-particle systems with finite and infinite interaction strength $g$ is calculated. Taking advantage of the fact that the $N$-boson and $N$-fermion systems with infinitely large coupling strength $g$ are analytically solvable for vanishing spin-orbit coupling strength $k_{so}$ and vanishing Raman coupling strength $\Omega$, we develop an effective spin model that is accurate to second-order in $\Omega$ for any $k_{so}$ and infinite $g$. The three- and four-particle systems are considered explicitly. It is shown that the effective spin Hamiltonian describes the transitions that these systems undergo with the change of $k_{so}$ as a competition between independent spin dynamics and nearest-neighbor spin interactions. [Preview Abstract] |
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C1.00007: Enhancement of the UV Photoluminescence and Defect Issues in ZnO films Dinesh Thapa, Jesse Huso, Hui Che, Amrah Canul, John Morrison, Caleb Corolewski, M.D. McCluskey, Leah Bergman ZnO is an environmentally-friendly material capable of emitting light in the Ultraviolet region of $\sim$ 3.4 eV with a potentially wide range of applications such as in solar cells, oil sensors and UV diodes for water purification. In view of realizing these applicative uses, an enhanced UV photoluminescence (PL) of ZnO is desirable. This study presents a route to enhance UV-PL via annealing and examines the origin of the resulting enhanced UV-PL. Native defects and morphological structural defects are discussed. We acknowledge the US Department of Energy, Office of Basic Energy Science, Division of Materials Science and Engineering under Grant No. DE-FG02-07ER46386. [Preview Abstract] |
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C1.00008: EXAFS Spectroscopy of Structurally Tunable Charge Density Wave Materials Nathan Turner, Sarah Kim, Matthew Marcus, Sirine Fakra, James Brozik, Susan Dexheimer We present EXAFS spectra and modeling of a series of quasi-one-dimensional mixed-valence platinum-halide linear chain materials. The materials exhibit a Peierls distortion, with alternating Pt-halide bond lengths, and fractional charge states on alternating Pt ions in the chain, giving rise to a charge density wave ground state. Varying the halide controls the strength of the charge density wave and the Peierls distortion. Oriented Pt LIII edge fluorescence and transmission EXAFS spectra were collected for each halide species for x-ray polarizations parallel and perpendicular to the chain axis. Modeling was carried out using FEFF9, allowing determination of the photoelectron threshold energies and mean-square relative displacement disorder parameters in addition to verifying bond lengths previously determined by x-ray diffraction. We find distinct photoelectron threshold values for the two inequivalent Pt ions in each of the mixed-valence chains, and find that the difference in threshold values varies systematically with the amplitude of the charge density wave. The disorder parameters correlate with the Peierls distortion and with the mass of the halide ion, reflecting thermal disorder from population of low-frequency chain-axis vibrational modes. [Preview Abstract] |
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C1.00009: Dynamics of Exciton and Polaron Formation in Molecular Electronic Materials Jason Leicht, Jason Mance, Susan Dexheimer We present measurements of the coupled electronic and vibrational dynamics of exciton and polaron formation using femtosecond wavepacket techniques. The experiments are carried out on the halide-bridged mixed-valence linear chain complex PtCl(en), a Peierls insulator with strong electron-phonon coupling. Earlier studies on longer time scales showed that excitation well above the optical gap energy can result in the formation of charged polarons in addition to the self-trapped excitons that form following excitation near the band edge, though the formation mechanism for polarons had not previously been established. Our measurements reveal formation of both types of excitations in $\sim$ 200 fs. Two distinct vibrational frequencies associated with the self-trapping process are observed: 176 cm$^{-1}$, associated with formation of self-trapped excitons, and upon excitation at higher energy, an additional component appears at 240 cm$^{-1}$, associated with the formation of polarons. The rapid formation of polarons, on the time scale of a single vibrational period following photoexcitation, together with the observation of accompanying vibrational coherence strongly suggests that the polarons form directly from the initial photoexcitation, rather than by dissociation of primary excitons. [Preview Abstract] |
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C1.00010: A tool for monitoring frequency combs in LIGO data Ryan Magee, Sukanta Bose, Gregory Mendell We describe a tool that we have developed for finding combs of frequencies in LIGO data in order to characterize the detector and assist in the search for astrophysical sources. Lines add to the overall noise estimates when filtering data, and can interfere with continuous and stochastic gravitational wave searches if they are not identified and vetoed. Locating combs will allow us to characterize the noise environment of subsystems, highlight potential problems with the interferometers, and identify features that we might try to mitigate in future commissioning work. The challenge is to create a method that will be able to find combs in real time to help us analyze the system. We have developed an algorithm to list both the tooth spacing and comb frequencies, and current extensions aim to use Chi-squared statistics to determine the false-alarm rates for these combs. [Preview Abstract] |
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C1.00011: \textit{Periscope:} Looking into learning in best-practices physics classrooms Stamatis Vokos, Rachel Scherr \textit{Periscope} is a set of instructional materials designed to support university physics instructors -- including teaching assistants, learning assistants, and faculty -- in learning to notice and interpret classroom events the way an accomplished teacher does. Periscope is organized into short lessons that highlight significant questions in the teaching and learning of physics, such as ``How do I bring out students' physics ideas?'' and ``Does it matter if students are unhappy in my class?'' Lessons are centered on captioned video episodes of introductory physics students in best-practices classrooms. By watching and discussing authentic teaching events, instructors enrich their experience with noticing and interpreting student behavior and practice applying lessons learned about teaching to actual teaching situations. \textit{Periscope} also gives instructors a view of other institutions' transformed courses, which can support and expand the instructors' vision of their own instructional improvement and support the transfer of course developments among faculty. \textit{Periscope} materials are free to educators. [Preview Abstract] |
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C1.00012: Biomedical Imaging in the Undergraduate Physics Curriculum Bethe Scalettar, James Abney In recent years, physics (and mathematics) have become very critical and conspicuous contributors to biology and medicine. One notable reason is the indispensable role that sophisticated imaging techniques now play in fundamental biological research and in diagnosing and treating many serious diseases. In light of this, we recently developed an undergraduate course in which imaging serves as a foundation for integrating physics with material that is engaging and relevant, especially to students majoring in physics and/or the life sciences. [Preview Abstract] |
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C1.00013: Student understanding of inner products in quantum mechanics Tong Wan, Gina Passante, Peter Shaffer Inner products play an important role in quantum mechanics, as they describe the overlap between two quantum states, and can be used to find the probabilities of measurement outcomes. We have found that many students struggle with this fundamental idea. We present data from a junior-level quantum mechanics course at the University of Washington that illustrate the difficulties students have calculating inner products for functions that have been represented graphically.~ In addition, we discuss how these difficulties impact students' ability to find the probabilities of measurement outcomes. [Preview Abstract] |
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C1.00014: Jet Asymmetries in the ATLAS Level 1 Calorimeter Trigger Johan Bonilla, Liese Marnard, Stephanie Majewski Boosted objects are reconstructed particle decay products with transverse momenta that are considerably greater than their respective rest masses. Such objects are interesting for new physics searches using the ATLAS detector at the Large Hadron Collider (LHC). We create and study algorithms used to better discern boosted objects in the Phase-I upgrade of the Level-I trigger electronics in ATLAS. In particular, we present an algorithm which exploits the asymmetries in the kinematics of jets arising from boosted top quarks compared to jets arising from gluons, using 0.2x0.2 towers (in $\eta$-$\phi$) of the global feature extractor (gFEX), a component of the Level-1 calorimeter trigger system for the Phase-I upgrade. The algorithm, whose parameters are optimized for signal efficiency and background rejection, has the potential to be used in field programmable gate arrays (FPGAs); thus simplicity, speed, and stability are emphasized. [Preview Abstract] |
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C1.00015: A Topological Clustering Algorithm for the ATLAS Level-1 Calorimeter Trigger Upgrades Luc Lisi, Elliot Parrish, Brianna Stamas, John Myers, Stephanie Majewski Topological clustering is the current method for calorimeter object reconstruction and suppression of multiple interactions per crossing (pileup) in the ATLAS detector at the Large Hadron Collider. We present simulation studies adopting this technique for the Level-1 Calorimeter trigger in the Phase-I and Phase-II upgrades of the trigger electronics. Applying a modified topological clustering algorithm to the 0.2x0.2 (in eta-phi) towers of the global feature extractor (gFEX), a component of the Level-1 trigger system for the Phase-I upgrade, we aim to improve the performance of the jet and missing transverse energy triggers. In particular, we focus on reconstructing so-called ``boosted'' objects, whose transverse momenta are large compared to their masses. The results of these studies are also applicable to a potential dedicated module with access to the full calorimeter granularity that may be implemented in the Phase-II upgrade. [Preview Abstract] |
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C1.00016: Prototype Power Regulation System for the Deterministic Preparation of an Ultracold Few-Fermionic System Justin Niedermeyer, Vincent Klinkhamer, Simon Murmann, Andrea Bergschneider, Selim Jochim Recently developed technology allows for the preparation of systems consisting of a few interacting ultracold fermionic particles (such as lithium-6). This allows for the study of a few-body quantum system consisting of one to ten particles with $\sim$ 90{\%} fidelity by creating magneto-optical microtraps with narrowly separated, tightly focused lasers. However, the components of the research apparatus undergo thermal drifts when exposed to the laser light and power fluctuations when varying the output parameters. To correct this, a prototype control system was created, and the proof of its concept was demonstrated. This prototype control-loop system was able to correct power fluctuations on the order of 500 Hz, and continuing development with higher-quality equipment will allow fluctuation correction on the order of 1 kHz. Once this threshold is achieved, new systems of multiple microtraps will become feasible. This will allow for the highly accurate study of systems which may further the understanding of high-temperature superconductors and may lead to the realization of quantum computing and spintronics. [Preview Abstract] |
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C1.00017: A new high-current (200 kA, 200 ns) pulser for x-pinch applications: low-inductance load testing and results Roman Shapovalov The $x$-pinch $x$-ray radiation has many proved applications in plasma physics, biology and more. However, to produce a ``good'' reliable $x$-pinch radiation source, the driver has to supply about 1 kA/ns (and more) current into the low-inductance load. We present a short-circuit, low-inductance load test data of a new $x$-pinch driver recently constructed at the Idaho Accelerator Center, which is an evolution of our earlier concepts. Test data reveals that the driver, when charged to 80 kV, can supply about 210-kA peak-current into a short-circuit load with about 210-ns current-rise time. Our driver contains no oil insulation, based on 2-LTD-bricks design combined into one, solid unit, and is very compact and portable. [Preview Abstract] |
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C1.00018: Biophysical Analysis of Dental Segmentation Using Computational Analysis Richard Kyung, Sonho Lee, Kyuyeol Kim Biometrics technology plays an important role in identifying the identity of individuals. Among the biometric system, characteristics of dental structures are one of the best biometric identifiers. Specifically, teeth segmentation from dental MRI image films is an essential step to achieve automated postmortem identification. In this paper, we presented a segmentation technique using physical and mathematical methods. Hybrid approach to enhance the quality of segmented image was carried out for the analysis of various cases. To improve the segmentation of the teeth from low contrast MRI films, high pass filter and specific filter(IMFILTER) in MATLAB was used. Also, noise removal of the magnetic resonance image using Fourier transform and mathematical morphology was presented, achieving a good tradeoff between resolution of the dental image and computer running time. Dental MRI images were digitized using computer code for the noise removal. [Preview Abstract] |
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C1.00019: Biophysical and Computational Analysis of Aortic Stenosis and Systemic Hypertension Richard Kyung, Jeong H. (Peter) Yoon, Yoon Ji Jung One of the most common cardiovascular diseases, along with hypertension and coronary artery disease, is aortic stenosis (AS). In today's society, the most frequent cause of AS is the formation of calcium salts on aortic valve tissues that impede new tissues from developing. AS is a disease that causes aortic valve openings to narrow, decreasing blood flow from the left ventricle to the aorta and increasing blood pressure in the left ventricle. Thirty to forty percent of AS patients are in risk of systemic hypertension. For this reason, the biophysical and computational cardiovascular models to evaluate the effect of AS on the left ventricle are shown in this paper. Numerical models and relationship between the transvalvular flow rate and the pressure difference are presented. The results demonstrate that there are patients who can be classified in AS category with mild or moderate Aortic Valve Velocity(AVV) and pressure gradient, which makes therapeutic management complicated. The data show the Aortic Valve Velocity(AVV) causing AS occurs at 3.0-3.5 cm/sec. [Preview Abstract] |
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C1.00020: 37 Years of High School Physics Olympics Competitions at the University of British Columbia Janis McKenna The Physics Olympics is an annual high school physics competition held at the University of British Columbia in Vancouver. This year, more than 400 students on 56 teams, with at least one teacher/coach per team, came from all over British Columbia to participate in the 37th Annual Physics Olympics. The competition consists of six hands-on events, of which two are pre-built by the students in the month before the competition. In recent years, a professional development workshop and networking opportunities have been offered to the physics teachers/coaches. We believe it is one of the largest annual physics high school outreach events in Canada. In addition to almost 500 high school students and teachers, more than 10 faculty members and more than 60 undergraduate and graduate students from UBC are involved in designing, prototyping and testing apparatus for the Olympic events and helping run the event on the big competition day. [Preview Abstract] |
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C1.00021: Disorder and Defects in Graphene Band Structures Jon Parnell, Sina Habibian, Christian Ast, Klaus Kern Calculating the electronic band structure of graphene provides an important insight into the electrical properties of this 2D carbon-based lattice. Of particular interest here is modelling disorder and defects within the lattice, and their effect on graphene's band structure. This includes varying levels of potential difference within the lattice, as well as varying symmetrical and asymmetrical defects - such as the ``585'' defect. Through a series of MATLAB scripts, these effects are theoretically modelled using a tight-binding model. Our results include a blurred band ``gap''--a result also seen, and speculated upon, experimentally. [Preview Abstract] |
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C1.00022: Maximum Path-Entropy Analysis of Aggregated Markov Models Roy Campbell The principle of maximum path entropy, which is also known as the principle of maximum caliber, is a generalization of the principle of maximum entropy to systems not necessarily close to equilibrium. The principle of maximum path entropy has recently been used to derive dynamical laws of transport, analyze single particle two-state dynamics, study few-state models of non-equilibrium processes, analyze the dynamics and fluctuations in biochemical reactions and cycles, and analyze ion-channel gating. It has been shown that when a system such as an ion channel is modeled using an aggregated Markov model, methods that use steady state gating statistics can typically find several models with different topologies that fit the data equally well. We explore the use of the principle of maximum path entropy to distinguish between different aggregated Markov models that all fit the steady state gating data but have different topologies. [Preview Abstract] |
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