Bulletin of the American Physical Society
15th Annual Meeting of the Northwest Section of the APS
Volume 59, Number 6
Thursday–Saturday, May 1–3, 2014; Seattle, Washington
Session D1: Poster Session (16:30 - 18:00) |
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Chair: Gina Passante, University of Washington Room: Alder Commons 102/103 (Common Area) |
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D1.00001: Search for hep neutrinos at the Sudbury Neutrino Observatory Timothy Major, Nikolai Tolich The sun fuses hydrogen into helium though a variety of pathways. All pathways produce neutrinos, but the energies of the neutrinos depend on the exact process producing them. The highest energy solar neutrinos are produced by the ``hep'' reaction, ${}^3$He${} + p \rightarrow {}^4$He${} + e^+ + \nu_e$. Despite their high energy, hep neutrinos remain undetected because of their small flux relative to other solar neutrinos. Previous analyses hint at the possibility of the flux of hep neutrinos being much higher than theory predicts. A new analysis of data from the Sudbury Neutrino Observatory is being conducted to measure or set the best possible limit on the flux of hep neutrinos by including data that was previously unused and applying a new fitter to distinguish signal events from backgrounds. [Preview Abstract] |
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D1.00002: Muon Capture on the Deuteron: The MuSun Experiment Michael Murray Basic few-body nuclear systems are increasingly understood in terms of QCD-based effective field theories (EFT). These calculations precisely predict electro-weak observables and establish rigorous relations between muon capture and fundamental astrophysical processes like p-p fusion and neutrino break-up of the deuteron. Experimentally, the muon capture rate on the deuteron tests this modern EFT description and determines the single, poorly known low-energy constant appearing in the two-nucleon sector. The MuSun experiment will achieve an order of magnitude improvement over previous measurements of this rate with the use of a cryogenic deuterium TPC target designed to be insensitive to muon atomic kinetics. The capture rate is measured via the lifetime of negative muons in deuterium, so it is critical to avoid decay-time-dependent event selection cuts. Data collected at the Paul Scherrer Institute in 2011 and 2013 is being analyzed and the MuSun collaboration is implementing detector upgrades for a beam period in 2014. [Preview Abstract] |
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D1.00003: Comparing Different Treatments Are Used for Mesothelioma Cancer Samira Rezaei The goal of this research was to survey the literature of studies on mesothelioma treatments and comparing their rates of success. The focus was on the radiation therapy which used with the chemotherapy or surgery treatment of this specific type of cancer. The research is based on the chosen treatment of the 13 patients shared in different websites to compare the number of survived years. The result shows that the average of survived years in patient who sued mind-body therapy is more than other patients who use radiation therapy with chemotherapy or surgery treatment and immune therapy as treatment for mesothelioma. The significant of this research was to find the best treatment for mesothelioma cancer and figure out the advantage of using radiation therapy in this specific type of cancer treatment. [Preview Abstract] |
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D1.00004: Searching for Tensor Current in $^6$He $\beta$-Decay Ran Hong, Yelena Bagdasarova, Kevin Bailey, Xavier Fl\'echard, Alejandro Garcia, Andreas Knecht, Arnaud Leredde, Etienne Lienard, Peter Mueller, Oscar Naviliat-Cuncic, Thomas O'Connor, Matthew Sternberg, Derek Storm, Erik Swanson, Frederik Wauters, David Zumwalt Precision measurement of the $\beta-\bar\nu_e$ angular correlation coefficient {\em a} can be used for searching for the Beyond-Standard-Model tensor-type weak currents. We produce $10^{10}$ $^6$He atoms per second using the Van de Graaff accelerator at CENPA, and deliver them to a magneto-optical trap (MOT) in a low background experiment hall. We measure the time-of-flight spectrum of the recoiling $^{6}{\rm Li}$ ions from $^6$He $\beta$-decay and then extract the $\beta-\bar\nu_e$ angular correlation coefficient {\em a}. The $\beta$-particles are detected by a multi-wire proportional chamber and a plastic scintillator, while the recoil ions are guided by an electric field and detected by a micro-channel plate. We developed a Monte Carlo simulation program to construct the fitting templates of the time-of-flight spectrum and study the systematic effects. We currently acquire coincidence data with the short term goal of reaching a 1\% uncertainty for a. [Preview Abstract] |
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D1.00005: Converter and Target Optimization for the Photonuclear Production of Radioisotopes Using Electron Linac Bindu KC, V. Starovoitova, D.P. Wells Photonuclear production of radioisotopes using an electron accelerator can be an excellent alternative method of radioisotope production to conventional methods that use nuclear reactors and cyclotrons. With the right choice of electron beam parameters, irradiation time, bremsstrahlung converter and target design, the specific activity of photo-produced radioisotopes may be increased significantly. An optimum converter thickness and target geometry was found for the photo-proton production of Cu-67 using an electron accelerator at the Idaho Accelerator Center. Considering four different geometries for a 40 gram zinc target, the specific activity of Cu-67 for each target shape were determined. In this study, the optimization procedure of bremsstrahlung converter and target for the photonuclear production of radioisotopes using electron linear accelerator was investigated in general, and the optimum bremsstrahlung converter thickness and target geometry for Cu-67 production through $^{68}$Zn($\gamma $,p)$^{67}$Cu reaction was found. [Preview Abstract] |
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D1.00006: Violating the Heisenberg Uncertainty Relation: An Entangled Approach Jacob Collings, Jean-Francois Van Huele Since Heisenberg introduced the relation p1 q1 $\sim$ h in 1927, great effort has been made to refine this expression and better understand its meaning. Recent work has shown that the term ``uncertainty'' applies to two different quantum properties. The first pertains to preparation uncertainty, the principle that one cannot prepare a quantum system such that two incompatible observables are arbitrarily well-defined. The second pertains to measurement uncertainty, the principle that the measurement with a certain degree of accuracy of one observable disturbs the subsequent measurement of a second incompatible observable. We review recent experiments showing evidence for a violation of the measurement uncertainty. We illustrate the different relations with examples using spin measurements. We explore how entanglement affects the difference components of the proposed relations. [Preview Abstract] |
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D1.00007: Toward Remote Entanglement with $^{138}$Ba$^{+}$ Carolyn Auchter, Thomas W. Noel, Chen Kuan Chou, Boris B. Blinov We present work toward remote ion entanglement using systems of singly trapped $^{138}$Ba$^{+}$ ions. Remote ion entanglement will be achieved through photon mediated entanglement swapping using spontaneously emitted 493 nm photons.\footnote{C. Simon and W. T. M. Irvine, Phys. Rev. Lett. \textbf{91}, 110405 (2003)} This scheme is an excellent candidate for a ``loophole-free'' Bell Inequality test due to the low decoherence and capability for fast control and detection of the $^{138}$Ba$^{+}$ qubit and the suitability of the relatively long wavelength of the emitted photons for fiber optic transmission. In order to improve the future rate of remote ion entanglement generation, we present work on employing ultrafast pulses from a mode-locked Ti:Sapphire laser to increase the rate of ion-photon entanglement and improve fidelity. Progress toward ion-ion entanglement of ions in adjacent traps will be reported. [Preview Abstract] |
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D1.00008: Ultracold Heteronuclear Mixture of Ground and Excited State Atoms William Dowd, Richard Roy, Rajendra Shrestha, Alaina Green, Subhadeep Gupta Ultracold atomic gases are fruitful systems in which to study exotic quantum phenomena such as Bose-Einstein condensation, superfluidity, and BCS pairing of fermions like that in superconductors. In this regard, single atomic species experiments have covered significant ground in studies of few and many-body physics. However, the addition of a second species opens up a large variety of new physics to be explored. Recent advances in the field of ultracold mixtures include the coherent production of heteronuclear diatomic molecules, from which point one can coherently control the many degrees of freedom of the molecule (e.g. rotational, vibrational, and electronic) with the use of external fields. This forms the starting point for realizing a number of quantum information and computation applications and studies of controlled chemical reactions. Here we report recent progress towards the creation of ultracold molecules of lithium and ytterbium, including the successful realization of a novel, long-lived mixture of ground state lithium and metastable excited state ytterbium atoms. [Preview Abstract] |
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D1.00009: Harmonically trapped two-atom systems: Interplay of short-range $s$-wave interaction and spin-orbit coupling X.Y. Yin, S. Gopalakrishnan, D. Blume We investigate the interplay between the single-particle spin-orbit coupling term of Rashba type and the short-range two-body $s$-wave interaction for cold atoms under external confinement. Treating the spin-orbit term with strength $k_{so}$ perturbatively, we determine the correction to the ground state energy for various parameter combinations. We find that the interplay between the spin-orbit coupling term and the $s$-wave interaction enters, depending on the exact parameter combinations of the $s$-wave scattering lengths, at order $k_{so}^2$ or $k_{so}^4$ for the ground state and leads to a shift of the energy of either sign. Additionally, we find that, for certain parameter combinations, the spin-orbit coupling term turns sharp crossings into avoided crossings with an energy splitting proportional to $k_{so}$. Our perturbative results are confirmed by numerical calculations that expand the eigenfunctions of the two-particle Hamiltonian in terms of basis functions that contain explicitly correlated Gaussians. [Preview Abstract] |
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D1.00010: Multiplexed Fluorescence Spectroscopy with Holographic Optical Tweezers Matthew Cibula, David McIntyre We are developing a multiplexed spectroscopy system which employs holographic optical tweezers to manipulate trapped sensor particles and an imaging spectrometer to simultaneously detect their fluorescence spectra. This system has potential applications to studying the internal or external environment of cells undergoing chemical reactions. Sensor particles incorporating quantum dots or fluorescent dyes are capable of monitoring environmental properties such as pH, ion concentration, temperature, and voltage by observing related changes in the sensor's fluorescence spectrum. A spatial light modulator controls the positions of infrared optical traps to manipulate sensors into regions of interest. The sensors are excited with a 532-nm laser source and the fluorescence of spatially separated sensors is detected on the spectrometer. The spectrometer aperture must remain open to view multiple sensors, so the spectral resolution is limited by the size of each sensor and the spectral data for each sensor are calibrated using the zeroth-order image. We will demonstrate the capabilities of our system by coating microspheres with quantum dots and measuring the spectral shift with respect to a change in temperature. [Preview Abstract] |
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D1.00011: Progress toward a polarization rotation measurement of the $6S_{1/2} \leftrightarrow 5D_{3/2}$ magnetic dipole transition amplitude in Ba$^{+}$ Anupriya Jayakumar, Spencer R. Willams, Matthew R. Hoffman, Boris B. Blinov, Norval Fortson We report our progress on the measurement of the magnetic dipole transition moment (\textit{M1}) in Ba$^{+}$ for the $6S_{1/2} (m)\leftrightarrow 5D_{3/2} (m^{'})$ transition with a linearly polarized 2051 nm laser. The motivation behind this study is to make a precise measurement of \textit{M1}, which is the leading source of systematic error in our planned parity nonconservation measurement. To date there are only two theory calculations that have been reported for \textit{M1} in Ba$^{+}$ which are $80\times 10^{-5}\mu_{B}$ [1] and $20 \times 10^{-5}\mu_{B}$ [2]. In our technique, the Rabi frequency was measured for the $6S_{1/2} \leftrightarrow 5D_{3/2} $ transition with $\Delta m=0$ and $\Delta m=2$ as a function of the linear polarization angle of the 2051 nm beam. We used the $\Delta m=2$ transition (that has no \textit{M1} contribution) as a check for systematics in the polarization of the beam. By measuring the polarization dependence of the $\Delta m=0$ transition Rabi frequency we can extract the ratio of the \textit{M1} to the much larger and well known electric quadrupole amplitude, from which we can extract \textit{M1}.\\[4pt] [1] PRA \textbf{74}, 062504\\[0pt] [2], PRA \textbf{88}, 034501. [Preview Abstract] |
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D1.00012: High Efficiency Collection and Fiber Coupling of Ion Florescence Richard Graham, John Wright, Zichao Zhou, Tomasz Sakrejda, Boris Blinov Efficient collection of fluorescence light from trapped ions is important for robust qubit state detection and for generating remote entanglement of states. Implementing a modular and scalable ion-trap quantum computer will require a low cost solution for fiber coupling a large fraction of the fluorescence light. We are developing a solution using custom aspheric lenses with a design collection efficiency of 38\%. [Preview Abstract] |
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D1.00013: Precision Measurements of Ba$^+$ Properties Matthew Hoffman, Spencer Williams, Anupriya Jayakumar, E.N. Fortson, Boris B. Blinov Single trapped barium ions continue to offer a wealth of information about atomic and nuclear structure, oscillator strengths, and polarizabilities. We report progress towards a series of precision measurements that will provide stringent tests of theorists' predictions of these various properties. The first of these is a measurement of the $6S_{1/2} \leftrightarrow 5D_{3/2}$ magnetic dipole transition moment (M1), using a frequency stabilized laser operating at 2051 nm.\footnote{S.R. Williams \emph{et al.}, PRA \textbf{88} 012515 (2013)} This measurement is of interest, as knowledge of M1 is necessary in a proposed measurement of atomic partity nonconservation (PNC).\footnote{E.N. Fortson, PRL \textbf{70} 2383 (1993)} The second is a radio-frequency (rf) spectroscopic measurement of the hyperfine structure of the $5D_{3/2}$, resulting in a measurement of the nuclear magnetic octupole moment of $^{137}$Ba$^+$. Finally, we have begun work on measuring the branching ratio of spontaneous decay from $5D_{5/2}$ to $6S_{1/2}$ and $5D_{3/2}$. The underlying theory and motivation behind these measurements will be presented, as well as experimental upgrades and recent results. [Preview Abstract] |
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D1.00014: Abnormal Superfluid Fraction of Harmonically Trapped Few-Fermion Systems Yangqian Yan, D. Blume Superfluidity is a fascinating phenomenon that, at the macroscopic scale, leads to dissipationless flow and the emergence of vortices. While these macroscopic manifestations of superfluidity are well described by theories that have their origin in Landau's two-fluid model, our microscopic understanding of superfluidity is far from complete. Using analytical and numerical \textit{ab initio} approaches, this work determines the superfluid fraction and local superfluid density of small harmonically trapped two-component Fermi gases as a function of the interaction strength and temperature. At low temperature, we find that the superfluid fraction is, in certain regions of the parameter space, negative. This counterintuitive finding is traced back to the symmetry of the system's ground state wave function, which gives rise to a diverging quantum moment of inertia $I_{\mathrm{q}}$. Analogous abnormal behavior of $I_{\mathrm{q}}$ has been observed in even-odd nuclei at low temperature. Our predictions can be tested in modern cold atom experiments. [Preview Abstract] |
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D1.00015: Ion-photon entanglement with trapped Ba-138 ions Thomas W. Noel, Carolyn Auchter, Chen-Kuan Chou, Boris B. Blinov We demonstrate entanglement between the polarization state of spontaneously emitted photons and the Zeeman state of a single trapped Barium ion. The Barium ion is weakly excited with a short ($\sim$20 ns) pulse of CW laser light. The ion subsequently decays emitting a single photon at 493 nm. Entanglement is verified by measuring the states of the ion and photon in multiple bases, yielding an overlap of 0.84 with the appropriate maximally entangled Bell state. Furthermore, the CHSH form of the Bell inequality is shown to be violated by over eight standard deviations. This work demonstrates elements of an apparatus which will make our long-term goal of achieving a loophole-free test of a Bell inequality possible. [Preview Abstract] |
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D1.00016: Design and Construction of a Super-Resolution Ground State Depletion Microscope to Optically Isolate GaAs Donors Sarah Harvey, Kai-Mei Fu, Todd Karin The ability to optically isolate single gallium arsenide electron donors has many implications both in quantum information science as well as semiconductor physics. However, conventional methods of fluorescence microscopy are fundamentally limited by diffraction, which sets a minimum resolvable feature size preventing the direct optical imaging of nanoscale structures. At the University of Washington Optical Spintronics and Sensing laboratory we are building a super-resolution optical microscope, based on ground state depletion, to isolate single GaAs donors. ~A critical component of the microscope is the raster scanning of laser beams over the sample, for which we have elected to use a piezoelectric fast-steering mirror. I have designed a scanning system capable of under 1 nm mechanical resolution, which will be sufficient for our target optical resolution of about 100 nm to isolate single donors. ~I will present preliminary results on the performance of the test system using a transmission electron microscopy (TEM) grid as a test sample, which will allow us to evaluate the achieved accuracy and resolution of the imaging due to its regular features. Isolating single donors in GaAs using this super-resolution microscopy technique may lead to new insights in how to localize and evaluate impurities such as donors and acceptors for quantum information as well as classical applications. [Preview Abstract] |
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D1.00017: Thermal conductivity measurements of amorphous metal thin films via the 3$\omega$ method Kai Zhan, Janet Tate, John McGlone, John Wager, Kris Olsen, Douglas Keszler Amorphous multicomponent metals have promising applications in novel electronic devices because of their atomically smooth surface morphology and lack of grain boundaries. It is important to understand the thermal transport properties of amorphous metals and an accurate measurement of their thermal conductivity will be essential for further improvement of device performance and reliability. Here, the 3$\omega$ method has been improved and extended to investigate the room temperature thermal conductivity of amorphous metals. Iterative, amorphous multicomponent metallic films are deposited on silicon substrate by magnetron sputter deposition. A thin layer of hafnium oxide film is deposited on top of amorphous metals by atomic layer deposition, providing a reliable insulation between an aluminum heater and the amorphous metal film. The room temperature thermal conductivities of thin-film hafnium oxide and silicon nitride are also measured to demonstrate the capability and reliability of the 3$\omega$ technique. [Preview Abstract] |
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D1.00018: Photometric study of single-shot energy-dispersive X-ray diffraction at a laser plasma facility Oliver Hoidn, Gerald Seidler The low repetition rates and possible shot-to-shot variations in laser-plasma studies place a high value on single-shot diagnostics. For example, white-beam scattering methods based on broadband backlighter x-ray sources are used to determine changes in the structure of laser-shocked crystalline materials by the evolution of coincidences of reciprocal lattice vectors and kinematically-allowed momentum transfers. We demonstrate that white-beam techniques can be extended to strongly-disordered dense plasma and warm dense matter (WDM) systems where reciprocal space is only weakly structured and spectroscopic detection is consequently needed to determine the static structure factor and thus the ion-ion radial distribution function. Specifically, we report a photometric study of energy-dispersive diffraction (ED-XRD) for structural measurement of high energy density systems at large-scale laser facilities such as OMEGA and the National Ignition Facility. We find that structural information can be obtained in single-shot ED-XRD experiments using established backlighter and spectrometer technologies. [Preview Abstract] |
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D1.00019: Volumetric adsorption isotherms of hydrogen on exfoliated graphite Oscar Vilches, Han Ye, Alex Podschwidt We report volumetric adsorption isotherm measurements of molecular hydrogen on a good quality exfoliated graphite foam substrate (H$_{\mathrm{2}}$/gr) at temperatures above 20K performed with the goal of understanding the initial stages of adsorption on this two-dimensional (2d) system at temperatures well above the known phase transitions of the monolayer H$_{\mathrm{2}}$/gr. We obtain the isosteric heat of adsorption of H$_{\mathrm{2}}$/gr as a function of coverage. On the very low coverage region below 10{\%} of a monolayer we are currently working towards obtaining (1) a measurement of the binding energy of non-interacting H$_{\mathrm{2}}$ on graphite, (2) the highest coverage at which heterogeneities in the substrate produce deviations from a linear dependence of the equilibrium 3d pressure vs. coverage (Henry's law), and (3) the 2d van der Waals coefficients of the weakly interacting 2d gas of H$_{\mathrm{2}}$ molecules We compare our results to the ones obtained with similar measurements using carbon nanotube bundles as the substrate. [Preview Abstract] |
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D1.00020: The Pressure Dependence of the Unscreened 4f Magnetic Moments of the Early Light Lanthanides Devon Mortensen, Magnus Lipp, Joseph Bradley, Paul Chow, Yuming Xiao, Gerald Seidler, William Evans Using the satellite structure of the L$\gamma $1 line in non-resonant x-ray emission spectra, we probe the high-pressure evolution of the bare 4f moments of the early light lanthanides at ambient temperature. For Ce and Pr this satellite peak experiences a sudden reduction concurrent with their respective volume collapse transitions. The partial persistence of this feature ($\sim$ 75{\%} for Ce and 60{\%} for Pr) indicates a complementary persistence in moment, arguing qualitatively in favor of the Kondo volume collapse model. Conversely, we find that Nd exhibits an unexpected increase in bare 4f moment that is independent of any reported structural or delocalization transition. All of these results differ sharply from prior state-of-the-art dynamical mean field theory calculations. These measurements emphasize the importance of studying microscopic observables, rather than macroscopic thermodynamic susceptibilities (e.g., the equation of state), to obtain the most discerning test of the underlying, fundamental f-electron phenomenon at high pressures. [Preview Abstract] |
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D1.00021: Evaluation of Electric Propulsion Systems for Asteroid Sample-Return Missions Andrew French, Sarah Gady, Ansh Sehgal This study evaluated the suitability of eight existing ion and Hall thrusters to meet some of the key requirements of sample-return missions to near Earth asteroids. The OSIRIS-REx mission was used as a baseline for evaluation, and all thrusters were expected to transport a dry mass of at least 750 kg to the asteroid 1999RQ36, land on it in 2019 and stay for an extended period, and return with a sample of the asteroid to Earth. Then, the values of the dry mass to be transported, required stay time on the target, and the mass of the sample to be returned were considered as parameters to be varied. The thrusters were evaluated for this mission at their measured performance levels, and their suitability was evaluated for various values of the specific mass of the power plant. The spacecraft was allowed to coast without thrust at appropriate places in its trajectory to reduce fuel consumption. The resulting values of total trip time and wet mass at LEO for the various cases are presented and are compared with the baseline case of the OSIRIS-REx mission. [Preview Abstract] |
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D1.00022: Searching for Evidence of White Dwarf Core Crystallization in 47 Tucanae Alysa C. Obertas, Harvey Richer, Jeremy Heyl White dwarfs (WDs) are remnants of stars like our Sun. About 98\% of all stars in the Galaxy will end their lives as white dwarfs. Young WDs are very hot, but lose energy initially by neutrinos and then by the emission of photons from the surface. Eventually, enough energy is lost that the core of the WD begins to crystallize. WD cooling is crucial for understanding a variety of issues from the formation of the Galaxy to the age of the Universe. Current cooling models incorporate crystallization of WDs and the release of latent heat that slows the cooling temporarily. In this poster, the cumulative luminosity function of white dwarfs in 47 Tuc is compared to modelled luminosity functions. The results suggest that crystallization is occurring at the expected age, verifying this component of current models used to age ancient star clusters. [Preview Abstract] |
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D1.00023: Dynamics of Laboratory Astrophysical Jets with Magnetized Helical Flows Eric Lavine, Jens Von Der Linden, Keon Vereen, Evan Carroll, Manuel Azuara Rosales, Alex Card, Morgan Quinley, Iman Datta, Setthivoine You A novel planar plasma gun experiment is under construction to investigate the dynamics of plasma jets with magnetized helical flows. The goal is to observe the effects of current profiles, flow profiles, and launch boundary conditions on the length, collimation, and stability of jets. The apparatus is carefully designed to provide boundary conditions relevant to astrophysical jets. The gun has three, planar, concentric electrodes that can be biased at different potentials to mimic an accretion disk rotation profile when coupled to the vacuum magnetic field. The dimensionless parameters are appropriate for protostellar jets and numerical simulations of astrophysical jets. Diagnostics include internal B-dot probes, and vector tomographic reconstruction of ion Doppler spectroscopic measurements capable of reconstructing 3D flow fields. Measurements will be interpreted with a two fluid model of canonical flux tube evolution that describes how magnetic helicity is converted into stabilizing shear helical flows while a system's total canonical helicity (sum of magnetic and fluid momentum helicity) is conserved. The study aims to address the questions: 1) Why are jets highly collimated, straight, and very long? 2) How are jet irregularities related to plasma instabilities and boundary conditions? [Preview Abstract] |
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D1.00024: Content knowledge for teaching energy: An example from middle-school physical scienc Amy Robertson, Rachel Scherr, Lane Seeley, Stamatis Vokos ``Content knowledge for teaching'' is the specialized content knowledge that teachers use in practice -- the content knowledge that serves them for tasks of teaching such as making sense of students' ideas, anticipating conceptual challenges students will face, selecting instructional tasks, and assessing student work. We examine a middle-school physical science teache's interactions with a group of students for evidence of content knowledge for teaching energy (CKT-E). Our aims are to develop our theory of CKT-E as well as criteria for its observational assessment. We identify CKT-E as potentially including elements of consensus energy models, elements of alternative energy models, elements of a sophisticated understanding of the nature of science, and a repertoire of instructional tasks or activities that exemplify or support instructional goals. [Preview Abstract] |
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D1.00025: Periscope: Looking into learning in best-practices physics classrooms Rachel Scherr, Renee Michelle Goertzen \textit{Periscope} is a set of materials to support university instructors in observing, discussing, and reflecting on best practices in university instruction. Periscope is organized into short ``video workshops,'' each introducing a significant topic in the teaching and learning of physics, such as formative assessment or cooperative learning. The workshops are appropriate for university professors, two-year college faculty, graduate student teaching assistants, and undergraduate learning assistants. Key topics in teaching and learning are introduced through captioned video episodes of introductory physics students in the classroom, chosen to prompt collaborative discussion. Video episodes from exemplary sites (including the University of Maryland, University of Colorado -- Boulder, Harvard University, and Florida International University) showcase a variety of research-tested instructional formats such as \textit{Peer Instruction} and \textit{Tutorials in Introductory Physics.} Discussion questions prompt participants who view the episode to reflect on their pedagogical beliefs, on their own practice, and on the results of physics education research. \textit{Periscope} materials may be flexibly adapted for settings ranging from brief introductory sessions to all-day workshops or weekly meetings. [Preview Abstract] |
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D1.00026: Learner understanding of energy degradation Abigail Daane, Stamatis Vokos, Rachel Scherr Learners' everyday ideas about energy often involve energy being ``used up'' or ``wasted.'' In physics, the concept of energy degradation can connect those ideas to the principle of energy conservation. Learners' spontaneous discussions about aspects of energy degradation have motivated us to introduce new learning goals into our K-12 teacher professional development courses. One of our goals is for teachers to recognize that since energy degradation is associated with the movement of some quantity towards equilibrium, the identification of energy as degraded or free depends on the choice of the objects involved. Teacher discussions of a particular energy scenario (about a wind-powered heating system) led to productive conversations about the nature of energy degradation and its possible dependence on the choice of what to include in the scenario. [Preview Abstract] |
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D1.00027: Models for Teaching Modern Physics Robert Close The great nineteenth century physicist William Thomson (Lord Kelvin) judged his understanding of physical phenomena by whether or not he could construct a mechanical model. Although this attitude is no longer in vogue, mechanistic models can still be useful in teaching modern physics to students. We present mechanistic models or analogues of special relativity, atomic spectra, Dirac wave functions, quantum operators, electromagnetic potentials, antimatter, and gravity. Mechanistic models may help to build intuition for all students of physics, and may also serve as an introduction to the mathematics of modern physics. [Preview Abstract] |
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D1.00028: Improving student reasoning about advanced electrostatics concepts Ryan Hazelton, Paula Heron This poster describes student difficulties with advanced electrostatic concepts related to electric potential and describes the results of tutorials developed for \textit{Tutorials in Introductory Physics}. After lecture instruction, the majority of students cannot correctly reason about advanced electrostatic concepts. Common incorrect reasoning patterns emerge in student responses about electric potential energy and electric potential difference, and about electric potential in conductors. We have developed tutorial worksheets that seek to address these incorrect reasoning patterns. Results from questions posed after the tutorials indicate that the tutorials are successful at improving student learning about these difficult and abstract ideas. [Preview Abstract] |
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D1.00029: Research as a guide for adapting curriculum on special relativity to a new population Alexis Olsho, Peter Shaffer Student understanding of special relativity has been examined by the Physics Education Group at the University of Washington over a period of many years. A Tutorial sequence on this topic had been developed for use in courses for advanced physics undergraduates. Special relativity, however, is being taught increasingly often in introductory physics courses. Preliminary research indicates that for many students, the current Tutorial curriculum is not sufficient for addressing common difficulties with the concepts of reference frames, observers, and causality. Post-tests on the relativity of simultaneity show only modest gains in student ability to determine the time order of events in different reference frames, and reveal significant gaps in student understanding of these fundamental concepts. The results are informing modifications to the tutorials in order to adapt them to this new population. [Preview Abstract] |
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D1.00030: Assessing effectiveness of lab curriculum in promoting student understanding of kinematics Chandler Dennison, Emily Granston, Andrew Boudreaux Prior research in physics education has identified specific aspects of the concepts of velocity and acceleration that introductory calculus-based physics (ICBP) students tend to struggle with (Trowbridge and McDermott, 1980, 1981; Shaffer and McDermott, 2005). At Western Washington University, ICBP students complete guided inquiry labs that target these difficulties explicitly. The labs draw on and adapt existing research based curricula such as \textit{Tutorials in Introductory Physics} (McDermott and Shaffer, 2001), use MBL sensors for real time data collection, include targeted use of PhET simulators, and ask students to reflect on changes in their understanding. Student learning has been assessed by administering free-response pre- and posttest questions similar to those used in prior studies. Three researchers collaboratively constructed rubrics to categorize student responses. Interrater reliability was found to be greater than 85{\%}. Results of the data will be presented as evidence for the effectiveness of the kinematics lab activities. [Preview Abstract] |
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D1.00031: Promoting quantitative reasoning in the PET curriculum with supplemental invention tasks Kelsey Mork, Andrew Boudreaux At Western Washington University, preservice elementary teachers take a required content course taught with the Physics and Everyday Thinking (PET) curriculum (Goldberg, Robinson, and Otero, 2008). While PET has led to consistent, strong gains in conceptual understanding and qualitative reasoning, informal observations of students have suggested that basic quantitative reasoning is not as well supported. Invention tasks, based on the approach of Dan Schwartz and colleagues, have been used to supplement the PET activities. In these tasks, students construct quantitative measures to make meaningful comparisons between contrasting cases. This poster describes the invention tasks and presents preliminary assessment data to both identify specific difficulties with quantitative reasoning and evaluate the effectiveness of the supplemental tasks. [Preview Abstract] |
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D1.00032: Research-based assessment resources to improve teaching in your classroom and department Sarah McKagan, Adrian Madsen, Eleanor Sayre Often physics faculty want to know how their students are doing compared to other ``students like mine.'' As part of the PER User's Guide (http://perusersguide.org), we are developing a national database of research validated assessment results and an accompanying data explorer. Here faculty can securely upload their students' anonymized assessment results and compare them to students from peer institutions and the national dataset, view a question-by-question breakdown and compare results over time. ``One-click analysis'' allows faculty members to visualize their data, view statistics and download a report of the results. Results can be used to improve teaching, to make a case for more resources, for accreditation reports, or for promotion and tenure. Additionally, we are developing guides to these research validated assessments and access to the tests themselves. We will showcase our new online system and provide information about how you can use it. [Preview Abstract] |
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D1.00033: Physicist Make Better Athletes: If You Understand Physics You Can Be Better At Sports Min Hyung Kim, Yeon Jae Lee, Sun Mee Lee Physics plays a dominant role in the way athletes perform and the way the sport is played. In high school, many students would complain because they do not know why they have to learn all about physics. Some will say that they would not need it in the future for they do not dream to be a physicist someday or they just cannot see the reason why. They say this because they do not know that physics can be used in relation to sports. How and why? If student athletes and their coaches were to better understand how physics is applied to sporting situations, they would be able to improve their performances and their teams' records - not just through repetitious conditioning on the field, but through conditioning of their minds to understand the basic laws and terms of physics. By illustrating how is physics related to sports, athletes can be taught to use their brain muscles to improve their athletes can control and improve their physical performances. This paper will help the people who do not know that physics can really help in understanding sports. It will define how fundamentals of various athletic performances can be significantly improved when the athlete understands the physics involved in his particular sports. This paper presents simple explanations of physics, defines relevant terms, and demonstrates the application of physics in various sports, and illustrate how to garner better results and records in sports. [Preview Abstract] |
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D1.00034: \textit{Internet} Promotes and Facilitates Learning Physics Yeon Jae Lee, Min Hyung Kim, Sun Mee Lee An ever-increasing amount of information in myriad of subjects is readily available on the \textit{Internet}; and students and teacher alike can access this vast array of information as learning aids. The idea presented in this article is to help both teachers and students realize how teaching-learning activities in physics can be creatively incorporated into currently popular youth-oriented websites and applications and procure the interest of young future physicists. The instructional resources and materials used nowadays in the teaching of physics in middle and secondary schools are still largely the same as those used in past years, books and charts. However, the way many young people obtain and retain information has been experiencing a dramatic change in light of the computer applications and materials that the young people use outside of schools in their personal lives; many receive majority of their information via internet, audio and video peripherals, World-Wide Web, etc. In contrast, the methodology many teachers of physics use in their teaching has not changed with the times. This paper presents how the internet and, in particular, computer-based resources and software programs, will be of great assistance to teachers in regard to their pedagogical activities. Also this paper shows instructors and students can engage in more dynamic and interactive learning methods by using those utilities and devices. [Preview Abstract] |
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D1.00035: Theoretical studies of asymmetric, multicomponent, lipid bilayers Ha Giang, Michael Schick We consider an asymmetric bilayer in which the two leaves are coupled solely by the fact that cholesterol can go back and forth between them rapidly. To model this, we require that the chemical potential of cholesterol in the two leaves be the same, and this provides the coupling. We examine two problems. First we consider how the transition temperature in one leaf is affected by the distribution of lipids in the other. In particular, we show that if the lipids are distributed very asymmetrically, as they are in the mammalian plasma membrane, phase separation can occur in one leaf and not the other. Secondly we consider the distribution of cholesterol in the bilayer. It is widely accepted that sphingomyelin has the greatest affinity for cholesterol. After that, the order of preference is phosphatidylserine, phosphatidylcholine, and lastly phosphatidylethanolamine. We show that, in spite of the affinity of cholesterol for sphingomyelin, which is located predominantly in the outer leaf of the plasma membrane, it is possible to have a majority of the cholesterol in the inner leaf. This situation has been observed in experiments on Chinese hamster ovary cells in which 70 percent of cholesterol was found in the inner leaf. [Preview Abstract] |
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D1.00036: Spatiotemporal-dependent dynamics of small molecules in Escherichia coli Stella Stylianidou, Nathan J. Kuwada, Paul A. Wiggins Despite its relative biological simplicity, many biophysical details of the bacterial cytoplasm remain unknown. In order to isolate active dynamics in \textit{E.~coli}, such as the chromosome segregation mechanism, we need to define totally passive motion. Using time-lapse wide-field fluorescence microscopy, we imaged small, non-functional fluorescent MS2-mRNA molecules throughout the entire \textit{E.~coli} cell cycle. By analyzing the trajectories of these molecules, we find that the dynamics of small non-functional molecules in the cell depend on spatial position along the long-axis of the cell as well as temporal location in the cell cycle lifetime. We present a biophysical model and possible consequences of these results on understanding passive and active transport systems in the cell. [Preview Abstract] |
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D1.00037: Characterizing the effect of temperature on gelation and inhomogeneity of type I collagen gels Christopher Jones, Bo Sun Type I collagen gels are commonly used as the substrate for experiments on cell mechanotransduction because collagen is the most abundant protein in the ECM of most animals. The gels are commonly approximated as homogeneous elastic materials; however, on smaller length scales, the inhomogeneity of the collagen fiber network becomes very apparent. During gelation, collagen fibers can group together to form larger fiber bundles, with the size, shape, and distribution of these bundles depending on the conditions during gelation. We study how the collagen concentration and temperature during gelation affect the inhomogeneity of collagen fiber networks. Confocal reflection microscopy is used to image the collagen as it polymerizes, and the collagen matrix is characterized by analyzing variations in fiber density and orientation. Gel homogeneity is quantified by calculating the spatial correlation of fiber orientation and density for various temperatures and collagen concentrations. We find that collagen gels formed at room temperature are inhomogeneous and show many fiber bundles, while gels formed at 37$^\circ$C are very homogeneous. We explore this transition by varying gelation temperatures from 23$^\circ$C to 37$^\circ$C for several different collagen concentrations. [Preview Abstract] |
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D1.00038: Macroscopic Phase Separation, Modulated Phases, and Microemulsions: A Unified Picture of Rafts Roy Shlomovitz, Lutz Maibaum, Michael Schick We simulate a simple phenomenological model describing phase behavior in a multi-component membrane, a model capable of producing macroscopic phase separation, modulated phases, and microemulsions, all of which have been discussed in terms of raft phenomena. We show that one effect of thermal fluctuations on the mean-field phase diagram is that it permits a direct transition between either one of the coexisting liquid phases to a microemulsion. This implies that one system which exhibits phase separation can be related to a similar system which exhibits the heterogeneities characteristic of a microemulsion. The two systems could differ in their average membrane composition or in the relative compositions of their exoplasmic and cytoplasmic leaves. The model provides a unified description of these raft-associated phenomena. [Preview Abstract] |
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D1.00039: Analysis of the Aortic Pressure Waveforms Using Numerical Method Doo Hyun Nam, Soo Yeon Kim, Richard Kyung Aortic valve disease is the most common valvular disease in our cardiovascular system.~It causes the calcification of the aortic valve leaflets, leading to obstruction to blood flow from the left ventricle to the Aorta. During the past couple of decades, the numerical analysis for the dynamics of blood flow and its relationship with disease has become appreciated by medical and biological researchers. Also numerical analysis of blood flow in the cardiovascular system has been considered as a key factor in both the cause of cardiovascular disease and the regulation of cellular biology in normal and diseased arteries. Modeling the biofluid systems experimentally and numerically is an important component to fundamental research of cardiovascular disease. However, numerical methods offer the advantage of changing flow variables that affecting the outcome quickly for the entire biofluid system. [Preview Abstract] |
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D1.00040: Study on the Knee Pressure Causing Fatigue in the Tibial Bone Soo Yeon Kim, Doo Hyun Nam, Richard Kyung Computational stress analysis is widely used in cases when figuring out the clinical conditions of patients is difficult.~The purpose of the present research is to evaluate stresses and fracture conditions in the tibial bone caused by various sports activities or accidents, using biomechanical and numerical analysis. The research procedures will include three steps : Examination of biomechanical properties of bones, development of biomechanical and mathematical modeling of the bone, and ~finding the solutions -stress and fracture conditions in the tibia. By using the above procedure together with the bone remodeling technique, the physiological solutions (maximum stress) of the bones and impact conditions causing the fracture in the bone can be found. The result can be compared to the empirical results found by other scientists and the data could help improve knee arthroplasty, which is a surgical treatment. For the computational ~and numerical analysis, the bone model can be meshed using a two dimensional element and the nodes on the bottom of the proximal tibial model will be constrained in all directions. To obtain stress distribution in the bone, pressure force will be applied on the top of the bone :~ For example, total load of 500 N ; 150 N on lateral and 350 N on medial compartment. In this paper, different loads on the lateral and medial compartment are applied to observe the variations in the stress distribution of the tibial component. [Preview Abstract] |
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D1.00041: A Novel Method of Line Detection without Noise Interferences using Pixel Voting Daniel Lin, Bo Sun Images generated by machines are often plagued with noises, or unwanted signals generated by machines, that might degrade the visibility of the images and thus make objects on them such as lines hard to be detected by computers and the naked eyes. Existing line detection algorithms, such as Canny Edge Detection, pre-processes the image using filtering algorithms such as Gaussian Smoothing to perform noise removal. However, most filters require the user to adjust their input parameters, which can add computational complexities to the algorithm depending on the parameter size. We designed a versatile line detection algorithm that can detect lines on images without the need of filters. The algorithm accepts a raw, unprocessed image, generates a noise-free reference image of the same size, and overlaps the reference image to the raw image. Our algorithm successfully detected fiber structures in the real confocal reflection images of collagen gel that was filled with various image noises. [Preview Abstract] |
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D1.00042: Evaluation of Gamma-Ray Spectroscopy Software for On-Site Inspection under the Comprehensive Nuclear-Test-Ban Treaty Brian Milbrath, David Jordan, Augustine Caffrey, Nathan Wimer The Comprehensive Nuclear-Test-Ban Treaty (CTBT) would ban all nuclear explosions worldwide. As part of the verification regime of the Treaty an On-Site Inspection (OSI) may be called to investigate a location to determine if a nuclear explosion has occurred. Per the Treaty, in order to protect sensitivities of the inspected country, the measurement of radioisotopes may be limited to those relevant to the inspection. This means, for example, that gamma spectroscopy detectors would be limited in their function so as to only detect certain gamma-rays (and their corresponding radioisotopes). How to impose this limitation in a robust and reliable manner is not currently agreed upon. In order to investigate this issue technically we have developed a gamma spectroscopy software that includes an information barrier called OSIRIS (OSI RadioIsotopic Spectroscopy). We have also developed a set of fission-product spectra, both Treaty compliant and non-compliant, for testing the software to compare its performance relative to expert analysis. An ORTEC Trans-SPEC-DX-100T HPGE spectrometer serves as the OSIRIS prototype instrument. [Preview Abstract] |
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D1.00043: Design Considerations for Implementing Halbach Arrays and High Temperature Superconductors for Contact-Free Flywheel Energy Storage Systems Christopher Mirabzadeh, Chris Birkinbine, Daniel Schneider, Joe Law, Christine Berven We have investigated the use of Halbach magnet arrays in combination with Type II High-Temperature Superconductors for use as a levitating thrust bearing for a fly-wheel energy storage system. Halbach arrays were selected because they have effectively one-sided flux and a greater flux gradient which would be expected to result in a greater levitation force and effective restoring force stiffness; each being beneficial in the design of such a system. To find the optimum orientation of the magnets for the arrays, we used Infolytica Magnet, a finite-element computation software package, to iterate over all permutations of magnet arrays costing of 3 and 5 magnets of single and double layers. The fields and levitation forces as well as the width of the magnet arrays relative to the width of the superconductor were analyzed. Within our given design constraints, we found that, compared to a single magnet, a single-pole Halbach array was predicted to increase levitation force and stability, reduce stray fields, focus the flux, and increase the bearing stiffness. We present our findings and suggest guidelines to increase levitation force of a superconducting magnetic bearing with qualifiers and rationale for optimizing such a system. [Preview Abstract] |
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D1.00044: Analysis of the Light Response of Lead Fluoride Crystals for the New (g-2) Experiment Kazimir Wall The new (g-2) experiment hopes to test the difference between the experimental and theoretical values of the anomalous magnetic moment of the muon out to a greater statistical precision than has been previously accomplished. Such a discovery would provide strong evidence of new physics such as dark photons, supersymmetry, or possibly something not yet considered. During the experiment, muons are injected into a large superconducting ring. A muon decays to an electron and the electron curls to the inside of the storage ring and strikes an array of lead fluoride crystals. When an electron hits a crystal, it produces light that is proportional in intensity to the energy of the electron. The energy and the time of its arrival help to indicate the direction of the spin which is used in the calculation of (g-2). My research investigates how light is propagated and distributed in these crystals and how different reflective or absorptive wrappings affect this distribution. I measure light yield and pulse width, which correspond to two different extremes of wrapping material. For maximum light yield, I use white Millipore paper, while shorter pulse widths are achieved using black Tedlar. I have developed a 2x2 array of crystals coupled to light sensitive photomultiplier tubes. This setup captures cosmic ray muons that hit the surface of the earth. Capturing these muons simulates the conditions of the experiment. I analyze the resulting data by fitting the pulses and extracting the functional form of the light distribution. The results of this research will ultimately contribute to the development of more complete theories of the fundamental building blocks of the universe. [Preview Abstract] |
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D1.00045: Liquid Helium Level Sensor Kevin Jamison The spins of electrons bound to donors are promising candidates as qubits for quantum information processing. The quantum properties of these donor-bound electrons are studied in high magnetic fields while immersed in liquid helium at 4K. For stability reasons, the level of liquid helium in the experiment must be monitored with a sensor. An effective way of implementing a sensor is with a superconducting wire. Super conductors have the property of having zero electrical resistance when they are cooled below a critical temperature. Above this critical temperature, the superconductor has significant electrical resistance. Using these characteristics, a superconducting wire can be used to construct a liquid helium level sensor. When current is run through a thin wire submerged in liquid helium, a relationship can be established between the voltage drop across the sensor and the amount of wire submerged in the liquid helium, allowing the liquid helium level to be measured. Results will be presented on the sensor design and performance. [Preview Abstract] |
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D1.00046: Heteroepitaxial ZnS Films on Si for Photovoltaic Applications Christopher Reidy, Peter Eschbach, Janet Tate Many novel photovoltaic devices have been designed recently that rely on heterojunctions to induce carrier multiplication. To that end, high quality ZnS thin films were grown on (111) and (100) oriented Si wafers via pulsed laser deposition. ZnS is a good candidate for such a device, since its band gap is wider than that of silicon, and the lattice constants of these materials differ by only 0.3{\%} at 25C. The ZnS growth was found to depend strongly on orientation and surface reconstruction of the silicon substrates. Epitaxial ZnS formed on (111) silicon at a substrate temperature between 300C and 350C. With optimized growth conditions, the film stoichiometry was 1:1 Zn:S as measured by energy dispersive x-ray spectroscopy and electron probe microanalysis. The structure of the films was investigated by convergent beam electron diffraction, and high-resolution transmission electron microscopy shows that the films formed with abrupt junctions and limited diffusion across the interface. [Preview Abstract] |
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D1.00047: Thermoelectric Properties of Cu$_{12}$Sb$_{4}$S$_{13}$ and Derivatives Rodney Snyder, Josh Mutch, Daniel Speer, Chris Reidy, Janet Tate, John Wager, Greg Angelos, Jaeseok Heo The room-temperature Seebeck coefficient and resistivity of thin film variants of the mineral tetrahedrite Cu$_{12}$Sb$_{4}$S$_{13}$ and its derivatives were measured. In bulk form, tetrahedrite has shown promise as a good thermoelectric material. Thin films of Cu$_{12-x}$M$_{x}$Sb$_{4}$S$_{13\, }$(M $=$ Cu, Zn) were produced by e-beam deposition, and we also produced films with a second metal on the Cu site. The Seebeck coefficients ranged from 10 to 113 $\mu $V/K and the resistivity from 8 to 50 m$\Omega $cm. Together, these values yield power factors S$^{2}$/$\rho $ ranging from 10$^{-7}$ to 10$^{-4}$ W/mK$^{2}$, approaching the range of their bulk counterparts at the upper end. As a comparison, the power factors for $n$- and $p$-doped silicon were measured and compared to published values. For both $p$-Si and $n$-Si, the power factor was 3.0$\cdot$10$^{-3}$ W/mK$^{2}$. [Preview Abstract] |
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D1.00048: Electrically tunable light-emitting diodes based on monolayer WSe2 p--n junctions Marie Scott, Jason Ross, Xiaodong Xu Following the discovery of graphene, other two-dimensional (2D) materials have been identified including a variety of truly 2D semiconductors. These new semiconductors are exciting candidates for next-generation optoelectronic devices because of their unique optical properties. Further, despite being atomically thin, techniques have recently been developed to transfer and stack these monolayer materials and produce arbitrarily complex heterostructures. Here, we present our adaptation of these transfer techniques in conjunction with electron beam lithography to produce the first monolayer LED using 2D crystals of tungsten diselendide(WSe2). We stack monolayer WSe2 along with boron nitride onto metal gates to from a lateral p--n junction. This structure allows effective injection of electrons and holes, and, combined with the high optical quality of WSe2, yields bright electroluminescence with 1,000 times smaller injection current and 10 times smaller linewidth than seen in MoS2 schottky junction electroluminescence. By increasing the injection bias we can tune the electroluminescence between regimes of impurity-bound, charged and neutral excitons. [Preview Abstract] |
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D1.00049: Low-Density Measurements of Gas Adsorption on Carbon Nanotubes Boris Dzyubenko, Denise Schmitz, Hao-Chun Lee, Oscar E. Vilches, David H. Cobden We have studied the adsorption of noble gases on suspended individual single-walled carbon nanotubes in the limit of low density (coverage). The coverage, determined from the shift of the mechanical resonance frequency of the nanotube due to mass loading is sensitive to about 30 atoms adsorbed on the entire nanotube. Due to the high homogeneity of the nanotube substrate and the sensitivity of the technique we are able to observe Henry's law, in which the coverage is proportional to the gas pressure. In this limit the adsorption isotherm is determined by single-atom effects, allowing unprecedentedly accurate $\pm$ 2{\%} determination of the single-particle binding energies of Ar and Kr to a nanotube. [Preview Abstract] |
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D1.00050: Electrical transport measurements on few-layer MX2 Zaiyao Fei, Joe Finney, Paul Nguyen, Bosong Sun, Xiaodong Xu, David Cobden Transition metal dichalcogenides (MX2) have recently been shown to have excellent optical properties, but their intrinsic electrical properties remain undetermined mainly due to a lack of good electrical contacts to these materials, especially at lower temperatures. We investigated a range of device geometries and contact techniques to improve the situation. So far we have achieved ambipolar gating of the linear-response conductance persisting at temperatures down to 4 K with contact resistance for both carrier of around 50 kiloohm at room temperature. Four terminal Hall-bar measurements is also been made to separate the contact resistance, sheet resistivity, carrier density and mobility. [Preview Abstract] |
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D1.00051: Observation of time-dependent PL intensity of excitonic transitions in III-V semiconductors Todd Karin, Russell Barbour, Patrick Wilhelm, Kai-Mei Fu We study the time dependence of the excitonic photoluminescence (PL) intensity under resonant and above-band excitation using pump-probe techniques in InP and GaAs. We find that the PL intensity of both free and bound excitons increases to a steady-state value on a microsecond time-scale upon optical excitation. The system recovers to its initial state on the time-scale of tens of microseconds in the absence of excitation. Understanding the mechanism of this time-dependent intensity is important for the interpretation of pump-probe measurements designed to measure the spin-relaxation time of bound carriers in III-V semiconductors. [Preview Abstract] |
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D1.00052: Second Harmonic Generation and Two-Photon Absorption in Few-Layer Transition Metal Dichalcogenides Kyle Seyler, John Schaibley, Sanfeng Wu, Jason Ross, Xiaodong Xu Atomically thin crystals of transition metal dichalcogenides (TMDs) have recently stimulated great interest due to their 2D optoelectronic properties, including strongly bound and tunable excitons and trions, and valley polarization and coherence. To date, most research efforts have been focused on the linear optical properties of TMDs. However, the recent observation of strong second harmonic generation and two-photon absorption in TMD monolayers suggests that the nonlinear optical properties may provide important insights into the excitonic physics of TMDs and lead to the observation of new phenomena. Here we present results of two-photon absorption and second harmonic generation experiments on monolayer and bilayer WSe2, under varied incident photon energy, photon polarization, and external electric field. We discuss the implications of these results on our understanding of the 2D excitonic physics in few-layer TMDs. [Preview Abstract] |
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D1.00053: Band Gap and Phase Stability in (Al$_{\mathrm{x}}$Ga$_{\mathrm{1-x}})_{2}$O$_{3}$ Alloy Films Benjamin Krueger, John Walseth, Fumio Ohuchi, Marjorie Olmstead Gallium oxide is a transparent semiconductor (E$_{\mathrm{g}}=$ 4.8 eV) that exhibits n-type conductivity; it has been proposed for a variety of uses ranging from ``solar-blind'' conductive coatings to chemical sensing. An intriguing possibility is development of transparent, high power transistors based on carrier accumulation at an epitaxial Ga$_{2}$O$_{3}$--(Al$_{\mathrm{x}}$Ga$_{\mathrm{1-x}})_{2}$O$_{3}$ alloy interface. Using pulsed laser deposition, composition-spread (Al$_{\mathrm{x}}$Ga$_{\mathrm{1-x}})_{2}$O$_{3}$ thin films were fabricated on sapphire and silicon substrates, with $x$ varying smoothly across the surface. Position-dependent X-ray diffraction revealed [-201]-oriented Ga$_{2}$O$_{3}$ on c-plane sapphire, and unoriented Ga$_{2}$O$_{3}$ on silicon with native oxide. Alloy (Al$_{\mathrm{x}}$Ga$_{\mathrm{1-x}})_{2}$O$_{3}$ films on sapphire remain in the $\beta $-Ga$_{2}$O$_{3}$ phase for $x$ \textless 0.30 then relax to the $\alpha $-Al$_{2}$O$_{3}$ phase, whereas films on silicon remain in the $\beta $-Ga$_{2}$O$_{3}$ phase for $x $\textless 0.35 and then relax into the cubic $\gamma $-Al$_{2}$O$_{3}$ phase. Photoemission spectroscopy shows core and valence levels shifting to higher binding energy and decreasing work function, while spectroscopic ellipsometry reveals the absorption edge moving to higher photon energy, consistent with a widening band gap. [Preview Abstract] |
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D1.00054: Dynein Motility Modeling David Roundy, Weihong Qiu, Karl Heldt, Elliott Capek Dynein is a motor protein which travels along microtubules. It is responsible for transporting organelles and other molecules around the cell. Dynein's stepping pattern is very irregular when compared to other motor proteins, which makes it particularly interesting. I will present a computational model of Dynein's motion, which takes into account the Brownian dynamics which are important for molecules of Dynein's size. I will discuss what is currently known about Dynein motion and the methods we use in modeling the protein's behavior. [Preview Abstract] |
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D1.00055: Quark Nugget Dark Matter Kyle Lawson While it is frequently assumed that the Dark Matter consists of a new fundamental particle an alternative possibility is that it represent a new phase of well know standard model particles. In this context I will discuss a model in which the dark matter consists of heavy ``nuggets'' of standard model quarks and antiquarks bound in a colour superconducting phase. After a brief review of the properties of these objects I will highlight a range of possible observational consequences and establish the current limits, and future detection prospects, for dark matter of this type. [Preview Abstract] |
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D1.00056: In Research of electromagnetic wave mass Yongquan Han 1, Einstein is pointed out that E $=$ mc$^{2}$. Assuming that the mass of an electromagnetic wave particle is m, according to Einstein's mass energy equation, an electromagnetic wave particle energy is: E $=$ mc$^{2}$. 2, Quantum mechanics, electromagnetic wave particle energy is the product of the Planck constant and the frequency of electromagnetic radiation, E$=$h$\gamma $. 3, For an electromagnetic wave particle, h$\gamma = $ mc$^{2}$, m $=$ h $\gamma$/c$^{2}$. Because h is Planck's constant, c$^{2}$ is the square of the speed of light is a constant, so the electromagnetic wave particle mass is related to the electromagnetic wave particle's frequency, the greater frequency is, the greater the mass od the electromagnetic wave particle is 4, analysis of Einstein's theory of relativity mass and velocity relationship can not be the photon mass confusion: electromagnetic wave particle mass is only related with the frequency of electromagnetic wave particle, it doesn't related to the electromagnetic wave particle velocity, although the propagation of electromagnetic wave particle velocity is as fast as the speed of light, the mass will not tend to infinity [Preview Abstract] |
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