Bulletin of the American Physical Society
National Mentoring Community (NMC) Conference
Friday–Sunday, October 9–11, 2015; Miami
Session GP: Graduate Poster Session |
Hide Abstracts |
Room: Bldg: PG6 100W1 Hallway |
Saturday, October 10, 2015 3:45PM - 5:00PM |
GP.00001: FABRICATION AND SIMULATION OF WAVEGUIDES FOR ALGAN NANOWIRE LEDS Emilio Codecido, ATM Sarwar, Brelon May, Roberto Myers Ultraviolet dopantless algan nanowire leds have been developed using composition gradients and polarization techniques. With the goal of accomplishing a side-emitting laser, we are fabricating and simulating waveguides to enhance the light propagation in the longitudinal direction. In this poster, I will present the outline and Progress of the fabrication process for such waveguides along with simulation results from meep, a finite-difference time-domain tool. [Preview Abstract] |
Saturday, October 10, 2015 3:45PM - 5:00PM |
GP.00002: Spatial Localization and Variation in Defect-Related Electron Traps in GaN Materials Kevin Galiano, Darryl Gleason, Pran Krishna Paul, Zeng Zhang, Drew Cardwell, Brian McSkimming, James Speck, Aaron Arehart, Steven Ringel, Jonathan Pelz High frequency transistors based on GaN have important applications in a variety of technologies, but can degrade due to defects of unknown origin. In particular, a class of defects with energy near 0.57 eV below the conduction band has been correlated with GaN device degradation [A. Arehart et al., Solid-State Electronics (2013)], has been observed for a wide variety of growth and processing conditions, and has been suggested to be clustered around physical defects [Z-Q Fang et al., J. Phys.: Condens. Matter (2002)]. We have used nm-scale Deep Level Transient Spectroscopy (nano-DLTS) [D. Cardwell et al., A.P.L. (2013)] on n-type GaN Schottky diodes grown by ammonia molecular beam epitaxy to confirm that these defects are indeed localized to “hotspots” with a density comparable to that of threading dislocations. Furthermore, our local nano-DLTS measurements reveal for the first time modest but distinct differences in trap energy and emission rate between hotspots, indicating that local conditions influence trap parameters even within a particular device. Ongoing work is directed towards determining the identity of the localized defects responsible for these detrimental traps, and what causes the trap parameters to vary with position. [Preview Abstract] |
Saturday, October 10, 2015 3:45PM - 5:00PM |
GP.00003: Computational Study on the Dynamics and Structural Conversion of RfaH Jeevan GC, Bernard Gerstman, Prem Chapagain RfaH undergoes major structural rearrangements to perform multiple functions. The C-terminal domain (CTD) of RfaH showed that it can exist as either an $\alpha $-helix bundle when interacting with the N-terminal domain (NTD), or as a $\beta $-barrel conformation when it is not interacting with the NTD. They perform different functions in these states and hence are labeled as ``Transformer Proteins''. We investigate the full RfaH using a variety of all-atom Molecular Dynamics (MD) simulation techniques. We find that the CTD-NTD domain-domain interactions constitute the major barrier in the CTD $\alpha $-helix to $\beta $-barrel structural conversion. The structural transformation of the CTD is relatively easy after the detachment of inter domain interactions. We pointed out important amino acids residues that play especially important roles in controlling the inter-domain motions. [Preview Abstract] |
Saturday, October 10, 2015 3:45PM - 5:00PM |
GP.00004: Holography Fluorescence Microscopy Juan Gomez Velez, Yamil Nieves, Justine Dupere, Myung Kim, David Clark Digital holography is a fast-growing research field that has drawn increasing attention leading to a myriad of new technological applications due to its powerful three-dimensional (3D) imaging capacity. Previously, fluorescent microscopy has been limited by the need of coherent light sources or two dimensional scanning. Recent developments in digital holography, including self-interference incoherent digital holography (SIDH), provide highly versatile capabilities for 3D holographic imaging with incoherent light that can remove the barrier between fluorescence and holography. Current progress in fluorescence cell imaging is presented using an SIDH module attached to a hand built customized fluorescence microscope. The module does not employ the use of coherent light sources or scanning devices. Methods are proven to be effective through imaging of fluorescent beads and preliminary images of drosophila eggs. Future work will include holography fluorescence microscopy of cellular processes, such as mitosis and motility of cells tagged with fluorescent proteins. [Preview Abstract] |
Saturday, October 10, 2015 3:45PM - 5:00PM |
GP.00005: Hunt for the Mysterious Prion Self-Replicator Olga Harrington Amyloid diseases such as Alzheimer's disease and type II diabetes are characterized by the self-assembly of partially denatured proteins into micron-sized rigid fibrils. There is increasing evidence that amyloid diseases share important similarities with prion diseases, such as Mad Cow Disease. Our own laboratory has recently reported that metastable precursors of rigid fibrils, so called oligomers and protofibrils, can undergo self-replication from natively folded monomers. This is the in vitro hallmark of prion diseases. However, it remains a mystery how such prion particles are able to catalyze their self-replication. We are trying to gain insight into the structure of protofibrils formed by hen egg white lysozyme by testing the resistance of these aggregates to enzymatic digestion and analyzing which portions of the aggregates remain preserved. Using this process we want to accomplish two goals: First, we want to identify which portion of the original monomers form the (readily digestible) outer segments and which portions forms the stable core of these prion aggregates. In a second step, we will test whether the enzymatically ablated aggregates still retain their capacity for self-replication -- thereby providing important insights into the structure of the mysterious prion self-replicator. [Preview Abstract] |
Saturday, October 10, 2015 3:45PM - 5:00PM |
GP.00006: Shear Thickening fluids for Impact Resistant Materials Jehnae Linkins, Tulio Freitas, Norman Wagner Athletes are frequently vulnerable to high Impact accidents such as concussions or broken bones. We believe that protective equipment retrofitted with shear thickening fluids (STFs) have been proved to offer exceptional defense against ballistic and impact threats. It has been recommended to use the STF nanocomposites to expand the protection for athletes, specifically soccer players, from the high impact and pressures of opposing forces. The STF moves like a liquid until an object strikes or agitates it forcefully; then it hardens in a few milliseconds. If there is a sudden impact of energy overwhelms the repulsive forces between particles, forming masses called Hydro clusters. When the energy stops the particles repel each other again and the solid substances become a liquid again. The fluid is a colloid that is made up of tiny particles suspended in a liquid. The particles repel each other slightly, so they float easily through the liquid without clumping together or settling at the bottom. [Preview Abstract] |
Saturday, October 10, 2015 3:45PM - 5:00PM |
GP.00007: Magnetic Tunnel Junctions with W Layers. Brian Zamarrripa Roman, Hamid Almasi, Weigang Wang Magnetic Tunnel Junctions with Perpendicular Magnetic Anisotropy are promising candidates for next generation of magnetic random access memories. Room-temperature tunneling magnetoresistance behavior has been analyzed in CoFeB/MgO/CoFeB perpendicular magnetic tunnel junctions with different buffer layers for annealing at 340\textdegree C and 380\textdegree C. Transport properties have been studied in these junctions. The TMR rapidly increased to a maximum within the first few minutes, up to 135{\%}, followed by a steady decline afterwards. These results highlight the importance of proper buffer/capping layer in perpendicular tunneling junction. [Preview Abstract] |
Saturday, October 10, 2015 3:45PM - 5:00PM |
GP.00008: Investigation of the structural properties of Na$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{6}}$ and Li$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{4}}$ Larry E. Rush Jr., N.A.W. Holzwarth Li-ion batteries were proposed in the 1970's and are currently commercially produced globally for many technological purposes; however, recent studies have suggested that Na-ion conducting materials might be a feasible alternative that could have some advantages over Li-ion batteries. First principles simulations are used in this investigation to examine the structural and physical properties of Na$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{6}}$, a$_{\mathrm{\thinspace }}$Na-ion conductor, in comparison with its Li-ion conducting analog, Li$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{4}}$. Four model structures are considered including the $C$2\textit{/m\textasciitilde }structure recently reported by Kuhn and co-workers from their analysis of single crystals of Na$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{6}}$ (ZAAC, 640(5):689-692, April 2014), and three structures related to the $P$6$_{\mathrm{3}}$\textit{/mcm }structure with P site disorder found in 1982 by Mercier and co-workers from their analysis of single crystals of Li$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{4}}$ (JSSC, 43(2):151-162, July 1982). The computational results indicate that both Na$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{6}}$ and Li$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{4}}$ have the same disordered ground state structures consistent with the P6$_{\mathrm{3}}$/mcm space group, while the optimized $C$2$/m $structures are meta-stable by 0.1 eV and 0.4 eV per formula unit for Na$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{6\thinspace }}$and Li$_{\mathrm{4}}$P$_{\mathrm{2}}$S$_{\mathrm{4}}$, respectively. [Preview Abstract] |
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