Bulletin of the American Physical Society
2017 Annual Spring Meeting of the APS Ohio-Region Section
Volume 62, Number 6
Friday–Saturday, May 5–6, 2017; Ypsilanti, Michigan
Session D3: Contributed: Condensed Matter, Soft Matter, and Chemical Physics |
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Chair: Natthi Sharma, Eastern Michigan University Room: Pray-Harrold 303 |
Saturday, May 6, 2017 8:36AM - 8:48AM |
D3.00001: Instability of Non-Ergodic Effects in Anharmonic Atomic Chains: Singular Dependence Christopher Watenpool, Donald Priour We use large scale molecular dynamics simulations to calculate equilibration times in anharmonic chains, with the anharmonicity being a quartic term in the interaction potential. In the latter case, where the system is thermally insulated from its environment, equilibration via internal dynamics is hampered, characterized by non-ergodic effects such as long term oscillations. We relax the isolation, allowing the ends of the chain to couple to external heat baths (implemented with the Langevin technique). In our calculations we quantify equilibration times using the decay exponents of the energy stored in the fundamental mode or the attainment of a specified threshold in a measure of mode engagement, finding in the thermodynamic limit a scaling form $\tau = A N^{\eta}$ with $\eta$ being a scaling exponent. Whether the anharmonicity is weak or strong, we find equilibration to be significantly hastened by the heat bath coupling. Moreover, we find singular behavior, in the sense that any finite coupling to the terminal heat baths leads not only to the same scaling exponent $\tau$, but also the same pre-factor $A$. Since a system realized in the experiment would be difficult to fully isolate suggesting that non-ergodic effects may be difficult to observe in practice in bulk systems. [Preview Abstract] |
Saturday, May 6, 2017 8:48AM - 9:00AM |
D3.00002: Superconducting behavior in the ZrNi$_{\mathrm{2}}$Ga$_{\mathrm{1-}}_{x}$In$_{x}$ system Alex Reigle, Adam Eggert, Yuliang Guo, Tyler Jamison, Scott Lee, Kelly Mason, Jessica Slattery, Vinoin Vincely, Darren Wong, Tiago Schaeffer, Saad Alzahrani, Jeffrey Brock, Mahmud Khan From both fundamental and applied viewpoints, the phenomenon of superconductivity remains an active research area. Here, we present an experimental study of the intermetallic ZrNi$_{\mathrm{2}}$Ga$_{\mathrm{1-}}_{x}$In$_{x}$ (0 $\le x\le $ 0.2) Heusler alloy system by means of X-ray diffraction, magnetization, and electrical resistivity measurements. At room temperature, the alloys were found to crystallize in the L2$_{\mathrm{1}}$ cubic Heusler structure. The magnetization and electrical resistivity as a function of temperature measurements revealed that all samples exhibit superconductivity at low temperatures despite the fact that the compounds contain ferromagnetic elements. The critical temperature decreases with In concentration, from 2.5 K ($x=$ 0) to less than 1.75 K ($x=$ 0.2). Additionally, magnetization as a function of applied magnetic field curves collected in the superconducting state exhibit behavior indicative of type-II superconductors. The experimental results and possible explanations as to mechanisms by which In impacts the superconducting properties will be discussed. [Preview Abstract] |
Saturday, May 6, 2017 9:00AM - 9:12AM |
D3.00003: A comparison of methods for the determination of the magnetocrystalline anisotropy constant in Fe$_3$O$_4$ nanoparticles Ronald Tackett, Megan Allyn, Gillian Ryan, Ronald Kumon, Cornel Rablau, Vijayendra Garg, Aderbal de Oliveira, Prev Vaishnava The dynamics of the relaxation behavior of superparamagnetic nanoparticles is governed by many factors such as the anisotropy constant, composition, size and nature of coating of the nanoparticles particles. We report values of the anisotropy constant ($K$) for magnetite nanoparticle (size $\sim$12 nm) coated with dextran and suspended in water by dc and ac magnetization measurements, Mössbauer spectroscopy and the temperature dependent specific absorption rate (SAR) measurement. The magnetite nanoparticles were synthesized by co-precipitation and characterized by x-ray diffraction (XRD) and Transmission electron microscopy (TEM). The $K$ values from dc magnetic susceptibility, M\"{o}ssbauer spectroscopy, ac magnetic susceptibility, and that obtained by temperature dependent SAR measurements are all within the range of the accepted values in the literature. Merits and demerits of the four methods of determining $K$ values will be discussed. We will also report on the temperature dependence of the anisotropy constant and the N\'{e}el relaxation constant. [Preview Abstract] |
Saturday, May 6, 2017 9:12AM - 9:24AM |
D3.00004: The Role of Actin Trails in Mediating Bulk Axonal Actin Transport Nilaj Chakrabarty, Archan Ganguly, Subhojit Roy, Peter Jung Actin is one of the key constituents of the neuronal cytoskeleton and is responsible for driving important cellular processes like axon elongation. Axonal actin is synthesized in the cell body and transported at rates of 0.25 $-$ 3 mm/day, as shown by in-vivo pulse-chase radiolabeling studies. However, the underlying transport mechanisms are unknown. Recent experiments in cultured neurons have revealed a dynamic network of metastable actin filaments (``actin trails''). Actin trails seem to originate from focal actin ``hotspots'' which colocalize with stationary endosomes. Interestingly, the number of actin trails extending anterogradely is higher than the ones extending retrogradely. We hypothesize that the bulk axonal transport of actin originates from this directional asymmetry of the number of actin trails. To test this, we constructed a computational model of actin trail growth and simulated the pulse-chase experiment. In our model, local, metastable trails, which grow with their barbed ends anchored to the hotspots, drive the bulk anterograde transport. Our results indicate that the observed bias of the nucleation probabilities and the elongation rate of actin trails are sufficient to drive the bulk transport of actin at rates that agree with in-vivo pulse chase experiments. [Preview Abstract] |
Saturday, May 6, 2017 9:24AM - 9:36AM |
D3.00005: Monitoring the flash-freezing of super-cooled water droplets using high speed imaging and temperature measurement Hok Wai Chang, Khalid Eid The freezing of water droplets on surfaces is relevant to many technological applications and has a rich behavior. We will present a systematic study of the super-cooling and flash freezing processes of individual water droplets. High speed imaging and rapid temperature measurements are used to compare and contrast that with the normal cooling and freezing of the same droplets. Water droplets can be `super-cooled' to a few degrees below freezing without changing to the solid phase. Once an initial ice micro-crystal forms, it spreads to the outer parts of the droplet within a few milliseconds, while the inside of the droplet remains in the liquid form. The latent heat released causes the temperature of the liquid part to rise to 0 $^{\mathrm{o}}$C instantly. The rest of the droplet then freezes gradually and the droplet takes a peculiar dome shape with a spike at the top. The role of droplet contact angle and surface roughness in this behavior will be discussed. [Preview Abstract] |
Saturday, May 6, 2017 9:36AM - 9:48AM |
D3.00006: Interplay of electric fields and strain effects on charge transport through DNA molecules Yong Joe, Eric Hedin, Sadeq Malakooti The combination of electric field effect and small mechanical strain perturbations is studied in the electron transport calculations of the poly(G)-poly(C) double-stranded (ds) DNA molecular electronic structure. We use an advanced two-dimensional tight-binding model including hopping integrals of the next nearest-neighbors and the implementation of strain-dependent DNA helix conformation in conjunction with the theories of Slater-Koster and linear elasticity. Determining on-site energies of each base and coupling parameters based on these effects, the transport properties of a 30 base-pair ds-DNA molecule tilted with respect to the inter-contact electric field direction with a mechanical strain are investigated. Specifically, we present single electron transmission spectra and current-voltage characteristics as functions of electron energy and source-drain voltage for both selected tilted angles and percentage strains. [Preview Abstract] |
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