Bulletin of the American Physical Society
2011 Fall Meeting of the APS Ohio-Region Section
Volume 56, Number 8
Friday–Saturday, October 14–15, 2011; Muncie, Indiana
Session EB: Biophysics, Chemcial Physics and Physics Education |
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Chair: Mahfuza Khatun, Ball State University Room: Cooper Science CP187 |
Saturday, October 15, 2011 8:30AM - 8:42AM |
EB.00001: Fault Tolerant Characteristics in Quantum-dot Cellular Automata Devices Mahfuza Khatun, Benjamin Padgett We present analytical results of fault tolerant properties of various quantum-dot cellular automata (QCA) devices. In any electronic computation device such as a computer, one needs digital signals for computation. In this model, the binary numbers are encoded from charge configurations in quantum dots. Data transfer, signal flow, and computations can be performed by electron polarization in the nanostructure. Our main focus is to investigate the functionality of a QCA device by studying the thermal and manufacturing defects. A Hubbard-type Hamiltonian and Inter-cellular Hartree approximation have been used for modeling, and a uniform random distribution has been implemented for the defect simulations. Simple devices such as quantum wire, logical gates, inverter, cross-over, XOR, and Full Adder will be discussed. Results show fault tolerance of a device is strongly dependent on the temperatures as well as on the manufacturing defects. [Preview Abstract] |
Saturday, October 15, 2011 8:42AM - 8:54AM |
EB.00002: A Perturbation Solution Of The Mechanical Bidomain Model Vanessa Punal, Brad Roth This research focuses on finding analytical solutions to the mechanical bidomain model of cardiac tissue. In particular, a perturbation expansion is used to analyze the equations, with the perturbation parameter being inversely proportional to the spring constant coupling the intracellular and extracellular spaces. The results indicate that the intracellular and extracellular pressures are not equal, and that the two spaces move relative to each other. This calculation is complicated enough to illustrate the implications of the mechanical bidomain model, but is nevertheless simple enough to solve analytically. The zeroth-order of the perturbation expansion reveals that the intracellular and extracellular displacements are equal, thus making it unnecessary to account for either space on an individual basis. Yet, in the first-order of the expansion we see a shift and the intracellular and extracellular displacements are unequal. One application of the calculation is to the mechanical behavior of active cardiac tissue surrounding an ischemic region. Also, a hypothesis for the physical meaning of the pressure inequality is if this inequality is held for an extended period of time it may cause fluid to flow across the cell membrane and in the tissue. [Preview Abstract] |
Saturday, October 15, 2011 8:54AM - 9:06AM |
EB.00003: Complete Phase Diagram of a Single Polymer Chain Mark Taylor, Wolfgang Paul, Kurt Binder The phase behavior of a single homopolymer chain is analogous to that of simple liquid, exhibiting an expanded coil (gas-like) phase, a collapsed globule (liquid-like) phase, and a compact solid phase. Using Wang-Landau sampling with bond-rebridging Monte Carlo moves we have studied the complete phase behavior of a flexible interaction-site polymer chain comprised of up to 256 square-well-spheres [1]. Here we present a finite-size scaling analysis for the phase behavior of a SW chain in the long chain limit. For a sufficiently short interaction range, the chain undergoes a direct freezing transition from the expanded coil without an intervening collapse transition. These results confirm the recent lattice model prediction that a collapsed-globule state is unstable with respect to a solid phase for polymers with sufficiently short-range monomer-monomer interactions [2]. \\[4pt] [1] M.P. Taylor, W. Paul, and K. Binder, J. Chem. Phys. 131, 114907 (2009).\\[0pt] [2] W. Paul, T. Strauch, F. Rampf, and K. Binder, Phys. Rev. E 75, 060801(R) (2007). [Preview Abstract] |
Saturday, October 15, 2011 9:06AM - 9:18AM |
EB.00004: Non-Adiabatic Atomic Transitions: Computational Cross Section Calculations of Alkali Metal - Noble Gas Collisions David Weeks, Charlton Lewis Optically pumped alkali lasers operate by first exciting an alkali atom from the ground $^{2}$S$_{1/2}$ state into the $^{2}$P$_{3/2}$ excited state. The alkali atom will then undergo a non-adiabatic fine structure transition from the $^{2}$P$_{3/2}$ state to the $^{2}$P$_{1/2}$ state. This establishes a population inversion between the $^{2}$P$_{1/2}$ excited state and the $^{2}$S$_{1/2}$ ground state required for the system to lase. In this type of laser, the working medium consists of alkali atoms at a fairly low partial pressure together with a buffer of noble gas atoms at a higher partial pressure. For potassium and rubidium, collisions with the noble gas atoms can cause the alkali atom to undergo fine structure transitions at a sufficiently high rate to lase. Scattering cross sections for the non-adiabatic fine structure transition between M + Ng pairs are therefore of interest and are computed for M + Ng pairs where M = K, Rb, Cs, and Ng = He, Ne, Ar. The calculations are performed with time dependent wave packet methods to first compute scattering matrix elements. A sum over scattering matrix elements for values of angular momentum J ranging from 1/2 to 501/2 is then used to compute associated fine structure cross sections. Theoretical cross sections are compared to experimental results where possible. [Preview Abstract] |
Saturday, October 15, 2011 9:18AM - 9:30AM |
EB.00005: Revisiting the GGA in density functional theory: Laplacian-based models for the exchange-correlation energy Antonio C. Cancio, Christopher E. Wagner We report recent work in developing a GGA-level density functional theory using primarily the Laplacian of the density $\nabla^2 n$ as an input beyond the LDA. Our starting point and motivation is a model fit to the exchange-correlation energy density of the valence shell of the Si crystal and other systems, as calculated by quantum Monte Carlo simulations, which show a strong, roughly linear dependence of this quantity on the Laplacian. The model respects the Lieb-Oxford bound for large positive Laplacian but suffers from a pole at negative values, such as exist near an atomic nucleus. A better treatment of $\nabla^2 n$ in this limit can be used to construct an all-electron extension of our model, and as an added benefit, avoid the singularity in the Kohn-Sham potential that gradient-based models suffer due to the cusp in electron density at the nucleus. We develop and test out an optimization method to minimize unwanted oscillations in the potential that can be a hazard with DFT's that use the Laplacian. [Preview Abstract] |
Saturday, October 15, 2011 9:30AM - 9:42AM |
EB.00006: Controlled Quantized Conductance Steps Using a Simple Mechanical System: An Undergraduate Lab Experiment Christopher Burnett, Robert Tolley, Antony Silvidi, Khalid Eid We demonstrate clear quantized conductance steps in mechanical break junctions (MBJ) based on a gold wire, a springy-steel bending beam, a micrometer, a 1.5V battery , and a Teflon disc that we rotate manually. The voltage across the wire is measured using a NI-DAQ assistant unit and a simple LabVIEW program. As the wire is stretched, its resistance (i.e. voltage across it) increases gradually then follows a stair-case- like shape, which is a hallmark of quantized conductance, with steps at values of 25.8 k$\Omega $/2n, where n is an integer. The resistance jumps are clearer and more distinct for smaller n and become closer for larger n, which is a demonstration of the Correspondence Principle. The quantization occurs when the wire is thin enough that its diameter is comparable to the de Broglie wave length of the current-carrying electrons and is a direct consequence of confinement. This experiment is designed for sophomore/junior level undergraduate labs. [Preview Abstract] |
Saturday, October 15, 2011 9:42AM - 9:54AM |
EB.00007: The Human Mind As General Problem Solver Henry Gurr Since leaving U Cal Irvine Neutrino Research, I have been a University Physics Teacher, and an Informal Researcher Of Human Functionality. My talk will share what I discovered about the best ways to learn, many of which are regularities that are to be expected from the Neuronal Network Properties announced in the publications of physicist John Joseph Hopfield. Hopfield's Model of mammalian brain-body, provides solid instructive understanding of how best Learn, Solve Problems, Live! With it we understand many otherwise puzzling features of our intellect! Examples Why 1) Analogies and metaphors powerful in class instruction, ditto poems. 2) Best learning done in physical (Hands-On) situations with tight immediate dynamical feedback such as seen in learning to ride bike, drive car, speak language, etc. 3) Some of the best learning happens in seeming random exploration, bump around, trial and error. 4) Scientific discoveries happen, with no apparent effort, at odd moments. 5) Important discoveries DEPEND on considerable frustrating effort, then Flash of Insight AHA EURIKA. [Preview Abstract] |
Saturday, October 15, 2011 9:54AM - 10:06AM |
EB.00008: Communicating science to students and the public Gordon Aubrecht Unless something is done, millennium-length consequences of the greenhouse gases we have already released will cause harm to the planet. Groups of people supported by political forces and money have decided that denial of scientific data is not only reasonable, but a moral force that opposes that of stewardship. I characterize these people as ``denialists,'' to distinguish them from true skeptics, scientists who must be skeptical to do their work. Denialists have succored the people who just want the problem to go away by sowing doubt about scientific integrity and distorting the meaning of scientific uncertainty. How scientists can change the framing of the issue and how individual scientists can influence the public through rea soning with fellow citizens and writing letters to their local papers countering misinformation is the focus of this work. [Preview Abstract] |
Saturday, October 15, 2011 10:06AM - 10:18AM |
EB.00009: Nine reasons to have confidence in anthropogenic climate change Gordon Aubrecht We present reasons supporting confidence that humans are responsible for climate change. [Preview Abstract] |
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