Frequency scaling of photo-induced tunneling

The DC current-voltage characteristics, induced by a driving electric field with frequency Omega, of a one dimensional electron channel with a tunnel barrier is calculated. Electron-electron interaction of finite-range is taken into account. For intermediate interaction strengths, the non-linear differential conductance shows cusp-like minima at bias voltages integer multiples of hbar Omega / e that are a consequence of the finite non-zero range of the interaction but are independent of the shape of the driving electric field. However, the frequency-scaling of the photo-induced current shows a cross-over between Omega^{-1} and Omega^{-2}, and depends on the spatial shape of the driving field and the range of the interaction.Comment: 7 pages, EURO-TeX, 3 figures, to appear in Europhysics Letter

Comparing Behavioural Models Using Data from Experimental Centipede Games

The centipede game posits one of the most well-known paradoxes of backward induction in the literature of experimental game theory. Given that deviations from the unique subgame perfect Nash equilibrium generates a Pareto improvement, several theoretical models have been employed in order to rationalize this kind of behavior in this social dilemma. The available explanations range from social preferences including fairness, altruism or cooperation motives, errors in playing, inability to perform backward induction or different depths of reasoning. In the present study, we use the Blavatskyy's theoretical contribution, and relax the assumptions of Expected Utility maximization and risk-neutral attitudes, to test an alternative explanation. We compare various probabilistic decision theory models in terms of their descriptive (in-sample) and predictive (out-of-sample fit) performance, using data from experimental centipede games. We find that introducing non-Expected Utility preferences to the Quantal Response Equilibrium model, along with a nonlinear utility function, provides a better explanation compared to alternative specifications such as the Level-k or the Quantal Response Equilibrium model with altruistic motives. (JEL C72, C92, D81, D82)

Heart Rate Response during Treadmill Running in Adidas _1 DLX Computerized Running Shoes at Various Shoe Settings

Advisor: David S. SenchinaBACKGROUND: Runners encounter a wide variety of terrains of varying hardness which can be modified by midsole cushioning. Cushioned shoes are recommended for athletes to decrease impact forces. The adidas_1 DLXTM shoe is advertised as being able to provide appropriate cushioning levels for different athletes on different terrains. PURPOSE: The purpose of the experiment was to investigate the effects of a commercially available computerized running shoe (adidas_l DLXTM) on heart rate and feelings of foot comfort. The data collected will be used to validate or refute some of the manufacturer's claims, and make recommendations to consumers about these types of shoes. HYPOTHESES: We hypothesized that the different settings on the adidas_l DLXTM shoe would influence heart rate and subjective foot comfort ratings. METHODS: Nine males (23 ± 3.6 yrs) ran 4 10-minute trials on a treadmill at a fixed speed, once in their own self-selected shoes and three times in the adidas_1 DLXTM shoes at automatic, manual hard, or manual soft settings. Heart rate was measured at 5, 7.5, and 10 minutes. Foot comfort was measured immediately after each trial. RESULTS: Shoe comfort ratings for all adidas_1 DLXTM settings were approximately 30% lower compared to self-selected shoes. There was no statistically-significant difference in heart rate between the trials. CONCLUSIONS: Mid-sole cushioning influences the comfort felt by runners. The data showed no significant relationship between mid-sole cushioning and heart rate, but did show that runners felt more comfortable in their own self-selected shoes versus the adidas_1 DLXTM shoes at any setting.Drake University, College of Arts and Sciences, Department of Biology and Biology Biochemistry, Cell and Molecular Biology Progra

Terahertz phase slips in striped La_2−xBa_xCuO₄

Interlayer transport in high-TC cuprates is mediated by superconducting tunneling across the CuO2 planes. For this reason, the terahertz frequency optical response is dominated by one or more Josephson plasma resonances and becomes highly nonlinear at fields for which the tunneling supercurrents approach their critical value IC. These large terahertz nonlinearities are in fact a hallmark of superconducting transport. Surprisingly, however, they have been documented in La2−xBaxCuO4 (LBCO) also above TC for doping values near x=1/8 and interpreted as an indication of superfluidity in the stripe phase. Here, electric-field-induced second harmonic is used to study the dynamics of time-dependent interlayer voltages when LBCO is driven with large-amplitude terahertz pulses, in search of other characteristic signatures of Josephson tunneling in the normal state. We show that this method is sensitive to the voltage anomalies associated with 2π Josephson phase slips, which near x=18 are observed both below and above TC. These results document a regime of nonlinear transport that shares features of fluctuating stripes and superconducting phase dynamics

Application of Volcano Plots in Analyses of mRNA Differential Expressions with Microarrays

Volcano plot displays unstandardized signal (e.g. log-fold-change) against noise-adjusted/standardized signal (e.g. t-statistic or -log10(p-value) from the t test). We review the basic and an interactive use of the volcano plot, and its crucial role in understanding the regularized t-statistic. The joint filtering gene selection criterion based on regularized statistics has a curved discriminant line in the volcano plot, as compared to the two perpendicular lines for the "double filtering" criterion. This review attempts to provide an unifying framework for discussions on alternative measures of differential expression, improved methods for estimating variance, and visual display of a microarray analysis result. We also discuss the possibility to apply volcano plots to other fields beyond microarray.Comment: 8 figure

Unusually large polarizabilities and "new" atomic states in Ba

Electric polarizabilities of four low-J even-parity states and three low-J odd-parity states of atomic barium in the range $35,600$ to $36,000\ $cm$^{-1}$are investigated. The states of interest are excited (in an atomic beam) via an intermediate odd-parity state with a sequence of two laser pulses. The odd-parity states can be excited due to the Stark-induced mixing with even-parity states. The polarizabilities are measured via direct spectroscopy on the second-stage transition. Several states have tensor and scalar polarizabilities that exceed the values that might be expected from the known energy levels of barium by more than two orders of magnitude. Two of the Stark-induced transitions cannot be identified from the known energy spectrum of barium. The observations suggest the existence of as yet unidentified odd-parity energy states, whose energies and angular momenta are determined in the present experiment. A tentative identification of these states as [Xe]$6s8p ^3P_{0,2}$ is suggested.Comment: 29 pages, 12 figure

The modelling cycle for collective animal behaviour

Collective animal behaviour is the study of how interactions between individuals produce group level patterns, and why these interactions have evolved. This study has proved itself uniquely interdisciplinary, involving physicists, mathematicians, engineers as well as biologists. Almost all experimental work in this area is related directly or indirectly to mathematical models, with regular movement back and forth between models, experimental data and statistical fitting. In this paper, we describe how the modelling cycle works in the study of collective animal behaviour. We classify studies as addressing questions at different levels or linking different levels, i.e. as local, local to global, global to local or global. We also describe three distinct approaches—theory-driven, data-driven and model selection—to these questions. We show, with reference to our own research on species across different taxa, how we move between these different levels of description and how these various approaches can be applied to link levels together