Near-Extreme Black Holes and the Universal Relaxation Bound

A fundamental bound on the relaxation time \tau of a perturbed thermodynamical system has recently been derived, \tau \geq \hbar/\pi T, where $T$ is the system's temperature. We demonstrate analytically that black holes saturate this bound in the extremal limit and for large values of the azimuthal number m of the perturbation field.Comment: 2 Pages. Submitted to PRD on 5/12/200

Nanowire Acting as a Superconducting Quantum Interference Device

We present the results from an experimental study of the magneto-transport of superconducting wires of amorphous Indium-Oxide, having widths in the range 40 - 120 nm. We find that, below the superconducting transition temperature, the wires exhibit clear, reproducible, oscillations in their resistance as a function of magnetic field. The oscillations are reminiscent of those which underlie the operation of a superconducting quantum interference device.Comment: 4 pages, 4 figures, 1 tabl

Universality at integer quantum Hall transitions

We report in this paper results of experimental and theoretical studies of transitions between different integer quantum Hall phases, as well as transition between the insulating phase and quantum Hall phases at high magnetic fields. We focus mainly on universal properties of the transitions. We demonstrate that properly defined conductivity tensor is universal at the transitions. We also present numerical results of a non-interacting electron model, which suggest that the Thouless conductance is universal at integer quantum Hall transitions, just like the conductivity tensor. Finite temperature and system size effects near the transition point are also studied.Comment: 20 pages, 15 figure

REGRESSION MODELING USING PRINCIPAL COMPONENTS

In this paper we present a new stepwise method for selecting predictor variables in linear regression models and its application to agricultural data analysis. This method is an extension of principal component regression, and it consists of iteratively selecting original predictor variables one at a time from repeatedly selected subsets of principal components. The reasoning behind the method and its implementation are discussed, and an example of applying the method to agricultural data is given. The example also demonstrates the advantages of the proposed method over some known methods

Improving the reliability of model-based decision-making estimates in the two-stage decision task with reaction-times and drift-diffusion modeling

A well-established notion in cognitive neuroscience proposes that multiple brain systems contribute to choice behaviour. These include: (1) a model-free system that uses values cached from the outcome history of alternative actions, and (2) a model-based system that considers action outcomes and the transition structure of the environment. The widespread use of this distinction, across a range of applications, renders it important to index their distinct influences with high reliability. Here we consider the two-stage task, widely considered as a gold standard measure for the contribution of model-based and model-free systems to human choice. We tested the internal/temporal stability of measures from this task, including those estimated via an established computational model, as well as an extended model using drift-diffusion. Drift-diffusion modeling suggested that both choice in the first stage, and RTs in the second stage, are directly affected by a model-based/free trade-off parameter. Both parameter recovery and the stability of model-based estimates were poor but improved substantially when both choice and RT were used (compared to choice only), and when more trials (than conventionally used in research practice) were included in our analysis. The findings have implications for interpretation of past and future studies based on the use of the two-stage task, as well as for characterising the contribution of model-based processes to choice behaviour

The quantized Hall effect in the presence of resistance fluctuations

We present an experimental study of mesoscopic, two-dimensional electronic systems at high magnetic fields. Our samples, prepared from a low-mobility InGaAs/InAlAs wafer, exhibit reproducible, sample specific, resistance fluctuations. Focusing on the lowest Landau level we find that, while the diagonal resistivity displays strong fluctuations, the Hall resistivity is free of fluctuations and remains quantized at its $\nu=1$ value, $h/e^{2}$. This is true also in the insulating phase that terminates the quantum Hall series. These results extend the validity of the semicircle law of conductivity in the quantum Hall effect to the mesoscopic regime.Comment: Includes more data, changed discussio

Phase Diagram of Integer Quantum Hall Effect

The phase diagram of integer quantum Hall effect is numerically determined in the tight-binding model, which can account for overall features of recently obtained experimental phase diagram. In particular, the quantum Hall plateaus are terminated by two distinct insulating phases, characterized by the Hall resistance with classic and quantized values, respectively, which is also in good agreement with experiments.Comment: 4 pages, RevTex, 4 PostScript figures; one new figure is added; minor modifications in the tex

Baryogenesis from Unstable Domain Walls

There exists a class of cosmic strings that turn matter into antimatter (Alice strings). In a GUT where the unbroken gauge group contains charge conjugation ($C$), such strings form when a phase transition renders $C$ a discrete symmetry. They become boundaries of domain walls at a later, $C$-breaking transition. These `Alice walls' are cosmologically harmless, but can play an important role in baryogenesis. We present a three-generation toy model with scalar baryons, where a quasi-static Alice wall (or a gas of such walls) temporarily gives rise to net baryogenesis of uniform sign everywhere in space. This becomes a permanent baryon excess if the wall shrinks away early enough. We comment on the possible relevance of a similar mechanism to baryogenesis in a realistic \soten unification model, where Alice walls would form at the scale of left-right symmetry breaking.Comment: SLAC-PUB-5828, May 92. 28 pp. Seven figures (not included). Use PHYZZ