A physical limitation of the Wigner "distribution" function in transport

We present an example revealing that the sign of the "momentum" $P$ of the Wigner "distribution" function $f(q, P)$ is not necessarily associated with the direction of motion in the real world. This aspect, which is not related to the well known limitation of the Wigner function that traces back to the Heisenberg's uncertainty principle, is particularly relevant in transport studies, wherein it is helpful to distinguish between electrons flowing from electrodes into devices and vice versa

Phase space formalisms of quantum mechanics with singular kernel

The equivalence of the Rivier-Margenau-Hill and Born-Jordan-Shankara phase space formalisms to the conventional operator approach of quantum mechanics is demonstrated. It is shown that in spite of the presence of singular kernels the mappings relating phase space functions and operators back and forth are possible.Comment: 15 pages, no figures, LATE

Spin tunneling through an indirect barrier

Spin-dependent tunneling through an indirect bandgap barrier like the GaAs/AlAs/GaAs heterostructure along [001] direction is studied by the tight-binding method. The tunneling is characterized by the proportionality of the Dresselhaus Hamiltonians at $\Gamma$ and $X$ points in the barrier and by Fano resonances. The present results suggest that large spin polarization can be obtained for energy windows that exceed significantly the spin splitting. We also formulate two conditions that are necessary for the existence of energy windows with large polarization.Comment: 19 pages, 7 figure

Charging effects in the ac conductance of a double barrier resonant tunneling structure

There have been many studies of the linear response ac conductance of a double barrier resonant tunneling structure (DBRTS). While these studies are important, they fail to self-consistently include the effect of time dependent charge density in the well. In this paper, we calculate the ac conductance by including the effect of time dependent charge density in the well in a self-consistent manner. The charge density in the well contributes to both the flow of displacement currents and the time dependent potential in the well. We find that including these effects can make a significant difference to the ac conductance and the total ac current is not equal to the average of non-selfconsitently calculated conduction currents in the two contacts, an often made assumption. This is illustrated by comparing the results obtained with and without the effect of the time dependent charge density included properly

Predicting Weight Loss in Post Surgical Laparoscopic Banding Patients

The present study was a retrospective chart review (N=128) that investigated the efficacy of profiles derived from the three factors of the Eating Inventory® test (EI) - cognitive restraint, disinhibition, and hunger - to predict successful weight loss in post surgical laparoscopic banding patients at 6 and 9 months post surgery. Although the EI is commonly used in bariatric presurgical assessment, few studies have found consistent relationships between presurgical factor scores and subsequent weight loss in this population. Based on restraint theory, 7 profiles (high CR, super high CR, high D, super high D, high H, super high H, and null) were derived from the raw scores on the subscales of the EI and tested for weight loss predictive ability using direct logistic regression. Results were mixed with high CR, super high CR, and null profiles accurately predicting successful weight loss. Raw scores on the three factors (cognitive restraint, disinhibition, and hunger) were tested individually for predictive ability using direct logistic regression. Overall results indicated that the profile model accurately predicted more cases than the general factor model. This study significantly contributes to both the bariatric presurgical assessment literature and the restraint theory literature. Suggestions for future research are offered

Effect of the Coulomb repulsion on the {\it ac} transport through a quantum dot

We calculate in a linear response the admittance of a quantum dot out of equilibrium. The interaction between two electrons with opposite spins simultaneously residing on the resonant level is modeled by an Anderson Hamiltonian. The electron correlations lead to the appearence of a new feature in the frequency dependence of the conductance. For certain parameter values there are two crossover frequencies between a capacitive and an inductive behavior of the imaginary part of the admittance. The experimental implications of the obtained results are briefly discussed.Comment: 13 pages, REVTEX 3.0, 2 .ps figures from [email protected], NUB-308