284,516 research outputs found
Signature of a Pairing Transition in the Heat Capacity of Finite Nuclei
The heat capacity of iron isotopes is calculated within the interacting shell
model using the complete -shell. We identify a signature of the
pairing transition in the heat capacity that is correlated with the suppression
of the number of spin-zero neutron pairs as the temperature increases. Our
results are obtained by a novel method that significantly reduces the
statistical errors in the heat capacity calculated by the shell model Monte
Carlo approach. The Monte Carlo results are compared with finite-temperature
Fermi gas and BCS calculations.Comment: 14 pages, 4 eps figures included, RevTe
Robust Η∞Control for a Class of Discrete Time-Delay Stochastic Systems with Randomly Occurring Nonlinearities
Copyright © 2014 Yamin Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.In this paper, we consider the robust Η∞ control problem for a class of discrete time-delay stochastic systems with randomly occurring nonlinearities. The parameter uncertainties enter all the system matrices; the stochastic disturbances are both state and control dependent, and the randomly occurring nonlinearities obey the sector boundedness conditions. The purpose of the problem addressed is to design a state feedback controller such that, for all admissible uncertainties, nonlinearities, and time delays, the closed-loop system is robustly asymptotically stable in the mean square, and a prescribed Η∞ disturbance rejection attenuation level is also guaranteed. By using the Lyapunov stability theory and stochastic analysis tools, a linear matrix inequality (LMI) approach is developed to derive sufficient conditions ensuring the existence of the desired controllers, where the conditions are dependent on the lower and upper bounds of the time-varying delays. The explicit parameterization of the desired controller gains is also given. Finally, a numerical example is exploited to show the usefulness of the results obtained.This work was supported in part by the National Natural Science Foundation of China under Grants 61374010,
61074129, and 61175111, the Natural Science Foundation of Jiangsu Province of China under Grant BK2012682, the Qing Lan Project of Jiangsu Province (2010), the 333 Project of Jiangsu Province (2011), and the Six Talents Peak Project of Jiangsu Province (2012)
Disorder effects on the spin-Hall current in a diffusive Rashba two-dimensional heavy-hole system
We investigate the spin-Hall effect in a two-dimensional heavy-hole system
with Rashba spin-orbit coupling using a nonequilibrium Green's function
approach. Both the short- and long-range disorder scatterings are considered in
the self-consistent Born approximation. We find that, in the case of long-range
collisions, the disorder-mediated process leads to an enhancement of the
spin-Hall current at high heavy-hole density, whereas for short-range
scatterings it gives a vanishing contribution. This result suggests that the
recently observed spin-Hall effect in experiment is a result of the sum of the
intrinsic and disorder-mediated contributions. We have also calculated the
temperature dependence of spin-Hall conductivity, which reveals a decrease with
increasing the temperature.Comment: 5 pages, 2 figures, Typos in the values of hole density correcte
Level Densities by Particle-Number Reprojection Monte Carlo Methods
A particle-number reprojection method is applied in the framework of the
shell model Monte Carlo approach to calculate level densities for a family of
nuclei using Monte Carlo sampling for a single nucleus. In particular we can
also calculate level densities of odd-even and odd-odd nuclei despite a new
sign problem introduced by the projection on an odd number of particles. The
method is applied to level densities in the iron region using the complete
-shell. The single-particle level density parameter and the
backshift parameter are extracted by fitting the microscopically
calculated level densities to the backshifted Bethe formula. We find good
agreement with experimental level densities with no adjustable parameters in
the microscopic calculations. The parameter is found to vary smoothly with
mass and does not show odd-even effects. The calculated backshift parameter
displays an odd-even staggering effect versus mass and is in better
agreement with the experimental data than are the empirical values.Comment: To be published in the proceedings of the Tenth International
Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, S. Wender,
ed., AIP Conference Proceedings (2000
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