Stability analysis of multiple nonequilibrium fixed points in self-consistent electron transport calculations

We present a method to perform stability analysis of nonequilibrium fixed points appearing in self-consistent electron transport calculations. The nonequilibrium fixed points are given by the self-consistent solution of stationary, nonlinear kinetic equation for single-particle density matrix. We obtain the stability matrix by linearizing the kinetic equation around the fixed points and analyze the real part of its spectrum to assess the asymptotic time behavior of the fixed points. We derive expressions for the stability matrices within Hartree-Fock and linear response adiabatic time-dependent density functional theory. The stability analysis of multiple fixed points is performed within the nonequilibrium Hartree-Fock approximation for the electron transport through a molecule with a spin-degenerate single level with local Coulomb interaction

Calculations of canonical averages from the grand canonical ensemble

Grand canonical and canonical ensembles become equivalent in the thermodynamic limit, but when the system size is finite the results obtained in the two ensembles deviate from each other. In many important cases, the canonical ensemble provides an appropriate physical description but it is often much easier to perform the calculations in the corresponding grand canonical ensemble. We present a method to compute averages in canonical ensemble based on calculations of the expectation values in grand canonical ensemble. The number of particles, which is fixed in the canonical ensemble, is not necessarily the same as the average number of particles in the grand canonical ensemble

Kramers problem for nonequilibrium current-induced chemical reactions

We discuss the use of tunneling electron current to control and catalyze chemical reactions. Assuming the separation of time scales for electronic and nuclear dynamics we employ the Langevin equation for the reaction coordinate. The Langevin equation contains current-induced forces and is used to define nonequilibrium, effective potential energy surface for current-carrying molecular systems. The current-induced forces are computed via Keldysh nonequilibrium Green's functions. Once the nonequilibrium, current-depended potential energy surface is defined, the chemical reaction is modeled as an escape of a Brownian particle from the potential well. We demonstrate that the barrier between the reactant and the product states can be controlled by the bias voltage. When the molecule is asymmetrically coupled to the electrodes, the reaction can be catalyzed or stopped depending on the polarity of the tunneling current.Comment: 4 pages, 2 figure

Second-order post-Hartree-Fock perturbation theory for the electron current

Based on the super-fermion representation of quantum kinetic equations we develop nonequilibrium, post-Hartree-Fock many-body perturbation theory for the current through a region of interacting electrons. We apply the theory to out of equilibrium Anderson model and discuss practical implementation of the approach. Our calculations show that nonequilibrium electronic correlations may produce significant quantitative and qualitative corrections to mean-field electronic transport properties. We find that the nonequilibrium leads to enhancement of electronic correlations

Coupled elastic membranes model for quantum heat transport in semiconductor nanowires

Presented here is a nanowire model, consisting of coupled elastic membranes with the purpose of investigating thermal transport in quasi-one-dimensional quantum systems. The vibrations of each elastic membrane are quantized and the flow of the vibrational energy between adjacent membranes is allowed. The ends of the nanowire are attached to thermal baths held at different temperatures. We derived quantum master equation for energy flow across the nanowire and obtained thermal currents and other key observables. We study the effects of a disordered boundary on the thermal current by randomizing the membrane radii. We evaluate the model as a nanowire analogue as well as study the effects of a disordered boundary on thermal conductivity. The calculations show that the membrane lattice model demonstrates diameter phonon confinement and a severe reduction in thermal conductivity due to surface roughness which is characteristic of semiconductor nanowires. The surface roughness also produces a length dependence of the thermal conductivity of the form $\kappa=\alpha L^{\beta}$, with $\beta$ dependent on disorder characteristics, in the otherwise ballistic regime. Finally, the parameters of the model are fitted to available experimental data for silicon nanowires and the results of the calculations are assessed against the experimental data.Comment: 12 Pages, 10 Figure

Gunn diodes and devices (bibliography for 1978-1980)

A listing of about 500 works from Soviet and foreign scientific literature on Gunn diodes and devices based on them is presented. The bibliography includes publications in which various questions pertinent to all (or several) types of semiconductor instruments in the superhigh frequency range are mentioned. A subject index is included

Thermal Bogoliubov transformation in nuclear structure theory

Thermal Bogoliubov transformation is an essential ingredient of the thermo field dynamics -- the real time formalism in quantum field and many-body theories at finite temperatures developed by H. Umezawa and coworkers. The approach to study properties of hot nuclei which is based on the extension of the well-known Quasiparticle-Phonon Model to finite temperatures employing the TFD formalism is presented. A distinctive feature of the QPM-TFD combination is a possibility to go beyond the standard approximations like the thermal Hartree-Fock or the thermal RPA ones.Comment: 8 pages, Proceedings of the International Bogolyubov Conference "Problems of Theoretical and Mathematical Physics", August 23 -- 27, 2009, Dubna, Russi

THE ISSUES OF ONLINE REPUTATION MANAGEMENT

The increased availability of communication technologies has caused people to use the Internet to form their opinion on products and services more often. Company's reputation remains an important resource that can provide a competitive advantage, but the current information environment specificity forces us to rethink the approaches to reputation management. Сurrent specificity has conditioned by the threats concerning spontaneous information spread in the Internet, as well as the need to develop the methods of exploiting new information dissemination channels. Under these circumstances, a new competitive struggle principle has formed: «If you win in the In-ternet, you win in real life». To win, one just needs to possess the necessary technologies and to re-act to information environment changes in time. The article considers the problems of the online reputation management and the given ways of their solution