694 research outputs found
Studies of concentration and temperature dependencies of precipitation kinetics in iron-copper alloys using kinetic monte carlo and stochastic statistical simulations
The earlier-developed ab initio model and the kinetic Monte Carlo method
(KMCM) are used to simulate precipitation in a number of iron-copper alloys
with different copper concentrations x and temperatures T. The same simulations
are also made using the improved version of the earlier-suggested stochastic
statistical method (SSM). The results obtained enable us to make a number of
general conclusions about the dependencies of the decomposition kinetics in
Fe-Cu alloys on x and T. We also show that the SSM describes the precipitation
kinetics in a fair agreement with the KMCM, and employing the SSM in
conjunction with the KMCM enables us to extend the KMC simulations to the
longer evolution times. The results of simulations seem to agree with available
experimental data for Fe-Cu alloys within statistical errors of simulations and
the scatter of experimental results. Comparison of results of simulations to
experiments for some multicomponent Fe-Cu-based alloys enables us to make
certain conclusions about the influence of alloying elements in these alloys on
the precipitation kinetics at different stages of evolution.Comment: 18 pages, 17 postscript figures, LaTe
Lie group analysis for multi-scale plasma dynamics
An application of approximate transformation groups to study dynamics of a
system with distinct time scales is discussed. The utilization of the
Krylov-Bogoliubov-Mitropolsky method of averaging to find solutions of the Lie
equations is considered. Physical illustrations from the plasma kinetic theory
demonstrate the potentialities of the suggested approach. Several examples of
invariant solutions for the system of the Vlasov-Maxwell equations for the
two-component (electron-ion) plasma are presented.Comment: Latex, 15 pages, 7 figure. This is an enlarged contribution to
Journal of Nonlinear Mathematical Physics v.18, Suppl. 1 (2011) p.163-175
with modest stylistic corrections introduced mainly in the third Sectio
PSR B0329+54: Statistics of Substructure Discovered within the Scattering Disk on RadioAstron Baselines of up to 235,000 km
We discovered fine-scale structure within the scattering disk of PSR B0329+54
in observations with the RadioAstron ground-space radio interferometer. Here,
we describe this phenomenon, characterize it with averages and correlation
functions, and interpret it as the result of decorrelation of the
impulse-response function of interstellar scattering between the
widely-separated antennas. This instrument included the 10-m Space Radio
Telescope, the 110-m Green Bank Telescope, the 14x25-m Westerbork Synthesis
Radio Telescope, and the 64-m Kalyazin Radio Telescope. The observations were
performed at 324 MHz, on baselines of up to 235,000 km in November 2012 and
January 2014. In the delay domain, on long baselines the interferometric
visibility consists of many discrete spikes within a limited range of delays.
On short baselines it consists of a sharp spike surrounded by lower spikes. The
average envelope of correlations of the visibility function show two
exponential scales, with characteristic delays of and , indicating the presence of two scales of
scattering in the interstellar medium. These two scales are present in the
pulse-broadening function. The longer scale contains 0.38 times the scattered
power of the shorter one. We suggest that the longer tail arises from
highly-scattered paths, possibly from anisotropic scattering or from
substructure at large angles.Comment: 15 pages, 6 figures, 3 tables; accepted by Astrophysical journa
Kinetics of exciton photoluminescence in type-II semiconductor superlattices
The exciton decay rate at a rough interface in type-II semiconductor
superlattices is investigated. It is shown that the possibility of
recombination of indirect excitons at a plane interface essentially affects
kinetics of the exciton photoluminescence at a rough interface. This happens
because of strong correlation between the exciton recombination at the plane
interface and at the roughness. Expressions that relate the parameters of the
luminescence kinetics with statistical characteristics of the rough interface
are obtained. The mean height and length of roughnesses in GaAs/AlAs
superlattices are estimated from the experimental data.Comment: 3 PostScript figure
Macroscopic quantum phenomena in Josephson structures
The Josephson effect is a probe with unparalleled capabilities for the study of a variety of macroscopic quantum phenomena. This is a survey of important achievements and challenging trends, in particular macroscopic quantum tunneling and energy level quantization. We focus on high-T-C superconducting structures and recent research on nanostructures
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