2,580 research outputs found
Mass Transfer Mechanism in Real Crystals by Pulsed Laser Irradiation
The dynamic processes in the surface layers of metals subjected activity of a
pulsing laser irradiation, which destroyed not the crystalline structure in
details surveyed. The procedure of calculation of a dislocation density
generated in bulk of metal during the relaxation processes and at repeated
pulse laser action is presented. The results of evaluations coincide with high
accuracy with transmission electron microscopy dates. The
dislocation-interstitial mechanism of laser-stimulated mass-transfer in real
crystals is presented on the basis of the ideas of the interaction of structure
defects in dynamically deforming medium. The good compliance of theoretical and
experimental results approves a defining role of the presented mechanism of
mass transfer at pulse laser action on metals. The possible implementation this
dislocation-interstitial mechanism of mass transfer in metals to other cases of
pulsing influences is justifiedComment: 10 pages, 2 figures, Late
Analytic model for a frictional shallow-water undular bore
We use the integrable Kaup-Boussinesq shallow water system, modified by a
small viscous term, to model the formation of an undular bore with a steady
profile. The description is made in terms of the corresponding integrable
Whitham system, also appropriately modified by friction. This is derived in
Riemann variables using a modified finite-gap integration technique for the
AKNS scheme. The Whitham system is then reduced to a simple first-order
differential equation which is integrated numerically to obtain an asymptotic
profile of the undular bore, with the local oscillatory structure described by
the periodic solution of the unperturbed Kaup-Boussinesq system. This solution
of the Whitham equations is shown to be consistent with certain jump conditions
following directly from conservation laws for the original system. A comparison
is made with the recently studied dissipationless case for the same system,
where the undular bore is unsteady.Comment: 24 page
On the temperature dependence of ballistic Coulomb drag in nanowires
We have investigated within the theory of Fermi liquid dependence of Coulomb
drag current in a passive quantum wire on the applied voltage across an
active wire and on the temperature for any values of . We assume
that the bottoms of the 1D minibands in both wires almost coincide with the
Fermi level. We come to conclusions that 1) within a certain temperature
interval the drag current can be a descending function of the temperature ;
2) the experimentally observed temperature dependence of the drag
current can be interpreted within the framework of Fermi liquid theory; 3) at
relatively high applied voltages the drag current as a function of the applied
voltage saturates; 4) the screening of the electron potential by metallic gate
electrodes can be of importance.Comment: 7 pages, 1 figur
Thermal Diffusion of a Two Layer System
In this paper thermal conductivity and thermal diffusivity of a two layer
system is examined from the theoretical point of view. We use the one
dimensional heat diffusion equation with the appropriate solution in each layer
and boundary conditions at the interfaces to calculate the heat transport in
this bounded system. We also consider the heat flux at the surface of the samle
as boundary condition instead of using a fixed tempertaure. From this, we
obtain an expression for the efective thermal diffusivity of the composite
sample in terms of the thermal diffusivity of its constituent materials
whithout any approximations.Comment: 16 pages, 1 figure, RevTeX v. 3.0 macro packag
Whitham systems and deformations
We consider the deformations of Whitham systems including the "dispersion
terms" and having the form of Dubrovin-Zhang deformations of Frobenius
manifolds. The procedure is connected with B.A. Dubrovin problem of
deformations of Frobenius manifolds corresponding to the Whitham systems of
integrable hierarchies. Under some non-degeneracy requirements we suggest a
general scheme of the deformation of the hyperbolic Whitham systems using the
initial non-linear system. The general form of the deformed Whitham system
coincides with the form of the "low-dispersion" asymptotic expansions used by
B.A. Dubrovin and Y. Zhang in the theory of deformations of Frobenius
manifolds.Comment: 27 pages, Late
Synthetic Turbulence Modeling for Evaluation of Ultrasonic Cross-Correlation Flow Measurement
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI linkPerformance of an ultrasonic cross-correlation flow measurement instrument may be significantly affected by turbulence at the location of the ultrasonic sensors. In this paper, a new method of generating Synthetic Turbulence is presented, to provide an effective tool for creating a variety of turbulent fields, which can be used to model and analyze instrument performance under different flow conditions. In the proposed method, a turbulent field is presented as a Fourier time-series in each point in space. Turbulence structures are defined by a spatial distribution of phase functions for each harmonic. Principles of designing a phase function to achieve the desirable distribution of turbulence scales, and two-point correlations, are outlined by considering the example of Uniform Isotropic Turbulence. One application of this method, presented in this work, is the mathematical modeling of ultrasonic cross-correlation flow measurement. Results predicted by the proposed mathematical model show good agreement with experimental data
Delayed feedback control of self-mobile cavity solitons
Control of the motion of cavity solitons is one the central problems in
nonlinear optical pattern formation. We report on the impact of the phase of
the time-delayed optical feedback and carrier lifetime on the self-mobility of
localized structures of light in broad area semiconductor cavities. We show
both analytically and numerically that the feedback phase strongly affects the
drift instability threshold as well as the velocity of cavity soliton motion
above this threshold. In addition we demonstrate that non-instantaneous carrier
response in the semiconductor medium is responsible for the increase in
critical feedback rate corresponding to the drift instability
Flux flow of Abrikosov-Josephson vortices along grain boundaries in high-temperature superconductors
We show that low-angle grain boundaries (GB) in high-temperature
superconductors exhibit intermediate Abrikosov vortices with Josephson cores,
whose length along GB is smaller that the London penetration depth, but
larger than the coherence length. We found an exact solution for a periodic
vortex structure moving along GB in a magnetic field and calculated the
flux flow resistivity , and the nonlinear voltage-current
characteristics. The predicted dependence describes well our
experimental data on unirradiated and irradiated
bicrystals, from which the core size , and the intrinsic depairing
density on nanoscales of few GB dislocations were measured for the
first time. The observed temperature dependence of
indicates a significant order parameter suppression in current channels between
GB dislocation cores.Comment: 5 pages 5 figures. Phys. Rev. Lett. (accepted
Whitham method for Benjamin-Ono-Burgers equation and dispersive shocks in internal waves in deep fluid
The Whitham modulation equations for the parameters of a periodic solution
are derived using the generalized Lagrangian approach for the case of damped
Benjamin-Ono equation. The structure of the dispersive shock in internal wave
in deep water is considered by this method.Comment: 8 pages, 4 figure
Formation of shock waves in a Bose-Einstein condensate
We consider propagation of density wave packets in a Bose-Einstein
condensate. We show that the shape of initially broad, laser-induced, density
perturbation changes in the course of free time evolution so that a shock wave
front finally forms. Our results are well beyond predictions of commonly used
zero-amplitude approach, so they can be useful in extraction of a speed of
sound from experimental data. We discuss a simple experimental setup for shock
propagation and point out possible limitations of the mean-field approach for
description of shock phenomena in a BEC.Comment: 8 pages & 6 figures, minor changes, more references, to appear in
Phys. Rev.
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