2,895 research outputs found
Orbital Magnetism in Two-dimensional Integrable Systems
We study orbital magnetism of a degenerate electron gas in a number of
two-dimensional integrable systems, within linear response theory. There are
three relevant energy scales: typical level spacing, the energy related to the
inverse time of flight across the system, and the Fermi energy.
Correspondingly, there are three distinct temperature regimes: microscopic,
mesoscopic, and macroscopic. In the first two regimes there are large
finite-size effects in the magnetic susceptibility, whereas in the third regime
the susceptibility approaches its macroscopic value. In some cases, such as a
quasi-one-dimensional strip or a harmonic confining potential, it is possible
to obtain analytic expressions for the susceptibility in the entire temperature
range.Comment: 28 pages, Latex, 4 Postscript figure
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
Thermal Fluctuations of the Electric Field in the Presence of Carrier Drift
We consider a semiconductor in a non-equilibrium steady state, with a dc
current. On top of the stationary carrier motion there are fluctuations. It is
shown that the stationary motion of the carriers (i.e., their drift) can have a
profound effect on the electromagnetic field fluctuations in the bulk of the
sample as well as outside it, close to the surface (evanescent waves in the
near field). The effect is particularly pronounced near the plasma frequency.
This is because drift leads to a significant modification of the dispersion
relation for the bulk and surface plasmons.Comment: Comments are welcom
Suppression of transverse instabilities of dark solitons and their dispersive shock waves
We investigate the impact of nonlocality, owing to diffusive behavior, on
transverse instabilities of a dark stripe propagating in a defocusing cubic
medium. The nonlocal response turns out to have a strongly stabilizing effect
both in the case of a single soliton input and in the regime where dispersive
shock waves develop "multisoliton regime". Such conclusions are supported by
the linear stability analysis and numerical simulation of the propagation
Detection of Quantum Noise from an Electrically-Driven Two-Level System
Quantum mechanics can strongly influence the noise properties of mesoscopic
devices. To probe this effect we have measured the current fluctuations at
high-frequency (5-90 GHz) using a superconductor-insulator-superconductor
tunnel junction as an on-chip spectrum analyser. By coupling this
frequency-resolved noise detector to a quantum device we can measure the
high-frequency, non-symmetrized noise as demonstrated for a Josephson junction.
The same scheme is used to detect the current fluctuations arising from
coherent charge oscillations in a two-level system, a superconducting charge
qubit. A narrow band peak is observed in the spectral noise density at the
frequency of the coherent charge oscillations.Comment: 16 pages, 4 figure
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
Towards an ASM thesis for reflective sequential algorithms
Starting from Gurevich's thesis for sequential algorithms (the so-called
"sequential ASM thesis"), we propose a characterization of the behaviour of
sequential algorithms enriched with reflection. That is, we present a set of
postulates which we conjecture capture the fundamental properties of reflective
sequential algorithms (RSAs). Then we look at the plausibility of an ASM thesis
for the class of RSAs, defining a model of abstract state machine (which we
call reflective ASM) that we conjecture captures the class of RSAs as defined
by our postulates
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