2,578 research outputs found
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
Formation of Quantum Shock Waves by Merging and Splitting Bose-Einstein Condensates
The processes of merging and splitting dilute-gas Bose-Einstein condensates
are studied in the nonadiabatic, high-density regime. Rich dynamics are found.
Depending on the experimental parameters, uniform soliton trains containing
more than ten solitons or the formation of a high-density bulge as well as
quantum (or dispersive) shock waves are observed experimentally within merged
BECs. Our numerical simulations indicate the formation of many vortex rings. In
the case of splitting a BEC, the transition from sound-wave formation to
dispersive shock-wave formation is studied by use of increasingly stronger
splitting barriers. These experiments realize prototypical dispersive shock
situations.Comment: 10 pages, 8 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
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