282 research outputs found
Unraveling the Landau's consistence criterion and the meaning of interpenetration in the "Two-Fluid" Model
In this letter we show that it is possible to unravel both the physical
origin of the Landau's consistence criterion and the specific and subtle
meaning of interpenetration of the "two fluids" if one takes into account that
in the hydrodynamic regime one needs a coarse-graining in time to bring the
system into local equilibrium. That is, the fuzziness in time is relevant for
the phenomenological Landau's consistency criterion and the meaning of
interpenetration. Note also that we are not questioning the validity of the
"Two-Fluid" Model.Comment: 8 pages, affiliation added, typos corrected, final version published
in Eur. Phys. J.
Sufficient stochastic maximum principle in a regime-switching diffusion model
We prove a sufficient stochastic maximum principle for the optimal control of
a regime-switching diffusion model. We show the connection to dynamic
programming and we apply the result to a quadratic loss minimization problem,
which can be used to solve a mean-variance portfolio selection problem
The stability of axisymmetric Taylor-Couette flow in hydromagnetics
The linear marginal instability of an axisymmetric MHD Taylor-Couette flow of
infinite vertical extension is considered. The dependence of the flow stability
on magnetic Prandtl number, Pm, and gap-width between rotating cylinders is
investigated. There is an unstability for flows with resting outer cylinder
even without a magnetic field. Nevertheless, there are solutions with smaller
critical Reynolds numbers for certain (weak) magnetic fields. These solutions,
however, exist for not too small Pm or large enough gap. For hydrodynamically
stable flow, we found that a magnetic field amplitude always exsits where the
critical Reynolds number is minimal. In all calculated cases the minimal
critical Reynolds numbers are running with 1/Pm for small Pm and the critical
Reynolds numbers exceed value of 10^6 for Pm of sodium (10^{-5}) or gallium
(10^{-6}).Comment: 8 pages, 17 figure
Dissipative dynamics of vortex arrays in anisotropic traps
We discuss the dissipative dynamics of vortex arrays in trapped
Bose-condensed gases and analyze the lifetime of the vortices as a function of
trap anisotropy and the temperature. In particular, we distinguish the two
regimes of the dissipative dynamics, depending on the relative strength of the
mutual friction between the vortices and the thermal component, and the
friction of the thermal particles on the trap anisotropy. We study the effects
of heating of the thermal cloud by the escaping vortices on the dynamics of the
system.Comment: RevTeX, 8 pages, 3 eps figure
Reconnections of Vortex Loops in the Superfluid Turbulent HeII. Rates of the Breakdown and Fusion processes
Kinetics of merging and breaking down vortex loops is the important part of
the whole vortex tangle dynamics. Another part is the motion of individual
lines, which obeys the Biot-Savart law in presence of friction force and of
applied external velocity fields if any. In the present work we evaluate the
coefficients of the reconnection rates and
. Quantity is a number (per unit of time and per unit of
volume) of events, when two loops with lengths and collide and
form the single loop of length . Quantity
describes the rate of events, when the single loop of the length breaks
down into two the daughter loops of lengths and . These
quantities ave evaluated as the averaged numbers of zeroes of vector
connecting two points on the loops of
and at moment of time . Statistics of the individual
loops is taken from the Gaussian model of vortex tangle. PACS-number 67.40Comment: 9 pages, 5 figures, To be submitted to JLT
Stable lyophilised gel vehicles for vaginal administration of recombinant C-clade HIV-1 trimeric CN54gp140
Spin-orbit final state interaction in the framework of Glauber theory for (e,e'p) reactions
We investigate the reactions D(e,e'p)n and D(\vec e,e'p)n at GeV energies and
discuss the opportunities to distinguish between different models for the
nuclear ground state by measuring the response functions. In calculating the
final-state interaction (FSI) we employ Glauber theory, and we also include
relativistic effects in the electromagnetic current. We include not only the
central FSI, but also the spin-orbit FSI which is usually neglected in (e,e'p)
calculations within the Glauber framework and we show that this contribution
plays a crucial role for the fifth response function. All of the methods
developed here can be applied to any target nucleus.Comment: 20 pages, 12 figures, minor change in figures 3 and 4 (changed beam
energy), correction of error in figure 4 in the previous replacemen
Eta invariants for flat manifolds
Using H. Donnelly result from the article "Eta Invariants for G-Spaces" we
calculate the eta invariants of the signature operator for almost all
7-dimensional flat manifolds with cyclic holonomy group. In all cases this eta
invariants are an integer numbers. The article was motivated by D. D. Long and
A. Reid article "On the geometric boundaries of hyperbolic 4-manifolds, Geom.
Topology 4, 2000, 171-178Comment: 18 pages, a new version with referees comment
The shrinking instability of toroidal liquid droplets in the Stokes flow regime
We analyze the stability and dynamics of toroidal liquid droplets. In
addition to the Rayleigh instabilities akin to those of a cylindrical droplet
there is a shrinking instability that is unique to the topology of the torus
and dominates in the limit that the aspect ratio is near one (fat tori). We
first find an analytic expression for the pressure distribution inside the
droplet. We then determine the velocity field in the bulk fluid, in the Stokes
flow regime, by solving the biharmonic equation for the stream function. The
flow pattern in the external fluid is analyzed qualitatively by exploiting
symmetries. This elucidates the detailed nature of the shrinking mode and the
swelling of the cross-section following from incompressibility. Finally the
shrinking rate of fat toroidal droplets is derived by energy conservation.Comment: 6 pages, 7 figure
Turbulent superfluid profiles in a counterflow channel
We have developed a two-dimensional model of quantised vortices in helium II
moving under the influence of applied normal fluid and superfluid in a
counterflow channel. We predict superfluid and vortex-line density profiles
which could be experimentally tested using recently developed visualization
techniques.Comment: 3 double figures, 9 page
- …