17,105 research outputs found
Two types of Hc2(T) dependences in Bi_2Sr_2Ca_(1-x)Y_xCu_2O_(8+delta) with different Yttrium content
We reanalyze the magnetization data collected on
Bi_2Sr_2Ca_(1-x)Y_xCu_2O_(8+y) samples (Kim at al, Phys. Rev. B 72, 64525
(2005)) and argue that the method, which was used for the analysis of
equilibrium magnetization data, is not adequate to the experimental situation.
As a result, the temperature dependencies of the upper critical field Hc2(T)
and the magnetic field penetration depth lambda (T), obtained in this work, are
misinterpreted. Using a different approach to analysis, we demonstrate that the
normalizedHc2(T) curves are rather different from those presented in the
original publication and do not follow predictions of the
Werthamer-Helfand-Hohenberg theory. Another important observation is that the
Hc2(T) dependencies for two samples with different levels of doping are
qualitatively different.Comment: 10 pages, 3 figure
Weakly nonlinear stability analysis of MHD channel flow using an efficient numerical approach
We analyze weakly nonlinear stability of a flow of viscous conducting liquid
driven by pressure gradient in the channel between two parallel walls subject
to a transverse magnetic field. Using a non-standard numerical approach, we
compute the linear growth rate correction and the first Landau coefficient,
which in a sufficiently strong magnetic field vary with the Hartmann number as
and
. These
coefficients describe a subcritical transverse velocity perturbation with the
equilibrium amplitude
which exists at Reynolds numbers below the linear stability threshold
We find that the flow
remains subcritically unstable regardless of the magnetic field strength. Our
method for computing Landau coefficients differs from the standard one by the
application of the solvability condition to the discretized rather than
continuous problem. This allows us to bypass both the solution of the adjoint
problem and the subsequent evaluation of the integrals defining the inner
products, which results in a significant simplification of the method.Comment: 16 pages, 10 figures, revised version (to appear in Phys Fluids
Multimode theory of measurement-induced non-Gaussian operation on wideband squeezed light
We present a multimode theory of non-Gaussian operation induced by an
imperfect on/off-type photon detector on a splitted beam from a wideband
squeezed light. The events are defined for finite time duration in the time
domain. The non-Gaussian output state is measured by the homodyne detector with
finite bandwidh . Under this time- and band-limitation to the quantm states,
we develop a formalism to evaluate the frequency mode matching between the
on/off trigger channel and the conditional signal beam in the homodyne channel.
Our formalism is applied to the CW and pulsed schemes. We explicitly calculate
the Wigner function of the conditional non-Gaussian output state in a realistic
situation. Good mode matching is achieved for BT\alt1, where the discreteness
of modes becomes prominant, and only a few modes become dominant both in the
on/off and the homodyne channels. If the trigger beam is projected nearly onto
the single photon state in the most dominant mode in this regime, the most
striking non-classical effect will be observed in the homodyne statistics. The
increase of and the dark counts degrades the non-classical effect.Comment: 20 pages, 14 figures, submitted to Phys. Rev.
Higher order first integrals of motion in a gauge covariant Hamiltonian framework
The higher order symmetries are investigated in a covariant Hamiltonian
formulation. The covariant phase-space approach is extended to include the
presence of external gauge fields and scalar potentials. The special role of
the Killing-Yano tensors is pointed out. Some non-trivial examples involving
Runge-Lenz type conserved quantities are explicitly worked out.Comment: 13 pages, references added, accepted for publication in MPL
On Inflation and Variation of the Strong Coupling Constant
Variation of constants in the very early universe can generate inflation. We
consider a scenario where the strong coupling constant was changing in time and
where the gluon condensate underwent a phase transition ending the inflation.Comment: 12 pages, 1 figure, accepted for publication in International Journal
of Modern Physics
T>0 ensemble state density functional theory revisited
A logical foundation of equilibrium state density functional theory in a
Kohn-Sham type formulation is presented on the basis of Mermin's treatment of
the grand canonical state. it is simpler and more satisfactory compared to the
usual derivation of ground state theory, and free of remaining open points of
the latter. It may in particular be relevant with respect to cases of
spontaneous symmetry breaking like non-collinear magnetism and orbital order.Comment: 7 pages, no figure
- …