3,871 research outputs found
Effect of fluctuations on vortex lattice structural transitions in superconductors
The rhombic-to-square transition field for cubic and tetragonal
materials in fields along [001] is evaluated using the nonlocal London theory
with account of thermal vortex fluctuations. Unlike extended Ginzburg-Landau
models, our approach shows that the line and the upper critical
field do not cross due to strong fluctuations near
which suppress the square anisotropy induced by the nonlocality. In increasing
fields, this causes re-entrance of the rhombic structure in agreement with
recent neutron scattering data on borocarbides.Comment: 4 pages, 2 figure
Neutrino dispersion in external magnetic fields
We calculate the neutrino self-energy operator Sigma (p) in the presence of a
magnetic field B. In particular, we consider the weak-field limit e B <<
m_\ell^2, where m_\ell is the charged-lepton mass corresponding to the neutrino
flavor \nu_\ell, and we consider a "moderate field" m_\ell^2 << e B << m_W^2.
Our results differ substantially from the previous literature. For a moderate
field, we show that it is crucial to include the contributions from all Landau
levels of the intermediate charged lepton, not just the ground-state. For the
conditions of the early universe where the background medium consists of a
charge-symmetric plasma, the pure B-field contribution to the neutrino
dispersion relation is proportional to (e B)^2 and thus comparable to the
contribution of the magnetized plasma.Comment: 9 pages, 1 figure, revtex. Version to appear in Phys. Rev. D
(presentation improved, reference list revised, numerical error in Eq.(41)
corrected, conclusions unchanged
On temperature-dependent anisotropies of upper critical field and London penetration depth
We show on a few examples of one-band materials with spheroidal Fermi
surfaces and anisotropic order parameters that anisotropies of the
upper critical field and of the London penetration depth
depend on temperature, the feature commonly attributed to multi-band
superconductors. The parameters and may have
opposite temperature dependencies or may change in the same direction depending
on Fermi surface shape and on character of the gap nodes. For two-band systems,
the behavior of anisotropies is affected by the ratios of bands densities of
states, Fermi velocities, anisotropies, and order parameters. We investigate in
detail the conditions determining the directions of temperature dependences of
the two anisotropy factors
Pair-breaking in iron-pnictides
The puzzling features of the slopes of the upper critical field at the
critical temperature , , and of the
specific heat jump of iron-pnictides are interpreted as
caused by a strong pair-breaking
On chaotic behavior of gravitating stellar shells
Motion of two gravitating spherical stellar shells around a massive central
body is considered. Each shell consists of point particles with the same
specific angular momenta and energies. In the case when one can neglect the
influence of gravitation of one ("light") shell onto another ("heavy") shell
("restricted problem") the structure of the phase space is described. The
scaling laws for the measure of the domain of chaotic motion and for the
minimal energy of the light shell sufficient for its escape to infinity are
obtained.Comment: e.g.: 12 pages, 8 figures, CHAOS 2005 Marc
Is the term "type-1.5 superconductivity" warranted by Ginzburg-Landau theory?
It is shown that within the Ginzburg-Landau (GL) approximation the order
parameters Delta1(r, T) and Delta2(r, T) in two-band superconductors vary on
the same length scale, the difference in the zero-T coherence lengths xi0_i
~vF_i/Delta_i(0), i = 1, 2 notwithstanding. This amounts to a single physical
GL parameter kappa and the classic GL dichotomy: kappa < 1/sqrt(2) for type-I
and kappa > 1/sqrt(2) for type-II.Comment: 5 pages, revised and extended version; previous title "Two-band
superconductors near Tc" change
Quantum amplification effect in a horizon fluctuations
The appearance of a few unevenly- spaced bright flashes of light on top of
Hawking radiation is the sign of the amplification effect in black hole horizon
fluctuations. Previous studies on this problem suffer from the lack of
considering all emitted photons in the theoretical spectroscopy of these
fluctuations. In this paper, we include all of the physical transition weights
and present a consistent intensity formula. This modifies a black hole
radiation pattern.Comment: 6 pages, 2 figure
Effect of graded physical load on the state of the liver from morphometric data and biochemical blood indices of rats against a background of hypokinesia
Tests were conducted on 100 sexually immature inbred August and Wistar male rats in order to determine the effects hypokinesia, physical load and phenamine on the liver. Weight and linear dimension fell in hypokinesia; total serum protein lowered and aldolase and cholesterol and beta-lipoprotein levels rose. Blood sugar content rose and liver glycogen fell. Interlinear differences of these indices are found. Rehabilitated physical loading against hypokinesia background diminished and at times completely prevented its negative effect. Extent of correction depended on animal species. Evidence of genotypical conditionality of organism adaptation to physical load in hypokinesia was found
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