1,635 research outputs found
Electronic structure, electron-phonon coupling and superconductivity of isotypic noncentrosymmetric crystals LiPdB and LiPtB
Electronic structure of recently discovered isotypic ternary borides
LiPdB and LiPtB, with noncentrosymmetric crystal structures, is
studied with a view to understanding their superconducting properties.
Estimates of the Fermi-surface averaged electron-phonon matrix element and
Hopfield parameter are obtained in the rigid ion approximation of Gaspari and
Gyorffy [Phys. Rev. Lett. {\bf 28} (1972) 801]. The contribution of the lithium
atoms to the electron-phonon coupling is found to be negligible, while both
boron and palladium atoms contribute equally strongly to the Hopfield
parameter. There is a significant transfer of charge from lithium, almost the
entire valence charge, to the B-Pd(Pt) complex. The electronic structure and
superconducting properties of LiPdB, thus, can be understood from the
viewpoint of the compound being composed of a connected array of B-Pd
tetrahedra decoupled from the backbone of Li atoms, which are connected by
relatively short bonds. Our results suggest that conventional s-wave
electron-phonon interaction without explicit consideration of SO coupling can
explain qualitatively the observed in LiPdB. However, such an
approach is likely to fail to describe superconductivity in LiPtB.Comment: 14 pages, 4 figures An erroneous statement following Eq. 6 in version
1 has been deleted. A statement regarding the possible inadequacy of Eq. 6
has been added following Eq. 6. At two places in the discussion Refs. 37,39
has been changed to 37-39, as it should b
Bulk Scale Factor at Very Early Universe
In this paper we propose a higher dimensional Cosmology based on FRW model
and brane-world scenario. We consider the warp factor in the brane-world
scenario as a scale factor in 5-dimensional generalized FRW metric, which is
called as bulk scale factor, and obtain the evolution of it with space-like and
time-like extra dimensions. It is then showed that, additional space-like
dimensions can produce exponentially bulk scale factor under repulsive strong
gravitational force in the empty universe at a very early stage.Comment: 7 pages, October 201
Interchange Slip-Running Reconnection and Sweeping SEP Beams
We present a new model to explain how particles (solar energetic particles;
SEPs), accelerated at a reconnection site that is not magnetically connected to
the Earth, could eventually propagate along the well-connected open flux tube.
Our model is based on the results of a low-beta resistive magnetohydrodynamics
simulation of a three-dimensional line-tied and initially current-free bipole,
that is embedded in a non-uniform open potential field. The topology of this
configuration is that of an asymmetric coronal null-point, with a closed fan
surface and an open outer spine. When driven by slow photospheric shearing
motions, field lines, initially fully anchored below the fan dome, reconnect at
the null point, and jump to the open magnetic domain. This is the standard
interchange mode as sketched and calculated in 2D. The key result in 3D is
that, reconnected open field lines located in the vicinity of the outer spine,
keep reconnecting continuously, across an open quasi-separatrix layer, as
previously identified for non-open-null-point reconnection. The apparent
slipping motion of these field lines leads to form an extended narrow magnetic
flux tube at high altitude. Because of the slip-running reconnection, we
conjecture that if energetic particles would be traveling through, or be
accelerated inside, the diffusion region, they would be successively injected
along continuously reconnecting field lines that are connected farther and
farther from the spine. At the scale of the full Sun, owing to the super-radial
expansion of field lines below 3 solar radii, such energetic particles could
easily be injected in field lines slipping over significant distances, and
could eventually reach the distant flux tube that is well-connected to the
Earth
Factorization of Seiberg-Witten Curves with Fundamental Matter
We present an explicit construction of the factorization of Seiberg-Witten
curves for N=2 theory with fundamental flavors. We first rederive the exact
results for the case of complete factorization, and subsequently derive new
results for the case with breaking of gauge symmetry U(Nc) to U(N1)xU(N2). We
also show that integrality of periods is necessary and sufficient for
factorization in the case of general gauge symmetry breaking. Finally, we
briefly comment on the relevance of these results for the structure of N=1
vacua.Comment: 24 pages, 2 figure
Exact solution of Schrodinger equation for Pseudoharmonic potential
Exact solution of Schrodinger equation for the pseudoharmonic potential is
obtained for an arbitrary angular momentum. The energy eigenvalues and
corresponding eigenfunctions are calculated by Nikiforov-Uvarov method.
Wavefunctions are expressed in terms of Jacobi polynomials. The energy
eigenvalues are calculated numerically for some values of l and n with n<5 for
some diatomic molecules.Comment: 10 page
Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT
The presence of a solar burst spectral component with flux density increasing
with frequency in the sub-terahertz range, spectrally separated from the
well-known microwave spectral component, bring new possibilities to explore the
flaring physical processes, both observational and theoretical. The solar event
of 6 December 2006, starting at about 18:30 UT, exhibited a particularly
well-defined double spectral structure, with the sub-THz spectral component
detected at 212 and 405 GHz by SST and microwaves (1-18 GHz) observed by the
Owens Valley Solar Array (OVSA). Emissions obtained by instruments in
satellites are discussed with emphasis to ultra-violet (UV) obtained by the
Transition Region And Coronal Explorer (TRACE), soft X-rays from the
Geostationary Operational Environmental Satellites (GOES) and X- and gamma-rays
from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz
impulsive component had its closer temporal counterpart only in the higher
energy X- and gamma-rays ranges. The spatial positions of the centers of
emission at 212 GHz for the first flux enhancement were clearly displaced by
more than one arc-minute from positions at the following phases. The observed
sub-THz fluxes and burst source plasma parameters were found difficult to be
reconciled to a purely thermal emission component. We discuss possible
mechanisms to explain the double spectral components at microwaves and in the
THz ranges.Comment: Accepted version for publication in Solar Physic
Normal-superconducting transition induced by high current densities in YBa2Cu3O7-d melt-textured samples and thin films: Similarities and differences
Current-voltage characteristics of top seeded melt-textured YBa2Cu3O7-d are
presented. The samples were cut out of centimetric monoliths. Films
characteristics were also measured on microbridges patterned on thin films
grown by dc sputtering. For both types of samples, a quasi-discontinuity or
quenching was observed for a current density J* several times the critical
current density Jc. Though films and bulks much differ in their magnitude of
both Jc and J*, a proposal is made as to a common intrinsic origin of the
quenching phenomenon. The unique temperature dependence observed for the ratio
J*/Jc, as well as the explanation of the pre-quenching regime in terms of a
single dissipation model lend support to our proposal.Comment: 10 pages, 10 figures, submitted to Physical Review
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