156 research outputs found
Effect of Multiple Scattering on the Critical Electric Field for Runaway Electrons in the Atmosphere
A simple method for taking into account the multiple Coulomb scattering in
construction of a separatrix (the line separating the regions of runaway and
decelerating electrons in an electric field) is described. The desired line is
obtained by solving a simple transcendental equation.Comment: 3 pages, 2 figure
Gamma Radiation by Neutralino Stars
A new model of gamma radiation (GR) generated by neutralino annihilation in
neutralino stars (NeS) is proposed. Diffuse Galactic and extragalactic GR is
calculated for this model and is shown to be in a reasonable agreement with
observations.
The point source component (P) is picked out among nonidentified discrete
gamma sources from EGRET catalog. This component is shown to be distributed
isotropically and homogeneously, as it should be for NeS. Gamma radiation from
significant part of P-sources is supposed to be the direct radiation from
individual NeS. This supposition is shown to be in agreement with observations.
The comparison of the theory with observed GR gives a possibility to establish
some important features of CDM particle.Comment: 12 pages, LaTe
Experimental Evidence of Giant Electron - Gamma Bursts Generated by Extensive Atmospheric Showers in Thunderclouds
The existence of a new phenomena - giant electron-gamma bursts is
established. The bursts are generated in thunderclouds as a result of the
combined action of runaway breakdown and extensive atmosphere showers (RB-EAS).
The experiments were fulfilled at the Tien Shan Mountain Scientific Station
using EAS-Radio installation. This specially constructed installation consists
of a wide spread EAS trigger array and a high time resolution
radiointerferometer.Comment: 30 pages, 16 figure
Thermal conductivity via magnetic excitations in spin-chain materials
We discuss the recent progress and the current status of experimental
investigations of spin-mediated energy transport in spin-chain and spin-ladder
materials with antiferromagnetic coupling. We briefly outline the central
results of theoretical studies on the subject but focus mainly on recent
experimental results that were obtained on materials which may be regarded as
adequate physical realizations of the idealized theoretical model systems. Some
open questions and unsettled issues are also addressed.Comment: 17 pages, 4 figure
Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen
The heat capacity Cm of polycrystalline fullerite C₆₀ doped with nitrogen has been measured in
the temperature interval 2–13 K. The contributions to the heat capacity from translational lattice
vibrations (Debye contribution), orientational vibrations of the C₆₀ molecules (Einstein contribution),
and from the motion of the N₂ molecules in the octahedral cavities of the C₆₀ lattice have
been estimated. However, we could not find (beyond the experimental error limits) any indications
of the first-order phase transformation that had been detected earlier in the dilatometric investigation
of the orientational N₂–C₆₀ glass. A possible explanation of this fact is proposed
Singularities of bi-Hamiltonian systems
We study the relationship between singularities of bi-Hamiltonian systems and
algebraic properties of compatible Poisson brackets. As the main tool, we
introduce the notion of linearization of a Poisson pencil. From the algebraic
viewpoint, a linearized Poisson pencil can be understood as a Lie algebra with
a fixed 2-cocycle. In terms of such linearizations, we give a criterion for
non-degeneracy of singular points of bi-Hamiltonian systems and describe their
types
The Whitham Deformation of the Dijkgraaf-Vafa Theory
We discuss the Whitham deformation of the effective superpotential in the
Dijkgraaf-Vafa (DV) theory. It amounts to discussing the Whitham deformation of
an underlying (hyper)elliptic curve. Taking the elliptic case for simplicity we
derive the Whitham equation for the period, which governs flowings of branch
points on the Riemann surface. By studying the hodograph solution to the
Whitham equation it is shown that the effective superpotential in the DV theory
is realized by many different meromorphic differentials. Depending on which
meromorphic differential to take, the effective superpotential undergoes
different deformations. This aspect of the DV theory is discussed in detail by
taking the N=1^* theory. We give a physical interpretation of the deformation
parameters.Comment: 35pages, 1 figure; v2: one section added to give a physical
interpretation of the deformation parameters, one reference added, minor
corrections; v4: minor correction
Hydrodynamic flow of expanding Bose-Einstein condensates
We study expansion of quasi-one-dimensional Bose-Einstein condensate (BEC)
after switching off the confining harmonic potential. Exact solution of
dynamical equations is obtained in framework of the hydrodynamic approximation
and it is compared with the direct numerical simulation of the full problem
showing excellent agreement at realistic values of physical parameters. We
analyze the maximum of the current density and estimate the velocity of
expansion. The results of the 1D analysis provides also qualitative
understanding of some properties of BEC expansion observed in experiments.Comment: 5 pages, 3 figures, RevTeX4. To appear in Physical Review
Critical flux pinning and enhanced upper-critical-field in magnesium diboride films
We have conducted pulsed transport measurements on c-axis oriented magnesium
diboride films over the entire relevant ranges of magnetic field 0 \alt H \alt
H_{c2} (where \hcu is the upper critical field) and current density 0 \alt j
\alt j_{d} (where is the depairing current density). The intrinsic
disorder of the films combined with the large coherence length and
three-dimensionality, compared to cuprate superconductors, results in a
six-fold enhancement of and raises the depinning current density
to within an order of magnitude of . The current-voltage
response is highly non-linear at all fields, resulting from a combination of
depinning and pair-breaking, and has no trace of an Ohmic free-flux-flow
regime.
Keywords: pair, breaking, depairing, superconductor, superconductivity, flux,
fluxon, vortex, mgb
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