330,307 research outputs found
Maximum Path Information and Fokker-Planck Equation
We present in this paper a rigorous method to derive the nonlinear
Fokker-Planck (FP) equation of anomalous diffusion directly from a
generalization of the principle of least action of Maupertuis proposed by Wang
for smooth or quasi-smooth irregular dynamics evolving in Markovian process.
The FP equation obtained may take two different but equivalent forms. It was
also found that the diffusion constant may depend on both q (the index of
Tsallis entropy) and the time t.Comment: 7 page
Electron screening and its effects on Big-Bang nucleosynthesis
We study the effects of electron screening on nuclear reaction rates
occurring during the Big Bang nucleosynthesis epoch. The sensitivity of the
predicted elemental abundances on electron screening is studied in details. It
is shown that electron screening does not produce noticeable results in the
abundances unless the traditional Debye-H\"uckel model for the treatment of
electron screening in stellar environments is enhanced by several orders of
magnitude. The present work rules out electron screening as a relevant
ingredient to Big Bang nucleosynthesis and ruling out exotic possibilities for
the treatment of screening, beyond the mean-field theoretical approach.Comment: 4 pages, 4 figures, more references included. To appear in Phys. Rev.
Analysis of the vertex with the light-cone QCD sum rules
In this article, we analyze the vertex with the light-cone QCD
sum rules. The strong coupling constant is an important
parameter in evaluating the charmonium absorption cross sections in searching
for the quark-gluon plasmas. Our numerical value for the is
consistent with the prediction of the effective SU(4) symmetry and vector meson
dominance theory.Comment: 6 pages, 1 figure, revised versio
Supernova Blastwaves in Low-density Hot Media: a Mechanism for Spatially Distributed Heating
Most supernovae are expected to explode in low-density hot media,
particularly in galactic bulges and elliptical galaxies. The remnants of such
supernovae, though difficult to detect individually, can be profoundly
important in heating the media on large scales. We characterize the evolution
of this kind of supernova remnants, based on analytical approximations and
hydrodynamic simulations. We generalize the standard Sedov solution to account
for both temperature and density effects of the ambient media. Although cooling
can be neglected, the expansion of such a remnant deviates quickly from the
standard Sedov solution and asymptotically approaches the ambient sound speed
as the swept-up thermal energy becomes important. The relatively steady and
fast expansion of the remnants over large volumes provides an ideal mechanism
for spatially distributed heating, which may help to alleviate the over-cooling
problem of hot gas in groups and clusters of galaxies as well as in galaxies
themselves. The simulations were performed with the FLASH code.Comment: 12 pages, 3 figures, 1 table, accepted for ApJ, uses aaste
Enhanced Thermoelectric Power and Electronic Correlations in RuSe
We report the electronic structure, electric and thermal transport properties
of RuIrSe (). RuSe is a semiconductor that
crystallizes in a cubic pyrite unit cell. The Seebeck coefficient of RuSe
exceeds -200 V/K around 730 K. Ir substitution results in the suppression
of the resistivity and the Seebeck coefficient, suggesting the removal of the
peaks in density of states near the Fermi level. RuIrSe
shows a semiconductor-metal crossover at about 30 K. The magnetic field
restores the semiconducting behavior. Our results indicate the importance of
the electronic correlations in enhanced thermoelectricity of RuSb.Comment: 6 pages, 4 figure
Rank-frequency relation for Chinese characters
We show that the Zipf's law for Chinese characters perfectly holds for
sufficiently short texts (few thousand different characters). The scenario of
its validity is similar to the Zipf's law for words in short English texts. For
long Chinese texts (or for mixtures of short Chinese texts), rank-frequency
relations for Chinese characters display a two-layer, hierarchic structure that
combines a Zipfian power-law regime for frequent characters (first layer) with
an exponential-like regime for less frequent characters (second layer). For
these two layers we provide different (though related) theoretical descriptions
that include the range of low-frequency characters (hapax legomena). The
comparative analysis of rank-frequency relations for Chinese characters versus
English words illustrates the extent to which the characters play for Chinese
writers the same role as the words for those writing within alphabetical
systems.Comment: To appear in European Physical Journal B (EPJ B), 2014 (22 pages, 7
figures
About the creation of proton-anti-proton pair at electron-positron collider in the energy range of the mass
The process of electron--positron annihilation into proton--antiproton pair
is considered within the vicinity of resonance. The interference
between the pure electromagnetic intermediate state and the state
is evaluated. It is shown that this interference is destructive and the
relative phase between these two contributions is large ().Comment: 16 pages, 6 figures. The authors included the long-range
contributions (D-meson loop) in their calculations. The conclusion of the
papers did not chang
Electronic structure of intentionally disordered AlAs/GaAs superlattices
We use realistic pseudopotentials and a plane-wave basis to study the
electronic structure of non-periodic, three-dimensional, 2000-atom
(AlAs)_n/(GaAs)_m (001) superlattices, where the individual layer thicknesses
n,m = {1,2,3} are randomly selected. We find that while the band gap of the
equivalent (n = m = 2) ordered superlattice is indirect, random fluctuations in
layer thicknesses lead to a direct gap in the planar Brillouin zone, strong
wavefunction localization along the growth direction, short radiative
lifetimes, and a significant band-gap reduction, in agreement with experiments
on such intentionally grown disordered superlattices.Comment: 10 pages, REVTeX and EPSF macros, 4 figures in postscript. e-mail to
[email protected]
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