2,914 research outputs found
Semiconductor effective charges from tight-binding theory
We calculate the transverse effective charges of zincblende compound
semiconductors using Harrison's tight-binding model to describe the electronic
structure. Our results, which are essentially exact within the model, are found
to be in much better agreement with experiment than previous
perturbation-theory estimates. Efforts to improve the results by using more
sophisticated variants of the tight-binding model were actually less
successful. The results underline the importance of including quantities that
are sensitive to the electronic wavefunctions, such as the effective charges,
in the fitting of tight-binding models.Comment: 4 pages, two-column style with 2 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#jb_t
Applications of the ACGT Master Ontology on Cancer
In this paper we present applications of the ACGT Master Ontology (MO) which is a new terminology resource for a transnational network providing data exchange in oncology, emphasizing the integration of both clinical and molecular data. The development of a new ontology was necessary due to problems with existing biomedical ontologies in oncology. The ACGT MO is a test case for the application of best practices in ontology development. This paper provides an overview of the application of the ontology within the ACGT project thus far
Astrophysical thermonuclear functions
As theoretical knowledge and experimental verification of nuclear cross
sections increases it becomes possible to refine analytic representations for
nuclear reaction rates. In this paper mathematical/statistical techniques for
deriving closed-form representations of thermonuclear functions are summarized
and numerical results for them are given.The purpose of the paper is also to
compare numerical results for approximate and closed-form representations of
thermonuclear functions.Comment: 17 pages in LaTeX, 8 figures available on request from
[email protected]
Constraints on the Variation of the Fine Structure Constant from Big Bang Nucleosynthesis
We put bounds on the variation of the value of the fine structure constant
, at the time of Big Bang nucleosynthesis. We study carefully all light
elements up to Li. We correct a previous upper limit on estimated from He primordial abundance and we find interesting new
potential limits (depending on the value of the baryon-to-photon ratio) from
Li, whose production is governed to a large extent by Coulomb barriers. The
presently unclear observational situation concerning the primordial abundances
preclude a better limit than |\Delta \alpha/\alpha| \lsim 2\cdot 10^{-2}, two
orders of magnitude less restrictive than previous bounds. In fact, each of the
(mutually exclusive) scenarios of standard Big Bang nucleosynthesis proposed,
one based on a high value of the measured deuterium primordial abundance and
one based on a low value, may describe some aspects of data better if a change
in of this magnitude is assumed.Comment: 21 pages, eps figures embedded using epsfig macr
Effects of Anomalous Magnetic Moment in the Quantum Motion of Neutral Particle in Magnetic and Electric Fields Produced by a Linear Source in a Conical Spacetime
In this paper we analyse the effect of the anomalous magnetic moment on the
non-relativistic quantum motion of a neutral particle in magnetic and electric
fields produced by linear sources of constant current and charge density,
respectively.Comment: 17 pages, no figur
Uptake of gases in bundles of carbon nanotubes
Model calculations are presented which predict whether or not an arbitrary
gas experiences significant absorption within carbon nanotubes and/or bundles
of nanotubes. The potentials used in these calculations assume a conventional
form, based on a sum of two-body interactions with individual carbon atoms; the
latter employ energy and distance parameters which are derived from empirical
combining rules. The results confirm intuitive expectation that small atoms and
molecules are absorbed within both the interstitial channels and the tubes,
while large atoms and molecules are absorbed almost exclusively within the
tubes.Comment: 9 pages, 12 figures, submitted to PRB Newer version (8MAR2K). There
was an error in the old one (23JAN2K). Please download thi
Strichartz estimates on Schwarzschild black hole backgrounds
We study dispersive properties for the wave equation in the Schwarzschild
space-time. The first result we obtain is a local energy estimate. This is then
used, following the spirit of earlier work of Metcalfe-Tataru, in order to
establish global-in-time Strichartz estimates. A considerable part of the paper
is devoted to a precise analysis of solutions near the trapping region, namely
the photon sphere.Comment: 44 pages; typos fixed, minor modifications in several place
Self-energy and Self-force in the Space-time of a Thick Cosmic String
We calculate the self-energy and self-force for an electrically charged
particle at rest in the background of Gott-Hiscock cosmic string space-time. We
found the general expression for the self-energy which is expressed in terms of
the matrix of the scattering problem. The self-energy continuously falls
down outward from the string's center with maximum at the origin of the string.
The self-force is repulsive for an arbitrary position of the particle. It tends
to zero in the string's center and also far from the string and it has a
maximum value at the string's surface. The plots of the numerical calculations
of the self-energy and self-force are shown.Comment: 15 pages, 4 Postscript figures, ReVTe
Fokker-Planck equations and density of states in disordered quantum wires
We propose a general scheme to construct scaling equations for the density of
states in disordered quantum wires for all ten pure Cartan symmetry classes.
The anomalous behavior of the density of states near the Fermi level for the
three chiral and four Bogoliubov-de Gennes universality classes is analysed in
detail by means of a mapping to a scaling equation for the reflection from a
quantum wire in the presence of an imaginary potential.Comment: 10 pages, 5 figures, revised versio
Fracture model with variable range of interaction
We introduce a fiber bundle model where the interaction among fibers is
modeled by an adjustable stress-transfer function which can interpolate between
the two limiting cases of load redistribution, the global and the local load
sharing schemes. By varying the range of interaction several features of the
model are numerically studied and a crossover from mean field to short range
behavior is obtained. The properties of the two regimes and the emergence of
the crossover in between are explored by numerically studying the dependence of
the ultimate strength of the material on the system size, the distribution of
avalanches of breakings, and of the cluster sizes of broken fibers. Finally, we
analyze the moments of the cluster size distributions to accurately determine
the value at which the crossover is observed.Comment: 8 pages, 8 figures. Two columns revtex format. Final version to be
published in Phys. Rev.
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