3,702 research outputs found
New shield for gamma-ray spectrometry
Gamma-ray shield that can be evacuated, refilled with a clean gas, and pressurized for exclusion of airborne radioactive contaminants effectively lowers background noise. Under working conditions, repeated evacuation and filling procedures have not adversely affected the sensitivity and resolution of the crystal detector
Self-steepening of light pulses
Self-steepening of light pulses due to propagation in medium with intensity-dependent index of refractio
Color separate singlets in annihilation
We use the method of color effective Hamiltonian to study the properties of
states in which a gluonic subsystem forms a color singlet, and we will study
the possibility that such a subsystem hadronizes as a separate unit. A parton
system can normally be subdivided into singlet subsystems in many different
ways, and one problem arises from the fact that the corresponding states are
not orthogonal. We show that if only contributions of order are
included, the problem is greatly simplified. Only a very limited number of
states are possible, and we present an orthogonalization procedure for these
states. The result is simple and intuitive and could give an estimate of the
possibility to produce color separated gluonic subsystems, if no dynamical
effects are important. We also study with a simple MC the possibility that
configurations which correspond to "short strings" are dynamically favored. The
advantage of our approach over more elaborate models is its simplicity, which
makes it easier to estimate color reconnection effects in reactions which are
more complicated than the relatively simple annihilation.Comment: Revtex, 24 pages, 7 figures; Compared to the previous version, 1 new
figure is added and Monte-Carlo results are re-analyzed, as suggested by the
referee; To appear in Phys. Rev.
Origin and evolution of the zodiacal dust cloud
The astrophysical importance of the zodiacal cloud became more apparent. The most useful source of information on the structure of the zodiacal cloud is the Infrared Astronomical Satellite (IRAS) observations. A substantial fraction of the extensive IRAS data set was analyzed. Also, a numerical model was developed (SIMUL) that allows to calculate the distribution of night-sky brightness that would be produced by any particular distribution of dust particle orbits. This model includes the effects of orbital perturbations by both the planets and solar radiation, it reproduces the exact viewing geometry of the IRAS telescope, and allows for the eccentricity of the Earth's orbit. SIMUL now is used to model not just the solar system dust bands discovered by IRAS but the whole zodiacal cloud
Unit circle elliptic beta integrals
We present some elliptic beta integrals with a base parameter on the unit
circle, together with their basic degenerations.Comment: 15 pages; minor corrections, references updated, to appear in
Ramanujan
Travelling waves for the Gross-Pitaevskii equation II
The purpose of this paper is to provide a rigorous mathematical proof of the
existence of travelling wave solutions to the Gross-Pitaevskii equation in
dimensions two and three. Our arguments, based on minimization under
constraints, yield a full branch of solutions, and extend earlier results,
where only a part of the branch was built. In dimension three, we also show
that there are no travelling wave solutions of small energy.Comment: Final version accepted for publication in Communications in
Mathematical Physics with a few minor corrections and added remark
The origin and evolution of the zodiacal dust cloud
We have now analyzed a substantial fraction of the IRAS observations of the zodiacal cloud, particularly in the 25 micron waveband. We have developed a gravitational perturbation theory that incorporates the effects of Poynting-Robertson light drag (Gomes and Dermott, 1992). We have also developed a numerical model, the SIMUL mode, that reproduces the exact viewing geometry of the IRAS telescope and calculates the distribution of thermal flux produced by any particular distribution of dust particle orbits (Dermott and Nicholson, 1989). With these tools, and using a distribution of orbits based on those of asteroidal particles with 3.4 micron radii whose orbits decay due to Poynting-Robertson light drag and are perturbed by the planets, we have been able to: (1) account for the inclination and node of the background zodiacal cloud observed by IRAS in the 25 micron waveband; (2) relate the distribution of orbits in the Hirayama asteroid families to the observed shapes of the IRAS solar system dustbands; and (3) show that there is observational evidence in the IRAS data for the transport of asteroidal particles from the main belt to the Earth by Poynting-Robertson light drag
Global well-posedness for a nonlocal Gross-Pitaevskii equation with non-zero condition at infinity
We study the Gross-Pitaevskii equation involving a nonlocal interaction
potential. Our aim is to give sufficient conditions that cover a variety of
nonlocal interactions such that the associated Cauchy problem is globally
well-posed with non-zero boundary condition at infinity, in any dimension. We
focus on even potentials that are positive definite or positive tempered
distributions.Comment: Communications in Partial Differential Equations (2010
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