479 research outputs found
Bose-Einstein Condensation and Casimir Effect of Trapped Ideal Bose Gas in between two Slabs
We study the Bose-Einstein condensation for a 3-d system of ideal Bose gas
which is harmonically trapped along two perpendicular directions and is
confined in between two slabs along the other perpendicular direction. We
calculate the Casimir force between the two slabs for this system of trapped
Bose gas. At finite temperatures this force for thermalized photons in between
two plates has a classical expression which is independent of . At
finite temperatures the Casimir force for our system depends on . For
the calculation of Casimir force we consider only the Dirichlet boundary
condition. We show that below condensation temperature() the Casimir force
for this non-interacting system decreases with temperature() and at
, it is independent of temperature. We also discuss the Casimir
effect on 3-d highly anisotropic harmonically trapped ideal Bose gas.Comment: 4 page
Stabilization of magnetic polarons in antiferromagnetic semiconductors by extended spin distortions
We study the problem of a magnetic polaron in an antiferromagnetic
semiconductor (ferron). We obtain an analytical solution for the distortion
produced in the magnetic structure of the d-spins due to the presence of a
charge carrier bound to an impurity. The region in which the charge carrier is
trapped is of the order of the lattice constant (small ferron) but the
distortion of the magnetic structure extends over much larger distance. It is
shown that the presence of this distortion makes the ferron more stable, and
introduces a new length scale in the problem.Comment: 5 pages, 1 figure, RevTex 4, submitted to PRB; v2: one reference
added, minor changes in the experiment discussion; v3: minor changes in tex
On tests of local realism by CP-violation parameters of K^0 mesons
Recently various papers have proposed to test local realism (LR) by
considering electroweak CP-violation parameters values in neutral pseudoscalar
meson systems. Considering the large interest for a conclusive test of LR and
the experimental accessibility to these tests, in this paper we critically
consider these results showing how they, albeit very interesting, require
anyway additional assumptions and therefore cannot be considered conclusive
tests of LR
Photoproduction of \eta mesons on protons in the resonance region:The background problem and the third S_11 resonance
We have constructed an isobar model for the -photoproduction on the
proton in the energy region up to the photon lab energy GeV. The data
base involved into the fitting procedure includes precise results for the cross
section and for the -asymmetry of the process near
threshold obtained at MAMI and ELSA as well as recent results for the
-asymmetry and for the angular distribution measured at higher energies
in Grenoble and also more recent measurements performed at JLab for the photon
energies up to 2 GeV. The model includes twelve nucleon resonances:
, , , ,,
, , , ,,
, , and the background consisting of the nucleon
pole term and the vector meson exchange in the -channel. To explain the
observed energy dependence of the integrated cross section, two -wave
resonances, and , have to be taken into account
along with the dominating . The integrated cross section as well
as the angular distribution and asymmetry predicted by the model are
in good agreement with the data. Above the photon energy GeV, the
calculated cross section exhibits an appreciable dependence on the - and
-meson contribution, whose coupling with nucleons is not well defined.
Several versions of extending the model to higher energies are considered.Comment: 7 pages, 8 figures, 2 tables, version to appear in Eur.Phys.J.A 22
(2004
Flavor changing neutral currents from lepton and B decays in the two Higgs doublet model
Constraints on the whole spectrum of lepton flavor violating vertices are
shown in the context of the standard two Higgs doublet model. The vertex
involving the mixing is much more constrained than the others, and
the decays proportional to such vertex are usually very supressed. On the other
hand, bounds on the quark sector are obtained from leptonic decays of the
mesons and from . We emphasize that
although the mixing restricts severely the
mixing vertex, the upper bound for this vertex could still give a sizeable
contribution to the decay respect to the standard
model contribution, from which we see that such vertex could still play a role
in the phenomenology.Comment: 9 pages, 2 figures, LaTeX2e. Minor typos corrected. References added
and corrected. Introduction change
Las islas Galápagos, Un viaje a través del espacio y el tiempo
Para hacer este maravilloso viaje, me equipé con todo lo que nos recomendó la persona encargada de la logística, pero, además, hice algo relativamente parecido a lo que hizo Darwin cuando se embarcó en el Beagle: así como él llevó algunos libros de científicos que le ayudarían a comprender sus observaciones (en especial llevó consigo un texto de Lyell y otro de Humboldt), del mismo modo yo viajé acompañado por su libro “El viaje del Beagle”. En lo que sigue, voy a describir algunas de las fotos que tomé en el archipiélago por medio de lo que dijo Darwin en 1835, año en el que lo visitó. Creo que no puede haber mejores descripciones que las que él hizo . Antes de entrar en materia, permítanme citar un texto muy diciente de Eduardo Galeano, el cual nos remonta al año en cuestión. Ah, se me olvidaba: digo que este viaje fue a través del espacio y del tiempo porque, de hecho, las islas se encuentran a cerca de 1000 Km de la costa ecuatoriana, y porque viajar a ese sitio en compañía del libro que he citado, es una manera de devolverse en el tiempo
Message from the President of the United States, transmitting, in compliance with a Senate resolution of July 7, 1876, information in relation to the hostile demonstrations of the Sioux Indians, and the disaster to the forces under General Custer
44-1Message on a Hostile Demonstration by the Sioux Indians. [1664] First news of the disaster regarding Gen. Custer's forces; observance of the treaty of 1868 by nearly all Sioux, save Sitting Bull's band.1876-13
Sisseton and Wahpeton Bands of Sioux Indians.
51-1Indian AffairsChicago, Milwaukee. and St. Paul Railway
Co. [2807] Railway has been constructed
through the Lake Traverse reservation
of the Sisseton and Wahpeton Sioux. but agreement on this has
not been ratified yet.1890-5
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