1,788 research outputs found
Bose-stimulated scattering off a cold atom trap
The angle and temperature dependence of the photon scattering rate for
Bose-stimulated atom recoil transitions between occupied states is compared to
diffraction and incoherent Rayleigh scattering near the Bose-Einstein
transition for an optically thin trap in the limit of large particle number, N.
Each of these processes has a range of angles and temperatures for which it
dominates over the others by a divergent factor as N->oo.Comment: 18 pages (REVTeX), no figure
Condensate fluctuations of a trapped, ideal Bose gas
For a non-self-interacting Bose gas with a fixed, large number of particles
confined to a trap, as the ground state occupation becomes macroscopic, the
condensate number fluctuations remain micrscopic. However, this is the only
significant aspect in which the grand canonical description differs from
canonical or microcanonical in the thermodynamic limit. General arguments and
estimates including some vanishingly small quantities are compared to explicit,
fixed-number calculations for 10^2 to 10^6 particles.Comment: 16 pages (REVTeX) plus 4 figures (ps), revision includes brief
comparison of repulsive-interaction vs. fixed-N fluctuation damping. To be
published in Phys. Rev.
Variation of parameters in Beckeâ3 hybrid exchangeâcorrelation functional
We have investigated the consequences of varying the three parameters in Becke's hybrid exchangeâcorrelation functional, which includes five contributions: HartreeâFock exchange, local exchange, Becke's gradient exchange correction, local correlation, and some form of gradient correlation correction. Our primary focus was upon obtaining orbital energies with magnitudes that are reasonable approximations to the electronic ionization potentials; however, we also looked at the effects on molecular geometries and atomization enthalpies. A total of 12 parameter combinations was considered for each of three different gradient correlation corrections: the LeeâYangâParr, the Perdewâ86, and the PerdewâWang 91. Five molecules were included in the study: HCN, N2, N2O, F2O, and H2O. For comparison, a HartreeâFock calculation was also carried out for each of these. The 6â31+G** basis set was used
A Lattice Study of Spectator Effects in Inclusive Decays of B-Mesons
We compute the matrix elements of the operators which contribute to spectator
effects in inclusive decays of -mesons. The results agree well with
estimates based on the vacuum saturation (factorization) hypothesis. For the
ratio of lifetimes of charged and neutral mesons we find
, where the first error represents
the uncertainty in our evaluation of the matrix elements, and the second is an
estimate of the uncertainty due to the fact that the Wilson coefficient
functions have only been evaluated at tree-level in perturbation theory. This
result is in agreement with the experimental measurement. We also discuss the
implications of our results for the semileptonic branching ratio and the charm
yield.Comment: 25 pages (figures are included). Revised version (some numerical
integrals have been recomputed
Color Confinement and Massive Gluons
Color confinement is one of the central issues in QCD so that there are
various interpretations of this feature. In this paper we have adopted the
interpretation that colored particles are not subject to observation just
because colored states are unphysical in the sense of Eq. (2.16). It is shown
that there are two phases in QCD distinguished by different choices of the
gauge parameter. In one phase, called the "confinement phase", color
confinement is realized and gluons turn out to be massive. In the other phase,
called the "deconfinement phase", color confinement is not realized, but the
gluons remain massless.Comment: 14 page
QCD Factorization for Decays: Strong Phases and CP Violation in the Heavy Quark Limit
We show that, in the heavy quark limit, the hadronic matrix elements that
enter meson decays into two light mesons can be computed from first
principles, including `non-factorizable' strong interaction corrections, and
expressed in terms of form factors and meson light-cone distribution
amplitudes. The conventional factorization result follows in the limit when
both power corrections in and radiative corrections in are
neglected. We compute the order- corrections to the decays
, and in the heavy
quark limit and briefly discuss the phenomenological implications for the
branching ratios, strong phases and CP violation.Comment: 6 pages, 1 figur
Higher Order Corrections at Zero Recoil
The general structure of the corrections at zero recoil is studied. The
relevant matrix elements are forward matrix elements of local higher
dimensional operators and their time ordered products with higher order terms
from the Lagrangian. These matrix elements may be classified in a simple way
and the analysis at the non recoil point for the form factor of heavy quark
currents simplifies drastically. The second order recoil corrections to the
form factor of the axial vector current, relevant for the
determination from decays, are estimated to be .Comment: LaTeX, 25 pages, one figure, appended after \end{document} as
uu-encoded and compressed eps file, uses epsf, CERN-TH.7162/9
Molecular dynamics simulations of liquid nitromethane
A potential energy function with harmonic intramolecular and Lennard-Jones plus Coulombic intermolecular terms was tested in molecular dynamics simulations of liquid nitromethane. Parameter values were adjusted iteratively until satisfactory agreement with density functional pair calculations and experimental data was achieved. The properties computed using the NVT and NPT ensembles were the heat of vaporization, dielectric constant, self-diffusion coefficient, density, heat capacity at constant pressure, pair correlation functions, single molecule and collective dipole moment reorientation times, the vibrational spectrum, and the effect of increasing pressure upon the CâN stretching frequency. Overall, the results were in reasonable accord with experimental results, the greatest discrepancy being for the dielectric constant. It was concluded, on the basis of the reorientation times and the calculated molecular
Peace Makers or Draft Dodgers: Haredi Resistance to Israeli Military Conscription
The haredim in Israel are an ultra-Orthodox Jewish religious group who uphold the most conservative of Jewish laws. Instead of serving in the Israel Defense Forces (IDF) as all other Israelis do, the haredim are exempted from the IDF\u27s policy of universal conscription. This thesis proposes three hypotheses to determine why Israel\u27s haredim do not serve in the IDF. First, the haredim do not serve in the IDF because they do not want to; second, the haredim do not serve because they hold pacifistic political opinions; and third, the haredim do not serve because Jewish religious tradition forbids military service. To test these hypotheses, data were gathered by conducting a literature review and studying Israeli newspapers, official Israeli Government statistics, and unofficial public opinion surveys. Accordingly, a close examination of both the haredi worldview and the cultural characteristics of Israel\u27s haredi communities suggests that the haredim do not want to serve in the IDF for self-interested reasons. Furthermore, a survey of haredi political opinions indicates that the majority of haredim exhibit a hawkish and aggressive political orientation. Finally, an analysis of individual haredi voices reveals that haredi yeshiva students consider their Torah studies to be an integral component to Israel\u27s wartime activities. Contrary to the expectations of this thesis, haredi resistance to military service is not defined by an aversion to war or a commitment to peace, and it therefore cannot serve as a model for advocates of conflict resolution to emulate
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