22,429 research outputs found
Electromagnetic Form Factors and the Localization of Quark Orbital Angular Momentum in the Proton
A new picture is given of generalized parton distributions probed in
experiments in which the probe scale and the momentum transfer
\DD^{2} are well separated. Application of this picture to the
dependence of the form factors shows that gauge invariant quark
orbital angular momentum can be measured and indeed {\it localized} in the
transverse profile of the proton. A previous prediction that
is generalized to GPD
language. This prediction appears to have been confirmed by recent CEBAF data.Comment: 6 pages, 1 figure. To appear in DIS 2001, 9th International Workshop
on Deep Inelastic Scattering, Bologna, 27 April - 1 May, 200
The Transverse Quark Distribution and Proton Electromagnetic Form Factors in Skew Distribution Formalism
Skew density matrices can be diagonalized to yield probability
interpretation. The power-counting prediction of perturbative QCD is found
consistent with recent CEBAF data on Comment: 4 pages, Presented May 23, 2000 by John Ralston. Published in the
Proceedings of the 7th International Conference on Intersections of Particle
and Nuclear Physics, (May 22-28, 2000 Quebec City), Edited by Z. Parseh and
W. Marciano, (AIP Conference Proceedings Number 549.
Eigenvalue spectrum for single particle in a spheroidal cavity: A Semiclassical approach
Following the semiclassical formalism of Strutinsky et al., we have obtained
the complete eigenvalue spectrum for a particle enclosed in an infinitely high
spheroidal cavity. Our spheroidal trace formula also reproduces the results of
a spherical billiard in the limit . Inclusion of repetition of each
family of the orbits with reference to the largest one significantly improves
the eigenvalues of sphere and an exact comparison with the quantum mechanical
results is observed upto the second decimal place for . The
contributions of the equatorial, the planar (in the axis of symmetry plane) and
the non-planar(3-Dimensional) orbits are obtained from the same trace formula
by using the appropriate conditions. The resulting eigenvalues compare very
well with the quantum mechanical eigenvalues at normal deformation. It is
interesting that the partial sum of equatorial orbits leads to eigenvalues with
maximum angular momentum projection, while the summing of planar orbits leads
to eigenvalues with except for L=1. The remaining quantum mechanical
eigenvalues are observed to arise from the 3-dimensional(3D) orbits. Very few
spurious eigenvalues arise in these partial sums. This result establishes the
important role of 3D orbits even at normal deformations.Comment: 17 pages, 7 ps figure
A flat space-time model of the Universe
We propose a model of the Universe based on Minkowski flat space-time metric.
In this model the space-time does not evolve. Instead the matter evolves such
that all the mass parameters increase with time. We construct a model based on
unimodular gravity to show how this can be accomplished within the framework of
flat space-time. We show that the model predicts the Hubble law if the masses
increase with time. Furthermore we show that it fits the high z supernova data
in a manner almost identical to the standard Big Bang model. Furthermore we
show that at early times the Universe is dominated by radiative energy density.
The phenomenon of recombination also arises in our model and hence predicts the
existence of CMBR. However a major difference with the standard Big Bang is
that the radiative temperature and energy density does not evolve in our model.
Furthermore we argue that the basic motivation for inflation is absent in our
model.Comment: 11 pages, no figures, changes in presentatio
An orphangyr B in the Mycobacterium smegmatis genome uncovered by comparative genomics
DNA gyrase is an essential topoisomerase found in all bacteria. It is encoded by gyrB and gyrA genes. These genes are organized differently in different bacteria. Direct comparison of Mycobacterium tuberculosis and Mycobacterium smegmatis genomes reveals presence of an additionalgyr B in M. smegmatis flanked by novel genes. Analysis of the amino acid sequence of GyrB from different organisms suggests that the orphan GyrB in M. smegmatis may have an important cellular role
Two-photon exchange in elastic electron-nucleon scattering
A detailed study of two-photon exchange in unpolarized and polarized elastic
electron--nucleon scattering is presented, taking particular account of nucleon
finite size effects. Contributions from nucleon elastic intermediate states are
found to have a strong angular dependence, which leads to a partial resolution
of the discrepancy between the Rosenbluth and polarization transfer
measurements of the proton electric to magnetic form factor ratio, G_E/G_M. The
two-photon exchange contribution to the longitudinal polarization transfer P_L
is small, whereas the contribution to the transverse polarization transfer P_T
is enhanced at backward angles by several percent, increasing with Q^2. This
gives rise to a small, ~3% suppression of G_E/G_M obtained from the
polarization transfer ratio P_T/P_L at large Q^2. We also compare the
two-photon exchange effects with data on the ratio of e^+ p to e^- p cross
sections, which is predicted to be enhanced at backward angles. Finally, we
evaluate the corrections to the form factors of the neutron, and estimate the
elastic intermediate state contribution to the ^3He form factors
Extreme value distributions for weakly correlated fitnesses in block model
We study the limit distribution of the largest fitness for two models of
weakly correlated and identically distributed random fitnesses. The correlated
fitness is given by a linear combination of a fixed number of independent
random variables drawn from a common parent distribution. We find that for
certain class of parent distributions, the extreme value distribution for
correlated random variables can be related either to one of the known limit
laws for independent variables or the parent distribution itself. For other
cases, new limiting distributions appear. The conditions under which these
results hold are identified.Comment: Expanded, added reference
Logarithmic temperature dependence of conductivity at half-integer filling factors: Evidence for interaction between composite fermions
We have studied the temperature dependence of diagonal conductivity in
high-mobility two-dimensional samples at filling factors and 3/2 at
low temperatures. We observe a logarithmic dependence on temperature, from our
lowest temperature of 13 mK up to 400 mK. We attribute the logarithmic
correction to the effects of interaction between composite fermions, analogous
to the Altshuler-Aronov type correction for electrons at zero magnetic field.
The paper is accepted for publication in Physical Review B, Rapid
Communications.Comment: uses revtex macro
A Rapid Review of COVID-19 Vaccine Prioritization in the U.S.: Alignment between Federal Guidance and State Practice.
BACKGROUND: Population groups to be prioritized for COVID-19 vaccinations in the U.S. have been determined at the Federal level, but there is variation in how States have implemented guidance. This review examines how the position of population groups in vaccine priority lists varies between Federal guidance and State practice. METHODS: An online search of State vaccination prioritization plans was conducted. Data were extracted on each population group included and their relative position. A standardized ranking method was applied to provide a directional measure of variability in prioritization between State and Federal guidance, for each population group. RESULTS: Healthcare workers and those in long-term care facilities were largely prioritized in line with Federal guidance. Aside from early education staff, essential workers were often excluded at State level. Almost all States included the 65-74 year age group and most assigned them to a higher position than recommended in Federal guidance. Those with underlying medical conditions were similarly highly prioritized, although there was more variability across States. Some socially vulnerable groups (not included in Federal guidance) were highly prioritized by many States. CONCLUSIONS: The prioritization of groups for COVID-19 vaccination has been highly variable despite clear Federal guidance. Future guidance must be relevant to local needs, values, and constraints, to minimize any unwarranted heterogeneity in vaccine access across populations
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