663 research outputs found
Quantum Monte Carlo Calculations of Pion Scattering from Li
We show that the neutron and proton transition densities predicted by recent
quantum Monte Carlo calculations for A=6,7 nuclei are consistent with pion
scattering from 6Li and 7Li at energies near the Delta resonance. This has
provided a microscopic understanding of the enhancement factors for quadrople
excitations, which were needed to describe pion inelastic scattering within the
nuclear shell model of Cohen and Kurath.Comment: 10 pages, REVTeX, 3 postscript figures; added calculation of elastic
and inelastic pion scattering from 6Li at multiple energie
The Shapes of Dirichlet Defects
If the vacuum manifold of a field theory has the appropriate topological
structure, the theory admits topological structures analogous to the D-branes
of string theory, in which defects of one dimension terminate on other defects
of higher dimension. The shapes of such defects are analyzed numerically, with
special attention paid to the intersection regions. Walls (co-dimension 1
branes) terminating on other walls, global strings (co-dimension 2 branes) and
local strings (including gauge fields) terminating on walls are all considered.
Connections to supersymmetric field theories, string theory and condensed
matter systems are pointed out.Comment: 24 pages, RevTeX, 21 eps figure
Kahler Potential for M-theory on a G_2 Manifold
We compute the moduli Kahler potential for M-theory on a compact manifold of
G_2 holonomy in a large radius approximation. Our method relies on an explicit
G_2 structure with small torsion, its periods and the calculation of the
approximate volume of the manifold. As a verification of our result, some of
the components of the Kahler metric are computed directly by integration over
harmonic forms. We also discuss the modification of our result in the presence
of co-dimension four singularities and derive the gauge-kinetic functions for
the massless gauge fields that arise in this case.Comment: 31 pages, Latex. Altered discussion of truncation of field content,
some typos corrected and references added. Version to appear in Phys. Rev .
A Compact Beam Stop for a Rare Kaon Decay Experiment
We describe the development and testing of a novel beam stop for use in a
rare kaon decay experiment at the Brookhaven AGS. The beam stop is located
inside a dipole spectrometer magnet in close proximity to straw drift chambers
and intercepts a high-intensity neutral hadron beam. The design process,
involving both Monte Carlo simulations and beam tests of alternative beam-stop
shielding arrangements, had the goal of minimizing the leakage of particles
from the beam stop and the resulting hit rates in detectors, while preserving
maximum acceptance for events of interest. The beam tests consisted of
measurements of rates in drift chambers, scintilation counter hodoscopes, a gas
threshold Cherenkov counter, and a lead glass array. Measurements were also
made with a set of specialized detectors which were sensitive to low-energy
neutrons, photons, and charged particles. Comparisons are made between these
measurements and a detailed Monte Carlo simulation.Comment: 39 pages, 14 figures, submitted to Nuclear Instruments and Method
Ghost D-branes
We define a ghost D-brane in superstring theories as an object that cancels
the effects of an ordinary D-brane. The supergroups U(N|M) and OSp(N|M) arise
as gauge symmetries in the supersymmetric world-volume theory of D-branes and
ghost D-branes. A system with a pair of D-brane and ghost D-brane located at
the same location is physically equivalent to the closed string vacuum. When
they are separated, the system becomes a new brane configuration. We generalize
the type I/heterotic duality by including n ghost D9-branes on the type I side
and by considering the heterotic string whose gauge group is OSp(32+2n|2n).
Motivated by the type IIB S-duality applied to D9- and ghost D9-branes, we also
find type II-like closed superstrings with U(n|n) gauge symmetry.Comment: 49 pages, 6 figures, harvmac. v2: references and acknowledgements
adde
Genome-wide enrichment analysis between endometriosis and obesity-related traits reveals novel susceptibility loci
Endometriosis is a chronic inflammatory condition in women that results in pelvic pain and subfertility, and has been associated with decreased body mass index (BMI). Genetic variants contributing to the heritable component have started to emerge from genome-wide association studies (GWAS), although the majority remain unknown. Unexpectedly, we observed an intergenic locus on 7p15.2 that was genome-wide significantly associated with both endometriosis and fat distribution (waist-to-hip ratio adjusted for BMI; WHRadjBMI) in an independent meta-GWAS of European ancestry individuals. This led us to investigate the potential overlap in genetic variants underlying the aetiology of endometriosis, WHRadjBMI and BMI using GWAS data. Our analyses demonstrated significant enrichment of common variants between fat distribution and endometriosis (P = 3.7 × 10(-3)), which was stronger when we restricted the investigation to more severe (Stage B) cases (P = 4.5 × 10(-4)). However, no genetic enrichment was observed between endometriosis and BMI (P = 0.79). In addition to 7p15.2, we identify four more variants with statistically significant evidence of involvement in both endometriosis and WHRadjBMI (in/near KIFAP3, CAB39L, WNT4, GRB14); two of these, KIFAP3 and CAB39L, are novel associations for both traits. KIFAP3, WNT4 and 7p15.2 are associated with the WNT signalling pathway; formal pathway analysis confirmed a statistically significant (P = 6.41 × 10(-4)) overrepresentation of shared associations in developmental processes/WNT signalling between the two traits. Our results demonstrate an example of potential biological pleiotropy that was hitherto unknown, and represent an opportunity for functional follow-up of loci and further cross-phenotype comparisons to assess how fat distribution and endometriosis pathogenesis research fields can inform each other
Thin-shell wormholes with a generalized Chaplygin gas in Einstein-Born-Infeld theory
We construct spherically symmetric thin-shell wormholes supported by a
generalized Chaplygin gas in Born-Infeld electrodynamics coupled to Einstein
gravity, and we analyze their stability under radial perturbations. For
different values of the Born-Infeld parameter and the charge, we compare the
results with those obtained in a previous work for Maxwell electrodynamics. The
stability region in the parameter space reduces and then disappears as the
value of the Born-Infeld parameter is modified in the sense of a larger
departure from Maxwell theory.Comment: 9 pages, 6 figures; v2: improved versio
Entrapment of a Network of Domain Walls
We explore the idea of a network of defects to live inside a domain wall in
models of three real scalar fields, engendering the Z_2 x Z_3 symmetry. The
field that governs the Z_2 symmetry generates a domain wall, and entraps the
hexagonal network formed by the three-junctions of the model of two scalar
fields that describes the remaining Z_3 symmetry. If the host domain wall bends
to the spherical form, in the thin wall approximation there may appear
non-topological structures hosting networks that accept diverse patterns. If
Z_3 is also broken, the model may generate a buckyball containing sixty
junctions, a fullerene-like structure. Applications to cosmology are outlined.Comment: Revtex, 4 pages, 2 ps figures; version to appear in Phys. Rev. D,
Rapid Communicatio
Rotating Black Branes in the presence of nonlinear electromagnetic field
In this paper, we consider a class of gravity whose action represents itself
as a sum of the usual Einstein-Hilbert action with cosmological constant and an
gauge field for which the action is given by a power of the Maxwell
invariant. We present a class of the rotating black branes with Ricci flat
horizon and show that the presented solutions may be interpreted as black brane
solutions with two event horizons, extreme black hole and naked singularity
provided the parameters of the solutions are chosen suitably. We investigate
the properties of the solutions and find that for the special values of the
nonlinear parameter, the solutions are not asymptotically anti-deSitter. At
last, we obtain the conserved quantities of the rotating black branes and find
that the nonlinear source effects on the electric field, the behavior of
spacetime, type of singularity and other quantities.Comment: 7 pages, 5 figures, to appear in EPJ
Nest and foraging‐site selection in Yellowhammers Emberiza citrinella: implications for chick provisioning
Capsule Vegetation structure and invertebrate abundance interact to influence both foraging sites and
nestling provisioning rate; when invertebrate availability is low, adults may take greater risks to provide
food for their young.
Aims To investigate nesting and foraging ecology in a declining farmland bird whose fledging success
is influenced by the availability of invertebrate prey suitable for feeding to offspring, and where perceived
predation risk during foraging can be mediated by vegetation structure.
Methods Provisioning rates of adult Yellowhammers feeding nestlings were measured at nests on arable
farmland. Foraging sites were compared with control sites of both the same and different microhabitats;
provisioning rate was related to habitat features of foraging-sites.
Results Foraging sites had low vegetation density, probably enhancing detection of predators, or high
invertebrate abundance at high vegetation density. Parental provisioning rate decreased with increasing
vegetation cover at foraging sites with high invertebrate abundance; conversely, where invertebrate
abundance was low, provisioning rate increased with increasing vegetation cover.
Conclusions Vegetation structure at foraging sites suggests that a trade-off between predator detection
and prey availability influences foraging site selection in Yellowhammers. Associations between parental
provisioning rate and vegetation variables suggest that where invertebrate abundance is high birds
increase time spent scanning for predators at higher vegetation densities; however, when prey are scarce,
adults may take more risks to provide food for their young
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