720 research outputs found
Sensitivity of spherical gravitational-wave detectors to a stochastic background of non-relativistic scalar radiation
We analyze the signal-to-noise ratio for a relic background of scalar
gravitational radiation composed of massive, non-relativistic particles,
interacting with the monopole mode of two resonant spherical detectors. We find
that the possible signal is enhanced with respect to the differential mode of
the interferometric detectors. This enhancement is due to: {\rm (a)} the
absence of the signal suppression, for non-relativistic scalars, with respect
to a background of massless particles, and {\rm (b)} for flat enough spectra, a
growth of the signal with the observation time faster than for a massless
stochastic background.Comment: four pages, late
Coarsening of Surface Structures in Unstable Epitaxial Growth
We study unstable epitaxy on singular surfaces using continuum equations with
a prescribed slope-dependent surface current. We derive scaling relations for
the late stage of growth, where power law coarsening of the mound morphology is
observed. For the lateral size of mounds we obtain with . An analytic treatment within a self-consistent mean-field
approximation predicts multiscaling of the height-height correlation function,
while the direct numerical solution of the continuum equation shows
conventional scaling with z=4, independent of the shape of the surface current.Comment: 15 pages, Latex. Submitted to PR
Tests of the random phase approximation for transition strengths
We investigate the reliability of transition strengths computed in the
random-phase approximation (RPA), comparing with exact results from
diagonalization in full shell-model spaces. The RPA and
shell-model results are in reasonable agreement for most transitions; however
some very low-lying collective transitions, such as isoscalar quadrupole, are
in serious disagreement. We suggest the failure lies with incomplete
restoration of broken symmetries in the RPA. Furthermore we prove, analytically
and numerically, that standard statements regarding the energy-weighted sum
rule in the RPA do not hold if an exact symmetry is broken.Comment: 11 pages, 7 figures; Appendix added with new proof regarding
violation of energy-weighted sum rul
Combined CI+MBPT calculations of energy levels and transition amplitudes in Be, Mg, Ca, and Sr
Configuration interaction (CI) calculations in atoms with two valence
electrons, carried out in the V(N-2) Hartree-Fock potential of the core, are
corrected for core-valence interactions using many-body perturbation theory
(MBPT). Two variants of the mixed CI+MBPT theory are described and applied to
obtain energy levels and transition amplitudes for Be, Mg, Ca, and Sr
Gravitational Wave Emission from Galactic Radio Pulsars
We consider in this work continuous gravitational wave (GW) emission from
non-axisymmetric radio pulsars. We treat in some detail the observational
issues related to the known radio pulsar sample with the aim of unveiling the
actual number of sources contributing to GW, which are likely to be the main
contributors of GWs. It is shown that the operation of spheroidal GW detectors
and full-size interferometers could detect this component of the radiation or
impose useful limits on the effective oblateness of young radio pulsars.Comment: 7 pages, RevTex , no figures , to appear in Phys. Rev.
Low birth weight is associated with chronic kidney disease only in men
The association of low birth weight and chronic kidney disease was examined in a screened volunteer population by the National Kidney Foundation's Kidney Early Evaluation Program. This is a free, community-based health program enrolling individuals aged 18 years or older with diabetes, hypertension, or a family history of kidney disease, diabetes, or hypertension. Self-reported birth weight was categorized and chronic kidney disease defined as an estimated glomerular filtration rate less than 60 ml per min per 1.73 m2 or a urine albumin/creatinine ratio ≥30 mg/g. Among 12 364 participants, 15% reported a birth weight less than 2500 g. In men, significant corresponding odds ratios were found after adjustment for demographic characteristics and health conditions to this low birth weight and chronic kidney disease, but there was no association among women. There was no significant interaction between birth weight and race for either gender. Efforts to clinically understand the etiology of this association and potential means of prevention are essential to improving public health
The detection of Gravitational Waves
This chapter is concerned with the question: how do gravitational waves (GWs)
interact with their detectors? It is intended to be a theory review of the
fundamental concepts involved in interferometric and acoustic (Weber bar) GW
antennas. In particular, the type of signal the GW deposits in the detector in
each case will be assessed, as well as its intensity and deconvolution. Brief
reference will also be made to detector sensitivity characterisation, including
very summary data on current state of the art GW detectors.Comment: 33 pages, 12 figures, LaTeX2e, Springer style files --included. For
Proceedings of the ERE-2001 Conference (Madrid, September 2001
Iron under Earth's core conditions: Liquid-state thermodynamics and high-pressure melting curve
{\em Ab initio} techniques based on density functional theory in the
projector-augmented-wave implementation are used to calculate the free energy
and a range of other thermodynamic properties of liquid iron at high pressures
and temperatures relevant to the Earth's core. The {\em ab initio} free energy
is obtained by using thermodynamic integration to calculate the change of free
energy on going from a simple reference system to the {\em ab initio} system,
with thermal averages computed by {\em ab initio} molecular dynamics
simulation. The reference system consists of the inverse-power pair-potential
model used in previous work. The liquid-state free energy is combined with the
free energy of hexagonal close packed Fe calculated earlier using identical
{\em ab initio} techniques to obtain the melting curve and volume and entropy
of melting. Comparisons of the calculated melting properties with experimental
measurement and with other recent {\em ab initio} predictions are presented.
Experiment-theory comparisons are also presented for the pressures at which the
solid and liquid Hugoniot curves cross the melting line, and the sound speed
and Gr\"{u}neisen parameter along the Hugoniot. Additional comparisons are made
with a commonly used equation of state for high-pressure/high-temperature Fe
based on experimental data.Comment: 16 pages including 6 figures and 5 table
Surface Kinetics and Generation of Different Terms in a Conservative Growth Equation
A method based on the kinetics of adatoms on a growing surface under
epitaxial growth at low temperature in (1+1) dimensions is proposed to obtain a
closed form of local growth equation. It can be generalized to any growth
problem as long as diffusion of adatoms govern the surface morphology. The
method can be easily extended to higher dimensions. The kinetic processes
contributing to various terms in the growth equation (GE) are identified from
the analysis of in-plane and downward hops. In particular, processes
corresponding to the (h -> -h) symmetry breaking term and curvature dependent
term are discussed. Consequence of these terms on the stable and unstable
transition in (1+1) dimensions is analyzed. In (2+1) dimensions it is shown
that an additional (h -> -h) symmetry breaking term is generated due to the
in-plane curvature associated with the mound like structures. This term is
independent of any diffusion barrier differences between in-plane and out
of-plane migration. It is argued that terms generated in the presence of
downward hops are the relevant terms in a GE. Growth equation in the closed
form is obtained for various growth models introduced to capture most of the
processes in experimental Molecular Beam Epitaxial growth. Effect of
dissociation is also considered and is seen to have stabilizing effect on the
growth. It is shown that for uphill current the GE approach fails to describe
the growth since a given GE is not valid over the entire substrate.Comment: 14 pages, 7 figure
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