106 research outputs found
Nuclear Effects on Bremsstrahlung Neutrino Rates of Astrophysical Interest
We calculate in this work the rates for the neutrino pair production by
nucleon-nucleon bremsstrahlung taking into account the full contribution from a
nuclear one-pion-exchange potential. It is shown that if the temperatures are
low enough (), the integration over the nuclear part can be done
for the general case, ranging from the completely degenerate (D) to the
non-degenerate (ND) regime. We find that the inclusion of the full nuclear
contribution enhances the neutrino pair production by and
bremsstrahlung by a factor of about two in both the D and ND limits when
compared with previous calculations. This result may be relevant for the
physical conditions of interest in the semitransparent regions near the
neutrinosphere in type II supernovae, cooling of neutron stars and other
astrophysical situations.Comment: 11 pages, no figures, LaTex file. submitted to PR
A polymorphism in the glucocorticoid receptor gene may be associated with and increased sensitivity to glucocorticoids in vivo
We investigated whether a polymorphism at nucleotide position 1220,
resulting in an asparagine-to-serine change at codon 363 in the
glucocorticoid receptor (GR) gene is associated with an altered
sensitivity to glucocorticoids. In a group of 216 elderly persons, 13
heterozygotes for the N363S polymorphism were identified by PCR/single
strand conformation polymorphism analysis. In 2 dexamethasone (DEX)
suppression tests (DSTs), using 1 and 0.25 mg DEX, the circulating
cortisol and insulin concentrations were compared between N363S carriers
and controls. In the 1-mg DST, there were no differences between N363S
carriers and controls, with respect to adrenal suppression, but there was
a significantly higher (P < 0.05) insulin response in N363S carriers. In
the 0.25-mg DST, a significantly larger (P < 0.05) cortisol suppression
and higher (P < 0.05) insulin response were seen in N363S carriers.
Comparison of blood pressure, body mass index (BMI), and bone mineral
density (BMD) between the N363S carriers and controls showed that N363S
carriers had a higher (P < 0.05) BMI but normal blood pressure. There was
an obvious trend towards lower age-, BMI-, and sex-adjusted BMD in the
lumbar spine in N363S carriers. GR characteristics measured in 41 controls
and 9 N363S carriers in peripheral mononuclear leucocytes showed no
differences between N363S carriers and controls, with respect to GR number
and ligand binding affinity. However, there was a trend towards greater
sensitivity to DEX in the carriers' lymphocytes, in a mitogen-induced cell
proliferation assay. In transfection assays, the capacity of the codon 363
variant to activate mouse mammary tumor virus promotor-mediated
transcription in COS-1 cells was unaltered, when compared with the
wild-type GR. We conclude that in 6.0% of our study population, a
polymorphism in codon 363 of the GR gene was found. Individuals carrying
this polymorphism seemed healthy at clinical examination but had a higher
sensitivity to exogenously administered glucocorticoids, with respect to
both cortisol suppression and insulin response. Life-long exposure to the
mutated allele may be accompanied by an increased BMI and a lowered BMD in
the lumbar spine but does not affect blood pressure
Free energy of colloidal particles at the surface of sessile drops
The influence of finite system size on the free energy of a spherical
particle floating at the surface of a sessile droplet is studied both
analytically and numerically. In the special case that the contact angle at the
substrate equals a capillary analogue of the method of images is
applied in order to calculate small deformations of the droplet shape if an
external force is applied to the particle. The type of boundary conditions for
the droplet shape at the substrate determines the sign of the capillary
monopole associated with the image particle. Therefore, the free energy of the
particle, which is proportional to the interaction energy of the original
particle with its image, can be of either sign, too. The analytic solutions,
given by the Green's function of the capillary equation, are constructed such
that the condition of the forces acting on the droplet being balanced and of
the volume constraint are fulfilled. Besides the known phenomena of attraction
of a particle to a free contact line and repulsion from a pinned one, we
observe a local free energy minimum for the particle being located at the drop
apex or at an intermediate angle, respectively. This peculiarity can be traced
back to a non-monotonic behavior of the Green's function, which reflects the
interplay between the deformations of the droplet shape and the volume
constraint.Comment: 24 pages, 19 figure
Astrophysical Axion Bounds
Axion emission by hot and dense plasmas is a new energy-loss channel for
stars. Observational consequences include a modification of the solar
sound-speed profile, an increase of the solar neutrino flux, a reduction of the
helium-burning lifetime of globular-cluster stars, accelerated white-dwarf
cooling, and a reduction of the supernova SN 1987A neutrino burst duration. We
review and update these arguments and summarize the resulting axion
constraints.Comment: Contribution to Axion volume of Lecture Notes in Physics, 20 pages, 3
figure
All-sky search for long-duration gravitational wave transients with initial LIGO
We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society
All-sky search for long-duration gravitational wave transients with initial LIGO
We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society
Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model
We present results from a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the J-statistic, and by analyzing data from Advanced LIGO's second observing run. In the frequency range searched, from 60 to 650 Hz, we find no evidence of gravitational radiation. At 194.6 Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of h095%=3.47×10-25 when marginalizing over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering. © 2019 American Physical Society
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω0T<5.58×10-8, Ω0V<6.35×10-8, and Ω0S<1.08×10-7 at a reference frequency f0=25 Hz. © 2018 American Physical Society
Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO-Virgo Run O3b
We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC-2020 March 27 17:00 UTC). We conduct two independent searches: A generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate. © 2022. The Author(s). Published by the American Astronomical Society
- …