1,271 research outputs found
Compact Binary Coalescences in the Band of Ground-based Gravitational-Wave Detectors
As the ground-based gravitational-wave telescopes LIGO, Virgo, and GEO 600
approach the era of first detections, we review the current knowledge of the
coalescence rates and the mass and spin distributions of merging neutron-star
and black-hole binaries. We emphasize the bi-directional connection between
gravitational-wave astronomy and conventional astrophysics. Astrophysical input
will make possible informed decisions about optimal detector configurations and
search techniques. Meanwhile, rate upper limits, detected merger rates, and the
distribution of masses and spins measured by gravitational-wave searches will
constrain astrophysical parameters through comparisons with astrophysical
models. Future developments necessary to the success of gravitational-wave
astronomy are discussed.Comment: Replaced with version accepted by CQG
The GEO600 squeezed light source
The next upgrade of the GEO600 gravitational wave detector is scheduled for
2010 and will, in particular, involve the implementation of squeezed light. The
required non-classical light source is assembled on a 1.5m^2 breadboard and
includes a full coherent control system and a diagnostic balanced homodyne
detector. Here, we present the first experimental characterization of this
setup as well as a detailed description of its optical layout. A squeezed
quantum noise of up to 9dB below the shot-noise level was observed in the
detection band between 10Hz and 10kHz. We also present an analysis of the
optical loss in our experiment and provide an estimation of the possible
non-classical sensitivity improvement of the future squeezed light enhanced
GEO600 detector.Comment: 8 pages, 4 figure
Interpolated kilonova spectra models: necessity for a phenomenological, blue component in the fitting of AT2017gfo spectra
In this work, we present a simple interpolation methodology for spectroscopic
time series, based on conventional interpolation techniques (random forests)
implemented in widely-available libraries. We demonstrate that our existing
library of simulations is sufficient for training, producing interpolated
spectra that respond sensitively to varied ejecta parameter, post-merger time,
and viewing angle inputs. We compare our interpolated spectra to the AT2017gfo
spectral data, and find parameters similar to our previous inferences using
broadband light curves. However, the spectral observations have significant
systematic short-wavelength residuals relative to our models, which we cannot
explain within our existing framework. Similar to previous studies, we argue
that an additional blue component is required. We consider a radioactive
heating source as a third component characterized by light, slow-moving,
lanthanide-free ejecta with , c,
and cm/g. When included as part of our radiative
transfer simulations, our choice of third component reprocesses blue photons
into lower energies, having the opposite effect and further accentuating the
blue-underluminosity disparity in our simulations. As such, we are unable to
overcome short-wavelength deficits at later times using an additional
radioactive heating component, indicating the need for a more sophisticated
modeling treatment.Comment: 11 pages, 7 figures, presenting at April APS session F13.0000
Transition density of diffusion on Sierpinski gasket and extension of Flory's formula
Some problems related to the transition density u(t,x) of the diffusion on
the Sierpinski gasket are considerd, based on recent rigorous results and
detailed numerical calculations. The main contents are an extension of Flory's
formula for the end-to-end distance exponent of self-avoiding walks on the
fractal spaces, and an evidence of the oscillatory behavior of u(t,x) on the
Sierpinski gasket.Comment: 11 pages, REVTEX, 2 postscript figure
Ablation of the canonical testosterone production pathway via knockout of the steroidogenic enzyme HSD17B3, reveals a novel mechanism of testicular testosterone production
Male development, fertility, and lifelong health are all androgen-dependent. Approximately 95% of circulating testosterone is synthesized by the testis and the final step in this canonical pathway is controlled by the activity of the hydroxysteroid-dehydrogenase-17-beta-3 (HSD17B3). To determine the role of HSD17B3 in testosterone production and androgenization during male development and function we have characterized a mouse model lacking HSD17B3. The data reveal that developmental masculinization and fertility are normal in mutant males. Ablation of HSD17B3 inhibits hyperstimulation of testosterone production by hCG, although basal testosterone levels are maintained despite the absence of HSD17B3. Reintroduction of HSD17B3 via gene-delivery to Sertoli cells in adulthood partially rescues the adult phenotype, showing that, as in development, different cell-types in the testis are able to work together to produce testosterone. Together, these data show that HS17B3 acts as a rate-limiting-step for the maximum level of testosterone production by the testis but does not control basal testosterone production. Measurement of other enzymes able to convert androstenedione to testosterone identifies HSD17B12 as a candidate enzyme capable of driving basal testosterone production in the testis. Together, these findings expand our understanding of testosterone production in males
Surrogate light curve models for kilonovae with comprehensive wind ejecta outflows and parameter estimation for AT2017gfo
The electromagnetic emission resulting from neutron star mergers have been
shown to encode properties of the ejected material in their light curves. The
ejecta properties inferred from the kilonova emission has been in tension with
those calculated based on the gravitational wave signal and numerical
relativity models. Motivated by this tension, we construct a broad set of
surrogate light curve models derived for kilonova ejecta. The four-parameter
family of two-dimensional anisotropic simulations and its associated surrogate
explore different assumptions about the wind outflow morphology and outflow
composition, keeping the dynamical ejecta component consistent. We present the
capabilities of these surrogate models in interpolating kilonova light curves
across various ejecta parameters and perform parameter estimation for AT2017gfo
both without any assumptions on the outflow and under the assumption that the
outflow must be representative of solar r-process abundance patterns. Our
parameter estimation for AT2017gfo shows these surrogate models help alleviate
the ejecta property discrepancy while also illustrating the impact of
systematic modeling uncertainties on these properties, urging further
investigation.Comment: 15 pages, 6 figures, data available in Zenodo
(https://zenodo.org/record/7335961) and GitHub
(https://github.com/markoris/surrogate_kne
Condensation of actin filaments pushing against a barrier
We develop a model to describe the force generated by the polymerization of
an array of parallel biofilaments. The filaments are assumed to be coupled only
through mechanical contact with a movable barrier. We calculate the filament
density distribution and the force-velocity relation with a mean-field approach
combined with simulations. We identify two regimes: a non-condensed regime at
low force in which filaments are spread out spatially, and a condensed regime
at high force in which filaments accumulate near the barrier. We confirm a
result previously known from other related studies, namely that the stall force
is equal to N times the stall force of a single filament. In the model studied
here, the approach to stalling is very slow, and the velocity is practically
zero at forces significantly lower than the stall force.Comment: 21 pages, 6 figures: Combined figures, fixed typos, added extra
material, altered symbolism to avoid confusion. Accepted by New Journal of
Physic
Constraining inputs to realistic kilonova simulations through comparison to observed -process abundances
Kilonovae, one source of electromagnetic emission associated with neutron
star mergers, are powered by the decay of radioactive isotopes in the
neutron-rich merger ejecta. Models for kilonova emission consistent with the
electromagnetic counterpart to GW170817 predict characteristic abundance
patterns, determined by the relative balance of different types of material in
the outflow. Assuming the observed source is prototypical, this inferred
abundance pattern in turn must match -process abundances deduced by other
means, such as what is observed in the solar system. We report on analysis
comparing the input mass-weighted elemental compositions adopted in our
radiative transfer simulations to the mass fractions of elements in the Sun, as
a practical prototype for the potentially universal abundance signature from
neutron-star mergers. We characterize the extent to which our parameter
inference results depend on our assumed composition for the dynamical and wind
ejecta and examine how the new results compare to previous work. We find that a
dynamical ejecta composition calculated using the FRDM2012 nuclear mass and
FRLDM fission models with extremely neutron-rich ejecta ()
along with moderately neutron-rich () wind ejecta composition
yields a wind-to-dynamical mass ratio of = 0.47 which
best matches the observed AT2017gfo kilonova light curves while also producing
the best-matching abundance of neutron-capture elements in the solar system.Comment: 16 pages, 9 figures, submitted to PR
A boron-coated CCD camera for direct detection of Ultracold Neutrons (UCN)
A new boron-coated CCD camera is described for direct detection of ultracold
neutrons (UCN) through the capture reactions B
(n,0)Li (6%) and B(n,1)Li (94%).
The experiments, which extend earlier works using a boron-coated ZnS:Ag
scintillator, are based on direct detections of the neutron-capture byproducts
in silicon. The high position resolution, energy resolution and particle ID
performance of a scientific CCD allows for observation and identification of
all the byproducts , Li and (electron recoils). A
signal-to-noise improvement on the order of 10 over the indirect method has
been achieved. Sub-pixel position resolution of a few microns is demonstrated.
The technology can also be used to build UCN detectors with an area on the
order of 1 m. The combination of micrometer scale spatial resolution, few
electrons ionization thresholds and large area paves the way to new research
avenues including quantum physics of UCN and high-resolution neutron imaging
and spectroscopy.Comment: 10 pages, 8 figure
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