5,134 research outputs found
Empirical constraints on the origin of fast radio bursts: volumetric rates and host galaxy demographics as a test of millisecond magnetar connection
The localization of the repeating FRB 121102 to a low-metallicity dwarf
galaxy at , and its association with a quiescent radio source,
suggests the possibility that FRBs originate from magnetars, formed by the
unusual supernovae in such galaxies. We investigate this via a comparison of
magnetar birth rates, the FRB volumetric rate, and host galaxy demographics. We
calculate average volumetric rates of possible millisecond magnetar production
channels such as superluminous supernovae (SLSNe), long and short gamma-ray
bursts (GRBs), and general magnetar production via core-collapse supernovae.
For each channel we also explore the expected host galaxy demographics using
their known properties. We determine for the first time the number density of
FRB emitters (the product of their volumetric birthrate and lifetime), Gpc, assuming that FRBs are predominantly emitted
from repetitive sources similar to FRB 121102 and adopting a beaming factor of
0.1. By comparing rates we find that production via rare channels (SLSNe, GRBs)
implies a typical FRB lifetime of 30-300 yr, in good agreement with
other lines of argument. The total energy emitted over this time is consistent
with the available energy stored in the magnetic field. On the other hand, any
relation to magnetars produced via normal core-collapse supernovae leads to a
very short lifetime of 0.5yr, in conflict with both theory and
observation. We demonstrate that due to the diverse host galaxy distributions
of the different progenitor channels, many possible sources of FRB birth can be
ruled out with host galaxy identifications. Conversely, targeted
searches of galaxies that have previously hosted decades-old SLSNe and GRBs may
be a fruitful strategy for discovering new FRBs and related quiescent radio
sources, and determining the nature of their progenitors
Using Wavelets to reject background in Dark Matter experiments
A method based on wavelet techniques has been developed and applied to
background rejection in the data of the IGEX dark matter experiment. The method
is presented and described in some detail to show how it efficiently rejects
events coming from noise and microphonism through a mathematical inspection of
their recorded pulse shape. The result of the application of the method to the
last data of IGEX is presented.Comment: 14 pages, 8 figures. Submitted to Astrop. Phy
Casimir energy between media-separated cylinders: the scalar case
We derive exact expressions for the Casimir scalar interaction energy between
media-separated eccentric dielectric cylinders and for the media-separated
cylinder-plane geometry using a mode-summation approach. Similarly to the
electromagnetic Casimir-Lifshitz interaction energy between fluid-separated
planar plates, the force between cylinders is attractive or repulsive depending
on the relative values of the permittivities of the three intervening media.Comment: New figure and discussion about the integration contour in the
complex plan
Case Notes
For decades, optical time-domain searches have been tuned to find ordinary supernovae, which rise and fall in brightness over a period of weeks. Recently, supernova searches have improved their cadences and a handful of fast-evolving luminous transients have been identified(1-5). These have peak luminosities comparable to type Ia supernovae, but rise to maximum in less than ten days and fade from view in less than one month. Here we present the most extreme example of this class of object thus far: KSN 2015K, with a rise time of only 2.2 days and a time above half-maximum of only 6.8 days. We show that, unlike type Ia supernovae, the light curve of KSN 2015K was not powered by the decay of radioactive elements. We further argue that it is unlikely that it was powered by continuing energy deposition from a central remnant (a magnetar or black hole). Using numerical radiation hydrodynamical models, we show that the light curve of KSN 2015K is well fitted by a model where the supernova runs into external material presumably expelled in a pre-supernova mass-loss episode. The rapid rise of KSN 2015K therefore probes the venting of photons when a hypersonic shock wave breaks out of a dense extended medium.NASA
NNH15ZDA001N
NNX17AI64G
Australian Research Council Centre of Excellence for All-sky Astrophysics
CE11000102
Simulation of High Conversion Efficiency and Open-circuit Voltages Of {\alpha}-si/poly-silicon Solar Cell
The P+ {\alpha}-Si /N+ polycrystalline solar cell is molded using the AMPS-1D
device simulator to explore the new high efficiency thin film poly-silicon
solar cell. In order to analyze the characteristics of this device and the
thickness of N+ poly-silicon, we consider the impurity concentration in the N+
poly-silicon layer and the work function of transparent conductive oxide (TCO)
in front contact in the calculation. The thickness of N+ poly-silicon has
little impact on the device when the thickness varies from 20 {\mu}m to 300
{\mu}m. The effects of impurity concentration in polycrystalline are analyzed.
The conclusion is drawn that the open-circuit voltage (Voc) of P+ {\alpha}-Si
/N+ polycrystalline solar cell is very high, reaching 752 mV, and the
conversion efficiency reaches 9.44%. Therefore, based on the above optimum
parameters the study on the device formed by P+ {\alpha}-Si/N+ poly-silicon is
significant in exploring the high efficiency poly-silicon solar cell.Comment: 8 pages 6figures, 1 table
On the accuracy of the PFA: analogies between Casimir and electrostatic forces
We present an overview of the validity of the Proximity Force Approximation
(PFA) in the calculation of Casimir forces between perfect conductors for
different geometries, with particular emphasis for the configuration of a
cylinder in front of a plane. In all cases we compare the exact numerical
results with those of PFA, and with asymptotic expansions that include the next
to leading order corrections. We also discuss the similarities and differences
between the results for Casimir and electrostatic forces.Comment: 17 pages, 5 figures, Proceedings of the meeting "60 years of Casimir
effect", Brasilia, 200
International standards for early fetal size and pregnancy dating based on ultrasound measurement of crown-rump length in the first trimester of pregnancy.
OBJECTIVES: There are no international standards for relating fetal crown-rump length (CRL) to gestational age (GA), and most existing charts have considerable methodological limitations. The INTERGROWTH-21(st) Project aimed to produce the first international standards for early fetal size and ultrasound dating of pregnancy based on CRL measurement.
METHODS: Urban areas in eight geographically diverse countries that met strict eligibility criteria were selected for the prospective, population-based recruitment, between 9 + 0 and 13 + 6 weeks' gestation, of healthy well-nourished women with singleton pregnancies at low risk of fetal growth impairment. GA was calculated on the basis of a certain last menstrual period, regular menstrual cycle and lack of hormonal medication or breastfeeding in the preceding 2 months. CRL was measured using strict protocols and quality-control measures. All women were followed up throughout pregnancy until delivery and hospital discharge. Cases of neonatal and fetal death, severe pregnancy complications and congenital abnormalities were excluded from the study.
RESULTS: A total of 4607 women were enrolled in the Fetal Growth Longitudinal Study, one of the three main components of the INTERGROWTH-21(st) Project, of whom 4321 had a live singleton birth in the absence of severe maternal conditions or congenital abnormalities detected by ultrasound or at birth. The CRL was measured in 56 women at < 9 + 0 weeks' gestation; these were excluded, resulting in 4265 women who contributed data to the final analysis. The mean CRL and SD increased with GA almost linearly, and their relationship to GA is given by the following two equations (in which GA is in days and CRL in mm): mean CRL = -50.6562 + (0.815118 × GA) + (0.00535302 × GA(2) ); and SD of CRL = -2.21626 + (0.0984894 × GA).
GA estimation is carried out according to the two equations: GA = 40.9041 + (3.21585 × CRL(0.5) ) + (0.348956 × CRL); and SD of GA = 2.39102 + (0.0193474 × CRL).
CONCLUSIONS: We have produced international prescriptive standards for early fetal linear size and ultrasound dating of pregnancy in the first trimester that can be used throughout the world
A Decline in the X-ray through Radio Emission from GW170817 Continues to Support an Off-Axis Structured Jet
We present new observations of the binary neutron star merger GW170817 at
days post-merger, at radio (Karl G. Jansky Very Large
Array; VLA), X-ray (Chandra X-ray Observatory) and optical (Hubble Space
Telescope; HST) wavelengths. These observations provide the first evidence for
a turnover in the X-ray light curve, mirroring a decline in the radio emission
at significance. The radio-to-X-ray spectral energy
distribution exhibits no evolution into the declining phase. Our full
multi-wavelength dataset is consistent with the predicted behavior of our
previously published models of a successful structured jet expanding into a
low-density circumbinary medium, but pure cocoon models with a choked jet
cannot be ruled out. If future observations continue to track our predictions,
we expect that the radio and X-ray emission will remain detectable until days post-merger.Comment: Accepted to ApJL. Updated version includes new VLA observations
extending through 2018 June
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