13,923 research outputs found
Using temporal distributions of transient events to characterize cosmological source populations
The brightest events in a time series of cosmological transients obey an
observation time dependence which is often overlooked. This dependence can be
exploited to probe the global properties of electromagnetic and gravitational
wave transients (Howell et al. 2007a, Coward & Burman 2005). We describe a new
relation based on a peak flux--observation time distribution and show that it
is invariant to the luminosity distribution of the sources (Howell et al.
2007b). Applying this relation, in combination with a new data analysis filter,
to \emph{Swift} gamma-ray burst data, we demonstrate that it can constrain
their rate density.Comment: published in proceedings of FRONTIERS OF FUNDAMENTAL AND
COMPUTATIONAL PHYSICS: 10th International Symposium, AIP,1246,203, (2010
An improved method for estimating source densities using the temporal distribution of Cosmological Transients
It has been shown that the observed temporal distribution of transient events
in the cosmos can be used to constrain their rate density. Here we show that
the peak flux--observation time relation takes the form of a power law that is
invariant to the luminosity distribution of the sources, and that the method
can be greatly improved by invoking time reversal invariance and the temporal
cosmological principle. We demonstrate how the method can be used to constrain
distributions of transient events, by applying it to Swift gamma-ray burst data
and show that the peak flux--observation time relation is in good agreement
with recent estimates of source parameters. We additionally show that the
intrinsic time dependence allows the method to be used as a predictive tool.
Within the next year of Swift observation, we find a 50% chance of obtaining a
peak flux greater than that of GRB 060017 -- the highest Swift peak flux to
date -- and the same probability of detecting a burst with peak flux > 100
photons s^{-1} cm^{-2} within 6 years.Comment: Submitted to ApJ Letter
Fringe Science: Defringing CCD Images with Neon Lamp Flat Fields
Fringing in CCD images is troublesome from the aspect of photometric quality
and image flatness in the final reduced product. Additionally, defringing
during calibration requires the inefficient use of time during the night to
collect and produce a "supersky" fringe frame. The fringe pattern observed in a
CCD image for a given near-IR filter is dominated by small thickness variations
across the detector with a second order effect caused by the wavelength extent
of the emission lines within the bandpass which produce the interference
pattern. We show that essentially any set of emission lines which generally
match the wavelength coverage of the night sky emission lines within a bandpass
will produce an identical fringe pattern. We present an easy, inexpensive, and
efficient method which uses a neon lamp as a flat field source and produces
high S/N fringe frames to use for defringing an image during the calibration
process.Comment: accepted to PAS
Experimental pressure distributions for a family of blunt bodies at Mach numbers from 2.49 to 4.63 and angles of attack from 0 deg to 15 deg
Pressure distributions for blunt body wind tunnel models at supersonic speeds and angles of attack from 0 to 15 degree
The plumes of IO: A detection of solid sulfur dioxide particles
Spectra of Io obtained during eclipse show a narrow deep absorption feature at 4.871 microns, the wavelength of the Nu sub 1 + Nu sub 3 band of solid SO2. The 4 micron radiation comes from volcanic hot spots at a temperature too high for the existence of solid SO2. It is concluded that the spectral feature results from SO2 particles suspended in plumes above the hot spots. The derived abundance of approximately 0.0003 gm/sq cm may imply an SO2 solid-to-gas ratio of roughly one for the Loki plume, which would in turn suggest that it is driven by the SO2 rather than by sulfur
Thanks, but no thanks: women's avoidance of help-seeking in the context of a dependency-related stereotype
The stereotype that women are dependent on men is a commonly verbalized, potentially damaging aspect of benevolent sexism. We investigated how women may use behavioral disconfirmation of the personal applicability of the stereotype to negotiate such sexism. In an experiment (N = 86), we manipulated female college studentsâ awareness that women may be stereotyped by men as dependent. We then placed participants in a situation where they needed help. Women made aware of the dependency stereotype (compared to controls who were not) were less willing to seek help. They also displayed a stronger negative correlation between help-seeking and post help-seeking affect - such that the more help they sought, the worse they felt. We discuss the relevance of these findings for research concerning womenâs help-seeking and their management of sexist stereotyping in everyday interaction. We also consider the implications of our results for those working in domains such as healthcare, teaching and counseling, where interaction with individuals in need and requiring help is common
Mathematical modelling of elastoplasticity at high stress
This paper describes a simple mathematical model for one-dimensional elastoplastic wave propagation in a metal in the regime where the applied stress greatly exceeds the yield stress. Attention is focussed on the increasing ductility that occurs in the over-driven limit when the plastic wave speed approaches the elastic wave speed. Our model predicts that a plastic compression wave is unable to travel faster than the elastic wave speed, and instead splits into a compressive elastoplastic shock followed by a plastic expansion wave
Transitions through Critical Temperatures in Nematic Liquid Crystals
We obtain âdynamicâ estimates for critical nematic liquid crystal (LC) temperatures with a slowly varying temperature-dependent control variable. We focus on two critical temperatures : the supercooling temperature below which the isotropic phase loses stability and the superheating temperature above which the ordered nematic states do not exist. In contrast to the static problem, the isotropic phase exhibits a memory effect below the supercooling temperature. This delayed loss of stability is independent of the rate of change of temperature and depends purely on the initial value of the temperature
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