64,656 research outputs found
Application of selective epitaxy to fabrication of nanometer scale wire and dot structures
The selective growth of nanometer scale GaAs wire and dot structures using metalorganic vapor phase epitaxy is demonstrated. Spectrally resolved cathodoluminescence images as well as spectra from single dots and wires are presented. A blue shifting of the GaAs peak is observed as the size scale of the wires and dots decreases
Observing mergers of non-spinning black-hole binaries
Advances in the field of numerical relativity now make it possible to
calculate the final, most powerful merger phase of binary black-hole
coalescence for generic binaries. The state of the art has advanced well beyond
the equal-mass case into the unequal-mass and spinning regions of parameter
space. We present a study of the nonspinning portion of parameter space,
primarily using an analytic waveform model tuned to available numerical data,
with an emphasis on observational implications. We investigate the impact of
varied mass ratio on merger signal-to-noise ratios (SNRs) for several
detectors, and compare our results with expectations from the test-mass limit.
We note a striking similarity of the waveform phasing of the merger waveform
across the available mass ratios. Motivated by this, we calculate the match
between our 1:1 (equal mass) and 4:1 mass-ratio waveforms during the merger as
a function of location on the source sky, using a new formalism for the match
that accounts for higher harmonics. This is an indicator of the amount of
degeneracy in mass ratio for mergers of moderate-mass-ratio systems.Comment: 13 pages, 11 figures, submitted to Phys. Rev.
The HI Environment of Nearby Lyman-alpha Absorbers
We present the results of a VLA and WSRT search for HI emission from the
vicinity of seven nearby clouds, which were observed in Lya absorption with HST
toward Mrk335, Mrk501 and PKS2155-304. We searched a volume of 40' x 40' x 1000
km/s. The HI mass sensitivity (5 sigma) varies from 5x10^6 to 5x10^8 Msun. We
detected HI emission in the vicinity of four out of seven absorbers. The
closest galaxy is a small dwarf galaxy at a projected distance of 68/h kpc from
the sight line toward Mrk335. It has the same velocity (V=1970 km/s) as one of
the absorbers, and has an HI mass of only 4x10^7 Msun. We found a more luminous
galaxy at the velocity (V=5100 km/s) of one of the absorbers toward
PKS2155-304, 230/h kpc from the sight line. Two other, stronger absorbers
toward PKS2155-304 at V=17,000 km/s are associated with a loose group of three
bright spiral galaxies, at projected distances of 300 to 600/h kpc. These
results support the conclusion that most nearby Lya forest clouds trace the
large-scale structures outlined by optically luminous galaxies. We do not find
any evidence for a physical association between an absorber and its closest
galaxy.Comment: 4 Tables, 11 Figures, to be published in Astron J. (Oct 1996) Vol 11
How Do Consumers Use Nutrition Labels on Food Products in the United States?
This study examined how consumers use food labels in the United States. Based on the results from the cluster analysis, eight nutrition label questions from the Health and Diet Survey fell into 2 categories of label usage: for shopping or for dietary decisions. Survey respondents reported equal or more consideration of nutrition-label information for dietary choices than for shopping decisions in 2008 compared with prior survey years. Female consumers, frequent label users, well-educated, consumers aged 50 to 59, or consumers with any health issues were significantly more likely to use food labels for all kinds of purposes than their corresponding counterparts
X-Ray Spectral Variability of PKS 2005-489 During the Spectacular November 1998 Flare
We report on monitoring of the BL Lac object PKS 2005-489 by the Rossi X-ray
Timing Explorer (RXTE) in October-December 1998. During these months, the
source underwent a spectacular flare; at its peak on November 10, its 2-10 keV
flux was , over 30 times
brighter than in quiescence. During the rising phase, the X-ray spectrum of PKS
2005-489 hardened considerably, reaching near maximum. During the declining phase, the X-ray spectrum
steepened rapidly, reaching , then became somewhat harder
towards the end of December (). While such behavior has been
seen before, the simplicity, magnitude and duration of this flare allowed us to
study it in great detail. We argue that this flare was caused by either the
injection of particles into the jet or {\it in situ} particle acceleration, and
that the spectral steepening which followed the flare maximum was the result of
synchrotron cooling. Contrary to other recently observed blazar flares (e.g.,
Mkn 501, 3C 279, PKS 2155-304), our results do not imply a major shift in the
location of the synchrotron peak during this flare.Comment: ApJ Letters in press, 6 pages, 2 figures Corrected reference
Testing of High Voltage Surge Protection Devices for Use in Liquid Argon TPC Detectors
In this paper we demonstrate the capability of high voltage varistors and gas
discharge tube arrestors for use as surge protection devices in liquid argon
time projection chamber detectors. The insulating and clamping behavior of each
type of device is characterized in air (room temperature), and liquid argon
(90~K), and their robustness under high voltage and high energy surges in
cryogenic conditions is verified. The protection of vulnerable components in
liquid argon during a 150 kV high voltage discharge is also demonstrated. Each
device is tested for argon contamination and light emission effects, and both
are constrained to levels where no significant impact upon liquid argon time
projection chamber functionality is expected. Both devices investigated are
shown to be suitable for HV surge protection applications in cryogenic
detectors.Comment: 22 pages, 18 figures v2: reduced file size for journal submissio
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