2,742 research outputs found
Beryllium fastener technology
Program was conducted to develop, produce, and test optimum-configuration, beryllium prestressed and blind fasteners. The program was carried out in four phases - phase 1, feasibility study, phase 2, development, phase 3, evaluation of beryllium alloys, and phase 4, fabrication and testing
Unravelling the Mysteries of the Leo Ring: An Absorption Line Study of an Unusual Gas Cloud
Since the 1980's discovery of the large (2x10^9 Msun) intergalactic cloud
known as the Leo Ring, this object has been the center of a lively debate about
its origin. Determining the origin of this object is still important as we
develop a deeper understanding of the accretion and feedback processes that
shape galaxy evolution. We present HST/COS observations of three sightlines
near the Ring, two of which penetrate the high column density neutral hydrogen
gas visible in 21 cm observations of the object. These observations provide the
first direct measurement of the metallicity of the gas in the Ring, an
important clue to its origins. Our best estimate of the metallicity of the ring
is ~10% Zsun, higher than expected for primordial gas but lower than expected
from an interaction. We discuss possible modifications to the interaction and
primordial gas scenarios that would be consistent with this metallicity
measurement.Comment: 11 pages, 7 figures, accepted Ap
Assessing Vulnerability of Selected Sectors Under Environmental Tax Reform: The Issue of Pricing Power. ESRI WP222. October 2007
This paper investigates pricing power, an important criterion for identifying sectors that would be vulnerable under environmental tax reform. Environmental tax reform, defined here as introduction of carbon taxes alongside reductions in labour taxes, could bear heavily on sectors that are energy intensive and highly traded, in particular if their options for adapting technology are limited. However, a sector with pricing power has less to fear as, rather than having to conform to the world price, it can set its price to accommodate a tax mark-up
Discovery of a Dwarf Post-Starburst Galaxy Near a High Column Density Ly-alpha Absorber
We report the discovery of a dwarf (M_B = -13.9) post-starburst galaxy
coincident in recession velocity (within uncertainties) with the highest column
density absorber (N_HI = 10^15.85 cm^{-2} at cz = 1586 km/s) in the 3C~273
sightline. This galaxy is by far the closest galaxy to this absorber, projected
just 71 kpc on the sky from the sightline. The mean properties of the stellar
populations in this galaxy are consistent with a massive starburst ~3.5 Gyrs
ago, whose attendant supernovae, we argue, could have driven sufficient gas
from this galaxy to explain the nearby absorber. Beyond the proximity on the
sky and in recession velocity, the further evidence in favor of this conclusion
includes both a match in the metallicities of absorber and galaxy, and the fact
that the absorber has an overabundance of Si/C, suggesting recent type II
supernova enrichment. Thus, this galaxy and its ejecta are the expected
intermediate stage in the fading dwarf evolutionary sequence envisioned by
Babul & Rees to explain the abundance of faint blue galaxies at intermediate
redshifts.Comment: 33 pages, 4 figures, ApJ in pres
Distinct requirements for the Rad32(Mre¹¹) nuclease and Ctp1(CtIP) in the removal of covalently bound topoisomerase I and II from DNA
For a cancer cell to resist treatment with drugs that trap topoisomerases covalently on the DNA, the topoisomerase must be removed. In this study, we provide evidence that the Schizosaccharomyces pombe Rad32Mre11 nuclease activity is involved in the removal of both Top2 from 5′ DNA ends as well as Top1 from 3′ ends in vivo. A ctp1CtIP deletion is defective for Top2 removal but overproficient for Top1 removal, suggesting that Ctp1CtIP plays distinct roles in removing topoisomerases from 5′ and 3′ DNA ends. Analysis of separation of function mutants suggests that MRN-dependent topoisomerase removal contributes significantly to resistance against topoisomerase-trapping drugs. This study has important implications for our understanding of the role of the MRN complex and CtIP in resistance of cells to a clinically important group of anticancer drugs
Relationships among pro-inflammatory and degradation-related biomarkers released by articular cartilage from osteoarthritic knees
"Orthpaedic Surgery, School of Medicine."Introduction: Osteoarthritis (OA) is a multifactorial disease often progressing from an initial insult or injury to whole-joint inflammation and degeneration causing pain and dysfunction ; Previous studies have indicated moderate to weak linear correlations between inflammatory and degradation related biomarker production levels by OA cartilage during culture ; This study was designed to characterize non-linear relationships among pro-inflammatory and degradation- related biomarkers produced by articular cartilage recovered from patients with knee OA."This study was funded by the Thompson Laboratory for Regenerative Orthopaedics."Neurological Surgery, University of Missouri School of Medicin
The Cosmic Background Imager
Design and performance details are given for the Cosmic Background Imager
(CBI), an interferometer array that is measuring the power spectrum of
fluctuations in the cosmic microwave background radiation (CMBR) for multipoles
in the range 400 < l < 3500. The CBI is located at an altitude of 5000 m in the
Atacama Desert in northern Chile. It is a planar synthesis array with 13 0.9-m
diameter antennas on a 6-m diameter tracking platform. Each antenna has a
cooled, low-noise receiver operating in the 26-36 GHz band. Signals are
cross-correlated in an analog filterbank correlator with ten 1 GHz bands. This
allows spectral index measurements which can be used to distinguish CMBR
signals from diffuse galactic foregrounds. A 1.2 kHz 180-deg phase switching
scheme is used to reject cross-talk and low-frequency pick-up in the signal
processing system. The CBI has a 3-axis mount which allows the tracking
platform to be rotated about the optical axis, providing improved (u,v)
coverage and a powerful discriminant against false signals generated in the
receiving electronics. Rotating the tracking platform also permits polarization
measurements when some of the antennas are configured for the orthogonal
polarization.Comment: 14 pages. Accepted for publication in PASP. See also
http://www.astro.caltech.edu/~tjp/CBI
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