335 research outputs found
Design guide for high pressure oxygen systems
A repository for critical and important detailed design data and information, hitherto unpublished, along with significant data on oxygen reactivity phenomena with metallic and nonmetallic materials in moderate to very high pressure environments is documented. This data and information provide a ready and easy to use reference for the guidance of designers of propulsion, power, and life support systems for use in space flight. The document is also applicable to designs for industrial and civilian uses of high pressure oxygen systems. The information presented herein are derived from data and design practices involving oxygen usage at pressures ranging from about 20 psia to 8000 psia equal with thermal conditions ranging from room temperatures up to 500 F
Emission-Line Properties of z > 4 Quasars
We present results of a program of high signal-to-noise spectroscopy for 44
QSOs at redshifts > 4 using the MMT and Keck observatories. The quasar spectra
cover 1100 -- 1700 A in the rest frame for sources spanning a luminosity range
of approximately 2 orders of magnitude. Comparisons between these data and
spectra of lower redshift quasars reveal a high degree of similarity, although
differences are present in the profiles and the strengths of some emission
features. An examination of the luminosity dependence of the emission lines
reveals evidence for a weak or absent Baldwin effect among z > 4 QSOs. We
compare measurements for objects in our sample with results from other high
redshift surveys characterized by different selection techniques. Distributions
of equivalent widths for these different ensembles are consistent with a common
parent population, suggesting that our sample is not strongly biased, or in any
case, subject to selection effects that are not significantly different from
other surveys, including the Sloan Digital Sky Survey. Based on this
comparison, we tentatively conclude that the trends identified here are
representative of high z QSOs. In particular, the data bolster indications of
supersolar metallicities in these luminous, high-z sources, which support
scenarios that assume substantial star formation at epochs preceding or
concurrent with the QSO phenomena.Comment: 26 pages (incl. 9 figures), AASTeX v5.0, to appear in The
Astrophysical Journa
Direct determination of quasar redshifts
We present observations of 11 quasars, selected in the range z = 2.2-4.1,
obtained with ESA's Superconducting Tunnel Junction (STJ) camera on the WHT.
Using a single template quasar spectrum, we show that we can determine the
redshifts of these objects to about 1%. A follow-up spectroscopic observation
of one QSO for which our best-fit redshift (z = 2.976) differs significantly
from the tentative literature value (z ~ 2.30) confirms that the latter was
incorrect.Comment: 4 pages, 3 figures; uses aa.cls, psfig.sty, natbib.sty; accepted for
publication in A&A Letter
A contemporaneous infrared flash from a long gamma-ray burst: an echo from the central engine
The explosion that results in a cosmic gamma-ray burst (GRB) is thought to
produce emission from two physical processes -- the activity of the central
engine gives rise to the high-energy emission of the burst through internal
shocking and the subsequent interaction of the flow with the external
environment produces long-wavelength afterglow. While afterglow observations
continue to refine our understanding of GRB progenitors and relativistic
shocks, gamma-ray observations alone have not yielded a clear picture of the
origin of the prompt emission nor details of the central engine. Only one
concurrent visible-light transient has been found and was associated with
emission from an external shock. Here we report the discovery of infrared (IR)
emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of
GRB 041219a. Our robotic telescope acquired 21 images during the active phase
of the burst, yielding the earliest multi-colour observations of any
long-wavelength emission associated with a GRB. Analysis of an initial IR pulse
suggests an origin consistent with internal shocks. This opens a new
possibility to study the central engine of GRBs with ground-based observations
at long wavelengths.Comment: Accepted to Nature on March 1, 2005. 9 pages, 4 figures, nature12.cls
and nature1.cls files included. This paper is under press embargo until print
publicatio
Discovery of the Optical Transient of the Gamma Ray Burst 990308
The optical transient of the faint Gamma Ray Burst 990308 was detected by the
QUEST camera on the Venezuelan 1-m Schmidt telescope starting 3.28 hours after
the burst. Our photometry gives , , , and for times ranging from 3.28 to 3.47
hours after the burst. The colors correspond to a spectral slope of close to
. Within the standard synchrotron fireball model,
this requires that the external medium be less dense than , the
electrons contain of the shock energy, and the magnetic field energy
must be less than 24% of the energy in the electrons for normal interstellar or
circumstellar densities. We also report upper limits of at 132 s
(with LOTIS), from 132-1029s (with LOTIS), at 28.2 min
(with Super-LOTIS), and a 8.5 GHz flux of at 110 days (with the
Very Large Array). WIYN 3.5-m and Keck 10-m telescopes reveal this location to
be empty of any host galaxy to and . The lack of a host
galaxy likely implies that it is either substantially subluminous or more
distant than a red shift of .Comment: ApJ Lett submitted, 5 pages, 2 figures, no space for 12 coauthor
The Team Keck Treasury Redshift Survey of the GOODS-North Field
We report the results of an extensive imaging and spectroscopic survey in the
GOODS-North field completed using DEIMOS on the Keck II telescope. Observations
of 2018 targets in a magnitude-limited sample of 2911 objects to R=24.4 yield
secure redshifts for a sample of 1440 galaxies and AGN plus 96 stars. In
addition to redshifts and associated quality assessments, our catalog also
includes photometric and astrometric measurements for all targets detected in
our R-band imaging survey of the GOODS-North region. We investigate various
sources of incompleteness and find the redshift catalog to be 53% complete at
its limiting magnitude. The median redshift of z=0.65 is lower than in similar
deep surveys because we did not select against low-redshift targets. Comparison
with other redshift surveys in the same field, including a complementary
Hawaii-led DEIMOS survey, establishes that our velocity uncertainties are as
low as 40 km/s for red galaxies and that our redshift confidence assessments
are accurate. The distributions of rest-frame magnitudes and colors among the
sample agree well with model predictions out to and beyond z=1. We will release
all survey data, including extracted 1-D and sky-subtracted 2-D spectra, thus
providing a sizable and homogeneous database for the GOODS-North field which
will enable studies of large scale structure, spectral indices, internal galaxy
kinematics, and the predictive capabilities of photometric redshifts.Comment: 17 pages, 18 figures, submitted to AJ; v2 minor changes; see survey
database at http://www2.keck.hawaii.edu/realpublic/science/tksurvey
Searches for the Shell Swept up by the Stellar Wind from Cyg OB2
We investigated the kinematics of ionized gas in an extended (20 degrees by
15 degrees) region containing the X-ray Superbubble in Cygnus with the aim of
finding the shell swept up by a strong wind from Cyg OB2. H-alpha observations
were carried out with high angular and spectral resolutions using a Fabry-Perot
interferometer attached to the 125-cm telescope at the Crimean Observatory of
the Sternberg Astronomical Institute. We detected high-velocity gas motions,
which could result from the expansion of the hypothetical shell at a velocity
of 25-50 km/s. Given the number of OB stars increased by Knoedlseder (2000) by
an order of magnitude, Cyg OB2 is shown to possess a wind that is strong enough
[Lw ~= (1-2)x10^39 erg/s] to produce a shell comparable in size to the X-ray
Superbubble and to a giant system of optical filaments. Based on our
measurements and on X-ray and infrared observations, we discuss possible
observational manifestations of the shell swept up by the wind.Comment: 14 pages, Astronomy Letter
Discovery of the optical transient of GRB 990308
The optical transient of the faint gamma-ray burst GRB 990308 was detected by the QUEST camera on the Venezuelan 1 m Schmidt telescope starting 3.28 hr after the burst. Our photometry gives V= 18.32 ± 0.07, R = 18.14 ± 0.06, B = 18.65 ± 0.23, and R = 18.22 ± 0.05 for times ranging from 3.28 to 3.47 hr after the burst. The colors correspond to a spectral slope of close to fv â v1/3. Within the standard synchrotron fireball model, this requires that the external medium be less dense than 104 cm-3, the electrons contain more than 20% of the shock energy, and the magnetic field energy be less than 24% of the energy in the electrons for normal interstellar or circumstellar densities. We also report upper limits of V \u3e 12.0 at 132 s (with LOTIS), V \u3e 13.4 from 132 to 1029 s (with LOTIS), V \u3e 15.3 at 28.2 minutes (with Super-LOTIS), and a 8.5 GHz flux of less than 114 ÎŒJy at 110 days (with the Very Large Array). Wisconsin-Indiana-Yale-NOAO 3.5 m and Keck 10 m telescopes reveal this location to be empty of any host galaxy to R \u3e 25.7 and K \u3e 23.3. The lack of a host galaxy likely implies that it is either substantially subluminous or more distant than a redshift of âŒ1.2
Association of polygenic risk score with the risk of chronic lymphocytic leukemia and monoclonal B-cell lymphocytosis
Inherited loci have been found to be associated with risk of chronic lymphocytic leukemia (CLL). A combined polygenic risk score (PRS) of representative single nucleotide polymorphisms (SNPs) from these loci may improve risk prediction over individual SNPs. Herein, we evaluated the association of a PRS with CLL risk and its precursor, monoclonal B-cell lymphocytosis (MBL). We assessed its validity and discriminative ability in an independent sample and evaluated effect modification and confounding by family history (FH) of hematological cancers. For discovery, we pooled genotype data on 41 representative SNPs from 1499 CLL and 2459 controls from the InterLymph Consortium. For validation, we used data from 1267 controls from Mayo Clinic and 201 CLL, 95 MBL, and 144 controls with a FH of CLL from the Genetic Epidemiology of CLL Consortium. We used odds ratios (ORs) to estimate disease associations with PRS and c-statistics to assess discriminatory accuracy. In InterLymph, the continuous PRS was strongly associated with CLL risk (OR, 2.49; P 5 4.4310294). We replicated these findings in the Genetic Epidemiology of CLL Consortium and Mayo controls (OR, 3.02; P 5 7.8 3 10230) and observed high discrimination (c-statistic 5 0.78). When jointly modeled with FH, PRS retained its significance, along with FH status. Finally, we found a highly significant association of the continuous PRS with MBL risk (OR, 2.81; P 5 9.8 310216). In conclusion, our validated PRS was strongly associated with CLL risk, adding information beyond FH.The PRS provides a means of identifying those individuals at greater risk for CLL as well as those at increased risk of MBL, a condition that has potential clinical impact beyond CLL
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