1,424 research outputs found
Strainrange partitioning behavior of an automotive turbine alloy
This report addresses Strainrange Partitioning, an advanced life prediction analysis procedure, as applied to CA-101 (cast IN 792 + Hf), an alloy proposed for turbine disks in automotive gas turbine engines. The methodology was successful in predicting specimen life under thermal-mechanical cycling, to within a factor of + or - 2
A search for gravitational lensing in 38 X-ray selected clusters of galaxies
We present the results of a CCD imaging survey for gravitational lensing in a
sample of 38 X-ray-selected clusters of galaxies. Our sample consists of the
most X-ray luminous (Lx>= 2x10^{44} erg s^{-1}) clusters selected from the
Einstein Observatory Extended Medium Sensitivity Survey (EMSS) that are
observable from Mauna Kea (dec > -40deg). The sample spans a redshift range of
0.15 0.5. CCD images of the
clusters were obtained in excellent seeing. There is evidence of strong
gravitational lensing in the form of giant arcs (length l > 8'', axis ratio l/w
> 10) in 8 of the 38 clusters. Two additional clusters contain shorter arclets,
and 6 more clusters contain candidate arcs that require follow-up observations
to confirm their lensing origin. Since the survey does not have a uniform
surface brightness limit we do not draw any conclusion based on the statistics
of the arcs found. We note, however, that 60% (3 of 5) of the clusters with Lx
> 10^{45} erg s^{-1}, and none of the 15 clusters with Lx < 4x10^{44} erg
s^{-1} contain giant arcs, thereby confirming that high X-ray luminosity does
identify the most massive systems, and thus X-ray selection is the preferred
method for finding true, rich clusters at intermediate and high redshifts. The
observed geometry of the arcs, most of which are thin, have large axis ratios
(l/w > 10), and are aligned orthogonal to the optical major axes of the
clusters, indicate the cluster core mass density profiles must be compact
(steeper than isothermal). In several cases, however, there is also some
evidence, in the form of possible radial arcs, for density profiles with finite
core radii.Comment: Latex file, 17 pages, 7 jpeg figures, to be published in Astronomy
and Astrophysics Supplement
PCV104 Timely Use Of Ace Inhibitors And Arbs After Newly Diagnosed Diabetes Among Older Adults With Hypertension In The U.S
A Systematic Search for High Surface Brightness Giant Arcs in a Sloan Digital Sky Survey Cluster Sample
We present the results of a search for gravitationally-lensed giant arcs
conducted on a sample of 825 SDSS galaxy clusters. Both a visual inspection of
the images and an automated search were performed and no arcs were found. This
result is used to set an upper limit on the arc probability per cluster. We
present selection functions for our survey, in the form of arc detection
efficiency curves plotted as functions of arc parameters, both for the visual
inspection and the automated search. The selection function is such that we are
sensitive only to long, high surface brightness arcs with g-band surface
brightness mu_g 10. Our upper limits on
the arc probability are compatible with previous arc searches. Lastly, we
report on a serendipitous discovery of a giant arc in the SDSS data, known
inside the SDSS Collaboration as Hall's arc.Comment: 34 pages,8 Fig. Accepted ApJ:Jan-200
Galaxy Groups in the SDSS DR4: I. The Catalogue and Basic Properties
We use a modified version of the halo-based group finder developed by Yang et
al. to select galaxy groups from the Sloan Digital Sky Survey (SDSS DR4). In
the first step, a combination of two methods is used to identify the centers of
potential groups and to estimate their characteristic luminosity. Using an
iterative approach, the adaptive group finder then uses the average
mass-to-light ratios of groups, obtained from the previous iteration, to assign
a tentative mass to each group. This mass is then used to estimate the size and
velocity dispersion of the underlying halo that hosts the group, which in turn
is used to determine group membership in redshift space. Finally, each
individual group is assigned two different halo masses: one based on its
characteristic luminosity, and the other based on its characteristic stellar
mass. Applying the group finder to the SDSS DR4, we obtain 301237 groups in a
broad dynamic range, including systems of isolated galaxies. We use detailed
mock galaxy catalogues constructed for the SDSS DR4 to test the performance of
our group finder in terms of completeness of true members, contamination by
interlopers, and accuracy of the assigned masses. This paper is the first in a
series and focuses on the selection procedure, tests of the reliability of the
group finder, and the basic properties of the group catalogue (e.g. the
mass-to-light ratios, the halo mass to stellar mass ratios, etc.). The group
catalogues including the membership of the groups are available at
http://gax.shao.ac.cn/data/Group.html and
http://www.astro.umass.edu/~xhyang/Group.htmlComment: 19 pages, 12 figures, Accepted for publication in ApJ. Group
catalogues are available at http://gax.shao.ac.cn/data/Group.html and
http://www.astro.umass.edu/~xhyang/Group.htm
Engine Component Retirement-For-Cause: A Nondestructive Evaluation (NDE) and Fracture Mechanics Based Maintainance Concep
Historically, cyclic life limited gas turbine engine components have been retired when they reach an analytically determined life where the first fatigue crack per 1000 parts could be expected. By definition, 99.9% of these components are being retired prematurely as they have considerable useful life remaining. Retirement for Cause is a procedure which would allow safe utilization of the full life capacity of each individual component. Since gas turbine engine rotor components are prime candidates and are among the most costly of engine components, adoption of a RFC maintenance philosophy could result in substantial engine systems life cycle cost savings. Two major technical disciplines must be developed and integrated to realize those cost savings: Fracture Mechanics and Nondestructive Evaluation. This paper discusses the methodology, and development activity required, to integrate these disciplines to provide a viable RFC system for use on military gas turbine engines, and illustrates potential benefits of its application
Identification of A-colored Stars and Structure in the Halo of the Milky Way from SDSS Commissioning Data
A sample of 4208 objects with magnitude 15 < g* < 22 and colors of main
sequence A stars has been selected from 370 square degrees of Sloan Digital Sky
Survey (SDSS) commissioning observations. The data is from two long, narrow
stripes, each with an opening angle of greater than 60 deg, at Galactic
latitudes 36 < abs(b) < 63 on the celestial equator. An examination of the
sample's distribution shows that these stars trace considerable substructure in
the halo. Large overdensities of A-colored stars in the North at (l,b,R) =
(350, 50, 46 kpc) and in the South at (157, -58, 33 kpc) and extending over
tens of degrees are present in the halo of the Milky Way. Using photometry to
separate the stars by surface gravity, both structures are shown to contain a
sequence of low surface gravity stars consistent with identification as a blue
horizontal branch (BHB). Both structures also contain a population of high
surface gravity stars two magnitudes fainter than the BHB stars, consistent
with their identification as blue stragglers (BSs). From the numbers of
detected BHB stars, lower limits to the implied mass of the structures are
6x10^6 M_sun and 2x10^6 M_sun. The fact that two such large clumps have been
detected in a survey of only 1% of the sky indicates that such structures are
not uncommon in the halo. Simple spheroidal parameters are fit to a complete
sample of the remaining unclumped BHB stars and yield (at r < 40 kpc) a fit to
a halo distribution with flattening (c/a = 0.65+/-0.2) and a density falloff
exponent of alpha = -3.2+/-0.3.Comment: AASTeX v5_0, 26 pages, 1 table, 20 figures, ApJ accepte
Improved constraints on H0 from a combined analysis of gravitational-wave and electromagnetic emission from GW170817
The luminosity distance measurement of GW170817 derived from GW analysis in
Abbott et al. 2017 (here, A17:H0) is highly correlated with the measured
inclination of the NS-NS system. To improve the precision of the distance
measurement, we attempt to constrain the inclination by modeling the broad-band
X-ray-to-radio emission from GW170817, which is dominated by the interaction of
the jet with the environment. We update our previous analysis and we consider
the radio and X-ray data obtained at days since merger. We find that the
afterglow emission from GW170817 is consistent with an off-axis relativistic
jet with energy
propagating into an environment with density , with preference for wider jets (opening angle
deg). For these jets, our modeling indicates an off-axis angle deg. We combine our constraints on with the
joint distance-inclination constraint from LIGO. Using the same
km/sec peculiar velocity uncertainty assumed in A17:H0 but with an inclination
constraint from the afterglow data, we get a value of \mbox{km/s/Mpc}, which is higher than the value of
\mbox{km/s/Mpc} found in A17:H0. Further,
using a more realistic peculiar velocity uncertainty of 250 km/sec derived from
previous work, we find km/s/Mpc for H0 from
this system. We note that this is in modestly better agreement with the local
distance ladder than the Planck CMB, though a significant such discrimination
will require such events. Future measurements at days of the
X-ray and radio emission will lead to tighter constraints.Comment: Submitted to ApJL. Comments Welcome. Revised uncertainties in v
A High-resolution Scintillating Fiber Tracker With Silicon Photomultiplier Array Readout
We present prototype modules for a tracking detector consisting of multiple
layers of 0.25 mm diameter scintillating fibers that are read out by linear
arrays of silicon photomultipliers. The module production process is described
and measurements of the key properties for both the fibers and the readout
devices are shown. Five modules have been subjected to a 12 GeV/c proton/pion
testbeam at CERN. A spatial resolution of 0.05 mm and light yields exceeding 20
detected photons per minimum ionizing particle have been achieved, at a
tracking efficiency of more than 98.5%. Possible techniques for further
improvement of the spatial resolution are discussed.Comment: 31 pages, 27 figures, pre-print version of an article published in
Nuclear Instruments and Methods in Physics Research Section A, Vol. 62
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