1,253 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
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
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
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
The Northern Sky Optical Cluster Survey II: An Objective Cluster Catalog for 5800 Square Degrees
We present a new, objectively defined catalog of candidate galaxy clusters
based on the galaxy catalogs from the Digitized Second Palomar Observatory Sky
Survey (DPOSS). This cluster catalog, derived from the best calibrated plates
in the high latitude (|b|>30) Northern Galactic Cap region, covers 5,800 square
degrees, and contains 8,155 candidate clusters. A simple adaptive kernel
density mapping technique, combined with the SExtractor object detection
algorithm, is used to detect galaxy overdensities, which we identify as
clusters. Simulations of the background galaxy distribution and clusters of
varying richnesses and redshifts allow us to optimize detection parameters, and
measure the completeness and contamination rates for our catalog. Cluster
richnesses and photometric redshifts are measured, using integrated colors and
magnitudes for each cluster. An extensive spectroscopic survey is used to
confirm the photometric results.
This catalog, with well-characterized sample properties, provides a sound
basis for future studies of cluster physics and large scale structure.Comment: 49 pages, 16 figures. Accepted to AJ; appearing in April. Version
with full resolution figures, and full length tables available at
http://dposs.caltech.edu:8080/NoSOCS.htm
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
The Lifetime of FRIIs in Groups and Clusters: Implications for Radio-Mode Feedback
We determine the maximum lifetime t_max of 52 FRII radio sources found in 26
central group galaxies from cross correlation of the Berlind SDSS group catalog
with the VLA FIRST survey. Mock catalogs of FRII sources were produced to match
the selection criteria of FIRST and the redshift distribution of our parent
sample, while an analytical model was used to calculate source sizes and
luminosities. The maximum lifetime of FRII sources was then determined via a
comparison of the observed and model projected length distributions. We
estimate the average FRII lifetime is 1.5x10^7 years and the duty cycle is
~8x10^8 years. Degeneracies between t_max and the model parameters: jet power
distribution, axial ratio, energy injection index, and ambient density
introduce at most a factor of two uncertainty in our lifetime estimate. In
addition, we calculate the radio active galactic nuclei (AGN) fraction in
central group galaxies as a function of several group and host galaxy
properties. The lifetime of radio sources recorded here is consistent with the
quasar lifetime, even though these FRIIs have substantially sub-Eddington
accretion. These results suggest a fiducial time frame for energy injection
from AGN in feedback models. If the morphology of a given extended radio source
is set by large-scale environment, while the lifetime is determined by the
details of the accretion physics, this FRII lifetime is relevant for all
extended radio sources.Comment: 18 pages, 7 figures. Accepted for publication in ApJ. High resolution
paper available at http://www.astronomy.ohio-state.edu/~bird/BMK07.pd
Cyber-infrastructure to Support Science and Data Management for the Dark Energy Survey
The Dark Energy Survey (DES; operations 2009-2015) will address the nature of
dark energy using four independent and complementary techniques: (1) a galaxy
cluster survey over 4000 deg2 in collaboration with the South Pole Telescope
Sunyaev-Zel'dovich effect mapping experiment, (2) a cosmic shear measurement
over 5000 deg2, (3) a galaxy angular clustering measurement within redshift
shells to redshift=1.35, and (4) distance measurements to 1900 supernovae Ia.
The DES will produce 200 TB of raw data in four bands, These data will be
processed into science ready images and catalogs and co-added into deeper,
higher quality images and catalogs. In total, the DES dataset will exceed 1 PB,
including a 100 TB catalog database that will serve as a key science analysis
tool for the astronomy/cosmology community. The data rate, volume, and duration
of the survey require a new type of data management (DM) system that (1) offers
a high degree of automation and robustness and (2) leverages the existing high
performance computing infrastructure to meet the project's DM targets. The DES
DM system consists of (1) a grid-enabled, flexible and scalable middleware
developed at NCSA for the broader scientific community, (2) astronomy modules
that build upon community software, and (3) a DES archive to support automated
processing and to serve DES catalogs and images to the collaboration and the
public. In the recent DES Data Challenge 1 we deployed and tested the first
version of the DES DM system, successfully reducing 700 GB of raw simulated
images into 5 TB of reduced data products and cataloguing 50 million objects
with calibrated astrometry and photometry.Comment: 12 pages, 3 color figures, 1 table. Published in SPIE vol. 627
Galaxy-Quasar correlations between APM galaxies and Hamburg-ESO QSOs
We detect angular galaxy-QSO cross-correlations between the APM Galaxy
Catalogue and a preliminary release (consisting of roughly half of the
anticipated final catalogue) of the Hamburg-ESO Catalogue of Bright QSOs as a
function of source QSO redshift using multiple cross-correlation estimators.
Each of the estimators yield very similar results, implying that the APM
catalogue and the Hamburg-ESO survey are both fair samples of the respective
true galaxy and QSO populations. Though the signal matches the expectations of
gravitational lensing qualitatively, the strength of the measured
cross-correlation signal is significantly greater than the CDM models of
lensing by large scale structure would suggest. This same disagreement between
models and observation has been found in several earlier studies. We estimate
our confidence in the correlation detections versus redshift by generating 1000
random realizations of the Hamburg-ESO QSO survey: We detect physical
associations between galaxies and low-redshift QSOs at 99% confidence and
detect lensing associations at roughly 95% confidence for QSOs with redshifts
between 0.6 and 1. Control cross-correlations between Galactic stars and QSOs
show no signal. Finally, the overdensities (underdensities) of galaxies near
QSO positions relative to those lying roughly 135 - 150 arcmin away are
uncorrelated with differences in Galactic extinction between the two regions,
implying that Galactic dust is not significantly affecting the QSO sample.Comment: 35 pages total, including 9 figures. Accepted by the Astrophysical
Journa
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