454 research outputs found
Hydrogen-Air-Steam Combustion Regimes In Large Volumes
Dangerous pressure waves can be generated by the combustion of H2-air-steam mixtures if ordinary deflagrations accelerate to high speed or undergo deflagration-to-detonation transition (DDT). The purpose of this paper is to estimate the potentially dangerous mixtures in large volumes. There is a limited experimental data base for flame acceleration and DDT of EL-airsteam mixtures in smaller geometries. There is concern about the possible explosive combustion in the Space Shuttle main engine exhaust duct at Vandenberg AFB. There are no relevant experimental data or valid theories at this large scale (duct width, W, ~ 10 m) to predict flame acceleration and DDT. We have estimated potentially dangerous mixtures by extrapolating correlations used at smaller scale based on the detonation cell width, X. In square ducts DDTs are possible if W/X \u3e 1. We delineate three combustion regions: nonflammable, weakly flammable, and strongly flammable and potentially detonable. The nonflammable region is the region outside the flammability limit where self-sustaining combustion cannot occur. Flammability limits are independent of scale in large volumes. The strongly flammable region, where dangerous flame acceleration or DDT is possible, is bounded by mixtures with X = 10 m. We estimate detonations are possible when there is less than 45% steam. The weakly flammable region, which lies between the other two, should support only slow combustion, where no significant pressure waves should be generated
A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory
Compact elliptical galaxies are characterized by small sizes and high stellar
densities. They are thought to form through tidal stripping of massive
progenitors. However, only a handful of them were known, preventing us from
understanding the role played by this mechanism in galaxy evolution. We present
a population of 21 compact elliptical galaxies gathered with the Virtual
Observatory. Follow-up spectroscopy and data mining, using high-resolution
images and large databases, show that all the galaxies exhibit old metal-rich
stellar populations different from those of dwarf elliptical galaxies of
similar masses but similar to those of more massive early-type galaxies,
supporting the tidal stripping scenario. Their internal properties are
reproduced by numerical simulations, which result in compact dynamically hot
remnants resembling the galaxies in our sample.Comment: 26 pages, 5 figures, 2 tables. Science in press, published in Science
Express on 1/Oct/2009. Full resolution figures in the supplementary online
material are available from the Science Magazine web-sit
A 3-D wavelet analysis of substructure in the Coma cluster: statistics and morphology
Evidence for clustering within the Coma cluster is found by means of a
multiscale analysis of the combined angular-redshift distribution. We have
compiled a catalogue of 798 galaxy redshifts from published surveys from the
region of the Coma cluster. We examine the presence of substructure and of
voids at different scales ranging from Mpc, using
subsamples of the catalogue, ranging from km/s to km/s.
Our substructure detection method is based on the wavelet transform and on the
segmentation analysis. The wavelet transform allows us to find out structures
at different scales and the segmentation method allows us a quantitative
statistical and morphological analysis of the sample. From the whole catalogue
we select a subset of 320 galaxies, with redshifts between cz=5858 km/s and
cz=8168 km/s that we identify as belonging to the central region of Coma and on
which we have performed a deeper analysis, on scales ranging from
kpc to Mpc. Our results are expressed in terms of the number of
structures or voids and their sphericity for different values of the threshold
detection and at all the scales investigated. According to our analysis, there
is strong evidence for multiple hierarchical substructure, on scales ranging
from a few hundreds of kpc to about Mpc. The morphology of these
substructures is rather spherical. On the scale of kpc we find two
main subclusters which where also found before, but our wavelet analysis shows
even more substructures, whose redshift position is approximatively marked by
these bright galaxies: NGC 4934 & 4840, 4889, 4898 & 4864, 4874 & 4839, 4927,
4875.Comment: 24 pages, 6 figures. ApJ (Main Journal), accepted for publication.
Added one section on statistical tests and slightly modified text and
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The Relationship between Arthritis and Muscular Strength in Older Women with Symptoms of Sarcopenia
Background: Sarcopenia classification is important for prevention or intervention of sarcopenia in the elderly. However, measures used for the current sarcopenia criteria, including muscular strength, could be impacted by forms of arthritis. Thus, it is crucial to understand the impact arthritis has on sarcopenia status. Objectives: The aim was to investigate if arthritis relates to sarcopenia classification via grip strength or single chair stand in older women. A secondary aim was to assess the relationship between grip strength and upper and lower body strength in those with arthritis. Design: A cross-sectional analysis. Setting and participants: Sixty-one community-dwelling older women (71.9±4.6 years) from Rhode Island. Measurements: Sarcopenia status was classified using established working definitions. Grip strength was measured using a hand grip dynamometer, chair stands were measured via a single chair stand test, and gait speed was assessed using a four-meter walk test. A segmental multifrequency bioelectrical impedance analysis assessed body composition and arthritis status was based on self-report. Upper and lower body muscular strength were measured using a chest press and leg press one repetition maximum. Results: No associations were observed between arthritis and sarcopenia status (p=0.36) nor arthritis and upper or lower body muscular strength and grip strength. Conclusions: The results of this study may indicate that arthritis is not associated with sarcopenia status but may affect other measures of muscular strength
Evidence of Substructure in the Cluster of Galaxies A3558
We investigate the dynamical properties of the cluster of galaxies A3558
(Shapley 8). Studying a region of one square degree ( 3 Mpc) centered
on the cluster cD galaxy, we have obtained a statistically complete photometric
catalog with positions and magnitudes of 1421 galaxies (down to a limiting
magnitude of ). This catalog has been matched to the recent velocity
data obtained by Mazure et al. (1997) and from the literature, yielding a
radial velocity catalog containing 322 galaxies. Our analysis shows that the
position/velocity space distribution of galaxies shows significant
substructure. A central bimodal core detected previously in preliminary studies
is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We
show that this central bimodal subtructure is nevertheless composed of a
projected feature, kinematically unrelated to the cluster, plus a group of
galaxies probably in its initial merging phase into a relaxed core. The cD
velocity offset with respect to the average cluster redshift, reported earlier
by several authors, is completely eliminated as a result of our dynamical
analysis. The untangling of the relaxed core component also allows a better,
more reliable determination of the central velocity dispersion, which in turn
eliminates the ``-problem'' for A3558. The cluster also shows a
``preferential'' distribution of subclumps coinciding with the direction of the
major axis position angle of the cD galaxy and of the central X-ray emission
ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication
in the Astrophysical Journa
Galaxy clusters in the CFHTLS. First matched filter candidate catalogue of the Deep fields
We apply a matched-filter cluster detection algorithm to the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) i-band data for the Deep-1, Deep-2, Deep-3 and Deep-4 fields covering a total of 4square degrees. To test the implemented procedure we carry out simulations for assessing the frequency of noise peaks as well as estimate the recovery efficiency. We estimate that up to z~0.7 the catalogue is essentially complete for clusters of richness class R>~1. The recovered redshifts are in general overestimated by dz=0.1 with a scatter of sigma_dz~0.1, except at redshifts z>~1 where the estimated redshifts are systematically underestimated. The constructed cluster candidate catalogue contains 162 detections over an effective area of 3.112 square degrees corresponding to a density of ~52.1 per square degree. The median estimated redshift of the candidates is z=0.6. The estimated noise frequency is 16.9+-5.4 detections per square degree. From visual inspection we identify systems that show a clear concentration of galaxies with similar colour. These systems have a density of ~20 per square degree
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SCOPE safety-controls optimization by performance evaluation: A systematic approach for safety-related decisions at the Hanford Tank Remediation System. Phase 1, final report
The Department of Energy`s Hanford Tank Waste Remediation system poses a significant challenge for hazard management because of the uncertainty that surrounds many of the variables that must be considered in decisions on safety and control strategies. As a result, site managers must often operate under excessively conservative and expensive assumptions. This report describes a systematic approach to quantifying the uncertainties surrounding the critical parameters in control decisions (e.g., condition of the tanks, kinds of wastes, types of possible accidents) through the use of expert elicitation methods. The results of the elicitations would then be used to build a decision support system and accident analysis model that would allow managers to see how different control strategies would affect the cost and safety of a facility configuration
The extreme ultraviolet excess emission in five clusters of galaxies revisited
Evidence for excess extreme ultraviolet (EUV) emission over a tail of X-ray
gas bremsstrahlung emission has been building up recently, but in some cases
remains controversial, mostly due to the moderate quality of the EUV data. In
order to improve the signal to noise ratio in the EUV, we have performed the
wavelet analysis and image reconstructions for five clusters of galaxies
observed both at EUV and X-ray energies with the EUVE and ROSAT satellites
respectively. The profiles of the EUV and X-ray reconstructed images all differ
at a very large confidence level and an EUV excess over a thermal
bremsstrahlung tail is detected in all five clusters (Abell 1795, Abell 2199,
Abell 4059, Coma and Virgo) up to large radii. These results, coupled with
recent XMM-Newton observations, suggest that the EUV excess is probably non
thermal in origin.Comment: accepted for publication in Astronomy & Astrophysics, final versio
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