1,246 research outputs found
Galaxy Cluster Masses at Moderate Redshifts
The masses of galaxy clusters are dominated by dark matter, and a robust determination of their masses has the potential of indicating how much dark matter exists on large scales in the universe, and the cosmological parameter Omega. X-ray observations of galaxy clusters provide a direct measure of both the gas mass in the intra-cluster medium, and also the total gravitating mass of the cluster. We used new and archival ROSAT observations to measure these quantities for a sample of intermediate redshift clusters which have also been subject to intensive dynamical studies, in order to compare the mass estimates from different methods. A direct comparison of dynamical mass estimates yielded surprisingly good results
Red Sequence Cluster Finding in the Millennium Simulation
We investigate halo mass selection properties of red-sequence cluster finders
using galaxy populations of the Millennium Simulation (MS). A clear red
sequence exists for MS galaxies in massive halos at redshifts z < 1, and we use
this knowledge to inform a cluster-finding algorithm applied to 500 Mpc/h
projections of the simulated volume. At low redshift (z=0.4), we find that 90%
of the clusters found have galaxy membership dominated by a single, real-space
halo, and that 10% are blended systems for which no single halo contributes a
majority of a cluster's membership. At z=1, the fraction of blends increases to
22%, as weaker redshift evolution in observed color extends the comoving length
probed by a fixed range of color. Other factors contributing to the increased
blending at high-z include broadening of the red sequence and confusion from a
larger number of intermediate mass halos hosting bright red galaxies of
magnitude similar to those in higher mass halos. Our method produces catalogs
of cluster candidates whose halo mass selection function, p(M|\Ngal,z), is
characterized by a bimodal log-normal model with a dominant component that
reproduces well the real-space distribution, and a redshift-dependent tail that
is broader and displaced by a factor ~2 lower in mass. We discuss implications
for X-ray properties of optically selected clusters and offer ideas for
improving both mock catalogs and cluster-finding in future surveys.Comment: final version to appear in MNRAS. Appendix added on purity and
completeness, small shift in red sequence due to correcting an error in
finding i
Dynamical Masses of RCS Galaxy Clusters
A multi-object spectroscopy follow-up survey of galaxy clusters selected from
the Red-sequence Cluster Survey (RCS) is being completed. About forty clusters
were chosen with redshifts from 0.15 to 0.6, and in a wide range of richnesses.
One of the main science drivers of this survey is a study of internal dynamics
of clusters. We present some preliminary results for a subset of the clusters,
including the correlation of optical richness with mass, and the mass-to-light
ratio as a function of cluster mass.Comment: 5 pages, 5 figures, to appear in the Proceedings of IAU Colloquium
195: "Outskirts of Galaxy Clusters: intense life in the suburbs", Torino
Italy, March 200
BENEFITS OF CONTROLLING SALINE WATER IN COLORADO
The Arkansas River in Colorado is confronted with a salinity issue; the majority of this salinity problem is due to agricultural runoff caused by irrigation. Reducing applications of irrigation water through adoption of more technically efficient irrigation systems is one means of improving water quality in the Arkansas River basin. This research uses positive mathematical programming to model the cropping practices of the farms along the Arkansas River. It examines the affect of acreage and profit levels of these farms given the choice of changing their irrigation technologies.Environmental Economics and Policy,
Phospholipid reactivation of plasmalogen metabolism
This report is concerned mainly with the properties of an enzyme from rat liver microsomes which hydrolyzes the alkenyl ether bond of 1â(1âČâalkâ1âČâenyl)âglyceroâ3âphosphorylâcholine (alkenylâGPC hydrolase).Destruction of the normal environment of the microsomes by treatment with phospholipases A or C caused inactivation of the alkenylâGPC hydrolase, which was then partially reactivated by the addition of exogenous phospholipids. Both sphingomyelin and diacylâGPC were efficient in restoring activity; diacylâGPE was less effective; and monoacylâGPC and monoacylâGPE were ineffective. The presence of two long hydrocarbon chains in the lipid activator is apparently required for reactivation, suggesting that interaction of hydrophobic areas of the enzyme with the phospholipid is necessary for maximal activity. High concentrations of sucrose mimicked the effect of phospholipids, and because the sucrose and diacylâGPC did not show an additive effect, they may reactivate the enzyme in a similar manner.Disrupting the enzymeâs environment by freezing and thawing the preparation also resulted in a loss of enzymatic activity, which was restored by added exogenous phospholipids.The alkenylâGPC hydrolase was inhibited by imidazole and some of its derivatives. Histidine and Nâacetyl histidine did not inhibit the enzyme, presumably due to the presence of a negative charge on the carboxyl group rather than the steric bulk of that group, since histidine methyl ester did inhibit the enzyme. Kinetic evidence showed imidazole to be a competitive inhibitor. The enzymatic activity of imidazoleâtreated microsomes also increased following addition of exogenous phospholipids. Imidazole inhibition differed from the phospholipase Aâinactivation in that it was partially reversed by KCl, but not by sucrose. Imidazole did not inhibit other microsomal enzymes tested, indicating that it is not a general inhibitor of membraneâassociated enzymes.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141883/1/lipd0111.pd
Detection of Mycobacterium avium ss. Paratuberculosis in Blau Syndrome Tissues
Background and Aim of the Work. Blau syndrome is an inherited granulomatous inflammatory disorder with clinical findings of uveitis, arthritis, and dermatitis. Although rare, Blau syndrome shares features with the more common diseases sarcoidosis and Crohn's disease. The clinical findings of Blau syndrome are indistinguishable from juvenile sarcoidosis; the mutations of Blau syndrome are on the same gene of chromosome 16 (CARD15) that confers susceptibility to Crohn's disease. The product of this gene is part of the innate immune system. Mycobacterium avium ss. paratuberculosis (MAP) is the putative cause of Crohn's disease and has been implicated as a causative agent of sarcoidosis. Methods. Archival tissues of individuals with Blau syndrome were tested for the presence of MAP. Results. DNA evidence of MAP was detected in all of the tissues. Conclusions. This article finds that MAP is present in Blau syndrome tissue and postulates that it has a causal role. The presence of MAP in Blau syndromeâan autosomal dominant, systemic inflammatory diseaseâconnects genetic and environmental aspects of âautoimmuneâ disease
- âŠ