3,810 research outputs found
A Bayesian Inference Analysis of the X-ray Cluster Luminosity-Temperature Relation
We present a Bayesian inference analysis of the Markevitch (1998) and Allen &
Fabian (1998) cooling flow corrected X-ray cluster temperature catalogs that
constrains the slope and the evolution of the empirical X-ray cluster
luminosity-temperature (L-T) relation. We find that for the luminosity range
10^44.5 erg s^-1 < L_bol < 10^46.5 erg s^-1 and the redshift range z < 0.5,
L_bol is proportional to T^2.80(+0.15/-0.15)(1+z)^(0.91-1.12q_0)(+0.54/-1.22).
We also determine the L-T relation that one should use when fitting the Press-
Schechter mass function to X-ray cluster luminosity catalogs such as the
Einstein Medium Sensitivity Survey (EMSS) and the Southern Serendipitous High-
Redshift Archival ROSAT Catalog (Southern SHARC), for which cooling flow
corrected luminosities are not determined and a universal X-ray cluster
temperature of T = 6 keV is assumed. In this case, L_bol is proportional to
T^2.65(+0.23/-0.20)(1+z)^(0.42-1.26q_0)(+0.75/-0.83) for the same luminosity
and redshift ranges.Comment: Accepted to The Astrophysical Journal, 20 pages, LaTe
Advocacy coalitions involved in California's menu labeling policy debate: Exploring coalition structure, policy beliefs, resources, and strategies.
Advocacy coalitions often play an important role in the state health policymaking process, yet little is known about their structure, composition, and behavior. In 2008, California became the first state to enact a menu labeling law. Using the advocacy coalition framework, we examine different facets of the coalitions involved in California's menu labeling policy debate. We use a qualitative research approach to identify coalition members and explore their expressed beliefs and policy arguments, resources, and strategies by analyzing legislative documents (n = 87) and newspaper articles (n = 78) produced between 1999 and 2009. Between 2003 and 2008, six menu labeling bills were introduced in the state's legislature. We found the issue received increasing media attention during this period. We identified two advocacy coalitions involved in the debate-a public health (PH) coalition and an industry coalition. State organizations acted as coalition leaders and participated for a longer duration than elected officials. The structure and composition of each coalition varied. PH coalition leadership and membership notably increased compared to the industry coalition. The PH coalition, led by nonprofit PH and health organizations, promoted a clear and consistent message around informed decision making. The industry coalition, led by a state restaurant association, responded with cost and implementation arguments. Each coalition used various resources and strategies to advance desired outcomes. PH coalition leaders were particularly effective at using resources and employing advocacy strategies, which included engaging state legislators as coalition members, using public opinion polls and information, and leveraging media resources to garner support. Policy precedence and a local policy push emerged as important policymaking strategies. Areas for future research on the state health policymaking process are discussed
A Search for X-Ray Bright Distant Clusters of Galaxies
We present the results of a search for X--ray luminous distant clusters of
galaxies. We found extended X--ray emission characteristic of a cluster towards
two of our candidate clusters of galaxies. They both have a luminosity in the
ROSAT bandpass of and a redshift of ;
thus making them two of the most distant X--ray clusters ever observed.
Furthermore, we show that both clusters are optically rich and have a known
radio source associated with them. We compare our result with other recent
searches for distant X--ray luminous clusters and present a lower limit of
for the number density of such high redshift
clusters. This limit is consistent with the expected abundance of such clusters
in a standard (b=2) Cold Dark Matter Universe. Finally, our clusters provide
important high redshift targets for further study into the origin and evolution
of massive clusters of galaxies. Accepted for publication in the 10th September
1994 issue of ApJ.Comment: 20 pages Latex file + 1 postscript figure file appende
CFHT AO Imaging of the CLASS Gravitational Lens System B1359+154
We present adaptive optics imaging of the CLASS gravitational lens system
B1359+154 obtained with the Canada-France-Hawaii Telescope (CFHT) in the
infrared K band. The observations show at least three brightness peaks within
the ring of lensed images, which we identify as emission from multiple lensing
galaxies. The results confirm the suspected compound nature of the lens, as
deduced from preliminary mass modeling. The detection of several additional
nearby galaxies suggests that B1359+154 is lensed by the compact core of a
small galaxy group. We attempted to produce an updated lens model based on the
CFHT observations and new 5-GHz radio data obtained with the MERLIN array, but
there are too few constraints to construct a realistic model at this time. The
uncertainties inherent with modeling compound lenses make B1359+154 a
challenging target for Hubble constant determination through the measurement of
differential time delays. However, time delays will offer additional
constraints to help pin down the mass model. This lens system therefore
presents a unique opportunity to directly measure the mass distribution of a
galaxy group at intermediate redshift.Comment: 12 pages including 3 figures; ApJL accepte
Ion beam effect on Ge-Se chalcogenide glass films: Non-volatile memory array formation, structural changes and device performance
The conductive bridge non-volatile memory technology is an emerging way to
replace traditional charge based memory devices for future neural networks and
configurable logic applications. An array of the memory devices that fulfills
logic operations must be developed for implementing such architectures. A
scheme to fabricate these arrays, using ion bombardment through a mask, has
been suggested and advanced by us. Performance of the memory devices is
studied, based on the formation of vias and damage accumulation due to the
interactions of Ar+ ions with GexSe1-x (x=0.2, 0.3 and 0.4) chalcogenide
glasses as a function of the ion energy and dose dependence. Blanket films and
devices were created to study the structural changes, surface roughness, and
device performance. Raman Spectroscopy, Atomic Force Microscopy (AFM), Energy
Dispersive X-Ray Spectroscopy (EDS) and electrical measurements expound the Ar+
ions behavior on thin films of GexSe1-x system. Raman studies show that there
is a decrease in area ratio between edge-shared to corner-shared structural
units, revealing occurrence of structural reorganization within the system as a
result of ion/film interaction. AFM results demonstrate a tendency in surface
roughness improvement with increased Ge concentration, after ion bombardment.
EDS results reveal a compositional change in the vias, with a clear tendency of
greater interaction between ions and the Ge atoms, as evidenced by greater
compositional changes in the Ge rich films
Optimizing future imaging survey of galaxies to confront dark energy and modified gravity models
We consider the extent to which future imaging surveys of galaxies can
distinguish between dark energy and modified gravity models for the origin of
the cosmic acceleration. Dynamical dark energy models may have similar
expansion rates as models of modified gravity, yet predict different growth of
structure histories. We parameterize the cosmic expansion by the two
parameters, and , and the linear growth rate of density fluctuations
by Linder's , independently. Dark energy models generically predict
, while the DGP model . To determine
if future imaging surveys can constrain within 20 percent (or
), we perform the Fisher matrix analysis for a weak lensing
survey such as the on-going Hyper Suprime-Cam (HSC) project. Under the
condition that the total observation time is fixed, we compute the Figure of
Merit (FoM) as a function of the exposure time \texp. We find that the
tomography technique effectively improves the FoM, which has a broad peak
around \texp\simeq {\rm several}\sim 10 minutes; a shallow and wide survey is
preferred to constrain the parameter. While
cannot be achieved by the HSC weak-lensing survey alone, one can improve the
constraints by combining with a follow-up spectroscopic survey like WFMOS
and/or future CMB observations.Comment: 18 pages, typos correcte
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