2,258 research outputs found
Evolution of the Cluster X-ray Luminosity Function
We report measurements of the cluster X-ray luminosity function out to z=0.8
based on the final sample of 201 galaxy systems from the 160 Square Degree
ROSAT Cluster Survey. There is little evidence for any measurable change in
cluster abundance out to z~0.6 at luminosities less than a few times 10^44
ergs/s (0.5-2.0 keV). However, between 0.6 < z < 0.8 and at luminosities above
10^44 ergs/s, the observed volume densities are significantly lower than those
of the present-day population. We quantify this cluster deficit using
integrated number counts and a maximum-likelihood analysis of the observed
luminosity-redshift distribution fit with a model luminosity function. The
negative evolution signal is >3 sigma regardless of the adopted local
luminosity function or cosmological framework. Our results and those from
several other surveys independently confirm the presence of evolution. Whereas
the bulk of the cluster population does not evolve, the most luminous and
presumably most massive structures evolve appreciably between z=0.8 and the
present. Interpreted in the context of hierarchical structure formation, we are
probing sufficiently large mass aggregations at sufficiently early times in
cosmological history where the Universe has yet to assemble these clusters to
present-day volume densities.Comment: 15 pages, 10 figures, accepted for publication in Ap
Statistical methods in cosmology
The advent of large data-set in cosmology has meant that in the past 10 or 20
years our knowledge and understanding of the Universe has changed not only
quantitatively but also, and most importantly, qualitatively. Cosmologists rely
on data where a host of useful information is enclosed, but is encoded in a
non-trivial way. The challenges in extracting this information must be overcome
to make the most of a large experimental effort. Even after having converged to
a standard cosmological model (the LCDM model) we should keep in mind that this
model is described by 10 or more physical parameters and if we want to study
deviations from it, the number of parameters is even larger. Dealing with such
a high dimensional parameter space and finding parameters constraints is a
challenge on itself. Cosmologists want to be able to compare and combine
different data sets both for testing for possible disagreements (which could
indicate new physics) and for improving parameter determinations. Finally,
cosmologists in many cases want to find out, before actually doing the
experiment, how much one would be able to learn from it. For all these reasons,
sophisiticated statistical techniques are being employed in cosmology, and it
has become crucial to know some statistical background to understand recent
literature in the field. I will introduce some statistical tools that any
cosmologist should know about in order to be able to understand recently
published results from the analysis of cosmological data sets. I will not
present a complete and rigorous introduction to statistics as there are several
good books which are reported in the references. The reader should refer to
those.Comment: 31, pages, 6 figures, notes from 2nd Trans-Regio Winter school in
Passo del Tonale. To appear in Lectures Notes in Physics, "Lectures on
cosmology: Accelerated expansion of the universe" Feb 201
A Suborbital Payload for Soft X-ray Spectroscopy of Extended Sources
We present a suborbital rocket payload capable of performing soft X-ray
spectroscopy on extended sources. The payload can reach resolutions of
~100(lambda/dlambda) over sources as large as 3.25 degrees in diameter in the
17-107 angstrom bandpass. This permits analysis of the overall energy balance
of nearby supernova remnants and the detailed nature of the diffuse soft X-ray
background. The main components of the instrument are: wire grid collimators,
off-plane grating arrays and gaseous electron multiplier detectors. This
payload is adaptable to longer duration orbital rockets given its comparatively
simple pointing and telemetry requirements and an abundance of potential
science targets.Comment: Accepted to Experimental Astronomy, 12 pages plus 1 table and 17
figure
Estimated population access to acute stroke and telestroke centers in the US, 2019
This cross-sectional study assesses US population access to emergency departments with acute stroke capabilities and telestroke capacity in 2019
Concordance of CSF measures of Alzheimer's pathology with amyloid PET status in a preclinical cohort: A comparison of Lumipulse and established immunoassays
INTRODUCTION: We assessed the concordance of cerebrospinal fluid (CSF) amyloid beta (Aβ) and tau measured on the fully automated Lumipulse platform with pre-symptomatic Alzheimer's disease (AD) pathology on amyloid positron emission tomography (PET). METHODS: In 72 individuals from the Insight 46 study, CSF Aβ40, Aβ42, total tau (t-tau), and phosphorylated tau at site 181 (p-tau181) were measured using Lumipulse, INNOTEST, and Meso Scale Discovery (MSD) assays and inter-platform Pearson correlations derived. Lumipulse Aβ42 measures were adjusted to incorporate standardization to certified reference materials. Logistic regressions and receiver operating characteristics analysis generated CSF cut-points optimizing concordance with 18F-florbetapir amyloid PET status (n = 63). RESULTS: Measurements of CSF Aβ, p-tau181, and their ratios correlated well across platforms (r 0.84 to 0.94, P < .0001); those of t-tau and t-tau/Aβ42 correlated moderately (r 0.57 to 0.79, P < .0001). The best concordance with amyloid PET (100% sensitivity and 94% specificity) was afforded by cut-points of 0.075 for Lumipulse Aβ42/Aβ40, 0.087 for MSD Aβ42/Aβ40 and 17.3 for Lumipulse Aβ42/p-tau181. DISCUSSION: The Lumipulse platform provides comparable sensitivity and specificity to established CSF immunoassays in identifying pre-symptomatic AD pathology
A meta-analytic review of stand-alone interventions to improve body image
Objective
Numerous stand-alone interventions to improve body image have been developed. The
present review used meta-analysis to estimate the effectiveness of such interventions, and
to identify the specific change techniques that lead to improvement in body image.
Methods
The inclusion criteria were that (a) the intervention was stand-alone (i.e., solely focused on
improving body image), (b) a control group was used, (c) participants were randomly
assigned to conditions, and (d) at least one pretest and one posttest measure of body
image was taken. Effect sizes were meta-analysed and moderator analyses were conducted.
A taxonomy of 48 change techniques used in interventions targeted at body image
was developed; all interventions were coded using this taxonomy.
Results
The literature search identified 62 tests of interventions (N = 3,846). Interventions produced
a small-to-medium improvement in body image (d+ = 0.38), a small-to-medium reduction in
beauty ideal internalisation (d+ = -0.37), and a large reduction in social comparison tendencies
(d+ = -0.72). However, the effect size for body image was inflated by bias both within
and across studies, and was reliable but of small magnitude once corrections for bias were
applied. Effect sizes for the other outcomes were no longer reliable once corrections for
bias were applied. Several features of the sample, intervention, and methodology moderated
intervention effects. Twelve change techniques were associated with improvements in
body image, and three techniques were contra-indicated.
Conclusions
The findings show that interventions engender only small improvements in body image, and
underline the need for large-scale, high-quality trials in this area. The review identifies effective
techniques that could be deployed in future interventions
Constraining dark energy with Sunyaev-Zel'dovich cluster surveys
We discuss the prospects of constraining the properties of a dark energy
component, with particular reference to a time varying equation of state, using
future cluster surveys selected by their Sunyaev-Zel'dovich effect. We compute
the number of clusters expected for a given set of cosmological parameters and
propogate the errors expected from a variety of surveys. In the short term they
will constrain dark energy in conjunction with future observations of type Ia
supernovae, but may in time do so in their own right.Comment: 5 pages, 3 figures, 1 table, version accepted for publication in PR
Geographically touring the eastern bloc: British geography, travel cultures and the Cold War
This paper considers the role of travel in the generation of geographical knowledge of the eastern bloc by British geographers. Based on oral history and surveys of published work, the paper examines the roles of three kinds of travel experience: individual private travels, tours via state tourist agencies, and tours by academic delegations. Examples are drawn from across the eastern bloc, including the USSR, Poland, Romania, East Germany and Albania. The relationship between travel and publication is addressed, notably within textbooks, and in the Geographical Magazine. The study argues for the extension of accounts of cultures of geographical travel, and seeks to supplement the existing historiography of Cold War geography
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