6,027 research outputs found
Optimal capture of non-Gaussianity in weak lensing surveys: power spectrum, bispectrum and halo counts
We compare the efficiency of weak lensing-selected galaxy clusters counts and
of the weak lensing bispectrum at capturing non-Gaussian features in the dark
matter distribution. We use the halo model to compute the weak lensing power
spectrum, the bispectrum and the expected number of detected clusters, and
derive constraints on cosmological parameters for a large, low systematic weak
lensing survey, by focusing on the - plane and on the dark
energy equation of state. We separate the power spectrum into the resolved and
the unresolved parts of the data, the resolved part being defined as detected
clusters, and the unresolved part as the rest of the field. We consider four
kinds of clusters counts, taking into account different amount of information :
signal-to-noise ratio peak counts; counts as a function of clusters' mass;
counts as a function of clusters' redshift; and counts as a function of
clusters' mass and redshift. We show that when combined with the power
spectrum, those four kinds of counts provide similar constraints, thus allowing
one to perform the most direct counts, signal-to-noise peaks counts, and get
percent level constraints on cosmological parameters. We show that the weak
lensing bispectrum gives constraints comparable to those given by the power
spectrum and captures non-Gaussian features as well as clusters counts, its
combination with the power spectrum giving errors on cosmological parameters
that are similar to, if not marginally smaller than, those obtained when
combining the power spectrum with cluster counts. We finally note that in order
to reach its potential, the weak lensing bispectrum must be computed using all
triangle configurations, as equilateral triangles alone do not provide useful
information.Comment: Matches ApJ-accepted versio
Metabolic efficiency of liver mitochondria in rats with decreased thermogenesis
AbstractWe have studied changes in hepatic mitochondrial efficiency induced by 24-h fasting or acclimation at 29°C, two conditions of reduced thermogenesis. Basal and palmitate-induced proton leak, which contribute to mitochondrial efficiency, are not affected after 24-h fasting, when serum free triiodothyronine decreases significantly and serum free fatty acids increase significantly. In rats at 29°C, in which serum free triiodothyronine and fatty acids decrease significantly, basal proton leak increases significantly, while no variation is found in palmitate-induced proton leak. The present results indicate that mitochondrial efficiency in the liver is not related to a physiological decrease in whole body thermogenesis
Constraining Cosmology with High Convergence Regions in Weak Lensing Surveys
We propose to use a simple observable, the fractional area of "hot spots" in
weak gravitational lensing mass maps which are detected with high significance,
to determine background cosmological parameters. Because these high-convergence
regions are directly related to the physical nonlinear structures of the
universe, they derive cosmological information mainly from the nonlinear regime
of density fluctuations. We show that in combination with future cosmic
microwave background anisotropy measurements, this method can place constraints
on cosmological parameters that are comparable to those from the redshift
distribution of galaxy cluster abundances. The main advantage of the statistic
proposed in this paper is that projection effects, normally the main source of
uncertainty when determining the presence and the mass of a galaxy cluster,
here serve as a source of information.Comment: 14 pages, 4 figures, accepted for publication in Astrophysical
Journa
Current and emerging diagnosis tools and therapeutics for giant cell arteritis
Introduction: Giant cell arteritis (GCA) is the most common large-vessel vasculitis in individuals older than 50 years from Western countries. The goal of the treatment is to achieve improvement of symptoms and clinical remission as well as decrease the risk of severe vascular complications.
Areas covered: The review summarizes the main epidemiological and clinical features of GCA and discusses in depth both the classic and the new therapies used in the management of GCA.
Expert commentary: Prednisone/prednisolone of 40-60 mg/day is the mainstay in GCA therapy. It yields improvement of clinical features and reduces the risk of permanent visual loss in patients with GCA. Other drugs are used in patients who experience relapses (flares of the disease) or side effects related to glucocorticoids. Methotrexate is the most common conventional immunosuppressive drug used as a glucocorticoid sparing agent. Among the new biologic agents, the most frequently used is the recombinant humanized anti-IL-6 receptor antibody, which is effective to improve clinical symptoms, decrease the cumulative prednisone dose and reduce the frequency of relapses in these patients. Anti-tumor necrosis factor-α therapy is not useful in GCA. Experience with other biologic agents, such as abatacept or ustekinumab, looks promising but it is still scarce
Weak lensing power spectra for precision cosmology: Multiple-deflection, reduced shear and lensing bias corrections
It is usually assumed that the ellipticity power spectrum measured in weak
lensing observations can be expressed as an integral over the underlying matter
power spectrum. This is true at second order in the gravitational potential. We
extend the standard calculation, constructing all corrections to fourth order
in the gravitational potential. There are four types of corrections:
corrections to the lensing shear due to multiple-deflections; corrections due
to the fact that shape distortions probe the reduced shear
rather than the shear itself; corrections associated with the non-linear
conversion of reduced shear to mean ellipticity; and corrections due to the
fact that observational galaxy selection and shear measurement is based on
galaxy brightnesses and sizes which have been (de)magnified by lensing. We show
how the previously considered corrections to the shear power spectrum
correspond to terms in our analysis, and highlight new terms that were not
previously identified. All correction terms are given explicitly as integrals
over the matter power spectrum, bispectrum, and trispectrum, and are
numerically evaluated for the case of sources at z=1. We find agreement with
previous works for the terms. We find that for ambitious
future surveys, the terms affect the power spectrum at
the ~ 1-5 level; they will thus need to be accounted for, but are
unlikely to represent a serious difficulty for weak lensing as a cosmological
probe.Comment: 14 pages, 3 figures; matches A & A accepted versio
Global coastal attenuation of wind-waves observed with radar altimetry
Coastal studies of wave climate and evaluations of wave energy resources are mainly regional
and based on the use of computationally very expensive models or a network of in-situ data.
Considering the significant wave height, satellite radar altimetry provides an established
global and relatively long-term source, whose coastal data are nevertheless typically flagged
as unreliable within 30 km of the coast. This study exploits the reprocessing of the radar
altimetry signals with a dedicated fitting algorithm to retrieve several years of significant
wave height records in the coastal zone. We show significant variations in annual cycle
amplitudes and mean state in the last 30 km from the coastline compared to offshore, in
areas that were up to now not observable with standard radar altimetry. Consequently, a
decrease in the average wave energy flux is observed. Globally, we found that the mean
significant wave height at 3 km off the coast is on average 22% smaller than offshore, the
amplitude of the annual cycle is reduced on average by 14% and the mean energy flux loses
38% of its offshore value
Golden gravitational lensing systems from the Sloan Lens ACS Survey. II. SDSS J1430+4105: A precise inner total mass profile from lensing alone
We study the SLACS strong lensing system SDSSJ1430+4105 at z=0.285. The
lensed source (z=0.575) of this system has a complex morphology with several
subcomponents. Its subcomponents span a radial range from 4 to 10kpc in the
lens plane. Therefore we can constrain the slope of the total projected mass
profile around the Einstein radius (R_E) from lensing alone. We measure a
density profile that is slightly but not significantly shallower than
isothermal at R_E. We decompose the mass of the lensing galaxy into a de
Vaucouleurs (deV) component to trace the stars and an additional dark
component. The spread of multiple image components over a large radial range
also allows us to determine the amplitude of the deV and dark matter components
separately. We get a mass to light ratio of M_deV/L_B~5.5\pm1.5M/L_sun,B and a
dark matter fraction within R_E of ~20 to 40%. Modelling the star formation
history assuming composite stellar populations at solar metallicity to the
galaxy's photometry yields a mass to light ratio of
M_star,salp/L_B~4.0_{-1.3}^{+0.6}M/L_sun,B and
M_star,chab/L_B~2.3_{-0.8}^{+0.3}M/L_sun,B for Salpeter and Chabrier IMFs,
respectively. Hence, the mass to light ratio derived from lensing is more
Salpeter-like, in agreement with results for massive Coma galaxies and other
nearby massive early type galaxies. We examine the consequences of the galaxy
group in which the lensing galaxy is embedded, showing that it has little
influence on the mass to light ratio obtained for the deV component of the
lensing galaxy. Finally, we decompose the projected, azimuthally averaged 2D
density distribution of the deV and dark matter component of the lensing signal
into spherically averaged 3D density profiles. We can show that the 3D dark and
luminous matter density within R_E~0.6R_eff of this SLACS galaxy is similar to
the values of Coma galaxies with the same velocity dispersions.Comment: 24 pages, 21 figures, 11 tables, accepted for publication by MNRA
Cosmology Using Cluster Internal Velocity Dispersions
We compare the distribution of internal velocity dispersions of galaxy
clusters for an observational sample to those obtained from a set of N-body
simulations of seven COBE-normalised cosmological scenarios: the standard CDM
(SCDM) and a tilted (n=0.85) CDM (TCDM) model, a CHDM model with 25% of massive
neutrinos, two low-density LCDM models with Omega_0=0.3 and 0.5, two open OCDM
models with Omega_0=0.4 and 0.6. Simulated clusters are observed in projection
so as to reproduce the main observational biases and are analysed by applying
the same algorithm for interlopers removal and velocity dispersion estimate as
for the reference observational sample. Velocity dispersions for individual
clusters can be largely affected by observational biases in a model-dependent
way: models in which clusters had less time to virialize show larger
discrepancies between 3D and projected velocity dispersions. From the
comparison with real clusters we find that both SCDM and TCDM largely
overproduce clusters. The CHDM model marginally overproduces clusters and
requires a somewhat larger sigma_8 than a purely CDM model in order to produce
the same cluster abundance. The LCDM model with Omega_0=0.3 agrees with data,
while the open model with Omega_0=0.4 and 0.6 underproduces and marginally
overproduces clusters, respectively.Comment: 28 pages, LaTeX uses Elsevier style file, 7 postscript figures (3
bitmapped to lower res.) included. Submitted to New Astronom
Unsupervised labelling of sequential data for location identification in indoor environments
In this paper we present indoor positioning within unknown environments as an unsupervised labelling task on sequential data. We explore a probabilistic framework relying on wireless network radio signals and contextual information, which is increasingly available in large environments. Thus, we form an informative spatial classifier without resorting to a pre-determined map, and show the potential of the approach using both simulated and real data sets. Results demonstrate the ability of the procedure to segregate structures of radio signal observations and form clustered regions in association to areas of interest to the user; thus, we show it is possible to differentiate location between closely spaced zones of variable size and shape
Alcohol consumption and lifetime change in cognitive ability:a gene × environment interaction study
Studies of the effect of alcohol consumption on cognitive ability are often confounded. One approach to avoid confounding is the Mendelian randomization design. Here, we used such a design to test the hypothesis that a genetic score for alcohol processing capacity moderates the association between alcohol consumption and lifetime change in cognitive ability. Members of the Lothian Birth Cohort 1936 completed the same test of intelligence at age 11 and 70 years. They were assessed for recent alcohol consumption in later life and genotyped for a set of four single-nucleotide polymorphisms in three alcohol dehydrogenase genes. These variants were unrelated to late-life cognition or to socioeconomic status. We found a significant gene × alcohol consumption interaction on lifetime cognitive change (p = 0.007). Individuals with higher genetic ability to process alcohol showed relative improvements in cognitive ability with more consumption, whereas those with low processing capacity showed a negative relationship between cognitive change and alcohol consumption with more consumption. The effect of alcohol consumption on cognitive change may thus depend on genetic differences in the ability to metabolize alcohol
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