2,528 research outputs found
Lyalpha versus X-ray heating in the high-z IGM
In this paper we examine the effect of X-ray and Lyalpha photons on the
intergalactic medium temperature. We calculate the photon production from a
population of stars and micro-quasars in a set of cosmological hydrodynamic
simulations which self-consistently follow the dark matter dynamics, radiative
processes as well as star formation, black hole growth and associated feedback
processes. We find that, (i) IGM heating is always dominated by X-rays unless
the Lyalpha photon contribution from stars in objects with mass M<10^8 Msun
becomes significantly enhanced with respect to the X-ray contribution from BHs
in the same halo (which we do not directly model). (ii) Without overproducing
the unresolved X-ray background, the gas temperature becomes larger than the
CMB temperature, and thus an associated 21 cm signal should be expected in
emission, at z<11.5. We discuss how in such a scenario the transition redshift
between a 21 cm signal in absorption and in emission could be used to
constraint BHs accretion and associated feedback processes.Comment: 7 pages, 3 figures, accepted for publication in MNRA
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Adaptations to Climate in Candidate Genes for Common Metabolic Disorders
Evolutionary pressures due to variation in climate play an important role in shaping phenotypic variation among and within species and have been shown to influence variation in phenotypes such as body shape and size among humans. Genes involved in energy metabolism are likely to be central to heat and cold tolerance. To test the hypothesis that climate shaped variation in metabolism genes in humans, we used a bioinformatics approach based on network theory to select 82 candidate genes for common metabolic disorders. We genotyped 873 tag SNPs in these genes in 54 worldwide populations (including the 52 in the Human Genome Diversity Project panel) and found correlations with climate variables using rank correlation analysis and a newly developed method termed Bayesian geographic analysis. In addition, we genotyped 210 carefully matched control SNPs to provide an empirical null distribution for spatial patterns of allele frequency due to population history alone. For nearly all climate variables, we found an excess of genic SNPs in the tail of the distributions of the test statistics compared to the control SNPs, implying that metabolic genes as a group show signals of spatially varying selection. Among our strongest signals were several SNPs (e.g., LEPR R109K, FABP2 A54T) that had previously been associated with phenotypes directly related to cold tolerance. Since variation in climate may be correlated with other aspects of environmental variation, it is possible that some of the signals that we detected reflect selective pressures other than climate. Nevertheless, our results are consistent with the idea that climate has been an important selective pressure acting on candidate genes for common metabolic disorders.</p
Altered vascular smooth muscle function in the ApoE knockout mouse during the progression of atherosclerosis
Objectives:
Relaxation of vascular smooth muscle (VSM) requires re-uptake of cytosolic Ca2+ into the sarcoplasmic reticulum (SR) via the Sarco/Endoplasmic Reticulum Ca2+ ATPase (SERCA), or extrusion via the Plasma Membrane Ca2+ ATPase (PMCA) or sodium Ca2+ exchanger (NCX). Peroxynitrite, a reactive species formed in vascular inflammatory diseases, upregulates SERCA activity to induce relaxation but, chronically, can contribute to atherogenesis and altered vascular function by escalating endoplasmic reticulum stress. Our objectives were to determine if peroxynitrite-induced relaxation and Ca2+ handling processes within vascular smooth muscle cells were altered as atherosclerosis develops.<p></p>
Methods:
Aortae from control and ApoE−/− mice were studied histologically, functionally and for protein expression levels of SERCA and PMCA. Ca2+ responses were assessed in dissociated aortic smooth muscle cells in the presence and absence of extracellular Ca2+.<p></p>
Results:
Relaxation to peroxynitrite was concentration-dependent and endothelium-independent. The abilities of the SERCA blocker thapsigargin and the PMCA inhibitor carboxyeosin to block this relaxation were altered during fat feeding and plaque progression. SERCA levels were progressively reduced, while PMCA expression was upregulated. In ApoE−/− VSM cells, increases in cytosolic Ca2+ [Ca2+]c in response to SERCA blockade were reduced, while SERCA-independent Ca2+ clearance was faster compared to control.<p></p>
Conclusion:
As atherosclerosis develops in the ApoE−/− mouse, expression and function of Ca2+ handling proteins are altered. Up-regulation of Ca2+ removal via PMCA may offer a potential compensatory mechanism to help normalise the dysfunctional relaxation observed during disease progression
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Adaptations to Climate-Mediated Selective Pressures in Humans
Humans inhabit a remarkably diverse range of environments, and adaptation through natural selection has likely played a central role in the capacity to survive and thrive in extreme climates. Unlike numerous studies that used only population genetic data to search for evidence of selection, here we scan the human genome for selection signals by identifying the SNPs with the strongest correlations between allele frequencies and climate across 61 worldwide populations. We find a striking enrichment of genic and nonsynonymous SNPs relative to non-genic SNPs among those that are strongly correlated with these climate variables. Among the most extreme signals, several overlap with those from GWAS, including SNPs associated with pigmentation and autoimmune diseases. Further, we find an enrichment of strong signals in gene sets related to UV radiation, infection and immunity, and cancer. Our results imply that adaptations to climate shaped the spatial distribution of variation in humans.</p
Detached binaries in the Large Magellanic Cloud. A selection of binaries suitable for distance determination
As a result of a careful selection of eclipsing binaries in the Large
Magellanic Cloud using the OGLE-II photometric database, we present a list of
98 systems that are suitable targets for spectroscopic observations that would
lead to the accurate determination of the distance to the LMC. For these
systems we derive preliminary parameters combining the OGLE-II data with the
photometry of MACHO and EROS surveys. In the selected sample, 58 stars have
eccentric orbits. Among these stars we found fourteen systems showing apsidal
motion. The data do not cover the whole apsidal motion cycle, but follow-up
observations will allow detailed studies of these interesting objects.Comment: 15 pages, 6 figures, accepted for publication in A&
Adaptations to Climate in Candidate Genes for Common Metabolic Disorders
Evolutionary pressures due to variation in climate play an important role in shaping phenotypic variation among and within species and have been shown to influence variation in phenotypes such as body shape and size among humans. Genes involved in energy metabolism are likely to be central to heat and cold tolerance. To test the hypothesis that climate shaped variation in metabolism genes in humans, we used a bioinformatics approach based on network theory to select 82 candidate genes for common metabolic disorders. We genotyped 873 tag SNPs in these genes in 54 worldwide populations (including the 52 in the Human Genome Diversity Project panel) and found correlations with climate variables using rank correlation analysis and a newly developed method termed Bayesian geographic analysis. In addition, we genotyped 210 carefully matched control SNPs to provide an empirical null distribution for spatial patterns of allele frequency due to population history alone. For nearly all climate variables, we found an excess of genic SNPs in the tail of the distributions of the test statistics compared to the control SNPs, implying that metabolic genes as a group show signals of spatially varying selection. Among our strongest signals were several SNPs (e.g., LEPR R109K, FABP2 A54T) that had previously been associated with phenotypes directly related to cold tolerance. Since variation in climate may be correlated with other aspects of environmental variation, it is possible that some of the signals that we detected reflect selective pressures other than climate. Nevertheless, our results are consistent with the idea that climate has been an important selective pressure acting on candidate genes for common metabolic disorders
The simulated 21 cm signal during the epoch of reionization : full modeling of the Ly-alpha pumping
The 21 cm emission of neutral hydrogen is the most promising probe of the
epoch of reionization(EoR). In the next few years, the SKA pathfinders will
provide statistical measurements of this signal. Numerical simulations
predicting these observations are necessary to optimize the design of the
instruments. The main difficulty is the computation of the spin temperature of
neutral hydrogen which depends on the gas kinetic temperature and on the level
of the local Lyman-alpha flux. A T_s >> T_cmb assumption is usual. However,
this assumption does not apply early in the reionization history, or even later
in the history as long as the sources of X-rays are too weak to heat the
intergalactic medium significantly. This work presents the first EoR numerical
simulations including, beside dynamics and ionizing continuum radiative
transfer, a self-consistent treatment of the Ly-alpha radiative transfer. This
allows us to compute the spin temperature more accurately. We use two different
box sizes, 20 Mpc/h and 100 Mpc/h, and a star source model. Using the redshift
dependence of average quantities, maps, and power spectra, we quantify the
effect of using different assumptions to compute the spin temperature and the
influence of the box size. The first effect comes from allowing for a signal in
absorption. The magnitude of this effect depends on the amount of heating by
hydrodynamic shocks and X-rays in the intergalactic medium(IGM). The second
effects comes from using the real, local, Lyman-alpha flux. This effect is
important for an average ionization fraction of less than 10%: it changes the
overall amplitude of the 21 cm signal, and adds its own fluctuations to the
power spectrum.Comment: 20 pages, 16 figures, 2 tables, To be publish A&A. High resolution
version available at http://aramis.obspm.fr/~baek/21cm_Lya.pd
Solving Nonlinear Parabolic Equations by a Strongly Implicit Finite-Difference Scheme
We discuss the numerical solution of nonlinear parabolic partial differential
equations, exhibiting finite speed of propagation, via a strongly implicit
finite-difference scheme with formal truncation error . Our application of interest is the spreading of
viscous gravity currents in the study of which these type of differential
equations arise. Viscous gravity currents are low Reynolds number (viscous
forces dominate inertial forces) flow phenomena in which a dense, viscous fluid
displaces a lighter (usually immiscible) fluid. The fluids may be confined by
the sidewalls of a channel or propagate in an unconfined two-dimensional (or
axisymmetric three-dimensional) geometry. Under the lubrication approximation,
the mathematical description of the spreading of these fluids reduces to
solving the so-called thin-film equation for the current's shape . To
solve such nonlinear parabolic equations we propose a finite-difference scheme
based on the Crank--Nicolson idea. We implement the scheme for problems
involving a single spatial coordinate (i.e., two-dimensional, axisymmetric or
spherically-symmetric three-dimensional currents) on an equispaced but
staggered grid. We benchmark the scheme against analytical solutions and
highlight its strong numerical stability by specifically considering the
spreading of non-Newtonian power-law fluids in a variable-width confined
channel-like geometry (a "Hele-Shaw cell") subject to a given mass
conservation/balance constraint. We show that this constraint can be
implemented by re-expressing it as nonlinear flux boundary conditions on the
domain's endpoints. Then, we show numerically that the scheme achieves its full
second-order accuracy in space and time. We also highlight through numerical
simulations how the proposed scheme accurately respects the mass
conservation/balance constraint.Comment: 36 pages, 9 figures, Springer book class; v2 includes improvements
and corrections; to appear as a contribution in "Applied Wave Mathematics II
Detection and extraction of signals from the epoch of reionization using higher-order one-point statistics
Detecting redshifted 21-cm emission from neutral hydrogen in the early Universe promises to give direct constraints on the epoch of reionization (EoR). It will, though, be very challenging to extract the cosmological signal (CS) from foregrounds and noise which are orders of magnitude larger. Fortunately, the signal has some characteristics which differentiate it from the foregrounds and noise, and we suggest that using the correct statistics may tease out signatures of reionization. We generate mock data cubes simulating the output of the Low Frequency Array (LOFAR) EoR experiment. These cubes combine realistic models for Galactic and extragalactic foregrounds and the noise with three different simulations of the CS. We fit out the foregrounds, which are smooth in the frequency direction, to produce residual images in each frequency band. We denoise these images and study the skewness of the one-point distribution in the images as a function of frequency. We find that, under sufficiently optimistic assumptions, we can recover the main features of the redshift evolution of the skewness in the 21-cm signal. We argue that some of these features ¿ such as a dip at the onset of reionization, followed by a rise towards its later stages ¿ may be generic, and give us a promising route to a statistical detection of reionization
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