143 research outputs found
N-Body Simulations of Alternate Gravity Models
Theories in which gravity is weaker on cosmological scales have been proposed
to explain the observed acceleration of the universe. The nonlinear regime in
such theories is not well studied, though it is likely that observational tests
of structure formation will lie in this regime. A class of alternate gravity
theories may be approximated by modifying Poisson's equation. We have run
N-body simulations of a set of such models to study the nonlinear clustering of
matter on 1-100 Mpc scales. We find that nonlinear gravity enhances the
deviations of the power spectrum of these models from standard gravity. This
occurs due to mode-coupling, so that models with an excess or deficit of
large-scale power (at k < 0.2/Mpc) lead to deviations in the power spectrum at
smaller scales as well (up to k ~ 1/Mpc), even though the linear spectra match
very closely on the smaller scales. This makes it easier to distinguish such
models from general relativity using the three-dimensional power spectrum
probed by galaxy surveys and the weak lensing power spectrum. If the potential
for light deflection is modified in the same way as the potential that affects
the dark matter, then weak lensing constrains deviations from gravity even more
strongly. Our simulations show that even with a modified potential,
gravitational evolution is approximately universal. Based on this, the
Peacock-Dodds approach can be adapted to get an analytical fit for the
nonlinear power spectra of alternate gravity models, though the recent Smith et
al formula is less successful. Our conclusions extend to models with
modifications of gravity on scales of 1-20 Mpc. We also use a way of measuring
projected power spectra from simulations that lowers the sample variance, so
that fewer realizations are needed to reach a desired level of accuracy.Comment: 26 pages, 10 figures, matches published versio
Quantifying Florida Bay Habitat Suitability for Fishes and Invertebrates Under Climate Change Scenarios
The Florida Bay ecosystem supports a number of economically important ecosystem services, including several recreational fisheries, which may be affected by changing salinity and temperature due toclimate change. In this paper, we use a combination of physical models and habitat suitability index models to quantify the effects of potential climate change scenarios on a variety of juvenile fish and lobster species in Florida Bay. The climate scenarios include alterations in sea level, evaporation and precipitation rates, coastal runoff, and water temperature. We find that the changes in habitat suitability vary in both magnitude and direction across the scenarios and species, but are on average small. Only one of the seven species we investigate (Lagodon rhomboides, i.e., pinfish) sees a sizable decrease in optimal habitat under any of the scenarios. This suggests that the estuarine fauna of Florida Bay may not be as vulnerable to climate change as other components of the ecosystem, such as those in the marine/terrestrial ecotone. However, these models are relatively simplistic, looking only at single species effects of physical drivers without considering the many interspecific interactions that may play a key role in the adjustment of the ecosystem as a whole. More complex models that capture the mechanistic links between physics and biology, as well as the complex dynamics of the estuarine food web, may be necessary to further understand the potential effects of climate change on the Florida Bay ecosystem
Spherical Collapse and Cluster Counts in Modified Gravity Models
Modifications to the gravitational potential affect the nonlinear
gravitational evolution of large scale structures in the Universe. To
illustrate some generic features of such changes, we study the evolution of
spherically symmetric perturbations when the modification is of Yukawa type;
this is non-trivial, because we should not and do not assume that Birkhoff's
theorem applies. We then show how to estimate the abundance of virialized
objects in such models. Comparison with numerical simulations shows reasonable
agreement: When normalized to have the same fluctuations at early times, weaker
large scale gravity produces fewer massive halos. However, the opposite can be
true for models that are normalized to have the same linear theory power
spectrum today, so the abundance of rich clusters potentially places
interesting constraints on such models. Our analysis also indicates that the
formation histories and abundances of sufficiently low mass objects are
unchanged from standard gravity. This explains why simulations have found that
the nonlinear power-spectrum at large k is unaffected by such modifications to
the gravitational potential. In addition, the most massive objects in
CMB-normalized models with weaker gravity are expected to be similar to the
high-redshift progenitors of the most massive objects in models with stronger
gravity. Thus, the difference between the cluster and field galaxy populations
is expected to be larger in models with stronger large-scale gravity.Comment: 9 pages, 8 figures Accepted by Phys. Rev.
PhyleasProg: a user-oriented web server for wide evolutionary analyses
Evolutionary analyses of biological data are becoming a prerequisite in many fields of biology. At a time of high-throughput data analysis, phylogenetics is often a necessary complementary tool for biologists to understand, compare and identify the functions of sequences. But available bioinformatics tools are frequently not easy for non-specialists to use. We developed PhyleasProg (http://phyleasprog.inra.fr), a user-friendly web server as a turnkey tool dedicated to evolutionary analyses. PhyleasProg can help biologists with little experience in evolutionary methodologies by analysing their data in a simple and robust way, using methods corresponding to robust standards. Via a very intuitive web interface, users only need to enter a list of Ensembl protein IDs and a list of species as inputs. After dynamic computations, users have access to phylogenetic trees, positive/purifying selection data (on site and branch-site models), with a display of these results on the protein sequence and on a 3D structure model, and the synteny environment of related genes. This connection between different domains of phylogenetics opens the way to new biological analyses for the discovery of the function and structure of proteins
BLAST Observations of the South Ecliptic Pole field: Number Counts and Source Catalogs
We present results from a survey carried out by the Balloon-borne Large
Aperture Submillimeter Telescope (BLAST) on a 9 deg^2 field near the South
Ecliptic Pole at 250, 350 and 500 {\mu}m. The median 1{\sigma} depths of the
maps are 36.0, 26.4 and 18.4 mJy, respectively. We apply a statistical method
to estimate submillimeter galaxy number counts and find that they are in
agreement with other measurements made with the same instrument and with the
more recent results from Herschel/SPIRE. Thanks to the large field observed,
the new measurements give additional constraints on the bright end of the
counts. We identify 132, 89 and 61 sources with S/N>4 at 250, 350, 500 {\mu}m,
respectively and provide a multi-wavelength combined catalog of 232 sources
with a significance >4{\sigma} in at least one BLAST band. The new BLAST maps
and catalogs are available publicly at http://blastexperiment.info.Comment: 25 pages, 6 figures, 4 tables, Accepted by ApJS. Maps and catalogs
available at http://blastexperiment.info
Crossing the Phantom Divide: Theoretical Implications and Observational Status
If the dark energy equation of state parameter w(z) crosses the phantom
divide line w=-1 (or equivalently if the expression d(H^2(z))/dz - 3\Omega_m
H_0^2 (1+z)^2 changes sign) at recent redshifts, then there are two possible
cosmological implications: Either the dark energy consists of multiple
components with at least one non-canonical phantom component or general
relativity needs to be extended to a more general theory on cosmological
scales. The former possibility requires the existence of a phantom component
which has been shown to suffer from serious theoretical problems and
instabilities. Therefore, the later possibility is the simplest realistic
theoretical framework in which such a crossing can be realized. After providing
a pedagogical description of various dark energy observational probes, we use a
set of such probes (including the Gold SnIa sample, the first year SNLS
dataset, the 3-year WMAP CMB shift parameter, the SDSS baryon acoustic
oscillations peak (BAO), the X-ray gas mass fraction in clusters and the linear
growth rate of perturbations at z=0.15 as obtained from the 2dF galaxy redshift
survey) to investigate the priors required for cosmological observations to
favor crossing of the phantom divide. We find that a low \Omega_m prior
(0.2<\Omega_m <0.25) leads, for most observational probes (except of the SNLS
data), to an increased probability (mild trend) for phantom divide crossing. An
interesting degeneracy of the ISW effect in the CMB perturbation spectrum is
also pointed out.Comment: Accepted in JCAP (to appear). Comments added, typos corrected. 19
pages (revtex), 8 figures. The numerical analysis files (Mathematica +
Fortran) with instructions are available at
http://leandros.physics.uoi.gr/pdl-cross/pdl-cross.htm . The ppt file of a
relevant talk may be downloaded from
http://leandros.physics.uoi.gr/pdl-cross/pdl2006.pp
Can Early Dark Energy be Detected in Non-Linear Structure?
We present the first study of early dark energy cosmologies using N-body
simulations to investigate the formation of non-linear structure. In contrast
to expectations from semi-analytic approaches, we find that early dark energy
does not imprint a unique signature on the statistics of non-linear structures.
Investigating the non-linear power spectra and halo mass functions, we show
that universal mass functions hold for early dark energy, making its presence
difficult to distinguish from CDM. Since early dark energy biases the
baryon acoustic oscillation scale, the lack of discriminating power is
problematic.Comment: 11 pages, 19 figures. Minor changes to match version accepted to
MNRA
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
Spitzer MIPS 24 and 70 micron Imaging near the South Ecliptic Pole: Maps and Source Catalogs
We have imaged an 11.5 sq. deg. region of sky towards the South Ecliptic Pole
(RA = 04h43m, Dec = -53d40m, J2000) at 24 and 70 microns with MIPS, the
Multiband Imaging Photometer for Spitzer. This region is coincident with a
field mapped at longer wavelengths by AKARI and the Balloon-borne Large
Aperture Submillimeter Telescope. We discuss our data reduction and source
extraction procedures. The median depths of the maps are 47 microJy/beam at 24
micron and 4.3 mJy/beam at 70 micron. At 24 micron, we identify 93098 point
sources with signal-to-noise ratio (SNR) >5, and an additional 63 resolved
galaxies; at 70 micron, we identify 891 point sources with SNR >6. From
simulations, we determine a false detection rate of 1.8% (1.1%) for the 24
micron (70 micron) catalog. The 24 and 70 micron point-source catalogs are 80%
complete at 230 microJy and 11 mJy, respectively. These mosaic images and
source catalogs will be available to the public through the NASA/IPAC Infrared
Science Archive.Comment: 30 pages, 9 figures, 4 tables. Submitted to ApJS. Maps and catalogs
can be downloaded from
http://blastexperiment.info/release/SEP_MIPS/sep-mips.php, and will be soon
be available through IRS
Ensembl 2005
The Ensembl (http://www.ensembl.org/) project provides a comprehensive and integrated source of annotation of large genome sequences. Over the last year the number of genomes available from the Ensembl site has increased by 7 to 16, with the addition of the six vertebrate genomes of chimpanzee, dog, cow, chicken, tetraodon and frog and the insect genome of honeybee. The majority have been annotated automatically using the Ensembl gene build system, showing its flexibility to reliably annotate a wide variety of genomes. With the increased number of vertebrate genomes, the comparative analysis provided to users has been greatly improved, with new website interfaces allowing annotation of different genomes to be directly compared. The Ensembl software system is being increasingly widely reused in different projects showing the benefits of a completely open approach to software development and distribution
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