104 research outputs found
How far do they go? The outer structure of dark matter halos
We study the density profiles of collapsed galaxy-size dark matter halos with
masses 1e11-5e12 Msun focusing mostly on the halo outer regions from the formal
virial radius Rvir up to 5-7Rvir. We find that isolated halos in this mass
range extend well beyond Rvir exhibiting all properties of virialized objects
up to 2-3Rvir: relatively smooth density profiles and no systematic infall
velocities. The dark matter halos in this mass range do not grow as one naively
may expect through a steady accretion of satellites, i.e., on average there is
no mass infall. This is strikingly different from more massive halos, which
have large infall velocities outside of the virial radius. We provide accurate
fit for the density profile of these galaxy-size halos. For a wide range
(0.01-2)Rvir of radii the halo density profiles are fit with the approximation
rho=rho_s exp(-2n[x^{1/n}-1])+rho_m, where x=r/r_s, rho_m is the mean matter
density of the Universe, and the index n is in the range n=6-7.5. These
profiles do not show a sudden change of behavior beyond the virial radius. For
larger radii we combine the statistics of the initial fluctuations with the
spherical collapse model to obtain predictions for the mean and most probable
density profiles for halos of several masses. The model give excellent results
beyond 2-3 formal virial radii.Comment: 15 pages, 10 figures, submitted to Ap
Statistical Tests for CHDM and \LambdaCDM Cosmologies
We apply several statistical estimators to high-resolution N-body simulations
of two currently viable cosmological models: a mixed dark matter model, having
contributed by two massive neutrinos (C+2\nuDM), and a Cold
Dark Matter model with Cosmological Constant (\LambdaCDM) with
and h=0.7. Our aim is to compare simulated galaxy samples with the
Perseus-Pisces redshift survey (PPS). We consider the n-point correlation
functions (n=2-4), the N-count probability functions P_N, including the void
probability function P_0, and the underdensity probability function U_\epsilon
(where \epsilon fixes the underdensity threshold in percentage of the average).
We find that P_0 (for which PPS and CfA2 data agree) and P_1 distinguish
efficiently between the models, while U_\epsilon is only marginally
discriminatory. On the contrary, the reduced skewness and kurtosis are,
respectively, S_3\simeq 2.2 and S_4\simeq 6-7 in all cases, quite independent
of the scale, in agreement with hierarchical scaling predictions and estimates
based on redshift surveys. Among our results, we emphasize the remarkable
agreement between PPS data and C+2\nuDM in all the tests performed. In
contrast, the above \LambdaCDM model has serious difficulties in reproducing
observational data if galaxies and matter overdensities are related in a simple
way.Comment: 12 pages, 10 figures, LaTeX (aaspp4 macro), in press on ApJ, Vol.
479, April 199
Insights into antiretroviral treatment changes in previously naĂŻve patients: results of a Portuguese cohort
Compositional analysis of flatworm genomes shows strong codon usage biases across all classes
In the present work, we performed a comparative genome-wide analysis of 22 species representative of the main clades and lifestyles of the phylum Platyhelminthes. We selected a set of 700 orthologous genes conserved in all species, measuring changes in GC content, codon, and amino acid usage in orthologous positions. Values of 3rd codon position GC spanned over a wide range, allowing to discriminate two distinctive clusters within freshwater turbellarians, Cestodes and Trematodes respectively. Furthermore, a hierarchical clustering of codon usage data differs remarkably from the phylogenetic tree. Additionally, we detected a synonymous codon usage bias that was more dramatic in extreme GC-poor or GC-rich genomes, i.e., GC-poor Schistosomes preferred to use AT-rich terminated synonymous codons, while GC-rich M. lignano showed the opposite behavior. Interestingly, these biases impacted the amino acidic usage, with preferred amino acids encoded by codons following the GC content trend. These are associated with non-synonymous substitutions at orthologous positions. The detailed analysis of the synonymous and non-synonymous changes provides evidence for a two-hit mechanism where both mutation and selection forces drive the diverse coding strategies of flatworms
Cosmic Voids and Galaxy Bias in the Halo Occupation Framework
(Abridged) We investigate the power of void statistics to constrain galaxy
bias and the amplitude of dark matter fluctuations. We use the halo occupation
distribution (HOD) framework to describe the relation between galaxies and dark
matter. After choosing HOD parameters that reproduce the mean space density
n_gal and projected correlation function w_p measured for galaxy samples with
M_r<-19 and M_r<-21 from the Sloan Digital Sky Survey (SDSS), we predict the
void probability function (VPF) and underdensity probability function (UPF) of
these samples by populating the halos of a large, high-resolution N-body
simulation. If we make the conventional assumption that the HOD is independent
of large scale environment at fixed halo mass, then models constrained to match
n_gal and w_p predict nearly identical void statistics, independent of the
scatter between halo mass and central galaxy luminosity or uncertainties in HOD
parameters. Models with sigma_8=0.7 and sigma_8=0.9 also predict very similar
void statistics. However, the VPF and UPF are sensitive to environmental
variations of the HOD in a regime where these variations have little impact on
w_p. For example, doubling the minimum host halo mass in regions with large
scale (5 Mpc/h) density contrast delta<-0.65 has a readily detectable impact on
void probabilities of M_r<-19 galaxies, and a similar change for delta<-0.2
alters the void probabilities of M_r<-21 galaxies at a detectable level. The
VPF and UPF provide complementary information about the onset and magnitude of
density- dependence in the HOD. By detecting or ruling out HOD changes in low
density regions, void statistics can reduce systematic uncertainties in the
cosmological constraints derived from HOD modeling, and, more importantly,
reveal connections between halo formation history and galaxy properties.Comment: emulateapj, 16 pages, 13 figure
Promoting a compassionate motivation in detained youth: A secondary analysis of a controlled trial with the PSYCHOPATHY.COMP program
This study aims to assess the efficacy of the PSYCHOPATHY.COMP in promoting a compassionate motivation among male detained youth, also testing its role as a potential mechanism of change on the reduction of psychopathic traits. A treatment group (n = 58) and a control group (n = 61) answered a set of self-report measures on psychopathic traits, shame, fears of compassion, social safeness, self-compassion, and compassion for others at three timepoints: baseline, posttreatment, and 6 monthsâ follow-up. Treatment participants attended the PSYCHOPATHY.COMP. Controls received the treatment as usual delivered at juvenile detention facilities. The treatment effects were tested with latent growth curve models. At baseline, no significant differences between groups were found. Results from latent growth curve models showed that condition was a significant predictor of change over time observed in all outcome measures, even after controlling for psychopathic traits scores. When compared with the control group, the treatment group showed a significant decrease on shame and fears of compassion and a significant increase on social safeness, self-compassion, and compassion for others over time (medium-to-large effect sizes; growth modeling analysis d ranging from .57 to .96). It was also observed that increases in self-compassion and, in some cases, decreases in fears of receiving compassion, were crucial to the decrease of psychopathic traits. These findings suggest that the PSYCHOPATHY.COMP is a promising approach to promote a compassionate motivation in these youth, strengthening their rehabilitation odds. Increasing self-compassion and decreasing fears of receiving compassion should be considered when designing intervention programs for detained youth.
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