1,092 research outputs found
Sub-horizon Perturbation Behavior in Extended Quintessence
In the general context of scalar-tensor theories, we consider a model in
which a scalar field coupled to the Ricci scalar in the gravitational sector of
the Lagrangian, is also playing the role of an ``Extended Quintessence'' field,
dominating the energy content of the Universe at the present time. In this
framework, we study the linear evolution of the perturbations in the
Quintessence energy density, showing that a new phenomenon, named here
``gravitational dragging'', can enhance the scalar field density perturbations
as much as they reach the non-linear regime. The possibility of dark energy
clumps formation is thus discussed.Comment: Proceedings of the 5th International UCLA Symposium on Sources and
Detection of Dark Matter and Dark Energy in the Universe (Dark Matter 2002),
Marina del Rey, California, USA, 20-22 February 200
Did most present-day spirals form during the last 8 Gyrs? A formation history with violent episodes revealed by panchromatic observations
(abridged) Studies of distant galaxies have shown that ellipticals and large
spirals were already in place 8 Gyr ago, leading to a very modest recent star
formation in intermediate mass galaxies. This is challenged by a recent
analysis (Heavens et al. 2004) of the fossil record of the stellar populations
of ~10^5 nearby galaxies, which show that intermediate mass galaxies have
formed or assembled the bulk of their stars 4 to 8 Gyr ago. Here we present
direct observational evidence supporting the Heavens et al's findings from a
long term, multi-wavelength study of 195 z>0.4 intermediate mass galaxies,
mostly selected from the CFRS survey. We show that a recent and efficient star
formation is revealed at IR wavelengths since ~15% of intermediate mass
galaxies at z>0.4 are indeed luminous IR galaxies (LIRGs), a phenomenon far
more common than in the local Universe. The star formation in LIRGs is
sufficient in itself to produce 38% of the total stellar mass of intermediate
mass galaxies and then to account for most of the reported stellar mass
formation since z=1. The high occurrence of LIRGs is easily understood only if
they correspond to episodic peaks of star formation, during which galaxies are
reddened through short IREs (infrared episodes). We examine how galaxy IREs can
be related to the emergence at high redshift, of the abundant population of
galaxies with small size, blue core and many irregularities. We show that
recent merging and gas infall naturally explain both morphological changes and
episodic star formation history in a hierarchical galaxy formation frame. We
propose a simple scenario in which 75+-25% of intermediate mass spirals have
experienced recently their last major merger event, leading to a drastic
reshaping of their bulges and disks during the last 8 Gyrs.Comment: 19 pages, 7 PS figures, 4 Tables. Accepted for publication in A&A,
revised versio
Fault kinematics in northern Central America and coupling along the subduction interface of the Cocos Plate, from GPS data in Chiapas (Mexico), Guatemala and El Salvador
International audienceNew GPS measurements in Chiapas (Mexico), Guatemala and El Salvador are used to constrain the fault kinematics in the North America (NA), Caribbean (CA) and Cocos (CO) plates triple junction area. The regional GPS velocity field is first analysed in terms of strain partitioning across the major volcano-tectonic structures, using elastic half-space modelling, then inverted through a block model. We show the dominant role of the Motagua Fault with respect to the Polochic Fault in the accommodation of the present-day deformation associated with the NA and CA relative motion. The NA/CA motion decreases from 18-22 mm yr−1 in eastern Guatemala to 14-20 mm yr−1 in central Guatemala (assuming a uniform locking depth of 14-28 km), down to a few millimetres per year in western Guatemala. As a consequence, the western tip of the CA Plate deforms internally, with ≃9 mm yr−1 of east-west extension (≃5 mm yr−1 across the Guatemala city graben alone). Up to 15 mm yr−1 of dextral motion can be accommodated across the volcanic arc in El Salvador and southeastern Guatemala. The arc seems to mark the northern boundary of an independent forearc sliver (AR), pinned to the NA plate. The inversion of the velocity field shows that a four-block (NA, CA, CO and AR) model, that combines relative block rotations with elastic deformation at the block boundaries, can account for most of the GPS observations and constrain the overall kinematics of the active structures. This regional modelling also evidences lateral variations of coupling at the CO subduction interface, with a fairly high-coupling (≃0.6) offshore Chiapas and low-coupling (≃0.25) offshore Guatemala and El Salvador
The physical properties of star forming galaxies in the low redshift universe
(modified) We present a comprehensive study of the physical properties of
\~10^5 galaxies with measurable star formation in the SDSS. By comparing
physical information extracted from the emission lines with continuum
properties, we build up a picture of the nature of star-forming galaxies at
z<0.2. We take out essentially all aperture bias using resolved imaging,
allowing an accurate estimate of the total SFRs in galaxies. We determine the
SFR density to be 1.915^{+0.02}_{-0.01}(rand.)^{+0.14}_{-0.42} (sys.) h70
10^{-2} Msun/yr/Mpc^3 at z=0.1 (for a Kroupa IMF) and we study the distribution
of star formation as a function of various physical parameters. The majority of
the star formation in the low redshift universe takes place in moderately
massive galaxies (10^10-10^11 Msun), typically in HSB disk galaxies. Roughly
15% of all star formation takes place in galaxies that show some sign of an
active nucleus. About 20% occurs in starburst galaxies. We show that the
present to past-average star formation rate, the Scalo b-parameter; is almost
constant over almost three orders of magnitude in mass, declining only at
M*>10^10 Msun. The volume averaged b parameter is 0.408^{+0.005}_{-0.002}
(rand).^{+0.029}_{-0.090} (sys.) h70^{-1}. We use this value constrain the star
formation history of the universe. In agreement with other work we find a
correlation between and morphological type, as well as a tight correlation
between the 4000AA break (D4000) and b. We discuss how D4000 can be used to
estimate b parameters for high redshift galaxies.Comment: Accepted for MNRAS. Replaced with accepted version. A section on
comparison with other methods of SFR estimation added and various updates
have been made. The main results are almost unchange
The VIMOS VLT Deep Survey: Tracing the galaxy stellar mass assembly history over the last 8Gyr
We selected a mass-limited sample of 4048 objects from the VIMOS VLT Deep
Survey in the redshift interval 0.5<z<1.3. We used the amplitude of the 4000
Balmer break (Dn4000) to separate the galaxy population and the EW[OII]3727
line as proxy for the star formation activity. We discuss to what extent
stellar mass drives galaxy evolution, showing for the first time the interplay
between stellar ages and stellar masses over the past 8Gyr. Low-mass galaxies
have small Dn4000 and at increasing stellar mass, the galaxy distribution moves
to higher Dn4000 values as observed in the local Universe. As cosmic time goes
by, we witness an increasing abundance of massive spectroscopically ET systems
at the expense of the LT systems. This spectral transformation is a process
started at early epochs and continuing efficiently down to the local Universe.
This is confirmed by the evolution of our type-dependent stellar mass function.
The underlying stellar ages of LT galaxies apparently do not show evolution,
likely as a result of a continuous formation of new stars. All star formation
activity indicators consistently point towards a star formation history peaked
in the past for massive galaxies, with little or no residual star formation
taking place in the most recent epochs. The activity and efficiency of forming
stars are mechanisms that depend on stellar mass, and the mass assembly becomes
progressively less efficient in massive systems as time elapses. The concepts
of star formation downsizing and mass assembly downsizing describe a single
scenario that has a top-down evolutionary pattern. The role of (dry) merging
events seems to be only marginal at z<1.3, as our estimated efficiency in
stellar mass assembly can possibly account for the progressive accumulation of
passively evolving galaxies.Comment: Accepted for pubblication in A&A, 14 pages, 5 figure
Measurement of the Forward-Backward Asymmetry in the B -> K(*) mu+ mu- Decay and First Observation of the Bs -> phi mu+ mu- Decay
We reconstruct the rare decays , , and in a data sample
corresponding to collected in collisions at
by the CDF II detector at the Fermilab Tevatron
Collider. Using and decays we report the branching ratios. In addition, we report
the measurement of the differential branching ratio and the muon
forward-backward asymmetry in the and decay modes, and the
longitudinal polarization in the decay mode with respect to the squared
dimuon mass. These are consistent with the theoretical prediction from the
standard model, and most recent determinations from other experiments and of
comparable accuracy. We also report the first observation of the {\mathcal{B}}(B^0_s \to
\phi\mu^+\mu^-) = [1.44 \pm 0.33 \pm 0.46] \times 10^{-6}27 \pm 6B^0_s$ decay observed.Comment: 7 pages, 2 figures, 3 tables. Submitted to Phys. Rev. Let
Measurements of the properties of Lambda_c(2595), Lambda_c(2625), Sigma_c(2455), and Sigma_c(2520) baryons
We report measurements of the resonance properties of Lambda_c(2595)+ and
Lambda_c(2625)+ baryons in their decays to Lambda_c+ pi+ pi- as well as
Sigma_c(2455)++,0 and Sigma_c(2520)++,0 baryons in their decays to Lambda_c+
pi+/- final states. These measurements are performed using data corresponding
to 5.2/fb of integrated luminosity from ppbar collisions at sqrt(s) = 1.96 TeV,
collected with the CDF II detector at the Fermilab Tevatron. Exploiting the
largest available charmed baryon sample, we measure masses and decay widths
with uncertainties comparable to the world averages for Sigma_c states, and
significantly smaller uncertainties than the world averages for excited
Lambda_c+ states.Comment: added one reference and one table, changed order of figures, 17
pages, 15 figure
Search for a New Heavy Gauge Boson Wprime with Electron + missing ET Event Signature in ppbar collisions at sqrt(s)=1.96 TeV
We present a search for a new heavy charged vector boson decaying
to an electron-neutrino pair in collisions at a center-of-mass
energy of 1.96\unit{TeV}. The data were collected with the CDF II detector
and correspond to an integrated luminosity of 5.3\unit{fb}^{-1}. No
significant excess above the standard model expectation is observed and we set
upper limits on . Assuming standard
model couplings to fermions and the neutrino from the boson decay to
be light, we exclude a boson with mass less than
1.12\unit{TeV/}c^2 at the 95\unit{%} confidence level.Comment: 7 pages, 2 figures Submitted to PR
The improbable transmission of Trypanosoma cruzi to human: the missing link in the dynamics and control of Chagas disease
Chagas disease has a major impact on human health in Latin America and is becoming of global concern due to international migrations. Trypanosoma cruzi, the etiological agent of the disease, is one of the rare human parasites transmitted by the feces of its vector, as it is unable to reach the salivary gland of the insect. This stercorarian transmission is notoriously poorly understood, despite its crucial role in the ecology and evolution of the pathogen and the disease. The objective of this study was to quantify the probability of T. cruzi vectorial transmission to humans, and to use such an estimate to predict human prevalence from entomological data. We developed several models of T. cruzi transmission to estimate the probability of transmission from vector to host. Using datasets from the literature, we estimated the probability of transmission per contact with an infected triatomine to be 5.8x10(-4) (95%CI: [2.6; 11.0] x 10(-4)). This estimate was consistent across triatomine species, robust to variations in other parameters, and corresponded to 900-4,000 contacts per case. Our models subsequently allowed predicting human prevalence from vector abundance and infection rate in 7/10 independent datasets covering various triatomine species and epidemiological situations. This low probability of T. cruzi transmission reflected well the complex and unlikely mechanism of transmission via insect feces, and allowed predicting human prevalence from basic entomological data. Although a proof of principle study would now be valuable to validate our models' predictive ability in an even broader range of entomological and ecological settings, our quantitative estimate could allow switching the evaluation of disease risk and vector control program from purely entomological indexes to parasitological measures, as commonly done for other major vector borne diseases. This might lead to different quantitative perspectives as these indexes are well known not to be proportional one to another
Immunoregulatory gene polymorphisms in women with preeclampsia
The costimulatory molecules CD28, cytotoxic T-lymphocyte antigen-4 (CTLA-4) (cytotoxic T-lymphocyte-associated antigen-4) and inducible costimulator (ICOS) are believed to have a critical modulatory role in the immune response. However, few studies have been performed on the role of these immune regulatory molecules and their polymorphisms in women with preeclampsia (PE). the aim of our study was to evaluate the CTLA4 (+49 A/G) (rs 231775), CD28 (+17 T/C) (rs 3116496) and ICOS (-1564 T/C) (rs 4675378) gene polymorphisms in Brazilian women with PE. This case-control study included 130 patients with PE and 261 control women without any obstetric or systemic disorders. Genomic DNA was extracted from peripheral blood, and the polymorphism genotyping was performed by digesting the PCR products with the restriction endonucleases BbvI (CTLA-4), Afel (CD28) and AluI (ICOS). Data were analyzed by X(2) or Fisher's exact test; a P-value of < 0.05 was considered as significant. There were significant differences in the ICOS genotype and allelic frequencies between the PE and control groups (P=0.01 and P=0.01, respectively). We found a significantly lower frequency of the ICOS (-1564) T allele in women with mild PE compared with the controls. There were no differences in the CTLA-4 (+49 A/G) and CD28 (+17 T/C) genotypes and allelic frequencies between the PE patients and controls. Our data suggest that PE is associated with ICOS, but is not associated with the CTLA-4 or CD28 gene polymorphisms. Hypertension Research (2011) 34, 384-388; doi:10.1038/hr.2010.247; published online 16 December 2010Fundacao de Amparo a PesquisaCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Universidade Federal de São Paulo, Dept Obstet, BR-01415002 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Obstet, BR-01415002 São Paulo, BrazilFundacao de Amparo a Pesquisa: 07/57446-0Web of Scienc
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