7,417 research outputs found
L'épidémiologie actuelle de la trypanosomiase humaine africaine et les problèmes qu'elle pose
La brucellose en Afrique occidentale et son incidence sur la santé publique. Résultats de dix enquêtes épidémiologiques effectuées en Côte-d'Ivoire, Haute-Volta et Niger de 1970 à 1973
Utilisant ring-tests, réactions allergologiques et sérologiques, les auteurs ont étudié l'épidémiologie de la brucellose en Afrique de l'Ouest au cours de dix enquêtes couplées, humaines et animales, où plus de 120 villages ont été prospectés par sondage aléatoire. Chez les animaux, 4 108 ring-tests et 1 225 sérologies et, chez l'homme, 12 739 intradermo-réactions et 11 990 sérologies ont été effectuées. La maladie animale existe partout et concerne les différentes espèces, en particulier les bovins, mais à des taux très variables selon les régions, le Sud étant plus atteint que le Nord. Chez l'homme, la maladie intéresse essentiellement les populations pastorales du sahel, tandis qu'ailleurs, elle affecte surtout les bergers et leurs familles, les réactions allergologiques positives étant plus fréquentes chez l'homme que chez la femme et chez l'adulte que chez l'enfan
Gravitational detection of a low-mass dark satellite at cosmological distance
The mass-function of dwarf satellite galaxies that are observed around Local
Group galaxies substantially differs from simulations based on cold dark
matter: the simulations predict many more dwarf galaxies than are seen. The
Local Group, however, may be anomalous in this regard. A massive dark satellite
in an early-type lens galaxy at z = 0.222 was recently found using a new method
based on gravitational lensing, suggesting that the mass fraction contained in
substructure could be higher than is predicted from simulations. The lack of
very low mass detections, however, prohibited any constraint on their mass
function. Here we report the presence of a 1.9 +/- 0.1 x 10^8 M_sun dark
satellite in the Einstein-ring system JVAS B1938+666 at z = 0.881, where M_sun
denotes solar mass. This satellite galaxy has a mass similar to the Sagittarius
galaxy, which is a satellite of the Milky Way. We determine the logarithmic
slope of the mass function for substructure beyond the local Universe to be
alpha = 1.1^+0.6_-0.4, with an average mass-fraction of f = 3.3^+3.6_-1.8 %, by
combining data on both of these recently discovered galaxies. Our results are
consistent with the predictions from cold dark matter simulations at the 95 per
cent confidence level, and therefore agree with the view that galaxies formed
hierarchically in a Universe composed of cold dark matter.Comment: 25 pages, 7 figures, accepted for publication in Nature (19 January
2012
Effect of nanostructuration on compressibility of cubic BN
Compressibility of high-purity nanostructured cBN has been studied under
quasi-hydrostatic conditions at 300 K up to 35 GPa using diamond anvil cell and
angle-dispersive synchrotron X-ray powder diffraction. A data fit to the Vinet
equation of state yields the values of the bulk modulus B0 of 375(4) GPa with
its first pressure derivative B0' of 2.3(3). The nanometer grain size (\sim20
nm) results in decrease of the bulk modulus by ~9%
Properties of Long Gamma-Ray Burst Host Galaxies in Cosmological Simulation
We use galaxy catalogues constructed by combining high-resolution N-body
simulations with semi-analytic models of galaxy formation to study the
properties of Long Gamma-Ray Burst (LGRB) host galaxies. We assume that LGRBs
originate from the death of massive young stars and analyse how results are
affected by different metallicity constraints on the progenitor stars. As
expected, the host sample with no metallicity restriction on the progenitor
stars provides a perfect tracer of the cosmic star formation history. When
LGRBs are required to be generated by low-metallicity stars, they trace a
decreasing fraction of the cosmic star formation rate at lower redshift, as a
consequence of the global increase in metallicity. We study the properties of
host galaxies up to high redshift (~9), finding that they typically have
low-metallicity (Z<0.5 Z_sun) and that they are small (M<10^9 M_sun), bluer and
younger than the average galaxy population, in agreement with observational
data. They are also less clustered than typical L_* galaxies in the Universe,
and their descendents are massive, red and reside in groups of galaxies with
halo mass between 10^{13} M_sun to 10^{14} M_sun.Comment: The paper contains 14 figures and 2 tables. Accepted MNRA
Q1208+1011: Search for the lensing galaxy
We present a high-resolution spectrum of the high redshift, lensed quasar
Q1208+1101, obtained with the echellette spectrograph on the Multiple Mirror
Telescope. We examine the new and published spectra and provide an updated list
of high-confidence metal-line absorption systems at z=1.1349, 2.8626, 2.9118,
2.9136, 2.9149. Combining this with a simple model of the gravitational lens
system allows us to constrain the possible lens redshifts. The high-redshift (z
> 2.5) and low-redshift (z < 0.4) candidates can be ruled out with high
confidence. The current spectra effectively probe about 40% of the redshift
range in which the lens is expected. In that range, there is only one known
metal-line absorption system, an MgII absorber at z=1.1349. We consider the
possibility that this system is the lensing galaxy and discuss the implied
parameters of the galaxy.Comment: Latex 24 pages, 6 figures. accepted for publication in Astrophysical
Journa
Structure and Dynamics of Liquid Iron under Earth's Core Conditions
First-principles molecular dynamics simulations based on density-functional
theory and the projector augmented wave (PAW) technique have been used to study
the structural and dynamical properties of liquid iron under Earth's core
conditions. As evidence for the accuracy of the techniques, we present PAW
results for a range of solid-state properties of low- and high-pressure iron,
and compare them with experimental values and the results of other
first-principles calculations. In the liquid-state simulations, we address
particular effort to the study of finite-size effects, Brillouin-zone sampling
and other sources of technical error. Results for the radial distribution
function, the diffusion coefficient and the shear viscosity are presented for a
wide range of thermodynamic states relevant to the Earth's core. Throughout
this range, liquid iron is a close-packed simple liquid with a diffusion
coefficient and viscosity similar to those of typical simple liquids under
ambient conditions.Comment: 13 pages, 8 figure
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Chemistry of hydrogen oxide radicals (HO_x) in the Arctic troposphere in spring
We use observations from the April 2008 NASA ARCTAS aircraft campaign to the North American Arctic, interpreted with a global 3-D chemical transport model (GEOS-Chem), to better understand the sources and cycling of hydrogen oxide radicals (HO_x≡H+OH+peroxy radicals) and their reservoirs (HO_y≡HO_x+peroxides) in the springtime Arctic atmosphere. We find that a standard gas-phase chemical mechanism overestimates the observed HO_2 and H_2O_2 concentrations. Computation of HO_x and HO_y gas-phase chemical budgets on the basis of the aircraft observations also indicates a large missing sink for both. We hypothesize that this could reflect HO_2 uptake by aerosols, favored by low temperatures and relatively high aerosol loadings, through a mechanism that does not produce H_2O_2. We implemented such an uptake of HO_2 by aerosol in the model using a standard reactive uptake coefficient parameterization with γ(HO_2) values ranging from 0.02 at 275 K to 0.5 at 220 K. This successfully reproduces the concentrations and vertical distributions of the different HO_x species and HO_y reservoirs. HO_2 uptake by aerosol is then a major HO_x and HO_y sink, decreasing mean OH and HO_2 concentrations in the Arctic troposphere by 32% and 31% respectively. Better rate and product data for HO_2 uptake by aerosol are needed to understand this role of aerosols in limiting the oxidizing power of the Arctic atmosphere
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