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Search Results: 1 - 10 of 200962 matches for " P. Brun "
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Production et morbidité des lapines reproductrices: étude comparative de quatre génotypes
P Coudert, JM Brun
Genetics Selection Evolution , 1989, DOI: 10.1186/1297-9686-21-1-49
Abstract:
Anisotropy test of the axion-like particle Universe opacity effect: a case for the Cherenkov Telescope Array
D. Wouters,P. Brun
Physics , 2013, DOI: 10.1088/1475-7516/2014/01/016
Abstract: The Universe opacity to gamma rays is still an open question, in particular anomalies may have been observed. Assuming that such anomalies find their origin in conventional physics like intrinsic source spectra or the density of the extragalactic background light, they would be evenly distributed over the sky. If they exist, axion-like particles (ALPs) would have a potential effect on the opacity of the Universe to gamma rays, possibly related to the anomalies in the spectral indices of distant gamma-ray sources. In the scenario where ALPs from distant sources convert back to photons in the Galactic magnetic field, their effect on the opacity is expected to depend on the position of the sources. In that case the anomaly is expected to exhibit peculiar correlations on the sky. We propose a method to test the origin of the opacity anomaly, based on angular correlations of spectral softening anomalies. Such a diagnosis requires a wide-field survey of high-energy gamma-ray sources over a broad range of energy. The future Cherenkov Telescope Array (CTA) is perfectly suited to perform such a study. It is shown that while the current sample of sources is not large enough to base conclusions on, with this method CTA will be sensitive to ALP couplings to gamma rays of the order of 3e-11 GeV^-1 for ALP masses below 1e-8 eV.
Observationnal constraints on the nature of the low redshift Lyman-alpha absorbers
V. Le Brun,J. Bergeron,P. Boisse
Physics , 1995,
Abstract: We present results from a spectroscopic and imaging survey of galaxies in the fields of quasars from the HST Quasar Absorption Line Key Project. The aim of this survey is to identify galaxies within 3.5' from the quasar sightline, to a limiting r-band magnitude mr = 22.5. The data are then compared to the HST homogeneous sample of Lyman-alpha-only absorbers in order to put constraints on the nature of these absorbers, and in particular on their relation to galaxies. The analysis of our sample combined with those of previous studies shows that: 1) the redshift agreements of the Ly-alpha absorber-galaxy associations cannot be due to chance coincidence; 2) there is no clear anti-correlation between the Ly-alpha rest-frame equivalent width and the impact parameter for the whole sample. Our results suggest that most Ly-alpha absorbers are not gaseous clouds that belong in a strict sense to galaxies, as is the case for MgII absorbers. The fraction of associations to the total number of galaxies at impact parameter < D as a function of D drops from 1 to 0.65 at D = 200 H50 kpc and flattens at larger values of D (> 300 H50 kpc), which leads to Ly-alpha galactic halos sizes about three times larger than the inner MgII halo region; 3) there is no correlation between the galaxy luminosity and the impact parameter. This again suggests that a significant Ly-alpha clouds do not belong to individual galaxies, but instead are distributed in the local large-scale structure. 4) the HWHM=120 km/s of the relative velocity distribution of the Ly-alpha absorber-galaxy associations is consistent with either galaxy rotation velocities or the local velocity dispersion in large-scale structures.
Influence of the Tachocline on Solar Evolution
A. S. Brun,J. P. Zahn
Physics , 2000, DOI: 10.1111/j.1749-6632.2000.tb06167.x
Abstract: Recently helioseismic observations have revealed the presence of a shear layer at the base of the convective zone related to the transition from differential rotation in the convection zone to almost uniform rotation in the radiative interior, the tachocline. At present, this layer extends only over a few percent of the solar radius and no definitive explanations have been given for this thiness. Following Spiegel and Zahn (1992, Astron. Astrophys.), who invoke anisotropic turbulence to stop the spread of the tachocline deeper in the radiative zone as the Sun evolves, we give some justifications for their hypothesis by taking into account recent results on rotating shear instability (Richard and Zahn 1999, Astron. Astrophys.). We study the impact of the macroscopic motions present in this layer on the Sun's structure and evolution by introducing a macroscopic diffusivity $D_T$ in updated solar models. We find that a time dependent treatment of the tachocline significantly improves the agreement between computed and observed surface chemical species, such as the $^7$Li and modify the internal structure of the Sun (Brun, Turck-Chi\`eze and Zahn, 1999, in Astrophys. J.).
Medical students from Parakou (Benin) and West-African traditional beliefs on death and cadavers
P Charlier, L Brun, GL de la Grandmaison, C Hervé
African Health Sciences , 2012,
Abstract: No
Granitoides asociados a zonas de desgarre: modelos analógicos y aplicación al macizo de Lizio (zona de cizalla surarmoricana)
Román Berdiel, T.,Gapais, D.,Brun, J. P.
Estudios Geologicos , 1997, DOI: 10.3989/egeol.97533-4235
Abstract: Granite intrusion in the upper crust along a crustal-scale shear zone has been modeled by injecting a Newtonian fluid (low-viscosity silicone putty) into a sandpack containing a ductile layer of silicone putty which acted as a potential décollement level along which the injected material could spread. The strike-slip regime was obtained using a mobile rigid basal plate sliding horizontally. Boundary conditions were chosen in order to analyze the influence of different rheologic profiles of the upper crust on the pattern of the intrusion. Experiments showed that: 1) intrusions are elongate and their long axis tends to track the principal stretching direction associated with the strike-slip regime, 2) intrusions are asymmetric shaped in horizontal view, with the development of a sheared tail trailing behind the intrusion, 3) the strike slip environment allowed local rising of the injected fluid along faults formed in the overburden, 4) when the crustal rheologic profile is similar in both sides of the shear zone, intrusions are asymmetric drop shaped, 5) when the viscosity of materials above the feeding pipe is higher that viscosity of materials of the other side of the shear zone, the asymmetric drop shape not appears. Lizio leucogranite of the South Armorican Shear Zone (South Brittany, France) emphasize that our experiments can explain the geometry of many syntectonic' granites emplaced along strike-slip zones. They further shed some light on mechanisms of pluton intrusion in the upper crust. El emplazamiento de granitoides en zonas de desgarre de la corteza superior se ha modelizado inyectando un fluido newtoniano en un paquete de arena en el cual se intercala una capa dúctil de silicona que actúa como un nivel de despegue potencial en el cual el material inyectado puede expandirse. El régimen de desgarre se obtiene utilizando una placa basal rígida y móvil que desliza horizontalmente. Se ha analizado la influencia de diferentes perfiles reológicos de la corteza superior en la forma de la intrusión. Los experimentos muestran que: 1) las intrusiones son alargadas y su eje mayor toma la dirección principal de elongación asociada al régimen de desgarre, 2) las intrusiones presentan forma asimétrica en planta, con el desarrollo de una cola en el sentido de cizalla, 3) el régimen de desgarre permite localmente la subida del fluido inyectado a lo largo de las fallas formadas en la cobertera, 4) cuando el perfil reológico de la corteza es igual a ambos lados de la zona de cizalla, las intrusiones presentan forma de gota asimétrica, 5) cuando la viscosidad de
Datation par thermoluminescence
Abba, F,Decamps, E. A,Brun, P,Bombre, F
Bulletin de l'Institut Francais d'études Andines , 1976,
Abstract: Depuis 1953, de nombreux chercheurs se sont intéressés à la datation par thermoluminescence de minéraux anciennement br lés ou cuits. Dans ce travail, après avoir rappelé quelques principes physiques de la thermoluminescence, on présente cette méthode de datation en mettant l'accent sur le mécanisme thermoluminescent dans une poterie. Ainsi la dose d'irradiation re ue par le matériau étant proportionnelle au temps écoulé depuis le 'zéro archéologique', il est possible de déterminer 'la dose archéologique' et d'en déduire l'age de l'échantillon après avoir calculé la dose d'irradiation annuelle. La réalisation pratique d'un tel ensemble de mesure est cependant très ardue. Dans un prochain article, E. A. Decamps et A. Roman montreront des résultats relatifs à la thermoluminescence d'échantillons de quartz naturels, purs et dopés et la mise au point d'une nouvelle méthode de datation. Desde 1953, muchos investigadores se han interesado en la datación por termoluminiscencia de minerales antiguamente quemados o cocidos. Dentro de este trabajo, luego de haber recordado algunos principios físicos de la termoluminiscencia, se presenta este método de datación poniendo mayor atención en el mecanismo termoluminescente en una vasija de metal o de barro. Siendo proporcional la dosis de irradiación recibida al tiempo transcurrido desde el 'cero arqueológico', es posible determinar 'la dosis arqueológica', y deducir la edad de la muestra luego de haber calculado la dosis de irradiación anual. La realización práctica de un trabajo de tal dimensión es sin embargo muy ardua. En un próximo artículo, E. A. Decamps y A. Román presentarán los resultados relativos a la termoluminiscencia de muestras de cuarzo naturales, puras y dopadas y la elaboración de un nuevo método de datación. Since 1953, a number of scientists have been concerned with the use of thermoluminescence for the dating of burned or fired minerals. After recalling some of the physical principles of thermoluminescence, this paper describes that dating process with emphasis upon the working of the thermoluminescent phenomenon in a piece of earthenware. The dose of irradiation received by the material being in direct ratio to the time elapsed since the 'archeological zero , it is possible to determine the 'archeological dose' and, after calculating the annual dose of irradiation, infer from it the age of the sample. Practically, however, carrying out such a set of measurements is arduous matter. In a forthcoming paper, E. A. Decamps and A. Roman will present some results about the thermoluminescence of samples o
Exploring the $P_{cyc}$ vs $P_{rot}$ relation with flux transport dynamo models of solar-like stars
L. Jouve,B. P. Brown,A. S. Brun
Physics , 2009, DOI: 10.1051/0004-6361/200913103
Abstract: Aims: To understand stellar magnetism and to test the validity of the Babcock-Leighton flux transport mean field dynamo models with stellar activity observations Methods: 2-D mean field dynamo models at various rotation rates are computed with the STELEM code to study the sensitivity of the activity cycle period and butterfly diagram to parameter changes and are compared to observational data. The novelty is that these 2-D mean field dynamo models incorporate scaling laws deduced from 3-D hydrodynamical simulations for the influence of rotation rate on the amplitude and profile of the meridional circulation. These models make also use of observational scaling laws for the variation of differential rotation with rotation rate. Results: We find that Babcock-Leighton flux transport dynamo models are able to reproduce the change in topology of the magnetic field (i.e. toward being more toroidal with increasing rotation rate) but seem to have difficulty reproducing the cycle period vs activity period correlation observed in solar-like stars if a monolithic single cell meridional flow is assumed. It may however be possible to recover the $P_{cyc}$ vs $P_{rot}$ relation with more complex meridional flows, if the profile changes in a particular assumed manner with rotation rate. Conclusions: The Babcock-Leighton flux transport dynamo model based on single cell meridional circulation does not reproduce the $P_{cyc}$ vs $P_{rot}$ relation unless the amplitude of the meridional circulation is assumed to increase with rotation rate which seems to be in contradiction with recent results obtained with 3-D global simulations.
Macroscopic Processes in the Solar Interior
A. S. Brun,S. Turck-Chieze,J. P. Zahn
Physics , 1998,
Abstract: With the recent results of helioseismology aboard SOHO, solar models are more and more constrained (Brun, Turck-Chieze and Morel 1998 (astro-ph/9806272)). New physical processes, mainly connected to macroscopic motions, must be introduced to understand these new observations. In this poster, we present solar models including a turbulent pressure in the outer layers and mixing due to the tachocline (Spiegel and Zahn 1992). Our results lead us to conclude that: - Turbulent pressure improves the absolute value of the acoustic mode frequencies (~ 10 microHz at 4mHz), - Mixing in a tachocline thickness of 0.05 +/- 0.03 Ro (Corbard et al. 1997) looks promising.
The nature of intermediate-redshift damped Ly-alpha absorbers
V. Le Brun,J. Bergeron,P. Boisse,J. -M. Deharveng
Physics , 1996,
Abstract: We present HST/WFPC2 high-spatial resolution images in the R and B bands of the close environment of the sightlines to seven quasars which spectra show either a damped Ly-alpha absorption line, 21cm absorption, or a very strong MgII/FeII absorption system at intermediate redshifts (0.4 < z < 1). Objects down to about 0.3", or 2.0 kpc at z=0.6 (H0 = 50 kms/s/Mpc, q0=0), and to a limiting magnitude m(702, lim)=25.9 could be detected for seven fields comprising eight absorbers (one at higher redshift z=1.78 towards MC 1331+170) with high HI column densities of at least 1x10^20 cm^-2. In each case, a candidate absorber with absolute magnitude Mb =-19.0 or much brighter has been detected. This small sample of gas-rich galaxies at intermediate redshifts covers a wide range in morphological types. There are three spiral galaxies of various sizes and luminosities (towards 3C 196, Q 1209+107 and MC 1331+170), three compact objects (towards EX 0302-223, PKS 0454+039 and, at high redshift, MC 1331+170), and two amorphous, low surface brightness galaxies (towards PKS 1229-021 and 3C 286). In the fields around 3C 196, PKS 1229-021 and Q 1209+107, there is an excess of galaxies in the PC2 images, suggestive of the presence of a group of galaxies associated with the damped Ly-alpha absorber, or maybe with the quasar itself for the two z = 1.0 cases. For 3C 196 and 3C 286, the quasar host galaxies have also tentatively been discovered.
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