The merging cluster of galaxies Abell 3376: an optical view

Abell 3376 is a merging cluster of galaxies at redshift z=0.046, famous mostly for its giant radio arcs, and shows an elongated and highly substructured X-ray emission, but has not been analysed in detail at optical wavelengths. We have obtained wide field images of Abell 3376 in the B band and derive the GLF applying a statistical subtraction of the background in three regions: a circle of 0.29 deg radius (1.5 Mpc) encompassing the whole cluster, and two circles centered on each of the two brightest galaxies (BCG2, northeast, coinciding with the peak of X-ray emission, and BCG1, southwest) of radii 0.15 deg (0.775 Mpc). We also compute the GLF in the zone around BCG1, which is covered by the WINGS survey in the B and V bands, by selecting cluster members in the red sequence in a (B-V) versus V diagram. Finally, we discuss the dynamical characteristics of the cluster implied by a Serna & Gerbal analysis. The GLFs are not well fit by a single Schechter function, but satisfactory fits are obtained by summing a Gaussian and a Schechter function. The GLF computed by selecting galaxies in the red sequence in the region surrounding BCG1 can also be fit by a Gaussian plus a Schechter function. An excess of galaxies in the brightest bins is detected in the BCG1 and BCG2 regions. The dynamical analysis based on the Serna & Gerbal method shows the existence of a main structure of 82 galaxies which can be subdivided into two main substructures of 25 and 6 galaxies. A smaller structure of 6 galaxies is also detected. The B band GLFs of Abell 3376 are clearly perturbed, as already found in other merging clusters. The dynamical properties are consistent with the existence of several substructures, in agreement with a previously published X-ray analysis.Comment: 11 pages, 12 figures, accepted for publication in A&

Quantum Brayton cycle with coupled systems as working substance

We explore the quantum version of Brayton cycle with a composite system as the working substance. The actual Brayton cycle consists of two adiabatic and two isobaric processes. Two pressures can be defined in our isobaric process, one corresponds to the external magnetic field (characterized by $F_x$) exerted on the system, while the other corresponds to the coupling constant between the subsystems (characterized by $F_y$). As a consequence, we can define two types of quantum Brayton cycle for the composite system. We find that the subsystem experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized by $F_x$), whereas the subsystem's cycle is of quantum Otto in another Brayton cycle (characterized by $F_y$). The efficiency for the composite system equals to that for the subsystem in both cases, but the work done by the total system are usually larger than the sum of work done by the two subsystems. The other interesting finding is that for the cycle characterized by $F_y$, the subsystem can be a refrigerator while the total system is a heat engine. The result in the paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance.Comment: 7 pages, 3 figures, accepted by Phys. Rev.

L'élevage traditionnel des petits ruminants au Sénégal. II. Pratiques de conduite et d'exploitation des animaux chez les éleveurs de la région de Louga

Les auteurs présentent ici une partie des résultats du programme "pathologie et productivité des petits ruminants en milieu traditionnel" (ISRA/IEMVT-CIRAD), à partir desquels ils analysent les pratiques et les stratégies des éleveurs de petits ruminants dans la région de Louga. La méthodologie s'appuie sur des enquêtes ponctuelles sur le terrain et l'analyse statistique des données micro-économiques recueillies lors d'un suivi hebdomadaire de 194 troupeaux de concession pendant une durée de 3 ans. Les enquêtes ont orienté le traitement des données, qui, à son tour, a soulevé des questions et généré de nouvelles enquêtes auprès des acteurs concernés. Les auteurs décrivent ensuite les conditions de l'élevage des petits ruminants: milieux naturel (zone sahélienne), humain (deux ethnies - Peul et Wolof - se partagent la région), et systèmes de production, puis les pratiques de conduite et de gestion économique, sensiblement différentes entre Peul et Wolof. Deux modes d'élevage sont toujours associés: l'élevage de case (surtout pratiqué par les Wolof), qui concerne les béliers les mieux conformés, restant à l'attache dans la concession et nourris à l'auge de 6 à 18 mois, avant d'être vendus au meilleur prix; l'élevage pastoral, qui concerne les autres ovins et les caprins partant pâturer la journée sous la conduite d'un berger et revenant le soir dans la concession où ils reçoivent une complémentation à l'auge. Le rôle de l'élevage de petits ruminants (production laitière, abattages festifs, épargne mobilisable en cas de besoin) est illustré par les résultats du suivi. Ceux-ci montrent clairement que les stratégies commerciales (choix des animaux à vendre ou à abattre, époque de vente, prix de vente, etc.) des deux ethnies sont tout à fait différentes et reflètent leurs objectifs majeurs: production laitière chez les Peul, ventes d'animaux chez les Wolof. (Résumé d'auteur

Integration of the Forward Detectors inside the LHC Machine

Several forward detectors have been installed in the LHC long straight sections located on each side of the experimental caverns. Most of these detectors have been designed by the LHC experiments to study the forward physics while some of them are dedicated to the measurement of the LHC luminosity. The integration and the installation of the forward detectors have required an excellent coordination between the experiments and the different CERN groups involved into the design and the installation of the LHC accelerator. In some cases the integration of these detectors has required a modification of the standard beam lines in order to maximise their physics potential. Finally, additional systems have been installed in the LHC tunnel to ensure the operation of the forward detectors in a high radiation environment

L'élevage traditionnel des petits ruminants au Sénégal. I. Pratiques de conduite et d'exploitation des animaux chez les éleveurs de la région de Kolda

Les auteurs présentent ici une partie des résultats du programme "pathologie et productivité des petits ruminants en milieu traditionnel" (ISRA/IEMVT-CIRAD), à partir desquels ils analysent les pratiques et les stratégies des éleveurs de petits ruminants dans la région de Kolda. La méthodologie utilisée s'appuie sur des enquêtes ponctuelles sur le terrain et l'analyse statistique des données micro-économiques recueillies lors d'un suivi hebdomadaire de 160 troupeaux de concession pendant une durée de 3 ans. Les enquêtes ont orienté le traitement des données, qui, à son tour a soulevé des questions et généré de nouvelles enquêtes auprès des acteurs concernés. Les auteurs décrivent ensuite les conditions de l'élevage des petits ruminants : milieux naturel (zone soudano-guinéenne), humain (petits villages peuls), systèmes de production où l'association entre agriculture et élevage est très poussée. Ils présentent les pratiques de conduite et de gestion économique des petits ruminants, qui divaguent en saison sèche et pâturent généralement au piquet en saison des pluies. Les niveaux de complémentation alimentaire sont faibles et la reproduction peu maîtrisée. Le rôle de l'élevage des petits ruminants (abattages festifs, épargne mobilisable en cas de besoin par la vente ou le troc d'animaux, capitalisation progressive par le troc d'ovins ou de caprins contre des bovins) est illustré par les résultats du suivi. (Résumé d'auteur

The Equation of State and the Hugoniot of Laser Shock-Compressed Deuterium

The equation of state and the shock Hugoniot of deuterium are calculated using a first-principles approach, for the conditions of the recent shock experiments. We use density functional theory within a classical mapping of the quantum fluids [ Phys. Rev. Letters, {\bf 84}, 959 (2000) ]. The calculated Hugoniot is close to the Path-Integral Monte Carlo (PIMC) result. We also consider the {\it quasi-equilibrium} two-temperature case where the Deuterons are hotter than the electrons; the resulting quasi-equilibrium Hugoniot mimics the laser-shock data. The increased compressibility arises from hot $D^+-e$ pairs occuring close to the zero of the electron chemical potential.Comment: Four pages; One Revtex manuscript, two postscipt figures; submitted to PR

Spin-dependent correlation in two-dimensional electron liquids at arbitrary degeneracy and spin-polarization: CHNC approach

We apply the classical mapping technique developed recently by Dharma-wardana and Perrot for a study of the uniform two-dimensional electron system at arbitrary degeneracy and spin-polarization. Pair distribution functions, structure factors, the Helmhotz free energy, and the compressibility are calculated for a wide range of parameters. It is shown that at low temperatures T/ T_F <0.1, T_F being the Fermi temperature, our results almost reduce to those of zero-temperature analyses. In the region T/ T_F >= 1, the finite temperature effects become considerable at high densities for all spin-polarizations. We find that, in our approximation without bridge functions, the finite temperature electron system in two dimensions remains to be paramagnetic fluid until the Wigner crystallization density. Our results are compared with those of three-dimensional system and indicated are the similarities in temperature, spin-polarization, and density dependencies of many physical properties.Comment: 8 pages, 9 figure

Isotopic distribution of fission fragments in collisions between 238U beam and 9Be and 12C targets at 24 MeV/u

Inverse kinematics coupled to a high-resolution spectrometer is used to investigate the isotopic yields of fission fragments produced in reactions between a 238U beam at 24 MeV/u and 9Be and 12C targets. Mass, atomic number and isotopic distributions are reported for the two reactions. These informations give access to the neutron excess and the isotopic distribution widths, which together with the atomic-number and mass distributions are used to investigate the fusion-fission dynamics.Comment: Submitted to PR

The Path Integral Monte Carlo Calculation of Electronic Forces

We describe a method to evaluate electronic forces by Path Integral Monte Carlo (PIMC). Electronic correlations, as well as thermal effects, are included naturally in this method. For fermions, a restricted approach is used to avoid the ``sign'' problem. The PIMC force estimator is local and has a finite variance. We applied this method to determine the bond length of H$_2$ and the chemical reaction barrier of H+H$_2\longrightarrow$H$_2$+H. At low temperature, good agreement is obtained with ground state calculations. We studied the proton-proton interaction in an electron gas as a simple model for hydrogen impurities in metals. We calculated the force between the two protons at two electronic densities corresponding to Na ($r_s=3.93$) and Al ($r_s=2.07$) using a supercell with 38 electrons. The result is compared to previous calculations. We also studied the effect of temperature on the proton-proton interaction. At very high temperature, our result agrees with the Debye screening of electrons. As temperature decreases, the Debye theory fails both because of the strong degeneracy of electrons and most importantly, the formation of electronic bound states around the protons.Comment: 18 pages, 10 figure