Relativistic Conic Beams and Spatial Distribution of Gamma-Ray Bursts

We study the statistics of gamma-ray bursts, assuming that gamma-ray bursts are cosmological and they are beamed in the form of a conical jet with a large bulk Lorentz factor $\sim 100$. In such a conic beam, the relativistic ejecta may have a spatial variation in the bulk Lorentz factor and the density distribution of gamma-ray emitting jet material. An apparent luminosity function arises because the axis of the cone is randomly oriented with respect to the observer's line of sight. The width and the shape of the luminosity function are determined by the ratio of the beam opening angle of the conical jet to the inverse of the bulk Lorentz factor, when the bulk Lorentz factor and the jet material density is uniform on the photon emitting jet surface. We calculate effects of spatial variation of the Lorentz factor and the spatial density fluctuations within the cone on the luminosity function and the statistics of gamma-ray bursts. In particular, we focus on the redshift distribution of the observed gamma-ray bursts. The maximum distance to and the average redshift of the gamma-ray bursts are strongly affected by the beaming-induced luminosity function. The bursts with the angle-dependent Lorentz factor which peaks at the center of the cone have substantially higher average gamma-ray burst redshifts. When both the jet material density and the Lorentz factor are inhomogeneous in the conical beam, the average redshift of the bursts could be 5 times higher than that of the case in which relativistic jet is completely homogeneous and structureless. Even the simplest models for the gamma-ray burst jets and their apparent luminosity distributions have a significant effect on the redshift distribution of the gamma-ray bursts.Comment: 15 pages, 4 figures, submitted to ApJ

The cost effectiveness of integrated care for people living with HIV including antiretroviral treatment in a primary health care centre in Bujumbura, Burundi

The incremental cost effectiveness of an integrated care package (i.e., medical care including antiretroviral therapy (ART) and other services such as psychological and social support) for people living with HIV/AIDS was calculated in a not-for-profit primary health care centre in Bujumbura run by Society of Women against AIDS-Burundi (SWAA-Burundi), an African non-governmental organisation (NGO). Results are expressed as cost-effectiveness ratio 2007, constant US$per disability-adjusted life year (DALY) averted. Unit costs are estimated from the NGO's accounting data and activity reports, healthcare utilisation is estimated from the medical records of a cohort of 149 patients. Effectiveness is modelled on the survival of this cohort, using standard calculation methods. The incremental cost of integrated care for people living with HIV/AIDS in the Bujumbura health centre of SWAA-Burundi is 258 US$ per DALY averted. The package of care provided by SWAA-Burundi is therefore a very cost-effective intervention in comparison with other interventions against HIV/AIDS that include ART. It is however, less cost effective than other types of interventions against HIV/AIDS, such as preventive activities

Asymmetric Franck-Condon factors in suspended carbon nanotube quantum dots

Electronic states and vibrons in carbon nanotube quantum dots have in general different location and size. As a consequence, the conventional Anderson-Holstein model, coupling vibrons to the dot total charge only, may no longer be appropriated in general. Here we explicitly address the role of the spatial fluctuations of the electronic density, yielding space-dependent Franck-Condon factors. We discuss the consequent marked effects on transport which are compatible with recent measurements. This picture can be relevant for tunneling experiments in generic nano-electromechanical systems.Comment: 4+ pages, 3 figures (2 color, 1 BW

South-West extension of the hard X-ray emission from the Coma cluster

We explore the morphology of hard (18-30 keV) X-ray emission from the Coma cluster of galaxies. We analyze a deep (1.1 Ms) observation of the Coma cluster with the ISGRI imager on board the \emph{INTEGRAL} satellite. We show that the source extension in the North-East to South-West (SW) direction ($\sim 17'$) significantly exceeds the size of the point spread function of ISGRI, and that the centroid of the image of the source in the 18-30 keV band is displaced in the SW direction compared to the centroid in the 1-10 keV band. To test the nature of the SW extension we fit the data assuming different models of source morphology. The best fit is achieved with a diffuse source of elliptical shape, although an acceptable fit can be achieved assuming an additional point source SW of the cluster core. In the case of an elliptical source, the direction of extension of the source coincides with the direction toward the subcluster falling onto the Coma cluster. If the SW excess is due to the presence of a point source with a hard spectrum, we show that there is no obvious X-ray counterpart for this additional source, and that the closest X-ray source is the quasar EXO 1256+281, which is located $6.1'$ from the centroid of the excess. The observed morphology of the hard X-ray emission clarifies the nature of the hard X-ray "excess" emission from the Coma cluster, which is due to the presence of an extended hard X-ray source SW of the cluster core.Comment: 7pages, 10 figure

DLI-CVD of TiO2–Cu antibacterial thin films: Growth and characterization

TiO2–Cu nanocomposite films were grown by pulsed direct liquid injection chemical vapor deposition (DLICVD) on stainless steel, silicon and glass substrates with the goal to produce bactericidal surfaces. Copper bis (2,2,6,6-tetramethyl-3,5-heptadionate), Cu(TMHD)2, and titanium tetra-iso-propoxide, TTIP, were used as metalorganic precursors. Liquid solutions of these compounds in xylene were injected in a flash vaporization chamber connected to a cold wall MOCVD reactor. The deposition temperature was typically 683 K and the total pressure was 800 Pa. The copper content of the layers was controlled by the mole fraction of Cu (TMHD)2 which was adjusted by the injection parameters (injection frequency and concentration of the starting solution). The chemical, structural and physical characteristics of the films were investigated by XRD, XPS, FEG-SEM and TEM. Copper is incorporated as metal particles with a relatively large size distribution ranging from 20 to 400 nm (with a large majority in 20–100 nm) depending on the copper content of the films. The influence of the growth conditions on the structural features and the antibacterial properties of the thin films are reported and discussed

Relativistic Winds from Compact Gamma-ray Sources: I. Radiative Acceleration in the Klein-Nishina Regime

We consider the radiative acceleration to relativistic bulk velocities of a cold, optically thin plasma which is exposed to an external source of gamma-rays. The flow is driven by radiative momentum input to the gas, the accelerating force being due to Compton scattering in the relativistic Klein-Nishina limit. The bulk Lorentz factor of the plasma, Gamma, derived as a function of distance from the radiating source, is compared with the corresponding result in the Thomson limit. Depending on the geometry and spectrum of the radiation field, we find that particles are accelerated to the asymptotic Lorentz factor at infinity much more rapidly in the relativistic regime; and the radiation drag is reduced as blueshifted, aberrated photons experience a decreased relativistic cross section and scatter preferentially in the forward direction. The random energy imparted to the plasma by gamma-rays can be converted into bulk motion if the hot particles execute many Larmor orbits before cooling. This `Compton afterburn' may be a supplementary source of momentum if energetic leptons are injected by pair creation, but can be neglected in the case of pure Klein-Nishina scattering. Compton drag by side-scattered radiation is shown to be more important in limiting the bulk Lorentz factor than the finite inertia of the accelerating medium. The processes discussed here may be relevant to a variety of astrophysical situations where luminous compact sources of hard X- and gamma-ray photons are observed, including active galactic nuclei, galactic black hole candidates, and gamma-ray bursts.Comment: LateX, 20 pages, 5 figures, revised version accepted for publication in the Ap

Highlighting boundary condition effects for granular matter flows with numerical simulations

International audienceGranular matter flows naturally occur on small or large bodies due to gravity. Their simulation allows a better understanding of the dynamics of these bodies. However many numerical simulations operate with periodic boundary conditions for convenience , or with static grain boundaries that do not reproduce the rolling and friction effects expected at the interface. This work not only shows that boundary conditions have a long-range effect within the flow , but that dissipative effects induced by flat walls cannot be neglected compared to using static grain boundaries