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

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

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

Is the distribution of Amblyomma variegatum influenced by interspecific competition with Amblyomma hebraeum? Preliminary study: distribution range in Mozambique

Widely spread in intertropical and subtropical areas of Africa, the southern distribution of Amblyomma variegatum in Mozambique seems to have its limit around the Save River, at the 22nd parallel South. This area also corresponds to the northern limit of another Amblyomma tick, A. hebraeum. Several authors use to explain the absence of A. variegatum more southwards by an interspecific competition with A. hebraeum. Whereas only A. variegatum is known to favor dermatophilosis, a skin disease that can cause important burden in ruminants, both species are good vectors of Ehrlichia ruminantium, the bacteria causing heartwater, a fatal disease of ruminants representing a major constraint for livestock development in Africa. However, their vector competence may be different and vary according to the strain of E. ruminantium. As a result, the bio-ecology and distribution of those vectors in the field may result in specific epidemiological patterns for the diseases they transmit and are important to understand to adopt proper sanitary control and prevention measures. Little information on current (last decade) Amblyomma distribution in Mozambique is available, and little is known on the factors influencing their distribution. More especially, the existence of a distribution overlap, as observed in Zimbabwe is not known in Mozambique. Indeed the extent of this overlap and the distribution of A. variegatum and A. hebraeum in this particular area represent useful information to assess potential interspecific competition. The objective of this study is to assess the current distribution of A. variegatum and A. hebraeum in this country and to better locate and characterize species limitation ranges around the Save River with a view to further identify the factors influencing their distribution. First, an exhaustive literature review was made to collect all published and unpublished data relating to the distribution of A. variegatum and A. hebraeum in Africa. A field entomological survey was then conducted in Mozambique between February and April 2012 to identify ticks collected on cattle, in the Inhambane, Manica and Sofala provinces, nearby the Save River. Sampling sites included dip-tanks and corridors, used for acaricides treatment by neighboring farmers, as well as farms which were selected by the local Veterinary Service. In each study site, about 60 animals were carefully examined for ticks presence and abundance, mostly in corridors and on 10 laid-down animals most heavily infested by ticks. Ticks, males and females, were collected to confirm species identification. Data on domestic ruminant population and movements as well as breeding practices including tick control were also collected through interviews with farmers and local and central veterinary services. The epidemiological unit is the sampling site. A site was considered positive for a given tick species if at least one animal was infested by at least one tick of that species, otherwise, it was considered negative. To better assess species presence in their limit of distribution, an attempt was made to interpret presence and absence data to distinguish well-established or occasionally present population and likely not detected or absent populations. This was done considering sampling method, tick abundance, study period against phenology, as well as other information: last acaricide treatment, animal introduction, etc. Data were entered in Access database and displayed on a Geographic Information System, ArcMap9.3 A map of the current A. variegatum and A. hebraeum distribution was produced and included 103 positive sites out of 113 sampled between 2000 and 2012. The field survey conducted in 30 study sites evidenced a distribution overlap of 30km (western side) to 100km (eastern side) width, along a slanting line northwest-southeast accross the Save River, where both species were found in three sites and coinfestation of few animals was observed. The current distribution o

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