The potential of discs from a "mean Green function"

By using various properties of the complete elliptic integrals, we have derived an alternative expression for the gravitational potential of axially symmetric bodies, which is free of singular kernel in contrast with the classical form. This is mainly a radial integral of the local surface density weighted by a regular "mean Green function" which depends explicitly on the body's vertical thickness. Rigorously, this result stands for a wide variety of configurations, as soon as the density structure is vertically homogeneous. Nevertheless, the sensitivity to vertical stratification | the Gaussian profile has been considered | appears weak provided that the surface density is conserved. For bodies with small aspect ratio (i.e. geometrically thin discs), a first-order Taylor expansion furnishes an excellent approximation for this mean Green function, the absolute error being of the fourth order in the aspect ratio. This formula is therefore well suited to studying the structure of self-gravitating discs and rings in the spirit of the "standard model of thin discs" where the vertical structure is often ignored, but it remains accurate for discs and tori of finite thickness. This approximation which perfectly saves the properties of Newton's law everywhere (in particular at large separations), is also very useful for dynamical studies where the body is just a source of gravity acting on external test particles.Comment: Accepted for publication in MNRAS, 11 page

Cosmic Evolution in Brans-Dicke Chameleon Cosmology

We have investigated the Brans-Dicke Chameleon theory of gravity and obtained exact solutions of the scale factor $a(t)$, scalar field $\phi(t)$, an arbitrary function $f(\phi)$ which interact with the matter Lagrangian in the action of the Brans-Dicke Chameleon theory and potential $V(\phi)$ for different epochs of the cosmic evolution. We plot the functions $a(t)$, $\phi(t)$, $f(t)$ and $V(\phi)$ for different values of the Brans-Dicke parameter. In our models, there is no accelerating solution, only decelerating one with $q>0$. The physical cosmological distances have been investigated carefully. Further the statefinder parameters pair and deceleration parameter are discussed.Comment: To be appear in "The European Physical Journal - Plus (EPJ Plus)",Extended version,15 pages, 17eps figure

Large-Eddy Simulations of Magnetohydrodynamic Turbulence in Heliophysics and Astrophysics

We live in an age in which high-performance computing is transforming the way we do science. Previously intractable problems are now becoming accessible by means of increasingly realistic numerical simulations. One of the most enduring and most challenging of these problems is turbulence. Yet, despite these advances, the extreme parameter regimes encountered in space physics and astrophysics (as in atmospheric and oceanic physics) still preclude direct numerical simulation. Numerical models must take a Large Eddy Simulation (LES) approach, explicitly computing only a fraction of the active dynamical scales. The success of such an approach hinges on how well the model can represent the subgrid-scales (SGS) that are not explicitly resolved. In addition to the parameter regime, heliophysical and astrophysical applications must also face an equally daunting challenge: magnetism. The presence of magnetic fields in a turbulent, electrically conducting fluid flow can dramatically alter the coupling between large and small scales, with potentially profound implications for LES/SGS modeling. In this review article, we summarize the state of the art in LES modeling of turbulent magnetohydrodynamic (MHD) ows. After discussing the nature of MHD turbulence and the small-scale processes that give rise to energy dissipation, plasma heating, and magnetic reconnection, we consider how these processes may best be captured within an LES/SGS framework. We then consider several special applications in heliophysics and astrophysics, assessing triumphs, challenges,and future directions

Effect of the sickle cell trait status of gametocyte carriers of Plasmodium falciparum on infectivity to anophelines

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Characterization of trypanosome infections by polymerase chain reaction (PCR) amplification in wild tsetse flies in Cameroon

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Une nouvelle glossine pour la faune de la Guinée Equatoriale (Dipt., Glossinidae)

For the first time, the authors report #Glossina caliginea$ Austen, 1911 in Equatorial Guinea (= Rio Mbini). Specimens of this species have been caught in "Vavoua type" traps settled down, in the Mbini area, during a survey on the epidemiology of human and animal trypanosomisasis. (Résumé d'auteur

Detection and identification of trypanosomes by polymerase chain reaction in wild tsetse flies in Cameroon

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Utilisation de la PCR sur sang pour le diagnostic des trypanosomoses porcines

La Polymerase Chain Reaction (PCR) sur sang a été réalisée sur du sang de porcs d'un village camerounais en utilisant des amorces de #T. brucei sl., #T. congolense, #T. simiae et #T. vivax. Les résultats montrent qu'alors que l'examen parasitologique mettait en évidence des trypanosomes chez 15,8% des porcs, la PCR permettait de diagnostiquer 84,2% de ceux-ci comme étant trypanosomés. Les perspectives ouvertes par cette technique pour l'étude des trypanosomes sont évoquées par les auteurs. (Résumé d'auteur