Les aspects parasitologiques de l'épidémiologie du paludisme dans le Sahara malien

Dans le cadre de l'évaluation épidémiologique de la Transsaharienne, une enquête transversale paludométrique a été réalisée d'Août 1988 à Septembre 1988 le long du tronçon malien. Neuf localités ont été visitées : Douentza, Gossi, Bourem, Almoustarat, Anefis, Aguel-Hoc, Tarlit, Tessalit, Kidal, Bouressa. 2185 unités ont été prélevées pour les études cliniques, parasitologiques et immunologiques. L'indice plasmodique global est de 5,3 % avec une grande variation du Sud (44,6 %) au Nord (0 %). L'indice gamétocytique et l'indice splénique sont très faibles. #P. falciparum est l'espèce dominante. #P. malariae a été décrit une fois en association avec #P. falciparum. #P. ovale n'a jamais été observé. Par contre un cas de #P. vivax a été décrit chez une jeune fille leucoderme de 8 ans à Kidal. #A. gambiae s.s. (forme Mopti) et #A. arabiensis sont les principaux vecteurs au Nord du Mali. Une hypothèse de circulation de #P. vivax dans le Sahara malien est émise. (Résumé d'auteur

Chaotic, memory and cooling rate effects in spin glasses: Is the Edwards-Anderson model a good spin glass?

We investigate chaotic, memory and cooling rate effects in the three dimensional Edwards-Anderson model by doing thermoremanent (TRM) and AC susceptibility numerical experiments and making a detailed comparison with laboratory experiments on spin glasses. In contrast to the experiments, the Edwards-Anderson model does not show any trace of re-initialization processes in temperature change experiments (TRM or AC). A detailed comparison with AC relaxation experiments in the presence of DC magnetic field or coupling distribution perturbations reveals that the absence of chaotic effects in the Edwards-Anderson model is a consequence of the presence of strong cooling rate effects. We discuss possible solutions to this discrepancy, in particular the smallness of the time scales reached in numerical experiments, but we also question the validity of the Edwards-Anderson model to reproduce the experimental results.Comment: 17 pages, 10 figures. The original version of the paper has been split in two parts. The second part is now available as cond-mat/010224

Metastable States in Spin Glasses and Disordered Ferromagnets

We study analytically M-spin-flip stable states in disordered short-ranged Ising models (spin glasses and ferromagnets) in all dimensions and for all M. Our approach is primarily dynamical and is based on the convergence of a zero-temperature dynamical process with flips of lattice animals up to size M and starting from a deep quench, to a metastable limit. The results (rigorous and nonrigorous, in infinite and finite volumes) concern many aspects of metastable states: their numbers, basins of attraction, energy densities, overlaps, remanent magnetizations and relations to thermodynamic states. For example, we show that their overlap distribution is a delta-function at zero. We also define a dynamics for M=infinity, which provides a potential tool for investigating ground state structure.Comment: 34 pages (LaTeX); to appear in Physical Review

Viral Load Distribution in SARS Outbreak

Airborne transmission may have resulted in an outbreak of SARS in Hong Kong

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics

Regional unit definition for the nucleus of comet 67P/Churyumov-Gerasimenko on the SHAP7 model

Open Acces publication. This article is available under the Creative Commons CC-BY-NC-ND license and permits non-commercial use of the work as published, without adaptation or alteration provided the work is fully attributed.The previously defined regions on the nucleus of comet 67P/Churyumov-Gerasimenko have been mapped back onto the 3D SHAP7 model of the nucleus (Preusker et al., 2017). The resulting regional definition is therefore self-consistent with boundaries that are well defined in 3 dimensions. The facets belonging to each region are provided as supplementary material. The shape model has then been used to assess inhomogeneity of nucleus surface morphology within individual regions. Several regions show diverse morphology. We propose sub-division of these regions into clearly identifiable units (sub-regions) and a comprehensive table is provided. The surface areas of each sub-region have been computed and statistics based on grouping of unit types are provided. The roughness of each region is also provided in a quantitative manner using a technique derived from computer graphics applications. The quantitative method supports the sub-region definition by showing that differences between sub-regions can be numerically justified.© 2018 The AuthorsThe team from the University of Bern is supported through the Swiss National Science Foundation and through the NCCR PlanetS. The project has also received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 686709. This work was supported by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 16.0008-2

Optimal Control of Nonlinear Switched Systems: Computational Methods and Applications

A switched system is a dynamic system that operates by switching between different subsystems or modes. Such systems exhibit both continuous and discrete characteristics—a dual nature that makes designing effective control policies a challenging task. The purpose of this paper is to review some of the latest computational techniques for generating optimal control laws for switched systems with nonlinear dynamics and continuous inequality constraints. We discuss computational strategiesfor optimizing both the times at which a switched system switches from one mode to another (the so-called switching times) and the sequence in which a switched system operates its various possible modes (the so-called switching sequence). These strategies involve novel combinations of the control parameterization method, the timescaling transformation, and bilevel programming and binary relaxation techniques. We conclude the paper by discussing a number of switched system optimal control models arising in practical applications