MARCOS, a numerical tool for the simulation of multiple time-dependent non-linear diffusive shock acceleration

We present a new code aimed at the simulation of diffusive shock acceleration (DSA), and discuss various test cases which demonstrate its ability to study DSA in its full time-dependent and non-linear developments. We present the numerical methods implemented, coupling the hydrodynamical evolution of a parallel shock (in one space dimension) and the kinetic transport of the cosmic-rays (CR) distribution function (in one momentum dimension), as first done by Falle. Following Kang and Jones and collaborators, we show how the adaptive mesh refinement technique (AMR) greatly helps accommodating the extremely demanding numerical resolution requirements of realistic (Bohm-like) CR diffusion coefficients. We also present the paral lelization of the code, which allows us to run many successive shocks at the cost of a single shock, and thus to present the first direct numerical simulations of linear and non-linear multiple DSA, a mechanism of interest in various astrophysical environments such as superbubbles, galaxy clusters and early cosmological flows.Comment: accepted for publication in MNRAS by the Royal Astronomical Society and Blackwell Publishin

Parametric studies of cosmic ray acceleration in supernova remnants

We present a library of numerical models of cosmic-ray accelerating supernova remnants (SNRs) evolving through a homogeneous ambient medium. We analyse distributions of the different energy components and diffusive shock acceleration time-scales for the models in various conditions. The library comprises a variety of SNR evolutionary scenarios and is used to map remnants with sufficiently known properties. This mapping constrains the respective ambient medium properties and the acceleration efficiency. Employing the library, we derive the ambient medium density, ambient magnetic field strength and the cosmic-ray acceleration efficiency for models of Tycho and SN 1006 remnants and refine the ages of SNR 0509-67.5 and SNR 0519-69.0.Comment: 13 pages, 9 figures, MNRAS accepte

Monogenous algebras. Back to Kronecker

In this note we develop some properties of those algebras (called here locally simple) which can be generated by a single element after, if need be, a faithfully flat extension. For finite algebras, this is shown to be in fact a property of the geometric fibers. Morphisms between rings of algebraic integers are locally simple. Expanding an idea introduced by Kronecker we show that much of the properties (in particular local simplicity) of a finite and locally free A-algebra B can be read through the characteristic polynomial of the generic element of B.Comment: Note ecrite en septembre 2003. 13 page

Sustainable intensification of rainfed lowland rice systems: A case study in Xieng Khouang Province in Lao PDR

With the growing concern about food security in the northern uplands of Laos, it is critical to address the issue of sustainable intensification of food production. The objective of the study was to characterize the variability in rice cropping practices and to evaluate their performance and sustainability in Lao PDR. One, name d Sustainable Rice System (SRS), was promoted by a national NGO as an adaptation of the System of Rice Intensification (SRI) to the local agro-ecological conditions. This innovation was compared to traditional rice growing practices in the study area in Kham Di strict, Xieng Khouang Province. The study has enabled actors to better understand the real diversity of practices. We found a distinct ion between single seedling and multiple seedling transplanting practices. Then, focusing on single seedling transplanting (referred as SRS), the study demonstrated that despite no signify cant yield increase, farmers are interested in adopting it because it provides other benefits. These are notably the increase in the return on labor (57.8%) and savings on the global labor requirement (28.4%). As labor scarcity is and will remain the main concern for Lao farmers, our study shows the importance of considering performance indicators beyond crop yields. Regarding the environmental aspect of SRS, our results highlight that the common use of chemical fertilizer does not really fit with agroecological principles. Nevertheless, the significant increase in the use of manure in comparison with other practices can anticipate a positive trend in term of environmental conservation. (Résumé d'auteur

Survey of children accessing HIV services in a high prevalence setting: time for adolescents to count?

OBJECTIVE: To establish the proportion of adolescents among children infected with human immunodeficiency virus (HIV) in Zimbabwe who receive HIV care and support, and what clinic staff perceives to be the main problems faced by HIV-infected children and adolescents. METHODS: In July 2008, we sent a questionnaire to all 131 facilities providing HIV care in Zimbabwe. In it we requested an age breakdown of the children (aged 0-19 years) registered for care and asked what were the two major problems faced by younger children (0-5 years) and adolescents (10-19 years). FINDINGS: Nationally, 115 (88%) facilities responded. In 98 (75%) that provided complete data, 196 032 patients were registered and 24 958 (13%) of them were children. Of children under HIV care, 33% were aged 0-4 years; 25%, 5-9 years; 25%, 10-14 years; and 17%, 15-19 years. Staff highlighted differences in the problems most commonly faced by younger children and adolescents. For younger children, such problems were malnutrition and lack of appropriate drugs (cited by 46% and 40% of clinics, respectively); for adolescents they concerned psychosocial issues and poor drug adherence (cited by 56% and 36%, respectively). CONCLUSION: Interventions for the large cohort of adolescents who are receiving HIV care in Zimbabwe need to target the psychosocial concerns and poor drug adherence reported by staff as being the main concerns in this age group