The Nonlinear Debye-Onsager Relaxation Effect in Weakly Ionized Plasmas

A weakly ionized plasma under the influence of a strong electric field is considered. Supposing a local Maxwellian distribution for the electron momenta the plasma is described by hydrodynamic equations for the pair distribution functions. These equations are solved and the relaxation field is calculated for an arbitrary field strength. It is found that the relaxation effect becomes lower with increasing strength of the electrical field.Comment: 4 pages, 1 figur

Formation of correlations in strongly coupled plasmas

The formation of binary correlations in plasma is studied from the quantum kinetic equation. It is shown that this formation is much faster than dissipation due to collisions. In a hot (dense) plasma the correlations are formed on the scale of inverse plasma frequency (Fermi energy). We derive analytical formulae for the time dependency of the potential energy which measures the extent of correlations. We discuss the dynamical formation of screening and compare with the statical screened result. Comparisons are made with molecular dynamic simulations.Comment: Proceedings of the 8th International Workshop on Atomic Physics for Ion-Driven Fusion, Heidelberg 1997, appear in Laser and Particle Beam

Model system development and uncertainty for the provisionary management of extreme floods in large river basins

International audienceA research project is introduced in which a modelling system is being developed to quantify risks of extreme flooding in large river basins. In the system, computer models and modules are coupled to simulate the functional chain: hydrology - hydraulics - polder diversion - dyke failure - flooding - damage estimate - risk assessment. In order to reduce uncertainty in flood frequency analyses, data sets are complimented with information from historical chronicles and artwork. Probable maximum precipitation and discharge are calculated to indicate upper bounds of meteorological and hydrological extremes. Uncertainty analysis is investigated for different degrees of model complexity and compared at different basin scales

Diversity and Ecological Correlates of Red Fluorescence in Marine Fishes

Marine environments at depths below -10 to -25 m are almost devoid of ambient red sunlight because water quickly attenuates long wavelengths. This stenospectral light environment presents unique opportunities for organisms that can transform ambient blue-green light into red light by fluorescence. Numerous marine fish species display intricate patterns of fluorescence. Because color vision is a key component of fish sensory ecology, several putative visual functions of red fluorescence have been proposed but are difficult to test experimentally. Here, we follow a comparative approach to assess the consistency between the phylogenetic distribution of red fluorescence with its presumed functions. We collected and analyzed the largest data set of red fluorescence in fishes to date, consisting of confirmed cases in 272 primarily diurnal fish species from 49 out of 90 surveyed fish families and 12 out of 21 surveyed fish orders, contrasted to 393 fish species with confirmed absence of red fluorescence. Based on a priori hypotheses on adaptive function, we compare the prevalence of red fluorescence among pre-defined sets of species based on ecological or biological characteristics while controlling for shared ancestry. When comparing between species, we find no evidence that red fluorescence is more prevalent in deep-water species, contrasting with our recent finding that fluorescence brightness increases with depth within species. There is also no evidence for a role in group-driven communication. Phylogenetic patterns are consistent, however, with three other predictions. First, fluorescence with a rather patchy distribution across the body occurred significantly more often among sit-and-wait predators or otherwise sedentary fish than in more mobile species, consistent with background matching for camouflage. Second, small, predatory fishes tended to show red fluorescent irides disproportionally often consistent with a proposed function in prey localization. Finally, sexually dimorphic species showed fluorescent fins more often, as predicted if relevant in sexual communication. From these findings, we derive predictions for experimental investigations of the presumed functions of red fluorescence

Close-to-community providers of health care: increasing evidence of how to bridge community and health systems.

This article was published in Human Resources for Health [© 2016 BioMed Central Ltd.] and the definite version is available at: https://human-resources-health.biomedcentral.com/articles/10.1186/s12960-016-0132-9Publishe

Comparison of Different Solvers and Geometry Representation Strategies for Dns of Rough Wall Channel Flow

In the present study we investigate an incompressible turbulent channel flow with heat transfer at Reτ = 180 with a deterministic surface topography consisting of truncated cones. Two solvers for each of the two boundary handling strategies are considered. With Nek5000 and OpenFOAM the influence of the roughness elements is directly accounted for by an unstructured body fitted mesh, whereas Xcompact3d and SIMSON utilize the immersed boundary method (IBM) to deal with the 3D geometry. The main focus of this work is on an evaluation of the usability of the IBM and a comparison of the parallel performance of the different solvers. Since usability is an ambiguous definition, various quantities are compared: global statistics like Nusselt number and friction coefficient, one-dimensional wall-normal profiles for first and second order statistics, as well as three-dimensional averages over roughness sections. In addition, the computational effort for each method is documented

Exploring perceptions of community health policy in Kenya and identifying implications for policy change

Background Global interest and investment in close-to-community health services is increasing. Kenya is currently revising its community health strategy (CHS) alongside political devolution, which will result in revisioning of responsibility for local services. This article aims to explore drivers of policy change from key informant perspectives and to study perceptions of current community health services from community and sub-county levels, including perceptions of what is and what is not working well. It highlights implications for managing policy change. Methods We conducted 40 in-depth interviews and 10 focus group discussions with a range of participants to capture plural perspectives, including those who will influence or be influenced by CHS policy change in Kenya (policymakers, sub-county health management teams, facility managers, community health extension worker (CHEW), community health workers (CHWs), clients and community members) in two purposively selected counties: Nairobi and Kitui. Qualitative data were digitally recorded, transcribed, translated and coded before framework analysis. Results There is widespread community appreciation for the existing strategy. High attrition, lack of accountability for voluntary CHWs and lack of funds to pay CHW salaries, combined with high CHEW workload were seen as main drivers for strategy change. Areas for change identified include: lack of clear supervisory structure including provision of adequate travel resources, current uneven coverage and equity of community health services, limited community knowledge about the strategy revision and demand for home-based HIV testing and counselling. Conclusion This in-depth analysis which captures multiple perspectives results in robust recommendations for strategy revision informed by the Five Wonders of Change Framework. These recommendations point towards a more people-centred health system for improved equity and effectiveness and indicate priority areas for action if success of policy change through the roll-out of the revised strategy is to be realized