Varieties of Cost Functions.

Regular cost functions were introduced as a quantitative generalisation of regular languages, retaining many of their equivalent characterisations and decidability properties. For instance, stabilisation monoids play the same role for cost functions as monoids do for regular languages. The purpose of this article is to further extend this algebraic approach by generalising two results on regular languages to cost functions: Eilenberg's varieties theorem and profinite equational characterisations of lattices of regular languages. This opens interesting new perspectives, but the specificities of cost functions introduce difficulties that prevent these generalisations to be straightforward. In contrast, although syntactic algebras can be defined for formal power series over a commutative ring, no such notion is known for series over semirings and in particular over the tropical semiring

Instabilities of a liquid layer locally heated on its free surface

International audienceWe report experimental results concerning patterns in a model experiment built to studybuoyant-thermocapillary-driven flows. The fluid is situated in a cooled cylindrical container andlocally heated on its free surface. The resulting temperature gradient induces a basic flow whichdraws the surface fluid from the hot center toward the cold boundary. When the gradient is increasedand depending on the height of liquid, the basic flow destabilizes into different stationary patterns.Above a second threshold, the patterns become time-dependent. These different instabilities arecharacterized and compared to recent theoretical results

Caesarean section rates in South Africa: A case study of the health systems challenges for the proposed National Health Insurance

Broader policy research and debate on the issues related to the planning of National Health Insurance (NHI) in South Africa (SA) need to be complemented by case studies to examine and understand the issues that will have to be dealt with at micro and macro levels. The objective of this article is to use caesarean section (CS) as a case study to examine the health systems challenges that NHI would need to address in order to ensure sustainability. The specific objectives are to: (i) provide an overview of the key clinical considerations related to CS; (ii) assess the CS rates in the SA public and private sectors; and (iii) use a health systems framework to examine the drivers of the differences between the public and private sectors and to identify the challenges that the proposed NHI would need to address on the road to implementation

On the properties of steady states in turbulent axisymmetric flows

We experimentally study the properties of mean and most probable velocity fields in a turbulent von K\'arm\'an flow. These fields are found to be described by two families of functions, as predicted by a recent statistical mechanics study of 3D axisymmetric flows. We show that these functions depend on the viscosity and on the forcing. Furthermore, when the Reynolds number is increased, we exhibit a tendency for Beltramization of the flow, i.e. a velocity-vorticity alignment. This result provides a first experimental evidence of nonlinearity depletion in non-homogeneous non-isotropic turbulent flow.Comment: latex prl-stationary-051215arxiv.tex, 9 files, 6 figures, 4 pages (http://www-drecam.cea.fr/spec/articles/S06/008/

Organotypic cultures as tools for optimizing central nervous system cell therapies

Stem cell therapy is a promising treatment for neurological disorders such as cerebral ischemia, Parkinson\u27s disease and Huntington\u27s disease. In recent years, many clinical trials with various cell types have been performed often showing mixed results. Major problems with cell therapies are the limited cell availability and engraftment and the reduced integration of grafted cells into the host tissue. Stem cell-based therapies can provide a limitless source of cells but survival and differentiation remain a drawback. An improved understanding of the behaviour of stem cells and their interaction with the host tissue, upon implantation, is needed to maximize the therapeutic potential of stem cells in neurological disorders. Organotypic cultures made from brain slices from specific brain regions that can be kept in culture for several weeks after injecting molecules or cells represent a remarkable tool to address these issues. This model allows the researcher to monitor/assess the behaviour and responses of both the endogenous as well as the implanted cells and their interaction with the microenvironment leading to cell engraftment. Moreover, organotypic cultures could be useful to partially model the pathological state of a disease in the brain and to study graft-host interactions prior to testing such grafts for pre-clinical applications. Finally, they can be used to test the therapeutic potential of stem cells when combined with scaffolds, or other therapeutic enhancers, among other aspects, needed to develop novel successful therapeutic strategies or improve on existing ones

Moving towards universal health coverage: Strengthening the evidence ecosystem for the South African health system

Health policy and systems research (HPSR) guides health system reforms and is essential for South Africa (SA)’s progress towards universal coverage of high-quality healthcare. For HPSR evidence to inform and strengthen health systems, it needs to flow efficiently between evidence producers, evidence synthesisers, evidence processers and disseminators and evidence implementors in an evidence ecosystem. A substantial body of evidence for health systems strengthening is generated in SA, and this informs national and international health system guidelines and guidance. In this manuscript, in celebration of the 50th anniversary of the SA Medical Research Council, we apply an evidence ecosystem lens to the SA health system, and discuss its current functioning in support of the achievement of a high-quality health system that is able to achieve universal health coverage. We use three case studies to describe successes, challenges and gaps in the functioning of the evidence ecosystem. The first case study focuses on using evidence to strengthen health-system governance and support for community health worker programmes. The second case focuses on managing the growing epidemic of drug-resistant tuberculosis, while the third case focuses on social protection, the child support grant and its impact on health. SA scientists are part of global initiatives to strengthen the health-systems evidence ecosystem, specifically through pioneering methods to synthesise evidence and produce evidence-informed guidelines to facilitate evidence use in health-system decision-making. SA institutes of health policy analysis facilitate involvement of evidence producers and synthesisers in the national health system policy-making process. A future priority is to further strengthen national initiatives to translate evidence into policy and practice and to sustain capacity for continuous technical support to health-systems policy development and implementation

Modeling nigrostriatal degeneration in organotypic cultures, a new ex vivo model of Parkinson’s disease

Parkinson’s disease (PD) is the second most frequent neurodegenerative disorder afflicting 2% of the population older than 65 years worldwide. Recently, brain organotypic slices have been used to model neurodegenerative disorders, including PD. They conserve brain three-dimensional architecture, synaptic connectivity and its microenvironment. This model has allowed researchers a simple and rapid method to observe cellular interactions and mechanisms. In the present study, we developed an organotypic PD model from rat brains that includes all the areas involved in the nigrostriatal pathway in a single slice preparation, without using neurotoxins to induce the dopaminergic lesion. The mechanical transection of the nigrostriatal pathway obtained during slice preparation induced PD-like histopathology. Progressive nigrostriatal degeneration was monitored combining innovative approaches, such as diffusion tensor magnetic resonance imaging (DT-RMI) to follow fiber degeneration and mass spectrometry to quantify striatal dopamine content, together with bright-field and fluorescence microscopy imaging. A substantia nigra dopaminergic cell number decrease was observed by immunohistochemistry against rat tyrosine hydroxylase (TH) reaching 80% after 2 days in culture associated with a 30% decrease of striatal TH-positive fiber density, a 15% loss of striatal dopamine content quantified by mass spectrometry and a 70% reduction of nigrostriatal fiber fractional anisotropy quantified by DT-RMI. In addition, a significant decline of medium spiny neuron density was observed from days 7 to 16. These sagittal organotypic slices could be used to study the early stage of PD, namely dopaminergic degeneration, and the late stage of the pathology with dopaminergic and GABAergic neuron loss. This novel model might improve the understanding of PD and may represent a promising tool to refine the evaluation of new therapeutic approaches