Stochastic and deterministic models for age-structured populations with genetically variable traits

Understanding how stochastic and non-linear deterministic processes interact is a major challenge in population dynamics theory. After a short review, we introduce a stochastic individual-centered particle model to describe the evolution in continuous time of a population with (continuous) age and trait structures. The individuals reproduce asexually, age, interact and die. The 'trait' is an individual heritable property (d-dimensional vector) that may influence birth and death rates and interactions between individuals, and vary by mutation. In a large population limit, the random process converges to the solution of a Gurtin-McCamy type PDE. We show that the random model has a long time behavior that differs from its deterministic limit. However, the results on the limiting PDE and large deviation techniques \textit{\`a la} Freidlin-Wentzell provide estimates of the extinction time and a better understanding of the long time behavior of the stochastic process. This has applications to the theory of adaptive dynamics used in evolutionary biology. We present simulations for two biological problems involving life-history trait evolution when body size is plastic and individual growth is taken into account.Comment: This work is a proceeding of the CANUM 2008 conferenc

Ex vivo TSM online monitoring of skin dehydration

International audienc

New wideband electromagnatic on-line system for microalgae production monitoring

International audienc

New ultrasonic technic for on-line encapsulation monitoring

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Influence of hydrophilic and hydrophobic SBA-15 and MCM-41 surfaces in CuII impregnation

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The missing bridge between ex vivo and in vivo models: the Perfex vivo system

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Skin surface nanoscale topography by light interferometry

International audienceThe skin is the first thing one perceives of a person. Unconsciously, its color, its radiance and its complexion give us a first impression of a person. This is why cosmetic care and makeup products are of great importance.But how to evaluate their activity?Many methods of in vivo measurements exist to evaluate its color or shine, but the evaluation of a product activity on skin surface is much more complicated.. The relief of the skin and even more its microrelief, are largely responsible for its optical properties and therefore the image it refers.Many products have a filling or a tensor effect, modifying the depth and width of the microfolds that compose the microrelief. It is consequently necessary to measure and characterize the skin surface before and after the application of a cosmetic product with great precision.More precise than 3D scanners, or the fringe projections in vivo, light interferometry allows making a topographical survey of the skin surface with an accuracy of a few tens of nanometers.The topography by light interferometry is developed by the Polytec company whose experience in measuring equipment is no longer to be proved.This technology used in particular in the control of mechanical parts of aeronautics, offers a lateral resolution of approximately 10 μm and a vertical resolution of less than 20 nm.Depending on the light interference reflected from the surface of the skin, this technology is sensitive to vibrations which avoids its in vivo use.To benefit from this technology usually reserved for the world of precision micromechanics, we have developed a support to put under tension a human living skin explant and to maintain it in survival ex vivo.This support specially designed and printed in 3D allows stretching the skin on a reservoir of culture medium while respecting a tension similar to the in vivo conditions.The tension of the skin was measured and verified by cutometry. This measurement can also be performed during the study which can last up to 10 days.The skin thus stretched can be topographed and treated by different products. So it will be very simple to measure the roughness of the surface of the skin, the depth of its folds or their width.We applied on the surface of the skin three products, two with smoothing and filling activity. We showed a decrease in the average depth of the cutaneous microfolds as well as a decrease of the roughness of the skin.If an immediate effect can be observed in a few minutes, the ex vivo character of this model also allows evaluating a biological activity which reinforces in depth this surface-visible effect.This new and original approach, coupling light interferometry technology and human living skin explant, offers all the precision and finesse necessary for an immediate evaluation of the activity of a product on skin surface proprieties and to investigate in parallel the cutaneous-linked biological effects

Immediate effects of cosmetic products on skin surface highlighted by nanoscale topography on ex vivo human skin

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Dispositif ex vivo de suivi en temps réel des propriétés mécaniques de peau maintenue en survie par microrhéologie ultrasonore

National audienc

Sulfonated polyimidesfor fuel cell electrode membrane assemblies (EMA)

International audienceThe state of the art in the field of fuel cell technol. shows that Nafion is a well-known std. for its use as polymeric proton exchange membrane. Indeed, this material is characterized by very high performance and durability. However, some limitations could prevent a wide industrial scale development such as the manufg. cost, and to some extent difficulties encountered to recycle the EMA related to the high chem. stability of the perfluorinated materials. However, over the last few years, an important research activity has been devoted to propose an alternative system and, as a consequence, has led to the synthesis of a large array of sulfonated non fluorinated polymers. In this perspective, we are interested in developing proton exchange membranes based on sulfonated polyimides. This work reports the performance obtained with such membranes, in a new design EMA