Speech Communication

Contains research objectives and reports on four research projects.U.S. Air Force (Electronic Systems Division) under Contract AF 19(628)-3325National Institutes of Health (Grant NB-04332-03

A techno-economic probabilistic approach to superheater lifetime determination

In the commonly used approach, the lifetime of a superheater is estimated by characteristic values of the production parameters and the operating conditions. In this approach, a lower bound for a superheater lifetime is based on some arbitrary safety factor that does not necessarily reflect real life, where unexpected failures do occur. The method proposed here suggests coping with this reality, by employing a techno-economic probabilistic approach. It comprises the following two models: • A probabilistic time to failure evaluation model that considers the variability of the lifetime determining parameters. • A model to optimise values of technical parameters and operating conditions and to determine a superheater’s optimal replacement policy, based on life cycle cost considerations. The proposed probabilistic time to failure evaluation model can help to identify the most influential parameters for planning for a minimal probability of failure. It is applied to a unique problematic steel T22 superheater of rather specific parameters: corrosion rate, the Larson Miller Parameter (LMP), diameter and wall thickness. Sensitivity analysis has shown that the dominant factor affecting variation in superheater lifetime is the variation in the LMP, while the effect of the other parameters is quite marginal. Decreasing the standard deviation of the LMP (by keeping a more uniform material) lowered the probability of failure. This resulted in a practical recommendation to perform periodical checks of the parameter wall thickness. We also tested the effect of changing the nominal values of these parameters on the lifetime distribution. Hence, we suggest that the selection of the nominal values should be based on life cycle cost considerations; and propose a model to calculate, for any given combination, the average life cycle cost. The latter model, the optimal parameters combination model, optimises the combination of changes in all the superheater’s parameters by minimising the average life cycle cost associated with the superheater. Demonstrating the usefulness of the proposed approach, in a problematic case, suggests that it can be beneficially employed in the more general case whenever the planned lifetime of a design is threatened

L'apoptose des cellules folliculaires: son implication dans les protocoles de stimulation ovarienne

National audienc

New Biophysical Approaches Reveal the Dynamics and Mechanics of Type I Viral Fusion Machinery and Their Interplay with Membranes

Protein-mediated membrane fusion is a highly regulated biological process essential for cellular and organismal functions and infection by enveloped viruses. During viral entry the membrane fusion reaction is catalyzed by specialized protein machinery on the viral surface. These viral fusion proteins undergo a series of dramatic structural changes during membrane fusion where they engage, remodel, and ultimately fuse with the host membrane. The structural and dynamic nature of these conformational changes and their impact on the membranes have long-eluded characterization. Recent advances in structural and biophysical methodologies have enabled researchers to directly observe viral fusion proteins as they carry out their functions during membrane fusion. Here we review the structure and function of type I viral fusion proteins and mechanisms of protein-mediated membrane fusion. We highlight how recent technological advances and new biophysical approaches are providing unprecedented new insight into the membrane fusion reaction

L'apoptose des cellules folliculaires: son implication dans les protocoles de stimulation ovarienne

National audienc

Involvement of theca cells and steroids in the regulation of granulosa cell apoptosis in rabbit preovulatory follicles

International audienc

Subtle temperature increase can interact with individual size and social context in shaping phenotypic traits of a coldwater fish

Temperature and individual egg size have been long studied in the development of fishes because of their direct effects on individual fitness. Here we studied the combined effects of three important factors for fish development, i.e. egg size, social environment and water temperature. Arctic charr (Salvelinus alpinus), a coldwater fish known to be phenotypically plastic, was used to investigate how these factors may affect growth and foraging behaviour of juvenile fish in a benign environment. We accounted for the social environment during early development by comparing fish raised in groups and in isolation. We examined the effect of egg size and a 2 degrees C difference on foraging behaviour, activity and growth a few weeks after first feeding. Growth trajectories of fish originating from large and small eggs were similar within each temperature: larger fish coming large eggs were at all time larger than smaller fish. There was no indication that small fish raised at a higher temperature grew faster than larger fish raised at a lower temperature. A 2 degrees C difference in temperature affected the behaviour of fish differently according to body size and/or social context. The foraging probability difference between fish raised in groups and fish briefly isolated was higher at 4.5 degrees C than at 6.5 degrees C for both size fish. Finally, there was no repeatability in foraging behaviour and mobility for isolated individuals. These results highlight the importance of small changes in temperature when evaluating growth and behaviour of fishes, and reveal the importance of considering the interaction of temperature with other factors, e.g. individual size and social environment, especially at early stages of development in fishes. We discuss these findings in the context of rapid changes in temperature and how temperature and its interaction with other factors may affect the phenotypes, ecology and evolution of coldwater fishes