Dynamics and organization of MAP kinase signal pathways

In the budding yeast, Saccharomyces cerevisiae, four separate but structurally related mitogen-activated protein kinase (MAPK) activation pathways are known. The best understood of these regulates mating. Pheromone binding to receptor informs cells of the proximity of a mating partner and induces differentiation to a mating competent state. The MAPK activation cascade mediating this signal is made up of Ste11 (a MEK kinase [MEKK]), Ste7 (a MAPK/ERK kinase [MEK]), and the redundant MAPK-related Fus3 and Kss1 enzymes. Another MAPK activation pathway is important for cell integrity and regulates cell wall construction. This cascade consists of Bck1 (a MEKK), the redundant Mkk1 and Mkk2 enzymes (MEKs), and Mpk1 (a MAPK). We exploited these two pathways to learn about the coordination and signal transmission fidelity of MAPK activation cascades. Two lines of evidence suggest that the activities of the mating and cell integrity pathways are coordinated during mating differentiation. First, cells deficient in Mpk1 are susceptible to lysis when they make a mating projection in response to pheromone. Second, Mpk1 activation during pheromone induction coincides with projection formation. The mechanism underlying this coordination is still unknown to us. Our working model is that projection formation generates a mobile second messenger for activation of the cell integrity pathway. Analysis of a STE7 mutation gave us some unanticipated but important insights into parameters important for fidelity of signal transmission. The Ste7 variant has a serine to proline substitution at position 368. Ste7-P368 has higher basal activity than the wild-type enzyme but still requires Ste11 for its function. Additionally, the proline substitution enables the variant to transmit the signal from mammalian Raf expressed in yeast. This novel activity suggests that Ste7-P368 is inherently more permissive than Ste7 in its interactions with MEKKs. Yet, Ste7-P368 cross function in the cell integrity pathway occurs only when it is highly overproduced or when Ste5 is missing. This behavior suggests that Ste5, which has been proposed to be a tether for the kinases in the mating pathway, contributes to Ste7 specificity and fidelity of signal transmission.     

Mechanical performance of ceramic matrix composite I-beams

Experimental studies have been performed on ceramic matrix composite (CMC) I-sections, which typify joint designs for CMC components. Axial loads and moments have been applied to activate delamination mechanisms. The maximum load bearing capacity has large variability, governed by the severity of manufacturing flaws located in the transition region of the I-section. This variability leads to an unsatisfactory design situation. Delaminations that form from these flaws arrest and behave in a stable manner, subject to a remanent load bearing capacity. This remanent capacity has minimal variability. Hence, design based on the remanent load would be robust. An expression for this design criterion is presented.     

e-LITE： A Concurrent Engineering Method Dedicated to E-learning Training Development for the Enhancement of Research Project Results

Scientific research projects aim to produce new knowledge generally in domains of high specialization.Some of these projects have goals of improving the performance of companies.In this case,the issues of the capitalization and transfer of scientific knowledge and its rapid transformation into professional skills are directly addressed.However,there is no method to derive e-learning teaching material from project results.So,this paper presents the e-LITE Method and its application to the ISTA3 project to support the process of developing a e-learning training.This application has allowed us to highlight the contributions of the method that promotes better knowledge sharing between partners of a research project and the development and transfer of research results to the professional world.So,after the presentation of the method,an application to the ISTA3 project will be presented.     

Temperature and magnetic field dependence of NbN film resistivity: 3D weak localization effects

Niobium nitride superconducting films have been deposited by reactive rf magnetron sputtering. Polyepitaxial growth on MgO-coated substrates greatly improves the superconducting properties. The overall film resistivity is found to be widely dependent on the total pressure of the gas mixture. Samples with a negative temperature coefficient of resistance exhibit 3D weak localization effects as characterized by magnetoresistance measurements. The inelastic scattering time is found to vary as T^–p with p2, in the temperature range T_c-3T_c.Laboratoire associé au C.N.R.S.     

Pulse chemical vapour infiltration of SiC in porous carbon or SiC participate preform using an r.f. heating system

SiC was infiltrated into a porous carbon or an SiC particulate preform from a gaseous system of 6% CH₃SiCl₃-H₂ using a pulse chemical vapour infiltration apparatus and r.f. heating at 1273 to 1423 K. At 1273 K, the SiC matrix infiltrated the porous carbon initially to half the thickness of the substrate and finally over the full thickness. After 10000 pulses, three-point flexural strength saturated at about 120MPa. SiC particulate preform made from an average particle size of 4m was infiltrated by SiC. After 30000 pulses at 1273 K, the flexural strength of the composite increased to 200 to 220 M Pa.     

An Operator-integration-factor splitting method for time-dependent problems: Application to incompressible fluid flow

In this paper we present a simple, general methodology for the generation of high-order operator decomposition (splitting) techniques for the solution of time-dependent problems arising in ordinary and partial differential equations. The new approach exploits operator integration factors to reduce multiple-operator equations to an associated series of single-operator initial-value subproblems. Two illustrations of the procedure are presented: the first, a second-order method in time applied to velocity-pressure decoupling in the incompressible Stokes problem; the second, a third-order method in time applied to convection-Stokes decoupling in the incompressible Navier-Stokes equations. Critical open questions are briefly described.     

A methodology for modeling the distributions of medical images and their stochastic properties

The probabilistic distribution properties of a set of medical images are studied. It is shown that the generalized Gaussian function provides a good approximation to the distribution of AP chest radiographs. Based on this result and a goodness-of-fit test, a generalized Gaussian autoregressive model (GGAR) is proposed. Its properties and limitations are also discussed. It is expected that the GGAR model will be useful in describing the stochastic characteristics of some classes of medical images and in image data compression and other applications.     

Color quantitation through image processing in dermatology

Classical color models and their applications to computer vision are reviewed. The performances of color quantitation from digitized images are compared with those derived from a chromameter. The color quantitation obtained from either digitized color slides or directly digitized images is proved to be more efficient than the conventional visual assessment of observers. A methodology is proposed for determining the specific color indices which are needed in dermatology. An application of this methodology is developed for designing a blanching quantitation index in order to replace the visual assessment during McKenzie tests.     

Modeling resonator frequency fluctuations induced by adsorbing and desorbing surface molecules

Resonator frequency fluctuations due to adsorption and desorption of molecules on plate electrodes are studied using the principle of mass-loading effects of adsorbed molecules. The study is based on a 525 MHz, AT-cut quartz resonator enclosed in a small crystal holder. Equations relating the surface adsorption rates of the crystal holder to pressure were derived and found to be quadratic polynomial functions of the adsorption rates. Calculations based on these equations show that a contaminant gas with a higher desorption energy creates larger changes in pressure when the temperature is varied. The function describing the frequency fluctuations due to any one contaminant site is a continuous-time Markov chain. Kolmogorov equations and an autocorrelation function for the Markov chain are derived. The autocorrelation and spectral density function of resonator frequency fluctuations are derived. The spectral density of frequency fluctuations at 1 Hz is studied as a function of pressure, temperature, and desorption energy of molecules. The noise levels for a contaminant gas with one type of molecules are found to be lower for lower desorption energies, and higher at lower pressures.