La relance du chêne-liège dans le Plan national de reboisement en Algérie -

En Algérie, la superficie forestière n'a cessé de régresser et, plus particulièrement, durant les deux dernières décennies. Aux causes multiples déjà connues, se sont rajoutés le terrorisme et les problèmes que risquent de poser les changements climatiques dont les effets ne sont pas encore bien cernés. Devant cette situation, les pouvoirs publics ont lancé un Plan national de reboisement (PNR), dont les réalisations à mi-parcours ne couvrent même pas la moitié de ce qui devrait être réalisé. Dans le même temps, les incendies ont brûlé plus que ce qui a été planté. S'agissant du chêne-liège, les techniques en usage sont loin de contribuer à la reconstitution de la subéraie. Sur la base des observations de terrain et l'analyse critique de ce qui s'est fait jusque-là, nous suggérons une nouvelle approche devant mener à une amélioration des résultat

Atomic motions in the αβ\alpha\beta-region of glass-forming polymers: Molecular versus Mode Coupling Theory approach

We present fully atomistic Molecular Dynamics simulation results on a main-chain polymer, 1,4-Polybutadiene, in the merging region of the $\alpha$- and $beta$-relaxations. A real space analysis reveals the occurrence of localized motions (``$\beta$-like'') in addition to the diffusive structural relaxation. A molecular approach provides a direct connection between the local conformational changes reflected in the atomic motions and the secondary relaxations in this polymer. Such local processes occur just in the time window where the $\beta$-process of the Mode Coupling Theory is expected. We show that the application of this theory is still possible, and yields an unusually large value of the exponent parameter. This result might originate from the competition between two mechanisms for dynamic arrest: intermolecular packing and intramolecular barriers for local conformational changes (``$\beta$-like'').Comment: 10 pages, 6 figure

Real-time Spectroscopic Ellipsometry Study of Ultrathin Diffusion Barriers for Integrated Circuits

The objective of this work is to monitor the growth process and the thermal stability of ultrathin tantalum nitride barrier nanostructures against copper diffusion in integrated circuits using real-time spectroscopic ellipsometry (RTSE). Single layers of copper and bilayer films of copper and tantalum nitride were produced on Si(111) substrates using unbalanced magnetron sputtering. The RTSE data was simulated using the Bruggeman effective medium approximation and a combined Drude-Lorentz model to obtain information about the growth process, film architecture, interface quality, and the conduction electron transport properties for these structures. The results deduced from the RTSE were verified by characterizing the structural and the chemical properties of the fabricated films using x-ray diffraction, Auger electron spectroscopy, and Rutherford backscattering. The effectiveness of the tantalum nitride barrier to stop the diffusion of copper into silicon was evaluated, monitoring their optical properties when annealed at 720 degreesC. The dielectric function of the films changed from a metallic to an insulating character when the diffusion proceeded. Also, the RTSE provided valuable information about the microstructure and the kinetics of the phase transformations that occur during heat treatment. (C) 2004 American Institute of Physics

Structural Relaxation and Mode Coupling in a Simple Liquid: Depolarized Light Scattering in Benzene

We have measured depolarized light scattering in liquid benzene over the whole accessible temperature range and over four decades in frequency. Between 40 and 180 GHz we find a susceptibility peak due to structural relaxation. This peak shows stretching and time-temperature scaling as known from $\alpha$ relaxation in glass-forming materials. A simple mode-coupling model provides consistent fits of the entire data set. We conclude that structural relaxation in simple liquids and $\alpha$ relaxation in glass-forming materials are physically the same. A deeper understanding of simple liquids is reached by applying concepts that were originally developed in the context of glass-transition research.Comment: submitted to New J. Phy

Bimodal Effect on Pancreatic β-Cells of Secretory Products From Normal or Insulin-Resistant Human Skeletal Muscle

OBJECTIVE: Type 2 diabetes is characterized by insulin resistance with a relative deficiency in insulin secretion. This study explored the potential communication between insulin-resistant human skeletal muscle and primary (human and rat) beta-cells. RESEARCH DESIGN AND METHODS: Human skeletal muscle cells were cultured for up to 24 h with tumor necrosis factor (TNF)-alpha to induce insulin resistance, and mRNA expression for cytokines was analyzed and compared with controls (without TNF-alpha). Conditioned media were collected and candidate cytokines were measured by antibody array. Human and rat primary beta-cells were used to explore the impact of exposure to conditioned media for 24 h on apoptosis, proliferation, short-term insulin secretion, and key signaling protein phosphorylation and expression. RESULTS: Human myotubes express and release a different panel of myokines depending on their insulin sensitivity, with each panel exerting differential effects on beta-cells. Conditioned medium from control myotubes increased proliferation and glucose-stimulated insulin secretion (GSIS) from primary beta-cells, whereas conditioned medium from TNF-alpha-treated insulin-resistant myotubes (TMs) exerted detrimental effects that were either independent (increased apoptosis and decreased proliferation) or dependent on the presence of TNF-alpha in TM (blunted GSIS). Knockdown of beta-cell mitogen-activated protein 4 kinase 4 prevented these effects. Glucagon-like peptide 1 protected beta-cells against decreased proliferation and apoptosis evoked by TMs, while interleukin-1 receptor antagonist only prevented the latter. CONCLUSIONS: Taken together, these data suggest a possible new route of communication between skeletal muscle and beta-cells that is modulated by insulin resistance and could contribute to normal beta-cell functional mass in healthy subjects, as well as the decrease seen in type 2 diabetes