Structural and electrical characterization of hybrid metal-polypyrrole nanowires

We present here the synthesis and structural characterization of hybrid Au-polypyrrole-Au and Pt- polypyrrole-Au nanowires together with a study of their electrical properties from room-temperature down to very low temperature. A careful characterization of the metal-polymer interfaces by trans- mission electron microscopy revealed that the structure and mechanical strength of bottom and upper interfaces are very different. Variable temperature electrical transport measurements were performed on both multiple nanowires - contained within the polycarbonate template - and single nanowires. Our data show that the three-dimensional Mott variable-range-hopping model provides a complete framework for the understanding of transport in PPy nanowires, including non-linear current-voltage characteristics and magnetotransport at low temperatures.Comment: Phys. Rev. B Vol. 76 Issue 11 (2007

Les protéines de choc thermique (heat shock proteins). I : Classification, structure, fonctions et implications dans les processus pathologiques

All living systems have evolved mechanisms to maintain homeostasis in the face of rapid environmental changes. When exposed to elevated temperatures, most of the cells activate the synthesis of a specific group of proteins called Heat Shock Proteins (Hsps). This heat shock response, under control of specific transcription factors, the Heat Shock factors (HSF), is an evolutionarily conserved mechanism, from bacteria to humans. Heat Shock Proteins are classified into families according to their molecular weight (Hsp 25, 40, 70, 90, 105). They play the role of molecular chaperones by binding and protecting other molecules (proteins, RNAs). The function of Hsp is to prevent accumulation of non-native proteins either by assisting proper folding of polypeptides or by driving them to proteosome pathway for degradation. Hsps are involved in various pathological processes that are accompanied by protein alterations such as chronic or degenerative diseases. This review describes structural and functional characteristics of the six main Hsps classes. It also focuses on their respective role in highly studied pathologies. The diversity of Hsps implications in these diseases explains that they became recently a strategic target in development of new therapeutic strategies.Tout organisme est doté de mécanismes lui permettant de résister à de brusques changements de son environnement. Exposées à une température anormalement élevée, la plupart des cellules activent l’expression d’une classe particulière de protéines appelées les protéines de choc thermique (Heat Shock Proteins, Hsps). Cette réponse cellulaire au choc thermique placée sous le contrôle de facteurs de trans-cription spécifiques, les facteurs de choc thermique (Heat shock factor, HSF) est un mécanisme conservé au travers de l’évolution depuis les bactéries jusqu’à l’homme. Les protéines de choc thermique qui sont divisées en familles désignées par leur masse moléculaire (Hsp25, 40, 70, 90, 105) font partie des molé-cules chaperons qui s’associent à d’autres molécules (protéines, ARNs) et en protègent la destinée. Le rôle des Hsp est d’empêcher l’accumulation de protéines anormales en aidant à conformer correctement les polypeptides ou en les dirigeant vers le protéosome qui les détruit. En tant que chaperons, les Hsp sont impliquées dans de nombreux processus pathologiques qui s’accompagnent d’altérations des protéines comme les maladies chroniques et dégénératives. Cette revue décrit les spécificités structurelles et fonc-tionnelles des six familles principales d'Hsp ainsi que leur intervention à différents niveaux dans les patho-logies les mieux étudiées. La multiplicité de l'implication des Hsp dans ces phénomènes pathologiques les désigne comme cibles privilégiées dans le développement de nouvelles stratégies thérapeutiques

Thermopower of Interacting GaAs Bilayer Hole Systems in the Reentrant Insulating Phase near ν=1\nu=1

We report thermopower measurements of interacting GaAs bilayer hole systems. When the carrier densities in the two layers are equal, these systems exhibit a reentrant insulating phase near the quantum Hall state at total filling factor $\nu=1$. Our data show that as the temperature is decreased, the thermopower diverges in the insulating phase. This behavior indicates the opening of an energy gap at low temperature, consistent with the formation of a pinned Wigner solid. We extract an energy gap and a Wigner solid melting phase diagram.Comment: to be published in Phys. Rev. Let

Long dephasing time and high temperature ballistic transport in an InGaAs open quantum dot

We report on measurements of the magnetoconductance of an open circular InGaAs quantum dot between 1.3K and 204K. We observe two types of magnetoconductance fluctuations: universal conductance fluctuations (UCFs), and 'focusing' fluctuations related to ballistic trajectories between openings. The electron phase coherence time extracted from UCFs amplitude is larger than in GaAs/AlGaAs quantum dots and follows a similar temperature dependence (between T^-1 and T^-2). Below 150K, the characteristic length associated with 'focusing' fluctuations shows a slightly different temperature dependence from that of the conductivity.Comment: 6 pages, 4 figures, proceedings of ICSNN2002, to appear in Physica

The information analysis center concept as developed by the Radiation Shielding Information Center in its computer codes activities

Information analysis center concept and computer codes for calculating radiation transport, and shield design

The far-ultraviolet main auroral emission at Jupiter - Part 1:dawn-dusk brightness asymmetries

The main auroral emission at Jupiter generally appears as a quasi-closed curtain centered around the magnetic pole. This auroral feature, which accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range, is related to corotation enforcement currents in the middle magnetosphere. Early models for these currents assumed axisymmetry, but significant local time variability is obvious on any image of the Jovian aurorae. Here we use far-UV images from the Hubble Space Telescope to further characterize these variations on a statistical basis. We show that the dusk side sector is ~ 3 times brighter than the dawn side in the southern hemisphere and ~ 1.1 brighter in the northern hemisphere, where the magnetic anomaly complicates the interpretation of the measurements. We suggest that such an asymmetry between the dawn and the dusk sectors could be the result of a partial ring current in the nightside magnetosphere

From START to FINISH : the influence of osmotic stress on the cell cycle

Peer reviewedPublisher PD