The spherical probe electric field and wave experiment

The experiment is designed to measure the electric field and density fluctuations with sampling rates up to 40,000 samples/sec. The description includes Langmuir sweeps that can be made to determine the electron density and temperature, the study of nonlinear processes that result in acceleration of plasma, and the analysis of large scale phenomena where all four spacecraft are needed

Reconnaissance automatique de fréquences de résonance à partir des données satellitaires de la mission spatiale CLUSTER

Dans cette communication, nous présentons une méthode automatique pour l'identification de la fréquence de résonance d'un plasma spatial. Les données satellitaires sont issues de deux instruments de mesure. Elles se présentent sous la forme d'un spectrogramme bruité et d'un signal. Ce signal permet de procéder automatiquement à un découpage adapté en temps des spectrogrammes et à une analyse en fréquence de chaque bande temporelle. La méthode mise en place exploite la distance de Fréchet comme critère de ressemblance. Une courbe de l'évolution de la fréquence plasma au cours du temps est ensuite reconstruite. Le logiciel développé permet l'étude systématique, dans certaines régions de la magnétosphère terrestre, des spectrogrammes de l'expérience WHISPER de la mission spatiale CLUSTER

Covalent Attachment of Proteins to Solid Supports and Surfaces via Sortase-Mediated Ligation

BACKGROUND: There is growing interest in the attachment of proteins to solid supports for the development of supported catalysts, affinity matrices, and micro devices as well as for the development of planar and bead based protein arrays for multiplexed assays of protein concentration, interactions, and activity. A critical requirement for these applications is the generation of a stable linkage between the solid support and the immobilized, but still functional, protein. METHODOLOGY: Solid supports including crosslinked polymer beads, beaded agarose, and planar glass surfaces, were modified to present an oligoglycine motif to solution. A range of proteins were ligated to the various surfaces using the Sortase A enzyme of S. aureus. Reactions were carried out in aqueous buffer conditions at room temperature for times between one and twelve hours. CONCLUSIONS: The Sortase A transpeptidase of S. aureus provides a general, robust, and gentle approach to the selective covalent immobilization of proteins on three very different solid supports. The proteins remain functional and accessible to solution. Sortase mediated ligation is therefore a straightforward methodology for the preparation of solid supported enzymes and bead based assays, as well as the modification of planar surfaces for microanalytical devices and protein arrays

Diagnostics dans les plasmas de densité et température électroniques faibles par mesure d'impédance mutuelle (sonde quadripolaire) et d'impédance propre (dipôle double sphère)

We have measured, in an isotropic plasma of simulation, the complex mutual impedance of quadrupole probes in square and linear configurations as well as the self impedance of a double sphere dipole probe. Each of these devices leads to one or several determinations of the electronic density and temperature, that we were able to compare.Nous avons mesuré, dans un plasma de simulation isotrope, l'impédance mutuelle complexe de sondes quadripolaires à configuration carrée ou linéaire, ainsi que l'admittance propre d'une sonde formée d'un dipôle double sphère. Chacun de ces systèmes donne accès à une ou plusieurs déterminations de la densité et de la température électronique, que nous avons pu comparer entre elles

The density minimum at the Earth's magnetic equator

Journal of Geophysical Research,Volume 97, pp. 1135-1150Observations of the density structure in the plasmapause region reveal the existence of a local minimum in the total electron density at the magnetic equator

Role of a distal pocket in the catalytic O2 reduction by cytochrome c oxidase models immobilized on interdigitated array electrodes

Five iron porphyrins with different superstructures were immobilized on self-assembled-monolayer (SAM)-coated interdigitated-array (IDAs) gold–platinum electrodes. The selectivity of the catalysts i.e., limited formation of partially reduced oxygen species (PROS) in the electrocatalytic reduction of dioxygen, is a function of 2 rates: (i) the rate of electron transfer from the electrode to the catalyst, which is controlled by the length, and conjugation of the linker from the catalyst to the electrode and (ii) the rate of bound oxygen (superoxide) hydrolysis, which correlates with the presence of a water cluster in the gas-binding pocket influencing the rate of oxygen binding; these factors are controlled by the nature of the porphyrin superstructure. The structurally biomimetic Tris-imidazole model is the most selective

Water may inhibit oxygen binding in hemoprotein models

Three distal imidazole pickets in a cytochrome c oxidase (CcO) model form a pocket hosting a cluster of water molecules. The cluster makes the ferrous heme low spin, and consequently the O2 binding slow. The nature of the rigid proximal imidazole tail favors a high spin/low spin cross-over. The O2 binding rate is enhanced either by removing the water, increasing the hydrophobicity of the gas binding pocket, or inserting a metal ion that coordinates to the 3 distal imidazole pickets