Ionic diode

Basic physical processes in an ionic diode with an external magnetic field are considered. Requirements are formulated for the magnetic field, which generates an electron cloud modifying the properties of the cathode surface in the diode. Mechanisms of ion emission from the anode surface are studied, and new experimental data concerning the operation of the diode are analyzed. Requirements for the accelerator, coil feeder, and vacuum system are stated. Basic engineering relationships necessary for the design of the diode are given.     

Improved image contrast with mangafodipir trisodium (MnDPDP) during MR-guided percutaneous cryosurgery of the liver

The present study was undertaken to measure the gain observed in the liver-to-tumor contrast of perioperative images when using mangafodipir trisodium, a liver-specific contrast agent, during percutaneous cryosurgery of the liver performed under the guidance of magnetic resonance images. Retrospective quantitative analyses of MR images were performed on eleven patients having a total of 30 liver tumors treated by MR-guided percutaneous cryosurgery. An initial group of four patients were treated with no contrast agent, and was compared with a second group of 7 patients who received an intravenous injection of 5 microM/kg of mangafodipir for their cryosurgery. The percutaneous cryosurgery was monitored under the near-real-time-imaging mode of a 0.5T open-configuration MRI system using a T(1)-weighted Gradient-recalled echo pulse sequence. A significant improvement in the liver-to-tumor contrast-to-noise ratio was observed with mangafodipir (p < 0.05, paired t test) in 0.5T preoperative images. Along with the stability of the mangafodipir contrast enhancement during the entire cryosurgical procedure, the resulting gain in contrast allowed for better visualizing the presence of residual untreated tumor margins at the periphery of the cryosurgery iceball directly from perioperative images acquired with patients under narcosis. Consequently, it not only became easier for the interventionalist to determine the need for an additional cryoprobe to increase the size of the iceball during the procedure, but also to decide on the appropriate end point of the cryosurgery.     

MIL-103, a 3-D lanthanide-based metal organic framework with large one-dimensional tunnels and a high surface area

A lanthanide-based metal organic framework, formulated Tb(C27H15O6)(H2O).2C6H11OH, has been solvothermally synthesized using the extended rigid tritopic ligand 1,3,5-tribenzoate. Included free solvent could be removed upon heating, and the resulting material presents large 1-D micropores (free diameter = 10 A) and a high surface area (SLangmuir > 1000 m2.g-1).     

Superparamagnetism of magnetite particles in C<Subscript>60</Subscript> fullerite powder

A new magnetic material, C₆₀ fullerite powder doped by magnetite (Fe₃O₄) nanoparticles, is obtained by heating a mixture of fullerite and iron(III) acetylacetonate. It is shown that the material offers superparamagnetic properties. Surface bonding between the nanoparticles and the fullerite is established.     

Décomposition des constantes de couplage nucléaires en éléments de symétrie à l'aide de la théorie des représentations

Sans résumé     

La transition vers l'instabilité pour les ondes de choc multi-dimensionnelles

We consider multi-dimensional shock waves. We study their stability in Hadamard's sense, following Erpenbeck and Majda's strategy. When the unperturbed shock is close to a Lax shock which is already -d unstable, we show, under a generic hypothesis, that it cannot be strongly stable. We also characterize strong instability in terms of a sign of an explicit quadratic form. In most cases, the instability under 1-d perturbations, which occurs for exceptional shock waves, characterizes a transition between weak stability and strong instability in the multi-dimensional setting.

RÉSUMÉ. Nous considérons la stabilité des ondes de choc multi-dimensionnelles, en suivant la stratégie d'Erpenbeck et Majda. Lorsque le choc non perturbé est proche d'un choc de Lax longitudinalement instable, nous montrons, moyennant une hypothèse générique, que des ondes de surface sont présentes, empêchant ainsi la stabilité forte. Nous donnons aussi un critère d'instabilité forte en termes de signe d'une certaine forme quadratique. L'instabilité -d d'un choc est en général facile à établir, car elle revêt un caractère exceptionnel. Elle apparaît comme une transition entre la stabilité faible et l'instabilité dans le contexte multi-d.