Electron kinetic effects on Raman backscatter in plasmas

We augment the usual three-wave cold-fluid equations governing Raman backscatter (RBS) with a new kinetic thermal correction, proportional to an average of particle kinetic energy weighted by the ponderomotive phase. From closed-form analysis within a homogeneous kinetic three-wave model and ponderomotively averaged kinetic simulations in a more realistic pulsed case, the magnitude of these new contributions is shown to be a measure of the dynamical detuning between the pump laser, seed laser, and Langmuir wave. Saturation of RBS is analyzed, and the role of trapped particles illuminated. Simple estimates show that a small fraction of trapped particles (approximately 6%) can significantly suppress backscatter. We discuss the best operating regime of the Raman plasma amplifier to reduce these deleterious kinetic effects.     

Inhomogeneous level splitting in Pr 2-x BixRu2O7

We report that Bi doping drives Pr 2-x BixRu2O7 from an antiferromagnetic insulator (x = 0) to a metallic paramagnet (x approximately 1) with a broad low T maximum in C/T. Neutron scattering reveals local low energy spin excitations (variant Planck's omega approximately 1 meV) with a spectrum that is unaffected by heating to k(B)T > variant Planck's omega. We show that a continuous distribution of splittings of the non-Kramers Pr3+ ground-state doublet such as might result from various types of lattice strain can account for all the data.     

Étude dans le système mercure solution acide des courbes I = f(E) relatives au dépôt et à la redissolution de traces de: Cu,Tl, Cd,Zn, Ni,Co, Fe

It is possible to redissolve in acid solution traces of Cu, Tl and Zu previously deposited on mercury without oxidising the mercury; the concentrations considered arcofthc order of 100y per ml of amalgam. Under the same conditions the redissolution of traces of Fe, Ni and Co can not be carried out without oxidation of the mercury.The constiuction in 1N H₂SO₄ medium of the curves I = f(E) for the Cu, Cd and Tl ions, the current I being negligible compared with the diffusion current, shows that. a. the variations in log I as a function of the potential E of the mercury or amalgam electrode are linear. b. the position of the curve log I — log a = f(E) is independent of the activity a of the element in solution or amalgam.Our experiments also show: 1° it is necessary to introduce a température coefficient for the coefficient relative to the overpotential of hydrogen on the mercury. 2° for cadmium, at weak current densities, a single electron is put into play in the case of deposition and in that of redissolving.     

Dosage gravimétrique rapide du béryllium dans les béryls

After attacking the beryl by fusing the powdered mineral with sodium peroxide and eliminating silica, beryllium is precipitated directly in the filtrate by mono-ammonium phosphate in the presence of complexon II or ethylene diamino-tetraacetic acid.Complexon II forms complexes and retains in the solution the other metals contained in beryl, but permits the quantitative precipitation of ammonium phosphate and beryllium which is calcined at 1000° and weighed out as beryllium pyrophosphate, Be2P2O7.     

Cinétique d'électrolyse de traces métalliques avec dégagement simultané d'hydrogène

The authors have determined, for analytical purposes, the influence of a certain number of factors affecting the kinetics of deposition of metallic traces on a platinum or mercury cathode when there is a simultaneous discharge of a large amount of hydrogen ions.The phenomenon of exaltation of the migration current of an ion in the presence of the simultaneous discharge of another chemical species allows an explanation of the parts played by the different factors considered.     

Local smoothing effects for the water-wave problem with surface tension

The water-wave problem with a one-dimensional free surface of infinite depth is considered, based on the formulation as a second-order nonlinear dispersive equation. The local smoothing effects are established under the influence of surface tension, stating that on average in time solutions acquire locally 1/4 derivative of smoothness as compared to the initial state. The analysis combines energy methods with techniques of Fourier integral operators. To cite this article: H. Christianson et al., C. R. Acad. Sci. Paris, Ser. I 347 (2009).