A rotational rheometer with a drag-cup torque transducer

A rotational cone-and-plate rheometer incorporating a drag-cup torque transducer and a frictionless, wire suspension has been designed and constructed. The instrument design provides for a controlled atmosphere for the sample, including anhydrous conditions necessary for studies on solutions of polymers in strong acids. The rheometer can be used to determine the shear deformation in response to an applied stress, including creep, recovery, and the shear stress in response to an applied steady shear. Both transient and steady-state measurements are possible. Illustrative examples of the instrument performance are given.     

Asymptotic scale invariance in two-dimensional theories: A massive Thirring model with bosons

The exact vanishing of all β functions of the Callan-Symanzik equation is proved in a two-dimensional model with Thirring and gradient couplings: $\text{(}\text{ψ}\text{γ}{}_{\mathrm{\mu }}\text{ψ)}{}^2$, $\text{(}\text{ψ}\text{γ}{}^5\text{γ}{}_{\mathrm{\mu }}\text{ψ)?}{}^{\mathrm{\mu }}\text{π}$ and $\text{(}\text{ψ}\text{γ}{}_{\mathrm{\mu }}\text{ψ)?}{}^{\mathrm{\mu }}\text{σ}$, where ψ, π and σ are fermion, pseudoscalar and scalar massive fields, respectively. The anomalous dimensions of scalar and pseudoscalar fields are also shown to be zero. Then we demonstrate that in two-dimensional models including at most one fermion field, only these three couplings can give asymptotic scale invariance.     

Collisionless Landau damping and stimulated compton scattering

Stimulated scattering by free electrons is first studied within a quantum model due to Schroedinger and subsequently within a classical “hydrodynamical” picture. In the latter case, it can be shown that a method initially introduced by Landau to study the damping of electronic vibrations in plasmas is well suited to this problem and provides a precise analysis of the experimental results recently obtained by a Stanford group.     

Microwave spectra of D217O and D218O

Forty lines of the microwave spectra of D₂¹⁷O and D₂¹⁸O have been measured in the region from 8 to 400 GHz and analyzed according to Watson's centrifugal distortion theory. Comparison of the results obtained for D₂¹⁶O, D₂¹⁷O, and D₂¹⁸O demonstrates their internal consistency. The transferability of the parameters according to the isotopic substitution rules is evidence for the validity of the model chosen for the study of the ground state of heavy water.The effective rotational constants deduced from the observed spectra are very close to the values calculated using Oka's second order theory. The values obtained in MHz are:

$\text{A = 456766.9,}\text{B = 218041.0,}\text{C = 144701.5}\text{(D}{}_2{}^{17}\text{O;)}$

$\text{A = 451891.9,}\text{B = 218045.2,}\text{C = 144201.7}\text{(D}{}_2{}^{18}\text{O;).}$

The hyperfine structure of the D₂¹⁷O lines has been analyzed using as a reference the corresponding quadrupole coupling tensor of HD¹⁷O with the appropriate rotation. The values of χ_gg in MHz used for the analysis are:

$\text{x}{}_{\mathrm{\chi \chi }}\text{= - 1.2104,}\text{x}{}_{\mathrm{yy}}\text{= 10.1068,}\text{x}{}_{\mathrm{zz}}\text{= - 8.8964.}$

     

Emissions Optiques Et Electroniques De Solides Intensement Eclaires

In order to analyze the processes involved in the optical and electronic emissions induced on various targets by laser pulses, we have developed pyrometric methods having a time resolution of 10⁻⁸ s. The initial temperature of the target is an important parameter which we control over a wide range. Our measurements suggest that many non-linear emission effects shown by various metals come from a non-metallic superficial layer and that they may not be accounted for by a simple heating effect. On tungsten and platinum, this superficial layer is easily destroyed in vacuum around 1200°C, which brings to the two photons photoelectric yield a decrease of at least three orders of magnitude.     

Anneau associé à une somme directe infinie de modules quasi-injectifs

Sans résumé     

Study of a new rate increasing "base effect" in the palladium-catalyzed amination of aryl iodides

Evidence for an interphase deprotonation of Pd(II)-amine complexes with weak carbonate base has been gained for the first time. When a rate-limiting deprotonation step is involved in the catalytic cycle, controlling the structure (shape and size of the particles) and/or molar excess of the carbonate base used can significantly increase the reaction rate of Buchwald-Hartwig aminations. By taking such a "base effect" into account a general protocol for the intermolecular amination of aryl iodides with all types of amines has been developed based on a standard Pd-BINAP catalyst, using cesium carbonate as the base.