Reductive Umpolung of Carbonyl Derivatives with Visible‐Light Photoredox Catalysis: Direct Access to Vicinal Diamines and Amino Alcohols via α‐Amino Radicals and Ketyl Radicals

Visible‐light‐mediated photoredox‐catalyzed aldimine–aniline and aldehyde–aniline couplings have been realized. The reductive single electron transfer (SET) umpolung of various carbonyl derivatives enabled the generation of intermediary ketyl and α‐amino radical anions, which were utilized for the synthesis of unsymmetrically substituted 1,2‐diamines and amino alcohols.     

Synthesis of Strained γ‐Lactams by Palladium(0)‐Catalyzed C(sp3)−H Alkenylation and Application to Alkaloid Synthesis

A variety of strained α‐alkylidene‐γ‐lactams were synthesized by palladium(0)‐catalyzed intramolecular C(sp³)?H alkenylation from easily accessible acyclic and monocyclic bromoalkene precursors. These lactams are valuable intermediates for accessing various classes of mono‐ and bicylic alkaloids containing a pyrrolidine ring, as illustrated with the synthesis of an advanced model of the marine natural product plakoridine A and of the indolizidine alkaloid δ‐coniceine.     

Analytic calculation of the stresses in an ensiled granular mediumCalcul analytique des contraintes dans un matériau granulaire ensilé

We present in this Note a new analytic approach, of continuous medium type, which improves the Janssen theory and enables us to calculate the stresses in an ensiled granular medium. This approach is based on the two dimensional equilibrium equations, coupled with the Mohr–Coulomb criterion and a slip condition at the walls of the silo. An analytic resolution is developed to compute the stresses for cohesive and non cohesive materials in the whole silo. To cite this article: O. Millet et al., C. R. Mecanique 334 (2006).     

Ionization of barium through a coherent excitation of two bound intermediate states

We have investigated theoretically the asymmetrical photoionization yields into the 6s _1/2, 5d _3/2 and 5d _5/2 continuum channels of atomic barium observed by Wang, Chen and Elliott [Phys. Rev. Lett. 77, 2416 (1996)] in the study of coherent control through two-color resonant interfering paths. The atomic parameters obtained from a theoretical approach based on a combination of jj-coupled eigenchannel R-matrix and Multichannel Quantum Defect Theory are used to analyze the photoionization spectra from the and 6s7p states with polarized light beams. The studied energy range includes the 6p7p autoionizing resonances. The dynamics of the two-color photoionization is governed by the coherent excitation of the 6s6p and intermediate states. This excitation is described as an adiabatic process in the rotating wave approximation. The influence of the radiative decay, spatial distribution of the intensities of the laser beams and hyperfine interaction is discussed. Received 28 September 1999     

Mössbauer Spectroscopic Study of Iron Containing Hydrotalcite Catalysts for the Reduction of Aromatic Nitro Compounds

Carbonated layered double magnesium hydroxides containing Fe with hydrotalcite structure which are active and selective catalysts for the reduction of aromatic nitro compounds by hydrazine hydrate have been prepared and characterized by X-ray diffraction and Mössbauer spectroscopy. Using these techniques we have shown that when the Fe/(Fe + Mg) ratio was greater than 0.2, which corresponds to the natural phase composition, ferrihydrite Fe₅HO₈?4H₂O was formed. This last phase, characterized at room temperature by a superparamagnetic doublet, leads after activation under nitrogen at 723 K to small particles of ferric oxide. An in-situ study of the activated catalysts allowed us to show that only iron cations present in this phase could undergo an oxido-reduction under the conditions of catalysis and that the catalytic properties must be related to this last phase.     

连续波锁模P_r~（3＋）：YLF激光器

本文报导了采用氩离子激光器来泵浦Ｒｒ￣（３＋）：ＹＬＦ晶体，应用声光调制器实现了主动锁模；同时应用振动─高反射平面镜也实现了被动锁模，两种锁模均得到了ｐｓ光脉冲。据作者了解这是这种晶体材料的第一次锁模运转。     

An Eulerian approach of non-linear membrane shell theory

The purpose of this article is to develop an asymptotic Eulerian approach in plate and shell theory valid for large displacements. With this Eulerian approach, the dead load assumption generally used with Lagrangian approaches can be dropped. We also obtain a membrane model which takes into account following forces, whose direction can vary during large displacements.     

Pneumatochemical impedance spectroscopy. 2. Dynamics of hydrogen sorption by metals

In this paper, pneumatochemical impedance spectroscopy is used to analyze multistep reaction mechanisms such as those observed in solid solution domains of LaNi5-H2(g) systems. It is shown that hydrogen sorption is a two-step mechanism including (i) dissociative surface chemisorption of molecular hydrogen and (ii) atomic hydrogen bulk transport by diffusion. Data fitting of experimental transfer functions with model equations yields the value of the kinetic parameter associated with each individual reaction step, i.e., surface sorption resistances and hydrogen bulk diffusion coefficients. The technique is used to follow the activation procedure of the sample as well as the degradation of sorption properties in oxygen-containing hydrogen atmospheres. A decrease in sorption kinetics is attributed to surface oxidation, whereas bulk properties remain unchanged. The perspectives offered by the technique which potentially can be used to optimize surface and bulk composition of IMC for increased sorption rates are discussed.