Reactivite d'hydrocarbures methylenecyclo-hexaniques—I : Stereochimie de la reaction d'oxymercuration-demercuration

Methylenecyclohexanes, prepared in excellent yield by Corey and Chaykovsky then Cornforth reactions, give on oxymercuration followed by reductive demercuration tertiary alcohols resulting from axial attack by solvent. The attack takes place trans to the substiuent when the latter is at the 2 position. α-Hydroxy or methoxy compounds behave similarly to each other. For acetoxy compounds, the cis alcohols are obtained preferentially, by intramolecular attack of acetoxy group on the mercurinium ion intermediate. The results can be explained satisfactorily on the assumption that the factors inducing stereochemistry are short distance interactions.     

Multiplicity studies and effective energy in ALICE at the LHC

In this work we explore the possibility to perform “effective energy” studies in very high energy collisions at the CERN large hadron collider (LHC). In particular, we focus on the possibility to measure in pp collisions the average charged multiplicity as a function of the effective energy with the ALICE experiment, using its capability to measure the energy of the leading baryons with the zero degree calorimeters. Analyses of this kind have been done at lower centre-of-mass energies and have shown that, once the appropriate kinematic variables are chosen, particle production is characterized by universal properties: no matter the nature of the interacting particles, the final states have identical features. Assuming that this universality picture can be extended to ion–ion collisions, as suggested by recent results from RHIC experiments, a novel approach based on the scaling hypothesis for limiting fragmentation has been used to derive the expected charged event multiplicity in AA interactions at LHC. This leads to scenarios where the multiplicity is significantly lower compared to most of the predictions from the models currently used to describe high energy AA collisions. A mean charged multiplicity of about 1000–2000 per rapidity unit (at η∼0) is expected for the most central Pb–Pb collisions at . In memory of A. Smirnitskiy     

Coding of shape from shading in area V4 of the macaque monkey

Background  

The shading of an object provides an important cue for recognition, especially for determining its 3D shape. However, neuronal mechanisms that allow the recovery of 3D shape from shading are poorly understood. The aim of our study was to determine the neuronal basis of 3D shape from shading coding in area V4 of the awake macaque monkey.     

Superconductors in parallel field: Electromagnetic properties at the surface

Summary In the framework of the boson transformation method, a general approach to the study of finite-dimensionality superconductors is applied to the investigation of the electromagnetic properties of a semiinfinite superconductor and of a film of arbitrary thickness in the presence of a parallel external magnetic field. The magnetic-field and current density distributions near the surfaces are computed and numerical results are given for some typical cases. As an application, an estimation of the superheating field for type-II superconductor is obtained and compared with previous results.

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Riassunto Nell'àmbito del metodo della trasformazione bosonica, una tecnica generale per lo studio di superconduttori a dimensione finita è applicata allo studio delle proprietà elettromagnetiche di un superconduttore semi-infinito e di un film di spessore arbitrario. Sono calcolate le distribuzioni del campo magnetico e della densità di corrente, e sono riportati risultati numerici per qualche caso tipico. Infine, si ottiene, e si confronta con precedenti risultati, una stima del campo di surriscaldamento per superconduttori del II tipo.

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Резюме В рамках метода бозонного преобразования общий подход для исследования конечно-мерных сверхпроводников применяется к изучению электромагнитных свойств полубесконечного сверхпроводника и пленки произвольной толщины в присутствии параллельного внешнего магнитного поля. Вычисляются распределения магнитного поля и плотности тока вблизи поверхностей. Приводятся численные результаты для некоторых типичных случаев. Оценивается поле супернагревания для сверхпроводника второго рода. Оценка сравнивается с имеющимися результатами.

     

Proton-proton correlations at small relative momentum in neon-nucleus collisions at E/A=400 and 800 MeV

Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed.