Decomposition de l'acide peroxydodecanoique dans CCl4 : role du solvant

The decomposition of peroxydodecanoic and in refluxing CCl₄ proceeds by a complex process involving ionic and radical reactions. In the latter, this study has confirmed the important role, shown previously,¹ of the character(nucleophilic or electrophilic) of the radical on the regioselectivity of the attack on the peracid.     

Remarks on finiteW algebras

The property of some finiteW algebras to be the commutant of a particular subalgebra of a simple Lie algebraG is used to construct realizations ofG. WhenGso(4, 2), unitary representations of the conformal and Poincaré algebras are recognized in this approach, which can be compared to the usual induced representation technics. WhenGsp(2,R) orsp(4,R), the anyonic parameter can be seen as the eigenvalue of aW generator in suchW representations ofG.Presented by P. Sorba at the 5th International Colloquium on Quantum Groups: Quantum Groups and Integrable Systems, Prague, 20–22 June 1996.P. Sorba would like to express his warm thanks to Professor estmír Burdík for the perfect organisation of the conference.     

Etude des reactions de substitution homolytique sur le noyau pyridinique; influence de l'acidite du milieu

Homolytic substitution by the l-n-undecyl radical at positions 2 and 4 of the pyridine nucleus results from thermal decomposition of dodecanoyl peroxide in acetic acid. Rate dependence on pH shows that pyridine protonation increases the rate of addition of the alkyl radical to the pyridine ring but decreases the rate of the reaction of the intermediate radical with the peroxide. Results are interpreted in terms of orbital interaction theory.     

Hidden colour and the isobar content of the deuteron

We show how experiments concerning the isobar content of the deuteron that apparently are contradicitng each other can be reconciled by the quark model with hidden colour.     

Generalization of the $$\mathcal{U} $$ q (gl(N)) Algebra and Staggered Models

We develop a technique for the construction of integrable models with a ₂ grading of both the auxiliary (chain) and quantum (time) spaces. These models have a staggered disposition of the anisotropy parameter. The corresponding Yang–Baxter equations are written down and their solution for the gl(N) case is found. We analyze in details the N = 2 case and find the corresponding quantum group behind this solution. It can be regarded as the quantum group , with a matrix deformation parameter q such that (q )² = q ². The symmetry behind these models can also be interpreted as the tensor product of the (–1)-Weyl algebra by an extension of _q (gl(N)) with a Cartan generator related to deformation parameter –1.     

Direct measurements of fractional quantum Hall effect gaps

We measure the chemical potential jump across the fractional gap in the low-temperature limit in the two-dimensional electron system of GaAs/AlGaAs single heterojunctions. In the fully spin-polarized regime, the gap for filling factor nu=1/3 increases linearly with the magnetic field and is coincident with that for nu=2/3, reflecting the electron-hole symmetry in the spin-split Landau level. In low magnetic fields, at the ground-state spin transition for nu=2/3, a correlated behavior of the nu=1/3 and nu=2/3 gaps is observed.     

Chemistry and formation process of Ga(Al)As oxide during local anodic oxidation nanolithography

We present our investigation on the early stage of the photon induced desorption of oxide nanostructures grown on GaAs/AlAs/GaAs heterostructures. The oxide structures were fabricated by local anodic oxidation performed by means of an atomic force microscope. We observed that after a first rapid evolution in which a thick layer of heterogeneous material is removed, the oxide composition remains almost constant. These results support our model in which the oxidation process on a layered material resembles a melting process and produces a mixed material whose composition is the average of the initial one.