Unexpected Formation of 10-Iodo- and 10-Chlorocamphor under Halosulfonylation Conditions, and Convenient Routes to 10-Chloro- and 10-Bromocamphor

The generation of camphor-10-sulfonyl iodide in situ under halosulfonylation conditions or exposure of camphor-10-sulfonyl chloride to copper(II) chloride under Asscher–Vofsi conditions leads unexpectedly to the formation of 10-iodocamphor or 10-chlorocamphor, respectively. Additionally, convenient syntheses of 10-bromocamphor and 10-chlorocamphor have been achieved by extension of a previously reported methodology

The euro at ten - lessons and challenges, 5th ECB Central Banking Conference, 13-14 November 2008

This volume contains a collection of papers, commentaries and speeches concerning the first decade of the euro and the recent global financial crisis.financial integration, optimal currency area

Magnetoresistance in Disordered Graphene: The Role of Pseudospin and Dimensionality Effects Unraveled

We report a theoretical low-field magnetotransport study unveiling the effect of pseudospin in realistic models of weakly disordered graphene-based materials. Using an efficient Kubo computational method, and simulating the effect of charges trapped in the oxide, different magnetoconductance fingerprints are numerically obtained in system sizes as large as 0.3 micronmeter squared, containing tens of millions of carbon atoms. In two-dimensional graphene, a strong valley mixing is found to irreparably yield a positive magnetoconductance (weak localization), whereas crossovers from positive to a negative magnetoconductance (weak antilocalization) are obtained by reducing disorder strength down to the ballistic limit. In sharp contrast, graphene nanoribbons with lateral size as large as 10nm show no sign of weak antilocalization, even for very small disorder strength. Our results rationalize the emergence of a complex phase diagram of magnetoconductance fingerprints, shedding some new light on the microscopical origin of pseudospin effects.Comment: 8 pages, 5 figure

Why does wurtzite form in nanowires of III-V zinc-blende semiconductors?

We develop a nucleation-based model to explain the formation of the wurtzite (WZ) crystalline phase during the vapor-liquid-solid growth of free-standing nanowires of zinc-blende (ZB) semiconductors. We first show that, in nanowires, nucleation generally occurs at the outer edge of the solid/liquid interface (the triple phase line) rather than elsewhere at the solid/liquid interface. In the present case, this entails major differences between ZB and WZ nuclei. Depending on the pertinent interface energies, WZ nucleation is favored at high liquid supersaturation. This explains our systematic observation of ZB during the early stages of nanowire growth.Comment: 4 pages with 4 figures Submitted to Physical Review Letter

Les espaces de l'halieutique

Les crevettes pénéides (essentiellement #Penaeus indicus$) sont capturées à Madagascar par trois grands types de pêcheries : industrielle, artisanale et traditionelle. La pêche traditionnelle exploite la frange la plus côtière avec des moyens restreints. Cette appellation recouvre un certain nombre de formes d'exploitation qui, au premier abord, n'ont souvent en commun que la ressource. Les systèmes d'exploitation que l'on rencontre tout au long du littoral peuvent se caractériser dans une première analyse par les engins de pêche utilisé (valakira, filets maillants, sennes à crevettes, kopiko) qui se répartissent de manière fractionnée. Cette répartition définit ainsi une structuration spatiale forte des zones d'exploitations et un découpage du littoral en entités homogènes. Dans chaque zone, l'impact des différentes formes d'exploitation sur la ressource montre des résultats totalement différents au niveau des rendements, des variations saisonnières et des quantités débarquées. Deux grands axes se profilent dont l'un met en opposition côte est et ouest et l'autre les régions nord et sud révélant des potentialités de pêche très inégales. Emboîtés dans ces gradients généraux se dessinent des espaces localisés d'exploitation liés aux conditions environnementales (présence de mangrove, baies, estuaires) et dépendants de la distribution du réseau hydrographique. Cette dissociation doit être nuancée en fonction des caractéristiques propres à chaque baie : nature du fond conditionnant la mise en oeuvre des engins, caractéristiques marines ou continentales du milieu. En définitive, cette division en plusieurs biotopes où des systèmes d'exploitations différents se sont développés renvoie à la disponibilité de la ressource, mais également à une adaptation des pêcheurs à des conditions particulières. (Résumé d'auteur

Companding technique for high dynamic range measurements using gafchromic films

We propose a methodology to perform dose measurements using gafchromic films which can span several decades of dose levels. The technique is based on a rescaling approach using different films irradiated at different dose levels. This is combined with a registration protocol correcting positioning and scaling factors for each film.Comment: Preprint submitted to Medical Physics, 10 pages, 4 figures, 1 tabl

Buried dislocation networks designed to organize the growth of III-V semiconductor nanostructures

We first report a detailed transmission electron microscopy study of dislocation networks (DNs) formed at shallowly buried interfaces obtained by bonding two GaAs crystals between which we establish in a controlled manner a twist and a tilt around a k110l direction. For large enough twists, the DN consists of a twodimensional network of screw dislocations accommodating mainly the twist and of a one-dimensional network of mixed dislocations accommodating mainly the tilt. We show that in addition the mixed dislocations accommodate part of the twist and we observe and explain slight unexpected disorientations of the screw dislocations with respect to the k110l directions. By performing a quantitative analysis of the whole DN, we propose a coherent interpretation of these observations which also provides data inaccessible by direct experiments. When the twist is small enough, one screw subnetwork vanishes. The surface strain field induced by such DNs has been used to pilot the lateral ordering of GaAs and InGaAs nanostructures during metal-organic vapor phase epitaxy. We prove that the dimensions and orientations of the nanostructures are correlated with those of the cells of the underlying DN and explain how the interface dislocation structure governs the formation of the nanostructures