LEED analysis of a dense lead monolayer on copper (100)

A LEED intensity analysis is reported for the c(5√2 × √2)R45° structure, which is formed by a dense lead monolayer on the (100) surface of copper. Evidence was found that the adsorbate atoms do not arrange pseudo-hexagonally (i.e. without sixfold intra-layer coordination) as expected for a dense two-dimensional package. It was confirmed that the lead atoms still tend to occupy the hollow sites of the (100) surface and arrange in the narrow domains of a strained c(2 × 2) structure. These domains are regularly intersected by dislocation lines, so that adjacent domains are in antiphase position. Within this arrangement the adsorbate atoms are mutually equidistant with closer spacings than in bulk lead. The growth of the monolayer and the epitaxial growth of lead on copper (100) in Stranski-Krastanov mode are correlated to this structure

Growth of epitaxially oriented Ag nanoislands on air-oxidized Si(111)-(7x7) surfaces: Influence of short range order on the substrate

Clean Si(111)-(7{x7) surfaces, followed by air-exposure, have been investigated by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). Fourier transforms (FTs) of STM images show the presence of short range (7x7) order on the air-oxidized surface. Comparison with FTs of STM images from a clean Si(111)-(7x7) surface shows that only the 1/7th order spots are present on the air-oxidized surface. The oxide layer is ~ 2-3 nm thick, as revealed by cross-sectional transmission electron microscopy (XTEM). Growth of Ag islands on these air-oxidized Si(111)-(7x7) surfaces has been investigated by in-situ RHEED and STM and ex-situ XTEM and scanning electron microscopy. Ag deposition at room temperature leads to the growth of randomly oriented Ag islands while preferred orientation evolves when Ag is deposited at higher substrate temperatures. For deposition at 550{\deg}C face centered cubic Ag nanoislands grow with a predominant epitaxial orientation [1 -1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si along with its twin [-1 1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si, as observed for epitaxial growth of Ag on Si(111) surfaces. The twins are thus rotated by a 180{\deg} rotation of the Ag unit cell about the Si [111] axis. It is intriguing that Ag nanoislands follow an epitaxial relationship with the Si(111) substrate in spite of the presence of a 2-3 nm thick oxide layer between Ag and Si. Apparently the short range order on the oxide surface influences the crystallographic orientation of the Ag nanoislands.Comment: 10 figure

Vanadium oxide supported on porous clay heterostructure for the partial oxidation of hydrogen sulphide to sulfur

Vanadium oxide supported on porous clay heterostructures (PCH) catalysts have been synthesized, characterized and evaluated in the selective oxidation of H2S to elemental sulfur. The catalysts were characterized by XRD, adsorption-desorption of N-2 at -196 degrees C, diffuse reflectance UV-vis, H-2-TPR, Raman spectroscopy and XPS. The catalysts with higher vanadium content are more active and selective, exhibiting a H2S conversion close to 70% after 360h on stream with a high selectivity toward elemental sulfur and a low formation of undesired SO2. The catalysts with V2O5 crystallites have shown a higher activity and resistance to the deactivation. The analysis of the spent catalyst has revealed the formation of V4O9 crystals during the catalytic test, which has been reported as the active phase in the selective oxidation of the H2S. (C) 2015 Elsevier B.V. All rights reserved.The authors would like to thank the DGICYT in Spain (Projects CTQ2012-37925-C03-01, CTQ2012-37925-C03-03 and FEDER funds, and MAT2010-19837-C06-05) and project of Excellence of Junta de Andalucia (project P12-RNM-1565) for financial support. A. Natoli thanks to SECAT (Spain) for a grant.Soriano Rodríguez, MD.; Cecilia, JA.; Natoli, A.; Jimenez-Jimenez, J.; López Nieto, JM.; Rodriguez Castellon, E. (2015). Vanadium oxide supported on porous clay heterostructure for the partial oxidation of hydrogen sulphide to sulfur. Catalysis Today. 254:36-42. https://doi.org/10.1016/j.cattod.2014.12.022S364225

Highly Regio- and Stereoselective Diels-Alder Cycloadditions via Two-Step and Multicomponent Reactions Promoted by Infrared Irradiation under Solvent-Free Conditions

Infrared irradiation promoted the Diels-Alder cycloadditions of exo-2-oxazolidinone dienes 1–3 with the Knoevenagel adducts 4–6, as dienophiles, leading to the synthesis of new 3,5-diphenyltetrahydrobenzo[d]oxazol-2-one derivatives (7, 9, 11 and 13–17), under solvent-free conditions. These cycloadditions were performed with good regio- and stereoselectivity, favoring the para-endo cycloadducts. We also evaluated the one-pot three-component reaction of active methylene compounds 20, benzaldehydes 21 and exo-2-oxazolidinone diene 2 under the same reaction conditions. A cascade Knoevenagel condensation/Diels-Alder cycloaddition reaction was observed, resulting in the final adducts 13–16 in similar yields. These procedures are environmentally benign, because no solvent and no catalyst were employed in these processes. The regioselectivity of these reactions was rationalized by Frontier Molecular Orbital (FMO) calculations

Les transformations du private equity

Changes in private equity Private equity funds have amassed real power in recent years. They have maintained the same objective of maximising the return on their investments, but are now adopting more sophisticated strategies and are having an increasing structuring effect on a number of industry sectors. Today’s financial crisis, which has made financing more expensive and harder to come by, will probably have only a temporary impact on the development of these funds. That said, the pressure they are facing is growing in pace with their impact on the stock markets and on the industry. Many have called for stepping up controls and transparency requirements on these unregulated entities. JEL Classification : G11, G23, G24Les fonds de private equity ont acquis au cours des dernières années une puissance considérable. Ils ont gardé le même objectif, maximiser le taux de rendement de leurs investissements, mais ils emploient désormais des stratégies plus sophistiquées et ont de plus en plus un effet structurant sur de nombreux secteurs industriels. La crise financière actuelle, qui raréfie l’endettement et renchérit son coût, n’aura probablement qu’un effet temporaire sur leur développement. Cependant, la pression sur ces acteurs croît en même temps que leur impact sur les Bourses et l’industrie. Des voix s’élèvent pour renforcer le contrôle et la transparence de ces entités non réglementées. Classification JEL : G11, G23, G24Argile Alain. Les transformations du private equity . In: Revue d'économie financière, n°93, 2008. Les fonds de private equity pp. 13-18

Using X11 Windows To Provide Shared Task Memory in Distributed Computer Systems

An X11 based shared memory system, permitting the implementation of a distributed water network monitoring and control software suite, is described in this paper. The application source code is in FORTRAN and accesses shared memory via a C library module requiring no other support packages. X11 based distributed mutual exclusion algorithms, based on the unconventional use of Lamport's bakery algorithm, are evaluated. The system is compared with other methods of providing distributed shared memory

Morphologie de cristallites de palladium sur support d'alumine Morphology of Palladium Crystallites Supported on Alumina

Nous avons étudié, par microscopie électronique à transmission, la structure tridimensionnelle des particules métalliques de catalyseurs Pd/Al2O3. Un modèle de cuboctaèdre tronqué est proposé pour des particules de taille de l'ordre de 30 nm. Pour des particules de taille inférieure (~ 5 nm) l'observation des profils et des orientations cristallographiques vis-à-vis du support sont compatibles avec un modèle cuboctaédrique. <br> Transmission electron microscopy has been used to study the three dimensional structure of metal particles in Pd/Al2O3 catalysts. A model in the form of a truncated cuboctahedron is proposed for particles of size about 30 nm. For smaller (~ 5 nm) particles observations of profiles and crystallographic orientations with respect to the support are compatible with a cuboctahedron model