Dissociation of water molecule at three-fold oxygen coordinated V site on the InVO4 (0 0 1) surface

Water molecule adsorption properties at the surface of InVO₄ have been investigated using an ab initio molecular dynamics approach. It was found that the water molecules were adsorbed dissociatively to the three-fold oxygen coordinated V sites on the (0 0 1) surface. The dissociative adsorption energy was estimated to be 0.8-0.9 eV per molecule. The equilibrium distance between V and O of the hydroxyl -OH was almost the same as the V-O distance of tetrahedra VO₄ in the InVO₄ bulk crystal (1.7-1.8 Å).     

Inversion of configuration of alcohols through nucleophilic displacement promoted by nitrate ions.

Inversion of configuration of hydroxy functionalities in biologically significant structures has been performed under mild conditions through nucleophilic displacement by nitrate ion.     

57Fe Mössbauer studies of oxisols

Mössbauer spectroscopy is a valuable complement to the standard analytical techniques of soil science for characterizing the iron content of soils, and for studying the mineralogical transformations that occur during pedogenesis from the point of view of the iron. The uses and limitations of Mössbauer spectroscopy in this field are illustrated by five selected examples. In each case, the starting point is a different question relating to the soil colour, mineralogy, magnetization or mode of formation.     

An efficient chemo-enzymatic approach to (+)-meroquinene

Meroquinene (+)-1 was prepared in an efficient and stereocontrolled fashion from (1R-2S)-4-cyclohexene dimethanol monoacetate (−)-8. Key steps are the enzyme-catalyzed hydrolysis of the available diacetate 5 to (−)-8 and of the intermediate diester 17 to hemiester 18, which allow the stereo- and regiocontrolled elaboration of the vicinal vinyl and carboxymethyl groups.     

Forza agente su una sfera in un fluido viscoso con memoria

Riassunto Si affronta il problema del moto di un corpo di forma sferica in un fluido viscoso incomprimibile, infinitamente esteso, con memoria non evanescente. Si assume che il fluido ed il corpo siano in quiete fino ad un istante fissato e che, successivamente, il corpo sia soggetto ad un moto traslatorio. In tali condizioni si determina il moto del fluido originato dal moto del corpo e l’azione del fluido sul corpo stesso.

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Summary The problem of the motion of a sphere in a viscous incompressible fluid of unlimited extent is examined, under the assumption that the memory of the fluid does not fade in time. The fluid and the sphere are assumed to be at rest up to a fixed time; subsequently the sphere is allowed to move without rotation. The motion of the fluid caused by the motion of the sphere and the action of the fluid on the sphere are determined.

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Lavoro eseguito nell’ambito del G.N.F.M. del Consiglio Nazionale delle Ricerche.     

Concave cost minimization on networks

The paper deals with the problem of finding a minimum cost multicommodity flow on an uncapacitated network with concave link costs. Problems of this type are the optimal design of a network in the presence of scale economies and the telpack problem.Two different definitions of local optimality are given and compared both from the point of view of the computational complexity and from the point of view of the goodness of the solution they may provide.A vertex following algorithm to find a local optimum is proposed. The computational complexity of each iteration of the algorithm is O(n³), where n is the number of nodes of the network, and is independent of the differentiability of the objective function.Experimental results obtained from a set of test problems of size ranging from 11 nodes and 23 arcs to 48 nodes and 174 arcs, with number of commodities up to 5, are given.     

New stereoselective beta-glycosylation via a vinyl oxirane derived from D-glucal

[reaction: see text] The reaction of the vinyl oxirane 1 derived from D-glucal with a series of O-nucleophiles (alcohols, phenol, and diacetone D-glucose) affords the corresponding 2-unsaturated beta-O-glycosides in a completely stereoselective way (syn 1,4-addition pathway). Epoxide 1 is generated in situ by treatment of the corresponding hydroxy mesylate 2 with t-BuOK in anhydrous benzene.