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.     

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.     

Symmetries in finite order variational sequences

We refer to Krupka's variational sequence, i.e. the quotient of the de Rham sequence on a finite order jet space with respect to a variationally trivial subsequence. Among the morphisms of the variational sequence there are the Euler-Lagrange operator and the Helmholtz operator.In this note we show that the Lie derivative operator passes to the quotient in the variational sequence. Then we define the variational Lie derivative as an operator on the sheaves of the variational sequence. Explicit representations of this operator give us some abstract versions of Noether's theorems, which can be interpreted in terms of conserved currents for Lagrangians and Euler-Lagrange morphisms.     

Energy-Dependent Phenomenological Metrics and Five-Dimensional Einstein Equations

We propose a new Kaluza-Klein-like scheme based on a five-dimensional Riemannian space in which energy plays the role of the fifth dimension and spacetime is deformed. The solutions of the five-dimensional Einstein equations in vacuum allow us to recover, as special cases, the energy-dependent phenomenological metrics, describing the four fundamental interactions, recently derived from the analysis of some experimental data.     

Superimposed normal and superconducting films

Tunneling characteristicsdI/dV have been taken on both sides of “dirty”In - Bi/Zn superimposed films, the temperatureT being such thatIn - Bi was superconducting and Zn normal. Most of the attention has been devoted to the regionT～T _c where the experimental curves can be compared with a reasonably accurate microscopic theory. We find reasonable agreement for the voltage scale and, more important, for theamplitude of the effects in the superconducting phase.     

Sull'equazione integrale non lineare di seconda specie di Fredholm

Nota dedicata aErich Kamke