Conformational effects on circular dichroism in the photoelectron angular distribution.

The B-spline density-functional method has been applied to the conformers of the (1R, 2R)-1,2-dibromo-1,2-dichloro-1,2-difluoroethane molecule. The cross section, asymmetry, and dichroic parameters relative to core and valence orbitals, which do not change their nature along the conformational curve, have been systematically studied. While the cross section and the asymmetry parameter are weakly affected, the dichroic parameter appears to be rather sensitive to the particular conformer of the molecule, suggesting that this dynamical property could be a useful tool for conformational analysis. The computational method has also been applied to methyl rotation in methyloxirane. Unexpected and dramatic sensitivity of the dichroic-parameter profile to the methyl rotation, both in the core and valence states, has been found. Boltzmann averaging over the conformers reproduces quite closely the profiles previously obtained for the minimum-energy conformation, which is in good agreement with the experimental results.     

Regioselective reductive demethoxylation of 3,4,5-trimethoxystilbenes

Selective removal of the 4-methoxy group of 3,4,5-trimethoxystilbenes was performed under electron transfer conditions from Na metal in THF. Careful control of reaction conditions and quenching procedure allowed the synthesis of either (E)-3,5-dimethoxystilbenes or 3,5-dimethoxybibenzyls.     

Quasidiagonal Solutions of the Yang–Baxter Equation, Quantum Groups and Quantum Super Groups

This paper answers a few questions about algebraic aspects of bialgebras, associated with the family of solutions of the quantum Yang–Baxter equation in Acta Appl. Math. 41 (1995), pp. 57–98. We describe the relations of the bialgebras associated with these solutions and the standard deformations of GL_n and of the supergroup GL(m|n). We also show how the existence of zero divisors in some of these algebras are related to the combinatorics of their related matrix, providing a necessary and sufficient condition for the bialgebras to be a domain. We consider their Poincaré series, and we provide a Hopf algebra structure to quotients of these bialgebras in an explicit way. We discuss the problems involved with the lift of the Hopf algebra structure, working only by localization.     

Il problema di Cauchy-Dirichlet per una classe di sistemi parabolici a coefficienti misurabili

Riassunto Si dimostrano teoremi di esistenza, di unicità e di regolarizzazione per la soluzione del problema di Cauchy-Dirichlet per una classe di sistemi parabolici a coefficienti misurabili.

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Summary We show that the Cauchy-Dirichlet problem for a class of parabolic systems with measurable coefficients admits a unique solution. We show, also, regularity's properties for the solution.

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Lavoro eseguito nell'ambito del gruppo G.N.A.F.A. del C.N.R.     

Bilateral evolution problems of non-variational type: Existence,uniqueness, Hölder-regularity and approximation of solutions

We study bilateral problems for a second order parabolic operator with principal part not of divergence form. We prove existence, uniqueness, Holder-continuity and approximation results for both strong and generalized solutions.     

Glass transition temperatures of some linear polymers containing phenyl side groups

The glass transition temperatures of a number of poly(vinyl phenyl ketones), poly-(vinyl benzoates), and poly(phenyl acrylates) have been measured by a refractometric method. The effects exerted on T_g by the nature and position of the ring substituents and by the different groups binding the pendant phenyl rings to the polyvinyl chain are discussed. The importance of knowledge of the side-group motions in the glassy state for the interpretation of glass temperature data is emphasized.     

When is a Cleft Extension H-Azumaya?

We show which H ^op -cleft extensions of k for a dual quasi-triangular Hopf algebra (H, r) are H-Azumaya. The result is given in terms of bijectivity of a map defined in terms of the universal r-form r and the 2-cocycle σ, generalizing a well-known result for the commutative and co-commutative case. We illustrate the Theorem with an explicit computation for the Hopf algebras of type E(n).Presented by A. Verschoren     

Turing vegetation patterns in a generalized hyperbolic Klausmeier model

The formation of Turing vegetation patterns in flat arid environments is investigated in the framework of a generalized version of the hyperbolic Klausmeier model. The extensions here considered involve, on the one hand, the strength of the rate at which rainfall water enters into the soil and, on the other hand, the functional dependence of the inertial times on vegetation biomass and soil water. The study aims at elucidating how the inclusion of these generalized quantities affects the onset of bifurcation of supercritical Turing patterns as well as the transient dynamics observed from an uniformly vegetated state towards a patterned state. To achieve these goals, linear and multiple-scales weakly nonlinear stability analysis are addressed, this latter being inspected in both large and small spatial domains. Analytical results are then corroborated by numerical simulations, which also serve to describe more deeply the spatio-temporal evolution of the emerging patterns as well as to characterize the different timescales involved in vegetation dynamics.