Towards SiC surface functionalization: an ab initio study

We present a microscopic model of the interaction and adsorption mechanism of simple organic molecules on SiC surfaces as obtained from ab initio molecular-dynamics simulations. Our results open the way to functionalization of silicon carbide, a leading candidate material for biocompatible devices.     

Concise total synthesis of (+/-)-aloperine and 6-epi-aloperine

[reaction: see text] Total synthesis of aloperine and 6-epi-aloperine is reported. The crucial steps of the synthetic strategy are an aza-annulation reaction and an intermolecular Diels-Alder reaction. The synthetic plan proceeds from commercially available piperidine-2-ethanol.     

-semigroups generated by second order differential operators with general Wentzell boundary conditions

Let us consider the operator where is positive and continuous in and is equipped with the so-called generalized Wentzell boundary condition which is of the form at each boundary point, where This class of boundary conditions strictly includes Dirichlet, Neumann and Robin conditions.

Under suitable assumptions on , we prove that generates a positive -semigroup on and, hence, many previous (linear or nonlinear) results are extended substantially.

     

Electron spin-echo envelope modulation at S-band. 2: Hyperfine and weak nuclear quadrupole interaction effects forI>1/2

The analysis of the nuclear modulation often observed in the electron spin-echo signals gives information on the structural arrangement around the paramagnetic center and on the interactions undergone by the spin system. Most applications to date have been carried out at X-band (≈9 GHz). However, to run experiments at different operating frequencies yields more accurate results and increases the number of experimental situations that can be investigated. Here we analyze the two- and three-pulse modulation patterns simulated at S-band (≈3 GHz) where the modulation is due to two different nuclei of experimental interest at different electron-nucleus distances, and comparison is done with the corresponding X-band patterns.²H (I=1) and⁷Li (I=3/2) nuclei are chosen due to their low quadrupole moment, so that comparison can be done between the effects due to weak nuclear quadrupole interaction at the two bands. It is shown that at short distances the complicated patterns due to hyperfine couplings are successfully interpreted by Fourier transform in the frequency domain, and that the use of S-band is really of some advantage with respect to X-band in detecting the presence of a weak nuclear quadrupole interaction.     

Local flat duality of abelian varieties

 Let K be a field complete for a discrete valuation and with algebraically closed residue field of positive characteristic p. We prove the existence of a non-degenerate pairing between the first (flat) cohomology group of an abelian variety A _K over K and the fundamental group of the Néron model of the dual abelian variety. This pairing extends to the p-primary components a pairing introduced by Shafarevich in [16]. We relate this pairing with Grothendieck's pairing. Received: 7 January 2002 / Revised version: 6 December 2002 Published online: 24 April 2003 Mathematics Subject Classification (2000): 14k05, 14F20, 14G22     

Photocatalytic oxidation of methyl-orange in aqueous suspension: comparison of the performance of different polycrystalline titanium dioxide

The photocatalytic oxidation of methyl-orange (C14H14N3SO3Na) dye was carried out in aqueous suspensions of polycrystalline TiO2 irradiated with artificial light until its complete mineralization was achieved. The performances of two widely used semiconductor powders were studied for comparison purposes. The dependence of dye photo-oxidation rate on various experimental parameters, including substrate concentration, semiconductor amount, and pH was investigated by using both catalysts. The observed dye degradation rates followed pseudo-first order kinetics with respect to the substrate concentration under the experimental conditions used. The two investigated TiO2 powders (Degussa P25 and Merck) showed different photoactivities. TOC analyses confirmed the complete mineralization achievable using both photocatalysts. Three main transient products still maintaining the chromophoric azo group were identified prior to their transformation into other degradation products which are non-absorbing in the visible region.     

Stabilizzabilita' di equazioni paraboliche

L'argomento di questo seminario è il problema della stabilizzabilità di equazioni paraboliche lineari del secondo ordine, con coefficienti costanti o periodici rispetto al tempo. Viene considerato sia il caso di controlli a parametri distribuiti che il caso di controlli sulla frontiera. The subject of this talk is the problem of stabilization of linear second order parabolic equations, with constant or periodic coefficients with respect to time. Both distributed parameter controls and boundary controls are considered.

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(Conferenza tenuta il 20 gennaio 1989)