Modeling the Adsorption of CO on Small Pt,Fe and Co Clusters for the Fischer–Tropsch Synthesis

The adsorption of CO on Fe, Pt and Co clusters was modeled by the DFT approach using the B3LYP and the BPW91 functionals together with the LANL2DZ and the 6-31G(d) basis set. These calculations show that although CO adsorbs more strongly on Pt than on either Fe or Co, the dissociation energy on Fe and on Co is lower than the corresponding dissociation energy on Pt. Therefore, the activation energy for dissociation is not determined by the adsorption energy. Additionaly, the CO bond distances also do not show any correlation to the adsorption energy.     

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.     

Multistep Methods for Conservative Problems

We discuss the use of linear multistep methods for the solution of conservative (in particular Hamiltonian) problems. Despite the lack of good results concerning their behaviour, linear multistep methods have been satisfactorily used by researchers in applicative fields. We try to elucidate the requirements that a linear multistep method should fulfill in order to be suitable for the integration of such problems, relating our analysis to their use as boundary value methods. We collect a number of results obtained for the linear autonomous case and also consider some numerical tests on the Kepler problem.Work supported by GNCS and MIUR.     

CR-struttura E geometria riemanniana delle ipersuperficie di ℂ n

For this work we study riemannian geometry of ? ⁿ hypersurfaces with reference to theirCR-structure. In particular we can obtain some properties of those hypersurfaces whose Levi's distribution is integrable.     

Preliminary 1H NMR study on archaeological waterlogged wood

Magnetic Resonance Relaxation (MRR) and Magnetic Resonance Imaging (MRI) are powerful tools to obtain detailed information on the pore space structure that one is unlikely to obtain in other ways. These techniques are particularly suitable for Cultural Heritage materials, because they use water 1H nuclei as a probe. Interaction with water is one of the main causes of deterioration of materials. Porous structure in wood, for example, favours the penetration of water, which can carry polluting substances and promote mould growth. A particular case is waterlogged wood from underwater discoveries and moist sites; in fact, these finds are very fragile because of chemical, physical and biological decay from the long contact with the water. When wood artefacts are brought to the surface and directly dried in air, there is the collapse of the cellular structures, and wood loses its original form and dimensions and cannot be used for study and museum exhibits. In this work we have undertaken the study of some wood finds coming from Ercolano's harbour by MRR and MRI under different conditions, and we have obtained a characterization of pore space in wood and images of the spatial distribution of the confined water in the wood.     

Electronic properties of b.c.c. transition metal solid solutions. a study of the Nr−Nb system

Summary Calculations of electron densities of states and of soft—X-ray absorption spectra in Zr−Nb alloys have been performed in the frame of the coherent potential approximation in its multiple-scattering version (KKR-CAP). It is shown that a lot of care is needed in applying the simple rigid-band model to these systems, in order to explain experimental data. Results are also diseussed in connection with existing experimental data and good agreement is found.

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Riassunto Sono stati eseguiti calcoli di densità di stati elettronici e di spettri di assorbimento di raggi X molli nella lega Zr−Nb a varie concentrazioni, nell'àmbito dell'approssimazione di potenziale coerente nella sua versione di scattering multiplo (KKR-CPA). Si mostra che è necessaria molta attenzione per poter interpretare dati sperimentali come semplice modello a bande rigide. I risultati sono inoltre, discussi in connessione con, i dati sperimentali esistenti con i quali si riscontra un buon accordo.

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Резюме в рамках приближения когерентного потенциала и его модификации для многократного рассеяния проводится вычисление плотностей электронных состояний и спектров поглощения мягких рентгеновских лучей в Zn−Nb сплавах. Показывается, что необходимо проявлять особое внимание при интерпретации экспериментальных данных с помощью простой модели недеформируемых зон. Полученные результаты обсуждаются в связи с имеющимися экспериментальными данными и овнаружено хорошее согласие.

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Work also sponsored by Assessorato Industria della Regione Siciliana.