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61.
A biased potential molecular dynamics simulation approach, accelerated molecular dynamics (AMD), has been implemented in the framework of ab initio molecular dynamics for the study of chemical reactions. Using two examples, the double proton transfer reaction in formic acid dimer and the hypothetical adiabatic ring opening and subsequent rearrangement reactions in methylenecyclopropane, it is demonstrated that ab initio AMD can be readily employed to efficiently explore the reactive potential energy surface, allowing the prediction of chemical reactions and the identification of metastable states. An adaptive variant of the AMD method is developed, which additionally affords an accurate representation of both the free-energy surface and the mechanism associated with the chemical reaction of interest and can also provide an estimate of the reaction rate. 相似文献
62.
Decio Levi Piergiulio Tempesta 《Journal of Mathematical Analysis and Applications》2011,376(1):247-258
We propose a new approach to the multiple-scale analysis of difference equations, in the context of the finite operator calculus. We derive the transformation formulae that map any given dynamical system, continuous or discrete, into a rescaled discrete system, by generalizing a classical result due to Jordan. Under suitable analytical hypotheses on the function space we consider, the rescaled equations are of finite order. Our results are applied to the study of multiple-scale reductions of dynamical systems, and in particular to the case of a discrete nonlinear harmonic oscillator. 相似文献
63.
D. Brunelli S. T. Levi P. Fragnoli A. Renzulli P. Santi E. Paganelli M. C. Martinelli 《Applied Physics A: Materials Science & Processing》2013,113(4):855-863
An integrated microchemical–petrographic approach is here proposed to discriminate the provenance of archaeological pottery artefacts from distinct production centres. Our study focuses on a statistically significant sampling (n=186) of volcanic temper-bearing potteries representative of the manufacturing and dispersion among the islands of the Aeolian Archipelago during the Bronze Age. The widespread establishment of new settlements and the abundant recovery of Aeolian-made ceramic in southern Italy attest for the increased vitality of the Archipelago during the Capo Graziano culture (Early Bronze Age–Middle Bronze Age 2; 2300–1430 BC). Potteries from three of the main known ancient communities (Lipari, Filicudi and Stromboli) have been studied integrating old collections and newly excavated material. Volcanic tempers have been first investigated through multivariate analyses of relative abundances of mineral and rock clasts along with petrographic characters. In addition, we performed in-situ mineral chemistry microanalyses by Electron Microprobe and Laser Ablation—Inductively Coupled Plasma Mass Spectrometry to assess major and trace element composition of the most common mineral phases. Four Temper Compositional Reference Units have been recognised based on compositional trends. Two units (AI and AX) are unequivocally distinct by their peculiar trace element enrichment and petrographic composition; they mostly contain samples from the sites of Lipari and Stromboli, respectively. Units AIV and AVIII, restricted to the sites of Filicudi and Stromboli, show distinct petrographic characters but overlapped geochemical fingerprints. 相似文献
64.
65.
Quantitative spot tests with a reflectance spectrometer have been developed for chloride (10–320 p.p.m.), sulphate (10–120 p.p.m.), phosphate (2–30 and 10–180 p.p.m.) and nitrite (1–35 and 10–100 p.p.m.). There are few interferences with these tests, and their effects can be overcome by standard techniques except for the interference from phosphate when it is present in the sulphate test, in large concentrations. 相似文献
66.
In this paper we prove that p-spaces and ?ech-complete spaces with Gδ-diagonals can be characterized by a familiar function extension property. 相似文献
67.
A new method for the determination of the compound nucleus coherence width at high excitation energy
N. Alamanos C. Levi C. Le Metayer W. Mittig L. Papineau 《Physics letters. [Part B]》1985,151(2):100-104
The coherence width of the compound nucleus can be obtained from cross correlations of the energy spectra taken at different energies instead of the correlation function of the excitation function. In this way it is sufficient to cover an incident energy interval of the order of the compound nucleus width. We have applied this method to the reaction 12C + 28Si. The coherence width of 40Ca is found in reasonable agreement with previous determinations. Indication is obtained for the presence of a second (smaller) coherence width which could correspond to anomalous long-living compound nucleus states. 相似文献
68.
Crystal growth occurs following widely different modes; in particular the transition from layer-by-layer to continuous growth, and the transition from stable to dendritic growth have attracted much theoretical attention. The former transition (corresponding, for equilibrium surfaces, to the roughening transition) is considered from the point of view of atom-surface scattering used as a tool to probe the state of the surface, and the effects of roughness on the height, width and shape of the incoherent peaks are studied. As an approach to the latter transition, simulations of cluster growth are considered where dendritic shapes are obtained by letting “atoms” fall along random straight trajectories from a “vapour” onto the growing cluster. Two geometries are considered: either the “atoms” fall along the cords from an outer large circle, or they fall obliquely on to a line from points of a parallel line. In both cases ramified structures are obtained, although less open that from diffusion-limited aggregation (DLA), and their fractal nature is studied. 相似文献
69.
The problem of atomic scattering from adsorbate-covered surfaces, treated earlier for the case of commensurate overlayers, is considered again in the eikonal approximation for incommensurate lattice phases and for fluid phases. Stochastic methods are employed and for a specific model (hard bosses on a plane) it is shown how the statistical and geometric problems can be separately solved. In order to explain the meaning of the coherent and incoherent scattering contributions a time-dependent theory is introduced and it is shown that the incoherent “elastic” scattering is in fact weakly inelastic and (for classical diffusion with diffusion coefficient D) has an energy width of the order ?DQ2, where Q is the parallel momentum transfer. The problem of the decay of substrate diffraction intensities when the coverage of random impurities is increased is also discussed. 相似文献
70.
F. W. Levi 《Archiv der Mathematik》1954,5(4-6):476-478
Ohne Zusammenfassung
Alexander Ostrowski zum 60. Geburtstag gewidmet 相似文献