Structure and dynamics of graphite-supported bimetallic nanoclusters

Molecular dynamics simulations are used to analyze the structure and dynamics of isolated bimetallic nanoclusters of 343 (Cu-Ni) and 1000 atoms (Cu-Ni and Pt-Au) deposited on a graphite substrate. The metal-metal interactions are modeled with the many-body Sutton-Chen potential, and a Lennard-Jones potential is used to describe the metal-carbon interactions. The nanocluster melting temperature is determined from caloric and heat capacity curves, and the atomic distribution is studied layer-by-layer as a function of temperature in a direction perpendicular to the substrate plane. Changes in the nanocluster shape as temperature increases are monitored through deformation parameters that show clear evidence of structural and melting transitions as well as of atomic surface diffusion in the cluster. Dynamic properties such as atomic and whole-cluster diffusion, and the motion of the metal atoms at the interface metal/graphite are characterized as a function of temperature.     

Signal velocity for transient waves in linear dissipative media

The aim of this paper is to discuss the concept of signal velocity for transient sinusoidal waves in linear dissipative media. The method of the steepest descent path, first introduced by Brillouin in this respect, is used to show whether the signal velocity may equal the group velocity or the phase velocity.     

Geometry and stability of BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters

Density functional theory B3PW91/6-31+G* calculations on BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters have been carried out to examine the effect of cluster size, relative composition, binding energy per atom, HOMO-LUMO gap, vertical ionization potential, and electron affinity on their relative stabilities. The most stable planar cyclic conformations of these clusters always show at least a set of two carbon atoms between two beryllium atoms, while structures where beryllium atoms cluster together, or allow the intercalation of one carbon atom between two of them, generally seem to be the least stable ones. Clusters containing 1, 2, and 3 beryllium atoms (Be2C8, Be3C6, Be2C6, BeC6, Be2C4, BeC4, Be2C2, and BeC2) are identified as clusters of "magic numbers" in terms of their high binding energy per atom, high HOMO-LUMO gap, vertical ionization potential, and second difference in energy per beryllium atom.     

Models based on Mittag-Leffler functions for anomalous relaxation in dielectrics

We revisit the Mittag-Leffler functions of a real variable t, with one, two and three order-parameters {α,β,γ}, as far as their Laplace transform pairs and complete monotonicity properties are concerned. These functions, subjected to the requirement to be completely monotone for t > 0, are shown to be suitable models for non–Debye relaxation phenomena in dielectrics including as particular cases the classical models referred to as Cole–Cole, Davidson–Cole and Havriliak–Negami. We show 3D plots of the relaxations functions and of the corresponding spectral distributions, keeping fixed one of the three order-parameters.