The structural evolution and dynamics of silver nanodrops Ag_2869 (4.4 nm in diameter) under rapid cooling conditions have been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modelled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the pair analysis technique are used to reveal the structural transition in the process of solidification. It is shown that Ag nanoparticles evolve into different nanostructures under different cooling processes. At a cooling rate of 1.5625 × 10(13) K s−1 the nanoparticles preserve an amorphous-like structure containing a large amount of 1551 and 1541 pairs which correspond to icosahedral symmetry. For a lower cooling rate (1.5625 × 1012 K s−1 ), the nanoparticles transform into a crystal-like struc...

The application of the iterative method of phase retrieval to series of images obtained at different defocus values is described and discussed. It is shown that the iterative scheme is robust in the presence of discontinuities in the phase. The application of these methods to a set of experimental images taken using X-ray imaging is investigated. A computer program which can reproduce the simulations and analyse experimental image data is briefly discussed.

El método de Dinámica Molecular fue aplicado al estudio de la nucleación y crecimiento de los clusters de Ag a partir de la fase gaseosa. Mediante el uso del potencial de interacción Tight-Binding SMA se estudia las propiedades energéticas y la cinética de formación de las partículas a diferentes densidades y temperaturas del sistema. Se estudia además la estructura y mecanismos de crecimiento de las nanopartículas de Ag durante el proceso de enfriamiento ultrarápido del gas. Se ha observado que la tasa de formación y tamaño promedio de las nanopartículas depende principalmente de la densidad del gas y en menor medida de la temperatura. La estructura de las nanopartículas de Ag luego del enfriamiento es más amorfa en la parte central e indicios de cristalinidad en las partes superficiales.

The kinetic energy distribution as a function of mass of final fragments (m) from low energy fission of U-234, measured with the Lohengrin spectrometer by Belhafaf et al., presents a peak around m = 109 and another around m = 122. The authors attribute the first peak to the evaporation of a large number of neutrons around the corresponding mass number; and the second peak to the distribution of the primary fragment kinetic energy. Nevertheless, the theoretical calculations related to primary distribution made by Faust et al. do not result in a peak around m = 122. In order to clarify this apparent controversy, we have made a numerical experiment in which the masses and the kinetic energy of final fragments are calculated, assuming an initial distribution of the kinetic energy without peaks on the standard deviation as function of fragment mass. As a result we obtain a pronounced peak...

The average of fragment kinetic energy () and the multiplicity of prompt neutrons (v) as a function of fragment mass (m*), as well as the fragment mass yield (Y (m*)) from thermal neutron induced fission of Pu-239, have been measured by Tsuchiya et al. In that work the mass and kinetic energy are calculated from the measured kinetic energy of one fragment and the diference of time of flight of the two complementary fragments. However they do not present their results about the standard deviation σE* (m*). In this work we have made a numerical simulation of that experiment, assuming an initial distribution of the primary fragment kinetic energy (E(A)) with a constant value of the standard deviation as function of fragment mass (σE (A)). As a result of that simulation we obtain the dependence σE* (m*) which presents an enhancement between m* = 92 and m* = 110, and a peak at m* = 1...