DEPENDENCE OF SOFT PION JET PROPERTIES IN THE SPACE OF RELATIVE FOUR-DIMENSIONAL VELOCITIES ON INITIAL ENERGY

In this paper experimental results obtained by studying of collective and fractal properties of soft pion jets in the space of relative four-dimensional velocities in intermediate energy domain 2–20 GeV are presented. Fractional values of cluster dimension are indicated on manifestation of fractal-like properties by pion jets. The changes of the mean square of the distance between secondary particles and jet axis, the mean kinetic energy of particles in jets and the cluster dimension with increasing of collision energy agree with the hypothesis of manifestation of quark degrees of freedom in processes of pion jet production at intermediate energies. For the first time the quantitative estimations are obtained for the low boundary energy at which quark degrees of freedom start to display itself in production of soft pion jets experimentally. The value of estimation for this parameter derived with taking into account of all used collective parameters is (2.8 ±0.6) GeV .

Fractal behaviour of the seismicity in the Southern Iberian Peninsula

The fractal behaviour of the seismicity in the Southern Iberian Peninsula is analysed by considering two different series of data: the distance and the elapsed time between consecutive seismic events recorded by the seismic network of the Andalusian Institute of Geophysics (AIG). The fractal analyses have been repeated by considering four threshold magnitudes of 2.5, 3.0, 3.5 and 4.0. The re-scaled analysis lets to determine if the seismicity shows strong randomness or if it is characterised by time-persistence and the cluster dimension indicates the degree of time and spatial clustering of the seismicity. Another analysis, based on the reconstruction theorem, permits to evaluate the minimum number of nonlinear equations describing the dynamical mechanism of the seismicity, its "loss of memory", its chaotic character and the instability of a possible predicting algorithm. The results obtained depict some differences depending on distances or elapsed times and the different threshold levels of magnitude also lead to slightly different results. Additionally, only a part of the fractal tools, the re-scaled analysis, have been applied to five seismic crises in the same area.

Electronic and Optical Properties of Silicon Nanocrystals: Structural Effects

The aim of this work is to investigate the structural, electronic and optical properties of hydrogenated Si nanoclusters (H-Si-nc) in their ground and excited state configurations. Structural relaxations have been fully taken into account in all cases through total energy pseudopotential calculations. Recent results about ab-initio calculations of Stokes shift as a function of the cluster dimension and of optical gain will be presented here. A structural model that can be linked to the four level scheme recently invoked to explain the experimental outcomes relative to the observed optical gain in Si-nc embedded in a SiO2 matrix will be suggested too.