Particle spectra from the ALCOR model

We introduce the Transchemistry Model as a dynamical extension of the Algebraic Coalescence Rehadronization (ALCOR) model in describing the hadronization of quark matter which is expected to be produced in relativistic heavy ion collisions. Results are presented for CERN SPS NA49 Pb+Pb experiment calculating hadron multiplicities and momentum spectra. The freeze-out properties of different hadrons are characterized by similar temperature, density and flow profiles in cylindrically symmetric geometry.     

Kaon interferometry

2-kaon and 2-pion correlation functions for an expanding thermalized source are compared. In the Yano-Koonin-Podgoretskii parametrization of the correlation function, the HBT radius parameters are shown to obeyM _∟-scaling in the absence of collective transverse flow. This scaling is broken by transverse flow. An accurate comparison of pion and kaon correlations can thus resolve issue whether the observedM _∟-dependence of the transverse radius parameter is due to transverse collective flow or other transverse gradients. Effects from resonance decays are shortly discussed.     

Strangelet search and particle production studies in Pb+Pb collisions at 158 AGeV/c at CERN SPS

We searched for long-lived strange quark matter particles, so-calledstrangelets, and studied particle and antiparticle production in Pb+Pb collisions at 158 GeV/c per nucleon at zero degree production angle. We give upper limits for the production of strangelets covering a mass to charge ratio up to 120 GeV/c ² and lifetimest _lab>1.2 μs and plot invariant differential production cross sections as a function of rapidity for a variety of particles.     

Complete theoretical ESR powder spectra by analytical and monte carlo methods

The theoretical ESR spectrum of spins in randomly oriented crystals is built from the distribution function, or powder pattern, of the spins in resonance magnetic field, the anisotropic transition probability and the elementary lineshape of the crystallites. It is shown to be given by the convolution of the product of the powder pattern and the transition probability function — the probability powder pattern — with the elementary lineshape function. Powder patterns in analytical forms, obtained by an isotimic method of integration, are shown to be a very convenient basis for building the theoretical spectra. For the axial field the powder pattern, being always the solution of an algebraic equation, is usually expressed in terms of algebraic irrational functions. Full analytical solutions are then shown to be always possible for Lorentzian elementary lineshapes. Some are derived and compared with full numerical solutions obtained in various fast PC's and supercomputers by a simple Monte Carlo method for synthesizing ESR powder spectra. Sample applications to known physical systems, Cr³⁺: anatase and Mn²⁺: calcite are also shown. An approximate method for first-derivative ESR spectra for the non-axial field is described and used on an orthorhombicg-system, for which an analytically exact powder pattern, recently derived by the isotimic method, is known. The result of its application to a suitable physical system, Cr³⁺: rutile, is also shown.     

Acceleration of femtosecond pulses to superluminal velocities by Gouy phase shift

The phase and the group velocities are calculated in a three-dimensional neighbourhood of the focus of an aberration-free lens illuminated by a spatially Gaussian beam. The Gouy phase shift caused by the diffraction results in superluminal pulse propagation on the optical axis within the Rayleigh range.     

The relaxation of a reconstructed metallic surface and its influence on the EFG acting on a substitutional PAC probe

The structure of the 1×2 reconstructed Au(110) surface, calculated using equivalent crystal theory, is studied. We perform point-charge calculations to estimate the electric field gradient (EFG) acting on a substitutional¹¹¹In probe deposited in that surface. The relaxation breaks the local symmetry producing an asymmetric EFG but the calculated asymmetry is lower than the experimental one. Comparing the computed orientations of the principal axes of the EFG to the experimental values we conclude that In probes prefer to substitute gold into the high coordinated sites at the bottom of the channels.     

Influence of oxygen concentration on optical properties of semi-insulating polycrystalline silicon films

Optical properties of semi-insulating polycrystalline silicon (SIPOS) films were investigated over the wide region of wavelengths. The vibrational modes of Si-O-Si and Si-Si bonds were studied by IR and Raman spectroscopy. A pronounced effect of oxygen content on the measured spectra was observed. Optical constants of SIPOS films have been compared with those of amorphous silicon and glassy silicon dioxide and their values have been successfully interpreted in terms of the theory of effective medium. The results have shown that the amorphous character prevails in the as-deposited SIPOS films.     

Photon down-shifting by energy transfer from Sm3+ to Eu3+ ions in sol-gel SiO2-LaF3 nano-glass-ceramics for photovoltaics

95SiO₂?C5LaF₃ sol-gel derived nano-glass-ceramics single doped with Eu³⁺ or Sm³⁺ and codoped with both of them were successfully obtained. XRD measurements confirm the precipitation of LaF₃ nanocrystals after the ceramming process, with mean size ranging from 10 to 20?nm which increases with the thermal treatment temperature. The incorporation of rare-earth ions into precipitated LaF₃ nanocrystals was confirmed from luminescence spectra. Intense yellow-red emissions were detected under UV and blue light excitation in single and codoped samples. The effect of codoping with Eu³⁺ and Sm³⁺ ions and the energy transfer mechanism between them have been analyzed in order to increase the yellow-red emissions.     

Implementation of an algorithm for detecting patterns in defocused scenes using binary joint transform correlation

An original method to detect images in defocused scenes by means of a binary joint transform correlation is presented. Defocused images are described in frequency domain as the product between the Fourier transform of the in-focus scene by the optical transfer function of the imaging lens. This function, which presents positive and negative values, introduces sign errors in the joint power spectrum. The goal of this study is to detect the sign of the optical transfer function starting from the defocused image by means of a digital algorithm. Information provided by the algorithm allows to compensate the sign errors in the binary joint power spectrum and to obtain invariant correlations with respect to defocusing. Theoretical analysis and digital experiments to test the procedure are provided.