Preconditioning by Projectors in the Solution of Contact Problems: A Parallel Implementation

A non-overlapping domain decomposition algorithm of the Neumann–Neumann type for solving contact problems of elasticity is presented. Using the duality theory of convex programming, the discretized problem turns into a quadratic one with equality and bound constraints. The dual problem is modified by orthogonal projectors to the natural coarse space. The resulting problem is solved by an augmented Lagrangian algorithm. The projectors ensure an optimal convergence rate for the solution of the auxiliary linear problems by the preconditioned conjugate gradient method. Relevant aspects on the numerical linear algebra of these problems are presented, together with an efficient parallel implementation of the method.     

Study of color centers produced in thulium doped YLF crystals irradiated by electron beam and femtosecond laser pulses

In this work, we report the influence of the presence of photochromic and color centers in the photobleaching of thulium ions blue emission in YLF (YLiF₄) crystals doped with 1 mol% Tm (3+). The samples were irradiated at room temperature both with electron beam and high intensity ultrashort pulses from a Ti:Sapphire CPA laser system. In both irradiations the production of photochromic and color centers was observed via the absorption bands in the UV and visible ranges. Pure LiF and pure and oxygen doped YLF crystals were used to identify the color centers produced and their optical properties. From a phenomenological model it was possible to study the interaction between color centers and thulium ions, and their effect in photobleaching and photodarkening behaviors. Finally, the blue up laser level population was computed using a rate equation analysis.     

Charged-particle multiplicity near midrapidity in central Au+Au collisions at sqrt[SNN]=56 and 130 GeV

We present the first measurement of pseudorapidity densities of primary charged particles near midrapidity in Au+Au collisions at sqrt[s(NN)] = 56 and 130 GeV. For the most central collisions, we find the charged-particle pseudorapidity density to be dN/deta|(|eta|<1) = 408+/-12(stat)+/-30(syst) at 56 GeV and 555+/-12(stat)+/-35(syst) at 130 GeV, values that are higher than any previously observed in nuclear collisions. Compared to proton-antiproton collisions, our data show an increase in the pseudorapidity density per participant by more than 40% at the higher energy.     

Experimental dynamic analysis of cracked free-free beams

The use of modal-analysis techniques as nondestructive methods for the detection of cracks in beams is a current field of interest for various researchers. However, an extensive search of the published literature shows that there is very little information on experimental results, thus making it almost impossible for theoretical researchers to use published experimental data to validate their models.The authors, who are currently working in the field of crack detection through modal analysis, performed an extensive experimental dynamic analysis of free-free beams with the objective of validating theoretical techniques, under development, for the prediction of the location and depth of cracks in straight beams. This paper describes the first part of the authors' work. The experimental techniques used are described and results obtained for various locations and depths of cracks in a straight free-free beam are presented.     

Rare earths in UAl2: quenching of spin fluctuations?

Experimental results involving the substitution of U atoms by Gd and Dy in the spin fluctuation system UAl₂ are studied in terms of the theory proposed by Doniach and Wohlfarth. Besides the intraband f-f Coulomb interaction, the model contains the Zener coupling between localized 4f spins and itinerant 5f states. The induced effective f-f interaction increases the proximity to a magnetic instability.     

Mode-locked ytterbium fiber laser tunable in the 980-1070-nm spectral range

Spectral tuning of a mode-locked Yb-doped fiber laser over a 90-nm range is reported. Using semiconductor saturable absorber mirrors in a fiber laser cavity incorporating a grating-pair dispersive delay line, we obtain reliable self-starting mode locking over the whole tuning range. The wide tuning range is achieved by optimization of reflection characteristics and bandgap energy of the multiple-quantum-well semiconductor saturable absorber and by proper engineering of the laser cavity.     

Hydrogen transport process in OH− doped KCl and KBr

It was investigated the kinectics of formation and destruction of hydrogen related defects originated from the randon aggregation of hydrogen atoms in their ground state that were allowed to diffuse through the crystal after the photodissociation of OH^? defects. Formation and activation energies for the several processes involved in three main steps were obtained utilizing 1st. order kinectics. A model for a new U_2x center is proposed.     

Elektrochemische Eigenschaften der halbleitenden TiO2-(Rutil)-Einkristallelektrode

Ohne Zusammenfassung     

Statistical mechanics of composite particles: I. General formulation using a projection technique for the fixed ion plasma model

This paper is concerned with the Statistical Mechanics of an hydrogenic plasma with randomly fixed ions. Starting from the “physical” problem we introduce an “ideal” problem (with an enlarged state space); the latter is defined in such a way that its dynamical evolution leads to the dynamical evolution of the former by means of a projection technique. The interesting features of the “ideal” problem are to be simpler than the “physical” one (usual commutation relations for the “ideal” creation and annihilation operators) and to have a two-particle hamiltonian (instead of an infinite number of particle-operators as in all previous works).