Software/parallel processing-Linda on the networks

The use of the coordination language Linda to facilitate the division of software tasks among several processors in parallel programming is considered. Linda's coordination facilities depend on a view of memory as object-oriented, associative, symmetric, and virtually shared, i.e., data are stored as simple data objects, with type signature and other properties, rather than as bits and bytes. To produce a parallel version of a language like C or Fortran, Linda adds just four major operations-in, out, rd, and eval.-to that language. The base language does the chores, such as arithmetic, loop control, I/O, and so on, for which it was designed, while Linda performs only coordination functions: process creation, interprocess communication and control     

Van Hove singularity in Raman scattering spectra of high-T c superconductors

Experimental data are presented which supporting observation of an extended van Hove singularity in Raman spectra of high-T _c superconductors. Excitation of large-momentum electron-hole pairs is proposed as a possible mechanism of the scattering. Fiz. Tverd. Tela (St. Petersburg) 40, 27–31 (January 1998)     

Copolymerizable initiator for improved polymer dispersed liquid crystal films

The problems of photoinitiator contamination are addressed for the liquid crystal phase in polymer dispersed liquid crystal films formed by photopolymerization induced phase separation of liquid crystal from monomer solutions. Initiator contamination lowers the clearing point of the liquid crystal phase, and decreases the photostability and resistivity of the polymer dispersed liquid crystal. These problems are minimized by replacing the conventional photoinitiators with copolymerizable initiators which become incorporated in the polymer phase as it separates. Copolymerizable photoinitiators are studied and used to form polymer dispersed liquid crystals with higher clearing point liquid crystal phases, higher resistivity, and better photostability than polymer dispersed liquid crystals formed with conventional photoinitiators. These improvements provide very significant advantages for many polymer dispersed liquid crystal applications.     

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The study of the neutral pion production in proton-proton collisions at beam momenta 1581 and 1683 MeV/c

The detailed investigation of the reaction has been carried out at two incident proton momenta. Momentum, angular and effective-mass distributions were analyzed in the framework of the one-pion exchange model. Taking into account only the P ₃₃-wave in the pole diagrams allows one to obtain a good agreement with experimental data on differential distributions. At the same time the predictions for total cross-sections are much lower than the experimental data.Received: 15 December 2003, Revised: 23 January 2004, Published online: 10 August 2004PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 13.85.Lg Total cross-sections - 25.40.Ep Inelastic proton scattering     

Two-dimensional t-J model at moderate doping

Using the method which retains the rotation symmetry of spin components in the paramagnetic state and has no preset magnetic ordering, spectral and magnetic properties of the two-dimensional t-J model in the normal state are investigated for the ranges of hole concentrations 0 ⩽ x ⩽ 0.16 and temperatures 0.01t ⩽ T ⩽ 0.2t. The used hopping t and exchange J parameters of the model correspond to hole-doped cuprates. The obtained solutions are homogeneous which indicates that stripes and other types of phase separation are not connected with the strong electron correlations described by the model. A series of nearly equidistant maxima in the hole spectral function calculated for low T and x is connected with hole vibrations in the region of the perturbed short-range antiferromagnetic order. The hole spectrum has a pseudogap in the vicinity of (0,π) and (π, 0). For x ≈ 0.05 the shape of the hole Fermi surface is transformed from four small ellipses around (±π/2,±π/2) to two large rhombuses centered at (0, 0) and (π,π). The calculated temperature and concentration dependencies of the spin correlation length and the magnetic susceptibility are close to those observed in cuprate perovskites. These results offer explanations for the observed scaling of the static uniform susceptibility and for the changes in the spin-lattice relaxation and spin-echo decay rates in terms of the temperature and doping variations in the spin excitation spectrum of the model. Received 14 November 2002 Published online 1st April 2003 RID="a" ID="a"e-mail: alexei@fi.tartu.ee     

The influence of the state of a compressed thermonuclear substance on the combustion of inertial fusion targets under direct ignition by a short radiation pulse

One-dimensional numerical calculations were performed to study the dependence of conditions for initiating thermonuclear combustion and of the target gain of direct-ignition inertial fusion targets ignited by a short radiation pulse on the initial temperature of a preliminarily compressed fuel and the initial heat energy distribution between plasma electrons and ions in the ignition region (igniter). The igniter parameters at which an effective thermonuclear target explosion with a G ～ 10³ target gain occurred were shown to substantially depend on the initial temperature of the major fuel fraction and the initial heat energy distribution between igniter electrons and ions. The heat energy of the igniter passed a minimum as the size of the igniter decreased. The dependences of these minimum energies on the temperature of the major fuel fraction at various initial energy distributions between igniter electrons and ions were determined. An increase in the temperature of the major fuel fraction was shown to decrease the target gain.     

A six-bowl carceplex that entraps seven guest molecules

A six-bowl carceplex that entraps seven guest molecules, 5.(DMSO)7, was synthesized and characterized. The dynamics of the host shell was studied in solution in the absence and presence of water. A multiple-molecule template was found to drive the formation of 5.(DMSO)x.G(7-x) (G = DMA, DMF; x = 5-7). Higher selectivity was found for species containing greater numbers of DMSO molecules.     

Study of the πn → π<Superscript>{-}</Superscript>π<Superscript>{-}</Superscript>p reaction at 430 MeV energy

The total cross-section for the ^{-}n ^{-}{-}p reaction has been measured at a pion kinetic energy of 430MeV in a deuterium bubble chamber. The cross-section value was found to be 0.197±0.016mb that is much smaller than the predictions of the chiral perturbation theory. The differential spectra are compared with calculations made in the framework of the model of Bolokhov et al. 13.60.LeMeson production [:AND:]13.85.LgTotal cross-sections