A positron annihilation study in some amorphous scintillators

Two organic scintillators — NE104 and a liquid solution of 2,5 diphenyloxazole (PPO) — were investigated through positron annihilation spectroscopy to study the influence of the structural order on the magnetic quenching effect on positron bound systems in solids.Preliminary note in [11]     

Synthesis of 4H-pyrans by O-cyclization of 1,5-diketones

Substituted 4H-pyrans were obtained in high preparative yields by the reaction of 1,5-diketones with acetic anhydride and boron trifluoride etherate in diethyl ether. It is assumed that the heterocyclization of 1,5-diketones includes a step involving the formation and transformations of an acyloxy carbonium ion.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 320–322, March, 1992.     

Large-scale computer simulation of fully developed turbulent channel flow with heat transfer

Recently, with the advent of supercomputers, there has been considerable interest in the use of direct numerical simulation to obtain information about turbulent shear flow at low Reynolds number. This paper presents a pseudospectral technique to solve the full three-dimensional time-dependent Navier-Stokes and advection-diffusion equations without the use of subgrid-scale modelling. The technique has not been previously used for fully developed turbulent channel flow simulation and is based on methods applied in other contexts. The emphasis of this paper is to provide a reasonably detailed account of how the simulation is done rather than to present new calculations of turbulence. The details of an algorithm for turbulent channel flow simulation and the grid and time step sizes needed to integrate through transient behaviour to steady state turbulence have not been published before and are presented here. Results from a Cray-2 simulation of fully developed turbulent flow in a channel with heat transfer are presented along with a critical comparison between experiment and computation. The first- and second-order moments agree well with experimental measurements; the agreement is poor for higher-order moments such as the skewness and flatness near the walls of the channel. Detailed information given about the effects of spatial grid resolution on a computed results is important for estimating the size of the computation required to study various aspects of a turbulent flow.     

Acoustic effect of pulsed high-energy proton beams

Experimental data on the generation of acoustic radiation in solid targets by pulsed high-energy proton beams are outlined. The features of ultrasound generation in solids by beams of heavy charged particles are analyzed, and the possibility of using the acoustic effect of heavy charged particles to investigate the interaction between radiation and condensed media and to determine particle energies is shown.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 95–99, August, 1991.     

INCENTIVE COMPATIBLE ENVIRONMENTAL REGULATIONS

This paper addresses the problem of designing environmental regulations when firms possess better information about the cost of pollution abatement than regulators. In the regulatory equilibrium derived in the paper, firms are induced to reveal the information they have concerning abatement costs through the judicious use of abatement standard-subsidy combinations. Offering firms a menu of regulatory contracts, each one specifying a required level of pollution abatement as well as a lump sum subsidy to be paid by the regulatory agency to the firm, is shown to be superior to optimal uniform standard-subsidy schemes. By appealing to the revelation principle and employing a second policy instrument (subsidies), albeit a costly one, in conjunction with an abatement standard, the incentive compatible approach to environmental regulation presented in the paper minimizes the economic inefficiency customarily attributable to a lack of initial information regarding pollution abatement costs.     

Fast switching ferroelectric side-chain liquid-crystalline polymer and copolymer

New ferroelectric side-chain liquid-crystalline polymers, a copolymer and a homopolymer, with siloxane backbone and a triaromatic mesogen as the side group have been synthesized. The materials exhibit a chiral smectic C phase over a large temperature range extending to room temperature. They possess high values of spontaneous polarization: 105 nC cm^-2 for the homopolymer and 180 nC cm^-2 for the copolymer. The electro-optic switching time in the chiral smectic C phase is extremely fast (150 μs). In the smectic A phase, an electroclinic effect with switching times less than 100 μs and with field induced tilt angles of 18° is observed.     

Superconvergence of recovered gradients of discrete time/piecewise linear Galerkin approximations for linear and nonlinear parabolic problems

Superconvergent error estimates in l₂(H¹) and l∞(H¹) norms are derived for recovered gradients of finite difference in time/piecewise linear Galerkin approximations in space for linear and quasinonlinear parabolic problems in two space dimensions. The analysis extends previous results for elliptic problems to the parabolic context, and covers problems in regions with nonsmooth boundaries under certain assumptions on the regularity of the solutions. © 1994 John Wiley & Sons, Inc.