Cosmological models with constant deceleration parameter

Berman presented elsewhere a law of variation for Hubble's parameter that yields constant deceleration parameter models of the universe. By analyzing Einstein, Pryce-Hoyle and Brans-Dicke cosmologies, we derive here the necessary relations in each model, considering a perfect fluid.     

Stresses in multispan triple-layer panels under static transverse flexure with a foam-plastic center layer foam-formed in the cavity of a structure

Results are shown of a study concerning the stresses in multispan panels under transverse flexure, with the center panel made of polyurethane foam plastic. The report contains data which have been obtained by static testing of such panels. The study has revealed that the stress field in the structural members of such panels depends on the mode of testing these panels for transverse flexure.     

Applications of ICP-MS in marine analytical chemistry

Summary The versatility of ICP-MS in marine analytical chemistry is illustrated with applications to the multielement trace analysis of two recently released marine reference materials, the coastal seawater CASS-2 and the non-defatted lobster hepatopancreas tissue LUTS-1, and to the determination of tributyltin and dibutyltin in the harbour sediment reference material PACS-1 by HPLC-ICP-MS. Seawater analyses were performed after separation of the trace elements either by adsorption on immobilized 8-hydroxy-quinoline or by reductive coprecipitation with iron and palladium. Simultaneous determination of seven trace elements in LUTS-1, including mercury, by isotope dilution ICP-MS, was achieved after dissolution by microwave digestion with nitric acid and hydrogen peroxide. Butyltin species in PACS-1 were separated by cation exchange HPLC of an extract of the sediment; method detection limits for tributyltin and dibutyltin in sediment samples are estimated to be 5 ng Sn/g and 12 ng Sn/g, respectively.Summer assistant 1988Summer assistant 1989     

Age of the universe and the density parameter

An exact formula for the age of the universe in terms of the density parameter is found that may be used instead of the approximate one in current use, among other purposes, for the estimate of an upper bound of relic particles in the present universe.     

A class of laplace transforms arising in a diffusion problem

It is shown that the function [α + (1 + 2s)^1/2]^?1, s ≥ 0, with fixed α ≥ ?1, is the Laplace transform of an explicitly given non-negative function g(x;α), × ≥ 0. This class of functions has easily computable convolutions. This property is used to identify the distribution of a sojourn time integral for the diffusion defined as Brownian motion on the real line with constant drift to the origin. © 1994 John Wiley & Sons, Inc.     

Efficient solution approaches for a discrete multi-facility competitive interaction model

In this paper, we present efficient solution approaches for discrete multi-facility competitive interaction model. Applying the concept of “Tangent Line Approximation” presented by the authors in their previous work, we develop efficient computational approaches—both exact and approximate (with controllable error bound α). Computational experiments show that the approximate approach (with small α) performs extremely well solving large scale problems while the exact approach performs very well for small to medium-sized problems.     

Stability of vibrations of finite amplitude in an electron-ion ring

The article discusses transverse vibrations of finite amplitude in an electron-ion ring. Far from the region of linear resonances, an equation is obtained for slowly varying amplitudes, and the conditions are found for the excitation of instability of the negative pressure type. Near the lower boundary of the region of linear instability, the conditions are found under which nonlinearity breaks down the stability of the vibrations with finite amplitudes.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 170–172, May–June, 1974.The author is indebted to B. V. Chirikov for his evaluation of the results of the work.     

Diastereoconvergent synthesis of anti-1,2-amino alcohols with N-containing quaternary stereocenters via selenium-catalyzed intermolecular C–H amination

We report a diastereoconvergent synthesis of anti-1,2-amino alcohols bearing N-containing quaternary stereocenters using an intermolecular direct C–H amination of homoallylic alcohol derivatives catalyzed by a phosphine selenide. Destruction of the allylic stereocenter during the selenium-catalyzed process allows selective formation of a single diastereomer of the product starting from any diastereomeric mixture of the starting homoallylic alcohol derivatives, eliminating the need for the often-challenging diastereoselective preparation of starting materials. Mechanistic studies show that the diastereoselectivity is controlled by a stereoelectronic effect (inside alkoxy effect) on the transition state of the final [2,3]-sigmatropic rearrangement, leading to the observed anti selectivity. The power of this protocol is further demonstrated on an extension to the synthesis of syn-1,4-amino alcohols from allylic alcohol derivatives, constituting a rare example of 1,4-stereoinduction.

We report a diastereoconvergent synthesis of anti-1,2-amino alcohols bearing N-containing quaternary stereocenters using an intermolecular direct C–H amination of homoallylic alcohol derivatives catalyzed by a phosphine selenide.