Intramolecular dehydrohalogenation during base-mediated reaction of diols with dihaloalkanes

Sodium alkoxides of a variety of diols were reacted with dibromoalkanes. It was found that the products of the reaction were alkenyl ethers resulting from intramolecular dehydrohalogenation of the initially formed monobromo ethers.     

A possible model for fifth force

Recent reanalysis of the data of the Eötvös experiment suggested the existence of a new force. We show that a negative energy massive scalar field minimally coupled to gravity in a background Schwarzschild metric naturally leads to a potential which can explain the small anomalous effect in the Eötvös experiment.     

Microwave-assisted Suzuki coupling on a KF-alumina surface: synthesis of polyaryls

A range of conjugated polyaryls has been synthesized through one-pot microwave assisted palladium-catalyzed consecutive Suzuki coupling reactions on a KF-alumina surface with notable features including rapid reaction times, solvent-free conditions, high yields, atom economic and air-insensitive reactions.     

Off-diagonal long-range order and currents in weakly coupled superconductors

Within the framework of quasi equilibrium approximation, Josephson’s expression for current in a weakly coupled superconducting system is derived without the use of any specific microscopic model. It is based only on the existence of the off-diagonal long-range order in the two-particle reduced density matrix. Allowing for deviations from the quasi equilibrium approximation, generalised Josephson equations are obtained which include ohmic terms. The effect of relaxation and thermal fluctuations is examined in detail to emphasise the physical origin of various terms in the expression for current.     

Single and double ionization of lead by electron impact

Theoretical calculations of electron impact single and double ionization cross-sections for ground state lead atoms have been performed in the binary encounter approximation (BEA) in the energy region ranging from respective near thresholds to 3000 eV. The accurate expression for (cross-section for energy transfer including exchange and interference as given by Vriens and Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. It is concluded that beyond 10.64 eV impact energy single ionization cross-sections are well explained by considering ionization of 6p and 6s shells only. The direct double ionization cross-sections obtained theoretically cannot explain the recent experimental observations. Inclusion of contributions of the Auger effect due to vacancy in 5d and 5p shells brings the results of double ionization cross-sections in reasonably good agreement with the experimental data. The identification of the shells whose ionization leads to the Auger effect contributing to double ionization is a remarkable aspect of the present investigation.Received: 15 January 2004, Published online: 30 March 2004PACS: 34.80.Dp Atomic excitation and ionization by electron impact     

A simple and readily integratable approach to toxicity prediction

A simple, highly extensible computational strategy to assess compound toxicity has been developed with the premise that a compound's toxicity can be gauged from the toxicities of structurally similar compounds. Using a reference set of 13645 compounds with reported acute toxicity endpoint dose data (oral, rat-LD(50) data normalized in mg/kg), a generic utility which assigns a compound the average toxicity of structurally similar compounds is shown to correlate well with reported values. In a leave-one-out simulation using the requirement that at least one structurally similar member in a "voting consortium" is present within a reference set, the strategy demonstrates a predictive correlation (q wedge 2) of 0.82 with 57.3% of the compounds being predicted. Similar leave-one-out simulations on a set of 1781 drugs demonstrate a q wedge 2 of 0.74 with 51.8% of the compounds being predicted. Simulations to optimize similarity cutoff definitions, consortium member size, and reference set size illustrate that a significant improvement in the quality and quantity of predictions can be obtained by increasing the reference set size. Similar application of the strategy to subchronic and chronic toxicity data should be possible given reasonably sized reference sets.     

Natural convection in vertical concentric annuli under a radial magnetic field

Exact solutions for fully developed natural convection in open-ended vertical concentric annuli under a radial magnetic field are presented. Expressions for velocity field, temperature field, mass flow rate and skin-friction are given, under more general thermal boundary conditions. It is observed that both velocity as well as temperature of the fluid is more in case of isothermal condition compared with constant heat flux case when gap between cylinders is less or equal to radius of inner cylinder while reverse phenomena occur when the gap between cylinders is greater than radius of inner cylinder.     

A Single-period Stochastic Inventory Model Under the Influence of Marketing Policies

A single-period stochastic inventory model is developed under different marketing policies using the concepts of fixed prices and fixed mark-up of prices where discounts are offered on bulk purchases. In the mathematical model shortages are allowed, and it is assumed that any unit unsold at the end of the period has no economic value. The model yields simple solutions for some particular demand distributions. It is illustrated with a suitable example.