Computational models for proton transfer in biological systems

A computational scheme based on a “mixed basis set” approach is applied to the study of the structure and the energetics in proton transfer systems. Five hydrogen-bonded systems of the type (CH₃H_nA ‥ H ‥ BH_mCH₃)⁺, where A and B can be N, O, or S, have been investigated with various minimal and extended basis sets. Calculations with the extended basis set yield double-well potential energy curves, which the minimal basis set is unable to reproduce. Calculations with the mixed basis set, constructed from an extended basis set on the atoms engaged in the hydrogen transfer part and a minimal basis set on the rest of the molecule, give predictions of geometries, potential energy curves, and relative energies similar to the results from the extended basis set. Inclusion of polarization functions in the mixed basis set becomes essential in systems that contain third row atoms. This scheme should become useful in studies of large molecules in which different parts can be represented at different levels of computational complexity.     

Linear programming based meta-heuristics for the weighted maximal planar graph

The weighted maximal planar graph (WMPG) is practically important in the laying out of facilities in modern manufacturing environments. Given a weighted complete graph, the WMPG seeks to find a sub-graph such that it is planar—it can be embedded on the plane without any arcs intersecting, and it is maximal—no additional arc can be added to the sub-graph without destroying its planarity, and it also has the maximal sum of arc weights. In this paper, an integer linear programming (ILP) model is newly introduced for the problem. Two meta-heuristics are then derived from the ILP relaxation. The first meta-heuristic considers all variables with fractional values greater than half in the ILP relaxation to build an initial sub-graph from which a planar sub-graph is extracted using greedy random adaptive search procedure (GRASP) and augmented by triangulation of faces. The second meta-heuristic considers only arcs with integer values in the ILP relaxation. The remaining arcs are then sorted in descending order of their weights, for selection and insertion with a planarity testing procedure, to obtain a feasible solution using GRASP. Computational results are reported on a set of 100 test instances of size varying from 20 to 100 facilities. The computational results demonstrate the tightness of the new upper bound when compared to the classical one as well as the good performance of the proposed metaheuristics when compared to the best-known procedures in the literature in terms of solution quality and computational requirement. Finally, the paper presents a successful integration of GRASP with classical optimisation approaches and should be attempted for other optimisation problems.     

Broad Nematic Phases with High Clearing Points

Unbranched 4-(4′-alkylbenzoyloxy)-, 4-(4′-methylanlinobenzoyloxy)- and 4-(4′dime thylaminobenzoyloxy)benzylidene-4″-cyanoanmlines were synthesized. They show broad nematic phases with high nematic isotropic transitions. Lateral Clsubstituents decrease the clearing points of these liquid crystals by about 80°. The intermediate 4-(4′-alkylbenzoyloxy)benzaldehydes are monotropic nematic.     

Photoredox laser chemistry of transition metal oxides

Received: 26 May 1997/Accepted: 17 July 1997     

Eriochrome black A as reagent for spectrophotometric microdetermination of cobalt in presence of nickel

Summary Eriochrome black A has been found to be a suitable reagent for the spectrophotometric determination of microgram quantities of cobalt in pure cobalt solutions and in the presence of nickel and some other cations by measuring the decrease in the absorbance of Eriochrome black A at p_H 10, caused by the presence of cobalt.Many foreign cations especially nickel were completely masked by EDTA. Amounts as low as about 0.9 to 3 g were determined with fair accuracy.     

Validation,verification, and testing techniques throughout the life cycle of a simulation study

Life cycle validation, verification, and testing (VV&T) is extremely important for the success of a simulation study. This paper surveys current software VV&T techniques and current simulation model VV&T techniques and describes how they can all be applied throughout the life cycle of a simulation study. The processes and credibility assessment stages of the life cycle are described and the applicability of the VV&T techniques for each stage is stated. A glossary is provided to explicitly define important terms and VV&T techniques.     

The deformation and orientation effect on reaction cross section with deformed targets

The reaction cross section (σ_R) for a deformed target nucleus and spherical projectile is calculated using the optical-limit approximation of the Glauber-Sitenko theory. A method is presented to include both the density-dependent NN interaction and the higher order deformations of the target nucleus in the collision process. We studied both the orientation and the deformation dependence of σ_R within the energy range 30–900 MeV/A. We found that the orientation of the heavy target nucleus (A ≥ 120) can produce a difference in the calculated σ_R up to 30%. The averaged σ_R over all directions of the symmetry axis of the deformed nucleus differs by less than 1% compared with σ_R calculated for a spherical target with the same rms matter radius as the deformed nucleus. For certain orientation, it was found that σ_R is highly dependent on the hexadecapole deformation. The orientation-averaged cross sections show almost no variation with either the sign or the value of the hexadecapole deformation. We compared the average cross section with the experimental data for several mass numbers; fair agreement is obtained.     

A primal-dual conjugate subgradient algorithm for specially structured linear and convex programming problems

This paper presents a primal-dual conjugate subgradient algorithm for solving convex programming problems. The motivation, however, is to employ it for solving specially structured or decomposable linear programming problems. The algorithm coordinates a primal penalty function and a Lagrangian dual function, in order to generate a (geometrically) convergent sequence of primal and dual iterates. Several refinements are discussed to improve the performance of the algorithm. These are tested on some network problems, with side constraints and variables, faced by the Freight Equipment Management Program of the Association of American Railroads, and suggestions are made for implementation.This research was supported by the Association of American Railroads.     

Stable Liquid Crystals with Large Negative Dielectric Anisotropy. Part IV

Stable liquid crystals with negative dielectric anisotropy containing the bicyclo [2.2.2]octyl group were synthesized. The incorporation of this moiety in the molecules increased the thermodynamic stability of the mesophase and lowered the smectic tendency. These new compounds can be useful in liquid crystal mixtures for homeotropic nematic displays.