Environmental effects on hydrogen bonded systems: A quantum chemical study of proton relay model systems

In this paper an application of a reaction field theory of solvent effects has been made to study proton transfer mechanisms in hydrogen bonded systems coupled to an environment. The latter is simulated with reaction fields having variable strength and direction (defined with respect to the supermolecule's total dipole moment direction), together with superposed uniform external electric fields. Changes in proton potential curves and some other properties of a model water dimer and a water trimer are reported. The results are discussed in relation to relevant phenomena in biology and biochemistry, namely proton relay systems in enzymatic catalysis.     

Kinetics Approximation Considering Different Reactivities of the Structural Units Formed by the Anionic Copolymerization of 1,3‐Butadiene and Styrene Using Al/Li/Ba as Initiator

The copolymerization reaction of butadiene and styrene copolymers prepared by anionic living polymerization using an initiator composed of alkyl aluminum, n‐butyl lithium, and barium alkoxide is studied using a kinetic model that considers the reactivity of active sites to be different; this assumption is justified by the varying geometric configurations. With the first‐order Markov model, the expressions for the fraction of active sites and dyad distribution are obtained. The rate constants are determined by fitting to the conversion and Bernoulli dyad data using the nonlinear least squares method. The conversion and dyad sequence distribution are correctly predicted, and the experimental results indicate that the microstructure and sequence distribution do not change with the conversion and temperature.

     

CVD diamond films: from growth to applications

The present review provides an up-to-date report on the main potential of CVD diamond films for industrial applications as well as on recent basic research which seeks to understand diamond deposition microwave plasma reactors. This review includes firstly an overview of diamond film applications. Elements which explain variations in diamond film characteristics as a function of synthesis conditions are given. Also experimental results are reported which show variations in diamond characteristics (quality, microstructure, growth rate, growth mechanisms) as four plasma variables (pressure, power, percentage of methane, substrate temperature) are systematically changed. In the second part, we discuss the effects of these variables on local parameters such as electron temperature, gas temperature, carbon-containing species and H-atom densities. Finally, based on these results, relationships between key local parameters and diamond characteristics are established and discussed.     

Self-consistent reaction field theory of solvent effects

A quantum-mechanical reaction field theory of solvent effects is proposed. It contains as a limiting case Onsager's model. It leads to an effective, non-linear, hamiltonian for the molecule in solution and hence to a tool for studying changes in charge distributions and molecular properties. Numerical examples are given.     

Investigations into the synthesis of 6-ethyl-5-(4-pyridinyl)-2,4-pyrimidinediamine as a potential antimalarial agent

The synthesis of 6-ethyl-5-(4-pyridinyl)-2,4-pyrimidinediamine ( 2 ), the pyridine analog of pyrimethamine, is described. Condensation of 4-pyridineacetonitrile ( 3 ) with methyl propionate afforded α-(1-oxopropyl)-4-pyridineacetonitrile ( 4 ). Treatment with triethyl orthopropionate gave primarily the undesired N-alkylated material. However reaction of the crude mixture with guanidine afforded 2 in low yield. This material was devoid of significant antimalarial activity.     

Complex interpolation between two weighted Bergman spaces on tubes over symmetric cones

We prove that the complex interpolation space [A_ν^p₀,A_ν^p₁]_θ, 0<θ<1, between two weighted Bergman spaces A_ν^p₀ and A_ν^p₁ on the tube in $\text{C}{}^{\mathrm{n}}$, n?3, over an irreducible symmetric cone of $\text{R}{}^{\mathrm{n}}$ is the weighted Bergman space A_ν^p with 1/p=(1?θ)/p₀+θ/p₁. Here, ν>n/r?1 and 1?p₀<p₁<2+ν/(n/r?1) where r denotes the rank of the cone. We then construct an analytic family of operators and an atomic decomposition of functions, which are related to this interpolation result. To cite this article: D. Békollé et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Selective Search for Global Optimization of Zero or Small Residual Least-Squares Problems: A Numerical Study

In this paper, we consider approximating global minima of zero or small residual, nonlinear least-squares problems. We propose a selective search approach based on the concept of selective minimization recently introduced in Zhang et al. (Technical Report TR99-12, Rice University, Department of Computational and Applied Mathematics MS-134, Houston, TX 77005, 1999). To test the viability of the proposed approach, we construct a simple implementation using a Levenberg-Marquardt type method combined with a multi-start scheme, and compare it with several existing global optimization techniques. Numerical experiments were performed on zero residual nonlinear least-squares problems chosen from structural biology applications and from the literature. On the problems of significant sizes, the performance of the new approach compared favorably with other tested methods, indicating that the new approach is promising for the intended class of problems.     

Local Behavior of the Newton Method on Two Equivalent Systems from Linear Programming

Newton's method is a fundamental technique underlying many numerical methods for solving systems of nonlinear equations and optimization problems. However, it is often not fully appreciated that Newton's method can produce significantly different behavior when applied to equivalent systems, i.e., problems with the same solution but different mathematical formulations. In this paper, we investigate differences in the local behavior of Newton's method when applied to two different but equivalent systems from linear programming: the optimality conditions of the logarithmic barrier function formulation and the equations in the so-called perturbed optimality conditions. Through theoretical analysis and numerical results, we provide an explanation of why Newton's method performs more effectively on the latter system.     

A quadratically convergent O(\sqrt n L)-iteration algorithm for linear programming

Recently, Ye, Tapia and Zhang (1991) demonstrated that Mizuno—Todd—Ye's predictor—corrector interior-point algorithm for linear programming maintains the O( L)-iteration complexity while exhibiting superlinear convergence of the duality gap to zero under the assumption that the iteration sequence converges, and quadratic convergence of the duality gap to zero under the assumption of nondegeneracy. In this paper we establish the quadratic convergence result without any assumption concerning the convergence of the iteration sequence or nondegeneracy. This surprising result, to our knowledge, is the first instance of a demonstration of polynomiality and superlinear (or quadratic) convergence for an interior-point algorithm which does not assume the convergence of the iteration sequence or nondegeneracy.Supported in part by NSF Grant DDM-8922636 and NSF Coop. Agr. No. CCR-8809615, the Iowa Business School Summer Grant, and the Interdisciplinary Research Grant of the University of Iowa Center for Advanced Studies.Supported in part by NSF Coop. Agr. No. CCR-8809615, AFOSR 89-0363, DOE DEFG05-86ER25017 and ARO 9DAAL03-90-G-0093.Supported in part by NSF Grant DMS-9102761 and DOE Grant DE-FG05-91ER25100.