Kinetics of gas-phase addition reactions of methyl radicals. I. Addition to ethylene,acetylene, and benzene

The reactions have been studied by a mass-balance method involving the photolysis of small amounts of biacetyl in the presence of a large excess of isobutane containing a small proportion of the unsaturated substrate. The following Arrhenius parameters have been derived:

Resistivity- and perturbed angular correlation-study of implanted nickel hydrides

Hyperfine Interactions -     

Linear algorithms for testing the sign stability of a matrix and for findingZ-maximum matchings in acyclic graphs

Summary Ann×n real matrixA=(a _ij ) isstable if each eigenvalue has negative real part, andsign stable (orqualitatively stable) if each matrix B with the same sign-pattern asA is stable, regardless of the magnitudes ofB's entries. Sign stability is of special interest whenA is associated with certain models from ecology or economics in which the actual magnitudes of thea _ij may be very difficult to determine. Using a characterization due to Quirk and Ruppert, and to Jeffries, an efficient algorithm is developed for testing the sign stability ofA. Its time-and-space-complexity are both 0(n ²), and whenA is properly presented that is reduced to 0(max{n, number of nonzero entries ofA}). Part of the algorithm involves maximum matchings, and that subject is treated for its own sake in two final sections.     

Chemical composition and in vitro antifungal and antioxidant activity of the essential oil and methanolic extract of Teucrium sauvagei Le Houerou

The chemical composition and the in vitro antifungal and antioxidant activity of the essential oil and the methanolic leaf extracts of Teucrium sauvagei Le Houerou, an endemic medicinal plant growing in Tunisia, have been studied. More than 35 constituents having an abundance >or=0.2% were identified in the oil. beta-Eudesmol, T-cadinol, alpha-thujene, gamma-cadinene, and sabinene were the prevalent constituents. Results of the antifungal activity tests indicated that the methanolic extract inhibited the in vitro growth of seven dermatophytes, whereas the essential oil showed average inhibition against only three dermatophytes. In vitro antioxidant properties of the essential oil and the methanolic extract were determined by DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulphonic acid)) assays and compared to those of the synthetic antioxidant Trolox. Due to their antifungal and antioxidant properties, the essential oil and the methanolic extract of T. sauvagei may be of use as natural preservative ingredients in food and/or pharmaceutical industries.     

Linear Convergence Rates for Variants of the Alternating Direction Method of Multipliers in Smooth Cases

In the present paper, we propose a novel convergence analysis of the alternating direction method of multipliers, based on its equivalence with the overrelaxed primal–dual hybrid gradient algorithm. We consider the smooth case, where the objective function can be decomposed into one differentiable with Lipschitz continuous gradient part and one strongly convex part. Under these hypotheses, a convergence proof with an optimal parameter choice is given for the primal–dual method, which leads to convergence results for the alternating direction method of multipliers. An accelerated variant of the latter, based on a parameter relaxation, is also proposed, which is shown to converge linearly with same asymptotic rate as the primal–dual algorithm.     

Development of the parametric tolerance modeling and optimization schemes and cost-effective solutions

Most of previous research on tolerance optimization seeks the optimal tolerance allocation with process parameters such as fixed process mean and variance. This research, however, differs from the previous studies in two ways. First, an integrated optimization scheme is proposed to determine both the optimal settings of those process parameters and the optimal tolerance simultaneously which is called a parametric tolerance optimization problem in this paper. Second, most tolerance optimization models require rigorous optimization processes using numerical methods, since closed-form solutions are rarely found. This paper shows how the Lambert W function, which is often used in physics, can be applied efficiently to this parametric tolerance optimization problem. By using the Lambert W function, one can express the optimal solutions to the parametric tolerance optimization problem in a closed-form without resorting to numerical methods. For verification purposes, numerical examples for three cases are conducted and sensitivity analyses are performed.     

Influence of Molar Mass and Concentration on the Thermogelation of Methylcelluloses

In this study, thermogelation of methylcelluloses is investigated in relation to the molar mass and concentration in aqueous medium. A large hysteresis between heating and cooling ramps was observed whatever the conditions. The heating process in particular was studied to analyze the two steps of gelation using rheometry. At low temperature, in the sol state, viscosity depends on the concentration and molar mass. Over 30°C a gel-like behavior was observed including two steps (the second step is a strong gel with phase separation) having storage moduli that are nearly independent of polymer molar mass but are directly related to polymer concentration.     

Thermoset modified with polyethersulfone: Characterization and control of the morphology

Thermoset (TS) epoxy resins can be toughened with a thermoplastic (TP) for high-performance applications. The final structure morphology has to be controlled to achieve high mechanical properties and high impact resistance. Four polyethersulfone-modified epoxy resins are considered. They consist of different epoxy monomer structure (TGAP, triglycidyl-p-aminophenol and TGDDM, tetraglycidyl diaminodiphenylmethane) and a fixed amount of thermoplastic, and they are cured with two different amounts of curing agent. A reaction-induced phase separation occurs for all formulations generating morphologies, different in shapes and scales. The aim is to control the final morphology and in particular its dominant length scale. This morphology depends on the phase separation process, from the initiation to its final stage. The initiation relies on the relative miscibility of the components and on the stoichiometry between epoxy and curing agent. The kinetics depends on the viscosity of the systems. The different morphologies are characterized by electron microscopy or neutron scattering. Dynamic mechanical analysis allows confirming the presence of a phase separation even when it is not observable by electron microscopy. Vermicular morphologies with few hundreds nanometer width are obtained for the systems containing the TGAP as epoxy monomer. Systems formulated with TGDDM presents morphologies on much smaller scale of order a few tens of nanometers. We interpret the different sizes of the morphologies as a consequence of a larger viscosity for the TGDDM systems as compared to the TGAP ones rather than by a latter initiation of phase separation.