A note on the stress singularity at a non-uniformly moving crack tip

The stress-singularity at a crack tip moving arbitrarily in an elastic plate under plane strain conditions is investigated. By formulating the wave-equations in a polar coordinate system attached to the crack-tip, it is found by an asymptotic analysis that the angle-dependence of the singularity is only dependent on the instantaneous cracktip velocity. This result is used to derive a relation between the dynamic stress-intensity factor and the energyrelease rate.     

Media Scheduling and Solution Approaches

A media model that selects and schedules advertisements over time subject to a budgetary constraint is formulated as a large-scale, zero-one, integer programming model. A solution to the model by means of standard optimization techniques is infeasible or impractical, because of its complex structure. Consequently, several computationally efficient alternative solution approaches are developed and evaluated. These are shown to provide good (often optimal) solutions to the model and also appear to have a wide range of applicability to other media models and optimization problems with similar structures.     

Use of oxiranes in the preparation of bonded phase supports

A variety of stationary phases were bonded to silaceous supports through an intermediate silane coupling agent, γ-glycidoxypropylsilane. Consequently, a series of ion-exchange, hydrophobic, and hydrophilic supports were prepared that are stable, withstand high mobile phase velocities, and have sufficient porosity to allow the partitioning of biopolymers. Liquid-liquid partition chromatography of proteins was achieved with phosphate buffers while the separation of a series of aromatic compounds was accomplished on the same columns with hexane.

Anion- and cation-exchange supports were found to have hemoglobin ion- exchange capacities similar to classical cross-linked dextrans while allowing separation speeds 10–20 times those of carbohydrate gel supports.     

Simple but powerful goal programming models for discriminant problems

Conventional statistical analysis includes the capacity to systematically assign individuals to groups. We suggest alternative assignment procedures, utilizing a set of interrelated goal programming formulations. We further demonstrate via simple illustration the potential of these procedures to play a significant part in addressing the discriminant problem, and indicate fundamental ideas that lay the foundation for other more sophisticated approaches.     

Vereinfachung der 1H- und 13C-NMR-spektren von benzylether-blockierten sacchariden. Eine leistungsfähige synthese von brommethyl-d2-benzol

An efficient synthesis of bromomethyl-d₂-benzene as reagent for protection of hydroxyl groups and its benefit in ¹H- and ¹³C-NMR-spectroscopical analysis of benzylether blocked saccharides is described.     

Iterating bonferroni bounds

A general method is presented for generating improved Bonferroni bounds whenever an improvement on Booles inequality holds.     

Time-resolved mass spectrometric study of the reaction H + Trans-2-Butene

The title reaction was studied in a discharge flow system using mass flow and modulated molecular beam sampling with phase-sensitive detection in order to obtain time-resolved mass spectrometric analysis. At total conversion exceeding 30%, the major products are methane and ethane when initially hydrogen atoms are in excess; when butene is in excess, the major products are ethane and propylene. No hydrocarbons with more than 4 carbon atoms were detected in the products. The reaction is a complicated one since the simplest reaction scheme that successfully simulates the experimental results comprises 20 elementary reactions. The simulation, coupled with sensitivity analysis, shows that with hydrogen atoms in excess, significant amounts of propylene formed in the initial decomposition of the butyl radical react further with hydrogen atoms to form methane and ethane. When butene is in excess, approximately [C₃H₆] ≈ [CH₄] + ½[C₂H₆] which means that this propylene does not react further and almost all methyl radicals end up as CH₄ or C₂H₆. At small conversion, simulation shows that the major product by far is propylene regardless of the [H]/[butene] ratio. The absence of higher hydrocarbons in the products is at variance with earlier results of Rabinovitch and coworkers; however the present work leads to a comparable value for the average rate constant ??_a = ωD/S where D and S is the amount of products arising from the decomposition and stabilization, respectively, of the butyl radical and ω is the collision frequency.     

Kinetics studies of oxidations of catechol and l-dopa as mediated by IrCli2−6 at polymer-coated glassy carbon electrodes

Rotating disk techniques were employed to measure the kinetics of the oxidations of catechol and l-dopa as mediated by IrCl^2?₆ at a glassy carbon rotating disk electrode coated with a mixture of two polycationic electrolytes. For both reactants the kinetic behavior matched that described by Andrieux et al. [1] for an “SR” case. Products of the cross-reaction rate constants and substrate partition coefficients derived from the data had values consistent with very similar reactivities of both substrates toward IrCl^2?₆ inside and outside of the coatings.     

BOOK REVIEW

Modeling Fluctuating Populations by R.M. Nisbet and W.S.C. Gurney, John Wiley and Sons, 1982, 379 pp.