A two-sided Arnoldi algorithm with stopping criterion and MIMO selection procedure

In this paper we introduce a two-sided Arnoldi method for the reduction of high order linear systems and we propose useful extensions, first of all a stopping criterion to find a suitable order for the reduced model and secondly, a selection procedure to significantly improve the performance in the multi-input multi-output (MIMO) case. One application is in micro-electro-mechanical systems (MEMS). We consider a thermo-electric micro thruster model, and a comparison between the commonly used Arnoldi algorithm and the two-sided Arnoldi is performed.     

Measuring the joint impact of governance form and economic regulation on airport efficiency

This paper examines the joint impact that governance structure and economic regulation has on airport efficiency. The previous literature has focused on one or the other of these factors but not both. The empirical investigation uses a semi-parametric Bayesian distance stochastic frontier model, as well as a Data Envelopment Analysis (DEA) model. Based on a panel of airports in several countries we find that the form of economic regulation is relatively more important than the type of governance in affecting efficiency. The article provides measures of changes in expected efficiency when either or both the governance form and price regulation changes.     

Stabilizer additives in ionizing radiation environments under oxidizing conditions

Very little work has been done with energy-scavenger additives in radiation environments under oxidizing conditions. In this study, the stabilizing effect of an energy scavenger (pyrene) and a radical scavenger (hindered phenol), which were incorporated in a polychloroprene rubber, has been evaluated in a γ-radiation environment in air under conditions which gave rise to oxidation throughout the sample. Both compounds were found to significantly inhibit changes in macroscopic tensile properties of the materials. The pyrene enhanced the material's radiation resistance when used alone and also when used in conjunction with the hindered phenol. The rate of radiation-induced chemical destruction of the two additives was monitored by gas chromatography after solvent-extraction from degraded samples. Following a dose of 3 × 10⁵ Gy, only a few per cent of the hindered phenol remained, whereas more than 90% of the pyrene was still present. The rate of disappearance of the hindered phenol was slower in samples which also contained the pyrene.     

Polymer degradation under ionizing radiation: The role of ozone

Gamma-radiation degradation of poly(butadiene-co-styene) [SBR rubber] and poly(butadiene-co-acrylonitrile) [Buna-n rubber] in the presence of air has been investigated. Using a recently-developed modulus profiling techniques, it is shown that the degradation of these materials is very heterogenous through the sample thickness. There is a broad, paraboloidally-shaped modulus profile through the sample interior, together with a dramatic change in modulus in the surface regions. Mechanistic investigations lead to the conclusion that the radiation-inducted degradatoin of these materials results from two different process: (1) the standard free radical-mediated radiation chemistry, which gives rise to oxidation involving O₂ dissolved in the polymer and which leads to heterogenous oxidation due to oxygen diffusion effects; and (2) ozone chemistry in the surface regions of the samples, which results from attack by O₃ generated by the action of the ionizing radiation on the air atmosphere surrounding the samples. It appears that the intense role which this ozone mechanism can play in radiation-induced oxidative degradation of polymers has not been widely appreciated. This study provides evidence that the simultaneous action of ozone and ionizing radiation can in fact be strongly synergistic in their effect on organic materials     

A kinetic study of the mechanism of esterification of 1-arylethanols in trifluoroacetic acid

Aryl substituent effects upon the rate constants for the esterification of a series of 1-arylethanols in trifluoroacetic acid are in accordance with a reverse A_AL1 mechanism, for which the Hammett reaction constant ? = ?3.69 has been determined by correlation with σ⁺ substituent constants. The rates of reaction are ca. 50-fold faster than those for corresponding benzyl alcohols which bear an electron-donating aryl substituent and which are also believed to undergo esterification in trifluoroacetic acid by the reverse A_AL1 mechanism; the reverse A_AC2 mechanism applies to benzyl alcohols which bear an electron- withdrawing aryl substituent.     

Impulsive inelastic scattering of O+(4S) by isotopic hydrogen molecules

We present experimental evidence that at relative energies above 10 eV the non-reactive inelastic scattering of O⁺ by H₂, D₂, and HD arises from impulsive elastic scattering of 0⁺ by individual H or D atoms. The relation of this impulsive non-reactive scattering to the reactive scattering from these systems is briefly discussed.     

Accelerated aging and lifetime prediction: Review of non-Arrhenius behaviour due to two competing processes

Lifetime prediction of polymeric materials often requires extrapolation of accelerated aging data with the suitability and confidence in such approaches being subject to ongoing discussions. This paper reviews the evidence of non-Arrhenius behaviour (curvature) instead of linear extrapolations in polymer degradation studies. Several studies have emphasized mechanistic variations in the degradation mechanism and demonstrated changes in activation energies but often data have not been fully quantified. To improve predictive capabilities a simple approach for dealing with curvature in Arrhenius plots is examined on a basis of two competing reactions. This allows for excellent fitting of experimental data as shown for some elastomers, does not require complex kinetic modelling, and individual activation energies are easily determined. Reviewing literature data for the thermal degradation of polypropylene a crossover temperature (temperature at which the two processes equally contribute) of 83 °C was determined, with the high temperature process having a considerably higher activation energy (107–156 kJ/mol) than the low temperature process (35–50 kJ/mol). Since low activation energy processes can dominate at low temperatures and longer extrapolations result in larger uncertainties in lifetime predictions, experiments focused on estimating E_a values at the lowest possible temperature instead of assuming straight line extrapolations will lead to more confident lifetime estimates.