Photostabilising action of nickel(II) bis(1-phenyl-3-methyl-4-decanoyl-5-pyrazolate), (sanduvor NPU) in polypropylene. Thermal antioxidant action and its relationship to photostabilisation,importance of hydroperoxide decomposition and light stability as a function of concentration

The thermal antioxidant action of Sanduvor NPU in polypropylene film has been examined at the 0.1% w/w concentration level. Infra-red and second-order derivative u.v.-visible spectroscopic techniques were used to monitor degree of oxidation in the films and stabiliser photodecomposition behaviour respectively. Hydroperoxide analysis was employed to determine the degree of thermal oxidation of films in an air oven. It was found that the behaviour of Sanduvor NPU in polypropylene films as a thermal stabiliser parallels its mode of action when used a melt stabiliser. The metal complex is highly effective in inhibiting hydroperoxide formation during extreme oxidative conditions. Hydroperoxide decomposition appears to play no part in this behaviour due to the inability of the complex to destroy these chromophores in solution, and the effect it has is attributed to the very effective chain breaking acceptor mechanism, i.e. macroalkyl radical scavenging. The relationship between embrittlement time and concentration was studied by varying the stabiliser content of the polymer over a wide range. As in the case of other metal chelates, the relationship is not linear, a limiting concentration behaviour is observed. This effect is attributed to the formation during photooxidation of products which promote the degradation of the polymer. This effect has implications on the efficiency of commercial systems.     

Propagation of gravitational waves in Robertson-Walker backgrounds

The electric and magnetic parts of the linearized Weyl tensor, when the stress-energy tensor is that of a perfect fluid and the background is of Robertson-Walker type, are known to satisfy wave equations that differ by the presence of a source term for the electric part. It is shown here that all of the allowed solutions of the inhomogeneous equation can be obtained by applying a differential operator to the solutions of the homogeneous equation; consequently, electric-type and magnetic-type gravitational waves have the same propagation properties. The results of a complete integration of the appropriately linearized Newman-Penrose equations are given.     

Self-reversed line profiles by scanning laser excitation

The theery of self-reversal is examined by observing the emission profile of the sodium D₂ line excited with light from a scanning tunable dye laser, as a function of vapour pressure.     

Difference approximations for wave equations via finite elements II. Error analysis

Difference-like schemes for the wave equation arise naturally from a Galerkin finite-element formulation, if we adopt certain quadrature rules in evaluating the mass and stiffness matrices. One can extend these schemes to problems involving sharp interfaces by applying the quadrature on a refinement of the finite-element grid that includes the interfaces. We develop error estimates for this modified scheme that corroborate numerical results for acoustic and elastic wave equations, presented in a companion article. © 1995 John Wiley & Sons, Inc.     

Optimizing material strength constants numerically extracted from taylor impact data

Advanced design requirements have dictated a need for the mechanical properties of materials at high strain rates. Mechanical testing for these data poses a significant problem for experimentalists. High-speed testing machines have a limited capability at rates approaching 10²/s. The split Hopkinson pressure bar is the most reliable alternative for rates approaching 10⁴/s. Plate impact experiments are capable of generating strain rates of 10⁸/s and higher. The Taylor impact test occupies a place of particular importance by providing data at strain rates on the order of 10⁴/s–10⁵/s. The issue at present is extracting the data. This paper provides a method for obtaining dynamic strength model material constants from a single Taylor impact test. A polynomial response surface is used to describe the volume difference (error) between the deformed specimen from the Taylor test and the results of a computer simulation. The volume difference can be minimized using an optimizer, with the result being an optimum set of material constants. This method was applied to the modified Johnson-Cook model for OFHC copper. Starting from a nominal set of material constants, the iterative process improved the relative volume difference from 23.1 percent to 4.5 percent. Other starting points were used that yielded similar results. The material constants were validated by comparing numerical results with Taylor tests of cylinders having varying aspect ratios, calibers and impact velocities.     

Use of cyclodextrin-bonded phases for liquid chromatographic separation of styrene polymers

The use of β- and γ-cyclodextrin bonded columns is successful for the separation of styrene polymers. Two retention mechanisms are involved: below 50% dichloromethane in heptane, normal adsorption behavior is observed; above 50%, a size-exclusion mode prevails. Good chromatograms under isocratic and gradient-elution conditions are shown, together with their applications in determination of molecular weights of polymers.     

A reflectivity equation for acoustic media with absorption

The wave equation which governs the propagation of dilatational stress (pressure) in viscoacoustic media can be reduced to the lossless acoustic wave equation by the introduction of a complex traveltime coordinate. An interesting property of this equation is that it contains a term which is proportional to the reflectivity function in its single scattering approximation.     

Continuity of the spectrum on closed similarity orbits

We present a useful case when the spectral radius of a norm limit of operator similar to a fixed operatorT still equals that ofT.This work was supported in part by grants from the National Science Foundation DMS-8811084, ECS-9001371, ECS-9122106, by the Air Force Office of Scientific Research AFOSR-90-0024 and AFOSR-90-0053, and by the Army Research Office DAAL03-91-G-0019.     

A parametric study of cochlear input impedance

In this paper various aspects of the cat cochlear input impedance Zc (omega) are implemented using a transmission line model having perilymph viscosity and a varying cross-sectional scalae area. These model results are then compared to the experimental results of Lynch et al. [J. Acoust. Soc. Am. 72, 108-130 (1982)]. From the model, the following observations are made about the cochlear input impedance: (a) Scalae area variations significantly alter the model Zc (omega); (b) the use of anatomically measured area improves the fits to the experimental data; (c) improved agreement between model and experimental phase is obtained when perilymph viscosity and tapering are included in the cochlear model for frequencies below approximately 150 Hz; (d) when model scalae tapering and perilymph viscosity are chosen to match physiological conditions, the effect of the helicotrema impedance on Zc (omega) is insignificant; and (e) the cochlear map, which is defined as the position of the basilar membrane peak displacement as a function of stimulus frequency, can have an important effect on Zc (omega) for frequencies below 500 Hz. A nonphysiological cochlear map can give rise to cochlear standing waves, which result in oscillations in Zc (omega). Scalae tapering and perilymph viscosity contribute significantly to the damping of these standing waves. These observations should dispel the previous notion that Zc (omega) is determined solely by parameters of the cochlea close to the stapes, and the notion that Zc (omega) is dominated by the helicotrema at low frequencies.