Narrow band laser-generated surface acoustic waves using a formed source in the ablative regime

A narrow band laser-generated acoustic signal was created using a 4-element lenticular array. This arrangement of the array produces an acoustical signal with frequency content that is compatible with the response of a noncontact and remote broadband receiver, such as a capacitive air-coupled transducer. To support the experimental observations, a simplified concept is presented to explain the effect of a line array source on the frequency content of a surface acoustic wave. The analytical model solution for the wave front shape is derived from the point load solution of Lamb's problem that represents the displacement of a surface acoustic wave generated by an ablative line array. The distribution function, which was used for the model to represent the laser light energy, was tailored to depict the actual energy distribution that illuminates the lenticular array. Filtering functions are applied to the resultant surface displacement function to retain frequencies similar to those detected by the broadband 50 kHz-2.25 MHz receiver. The theoretical model showed good agreement with experimental results.     

Evaluation of sulfur, selenium and tellurium catalysts with antioxidant potential

Oxidative stress is implicated, either directly or indirectly, in the pathology of a range of human diseases. As a consequence, the development of efficient antioxidants for medical use has become increasingly important. We have synthesised a range of structurally related organo-sulfur, -selenium and -tellurium agents and demonstrated that a combination of electrochemical methodology, in vitro assays and cell culture tests can be used to rationalise the antioxidant activity of these catalytic agents. Based on its exceptionally low anodic oxidation potential (Epa) and high activity against the representative oxidative stressors tert-butyl hydroperoxide and peroxynitrite, 4,4'-dihydroxydiphenyltelluride is predicted to be a potent antioxidant. This compound exhibits a correspondingly high activity with a remarkably low IC50 value of 20 nM, when tested in PC12 cell culture using a bioassay indicative of the early stages of Alzheimer's disease.     

Evidence for changing of cosmic ray composition between 10(17) and 10(18) eV from multicomponent measurements

The average mass composition of cosmic rays with primary energies between 10(17) and 10(18) eV has been studied using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum and the muon density as a function of energy. The results show that the composition is changing from a heavy to lighter mix as the energy increases.     

Elastic waves in fibre composite laminates

This paper considers the propagation of elastic waves in an eight-ply quasi-isotropic laminate arising from line sources of dislocation located at each of the seven interfaces in turn. The line source sets up a straight crested wave travelling along the laminate in a direction normal to the load line, and the elastodynamic equations within each layer are solved by taking the Laplace transform with respect to time and the Fourier transform with respect to the spatial coordinate in the direction of propagation. The resulting system of six first-order differential equations in each layer is solved to obtain the transforms of the displacement and stress components throughout the laminate. The time history of any displacement or stress component at any location may then be recovered by numerical inversion of the double transform. Examples are shown of the time history of the normal displacement of the top surface of the laminate at a distance of 20 plate thicknesses from the plane of action of the sources. The numerical inversion involves a summation over different modes of Rayleigh-Lamb waves in the laminate and contributions to the overall response from some of the individual modes are displayed.     

IBA-2 model calculation on even mass tellurium isotopes compared with results of recent nuclear orientation experiments

Calculations using the IBA-2 model code are presented for even-even tellurium isotopes¹¹⁸Te to¹²⁴Te. Three parameter sets are used, two from previous work and a third chosen to give optimum fit to experimental positive parity energy levels and B(E2) ratios. With only two additional parameters, each with simple physical interpretation, the three parameter sets are shown to give excellent fits to the known collective negative parity states in these isotopes. Failure to fit the O ₂ ⁺ ,O ₃ ⁺ and 2 ₃ ⁺ levels suggests these may be 4p-2h intruder states, although their Behaviour with varying neutron number is not as clearly characteristic of such configurations as is found for the 2p-4h states in Cd isotopes.