Andreev states near short-ranged pairing potential impurities

We study Andreev states near atomic scale modulations in the pairing potential in both s- and d-wave superconductors with short coherence lengths. For a moderate reduction of the local gap, the states exist only close to the gap edge. If one allows for local sign changes of the order parameter, however, resonances can occur at energies close to the Fermi level. The local density of states (LDOS) around such pairing potential defects strongly resembles the patterns observed by tunneling measurements around Zn impurities in Bi2Sr2CaCu2O8+x (BSCCO). We discuss how this phase impurity model of the Zn LDOS pattern can be distinguished from other proposals experimentally.     

Semiclassical calculations of half-widths and line shifts for transitions in the 30012←00001 and 30013←00001 bands of CO2 II: Collisions with O2 and air

The complex Robert–Bonamy (CRB) formalism was used to calculate the half-width, its temperature dependence, and the line shift for CO₂ for transitions in the 30012←00001 and 30013←00001 bands with O₂ as the perturbing gas. The calculations were done for rotational quantum numbers from J=0 to J=120 with no ad hoc scaling of the line shape equations. The intermolecular potential parameters are adjusted on accurate experimental measurements of the half-widths, its temperature dependence, and the pressure-induced line shifts so that a single intermolecular potential reproduces all three parameters. Using the results of this work and previous results for N₂-broadening, air-broadening line shape parameters were also determined. The comparison of the CRB calculations with the experimental data available in the literature for the three line shape coefficients demonstrates the quality of the present calculations for the both bands under study.     

Stimulated luminescence emission from localized recombination in randomly distributed defects

We present a new kinetic model describing localized electronic recombination through the excited state of the donor (d) to an acceptor (a) centre in luminescent materials. In contrast to the existing models based on the localized transition model (LTM) of Halperin and Braner (1960 Phys. Rev. 117 408-15) which assumes a fixed d?→?a tunnelling probability for the entire crystal, our model is based on nearest-neighbour recombination within randomly distributed centres. Such a random distribution can occur through the entire volume or within the defect complexes of the dosimeter, and implies that the tunnelling probability varies with the donor-acceptor (d-a) separation distance. We first develop an 'exact kinetic model' that incorporates this variation in tunnelling probabilities, and evolves both in spatial as well as temporal domains. We then develop a simplified one-dimensional, semi-analytical model that evolves only in the temporal domain. An excellent agreement is observed between thermally and optically stimulated luminescence (TL and OSL) results produced from the two models. In comparison to the first-order kinetic behaviour of the LTM of Halperin and Braner (1960 Phys. Rev. 117 408-15), our model results in a highly asymmetric TL peak; this peak can be understood to derive from a continuum of several first-order TL peaks. Our model also shows an extended power law behaviour for OSL (or prompt luminescence), which is expected from localized recombination mechanisms in materials with random distribution of centres.     

Fatigue performance of glass/polyester laminates and the monitoring of material degradation

Experiments are performed on glass/polyester composites under fatigue loading. The stiffness degradation is recorded as an indirect measure of material damage. The stiffness decrease rate is described by a power dependence on stress; this relationship allows the fatigue law to be derived. Stiffness-controlled fatigue curves are generated and presented in an S-N-diagram based on normalized stress (equivalent to strain). Such stiffness controlled fatigue curves can be used as a basis for design criteria for components.Presented at the 9th International Conference on Mechanics of Composite Materials, 17–20 October 1995, Riga, Latvia.Materials Department, Risø National Laboratory, Roskilde, Denmark. Published in Mekhanika Kompozitnykh Materialov, Vol. 32, No. 1, pp. 32–41, January–February, 1996.     

A computational study of the error in the vortex method associated with discontinuous vorticity

We investigate computationally the error computed by the vortex method for a discontinuous patch of vorticity. Specifically, the computed velocity and vorticity of an elliptical path of constant vorticity, known as the Kirchhoff ellipse, are compared to the analytic velocity and vorticity. The error in the velocity and the vorticity for the Kirchhoff ellipse as computed by the vortex method is presented. This error is studied as a function of the aspect ratio of the ellipse, the blob function, the spacing between the centers of the computational elements, and the blob radius. Both the error at the initial time and the error after three revolutions of the ellipse are discussed. © 1996 John Wiley & Sons, Inc.