Air-cushioning in impact problems

This paper concerns the displacement potential formulation to study the post-impact influence of an aircushioning layer on the two-dimensional impact of a liquid half-space by a rigid body. The liquid and air are both ideal and incompressible and attention is focussed on cases when the density ratio between the air and liquid is small. In particular, the correction to classical Wagner theory is analysed in detail for the impact of circular cylinders and wedges

On the nature of the phase transitions in two-dimensional type II superconductors

We have simulated the thermodynamics of vortices in a thin film of a type-II superconductor. We make the lowest Landau level approximation, and use quasi-periodic boundary conditions. Our work is consistent with the results of previous simulations where evidence was found for an apparent first order transition between the vortex liquid state and the vortex crystal state. We show, however, that these results are just an artifact of studying systems which are too small. There are substantial difficulties in simulating larger systems using traditional approaches. By means of the optimal energy diffusion algorithm we have been able to study systems containing up to about one thousand vortices, and for these larger systems the evidence for a first order transition disappears. By studying both crystalline and hexatic order, we show that the KTHNY scenario seems to apply, where melting from the crystal is first to the hexatic liquid state and next to the normal vortex liquid, in both cases via a continuous transition.Comment: 26 pages, 26 composite figures. Pre-proof versio

Three-dimensional oblique water-entry problems at small\ud deadrise angles

This paper extends Wagner theory for the ideal, incompressible normal impact of rigid bodies that are nearly parallel to the surface of a liquid half-space. The impactors considered are three-dimensional and have an oblique impact velocity. A variational formulation is used to reveal the relationship between the oblique and corresponding normal impact solutions. In the case of axisymmetric impactors, several geometries are considered in which singularities develop in the boundary of the effective wetted region. We present the corresponding pressure profiles and models for the splash sheets

The ultraviolet excess of quasars 3: The highly polarized quasars PKS 0736+017 and PKS 1510-089

Ultraviolet/optical/infrared spectrophotometry of the highly-polarized quasars (HPQ's) PKS 0736+017 and PKS 1510-089 is analyzed. A blazar continuum component like that in BL Lac objects (e.g. with violent variability, high polarization, and a steep power-law shape) contributes about half the visual light of 1510-089, and at least three-quarters of that in 0736+017. The remaining light has the same spectrum as normal (low-polarization) quasars, including an ultraviolet excess or blue bump, which is easily detected in the IUE spectra of 1510-089, and weakly detected in 0736+017. The line fluxes do vary, but not as much as the continuum. The ratios of the broad emission lines, and the Balmer continuum are normal in both quasars

Effect of casing treatment of overall performance of axial-flow transonic fan stage with pressure ratio of 1.75 and tip solidity of 1.5

The effect of a number of casing treatments on the overall performance of a 1.75-pressure-ratio, 423-m/sec-tip-speed fan stage was evaluated. The skewed slot configuration with short-open slots over the midportion of the rotor had a stall margin of 23.5 percent, while the solid casing had a stall margin of 15.0 percent. The skewed slot configuration with long open slots extending ahead of and over portion of rotor displaced the stall line to the lowest flow at all speeds tested. At design speed, the peak efficiency for the long, forward open slots was 1 point less than that for the short midopen slots and 3 points less than that for the solid casing

A note on oblique water entry

An apparently minor error in Howison, Ockendon & Oliver (J. Eng. Math. 48:321–337, 2004) obscured the fact that the points at which the free surface turns over in the solution of the Wagner model for the oblique impact of a two-dimensional body are directly related to the turnover points in the equivalent normal impact problem. This note corrects some results given in Howison, Ockendon & Oliver (2004) and discusses the implications for the applicability of the Wagner\ud model

Atmosphere Behavior in Gas-Closed Mouse-Algal Systems: An Experimental and Modelling Study

A dual approach of mathematical modelling and laboratory experimentation aimed at examining the gas exchange characteristics of artificial animal/plant systems closed to the ambient atmosphere was initiated. The development of control techniques and management strategies for maintaining the atmospheric levels of carbon dioxide and oxygen at physiological levels is examined. A mathematical model simulating the atmospheric behavior in these systems was developed and an experimental gas closed system was constructed. These systems are described and preliminary results are presented

The Semiclassical and Quantum Regimes of Superradiant Light Scattering from a Bose-Einstein Condensate

We show that many features of the recent experiments of Schneble et al. [D. Schneble, Y. Torii, M. Boyd, E.W. Streed, D.E. Pritchard and W. Ketterle, Science vol. 300, p. 475 (2003)], which demonstrate two different regimes of light scattering by a Bose-Einstein condensate, can be described using a one-dimensional mean-field quantum CARL model, where optical amplification occurs simultaneously with the production of a periodic density modulation in the atomic medium. The two regimes of light scattering observed in these experiments, originally described as ``Kapiza-Dirac scattering'' and ``Superradiant Rayleigh scattering'', can be interpreted as the semiclassical and quantum limits respectively of CARL lasing.Comment: 10 pages, 5 figures - to appear in Journal of Optics

Interconnect fatigue design for terrestrial photovoltaic modules

The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable (1) the prediction of cumulative interconnect failures during the design life of an array field, and (2) the unambiguous--ie., quantitative--interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field

Structure of the Alkali-metal-atom-Strontium molecular ions: towards photoassociation and formation of cold molecular ions

The potential energy curves, permanent and transition dipole moments, and the static dipolar polarizability, of molecular ions composed of one alkali-metal atom and a Strontium ion are determined with a quantum chemistry approach. The molecular ions are treated as effective two-electron systems and are treated using effective core potentials including core polarization, large gaussian basis sets, and full configuration interaction. In the perspective of upcoming experiments aiming at merging cold atom and cold ion traps, possible paths for radiative charge exchange, photoassociation of a cold Lithium or Rubidium atom and a Strontium ion are discussed, as well as the formation of stable molecular ions