Simulation of leachate migration in leaky aquifers

A two-dimensional cross-section finite difference model is presented to simulate density dependent leachate migration in leaky aquifers. Unlike existing models, a new approach is adopted to couple the groundwater-flow equation and the hydrodynamic dispersion equation with the elimination of the intermediate step of calculating velocities. The concept of the reference density is employed, permitting increased accuracy (over pressure-based models) in the representation of the transport process. The model is then used to study the effect of several hydraulic and transport parameters on the flow pattern and plume migration which are found to be very sensitive to most of these parameters. Equiconcentration and equipotential lines are overlapped to provide a better understanding of the coupling effect.     

Consequences of structural disorder on laser properties in quantumwire lasers

The effect of interface-roughness-related disorder on the electronic and optoelectronic properties of a quantum wire structure are studied. It is seen that the disorder causes strong localization in the quasi-one-dimensional system. While the electronic states are seriously perturbed, the density of states is not affected drastically. Optoelectronic properties as reflected in the interband transition related phenomenon are not found to suffer significant deterioration as a result of the disorder. However, the results suggest that intraband relaxation processes may be seriously affected because of electron (hole) states being localized in different regions of the wire     

Non-linear analysis of frames

A simple and easily programmable technique is proposed for the second-order analysis of frames. This technique involves the iterative process with modification of the stiffness matrix as well as the load vector in each iteration. Both curvature and sway effects are included. A numerical example is included to illustrate the results.     

A model for electroluminescence in SrS:Ce ACTFEL display devices

An analytical model for electroluminescence in SrS:Ce AC thin-film electroluminescent display devices is presented. The model incorporates an exact calculation of the electric field and the effect of activator ionization and bulk traps. Activator ionization is needed to explain several features of luminescence behavior in SrS:Ce devices. These features include the second luminescence peak at the trailing edge of the voltage pulse and the time lag between the luminescence and the applied voltage when the applied voltage consists of bipolar trapezoidal pulses and rectangular pulses of low voltage amplitudes. As a mechanism for the ionization of activators, field-assisted tunneling is shown to be more likely than impact ionization by hot electrons. Physical processes are described in terms of rate equations, and field, current, and luminescence waveforms are calculated for one set of device parameters. The calculated and experimental luminescence waveforms agree     

Two-dimensional grain growth in rapidly solidified succinonitrile films

The kinetics and topological mechanisms of normal grain growth have been examined throughin situ dynamic studies on rapidly solidified succinonitrile (SCN). Thein situ studies allowed for continuous monitoring of the evolution of individual grains during growth. We have assessed the Mullins—Von Neumann topological grain growth law and the Burke—Turnbull parabolic rate law and have determined rate constants that describe grain growth. This work demonstrates that both laws are both obeyed globally and consistently. Thesein situ studies permit one to follow the unit operations associated with grain growth kinetics. This article demonstrates the usefulness of succinonitrile as a model analog system for studying grain growth. This article is based on a presentation made in the symposium “Fine Grains And Their Growth in Rapidly Solidified Materials,” TMS Materials Week ’93, Pittsburgh, PA, October 18–21, 1993.     

Incremental maintenance of aggregate and outerjoin expressions

Views stored in a data warehouse need to be kept current. As recomputing the views is very expensive, incremental maintenance algorithms are required. Over recent years, several incremental maintenance algorithms have been proposed. None of the proposed algorithms handle the general case of relational expressions involving aggregate and outerjoin operators efficiently.