News: EPA report targets 10 key research areas

Science.     

An Iterative Model for the Steady-State Current Distribution in Oxide-Confined VCSELs

This paper presents an iterative model for the analysis of the current distribution in vertical-cavity surface-emitting lasers (VCSELs) using a SPICE-like approach. The model includes a degeneracy correction for operation at and above threshold. The effect of the resistance due to the p-distributed Bragg reflector (p-DBR) mirror layers and the oxide layer on performance is investigated. Higher sheet resistance under the oxide layer reduces the threshold current, but reduces the current range over which single transverse mode operation occurs. The voltage drop across the p-DBR region dominates spatial hole burning, which is moderated by lateral drift and diffusion. This simple iterative model is applied to commercially available oxide-confined VCSELs.     

The effect of spherical projectile speed in ricochet off water and sand

Experimental results are reported for the ricochet of steel and duralumin spheres ( and 1 in. dia.), from shallow depths of water and dry sand. The critical angle for ricochet off water is shown to increase with speed to approach the theoretical limit of . For ricochet off sand the critical angle decreases with speed but a cut-off angle exists, , for which no ricochet occurs at any speed.     

Plastic yielding of I-beams under shear, and shear and axial loading

Plane strain and plane stress slip-line field solutions previously published by the authors for cantilevers of rectangular cross-section are utilized to estimate the plastic collapse loads of corresponding I-sectioned beams. Uniform I-beams, tapered and haunched beams, and beams with rectangular holes and castellated beams are studied. Previous works in each case are reviewed and for uniform-section cantilevers with end shear loading, the results are compared with the theoretical results of others and with the experimental results of Green and Hundy.     

Low-energy electron-enhanced etching of HgCdTe

Low-energy electron-enhanced etching (LE4) is applied to HgCdTe to eliminate ion-induced surface damage. First, LE4 results for patterned samples are illustrated. The LE4 mechanism is understood from a mechanistic study in terms of three etch variables: direct current (DC) bias, gas composition, and sample temperature. For this paper, the effects of DC bias (electron energy) and gas composition (CH₄ concentration) are summarized qualitatively, followed by quantitative evidence. Etch rate, the amount of polymer, surface stoichiometry, and surface roughness have specific relations with each etch variable under competition between pure LE4 and polymer deposition.     

The relationship between the matched-filter operator and the targetsignature space-orthogonal projection classifier

An operator called the target signature space-orthogonal projection classifier (TSC) was recently introduced. The author shows that the TSC is actually a scaling of the familiar matched-filter operator. It is also proved that scaling the matched-filter operator does not alter its receiver operating characteristic (ROC) curve. Therefore, the TSC has the same performance as the matched-filter operator but requires more computations     

Die zweite Phase der Feldbusentwicklung

The past decade may be regarded as the phase of the fundamental developments in fieldbus systems that were based on the OSI model. Today we are entering a second stage. It is the objective of this issue to present the current state and where the further developments will lead to. This introductory article is intended to give an overview on the subject.     

Auswirkungen von Blitzschlägen auf 20-kV-Energiekabel

Recently appeared defects on high voltage cables have required an urgent evaluation of the impact of lightning strikes necessary. In some cases overvoltages between the copper wire screen of the cable and earth may appear which cause damages of the cablesheath. Field measurements with a classification of the voltage impulses at the copper wire screen have been made to evaluate the number of events. Additionally a numerical model was developed to study the effects of atmospheric discharges on underground cables with emphasis to the influence on the cablesheath. This numeric method was also applied to estimate the effectiveness of different protection arrangements. This contribution presents evaluation methods for overvoltages of cables and a model used firstly for calculating the stress caused by differential voltages and secondly to determinate the influence of protection measures.