Quasi-exact optical analysis of oxide-apertured microcavity VCSELsusing vector finite elements

We report a new full vector finite element model for analyzing the optical properties of azimuthally symmetric oxide-apertured vertical-cavity surface emitting lasers (VCSELs). Our model allows for quasi-exact calculation of the lasing mode blueshift, threshold gain, and field profile. Through a detailed analysis of a sample VCSEL, we ascertain the physical effects which determine diffractive or parasitic mode loss. They are: 1) the background density of parasitic modes and 2) the coupling strength between the lasing mode and the parasitic mode continuum. The coupling strength is in turn determined by the relative alignment between the lasing and parasitic mode propagation vectors and the lasing mode penetration into the oxide region. This analysis improves our understanding of the optical physics of apertured VCSELs and should enable the next leap down in lasing threshold     

Charge storage in InAlAs/InGaAs/InP floating gate heterostructures

Charge retention in floating gate InAlAs/InGaAs/InP field effect transistors is limited by lateral electron motion along the storage channel, a different direction for motion than found for AlAs/GaAs devices. Storage times as a function of temperature for the InP based alloy devices are reported and compared with similar AlAs/GaAs devices by using Poisson equation models.<>     

The nephelometric determination of selenium with 2,3-diaminonaphthalene

A nephelometric determination of selenium has been developed in the concentration range from 10 to 300 ppm based on the reaction of Se(IV) with 2,3-diaminonaphthalene. The method is inexpensive, simple, and requires little operator time or skill.     

Optimal transport and Perelman’s reduced volume

We show that a certain entropy-like function is convex, under an optimal transport problem that is adapted to Ricci flow. We use this to reprove the monotonicity of Perelman’s reduced volume. This research was partially supported by NSF grant DMS-0604829.     

Reduced power consumption in GaAs-based bipolar cascade lasers

A systematic study of GaAs tunnel junctions for use in bipolar cascade laser diodes was performed. The current voltage characteristics of individual degenerately doped n/sup +/ and p/sup +/ regions grown by MBE were investigated and the most promising designs were placed within the individual laser substructures. This resulted in a 1 V reduction in operating voltage, as verified by comparing the lasing characteristics of several edge-emitting laser devices.     

Assessment Methods for Demonstrating Compliance With Safety Limits of Wireless Devices Used in Home and Office Environments

Short-range wireless radio-frequency devices are rapidly pervading home and office environments. Nevertheless, their contribution to the electromagnetic field exposure of humans has not yet been systematically assessed, nor have the procedures for testing compliance been developed. In this paper, we have assessed the range of exposure in terms of the dosimetric and incident field quantities for devices of the most common technologies, i.e., digital enhanced cordless telecommunications, wireless local area networks and Bluetooth, as well as wireless communication devices based on proprietary standards in the frequency range from 30 MHz to 6 GHz. Well-defined procedures to obtain the worst case operational modes are presented. Since operation in the near-field of these devices cannot be excluded, dosimetric evaluation is the most straightforward technique for testing compliance when low-power exclusions are not applicable. The suitability of the suggested methods is demonstrated through the examination of five classes of short-range transmitters.     

Gunshot residue determination by high-performance liquid chromatography with electrochemical detection

A procedure for the detection of gunshot residue via the organic constituent diphenylamine is described. The method incorporates high-performance liquid chromatography with electrochemical detection.