Microwave permittivity determination in agricultural products.

Applications of microwave measurement techniques, including frequency-domain and time-domain methods, for determining the permittivity of agricultural products (seeds, plants, grains, fruits, meat, etc.) are reviewed. Graphical data illustrating the dependence of the dielectric constants and loss factors of such products on moisture content, frequency of the applied fields, temperature, and bulk density of granular materials are provided for selected materials. Finally, recommendations are offered for further study and applications of permittivity measurements.     

Quantitative prediction of semiconductor laser characteristicsbased on low intensity photoluminescence measurements

A general scheme for the determination of vital operating characteristics of semiconductor lasers from low intensity photoluminescence spectra is outlined and demonstrated. We describe a comprehensive model that allows us to determine properties of the running device like gain spectra, peak gain wavelengths, bandwidths or differential gains, as well as inhomogeneous broadening and actual carrier densities of PL-signals. This information can then be used to compute characteristics like the temperature dependence of the gain, threshold densities, optical field distributions or near-field and far-field outputs     

Photochemistry of Tetracene Adsorbed on Dry Silica: Products and Mechanism

The photochemistry of tetracene (1) has been studied on dry silica at very low surface coverages (less than 3% of a monolayer). Irradiation of degassed samples of 1 adsorbed on silica surface proceeds very slowly to produce both syn (2) and anti (3) dimers. Under aerated conditions photolysis of 1 at surface coverages <1% of a monolayer gives mainly tetracene-5, 12-endoperoxide (4) and very little dimer. The endoperoxide slowly decomposes to form 5, 12-tetracenequinone (5), 5, 12-dihydroxytetracene (6) and 5, 12-dihydro-5, 12-dihydroxytetracene (7), respectively. As the surface coverage is increased above 1% of a monolayer, dimerization becomes more pronounced as a result of pairing and/or aggregation. The photooxidation process is mediated by the addition of singlet molecular oxygen to 1. Tetracene also undergoes a dark oxidation reaction on the silica surface to give 5 (major), 6 and 7 (minors) as products. The first-order rate constant for this Lewis acid-catalyzed oxidation was determined to be 1 × 10⁵ S^?1.     

Lagrangean decomposition for integer nonlinear programming with linear constraints

We present a Lagrangean decomposition to study integer nonlinear programming problems. Solving the dual Lagrangean relaxation we have to obtain at each iteration the solution of a nonlinear programming with continuous variables and an integer linear programming. Decreasing iteratively the primal—dual gap we propose two algorithms to treat the integer nonlinear programming.This work was partially supported by CNPq and FINEP.     

565 Mbaud 100 km optical system trial using a ridge waveguide DFB laser at 1.478 ?m

565 Mbaud transmission over 100 km of step-index mono-mode fibre using a new ridge waveguide distributed feedback (DFB) laser structure operating at 1.478 ?m and a Ge APD receiver has been demonstrated. No residual dispersion penalty was observed.     

Cosmic ray soft error rates of 16-Mb DRAM memory chips

Manufactured 16-Mb DRAM memory chips use three different cell technologies for bit storage: stacked capacitors, trenches with internal charge, and trenches with external charge. We have measured the soft fail probability of 26 different 16-Mb chips produced by nine vendors to evaluate whether the different cell technologies have an impact on the chip soft error rate. This testing involved irradiation with neutrons, protons, and pions, the principle hadrons of terrestrial cosmic rays. The results show clear differences in soft-fail sensitivity, which appears to be related to the cell structure     

The structure of red sprites determined by VLF scattering

Red sprites occur high above the stratosphere, just under the ionosphere. Although the first reported observation was over 100 years ago, and the first theory was 40 years ago, only over the last year or so has the subject spread into the popular science magazines, and into the secular media. Most of the studies of the sprite structure have been optical, using the light they emit for a few tens of milliseconds for imaging (low-light video and photography) and spectroscopy. Here, we concentrate on the scattering by sprites of man-made VLF radio waves. This scattering shows that the columnar elements of sprites have a substantial electrical conductivity     

Low threshold 1.55 ?m InGaAsP lasers double clad with InGaAsP confining layers

Preliminary results for 1.55 ?m InGaAsP double-heterostructure lasers with symmetrical InGaAsP confining layers are presented. The lowest broad-area threshold is 1.36 kA/cm2, which is 30% lower than the best value previously reported for 1.55 ?m lasers. This improvement is believed to be related to the absence of terracing on InGaAsP confining layers.     

Business and residential services for the evolving subscriber loop

The role of new loop technologies in providing new and valuable services from increasingly dynamic and intelligent networks is examined. Important market trends in business services are discussed, and the needs of large business customers are considered. Evolutionary service opportunities for the low-end market are identified. It is shown that meeting the total communications needs of large corporate enterprises necessarily involves providing much improved communications capabilities to the low end of the market. The role of the advanced intelligent network is considered