Recent progress in high-power blue-violet lasers

The property of GaInN-AlGaN heterostructures and GaInN multiple quantum well (MQW) gain GaInN laser diodes with low internal loss are described. GaInN blue-violet laser diodes have been developed as a light source for optical disk recording. However, the threshold current density of these diodes has been difficult to reduce and remains high at around 3-4 kA/cm/sup 2/. This is thought to be due to the large transparency current density Jt and the large optical internal loss /spl alpha//sub i/. Recently, the internal loss was successfully reduced to 13.6 cm/sup -1/ by optimizing the design of the near active region and achieved stable continuous operation under 50-mW continuous wave at 70/spl deg/C. Other laser characteristics such as far-field patterns and laser noise have also been improved for optical disk use.     

Risk-informed design of IRIS using a level-1 probabilistic risk assessment from its conceptual design phase

In this study, a probabilistic risk assessment (PRA) for the International Reactor Innovative and Secure (IRIS) has been generated to address two key areas as a part of the effort for the pre-application licensing of the IRIS design.First, the IRIS PRA is supporting the evaluation of IRIS design by providing design insights as well as a solid risk basis for the pre-licensing evaluation of the IRIS design. Second, the current PRA task is beginning the preparation of the more complete PRA analyses and documentation that will be required for Design Certification. The initial IRIS PRA is an at-power, Level-1 PRA for internal events that focuses on the evaluation of the IRIS design features to support the risk-informed design of IRIS by application of the PRA insights and the risk information to the design. To accomplish the evaluation, a reasonably complete Level-1 PRA model has been developed.The use of PRA in the early stages of the design has allowed a selection of design and performance features and an optimization of the design of several systems to reduce the potential for events that could lead to core damage via both enhanced prevention and mitigation of challenges. As a result, the total core damage frequency for internal events for the IRIS design has been calculated as 1.2×10⁻⁸ per year.     

A Microprocessor-Based Motor Speed Regulator Using Fast-Response State Observer for Reduction of Torsional Vibration

A new state observer, which is suitable for microprocessor-based motor drives, and its application to suppression control of shaft torsional vibration are described. A distinct feature of the state observer is that a fast-response load torque estimation is obtained by processing the detected motor current and the encoder output pulses by a hardware circuit for each encoder pulse generation. Suppression control of the shaft torsional vibration is achieved by calculating a compensation signal from the estimated load torque with the microprocessor software. A microprocessor-based speed regulator for dc motor drives, which utilizes the state observer and suppression control of the shaft torsional vibration, was developed for evaluation purposes and tested with a 15-kW dc motor. The load torque of the motor can be estimated accurately, even with a 15-Hz vibration frequency, and the torsional vibration can be eliminated with the proposed suppression control.     

Decrease in Charge of Sharp-Edged Ellipsoidal Particles by Self-Discharge

The saturation charge of conductive sharp-edged ellipsoidal particles imparted by field charging is measured and found to be in agreement with the theoretical value. The saturation charge decreases, however, when the charging electric field exceeds a certain value. When the decrease in the saturation charge takes place, a corona discharge is observed from the particle at its one edge facing downstream in the ion flow. This discharge is referred to as the self-discharge. A theoretical initiation condition of the self-discharge is calculated, considering the field around the ellipsoidal particles. The theoretical initiation condition of the self-discharge is checked by an experiment to measure the electric field strength to initiate the decrease in the saturation charge of two conductive ellipsoidal particles with a = 3.5 mm focal length, ?o = 0.068 eccentricity, and a = 1.87 mm, ?o = 0.1. The theoretical initiation condition of the self-discharge for various sizes of ellipsoidal particles is also calculated to discuss the possibility of the self-discharge taking place with crushed or agglomerated particles.     

Influence of initial CaCl2 concentration on the phase and morphology of CaCO3 prepared by carbonation

Calcium carbonate particles were prepared by bubbling the mixed gas CO₂/N₂ into CaCl₂ solution. The effect of initial CaCl₂ concentration on the morphology and phase of CaCO₃ was discussed with the help of XRD and SEM measurements. The samples prepared at low CaCl₂ concentration composed mainly of spherical vaterite. With the increase of CaCl₂ concentration, more and more rhombic particles were formed and mixed with spherical particles. When the initial CaCl₂ concentration increased to 0.3 mol/L, only rhombic calcite was formed in the final product. The change of CaCO₃ morphology with the increase of CaCl₂ concentration was attributed to the excess of Ca²⁺, which speeded the transformation of vaterite to calcite, thus more rhombic calcite was formed at higher CaCl₂ concentration.     

Influence of crystal orientation on ECAP of aluminum single crystals

A single crystal of high purity aluminum, oriented with the {1 1 1} slip plane and the 1 1 0 slip direction rotated by 20° in a clockwise sense from the theoretical shear plane and the shear direction, was processed by equal-channel angular pressing (ECAP) through a single pass. This configuration was designated the 20° orientation and the results are compared with earlier data obtained on a similar high purity aluminum single crystal in the 0° orientation with the (1 1 1) slip plane and the 1 1 0 slip direction lying parallel to the shear plane and the shear direction. The results show that in both orientations the long axes of the subgrains lie parallel to the slip traces of the primary slip system and the average subgrain widths are 1.3 μm. However, the shearing characteristics are different because the 0° specimen exhibited a conventional B-type rolling texture whereas the 20° specimen deformed by slip on the primary slip system and this system rotated by 40° in a counter-clockwise sense as the specimen passed through the shear zone of the ECAP die.     

Increased enzyme activity in immobilised cell composites with a highly hydrophilic polymer matrix

Streptomyces phaeochromogenes cells were immobilised by radiation polymerisation of hydrophilic monomers; highest levels of glucose isomerase activity were found in immobilised cell composites with highly hydrophilic polymer matrices. The enzyme activity in the composites from the copolymerisation of hydroxyethyl acrylate (or methacrylate) and N-vinyl-2-pyrrolidone monomer increased markedly with increase in the content of the N-vinyl-2-pyrrolidone monomer, owing to the higher water absorption by the polymer matrix, and was close to that of the non-immobilised cells. The enzyme activity was affected by monomer concentration, the hydrophilicity, and chemical structure of the polymer matrix. The Michaelis constant of the composites from hydrophilic monomers was close to that of the intact cells.     

Immobilization of microbial cells on cellulose–polymer surfaces by radiation polymerization

Streptomyces phaeochromogenes cells were immobilized on cellulose–polymer surfaces by radiation polymerization using hydrophilic monomers and paper. The enzyme activity of immobilized cell sheets was higher than that of immobilized cell composites obtained by the usual radiation polymerization technique. The enzyme activity of the sheets was affected by monomer concentration, the thickness of paper, and the degree of polymerization of paper. The copolymerization of hydroxyethyl methacrylate and methoxytetraethyleneglycol methacrylate in the sheets led to a further increase of the enzyme activity due to the increase of the hydrophilicity of the polymer matrix. The Michaelis constant of the sheets from low monomer concentration was close to that of intact cells.     

Carrier trapping centers and interface states induced by r.f. sputtering of molybdenum electrodes in MOS-structure diodes

Electronic properties of interface and oxide layers of Si MOS diodes with an r.f. sputtered molybdenum metal electrodes have been studied. A remarkable density increase of both oxide charge and interface states by the sputtering has been found. IMA data show that the sputtered Mo atoms are implanted into the SiO₂ less than 100 Å from the surface. It is also found from photo I–V data that the charge centroid in the SiO₂ is shifted to a depth of 100 Å below the SiO₂ surface. The energy distribution of the carrier trapping centers having a capture cross section of the order of 10^?13 to 10^?16 cm² has been observed. The interface states density can be reduced about one order of magnitude by an annealing in N₂ 10 min/H₂ 15 min/N₂ 10 min at 450°C. The mechanism of the increase of the carrier trapping centers and the interface states is also studied. Especially it is concluded that the increase of the interface states originates from the ultraviolet-light irradiation emitted from the plasma during the r.f. sputtering.