Growth of highly strained GaInAs-GaAs quantum wells on patterned substrate and its application for multiple-wavelength vertical-cavity surface-emitting laser array

We carried out the growth of highly strained GaInAs-GaAs quantum wells (QWs) on a patterned substrate for extending emission wavelength on a GaAs substrate. We examined the shift of photoluminescence wavelength of the QWs and showed a large wavelength shift due to the spatial modulation in well thickness and indium composition. We demonstrated a single-mode multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) array on a patterned GaAs substrate covering a new wavelength window of 1.1-1.2 /spl mu/m. By optimizing pattern shape, we achieved multiple-wavelength operation with widely and precisely controlled lasing wavelengths. The maximum lasing span is as large as 77 nm. We carried out a data transmission experiment through 5-km of single-mode fiber with a 2.5 Gb/s/channel. The total throughput reaches 10 Gb/s. The VCSEL-based wavelength-division-multiplexing (WDM) source would be a good candidate for WDM-LAN beyond 10 Gb/s.     

An analytical study of the effect of a support geometry on frequency shift and support loss of piezoelectric ring-shaped resonators for healthcare and environmental applications

Ring-shaped resonators with one support have been designed in this work. The ring-shaped resonator reacts with a mass perturbation to provide eigenstate or frequency shifts which could transfer to electrical signals by piezoelectric effect. The aforementioned ring-shaped resonator is mainly comprised with a multilayer of Pt/Ti/PZT/Pt/Ti/SiO₂ deposited on the silicon-on-insulator wafer and expected to be a contour mode. In order to estimate the sensitivity of the ring-shaped resonator against the mass perturbation, the theoretical analysis was conducted by ANSYS from two aspects including: (a) the effect of support geometry on frequency shift and support loss (from view point of vibration mode shape); and (b) the mass application methodology. It is found that low-amplitude vibration area is smaller at narrow support, and frequency shift of trapezoid support is higher than that of rectangle support.     

Passive piezoelectric single-side MEMS DC current sensor with five parallel PZT plates applicable to two-wire DC electric appliances without using cord separator

A passive (power-less), non-contact macro-scale piezoelectric bimorph DC current sensor to satisfy the increasing needs of DC power supply for monitoring the electricity consumption by either one-wire or two-wire appliance cord was proposed at our laboratory previously. In present study however, a MEMS-scale piezoelectric single-side DC current sensor, comprised of five parallel PZT plates, was further proposed and micro-fabricated for preliminarily examination. A micro magnet was fixed by manipulator onto the PZT cantilever tip to the theoretically pinpointed position of the center plate. Different from the results of the macro-scale piezoelectric bimorph DC current sensor, impulsive piezoelectric output voltages accompanying with a gradual decrease in decay were detected when the applied DC electric current was varied from 0.5 to 2.5 A. A linear relationship between the detected peak value of the impulse output voltage and the applied DC electric current was also obtained but with a higher slope compared to the result of the macro-scale piezoelectric bimorph DC current sensor.     

An anaerobic bacterium isolated from Japanese spiny lobster Panulirus japonicus

Eight strains of bacteria which could not grow under aerobic conditions, were isolated from Japanese spiny lobster. All the strains were Gram-positive, non-sporeforming cocci, and grew well under anaerobic conditions. The strains required a decreased oxygen tension rather than an increased CO₂ tension. Catalase, oxidase, nitrate reductase and urease were not produced. The strains fermented glucose, cellobiose, trehalose and levulose. Indole and H₂S were not produced. Macromolecule substances including starch, esculin, casein, gelatin and chitin were not hydrolyzed. Lactic acid was the sole product from peptone-yeast extract-Fildes solution-glucose broth. Fermentable carbohydrates were not required. The strains could grow at 20 to 37°C, and required NaCl for growth. From the above results, the strains were identified as anaerobic (aerotolerant) Streptococcus sp.     

Effect of different features to drill-wear prediction with back propagation neural network

In this paper, a back propagation neural network (BPNN) has been applied to predict the corner wear of a high speed steel (HSS) drill bit for drilling on different workpiece materials. Specially defined static and dynamic features extracted by a wavelet packet transform (WPT) from the resultant force converted from thrust and torque together with the cutting conditions (workpiece material, spindle speed, drill diameter, feed rate) are used as inputs to train the network to obtain a better output, drill corner wear. Drilling experiments have been carried out over a wide range and, features newly defined and conventional ones, features extracted from different frequency bands are compared.     

Application of nuclear energy for environmentally friendly hydrogen generation

It is universally admitted that hydrogen is one of the best energy media and its demand will increase greatly in the near future. However, little hydrogen exists naturally, so that how to generate hydrogen without bringing forth much CO₂${}_2$ will be very important research subject. Hydrogen generation from water using nuclear energy is one of the solutions for this problem. Especially, the high temperature gas cooled reactor (HTGR) has a possibility to generate hydrogen economically compared with other types of nuclear reactors. As for long-lived radioactive waste to be generated by nuclear reactors, it is expected to significantly reduce its burden to the human environment by applying transmutation technologies. This report describes the feature of the hydrogen generation with HTGR and the development of the accelerator-driven subcritical system to reduce radioactive waste ongoing at JAEA.     

Novel SiC synthesis method applicable to SiC solid phase sintering

Most of the present production processes of SiC sintered bodies require some powder mixing using a mechanical milling process (ball milling, and so on). In this case, relatively long hours are required, and there is the problem of contamination during the preparation process. To avoid these problems, we developed a new process for obtaining a self-sinterable, stoichiometric SiC powder, whose precursor material is water-soluble; the precursor material was synthesized from aqueous silica and citric acid containing a small amount of aluminum compound. In order to obtain the stoichiometric SiC composition, the above aqueous precursor material was adequately cured in air (200°C-400°C); subsequently carbonization reaction (~800°C) in nitrogen atmosphere, carbothermal reduction (~1600°C) in argon atmosphere, and pressureless sintering (~1900°C) were performed. Among these processes, the curing process (cross-linking process) is very important for obtaining the equivalent composition (silica and carbon) for the subsequent carbothermal reduction. In this study, the adequate curing temperature and suitable preparation condition for the carbothermal reduction were investigated for the production of stoichiometric self-sinterable SiC powder. The pressureless sintered body achieved using the obtained SiC powder demonstrated a desirable trans-crystalline fracture behavior.     

Electron cyclotron resonance plasma production by using pulse mode microwaves and dependences of ion beam current and plasma parameters on the pulse condition

We measure the ion beam current and the plasma parameters by using the pulse mode microwave operation in the first stage of a tandem type ECRIS. The time averaged extracted ion beam current in the pulse mode operation is larger than that of the cw mode operation with the same averaged microwave power. The electron density n(e) in the pulse mode is higher and the electron temperature T(e) is lower than those of the cw mode operation. These plasma parameters are considered to cause in the increase of the ion beam current and are suitable to produce molecular or cluster ions.