High radiance InGaAsP/InP lensed LED́s for optical communication systems at 1.2-1.3 µm

The fabrication of high radiance InGaAsP/InP double-heterostructure (DH) surface-emitting LED's at 1.27 μm wavelength has been described. The elimination of the junction misplacement as well as the optimization of the active layer thickness has been found to be important in realizing high quantum efficiency. An ideal DH, free from the junction misplacement, has been fabricated by using Cd as the dopant in the InP carrier confining layer. The active layer thickness for maximum output power has been determined to be1-1.5 mum. Furthermore, a new fabrication technique has been developed and the LED structure, which has a lens monolithically formed on the InP substrate, has been fabricated for the first time at this wavelength. This lensed LED improves the coupling efficiency greatly, 2.7 times that of the flat LED's. A maximum coupled power of approximately 0.20 and 0.31 mW has been attained at 100 mA for 85 μm core, 0.16 NA and 100 μm core, 0.25 NA step index fibers, respectively.     

Design and Performance of a DSI Terminal for Domestic Applications

The development of a microprocessor-controlled 96/48 DSI terminal is described. The terminal is intended for domestic use, and is designed so as to maximize compatibility with existing digital carrier systems, it merges four T1 signals into two T1 compatible bit streams for transmission. The terminal is given sufficient excess capacity to accommodate voiceband data, while retaining toll-grade transmission quality for speech. Implementation approaches and considerations in both calculated and measured system characteristics are described.     

MULTI-OBJECTIVE OPTIMIZATION OF AN AERATION VESSEL FOR WASTE WATER TREATMENT

Aeration is one of the most important processes for waste water treatment. Traditionally, only the cost has been taken into account as a criterion to be optimized in the design of the aeration process. It is highly desirable that two additional criteria be considered. They are satisfaction of the environmental constraint and reduction of the uncertainty caused by the variation in the rate of waste water inflow. Consideration of the three criteria naturally gives rise to a multi-objective optimization problem. The ε-constraint method is employed to generate the trade-off surface that contains the non-inferior solutions. The interactive coordinatewise optimization method, a version of the SWT method, is employed for selection of the preferred solution. In conjunction with these methods, the maximum principle and the max-sensitive method are used.     

Molecular beam epitaxy of CdTe and Hg1-xCdxTe ON GaAs (100)

Using the molecular beam epitaxial (MBE) technique, CdTe and Hg_1-xCd_xTe have been grown on Cr-doped GaAs (100) sub-strates. A single effusion cell charged with polycrystal-line CdTe is used for the growth of CdTe films. The CdTe films grown at 200 °C with a growth rate of ~ 2 μm/hr show both streaked and “Kikuchi” patterns, indicating single crystalline CdTe films are smoothly grown on the GaAs sub-strates. A sharp emission peak is observed at near band-edge (7865 Å, 1.577 eV) in the photoluminescence spectrum at 77 K. For the growth of Hg_1-xCd_xTe films, separate sources of HgTe, Cd and Te are used. Hg_0.6Cd_0.4Te films are grown at 50 °C with a growth rate of 1.7 μm/hr. The surfaces are mirror-smooth and the interfaces between the films and the substrates are very flat and smooth. As-grown Hg_0.6Cd_0.4Te films are p-type and converted into n-type by annealing in Hg pressure. Carrier concentration and Hall mobility of an annealed Hg_0.6Cd_0.4Te film are 1 × 10¹⁷ cm^?3 and 1000 cm²/V-sec at 77 K, respectively.     

Development of in-vessel components of the microfission chamber for ITER

Microfission chambers (MFCs) will measure the total neutron source strength in ITER. The MFCs will be installed behind blanket modules in the vacuum vessel (VV). Triaxial mineral insulated (MI) cables will carry signals from the MFCs. The joint connecting triaxial MI cables in the VV must be considered because the MFCs and the MI cables will be installed separately at different times. Vacuum tight triaxial connector of the MI cable has been designed and a prototype has been constructed. Performance tests indicate that the connector can be applied to the ITER environment. A small bending-radius test of the MI cable indicates no observed damage at a curvature radius of 100 mm.     

Development of lateral displacement sensor for real‐time detection of structural damage

We have developed a novel sensor that enables us to measure the relative story displacement of a building structure in real time. This lateral displacement sensor (LDS) is composed of a light‐emitting diode (LED) array, which is fixed on the ceiling, and a position‐sensitive detector (PSD) unit, which is placed on the floor. We optimized the LDS to achieve high accuracy in lateral displacement measurement. The accuracy was evaluated to be 60 µm by conducting shaking table tests. Two LDSs were implemented in an actual building equipped with an active variable stiffness (AVS) system, and the building was vibrated with seismic waveforms by an exciter placed on the rooftop. The seismic displacement of the second floor relative to the first floor was measured using the LDS. Furthermore, the inclination angle of the second floor could be measured using the LDS during the seismic vibration. Using the AVS system, we realized the residual displacement of the second floor without inducing damage to the building, and succeeded in real‐time residual displacement measurement for the first time. These results indicate that the LDS is useful for the health diagnosis of a building structure. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Numerical simulation of particulate cake formation in cross-flow microfiltration: Effects of attractive forces

We present a two-dimensional simulation model to explore cake formation in cross-flow filtration. The model uses the lattice Boltzmann method (LBM) for fluid computation and the discrete element method (DEM) for particle computation; they were fully coupled with the smoothed profile method. We verified our model by simulating filtration under different transmembrane pressures. We then investigated the effects of attractive forces and particle concentration on the cake formation mechanism. Generally, as the attractive interaction and particle concentration increased, the particles formed a cake layer with a looser body and rough surface, due to the decrease in the mobility of the particles in contact with the cake surface. It is concluded that the effects of particle concentration are affected by the different conditions of attractive interactions between the particles.     

Japanese contribution to the DEMO-R&D program under the Broader Approach activities

Several technical R&D activities mainly related to the blanket materials are newly launched as a part of the Broader Approach (BA) activities, which was initiated by the EU and Japan. According to the common interests for these parties in DEMO, R&Ds on reduced activation ferritic/martensitic (RAFM) steels as structural material, SiC_f/SiC composites as a flow channel insert material and/or alternative structural material, advanced tritium breeders and neutron multipliers, and tritium technology are carried out through the BA DEMO R&D program, in order to establish the technical bases on the blanket materials and the tritium technology required for DEMO design. This paper describes overall schedule of those R&D activities and recent progress in Japan carried out by JAEA as the domestic implementing agency on BA, collaborating with Japanese universities and other research institutes.     

A 128 Kb/s Hi-Fi audio codec based on adaptive transform codingwith adaptive block size MDCT

A Hi-Fi audio codec with an improved adaptive transform coding (ATC) algorithm is presented using digital signal processors (DSPs). An audio signal with a 20 kHz bandwidth sampled at 48 kHz is coded at a rate of 128 kb/s. The algorithm utilizes adaptive block size selection, which is effective for preecho suppression. A modified discrete cosine transform (MDCT) with a simple window set is employed to reduce block boundary noise without decreasing the performance of transform coding. In addition, a fast MDCT calculation algorithm, based on a fast Fourier transform, is adopted. Weighted bit allocation is employed to quantize the transformed coefficients. The codec was realized by a multiprocessor system composed of newly developed DSP boards. Subjective tests with the codec show that the coding quality is comparable to that of compact disc signals     

Tandem Transcoding Without Distortion Accumulation

A simple and universal PCM/ADPCM transcoding algorithm, which does not accumulate distortion in multiple code conversions between PCM and ADPCM, has been derived by thoroughly investigating the PCM-ADPCM-PCM code conversion process. Conditions to avoid distortion in code conversions are clarified by newly introduced mathematical expressions for ADPCM and PCM quantization processes. These expressions can be utilized to simplify a code conversion process without losing generality. Distortion reduction on a code conversion can be realized by adding some functions to the ADPCM decoder output portion. This distortion reduction technique is shown to assure no distortion accumulation in tandem code conversions. In contrast to other reported techniques for tandem conversions, the proposed method is free from applied ADPCM structures, as well as being the simplest among them. As the mathematical treatment is so general, this technique can be applied to code conversions other than PCM/ADPCM conversions.