Photocatalytic activities of CdS crystallites embedded in TiO2 gel as a stable semiconducting matrix

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Optimizing the design of large-scale ground-coupled heat pump systems using groundwater and heat transport modeling

In order to predict the long-term performance of large-scale ground-coupled heat pump (GCHP) systems, it is necessary to take into consideration well-to-well interference, especially in the presence of groundwater flow. A mass and heat transport model was developed to simulate the behavior of this type of system in the Akita Plain, northern Japan. The model was used to investigate different operational schemes and to maximize the heat extraction rate from the GCHP system.     

Development of a new seminested PCR method for detection of Legionella species and its application to surveillance of legionellae in hospital cooling tower water

The presence of PCR inhibitors in water samples is well known and contributes to the fact that a practical PCR assay has not been developed for legionella surveillance. In this study, we devised a new seminested PCR assay for detection of Legionella spp. in water samples as a means of overriding the PCR inhibitors without loss of sensitivity. The seminested PCR assay utilized primers to amplify the 16S rRNA gene (LEG primers) of 39 Legionella spp. The assay was specific to legionellae, and the sensitivity was 1 fg of extracted Legionella DNA in laboratory examination. To evaluate the feasibility and sensitivity of the PCR assay in identifying the presence of legionellae, it was used to survey Legionella contamination in the water of 49 cooling towers of 32 hospitals. A commercially available EnviroAmp Legionella kit and a culture method were also used in the survey for comparison with the seminested PCR assay. The detection rates of legionellae in the samples were 91.8% (45 of 49) by the PCR assay and 79.5% (39 of 49) by the culture method. The EnviroAmp kit revealed that 30.6% of the water samples (15 of 49) contained inhibitors of the PCR amplification. However, the seminested PCR assay could produce the Legionella-specific DNA bands in 14 of the 15 samples. Although 8 of the 14 samples were positive in the first-step PCR, 6 of the 14 samples became positive in the second-step PCR. These results suggest that the effect of PCR inhibitors in samples, if any, can be reduced because of the dilution of the sample in the second-step PCR and that sensitivity of detection can be increased by the second-step PCR. Thus, the seminested PCR assay with LEG primers to amplify the 16S rRNA gene of 39 Legionella spp. was a practical and sensitive method to detect Legionella spp. in water samples.     

Nanocrystallization of Fe73.5Si13.5B9Nb3Cu1 soft-magnetic alloy from amorphous precursor in a magnetic field

The effect of a magnetic field on the nature of nanocrystallization from a melt-spun Fe_73.5Si_13.5B₉Nb₃Cu₁ amorphous precursor has been studied with the aim of controlling microstructures and magnetic properties. Annealing for magnetic crystallization was carried out at temperatures between the Curie temperature of the amorphous phase (586 K) and that of the crystalline phase (920 K). It was found that the {110} texture component in crystallized α-Fe(Si) phase increased in importance with increasing magnetic-field strength. An X-ray diffraction analysis based on the Shultz method revealed that the magnetic field caused preferential formation of {110}-oriented nuclei. In addition, the applied field enhanced crystallization kinetics, particularly the nucleation rate. No significant difference in grain growth behavior was observed as a result of applying a magnetic field. We therefore conclude that the development of the {110} texture by magnetic crystallization is predominantly attributable to preferential nucleation, rather than preferential growth, of {110}-oriented nuclei. The saturation magnetization of nanocrystallized specimens, evaluated using a vibrating sample magnetometer (VSM), was increased by the application of a magnetic field up to 4T during nanocrystallization.     

Mode characteristics of the multiple-stripe laser effects of the loss embedded in the outer unpumped region

The criteria for the mode selections in multiple-stripe lasers are presented. It is shown that the couplings of the higher-order modes of each stripe, which constitute the multiple-stripe laser, play important roles in the mode selections. Based on this analysis, a method for realizing 0° phase-shift mode oscillations is proposed. The method involves loss embedment in the outer unpumped region and the use of multiple stripes with fine center-to-center spacings. For the realization of this scheme, a grating-incorporated channeled-substrate planar (GICSP) laser is proposed and is fabricated. It is demonstrated that the 180° phase-shift mode is completely suppressed with this scheme. Single-longitudinal mode oscillations of well-defined index-guided 0° modes are observed for wide-channel CSP lasers.     

Growth and led evaluation ofN-type conductive lec gaas co-doped with in and si

Dislocation-free and low dislocation densityn-type conductive GaAs crystals, 50 mm in diameter, were grown by the In and Si co-doping LEC technique. Two-dimensional LED arrays were fabricated on substrates obtained from these crystals by the MOCVD technique and the influence of the In doping on the LED characteristics was examined. The light output power of LEDs fabricated on co-doped substrate with an In concentration of 1 ×10²⁰atoms/cm³ are low and are non-uniformly distributed, as compared with the boat-grown substrate, even though the co-doped substrate is dislocation-free. However, the LED properties of a substrate with an In concentration of 2 × 10¹⁸atoms/cm³ are the same as those of a boat-grown substrate. The light output power of the LEDs becomes higher as the In concentration in the substrate decreased.     

Nondestructive inspection of thermal barrier coating of gas turbine high temperature components

A thermal barrier coating (TBC) is applied to high‐temperature components in gas turbines, and consists of a ceramic topcoat and a metallic bondcoat. Various kinds of TBC degradation and damage occur in high‐temperature components during service, such as topcoat thinning, topcoat delamination, and formation of a thermally grown oxide (TGO) layer below the topcoat, each of which can be examined using a suitable nondestructive inspection technique. Topcoat thinning can be detected by topcoat thickness measurement using terahertz waves, which are electromagnetic waves in the frequency region between optical and radio waves. The measurement resolution is about 10 μm, which is comparable to microscopic observation of the cross section in destructive inspection. Topcoat delamination can be detected by active thermography, in which the topcoat surface is scanned by a heating laser and the surface temperature distribution is measured by a thermal infrared camera. The combination of temperature peak and residual thermal image detection is effective in eliminating false detection. The TGO layer can be detected using photoluminescence, in which the Cr³⁺ ions included as an impurity in Al₂O₃ are detected. Since delamination tends to occur at locations at which the TGO layer has grown, TGO layer detection provides an effective method to select regions where delamination has occurred or is likely to occur. An inspection flow based on these techniques is proposed, which is expected to aid the establishment of condition‐based maintenance strategies of high‐temperature components. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

High-temperature formation phases and crystal structure of hot-pressed thermoelectric compounds with chalcopyrite-type structure

In this study, we introduced the temperaturedependent formation phases and crystallographic parameters of hot-pressed silver gallium telluride AgGaTe_2 and copper gallium telluride CuGaTe_2 with chalcopyrite structure from 300 to 800 K. These two compounds are potential thermoelectric materials in the intermediate temperature range; however, the temperature-dependent formation phases and crystallographic parameters of hotpressed samples have not yet been analyzed in detail. The crystal structure analysis based on synchrotron X-ray diffraction(SXRD) measurements clarifies that impurity phases such as Te and Ag_2 Te in the AgGaTe_2 matrix and Te and CuTe in the CuGaTe_2 matrix appear at some temperature regions above 300 K. The existence of such impurity phases could be correlated with the increases of the electrical resistivity and Seebeck coefficient of the samples after multiple measurement cycles of the temperature-dependent transport properties from 300 to 800 K.The tetragonal lattice parameters a and c, tetragonal lattice volume, thermal expansion coefficients, tetragonal distortion, anion displacement parameter, and isotropic displacement parameter of the hot-pressed AgGaTe_2 and CuGaTe_2 were also analyzed. These crystallographic parameters are expected to substantially affect the thermoelectric properties of AgGaTe_2 and CuGaTe_2. Our results provide prospect of the long-term high-temperature stability and clues of the detailed analysis on the transport properties of hot-pressed AgGaTe_2 and CuGaTe_2, which should aid their development for thermoelectric applications.