Control of SF6 discharge gap switch by XeCl excimer laser

Experimental studies have been carried out on triggering characteristics of the SF₆ discharge gap switch by use of XeCl excimer laser (wavelength = 308 nm). First, laser irradiation characteristics are studied on a pure SF₆ in the pressure range of p = 160 ～ 3,800 torr. Using a lens of f (focal length) = 133 mm, the laser is irradiated into the gas, where the energy absorption is studied. If the laser is injected into the gas with the energy above a certain threshold for the breakdown, the rate of energy absorption is found to be ～ 17 percent of the incident energy at p > 760 torr. Injecting the laser into the SF₆-filled gap switch (gap length = 7 mm, p = 760 torr), we have studied the triggering characteristics. Excellent triggering characteristics were obtained; delay time for the discharge ～ 20 ns, and the jitter ～ 260 ps when the gap voltage is operated at 99 percent of the self-breakdown voltage. In addition, the triggering characteristics are studied by changing the focusing point axially. It is found that both the delay time and the jitter decrease when the focusing point tends to approach the high-voltage electrodes.     

Electrochemical characteristics of iron carbide as an active material in alkaline batteries

Electrochemical properties of iron carbide (Fe₃C) for use as an alkaline battery anode were investigated during charge–discharge cycles. Results of electrochemical measurements and Mössbauer spectroscopy suggested that Fe₃C is oxidized irreversibly to Fe₃O₄ during discharge processes and that the produced Fe₃O₄ is subsequently changed to Fe(OH)₂ and Fe during the charging process, raising the discharge/charge capacity in further galvanostatic cycles. In addition, the electrode particles were observed to be less than 100 nm in diameter and to be highly dispersed on the surface of carbon black. These phenomena seems to be caused by dissolution and deposition of Fe(OH)₂ and Fe via intermediate iron species, leading to exposure of a fresh Fe₃C surface to the electrolyte after the second discharge.     

Development of a 3-D simulation analysis system for PWR control rod drive mechanism

A 3-D virtual analysis system to analyze the motion of control rod drive mechanism (CRDM) was developed. The analysis system consists of a 3-D model established as per the actual dimensions and interfaces of CRDM parts and a routine to calculate the forces acting on the mechanism, and was verified by mock-up test using the same equipment as the actual product. The analysis system is useful for functional evaluation in maintenance or to factor out root causes in the case of malfunction of CRDM.     

Heat transfer and pressure loss characteristics of a heat exchanger for recovering latent heat (effects of straight fin length and fin pitch on the heat transfer and pressure loss characteristics)

In recent years, the requirement for the reduction of energy consumption has been increasing to solve the problems of global warming and the shortage of petroleum resources. A latent heat recovery type heat exchanger is one of the effective methods for improving thermal efficiency by recovering latent heat. This paper describes the heat transfer and pressure loss characteristics of a latent heat recovery type heat exchanger having straight fins (fin length: 65 mm or 100 mm, fin pitch: 2.5 mm or 4 mm). These were clarified by measuring the exchange heat quantity, the pressure loss of the heat exchanger, and the heat transfer coefficient between the outer fin surface and gas. The effects of fin length and fin pitch on heat transfer and pressure loss characteristics were clarified. Furthermore, equations for predicting the heat transfer coefficient and pressure loss which are necessary for heat exchanger design were proposed. ©2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(4): 230– 247, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20153 Copyright © 2004 Wiley Periodicals, Inc.     

Simultaneous induction of calcium transients in embryoid bodies using microfabricated electrode substrates

Precise control of differentiation processes of pluripotent stem cells is a key component for the further development of regenerative medicine. For this purpose, combining a cell-aggregate-size treatment for regulating intercellular signal transmissions and an electrical stimulation technique for inducing cellular responses is a promising approach. In the present study, we developed microfabricated electrode substrates that allow simultaneous stimulation of embryoid bodies (EBs) of P19 cells. Mouse embryonal carcinoma P19 cells can be induced to differentiate into three germ layers and serve as a promising stem cell model. Microcavity–array patterns were fabricated onto indium–tin–oxide (ITO) substrates using a standard photo-lithography technique, and uniform-sized EBs of P19 cells were inserted into each microcavity. Electrical stimulation was applied to the EBs through substrate electrodes and stimulus-induced intracellular calcium transients were monitored. We confirmed that the developed electrode device could simultaneously stimulate smaller (200 μm diameter) and larger (500 μm diameter) EBs inserted in the microcavities and induce specific spatio-temporal patterns of intracellular calcium transients in the EBs with fine reproducibility. We concluded that the developed microcavity array with embedded electrodes could simultaneously and effectively stimulate uniform-sized EBs inserted in it. Therefore, it is a promising experimental tool for precisely controlling cell differentiation processes.     

Photo atomic layer deposition of transparent conductive ZnO films

Low-resistivity ZnO films were grown by photo atomic layer deposition (photo-ALD) technique using diethylzinc (DEZ) and H₂O as reactant gases. Self-limiting growth was achieved for the temperature range from 105°C to 235°C. It was found that UV light irradiation was very effective to increase the electron concentration of the films and the electron concentration of 5 × 10²⁰ cm⁻³ was achieved even in undoped ZnO. Thus, the resistivity of the films grown with UV irradiation was one order of magnitude less than that grown without UV irradiation. The minimum resistivity of 6.9 × 10⁻⁴Ω cm was obtained by photo- ALD method without any intentional doping.     

Fabrication of dense β-calcium orthophosphate with submicrometer-sized grains and its high-temperature superplastic deformation

High-density β-calcium orthophosphate (β-Ca₃(PO₄)₂, also called β-tricalcium phosphate: β-TCP) ceramics with submicrometer-sized grains were fabricated using a pulse-current pressure firing route. The maximum relative density of the β-TCP compacts was 98.7% at 1050 °C and this was accompanied by a translucent appearance. The mean grain size of the β-TCP compacts increased slightly with temperature to reach 0.78 μm at 1000 °C. However, upon further increasing the firing temperature to 1050 °C the mean grain size increased significantly to 1.6 μm. The extent of plastic deformation during tensile testing was examined at temperatures between 900 and 1100 °C using a strain rate in the range 9.26 × 10⁻⁵ to 4.44 × 10⁻⁴ s⁻¹. The maximum tensile strain achieved was 145% for a test temperature of 1000 °C and strain rate of 1.48 × 10⁻⁴ s⁻¹ and this was attributed to the relatively high density and small grain size.     

Control of wetting on Ti-based bulk metallic glass surfaces by a hydrothermal method

The surfaces of the Ti-based bulk metallic glasses (Ti₅₀Ni₂₀Cu₂₅Sn₅) were modified by a hydrothermal method using sodium hydroxide (NaOH) solution, and the surface wettability was investigated. No reflections were observed in the XRD patterns of the NaOH-treated samples even though there was a clear change of the color, indicating formation of amorphous oxide phases. The Raman spectra showed peaks attributed to sodium titanate compounds (Na–O–Ti) and titanium oxide. Some of the samples were observed to have a very rough surface microstructure such as a “house-of-cards” or leaf-like structure. The water contact angle of the treated samples decreased with increasing treatment temperature and time. These results indicate that the wettability of the sample surface was able to be controlled from hydrophobic to hydrophilic by changing the conditions of the hydrothermal treatment.     

Effects of heating rate and particle size on pulse electric current sintering of alumina

Two Al₂O₃ powders with different particle sizes were sintered by pulse electric current sintering method at different heating rates. Rapid heating reduced grain growth rate, and the level of reduction depended on the initial powder size and sintering temperature. Under certain conditions, rapid heating could enhance densification.     

Dynamics of an HVDC system in the presence of unbalanced AC transmission line faults and a stabilization scheme

The introduction of an HVDC system into the trunk power supply system requires transmitting as much dc power as possible for improving the whole ac/dc system stability. The continued operation scheme of an HVDC system which makes it possible to operate even under very low commutation bus voltage is adopted to cope with such system requirement. Further stability improvement can be achieved by adding damping control which modulates converter active and/or reactive power. To take full advantage of these control effects, it is essential that the HVDC system can maintain stable operation during the ac system faults and reclosing. Particular attention should be given to a repetitive commutation failure following the unbalanced ac transmission line faults. This paper discusses first the cause of the repetitive commutation failure when supplied with unbalanced ac system voltage based on an experiment using the CRIEPI AC-DC Power System Simulator. Then a stabilization control scheme with an on-line extinction angle estimation is proposed and the effect is verified by digital simulation.