Development of high-performance planar borohydride fuel cell modules for portable applications

Direct borohydride fuel cell (DBFC) as a liquid type fuel cell is promising for portable applications. In this study, we report our recent progress in the micro-fuel cell development. A power density of 80 mW cm⁻² was achieved in passive mode at ambient conditions when using the anode containing nickel, carbon-supported Pd catalyst and Nafion ionomer. Current efficiency was also found to be greatly increased due to the use of Nafion rather than polytetrafluoroethylene (PTFE). Based on improvements on single cell performance, planar multi-cell power modules were assembled to study the feasibility of making high-performance and practical DBFC power units. A power of 2.5 W was achieved in a fully passive eight-cell module after significantly simplifying cell structure.     

Throughput and delay analysis of free access tree algorithm withminislots

An analysis is made of the throughput and delay performance of two classes of free-access tree algorithms with minislots. In one class, binary feedback information is available in minislots, and in the other, ternary feedback information is available. It is shown that the highest maximum throughput 0.56714 is achieved in the limiting case where the number of minislots in a (large) slot is infinity and minislot overhead is zero. A lower bound of the average transmission delays in these algorithms is analytically derived. The obtained lower bound is also a lower bound of the average delay of the whole class of the free-access algorithms     

Mixing of nickel and silicon by incoherent-light-pulse annealing

Mixed layers of Ni and Si were formed by pulsed incoherent-light annealing of Ni thin films evaporated on Si substrates. Incoherent light pulse of 36 μs produced in an arc-discharge plasma system was used as the energy source for annealings. A thin layer (300 Å) of amorphous silicon (a-Si) deposited on 800–1000 Å thick Ni films was found to increase light absorption significantly. The light energy needed to form uniform mixing was measured to be about 23 J/cm². Rutherford backscattering and Auger electron spectroscopy techniques were used for qualitative analysis of a-Si/Ni/Si samples. Optimum operating conditions of the light source was determined.     

Improvement of sensing characteristics of self‐sensing active magnetic bearings

A winding‐current interference model of self‐sensing magnetic bearings (AMBs) and an improvement technique of position‐sensing characteristics are proposed. In the self‐sensing AMB systems, the electromagnets work not only as actuators suspending the rotor but also as position sensors. The self‐sensing position signal, however, includes errors because of nonlinearity of the magnetic circuits. In the proposed model, the current is directly transmitted to the self‐sensing position signal. This transmission means degradation of the self‐sensing characteristics. This winding‐current interference to the self‐sensing signal is reduced by the proposed compensation method. The characteristics of the proposed self‐sensing method agree well with a reference sensor signal up to over 1 kHz. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(2): 70– 77, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20732 Copyright © 2004 Wiley Periodicals, Inc.     

Solid-state diffusion bonding of silicon nitride using titanium foils

This article presents an effective way to control the interfacial reaction during solid-state diffusion bonding of silicon nitride (Si₃N₄) using titanium foils. The interfacial structure and its growth kinetics were analyzed in detail with scanning electron microscopy (SEM), electron-probe microanalysis (EPMA), and X-ray diffraction (XRD). The actual phase sequence of the joint interfaces bonded at temperatures between 1473 and 1673 K is concluded to be Si₃N₄/Ti₅Si₃(N)/α-Ti(N)+Ti₅Si₃(N), which is different from the phase sequence observed at room temperature after bonding. The joints are very weak due to the formation of a brittle Ti₅Si₃(N) layer at the interface. To suppress the growth of the Ti₅Si₃ layer, a nitrogen-solution treatment of titanium foils prior to each bonding experiment is implemented. Although a perfect prevention of the Ti₅Si₃(N) layer formation is not achieved with this treatment, it is shown that the growth of the layer is effectively suppressed enough to improve the joint strength to a level 3 times higher than the case in which pure titanium is employed.     

1330 V, 67 m/spl Omega//spl middot/cm/sup 2/ 4H-SiC(0001) RESURF MOSFET

Design and fabrication of 4H-SiC(0001) lateral MOSFETs with a two-zone reduced surface field structure have been investigated. The dose dependencies of experimental breakdown voltage show good agreement with simulation. Through the optimization of implant dose, high-temperature (1700/spl deg/C) annealing after ion implantation, and reduction of channel length, a breakdown voltage of 1330 V and a low on-resistance of 67 m/spl Omega//spl middot/cm/sup 2/ have been obtained. The figure-of-merit (V/sub B//sup 2//R/sub on/) of the present device reaches 26 MW/cm/sup 2/, being the best performance among lateral MOSFETs reported. The temperature dependence of static characteristics is also presented.     

Ortho-deuterium Raman laser using the S0(2) rotationaltransition in the mid-infrared region

Based on a calculation for the Raman gain coefficient of the S₀(2) transition in ortho-D₂, we have demonstrated the generation of first Stokes waves in the 15-16-μm spectral region. Use of ortho-D enriched by a catalytic converter enabled us to realize efficient conversion at room temperature. Stokes energies as high as 400 mJ were obtained     

X-ray absorption fine structure analysis of local structure of CeO2–ZrO2 mixed oxides with the same composition ratio (Ce/Zr=1)

Three types of CeO₂–ZrO₂ (Ce:Zr=1:1 molar ratio) compounds with different oxygen storage/release capacities (OSCs) were characterized by means of the Ce K-edge and Zr K-edge X-ray absorption fine structure (XAFS). In order to investigate the relationship between the OSC and local structure, the quantitative EXAFS curve-fitting analysis was applied. By enhancing the homogeneity of the Ce and Zr atoms in the CeO₂–ZrO₂ solid solution, the OSC performance increased. Especially, the atomically homogeneous Ce_0.5Zr_0.5O₂ solid solution exhibited the highest OSC among these CeO₂–ZrO₂ samples. Additionally, the local oxygen environment around Ce and Zr was remarkably modified by enhancing the homogeneity of the CeO₂–ZrO₂ solid solution. It was postulated that the enhancement of the homogeneity of the CeO₂–ZrO₂ solid solution and the modification of the oxygen environment would be the source for the OSC improvement.     

Quantum flux parametron: a single quantum flux device for Josephsonsupercomputer

A quantum flux parametron (QFP), a single quantum flux superconductive device that has a potential of up to 100-GHz switching with nW-order power dissipation, is considered. The potential of the QFP and key technologies when QFPs are applied to a Josephson supercomputer are described. Switching speed, stability, and power dissipation of a QFP are discussed. QFP gates, circuits, and systems are next described. Then, ultra-fast clock distribution using a standing wave is explained. High-speed operation at more than 10 GHz and 10¹⁴ error-free operations per QFP have been demonstrated. Finally described is a high-density packaging scheme by three-dimensional integration, which is very important for ultra-high speed circuits because the propagation delay becomes dominant in such circuits