Breakdown of YBCO thin films during current limiting and methods of improving current limiting performance

We performed fault current limiting tests using YBCO thin films and investigated the reasons for their breakdown during current limiting. There were two patterns of film breakdown. One occurred immediately after current limiting and the other occurred during current limiting. In film breakdown, the quench propagation speed showed almost no change with increasing energy consumption per unit time, but the energy consumption per unit area increased with increasing energy consumption per unit time. Therefore, local areas of the film reached the melting point and arcing occurred. It is therefore concluded that the performance of the films can be improved by decreasing the energy consumption per unit time. Connecting a parallel capacitor to the film in order to limit the energy consumption per unit time is proposed and tested as a measure to improve the current limiting performance of thin films. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(1): 20–27, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20709     

一个NT平台上分布式对象数据库服务器系统

FISH系统是一个用于支持先进应用(如GIS,EC,CIMS)的新一代分布式对象数据库系统.该系统采用了许多新颖技术,如DSVM(distributed shared virtual memory)、持久堆、页式对象、透明锁、紧凑提交等.重点介绍了该系统的总体结构和设计思想,特别是FISH系统在Windows NT上实现所涉及的底层技术,包括内存映射、共享内存、远程过程调用、多线索连接、页面故障处理等.基于OO7的性能测试表明,FISH系统在NT机群环境下取得了与在分布式UNIX环境下同样高的分布执行效率     

High-intensity laser-driven particle and electromagnetic wave sources for science, industry, and medicine

We simultaneously observed both the fast proton generation and terahertz (THz) radiation in the laser pulse interaction with a thin-foil target.The maximum proton energy of ～2.3 MeV and an intense THz radiation were observed at the pulse duration of ～30fs.We also measured the proton beam and UV harmonics from a thin-foil target by changing the laser pulse duration.In the case of the ～500 fs, peaks of UV harmonics up to fourth order appeared.This unique combination of the multiple beams will provide useful applications such as pump-probe experiments.     

Experimental study of squirrel-caged damper structure for superconducting generator

In this paper a double-layer damper is developed which will consist of a squirrelcaged warm damper and a cylindrical cold damper as a part of a 70-MW superconducting generator development project. To evaluate the characteristics of unbalance current capability, magnetic shielding and damping for rotor swing, a one-half scale rotor model is constructed and an experimental study is made. From analysis of the experimental results, design guidelines have been developed and the FEM magnetic field analysis technique is refined. The main results are summarized as follows:

• 1 The squirrel-caged warm damper has sufficient capability against negative sequence current;
• 2 Damping characteristics can be designed to be effective near the rotor swing frequency;
• 3 Flux shielding at low frequencies corresponding to quick response excitation is sufficiently small so as not to prevent field flux change; and
• 4 Magnetic field can be analyzed by the refined FEM field analysis technique which now takes into account the effects of the rotor end region by estimating the end resistance based on the eddy current flow path.

     

Decomposition of nitrous oxide over supported rhodium catalysts and dependency on feed gas composition

The catalytic decomposition of nitrous oxide to nitrogen and oxygen was studied overRh/ZnO, Rh/CeO₂, Rh/ZSM-5, CuZSM-5 and CoAlCO₃HT (hydrotalcite). The effects of metal loading and calcination conditions upon the catalytic performance were examined on Rh/ZnO. A 0.5 wt.% Rh/ZnO catalyst was found to be the most active catalyst, whose reaction rate was 4.0 × 10⁴ μmol(N₂O) · g⁻¹ · h⁻¹ under the conditions of 950 ppm N₂O and 5% O₂ at 300°C. The oxidized Rh/ZnO showed a higher activity than that calcined in a reducing atmosphere. The TEM and EDX observations revealed the formation of particles of ca. 50Åin diameter. They consisted of rhodium and zinc oxides as major and minor components, respectively. The activities of all these catalysts decreased when NO₂ and H₂O were added to the feed.     

Effect of salt on the elastic modulus of poly(N-isopropylacrylamide) gels

The measurement of tensile modulus of poly(N-isopropylacrylamide) (PNIPA) gel in the solution of NaCl, NaI, LiNO₃ and NaNO₃ was carried out. It was confirmed that the tensile modulus of PNIPA gel in the solution of salt depends on the volume of gel regardless of the kind and concentration of salts. This result leads us to the conclusion that the addition of salt effect only on the mixing contribution to the Flory's type free energy of gel especially in the swollen state. Therefore, our result is in agreement with a recent remarkable discovery that the volume of PNIPA gel depends only on the chemical potential of water in spite of the kind of additives. On the other hand, it was found that on the volume phase transition point and in the deswollen state, the elasticity of PNIPA gel depended on the concentration and kind of the salt because the viscoelasticity emerged due to the shrinkage of polymer network.     

Carbon oxidation with platinum supported catalysts

The effect of the support oxide, Pt precursor and reactant gas composition on the catalysis of soot oxidation was investigated using carbon black as a model soot and simulated exhaust gases. The Pt precursors used were Pt(NH₃)₄(OH)₂, H₂PtCl₆·6H₂O, Pt(NH₃)₄(NO₃)₂, and Pt(NH₃)₄Cl₂. The support metal oxides used were SiO₂, Al₂O₃, and ZrO₂. Pt/SiO₂ prepared from Pt(NH₃)₄(OH)₂ showed the highest carbon oxidation activity. It had much higher activity in the condition of N₂+O₂+H₂O+NO+SO₂ than without NO and SO₂.     

Burning velocity measurement of fluorinated compounds by the spherical-vessel method

Burning velocity has been measured using the spherical-vessel (SV) method for four hydrofluorocarbons (HFCs), i.e., difluoromethane (HFC-32), 1,1,2-trifluoroethane (HFC-143), 1,1,1-trifluoroethane (HFC-143a), and 1,1-difluoroethane (HFC-152a). Experiments were conducted for initial pressures in the range 78-108 kPa and initial temperatures in the range 280-330 K, over wide ranges of HFC-air equivalence ratios. The burning velocities were determined from the rate of pressure increase by applying a spherical-flame propagation model. Flame propagation behavior was observed in a cylindrical vessel equipped with optical windows by employing schlieren photography. It was found that the values of burning velocity derived from the spherical-vessel method are in good agreement with the ones obtained with schlieren method. It is found that the SV method is adequate for determining the burning velocity for weakly flammable HFCs as well as for moderately flammable compounds. The burning velocity of each HFC was obtained as a function of temperature, pressure, and equivalence ratio. The maximum burning velocities of HFC-32, HFC-143, HFC-143a, and HFC-152a were determined to be 6.7, 13.1, 7.1, and 23.6 cm s⁻¹, respectively. The maximum burning velocity occurred for slightly fuel-rich concentrations. The magnitude of the burning velocity is strongly dependent on the ratio of H atoms to F atoms in the HFC molecules.     

Effect of vessel size and shape on experimental flammability limits of gases

The flammability limits of methane and propane have been measured using cylindrical vessels of various sizes and one spherical vessel. An ac discharge ignition method has been employed. For a cylindrical vessel of small diameter with a large height, the flammability limits are primarily determined by the quenching effect of the wall. For cylindrical vessels of smaller heights, the experimental flammability limits are affected by hot gas accumulation at the vessel ceiling, unburned gas heating, self heating of the incipient flame by the reflection both from walls and ceiling, and the quenching effect of the walls. If the vessel size is large enough so that all these effects become negligible, the experimental values of flammability limits may approach to the values that would be obtained in free space. In order to approach this condition for a cylindrical vessel, it is desirable to use a container at least 30 cm in diameter and 60 cm in height. For comparison purpose, the measurement has also been done using ASHRAE type 12l spherical flask.     

A middleware for a tabletop procedure-aware information display

In this article, we propose a middleware that supports a developer to build tabletop information display systems. We focus on an application that projects information close to a particular object on a table. To let a user focus on his/her primary task, the information is presented based on a current phase in a procedure, which we call procedure-awareness. Here, a current phase is recognized through the utilization of objects. The proposed middleware separates information from acquisition and presentation mechanisms: sensors for operational context recognition, sensors for object identification/tracking for “nearby presentation”, and projecting information near an object. A developer just needs to write a set of rules, i.e. application logic, that represent contents for particular operational contexts. Also, by implementing appropriate handlers, any content can be provided. We present the design and the implementation of the middleware and validate the expressiveness of application logics through prototype development.