Field test and EMTP simulation of transient voltages when clearing a transformer secondary fault

A field test was carried out to investigate a fault clearing transient due to current interruption of a three‐phase to ground fault at the secondary side of a 3‐MVA, 22/6.6‐kV transformer by a vacuum circuit breaker. EMTP simulations in comparison with the measured results have made it clear that the capacitance C_p of a CR divider to measure voltages reduces dv/dt of transient recovery voltage across the circuit breaker by the ratio of (C_t/(C_t + C_p) where C_t is the transformer stray capacitance. The leakage inductance evaluated from the transformer rating has been found to be noticeably greater than that determined from the measured fault current possibly due to the transformer saturation. Considering the transformer magnetizing conductance and selecting an appropriate interrupted current, EMTP simulation gives a satisfactory result compared with a field test. © 1999 Scripta Technica, Electr Eng Jpn, 130(2): 40–48, 2000     

添加合金元素对奥氏体不锈钢等离子渗氮和渗碳的影响

奥氏体不锈钢众所周知有良好的耐蚀性,但是在工业上没有用于承受摩擦的工件上,因为它的硬度低,摩擦磨损性能差。奥氏体不锈钢经低温等离子体渗氮或渗碳能生成一层特殊的氮化物或碳化物层,称为S相,它具有高的硬度和优良的耐蚀性。这项研究中各种奥氏体不锈钢都经低温等离子体渗氮或渗碳,用各种分析技术研究了添加合金元素对S相特性的影响,用了光学显微镜和电子显微镜观察,做了X射线衍射分析,在5%H2SO4溶液中测量阳极极化,用球对平面摩擦装置做摩擦磨损测试。氮化物或碳化物层厚度随处理温度增加而加厚,AISI316钢上生成的渗层厚度是所有的基体钢材中最厚的。超过临界温度,由于氮化铬工碳化铬沉淀使耐蚀性降低。临界温度由渗氮的基材决定。另一方面,在渗碳层中临界温度不随基材变化。大部分样品上S相层的耐蚀性比没有处理的不锈钢的低。但是,AISI316和JIS-SUS304J3钢在400℃渗碳后都有和未处理钢一样优良的耐蚀性。每种不锈钢经渗氮或渗碳后耐磨性都有明显的改进。     

Influence of Slurry Flocculation on the Character and Compaction of Spray-Dried Silicon Nitride Granules

The effect of slurry flocculation on the characteristics of silicon nitride granules prepared by the spray drying process is investigated. The flocculation state of an aqueous silicon nitride slurry is controlled by adding nitric acid and evaluated as a function of pH. Dense and hard silicon nitride granules result from a well-dispersed slurry having a high pH (e.g., 10.8). These hard granules retain their shape in green compacts and form detrimental defects. Lowering the pH of the slurry to a certain value (e.g., pH 7.9) results in slurry flocculation. Granules prepared from this flocculated slurry have low density and low diametral compression strength and contribute to the elimination of large pores in green compacts.     

Enhanced growth inhibition of hepatic multicellular tumor spheroids by lactosylated poly(ethylene glycol)-siRNA conjugate formulated in PEGylated polyplexes

PEGylated polyplexes (lac-PEGylated polyplexes) composed of poly(L-lysine) and lactosylated poly(ethylene glycol)-small interfering RNA conjugate, which inhibits the RecQL1 gene product, were revealed to show an appreciable growth inhibition of multicellular HuH-7 spheroids (human hepatocarcinoma cell lines) for up to 21 days (IC(50)=6 nM); this system used as an in vitro three-dimensional (3D) model mimicking the in vivo biology of tumors. The PEGylated polyplexes thus prepared had a size of approximately 110 nm with clustered lactose moieties on their periphery as targeting ligands for the asialoglycoprotein-receptor-expressing HuH-7 cells. In contrast, OligofectAMINE/siRNA (cationic lipoplex) was observed to have almost no growth-inhibitory effect against HuH-7 spheroids, even though the lipoplex showed a stronger growth-inhibitory effect than the lac-PEGylated polyplexes on conventional monolayer-cultured HuH-7 cells. The FITC-tagged conjugate in the lac-PEGylated polyplexes showed smooth penetration into the HuH-7 spheroids compared with that in the lipoplexes, as observed by confocal fluorescence-scanning microscopy. This indicates that the small size of approximately 100 nm and the reduced nonspecific interaction due to the nonionic and hydrophilic lactosylated PEG layer contributes to the smooth penetration of the PEGylated polyplexes into the spheroid interior, eventually facilitating their uptake into the cells composing the spheroids. Cellular apoptosis indicating programmed cell death was also observed in the HuH-7 spheroids treated with the PEGylated polyplexes, revealing that the observed growth inhibition was indeed induced by the RNAi of the RecQL1 siRNA. These data suggest that the smart PEGylated polyplexes can indeed penetrate into the multiple cell layers of 3D tumor masses in vivo, exerting therapeutic effects through the RNAi.     

Synthesis of Optically Active Dendrimers Having Chiral Bisphosphine as a Core

Summary First and second generation chiral dendrimers P-1G1, P-2G1, P-1G2 and P-2G2 containing chiral bisphosphine as a core were synthesized via a reaction of chiral bisphosphine compound (S,S)-1 with benzyl ether dendrons. This is the first example of chiral dendrimers containing chiral phosphorus atoms. To investigate the effect of chiral phosphorus atoms on their conformations, optically inactive dendrimer P′-2G1 was synthesized as well using optically inactive initiator 1′ which was the mixture of rac-1 ((S,S)-1 and (R,R)-1) and meso-1. Their structures were characterized by ¹H, ¹³C, ³¹P NMR, and HRMS. According to CD measurement, optically active dendrimers exhibited the Cotton effect induced by the chirality of phosphorus atoms, while optically inactive dendrimer P′-2G1 showed no Cotton effect.     

Accuracy of black carbon measurements by a filter-based absorption photometer with a heated inlet

Long-term measurements of black carbon (BC) aerosols by filter-based absorption photometers with a heated inlet (COSMOS) in different regions have been useful in elucidating spatial variations and radiative impacts of BC. Evaluations of mass concentrations of BC (M_BC) measured by the COSMOS have been made by our previous studies through comparisons with other measurement techniques. However, how variations in the microphysical properties of BC and the co-existing light scattering aerosols affect the COSMOS measurements should be evaluated in more detail. In this study, we assessed these potential effects under various field environments in the Arctic and in the East Asia. From the slopes of the correlation plots between the M_BC values measured by the COSMOS and a single-particle soot photometer, the average accuracy of the COSMOS was estimated as ～10% in the M_BC range 1–3000?ng m^?3. On an hourly basis, the estimated sensitivity of the COSMOS M_BC values to the changes in the BC size distributions was less than 10%, within the typical variabilities of BC size at individual observation sites. The COSMOS measurements depended little on the mixing states of BC and the concentrations of co-existing light scattering aerosols, except in the maritime air masses of East Asia, where the relative abundance of sea salt to BC was very high. The M_BC measured by COSMOS also well agreed with elemental carbon measurements. Our results demonstrate the high reliability of COSMOS measurements under various environments.

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