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81.
In GaN high-electron-mobility transistors, electrical degradation due to high-voltage stress is characterized by a critical voltage at which irreversible degradation starts to take place. Separately, cross-sectional TEM analysis has revealed significant crystallographic damage for severely degraded devices. Furthermore, a close correlation between the degree of drain current degradation and material degradation has been reported. However, the role of the critical voltage in physical degradation has not been explored. In this work, we investigate the connection between electrical degradation that occurs around and beyond the critical voltage and the formation of crystallographic defects through detailed electrical and TEM analysis, respectively. We find that a groove in the GaN cap starts to be generated around the critical voltage. At higher voltages, a pit develops that penetrates into the AlGaN barrier. The size of the pit increases with stress voltage. We also observe a good correlation between electrical and material degradation. 相似文献
82.
Anna Ostroverkh Martin Dubau Peter Kúš Stanislav Haviar Michal Václavů Břetislav Šmíd Roman Fiala Yurii Yakovlev Yevhenii Ostroverkh Viktor Johánek 《国际能源研究杂志》2020,44(6):4641-4651
An ultra-low-platinum catalyst based on finely dispersed platinum (Pt) deposited on a highly porous complex microporous layer was investigated as a candidate of durable anode catalyst for hydrogen oxidation reaction (HOR) in proton exchange membrane fuel cells. Etching of teflonated and nitridized base carbon substrate in oxygen plasma and simultaneous deposition of cerium oxide were applied to increase active surface area and electrochemical activity of the platinum nanocatalyst. Ultra-low loadings of Pt (between 0.85 and 8.5 μg cm−2) deposited by magnetron sputtering on this substrate were assembled with Nafion 212 membrane and commercially available Pt/C cathodes (300-400 μg cm−2 Pt). Such membrane electrode assembly (MEA) with extremely low Pt content at anode can deliver high output power densities, reaching 0.95 W cm−2 or 0.65 W cm−2 with only 1.7 μg cm−2 of Pt, using H2 as fuel and pure O2 or air as an oxidant, respectively. Although electrocatalysts with highly dispersed active metals are known to often suffer from irreversible degradation, the above MEAs proved to be very stable when the cell was subjected to a durability test under heavy duty conditions of on/off cycling. The system with lower Pt content is more prone to water flooding which can, however, be eliminated by maintaining better control over the fuel humidity. Average decay of the cell voltage less than 50 μV h−1 was obtained in the cycling regime, while excellent stability <10 μV h−1 is achievable under the static load of 0.4 A cm−2. 相似文献
83.
Three experiments investigated whether 14- and 15-month-old infants use information for both friction and slant for prospective control of locomotion down slopes. In Experiment 1, high- and low-friction conditions were interleaved on a range of shallow and steep slopes. In Experiment 2, friction conditions were blocked. In Experiment 3, the low-friction surface was visually distinct from the surrounding high-friction surface. In all three experiments, infants could walk down steeper slopes in the high-friction condition than they could in the low-friction condition. Infants detected affordances for walking down slopes in the high-friction condition, but in the low-friction condition, they attempted impossibly slippery slopes and fell repeatedly. In both friction conditions, when infants paused to explore slopes, they were less likely to attempt slopes beyond their ability. Exploration was elicited by visual information for slant (Experiments 1 and 2) or by a visually distinct surface that marked the change in friction (Experiment 3). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
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86.
Chimeric MLL products with a Ras binding cytoplasmic protein AF6 involved in t(6;11) (q27;q23) leukemia localize in the nucleus 总被引:1,自引:0,他引:1
T Joh K Yamamoto Y Kagami H Kakuda T Sato T Yamamoto T Takahashi R Ueda K Kaibuchi M Seto 《Canadian Metallurgical Quarterly》1997,15(14):1681-1687
In infantile leukemias and therapy-related leukemias, the MLL gene is frequently found to be disrupted and fused to various translocation partner genes, such as AF4/FEL, LTG9/AF9 and LTG19/ENL as a result of 11q23 translocations. We previously showed that the N-terminal portion common to various chimeric MLL products, as well as to MLL-LTG9 and MLL-LTG19, localizes in the nuclei, and therefore suggested that it might play an important role in leukemogenesis. In the present study, MLL-AF6 chimeric products found in the t(6;11)(q27;q23) translocation were analysed since AF6, a Ras-binding protein, exhibits a different subcellular localization from that of LTG9/AF9 and LTG19/ENL. Immunofluorescence staining data and cell fractionation analyses demonstrated that MLL-AF6 chimeric products localize in the nuclei despite the fact that AF6 itself localizes in the cytoplasm, confirming the importance of the nuclear localization of chimeric MLL products. The region in the N-terminal portion of MLL responsible for this nuclear localization was examined and found to be a region containing AT-hook motifs. 相似文献
87.
Viktor Johánek Petr Švenda Karel Mašek 《International Journal of Hydrogen Energy》2021,46(33):17197-17208
Methanol oxidation catalyzed by bi-layered or mixed oxides of cobalt and cerium was studied at atmospheric pressure by temperature-programmed reaction technique. The catalysts were deposited in the form of thin films by magnetron sputtering from Co and CeO2 targets, forming double layer structures of CeO2/CoOx or CoOx/CeO2. Reaction selectivity and hydrogen production rates were monitored at O2:CH3OH reactant stoichiometries varied in the range 4:1–1:4, spanning from oxygen rich to oxygen lean reaction conditions. A complementary information in regard to thermal stability of the catalytic layers was obtained by X-ray photoelectron spectroscopy. A strong synergistic interaction between cerium and cobalt within the mixed oxide (driving dynamics of the Co2+/Co3+ and Ce4+/Ce3+ redox pairs and oxygen exchange) leads to a bi-functional catalyst. Particularly the CeO2/CoOx configuration proved to be significantly more active than the CoOx alone and more stable, especially under reducing environments. Further optimization of reactivity can be provided via control of the adlayer coverage. 相似文献
88.
We have electrically stressed GaN High Electron Mobility Transistors on Si substrate at high voltages. We observe a pattern of device degradation that differs markedly from previous reports in GaN-on-SiC HEMTs. Similarly to these devices, the gate leakage current of GaN-on-Si HEMTs increases by several orders of magnitude at a certain critical voltage and this increase is irreversible. However, in contrast with devices on SiC, the critical voltage varies substantially across the wafer, even over short distances, with values as high as 75 V being observed. In addition, for voltages below the critical voltage, we observe a prominent degradation in the drain current and the source and drain resistances, something not observed in devices on SiC. This degradation is almost completely recoverable under UV illumination. We attribute these results to the high mismatch that exists between GaN and Si that leads to a large concentration of electrically active traps and a lower and non-uniform initial strain in the AlGaN barrier. This is evidenced by observed correlations between threshold voltage and maximum drain current in fresh devices and their corresponding critical voltages. 相似文献
89.
Moriyama T Shindoh K Taguchi Y Watanabe H Yasui A Joh T 《Shokuhin eiseigaku zasshi. Journal of the Food Hygienic Society of Japan》2003,44(3):145-149
Milled rice and bran were prepared from brown rice (Oryza sativa japonica) using a commercial scale rice-mill to investigate the changes in cadmium (Cd) content caused by the milling process. Rice sample solution was prepared by microwave digestion using HNO3 and HF, then analyzed by ICP-MS. Cd was measured at m/z 114 in interference correction with MoO and Sn. The digestion method was validated with 4 kinds of certified reference material of "rice flour". We found that the Cd content was reduced only slightly by the milling process. When the Cd concentration of brown rice was regarded as 100, the relative content of the milled rice was 97 (average of 6 samples). In addition, the reduction of the Cd content was only slight when milled rice was processed to "wash-free" rice. The relative Cd content of the bran was 139 when that of brown rice was regarded as 100. These results support the hypothesis that the Cd content is not greatly decreased by the milling process. 相似文献
90.
A rapid and inexpensive procedure to detect polychlorinated biphenyls (PCBs) in transformer oil is needed to facilitate identification and removal of PCB contaminated transformers. Here we describe a simple two-step liquid-liquid extraction using acidic dimethyl sulfoxide in conjunction with an immunoassay for detecting PCBs in transformer oil. The process described is faster and simpler than any previous immunoassay while maintaining comparable detection limit and false negative rate. Cross reactivity data, characterizing the immunoassay response to the four Kanechlor technical mixtures of PCBs in oil, are presented. Forty-five used transformer oil samples were analyzed by gas chromatography-high-resolution mass spectrometry and were also evaluated using the immunoassay protocol developed. Results presented show zero false negatives at a 1.4 ppm nominal cutoff for the transformer oils analyzed. 相似文献