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741.
Microcystin-LR(MC-LR) is the most abundant and toxic microcystin congener and has been classified as a potential human carcinogen(Group 2B) by the International Agency for Research on Cancer. However, the mechanisms underlying the genotoxic effects of MC-LR during chronic exposure are still poorly understood. In the present study, human–hamster hybrid(AL) cells were exposed to MC-LR for varying lengths of time to investigate the role of nitrogen radicals in MC-LR-induced genotoxicity. The mutagenic potential at the CD59 locus was more than 2-fold higher(p 0.01) in ALcells exposed to a cytotoxic concentration(1 μmol/L) of MC-LR for 30 days than in untreated control cells, which was consistent with the formation of micronucleus. MC-LR caused a dose-dependent increase in nitric oxide(NO) production in treated cells. Moreover, this was blocked by concurrent treatment with the NO synthase inhibitor NG-methyl-L-arginine(L-NMMA), which suppressed MC-LRinduced mutations as well. The survival of mitochondrial DNA-depleted(ρ0) ALcells was markedly decreased by MC-LR treatment compared to that in ALcells, while the CD59 mutant fraction was unaltered. These results provided clear evidence that the genotoxicity associated with chronic MC-LR exposure in mammalian cells was mediated by NO and might be considered as a basis for the development of therapeutics that prevent carcinogenesis. 相似文献
742.
The dyadic level of conceptualization and analysis: A missing link in multilevel OB research? 下载免费PDF全文
Despite burgeoning multilevel research in organizational behavior over the past two decades, our understanding of dyadic relationships at work remains underdeveloped. Focusing on leader–member exchange, we discuss conceptual and methodological challenges that have hampered research at this level and illustrate how and why such analysis might provide new insights. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
743.
Flame regime of gasoline-air mixture explosion is related to chemical reaction, turbulent flow and heat and mass transfer. Experimental data of gas velocity, pressure and flame temperature of gasoline-air mixture explosion in a tube at the equivalence ratio of 0.72, 1.00 and 1.28 were preliminarily acquired. Then, fluctuating velocities, overpressures, and burned and unburned gas temperatures at early stage (50 ms), intermediate stage (150 ms) and last stage (250 ms) in three explosions were determined through the analysis of the experimental data. Finally, the Damköhler number and Reynolds number of the early, intermediate and late stage were calculated respectively, and the flame regimes for each stage were estimated through the Damköhler number vs. Reynolds number diagram. Results show that all the flames at early, intermediate and late stage of the three explosions have the same regime of flamelets-in-eddies. The conclusions can provide some useful references for further study of the flame regime and the numerical analysis model selection of gasoline-air mixture explosion. 相似文献
744.
以型钢高强混凝土(SRHSC)梁为研究对象,结合SRHSC梁受力机理及承载能力的试验研究成果,提出了极限状态下的承载能力是评价梁力学性能的关键指标,将损伤前后梁正截面抗弯承载力之比和斜截面抗剪承载力之比的均值作为自变量,给出了SRHSC梁损伤表征函数,并借助"预定损伤法",揭示了主要设计参数对SRHSC梁损伤演化的影响规律。研究成果将为建立地震激励下SRHSC框架结构楼层损伤模型提供理论和数据支持。 相似文献
745.
746.
747.
用2,3-二羟基苯甲酸经羟基保护、酰胺化、酯化和去保护4步反应,生成一种新型的四齿丙二酸二(2-(2,3-二羟基苯甲酰胺)乙基)酯配体.采用傅里叶变换红外光谱(FT-IR)、紫外-可见光谱(UV-Vis)、核磁共振氢谱(1H NMR)、核磁共振碳谱(13C NMR)和质谱(MS)对其结构进行了表征.在中性pH值条件下,研究了这种配体对铀酰离子的络合能力.结果表明,丙二酸二(2-(2,3-二羟基苯甲酰胺)乙基)酯配体与铀酰离子的螯合常数为23.2. 相似文献
748.
Objective: This article estimates the safety potential of a current commercially available connected vehicle technology in real-world crashes.Method: Data from the Centre for Automotive Safety Research's at-scene in-depth crash investigations in South Australia were used to simulate the circumstances of real-world crashes. A total of 89 crashes were selected for inclusion in the study. The crashes were selected as representative of the most prevalent crash types for injury or fatal crashes and had potential to be mitigated by connected vehicle technology. The trajectory, speeds, braking, and impact configuration of the selected in-depth cases were replicated in a software package and converted to a file format allowing “replay” of the scenario in real time as input to 2 Cohda Wireless MK2 onboard units. The Cohda Wireless onboard units are a mature connected vehicle technology that has been used in both the German simTD field trial and the U.S. Department of Transport's Safety Pilot project and have been tuned for low false alarm rates when used in the real world. The crash replay was achieved by replacing each of the onboard unit Global Positioning System (GPS) inputs with the simulated data of each of the involved vehicles. The time at which the Cohda Wireless threat detection software issued an elevated warning was used to calculate a new impact speed using 3 different reaction scenarios and 2 levels of braking.Results: It was found that between 37 and 86% of the simulated crashes could be avoided, with highest percentage due a fully autonomous system braking at 0.7 g. The same system also reduced the impact speed relative to the actual crash in all cases. Even when a human reaction time of 1.2 s and moderate braking of 0.4 g was assumed, the impact speed was reduced in 78% of the crashes. Crash types that proved difficult for the threat detection engine were head-on crashes where the approach angle was low and right turn–opposite crashes.Conclusions: These results indicate that connected vehicle technology can be greatly beneficial in real-world crash scenarios and that this benefit would be maximized by having the vehicle intervene autonomously with heavy braking. The crash types that proved difficult for the connected vehicle technology could be better addressed if controller area network (CAN) information is available, such as steering wheel angle, so that driver intent can be inferred sooner. More accurate positioning in the real world (e.g., combining satellite positioning and accelerometer data) would allow the technology to be more effective for near-collinear head-on and rear-end crashes, because the low approach angles that are common in such crashes are currently ignored in order to minimize false alarms due to positioning uncertainty. 相似文献
749.
为研究前车突然切入对驾驶人生理负荷的影响,利用MP150生理监测系统对22名被试进行虚拟驾驶试验。采集记录前车突然切入时被试的生理参数。研究驾驶人心率增长率和心率变异性(HRV)指标与车速、应激距离之间的关系。结果表明:自车速度为100 km/h时,随着前车切入距离从55.6 m减小到27.8 m,被试的平均心率增长率从16.21%增大到23.27%,HRV参数低频(LF)值也呈现下降趋势。前车切入距离一定,随着自车车速从60 km/h增加到120 km/h,被试的平均心率增长率存在显著性差异,平均从13.05%上升到21.85%。差异性检验结果表明,前车切入距离和自车速度发生变化时驾驶人的生理负荷变化趋势一致,但自车速度因素对驾驶人生理负荷的影响程度高于切入距离因素。 相似文献
750.
为揭示可控飞行撞地(CFIT)事故致因规律,根据Reason-SHEL模型得出的10个CFIT事故致因因子,分析从飞行安全基金会数据库中整理出的2006—2011年间40起CFIT事故。在此基础上建立CFIT事故年份-成因列联表,再利用SPSS软件对表格进行对应分析。将事故成因和年份同时反映在二维散点图中,实现数据可视化。最后对图形进行向量、圆心接近点以及区域化等3项分析。根据结果得出,CFIT事故的主成因是人因操作和外界环境;随着年份增加,飞行员状态(药物/疲劳、经验不足)对造成CFIT事故的重要性越来越明显;不同年份有不同的重要致因因子。 相似文献