高压P-i-N二极管关断瞬态综合失效机理分析

针对商用高电压大功率多芯片P-i-N二极管在钳位型电感负载电路中,在额定电气参数下发生的瞬态失效现象,分别从电路布局和器件机理层面讨论了各因素对二极管芯片失效的作用影响。首先,通过考察二极管模块内部失效芯片的位置和故障波形,得出整个电力电子装置的可靠性是由失效风险最高的局部芯片决定而非由功率模块的坚固性决定。其次,根据二极管芯片在深度动态雪崩情况下所产生丝状电流的现象,得出由芯片电流密度不均所引发的结温-电流密度正反馈机制是导致多芯片功率模块失效的最终原因。最后,根据失效表征与测试条件,提出了由综合失效诱因导致的多芯片模块动态失效新模式。结论表明本文讨论的大功率多芯片模块所发生的失效现象,是多失效诱因综合作用所引发的,而非单一因素超限的结果。

Ground response and failure mechanism of gob-side entry by roof cutting with hard main roof

This study is the result of long-term efforts of the authors’team to assess ground response of gob-side entry by roof cutting(GSERC)with hard main roof,aiming at scientific control for GSERC deformation.A comprehensive field measurement program was conducted to determine entry deformation,roof fracture zone,and anchor bolt(cable)loading.The results indicate that GSERC deformation presents asymmetric characteristics.The maximum convergence near roof cutting side is 458 mm during the primary use process and 1120 mm during the secondary reuse process.The entry deformation is closely associated with the primary development stage,primary use stage,and secondary reuse stage.The key block movement of roof cutting structure,a complex stress environment,and a mismatch in the supporting design scheme are the failure mechanism of GSERC.A controlling ideology for mining states,including regional and stage divisions,was proposed.Both dynamic and permanent support schemes have been implemented in the field.Engineering practice results indicate that the new support scheme can efficiently ensure long-term entry safety and could be a reliable approach for other engineering practices.

Soil Erosion Changes over the Past Five Decades in the Red Soil Region of Southern China

This paper reports the dynamic changes of soil and water loss in the red soil region of Southern China since the 1950s. The red soil region covers eight provinces: Jiangxi, Zhejiang, Fujian, Anhui, Hubei, Hunan, Guangdong and Hainan. From the 1950s to 1986, the annual rate of soil erosion increased by 3.4%. From 1986 to 1996 and from 1996 to 2000, the annual rates of soil erosion decreased by 2.0% and 0.32%, respectively. Field surveys showed that from 2000 to 2005, the area of soil and water loss decreased annually by 1.2%. This decrease was a result of large-scale erosion control activities across China. Although the eroded soil has been restored, the restoration process is very slow and full restoration will take a long time. Our report suggests that controlling soil and water loss is a challenging task, and additional measures must be taken to effectively control the soil erosion in the red soil region.

Research on Occurrence Mechanism of Public Security Emergency from the perspective of the Structure Box

Public security emergency is a public crisis event, and we cannot anticipate the specific time, actual scale, specific situation and influence depth of emergencies. If the emergencies are not under control, the crisis will get worse and its destructive energy will be released quickly.Structure box is an invisible closed system which is constructed by local politics, economy, and culture. Namely, structure box is local social ecological environment. Structure box is a closed area which is full of anger. Therefore, in such environment with too much pressure, we need an outlet to release pressure. Anger is the social and psychological basis of the emotional resonance of onlooker, when the fuse incident occurred, so that the widespread anger in structure box will find the spotlight. The words and actions of the leaders in the informal group will produce a great social infection and circulatory response, and groups’ stirring will cause emotional resonance which is easy to burst. Thus, irrational behavior may caused by people. This processcan use five links to describe： occurrence of fuse events, information diffusion, emotional resonance, situational catalysis, control failure, and occurrence of public security emergency. This is the occurrence mechanism of public security emergency.

旋流中钉螺运动数值模拟

钉螺是日本血吸虫的唯一中间宿主,研究其在水中的沉降特性与运动特征对防治血吸虫病具有重要意义。该文运用文献中的实测资料对钉螺自由态以及失控态的沉降速度及阻力系数进行了研究;提出了旋流排螺的设想,构建了三维数学模型模拟旋流装置中的水流及钉螺的运动,并对该模型进行了验证计算,结果表明,模型验证的计算成果与已有实测资料吻合良好。