Inhibition of small G proteins by clostridium sordellii lethal toxin activates cdc2 and MAP kinase in Xenopus oocytes

The lethal toxin (LT) from Clostridium sordellii is a glucosyltransferase that modifies and inhibits small G proteins of the Ras family, Ras and Rap, as well as Rac proteins. LT induces cdc2 kinase activation and germinal vesicle breakdown (GVBD) when microinjected into full-grown Xenopus oocytes. Toxin B from Clostridium difficile, that glucosylates and inactivates Rac proteins, does not induce cdc2 activation, indicating that proteins of the Ras family, Ras and/or Rap, negatively regulate cdc2 kinase activation in Xenopus oocyte. In oocyte extracts, LT catalyzes the incorporation of [14C]glucose into a group of proteins of 23 kDa and into one protein of 27 kDa. The 23-kDa proteins are recognized by anti-Rap1 and anti-Rap2 antibodies, whereas the 27-kDa protein is recognized by several anti-Ras antibodies and probably corresponds to K-Ras. Microinjection of LT into oocytes together with UDP-[14C]glucose results in a glucosylation pattern similar to the in vitro glucosylation, indicating that the 23- and 27-kDa proteins are in vivo substrates of LT. In vivo time-course analysis reveals that the 27-kDa protein glucosylation is completed within 2 h, well before cdc2 kinase activation, whereas the 23-kDa proteins are partially glucosylated at GVBD. This observation suggests that the 27-kDa Ras protein could be the in vivo target of LT allowing cdc2 kinase activation. Interestingly, inactivation of Ras proteins does not prevent the phosphorylation of c-Raf1 and the activation of MAP kinase that occurs normally around GVBD.     

抗氧化三维纤维增强酚醛气凝胶的性能

采用低密度三维刚性结构作为增强体,利用Si-B-C陶瓷先驱体对纤维进行抗氧化防护,并在纤维骨架的孔隙中填充纳米隔热酚醛树脂,形成了一种抗氧化三维纤维增强酚醛气凝胶材料(三维结构热防护材料).该材料密度从0. 3 g/cm3 提升至0. 7 g/cm3 ,其弯曲强度从12 MPa提升至57 MPa,拉伸强度从10 MPa提升至46 MPa,压缩强度从2 MPa提升至18 MPa,比热容维持在1. 07～1. 1 J/(g·K),热导率从0. 078 W/(m·K)提升至0. 12 W/(m·K).经15 min、2 000 ℃的电弧风洞烧蚀后,该材料后退量为10 mm.综合热力性能测试表明,该材料具有优异的力学强度和抗失效能力,而且纤维采用先进的抗氧化处理,在烧蚀过程中利用原位陶瓷化反应,提升了高温抗烧蚀能力,这种三维结构能够实现多种复杂构型近净尺寸成型,有效提升了防热材料的一体化制备、高效装配的任务适应能力.该类材料在载人航天、高超飞行器防热结构中具有广阔的应用前景.     

铸造Al-Pb轴承合金的组织和性能

利用一种新的搅拌铸造技术生产系列铸造铝铅合金,含铅量的变化范围在ω（Ｐｂ）－０￣２５％,试验中,研究了铸态铝铅合金的显微组织和力学性能。结果表明,在研究的含铅量范围内,铸态合 硬度、抗拉强度和虎率都随铅的质量分数的增加而下降。断口分析表明,随质量分数的增加断口特征逐渐由塑性向脆性转变。而摩擦磨损性能随铅的质量分数的增加有一最佳值,即铅的质量分数为１５－２０％时,其磨损量和摩擦系数最小。     

高模量碳纤维在中国宇航结构产品上的应用现状及实现自我保障的建议

实现高模量碳纤维复合材料的自我保障对中国国防建设与航天事业发展具有重要的战略与实践意义.重点介绍了高模量碳纤维在中国宇航结构产品上的应用现状及需求,阐述了高模量碳纤维的特点、制备工艺、关键技术及研究现状等,分析了现阶段中国高模量碳纤维发展存在的主要问题,有针对性的提出了实现自我保障的建议.     

用方坯连铸机生产焊条钢

论述采用连铸工艺生产焊条钢时在冶炼、脱氧合金化、浇注等过程中出现的问题，并提出了解决这些问题的相应措施。     

Amebic liver abscess of unusual presentation

A 35-year-old male who had travelled extensively in the tropics presented with severe anorexia and vomiting associated with fever of 39-40 degrees C during a 4-day period. The clinical findings were entirely negative. In 1973, he had been given metronidazole for amebic dysentery, since when recurrent attacks of diarrhea and abdominal pain had been treated with iodoquinoleines. Stool examination was negative for amebae. Liver scan revealed a suspect "expansive process" in the right lobe. The presumptive diagnosis of amebic abscess was made and metronidazole therapy was started. In less than 24 h the patient became afebrile. The abscess was confirmed by a further liver scan. The definitive diagnosis of amebiasis was established 16 days later when the immunofluorescence level, which had been previously negative, became positive 1/480. This case demonstrates the dangers of the indiscriminate use of iodoquinoleines in patients who have travelled in tropical countries. The amebic liver abscess may be silent locally while causing systemic manifestations such as fever. Early treatment of hepatic amebiasis is recommended even with a presumptive diagnosis. Serological tests during the development of an amebic abscess may be negative and should be repeated after several days of therapy.     

Discrete modelling of debris flows for evaluating impacts on structures

Bulletin of Engineering Geology and the Environment - Lahars (volcanic debris flows) are natural phenomena that can generate severe damage and wreak havoc in densely populated urban areas. The...     

武汉火车站玻璃幕墙减振装置模型疲劳试验研究

在分析武汉火车站内桥轨在列车行车激励下的振动规律基础上,提出进站口幕墙与桥轨采取嵌套式自润滑减振滑动支撑连接,采用1∶1减振装置模型在INSTRON疲劳试验机上进行疲劳试验。结果显示该减振装置完好,减振橡胶没有出现损坏现象,说明该装置具有良好的使用寿命,能够减少幕墙的振动响应。本结构设计新颖,维护、更换方便,具有很好的推广使用价值。     

武汉火车站玻璃幕墙减振结构性能研究

桥建合一综合结构体系的提出与应用是大型铁路客运站建设中的一项重大创新,但也带来一系列诸如列车荷载引起结构振动的设计难题.针对武汉火车站工程中铁轨桥梁底部的玻璃幕墙结构进行了静力有限元分析和动力减振性能足尺模型试验研究,检测了玻璃幕墙结构在给定动荷载作用下的整体受力状态及基本工作性能,并对减振装置提出优化的合理性建议.     

航天器用支架复合材料轻量化研究

支架是航天器总装设计的重要组成部分,目前主要采用金属材质铸造成型,质量较大,成品率较低。复杂的太空环境要求支架具有非常高的尺寸稳定性。因此为提高结构刚度和减重,选取典型结构的支架进行轻量化研究。首先,根据碳纤维复合材料的性能参数和支架边界条件建立有限元模型并进行仿真分析;其次,在突破复合材料支架成型技术的基础上完成了复合材料支架的制备;最后,制定试验方案,通过评估金属与碳纤维复合材料支架在正弦与随机振动时的响应,对比了2种支架的力学性能。结果表明:碳纤维复合材料支架具有更优异的力学性能和更轻的质量。