Electron irradiation-induced destruction of carbon nanotubes in electron microscopes

Observations of carbon nanotubes under exposure to electron beam irradiation in standard transmission electron microscope (TEM) and scanning electron microscope (SEM) systems show that such treatment in some cases can cause severe damage of the nanotube structure, even at electron energies far below the approximate 100 keV threshold for knock-on damage displacing carbon atoms in the graphene structure. We find that the damage we observe in one TEM can be avoided by use of a cold finger. This and the morphology of the damage imply that water vapour, which is present as a background gas in many vacuum chambers, can damage the nanotube structure through electron beam-induced chemical reactions. Though, the dependence on the background gas makes these observations specific for the presently used systems, the results demonstrate the importance of careful assessment of the level of subtle structural damage that the individual electron microscope system can do to nanostructures during standard use.     

微米Wp/Cu基复合材料耐磨行为

以微米级的钨粉和铜粉为原料,采用冷压烧结方法制备出Wp/Cu基复合材料,并进行了热挤压加工,考察了该材料的耐磨行为。结果表明:该复合材料不仅具有良好的抗磨性能,而且适宜同40Cr钢组成在油润滑条件下工作的摩擦副;在油润滑条件下,其磨损体积损失仅是QSn6.5-0.4的11.6%,磨损表面呈Cu基体、凸出Wp和少量孔隙的耐磨组织,并且未发现来自40Cr钢的转移物。     

基于SPS-热轧法钨颗粒增强铝基复合材料微观组织及力学性能研究

本文采用放电等离子烧结→热轧制方法制备了颗粒含量为1～7%的钨颗粒增强铝基复合材料,研究钨颗粒含量对复合材料的微观组织、机械性能和导电性能的影响。研究结果表明：钨颗粒均匀的分布在基体铝合金当中,W/Al界面之间达到了冶金结合,在界面处存在元素扩散和WAl12金属间化合物的生成。在复合材料中,随着钨颗粒含量的增加,复合材料的致密度和韧性降低而拉伸强度呈现先升高后降低的趋势。其中,1和3 vol.% W/Al复合材料的拉伸强度和断裂韧性分别为192.85 MPa (16.84%) 和315.18 MPa (11.93%)。此外,W/Al复合材料具有良好的电导率,W颗粒的含量对复合材料的影响较小。     

基于集合覆盖的Wp方法测试集约简方法

为了提高测试效率,提出一种基于集合覆盖的测试集约简方法.该方法对有限状态机(finite state machine,FSM)模型中经典的测试生成算法Wp方法(部分W方法)所生成的测试集进行冗余约简.通过分析Wp方法的特点,找出测试序列之间包含关系的规律,删除冗余的测试用例.理论分析和实验结果表明:该方法能够有效约简测试集,并且不改变故障检测能力.     

Swift heavy ion induced modifications of fullerene C70 thin films

Modifications of the C₇₀ molecule (fullerene) under swift heavy ion irradiation are investigated. C₇₀ thin films were irradiated with 120 MeV Au ions at fluences from 1 × 10¹² to 3 × 10¹³ ions/cm². The energetic ion impacts lead to the destruction of the C₇₀ molecule. To investigate the stability of C₇₀ fullerene, the damage cross-section and radius of the damaged cylindrical zones are evaluated by fitting the evanescence of C₇₀ vibration modes recorded by Raman spectroscopy. Conductivity measurements together with Raman and optical absorption studies revealed that an irradiation fluence of 3 × 10¹³ ions/cm² results in complete amorphization of the carbon structure of the fullerene molecules.     

基于UML时序图的集成测试序列自动生成

该文研究了基于UML时序图的集成测试序列自动生成方法。该方法分析了时序图的语义信息并添加语义约束规约生成可测试模型,从中提取相关信息生成有限状态机;然后使用Wp方法构造测试序列;最后使用中国邮递员算法对Wp方法进行改进生成最优测试序列。该方法生成的测试序列长度相对较短,并能充分满足测试用例覆盖需求。