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81.
Bending tests of crystalline nanotubes composed of fullerene C60 molecules are performed inside a high-resolution transmission electron microscope. We fixed one side of a C60 nanotube with a body-centered tetragonal structure with typical inner and outer diameters, i.e., 180 nm and 510 nm, respectively, and then applied concentrated forces on the other side using piezomanipulation of a silicon nanotip. The bending process was observed in situ by transmission electron microscopy with simultaneous measurements of the forces by an optical deflection method. It was found that the Young’s modulus of the nanotube was estimated to be 62–107 GPa, which was 1.1–3.3 times larger than that of C60 nanowhiskers. The result concerning the increase in the Young’s modulus of the C60 nanotube provided an experimental evidence for the structural model composed of an inner core and a surface shell for C60 nanowhiskers. 相似文献
82.
将3组不同纤维体积分数的整体毡采用等温CVD进行沉积热解炭增密,结合CVD沉积过程中整体毡内气体传质数学模型,研究了整体毡的纤维体积分数对CVD增密过程的影响,研究结果表明:纤维体积低的整体毡沉积时增重率高;纤维体积分数高的整体毡容易获得较高密度的C/C复合材料;纤维体积分数超过35%的整体毡经过300 h的化学气相沉积,坯体的体积密度能达到1.52 g/cm~3。 相似文献
83.
84.
Zeolite beta with a low SiO2/Al2O3 ratio was synthesized by a novel two-step process.The synthesized sample was characterized with XRD,SEM,FTIR,and N2 adsorption-desorption and solid-state MAS NMR.The results showed that aluminium species were inserted into the framework of zeolite beta.The BET surface area,volume,and particle size of the zeolite beta sample decreased with decreasing SiO2/Al2O3 ratio.Our process was proved an efficient route to synthesize zeolite beta with a low SiO2/Al2O3 ratio. 相似文献
85.
We investigated the effect of controlled damage on the residual strength, failure mechanism and acoustic emission (AE) activity of graphite epoxy composites. The controlled damage was introduced by indenting unidirectional tensile specimens using a hardness machine with a diamond indentor. The specimens were loaded parallel to the fiber direction. The damage progression mechanisms operating upon subsequent loading and the failure modes were found to be different for sound and indented specimens. The difference in mechanical behavior affected also the AE, as displayed by the statistical moments of the peak amplitude distribution. Specifically, the variation of moment values with stress level were found to be different for the two groups. This difference can be used to sort sound from defective material during loading. In addition, this approach can in future be used as a means to ratify the soundness of structures, if a reliable database can be generated. 相似文献
86.
87.
甲醇气相氧化羰化合成碳酸二甲酯 Ⅲ.复合载体铜基催化剂的表征 总被引:4,自引:0,他引:4
采用X射线衍射、表面物理吸附、CO原位吸附红外光谱、X射线光电子能谱以及热重分析方法对甲醇直接气相氧化羰化合成碳酸二甲酯的复合载体铜基催化剂(Cu(Ⅱ)/Naβ-AC)的物化性能进行了表征。实验结果表明,微波辐射条件下制备的Cu(Ⅱ)/Naβ-AC催化剂中,活性组分CuC l2一方面与分子筛载体间发生了固相离子交换反应,并形成了铜分子筛物种,另一方面,可直接高度分散在复合载体表面。反应后Cu(Ⅱ)/Naβ-AC催化剂中部分Cu2+被还原为Cu+或Cu0,Cu2+的结合能峰向低结合能方向迁移,但微波辐射处理并未破坏分子筛载体的骨架结构。采用复合载体增加了催化剂的比表面积,并产生一定量的微孔,从而提高了催化剂的氧化羰化反应活性。热重分析表明,当温度低于350℃时,Cu(Ⅱ)/Naβ-AC催化剂稳定性较好。 相似文献
88.
89.
1 INTRODUCTIONSkeletalreconstructionorregenerationisre quiredincasesinvolvinglargedefectscreatedbytu morresection ,trauma ,andskeletalabnormalities .Graftsandflapsofautogenoustissuearetwoofthemostsuccessfulmeansofreconstructionbecausetheyallowthetransplantationofbonecontainingbioactivemolecules,livecells ,andfrequently ,avascularsup plythatallowthetransplanttosurviveandremodeleveninhostileradiatedenvironments .However ,onlyaminimalamountoftissuecanbeharvestedforauto grafts,anditisverydiff… 相似文献
90.
Pressure to compress the development life cycle and reduce the duration and resources committed to testing lead to experimentation in testing at the NASA Goddard Space Flight Centerís Software Engineering Laboratory. This study investigates the trend to reduce developer testing and increasingly rely upon inspection techniques and independent functional testing to shorten the development life cycle, improve testing productivity, and improve software quality.An approach is developed to conduct this comparison. In particular, the problem faced by software researchers, having a comprehensive characterization of software projects so similar types may be identified for comparative studies, is addressed using expert opinion. 相似文献