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991.
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994.
Effect of Nanopores on the Phonon Conductivity of Crystalline CoSb3: A Molecular Dynamics Study 总被引:1,自引:0,他引:1
Xu-qiu Yang Peng-cheng Zhai Li-sheng Liu Gang Chen Qing-jie Zhang 《Journal of Electronic Materials》2014,43(6):1842-1846
Molecular dynamics simulations have been performed to investigate the effect of nanometer-size pores on the phonon conductivity of single-crystal bulk CoSb3. The cylindrical pores are uniformly distributed along two vertical principal crystallographic directions of a square lattice. Because pore diameter and porosity are two key factors that could affect the performance of the materials, they were varied individually in the ranges a 0–6a 0 and 0.1–5%, respectively, where a 0 is the lattice constant of CoSb3. The simulation results indicate that the phonon conductivity of nanoporous CoSb3 is significantly lower than that of no-pore CoSb3. The reduction of phonon conductivity in this simulation was consistent with the ballistic–diffusive microscopic effective medium model, demonstrating the ballistic character of phonon transport when the phonon mean-free-path is comparable with or larger than the pore size. Reducing pore diameter or increasing porosity are alternative means of effective reduction of the thermal conductivity of CoSb3. These results are expected to provide a useful basis for the design of high-performance skutterudites. 相似文献
995.
Xu-qiu Yang Peng-cheng Zhai Chang Cai Li-sheng Liu Qing-jie Zhang 《Journal of Electronic Materials》2014,43(6):1837-1841
The effects of nanometer-size pores on the uniaxial tensile mechanical properties of single-crystal bulk CoSb3 were investigated by classical molecular dynamics simulation. The pores were assumed to be cylindrical and uniformly distributed along two vertical principal crystallographic directions of a square lattice. The dependence of the effects of pores on pore diameter and porosity was examined separately, by varying pore diameter and porosity in the ranges a 0–6a 0 and 0.1–5%, respectively, where a 0 is the lattice constant of CoSb3. The results from simulation indicate that, at constant porosity, Young’s modulus remains almost constant whereas ultimate strength decreases as pore diameter increases. At constant pore diameter, Young’s modulus decreases monotonically as porosity increases exponentially; interestingly, variation of the ultimate strength is negligible. Numerically, the mechanical performance of systems containing nanopores is still desirable, although no better than that of the no-pore system. The results provide useful information for realistic application of skutterudites. 相似文献
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997.
A. MU?AN 《Journal of sound and vibration》2002,258(1):45-63
The singular-value decomposition (SVD) is employed to study the effects of localization phenomena on input-output relationships, and power and energy transmission ratios of structures. For weakly and strongly coupled systems, existence of strong localization of singular vectors and abrupt veering of singular value loci are shown. Occurrence of strong localization causes abrupt changes in input-output directional properties. In contrast to eigenvalues, singular values do not veer away by introducing a disorder in weakly coupled systems. In particular, the use of singular values and vectors is computationally advantageous in considering multiple load cases. While eigenvalue-based analyses give information about the resonance frequencies and vibration modes of a structure, singular values of the structure are related to the forced response characteristics and give the dynamic behavior in the frequency domain. Representative examples in structural dynamics are presented. 相似文献
998.
用1-甲基-2-萘甲酰基替换N-苯甲酰苯基羟胺(BPHA)的苯甲酰基,合成了一种新显色剂N-苯基-1-甲氧基-2-萘甲酰氧肟酸(N-phenyl-1-methoxy-2-naphthoyl hydroxamic acid,缩写为PMNHA)。根据元素分析、差热分析、质谱分析、核磁共振、红外光谱分析,确定PMNHA的组成和结构为 。该试剂的三氯甲烷溶液能很快从2.25-4.50mol/L HCl中萃取钒(V)的紫色配合物,其配合物最大吸收在540nm,很多外来离子,特别是大量的钛不干扰钒的测定,钒含量在0-28μg·g^-1范围遵守比耳定律。我们建立了一个高选择性和简便的用显色剂PMNHA分光光度测定钒的方法。 相似文献
999.
Costas阵列编码与线性调频SFR信号分析 总被引:2,自引:0,他引:2
线性调频-Costas频率步进雷达信号是一种很有研究价值的雷达信号。针对线性调频-Costas频率步进雷达信号的需要研究总结了一套生成N阶Costas序列的方法,同时结合实际需要生成了多组64阶Costas序列。这些Costas阵列是具有良好相关特性的最佳离散信号,将Costas阵列编码与线性调频频率步进雷达信号结合起来构成了线性调频-Costas频率步进雷达信号。通过对该信号的模糊特性的理论和仿真结果的分析表明,这种信号不仅能够较大地抑制信号的模糊旁瓣的幅度。而且能解决距离-速度的多普勒耦合问题。 相似文献
1000.
用卢瑟福背散射/沟道技术研究了1MeVSi+在衬底加温和室温下以不同剂量注入Al0.3G0.7As/GaAs超晶格和GaAs后的晶格损伤。在衬底加温下,观察到Al0.3Ga0.7As/GaAs超晶格和GaAs都存在一个动态退火速率与缺陷产生速率相平衡的剂量范围,以及两种速率失去平衡的临界剂量。超晶格比GaAs更难以损伤,并且它的两种速率失去平衡的临界剂量也大于GaAs中的相应临界剂量,用热尖峰与碰撞模型解释了晶格损伤积累与注入剂量和衬底温度的关系。用CNDO/2量子化学方法计算了GaAs和AlxGa1-xAs中化学键的相对强度,并根据计算结果解释了注入过程中Al0.3Ga0.7As/GaAs超晶格和GaAs中晶格损伤程度的差别。
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