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1.
从激光推进的要求出发,阐述了用于激光推进的高功率激光器的选择原则,即激光器必须满足:(1)高的平均功率和峰值功率;(2)高的单脉冲能量;(3)高的重复频率;(4)优良的大气传输特性。主要分析了目前YAG固体激光器、自由电子激光器和TEA脉冲CO2激光器的特点,通过上述4个方面性能的比较,认为在目前水平下,TEA脉冲CO2激光器是进行激光推进的首选强激光源,其优点表现在:功率可达10kW量级,单脉冲能量可达0.5~1kJ,重复频率为20~40Hz;激光波长处于大气传输窗口,对大气变化不敏感;工作物质快速流动,不存在热透镜效应和破坏阈值;相关光学元件易于制造;光束质量较好;运行成本低。 相似文献
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Chengzhe Zhao Guangfeng Wu Chao Zhou Haidong Yang Huixuan Zhang 《Journal of Polymer Science.Polymer Physics》2006,44(4):696-702
A series of acrylic impact modifiers (AIMs) with different particle sizes ranging from 55.2 to 927.0 nm were synthesized by seeded emulsion polymerization, and the effect of the particle size on the brittle–ductile transition of impact‐modified poly(vinyl chloride) (PVC) was investigated. For each AIM, a series of PVC/AIM blends with compositions of 6, 8, 10, 12, and 15 phr AIM in 100 phr PVC were prepared, and the Izod impact strengths of these blends were tested at 23 °C. For AIMs with particle sizes of 55.2, 59.8, 125.2, 243.2, and 341.1 nm, the blends fractured in the brittle mode when the concentration of AIM was lower than 10 phr, whereas the blends showed ductile fracture when the AIM concentration reached 10 phr. It was concluded that the brittle–ductile transition of the PVC/AIM blends was independent of the particle size in the range of 55.2–341.1 nm. When the particle size was greater than 341.1 nm, however, the brittle–ductile transition shifted to a higher AIM concentration with an increase in the particle size. Furthermore, the critical interparticle distance was found not to be the criterion of the brittle–ductile transition for the PVC/AIM blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 696–702, 2006 相似文献
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An atomic-absorption spectrometric method is reported for the determination of cobalt, nickel, and copper in a variety of geological materials including iron- and manganese-rich, and calcareous samples. The sample is decomposed with HP-HNO3 and the residue is dissolved in hydrochloric acid. Ammonium fluoride is added to mask iron and 'aluminum. After adjustment to pH 6, cobalt, nickel, and copper are chelated with sodium diethyl-dithiocarbamate and extracted into methyl isobutyl ketone. The sample is set aside for 24 h before analysis to remove interferences from manganese. For a 0.200-g sample, the limits of determination are 5–1000 ppm for Co, Ni, and Cu. As much as 50% Fe, 25% Mn or Ca, 20% Al and 10% Na, K, or Mg in the sample either individually or in various combinations do not interfere. Results obtained on five U.S. Geological Survey rock standards are in general agreement with values reported in the literature. 相似文献
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The complete infrared and Raman spectra of 1,1-difluoro-1-silacyclopentane and 1,1-dichloro-1-silacyclopentane have been recorded and analyzed. Furthermore, a number of the vibrational frequencies of the silacyclopentane and silacyclopentane-1, 1-d2 molecules have been reassigned.A normal coordinate calculation for each of these molecules was carried out and this demonstrated the validity of the assignments. Considerable mixing of the modes was found especially where ring vibrations and SiX2 motions were involved. 相似文献
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We have derived a new multipolar expansion for intermolecular potential-energy functions with applications in molecular physics, theoretical chemistry, and mathematical physics. The new formulation employs a separation of radial and angular terms with a simple index structure that leads to computational efficiency and ease of physical interpretation. For the case of the Coulomb interaction, we compare the present formulation with two conventional multipole expansions: the Cartesian tensor and the irreducible spherical tensor expansions. The new formalism leads to efficient numerical algorithms that are useful for general applications beyond intermolecular potentials. In addition to the electrostatic Coulomb interaction, we illustrate the formalism with applications to special function theory and a bipolar expansion involved in potential theory. 相似文献
8.
George Odian Richard Henry Raymond Koenig D. Mangaraj Le Doan Trung Bou Chao Arif Derman 《Journal of polymer science. Part A, Polymer chemistry》1975,13(3):623-643
A theoretical analysis has been made of the graft polymerization process in terms of the quantitative interrelationship between the initiation rate Ri, the kp/kt1/ ratio of the monomer, the equilibrium solubility M of the monomer in the polymer, the polymer film thickness L, and the diffusivity D of the monomer in the polymer. It is shown how the values of these parameters in any grafting system interact to lead to diffusion-controlled graft polymerization. Whether graft polymerization is diffusion-free or diffusion-controlled depends on the values of Kp, d, kp/kp1/2, and L as gathered in the parameter A = [(Kp/kt1/2)Ri, D,/1/2] L/2. When the values of the various terms are such that A is less than 0.1 (i.e., D is large while Ri, kp, and L are small), the reaction is diffusion-free. When A is greater than 3 (i.e., D is small while Ri, kp, and L are large), the reaction is diffusion-controlled. The derived equations showing the relationship between kinetic and diffusional parameters are theoretically applicable to all grafting systems, i.e., for all monomer-polymer combinations under all conditions of reaction temperature, radiation intensity and polymer film thickness. The theoretical analysis has been verified for the rate and degree of polymerization for the radiation-induced graft polymerization of styrene to polyethylene. 相似文献
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High-resolution solid-state 29Si NMR has been applied to the study of partially exchanged Li, K, and Cs NaY zeolites. The order of the 29Si chemical shifts of dehydrated samples is Li, Na-Y < Na-Y < K, Na-Y. The correlation between the 29Si chemical shift and the Li or K loading on Li, Na-Y or K, Na-Y was rationalized in terms of the interaction between the framework and the cations inside the small cages. Because of the restrictive migration of large Cs+ ions from the supercages to the small cages, the 29Si chemical shift of Cs, Na-Y was found to be similar to that of Na-Y. 相似文献
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目的:建立不同产地半夏无机元素的分析方法和溯源体系,为半夏药材的质量控制和道地性评价提供技术支持。方法:采用电感耦合等离子体质谱法(ICP-MS)和电感耦合等离子体原子发射光谱法(ICP-AES)对我国6个主产区72份半夏样品中K、Ca、Na、Mg、Al等37种无机元素的含量进行测定,并采用方差分析、主成分分析、因子分析等计量学方法进行统计与评价。通过对比BP-神经网络算法、K-最近邻算法、最小二乘支持向量机等多种模式识别方法,探索适合半夏产地溯源的最佳模型。结果:不同产地半夏中无机元素的构成各具特征,各无机元素含量在产地间差异显著(P<0.05),其中La、Pb、As、Na、Bi、Hg、Sn、Cd、Ag 9种元素在不同产区间的差异最为明显;3D-plots图显示不同产地半夏样品分布相对集中,具备产地分类的可行性;KNN分类模型(曼哈顿距离)是半夏产地溯源的最佳方法,测试集的正确率达到100%。结论:无机元素分析技术结合适当的计量学模型可以实现半夏的产地溯源。 相似文献