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991.
Acetyl acrylic anhydride (CH(3)C(O)OC(O)CHCH(2)) and its halogen-substituted derivatives (CF(3)C(O)OC(O)CHCH(2) and CCl(3)C(O)OC(O)CHCH(2)) were prepared by the heterogeneous reaction of gaseous CH(2)═CHC(O)Cl with CX(3)C(O)OAg (X = H, F, or Cl). The molecular conformations and electronic structure of these three compounds were investigated by HeI photoelectron spectroscopy, photoionization mass spectroscopy, FT-IR, and theoretical calculations. They were theoretically predicted to prefer the [ss-c] conformation, with each C═O bond syn with respect to the opposite O-C bond and the C═C bond in cis orientation to the adjacent C═O bond. The experimental first vertical ionization potential for CH(3)C(O)OC(O)CHCH(2), CF(3)C(O)OC(O)CHCH(2), and CCl(3)C(O)OC(O)CHCH(2) was determined to be 10.91, 11.42, and 11.07 eV, respectively. In this study, the rule of the conformation properties of anhydride XC(O)OC(O)Y was improved by analyzing the different conformations of anhydrides with various substitutes. 相似文献
992.
考察人体口腔异味现象,利用恒化器建模方法,改进了人体口腔系统中微生物种群关系的模型,利用Lyapunov稳定性理论分析了系统的平衡点及其稳定性.进而得到结论,口腔异味作为疾病,需要专业医治才能治愈.数值模拟结果证实了理论分析的正确性. 相似文献
993.
Constant‐weight codes (CWCs) have played an important role in coding theory. To construct CWCs, a K‐GDD (where GDD is group divisible design) with the “star” property, denoted by K‐*GDD, was introduced, in which any two intersecting blocks intersect in at most two common groups. In this paper, we consider the existence of 4‐*GDDs. Previously, the necessary conditions for existence were shown to be sufficient for , and also sufficient for with prime powers and . We continue to investigate the existence of 4‐*GDD(6n)s and show that the necessary condition for the existence of a 4‐*GDD(6n), namely, , is also sufficient. The known results on the existence of optimal quaternary (n, 5, 4) CWCs are also extended. 相似文献
994.
A new method for information retrieval in two-dimensional grating-based X-ray phase contrast imaging
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Grating-based X-ray phase contrast imaging has been demonstrated to be an extremely powerful phase-sensitive imaging technique.By using two-dimensional(2D) gratings,the observable contrast is extended to two refraction directions.Recently,we have developed a novel reverse-projection(RP) method,which is capable of retrieving the object information efficiently with one-dimensional(1D) grating-based phase contrast imaging.In this contribution,we present its extension to the 2D grating-based X-ray phase contrast imaging,named the two-dimensional reverseprojection(2D-RP) method,for information retrieval.The method takes into account the nonlinear contributions of two refraction directions and allows the retrieval of the absorption,the horizontal and the vertical refraction images.The obtained information can be used for the reconstruction of the three-dimensional phase gradient field,and for an improved phase map retrieval and reconstruction.Numerical experiments are carried out,and the results confirm the validity of the 2D-RP method. 相似文献
995.
Preparation and the physical properties of antiperovskite-type compounds Cd<sub>1-x</sub>In<sub>x</sub> NNi<sub>3</sub>(0 ≤x≤ 0.2) and Cd<sub>1-y</sub>Cu<sub>y</sub>NNi<sub>3</sub>(0≤y≤0.2)
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Two series of Cd1-xInx NNi3(0 ≤x≤ 0.2) and Cd1-yCuyNNi3(0≤y≤0.2) samples were prepared from CdO, In2O3 , CuO, and nickel powders under NH3 atmosphere at 773K. The structural and physical properties were investigated by means of X-ray powder diffraction temperature-dependent resistivity and magnetic measurements. X-ray powder diffraction results showed that the Cd 1 x In x NNi 3 and Cd 1 y Cuy NNi 3 compounds have a typical antiperovskite structure, and the CdNNi3, Cd0.9 In 0.1 NNi3 , and Cd0.9Cu0.1NNi3 compounds show metallic temperature-dependent resistivity and exhibit a Fermi liquid behavior at low temperature. In contrast to the paramagnetism previously reported, the CdNNi 3 sample exhibits very soft and weak ferromagnetism, and no superconductivity was found in the Cd 1 x In x NNi 3 and Cd 1 y Cu y NNi 3 samples down to 2 K. Each sample exhibited very soft and weak ferromagnetism, and the temperature dependence of the magnetization of the Cd 1-xInx NNi 3 and Cd1-y Cu y NNi 3 samples can be well fitted to the combination of a Bloch term and a Curie–Weiss term. 相似文献
996.
997.
基于位移和应力灵敏度的结构拓扑优化设计 总被引:3,自引:0,他引:3
针对仅有应力约束以及含位移和应力约束的重量最小结构拓扑优化问题,基于ICM(独立、连续、映射)方法和渐进结构优化方法的思路,提出了一种结构拓扑优化方法. 在优化迭代循环的每一轮子循环迭代求解开始时,通过形成和引进新的位移和应力约束限, 自动构建设计变量移动限.将结构应力约束归并为几个最可能的有效应力约束,大大减少了应力灵敏度的分析量. 另外,建立了单元删除阈值和几轮迭代循环的单元删除策略. 为了确保优化迭代中结构非奇异和方法具有增添单元的功能,在结构孔洞和边界周围引入了一层人工材料单元,构建了其等效的优化模型. 结合位移和应力灵敏度分析,形成了一种新的连续体结构的拓扑优化方法. 给出的算例验证了该方法的正确性和有效性. 相似文献
998.
三电平大功率并联逆变电源在EAST系统中的应用 总被引:1,自引:0,他引:1
针对EAST超导托卡马克装置中的等离子体位移快控电源大电流快速响应的要求,采用三电平结合移相PWM多重化技术,实现多组变流器并联运行,提高了变流器的等效开关频率控制性能,从而改善了电流波形品质。分析了快控电源系统的设计方案和控制方法,并针对移相PWM多重化技术,采用Matlab进行了仿真,验证了设计思想。实验结果表明,该系统设计方案合理、控制策略有效,具备良好的大电流输出和快速响应能力。 相似文献
999.
研究了皮疹患者和健康人血清的表面增强拉曼光谱。结果表明: 皮疹患者血清中蛋白质主链酰胺Ⅰ的谱线出现在1 648 cm-1处,而在健康人血清中此峰消失。蛋白质侧链C—S键扭曲构象的谱线637 cm-1的相对强度增加了23%,而反式构象的谱线725 cm-1的相对强度减少了60%,说明C—S键的反式构象部分转成扭曲构象,表明皮疹患者血清中蛋白质的有序结构发生变化。类脂物特征峰1 449 cm-1的相对强度增加了近一倍,D-甘露糖的谱线1 099 cm-1消失,表明患者血清中糖蛋白、糖质发生了变化。这些拉曼特征峰为皮疹的诊断以及生化机理研究提供了有力的实验依据。最后用主成分分析(PCA)方法对健康人和皮疹患者血清的表面增强拉曼光谱进行分析,发现皮疹患者血清的主成分分布相对健康人较分散,并且此方法能准确的区分开这2种血清。 相似文献
1000.