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81.
Tang Chak-yin Fan Jianping Tsui Chi-pong Lee Tai-chiu Chad Luen-chow Rao Bin 《Acta Mechanica Solida Sinica》2007,20(1):57-64
Shear damage may occur in the process of metal machining such as blanking and cutting, where localized shear deformation is developed. Experimental findings indicate that microscopic shear damage evolution in aluminium alloy 2024T3 (A1 2024T3) is a multi-stage mechanism, including particle cracking, micro-shear banding, matrix microcracking and coalescence of microcracks. This study is an attempt to use a set of equations to describe the multi-stage shear damage evolution in Al 2024T3. The shear damage variables in terms of multi-couple parameters of a power-law hardening material have been defined. An evolution curve of shearing damage has been calculated from experimental data. The values of the shear damage variable at different stages of damage have also been calculated. By making use of the findings, the relation between the microscopic shear damage evolution and the macroscopic shear response of the material has been discussed. 相似文献
82.
YU Jian-Chang WANG Chang-Yun 《结构化学》2007,26(10):1139-1144
In this paper,zinc acetate,manganese acetate and thiacetamide are used as raw materials to successfully synthesize monodispersed ZnS:Mn2+ microspheres by using hydrothermal method and taking P123 surfactant as a template. The products were characterized by XRD,STEM,FT-IR and N2 adsorption-desorption. And the results show that the diameter of this microsphere is 1.0 μm or so,which is larger than that of ZnS microsphere without Mn2+ doping,and it has monodispersion,smooth surface and uniform size. The doping of Mn2+ does not obviously change the structure of monodispersed ZnS microsphere. The photoluminescence peak lies in a wide band ranging from 450 to 650 nm,and the microspheres emit orange light; with the increase of Mn2+ concentration,fluorescence intensity of ZnS:Mn2+ microsphere changes,and when the mole ratio of Mn2+:Zn2+ is 0.3:1,the fluorescence intensity is the strongest. 相似文献
83.
3d过渡金属碳化物相稳定性和化学键的第一性原理研究 总被引:3,自引:2,他引:3
采用第一性原理方法对具有NaCl相、CsCl相以及WC相结构的3d过渡金属碳化物MC(M=Sc~Ni)的电子结构进行了详细研究,研究结果表明,对于同一类型相结构的Mc化合物具有相似的能带结构,均可用刚性带模型来描述,并由此得到了三种相统一的态密度(1DOS)分布.基于该DOS分布,通过分析费米能级附近DOS的大小并结合体系的结合能,对三种相的稳定性进行了探讨.结果表明,CsCl相构型最不稳定;对于3d电子数较少的MC化合物(M=Sc~V),以NaCl相为稳定构型;对于M=Cr~Ni的MC化合物,则以WC相为稳定相.此外,通过采用双子晶格模型,进一步从化学键角度对影响三种相稳定性的内在原因进行了探讨. 相似文献
84.
Er3Pd7P4 — Crystal Structure Determination and Extended Hückel Calculations Er3Pd7P4 was prepared by heating the elements (1050°C) and investigated by means of single-crystal X-ray methods. The compound crystallizes in a new structure (C2/m; a = 15.180(3) Å, b = 3.955(1) Å, c = 9.320(1) Å, β = 125,65(1)°; Z = 2) with a three-dimensional framework of Pd and P atoms and with Er atoms in the holes. The Pd atoms are surrounded tetrahedrally, trigonally or linearly by P atoms, which are coordinated by nine metal atoms in the form of a tricapped trigonal prism. Therefore the atomic arrangement of Er3Pd7P4 is related to the structures of ternary transition metal phosphides with a metal: phosphorus ratio of 2:1. Band calculations using the Extended Hückel method show strong covalent Pd? P bonds and weak bonding interactions between Pd atoms with Pd? Pd distances shorter than 2.9 Å. 相似文献
85.
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87.
Shi-jun Zheng Qun Xu Shao-kui Cao 《高分子科学》2007,(2):171-179
The novel shish-kebab-type liquid crystalline cross-conjugated (p-phenylene)s-poly(p-phenylenevinylene)s hybrid was synthesized through Gilch polymerization. Their structures and properties were characterized by NMR, GPC, DSC, X-ray diffraction and polarizing optical microscope (POM). ^1H-NMR investigation of the polymers indicates that the shish-kebab-structure has a strong ability to suppress the structural defects in the polymers. The polymers are enantiotropic liquid crystals. The melting point (Tm) of the polymers decreases when the length of the alkoxy tails of the mesogenic units increases. The mesophase was identified by X-ray diffraction method. They showed not only a smectic LC phase, but also a strong green fluorescence in chloroform. The maximum absorption band of the "kebabs" of the two, 5-bis(4'- alkoxyphenyl)benzene at 280 nm did not appear in absorption spectra of the polymers. The same phenomena were also observed in the fluorescence spectra. These results imply that the polymers have formed a cross-conjugated uniform structure and achieved an extended n-conjugation polymer. 相似文献
88.
本文用水作为分散介质,掺杂一定量的ZnO于Bi_4Ti_3O_(12)中,采用高能球磨法制备了异质结型光催化剂ZnO/Bi_4Ti_3O_(12).利用UV-Vis、XRD、SEM和PL等仪器对样品进行了分析与表征.以375 W中压汞灯为光源,通过对亚甲基蓝的氧化来研究其光催化活性.结果表明,对于光氧化亚甲基蓝(MB),异质结型光催化剂ZnO/Bi_4Ti_3O_(12)光催化活性高于钛酸铋的光催化活性.当ZnO的掺杂量分别是0.0和0.5wt.%,异质结型光催化剂ZnO/Bi_4Ti_3O_(12)对亚甲基蓝光氧化率分别达到50.2和80.3 %. 相似文献
89.
W. Russ Algar 《Analytica chimica acta》2010,673(1):1-25
A comprehensive review of the development of assays, bioprobes, and biosensors using quantum dots (QDs) as integrated components is presented. In contrast to a QD that is selectively introduced as a label, an integrated QD is one that is present in a system throughout a bioanalysis, and simultaneously has a role in transduction and as a scaffold for biorecognition. Through a diverse array of coatings and bioconjugation strategies, it is possible to use QDs as a scaffold for biorecognition events. The modulation of QD luminescence provides the opportunity for the transduction of these events via fluorescence resonance energy transfer (FRET), bioluminescence resonance energy transfer (BRET), charge transfer quenching, and electrochemiluminescence (ECL). An overview of the basic concepts and principles underlying the use of QDs with each of these transduction methods is provided, along with many examples of their application in biological sensing. The latter include: the detection of small molecules using enzyme-linked methods, or using aptamers as affinity probes; the detection of proteins via immunoassays or aptamers; nucleic acid hybridization assays; and assays for protease or nuclease activity. Strategies for multiplexed detection are highlighted among these examples. Although the majority of developments to date have been in vitro, QD-based methods for ex vivo biological sensing are emerging. Some special attention is given to the development of solid-phase assays, which offer certain advantages over their solution-phase counterparts. 相似文献
90.