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51.
地下环境中电子设备的腐蚀与防护 总被引:3,自引:0,他引:3
程环境中电子设备所承受的湿度、温度、腐蚀性气体、空气沉积物、微生物等环境应力因素及其腐蚀效应,概述总结了电子设备腐蚀机制及主要类型,并提出电子设备设计与使用中抑制腐蚀的措施. 相似文献
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The objective of this study is to identify defects such as surface cracks, subsurface defects and metal losses using feature based pulsed eddy current sensors. A new feature, termed as the rising point, related to the propagation time of electromagnetic waves in metallic targets is proposed for defect classification. Experimental studies of the validation, robustness of the new feature of rising time are reported. In addition to other features, defects can be detected and quantified robustly and lift-off can also be derived from the rising time. Conclusion and further work are derived on the basis of the findings. 相似文献
53.
通过B2O3蒸汽掺杂,钛酸钡晶胞膨胀,表明硼离子可以进入钛酸钡晶格中形成硼间隙。B2O3蒸汽掺杂使含Y钛酸钡陶瓷室温电阻率下降,升阻比提高。同样的烧结条件下,钛酸钡陶瓷的PTCR效应随B2O3蒸汽掺杂源的浓度升高而升高。硼间隙和/或相关缺陷络合物可以形成电子捕获中心,从而提高PTCR效应。 相似文献
54.
磁致冷材料研究进展 总被引:4,自引:0,他引:4
介绍了磁致冷材料磁热效应的表征方法,概述了国内外各温度区间磁致冷材料的研究进展。在20K以下温区,磁致冷材料研究主要集中在具有高导热率、低点阵热容和极低有序化温度的石榴石,如Gd3Ga5O12(GGG),Dy3Al5O12(DAG),Gd3Ga5-xFexO12(GGIG)及Er基磁致冷材料;20K~77K温度区间,磁致冷材料研究主要集中在重稀土金属间化合物中,如(Dy1-xErx)Al2复合材料等;在室温附近,具有大磁热效应的磁致冷材料以稀土Gd,Gd5(SixGe1-x)4(0≤x≤0.5)和MnFeP1-xAsx(0.15≤x≤0.66)合金为代表,特别是Gd5Si2Ge2(Tc=274K)和MnFeP0.45As0.55(Tc=300K)合金,在磁场5T下具有巨磁热效应,是Gd的2倍以上。总结了各温度区间磁致冷材料的选择依据。重点评述了室温磁致冷材料的最新研究成果,展望了室温磁致冷材料的发展前景。 相似文献
55.
Experiment and simulation study of 3D magnetic field sensing for magnetic flux leakage defect characterisation 总被引:1,自引:0,他引:1
Magnetic flux leakage (MFL) testing is widely used to detect and characterise defects in pipelines, rail tracks and other structures. The measurement of the two field components perpendicular to the test surface and parallel to the applied field in MFL systems is well established. However, it is rarely effective when the shapes of the specimens and defects with respect to the applied field are arbitrary. In order to overcome the pitfalls of traditional MFL measurement, measurement of the three-dimensional (3D) magnetic field is proposed. The study is undertaken using extensive finite element analysis (FEA) focussing on the 3D distribution of magnetic fields for defect characterisation and employing a high sensitivity 3-axis magnetic field sensor in experimental study. Several MFL tests were undertaken on steel samples, including a section of rail track. The experimental and FEA test results show that data from not only the x- and z-axes but also y-axis can give comprehensive positional information about defects in terms of shape and orientation, being especially advantageous where the defect is aligned close to parallel to the applied field. The work concludes that 3D magnetic field sensing could be used to improve the defect characterisation capabilities of existing MFL systems, especially where defects have irregular geometries. 相似文献
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Metallothionein is a ubiquitous protein with a wide range of proposed physiological roles, including the transport, storage and detoxification of essential and nonessential trace metals. The amino acid sequence of isoform 2a of rabbit liver metallothionein, the isoform used in our spectroscopic studies, includes 20 cysteinyl groups out of 62 amino acids. Metallothioneins in general represent an impressive chelating agent for a wide range of metals. Structural studies carried out by a number of research groups (using (1)H and (113)Cd NMR, X-ray crystallography, more recently EXAFS, as well as optical spectroscopy) have established that there are three structural motifs for metal binding to mammalian metallothioneins. These three structures are defined by metal to protein stoichiometric ratios, which we believe specifically determine the coordination geometry adopted by the metal in the metal binding site at that metal to protein molar ratio. Tetrahedral geometry is associated with the thiolate coordination of the metals in the M(7)-MT species, for M = Zn(II), Cd(II), and possibly also Hg(II), trigonal coordination is proposed in the M(11-12)-MT species, for M = Ag(I), Cu(I), and possibly also Hg(II), and digonal coordination is proposed for the metal in the M(17-18)-MT species for M = Hg(II), and Ag(I). The M(7)-MT species has been completely characterized for M = Cd(II) and Zn(II). (113)Cd NMR spectroscopic and x-ray crystallographic data show that mammalian Cd(7)-MT and Zn(7)-MT have a two domain structure, with metal-thiolate clusters of the form M(4)(S(cys))(11) (the alpha domain) and M(3)(S(cys))(9) (the beta domain). A similar two domain structure involving Cu(6)(S(cys))(11) (alpha) and Cu(6)(S(cys))(9) (beta) copper-thiolate clusters has been proposed for the Cu(12)-MT species. Copper-, silver- and gold-containing metallothioneins luminesce in the 500-600 nm region from excited triplet, metal-based states that are populated by absorption into the 260-300 nm region of the metal-thiolate charge transfer states. The luminescence spectrum provides a very sensitive probe of the metal-thiolate cluster structures that form when Ag(I), Au(I), and Cu(I) are added to metallothionein. CD spectroscopy has been used in our laboratory to probe the formation of species that exhibit well-defined three-dimensional structures. Saturation of the optical signals during titrations of MT with Cu(I) or Ag(I) clearly show formation of unique metal-thiolate structures at specific metal:protein ratios. However, we have proposed that these M=7, 12 and 18 structures form within a continuum of stoichiometries. Compounds prepared at these specific molar ratios have been examined by X-ray Absorption Spectroscopy (XAS) and bond lengths have been determined for the metal-thiolate clusters through the EXAFS technique. The stoichiometric ratio data from the optical experiments and the bond lengths from the XAS experiments are used to propose structures for the metal-thiolate binding site with reference to known inorganic metal-thiolate compounds. 相似文献
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