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101.
102.
对于半导体瞬态问题的数学模型,我们采用Lagrange型分片二次多项式空间和分片常数函数空间分别作为试探函数和检验函数空间,构造了该问题的全离散二次有限体积元格式,并进行误差分析,得到了次优阶L2模误差估计结果。 相似文献
103.
《Materials Research Bulletin》2006,41(8):1437-1446
Yttria stabilised zirconia has been prepared using a simple sol-powder coating technique. The polymeric yttria sol, which was prepared using 1,3 propanediol as a network modifier, was homogeneously mixed with nanocrystalline zirconia powder and it showed a dual function: as a binder which promoted densification and a phase modifier which stabilised zirconia in the tetragonal and cubic phases. Thermal analysis and X-ray diffraction revealed that the polymeric yttria sol which decomposed at low temperature into yttrium oxide could change the m → t phase transformation behaviour of the zirconia, possibly due to the small particle size and very high surface area of both yttria and zirconia particles allowing rapid alloying. The sintered samples exhibited three crystalline phases: monoclinic, tetragonal and cubic, in which cubic and tetragonal are the major phases. The weight fractions of the individual phases present in the selected specimens were determined using quantitative Rietveld analysis. 相似文献
104.
给出属性下界值,属性上界值的数据生成概念,给出属性下界值的数据生成模型,属性上界值的数据生成模型;提出金属材料的遗传一进化定理,金属材料的遗传进化一遗传变异原理.利用这些数据模型讨论了发现新金属材料的方法;对于新发现的新金属材料用例子证明它的存在,本文的例子说明,S-粗集和它的属性值模型是材料科学中新材料发现的一个新的工具。 相似文献
105.
Hongxia Li Huaijin Zhang Guangwei Yu Liang Fang Zhaoyuan Ning Shiling Li Keming Wang 《Materials Research Bulletin》2005,40(11):1915-1921
High quality Nd-doped lutecium vanadate thin films on silica glass substrates were fabricated successfully by using a pulsed laser deposition technique. The properties of the samples were characterized by using X-ray diffraction, Rutherford backscattering, atomic force microscopy (AFM), and prism-coupling measurements. The RBS shows that the ratio of Lu/V in the film is 0.991, which is in good agreement with the target composition. X-ray diffraction results show that the degree of crystal orientation along (2 0 0) increases with increasing oxygen pressure up to 20 Pa. The refractive indices of the films determined with dark-mode prism coupling measurements are slight, smaller than that of the bulk crystal. An optimum 20 Pa oxygen pressure, at which the oxygen was leaked into the chamber as the reactive ambient, was determined. 相似文献
106.
《Materials Letters》2005,59(14-15):1866-1870
Tetrapod-like zinc oxide (ZnO) nanoneedles were fabricated using a simple and economical method of rapid heating high purity zinc powders at 900 °C. No catalyst and vacuum were employed in the experiment. Field-emission measurements showed that the turn-on field of the synthesized tetrapod-like ZnO nanoneedles was as low as 1.8 V/μm at the emission current density of 1.0 μA/cm2 and the emission current density reached 1.0 mA/cm2 under an applied field of about 3.9 V/μm. The low turn-on field, high emission current density, and good electron emission stability make the ZnO nanoneedles one of the promising candidates for field-emission displays. 相似文献
107.
《Materials Letters》2005,59(24-25):3069-3072
The nanocrystalline ribbons Fe90.3−xZr7B2.7Cux with low Cu contents can be directly obtained through melt-spinning technique with an appropriate low quenching speed such as 22 m/s. Sizes of bcc-Fe grains precipitated in Fe90.3−xZr7B2.7Cux as-spun ribbons were 17 nm for x = 0.75, 15 nm for x = 1 and 12 nm for x = 1.25. The addition of Cu reduces grain size of bcc-Fe in as-spun nanocrystalline Fe90.3−xZr7B2.7Cux ribbons. Among the investigated samples (0.5 ≤ x ≤ 1.5), the largest magnetoimpedance can be obtained in the nanocrystalline Fe80.3Zr7B2.7Cu1 as-spun ribbon with x = 1. The value of magnetoimpedance (Z(H) − Z(0)) / Z(0) under H = 90 Oe for Fe80.3Zr7B2.7Cu1 as-spun ribbon reaches − 28.2% at a frequency of 1 MHz. 相似文献
108.
109.
An adaptive neural network controller is developed to achieve output-tracking of a class of nonlinear systems. The global L2 stability of the closed-loop system is established. The proposed control design overcomes the limitation of the conventional adaptive neural control design where the modeling error brought by neural networks is assumed to be bounded over a compact set.Moreover,the generalized matching conditions are also relaxed in the proposed L2 control design as the gains for the external disturbances entering the system are allowed to have unknown upper bounds. 相似文献
110.
Hongwei QIN Jifan HU Juan CHEN Hongdong NIU Luming ZHU Zhuo WANG Department of Physics Shandong University Jinan China State Key Laboratory for Crystal Materials Shandong University Jinan China 《材料科学技术学报》2004,(3)
With substitution of La by Tb in (La_(1-x)Tb_x)_(0.67)Sr_(0.33)MnO_3, the room temperature magnetoresistance △R/R_0drops at first, then undergoes an increase near x≈0.1, and finally drops again. The value of room temperaturemagnetoresistance at a field H=12 kOe for (La_(0.9)Tb_(0.1))_(0.67)Sr_(0.33)MnO_3 is -3.56%. The enhancement of the roomtemperature magnetoresistance induced by an appropriate Tb substitution in (La_(1-x)Tb_x)_(0.67)Sr_(0.33)MnO_3 is correlatedwith the shifts of the Curie temperature and metal-insulator temperature to near room temperature. The drop ofthe room temperature magnetoresistance at large Tb doping-contents may be due to its lower T_C and T_(MI) far fromthe room temperature. 相似文献