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排序方式: 共有93条查询结果,搜索用时 46 毫秒
71.
HUANG Qing-Ming ② YU Jian-Chang WANG Yun-Min WU Wan-Guo 《结构化学》2005,24(6):691-695
1 INTRODUCTION The structure of material has a close and com- plicated relationship with its physical property. Knowledge on the structure of material is fundamen- tal to the process of material research, where the ma- terial structure analysis plays an important role. In the past, structures of many materials were known by synthesizing their single crystals and using the single crystal diffraction instrument to collect crys- talline structure data. But now, it is difficult to obtain the… 相似文献
72.
六方相磷酸铈一维纳米材料的合成与表征 总被引:1,自引:0,他引:1
以磷酸钠、硝酸铈为原料, 利用P123表面活性剂的水溶液形成的胶束为反应模板, 采用水热法合成工艺, 在反应溶液的pH=1, 反应温度为140 ℃, 反应时间为24 h的条件下成功合成了六方相的CePO4一维纳米发光材料, 并提出其可能的形成机理. 通过XRD, TEM, FT-IR, UV-Vis, PL测试表征, 发现制备的磷酸铈一维纳米材料最长可以达到1 μm左右, 而直径为10~25 nm, 轴径比较高; 其在紫外光区的荧光发射性能与普通的纳米颗粒相比得到了很大程度的提高; 六方相磷酸铈一维纳米材料以其独特的荧光发射性能, 有望在光、电等领域发挥其潜在的应用价值. 相似文献
73.
74.
The photoluminescence (PL) property effect of Sc3+ on the Er3+/Y3+/Yb3+ doped Al2O3 powders prepared by sol-gel method has been investigated. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) implied that the distribution of dopants (Er3+ , Y3+ , Yb3+ , Sc3+) was improved effectively with the rise of Sc3+ concentration. The Fourier transform infrared spectra (FTIR) results demonstrated that the ligand around the quenching center -OH and the population of -OH were altered by introducing different amounts of Sc3+ . The PL intensity centered at 1530 nm was increasingly improved with the rise of Sc3+ concentration, as well as the corresponding full widths at the half maximum (FWHM) and lifetime. The optimized PL intensity was 4.7 times higher than that non-Sc3+ doped sample for the Al2O3 powders codoped with 10mol% Sc3+ . This material can be promising candidates for optical fiber amplifier. 相似文献
75.
Giant negative temperature coefficient of resistance (TCR) was observed in ZnO/Si (111) thin films. The films were grown using the pulsed laser deposition (PLD) technique, taking Si (111) wafer as substrates, with a substrate at the temperature below 450°C in the PLD. It is found that both TCR-temperature behavior and TCR value are strongly affected by deposition temperature. The maximal TCR value over -10.9%K-1 can be observed at the deposition temperature from 20°C to 350°C and reaches to -13%K-1 at deposition temperature 20°C where the film shows X-ray diffraction amorphous. The results suggest that the ZnO/Si films demonstrate great potentials when used in a low-cost, high-performance, non-cooling and highly sensitive bolometer. 相似文献
76.
肝纤维化程度以及纤维化速率的精确判断对于相应治疗手术的选择以及治疗预后评估都是至关重要的.临床上需要发展一种非侵入性的肝纤维化定量检查手段.核磁共振弹性成像技术成为实现肝纤维化分级研究的最具发展前景的技术之一.我们研制开发了可用于进行肝纤维化分级研究的实验平台,并讨论了激励装置和位移相位成像序列的技术细节,最后给出了体模的初步实验结果并对结果进行了分析.为后续体模深入研究和临床应用实验奠定基础. 相似文献
77.
Qing-Ming Cheng Guangyue Huang Guoxin Wei 《Calculus of Variations and Partial Differential Equations》2010,38(3-4):409-416
For a bounded domain Ω in a complete Riemannian manifold M n , we study estimates for lower order eigenvalues of a clamped plate problem. We obtain universal inequalities for lower order eigenvalues. We would like to remark that our results are sharp. 相似文献
78.
Density functional theory (DFT) with local density approximation (LDA) is employed to study the structural and electronic properties of the high explosive octahydro- 1,3,5, 7-tetranitro-1,3, 5, 7-tetrazocine (HMX) under high pressure compression up to 40 GPa. Pressure dependences of the cell volume, lattice constants, and molecular geometry of solid β-HMX are presented and discussed. It is found that N-N and N-C bonds are subject to significant change. This may implies that these bonds may be related to the sensitivity. The band gap is calculated and plotted as a function of pressure. Compared the experimental results with other theoretical works we find that LDA gives good results. 相似文献
79.
In this paper, we will introduce the notion of harmonic stability for complete minimal hypersurfaces in a complete Riemannian
manifold. The first result we prove, is that a complete harmonic stable minimal surface in a Riemannian manifold with non-negative
Ricci curvature is conformally equivalent to either a plane R
2 or a cylinder R × S
1, which generalizes a theorem due to Fischer-Colbrie and Schoen [12].
The second one is that an n ≥ 2-dimensional, complete harmonic stable minimal, hypersurface M in a complete Riemannian manifold with non-negative sectional curvature has only one end if M is non-parabolic. The third one, which we prove, is that there exist no non-trivial L
2-harmonic one forms on a complete harmonic stable minimal hypersurface in a complete Riemannian manifold with non-negative
sectional curvature. Since the harmonic stability is weaker than stability, we obtain a generalization of a theorem due to
Miyaoka [20] and Palmer [21].
Research partially Supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science
and Technology, Japan.
The author’s research was supported by grant Proj. No. KRF-2007-313-C00058 from Korea Research Foundation, Korea.
Authors’ addresses: Qing-Ming Cheng, Department of Mathematics, Faculty of Science and Engineering, Saga University, Saga
840-8502, Japan; Young Jin Suh, Department of Mathematics, Kyungpook National University, Taegu 702-701, South Korea 相似文献
80.
In this paper, we investigate an eigenvalue problem for a biharmonic operator on a bounded domain in an n-dimensional Euclidean space, which is also called a buckling problem. We introduce a new method to construct ``nice' trial
functions and we derive a universal inequality for higher eigenvalues of the buckling problem by making use of the trial functions.
Thus, we give an affirmative answer for the problem on universal bounds for eigenvalues of the buckling problem, which was
proposed by Payne, Pólya and Weinberger in [14] and this problem has been mentioned again by Ashbaugh in [1].
Research partially supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science.
Research partially supported by SF of CAS 相似文献