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71.
72.
Longitudinal study has become one of the most commonly adopted designs in medical research. The generalized estimating equations (GEE) method and/or mixed effects models are employed very often in causal inferences. The related model diagnostic procedures are not yet fully formalized, and perhaps never will be. The potential causes of major problems are the high variety of the dependence within subjects and/or the number of repeated measurements. A single testing procedure, e.g., run test, is not possible to resolve all model diagnostics problems in longitudinal data analysis. Multiple quantitative indexes for model diagnostics are needed to take into account this variety. We propose eight testing procedures for randomness accompanied with some conventional and/or non-conventional plots to remedy model diagnostics in longitudinal data analysis. The proposed issue in this paper is well illustrated with four clinical studies in Taiwan. 相似文献
73.
H.L. Li H.T. Lin Y.H. Wu T. Liu Z.L. Zhao G.C. Han T.C. Chong 《Journal of magnetism and magnetic materials》2006
We report on the growth and characterization of delta-doped amorphous Ge:Mn diluted magnetic semiconductor thin films on GaAs (0 0 1) substrates. The fabricated samples exhibit different magnetic behaviors, depending on the Mn doping concentration. The Curie temperature was found to be dependent on both the Mn doping concentration and spacing between the doping layers. A sharp drop in magnetization and rise in resistivity are observed at low temperature in samples with high Mn doping concentrations, which is also accompanied by a negative thermal remanent magnetization (TRM) in the higher temperature range. The temperature at which the magnetization starts to drop and the negative TRM appears show a correlation with the Mn doping concentration. The experimental results are discussed based on the formation of ferromagnetic regions at high temperature and antiferromagnetic coupling between these regions at low temperature. 相似文献
74.
就如何在4英寸热氧化硅衬底上沉积高质量的磁性隧道结纳米多层薄膜材料和如何利用光刻方法微加工制备均匀性较好的磁性隧道结方面做了初步研究,并对磁性隧 道结的磁电性质及其工作特性进行了初步测量和讨论.利用现有的光刻设备和工艺条 件在4英寸热氧化硅衬底上直接制备出的磁性隧道结,其结电阻与面积的积 矢的绝对误差在10% 以内,隧穿磁电阻的绝对误差在7% 以内,样品的磁性隧道结性质具有较好的均匀性和一致性,可以满足研制磁随机存储器存储单元演示器件的基本要求.
关键词:
磁性隧道结
隧穿磁电阻
磁随机存储器
4英寸热氧化硅衬底 相似文献
75.
It is well known that topology and dynamics are two major aspects to determine the function of a network. We study one of the dynamic properties of a network: trajectory convergence, i.e. how a system converges to its steady state. Using numerical and analytical methods, we show that in a logical-like dynamical model, the occurrence of convergent trajectory in a network depends mainly on the type of the fixed point and the ratio between activation and inhibition links. We analytically proof that this property is induced by the competition between two types of state transition structures in phase space: tree-like transition structure and star-like transition structure. We show that the biological networks, such as the cell cycle network in budding yeast, prefers the tree-like transition structures and suggest that this type of convergence trajectories may be universal. 相似文献
76.
77.
Chirped fiber grating was used in dispersion compensator. We tried to use the same phase mask to write fiber grating of different wavelength with two methods to reduce the price of the fiber grating. 相似文献
78.
Yu-hai WU~ 《中国科学A辑(英文版)》2007,50(7):925-940
This paper concerns the number and distributions of limit cycles in a Z_2-equivariant quintic planar vector field.25 limit cycles are found in this special planar polynomial system and four different configurations of these limit cycles are also given by using the methods of the bifurcation theory and the qualitative analysis of the differential equation.It can be concluded that H(5)≥25=5~2, where H(5)is the Hilbert number for quintic polynomial systems.The results obtained are useful to study the weakened 16th Hilbert problem. 相似文献
79.
80.
Using the theoretically calculated point-defect total-energy values of Baraff and Schlüter in GaAs, anamphoteric-defect model has been proposed by Walukiewicz to explain a large number of experimental results. The suggested amphoteric-defect system consists of two point-defect species capable of transforming into each other: the doubly negatively charged Ga vacancyV
Ga
2–
and the triply positively charged defect complex (ASGa+V
As)3+, with AsGa being the antisite defect of an As atom occupying a Ga site andV
As being an As vacancy. When present in sufficiently high concentrations, the amphoteric defect systemV
Ga
2–
/(AsGa+V
As)3+ is supposed to be able to pin the GaAs Fermi level at approximately theE
v
+0.6 eV level position, which requires that the net free energy of theV
Ga/(AsGa+V
As) defect system to be minimum at the same Fermi-level position. We have carried out a quantitative study of the net energy of this defect system in accordance with the individual point-defect total-energy results of Baraff and Schlüter, and found that the minimum net defect-system-energy position is located at about theE
v
+1.2 eV level position instead of the neededE
v
+0.6 eV position. Therefore, the validity of the amphoteric-defect model is in doubt. We have proposed a simple criterion for determining the Fermi-level pinning position in the deeper part of the GaAs band gap due to two oppositely charged point-defect species, which should be useful in the future. 相似文献