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111.
112.
Composite materials often exhibit local fluctuations in the volume fraction of their individual constituents. This paper studies the influence of such small fluctuations on the effective properties of composites. A general asymptotic expansion of these properties in terms of powers of the amplitude of the fluctuations is given first. Then, this general result is applied to porous materials.As is well-known, the effective yield surface of ductile voided materials is accurately described by Gurson's criterion. Suitable extensions for viscoplastic solids have also been proposed. The question addressed in the present study pertains to nonuniform distributions of voids in a typical volume element or in other words to the presence of matrix-rich and pore-rich zones in the material. It is shown numerically and analytically that such deviations from a uniform distribution result in a weakening of the macroscopic carrying capacity of the material. 相似文献
113.
Zhuang Wajin 《东北数学》1995,(1)
PartialOrderingsintheCategoryofMatricesovertheQuaternionFieldZhuangWajin(庄瓦金)(DepartmentofMathematics,ZhangNormalCollege,Fuji... 相似文献
114.
An effective method is developed and used to investigate the antiplane problem of a rigid line in a confocal elliptic inhomogeneity
embedded in an infinite medium. The analytical solution is obtained. The proposed method is based upon the use of conformal
mapping and the theorem of analytic continuation. Special solutions which are verified by comparison with existing ones are
provided. Finally, the characteristics of stress singularity at the tip of the rigid line inhomogeneity are analyzed and the
extension forces for the crack and the rigid line inhomogeneity are derived.
The project supported by the National Natural Science Foundation of China, the State Education Commission Foundation and the
Failure Mechanics Lab of SEdC. 相似文献
115.
The forward current-voltage (I-V) characteristics of polycrystalline CoSi2/n-Si(100) Schottky contacts have been measured in a wide temperature range. At low temperatures (≤200K), a plateau-like section is observed in the I-V characteristics around 10-4A·cm-2. The current in the small bias region significantly exceeds that expected by the model based on thermionic emission (TE) and a Gaussian distribution of Schottky barrier height (SBH). Such a double threshold behaviour can be explained by the barrier height inhomogeneity, i.e. at low temperatures the current through some patches with low SBH dominates at small bias region. With increasing bias voltage, the Ohmic effect becomes important and the current through the whole junction area exceeds the patch current, thus resulting in a plateau-like section in the I-V curves at moderate bias. For the polycrystalline CoSi2/Si contacts studied in this paper, the apparent ideality factor of the patch current is much larger than that calculated from the TE model taking the pinch-off effect into account. This suggests that the current flowing through these patches is of the tunnelling type, rather than the thermionic emission type. The experimental I-V characteristics can be fitted reasonably well in the whole temperature region using the model based on tunnelling and pinch-off. 相似文献
116.
MODAL ANALYSIS OF A SLOTTED WAVEGUIDE: COMPARISON BETWEEN ANALYTIC SOLUTION AND COMPUTER SIMULATIONS
Because of the complicated geometry of the slotted structure, analytical theories of such structures are inevitably developed
on the basis of simplifying assumptions. On the other hand, the accuracy of the theory is of importance to the design of microwave
interaction structures. In this study, modes of the slotted waveguide are investigated analytically and simulated with the
HFSS code. It is shown that, in spite of the approximations made, the dispersion relation and field patterns of the standard
analytical theory are in excellent agreement with the HFSS simulations over the complete range of the slot depth. Modes not
built into the theory will also be noted. 相似文献
117.
非圆截面环流器FY-1实验(Ⅰ)——被动运行部分 总被引:1,自引:1,他引:0
本文简略地描述了FY-1装置结构、等离子体基本参数的测量和等离子体位形的调试,初步考察了硬X射线产额与工作气压的关系。实验分析表明,FY-1装置已形成的等离子体环流放电属于逃逸放电。在场成形线圈作被动运行时,通过改变其回路连接方式和外串电感值,可适当调节等离子体平衡位置和位形。MHD平衡计算与实验测量拟合结果表明,等离子体截面可调节为不同截面积和拉长比(k=1.1—1.4)的椭圆。 相似文献
118.
119.
Ji Chungang 《东北数学》1998,(1)
in this paper, let K = Q ( ) be an abelian number field,where mi's are distinct square-free integers and Gal (K/Q ) (Z/2Z )n+1, and let k Q(M). When k is imaginary or k is real and has a unit of norm -1, we give a necessaryand sufficient condition for K/k to have a normal integral basis. 相似文献
120.
Carbon-containing gases usually present when preparing carbon nanotubes, and can affect the field emission of carbon nanotubes. Water vapor is also an important kind of gas for field emission, concerned by both experimental and theoretical studies. Under strong electric field, the gas molecules may be decomposed to radicals. Using DMol3 code based on density-functional theory, we calculated the adsorption of the gas molecules CH4, CO and H2O and the CH3 and OH radicals under emission conditions. We found that the H2O and the methyl have advantages to field emission and the CH4, CO and the hydroxyl have disadvantages. The results of H2O and CO are consistent with experiments, and the enhancement of current by CH4 in the experiment may be due to the methyl decomposed from the CH4. 相似文献