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排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Let R be a ring and S a class of R-modules. S-superfluous epimorphisms and S-essential monomorphisms are introduced and studied in this article. As appli-cations, some new characterizations of yon Neumann regular rings and perfect rings are given. Finally, these notions are also used to study minimal homomorphisms. 相似文献
992.
993.
In this paper, we use a semi-discrete and a padé approximation method to propose a new difference scheme for solving convection–diffusion problems. The truncation error of the difference scheme is O(h4+τ5). It is shown through analysis that the scheme is unconditionally stable. Numerical experiments are conducted to test its high accuracy and to compare it with Crank–Nicolson method. 相似文献
994.
本文利用文[2]提供的方法,得到了代数特征值反问题解几乎处处扰动存在及连续性的结论。 相似文献
995.
The free vibration of a functionally graded material hollow sphere submerged in a compressible fluid medium is exactly analyzed.
The sphere is assumed to be spherically isotropic with material constants being inhomogeneous along the radial direction.
By employing a separation technique as well as the spherical harmonics expansion method, the governing equations are simplified
to an uncoupled second-order ordinary differential equation, and a coupled system of two such equations. Solutions to these
equations are given when the elastic constants and the mass density are power functions of the radial coordinate. Numerical
examples are finally given to show the effect of the material gradient on the natural frequencies.
The project is supported by the National Natural Sciences Foundation of China(No. 19872060). 相似文献
996.
Huming Ren Yanhuai Ding Yong Jiang Fu Xu Zhilin Long Ping Zhang 《Journal of Sol-Gel Science and Technology》2009,52(2):287-290
ZnO nanofibers were prepared from zinc acetate/polyvinyl alcohol (PVA) by electrospun method. The morphological features,
crystallinity, mechanical and optical properties of the ZnO nanofibers were studied. The results show the specific surface
area of the ZnO nanofibers was influenced by the electrospun conditions. The specific surface area reached 389.7 m2g−1 as the average diameter was 232 nm. The XRD date reveals the nanofibers consist of a single phase of well-crystallized ZnO
with hexagonal structure. The elastic modulus of a single ZnO nanofiber was also characterized by nano-scale three-point bending
test. 相似文献
997.
两同心球间旋转流动类Lorenz方程组的静态分歧 总被引:3,自引:0,他引:3
对同心球间旋转流动的N av ier-S tokes方程谱展开后进行三模态截断,讨论了所得到的类Lorenz型方程组的分歧问题.给出了静态奇异点的条件,并计算出解分支.首先,简要介绍了Lorenz方程组以及用Lorenz截断法讨论非线性问题的意义,其次,推导同心球间旋转流动N av ier-S tokes方程的流函数-涡度形式,最后,讨论同心球间旋转流动的类Lorenz型方程组的分歧问题. 相似文献
998.
999.
搜索区传递2-(q,4,1)设计 总被引:1,自引:0,他引:1
对于区传递但非旗传递的可解2-(q,4,1)设计,Camina指出,当q=13,37,61,109,157,181时有具体的例子,但是否有更多的q产生具体例子有待研究。主要结果:设q是素数幂且q=13(mod24),则对于每个q〈2000,总存在区传递但非旗传递的2-(q,4,1)设计。 相似文献
1000.
Min-Sheng Hung Pei-Pei Ding Ping-Hei Chen 《Experimental Thermal and Fluid Science》2009,33(2):292-305
The present study employs a transient liquid crystal thermography to measure film cooling performance over constant curvature of concave and convex surfaces. This work investigates detailed distributions of both film cooling effectiveness and heat transfer coefficient on concave and convex surfaces with one row of injection holes inclined stream-wise at 35° at four blowing ratios (0.5, 1.0, 1.5 and 2.0) on four test pieces with different hole configurations. All test models have a row of discrete holes with a stream-wise injection angle (γ of 35° and a pitch-to-diameter ratio (P/d) of 3. The current work examines four different injection configurations, one with simple and three with 8° forward-expanded holes. Three compound angles of 0, 45 and 90° with air (ρc/ρm = 0.98) as coolants are tested under the mainstream Reynolds number (Red) of 2300 on concave surface, and 1700 on convex surface. Measured results of the concave surface show that both the span-wise averaged heat transfer coefficient and film cooling effectiveness increase with blowing ratios for all tested models. Higher heat transfer levels induced by large flow disturbance of compound-angle injection also lead to poorer overall film cooling performance, especially at high blowing ratio and large span-wise injection angle. Present results show that the best surface protection on the concave surface over the widest range of M can be provided by the forward-expanded holes with β = 0° (Model-B), followed by the forward-expanded holes with β = 45° (Model-C). Convex surface results show that the compound-angle injection indicates increases in both film cooling effectiveness and heat transfer at moderate and high blowing ratios. The forward-expanded hole with simple-angle injection provides the best film performance because of high film cooling effectiveness and low heat transfer coefficient at blowing ratio of 0.5. 相似文献