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11.
奚欧根 《宁波大学学报(理工版)》1991,(1)
本文定义了Γ-环的b-理想与拟b-理想,论述了Γ-环中都有一个Baer根,一个b-根与一个拟强b-根,并且还证得了Γ-环的Baer根=b-根=拟b-根。 相似文献
12.
13.
James Tanton 《Mathematical Intelligencer》2007,29(3):55-59
This column is a place for those bits of contagious mathematics that travel from person to person in the community, because
they are so elegant, suprising, or appealing that one has an urge to pass them on.
Contributions are most welcome. 相似文献
14.
The shock structure problem is one of the classical problems of fluid mechanics and at least for non-reacting dilute gases it has been considered essentially solved. Here we present a few recent findings, to show that this is not the case. There are still new physical effects to be discovered provided that the numerical technique is general enough to not rule them out a priori. While the results have been obtained for dense fluids, some of the effects might also be observable for shocks in dilute gases. 相似文献
15.
It is shown that time-dependent temperatures in a transient, conductive system can be approximately modeled by a fractional-order
differential equation, the order of which depends on the Biot number. This approximation is particularly suitable for complex
shapes for which a first-principles approach is too difficult or computationally time-consuming. Analytical solutions of these
equations can be written in terms of the Mittag-Leffler function. The approximation is especially useful if a suitable fractional-order
controller is to be designed for the system. 相似文献
16.
因特网防御DoS攻击技术评述Ⅰ--攻击分类与特征·包过滤·攻击检测与防御 总被引:1,自引:0,他引:1
概述了因特网上DoS攻击的相应分类及基本特征,评述了包过滤、攻击检测及防御技术的最新成果.前一部分介绍了入口过滤、基于路由的过滤网和有效源地址强制协议.后一方面主要讨论了适合于检测攻击包的技术,介绍了新近提出的频谱分析方法和泛滥检测系统.简要评述了已有的防御SYN泛滥攻击的技术措施,介绍了Cisco的TCP拦截技术,提出了改进策略. 相似文献
17.
A numerical simulation is performed to investigate the flow induced by a sphere moving along the axis of a rotating cylindrical container filled with the viscous fluid. Three‐dimensional incompressible Navier–Stokes equations are solved using a finite element method. The objective of this study is to examine the feature of waves generated by the Coriolis force at moderate Rossby numbers and that to what extent the Taylor–Proudman theorem is valid for the viscous rotating flow at small Rossby number and large Reynolds number. Calculations have been undertaken at the Rossby numbers (Ro) of 1 and 0.02 and the Reynolds numbers (Re) of 200 and 500. When Ro=O(1), inertia waves are exhibited in the rotating flow past a sphere. The effects of the Reynolds number and the ratio of the radius of the sphere and that of the rotating cylinder on the flow structure are examined. When Ro ? 1, as predicted by the Taylor–Proudman theorem for inviscid flow, the so‐called ‘Taylor column’ is also generated in the viscous fluid flow after an evolutionary course of vortical flow structures. The initial evolution and final formation of the ‘Taylor column’ are exhibited. According to the present calculation, it has been verified that major theoretical statement about the rotating flow of the inviscid fluid may still approximately predict the rotating flow structure of the viscous fluid in a certain regime of the Reynolds number. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
18.
This paper presents the applications of digital image correlation technique to the mesoscopic damage and fracture study of
some granular based composite materials including steelfiber reinforced concrete, sandstone and crystal-polymer composite.
The deformation fields of the composite materials resulted from stress localization were obtained by the correlation computation
of the surface images with loading steps and thus the related damage prediction and fracture parameters were evaluated. The
correlation searching could be performed either directly based on the gray levels of the digital images or from the wavelet
transform (WT) coefficients of the transform spectrum. The latter was developed by the authors and showed higher resolution
and sensitivity to the singularity detection. Because the displacement components came from the rough surfaces of the composite
materials without any coats of gratings or fringes of optical interferometry, both surface profiles and the deformation fields
of the composites were visualized which was helpful to compare each other to analyze the damage of those heterogeneous materials.
The project supported by the National Natural Science Foundation of China (10125211 and 10072002), the Scientific Committee
of Yunnan Province for the Program of Steel Fiber Reinforced Concrete, and the Institute of Chemical Materials, CAEP at Mianyang 相似文献
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