偏心支撑钢框架延性抗震设计探讨

偏心支撑钢框架结构体系是一种非常适合强震地区的抗震结构体系.国内外许多高层建筑采用了该结构体系,尤其在美国与日本的高地震烈度地区.国内外现行规范对该体系的设计均未能充分体现其良好的延性与耗能能力,但只有通过结构的延性设计才能使结构真正具有耗能能力.本文从不同支撑类型的刚度、高跨比、延性和双重体系探讨了支撑类型的选择与布置形式,分析了耗能梁长度与截面设计以及耗能梁与支撑、柱的连接形式对偏心支撑钢框架结构体系延性和耗能能力的影响,提出了偏心支撑钢框架结构体系延性抗震设计的建议与思路,为规范修订和工程应用提供一些参考.     

软切换FSO/RF链路混合编码调制算法性能分析

将自由空间光(FSO)通信链路的高速率优势与射频(RF)链路的可靠性优势互补结合,针对FSO/RF混合通信链路组网的物理层数据可靠传输问题,研究软切换机制下采用LDPC混合编码与2-PPM和16QAM调制的系统方案性能。混合系统FSO链路在Gamma-Gamma信道不同湍流强度与RF链路在Rician信道不同信噪比条件下的仿真结果表明,所述方案在软切换下达到1×10~(-6)误比特率时,不同条件下可获得1.3~8.0 dB不等的性能增益改善,显著提高在不同链路条件下FSO/RF混合通信系统的数据传输可靠性。     

Study of a new type of steel slit shear wall with initially twisted links

To address the issue of strength and stiffness degradation of steel slit shear walls (SSSWs) after the occurrence of out‐of‐plane buckling at large lateral deformation, a new type of SSSW made by assembling initially twisted steel plate links is proposed in the present work. Three types of SSSW specimens, with vertical slits, narrow rhomboid openings, and initially twisted steel plate links, respectively, were manufactured and tested under quasi‐static cyclic loading. Test results showed that the SSSW assembled by initially twisted steel plate links had no strength degradation and a nearly constant positive second stiffness throughout the whole loading process with a maximum drift ratio of 6%, whereas the other two SSSW specimens exhibited obvious degradation of strength, stiffness and energy dissipation capacity. The new SSSW also had much smaller residual strength, and its deformation capacity was largely improved. The method to predict the elastic stiffness of the new SSSW was proposed, by which the predicted results agreed well with test results. A user‐defined macromodel was developed to simulate its force‐deformation hysteretic behavior.     

无线传感器网络中自修复密钥颁布机制中滑动窗口的动态性探讨

在很多自修复密钥颁布机制中,滑动窗口大小影响着密钥的修复性能和通信开销.本文利用概率知识,首次建立了滑动窗口和丢包率对节点密钥同步性能、组安全关联性能和安全服务性能的数学模型.设计了适应链路动态变化特性的滑动窗口选择机制,采用查找表方式优化了计算和存储开销.仿真验证了该机制具有动态适应性,可以高概率的保证网络的安全服务性能.与已有机制相比,所提机制显著降低了通信开销,具有可行性和高效性,进一步推动了自修复密钥颁布机制的实际应用.     

Faculty Begin to Replace Textbooks with “Freely” Accessible Online Resources

ABSTRACT

More and more students are financially unable to acquire, or deliberately choose to go without course textbooks. A variety of commercial and noncommercial initiatives have materialized to address the student success challenge of learning material access inequality in the classroom. There is a gap between how higher education faculty plan to teach a course and the actual learning environment that exists in practice. Faculty are beginning to experiment with freely available and licensed library materials as a substitute for commercial textbooks and course packages to address the failure of textbook publishers to reach a price point that entices students to buy textbooks. The results thus far are promising. Some courses can be delivered today using only “freely available” learning resources, some using a mix of fee based and free, while others cannot be delivered using any freely available resources at all due to a lack of availability.     

兼顾稳定性与经济性的交直流系统直流落点选择方法

直流电系统落入受端交流电网的落点选择需要考虑交直流系统的相互作用,主要包括有效短路比、静态电压稳定指标和受端系统的有功功率损耗。文中提出一种兼顾稳定性与经济性的直流落点选择方法。基于数学上解决多目标决策问题的线性加权和法,首先设置各指标的门槛值,然后对其进行归一化处理,采用组合赋权法合理确定权系数,建立目标函数,选出最...     

Tools for consistency management between design products

Consistency between different design documents is most important, as these documents are usually elaborated by different persons. Consistency means that structures within different documents “match” each other and also the values of corresponding attributes. Interactive and incremental tools for building up and maintaining consistency - so-called integrators - install fine-grained relations (semantic links) between objects of these documents. Such integrators have been investigated for some time in different application domains (Nagl, 1996).This paper deals with two extensions of integrators ( [K?rtgen, 2009a] and [K?rtgen, 2009b]). Both are devoted to speed up the (re-)integration process. The first extension makes use of the still valuable information of links damaged due to changes of documents. The second reuses consistent documents of past projects, to find out big and suitable related parts of design documents or of corresponding underlying knowledge. This paper is written for a chemical engineer and, therefore, emphasizes the tool functionality side.     

Complementary geometric formulations for electrostatics

The simultaneous use of a pair of complementary discrete formulations for electrostatic boundary value problems (BVPs) allows to accurately compute electromagnetic quantities, such as capacitance or electrostatic force with a minimum computational effort. In fact, the two formulations provide the upper and lower bounds for these quantities and their averages result quite close to the exact solution even for extremely coarse meshes. Despite the potential benefit to the many three‐dimensional large‐scale applications, taking advantage of this feature is not exploited in practice due to theoretical difficulties in the potential design. The aim of this paper is to fill this gap by rigorously introducing a pair of three‐dimensional complementary geometric formulations to solve electrostatic BVPs on domains covered by conformal polyhedral meshes. In particular, an original formulation based on a vector potential is introduced by using cohomology theory with integer coefficients. It is shown how the so‐called thick links are needed, which are representatives of the second cohomology group generators of the dielectric region. Two easy‐to‐implement graph‐theoretic algorithms to automatically find such a basis with optimal computational complexity are described. Some benchmark problems are presented to show how the simultaneous use of both formulations yields to a sensible computational advantage. Therefore, solvers based on complementary formulations should be embedded in the next‐generation of electromagnetic Computer‐Aided Engineering (CAE) softwares. Copyright © 2010 John Wiley & Sons, Ltd.     

圆环链链轮传动力学模型的建立与计算方法

建立了清晰的圆环链—链轮传动的力学模型 ,识别了决定传动形式的齿形、自锁、啮入过程等关键细节问题 ,并探讨了在这一力学模型下借用图形学专业软件来计算链环受力的方法 ,突破了传统分析轻重不分不建理论模型的缺陷 ,能做到定量计算