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针对自由空间光通信链路性能易受大气湍流影响的问题,构造了一种适用于自由空间光通信的多输人多输出(MIMO)极化编码方法.基于通用偏序法、极化编码、调制及MIMO技术联合优化快速构造极化码,并在大气湍流信道下进行仿真分析.实验结果表明,在不同构造方法及编码方案下,MIMO极化编码方法能在保持低复杂度的同时使系统获得更好的性能.在强湍流条件且误码率为10-4时,相比Monte Carlo方法,偏序法的编码增益约为0.2dB,且离线构造的计算复杂度可忽略不计;强弱湍流条件下,相比单输入单输出(SISO)-polar方式,MIMO(2×2)-polar方式的编码增益约为1.1~1.6 dB,具有明显的分集优势. 相似文献
95.
László Gyarmati András Gulyás Balázs Sonkoly Tuan A. Trinh Gergely Biczók 《Computer Networks》2013,57(8):1758-1773
The increasing popularity of both small and large private clouds and expanding public clouds poses new requirements to data center (DC) architectures. First, DC architectures should be incrementally scalable allowing the creation of DCs of arbitrary size with consistent performance characteristics. Second, initial DC deployments should be incrementally expandable supporting small-scale upgrades without decreasing operation efficiency. A DC architecture possessing both properties satisfies the requirement of free-scaling.Recent work in DC design focuses on traditional performance and scalability characteristics, therefore resulting in symmetric topologies whose upgradability is coarse-grained at best. In our earlier work we proposed Scafida, an asymmetric, scale-free network inspired DC topology which scales incrementally and has favorable structural characteristics. In this paper, we build on Scafida and propose a full-fledged DC architecture achieving free-scaling called FScafida. Our main contribution is threefold. First, we propose an organic expansion algorithm for FScafida; this combined with Scafida’s flexible original design results in a freely scalable architecture. Second, we introduce the Effective Source Routing mechanism that provides near-shortest paths, multi-path and multicast capability, and low signaling overhead by exploiting the benefits of the FScafida topology. Third, we show based on extensive simulations and a prototype implementation that FScafida is capable of handling the traffic patterns characteristic of both enterprise and cloud data centers, tolerates network equipment failures to a high degree, and allows for high bisection bandwidth. 相似文献
96.
Evaluation of Flow Resistance in Smooth Rectangular Open Channels with Modified Prandtl Friction Law
Nian-Sheng Cheng Hoai Thanh Nguyen Kuifeng Zhao Xiaonan Tang 《Canadian Metallurgical Quarterly》2011,137(4):441-450
Flow resistance in open channels is usually estimated by applying the approach that is developed originally for pipe flows. Such estimates may be useful for engineering applications but always differ from measurements to some extent. This paper first summarizes empirical approaches that have been proposed in the literature to reconcile the resistance difference. These include various modifications of the pipe friction for applications to rectangular ducts and open channel flows. An improved friction equation is then derived for evaluating flow resistance of smooth rectangular open channels. Comparisons are made with experimental data reported by previous researchers and those collected in the present study. It is shown that the new proposed equation is applicable for both narrow and wide channels and is more accurate than those available in the literature. 相似文献
97.
From Biomimetic Concept to Engineering Reality – A Case Study on the Design of Ceramic Reinforcement
The applications of ceramics are limited by their brittleness. Though the toughness of ceramics can be improved by adding hard and strong toughening agents, their damage tolerance is still poor. Novel concept derives from fish scale is explored and used to design alternative toughening agent. The microstructure of fish scale exhibits hierarchical complexity and many weak layers are present. As fish scales are used directly as the toughening agent, the toughness of ceramics can be enhanced. Furthermore, a new toughening mechanism involving crack deflection within fish scale is observed. Based on such observation, the toughening agents with internal weak interfaces are recommended as the toughening agent. Many ceramic/metal interfaces are present within the multilayer ceramic capacitors (MLCCs). The addition of MLCCs into brittle glass improves its crack resistance considerably. 相似文献
98.
Nguyen Dang Manh Anton Evgrafov Allan Roulund Gersborg Jens Gravesen 《Computer Methods in Applied Mechanics and Engineering》2011,200(13-16):1343-1353
We consider a model problem of isogeometric shape optimization of vibrating membranes whose shapes are allowed to vary freely. The main obstacle we face is the need for robust and inexpensive extension of a B-spline parametrization from the boundary of a domain onto its interior, a task which has to be performed in every optimization iteration. We experiment with two numerical methods (one is based on the idea of constructing a quasi-conformal mapping, whereas the other is based on a spring-based mesh model) for carrying out this task, which turn out to work sufficiently well in the present situation. We perform a number of numerical experiments with our isogeometric shape optimization algorithm and present smooth, optimized membrane shapes. Our conclusion is that isogeometric analysis fits well with shape optimization. 相似文献
99.
用溶胶-凝胶技术在Bi(100)衬底上制备了单层和渐变型多层的BaxSr(1-X)TiO3薄膜,其膜层组分分别为:Ba0.7Sr0.3TiO3,Ba0.8Sr0.2TiO,Ba0.9Sr0.1TiO3,BaTiO3,对生长制备出的多层BaxSr(1-X)TiO3薄膜进行了变角度椭偏光谱测量,通过椭偏光谱解谱分析研究,首次得到了BaxSr(1-X)TiO3多层膜结构不同膜层的膜厚和光学常数,其结果显示:椭偏光谱分析得到的不同膜层的膜厚与卢瑟福背向散射测量得到的结果基本相符;渐变型多层膜中BaTiO3薄膜的折射率比单层BaTiO3薄膜折射率大许多,与体BaTiO3的折射率相接近,这说明渐变型多层膜中BaTiO3薄膜的光学性质与体材料的光学性质接近。 相似文献
100.
Large parabolic dish concentrators have been widely employed in solar thermal applications. The supporting structure of a solar dish concentrator consists of a circular frame, a central post, and front and rear cables connecting the frame to the post. The tensions in the cables cause compressive stresses in the circular frame and the central post, and this support structure must be designed for stability. In this paper, the nonlinear buckling behavior of the supporting structure of a cable-stayed circular frame is studied in detail. A three-dimensional finite element model of the supporting structure is developed to predict the critical cable tensions that would cause buckling of the circular frame and to determine the associated buckling mode shapes of the supporting structural system. The results show that the buckling load of a cable-stayed circular frame depends not only upon the cross-section of the frame, but also upon the number of cables and the inclinations of the cables. In all cases, in-plane buckling modes are predominant. The concentrated torques resulting from unbalanced cable tensions tend to induce the out-of-plane buckling modes. 相似文献