Landing domain analysis of shuttle re-entry vehicles

With increasing frequency in space shuttle operation, it is of interest to have more than one or two landing fields within the boundary of the reachable area of the reentry vehicle. This boundary, called the footprint, depends on the aerodynamic characteristics of the vehicle. It has been investigated previously but unfortunately was not completely constructed, especially the minimum range on the longitudinal axis and the left end portion of the footprint. In this paper, the previous work using the facilities of the continuation method and the multiple shooting method is extended, and a complete footprint is constucted. At first, the optimal trajectories are solved in the vertical plane and in the three-dimensional space to minimize the final range on the longitudinal axis, θ _{? min},. After comparison of the obtained minimum longitudinal ranges, we find that the three-dimensional optimal trajectory is the global optimal trajectory for θ _{? min},. With the application of the techniques of rotating the coordinates, based on this θ _{? min}, we obtain the complete footprint by the optimal lift and bank modulations for three-dimensional re–entry trajectories with lift constraint.     

Multivariable control design for stochastic systems with saturated driving: LQG optimal approach

A stability criterion for stochastic multivariable feedback systems with saturated actuators is derived. An algorithm is proposed to choose an appropriate linear-quadratic-gaussian (LQG) performance index scalar to satisfy the stability criterion, and then a robust LQG optimal controller is obtained to override the limit cycle or instability incurred by saturated actuators employed in control systems. Finally, a simulation is given to support the results.     

Stable-throughput analysis and optimization of cooperative cognitive radio networks based on information and energy cooperation

According to the unsaturated data traffic in wireless communications, this paper studies the interaction between primary users (PUs) and secondary users (SUs) in a cooperative cognitive radio network which is based on information and energy cooperation, and optimizes the stable-throughput of SUs. A probabilistic cooperation scheme has been proposed and the stable-throughput region has been characterized in order to reflect the interaction between PUs and SUs by using the Queuing Theory. Then by deriving the optimal value of the relaying probability, the stable-throughput of secondary users can be maximized under the constraint of the primary queue stability. Simulation results and theoretical analysis show that the probabilistic cooperation scheme can achieve maximal stable-throughputs for SUs, and meanwhile PUs can also have a better performance compared to the non-cooperative case.     

认知无线电中继协助网络资源分层优化算法

在认知多用户中继网络系统场景下,针对时变信道完全DF中继两跳传输的差异性问题,采用纳什议价公平性准则效用函数,提出了联合用户传输模式选择、子载波配对、信道分配和功率分配的分层优化模型。利用拉格朗日对偶理论实现模型分层求解,在降低算法复杂度的同时提升了系统效用及吞吐量。仿真结果表明:相对于完全中继、直传网络和非载波配对的中继网络,所提算法在兼顾用户速率需求和公平性的同时可使系统吞吐量获得较大提高。     

避免非视距影响的蒙特卡罗移动节点定位方法简

Enhanced Monte Carlo Boxed (EMCB), based on the broadcasting messages of one-hop neighbor nodes, is proposed in a mobile wireless sensor network for NLOS environment. The utilization efficiency of nodes is improved in the way of message flooding. The located nodes are used as the virtual anchor nodes in order to improve the location precision in the network with few anchors, optimizing the sample boxes of the neighbor nodes. Besides, both the theoretical limit of connectivity and the previous location information are used to enhance the filtering performance. Taking advantage of the one-hop messages, all the nodes are located layer-by-layer. Finally, the results of simulation show that the location precision is improved compared with the traditional algorithms in any situation. Especially, a good performance is achieved with fewer anchor nodes.     

A practical approach to scheduling a multistage,multiprocessor flow-shop problem

This paper describes a rubber manufacturing system and the numerous technological, operating and quality constraints governing its scheduling process. The complex system resembles a flow-shop problem where all jobs share the same general processing order on a progression of machines. The manufacturing system is defined in terms of production stages and parallel processing lines. One stage can process two or more jobs simultaneously. Jobs are often split on the last stage so that two or more parallel processing lines process the same job simultaneously. The scheduling for such a multistage, multiprocessor flow shop is dominated by the quality constraints. A pragmatic approach is provided in which a schedule is constructed through extensive iterations of analysis and simulation.     

Valence Distribution in ATxV6-xO11 Compounds

1-IntroductionAVoOll(A,Alkalineoralkalineearthmetal)-typecompoundsaretheonlyphaseswhichshowferromag-neticbehaviorandmetallicconductivityamongvar-iousVs+~V`+mixedvalenceoxidesI1~3].Tohaveagoodunderstandingofthestructure-propertyre-lationship,manypapershavebeenpublishedtore-vealthecrystalstructuresofthesecompoundsinthelatesty6ars.DeRoyetal.l4]determinedcrystalstructureofNaV6O11forthefirsttimewithspacegroupP-62c.Kankeetal.l5lstudiedthecrystalstructuresofSrV6O11,SrTi.V6-.o11(o相似文献   

Solution of variational problems using the Fourier series operational matrix

There are many functions having the property of orthogonality. Among them are Walsh functions, block-pulse functions, Chebyshev functions and Legendre functions. Recently, many scholars and researchers made new approaches to solving variational problems via orthogonal functions. This paper suggests a more simple and powerful orthogonal method—the Fourier series operational matrix for integration—which is derived and used to solve a variational problem.     

Robust stability of linear perturbed discrete systems with saturating actuators

This paper is concerned with the robust stability conditions for linear perturbed systems with saturating actuators in the discrete-time case. Both non-linear and linear perturbations are considered. Two types of controller, a state feedback and a dynamic controller, are introduced to guarantee asymptotic stability of the perturbed system.     

工业工程课程的最新沿革

简要回顾了传统工业工程课程的发展历史,分析了传统工业工程课程的五大局限。之后,根据当代产业的特点和发展需求,以及工业工程学科本身发展的需要,提出了具有现代化活力的工业工程新课程。新课程具有六大特点,其目的是培养学生成为符合现代生产和制造特点的工业工程师。