乡村人口收缩背景下经济发达地区村庄用地演变：以江苏省常熟市为例

在乡村人口收缩背景下,部分地区村庄用地规模持续增长。为研究这一现象,以经济发达的江苏省常熟市为例,基于2009-2013年土地利用变更调查数据,结合多时相高清卫星影像识别村庄用地类型,阐释村庄用地的演变特征,并从土地供需角度探究村庄用地持续扩张的机制。将村庄用地划分为村庄商服住宅用地、村庄工业用地和其他村庄用地3类。分析结果表明：1）2009-2013年,常熟市村庄工业用地净增量占比53.92%,是乡村空间扩展的主要原因,商服住宅用地净增量占17.88%,且以住宅用地的增长为主;2）常熟市村庄住宅用地持续增长主要源于地方政府对农村社区建设用地补偿过量,村庄工业用地的快速扩张则主要源于乡村工业化的持续推进、企业生产利益追逐及地方政府对财税和经济增长的追求。乡村价值回归提升趋势下,人口收缩的乡村发展转型和土地节约集约利用势在必行。乡村生活空间合理集中化、生产空间进一步集约化、保留和改善生态空间,从而实现乡村“三生一体”。     

Bivariate grid-connection speed control of hydraulic wind turbines

The requirement for An electrical grid-connected wind turbine is that the synchronous generator speed is stable within a required speed range for the electrical grid. In this paper, a hydraulic wind turbine (HWT) system is considered, and the working principle and working conditions of the HWT are introduced. A novel speed control method is proposed in this paper, using both a proportional flow control valve and a variable displacement motor, which are adjusted in combination to control the speed of the HWT. By establishing a state space model of the HWT and solving the nonlinear system with a feedback linearization method, a bivariate tracking controller is constructed to realize accurate speed control under fluctuating wind speed and the load disturbance conditions. The effectiveness of the control method is verified by simulation, but experimental results highlight problems with the method. The theoretical controller is simplified to reduce sensitivity to measurement noise and modeling error. The control effect has been improved to some extent, but it is limited. Based on these results, combined with the sliding mode variable structure control method and the feedback linearization method to solve the problem of measurement noise and modeling error, and the effectiveness of the control law is finally verified experimentally. It lays a theoretical foundation for the practical application of HWT.     

Novel delay-partitioning approaches to stability analysis for uncertain Lur’e systems with time-varying delays

This work deals with the problem of absolute stability analysis for a class of uncertain Lur’e systems with time-varying delays. Novel delay-partitioning approaches are presented, which are dividing the variation interval of the delay into three subintervals. Some new augment Lyapunov–Krasovskii functionals (LKFs) are defined on each of the obtained subintervals which can efficiently make use of the information of the delay and relate to the reciprocally convex combination technique and the Wirtinger-based integral inequality method. Several improved delay-dependent criteria are derived in terms of the linear matrix inequalities (LMIs). The merit of the proposed criteria lies in their less conservativeness and lower numerical complexity than relative literature. Two numerical examples are included to illustrate the effectiveness and the improvement of the proposed method.     

Asynchronous non-fragile control for persistent dwell-time switched singularly perturbed systems with strict dissipativity

This paper focuses on the problem of asynchronous non-fragile dissipativity control for a class of switched singularly perturbed systems (SPSs) governed by the persistent dwell-time (PDT) switching mechanism in the discrete-time context. Unlike some previous results, the modes of system and controller in this paper are assumed to be asynchronized, which conforms better with the practical scenarios. Besides, considering the case that the controllers may be affected by uncertain factors and can not be realized accurately during system operation, the non-fragile mechanism is introduced in the process of controller design to enhance the reliability and security of the SPSs. Based on Lyapunov stability theory and stochastic analysis theory, some sufficient conditions are obtained, which can ensure the exponentially mean-square stable (EMSS) and strict dissipative performance of the closed-loop system. Furthermore, the asynchronous non-fragile slow state variables feedback (SSVF) controller gains are obtained by solving a set of linear matrix inequalities (LMIs). Finally, a numerical example and an inverted pendulum model are applied to demonstrate the superiority and the practicability of the developed control mechanism.     

Adaptive leaderless consensus control of a class of strict feedback nonlinear systems with guaranteed transient performance under actuator faults

The problem of adaptive leaderless consensus control of a class of uncertain strict feedback nonlinear systems with guaranteed transient performance is investigated in this paper. The system model is a class of strict feedback nonlinear systems with parametric uncertainty, actuator fault and external disturbance. How to guarantee the transient performance of consensus error is involved. To solve this problem, the consensus is transmitted into stabilization of a new variable. Ultimately the consensus errors will asymptotically converge to zero and faster than a given exponentially converging variable. Finally, simulation results show the effectiveness of proposed control scheme.     

Linear active disturbance rejection control for oscillatory systems with large time-delays

Oscillatory systems with time delays exist widely in actual industrial process. This paper discusses the design and tuning of linear active disturbance rejection controller (LADRC) for the oscillatory systems with large time delays. First, internal model controllers (IMC) are designed for the oscillatory systems to compensate the time-delay and cancel the complex poles; then they are implemented with the general LADRC structures and approximated with observer-bandwidth-based LADRCs. Afterwards, the third-order LADRC tuning formulas for oscillatory systems are derived from the IMC controllers. Simulation examples and load frequency control(LFC) in power system with communication delay are used to test the applicability of the proposed tuning formula.     

西部老少边穷地区农民体育健身的思考

关注西部老少边穷地区的农民体育健身问题,不单纯是一个体育问题,也是一个事关民族团结、社会和谐、政治稳定、国家安全的全局性问题。结合国家高度重视三农的时代背景,对当前我国西部老少边穷地区农民体育健身问题进行了理性分析和宏观思考,认为:必须从国家发展的战略高度认识西部老少边穷地区农民体育健身问题;应从国家层面、操作层面、受体层面全方位考虑解决西部老少边穷地区农民体育健身问题;应根据西部老少边穷地区的区域特点探寻农民体育健身的发展路径。     

发达国家学生水上安全教育的经验及启示

通过文献资料法和逻辑推理法,对国外发达国家水上安全教育体系及相关研究成果进行分析,结合我国水上安全教育的现状,旨在引进国外水上安全教育的成功经验,从而促进我国学生水上安全教育的发展。     

超声波理疗复方中药导入制剂的研究与配制

超声波理疗可治疗疾患和促进机体康复。针对复方中药超声波导入液的配制进行研究,按照中药复方的"君"、"臣"、"佐"、"使"的组方原则进行药方选定,据各单味药的醇类、油脂类、水溶性的药性进行提纯融合,并跟最适合比例的芦荟、基质进行配制,其应用前景广阔。     

大学生心理健康水平对体质影响的研究——以深圳大学为例

文章通过深圳大学学生心理健康水平的514份问卷调查以及体质检测的统计数据,对深圳大学学生心理健康水平对体质达标现状的影响进行分析。研究结果深圳大学学生不同性别心理健康存在显著差异;不同年级的体质得分测试结果存在显著差异;男子体质综合得分较差组与优良组在强迫因子得分上有显著差异(P<0.05),女子体质综合得分较差组与优良组在焦虑强迫因子得分上和偏执强迫因子得分上有显著差异(P<0.05),结论大学生某些方面的心理因素对体质水平存在影响。