排序方式： 共有36条查询结果，搜索用时 15 毫秒
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We consider the problem of controlling the model of one-dimensional fluid flow through a soil packed tube in which a contaminant is initially distributed. A fluid is pumped through a tube to remove the contaminant. The control problem is to determine the optimal convective velocity due to the fluid being pumped by minimizing a given performance criterion. The performance criterion is chosen to be a combination of the total contaminant at the final time and the cost of the control. The set of orthogonal Fourier trigonometry series is used as a basis function of the Galerkin procedure to lump the distributed parameter system. A Legendre wavelet operational matrix of derivative is used to approximate the control and modal state variables. The main characteristics of this technique is that it reduces these problems to those of solving a system of algebraic equations, thus greatly simplifying the problem. The effectiveness of the proposed approach is illustrated numerically and the results are quite satisfactory. 相似文献
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Nicolas Faysse Mohamed Taher Sraïri Mostafa Errahj 《The Journal of Agricultural Education and Extension》2013,19(3):285-299
Abstract Purpose: The study investigated to what extent local farmers' organisations are spaces where farmers discuss, learn and innovate. Design/methodology/approach: Two milk collection cooperatives in Morocco were studied. The study analysed the discussion networks, their impacts on farmers' knowledge and innovation, and the performance of collective action at cooperative level. Findings: In both cooperatives, only two-thirds of the farmers regularly discussed dairy practices with other farmers. Most leaders of one cooperative were acknowledged to be experienced farmers and played key roles as advisors on dairy farming. Farmers' involvement in dialogue networks in this cooperative improved their capacity to innovate in dairy farming, even though their knowledge on some issues related to cattle, health and nutrition was not improved. In the other cooperative, experienced farmers did not share their knowledge and farmers' involvement in dialogue networks at cooperative level had no impact on their knowledge and practices. Dialogue networks and collective action were found to influence each other, since in the first cooperative, collective action was considered by members to be efficient, whereas in the second collective action was limited to milk collection. Practical implications: The study enabled identification of stumbling blocks which need to be addressed to get local farmers’ organisations involved in farmer capacity-building. Originality/value: While the importance of local discussion networks for knowledge creation and diffusion is widely acknowledged, taking such networks into account in farmers' capacity-building programmes in developing countries has been hindered by their informality. Combining the analysis of dialogue networks and collective action proved to be a productive way to assess the potentialities of working with farmers' organisations with the aim of establishing a connection with local discussion networks. 相似文献
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Imran Ghous Zhaoxia Duan Jahanzeb Akhtar Muhammad Jawad 《Journal of The Franklin Institute》2019,356(16):9407-9431
This paper aims to solve the problem of sliding mode control for an uncertain two-dimensional (2-D) systems with states having time-varying delays. The uncertainties in the system dynamics are constituted of mismatched uncertain parameters and the unknown nonlinear bounded function. The proposed problem utilizes the model transformation approach. By segregating the proper Lyapunov–Krasovskii functional in concert with the improved version of Wirtinger-based summation inequality, sufficient solvability conditions for the existence of linear switching surfaces have been put forward, which ensure the asymptotical stability of the reduced-order equivalent sliding mode dynamics. Then, we solve the controller synthesis problem by extending the recently proposed reaching law to 2-D systems, whose proportional part is appropriately scaled by the factor that does not depend on some constant terms but rather on current switching surface’s value, which in turn ensures the faster convergence and better robustness against uncertainties. Finally, the proposed results have been validated through an implementation to a suitable physical system. 相似文献
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Application of honey-bee mating optimization on state estimation of a power distribution system including distributed generators 总被引：1，自引：0，他引：1
Taher Niknam 《浙江大学学报(A卷英文版)》2008,9(12):1753-1764
We present a new approach based on honey-bee mating optimization to estimate the state variables in distribution networks including distributed generators. The proposed method considers practical models of electrical equipments such as static var compensators, voltage regulators, and under-load tap changer transformers, which have usually nonlinear and discrete characteristics. The feasibility of the proposed approach is demonstrated by comparison with the methods based on neural networks, ant colony optimization, and genetic algorithms for two test systems, a network with 34-bus radial test feeders and a realistic 80-bus 20 kV network. 相似文献
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In 1975/76 Kuwait University was transferred to an Elective System and initially, the article reviews the rationale and objectives of such a change. Guidance or advisement is considered a key means to achieve these objectives. The major focus of the article is an examination of several attempts to assess/evaluate the implementation and effectiveness of advisement. Recommendations for practical solutions to those problems which surround this practice are also discussed.Paper submitted to the International Consultation Conference on Career Guidance in Higher Education convened by IRTAC and Robinson College — Cambridge University, 13–17 December 1981, Robinson College, Cambridge, England. 相似文献
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Taher A. Razik Patrick J. Nalbone 《Educational technology research and development : ETR & D》1990,38(1):65-76
Technological change and social change are viewed as interdependent in this paper. At the same time technology's push is seen as outpacing the capability of social institutions to respond. Consequently, America risks losing its competitive edge economically and, further, is rapidly evolving toward a two-tiered occupational and social structure. This paper examines the relationship between technological and social change, the nature and significance of technological innovation and dissemination, and impacts on organizational life. Finally, the paper explores the role of higher education as well as strategies the university must adopt if it is to participate effectively in addressing the changes that are emerging as society moves from being production-and-material based to an information-based system. 相似文献