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91.
This article presents a new approach for solving the Optimal Control Problem (OCP) of linear time-delay systems with a quadratic cost functional. The proposed method can also be used for designing optimal control time-delay systems with disturbance. In this study, the Variational Iteration Method (VIM) is employed to convert the original Time-Delay Optimal Control Problem (TDOCP) into a sequence of nonhomogeneous linear two-point boundary value problems (TPBVPs). The optimal control law obtained consists of an accurate linear feedback term and a nonlinear compensation term which is the limit of an adjoint vector sequence. The feedback term is determined by solving Riccati matrix differential equation. By using the finite-step iteration of a nonlinear compensation sequence, we can obtain a suboptimal control law. Finally, Illustrative examples are included to demonstrate the validity and applicability of the technique. 相似文献
92.
93.
This paper presents a three-dimensional extension of graphic statics using polyhedral form and force diagrams for the design of compression-only and tension-only spatial structures with externally applied loads. It explains the concept of 3D structural reciprocity based on Rankine’s original proposition for the equilibrium of spatial frames. It provides a definition for polyhedral reciprocal form and force diagrams that allows including external forces and discusses their geometrical and topological characteristics. This paper furthermore provides a geometrical procedure for constructing a pair of reciprocal polyhedral diagrams from a given polyhedron representing either the form or force diagram of a structural system. Using this method, this paper furthermore suggests a design strategy for finding complex funicular spatial forms in pure compression (or tension), based on the construction of force diagrams through the aggregation of convex polyhedral cells. Finally, it discusses the effect of changes in the geometry of the force diagram on the geometry of the form diagram and the distribution of forces in it. 相似文献
94.
Computer-Supported Collaborative Learning (CSCL) is concerned with how Information and Communication Technology (ICT) might facilitate learning in groups which can be co-located or distributed over a network of computers such as Internet. CSCL supports effective learning by means of communication of ideas and information among learners, collaborative access of essential documents, and feedback from instructors and peers on learning activities. As the cloud technologies are increasingly becoming popular and collaborative learning is evolving, new directions for development of collaborative learning tools deployed on cloud are proposed. Development of such learning tools requires access to substantial data stored in the cloud. Ensuring efficient access to such data is hindered by the high latencies of wide-area networks underlying the cloud infrastructures. To improve learners’ experience by accelerating data access, important files can be replicated so a group of learners can access data from nearby locations. Since a cloud environment is highly dynamic, resource availability, network latency, and learner requests may change. In this paper, we present the advantages of collaborative learning and focus on the importance of data replication in the design of such a dynamic cloud-based system that a collaborative learning portal uses. To this end, we introduce a highly distributed replication technique that determines optimal data locations to improve access performance by minimizing replication overhead (access and update). The problem is formulated using dynamic programming. Experimental results demonstrate the usefulness of the proposed collaborative learning system used by institutions in geographically distributed locations. 相似文献
95.
高理想 《黑龙江工程学院学报》2015,(2)
"思想道德修养与法律基础"课程是高校思想政治理论课的重要组成部分。把基础课课堂魅力作为研究内容,通过课堂观察法和自身授课经验总结法,对影响基础课课堂魅力的因素进行分析,发现教师自身和教学方式是主要影响因素。提升基础课教师自身魅力和教学方式魅力可有效解决基础课课堂实效性差等问题,为顺利实现教学目标,有效发挥思想政治教育作用奠定基础。 相似文献
96.
《International Journal of Hydrogen Energy》2020,45(27):13975-13984
An intervening barrier for photocatalytic water decomposition and pollutant degradation is the frustratingly quick recombination of e− - h+ pairs. Delicate design of heterojunction photocatalysts by coupling the semiconductors at nanoscale with well-matched geometrical and electronic alignments is an effective strategy to ameliorate the charge separation. Here a facile and environment-friendly l-cysteine-assisted hydrothermal process under weakly alkaline conditions is demonstrated for the first time to fabricate ZnIn2S4/In(OH)3 hollow microspheres with intimate contact, which are verified by XRD, SEM, (HR)TEM, XPS, N2 adsorption-desorption, UV–Vis DRS and photoluminescence spectra. ZnIn2S4/In(OH)3 heterostructure (L-cys/Zn2+ = 4, molar ratio) with a band-gap of 2.50 eV, demonstrates the best photocatalytic performance for water reduction and MB degradation under visible light, outperforming its counterparts (In(OH)3 and ZnIn2S4). The excellent activity of ZnIn2S4/In(OH)3 heterostructure arises from the intercrossed band-edge positions as well as the unique hollow structure with large surface area and wide pore-size distribution, which are beneficial for the efficient charge migration from bulk to surface as well as at the interface between ZnIn2S4 and In(OH)3. This work provides an efficient and eco-friendly strategy for one-pot synthesis of heterostructured composites with intimate contact for photocatalytic application. 相似文献
97.
98.
99.
《International Journal of Hydrogen Energy》2022,47(72):31014-31057
In the scope of the rapid technological advancements, nanoparticles (NPs) have gained prominence due to their excellent and tunable biological, and physicochemical properties. Nowadays, different methods are used for their synthesis. In particular, the green synthesis of metal precursors for the synthesis of NPs, represents a cost-effective, environmentally friendly, and hazardous chemical-free method for developing a large variety of NPs. By exploiting plant extracts, the production rate of NPs is relatively faster. Due to fossil reserves and high fuel consumption, renewable and clean energy materials are urgently needed to improve environmental sustainability. With outstanding electrochemical and physicochemical characteristics, molybdenum-based NPs (Mo-NPs) are gaining increasing attention in the fields of energy conversion and storage. Considering the significance of Mo-NPs synthesized from greener routes and their energy applications, it is necessary to review recent trends and developments in this field. This review summarizes important research studies and future research guidelines for the preparation of Mo-NPs through green routes and their applications to meet global energy and environmental demands. Moreover, future research directions are also highlighted to achieve sustainable greener precursors and Mo-NPs based energy storage devices. 相似文献
100.
《International Journal of Hydrogen Energy》2022,47(9):5757-5765
At present, as the demand for electricity increases in all sectors, there is an urgent need to introduce alternative renewable energy sources into modern energy systems. Renewable energy sources, which consist of solar (photovoltaic, PV), wind and hydro power, are key alternative sources of “green energy’’ energies, but it can also be used to produce “green” hydrogen. Thanks to scientific and technological progress, the cost of photovoltaic solar radiation converters is constantly decreasing at a high rate, which makes it possible to build solar power plants of sufficiently large capacity. In the coming decades, solar energy will become an incentive for the economic development of countries that have the maximum “solar” resource. The Republic of Tajikistan is one of these countries with a high potential for solar energy.The article presents an analysis of the resources and potential of solar energy in the Republic of Tajikistan. The study of electromagnetic transients in networks with photovoltaic solar power plants is performed. The main equations, simulation model and calculations of transients are presented, taking into account changes in voltage on DC buses. An algorithm for controlling the system of automatic control of output parameters is proposed. The analysis of dynamic and static modes in parallel operation of a solar power plant with the grid is carried out. A block diagram and computer model is constructed in the MATLAB package together with Simulink and Power System Blockset. 相似文献