共查询到20条相似文献，搜索用时 78 毫秒
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This paper presents a second order sliding mode observer (SOSMO) design for discrete time uncertain linear multi-output system. The design procedure is effective for both matched and unmatched bounded uncertainties and/or disturbances. A second order sliding function and corresponding sliding manifold for discrete time system are defined similar to the lines of continuous time counterpart. A boundary layer concept is employed to avoid switching across the defined sliding manifold and the sliding trajectory is confined to a boundary layer once it converges to it. The condition for existence of convergent quasi-sliding mode (QSM) is derived. The observer estimation errors satisfying given stability conditions converge to an ultimate finite bound (within the specified boundary layer) with thickness O(T2) where T is the sampling period. A relation between sliding mode gain and boundary layer is established for the existence of second order discrete sliding motion. The design strategy is very simple to apply and is demonstrated for three examples with different class of disturbances (matched and unmatched) to show the effectiveness of the design. Simulation results to show the robustness with respect to the measurement noise are given for SOSMO and the performance is compared with pseudo-linear Kalman filter (PLKF). 相似文献
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K.S. Bajaj 《Journal of The Franklin Institute》1975,300(3):193-196
A method for simulation by resistive networks is given for numbers like nm and n?m for 0 < m < 1. The method is based on Cauchy-type integral representations for irrational functions. An algorithm to get networks from Cauchy-type integrals is used in the paper. A similar method is used for simulation of transcendental numbers. Tapered resistive networks are obtained, which are easier to build by using integrated circuit technology. 相似文献
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从诺贝尔科学奖看创造性人才的培养与管理 总被引：2，自引：0，他引：2
诺贝尔科学奖不仅是20世纪科学技术发展的缩影,也是创造性人才培养的典范。文章从六个方面对此进行了阐述:良好的家庭教育和熏陶是创造性人才成长的“第一基石”;自身的不懈努力和奋斗是创造性人才成长的“内在动力”;良师的精心指导和帮助是创造性人才成长的“快速通道”;自由的研究环境和交流是创造性人才成长的“肥沃土壤”;选准研究方向和课题是创造性人才成长的“捷径”;善于把握机遇和创新是创造性人才成长的“关键”。 相似文献
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This paper investigates the finite-time control problems for a class of discrete-time nonlinear singular systems via state undecomposed method. Firstly, the finite-time stabilization problem is discussed for the system under state feedback, and a finite-time stabilization controller is obtained. Then, based on which, the finite-time H∞ boundedness problem is studied for the system with exogenous disturbances. Finally, an example of population distribution model is presented to illustrate the validity of the proposed controller. Because there is no any constraint for singular matrix E in the paper, controllers can be designed for more discrete-time nonlinear singular systems. 相似文献
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The dynamics of multi-DOF aerial manipulators is complex system evolving in non-Euclidean Lie group, making design and tuning of the control of such systems challenge. In this paper we consider the nonlinear geometric control for aerial manipulation system. The linearized tracking error kinematic equation of motion on SO(3) is obtained from the variation on SO(3). Based on the linearized tracking error kinematic equation of motion on SO(3), the trajectory linearization control for the kinematics on SO(3) is investigated. The decoupled dynamics of multi-DOF aerial manipulator enables us to apply the results of trajectory linearization control for the kinematics on SO(3). We then design the entire controller for aerial manipulation system by composing different trajectory linearization control loops. Such controller structure eases the controller implementation and tuning procedure. The stability of the proposed controlled system is analyzed using Lyapunov’s method. The proof is finished from inner loop to outer loop. It is proven that the closed loop shape system is exponentially stable. The attraction basin of the configuration error for the shape system can almost cover the whole . The stability of the system considering the actuator dynamics and perturbations is also discussed in this paper. From the stability of the shape system, the stability of the entire system is proven. The stability analysis results are further verified through several numerical simulations. 相似文献
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Even though isoelectric focusing (IEF) is a very useful technique for sample concentration and
separation, it is challenging to extract separated samples for further processing. Moreover, the
continuous sample concentration and separation are not possible in the conventional IEF. To overcome
these challenges, free flow IEF (FFIEF) is introduced in which a flow field is applied in the
direction perpendicular to the applied electric field. In this study, a mathematical model is developed for FFIEF to understand
the roles of flow and
electric fields for
efficient design of microfluidic
chip for continuous separation of proteins from an initial well mixed solution. A finite volume based
numerical scheme is implemented to simulate two dimensional FFIEF in a microfluidic chip. Simulation results
indicate that a pH gradient forms as samples flow downstream and this pH profile agrees well with
experimental results validating our model. In addition, our simulation results predict the experimental behavior of
pI markers in a FFIEF microchip. This numerical model is used to predict the separation
behavior of two proteins
(serum albumin and cardiac troponin I) in a two-dimensional straight microchip. The effect of
electric field is
investigated for continuous separation of proteins. Moreover, a new channel design is presented to increase the separation
resolution by introducing cross-stream flow velocity. Numerical results indicate that the separation
resolution can be improved by three folds in this new design compare to the conventional straight
channel design. 相似文献
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A procedure is described for determining the characteristics of adiabatic flow through a rocket nozzle with and without composition change. The method of calculation is illustrated for the expansion of pure hydrogen gas from a chamber temperature of 306° K. and a pressure of 20.42 atm. to atmospheric pressure.The study indicates that the exhaust velocity and temperature are highest for flow where complete equilibrium is reached at each temperature with respect to the reaction Flow with composition change requires a nozzle exit to nozzle throat area ratio somewhat greater than that determined for adiabatic flow without composition change for the same ratio of chamber pressure to exit pressure.The residence time in a given temperature range is computed as a function of gas temperature for the two types of flow. The results of this calculation may be used to determine the minimum required reaction rates which allow composition changes during flow through the nozzle. 相似文献
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This paper presents a stochastic multi-parameters divergence method for online parameter optimization of fractional-order proportional–integral–derivative (PID) controllers. The method is used for auto-tuning without the need for exact mathematical plant model and it is applicable to diverse plant transfer functions. The proposed controller tuning algorithm is capable of adaptively responding to parameter fluctuations and model uncertainties in real systems. Adaptation skill enhances controller performance for real-time applications. Simulations and experimental observations are carried on a prototype helicopter model to confirm the performance improvements obtained by the online auto-tuning of fractional-order PID structure in laboratory conditions. 相似文献
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This paper investigates the Riemannian trust-region method for H2 model reduction of bilinear systems. The H2 error norm is treated as a cost function on the Stiefel manifold such that the orthogonality constraint for the projection matrix is plainly satisfied. The property related to the Euclidean gradient is studied. Then, the inner product associated with the Riemannian Hessian is derived, which can simplify the expression of the trust-region subproblem. The trust-region method for H2 model reduction is accordingly established and the convergence is further discussed. Finally, two numerical examples are employed to demonstrate the performance of the proposed method. 相似文献
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In this paper, switched circuits are modeled based on wavelet decomposition and neural network. Also describes the usage of wavelet decomposition and neural network for modeling and simulation of nonlinear systems. The switched circuits are piecewise-linear circuits. At each position of switch the circuit is linear but when considered all switching positions of the circuit it becomes nonlinear. An important problem which arises in modeling switched circuit is high structural complexity. In this study, wavelet decomposition is used for feature extracting from input signals and neural network is used as an intelligent modeling tool. Two performance measures root-mean-square (RMS) and the coefficient of multiple determinations (R2) are given to compare the predicted and computed values for model validation. The evaluated R2 value is 0.9985 and RMS value is 0.0099. All simulations showed that the proposed method is more effective and can be used for analyzing and modeling switched circuits. When we consider obtained performance, we can easily say that the proposed method can be used efficiently for modeling any other nonlinear dynamical systems. 相似文献
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中国正处在城市化的快速发展阶段,家庭能源消费和CO2排放不断增长.本文以1991年-2010年为样本期,对城乡家庭直接能源消费和CO2排放的变化特征和原因进行分析,并对二者的差异进行比较.分析表明,城镇和农村户均直接能源消费和CO2排放以及总量变化,都呈现出以1998年为拐点的先下降后上升特征.原因在于1998年之前,直接能源消费强度下降与家庭规模缩小的节能减排效应大于消费水平提高的增能增排效应,而1998年之后,后者超过了前者.城镇和农村家庭直接能源消费结构变化促使户均直接能源消费CO2排放增加,原因在于电力的CO2排放不断增加.城镇的户均直接能源消费和CO2排放一直高于农村,但差距正在缩小,原因在于城镇直接能源消费强度下降、直接能源消费结构优化、家庭规模缩小所产生的节能减排效应逐步增大,抵消了人均消费水平提高所产生的增能增排效应. 相似文献
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Annalisa Caloffi Marco Mariani Federica Rossi Margherita Russo 《Research Policy》2018,47(8):1437-1447
We analyse whether public subsidies supporting collaborative research and development (R&D) projects in small and medium-sized enterprises (SMEs) are able to encourage persistent R&D investment and interorganisational networking more than subsidies supporting individual R&D projects. Adopting a counterfactual approach to policy evaluation, we compare subsidies for collaborative R&D and for individual R&D implemented in the same Italian region in the same period. Our findings suggest that, once public support is no longer available, the two subsidies have different effects on different types of SMEs. If the policymakers’ objective is to increase the number of R&D-performing SMEs over time, they should provide subsidies for collaborative R&D to firms with modest R&D experience. If their objective is to increase the amount of spontaneous R&D investment over time, they should target SMEs with some prior R&D experience, using either subsidy. Finally, if their objective is to induce SMEs to network with external organisations, subsidies for collaborative R&D projects should be preferred to subsidies for individual R&D projects. 相似文献
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如何引导和支持在华R＆D机构本土化发展，是学术界和政府共同关注的热点问题。本文基于对近30个跨国公司在华R＆D机构经理的访谈调研，归纳了跨国公司R＆D本土化过程中遇到的各类问题，并深入分析了R＆D经理的个人经历和R＆D机构城市分布对跨国公司在华R＆D机构面临问题的影响。基于上述研究，总结得出相应的政策启示。 相似文献
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Sequences of integers are common data types, occurring either as primary data or ancillary structures. The sizes of sequences can be large, making compression an interesting option. Effective compression presupposes variable-length coding, which destroys the regular alignment of values. Yet it would often be desirable to access only a small subset of the entries, either by position (ordinal number) or by content (element value), without having to decode most of the sequence from the start. Here such a random access technique for compressed integers is described, with the special feature that no auxiliary index is needed. The solution applies a method called interpolative coding, which is one of the most efficient non-statistical codes for integers. Indexing is avoided by address calculation guaranteeing sufficient space for codes even in the worst case. The additional redundancy, compared to regular interpolative coding, is only about 1 bit per source integer for uniform distribution. The time complexity of random access is logarithmic with respect to the source size for both position-based and content-based retrieval. According to experiments, random access is faster than full decoding when the number of accessed integers is not more than approximately 0.75 · n/log2n for sequence length n. The tests also confirm that the method is quite competitive with other approaches to random access coding, suggested in the literature. 相似文献
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This paper mainly considers the consensus for first-order discrete-time multi-agent systems w.r.t. two key parameters, the step size T and the delay τ. First, the consensus is recast into the concurrent stability for a series of trinomials. Then, for each associated trinomial, we derive a necessary and sufficient stability condition, based on proving the two invariance properties for the asymptotic behavior of the critical unitary roots. As a result, the exhaustive consensus region in the parameter space (i.e., the parameter set such that the multi-agent system reaches a consensus iff T and τ belong to that set) is determined. Furthermore, we show that the obtained result also applies to systems with diverse input delays, through an extra sufficient consensus condition. Finally, two illustrative examples are presented. 相似文献