Input-output approach to robust stability and stabilization for uncertain singular systems with time-varying discrete and distributed delays   总被引：3，自引：0，他引：3  

Hui-jiao Wang  An-ke Xue  Yun-fei Guo  Ren-quan Lu 《浙江大学学报(A卷英文版)》2008,9(4):546-551

Based on input-output approach, the robust stability and stabilization problems for uncertain singular systemswith time-varying delays are investigated. The parameter uncertainties are assumed to be norm-bounded and the time-varying delays include both discrete delay and distributed delay. By introducing a new input-output model, the time-delay system is embedded in a family of systems with a forward system without time delay and a dynamical feedback uncertainty. A sufficient and necessary condition, which guarantees the system regular, impulse-free and stable for all admissible uncertainties, is obtained. Based on the strict linear matrix inequality, the desired robust state feedback controller is also obtained. Finally, a numerical example is provided to demonstrate the application of the proposed method.  相似文献   

A cross-layer design approach on spectrum allocation and resource scheduling in cognitive PMP networks     

Jie Chen  Min-jian Zhao  Qiao Zhou  Shi-ju Li 《浙江大学学报(A卷英文版)》2008,9(4):435-444

We propose the spectrum allocation and resource scheduling algorithms in cognitive point to multipoint （PMP） networks with rapid changes of spectrum opportunities and present a media access control （MAC） protocol based on these algorithms. The objective of spectrum allocation is to make efficient use of the spectrum while maintaining the transceiver synchronization on frequency and time in the network. The objective of resource scheduling is to guarantee the quality of service （QoS） requirements of different kinds of connections and to minimize the total energy consumption in the network as well. By sensing only a small set of possible channels in each slot based on the state transition probability of each channel, our spectrum allocation algorithm achieves high spectrum efficiency in the network. The resource scheduling problem is divided into three sub problems and we derive optimal solutions to these problems by greedy algorithm and convex optimization. The simulation results show that our algorithm can make efficient use of the spectrum and the network resources at a cost of low computational complexity.  相似文献   

Eccentricity and thermoviscous effects on ultrasonic scattering from a liquid-coated fluid cylinder     

Seyyed M. Hasheminejad  M. A. Alibakhshi 《浙江大学学报(A卷英文版)》2008,9(1):65-78

Calculation of the scattered field of the eccentric scatterers is an old problem with numerous applications. This study considers the interaction of a plane compressional sound wave with a liquid-encapsulated thermoviscous fluid cylinder submerged in an unbounded viscous thermally conducting medium. The translational addition theorem for cylindrical wave functions, the appropriate wave field expansions and the pertinent boundary conditions are employed to develop a closed-form solution in the form of infinite series. The analytical results are illustrated with a numerical example in which the compound cylinder is insonified by a plane sound wave at selected angles of incidence in a wide range of dimensionless frequencies. The backscattered far-field acoustic pressure amplitude and the spatial distribution of the total acoustic pressure in the vicinity of the cylinder are evaluated and discussed for representative values of the parameters characterizing the system. The effects of incident wave frequency, angle of incidence, fluid thermoviscosity, core eccentricity and size are thoroughly examined. Limiting case involving an ideal compressible liquid-coated cylinder is considered and fair agreement with a well-known solution is established.  相似文献   

Zero-voltage switching converter absorbing parasitic parameters for super high frequency induction heating     

Zheng-shi Wang  Hui-ming Chen 《浙江大学学报(A卷英文版)》2008,9(4):564-571

This paper presents a novel mega-Hz-level super high frequency zero-voltage soft-switching converter for induction heating power supplies. The prominent advantage of this topology is that it can absorb both inductive and capacitive parasitic components in the converter. The switch devices operate in a zero-voltage soft-switching mode. Consequently, the high voltage and high current spikes caused by parasitic inductors or capacitors oscillation do not occur in this circuit, and the high power loss caused by high frequency switching can be greatly reduced. A large value inductor is adopted between the input capacitor and the switches, thus, this novel converter shares the benefits of both voltage-type and current-type circuits simultaneously, and there are no needs of dead time between two switches. The working principles in different modes are introduced. Results of simulation and experiments operated at around 1 MHz frequency verify the validity of parasitic components absorption and show that this convener is competent for super high frequency applications.  相似文献   

Bubble counter based on photoelectric technique for leakage detection of cryogenic valves     

Tao Jin  Bin Xu  Ke Tang  Jian-ping Hong 《浙江大学学报(A卷英文版)》2008,9(1):88-92

In order to overcome the inconvenience of manual bubble counting, a bubble counter based on photoelectric technique aiming for automatically detecting and measuring minute gas leakage of cryogenic valves is proposed. Experiments have been conducted on a self-built apparatus, testing the performance with different gas inlet strategies （bottom gas-inlet strategy and side gas-inlet strategy） and the influence of gas pipe length （0, 1, 2, 4, 6, 8, 10 m） and leakage rate （around 10, 20, 30, 40 bubbles/min） on first bubble time and bubble rate. A buffer of 110 cm^3 is inserted between leakage source and gas pipe to simulate the downstream cavum adjacent to the valve clack. Based on analyzing the experimental data, experiential parameters have also been summarized to guide leakage detection and measurement for engineering applications. A practical system has already been successfully applied in a cryogenic testing apparatus for cryogenic valves.  相似文献   

Time-domain training sequences design for MIMO OFDM channel estimation     

Zhen Lu  Jian-hua Ge 《浙江大学学报(A卷英文版)》2008,9(4):464-469

This paper describes a Least Squares （LS） channel estimation scheme for MIMO OFDM systems based on time-domain training sequence. We first compute the minimum mean square error （MSE） of the LS channel estimation, and then derive the optimal criteria of the training sequence with respect to the minimum MSE. It is shown that optimal time-domain training sequence should satisfy two criteria. First, the autocorrelation of the sequence transmitted from the same antenna is an impulse function in a region longer than the channel maximum delay. Second, the cross-correlation between sequences transmitted from different antennas is zero in this region. Simulation results show that the estimator using optimal time-domain training sequences has better performance than that using optimal frequency training sequence at low signal-to-noise ratio （SNR）. To reduce the training overhead, a suboptimal training sequence is also proposed. Comparing with optimal training sequence, it has low computation complexity and high transmission efficiency at the expense of little performance degradation.  相似文献   

Beyond Archaeology and Genealogy     

Dany Nobus 《Metascience》2005,14(3):419-421

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Remembering Gould     

John S. Wilkins 《Metascience》2007,16(1):169-173

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Editorial     

Jérôme Rossier 《International Journal for Educational and Vocational Guidance》2016,16(1):5-8

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A new patch antenna with metamaterial cover   总被引：6，自引：0，他引：6  

胡骏阎春生  林青春 《浙江大学学报(A卷英文版)》2006,7(1):89-94

INTRODUCTION Investigation of metamaterials is currently one of the most active frontiers in engineering and physics. Metamaterials are also called backward-wave mate- rials, double-negative materials, or left-handed mate- rials. Left-handed materials were proposed by Vese- lago (1968). The applications of metamaterials are widely spread in many fields (Pendry, 2000; Grbic and Eleftheriades, 2003; Foteinopoulou et al., 2003), such as imaging apparatus, planar light wave circuits, optica…  相似文献