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排序方式: 共有534条查询结果,搜索用时 17 毫秒
91.
V.V. Joshi L.B. Xie J.J. Park L.S. Shieh Y.H. Chen K. Grigoriadis J.S.H. Tsai 《Applied Mathematical Modelling》2012
Distributed power grid (DPG) control systems are so highly interconnected that the effects of local disturbances as well as transmission time delays can be amplified as they propagate through a complex network of transmission lines. These effects deteriorate control performance and could possibly destabilize the overall system. In this paper, a new approximated discretization method and digital design for DPG control systems with multiple state, input and output delays as well as a generalized bilinear transformation method are presented. Based on a procedure for the generation of impulse response data, the multiple fractional/integer time-delayed continuous-time system is transformed to a discrete-time model with multiple integer time delays. To implement the digital modeling, the singular value decomposition (SVD) of a Hankel matrix together with an energy loss level is employed to obtain an extended discrete-time state space model. Then, the extended discrete-time state space model of the DPG control system is reformulated as an integer time-delayed discrete-time system by computing its observable canonical form. The proposed method can closely approximate the step response of the original continuous time-delayed DPG control system by choosing various energy loss levels. For completeness, an optimal digital controller design for the DPG control system and a generalized bilinear transformation method with a tunable parameter are also provided, which can re-transform the integer time-delayed discrete-time model to its continuous-time model. Illustrative examples are given to demonstrate the effectiveness of the developed method. 相似文献
92.
Shieh DL Lin YS Yeh JH Chen SC Lin BC Lin JL 《Chemical communications (Cambridge, England)》2012,48(19):2528-2530
Nitrogen-doped, porous rutile has been prepared by hydrothermal reaction of TiN in nitric acid, with the nitrogen atoms present in the interstitial sites and in the form of adsorbed nitrate ions. The N-rutile powder exhibits outstanding photocatalytic activity toward degradation of adsorbed methylene blue under visible light irradiation. 相似文献
93.
ZHU Jia-Min LU Zhi-Ming LIU Yu-Lu 《理论物理通讯》2008,49(6):1403-1406
One of the advantages of the variational iteration method is the free choice of initial guess. In this paper we use the basic idea of the Jacobian-function method to construct a generalized trial function with some unknown parameters. The Jaulent-Miodek equations are used to illustrate effectiveness and convenience of this method, some new explicit exact travelling wave solutions have been obtained, which include bell-type soliton solution, kink-type soliton solutions, solitary wave solutions, and doubly periodic wave solutions. 相似文献
94.
Ching-Sung Shieh Chin-Teng Lin 《Antennas and Propagation, IEEE Transactions on》2000,48(7):1115-1124
A new high-resolution direction of arrival (DOA) estimation technique using a neural fuzzy network based on phase difference (PD) is proposed. The conventional DOA estimation method such as MUSIC and MLE, are computationally intensive and difficult to implement in real time. To attack these problems, neural networks have become popular for DOA estimation. However, the normal neural networks such as the multilayer perceptron (MLP) and radial basis function network (RBFN) usually produce the extra problems of low convergence speed and/or large network size (i.e., the number of network parameters is large). Also, the may to decide the network structure is heuristic. To overcome these defects and take use of neural learning ability, a powerful self-constructing neural fuzzy inference network (SONFIN) is used to develop a new DOA estimation algorithm. By feeding the PDs of the received radar-array signals, the trained SONFIN can give high-resolution DOA estimation. The proposed scheme is thus called PD-SONFIN. This new algorithm avoids the need of empirically determining the network size and parameters in normal neural networks due to the powerful on-line structure and parameter learning ability of SONFIN. The PD-SONFIN can always find itself an economical network size in the fast learning process. Our simulation results show that the performance of the new algorithm is superior to the RBFN in terms of convergence accuracy, estimation accuracy, sensitivity to noise, and network size 相似文献
95.
Z-pinch experiments with two arrays consisting, respectively, of 32
4-μm- and 6-μm-diameter tungsten wires have been carried out on
QiangGuang-1 facility with a current rising up to 1.5MA in 80ns. At early
time of implosion, x-ray framing images show that the initial emission comes
from the central part of arrays, and double clear emission rings, drifting
to the anode and the cathode at 5×106cm/s and 2.4×107cm/s respectively, are often produced near the electrodes. Later,
in a 4-μm-diameter tungsten wire array, filamentation caused by ohmic
heating is prominent, and more than ten filaments have been observed. A
radial inward shift of arrays starts at about 30\,ns earlier than the
occurrence of the x-ray peak power for both kinds of arrays, and the
shrinkage rate of emission region is as high as 1.7×107cm/s in
a 4-μm-diameter tungsten wire array, which is two times higher than
that in a 6-μm one. Emission from precursor plasmas is observed in
implosion of 6-μm-diameter tungsten wire arrays, but not in implosion
of a 4-μm-diameter tungsten wire array. Whereas, in a 4-μm-diameter tungsten wire array, the soft x-ray emission shows the growth of
m=1 instability in the plasma column, which is caused by current. The
reasons for the discrepancy between implosions of 4-μm- and 6-μm-diameter tungsten wire arrays are explained. 相似文献
96.
ZHU Jia-Min MA Zheng-Yi 《理论物理通讯》2006,46(3):393-396
In this paper, using the variable coefficient generalized projected Rieatti equation expansion method, we present explicit solutions of the (2+1)-dimensional variable coefficients Broer-Kaup (VCBK) equations. These solutions include Weierstrass function solution, solitary wave solutions, soliton-like solutions and trigonometric function solutions. Among these solutions, some are found for the first time. Because of the three or four arbitrary functions, rich localized excitations can be found. 相似文献
97.
Fractal localized structures related to Jacobian elliptic functions in the higher-order Broer-Kaup system 下载免费PDF全文
This work reveals a novel phenomenon—that the localized coherent structures of a (2﹢1)﹣dimensional physical model possesses fractal behaviours. To clarify the interesting phenomenon, we take the (2﹢1)﹣dimensional higher-order Broer-Kaup system as a concrete example. Starting from a B?cklund transformation, we obtain a linear equation, and then a general solution of the system is derived. From this some special localized excitations with fractal behaviours are obtained by introducing some types of lower-dimensional fractal patterns that related to Jacobian elliptic functions. 相似文献
98.
A general mapping approach and new travelling wave solutions to the general variable coefficient KdV equation 下载免费PDF全文
A general mapping deformation method is applied to a generalized variable coefficient KdV equation. Many new types of exact solutions, including solitary wave solutions, periodic wave solutions, Jacobian and Weierstrass doubly periodic wave solutions and other exact excitations are obtained by the use of a simple algebraic transformation relation between the generalized variable coefficient KdV equation and a generalized cubic nonlinear Klein-Gordon equation. 相似文献
99.
100.
“能量”是学生认识化学变化的重要维度,本实验借助手持红外热成像仪“看到”化学反应中的能量变化。在实验中通过拍摄等量的不同酸溶液与氢氧化钠溶液混合反应时的热成像图,从“温度”高低间接反映出热量变化,从宏观的能量变化建立模型,推理微观的成键、断键等过程,探究酸碱中和反应过程的放热以及弱酸电离过程的吸热,并培养学生的证据推理能力和科学探究意识。 相似文献