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Ling Xu,Hai-Yan Xu,Feng Wang,Feng-Jun Zhang,Ze-Da Meng,Wei Zhao,오원춘 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.2
Flower-like and plate-like CuO nanopowder has been successfully synthesized using a facile microwave-assisted synthetic route. The morphology and size of the final products strongly depended on microwave power. The phase, structures and morphologies of the as-prepared products were investigated in detail by BET surface area analysis, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). In addition, the chemical oxygen demand of polluted lake water was employed for characterization of these new photocatalysts. The results showed correlations between the morphology of CuO micro-crystals and their catalytic properties.
Separable Recursive Gradient Algorithm for Dynamical Systems Based on the Impulse Response Signals
Ling Xu,Feng Ding,Erfu Yang 제어·로봇·시스템학회 2020 International Journal of Control, Automation, and Vol.18 No.12
The identification for process control systems is considered in this paper based on the impulse response signals from the discrete measurements. By taking advantage of impulse signals and through the model parameter decomposition, two dependent identification models are constructed and two identification sub-algorithms are presented based on the nonlinear gradient optimization. In terms of the associated items of the parameters to be estimated between two derived sub-algorithms, a separable recursive gradient parameter estimation method is proposed by designing an interactive and recursive estimation. The performance tests and the comparison experiments are carried out by the simulation examples.
Ling Xu 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.2
Many control techniques rely on the mathematical models of the systems to be controlled. This paper copes with the modelling problem of dynamical systems aiming to develop highly accurate modelling approaches. By an impulse response identification experiment, the dynamical observations with increasing data length are designed for the purpose of capturing the real-time information of systems and serving for on-line identification. According to the different features of the parameters of the systems to be identified, two separable identification models are constructed through the parameter decomposition and the model decomposition for simplifying the structure of the original identification model. On basis of the separable identification models, a separable Newton recursive parameter estimation approach is developed by means of the Newton search for acquiring highly accurate parameter estimates. In terms of the coupled terms in the separated sub-algorithms, a joint estimation algorithm is presented for removing the coupled terms. The experimental results through the Monte-Carlo tests show that the obtained parameter estimates through the separable algorithm are more accurate than those obtained by the Newton recursive estimation method without the model separation.
Parameter Estimation for Nonlinear Functions Related to System Responses
Ling Xu 제어·로봇·시스템학회 2023 International Journal of Control, Automation, and Vol.21 No.6
This paper considers the parameter estimation problem of nonlinear models, which are related to the impulse or step response functions of linear time-invariant (LTI) dynamical systems, based on the response data. In terms of the nonlinear characteristic of the models, the nonlinear dynamical optimization scheme is adopted for obtaining the system parameter estimates. By constructing a gradient criterion function, a gradient recursion algorithm is derived. In order to overcome the difficulty of determining the step-size in the gradient recursion algorithm, a trying method and a numerical approach are proposed to achieve the step-size. On this basis, a stochastic gradient estimation method is presented by using a recursive step-size. Furthermore, a multi-innovation stochastic gradient method is deduced for enhancing the estimation accuracy by using the dynamical window data. Finally, a dynamical length stochastic gradient estimation technique is offered to obtain more accurate parameter estimates by using dynamical length measured data from the step response. The examples are provided to examine the algorithm performance and the simulation results indicate that the presented approaches are effective.
Hierarchical Parameter Estimation for the Frequency Response Based on the Dynamical Window Data
Ling Xu,Weili Xiong,Ahmed Alsaedi,Tasawar Hayat 제어·로봇·시스템학회 2018 International Journal of Control, Automation, and Vol.16 No.4
This paper studies the problem of parameter estimation for frequency response signals. For a linear system, the frequency response is a sine signal with the same frequency as the input sine signal. When a multifrequency sine signal is applied to a system, the system response also is a multi-frequency sine signal. The signal modeling for multi-frequency sine signals is very difficult due to the highly nonlinear relations between the characteristic parameters and the model output. In order to obtain the parameter estimates of the multi-frequency sine signal, the signal modeling methods based on statistical identification are proposed by means of the dynamical window discrete measured data. By constructing a criterion function with respect to the model parameters to be estimated, a hierarchical multi-innovation stochastic gradient estimation method is derived through parameter decomposition. Moreover, the forgetting factor and the convergence factor are introduced to improve the performance of the algorithm. The simulation results show the effectiveness of the proposed methods.
Parameter Estimation for Control Systems based on Impulse Responses
Ling Xu,Feng Ding 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.6
The impulse signal is an instant change signal in very short time. It is widely used in signal processing,electronic technique, communication and system identification. This paper considers the parameter estimationproblems for dynamical systems by means of the impulse response measurement data. Since the cost function ishighly nonlinear, the nonlinear optimization methods are adopted to derive the parameter estimation algorithms toenhance the estimation accuracy. By using the iterative scheme, the Newton iterative algorithm and the gradientiterative algorithm are proposed for estimating the parameters of dynamical systems. Also, a damping factor isintroduced to improve the algorithm stability. Finally, using simulation examples, this paper analyzes and comparesthe merit and weakness of the proposed algorithms.
Lingxu Wang,Huiying Liu,Liqiang Liu,Fengqing Zhang 한양대학교 세라믹연구소 2021 Journal of Ceramic Processing Research Vol.22 No.1
In order to studying the effect of the annealing atmospheres (nitrogen and air) on the films, two kinds of Bi4Ti3O12 (BIT) samples were prepared by the sol-gel and layer-by-layer thermal annealing method. Various factors, including lesser VO••, more V'B'i and greater grain size in the air-annealed samples, interacted on the ferroelectric and light absorption properties. However, more (V'B'i)-(VO••) reinforced the imbalance of electron capture in the ITO/BIT/Au capacitors, resulting in stronger imprinting. And the arrangement of (V'B'i)-(VO••) and the domain pinning in the air-annealed films resulted in more serious aging effect.
Prediction of the effective thermal conductivity of microsphere insulation
Lingxue Jin,박지호,이천규,서만수,정상권 한국초전도.저온공학회 2014 한국초전도저온공학회논문지 Vol.16 No.1
Since glass microsphere has high crush strength, low density and small particle size, it becomes alternative thermal insulation material for cryogenic systems, such as storage and transportation tank for cryogenic fluids. Although many experiments have been performed to verify the effective thermal conductivity of microsphere, prediction by calculation is still inaccurate due to the complicated geometries, including wide range of powder diameter distribution and different pore sizes. The accurate effective thermal conductivity model for microsphere is discussed in this paper. There are four mechanisms which contribute to the heat transfer of the evacuated powder: gaseous conduction (kg), solid conduction (ks), radiation (kr) and thermal contact (kc). Among these components, kg and ks were calculated by Zehner and Schlunder model (1970). Other component values for kc and kr, which were obtained from experimental data under high vacuum conditions were added. In this research paper, the geometry of microsphere was simplified as a homogeneous solid sphere. The calculation results were compared with previous experimental data by R. Wawryk (1988), H. S. Kim (2010) and the experiment of this paper to show good agreement within error of 46%, 4.6% and 17% for each result