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A New Control Strategy for a Three-Phase PWM Current-Source Rectifier in the Stationary Frame
Guo, Qiang,Liu, Heping,Zhang, Yi The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4
This paper presents a novel power control strategy for PWM current-source rectifiers (CSRs) in the stationary frame based on the instantaneous power theory. In the proposed control strategy, a virtual resistance based on the capacitor voltage feedback is used to realize the active damping. In addition, the proportional resonant (PR) controller under the two-phase stationary coordinate is designed to track the ac reference current and to avoid the strong coupling brought about by the coordinate transformation. The limitations on improving steady-state performance of the PR controller is investigated and mitigated using a cascaded lead-lag compensator. In the z-domain, a straightforward procedure is developed to analyze and design the control-loop with the help of MATLAB/SISO software tools. In addition, robustness against parameter variations is analyzed. Finally, simulation and experimental results verify the proposed control scheme and design method.
GLOBAL CONVERGENCE PROPERTIES OF TWO MODIFIED BFGS-TYPE METHODS
Guo, Qiang,Liu, Jian-Guo 한국전산응용수학회 2007 Journal of applied mathematics & informatics Vol.23 No.1
This article studies a modified BFGS algorithm for solving smooth unconstrained strongly convex minimization problem. The modified BFGS method is based on the new quasi-Newton equation $B_k+1{^s}_k=yk\;where\;y_k^*=yk+A_ks_k\;and\;A_k$ is a matrix. Wei, Li and Qi [WLQ] have proven that the average performance of two of those algorithms is better than that of the classical one. In this paper, we prove the global convergence of these algorithms associated to a general line search rule.
GLOBAL CONVERGENCE OF A MODIFIED BFGS-TYPE METHOD FOR UNCONSTRAINED NON-CONVEX MINIMIZATION
Guo, Qiang,Liu, Jian-Guo 한국전산응용수학회 2007 Journal of applied mathematics & informatics Vol.24 No.1
To the unconstrained programme of non-convex function, this article give a modified BFGS algorithm associated with the general line search model. The idea of the algorithm is to modify the approximate Hessian matrix for obtaining the descent direction and guaranteeing the efficacious of the new quasi-Newton iteration equation $B_{k+1}s_k=y^*_k,\;where\;y^*_k$ is the sum of $y_k\;and\;A_ks_k,\;and\;A_k$ is some matrix. The global convergence properties of the algorithm associating with the general form of line search is proved.
Nanocarbon-reinforced metal-matrix composites for structural applications
Guo, Qiang,Kondoh, Katsuyoshi,Han, Seung Min Cambridge University Press (Materials Research Soc 2019 MRS bulletin Vol.44 No.1
<▼1><B>Abstract</B><P/></▼1><▼2><P>Nanocarbon materials, such as carbon nanotubes, graphene, and their derivatives, are regarded as promising reinforcing agents in metal matrix composites (MMCs) because of their excellent intrinsic mechanical properties. Considering the various types of nanocarbons with different defect states and intrinsic properties, there is a potential for tailoring the mechanical behavior of nanocarbon-reinforced MMCs. This article reviews recent developments in both the processing and the structure-property correlations of these composites. Particular emphasis is given to the structure and properties of the nanocarbon-metal interfaces, as the external mechanical load is transferred between the nanocarbon and the metal matrix across their interfaces. Moreover, in addition to the intuitive load-bearing effect of the nanocarbon reinforcements, a copious interplay between nanocarbons and dislocations in the metal matrix has been found, which alters the deformation behavior that leads to additional strengthening. For structural applications, scalable fabrication routes for the nanocarbon-metal composites need to be developed, and studies on the mechanical behavior under real service conditions are needed.</P></▼2>
Method for Feature Extraction of Radar Full Pulses Based on EMD and Chaos Detection
Guo, Qiang,Nan, Pulong The Korea Institute of Information and Commucation 2014 Journal of communications and networks Vol.16 No.1
A novel method for extracting frequency slippage signal from radar full pulse sequence is presented. For the radar full pulse sequence received by radar interception receiver, radio frequency (RF) and time of arrival (TOA) of all pulses constitute a two-dimensional information sequence. In a complex and intensive electromagnetic environment, the TOA of pulses is distributed unevenly, randomly, and in a nonstationary manner, preventing existing methods from directly analyzing such time series and effectively extracting certain signal features. This work applies Gaussian noise insertion and structure function to the TOA-RF information sequence respectively such that the equalization of time intervals and correlation processing are accomplished. The components with different frequencies in structure function series are separated using empirical mode decomposition. Additionally, a chaos detection model based on the Duffing equation is introduced to determine the useful component and extract the changing features of RF. Experimental results indicate that the proposed methodology can successfully extract the slippage signal effectively in the case that multiple radar pulse sequences overlap.
A MODIFIED BFGS BUNDLE ALGORITHM BASED ON APPROXIMATE SUBGRADIENTS
Guo, Qiang,Liu, Jian-Guo The Korean Society for Computational and Applied M 2010 Journal of applied mathematics & informatics Vol.28 No.5
In this paper, an implementable BFGS bundle algorithm for solving a nonsmooth convex optimization problem is presented. The typical method minimizes an approximate Moreau-Yosida regularization using a BFGS algorithm with inexact function and the approximate gradient values which are generated by a finite inner bundle algorithm. The approximate subgradient of the objective function is used in the algorithm, which can make the algorithm easier to implement. The convergence property of the algorithm is proved under some additional assumptions.
BIAXIALLY ORIENTED POLYPROPYLENE FILM FOR AFM TIP CHARACTERIZATION
GUOQIANG HAN,YUQIN CHEN,BINGWEI HE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2014 NANO Vol.9 No.3
Atomic force microscopy (AFM) investigating the sample morphology is the process of directinteraction between tip and surface features. The geometry of probe tip is a determining factor incorrecting AFM images distorted by tip size itself. A quantitative knowledge of the current tipshape is needed to improve the reliability of AFM images. The biaxially oriented polypropylene(BOPP) ¯lm was fabricated and used as tip characterizer to estimate the morphology of AFM Sitip based on the blind reconstruction algorithm. The surface of the BOPP ¯lm was covered bynanometer-scale-sized structures which ensure that the tip pro¯le can be determined accurately. Without independent knowledge of the sample, the three-dimensional (3D) shape of Si probe tipwas obtained with high aspect ratio. BOPP ¯lm is not only a simple, cheap material but also asoft one which can also avoid tip damage in scanning. It was demonstrated reliable and suitablefor tip characterization.
Drought stress-induced changes of microRNAs in diploid and autotetraploid Paulownia tomentosa
Guoqiang Fan,Xibing Cao,Lin Cao,Minjie Deng,Zhenli Zhao,Suyan Niu,Zhe Wang,Yuanlong Wang 한국유전학회 2017 Genes & Genomics Vol.39 No.1
Drought stress adversely affects plant productivity. Growth and timber production of Paulownia trees are limited under drought stress. Changes in gene expression patterns and miRNA in different ploidy of Paulownia tomentosa have been investigated. However, the responses of P. tomentosa to drought stress at the microRNA (miRNA) level have not been reported so far. To identify miRNA candidates and their target genes involved in the drought stress response in diploid and tetraploid P. tomentosa, four small RNA and four degradome libraries from diploid and autotetraploid P. tomentosa under normal and drought stress conditions were constructed and sequenced. A total of 41 conserved and 90 novel miRNAs were identified. Among these miRNAs, 67 (26 conserved and 41 novel) and 53 (six conserved and 47 novel) were significantly differentially expressed in response to drought stress in diploid and autotetraploid P. tomentosa, respectively. Degradome analysis identified 356 candidate miRNA target genes that encoded proteins with functions that included plant defense, transcriptional regulation, and hormone metabolism. In particular, miR4 and miR156 were identified only in autotetraploid P. tomentosa under drought stress. These results will help us build a foundation for future studies of the biological functions of miRNAmediated gene regulation in P. tomentosa.