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Articles by Xiaoping Xu
Total Records ( 3 ) for Xiaoping Xu
  Guangjun Liu , Feng Wang , Xiaoping Xu and Long Liu
  Nonlinear system identification has been received more attention especially for control purposes. In this study, a new identification method is presented for nonlinear system model. Its basic idea is as follows. At first, the identification problem of nonlinear system is changed into a nonlinear function optimization problem over parameter space. Then, the estimates of the parameters of the nonlinear system are obtained using a proposed particle swarm optimization algorithm. Finally, in simulation, the method is applied to several different nonlinear systems and simulation results indicated that the presented method is feasible and reasonable.
  Xiaoping Xu , Bo Bai , Feng Wang and Fucai Qian
  Present study proposed new identification method for the nonlinear dynamic system. Firstly, suppose that the original system is expressed by Hammerstein model then the transfer function of the model can be changed into a linear form, thus generating a middle model. The parameters of the middle model are obtained by a Bacterial Chemotaxis Optimization (BCO) algorithm. Finally, through the relationships of the parameters of middle model and those of Hammerstein model, the parameters of Hammerstein model are derived. Thus, the original system is identified. The feasibility and efficiency of the presented algorithm are demonstrated using numerical simulations.
  Lianrui Chu , Yanlai Lai , Xiaoping Xu , Scott Eddy , Shuang Yang , Li Song and David Kolodrubetz
  The metabolism of glutathione by the periodontal pathogen Treponema denticola produces hydrogen sulfide, which may play a role in the host tissue destruction seen in periodontitis. H2S production in this organism has been proposed to occur via a three enzyme pathway, γ-glutamyltransferase, cysteinylglycinase (CGase), and cystalysin. In this study, we describe the purification and characterization of T. denticola CGase. Standard approaches were used to purify a 52-kDa CGase activity from T. denticola, and high pressure liquid chromatography electrospray ionization tandem mass spectrometry analysis of this molecule showed that it matches the amino acid sequence of a predicted 52-kDa protein in the T. denticola genome data base. A recombinant version of this protein was overexpressed in and purified from Escherichia coli and shown to catalyze the hydrolysis of cysteinylglycine (Cys-Gly) with the same kinetics as the native protein. Surprisingly, because sequence homology indicates that this protein is a member of a family of metalloproteases called M17 leucine aminopeptidases, the preferred substrate for the T. denticola protein is Cys-Gly (kcat/Km of 8.2 µM–1 min–1) not L-Leu-p-NA (kcat/Km of 1.1 µM–1 min–1). The activity of CGase for Cys-Gly is optimum at pH 7.3 and is enhanced by Mn2+, Co2+, or Mg2+ but not by Zn2+ or Ca2+. Importantly, in combination with the two other previously purified T. denticola enzymes, γ-glutamyltransferase and cystalysin, CGase mediates the in vitro degradation of glutathione into the expected end products, including H2S. These results prove that T. denticola contains the entire three-step pathway to produce H2S from glutathione, which may be important for pathogenesis.

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