Showing papers by "Yanshan University published in 2009"

Adaptive Fuzzy Output-Feedback Controller Design for Nonlinear Time-Delay Systems With Unknown Control Direction

Abstract: In this paper, the robust-control problem is investigated for a class of uncertain nonlinear time-delay systems via dynamic output-feedback approach. The considered system is in the strict-feedback form with unknown control direction. A full-order observer is constructed with the gains computed via linear matrix inequality at first. Then, with the bounds of uncertain functions known, we design the dynamic output-feedback controller such that the closed-loop system is asymptotically stable. Furthermore, when the bound functions of uncertainties are not available, the adaptive fuzzy-logic system is employed to approximate the uncertain function, and the corresponding output-feedback controller is designed. It is shown that the resulting closed-loop system is stable in the sense of semiglobal uniform ultimate boundedness. Finally, simulations are done to verify the feasibility and effectiveness of the obtained theoretical results.

A Simple Nonlinear Logical Torque Sharing Function for Low-Torque Ripple SR Drive

Abstract: A novel and simple nonlinear logical torque-sharing function (TSF) for a switched reluctance motor (SRM) drive is proposed. This novel scheme using nonlinear TSF manipulates currents in two adjacent phases during commutation, so that efficiency and torque ripple in an SRM drive can be considerably improved. For constant torque generation, the switching of one-phase windings is regulated, and torque reference for the other phase stays at the previous state under the condition of a certain current limit given by the overall drive power rating. Every torque state monitored by the nonlinear logical condition determines a regulated or nonregulated torque control among two phases overlapped in commutation region, where one phase is incoming to produce the majority of torque and the outgoing current in the other phase is decreasingly controlled by the logical condition. Due to the same switching state in a nonregulated phase and the reduction of commutation period by the proposed control method, the switching number can be significantly reduced, and hence, the switching loss can be reduced. In case that one-phase regulation cannot satisfy a proper torque reference required for minimum torque ripple operation, a two-phase regulation mode is employed in the novel nonlinear TSF. In order to include magnetic nonlinearity in torque control and decrease a current tail at the end of commutation, the current of the incoming phase needs to be controlled in an increasing manner, and at the same time, the outgoing phase current tracks on an opposite direction so that torque sharing between two phases can be smoothly achieved with a minimum current crossover. The proposed control scheme is verified by some computer simulations and experimental results.

Microwave-absorbing properties of shape-optimized carbonyl iron particles with maximum microwave permeability

Abstract: The microwave-absorbing properties for different shapes of carbonyl-iron particles prepared by the high-energy planetary ball milling with 40 vol% in epoxy resin matrix have been investigated. Higher value of magnetic permeability and permittivity can be obtained in the composites for thin flake carbonyl iron than spherical powders. The results are attributed to reduction of eddy current loss, orientation of magnetic moment and space–charge polarization with the shape change from spherical powders to thin flake particles. As the iron flakes with 0.4 μm in thickness as the absorbent fillers, the minimum RL value of −6.20 dB was observed at 4.57 GHz with thickness of 1 mm. The minimum reflection loss (RL) shifts to lower frequency and the value declines with change from spherical powders to thin flakes. It results from the considerable dielectric loss in the absorbing materials.

Antidiabetic and antioxidant effects of oleanolic acid from Ligustrum lucidum Ait in alloxan-induced diabetic rats.

Abstract: The present study evaluated the antidiabetic and antioxidant effects of oleanolic acid (OA) from Ligustrum lucidum Ait (LLA) in alloxan-induced diabetic rats. OA in the alloxan-induced diabetic rats showed significant hypoglycemic activity by lowering blood glucose (at doses of 60 and 100 mg/kg for 40 days). The levels of serum total cholesterol (TC), triglycerides (TG) and low-density lipoprotein cholesterol (LDL-c) in the OA-treated diabetic rats were lower, and the high-density lipoprotein cholesterol (HDL-c) level was higher than in the control diabetic rats. A significant reduction in the serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) levels of diabetic rats following OA treatment was also observed. Furthermore, OA treatment decreased the malondialdehyde (MDA) level, but increased superoxide dismutase (SOD) and glutathione peroxidase (GSH-px) activities of the liver and kidney in diabetic rats. These results indicate that OA could protect the liver function avoiding alloxan-induced damage; OA had hypoglycemic, hypolipidemic and antioxidant efficacy in the diabetic rats. The antioxidant ability of OA might be one of the mechanisms of its hypoglycemic and hypolipidemic effects.

Parameter estimation for time-delay chaotic system by particle swarm optimization

Abstract: The knowledge about time delays and parameters is very important for control and synchronization of time-delay chaotic system. In this paper, parameter estimation for time-delay chaotic system is given by treating the time delay as an additional parameter. The parameter estimation is converted to an optimization problem, which finds a best parameter combination such that an objective function is minimized. Particle swarm optimization (PSO) is used to optimize the objective function through particles’ cooperation and evolution. Two illustrative examples are given to show the validity of the proposed method.

A general methodology for mobility analysis of mechanisms based on constraint screw theory

Abstract: It is well known that the traditional Grubler-Kutzbach formula fails to calculate the mobility of some classical mechanisms or many modern parallel robots, and this situation seriously hampers mechanical innovation. To seek an efficient and universal method for mobility calculation has been a heated topic in the sphere of mechanism. The modified Grubler-Kutzbach criterion proposed by us achieved success in calculating the mobility of a lot of highly complicated mechanisms, especially the mobility of all recent parallel mechanisms listed by Gogu, and the Bennett mechanism known for its particular difficulty. With wide applications of the criterion, a systematic methodology has recently formed. This paper systematically presents the methodology based on the screw theory for the first time and analyzes six representative puzzling mechanisms. In addition, the methodology is convenient for judgment of the instantaneous or full-cycle mobility, and has become an effective and general method of great scientific value and practical significance. In the first half, this paper introduces the basic screw theory, then it presents the effective methodology formed within this decade. The second half of this paper presents how to apply the methodology by analyzing the mobility of several puzzling mechanisms. Finally, this paper contrasts and analyzes some different methods and interprets the essential reason for validity of our methodology.

The cryoprotective effect of trehalose supplementation on boar spermatozoa quality.

Abstract: In order to improve boar sperm quality during frozen-thawed process, the influence of the presence of trehalose on success of cryopreservation of boar sperm were investigated. We evaluated freeze-thawing tolerance of boar spermatozoa in a base cooling extender with the addition of different trehalose concentrations (0, 25, 50, 100 and 200 mm), and try to determine the optimum concentration of trehalose. We chose sperm motility, mitochondrial activity, acrosome integrity and membrane integrity as parameters to evaluate cryopreservation capacity of boar spermatozoa. We obtained the best results for 100 mm trehalose-supplemented extenders, with values of 49.89% for motility, 44.69% for mitochondrial activity, 66.52% for acrosome integrity and 44.61% for membrane integrity, while freeze-thawing tolerance diminished significantly for 200 . The synergic effect of trehalose and glycerol resulted in better cryosurvival of boar spermatozoa than that of a single cryoprotectant. In conclusion, when trehalose-supplementation was added up to 100 mm, trehalose confers a greater cryoprotective capacity to the extender, and the sperm motility, mitochondrial activity, membrane integrity and acrosome integrity parameters were significantly improved during frozen-thawed process.

The open hole tensile test - a challenge for virtual testing of composites

Abstract: The open hole tension strength is an important parameter for composite structures since it is can be a limiting factor in design. It is also difficult to characterise and predict through analytical or numerical methods since there exists a wide variation in experimental results depending on testing configuration. Here a range of such variations are presented and the behaviour explained in terms of the development of sub-critical damage in the form of intra-ply splits and inter-ply delaminations and their interaction with each other and also with fibre failure. A finite element based numerical analysis technique has been developed and applied to each case in turn, successfully predicting the failure modes, trends and strengths. This is sufficiently robust to form the basis for a virtual testing framework for the open hole tensile strength of composite materials.

Density-Based Data Streams Clustering over Sliding Windows

Abstract: Data stream clustering is an important task in data stream mining. In this paper, we propose SDStream, a new method for performing density-based data streams clustering over sliding windows. SDStream adopts CluStream clustering framework. In the online component, the potential core-micro-cluster and outlier micro-cluster structures are introduced to maintain the potential clusters and outliers. They are stored in the form of Exponential Histogram of Cluster Feature (EHCF) in main memory and are maintained by the maintenance of EHCFs. Outdated micro-clusters which need to be deleted are found by the value of t in Temporal Cluster Feature (TCF). In the offline component, the final clusters of arbitrary shape are generated according to all the potential core-micro-clusters maintained online by DBSCAN algorithm. Experimental results show that SDStream which can generate clusters of arbitrary shape has a much higher clustering quality than CluStream which generates spherical clusters.

Analysis of the M/G/1 queue with exponentially working vacations--a matrix analytic approach

Abstract: In this paper, an M/G/1 queue with exponentially working vacations is analyzed. This queueing system is modeled as a two-dimensional embedded Markov chain which has an M/G/1-type transition probability matrix. Using the matrix analytic method, we obtain the distribution for the stationary queue length at departure epochs. Then, based on the classical vacation decomposition in the M/G/1 queue, we derive a conditional stochastic decomposition result. The joint distribution for the stationary queue length and service status at the arbitrary epoch is also obtained by analyzing the semi-Markov process. Furthermore, we provide the stationary waiting time and busy period analysis. Finally, several special cases and numerical examples are presented.

Antitumor and immunomodulating effects of polysaccharides isolated from Solanum nigrum Linne.

Abstract: We have examined the effects of the crude polysaccharides isolated from Solanum nigrum Linne (SNL-P) in vitro and in vivo against U14 cervical cancer. SNL-P showed no antiproliferative effects in vitro at a dose up to 1 mg/ml. In vivo administration with SNL-P (90, 180, 360 mg/kg b.w., p.o.) decreased the number of ascites tumor cells and prolonged the survival time of U14 cervical-cancer-bearing mice. FACScan flow cytometer analysis showed that most of the ascites tumor cells were arrested in G2/M phase of cell cycle and the ratio of CD4+/CD8+ peripheral blood T-lymphocyte subpopulations were restored following treatment of SNL-P. Furthermore, the treatment with SNL-P also caused a significant increment in IFN-gamma (p < 0.01, 90, 180 and 360 mg/kg b.w.) and a remarkable decrease in Il-4 (p < 0.01, 90, 180 mg/kg b.w.; p < 0.05, 360 mg/kg b.w.) by the method of ELISA. These data showed that SNL-P possess potent antitumor activity and SNL-P might exert antitumor activity via activation of different immune responses in the host rather than by directly attacking cancer cells on the U14 cervical cancer bearing mice. Thus, SNL-P could be used as an immunomodulator and an anticancer agent.

Robust Adaptive Controller Design for Nonlinear Time-Delay Systems via T–S Fuzzy Approach

Abstract: The robust control problem is investigated for a class of uncertain nonlinear time-delay systems. Via the Takagi-Sugeno (T-S) fuzzification, we obtain the T-S fuzzy systems with each local model in the form of time-delay systems with uncertain nonlinear functions. The mismatched nonlinear functions satisfy the Lipschitz condition, while the matched parts are bounded by nonlinear functions with unknown coefficients. Based on the input matrix, the system is decomposed into two cascade subsystems. The virtual controller is designed for the first subsystem, and then, a memoryless adaptive controller is presented. By employing a new Lyapunov Krasovskii functional, we show that the resulting closed-loop system is exponentially stable and the solutions are uniformly ultimately bounded. Finally, simulation examples are given to show the effectiveness of our main results.

Processing maps and hot workability of Super304H austenitic heat-resistant stainless steel

Abstract: Hot-compression and hot-tension experiments were conducted on a Gleeble3500 thermal–mechanical simulator, and the microstructure diagram of Super304H austenitic heat-resistant stainless steel as well as its thermoplastic diagram under different deformation conditions was obtained. Based on the dynamic material model theories and Prasad instability criterion, its hot processing maps were developed. The deformation mechanisms of different regions in the maps were analyzed, and corresponding microstructures were investigated. The results show that for Super304H steel, the critical Z value, below which the complete dynamic recrystallization may occur, is about 4.23 × 10 20 . During the hot tension at 0.1 and 1 s −1 , the total elongation and reduction in area increased with the increase of deformation temperature ranging from 800 to 1100 °C. As for the hot working of Super304H austenitic heat-resistant stainless steel, large-strain deformation can be carried out at 1100 °C and at the strain rate above 0.5 s −1 .

Stability analysis for periodic solution of neural networks with discontinuous neuron activations

Abstract: In this paper, we present a general class of neural networks with discontinuous neuron activations and varying coefficients, where the neuron activation function is a discontinuous monotone increasing and bounded function. By using the fixed point theorem in differential inclusion theory and constructing suitable Lyapunov functions, a condition is derived which ensures the existence and global exponential stability of a unique periodic solution for the neural network. Furthermore, under certain conditions global convergence in finite time of the state is investigated. The obtained results show that Forti’s conjecture for neural networks without delays is true. Finally, two numerical examples are given to demonstrate the effectiveness of the results obtained in this paper.

Enthalpy relaxation upon glass transition and kinetic fragility of molecular liquids.

Abstract: Relaxation enthalpies in the vicinity of glass transitions were recorded on the basis of the heat capacity curves measured in nine glass-forming molecular liquids and solutions in the well defined cooling and subsequent heating cycles. It is observed that enthalpy hysteresis in the cooling/heating cycles is less significant in liquids with increasing fragility. A notable correlation of the fragility index m with relaxation enthalpy ΔHR, glass transition temperature, and heat capacity jump from glasses to liquids is demonstrated. The introduction of ΔHR favors the thermodynamic evaluation of fragility in the glass forming multicomponent systems such as solutions and alloys.