• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1599-1603
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• 2004

Based on the idea that nonlinear PWM controller design can be directly applied to the attitude tracking problem of thruster-controlled spacecraft because it constitutes a sub-class of nonlinear PWM controlled system, nonlinear and output error feedback PWM controlled system is considered to describe the behavior of thruster-controlled spacecraft, and to determine actual thruster on-time which guarantees system stability. A differential geometric approach is utilized to show an asymptotical stability of average PWM system, which finally guarantees the stability of closed loop PWM controlled system. Simulation results show that the motions of PWM controlled system occurs very closely around those of the average model of PWM controlled system.

• Journal of applied mathematics & informatics
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• v.31 no.3_4
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• pp.385-398
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• 2013

In this paper, a turbidostat model with ratio-dependent growth rate and impulsive state feedback control is considered. We obtain sufficient conditions of the globally asymptotically stable of the system without impulsive state feedback control. We also obtain that the system with impulsive state feedback control has periodic solution of order one. Sufficient conditions for existence and stability of periodic solution of order one are given. In some cases, it is possible that the system exists periodic solution of order two. Our results show that the control measure is effective and reliable.

• Bulletin of the Korean Mathematical Society
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• v.46 no.6
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• pp.1237-1248
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• 2009

The domain of attraction of a nonlinear differential equations is the region of initial points of solution tending to the equilibrium points of the systems as the time going. Determining the domain of attraction is one of the most important problems to investigate nonlinear dynamical systems. In this article, we first present two algorithms to determine the domain of attraction by using the moment matrices. In addition, as an application we consider a class of SIRS infection model and discuss asymptotical stability by Lyapunov method, and also estimate the domain of attraction by using the algorithms.

• Bulletin of the Korean Mathematical Society
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• v.48 no.3
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• pp.555-574
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• 2011

It is well known that the mathematical models provide very important information for the research of human immunodeciency virus type. However, the infection rate of almost all mathematical models is linear. The linearity shows the simple interaction between the T-cells and the viral particles. In this paper, a differential equation model of HIV infection of $CD4^+$ T-cells with Crowley-Martin function response is studied. We prove that if the basic reproduction number $R_0$ < 1, the HIV infection is cleared from the T-cell population and the disease dies out; if $R_0$ > 1, the HIV infection persists in the host. We find that the chronic disease steady state is globally asymptotically stable if $R_0$ > 1. Numerical simulations are presented to illustrate the results.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.74.3-74
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• 2001

This paper proposes a nonlinear adaptive controller based on back-stepping method for tracking reference substrate concentration by manipulating dilution rate in a continuous baker´s yeast cultivating process in stirred tank bioreactor. Control law is obtained from Lyapunov control function to ensure asymptotical stability of the system. The Haldane model for the specific growth rate depending on only substrate concentration is used in this paper. Due to the uncertainty of specific growth rate, it has been modified as a function including the unknown parameter with known bounded values. The substrate concentration in the bioreactor and feed line are measured. The deviation from the reference is observed when the external disturbance such as the change of the feed is introduced to the system ...

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.198-201
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• 2005

This study investigates the difference between single-cell and multi-cell cross-sections of thin-walled beams. The variationally and asymptotically consistent theory is used in order to model the two-cell thin- walled beam. The theory is based on an asymptotical analysis of two-dimensional shell energy. In addition, the method allows for the development of closed-form expressions for the displacement, stress field and beam stiffness coefficients. The numerical results show the difference between the cross-sectional stiffness of single-cell and that of multi-cell.

• Transactions on Control, Automation and Systems Engineering
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• v.4 no.4
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• pp.277-282
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• 2002

This paper proposes a nonlinear adaptive controller based on back-stepping method for tracking reference substrate concentration by manipulating dilution rate in a continuous baker's yeast cultivating process in stirred tank bioreactor. Control law is obtained from Lyapunov control function to ensure asymptotical stability of the system. The Haldane model for the specific growth rate depending on only substrate concentration is used in this paper. Due to the uncertainty of specific growth rate, it has been modified as a function including the unknown parameter with known bounded values. The substrate concentration in the bioreactor and feed line are measured. The deviation from the reference is observed when the external disturbance such as the change of the feed is introduced to the system. The effectiveness of the proposed controller is shown through simulation results in continuous system.

• Communications for Statistical Applications and Methods
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• v.25 no.1
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• pp.43-60
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• 2018

This paper considers the use of classical and Bayesian inference methods to analyze data generated by variables whose natural behavior can be modeled using asymmetric distributions in the presence of left censoring. Our approach used a $L{\grave{e}}vy$ distribution in the presence of left censored data and covariates. This distribution could be a good alternative to model data with asymmetric behavior in many applications as lifetime data for instance, especially in engineering applications and health research, when some observations are large in comparison to other ones and standard distributions commonly used to model asymmetry data like the exponential, Weibull or log-logistic are not appropriate to be fitted by the data. Inferences for the parameters of the proposed model under a classical inference approach are obtained using a maximum likelihood estimators (MLEs) approach and usual asymptotical normality for MLEs based on the Fisher information measure. Under a Bayesian approach, the posterior summaries of interest are obtained using standard Markov chain Monte Carlo simulation methods and available software like SAS. A numerical illustration is presented considering data of thyroglobulin levels present in a group of individuals with differentiated cancer of thyroid.

• Journal of Mechanical Science and Technology
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• v.19 no.3
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• pp.756-767
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• 2005

This paper presents a decentralized motion control method of welding mobile manipulators which use for welding in many industrial fields. Major requirements of welding robots are accuracy, robust, and reliability so that they can substitute for the welders in hazardous and worse environment. To do this, the manipulator has to take the torch tracking along a welding trajectory with a constant velocity and a constant heading angle, and the mobile-platform has to move to avoid the singularities of the manipulator. In this paper, we develop a kinematic model of the mobile-platform and the manipulator as two separate subsystems. With the idea that the manipulator can avoid the singularities by keeping its initial configuration in the welding process, the redundancy problem of system is solved by introducing the platform mobility to realize this idea. Two controllers for the mobile-platform and the manipulator were designed, respectively, and the relationships between two controllers are the velocities of two subsystems. Control laws are obtained based on the Lyapunov function to ensure the asymptotical stability of the system. The simulation and experimental results show the effectiveness of the proposed controllers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.12
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• pp.3037-3054
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• 2013

Interference between primary user (PU) and secondary user (SU) transceivers should be mitigated in order to implement underlay spectrum sharing in cognitive radio networks (CRN). Considering this scenario, an improved joint subcarrier and bit allocation scheme for cognitive user with primary users' cooperation (PU Coop) in CRN is proposed. In this scheme, the optimization problem is formulated to minimize the average interference power level at the PU receiver via PU Coop, which guarantees a higher primary signal to interference plus noise ratio (SINR) while maintaining the secondary user total rate constraint. The joint optimal scheme is separated into subcarrier allocation and bit assignment in each subcarrier via arith-metric geo-metric (AM-GM) inequality with asymptotical optimization solution. Moreover, the joint subcarrier and bit optimization scheme, which is evaluated by the available SU subcarriers and the allocated bits, is analyzed in the proposed PU Coop model. The performance of cognitive spectral efficiency and the average interference power level are investigated. Numerical analysis indicates that the SU's spectral efficiency increases significantly compared with the PU non-cooperation scenario. Moreover, the interference power level decreases dramatically for the proposed scheme compared with the traditional Hughes-Hartogs bit allocation scheme.