K S Lee’s research while affiliated with Dong-A University and other places

Interior noise cancellation for railway train systems is an important means of enhancing passenger comfort and quality of service. This study proposes a novel active noise control (ANC) approach that uses an finite impulse response (IIR) filter and neural network techniques to effectively reduce interior noise. The authors construct a multiple-channel IIR filter module that is a linearly augmented framework with a generic IIR model to generate a primary control signal. A three-layer perceptron neural network is employed for establishing a secondary-path model to represent air channels among noise fields. Since the IIR module and neural network are connected in series, the output of an IIR filter is transferred forward to the neural model to generate a final ANC signal. A gradient descent optimisation-based learning algorithm is analytically derived for the optimal selection of the ANC parameter vectors. Moreover, re-estimation of partial parameter vectors in the ANC system is proposed for online learning. Sufficient stability conditions are derived for the proposed ANC system. Lastly, the authors present the results of a numerical study to test their ANC methodology with realistic interior noise measurement obtained from Korean railway trains.

Ag doped SnO2 (Ag:SnO2) films were prepared on glass substrates by pulsed dc magnetron sputtering. The effect of thermal annealing treatments on the physical properties of the films was investigated. Several analytical techniques such as X-ray diffraction, electron probe microanalysis, scanning electron microscopy, atomic force microscopy, four-point probe and double beam spectrophotometer were used to examine the changes in structural, compositional, surface morphology, electrical and optical properties. XRD results showed that the films were grown with (1 1 0) preferential orientation with an average grain size in the range from 4.8 to 8.9 nm. The smoothness of the films increased with annealing temperature. The films annealed at 500 °C presented an electrical resistivity of 0.007 Ω cm. The as deposited films exhibited the highest optical transmittance of 95% with band gap of 3.23 eV.

The authors present a robust adaptive control approach using model reference adaptive control (MRAC) for autonomous robot systems with random friction. First, a non-linear model of the robot system is approximated by feedback linearisation to derive a nominal control law. Next, a least square observer is constructed for the online estimation of friction dynamics. The authors derive a perturbed system model governing the friction estimation error and design an MRAC control to mitigate its effect. Also, stability conditions for the perturbed system model using the Lyapunov stability theory are derived. The authors demonstrate the success of the proposed control methodology through computer simulation, including a comparison to a traditional controller based on nominal dynamics.

This paper presents a novel control methodology for communication network based nonlinear systems with time delay nature. We construct a nominal nonlinear control law for representing a linear model and a reset control system which is aimed for corrective control strategy to compensate system error due to uncertain time delay through wireless communication network. Next, online neural control approach is proposed for overcoming nonstationary statistical nature in the network topology. Additionally, DBN (Dynamic Bayesian Network) technique is accomplished for modeling of its dynamics in terms of casuality, which is then utilized for estimating prediction of system output. We evaluate superiority and reliability of the proposed control approach through numerical simulation example in which a nonlinear inverted pendulum model is employed as a networked control system.

Chaos in motor systems is undesirable in real-time implementation because it results in motor speed oscillations changes in steady-state torque. This paper presents an adaptive control approach for time-varying permanent-magnet synchronous motor (PMSM) systems with chaotic behavior. We consider bounded perturbations in the system parameters. First, we transform the nonlinear PMSM model to derive a nominal linear control strategy. Then, we design an auxiliary control to compensate for real-time control errors due to parameter changes using Lyapunov stability theory. We numerically simulate our PMSM controller and demonstrate its efficiency and reliability when compared to traditional controllers.

Recent studies have suggested that virulent strains of Mycobacterium tuberculosis induce apoptosis in macrophages less often than do attenuated strains. K-strain, which belongs to the Beijing family, is the most frequently isolated clinical strain of M. tuberculosis in Korea. In this study, we investigated the differential induction of cell death in human monocytic THP-1 cells by K-strain and H37Rv, a virulent but laboratory-adapted strain of M. tuberculosis. Although no significant difference in growth rate was observed between the cells exposed to K-strain and those exposed to H37Rv, the levels of protective cytokines such as tumour necrosis factor (TNF)-alpha, interleukin (IL)-6 and IL-12p40 were lower in K-strain-infected cells than in H37Rv-infected cells. Cell viability assays showed that both K-strain and H37Rv, but not heat- or streptomycin-killed bacteria, induced THP-1 cell death in a TNF-independent manner. In contrast, double staining with fluorochrome-labelled inhibitors of caspase and propidium iodide and lactate dehydrogenase release assays revealed that K-strain induced significantly higher levels of necrotic cell death, rather than apoptosis, in THP-1 cells than did H37Rv. Anti-apoptotic Bcl-2, Mcl-1, Bfl-1 and Bcl-xL in the cells were significantly upregulated following infection with K-strain compared with H37Rv, whereas Bax was slightly upregulated in response to infection with both H37Rv and K-strain. These results suggest that the highly virulent K-strain keeps cellular apoptosis as a host defense mechanism to a minimum and induces necrosis in macrophages.