• Proceedings of the KIPE Conference
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• 2004.07a
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• pp.147-150
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• 2004

Maximum power point tracking for PV systems traditionally uses either perturbation and observation method or incremental conductance method. Both methods require modulation of the output voltage and this leads to significant power loss. In this paper, a method, which senses output circuit voltage and short circuit current and use the above two parameters for optimum control with a fuzzy controller, is introduced. The short circuit current of PV cell represents illumination, and the output circuit voltage carry on information about the temperature. PCS(power conditioning system) is controlled not only feed to inverter for stability voltage variation despite of variety external environment, but also operate in order to feeding voltage and current at maximum power point by boost type chopper.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.666-671
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• 1993

A new robust control law is proposed for uncertain rigid robots and two composite robust control laws for flexible-joint manipulators which contain uncertainties. The uncertainty, is nonlinear and (possibly fast) time-varying. Therefore, the uncertain factors such as imperfect modeling, function, payload change, and external disturbances are all addressed. Based only on the possible bound of the uncertainty, a robust controller is constructed for the rigid counterpart of the flexible-joint robot Some feedback control terms are then added to the robust control law to stabilize the elastic vibrations at the joints. To show that the proposed composite robust control laws are indeed applicable to flexible-joint robots, a singular perturbation approach and the stability study based on Lyapunov function are proposed.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.722-725
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• 1996

This paper presents a new control strategy for the position and force control of a flexible manipulator. The governing equation of motion of a two-link flexible manipulator which features a piezoceramic actuator is derived via Hamilton's principle. The control torque of the motor to command desired position and force is determined by a sliding mode controller. This controller is formulated to take account of parameter uncertainties and external disturbances. During the commanded motion, undesirable oscillation is actively suppressed by applying a feedback control voltage to the piezoceramic actuator. Consequently, an accurate compliant motion control of the flexible manipulator is achieved. Computer simulations are undertaken in order to demonstrate the effectiveness of the proposed control methodology.

• Journal of the Korean Ceramic Society
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• v.47 no.1
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• pp.39-46
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• 2010

The kinetics of cation reequilibration have been studied theoretically and experimentally in complex oxides after an external perturbation of equilibrium by temperature jumps. A general kinetic model for cation redistribution amongst non-equivalent sites in complex oxides is derived based on a local homogeneous point defect mechanism involving cation vacancies. Temperature-jump optical relaxation spectroscopy has been established to investigate cation kinetic processes in spinels and olivines. The kinetic model satisfactorily describes the experimental absorbance relaxation kinetics in cobalt containing olivines and in nickel containing spinels. It is found that the kinetics of cation redistribution in complex oxides shows a strong temperature- and composition-dependence. Activation energies for cation redistribution in Co-Mg olivines are found to range between 200 and 220 kJ/mol whereas an energy barrier of about 230 kJ/mol is observed in the case of nickel gallate spinel.

• Carbon letters
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• v.13 no.4
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• pp.226-229
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• 2012

Polyacetylene (PA) films with vertically aligned fibril morphology were synthesized in homeotropic nematic liquid crystal (N-LC) solvent by using a magnetic field of 5 Tesla as an external perturbation. Scanning electron microscope (SEM) photographs indicated that the lengths of fibrils from the substrate were $5-35{\mu}m$, depending on polymerization time. Carbonization was carried out using iodine-doped PA film and a morphology-retaining carbonization method. From the SEM results, we confirmed that the vertical morphology of the PA remains unchanged even after carbonization at $800^{\circ}C$. The weight loss of the films due to carbonization at $800^{\circ}C$ is about 20% of the weight of the film before iodine doping. It is expected that vertically aligned carbon might be a precursor for preparing vertical graphite materials, which materials could be useful for electrochemical energy storage and cell electrodes.

• Korea-Australia Rheology Journal
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• v.20 no.4
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• pp.189-196
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• 2008

The pulsatile flow of blood through a stenosed artery under the influence of external periodic body acceleration is studied. The effect of non-Newtonian nature of blood in small blood vessels has been taken into account by modeling blood as a Casson fluid. The non-linear coupled equations governing the flow are solved using perturbation analysis assuming that the Womersley frequency parameter is small which is valid for physiological situations in small blood vessels. The effect of pulsatility, stenosis, body acceleration, yield stress of the fluid and pressure gradient on the yield plane locations, velocity distribution, flow rate, shear stress and frictional resistance are investigated. It is noticed that the effect of yield stress and stenosis is to reduce flow rate and increase flow resistance. The impact of body acceleration is to enhance the flow rate and reduces resistance to flow.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.5
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• pp.779-787
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• 2001

The multi degree of freedom system using magnetic levitation has been implemented successfully. Differently from another noncontact systems, the developed system was focused on the maximization of the system stiffness under the constraint of a limited input. The variation of a relative adopting point between the magnetic pair, its location on the fixed base, and the selection of optimal specifications for the main active magnetic elements give us another chance to realize the increased robustness against external disturbances with the less control inputs. In this paper, the overall development procedures are given including the optimal design, the dynamic modeling, the various control tests, and the main issues to be solved.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.74.2-74.2
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• 2011

We probe the tidal perturbation parameter f of Virgo cluster galaxies. The goal is to measure the strength of tidal fields around individual galaxies to get better understanding gravitational processes that can affect galaxy evolution in the cluster environment. The f-value is defined as a logarithmic ratio between the net internal gravitational force within a galaxy and the external tidal force exerted by a neighboring galaxy. Hence, it provides one way to quantify the tidal field strength of galaxies, in particular, due to galaxy neighbors. In this study, we determine f-values of the VIVA galaxies, samples of the VLA Imaging study of Virgo galaxies in Atomic gas, using the Extended Virgo Cluster Catalog (EVCC) which is the most complete Virgo cluster catalog to date. With diagnostics based on the HI gas and R-band morphologies, we discuss the impact of the tidal fields on the evolution of the VIVA sample. Also, we compare the tidal field strength to the intra cluster medium (ICM) pressure for each sample galaxy to pin down environmental processes at work.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.883-885
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• 2009

We proposed intriguing and simple technique for fabricating flexible plastic liquid crystal (LC) devices. We made a preliminary version of a flexible LC display employing this concept, and we confirmed this technique was useful for the flexible LC display; the electro-optical reproducibility of the flexible LC device fabricated here was remarkably improved against external perturbation compared with the conventional one.

• Current Optics and Photonics
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• v.7 no.1
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• pp.33-37
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• 2023

Real-time adaptive control of laser output polarization is presented in a 10-W-level non-polarization-maintaining (non-PM) fiber amplifier. While the output polarization from a non-PM fiber amplifier tends to be irregular, depending on output power, time, and perturbation, closed-loop polarization control can maintain the polarization extinction ratio at higher than 20 dB. Real-time polarization control can attain the target linear polarization mostly within 1.4-25 ms and shows stability against external perturbations. This approach can satisfy both linear polarization and high output power in a non-PM amplifier, and facilitates optimization of laser performance and maintenance-free operation.