• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.263-268
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• 2004

In the present study, a Nd;YAG Laser (pulse type) was used to emit ultrasonic signals to a test material. In addition, a total ultrasonic investigation system was designed by adopting a Fabry-Perot interferometer, which receives ultrasonic signals without any contact. For non-destructive test SM45C, which contains some flaws was used as a test material. Because it is easy to align light beam in receiver, and the length of the light beam does not change much even if convex mirror leans towards one side, confocal Fabry-Perot interferometer, which has stable frequency, and PI control are used to correct interfered and unstable signals from temperature, fluctuation and time shift of laser frequency. Stable signals are always obtained by the feedback of PI circuit signals in the confocal Fabry-Perot interferometer. The type, size and position of flaws inside the test material were examined by achieving the stabilization of an interferometer. This study presented a useful method, which could quantitatively investigate the fault of objects by using a Fabry-Perot interferometer.

• Journal of IKEEE
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• v.23 no.2
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• pp.652-658
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• 2019

This paper proposes the selective voltage balancing scheme of a modular multilevel DC-DC converter for solid-state transformers. In general, the sub-module capacitor voltage can be controlled uniformly by individual feedback controllers, however computation time increases according to the number of modules. The voltage balance control scheme in this paper can reduce the computation time by selecting and controlling sub-module of maximum/minimum voltage momentarily. The performance of the proposed selective voltage balancing scheme is verified by simulation.

• Journal of the Semiconductor & Display Technology
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• v.21 no.1
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• pp.50-55
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• 2022

Due to the wavelength shift problem of micro LED caused by the change of current density, the active matrix driving pixel circuit that is used in OLED cannot be applied to micro LED displays. Therefore, we need a gray scale method based on modulation of duration time of light emission. In this study, we propose the PWM-controlled micro LED pixel circuit based on CMOS thin film transistors (TFTs). By adopting CMOS inverter structure, we can reduce the number of storage capacitors from the circuit and make the operating speed of the circuit faster. Most of all, our circuit is designed to make operating speed of PWM circuit faster by adopting feedback effect through double gate TFT structure. As a result, it takes about 4.7ns to turn on the LED and about 5.6ns to turn it off. This operating time is short enough to avoid the color distortion and help the precise control of the gray scale.

• IMMUNE NETWORK
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• v.3 no.3
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• pp.201-210
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• 2003

Objective: The role of prostaglandin $E_2$ (PGE2) in the etiopathogenesis of immune and inflammatory diseases has become the subject of recent debate. To determine the role of PGE2 in rheumatoid arthritis (RA), we tested the effect of exogenous PGE2 on the production of cyclooxygenase-2 (COX-2) by rheumatoid synoviocytes. Methods: Fibroblast-like synoviocytes (FLS) were prepared from the synovial tissues of RA patients, and cultured in the presence of PGE2. The COX-2 mRNA and protein expression levels were determined by RT-PCR and Western blot analysis, respectively. The PGE2 receptor subtypes in the FLS were analyzed by RT-PCR. Electrophoretic mobility shift assay (EMSA) was used to measure the NF-${\kappa}B$ binding activity for COX-2 transcription. The in vivoeffect of PGE2 on the development of arthritis was also tested in collagen induced arthritis (CIA) animals. Results: PGE2 ($10^{-11}$ to $10^{-5}M$) dose-dependently inhibited the expression of COX-2 mRNA and the COX-2 protein stimulated with IL-$1{\beta}$, but not COX-1 mRNA. NS-398, a selective COX-2 inhibitor, displayed an additive effect on PGE2-induced COX-2 downregulation. The FLS predominantly expressed the PGE2 receptor (EP) 2 and EP4, which mediated the COX-2 suppression by PGE2. Treatment with anti-IL-10 monoclonal antibodies partially reversed the PGE2-induced suppression of COX-2 mRNA, suggesting that IL-10 may be involved in modulating COX-2 by PGE2. Experiments using an inducer and an inhibitor of cyclic AMP (cAMP) suggest that cAMP is the major intracellular signal that mediates the regulatory effect of PGE2 on COX-2 expression. EMSA revealed that PGE2 inhibited the binding of NF-${\kappa}B$ in the COX-2 promoter via a cAMP dependent pathway. In addition, a subcutaneous injection of PGE2 twice daily for 2 weeks significantly reduced the incidence and severity of CIA as well as the production of IgG antibodies to type II collagen. Conclusion: Our data suggest that overproduced PGE2 in the RA joints may function as an autocrine regulator of its own synthesis by inhibiting COX-2 production and may, in part, play an anti-inflammatory role in the arthritic joints.