• The Korean Journal of Ceramics
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• 제6권3호
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• pp.267-271
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• 2000

The influence of photoexcited nonequilibrium carriers on domain switching and photovoltaic current was investigated in two kinds of poled La-modified PbTiO$_3$ferroelectric ceramics, (Pb$_{0.85}$La$_{0.15}$)TiO$_3$and (Pb$_{0.76}$La$_{0.24}$)TiO$_3$, under illumination in the absence of external electric field. Both photovoltaic current and cumulative AE event counts increased with illumination time. The observed nonsteady-state photovoltaic current could be explained on the basis of the cycles of a series of physical events consisting the establishment of space charge field by photoexcited carriers trapped at the grain boundaries, the photoinduced domain switching, and the increase in the remanent polarization. An analysis of energy distribution of the observed AE signals also revealed that the space charge field in (Pb$_{0.85}$La$_{0.15}$)TiO$_3$allowed both 18$0^{\circ}C$ and 90$^{\circ}$domains to be switched during illumination.

• 한국IT서비스학회지
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• 제2권2호
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• pp.15-29
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• 2003

This thesis suggests a R&D model for Korean SI companies who aggressively drive oversea business to overcome domestic market limitation and to become world class SI players. Even though there have been a lot of discussions on IT technologies and new business models, scientific approach to a R&D model for SI companies is rare due to its natural distinctiveness from manufacturing and general service domain. Therefore, this will be a flagship thesis to keep up our study. As business market environment gets more competitive, major Korean SI players will be confronted with much more keen competition among themselves. And as they are willing to expand their oversea market presence, they can not help struggling against global SI players. So, here we are presenting SI players the reinforcement of R&D as one of the key components to build up their own core competencies. That is, SI players have to adopt and evaluate fast changing and complicated IT technologies at the right time, and to apply them into a real business with cost-effective service delivery and operation processes internally. The ultimate purpose of all of these activities is to offer a SI company the value added business model based on its innovative technical capabilities and well refined service deliver model. For this purpose, we suggests, SI company's R&D has to play an important role of emerging technology verification/evaluation/utilization, value added business model creation, future innovation lead, standard body participation, and effective service delivery and quality system development. To become a more effective R&D organization, hybrid R&D, in which central R&D and divisional sub R&D work together, is considered as an idea model. The reliability of the R&D model for Korean SI companies', here we suggest, has been checked by SI companies R&D specialists and on-site business people.

• Current Photovoltaic Research
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• 제4권2호
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• pp.64-67
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• 2016

We investigated the influences of Ag nanoparticle (NP) arrays and surface nanohole (NH) patterns on the optical characteristics of 10-${\mu}m$-thick c-Si wafers using finite-difference time-domain (FDTD) simulations. In particular, we comparatively studied the plasmonic effects of both monomer arrays (MA) and heptamer arrays (HA) consisting of identical Ag NPs. HA improved the optical absorption of the c-Si wafers in much wider wavelength range than MA, with the help of hybridized plasmon modes. The light trapping capability of the NH array pattern is superior to that of the Ag plasmonic NPs. We also found that the addition of the Ag HA on the wafers with surface NH patterns further enhanced optical absorption: the expected short-circuit current density was as high as $34.96mA/cm^2$.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.529-535
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• 2005

This paper presents a system identification (SI) scheme in time domain using measured acceleration data. The error function is defined as the time integral of the least squared errors between the measured acceleration and the calculated acceleration by a mathematical model. Damping parameters as well as stiffness properties of a structure are considered as system parameters. The structural damping is modeled by the Rayleigh damping. A new regularization function defined by the L1-norm of the first derivative of system parameters with respect to time is proposed to alleviate the ill-posed characteristics of inverse problems and to accommodate discontinuities of system parameters in time. The time window concept is proposed to trace variation of system parameters in time. Numerical simulation study is performed through a two-span continuous truss subject to ground motion.

• Current Photovoltaic Research
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• 제5권2호
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• pp.55-58
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• 2017

We investigated the influences of dielectric thin film coating on the optical characteristics of c-Si wafers with nanocone (NC) arrays using finite-difference time-domain (FDTD) simulations. Dielectric thin films on high-refractive-index surface can lower optical reflection and reflection dips appear at the wavelengths where destructive interference occurs. The optical reflection of the NC arrays was lower than that of the dielectric-coated planar wafer in broad wavelength range. Remarkable antireflection effects of the NC array could be attributed to beneficial roles of the NCs, including the graded refractive index, multiple reflection, diffraction, and Mie resonance. Dielectric thin films modified the optical reflection spectra of the NC arrays, which could not be explained by the interference alone. The optical properties of the dielectric-coated NC arrays were determined by the inherent optical characteristics of the NC arrays.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.179.1-179.1
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• 2014

Si nanowires have exhibited unique optical characteristics, including nano-antenna effects due to the guided mode resonance, significant optical absorption enhancement in wide wavelength and incident angle range due to resonant optical modes, graded refractive index, and scattering. Since Si poor optical absorption coefficient due to indirect bandgap, all such properties have stimulated proposal of new optoelectronic devices whose performance can surpass that of conventional planar devices. We have carried out finite-difference time-domain simulation studies to design optimal Si nanowire array for solar cell applications. Optical reflectance, transmission, and absorption can be calculated for nanowire arrays with various diameter, length, and period. From the absorption, maximum achievable photocurrent can be estimated. In real devices, serious recombination loss occurring at the surface states is known to limit the photovoltaic performance of the nanowire-based solar cells. In order to address such issue, we will discuss how the geometric parameters of the array can influence the spatial distribution of the optical field (resulting optical generation rate) in the nanowires.

• Journal of Power Electronics
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• 제18권3호
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• pp.892-901
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• 2018

SiC MOSFETs have been used to improve system efficiency in high frequency converters due to their extremely high switching speed. However, this can result in undesirable parasitic oscillations in practical systems. In this paper, models of the key components are introduced first. Then, theoretical formulas are derived to calculate the switching oscillation frequencies after full turn-on and turn-off in clamped inductive circuits. Analysis indicates that the turn-on oscillation frequency depends on the power loop parasitic inductance and parasitic capacitances of the freewheeling diode and load inductor. On the other hand, the turn-off oscillation frequency is found to be determined by the output parasitic capacitance of the SiC MOSFET and power loop parasitic inductance. Moreover, the shifting regularity of the turn-off maximum peak voltage with a varying switching speed is investigated on the basis of time domain simulation. The distortion of the turn-on current is theoretically analyzed. Finally, experimental results verifying the above calculations and analyses are presented.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.237.1-237.1
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• 2014

Etching is one of the most important steps in semiconductor manufacturing. In etch process control a critical task is to stop the etch process when the layer to be etched has been removed. If the etch process is allowed to continue beyond this time, the material gets over-etched and the lower layer is partially removed. On the other hand if the etch process is stopped too early, part of the layer to be etched still remains, called under-etched. Endpoint detection (EPD) is used to detect the most accurate time to stop the etch process in order to avoid over or under etch. The goal of this research is to develop a hardware and software system for EPD. The hardware consists of an Optical Plasma Monitor (OPM) sensor which is used to continuously monitor the plasma optical emission intensity during the etch process. The OPM software was developed to acquire and analyze the data to perform EPD. Our EPD algorithm is based on the following theory. As the etch process starts the plasma generated in the vacuum is added with the by-products from the etch reactions on the layer being etched. As the endpoint reaches and the layer gets completely removed the plasma constituents change gradually changing the optical intensity of the plasma. Although the change in optical intensity is not apparent, the difference in the plasma constituents when the endpoint has reached leaves a unique signature in the data gathered. Though not detectable in time domain, this signature could be obscured in the frequency spectrum of the data. By filtering and analysis of the changes in the frequency spectrum before and after the endpoint we could extract this signature. In order to do that, first, the EPD algorithm converts the time series signal into frequency domain. Next the noise in the frequency spectrum is removed to look for the useful frequency constituents of the data. Once these useful frequencies have been selected, they are monitored continuously in time and using a sub-algorithm the endpoint is detected when significant changes are observed in those signals. The experiment consisted of three kinds of etch processes; ashing, SiO2 on Si etch and metal on Si etch to develop and evaluate the EPD system.

• 대한음성학회지:말소리
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• 제64호
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• pp.89-103
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• 2007

In this paper, we introduce mel-cepstrum modulation energy (MCME) for a feature to discriminate speech and music data. MCME is a mel-cepstrum domain extension of modulation energy (ME). MCME is extracted on the time trajectory of Mel-frequency cepstral coefficients, while ME is based on the spectrum. As cepstral coefficients are mutually uncorrelated, we expect the MCME to perform better than the ME. To find out the best modulation frequency for MCME, we perform experiments with 4 Hz to 20 Hz modulation frequency. To show effectiveness of the proposed feature, MCME, we compare the discrimination accuracy with the results obtained from the ME and the cepstral flux.

• 한국전기전자재료학회논문지
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• 제18권12호
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• pp.1129-1132
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• 2005

The purpose of this reserch is to establish the new design technology for microwave Coplanar structure. The components in microwave circuit are classified to transmission devices, EM devices, and quasi-TEM devices. After design of these devices, we analyzed these CPWs electromagnetically using FDTD method, and suggested optimum CPW structure. In oder to realize a CPW module up to 30 GHz-100 GHz band, we research on a technology of 3-dimensional microwave CPW, and GaAs substrate with Si layer for ohmic loss. As a result this research, we suppressed the leakage, resonance, coupling, and radiation of CPW EMI, and improved resonance quality of CPW.