• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2015년도 춘계학술대회
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• pp.685-688
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• 2015

기존의 컨버터에서 널리 사용되는 위상천이 풀브리지 컨버터(Phase-Shifted Full-Bridge Converter) 경우 입력 전원 변화에 출력 전압의 변동이 있는 경우 듀티 변화에 따른 Freewheeling 구간이 존재하게 되며 효율을 감소시키는 요인이 된다. 본 논문에서는 고효율을 요구하는 ESS 시스템에서 컨버터/인버터의 효율 향상 방안을 제시한다. Freewheeling 구간에서 ZVS(Zero Voltage Switching) 실패문제를 해결하기 위한 듀티 제어 기법을 사용하여 구현하였으며 실험 결과 효율을 향상시켰다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권9호
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• pp.4390-4407
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• 2019

The paucity of pilot signals in Massive MIMO system is a vital issue. To accommodate substantial number of users, pilot signals are reused. This leads to interference, resulting in pilot contamination and degrades channel estimation at the Base Station (BS). Hence, mitigation of pilot contamination is exigency in Massive MIMO system. The proposed Time Shifted Pilot Signal Transmission with Pilot signal Hopping (TSPTPH), addresses the pilot contamination issue by transmitting pilot signals in non-overlapping time interval with hopping of pilot signals in each transmission slot. Hopping is carried by switching user to new a pilot signal in each transmission slot, resulting in random change of interfering users. This contributes to the change in channel coefficient, which leads to improved channel estimation at the BS and therefore enhances the efficiency of Massive MIMO system. In this system, Uplink Signal Power to Interference plus Noise Power Ratio (SINR) and data-rate are calculated for pilot signal reuse factor 1 and 3, by estimating the channel with Least Square estimation. The proposed system also reduces the uplink Signal power for data transmission of each User Equipment for normalized spectral efficiency with rising number of antennas at the BS and thus improves battery life.

• Journal of Power Electronics
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• 제14권2호
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• pp.271-281
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• 2014

Fluctuating wind conditions necessitate the use of a variable speed wind turbine (VSWT) with a AC/DC/AC converter scheme in order to harvest the maximum power from the wind and to decouple the synchronous generator voltage and frequency from the grid voltage and frequency. In this paper, a combination of a three phase diode bridge rectifier (DBR) and a modified topology of the diode clamped multilevel inverter (DCMLI) has been considered as an AC/DC/AC converter. A control strategy has been proposed for the DCMLI to achieve the objective of grid interface of a wind power system together with local load compensation. A novel fixed frequency current control method is proposed for the DCMLI based on the level shifted multi carrier PWM for achieving the required control objectives with equal and uniform switching frequency operation for better control and thermal management with the modified DCMLI. The condition of the controller gain is derived to ensure the operation of the DCMLI at the fixed frequency of the carrier. The converter current injected into the distribution grid is controlled in accordance with the wind power availability. In addition, load compensation is performed as an added facility in order to free the source currents being fed from the grid of harmonic distortion, unbalance and a low power factor even though the load may be unbalanced, non-linear and of a poor power factor. The results are validated using PSCAD/EMTDC simulation studies.

• 멤브레인
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• 제6권4호
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• pp.250-257
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• 1996

글루탈알데히드와 황산을 이용하여 가교된 키토산 복합막을 제조하였다. 제조된 복합막은 글루탈알데히드와 황산용액을 이용하여 표면말을 선택적으로 가교하엿다. 제조된 키토산 막에서의 키토산과 아세트산간의 착체형성의 영향을 관찰하기 위하여 수산화나트륨으로 중화하여 성능을 비교하였다. 황산으로 표면을 가교한 경우 코팅된 활성층의 투과증발에 대한 영향을 관찰하였다. 글루탈알데히드로 가교된 키토산복합막은 지지체의 종류를 변화시키면서 투과증발성능을 비교하였다. 지지체의 순수투과성능이 증가할수록 투과유량은 비슷한 값들을 유지하였으며, 선택도는 증가하다가 다시 감소하는 경향을 나타내었다. 수산화나트륨으로 키토산을 중화시킨 경우에는 선택도는 감소하였고 투과유량은 유지되는 경향을 나타내었다. 황산을 이용하여 표면을 이온가교시킨 경우 키토산 복합막은 활성충우ㅏ 두께가 증가할수록 가교시간이 증가하여야 최적의 가교조건을 나타내었다.

• 한국기계가공학회지
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• 제10권4호
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• pp.38-43
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• 2011

Industrial reducer is in general use to Deck Crane. High-precision and high-efficient reducer is minimized the power-loss and energy-loss of a machine. So it contribute the price reduction and life extension. Reducer is usually using the Planetary gear reducer. Planetary gear reducer is composed the sun gear, planet gear, internal gear and casing. Industrial reducer's wear and breakage have a short-life. To solve this problem, it is using the profile-shifted-gear or tooth modification. This study was carried out the effect of addendum modification coefficient on tooth fillet bending strength to planetary reducer. Tooth fillet bending stress is calculate. And all parameter were expressed the function of addendum modification coefficient. And then stress concentration factor of tooth fillet curve was express the function of addendum modification coefficient using comparison between theory and finite element analysis.

• Journal of information and communication convergence engineering
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• 제6권1호
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• pp.34-37
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• 2008

Effects of the addition of Cr adhesion layer to $W/SiO_2$ multilayer Bragg reflectors on the resonance characteristics of film bulk acoustic wave resonator (FBAR) devices are presented. Main resonance peaks could be significantly shifted to higher frequency, mainly due to the addition of Cr adhesion layer to multilayer Bragg reflectors and control of the bottom electrode thickness as well. The FBAR devices with the Cr adhesion layer in Bragg reflectors could result in much more improved resonance characteristics at about 3 GHz in terms of return loss and Q-factor.

• 한국실내디자인학회논문집
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• 제22호
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• pp.110-116
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• 2000

After the industrial revolution, interior of living space have shifted from the spacial structure of existing wall partitions to visually and spacially continuous open space. And these open space can be recognized mostly in the common space of housing architecture of living, dining, and kitchen space composition. In order to understand the characteristics of space and compositional method, the works of Le Corbusier, W. Grupius, and F.L. Wright in their living, dining, and kitchen space design have been analized from the collected materials to make evaluation for the similarities and significance of their space compositional factors. therefore, this study is to analize space composition and design factor of the modern housing space of Living, Dining, and kitchen space variation and character of open space design factor for the practical use as an index of designing contemporary living space.

• EDISON SW 활용 경진대회 논문집
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• 제3회(2014년)
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• pp.287-299
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• 2014

Bicarbonate anion ($HCO_3{^-}$) takes the role of major buffer systems in our body by maintaining the pH at 7.4. Epithelial $HCO_3{^-}$ secretion also hydrolyzes the mucus which protects body from noxious infections. It has been widely known that such infections are closely related to $HCO_3{^-}$ permeability through membrane and, thus, increasing the $HCO_3{^-}$ permeability is essential. To evaluate the $HCO_3{^-}$ permeability through ion channels, the free energy changes relevant to ion pumping are calculated with the Integral Equation Formalism-PCM (IEF-PCM) theory. Molecular structures of various anions including $HCO_3{^-}$ were optimized with the density functional theory at the level of B3LYP/6-311++G(d,p) in gas and solution phase. In addition, the anion permeability is significantly influenced by the relative size of the anion and pore. We introduce a shifted volume factor model that describes the pore size effect when the charged solutes transfer through ion channels. We found excellent agreement between experimental and calculated permeability when our novel model of the size effect was taken into account to.

• Transactions on Electrical and Electronic Materials
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• 제2권3호
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• pp.18-23
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• 2001

For the piezoelectric transformer application, Pb(Sb$\_$1/2/ Nb$\_$1/2/)O$_3$-Pb(Zr,Ti)O$_3$ ceramics were produced by attrition milling. Microstructural, dielectric and piezoelectric characteristics of the ceramics were investigated as a function of milling time. The particle size and grain size decreased while dielectric constant, density and mechanical quality factor (Q$\_$m/) increased with milling time. Temperature coefficient of resonant frequency (TCf$\_$r/) was shifted to positive side with increasing milling time. The attrition milling process proved to be one of the effective routes to produce transformers for high power application.

• 한국지능시스템학회논문지
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• 제12권3호
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• pp.255-260
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• 2002

This paper describes a fuzzy-based system for analyzing the stress intensity factors (SIFs) of three-dimensional (3D) cracks. A geometry model, i.e. a solid containing one or several 3D cracks is defined. Several distributions of local node density are chosen, and then automatically superposed on one another over the geometry model by using the fuzzy knowledge processing. Nodes are generated by the bucketing method, and ten-coded quadratic tetrahedral solid elements are generated by the Delaunay triangulation techniques. The singular elements such that the mid-point nodes near crack front are shifted at the quarter-points, and these are automatically placed along the 3D crack front. The complete finite element(FE) model is generated, and a stress analysis is performed. The SIFs are calculated using the displacement extrapolation method. To demonstrate practical performances of the present system, semi-elliptical surface cracks in a inhomogeneous plate subjected to uniform tension are solved.