• Transactions on Electrical and Electronic Materials
• /
• 제8권6호
• /
• pp.241-245
• /
• 2007

[ $(Ba_{0.9-x}Sr_xCa_{0.10})TiO_3$ ] (x=0.33, 0.36) powders were prepared by sol-gel method. $(Ba,Sr,Ca)TiO_3$(BSCT) thick films, undoped and doped with $MnCO_3$ and $Yb_2O_3(0.1{\sim}0.7mol%)$, were fabricated by the screen printing method on the alumina substrate. The coating and drying procedure was repeated 6-times. The Pt bottom electrode was screen printing method on the alumina substrate. These BSCT thick films were annealed at $1420^{\circ}C$ for 2 hr in atmosphere. The upper electrodes were fabricated by screen printing the Ag paste and then firing at $590^{\circ}C$ for 10 min. And then the structured and dielectric properties as a function of the doping amount of $Yb_2O_3$ were studied. As a result of the TG-DTA, exothermic peak was observed at around $670^{\circ}C$ due to the formation of the polycrystalline perovskite phase. All BSCT thick films showed XRD patterns of typical cubic peroveskite structure. The average thickness of BSCT thick films was about $70^{\mu}m$. The curie temperature and the dielectric constant decreased with increasing $Yb_2O_3$ doped content and the relative dielectric constant of the specimen, doped with 0.5 mol% $Yb_2O_3$ at BSCT(54/36/10), showed a best value of 5018 at curie temperature.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제7권2호
• /
• pp.227-243
• /
• 2015

In this paper, the effects of nonlinear soft clay on dynamic embedment of offshore pipeline were investigated. Seabed embedment by pipe-soil interactions has impacts on the structural boundary conditions for various subsea structures such as pipeline, riser, pile, and many other systems. A number of studies have been performed to estimate real soil behavior, but their estimation of seabed embedment has not been fully identified and there are still many uncertainties. In this regards, comparison of embedment between field survey and existing empirical models has been performed to identify uncertainties and investigate the effect of nonlinear soil parameter on dynamic embedment. From the comparison, it is found that the dynamic embedment with installation effects based on nonlinear soil model have an influence on seabed embedment. Therefore, the pipe embedment under dynamic condition by nonlinear parameters of soil models was investigated by Dynamic Embedment Factor (DEF) concept, which is defined as the ratio of the dynamic and static embedment of pipeline, in order to overcome the gap between field embedment and currently used empirical and numerical formula. Although DEF through various researches is suggested, its range is too wide and it does not consider dynamic laying effect. It is difficult to find critical parameters that are affecting to the embedment result. Therefore, the study on dynamic embedment factor by soft clay parameters of nonlinear soil model was conducted and the sensitivity analyses about parameters of nonlinear soil model were performed as well. The tendency on dynamic embedment factor was found by conducting numerical analyses using OrcaFlex software. It is found that DEF was influenced by shear strength gradient than other factors. The obtained results will be useful to understand the pipe embedment on soft clay seabed for applying offshore pipeline designs such as on-bottom stability and free span analyses.

• 한국콘텐츠학회:학술대회논문집
• /
• 한국콘텐츠학회 2008년도 춘계 종합학술대회 논문집
• /
• pp.161-165
• /
• 2008

본 연구는 지식정보화 사회의 경쟁력인 창의성을 기르기 위하여 수정된 ASSURE 모델을 기반으로 한 영상제작 활동 교수 학습 과정을 설계하고 적용하는 데 그 목적이 있다. 연구의 목적을 달성하기 위하여 다음과 같은 절차와 방법을 수행하였다. 먼저 영상매체 교육과 창의성 교육에 대하여 이론적 고찰을 한 후, 이 둘의 관계를 규명 해보고 그 결과로 수정된 ASSURE 모델을 적용한 교수 학습과정을 설계하였다. 그리고 영상제작 활동 교수 학습과정 전개 시 창의성 계발학습 모형을 적용하여 수업의 효과성을 높였다. 본 연구 결과 및 의의는 다음과 같다. 첫째, 영상제작활동 교수학습과정 적용의 결과 학생들의 창의적 성향이 신장되었다. 적용 전에 이던 것이 적용 후에는 로 나타났으며 통계적으로는 t=(p<0.05)의 유의미한 차이가 있다. 둘째, 영상제작 활동 교수학습 과정 적용을 통하여 문화적 프로슈머의 발판을 마련하였다. 덧붙여서 본 연구를 함께 한 모든 학생이 디지털미디어 시대의 리더그룹으로 성장하기를 기대해 본다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2007년도 제38회 하계학술대회
• /
• pp.1283-1284
• /
• 2007

The barium strontium calcium titanate((Ba,Sr,Ca)$TiO_3$) powders prepared by the sol-gel method and $MnCO_3$ as acceptor were mixed oxide method. The microstructure was investigated with variation of $Pr_{2}O_{3}$ amount. The BSCT powder and $Pr_{2}O_{3}$ were mixed with organic vehicle(Ferro. B75001). BSCT thick films were fabricated by the screen-printing method on alumina substrates. The bottom electrode was Pt and upper electrode was Ag, respectively. All BSCT thick films were sintered at $1420^{\circ}C$, for 2h. The result of the differential thermal analysis(DTA), exothermic peak at around $654^{\circ}C$ due to the formation of the polycrystalline perovskite phase. In the X-ray diffraction(XRD) patterns, all BSCT thick films showed the typical perovskite polycrystalline structure and no pyrochlore phase was dbserved. The microstructure investigated by scanning electron microscope(SEM). Pore and grain size of BSCT thick films were decreased with increasing amount of $Pr_{2}O_{3}$ dopant. And the average grain size and thickness of BSCT thick films doped with 0.1 mol% $Pr_{2}O_{3}$ was $3.09{\mu}m$, $60{\mu}m$, respectively. The relative dielectric constant decreased and dielectric loss decreased with increasing amount of $Pr_{2}O_{3}$ dopant, the values of the BSCT thick films no doped with $Pr_{2}O_{3}$ were 7443 and 4 % at 1 kHz, respectively.

• 한국표면공학회지
• /
• 제47권5호
• /
• pp.239-243
• /
• 2014

The electrical and optical properties of amorphous In-Tin-Zinc-Oxide(ITZO) deposited at room temperature using rf-magnetron sputtering were investigated. The amorphous ITZO thin films were obtained at the composition of In:Sn:Zn = 6:2:2, 4:3:3, and 2:4:4, but the ITZO (8:1:1) showed a crystalline phase of bixbyite structure of In2O3. The resistivity of ITZO could be controlled by oxygen pressure in the sputtering ambient. The resistivity of post-annealed ITZO thin films exhibited the dependence on the amount of Indium. Optical energy band gap and transmittance increased as the amount of indium in ITZO increased. For the device application with ITZO, the bottom-gated thin-film transistor using ITZO as a active channel layer was fabricated. It showed a threshold voltage of 1.42V and an on/off ratio of $5.63{\times}10^7$ operated with saturation field-effect mobility of $14.2cm^2/V{\cdot}s$.

• 한국정보통신학회논문지
• /
• 제11권2호
• /
• pp.344-348
• /
• 2007

본 논문에서 높은 투과율을 가질 수 있는 PVA (Patterned Vertical Aligned) 액정 셀의 전극 구조를 제안하였다. 제안한 전극 구조의 결과를 확인하기 위해서 광학적 특성과 그리고 디렉터 모양의 계산은 'TechWiz LCD'라는 상용 시뮬레이터를 사용하였다. 보통 PVA 액정 셀의 투과율은 전극의 모양과 셀갭에 의해 크게 영향을 받는다. 본 논문에서 제안한 전극 구조의 게이트 라인과 데이터 라인 사이의 거리는 기존의 PVA 셀과 같다. 대신 전극의 끝단 (edge) 지역에서의 광손실을 줄이기 위하여 상층부 전극과 하층부 전극의 모양을 수정하였다. 결과를 비교하기 위하여 기존의 PVA 액정 셀과 제안한 PVA 액정 셀의 투과율을 비교하였다. 그 결과, 제안된 구조에 의해서 전극부근에서 발생하는 광학적 손실이 감소되는 것을 확인 할 수 있었다.

• 전력전자학회논문지
• /
• 제26권5호
• /
• pp.325-333
• /
• 2021

A 3 kW grid-tied PV inverter with Gallium nitride high-electron mobility transistor (GaN HEMT) for domestic commercialization was developed using boost converter and full-bridge inverter with LCL filter topology. Recently, many GaN HEMTs are manufactured as surface mount packages because of their lower parasitic inductance characteristic than standard TO (transistor outline) packages. A surface mount packaged GaN HEMT releases heat through either top or bottom cooling method. IGOT60R070D1 is selected as a key power semiconductor because it has a top cooling method and fairly low thermal resistances from junction to ambient. Its characteristics allow the design of a 3 kW inverter without forced convection, thereby providing great advantages in terms of easy maintenance and high reliability. 1EDF5673K is selected as a gate driver because its driving current and negative voltage output characteristics are highly optimized for IGOT60R070D1. An LCL filter with passive damping resistor is applied to attenuate the switching frequency harmonics to the grid-tied operation. The designed LCL filter parameters are validated with PSIM simulation. A prototype of 3 kW PV inverter with GaN HEMT is constructed to verify the performance of the power conversion system. It achieved high power density of 614 W/L and peak power efficiency of 99% for the boost converter and inverter.

• 한국재료학회지
• /
• 제29권1호
• /
• pp.1-6
• /
• 2019

Recent industrialization has led to a high demand for the use of fossil fuels. Therefore, the need for producing hydrogen and its utilization is essential for a sustainable society. For an eco-friendly future technology, photoelectrochemical water splitting using solar energy has proven promising amongst many other candidates. With this technique, semiconductors can be used as photocatalysts to generate electrons by light absorption, resulting in the reduction of hydrogen ions. The photocatalysts must be chemically stable, economically inexpensive and be able to utilize a wide range of light. From this perspective, cuprous oxide($Cu_2O$) is a promising p-type semiconductor because of its appropriate band gap. However, a major hindrance to the use of $Cu_2O$ is its instability at the potential in which hydrogen ion is reduced. In this study, gold is used as a bottom electrode during electrodeposition to obtain a preferential growth along the (111) plane of $Cu_2O$ while imperfections of the $Cu_2O$ thin films are removed. This study investigates the photoelectrochemical properties of $Cu_2O$. However, severe photo-induced corrosion impedes the use of $Cu_2O$ as a photoelectrode. Two candidates, $TiO_2$ and $SnO_2$, are selected for the passivation layer on $Cu_2O$ by by considering the Pourbaix-diagram. $TiO_2$ and $SnO_2$ passivation layers are deposited by atomic layer deposition(ALD) and a sputtering process, respectively. The investigation of the photoelectrochemical properties confirmed that $SnO_2$ is a good passivation layer for $Cu_2O$.

• 생태와환경
• /
• 제42권3호
• /
• pp.340-349
• /
• 2009

2007년 4월부터 2008년 10월까지 갑천의 자연형 구간 가운데 7개 지점을 선정하여 각 서식처별 어류군집의 생태적 특성을 연구하였다. 조사지점은 폐쇄형 웅덩이(Closed pool), 평여울(Runs), 급여울(Riffles), 내만형 웅덩이(Opened pool), 소(Pool), 징검여울(Rock-scattered riffles), 댐형 웅덩이(D-type pool)등으로 구분하였다. 채집된 어류는 총 8과 29종이 출현하였으며, 서식처를 대표하는 표징종은 붕어 (Corassius ouratus, St. 1), 쉬리 (Coreoleuciscus splendidus, St. 3), 납자루(Acheilognathus lanceolatus, St. 4), 피라미 (Zacco platypus St. 2, 5, 6, 7) 정도로 구분하였다. 붕어(C. auratus)는 폐쇄형 웅덩이(St. 1)와 같이 하상구조가 대부분 모래로 구성되고 수심은 65$\sim$90 cm 정도로 다소 깊으며 유속이 거의 정체된 수역을 선호하는 것으로 나타났다. 쉬리 (C. splendidus)는 급여울(St. 3)과 같이 수심이 8$\sim$38cm정도, 유속 $0.14\sim0.85\;m\;sec^{-1}$ 정도, 그리고 하상구조는 작은돌과 조약돌이 산재된 곳에 주로 서식하며 유속이 빠르기 때문에 BOD, COD, TN, TP, SS의 농도는 낮으며 DO는 높게 나타나는 곳을 선호하였다. 납자루(A. lanceolatus)는 개방형 웅덩이 (St. 4)와 같이 수심이 3$\sim$44cm정도,유속은 $0.01\sim0.02\;m\;sec^{-1}$로 낮은 수심과 느린 유속을 선호하는 것으로 나타났다. 피라미 (Z. platypus)는 평 여울(St. 2), 소(St. 5), 징검 여울(St. 6)댐형 웅덩이(St. 7)등 여러 서식처에서 우점하였는데 주로 유량이 풍부하고 하상구조가 다양한 지점을 선호하는 것으로 나타났다. 한편 징검여울(St. 6)에서 미호종개(Iksookimia choii)가 4개체 출현하였는데 본 연구에서 출현한 미호종개(I. choii)의 서식지는 하폭 24 m 정도, 수심 이 3$\sim$35 cm 정도, 유속은 $0.01\sim0.49\;m\;sec^{-1}$ 정도를 나타내며 하상구조는 큰돌부터 모래까지 다양한 구조를 이루고 있었다. 또한 수질측정 결과 수온, EC, BOD, COD, TN, TP의 농도가 비교적 낮게 나타났고 DO, SS의 농도가 비교적 높은 범위를 나타내어 이와 비슷한 물리, 화학적인 서식 환경이 조성되어야만 미호종개(I. choii)가 서식할 수 있을 것으로 판단된다.

• 한국전자파학회논문지
• /
• 제19권4호
• /
• pp.477-483
• /
• 2008

본 논문에서는 미엔더 라인 피파 구조와 기생 패치를 이용하여 휴대 단말기용 다중 대역 칩 안테나를 제안하였다. 제안된 안테나는 FR-4 기판을 사용하였으며, 상층은 GSM900 대역을 구현하기 위해 미엔더 라인 PIFA 구조로 구성하였고, 최대한 공간 효율을 높이기 위해 비아홀로 각 패드에 미엔더 라인을 연결하였다. 중간층은 DCS, PCS 대역을 구현하기 위해 급전선과 간격을 주어 설계했으며, 하층은 그라운드 접지면에 기생 패치를 추가하여 중간층의 방사체와 커플링 결합으로 주파수와 임피던스 특성을 조절할 수 있음을 보였다. 안테나 크기는 $28{\times}6{\times}4\;mm^3$, 그라운드 조건은 $45{\times}90\;mm$로 제작하였으며, 설계를 위한 모의 실험은 CST 시뮬레이터로 해석하였다. 측정된 대역폭(VSWR<3)은 GSM900 대역에서 90($875{\sim}965$) MHz, DCS, PCS 대역에서는 380($1,670{\sim}2,050$) MHz을 얻었다. 각 공진 주파수의 최대 이득은 0.25 dBi, 3.65 dBi, 3.3 dBi이며, 무지향성 방사 패턴 특성을 보였다.