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천민철,박솔민,박상현,박가연,강보수 한국물리학회 2019 Current Applied Physics Vol.19 No.4
We investigated the effect of repetitive switching of polarization on the ferroelectric Pt/Pb(Zr0.52Ti0.48)O3/Pt thin film capacitor by using impedance spectroscopy. From the Cole-Cole plot, the equivalent circuit is described as a combination of the bulk part (a capacitor), the interface part (the constant phase element (CPE), and a parallelly-connected resistor). The circuit parameters were analyzed at various stages of switching. An early increase and a subsequent decrease of the bulk capacitance may represent the wake-up and fatigue phenomena, respectively. The change in the interface part was characterized by an increase in resistance and the growth of n, the exponent of CPE, which may have come from a reduction of defects and the diminished inhomogeneity in the interfacial layer, respectively. The change in the resistance and the coefficient of the CPE in the interface part collectively resulted in an increase in the interfacial impedance. The coercive voltage, which may have intrinsically increased due to the repetitive switching, was even larger as a result of the increased interfacial impedance.
Negative capacitance phenomena depending on the wake-up effect in the ferroelectric Si:HfO2 film
박상현,천민철,박솔민,박가연,정문영,노영지,안승언,강보수 한국물리학회 2019 Current Applied Physics Vol.19 No.3
Negative capacitance (NC) phenomena is recently suggested as a breakthrough that can lead to the improved transistor by decreasing the subthreshold swing. To understand the NC phenomena, we investigated the effects of the ferroelectric properties such as the remnant polarization depending on the switching cycles in Si-doped HfO2 thin film capacitor. The ferroelectric properties were controlled by using the wake-up effect, in which the remnant polarization enhances as the number of switching cycles increase. The relation between the wake-up effect and the voltage drop region with the negative differential capacitance were elucidated. The dynamic hysteresis loops were fitted based on Landau-Khalatnikov equation, and the free energy as a function of polarization was obtained. The Landau coefficients showed that the double-well feature of the free energy becomes more apparent due to the wake-up. Based on the wake-up effect on NC phenomena, we show that the NC phenomena is well described by Landau-Ginzburg theory of ferroelectrics.
금강 하구역 미세-점착성 퇴적물의 침강특성에 관한 연구
류홍렬(Ryu, Hong-Ryul),천민철(Chun, Min-Chul),황규남(Hwang, Kyu-Nam) 한국해안해양공학회 2006 한국해안해양공학회 논문집 Vol.18 No.3
본 연구의 목적은 금강 하구역 미세-점착성 퇴적물의 침강속도를 정량적으로 산정하고, 그 침강특성의 금강 하구 내에서의 지엽적 변화 및 계절적 변화와 타 지역 침강속도 결과와의 비교/분석을 통한 공간적 변화를 해석하는데 있다. 또한 실험분석을 통하여 점착성 퇴적물의 물리 화학적 특성 즉, 입경분포, 유기물함량, 광물질구성 등의 공간적 변화를 정량적으로 조사한 후, 이러한 특성들과 침강속도간의 상관관계 및 침강속도의 정량적 변화에 미치는 영향에 대해서도 해석하였다. 침강실험의 결과로서, 금강 하구역 미세점착성 퇴적물은 부유사 농도 값이 0.1 < C < 80 g/L에서 0.01<W<sub>s</sub><1mm/sec의 침강속도 값을 갖는 것으로 확인되었으며, 산정된 침강 속도는 다른 지역(새만금, Tampa만, Severn하구, Okeechobee호)과 비교해 정량적으로 상당한 차이를 보였으나 금강 하구역 내에서의 지엽적 변화 및 계절적 변화는 미미한 것으로 나타났다. The purpose of this study is to quantitatively estimate the settling property for fine-cohesive sediments in Keum Estuary and to evaluate the spatial variation by analyzing and comparing the local and seasonal variation of the settling properties in Keum Estuary with that of the settling properties in the other sites. After the spatial variation of physico-chemical properties such grain size distribution, the percentage of organic contents, mineralogical composition etc is investigated through experiments and analyses, interrelation between the physico-chemical properties and settling velocities and effect that the physico-chemical properties have on the quantitative variation of settling velocities were also analyzed in this study. Experimental results of settling tests shows that settling velocities of Keum Estuary mud vary in the range of two orders of magnitude (from 0.01 to 1mm/sec) over the corresponding concentration range of 0.1 to 80 g/L, and a feature of settling velocity profile is quite different in quantity as compared to those of previous studies with mud of other regions: Saemankuem, Tampa Bay, Sevem Estuary and lake Okeechobee. However, their local and seasonal variabilities within Keum Estuary appear to be insignificant.
Deep Mixing Technology to Mitigate Ground Vibration Inducedby High-Speed Trains
김진호(Kim Jin-Ho),박옥정(Park Ok-Jeoung),천민철(Chun Min-Chul) 한국철도학회 2004 한국철도학회 학술발표대회논문집 Vol.- No.-
최근에 철도의 고속화 운행이 유럽, 동아시아, 북아메리카에 이르기까지 빠르게 확장됨으로 인하여 수반되는 지반진동에 대한 문제가 관심이 되고 있다. 건설현장에서 널리 적용되고 있는 Deep Mixing 기술은 철도의 고속화에 따른 진동의 피해를 줄이는 방법으로도 사용되고 있다. Deep Mixing 공법은 특별히 설계된 장비를 사용하여 접착성재료와 통양을 혼합하여 생산된 기둥벽을 이용하는 지반개량공법이다. 본 논문의 목적은 유럽이나 일본에서 진동제어로 사용되어지는 최근의 Deep Mixing 공법을 종합 검토하고자 함이다. 스웨덴과 일본의 현장계측 결과와 함께 해석적 수치적 해에 근거하여 개선된 지반의 거동을 해석 및 예측한다. 수치해석결과는 Deep Mixing 공법의 진동저감에 대한 예측에 있어서 유용한 도구임을 보여준다.