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RISS 인기검색어
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- 저자 : Cho Jinhyung (검색결과 72 건)
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Capping layers and their roles in polar catastrophe scenario of LaAlO3/SrTiO3 (001) systems
Cho Jinhyung,Jeen Hyoungjeen 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.10
Under the assumption that epitaxially strained growth is taking place under strained growth conditions, the metallic and insulating properties of LaAlO3 (LAO) flms grown on TiO2-terminated SrTiO3 (STO) (001) substrates are theoretically investigated in this study. We studied the electronic properties LaAlO3/SrTiO3 flms grown on the periodic superstructure of √2 × √2 in-plane squares of STO substrate to accommodate the structural strain of heterogeneous flm by allowing tilting of octahedra, as well as distortion. This enables us to study electronic and structural properties by allowing structural relaxation in a more realistic manner. This study examined spin-polarized Ti density functional calculations which promote metal–insulator transition toward thinner LAO/STO than in cases without spin polarization. Using the density of states at the Fermi level obtained from fully relaxed structures, the study shows that a capping layer of LaAlO3, Al2O3, and La2O3 on top of a stoichiometric AlO2 layer promotes toward-metallic transition, causing thin LAO flms to undergo metallic transitions sooner than stoichiometric LAO flms to do so.
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Cho, Jinhyung,Lee, Kun Sang Taylor Francis 2016 Petroleum science and technology Vol.34 No.4
<P>The addition of hydrocarbon solvent such as liquefied petroleum gas (LPG) to the CO2 stream leads to miscible conditions in reservoirs at lower pressures by reducing the minimum miscibility pressure (MMP). Under miscible conditions, improved displacement and vertical sweepout occur simultaneously. The influences of LPG concentration and composition on the displacement and sweep efficiencies during CO2-LPG enhanced oil recovery (EOR) were investigated. Enhanced displacement efficiency was assessed through oil viscosity reduction and oil saturation change. Moreover, the miscible flooding induced by LPG addition, which resulted in increased solvent viscosity and a lower density difference between the injected fluid and reservoir oil, provided a smaller viscous gravity number, and improved the sweep efficiency, alleviating the impact of solvent gravity override. For CO2-LPG EOR, oil recovery increased up to 52% as compared with that for CO2 flooding. The amount of incremental oil recovery with 100% butane in the LPG was 16%, as compared with the 100% propane case. Mitigated gravity override enabled CO2-LPG EOR to enhance sweep efficiency. Results indicated that the compositional modeling of the EOR process with the addition of LPG provided more accurate prediction on the performance of CO2-LPG EOR.</P>
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Cho, Jinhyung,Kim, Tae Hong,Lee, Kun Sang Elsevier 2016 Journal of petroleum science & engineering Vol.146 No.-
<P><B>Abstract</B></P> <P>Once asphaltenes have been precipitated from oil due to pressure, temperature, or oil composition changes, they can affect reservoir performance by reducing porosity and permeability and altering wettability. Moreover, they can cause plugging of wellbore and surface production facilities. The addition of liquefied petroleum gas (LPG) into the CO<SUB>2</SUB> stream during CO<SUB>2</SUB> flooding reduces oil viscosity, interfacial tension (IFT), and oil swelling, resulting in improved displacement efficiency, but also causes asphaltene precipitation because of a change in oil composition. When toluene is introduced into the LPG and CO<SUB>2</SUB> stream to overcome the limitations of a CO<SUB>2</SUB>-LPG flood, it acts as an inhibitor of asphaltene precipitation. This research systematically examines the mechanism of asphaltene precipitation and how to mitigate problems associated with asphaltene deposition based on compositional simulations. Solid deposition model that included adsorption, pore throat plugging, and re-entrainment was considered. A compositional equation of state (EOS) model was developed to analyze the effects of LPG and toluene on asphaltene deposition and formation damage. At the center of reservoir, the amount of asphaltene deposition reached the maximum for 10% LPG-added CO<SUB>2</SUB>-LPG flooding, which was 12% higher than that from CO<SUB>2</SUB> flooding. When 1% toluene was added into the CO<SUB>2</SUB>-LPG flood, the amount of asphaltene deposited declined by 2%. Oil resistance factor had the same tendency because of porosity reduction due to decreased deposition of asphaltene. Oil recovery for the CO<SUB>2</SUB>-LPG flood was enhanced by 4% compared to the CO<SUB>2</SUB> flood, despite an increment in asphaltene deposition, and by 9% for the CO<SUB>2</SUB>-LPG-toluene flood. Results from this study indicate that LPG addition causes increased asphaltene deposition, which can be mitigated by using toluene as an inhibitor.</P>
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Collaborative Filtering Using Dual Information Sources
Cho, Jinhyung,Kwon, Kwiseok,Park, Yongtae IEEE 2007 IEEE INTELLIGENT SYSTEMS Vol.22 No.3
<P>With the proliferation of e-commerce on the Web, e-commerce providers will need to offer recommender systems if they wish to remain competitive. One of the most successful recommendation methods is collaborative filtering. To provide recommendations, conventional CF methods use only a single recommender group (that is, a single information source). Consequently, they have several limitations that make them unsuitable for high-involvement, knowledge-intensive product domains such as e-learning. A new CF method, based on group behavior theory from consumer psychology, attempts to overcome these limitations. To adapt CF to Web-based e-learning content services, this method forms dual recommender groups: similar users and expert users. In experiments, a recommender system employing this method outperformed conventional CF methods in situations involving variations in the product domain and in data sparsity. This article is part of a special issue on recommender systems.</P>
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마이크로셀 환경에서 혼합 데이타를 지원하는 다중 액세스 기법
조진형(Jinhyung Cho),최양희(Yanghee Choi),김종상(Chong Sang Kim) 한국정보과학회 1995 한국정보과학회 학술발표논문집 Vol.22 No.2B
본 논문에서는 전파지연시간이 전송시간에 비해 무시될 정도로 작고 전송중 오류의 가능성이 비교적 작은 마이크로셀 환경에서 실시간 데이타 및 비실시간 데이타를 효율적으로 전송 할 수 있는 다중 액세스 기법을 제안한다. 실시간 데이타는 전송 지연을 줄이기 위해 TDMA와 유사하게 채널이 예약 할당된다. 실시간 데이타에 할당된 슬롯에 트래픽이 잠시 없는 경우에 다른 비실시간 데이타의 전송이 허용되며 따라서 채널의 이용률이 증가한다. 또한 예약을 위한 별도의 슬롯을 두지 않기때문에 전송 준비가 된 단말기는 다음 프레임까지 기다리지 않고 즉시 전송을 시도할 수가 있다. 시뮬레이션을 통해 전송지연과 채널의 이용률을 중심으로 성능을 평가한다.
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강환수(Hwan Soo Kang),조진형(Jinhyung Cho),김희천(Heechern Kim) 한국디지털콘텐츠학회 2013 한국디지털콘텐츠학회논문지 Vol.14 No.4
Recently student portfolio is widely used as an evaluation method for self-directed performance in engineering education of the university. Especially, as many of the Innovation Centers for Engineering Education and ABEEK held student portfolio competitions, a lot of students in engineering college participate in student portfolio includes the contents and careers of the entire process of university. However, except for courses related to capstone design, there are few regular courses applied to Learning Portfolio in engineering education. Through using Learning Portfolio in courses, students take opportunities of organized collection of learning contents and critical reflection. Under these background study, the regular course in engineering education is may be appropriate for using Learing Portfolio in lecture. In this paper, we present the case study for the Data Structure course opened in the first semester of 2013 which is organized as a Learning Portfolio. According to the results of applying Learning Portfolio to the regular course, it turns out that learners can develope self-directed learning ability in exploring the learning process, and manage a learning process systematically through self-reflection in learning process.
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Cho, Sung-Yong,Kim, Sungwoo,Choo, Min-Seong,Ko, Han-Gon,Lee, Jinhyung,Bae, Woorham,Jeong, Deog-Kyoon IEEE 2018 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS PART 1 R Vol.65 No.9
<P>A 2.5–5.6 GHz low-phase-noise subharmonically injection-locked sub-sampling all-digital phase-locked loop with a dual-edge complementary switched injection technique is presented. While previously reported injection-locked phase-locked loops (ILPLLs) require additional circuitry for resolving a phase alignment mismatch between the PLL loop and injection path, the presented ILPLL exhibits a simplified architecture owing to the proposed injection technique and sub-sampling bang-bang phase detector (SSBBPD). Because the proposed injection technique exploits dual-edge injection, we analyze the performance impact of dual-edge injection when inaccurate injection timing occurs. This paper also offers an analysis of the injection technique based on the charge transfer and derives the realignment factor of the injection. With the proposed injection technique and the direct connection of the digitally controlled oscillator (DCO) clock to the SSBBPD, the timing mismatch between the PLL loop and injection path becomes insensitive to voltage and temperature drift. The proposed ILPLL prototype is fabricated in a 65-nm CMOS process and achieves a 168-fs integrated rms jitter over 1 kHz to 40 MHz at a 5-GHz output frequency with 156.25-MHz reference clock while consuming 15.4 mW with an active area of 0.06 mm<SUP>2</SUP>.</P>
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