Performance of a Microbial Fuel Cell using a Magnet Attached Cathode

Changho Choi,Mia Kim,홍석원,최용수,Young Il Song,Sunghyun Kim,김형주 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.6

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Development of an Easy User Interface for Constitutive Modeling of Fine-Grained Soil

Changho Choi 대한토목학회 2006 KSCE journal of civil engineering Vol.10 No.6

The successful performance of any numerical geotechnical simulation depends on the accuracy of the constitutive model used to simulate the stress-strain (constitutive) response of the soil. To date, several constitutive models have been developed for soils. Unfortunately, most of them are comprised of numerous mathematical equations which, in general, are difficult to conceptualize and follow. In this paper a new windows-based constitutive driver, EVER-CD, is presented. The major role of EVER-CD is to bridge between the user and constitutive models and to enable easy assessment to the models. The distinctive features of the driver are: (1) it is easy to use by the non-specialist, (2) loading histories can be easily created and validated, (3) runs are relatively easy compared to traditional command line interfaces, (4) results can be easily visualized utilizing a user-friendly graphical interface, and (5) the accessible features of EVER-CD encourage the user to understand constitutive modeling. The usability of the new tool has been verified by simulating conventional triaxial experimental results. The results show the capabilities of the new interface to successfully predict the mechanical behavior of soils.

A Procedure Qualification Study on ISO Phased Array Ultrasonic Testing (PAUT) for API 2W 60 Piping Weld

Changho Choi(최창호),Sangho Lee(이상호),Younghee Lee(이용희) 대한인간공학회 2021 대한인간공학회 학술대회논문집 Vol.2021 No.11

Objective: This study was conducted for the purpose of verifying the reliability of the inspection results when performing non-destructive inspection of API 2W 60 pipe welds according to the ISO standard PAUT procedure. Background: Radiography Test (RT) of welds has problems in terms of safety for the human body and limitations in the detection capability of plane defects. To supplement this, the PAUT test, which can acquire the test result data file, is used by replacing the film, which is the test record of RT. However, most of the studies on PAUT have been conducted based on the American Society of Mechanical Engineers (ASME) or American Society of Welding (AWS) codes. However, recent customer specifications require international ISO standards. Therefore, specific experimental analysis for the ISO standard PAUT procedure certification of the pipe welding part is absolutely necessary. Method: API 2W60 pipe calibration test specimen and ISO PAUT procedure accreditation test specimen were prepared with reference to previous studies on PAUT theory, research trends, and reliability analysis model of non-destructive testing. The acoustic anisotropy of TMCP steel and the transverse wave velocity of ultrasonic waves were measured using the calibration specimen. Next, the RT and PAUT volumetric non-destructive testing experiments were performed using the test specimens for approval, and the PAUT reliability was verified by comparative analysis of the measured results. Results: The effect of the acoustic anisotropy in the rolling direction and the direction perpendicular to the rolling direction of API 2W60 material on the change in the refraction angle of the ultrasonic beam and the speed of the transverse wave was confirmed. The reliability of PAUT inspection was secured by comparative analysis of RT and PAUT results related to the acceptance of ISO PAUT procedures for pipe welds. Conclusion: The acoustic anisotropy of API 2W60 material was confirmed by decreasing the measured refraction angle in the rolling direction and increasing the measured refraction angle in the transverse direction. In addition, as a result of a comparative verification experiment on RT and PAUT for pipe welds, the reliability of the PAUT result was high, so the verification of the ISO PAUT procedure was confirmed. Application: The contents and results of this study are expected to be utilized as an example of the application of ultrasonic inspection (UT) of welds of acoustic anisotropic materials. Furthermore, it is expected to be used in various ways for accreditation of ISO PAUT procedures for pipe welds.

Spin-dependent Transport in Granular TbN-Co Films

Changho Choi,Taewan Kim,Kyujoon Lee,Jungbum Yoon,Chun-Yeol You,Myung-Hwa Jung 한국자기학회 2010 한국자기학회 학술연구발표회 논문개요집 Vol.2010 No.12

Modeling of Radiation Effects for 1-D RLH-TL Using Extraction of Circuit Parameters

Changho Choi(최창호),Bomson Lee(이범선) 한국전자파학회 2008 한국전자파학회논문지 Vol.19 No.2

일반적으로 손실이 없는 우형 전송선 모델에 직렬 커패시터와 병렬 인덕터를 삽입하여 만든 우좌형 전송 선로에 손실을 고려한 등가 회로를 제안한다. 제안된 식을 이용하면 원하는 주파수에서의 위상 조절이 가능하며, 단위 셀을 점차 늘려갈수록 발생하는 방사율에 대한 조정 역시 용이하게 된다. 단위 셀의 구조의 증가는 안테나의 배열과 같으며, 이러한 배열 구조에서는 균등한 방사가 요구된다. 따라서 방사율의 조정을 위한 식은 일반적인 마이크로스트립 기판에 제작된 평면 안테나에 비해 소형화된 안테나를 구성하는데 적용될 수 있다. 그리고 회로 시뮬레이션과 EM 시뮬레이션 사이에서 발생하는 방사율에 대한 편차는 수정된 식을 적용하면 부합된 결과를 얻을 수 있으므로 간단한 방사 구조의 설계시 간편하게 이용할 수 있을 것으로 기대된다. The equivalent circuit for the RLH-TL is proposed considering radiation effects due to the inclusion of a series capacitor and shunt inductor in a unit cell for the right/left-handed transmission line(RLH-TL). The design equations to realize a specific phase shift at a given frequency is also provided. The S-parameters for unit cells with N=1, 3, 5, and 10 are analyzed in various aspects based on the EM and circuit simulations especially for the purpose of controlling radiation along RLH-TL’s. A modification formula for the radiation rate per unit cell is also proposed for good agreement between the EM and circuit simulation results.

Development of an Easy User-Interface for Constitutive Modeling of Fine-Grained Soil

Changho Choi 대한토목학회 2006 KSCE Journal of Civil Engineering Vol.10 No.6

The successful performance of any numerical geotechnical simulation depends on the accuracy of the constitutive model used to simulate the stress-strain (constitutive) response of the soil. To date, several constitutive models have been developed for soils. Unfortunately, most of them are comprised of numerous mathematical equations which, in general, are difficult to conceptualize and follow. In this paper a new windows-based constitutive driver, EVER-CD, is presented. The major role of EVER-CD is to bridge between the user and constitutive models and to enable easy assessment to the models. The distinctive features of the driver are: (1) it is easy to use by the non-specialist, (2) loading histories can be easily created and validated, (3) runs are relatively easy compared to traditional command line interfaces, (4) results can be easily visualized utilizing a user-friendly graphical interface, and (5) the accessible features of EVER-CD encourage the user to understand constitutive modeling. The usability of the new tool has been verified by simulating conventional triaxial experimental results. The results show the capabilities of the new interface to successfully predict the mechanical behavior of soils.

The fluctuation effect of BaFe_1.8Co_0.2As₂ single crystals from reversible magnetization

Choi, Changho,Hyun Kim, Soo,Choi, Ki-Young,Jung, Myung-Hwa,Lee, Sung-Ik,Wang, X F,Chen, X H,Wang, X L IOP Publishing Ltd 2009 Superconductor science & technology Vol.22 No.10

<P>We present reversible magnetization measurements for applied fields in the range from 0.5 to 7 T made while varying the temperature for optimally doped BaFe<SUB>1.8</SUB>Co<SUB>0.2</SUB>As<SUB>2</SUB> single crystals with <I>T</I><SUB>c</SUB> = 23.6 K. The rounding fluctuating magnetization was observed in the reversible range of magnetization for temperatures above 18 K. This fluctuation effect is quite small compared with that in high temperature cuprate superconductors, but is still large enough for obtaining the essence of the physical properties in this iron pnictide superconductor. This reversible magnetic fluctuation follows a three-dimensional scaling form in the critical fluctuation region for fields above 0.5 T, which indicates that this iron pnictide superconductor belongs to the class of three-dimensional superconductors. </P>

객체 분할에 Dilated Convolution이 미치는 영향

최창호(Changho Choi),박운상(Unsang Park) 대한전기학회 2019 대한전기학회 학술대회 논문집 Vol.2019 No.7

중소해양도시 크루즈관광 여건 및 활성화 방안

최창호(Changho Choi),임영태(Youngtae Lim) 한국항만경제학회 2013 韓國港灣經濟學會誌 Vol.29 No.2

최근 우리나라에 기항하는 국제해양크루즈가 급증하면서 크루즈관광 활성화에 대한 정부와 지자체의 관심이 고조되고 있으나, 우리나라의 크루즈관광 정책과 시설확충 계획은 부산, 인천, 제주 등 크루즈 기항실적이 많은 도시의 거점항 위주로 이루어지는 경향이 있다. 하지만 연근해를 대표하는 중소해양도시의 지역항도 크루즈관광 매력을 갖추고 크루즈 유치를 위해 노력하고 있으므로 이들 도시의 크루즈관광 활성화를 위한 지원도 필요하다. 본 연구는 우리나라 중소해양도시의 크루즈관광 여건을 살펴보고 중소해양도시의 크루즈관광 활성화 방안을 모색하였다. 그리고 이를 토대로 항만 서비스, 교통 접근성과 도시 편의성, 관광활동 지원 분야에 대한 개선방안과 이를 위한 공공과 민간 등의 역할을 제시하였다. 사례연구 지역으로 전라남도 여수시를 선정하여 중소해양도시의 여건과 개선방안, 그리고 거점항과의 차이를 분석하였다. 크루즈 기항항이 되기 위해서는 거점항과 지역항의 차이가 없이 크루즈관광과 관련된 전 분야에서 많은 개선 노력이 이루어져야 한다. 특히 중소해양도시에 속한 지역항은 모항으로 성장할 가능성이 낮기 때문에 기항항으로 선정되는데 초점을 둔 정책과 관광 프로그램 개발이 추진되어야 한다. The recent rapid increase of international ocean cruises calling at Korea has prompted the interests of central and local governments in promotion of cruise ship tour. Korea"s cruise tour policies and facility improvement plans tend to be focused only on main ports of cities with high calls at cruise port, such as Busan, Incheon, and Jeju. However, small and medium-sized ocean cities which represent the coastal areas are also seeking to activate cruise ship tour and attract investment, and therefore they merit governmental support as well. This study looks at the current conditions of cruise tourism in small and medium-sized ocean cities and searches for the means to activate cruise tours. It suggests improvement policies for port services, transport accessibility, urban facilities and tour activity support, as well as expected roles of public and private sector. As a case study of Yeosu in Jeollanam-do, it analyzes the present state and discusses possible future activation programs, comparing small and medium-sized cities with cities with main ports. In order to be a port of call, steady exertions for improvement are required in all areas regarding cruise tourism whether it"s main or local. Especially, since local ports in small and medium-sized ocean cities are relatively unlikely to be developed into home ports, policies and tourism programs should be established to support them in being chosen as ports of call.

2단계 계산 방식을 적용한 고속 CRC 구현

최창호(Changho Choi),정해원(Haewon Jung),이형호(Hyoungho Lee) 한국통신학회 2002 한국통신학회 학술대회 및 강연회 Vol.2002 No.4