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Jeon, Dongho,Yum, Woo Sung,Song, Haemin,Sim, Sungwon,Oh, Jae Eun Elsevier 2018 Construction and Building Materials Vol.190 No.-
<P><B>Abstract</B></P> <P>This study reports the temperature-dependent strength improvement and retardation in Ca(OH)<SUB>2</SUB>-Na<SUB>2</SUB>CO<SUB>3</SUB>-activated fly ash binders with sugar. Without sugar, the system exhibited rapid stiffening due to the calcite formation. The addition of sugar clearly removed the false set; however, at room temperature, it retarded strength development because the calcium complexation of sugar inhibits the dissolved calcium ions from participating in calcite and C-S-H formation. However, at 90 °C, the use of sugar significantly improved the compressive strength by increasing the (1) degree of dissolution of fly ash and Ca(OH)<SUB>2</SUB>, (2) C-S-H formation, and (3) reduction of overall pore size and volume.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fly ash was activated with Ca(OH)<SUB>2</SUB>, Na<SUB>2</SUB>CO<SUB>3</SUB>, and sugar at different temperatures. </LI> <LI> The use of sugar delayed the rapid set of the cementless binder at room temperature. </LI> <LI> At the high curing temperature, the use of sugar improved the strength of the binder. </LI> <LI> The high temperature removed calcium complexation of sugar, increasing strength. </LI> </UL> </P>
Control of Phase and Phase Slope with Reinvestigation of 1D CRLH Transmission Lines
Dongho Jeon,Bomson Lee 한국전자파학회JEES 2012 Journal of Electromagnetic Engineering and Science Vol.12 No.4
The conventionally classified waves are reclassified in this paper, including the waves associated with metamaterial (MTM) transmission lines. Various types of guided waves in periodic structures are analyzed for 1D Composite Right/Left Handed (CRLH) transmission lines (TL). In addition, dispersion diagrams for 1D CRLH, RH, and LH TLs are presented in terms of radiation conditions. We have refined the design equations of the conventional 1D CRLH TL and proposed a condition to realize the desired phase shift and its slope per unit cell. This condition has been applied to the conventional Wilkinson power divider and realized into MTM added 90° hybrid coupler. Based on the 10 dB return loss and the 90±10° phase shift, the bandwidths of the MTM added 90° hybrid coupler are 82.25 % and 103.5 % against the conventional 23 % and 52.5 %, respectively.
Properties of quicklime(CaO)-activated Class F fly ash with the use of CaCl<sub>2</sub>
Jeon, Dongho,Yum, Woo Sung,Jeong, Yeonung,Oh, Jae Eun Elsevier 2018 Cement and concrete research Vol.111 No.-
<P><B>Abstract</B></P> <P>This study reports the significant effect of CaCl<SUB>2</SUB> on strength improvement in CaO-activated Class F fly ash system. In these systems, the presence of CaCl<SUB>2</SUB> promotes (1) a higher degree of fly ash dissolution, (2) increasing C-S-H formation, and (3) an overall reduction of pore size and volume, resulting in increased strength. However, while more C-S-H, which is responsible for strength increase, was produced with higher CaCl<SUB>2</SUB> content, extreme doses of CaCl<SUB>2</SUB> resulted in strength degradation; more importantly, the best quantity of CaCl<SUB>2</SUB> for the greatest strength was dependent on the water-to-binder weight ratio (w/b). This dependency was closely related to the formation of calcium oxychloride, which generally causes severe expansive cracking and depends on w/b.</P>
Fully Printed Chipless RFID Tags Using Dipole Array Structures with Enhanced Reading Ranges
Dongho Jeon,Min-Sik Kim,Seung-Jin Ryu,Dae-Heon Lee,Jong-Kyu Kim 한국전자파학회JEES 2017 Journal of Electromagnetic Engineering and Science Vol.17 No.3
This article proposes a design of chipless RFID tag with dipole array structure that is fully printable using conductive ink. The proposed tags encode data based on spectral signature modulations. The reading range is considerably increased (2 m) while maintaining low transmission power (1 mW). Several prototype chipless RFID tags were fabricated and measured in the SHF and UHF bands. The proposed dipole array structure enhances the antenna gain of the passive tags and contributes to overcoming the low conductivity of conductive ink. In order to verify the utility of our proposal, the tags are manufactured on paper, using conductive ink, for the purpose of economic mass production.
Jeon, Dongho,Jun, Yubin,Jeong, Yeonung,Oh, Jae Eun Elsevier 2015 Cement and concrete research Vol.67 No.-
<P><B>Abstract</B></P> <P>This study explores the beneficial effects of Na<SUB>2</SUB>CO<SUB>3</SUB> as an additive for microstructural and strength improvements in a Ca(OH)<SUB>2</SUB>-activated fly ash system. NaOH-activated fly ash samples were also tested to compare the effect of Na<SUB>2</SUB>CO<SUB>3</SUB>. Compressive strength testing, XRD, SEM/BSE/EDS, <SUP>29</SUP>Si/<SUP>27</SUP>Al MAS-NMR, MIP and TGA were performed. The testing results indicate that the use of Na<SUB>2</SUB>CO<SUB>3</SUB> for Ca(OH)<SUB>2</SUB>-activation led to a noticeable improvement in strength and microstructure, primarily due to (1) more dissolution of raw fly ash at an early age, (2) more formation of C–S–H [or C–S–H(I)], (3) porosity reduction, and (4) pore-size refinement. We also found that (1) an early high alkalinity from the NaOH formation was not a major cause of strength, (2) geopolymer was not formed despite the early NaOH formation, and (3) no visible pore-filling action of CaCO<SUB>3</SUB> was observed. However, Na<SUB>2</SUB>CO<SUB>3</SUB> did not produce any improvement in strength for NaOH-activated fly ash.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The use of Na<SUB>2</SUB>CO<SUB>3</SUB> significantly improved strength and microstructure. </LI> <LI> The use of Na<SUB>2</SUB>CO<SUB>3</SUB> induced more dissolution of raw fly ash at early ages. </LI> <LI> The use of Na<SUB>2</SUB>CO<SUB>3</SUB> promoted more C–S–H [or C–S–H(I)] formation. </LI> <LI> The use of Na<SUB>2</SUB>CO<SUB>3</SUB> reduced total porosity and refined pore-size distribution. </LI> <LI> The use of Na<SUB>2</SUB>CO<SUB>3</SUB> produced neither geopolymer formations nor pore-filling actions from CaCO<SUB>3</SUB>. </LI> </UL> </P>
Simplified Modeling of Ring Resonators and Split Ring Resonators Using Magnetization
Dongho Jeon,Bomson Lee 한국전자파학회JEES 2013 Journal of Electromagnetic Engineering and Science Vol.13 No.2
This paper examines various aspects of the electromagnetic responses of the ring resonator located in the transverse electromagnetic cell. In addition, an equivalent circuit for the ring resonator is proposed and analyzed based on the electromagnetic phenomenon of the resonator. The equivalent circuit was simply modeled based on the concept of magnetization. A method for achieving a wider operating bandwidth of the negative permeability is provided. The ring resonator with its resonant frequency of 13.56 ㎒ was designed and its characteristics were examined in terms of S-parameters, effective permeability, loss rate, bandwidth, etc. The circuit and electromagnetic simulation results show an excellent agreement as well as that of theory.
합성곱 신경망 학습을 이용한 전기저항 토모그래피 기반 철근 위치 탐지 자동화 기술 개발
전동호(Jeon, Dongho),김민경(Kim, Minkyoung),김동주(Kim, Dongjoo),윤세윤(Yoon, Seyoon) 한국콘크리트학회 2021 한국콘크리트학회 학술대회 논문집 Vol.33 No.2
본 연구는 기 개발된 주파수 차이 ERT 방식과 합성곱 신경망 학습을 결합하여 콘크리트에 매립된 철근의 탐지를 시도하였고, 그 결과 높은 정확도로 철근의 지름별 위치, 각도별 위치를 탐지해내었다. In this study, a CT technology (electrode installation and analysis algorithm) using electrical impedance was developed and applied to real concrete samples in order to develop a non-destructive test technology to check the condition (crack and rebar position) inside the concrete.
15년간 사용된 KTX 콘크리트 침목에서 발생한 열화 현상 분석
전동호(Jeon, Dongho),유주안(Yoo, Juan),김지환(Kim, Jiwhan),배영훈(Bae, Younghoon),오재은(Oh, Jaeeun) 한국콘크리트학회 2021 한국콘크리트학회 학술대회 논문집 Vol.33 No.1
본 연구는 PSC침목의 재료적 측면에서 결함 요인을 알아보기 위하여 경부고속철도에서 사용된 PSC침목을 회수하여 4개의 상태로 분류하고, 각 분류 별 침목 내부에서 콘크리트 시료를 채취하여 상태 별 미세구조를 분석하였다. In this study, PSC sleepers used in Gyeongbu High-speed Railway were collected and classified into four states in order to find out the cause of defects in the material aspect of PSC sleepers.