• Advances in concrete construction
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• 제12권6호
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• pp.517-525
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• 2021

More underground structures are increasingly being constructed such as box culverts for electric power transmission, and the life extension of these structures is very important. It is well known that the steel embedded in concrete is usually invulnerable to corrosion because the high alkalinity of the pore solution in concrete generates a thin protective oxide layer on the surface of the steel. Recent observations in the field and experimental evidence have shown that even steel in concrete can be corroded through the carbonation reaction of cover concrete. Carbonation-induced corrosion in concrete may often occur in a high carbon dioxide environment. In this study, the risk of carbonation of underground box culverts in Korea was evaluated by measuring the car¬bonation rate and concrete cover depth in the field. Then, the carbonation-free service life for the cover depth of the steel was calcu¬lated with in situ information and Monte Carlo simulation. Additionally, an accelerated carbonation test for a cracked beam specimen was performed, and the effect of a crack on the service life of a box culvert was numerically investigated with Monte Carlo simulation based on experimental results.

• Journal of Electrochemical Science and Technology
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• 제13권3호
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• pp.354-361
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• 2022

In a direct methanol fuel cell system (DMFC), one of the drawbacks is methanol crossover. Methanol from the anode passes through the membrane and enters the cathode, causing mixed potential in the cell. Only Pt-based catalysts are capable of operating as cathode for oxygen reduction reaction (ORR) in a harsh acidic condition of DMFC. However, it causes mixed potential due to high activity toward methanol oxidation reaction of Pt. To overcome this situation, developing Pt-based catalyst that has methanol tolerance is significant, by controlling reactant adsorption or reaction kinetics. Pt/C decorated with phosphate ion was prepared by modified polyol method as cathode catalyst in DMFC. Phosphate ions, bonded to the carbon of Pt/C, surround free Pt surface and block only methanol adsorption on Pt, not oxygen. It leads to the suppression of methanol oxidation in an oxygen atmosphere, resulting in high DMFC performance compared to pristine Pt/C.

• Steel and Composite Structures
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• 제44권2호
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• pp.255-270
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• 2022

This manuscript illustrates the dynamic response of nanoscale carbon nanotubes (CNTs) embedded in an elastic media under moving load using doublet mechanics theory, which not considered before. CNTs are modelled by Timoshenko beam theory (TBT) and a bottom to up modelling nano-mechanics is simulated by doublet mechanics theory to capture the size effect of CNTs. To explore the influence of the CNTs configurations on the dynamic behaviour, both armchair and zigzag configurations are considered. The governing equations of motion and the associated boundary conditions are obtained using the Hamiltonian principle. The Navier solution methodology is applied to obtain the solutions for both orientations. Free vibration and forced response under moving loads are considered. The accuracy of the developed procedure is verified by comparing the obtained results with available previous algorithms and good agreement is observed. Parametric studies are conducted to demonstrate effects of doublet length scale, CNTs configurations, moving load velocities as well as the elastic media parameters on the dynamic behaviours of CNTs. The developed procedure is supportive in the design and manufacturing of MEMS/NEMS made from CNTs.

• 한국기계가공학회지
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• 제21권2호
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• pp.137-143
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• 2022

Composite materials, being light-weight and of high mechanical strength, are increasingly used in various industries such as the aerospace, automobile, sporting-goods manufacturing, and ship-building industries. Recently, manufacturing of composite materials using 3D printers has increased. 3D-printed composite materials are made in free-form and adapted for end-use by adjusting the fiber content and orientation. However, research on the machining of 3D printed composite materials is limited. The aim of this study is to develop a machine learning method to select machining conditions for machining of 3D-printed composite materials. The composite material was composed of Onyx and carbon fibers and stacked sequentially. The experiments were performed using the following machining conditions: spindle speed, feed rate, depth of cut, and machining direction. Cutting forces of the different machining conditions were measured by milling the composite materials. PCA, a method of machine learning, was developed to select the machining conditions and will be used in subsequent experiments under various machining conditions.

• 멤브레인
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• 제33권1호
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• pp.46-51
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• 2023

본 연구의 목적은 스마트시티 구축의 핵심인 수소연료전지의 활용형태를 분석하고 해결방안을 제시하는 것이다. 수소연료전지를 활용하는 발전소의 경우 간헐성 문제가 없다는 장점 때문에 향후 가장 유망한 사용 형태로 분석됐다. 다만 많은 장점에도 불구하고 폭발 우려와 특정 수소 생산방식의 경우 이산화탄소 발생 문제 등으로 지역주민들의 반발이 지속적으로 나타나고 있어 이를 해결하는 것이 스마트시티 구축의 주요 관건이 될 것으로 분석된다. 마지막으로 현재의 수소 생산방식을 분석하고 이에 따른 문제점을 파악하여 스마트시티의 완전한 구축을 위한 해결책을 제시하였다.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4335-4349
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• 2023

Nuclear marine propulsion has been emerging as a next generation carbon-free power source, for which proper passive residual heat removal systems (PRHRSs) are needed for long-term safety. In particular, the characteristics of unlimited operation time and compact design are crucial in maritime applications due to the difficulties of safety aids and limited space. Accordingly, a compact and long-term-operable PRHRS has been proposed with the key design concept of using both air cooling and seawater cooling in tandem. To confirm its feasibility, this study conducted system design and a transient analysis in an accident scenario. Design results indicate that seawater cooling can considerably reduce the overall system size, and thus the compact and long-term-operable PRHRS can be realized. Regarding the transient analysis, the Multi-dimensional Analysis of Reactor Safety (MARS-KS) code was used to analyze the system behavior under a station blackout condition. Results show that the proposed design can satisfy the design requirements with a sufficient margin: the coolant temperature reached the safe shutdown condition within 36 h, and the maximum cooling rate did not exceed 40 ℃/h. Lastly, it was assessed that both air cooling and seawater cooling are necessary for achieving long-term operation and compact design.

• 한국자원식물학회지
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• 제26권2호
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• pp.303-309
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• 2013

본 연구는 바이러스 무병묘의 대량 증식을 위한 기초 자료를 얻고자 포도 '자랑' 품종의 신초와 뿌리의 형성 및 생장에 미치는 배지조성물질과 생장조절제의 영향을 구명하고자 수행되었다. 배지의 무기염 농도가 낮을수록 신초의 형성은 많아지는 경향으로, 특히 1/2MS배지에서 신초의 형성 및 생장이 가장 양호하였다. 부정근의 형성은 무기염의 농도가 높아질수록 양호하여 2MS배지에서 부정근의 수가 2.1개로 가장 많았다. Sucrose의 경우, 신초의 형성은 1%, 부정근의 형성은 3%, 생장은 1% 농도구에서 가장 좋았다. 활성탄의 0.05% 첨가에 의해 신초의 생장은 양호했으며, 특히, 부정근의 형성 및 생장에 효과적이었다. '자랑'의 대량 증식을 위한 배지의 pH는 6.8이 가장 적합하여 신초의 마디수와 길이가 각각 3.9개와 1.3 cm로 가장 좋았다. 기내 대량증식에 미치는 생장조절제의 영향으로 BA 1.0 mg/L에서 신초의 생장이 가장 왕성하였으며, NAA 1.0 mg/L에서 절편체당 16.9개의 신초가 형성되어 양호한 결과를 얻었다.

• 한국응용과학기술학회지
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• 제36권4호
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• pp.1143-1152
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• 2019

양이온성 계면활성제 (DTAB, TTAB 및 CTAB)에 의한 아닐린의 가용화현상을 연구하기 위하여 UV-Vis법을 이용하여 가용화상수(K_s)와 열역학 함수들을 계산하고 비교하였다. 그리고 이온염과 유기물의 첨가가 가용화상수에 어떠한 영향을 미치는지를 조사하였다. 또한 온도변화에 따른 K_s값의 변화를 계면활성제 종류별로 비교하고 분석하였으며, 가용화상수로부터 구한 여러 열역학적 함수를 비교하고 검토함으로써 아닐린의 가용화현상을 미시적으로 분석하고 해석하고자 하였다. 그 결과 양이온성 계면활성제에 의한 아닐린의 가용화현상에 대한 Gibbs 자유에너지와 엔탈피 변화 값은 모두 음의 값을 그리고 엔트로피 변화값은 모두 양의 값을 나타내었다. 가용화상수 값은 온도가 증가함에 따라 감소하고 계면활성제의 탄소사슬의 길이가 증가할수록 증가하였다. 이온염의 농도가 증가함에 따라 가용화에 대한 Gibbs 자유에너지값은 증가하다가 감소하는 경향을 보였다. 그리고 n-부탄올의 농도가 증가함에 따라 Gibbs 자유에너지는 계속 증가하는 경향을 보였다.

• 대기
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• 제29권5호
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• pp.511-523
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• 2019

A new Korean Meteorological Administration (KMA) airborne measurement platform has been established for regular observations for scientific purpose over South Korea since late 2017. CRDS G-2401m analyzer mounted on the King Air 350HW was used to continuous measurement of CO₂, CH₄ and CO mole fraction. The total uncertainty of measurements was estimated to be 0.07 ppm for CO₂, 0.5 ppb for CH₄, and 4.2 ppb for CO by combination of instrument precision, repeatability test simulated in-flight condition and water vapor correction uncertainty. The airborne vertical profile measurements were performed at a regional Global Atmosphere Watch (GAW) Anmyeon-do (AMY) station that belongs to the Total Carbon Column Observing Network (TCCON) and provides concurrent observations to the Greenhouse Gases Observing Satellite (GOSAT) overpasses. The vertical profile of CO₂ shows clear altitude gradient, while the CH₄ shows non-homogenous pattern in the free troposphere over Anmyeon-do. Vertically averaged CO₂ at the altitude between 1.5 and 8.0km are lower than AMY surface background value about 7 ppm but higher than that observed in free troposphere of western pacific region about 4 ppm, respectively. CH₄ shows lower level than those from ground GAW stations, comparable with flask airborne data that was taken in the western pacific region. Furthermore, this study shows that the combination of CH₄ distribution in free troposphere and trajectory analysis, taking account of convective mixing, is a useful tool in investigating CH₄ transport processes from tropical region to Korean region in winter season.

• KSBB Journal
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• 제15권6호
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• pp.621-629
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• 2000

전남의 여수지역의 해양에서 carotenoid를 생산하는 세균을 분리하여 상용하였으며, 이 세균은 Curtobacterium sp.으로 동정되었다. 해양세균 Curtobacterium sp.의 carotenoid 생산 최적조건은 pH 7.0, 최적온도 $25^{\circ}C$, 탄소원으로서는 4 mM의 fructose, 질소원으로서는 0.07%의 tryptone, 미량원소 및 growth로서는 각각 0.5 mM의 $Mg^{+2}$ 이온, $1{\;}\mu\textrm{m}$의 cytocobalamine이었으며, 이 최적조건에서의 carotenoid의 생산량은 $13.0{\;}mg/\ell$ 였다. 해양세균 Curtobacterium sp.로 부터 생산된 carotenoid는 tunaxanthi (86.6%), diatoxanthin (7.1%), ${\beta}-carotene$ (2.1%), canthaxanthin (19.1%), cynthiaxanthin (1.9%) 5가지의 다른 성분으로 구성되어 있었으며, 주로 tunaxanthin을 생산하는균주로 사료된다. 그리고 분리 정제하지 않은 crude corotenoid을 이용한 생리활성 시험에서 E. coli 및 L. bulgaricus 등에 대해서는 항균활성은 나타내지 않았으나, HepG2 (hepatocellular carcinoma, human, ATCC HB-8065) 및 HeLa (cervical carcinoma, human, ATCC CCL-2) 등의 암세포에 대하여 각각 86.4% 및 39.2%의 강한 저해 활성을 나타내었다. CCL-13 (diploid, monotypic hepatocyte, huma, ATCC CCL-13) 세포를 사용한 항산화 활성은 $50{\;}\mu\textrm{g}/m{\ell}$의 carotenoid의 농도에서 83%의 강한 항산화 활성을 보였고, DPPH법에 의한 Free radical의 소거 기능도 43.4%의 높은 활성을 나타내었다. 따라서 해양세균 Curtobacterium sp.로부터 생산된 이 carotenoid는 정제하지 않은 상태로도 어류 및 축산사료, 첨가물, 항산화제, 의약품 등의 다양한 분야에 사용이 가능할 것으로 판단된다.