• 한국해양환경ㆍ에너지학회지
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• 제16권2호
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• pp.115-120
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• 2013

본 연구에서는 순환골재를 이용하여 수용액상에서 혼합중금속의 제거능을 평가하였다. 순환골재는 주요 성분인 CaO, $SiO_2$, $Al_2O_3$, $Fe_2O_3$가 약 95% 함유되어 흡착제로서 유리한 조성을 가지고 있다. 동적흡착결과를 유사 1차 모델과 유사 2차 모델로 분석한 결과 두 모델 모두 실험결과에 잘 부합하는 것으로 나타났다. 평형흡착 실험은 Langmuir 모델에 잘 부합했고, $Cu^{2+}$ > $Pb^{2+}$ > $$Zn^{2+}{\simeq_-}Ni^{2+}$$ > $Cd^{2+}$순으로 흡착량이 높았다. 용액의 pH가 6에서 10로 증가함에 따라서 흡착률은 증가하는 것으로 나타났다. 또한, 순환골재의 양이 증가함에 따라서 중금속의 흡착률은 증가하였지만, 단위 질량당 흡착량은 감소하였다. 본 연구 결과를 통해 순환골재는 중금속을 효율적으로 제거할 수 있는 흡착제로 판단된다.

• 한국지반환경공학회 논문집
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• 제14권3호
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• pp.5-11
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• 2013

본 연구는 홍수 시 교량하부에서 발생되는 세굴에 의한 문제점을 조사하기 위한 연구로서 실제 현장에서 실험에 의하여 규명이 쉽지 않은 세굴과 관련된 교량하부구조 거동에 대한 해석적 연구이다. 본 연구에서 제시된 해석모델의 경우 도로교 시방규정에서 제시한 표준하부구조 단면을 기준으로 세굴에 따른 3축 지반지지력 표현 및 손실이 가능하도록 유한요소 모델링을 수행하였고 상용유한요소해석 프로그램인 ANSYS를 이용하여 해석을 수행하였다. 고려된 하중조건으로는 시간에 따른 유량변화를 단계적으로 고려하였으며 다양한 형태의 세굴조건과 지반지지력 변화에 대하여 교량하부구조 거동을 조사하였다. 최종적으로 교량하부구조의 거동은 세굴발생 면적 및 형태에 따라서 다양한 결과들을 보여주었으며, 이들 결과들은 향후 교량하부구조 세굴보호공 설계기준 마련을 위한 기초자료로 유용하게 활용될 수 있을 것이다.

• Computers and Concrete
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• 제22권2호
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• pp.167-182
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• 2018

The modeling of loss of bond between reinforcing bars (rebars) and concrete due to corrosion is useful in studying the behavior and prediction of residual load bearing capacity of corroded reinforced concrete (RC) members. In the present work, first the possibility of using different methods to simulate the rebars-concrete bonding, which is used in three-dimensional (3D) finite element (FE) modeling of corroded RC beams, was explored. The cohesive surface interaction method was found to be most suitable for simulating the bond between rebars and concrete. Secondly, using the cohesive surface interaction approach, the 3D FE modeling of the behavior of non-corroded and corroded RC beams was carried out in an ABAQUS environment. Experimental data, reported in literature, were used to validate the models. Then using the developed models, a parametric study was conducted to examine the effects of some parameters, such as degree and location of the corrosion, on the behavior and residual capacity of the corroded beams. The results obtained from the parametric analysis using the developed model showed that corrosion in top compression rebars has very small effect on the flexural behaviors of beams with small flexural reinforcement ratio that is less than the maximum ratio specified in ACI-318-14 (singly RC beam). In addition, the reduction of steel yield strength in tension reinforcement due to corrosion is the main source of reducing the load bearing capacity of corroded RC beams. The most critical corrosion-induced damage is the complete loss of bond between rebars and the concrete as it causes sudden failure and the beam acts as un-reinforced beam.

• 한국지진공학회논문집
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• 제19권1호
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• pp.37-43
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• 2015

This paper presents a detailed procedure for a nonlinear soil-structure interaction of a seismically isolated NPP(Nuclear Power Plant) structure using the boundary reaction method (BRM). The BRM offers a two-step method as follows: (1) the calculation of boundary reaction forces in the frequency domain on an interface of linear and nonlinear regions, (2) solving the wave radiation problem subjected to the boundary reaction forces in the time domain. For the purpose of calculating the boundary reaction forces at the base of the isolator, the KIESSI-3D program is employed in this study to solve soil-foundation interaction problem subjected to vertically incident seismic waves. Wave radiation analysis is also employed, in which the nonlinear structure and the linear soil region are modeled by finite elements and energy absorbing elements on the outer model boundary using a general purpose nonlinear FE program. In this study, the MIDAS/Civil program is employed for modeling the wave radiation problem. In order to absorb the outgoing elastic waves to the unbounded soil region, spring and viscous-damper elements are used at the outer FE boundary. The BRM technique utilizing KIESSI-3D and MIDAS/Civil programs is verified using a linear soil-structure analysis problem. Finally the method is applied to nonlinear seismic analysis of a base-isolated NPP structure. The results show that BRM can effectively be applied to nonlinear soil-structure interaction problems.

• 분석과학
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• 제16권3호
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• pp.226-231
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• 2003

국내와 국외에서 생산된 두 가지 종류의 AAS 기기를 이용하여 대기분진 시료를 분석하였다. 국내에서 생산된 제품의 경우, 단색화 장치의 성능면에서 선택된 파장들에 대한 광량의 세기가 우수하게 관찰되었다. 그리고 원자화장치의 경우, 재현성을 높이기 위하여 미세방울을 제외한 모든 큰 방울을 폐기 잔유물이 남지 않도록 하였다. 기기의 검출부에서는 저역 통과 filter를 사용하여, 데이터의 노이즈를 줄였다. Au 표준 용액을 이용한 검출한계 실험 분석치는 약 $0.015{\mu}g/L$ 수준의 높은 감도로서 외국사의 성능과 뚜렷한 큰 차이를 구분하기는 어려웠다. 본 연구진은 이러한 분석기법을 활용하여 서울시내 7개 지역 주요 관측점을 중심으로 2001년부터 2002년 봄까지 일년 동안 대기보전시료를 채취하였다. 이들 시료를 이용하여 분진 중에 결합된 중금속성분의 (Pb, Cu, Mn, Cd, Ni, Fe, Cr, Co, Mg, Al) 농도를 분석하였다.

• Smart Structures and Systems
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• 제6권5_6호
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• pp.579-593
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• 2010

Low-power radio frequency (RF) chip transceiver technology and the associated structural health monitoring platforms have matured recently to enable high-rate, lossless transmission of measurement data across large-scale sensor networks. The intrinsic value of these advanced capabilities is the allowance for high-quality, rapid operational modal analysis of in-service structures using distributed accelerometers to experimentally characterize the dynamic response. From the analysis afforded through these dynamic data sets, structural identification techniques can then be utilized to develop a well calibrated finite element (FE) model of the structure for baseline development, extended analytical structural evaluation, and load response assessment. This paper presents a case study in which operational modal analysis is performed on a three-span prestressed reinforced concrete bridge using a wireless sensor network. The low-power wireless platform deployed supported a high-rate, lossless transmission protocol enabling real-time remote acquisition of the vibration response as recorded by twenty-nine accelerometers at a 256 Sps sampling rate. Several instrumentation layouts were utilized to assess the global multi-span response using a stationary sensor array as well as the spatially refined response of a single span using roving sensors and reference-based techniques. Subsequent structural identification using FE modeling and iterative updating through comparison with the experimental analysis is then documented to demonstrate the inherent value in dynamic response measurement across structural systems using high-rate wireless sensor networks.

• 소성∙가공
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• 제31권6호
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• pp.365-375
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• 2022

The microstructure and high-temperature plastic deformation behavior of the modified Al-0.7Mn alloy were investigated and compared with the conventional Al-0.3Mn (Al3102) alloy. α-Al (matrix) and Al₆(Mn, Fe) phases were identified in both alloys. As a result of microstructure observation, both alloys showed equiaxed grains, and Al-0.7Mn alloy showed larger grain size and higher Al₆(Mn, Fe) fraction than Al-0.3Mn alloy. High temperature compressive tests, the deformation temperatures of 410℃, 450℃, 490℃, 530℃ and strain rats of 10^-2/s, 10^-1/s, 1/s, 10/s, were conducted using Gleeble equipment. The flow stress values of Al-0.7Mn alloy were higher than that of Al-0.3Mn alloy at all strain rates and temperature conditions. Constitutive equations were presented using the flow stresses obtained from experimental results and the Zener-Hollomon parameter. In the true stress-true strain curves of the two alloys, the experimental and predicted values were in good agreement with each other. Based on the dynamic material model, eutectic deformation maps of Al-0.7Mn and Al-0.3Mn alloys were suggested, and the plastic instability region was presented. The modified Al-0.7Mn alloy showed a wider plastic instability region than that Al-0.3Mn alloy. Based on the process deformation maps, the MPE tube parts could be manufactured through the actual extrusion process using the suggested conditions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권7호
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• pp.1773-1793
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• 2023

Automated machine learning, often referred to as "AutoML," is the process of automating the time-consuming and iterative procedures that are associated with the building of machine learning models. There have been significant contributions in this area across a number of different stages of accomplishing a data-mining task, including model selection, hyper-parameter optimization, and preprocessing method selection. Among them, preprocessing method selection is a relatively new and fast growing research area. The current work is focused on the recommendation of preprocessing methods, i.e., feature subset selection (FSS) algorithms. One limitation in the existing studies regarding FSS algorithm recommendation is the use of a single learner for meta-modeling, which restricts its capabilities in the metamodeling. Moreover, the meta-modeling in the existing studies is typically based on a single group of data characterization measures (DCMs). Nonetheless, there are a number of complementary DCM groups, and their combination will allow them to leverage their diversity, resulting in improved meta-modeling. This study aims to address these limitations by proposing an architecture for preprocess method selection that uses ensemble learning for meta-modeling, namely AutoFE-Sel. To evaluate the proposed method, we performed an extensive experimental evaluation involving 8 FSS algorithms, 3 groups of DCMs, and 125 datasets. Results show that the proposed method achieves better performance compared to three baseline methods. The proposed architecture can also be easily extended to other preprocessing method selections, e.g., noise-filter selection and imbalance handling method selection.

• 한국산업융합학회 논문집
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• 제27권4_2호
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• pp.833-840
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• 2024

According to recent data from the Korea Meteorological Administration(KMA), the frequency of typhoons around the Korea Peninsula is almost unchanged, but the intensity is on the rise due to climate change. A typhoon that has become so powerful can cause partial or complete damage to the traffic signal structures, limiting the operation of the vehicle and causing traffic congestion. If the traffic signal structure fails to function properly due to the influence of the typhoon, not only the v ehicle operation will be disrupted, but also direct damage to the traffic signal structure will occur. In addition, if the social overhead cost of traffic congestion is included, the recovery cost caused by the typhoon will increase to an extent that it is difficult to estimate. Therefore, in this study, a wind tunnel experiment was performed by producing a wind tunnel model of an existing fixed traffic signal structure and a traffic signal structure in which signs and traffic lights are hinged. Also, The fixed and hinge structures were modeled as 3D finite elements, and wind-resistant analysis was performed by wind speed, and, wind-resistant safety of traffic signal structures were analyzed and examined through wind-resistant analyses. From the comparative analysis of the results of experiment and FE analysis, it was known that the stress reduction rate of the hinge connection structure was at least 30% compared to that of the fixed connection structure from the results of the wind tunnel experiment and FE analysis. And As a result of finite element analysis for the maximum design wind speed of 50m/s, it was found that the maximum stress generated in the existing structure exceeded all the yield stress, but the maximum stress of the hinge connection structure was within the yield stress. Finally The hinge connection structure showed a relatively large stress reduction rate as the wind speed increased and the length of the lateral beam was shorter at the same wind speed.

• 한국식품과학회지
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• 제39권1호
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• pp.20-24
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• 2007

된장모델로서 0.1M glucose-0.1M glutamic acid 모델을 선정하고 0.2mM $FeCl_{2}$의 존재 하에 갈변억제제인 50mM citric acid와 이의 synergist로 5종의 phenolic acids를 첨가하여 조제한 시료를 $4^{\circ}C$와 $30^{\circ}C$에서 4주간 저장하면서 phenolic acids가 갈변억제에 미치는 영향을 알아보았다. 그 결과 phenolic acids 첨가에 따른 갈변억제효과는$4^{\circ}C$의 저온에서보다 $30^{\circ}C$의 실온에서 저장시 pH의 변화 없이 더욱 효과적인 것으로 나타났다. 5종의 phenolic acids 중에서 hydroxybenzoic acid는 갈변억제능이 가장 높아, 갈변억제능은 $30^{\circ}C$에서 4주간 저장후 phenolic acids 무첨가구보다 13%가 높았다. Caffeic acid와 protocatechuic acid와 같이 OH기가 2개 치환된 phenolic acid는 Maillard 반응의 촉매로 작용하는 철 이온과의 결합능이 높아 Maillard 반응이 보다 더 억제되어 3-DG 및 형광화합물과 같은 중간반응산물의 생성을 가장 억제하였으나, 이들 phenolic acids는 유색의 착체를 형성하여 동일계의 OH기가 0, 1개 치환된 phenolic acids보다 갈변도는 오히려 증가하였다. Hydroxybenzoic acid는 실제 된장에도 사용가능한 첨가물로서 citric acid를 갈변억제제로 사용시 이의 synergist로 사용이 가능할 것으로 생각되었다.