• 한국지구과학회지
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• 제39권5호
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• pp.436-457
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• 2018

본 연구에서는 3차원 순환 모델인 MOHID (MOdelo $HIDrodin{\hat{a}}mico$) 모델을 적용하여 한반도를 포함한 동아시아 해역의 2016년 해황 변동을 재현하였다. 재현 결과는 객관 분석장(EN4, ARMOR3D, AVISO, SIO 자료)과 현장 관측 자료(정선 해양 자료, 부이 자료)를 사용하여 검증하였다. 검증 결과 MOHID로 재현된 수온, 해면 고도 편차, 표층 유속 및 혼합 층 깊이 등의 전반적인 해황 구조가 동아시아 해역의 객관 분석 자료들과 유사하게 나타났다. 특히 연안의 부이 자료와 비교하였을 때, 표층 수온 및 해면 고도 편차의 상관 계수는 모두 0.8 이상이며, 표준화된 표준편차는 0.85-1.15의 값을 보였다. 그러나 여름철 동해의 수온 약층의 구조 및 황해와 남해의 강한 성층 현상 재현에 관한 추가적인 개선이 필요할 것으로 분석되었다.

• 대기
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• 제29권5호
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• pp.689-698
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• 2019

Air pollution in urban areas has become a serious problem in the recent years. Especially, high concentrations of particulate matter (PM) cause negative effects on human health. Several studies suggest urban forest as a tool for improving air quality because of the capability of forests in reducing PM concentrations through deposition and adsorption using leaf area. For this reason, the National Institute of Forest Science plans to install in-situ observation stations for PM and biogenic volatile organic compounds (BVOCs) on a national scale to verify the net effect of forests on urban air pollution. To measure the quantitative change of PM concentrations due to the urban forest, stations should be located within and outside the forest area with respect to atmospheric circulation. In this study, we analyze the wind direction at the potential measurement sites to assess suitable locations for detecting the effect of urban forests on air quality in five cities (i.e. Gwangju, Daegu, Busan, Incheon, and Ilsan). This technical note suggests effective locations of in-situ measurements by considering main wind direction in the five cities of this study. A measurement station network created in the future based on the selected locations will allow quantitative measurements of PM concentration and BVOCs emitted from the urban forest and help provide a comprehensive understanding of the forest capabilities of reducing air pollution.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.86.1-86.1
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• 2012

나노재료와 나노기술의 연구개발 지원을 위하여 국가나노인프라인 나노종합팹센터에서 개발되고 있는 나노재료/나노현상의 실시간 관찰을 위한 SiN membrane chip 기술 및 나노그래핀 기반구축에 대한 최근 결과와 향후계획을 소개하고자 한다. 나노재료의 합성, 배열, 구조 등의 실시간 관찰을 가능하게 하기 위하여 제작된SiN membrane chip은 투과전자현미경(transmission electron microscope, TEM)에서 투명한 기판으로, 그 위에 나노재료를 합성, 배열하고 원하는 모양의 전극을 형성하여 나노재료 및 나노소자의 온도변화 및 전기적 특성 측정 등이 가능하다. 이러한 기술은 Ag, Sn, Cu 등 nano-cluster의 percolation 소자, SiN 및 Graphene 나노기공 소자, SiGe, BiTe, Si, ZnO 나노선 및 CNT의 내부구조변화, 상변화 등 다양한 나노재료/나노소자의 나노현상 관찰 및 해석에 적용되었다.

• 대기
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• 제24권2호
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• pp.173-188
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• 2014

The KMA has cooperated with the Oklahoma University in USA to develop a Polarimetric Radar Data (PRD) simulator to improve the microphysical processes in Korea Local Analysis and Prediction System (KLAPS), which is critical for the utilization of PRD into Numerical Weather Prediction (NWP) field. The simulator is like a tool to convert NWP data into PRD, so it enables us to compare NWP data with PRD directly. The simulator can simulate polarimetric radar variables such as reflectivity (Z), differential reflectivity ($Z_{DR}$), specific differential phase ($K_{DP}$), and cross-correlation coefficient (${\rho}_{hv}$) with input of the Drop Size Distribution (DSD) and scattering calculation of the hydrometeors. However, the simulator is being developed based on the foreign observation data, therefore the PRD simulator development reflecting rainfall characteristics of Korea is needed. This study analyzed a potential application of the 2-Dimension Video Disdrometer (2DVD) data by calculating the raindrop axis ratio according to the rain-types to reflect Korea's rainfall characteristics into scattering module in the simulator. The 2DVD instrument measures the precipitation DSD including the fall velocity and the shape of individual raindrops. We calculated raindrop axis ratio for stratiform, convective and mixed rainfall cases after checking the accuracy of 2DVD data, which usually represent the scattering characteristics of precipitation. The raindrop axis ratio obtained from 2DVD data are compared with those from foreign database in the simulator. The calculated the dual-polarimetric radar variables from the simulator using the obtained raindrop axis ratio are also compared with in situ dual-polarimetric observation data at Bislsan (BSL). 2DVD observation data show high accuracies in the range of 0.7~4.8% compared with in situ rain gauge data which represents 2DVD data are sufficient for the use to simulator. There are small differences of axis ratio in the diameter below 1~2 mm and above 4~5 mm, which are more obvious for bigger raindrops especially for a strong convective rainfall case. These differences of raindrop axis ratio between domestic and foreign rainfall data base suggest that the potential use of disdrometer observation can develop of a PRD simulated suitable to the Korea precipitation system.

• 터널과지하공간
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• 제23권4호
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• pp.297-307
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• 2013

본 연구에서는 시추공히터시험의 실측 결과를 FEM 해석코드인 ABAQUS ver 6.10을 이용하여 열 해석을 수행하였다. 현장시험 전 암석 코아에 대한 실내 실험을 통해 결정된 열, 역학적 암반물성과 실험구간 내 대기특성을 해석 초기조건으로 입력하였다. 현장시험과 열 해석의 결과를 비교했을 때, 히터로부터 0.9 m 이격된 C3 관측공의 온도는 상당히 유사한 패턴과 수치(약 $1.3^{\circ}C$ 차이)를 보였으나, A와 B 관측공의 현장시험 결과와는 최대 $15^{\circ}C{\sim}20^{\circ}C$가량의 큰 차이를 나타냈다. 이러한 결과의 이유를 찾고자 A1과 B1 관측공을 대상으로 over-coring을 실시하였다. 육안으로 시추된 코어를 확인한 결과, 센서의 위치, 개수는 문제가 없었지만, 관측공내 시멘트의 주입 상태가 불량하였다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.197-201
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• 2009

A lot of work is carried out concerning to acicular ferrite formation in the weld metal of high strength and low-alloy steel. Those results are suggesting that oxides that contain titanium elements provides nucleation site of intragranular ferrite, referred as acicular ferrite. Thus, when intragranular ferrite is expected to form in heat-affected zone, oxide containing titanium element should be formed in the steel. However, normal steel is deoxidized by using aluminum element (Al-killed steel) with little oxygen content. It means almost oxygen is deoxidized with aluminum elements. In the present work, in order to form the acicular ferrite in the heat affected zone, with the same concept in the case of weld metal, the steel deoxidized with titanium element (titanium killed-steel) is prepared and the acicular ferrite formation is observed in detail by using laser-conforcal microscopy technique. The confocal technique makes it possible that the morphological change along the phase transformation from austenite to ferrite is in-situ tracked. Thus, the inclusion that stimulated the ferrite nucleation could be directly selected from the observed images, in the HAZ of the Ti-killed steel. The chemical composition of the selected inclusion is analyzed and the nucleation potential is discussed by changing the nucleation site with boron element. The potency for the ferrite nucleation is summarized and the existence of effective and ineffective manganese sulfide for nucleation is made clear.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.264-265
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• 2008

While the reliability of bulk insulation has become important particularly in multilayer boards and embedded boards, electronics are to be used under various environments such as at high temperature and in high humidity. We observed internal space charge behavior for two types of epoxy composites under dc electric fields to investigate the influence of water at high temperature. In the case of glass/epoxy specimen, homocharge is observed at water-treated specimen, and spatial oscillations become clearer in the water-treated specimens. Electric field in the vicinity of the electrodes shows the injection of homocharge. In aramid/epoxy specimens, heterocharge is observed at water-treated specimens, i.e. negative charge accumulates near the anode, while positive charge accumulates near the cathode. Electric field is enhanced just before each electrode. In order to further examine the mechanism of space charge formation, we have developed a new system that allows in situ space charge observation during ion migration tests at high temperature and high humidity. Using this in situ system.

• Elastomers and Composites
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• 제53권2호
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• pp.57-66
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• 2018

Styrene-butadiene rubber (SBR), reinforced with different contents of silica (with or without modification using silane coupling agents), was prepared by a modified sol-gel method involving hydrolyzation of tetraethoxysilane over an acid catalyst. The structures of the as-prepared samples were characterized using various techniques, such as scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The mechanical properties of the as-prepared samples were discussed in detail. The results revealed an increasing of the storage modulus (G') with increase in the silica content without modification. In contrast, G' decreased after modification using silane coupling agents, indicating a reduction in the silica-silica interaction and improved dispersion of silica in the SBR matrix. Both tensile stress and hardness increased with increase in the silica content (with modification) in the SBR matrix, albeit with low values compared to the samples with un-modified silica, except for the case of silica modified using (3-glycidyloxypropyl) trimethoxysilane (GPTS). The latter observation can be attributed to the special structure of GPTS and the effort of oxygen atom lone-pair.

• Smart Structures and Systems
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• 제8권5호
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• pp.471-486
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• 2011

Various types of strain sensors have been developed and widely used in the field for monitoring the mechanical deformation of structures. However, conventional strain sensors are not suited for measuring large strains associated with impact damage and local crack propagation. In addition, strain sensors are resistive-type transducers, which mean that the sensors require an external electrical or power source. In this study, a gold nanoparticle (GNP)-based polymer composite is proposed for large strain sensing. Fabrication of the composites relies on a novel and simple in situ GNP reduction technique that is performed directly within the elastomeric poly(dimethyl siloxane) (PDMS) matrix. First, the reducing and stabilizing capacities of PDMS constituents and mixtures are evaluated via visual observation, ultraviolet-visible (UV-Vis) spectroscopy, and transmission electron microscopy. The large strain sensing capacity of the GNP-PDMS thin film is then validated by correlating changes in thin film optical properties (e.g., maximum UV-Vis light absorption) with applied tensile strains. Also, the composite's strain sensing performance (e.g., sensitivity and sensing range) is also characterized with respect to gold chloride concentrations within the PDMS mixture.

• Corrosion Science and Technology
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• 제16권4호
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• pp.194-200
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• 2017

Stress-corrosion cracking (SCC) of alloy 600 and alloy 800 in 0.5 mol/L thiosulfate solution during constant strain was investigated using electrochemical noise (EN) combined with 3-D microscope techniques. The in-situ morphology observation and EN results indicate that the SCC process could be divided into three stages: (1) passive film stabilization and growth, (2) crack initiation, (3) and crack growth. Power Spectral Density (PSD) and the probability distribution obtained from EN were used as the "fingerprint" to distinguish the different processes. During passive film stabilization and growth, the current noise signals resembled "white noise": when the crack initiated, many transient peaks could be seen in the current noise and the wavelet energy at low frequency as well as the noise resistance decreased. After crack propagation, the noise amplitudes increased, particularly the white noises at low and high frequencies ($W_L$ and $W_H$) in the PSDs. Finally, the detection of metal structure corrosion in a simulated sea splash zone and pipeline corrosion in the atmosphere are established.