• Wind and Structures
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• 제25권5호
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• pp.433-457
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• 2017

As a novel typical wind-sensitive structure, the wind load and wind-induced structural behaviors of super-large straight-cone cooling towers are in an urgent need to be addressed and studied. A super large straight-cone steel cooling tower (189 m high, the highest in Asia) that is under construction in Shanxi Power Plant in China was taken as an example, for which four finite element models corresponding to four structural types: the main drum; main drum + stiffening rings; main drum + stiffening rings + auxiliary rings (auxiliary rings are hinged with the main drum and the ground respectively); and main drum + stiffening rings + auxiliary rings (auxiliary rings are fixed onto the main drum and the ground respectively), were established to compare and analyze the dynamic properties and force transferring paths of different models. After that, CFD method was used to conduct numerical simulation of flow field and mean wind load around the cooling tower. Through field measurements and wind tunnel tests at home and abroad, the reliability of using CFD method for numerical simulation was confirmed. On the basis of this, the surface flow and trail characteristics of the tower at different heights were derived and the wind pressure distribution curves for the internal and external surfaces at different heights of the tower were studied. Finally, based on the calculation results of wind-induced responses of the four models, the effects of stiffening rings, auxiliary rings, and different connecting modes on the dynamic properties and wind-induced responses of the tower structure were derived and analyzed; meanwhile, the effect mechanism of internal suction on such kind of cooling tower was discussed. The study results could provide references to the structure selection and wind resistance design of such type of steel cooling towers.

• 콘크리트학회논문집
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• 제16권4호
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• pp.501-509
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• 2004

제안된 모델은 FRP 구속 콘크리트에 대한 압축거동 예측을 위한 것이다. FRP로 구속된 콘크리트의 모델링을 위하여, 3축 응력상태의 콘크리트 아탄성 구성관계를 제시하였다. FRP 구속에 따른 콘크리트 강도 증진은 3축 응력공간의 파괴기준에 따라 결정되며, 이에 대응하는 최대 압축변형률은 본 연구에서 제안된 변형률 증진계수로부터 결정된다. 따라서, 기존의 모델들이 하중단계에 관계없이 구속조건이 초기부터 파괴까지 일정하게 고려되는 반면에, 제안된 모델은 FRP로 구속된 콘크리트의 구속현상을 하중단계에 의존적인 비선형 관계로 제시하였다. FRP 층은 2차원의 적층된 복합재료의 해석에 기초하여 모델링되었다. 개발된 해석모델은 증분법에 의한 압축거동실험에 대한 해석을 수행할 수 있도록 하였다. FRP로 구속된 콘크리트 실린더의 대한 여러 연구자들의 실험 결과와 본 예측모델을 비교한 결과, 제안된 모델은 축방향 변형 뿐만 아니라 횡방향 변형을 포함하여 FRP 층으로 인한 콘크리트의 구속효과의 증진에 관한 거동 특성들을 잘 예측해 주었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 센서 박막재료 반도체재료 기술교육
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• pp.55-61
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• 2002

Ultra-fine particles of $SnO_{2}$ was synthersized by the sol-gel powder processing using tin(II) chloride dihydrate$(SnCl_{2}{\cdot}2H_{2}O)$ and ethanol$(C_{2}H_{5}OH)$ as raw materials. Gel powders can be obtained by drying of sol at $120^{\circ}C$ after aging 72hrs and 168hrs. The amount of $SnO_{2}$ phase was increased with temperature because of the evaporation of volatile components, and the creation of $SnO_{2}$ phase was almost done by the heat treatment at $700^{\circ}C/30min$ The grain sizes after firing are about 20-30nm, and it showed the narrow distribution of grain size. The specimens to measure electrical properties were fabricated by the thick film screen printing technique on the alumina substrates. The conductance of $SnO_{2}$ was increased with temperature up to $380^{\circ}C$ by the typical conduction mechanism of semiconducting ceramics. There was a region of constant conductance between about $200^{\circ}C$ and $380^{\circ}C$ due to the increment of electron concentration with temperature and the annihilation of conduction carriers by the absorption and electron trapped-ionization of oxygen on the surface of $SnO_{2}$, It was finally showed the intrinsic behaviors above $450^{\circ}C$. The sensing properties of response time, recovery, and sensitivity of CO were improved with aging time.

• 한국도로학회논문집
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• 제11권2호
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• pp.205-216
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• 2009

본 논문에서는 기 발표된 연구를 바탕으로 도로하부구조 안정처리기법 적용시 아스팔트 포장에서의 구조적인 거동을 비교 분석하였다. 도로하부재료의 비선형성을 고려한 유한요소법을 활용하여 단축 표준하중 하에서 공용성 지수를 추정하였으며 안정처리된 지반재료의 물리적 역학적 성질들은 실내시험 결과를 통하여 평가되었다. 유한요소 수치해석에 기초한 분석을 통하여 다양한 층두께와 안정제 함량에 따라 포장체에서 변형에 기초한 반응을 분석하였다. 결과 안정처리된 도로에 대한 구조적인 성능은 층두께와 안정제 함량에 따라 많은 영향을 받고 있었으며 결과를 분석하여 조립질 도로하부 안정처리인 경우에 대한 안정처리층의 적정한 두께와 안정제의 최소함량을 각각 제안하였다.

• Journal of Electrochemical Science and Technology
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• 제10권4호
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• pp.361-372
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• 2019

The silver nanoparticles/polyaniline/reduced graphene oxide nanocomposite modified glassy carbon electrode (Ag/PANI/RGO/GCE) was prepared by the electrochemical method. The Ag/PANI/RGO nanocomposite was characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, X-ray diffraction (XRD), and electrochemical impedance spectroscopy (ESI). Two electrochemical techniques namely differential pulse voltammetry (DPV) and cyclic voltammetry (CV) were used to the electrochemical behaviors investigation of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The Ag/PANI/RGO/GCE exhibited remarkable electrocatalytic activity towards the oxidation reaction of AA, DA, and UA in Britton-Robinson (BR) solution (pH=4.0). Under the optimal conditions, the determinations of AA, DA, and UA were accomplished using DPV. AA-DA and DA-UA peak potential separations were 130 and 180 mV, respectively. For simultaneous detection, the linear response ranges were in the two concentration ranges of 0.05-0.8 mM and 2.0-16.0 mM with detection limit 0.412 μM (S/N = 3) for AA, 0.7-90.0 μM and 90.0-1000.0 μM with detection limit 0.023 μM (S/N = 3) for DA, and 0.8-70.0 μM and 70.0-1000.0 μM with detection limit 0.050 μM (S/N = 3) for UA. This modified electrode showed good sensitivity, selectivity, and stability with applied to determine AA, DA, and UA in human urine and drug.

• 센서학회지
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• 제18권1호
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• pp.54-62
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• 2009

${Co_3}{O_4}$ and ${Co_3}{O_4}$-based thick films with additives such as ${Co_3}{O_4}-{Fe_2}{O_3}$(5 wt.%), ${Co_3}{O_4}-{SnO_2}$ (5 wt.%), ${Co_3}{O_4}-{WO_3}$(5 wt.%) and ${Co_3}{O_4}$-ZnO(5 wt.%) were fabricated by screen printing method on alumina substrates. Their structural properties were examined by XRD and SEM. The sensitivities to iso-${C_4}H_{10}$, $CH_4$, CO, $NH_3$ and NO gases were investigated with the thick films heat treated at $400^{\circ}C$, $500^{\circ}C$ and $600^{\circ}C$. From the gas sensing properties of the films, the films showed p-type semiconductor behaviors. ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film heat treated at $600^{\circ}C$ showed higher sensitivity to i-${C_4}H_{10}$ and CO gases than other thick-films. ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film heat treated at $600^{\circ}C$ showed the sensitivity of 170 % to 3000 ppm iso-${C_4}H_{10}$ gas and 100 % to 100 ppm CO gas at the working temperature of $250^{\circ}C$. The response time to i-${C_4}H_{10}$ and CO gases showed rise time of about 10 seconds and fall time of about $3{\sim}4$ minutes. The selectivity to i-${C_4}H_{10}$ and CO gases was enhanced in the ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film.

• 한국토양비료학회지
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• 제45권1호
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• pp.30-36
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• 2012

The active fraction of soil organic matter, which includes organic debris and light organic fraction, plays a major role in nutrient cycling. In addition, particulate organic matter is a valuable index of labile soil organic matter and can reflect differences in various soil behaviors. Since soil organic matter bound to soil mineral particles has its density lower than soil minerals, we partitioned soil organic matter into debris ($<1.5g\;cm^{-3}$), light fraction ($1.5-2.0g\;cm^{-3}$), and heavy fraction ($>2.0g\;cm^{-3}$), based on high density $ZnCl_{2-}$ sucrose solutions. Generally, partitioned organic bands were clearly separated, demonstrating that the $ZnCl_{2-}$ sucrose solutions are useful for such a density gradient centrifugation. The available gradient ranges from 1.2 to $2.0g\;cm^{-3}$. Although there was not a statistically meaningful difference in organic debris and organomineral fractions among the examined soils, there was a general trend that a higher content of organic debris resulted in a higher proportion of light organomineral fraction. In addition, high clay content was associated with increased fraction of light organomineals. Partitioning of soil organic carbon revealed that carbon content is reduced in the heavy fraction than in the light fraction, reflecting that the light fraction contains more fresh and abundant carbon than the passive resistant fraction. It was also found that carbon contents in the overall organic matter, debris, light fraction, and heavy fractions may differ considerably in response to different farming practices.

• 대한교통학회지
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• 제19권3호
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• pp.19-32
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• 2001

본 연구에서는 주차정책의 변화에 따른 운전자의 주차행동 변화를 예측하고, 나아가서 주차시설별 주차수요의 예측이 가능한 주차장 선택모형을 개발하기 위하여, 대구광역시 운전자의 선호의식자료를 이용한 다항로짓과 네스티드로짓 주차장 선택모형을 추정하고, 모형에 대한 탄력성분석을 실시하였다. 설명변수로서는 성별 연령 등의 대안특유 사회경제적 변수와 주차장 탐색 및 입고시간, 목적지까지의 도보거리, 주차요금, 불법주차 단속횟수 등의 주차관련 특성변수를 적용하였다. 모형의 추정결과에 의하면, 각 설명변수에 대한 추정 파라메타의 부호는 논리적으로 타당하였으며, 모형의 적합도 역시 양호하게 나타났다. 또한, 주차정책변수의 변화에 대한 모형의 탄력성 분석을 실시한 결과에 의하면, 주차비용의 탄력성이 가장 높았고, 주차시설 접근시간보다 목적지까지의 도보거리의 탄력성이 높은 것으로 나타났다. 이는 주차시설의 입고 편의성보다 주차시설과 목적지간의 근접성이 더욱 중요하다는 것을 의미한다. 따라서, 앞으로의 주차시설은 목적지 주변에 소형주차장을 분산하여 공급할 필요가 있을 것이다. 상기와 같이, 본 연구의 결과는 주차정책 수립을 위한 중요한 기초자료를 제공할 수 있을 것으로 기대된다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.137-137
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• 2003

Conducting PPy/PVA composite and pure PPy gas sensors were prepared by in-situ vaporstate polymerization method in a vaporization chamber under N2 condition, by exposing the pre-coated electrode with PVA/FeC13 to distilled pyrrole monomer. The various electrical sensing behaviors of both types of sensors were systematically investigated by a flow measuring system including mass flow controller (MFC) and bubbling bottle. The FT-Raman spectroscopy of vapor state polymerized PPy was identical to that of chemically polymerized PPy, confirming the same chemical structure. Both types of sensors had positive sensitivity when exposed to methanol gas. The sensitivity varied linearly with gas concentration in the range of 50ppm to 1059ppm. The detection limit of PPy/PVA sensor was believed to be as low as 10ppm. The sensitivity of PPy/PVA composite sensor was higher than that of pure PPy sensor. Both the response time and recovery time of PPy/PVA composite sensors were longer than those of pure PPy sensors. The thickness of the sensing film affected the sensitivity this way that the sensor having thinner film had higher sensitivity, indicating that the resistance of polymer film involved in the sensing behavior was bulk resistance rather than surface resistance. The reproducibility of PPy/PVA composite sensor was excellent during eight on-off cycles by switching between N2 and 3000ppm methanol gas. The sensitivity of PPy/PVA composite sensor was only maintained for two weeks, while the sensitivity of pure PPy sensor was maintained over two months.

• 한국콘텐츠학회논문지
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• 제11권12호
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• pp.182-189
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• 2011

본 연구는 유아용 증강현실 그림책의 사용성을 평가하기 위해 실시되었다. 사용성 평가를 위해 유치원 5세 학급의 유아 17명에게 증강 그림책을 읽게 하고 다음의 세 가지 측면에 대한 관찰과 인터뷰를 진행하였다; 1) 증강현실 그림책 읽기에서 유아의 실행정도, 2) 그림책을 읽는 과정에서 보이는 유아의 반응, 3) 증강 현실 그림책 읽기에 대한 유아의 만족도 연구 결과, 대부분의 유아들은 증강현실 그림책 읽기에서 웹캠과 그림책의 각도와 거리를 적절하게 조절하여 동영상 이미지를 떠오르게 할 수 있었고, 그림책 읽는 과정에서 유아들은 놀라움이나 기쁨을 표현하기, 질문하기, 실망과 좌절감을 표현하는 등의 언어적, 비언어적 행동을 보였다. 유아는 증강현실 그림책에 대한 흥미도와 난이도에 있어서 대체적으로 재미있고 쉽다는 반응을 보였다. 본 연구의 결과는 추후 개발될 증강현실 인터페이스의 개발과 성인-유아의 증강 그림책 읽기에 관한 시사점을 제공할 것으로 기대된다.