• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1126-1129
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• 2004

Because of the various length condition of carbon nanotube, it is very confined the application area of the single CNT tip. In this paper, it was proposed the cutting technique of single CNT tip and the relationship between the etched volume and the amount of the applied charge. It is possible to control the length of single CNT tip arbitrary using this technique. The etched volume and length in the single CNT tip can be predicted with the amount of the applied charge. It is very easy to make a single CNT tip with proper length using this technique and to make nanotweezer that was composed two single CNT tips.

• 콘크리트학회논문집
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• 제19권6호
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• pp.803-810
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• 2007

FRP 합성재료로 구속된 콘크리트의 응력-변형률 응답을 합리적으로 예측할 수 있는 해석 모델이 제시되었다. 제안된 모델은 하중이 증가함에 따라 점진적으로 발생하는 미세균열에 의한 부피팽창이 미세 재료 구조의 손상을 나타내는 중요한 척도이며, 이에 손상 정도에 따라 하중 지지 능력을 일관되게 산정할 수 있다는 기본 개념에 근거한다. 이를 위하여 제안 모델은 면적 변형률 및 공극의 함수로 표시된 탄성계수, 팽창 콘크리트와 구속 매체의 상호작용을 나타내는 에너지 평형식, 변화하는 구속력 및 점증 계산 논리를 포함한다. 따라서 실험으로부터 유도된 팽창비 관계식으로부터 횡방향 혹은 부피팽창변형률을 산정하는 기존의 해석 모델과는 달리 역학적 거동 및 에너지 평형식으로부터 연속적으로 변화하는 횡방향 변형률을 산정한다. 구속된 콘크리트의 전체 응답을 예측할 수 있는 기존의 여러 해석 모델에 대하여 검토하였으며, 특히 부피 팽창을 고려하는 방법에 초점을 맞추어 토의하였다. 제안된 모델 및 기존 Samaan의 2선식 모델을 사용하여 실험 결과를 예측한 결과, 만족할 만한 범위 내에서 일치를 나타냈으나, Samaan의 2선식 모델은 부피 팽창 거동을 위하여 단지 초기 포아송비와 최종 수렴 팽창변화율 만을 고려하기 때문에 횡방향 변형률 응답을 예측하는 데는 한계가 있는 것으로 판단된다. 제안된 모델은 역학적 거동에 근거하여 다양한 관련 응답을 산정하므로 다른 분야에도 쉽게 적용할 수 있다.

• 한국강구조학회 논문집
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• 제22권2호
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• pp.139-150
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• 2010

기둥은 하중 상태에 따라서 축하중과 횡하중 등에 영향을 받는 주부재로서 많이 사용되어지고 있다. 일반적으로 철근 콘크리트(Reinforced Concrete Column, R.C. Column)이 가장 많이 설계 및 시공되고 있으며, 그 밖에도 콘크리트 충전 강관(.Concrete Filled Tube, CFT) 기둥과 같은 복합재료의 기둥이 최근 현장에 많이 적용되어 건설이 진행되고 있는 실정이다. 철근 콘크리트 기둥의 자중의 감소와 사용 재료의 절감을 위하여, 기존의 기둥에 중공부를 두는 중공 R.C 기둥이 사용되고 있다. 중공 RC의 경우 동일 단면적을 갖는 일반 R.C기둥에 비하여 큰 단면이차모멘트를 갖게 되므로 더 효율적인 단면 활용이 가능하다. 그러나 위와 같은 장점이 있는 것과는 반대로, 중공 R.C 기둥은 내측면의 취성파괴로 인하여 낮은 연성 거동을 할 가능성이 높다. 이러한 내측면의 취성 파괴는 기둥 외측면의 경우 횡철근에 의해 구속되어 있으나, 내측면의 콘크리트에는 구속력이 작용하지 않는다. 이러한 단점을 극복하기 위하여 중공면에 구속력을 작용시켜, 콘크리트를 3축 구속 상태로 만들어 주어야 한다. 이를 해결하기 위해서 중공 R.C. 기둥 중공부에 강관을 삽입함으로서 중공 기둥 내의 콘크리트를 3축 구속 상태로 만들어주는 내부 구속 중공 R.C 기둥(Internally Concfined Hollow Reinforced Concrete, ICH R.C)이 기존연구자에 의해서 제시되어졌다.(Kang & Han, 2005) 본 연구에서는 ICH RC 기둥의 열전달 해석 및 비선형 재료모델 프로그램을 이용하여 내화 성능을 분석하였으며, 중공비, 피복콘크리트의 두께, 내부강관의 두께를 변수로 선정하여 매개변수를 수행함으로서 내부 구속 중공 RC 기둥의 내화 성능을 증가 시켜주는 인자를 찾아내고 분석하였다.

• 한국산업보건학회지
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• 제7권2호
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• pp.181-195
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• 1997

The purpose of this study was to investigate factors affecting the composition and concentrations of fumes generated from various types of welding processes. The results are as follows. 1. Iron(Fe), zinc(Zn) and manganese(Mn) were predominant in Welding fumes. The Fe content in total fumes was 25.5% in coated electrode and 28.2% in $CO_2$ are welding, and the Zn content was 4.5% and 9.1%, respectively, and the Mn was 3.6% and 7.8%, respectively. 2. It was found that the important factors determining composition and concentration of fumes were type of industries, type of welding processes, type and composition of electrodes, composition of base metals, confinement of workplaces or condition of ventilation, work intensity, coated metals such as lead and Zn in paint. 3. The Mn content in airborne fumes was highly correlated with that of electrode(r=0.77, p<0.01) and was about 4 times higher than that in electrodes or base metals. The results lindicate that Mn is well evaporated into air during welding. The higher vapor pressure of Mn may explain this phenomenon. 4. the airborne total fume concentrations were significantly different among types of industries(p<0.001). The airborne total fume concentration was higher in order of sleel-structure manufacturing($GM=15.1mg/m^3$), shipbuilding($GM=13.2mg/m^3$), automobile-component manufacturing ($GM=7.8mg/m^3$) and automobile assembling industry($GM=3.0mg/m^3$) 5. The airbone total fume concentration was 6 times higher in $CO_2$ welding than in coated electrode welding, and approximately 3 times higher in confined area than in open area, in steel-structure manufacturing industry. 6. The concentration of welding fume outside welding helmet was about 2 times higher than that inside it. It is recommened that air sampling be done inside helmet to evaulate worker's exposure accurately, for it has an outstanding effect on reducing worker exposure to fumes and other contaminants.

• Structural Engineering and Mechanics
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• 제65권6호
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• pp.679-687
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• 2018

In composite materials technology, the fiber-reinforced polymers (FRP) have opened up new horizons in infrastructural engineering field for strengthening existing structures and components of structure. The Carbon fiber reinforced polymer (CFRP) sheets are well suited for RC columns to this application because of their high strength to weight ratio, good fatigue properties and excellent resistance to corrosion. The main focus of present experimental work is to investigate effect of shapes on axial behavior of CFRP wrapped RC columns having same cross-sectional area and slenderness ratio. The CFRP volumetric ratio and percentage of steel are also adopted constant for all the test specimens. A total of 18 RC columns with slenderness ratio four were cast. Nine columns were control and the rest of nine columns were strengthened with one layer of CFRP wrap having 35 mm of corner radius. Columns confined with CFRP wrap were designed using IS: 456:2000 and ACI 440.2R.08 provisions. All the test specimens were loaded for axial compression up to failure and failure pattern for each shaped column was investigated. All the experimental results were compared with analytical values calculated as per the ACI-440.2R-08 code. The test results clearly demonstrated that the axial behavior of CFRP confined RC columns is affected with the change in shapes. The axial deformation is higher in CFRP wrapped RC circular column as compared to square and rectangular columns. Stress-strain behaviour revealed that the yield strength gained from CFRP confinement was significant for circular columns as compare to square and rectangular columns. This behaviour may be credited due to effect of shape on lateral deformation in case of CFRP wrapped circular columns at effective confinement action.

• Structural Engineering and Mechanics
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• 제74권3호
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• pp.395-406
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• 2020

Many prefabricated concrete frame joints have been proposed, and most of them showed good seismic performance. However, there are still some limitations in the proposed fabricated joints. For example, for prefabricated prestressed concrete joints, prefabricated beams and prefabricated columns are assembled as a whole by the pre-stressed steel bar and steel strand in the beams, which brings some troubles to the construction, and the reinforcement in the core area of the joints is complex, and the mechanical mechanism is not clear. Based on the current research results, a new type of fabricated joint of prestressed concrete beams and confined concrete columns is proposed. To study the seismic performance of the joint, the quasi-static test is carried out. The test results show that the nodes exhibit good ductility and energy dissipation. According to the experimental fitting method and the "fixed point pointing" law, the resilience model of this kind of nodes is established, and compared with the experimental results, the two agree well, which can provides a certain reference for elasto-plastic seismic response analysis of this type of structure. Besides, based on the analysis of the factors affecting the shear capacity of the node core area, the formula of shear capacity of the core area of the node is proposed, and the theoretical values of the formula are consistent with the experimental value.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.763-768
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• 2001

The purpose of this study is to research a specific material characteristics of top down concrete at column joint and to reduce column joint opening. Based on the established top down study, the experiment to apply an real construction case is performed. When the concrete placed into joint of top down column, raised air bubble is left as opening. This study is examined the incomplete packing reason in the top down column and found to air deflation method. The result of study is below (1) As the method to minimize column opening caused from confined air, it is required that an air exhaust port installation in joint column. (2) From air exhaust port installation, most of air bubble in column part is exhausted. As the concrete placing height is going up, air bubble size is going smaller.

• Journal of Biosystems Engineering
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• 제29권2호
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• pp.175-186
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• 2004

The study was designed to forecast and derive future core technologies using Delphi method in Korea agriculture. The technologies will make agriculture for core and strategic industry that has high value-added in 21 century. Questions were given to specialists by each technology in order to survey importance, realization time, level of R＆D in Korea and foremost country, leading group of R＆D, effective policy, etc. for each technology. The target of the survey for Delphi is confined specialists in the area of Bioystems Engineering. 55 core technologies were derived and 31 specialists answered the survey.

• Interaction and multiscale mechanics
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• 제1권4호
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• pp.411-422
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• 2008

Atomistic simulation of nanoindentation with spherical indenters was carried out to study dislocation structures, mean contact pressure, and nanohardness of Au and Al thin films. Slip vectors and atomic stresses were used to characterize the dislocation processes. Two different characteristics were found in the induced dislocation structures: wide-spread slip activities in Al, and confined and intact structures in Au. For both samples, the mean contact pressure varied significantly during the early stages of indentation but reached a steady value soon after the first apparent load drop. This indicates that the nanohardness of Al and Au is not affected by the indentation depth for spherical indenters, even at the atomistic scale.

• 대한수의학회지
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• 제10권1호
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• pp.33-38
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• 1970

1. Hepatic ascariasis represented by milk spots on the liver surface was found in 475(31.7%) out of 1,500 pigs. 2. For histopathological studies, 170 cases were collected at random from the milk spotted liver From these cases ascaris larva was found in 14 cases(8.2%). 3. Grossly, the occurrence of milk spots was not confined to any particular lobes of the liver. The lesions, however, were more frequently found in the diaphragmatic surface than in the visceral surface. The extent of the spots was limited to the subcapsular region and the deeper tissue was not affected. 4. Histologically, hemorrhage and eosinophilic infiltration were observed in the area invaded by the larva. The increase of connective tissue followed by a form of chronic lymphocytic hepatitis was observed at the late stage of infection. There was numerous eosinophilic infiltration around the larva trapped in the liver tissue. Consequently, encapsulation of the larva was followed by organization and calcification.