• 조명전기설비학회논문지
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• 제17권5호
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• pp.51-59
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• 2003

전력회사와 수용가들은 유도성 부하에 무효전력을 공급하여 역률(수용가)이나 전압(전력회사)을 조절하기 위해 커패시터 뱅크(전력회사는 스타콘이라 함)를 설치 운영하고 있다. 본 논문에서는 전력회사의 스타콘 투입시 발생되는 과도 전압 상승과 고조파를 분석하고자 한다. 과도 전압과 고조파를 저감시키는 간단한 수단중의 하나는 수용가의 커패시터 뱅크를 전력회사의 스타콘을 투입한 후에 과도상태가 지난뒤에 투입하는 방법이다. EDSA프로그램으로 컴퓨터 시뮬레이션을 수행하여 수용가에서의 과도 전압 상승과 고조파 저감 효과를 검증 하였다. 그리고 수용가에서 발생하는 고조파를 잘 알려진 국제 고조파 관리 기준인 IEEE 519와 IEC 1000으로 비교해 보았다.

• Structural Engineering and Mechanics
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• 제67권3호
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• pp.255-265
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• 2018

The prestress force effect on the fundamental frequency and deflection shape of Prestressed Concrete I (PCI) beams was studied in this paper. Currently, due to the conflicts among existing theories, the analytical solution for properly considering the structural behavior of these prestressed members is not clear. A series of experiments were conducted on a large-scale PCI beam of high strength concrete with an eccentric straight unbonded tendon. Specifically, the simply supported PCI beam was subjected to free vibration and three-point bending tests with different prestress forces. Subsequently, the experimental data were compared with analytical results based on the Euler-Bernoulli beam theory. It was proved that the fundamental frequency of PCI beams is unaffected by the increasing applied prestress force, if the variation of the initial elastic modulus of concrete with time is considered. Vice versa, the relationship between the deflection shape and prestress force is well described by the magnification factor formula of the compression-softening theory assuming the secant elastic modulus.

• Applied Microscopy
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• 제39권1호
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• pp.73-77
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• 2009

Contaminative artifacts such as carbonaceous materials on carbon-coated microgrids are unavoidable, which is induced by electron beam exposure inside electron microscopes. This phenomenon raise a source to produce confusing information to the samples investigated by analytical TEM, which should be alleviated as much as possible. As experimental precautions for reducing this unwanted effect, the use of $LN_2$ cooled anti-contaminator and pre-illumination of electron beam at low magnification can be helpful. Nevertheless, we should be cautious to set an illumination condition for microanalysis because the contaminative effect is dependent with the types of irradiation situations, which is well known to be a decisive factor for causing the carbonaceous artifacts. Accordingly, it is necessary that optimal illumination to minimize the contaminative effect should be selected for improving the accuracy of microanalysis. In this paper, we introduce the practical method to determine the optimal illumination condition by evaluating the contaminative effect as a function of instrumental spot size, which is directly linked with electron current density.

• 한국철도학회논문집
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• 제8권1호
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• pp.41-50
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• 2005

Steel -Concrete Composite two girder railway bridges applying high performance steel with extra thick plate have economic and aesthetic advantages due to the simplification of manufacturing and construction process. However, steel bridges are seldom adopted in domestic railway bridge, since steel bridges are not efficient as R.C bridges considering dynamic characteristics and noise, etc. While highway bridges do not have lower horizontal bracing and larger interval of diaphragm cross beam, railway bridges install lower horizontal bracings to control the torsion due to heavy eccentrical line load. Accurate finite element analysis were performed with the parameters of existence of bracing and bracing shape, with the cross beam interval and stiffness, etc. To find out the effects of secondary members such as horizontal bracings and diaphragms, static md dynamic analysis have been performed by using finite element method. In this study, few member plate-girder bridges are analyzed with variable span lengths to examine the dynamic behavior and limits of damping. And though lateral bracings are members against torsion, but lateral bracing's absence is no big problem. Time history analysis using mode superposition method makes proof of this result.

• Structural Engineering and Mechanics
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• 제69권1호
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• pp.95-104
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• 2019

The Standard ASCE 61-14 proposes the Substitute Structure Method (SSM) as a Nonlinear Static Procedure (NSP) to estimate nonlinear displacement demands at the center of mass of piers or wharves under seismic actions. To account for bidirectional earthquake excitation according to the Standard, results from independent pushover analyses in each orthogonal direction should be combined using either a 100/30 directional approach or a procedure referred to as the Dynamic Magnification Factor, DMF. The main purpose of this paper is to present an evaluation of these NSPs in relation to four wharf model structures on soil conditions ranging from soft to medium dense clay. Results from nonlinear static analyses were compared against benchmark values of relevant Engineering Design Parameters, EDPs. The latter are defined as the geometric mean demands that are obtained from nonlinear dynamic analyses using a set of 30 two-component ground motion records. It was found that SSM provides close estimates of the benchmark displacement demands at the center of mass of the wharf structures. Furthermore, for the most critical pile connection at a landside corner of the wharf the 100/30 and DMF approaches produced displacement, curvature, and force demands that were reasonably comparable to corresponding benchmark values.

• Structural Engineering and Mechanics
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• 제77권1호
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• pp.1-17
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• 2021

The influence of prestress force on the fundamental frequency and static deflection shape of uncracked Prestressed Concrete (PC) beams with a parabolic bonded tendon was examined in this paper. Due to the conflicts among existing theories, the analytical solutions for properly considering the dynamic and static behavior of these members is not straightforward. A series of experiments were conducted for a total period of approximately 2.5 months on a PC beam made with high strength concrete, subsequently and closely to the 28 days of age of concrete. Specifically, the simply supported PC member was short term subjected to free transverse vibration and three-point bending tests during its early-age. Subsequently, the experimental data were compared with a model that describes the dynamic behavior of PC girders as a combination of two substructures interconnected, i.e., a compressed Euler-Bernoulli beam and a tensioned parabolic cable. It was established that the fundamental frequency of uncracked PC beams with a parabolic bonded tendon is sensitive to the variation of the initial elastic modulus of concrete in the early-age curing. Furthermore, the small variation in experimental frequency with time makes doubtful its use in inverse problem identifications. Conversely, the relationship between prestress force and static deflection shape is well described by the magnification factor formula of the "compression-softening" theory by assuming the variation of the chord elastic modulus of concrete with time.

• Wind and Structures
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• 제25권1호
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• pp.1-24
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• 2017

This paper presents a 1:25 multi-freedom aero-elastic model for a high lighting pole at the Zhoushan stadium. To validate the similarity characteristics of the model, a free vibration test was performed before the formal test. Beat phenomenon was found and eliminated by synthesis of vibration in the X and Y directions, and the damping ratio of the model was identified by the free decay method. The dynamic characteristics of the model were examined and compared with the real structure; the similarity results were favorable. From the test results, the major along-wind dynamic response was the first vibration component. The along-wind wind vibration coefficient was calculated by the China code and Eurocode. When the peak factor equaled 3.5, the coefficient calculated by the China code was close to the experimental result while Eurocode had a slight overestimation of the coefficient. The wind vibration coefficient during typhoon flow was analyzed, and a magnification factor was suggested in typhoon-prone areas. By analyzing the power spectrum of the dynamic cross-wind base shear force, it was found that a second-order vortex-excited resonance existed. The cross-wind response in the test was smaller than Eurocode estimation. The aerodynamic damping ratio was calculated by random decrement technique and the results showed that aerodynamic damping ratios were mostly positive at the design wind speed, which means that the wind-induced galloping phenomenon is predicted not to occur at design wind speeds.

• Ocean and Polar Research
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• 제38권2호
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• pp.139-148
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• 2016

The activity concentrations of $^{210}Po$ and $^{210}Pb$ within phytoplankton-zooplankton-anchovy-mackerel in the coastal water of the Jeju Island were determined to understand their distribution and bio-accumulation along the trophic level. In the surface water, the total activity concentrations of $^{210}Po$ and $^{210}Pb$ were $0.83{\pm}0.004mBq\;kg^{-1}$ and $1.27{\pm}0.03mBq\;kg^{-1}$. And the dissolved activity concentration of $^{210}Po$ and $^{210}Pb$ were $0.75{\pm}0.06mBq\;kg^{-1}$ and $1.22{\pm}0.09mBq\;kg^{-1}$ respectively. In the phytoplankton, the concentration factor (CF) of $^{210}Po$ and $^{210}Pb$ were $1.5{\times}10^5$ and $2.6{\times}10^4$ shows $^{210}Po$ is 5 times higher compared to $^{210}Pb$. The similar CF factor in the zooplankton of $^{210}Po$ was derived as $1.4{\times}10^5$. The CF of $^{210}Po$ in anchovy was increased twice compared to that in plankton. This is the evidence that there is $^{210}Po$ bio-magnification in the trophic level of plankton-anchovy. However the $^{210}Po$ activity concentration in the muscle tissue of mackerel was one-hundred times lower than that in anchovy. This reflects that in the trophic level of anchovy-mackerel, the bio-accumulation of $^{210}Po$ is decreased. The activity concentrations of $^{210}Po$ in the internal organs of anchovy and mackerel were 8 to 38 times higher than those in muscle tissues. In phytoplankton-zooplankton-anchovy, the CF of $^{210}Pb$ was decreased five times along the trophic level in order. In anchovy-mackerel it was decreased by 30-70%.

• 한국지진공학회논문집
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• 제15권3호
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• pp.1-9
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• 2011

자기부상열차가 중 저속 및 초고속 주행 시 차량의 주행특성 및 교량의 동적 응답 결과를 제시하고자 한다. 수직 자유도 및 회전 자유도를 포함한 10자유도 자기부상열차에 대한 운동방정식을 유도하고, 모드 중첩법을 이용하여 교량의 운동방정식을 구성하였다. 또한 제어 방법으로 UTM01제어기법을 적용하여 수치해석을 수행하였다. 해석 예제로 노면조도, 가이드웨이의 처짐비, 차량 속도 등이 교량의 처짐과 차량의 부상공극 및 여러 가지 변수에 미치는 영향을 파악하였다. 부상공극은 조도의 조건에 따라 그 차이가 확연히 드러나고 또한 자기부상열차의 속도가 증가함에 따라 부상공극이 증가함을 알 수 있었다. 그리고 자기부상열차가 중, 저속 주행 시에는 교량에 대한 영향이 미비하지만 초고속 주행 시 교량에 대한 동적확대계수가 큰 값을 보여주었다.

• Journal of Chest Surgery
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• 제36권2호
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• pp.86-90
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• 2003

폐 형성에 활성적인 또는 억제적인 기능을 갖고 있다고 알려져 있는 FGF-7 성장인자, BMP수용체 II, 그리고 TGF-$\beta$ 수용체 II 유전자의 비정상 발현이 폐기포 생성에 관여하는지를 각각의 단일성 클론 항체를 사용하여 수술로 절제된 자연기흉 환자의 폐기포 조직들을 면역조직염색 방법으로 염색하여 관찰하였다. 대상 및 방법: 재발성 또는 지속성 기흉으로 흉강경 또는 개흉술로 폐기포 절제술을 실시한 환자들을 대상으로 하였다. 총 31명의 환자로 15세에서 39세까지 연령분포를 보였으며 남자 30명, 여자 1명이었다. 폐기포 절제는 비디오흉강경이나 소절개개흠술을 통하여 폐기포벽에 손상을 가하지 않게 주의하면서 비디오흉강경용 스태플러(Endo GIA stapler)를 이용하여 절제하였으며 가능한 원형을 유지하여 신선한 상태로 포르마린에 고정하여 면역조직화학적 연구를 위한 표본을 만들었다. 폐기포 조직 슬라이드를 단일클론성 항 TGF-$\beta$ 수용체 II, BMP수용체 II 그리고 FGF-7인자 항체를 이용하여 면역조직학적 염색방법으로 관찰하였다. 결과: 전체 환자 31명중 TGF-$\beta$ 수용체 II항체에 양성 반응을 나타낸 환자수는 모두 24명이었다. 이들 중에는 18명이 강한 양성 반응을 보였고, 6명이 약한 양성 반응을 보였다 면역조직화학적 염색 결과를 고배율 현미경으로 살펴보면, TGF-$\beta$ 수용체 II의 염색이 기흉과 정상 폐조직 경계 부위에서 측히 강하게 염색됨이 관찰되었다. 이에 반하여, BMP수용체 II 그리고 FGF-7인자의 항체를 이용한 면역조직학적 염색 결과는 모든 환자의 조직들에서 음성으로 관찰되었다. 결론: 폐 조직이 형성될 때, 억제유전자의 역할을 담당하고 있다고 알려진 TGF-$\beta$ 수용체 II의 발현이 증가되면서 폐기포가 생성될 수 있다는 가능성을 제시하였다. 이번 결론은 면역조직학적 염색 실험 결과만으로 밝혀진 사실임으로 좀 더 체계적인 분자생물학적 인 연구가 요구된다.