• 한국농공학회지
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• 제38권1호
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• pp.79-89
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• 1996

It is expected that the soil hehaviours in the seahed subjected to cyclic wave loads are much different from that on the ground Cyclic shear stresses developed below the ocean bed as a result of a passing wave train may progressively build up pore pressure in certain soils. Such build-up pore pressure may be developed dynamic behaviour such as liquefaction and significant deformation of the seabed. Currently available analytical and testing methods for the seabed subjected to cyclic wave loads are not general. The purpose of the study are to provide a test method in laboratory and to analyse the mechanism of wave-induced stresses and liquefactions potentials of the unsaturated silty marine sand. It is showed that the test set-up made especially for this study delivers exactly oscillatory wave pressures of the form of sine function. Laboratory test results defining the cyclic shear strength of the unsaturated porous medium that is homogenously sedimented. It is understood that the pore water pressure due to induced-waves is not accumulated as the wave number increases but reveals periodical change on the still water surface. The magnitude of the pore water pressure tends to be attenuated radically with a certain time lag under the action of both high and low waves as depth increases.

• Nuclear Engineering and Technology
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• 제45권1호
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• pp.89-98
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• 2013

In recent years steel-concrete composite shear walls have been widely used in enormous high-rise buildings. Due to high strength and ductility, enhanced stiffness, stable cycle characteristics and large energy absorption, such walls can be adopted in the auxiliary building; surrounding the reactor containment structure of nuclear power plants to resist lateral forces induced by heavy winds and severe earthquakes. This paper demonstrates a set of nonlinear numerical studies on I-shaped composite steel-concrete shear walls of the nuclear power plants subjected to reverse cyclic loading. A three-dimensional finite element model is developed using ABAQUS by emphasizing on constitutive material modeling and element type to represent the real physical behavior of complex shear wall structures. The analysis escalates with parametric variation in steel thickness sandwiching the stipulated amount of concrete panels. Modeling details of structural components, contact conditions between steel and concrete, associated boundary conditions and constitutive relationships for the cyclic loading are explained. Later, the load versus displacement curves, peak load and ultimate strength values, hysteretic characteristics and deflection profiles are verified with experimental data. The convergence of the numerical outcomes has been discussed to conclude the remarks.

• Earthquakes and Structures
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• 제16권5호
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• pp.533-546
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• 2019

This study presents an experimental investigation on six beam-column joint specimens under the lateral cyclic loading. The aim was to explore the effectiveness of steel fiber-reinforced concrete (SFRC) in reducing the transverse shear stirrups in beam-column joints of the reinforced concrete (RC) frames with strong-columns and weak-beams. Two RC and four SFRC specimens with different types of reinforcement detailing and steel fibers of volume fraction in the range of 0.75-1.5% were tested under gradually increasing cyclic displacements. The main parameters investigated were lateral load-resisting capacity, hysteresis response, energy dissipation capacity, stiffness degradation, viscous damping variation, and mode of failure. Test results showed that the diagonally bent configuration of beam longitudinal bars in the beam-column joints resulted in the shear failure at the joint region against the flexural failure of beams having straight bar configurations. However, all SFRC specimens exhibited similar lateral strength, energy dissipation potential and mode of failure even in the absence of transverse steel in the beam-column joints. Finally, a methodology has been proposed to compute the shear strength of SFRC beam-column joints under the lateral loading condition.

• Journal of Astronomy and Space Sciences
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• 제31권2호
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• pp.145-148
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• 2014

There was a research on the prolongation of solar cycle 23 by the solar cyclic variation of solar, interplanetary geomagnetic parameters by Oh & Kim (2013). They also suggested that the sunspot number cannot typically explain the variation of total solar irradiance any more. Instead of the sunspot number, a new index is introduced to explain the degree of solar activity. We have analyzed the frequency of sunspot appearance, the length of solar cycle, and the rise time to a solar maximum as the characteristics of solar cycle. Then, we have examined the predictability of solar activity by the characteristics of preceding solar cycle. We have also investigated the hemispheric variation of flare index for the periods that the leading sunspot has the same magnetic polarity. As a result, it was found that there was a good correlation between the length of preceding solar cycle and spotless days. When the length of preceding solar cycle gets longer, the spotless days increase. It is also shown that the shorter rise time to a solar maximum is highly correlated with the increase of sunspots at a solar maximum. Therefore, the appearance frequency of spotless days and the length of solar cycle are more significant than the general sunspot number as an index of declining solar activity. Additionally, the activity of flares leads in the northern hemisphere and is stronger in the hemisphere with leading sunspots in positive polarity than in the hemisphere with leading sunspots in negative polarity. This result suggests that it is necessary to analyze the magnetic polarity's effect on the flares and to interpret the period from the solar maximum to solar maximum as the definition of solar cycle.

• 한국자동차공학회논문집
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• 제17권1호
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• pp.87-95
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• 2009

EGR(Exhaust gas recirculation) provides an important contribution in achieving the development targets of low fuel consumption and low exhaust emission levels on gasoline engine for hybrid vehicles while allowing stoichiometric fuelling to be retained for applications using the three-way catalysts. However, the occurrence of excessive cyclic variation with high EGR normally prevents substantial fuel economy improvements from being achieved in practice. Therefore, the optimum EGR rate in gasoline engine for hybrid vehicles should be carefully determined in order to achieve low fuel consumption and low exhaust emission. In this study, 2 liters gasoline engine with E-EGR system was used to investigate the effects of EGR with optimum EGR rate on fuel economy, combustion stability, engine performance and exhaust emissions. As the engine load becomes higher, the optimum EGR rate tends to increase. The increase in engine load and reduction in engine speed make the fuel consumption better. The fuel consumption was improved by maximum 5.5% at low speed, high load operating condition. As the simulated EGR variation on a cylinder is increased, due to the increase in cyclic variation, the fuel consumption and emissions characteristics were deteriorated simultaneously. To achieve combustion stability without a penalty in fuel consumption and emissions, the cylinder-to-cylinder variations must be maintained under 10%.

• 한국음향학회지
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• 제36권5호
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• pp.361-369
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• 2017

뇌혈관 질환의 발생 및 진행 기작을 이해하고 그 질환의 조기진단과 진행예측을 위해서는 경동맥 분지에서의 혈류역학 정보가 매우 중요하다. 본 논문에서는 정상인 경동맥 분지 탄성 모형 혈관과 생체 외 돼지혈액을 이용하여 모의박동 혈액 순환 시스템을 구축하여 혈류를 조절하면서 혈관과 혈액의 초음파 영상을 내부 압력과 시간 동기화하여 측정하였다. 박동 펌프의 박동률이 분당 20회, 40회, 60회(r/min)일 때의 초음파 영상의 에코 값, 혈류속도, 혈관 벽의 움직임, 혈압을 펌프의 5주기 동안 평균하여 한 주기의 데이터를 추출하였다. 결과로 박동률이 20 r/min, 40 r/min, 60 r/min일때 수축기 최고 혈류 속도는 각각 20 cm/s, 25 cm/s, 40 cm/s, 혈압 차는 각각 30 mmHg, 70 mmHg, 85 mmHg, 동맥벽은 각각 0.05 mm, 0.15 mm, 0.25 mm로 확장 하였다. 에코의 주기적 변화는 혈류속도와 압력과는 시간 지연이 있었으며 20 r/min에서는 변화량이 최소였다. 이러한 시간 동기화된 인자들의 주기적 변화는 전산혈류역학 실험의 정확한 입력정보와 검증을 위한 중요한 정보이며 경동맥 협착 질환의 발생 및 진행 기작을 밝히는데도 유용한 정보를 제공할 것이다.

• Journal of the Korean Wood Science and Technology
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• 제43권5호
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• pp.539-547
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• 2015

To investigate dimensional responses of wood under dynamic temperature condition, poplar (populous euramericana Cv.) specimens, 20 mm in radial (R) and tangential (T) directions with two thicknesses of 4 and 10 mm along the grain, were exposed to cyclic temperature changes in square wave between $25^{\circ}C$ and $40^{\circ}C$ at 60% relative humidity (RH) for three different cycling periods of 6 h, 12 h and 24 h. R and T dimensional changes measured during the cycling gave the following results: 1) Transverse dimensional changes of the specimens were generally square but at an opposite phase and lagged behind the imposed temperature changes. The phase lag was inversely correlated with cycling period, but positively related to specimen thickness, while the response amplitude was directly proportional to cycling period, but in a negative correlation with specimen thickness. 2) The specimens showed swelling hysteresis behavior. The heat shrinkage coefficient (HSC) became greater as cycling period increased or specimen thickness decreased. 3) Dimensional changes of the specimens produced deformation accumulation during repeated adsorption and desorption. The deformation accumulating ratio decreased with an increase in cycling period and specimen thickness. 4) Wood suffered 1.5 times as many dimensional changes per unit temperature variation as per unit humidity variation, and this deformation behaved even more seriously under static condition.

• 열처리공학회지
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• 제4권3호
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• pp.31-38
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• 1991

Effect of thermal cycling on shape memory effect and stabilization of austenite was investigated in Fe-21%Mn alloy. The thermal cyclic treatment was carried out with two types, room temperature${\leftrightarrow}215^{\circ}C$ and room temperature${\leftrightarrow}260^{\circ}C$. In case of the room temperature${\leftrightarrow}215^{\circ}C$, the SME was rapidly increased up to 3 cycles and maintained nearly constant value regardless of further cycles. In case of the room temperature${\leftrightarrow}260^{\circ}C$, however, the SME was increased with increasing the thermal cycle up to 5 cycles and decreased gradually with further cycle. The variation of the ${\varepsilon}$ martensite volume pet with the thermal cycle was in good agreement with the variation of the SME. Therefore, the change of the SME due to the cyclic treatment was explained with the change of the ${\varepsilon}$ martensite content. As the thermal cycle was increased, the $M_s$ temperature was decreased, and the $A_s$ and $A_f$ temperatures were increased, respectively.

• 멤브레인
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• 제21권1호
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• pp.13-21
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• 2011

본 연구는 폴리에틸렌 정밀여과 막을 이용한 $Al_2O_3$ 콜로이드 현탁액의 운전압력 순환변화에 따른 투과거동을 검토하였다. 운전압력의 순환은 0.49에서 1.96 bar까지 증가시키는 증압운전 후 다시 0.49 bar로 감소시키는 감압운전으로 행하였다. 연속적으로 운전압력을 순환변화 시킨 결과, 증압운전과 감압운전의 투과유속이 서로 다른 이력(hysteresis)을 나타냈다. 현탁액의 투과저항은 감압운전의 경우가 증압운전의 경우보다 컸으며, 투과저항 증가율도 컸다. 막오염 형태는 증압운전과 감압운전 모두 운전초기에 케익오염이 강하게 나타났으며, 막오염의 크기는 감압운전의 오염이 증압운전의 오염보다 컸다.

• 전기전자학회논문지
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• 제27권3호
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• pp.234-238
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• 2023

본 논문에서는 PVT(process, voltage, and temperature) 변화에 대한 보상기능을 가지는 시간-디지털 변환기(time-to-digital converter : TDC)를 제안한다. 일반적인 지연 라인(delay line) 기반의 TDC는 인버터의 전파 지연을 기반으로 시간을 측정하기 때문에 근본적으로 PVT 변화에 민감하다. 이 논문은 PVT 변화에 의한 전파 지연을 보상하여 TDC의 해상도 변화를 최소화시키는 방법을 제안한다. 또한 넓은 입력 측정 범위(detection range)를 갖기 위해 Cyclic Vernier TDC (CVTDC) 구조를 채택한다. 제안하는 PVT보상 기능의 CVTDC는 45nm CMOS 공정으로 설계되어, 8mW의 전력을 소모하며, 5 ps의 TDC 해상도 및 약 5.1 ns 입력 측정 범위를 갖는다.