• 대한기계학회논문집A
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• 제34권10호
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• pp.1437-1442
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• 2010

슬리퍼 메탈은 열간 압연 공정의 동력전달 부품이다. 슬리퍼 메탈은 스핀들과 커플링을 연결한다. 그러므로 슬리퍼 메탈이 심각하게 손상되면 스핀들과 커플링은 서로 충돌할 것이다. 슬리퍼 메탈의 파손을 방지하는 것은 기계적 수명을 연장하는 필수적인 요소이다. 본 연구에서는 슬리퍼 메탈의 수명 연장을 위하여 유한요소법을 사용하여 구조해석 및 형상 설계를 수행하였다. 수정된 슬리퍼 메탈과 스핀들 조립의 간섭을 검증하기 위해 다양한 체결 타입과 동적 경계 조건을 적용하여 동적 시뮬레이션을 수행하였다. 슬리퍼 메탈의 구조 해석과 형상 설계의 결과로써 수정된 슬리퍼 메탈의 최대응력은 초기 모델과 비교하여 22 % 감소하였다.

• 한국농공학회지
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• 제32권4호
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• pp.71-80
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• 1990

Model tests for the ultimate pullout resistance of anchorages and investigation of failure behaviors in cohesionless soil have been conducted. The factors affecting the anchorage are mostly the geometry of the system, and soil properties of sands. The main conclusions of the experimental work were as follows. 1. The load - displacement relationship can be a form of parabolic curve for all plates. 2. The change in ultimate pullout resistance of anchor is mostly affected by embedment ratio and size of anchor, and influenced to a lesser degree by its shape. 3. Critical embedment ratio which is defined as the failure mode changes from shallow to deep mode is increased with increasing height of anchor. 4. For a constant anchor height, as the width of anchor increases the ultimate pullout resistance also increases. However, considering the efficiency of anchor for unit area, width of anchor does not appear to have any sigrnificant contribution on increasing anchor city. 5. Anchor capacity has a linear relation to sand density for any given section and the rate of change increases as the section increases. Critical depth determining the failure patterns of anchor is decreased with a decrease of sand density. 6. With increasing inclination angle, size of anchor, and decreasing embedment ratio, the ultimate pullout resistance of anchor under inclined loading is significantly decreased. 7. The ultimate pullout resistance of double anchor, a method of improving single of anchor capacity, is influenced by the center - to - center spacing adjacent anchors. It is also found that tandem and parallel anchor rigging arrangements decrease the anchor system capacity to less than twice the single anchor capacity due to anchor interference.

• Reproductive and Developmental Biology
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• 제38권3호
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• pp.99-105
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• 2014

In this study, to further understand the mechanism of animal growth and to develop a miniature transgenic animal model, we constructed and tested tetracycline-inducible RNAi system using shRNA targeting the mRNA of mouse insulin-like growth factor (mIGF-1) or mouse growth hormone receptor (mGHR) gene. Quantitative real-time PCR analysis of mouse liver cell (Hepa1c1c7) cells transfected with these vectors showed 85% or 90% of expression inhibition effect of IGF-1 or GHR, respectively. In ELISA analysis, the protein level of IGF-1 in the cells expressing the shRNA targeting IGF-1 mRNA was reduced to 26% of non-transformed control cells. Unexpectedly, in case of using shRNA targeting GHR, the IGF-1 protein level was decreased to 75% of control cells. Further experiments are needed to explain the lower interference effect of GHR shRNA in IGF-1 protein. Accumulated knowledge of this approach could be applicable to a variety of related biological area including gene function study, gene therapy, development of miniature animals, etc.

• International Journal of Aeronautical and Space Sciences
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• 제18권4호
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• pp.797-806
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• 2017

In this study, the reflection coefficient (RC) and the flame transfer function (FTF) were measured by applying acoustic excitation to a duct-type model combustor and were used to predict the frequency of the combustion instability (CI). The RC is a value that varies with the excitation frequency and the geometry of the combustor as well as other factors. Therefore, in this study, an experimentally measured RC was used to improve the accuracy of prediction in the cases of 25% and 75% hydrogen in a mixture of hydrogen and methane as a fuel. When the measured RCs were used, an unstable condition was correctly predicted, which had not been predicted when the RCs had been assumed to be a certain value. The reason why the CI occurred at a specific frequency was also examined by comparing the peak of the FTF with the resonance frequency, which was calculated using Helmholtz's resonator analysis and a resonance frequency equation. As the CI occurred owing to the interaction between the perturbation in the rate of heat release and that in the pressure, the CI was frequent when the peak of the FTF was close to the resonance frequency such that constructive interference could occur.

• 한국위성정보통신학회논문지
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• 제2권2호
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• pp.1-9
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• 2007

본 논문은 고속철도 채널환경에서의 위성을 통한 Satellite Wibro 시스템의 성능열화특성과 이에 따른 보상기법에 대해 서술하였다. 고속철도 채널환경은 LOS채널 과 터널환경으로 구분되고 LOS 환경에서는 고속철도 파워 급전선에 의한 신호블로킹에 의한 문제와 터널내 에서는 Optic Fiber내에서와 같은 다중경로 간섭문제가 발생한다. 이러한 전형적인 두 채널 공간에서의 위성 와이브로 시스템 성능열화 특성을 해석적으로 규명하고 컴퓨터 시뮬레이션을 통하여 확인 하였다. 아울러 300 km/h 이상으로 이동하는 고속철도에서 발생되는 OFDM 시스템의 도플러 효과에 의한 ICI 현상과 이를 보상할 수 있는 기법을 해석적, 실험적 결과를 통하여 증명하였다.

• 한국항해항만학회지
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• 제31권6호
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• pp.485-490
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• 2007

부표시스템 침수체의 주요형상인 실린더에 원형 제어봉을 부착하여 2차원 단면의 유동특성에 대해서 수치해석을 수행하였다. 유속을 0.1m/s에서 0.5m/s로 변화시키면서 부표시스템 주위의 유동현상을 파악하고, 부표시스템의 효과적인 유동제어를 위해 실린더 (D=50mm)에 제어봉의 직경을 0.1D 에서 0.5D까지 부착하여 조류에 의한 압력분포를 조사하였다. 유동장내의 속도분포는 PIV 계측기법 중 2프레림 입자추적 법을 사용하여 수치해석의 정도를 높이고자 0.3m/s에서 비교 평가하였다. 실린더 주위의 압력분포는 0.2D의 제어봉을 부착하였을 경우, 유속의 변화에 관계없이 가장 양호한 경향을 보이는 것을 알 수 있었다.

• 전자공학회논문지
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• 제51권10호
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• pp.3-10
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• 2014

본 논문에서는 인지 기반 중첩 융합 네트워크 환경 하에서의 사용자의 위치정보를 토대로 사용자 단말기의 전력소모감소와 간섭신호의 저감효과를 극대화하기 위한 기본적인 D2D(device-to-device)시스템을 제시하고 무선 전송 환경에서의 시스템 성능을 분석하고자 한다. 단말기의 기능성이 좋아짐에 따라 스마트한 지능을 기반으로 자원의 효과적 활용에 적합한 개별 이종 네트워크의 특성분석과 특성을 반영하는 시스템 측면의 최적화가 중요하다고 할 수 있다. 본 논문에서는 사용자 이동특성에 기반하여 인접 단말기와의 직접 통신하는 절차를 구성하여 단말기 간 직접 통신에 다중안테나 기술을 적용할 경우 이에 따른 FER(frame error rate) 등의 성능특성을 살펴보고자 한다.

• Journal of Ecology and Environment
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• 제29권2호
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• pp.113-124
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• 2006

Landscape structure, habitat types, vegetation structure and biodiversity in the Bokha stream chosen as a reference stream were investigated to get ecological information necessary for restoration of urban stream degraded by excessive artificial interference. Landscape structure showed a slight change between before and after flooding. Habitat types of nine sorts were identified based on ecological information obtained from field survey such as micro-topography, hydrological characteristics, disturbance regime, and so on. Each habitat holds specific organisms to each site. Consequently, the number of plant communities, and species of benthos and fish increased as the kinds of habitat type increase. Ordination of habitat types based on vegetation, benthos, and fish data reorganized them into three groups of pool types of two kinds depending on whether they are connected to the water course or not and riffle one. Vegetation showed different stratification and species composition depending on topographical position in relation to disturbance cycle. Based on the results from this study, relationship between environmental heterogeneity and biodiversity was discussed and a restoration plan was suggested in a viewpoint of vegetation.

• Journal of Advanced Marine Engineering and Technology
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• 제32권1호
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• pp.82-93
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• 2008

The flowfield behind two cylinders and flow-induced noise generated from the cylinders in various arrangement are numerically investigated based on the finite difference lattice Boltzmann model with 21 velocity bits. which is introduced a flexible specific heat ${\gamma}$ to simulate diatomic gases like air. In an isolated cylinder with two type of mesh. some flow parameters such as Strouhal number $S_t$ and acoustic pressure ${\Delta}p$ simulated from the solution are given and quantitatively compared with those provided the previous works. The effects of the center-to-center pitch ratio $L_{cc}/d=2.0$ in staggered circular cylinders as shown in Fig. 1 and angles of incidence ${\alpha}=30^{\circ}(T_{cc}/d=0.5)$, $45^{\circ}(T_{cc}/d =0.707)$ and $60^{\circ}\;(T_{cc}/d=0.866)$, respectively, are studied. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in staggered arrangement. With the results of drag $C_d$ and lift $C_l$ coefficients and vorticity contours. the mechanisms of the interference phenomenon and its interaction with the two-dimensional vortical structures are present in the flowfields under $Re\;{\le}\;200$. The results show that we successively capture very small pressure fluctuations, with the same frequency of vortex shedding, much smaller than the whole pressure fluctuation around pairs of circular cylinders. The upstream cylinder behaves like an isolated single cylinder, while the downstream one experiences wake-induced flutter. It is expected that, therefore, the relative position of the downstream cylinder has significant effects on the flow-induce noise, hydrodynamic force and vortex shedding characteristics of the cylinders.

• 대한공간정보학회지
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• 제13권3호
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• pp.53-57
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• 2005

환경의 변화에 민감하여 인위적 간섭에 매우 취약한 생태계가 바로 습지이다. 이 자연자산은 인간생활에 매우 중요하다. 따라서 습지의 보전과 관리대책 마련이 필요하다. 습지 분포지역의 명확한 위치정보를 수록하고 있는 수치지도를 활용한 습지의 공간 DB를 구축하고 정보를 공유하며 지리정보시스템(GIS)를 이용한 체계적인 시스템 관리가 필요하다. 본 연구에서는 산지습원에 대한 통합 DB로서 습지관리의 기초자료를 구축하는 것을 우선하였다. 기준점 측량방식을 이용하여 정확한 위치를 규정하였고 습지분포 수치지도를 표준화하였다. 특히, 친환경 건설계획 수립 시 GIS를 활용하여 중요한 자연자산인 습지를 보존하는데 주안점을 두었다. 현재 환경부에서 지정하고 있는 보존습지의 구성인자 지형, 지질, 동 식물상 분포를 분석하여 GIS를 적용함으로써 발견되지 않은 습지 분포지역을 예측 할 수 있도록 모델을 제시하였다.