• Water Engineering Research
• /
• 제5권4호
• /
• pp.195-206
• /
• 2004

This paper deals with oxygen transfer by air entrainment and energy dissipations by flow characteristics at the stepped drop structure. Nappe flow occurred at low flow rates and for relatively large step height. Dominant flow features included an air pocket, a free-falling nappe impact and a subsequent hydraulic jump on the downstream step. Most energy was dissipated by nappe impact and in the downstream hydraulic jump. Skimming flow occurred at larger flow rates with formation of recirculating vortices between the main flow and the step comers. Oxygen transfer was found to be proportional to the flow velocity, the flow discharge, and the Froude number. It was more related to the flow discharge than to the Froude number. Energy dissipations in both cases of nappe flow and skimming flow were proportional to the step height and were inversely proportional to the overflow depth, and were not proportional to the step slope. The stepped drop structure was found to be efficient for water treatment associated with substantial air entrainment and for energy dissipation.

• Advances in Energy Research
• /
• 제2권2호
• /
• pp.73-84
• /
• 2014

Fuel cells of proton exchange membrane type (PEMFC) working with hydrogen in the anode and ambient air in the cathode ('air breathing') have been prepared and characterized. The cells have been studied with variable thickness of the cathode catalyst layer ($L_{CL}$), maintaining constant the platinum and ionomer loads. Polarization curves and electrochemical active area measurements have been carried out. The polarization curves are analyzed in terms of a model for a flooded passive air breathing cathode. The analysis shows that $L_{CL}$ affects to electrochemical kinetics and mass transport processes inside the electrode, as reflected by two parameters of the polarization curves: the Tafel slope and the internal resistance. The observed decrease in Tafel slope with decreasing $L_{CL}$ shows improvements in the oxygen reduction kinetics which we attribute to changes in the catalyst layer structure. A decrease in the internal resistance with $L_{CL}$ is attributed to lower protonic resistance of thinner catalyst layers, although the observed decrease is lower than expected probably because the electronic conduction starts to be hindered by more hydrophilic character and thicker ionomer film.

• Structural Engineering and Mechanics
• /
• 제53권4호
• /
• pp.725-744
• /
• 2015

In this paper, a new damage indicator based on mode shape data is introduced to identify damage in beam structures. In order to construct the indicator proposed, the mode shape, mode shape slope and mode shape curvature of a beam before and after damage are utilized. Mode shape data of the beam are first obtained here using a finite element modeling and then the slope and curvature of mode shape are evaluated via the central finite difference method. In order to assess the robustness of the proposed indicator, two test examples including a simply supported beam and a two-span beam are considered. Numerical results demonstrate that using the proposed indicator, the location of single and multiple damage cases having different characteristics can be accurately determined. Moreover, the indicator shows a better performance when compared with a well-known indicator found in the literature.

• 한국방재학회:학술대회논문집
• /
• 한국방재학회 2007년도 정기총회 및 학술발표대회
• /
• pp.399-402
• /
• 2007

This project is the 1st. stage for the foreshore reclamation at Jang-Hang area and its scope is to construct a seawall as outer facilities, road adjacent to the seawall and drainage gate. for the safe protections of the facilities at the reclaimed land hereafter, we adopted the mild slope rubble mound type for the seawall structure which was excellent in interrupting the wave overtopping, as a result of numerical & hydraulic model test about alternative 4 sections. For the flooding prevention of the reclaimed land, we planned the drainage system that could make the flood water level lower than the reclaimed land level. Also, we planned the eco-friendly waterfront area with 8 nature themes through the whole seawall sections.

• 자원환경지질
• /
• 제33권6호
• /
• pp.547-556
• /
• 2000

The purpose of this study is to analyze shear fracture system using landslide location occurred 1998 at Janghung area. For the geological implication, foliation was surveyed and analyzed, and location of landslide, geological structure and topography were constructed into spatial database using GIS. With the constructed spatial database, shear fracture system was assessed by the relation analysis between strike and dip of the foliation and aspect and slope of the topography. We compared strike and dip of foliation and aspect and slope of topography and recognized the typical fracture pattern, strike and dip of joint, that coincided with shear fracture system. The result tells us that foliation of gneiss has geometrical relation to joint or fault that leading landslide. GIS was used to analyze vast data efficiently and the result can be used to assess the landslide susceptibility as important factor.

• 한국안전학회지
• /
• 제12권3호
• /
• pp.147-154
• /
• 1997

The main purpose of this study is to investigate the failure surface in a soil mass by a excavation of the model ground. The failure mechanism of an earth structure is usually determined from field failure observations or from laboratory model tests at failure. To study the failure surface for the excavated slope, laboratory model tests were performed by changing the angle of the excavated slope and the ground condition. Results of the laboratory model tests were compared with those obtained with theoretical solutions using limit equilibrium analysis method. The results of model tests show that, there is a failure to create a straight line in the low angle of excavated surface and a create a circle as the angle increases. As the angle of excavated surface is increasing, the angle of the failure surface increases too. In the angle of the failure surface, the submerged ground is less than the dry ground at $3.2^{\circ}$.

• 한국지반공학회논문집
• /
• 제19권6호
• /
• pp.99-106
• /
• 2003

본 연구에서는 장비하중이 고려된 폐기물 매립지 라이닝 시스템의 단면 설계를 위하여 제안된 개별요소법에 근거한 안정해석 기법과 실수형 유전자 알고리즘이 적용된 새로운 최적화 설계기법이 제안되었다. 개별요소법에 근거하여 제안된 해석기법을 장비하중이 적용된 폐기물 매립지의 라이닝 시스템 해석에 적용함으로써, 라이닝 시스템의 구성요소 중의 하나인 덮개 흙의 단면 변화에 따른 영향이 검토되었다. 또한 폐기물 매립 용량을 최대화할 수 있는 매립지라이닝 사면 형상을 결정하기 위하여, 실수형 유전자 알고리즘에 근거한 최적화 과정을 통한 최적설계 예제해석이 수행되었다.

• Transactions on Electrical and Electronic Materials
• /
• 제11권6호
• /
• pp.253-256
• /
• 2010

Different active layer thicknesses for zinc oxide (ZnO) bottom-contact thin-film transistors (TFTs) were fabricated with a poly-4-vinyphenol polymeric dielectric using injector type atomic layer deposition. The properties of the ZnO TFTs were influenced by the active thickness and width-to-length (W/L) ratio of the device. The threshold voltage of ZnO TFTs shifted positively as the active layer thickness decreased, while the subthreshold slope decreased. The W/L ratio of ZnO TFTs also affected the mobility and subthreshold slope. An optimized TFT structure exhibited an on-tooff current ratio of above 106 with solid saturation.

• 한국환경생태학회지
• /
• 제14권1호
• /
• pp.67-79
• /
• 2000

지리산국립공원 동부지역의 해발고와 사면에 따른 식물군집구조를 파악하기 위하여 1999년 7월에 49개의 조사구(20m$\times$15m)를 설치하여 조사하였다 해발고가 올라감에 따라 북사면에 위치한 조사구에서는 구상나무와 신갈나무의 평균상대우점치가 증가하였고 천왕봉 해발 1,700m이상 지역에서는 가문비나무가 우점종이었으며 해발고가 올라갈수록 상대우점치는 증가하였다 반면 남사면에 위치한 조사구에서는 해발고가 올라감에 따라 신갈나무의 평균상대우점치는 감소하였고 구상나무의 평균상대우점치는 증가하였다 해발고에 따른 북사면과 남사면의 종수와 개체수는 북사면에서보다 남사면에서 많았고 입지환경과 종간상관관계에서는 가문비나무 신갈나무, 잣나무가 해발고와 정의 상관관계를 나타냈으며 서어나무는 부의 상관관계를 나타내었다 동일 해발고에서도 사면상 위치에 따라 식물군집구조 및 종구성의 차이를 나타내었다.

• 천문학회보
• /
• 제35권1호
• /
• pp.66.2-66.2
• /
• 2010

We have studied the properties of interstellar turbulence as observed by Boston University-Five College Radio Astronomy Observatory (BU-FCRAO) Galactic Ring Survey (GRS). This observation uses 13CO J=$1{\rightarrow}0$ emission with high spectral resolution of 0.21 kms-1 and covers wide galactic plane regions ($18^{\circ}$ < 1 < $55.7^{\circ}$ and -1 < b < $1^{\circ}$). Firstly, we measured the one dimensional power spectrum of 13CO intensity along the galactic longitude and along the galactic latitude. We found the slope of the power spectrum changes around the molecular ring structure and the center of the galactic plane. Secondly, we explored how the power spectral slope is related with the velocity dispersion of supersonic giant molecular clouds in the GRS. Finally, we suggest the turbulent nature of the interstellar medium is connected with star formation activities in spiral arms.