• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2004년도 학술발표회
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• pp.72-76
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• 2004

Wetland is an important eco-system on the earth and can effectively control agricultural non-point source pollution. Reed is a typical wetland plant for land/inland water ecotone in north China. The studies indicated that reed had a underground rooted-stem, which formed a 'high speeded-connecting vessels' i.e. reed root channel (RRC) in Baiyangdian lake of Hebei province. It spread predominantly along horizontal direction underground and are mainly distributed at 18-75 cm. The results of field work from healthy reed-wetland (HRW) and regarded reed-wetland (RRW) showed that the reed, averagely, in HRW is 4.2 m height, 1 cm diameter, 65/m2 density; in RRW is 2.4 m height, 3 mm diameter, 86/m2 density. These results indicated the regradation of the function of RRC in RRW. The results of laboratory work of sewage purification from reed soil column (RSC) $(0\~100cm)$ and wheat soil column (WSC) showed that the efficiency of purification to sewage, in RSC, is high than in WSC, especially for phosphorus. The efficiency of purification, in RSC, is $92.6\%$ for total phosphorus, $43.5\%$ for total nitrogen, $54.1\%$ fur COD, respectively; in WSC, is $86.0\%$ for total phosphorus, $241.3\%$ for total nitrogen, $29.8\%$ for COD, respectively.

• 지질공학
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• 제4권2호
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• pp.187-206
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• 1994

전산모형시험을 통하여 고해상도 해양반사파 탐사를 위한 최적 장비구성과 자료획득변수를 결정하였다. 조사선 온누리호에 탑재된 각기 다른 6종류의 독립 에어건과 1쌍의 cluster에 대하여 시간 및 주파수 영역에서 분석한 원거리장 파형특성은 내부용적 $2.46{\ell}$의 슬리브건 2개로 구성된 cluster를 2m 정도의 깊이에서 발파할 경우에 고해상도 탐사시 적합한 원거리장 파형이 발생될 수 있음을 보인다. 온누리호의 12채널 스트리머는 96채널 스트리머와 비교할 때, 신호대 잡음비가 다소 낮은 문제가 있으나, 높은 수직 및 수평 해상도를 얻을 수 있어 천부 반사파탐사에 적합한 것으로 분석된다. 기타 획득변수는, 대상심도, 주파수범위, 에어건 내부용적, 수신 채널수, 콤프세샤 용량 등 제반요소를 고려할 때, 기록시간 1m, 샘플간격 1ms, 발파간격 3.125m 혹은 6.25m가 적당한 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제51권8호
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• pp.1897-1904
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• 2019

Three-layer back propagation network (BPN) and genetic neural network (GNN) were developed in this study to predict the flow boiling heat transfer coefficient (HTC) in conventional and small-diameter channels. The GNN has higher precision than BPN (with root mean square errors of 17.16% and 20.50%, respectively) and other correlations. The inputs include vapor quality x, mass flux G, heat flux q, diameter D and physical parameter φ, and the predicted flow boiling HTC is set as the outputs. Influences of input parameters on the flow boiling HTC are discussed based on the trained GNN: nucleate boiling promoted by a larger saturated pressure, a larger heat flux and a smaller diameter is dominant in small channels; convective boiling improved by a larger mass flux and a larger vapor quality is more significant in conventional channels. The HTC increases with pressure both in conventional and small channels. The HTC in conventional channels rises when mass flux increases but remains almost unaffected in small channels. A larger heat flux leads to the HTC growth in small channels and an increase of HTC was observed in conventional channels at a higher vapor quality. HTC increases inversely with diameter before dry out.

• 지구물리와물리탐사
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• 제4권2호
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• pp.34-44
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• 2001

종래의 탄성파 모델링은 지표를 수평면으로 가정하고 그 아래쪽에 여러 개의 반사면에 대한 모델링이 대부분 이었다. 그러나, 실제 탐사에서는 복잡한 지형을 가진 지표에서 탐사가 수행되기 때문에 탄성 매질에서의 반응을 명확하게 구분해 내는 것이 힘들다. 지표에 탄성파 전파특성을 규명하기 위하여 모델에 지형을 고려할 수 있도록 하여 시간영역 유한요소법을 이용하여 매질의 반응을 구하였다. 이러한 이러한 알고리즘을 이용하여 지표에서 진원을 가했을 때 수평 및 제방(mound), 채널(channel)등의 구조로부터 지표의 수신기에서 합성 탄성파 기록을 관찰하고, 스냅사진(snapshot)을 얻어냄으로써 해석해와 잘 일치함을 확인하였고, 지표 및 지하 반사면에 의한 복잡한 탄성파의 전파 양상을 파악할 수 있었다. 불규칙 지표면을 따라 전파하는 표면파가 모서리에서 새로운 진원으로 작용하여 큰 잡음이 생성됨을 관찰하였고, 지표를 따라 전파하는 높은 에너지의 레일리파, 상대적으로 낮은 압축파, 전단파 등의 전파 양상으로부터 파의 천이 상태를 관찰할 수 있었다.

• 한국해양학회지
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• 제29권2호
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• pp.95-106
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• 1994

김 등 (1993)에 의해 개발된 3차원 해수유동 수치모델을 사용하여 진해만의 조류 및 취송류를 해석하였다. 만내의 흐름은 주로 지형, 바람 및 하천유출에 의해 지배되 며, 만 입구의 수로보다 내만에서 바람 의 영향을 더 강하게 받는다. 계산된 조류는 현장관측과 잘 일치한다. 조류 및 조석잔차류의 수평 및 연직 유속은 만 입구의 수로 에서는 강하나, 진해만의 서부해역과 북부해역에서는 상대적으로 약하게 일어났다. 저 층과 표층 사이에 유속우 위상차가 일어나며, 위상차는 소조기보다 소조기보다 대조기 에 더 뚜렷하게 나타났다. 또한 만내에서 표층흐름은 바람 및 하천유출류에 의해 강하 게 지배되며, 이러한 현상은 대조기보다 소조기에 더 뚜렷하게 나타났다.

• 한국해안·해양공학회논문집
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• 제29권2호
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• pp.92-108
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• 2017

본 연구에서는 Navier-Stokes solver에 기초한 3차원혼상류해석법인 TWOPM-3D를 적용하여 고립파와 연안교량과의 상호작용을 수치해석적으로 수행하였다. 이 때, 고립파는 수치파동수로에서 수치조파되었고, 작용파력의 타당성은 본 수치해석결과와 기존의 실험결과와의 비교 분석으로부터 검증되었다. 이로부터 고립파의 파고, 교량의 종류와 위치 및 거더 수 등의 변화에 따른 수위변화와 유속변화를 포함하여 수평파력과 연직파력(연직상방파력과 연직하방파력)의 변동특성을 면밀히 검토하였다. 거더교의 경우 입사파고의 증가에 따라 수평파력과 연직파력의 각 최대치는 증가하는 경향을 나타낸 반면, 거더 수의 변화에 따라서는 서로 상이한 변동특성을 나타내었으며, 연직파력에 수중에 연행되는 공기가 큰 영향을 미치는 것 등을 결과로부터 알 수 있었다.

• Journal of Positioning, Navigation, and Timing
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• 제7권4호
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• pp.295-305
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• 2018

Network RTK is a highly practical technology that can provide high positioning accuracy at levels between cm~dm regardless of user location in the network by extending the available range of RTK using reference station network. In particular, unlike other carrier-based positioning techniques such as PPP, users are able to acquire high-accuracy positions within a short initialization time of a few or tens of seconds, which increases its value as a future navigation system. However, corrections must be continuously received to maintain a high level of positioning accuracy, and when a time delay of more than 30 seconds occurs, the accuracy may be reduced to the code-based positioning level of meters. In case of SSR, which is currently in the process of standardization for PPP service, the corrections by each error source are transmitted in different transmission intervals, and the rate of change of each correction is transmitted together to compensate the time delay. Using these features of SSR correction is expected to reduce the performance degradation even if users do not receive the network RTK corrections for more than 30 seconds. In this paper, the simulation data were generated from 5 domestic reference stations in Gunwi, Yeongdoek, Daegu, Gimcheon, and Yecheon, and the network RTK and SSR corrections were generated for the corresponding data and applied to the simulation data from Cheongsong reference station, assumed as the user. As a result of the experiment assuming 30 seconds of missing data, the positioning performance compensating for time delay by SSR was analyzed to be horizontal RMS (about 5 cm) and vertical RMS (about 8 cm), and the 95% error was 8.7 cm horizontal and 1cm vertical. This is a significant amount when compared to the horizontal and vertical RMS of 0.3 cm and 0.6 cm, respectively, for Network RTK without time delay for the same data, but is considerably smaller compared to the 0.5 ~ 1 m accuracy level of DGPS or SBAS. Therefore, maintaining Network RTK mode using SSR rather than switching to code-based DGPS or SBAS mode due to failure to receive the network RTK corrections for 30 seconds is considered to be favorable in terms of maintaining position accuracy and recovering performance by quickly resolving the integer ambiguity when the communication channel is recovered.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2408-2413
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• 2007

Since the heat generation in a chip increases as the components are miniaturized and the computing speed becomes faster, suitable heat dissipation has become one of the primary limiting factors to ensure the reliable operation of the electronic devices. A pin-fin array could be used as an alterative cooling system of the electronic equipment. In this study, convective heat transfer through the pin-fin array is analyzed experimentally based on porous medium approach. The influence of the structure of the pin-fin array including the pin-fin spacing, the pin diameter and plate length on heat transfer characteristics is investigated and compared with the previous analytical results and existing correlation equations. Nowadays, electronic and mechanical devices become smaller and smaller. In this sense, the main purpose of this study is to decide the optimum pin-fin arrangement to get similar heat transfer performance when the length of the existing cooling system is reduced as a half.

• The Korean Journal of Physiology
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• 제27권2호
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• pp.163-174
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• 1993

Vertebrate retinal neurons, like brain tracts farm complex synaptic relations in the enter and inner plexiform layers which ape equivalent to the central nervous system nuclei. The effects of $\gamma-aminobutyric$ acid(GABA) and glycine on retinal neurons were explored to discern the mechanisms of action of neurotransmitters. Experiments were performed in the superfused retina-eyecup preparation of the channel catfish, Ictalurus punctatus, using intracellular electrophysiological techniques. The roles of GABA and glycine as inhibitory neurotransmitters are well established in the vertebrate retina. But, we found that the depolarizing action of GABA and glycine on third-order neurons in the catfish retina. GABA and glycine appeared to act on retinal ueurons based on the observations that (1) effects on photoreceptors were not observed, (2) horizontal cells were either hyperpolarized $({\sim}33%)$ or depolarized $({\sim}67%)$, (3) bipolar cells were all hyperpolarized (4) amacrine and ganglion cells were either hyperpolarized $({\sim}37%)$ or depolarized $({\sim}63%)$, (5) GABA and glycine may be working to suppress presynaptic inhibition. The results suggest that depolarization of third-order neurons by GABA and glycine is due to at least two mechanisms; a direct postsynaptic effect and an indirect effect. Therefore, in the catfish retina, a mechanism of presynaptic inhibition or disinhibition including the direct postsynaptic effect may exist in the third-order neurons.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권2호
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• pp.547-566
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• 2014

This study investigates the decisive factors affecting the survival or collapse of cable networks in the Korean paid broadcasting market from 1993 to 2010. The effects of performance variables discussed in previous studies were verified through survival analyses. According to the results, the most influential factors in the survival of cable networks were horizontal integration (MPP), channel genre, the scheduling of HDTV content, and the proportion of access program scheduling. These findings imply that the differentiation strategy of content suppliers is the most decisive factor among all business performance-related factors. Specifically, the content supply power and strategy of the program provider (PP) have the greatest influence on cable network viability. The present study is meaningful as the first attempt to establish the performance of PPs in Korean pay broadcasting markets through the viewpoint of organizational mortality. Accordingly, the present study can supplement the results of cross-sectional studies conducted with smaller samples.