• 한국전자파학회논문지
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• 제16권6호
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• pp.615-621
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• 2005

본 논문에서는 산악지대, 논, 채소밭, 풀밭, 도로, 수면 등을 포함하는 지표면에 대한 합성 개구면 레이다(SAR) 영상을 생성하여 주는 시뮬레이션 모델을 선보인다. 우선 토양, 수면, 논, 밭과 같은 풀 층과 나무 숲 등에서의 산란 모델을 개발하였다. 그런 다음에, 표고 데이터와 지형 데이터를 이용하여 SAR 영상을 생성하였다. 이용된 지형 변수로는 토양 수분 함유량, 표면 거칠기, 초목 층 높이, 잎 넓이, 잎 길이, 잎 밀도, 가지 길이, 가지 밀도, 나무 기둥 길이, 나무 기둥 밀도를 포함하는 10개이다. 개발된 산란 모델들은 실험 데이터와 비교하는 방식으로 정확성을 증명하였고, 특정 지역에서의 SAR 영상을 생성하였다.

• 대한토목학회논문집
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• 제33권5호
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• pp.1829-1840
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• 2013

수리구조물의 효과적 운영과 홍수기 피해저감을 위해서는 하천수리특성에 대한 적절한 이해가 필수적이기 때문에 본 연구에서는 낙동강 수계 금호강 유입지점 하류를 대상으로 준설 및 수리시설물 운영에 따른 수리특성 영향을 분석하였다. 수리특성 분석을 위해 HEC-RAS 모형을 이용하였으며, 부정류 흐름 해석을 통해 흐름의 천이를 반영하고 수리시설물 운영을 위한 다기능보 제원을 적용하였다. 조도계수와 조고값의 관계, 정류와 부정류 흐름해석, 사업 전과 후 하천 단면 그리고 다기능보 운영에 따른 하천 흐름에 대해 다각도로 연구를 하였다. 낙동강 수계 주요 관심구간을 중심으로 급격한 지형변화 및 수리구조물 운영에 의한 홍수에 대비하고 주요지점별 유량 전달에 의한 홍수파에 대해 분석된 자료는 합리적인 하천관리를 위한 기초자료로 활용될 수 있을 것이다.

• Journal of Biosystems Engineering
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• 제21권4호
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• pp.429-435
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• 1996

A wind tunnel consisting of two air flow conditioners with polycarbonate pipes, a plant growth room, a suction fan and fan controller, and fluorescent lamps, was designed to investigate the interactions between the growth of plug seedlings under artificial light and their Physical environments. Light transmissivities in the plant growth room based on the photosynthetic photon flux density and photosynthetically active radiation was appeared to be 96.3% and 96.8%, respectively. Measurement showed a uniformity in the vertical profiles of air current speed at the middle and rear regions of plug trays in wind tunnel. This result indicated that the development of a wind tunnel based on the design criteria of the American Society of Mechanical Engineers was adequate. Air current speed inside the plug stand was significantly decreased due to the resistance by the leaves of plug seedlings and boundary layer developed over and below the plug stand. Driving force to facilitate the diffusion of gas inside the plug stand might be regarded as extremely low. Aerodynamic characteristics above the plug stand under artificial light were investigated. As the air current speed increased, zero plane displacement decreased but roughness length and frictional velocity increased. Zero plane displacement linearly increased with the average height of plug seedlings. The wind tunnel developed in this study would be useful to investigate the effects of air current speed on the microclimate over and inside the plug stand and to collect basic data for a large-scale plug production under artificial light in a semi-closed ecosystem.

• Tribology and Lubricants
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• 제32권2호
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• pp.61-66
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• 2016

Total thickness variation (TTV), BOW, and surface roughness are essential characteristics for high quality sapphire substrates. Many researchers have attempted to increase removal rate by controlling the key process parameters like pressure and velocity owing to the high cost of consumables in sapphire chemical mechanical polishing (CMP). In case of the pressure approach, increased pressure owing to higher deviation of pressure over the wafer leads to significant degradation of the TTV. In this study, the authors focused on reducing TTV under the high-pressure conditions. When the production equipment polishes multiple wafers attached on a carrier, higher loads seem to be concentrated around the leading edge of the head; this occurs because of frictional force generated by the combination of table rotation and the height of the gimbal of the polishing head. We believe the skewed pressure distribution during polishing to be the main reason of within-wafer non-uniformity (WIWNU). The insertion of a hub ring between the polishing head and substrate carrier helped reduce the pressure deviation. Adjusting the location of the hub ring enables tuning of the pressure distribution. The results indicated that the position of the hub ring strongly affected the removal profile, which confirmed that the position of the hub ring changes the pressure distribution. Furthermore, we analyzed the deformation of the head via finite element method (FEM) to verify the pressure non-uniformity over the contact area Based on experiment and FEM results, we determined the optimal position of hub ring for achieving uniform polishing of the substrate.

• 한국물환경학회지
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• 제29권4호
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• pp.559-567
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• 2013

In recent years, NF (nanofiltration) membrane has been receiving great attention for hardness removal and has begun to replace traditional lime soda ash softening process, particularly in Florida, USA, mainly due to less sludge production and easy operation. This study aimed to provide detailed surface characteristics of various commercial NF membranes by performing sophisticated surface analysis, which would help more fundamentally understand the performance of NF membranes. More specifically, a total of 7 NF membranes from top NF/RO manufacturers in the world were examined for basic performance tests, surface analysis, and fouling potential assessment. The results demonstrated that NF membranes are classified into two groups in terms of surface zeta potential; they are highly negatively charged ones, and neutral and/or less negatively charged ones. Their hydrophobicities, measured by contact angle, varied from hydrophilic to slightly hydrophobic ones. The AFM measurements showed various surface roughness, ranging from 23 nm (smooth) to 162 nm (rough) of average peak height. Lab-scale fouling experiments were performed using feedwater obtained from conventional water treatment plants in the province of Korea, and their results attempted to correlate to surface characteristics of NF membranes. However, unlike typical RO membranes, no clear correlation was found in this study, indicating that fouling mechanisms of NF membrane may be different from those of typical RO membranes, and both cake deposition and pore blocking mechanisms should be considered simultaneously.

• The Journal of Advanced Prosthodontics
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• 제9권5호
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• pp.335-340
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• 2017

PURPOSE. Bacterial adhesion on provisional crown materials retained for a long time can influence the duration for which permanent prosthetic restorations can be healthily worn in the oral cavity. The aim of this study was to compare seven different commonly used provisional crown materials with regard to Streptococcus mutans and Candida albicans surface adhesion. MATERIALS AND METHODS. For each group, twenty specimens of the provisional fixed prosthodontic materials TemDent ($Sch{\ddot{u}}tz$), Imident (Imicryl), Tab 2000 (Kerr), Structur Premium (Voco), Systemp (Ivoclar Vivadent), Acrytemp (Zhermack), and Takilon-BBF (Takilon) were prepared (diameter, 10.0 mm; height, 2.0 mm). Surface roughness was assessed by atomic force microscopy. Each group was then divided into 2 subgroups (n=10) according to the microbial suspensions used: S. mutans and C. albicans. The specimens were incubated at $37^{\circ}C$ with S. mutans or C. albicans for seven days. Bacterial adherence on surfaces was assessed using the 2,3-bis[2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT) assay. RESULTS. S. mutans showed maximum adhesion to Structur, followed by Systemp, Acrytemp, Takilon, Tab 2000, Imident, and TemDent (P<.05). The highest vital C. albicans adhesion was noted on Takilon, followed by Imident and Tab 2000; the lowest adhesion was noted on Systemp (P<.05). CONCLUSION. The materials showed significant differences in the degree of bacterial adhesion. C. albicans showed higher surface adhesion than S. mutans on provisional crown and fixed partial denture denture materials.

• 대기
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• 제25권4호
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• pp.707-718
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• 2015

This study investigates the characteristics of turbulent fluxes observed at Ieodo Ocean Research Station (IORS) in autumn 2014. The 10 Hz IORS data is quality controlled and calculated to be the 30 minutes turbulent fluxes. The quality control consists of five steps: a weather check, Vickers and Mahrt (VM) sequential check, VM parallel check, flag check, and direction check. Since the IORS is an open-sea station with no orographic influence, there are no significant diurnal variations for the turbulent fluxes and 10 m wind speed. According to stabilities, the unstable and semi-unstable states appear more than 28% and 70% in autumn, respectively and they have strong winds of over $10m\;s^{-1}$. In addition, the turbulent fluxes increase with increasing wind speed. In particular, the latent heat flux and its deviations are clearly shown because the latent heat flux is influenced by the change of both the sea surface roughness and wave height induced by the wind. To demonstrate the changes of the turbulent fluxes before and after typhoon, Vongpong (1419), which is the most intense typhoon affecting the Korean Peninsula in 2014, is considered. The turbulent flux fluctuates in accordance with the location of Vongpong. The turbulent fluxes have a large (small) variation when Vongpong approaches (retreats) at the IORS. The overall results represent that the IORS data helps us understand physical processes related to air-sea interaction by providing the valuable and reliable observed data.

• 한국해안·해양공학회논문집
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• 제24권6호
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• pp.400-403
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• 2012

본 연구에서 건물이 밀집되어 있는 해안도시에서의 지진해일 범람에 대한 평면수리모형실험을 수행하였다. 해안도시는 미국 서해안에 위치한 도시인 Seaside를 1/50으로 축소하여 평면수조에 설치하였다. 본 실험에서 범람지역에서의 지진해일의 파고 및 수평속도 측정하였는데, 31개 지점에서 계측하였으며 입사된 지진해일의 파고는 원형 스케일 10 m로 설정하였다. 범람양상과 속도는 건물의 위치 및 배열상태에 따라 크게 다르게 계측되었다. 또한, 도시의 주요 도로를 따라 계측된 지진해일 범람 파고 및 수평속도를 이용하여 모멘텀 플럭스(Momentum flux)를 계산하였다. 모멘텀 플럭스는 해안선에서부터 육지방향으로 파가 진행하면서 감소하는 일반적인 경향을 나타내었다. 범람파고와 모멘텀 플럭스는 도로가 형성된 구역에서 감쇄가 적게 나타났다. 본 연구를 통해 수평 유속이 구조물에 미치는 외력에 중요한 영향을 준다는 것을 알게 되었다.

• Tribology and Lubricants
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• 제33권2호
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• pp.59-64
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• 2017

This study investigates friction and wear characteristics of anodized aluminum (Al) alloy 6061 by using a reciprocating tribotester. The diameter and height of the specimen are 30 mm and 10 mm, respectively. The surface roughness of the mirrored-surface is approximately $0.01{\sim}0.02{\mu}m$, and it is used throughout the current study. As a result of anodizing, the depth and diameter of the nanopore are approximately $25{\mu}m$ and 30-40 nm, respectively. The testing conditions are as follows: loads of 1, 3, and 5 N; a frequency of 1 Hz; a stoke of 3 mm; and a duration of 1800 s. We use deionized water with a volume of approximately $25{\mu}l$, as the lubricant. Micro Vickers hardness measurements show that mirrored-surface specimens had lower hardness values than anodized specimens. Further, their coefficients of friction are lower than those of the anodized samples, and the width of their wear track increases with load, as expected. The anodized specimens' coefficients of friction increase with stable frictional behavior and exhibit insignificant load dependence. Further, we observe that the width of the wear track is less than that of the mirrored-surface specimens, and micro cracks are present near it. Moreover, the anodizing process increases the hardness of the samples, improving their wear resistance. These results indicate that nanoporous structures are not effective in lowering friction under the water-lubricated condition.

• 한국수자원학회논문집
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• 제33권3호
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• pp.331-340
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• 2000

본 연구의 목적은 하천에서의 실시간 범람위험도 해석을 위해서 DAMBRK 모형과 Kalman filter를 연계한 수치모형을 개발하는데 있다. 본 모형은 1차원 동역학 방정식의 비선형 유한차분 근사해인 음해법을 기본으로 하고 있다. 추계학적 추정법으로서 최적의 갱신 예측치를 얻기 위해 확장된 Kalman filter 기법을 사용하였다. 이 과정은 확정론적 모형에 의한 예측치를 Kalman filter gain factor에 의해 보정된 실시간 관측치와 조합함으로써 수행되었다. 홍수범람위험도는 하도단면의 기하형상과 Manning 조도계수의 변동성을 고려하여 Monte Carlo 모의를 적용하여 예측되었다. 본 모형은 1990년 9월과 1995년 8월의 남한강 홍수에 적용하여 검증하였다. Kalman filter에 의한 해석은 이 기간 동안에 확정론적 해석결과와 비교하여 실측자료와 잘 일치되는 양상이 나타났으며, 이에 따라 제방의 월류위험도를 모의된 홍수위와 제방고를 비교함으로써 얻을 수 있었다.