• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.274-274
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• 2019

최근 하천에서 실시간 유량측정을 위하여 유수에 접촉 또는 비접촉 유속측정방식을 이용한 자동유량측정시스템이 설치 운영되고 있으며, 주로 지표유속법(index velocity method)이 적용되고 있다. 지표유속법 적용을 위해서는 다양한 범위에서 측정된 지표유속과 평균유속관계를 분석해야한다. 그러나 유속계 설치초기에는 측정된 유속이 없기 때문에 측정된 유량을 신뢰하기가 어렵다. 본 연구에서는 비접촉 유속계인 전자파표면유속계(MU2720)로 측정된 표면유속과 지표유속법을 이용하여 일반적인 하천에서 비접촉(레이다 또는 전자파표면유속계 등) 방식에 의한 자동유량측정 시스템 운영초기에 적용 가능한 경험적 지표-평균유속 관계식을 개발하여 검토하였다. 연구 대상지점은 한탄강(1개소), 홍천강(3개소), 내린천(2개소), 북천(1개소), 탄천(1개소), 섬강(1개소) 등 6개 하천 9개 지점이며, 2016~2018년에 지점별로 측정된 총 103개(6~26개)의 측정자료를 이용하여 분석하였다. 지점별 최대유속이 발생하는 지표유속과 평균유속과의 관계를 분석한 결과 결정계수(R2)가 0.8848(원주시(문막교))~0.9874(서울시(대곡교))로 평균 0.9626를 보여 매우 높은 상관성을 보였다. 또한 9개 지점의 모든 유속자료를 통합하여 지표-평균유속 관계식을 개발하였다. 그 결과 결정계수는 0.9247를 보였으며, 유속분포가 일반적이지 않은 홍천강의 홍천군(반곡교), 섬강의 원주시(문막교) 지점 자료를 제외한 7개 지점의 자료만으로 지표-평균유속 관계식을 개발한 결과 결정계수가 0.9603으로 매우 높은 상관성을 보였다. 이러한 결과를 볼 때 일반적인 유속분포(포물선형태)를 가진 하천은 본 연구에서 7개 지점으로 개발된 지표-평균유속 관계식을 운영초기에 활용할 수 있을 것으로 판단된다.

• Journal of Oral Medicine and Pain
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• v.35 no.1
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• pp.75-81
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• 2010

By repeating nocturnal bruxism occlusal appliance's wearing condition that is used to cure temporomandibular disorders into the vitro experiment, research aims to find out how moisture infiltrated and drying cycle process affects on the surface microhardness of the resin for occlusal appliance and flexural strength. By utilizing resin for occlusal appliance which is the main component of poly methyl methacrylate, bar shaped sample was produced. For the resin sample utilized as the controlled group 1, the sample was infiltrated in the moisture for 7 days in the temperature of 37C. Then, the resin sample of the controlled group 2 was maintained in a dry condition for 7 days in the normal temperature. After that, each sample's surface microhardness and flexural strength were measured. For the resin sample that is utilized as the experimental sample, the sample was infiltrated in the moisture for 7 days in the temperature of 37C. Then, it was inundated for 8 hours a day and dried in the normal temperature for 16 hours with the continuous process of moisture infiltration and dry cycle process for 30 days. During this cycle process, sample's surface and flexural strength were measured in the 1st day, 7th day, and 30th day. Then, it was statistically analyzed to find out the difference of controlled and experiment group's surface microhardness and flexural strength. Results are 1. For the experimental and controlled group's surface microhardness of the resin for the occlusal appliance, it did not show any significant differences after moisture infiltration and dry cycle process repetition. 2. In case of the flexural strength for resin for the occlusal appliance, experimental group with moisture infiltration and dry cycle for 30 day process had greater effect than the experimental group at the 1st day and controlled group These results can be considered to be utilized from the patients of the temporomandibular disorders towards occlusal appliance used and maintained method.

• Membrane Journal
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• v.33 no.1
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• pp.1-12
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• 2023

In this review, surface modification methods of hydrophobic poly(tetrafluoroethylene) (PTFE) membrane are introduced and their improved hydrophilicity results are discussed. Fluoropolymer based membranes, represented by PTFE membranes have been used in various membrane separation processes, including membrane distillation, oil separation and gas separation. However, despite excellent physical properties such as chemical resistance, heat resistance and high mechanical strength, the strong hydrophobicity of PTFE membrane surface has become a challenging factor in expanding its membrane separation application. To improve the separation performance of PTFE membranes, wet chemical, hydrophilic coating, plasma, irradiation and atomic layer deposition are applied, modifying the surface property of PTFE membranes while maintaining their inherent properties.

• Journal of Wetlands Research
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• v.17 no.1
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• pp.101-111
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• 2015

This study conducted a field experiment to estimate the characteristics of the rain garden installed at the site near Haman, also proposed a one-dimensional model to simulate the infiltration and runoff from the rain garden. This model was used to evaluate the rain garden using the rainfall data after the installation and during the last 10 years. Also, this model was applied to the annual maximum rainfall events to quantify the size of the impervious area that the rain garden can offset the adverse effect. The results are summarized below. (1) Hydraulic conductivity of the rain garden was estimated to be about 0.0188 m/hr by the variable-stage experiment. Also, the simulation experiment using the last 10 years rainfall data over the entire roof area showed that the infiltration amount is about 90.38% out of the total rainfall. (2) Infiltration simulation of the annual maximum rainfall events during last 10 years showed that the rain garden can offset the impervious area with its size about 30 times of the rain garden surface.

• Journal of Digital Convergence
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• v.14 no.11
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• pp.449-457
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• 2016

At this study, we select five colorful and high-acid fruits: grape, lemon, orange, grapefruit and kiwi, and we made a composite resin specimen and dipped into fruit juice in order to figure out influence that affects on surface corrosion and coloring. We dipped resin specimen into fruit juice by three-day and seven-day interval at $37^{\circ}C$. Control group used the resin that was not dipped into fruit juice. For surface change according to the time, it was observed by using scanning electron microscopy, and it was measured by using spectrophotometer for change of coloring degree. As a result of surface change of resin by using scanning electron microscopy, furrow size between surface particles increased, and rectangular rod-shape structure was emerged, and small prominent particles on bumps disappeared. As a result of coloring degree of resin by measuring spectrophotometer, a difference between experimental group appears with the darkest brightness in the case where it is dipped into grape extracts.

• Membrane Journal
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• v.15 no.4
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• pp.320-329
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• 2005

Polyamide membrane degradation by chlorine has been studied to improve membrane durability. In this study, it was found that the salt rejection was reduced rapidly and flux of the membrane was increased slowly far membrane treated under chlorine condition. In order to improve resistance to chlorine of the polyamide reverse osmosis membrane, fluorine-containing silane coupling agent (FSCA) was introduced to surface modification. Surface properties and chlorine resistance of silane modified membrane were compared with virgin membrane. It was found that the surface of silane modified membrane has dense structure according to FSCA concentration increasing. The results of surface analysis suggest that FSCA retrieved a severe change in the hydrophobicity and surface roughness. In addition, it appears that FSCA can enhance chlorine resistance due to the interaction of such substance with free radical chlorine.

• Membrane Journal
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• v.23 no.6
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• pp.439-449
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• 2013

This study investigated the aromatic polyamide reverse osmosis membrane was modified with diphenylamine (DPA) for enhanced chlorine and fouling resistance and how to optimize. DPA has high reactivity and thermo chemical stability. The performance of a modified membranes was investigated and its surface analyzed using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurement. The experiment was conducted while changing the conditions of temperature and DPA solution concentration.

• Membrane Journal
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• v.15 no.3
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• pp.233-240
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• 2005

Surface modification of polypropylene hollow fiber membranes was performed in order to develop blood-compatibility biomaterials for use in the blood contacting surfaces and oxygenation membranes of a lung assist device (LAD), important medical device even more useful. Blood compatibility of materials was determined by using anticoagulation blood and evaluating formation of blood clots on their surfaces as well as activation of plasma coagulation cascade, platelet adhesion, and aggregation. It was verified that the number of platelets on the silicone coated fibers was significantly lower than that on untreated fiber membrane, indicating improved blood compatibility. It was also found that the polypropylene hollow fiber membranes using plasma treatment exhibited suppression of complement activation in blood compatibility test.

• Membrane Journal
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• v.10 no.4
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• pp.186-191
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• 2000

The recovery of three ethyl esters (aroma model compounds; ethyl acetate, ethyl propionate. ethyl butyrate) from aqueous solutions was studied for vapor permeation with surface-modified hydrophobic alumina membrane, Although the driving force of ethyl butyrate is the highest, the ethyl butyrate concentration in permeate is lower than those of propionate and acetate. Since the solubility of aroma compounds for water is very low, phase separation occurred in permeate, and we could obtain pure ethyl esters. The experimental results showed that the porous hydrophobic alumina membrane had high selectivity and permeation flux on the ester-model compounds.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.5
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• pp.371-380
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• 2013

Though MBR process has many advantages, the greatest risk factors in operating MBR process are occurrence of membrane fouling and decrease of flux. It is very difficult to find exact mechanism due to complex influence by many effects, although there have been recently many studies of membrane fouling. The purposes of this study are firstly evaluating bioreactor of lab-scale and micro-filtration hollow fiber membrane, secondly investigating correlation between foulants affecting membrane performance and membrane fouling, and lastly evaluating various parameters affecting fouling and applicability of membrane fouling reducer. This study found that TMP was increasing rapidly and showed 0.32 bar and the average of flux was 88 LMH. EPS concentration tends not to change much above MLSS concentration (6,000 mg/L). However, EPS concentration variation is wide below MLSS concentration (6,000 mg/L). Also, from results of membrane surface condition and element analysis using SEM/EDX, carbon and fluorine were founded to be the highest percentage in membrane because of characteristics of membrane material. In operating continuously, inorganic fouling was generated by increase of these inorganic substances such as $Al^{3+}$ and $Mg^{2+}$. Lastly, the best filtration performance was obtained for 0.03 mg MFR/mg MLSS by results of particle size, zeta potential, $SCOD_{cr}$, EPS and MLSS concentration.