• Journal of the Korean Geographical Society
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• v.38 no.2
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• pp.145-155
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• 2003

In this research, the primary factors affected to the formation of lake current of surface layer and thermal stratification of temperate lake have been analyzed, the daily change of water temperature, relationship with lake current and the research about the elements of meteorological phenomenon have been implemented. As a result, the lake current of surface layer occurring while the period of thermal stratification is showing the proportional difference of water temperature, thermal exchange caused by this has been known as the main energy source, and this is, secondly, considering as the interaction of the wind driven current by the prevailing wind. On the other hand, during the night time when the water surface is cooled, and it is considering as the vertical convection is occurring than horizontal circumfluence. Also, there exists the water mass, which is circumfluent counterclockwise and clockwise direction separately. The prevailing md is rather affected to the moving direction and moving speed of water mass, but it doesn't affect to the whole flowing direction.

• Membrane Journal
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• v.15 no.1
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• pp.44-51
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• 2005

Polyurethane-polysiloxanes (PU/PDMS) was synthesized using 4,4'-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) to overcome the weakness to the organic chemicals. The composite membranes were prepared onto porous poly(tetrafluoroethylene) (PTFE) supports. In vapor permeation experiments, the flux increased with increasing operating temperatures and feed concentrations while the separation factors showed the opposite trend, so-called 'trade-off'. In this study, the effect of the flux on the operating temperatures was not severe since the content of the soft segments is fairly higher than that of the hard segments. The composite membrane type of PU/PDMS maintained high flux and separation factor as well when comparing with the dense type membranes.

• Membrane Journal
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• v.30 no.6
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• pp.433-442
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• 2020

In this study, in order to build a molecular dynamics simulation model of ionomer for water electrolysis, an ionomer model that reflects the characteristics of a water electrolysis system in which excess water molecules exist was compared to an ionomer built according to the conventional simulation method of the fuel cells membrane. The final ionomer MD models have a strong phase separation and water channel that is one of the important characteristics of the perfluorinated ionomer, and are stable and water-insoluble under excessive water and high temperature conditions. In the ionomer MD models built in this study, the excess water molecules decrease an ion conductivity due to the dilution of ions, but increase a hydrogen diffusivity. Therefore, it is necessary to design the molecular structure of ionomers for water electrolysis in experimental studies as well as molecular dynamics studies according to the characteristics of the water electrolysis system reported in this study.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.280-280
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• 2023

강수의 정확한 시·공간적 추정은 홍수 대응, 가뭄 관리, 수자원 계획 등 수문학적 모델링의 핵심 기술이다. 우주 기술의 발전으로 전지구 강수량 측정 프로젝트(Global Precipitation Measurement, GPM)가 시작됨에 따라 위성의 여러 센서를 이용하여 다양한 고해상도 강수량 자료가 생산되고 있으며, 기후변화로 인한 수재해의 빈도가 증가함에 따라 준실시간(Near-Real-Time) 위성 강수 자료의 활용성 및 중요성이 높아지고 있다. 하지만 준실시간 위성 강수 자료의 경우 빠른 지연시간(latency) 확보를 위해 관측 이후 최소한의 보정을 거쳐 제공되므로 상대적으로 강수 추정치의 불확실성이 높다. 이에 따라 본 연구에서는 앙상블 머신러닝 기반 수집된 위성 강수 자료들을 관측 자료와 병합하여 보정된 준실시간 강수량 자료를 생성하고자 한다. 모형의 입력에는 시단위 3가지 준실시간 위성 강수 자료(GSMaP_NRT, IMERG_Early, PERSIANN_CCS)와 방재기상관측 (AWS)의 온도, 습도, 강수량 지점 자료를 활용하였다. 지점 강수 자료의 경우 결측치를 고려하여 475개 관측소를 선정하였으며, 공간성을 고려한 랜덤 샘플링으로 375개소(약 80%)는 훈련 자료, 나머지 100개소(약 20%)는 검증 자료로 분리하였다. 모형의 정량적 평가 지표로는 KGE, MAE, RMSE이 사용되었으며, 정성적 평가 지표로 강수 분할표에 따라 POD, SR, BS 그리고 CSI를 사용하였다. 머신러닝 모형은 개별 원시 위성 강수 자료 및 IDW 기법보다 높은 정확도로 강수량을 추정하였으며 공간적으로 안정적인 결과를 나타내었다. 다만, 최대 강수량에서는 다소 과소추정되므로 이는 강수와 관련된 입력 변수의 개수 업데이트로 해결할 수 있을 것으로 판단된다. 따라서 불확실성이 높은 개별 준실시간 위성 자료들을 관측 자료와 병합하여 보정된 최적 강수 자료를 생성하는 머신러닝 기법은 돌발성 수재해에 실시간으로 대응 가능하며 홍수 예보에 신뢰도 높은 정량적인 강수량 추정치를 제공할 수 있다.

• Membrane Journal
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• v.22 no.2
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• pp.120-127
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• 2012

In this study, separation of ethylbenzene from mixed xylene was performed by using TS-1 zeolite membrane. TS-1 zeolite membranes were prepared by microwave synthesis and changing the reaction temperature. MFI-type TS-1 membranes are synthesized on alumina tubes by functional coating using 3-chloropropyltrimethoxysilane (3CP-TMS). On top surface of interlayer, nano TS-1 crystals were seeded. To form interlayer, microwave-assisted growth of TS-1 zeolite was carried out and thin zeolite layers were produced. All of the prepared membranes are tested to separate ethylbenzene from mixed xylene at different operating temperatures. TS-1 membrane with zeolite seed synthesized at $170^{\circ}C$ compared to 120, $140^{\circ}C$ shows the best ethylbenzene separation at the operation temperature of $200^{\circ}C$ from ternary mixed xylene containing certain composition of ethylbenzene/p-xylene/m-xylene. (separation factor : 2.64, ethylbenzene flux : 1703.0 mol/$m^2{\cdot}s{\cdot}Pa$).

• Membrane Journal
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• v.23 no.4
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• pp.283-289
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• 2013

Poly(vinyl alcohol) (PVA) coating solution containing glutaraldehyde (GA) and maleic anhydride (MA) as crosslinking agents was coated onto hydrolyzed poly acrylonitrile (PAN) hollow fiber membranes. The permselectivities of the resulting composite membranes prepared varying the reaction temperature and the concentration of the crosslinking agents were tested for 90 wt% ethanol aqueous mixtures by the pervaporation technique at $60^{\circ}C$. In general, the flux decreased while the selectivity increased for the increases of the reaction temperature and the crosslinking concentration. In case of GA as a crosslinking, the flux $165g/m^2hr$ and the separation factor 81 were obtained at GA 11 wt% and the reaction temperature $120^{\circ}C$. And for the case of MA, the flux $174g/m^2hr$ and the separation factor 73 were obtained at MA 11 wt% and the reaction temperature $120^{\circ}C$.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.15-23
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• 2019

The sprayable waterproofing membrane is a recently introduced material in the civil engineering field, and is a material that sprays and attaches a single phase or two phase powder or liquid material to a surface to be covered using a pump and nozzle. Although the material properties are gradually reported through researches, there is a lack of studies on long-term performance compared to concrete materials used with the membranes. In this study, the long-term performance of materials was estimated using the Arrhenius equation. The temperature conditions used in this study were 65℃, 80℃ and 95℃, and the temperature was maintained with the membrane attached to the concrete block for long-term behavior. Then the membranes were tested for tensile strength and adhesion strength in the order of 30, 90, 150, 200, and 300 days. The long-term performance of the material was determined from a long-term perspective by estimating the activation energy by the Arrhenius equation. Consequently, the time to reach 50% of the performance standard could be estimated by long-term test.

• Journal of Korean Society of Steel Construction
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• v.17 no.6 s.79
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• pp.673-679
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• 2005

According to continuous welded rails on a bridge, temperature changes bring about the expansion of the bridge deck,adding axial forces on the track. Moreover, the ballast on the bridge deck expansion joint is moved due to the bridge deck. The longer the bridge deck is, the greater the influence will be, loosening the ballast, causing track irregularities, and deteriorating passenger comfort. Considering the structure of the bridge itself and tolerance for track irregularities caused by the loosened ballast on the bridge, the maximum length of the deck should be less than 80 m, which is the same as the standard of French railways. In this study, the interaction between the expansion related to the bridge length and the irregularity in the longitudinal level, referring to measurements and maintenance work performed in high-speed railways, was analyzed. This research shows that the installation of a sliding plate or a vertical ballast stopper is not a good option, since it is difficult. On the other hand, the installation of a ZLR fastener or gluing is easy, but its influence is insignificant. In conclusion, switch tie tamping or manual tamping is more effective than other methods of what?

• Membrane Journal
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• v.13 no.4
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• pp.246-256
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• 2003

For the olefin recovery from polyolefin off-gas, the permeation behaviors of olefins and nitrogen were investigated through three kinds of PDMS membranes - cross-linked PDMS membranes, a polysiloxaneimide membrane, and oligo-PDMS modified PDMS membranes. Their pure gas permeabilities were measured as a function of operation temperature(-20 to $50^{\circ}C$) and pressure(1 to 25 atm) with ethylene($C_2\;H_4$), propylene($C_3\;H_6$), butylene($C_4\;H_8$), and nitrogen($N_2$) gases. The permeabilities of olefins and nitrogen highly depended upon the nature of PDMS membranes. Among these membranes, cross-linked PDMS membranes showed stable and high olefin/nitrogen selectivities over a wide operation pressure range and further study in various test conditions. Their permeability of olefin and nitrogen were governed by the condensation temperature(solubility selectivity) and plasticization, not the order of the size(diffusivity selectivity) of gases, which matched well with the general permeation behavior of rubbery polymeric membranes for condensable and non-condensable gases. With increasing feed pressure or decreasing feed temperature, the permeabilities of more condensible olefins increase highly, presumably due to high solubility and plasticization, but that of non-condensible nitrogen decreases slightly and thus, the selectivities of olefin/nitrogen increase highly.

• Membrane Journal
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• v.26 no.1
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• pp.70-75
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• 2016

The reuse of wastewater is being diffused to manage and develop the water resources. Generally, the treated wastewater is discharged to the river after being treated to meet the effluent quality standard or reused for diverse uses through the reprocessing. And recently, as the reuse of the treated wastewater is activated, the technologies to utilize for the high quality water resources such as industrial water by reusing the wastewater with Membrane Distillation (MD) are under development. In this study, the direct contact membrane distillation (DCMD) process has been applied to treat sewage discharge water for water reuse. The laboratory scale experiment was performed by using a hydrophobic PVDF membrane with the pore size of $0.22{\mu}m$. The influence of operating parameters, such as feed temperature, feed flow rate, feed concentration, on the permeate flux and rejection has been investigated. All filtration tests were conducted till the feed volume reached a concentration factor of 3.0. Thus, the operating period ranged between 19 hr and 49 hr depending on filtration performance. The results showed that above 92% of TN, TP, COD and TOC in the feed could be rejected regardless of an operating condition. The water flux was ranged from 13.8 to 20.3 LMH. The lowest flux was obtained at the operating condition with the feed temperature of $50^{\circ}C$ and feed flow velocity of 500 mL/min while the highest one was measured with $60^{\circ}C$ and 900 mL/min. When the concentration factor reached 3.0, water flux declined by approximately ranged from 14.5% to 33.3%. But the fouling in MD is almost fully reversible, with more than 90% recovery of permeate water flux following a DI water rinse without the addition of chemical cleaning reagents.