• 한국수소및신에너지학회논문집
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• 제29권1호
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• pp.41-55
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• 2018

General polymer electrolyte fuel cell (PEMFC) operates at less than $80^{\circ}C$. Therefore liquid phase water resulting from electrochemical reaction accumulates and floods the cell which in turn increases the mass transfer loss. To prevent the flooding, it is common to employ serpentine flow channel, which can efficiently export liquid phase water to the outlet. The major drawback of utilizing serpentine flow channel is the large pressure drop that happens between the inlet and outlet. On the other hand, in the high temperature polymer electrolyte fuel cell (HT-PEMFC), since the operating temperature is 130 to $180^{\circ}C$, the generated water is in the state of gas, so the flooding phenomenon is not taken into consideration. In HT-PEMFCs parallel flow channel with lower pressure drop between the inlet and outlet is employed therefore, in order to circulate hydrogen and air in the cell less pumping power is required. In this study we analyzed HT-PEMFC's different flow channels by parallel computation using previously developed 3-D isothermal model. All the flow channels had an active area of $25cm^2$. Also, we numerically compared the performance of HT-PEMFC parallel flow channel with different manifold area and Rib interval against the original serpentine flow channel. Results of the analysis are shown in the form of three-dimensional contour polarization curves, flow characteristics in the channel, current density distribution in the Membrane, overpotential distribution in the catalyst layer, and hydrogen and oxygen concentration distribution. As a result, the performance of a real area fuel cell was predicted.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2672-2677
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• 2007

An investigation of low Reynolds number flow in nozzles and diffusers which are widely used in the valveless micropump is presented. Flow characteristics in the nozzle and diffuser are explained in view of viscous effect and flow oscillation induced by pumping membrane. These calculation results show that the rectification property of valveless micropump is due to a flow separation in the diffuser and the separation is largely originated from the flow oscillation. Under the assumptions of steady flow velocity profile and flow separation in the diffuser, simplified analytical models are provided to see the dependency of rectification on the micropump geometry. Geometric parameters of channel length, nozzle throat, chamber size, and converging/diverging angle are depicted through the analytical models in low Reynolds number flow, and the prediction and experimental results are compared. This theoretical study can be used to determine the optimum geometry of valveless micropump.

• 대한기계학회논문집B
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• 제27권2호
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• pp.236-242
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• 2003

Thermal bubbles find their diverse application areas in the MEMS (MicroElectroMechanial Systems) technology, including bubble jet printers, microactuators, micropumps, etc.. Especially, microactuators and micropumps, which use a microbubble growing by a controlled heat input, frequently involve mechanical and thermal interaction of the bubble with a solid structure, such as a cantilever beam and a membrane. Although the concept is experimentally verified that an internal pressure of the bubble can build up high enough to deflect a thin solid plate or a beam, the physics of the entire process have not yet been thoroughly explored. This work reports the experimental study of the growth of a thermal bubble while deflecting a thin cantilever beam. A physical model is presented to predict the elastic response of the cantilever beam based on the experimental measurements. The scaling law constructed through this work can provide a design guide for micro- and nano-systems that employ a thermal bubble for their actuation/pumping mechanism.

• Biomolecules & Therapeutics
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• 제18권4호
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• pp.375-385
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• 2010

Conventional cancer chemotherapy is seriously limited by tumor cells exhibiting multidrug resistance (MDR), which is caused by changes in the levels or activity of membrane transporters that mediate energy-dependent drug efflux and of proteins that affect drug metabolism and/or drug action. Cancer scientists and oncologists have worked together for some time to understand anticancer drug resistance and develop pharmacological strategies to overcome such resistance. Much focus has been on the reversal of the MDR phenotype by inhibition of ATP-binding cassette (ABC) drug transporters. ABC transporters are a family of transporter proteins that mediate drug resistance and low drug bioavailability by pumping various drugs out of cells at the expense of ATP hydrolysis. Many inhibitors of MDR transporters have been identified, and though some are currently undergoing clinical trials, none are in clinical use. Herein, we briefly review the status of MDR in human cancer, explore the pathways of MDR in chemotherapy, and outline recent advances in the design and development of MDR modulators.

• EDISON SW 활용 경진대회 논문집
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• 제3회(2014년)
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• pp.287-299
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• 2014

Bicarbonate anion ($HCO_3{^-}$) takes the role of major buffer systems in our body by maintaining the pH at 7.4. Epithelial $HCO_3{^-}$ secretion also hydrolyzes the mucus which protects body from noxious infections. It has been widely known that such infections are closely related to $HCO_3{^-}$ permeability through membrane and, thus, increasing the $HCO_3{^-}$ permeability is essential. To evaluate the $HCO_3{^-}$ permeability through ion channels, the free energy changes relevant to ion pumping are calculated with the Integral Equation Formalism-PCM (IEF-PCM) theory. Molecular structures of various anions including $HCO_3{^-}$ were optimized with the density functional theory at the level of B3LYP/6-311++G(d,p) in gas and solution phase. In addition, the anion permeability is significantly influenced by the relative size of the anion and pore. We introduce a shifted volume factor model that describes the pore size effect when the charged solutes transfer through ion channels. We found excellent agreement between experimental and calculated permeability when our novel model of the size effect was taken into account to.

• 한국유체기계학회 논문집
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• 제10권5호
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• pp.27-33
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• 2007

Rarefied gas flows through two-dimensional micro channels are studied numerically for the performance optimization of a nanomembrane-based Knudsen compressor. The effects of the wall temperature distributions on the thermal transpiration flow patterns are examined. The flow has a pumping effect, and the mass flow rates through the channel are calculated. The results show that a steady one-way flow is induced for a wide range of the Knudsen number. The DSMC(direct simulation Monte Carlo) method with VHS(variable hard sphere) model and NTC(no time counter) techniques has been applied in this work to obtain numerical solutions. A critical element that drives Knudsen compressor Is the thermal transpiration membrane. The membranes are based on aerosol or machined aerogel. The aerogel is modeled as a single micro flow channel.

• 한국환경보건학회지
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• 제1권1호
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• pp.28-31
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• 1974

A study was conducted to find out the biological contamination of wells in Chon Ho Dong areas, Seoul, Korea from May 4, 1971 through May 18 1971. Coliform groups were detected by membrane filter method and general sanitary conditions were checked. The results obtained were summarized as follows: 1) 61 wells (81.3%) out of 75 wells showed the evidence of coliform group. In urban areas it is recommended to use disinfectants for wells pretty frequently. 2) The wells in native villages were less contaminated than those in new villages established by poor people from slum areas of Seoul. 9 out of 15 wells at Song Pa Dong, which is However, at Bang E Dong's new village, 19 out of 20 wells were contaminatd by coliform groups. 3) Coliform groups were positive at 57 out of 61 open wells, while only 4 out of 14 pumping wells showed the evidence of coliform groups. 4) 38 out of 40 poorly drained wells were contaminated, however, 13 out of 25 well drained wells were coliform organisms positive.

• KSBB Journal
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• 제14권2호
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• pp.230-234
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• 1999

한외여과공정에서 압력구배를 주기적으로 변화시켜 막 표면의 용질층을 불안정화시켜 여과 flux의 총괄적 향상을 유도한 실험을 수행하였다. 일정압력에서의 여과 flux 감소현상을 Hernia 식을 사용하여 모사하였고, 또한 압력구배의 주기적 변화를 Fourer series로 표현하여 압력구배의 변화에 따른 flux 변화를 수학적으로 모사하였고 이 결과를 실제의 실험결과와 비교하여 보았다. 수학적 모사결과 압력변화의 형태, 진폭, 주기 등의 변화에 따른 평균 flux의 변화는 미미하였다. 하지만 실제실험결과 주기적으로 압력구배를 변화시킨 경우 약 11%의 향상을 관찰할 수 있었다. 이는 압력구배가 주기적으로 변하는 과정에서의 응질층의 압축이완속도가 다른 것에 기인하는 것으로 유추된다. 주기적 압력구배변화외에 feed pump interruption을 이용하여 평균총괄 flux를 약 32%까지 향상 시켰다. 역확산에 의한 용질층의 이완에는 일정한 시간이 필요함을 찾아내었고 interruption은 용질층이 형성되기 전부터 시작하는 것이 유리하다고 판단되었다. 본 실험을 위하여 한외여과의 자동제어 시스템을 설계제작하여 다양한 압력함수를 이용할 수 있었고, 공정운영 중 압력구매와 여과 flux를 실시간 모니터링 및 제어할 수 있었다. 자동제어 시스템을 통해 압력구매를 주기적으로 변화시켜 총괄 flux의 극대화를 도모하는 기법은 기존장치를 최소로 변경시키면서 한외여과성능을 극대화시킬 수 있는 방법으로 기대된다.

• 미생물학회지
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• 제47권1호
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• pp.22-29
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• 2011

Chromophore로 레티날(vitamin A)을 사용하는 막 단백질인 로돕신은 7개의 막 단백질로 이루어진다. 최근 광화학/생물리학 측정 방법이 다양해지면서, 그에 따른 새로운 특성도 함께 다양하게 보고되고 있다. 하지만, 다양한 측정 환경에 따른 그 광화학/생물리학 특성의 차이점에 대한 비교연구는 없는 상태이다. 첫째, 빛 에너지를 이용하여 수소 이온 펌프 역할 하는 것으로 잘 알려져 있는 roteorhodopsin (PR)은 해양 proteobacteria에서 발견 되었다. 둘째, 한 오페론에서 14 kDa 전달자와 같이 발현되면서 신호 전달 기능을 하는 Anabaena sensory rhodopsin (ASR)이 있다. 이에 본 연구에서는 이 두 미생물 로돕신을 이용하여 다양한 조건에서 그 차이를 살펴보았다. 각 단백질이 막에 끼어 있는 상태(membrane state), polyacrylamide gel에 고정되어 있는 상태, nonionic detergent일종인 DDM (n-dodecyl-${\beta}$-D-maltopyranoside)과, OG (octyl-${\beta}$-D-glucopyranoside)에 녹아 있는 상태, 좀더 자연상태와 유사한 환경을 위해 단백질만 깨끗하게 정제한 다음 다시 Escherichia coli의 지질인 DOPC (1,2-didecanoyl-sn-glycero-3-phosphocholine)에 재조립한 상태, 이렇게 5가지 조건에서 각각의 광화학/생물리학 특징을 흡수스펙트럼(absorption spectrum), 빛-어둠 차이 흡수스펙트럼(light-induced difference spectrum), 포토사이클(photocycle)을 측정하였다. 그 결과 DDM에 녹아 있는 PR과 ASR에서 각 다른 파장에서 M과 O state와 같은 선명한 photointermediate를 가지고, 가장 signal/noise 비율이 좋았다. 본 연구를 통해 막단백질의 다양한 측정 환경에 대한 그 특성의 차이점을 살펴봄으로써 앞으로 다양한 종류의 로돕신 연구에 기초 기반이 될 것으로 사료된다.

• 대한기계학회논문집B
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• 제34권2호
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• pp.105-111
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• 2010

양극산화법과 DRIE 법으로 제작된 다공성 실리콘막을 이용하여 두 종류의 전기침투 펌프를 제작하였다. 펌프의 성능은 유기용매를 이용하여 유량과 단위전류당 유량으로 측정하였다. 두 종류 펌프 모두 기존의 다공성 유리막으로 제작된 전기침투 펌프보다 성능이 우월했다. 특히 DRIE 법으로 제작된 다공성 실리콘막은 유량과 단위전류당 유량이 모두 월등한 성능을 보였다. DRIE 법은 널리 알려진 방법이기에 이와 같이 제작된 펌프는 다양한 응용 분야에 비교적 쉽게 적용될 것으로 기대된다.