• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.489-495
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• 2006

Proton exchange membrane (PEM) should be sufficiently hydrated with a careful consideration of heat and water management. Water management has been a critical operation issue for better understanding the operation and optimizing the performance of a PEM fuel cell. The flooding on cathode side resulting from excess water can limit the fuel cell performance. In this study, the visual cell was designed and fabricated fur the visualization of liquid water droplet dynamics related to cathode flooding in flow channels. The experiment was carried out to observe the formation, growth and removal of water droplets using CCD imaging system. Effects of operating conditions such as cell temperature, air flow rate and air relative humidity on cathode flooding characteristics were mainly investigated. Based on this study, we can get the basic insight into flooding phenomena and its two-phase flow nature. It is expected that data obtained can be effectively used fur the setup and validation of two-phase PEM fuel cell models considering cathode flooding.

• Journal of Surface Science and Engineering
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• v.36 no.4
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• pp.301-306
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• 2003

Multilayered WC-Ti/suv $1-x/Al_{x}$ N coatings were deposited on AISI D2 steel using cathodic arc deposition (CAD) method. These coatings contain structural defects such as pores or droplets. Thus, the substrate is not completely isolated from the corrosive environment. The growth defects (pores, pinholes) in the coatings are detrimental to corrosion resistance of the coatings used in severe corrosion environments. The localized corrosion behavior of the coatings was studied in deaerated 3.5 wt.% NaCl solution using electrochemical techniques (potentiodynamic polarization test) and surface analyses (GDOES, SEM, AES, TEM). The porosity was calculated from the result of potentiodynamic polarization test of the uncoated and coated specimens. The calculated porosity is higher in the $WC-Ti_{0.6}$ $Al_{0.4}$ N than others, which is closely related to the packing factor. The positive effects of greater packing factor act on inhibiting the passage of the corrosive electrolyte to the substrate and lowering the localized corrosion kinetics. From the electrochemical tests and surface analyses, the major corrosion mechanisms can be classified into two basic categories: localized corrosion and galvanic corrosion.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2006.04a
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• pp.55-56
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• 2006

This thesis describes the use of measured aerosol size distributions and size-resolved hygroscopic growth to examine the physical and chemical properties of several particle classes. The primary objective of this work was to investigate the optical and cloud forming properties of a range of ambient aerosol types measured in a number of different locations. The tool used for most of these analyses is a differential mobility analyzer / tandem differential mobility analyzer (DMA / TDMA) system developed in our research group. To collect the data described in two of the chapters of this thesis, an aircraft-based version of the DMA / TDMA was deployed to Japan and California. The data described in two other chapters were conveniently collected during a period when the aerosol of interest came to us. The unique aspect of this analysis is the use of these data to isolate the size distributions of distinct aerosol types in order to quantify their optical and cloud forming properties. I used collected data during the Asian Aerosol Characterization Experiment (ACE-Asia) to examine the composition and homogeneity of a complex aerosol generated in the deserts and urban regions of China and other Asian countries. An aircraft-based tandem differential mobility analyzer was used for the first time during this campaign to examine the size-resolved hygroscopic properties of particles having diameters between 40 and 586 nm. Asian Dust Above Monterey (ADAM-2003) study was designed both to evaluate the degree to which models can predict the long-range transport of Asian dust, and to examine the physical and optical properties of that aged dust upon reaching the California coast. Aerosol size distributions and hygroscopic growth are measured in College Station, TX to investigate the cloud nucleating and optical properties of a biomass burning aerosol generated from fires on the Yucatan Peninsula. Measured aerosol size distributions and size-resolved hygroscopicity and volatility were used to infer critical supersaturation distributions of the distinct particle types that were observed during this period. The predicted CCN concentrations were used in a cloud model to determine the impact of the different aerosol types on the expected cloud droplet concentration. RH-dependent aerosol extinction coefficients are calculated at a wavelength of 550 nm.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.2 no.2
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• pp.11-19
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• 1992

$SrTiO_3$powders were synthesized from the chloride and the nitrate aqueous solution by spray pyrolysis method using ultrasonic vibrator. The concentration of mother solution was prepared 0.05M and O.lM. The carrier gas flow rate was 0.5cm/sec and 1.5cm/sec, respectively. The formation processing was investigated in the 0.05M and 0.05cm/sec. The $SrTiO_3$powders could not be synthesized from chloride aqueous solution. The prepared powders from nitrate aqueous solution was SrTi03 with cubic structure and nearly sphere particle for all samples. Mean particle size was increased from $0.49{\mu}m$ to $0.67{\mu}m$ by changing the carrier gas flow rate from O.5cm/sec to 1.5cm/sec. Also, mean particle size increased from $0.49{\mu}m$to $0.55{\mu}m$by changing the concentration of mother solution from O.05M to O.1M. Atomizing droplet size was $14.3{\mu}m$. The shape of particles was very porous by evaporation of solvent at the initial step. But through the each step upwards, shape of particles was formed themselves into a nearly roundish.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.23-29
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• 2003

Transonic two-phase flow of Saturated humid air, in which relative humidity is 100%, with various condensation processes around thin airfoils is investigated. The study uses an extended transonic small-disturbance(TSD) model of Rusak and Lee [11, 12] which includes effects of heat addition to the flow due to condensation. Two possible limit types of condensation processes are considered. In the nonequilibrium and homogeneous process, the condensate mass fraction is calculated according to classical nucleation and droplet growth rate models. In the equilibrium process, the condensate mass fraction is calculated by assuming an isentropic process. The flow and condensation equations are solved numerical1y by iterative computations. Results under same upstream conditions describe the flow structure, field of condensate, and pressure distribution on airfoil's surfaces. It is found that flow characteristics, such as position and strength of shock waves and airfoil’s pressure distribution, are different for the two condensation processes. Yet, in each case, heat addition as a result of condensation causes significant changes in flow behavior and affects the aerodynamic performance of airfoils.

• Microbiology and Biotechnology Letters
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• v.42 no.1
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• pp.41-50
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• 2014

In this study, the performances of PVA-encapsulation and non-encapsulation in a fed-batch bioreactor system were compared for biohydrogen production. Hydrogen production in the PVA-encapsulation bioreactor was not significantly different in comparison to the non-encapsulation bioreactor. However, the hydrogen gas in the encapsulation bioreactor could be stably produced when it was exposed to environmental difficulties such as pH impact by the accumulation of organic acids as fermentative metabolic products. Bacterial communities by DGGE analysis were differently shifted between the PVA-encapsulation and non-encapsulation bioreactors from the initial sludge. The community of hydrogen producing bacteria was stable during the experimental period in the PVA-encapsulation bioreactor compared to the non-encapsulation method. The absolute quantitation of the DNA copy number by a high-throughput droplet digital PCR system for six genera contributed to hydrogen production showing that the numbers of dominant bacteria existed at similar levels in the two bioreactors regardless of encapsulation. In both of two bioreactors, not only Clostridium and Enterobacter, which are known as anaerobic hydrogen producing bacteria, but also Firmicutes, Ruminococcus and Escherichia existed with $1{\times}10^5-1{\times}10^6$ copy numbers of ml-samples exhibiting rapid growth during the initial operation period.

• Journal of Life Science
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• v.24 no.10
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• pp.1085-1091
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• 2014

The purpose of this study was to determine the effect of selenate on adipocyte differentiation and to identify genes involved in the modulation of adipogenesis in 3T3-L1 cells. To test the effect of selenate on adipocyte differentiation, adipogenesis was induced in cells using various concentrations ($0-100{\mu}M$) of selenate. Various phases of adipogenesis were induced: postconfluent (PC), early phase (EP, d0-d2), postmitotic growth arrest (PM, d2-d4), and all period (AP). The PC cells exposed to selenate for 24 h displayed dose-dependent inhibition of intracellular lipid droplet accumulation on day 6 of adipogenesis. Two days of selenate treatment at EP or AP inhibited adipogenesis, with an approximately 20-80% reduction in lipid accumulation compared to that of a control (p<0.05). When preadipocytes were exposed to selenate during the PM period, the antiadipogenic effect of selenate was attenuated. Two types of selenoprotein genes (Seps1 and Sepp1) were up-regulated by the selenate treatment during mitotic clonal expansion, whereas these genes were down-regulated during PM growth arrest (p<0.05). The findings demonstrate the antiadipogenic function of selenate and the possible involvement of Sepp1 and Seps1 genes in selenate-inhibited adipogenesis in 3T3-L1 cells.

• Korean Journal of Pharmacognosy
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• v.41 no.4
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• pp.270-274
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• 2010

Obesity is caused from an imbalance between energy intake and expenditure, which may lead to pathologic growth of adipocytes and accumulation of fat in tissue. We examined the inhibitory effects of Eriobotrya japonica leaf and seed extracts on lipid absorption in vitro and fat accumulation during the differentiation of 3T3-L1 to adipocytes. 3T3-L1 preadipocytes were stimulated with DMEM media containing 10% FBS, 0.5 mM 3-isobuthyl-1-methyxanthine (IBMX), $5\;{\mu}g/ml$ insulin, and $1\;{\mu}g/ml$ dexamethasone for differentiation to adipocytes. E. japonica leaf extract at concentration of 0.5 or 1 mg/ml inhibited pancreatic lipase activity. The cell viability of 3T3-L1 adipocytes slightly reduced about 3% by treatment of E. Japonica leaf and seed extracts. The leaf and seed extracts of E. japonica effectively inhibited the accumulations of lipid droplet and expression of $C/EBP{\alpha}$ promoting adipogenesis. Thus, this data suggest that E. japonica leaf and seed extracts inhibit fat accumulation through regulation of $C/EBP{\alpha}$, and leaf extract is more effective in lipid absorption and adipogenesis than seed extract.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.21-29
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• 2002

In the present study, a passive control method, using a porous wall and cavity system, is applied to the shock wave/boundary layer interactions in transonic moist air flow. The two-dimensional, unsteady, compressible, Navier-Stokes equations, which are fully coupled with a droplet growth equation, are solved by the third-order MUSCL type TVD finite difference scheme. Baldwin-Lomax model is employed to close the governing equations. In order to investigate the effectiveness of the present control method, the total pressure loss of the flow and the time-dependent behaviour of shock motions are analyzed in detail. The computed results show that the present passive control method considerably reduces the total pressure losses due to the shock wave/boundary layer interaction in transonic moist air flow and suppresses the unsteady shock wave motions over the airfoil as well. It is also found that the location of the porous ventilation significantly affects the control effectiveness.

• Journal of Embryo Transfer
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• v.15 no.3
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• pp.271-277
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• 2000

This study was conducted to establish the optimal culture conditions for in vitro production of bovine embryos derived from slaughter house ovaries. Cumulus-oocyte- complexes (COCs) collected by aspiration from follicles of 2~7 mm in diameter were matured in Ham's F-10 medium supplemented with 0.01 $\mu\textrm{g}$/m1 epidermal growth factor (EGF) at 39$^{\circ}C$ in a humidified atmosphere of 5% $CO_2$in air. After 24 hrs of culture, the oocytes were co-cultured with epididymal sperm selected off by Percoll-density gradient in TALP medium for 24 hrs. The presumptive zygotes were cultured in HECM-6 medium for 3 d post-insemination, and followed by cultured in TCM199 medium until 7 to 10d post-insemination. The cultures were compared of their cleavage and development into later stage in culture medium by additions of different protein sources (PVA, BSA and BCS) and by different embryo density. The rates of cleavage and development rates into blastocyst were not significantly (P<0.05) different among the culture media containing with BSA (75.0% and 40.5%), BCS (76.7% and 38.0%) and PVA (72.5% and 42.2%), respectively. Significantly (P<0.05) higher blastocysts rates were obtained in culturing of 30 and 40 embryos in each 50$\mu$l droplets of culture medium than in 5, 10 and 20 embryos. These results indicate that the optimal density of embryos is 30~40 embryos in a 50$\mu$l droplet of culture medium. Furthermore there is no effect of different protein sources on early embryonic development.