• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.174-179
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• 2004

The growth of the critical size bubble by diffusion process in viscoelastic medium was treated by an integral method for the concentration boundary layer adjacent to the bubble wall. In this study, we obtained a set of the first order time dependent equations to obtain bubble radius and gas pressure inside the bubble simultaneously. The calculated final cell sizes depending on the initial saturation pressure are in close agreement with the observed ones. The governing equations developed in this study may be used in polymer processing of microcellular foams.

• KIEAE Journal
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• 제2권3호
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• pp.33-38
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• 2002

The intermediate range of temperatures($100{\sim}300^{\circ}C$) which can be achieved with CPCs(Compound Parabolic Concentrators) without tracking device provides both economic and thermal advantages for solar collector design. The present paper summarizes critical design considerations for CPC with cylindrical absorber and its optical performance using ray tracing program. Concentration ratios vary as acceptance half angle, ratio of reflector height to aperture width and ratio of reflector area to aperture area. This effects showed that the concentration ratio was increased as acceptance angle but optimum ratio of reflector height to aperture width existed at critical value. As a result of ray tracing, solar ray losses was maximized at acceptance half angle and this problem was solved by increasing absorber tube diameter. The concentrating flux distribution on the absorber surface was uniform but peak flux existed.

• Biotechnology and Bioprocess Engineering:BBE
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• 제7권6호
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• pp.362-366
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• 2002

A mathematical model has been developed for describing the oxygen concentration during the exponential growth of microorganisms, in a static solid substrate bed supported on a tray fermentor. The model equations comprise of one partial differential equation for mass transfer and an ordinary differential equation of growth. After nondimensionlisation, analytical solution tn the model has been obtained by the method of Laplace transforms. An expression for critical thickness of bed is deduced from the model equation. The significance of the model in the design of tray fermentors is discussed. The validity of the discussion is verified by taking an illustration from the literature.

• Bulletin of the Korean Chemical Society
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• 제12권4호
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• pp.411-413
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• 1991

The effects of electrolyte on the critical micelle concentration (cmc) and bromide counterion binding in the micelles of cetylpyridinium bromide (CPB) have been investigated by UV spectroscopy and conductance measurements. Salts used in this study decreased cmc in the order $Cl^-\;<\;Br^-\;<\;NO3^-$ (which parallels the lyotropic series for the inorganic anions) and the effects on cmc followed the equation proposed by Shinoda: log cmc = A - B log (cmc + [NaX]). In the equation, constant B represents the counterion binding to the micelles at cmc and for the micelle of CPB at $25^{\circ}C$, B=80.76%. The association constant for the binding of counterions to long chain cations within micelles was also derived from the cmc values and counterion binding constant to the micelles.

• Advances in Traditional Medicine
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• 제3권2호
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• pp.51-55
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• 2003

Resibufogenin is a single compound isolated from the skin venom gland of the toad (Bufo bufo gargarizans cantor). Formulations containing toad venom have been widely used as complementary and alternative medicines. However, like digitalis, resibufogenin possesses both pharmacological and toxicological activities. Our previous data indicated that resibufogenin induces electro-toxicity, including delayed afterdepolarization and triggered arrhythmias at high concentration, both in cardiac fiber in vitro and in beating heart in vivo.

• Bulletin of the Korean Chemical Society
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• 제25권9호
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• pp.1392-1396
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• 2004

The micellization of dodecylpyridinum chloride (DPC) assembled on aqueous gold nanoparticles has been studied as a function of concentration using Surface-Enhanced Raman Scattering (SERS). At the low concentration, the strong SERS band of the benzene ring moiety was observed at 1025 $cm^{-1}$, and assigned to “trigonal ring breathing”. According to high concentration of DPC, a new strong band was also appeared at 1012 $cm^{-1}$, which was assigned to “totally symmetry ring breathing”. The difference of two spectra seems to ascribe to the geometry of polar head group, i.e., pyridinium cation. These geometry exist flat-down at low concentration, whereas standing-up or tilted geometry at high concentration. The critical micelle concentration (CMC) was first obtained from the ratio of intensities of the two bands related to the benzene ring moiety by vibrational spectroscopy, and was about 28 mM. After the CMC, the benzene ring moiety in the micelle state was more restricted than in monomer state because there is no more change of intensities at 1012 $cm^{-1}$. In addition, the size of gold-assembled micelle was estimated using light scattering and it was about 328.3 nm.

• 청정기술
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• 제7권4호
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• pp.291-297
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• 2001

본 연구는 중금속 추출 공정에 쓰이는 사차 암모늄 염인 Aliquat 336을 포함하는 콜로이드 액상 에이프런 (colloidal liquid aphrons, CLAs)을 지용성 계면활성제와 수용성 계면활성제를 사용하여 제조하였고 연속상에서 농축된 CLAs의 안정성을 표면으로 떠오르는 유기 용매의 양을 시간에 따라 측정하여 평가하였다. 다양한 조건에서 CLAs의 안정성을 비교하기 위해서 반감기가 도입되었다. 전해질의 첨가나 pH의 변화와 같은 연속상의 상태 변화는 CLAs의 파괴(break-up) 속도에 상당히 영향을 미치는데 이 파괴 속도가 급격히 변화하는 임계 응집 농도가 존재한다. pH의 변화에 따른 임계 응집 농도를 측정하였고 이온의 세기, 수용성 계면활성제 Sodium Dodecyl Sulfonate (SDBS)의 농도에 대한 CLAs의 안정성에 대한 영향을 고찰하였다.

• 멤브레인
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• 제17권2호
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• pp.112-117
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• 2007

The application of membrane bioreactors for the depuration of wastewater coming from the washing of mineral oil storage tanks is described. Microfiltration hollow-fibre membranes were used in the submerged configuration. Filtration tests were carried out with a biomass concentration of about 15 g/L in order to assess the critical flux of the hollow fibre membrane used. Then particular care was taken in carrying out the performance runs in the sub-critical flux region. The reactor performance was very high, with removal efficiencies ranging between 93% and 97% also when the concentration of hydrocarbon was very high. Some kinetic parameters for the COD and the hydrocarbon removal were estimated.

• 한국응용과학기술학회지
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• 제23권2호
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• pp.160-168
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• 2006

The conductances of trimethyltetradecylammonium bromide (TTAB) plus triphenyltetradecyl phosphonium bromide (TTPB) and TTAB plus trimethylhexadecylammonium bromide (HTAB) over the entire mole fraction range of TTAB were measured in water and in cyclodextrin plus water mixtures at fixed 4 and 8 mM of cyclodextrin at $30^{\circ}C$. The conductivity plot for both binary mixtures shows a single break from which the mixed critical micelle concentration and degree of micelle ionization were computed. From the slope of the conductivity curve, the equivalent ionic conductivities of the monomeric, associated, and the micelle states were calculated and discussed with respect to the surfactant-cyclodextrin complexation in the whole mole fraction range of both surfactant binary mixtures. The association constant K between the respective monomeric surfactant and cyclodextrin cavity of fixed 4 mM cyclodextrin was computed by considering 1:1 association from the surface tension measurement. A comparison among the K values for HTAB-cyclodetrin, TTAB-cyclodextrin, and TTPB-cyclodextrin shows that the former complexation is significantly stronger in comparison to the other ones due to the longer hydrophobic tail.

• 한국응용과학기술학회지
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• 제18권4호
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• pp.325-331
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• 2001

The critical micelle concentration (CMC) at which micelles start to form from a surfactant solution is usually measured in terms of conventional concentration units. However, the thermodynamic potentials are expressed in terms of mole fraction $X_{CMC}$ and $X_{CMC}$ cannot be directly measured experimentally. The Gibbs free energy, ${\Delta}G^{\ast}_{mic}$, in particular is related to $X_{CMC}$ through ${\Delta}G^{\ast}_{mic}$ = $RTlnX_{CMC}$. When it comes to CMC, the molar CMC, $C_{CMC}$, differs only by the proportionality $C^{-1}_{w}$ with $C_{w}$ being the molarity of water. Hence, $C_{CMC}$ is found to be a proper representation of CMC. However, in calculation of ${\Delta}G^{\ast}_{mic}$ and other thermodynamic potentials from the CMC, $X_{CMC}$ or $C_{CMC}/C_{w}$ should be used.