• 한국분무공학회지
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• 제24권4호
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• pp.157-162
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• 2019

This numerical study was analyzed to predict the flammability limits of biodiesel and diesel fuels in the high temperature and pressure conditions. To achieve this, the biodiesel fuel was simulated with the chemical species of n-heptane (n-C₇H₁₆), methyl decanoate (C₁₁H₂₂O₂), and methyl-9-decenoate (C₁₁H₂₀O₂), and the diesel fuel was substituted the chemical species of n-heptane. The closed 0-D homogeneous reactor model which was employed the 1100 K of ambient temperature and 35 atm of ambient pressure was used for the simulation of constant volume combustion, and the equivalence ratio was changed from 0.3 to 2.5 conditions. In addition, a comparative analysis study was conducted with the results of HCCI engine simulation and flammability limits according to the changes of equivalence ratio. The results of combustion temperature, pressure, and ignition delay were increased when the equivalence ratio elevated from 0.3 to 1.3 conditions because the increase in fuel oxidation rate affects the chemical reaction of the overall combustion process. Furthermore, the CO and NO_X production under the rich combustion conditions are considered to have a trade off relationship since the OH radicals and O₂ chemical species are greatly affected the CO and NO_X production and oxidation processes.

• KSBB Journal
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• 제4권3호
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• pp.229-234
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• 1989

보효소고분자화를 위한 담체로서 $\beta$ - casein에 NAD$/^+$ 를 효소법으로 고정화하였다. 21개의 glutamine 잔기를 함유하는 수용성고분자물질로서 transglutaminase 촉매작용에 의해 NAD$/^+$analog의 amino기와 r-glutamylamine bond를 형성하여 결합하였다. $\beta$-Casein은 $/_a_s_1+$(1분자내에 15개의 glutamine잔기를 함유)에 비하여 효과적인 고정화담체이었으며 8-(6-amino hexyl) aminonicotinamide ade-nine dinucleotide는 N$^6$-[(6-aminohexyl)-carba-moylmethy]-NAD$^+$에 비하여 고정화수율이 높았다. 고정화에 있어 NAN$_3$의 첨가는 필수적이었다. 고정화 NAD$^+$ Km치는 NAD$^+$또는 NAD$^+$analog와 비슷하였으나 max.rate는 고정화하므로써 31% 감소되었다. 그러나 고정화하므로써 NAD$^+$의 alkaline pH에서의 안정성은 증대되었으며, 고정화 보효소를 칼슘침전하여 분리회수하였을 경우에도 보효소 활성을 유지, NAD$^+$형 (산화형)과 NADH형(환원형)으로 상호전환되므로써 재생되었다.

• Journal of Microbiology and Biotechnology
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• 제26권12호
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• pp.2087-2097
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• 2016

Most cold-adapted enzymes possess higher $K_m$ and $k_{cat}$ values than those of their mesophilic counterparts to maximize the reaction rate. This characteristic is often ascribed to a high structural flexibility and improved dynamics in the active site. However, this may be less convincing to cold-adapted metabolic enzymes, which work at substrate concentrations near $K_m$. In this respect, cold adaptation of a shikimate kinase (SK) in the shikimate pathway from psychrophilic Colwellia psychrerythraea (CpSK) was characterized by comparing it with a mesophilic Escherichia coli homolog (EcSK). The optimum temperatures for CpSK and EcSK activity were approximately $30^{\circ}C$ and $40^{\circ}C$, respectively. The melting points were $33^{\circ}C$ and $45^{\circ}C$ for CpSK and EcSK, respectively. The ${\Delta}G_{H_2O}$ (denaturation in the absence of denaturing agent) values were 3.94 and 5.74 kcal/mol for CpSK and EcSK, respectively. These results indicated that CpSK was a cold-adapted enzyme. However, contrary to typical kinetic data, CpSK had a lower $K_m$ for its substrate shikimate than most mesophilic SKs, and the $k_{cat}$ was not increased. This observation suggested that CpSK may have evolved to exhibit increased substrate affinity at low intracellular concentrations of shikimate in the cold environment. Sequence analysis and homology modeling also showed that some important salt bridges were lost in CpSK, and higher Arg residues around critical Arg 140 seemed to increase flexibility for catalysis. Taken together, these data demonstrate that CpSK exhibits characteristics of cold adaptation with unusual kinetic parameters, which may provide important insights into the cold adaptation of metabolic enzymes.

• 한국재료학회지
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• 제10권6호
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• pp.450-455
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• 2000

실리콘 소자가 더욱 미세화되면서, 발생되는 power consumption, crosstalk와 interconnection delay 등을 감소시키기 위해 $SiO_2$ 대신에 저유전 상수막의 적용이 고려되어진다. 본 논문에서는, 저유전 상수 층간 절연막 재료로 유망한 폴리이미드의 식각 특성에 $O_2/SF_6$ 가스가 미치는 영향을 연구하였다. 폴리이미드의 식각률을 SF(sub)6 가스의 첨가에 따라 산소와 hydrocarbon 폴리머 간의 반응을 억제하는 비휘발성 물질은 fluorine 화합물의 형성에 의해 감소되었다. 반면에, 기판 전극의 전압 증가는 물리적인 충격을 통해 식각 공정을 증가시켰다. 또한 작은 량의 SF(sub)6 가스 첨가는 식각 topography에 바람직하였다. 폴리이미드 식각을 위한 $SiO_2$ hard mask 사용은 산소 플라즈마 식각 하에서 효과적이었다(선택비-30). 반면에 $O_2SF_6$ 가스 조성은 식각 선택비를 4로 저하시키게 되었다. 이러한 결과를 기초로, $1-2\mu\textrm{m}$ 선폭을 가진 PI 2610의 식각을 원활히 수행할 수 있었다.

• 한국수소및신에너지학회논문집
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• 제13권2호
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• pp.110-118
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• 2002

The hydrogen storage vessel having a good heat conductivity along with a simple structure and a low cost for these alloys was designed and manufactured, and then its characteristic properties were studied in this study. The various parts in hydrogen storage vessel consisted of copper pipes and stainless steel of 250 mesh reached the setting temperature after 4~5 minutes, which indicated that storage vessel had a good heat conductivity that was required in application. And also the storage vessel had a good property of hydrogen transport considering that the reaction time between hydrogen and rare-earth metal alloys in storage vessel was found to be within 10 min at $18^{\circ}C$ under 10 atmospheric pressure. It showed that the average capacity of discharged hydrogen volume was found to be $120{\ell}$ for $MmNi_{4.5}Mn_{0.5}$ under discharging conditions of $40^{\circ}C{\sim}80^{\circ}C$ at a constant flow rate of $5{\ell}$/min. It was found that the optimum discharging temperature for obtaining an appropriate pressure of 3atm was determined to be $60^{\circ}C$ for $MmNi_{4.5}Mn_{0.5}$ hydrogen storage alloy.

• 대한화학회지
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• 제35권3호
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• pp.233-239
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• 1991

합성된 2-chloroethyl acrylate를 출발물질로 이용하여 5-fluorouracil의 $N_1$-위치에 각각 hydroxyethyl, acryloyloxyethyl, poly(acryloyloxyethyl)기를 가진 5-fluorouracil 유도체를 높은 수율로 얻었다. 이들 유도체들과 HCl과의 가수분해속도를 물-에탄올(1:1) 혼합용매에서 UV 분광기를 이용하여 측정하였다. 1-hydroxyethyl-5-fluorouracil, 1-acryloyloxyethyl-5-fluorouracil 및 Poly(1-acryloyloxyethyl-5-fluorouracil)의 가수분해속도는 각각 $k=1.38{\times}10^{-4}$sec, $9.25{\times}10^{-5}$/sec, $4.16{\times}10^{-5}$/sec 이었다. 또한, 합성된 5-fluorouracil 유도체의 열분해성에 대해 논의하였다.

• 상하수도학회지
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• 제29권3호
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• pp.407-414
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• 2015

The effect of activated carbon particle diameter (i.e. US sieve No. $8{\times}10$ ($d_p{\approx}2.19mm$), $18{\times}20$ ($d_p{\approx}0.92mm$), $50{\times}60$ ($d_p{\approx}0.27mm$) and $170{\times}200$ ($d_p{\approx}0.081mm$) on caffeine adsorption is investigated. BET surface area was increased with decreasing particle diameter ($d_p$), and caffeine adsorption rates increased with decreasing $d_p$. Moreover, pseudo-second order model is predicted the experimental data more accurately than pseudo-first order model, and the fastest rate constant ($k_2$) was $1.7g\;mg^{-1}min^{-1}$ when $d_p$ was 0.081 mm. Surface diffusion coefficient (Ds) was decreased with decreasing $d_p$ based on the minimum sum of square error (SSE). Practically, certain ranges of Ds are acceptable with high reliability ($R^2$) and it is determined that the effect of $d_p$ on Ds is unclear. The effect of pH on caffeine adsorption indicated the dependency of m/L ratio (mass liquid ratio) and $pH_{pzc}$. The $pH_{pzc}$ (i.e. $7.9{\pm}0.2$) was not affected by $d_p$. The higher caffeine adsorption at pH 4 and pH 7 than at pH 10 is due to $pH_{pzc}$, not $pk_a$ of caffeine.

• 한국세라믹학회지
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• 제46권5호
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• pp.456-461
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• 2009

Chemical composition and status of chemical bonding of the YAG($Y_3Al_5O_{12}$) ceramics after the exposure to fluorine plasma have been investigated using X-ray photoelectron spectroscopy, with the analysis on its erosion behavior. On the surface, F showed the maximum content, decreasing with depth, meanwhile the cation composition remained almost constant, irrespective of the position. The peaks due to Y in the reaction layer consisted of two kinds, showing the Y-O and Y-F bonds. These surface modifications under fluorine plasma seem to promote the erosion of the YAG ceramics. Excess addition of $Al_2O_3$ or $Y_2O_3$ into stoichiometric YAG produced 2nd phases of $Al_2O_3$ and $YAlO_3$, respectively, resulting in the slight difference in the local erosion rates. But, the overall average erosion rate was not sensitive to such excess additions of $Al_2O_3$ or $Y_2O_3$.

• 대한화학회지
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• 제31권6호
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• pp.527-533
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• 1987

아쿠아옥소몰리브덴(IV) 삼합체와 티오시안산이온과의 착물생성반응에 대한 속도론적 연구를 분광광도법으로 행하였다. 이 반응의 관찰된 속도상수, $k_{obsd}$는 다음과 같이 주어진다. $k_{obsd}\;=\;{k_O + k_H[H^+]^2}(SCN^-) + k_r$. 이온세기가 2.30이고 온도가 25$^{\circ}$C일때 $k_f$ 와 $k_r$의 값은 각각 $(3.78 {\pm} 0.61) {\times} 10^{-4}M^{-1}s^{-1}$ 과 $(6.93 {\pm} 2.39) {\times} 10^{-4}s^{-1}$이다. 활성화파라미터는 ${\Delta}H^*\;=\;50.71{\pm}6.91 kJmol^{-1}$이고 ${\Delta}S^*\;=\;-121.65JK^{-1}mol^{-1}$이다. 이 반응의 메카니즘에 대하여 논의된다.

• 대한화학회지
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• 제40권9호
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• pp.640-648
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• 1996

Chitin을 epichlorohydrin과 반응시켜 가교 chitin을 합성하고, $C_2$ 위치의 아세트아미드기를 탈아세틸화하여 가교 chitosan을 얻었다. 가교 chitosan을 증류수에 팽윤시킨 다음 글리세린과 silver sulfadiazine을 가하여 고분자 matrix를 제조하였다. 이렇게 제조된 matrix로부터 in vitro에서의 약물 방출 pattern을 고찰하기 위해 pH7.4 인산염 완충용액 중에서 약물의 함유량, 글리세린의 농도 변화 및 matrix 두께변화에 미치는 인자들에 관하여 연구 검토 하였다. 고분자 matrix내의 약물의 함유량과 matrix의 두께가 증가할수록 약물 방출 지속 시간은 지연되었다. 그러나 글리세린의 함유량이 증가함에 따라 약물 방출 지속 시간은 오히려 감소 하였다. 또한 약물의 함유량과 글리세린의 함유량이 증가할수록 겉보기 방출속도상수 (K)값도 증가하였으나, matrix 두께가 증가함에 따라서는 겉보기 방출속도상수(K)값이 일정하였다. 이상과 같이 가교 chitosan은 약품의 방출 조절형 제제로서 사용 가능성을 나타냈으며, 약물로 사용된 silver sulfadiazine의 방출거동은 Higuchi model에 따른 확산으로 생각되었다.