• Bulletin of the Korean Chemical Society
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• 제31권2호
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• pp.303-308
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• 2010

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for nucleophilic substitution reactions of 4-nitrophenyl benzoate (5a), 4-nitrophenyl 4-methoxybenzoate (5b), and 4-nitrophenyl 4-hydroxybenzoate (5c) with alkali metal ethoxides, $EtO^-M^+$ ($M^+=Li^+$, $Na^+$ and $K^+$) in anhydrous ethanol (EtOH) at $25.0{\pm}0.1^{\circ}C$. The plots of $k_{obsd}$ vs. [$EtO^-M^+$] exhibit upward curvatures in all cases, indicating that $M^+$ ions catalyze the reactions and ionpaired $EtO^-M^+$ species are more reactive than dissociated $EtO^-$. Second-order rate constants for reactions with dissociated $EtO^-$ and ion-paired $EtO^-M^+$ (i.e., $k_{EtO^-}$ and $k_{EtO^-M^+}$, respectively) have been calculated from ion-pair treatment for the reactions of 5a and 5b. However, such ion-pair treatment has failed to determine $k_{EtO^-}$ and $k_{EtO^-M^+}$ values for the reactions of 5c. It has been concluded that reactions of 5a and 5b are catalyzed by one metal ion, which increases electrophilicity of the reaction center through coordination on the carbonyl oxygen. In contrast, reactions of 5c have been suggested to involve two metal ions, i.e., the one coordinated on the carbonyl oxygen increases the electrophilicity of the reaction center while the other one associated on the phenoxy oxygen decreases the charge repulsion between the anionic reagents (i.e., $EtO^-$ and deprotonated 5c). It has been found that the rate equation derived from the mechanism involving two metal ions fits nicely to the kinetic results obtained for the reactions of 5c.

• Bulletin of the Korean Chemical Society
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• 제31권7호
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• pp.1988-1992
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• 2010

4-Amino-1,2,4-triazole copper complex (4-ATzCu) was synthesized, and its thermal behaviors, nonisothermal decomposition reaction kinetics were studied by DSC and TG-DTG techniques. The thermal decomposition reaction kinetic equation was obtained as: $d\alpha$ / dt =$10^{22.01}$ (1-$\alpha$)[-ln(1-$\alpha$)]$^{1/3}$ exp($-2.75\times10^4$ /T). The standard mole specific heat capacity of the complex was determined and the standard molar heat capacity is 305.66 $J{\cdot}mol^{-1}{\cdot}K^{-1}$ at 298.15 K. The entropy of activation $({\Delta}S^{\neq})$, enthalpy of activation $({\Delta}H^{\neq})$, and Gibbs free energy of activation $({\Delta}G^{\neq})$ are calculated as 171.88 $J{\cdot}mol^{-1}{\cdot}K^{-1}$ 225.81 $kJ{\cdot}mol^{-1}$ and 141.18 $kJ{\cdot}mol^{-1}$, and the adiabatic time-to-explosion of the complex was obtained as 389.20 s.

• 공업화학
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• 제9권6호
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• pp.857-863
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• 1998

Beer의 법칙을 이용하여 lysozyme-M. lysodeikticus cell의 용해반응속도 및 lysozyme의 활성을 측정할 수 있는 간단하고 새로운 실험방법을 제시하였다. M.lysodeikticus cell의 농도에 따라 용액의 UV 투과도를 측정하였으며 이것은 Beer의 법칙에 따르는 것으로 나타났다. 또한 용액 내의 lysozyme 농도 및 용해반응에 의해 생성되는 생성물은 UV 투과도에 전혀 영향을 미치지 않는 것으로 실험적으로 증명되었다. 따라서 lysozyme의 용해반응이 진행되는 동안 용액내에 존재하는 M. lysodeikticus cell의 농도는 UV-분광광도계를 이용하여 in-situ로 측정될 수 있었다. 이렇게 얻어진 M. lysodeikticus cell의 농도변화를 Michaelis-Menten식을 이용하여 lysozyme-M. lysodeikticus cell의 용해 반응속도 상수들을 결정하였다. 최대반응속도상수 $k_3$은 약 $0.1734sec^{-1}$로 나타났으며 Michaelis-Menten 상수는 약 $9.83{\times}10^{-6}M$으로 나타났다. Lysozyme의 용해반응속도가 활성에 의존하므로 이와 같은 측정을 통해 lysozyme의 활성도도 측정할 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제25권7호
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• pp.969-976
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• 2004

Cassava peelings waste, which is both a waste and pollutant, was chemically modified using mercaptoacetic acid (MAA) and used to adsorb $Cu^{2+}\;and\;Cd^{2+}$ from aqueous solution over a wide range of reaction conditions at $30^{\circ}C$. Acid modification produced a larger surface area, which significantly enhanced the metal ion binding capacity of the biomass. An adsorption model based on the $Cu^{2+}/Cd^{2+}$ adsorption differences was developed to predict the competition of the two metal ions towards binding sites for a mixed metal ion system. The phytosorption process was examined in terms of Langmuir, Freundlich and Dubinin-Radushkevich models. The models indicate that the cassava waste biomass had a greater phytosorption capacity, higher affinity and greater sorption intensity for $Cu^{2+}\;than\;Cd^{2+}$. According to the evaluation using Langmuir equation, the monolayer binding capacity obtained was 127.3 mg/g $Cu^{2+}$ and 119.6 mg/g $Cd^{2+}$. The kinetic studies showed that the phytosorption rates could be described better by a pseudo-second order process and the rate coefficients was determined to be $2.04{\times}10^{-3}\;min^{-1}\;and\;1.98{\times}10^{-3}\;min^{-1}\;for\;Cu^{2+}\;and\;Cd^{2+}$ respectively. The results from these studies indicated that acid treated cassava waste biomass could be an efficient sorbent for the removal of toxic and valuable metals from industrial effluents.

• 한국식품저장유통학회지
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• 제12권3호
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• pp.204-208
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• 2005

오가피 열수추출액의 유통 품질의 변화특성을 규명하기 위하여, 오가피($8{\sim}20$ mesh)를 열수 추출한 액을 nylon/PE(0.08 mm) pouch로 밀봉포장하거나 포장하지 않고, 가온조건(40, $60^{\circ}C$)에서 10일간 보관하면서 1일 간격으로 이화학적 품질특성을 조사하였다. 보관 중 추출액의 탁도, pH, 총폴리페놀 함량 및 DPPH 유리기 소거능 등은 감소하는 경향을 보였으나 저온과 포장에 의해 감소가 억제됨을 보였다. 적정산도는 고온에서 증가함을 보였으나 포장에 의해 증가가 억제되는 경향이었다. 가용성 고형분 함량은 포장과 온도의 영향을 받지 않고 거의 일정하게 유지되었다. 품질변화 kinetics를 model화 하기 위하여 반응속도론에 상사시켜 본 결과 오가피 추출액의 품질변화는 1차반응 속도식이 적합하였으며 품질변화 속도상수에 대한 온도의 영향은 Arrhenius 식에 잘 따른다고 할 수 있었다. 이상의 결과로 볼 때, 오가피 열수추출액의 부패억제와 항산화능 유지를 위해서는 포장과 저온유통이 필수적인 것으로 판단된다.

• 한국세라믹학회지
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• 제39권11호
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• pp.1028-1034
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• 2002

용융침투법을 이용 스피넬/지르코니아-유리 복합체를 제조하여 지르코니아 첨가가 복합체의 기계적 특성에 미치는 영향을 조사하였다. 유리 침투시간이 증가할수록 침투깊이는 Washburn식에 의한 포물선 관계로 증가하였으며 유리 침투상수 K는 기공 크기의 함수로 지르코니아 첨가량이 증가할수록 감소하였다. 지르코니아가 20 wt% 첨가되었을 때 스피넬/지르코니아-유리 복합체의 최적의 강도값(308 MPa)이 관찰되었지만 지르코니아 양이 증가함에 따라 유리 침투 상수와 투과율(transmittance)이 감소하였다. 지르코니아 첨가가 스피넬/지르코니아-유리 복합체의 기계적 특성 향상에 미치는 증진 효과는 크지 않은 것으로 관찰되었다.

• 한국환경과학회지
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• 제26권6호
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• pp.719-728
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• 2017

In order to investigate the adsorption characteristics for Sr ion using the Na-X zeolite synthesized from coal fly ash, batch tests and response surface analyses were carried out. The adsorption kinetic data for Sr ions, using Na-X zeolite, fitted well with the pseudo-second-order model. The uptake of Sr ions followed the Langmuir isotherm model, with a maximum adsorption capacity of 196.46 mg/g. Thermodynamic studies were conducted at different reaction temperatures, with the results indicating that Sr ion adsorption by Na-X zeolite was an endothermic (${\Delta}H^o$>0) and spontaneous (${\Delta}G^o$<0) process. Using the response surface methodology of the Box-Behnken method, initial Sr ion concentration ($X_1$), initial temperature ($X_2$), and initial pH ($X_3$) were selected as the independent variables, while the adsorption of Sr ions by Na-X zeolite was selected as the dependent variable. The experimental data fitted well with a second-order polynomial equation by multiple regression analysis. The value of the determination coefficient ($R^2=0.9937$) and the adjusted determination coefficient (adjusted $R^2=0.9823$) was close to 1, indicating high significance of the model. Statistical results showed the order of Sr removal based on experimental factors to be initial pH > initial concentration > temperature.

• 한국축산식품학회지
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• 제34권1호
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• pp.80-87
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• 2014

Ready-to-eat (RTE) Jokbal (Pig's trotter), which consists of pig's feet cooked in soy sauce and various spices, is a very popular and widely sold in Korean retail markets. Commercially, the anaerobically packed Jokbal have also become a popular RTE food in several convenience stores. This study evaluates the effects of storage temperature and packaging methods for the growth of C. perfringens in Jokbal. Growth kinetic parameters of C. perfringens in aerobically and anaerobically packed Jokbals are determined at each temperature by the modified Gompertz equation. The lag time, specific growth rate, and maximum population density of C. perfringens are being analyzed as a function of temperature and packaging method. The minimum growth temperature of C. perfringens in aerobically and anaerobically packed Jokbal is $24^{\circ}C$ and $18^{\circ}C$, respectively. The C. perfringens in Jokbal did not grow under conditions of over $50^{\circ}C$ regardless of the packaging methods, indicating that the holding temperature of Jokbal in markets must be maintained at above $50^{\circ}C$ or below $18^{\circ}C$. Growth of C. perfringens in anaerobically packed Jokbal is faster than in aerobically packed Jokbal when stored under the same conditions. This indicates that there are a higher risks associated with C. perfringens for anaerobically packed meat products.

• Journal of Advanced Marine Engineering and Technology
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• 제35권5호
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• pp.616-624
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• 2011

본 연구에서는 사각채널내에 주유속 방향에 가로지르게 배치된 반원 리브의 난류 유동에 대한 유동 특성과 열전달 증대에 관해 수치해석적으로 살펴보았다. 사각채널의 종횡비는 5이고, 수력직경 대비 리브 높이비는 0.07, 사각채널 높이 대비 리브 높이비는 0.117로서 리브 높이 대비 리브 피치비가 8~14인 리브를 주기적으로 배열하여 연구를 수행하였다. 난류 모델의 선정은 실제 현상과 근접한 벽 근처 유동 특성과 열전달을 위해 SST k-${\omega}$ 난류 모델과 v2-f 난류 모델을 이용하였다. 수치해석의 결과는 실험에 의 해 관찰된 난류 유동 특성, 열전달 및 마찰계수의 결과를 잘 예측함을 보여준다. 본 결과에서 난류 운동 에너지가 재순환류 영역의 확산과 밀접한 관련이 있음을 알 수 있고 v2-f 난류 모델이 SST k-${\omega}$ 난류 모델에 비해 실험결과를 더 잘 예측하였다.

• 한국농공학회논문집
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• 제58권6호
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• pp.55-69
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• 2016

RUSLE (Revised Universal Soil Loss Equation) is the empirical formular widely used to estimate rates of soil erosion caused by rainfall and associated overland flow. Among the factors considered in RUSLE, rainfall erosivity factor (R factor) is the major one derived by rainfall intensity and characteristics of rainfall event. There has been developed various methods to estimate R factor, such as energy based methods considering physical schemes of soil erosion and simple methods using the empirical relationship between soil erosion and annual total rainfall. This study is aimed to quantitatively evaluate the variation among the R factors estimated using different methods for South Korea. Station based observation (minutely rainfall data) were collected for 72 stations to investigate the characteristics of rainfall events over the country and similarity and differentness of R factors calculated by each method were compared in various ways. As results use of simple methods generally provided greater R factors comparing to those for energy based methods by 76 % on average and also overestimated the range of factors using different equations. The variation coefficient of annual R factors was calculated as 0.27 on average and the results significantly varied by the stations. Additionally the study demonstrated the rank of methods that would provide exclusive results comparing to others for each station. As it is difficult to find universal way to estimate R factors for specific regions, the efforts to validate and integrate various methods are required to improve the applicability and accuracy of soil erosion estimation.