• Wind and Structures
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• 제19권6호
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• pp.687-708
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• 2014

The performance of the $k-{\varepsilon}$ and $k-{\omega}$ two-equation turbulence models was investigated in computational simulations of the neutrally stratified atmospheric boundary layer developing above various terrain types. This was achieved by using a proposed methodology that mimics the experimental setup in the boundary layer wind tunnel and accounts for a decrease in turbulence parameters with height, as observed in the atmosphere. An important feature of this approach is pressure regulation along the computational domain that is additionally supported by the nearly constant turbulent kinetic energy to Reynolds shear stress ratio at all heights. In addition to the mean velocity and turbulent kinetic energy commonly simulated in previous relevant studies, this approach focuses on the appropriate prediction of Reynolds shear stress as well. The computational results agree very well with experimental results. In particular, the difference between the calculated and measured mean velocity, turbulent kinetic energy and Reynolds shear stress profiles is less than ${\pm}10%$ in most parts of the computational domain.

• BMB Reports
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• 제33권3호
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• pp.228-233
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• 2000

The steady-state investigation of the mechanism of Dhydroxyisovalerate dehydrogenase was performed in order to understand this type of kinetic patterns. The initial velocity was measured with various amounts of both substrates, NADPH and 2-ketoisovalerate. Double reciprocal plots gave patterns that conversed on or near the abscissa. Binding studies indicated that NADPH bound first to the enzyme. The product $NADP^+$ was found to be a competitive inhibitor with respect to NADPH at a constant concentration of 2-ketoisovalerate. However, it showed noncompetitive inhibition against 2-ketoisovalerate at a fixed amount of NADPH. Another product, D-hydroxyisovalerate, was a non-competitive inhibitor versus NADPH and 2-ketoisovalerate at constant levels of 2-ketoisovalerate and NADPH, respectively. These results were comparable with an ordered bi-bi mechanism, in which NADPH bound first to the enzyme, followed by the binding of 2- ketoisovalerate. $NADP^+$ is the last product to be released. The ordered reaction manner of D-hydroxyisovalerate dehydrogenase from 2-ketoisovalerate to D-hydroxyisovalerate allows the accurate regulation of valine metabolism and it may lead to the regulation of total biosynthesis of enniatins in the Fusarium species.

• 대한화학회지
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• 제32권5호
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• pp.416-421
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• 1988

메탄올-아세토니트릴 혼합 용매계에서 할로겐화 벤질(파라 치환된 브롬화 벤질과 요오드화 벤질)과 피리딘 사이의 친핵성 치환반응을 속도론적으로 연구하여 반응메카니즘을 밝혔다. 치환기 상호 작용 계수 ${\rho}_{XY}$값으로 부터 할로겐화 벤질과 피리딘 사이의 반응은 전이 상태에서 dissociative S$_N$2 메카니즘으로 진행되고 있음을 알 수 있었다. Hammett ${\rho}$(${\rho}_X$, ${\rho}_Y$) 값, Br${\o}$nsted ${\beta}_N$값, 분광 용매화 관계식의 계수 a, s 및 a/s 값을 이용하여 비교하였다. PES 모형과 QM 모형의 분석결과 QM 모형 해석에 잘 적용 됨을 알수 있었다.

• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4304-4308
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• 2011

Kinetic studies of the reactions of O,O-dimethyl Z-S-aryl phosphorothioates with X-benzylamines have been carried out in dimethyl sulfoxide at $85.0^{\circ}C$. The Hammett (log $k_2$ vs ${\sigma}_X$) and Br$\ddot{o}$nsted [log $k_2$ vs $pK_a$(X)] plots for substituent X variations in the nucleophiles are discrete with a break region between 4-Me and H, while the Hammett plots (log $k_2$ vs ${\sigma}_Z$) for substituent Z variations in the leaving groups are linear. The sign of the cross-interaction constant (${\rho}_{XZ}$) is positive for both the strongly and weakly basic nucleophiles. Greater magnitude of ${\rho}_{XZ}$ (= 2.54) value is observed with the weakly basic nucleophiles compared to with the strongly basic nucleophiles (${\rho}_{XZ}$ = 0.17). The deuterium kinetic isotope effects ($k_H/k_D$) involving deuterated benzylamines [$XC_6H_4CH_2ND_2$] are primary normal ($k_H/k_D$ > 1). The proposed mechanism is a stepwise with a rate-limiting leaving group expulsion from the intermediate involving a frontside nucleophilic attack with a hydrogen bonded, four-center-type transition state for both the strongly and weakly basic nucleophiles.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2471-2476
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• 2014

The aim of the present study is to explore the possibility of utilizing loess for the adsorption of total phosphorous (T-P) and total nitrogen (T-N) in water. Batch adsorption studies were performed to evaluate the influences of various factors like initial concentration, contact time and temperature on the adsorption of T-P and T-N. The adsorption data showed that loess is not effective for the adsorption of T-N. However, loess exhibited much higher adsorption capacity for T-P. At concentration of $1.0mgL^{-1}$, approximately 97% of T-P adsorption was achieved by loess. The equilibrium data were fitted well to the Langmuir isotherm model. The pseudo-second-order kinetic model appeared to be the better-fitting model because it has higher $R^2$ compared with the pseudo-first-order and intra-particle kinetic model. The theoretical adsorption equilibrium $q_{e,cal}$ from pseudo-second-order kinetic model was relatively similar to the experimental adsorption equilibrium $q_{e,exp}$. The thermodynamic parameters such as free energy ${\Delta}G$, the enthalpy ${\Delta}H$ and the entropy ${\Delta}S$ were also calculated.

• 한국수산과학회지
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• 제15권3호
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• pp.179-184
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• 1982

Lartobacillus bulgricus를 glucose를 제한기질로 하는 합성배지에서 연속배양한 결과를 요약하면 다음과 같다. 1. 본 실험 model은 Monod의 chemostat 이론을 적용시킬 수 있다. 2. 본 실험 model에서의 최대 cell production rate는 $0.178 g/1{\cdot}hr$로서 회석율 $0.414hr^{-1}$ 일 때이다. 3. 연속배양 결과 saturation constant($K_s$)는 7.69g/l, 최대비증식속도$(V_{max})$는 $0.62hr^{-1}$ 이었다. 4. wash out 현상은 $0.51hr^{-1}$에서 일어났으며cell yield coefficient는 0.016g/l 이었다.

• 한국환경과학회지
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• 제27권3호
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• pp.167-177
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• 2018

The removal characteristics of As and Se ions from aqueous solution by hexadecyl trimethyl ammonium bromide (HTMAB) modified anthracite (HTMAB-AT) were investigated under various conditions of contact time, pH and temperature. When the pH is 6, the zeta potential value of anthracite (AT) is -24 mV and on the other hand, the zeta potential value of the HTMAB-AT is +44 mV. It can be seen that the overall increase of about 60 mV. Increasing the (+) potential value indicates that the surface of the adsorbent had a stronger positive charge, so adsorption for the anion metal was increased. The isotherm data was well described by Langmuir and Temkin isotherm model. The maximum adsorption capacity was found to be 7.81 and 6.89 mg/g for As and Se ions from the Langmuir isotherm model at 298 K, respectively. The kinetic data was tested using pseudo first and pseudo second order models. The results indicated that adsorption fitted well with the pseudo second order kinetic model. The mechanism of the adsorption process showed that adsorption was dependent on intra particle diffusion model according to two step diffusion. The thermodynamic parameters(${\Delta}G^{\circ}$, ${\Delta}H^{\circ}$, and ${\Delta}S^{\circ}$) were also determined using the equilibrium constant value obtained at different temperatures. The thermodynamic parameters indicated that the adsorption process was physisorption, and also an endothermic and spontaneous process.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.74.1-74.1
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• 2011

As a demand for energy, many studies are increasing about energy resource. One of these resources is coal which reserves of underground. A lot of research to use coal is going on as method of IGCC (Integrated Gasification Combined Cycle). In addition, SNG(Substitute Natural Gas) and IGFC (Integrated Gasification Fuel Cell) are also being developed for fuel & electricity. This technology which uses synthesis gas after gasification is to produce electricity from the Fuel Cell. At this point, important thing is the components of synthesis gas. The main objective is to increase the proportion of methane and hydrogen in synthesis gas. The catalytic gasification is suitable to enhance the composition of methane and hydrogen. In this study, Exxon Predevelopment catalyst gasification study was served as a good reference and then catalytic gasification simulation process is conducting using Aspen Plus in this research. For this modelling, kinetic value should be calculated from Exxon's report which is used for modeling catalytic gasification. Catalytic gasification model was performed by following above method and was analyzed by thermodynamic method through simulation results.

• 한국자동차공학회논문집
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• 제6권4호
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• pp.166-177
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• 1998

Combustion characteristics of natural gas premixed flames is studied experimently and numerically by adopting a counterflow as a flamelet model in turbulent flames. Flame speeds are measured by employing LDV, and the results show that flame speed increases linearly with strain rate, which agrees well with numerical results. Parametric dependences of extinction strain rates are studied numerically with detailed kinetic mechanism to show that the addition of ethand to a methane premixed flame makes the flame more resistant to strain rate. The effect of pressure on the extinction strain rate is that the extinction strain rate increases up to 10 atm and them decreases, which is explained by competition of chain branching H+O2=OH+O and recombination reaction H+O2+M=HO2+M. Detailed mechanism having seventy-four step is systematically reduced to a nine-step and a five-step thermal NOx chemistry is reduced to two-step. Comparison between the results of the detailed and the reduced mechanisms demonstrates that the reduced mechanism successfully describes the essential features of natural gas premixed flames including extinction strain rate and NOx production.

• 한국초지조사료학회지
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• 제3권2호
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• pp.77-85
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• 1983

본(本) 보고(報告)는 광합성(光合成)의 동력학(動力學)에 관하여 연구(硏究)한 결과(結果)이며 더욱 동력학식(動力學式)의 타당성과 확실성(確實性)을 해바라기의 광합성실험(光合成實驗)으로 구명(究明)되었다. 광합성(光合成)의 동력학식(動力學式)은 물질(物質)의 동화작용(同化作用)과 이화작용(異化作用)의 수식화(數式化)로 부터 유도되었으며 그 결과(結果)는(6), (7)식(式)과 같다. 한편 해바라기를 재료(材料)로 한 제환경조건(諸環境條件)에 관계하는 광합성실험(光合成實驗) 결과(結果)로 얻어진 (8)식(式)에 의하여 동력학식(動力學式)에 대한 타당성이 입증되었다.