• Title/Summary/Keyword: kinetics

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Polymorphism of Sulpiride and its Pharmaceutical Applications(II) Transformation Kinetics of Sulpiride Polymorphs (Sulpiride의 Polymorphism 및 그 약제학적 연구(II) Polymorph 상호간의 Transformation Kinetics)

  • 김길수;이민화
    • YAKHAK HOEJI
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    • v.26 no.4
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    • pp.231-237
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    • 1982
  • The transformation kinetics between polymorphs of sulpiride and the effect of additives on the transformation kinetics were studied. The results could be summarized as follows. 1. Transformation kinetics of the polymorph form I to form II in water suspenion was first order type and transformation rate constant at $25^{\circ}C$ is $2.61{\times}10^{-2}min^{-1}$, the half life of form I was about 27 minutes and the activation energy for transformation was 21.35 Kcal/mole. 2. Glycerine and coloring agents increased the rate of transformation., In the case of polysorbate 80, the rate constant increased in proportion to the concentration of polyserbate 80. Simple syrup showed no effect 3n transformation kinetics.

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Accumulation and Decay of Macroscopic Correlations in Elementary Reactions Kinetics

  • Doktorov, Alexander B.;Kipriyanov, Alexander A.;Kipriyanov, Alexey A.
    • Bulletin of the Korean Chemical Society
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    • v.33 no.3
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    • pp.941-952
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    • 2012
  • In the present contribution the Encounter Theory (ET) (the prototype of the classical Collision Theory in rarefied gases) concepts for widely occurring diffusion assisted irreversible bulk reactions A + A ${\rightarrow}$ C and A + B ${\rightarrow}$ C in liquid solutions examined by the authors in the literature are analyzed and compared with each other for these different types of reactions. It is shown that for a particular case of equal initial concentrations $[A]_0=[B]_0$ in the reaction A + B ${\rightarrow}$ C, when the kinetics of both reactions A + A ${\rightarrow}$ C and A + B ${\rightarrow}$ C in the framework of formal chemical kinetics and ET are the same, the accumulation of macroscopic correlations breaking the concepts of independent encounters and leading to the Generalized Encounter Theory (GET) are drastically different. The influence of the force interaction and the decay of nonstable reactants on the time behavior the macroscopic correlations is also briefly discussed.

Investigation on the Prediction Performance of the Chemical Kinetics for the Numerical Simulation of MILD Combustion (마일드 연소장 수치계산을 위한 화학반응기구의 예측성능 검토)

  • Kim, Yu Jeong;Oh, Chang Bo
    • 한국연소학회:학술대회논문집
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    • 2012.11a
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    • pp.341-344
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    • 2012
  • The prediction performance of the chemical kinetics for the numerical simulation of MILD combustion was investigated. A wall-confined turbulent methane jet combustor was adopted as a configuration. Four chemical kinetics, such as a global 3-step, WD4, Skeletal, and DRM-19, were investigated, The air stream of the wall-confined MILD jet combustor was diluted with combustion products. It was found that the DRM-19 was optimal for the numerical simulation of the MILD combustion.

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Induction Parameter Modeling of Hydrocarbon Fuel/Oxidizer for Detonation Wave Analysis (데토네이션 파 해석을 위한 탄화수소 연료/산화제의 Induction Parameter Modeling)

  • Choi, Jeong-Yeol;Yang, Vigor
    • 한국연소학회:학술대회논문집
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    • 2003.05a
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    • pp.57-62
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    • 2003
  • A general procedure of obtaining reliable one-step kinetics model for hydrocarbon mixture from the fully detailed chemistry is described iin this study. One-step theoretical formulation of the induction parameter model IPM uses a theoretical reconstruction of the induction time database obtained from a detailed kinetics library. Non-dimensional induction time calculations is compared with that of detailed kinetics. The IPM was latter implemented to fluid dynamics code and applied for the numerical simulation of detonation wave propagation. The numerical results including the numerical smoked-foil record show the all the details of the detonation wave propagation characteristics at the cost around 1/100 of the detailed kinetics calculation.

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FURTHER EVALUATION OF A STOCHASTIC MODEL APPLIED TO MONOENERGETIC SPACE-TIME NUCLEAR REACTOR KINETICS

  • Ha, Pham Nhu Viet;Kim, Jong-Kyung
    • Nuclear Engineering and Technology
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    • v.43 no.6
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    • pp.523-530
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    • 2011
  • In a previous study, the stochastic space-dependent kinetics model (SSKM) based on the forward stochastic model in stochastic kinetics theory and the Ito stochastic differential equations was proposed for treating monoenergetic space-time nuclear reactor kinetics in one dimension. The SSKM was tested against analog Monte Carlo calculations, however, for exemplary cases of homogeneous slab reactors with only one delayed-neutron precursor group. In this paper, the SSKM is improved and evaluated with more realistic and complicated cases regarding several delayed-neutron precursor groups and heterogeneous slab reactors in which the extraneous source or reactivity can be introduced locally. Furthermore, the source level and the initial conditions will also be adjusted to investigate the trends in the variances of the neutron population and fission product levels across the reactor. The results indicate that the improved SSKM is in good agreement with the Monte Carlo method and show how the variances in population dynamics can be controlled.

Effect of Ga, Nb Addition on Disproportionation Kinetics of Nd-Fe-B Alloy

  • Kwon, H.W.;Yu, J.H.
    • Journal of Magnetics
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    • v.14 no.4
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    • pp.150-154
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    • 2009
  • The effect of Ga and, Nb addition on the kinetics and mechanism of the disproportionation of a Nd-Fe-B alloy were investigated by isothermal thermopiezic analysis (TPA) using $Nd_{12.5}Fe_{(81.1-(x+y))}B_{6.4}Ga_xNb_y$ (x=0 and 0.3, y= 0 and 0.2) alloys. The addition of Ga and Nb retarded the disproportionation kinetics of the Nd-Fe-B alloy significantly, and increased the activation energy of the disproportionation reaction. The disproportionation kinetics of the $Nd_{12.5}Fe_{(81.1-(x+y))}B_{6.4}Ga_xNb_y$ alloys measured under an initial hydrogen pressure of 0.02 MPa were fitted to a parabolic rate law. This suggested that during the disproportionation of $Nd_{12.5}Fe_{(81.1-(x+y))}B_{6.4}Ga_xNb_y$ alloys with an initial hydrogen pressure of 0.02 MPa, a continuous disproportionation product is formed and the overall reaction rate is limited by the diffusion of hydrogen atoms (or ions).

Theoretical and Experimental Studies on the Kinetics of Cation Redistribution Processes in Complex Oxides

  • Shi, Jianmin;Becker, Klaus-Dieter
    • Journal of the Korean Ceramic Society
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    • v.47 no.1
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    • pp.39-46
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    • 2010
  • The kinetics of cation reequilibration have been studied theoretically and experimentally in complex oxides after an external perturbation of equilibrium by temperature jumps. A general kinetic model for cation redistribution amongst non-equivalent sites in complex oxides is derived based on a local homogeneous point defect mechanism involving cation vacancies. Temperature-jump optical relaxation spectroscopy has been established to investigate cation kinetic processes in spinels and olivines. The kinetic model satisfactorily describes the experimental absorbance relaxation kinetics in cobalt containing olivines and in nickel containing spinels. It is found that the kinetics of cation redistribution in complex oxides shows a strong temperature- and composition-dependence. Activation energies for cation redistribution in Co-Mg olivines are found to range between 200 and 220 kJ/mol whereas an energy barrier of about 230 kJ/mol is observed in the case of nickel gallate spinel.

Effects of Temperature on Flocculation Kinetics Using Fe(III) Coagulant in Water Treatment (정수처리시 Fe(III) 응집제를 사용한 응집동력학에 대한 온도의 영향)

  • 강임석
    • Journal of Environmental Science International
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    • v.4 no.2
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    • pp.181-194
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    • 1995
  • Flocculation kinetics using ferric nitrate as a coagulant to coagulate kaolin clay in water was examined as a tool to investigate the effect of low temperature under tightly controlled treatment conditions. Both the particle size distribution data obtained from Automatic Image Analysis (AIA) system and the on-line measurement of the degree of turbidity fluctuation in a flowing suspension by Photometric Dispersion Analyzer (PDA) were used to measure flocculation kinetics. Results show that cold water temperature had a pronounced detrimental effect on flocculation kinetics. For improving flocculation kinetics at low water temperature, maintaining constant pOH to adjust water chemistry for temperature changes was found to be partially effective only in the more acidic pH range studied.

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A Kinetic Studies of Pyrolysis and Combustion of Sewage Sludge (하수 슬러지의 열분해 및 연소 Kinetics 연구)

  • Roh, Seon Ah
    • Resources Recycling
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    • v.23 no.6
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    • pp.47-53
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    • 2014
  • Effective treatment and energy conversion technologies are necessary due to the ban of the dumping of organic waste including the sewage sludge. In this study, the kinetics of pyrolysis and combustion were derived in a TGA and thermobalance reactor, which is essential for thermal conversion of sewage sludge to energy. Three steps are shown for the pyrolysis in TGA and the different pre-exponential factors and activation energies are derived depending on the temperature range. Three models of gassolid reaction were applied to the reaction kinetics analysis for the combustion of sewage sludge char and shrinking core model was an appropriated model. Apparent activation energy and pre-exponential factor were evaluated and the effect of oxygen partial pressure was examined.

Folding Mechanism of WT* Ubiquitin Variant Studied by Stopped-flow Fluorescence Spectroscopy

  • Park, Soon-Ho
    • Bulletin of the Korean Chemical Society
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    • v.31 no.10
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    • pp.2877-2883
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    • 2010
  • The folding kinetics of $WT^*$ ubiquitin variant with valine to alanine mutation at sequence position 26 (HubWA) was studied by stopped-flow fluorescence spectroscopy. While unfolding kinetics showed a single exponential phase, refolding reaction showed three exponential phases. The semi-logarithmic plot of urea concentration vs. rate constant for the first phase showed v-shape pattern while the second phase showed v-shape with roll-over effect at low urea concentration. The rate constant and the amplitude of the third phase were constant throughout the urea concentrations, suggesting that this phase represents parallel process due to the configurational isomerization. Interestingly, the first and second phases appeared to be coupled since the amplitude of the second phase increased at the expense of the amplitude of the first phase in increasing urea concentrations. This observation together with the roll-over effect in the second folding phase indicates the presence of intermediate state during the folding reaction of HubWA. Quantitative analysis of Hub-WA folding kinetics indicated that this intermediate state is on the folding pathway. Folding kinetics measurement of a mutant HubWA with hydrophobic core residue mutation, Val to Ala at residue position 17, suggested that the intermediate state has significant amount of native interactions, supporting the interpretation that the intermediate is on the folding pathway. It is considered that HubWA is a useful model protein to study the contribution of residues to protein folding process using folding kinetics measurements in conjunction with protein engineering.