• Bulletin of the Korean Chemical Society
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• v.8 no.3
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• pp.193-196
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• 1987

The gas phase pyrolyses of eight esters have been studied by MNDO-MO method. In the ethylformate pyrolysis, ${\alpha}$-methylation had a steric releasing effect whereas ${\beta}$-methylation had a steric crowding in the transition state; the latter, however, is over-compensated by a greater electronic repulsion resulting in a net steric releasing effect. Considerations of formal charges and geometrical changes involved in the activation led us to propose a pyrolysis mechanism in which a preequilibrium of acidic proton transfer is followed by the rate-limiting bond polarization of $C_{\alpha}$-O bond in a cyclic transition state.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.222-222
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• 1999

From extensive measurements of the resistance and the dynamic resistance as functions of magnetic field and temperature, we find that the transport in the insulating state beyond the superconductor-insulator (S-I) transition is dominated by bosons(Cooper pairs and/or vortices) and cannot be described by the theory of the fermionic insulating phase. The maximum of the magnetoresistance at B = B$_m$ and the following negative slope in R(B) with increasing field can be explained by the crossover from the "Bose-glass" to the "Fermi-glass" phase as suggested by Paalanen, Hebard, and Ruel. The zero bias peak in dv/dl for biases below the characteristic voltage V$_c$ (or current $I_c$), gives a clue for the assumption of the "dirty boson" model which states that the insulating state above the critical magnetic field is the phase where Cooper pairs are localized due to the Coulomb blockade with a nonvanishing order parameter. The shift to a lower value of the critical magnetic field by overlaying thin Au layer, which is known as a strong spin-orbit scatterer, also supports the bosonic nature of the S-I transition.

• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3634-3640
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• 2011

We have performed quantum mechanical calculations to study the geometries and binding energies of biologically important, cyclic hydrogen-bonded complexes, such as formic acid + $H_2O$, formamidine + $H_2O$, formamide + $H_2O$, formic acid dimer, formamidine dimer, formamide dimer, formic acid + formamide, formic acid + formamidine, formamide + formamidine, and barrier heights for the double proton transfer in these complexes. Various ab initio, density functional theory, multilevel methods have been used. Geometries and energies depend very much on the level of theory. In particular, the transition state symmetry of the proton transfer in formamidine dimer varies greatly depending on the level of theory, so very high level of theory must be used to get any reasonable results.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.133-133
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• 2015

Recently, it has been shown that the ${\omega}B97X-D/aVTZ$ method is strongly recommended as the best practical density functional theory(DFT) for rigorous and extensive studies of saturated or unsaturated $C_4F_8$ species because of its high performance and reliability especially for van der Waals interactions. All the feasible isomerization and dissociation paths of $C_4F_8$ molecules were investigated at this theoretical level and rate constants of their chemical reactions were computed by using variational transition-state theory for a deep insight into $C_4F_8$ reaction mechanisms. Fates and roles of C4F8 molecules and their fragments in plasma phases could be clearly explained based on our computational results.

• Bulletin of the Korean Chemical Society
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• v.10 no.1
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• pp.50-57
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• 1989

A pressure effect of the dehydrogenation of ethylalcohol catalyzed by alcoholdehydrogenase was observed in Tris-HCl buffer, pH 8.8 from $25^{\circ}C$ to $35^{\circ}C$ under high pressure system by using our new theory. The theory makes it possible for us to obtain all rate and equilibrium constants for each step of all enzymatic reaction with a single intermediate. We had enthalpy and volume profiles of the dehydrogenation to suggest a detail and reasonable mechanism of the reaction. In these profiles, both enthalpy and entropy of the reaction are positive and their values decrease with enhancing pressure. It means that the first step is endothermic reaction, and its strength decrease with elevating pressure. At the same time, all activation entropies have large negative values, which prove that not only a ternary complex has a more ordered structure at transition state, but also water molecules make a iceberg close by the activated complex. In addition to this fact, the first and second step equilibrium states are controlled by enthalpy. The first step kinetic state is controlled by enthalpy but the second step kinetic state is controlled by entropy.

• Journal of the Korean Chemical Society
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• v.34 no.6
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• pp.593-599
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• 1990

A series of new, square planar, and mixed-ligand complexes of Ni(Ⅱ), Pd(Ⅱ), and Pt(Ⅱ) have been prepared. From the observation of electronic spectrum for the variation of the ligand substituents, the very intense absorption band in the visible range is by the electronic transition of dithiolene to diimine ligand, HOMO to LUMO. In the various solvent systems the IT band shows the similar behavior to IT transition of mixed-valence dinuclear complexes followed with Hush theory, happens rto dominently by the inner sphere charge transfer transition. The negative solvatochromism represents that the excited-state electric dipole is reduced or reversed by the electronic transition.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.897-900
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• 2012

We examined theory for force-induced unbinding on a two-dimensional free energy surface where the internal dynamics of biomolecules is coupled with the rupture process under constant tension f. We show that only if the transition state ensemble is narrow and activation barrier is high, the f-dependent rupture rate in the 2D potential surface can faithfully be described using an effective 1D energy profile.

• Bulletin of the Korean Chemical Society
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• v.16 no.5
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• pp.427-432
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• 1995

A model based on two coupled generalized Langevin equations is proposed to investigate the trans-stilbene photoisomerization dynamics. In this model, a system which has two independent coordinates is considered and these two system coordinates are coupled to the same harmonic bath. The direct coupling between the system coordinates is assumed negligible and these two coordinates influence each other through the frictional coupling mediated by solvent molecules. From the Hamiltonian which is equivalent to the coupled generalized Langevin equations, we obtain the transition state theory rate constants of the stilbene photoisomerization. The rates obtained from this model are compared to experimental results in n-alkane solvents.

• Journal of the Korean Chemical Society
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• v.64 no.3
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• pp.145-152
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• 2020

Flip-flop rate constants were measured by dithionite assay of NBD-PE fluorescence in DMPC/POPC vesicles made of various DMPC/POPC ratios. The activation energy, enthalpy, entropy, and free energy were determined based on the transition state theory. We found that the activation energy, enthalpy, and entropy increased as the amount of POPC increased, but the activation free energy was almost constant. These experimental results and other similar studies allow us to propose that the POPC molecules included in DMPC vesicles affect the flip-flop motion of NBD-PE in DMPC/POPC vesicles via increasing the packing order of the ground state of the bilayer of the vesicles. The increase in the packing order in the ground state seems to be a result of the effect of the overall molecular shape of POPC with a monounsaturated tail group, rather than the effect of the longer tail group.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.3
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• pp.213-220
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• 2008

The object of this paper is to propose a method to deal with the problem of modeling user specifications in approaches based on supervisory control and Petri nets. However, most of Petri Net approaches are based on forbidden states specifications, and these specifications are suitable the use of tool such as the reachability graph. But these methods were not able to show the user specification easily and these formalisms are generally limited by the combinatorial explosion that occurs when attempting to model complex systems. Herein, we propose a new efficient method using FSSTP (Forbidden Sequences of State-Transitions Problem) and theory of region. Also, to detect and avoid the deadlock problem in control process, we use DAPN method (Deadlock Avoidance Petri nets) for solving this problem in control model.