• Journal of the Korean Chemical Society
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• v.26 no.3
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• pp.117-127
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• 1982

In order to analyze the role of axial carbon atoms in rotational barrier of ethane, we take the carbonless ethane, as a model, which is made of six hydrogens in coordinates of ethane. The energy of the system is calculated by McWeeny's open-shell restricted Hartree-Foch selfconsistent-field (RHF-SCF) method, and the transition density on the staggered-to-eclipsed rotation is examined. As being expected, the eclipsed form of the model is more stable than the staggered one. Through the transition density comparison of this model and real ethane, it is found that the existence of the axial carbon atoms induces the electronic density to be diluted in the vicinity of protonic sites and to be attracted to the region of carbon atoms or further to C-C bond region as the barrier is traversed. This migration of electronic charge tell us that the barrier to the internal rotation of ethane originates from the fact that the magnitude of electronic energy depression is not large enough to offset the increased nuclear-nuclear repulsion on the staggered-to-eclipsed rotation.

• Structural Engineering and Mechanics
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• v.18 no.5
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• pp.645-669
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• 2004

In seismic analysis of moment-resisting frames, beam-column connections are often modeled with rigid joint zones. However, it has been demonstrated that, in ductile reinforced concrete (RC) moment-resisting frames designed based on current codes (to say nothing of older non-ductile frames), the joint zones are in fact not rigid, but rather undergo significant shear deformations that contribute greatly to global drift. Therefore, the "rigid joint" assumption may result in misinterpretation of the global performance characteristics of frames and could consequently lead to miscalculation of strength and ductility demands on constituent frame members. The primary objective of this paper is to propose a rational method for estimating the hysteretic joint shear behavior of RC connections and for incorporating this behavior into frame analysis. The authors tested four RC edge beam-column-slab connection subassemblies subjected to earthquake-type lateral loading; hysteretic joint shear behavior is investigated based on these tests and other laboratory tests reported in the literature. An analytical scheme employing the modified compression field theory (MCFT) is developed to approximate joint shear stress vs. joint shear strain response. A connection model capable of explicitly considering hysteretic joint shear behavior is then formulated for nonlinear structural analysis. In the model, a joint is represented by rigid elements located along the joint edges and nonlinear rotational springs embedded in one of the four hinges linking adjacent rigid elements. The connection model is able to well represent the experimental hysteretic joint shear behavior and overall load-displacement response of connection subassemblies.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.251-262
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• 2011

Human ether-a-go-go related gene (hERG) potassium channel blockade, an undesirable side effect which might cause sudden cardiac death, is one of the major concerns facing the pharmaceutical industry. The purpose of this study is to develop an in silico QSAR model which uncovers the structural parameters of T-type calcium channel blockers to reduce hERG blockade. Comparative molecular similarity indices analysis (CoMSIA) was conducted on a series of piperazine and benzimidazole derivatives bearing methyl 5-(ethyl(methyl)amino)-2-isopropyl-2-phenylpentanoate moieties, which was synthesized by our group. Three different alignment methods were applied to obtain a reliable model: ligand based alignment, pharmacophore based alignment, and receptor guided alignment. The CoMSIA model with receptor guided alignment yielded the best results : $r^2$ = 0.955, $q^2$ = 0.781, $r^2_{pred}$ = 0.758. The generated CoMSIA contour maps using electrostatic, hydrophobic, H-bond donor, and acceptor fields explain well the structural requirements for hERG nonblockers and also correlate with the lipophilic potential map of the hERG channel pore.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.27-31
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• 2012

This study was designed to examine the feasibility of functionalized mesoporous silica as the adsorbent for benzene, toluene, ethylbenzene, and xylene isomers (BTEX) in groundwater. p-Xylene was used as the model compound of BTEX. A series of functionalized mesoporous silica with MCM-41 type of structure was synthesized using a co-condensation method. Monoamine, triamine, nitrile, phenyl, and octyl groups were functionalized to the mesoporous silica structure. Adsorption sites for p-Xylene in a functionalized mesoporous silica were Si-O-Si covalent bond, the surfactant, and the functional group. Octyl-functionalized mesoporous silica with stearyltrimethylammonium chloride as a surfactant showed the highest adsorption ability. The maximum xylene adsorption capacity of the octyl-functionalized mesoporous silica with stearyltrimethylammonium chloride based on Langmuir model was 4.17 mmol/g on $20^{\circ}C$, which was 2.9 times higher than that of MCM-41.

• Analytical Science and Technology
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• v.7 no.4
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• pp.505-515
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• 1994

$^1H$ NMR spectra for monocyanide ligated ferriprotoporphyrin(hemin) complex and dicyanide coordinated hemin complex in dimethylsulfoxide(DMSO-$d_6$) solution have been recorded and analyzed. NMR spectra of hemin-cyanide complexation in DMSO-$d_6$ exhibit that the cyanide ligation to hemin is temperature-dependent. Thermodynamic parameters for the monocyanide ligated hemin to dicyanide ligated hemin are consistent with endothermic process with ${\Delta}H^{\circ}=736.6cal/mol$ and ${\Delta}S^{\circ}=16.4eu$. Detailed analysis of the anomalous deviation from Curie behavior for CN/DMSO coordinated hemin complex demonstrates the presence of a high spin character, and this weaker axial field relative to the purely low-spin dicyanide hemin complex is supposed to attribute to instantaneously ruptured iron-DMSO bond. This complex may serve as a useful model to characterize electronic/molecular structure of hemoproteins, which one of axial ligands is weak.

• Journal of the Korean Magnetic Resonance Society
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• v.8 no.2
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• pp.77-85
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• 2004

$^1$H-detected $^{15}$N NMR was employed to investigated the effect of mutation (Y14F) on the dynamic properties of catalytic residues in ${\Delta}^5$-3- ketosteroid isomerase (KSI) from Conamonas testosteroni. In particular, the backbone dynamics of the catalytic residues have been studied in free enzyme and its complex with a steroid ligand, 19-nortestosterone hemisuccinate, by $^{15}$N relaxation measurements. The relaxation data were analyzed using the model-free formalism to extract the model-free parameters (S$^2$, ${\tau}_e$, and R$_{ex}$). The results show that the mutation causes a significant decrease in the order parameter (S$^2$) for the catalytic residues of free Y14F KSI, presumably due to breakdown of the hydrogen bond network by mutation. In addition, the order parameters of Phe-14 and Asp-99 increased slightly upon ligand binding, indicating a slight restriction of the high-frequency (pico- to nanosecond) internal motions of the residues in the complexed Y14F KSI, while the order parameter of Tyr-55 decreased significantly upon ligand binding.

• Bulletin of the Korean Chemical Society
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• v.16 no.2
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• pp.112-120
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• 1995

The conformational study on malonic acid, hydrogen malonate, malonate, malonyl methyl sulfide, and malonyl methyl sulfide anion, as the model compounds of malonyl-CoA, was carried out using the semiempirical MO methods (MNDO, AM1, and PM3) and hydration shell model. On the whole, the feasible conformations of malonic acid, hydrogen malonate, and malonate seem to be similar to each other. In malonic acid and malonate, two carboxyl groups are nearly perpendicular to the plane of the carbon skeleton, despite of different orientation of two carboxyl groups themselves. In particular, two carboxyl groups of hydrogen malonate are on the plane formed by carbon atoms with an intramolecular hydrogen bond. The calculated results on the geometry and conformation of three compounds are reasonably consistent with those of X-ray and spectroscopic experiments as well as the previous calculations. The orientation of two carbonyl groups of malonyl methyl sulfide is quite similar to that of malonic acid, but different from that of its anion. Especially, the computed probable conformations of the sulfide anion by the three methods are different from each other. The role of hydration seems not to be crucial in stabilizing the overall conformations of malonic acid, hydrogen malonate, malonate, and malonyl methyl sulfide. However, the probable conformations of the unhydrated sulfide anion obtained by the MNDO and AM1 methods become less stabilized by including hydration. The AM1 method seems to be appropriate for conformational study of malonyl-CoA and its model compounds because it does not result in the formation of too strong hydrogen bonds and significant change in conformational energy from one compound to another.

• Advances in nano research
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• v.7 no.1
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• pp.39-49
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• 2019

This paper focuses on two main objectives. The first one is to exploit an energy equivalent model and finite element method to evaluate the equivalent Young's modulus of single walled carbon nanotubes (SWCNTs) at any orientation angle by using tensile test. The calculated Young's modulus is validated with published experimental results. The second target is to exploit the finite element simulation to investigate mechanical buckling and natural frequencies of SWCNTs. Energy equivalent model is presented to describe the atomic bonding interactions and their chemical energy with mechanical structural energies. A Program of Nanotube modeler is used to generate a geometry of SWCNTs structure by defining its chirality angle, overall length of nanotube and bond length between two adjacent nodes. SWCNTs are simulated as a frame like structure; the bonds between each two neighboring atoms are treated as isotropic beam members with a uniform circular cross section. Carbon bonds is simulated as a beam and the atoms as nodes. A finite element model using 3D beam elements is built under the environment of ANSYS MAPDL environment to simulate a tensile test and characterize equivalent Young's modulus of whole CNT structure. Numerical results are presented to show critical buckling loads, axial and transverse natural frequencies of SWCNTs with different orientation angles and lengths. The understanding of mechanical behaviors of CNTs are essential in developing such structures due to their great potential in wide range of engineering applications.

• Structural Engineering and Mechanics
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• v.85 no.3
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• pp.337-351
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• 2023

In this paper, the shear behavior of soft filling in rectangular-hollow concrete specimens was simulated using the 2D particle flow code (PFC2D). The laboratory-measured properties were used to calibrate some PFC2D micro-properties for modeling the behavior of geo-materials. The dimensions of prepared and modeled samples were 100 mm×100 mm. Some disc type narrow bands were removed from the central part of the model and different lengths of bridge areas (i.e., the distance between internal tips of two joints) with lengths of 30 mm, 50 mm, and 70 mm were produced. Then, the middle of the rectangular hollow was filled with cement material. Three filling sizes with dimensions of 5 mm×5 mm, 10 mm×5 mm, and 15 mm×5 mm were provided for different modeled samples. The parallel bond model was used to calibrate and re-produce these modeled specimens. Therefore, totally, 9 different types of samples were designed for the shear tests in PFC2D. The shear load was gradually applied to the model under a constant loading condition of 3 MPa (σc/3). The loading was continued till shear failure occur in the modeled concrete specimens. It has been shown that both tensile and shear cracks may occur in the fillings. The shear cracks mainly initiated from the crack (joint) tips and coalesced with another one. The shear displacements and shear strengths were both increased as the filling dimensions increased (for the case of a bridge area with a particular fixed length).

• Industry Promotion Research
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• v.7 no.4
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• pp.97-108
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• 2022

This paper examined the impact of financing structure on the innovation efficiency of SMEs by constructing an econometric model using panel data of SMEs listed on the SME board from 2010 to 2020 as the research sample. The innovation efficiency of SMEs was measured by the Stochastic Frontier Analysis (SFA), the relationship between financing structure and innovation efficiency of SMEs was examined with the help of the Tobit model, and the corresponding heterogeneity analysis was conducted. Finally, the robustness of the model was tested. It was concluded that the effects of debt and equity financing on the quantitative efficiency of innovation were non-linear and mainly showed an inverted "U" shaped relationship. For innovation quality efficiency, bond financing could positively contribute, while equity financing negatively inhibits. Finally, the corresponding advice was given.