• Bulletin of the Korean Chemical Society
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• v.14 no.1
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• pp.101-107
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• 1993

Ab initio calculations are carried out at the 6-311G$^{**}$ level for the $C_{2v}$ interactions of Be and Li atoms with acetylene molecule. The main contribution to the deep minima on the $^3B_2\;BeC_2H_2\;and\;^2B_2 LiC_2H_2$ potential energy curves is the b_2\;(2p(3b_2)-l{\pi}_g^*(4b_2))$ interaction, the $a_1\;(2s(6a_1)-I{\pi}_u(5a_1))$ interaction playing a relatively minor role. The exo deflection of the C-H bonds is basically favored, as in the $b_2$ interaction, due to steric crowding between the metal and H atoms, but the strong in-phase orbital interaction, or mixing, of the $a_1$ symmetry hydrogen orbital with the $5a'_1,\;6a'_1,\;and\;7a'_1$ orbitals can cause a small endo deflection in the repulsive complexes. The Be complex is more stable than the Li complex due to the double occupancy of the 2s orbital in Be. The stability and structure of the $MC_2H_2$ complexes are in general determined by the occupancy of the singly occupied frontier orbitals.

• The Journal of the Korea Contents Association
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• v.18 no.12
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• pp.229-237
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• 2018

This paper considers effective timetable modules in order to easily satisfy various user requirements during scheduling timetables in universities. Noticing that the methods for allocating time blocks change according to the timetable modules, we suggest six models of symmetric timetable modules composed of 4 blocks, and show that our models have more benefits without any loss from the viewpoint of customers, if the suppliers consider the decreasing upper bound of ratio utilizing space resources. By adapting a concept of potentially determined blocks and suggesting their management strategies, finally, we accomplish a method for supporting flexibility and controllability when the universities timetables are scheduled.

• Bulletin of the Korean Chemical Society
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• v.6 no.6
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• pp.362-366
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• 1985

The hydrogen atom transfer reaction between substituted methane, $CH_3X,$ and its radical, $CH_2X(X=H,F,CH_3,CN,OH\;and\;NH_2$ was studied by MINDO/3 method. The transition state(TS) structure and energy barriers were determined and variation of the transition state and of the reactivity due to the change of X were analyzed based on the potential energy surface characteristics. It was found that the greater the radical stabilization energy. the looser the TS becomes; the TS occurs at about 15% stretch of the C-H bond, which becomes longer as the radical stabilization energy of $CH_2X$ increasers. The intrinsic barrier, ${\Delta}E*_{x.x},$ of the reaction with X was found to increase in the order $H The degree of bond stretch of the C-H bond stretch of the C-H bond at the TS also had the same order indicating that the homolytic bond cleavage of the C-H bond is rate-determining. Orbital interactions at the TS between LUMO of the fragment $C{\ldots}H{\ldots}C$ and the symmetry adapted pair of nonbonding, $n{\pm}(=n_1{\pm}n_2),$ or pi orbitals of the two X atoms were shown to be the dominant contribution in determining tightness or looseness of the TS. The Marcus equation was shown to apply to the MINDO/3 barriers and energy changes of the reaction.

• Geophysics and Geophysical Exploration
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• v.25 no.1
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• pp.44-49
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• 2022

Closed-form expressions of vector gravity and gravity gradient tensor based on a line segment are derived. If a cylindrical object with axial symmetry is observed from a distance, it is possible to approximate it as a line segment; therefore, it is necessary to compute the gravity and the gravity gradient tensor due to a line source by using closed-form expressions. The gravitational potential for a line segment is defined as a one-dimensional integral, and this integral is differentiated with respect to the Cartesian coordinate system to derive the vector gravity. The expressions of the gravity gradient tensor are derived by differentiating the vector gravity once more in the same coordinate system.

• Structural Engineering and Mechanics
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• v.82 no.1
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• pp.41-53
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• 2022

We developed an accurate and simple vibration model to calculate the natural frequencies and their corresponding vibration modes for multi-span beam bridges with non-uniform cross-sections. A closed set of characteristic functions of a single-span beam was used to construct the vibration modes of the multi-span bridges, which were considered single-span beams with multiple constraints. To simplify the boundary conditions, the restraints were converted into spring constraints. Then the functional of the total energy has the same form as the penalty method. Compared to the conventional penalty method, the penalty coefficients in the proposed approach can be calculated directly, which can avoid the iteration process and convergence problem. The natural frequencies and corresponding vibration modes were obtained via the minimum total potential energy principle. By using the symmetry of the eigenfunctions or structure, the matrix size can be further reduced, which increases the computational efficiency of the proposed model. The accuracy and efficiency of the proposed approach were validated by the finite element method.

• Bulletin of the Korean Chemical Society
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• v.27 no.9
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• pp.1405-1417
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• 2006

The geometrical structures, potential energy surfaces, and energetics for the ligand exchange reactions of tetracoordinated platinum $(PtY_2L_2\;:\;Y,\;L=Cl^-,\;OH^-,\;OH_2,\;NH_3)$ complexes in the ligand-solvent interaction systems were investigated using the ab initio Hartree-Fock (HF) and Density Functional Theory (DFT) methods. The potential energy surfaces for the ligand exchange reactions used for the conversions of $(PtCl_4\;+\;H_2O)^{^\ast_\ast}\;to\;[PtCl_3(H_2O)\;+\;Cl^-]$ and $[Pt(NH_3)_2Cl_2\;+\;H_2O]$$[Pt(NH_3)_2Cl_2\;+\;H_2O]$ to $[Pt(NH_3)_2Cl(H_2O)\;+\;Cl^-] $ were investigated in detail. For these two exchange reactions, the transition states $([PtY_2L_2{\cdot}{\cdot}{\cdot}L^\prime])^{^\ast_\ast} $ correspond to complexes such as $(PtCl_4{\cdot}{\cdot}{\cdot}H_2O)^{^\ast_\ast}$ and $[Pt(NH_3)_2Cl_2{\cdot}{\cdot}{\cdot}H_2O]^{^\ast_\ast}$, respectively. In the transition state, $([PtCl_4{\cdot}{\cdot}{\cdot}H_2O]^{^\ast_\ast}$ and $[Pt(NH_3)_2Cl_2{\cdot}{\cdot}{\cdot}H_2O]]^{^\ast_\ast})$ have a kind of 6-membered $(Pt-Cl{\cdot}{\cdot}{\cdot}HOH{\cdot}{\cdot}{\cdot}Cl)$ and $(Pt-OH{\cdot}{\cdot}{\cdot}Cl{\cdot}{\cdot}{\cdot}HN)$ interactions, respectively, wherein a central Pt(II) metal directly combines with a leaving $Cl^-$ and an entering $H_2O$. Simultaneously, the entering $H_2O$ interacts with a leaving $Cl^-$. No vertical one metal-ligand interactions $([PtY_2L_2{\cdot}{\cdot}{\cdot}L^\prime]) $ are found at the axial positions of the square planar $(PtY_2L_2)$ complexes, which were formed via a vertically associative mechanism leading to $D_{3h}$ or $C_{2v}$-transition state symmetry. The geometrical structure variations, molecular orbital variations (HOMO and LUMO), and relative stabilities for the ligand exchange processes are also examined quantitatively. Schematic diagrams for the dissociation reactions of {PtCl4(H2O)n(n=2,4)} into {$PtCl_3(H_2O)_{(n-2)}\;+\;Cl^-(H_2O)_2$} and the binding energies {$PtCl_4(H_2O)_n$(n = 1-5)} of $PtCl_4$ with water molecules are drawn.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.3
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• pp.180-188
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• 1999

The dynamic elastic properties of metal matrix composites were investigated by resonant ultrasound spectroscopy(RUS). The composites used in this study consisted of 2124 aluminum alloy reinforced with different concentrations of SiC particles. RUS can determine the nine independent elastic stiffness($C_{ij}$) for the orthorhombic symmetry on a small specimen simultaneously. The elastic constants were determined as a function of the volume fraction. A concept of effective aspect ratio. which combine the aspect ratio and the orientation of reinforcement. was used to calculate the initial moduli from Mori-Tanaka theory for the input of RUS minimization code. Young's moduli can be obtained from the measured stiffnesses. The results show that the elastic stiffness increases with increment of the particle content. The behavior of elastic stiffness indicates that the particle redistribution induced by the extrusion process enlarges the transversely isotropic symmetry as the fraction of reinforced particles increase. This relationship could be used for determination of the volume fractions of reinforcement as a potential tool of nondestructive material characterization.

• Journal of Intelligence and Information Systems
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• v.18 no.2
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• pp.177-192
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• 2012

This is a study of match-making systems that considers the mutual satisfaction of matching partners. Recently, recommendation systems have been applied to people recommendation, such as recommending new friends, employees, or dating partners. One of the prominent domain areas is match-making systems that recommend suitable dating partners to customers. A match-making system, however, is different from a product recommender system. First, a match-making system needs to satisfy the recommended partners as well as the customer, whereas a product recommender system only needs to satisfy the customer. Second, match-making systems need to include as many participants in a matching pool as possible for their recommendation results, even with unpopular customers. In other words, recommendations should not be focused only on a limited number of popular people; unpopular people should also be listed on someone else's matching results. In product recommender systems, it is acceptable to recommend the same popular items to many customers, since these items can easily be additionally supplied. However, in match-making systems, there are only a few popular people, and they may become overburdened with too many recommendations. Also, a successful match could cause a customer to drop out of the matching pool. Thus, match-making systems should provide recommendation services equally to all customers without favoring popular customers. The suggested match-making system, called Mutually Beneficial Matching (MBM), considers the reciprocal satisfaction of both the customer and the matched partner and also considers the number of customers who are excluded in the matching. A brief outline of the MBM method is as follows: First, it collects a customer's profile information, his/her preferable dating partner's profile information and the weights that he/she considers important when selecting dating partners. Then, it calculates the preference score of a customer to certain potential dating partners on the basis of the difference between them. The preference score of a certain partner to a customer is also calculated in this way. After that, the mutual preference score is produced by the two preference values calculated in the previous step using the proposed formula in this study. The proposed formula reflects the symmetry of preferences as well as their quantities. Finally, the MBM method recommends the top N partners having high mutual preference scores to a customer. The prototype of the suggested MBM system is implemented by JAVA and applied to an artificial dataset that is based on real survey results from major match-making companies in Korea. The results of the MBM method are compared with those of the other two conventional methods: Preference-Based Matching (PBM), which only considers a customer's preferences, and Arithmetic Mean-Based Matching (AMM), which considers the preferences of both the customer and the partner (although it does not reflect their symmetry in the matching results). We perform the comparisons in terms of criteria such as average preference of the matching partners, average symmetry, and the number of people who are excluded from the matching results by changing the number of recommendations to 5, 10, 15, 20, and 25. The results show that in many cases, the suggested MBM method produces average preferences and symmetries that are significantly higher than those of the PBM and AMM methods. Moreover, in every case, MBM produces a smaller pool of excluded people than those of the PBM method.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.170.1-170.1
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• 2016

$Bi_2Te_3$ has long been studied for its excellent thermoelectric characteristics. Recently, this material has been known as a topological insulator (TI). The surface states within the bulk band gap of a TI, which are protected by the time reversal symmetry, contribute to the conduction at the surface, while the bulk is in insulating state. In contrast to the bulk defects tuning the chemical potential to the Dirac energy, the native defects near the surface are expected not to change the shape of the Fermi surface and the related spin structure. Using scanning tunneling microscopy (STM), we have systematically characterized surface or near surface defects in p- and n- doped $Bi_2Te_3$, and identified their structure by first principles calculations. In addition, bias-polarity dependences of STM images revealed the electron donor/acceptor nature of each defect. A detailed theoretical study of the surface states near the Dirac energy reveals the robustness of the Dirac point, which verifies the effectiveness of the disturbance on the backscattering from various kinds of defects.

• Progress in Superconductivity and Cryogenics
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• v.15 no.4
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• pp.53-58
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• 2013

KSTAR in-vessel cryo-pump has been installed in the vacuum vessel top and bottom side with up-down symmetry for the better plasma density control in the D-shape H-mode. The cryogenic helium lines of the in-vessel cryo-pump are located at the vertical positions from the vacuum vessel torus center 2,000 mm. The inductive electrical potential has been optimized to reduce risk of electrical breakdown during plasma disruption. In-vessel cryo-pump consists of three parts of coaxial circular shape components; cryo-panel, thermal shield and particle shield. The cryo-panel is cooled down to below 4.5 K. The cryo-panel and thermal shields were made by Inconel 625 tube for higher mechanical strength. The thermal shields and their cooling tubes were annealed in air environment to improve the thermal radiation emissivity on the surface. Surface of cryo-panel was electro-polished to minimize the thermal radiation heat load. The in-vessel cryo-pump was pre-assembled on a test bed in 180 degree segment base. The leak test was carried out after the thermal shock between room temperature to $LN_2$ one before installing them into vacuum vessel. Two segments were welded together in the vacuum vessel and final leak test was performed after the thermal shock. Commissioning of the in-vessel cryo-pump was carried out using a temporary liquid helium supply system.