• Computers and Concrete
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• v.1 no.3
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• pp.249-260
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• 2004

The stress transmission mechanism in pretensioned concrete beams, though very interesting from an economical point of view, is very complex, integrating various phenomenons such as sliding, bond, bursting. For long the complexity of this mechanism has led engineers to provide a massive rectangular anchorage zone at each end of the beam. The necessity of using such a concrete reinforcement is certainly unquestionable in post-tensioned beams. However in pretensioned elements the stresses induced in concrete in the anchorage zone are smaller than in post-tensioned elements. In this article the stress field in the end zone is calculated numerically and from this analysis the possible reduction of the cross-section of the anchorage block is examined.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.10a
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• pp.21-24
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• 2000

Traction motors driven by several type inverters have been subjected to increasing demands for higher operating temperature, more demands for duty cycles, higher starting current, frequent voltage transients and finally severe environmental exposure. For applications to inverter duty, traction motors needs a special insulation system, which has characteristics of increased bond strength, lower operating temperature and higher turn-to-tum insulation. Also it needs major contributors to insulation life and reliability of motors, which more considered by temperature, voltage, frequency, rise time, pulse configuration, wire thickness and insulation materials. In this paper, to evaluate of reliability and expected life, it is analyzed the several stresses and their degradation mechanism on insulation system of AC traction motor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.6 s.237
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• pp.852-859
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• 2005

Molecular dynamics simulations of nanoimprint lithography in which a stamp with patterns is pressed onto amorphous poly-(methylmethacrylate) (PMMA) surface are performed to study the deformation of polymer. Force fields including bond, angle, torsion, inversion, van der Waals and electrostatic potential are used to describe the intermolecular and intramolecular force of PMMA molecules and stamp. Periodic boundary condition is used in horizontal direction and Nose-Hoover thermostat is used to control the system temperature. As the simulation results, the adhesion forces between stamp and polymer are calculated and the mechanism of deformation are investigated. The effects of the adhesion and friction forces on the polymer deformation are also studied to analyze the pattern transfer in nanoimprint lithography. The mechanism of polymer deformation is investigated by means of inspecting the indentation process, molecular configurational properties, and molecular configurational energies.

• Journal of the Korean Magnetic Resonance Society
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• v.5 no.2
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• pp.130-137
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• 2001

Backbone dynamics of the catalytic residues in free and steroid-bound $\Delta$$^{5}$ -3- ketosteroid isomerase from Pseudomonas testosteroni has been examined by $^{15}$ N relaxation measurements. The relaxation data were analyzed using the model-free formalism to extract the model-free parameters (S$^2$, $\tau$$_{e}$, and R$_{ex}$). Tyr-34 and Asp-99 exhibit enhanced high-frequency (pico- to nanosecond) internal motions in the free enzyme, which are restricted upon ligand binding, while Asp-38 experiences severe restriction of the internal motions in the fee enzyme, suggesting that Tyr-14 and Asp-99 are more actively involved in the ligand binding than Asp-38. The results also indicate that the H-bond network in the catalytic cavity might be slightly strengthened upon ligand binding, which may have some implications on the enzyme mechanism.he enzyme mechanism.m.

• Tribology and Lubricants
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• v.15 no.2
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• pp.212-217
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• 1999

The wear characteristics and wear mechanisms of dental composite resins were investigated. Composite resins such as Metafil, Silux Plus, Heliomolar and Palfique Estelite were selected as specimens and contents of filler in specimens in order to evaluate the effect of Prepolymerized Particle Fillers in friction and wear characteristics. Ball on flat wear tester was used for the wear test at room temperature. The friction coefficient of Metafil was quite high relatively, and the wear resistances of Silux Plus and Palfique Estelite were better than that of Metafil and Heliomolar at the same experimental condition. It was found that The main wear mechanism is plastic flow and abrasive wear by failure of filler's bond to the matrix.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 1999.11b
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• pp.109-114
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• 1999

The deposition kinetics of fines on fibres was studied to elucidate the flocculation mechanism of a PAM/bentonite retention aid. It is shown that polymer-induced co-flocculation is not permanent. This phenomenon is attributed to a stabilising effect of polymer transfer between surfaces. The resulting polymer layers have a reduced bridging ability with naked surfaces. The addition of bentonite increases the bond strength between fibres and fines, and links non-briding layers. These results explain the positive influence of bentonite on fines retention.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.301-301
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• 2011

We present theoretical investigations of the self-assembled growth of one-dimensional (1D) molecular lines directed across the dimer rows on the H-terminated Si(001) surface [1]. Based on density-functional theory calculations, a new growth mechanism of the 1D acetylacetone line is proposed [2], which involves the radical chain reaction initiated at two dangling-bond sites on one side of two adjacent Si dimers. It is also enabled that, if an H-free Si dimer were employed as the initial reaction site, a 1D acetylacetone line can grow along the dimer row. Our findings represent the first insight into the growth of 1D molecular lines not only across but also along the dimer rows on the H-terminated Si(001) surface.

• Journal of Welding and Joining
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• v.15 no.6
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• pp.32-40
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• 1997

Solid state diffusion bonding is the joining process performed by creep and diffusion, which is accelerated by heating below melting temperature and proper pressing, in vacuum or shielding gas atmosphere. By this process we can obtain sufficient joint which can't be expected from the fusion welding. For Ti-6Al-4V alloy, the optimum solid state diffusion bonding condition and mechanical properties of the joint were found, and micro void morphology at bond interface was observed by SEM. The results of tensile test showed sufficient joint, whose mechanical properties are similar to that of base metal. 850$^{\circ}$C, 3MPa is considered as the optimum bonding condition. Void morphology at interface is long and flat at the initial stage. As the percentage of bonded area increases, however, small and round voids are found. Variation of void shape can be explained as follows. As for the void shrinkage mechanism, at the initial stage, power law creep is the dominant, but diffusion mechanism is dominant when the percentage of bonded area is increased.

• Journal of the Korean Chemical Society
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• v.19 no.3
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• pp.179-185
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• 1975

A new mechanism is proposed for aromatic substitution, involving the formation of pseudo molecular complexes at the transition state. It accounts for the addition reactions of aromatic compounds with double bond reagents such as ozone, somium tetraoxide and carbene as well as all of the features of electrophilic substitution reactions. The pseudo molecular complex has been proved to be formed by quantum-chemical considerations using the simple Huckel method.

• Bulletin of the Korean Chemical Society
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• v.29 no.9
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• pp.1769-1773
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• 2008

fThe kinetics and mechanism of the reactions of Y-O-aryl phenylphosphonochloridothioates with X-pyridines are investigated in acetonitrile at 35.0 ${^{\circ}C}$. The negative value of the cross-interaction constant, $\rho$XY = −0.46, indicates that the reaction proceeds by concerted $S_N2$ mechanism. The observed $k_H/k_D$ values involving d-5 pyridine ($C_5D_5N$) nucleophiles are greater than unity (1.05-1.11). The net primary deuterium kinetic isotope effects, $(k_H/k_D)_{net}$ = 1.28-1.35, excluding the increased $pK_a$ effect of d-5 pyridine are obtained. The transition state with a hydrogen bond between the leaving group Cl and the hydrogen (deuterium) atom in the C-H(D) is suggested for the studied reaction system.