• Proceedings of the KIEE Conference
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• 1997.07c
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• pp.1025-1027
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• 1997

In this paper, the digital distance relay of transmission lines under fault conditions is discussed. Distance relay is used to protect transmission lines. The principle of distance relay is well-known ; the impedance measured by a relay is Proportional to the distance from the relay to the fault. Hence, by measuring the impedance, it can be determined whether the line is faulted or not. Unfortunately, the measurement of the fault distance is distorted by Mutual Coupling. To implement more reliable and practical digital distance relay, the mutual coupling effect has to be considered.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.42-48
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• 2013

Potassium N-heterobiaryltrifluoroborates were successfully prepared via a selective Cu-catalyzed C-N coupling reaction. The $BF_3K$ moiety was well tolerated under the reaction conditions involving CuI and dimethyl-ethylenediamine (DMEDA) in the presence of DMSO. The Pd-catalyzed Suzuki-Miyaura cross couplings of potassium N-heterobiaryltrifluoroborates with bromoarenes were studied to prepare the N-heterotriaryl compounds. Moreover, homocoupling, iodination, and hydroxylation of potassium N-heterobiaryltrifluoroborates provided the corresponding products in high yields.

• Journal of the Optical Society of Korea
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• v.9 no.3
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• pp.99-102
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• 2005

Directional couplers of gradient-index plastic optical fibers were fabricated and characterized. In particular, we have employed a core-facet technique to make the directional couplers, which require mechanical side polishing and linkage. We have measured insertion loss, excess loss, and coupling ratio of the fabricated couplers as a function of polishing depth and coupling length. We found that polishing depth of $\~300{\mu}m$ and coupling length of $\~35mm$ are optimum conditions for minimizing the insertion and excess losses and for achieving 1: 1 coupling ratio.

• Journal of the Korean Chemical Society
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• v.21 no.3
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• pp.180-186
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• 1977

The preparation of 1-chloro-2-iodoperfluorocycloalkenes was achieved with a short reaction time and a high yield when the starting compound was iodinated via the metalation process using an alkyllithium reagent. Especially, the high yield of 1-chloro-2-iodo-perfluorocyclohexene was obtained when 1,2-dichloroperfluorocyclohexene was iodinated via the same reaction conditions. The coupling reaction of 1,2-dihaloperfluorocycloalkenes was also achieved with a lower reaction temperature and a shorter reaction time when the equal slurry mixture of fluorocycloolefines and DMF was reacted at a high pressure in a sublimer. The yield of the coupling product was greatly improved by this process. For a typical example, the coupling reaction of the 1-chloro-2-iodotetrafluorocyclobutene was proceeded with a higher yield of the product than that of the reported reaction, when the present method was adopted. A plausible reaction mechanism of the present coupling reactiont was proposed and the physical characteristics of the coupling product were confirmed.

• Tribology and Lubricants
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• v.34 no.1
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• pp.23-32
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• 2018

Coupling is a mechanical component that transmits rotational force by connecting two shafts. Curvic coupling is widely used in high-performance systems because of its excellent power transmission efficiency and easy machining. However, coupling applications change dynamic behavior by reducing the stiffness of an entire system. Contact surface stiffness is an important parameter that determines the dynamic behavior of a system. In addition, the roughness profile of a contact surface is the most important parameter for obtaining contact stiffness. In this study, we theoretically establish the process of contact and bending stiffness analysis by considering the rough surface contact at Curvic coupling. Surface roughness parameters are obtained from Nayak's random process, and the normal contact stiffness of a contact surface is calculated using the Greenwood and Williamson model in the elastic region and the Jackson and Green model in the elastic-plastic region. The shape of the Curvic coupling contact surface is obtained by modeling a machined shape through an actual machining tool. Based on this modeling, we find the maximum number of gear teeth that can be machined according to the contact angle. Curvic coupling stiffness is calculated by considering the contact angle, and the calculation process is divided into stick and slip conditions. Based on this process, we investigate the stiffness characteristics according to the contact angle.

• Bulletin of the Korean Chemical Society
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• v.34 no.7
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• pp.2099-2104
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• 2013

We present here an efficient and simple method for preparation of highly active Pd heterogeneous catalyst (CNT-Pd), specifically by reaction of dichlorobis(triphenylphosphine)palladium ($Pd(PPh_3)_2Cl_2$) with thiolated carbon nanotubes (CNTs). The as-prepared CNT-Pd catalysts demonstrated an excellent catalytic activity for the carbon-carbon (C-C) cross-coupling reactions (i.e. Suzuki, Stille, and decarboxylative coupling reactions) under mild conditions. The CNT-Pd catalyst could easily be removed from the reaction mixture; additionally, in the decarboxylative coupling of iodobenzene and phenylpropiolic acid, it showed a six-times recyclability, with no loss of activity. Moreover, once its activity had decreased by repeated recycling, it could easily be reactivated by the addition of phosphine ligands. The remarkable recyclability of the decarboxylative coupling reaction is attributable to the high degree of dispersion of Pd catalysts in CNTs. Aggregation of the Pd catalysts is inhibited by their strong adhesion to the thiolated CNTs during the chemical reactions, thereby permitting their recycling.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.309-315
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• 1996

An analysis is presented on the stability of elastic cantilever column subjected to uniformly distributed follower forces as to the influence of the elastic restraints and a tip mass at the free end. The elastic restraints are formed by both the translational and the rotatory springs. For this purpose, the governing equations and boundary conditions are derived by using Hamilton's principle, and the critical flutter loads and frequencies are obtained from the numerical evaluation of the eigenvalue functions of this elastic system. The added tip mass increases as a whole the critical flutter load in this system, but the presence of its moment of inertia of mass has a destabilizing effect. The existence of the translational and rotatory spring at the free end increases the critical flutter load of the elastic cantilever column. Nevertheless their effects on the critical flutter load are not uniform because of their coupling. The translational spring restraining the end of cantilever column decreases the critical flutter load by coupling with a large value of tip mass, while by coupling with the moment of inertia of tip mass its effect on the critical flutter load is contrary. The rotatory spring restraining the free end of cantilever column increases the critical flutter load by coupling with the tip mass, but decreases it by coupling with the moment of inertia of tip mass.

• Journal of KSNVE
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• v.7 no.1
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• pp.91-97
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• 1997

An analysis is presented on the stability of an elastic cantilever column having the elastic restraints at its free end, carrying an added tip mass, and subjected to uniformly distributed follower forces. The elastic restraints are formed by both a translational spring and a rotatory spring. For this purpose, the governing equations and boundary conditions are derived by using Hamilton's principle, and the critical flutter loads and frequencies are obtained from the numerical evaluation of the eigenvalue functions of this elastic system. The added tip mass increases as a whole the critical flutter load of the elastic cantilever column, but the presence of its moment of inertia of mass has a destabilizing effect. The existence of the translational and rotatory springs at the free end increases the critical flutter load of the elastic cantilever column. Nevertheless, their effects on the critical flutter load are not uniform because of their coupling. The translational spring restraining the free end of the cantilever column decreases the critical flutter load by coupling with a large value of tip mass, while by coupling with the moment of inertia of tip pass its effect on the critical flutter load is contrary. The rotatory spring restraining the free end of the cantilever column increases the critical flutter load by coupling with the tip mass, but decreases it by coupling with the moment of inertia of the tip mass.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.28-33
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• 2004

An in-line fiber coupler, based on side-polished single-mode fibers covered with an intermediate coupling layer and a planar waveguide, is analyzed by modeling the interaction region as an equivalent multi-layered planar waveguide. The reflectance for the multi-layered structure with and without buffer layer is illustrated as a function of the refractive index and thickness of the overlay waveguides. When the refractive index of the overlay waveguides is greater than that of the fiber core, the conditions for the intermediate coupling layer to increase the power coupling from the fiber to the overlays is also explained. Through the experimental results using a LiNbO$_3$planar waveguide, we show that the theoretical analysis is reasonable and in good agreement with the measured values.

• Textile Coloration and Finishing
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• v.9 no.4
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• pp.47-53
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• 1997

To improve the interfacial bonding of carbon fiber-nylon 6 composite, carbon fiber(CF) were oxidized by nitric acid treatment, and two types of graft polymer(GP) of nylon 6-g-polyacrylamide (PAAm) -water dispersable GP(WDGP) and m-cresol solu ble GP(CSGP) were treated as coupling agents. Introduction of polar groups such as -COOH, -OH, etc, on the surface of the oxidized CF was confirmed by IR spectra. The stem polymer of nylon 6 in the coupling agent (GP) could be compatible with'matrix nylon 5, and the grafted branch of PAAm on GP could react to the polar groups on the oxidized CF in composite. The interfacial strength was measured by the transverse tensile test to the fiber direction for single CF embedded nylon 6 film especially prepared and by the pull-out test method. The interfacial strength of the composite reinforced with oxidized CF is greater than that reinforced with unoxidized CF. The interfacial strength of the composite was increased by treatment of coupling agents(GPs) considerably, and the increasing tendency by the WDGP is greater than that by the CSGP. The optimum conditions of coupling agent treatment are as follows: the concentration, adsorption tlme of GP, and curing temperature are 2%, 20 minutes, and $170^{\circ}$, respectively.