• Proceedings of the Korean Operations and Management Science Society Conference
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• 2003.05a
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• pp.409-416
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• 2003

We consider the problem of grouping orders into lots. The problem is modelled by a graph G = (V, E). where each node $\nu\;\in\;V$ denotes order specification and its weight $\omega(\nu)$ the orders on hand for the specification. We ran construct a lot simply from orders or single specification For a set of nodes (specifications) $\theta\;\subseteq\;V$, if the distance or any two nodes in $\theta$ is at most d, it is also possible to make a lot using orders on the nodes. The objective is to maximize the number of lots with size exactly $\lambda$. In this paper, we prove that our problem is NP-Complete when d = 2, $\lambda\;=\;3$ and each weight is 0 or 1. Moreover, it is also shown to be NP-Complete when d = 1, $\lambda\;=\;3$ and each weight is 1, 2 or 3

• Proceedings of the IEEK Conference
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• 2001.06e
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• pp.131-134
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• 2001

This paper proposes a stable control rule for nonlinear unicycle-type mobile robot. The control method uses a local error coordinate system, velocity and distance constants $\kappa$$\_$x/, $\kappa$$\_$y/, and he. Stability of control rule is proved Liapunov function. System input to the mobile robot is reference posture ($\chi$$\_$r/, y$\_$r/, $\theta$$\_$r/)/sup/ $\tau$/ and reference e velocity (ν$\_$r/,$\omega$$\_$r/)$\^$$\tau$/. System output of the mobi-le robot is velocity of driving wheels. We introduce limit velocity for preventing high initial speed. From simulation results, we can see the proposed control rule is stable.

• Journal of Korean Institute of Industrial Engineers
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• v.29 no.4
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• pp.253-258
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• 2003

We consider the problem of grouping orders into lots. The problem is modelled by a graph G=(V,E), where each node ${\nu}{\in}V$ denotes order specification and its weight ${\omega}(\nu)$ the orders on hand for the specification. We can construct a lot simply from orders of single specification. For a set of nodes (specifications) ${\theta}{\subseteq}V$, if the distance of any two nodes in $\theta$ is at most d, it is also possible to make a lot using orders on the nodes. The objective is to maximize the number of lots with size exactly $\lambda$. In this paper, we prove that our problem is NP-Complete when $d=2,{\lambda}=3$ and each weight is 0 or 1. Moreover, it is also shown to be NP-Complete when $d=1,{\lambda}=3$ and each weight is 1,2 or 3.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.131-135
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• 2003

Zinc Oxide(ZnO) thin films on Si (100) substrate were deposited by RF magnetron sputter with changing sputtering conditions such as argon/oxygen gas ratios, RF power, and substrate temperature, chamber pressure and target-substrate distance. To analyze a crystallographic properties of the films, $\theta/2\theta$ mode X-ray diffraction, SEM, and AFM analyses. C-axis preferred orientation, resistivity, and surface roughness highly depended on $Ar/O_2$ gas ratios. The resistivity of ZnO thin films rapidly increased with increasing oxygen ratio and the resistivity value of $9{\times}10^7{\Omega}cm$ was obtained at a working pressure of 10 mTorr with $Ar/O_2$=50/50. The surface roughness was also improved with increasing oxygen ratio and the ZnO films deposited with $Ar/O_2$=50/50 showed the excellent roughness value of $28.7{\AA}$.

• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.26-35
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• 1997

This paper deals with establishing correspondent points of feature pints and sampling period when we estimate object motion parameters from image information of freely moving objects in space of gravity-free state. Replacing the inertial coordinate system with the camera coordinate system which is equipped within a space robot, it is investigated to be able to analyze a problem of correspond points from image information, and to obtain sequence of angular velocity $\omega$ which determine a motion of object by means of computer simulation. And if a sampling period ${\Delta}t$ is shortened, the relative errors of angular velocity are increased because the relative errors against moving distance of feature points are increased by quantization. In reverse, if a sampling period ${\Delta}t$ is lengthened too much, the relative error are likewise increased because a sampling period is long for angular velocity to be approximated, and we confirmed the precision that grows according to ascending of resolution.

• Journal of the Korean Magnetics Society
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• v.12 no.2
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• pp.51-56
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• 2002

Permalloy thin films fabricated by rf magnetron sputtering showed the excellent magnetic properties, i.e., an effective permeability of over 2000 at 1$\mu\textrm{m}$ thick up to 10 MHz, a saturation magnetization of 10∼12 kG, a coercive force of 0.2∼1 Oe, resistivity (p) is 20 ${\mu}$$\Omega$cm. In order to control the magnetic anisotropy direction of the films in a wafer scale, two parallel Nd-Fe-B permenant mangnets were used to provide the magnetic field during the sputtering process. As a result, the anisotropy direction was successfully controlled when the two magnets were seperated with a distance of 70 mm. 3D simmulation of the magnteic fields around the wafer during sputtering were in accord with the above result.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1646-1649
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• 2012

The $O_2$ annealing technique has considerably suppressed the leakage current of GaN power devices, but this forms NiO at Ni-based Schottky contact with increasing on-resistance. The purpose of the present study was to fabricate 1.5 kV GaN Schottky barrier diodes by improving $O_2$-annealing process and GaN buffer. The proposed $O_2$ annealing performed after alloying ohmic contacts in order to avoid NiO construction. The ohmic contact resistance ($R_C$) was degraded from 0.43 to $3.42{\Omega}-mm$ after $O_2$ annealing at $800^{\circ}C$. We can decrease RC by lowering temperature of $O_2$ annealing. The isolation resistance of test structure which indicated the surface and buffer leakage current was significantly increased from $2.43{\times}10^7$ to $1.32{\times}10^{13}{\Omega}$ due to $O_2$ annealing. The improvement of isolation resistance can be caused by formation of group-III oxides on the surface. The leakage current of GaN Schottky barrier diode was also suppressed from $2.38{\times}10^{-5}$ to $1.68{\times}10^{-7}$ A/mm at -100 V by $O_2$ annealing. The GaN Schottky barrier diodes achieved the high breakdown voltage of 700, 1400, and 1530 V at the anode-cathode distance of 5, 10, and $20{\mu}m$, respectively. The optimized $O_2$ annealing and $4{\mu}m$-thick C-doped GaN buffer obtained the high breakdown voltage at short drift length. The proposed $O_2$ annealing is suitable for next-generation GaN power switches due to the simple process and the low the leakage current.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.259-264
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• 2016

In this study, the properties of a patch antenna fed by a coplanar waveguide with ground (CPWG) and design method were studied. The antenna was impedance-matched to the CPWG feedline by adjusting the width, length, and position of the patch. To improve the frequency properties of the CPWG type antenna, patch length, patch width, patch position, and ground distance were simulated using HFSS (High Frequency Structure Simulator) simulation program. A CPWG antenna of 1.8 GHz for LTE band was designed and fabricated by photolithography on an FR4 substrate (dielectric constant of 4.4 and thickness of 0.8 mm). The fabricated antenna was analyzed using a network analyzer. The measured results agree well with the simulations, which confirmed the validity of this study. The fabricated CPWG antenna showed a center frequency, minimum return loss and -10dB bandwidth of 1.8GHz, -32.1dB, 22MHz and $50.2{\Omega}$ respectively. The proposed antenna is expected to be applicable to the LTE band.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.396-399
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• 2003

4H-SiC un diodes with field limiting rings(FLRs) were fabricated and characterized. The dependences of reverse breakdown voltage on the number of FLRs, the distance between p-base main junction and first FLR, and activation temperatures, were investigated. Al and B ions were implanted and activated at high temperature to form p-base region and p+ region in the n-epilayer. We have obtained up to 1782V of reverse breakdown voltage in the un diode with two FLRs on loom thick epilayer. The differential on-resistances of the fabricated diode are $5.3m{\Omega}cm^2$ at $100A/cm^2$ and $2.7m{\Omega}cm^2$ at $1kA/cm^2$, respectively. All pn diodes with FLRs have higher avalanche breakdown voltages than that of diode without an FLR. Regardless of the activation temperature, the un diode with a FLR located 5um apart from main junction has the highest mean breakdown voltage around 1600V among the diodes with one ring. On the other hand, the pn diode with two rings showed different behavior with activation temperature. It reveals that high voltage SiC pn diodes with low on-resistance can be fabricated by using the FLR edge termination.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.291-295
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• 2007

The oxidation treatment of needle cokes with 70 wt% of nitric acid and sodium chlorate ($NaClO_3$) was attempted to achieve an electrochemically active material with a large capacitance. The structure of needle cokes was changed to graphite oxide after oxidation treatment of needle cokes with acidic solution having the composition ratio, $NaClO_3$/needle cokes, of 7.5, and the inter-layer distance of the oxidized needle cokes was extended to $6.9{\AA}$with increasing oxygen content. On the other hand, the electrochemical performance of oxidized needle cokes as a polarized electrode for an Electric Double Layer Capacitor (EDLC) was examined with an electrolyte of 1.2 M $TEABF_4$ (tetraethylammonium tetrafluoroborate) and $TEABF_4$ (triethylmethylammonium tetrafluoroborate) in acetonitrile. The capacitor cell using 1.2 M $TEABF_4$/acetonitrile has exhibited smaller electric resistance of $0.05{\Omega}$, and larger capacitance per weight and volume of 32.0 F/g and 25.5 F/mL at the two-electrode system in the potential range 0~2.5 V than that of the capacitor cell using $TEABF_4$. The observed electrochemical performance was discussed with the correlation between the inter-layer distance in graphite oxide structure and the anionic size of electrolyte.