• Journal of Korean Institute of Industrial Engineers
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• v.29 no.2
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• pp.172-178
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• 2003

In the recent researches, a variety of ways for determining the locations of RBF centers have been proposed assuming that the number of RBF centers is known. But they have also many numerical drawbacks. We propose a new method to overcome such drawbacks. The strength of our method is to determine the locations and the number of RBF centers at the same time without any assumption about the number of RBF centers. The proposed method consists of two phases. The first phase is to determine the number and the locations of RBF centers using bi-section search method and enhanced k-medoids clustering which overcomes drawbacks of clustering algorithm. In the second phase, network weights are computed and the design of RBF network is completed. This new method is applied to several benchmark data sets. Benchmark results show that the proposed method is competitive with the previously reported approaches for center selection.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.11 s.114
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• pp.1096-1104
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• 2006

In this paper, the broadband antenna for the combined base station of Cellular/PCS/IMT-2000/Wibro and S-DMB services is designed and the proposed antenna allows having sufficient coverage for each service band. In order to get the broadband impedance matching, the tapered sections are applied on the both terminus of hi-conical respectively. The design parameter is calculated and simulated by using FDTD method. As a result, the measured bandwidth of the proposed antenna is $0.79GHz{\sim}2.93GHz$ and the gain is distributed from 5.5 dBi up to 8.19 dBi.

• Progress in Superconductivity and Cryogenics
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• v.1 no.2
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• pp.15-19
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• 1999

For large scale applications of high temperature superconductor (HTS) such as transmission cables, motors and generators, long length of flexible HTS conductor is required. Currently, Bi-2223 HTS tape is capable of being fabricated in longer than 100 m length by industrial processes. In this study, we fabricated 100 m 19 filamentary Bi-2223 ($Bi_{1.8}Pb_{0.4}Sr_2Ca_2O_{10+x}$) HTS tape by PIT (Power in Tube) process. Critical current(IC) of this long length tape was measured 18.5 A at 77K, self field. Critical current of 100 m length tape was mainly resulted from the increase of inhomogeneity in oxide from the increase of inhomogeneity in oxide layer. Engineering critical current (Je=Ic/total tape cross-section area) that is important factor for practical applications and fabrication cost was measured 2.2 kA/cm2.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.6
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• pp.2422-2443
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• 2020

This paper studies a single-user Mobile Edge Computing (MEC) system where mobile device (MD) includes an application consisting of multiple computation components or tasks with dependencies. MD can offload part of each computation-intensive latency-sensitive task to the AP integrated with MEC server. In order to accomplish the application faultlessly, we calculate out the optimal task offloading strategy in a time-division manner for a predetermined execution order under the constraints of limited computation and communication resources. The problem is formulated as an optimization problem that can minimize the energy consumption of mobile device while satisfying the constraints of computation tasks and mobile device resources. The optimization problem is equivalently transformed into solving a nonlinear equation with a linear inequality constraint by leveraging the Lagrange Multiplier method. And the proposed dual Bi-Section Search algorithm Bi-JOTD can efficiently solve the nonlinear equation. In the outer Bi-Section Search, the proposed algorithm searches for the optimal Lagrangian multiplier variable between the lower and upper boundaries. The inner Bi-Section Search achieves the Lagrangian multiplier vector corresponding to a given variable receiving from the outer layer. Numerical results demonstrate that the proposed algorithm has significant performance improvement than other baselines. The novel scheme not only reduces the difficulty of problem solving, but also obtains less energy consumption and better performance.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.

• Journal of Advanced Navigation Technology
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• v.12 no.3
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• pp.201-207
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• 2008

Design rule of optical transmission link consisted of dispersion management (DM) controlling accumulated dispersion in total fiber length by precompensation and postcompensation, and optical phase conjugator (OPC) positioned at mid-way are proposed. DM schemes investigated in this paper are 2 types depending on the position of precompensation and postcompensation; bi-end type and concentration type. It is confirmed that effective residual dispersion ranges, as a design parameter of optical link, of transmission section from transmitter to OPC and transmission section from OPC to receiver are independence on the positions of dispersion compensating fiber (DCF) accomplishing precompensation and postcompensation, if both DCF position is symmetry with respect to OPC.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.172-179
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• 2004

Average Bi-directional flow tube was suggested to measure single and two phase flow rate. Its working principle is similar with Pilot tube, however, it makes it possible to eliminate the cooling system which is normally needed to prevent from flashing in the pressure impulse line of Pilot tube when it is used in the depressurization condition. The suggested instrumentation was tested in the air-water vertical test section which has 80mm inner diameter and 10m length. The flow tube was installed at 120 of L/D from inlet of test section. From the test, single air and water flow rate was measured successfully. For the emasurement of two phase flow rate, Chexal drift-flux correlation was used. In the test a new correlation of momentum exchange factor was suggested. The test result shows that the suggested instrumentation using the measured void fraction and Chexal drift-flux correlation can predict the mass flow rates within $10\%$ error of measured data.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.1
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• pp.19-25
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• 2001

In this paper, the design and simulation results of IF frequency synthesizer section has been described. We has been used 0.8 $\mu\textrm{m}$ BiCMOS device and library of the AMS. IF frequency synthesizer section has been contained IF VCO, Phase Detector, Divide_by_8, Charge Pump and Loop Filter. IF frequency synthesizer has been shown operating voltage of 2.7~3.6 V, control voltage of 0.5~2.7 V and supply current of 11 mA. The measured results have been showed good agreement with the simulation results about supply current.

• KIEE International Transactions on Power Engineering
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• v.3A no.2
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• pp.100-108
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• 2003

This paper presents the design and performance results of a pair of 6-kA high-temperature superconducting (HTS)-copper current leads, in which, over a short length at the warm end (e.g.,77K) of each HTS section, comprised of paralleled Bi-2223/Ag-Au tapes, is operated in the current-sharing mode. Because of their reliance on vapor cooling, the leads are applicable only to liquid helium cooled superconducting magnets such as those used in high-energy Physics accelerators and fusion machines. The experimental measurements have demonstrated that key performance data of the new 6-kA HTS-Copper leads agree reasonably well with those expected from design.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.6
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• pp.1035-1038
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• 2007

We designed and manufactured a 1.8T high temperature superconducting(HTS) insert coil for a NMR magnet operated at 4.2 K. Suitable HTS superconductor and HTS coil were carefully designed and developed. We have selected multi-filamentary Bi2223 conductor fabricated by American Superconductor Corporation(AMSC). The selected conductor consists of Bi2223 filaments of 55, silver stabilizer and stainless steel reinforcement tapes. Therefore, it shows good hoop strength as well as compression tolerance. The conductor has a tape cross-section of 0.31mm x 4.8mm. the Bi2223 conductor shows large anisotropy of critical current. The critical current of conductor in magnetic field parallel to the flat surface are much higher than that in magnetic field perpendicular. The HTS coil has an inner diameter of 78 mm, an outer diameter of 127 mm and a coil length of 600 mm. In this paper, the detailed design, fabrication and test results on the HTS insert coil are presented.