• Journal of Industrial Technology
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• v.18
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• pp.117-124
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• 1998

In recently, according to increase the construction rate of steel bridge, it is necessary to develop the high strength, high toughness steel. Thus, this study show to evaluate the fatigue characteristic of SWS 570 B first used within a country. With the weld-joined compact tension specimens compared with each other, that is, transverse and lengthwise about the crack propagation, high and low in the input heat level, the fatigue test were performed. The log-log curves between the fatigue crack propagation rate da/dN and the transition range of the stress intensity factor ${\Delta}K$ ahead the crack tip were drawed, with these data. By using this curve, we obtained C and m which is material constant from Paris-Erdogan power law. The obtained results from this study indicate that fatigue crack growth rate of SWS 570 B is not influenced by softening effect which occurs in the HAZ(heat-affected zone) when high and low heat input weld is carried out. Softening effects, which affect fatigue properties, are shown that it is not affected to the fatigue growth rates significantly.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.1
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• pp.42-48
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• 2016

This study presents an experiment investigation on natural convection heat transfer of air-cooling Proton exchange membrane fuel cells (PEMFCs) in a enclosure system for unmanned aerial vehicles (UAVs). Considered are replacing fuel cell stack with Aluminum block for heat generating inside a enclosure chamber. The volume ratio of fuel cell stack and chamber for simulation to the actual size of aerial vehicle is 1 to 15. The parameters considered for experimental study are the environmental temperature range from $25^{\circ}C$ to $-60^{\circ}C$ and the block heat input of 10 W, 20 W and 30 W. Effect of the thermal conductivity of the block and power level on heat transfer in the chamber are investigated. Experimental results illustrate the temperature rise at various locations inside the chamber as dependent upon heat input of fuel cell stack and environmental temperature. From the results, dimensionless correlation in natural convection was proposed with Nusselt number and Rayleigh number for designing air-cooling PEMFC powered high altitude long endurance (HALE) UAV.

• Journal of the Korean institute of surface engineering
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• v.40 no.4
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• pp.165-169
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• 2007

Compared to conventional Indium Tin Oxide (ITO) film deposition methods, cesium (Cs) assisted sputtering offers higher film characteristics in terms of electrical, mechanical and optical properties. However, it showed highly non-linear characteristics between process input factors and equipment responses. Therefore, to maximize film quality, optimization of manufacturing process is essential and process characterization is the first step for process optimization. For this, we designed 2 level design of experiment (DOE) to analyze ITO film characteristics including film thickness, resistivity and transmittance. DC power, pressure, carrier flow, Cs temperature and substrate temperature were selected for process input variables. Through statistical effect analysis methods, relation between three types of ITO film characteristics and five kinds of process inputs are successfully characterized and eventually, it can be used to optimize Cs assisted sputtering processes for various types of film deposition.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.11 s.353
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• pp.175-184
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• 2006

In this paper, we describe a 900MHz CMOS RF transceiver using an ISM band for ZigBee applications. The architecture of the designed rx front-end, which consists of a low noise amplifier, a down-mixer, a programmable gain amplifier and a band pass filter. And the tx front-end, which consists of a band pass filter, a programmable gain amplifier, an up-mixer and a drive amplifier. A low-if topology is adapted for transceiver architecture, and the total current consumption is reduced by using a low power topology. Entire transceiver is verified by means of post-layout simulation and is implemented in 0.18um RF CMOS technology. The fabricated chip demonstrate the measured results of -92dBm minimum rx input level and 0dBm maximum tx output level. Entire power consumption is 32mW(@1.8VDD). Die area is $2.3mm{\times}2.5mm$ including ESD protection diode pads.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.4C
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• pp.362-369
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• 2007

APSK (Amplitude Phase Shift Keying) digital modulation is characterized by the circular positioning of the transmission symbols in the constellation diagram. Due to such structural characteristics, the peak-to-average power ratio of the APSK modulation is lower than that of the QAM (Quadrature Amplitude Modulation), and the amount of performance degradation over nonlinear channels can be mitigated. The APSK modulation scheme has recently been adopted as satellite communication system standards including the DVB-S2 (Digital Video Broadcasting - Satellite, Version 2). In this paper, a BER (Bit Error Rate) upper bound approximation formula is derived using the channel model with the output power saturation characteristics, and its accuracy is demonstrated. Using the derived formula, the input power level that minimizes the BER is determined. The optimized performance based on the radii ratio of the 16APSK constellation and the channel saturation level is also presented.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.4
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• pp.329-346
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• 2008

Post-closure safety assessment for the Wolsong Low- and Intermediate-level radioactive waste Disposal Center is described. Based on assessment context, closure concept and ground water flow characteristics of the disposal site, brief descriptions are included on the assessment scenarios, models, input parameters and tools. Radionuclide transport modeling in the near-field and far-field, gas generation and transport modeling, human intrusion and biosphere transport are also described briefly. Assessment results for each scenarios are shown to meet the performance criteria of regulatory body. Further and continuous efforts to improve the safety of disposal facility will be made during the construction and operational period.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.3
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• pp.240-248
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• 2017

This paper describes the development of a powertrain for a 20 kW experimental electric vehicle using a surface-mounted permanent magnet synchronous motor (SPMSM) and its application to a test vehicle. Two 10 kW SPMSMs are used in the powertrain, and two-level inverters are developed by using IGBTs to derive these motors. To control the SPMSM, a control board based on a TMS320F28335 DSP module, which has fast arithmetic function and floating point operator, is used. We develop a 100 V/40 A battery pack, which includes $32{\times}4$ LiFePO4 battery cells using commercial BMS. A commercial on-board charger with 220 V (AC) input and 100 V (DC) and 18 A output is used to charge the battery pack. The performance of the developed vehicle, such as acceleration availability, maximum speed, and maximum power, is estimated based on vehicle dynamics and verified through experiments.

• Environmental and Resource Economics Review
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• v.27 no.2
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• pp.339-362
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• 2018

In this paper, we simulate the contribution of an increasing renewable energy to demands for fossil fuels and power supply price by estimating a cost function for the Korean electric power generation sector. Since the renewable energy is a composite input, it is not feasible to compute the price index for renewable energy due to data limit. We estimate a restricted cost function, which is derived by minimizing the costs of fossil fuels conditional on the quantity of renewable energy set to its optimal level, jointly with supply relation. In particular, derivation of the shadow price of renewable energy would make it possible to analyze potential costs incurred by power plants.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.5
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• pp.1000-1006
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• 2007

This paper presents a power detector circuit which monitors the transmitting power for the application in CDMA cell phones. The proposed power detector are composed of coupler for coupling output power and detector fur monitoring output power. The designed coupler has low loss characteristic because it adopts the stripline structure which consists of two ground planes at both sides of signal plane. The design frequency is 824-849MHz which is the Tx band fur CDMA mobile terminal, and the coupling factor of the stripline coupler is -20dB. A schottky barrier diode is adopted for detector design because of its high speed operation with minimized loss. The required impedance matching is performed to improve the linearity and sensitivity of output voltage at relatively low detector input level where the nonlinear characteristic of diode exists. The package parasitics as well as intrinsic diode model are considered for simulation of the detector. The predicted performances agree well with the measured results.

• Clean Technology
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• v.12 no.3
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• pp.138-144
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• 2006

Conversion of methane to synthesis gas in a capacitive rf plasma at low pressure was experimentally studied. In this plasma, electrons which had sufficient energy-level collided with the molecules of methane or oxygen-containing gas, which were than activated and converted to synthesis gas. The effect of input power, various oxygen-containing gas and composition of the gas mixture were investigated. The conversion of methane reached up to 100%. In all cases, hydrogen and carbon oxide were produced as primary products, and other compounds was generated. The conversion of methane and the yield of hydrogen and carbon oxides were increased with increasing the input power. Depending on the oxygen-containing gases, the composition of synthesis gas was varied.