• Journal of Power Electronics
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• 제15권2호
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• pp.487-496
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• 2015

In order to ensure that photovoltaic (PV) systems work at the maximum power point (MPP) and maximize the economic benefits, maximum power point tracking (MPPT) techniques are normally applied to these systems. One of the most widely applied MPPT methods is the incremental conductance (INC) method. However, the choice of the step size still remains controversial. This paper presents an improved variable step size INC MPPT algorithm that uses four different step sizes. This method has the advantages of INC but with the ability to validly adjust the step size to adapt to changes of the PV's power curve. The presented algorithm also simultaneously achieves increased rapidity and accuracy when compared with the conventional fixed step size INC MPPT algorithm. In addition, the theoretical derivation and specific applications of the proposed algorithm are presented here. This method is validated by simulation and experimental results.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.539-544
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• 2002

Titanium and titanium alloy are excellent in corrosion resistance and specific intensity, and also in the biocompatibility. On the other hand, the brazing is bonding method of which productivity and reliability are high, when the complicated and precise structure of the thin plate is constructed. However, though conventional titanium-based brazing filler metal was excellent in bond strength and corrosion resistance, it was disadvantageous that metal structure and mechanical property of the base metal deteriorated, since the brazing temperature (about 1000 C) is considerably high. Authors developed new brazing filler metal which added Zr to Ti-Cu (-Ni) alloy which can be brazed at 900 C or less about 15 years ago. In this paper, the development of more low-melting-point brazing filler metal was tried by the addition of the fourth elements such as Ni, Co, Cr for the Ti-Zr-Cu alloy. As a method for finding the low-melting-point composition, eutectic composition exploration method was used in order to reduce the experiment point. As the result, several kinds of new brazing filler metal such as 37.5Ti-37.5-Zr-25Cu alloy (melting point 825 C) and 30Ti-43Zr-25Cu-2Cr alloy (melting point: 825 C) was developed. Then, the brazing joint showed the characteristics which were almost equal to the base metal from the result of obtaining metallic structure and strength of joint of brazing joint. However, the brazing filler metal composition of the melting point of 820 C or less could not be found. Consequentially, it was clarified that the brazing filler metal developed in this study could be practically sufficiently used from results such as metal structure of brazing joint and tensile test of the joint.

• 항공우주기술
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• 제12권2호
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• pp.1-6
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• 2013

저궤도 위성은 지상국과의 접속 중에 X-band 안테나를 이용해 촬영한 영상을 전송한다. X-band 안테나는 교신 시간 동안 TPF (tracking parameter file)에 따라 움직이며 지상국의 안테나를 지속적으로 지향한다. TPF 생성 소프트웨어는 위성의 궤도 및 자세 정보와 촬영 및 다운링크 임무 정보를 이용해 X-band 안테나가 지상국을 지향하도록 하는 Azimuth, Elevation 정보를 생성한다. 위성이 지상국 상공을 지나가는 경우 X-band 안테나 특성 상 방위각 속도가 급격하게 증가하며, 특정 각속도로 회전하는 경우 위성의 지터를 유발할 수 있다. 영상촬영과 다운링크를 동시에 수행하는 실시간 임무의 경우 지터에 의한 영상 열화를 방지하기 위해 Azimuth 각속도를 일정 수준 이하로 낮춰야 한다. 현재 사용하는 방법인 한 점의 가상 지상국을 지향하는 방법으로는 각속도를 낮추는데 한계가 있다. 이 논문에서는 방위각 고정 기법을 이용해 X-band 안테나의 Azimuth 각속도를 낮추는 방법을 제안한다. 시뮬레이션 결과는 제안된 방법을 이용해 방위각 속도가 현저하게 감소함을 나타낸다.

• 한국의류학회지
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• 제26권8호
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• pp.1228-1238
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• 2002

This study attempted to identify that how the meaning of clothes and clothing behavior were extended, and to examine that they, produce what kinds of meaning in the specific contort in a novel, the Honpul. The Frame of meaning analysis proposed by Beaugrande, Dressier, and Damesteter was used as an analyzing method. The 100 texts were collected for analysis from the Honpul volume 1 to 10. Psychological meanings were categorized to sensitivity meaning, disposition meaning and incantation meaning. Those had not only a basic meaning which could be gotten from the practical clothing but also second and third extended meanings. The point of this study was to present a new method and possibility for analyzing the code of costume culture by the extended meanings in novels.

• Journal of Advanced Marine Engineering and Technology
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• 제28권6호
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• pp.962-971
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• 2004

This paper has dealt with thermo-physical properties of microencapsulated phase change material slurry as a latent heat storage material having a low melting point. The measured results of the thermo-physical properties of the test microencapsulated phase change material slurry, those are, density, specific heat, thermal conductivity and viscosity, were discussed for the temperature region of solid and liquid phases of the dispersion material (paraffin). The measurements of these properties of microencapsulated phase change material slurry have been carried out by using a specific-gravity meter, a water calorimeter, a differential scanning calorimeter(DSC), a transient hot wire method and rotating type viscometer, respectively. It was clarified that the additional properties law could be applied to the estimation of the density and specific heat of microencapsulated phase change material slurry and also the Euckens equation could be applied to the estimation of the thermal conductivity of this slurry.

• 대한기계학회논문집
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• 제18권9호
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• pp.2413-2422
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• 1994

The effects of compressor design conditions on the off-design performance of a single-shaft gas turbine engine have been studied. Three different geometric design conditions are considered and three different values for the specific mass flow rate at the inlet to the compressor are assumed. For each of nine compressor design, the off-design performance of the gas turbine engine is predicted using the method previously proposed by present authors. Results show that the predicted off-design performances are quite different from each other even though they have the same performance at design point: it means that compressor design conditions should be determined in consideration of the off-design performance of the engine. The specific mass flow rate at the inlet to the compressor is also shown that it might be optimized with respect to the net power of the engine.

• 전력전자학회논문지
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• 제27권5호
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• pp.446-454
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• 2022

This study proposes a carrier-based pulse width modulation (PWM) method for leakage current reduction and neutral point (NP) current control in a three-phase three-level converter, which is a carrier-based PWM version of the previously proposed low-frequency common mode voltage PWM. Three groups of space vectors with the same common mode voltage are used. When the averaged NP current needs to be positive or negative, the specific groups are employed to produce low-frequency common mode voltages. The validity of the proposed PWM method is verified through experiments.

• 한국대기환경학회지
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• 제17권1호
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• pp.51-56
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• 2001

This study was carried out to interpret mathematically hydraulic behaviour in packing tower which packed 50 mm plastic Hiflow-ring with a dimension of 300 mm wide and 1,400 mm high. In view of energy saving, the recent packing. 50 mm plastic Higlow-ring was superior to conventional packings because of low pressure drop in high loads. As relative error between numerically predicted and experimentally obtained values was less then 6% in the loading and flooding point, it found that therir results appeared to be adequate. Comparison of hose two values in both dry and wet packing conditions. relative errors amount to 3.96 and 5.6%, respectively. In order to evaluate the operating characteristics of packing, the type, size, and material for packings must be estimated in various system and loads. This study is able to calculated pressure drop, hold-up, gas and liquid loads using mathematical interpretation. For these calculation, the specific constants of each packings must be calculated first all. The method of mathematical interpretation in this study turned out to be superior to the existing methods because of reduced errors at loading and flooding point.

• 분석과학
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• 제16권3호
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• pp.232-239
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• 2003

청주시 석남천 유역의 4개 지점, 미호천 유역의 1개 지점, 석남천과 미호천 합류지역의 1개 지점 등 6개 지점을 기준지점으로 택하고, 각 지점의 상층, 중층, 하층에서 침전물을 채취하여 조사용 시료를 제작하였다. 한국원자력연구소의 연구용 원자로(HANARO)의 중성자 선을 이용한 중성자 방사화 분석법으로 원소함량을 분석하였다. 미국 표준연구원(NIST)의 인증표준물질을 이용하여 시료 중의 30 개 원소들의 함량을 비교법으로 분석하였다. 그 분석 결과로부터 하천오염원지역에서 하류로 이어지는 지역의 침전물 오염도분포조사 및 예측시 오염물질의 원소비중과 유속을 고려해야 하며 하천침전물의 함량분석을 위한 시료를 채취할 때 시료의 지역적 대표성을 확립하기 위해서는 원소의 비중과 유속 등을 고려하여 수직적 범위를 정할 필요가 있음을 알았다.

• Korean Journal of Hydrosciences
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• 제5권
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• pp.99-114
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• 1994

Three purposes of this study are as follows : The first was the development of the extension method for the limited data observed in an urban drainage basin. The second was the analysis of the correlation between storm water runoff and NPS(non-point source) Pollutant discharge. The last was the calculation of the monthly and annual specific NPS loads using the established correlation. The selected model was the SWMM(Storm Water Management Model) developed by the US EPA(Environmental Protection Agency). As a result of this study, the best correlation between storm water runoff and NPS pollutants discharge was produced by the nonlinear correlation between runoff rate(mm/hr) and specific loads rate(kg/ha) for all pollutants studied : SS, COD, BOD, and TN. The best correlation through the analysis based on evently total mass was made by the linear correlation between the by the nonlinear correlation for CASE2. The NPS annual specific loads for the urban basin studed were 4,993 kg/ha/year for SS, 775 kg/ha/year for BOD, 3,094 kg/ha/year for COD, 257 kg/ha/year for TN, respectively. And the proportion of the NPS annual specific loads to the total annual specific loads were 41 % for SS, 13 % for BOD, 29 % for COD, and 21 % for TN.