• Journal of Power Electronics
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• 제13권5호
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• pp.854-860
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• 2013

The voltage variation problem at the point of common coupling (PCC) in a grid-connected wind turbine is investigated. The voltage variation problem is one of the most frequent power quality issues for the grid connection of large amounts of input power in a weak grid. Through the simplified modeling of the wind turbine and power network, the magnitude of PCC voltage variation is calculated by using the equivalent circuit parameters and output power of the wind turbine. The required amount of reactive power that can compensate the voltage variation is also presented analytically by using the vector diagram method. The proposed calculation and compensation method of the PCC voltage variation is verified by computer simulations and experiments.

• International Journal of CAD/CAM
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• 제6권1호
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• pp.65-71
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• 2006

Based on the smoothness criterion of minimum curvature variation of the curve, tangent angle constraints guaranteeing an optimized geometric Hermite (OGH) curve both mathematically and geometrically smooth is given, and new methods for constructing composite optimized geometric Hermite (COH) curves are presented in this paper. The comparison of the new methods with Yong and Cheng's methods based on strain energy minimization is included.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(4)
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• pp.295-299
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• 1996

This analysis is to investigate the benefits and disadvantages of increasing the pressure tube wall thickness for CANDU reactor. Creep analysis of the pressure tube was performed for slightly enriched uranium (SEU) to establish the reduction in axial elogation and diametral creep provided by a thicker wall pressure tube.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2011년도 학술대회 및 정기총회
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• pp.75-76
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• 2011

• 신재생에너지
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• 제7권4호
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• pp.30-36
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• 2011

The objective of this study is to investigate the effects of the refrigerant charge amount on the performance of a water-to-water ground source heat pump with a variation of compressor speed and the secondary fluid flow rate. The water-to-water ground source heat pump was tested by varying refrigerant charge amount from -40% to 20% of full charge. Compressor speed was changed from 30 Hz to 75 Hz and the secondary fluid flow rate was adjusted from 6 LPM to 14 LPM. For all test conditions, EWTs of an indoor heat exchanger and an outdoor heat exchanger were maintained at standard conditions of ISO 13256-2. The slope of the COP with the variation of charge amount is much steeper at undercharged conditions than that at overcharged conditions. For all compressor speed, the variation of the system performance according to charge amounts showed the similar trends. However, the optimum charge amount of the system increased a little with an increment of compressor speed. When the secondary fluid flow rate decreased, the system was optimized at higher refrigerant charge amount conditions.

• 대한방사선치료학회지
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• 제20권1호
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• pp.31-36
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• 2008

목 적: X선이 조사된 물질의 색변화를 통하여 방사선 측정 및 선량분포확인을 위한 물질로서의 가능성에 대하여 평가하고자 한다. 대상 및 방법: 순수한 KCl과 KCl에 희토류 물질인 Eu를 0.5 mol% 첨가하여 초크랄스키 방법으로 각각의 단결정을 성장시키고 선형가속기를 이용하여 X선조사선량에 따른 KCl결정의 색 변화를 관찰하였다. 결 과: 고 에너지 X선조사에 의해 KCl:Eu 단결정은 가시광의 푸른색 형광과 함께 자주색을 나타내었고 순수한 KCl 단결정은 눈으로 확인할 수 있을 정도의 형광은 관찰되지 않았지만 보라색으로 착색되었다. 결 론: KCl 단결정의 색 변화는 X선으로 인하여 안정된 색 중심이 생기고 이러한 색변화는 X선 측정물질과 펜톰으로 유용하게 사용되어질 것이다.

• Journal of Nutrition and Health
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• 제29권9호
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• pp.1028-1034
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• 1996

This study examined within-and between-individual variation in nutrient intakes in order to estimate the degrees of precison in dietary assessment among 59 female volunteers aged 21-23 years. Self-recorded 7-day dietary recalls and records were collected by during a 3 month period. Between the recall and record methods, there were little difference of within-and between-individual variations. Within-to-between individual variation ratios were > 2.0 for most of the nutrients examined, and were higher for niacin, vitamin A and C (>2.5) in the recals and for calcium, iron, vitamin A and C(>3.0) in the records. With 7-day dietary data, observed nutrient intakes were estimated to within 26-107% of the subjects' true(usual) intakes, among those vitamin C and energy showed the highest and lowest values, respectively. Correlation coefficients between observed and true nutrient intakes were 0.73-0.81 for the recalls and 0.68-0.77 for the records. In order to estimate with 20% precision, 12-13 days of dietary study were required for energy, 46 for calcium, 71-72 for vitamin A, and 199-200 for vitamin C. Attenuation factor ranged 0.73-0.81 for the recalls and 0.68-0.77 for the records. This study implies that commonly used 1 or 3 day dietary studies may not be appropriate for assessing individuals' nutrient intakes. Further research focusing on the methodological issues in the assessment of Korean diet are needed for between understanding of the relationship between diet and health in Koreans.

• 임산에너지
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• 제19권1호
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• pp.38-48
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• 2000

한국산 참나무아속 화분형태의 유사관계 및 종내변이를 조사하기 위하여 화분립의 국축길이, 적도면 폭, 구의 길이, 구의 폭을 측정하고 화분립의 국축길이에 대한 적도면 폭의 비율을 계산하였다. 본 연구 결과를 근거로 하여 군집분석을 수행한 결과 상수리나무와 굴참나무의 화분형태가 가장 유사관계가 높은 것으로 나타났다. 조사된 수종 중 화분립의 크기에 있어서 폭 넓은 변이를 나타내는 떡갈나무의 경우에는 polypoid와 (또는) aneuploid의 형태가 존재하는 것으로 추정되었다. 참나무아속 수종들의 ploidy levels에 대한 연구가 수행되어야 할 것이다.

• 풍력에너지저널
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• 제9권4호
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• pp.47-56
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• 2018

This paper introduces an active power dependent standard characteristic curve, Q(P) to compensate for voltage variations due to the output of distributed generation. This paper presents an efficient control method of grid-connected inverters by comparing and analyzing voltage variation magnitude and line loss according to the compensation method. Voltage variations are caused not only by active power, but also by the change of reactive power flowing in the line. In particular, the system is in a relatively remote place in a coastal area compared with existing power plants, so it is relatively weak and may not be suitable for voltage control. So, since it is very important to keep the voltage below the normal voltage limit within the specified inverter capacity and to minimize line loss due to the reactive power. we describe the active power dependent standard characteristic curve, Q(P) method and verify the magnitude of voltage variation by simulation. Finally, the characteristics of each control method and line loss are compared and analyzed.

• 한국지하수토양환경학회지:지하수토양환경
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• 제16권5호
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• pp.82-89
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• 2011

Understanding snowmelt movement to the watershed is crucial for both climate change and hydrological studies because the snowmelt is a significant component of groundwater and surface runoff in temperature area. In this work, a new energy balance budget algorithm has been developed for melting snow from a snowpack at the Central Sierra Snow Laboratory (CSSL) in California, US. Using two sets of experiments, artificial rain-on-snow experiments and observations of diel variations, carried out in the winter of 2002 and 2003, we investigate how to calculate the amount of snowmelt from the snowpack using radiation energy and air temperature. To address the effect of air temperature, we calculate the integrated daily solar radiation energy input, and the integrated discharge of snowmelt under the snowpack and the energy required to generate such an amount of meltwater. The difference between the two is the excess (or deficit) energy input and we compare this energy to the average daily temperature. The resulting empirical relationship is used to calculate the instantaneous snowmelt rate in the model used by Lee et al. (2008a; 2010), in addition to the net-short radiation. If for a given 10 minute interval, the energy obtained by the melt calculation is negative, then no melt is generated. The input energy from the sun is considered to be used to increase the temperature of the snowpack. Positive energy is used for melting snow for the 10-minute interval. Using this energy budget algorithm, we optimize the intrinsic permeability of the snowpack for the two sets of experiments using one-dimensional water percolation model, which are $52.5{\times}10^{-10}m^2$ and $75{\times}10^{-10}m^2$ for the artificial rain-on-snow experiments and observations of diel variation, respectively.