• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계합동학술대회 논문집
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• pp.112-116
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• 2002

A sensorless control strategy for permanent magnet synchronous motors is presented in this paper. A speed control scheme based on the measurement and observation of stator current, voltage. and flux vector is proposed. Two phase voltages and two stator currents are measured and processed in discrete form in DSP. The rotor position and speed are estimated through the stator flux and its derivative estimation. Flux and its derivative are calculated in the stationary reference frame and used to estimate the speed and position. The rotor position angle is then used in a microcontroller to produce the appropriate stator current command signals for the hysteresis current controller of the inverter. The closed-loop speed control has been shown to be effective from standstill to rated speed. Moreover, a flux drift problem caused by the integration can be eliminated so that a stable sensorless starting and running operation can be achieved. Computer simulation and experimental results are presented to demonstrate the effectiveness of the proposed scheme.

• 천문학회보
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• 제40권1호
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• pp.66.3-67
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• 2015

Without scrutinizing reflection, the plasma comprising a coronal loop is usually regarded to reside within a flux rope. This picture seems to have been adopted from laboratory plasma pinches, in which a plasma of high density and pressure is confined in the vicinity of the flux rope axis by magnetic tension and magnetic pressure of the concave inward magnetic field. Such a configuration, in which the plasma pressure gradient and the field line curvature vector are almost parallel, however, is known to be vulnerable to ballooning instabilities (to which belong interchange instabilities as a subset). In coronal loops, however, ideal MHD (magnetohydrodynamic) ballooning instabilities are impeded by a very small field line curvature and the line-tying condition. We, therefore, focus on non-ideal (resistive) effects in this study. The footpoints of coronal loops are constantly under random motions of convective scales, which twist individual loop strands quite randomly. The loop strands with the axial current of the same direction tend to coalesce by magnetic reconnection. In this reconnection process, the plasma in the loop system is redistributed in such a way that a smaller potential energy of the system is attained. We have performed numerical MHD simulations to investigate the plasma redistribution in coalescence of many small flux ropes. Our results clearly show that the redistributed plasma is more accumulated between flux ropes rather than near the magnetic axes of flux ropes. The Joule heating, however, creates a different temperature distribution than the density distribution. Our study may give a hint of which part of magnetic field we are looking to in an observation.

• 천문학회보
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• 제37권1호
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• pp.90.2-90.2
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• 2012

Geosynchronous electron flux dropouts are most likely due to fast drift loss of the particles to the magnetopause (or equivalently, the "magnetopause shadowing effect"). A possible effect related to the drift loss is the radial diffusion of PSD due to gradient of PSD set by the drift loss effect at an outer L region. This possibly implies that the drift loss can affect the flux levels even inside the trapping boundary. We recently investigated the details of such diffusion process by solving the diffusion equation with a set of initial and boundary conditions set by the drift loss. Motivated by the simulation work, we have examined observationally the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropouts. For this work, we have first identified a list of geosynchronous flux dropout events for 2007-2010 from GOES satellite electron measurements and solar wind pressures observed by ACE satellite. We have then used the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements to investigate the particle fluxes. The five THEMIS spacecraft sufficiently cover the inner magnetospheric regions near the equatorial plane and thus provide us with data of much higher spatial resolution. In this paper, we report the results of our investigations on the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropout events and discuss implications on the effects of the drift loss on the flux levels at inner L regions.

• 대기
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• 제29권5호
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• pp.567-583
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• 2019

In this study, the high-resolution numerical simulations considering detailed anthropogenic heat, albedo, emission and roughness length are analyzed by using single layer Urban Canopy Model (UCM) in Weather Research Forecast (WRF). For this, improved urban parameter data for Seoul Metropolitan Area (SMA) was collected from global data. And then the parameters were applied to WRF-UCM model after it was processed into 2-dimensional topographical data. The 6 experiments were simulated by using the model with each parameter and verified against observation from Automated Weather Station (AWS) and flux tower for the temperature and sensible heat flux. The data for sensible heat flux of flux towers on Jungnang and Bucheon, the temperature of AWS on Jungnang, Gangnam, Bucheon and Neonggok were used as verification data. In the case of summer, the improvement of simulation by using detailed anthropogenic heat was higher than the other experiments in sensible flux simulation. The results of winter case show improved in all simulations using each advanced parameters in temperature and sensible heat flux simulation. Improvement of urban parameters in this study are possible to reflect the heat characteristics of urban area. Especially, detailed application of anthropogenic heat contributed to the enhancement of predicted value for sensible heat flux and temperature.

• 한국습지학회지
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• 제11권1호
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• pp.105-113
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• 2009

연안습지 생태계에서 열에너지 교환 과정은 매우 중요하다. 지표 열에너지 평형을 이루는 요소인 순복사플럭스, 현열 플럭스, 잠열 플럭스 그리고 토양열 플럭스를 전라남도 고흥에 위치한 수평적으로 균질하다고 판단되는 지역인 고흥만 간척지에서 관측하고 분석하였다. 열의 수송을 평가하기 위해서 5회의 집중관측 기간에 대기 난류를 측정하였고, 특히 갈대로 덮여있는 간척지에서 지표층 열에너지 수지를 분석하기 위해서는 물과 매우 미세한 입자로 구성된 토양 그리고 계절에 따라 색깔과 밀도가 변하는 식생캐노피를 고려하였다. 순복사 플럭스, 현열 플럭스, 잠열 플럭스, 토양열 플럭스를 기존의 에너지 수지방정식에 적용하여 식생과 토양과 같은 지표면 특성에 따른 열 플럭스의 특징을 조사하여 습지의 기온조절 효과에 대해 알아보았다. 에너지 수지비로 식생 성장기에는 주로 잠열 플럭스에 의해 열이 대기로 전달되는 것을 알 수 있었다. 또한 식생층은 열을 저장하여 기온의 일교차를 줄이는 역할을 한다. 여름철에 집중관측지의 기온이 주변 지역의 기온보다 보다 낮고 겨울철에는 다소높게 나타난 결과는 식생층을 포함하는 연안습지가 열환경을 조절함을 보여주었다.

• 한국농림기상학회:학술대회논문집
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• 한국농림기상학회 2013년도 추계 학술발표논문집
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• pp.30-31
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• 2013

Land use and land cover change (LULCC) due to human activities directly affects natural systems and contributes to changes in carbon exchange and climate through a range of feedbacks. How land use and land cover changes affect carbon exchanges can be assessed using multiyear measurement data from micrometeorological flux towers. The objective of the research is to assess the impact of land use and land cover change on carbon exchange in a heterogeneous cropland area. The heterogeneous cropland area in Haenam, South Korea is also subjected to a land conversion due to rural development. Therefore, the impact of the change in land utilization in this area on carbon exchange should be assessed to monitor the cycle of energy, water, and carbon dioxide between this key agricultural ecosystem and the atmosphere. We are currently conducting the research based on 10 years flux measurement data from Haenam Koflux site and examining the LULCC patterns in the same temporal scale to evaluate whether the LULCC in the surrounding site and the resulting heterogeneity (or diversity) have a significant impact on carbon exchange. Haenam cropland is located near the southwestern coast of the Korean Peninsula with land cover types consisting of scattered rice paddies and various croplands (seasonally cultivated crops). The LULCC will be identified and quantified using remote sensing satellite data and then analyzing the relationships between LULCC and flux footprint of $CO_2$ from tower flux measurement. We plan to calculate annual flux footprint climatology map from 2003 to 2012 from the 10 years flux observation database. Eventually, these results will be used to quantify how the system's effective performance and reserve capacity contribute to moving the system towards more sustainable configuration. Broader significance of this research is to understand the co-evolution of the Haenam agricultural ecosystem and its societal counterpart which are assumed to be self-organizing hierarchical open systems.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.508-508
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• 1996

;The growth of films have considerable interest in the field of superlattice structured multi-layer epitaxy led to realization of new devices concepts. Molecular beam epitaxy (MBE) with in situ observation by reflection high-energy electron diffraction (RHEED) is a key technology for controlled layered growth on the atomic scale in oxide crystal thin films. Also, the combination of radical oxygen source and MBE will certainly accelerate the progress of applications of oxides. In this study, the growth process of single crystal films using by MBE method is discussed taking the oxide materials of Bi-Sr-Ca-Cu family. Oxidation was provided by a flux density of activated oxygen (oxygen radicals) from an rf-excited discharge. Generation of oxygen radicals is obtained in a specially designed radical sources with different types (coil and electrode types). Molecular oxygen was introduced into a quartz tube through a variable leak valve with mass flowmeter. Corresponding to the oxygen flow rate, the pressure of the system ranged from $1{\;}{\times}{\;}10^{-6}{\;}Torr{\;}to{\;}5{\;}{\times}{\;}10^{-5}$ Torr. The base pressure was $1{\;}{\times}{\;}10^{-10}$ Torr. The growth of Bi-oxides was achieved by coevaporation of metal elements and oxygen. In this way a Bi-oxide multilayer structure was prepared on a basal-plane MgO or $SrTiO_3$ substrate. The grown films compiled using RHEED patterns during and after the growth. Futher, the exact observation of oxygen radicals with MBE is an important technology for a approach of growth conditions on stoichiometry and perfection on the atomic scale in oxide. The oxidization degree, which is determined and controlled by the number of activated oxygen when using radical sources of two types, are utilized by voltage locked loop (VLL) method. Coil type is suitable for oxygen radical source than electrode type. The relationship between the flux of oxygen radical and the rf power or oxygen partial pressure estimated. The flux of radicals increases as the rf power increases, and indicates to the frequency change having the the value of about $2{\times}10^{14}{\;}atoms{\;}{\cdots}{\;}cm^{-2}{\;}{\cdots}{\;}S^{-I}$ when the oxygen flow rate of 2.0 seem and rf power 150 W.150 W.

• 한국수자원학회논문집
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• 제46권5호
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• pp.465-476
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• 2013

방출장파복사량은 수치예보모형, 수문모형, 증발산 등에 사용되는 인자로 지구의 에너지 균형을 이해하는데 필수적이다. 현재 국내외에서는 이를 정확하게 관측하기가 어려우며, 또한 공간적인 제약이 따른다. 따라서, 본 연구에서는 원격탐사 기술을 적용함으로써 지상관측의 단점을 보완하기 위해 정지궤도 위성인 Communication, Ocean and Meteorological Satellite (COMS)를 사용하여 방출장파복사량(Outgoing Longwave Radiation, $R_{lu}$ )를 계산하였다. 이 자료의 검증을 위해 유량조사사업단에서운영 관리하는 청미천/설마천 Flux Tower의 자료를 사용하여 계산된 $R_{lu}$ 와 MODIS 위성자료를 사용하여 계산된 $R_{lu}$ 를 비교 및 검증하였다. 전반적으로 COMS의 자료가 높은 상관계수를 나타내어 COMS의 사용가능성을 보여주었다. 이러한 결과를 바탕으로 향후 COMS를 이용한 증발산 산정 연구를 할 계획이다.

• 대한원격탐사학회지
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• 제29권1호
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• pp.137-149
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• 2013

표면도달일사량은 태양과 지구에너지시스템을 이해하는데 중요하며, 대기-지표면의 흐름, 농업 생산량, 태양발전에 필요한 에너지 연구 등과 같은 많은 분야에 활용되고 있는 중요한 변수이다. 대부분의 태양에너지는 지상관측지점에서 관측하는 경우가 많이 있지만, 공간적인 분포를 판단하기에는 한계성을 지니고 있다. 이에 반해 인공위성을 활용한 원격탐사 기법은 지속적인 자료 제공과 더불어 광역범위의 공간적 분포를 파악하는 장점이 있다. 본 연구에서는 COMS 위성자료 중 표면도달일사량 (Solar Insolation, INS)의 정확성 판단하기 위해 플럭스 타워에서 측정된 지점 자료와의 비교, 검증을 실시하였다. 결론적으로 볼 때, 30분 간격의 자료와 일평균의 자료에서 높은 상관계수를 보임에 따라 천리안 위성자료의 한반도 적용가능성이 높다고 판단된다.

• 한국농림기상학회지
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• 제12권4호
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• pp.241-263
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• 2010

KoFlux는 한국의 주요 육상생태계와 대기간의 에너지, 물, 이산화탄소의 순환을 감시하기 위해 구축한 에디 공분산 기술을 기반으로 하는 미기상학 플럭스 타워 관측지의 국내 관측망이다. KoFlux의 사명은 AsiaFlux와 동일하게 지구상의 생명의 질과 지속가능성을 보장하기 위해 아시아의 주요 생태계를 감시하고 돌보는 것이다. 구체적인 KoFlux의 목적은 (1) 생태계를 감시하고, 자료를 수집, 저장하고 배포를 가능하게 하는 하부구조와 (2) 이에 관련된 지식과 자료를 효과적으로 적용하고 배포하기 위해 정기적으로 포럼과 단기 훈련과정을 과학공동체에 제공하는 것이다. KoFlux는 아시아의 주요 육상생태계의 탄소/물/에너지 교환에 관한 생태계과학 정보와 지식을 창출하고, 과학적 연구와 적용에 있어서 다학문간 협력과 융합을 촉진하고, 지속적인 생태계 서비스를 지역사회에 제공함으로써 AsiaFlux의 비전인 "사고하는 공동체, 배움의 프런티어"를 추구하며 실천해 나간다. 현재 KoFlux 네트워크는 총 일곱 개의 관측지로 구성되어 있는데 국내의 경우 활엽수림, 침엽수림, 혼효림, 논과 비균질 농경지를 포함하며, 국외의 경우 남극과 북극의 툰드라 생태계에 위치해 있다. 등재된 관측지는 모두 표준화된 프로토콜을 사용하여 자료를 체계적으로 처리하고 있으며 자유롭게 자료 활용이 가능하도록 품질 검증된 플럭스 자료의 데이터베이스를 지속적으로 구축해 가고 있다. KoFlux는 정기적인 학술 논문 출판, 포럼 및 훈련과정을 통해, 네트워크를 성장시키고, 플럭스 관측 및 모델링 전문가간의 연결 및 정보교환을 위한 아고라를 제공하며, 관측 및 자료 분석을 위한 전문인력 양성을 위한 교육에 힘쓰고 있다. 그러나 이러한 지속적인 노력에도 불구하고 KoFlux에 등재된 산학연기관을 제외하고는 아직까지 네트워크의 성장이 제한되어 있는 실정이다. 이러한 학문간의 벽을 허물고, 네트워크에 대한 동반자 및 주인 의식을 고취시키기 위해 KoFlux는 2011년부터 서울대학교에 설립된 국가농림기상센터를 중심으로 NCAM의 주요 서비스를 담당하게 될 것이다. 이러한 일치된 협력은 현재의 감시 네트워크를 더욱 보강시키고, 차세대 과학자들을 길러내며, 우리 사회에 지속가능한 생태계 서비스의 제공을 보장할 수 있도록 이끌어 줄 것이다.