• Journal of international Conference on Electrical Machines and Systems
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• 제3권2호
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• pp.155-161
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• 2014

Industrial Static Var Generator (SVG) is typically applied at or near the load center to mitigate voltage fluctuation, flicker, phase unbalance, non-sine distortion or other load-related disturbance. Special attention is paid to the influence of grid voltage quality on SVG current, the non-sine distortion and unbalance of grid voltage causes not only the AC current distortion and unbalance but also the DC voltage fluctuation. In order to let the inverter voltage contain the fundamental negative sequence and harmonic component corresponding to the grid voltage, a new dual-loop control scheme is proposed to suppress the influence in this paper. The harmonic and negative sequence voltage decomposition algorithm and DC voltage control are also introduced. All these analyses can guide the practical applications. The simulation results verify the feasibility and effectiveness of the present control strategy and analyses.

• 연구논문집
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• 통권30호
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• pp.33-42
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• 2000

We must stabilize quickly increasing waste matters in urban life and livestock industry. Biogas including landfill gas and digester gas is byproduct of anaerobic decomposition of organic waste matter and contains 40%-70% methane, which can be used for energy purposes. Utilization of biogas reduce the emission of methane into the atmosphere to minimize greenhouse effect and the carbon dioxide (CO2) emitted when biogas is converted to energy has been taken out of the atmosphere by growing plant. Recently, bioenergy is world-widely noticeable as all contributing to the greenhouse effect. This paper presents development process of a biogas engine for cogeneration system and results of application to digester gas and landfill gas in site. The biogas engine is a dual fuel engine operated on biogas with a diesel pilot. At present, the engine can substitute biogas for diesel fuel up to 85%. but it can be said that there is a possibility of improvement in performance.

• Journal of Information Processing Systems
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• 제13권6호
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• pp.1628-1639
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• 2017

The combination texture feature extraction approach for texture image retrieval is proposed in this paper. Two kinds of low level texture features were combined in the approach. One of them was extracted from singular value decomposition (SVD) based dual-tree complex wavelet transform (DTCWT) coefficients, and the other one was extracted from multi-scale local binary patterns (LBPs). The fusion features of SVD based multi-directional wavelet features and multi-scale LBP features have short dimensions of feature vector. The comparing experiments are conducted on Brodatz and Vistex datasets. According to the experimental results, the proposed method has a relatively better performance in aspect of retrieval accuracy and time complexity upon the existing methods.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.97-104
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• 2008

Most of engine control systems for helicopter turboshaft engines are equipped with dual sensors. For the system with dual redundancy, analytic methods are used to detect faults based on the system dynamical model. Helicopter engine dynamics are affected by aerodynamic torque induced from the dynamics of the main rotor. In this paper an engine model including the rotor dynamics is constructed for the T700-GE-700 turboshaft engine powering UH-60 helicopter. The singular value decomposition(SVD) method is applied to the developed model in order to detect sensor faults. The SVD method which do not need an additional computation to generate residual uses the characteristics that the system outputs in direction of the left singular vector if an input is applied in direction of the right singular vector. Simulations show that the SVD method works well in detecting and isolating the sensor faults.

• Current Optics and Photonics
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• 제7권4호
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• pp.428-434
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• 2023

The compensators used in spectroscopic ellipsometers are usually assumed to be ideal linear waveplates. In reality, however, they are elliptical waveplates, because they are usually made by bonding two or more linear waveplates of different materials with slight misalignment. This induces systematic error when they are modeled as linear waveplates. We propose an improved calibration method based on an optical model that regards an elliptical waveplate as a combination of a circular waveplate (rotator) and a linear waveplate. The method allows elimination of the systematic error, and the residual error of optic axis measurement is reduced to 0.025 degrees in the spectral range of 450-800 nm.

• Korean Journal of Radiology
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• 제22권6호
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• pp.970-982
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• 2021

Dual-energy CT (DECT) provides insights into the material properties of tissues and can differentiate between tissues with similar attenuation on conventional single-energy imaging. In the conventional CT scanner, differences in the X-ray attenuation between adjacent structures are dependent on the atomic number of the materials involved, whereas in DECT, the difference in the attenuation is dependent on both the atomic number and electron density. The basic principle of DECT is to obtain two datasets with different X-ray energy levels from the same anatomic region and material decomposition based on attenuation differences at different energy levels. In this article, we discuss the clinical applications of DECT and its potential robust improvements in performance and postprocessing capabilities.

• Journal of Power Electronics
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• 제11권4호
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• pp.401-407
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• 2011

In order to enhance torque density of five-phase permanent magnetic synchronous motor with third harmonic injection for electric vehicles (EVs) applications, optimum seeking method for injection ratio of third harmonic was proposed adopting theoretical derivation and finite element analysis method, under the constraint of same amplitude for current and air-gap flux. By five-dimension space vector decomposition, the mathematic model in two orthogonal space plane, $d_1-q_1$ and $d_3-q_3$, was deduced. And the corresponding dual-plane vector control method was accomplished to independently control fundamental and third harmonic currents in each vector plane. A five-phase PMSM prototype with quasi-trapezoidal flux pattern and its fivephase voltage source inverter were designed. Also, the dual-plane vector control was digitized in a single XC3S1200E FPGA. Simulation and experimental results prove that using the proposed optimum seeking method, the torque density of five-phase PMSM is enhanced by 20%, without any increase of power converter capacity, machine size and iron core saturation.

• 대한전자공학회논문지TC
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• 제49권7호
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• pp.23-31
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• 2012

스케쥴링 및 데이터율의 결합 제어와 같은 자원할당 기술은 전파인지 네트워크에서는 매우 중요한 문제이다. 그러나 전파인지 네트워크에서는 주사용자 채널의 스토케스틱 특성으로 인하여 데이터율 및 스케쥴링을 결합하여 제어하는 것은 매우 어렵다. 본 논문에서는 전파인지 네트워크에서 신뢰성 제한 조건들을 고려한 비대칭 데이터율 및 스케쥴링 결합 제어 기법을 제안한다. 데이터율 및 스케쥴링 문제를 컨벡스 최적화 기법으로 공식화하고 쌍대성 분해 기법을 사용하여 부분 문제로 변환하여 분산화 하였다. 본 논문에서는 전체 시스템의 효용함수를 최대화 하도록 분산 노드들의 데이터율을 분산적으로 제어하는 알고리즘을 제안 하였다. 반면, 스케줄링은 기지국이 최적화하는 비대칭 기법을 제안하였다. 본 논문에서 제안한 비대칭 결합 제어 알고리즘은 전체 최적화 해로 수렴하는 것을 수치해석 기법으로 검증하였다.

• 공업화학
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• 제31권3호
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• pp.317-322
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• 2020

수산화암모늄나이트레이트(HAN; NH₃OHNO₃)는 낮은 용융점과 증기압의 특성을 가지고 있고, 상대적으로 높은 산소균형을 이루고 있는 이온성 화합물이다. 본 연구에서는 높은 함량의 액상추진제를 제조하기 위한 산화제로 활용하기 위하여 이중용매를 적용하여 고체입자상으로 얻었다. 감압 하에서 액상의 HAN으로부터 수분을 증발시킨 후, 반용매로서 아세톤과 에탄올을 적용하여 추출한 입자상의 HAN에는 13.8 wt%의 수분이 포함되어 있었다. 아세톤을 단독으로 적용하였을 때, 합성수율은 질량기준으로 최대 88%이었고, TGA로 측정된 최대 함량은 86.2%, 분해온도는 160~205℃ 범위로 나타났다.

• 한국결정성장학회지
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• 제29권1호
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• pp.6-11
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• 2019

본 연구에서는 페로브스카이트 태양전지의 광흡수체로 사용되는 메틸암모늄 할로젠화 납(methylammonium lead halide, $MAPbX_3$, X = I, Br) 페로브스카이트(perovskite) 박막을 이중주입 초음파분무법을 이용하여 제조하였다. 이중주입 초음파 분무법을 통해 $60^{\circ}C$ 이하의 기판온도에서 분무한 후, $75^{\circ}C$에서 5분간 최종열처리 후 $MAPbI_3$ 단일상을 제조할 수 있었다. $80^{\circ}C$ 이상의 온도에서 분무 증착 시에는 페로브스카이트 상의 분해로 인해 구형의 결정립이 막대형태의 프렉탈(fractal) 구조로 변화되었다. $MAPbI_3$ 용액과 $MAPbIBr_2$ 용액의 이중주입을 통해, $MAPbI_3$ 박막에 비해 높은 $100^{\circ}C$의 열처리로 $MAPbI_{3-x}Br_x$ 박막을 제조할 수 있었다.