• Journal of Power Electronics
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• 제17권6호
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• pp.1683-1693
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• 2017

This paper analyses the harmonic pollution to power grids caused by thyristor-controlled devices. It also formulates a mathematic derivation for the voltage spikes in thyristor-controlled branches to explain the harmonic and EMI derived from the reverse-recovery characteristics of the thyristor. With an equivalent nonlinear time-varying voltage source, a detailed simulation model is established, and the periodic dynamic switching characteristic of the thyristor can be explicitly implied. The simulation results are consistent with the probed results from on-site measurements. An improved trigger system with gate-shorted circuit structure is proposed to reduce the voltage spikes that cause EMI. The experimental results indicate that a prototype with the improved trigger system can effectively suppress the voltage spikes.

• Advances in nano research
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• 제12권2호
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• pp.167-183
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• 2022

In this paper, the free and forced vibration analysis of rotating cantilever nanoscale cylindrical beams and tubes is investigated under the external dynamic load to examine the nonlocal effect. A couple of nonlocal strain gradient theories with different beams and tubes theories, involving the Euler-Bernoulli, Timoshenko, Reddy beam theory along with the higher-order tube theory, are assumed to the mathematic model of governing equations employing the Hamilton principle in order to derive the nonlocal governing equations related to the local and accurate nonlocal boundary conditions. The two-dimensional functional graded material (2D-FGM), made by the axially functionally graded (AFG) in conjunction with the porosity distribution in the radial direction, is considered material modeling. Finally, the derived Partial Differential Equations (PDE) are solved via a couple of the generalized differential quadrature element methods (GDQEM) with the Newmark-beta techniques for the time-dependent results. It is indicated that the boundary conditions equations play a crucial task in responding to nonlocal effects for the cantilever structures.

• Journal of Power Electronics
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• 제18권5호
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• pp.1545-1554
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• 2018

This paper proposes a modified control strategy to improve the performance of three-phase four-leg shunt active power filters (APFs) for the compensation of three phase unbalanced loads. Unbalanced current cannot be obtained accurately by a harmonic detector due to the lower frequency. The proposed control strategy eliminates conventional harmonic detectors by directly regulating the source current. Therefore, the computational complexity is greatly reduced and the performance of the APF is improved. A mathematic model has been developed based on the source currents. The corresponding controllers have been designed based on the sinusoidal internal model principle. The proposed control strategy can guarantee excellent compensation performance and stable operation after an extreme disturbance such as a short circuit fault. In addition, the proposed technique can selectively compensate specific harmonics. A 50kVA prototype APF is implemented in the laboratory to validate the feasibility and performance of the proposed control strategy.

• 한국기계가공학회지
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• 제16권2호
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• pp.88-93
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• 2017

Due to the requirement of the development of the precision manufacturing industry, the accuracy of machine tools has become a key issue in this field. A critical factor that affects the accuracy of machine tools is the feed system, which is generally driven by a ball screw. Basically, to improve the performance of the feed drive system, which will be thermally extended lengthwise by continuous usage, a thermal error compensation system that is highly dependent on the feedback temperature or positioning data is employed in the machine tool system. Due to the overdependence on measuring technology, the cost of the compensation system and low productivity level are inevitable problems in the machine tool industry. This paper presents a novel feed drive thermal error compensation system method that could compensate for thermal error without positioning or temperature feedback. Regarding this thermal error compensation system, the heat generation of components, principal of compensation, thermal model, mathematic model, and calculation method are discussed. As a result, the test data confirm the correctness of the developed feed drive thermal error compensation system very well.

• 한국식품영양학회지
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• 제16권3호
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• pp.180-186
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• 2003

가열살균 처리시의 온도값을 이용하여 다양한 미생물들의 가열살균 효과를 D값, z값 등의 미생물 내열성 특성치와 kinetic 모델 및 수식을 이용하여 살균치 계산을 컴퓨터를 이용하여 수행함으로써 target 미생물의 살균정도를 예측하고자, Excel과 Visual Basic을 연동하여 작성된 시스템으로 Excel을 기본으로 사용한 프로그램을 개발하였다. 가열살균 target 미생물을 선택하고자 야채식품을 기반으로 하는 식품에서의 미생물을 검토하여, 내열성인 가장 큰 호기성 포자형성균인 Bacillus spp. 계통이 산을 형성하여 맛 등의 품질을 저하시켜 변패를 유발하며, 위생적인 면에서 포자수를 줄이거나 사멸할 필요가 있어서 선택하였다. 병원성 균 중에서 $D_{121.1}$이 0.0065분, z값이 7.8$^{\circ}C$인 Bacillus cereus와 부패현상 관련 균 중에서 $D_{121.1}$이 0.5분, z값이 12$^{\circ}C$인 Bacillus subtilis를 대상으로 해서 개발되었으며, 필요시에는 D값과 z값을 직접 대입하므로서, 여러 가지 미생물에 대해서도 적용이 가능하게 하였다.

• 대한한의학방제학회지
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• 제18권2호
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• pp.227-239
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• 2010

Objective : The purpose of this study was to develop the simulator which can analyze the anti-inflammatory effects of herbs based on e-cell, or the virtual cell. Method : We have ensured the medical herbs and its active compounds by investigating the oriental medicine records and NBCI(Biomedicine database). Also we have developed the web-based search system for confirming database related to anti-inflammation. We have researched the cell signal pathway related with inflammatory response control and established the mathematical model of herb interaction on selected signal pathway in e-cell. Finally we have developed the prototype which can confirm the result of this model visibly. Results : We constructed the database of 62 cases of anti-inflammatory active compounds in 61 cases of medical herbs which have been known anti-inflammation effects in the paper, 16 cases of inflammatory factors, 10 cases of signal pathways related with inflammatory response and 6,834 cases of URL(Uniform Resource Locator) of referenced papers. And we embodied the web-based research system, which can research this database. User can search basic and detailed information of medical plants related with anti-inflammatory by using information system. And user can acquire information on an active compounds, a signal pathway and a link URL of related paper. Among investigated ten pathways, we selected NF-${\kappa}B$, which plays important role in activation of immune system, and we searched the mechanisms of actions of proteins which could be components of this pathway. We reduced total network into IKK-$I{\kappa}B$ - NF-${\kappa}B$, and completed mathematic modeling by using ordinary differential equations and response variables of $I{\kappa}B-NF-{\kappa}B$ signaling model network which is suggested by Baltimore Group. We designed OED(Ordinary Differential Equation) for response of IKK, $I{\kappa}B$, $NF-{\kappa}B$ in e-cell's cytoplasm and nucleus, and measured whether an active compound of medicinal plants which is inputted by an user would have a anti-inflammation effects in obedience to change in concentration over time. The proposed model was verified by using experimental results of the papers which are listed on NCBI.

• 한국정보통신학회논문지
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• 제18권5호
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• pp.1013-1021
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• 2014

정부의 입장에서 R&D 과제간의 유사도를 분석하는 것은 불필요한 예산의 낭비를 없애고, R&D 투자의 효과를 높이는데 있어서 매우 중요한 문제이다. 그 동안, 문서의 내용을 대표하는 키워드를 중심으로 두 문서간의 유사도를 분석하거나, 문장 단위로 유사도를 분석함으로써, R&D 과제의 중복 여부를 판단하기 위한 연구들이 시도되어 왔으나, 여러 가지 이유로 아직까지 그 정확도는 매우 낮은 실정이다. 이에, 본 연구는 기 수행된 R&D 관련 특허를 조사, 수집하는 정부 R&D 특허기술동향조사사업의 특허분석 DB를 활용하여 R&D 과제간의 유사도를 분석할 수 있는 방안을 제시하고자 한다. 이를 위해, 집합 이론 및 확률 이론을 기반으로 한 유사도 측정 모델을 제시하였다. 또한, 제시한 모델의 검증을 위해 156개 과제, 160,218개의 유효특허를 기반으로 유효특허기반 과제 유사도 측정 실험을 수행하고, 그 사례를 제시하였다.

• Journal of Power Electronics
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• 제15권5호
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• pp.1305-1317
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• 2015

Distributed generation systems (DGSs) have been getting more and more attention in terms of renewable energy use and new generation technologies in the past decades. The self-excited induction generator (SEIG) occupies an important role in the area of energy conversion due to its low cost, robustness and simple control. Unlike synchronous generators, the SEIG has to absorb capacitive reactive power from the outer device aiming to stabilize the terminal voltage at load changes. This paper presents a novel static VAR compensator (SVC) called a magnetic energy recovery switch (MERS) to serve as a voltage controller in SEIG powered DGSs. In addition, many small scale SEIGs, instead of a single large one, are applied and devoted to promote the generation efficiency. To begin with, an expandable mathematic model based on a d-q equivalent circuit is created for parallel SEIGs. The control method of the MERS is further improved with the objective of broadening its operating range and restraining current harmonics by parameter optimization. A hybrid control strategy is developed by taking both of the stand-alone and grid-connected modes into consideration. Then simulation and experiments are carried out in the case of single and double SEIG(s) generation. Finally, the measurement results verify that the proposed DGS with SVC-MERS achieves a better stability and higher feasibility. The major advantages of the mentioned variable reactive power supplier, when compared to the STATCOM, include the adoption of a small DC capacitor, line frequency switching, simple control and less loss.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2004년도 제29회 추계학술대회 발표논문집
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• pp.132-135
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• 2004

본 연구는 호흡시에 내부 장기가 움직일 때 시간에 따른 threshold 값을 주어졌을 때 선량분포에 대한 연구를 수행한 것이다. 이전 연구에서 보고 된 것처럼 일정 시간에 따라 움직이는 내부 장기의 움직임은 Rujan 등에 의해 보고된 3차원적 수학적 계산방법에 의해 장기의 위치를 나타내었다. 그 결과 처음exhale에서 1초동안 간의 움직임은 2mm이내에 위치하는 것을 알게 되었다. 그래서 이 연구에서 TGT는 간의 움직임이 가장 적은 처음 exhale에서 1초동안 움직일 때의 선량분포를 평가하였다. TGT 값을 주었을 때 선량분포를 비교하기 위해 다음 조건으로 방사선을 조사하였다. 1) threshold 범위에서 target이 움직일 때(1초, 1.5호), 2) threshold 없이 target이 움직일 때, 3) target이 움직이지 않을때. 각각 조건의 선량분포를 비교 평가하였다

• 대한수학교육학회지:학교수학
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• 제13권4호
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• pp.581-598
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• 2011

학교 교육과정의 초기 단계에서부터 대수를 가르쳐야 한다는 주장이 국제적인 공감을 얻으면서, 초등학교에서 적절한 대수 지도 방안을 찾는데 관심이 높아지고 있다. 그러나 초등학교에서 대수적 추론 능력을 향상시키기 위해 수학 수업이 어떻게 이루어져야 하는가에 관한 실제적인 연구는 여전히 부족한 상황이다. 본 연구는 초등학교에서의 효과적인 대수 교수-학습에 대한 구체적이고 실질적인 정보를 얻기 위해, 곱셈의 결합법칙 탐구를 강조한 4학년 수업 사례를 중심으로 탐구적 질적 사례 연구를 실시하였다. 체계적인 수업 분석을 통해 본 연구는, 구체적인 상황에서 수와 연산의 성질에 초점 맞추기, 충분한 사례 탐구를 통해 수와 연산의 성질 발견하기, 임의의 수 상황에서 연산의 성질 일반화하기의 세 단계에 따라 교사가 어떤 활동들을 구성할 수 있으며 학생들은 어느 정도의 대수적 추론을 발현할 수 있는지를 구체적인 사례를 통해 밝히고자 하였다.