• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1259-1261
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• 2003

고정밀 와이어컷 방전가공기는 높은 정밀도를 갖는 금형제작에 사용되고 있는 공작기계로서 최근 나노단위의 가공기술이 요구되는 산업추세에 발맞추어 고속, 고정밀 가공특성을 갖추도록 전반적인 성능개선이 이루어지고 있다. 본 논문에서는 기존 Thyristor를 이용한 위상제어 방식보다 우수한 특성을 갖는 스위칭모드 방식의 10kW급 직류 전원장치의 개발에 대해 기술하고있다.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.3 no.3
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• pp.73-80
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• 2010

Complex-valued blind algorithms which are based on constant modulus error and Euclidian distance (ED) between two probability density functions show relatively poor performance in spite of the advantages of information theoretic learning since the inherent characteristics of the constant modulus error prevent the algorithm from coping with the symbol phase rotation caused by the complex channels. In this paper, we show that the symbol phase rotation problem can be avoided and the advantages of information theoretic learning can be preserved by introducing decision-directed mode to the blind algorithm whenever the equalizer output power lies in the neighborhood of multi-modulus levels. Simulation results through MSE convergence and constellation comparison for severely distorted complex channels show significantly enhanced performance of symbol-point concentration and no phase rotation problems caused by the complex channel models.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.10
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• pp.1968-1976
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• 2007

This paper proposes a hybrid pseudo-noise (PN) code acquisition scheme for Multicarrier Direct Sequence - Code Division Multiple Access (MC DS-CDMA) mobile communication systems on the code acquisition performance for Nakagami-m fading channel. The hybrid acquisition scheme combines parallel search with serial search to cover the whole uncertainty region of the input code phase. It has a much simpler acquisition hardware structure than the total parallel acquisition and can achieve the mean acquisition time (MAT) slightly inferior to that of the total parallel acquisition. The closed-form expressions of the detection and false-alarm probabilities are derived.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.30-37
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• 1998

This paper investigates the linear stability of wakes with special emphasis on the effect of chemical reaction. Velocity and density profiles for laminar flows are obtained from analytic profiles as well as from simulation. Wakes have two generalized inflection points and two unstable modes-sinuous and varicose modes. For analytical laminar profiles, sinuous modes are more unstable than varicose modes irrespective of density variation, which shows wakes will be destabilized by sinuous modes. Large velocity difference and density difference lead to more unstable wakes due to large momentum difference. For simulated laminar profiles, chemical reaction with stoichiometric chemistry increases temperature and stabilizes the flow due to increase in compressible reacting wades, flow becomes stable as velocity increases due to viscous dissipation.

• Journal of the Korean Wood Science and Technology
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• v.27 no.3
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• pp.1-6
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• 1999

European spruce and maple were to be estimated as raw material of violin family instruments with linear modal analysis to provide the information data for the design of their bodies. Wood specimens cut in different direction were excited by impact hammer to measure the resonant frequency with typical vibrational modes. In spite of lower density than maple, European spruce showed the excellent acoustical properties with higher resonant frequency. And edge-grained spruce had more even frequencies than flat-grained ones to be more acceptable as front plate of violin. Resonant frequency was positively correlated with wood density of each specimen and the coefficients of edge-grained specimens were higher than those of flat-grained specimens of both wood species.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4C
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• pp.476-483
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• 2009

Tracking and detecting targets by the microwave seeker is affected by the clutter reflecting from the earth's surface. In order to detect retreating targets in look-down scenario, which appear in the sidelobe clutter (SLC) region, in the microwave seeker of high pulse repetition frequency (HPRF) mode, it is necessary to understand statistical characteristics of the surface SLC. Statistical analysis of SLC has been conducted for several kinds of the surface using data obtained by the captive flight test of the microwave seeker in the HPRF mode. The probability density function (PDF) fitting is conducted for several kinds and conditions of the surface. PDFs and PDF parameters, which best describe statistical distribution of the SLC power, are estimated. By using the estimated PDFs and PDF parameters, analyses for setting the target-detection thresholds, which give a desired level of target-detection false alarm probability, are made. These analysis materials for statistical characteristics of SLC power and the target-detection threshold can be used in various fields, such as development of a target-detection method, the constant false alarm rate processing.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.172-175
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• 2003

새로운 전력 반도체 소자로 주목받고 있는 MOS 구동 사이리스터 중 대 전력용으로 사용되는 EST는 높은 전류 밀도에서 게이트에 의한 전류 조절이 가능할 뿐만 아니라 다른 MOS 구동 사이리스터 소자와는 달리 전류 포화 특성을 지녀 차세대 전력 반도체로 각광 받고 있는 소자이다. 하지만 소자의 동작 시에 스냅-백 특성을 지녀 전력의 손실을 유발할 뿐만 아니라 오동작을 일으킬 가능성이 있다. 따라서 본 논문에서는 기존의 EST에서 스냅-백 특성의 제거와 저지 전압의 향상을 위해 트랜치 전극을 가지는 새로운 구조를 제안하고 게이트 전극과 캐소드 전극의 트랜치 화에 따른 특성 변화 양상을 살펴보기 위해 게이트 전극만 트랜치로 구성한 경우와 캐소드 전극만 트랜치로 구성한 경우를 시뮬레이션을 통해 해석하였다. 그 결과 기존의 EST에서 게이트 전극만을 트랜치 형태로 바꾼 경우에는 스냅-백 특성이 1.1 V의 애노드 전압과 91 A/cm2의 전류 밀도에서 발생하고 순방향 저지 모드 시의 저지 전압은 800 V로 기존의 257에 비해 월등한 전기적 특성 향상을 가져왔다. 그러나 기존의 EST에서 캐소드 전극만을 트랜치 형태로 바꾼 경우에는 스냅-백 특성이 1.72 V의 애노드 전압과 25 A/cm2의 전류 밀도에서 발생하고 순방향 저지 모드 시의 저지 전압은 613 V로 스냅-백 특성은 향상되었으나 저지 전압은 기존의 EST 보다 감소하였다. 결국 기존의 EST에서 게이트 전극만을 트랜치 전극 형태로 구성한 경우에 가장 탁월한 전기적 특성을 갖는 것으로 나타났다.

• Journal of KIISE
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• v.41 no.12
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• pp.1050-1057
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• 2014

Electroencephalogram (EEG)-based brain-computer interfaces (BCI) can be used for a number of purposes in a variety of industries, such as to replace body parts like hands and feet or to improve user convenience. In this paper, we propose a method to decompose and extract motor imagery EEG signal using Empirical Mode Decomposition (EMD) and Fast Fourier Transforms (FFT). The EEG signal classification consists of the following three steps. First, during signal decomposition, the EMD is used to generate Intrinsic Mode Functions (IMFs) from the EEG signal. Then during feature extraction, the power spectral density (PSD) is used to identify the frequency band of the IMFs generated. The FFT is used to extract the features for motor imagery from an IMF that includes mu rhythm. Finally, during classification, the Support Vector Machine (SVM) is used to classify the features of the motor imagery EEG signal. 10-fold cross-validation was then used to estimate the generalization capability of the given classifier., and the results show that the proposed method has an accuracy of 84.50% which is higher than that of other methods.

• Journal of the Korea Convergence Society
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• v.9 no.4
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• pp.1-7
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• 2018

Electric motors for electric vehicles differ in efficiency characteristics depending on the operation modes, studies for evaluating high efficiency characteristics in low speed and high speed operation modes are very important. Therefore, it is necessary to design method that can change the high torque, high output density, and high efficiency characteristics of driving motors for electric vehicles. In this paper, the diameter ratio of stator and rotor for the interior permanent magnet synchronous motor is change of designed 0.62, 0.65, and 0.68, respectively, and the efficiency characteristics of the entire operation section, average efficiency characteristics of the city driving modes and express highway driving modes are analyzed. As a result of analyzing the efficiency characteristics of the entire operating section, it was confirmed that as the diameter ratio increases, the high efficiency section moves to the low speed and low torque section and the high efficiency section moves to the high speed and low torque neighborhood as the diameter ratio decreases. As a result of analyzing the average efficiency characteristics in the city driving modes and express highway driving modes, the average efficiency of 0.68 model is analyzed to be more efficient than the 0.63 and 0.65 model ratio, and it is confirmed that it is suitable for city driving modes and express highway driving modes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7A
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• pp.672-677
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• 2007

A novel method for stabilizing the bias of an Electro-Optic Mach-Zehnder modulator has been proposed and demonstrated to maximize the switching extinction ratio in burst mode packet traffic. By sampling and minimizing the off-level output power of the modulator, a high extinction optical gate switch in obtain regardless of the variation of the packet traffic density.