• 전기의세계
• /
• v.10
• /
• pp.55-61
• /
• 1963

본 논문에서 취급한 제동권선이 없는 철극선의 3상단락현상을 해명하는데 있어 우선 임의력율의 전류를 횡축분과 직축분으로 분리해서 취급하는 소위 Blonde의 2반작용법(two reaction method)를 썼고, 각종 Reactance를 표시하는데는 편리한 단위법(perunit notation)을 사용했으며, 전기자의 1상저항은 각종 Reactance ( $X_{x}$, $X_{q}$ )의 어느것 보담도 극소치임으로 실제계산에는 무시했으나 과도전류의 변화를 좌우하는 감쇠정수[decrement factor)에는 큰 영향을 준다는 것이 규명되었다. 해석결과로서 3상단락전류의 초기치는 특수치보다 훨씬 큰 이유로서 단락전류가 계자자속을 약하게 만들어 그 반동으로 계자회로에 일정자속을 유지하기 위하여 부문적으로 개자전류가 증대함을 알게되었고, 단락전류의 직축분과 횡축분의 구성분이 규명검토되었고, 발전기의 돌발단락저류는 일반적으로 직류분, 기본파교류분 및 제2조파등을 포함하나 그 전부가 시정수의 역수인 감쇠정수에 지배되어서 지수함수곡선에 따라 감쇠되어 결국에는 지속단락전류에 귀착한다는 사실과 3상단락은 평형단락사고임으로 영상전류는 영이며 각상과도전류의 위상차가 120.deg.라는 것엔 변함이 없다는 것과 끝으로 철극기를 정격속도로 운전해 놓고 이것을 여자해서 무부하전압을 수기시켜 그의 3상전단자를 돌연 단락해서 그의 과도전류의 파형을 Oscillograph로 촬영하면 본론에서 해석한 결과식의 그것과 일치하게 됨을 알 수 있을 것이다.것이다.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.43 no.12 s.354
• /
• pp.61-67
• /
• 2006

This paper proposes the algorithm for tracking of the residual phase errors incurred by carrier frequency offset and sampling frequency offset in the orthogonal frequency division multiplexing (OFDM) systems which are suitable for high data rate wireless communications. In the OFDM systems the subcarriers which are orthogonal to each other are modulated by digital data and transmitted simultaneously. The carrier frequency offset causes degradation of signal to noise ratio(SNR) performance and interference between the adjacent subcarriers. The errors in the sampling timing caused by the sampling frequency difference between the transmitter and the receiver sides also cause a major performance degradation in the OFDM systems. The residual error tracking and compensation mechanism is essential in the OFDM system since the carrier and the sampling frequency offset cause the loss of orthogonality resulting in the system performance loss. This paper proposes the scheme where the channel gain and the payload data information are reflected in the residual error tracking process which results in the reduction of the estimation error and the tracking performance improvements under the frequency selective fading wireless channels.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.40 no.3
• /
• pp.172-180
• /
• 2003

The purpose of this study is to observe the heat transfer process in in-vivo human muscle based on Proton Resonance Frequency(PRF) method in Magnetic Resonance Imaging(MRI). MRI was obtained to measure the temperature variation according to the heat transfer in phantom and in-vivo human calf muscle. A phantom(2% agarose gel) was used in this experiment. MR temperature measurement was compared with the direct temperature measurement using a T-type thermocouple. After heating agarose gel to more than 5$0^{\circ}C$ in boiling hot water, raw data were acquired every 3 minutes during one hour cooling period for a phantom case. For human study heat was forced to deliver into volunteer's calf muscle using hot pack. Reference data were once acquired before a hot pack emits heat and raw data were acquired every 2 minutes during 30minutes. Acquired raw data were reconstructed to phase-difference images with reference image to observe the temperature change. Phase-difference of the phantom was linearly proportional to the temperature change in the range of 34.2$^{\circ}C$ and 50.2$^{\circ}C$. Temperature resolution was 0.0457 radian /$^{\circ}C$(0.0038 ppm/$^{\circ}C$) in phantom case. In vivo-case, mean phase-difference in near region from the hot pack is smaller than that in far region. Different temperature distribution was observed in proportion to a distance from heat source.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.2C
• /
• pp.203-209
• /
• 2010

In this paper, we propose a new selected mapping (SLM) scheme for reducing peak to average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals modulated with quadrature amplitude modulation (QAM), called amplitude and phase variant SLM (APSLM). Contrary to the conventional SLM which rotates the phases of QAM symbols in the frequency domain, the proposed scheme changes the magnitudes as well as the phases of QAM symbols by applying binary sequences to the binary data sequence before mapped to QAM symbols. Simulation results show that the proposed scheme has better PAPR reduction performance than the conventional SLM scheme for the QAM modulated OFDM signals, especially for the small number of subcarriers.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.4
• /
• pp.424-434
• /
• 2015

Adaptive beamforming algorithms have been widely used to remove interference and jamming in the phased array radar system. Advances in the field programmable gate array(FPGA) technology now make possible the real time processing of adaptive beamforming (ABF) algorithm. In this paper, the FPGA based real-time implementation method of adaptive beamforming system(beamformer) in the pre-processor module for active electronically scanned array(AESA) radar is proposed. A compact FPGA-based adaptive beamformer is developed using commercial off the shelf(COTS) FPGA board with communication via OpenVPX(Virtual Path Cross-connect) backplane. This beamformer comprises a number of high speed complex processing including QR decomposition & back substitution for matrix inversion and complex vector/matrix calculations. The implemented result shows that the adaptive beamforming patterns through FPGA correspond with results of simulation through Matlab. And also confirms the possibility of application in AESA radar due to the real time processing of ABF algorithm through FPGA.

• Korean Journal of Optics and Photonics
• /
• v.18 no.2
• /
• pp.122-129
• /
• 2007

Generally, many kinds of phase unwrapping algorithm are used to obtain three-dimensional features in digital holography. The Goldstein algorithm is ra epresentative method. which requires small memory capacity and short execution time fer an unwrapping process. However, the Goldstein algorithm has some problems when the dipole residue is located at the boundary. When the opposite residues are located at the boundary and the distance between the opposite residues is longer than the boundary, an incorrect branch cut occurs and results in incorrect calculation. We have modified the Goldstein algorithm to solve the incorrect calculation problem using boundary information. We found that the modified Goldstein algorithm could resolve the Goldstein algorithm's problem.

• Journal of Advanced Navigation Technology
• /
• v.26 no.1
• /
• pp.22-28
• /
• 2022

In order to install ultra wide band and ultra long-haul transmission link based on standard single mode fiber, optical signal distortion due to chromatic dispersion and nonlinear Kerr effect must to be compensated. In this paper, optical link consisted of dispersion management and optical phase conjugation is proposed for compensation of the distorted wavelength division multiplexed (WDM) channels. Dispersion map profile in the proposed dispersion-managed link is configured by periodic repetitive shape, and optical phase conjugator is placed at various position including the midway of total transmission length. It is confirmed from simulation results that when the residual dispersion per span (RDPS) selected in the proposed dispersion-managed link to be large, the compensation of distorted WDM channels in the non-midway OPC system is more improved than the conventional dispersion-managed link.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.13 no.1
• /
• pp.23-30
• /
• 1976

In this paper, a method is proposed for the recognition of hand-written Hangeul. This is peiformed by extraction of the concave structural segments by phase rotation. Character patterns can be decomposed into the fundamental concave structural segments which are also categorized into segment sects, and the closure and phase features of each segment in set is represented by logics. By rotating the logic pattern, the topological and phase features of segment are extracted for the reliable recognition of the character. It is also evaluated that this method applies to a wide variety of shape, position and declination of the character.

• Korean Journal of Optics and Photonics
• /
• v.12 no.1
• /
• pp.5-9
• /
• 2001

A wavemeter was realized using the phenomena that the phase lag between principal polarization states in an optical retarder is a function of wavelength. The change in the polarization state of the optical beam as it passes through the optical retarder is dependent on wavelength. The wavelength of the optical beam is determined by comparing the power difference between principal polarization states. A prototype wavemeter was successfully implemented using a polarization maintaining fiber with birefringence $3\times10^{-4}$ and length 100 mm as the optical retarder. The measurement resolution was 0.08 nm over a wavelength region of 1554.38 nm-1557.l9 nm, which agreed well with theoretically calculated results. In addition, the dependence of operating characteristics on temperature was analyzed theoretically and experimentally.mentally.

• Proceedings of the KIPE Conference
• /
• 2013.11a
• /
• pp.56-57
• /
• 2013

불평형 및 왜곡 상태에서 정상분 추출은 기존 여러 가지 방법이 제시되어 있다. 여기에 PLL(Phase Locked Loop) 방식에 따라 다양한 특성이 나타나게 된다. 본 논문에서는 4가지 정상분 추출 방법과 2가지 PLL 방법을 적용하여 각각의 성능을 시뮬레이션 및 실험을 통해 비교 분석하였다.