• 전기학회논문지
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• 제64권7호
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• pp.978-983
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• 2015

This paper presents Frequency Bias setting for the adequate AGC(Automatic Generator Control) operation based on the frequency response of power system in Korea. AGC frequency control recovers the frequency up to 60Hz following a primary control when the frequency suddenly drops due to a fault in power system. AGC can compensate an appropriate amount of generation by calculating ACE(Are Control Error) from the frequency deviation with the AGC frequency bias set from the actual frequency response in power systems. An appropriateness of the proposed AGC bias setting is verified through case studies employing the simulation model.

• 한국광학회:학술대회논문집
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• 한국광학회 2008년도 하계학술발표회 논문집
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• pp.297-298
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• 2008

• 음성과학
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• 제13권3호
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• pp.35-48
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• 2006

The present study examined whether words with higher frequency have more exposure to the lenition process such as intervocalic stop voicing or /h/ reduction in the production of the Korean speakers. Experiment 1 and Experiment 2 tested if word-internal intervocalic voicing and /h/ reduction occur more often in the words with higher frequency than less frequent words respectively. Results showed that the rate of voicing was not significantly different between the high frequency group and the low frequency group; rather both high and low frequency words were shown to be fully voiced in this prosodic position. However, intervocalic /h/s were deleted more in high frequency words than in low frequency words. Low frequency words showed that other phonetic variants such as [h] and [w] were found more often than in high frequency group. Thus the results of the present study are indefinitive as to the relationship between the word frequency and lenition with the data at hand.

• 한국컴퓨터정보학회논문지
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• 제23권1호
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• pp.1-7
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• 2018

The Korean Air Force FA-50 aircraft currently operating in the Air Force is using Ultra High Frequency (UHF) frequency communications for navigation communications with ground control stations or other aircraft. The pilot communicates by changing frequency at any time during flight, and performs communication by directly inputting from the Integrated Up-Front Controller installed in the cockpit. The frequency is designated as secret, and the pilot receives the task with the frequency channel number (001~xxx) and finds the frequency of the channel in the list of 4,000 frequency channels and inputs it manually. This reduces the safety and convenience of pilots' operations and exposes them to hazards that may occur especially during night flight missions. In this paper, we propose a function to embed the frequency corresponding to the frequency channel list in IMDC, the aircraft mission computer, and to automatically change the frequency when the pilot only inputs the channel number.

• 한국광학회지
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• 제34권6호
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• pp.225-234
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• 2023

모드 잠금 레이저는 주기성을 가지고 짧은 시간 동안 레이저 출력이 펄스로 동작한다. 그러나 시간-주파수 영역에서 모드 잠금된 펄스 레이저의 펄스 반복률의 주기성은 푸리에 변환으로 일정한 주파수 간격을 가진 광 주파수 빗과 같이 이해된다. 이때 광 주파수 빗의 각 주파수 성분은 연속적으로 발진하는 수십만 개의 단일 주파수 성분을 가진 continuous-wave 레이저들과 같다. 광 주파수 빗은 약 20년 전에 개발되어 세계에서 가장 정밀한 원자 시계의 개발을 가능케 하고 안정된 광 주파수를 정밀하게 전송하는 데에 사용되었으며, 다양한 응용연구로도 발전했다. 본 논문에서는 광 주파수 빗의 단일 주파수 구성 요소를 선택적으로 추출하고, 광 빗의 주파수 구성 요소를 제어하는 연구를 소개한다. 또한 광 주파수 빗의 개념과 원리를 해설함으로써 시간-주파수 도메인에서 빛의 특성을 이해하고, 광 주파수 빗을 활용한 다양한 응용 연구를 개발하는 데 도움을 주고자 한다.

• Journal of the Optical Society of Korea
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• 제7권3호
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• pp.131-134
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• 2003

We demonstrated an optical frequency synthesizer based on a femtosecond (fs) mode-locked Ti:sapphire (Ti:s) laser by simultaneously stabilizing the carrier-offset frequency, $f_{ceo}$, and repetition rate, $f_{ rep}$, referenced to the Cs atomic frequency standard. By using two wide-band digital phase-detectors we realized a phase-coherent link between $f_{rep} and f_{ceo} with the relation f_{ceo} = f_{AOM} 5/6f_{rep} ≡ 0, where f_{AOM} = 5/6f_{rep}$ is the phase-locked driving frequency of an acousto-optic modulator (AOM) in a self-referencing interferometer and $f_{rep}$ = 100 MHz. As a result, we could stabilize all components of the fs laser comb at once with an equal frequency separation $f_{rep}$ = 100 MHz with $f_{ceo}$ = 0. In our optical frequency synthesizer, the frequency of the nth component ($f_{n}$) is given exactly by the simple relation $f_n = nf_{rep}$, enabling us to use the fs laser comb as a frequency ruler in the optical frequency metrology.

• 대한음성학회지:말소리
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• 제62호
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• pp.51-68
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• 2007

Two experiments were conducted to determine the exact locus of the frequency effect in speech production. Experiment 1 addressed the question as to whether the word frequency effect arise from the stage of lemma selection. A picture-word interference task was performed to test the significance of interactions between the effects of target frequency, distractor frequency and semantic relatedness. There was a significant interaction between the distractor frequency and the semantic relatedness and between the target and the distractor frequency. Experiment 2 examined whether the word frequency effect is attributed to the lexeme level which represent phonological information of words. A methodological logic applied to Experiment 2 was the same as that of Experiment 1. There was no significant interaction between the distractor frequency and the phonological relatedness. These results demonstrate that word frequency has influence on the processes involved in selecting a correct lemma corresponding to an activated lexical concept in speech production.

• 전기학회논문지P
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• 제55권1호
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• pp.1-5
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• 2006

In this paper, the frequency estimator and DFT filter gain compensation for UFR(Under Frequency protection Relay) is introduced. Due to the sudden appearance of generator loads or faults in power system, the frequency is supposed to deviate from its nominal value. Because a frequency calculation is based on phase information, it needs sufficient sampling data to figure out a precious frequency. Therefore the frequency measurement for UFR needs excellent qualities such as high speed and precision with low sampling frequency Authors propose the frequency estimator which compares the vector differences and the DFT filter gain compensation which identifies DFT filter error and correct it. Using the frequency estimator and compensation, UFR which has the 0.01[ms] calculation delay and 0.003[Hz] measurement error is implemented with digital processor.

• 전기학회논문지
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• 제62권7호
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• pp.891-897
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• 2013

The power system frequency plays an important role in monitoring and controlling the power system. The frequency can be measured through discrete Fourier transform (DFT) coefficients of its positive fundamental frequency. The accuracy of the frequency estimate is severely affected by noise in the power system signal and the leakage effect of the negative fundamental frequency in DFT. This paper proposes a DFT-based frequency estimation algorithm to cope with the noise as well as the leakage effect. In this algorithm, two suitable digital filters are introduced to reduce efficiently frequency estimate error due to the noise. These filters are designed to use a digital bandpass filter and a second-degree integrator. The effectiveness of the proposed algorithm in reduction of frequency estimate error is verified through simulations on noise, harmonics and frequency deviation.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
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• pp.197-201
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• 2007

The reattachment characteristics of propane lifted flames in laminar coflow jets influenced by AC electric fields have been investigated experimentally in low AC frequency range. The reattachment velocity and height have been measured by varying the applied AC voltage and frequency. The results showed that the reattachment of lifted flame occurred at relatively higher jet velocity with AC electric fields, comparing to that without having AC electric fields. The effect of AC electric fields became more effective at higher voltage and lower frequency in the AC frequency range larger than 30 Hz. However, in the low frequency range below 30 Hz, the reattachment velocity decreased with decreasing frequency. Consequently, there existed a transition regime, for the frequency smaller than about 30 Hz. Also, when the AC voltage was applied to the fuel nozzle at very low frequency, the reattachment process exhibited an oscillatory behavior, synchronized with the applied AC frequency.