• 한국지역지리학회지
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• 제11권4호
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• pp.429-439
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• 2005

본 연구는 한국에 있어서 동계한발의 지역적 출현빈도 분포특성과 한발시 해면기압장 및 500hPa면의 종관기후학적 특성을 평년과 비교 분석한 연구이다. 한국의 동계한발의 출현빈도 분포는 월별 지역적 강수변동률의 분포를 반영하여 1 12월은 강수변동률이 높은 한국의 동부가 높고 강수변동률이 낮은 서부가 낮아서 동고 서저유형, 2월은 북고 남저유형을 나타내고 있다. 해면기압 및 500hPa면 고도편차 분포에서 1, 2월의 한발시 한반도 주변 및 시베리아 고기압 지역은 양의 편차, 알류샨 저기압 지역 및 북태평양 서안은 음의 편차를 나타내므로 서고 동저형의 기압배치가 탁월하여 남동쪽으로부터 온난습윤한 공기의 유입이 차단될 때 한발이 출현한다. 따라서 이 때 한반도 주변은 동서풍의 풍속은 강하다. 12월의 한발 시에는 한반도를 포함한 동아시아의 중위도 전역이 양의 편차를 나타내어 남쪽으로부터 온난습윤한 공기의 유입이 적을 뿐만 아니라 저기압 통과의 빈도가 적음을 반영하고 있다.

• 대한화학회지
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• 제61권3호
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• pp.104-111
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• 2017

이 연구에서는 스마트 기기를 활용한 소집단 과학 학습 과정에서 사전 성취 수준에 따른 언어적 상호작용을 분석하였다. 서울시의 한 남녀 공학 고등학교에서 사전 성취 수준 측면에서 이질적으로 구성된 4개의 소집단이 참여하였다. 스마트 기기를 활용한 소집단 과학 학습 과정에서 일어나는 언어적 상호작용을 녹음 및 녹화하고 기록 원고를 작성한 뒤 분석하였다. 학생들 사이의 언어적 상호작용은 개별 진술과 상호작용 단위 수준에서 분석하였다. 연구 결과, 스마트 기기를 활용한 소집단 학습에서 학생 사이의 언어적 상호작용은 과제 관련 진술의 빈도가 높았는데, 특히 정보 설명, 정보 질문, 기준 반성의 빈도가 높았다. 방향 설명, 기준 반성, 진행에서는 사전 성취 수준 상위 학생들의 진술 빈도가 높게 나타났고, 방향 질문, 정보 설명에서는 하위 수준 학생들의 진술 빈도가 높게 나타났다. 상호작용 단위에서는 지식 구성 상호작용 중 대칭적 정교화 상호작용의 빈도가 높았는데, 특히 누적형과 평가형이 높게 나타났다.

• Journal of Radiation Protection and Research
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• 제40권3호
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• pp.132-146
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• 2015

To develop tailored elementary, middle, and high school textbooks suitable for understanding the nuclear energy and radiation, quantitative and qualitative research was carried out in parallel, which included nine steps to ensure the validity of content and structure. The elementary, middle, and high school students wanted to acquire information used in their daily lives, including the definition of nuclear energy and radiation, principles and status of nuclear power generation, and information about irradiated food, medical radiation, and radiation in life. In the evaluation of the effects of textbook contents according to the educational requirements of each school level, high suitability frequencies (>80%) were shown for the human character, education goals, curriculum goals, evaluation method, and education time. At some levels, the high suitability frequencies (>70%) were shown for the education grade, education type, and textbook type.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1936-1941
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• 2003

Characteristics of the high frequency and pulsatile flow investigated experimentally to understand the flow phenomena in the hydraulic system. In the study, I axis fatigue tester which are widely used for automobile filed are selected. 4 Pressure transducer, amplifier, A/D convertor are used to analyse and to obtain the pulsatle pressure waveform with high frequencies in hydraulic system. Matlab are used. to analyse the characteristics of frequency. Variation of pump input pressure and actuator acceleration frequency, pressure wave are measured with or without accumulators. For with accumulator, frequency amplitude of pressure are very lower than those of without accumulator due to absorbing function of accumulator. As the actuator acceleration frequency increased, effect of accumulator are very important to decrease the pulsatile pressure waveform with high frequencies.

• 한국컴퓨터정보학회논문지
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• 제22권11호
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• pp.49-55
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• 2017

Recently, for safety of people, there are proposed so many technologies which detect density of people at the specific place or space. The representative technology for crowd density estimation was using image analysis method from CCTV images. However, this method had a weakness which could not be used and which's accuracy was lower at the dark or smog space. Therefore, in this paper, to solve this problem, we proposed a user density estimation system at closed space using high frequency and smart device. The system send inaudible high frequencies to smart devices and it count the smart devices which detect the high frequencies on the space. We tested real-time user density with the proposed system and ten smart devices to evaluate performance. According to the testing results, we confirmed that the proposed system's accuracy was 95% and it was very useful. Thus, because the proposed system could estimate about user density at specific space exactly, it could be useful technology for safety of people and measurement of space use state at indoor space.

• Structural Engineering and Mechanics
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• 제56권3호
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• pp.423-442
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• 2015

This study examines the wavelet transform for output-only system identification of ambient excited engineering structures with emphasis on its utilization for modal parameter estimation of high-order and closely-spaced modes. Sophisticated time-frequency resolution analysis has been carried out by employing the modified complex Morlet wavelet function for better adaption and flexibility of the time-frequency resolution to extract two closely-spaced frequencies. Furthermore, bandwidth refinement techniques such as a bandwidth resolution adaptation, a broadband filtering technique and a narrowband filtering one have been proposed in the study for the special treatments of high-order and closely-spaced modal parameter estimation. Ambient responses of a 5-story steel frame building have been used in the numerical example, using the proposed bandwidth refinement techniques, for estimating the modal parameters of the high-order and closely-spaced modes. The first five natural frequencies and damping ratios of the structure have been estimated; furthermore, the comparison among the various proposed bandwidth refinement techniques has also been examined.

• Advances in concrete construction
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• 제9권3호
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• pp.301-312
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• 2020

This research deals with the study of the orthotropic vibrational features of single-walled carbon nanotubes according to Kelvin's model and to check the accuracy of the models, the results have been compared with earlier modeling/simulations. Obtaining rough approximations of the natural frequencies of CNTs using continuum equations are still a common procedure, even at high harmonics. The effects of different physical and material parameters on the fundamental frequencies are investigated for zigzag and chiral single-walled carbon nanotubes invoking Kelvin's theory. By using nonlocal Kelvin's model, the fundamental natural frequency spectra for two forms of single-walled carbon nanotubes (SWCNTs) have been calculated. The influence of frequencies with nonlocal parameters and bending rigidity are investigated in detail for these tubes. Computer software MATLAB is utilized for the frequencies of SWCNTs and current results shows a good stability with comparison of other studies.

• 천문학회보
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• 제39권2호
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• pp.79.2-79.2
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• 2014

Galactic radio pulsar population is diverse. So far about 2300 radio pulsars are known in the Milky Way, in addition to Large and Small Magellanic Clouds. Radio pulsar observations at a few hundreds MHz up to ~10 GHz have been active and they are proved to be fruitful. Low frequencies are preferred mainly because of the steep ratio spectrum of pulsars. However, developments in pulsar backends (e.g. a wide-band spectrometer) and improved system sensitivities make it possible to observe pulsars at higher frequencies using large, single-dish telescopes up to ~18 GHz. Going forward, mm-wavelength observations is expected to open a new window in pulsar astronomy. In particular, frequencies well above ~15 GHz are pre-requisite to detect pulsars in the Galactic Center where radio pulsed signals are severely scattered by interactions with the interstellar medium. Recent discoveries strongly imply that there are subsets of pulsars with an apparently flat spectrum, such as magnetars. In April 2014, the first pulsar (magnetar) was discovered only 3 arcmin from Sgr A*, PSR J1745-2900. We will present a brief overview on pulsar populations focusing on those observable at high frequencies. We will also discuss prospects of pulsar observations in mm-wavelengths and how we can utilize the Korean VLBI network.

• 한국안전학회지
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• 제26권6호
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• pp.97-103
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• 2011

This study compared the effects of different frequencies of self-monitoring on safe sitting postures. Participants were four office workers. The dependent variable was the safety percentage for four body positions. The independent variable was self-monitoring frequency: high and low self-monitoring frequencies. Results showed that the safety percentage increased when self-monitoring was introduced. However, the effects of the two different self-monitoring frequencies on safe performance were not statistically different.

• Structural Engineering and Mechanics
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• 제36권6호
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• pp.679-695
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• 2010

In-plane vibrations of slightly curved beams having cracks are investigated numerically and experimentally. The curvature of the beam is circular and stays in the plane of vibration. Specimens made of steel with different lengths but with the same radius of curvature are used in the experiments. Cracks are opened using a hand saw having 0.4 mm thickness. Natural frequencies depending on location and depth of the cracks are determined using a Bruel & Kjaer 4366 type accelerometer. Then the beam is assumed as a Rayleigh type slightly curved beam in finite element method (FEM) including bending, extension and rotary inertia. A flexural rigidity equation given in literature for straight beams having a crack is used in the analysis. Frequencies are obtained numerically for different crack locations and depths. Experimental results are presented and compared with the numerical solutions. The natural frequencies are affected too much due to larger moments when the crack is around nodes. The effect can be neglected when it is at the location of maximum displacements. When the crack is close to the clamped end, the decrease in the frequencies in all modes is very high. The consistency of the results and validity of the equations are discussed.