• Earthquakes and Structures
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• 제12권1호
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• pp.91-108
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• 2017

Superstructures and isolation systems of seismically isolated buildings located close to active faults may observe increased seismic demands resulting from long-period and high-amplitude velocity and displacement pulses existent in near-fault ground motions as their fundamental periods may be close to or coincident with these near-fault pulse periods. In order to take these effects into account, the 1997 Uniform Building Code (UBC97) has specified near-source factors that scale up the design spectrum depending on the closest distance to the fault, the soil type at the site, and the properties of the seismic source. Although UBC97 has been superseded by the 2015 International Building Code in the U.S.A., UBC97 near-source factors are still frequently referred in the design of seismically isolated buildings around the world. Therefore it is deemed necessary and thus set as the aim of this study to assess the necessity and the adequacy of near-source factors for seismically isolated buildings. Benchmark buildings of different heights with isolation systems of different properties are used in comparing seismic responses obtained via time history analyses using a large number of historical earthquakes with those obtained from spectral analyses using the amplified spectrums established through UBC97 near-source factors. Results show that near-source factors are necessary but inadequate for superstructure responses and somewhat unconservative for base displacement response.

• 한국음향학회지
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• 제19권2호
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• pp.54-60
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• 2000

어레이를 이용한 음원 탐지는 음원의 모델을 가정하고 있다. 원거리 음원의 경우에는 평면파 모델을 적용하여 널리 적용되고 있으나, 근거리 음원의 경우에는 단극 음원을 가정한 음원 탐지법이 시도되고 있는 상황이다. 이 논문에서는 보다 효과적인 근거리 음원 추정을 위해 쌍극 음원 모델과, 삼극 음원 모델을 유도하여 MUSIC 방법에 적용할 수 있는 주사벡터(scan vector)를 제안하였다. 제안된 삼극 음원 모델의 경우, 실제 음원이 순수 쌍극 음원인 경우에 음원 탐지 성능이 다소 떨어지나, 단극 및 사극 음원이거나, 이들의 조합에 의한 음원이거나에 관계 없이 적용 가능함을 알 수 있었다. 따라서 일반적인 음원 탐지에 활용할 수 있는 효과적인 음원 모델임을 알 수 있었다.

• 대한조선학회논문집
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• 제46권2호
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• pp.105-113
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• 2009

A theoretical study on the pressure fluctuation induced by a propeller was carried out in this study. The main objective of this study is to analyze the source mechanism of the pressure fluctuation induced by propeller sheet cavitation. To analyze the pressure fluctuation induced by propeller sheet cavitation, modern acoustic theory was applied. Governing equation of pressure fluctuation induced by sheet cavitation was derived using Ffowcs Williams proposed time domain acoustic approaches. Several factors affecting pressure fluctuation were analyzed based on the derived governing equation. Pressure fluctuation result was represented by combined results of the far field term and near field term. Finally, the physical mechanism of pressure fluctuation at the blade rate frequency was analyzed using numerically generated cavitation volume variation.

• 천문학회보
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• 제46권1호
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• pp.44.2-45
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• 2021

As implied by the zodiacal light and spacecraft impact measurements, the space between large bodies in our Solar System is filled with interplanetary dust particles (IDPs). IDPs give us deeper insight into the composition and evolution of the Solar System, as well as being a crucial reference for extrasolar research. IDPs can be interpreted as bearers of carbon and organic materials, and thus, their interaction with Earth can be considered as important factors for the birth of terrestrial life. One of the key routes of IDPs entering Earth is via meteoroid streams (Love and Brownlee 1993). The Geminid meteoroid stream is a notable example. Together with its source asteroid (3200) Phaethon, the Phaethon-Geminid stream complex (PGC) (Whipple 1983; Gustafson 1989) can potentially provide information on the properties and evolution of IDPs in near-Earth space. DESTINY+* is a JAXA/ISAS spacecraft planned to launch in 2024 to explore the physical and chemical features of near-Earth IDPs and uncover the dust ejection mechanism of active near-Earth asteroids, especially Phaethon (Arai et al. 2018). Previous studies on the dust ejection mechanism of Phaethon have various degrees of success in explaining the ejection of submillimeter particles and try to recreate the dust replenishment rate of the Geminid stream. However, none of them are satisfactory for explaining the observed Geminid stream, especially for larger particles of a millimeter and centimeter scales. Inspired by the discovery of rotational mass shedding in the Main Belt region (Jewitt et al., 2014), we investigate a dust ejection scenario by rotational instability on Phaethon. Using the N-body integrator MERCURY6 (Chambers 1999; modified by Jeong 2014), we performed a long-term integration of dust particles of various sizes ejected at ~1 m/s. Through this process, we discuss the implications Phaethon's rotation may have on its ejection, the formation and evolution of IDP by this mechanism, and contribute to the DESTINY+ mission.

• 소음진동
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• 제6권6호
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• pp.843-849
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• 1996

Locations and emission characteristics of noise source of motor vehicles are great important factors to control the road traffic noise in effective ways. From results of this study on emission characteristics of engine and exhaust noise, we could find that every noise emission of different kind of vehicles has smilar pattern. The main emission locations of engine noise for the front of vehicle became the space between the road surface and bottom of the body and radiator grill, and for the side of vehicle became the space between the road surface and bottom nearby the front wheel. In case of exhaust noise of passenger-car and light truck, all the highest sound intensity level located near surface of road. But it is hard to conclude the height of noise source of driving vehicles with only results of this study. So further studies are needed to check the emission characteristics of noise.

• 보건행정학회지
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• 제9권3호
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• pp.21-32
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• 1999

The purpose of this study is to assess individual decisive factors for distribution of medical specialists in Korea. A data set was constructed using several published data sources. including the Korean Medical Association's physician master file as a principal source for physician information. Linear logistic regression analysis was performed to assess the relationship between the location of private specialist clinic for practice with six variables related with individual characteristics: age. sex. location of postgraduate training hospital. location of medical school graduated, size of hospital for training, and specialty. Analysis showed that location of practice. classified into urban and rural areas, was significantly associated with the variables of sex. location of postgraduate training hospital. location of medical school. In addition, significant association was found between the location of practice which was categorized into "near-Seoul area" and others, and sex, location of postgraduate training hospital. and location of medical school. We could conclude that to improve area maldistribution of physicians locations of hospitals for training and medical schools have to have the highest priority in the policymaking.icymaking.

• 미생물학회지
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• 제13권1호
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• pp.1-23
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• 1975

This experiment was designed to elucidate the environmental factors in rhizosphers of bamboo forest that affect the distribution and the population size of Azotobacter, and also to estimate the annual productivities of nitrogen fixed by Azotobacter species. The results of this experiment can be summarized as follows ; The rhizosphere of bamboo forest contained high free sugars as of 3-8 times more than non-rhizosphere (Bacon, 1968), and the contents of organic matter and amino acids of that are reltively higher than this. Because of high content of potassium, average of soil pH is near at 7.0. As above-mentioned enviromental factors, the population sizes of Actinomycetes, general fungi, general bacteria and Azotobacters are larger than those of non-rhizosphere and the ofllowings are general fungi and general bacteria by turns. Azotobacter is dependent upon the antagonistic Actinomycetes. The main carbon source for Azotobacter in nitrogn flxation at the rhizosphere was glucose and minors were fructose, maltose and sucrose by turns. Annual gains of nitrogen by Azotobacters in soil of bamboo forest within 10cm from surface are estimated as of 88.94 kg/ha at site A, 60.4kg/ha at site B and 67.38kg/ha at site C, respectively.

• Journal of Radiation Protection and Research
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• 제22권4호
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• pp.299-307
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• 1997

점선원 주위에 형성되는 방사상의 감마선장에서 개인선량당량 $H_p$, 유효선량 E, 성별 유효선량 $E^m$과 $E^f$를 MIRD형 남녀 모의 피폭체를 이용하여 평가하였다. 선원은 신체의 전방 각각 15, 40 및 100 cm 거리의 여러 높이에 있는 것으로 하였고 방사성 핵종으로는 시범적으로 $^{137}Cs$과 $^{131}I$을 선정하였다. 성별 유효선량에서는 일부 예외적인 경우-예를 들면 선원이 생식선 앞에 위치할 때-를 제외하고는 대체로 여성의 경우가 크게 나타났으나, 남녀 평균값과의 차이는 크지않아 방사상 감마선장에서 성별 유효선량환산인자를 사용할 필요성은 없었다. 선량계를 가슴에서 하복부까지의 몸통 전방에 착용할 경우에는 $H_p$/E의 비가 약$1{\sim}3$의 범위에 있었고 극단적인 경우는 0.34에서 6.5까지 큰 편차를 보였다. 그러나 일반적인 방사선원 취급방법과 선량계 착용위치(흉곽 전방)를 가정하고, 선량계가 넓고 평행한 방사선장에서 유효선량에 대해 교정된다면 평행하지는 않지만 넓은 빔인 방사상 감마선장에 대해서는 용인할 수 있는 오차의 범위에서 유효선량 평가치를 제공할 수 있을 것으로 나타났다.

• Radiation Oncology Journal
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• 제9권2호
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• pp.333-336
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• 1991

충남대학교병원 치료방사선과내 설치되어 있는 6MV선형가속기를 이용하여 음영을 측정하여 다음과 같은 결과를 얻었다. 1) 조사면 크기가 커질수록 음영폭은 중가하였으며 10x10 Cm 이상의 조사면에서는 계산한 음영폭보다 측정치가 대개 크게 나타났다. 조사면이 커질수록 이 차이는 더욱 증가하였다. 2) 깊이가 증가하면 음영폭도 증가하였다. 3) $90\%\~20\%$의 음영폭이 $80\%\~20\%$의 음영폭보다 컸으며 조사면이 커지고, 깊이가 증가할 수록 이 차이는 더 커졌다.

• 대한교통학회지
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• 제30권2호
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• pp.79-89
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• 2012

도시고속도로 주변 지역에 인접한 주거지역의 도로교통소음은 매우 심각한 실정이다. 도시고속도로 주변의 주거지역은 90년대 들어 크게 증가하였으나 많은 교통량과 높은 속도로 인해 거주민들의 삶의 질은 계속 저하되고 있다. 본 연구에서는 이러한 도시고속도로 주변의 주거지역에 대해 교통조건을 고려한 소음도에 영향을 미치는 인자(교통량, 속도, 수음점에서의 거리 등)에 대해 고찰하였다. 소음도에 대한 교통량과 속도와의 관계를 고찰해보기 위해 이 식에서 주요 요인으로 사용한 교통량과 속도의 두 요인 중에서 무엇이 더 큰 영향을 가지는지를 상관관계 분석과 회귀분석을 통해 교통량이 속도보다 더 밀접한 관계가 있음을 알 수 있었다. 따라서, 도시고속도로 구간에서 도로교통소음을 저감하기 위해서는 차량의 속도도 중요하지만 근본적으로 교통량을 저감하기 위한 대책이 더 중요하다고 볼 수 있다.