• 한국환경보건학회지
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• 제26권2호
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• pp.108-115
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• 2000

The mass fraction of PM10 had a bimodal distribution in the middle of between 2.1 ${\mu}{\textrm}{m}$, and the average mass fraction of particles less than 2.1~3.1 ${\mu}{\textrm}{m}$ was 54.1% for Pb and 890.8 ng/㎥ for Fe, respectively. For the concentration of PM10 and metallic elements by seasonal variation, PM10 showed bimodal distribution, while metallic elements showed different distributions by their sources. The ratios of fine particles to total mass were 0.45 for PM10, 0.41 for Cr, and 0.20 for Fe, 0.57 for Zn, 0.68 for Cd and 0.63 for Pb, respectively. That facts indicated that PM10, Zn, Cd, Cr and Pb were from anthropogenic sources, and Fe was from natural source. The geometric means and geometric standard deviations by seasonal variations were 3.6 ${\mu}{\textrm}{m}$ , 2.31 ${\mu}{\textrm}{m}$ in winter, 3.0 ${\mu}{\textrm}{m}$ , 2.49 ${\mu}{\textrm}{m}$ in spring, 2.7 ${\mu}{\textrm}{m}$ , 2.03 ${\mu}{\textrm}{m}$ in summer respectively. And, total efficiency of cascade impactor by seasonal variations were 49.6% in winter, 45.9% in spring and 44.5% in summer.

• 한국대기환경학회지
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• 제24권5호
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• pp.584-593
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• 2008

The surface $O_3,\;CO,\;NO_x,\;and\;SO_2$ were measured at Gosan in Jeju Island from May 2004 to April 2005. Over this period, the mean concentrations $({\pm}s.d.)$ of each gas was 40.06 $({\pm}16.01)$ ppbv for $O_3,\;264.92({\pm}115.73)ppbv\;for\;CO,\;1.98({\pm}2.73)ppbv\;for\;SO)_2,\;and\;4.64 ({\pm}3.24) ppbv\;for\;NO_x$. The monthly variations and the diurnal variations of these gases show that the Gosan site is situated in a relatively clean region. However, there were episodic simultaneous peaks in CO and $SO_2$, especially in winter and early spring. Using cluster analysis with air mass back- ward trajectory analysis, we suggest that these episodes are due to the influence of transportation of polluted air mass from polluted regions. In the cluster, which was under the dominant influence of clean maritime air mass, low levels of $O_3,\;CO,\;and\;SO_2$ were observed. The levels of these species were elevated in the other two clusters which had the air mass influenced by polluted continental regions. In addition, ratios of the chemical species such as $CO/NO_x,\;SO_2/NO_x,\;and\;CO/SO_2$ revealed the somewhat different characteristics of emission sources influencing each cluster. The differences in concentration of trace gases among clusters with different origin and transport pathways imply that Gosan is under the effect of pollution transported from other regions.

• 에너지공학
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• 제22권2호
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• pp.197-204
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• 2013

A cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under idling conditions. The coefficient of variation (COV) in indicated mean effective pressure (IMEP) defines the cyclic variability in indicated work per cycle, and it has been found that vehicle drivability problems usually result. For analysis of the cyclic variations in spark ignition engines at idling, the results show that cyclic variability by the COV, COV of IMEP, the lowest normalized value (LNV), and burn angles can help to design the spark ignition engine.

• 대한영양사협회학술지
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• 제7권2호
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• pp.153-158
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• 2001

This study examined the age-related patterns in body composition cross-sectionally using Segmental bioelectrical impedance analysis(SBIA), specifically its two components, lean body mass(LBM) and body fat mass, in 1,452 men and 1,436 women with an age range of 19 to over 70 years . Mean height of male subjects was 174.1cm at peak in early 20's and was decreased continuously 0.2-0.3 cm every year. Mean weight was greatest between late 20's and 40's, and was decreased quickly in 70's. Body fat mass was increased steadily before 30's and remained thereafter. Because decreasing lean body mass (LBM), percentage of body fat(PBF) increased continuously with aging. Mean height of female subjects was 161.7 cm at peak in 20's and was decreased steadily around 0.2 cm every year and thus an individual's height was decreased approximately 10 cm in their life cycle. Body weight was increased steadily until 50's and then was decreased. Body fat mass was increased continuously and LBM remained constant and thus PBF was increased steadily with aging. SBIA can be used to compare body composition between genders and between ages. In future studies, SBIA could be applied widely to evaluate variations of body composition in subjects with different nutritional problems.

• 천문학회지
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• 제22권2호
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• pp.113-126
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• 1989

The initial mass functions (IMF) of 15 selected open clusters are investigated by making use of C-M diagrams and theoretical evolutionary tracks. Among 15 clusters 13 have peaks in their IMFs and it is thought to be not due to incomplete photometry but to intrinsic property. The mass where IMF peaks is about $2\;M_{\odot}$ and it is similar to that of the second peak in the IMF of nearby field stars. The mean slope of the IMF in the high mass part is $1.9{\pm}0.6$ with some variations among clusters. But there seems to be no correlation between the slope and physical parameters such as ages, diameters, and metal abundances.

• 한국해양학회지:바다
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• 제8권2호
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• pp.59-69
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• 2003

제주도 남부해역의 미세생물 먹이망 구조에 관한 연구의 일환으로써 부유성 유종섬모충(tintinnids)과 빈섬모충(aloricate oligotrichs)의 종 조성과 생물량의 계절 변화 특성에 대하여 중문주변해역의 6개 정점에서 1998년 7월부터 2000년 6월까지 매월 조사를 실시하였다. 조사기간 동안 출현한 유종섬모충은 총 39종으로 세포수 범위는 100~5,400 cells. 1$^{-1}$(평균 314 cells . 1$^{-1}$) 이었고 가을철과 겨울철에는 외양성 종류가 주로 우점하였으며 봄철과 여름철은 외양성 보다 연안성 종류가 우세하였다. 빈섬모충은 총 15종이 동정되었고 세포수 범위는 140~21,000 cells.1$^{-1}$(평균 2,356 cells.1$^{-1}$)로써 Strombidium속의 종들이 전 계절에 걸쳐 우점하였다. 계절에 따른 종 다양성과 생물량 변화는 유종섬모충의 경우 차이가 컸지만 빈섬모충은 큰 차이가 없었다. 유종섬모충의 계절별 수괴지표 특성은 연구 해역의 해양환경변화에 따라 영향을 받고 있었으나 빈섬모충은 특이한 수괴지표 특성을 보이지 않았다. 해역별로 보면 외해역 보다는 해안역에서 세포수가 높았고 종 다양성도 높았다 섬모충의 총 탄소량의 범위는 0.01~136.06 $\mu\textrm{g}$C.1$^{-1}$(평균 5.01 $\mu\textrm{g}$C.1$^{-1}$)로 탄소량과 세포수의 월별 변동이 반드시 일치하지는 않았다. 유종섬모충과 빈섬모충의 수심별세포수 분포는 모두 20 m층에서 가장 높았고 수직분포의 경향도 비슷하였으며, 엽록소 a 량의 수직분포와도 일치하고 있어 식물플랑크톤과 섬모충은 피식과 포식의 상관성을 보이고 있었다.

• 천문학회보
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• 제40권1호
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• pp.66.1-66.1
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• 2015

We present the first observational detection of radial and azimuthal oscillations in full halo coronal mass ejections (HCMEs). We analyze nine HCMEs well-observed by LASCO from Feb 2011 to Jun 2011. Using the LASCO C3 running difference images, we estimated the instantaneous apparent speeds of the HCMEs in different radial directions from the solar disk center. We find that the development of all these HCMEs is accompanied with quasi-periodic variations of the instantaneous radial velocity with the periods ranging from 24 to 48 mins. The amplitudes of the instant speed variations reach about a half of the projected speeds. The amplitudes are found to anti-correlate with the periods and correlate with the HCME speed, indicating the nonlinear nature of the process. The oscillations have a clear azimuthal structure in the heliocentric polar coordinate system. The oscillations in seven events are found to be associated with distinct azimuthal wave modes with the azimuthal wave number m=1 for six events and m=2 for one event. The polarization of the oscillations in these seven HCMEs is broadly consistent with those of their position angles with the mean difference of $42.5^{\circ}$. The oscillations may be connected with natural oscillations of the plasmoids around a dynamical equilibrium, or self-oscillatory processes, e.g. the periodic shedding of Alfvenic vortices. Our results indicate the need for advanced theory of oscillatory processes in CMEs.

• 대한기계학회논문집B
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• 제21권12호
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• pp.1701-1709
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• 1997

The diagnostic used to observe the early flame development was a fiber optic spark plug, which enabled measurement of the flame front arrival times on a cycle-to-cycle basis. The data obtained with this fiber optic spark plug were analyzed to obtain two parameters to describe the behavior of the flame kernel : an expansion speed and a convection velocity. In addition, synchronized cylinder pressure data were taken to compare with the fiber optic spark plug data on a cyclic basis. Heat release analysis was performed on the cylinder pressure data to obtain the mass burning profile of the charge for each cycle. There was a significant correlation observed in the initial flame duration and the kernel expansion speed with dwell angle.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.90-96
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• 2003

Numerical analyses have been performed to obtain the absorption heat and mass transfer coefficients and the absorption mass flux from a falling film of LiBr solution. In the present study, the behavior of laminar-wavy falling film in the vertical absorber was studied analytically and experimentally. The change of absorption performance on mean film thickness, wave amplitude, wave celerity was analysed. The heat and mass transfer equations are solved simultaneously to give the temperature and concentration variations at the LiBr solution/refrigeration vapor interface and at the wall. Effects of uniform film, wavy film and film Reynolds number on the heat and mass transfer coefficients have been estimated. The analytical results of the uniform and wavy falling film in the bare tube was higher than experimental result for $Rd_{t}<100$. The absorption performance showed the maximum at the wavy film by the insert device(spring).

• 한국공간구조학회논문집
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• 제18권1호
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• pp.77-84
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• 2018

The identification of damping ratios in buildings is a well-known problem and appears to be of important and crucial interest in the safety and serviceability design. When compared to an estimation of the stiffness, i.e. natural frequency, and mass, the damping ratio is the most difficult quantity to determine. Many previous studies have examined the characteristics of damping ratios from ambient vibration, but the measurement time is roughly within 2 hours. In this paper, characteristics of damping ratios and natural frequencies of 4 story RC building were investigated using long-term ambient vibration. Free vibrations were obtained using random decrement technique, and damping ratios were evaluated by the envelop function, continuous wavelet transform, and logarithmic decrement. It was found that although the natural frequencies show little variations with time, the damping ratios show some variations with time and the largest variations found in the damping ratios obtained from the continuous wavelet transform. The damping ratios from the envelop function showed the smallest mean and standard deviation. And the probability distribution of damping ratios seems to follow the logarithmic normal distribution.