• Journal of Korean Association for Spatial Structures
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• v.7 no.5
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• pp.75-82
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• 2007

The present work measured and analyzed changes in the acoustics of a sound field which has a retractable ceiling. An 1/20 scale model of an openable space was built and measurement was carried out by varying the opened area of a ceiling. The most widely used room acoustic and design parameters, RT, EDT, and D50 were investigated. The results suggest that the use of RT as an acoustic design parameter may not be proper in an openable space and further it is likely to mislead the initial acoustic design of such spaces. It is mainly due to the characteristics of RT in which non-exponential decay processes are linearly fitted. Early decay times were found to be decreased in proportion to increaing the ratio of opened area. D50, an index of speech intelligibility, was effectively shows the influence of openings on the acoustics. It is also found that EDT and D50 at the seats, not directly exposed to the opened part of a ceiling, were almost linearly decreased in proportion to the ratio of opened area, while little influence was found for the opening ratio larger than 40% at the directly exposed seats to the opened part of a ceiling.

• The Journal of the Acoustical Society of Korea
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• v.35 no.2
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• pp.92-101
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• 2016

There are many results in which acoustical conditions of a classroom play an important role for studying effects and academic achievement of students. However, there are very few guidelines or design proposals which could make appropriate acoustic environment when classrooms are built or renovated. The present study suggests various design proposals satisfying acoustic standards of classrooms based on theoretical calculation and acoustic field experiments. At first, minimum area of sound absorption was calculated which is required to satisfy the acoustic standard for domestic middle and high schools. Also, room acoustic measurements were carried out in order to investigate the acoustic performance of an existing classroom by changing interior finishing materials on ceiling and rear walls. As a result, it was revealed that reverberation time standard below 0.8 s can be acquired even if there is no sound absorption on ceiling which is a general practice executed in Korea. Specially, it was found that if partial area of ceiling would be treated as reflective with the ratio of sound absorption and reflection as 2:1, almost similar acoustic parameters of $C_{50}$, $D_{50}$, RASTI (Rapid Speech Transmission Index) and higher sound levels could be acquired in comparison with the case of entire sound absorption on ceiling.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.22 no.1
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• pp.42-51
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• 2012

Objectives: To compare the exposure level of extremely low frequency (ELF) magnetic fields among semiconductor workers, shipyard welders and office workers. Methods: To measure the ELF magnetic field concentration, EMDEX LITE (Enertech, USA) were used and monitored for eight hours continuously. Five companies handling the electric and magnetic field (EMF) source were investigated, which the exposure groups were classified into three groups: semiconductor workers, welders, and office workers. Welder group was chosen as a high exposed group and office group as a low exposed group. Results: The arithmetic mean (${\pm}SD$) and geometric mean (GSD) of personal exposure level of semiconductor workers were 0.73 (${\pm}1.33$) ${\mu}T$, 0.43 (2.88) ${\mu}T$, respectively. The ceiling value ranged between 0.18 and 123.2 ${\mu}T$. Welders were exposed high with the arithmetic mean value of 3.46 (${\pm}\;13.46$) ${\mu}T$ and geometric mean value of 0.45 (4.70) ${\mu}T$, respectively, and ceiling value range of 75.5~129.6 ${\mu}T$. The exposure levels of office workers were low compared to other exposed groups; the arithmetic mean 0.05 (${\pm}0.13$) ${\mu}T$, geometric mean 0.03 (2.38) ${\mu}T$ and ceiling value range 0.37~3.35 ${\mu}T$. This study revealed statistically significant differences of the mean ELF magnetic field exposure doses among three groups (p < 0.01). Conclusions: The average ELF magnetic field exposure doses of semiconductor workers were much higher than those of office workers in control group, but were lower than those of welders in high exposure group.

• Korean Journal of Heritage: History & Science
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• v.47 no.2
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• pp.68-84
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• 2014

The royal tombs of Baekje(백제), after the transfer of the capital to the Geumgang(riv)(금강) basin, changed to Songsanri(송산리) style(stone chamber) ${\rightarrow}$ Southern dynastic(남조) style(brick chamber) ${\rightarrow}$ Neungsanri(능산리) style(stone chamber). The most special feature of this process is the change of the ceiling structure. The ceiling had been changed from dome(Songsanri style) ${\rightarrow}$ tunnel ceiling(transition period of brick tombs and Neungsanri style) ${\rightarrow}$ a roof style(is Neungsanri style of three imitate type, trapezoid, triangle, flattened ceiling). The most special feature among this process is Neungsanri style(stone chamber), created especially in Baekje. The royal tombs of Baekje didn't lay stress on the mound, so the mound is not noticeable. It is result that they more stressed on basin of the boundary than showed off individual tomb, and this is count as an element of China Southern dynasty. Boundary of the royal tomb of Baekje, after the transfer of the capital to south, were changed from royal family's boundary to single independent's. Those are Songsanri's and Neungsanri's, these are the pair tombs(쌍릉) of Iksan(익산). That is influence of the Southern dynasty, reflect the theory of divination based on topography completely, this is influence of the China Sui(수) and the early Tang(당) dynasty's system of boundary of the royal tomb. Besides the royal tomb, they also buried a closely related person, in the boundary of the royal tomb. And facilities for memorial ceremony were existed too. An altar was equipped in Songsanri's boundary of the royal tomb, it was seen a kind of character of a sanctuary for progenitor. Neungsanri's boundary of the royal tomb were equipped with an open-aired altar that performed memorial ceremony about communal royal tombs, and also equipped a temple, was needed to pray for the happiness of the dead. This structure and arrangement are very similar to Seoakdong(서악동) of Silla(신라).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.325-326
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• 2008

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.722-723
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• 2008

• Proceedings of the SAREK Conference
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• 2006.11a
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• pp.64-64
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• 2006

• Fire Protection Technology
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• s.16
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• pp.13-19
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• 1994

An Experimental study on the relation between responsiveness and elapse of years This experiment study is to appraise a fire detector's durability & reliability. Fire detector is located in office, temp range 10-27 고 65 15%, installed in the ceiling with power on. This is the experiment report of elapsed 5 years.

• Proceedings of the Korean Fiber Society Conference
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• 1998.04a
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• pp.285-290
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• 1998

The purpose of this study is the design of the climate chamber. Experiments was performed in a climate chamber that was running Under Floor Air-Conditioning System(UFAC). The chamber has a diffuser in the middle of the floor, and exhausts on the ceiling, simulating underfloor air conditioning system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.275-276
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• 2009