• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.888-892
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• 2014

This paper evaluates $C_{50}$ in elementary school classrooms and considers utilization of $C_{50}$ as an assessment indicator of acoustic performance. $C_{50}$ is early-to-late arriving sound ratio, recent study reported that $C_{50}$ is more appropriate as a measure of clarity and speech intelligibility than D50 because it is linearly related to subjective responses. The average of $C_{50}$ in elementary school classrooms appeared to be about +2 dB ~ +3 dB throughout 500 Hz ~ 4 kHz. However, absolute evaluation is difficult because there is no suitable reference or standard yet. As deviation of $C_{50}$ according to location is larger than reverberation time, it is expected that $C_{50}$ will be more sensitive when someone assesses acoustic performance of classrooms. Correlation between $C_{50}$ and reverberation time is very high. From logarithmic regression equation, we can estimate appropriate range of $C_{50}$ in elementary school classrooms indirectly, using standard of reverberation time in ANSI.

• The Journal of the Korean dental association
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• v.50 no.7
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• pp.394-406
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• 2012

Objective: The adhesion capabilities of different types of self-ligating brackets were measured with respect to Streptococcus mutans and Streptococcus sobrinus. Methods: Five types of self-ligating brackets (Clippy-C; Mini Clippy; Clarity-SL; Speed; Damon 3) were used for the experiment group and composite resin brackets (Spirit-MB), metal brackets (Victory) and polycrystalline alumina brackets (Clarity) were used for the control group. In order to assess adhesion of bacteria to the brackets, the brackets were cultured for 3, 6 and 24 hours in media containing bacteria and 20% sucrose. Results: There was no statistic difference in adhesion amount of Streptococcus mutans and Streptococcus sobrinus according to the types of brackets. A total adhesion amount according to bracket type was different. An extended incubation time increased adhesion amount. Observation under scanning electron microscope showed that Streptococcus sobrinus adhered more to Clippy-C and Victory rather than to Clarity-SL. Conclusions: Clarity-SL, a self-ligating esthetic bracket was confirmed to show lower bacterial adhesion to cariogenic bacteria, Streptococcus mutans and Streptococcus sobrinus group than other self-ligating brackets or conventional brackets, which suggests that proper use of self-ligating esthetic brackets might even be better in preventing tooth surface decalcification.

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.558-567
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• 2019

When used for broadcasting, multipurpose halls need to accommodate various types of programs such as speeches, Korean traditional music, musicals, pop music, and concerts. Therefore, multipurpose halls must meet a wide range of electric and architectural acoustic demands. However, there are few ways to alter acoustic environments for multipurpose halls, given these different demands. The current study investigates the effects of banners on acoustic environments in the presence of an acoustic shell or electric acoustic system. The results indicate that the installation of a 15% banner of wall area could vary the range of reverberation time ($T_{30}$) by 0.12 s, EDT (Early Decay Time) by 0.15 s, clarity of music ($C_{80}$) by 0.76 dB, and clarity of speech ($D_{50}$) by 6.43 % under different measurement circumstances. A computer simulation that enlarges the banner size to 40 % of the wall area varies the reverberation time from 0.11 s to 0.55 s depending on the room environment.

• The Journal of the Acoustical Society of Korea
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• v.34 no.2
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• pp.146-156
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• 2015

This study investigated how the location of sound absorptive materials and sound diffusers affects the acoustic performance of small auditoriums. It was conducted for a standard model established with the averaged dimension of 36 auditoriums which had opened since 2000 in Daehak-ro, Seoul. In this study, the installation area of finishing materials was calculated upon a back wall which had the smallest installation effective area of finishing materials. To analyze the changes of acoustic performance according to installation location of finishing materials, experiments were carried out using the 1/10 down scale models for 8 cases which were made by classifying the installation location of ceiling and side wall into the front, middle and rear part.The used acoustic parameters were reverberation time (RT), early decay time (EDT), clarity (C80), definition (D50) and speech transmission index (STI). In result, the index related to the amount of reverberant sound (RT, EDT) showed the great changes when evaluating it through just noticeable difference (JND), but the one related to clarity (C80, D50, STI) hardly indicated the changes. In case to obtain short reverberation time, it was most effective to control reverberation time through the side walls when installing sound absorptive and diffusive materials, and side wall front was the location which could get the shortest reverberation time.

• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.363-368
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• 2018

Recently a slat type ceiling is widely used in various spaces, such as music performance spaces and concourse of airport and a general reception area of a building. However, it is hard to find a proper design guideline or material useful in designing such spaces, due to the lack of relevant researches on the effect of a slat ceiling on room acoustics. The present work investigated the effect of a slat type ceiling using a physical scale model method. A 1/20 scale model of a small shoe-box type music performance hall was built and a slat ceiling with different configurations was installed. 6 cases of different ceiling configurations were considered with the combination of 2 slat ceiling height cases and 3 distance cases between slats. The effect of a slat ceiling on the acoustics of a room was evaluated by measuring reverberance($T_{30}$), intelligibility and clarity($D_{50}$ and $C_{80}$), and loudness(G and $G_{80}$).

• Journal of Distribution Science
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• v.14 no.4
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• pp.103-110
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• 2016

Purpose - This study investigates the improvement of rationalization of distribution structure in Korean diamond market. It also explores the international distribution of diamond and how the distribution of Korean diamond market system was improved. This study also for providing the evaluation method in case of purchasing diamond on the consumers. Research Design, Data, and Methodology - The research investigates how international diamond distribution market has been changed since 1933 by De Beers. The international Diamond rough stone has been deregulated in supply and demand by Debeers since July, 2000, therefore, the price maintenance policy of diamond market also has been changed. In the short term, the diamond price in market has been down, whereas, in the long term, the market share of Debeers has affected the high quality of diamond price in world market. Before 1985, both G color and VVS1 clarity were used as the level of percentages in the diamond certificate of authenticity in Korea. But, after 1985, the diamond certificate of authenticity uses Diamond Grading Report. Results - Between the 1970's and 1980's, Debeers had controlled about 80 percentages of international diamond supply market. But, Debeers share in diamond market fell by 60 percentages in 2000's. Debeers supplied 31%(4390 carets) of international diamond supply and 41%(39 billion dollars) in 2003. However, Debeers shares 50% of market shares in the diamond supply market by Alosa in Russia. In Korea, the diamond grading report system has been used since 1985. But, the diamond grading report system has price bubbles and much irrational parts in grading system methods. Conclusions - 4C, the grading system of diamond, is a method for comparing and evaluating diamond objectively. Diamond is graded according to its color, cut, clarity, and carat. The price of diamond is determined based on its each item. Consumers purchase diamond for the purpose of investment and wearing. In terms of investment, it is recommended to purchase diamond with color of D grade, cut with Excellent or Very Good Cut grade, Clarity of FL or IF, and more than 3 carat. As for wearing purpose, it is highly recommended for diamond to have color of F or G grade, cut of Excellent or Very Good Cut, clarity of VS2 or SI1, and more than 1 carat Before 2000, Central Selling Organization(CSO) distributed about 80 percentages rough diamond to world market exclusively by purchase, classification, assessment, and sales. After 2000, Dbeers diamond company looses slowly market shares, while Almosa diamond company etc. in Russia are taking over world market shares more and more. Debeers market shares have been falling over the years, and the international diamond markets are gradually growing by other international diamond companies. But, there is no change in Korean diamond market after 1980's. Korean diamond distribution needs to follow international level of Diamond Grading System. By using different grading systems with different panel members, Korean diamond grading system needs to follow international perfect grading systems to grow diamond markets and maintain within top 10 diamond markets countries.

• Journal of the Korean Institute of Educational Facilities
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• v.18 no.5
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• pp.3-11
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• 2011

In this study, the effect of treating 1-dimensional diffusers on the classroom acoustics was investigated to determine if the diffuser are beneficial for performing the preferred acoustical conditions for speech. A 1/10 scale model of a classroom was used to measure the acoustical parameters, T30, $C_{50}$, STI and SNR in that room. The room acoustical conditions were varied by treating diffusers either on the front or side walls of the classroom. When the diffusers were treated on the side walls around the student's areas, a shorter reverberation time at low frequencies was obtained and resulted in performing uniform reverberation times across the frequency bands. The $C_{50}$ values at mid- and high-frequencies were increased by treating the diffusers either on front or side wall surfaces. The highest STI and SNR values were obtained when the diffuser was treated on the front wall around the teacher's areas. It is found that diffusers are beneficial to increase the intelligibility of speech for the rear seats of the rooms.

• Journal of the East Asian Society of Dietary Life
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• v.14 no.2
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• pp.123-130
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• 2004

The physicochemical and sensory qualities of pumpkin jams replaced sucrose with sugar alcohols were investigated during storage at 2$0^{\circ}C$. Pumpkin jam was prepared with steamed ground pumpkin, mixed with sucrose only(50%), sorbitol (sucrose 30%＋sorbitol 20%) or maltitol (sucrose 30%＋maltitol 20%). Final sweetness of each pumpkin jam was 64$^{\circ}$ Brix. During 60 days of storage there were no differences in acidity and pH among treatments. Reducing sugar content was higher in sucrose, compared to maltitol or sorbitol. During storage, Hunter L, a and b values increased; L and b values were the highest in maltitol and a value were the highest in sucrose compared to the other sugars. Adhesiveness and hardness of textural properties were the highest in sugar and the lowest in maltitol. Sensory evaluation results showed that the mean scores of color, clarity, flavor and overall acceptability were the highest in maltitol, compared to sucrose or sorbitol. Physicochemical and sensory characteristics of pumpkin jams during storage in a PCA plot comprised of first principal component (58.79%) and second principal component (20.94%).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.468-473
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• 2000

Recently the acoustic design has been considered the important part of architectural design. However, in the design of Catholic churches the exterior beauty is still main point. This study aims to find out the acoustical characteristics in the main hall of Catholic churches. Six catholic churches were selected for this experiment and the physical parameters which represent the acoustic characteristics of room were compared by the plan type and the architectural factor. The physical parameters compared and analyzed were SD(Stand deviation) of SPL(sound pressure level), RT(reverberation time), $D_{50}$(definition), $C_{80}$(clarity) and STI(speech transmission index).

• Korean Journal of Plant Resources
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• v.8 no.2
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• pp.183-188
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• 1995

This experiment was carried out to clarity the effect of summer softening cultivation on bud yield of Aralia continentalis Kita. Bulbous plant harvested on March 25 and stored in low temperature storage room($0-2^{\circ}C$) were transplanted in May, June, July and August. The bulbous plants were grown under black PE film and 50%(T-2250) silver shading nets. The results obtained are summerized as fallows. Harvesting time in Jul. and Aug. transplanting was 15days and was speeling 5days in May transplanting. The accumulative temperature of whole growth period was about $400^{\circ}C$. But yield of soft stems in June transplanting was 6.64(ton/ha), which was more than others. High temperature induced low-quality of soft stem in transplanting in July. Net income was 18000(1000won/ha) in transplanting in May or June.