• Journal of Plant Biotechnology
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• v.32 no.1
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• pp.23-29
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• 2005

Shoots of balloon flower (Platycodon grandiflorum A. DC.) derived from in vitro germinated seeds were cultured on MS medium containing $0.1\;\cal{mg/L}$ NAA under various photosynthetic photon flux (PPF) 33, 66, and $99\;{\mu}mol\;m^{-2}s^{-1}$ with or without membrane filter. Number of air exchanges per hour (NAEH) of the culture vessel with membrane filter on the lid was $4.9 h^{-1}$ and that without membrane filter was $0.1 h^{-1}$ Plantlets grown in $4.9 h^{-1}$ NAEH showed greater growth than in $0.1 h^{-1}$ NAEH. According to increase of PPF, plantlets growth decreased in $0.1 h^{-1}$ NAEH while it increased in $4.9 h^{-1}$ NAEH. At the same PPF, fresh weight and sugar content in plantlets in $4.9 h^{-1}$ NAEH were above 1.9, 2.0 times higher than those in $0.1 h^{-1}$ NAEH, respectively. Also they were enhanced in $4.9 h^{-1}$ NAEH by increase of PPF whereas no significance in $0.1 h^{-1}$ NAEH. The percentage of water content of plantlets in $4.9 h^{-1}$ NAEH was $4.2\~5.5\%$ lower than those in $0.1 h^{-1}$ and no difference in PPF. The content of total chlorophyll in plantlets in $4.9 h^{-1}$ NAEH was higher $0.27\~0.79\;\cal{mg/g}$ F.W. than that in $0.1 h^{-1}$ NAEH. By increase of PPF, it was decreased in $0.1 h^{-1}$ NAEH while had no significant difference in $4.9 h^{-1}$ NAEH. Guard and subsidiary cells of leaves in $4.9 h^{-1}$ NAEH were more developed than in $0.1 h^{-1}$ NAEH. Especially, in $99\;{\mu}mol\;m^{-2}s^{-1}$ leaves in $0.1 h^{-1}$ NAEH had undeveloped subsidiary cells and wide open stomata whereas those in $4.9 h^{-1}$ NAEH had well-developed subsidiary cells.

• Journal of the Korean Society of Marine Environment & Safety
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• v.30 no.2
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• pp.165-175
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• 2024

Hydrogen is being touted as one of the energy sources to combat the climate change crisis. However, hydrogen can leak into enclosed spaces, rise to the ceiling, accumulate, and cause fires and explosions if it encounters an ignition source. In particular, ships that transport hydrogen or use it as a fuel comprise multiple enclosed spaces. Therefore, the dif usion characteristics within these spaces must be understood to ensure the safe use of hydrogen. The purpose of this study is to experimentally determine the diffusion characteristics of helium, which has similar properties to hydrogen, in a closed space on board a ship, and to determine the change in the oxygen concentration along the leakage direction as the air change per hour(ACH) increases to 25, 30, 35, 40, and 45 through CFD simulation. The study, results revealed that the oxygen concentration reduction rate was 2% for leakage in the -z direction and 1% for leakage in the +x and +z directions, and the ventilation time was 15 min 30 s for leakage in the -z direction, 7 min for leakage in the +x direction, and 9 min for leakage in the +z direction, showing that differences existed in the oxygen concentration and ventilation time depending on the leakage direction. In addition, no significant difference was observed in the rate of oxygen concentration reduction and ventilation time in all leakage directions from the ACH of 35 and above in the experimental space. Therefore, because the oxygen concentration and ventilation time were not improved by increasing the ACH, 35 was noted as the optimal ACH in this experimental environment.

• Land and Housing Review
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• v.13 no.3
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• pp.93-106
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• 2022

Ventilation plays an important role in controlling indoor air quality. Due to the recent spread of infectious diseases such as COVID-19 and with people spending more time indoors, there's been increased attention on the importance of ventilation performance. In many countries, ventilation is regulated by airflow rates and the number of air changes per hour (ACH). However, airflow rates and ACH alone do not provide an accurate account of actual indoor pollutant removal and ventilation uniformity in a space. This study looked into the ventilation performance of an actual residential unit using several sampling points instead of basing it off of airflow and air change rates. Literature review was used to derive relevant influencing factors and the tracer gas dilution method was used for the field test. The study measured air velocity, age of air, and ventilation efficiency at several locations and compared them to the average value at the center of the test space to determine the differences in ventilation performance at the selected measurement points. The study showed that different sampling locations resulted in different ventilation values. Findings of this study will be used to develop an experimental procedure for evaluating indoor ventilation performance of actual residential spaces.

• Journal of Bio-Environment Control
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• v.4 no.2
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• pp.223-231
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• 1995

Judicious control of high temperature is the most important task for a successful intensive - cultivation in greenhouses during the hot summer. Therefore, the climatological data at 31 locations in Korea were calculated using the modified model equation for ventilated in glasshouses during summer. Furthermore, the adequate number of air- changes or frequency of ventilation was estimated based on temperature settings, which is considered to be more active means of controlling summer glasshouse temperatures, was investigated. The major results can be summarized as follows: Forced ventilation of one air change per minutes was effective in maintaining the maximum air temperature below 35$^{\circ}C$ in the glasshouse haying 40% shading. It was impossible, however, to maintain air temperature below 3$0^{\circ}C$ in 40% shaded glasshouse with forced ventilation only.

• Journal of Bio-Environment Control
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• v.18 no.3
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• pp.208-214
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• 2009

In this study, we investigated the effects of the number of air exchanges (NAE) on shape fruit body in two oyster mushrooms, Chunchu 2# and Suhan 2#. The suitable NAEs of Chunchu 2# were $1/10h^{-1}$ at primordial induction, $1/6h^{-1}$ at early stage of growth, $1/4h^{-1}$ at middle stage of growth, $1/4h^{-1}$ at late stage of growth and those of Suhan 2# were $1/6h^{-1}$ at primordial induction, $1/6h^{-1}$ at early stage of growth, $1/4h^{-1}$ at middle stage of growth, and $1/2h^{-1}$ at late stage of growth. In those conditions, the fruit bodies grew well. $CO_2$ concentration hardly affected the primordial formation of both mushrooms. However there were ventilation disturbances over 1500ppm. For instance, the end of pileus rolled up etc. As a result, Suhan 2# required higher ventilation compared with Chunchu 2# and the lower NAE was favorable for growth.

• Journal of Bio-Environment Control
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• v.28 no.3
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• pp.225-233
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• 2019

In the summer season, natural ventilation is commonly used to reduce the inside air temperature of greenhouse when it rises above the optimal level. The greenhouse shape, vent design, and position play a critical role in the effectiveness of natural ventilation. In this study, computational fluid dynamics (CFD) was employed to investigate the effect of different roof vent designs along with side vents on the buoyancy-driven natural ventilation. The boussinesq hypothesis was used to simulate the buoyancy effect to the whole computational domain. RNG K-epsilon turbulence model was utilized, and a discrete originates (DO) radiation model was used with solar ray tracing to simulate the effect of solar radiation. The CFD model was validated using the experimentally obtained greenhouse internal temperature, and the experimental and computed results agreed well. Furthermore, this model was adopted to compare the internal greenhouse air temperature and ventilation rate for seven different roof vent designs. The results revealed that the inside-to-outside air temperature differences of the greenhouse varied from 3.2 to $9.6^{\circ}C$ depending on the different studied roof vent types. Moreover, the ventilation rate was within the range from 0.33 to $0.49min^{-1}$. Our findings show that the conical type roof ventilation has minimum inside-to-outside air temperature difference of $3.2^{\circ}C$ and a maximum ventilation rate of $0.49min^{-1}$.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2023.11a
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• pp.335-336
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• 2023

최근 환경에 대한 관심이 지속적으로 증가함에 따라 실내 공기질에 대한 관심 역시 증폭되었다. 이에 따라 실내 공기질을 결정 짓고 흡연에 이어 폐암 사망률이 높은 라돈에 대한 관심 역시 증가하였다. 따라서 본 연구에서는 실내 라돈가스의 농도를 낮추기 위한 방법을 찾기 위해 RADON EYE RD200을 이용하여 교육연구시설에서의 세 강의동을 대상으로 라돈 방출량을 측정하고, 환기를 통해 라돈의 감소량을 측정한다. 세 강의동 모두 현재 기준치인 148 Bq/m³을 초과하는 수치를 기록하였고, 강의실을 10분간 환기한 결과 1회 환기 시 평균 77 Bq/m³만큼 감소하였고, 2회 환기 시 평균 56 Bq/m³만큼 감소하였다. 본 연구를 통해 라돈의 실태 및 위험성을 인지하고 라돈에 관련된 시설물 지침 및 환기를 강조하는 방안에 대한 마련이 필요하다고 판단된다.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.7 no.1
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• pp.48-53
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• 2004

Purpose: Besides interferencence of esophageal motor function by the nasogastric tube, a decline of the positive gastro-esophageal pressure gradient caused by intermittent positive pressure ventilation seems to have a major role in the pathogenesis of gastroesophageal reflux (GER) in mechanically ventilated preterm infants. The aim of this study was to determine the incidence of GER and associated risk factors in mechanically ventilated preterm infants. Methods: Twenty four hour esophageal pH monitorings were performed using a antimony electrode on 11 mechanically ventilated preterm infants in Neonatal Intensive Care Unit in Pusan National University Hospital. We evaluated the following reflux parameters; reflux index, reflux episodes/hour, reflux episodes ${\geq}5min/hour$, duration of longest episode, and percent episodes ${\geq}5min$. Patients were considered to have significant GER if more than 2 among 5 parameters were satisfied. Results: The mean gestational age of the patients was 30.9 weeks, mean birth weight was 1,568 g, and mean age at the time of pH monitoring was 2.8 days. Significant GER was detected in 4 patients (36.4%). There was no relationship between the incidence of GER and gestational age, birth weight, postnatal age, or the ventilator settings. Conclusion: The incidence of GER in mechanically ventilated preterm infants was similar, compared with other previous studies. Associated risk factors of GER in these patients were not detected. Therefore, mechanical ventilation in preterm infants does not seem to be the high risk factor of GER.

• Air Cleaning Technology
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• v.27 no.1
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• pp.56-70
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• 2014

• Journal of dental hygiene science
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• v.11 no.4
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• pp.353-359
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• 2011

This study was designed to identify a subjective symptom level by Indoor air according to ventilation system in Dental Clinic. The number of respondents was 582 who work in dental clinic and period of investigation was October 2010 through January 2011. A structured questionnaire was employed to evaluate the level of participants' sociodemographics, job-related factors, work place condition, a subjective symptom. Most of respondents were answered that time for symptom to begin was at around 2 P.M. and time for symptom to feel serve pain was at around 3 P.M. and ventilation frequency per a day was often in case of individual cooling and heating system. More often natural ventilation and in case of individual cooling and heating system, the level of subject symptom was low and multiple regression analysis has found that indoor air quality related elements were main factors that influence to the feeling of satisfaction in work place. The results of this study suggest that more often natural ventilation was very important to reduce the level of subjective symptom. Thus, a management program for indoor air quality is strongly recommended by natural ventilation, maintenance man for promotion of quality of life in dental hygienist and to improve dental service and competitiveness.