• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.6
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• pp.459-471
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• 1991

The community structure and micro-scale distribution of plankton in relation to hydrography were investigated in Masan Bay, Korea in October 1989. Warmer and less saline waters with stratification was located in the inner part of the Pudo Strait, and chlorophyll-a and nutrients were higher. Both phytoplankton biomass and nutrients was changed dramatically around the Strait. Offshore/oceanic species in phytoplankton i.e., Chaetoceres decipiens, Rhizosolenia stolterforthii, Rhizosolenia styliformis and Ceratium trichoceros and zooplankton i.e., Sagitta enflata, Oncaea uenusta and Oikopluera longicaudata occurred mainly in well mixed waters of the outer part. This suggests that discontinuous layer seems to play an important role as an approximate border for the plankton population. This layer was located between Station 3 and Station 4 near the Pudo Strait, since the layer consisted of a series of micro-scale discontinuties of salinity and dissolved inorganic nutrients gradient. Phytoplankton patchs of more than 801e1 were found only in the inner part of the bay. Depletion of silicate caused by a rapid assimilation of phytoplankton in the inner part of the bay seemed to be responsible for the decline of blooms.

• Korean Journal of Environmental Biology
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• v.24 no.1 s.61
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• pp.7-18
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• 2006

Samples were collected from five stations monthly from October 2003 to September 2004 to investigate seasonal variation of size structure of phytoplankton and relationship between size-fractionated phytoplankton and environmental factors in the Asan Bay. The contribution of large cells (microphytoplankton, $>20\;{\mu}m$) to total concentrations of chlorophyll $\alpha$ was higher than small cells (nanophytoplankton, $3\sim20\;{\mu}m$; picophytoplankton, $<3\;{\mu}m$) during the sampling period. Especially, large cells contributed 80% to the total chlorophyll a from February, 2004 to April 2004 when chlorophyll $\alpha$ concentrations were high. The size structure of phytoplankton shifted from micro-size class to nano-size class and picophytoplankton rapidly increased when phytoplankton biomass decreased in May 2004. Microphytoplankton exhibited a high biomass in the upper region during winter-spring season whereas nano- and picophytoplankton showed two peaks in the middle-lower regions (Station 3,5) during spring and summer. Microphytoplankton are most likely controlled by water temperature and nutrient supply during the cold season whereas nano- and picophytoplankton may be affected by stratification, light exposure during the warm season.

• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2204-2220
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• 2020

An open-pool type research reactor is designed and operated considering the accessibility around the pool top area to enhance the reactor utilization. The reactor structure assembly is placed at the bottom of the pool and filled with water as a primary coolant for the core cooling and radiation shielding. Most radioactive materials are generated from the fuel assemblies in the reactor core and circulated with the primary coolant. If the primary coolant goes up to the pool surface, the radiation level increases around the working area near the top of the pool. Hence, the hot water layer is designed and formed at the upper part of the pool to suppress the rising of the primary coolant to the pool surface. The temperature gradient is established from the hot water layer to the primary coolant. As this temperature gradient suppresses the circulation of the primary coolant at the upper region of the pool, the radioactive primary coolant rising up directly to the pool surface is minimized. Water mixing between these layers is reduced because the hot water layer is formed above the primary coolant with a higher temperature. The radiation level above the pool surface area is maintained as low as reasonably achievable since the radioactive materials in the primary coolant are trapped under the hot water layer. The key to maintaining the stable hot water layer and keeping the radiation level low on the pool surface is to have a stable flow of the primary coolant. In the research reactor with a downward core flow, the primary coolant is dumped into the reactor pool and goes to the reactor core through the flow guide structure. Flow fields of the primary coolant at the lower region of the reactor pool are largely affected by the dumped primary coolant. Simple, circular, and duct type discharge headers are designed to control the flow fields and make the primary coolant flow stable in the reactor pool. In this research, flow fields of the primary coolant and hot water layer are numerically simulated in the reactor pool. The heat transfer rate, temperature, and velocity fields are taken into consideration to determine the formation of the stable hot water layer and primary coolant flow. The bulk Richardson number is used to evaluate the stability of the flow field. A duct type discharge header is finally chosen to dump the primary coolant into the reactor pool. The bulk Richardson number should be higher than 2.7 and the temperature of the hot water layer should be 1 ℃ higher than the temperature of the primary coolant to maintain the stability of the stratified thermal layer.

• Korean Journal of Heritage: History & Science
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• v.48 no.2
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• pp.4-29
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• 2015

This article considered generally gradational change aspect, character of community for the tombs of the Three kingdoms prepared by some certain homogenous groups. It was completed by tracing the transfering process to grasp character of social structure and organizing System in the community. For this reason, it's analyzed that Wooden chamber tomb was formed in some certain Time-Space of the Yaksadong Buk-dong archaeological site in the Three Kingdom Period. Constructed group was distinguished by the five classes. So perhaps scale of Wooden chamber and sort, material of burial relics, the top layer and the upper layer were established two status those are active the ruling class led the Wooden chamber tomb's society, the general public hold a large majority from the middle class to the lowest class. And it depends on age(nonage-adult) that differed in relation of arrangement, character. It's changed with function or roles, property, purpose etc. of social community in accordance with these individual position, age. Received signification, value of social status were considered with social worth, faith. Members in a community had been conducted under premeditated, organised system for common target, relatedness. Also it seems to attempt organization's own maintenance, persistiveness in norms that given at common law. To do that, relation for combination between members who consisted systems had to be organic. The relation for combination was considered to form relation for the much larger community in based on blood relationship that most vital part. One social structure had established family(house, household) community in based on individual blood relationship, family communities gather up to develop into relative(blood relative, same race) community gradually. Furthermore, relative(blood relative, same race) communities, that focus on the public good gather up to develop into social community in based on regionalism. It's considered to go through the Development Process of family(house, household) community - relative(blood relative, same race) community - social community.

• Korean Journal of Environment and Ecology
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• v.35 no.4
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• pp.408-423
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• 2021

We established and monitored survey sites in seven regions of Mt. Jiri to investigate population decline and change of the Korean fir (Abies koreana) over a ten-year period from 2009 to 2018. With the exception of one site (Seseok), the six remaining ones all showed a four-layer stratification structure. The importance value of Korean firs in all of the survey areas decreased significantly by 28.5%, from 55.7% in 2009 to 39.8% in 2018. The average population of objects with a diameter at breast height (DBH) of 5cm or more in all survey sites was 711 objects/ha in 2018, and the cumulative death rate from 2009 to 2018 was 10.8%. Among the death types, DS (dead standing) was the most dominant, comprising 82.4% of the total survey area. However, in Banyabong 1, which had a high gradient of 35°, the death types other than DS accounted for 44.2%. We estimate that A. koreana can maintain a stable population as its distribution type for each diameter class in the Saeseokpyeongjeon site showed a reverse-J shape. The average annual ring growth in all survey sites was 1.09 mm/year, with the most abundant growth observed in the Seseokpyeongjeon site, which was formed mainly by a subtree layer. The growth ring survey showed the estimated average age of A. koreana population in the Byeoksoryeong and Banyabong 1 sites to be 102 and 91 years, respectively, a general downward trend of vitality since 2013.

• Journal of Marine Life Science
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• v.4 no.2
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• pp.53-62
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• 2019

Heterotrophic bacteria are a major member of the microbial loop in the marine ecosystem and play an important role in the biogeochemical cycle decomposing organic matter. Therefore study of bacterial variation is important to understand the material cycle and energy flow of marine ecosystems. We investigated the monthly variations of bacteria and environmental factors in the Youngsan River estuary, and the correlation between bacteria and phytoplankton biomass (chlorophyll-a) including size-structure. As a result, bacteria of the Youngsan River estuary were higher in the surface than in the bottom layer, and higher in the summer than in winter. And the closer to the dike, the abundance increased, and it increased to the peaks in August, September, and June 2019 at the station closest to the dike. The chlorophyll-a also increases at the stations and time when the bacterial abundance was high and they correlates positively displaying no difference between size fractions. The results indicate that organic matter derived from phytoplankton has an effect on bacterial variation but no size-dependent effects. In addition, the seasonal pattern of bacteria increasing in proportion to the water temperature suggests the effect of water temperature on the growth of bacteria. No association of bacterial abundance variation with nutrient supply due to freshwater input was observed. In this study, dissolved oxygen was depleted and hypoxia was observed for a short time when a strong stratification was not developed. This may be resulted from the supply of organic matter from phytoplankton and the consumption of oxygen due to bacterial decomposition.

• The Journal of Korean Society for School & Community Health Education
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• v.25 no.1
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• pp.17-28
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• 2024

Background & Objectives: This study aimed to examine the relationship between subjective health perception and health behaviors among adolescents, utilizing raw data from the 8th Korea National Health and Nutrition Examination Survey (2019-2021) while distinguishing between genders. Methods: The study employed data from the 8th Korea National Health and Nutrition Examination Survey (2019-2020), recruiting students from 1st to 3rd grades in middle and high schools nationwide. Through population stratification, sample distribution, and sampling stages, a final sample of 1,065 adolescents aged 12 to 18 years was selected. The collected data were analyzed using SPSS 28.0 (IBM Corp., Armonk, NY, USA) at a significance level of .05. Results: Regarding the general characteristics of the subjects, no statistically significant differences were observed among male students based on school, family structure, and income. However, among female students, a significant difference in subjective health perception was noted, with higher perception among high school students compared to middle school students (p=.001). Significant differences in health behaviors were identified based on family structure for male adolescents, where those living with both parents exhibited more health-promoting behaviors than single-parent adolescents (p=.011). However, no significant difference was observed among female adolescents. In terms of health behaviors related to gender, regular exercise was found to significantly impact subjective health perception in male adolescents (p=.013), while breakfast habits were identified as significant influencers for female adolescents (p<.001). Conclusions: This study revealed gender differences in subjective health perception and health behaviors among adolescents. Based on these findings, there is a perceived need for the development of health promotion programs tailored to the unique needs of male and female adolescents.

• Geophysics and Geophysical Exploration
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• v.13 no.1
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• pp.102-108
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• 2010

The internal structure of a river embankment must be delineated as part of investigations to evaluate its safety. Geophysical methods can be most effective means for that purpose, if they are used together with geotechnical methods such as the cone penetration test (CPT) and drilling. Since the dyke body and subsoil in general consist of material with a wide range of grain size, the properties and stratification of the soil must be accurately estimated to predict the mechanical stability and water infiltration in the river embankment. The strength and water content of the levee soil are also parameters required for such prediction. These parameters are usually estimated from CPT data, drilled core samples and laboratory tests. In this study we attempt to utilise geophysical data to estimate these parameters more effectively for very long river embankments. S-wave velocity and resistivity of the levee soils obtained with geophysical surveys are used to classify the soils. The classification is based on a physical soil model, called the unconsolidated sand model. Using this model, a soil profile along the river embankment is constructed from S-wave velocity and resistivity profiles. The soil profile thus obtained has been verified by geotechnical logs, which proves its usefulness for investigation of a river embankment.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.2
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• pp.103-111
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• 2013

In this study, field measurements were conducted in the section about 7 km from sea dike to westward. The observations of along channel current were carried out, and water temperature and salinity were measured simultaneously at 10 stations during one tidal cycle, and sampling interval is 1 hour. The maximum ebb current is about 1.5 m/s at the surface layer but flood current is 0.4 m/s at the bottom layer during discharge period. Residual current during river discharge shows two layer structures which is typical characteristic of the estuary system. On the other hand, residual current during a period with no discharge has shown multi-layer structure different from general estuarine systems. The distribution of high salinity can be seen at the bottom layer as the effect of discharge does not reach down to the bottom layer during discharge. As a result, freshwater is not effected at the bottom layer during observation, and mixing of surface layer to bottom layer is reduced by stratification.

• Journal of Navigation and Port Research
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• v.28 no.6
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• pp.565-572
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• 2004

Residual current plays more important role than the tidal current for long-term material transport in coastal areas. The main component of residual current is tide-induced residual current. Otherwise, wind driven current and buoyancy-driven current are important components which change the residual current. To clarify the characteristic of coastal current, application of a three -dimensional model is necessary. This study focuses on clarifying the stratified systems of coastal water affected by freshwater runoff from a river and analyzes the structure of current at Ulsan bay by applying a three-dimensional buoyancy-driven current model. According to the result of “Ulsan bay” study, it shows that the surface layer in semi-enclosed estuaries, which affected by freshwater runoff. has flows going out, and the bottom layer has flows coming in. Besides when the wind blows toward inside of the bay, the surface layer has flows coming in and the bottom layer has flows going out as compensation flows for the surface circulation. The results of simulation could be applicable to examine vertical upwelling, which might be caused by construction of artificial fishing reef to build aqua farm, submerged breakwater to control coastal sediment, and the formulation of oceanic ridge, or a basic study on application to the usage of deep water.