• The Korean Journal of Ecology
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• v.16 no.2
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• pp.135-149
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• 1993

In order to study and ecotypic variation of Phragmites communis Trin., we investigated germination rates, velocities, and protein band patte군 of seeds of three population of salt marsh, estuary and fresh water areas of Muan Peninsular in southwestern coast of Korea from March, 1990 to October, 1992. The highest germination rates of seeds were observed at $25^{\circ}C$; those of population of the estuary and fresh water are were 100% and that of the salt marsh was 95%. Similar germination rates were observed from the populations of estuary and fresh water areas at $30^{\circ}C$ and $20^{\circ}C$, but they decreased at $15^{\circ}C$. The onset of germination of seeds of three population was earlier $^{\circ}C$, but they decreased at $15^{\circ}C$. The onset of germination of seeds of th three populations was earlier at both $25^{\circ}C$, which was higher than those of any other areas, while that of fresh water areas was the lowest. were different; those of salt marsh and estuary decreased to 30% and 2.5%, respectively, at 3.0% of salt content, but seeds of the fresh water area did not germinate at all at the same salt content. The onset of germination was delayed in the order of the salt marsh, esturay and fresh water areas as salt content of culture solution increased. Germination of seeds from the population of salt marsh was found to begin earliest. The highest germination velocity of three populations was observed in the culture containing no salt. The germination velocity constant decreased as salt content of culture solution increased from 0.5% to 3.0%: those of the populations of the salt marsh, estuary, and fresh water areas were 9.50, 0.75 and 0.00, respectively, at the salt concentration of 3.0%. Soluble protein patterns of seedings from the three populations were analyzed by SDS-PAGE method. The results showed that protein patterns of the three populations were distinctly different qualitatively and quantitatively. The present study suggests that populations of Phragmites communis Trin. in the coast of Korea had taken ecotypic variations of habitats, i.e., fresh water, estuary, and salt marsh types, according to the salt content.

• Economic and Environmental Geology
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• v.47 no.1
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• pp.39-48
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• 2014

In coastal region, estuaries have complex environments where dissolved and particulate matters are mixed with marine water and substances. Suspended sediment (SS) dynamics in coastal water, in particular, plays a major role in erosion/deposition processes, biomass primary production and the transport of nutrients, micropollutants, heavy metals, etc. Temporal variation in suspended sediment concentration (SSC) can be used to explain erosion/sedimentation patterns within coastal zones. Remotely sensed data can be an efficient tool for mapping SS in coastal waters. In this study, we analyzed the variation in SSC in coastal water using the Geostationary Ocean Color Imager (GOCI) and Landsat Enhanced Thematic Mapper Plus (ETM+) in Gyeonggi-bay. Daily variations in GOCI-derived SSC showed low values during ebb time. Current velocity and water level at 9 and 10 am is 37.6, 28.65 $cm{\cdot}s^{-1}$ and -1.23, -0.61 m respectively. Water level has increased to 1.18 m at flood time. In other words, strong current velocity and increased water level affected high SSC value before flood time but SSC decreased after flood time. Also, we compared seasonal SSC with the river discharge from the Han River and the Imjin River. In summer season, river discharge showed high amount, when SSC had high value near the inland. At this time SSC in open sea had low value. In contrast, river discharge amount from inland showed low value in winter season and, consequently, SSC in the open sea had high value because of northwest monsoon.

• Journal of Bio-Environment Control
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• v.28 no.4
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• pp.335-341
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• 2019

In order to provide basic data for uniformization of temperature distribution in heating greenhouses, heating experiments were performed in two greenhouses with a hot water heating system. By analyzing heat transfer characteristics and improving pipes layout, measures to reduce the variation of pipe surface temperature and to improve the uniformity were derived. As a result of analyzing the temperature distributions of two different greenhouses and examining the maximum deviation and uniformity, it was found that the temperature deviation of greenhouses with a large amount of hot water flow and a short heating pipe was small and the uniformity was high. And it was confirmed that the temperature deviation was reduced and the uniformity was improved when the circulating fan was operated. The correlation between the surface temperature of the heating pipe and the indoor air temperature was a positive correlation and statistically significant(p<0.01) in both greenhouses. It was confirmed that the indoor temperature distribution in a hot water heating greenhouse was influenced by the surface temperature distribution of heating pipe, and the uniformity of indoor temperature distribution could be improved by arranging the heating pipe to minimize the temperature deviation. Analysis of the heat transfer characteristics of heating pipe showed that the temperature deviation increased as the pipe length became longer and the temperature deviation became smaller as the flow rate in pipe increased. Therefore, it was considered that the temperature distribution and the uniformity of environment in a greenhouse could be improved by arranging the heating pipe to shorten the length and controlling the flow velocity in pipe. In order to control the temperature deviation of one branch pipe within $3^{\circ}C$ in the tube rail type hot water heating system most used in domestic greenhouses, when the flow velocity in the pipe is 0.2, 0.4, 0.6, 0.8, $1.0m{\cdot}s^{-1}$, the length of a heating pipe should be limited to 40, 80, 120, 160, 200m, respectively.

• Journal of Biosystems Engineering
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• v.12 no.2
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• pp.16-27
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• 1987

Greenhouse farming was introduced to the Korean farmers in the middle of 1950's and its area has been increased annually. The plastic greenhouse, which is covered with polyethylene or polyvinyl chloride film, has been rapidly spread in greenhouse farming since 1970. The greenhouse farming greatly contributed to the increase of farm household income and the improvement of crop productivity per unit area. Since the greenhouse farming is generally practiced during winter, from November to March, the thermal environment in the plastic greenhouse should be controlled in order to maintain favorable condition for plant growing. Main factors that influence the thermal environment in the plastic greenhouse are solar radiation, convective and radiative heat transfer among the thermal component of the greenhouse, and the use of heat source. The objective of this study was to develop a simulation model for thermal environment of the plastic greenhouse in order to determine the characteristics of heat flow and effects of various ambient environmental conditions upon thermal environments within the plastic greenhouse. The results obtained are summarized as follows: 1. Simulation model for thermal environment of the plastic greenhouse was developed, resulting in a good agreement between the experimental and predicted data. 2. Solar radiation being absorbed in the plant and soil during the daytime was 75 percent of the total solar radiation and the remainder was absorbed in the plastic cover. 3. About 83 percent of the total heat loss was due to convective and radiative heat transfer through the plastic cover. Air ventilation heat loss was 5 to 6 percent of total heat loss during the daytime and 16 to 17 percent during the night. 4. The effectiveness of thermal curtain for the plastic greenhouse at night was significantly increased by the increase of the inside air temperature of the greenhouse due to the supplementary heat. 5. When the temperature difference between the inside and outside of the greenhouse was small, the variation of ambient wind velocity did not greatly affect on the inside air temperature. 6. The more solar radiation in the plastic greenhouse was, the higher the inside air temperature. Because of low heat storage capacity of the plant and soil inside the greenhouse and a relatively high convective heat loss through the plastic cover, the increase of solar radiation during the daytime could not reduce the supplymentary heat requirement for the greenhouse during the night.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.24-33
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• 2017

Domestic urban railway underground station structures, which were built in the 1970s ad 1980s, had been constructed as Cut-and-Cover construction system without seismic design. Because the trends of earthquake occurrence is constantly increasing all over the world as well as the Korean Peninsula, massive human casualties and severe properties and structures damage might be occurred in an non-retrofitted underground station during an earthquake above a certain scale. Therefore, to evaluate the retrofit effect and soil-structure interaction of seismic retrofitted underground station, a centrifugal shaking table test with enhanced stiffness on its structural main member are carried out on 1/60 scaled model using the Kobe and Northridge earthquakes. The seismic retrofitted members, which are columns, side walls, and slabs, are evaluated to comparing with existing non-retrofitted centrifuge test results Also, to simulate the scaled ground using variation of shear velocity according to site conditions such as ground depth and density, resonant column test is performed. From the test results, the relative displacement behavior between ground and structures shows comparatively similar in ground, but is increased on ground surface. The seismic retrofit effects were measured using relative displacements and moment behavior of column and side walls rather than slabs. Additionally, earthquake wave can be used to main design factor due to large structural deformation on Kobe earthquake wave than Norhridge earthquake wave.

• Journal of the Korean Geotechnical Society
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• v.31 no.7
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• pp.13-28
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• 2015

This study extended the Lee et al.'s (2015a) solution which improved the existing analytical solution for prediction of the residual pore water pressure into progressive wave and flow coexisting field. At this time, the variation of incident wave period and wave length should be incorporated to Lee et al.'s (2015a) analytical solution, which does not consider flow. For the case of infinite thickness, the new analytical solution using Fourier series was compared to the analytical solution using Laplace transformation proposed by Jeng and Seymour (2007). It was verified that the new solution was identical to the Jeng and Seymour's solution. After verification of the new analytical solution, the residual pore water pressure head was examined closely under various given values of flow velocity's magnitude, direction, incident wave's period and seabed thickness. In each proposed analytical solution, asymptotic approach to shallow depth with the changes in the soil thickness within finite soil thickness was found possible, but not to infinite depth. It is also identified that there exists a discrepancy case between the results obtained from the finite and the infinite seabed thicknesses even on the same soil depth.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.42-57
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• 1995

An efficient and accurate scheme has been constructed by taking advantages of the hi-quadratic spline scheme and the higher-order boundary element method selectively depending on computation domains. Boundary surfaces are represented by 8-node boundary elements to describe curved surfaces of a ship and its neighboring free surface more accurately. The variation of the velocity potential complies with the characteristics of the 8-node element on the body surface. But on the free surface, it is assumed to follow that of the hi-quadratic spline scheme. By which, the free surface solution is free from numerical damping and has better numerical dispersion property. As numerical examples, steady and unsteady Neumann-Kelvin problems are considered. Numerical results for a submerged spheroid, Series 60($C_B=0.6$) and a modified support the proposed method. Finally, a new upstream radiation condition is derived using a wave equation operator in order to deal with problems for subcritical reduced frequency. The relevance of this operator has been confirmed in the case of unsteady Kelvin source potential.

• Journal of Korea Water Resources Association
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• v.40 no.10
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• pp.833-840
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• 2007

The experimental study was carried out to investigate propagation distance of flood wave due to levee breach in a flat inundation area without obstacle. Hitter solution was considered to formulate the experimental results and a representative form was written referring to existing researches. As a result of experiments, it was found that the propagation velocity of the wave front in inundation area was significantly influenced by the initial water level in a channel, which was similar to flow in a channel due to dam break. An empirical formula was also suggested using the experimental results. The dimensionless propagation distance L can be written as the power function of dimensionless time T Coefficients k and m were varied with the dimensionless time T whereas k and m in Ritter solution were 2 and 0, respectively. The variation of coefficients in the relationship between L and T was influenced by the water depth in the inundation area and the fact proved that the changing points of L in the slope of relationship between L and T are the same to those of relationship between the dimensionless maximum water depth in the inundation area, $h_{max}$ and L.

• Investigative Magnetic Resonance Imaging
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• v.6 no.1
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• pp.41-46
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• 2002

The Fourier transform arteriography (FTA) exploits the periodic variation of arterial flow velociety of arterial flow velocity in stnchronized with cardiac cycles. This technique is intrinsically unique compared to other modern techniques. This technique separates the arteries from the veins using the pulsatile arterial flow without using the presaturation RF pulses. Therefore, it has less RF deposition and is free from the dark band artifacts that can arise from retrograde flow and curved arteries. Furthermore, it is free from the artifacts induced by eddy currents. However, there are some drawbacks such as a single projection view and the saturation of arteries at the end of an imaging slab. These drawbacks are circumvented by applying recently developed techniques. The fast gradient switching capability of modern MRI systems enabled us to incorporate dual projection views into the conventional FTA sequence without increasing the repetition time. In addition, signals from the distal arteries were enhanced by use of a ramped RF pulse and therefore the distal arteries were less saturated. By use of the FTA sequence with dual projection views and the ramped RF pulse, we acquired the sagittal and coronal projection views of femoral arteriograms simultaneously with more enhanced signals of distal arteries than the conventional FTA.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.37 no.1
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• pp.45-51
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• 2001

In order to investigate the optimal design weight of sinkers for preventing cage net from deforming in current, the model experiment on 2 types of square cage nets with different S sub(n)/S, the ratio of total area of netting projected to the perpendicular to the water flow S sub(n) to wall area of netting S, and 4 kinds of sinkers was carried out in circulation water channel. The model cage nets were made in 1/10 scale and the total weight in water of 4 sinkers attached to each corner of their bottom frames was 18, 54, 90, and 126g, respectively equivalent to 0.1, 0.3, 0.5, and 0.7 kg per unit area of prototype net. The results obtained can be summarizes as follows; Due to the deformation of each net where it was lifted towards the surface in severe conditions, its volume was reduced. This depended highly on the weight of sinkers placed in the bottom corner of cage nets, even if the variation of S sub(n)/S had a little effect on their deformation in current less than 0.4 m/s. In addition, it was observed that the total weight of sinkers for preventing the net from deforming to the extent of less than 50% inside its initial volume was 31 to 245 kg in the range of 0.3 to 0.6 m/s and the adequate design weight of sinker was approximately 0.5 kg per its unit area.