• Journal of Wetlands Research
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• v.21 no.4
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• pp.257-266
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• 2019

In this study, we selected 6 vegetation sites (reed community) and 6 non-vegetation sites (tidal flat) in the Muan tidal flat of Hampyeong Bay, and observed seasonal changes in carbon dioxide concentration, flux and soil temperature at low tide conditions. The study was conducted to identify the characteristics of seasonal changes in vegetation and non-vegetation areas through the data observed in May 30, August 8, 2012 and January 31, 2013. The average carbon dioxide concentration in the vegetation area was the highest in winter, followed by spring and summer, and the non-vegetation area showed the same concentration change as the vegetation area. The carbon dioxide flux in the vegetation area showed a positive (+) value in both spring and summer, but it was negative (-) in the winter. The average value of carbon dioxide flux was the highest in spring, but it was almost similar to summer, and winter was the lowest negative value. Non-vegetation areas showed positive emission in spring, and negative uptake in summer and winter; mean values were the highest in spring, and the difference between summer and winter was small. In summary of seasonal change characteristics of the research area, the emission of carbon dioxide was dominant in both areas in spring. In summer, carbon dioxide emission was dominant in the vegetation area, and the non-vegetation area was observed to uptake by photosynthesis of phytoplankton, but it was very small. In winter, changes in flux in both areas were very slight.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.3
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• pp.85-91
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• 2007

This study was carried out to minimize the lifting force of a two hinge type stand mechanism. This unit is designed for the display devices in order to enhance the ergonomics for effective height adjustment and maintenance at any preferred position. The unit will be very useful for the mechanism fabricated with a coil spring and disc springs as a torque generator. The maximum and the minimum torque value should be calculated initially for the smooth lift. And the reasonable torque distribution is necessary to prevent any auto lift and auto dropping at any position because the torque generated by coil spring is more sensitive than disc spring in tilting the position. Therefore, the analysis of the coil spring is requisite to issue the specific torque value depending on the distorted angle with securing reliability of a long time storage condition. After the theoretical torque value was calculated, the evaluation was carried out by making a proto-type sample, then distorted angle was updated by experiment. The result of this study can readily be applied to various units for the optimization of the smooth lift.

• Journal of the Korean earth science society
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• v.26 no.3
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• pp.253-267
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• 2005

Seasonal and spatial variations of tidal flat sediments were studied in Yeoja Bay. Results of the yearly observation of tidal flat transect lines indicated that the monthly change of grain size composition was not distinct from each tidal flat transect line, but it was quite clear that clay covered $40\~70\%$ of the sediment composition. Clay composed most highest in the northern part of the bay, and lowest in the western. As clay content increased, water and organic matter showed a tendency of increase, while the mean grain size was fixed per clay amount. Shear strength came out as 0 kPa as a whole. Seasonal variations of clay contents in each tidal flat were higher in winter and spring, but lower in summer and autumn. Thefine sediments were likely to be accumulated in the winter and spring. The average accumulation rate of each tidal flat was $-14.62\~38.57mm{\cdot}yr^{-1}$. The numbers showed $32.13mm{\cdot}yr^{-1}$ in the northern, $-14.62mm{\cdot}yr^{-1}$in the western, and $6.46mm{\cdot}yr^{-1}$ in the eastern part. During the coarse of this study sediment accumulation rates indicated that the sediments deposited continuously in the northern part of tidal flat, whereas erosion occurred in the western part. However, there was no distinct change in the eastern part. It was due to the clockwise lateral circulation in Yeoja Bay. Seasonally, sedimentation happened during the dry season (winter and spring) and erosion during the wet season (summer and autumn).

• The Korean Journal of Malacology
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• v.32 no.1
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• pp.31-36
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• 2016

In the present study, we observed a unique association of the flat oyster, Ostrea denselamellosa obtained from a muddy substrate at Haechang Bay, the south coast of Korea in the spring of 2013. Fossilized or semi-fossilized veneriid clam shells, possibly Ruditapes philippinarum, were found adhering to the umbonal area of the flat oyster valves. This unique association of the flat oyster shells with the fossilized clam shells suggested that the flat oyster larvae utilized the clam shells as substrate during settlement. Since availability of clam shells in the muddy subtidal environment is limited, this unique substrata for the flat oyster larvae may limit recruitment of the flat oysters in the bay.

• Ocean and Polar Research
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• v.24 no.4
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• pp.331-343
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• 2002

The southern tidal flat of Kanghwa Island with an area of approximately $90km^2$ is one of the biggest flats on the west coast of Korea. Surface sediments for sedimentary analyses were sampled at 83 stations in August 1997, September 1999 and August 2000. The very poorly-sorted mud sediments were predominant in the eastern part of the tidal flat, whereas the poorly-sorted sand-mud mixed sediments were dominant in the western part. The area of muddy sediment distribution diminished, but that of sandy mud sediment extended to southeastward tidal flat for three years. In the western part of tidal flat, deposition occurred during the period of spring to summer, whereas erosion occurred in winter. Sediment accumulation rates during three years indicated that the sediments deposited continuously in the eastern part of tidal flat, whereas eroded in the western part of tidal flat. Recently, construction of artificial structures such as new airport, island-connecting bridges and dikes near the tidal flat might change tidal current and river flow pattern. In order to reduce the ecological damage and to preserve tidal-flat environment, it is necessary to Investigate long-term impacts on sedimentary environment and ecology.

• KSTLE International Journal
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• v.4 no.1
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• pp.31-36
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• 2003

Sliding and impact/sliding wear test in room temperature air and water were performed to evaluate the effect of spring shapes on the wear mechanism of a fuel rod. The main focus was to quantitatively compare the wear behavior of a fuel rod with different support springs (i.e. two concaves, a convex and a flat shape) using a ratio of wear volume to worn area (De)-The results indicated that the wear volumes at each spring condition were varied with the change of test environment and loading type. However, the relationship between the wear volume and worn area was determined by only spring shape even though the wear tests were carried out at different test conditions. From the above results, the optimized spring shape which has more wear-resistant could be determined using the analysis results of the relation between the variation of De and worn surface observations in each test condition.

• Tribology and Lubricants
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• v.37 no.2
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• pp.77-80
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• 2021

In this study, we investigated the effect of the spring constant on frictional behavior at a nanoscale through molecular dynamics simulation. A small cube-shaped tip was modeled and placed on a flat substrate. We did not apply the normal force to the tip but applied adhesive force between the tip and the substrate. The tip was horizontally pulled by a virtual spring to generate relative motion against the substrate. The controlled spring constant of the virtual spring ranged from 0.3 to 70 N/m to reveal its effect on frictional behavior. During the sliding simulation, we monitored the frictional force and the position of the tip. As the spring constant decreased from 70 to 0.3 N/m, the frictional force increased from 0.1 to 0.25 nN. A logarithmic relationship between the frictional force and spring constant was established. The stick-slip instability and potential energy slope increased with a decreasing spring constant. Based on the results, an increase in the spring constant reduces the probability of trapping in the local minima on the potential energy surface. Thus, the energy loss of escaping the potential well is minimized as the spring constant increases.

• The Korean Journal of Zoology
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• v.9 no.1
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• pp.1-6
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• 1966

Frequently , large masses of the young short necked clam, Tapes japonica , die at their tidal flats in summer and this phenomenon has not been explained clearly. The purpose of the present investigation is to study the thermal condition and the chlorinity level of tidal flats in which the young clam appears to be injured. A study is also mad efor the burrowing organism in the lower layer of the esturay over which the fresh water flow during the low tide. Observation are made at five places of the tidal flat near Ikawazu Fixheries Laboratory of Tokyo University during the ebb and flow tide period of the spring tide. The diurnal and monthly changes of tidal temperatures and chlorinities are measured. Results of the study are ; 1. The surface temperature of the tidal flat increases with the ebb tide, reaches the highest between 12-14PM, and gradually decreases thereafter. The temperatures of tidal flat below 5 and 10 cm increase gradually until the flow tide reaches the surface. 2. At the spring tide in summer , the diurnal change of surface of the tidal flat temperature is very extensive ; it reaches 37-39$^{\circ}C$ in August. At the depths of 5 and 10 cm the temperature remains at 33 $^{\circ}C$ and 31$^{\circ}C$ , respectively. 3. The chlorinity of the tidal flat is higher during May through June and lower July through August, and this seems to be related to the amount of rainfall. 4. The chlorinity of the surface of tidal flat increases slightly during the ebb and flow tide periods. The observed higher chlorinity of surface of the tidal flat was 18.82% Cl. 5. At near the esturay, the fresh water that overflows the tidal flat affects the chlorinity of the surface but no such influence to the depth of the flat. 6. From above observations, it is assumed that the young short necked clam in the tidal flat could be exposed to the severe change of environmental conditions. The high temperature of the tidal flat in summer and the low chlorinity of it at flood period may be considered as the change in environment.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.43 no.5
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• pp.521-531
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• 2010

This study examined the community structure and temporal variation of the macro-crustaceans on Jangbong tidal flat, Incheon, Korea. Macro-crustaceans on this tidal flat were collected using a modified otter trawl from November 1999 to January 2001. The macro-crustaceans comprised 32 species, 7,741 individuals, and 29,211.3 gWWt during the study period. The Jangbong tidal flat was dominated numerically by three shrimp (Palaemon carinicauda, Crangon affinis, and Metapenaeus joyneri) and two portunid crabs (Charybdis japonica and Portunus trituberculatus). The macro-crustacean assemblages were divided into two different season and species groups based on the q-mode and r-mode clustering methods. In terms of q-mode, they consisted of a winter species group from December through April and a summer species group from May through November. The r-mode analysis showed that the species group visiting the tidal flat in winter was dominated numerically by palaemonid and crangonid shrimps, while a species group characterized by an abundance of portunid crabs and penaeid shrimps was more frequent in spring, summer, and autumn. In conclusion, our study revealed distinct temporal variation in the tidal flat use by macro-crustaceans around Jangbong Island, Incheon, Korea.

• The Korean Journal of Malacology
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• v.15 no.1
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• pp.21-30
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• 1999

This study was carried out to describe the growth of Ruditapes philippinarum on Chohwa and Toksan tidal flat in Kwangyang Bay, from June 1994 to July 1995. On the Chohwa tidal flat, the mean gran size, organic content and chlorophyll-a of the surface sediment were the range of 2.50-4.46 , 4.99-5.11%, 14.53-19.90 $\mu\textrm{g}$ cm$\^$-3/, and on the Toksan tidal flat, 0.83-1.66 , 2.22-2.34%, 6.20-6.90 $\mu\textrm{g}$ cm$\^$-3/, respectively. The shell length of R. philippinarum increased rapidly from spring to summer, and gently from summer to autumn, and ceased during winter. Fresh weight increased during spring and autumn, and decreased during summer and winter. condition factors also showed the same variations of weights. Synthesized annual growth pattern of 4 year classes in shell length fitted the von Bertalnffy growth model well. The annual growth of weight fitted the Gompertz model relatively well. The values of w, initial shell growth rate, and AGR$\sub$max/, maximum weight growth rate, on the Chohwa tidal flat were lower than those on the Toksan tidal flat. Comparing the growth patterns in the same tidal flat, growth rate was higher on the lover tidal flat than those on the higher tidal flat. In conclusion, the Chohwa tidal flat maintaining higher density showed lover growth rate, because of relatively insufficient food supply and inhabiting space.