• Composites Research
• /
• v.23 no.1
• /
• pp.44-50
• /
• 2010

In this paper, two different experiments, namely, salt water spray and salt water immersion, were performed to reproduce the contact of composites with the seawater for three kinds of woven fabric composite material systems which would be used for the WIG(wing in ground effect)craft. After aging 140 days in the salt water environment, material properties of carbon/epoxy and glass/epoxy composite such as tensile, compressive and shear stiffness and strength, and inter-laminar shear strength (ILSS) were measured. By comparing baseline material properties with degraded ones, the effects of the salt water environment on the composite mechanical properties were evaluated. From the experiments, it was confirmed that the difference in aging conditions had very small influence on composite properties. And it was found that tensile strength of carbon/epoxy composites showed little degradation, but much more degradation was observed in glass/epoxy composites. And large degradations on matrix dominant properties were observed. The salt water could damage the fiber-matrix interface, matrix properties and the glass fiber.

• Asian-Australasian Journal of Animal Sciences
• /
• v.13 no.7
• /
• pp.967-973
• /
• 2000

A metabolism trial was conducted with 28 Najdi rams allocated into seven dietary groups to evaluate the effect of dietary inclusion of Salicornia bigelovii Torr biomass on nutrient digestibility, rumina I fluid metabolites and nitrogen and mineral balances. Either the stems (ST) or spikes (SP) of this seawater-irrigated halophyte were incorporated into complete diets at rates of 0, 10, 20 and 30% levels, replacing equal amounts of rhodesgrass hay in a ground mixed control diet. Digestibility of DM, OM, EE, NFE and fecal and urinary nitrogen were not affected by increased level of ST in the diet. As level of ST increased from 0 to 20% in the diets, CP digestibility and nitrogen retention approached their maximum (p<0.01), whereas CF digestibility reached its minimum (p<0.01). On the other hand, except for EE, digestion of all nutrients and nitrogen retention were linearly depressed (p<0.01) as SP increased in the diets from 10 to 30% level. Concentration of ammonia-N, total VFA and pH values in the rumen fluid were lower (p<0.01) with the ST- or SP-fed diets than with the control diet. Increasing level of ST or SP in the diet was associated with an increase (p<0.01) in the proportion of acetate and a decline (p<0.01) in molar percentage of propionate in the ruminal fluid. Sodium absorption increased (p<0.01) with increased ST and SP in the diets up to the 10 and 20% level, respectively, followed by constant absorption values up to the 30% level. When the level of ST in the diet gradually increased to 30%, a concomitant increased (p<0:01) in Ca and P absorption were obvious; whereas, increased level of SP in the diets from 0 to 30% resulted in noticeable (p<0.01) depression in Ca and P apparent absorption.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.53 no.5
• /
• pp.773-783
• /
• 2020

In order to evaluate the recovery of fishing ground environment after the cessation of aquaculture farming, we examined the variation in sediment quality over time using different geochemical factors and investigated whether these factors are indicators of sediment quality recovery. The study area was an oyster Crassostrea gigas, farm in Tongyeong, Geyongsangnam-do, South Korea, where aquaculture activities had been carried out for 20 years, and the changes in water and sediment environment were monitored for 14 months after the abandonment of the farm. The mean water depth was 14 m, with a tidal range of 3 m, and seawater current velocity ranged from 4.7 to 7.0 cm/s. After the abandonment of the farm, total organic carbon and total nitrogen concentrations in the surface sediments decreased significantly over time compared to those in the control site; in particular, immediately after farm abandonment, acid-volatile sulfide concentrations decreased relatively rapidly. Carbohydrate and protein concentrations in the sediments showed no significant changes; however, lipid concentrations markedly decreased. Further studies on other aquaculture taxa and various aquaculture areas are needed to establish new policies for environmental management of fishing grounds, such as relocation of fishing grounds and determination of optimal fallowing periods.

• Geophysics and Geophysical Exploration
• /
• v.21 no.4
• /
• pp.244-254
• /
• 2018

The first geophysical technique applied to the agricultural sector in Korea was electrical resistivity sounding and conducted in purpose of groundwater exploitation in the 1970s. According to the diversity of agricultural activities since the 1990s, various geophysical methods including electrical resistivity, electromagnetic induction, and self-potential method were applied to several agricultural fields such as soil characterization with saline concentration in vast reclaimed area, delineation of seawater intrusion regions in costal aquifer, safety inspection of embankment dikes with leakage problem, detection of ground subsidence from overpumping and tracing of groundwater aquifer contamination by leachate from livestock mortality burial or waste burial site. This paper introduces representative geophysical techniques that have been utilized in various agricultural fields and suggests several ways to develop the geophysical methods required for the precision agriculture field in the near future based on the past achievements.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.16 no.1
• /
• pp.157-164
• /
• 2021

Wind and temperature were measured with a three-dimensional ultrasonic anemometer and the carbon dioxide concentration was measured using an infrared sensor in the tidal flat of Suncheon Bay. In general, as the temperature increases, the concentration of carbon dioxide increases, and as the temperature decreases, the carbon dioxide also decreases in the atmosphere. However, since photosynthesis declined immediately after the sunset, the concentration of carbon dioxide increased as the temperature decreased. In addition, near the high tide when the tidal flat is covered with seawater, the atmospheric turbulence was strong despite an increase in temperature, resulting in a decrease in carbon dioxide concentration. It is necessary to quantitatively evaluated the effects of photosynthesis, respiration and atmospheric turbulence on the change of carbon dioxide concentration over tidal flat ecosystems.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.4A
• /
• pp.365-371
• /
• 2009

It is time-consuming to estimate chloride diffusivity of concrete by concentration difference test. For the reason chloride diffusivity of concrete is mainly tested by electrically accelerated method, which is accelerating the movement of chloride ion by potential difference. In this study, portland cement concrete and concrete containing with ground granulated blast-furnace slag (40 and 60% of cement by weight) with water-cementitious material ratio 40, 45, 50 and 60% were manufactured. To compare with chloride diffusivity calculated from the electrically accelerated test and immersed test in artifical seawater, chloride diffusivity tests were conducted. From the results of regression analysis, regression equation between accelerated chloride diffusivity and immersed chloride diffusivity was linear function. And the determinant coefficient was 0.96 for linear equation.

• Journal of Aquaculture
• /
• v.21 no.2
• /
• pp.111-122
• /
• 2008

This study was conducted to assess the usefulness of the temperature characteristics of the tidal flat sediments during low tide as a environmental factor, and burrowing behaviour, fatness, total hemocyte counts(THCs) and differential hemocyte counts(DHCs) of hard clam Meretrix lusoria as biological activity indices for the management of hard clam farms located in Taean(Chungnam province) and Gimje(Jeonbuk province) tidal flat in Korea. Temperature ranges of the sediment at 1cm depth during spring(March to May) and summer(June to August) in Taean(where the exposure time was about $5.5{\sim}6$ hours during low tide) were $8.7{\sim}26.8^{\circ}C\;and\;27.6{\sim}32.8^{\circ}C$, respectively. Even though there was no significant difference(P>0.05), temperatures of the surface sediment where submerged with remained seawater were generally higher than that of uncovered with seawater. Burrowing depths of normally digged hard clams were 0.9{\sim}3.6cm from March to October, 2002. In the field experiment performed at Taean farming ground covered with seawater, burrowing times of the clams under natural water temperatures were $41.6{\pm}10minutes$ in February and $5.4{\pm}1.3minutes$ in August, respectively, and these were influenced by water temperatures. Fatness of hard clams began to decrease from May(at Taean tidal flat) and June(at Gimje tidal flat), showed the lowest level in August and increased again from September. Total hemocytes counts in the hemolymph of the hard clams were decreased to the lowest level in July($24.7{\times}10^4cells/mL$, at Taean tidal flat) and August($28.2{\times}10^4cells/mL$, at Gimje tidal flat), and significantly increased again from September(at Taean tidal flat, P<0.01) and October(at Gimje tidal flat, P<0.001), respectively. We observed three types of hemocytes from the hemolymph of hard clams according to whether hemocytes retain the granules or not and the size of the granules. As a results, we could found that periodical monitoring of the sediment temperatures, clam burrowing behaviour and hemocyte parameters were very helpful for the management of hard clam farming.

• Economic and Environmental Geology
• /
• v.44 no.3
• /
• pp.239-246
• /
• 2011

Groundwater in small islands is used as main water resource but the overuse of groundwater may cause seawater intrusion and temperature decrease in geothermal wells. This study aimed to characterize the hydrogeology of Maeum-ri area in Seokmo Island of Ganghwagun using long-term monitoring at groundwater wells and geothermal wells. In the monitoring period seasonal water level change, consistent drop or increase of water levels are not detected. The groundwater temperature about 10m below ground surface shows year cycle variation having two to five months difference with ambient temperature cycle. The storativity was calculated by tidal method. The storativity estimated by adapting tidal efficiency factor showed some larger values than that by using tidal time lag. The result suggested that the tidal method assuming several assumptions on aquifer condition may produce broad ranges but the calculated ranges at this application are reasonable. The similar shape of groundwater level change and tidal effects was observed at several wells clustered east-south-east direction which may implicate the distribution of vertical fracture system strongly related with groundwater flow channels. The applied methodology and study results will bc valuable to evaluate optimal pumping rate for the preservation of groundwater resources, and to manage geothermal development.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.4 no.3
• /
• pp.226-236
• /
• 1999

Growth, reproduction, mortality, and production of Laminaria japonica were experimentally studied at a cultivation ground on the coast of llkwang, where the largest amount of cultivated Laminaria has been produced in Korea. For this experiment, young sporophytes (0.33 cm in mean length) grown in the laboratory were transplanted at the depth of 3 m and field surveys on them were conducted twice a month from December, 1995 to August, 1996. Plants exhibited an annual life span; they were completely dead by August. Frond width, thickness, and wet weight showed similar pattern of seasonal growth and reached their maxima in July, but frond length showed no more increment after May. Maximum mean frond length and weight were 199.8 cm and 333.0 g wet wt., respectively. Overall meristematic growth in length and weight were 384.0 cm and 393.6 g wet wt., respectively. Absolute growth rates (AGR) which were calculated from the length of tissue developed from meristem varied seasonally; AGR of length and weight reached maxima in March (3.6 $cm{\cdot}d^{-1}$) and May (3.8 g wet $wt{\cdot}d^{-1}$), respectively. Absolute attrition rates gradually increased from February to July. Seasonal differences in growth and attrition rates appeared to be related to seawater temperature and nitrogen concentration in seawater. Reproductive sporophytes bearing sprorangium sorus began to occur from April, and the ratio of sorus area to blade area reached its maximum in July (0.034). Survival rate was exponentially decreased; more than 90% of plants decayed within 56 days after outplanting. After February, mortality was size-specific; mortality of smaller plants less than 30 cm in length were relatively higher. Maximum biomass occured in July (285.6 kg wet $wt{\cdot}m^{-2}$) and annual production was 758.7 kg wet $wt{\cdot}m^{-2}$.

• Journal of Aquaculture
• /
• v.3 no.1
• /
• pp.89-125
• /
• 1990

In order to improve top shell seed production techniques spawning and larvae rearing were done in rearing tanks. Growth of young top shell in the nursing ground were also investigated. For induced spawning, top shells were maintained in still water during night time. Then they were treated with ultra violet iradiated sea water after dried up in air for 60 minutes. Spawning rate were 10 to $39.77\%$. It was found that young top shells moved in the growing grounds from nursing grounds when they reached approximately 30-40mm in shell heignt. Among main food algae for top shell in the natural growing grounds, sea mustard were melted away during June. Therefore, presence of another food algae such as Ecklonia cava or Sargassum spp. seems to be the main limiting factor for survival of top shell during summer. The tolerance of top shells ranging from 30mm to 60mm to low density of seawater for were tested at the temperature between 29.5 and $31.4^{\circ}C$. Hundred percent mortality occoured in 20, 55 and 90 hours after first stocking at the specific gravity of 1.010, 1.015, and 1.020, respectively.