• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.3 no.1
• /
• pp.45-52
• /
• 1998

The transport of suspended matter was interpreted in the coastal zone off Taean Peninsula during the summer (June) in 1996. Coastal waters were homogenous in water temperature and salinity, whereas offshore waters were characterzed by the strong thermocline. Mixing between coastal and offshore waters are negligeable, largely lessened, due to the existence of strong tidal front between the two water masses. In the offshore area, less saline coastal waters from the Kyunggi Bay are considered to be transported southward along the mid-depth layer of thermocline. Concentration of suspended matters was higher than 5 mg/l in the northern coastal area near the Kyunggi Bay, but generally less than 2 mg/l in the offshore area. Less saline waters along the mid-depth layer in the offshore area sustain maximum turbidities throughout the water column. Therefore suspended matters supplied from the coastal area of Kyunggi Bay are considered to be transported southward by the advective movement of less saline coastal waters. Mean particle size of the suspended matters shows 2~9 ${\mu}m$. Coarse grains (mean size larger than 7 ${\mu}m$) are predominant in the less saline coastal waters extending to the offshore mid-depth waters. Such size distributions of suspended matters together with the characteristics of water masses are considered to be an indicator for the southward movement of suspended matters derived from Kyunggi Bay.

• Applied Chemistry for Engineering
• /
• v.10 no.4
• /
• pp.523-530
• /
• 1999

Acrylic pressure-sensitive adhesive has been made utilizing organic solvents, but nowadays it is made by solvent-free system due to environmental problems. In this study, emulsion polymerization were carried out at $40^{\circ}C$ with methacrylic acid(MAA), n-butyl acrylate(n-BA) and 2-ethylhexyl acrylate(2-EHA) as monomers in the presence of anionic(sodium dodecyl sulfate, SDS) and nonionic(ethylene oxide types) surfactant mixtures. The overall conversion of the polymerization reaction in a mixed surfactant system was found to be higher than that in a single surfactant system. Emulsion stability in mixed or anionic surfactant systems was found to be over 12 week, which was better than that in nonionic surfactant system. Emulsion particle size decreased as surfactant content increased. The Tg and molecular weight of emulsion polymer were inependent of the type, the amount and the mixing ratio of surfactant. Based on the results of stability and peel strength, the optimum nonionic surfactant ratio in total 4 g of surfactant mixture systems is found to be 40~60% by weight where the nonionic surfactant has 50 ethylene oxide groups and 16~18 carbon atoms in hydrophobic alkyl chain.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.16 no.3
• /
• pp.101-105
• /
• 2006

We fabricated the nano $TiN_x$ by making of reaction between titanium powder and $Si_3N_4$ during planetary milling. The $TiN_x$ powder was sintered by spark plasma sintering machine after mixing with 50 wt% of titanium powder, and the sintered body was heat-treated at $850^{\circ}C$ in order to investigate its hardness property at the elevated temperature. We analyzed crystal structure by XRD. We observed the peaks of $TiN_{0.26}$ and TiN after 10 hours milling, and we observed TiN peak mainly after 20 hours milling. The reacted particle size distribution was investigated by FE-SEM. Increase of milling time, the size of reacted particles was decreased and the $10{\sim}20nm$ size of $TiN_x$ on the surface of titanium and $TiN_x$ was observed after 20 hours milling. The micro-Vickers hardness of mixed sintered body was about $1050kgf/mm^2$.

• Journal of the Korean Geosynthetics Society
• /
• v.10 no.4
• /
• pp.123-130
• /
• 2011

In the precedent study it was presented that the comparison of thermal resistivity using various backfill materials including river sand regarding water content, dry unit weight and particle size distribution. Based on the precedent study, this study focused on developing the optimized backfill material that would improve the power transfer capability and minimize the thermal runaway due to an increase of power transmission capacity of underground power cables. When raw materials, such as river sand, recycled sand, crush rock and stone powder, are used for a backfill material, they has not efficient thermal resistivity around underground power cables. Thus, laboratory tests are performed by mixing Fly-ash, slag and floc with them, and then it is found that the optimized backfill material are required proper water content and maximum density. Through various experimental test, when coarse material, crush rock, is mixed with recycled sand, stone powder, slag or floc for a dense material, the thermal resistivity of it has $50^{\circ}C$-cm/Watt at optimum moisture content, and the increase of thermal resistivity does not happen in dry condition. The result of experiments approach the optimization of the backfill materials for underground power cables.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.17 no.2
• /
• pp.141-151
• /
• 2015

A new rock excavation method using an abrasive injection waterjet system has been developed to enhance the efficiency and reduce the vibration of tunnel excavation. The abrasive feed rate is an important factor for the cutting performance and the economical efficiency of waterjet-based excavation. In this study, various experiments were performed to explore the effects of major process parameters for both the abrasive feed rate and the suction pressure occurring inside the mixing chamber when the abrasives are inhaled. Experimental results reveal that the abrasive feed rate is affected by geometry parameters (abrasive pipe height, length, and tortuosity), abrasive parameters (abrasive particle size), and jet energy parameters (water pressure and water flow rate). In addition, the relation between the cutting performance and the abrasive feed rate was discussed on the basis of the results of an experimental study. The cutting performance can be maximized when the abrasive feed rate is controlled appropriately via careful management of major process parameters.

• Atmosphere
• /
• v.27 no.1
• /
• pp.41-54
• /
• 2017

Organic carbon (OC) and elemental carbon (EC) in $PM_{2.5}$ were measured using Sunset OC/EC Field Analyzer at Seoul Hwangsa Monitoring Center from March to April, 2016. The mean concentrations of OC and EC during the entire period were $4.4{\pm}2.0{\mu}gC\;m^{-3}$ and $1.4{\pm}0.6{\mu}gC\;m^{-3}$, respectively. OC/EC ratio was $3.4{\pm}1.0$. The average concentrations of $PM_{10}$ and $PM_{2.5}$ were $57.4{\pm}25.9$ and $39.7{\pm}19.8{\mu}g\;m^{-3}$, respectively, which were detected by an optical particle counter. The OC and EC peaks were observed in the morning, which were impacted by vehicle emission, however, their diurnal variations were not noticeable. This is determined to be contributed by the long-range transported OC or secondary formation via photochemical reaction by volatile organic compounds at afternoon. A conditional probability function (CPF) model was used to identify the local source of pollution. High concentrations of $PM_{10}$ and $PM_{2.5}$ were observed from the westerly wind, regardless of wind speed. When wind velocity was high, a mixing plume of dust and pollution during long-range transport from China in spring was observed. In contrast, pollution in low wind velocity was from local source, regardless of direction. To know the effect of long-range transport on pollution, a concentration weighted trajectory (CWT) model was analyzed based on a potential source contribution function (PSCF) model in which 75 percentiles high concentration was picked out for CWT analysis. $PM_{10}$, $PM_{2.5}$, OC, and EC were dominantly contributed from China in spring, and EC results were similar in both PSCF and CWT. In conclusion, Seoul air quality in spring was mainly affected by a mixture of local pollution and anthropogenic pollutants originated in China than the Asian dust.

• Asian-Australasian Journal of Animal Sciences
• /
• v.29 no.12
• /
• pp.1719-1724
• /
• 2016

The objective of this study was to determine the effects of physically effective neutral detergent fiber (peNDF) content in total mixed ration (TMR) on dry matter intake, digestibility, and chewing activity in fattening Hanwoo (Bos taurus coreanae) heifers. The experiment was designed as a replicated $3{\times}3$ Latin square using 12 heifers. Fattening heifers were offered one of three diets [high (T1), medium (T2), and low (T3) peNDF] obtained by different mixing times (3, 10, and 25 min) for the same TMR feed. The peNDF content of TMR was determined by multiplying the proportion of dry matter retained by a 1.18 mm-screen in a Penn State Particle Separator by the dietary NDF content. The $peNDF_{1.18}$ content was 30.36%, 29.20%, and 27.50% for the T1, T2, and T3 diets, respectively (p<0.05). Dry matter intake was not affected by peNDF content in TMR. Total weight gain in T1 group was significantly higher (p<0.05) than in T2 and T3 groups. However, weight gain did not differ between T2 and T3 groups. The feed conversion ratio decreased with an increase in the peNDF content (T1: 12.18, T2: 14.17, and T3: 14.01 g/g). An increase in the peNDF content of TMR was associated with a linear increase in the digestibility of dry matter, crude protein, crude fiber, neutral detergent fiber, and acid detergent fiber (p<0.05). Also, an increase in peNDF content of the TMR resulted in a linear increase in the number of chews in eating and ruminating (p<0.05), and consequently in the number of total chews (p<0.05). These results indicate that peNDF content affects digestibility and chewing activity. Consequently, the peNDF content of TMR should be considered for improving feed efficiency, digestibility, body weight gain, and performance in fattening heifers.

• Economic and Environmental Geology
• /
• v.43 no.2
• /
• pp.177-184
• /
• 2010

When cement grout is used for waterproofing of grounds, important roles are played by fluidity, particle size and bleeding. The most important element which determines their characteristics is the water/cement ratio of grout. Moreover in order to improve the efficiency of soil permeation, micro cement with a smaller average diameter is used in addition to ordinary portland cement. Besides the mixing ratio and cement diameter, the condition of ground is also of fundamental importance in the efficiency of permeation. In order to evaluate grout in terms of permeation ability into ground, we need a field test of grounting, which is cost and time consuming. In this paper we present a laboratory test method in which the suitability and efficiency of grouts are simply and more practically tested. In Korea neither a test standard nor devices are available to simulate grouting in a laboratory. We devised a grout injection equipment in which grouting was reproduced in the same condition with different materials, and suggested a standard for the production of specimens. Our tests revealed that the efficiency of injection increases with the water/cement ratio. We also found that more efficiently injected is the grout with the order of decreasing size; MS8000, micro cement, and ultra fine cements, and colloidal super cement.

• Journal of the Korean Wood Science and Technology
• /
• v.35 no.6
• /
• pp.91-99
• /
• 2007

Activities of the extracellular enzyme from Fomitopsis palustris, a brown-rot fungi, and by which crystallinity changes of cellulose in the various softwoods, such as Larix leptolepsis, Finns rigida, Finns koraiensis and Finns densiflora by liquid culture, were investigated. Activity of Cellobiohydrolase (CBH) from F. palustris was detected in the every test softwoods culture, showing activities of the Endoglucanase (EG), $\beta$-glucosidase (BGL) and $\beta$-1,4-xylosidase (BXL). It was shown high enzyme activities in the sapwood culture than heartwood of the same wood species, However, the enzyme activities in most of test wood cultures increased with longer incubation time, indicating a possibility of intermix sapwood and heartwood for degradation process by enzyme. Also it was shown that protein patterns of the extracellular enzyme from F. palustris in wood particle substrate of the several domestic softwoods were similar with each other wood species, which suggested the possibility of mixing all softwoods in saccharification by enzyme from F. palustris. Crystallinity reduction value of cellulose by F. palustris was 4.2~20.4% in 4 weeks cultivation, 12.9~28.9% in 8 weeks.

• Korean Journal of Microbiology
• /
• v.30 no.5
• /
• pp.383-390
• /
• 1992

In the periods of July 31 to August 10. 1988 and March 9 to 13. 1989. sediment samples were collected from the South Sea stations (010] to 092]) located in the area from $N 32^{\circ}$/30' to $34^{\circ}$/30', of latitude and from E $123^{\circ}$ 30' to $128^{\circ}$30' of longitude. These samples were analyzed for the number of total heterotrophic bacteria and extracellular digesting enzyme activities. In the 1989 spring period the number of heterotrophic bacteria in the sediment surface layer was increased more than 100 times at the maximum compared to that in the 1988 summer period. The proportion of fresh water bacteria to total heterotrophic bacteria was also higher in the spring period than the summer period. The extracellular digesting enzyme activities were higher in spring season than summer. Although the water content of sediment in the spring period was lower than that the summer period. the ash weight indicating organic material content was higher. These results means that the diameters of sediment particles were larger in spring than summer but the input of organic material into the sediment was greater. Based on these results bacterial distributions in the sediment layer of South Sea depend greatly on the season due to the effect of fresh water. During the spring season plankton could grow extensively owing to the inorganic nutrients input by the vertical mixing in the water column, then be precipitated into the sediment. Organic nutrients supplied from enzymatic degradation of polymeric particle from plankton can increase the bacterial number, too.