• Journal of Korean Society for Atmospheric Environment
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• v.31 no.2
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• pp.164-172
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• 2015

Seoul subway plays an important part for the public transportation service in Seoul metropolitan area. As the subway system is typically a closed environment, frequent air pollution problems occurred and passengers get malhealth impact. Especially particulate matters (PM) is well known as one of the major pollutants in subway environments. The purpose of this study was to compare the concentrations of $PM_{10}$ and $PM_{2.5}$ in the Seoul subway system and to provide fundamental data in order to management of subway system. $PM_{10}$ and $PM_{2.5}$ samples were collected in the M station platform and tunnel of Subway Line 4 in Seoul metropolitan and in an outdoor location close to it from Apr. 21, 2010~Oct. 27, 2013. The samples collected on teflon filters using $PM_{10}$ and $PM_{2.5}$ mini-volume portable samplers and PM sequential sampler. The PM contributions were $48.6{\mu}g/m^3$ (outdoor), $84.6{\mu}g/m^3$ (platform) and $204.8{\mu}g/m^3$ (tunnel) for $PM_{10}$, and $34.6{\mu}g/m^3$ (outdoor), $49.7{\mu}g/m^3$ (platform) and $83.1{\mu}g/m^3$ (tunnel) for $PM_{2.5}$. The $PM_{10}$ levels inside stations and outdoors are poorly correlated, indicating that $PM_{10}$ levels in the metro system are mainly influenced by internal sources. In this study, we compared PM concentrations before and after operation of ventilation and Electrostatic Precipitator (EP). Despite the increased PM concentration at outdoor, $PM_{10}$ concentration at platform and tunnel showed the 31.2% and 32.3% reduction efficiency after operation the reduction system. The overall results of this study suggest that the installation and operation of the ventilating system and EP should have served as one of the important components for maintaining the air quality in the subway system.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.23-32
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• 2016

A single particle crushing test was carried out for recycled aggregates from waste concrete while demolishing various structures. When the recycled aggregates were used for backfill or road subbase materials, load-displacement and crushing characteristics were analyzed. The recycled aggregates with hydrates and aggregates were sorted into 40 mm size (75-40 mm) and 20 mm size (40-20 mm). At initial loading, their irregular surface was closed to and then crushed by loading plate. Such first crushing stage was called 'Surface crushing'. Further loading, some hydrate was crushed and detached from aggregate, and such process repeated several times. This state is called 'hydrate crushing'. The final state is called 'aggregate crushing' in which aggregate crushed and following load suddenly dropped down. As the load increased, such crushing cycle is repeated several times. The shapes of aggregates are round or square, and triangle or long shaped. Depending on their shapes and surface conditions, they crushed in different ways. The 63% of aggregates showed more than 50% load reduction due to aggregate crushing. The 90% load reduction occurred at 15% of aggregates. The 40 mm aggregate crushed at maximum load between 3.05-4.38 kN and 70% of crushed aggregates were less than 20 mm.

• The korean journal of orthodontics
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• v.20 no.2
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• pp.363-379
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• 1990

The purpose of this study was to evaluate the effects of the mandibular retractive force on the mandibular condyle of growing dog. The experimental animals were six mongrel dogs of two-month old. Their deciduous dentition were completed. Two of them was used as control group, and experimental group was composed of remaining four. Head band and chin cup were made of cotton tape, and hooks are fabricated on the chin cup and had band for closed coil. Mandibular retractive force was 100g/side and chin cap appliance was used for 14 hours/day during night. Experimental group were sacrificed at 2, 4, 6, 8 weeks from beginning of the experiment. Right TMJ was prepared for histologic study and left TMJ was examined grossly for disc, fossa, and condyle. The conclusions are: 1. Two-month old control animal showed active cartilaginous growth on the mandibular condyle, therefore showed thick proliferative and hypertrophic zones. Remodeling process in the condyle head was observed in which there were bone resorption on the anterior surface and bone apposition on the posterior surface. 2. Four-month old control animal showed marked reduction of hypertrophic zone but the condylar bone remodeling was more pronounced. 3. In experimental group, there are marked reduction of hypertrophic zone at 4 weeks from beginning of experiment, and hypertrophic zone disappeared at posterior-superior portion of condyle in 6-week experimental animal. 8 week experimental animal showed slight recovery of hypertrophic zone. 4. In experimental group, bone deposition was increased at anterior surface of condyle, and bone resorption was increased at posterior surface of condyle. 5. In control group, the glenoid fossa and surrounding bone showed mainly bone apposition. But experimental group showed bone resorption at anterior surface of articular eminence and increased bone apposition at posterior surface of postglenoid spine. 6. No marked traumatic change was seen but 4 weeks and 8 weeks experimental animal showed flattening of posterior surperior condylar surface. Bone marrow of condyle showed minute focal bleeding in 2 weeks and 4 weeks experimental animal, and congestion and depression of hematopoietic bone marrow during all experimental period.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.4
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• pp.1740-1748
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• 2011

The purpose of this study was to investigate effects of the long-term high-frequency transcutaneous electrical nerve stimulation(TENS) on the spasticity and the balance in chronic stroke patients. Twenty-six subjects with spasticity over lower limbs were allocated randomly into two groups under standard rehabilitation: (1) TENS group, (2) placebo-TENS group. TENS stimulation was applied on the both the gastrocnemius for 30 minutes, 5 days a week for 4 weeks(100 Hz, 0.25 ms, 2 times sensory threshold). The Modified Ashworth Scale(MAS) and Hand-held manual muscle tester were used to assess the ankle plantarflexor spasticity. Balance function under three conditions was measured by using force-plate and the amount of postural sway was assessed; in (1) the condition of standing with eyes opened, (2) with eyes closed and (3) the condition of standing on unstable surface with eyes opened. Both groups showed significant improvement in spasticity and balance function after treatment for 4 weeks(p<.05). Especially, TENS group showed a significant reduction of spasticity compared to placebo-TENS group(p<.05). These results suggested that additional stimulation of a long-term high-frequency TENS to standard rehabilitation induced an improved balance function and a spasticity reduction. The long-term application of high-frequency TENS will be an effective intervention for reducing spasticity and increasing balance ability in the chronic stroke patients.

• Archives of Plastic Surgery
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• v.36 no.5
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• pp.623-628
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• 2009

Purpose: In cases where nasal fractures involve frontal process of maxilla or perpendicular plate of ethmoid, 4 - 5 days of nasal packing may not provide sufficient support for avoiding displacement after packing removal. Therefore a single Kirschner - wire(K - wire) is used as an internal splint when nasal fractures involve the above two areas. Methods: Thirty five patients during the last 3 practical years were treated with a K -wire pinning according to the anatomic locations of nasal fractures. We performed a retrospective study using 13 nasal fractures out of total 35 patients. Among 13 cases, 10 patients involved frontal process of maxilla, and 3 patients were diagnosed as bilateral nasal side wall fractures accompanied with fractures of perpendicular plate of ethmoid. One patient of the last three cases had been augmented with dorsal silicone implant long before the trauma. We analyzed the anteroposterior displacement of key stone area and the width between both lateral walls by comparing immediate postoperative radiographs with 2 month follow - ups. To reduce the errors, the same measurements were taken by two different inspectors, and the mean of each inspector's measurements was compared. Patient satisfaction was analyzed using a questionnaire regarding the esthetic and functional outcomes. Results: Ten patients underwent a longitudinal K - wire fixation in submucoperiosteal plane underneath the frontal process of maxilla. And three patients underwent a transverse K - wire fixation from the one side of lateral wall to the perpendicular plate of ethmoid and to the other side of lateral wall. The mean postoperative anteroposterior displacement of the key stone area measured by two inspectors were 1.84% and 3.06%; mean narrowing of bony pyramid were 1.33% and 1.48%, respectively. Subjective satisfaction scores regarding the esthetic appearance and the maintenance of nasal shape compared with immediate post - operative state with the long term ones were not different (p>0.05). Conclusion: K - wire pinning after closed reduction is a reliable and useful method for the treatment of nasal fractures involving frontal process of maxilla or perpendicular plate of ethmoid. This is because it achieves longer intranasal support after reduction. This method also leaves conspicuous external scar, and minimal soft - tissue injury.

• Journal of the Korean Society of Marine Environment & Safety
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• v.30 no.2
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• pp.165-175
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• 2024

Hydrogen is being touted as one of the energy sources to combat the climate change crisis. However, hydrogen can leak into enclosed spaces, rise to the ceiling, accumulate, and cause fires and explosions if it encounters an ignition source. In particular, ships that transport hydrogen or use it as a fuel comprise multiple enclosed spaces. Therefore, the dif usion characteristics within these spaces must be understood to ensure the safe use of hydrogen. The purpose of this study is to experimentally determine the diffusion characteristics of helium, which has similar properties to hydrogen, in a closed space on board a ship, and to determine the change in the oxygen concentration along the leakage direction as the air change per hour(ACH) increases to 25, 30, 35, 40, and 45 through CFD simulation. The study, results revealed that the oxygen concentration reduction rate was 2% for leakage in the -z direction and 1% for leakage in the +x and +z directions, and the ventilation time was 15 min 30 s for leakage in the -z direction, 7 min for leakage in the +x direction, and 9 min for leakage in the +z direction, showing that differences existed in the oxygen concentration and ventilation time depending on the leakage direction. In addition, no significant difference was observed in the rate of oxygen concentration reduction and ventilation time in all leakage directions from the ACH of 35 and above in the experimental space. Therefore, because the oxygen concentration and ventilation time were not improved by increasing the ACH, 35 was noted as the optimal ACH in this experimental environment.

• FLOWER RESEARCH JOURNAL
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• v.18 no.4
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• pp.238-243
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• 2010

This study was conducted to investigate effects of nutrient solution pH control agent and foliar spray of ethephon on the reduction of stem inside-cavity and improvement of flower quality in chrysanthemum 'Baekma'. Changes of pH in nutrient solution as affected by the kind of pH control agent showed more settled pattern in the plot of KOH treatment than in others. Plant growth and development such as cut flower length, leaf numbers, cut flower weight and petal number were the greatest in the plot of KOH. However, the size and area of stem cavity was large in KOH rather than $KHCO_3$. As changes in the absorbing patterns of mineral elements as affected by nutrient solution pH control agent in closed system, contents of total nitrate, phosphorus, potassium and calcium by $KHCO_3$ was absorbed into the plant less than KOH, so that it remained a lot of mineral element residues rather than KOH in closed system. Plant growth as affected by the foliar spray of ethephon showed growth retardation effect in the plot of solution diluted to 1 : 500 and growth promotion effect in the plot of solution diluted to 1 : 1,000 or 1 : 2,000. The number of petals was the best in the plot of foliar spray of ethephon solution diluted to 1 : 1,000 before flowering at 45 days showing 331 petals compared to control showing 302 petals. The size and area of stem cavity as affected the foliar spray of ethephon was smaller 1 mm and 7%, respectively, in the plot of solution diluted to 1 : 2,000 before flowering at 30 days than in control. Therefore, treating pH stabilization using KOH after floral initiation stage with the foliar spray of ethephon solution diluted to 1 : 2,000 before flowering at 30 days would help to reduce stem cavity size and improve flower quality in hydroponically grown chrysanthemum 'Baekma'.

• Journal of Bio-Environment Control
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• v.7 no.1
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• pp.43-54
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• 1998

This experiment was conducted to develop optimal nutrient solution for tomato plants, according to the plant growth stages in closed system. Perlite substrate was supplied with 1/2 and 1 strength of the solution of National Horticultural Research Station in Japan. Plants grew better and the nutrient_contents in the leaves were also proper in 1 strength. Based on these results, optimal nutrient solution in perlite was composed by n/w of 1 strength according to the plant growth rates ： N 13.5, P 3.3, K 7.0, Ca 7.0, Mg 3.5 me.L$^{-1}$ in seedling stage, N 14.2, P 3.3, K 8.0, Ca 7.5, Mg 4.0 me.L$^{-1}$ in vegetative stage and N 10.0, P 3.0, K 7.0, Ca 6.0, Mg 3.0 me.L$^{-1}$ in reproductive stage. To examine the suitability of the nutrient solution developed in this experiment, tomato plants were grown in rockwool and supplied with two different composition and concentration of nutrient solution composed by n/w of 1 strength in perlite (SCUT) and by Research Station for Greenhouse Vegetable and Floriculture on the Netherlands (PBG). PH and EC in SCUT were changed little in 1 strength but a significant change of PH was shown in 1/2 strength. Later, drained solutions in rockwool were also analyzed according to the Plant growth stages. Low concentrations of N and P in root zone were shown in early growth stage but N was increased in reproductive stage, while, K, Ca, Mg concentration was consistent through the whole growth stage. Considering these results, we found that the rebalance of N and P was needed, that is, reduction of N concentration in reproductive stage and increasing of P concentration in vegetative stage.

• KDI Journal of Economic Policy
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• v.14 no.2
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• pp.29-54
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• 1992

Recent studies on the economic effects of trade liberalization and economic integration have emphasized the significant gains associated with product differentiation and scale economies. Securing access to markets in other countries will make it possible to increase product variety and capture scale economies, thus, expanding the gains from trade. Liberalization is also expected to introduce foreign competition into the previously closed market. Concurrently, the liberalization will improve the competitive market environment for firms selling in the domestic market. Firms will be pressed to either exit or reduce cost. The output per firm, then, will increase due to the exit of rival firms, and the average total cost will decline due to the economies of scale. 'Rationalization' of the production process will eventually follow. This paper addresses the economic effects of (counterfactual) bilateral tariff elimination between Korea and Japan. It computationally assesses the gains from liberalization as well as the resource allocations and welfare effects associated with the tariff reduction. The endogenous determination of the key parameters distinguishes this paper from others. The firm's perceived elasticity of demand and elasticity of substitution in the present model are calibrated to be consistent with the base year data. Korea, Japan, and the rest of the world are modeled explicitly. The sectoral coverage of the model includes twenty-three tradable product categories based on three-digit SITC industries and seven nontradable categories based on one-digit SITC industries. Product categories are also classified into perfectly competitive and imperfectly competitive ones. In the imperfectly competitive industries, product differentiation exists at the firm level, while the perfectly competitive industries are characterized by national product differentiation. The simulation results of bilateral tariff reduction are reported. Tariff elimination tends to increase intra-industry trade flows so that the total amount of exports and imports of both countries expand. Yet, Japan is expected to increase the bilateral trade surplus in the wake of the mutual tariff reduction. Terms-of-trade for Korea will not change, while for Japan it will deteriorate. Equivalent variations reflecting the change in consumer surplus (welfare) will favor Korean consumers. Total output, however, will not change substantially, recording 0.5 and 0.6% for Japan and Korea, respectively. An interesting finding in the analysis is that the gains from increased competition and scale efficiency are not as prevailing as expected in theory.

• Journal of Bio-Environment Control
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• v.26 no.4
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• pp.393-401
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• 2017

The nitrate ($NO_3{^-}$) accumulation of hydroponically grown leafy vegetables may increase in the condition of a closed-type plant production system with low light intensity due to low activity of enzymes involved in nitrogen assimilation and the use of $NO_3-N$ as major nitrogen source. The objective of this study is to investigate the effects of light intensities, nutrient solution compositions and the time of nutrient solution removal before harvest on nitrate contents of hydroponically-grown lettuces in a closed plant production system. The reduction of nitrate contents in leafy lettuces 'Cheongchima' was higher in the treatments of 'TW' (nutrient solution removal) and '$(NH_4)_2CO_3$' (use of ammonium carbonate as nitrogen source) than those in other treatments, which significantly lowered fresh weight and leaf area of the plants. In the light intensity of $100{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, the nitrate content was effectively reduced without causing any growth retardation, by substitution of the nutrient solution composition that $NO_3-N$ was removed ('$NO_3-N$ removal' treatment) or the half strength of standard nutrient solution was applied ('1/2 S' treatment), for 7days before harvest. The effects of light intensity and the time of nutrient solution removal before harvest on growth and nitrate contents in leafy lettuces were investigated. The nitrate contents in leaves under the light condition of $300{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ before nutrient solution removal were lower than those of 100 or $200{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$. The removal of nutrient solution for 7 days before harvest quickly reduced the amount of nitrates in leaves in all the light intensities with a greater degree under the $300{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ of light condition, while the 7 days-removal with both 200 and $300{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ of light conditions caused decrease in 16~31% of leaf area and 20~35% of fresh weight, compared to the 3 days-removal treatment. The nitrate contents were greatly reduced from 3,018 to 1,035 in $200{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, and 2,021 to 480 ppm in the light condition of $300{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, with the nutrient solution removal for 3 days before harvest, without causing any deterioration in growth and product quality. The vitamin C contents in leaves were higher in the treatment of nutrient solution removal for both 3 and 5 days before harvest with the light condition of $300{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ than those in the light condition of 100 or $200{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$.