• Korean Journal of Agricultural Science
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• v.31 no.1
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• pp.53-75
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• 2004

This study is aimed at identifying the national economic value of the irrigation facilities by reviewing the existing papers on economic values of the irrigation facilities and presenting current status of dual O & M problems of the irrigation facilities. This study suggested the unified O & M system rather than continuing the existing dual O & M system of irrigation facilities based on the surveyed results of the activities of irrigation fraternities in Chungnam Province. The findings and proposals for the successful unified and mono O & M system of the irrigation facilities are as follows: (1) Total number of irrigation facilities in the nation accounts for 67,582, while the total length of irrigation and drainage canals amounted to about 174,259km. On account of the total length of structural canals was estimated at 31%, much losses of water and much O & M costs have been inevitable for the full irrigation rice culture. In spite of the past heavy investment for irrigation facilities, the ratio of rain-fed and partially irrigated paddy fields accounts for 23% in 2003. Both Korea Agricultural and Rural Infrastructure Corporation (KARICO) and the city and Gun Governments have managed the irrigation facilities separately by irrigation fraternities. The KARICO have commanded 59% of irrigation paddy area with 18% of the total irrigation facilities, while the city and Gun governments covered 41% of irrigation paddy area with 82% of the existing number of irrigation facilities representing small and medium scale. (2) The 1999 demand prices of irrigation water per ton expressed in 2000 constant market price was estimated at 388 won, the supply price was amounted to 184 won per ton. Considering the supply and demand curve of the irrigation water, the existing irrigation facilities could not satisfy the demand of irrigation water. (3) In 1999, total present added value of the irrigation facilities during the economic life accounted for 48 trillion won, while total supply cost was 44.7 trillion won. The marginal benefit and cost ratio of irrigation water was 1.08. (4) The total O & M cost per year amounting to 681.1 billion won have been required to maintain and repair the existing irrigation facilities in Korea. For the successful unified O & M of irrigation facilities covering whole irrigated paddy field in Korea, 950 billion won of O & M costs are required to keep up the marginal benefit of irrigation water as 2,800 billion won per year. The total O & M cost as 950 billion won should be allocated 40%, 380 billion won for O & M costs of irrigation facilities and 60%, 570 billion won for improvement of irrigation facilities. (5) The study investigated and reviewed the present O & M status of the irrigation facilities by small and medium irrigation fraternities. Most of the farmers belong to the irrigation fraternities preferred not only unified O & M but also KARICO take-over of the whole O & M activities of the irrigation facilities. The prevailing O & M cost per 10a expended by the Corporation was amounted to 104,890 won, while that of city and Gun governments was only amounted to 4,600 won per 10a. regarding the small amount of O & M cost expended by city and Gun governments, it is evident that the existing irrigation system have been managed ineffectively and deteriorated the facilities comparing that of KARICO. In conclusion, the Government could not satisfied the demand of irrigation water by suppling water with existing irrigation facilities. Therefore new additional investment and financial support for irrigation water development should be made to convert rain-fed and partially irrigated paddy fields into fully irrigated ones. The operation and maintenance cost should be supported to keep the marginal values of rice production of existing irrigation facilities in the national economy and to modernize the obsolete irrigation facilities. By unifying the existing dual O & M systems, all the farmers belong to the irrigated paddy fields have to be equally benefited and could be increased their farm income and be stabilized their rural lives.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.4
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• pp.346-353
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• 2011

Purpose: The peri-implant soft tissue is remodeled by the initial marginal bone resorption affecting the prognosis and esthetic result of treatment. Thus various designs on implant neck design are studied to preserve peri-implant bone. The purpose of this study is to review on the causes of initial marginal bone resorption, the configuration of peri-implant soft tissue, and the implant crestal module favorable in preserving peri-implant tissue. Materials and methods: The studies on the causes of initial marginal bone resorption and the implant crestal modules are researched and reviewed using Pubmed database. The implant crestal modules including one piece and two-piece implant, internal and external hex abutment, taper and butt joint connection, scalloped design abutment, and platform switching concept are reviewed. Results: A number of clinical and experimental studies preferred one piece implant to two-piece in preserving initial peri-implant tissue. For two piece implants, internal hex abutment and taper joint connection appear more favorable than external hex abutment and butt joint connection relatively. Controversial issues still exist on scalloped design requiring more studies on it. Although the rationale is not certain, the concept of platform switching seems favorable in preserving initial peri-implant tissue based on clinical and experimental studies. Conclusion: Each implant crestal module contains its own advantages and disadvantages with various controversial issues. In the aspect of preservation of initial peri-implant tissue, however, one-piece implant seems beneficial. In cases when two-piece implant is more appropriate due to prosthodontic concerns or any other problems, the application of platform switching concept, internal connection abutment, and taper joint connection may be favorable for the preservation of peri-implant tissues.

• Journal of the korean society of oceanography
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• v.31 no.4
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• pp.155-163
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• 1996

CREAMS (Circulation Research of the East Asian Marginal Seas) is an international research program, which began in 1993 in order to understand the water mass structure and circulation in the East Sea. Since the beginning of CREAMS, there have been four cruises in the summer and two in the winter, covering most parts of the East Sea for the first time in more than 60 years since the historical survey reported by Uda (1934). CREAMS investigations have provided many new insights into the various aspects of oceanographic problems in the East Sea such as water masses, deep sea currents and circulation, eddies, particle fluxes and so on. In this paper, we briefly review understandings before CREAMS and summarize initial new findings from CREAMS expeditions in terms of water masses and currents.

• Geomechanics and Engineering
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• v.13 no.1
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• pp.25-41
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• 2017

In recent years, the amount of sludge ash (SA) has considerably increased due to rapid urbanization and population growth. In addition, its storage in landfills induces environmental pollution and health problems. Therefore, its disposal in an environmentally friendly way has become more important. The main goal of this study is to investigate the reusability of sludge ash as an additive with polypropylene fiber (PF) to stabilize marginal sand based on the compressive strength performances from UCS tests. For this purpose, a series of UCS tests was conducted. Throughout the experimental study, the used inclusion rates were 10, 15, 20 and 30% for sludge ash and 0, 0.5 and 1% for polypropylene fiber by total dry weight of the sand+sludge ash mixture and the prepared samples were cured for 7 and 14 days prior to the testing. Freezing and thawing resistance of the mixture including 10% sludge ash and 0, 0.5 and 1% polypropylene fiber was also examined. On the basis of UCS testing results, it is said that sludge ash inclusion remarkably enhances UCS performance of sand. Moreover, the addition of polypropylene fiber to the admixtures including sand and sludge ash significantly improves their stress-strain characteristics and post-peak strength loss as well as UCS. As a result of this paper, it is suggested that sludge ash be successfully reused with polypropylene fiber for stabilizing sand in soil stabilization applications. It is also believed that the findings of this study will contribute to some environmental concerns such as the disposal problem of sludge ash, recycling, sustainability, environmental pollution, etc. as well as the cost of an engineering project.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.34 no.3
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• pp.186-199
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• 2012

Purpose: Single implants, of which screw loosening has been observed frequently, presents problems such as fixtures fractures, marginal bone loss, and inflammation of the soft tissue around the implant. However, the single implant is more conservative, cost effective, and predictable compared to the 3 unit bridge with respect to the long-term outcome. This study evaluated the survival rate as well as future methods aimed at increasing the survival rate in single implants in posterior teeth. Methods: Among the implants placed in the Dankook University Dental Hospital department of Oral & Maxillofacial surgery from January 2001 to June 2008, 599 implants placed in the maxillar and mandibular posterior were evaluated retrospectively. Survival rates were investigated according to implant location, cause of tooth loss, gender, age, general disease, fixture diameter and length, surface texture, implant type and shape, presence of bone graft, surgery stage, surgeons, bone quality and opposite teeth. Results: Out of 599 single implants in posterior teeth, 580 implants survived and the survival rate was 96.8%. The difference in survival rate was statistically significant according to the implant location. The survival rate was low (84.2%) in implants exhibiting a wide diameter (${\geq}5.1mm$) and the surface treated by the acid etching group demonstrated a significantly lower survival rate (91.1%). One stage surgical procedure, which implemented a relatively better bone quality survival rate (100%), was higher than the two stage surgical procedure (96.1%). The survival rate of type IV bone quality (75%) was significantly lower than the other bone quality. Conclusion: Single posterior teeth implant treatments should use an improved surface finishing fixture as well as careful and safe procedures when performing implant surgery in the maxilla premolar and molar regions since bone quality is poor.

• Journal of Korea Water Resources Association
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• v.42 no.4
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• pp.281-295
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• 2009

This study estimates the value of irrigation water in Korea using an economic programming model that is constructed with all the resource endowment constraints, technology restrictions and policy variables. The variability and uncertainty of water resource endowment are incorporated into the model through the chance-constrained technique. Solving the profit maximization problems with gradually reduced water endowments, we derive a series of shadow values of irrigation water. It has been found that uncertainty in water supply raises the damage from water loss, and the marginal damage increases in water loss.

• The Journal of the Petrological Society of Korea
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• v.11 no.3_4
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• pp.121-137
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• 2002

Metamorphic evolution of the Ogcheon metamorphic belt has been studied by many investigators for the past few decades. P-T conditions of the Ogcheon metamorphic belt were estimated as 4.2-9.4 kbar and $490-630^{\circ}C$, corresponding to the medium-pressure type. In addition, the clockwise P-T-t path suggests a crustal-thickening event in association with the formation of thrust nappes. However, some details on deformation and orogeny of the Ogcheon metamorphic belt have been ambiguous yet. Although the metamorphic age has been also equivocal, recent isotopic studies strongly suggest that the peak metamorphism in the Ogcheon metamorphic belt has occurred at ca. 300-280 Ma between Late Carboniferous and Early Permian. It is thus inferred that the Ogcheon metamorphic belt and the Taebaegsan basin have evolved as separate terranes and that both were sutured at ca. 250-220 Ma. These results are partly in contrast with those of previous workers and require a revised framework for tectonic evolution of the Ogcheon belt. In addition, it is likely that the Ogcheon belt is correlative with the Hida marginal belt and the Hida metamorphic belt.

• Archives of Plastic Surgery
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• v.33 no.6
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• pp.711-714
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• 2006

Purpose: Contralateral reduction mammaplasty at the time of breast reconstruction using autogenous tissue gives aesthetically improved results in the patients with mammary hypertrophy or ptosis. It also reduces required flap size for reconstruction and permits discarding zones of poor perfusion, decreasing flap size-related problems such as partial flap loss or fat necrosis. Considering the high rate of bilaterality of breast cancer, it also provides a good opportunity for exploration and occult cancer diagnosis in such high risk group patients. Methods: We retrospectively reviewed 45 consecutive patients who underwent simultaneous breast reconstruction and contralateral reduction mammaplasty was performed about surgical technique, pathologic diagnosis, and subsequent treatment. Results: Three occult breast cancers were found in 45 patients(6.7%); one was microinvasive, and the other two were invasive carcinomas and their mean diameter was 1.2 cm. One patient underwent subsequent breast conserving mastectomy, adjuvant radiation and chemotherapy. The others underwent only radiation and hormone therapy. They were followed up for 10 to 42 months without evidence of recurrence or metastasis. Conclusion: Occult breast cancer diagnosed in reduction mammaplasty specimen will lead to good prognosis due to its early detection. Treatment options depend on pathologic finding, stage, marginal status, and the timing of diagnosis. We recommend adequate markings for orientation and margins, excision with sufficient margin, and confirmation by frozen biopsy for suspected lesions.

• Journal of The Korean Society of Agricultural Engineers
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• v.58 no.6
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• pp.9-21
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• 2016

Agricultural reservoirs in Korea have been recognized as an emerging resource for recreational and cultural activities for residents. However, most of the reservoirs are eutrophic and showing high level of contamination with nuisance algal bloom and offensive odor during the summer. For better management and restoration of the reservoirs' water quality, scientific modeling approaches could be used to diagnose the problems and evaluate the efficacy of alternative control measures. The objectives of this study were to validate the performance of a three-dimensional (3D) hydrodynamic and water quality model (Environmental Fluid Dynamics Code, EFDC) for a eutrophic agricultural reservoir and assess the effect of bypassing of the effluent from a wastewater treatment plant on the reservoir water quality. The 3D model successfully simulated the temporal variations of water temperature, DO, TOC, nitrogen and phosphorus species and Chl-a observed in 2014 and also captured their spatial heterogeneity in the reservoir. The simulation results indicated that the point source bypassing may reduce the T-N and T-P concentrations of the reservoir by 6.6 ~ 8.2 %, and 1.7 ~ 16.8 %, respectively. The bypassing, however, showed a marginal effect on the control of TOC due to the increased algal biomass associated with the increased water retention time after bypassing as well as the lower TOC level of the effluent compared to the ambient reservoir water.

• Journal of the Korean Society for Railway
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• v.10 no.6
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• pp.742-750
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• 2007

This paper presents a mathematical model for a double-fleet operation in Korean high speed rail (HSR). KORAIL has a plan to launch new HSR units in 2010, which are composed of 10 railcars. The double-fleet operation assigns a single-unit or two-unit fleet to a segment, accommodating demand fluctuation. The proposed model assumes stochastic demand and uses chance-constrained constraints to assure a preset service level. It can be used in the tactical planning stage of the rail management as it includes several real-world conditions, such as the capacities of the infra-structures and operational procedures. In the solution approach, the expected revenue in the objective function is linearized by using expected marginal revenue, and the chance-constrained constraints are linearized by assuming that demands are normally distributed. Subsequently, the model can be solved by a mixed-integer linear programming solver fur small size problems. The test results of the model applied to Friday morning train schedules for one month sample data from KTX operation in 2004 shows that the proposed model could be utilized to determine the effectiveness of double-fleet operation, which could significantly increase the expected profit and seat utilization rates when properly maneuvered.