• Asia pacific journal of information systems
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• v.20 no.1
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• pp.127-140
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• 2010

The benefit that a consumer derives from the use of a good often depends on the number of other consumers purchasing the same goods or other compatible items. This property, which is known as network externality, is significant in many IT related industries. Over the past few decades, network externalities have been recognized in the context of physical networks such as the telephone and railroad industries. Today, as many products are provided as a form of system that consists of compatible components, the appreciation of network externality is becoming increasingly important. Network externalities have been extensively studied among economists who have been seeking to explain new phenomena resulting from rapid advancements in ICT (Information and Communication Technology). As a result of these efforts, a new body of theories for 'New Economy' has been proposed. The theoretical bottom-line argument of such theories is that technologies subject to network effects exhibit multiple equilibriums and will finally lock into a monopoly with one standard cornering the entire market. They emphasize that such "tippiness" is a typical characteristic in such networked markets, describing that multiple incompatible technologies rarely coexist and that the switch to a single, leading standard occurs suddenly. Moreover, it is argued that this standardization process is path dependent, and the ultimate outcome is unpredictable. With incomplete information about other actors' preferences, there can be excess inertia, as consumers only moderately favor the change, and hence are themselves insufficiently motivated to start the bandwagon rolling, but would get on it once it did start to roll. This startup problem can prevent the adoption of any standard at all, even if it is preferred by everyone. Conversely, excess momentum is another possible outcome, for example, if a sponsoring firm uses low prices during early periods of diffusion. The aim of this paper is to analyze the dynamics of the adoption process in markets exhibiting network effects by focusing on two factors; switching and agent heterogeneity. Switching is an important factor that should be considered in analyzing the adoption process. An agent's switching invokes switching by other adopters, which brings about a positive feedback process that can significantly complicate the adoption process. Agent heterogeneity also plays a important role in shaping the early development of the adoption process, which has a significant impact on the later development of the process. The effects of these two factors are analyzed by developing an agent-based simulation model. ABM is a computer-based simulation methodology that can offer many advantages over traditional analytical approaches. The model is designed such that agents have diverse preferences regarding technology and are allowed to switch their previous choice. The simulation results showed that the adoption processes in a market exhibiting networks effects are significantly affected by the distribution of agents and the occurrence of switching. In particular, it is found that both weak heterogeneity and strong network effects cause agents to start to switch early and this plays a role of expediting the emergence of 'lock-in.' When network effects are strong, agents are easily affected by changes in early market shares. This causes agents to switch earlier and in turn speeds up the market's tipping. The same effect is found in the case of highly homogeneous agents. When agents are highly homogeneous, the market starts to tip toward one technology rapidly, and its choice is not always consistent with the populations' initial inclination. Increased volatility and faster lock-in increase the possibility that the market will reach an unexpected outcome. The primary contribution of this study is the elucidation of the role of parameters characterizing the market in the development of the lock-in process, and identification of conditions where such unexpected outcomes happen.

• Korean Journal of Ecology and Environment
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• v.49 no.4
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• pp.354-374
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• 2016

This study explored spatiotemporal variability of water quality in correspondence with hydrometeorological factors in the five stations of Paldang Reservoir located in the Han River during 4 years from May 2012 to December 2015. Variability of basic water quality factors were largely related with seasonal fluctuations of hydrology. Temperature stratification occurred in the deep dam station, and prolonged hypoxia was observed during the draught year. Nitrogen nutrients were increased with decreasing inflow in which changing pattern of $NH_4$ reversed to $NO_3$ by the effect of treated wastewater effluent. Phosphorus increase was manifest during the period of high inflow or severe drought. Chl-a variation was reversely related with both flow change and AGP(algal growth potential) variations. Our study demonstrated that water quality variability in Paldang Reservoir was largely attributed to both natural and operational changes of inflow and outflow (including water intake) based on major pollution source of the treated wastewater (total amount of $472{\times}10^3m^3d^{-1}$) entering to the water system from watershed. In the process of water quality variability, meteorological (e.g., flood, typhoon, abnormal rainfall, scorching heat of summer) and hydrological factors (inflow and discharge) were likely to work dynamically with nutrients pulse, dilution, absorption, concentration and sedimentation. We underline comprehensive limnological study related to hydro-meteorolology to understand short- and long-term water quality variability in river-type large reservoir and suggest the necessity of P-free wastewater treatment for the effective measure of reducing pollution level of Paldang drinking water resource.

• Journal of The Korean Society of Grassland and Forage Science
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• v.36 no.2
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• pp.109-114
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• 2016

This study was conducted to determine grazing intensity of growing Korean native goats (Capra hircus coreanae) on mountainous pasture. It was carried out to obtain basic information for improvement of mountainous pasture management and establishing feeding system of Korean native goats. Castrated, male goats (n=10) with average initial body weight (BW) of $23.33{\pm}2.15kg$ and an average age of 4 months were used in this study. Grazing goats were supplemented by concentrates with 1.0% of BW. The crude protein content of forage was the highest in October ($22.71{\pm}0.25%$) and there were significantly differences (p<0.05) in monthly comparison. The forage productivity of pasture was the highest from May to June ($1718.7{\pm}207.5{\sim}1672.0{\pm}422.8kg/ha$ but it was decreased in July ($1356.0{\pm}103.8kg/ha$) because of drought and summer depression. Average daily gains (ADG) of goats were the highest in June ($99.5{\pm}6.4d/g$). Grazing intensity was calculated by forage productivity and dry matter intake (DMI) and was the highest in May (65 head/ha). As shown in the results of this research, grazing intensity was suggested to average 39 head/ha from May to October. It is desirable that adequate grazing intensity was maintained by adjusting supplemental feed.

• Journal of Food Hygiene and Safety
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• v.27 no.4
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• pp.366-374
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• 2012

Recently pathogenic E. coli is one of the main foodborne pathogens resulting in many patients in Korea. To understand the characteristics of pathogenic E. coli outbreaks in Korea, the epidemiological investigation reports of pathogenic E. coli outbreak in 2009 (41 reports) and in 2010 (27 reports) were collected in the web site of the Korea Centers for Disease Control and Prevention, reviewed and analysed in this study. The main places of the pathogenic E. coli outbreaks were food catering service area (64.8%) and restaurants (25.0%). The main type of the pathogens were EPEC (44.7%) and ETEC (34.2%). EAEC and EHEC was responsible for 10.5 and 9.2%, respectively. Eight of 68 outbreak cases were caused by more than 2 types of pathogenic E. coli which implicates the complicated contamination pathways of pathogenic E. coli. The incidence rate of pathogenic E. coli was $33.6{\pm}30.5%$ and the main symptoms were diarrhea, stomach ache, nausea, vomiting, and fever etc. The two identified food sources were identified as frozen hamburger pattie and squid-vegetable mixture. To improve the food source identification by epidemiological investigation, food poisoning notification to the agency should not be delayed, whole food items attributed the outbreak should be collected and detection method of the various pathogenic E. coli in food has to be improved. In conclusion, the characteristics between the EHEC outbreaks in the western countries and the EPEC or ETEC outbreaks in Korea needs to be distinguished to prepare food safety management plan. In addition, the development of the trace back system to find the contamination pathway with the improved detection method in food and systemic and cooperative support by the related agencies are necessary.

• Journal of Food Hygiene and Safety
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• v.29 no.4
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• pp.260-267
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• 2014

To evaluate microbiological and aflatoxin safety on traditional dried persimmon, a total of 315 samples were collected from 105 farms. The collected samples were assessed on aflatoxin and microorganisms (Aerobic plate count, coliform count, Escherichia coli, Escherichia coli O157:H7, Salmonella spp., Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus). The the APC of sliced dried persimmon, dried persimmon, and semi dried persimmon were $3.93{\pm}0.96$, $2.12{\pm}0.93$, and $1.50{\pm}1.08{\log}\;CFU/g$, respectively. S. aureus was detected in 40.0% of sliced dried persimmon, 29.5% of dried persimmon, and 23.5% of semi dried persimmon. E. coli recovered from dried persimmon and semi dried persimmon was 6.6%, and 2.9%, respectively. However, E. coli O157:H7, Salmonella spp., and L. monocytogenes were not detected. According to the result of aflatoxin by ELISA and UPLC, aflatoxin was not detected in any sample. These data suggested that safety management system should be introduce to the farms producing traditional dried persimmon to enhance the safety of traditional dried persimmon.

• Korean Journal of Food Science and Technology
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• v.38 no.1
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• pp.104-108
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• 2006

Water extracts of Jehotang were evaluated for their growth-promoting effects on Bifidobacterium longum, Lactobacillus sp., L. acidophilus, and Clostridium perfringens. Addition of Jehotang water extract to modified EG media at 0.1 mg/mL increased growths of B. longum, Lactobacillus sp., and L. acidophilus, with 1.8-fold increase in growth of L. acidophilus compared to that of control. Studies on these strains by agar diffusion method showed Lactobacillus sp. and L. acidophilus were activated by addition of Jehotang extract at 10 mg/disc. Proliferation responses of mice splenocytes and Peyer's patch cells to ConA by LPS-stimulation at 500 mg/kg B.W./day Jehotang extract were investigated in vitro. Upon treatment of 1 mg/mL Jehotang water extract to mice, proliferations of splenocytes and Peyer's patch cells increased 1.4- and 1.6-fold compared to control, respectively. In mice administered Jehotang extract, production of intestinal secretory IgA (sIgA) increased 2.4-fold compared to control. These results indicate water extract of Jehotang stimulated intestinal immune system of mice. In mice treated with Jehotang extract, production of lymphocytes was 4% lower, whereas those of granulocytes and platelets were 4% and slightly higher than control, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4346-4353
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• 2010

The purpose of this study was to estimate the cervical range of motion and the effects of massage and static stretching in their 20s of normal adult. One hundred participants(massage=50, stretching=50) with no musculoskeletal and nervous system problems volunteered for this study. Massage and static stretching were applied to sternocleidomstoid, scalenes, trapezius, semispinalis, splenius, suboccipital, multifidi and rotatores. Both groups received intervention for 3 times in a week. The time the intervention was applied was for 10minutes. Effleurage, petrissage and stripping technique was applied to massage group and static stretching technique was applied to stretching group. The cervical range of motion (CROM) instrument was used to measure eight cervical motions (suboccipital flexion, suboccipital extension, neck flexion and extension, and left and right lateral flexion, left and right rotation). As a result of making a statistical analysis of the data, the following findings were given: First, normal cervical range of motion revealed; suboccipital flexion($2.39^{\circ}$) and extension($38.36^{\circ}$), flexion($54.11^{\circ}$) and extension($69.39^{\circ}$), lateral flexion on left($43.50^{\circ}$) and right($41.28^{\circ}$), rotation on left($66.39^{\circ}$) and right($65.94^{\circ}$) in male and suboccipital flexion($5.14^{\circ}$) and extension($36.47^{\circ}$), flexion($55.92^{\circ}$) and extension($71.22^{\circ}$), lateral flexion on left($43.34^{\circ}$) and right($41.06^{\circ}$), rotation on left($69.38^{\circ}$) and right($68.63^{\circ}$) in female. Second, women had greater range of motions than men in suboccipital flexion, left and right rotation(p<0.05). Third, it showed significantly increasing cervical range of motion in all directions within groups following treatments but not between groups(p<0.05). Our results suggest that massage and static stretching are an appropriate intervention to increase cervical range of motion by muscle relaxation and stretching and may be provided a basis for future studies investigating the cervical range of motion.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.31 no.4
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• pp.95-112
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• 2013

Jangchungdan Park is now perceived as a mere park at the foot of Namsan mountain, but originally it was created to commemorate soldiers of Korean Empire on a site which name was Namsoyeong(南小營) during Joseon Dynasty. During the period of Japanese colonial rule, it was transformed into a park due to the rapidly changing circumstances, so the components expressing the validity of the colonial rule were introduced into the park. This paper examines the time sequential changes of Jangchungdan Park during the period of Japanese colonial rule, and the conclusions can be summarized as given below. Firstly, the park originally was a space to commemorate the soldiers who fought for the Korean Empire. It was built on formerly restricted area at the foot of Namsan Mountain in 1900, and it was arranged putting the ceremonial shrine Dansa (壇祠) as a central building and the annexes in the surroundings of it. The memorial ceremonies were held regularly in spring and autumn until 1909. Secondly, it became a city park for citizens of Gyeongseong-bu(the name of Seoul under the Japanese colonial rule). The authorities of Gyeongseong-bu reorganized Jangchungdan as a park in 1919, prohibited the performance of memorial ceremonies, and the existing buildings except the ceremonial shrine Dansa began to be used as park management facilities. Resting areas and amenities were supplemented for the usage of people from various backgrounds, and the large scale planting of cherry trees made the park a famous place to enjoy cherry-blossoms and other flowers in spring. Thirdly, it was reconstructed as a space to honor the influential personalities of Japanese colonial system. In 1932, Bankmun temple (博文寺) to commemorate Ito Hirobumi was constructed at a location that made it possible for a number of people to overlook Jangchungdan area. During that time, the buildings of traditional Joseon architecture were removed and reconstructed to serve as annexes to Bankmun temple. Due to the strategy to make Jangchungdan park a tourist attraction, Bankmun temple was included into the Gyeongseong sightseeing course, since the wide panorama of Jangchungdan Park and the whole city of Gyeongseong was opening from the temple. Various different components were introduced into Jangchungdan Park due to the rapidly changing circumstances; therefore the nature of the park was either altered or reproduced. Hopefully, the park rearrangement works will be executed paying respects to the memories of the past hereafter.

• Journal of Nutrition and Health
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• v.45 no.5
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• pp.489-499
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• 2012

The purpose of this study is to present basic data for an improvement of school foodservice by identifying students' preference level for school meal menu. A survey was carried out in two high schools provided with different types of consignment service in Daegu. Study subjects were consisted of 100 high school students from a school with on-site service and 119 students from the other school with external transporting service. More than half of students (54.2% of male and 68.3% of female) had normal weights while 13.5% of male and 30.1% of female students had underweights. 'Taste' and 'family' were the most important factors in meal choices and in eating habits, respectively of all the study subjects. Students who answered to have unbalanced diet (33.0%) were less in school with on-site service than those (56.1%) with external transporting service. Compared with on-site service, preferences for meats fruit and milk were higher and as cooking method, preference for blanching lower but stew, roasting and frying higher in the school with external transporting service. Various types of cooking methods and food materials were better accepted by the students with on-site service than those with external transporting service who preferred meat more exclusively regardless of cooking methods of main dish. Most kinds of kimchi was less liked by the students with external transporting service. It is concluded that low preference for most menus provided by the external transporting service is attributed by limitation in food materials, cooking methods and maintenance of food temperature. The limitation could be overcome by more intensive efforts for developing menus and using more efficient facilities and ultimately by changing meal service system in cooperation with school administrators, dietitians and parents.

• Journal of agriculture & life science
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• v.46 no.3
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• pp.97-108
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• 2012

Physical, chemical and biological hazards of strawberry farms at the cultivation stage were analyzed to establish the GAP(Good Agricultural Practice) system. Samples were collected from the plants, cultivation environments(water, soil and air), and personal hygiene (hand, glove, and clothes) of three strawberry farms(A, B, and C) and were tested to analyze physical, chemical (heavy metals and pesticide residues), and biological(sanitary indications and foodborne pathogens) hazards. Physical hazards such as insects and pieces of metal and glass were found in the strawberry farms and can be potential bow for strawberry products. Heavy metal and pesticide residue as chemical hazards were detected at levels lower than the regulation limit. In case of biological hazards, total bacteria and coliform were detected at the levels of 1.6~7.3 and 1.3~5.6 log CFU/g, leaf, mL, hand or $100cm^2$. However, Escherichia coli was not detected in all samples. Bacillus cereus and Staphylococuus aureus were detected at levels of ${\leq}$ 1.1~6.1 log CFU and 4.7~5.4 log CFU/g, mL, hand or $100cm^2$, whereas Listeria monocytogenes, E. coli O157 and Salmonella spp. were not detected in all samples. This study demonstrates that various harzards were in strawberry farms at the growing stage. Therefore proper management such as GAP is needed to prevent the occurrence of food poisoning associated with the hazards revealed in this study.