• Journal of Environmental Policy
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• v.6 no.1
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• pp.83-109
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• 2007

This study evaluates citizen's willingness-to-pay for the benefits from improved water quality of the Taehwa river in Ulsan, Korea, using a contingent valuation method with double-bounded dichotomous choice. The estimation results of the bivariate probit model shows the amounts of willingness-to-pay are monthly 3,458.5 Korean Won per household and yearly 14,760 million Korean Won for total households in Ulsan, Korea. These estimates are equivalent to the social values of improved water quality of the Taehwa river. This study also tests the inter-dependence between two answers, which may occur in the responses of the questions for the double-bounded dichotomous choice, and all the null hypotheses on the inter-dependence are rejected in this study.

• Journal of Applied Tourism Food and Beverage Management and Research
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• v.16 no.2
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• pp.33-56
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• 2005

The purpose of this study is to understand the critical role of customers' perceived service quality. in relationship marketing. This paper examined the relationships of service quality with customer satisfaction, and investigated the effects of trust and commitment. Data were collected from 242 people at hotel located in Taegu city. LISREL provided satisfactory model-fits in measurement model and structural equation model. The empirical results indicated that first, service quality takes strong effect on customer satisfaction and trust but not on commitment. Second, trust and commitment are importantly influenced by customer satisfaction. Third, service quality was found to indirectly contribute to trust and commitment. Finally, customer satisfaction is effective mediators linking service quality to trust and commitment. The effects of these variables on trust and commitment, which are based on social exchange theory, were empirically confirmed.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.4 s.316
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• pp.42-47
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• 2007

To reduce the chattering errors of reed switch sensors in the automatic remote measurement of water meter a reed switch sensor was analyzed and improved. The operation of reed switch sensors can be described as a mechanical contact switch by approximation of permanent magnet piece to generate an electrical pulse. The reed switch sensors are used mostly in measurement application to detect the rotational or translational displacement. To apply for water flow measurement devices, the reed switch sensors should keep high reliability. They are applied for the electronic digital type of water flow meters. The reed switch sensor is just mounted simply on the conventional mechanical type flow meter. A small magnet is attached on a pointer of the water meter counter rotor. Inside the reed sensor two steel leaf springs make mechanical contact and apart repeatedly as rotation of flow meter counter. The counting electrical contact pulses can be converted as the water flow amount. The MCU sends the digital flow rate data to the server using the wireless communication network. But the digital data is occurred difference or won by chattering noise. The reed switch sensor contains chattering error by it self at the force equivalent position. The vibrations such as passing vehicle near to the switch sensor installed location causes chattering. In order to reduce chattering error, most system uses just software methods, for example using filter algorithm and also statistical calibration methods. The chattering errors were reduced by changing leaf spring structure using mechanical characteristics.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2014.06a
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• pp.73-75
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• 2014

Marine transportation facility is public goods for the general public and their safety. The study used the Contingent Valuation Method (CVM), a method to estimate economic value of non-market goods, such as environmental goods. In order to analyze economic effects of marine accidents preventable by the VTS, the study estimated costs caused by marine accident cases. It conducted surveys with people and shipping companies in local areas where VTS is to be established in the future. According to a survey with people in areas where marine transportation control center is to be built (Tongyoung), the yearly benefit from building new VTS is estimated at KRW 11billion. If fees are paid in the form of income tax for five years from 2014, corresponding benefits during the same period will reach KRW 47.3 billion in current value. An analysis on economic validity of VTS establishment in Tongyong showed the B/C ration stood at 3.193, far higher than 1. The Net Present Value (NPV) was KRW 32.5 billion and the Internal Rate of Return (IRR) turned out to be 37.4% which was higher than social discount rates of 53.5%. On balance, the establishment has reasonable economic validity.

• Journal of Chest Surgery
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• v.43 no.6
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• pp.602-613
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• 2010

Background: As life expectancy has been increased, the cardiac valve disease has been increased. In past, mechanical valve for valve replacement surgery was used widely, but it has many weaknesses, such as hemorrhage, teratogenic effect caused by warfarin, acute mechanical failure, taking warfarin during life, etc. So, the tissue valve is used widely and researches for durability of tissue valve are in progress. Tissue valves being used are all imported in Korea, and there is a lack of information on its geometry and design. So, we studied the geometry of porcine aortic and pulmonary valve, and tried to suggest theoretical basis for making the aortic and pulmonary valve. Material and Method: We harvested aortic and pulmonary valves of 25 pigs and measured the geometry of valve at fresh and glutaraldehyde (GA) fixed state. In each group, we measured the diameter of the base, diameter of commissure, valve height, commissural height, etc. Also, for making implantable porcine and bovine pericardial valve, we designed the valve stent form, thickness, height, and leaflet size, form, thickness by different size of valve. Result: The aortic and pulmonary valve geometry and ratio were measured in each group. The right coronary cusp of aortic valve and right facing cusp of pulmonary valve was bigger than other cusps and non coronary cusp was smaller than others (RCC: NCC : LCC=1 : 0.88 : 1). Valve height was correlated to the leaflet size. We designed the outer diameter of stented porcine aortic valve from 19 mm to 33 mm and designed stent height and width, using previous measured ratio of each structure, stent thickness, working thickness (for making valve). Also, we designed the size of stent and form for stented bovine pericardial valve, considering diameter of valve, leaflet length, height and leaflet minimum coaptation area. Conclusion: By measuring of 25 pig's aortic and pulmonary valve geometry and ratio, we can make theoretical basis for making implantable stented porcine valve and bovine pericardial valve in various size. After making implantable valve using these data, it is necessary to do in vivo and in vitro researches, furthermore.

• Information Systems Review
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• v.23 no.3
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• pp.159-176
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• 2021

Obviating user churn is a prominent strategy to capitalize on online games, eluding the initial investments required for the development of another. Extant literature has examined factors that may induce user churn, mainly from perspectives of motives to play and game as a virtual society. However, such works largely dismiss the service aspects of online games. Dissatisfaction of user needs constitutes a crucial aspect for user churn, especially with online services where users expect a continuous improvement in service quality via software updates. Hence, we examine the relationship between a game's quality management and its user base. With text mining and survival analysis, we identify complaint factors that act as key predictors of user churn. Additionally, we find that enjoyment-related factors are greater threats to user base than usability-related ones. Furthermore, subsequent quasi-experiment shows that improvements in the complaint factors (i.e., via game patches) curb churn and foster user retention. Our results shed light on the responsive role of developers in retaining the user base of online games. Moreover, we provide practical insights for game operators, i.e., to identify and prioritize more perilous complaint factors in planning successive game patches.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.648-648
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• 2015

이 연구는 수자원 환경을 전반적으로 객관화, 계량화하는 새로운 방법이 성공적임을 소개한다. 기존의 계량법이 일강수량, 월 강수량, 년 강수량 등등, 단순한 수학적 합계에 치중한 결과 가중 중요한 강수의 시간 분포를 간과하였다. 이 단점을 해결하여, 1) 구체적으로 매 시간, 매일 남아 있다고 추정되는 물의 양 만을 합산하는 방법을 택했다. 시간적 감소함수를 이용하여, 강수 후 유출과 증발 등으로 사라지는 물의 양을 고려한 것이다. 2) 합산기간을 객관화하였다. 기본 합산 기간을 365일로 하고, 물 부족 또는 물 과잉이 지속될 경우는 지속되는 기간만큼, 합산기간을 늘이는 방법을 택했다. 따라서 다른 지수들이 임의로 3개월 또는 12개월 등등으로 기간을 결정하는 단점을 해결했다. 이렇게 계산되는 4차원 강수지수(4-Dimensional Rain Index, 4RI)는 1) 일별유효강수지수 (AWRI), 2) 일별가뭄지수(EDI), 3) 일별 홍수지수(FI), 4) 시간별 장기 물지수(LWI), 5) 시간별 단기 물지수(SWI) 등 5개가 기본지수이다. AWRI는 매일 남아 있는 물의 양이다. 이로 인해, 전 지구의 수자원과 재해위험의 시공간적 분포의 정량화 분석이 정밀해졌다. 지구상에서 물 집중이 가장 강한 곳은 캄보디아 내의 한 지점이며 시기는 7월 말이고, 가장 약한 곳은 사하라 사막의 한 지역임이 확인되었다. 또 한국에서 발생하는 갈수기와 풍수기가 정의되었고, 이들의 각 지역별 특성과 차이가 정량적으로 드러났다. 시간적 분포 또한 명확하게 드러나, 각종 저수지의 물 관리나 농?임산물의 생산관리에 획기적 전환점이 마련되었다. 각 국가별로, 각 지역별로 이런 분석은 향후도 무수히 시도되어야 할 것이다. EDI는 매일의 AWRI를 그 날짜의 평균치와 비교한 값이다. 장기가뭄 및 단기가뭄의 강도를 모두 가장 정밀하게 표현한다. FI는 일별로 홍수, 산사태, 침수, 토사 (이하 홍수 등이라 칭함)의 위험을, LWI는 장기 누적된 강수량에 의한 돌발적 홍수 등의 위험을, SWI는 단기 누적된 강수량에 의한 돌발적 홍수 등의 위험을 잘 반영한다. 이들은 모두 시간적으로 산발적인 호우에 의한 홍수 등의 위험을 한 개의 지수로 표현해 주는 장점이 있다. 강수 후 홍수가 발생하기 까지는 시간차이가 있기 때문에, 특히 호우 경보에는 SWI가, 홍수 경보에는 LWI가 아주 효과적이다. 결론적으로 5개의 4차원 강수지수는 물환경의 시공간적 분포진단과 예측, 그리고 조기경보에 혁명적 진화를 초래함이 확인되었다. 따라서 추후 모든 강수기후와 연관된 연구는 연강수량 등의 단순 합산보다, 4차원 강수지수를 먼저 사용하는 것이 바람직 할 것임이 제안되었다.

• Journal of Korea Spatial Information System Society
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• v.8 no.1 s.16
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• pp.107-118
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• 2006

In this paper, several network algorithms were tested to find an optimal one for telecommunication network design. Algorithms such as Dijkstra's shortest path algorithm, Ford-Bellman's shortest path algorithm, Prim's minimum spanning tree algorithm, and Kruscal's minimum spanning tree algorithm were reviewed and compared in terms of feasibility and resulted network construction cost. Then an optimal algorithm that is most suitable for telecommunication network design was selected. For more specific and quantitative analysis of the selected algorithm, it was implemented to a real telecommunication network construction site. The analyzed results showed that the suggested design method when compared with the conventional one, reduced the network construction cost considerably. The total network length estimated by the conventional method were 5267 meters while the suggested method resulted in 4807 meters. Thus the new method reduced the total network length by 8.7 percent which is equivalent to 97,469,000 Won of construction cost. Considering the frequent telecommunication network constructions, due to new urban developments in the nation, the economic benefit of the suggested telecommunication network design method will be significant. In addition to the construction cost savings, the suggested telecommunication network design procedure possesses several other economic benefits. Since the design procedure can be standardized and automatized, it can reduce the design cost itself and the skill acquirement periods required for new or inapt design crews. Further, due to the standardized and automatized design procedure, any telecommunication network design results can accessed more objectively.

• Journal of Advanced Navigation Technology
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• v.26 no.3
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• pp.172-178
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• 2022

In this paper, water meter AMR(automatic meter reading), one of the core technologies of smart water grid, using LoRa IoT network is studied. The main content of the research is to develop the network system and show the test results that one PC server receives the readings of water meters from multiple households through LoRa communication and stores them in the database, and at the same time sends the data to the web server database through internet. The system also allows users to monitor the meter readings using their smartphones. The hardware and firmware of the main board of the digital water meter are developed. For a PC server program, MDMS(meter data management system) is developed using Visual C#. The app program running on the user's smartphone is also developed using Android Studio. By connecting each developed parts, the total network system is mounted on a flow test bench in the laboratory and tested. For the fields test, 5 places around the university are selected and the transmission distances are tested. The test result show that the developed system can be applied into the real field. The developed system can be expanded to various social safety nets such as monitoring the living alone or elderly with dementia.

• Journal of Distribution Research
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• v.6 no.2
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• pp.41-64
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• 2002

Since its market opening in the year 1996, Korea's retail sector has witnessed the emergence of various new retail formats such as discount stores and Internet shopping malls. Given the competition among various retail formats, it is needed to analyze the previous trends and to measure the future potential of the market with more careful economic models. Using Time Series Analysis on Korean economy and distribution industry, we aim to economic models to follow the trends and to measure the future growth of competing retail formats such as department stores, discount stores and convenience stores. We have found that the growth of department stores, convenience stores and specialty store format is very closely related with the private consumption expenditure. On the other hand, private consumption expenditure is not a good variable to explain the growth of discount stores and the supermarket sector. Following an extensive data analysis, three year forecasting of Korean distribution market including six different retail sectors is proposed. In addition, several discussion points including statistical classification of retail formats are argued.