• Restorative Dentistry and Endodontics
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• 제37권4호
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• pp.201-206
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• 2012

Objectives: The purpose was to investigate the preference and usage technique of NiTi rotary instruments and to retrieve data on the frequency of re-use and the estimated incidence of file separation in the clinical practice among general dentists. Materials and Methods: A survey was disseminated via e-mail and on-site to 673 general dentists. The correlation between the operator's experience or preferred technique and frequency of re-use or incidence of file fracture was assessed. Results: A total of 348 dentists (51.7%) responded. The most frequently used NiTi instruments was ProFile (39.8%) followed by ProTaper. The most preferred preparation technique was crown-down (44.6%). 54.3% of the respondents re-used NiTi files more than 10 times. There was a significant correlation between experience with NiTi files and the number of re-uses (p = 0.0025). 54.6% of the respondents estimated experiencing file separation less than 5 times per year. The frequency of separation was significantly correlated with the instrumentation technique (p = 0.0003). Conclusions: A large number of general dentists in Korea prefer to re-use NiTi rotary files. As their experience with NiTi files increased, the number of re-uses increased, while the frequency of breakage decreased. Operators who adopt the hybrid technique showed less tendency of separation even with the increased number of re-use.

• Current Optics and Photonics
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• 제1권4호
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• pp.344-350
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• 2017

We present a new design approach and an example design for an image-space telecentric two-mirror system that has a fast f-number and a wide-field line image. The initial design of the telecentric mirror system is a conventional axially symmetric system, consisting of a flat primary mirror with fourth-order aspheric deformation and an oblate ellipsoidal secondary mirror to correct spherical aberration, coma, and field curvature. Even though in the optimized design the primary mirror is tilted, to avoid ray obstruction by the secondary mirror, the image-space telecentric two-mirror system shows quite good imaging performance, for a line imager.

• Investigative Magnetic Resonance Imaging
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• 제20권4호
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• pp.207-214
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• 2016

Purpose: The purpose of this study was to investigate the effect of the number of measurement points on the calculation of transverse relaxation time (T2) with a focus on muscle T2. Materials and Methods: This study assumed that muscle T2 was comprised of a single component. Two phantom types were measured, 1 each for long ("phantom") and short T2 ("polyvinyl alcohol gel"). Right calf muscle T2 measurements were conducted in 9 healthy male volunteers using multiple-spin-echo magnetic resonance imaging. For phantoms and muscle (medial gastrocnemius), 5 regions of interests were selected. All region of interest values were expressed as the mean ${\pm}$ standard deviation. The T2 effective signal-ratio characteristics were used as an index to evaluate the magnetic resonance image quality for the calculation of T2 from T2-weighted images. The T2 accuracy was evaluated to determine the T2 reproducibility and the goodness-of-fit from the probability Q. Results: For the phantom and polyvinyl alcohol gel, the standard deviation of the magnetic resonance image signal at each echo time was narrow and mono-exponential, which caused large variations in the muscle T2 decay curves. The T2 effective signal-ratio change varied with T2, with the greatest decreases apparent for a short T2. There were no significant differences in T2 reproducibility when > 3 measurement points were used. There were no significant differences in goodness-of-fit when > 6 measurement points were used. Although the measurement point evaluations were stable when > 3 measurement points were used, calculation of T2 using 4 measurement points had the highest accuracy according to the goodness-of-fit. Even if the number of measurement points was increased, there was little improvement in the probability Q. Conclusion: Four measurement points gave excellent reproducibility and goodness-of-fit when muscle T2 was considered mono-exponential.

• Journal of Computing Science and Engineering
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• 제4권2호
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• pp.173-187
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• 2010

Recent technological advances in mobile communication systems have made explosive growth in the number of mobile device users worldwide. One of the most important issues in designing a mobile computing system is location management of users. The hierarchical systems had been proposed to solve the scalability problem in location management. The scalability problem occurs when there are too many users for a mobile system to handle, as the system is likely to react slow or even get down due to late updates of the location databases. In this paper, we propose a top-down clustering algorithm for hierarchical location database systems in a wireless network. A hierarchical location database system employs a tree structure. The proposed algorithm uses a top-down approach and utilizes the number of visits to each cell made by the users along with the movement information between a pair of adjacent cells. We then present a modified algorithm by incorporating the exhaustive method when there remain a few levels of the tree to be processed. We also propose a capacity constraint top-down clustering algorithm for more realistic environments where a database has a capacity limit. By the capacity of a database we mean the maximum number of mobile device users in the cells that can be handled by the database. This algorithm reduces a number of databases used for the system and improves the update performance. The experimental results show that the proposed, top-down, modified top-down, and capacity constraint top-down clustering algorithms reduce the update cost by 17.0%, 18.0%, 24.1%, the update time by about 43.0%, 39.0%, 42.3%, respectively. The capacity constraint algorithm reduces the average number of databases used for the system by 23.9% over other algorithms.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2015년도 추계학술대회
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• pp.268-269
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• 2015

해양수산부 해양측위정보원은 현재 총 17개소의 DGPS 기준국을 운영 중이다. 그러나 남한의 면적을 고려할 때 지나치게 많은 기준국을 운영하고 있다는 판단에서 3-4개소의 기준국만으로 균일한 정확도의 DGPS 서비스가 가능하도록 보정정보를 효율적으로 생성하는 방법을 적용하였다.

• 농촌지도와개발
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• 제9권1호
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• pp.11-27
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• 2002

The objectives of this study were to categorize agriculture, to analyze perception of sustainable agriculture and to suggest the directions for improving farming practices in Korea. This study was conducted by review of literature and mail survey. The data was collected from 225 purposively sampled agricultural students by questionnaire. Major findings of the study were as follows; 1) According to the respondents, sustainable agriculture may bring positive effects on the betterment of land conservation, water management and animal protection. 2) The respondents expected that the sustainable agricultural practices may diminish the use of agricultural chemicals and increase safe agricultural products. 3) Sustainable agriculture needs more labor power, however, the number of small and middle-size farms in Korea would not be increased. 4) Even though the price of sustainable agriculture products increases, the respondents expected that rural economic condition would not be much improved because of sustainable agriculture. 5) Agricultural students responded that number of farmers in sustainable agriculture would be increased in the future.

• 대한안전경영과학회지
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• 제11권4호
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• pp.25-33
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• 2009

Since it's first adaptation in Germany in 1884, the industrial accident compensation insurance system has been on the most widely used social security systems, and in was first enforced in Korea in 1964. Today's society has been industrialized and number of business places for workers accident. As the welfare of workers improves in korea, the number of beneficiaries of industrial accident compensation insurance is increasing. Even though such trend is desirable in many respects, there is a growing social problem caused by abnormal insurance claims.

• 농업과학연구
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• 제25권1호
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• pp.138-147
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• 1998

U-turn migration is one of the prominent phenomenon after IMF controlled Korean economy. However a number of U-turn migrants were settled in rural area before that time. This paper is aims at studying the socio-economic effects of U-turn migration in rural area. The study results are summarized as follows; First, migrants are relatively young and engaged in overall parts of the farming. The farmer with age under 50 is represented at 71.4% of migrants comparing with 53.7% of those farmers in rural area. Second, owing to the increasing number of U-turn migrants, the decreasing price of rural wages, the decreasing of idle land, and the increasing price of farm land are the outstanding phenomenon at present. Third, even though there are many kinds of supporting systems for U-turn migrants, the systems are not so successfully functioned. For the successful supporting system they must be changed for the individual migrant rather than target group.

• 산업공학
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• 제23권4호
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• pp.327-336
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• 2010

We consider a supply chain consisting of a make-to-order manufacturer and N component suppliers and study the impacts of the number of suppliers on component inventory management. The manufacturer has full information and continuously observes the state of both component inventory level and customer backorders. Based on this information, the manufacturer determines whether or not to place a component purchasing order to a supplier among N suppliers even though some orders are in process by other suppliers. The goal of this paper is to numerically identify the manufacturer's purchasing policy which minimizes the total supply chain cost and the best choice of N. Our model contributes to the current literature in that the problem of simultaneously considering multiple outstanding orders and incorporating order setup cost into the model has not been covered yet. From numerical experiment, we investigate how much the policy with N suppliers can contribute to reducing the supply cost compared to the policy with a single supplier.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제11권4호
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• pp.286-292
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• 2011

Biometrics systems are used in a wide range of areas, including the area of crime prevention, due to their unique characteristics. However, serious problems can occur if biometric information is disclosed to an unauthorized user. To address these issues, this paper proposes a real valued fuzzy vault method, which adopts a real number error correction code to implement a fuzzy vault scheme for protecting fingerprint temples. The proposed method provides the benefit of allowing the private key value to be changed at any time, unlike biometric template such as a fingerprint, which is not easily renewable even if its security has been breached. The validity of the proposed method is verified for fingerprint verification.