• Journal of Positioning, Navigation, and Timing
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• v.4 no.3
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• pp.123-130
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• 2015

In this study, a carrier smoothed global positioning system / dead reckoning (CSGPS/DR) integrated system for high-precision trajectory estimation for the purpose of vehicle navigation was proposed. Existing code-based GPS has a low position accuracy, and carrier-phase differential global positioning system (CPDGPS) has a long waiting time for high-precision positioning and has a problem of high cost due to the establishment of infrastructure. To resolve this, the continuity of a trajectory was guaranteed by integrating CSGPS and DR. The results of the experiment indicated that the trajectory precision of the code-based GPS showed an error performance of more than 30cm, while that of the CSGPS/DR integrated system showed an error performance of less than 10cm. Based on this, it was found that the trajectory precision of the proposed CSGPS/DR integrated system is superior to that of the code-based GPS.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.2131-2136
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• 2003

Since the number of user-requests increases dramatically on the Internet, the servers and networks can be swamped unexpectedly without any prior notice. Therefore, the end-users are waiting or refused for the responses of the contents from the originating servers. To solve this problem, it has been considered that a distributed web caching system efficiently utilizes structural elements of the network. Because a distributed web caching system uses the caches that are close to end-users on the network, it transmits the contents to users faster than the original network system. This paper proposes a simple client-based distributed web caching system(2HRCS) that client can directly perform object allocation and load balancing without an additional DNS for load balancing in CARP (Cache Array Routing Protocol) and GHS (Global Hosting System) that are the recent distributed web caching system protocol. The proposed system reduces the cost of setup and operation by removing DNS that needs to balance the load in the existing system. The system has clients with consistent hashing method, so it extends its environment to other distributed web caching system that has caches of different capacity. A distributed web caching system is composed and tested to evaluate the performance. As a result, it shows superior performance to consistent hashing system. Because this system can keep performance of the existing system and reduce costs, it has the advantage of constructing medium or small scale CDN (Contents Delivery Network).

• Journal of the military operations research society of Korea
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• v.2 no.1
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• pp.177-184
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• 1976

As the organizational size of a military service or business increases and its management becomes complex, the success in its management depends less on static type of management but more on careful, dynamic type of management. In this thesis, an operations research technique is applied to the problems of determining optimal air traffic control rule and of optimal capacity of air base for a military air base. An airport runway is regarded as the service facility in a queueing mechanism, used by landing, low approach, and departing aircraft. The usual order of service gives priority different classes of aircraft such as landings, departures, and low approaches; here service disciplines are considered assigning priorities to different classes of aricraft grouped according to required runway time. Several such priority rules are compared by means of a steady-state queueing model with non-preemptive priorities. From the survey conducted for the thesis development, it was found that the flight pattern such as departure, law approach, and landing within a control zone, follows a Poisson distribution and the service time follows an Erlang distribution. In the problem of choosing the optimal air traffic control rule, the control rule of giving service priority to the aircraft with a minimum average waiting cost, regardless of flight patterns, was found to be the optimal one. Through a simulation with data collected at K-O O Air Base, the optimal take-off interval and the optimal capacity of aircraft to be employed were determined.

• The Journal of Korean Physical Therapy
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• v.9 no.1
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• pp.37-50
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• 1997

Low back Pain(LBP) is a common problem, and the resulting disability frequently contains nonorganic, psycho-logical and social elements that are difficult for the physical therapists to manage. The physical therapist-patient relationship is the most important factors in the management of low back pain as chronic disease. The purpose of this study was to evaluate and to identify factors that had influenced low, back pain patients satisfaction with physical therapist The subjects of this study were 223 out-patients(116 males and 107 females) who had been visited to physical therapy room of medical institutions in Seoul and Uijgngbu city. They were examined by the questionaire of Dimatteo and Hays which was amended to serve the purpose of this study by author. The collected data was analyzed by ANOVA according to the purpose of this study. There was no difference with statistic value in LBP patient's satisfaction according to occupation, sex, schooling, religion, marital status, medical security, duration of disease, the tine required, recurrence, but was a difference according to age, income, period of treatment, cost, diagnosis, waiting time, the number of physical therpy's sort, sex ane age of physical therapists (p<.05). LBP patients was satisfied with physical therapist's communicative behavior, but was dissatisfied with physical therapist's competence.

• Journal of Information Technology Services
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• v.10 no.2
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• pp.259-269
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• 2011

The B$\'{e}$k$\'{e}$sy audiometer is used to determine not only hearing threshold but also assumption of recruit phenomenon and cause of disease. However, current B$\'{e}$k$\'{e}$sy audiometer takes an operational model, so called face-to-face model, in which model one audiometrist can assess only one subject at a time. As a result, the face-to-face model leads to high audiometrist's labor cost and long waiting time when there exist many subjects. To improve such weakness, this paper extends PC based B$\'{e}$k$\'{e}$sy audiometer to support client/server model in which model one audiometrist enables to concurrently access several subjects. As providing capabilities such as real-time transfer of assessment result, video monitoring of subject and video chat, the same effect as face-to-face model but overcomes weakness of face-to-face model.

• Journal of KIISE:Software and Applications
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• v.30 no.7_8
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• pp.780-791
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• 2003

Caching is a useful technique to improve the response time by reducing contention of requests in mobile computing environments with a narrow bandwidth. in the traditional cache-based systems, to improve the hit ratio has been usually one of main concerns for the time. However, in mobile computing environments, it is necessary to consider the cost of cache miss as well as the hit ratio. In this paper, we propose a new cache replacement strategy in pull-based data dissemination systems. Then, we evaluate performance of the proposed strategy by a simulation approach. The proposed strategy considers both the popularity and the wating time together, so the page with the smallest value of multiplying popularity by waiting time is selected as a victim.

• Proceedings of the KIEE Conference
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• 2009.04a
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• pp.195-197
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• 2009

It is a proven fact with the opening of the Seoul metro line number 1 in 1974 traffic congestion on the roads has decreased and the efficiency of people transportation in general has greatly been enhanced in the downtown and surrounding areas of Seoul. Even today construction of new subway lines are under way and many more are being planned due to the easy access to stations, short waiting and average travel times, compared with personal vehicles, contributing to the efficiency of the public transportation systems that are linking the downtown areas and also the intercity systems in moving passengers during rush hour and times of special event. Since the labour costs of the train operator in any large city based subway system accounts for a major part of the operating costs per kilometer and to ensure cost efficient operations, especially during non-peak hours, it is necessary to implement an unmanned(auto-driven) subway system. In order to implement such a system it is imperative that the on-board and wayside signalling control systems be fully automated as well. Only through proper examination of safety procedures not only by the AUGT(Automated Urban Guided Transport)system but also by ail the international standards organizations involved can safely and stability be ensured.

• Journal of the Korea Society for Simulation
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• v.23 no.4
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• pp.229-235
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• 2014

Improving the time and cost efficiency of production systems is one of the important means of building competitive advantage and staying profitable in the ever increasing competitive business environment. Among others, CONWIP (constant work-in-process) and DBR (drum-buffer-rope) methods are widely used in improving production process efficiency. In this study, we have developed simulation models for a real button factory production system. We have tried to improve the efficiency of the production process by implementing these two approaches to our model. According to our results, both CONWIP and DBR production approaches were found to have equivalently better results in reducing the waiting time of the bottleneck process. By applying either of the two production systems, efficiency of the real production process can be significantly improved as the simulated model results demonstrate.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.5
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• pp.41-50
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• 2020

The paper investigates the factors that affect the demand for a voluntary audit of small and medium-sized enterprises (SMEs) in Vietnam. A structured questionnaire survey of 284 SMEs was employed, preceded by in-depth interviews with auditors and SMEs' managers. The research used logistic regression estimator to address econometric issues and to improve the accuracy of the regression coefficients. The results show that the degree of director's view on voluntary audit, related stakeholder, degree of recommendation, and firm size have a statistically significant positive effect on audit decisions of SMEs while degree of audit fee has a statistically significant negative effect, and degree of subjective norm does not affect. This indicated that SMEs are more likely to have an external audit if they have some typical features: it is becoming larger in terms of size, and the directors consider that the audit has a relative benefit outweighing its cost. The research results suggested that Vietnam Government should make a statutory audit of SMEs' financial statements rather than make it an option for SMEs. The auditing firms were also recommended to actively take their audit services to SMEs rather than waiting for the SMEs' managers to contact them for their services.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.5
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• pp.2499-2522
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• 2017

Multi-hop networks are a low-setup-cost solution for enlarging an area of network coverage through multi-hop routing. Carrier sense multiple access with collision avoidance (CSMA/CA) is frequently used in multi-hop networks. Multi-hop networks face multiple problems, such as a rise in contention for the medium, and packet loss under heavy-load, saturated conditions, which consumes more bandwidth due to re-transmissions. The number of re-transmissions carried out in a multi-hop network plays a major role in the achievable quality of service (QoS). This paper presents a statistical, analytical model for the end-to-end delay of contention-based medium access control (MAC) strategies. These strategies schedule a packet before performing the back-off contention for both differentiated heterogeneous data and homogeneous data under saturation conditions. The analytical model is an application of Markov chain theory and queuing theory. The M/M/1 model is used to derive access queue waiting times, and an absorbing Markov chain is used to determine the expected number of re-transmissions in a multi-hop scenario. This is then used to calculate the expected end-to-end delay. The prediction by the proposed model is compared to the simulation results, and shows close correlation for the different test cases with different arrival rates.