• Journal of Korean Institute of Industrial Engineers
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• v.33 no.4
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• pp.487-493
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• 2007

In this paper, we deal with an optimal software-release problem of determining the time to stop testing and release the software system to the user. The optimal release time problem is considered from maintenance like the periodic distribution of service packs and the unpredictable distribution of patches after the release. Moreover, the environment of software error-detection during operation differs from the environment during testing. This paper proposes the software reliability growth model which incorporates periodic service packs, unpredictable patches and operational environment. Based on the proposed model, we derive optimal release time to minimize total cost composed of fixing an error, testing and maintenance. Using numerical examples, optimal release time is determined and illustrated.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.57.2-57
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• 2001

Timed token protocols inadequately provide periodic communication service, although this is crucial for hard real time systems. We propose an approach to guaranteeing periodic communication service on a timed token protocol network. In this approach, we allocate bandwidth to each node so that the summation of bandwidth allocations is Target Token Rotation Time (TTRT). If a node cannot consume the allocated time, the residual time can be used by other nodes for non-periodic service using a timer which contains the unused time value and is appended to the token. This approach can always guarantee transmission of real-time messages before their deadlines when the network utilization is less than 50%.

• Journal of Information Processing Systems
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• v.6 no.4
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• pp.575-596
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• 2010

Video-on-Demand services are increasing rapidly nowadays. The load on servers can be very high, even exceeding their capacity. For popular contents, we can use a Periodic Broadcast (PB) strategy using multicast to serve all clients. Recent development of PB uses multiple channels broadcasting for segments of movies in certain patterns, so that users only need to wait for a small segment to start the service. However, users need higher download capacity to download multiple segments at a time. In order to compensate for this, a proxy server can help to reduce download bandwidth requirements by holding some segments for a certain time. This research will focus on more recent PB schemes that couldn't be covered by previous Proxy-Assisted Periodic Broadcast strategies.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.38 no.3
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• pp.8-13
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• 2015

One of the most usual indicators to measure the performance of any inventory policy is the mean physical stock. In general, when estimating the mean physical stock in periodic review inventory systems, approximate approaches are often utilized by practitioners and researchers. The mean physical stock is generally calculated by a simple approximation. Still these simple methods are frequently used to analyze various single stockpoint and multi-echelon inventory systems. However, such a simple approximation can be very inaccurate. This is particularly true for low service levels. Even though exact methods to calculate the mean physical stock have been derived, they are available for specific cases only and computationally not very efficient, and therefore less useful in practice. In literature, approximate approaches, such as the simple, the linear, and Simpson approximations, were derived for the periodic review inventory systems that allow backorders. This paper modifies the approximate approaches for the lost sales case and evaluates the modified approximate approaches. Through computational experiments, average (and maximum) percentage deviations of mean physical stock between the exact method and the modified approximations are compared in the periodic review inventory system with lost sales. The same comparison between the modified and the original approximations are also conducted, in order to examine the performance of modified approximations. The results show that all modified approximations perform well for high service levels, but also that the performance may deteriorate fast with decreasing service level. The modified Simpson approximation is clearly better. In addition, the comparison between the modified and the original approximations in the periodic review inventory system with lost sales shows that the modified approximation outperforms the original approximation.

• Korean Journal of Occupational Health Nursing
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• v.9 no.1
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• pp.30-38
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• 2000

This study was carried out to investigate what factors affect satisfaction of periodic health examination undertaken by employees. The purpose of the study was to improve quality of periodic health examination and to increase the rate of workers participation in the screening test. The content of questionnaire was designed with focus on the satisfaction and attitude on the periodic health examination. Data were analyzed with 212 males, 181 females among 393 samples who took periodic examination at a general hospital in Seoul. Korea. The results were as follows: 1. Respondents were mainly in the thirties(42.7%), married(58.5%), more than 3 years working experiences(66.7%) and employed in Sales & Customers service industry(60.1%). 2. There were significant differences in the scores of satisfaction by general characteristics among the respondents. The highly educated and the single showed higher satisfaction on the periodic health examination than other respondents. 3. The scores of satisfaction in periodic health examination showed highly influenced by level of age, work duration, level of knowledge to the health screening and income. Based on the results, this study concluded that the periodic health examination might be necessary to modify its items according to the clients characteristics and their individual demands for maintenance of healthy life.

• Journal of the Korean association of regional geographers
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• v.2 no.1
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• pp.133-150
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• 1996

This study is to clarify the market cycle of travelling merchants and the spatial behavior of consumer's commodity purchasing. its reasons and purchasing region of each commodity in Chongsan of Chongsan Myun(village) periodic markets, that is one of the lowest central places in Okchon county. The data used are the results of interviews with 58 travelling merchants on June 22 and July 17, 1994, and questionaire survey taken to parents of students of Chongsan middle school of Chongsan Myun in Okchon county. Study area is typical agricultural regions taking the role of central places to provide rural service and is comparatively important periodic markets. Some of findings are summarized as follows: (1) Until 1980's. appearance of closed periodic markets is caused by the population decrease in rural region, income increase, and rising of living level according to the Five Years Planning of Economic Development, appearance of chain stores of agricultural co-coperative and of supermarkets,. changes in distribution mechanisim by increasing consignment volume of agricultural products through agricultural co-coperative, and the development of transportation in Okchon county. These, too, became the reasons for the decline of the Chongsan periodic markets in Okchon county. (2) Most of the travelling merchants visiting the Chongsan periodic markets are in their 50's of age, and they sell the miscellaneous commodities and agricultural products. And about one-fourths of travelling merchants reside in regions with periodic markets and in Okchon of higher order central places. (3) Travelling routes visting periodic markets can be simplified to five types. Major types of travelling routes are Chongsan periodic market$\rightarrow$Wonnam$\rightarrow$Boun, and Chongsan periodic market$\rightarrow$Yungdong$\rightarrow$Yongsan. The patterns of travelling merchants visiting periodic markets are classified into the type of everyday visiting of periodic markets over three days of five days from merchant's residence to market, and the type of merchants or consumers visiting one day's of five days. On days that travelling merchants don't visit periodic markets they purchase the commodities in Seoul, Taejon and Chongju. (4) Consumers who use periodic markets are from thirties to fifties years of age and most of them are employed in agriculture. Consumers visit periodic markets on foot or by bus, and visit two or three times in a month, and mainly purchase the commodities for one or two hours from about ten o'clock in the morning. (5) Consumers purchase the necessaries of life in periodic markets, and other commodities are purchased in Taejon city, Youngdong, and Boun Eup(town). But consumers purchase the goods(convenience goods, shopping goods, and specialied goods) largerly in Chongsan, because additional expense and disadvantage after service with poor transportation service for purchased goods in others regions. Therefore, the hierarchies of central places by the consumer's purchasing behaviour can not be seem in dewellers in Chongsan and Chongseong Myun.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.350-353
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• 2004

The increasing use of Ethernet-TCP/IP network in industry has led to the growing interest in its reliability in real-time applications such as automated manufacturing systems and process control systems. However, stochastic behavior of its medium access scheme makes it inadequate for time-critical applications. In order to guarantee hard real-time communication service in Ethernet-TCP/IP network, we proposed an algorithm running over TCP/IP protocol stack without modification of protocols. In this paper, we consider communication services guaranteeing deadlines of periodic real-time messages over MAC protocols that have unbounded medium access time. We propose a centralized token scheduling scheme for multiple access networks. The token is used to allow a station to transmit its message during the time amount that is appended to the token. The real-time performance of the proposed algorithm has been described.

• Journal of KIISE:Computing Practices and Letters
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• v.12 no.3
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• pp.149-159
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• 2006

To provide on-demand video streaming services through the network, video objects with both high and low client request rates should be served efficiently. In this paper, we propose a dynamic on-demand streaming approach for providing services efficiently regardless of the client request rate. This approach can maintain QoS by transitioning the service scheme according to the request rate. The server provides services by the Heuristic broadcasting approach when the client request rate is low and by Striping broadcast, one of many Periodic broadcast approaches, when the client request rate is high. The server knows the variations of client request rates by the number of service channels and decides the transition to more efficient service schemes on its own. We simulated this scheme transition with various client request intervals and traces from a company providing streaming services. The results show that the performance of our approach is reasonable.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.3
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• pp.170-176
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• 2017

In this paper, we proposed the miniaturized structure of the Log-Periodic Dipole Array(LPDA) antenna for PS-LTE(Pubic Safety-Long Term Evolution) service. The length of array dipole was shortened by adding a fractal tree element with iteration to the array dipole to miniaturize the LPDA antenna. As the result, the proposed LPDA antenna was reduced up to 25 %, compared a typical LPDA antenna. To validation of the proposed LPDA antenna specification, the proposed LPDA antenna is fabricated using aluminum with 1.5 mm thickness and performances are measured. Comparison between simulation result and experiment shows good agreement.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.1
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• pp.77-88
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• 1997

Fieldbus is the lowest level communication network in factory automation and process control systems. Performance of factory automation and process control systems is directly affected by the data delay induced by network traffic. Data generated from several distributed field devices can be largely divided into three categories: sporadic real-time, periodic real-time and non real-time data. Since these data share one fieldbus network medium, the limited bandwidth of a fieldbus network must be appropriately allocated to the sporadic real-time, periodic real-time and non real-time traffic. This paper introduces a new fieldbus design scheme which allocates the limited bandwidth of fieldbus network to several different kinds of traffic. The design scheme introduced in this study not only satisfies the performance requirements of application systems interconnected into the fieldbus but also fully utilizes the network resources. The design scheme introduced in this study can be applicable to cyclic service protocols operated under single-service discipline. The bandwidth allocation scheme introduced in this study is verified using a discrete-event/continuous-time simulation experiment.