• Journal of Korean Society of Transportation
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• v.30 no.3
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• pp.95-106
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• 2012

The railway service in the Seoul metropolitan area is facing variety of l changes such as extension of service coverage, new construction, and introduction of express service which in turn causes changes on demands. The demand affects train operation characteristics (frequency of service, train formation) as well as on the congestion rate which is one of the major evaluation index in metropolitan area user service. For the efficient operation of the train, the relationship among the minimization of fleet number, operating cost, and service level has been analyzed. Using the Powersim, which is a system dynamics (System Dynamics) simulation program for realizing optimized simulation for train-formation, this paper identified that some stations of Gyeong-bu line exceeded limit congestion rate(150%) of a fleet already that means it is best to maintain current condition of the line; however, the Gyeong-in line and the Gwa-chon line showed no excess of the limit congestion rate so that it is possible to reduce 2-4 fleets of train for efficient operation. In addition, in case of Jang-hang line between Cheon-an and Sin-chang, a train consisting of 10 fleets provides services which is same formation of train for Gyeong-bu line. This study proved that the congestion rate will not rise greatly with only 4 fleets of a train for the service in Jang-hang line, and it is considered that a study for shuttle service between Cheon-an and Sin-chang is necessary.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.21 no.1
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• pp.33-39
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• 2011

The present study was carried out to investigate the potential acute toxicity of methylcyclohexane (MCH) by a single oral dose in female rats. The test chemical was administered once by gavage to female rats at dose levels 0, 1,250, 2,500, and 5,000 mg/kg. Mortalities, clinical findings, and body weight changes were monitored for the 14-day period following the administration. At the end of 14-day observation period, all animals were sacrificed and complete gross postmortem and histopathological examinations were performed. Treatment-related clinical signs, as evidenced by depression, soft feces, decreased locomotion activity, solid perineal region, crouching position, and anorexia were observed in all treatment groups in a dose-dependent manner. At the dose level of 5,000 mg/kg, decreased or suppressed body weight gain was found during the study period. At the scheduled necropsy, one case of congestion of the intestine and an increase in the weights of liver and kidney were observed in the 5,000 mg/kg group. Histopathological examinations exhibited an increased incidence of glomerular atrophy, congestion/hemorrhage, and focal degeneration/necrosis in the liver and an increased incidence of congestion, and inflammatory cell infiltration in the kidney. On the basis of the results, it was concluded that a single oral administration of MCH resulted in some adverse effects on clinical sign, body weight gain, and organ weight and histopathology in the liver and kidney in female rats. In the experimental conditions, the minimal lethal dose ($LD_{10}$) of MCH was greater than 5,000 mg/kg.

• Journal of Environmental Health Sciences
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• v.37 no.6
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• pp.460-466
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• 2011

Objectives: Students in elementary schools usually wash their hands in a washstand. However, little attention is paid to the washstand itself. Today, the importance of personal sanitation and hygiene is greatly emphasized. Therefore students' parents and the public are growing increasingly interested in accessibility to washstands by elementary school students in their schools. Methods: With respect to this study, a survey of students and teachers inelementary schools was performed on the installation of washstands in order to determine the proper number of washstands per school. Results: The results show that 1.1 boys (per class) need a washstand, while 1.8 girls (per class) do so in order to maintain a 50% level of crowdedness. By of the regression equation, to maintain 50% congestion (50% of all students feel congestion) there should be 18.5 boys, and the 15.76 girls per washstand. Table 3 is based on the above results, the number of students per washstand (x) and congestion (y), separated by gender according to the results of regression analysis, the correlation of male models in the linear regression analysis and correlation of girls in the regression equation can be obtained. The linear regression fit of less than 0.7 determines that the coefficients of determination are 0.5399 and 0.4195, respectively. Significance was much smaller. Also, according to the simulation using the diffusion model, with 29 students per class more than one washstand should be provided in a school. Girls (per class) need 0.7 more washstands than boys (per class). Conclusions: More washstand facilities for girls than boys are needed. If the target is based on school class size two washstands should be installed. Finally, guidelines and/or standards in the Schools Health Act of Korea forin elementary school washstands is considerably needed.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.15 no.5
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• pp.29-41
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• 2016

V2X environment is the most popular part of the C-ITS based on the high technologies. To evaluate V2X environment technologies, radio communication range and market penetration rate of V2X vehicle are used. This paper studies the V2X environment considering various traffic congestion level, radio communication range and market penetration rate of V2X vehicle using the microscopic simulation (VISSIM) based on proper parameters and algorithm. In conclusion, V2X environment can reduce the congestion in proper traffic volume. However, if traffic volume is almost near the capacity, even V2X environment can't relieve the road condition. Furthermore, increase of the radio communication range does not always mean the decrease of the congestion and even with the small market penetration rate, it can also have an impact on the V2X environment. This result will be the foundation for the V2X environment much better.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.48 no.6
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• pp.140-148
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• 2011

Multimedia streaming service is susceptible to loss and delay of data as it requires high bandwidth and real time processing. Therefore QoS cannot be guaranteed due to data loss caused by heavy network traffic. To deal with these problems, a study on algorithm that can provide high quality multimedia service by considering both network congestion and characteristics of multimedia data is required. In this paper, we propose APQM algorithm which probabilistically removes packet by the congestion level of the queue in wireless station. The comparison with other existing scheduling algorithms shows tht congestion in the network is reduced and multimedia service quality of the proposed algorithm is improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.965-973
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• 2007

We analyzed that the loss of data in TCP protocol based wireless networks caused by overlapped responses in bi-directional nodes that were resulted in out of the data sequence. This loss can be prevented by using revised TCP rate control algorithm and the performance of throughput can also be improved. The rate control algorithm is applied when the congestion happens between nodes while traffic packets are retransmitting in TCP bandwidth. In addition to applying the rate control algorithm, we determine the number of system clients in bandwidth and the average of pausing time between transmitting serial files to produce a competitive level so that an efficient performance of rapid retransmitting for the loss of multi-packets. This paper discusses the improvement of congestion control in that the decrease of the loss, firstly, as ensuring an efficient connection rate and, secondly, as using sliding window flow control.

• Smart Media Journal
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• v.2 no.4
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• pp.51-59
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• 2013

With increasing transmission speed of backbone networks, it is getting to provide enough available bandwidth. However, the bandwidth is not effectively utilized in volumetric data transfer. This mainly comes from the transmission protocol, TCP, which is used for most applications. TCP is inherently difficult to adapt the available bandwidth because of it's own characteristic of transfer mechanism. UDT is a prominent application level data transfer protocol which is targeting high speed network. In this paper, we propose UDT parallel transfer technologies which is adaptive to network status and then evaluate their performance in two points of view. Firstly, we measure data transfer rate of UDT with rate congestion control methods, and compare them with basic UDT. Secondly, we apply parallel transfer technologies adapted to network status, and measure their performance. Experimental results showed that UDT rate congestion control method outperforms UDT with 106% improvement in RTT 100ms section set with jitter 30ms. In addition, performance of parallel transfer with rate congestion control method showed 107% improvement than that of parallel transfer in RTT 400ms section set with jitter 20ms.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.44 no.2
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• pp.1-14
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• 2021

It is highly challenging to measure the efficiency of electric vehicle charging stations (EVCSs) because factors affecting operational characteristics of EVCSs are time-varying in practice. For the efficiency measurement, environmental factors around the EVCSs can be considered because such factors affect charging behaviors of electric vehicle drivers, resulting in variations of accessibility and attractiveness for the EVCSs. Considering dynamics of the factors, this paper examines the technical efficiency of 622 electric vehicle charging stations in Seoul using data envelopment analysis (DEA). The DEA is formulated as a multi-period output-oriented constant return to scale model. Five inputs including floating population, number of nearby EVCSs, average distance of nearby EVCSs, traffic volume and traffic congestion are considered and the charging frequency of EVCSs is used as the output. The result of efficiency measurement shows that not many EVCSs has most of charging demand at certain periods of time, while the others are facing with anemic charging demand. Tobit regression analyses show that the traffic congestion negatively affects the efficiency of EVCSs, while the traffic volume and the number of nearby EVCSs are positive factors improving the efficiency around EVCSs. We draw some notable characteristics of efficient EVCSs by comparing means of the inputs related to the groups classified by K-means clustering algorithm. This analysis presents that efficient EVCSs can be generally characterized with the high number of nearby EVCSs and low level of the traffic congestion.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.1
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• pp.56-65
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• 1994

As a method to control the congestion, priority mechanism which gives two-level priority to various traffics using CLP bit in cell haeder is carried in ATM network. In this paper, we proposed PBS(partial buffer sharing) mechanism with two threshold for provide three-level priority using CLP bit and Res. bit. By performance analysis proposed mechanism, we knew that provides flexibility to satisfy requirements of various quality of service, compare to existing mechanism with two-level priority.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.8
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• pp.1407-1417
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• 2016

In this paper, we propose a multi-level content transmission mechanism for intelligent quality of service (QoS) in social networking services (SNSs). Because existing SNSs and related work send image content to a client with a single fixed mechanism, they cannot consistently support content accessibility according to different conditions of QoS factors such as network congestion and throughput. In the proposed image transmission mechanism, our communication middleware (CM) provides an SNS developer with three transmission modes so that an SNS server or client can dynamically change the quality of images if required. In each transmission mode, an SNS server can send images to a requesting client with original high quality, thumbnail quality, or send only text information. With varying qualities of downloaded images, an SNS developed on top of CM can provide users with consistent QoS for access to SNS content.