• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.5C
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• pp.422-434
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• 2002

We propose 3-layered hierarchical fiber-optic backbone transmission network composed of B-DCS, Backbone ring, Edge ring for efficient transmission of high capacity traffic and consider design method to ensure network survivability of each layer at affordable cost. Mathematical ring-construction cost minimization using MIP(Mixed Integer Programming) models results in NP-complete problem. So, it is hard to solve it within reasonable computing time. on a large-scale network. Therefore we develop heuristic algorithms solving WSCAP(Working and Spared Channel Assignment Problem) for B-DCS, MRLB(Multi-Ring Load Balancing) problem for Backbone ring, and ORLB(Overlayed Ring Load Balancing) problem for Edge ring and show their usefulness through case study.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.1
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• pp.51-62
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• 2010

The purpose of this study was to investigate the performance of hollow precast segmental PSC bridge columns. The proposed system can reduce work at a construction site and makes construction periods shorter. Shortened construction times, in turn, lead to important safety and economic advantages when traffic disruption or rerouting is necessary. Two hollow precast segmental PSC bridge columns were tested under a constant axial load and a quasistatic, cyclically reversed horizontal load. A computer program, RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures, was used. The proposed numerical method gives a realistic prediction of performance throughout the loading cycles for several test specimens investigated.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.494-499
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• 2007

The ballast, one of a track components, plays an essential role as intermedium in transmitting train traffic-load to subgrade safely, and deterioration of ballast caused by cumulative load effects growth of track irregularity. Especially in the case of Gyeongbu high-speed railway, the deteriorating speed of ballast by dynamic vibration is faster than conventional line because KTX is longer than normal trains in length and it's velocity is very fast with high speed of 300km/h as well. In addition, ballast is a nonlinear material contrary to ordinary metal which has homogeneous property and this property of ballast may cause transformation of ballast. Therefore the theoretical modeling of ballast is quite complicated and it is hard to ensure the reliability of the result. The objective of this paper is to examine the availability of GPR(Ground Penetrating Radar) in estimating the thickness and the degree of deterioration of ballast. First, We figured out the principle of GPR which is the technique of evaluating the condition of ballast and then analyzed data which were measured at Gyeongbu high-speed railway where KTX is running now.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.280-285
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• 2000

With recent development of technology of high stiffness material and the structural design, the construction of high rise structures such as tall building, tower has increased. The more flexible and slender structure is vulnerable to the internal and external dynamic loads induced by earthquake, wind and traffic load. There have been great effort and many researches to minimize the influence of dynamic loads on the structure. The traditional and stable method, the application of the passive damper, is not able to comply with various dynamic loads, while the mass damper which active control technology is integrated can effectively comply with load types. Therefore, the application of active control of huge structures with AMD(Active mass damper) or HMD(Hybrid Mass damper) is increasing. Up to now, most of actuators are servomotor and hydraulic actuator. But it is known that the electromagnetic actuator applies non contacting control force, which makes the control system easier with no characteristic change depending on time. In this paper, Hybrid mass damper with electromagnetic actuator was designed and applied to building scaled structure. The performance of designed HMD tested by shake table test is included.

• The Journal of the Acoustical Society of Korea
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• v.17 no.4E
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• pp.28-34
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• 1998

In most switching system, the processing unit is designed to work efficiently even at relatively high loads, but when the offered traffic exceeds a particular level, the rate of completed calls can fall drastically. A single call handled by the switching system consists of a sequence of events or messages that has to be processed by the control unit. The control unit is not only incapable of handling all of the offered calls, but also its call handling capability can drop as the offered load increases. The real time available for call processing is a critical resource that requires careful management. Therefore, the overloading of this resource must be detected by a subscriber in the from of a dial tone delay or an uncompleted call which is either blocked or mishandled. The subscriber may respond by either dialing prematurely or by re-attempting a call. This action can further escalate the processors load, which is spent for uncompleted calls. Unless a proper control is used, the switching system can finally break down. In this paper, we paper, we propose a fuzzy overload detection and control method for switching systems, which can by generating fuzzy rules via fuzzy aggregation networks. Simulation results involving a switching system is given.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9A
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• pp.1075-1082
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• 2004

Wireless LAN is a rather mature communication technology connecting mobile terminals. IEEE 802.11 is a representative protocol among Wireless LAN technologies. The basic medium access control (MAC) mechanism of IEEE 802.11 is called distnbuted coordination function (DCF). DCF shows poor throughput and high drop rate as the number of stations and offered traffic load increase. In this paper we propose an effective mechanism using dynamic mimmum contention window(CWmin) in wireless LAN~ and show that performance improves via simulations. Proposed dynamic CWmin scheme exhibits superior performance as the number of stations and offered load grow. As, our proposed scheme is expected to be more effective in highly densed wireless LAN environment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.237-252
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• 2017

In recent years, data centers have become the core infrastructure to deal with big data processing. For these big data applications, network transmission has become one of the most important factors affecting the performance. In order to improve network utilization and reduce job completion time, in this paper, by real-time monitoring from the application layer, we propose job-aware priority scheduling. Our approach takes the correlations of flows in the same job into account, and flows in the same job are assigned the same priority. Therefore, we expect that flows in the same job finish their transmissions at about the same time, avoiding lagging flows. To achieve load balancing, two approaches (Flow-based and Spray) using ECMP (Equal-Cost multi-path routing) are presented. We implemented our scheme using NS-2 simulator. In our evaluations, we emulate real network environment by setting background traffic, scheduling delay and link failures. The experimental results show that our approach can enhance the Hadoop job execution efficiency of the shuffle stage, significantly reduce the network transmission time of the highest priority job.

• The KIPS Transactions:PartC
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• v.10C no.7
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• pp.937-942
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• 2003

In this paper, we measured and examined RTT delays and packet losses according to the changes of stationary loads for two typical stream-type traffics, a DV and a MPGE2 on the R＆D Gigabit Network testbed, JGN. As the result of our actual measurements, we realized that the packet size of stationary load have no effects on a DV and a MPGE2 stream on the very high-speed network(50Mbps, IP over ATM). When its bandwidth and stationary load exceeds 95％ of network bandwidth, packet losses appeared and RTT delay increased rapidly. Also we realized that the number and size of Receive ＆ Transmit buffer on the end systems have no effects on packet losses and RTT delays.

• Steel and Composite Structures
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• v.11 no.1
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• pp.1-19
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• 2011

The introduction of the Eurocodes makes plastic design criteria available also for composite bridges, leading to more economical solutions compared with previous elastic design rules. Particularly for refurbishment old bridges with higher actual traffic loads, up to date outside the scope of the Eurocodes, strengthening should therefore be avoidable or at least be necessary only to a minor extent. For bridges with smaller spans and compact cross sections, the plastic load bearing capacity is clearly justified. In this work, however, the focus is placed on long span continuous composite bridges with deep, longitudinally stiffened girders, susceptible to local buckling. In a first step, the elastic - plastic cross section capacity of the main girder in bending is studied as an isolated case, based on high preloads acting on the steel girder only, due to the common assembling procedure without scaffolding. In a second step, the effects on the whole structure are studied, because utilising the plastic section capacity at midspan leads to a redistribution of internal forces to the supports. Based on the comprehensive study of an old, actual strengthened composite bridge, some limitations for plastic design are identified. Moreover, fully plastic design will sometimes need additional global analysis. Practical recommendations are given for design purposes.

• Journal of the Korea Society of Computer and Information
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• v.15 no.8
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• pp.79-87
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• 2010

It is widely accepted that the coverage with high user densities in mobile multimedia environments can only be achieved with small cell such as micro- and pico-cell. If handover events occur during the transmission of multimedia, the efficient resource reservation and handover methods are necessary in order to maintain the same QoS of transmitted multimedia traffic because the QoS may be defected by some delay and information loss. In this paper, we propose a resource allocation method in the next generation mobile communication systems, in which the resource allocation process has a tight relation with call admission, call load, and packet scheduling. The simulation results show that our proposed method provides a excellent performance.