• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.7
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• pp.2512-2531
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• 2014

We propose a new Distributed Denial of Service (DDoS) defense mechanism that protects http web servers from application-level DDoS attacks based on the two methodologies: whitelist-based admission control and busy period-based attack flow detection. The attack flow detection mechanism detects attach flows based on the symptom or stress at the server, since it is getting more difficult to identify bad flows only based on the incoming traffic patterns. The stress is measured by the time interval during which a given client makes the server busy, referred to as a client-induced server busy period (CSBP). We also need to protect the servers from a sudden surge of attack flows even before the malicious flows are identified by the attack flow detection mechanism. Thus, we use whitelist-based admission control mechanism additionally to control the load on the servers. We evaluate the performance of the proposed scheme via simulation and experiment. The simulation results show that our defense system can mitigate DDoS attacks effectively even under a large number of attack flows, on the order of thousands, and the experiment results show that our defense system deployed on a linux machine is sufficiently lightweight to handle packets arriving at a rate close to the link rate.

• Journal of Korean Academy of Nursing
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• v.42 no.4
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• pp.579-588
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• 2012

Purpose: The purpose of this study was to identify the effects of heating on the non-affected hand on blood flow velocity, wound healing, and pain for hand microsurgery patients. Methods: This study was designed using the nonequivalent control group pretest-posttest design. Thirty-nine patients were assigned either to the experimental group (20 patients) or control group (19 patients). Data were analyzed with $x^2$-test, Fisher's exact test, t-test, and repeated measure ANOVA using SPSS/WIN 17.0 program. Results: After treatment in this program, blood flow velocity (F=5.13, p=.008) and wound healing (F=4.11, p=.020) improved significantly in the experimental group compared to the control group. But there was no significant improvement in pain in the experimental group compared to the control group (F=2.40, p=.097). Conclusion: Based upon these results, the non-affected side hand heating was recommended as an independent nursing intervention for the patients who need improvement in blood flow velocity and wound healing such as patients who have microsurgery. As the heating was effective even when applied on the non-affected side, it is the applicable to patients who cannot tolerate any therapy on affected side.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.373-378
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• 2003

It is important that overheat protection of super heated tube in boiler operation and maintenance. The overheat of super heat tube can make damage and rupture of tube material, which causes accidental shutdown of boiler. The super heated tube overheat is almost due to the lack of uniformity of gas temperature distribution. There are two ways to protect overheat of super heated tube. The one is to control hot gas operation pattern which is temperature or flow distribution. the other is to control super heated steam flow distribution. The former is difficult than the later, because of control device design. In this paper steam flow control method which uses orifices is proposed to protect overheat of super heat tube.

• Journal of Communications and Networks
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• v.11 no.3
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• pp.297-305
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• 2009

Multiprotocol label switching (MPLS) networks require dynamic flow admission control to guarantee end-to-end quality of service (QoS) for each Internet protocol (IP) traffic flow. In this paper, we propose to tackle the joint routing and admission control problem for the IP traffic flows in MPLS networks without rerouting already admitted flows. We propose two mathematical programming models for this problem. The first model includes end-to-end delay constraints and the second one, end-to-end packet loss constraints. These end-to-end QoS constraints are imposed not only for the new traffic flow, but also for all already admitted flows in the network. The objective function of both models is to minimize the end-to-end delay for the new flow. Numerical results show that considering end-to-end delay (or packet loss) constraints for all flows has a small impact on the flow blocking rate. Moreover, we reduces significantly the mean end-to-end delay (or the mean packet loss rate) and the proposed approach is able to make its decision within 250 msec.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.11
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• pp.876-880
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• 2009

A control flow graph(CFG) is an essential data structure for program analyses based on graph theory or control-/data- flow analyses. Esterel is an imperative synchronous language and its synchronous parallelism makes it difficult to construct a CFG of an Esterel program. In this work, we present a method to construct over-approximated CFGs for Esterel. Our method is very intuitive and generated CFGs include not only exposed paths but also invisible ones. Though the CFGs may contain some inexecutable paths due to complex combinations of parallelism and exception handling, they are very useful for other program analyses.

• Wind and Structures
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• v.32 no.1
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• pp.1-9
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• 2021

Vortex generators are commonly used in mechanical engineering and the aerospace industry to suppress flow separation owing to their advantages of simple structure, economic viability, and high level of efficiency. Owing to the flow separation of the incoming wind on the leading edge, a suction area is formed on the roof surface, which results in a lifting effect on the roof. In this research, vortex generators were installed on the windward surface of a flat roof and used to disturb to roof flow field and reduced suction based on flow control theory. Computational fluid dynamics (CFD) simulations were performed in this study to investigate the effects of vortex generators on reduce suction. It was determined that when the vortex generator was installed on the top of the roof on the windward surface, it had a significant control effect on reduce suction on the roof leading edge. In addition, the influence of parameters such as size, placement interval, and placement position of the vortex generator on the control effect of the roof's suction is also discussed.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.2
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• pp.219-227
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• 2021

In the present study, the effect of command signals of the flow control valve on performance of underwater discharge systems using a linear pump was investigated numerically. For that, the improved mathematical model was developed. The improvement is to calculate the flow leakage between the water cylinder and the piston. Also the model of the hydraulic cylinder is simplified. To validate the improved model, calculation results were compared with experiment results. The results of the study is as follows: Double ramp command signals of the flow control valve had an advantage over single ramp signals. The parametric study on the effect of double ramp command signals on performance of the system was performed. In case of using double ramp signals, the maximum acceleration of the underwater vehicle was reduced by approximately 50 % compared with using single ramp signals.

• Journal of Korean Physical Therapy Science
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• v.29 no.2
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• pp.48-56
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• 2022

Background: This study was to identify the effects of blood flow restriction on gluteus muscles thickness, density, and white area index for children with cerebral palsy. Design: Randomized controlled trial. Methods: Twenty children with cerebral palsy were assigned randomly to an experimental (n=10) or control (n=10) group. The experimental group performed a bicycle exercise after blood flow restriction. The control group performed a bicycle exercise. The study used an ultrasonic instrument to measure gluteus muscles thickness, density, and WAI. Wilcoxon signed ranks test was used for determination of differences before and after treatment, and a Mannn-whitney U test was used for determination of differences between treatment groups. Results: As a result of comparison within groups, the experimental and control group showed significant difference for gluteus muscles thickness, density, and WAI after the experiment (p<0.05). In comparison between two groups, the experimental group showed more significant difference in gluteus muscles thickness, density, and WAI than the control group (p<0.05). Conclusion: Based on these results, a bicycle exercise after blood flow restriction effectively improved the gluteus muscles thickness, density, and WAI of children with cerebral palsy.

• PNF and Movement
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• v.20 no.1
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• pp.31-39
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• 2022

Purpose: The purpose of this study was to identify the effects of general exercise after blood flow restriction on trunk muscles thickness in children with spastic cerebral palsy. Methods: Twenty children with cerebral palsy were assigned randomly to an experimental (n = 10) or a control (n = 10) group. The experimental group performed general exercise after blood flow restriction, while the control group performed general exercise alone. The study used an ultrasonic instrument to measure trunk muscles thickness. The Wilcoxon signed-rank test was used to determine differences before and after treatment, and the Mann-Whitney U test was used to determine differences between treatment groups. Results: From a comparison within the groups, the experimental and control groups showed significant difference in trunk muscle thickness after the experiment (p < 0.05). In a comparison between the two groups, the experimental group showed more significant difference in trunk muscle thickness than the control group (p < 0.05). Conclusion: Based on these results, general exercise after blood flow restriction effectively improves trunk muscle thickness in children with cerebral palsy.

• International Journal of Control, Automation, and Systems
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• v.3 no.spc2
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• pp.315-321
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• 2005

Interactions among multiple control functions of a UPFC installed in a power system have been observed in power system simulation and been reported in authors' previous publications [1,2]. This paper presents new analytical results about these observed interactions and concludes that they are due to the control conflict between the series and shunt part of the UPFC, which are connected through the internal common capacitor inside the UPFC. Investigation in the paper reveals, for the first time as far as the authors are aware of, that the linkage pattern of UPFC series and shunt part decides whether the control functions implemented by the UPFC series and shunt part conflict each other or not. This linkage pattern of UPFC series and shunt part can be described by the flow of active power through the UPFC at steady-state operation of the power system. Hence in order to predict the possible interactions among multiple control functions of the UPFC, an interaction indicator is proposed in the paper which is the direction and amount of active power flow through the internal link of the UPFC series and shunt part at steady-state operation of the power system. This proposed interaction indicator can be calculated from power system load flow solution without having to run simulation of the power system with UPFC controllers installed. By using the indicator, the interactions among multiple control functions of the UPFC caused by badly set controller's parameters are excluded. Therefore the indicator only identifies the possible existence of inherent control conflict of the UPFC.