• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.9
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• pp.4529-4548
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• 2016

DDoS attacks have had a devastating effect on the Internet, which can cause millions of dollars of damage within hours or even minutes. In this paper we propose a practical dynamic defense approach that overcomes the shortage of static defense mechanisms. Our approach employs a group of SDN-based proxy switches to relay data flow between users and servers. By substituting backup proxy switches for attacked ones and reassigning suspect users onto the new proxy switches, innocent users are isolated and saved from malicious attackers through a sequence of remapping process. In order to improve the speed of attacker segregation, we have designed and implemented an efficient greedy algorithm which has been demonstrated to have little influence on legitimate traffic. Simulations, which were then performed with the open source controller Ryu, show that our approach is effective in alleviating DDoS attacks and quarantining the attackers by numerable remapping process. The simulations also demonstrate that our dynamic defense imposes little effect on legitimate users, and the overhead introduced by remapping procedure is acceptable.

• East Asian mathematical journal
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• v.40 no.2
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• pp.149-166
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• 2024

This study is to establish the domains and the standards of instructional evaluation on the teacher knowledge dealing with the knowledge of 'teaching and learning methods and assessment'. Especially, in this study, the instruction assessment standards are developed focused on the five types of mathematics competencies such as problem solving, communication, reasoning, connection, information and handling, which were emphasized in the mathematical curriculum revised in 2022. By the result, ten domains such as an instruction involving instruction goal and content, problem-solving competency, data treatment competency, learners' achievement level and attitude, communication competency, reasoning competency, connection competency, the assessment method and procedure based on the competency, the assessment tool development based on the competency, assessment result based on the competency were new established. According to those domains, the total 20 instructional evaluation standards were developed. This study is limited to consider the domain of 'teaching and learning methods and assessment' among the domains of teacher knowledge, while dealing with the elements of mathematics competencies in the standards. However, instructional evaluation standards reflecting these competencies should be developed in the other diverse domains of teacher knowledge.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.89-96
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• 2005

Numerical procedure of design optimality evaluation is studied for caisson structural systems. Two kinds of evaluation methods can be considered; mathematical optimality criteria method (MOCM) and numerical optimization method (NOM). The choice of the method depends on the available information of the system MOCM can be used only when the information of all function values, gradients and Lagrange multipliers is available, which may not be realistic in practice. Therefore, in this study, NOMs are applied for the structural optimality evaluation, where only design variables are necessary. To this end, Metropolis genetic algorithm (MGA) is advantageously used and applied for a standard optimization model of caisson composite breakwater. In the numerical example, cost and constraint functions are assumed to be changed from the orignal design situation and their effects are evaluated for optimality. From the theoretical consideration and numerical experience, it is found that the proposed optimality evaluation procedure with MGA-based NOM is efficient and practically applicable.

• Journal of the Korean Operations Research and Management Science Society
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• v.24 no.2
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• pp.81-94
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• 1999

ATM network design procedure is different from the current circuit or packet networks design procedure because of the variety of the offered services and the variability of requested bandwidth for each connection of ATM network. A number of optimization models for the link dimensioning of ATM network design have been proposed in the literature. However, most of the literature did not consider the modularity of resources allocated to a transmission path and the non-bifurcation of a VP link over the more than one TP, which are standardized in recent ITU-T Recommendations. In thIs paper, we propose a mathematical model for link dimensioning of ATM networks, based on the network synthesis method and a generalized bin-packing problem. The suggested model satisfies the constraints mentioned in the ITU-T Recommendations. We also propose efficient and practical algorithms for the suggested model. Computational experiment shows that the suggested algorithm gives efficient solutions even for moderate and large-sized networks within reasonable time.

• Industrial Engineering and Management Systems
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• v.7 no.2
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• pp.182-188
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• 2008

Automated parking systems, which automatically park and retrieve vehicles, have been steadily replacing conventional parking systems. The spiral parking system is a type of automated parking systems that has cylindrical parking tower. We develop an economic design model of spiral parking system based on a recursive optimization and simulation procedure in which the dynamic nature of the parking system can be integrated into the mathematical programming model. The optimal values of design parameters are found that gives the minimum total cost while complying with the desired performance of the system.

• Journal of Power Electronics
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• v.9 no.6
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• pp.929-939
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• 2009

This paper presents a new soft-switching boost converter based on the LC resonance and passive clamping technique without additional active switches. The circuit achieves high efficiency and low voltage stress by adopting a soft switching method using LC resonance. This paper gives a mathematical analysis of each mode and a detailed design procedure of the proposed boost converter. First of all, the operational principles are verified through simulation results. Then, according to the design procedure, we designed and built a 1.5[kW] prototype soft switching boost converter. Through the experimental results, we demonstrated the validity and usefulness of the proposed boost converter.

• Journal of Applied Reliability
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• v.12 no.3
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• pp.225-238
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• 2012

In this paper determined is the quantity of repairable concurrent spare parts(CSP) of a new equipment system to maximize the operational availability under budget constraint and cannibalization allowed. When a part fails, the part is replaced and the failed part is repaired for later use while cannibalization is allowed. The failure of a part is assumed to follow a Poisson process and the availability in CSP is defined. The solution procedure consists of two parts. Firstly, a mathematical model is developed under the assumption that the failure rate is constant during the CSP period and cannibalization is not allowed. Secondly, proposed is a simulation search procedure which improves the heuristic solution to the near optimal solution in a reasonable amount of time under the assumption that the cannibalization is allowed.

• Structural Engineering and Mechanics
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• v.23 no.3
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• pp.249-262
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• 2006

In this paper, a simplified mathematical procedure is presented to incorporate nonlinearity in soil material to predict the deceleration time history, penetration depth and other relevant parameters for normal impact of missiles into soil targets. Numerical method is employed for these predictions. The results of the study are compared with experimental observations and predictions available in the literature. A good agreement is found with experimental observations and an improvement is observed with existing predictions. A comparison is also made with linear soil model. Some parametric studies are also carried out to obtain the results of practical interest.

• Journal of Applied Reliability
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• v.4 no.2
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• pp.91-104
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• 2004

In this paper we consider the concurrent spare part(CSP) requirements problem of new equipment system. When a part fails, the part is replaced and the repair of failed part is impossible and cannibalization is allowed. We assume that the failure of a part knows a Poisson process. The operational availability concept in CSP is defined, and derive a formula to calculate the operational availability using expected machine operating time during CSP period. A mathematical model is derived for making an CSP requirement determination subject to the constraint of satisfying any given operational availability limitation and an heuristic solution search procedure is derived. An illustrative example is shown to explain the solution procedure.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.23 no.58
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• pp.17-27
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• 2000

In FMS where tool movement policy is adopted, a mathematical model has been developed which determines the selection of a tool type for each operation and tool loading-part assignment simultaneouly. The objective is to minimize the total cost of operation including machining time cost, tool cost, tool replacement and loading time cost, and tool change time cost. Due to the complexity of the problem, an approximate solution procedure has been developed utilizing the special structure of the model. Tool selection was determined first to allocate one tool type to each operation considering more than one tool type alternatives for each operation. Tool loading-part assignment was determined to minimize tile total number of tool changes due to part mix based on the tool selection.