• Journal of the Korea Society for Simulation
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• v.15 no.4
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• pp.29-39
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• 2006

Sensor networks consist of small nodes with sensing, computation, and wireless communications capabilities. A number of routing protocols to transmit the data between the base station and sensor nodes have been proposed. Intanagonwiwat et al. proposed the directed diffusion in which the base station sends interest messages and waits for data from the nodes in the specific regions. Since the directed diffusion propagates every interest message to whole nodes in the network, it causes energy dissipation of nodes. In this paper, we propose a novel data propagation method, which limits the data transmission area according to a threshold value for reducing the energy consumption in the network. A fuzzy logic is exploited to determine the threshold value by considering the energy and density of all the deployed nodes. The simulation models are designed and implemented based on DEVS formalism which is theoretically well grounded means of expressing discrete event simulation models.

• Journal of the Korea Society for Simulation
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• v.23 no.2
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• pp.1-6
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• 2014

CPS (cyber-physical systems) which consists of connected and diverse embedded systems and physical systems are a new paradigm. Traditional systems were usually considered to be passive and dumb parts in physical systems, but with CPS, we have to take into account what are being moved or changed in the physical systems. So, as increasing the complexity of CPS, potential errors in the systems also increase. In this paper, for enhancing the reliability of CPS, we exploit an executable-model-based design methodology and propose a distributed simulation method to verify the design of CPS. For the design of the systems including discrete and continuous factors, we apply DEV&DESS formalism and simulate models in distributed simulation environments through DDS middleware. We also illustrate the applications of CPS with our modeling tool.

• Bulletin of the Korean Chemical Society
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• v.35 no.2
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• pp.494-500
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• 2014

Indium-doped zinc oxide nanocrystals (IZO NCs), capped with stearic acid (SA) of different sizes, were synthesized using a hot injection method in a noncoordinating solvent 1-octadecene (ODE). The ligand exchange process was employed to modify the surface of IZO NCs by replacing the longer-chain ligand of stearic acid with the shorter-chain ligand of butylamine (BA). It should be noted that the ligand-exchange percentage was observed to be 75%. The change of particle size, morphology, and crystal structures were obtained using a field emission scanning electron microscope (FE-SEM) and X-ray diffraction pattern results. In our study, the 5 nm and 10 nm IZO NCs capped with stearic acid (SA-IZO) were ligand-exchanged with butylamine (BA), and were then spin-coated on a thermal oxide ($SiO_2$) gate insulator to fabricate a thin film transistor (TFT) device. The films were then annealed at various temperatures: $350^{\circ}C$, $400^{\circ}C$, $500^{\circ}C$, and $600^{\circ}C$. All samples showed semiconducting behavior and exhibited n-channel TFT. Curing temperature dependent on mobility was observed. Interestingly, mobility decreases with the increasing size of NCs from 5 to 10 nm. Miller-Abrahams hopping formalism was employed to explain the hopping mechanism insight our IZO NC films. By focusing on the effect of size, different curing temperatures, electron coupling, tunneling rate, and inter-NC separation, we found that the decrease in electron mobility for larger NCs was due to smaller electronic coupling.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.3
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• pp.173-182
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• 2014

The mixed convolved action principle provides a new rigorous weak variational formalism for a broad range of initial boundary value problems in mathematical physics and mechanics in terms of mixed formulation, convolution, and fractional calculus. In this paper, its potential in the development of numerical methods for transient problems in various dynamical systems when adopting temporally second order approximation is investigated. For this, the classical single-degree-of-freedom linear elastic dynamical systems are primarily considered to investigate computational characteristics of the developed algorithms. For the undamped system, all the developed algorithms are symplectic with respect to the time step. For the damped system, they are shown to be accurate with good convergence characteristics.

• Nuclear Engineering and Technology
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• v.7 no.4
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• pp.267-275
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• 1975

The low-lying resolved resonance structure of U-233 is investigated in terms of the Adler-Adler multilevel formalism. The resonance capture and fission cross sections of U-233 below 60 eV are calculated using Adlers' effective resonance parameters. The infinite dilution resonance integrals of U-233 are computed with the use of the Alders' parameters adjusted to fit the cross section data. It is found that the agreement of calculations with experiments is generally good over most of the energy region covered. A transformation of the Adlers' multilevel parameters into an equivalent set of the single level pseudoparameters is made for the use of the existing computer codes which are useful in the reactor calculations but do not have capability to use the multilevel parameters. The results of this transformation are presented in the form of a table.

• Journal of the Korean Operations Research and Management Science Society
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• v.20 no.2
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• pp.159-178
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• 1995

Supervisory control is an approach based on formal language. it is used to model and control discrete event systems in which each discrete event process is represented as an automation. A supervisor is a generator that switches control patterns in such a way that a given discrete evenet process behaves in obedience to various constraints. A flexible manufacturing cell (FMC) is one of discrete evenet systems. Functions necessary for the operation of an FMC are characterized by operational components and informational compoments. The operational components can be modeled using the finite state machines and the informational components can be modeled using the abstract formalism which describes supporting operations of the cell controller. In this paper, we addressed function required for FMC control specification, software engineering aspects on FMC control based on supervisory control, a concept of event queue for resolving synchronization problem, and complexity reduction. Based on the mathematical model of an FMC. we synthesized the controller by integrating a supervisor for FMC with control specification that specifies event-driven operation of the cell controller. The proposed control scheme is stable mathematically so that the system always behaves on a controlled way even under the existence of uncontrollable events. Furthermore, using an event queue concept, we can solve a synchronization problem caused by the violation of instantaneity assumption of supervisory control theory in real life situation. And also, we can propotype a control software rapidly due to the modularity of the proposed control scheme.

• The Journal of the Korea Contents Association
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• v.3 no.4
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• pp.38-47
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• 2003

Distributed problem solving is the cooperative solution of problem by a decentralized and loosely couped collection of knowledge-sources (KS's), located in a number of distinct processor nodes. The contract net protocol has been developed to specify problem-solving communication and control for nodes in a distributed problem solver. Task distribution is affected by a negotiation process, a discussion carried on between nodes with tasks to be executed and nodes that may be able to execute tasks In this paper, we present the coordination method among distributed intrusion detection system and firewall by the contract net protocol. The method enhances the intrusion detection performance and provides the communication methods. To mode IDS and firewall, security models hue been hierarchically constructed based on the DEVS (Discrete Event system Specification) formalism. Each ID agent cooperates through the contract net protocol for detecting intrusions. The IDS which detects the intrusion informs to firewall, so the harmful network traffic is blocked. If an agent detects infusions, the agent transfers attacker's information to a firewall. Using this mechanism attacker's packets detected by In can be prevented from damaging the network.

• Journal of the Korea Society for Simulation
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• v.24 no.4
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• pp.11-21
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• 2015

If the cloud computing environment is not sufficiently provide the required resources due to the number of virtual server to process the request, may cause a problem that the load applied to the specific server. Migration administrator receive the resources of each physical server for improving the efficiency of the virtual server that exists in the physical servers, and determines the migration destination based on the simulation results. But, there is more overhead predicting the future resource consumption of all the physical server to decide the migration destination through the simulation process in large and complex cloud computing environments. To solve this problem, we propose an improved prediction method with the simulation-based approach. The proposed method is a fuzzy-logic based priority model for VM migration. We design a proposed model with the DEVS formalism. And we also measure and compare a performance and migration count with existing simulation-based migration method. FPLM shows high utilization.

• Journal of the Korea Society for Simulation
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• v.16 no.3
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• pp.75-87
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• 2007

As the VoIP service quality is getting better and many shortcomings are being overcome, users are getting interested in this service. Also, there are several additional features that provide a convenience to users such as presence service, instant messaging service and so on. But, as there are always two sides of rein, some security issues have users hesitate to make use of it. This paper deals with one of the issues, the VoIP spam problem. We took into account the signal pattern of voice message in spam call and we have constructed voice signal models of normal call, normal call with noise and spam call. Each voice signal case is inserted into our spam decision algorithm which detects the spam calls based on the amount of information in the call signal. We made use of the DEVS-$Java^{TM}$ for our modeling and simulation. The contribution of this work is in suggestion of a way to detect voice spam call signal and testing of the method using modeling and simulation methodology.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1B
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• pp.1-7
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• 2010

In this paper, a high-performance fault-tolerant switching network using a deflection self-routing was proposed. From an abstract algebraic analysis of the topological properties of the Delta network, which is a baseline switching network, we derive the Multidimensional Ring-Delta network: a multipath switching network using a deflection self-routing algorithm. All of the links including already existing links of the Delta network are used to provide the alternate paths detouring faulty/congested links. We ran a simulation analysis under the traffic loads having the non-uniform address distributions that are usual in Internet. The throughput of $1024\;{\times}\;1024$ switching network proposed is better than that of the 2D ring-Banyan network by 13.3 %, when the input traffic load is 1.0 and the hot ratio is 0.9. The reliability of $64\;{\times}\;64$ switching network proposed is better than that of the 2D ring-Banyan network by 46.6%.