• ETRI Journal
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• v.37 no.4
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• pp.696-706
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• 2015

This paper presents an achievable secure videoconferencing system based on quantum key encryption in which key management can be directly applied and embedded in a server/client videoconferencing model using, for example, OpenMeeting. A secure key management methodology is proposed to ensure both a trusted quantum network and a secure videoconferencing system. The proposed methodology presents architecture on how to share secret keys between key management servers and distant parties in a secure domain without transmitting any secrets over insecure channels. The advantages of the proposed secure key management methodology overcome the limitations of quantum point-to-point key sharing by simultaneously distributing keys to multiple users; thus, it makes quantum cryptography a more practical and secure solution. The time required for the encryption and decryption may cause a few seconds delay in video transmission, but this proposed method protects against adversary attacks.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.4
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• pp.34-40
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• 2012

In wireless communication system, fading is an unavoidable problem. Hence, errors in form of BER are introduced with the transmitted signal. It is necessary to recognize the behavior of these errors in different fading channels. To obtain the mathematical solution for the average bit error rate(BER) of coherent MPSK, some techniques are presented. In this paper, the impact of diversity is also analyzed over slow and flat Rician fading channel. In here, the value of modulation index, M is varied and the effects of its variation are also depicted. So, these performance curves with different diversity values and fading parameter are useful to design and evaluate the radio channel for faithful communication system.

• Particle and aerosol research
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• v.4 no.1
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• pp.21-25
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• 2008

$Pb(Zr_{0.53}Ti_{0.47})O_3$ (PZT) was synthesized by a multiple wet dry process. Precipitates prepared from reaction between $ZrOCl_2{\cdot}8H_2O$ and $TiOCl_2$ and $NH_4OH$ in an aqueous solution was dried at $100^{\circ}C$, and calcined at $500^{\circ}C$ and $700^{\circ}C$. The mixture mixed with PbO and as-dried or calcined $Zr_{0.53}Ti_{0.47}O_4$ (ZT) powders was calcined again at 700 and $800^{\circ}C$. Well crystallized ZT and PZT were formed at even $700^{\circ}C$. PZT piezoelectric ceramics of more than 98.5% in a relative density was obtained by sintering at as low as $900^{\circ}C$.

• 한국HCI학회:학술대회논문집
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• 2008.02c
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• pp.224-224
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• 2008

Recent advances in model acquisition, computer-aided design, and simulation technologies have resulted in massive databases of complex geometric data occupying multiple gigabytes and even terabytes. In various graphics/geometric applications, the major performance bottleneck is typically in accessing these massive geometric data due to the high complexity of such massive geometric data sets. However, there has been a consistent lower growth rate of data access speed compared to that of computational processing speed. Moreover, recent multi-core architectures aggravate this phenomenon. Therefore, it is expected that the current architecture improvement does not offer the solution to the problem of dealing with ever growing massive geometric data, especially in the case of using commodity hardware. In this tutorial, I will focus on two orthogonal approaches--multi-resolution and cache-coherent layout techniques--to design scalable graphics/geometric algorithms. First, I will discuss multi-resolution techniques that reduce the amount of data necessary for performing geometric methods within an error bound. Second, I will explain cache-coherent layouts that improve the cache utilization of runtime geometric applications. I have applied these two techniques into rendering, collision detection, and iso-surface extractions and, thereby, have been able to achieve significant performance improvement. I will show live demonstrations of view-dependent rendering and collision detection between massive models consisting of tens of millions of triangles on a laptop during the talk.

• Journal of Communications and Networks
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• v.18 no.1
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• pp.112-122
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• 2016

Cognitive radio (CR) is considered an attractive technology to deal with the spectrum scarcity problem. Multi-radio access technology (multi-RAT) can improve network capacity because data are transmitted by multiple RANs (radio access networks) concurrently. Thus, multi-RAT embedded in a cognitive radio network (CRN) is a promising paradigm for developing spectrum efficiency and network capacity in future wireless networks. In this study, we consider a new CRN model in which the primary user networks consist of heterogeneous primary users (PUs). Specifically, we focus on the energy-efficient resource allocation (EERA) problem for CR users with a special location coverage overlapping region in which heterogeneous PUs operate simultaneously via multi-RAT. We propose a two-tier crossover genetic algorithm-based search scheme to obtain an optimal solution in terms of the power and bandwidth. In addition, we introduce a radio environment map to manage the resource allocation and network synchronization. The simulation results show the proposed algorithm is stable and has faster convergence. Our proposal can significantly increase the energy efficiency.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.3
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• pp.457-463
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• 2011

As computer related technologies are developed, interests in augmented reality technologies are greatly increasing. Augmented reality is a technology that composes digital contents from the real input images through camera and it enables interaction with users. This study designed a directional marker using LED light that emits infrared ray, then, provided a detection algorithm and a marker information extraction method that can realize various virtual objects as augmented reality from one marker. The newly designed method provides a solution to settle the problems in existing marker technologies such as decrease of immersiveness and read rate and single information expression, and at the same time it can minimize the cost or time consumption in marker information storage.

• Industrial Engineering and Management Systems
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• v.11 no.3
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• pp.288-298
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• 2012

Lot sizing and shipment scheduling are two interrelated decisions made by a manufacturing plant and a third-party logistics distribution center. This paper analyzes a dynamic inbound ordering problem and shipment problem with a freight container cost, in which the order size of multiple products and single container type are simultaneously considered. In the problem, each ordered product placed in a period is immediately shipped by some freight containers in the period, and the total freight cost is proportional to the number of containers employed. It is assumed that the load size of each product is equal and backlogging is not allowed. The objective of this study is to simultaneously determine the lot-sizes and the shipment schedule that minimize the total costs, which consist of production cost, inventory holding cost, and freight cost. Because the problem is NP-hard, we propose three meta-heuristic algorithms: a simulated annealing algorithm, a genetic algorithm, and a new population-based evolutionary meta-heuristic called self-evolution algorithm. The performance of the meta-heuristic algorithms is compared with a local search heuristic proposed by the previous paper in terms of the average deviation from the optimal solution in small size problems and the average deviation from the best one among the replications of the meta-heuristic algorithms in large size problems.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1586-1595
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• 2018

For the problem that the complexity of 3-D modeling and multi parameter optimization, as well as the uncertainty of the winding factor of axial flux permanent magnet generator with coreless windings. The complex 3-D model was simplified into 2-D analytic model, and an analytical formula for the winding factor that adapting different coreless stator winding is proposed in this paper. The analytical solution for air-gap magnetic fields, no-load back EMF, electromagnetic torque, and efficiency are calculated by using this method. The multiple objective and multivariable optimization of the maximum fundamental and the minimum harmonic content of back EMF are performed by using response surface methodology. The proposed optimum design method was applied to make a generator. The generator was tested and the calculated results are compared with the proposed method, which show good agreements.

• Journal of KIISE:Computer Systems and Theory
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• v.31 no.9
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• pp.495-502
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• 2004

A rapid growth of the Internet user and rich media content cause an excessive server load and high network traffic, and thus it decreases the quality of service. A solution to this problem is to distribute the content on multiple replicated servers. However, in this circumstance, clients face additional task of selecting the best server to provide proper so${\gamma}$vice which clients request. This paper is intended to propose an adaptive server selection mechanism for a client request based on distance and server load. This will offer a fast and scalable service in response to the increase of massive and realtime multimedia content and contribute to floating a new business model of digital content service.

• Journal of Powder Materials
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• v.27 no.4
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• pp.305-310
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• 2020

In this study, partially dry transfer is investigated to solve the problem of fully dry transfer. Partially dry transfer is a method in which multiple layers of graphene are dry-transferred over a wet-transferred graphene layer. At a wavelength of 550 nm, the transmittance of the partially dry-transferred graphene is seen to be about 3% higher for each layer than that of the fully dry-transferred graphene. Furthermore, the sheet resistance of the partially dry-transferred graphene is relatively lower than that of the fully dry-transferred graphene, with the minimum sheet resistance being 179 Ω/sq. In addition, the fully dry-transferred graphene is easily damaged during the solution process, so that the performance of the organic photovoltaics (OPV) does not occur. In contrast, the best efficiency achievable for OPV using the partially dry-transferred graphene is 2.37% for 4 layers.