• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.11
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• pp.2547-2552
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• 2013

To achieve better performance in dynamic spectrum access networks, each secondary user tracks channels and chooses a good channel to transmit its packet. When all secondary users adopt the same dynamic spectrum access policy, they have similar channel information, which leads secondary users to choose the same channel and more collisions among them. To relieve this problem, we propose an access policy using belief vector tracking method for other competing secondary users. Simulation results are provided to show that the proposed policy yields better performance than the existing policies which do not take into account what other secondary users are doing.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.2
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• pp.144-152
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• 2018

This study aims to establish a mathematical formula to provide rapid and safety estimation of the damaged double hull tankers under ship-ship collision. Difference in heights between the striking and struck ships 'h' and penetration depth 'x' were considered as the main parameters. In ship-ship interaction, Large oil tankers are selected as target struck vessels, and they are struck by Very Large Crude-Oil Carrier (VLCC) class oil tanker. The residual strength of damaged ship at several locations and collision scenarios were carried out using Intelligent Supersize Finite Element Method (ISFEM) which considers the progressive collapse behavior of ship hulls strength. Based on these results, satisfactory was achieved and empirical formula was successfully established using the regression analysis method by deploying the height difference 'h' and penetration depth 'x' as the observed parameters.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2017.11a
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• pp.21-23
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• 2017

본 논문에서는 스펙트럼 감지 무선 인지 네트워크에서 동기화 에러가 존재하는 환경을 고려한다. 동기화에러가 존재 할 때 주어지는 오검출 확률(miss detection probability)을 이용하여 일차 사용자와 이차 사용자들 간의 충돌 확률(collision probabliyt)를 유도한다. 유도된 수식을 몬테 카를로 모의실험(Monte Carlo simulation)을 통해 확인한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.401-403
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• 2013

Myopic method which is one of dynamic spectrum access method is an advantage that it maximizes immediate throughput is not complicated, and the simple and effective. The disadvantage of myopic method is that there may become less efficient because of conflicts between users secondary secondary user becomes many. Between the secondary if the secondary all users, select a channel to maximize the throughput of their own without considering the secondary other users, but it will try transfer secondary most users select the same channel collision will be more. Myopic / CA method has been proposed to solve this problem. Instead of selecting one channel to maximize their performance, select a candidate channels plurality of their advantage, the secondary user transfers to randomly selected channel that one in this way is a scheme. In this paper, we analyze whether it can be defined in a number of the channel number of candidates, depending on the network environment, maximizes the performance of the entire network.

• Journal of ILASS-Korea
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• v.4 no.2
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• pp.10-18
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• 1999

The droplet/wall impingement processes in the diesel-like environment are numerically modeled. In order to evaluate the predictive capability of the droplet/wall impingement model developed in this study, computations are carried out for two ambient temperature conditions. Numerical results indicate that the present droplet/wall impingement model reasonably well predicts the basic features of the impinging spray dynamics.

• IEIE Transactions on Smart Processing and Computing
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• v.3 no.4
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• pp.173-180
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• 2014

Random access protocols feature inherent sensing functionality and distributed coordination, making them suitable for cognitive radio communication environments, where secondary users must detect the white space of the primary spectrum and utilize the idle primary spectrum efficiently without centralized control. These characteristics have led to the adoption of carrier-sensing-multiple-access/collision-avoidance (CSMA/CA) in cognitive radio. This paper proposes a new analytical framework for evaluating the performance of a CSMA/CA protocol that considers the characteristics of idle periods based on the primary traffic behavior in cognitive radio systems. In particular, the CSMA/CA-based secondary network was analyzed in the terms of idle period utilization, which is the average effective data transmission time portion in an idle period. The use of the idle period was maximized by taking its statistical features into consideration.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1255-1257
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• 2005

The increase of secondary electron-emitting coefficient is effective to reduce the discharge voltage as well as to improve the luminance efficiency of PDP. We investigated the properties of ${\gamma}$ with composition and different dielectric constants, and the microstructure of dielectric after ion collision. As a result the dielectric of PbO system showed higher ${\gamma}$ compared with Pb-free system. However, there was no difference in ${\gamma}$ when the MgO protective layer was covered.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1C
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• pp.54-62
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• 2012

A Wi-Fi mesh network providing multi-hop wireless connections based on IEEE 802.11 PHY/MAC technology has recently received a significant attention as a network infrastructure that interconnects RFID systems and wireless sensor networks (WSNs). However, the current IEEE 802.11 contention-based MAC protocol cannot fully utilize the network capacity due to eithor frame collisions or unused network resources. In this paper, we propose a novel multi-channel scheduling MAC (MCS-MAC) protocol for Wi-Fi mesh networks. Under the secondary interference model of Wi-Fi mesh networks, the MCS-MAC protocol can maximize the network throughput via activation of collision-free links that has a maximal link weight. Through the simulations, we show that the throughput of the MCS-MAC protocol is at least three times higher than that of existing MAC protocols in Wi-Fi mesh networks.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.7
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• pp.1583-1588
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• 2013

According to 2008 statistics, there is a need for sailing lookout to minimize the ships collision that caused a secondary damage such as environment pollution and it happened 25 percentage rate. The aim of this study is to construct the object targeting system for notifying the sailing and ship information as monitoring the marine with CCTV having a zoom, rotation, and tile function. In this study we expected to induce the safety sailing by offering the CCTV automatic treatment.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.557-560
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• 2008

A two-dimensional particle-in-cell(PIC) simulation with a Monte-Carlo Collision(MCC) has been developed to investigate the discharge characteristics of the acceleration channel of a HET. The dynamics of electrons and ions are treated with PIC method at the time scale of electrons in order to investigate the particle transport. The densities of charged particles are coupled with Poisson's equation. Xenon neutrals are injected from the anode and experience elastic, excitation, and ionization collisions with electrons, and are scattered by ions. These collisions are simulated by using an MCC model. The effects of control parameters such as magnetic field profile, electron current density, and the applied voltage have been investigated. The secondary electron emission on the dielectric surface is also considered.