• Proceedings of the Korean Nuclear Society Conference
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• 2003.05a
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• pp.61.1-61.1
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• 2003

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.6
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• pp.2686-2708
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• 2020

This paper investigates the energy efficiency of energy harvesting (EH) bidirectional cooperative sensor networks, in which the considered system model enables the uplink information transmission from the sensor (SN) to access point (AP) and the energy supply for the amplify-and-forward (AF) relay and SN using power-splitting (PS) or time-switching (TS) protocol. Considering the minimum EH activation constraint and quality of service (QoS) requirement, energy efficiency is maximized by jointly optimizing the resource division ratio and transmission power. To cope with the non-convexity of the optimizations, we propose the low complexity iterative algorithm based on fractional programming and alternative search method (FAS). The key idea of the proposed algorithm first transforms the objective function into the parameterized polynomial subtractive form. Then we decompose the optimization into two convex sub-problems, which can be solved by conventional convex programming. Simulation results validate that the proposed schemes have better output performance and the iterative algorithm has a fast convergence rate.

• Journal of the Korea Society for Simulation
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• v.17 no.4
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• pp.81-88
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• 2008

It is important to study the energy efficient MAC protocol in sensor networks. We propose a new protocol named as ELM?MAC (Energy efficient Link Management MAC) to increase energy efficiency in sensor networks. ELM-MAC protocol operates, uses, and manages the optimized transmission power level to increase energy efficiency in MAC layer. It includes mechanism that uses the adaptive method in change of surround environment for guarantee of link quality. In this paper we implement ELM-MAC and evaluate its performance.

• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2299-2305
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• 2020

Zr alloy specimens were coated with Cr-Al alloy to enhance their resistance to oxidation. The coated samples were oxidized at 1200 ℃ in a steam environment for 300 s and showed extremely low oxidation when compared to uncoated Zr alloy specimens. The microstructure and elemental distribution of the oxides formed on the surface of Cr-Al alloys have been investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A very thin protective layer of Cr₂O₃ formed on the outer surface of the Cr-Al alloy, and a thin Al₂O₃ layer was also observed in the Cr-Al alloy matrix, near the surface. Our results suggest that these two oxide layers near the surface confers excellent oxidation resistance to the Cr-Al alloy. Even after exposure to a high temperature of 1200 ℃, inter-diffusion between the Cr-Al alloy and the Zr alloy occurred in very few regions near the interface. Analysis of the inter-diffusion layer by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) measurement confirmed its identity as Cr₂Zr.

• Journal of the Korean Solar Energy Society
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• v.24 no.3
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• pp.55-63
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• 2004

빛이 입사각별로 태양투과율이 제어되어지는 첨단 창과 같은 물체를 통과할 때 투과되는 성분은 직달투과와 산란투과성분으로 볼 수 있다. 직달투과는 물체를 통과하면서 일정한 방향으로 굴절되어 투과되는 성질을 말하고, 산란투과는 직달투과를 제외한 나머지 방향의 성분들의 형태를 말한다. 이러한 첨단 창의 냉난방부하에 미치는 에너지성능을 평가하기 위해서는 산란투과에 대한 정보가 필요하고, 이에 대한 물리적 변수는 입사각, 출력각, 양방향 투과율 분산함수인 BTDF로 정의된다. 본 논문에서는 3개의 서로 나른 첨단 창 (1) $42^{\circ}/5^{\circ}$ 프리즘 창 판넬, (2) 레이저 컷 판넬 (3) $45^{\circ}$ 프리즘 3M 필름의 BTDF 데이터 획득을 위한 실험 방안을 소개하고, 실험을 통해 획득한 정보를 이용하여 계산식과 비교 검증을 하였다. 따라서 이 검증된 방안을 이용하여 지역별 냉난방 부하를 최소화 할 수 있는 입사각별로 태양 투과율 제어 판넬을 선정할 수 있게 되었다.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.3
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• pp.175-183
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• 2008

In wireless sensor networks with ad hoc networking capability, sensor nodes are battery operated and are usually disposable once deployed. As a result, each sensor node senses and communicates with limited energy and, thus, energy efficiency has been studied as a key design factor which determines lifetime of a wireless sensor network, and it is more improved recently by using so-called cross-layer optimization technique. In this paper, we propose and implement a new energy saving mechanism that reduces energy consumption during data collection by controlling transmission power at sensor nodes and then measure its performance in terms of lifetime improvement for the wireless sensor network platform ZigbeX. When every sensor node transmits sensed data to its clusterhead, it controls its transmission power down to as low level as communication is possible, resulting in energy saving. Each sensor node controls its transmission power based on RSSI(Received Signal Strength Indicator) of the packet received from its clusterhead. In other words, the sensor node can save energy by controlling its transmission power down to an appropriate level that its clusterhead safely receives the packet it transmits. According to the repetitive experiment of the proposed scheme on the ZigbeX platform using the packet analyzer developed by us, it is observed that the network lifetime is prolonged by up to 21.9% by saying energy during the data collection occupying most amount of network traffic.

• KEPCO Journal on Electric Power and Energy
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• v.5 no.3
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• pp.141-147
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• 2019

Recently, the biggest issue in the electricity industry is the increase in renewable energy, and various technologies are being developed to ensure the capacity of the power system. In addition, super-grids linking power systems are being pushed to utilize eco-friendly energy between countries and regions worldwide. The HVDC transmission technology is required to link the power network between regions with different characteristics of the power system such as frequency and voltage. Until now, Korea has applied HVDC transmission technology that connects mainland and Jeju Island with submarine cables. But, the HVDC transmission technology is still developing for long-distance high-capacity power transmission from power parks on the east coast to load-tight areas near the metropolitan area. Considering the high population density and mountainous domestic environment, it is pushing for commercialization of the design technology of the ${\pm}500kV$ Double Bipole with metallic return wire transmission line to transmit large-scale power of 8 GW using minimal right of ways. In this paper, the insulation characteristics were studied for the design of double-bipole transmission tower with metallic return wire, which is the first time in the world. And the air insulation characteristics resistant to the various overvoltage phenomena occurring on transmission lines were verified through a full-scale impulse voltage test.

• International Journal of Control, Automation, and Systems
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• v.3 no.4
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• pp.533-541
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• 2005

In this paper, a wind turbine with power splitting transmission, which is realized through a novel three-shaft planetary, is presented. The input shaft of the transmission is driven by the rotor of the wind turbine, the output shaft is connected to the grid via the main generator (asynchronous generator), and the third shaft is driven by a control motor with variable speed. The dynamic models of the sub systems of this wind turbine, e.g. the rotor aerodynamics, the drive train dynamics and the power generation unit dynamics, were given and linearized at an operating point. These sub models were integrated in a multidisciplinary dynamic model, which is suitable for control syntheses to optimize the utilization of wind energy and to reduce the excessive dynamic loads. The important dynamic behaviours were investigated and a wind turbine with a soft main shaft was recommend.

• Journal of Korea Multimedia Society
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• v.18 no.4
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• pp.492-498
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• 2015

In general, data packets from sensor nodes are transferred to the sink node in a wireless sensor networks. So many data packets are gathered around the sink node, resulting in significant packet collision and delay. In this paper, we propose an efficient packet transmission mechanism for multi-hop wireless sensor networks. The proposed mechanism is composed of two modes. One mode works between sink node and 1-hop nodes from sink. In this mode, data packets are transmitted in predefined time slots to reduce collisions. The other mode works between other nodes except sink node. In this mode, duplicated packets from neighbor nodes can be detected and dropped using some control signals. Our numerical analysis and simulation results show that our mechanism outperforms X-MAC and RI-MAC in terms of energy consumption and transmission delay.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.23 no.3
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• pp.205-211
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• 2013

Objectives: 21 sepiolite substances produced in China were investigated for the presence of asbestos in their materials. Materials and methods: In order to identify asbestos in sepiolite substances, test materials were analyzed using a transmission electron microscope equipped with energy dispersive X-ray spectrometer (TEM-EDS) for confirming their shape and components (atomic %). Results: Five of 21 sepiolte substances were asbestos-containing materials. Two chrysotile containing sepiolite proved to be asbestoscontaining materials, as did two chrysotile mixed with tremolite containing sepiolite. 16 sepiolite substances did not contain asbestos materials. Conclusions: When importing sepiolite substances, they must be analyzed to determine if there is asbestos in their materials.