• Journal of KIISE:Information Networking
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• v.34 no.4
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• pp.269-275
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• 2007

Since being constructed without any infrastructure-based network, ad hoc network has been received much attention as a key technology for ubiquitous networks. Due to high bit error rate and dynamically changing network topology in ad hoc network, the routing protocol that provides stable multi-hop communication path is the one of the key issues to address. The previously proposed ad hoc routing protocols have their limitations on network overhead, stability, and scalability. In this paper, we consider hybrid wireless network, which can overcome shortcomings of ad hoc network, and propose a novel routing protocol called zone master-based routing protocol. We verify with computer simulations that the proposed routing protocol outperforms other existing routing protocols in the various wireless environments.

• Journal of Astronomy and Space Sciences
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• v.4 no.2
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• pp.81-88
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• 1987

There are more oxygen ions than hydrogen ions in the auroral field zone. We consider both analytic and numerical simulation study of the heating of hydrogen and oxygen ions by auroral electrons. With the low drift speed of electron beams, the ion-ion hybrid wave becomes unstable instead of the lower hydrid wave so that a preferential heating of oxygen ions occurs.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.656-661
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• 2016

4H- and 6H-SiC grown by physical vapor transport method were investigated by transmission electron microscopy (TEM). From the TEM diffraction patterns observed along the [11-20] zone axis, 4H- and 6H-SiC were identified due to their additional diffraction spots, indicating atomic stacking sequences. However, identification was not possible in the [10-10] zone axis due to the absence of additional diffraction spots. Basal plane dislocations (BPDs) were investigated in the TEM specimen prepared along the [10-10] zone axis using the two-beam technique. BPDs were two Shockley partial dislocations with a stacking fault (SF) between them. Shockley partial BPDs arrayed along the [0001] growth direction were observed in the investigated 4H-SiC. This arrayed configuration of Shockley partial BPDs cannot be recognized from the plan view TEM with the [0001] zone axis. The evaluated distances between the two Shockley partial dislocations for the investigated samples were similar to the equilibrium distance, with values of several hundreds of nanometers or even values as large as over a few micrometers.

• Land and Housing Review
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• v.6 no.3
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• pp.129-138
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• 2015

The building structure in Korea is planned to maximize the use of space in recent. The hybrid OCB(Optimized Composite Beam) beam is developed to take advantage of using the space. The OCB beam is composed of the steel H-beam section reinforced by open strands in negative moment zone and the pretensioned PSC concrete section in positive zone. Flexural behavior of typical architectural hybrid OCB beam section was investigated by F.E.M. The 15m, 20m, 30m OCB models were tested on nonlinear material and geometry under static loading system. Following results are obtained from the analysis; 1)The OCB beam develop initial flexural cracking over full service loading. 2)Overall deflections of OCB beam under the service loads are less than those of the allowable limits in KCI Code(2012). 3)The ultimate load capacity get over the nominal strength of the OCB main section. The OCB beam is verified of structural reliability from the finite element analysis.

• Journal of Welding and Joining
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• v.27 no.3
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• pp.52-59
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• 2009

Flash butt welding is applied in many industries. New technology was developed recently for joining billets which called "EBROS (Endless Bar Rolling System)". After reheating billets in furnace, two billets were joined using flash butt welding. The objective of this study was to investigate the effect of alloying elements on mechanical properties of flash butt welded zone of hot rolled steel bar. The tensile properties on welded zone of Fe-Mn steel and Fe-Mn-V steel were dropped as compared with non-welded zone. Fe-Mn-Nb steel was opposed to the former. It was found that the white band at the welded zone had high ferrite volume fraction and large ferrite grain size. The vertical white band between flash butt welded billets was transformed into an arrowhead it of steel bar. According to this band, softening has been appeared. There was a interesting phenomenon with HAZ of Fe-Mn-Nb Steel, 40nm scale of particles were observed and hardness of HAZ was higher than non-welded zone.

• Journal of Electrical Engineering and Technology
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• v.4 no.4
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• pp.429-437
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• 2009

This paper proposes a hybrid voltage controller based on a hierarchical control structure for implementation in the Jeju power system. The hybrid voltage controller utilizes the coordination of various reactive power devices such as generators, switched shunt devices and LTC to regulate the pilot voltage of an area or zone. The reactive power source can be classified into two groups based on action characteristics, namely continuous and discrete. The controller, which regulates the pilot bus voltage, reflects these characteristics in the coordination of the two types of reactive power source. However, the continuous type source like generators is a more important source than the discrete type for an emergency state such as a voltage collapse, thereby requiring a more reactive power reserve of the continuous type to be utilized in the coordination in order to regulate the pilot bus voltage. Results show that the hybrid controller, when compared to conventional methods, has a considerable improvement in performance when adopted to control the pilot bus voltage of the Jeju island system.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.10
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• pp.108-115
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• 2009

Although nanosecond pulsed laser drilling and milling are rapid and non-wear processes in micromachining, the quality cannot meet the precision standard due to the recast layer and heat affected zone. On the other hand, electrical discharge machining (EDM) is a well-known high precision machining process in micro scale; however, the low material removal rate (MRR) and tool wear remain as drawbacks. In this paper, hybrid process of laser beam machining (LBM) using nanosecond pulsed laser and micro EDM was studied for micro drilling and milling. While the quality of the micro structure fabricated by this hybrid process remains as high as direct EDM, the machining time and tool wear can be reduced. In addition, variable depth of layer was introduced as an effective method improving efficiency of hybrid milling.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.22 no.52
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• pp.117-139
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• 1999

This paper is concerned about the hybrid tandem configuration as the design of the automated guided vehicle system(AGVs). The hybrid tandem configuration is that the manufacturing system is divided into several non-overlapping zones, workstations of each zone are linked by network configuration including loop. That is, the manufacturing system is divided into several non-overlapping small size networks, and at most two automated guided vehicles can be available in each network. The transit point is located at proper point between adjacent networks. The parts are transported to workstations in other network through the transit points. One of the objective functions in dividing into the hybrid tandem configuration is to minimize the maximum travel time of the divided networks, and other is to minimize the total travel distance of parts moved to workstations in other networks for the next processing. The model formulation is presented, and a numerical example is shown. Also, the performances of system for the hybrid tandem, tandem and network configuration are compared through the simulation. The results of this research will contribute to the development of material handling systems in the manufacturing system. Also, it will be applied in determining the transportation area of transportation vehicles and the number and size of the transportation fleet in the transportation problem of logistics management.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.119-122
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• 2004

This mobile oriented Ad-hoc network yet steps on development level, related issues and standardization are progressing. This paper presented ad-hoc network's overview and overall property, followed by routing scheme that must be setup for communication between each nodes. Among several routing scheme proposed for standardization, ZRP that is foaled by this paper, is hybrid type algorithm, and only includes advantages of others This paper presented running process and implementation method, result that is made from network simulation, shows analysis of each parameter values's change. Each parameters changed with many differences according to Zone radius and communication node's location from simualtion that was performed changing a number of nodes and a velocity of nodes.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.121-139
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• 2008

For mechanical drive steam turbines, the investigation results of corrosion fatigue phenomena in the transient zone are introduced, including basic phenomena on expansion line and actual design and damage experience. These results were analyzed from the standpoint of stress intensity during the start of cracking. In order to resolve such problems, preventive coating and blade design methods against fouling and corrosive environments are developed. Detailed evaluation test results are given for coating performance using a unique test procedure simulating fouling phenomena and washing conditions. Finally, the results of the successful modification of internals and on-line washing results on site are introduced.