• Journal of KIISE:Computer Systems and Theory
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• v.30 no.11
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• pp.629-654
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• 2003

A new multiresolutional scheme that reconstructs a polygonal mesh from the set of contours is presented. In the first step, we apply a radial gradient method to extract the contours on the sampled slices from a volume data. After classifying the types of the edges on the contours, we represent the contour using the context-free grammar. The polygons between two neighboring contours are generated through the traversal of the derivation trees of the context-free grammar. The polygonal surface of the coarsest resolution is refined through the refinement of the contours, which is executed by casting more rays on the slices. The topologies between the polygonal surfaces of various resolutions are maintained from the fact that the radial gradient method preserves the topologies of the contours of various resolutions. The proposed scheme provides efficient computation and compression methods for the tiling procedure with the feature preservation.

• Journal of Life Science
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• v.13 no.2
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• pp.168-174
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• 2003

The chemical compositions and antioxidant activity of green tea extracts in medilite-extraction water were compared to that of distilled water(DW). Antioxidant activity was fetermined by the formation of thiobarbituric acid reactive substances (TBARS) in rat liver homogenates and microsomes and the scavenging activity of free radicals by DPPH ($\alpha$, $\alpha$'-diphenyl-$\beta$-picrylhydrazyl). The order of total polyphenolic compounds and extracted yield by extracts was medilite 325 mesh-extraction water, medilite 600 mesh-extraction water and distilled water(DW). The ranges of scavenging activity of green tea extracts in DPPH method were 60.95% - 64.51%. The inhibition ratios of TBARS formation in the rat liver homogenates and microsomal fractions were significantly lower with green tea extracts by DW-extraction than with both medilite 325 mesh and 600 mesh-extraction water. The concentration of iron ion of water containing medilite 325 mesh and green tea extracts and of water containing medilite 600 mesh and green tea extracts were significantly higher compared to DW. Therefore, this result suggested that enhanced concentration of iron ion in green tea extracts by medilite-extraction water containing high iron ion content was associated with enhanced peroxidation of the rat liver microsomal fractions. These results showed that total polyphenolic compounds, the % of yield and mineral compounds of green tea extracts were increased using medilite 325 mesh and 600 mesh-extraction water.

• ETRI Journal
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• v.35 no.5
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• pp.775-785
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• 2013

Because of their exclusive features, millimeter wave directive mesh networks can be considered for small cell backhaul support in urban environments. For this purpose, a network of closely spaced stations has been considered with very directive line-of-sight links operating in the 60-GHz band. An attempt is made to evaluate channel response and interference behavior in such a network, taking into account the effect of building blockage. A simple grid of building blocks is considered as the propagation environment, and wave propagation is simulated using 2.5-dimensional (2.5D) ray tracing (2D with ground effect) to calculate the received signal at different nodes in the network. The results are compared with free space predictions and used to evaluate interference at all nodes in the channel and describe certain characteristics of links, such as the delay profile and the correlation length.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.112-119
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• 2002

In this paper, an Extended Finite Element Method is proposed by adding discontinuity and singularity enrichment functions to the standard FEM approximation. In this method, the singularity and the discontinuity of the crack are efficiently modeled by using initial regular mesh without refining mesh near the crack tip, so that it enables express the asymptotic stress field near crack tip and crack surface successfully. The developed method was verified by evaluating crack tip stress profile and stress intensity factor of mode Ⅰ/mode Ⅱ fracture problems and the results showed the effectiveness and robustness for fracture problem.

• Journal of Power System Engineering
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• v.4 no.1
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• pp.60-67
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• 2000

As the speed of rotating machines increases and also their weight decreases, the coupling between lateral and torsional vibrations must be considered. In the past, rotordynamics and geardynamics have tended to treat the lateral and torsional vibrations of the system elements as separate and decoupled mechanisms. In the paper, the coupled lateral-torsional free and forced vibration of rotors trained by gears is analyzed using finite element method. Also the complicated variation of the meshing stiffness as a function of contact point along the line of action is estimated correctly. The gear mesh model is assumed to be linear with constant average mesh stiffness.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2A
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• pp.113-123
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• 2009

Wireless mesh networks have been studied as the next generation technology to solve problems of conventional wireless networks. Particularly, mobile WiMAX based wireless mesh networks are noticed due to many advantages. In this paper, we propose a layer-2 handover scheme for mobile WiMAX based wireless mesh networks. A layer-2 handover scheme based on mobile WiMAX causes many handover failures over mobile WiMAX based wireless mesh networks because it does not consider the characteristics of wireless mesh networks. The proposed scheme does not bring about packet losses achieving lower handover latency than a conventional handover scheme. Simulation results show that the proposed scheme achieves loss-free and low handover latency during the layer-2 handover.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.40 no.6
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• pp.9-21
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• 2003

In this paper, we propose a new submesh allocation scheme which improves the performance of multicomputer systems. The key idea of this allocation scheme is to reduce waiting time of task by minimizing the submesh search time and the submesh a]location delay caused by external fragmentation. This scheme reduces the submesh search time by classifying independent free submeshes according to their types (square, horizontal rectangle, vertical rectangle) and searching a best-fit submesh from the classified free submesh list. If a submesh allocation delay occurs due to external fragmentation, the proposed scheme relocates tasks, executing In allocated submeshes, to another free submeshes and compacts processor fragmentation. This results in reducing the submesh allocation delay. Through simulation, we show that it is more effective to reduce the submesh allocation delay due to external fragmentation than reducing the submesh search time with respect to the waiting time of task. We also show that the proposed strategy improves the performance compared to previous strategies.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.10
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• pp.2509-2528
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• 2012

Time division multiple access (TDMA) is a widely used media access control (MAC) technique that can provide collision-free and reliable communications, save energy and bound the delay of packets. In TDMA, energy saving is usually achieved by switching the nodes' radio off when such nodes are not engaged. However, the frequent switching of the radio's state not only wastes energy, but also increases end-to-end delay. To achieve high energy efficiency and low delay, as well as to further minimize the number of time slots, a multi-objective TDMA scheduling problem for industrial wireless mesh networks is presented. A hybrid algorithm that combines genetic algorithm (GA) and simulated annealing (SA) algorithm is then proposed to solve the TDMA scheduling problem effectively. A number of critical techniques are also adopted to reduce energy consumption and to shorten end-to-end delay further. Simulation results with different kinds of networks demonstrate that the proposed algorithm outperforms traditional scheduling algorithms in terms of addressing the problems of energy consumption and end-to-end delay, thus satisfying the demands of industrial wireless mesh networks.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.2
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• pp.149-155
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• 2011

The viscous flow in an axisymmetric nozzle was analyzed while accounting for the mesh sizes in both in the free stream and the boundary layer. The Navier-Stokes equations were resolved using the finite volume method in order to determine the supersonic flow parameters at the exit of the converging-diverging nozzle. The numerical technique in the aforementioned method uses the flux vector splitting of Van Leer. An adequate time stepping parameter, along with the Courant, Friedrich, Lewis coefficient and mesh size level, was selected to ensure numerical convergence. The boundary layer thickness significantly affected the viscous flow parameters at the exit of the nozzle. The best solution was obtained using a very fine grid, especially near the wall at which a strong variation of velocity, temperature and shear stress was observed. This study confirmed that the boundary layer thickness can be obtained only if the size of the mesh is lower than a certain value. The nozzles are used at the exit of the shock tube in order to obtain supersonic flows for various tests. They also used in propulsion to obtain the thrust necessary to the displacement of the vehicles.

• Journal of Biosystems Engineering
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• v.30 no.4 s.111
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• pp.195-201
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• 2005

The output of Stirling engine is influenced by the regenerator effectiveness. The regenerator effectiveness is influenced by heat transfer and flow friction loss of the regenerator matrix. In this paper, in order to provide a basic data for the design of regenerator matrix, characteristics of heat transfer and flow friction loss were investigated by a packed method of matrix in the oscillating flow as the same condition of operation in a Stirling engine. As matrices, several kinds of combined wire screen meshes were used. The results are summarized as follows; The packed meshes with high mesh no. in the side of heater part of regenerator showed effective than the packed meshes with low mesh no. in the side of cooler part of regenerator. The temperature difference and pressure drop of the regenerator were not made by the specific surface area of wire screen meshes but by the minimum free-flow area to the total frontal area. Among the No. 150 single screen meshes, 200-60 combined meshes, the 200-150-100 combined meshes showed the highest in effectiveness.