• Korean Journal of Optics and Photonics
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• v.26 no.3
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• pp.168-171
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• 2015

The heat flow characteristics of a high-power optical semiconductor source have been analyzed using a 3D CFD commercial tool, and the thermal resistance values for each of the layers revealed the places for thermal bottlenecks to be improved. As the heat source of a LD (Laser Diode) has a small volume and a narrow surface, the effective thermal cross-sectional area near it is also quite small. It was possible to expand the cross-sectional area effectively by using graphene layers on the TIM (Thermal Interface Material) layers of a LD chip. The effective values of heat resistance for the layers are compared to confirm the improvement effect of the graphene layers before and after, which can be considered to expand the thermal cross section of the heat transfer path.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4D
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• pp.519-526
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• 2011

In this study, the characteristics of transfer station are analyzed using the data of public transportation. The traffic card of Daegu does not include boarding information. The boarding data are calculated using traffic card data and the BMS data. It is found that transfer has increased by the distance from CBD and the numbers of routes, and decresed by the waiting time. Oneway ANNOVA are carried out to find the optimal number of clusters. Three clusters are chosen in this study. The center of the first cluster shows 2.99, so it has a characteristic of CBD. The second is 6.73, the outskirts of town, and the third is 12.78, the outlying areas.

• Journal of Korea Water Resources Association
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• v.45 no.4
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• pp.349-360
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• 2012

A horizontally curvilinear non-hydrostatic free surface model that was applicable to three-dimensional viscous flows was developed. The proposed model employed a top-layer equation to close kinematic free-surface boundary condition, and an isotropic k-${\varepsilon}$ model to close turbulence viscosity in the Reynolds averaged Navier-Stokes equation. The model solved the governing equations with a fractional step method, which solved intermediate velocities in the advection-diffusion step, and corrects these provisional velocities by accounting for source terms including pressure gradient and gravity acceleration. Numerical applications were implemented to the wind-driven currents in a two-dimensional closed basin, the flow in a steep-sided trench, and the flow in a strongly-curved channel accounting for secondary current by the centrifugal force. Through the numerical simulations, the model showed its capability that were in good agreement with experimental data with respect to free surface elevation, velocity, and turbulence characteristics.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.74-80
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• 2012

Past few years have seen the growing importance of micro shock tubes in various engineering applications like micro combution, micro propulsion, particle delivery systems. But in order to efficiently apply Micro Shock Tube to such areas require the detailed knowledge of shock characteristics and flow field inside a micro shock tube. Due to many factors such as boundary layer, low Reynolds number and high Knudsen number shock propagation inside micro shock tubes will be quite different from that of the well established macro shock tubes. In the present study, experimental studies were carried out on micro shock tubes of two diameters to investigate flow characteristics and shock propagation. Pressure values were measured at different locations inside the driven section. From the experimental values other parameters like shock velocity, shock strength were found and shock wave diagram was constructed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.137-147
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• 2013

It is essential to understand the hydraulic characteristics of rivers for increasing flood-control capacity and operating hydraulic structures efficiently. Multi-dimensional models can be the proper measures to obtain the detailed information on the hydraulic characteristics of rivers. But huge amount of data and time-consuming work have been the obstacle for applying multi-dimensional models. In this study, simulation technique with multi-dimensional model(EFDC), coupled with COSFIM and FLDWAV, has been developed and applied to the real river system for verification. Developed technique can offers spatial and grid unit information as well as line and section unit information from 1-D modeling. It is considered that the coupling simulation technique can provide useful hydraulic information for river management and treatment.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.1
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• pp.42-48
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• 2011

In this paper, a passive load-pull using a GaN HEMT (Gallium Nitride High Electron Mobility Transistor) bare-chip in X-band is presented. To obtain operation conditions that characteristic change by self-heating was minimized, pulsed drain bias voltage and pulsed-RF signal is employed. An accuracy impedance matching circuits considered parasitic components such as wire-bonding effect at the boundary of the drain is accomplished through the use of a electro-magnetic simulation and a circuit simulation. The microstrip line length-tunable matching circuit is employed to adjust the impedance. The measured maximum output power and drain efficiency of the pulsed load-pull are 42.46 dBm and 58.7%, respectively, across the 8.5-9.2 GHz band.

• Journal of the Korean association of regional geographers
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• v.22 no.3
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• pp.655-665
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• 2016

The meanings and roles of community have been changed. Traditional community theories hinged on the neighborhood have been threatened by the alternative concept of 'communities without propinquity'. Embracing unprecedented development of transportation, information and communication technologies, Propinquity of community has not been a precondition. This paper reviews the development of community theories with a frame of 'communities without propinquity'. Furthermore, applying social network analysis(SNA) approaches, it explores the communality of Topgol Comic Book Space, located in Goesan, Chungbuk and examines spatial characters. Visitors' networks of Topgol Comic Book Space builda up national coverage and expands. It functions as a field of testing various activities without explicit 'fixed purpose'. The case exemplifies a community, continuously enlarging the spatial and social boundaries, performing a series of activities, and connecting both the outside and the local.

• Korean Journal of Environmental Biology
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• v.33 no.1
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• pp.63-74
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• 2015

The purpose of this study is to provide the basis information for ecological conservation and restoration of Jangdo wetland conservation area through the survey of vegetation diversity and spatial distribution characteristics. Syntaxonomic account of plant communities were carried out field survey by Z.-M. school method at 14 sites and relationship analysis between plant community and environment variables with Principal Coordinate Analysis (PCoA). Based on the floristic composition, all the plots were classified into xeric and hydric type and arranged in seven plant communities. Spatial distribution of plant communities is determined primarily by the soil moisture condition and amount of organic matter. Hydric vegetation is around 8% ($7,337m^2$) of the protected area and distributed swamp forest of dominating willows under 18 years. Proliferation of willows are recognised extended from edge to centre after in 1990's caused by fallow and control of livestock grazing on wetland. Jangdo wetland will have to readjust the protection boundary because wet meadow zone and swamp forest have been distributed outside the protection area.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.7
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• pp.4849-4854
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• 2015

It has been often occurred for the outside components(BU, SVaC, DB) of UM71c AF track circuits to be broken down caused by some pieces of falling ice in the winter time or by infrastructure repairing equipments while facility maintenance works since 2004, opening of Kyeongbu High Speed Rail Express. In this paper, we proposed that we could move the outside components of UM71c track circuit out of wayside from present place. Then we can assure that the life time of those components would be extended. So we simulated the electrical characteristics by changing cable length using MATLAB Simulinks and we designed the compensation capacitor. Also, we obtained the same results as those of simulation by field demonstration test on site. The design specifications obtained from this field verification test could be applied in the absent section of track circuit, if only have a little more intensified research to compensate changed electrical characteristics and to redesign inner impedance of the track circuit.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.377-383
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• 2016

The effect of long-term aging degradation on magnetic properties of ferritic 11Cr low-carbon steel was investigated. Coercivity and hysteresis loss measured from the hysteresis loops decreased with long-term aging time and showed that the relation was well fitted by a second order exponential function. Vickers hardness also decreased with aging time and resulted in mechanical softening. In addition, the microstructural evolution was observed by the scanning electron microscopy, backscattered electron image and X-ray diffraction. The $Cr_{23}C_6$ precipitates along grain boundary grew fast and Laves ($Fe_2W$) phase on martensitic lath boundaries in interior grains was developed. The solid solution atoms depleted in matrix and lath subgrains recovered owing to precipitate coarsening with long-term aging degradation. There was a close relation with softening of magnetic and mechanical properties.