• Proceedings of the KSR Conference
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• 2010.06a
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• pp.664-670
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• 2010

The study on mechanical behavior of the structure at the site includes experimental method and numerical analysis method. Experimental method is categorized into true-scale test and laboratory model test. A laboratory model test is to monitor the failure mechanism with a model simulated similar with a real ground so as to identify the quantitative result, while a true-scale model test is the approach which enables to identify the potential problems that may occur with a simulated construction situation similar with a real site circumstance. Thus this study was intended to carry out the experimental test of non open-cut excavation by pipe roof method which is mostly common in domestic sites. as well as was aimed at identifying the ground behavior occurred during pipe penetration using laboratory model test. Appropriate reduced-scale model was selected, taking into account of domestic geological characteristics and operation characteristics of traditional and high-speed rail trains and the qualitative evaluation of displacement was carried out based on a certain ground loss volume depending on excavation after categorizing trackbed settlement pattern by depth of top soil.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1864-1874
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• 2007

Korean trains pass many mountain areas, so the volume of structures like bridge and tunnel has large part of railway lines. Train speed-up naturally needs a straight line in railway, then structures are increasing, and the length of structure has more than 70% in Kyongbu high-speed railway. The stiffness of bridge and tunnel is higher than the soil in the roadbed in spite of dynamic difference in vibration and displacement. Differences in stiffness have more dynamic effects and increase the deformation and destruction in the track and roadbed. This influences passenger's comfort and the safety of operation, and it needs more track maintenance. This study selected tunnel with ballast track, tunnel with concrete track, and structure's approaches with short maintenance cycle in the roadbed and had track acceleration tests and track liner inspections using track master in the field. This study will measure periodically to structure's approaches which have very fast track irregularity and analyze dynamic differences and track irregularity near structure's approaches, so realize the cause of track irregularity of structure's approaches and use basic data for reasonably strengthening method of structure's approaches.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.575-582
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• 2004

We analyse the beam characteristics of the thermal-birefringence compensated symmetric resonator which consists of two laser rods with rod-end curvatures. The numerical results show that the stability and the beam quality can be improved in high power operation region when the rod-ends are made in the form of a negative lens. The thermal birefringence of the symmetric two-rods resonator is shown to be well compensated when the two rods closely contact each other.

• Journal of Korean Society of Transportation
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• v.12 no.4
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• pp.35-52
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• 1994

In order to operate the computerized traffic signal system, it requires the detectors which ensure the exact detections of actual traffic data (e.g., traffic volume, occupancy and velocity of vehicles). The octagonal detectors are used currently in Korea. However, the maintenance of the detectors has many problems with the road repairs and the constructions on the pavement, and failure due to the disconnection of the wires. Serious delay due to the long installation time of loops also causes the traffic disturbances. The low sensitivities and splash-over effect can sometimes create error data after installation of the octagonal loops. The mai purpose of this study is to evaluate the feasibility of domestic use of the round (circular) inductive loops which developed recently in U.S.A. It was found that the round loops are comparable to the existing octagonal loops. In addition, the use of the high quality of materials in the round loop system can reduce the current problems and weakpoints of the octagonal loops. The installation cost of the round loop was found out as economic as the octagonal loop. The installation time of the round loop system can be reduced with the specially equipped loop truck, and wide/deep slots without sharp corners can extend the durability without serious stress of loop head wires. In conclusion, the round loop is superior to the octagonal type in overall points. It is recommended that the localization of the materials and equipments of round loop system is required to carry out the extensive local installations. Also, several contractors to meet the nationwide demand should be arranged to gurantee the proper maintenance and operation of the systems.

• Asian-Australasian Journal of Animal Sciences
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• v.23 no.2
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• pp.279-286
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• 2010

Livestock production in Vietnam is, as in most Asian countries, increasing rapidly and changing into specialized highly intensified operations. The volume of animal excreta generated exceeds the capacity of the operation land base and cannot be utilized efficiently. As a consequence, there is a loss of plant nutrients from livestock farms that causes environmental pollution. This study carried out a feed and excretion experiment measuring fecal characteristic, daily fecal production, daily nitrogen and phosphorous excretion from grower-finisher pigs fed prevalent rations in Vietnam. Furthermore, equations for assessing the excretion were tested, which can be used in farm models for optimal recycling of manure while focusing on reducing pollution. The results indicated that fecal production and nutrient excretion were affected by the different rations tested. This study showed that five selected equations for predicting excretion from grower-finisher pigs in Danish conditions can also be used with precision in Vietnamese pig farming systems. The equations have been proven valid and can, therefore, be used as a much needed tool for assessing fecal production and nitrogen in excreta on pig farms. The study also showed that about 12% of nitrogen excreted was emitted during housing. Waste water contains more than half of the nitrogen excreted, mainly in ammonium form which has a high potential for gaseous emission.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.387-391
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• 2011

Since MEMS based micro actuators or generating devices have high efficiency per volume, plenty of research are ongoing. Among them, MEMS based millimeter-scale micro gas' turbine is one of the most powerful issue for replacing chemical batteries. However, since limiting of MEMS manufacturing technique, it is very difficult that makes wide turbine bearing area. It causes low DN number, so sufficient bearing force is hard to achieve. Thus, the most important issue on micro gas turbine is proper bearing design which can keep rotor stable during operation. In order to that, micro-scale gas-lubricated bearing is generally used. In this paper, basic feasibility study and design of journal bearing for 10mm diameter micro gas turbine is described Journal bearing is hydrostatic gas-lubricated type. Numerical simulation is performed with ANSYS CFX 11.0 which is commercial numerical tool. Repulsive force when there is radial displacement in bearing and returning time is calculated using steady and unsteady cases. Auto re-meshing technic is used for moving mesh unsteady cases which simulate displacement of axis and its movement. The simulation results are used for further design of micro gas turbine, and experiment will be done later.

• International Journal of Automotive Technology
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• v.8 no.1
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• pp.1-7
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• 2007

The effect of the di-tertiary butyl peroxide (DTBP) additive on the heat release rate and emissions of a homogeneous charge compression ignition (HCCI) engine fueled with high Research Octane Number (RON) fuels were investigated. The experiments were performed using 0%, 1%, 2%, 3%, and 4% (by volume) DTBP-RON90 blends. The RON90 Fuel was obtained by blending 90% iso-octane with 10% n-heptane. The experimental results show that the operation range was remarkably expanded to lower temperature and lower engine load with the DTBP additive in RON90 fuel. The first ignition phase of HCCI combustion was observed at 850 K and ended at 950 K while the hot ignition occurred at 1125 K for all fuels at different engine working conditions. The chemical reaction scale time decreases with the DTBP addition. As a result, the ignition timing advances, the combustion duration shortens, and heat release rates were increased at overall engine loads. Meanwhile, the unburned hydrocarbon (UHC) and CO emissions decrease sharply with the DTBP addition while the NOx emissions maintain at a lower level.

• Journal of Astronomy and Space Sciences
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• v.13 no.2
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• pp.30-40
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• 1996

The telecommand system of KITSAT micorsatellite receives commands from ground stations or on-board computers. It decodes, validates and delivers commands to sub-system. The telemetry system is to collect, process and format satellite housekeeping and mission data for use by on-board computer and ground station. It is crucial for the telemetry and telecommand system to have high reliability since the spacecraft operation is mostly based on the function of this system. The telemetry and telecommand(TTC) systems for KITSAT-1 and 2 had been developed under the consideratin of the space environment of Low-Earth-Orbit and the limited mass, volume and power of micorsatellite. Since both satellites were launched in August 1992 and September 1993 respectively, the have shown to be working successfully as well as the TTC systems on-board both satellites.

• International Journal of High-Rise Buildings
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• v.6 no.1
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• pp.101-111
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• 2017

The objective of this study is to determine the effectiveness of a modified air-side economizer in improving indoor air quality (IAQ). An air-side economizer, which uses all outdoor air for cooling, affects the building's IAQ depending on the outside air quality and can significantly affect the occupants' health, leading to respiratory and heart disease. The Air Quality Index (AQI), developed by the US Environmental Protection Agency (US EPA), measures air contaminants that adversely affect human beings: PM10, PM2.5, SO2, NO2, O3, and CO. In this study, AQI is applied as a control for the operation of an air-side economizer. The simulation is analyzed, comparing the results between the differential enthalpy economizer and AQI-modified economizer. The results confirm that an AQI-modified economizer has a positive effect on IAQ. Compared to the operating differential enthalpy economizer, energy increase in an operating AQI-modified economizer is 0.65% in Shanghai and 0.8% in Seoul.

• Journal of Korea Society of Digital Industry and Information Management
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• v.15 no.4
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• pp.9-17
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• 2019

Sun power generation systems which use large capacity centralized inverters have loss of power generation due to cloud and building shadows, pollution, cell deterioration, etc. To minimize loss of power generation, decentralized solar power systems using multiple micro-inverters are being proposed as an alternative. A distributed solar power system consisting of a system-connected system uses power line communication to collect data from the micro-inverters. Power line communication has the advantage of using power lines without separate lines for data transmission, but in distributed solar power generation systems that use a large number of micro-inverters, the bit error rate is less reliable due to the phenomenon caused by limited transmission power, high load interference and noise, variable signal attenuation, and impedance characteristics. So we proposed wireless intelligent controller for micro-inverter that is used to build distributed solar power systems. and we design and implement that. Further, the proposed wireless intelligent controller for micro-inverter was used to establish a small-volume solar power plant to check its function and operation.