• Tunnel and Underground Space
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• v.27 no.1
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• pp.12-25
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• 2017

In local underground mines heavily depending on the natural ventilation, ducted fan auxiliary ventilation system is strongly recommended instead of the total mine ventilation system requiring large capital and operating costs. Optimizing the installation of ducted fans in series in long large-opening mines is required to assure the economy and efficiency of the ventilation system. The two most critical design parameters for optimization are the wall separation distance and gap length between adjoining ducts. This study aims at deriving the optimal values for those two parameters concerning the economic and environmental aspects through the extensive CFD analysis, which minimizes pressure loss, leakage and entrainment of the contaminated air in the gap space. The ranges of the wall separation distance and gap length for study are selected by taking into consideration the existing recommendations and guidelines. The ultimate goal is to optimize the auxiliary ventilation system using ducted fans in series to provide a reliable and efficient solution to maintain clean and safe workplace environment in local long underground mines.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.212-219
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• 2021

Chemical accidents caused by transport vehicles account for 20% of all chemical accidents every year, but there are difficulties in the accident-response process due to repeated situations where the impact assessment information is unknown. In this study, we developed a calculation table and formula for predicting the range of damage for chlorine and hydrogen fluoride, which have a high domestic usage, high risk of accidents, and high accident frequency in the last 7 years. The calculation table is based on the leakage rate, wind speed, and temperature, and the calculation formula was derived using R software for special situations where it is difficult to apply the calculation table. The calculation table and formula could be used on site by related organizations to obtain important information for decision making, which could help in minimizing damage from chemical accidents, setting separation distances, and deciding to evacuate residents.

• Journal of the Korea Institute of Building Construction
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• v.18 no.4
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• pp.337-345
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• 2018

In this study, observations of oil leakage samples taken from the actual site were performed to identify the causes of the oil leakage phenomenon. As a result, the separation of the material components was determined as the main cause of the oil leakage phenomenon based on the changes in the surface conditions, and verification of this was conducted. The evaluation results confirmed that the filler component of the asphalt mastic subsided with the lapse of the settling time, and that the difference ratio of the filler contents of the upper and lower specimens was up to 23.8% after day 28. Based on these results, a hypothesis on the oil leakage mechanism of asphalt mastic was established, and then modeling of the entire process of oil leakage was performed.

• Journal of electromagnetic engineering and science
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• v.3 no.1
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• pp.1-6
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• 2003

In this paper, a sub-harmonic dual-gate FET mixer is suggested to improve the isolation characteristic between LO and RF ports of an unbalanced mixer. The mixer was designed by using single-gate FET cascode structure and driven by the second harmonic component of LO signal. A dual-gate FET mixer has good isolation characteristic since RF and LO signals are injected into gatel and gate2, respectively. In addition, the isolation characteristic of a sub-harmonic mixer is better than that of a fundamental mixer due to the large frequency separation between the LO and RF frequencies. As RF power was -30 ㏈m and LO power was 0 ㏈m, the designed mixer yielded the -47.17 ㏈m LO-to-RF leakage power level, 10 ㏈ conversion gain, -2.5 ㏈m OIP3, -12.5 ㏈m IIP3 and -1 ㏈m 1 ㏈ gain compression point. Since the LO-to-RF leakage power level of the designed mixer is as good as that of a double-balanced mixer, the sub-harmonic dual-gate FET mixer can be utilized instead.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.601-612
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• 2005

In mountainous area, Two parallel tunnels have been usually recognized as a road tunnel which has benefits in aspects of cost and stability. However, Design and construction of 2-Arch road tunnel are growing recently due to environmental destruction, compensation of land and difficulty of route separation. As studies are mainly undergoing on only guaranteeing stability and developing a waterproofing-drainage system to avoid water leakage through comprehension for characteristics of 2-arch tunnel behaviors, there is a tendency to evaluate quantity of support by empirical method with a tunnel which has a complicated cross-section and lack of construction ability. In this study, therefore, we made a plan of tunnel cross-section which had shown good construction ability and developed the waterproofing-drainage system which is able to solve the water leakage problem fundamentally by analyzing precedented 2-arch tunnels and investigating their sites in and out of nation. We also determined fixed quantity of support by a large-scale model test and numerical analysis. We want to contribute to 2-arch tunnel design hereafter introducing design procedure and method applied here.

• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2201-2206
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• 2010

To improve the separation property and stability of metal chelate Cu(II) column, three new kinds of multidentate aminocarboxy silica columns with cation-exchange properties were synthesized using glutamic acid (Glu), glutamic acidbromoacetic acid (Glu-BAA), glutamic acid-bromosuccinic acid (Glu-BSUA) as ligands and silica gel as matrix. The standard proteins were separated with prepared chromatographic columns. The stationary phases exhibited the metal chelate property after fixing copper ion (II) on the synthesized multidentate ligand silica columns. The binding capacity of immobilized metal ion was related with the dentate number of multidentate ligands. Chromatographic behavior of proteins and the leakage of immobilized metal ion on multidentate chelate Cu(II) columns were affected by the dentate number of multidentate ligands and competitive elution system directly. The results showed that quinquedentate Glu-BSUA-Cu(II) column exhibited better chromatographic property and stability as compared with tridentate Glu-Cu(II) column, tetradentate Glu-BAA-Cu(II) column and commonly used IDA-Cu(II) column.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.40 no.4
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• pp.407-412
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• 1995

Experiments were conducted to obtain information on separation of nonviable seeds from seed lots by the nondestructive ways. Seeds of sesame, welsh onion and lettuce were artificially aged at 90% relative humidity and 45$^{\circ}C$ to get different seed qualities. The relationships between seed quality and leakage of total sugars, amino acids, and proteins into soaking water were determined to know a possibility of grading seeds. Dead seeds of lettuce leaked significant amounts of total sugars, amino acids, and proteins, while high quality seeds leaked negligeable amounts of total sugars and some of amino acids and proteins. Dead seeds of welsh onion leaked significant amounts of amino acids and some total sugars and proteins, while high quality seeds leaked negligeable amounts of these compounds. Sesame seeds leaked little total sugars, amino acids, and proteins regardless of seed quality.

• Journal of Mechanical Science and Technology
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• v.19 no.8
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• pp.1544-1553
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• 2005

In this article, a micro cantilever array actuated by PZT films is designed and fabricated for micro fluidic systems. The design features for maximizing tip deflections and minimizing fluid leakage are described. The governing equation of the composite PZT cantilever is derived and the actuating behavior predicted. The calculated value of the tip deflection was 15 ${\mu}m$ at 5 V. The fabrication process from SIMOX (Separation by oxygen ion implantation) wafer is presented in detail with the PZT film deposition process. The PZT films are characterized by investigating the ferroelectric properties, dielectric constant, and dielectric loss. Tip deflections of 12 ${\mu}m$ at 5 V are measured, which agreed well with the predicted value. The 18 ${\mu}l/s$ leakage rate of air was observed at a pressure difference of 1000 Pa. Micro cooler is introduced, and its possible application to micro compressor is discussed.

• Journal of the Semiconductor & Display Technology
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• v.5 no.3 s.16
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• pp.29-32
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• 2006

Because of new requirements related to the employment of SMT(Surface Mounting Technology) manufacturing and the diversity of components on high density PCB(Printed Circuit Boards), Thermal control of the reflow process is required in order to achieve acceptable yields and reliability of SMT assemblies. Accurate control of the temperature distribution during the reflow process is one of the major requirements, especially in lead-free assembly. This study has been performed for reflow process using the commercial CFD(Computational Fluid Dynamics) tool for predicting flow and temperature distributions. Porous plate was installed to prevent leakage flow which was one of the major problem of temperature uniformity in the reflow process. There is a separation region where the flow is turned. Outside wall made of porous plate is to prevent and minimize separation region for acquiring uniform temperature during operation. This paper provided design concept from CFD results of the steady state temperature distribution and flow field inside a reflow oven.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.165-166
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• 2014

The Composite waterproofing began to rise gradually 2000s in domestic. However, the sheet-membrane composite waterproofing method also acts as an abutment vulnerability that was a problem in a single method, and had the problem of damage to the formation of leakage paths. The existing non-overlap method, through vigorous research abutting sheet shall or could be developed to improve the seal performance of this method with the I-type joint coating material. Nevertheless, it has an integral top coat paint membrane and a sheet abutment limitation, damage to the upper membrane is damaged junction coating membranes has been generated. In this study, a method that has a layer of insulation on the joint bond breaker concept development, and to determine the physical properties with insulated joints to determine the breaking off of the upper joint is damaged coating membrane and tensile performance.