• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.135-140
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• 2005

This paper summarizes the recent progress made by our group at Seoul National University on studies of the evolution and formation of distant galaxies. Various research projects are currently underway, which include: (i) the number density of distant early-type galaxies (z < 1); (ii) the optical-NIR color gradient of nearby early-type galaxies; (iii) J - K-selected Extremely Red Objects (EROs) in field (CDF-S) and the cluster environment; and (iv) the Lyman-break galaxies in the Spitzer First Look Survey (FLS) field. These works will constrain the mass evolution and the star formation history of galaxies in different environments, and the results will serve as useful contraints on galaxy formation models.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.105-108
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• 2002

Polyimide-epoxysilane (coupling agent) composites were reacted with oligomeric PDMS, a condensation product of difunctional silane, by a sol-gel process and were then dried into films. And then, the surface, mechanical, and electric properties were measured. The study showed that PDMS existed in the polyimlde matrix by the use of FT-IR. In the mechanical properties, the maximum elongation and toughness was increased in the polyimide with silane-groups. But the maximum tensile strength was slightly decreased. And the intensive dispersion of the silane-groups on the surface of polyimide was ascertained through XPS measurement. In the electric properties, AC break down voltage was increased by increasing the amount of difunctional silane. This experiment showed that PDMS added polyimide had better mechanical and electric properties than classical materials.

• Proceedings of the KIEE Conference
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• 2006.04b
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• pp.185-187
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• 2006

The line-start permanent magnet synchronous motor has a high efficiency and an advantage in constant speed operation regardless of the effect of load variation. However it is difficult to predict the performance of characteristics accurately, because of the unbalanced starting torque with the initial starting position of the rotor and the generation of a break torque. In this paper the dynamic characteristics of the line-start permanent magnet synchronous motor are described and compared with those of the squirrel-cage induction motor through the simulation to find the characteristics of the permanent magnets and the rotor bars in the line-start permanent magnet synchronous motor.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.8 no.2
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• pp.76-82
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• 2009

In this papers, Study on the Bonding property and Strength Evaluation in Bonding interface Joints of Dissimilar material using DOE. We found optimal condition that uses experimental design method (Response Surface Analysis, DOE) used temperature, pressure, time on experiment factor. And we could get bonding condition and strength that break and crack do not happen in mechanical processing about united dissimilar material. And progress 3 point bending tests and verified result.

• Tunnel and Underground Space
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• v.7 no.4
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• pp.267-273
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• 1997

Rock fragmentation with plasma blasting technique has advantageous properties in contrast to the conventional blasting method in controlling of flying rocks and ground vibrations, when residents are complaining or surrounding structures stay in protection from blasting operations. The experiences show in urban construction works that the plasma blasting is the most possible method to prevent damages and minimize adverse environmnetal impacts. The fragmentation energy level is evaluated by numerical simulation using PFC-2D for various drill hole pattern and tested accordingly to get the feasibility. The energy output of plasma blasting system has been improved to a level of 1 MJ, which can break a 2~3 ㎥ granite boulder or 1.5 m height bench face. Measurements are carried out to get the ground vibration level and propagation equation, so that the control of the blasting operations can be performed more precisely and safely.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.1
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• pp.46-51
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• 2007

Environmental contamination creates shortages of potable water. In such situations, the leakage of water due to breakage or aging of rubber valve seats is a serious problem. Rubber is apt to break when it is placed between two materials that contact each other. One way to avoid water leakage due to rubber damage and breakdown is to replace the rubber with metal, which is currently taking place in water distribution systems. In tribology, a severe form of wear is characterized by local macroscopic material transfer or removal, or by problems with sliding protrusions when two solid surfaces experience relative sliding under load. One of the major problems when metal slides is the occurrence of galling. Experimentally, various conditions influence incipient galling, such as hardness, surface roughness, temperature, load, velocity, and the external environment. This study sought to verify the galling tendencies of metal according to its hardness, surface roughness, load, and sliding velocity, and determine the quantitative effect of each factor on the galling tendencies.

• Macromolecular Research
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• v.9 no.1
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• pp.30-36
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• 2001

Polybutadiene latex grafted (g-PB) in g-PB/SAN blends, i.e., acrylonitrile-butadiene-styrene terpolymer (ABS) were partially replaced by acrylonitrile-butadiene copolymer (NBR) with various acrylonitrile (AN) contents. Changes in morphology, physical and rheological properties were examined. The dispersed size of NBR was decreased as the miscibility with matrix SAM, was increased by increasing AN content in NBR upto 50 wt%. Impact strength was enhanced about two-fold due to the NBR dispersed with a slight larger size than the original g-PB. Gloss was effectively reduced as the particle size of NBR was increased. Tensile yield strength was decreased, and elongation at break or yield behavior at low shear rate were increased as g-PB was partially replaced by NBR having AN content less that 40 wt%.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• autumn
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• pp.292-295
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• 2002

A purpose of subcontractor management succeed in construction project. Specially in the subcontractor management of quality management, it is necessary that subcontractors not only acquire ISO 9000 quality system certification but also continuously and without a break fulfill ISO 9000 quality system. As a result, we proposed that a general contractor play an important role in a manager of subcontractors to keep up the ISO 9000 duality system of subcontractors.

• Journal of the Korean Society of Safety
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• v.17 no.3
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• pp.90-95
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• 2002

Den have been many construction projects in urban n We have a lot of problems which have to be solved especially against residence complaints existing building damage due to construction worts. We sometimes have to pay a certain amount of cost to solve the above problem, not in planning. In addition to, we have to suffer from work delay due to confronting problem. Almost all of these are due to blasting work to break solid rock to be excavated. Therefore, this study is focused on finding out how to reduce noise more cheaply. Four cases(4) as cheaper but more effective way have been tested to find out which way of local fence will have better moise reduce function in a field site. Where five(5) large breakers are being operated. It is concluded that more form and shape of local movable panel than the site of panel can be influenced on noise reduce.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1599-1607
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• 2003

The characteristics of elastic waves emanated from crack initiation in 6061 aluminum alloy subjected to fatigue loading are investigated through experiments. The objective of the study is to determine the differences in the properties of the signals generated from fatigue test and also to examine if the sources of the waves could be identified from the temporal and spectral characteristics of the acoustic emission (AE) waveforms. The signals are recorded using nonresonant, flat, broadband transducers attached to the surface of the alloy specimens. The time dependence and power spectra of the signals recorded during the tests were examined and classified according to their special features. Six distinct types of signals were observed. The waveforms and their power spectra were found to be dependent on the crack propagation stage and the type of fracture associated with the signals. The potential application of the approach in health monitoring of structural components using a network of surface mounted broadband sensors is discussed.