• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.402.1-402.1
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• 2014

Photonic force microscopy (PFM) is an optical tweezers-based scanning probe microscopy, which measures the forces in the range of fN to pN. The low stiffness leads proper to measure single molecular interaction. We introduce a novel photonic force microscopy to stably map various chemical properties as well as topographic information, utilizing weak molecular bond between probe and object's surface. First, we installed stable optical tweezers instrument, where an IR laser with 1064 nm wavelength was used as trapping source to reduce damage to biological sample. To manipulate trapped material, electric driven two-axis mirrors were used for x, y directional probe scanning and a piezo stage for z directional probe scanning. For resolution test, probe scans with vertical direction repeatedly at the same lateral position, where the vertical resolution is ~25 nm. To obtain the topography of surface which is etched glass, trapped bead scans 3-dimensionally and measures the contact position in each cycle. To acquire the chemical mapping, we design the DNA oligonucleotide pairs combining as a zipping structure, where one is attached at the surface of bead and other is arranged on surface. We measured the rupture force of molecular bonding to investigate chemical properties on the surface with various loading rate. We expect this system can realize a high-resolution multi-functional imaging technique able to acquire topographic map of objects and to distinguish difference of chemical properties between these objects simultaneously.

• Journal of the Korean Geosynthetics Society
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• v.9 no.3
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• pp.39-45
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• 2010

When the ground temperature drops below $0^{\circ}C$, wet soils expand due to the ice formation in their porous space. This results in frost heave which causes structural stability problems. Frost heave is attributed by several factors such as physical soil properties and heat transfer including pore water phase change. Due to the complex physical phenomena, reliable and verified multi-dimensional numerical models for frost heave problems are still in a research stage. This study presents an efficient and simple method of overcoming numerical problems associated with sudden jump of heat capacity due to the phase change from water to ice in the pore space. This paper proposes heat transfer equation and finite element method when the saturated soils or porous rocks are subjected to freezing. Numerical analyses using the proposed method agree well with the known closed form solution and the laboratory test results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.235-249
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• 2011

A new form of I-type PSC bridge girder, which has hole in the web, is proposed in this paper. Three different concepts were combined and implemented in the design. First of all, a girder was precast at a manufacturing plant as divided pieces and assembled at the construction site using post-tensioning method, and the construction period at the site will be reduced dramatically. In this way, the quality of concrete can be assured at the manufacturing factory and concrete curing can be well controlled, and the spliced girder segments can be moved to the construction site without a transportation problem. Secondly, a numerous number of holes was made in the web of the girder. This reduces the self-weight of the girder. But more important thing related to the holes is that about half of the total anchorages can be moved from the girder ends into individual holes. The magnitude of negative moment developed at girder ends will be reduced. Also, since the longitudinal compressive stresses are reduced at ends, thick end diaphragm is not necessary. Thirdly, Prestressing force was introduced into the member through multiple stages. This concept of multi-stage prestressing method overcomes the prestressing force limit restrained by the allowable stresses at each loading stage, and maximizes the magnitude of applicable prestressing force. It makes the girder longer and shallower. Two 50 meter long full scale girders were fabricated and tested. One of them was non-spliced, or monolithic girder, made as one piece from the beginning, and the other one was assembled using post-tensioning method from five pieces of segments. It was found from the result that monolithic and spliced girder show similar load-deflection relationships and crack patterns. Girders satisfied specific girder design specification in flexural strength, deflection, and live load deflection control limit. Both spliced and monolithic holed web post-tensioned girders can be used to achieve span lengths of more than 50m with the girder height of 2 m.