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- 저자 : K. Usami (검색결과 2 건)
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Confinement evaluation of concrete-filled box-shaped steel columns
K.A.S. Susantha,Hanbin Ge,Tsutomu Usami 국제구조공학회 2001 Steel and Composite Structures, An International J Vol.1 No.3
This paper presents a three-dimensional finite element analysis methodology for a quantitative evaluation of confinement in concrete-filled box-shaped unstiffened steel columns. The confinement effects of concrete in non-circular sections can be assessed in terms of maximum average lateral pressure. A brief review of a previous method adopted for the same purpose is also presented. The previous method is based on a two-dimensional finite element analysis method involving a concrete-steel interaction model. In both the present and previous methods, average lateral pressure on concrete is computed by means of the interaction forces present at the concrete-steel interface. Subsequently, the strength enhancement of confined concrete is empirically related to the maximum average lateral pressure. The results of the former and latter methods are then compared. It is found that the results of both methods are compatible in terms of confined concrete strengths, although the interaction model yields a somewhat overestimated estimation of confinement than those of the present method when relatively high strength concrete is used. Furthermore, the confinement in rectangular-shaped sections is investigated and the reliability of previously adopted simplifications in such cases is discussed.
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High-density assembly of nanocrystalline silicon quantum dots
A. Tanaka,G. Yamahata,Y. Tsuchiya,K. Usami,H. Mizuta,S. Oda 한국물리학회 2006 Current Applied Physics Vol.6 No.3
This paper reports on a new bottomup technique of forming silicon nanostructures based on assembly of nanocrystalline (nc) Si dotsfrom the solution. The nc-Si dots with a diameter of 8 ± 1 nm were fabricated by using VHF plasma decomposition of pulsed SiH4 gassupply and deposited on the substrate randomly. We rst studied the method of making the nc-Si dot dispersion solution by immersingthe deposited wafer into various kinds of solvent with ultra sonic treatment. We found that methanol works as a suitable solvent for nc-Sidots. We then add a drop of the nc-Si dot solution onto other substrates and evaporated it. During the evaporation the nc-Si dots wereassembled in the solution via the lateral capillary meniscus force which works as an attractive force between the dots. Use of SiO2 sub-strate with good surface wettability with the solution was found vital to have the maximum meniscus force and to have two-dimensionalassembly of the dots. The evaporation speed was carefully controlled via temperature and evaporation pressure to achieve high dot den-scale patterning and succeeded in making the nc-Si dots cluster bridging between the nanoelectrodes with a gap of as small as 20 nm.
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