• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.107-114
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• 2003

The influence of property difference in refraction index on micro PIV measurement of two-fluid flow in a microchannel was analyzed. The difference of measurement planes in two fluids would bring misunderstanding of the physics. The objective-imaging system for two-fluid flow measurement was presented, and the condition for measurement of valid velocity profile across two-fluid interface was derived. A micro PIV experimental system was set up to measure two-fluid flow inside a Y-shape microchannel. Under the conditions, three cases of two-fluid flow of glycerol solutions at different concentration (${\phi}$), e.g., (${\phi}=0\;and\;{\phi}=0.2,\;{\phi}=0.1\;and\;{\phi}=0.5,\;{\phi}=0\;and\;{\phi}=0.6$, were measured. Close agreement of experimental and numerical results was found.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.7-11
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• 2017

This paper describes a design concept of NPC1 power stack for 1500VDC megawatt level solar inverter. This stack uses three latest half-bridge IGBT modules with highest power density and operation junction temperature, which enable realization of power level beyond 1MW without paralleling. Critical design concept on loop inductance is explained. Dynamic characteristics are verified by double-pulse test. Thermal characteristics and output power limits are verified by thermal test. Temperature-sensitive component on PCB as output power constraint is identified. Different PCB repositioning solutions are tested to give the overall output power thermal derating curves, which enable output power of 1.15MW at $T_A=55^{\circ}C$ with $15^{\circ}C$ thermal margin. The power stack characteristic and performance change under different thermal environment is further analyzed.

• Journal of the Korea Furniture Society
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• v.17 no.4
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• pp.15-26
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• 2006

This article is composed of three parts in this article. The first part reviews, in the general, condition on Chinese forest resource history and analyzes the change in different historical times. The present condition and existing problems are discussed in the second part, where analyzes the existing problems in different distribution areas. In the third part, the solutions are raised to solve the problems mentioned in the second part. Finally the objective and strategy for sustainable development of Chinese forest resources are put forward.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.25 no.3
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• pp.117-131
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• 2021

The problem of generalized thermoelasticity of two-temperature for finite piezoelectric rod will be modified by applying three different types of heating applications namely, thermal shock, ramp-type heating and harmonically vary heating. The solutions will be derived with direct approach by the application of Laplace transform and the Caputo-Fabrizio fractional order derivative. The inverse Laplace transforms are numerically evaluated with the help of a method formulated on Fourier series expansion. The results obtained for the conductive temperature, the dynamical temperature, the displacement, the stress and the strain distributions have represented graphically using MATLAB.

• Current Optics and Photonics
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• v.5 no.3
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• pp.278-288
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• 2021

We propose a characterization method for the scattering property of microspheres using spectroscopic optical coherence tomography (OCT). To prove the effectiveness of the proposed method, we prepare solutions of different concentrations using microspheres ranging from 28 to 2300 nm in diameter. Time-frequency analysis is performed on the measured interference spectrum of each solution, and the resulting spectroscopic information is converted into histograms for centroid wavelengths. The histograms present a very sensitive response to changes in the concentration and size of microspheres. We classify them into three categories according to their characteristics. When the histogram of each category is replaced with the corresponding calculated value of the scattering coefficient, each category is mapped to a different scattering-coefficient region. It is expected that the proposed method could be used to investigate the optical characteristics of a biological sample from OCT images, which would be helpful for optical diagnostic and therapeutic applications.

• Journal of Environmental Science International
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• v.23 no.7
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• pp.1223-1232
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• 2014

Density currents have been easily observed in environmental flows, for instance turbidity currents and pollutant plumes in the oceans and rivers. In this study, we explored the propagation dynamics of density currents using the FLOW-3D computational fluid dynamics code. The renormalization group (RNG) $k-{\varepsilon}$ scheme, a turbulence numerical technique, is employed in a Reynold-averaged Navier-Stokes framework (RANS). The numerical simulations focused on two different types of intrusive density flows: (1) propagating into a two-layer ambient fluid; (2) propagating into a linearly stratified fluid. In the study of intrusive density flows into a two-layer ambient fluid, intrusive speeds were compared with laboratory experiments and analytical solutions. The numerical model shows good quantitative agreement for predicting propagation speed of the density currents. We also numerically reproduced the effect of the ratio of current depth to the overall depth of fluid. The numerical model provided excellent agreement with the analytical values. It was also clearly demonstrated that RNG $k-{\varepsilon}$ scheme within RANS framework is able to accurately simulate the dynamics of density currents. Simulations intruding into a continuously stratified fluid with the various buoyancy frequencies are carried out. These simulations demonstrate that three different propagation patterns can be developed according to the value of $h_n/H$ : (1) underflows developed with $h_n/H=0$ ; (2) overflows developed when $h_n/H=1$ ; (3) intrusive interflow occurred with the condition of 0 < $h_n/H$ < 1.

• Restorative Dentistry and Endodontics
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• v.17 no.2
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• pp.263-286
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• 1992

This study was performed to evaluate and compare the cytotoxic effects of five root canal sealers to several different cell lines. Five root canal sealers were AH-26, N2, Sealapex, Tubliseal, and Vitapex. Each sealers were mixed according to the manufacturer's instructions, and culture media were added to each sealers immediately after mixing (the immediate group) and after three days (the third day group) and seven days (the seventh day group) respectively. And every sealer solutions were diluted to 1:1, 1:2, 1:3 and 1:4. Three different permanent cell lines (HEp-2, McCoy, MRC-S) and human gingival fibroblasts and mononuclear cells were challenged by each sealer solution and the cytopathic effects were evaluated using MTT-ELISA, MTT-microscopy, and lactate dehydrogenase (LD) activity. The results were as follows: 1. In HEp-2 and MRC-5 cells, Vitapex was the least cytotoxic sealers. 2. AH-26 showed mild cytotoxic effects to HEp-2, gingival fibroblast and mononuclear cells. 3. N2 was the most toxic sealer to gingival fibroblast and it showed relatively strong cytotoxicity to HEp-2, McCoy and MRC-S cells. 4. Tubliseal showed strong cytotoxic effects to HEp-2, McCoy, MRC-S, and mononuclear cells. 5. Sealapex showed strong cytotoxic effect to HEp-2, McCoy, and gingival fibroblasts.

• Computers and Concrete
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• v.26 no.6
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• pp.533-546
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• 2020

The prediction of spall response of reinforced concrete members like columns and slabs have been attempted by earlier researchers with analytical solutions, as well as with empirical models developed from data generated from physical or numerical experiments, with different degrees of success. In this article, compared to the empirical models, more versatile and accurate models are developed based on model-free approach of artificial neural network (ANN). Synthetic data extracted from the results of numerical experiments from literature have been utilized for the purpose of training and testing of the ANN models. For two concrete members, namely, slabs and columns, different sets of ANN models were developed, each of which proved to have definite advantages over the corresponding empirical model reported in literature. In case of slabs, for all three categories of spall, the ANN model results were superior to the empirical models as evaluated by the various performance metrics, such as correlation, root mean square error, mean absolute error, maximum overestimation and maximum underestimation. The ANN models for each category of column spall could handle three variables together: namely, depth, spacing of longitudinal and transverse reinforcement, as contrasted to the empirical models that handled one variable at a time, and at the same time yielded comparable performance. The application of the ANN models for spall prediction of concrete slabs and columns developed in this study has been discussed along with their limitations.

• Korean Journal of Human Ecology
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• v.6 no.1
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• pp.27-34
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• 2003

We investigated the bacterial and chemical retting conditions of ramie grown in Hansan. Bacterial retting was done in troughs at a temperature of 30${\pm}$2$^{\circ}C$ for 1, 2, 3, 4, 5, 6 and 10 days. Chemical retting(CR) was done at the different conditions using sodium silicate (Na$_2$SiO$_3$), sodium carbonate(Na$_2$CO$_3$) and sodium hydroxide(NaOH) as alkali solutions. The retting solution was boiled during 1. 2, 4 and 6 hours respectively at the different concentration(0.5, 2.0, 4.0, 6.0. 8.0 %) with decorticated ramie stems submerged in it. The treated ramie was then rinsing with running tap water thoroughly, which was further soaker in 0.5% acetic acid (v/v) solution for three minutes and washed thoroughly with distilled water. Finally ramie was dried for 2 hours in vacuum oven at 100 $^{\circ}C$. To know change of ramie fiber characteristics retted at the different conditions, weight loss, fiber bundle strength were tested and color, texture, luster etc. were also sensually evaluated. The results were as follows. $.$ Weight loss of ramie retted in each alkali solutions were about 10%, 20% and 30% in sodium silicate, sodium carbonate and sodium hydroxide, respectively. $.$ Chemical retting was faster than bacterial retting, but the color of chemically retted ramies were worse than that of bacterially retted ramies. $.$ The combination of bacterial and chemical processing showed some merits. A combination of either 2 or 3 days of bacterial and then chemical retting might provide the best quality ramie. $.$ Ramie fiber became cottonized ramie when retted in 8% NaOH solution for 6-8hours.

• Earthquakes and Structures
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• v.12 no.3
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• pp.359-374
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• 2017

The seismic events in Northern Italy, May 2012, have revealed the seismic vulnerability of typical Italian precast industrial buildings. The aim of this paper is to present a seismic fragility model for Italian RC precast buildings, to be used in earthquake loss estimation and seismic risk assessment by comparing two building typologies and three different codes: D.M. 3-03-1975, D.M. 16-01-1996 and current Italian building code that has been released in 2008. Based on geometric characteristics and design procedure applied, ten different building classes were identified. A Monte Carlo simulation was performed for each building class in order to generate the building stock used for the development of fragility curves trough analytical method. The probabilistic distributions of geometry were mainly obtained from data collected from 650 field surveys, while the material properties were deduced from the code in place at the time of construction or from expert opinion. The structures were modelled in 2D frameworks; since the past seismic events have identified the beam-column connection as the weakest element of precast buildings, two different modelling solutions were adopted to develop fragility curves: a simple model with post processing required to detect connection collapse and an innovative modelling solution able to reproduce the real behaviour of the connection during the analysis. Fragility curves were derived using both nonlinear static and dynamic analysis.