• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2274-2279
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• 2008

This paper numerically investigates thermo-flow characteristics of offset strip fins to obtain a correlation of heat transfer and pressure drop. The flow is divided into three regimes, i.e. laminar, transition and turbulent. The predicted j and f values from the SST k-w turbulence model agree with previous correlations with the error less than 20% in transition and turbulent regimes. Prandtl number is varied from 0.5 to 40 and a correlation to predict heat transfer and pressure drop for offset strip fins is suggested.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.694-700
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• 1998

A novel zero-voltage-transition (ZVT) isolated PWM boost converter for single stage power factor correction (PFC) is presented to improve the performance of the previously presented ZVT converter[8]. A simple auxiliary circuit which includes only one active switch provides zero-voltage-switching (ZVS) condition to all semiconductor devices. (Two active switches are required for the previous ZVT converter) This leads to reduced cost and simplified control circuit comparing to the previous ZVT converter. The ZVS is achieved for wide line and load ranges with minimum device voltage and current stresses. Operation principle, control strategy and features of the proposed converter are presented and verified by the experimental results from a 1.5 kW, 100 KHz laboratory prototype.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.305-314
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• 2001

A modified model is proposed for calculation of transitional boundary layer flows. In order to develop the eddy viscosity model for the problem, the flow is divided into three regions; namely, pre-transition region, transition region and fully turbulent region. The pre-transition eddy-viscosity is formulated by extending the mixing length concept. In the transition region, the eddy-viscosity model employs two length scales, i.e., pre-transition length scale and turbulent length scale pertaining to the regions upstream and the downstream, respectively, and a universal model of stream-wise intermittency variation is used as a function bridging the pre-transition region and the fully turbulent region. The proposed model is applied to calculate three benchmark cases of the transitional boundary layer flows with different free-stream turbulent intensity (1%∼6%) under zero-pressure gradient. It was found that the profiles of mean velocity and turbulent intensity, local maximum of velocity fluctuations, their locations as well as the stream-wise variation of integral properties such as skin friction, shape factor and maximum velocity fluctuations are very satisfactorily predicted throughout the flow regions.

• Proceedings of the Zoological Society Korea Conference
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• 1994.10a
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• pp.178.1-178
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• 1994

No Abstract, See Full Text

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.9
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• pp.4137-4142
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• 2015

The zinc finger transcription factor EGR 1 has a role in controlling synaptic plasticity, wound repair, female reproductive capacity, inflammation, growth control, apoptosis and tumor progression. Recent studies mainly focused on its role in growth control and apoptosis, however, little is known about its role in epithelial-mesenchymal transition (EMT). Here, we aim to explore whether EGR 1 is involved in TGF-${\beta}1$-induced EMT in non-smallcell lung cancer cells. Transforming growth factor (TGF)-${\beta}1$ was utilized to induce EMT in this study. Western blotting, RT-PCR, and transwell chambers were used to identify phenotype changes. Western blotting was also used to observe changes of the expression of EGR 1. The lentivirus-mediated EGR 1 vector was used to increase EGR 1 expression. We investigated the change of migration to evaluate the effect of EGR 1 on non-small-cell lung cancer cells migration by transwell chambers. After stimulating with TGF-${\beta}1$, almost all A549 cells and Luca 1 cells (Non-small-cell lung cancer primary cells) changed to mesenchymal phenotype and acquired more migration capabilities. These cells also had lower EGR 1 protein expression. Overexpression of EGR 1 gene with EGR 1 vector could decrease tumor cell migration capabilities significantly after adding TGF-${\beta}1$. These data s howed an important role of EGR 1 in the EMT of non-small-cell lung cancer cells, as well as migration.

• Nutrition Research and Practice
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• v.11 no.2
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• pp.83-89
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• 2017

BACKGROUND/OBJECTIVES: Epithelial-mesenchymal transition (EMT) is involved in not only cancer development and metastasis but also non-cancerous conditions. Hypoxia is one of the proposed critical factors contributing to formation of chronic rhinosinusitis or nasal polyposis. Wheatgrass (Triticum aestivum) has antioxidant, anti-aging, and anti-inflammatory effects. In this study, we analyzed whether wheatgrass has an inhibitory effect on the EMT process in airway epithelial cells. MATERIALS/METHODS: A549 human lung adenocarcinoma cells were incubated in hypoxic conditions ($CO_2$ 5%/$O_2$ 1%) for 24 h in the presence of different concentrations of wheatgrass extract (50, 75, 100, and $150{\mu}g/mL$) and changes in expression of epithelial or mesenchymal markers were evaluated by immunoblotting and immunofluorescence. Accordingly, associated EMT-related transcriptional factors, Snail and Smad, were also evaluated. RESULTS: Hypoxia increased expression of N-cadherin and reduced expression of E-cadherin. Mechanistically, E-cadherin levels were recovered during hypoxia by silencing hypoxia inducible factor (HIF)-$1{\alpha}$ or administering wheatgrass extract. Wheatgrass inhibited the hypoxia-mediated EMT by reducing the expression of phosphorylated Smad3 (pSmad3) and Snail. It suppressed the hypoxia-mediated EMT processes of airway epithelial cells via HIF-$1{\alpha}$ and the pSmad3 signaling pathway. CONCLUSION: These results suggest that wheatgrass has potential as a therapeutic or supplementary agent for HIF-1-related diseases.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.63-69
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• 2022

Vanadium dioxide shows a unique and interesting property of metal-insulator transition, which has attracted great attention from the viewpoints of fundamental materials science and industrial applications. In this study, the effect of Mg and W addition on the metal-insulator transition of VO₂ were investigated for the bulk materials that are prepared by spark plasma sintering. The X-ray diffraction analysis of the sintered specimens revealed that the lattice parameters barely change, and the secondary phases are present. The transition temperature of MIT appears in the range of 64.2-64.6℃, regardless of the impurity element and content. On the other hand, the addition of Mg and W alters the electrical conductivity, i.e., the electrical conductivity increases by a factor of up to 2.4 or decrease by a factor of up to 57.4 depending on the impurity type and its content. The thermal conductivity showed the values of 1.8~2.5 W/m·K below the transition temperature, and the values of 1.9~2.8 W/m·K above the transition temperature. These changes in electrical and thermal conductivities can be attributed to the combination of the change in charge carrier density, the impurities as scattering centers, and the change in microstructures.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.1
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• pp.51-60
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• 2005

This paper reviews the studies on the pressure drop and the heat transfer in microchannels. Although a lot of studies about the single-phase flow have been done until now, conflicting results are occasionally reported about flow transition from laminar flow to turbulent flow, friction factor, and Nusselt number. Some studies reported the early flow transition due to relatively greater wall effect like surface roughness, but the other studies showed that the flow transition occurred at the Reynolds number of about 2300 and the early flow transition might be due to less accurate measurement of the channel geometry. Also, there have been arguments whether the conventional relation based upon continuum theory can be applied to the fluid flow and the heat transfer in microchannels without modification or not. The studies about the two-phase flow in microchannels have been mostly about investigating the flow pattern and the pressure drop in rectangular channels using two-component, two-phase flow like air/water mixture. Some studies proposed correlations to predict two-phase flow pressure drop in microchannels. They were mostly based on Lockhart-Martinelli model with modification on C-coefficient, which was dependent on channel geometry, Reynolds number, surface tension, and so on. Others investigated the characteristics of flow boiling heat transfer in microchannels with respect to test parameters such as mass flux, heat flux, system pressure, and so on. The existing studies have not been fully satisfactory in providing consistent results about the pressure drop and the heat transfer in microchannels. Therefore, more in-depth studies should be done for understanding the fundamentals of the transport phenomena in the microchannels and giving the basic guidelines to design the micro devices.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.8
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• pp.62-69
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• 2005

This paper presents the improved AC/DC PFC(Power-Factor-Correction) ZVT(Zero-Voltage-Transition) Boost Converter. The conventional AC/DC PFC ZVT Boost Converter minimizes the switching loss of the main switch within all of the load range. That is because AC/DC PFC ZVT Boost converter makes the main switch and the auxiliary switch turn on simultaneously so that it makes ZVS (Zero-Voltage-Switching) possible at the light load. However, it has two problems that ale large loss of the auxiliary switch and the increasing of the reverse current of the main switch. Therefore this research presents high efficiency to reduce the current stress of the auxiliary switch and the reverse current of main switch by adding a diode to the conventional ZVT converter. The prototype of 640[W], 100[kHz] system using MOSFET is implemented for this experimental verification.

• Journal of the Korean Ceramic Society
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• v.45 no.5
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• pp.263-267
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• 2008

$(Bi_{1/2}Na_{1/2})TiO_3$-based ceramics have been intensively studied as lead-free piezoelectric ceramics. In this study, the piezoelectric properties and phase transition behaviors of BNT based solid solution $(Bi_{0.5}Na_{0.5})_{1-x}Ca_xTiO_3$ ($X=0.01{\sim}0.25$) were investigated. The morphotropic phase boundary(MPB) zone which BNT is transformed from rhombohedral to cubic structure was appeared by adding $CaTiO_3$ with 0.12 mol by the measurement of permittivity and X-ray diffraction. The behavior which ferroelectric BNT with adding $CaTiO_3$ was changed to antiferroelectric and paraelectric state was confirmed by the measurement ofhysterisis loop and depolarization temperature as a function of temperature. As $CaTiO_3$ concentration was increased, the phase transition temperature was decreased. The piezoelectric properties were highest at 0.01 mol of $CaTiO_3$ concentration. The electromechanical coupling factor($K_t$) and mechanical quality factor($Q_m$) were 42% and 254, respectively.