• Biomaterials and Biomechanics in Bioengineering
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• v.3 no.1
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• pp.1-14
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• 2016

Well-ordered porous materials are very promising in orthopedics since they allow tailoring the mechanical properties. Finite element (FE) analysis is commonly used to evaluate the mechanical behavior of well-ordered porous materials. However, FE results generally differ importantly from experimental data. In the present article, three types of manufacturing irregularities were characterized on an additive manufactured porous titanium sample having a simple cubic unit-cell: strut diameter variation, strut inclination and fractured struts. These were included in a beam FE model. Results were compared with experimental data in terms of the apparent elastic modulus (Eap) and apparent yield strength (SY,ap). The combination of manufacturing irregularities that yielded the closest results to experimental data was determined. The idealized FE model resulted in an Eap one order of magnitude larger than experimental data and a SY,ap almost twice the experimental values. The strut inclination and fractured struts showed the strongest effects on Eap and SY,ap, respectively. Combining the three manufacturing irregularities produced the closest results to experimental data. The model also performed well when applied to samples having different structural dimensions. We recommend including the three proposed manufacturing irregularities in the FE models to predict the mechanical behavior of such porous structures.

• Advances in materials Research
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• v.2 no.2
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• pp.119-131
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• 2013

Impedance and electrical conduction studies of $Ba(Nd_{1/2}Nb_{1/2})O_3$ ceramic prepared using conventional high temperature solid-state reaction technique are presented. The crystal symmetry, space group and unit cell dimensions were estimated using Rietveld analysis. X-ray diffraction analysis indicated the formation of a single-phase cubic structure with space group $Pm\bar{3}m$. Energy dispersive X-ray analysis and scanning electron microscopy studies were carried to study the quality and purity of compound. The circuit model fittings were carried out using the impedance data to find the correlation between the response of real system and idealized model electrical circuit. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type and negative temperature coefficient of resistance character. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in $Ba(Nd_{1/2}Nb_{1/2})O_3$. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy.

• Journal of the Korean Solar Energy Society
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• v.28 no.5
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• pp.28-35
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• 2008

The aim of this study was to analysis the Heating/cooling performance of movable insulation system built in apartments. The process of this study is as follows: 1) Test-cells of movable insulation are designed through the investigation of previous paper and work. The type of the movable insulation used in test-cell is low emissivity(5%) insulation, measured for heating season and the thermal effects are analyzed. 2) The simulation program(Design Builder) was used in energy performance analysis. the reference model of simulation was made up to analysis energy performance on movable insulation system. 3) Selected reference model(Floors:15, Area of Unit:115.5$m^2$) for heating/cooling energy analysis, Energy performance simulation with various variants, such as slate angle of movable insulation(5$^{\circ}$, 30$^{\circ}$, 50$^{\circ}$) and position of movable insulation. Consequently, When movable insulation system is equipped with balcony window of Apartment, Annual heating energy of reference model was cut down at the average of 5.4kWh/$m^2$ or 4.6% of heating/cooling energy.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.191-195
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• 2007

In this study, we estimated the performance of PEMFC's unit cell as changing operating temperature in different inlet humidity condition at cathode side but anode dry, and tried to match experimental results with 1-dimensional simulation. We used $Nafion^{\circledR}112$ membrane and a self-manufactured PEMFC with active area of $25cm^{2}$ was used in this study. The range of operating temperature was $40{\sim}70^{\circ}C$ and oxygen through bubbled humidity chamber was supplied $0{\sim}80$% humidity condition as changing water temperature in humidity chamber. For figuring out governing equations, represent water contents in electrolyte membrane, the linear forward difference method was applied about time progress and quadratic central difference method was used about space progress. It was assumed that pressure terms were linearly changed due to thin electrolyte membrane. In low operating temperature condition, $40{\sim}60^{\circ}C$, increasing temperature rarely effected cell performance but we can see performance drop at $70^{\circ}C$. By modifying Henrry's constant and/or diffusion coefficient, the modified one-dimensional model was accomplished for calculation.

• Journal of Physiology & Pathology in Korean Medicine
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• v.22 no.1
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• pp.82-88
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• 2008

We evaluated the potential protective activity of the traditional Korean medicinal herb, Corni fructus (CF), in an experimental model of hepatotoxicity induced by carbontetrachloride $(CCl_4)$. The CF exhibited a hepatoprotective activity against Chang cell. And The expression of cytochrome P450 2E1 (CYP2E1), measured by RT-PCR and western blot, was significantly decreased in the CF treated Chang cell. But $CCl_4$ and CF has no significant effect on 1A1 and 3A1 isoform of cytochrome P450. Based on these findings, it is suggested that hepatoprotective effects of CF possibly related to antioxidative effects and downregulation of CYP2E1 expression.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.4
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• pp.104-109
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• 2005

The catalyst layer design is one of the most important factors to enhance the performance of PEMFC(Proton Exchange Membrane Fuel Cell) system. The hydrophobic and ion conductive type is studied for the MEA(Membrane Electrolyte Assembly). It is found that those have some limitations for performance enhancement when they are used separately. Thus, the dual catalyst type, a mixed model, is developed for the better MEA performance. In the meantime, the design of flow field plate is subsequently carried out in order to give more enhanced output during its operation. The conductivity of flow field plate showed better performance in the case of manufactured by the more compressed process(20MPa) than by the less compressed process(10MPa). The micro-structure of the flow field plate is examined in details using SEM(Scanning Electron Microscope) to analyse the effects on the different compression processes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.12
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• pp.5898-5916
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• 2018

In this paper, the downlink performance of multi-cell distributed antenna systems (DAS) with a single user in each cell is investigated. Assuming the channel state information is available at the transmitter, four transmission modes are formulated as combinations of remote antenna units (RAUs) selection and cooperative transmission, namely, non-cooperative transmission without RAU selection (NCT), cooperative transmission without RAU selection (CT), non-cooperative transmission with RAU selection (NCT_RAUS), and cooperative transmission with RAU selection (CT_RAUS). By using probability theory, the cumulative distribution function (CDF) of a user's signal to interference plus noise ratio (SINR) and the system ergodic capacity under the above four modes are determined, and their closed-form expressions are obtained. Furthermore, the system energy efficiency (EE) is studied by introducing a realistic power consumption model of DAS. An expression for determining EE is formulated, and the closed-form tradeoff relationship between spectral efficiency (SE) and EE is derived as well. Simulation results demonstrate their consistency with the theoretical analysis and reveal the factors constraining system EE, which provide a scientific basis for future design and optimization of DAS.

• Journal of Physiology & Pathology in Korean Medicine
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• v.18 no.5
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• pp.1317-1321
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• 2004

The differentiation of the sebaceous gland is remarkably species-specific and sebocytes may play crucial parts in the pathophysiologic processes and disorders of pilosebaceous unit SZ95 cell is an immortalized human sebaceous gland cell line that shows characteristics of normal human sebocytes, In this study, we investigated the effect of testosterone and the anti-androgenic effect of 13-cis-retinoic acid (13-cis-RA) on lipid synthesis in SZ95 cells. Cytoplasmic lipid droplets were shown by Oil-red staining. The majority of the SZ95 cells positively labeled with Oil-red dye, while HaCaT cells negatively labeled with Oil red dye. Total lipid level of SZ96 cells is higher 4 times than that of HaCat cells. Testosterone markedly increased 2 times lipid synthesis of SZ95 cells in compared with control. 13-cis-RA significantly inhibited lipid synthesis and cell proliferation in SZ95 cells. Combined treatment with testosterone and 13-cis-RA resulted in a lower total lipid levels than that with androgen alone. In conclusion, SZ95 cells well resembled the morphologic and functional characteritics of normal human sebocytes. This in vitro model could provide a valuable tool for the study of sebocytes with a key role in pathophysiology and differentiation of sebaceous glands.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1609-1618
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• 2015

DC microgrids are considered as prospective systems because of their easy connection of distributed energy resources (DERs) and electric vehicles (EVs), reduction of conversion loss between dc output sources and loads, lack of reactive power issues, etc. These features make them very suitable for future industrial and commercial buildings' power systems. In addition, the bipolar-type dc system structure is more popular, because it provides two voltage levels for different power converters and loads. To keep voltage balanced in such a dc system, a bidirectional dual buck-boost voltage balancer with direct coupling is introduced based on P-cell and N-cell concepts. This results in greatly enhanced system reliability thanks to no shoot-through problems and lower switching losses with the help of power MOSFETs. In order to increase system efficiency and reliability, a novel burst-mode control strategy is proposed for the dual buck-boost voltage balancer. The basic operating principle, the current relations, and a small-signal model of the voltage balancer are analyzed under the burst-mode control scheme in detail. Finally, simulation experiments are performed and a laboratory unit with a 5kW unbalanced ability is constructed to verify the viability of the bidirectional dual buck-boost voltage balancer under the proposed burst-mode control scheme in low-voltage bipolar-type dc microgrids.

• Transactions of the Korean hydrogen and new energy society
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• v.3 no.2
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• pp.55-62
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• 1992

To improve the MCFC performance it is important to distingush between polarization losses occuring in the individual electrodes and other components. In this study a current interruption technique has been applied to a MCFC unit cell having a reference electrode to separately study the contributions of IR loss and other polarization losses. At a current density of $150mA/cm^2$ the IR-free polarization of a Ni anode was about 60mV while that of a NiO cathode was 130mV and the Ohmic loss of the cell was as large as 170mV suggesting that both the cathode and the cell structure need further improvement. The thin-film electrode model was used to simulate the performance of the electrodes. Both andoe data and cathode data were successfully fitted.