• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.616-624
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• 2011

The flow characteristics and heat transfer augment on the periodically arranged semi-circular ribs in a rectangular channel for turbulent flow has been investigated numerically. The aspect ratio of the rectangular channel was AR=5, the rib height to hydraulic diameter ratio were 0.07 and rib height to channel height ratio was set as e/H=0.117 for various PR(rib pitch-to-rib height rate) between 8~14, respectively. The SST k-${\omega}$ turbulence model and v2-f turbulence model were used to find out the heat transfer and the flow characteristics of near the wall which are suited to obtain realistic phenomena. The numerical analysis results show turbulent flow characteristics, heat transfer enhancement and friction factor as observed experimentally. The results predict that turbulent kinetic energy(k) is closely relative to the diffusion of recirculation flow. and v2-f turbulence model simulation results have a good agreement with experimental values.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.101-104
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• 2007

Mechanical behavior in metal bipolar plate of a fuel cell stack was studied using finite element analysis. The fuel stack is essentially composed of a metal bipolar plate (metal BP), a gasket, an end plate, a membrane electrolyte assembly (MEA), and a gas diffusion layer (GDL). It is important to maintain a suitable fastening force of Metal BP, because it influences the power efficiency of the fuel cell stack. After a gasket and a GDL are placed on the metal BP, the reaction force with the displacement is measured. The channel of metal bipolar plate is replaced by a simple geometrical plate. The results of FEM are similar to those of experiment. Therefore mechanical behavior in metal BP of a fuel cell stack can be estimated by using FEM.

• Journal of Pharmaceutical Investigation
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• v.37 no.2
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• pp.73-78
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• 2007

The aim of this study was to investigate the absorption properties of ketoprofen. The in-situ perfusion model has advantages over in vitro models as it provides intact lymphatic and blood flow circulation. The absorption properties of six different concentrations of ketoprofen have been studied in single pass in-situ rat intestine model. $^{14}C-PEG$ 4000 was used as a permeability marker and the possibility of an energy dependent contribution to ketoprofen absorption was also Investigated using the metabolic inhibitor sodium azide. Three different concentrations of sodium azide were studied to examine its effect on absorption of ketoprofen from the rat intestine. The findings of this study suggest that mono-carboxylic type drugs like ketoprofen cause permeability changes in the intestine. This is shown by the increase in absorption of $^{14}C-PEG$ 4000 as the concentration of ketoprofen is increased. However, the trend for ketoprofen permeability is to decrease over the concentration ranges. It was observed that the Papp values for ketoprofen with sodium azide shows a trend towards reduction in the amount of ketoprofen absorbed from the rat intestine which was significantly different (p<0.05) from that of ketoprofen with sodium azide 3.0mM. This indicates that sodium azide has an affect on the absorption of ketoprofen. The pH of all the perfusion solutions was altered to ${\sim}pH\;6.7$ by the buffering capacity of the small intestine secretions. The results suggest that mechanisms other than passive diffusion may be involved in ketoprofen absorption. This would be consistent with the involvement of active transport or saturatable processes in the absorption of drugs containing monocarboxylic acid group, as has been previously suggested from in vitro data.

• Journal of Pharmaceutical Investigation
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• v.40 no.3
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• pp.167-173
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• 2010

Repeated oral administration of hydrochlorothiazide, a loop diuretic, due to transient high blood levels, may cause adverse effects such as gastric disturbance, nausea, high blood sugar, and hyper lipidemia. Transdermal administration could avoid some of these systemic side effects and gastric disorders. We have developed a matrix using ethylene-vinyl acetate (EVA), a heat-processible and flexible material, for transdermal delivery of hydrochlorothiazide. Drug solubility was highest at 40% PEG-400 volume fraction. Drug release increased as concentration increased with a linear relationship between the release rate and the square root of loading dose. Increasing temperature increased drug release from the EVA matrix. The activation energy, measured from the slope of log P versus 1000/T, was 11.9 kcal/mol for a 2.5% loading dose from EVA matrix. Diethyl phthalate had the highest plasticizing effects on the release of hydrochlorothiazide. To increase the skin permeation of hydrochlorothiazide from the EVA matrix, enhancers such as the saturated fatty acids, the unsaturated fatty acids, and the non-ionic surfactants were added to the EVA matrix, and skin permeation was evaluated using a modified Keshary-Chien diffusion cell fitted with intact excised rat skin. Polyoxyethylene 23-lauryl ether showed the highest enhancing effects. In conclusion, transdermal delivery of hydrochlorothiazide could be improved from an EVA matrix containing plasticizer and permeation enhancer.

• Membrane and Water Treatment
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• v.2 no.1
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• pp.25-37
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• 2011

PES UF membranes containing silver were prepared to impart antibacterial properties for waste water treatment. Asymmetric membranes for antibacterial application were prepared from polyethersulfone (PES) and silver nitrate ($AgNO_3$) (PES/$AgNO_3$=15/2 by weight) solution in N-Methyl-2-pyrrolidone (NMP) via simple wet phase inversion technique. These membranes were characterized by polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) of different molecular weights (1000 ppm in water) at room temperature and on operating pressure of 5 bars. It was observed that the water flux of PES-$AgNO_3$ membrane is slightly lower than virgin PES but still increased linearly with the increment of pressure applied. The morphology of the resulting membranes was examined using Field-Emission Scanning Electron Microscope (FESEM) coupled with Energy Dispersive Spectroscopy (EDS). Elemental analysis using EDS proved that silver is successfully loaded on the membrane surfaces. Due to the success of loading silver on membrane surfaces, antibacterial activities were evaluated via agar diffusion method against Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) culture. By incorporating 2 wt% of silver nitrate, PES-$AgNO_3$ showed significant inhibition ring on both E.coli and S.aureus. Filtration of E.coli solution (OD 0.31) showed satisfactory rejection data with ~100% inhibition growth after 24 hours incubation at $37^{\circ}C$. Resultant membranes also exhibit better tensile strength (compared to virgin PES) up to 71% may be due to the suggested interactions. The residual silver during fabrication was measured using ICP-MS and result showed that the residual silver content of PES-$AgNO_3$ membrane was only ~1% of the original silver added in the polymer solution. These studies have shown that PES-$AgNO_3$ UF membranes are potential in improving the filtration in water treatment.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.3
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• pp.1299-1306
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• 2014

Background: Nano-biotechnology is recognized as offering revolutionary changes in various fields of medicine. Biologically synthesized silver nanoparticles have a wide range of applications. Materials and Methods: Silver nanoparticles (AgNPs) were biosynthesized with an aqueous extract of Pterocladiella (Pterocladia) capillacea, used as a reducing and stabilizing agent, and characterized using UV-VIS spectroscopy, Fourier Transform Infra red (FT-IR) spectroscopy, transmission electron microscopy (TEM) and energy dispersive analysis (EDX). The biosynthesized AgNPs were tested for cytotoxic activity in a human hepatocellular carcinoma ($HepG_2$) cell line cultured in Dulbecco's modified Eagle medium supplemented with 10% fetal bovine serum, 1% antibiotic and antimycotic solution and 2 mM glutamine. Bacterial susceptibility to AgNPs was assessed with Staphylococcus aureus, Bacillus subtilis [Gram+ve] and Pseudomonas aeruginosa and Escherichia coli [Gram-ve]. The agar well diffusion technique was adopted to evaluate the bactericidal activity of the biosynthesized AgNPs using Ampicillin and Gentamicin as gram+ve and gram-ve antibacterial standard drugs, respectively. Results: The biosynthesized AgNPs were $11.4{\pm}3.52$ nm in diameter. FT-IR analysis showed that carbonyl groups from the amino acid residues and proteins could assist in formation and stabilization of AgNPs. The AgNPs showed potent cytotoxic activity against the human hepatocellular carcinoma ($HepG_2$) cell line at higher concentrations. The results also showed that the biosynthesized AgNPs inhibited the entire panel of tested bacteria with a marked specificity towards Bacillus subtillus. Conclusions: Cytotoxic activity of the biosynthesized AgNPs may be due to the presence of alkaloids present in the algal extract. Our AgNPs appear more bactericidal against gram-positive bacteria (B. subtillus).

• Journal of Powder Materials
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• v.12 no.6 s.53
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• pp.447-452
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• 2005

The synthesis and consolidation of titanium silicide by electro-discharge-sintering has been investigated. As-received Ti powder was in flaky shape and the mean particle size was $45.0{\mu}m$, whereas the mean particle size of the pre-milled Si powder with angular shape was $8.0{\mu}m$. Single pulse of 2.5 to 5.0 kJ/0.34g-elemental Ti and pre-milled Si powder mixture with the composition of $Ti-37.5at.\%$ Si was applied using $300{\mu}F$ capacitor. The solid with $Ti_5Si_3$ phase has been successfully fabricated by the discharge with the input energy more than 2.5kJ in less than $129{\mu}sec.$ Hv values were found to be higher than $1000kgf/mm^2$. The formation of $Ti_5Si_3$ occurred through a fast solid state diffusion reaction.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.189-195
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• 1999

We have studied the vortex dynamics in YBa$_2Cu_3O_7$ single crystals with columnar defects using micro Hall-probe array. The Hall-probe array technique allowed a simultaneous measurement of the time and spatial dependence of the vortex density so that more detailed information on flux dynamics could be obtained. We found that field profiles inside sample were similar to the Bean's critical state model from the magnetic hysteresis measurement. Normalized relaxation rates were maximum near the center and decreased toward the edge if applied field H$_{app}$ is greater than the penetration field H. But applied magnetic field H$_{app}$ is less than H, relaxation rates were minimum near the center and increased toward edge. We found that glassy exponent ${\mu}$ has the value of ${\sim}$ 1 whose corresponding vortex motion is half-loop excitation. However, single vortex creep, ${\mu}$ ${\sim}$ 1/7, was also found at 30 K and H$_{app}$ ${\cong}$ H'. Calculation of activation energy, U, was possible from direct analysis of the local relaxation data using the basic diffusion equation. From these results, we found that U increases logarithmically with time and U around center was lower than that at the edge.

• Journal of Electrochemical Science and Technology
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• v.2 no.2
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• pp.110-115
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• 2011

The effect of $TiO_2$ nanotube (TNT) and nanoparticle (TNP) composite photoelectrode and the role of TNT to enhance the photo conversion efficiency in dye-sensitized solar cell (DSSC) have investigated in this study. Results demonstrated that the increase of the TNT content (1-15 %) into the electron collecting TNP film increases the open-circuit potential ($V_{oc}$) and short circuit current density ($J_{sc}$). Based on the impedance analysis, the increased $V_{oc}$ was attributed to the suppressed recombination between electrode and electrolyte or dye. Photochemical analysis revealed that the increased Jsc with the increased TNT content was due to the scattering effect and the reduced electron diffusion path of TNT. The highest $J_{sc}$ (12.6 mA/$cm^2$), Voc (711 mV) and conversion efficiency (5.9%) were obtained in the composite photoelectrode with 15% TNT. However, $J_{sc}$ and $V_{oc}$ was decreased for the case of 20% TNT, which results from the significant reduction of adsorbed dye amount and the poor attachment of the film on the fluorine-doped tin oxide (FTO). Therefore, application of this composite photoelectrode is expected to be a promising approach to improve the energy conversion efficiency of DSSC.

• ETRI Journal
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• v.38 no.2
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• pp.265-271
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• 2016

We analyzed the interface characteristics of Zn-based thin-film buffer layers formed by a sulfur thermal cracker on a $Cu(In,Ga)Se_2$ (CIGS) light-absorber layer. The analyzed Zn-based thin-film buffer layers are processed by a proposed method comprising two processes - Zn-sputtering and cracker-sulfurization. The processed buffer layers are then suitable to be used in the fabrication of highly efficient CIGS solar cells. Among the various Zn-based film thicknesses, an 8 nm-thick Zn-based film shows the highest power conversion efficiency for a solar cell. The band alignment of the buffer/CIGS was investigated by measuring the band-gap energies and valence band levels across the depth direction. The conduction band difference between the near surface and interface in the buffer layer enables an efficient electron transport across the junction. We found the origin of the energy band structure by observing the chemical states. The fabricated buffer/CIGS layers have a structurally and chemically distinct interface with little elemental inter-diffusion.