• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.965-975
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• 2014

Pretension PSC (Prestressed Concrete) members are subjected to a certain limit of size as they are generally produced in the off-site plant and transferred to the site due to the large scale of the product on system. In this study, a portable pretensioning production system has been developed, which allow us to apply the pretension method on site. Considering that a 50m span PSC girder using the pretension method requires a pressing device to endure a large jacking force, the portable pretension production system has to ensure safety against such a large pretension jacking force. In this study, the portable pretensioning system to produce a 50m span pretension girder was manufactured by using CFT (Concrete Filled steel Tube) members. In order to understand the stability of the system and the behavior of the elements, a static loading test was conducted and the stability of the proposed portable pretensioning production system was confirmed. The developed portable pretension system was applied to several construction sites and was investigated the problems on site. During the pretension girder and slab members that was producted by this pretension system in construction site, it has be found the several advantages such as simple fabrication processes, reduction of prestress-loss, and a decrease of 15% compared with the fabrcation cost of post-tension girder. After due consideration of the problems, this portable pretension system will be improved.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.5
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• pp.501-513
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• 2004

Purpose : The purpose of this study was to evaluate the effects of etching time on shear bond strength of four resin cements to IPS Empress 2 ceramic. Material and Methods: Forty rectangular shape ceramic specimens ($10{\times}15{\times}3.5mm$ size) were used for this study. The ceramic specimens divided into four groups and were etched with 10% hydrofluoric acid for 0, 10, 30, 60, 180, 300, 420, 600, and 900 seconds respectively. Etched surfaces of ceramic specimens were coated with ceramic adhesive system and bonded with four resin cement (Variolink II, Panavia F, Panavia 21, Super-Bond C&B) using acrylic glass tube. All cemented specimens were tested under shear loading untill fracture on universal testing machine at a crosshead speed 1mm/min: the maximum load at fracture (kg) was recored. Shear bond strengh data were analyzed with oneway analysis of variance and Tukey HSD tests (p<.05). Etched ceramic surfaces (0-, 60-, 300-, and 600-seconds etching period) and fracture surfaces after shear testing were examined mophologically using scanning electron microscopy. Results : Ceramic surface treatment with 10% hydrofluoric acid improved the bond strength of three resin cement except for Super-Bond C&B cement. Variolink II (41.0$\pm$2.4 MPa) resin cement at 300-seconds etching time showed statistically higher shear bond strength than the other resin cements (Panavia F: 28.3$\pm$2.3 MPa, Panavia 21: 21.5$\pm$2.2 MPa, Super-Bond C&B: 16.7$\pm$1.6 MPa). Ceramic surface etched with 10% hydrofluoric acid for 300 seconds showed more retentive surface texture. Conclusion: Within the limitation of this study, Variolink II resin cement are suitable for cementation of Empress 2 all-ceramic restorations and etching with 10% hydrofluoric acid for 180 to 300 seconds is required to enhance the bond strength.

• Korean Journal of Environmental Biology
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• v.28 no.3
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• pp.115-124
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• 2010

In order to find out the short-term phytoplankton dynamics during summer season in Jinhae Bay, we investigated the environmental factors and phytoplankton population densities at 16 stations. A total of 66 phytoplankton species were appeared, diatoms occupied more than 80% of total species, and the others were dinoflagellates and raphidophyceaes. The dominant species were diatoms Chaetoceros affinis, C. didymus, C. pseudocurvisetus, Leptocylindrus danicus, Pseudonitzchia pungens, Skeletonema costatum and dinoflagellates Cochlodinium polykrikoides, Gymnodinium impudicum, Karenia mikimotoi, Prorocentrium minimum, Protoperidinium bipes and Scrippsiella trochoidea. According to multidimensional scaling (MSD) and cluster analysis based on phytoplankton community data from each station, the Jinhae bay was divided into two groups. The first group included stations in the inner part of Masan Bay, which is strongly influenced by high nitrogen loading and low salinity by river discharge. The second group included the other remained stations. Based on canonical correspondence analysis (CCA), small-size dinoflagellates K. mikimotoi, P. minimum, P. bipes and S. trochoidea and centric diatom C. pseudocurvisetus and S. costatum, which is dominanted in the inner area of bay, were related with DIN (ammonium, nitrate, nitrite). These results imply that the study area was grouped into the two water masses (inner and outer water of Masan Bay) and inner waters had higher phytoplankton abundances and Chl.a concentration than outer waters. As a result, summer phytoplankton peaks in the inner shallow bay were stimulated by increases in nitrogen and temperature.

• Journal of Veterinary Clinics
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• v.32 no.3
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• pp.224-230
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• 2015

This study was designed in the fabricated poly (L-Lactic-co-${\varepsilon}$-Caprolactone) (PLCL) scaffold using chitosan-alginate hydrogel, which would be more suitable to maintain the biological and physiological functions continuing three dimensional spatial organizations for chondrocytes. As a scaffold, hydrogels alone is weak at endure complex loading within the body. In this study, we made cell hybrid scaffold constructs with poly (L-Lactic-co-${\varepsilon}$-Caprolactone) (PLCL) scaffold and hydrogels to make a three-dimensional composition of cells and extracellular matrix, which would be a mimic of a native cartilage. Using a particle leaching technique with NaCl, we fabricated a highly-elastic scaffold from PLCL with 85% porosity and $300-500{\mu}m$ pore size. A mixture of bovine chondrocytes and chitosan-alginate gel was seeded and compared with alginate as a control on the PLCL scaffold. The cell maturation, proliferation, extracellular matrix synthesis, glycosaminoglycans (sGAG) production and collagen type-II expressions were better in chondrocytes seeded in chitosan-alginate hydrogel than in alginate only. These results indicate that chondrocytes with chitosan-alginate gel on PLCL scaffolds provide an appropriate biomimetic environment for cell proliferation and matrix synthesis, which could successfully be used for cartilage repair and regeneration.

• Journal of Korean Society on Water Environment
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• v.23 no.6
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• pp.945-950
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• 2007

The stormwater runoff from paved area are highly polluted because of particulate materials as well as metals from various vehicular activities. The Division of Road Maintenance in Ministry of Construction and Transportation was recently developed the Guidelines of Environment-kindly Road Maintenance. It is actually requiring the BMP construction to control the nonpoint source pollution as based on the TMDL program. This research is carried out in order to define the characteristics of stormwater runoff from the toll-gate of highways since 2006, which is actually one of the main pollutant sources of paved areas. This monitoring is the first phase work for establishing the treatment facilities in the toll-gates. The one of the main characteristics from toll-gate runoff is the first flush phenomenon containing lots of sediments and metal compounds at the beginning of a storm event. Usually it is used to determine the size of treatment facilities and to calculate the reduced pollutant mass in the facility. The research results shows that the mean EMC vaules for heavy metals are determined to $274.3{\mu}g/L$ for Cd, $1,273.4{\mu}g/L$ for Cr, $1,822.0{\mu}g/L$ for Cu, $6,504.9{\mu}g/L$ for Fe, $14,930.3{\mu}g/L$ for Pb, and $714.1{\mu}g/L$ for Zn. Also the metal mass loadings from the toll-gates are calculated using EMC, watershed area and storm duration.

• Applied Chemistry for Engineering
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• v.4 no.2
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• pp.365-372
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• 1993

$CO_2$ methanation was performed over Ni supported on cation-exchanged Y zeolites under atmospheric pressure at $250{\sim}550^{\circ}C$ and $H_2/CO_2$ mole ratio of 4. Adsorption strength between carbon dioxide and nickel was found to be Influenced by the cation exchanged in the zeolite. TPD(Temperature-programmed desorption) results show that the adsorption strength decreases in the order of Ni/NaY>Ni/MaY>Ni/HY. TPSR(Temperature-programmed surface reaction) results indicate that enhanced methanation activity is obtained when the adsorption strength between carbon dioxide and nickel is stroing. As the reduction temperature increases, the methantion activity of the catalyst increase. From this result the larger size nickel particle seems advantageous for $CO_2$ methanation reaction. The maximum activity is obtained when nickel loading is 3.3wt%. Carbon monoxide is produced as a by-product throughout the reaction temperature range, and as the contact time increases, the selectivity to methane increases and the selectivity to carbon monoxide decreases steadily. Thus methane seems to be produced from $CO_2$ via CO as an intermediate species. In the temperature range of $410{\sim}450^{\circ}C$, the methane production rate is found to be dependent on the orders of 3.3~-0.5 and 1.4~3.6 with respect to $CO_2$ and $H_2$ partial pressures, respectively. This clearly shows that $CO_2$ and $H_2$ are competing for adsorption sites and as the reaction temperature increases, it becomes increasingly difficult for $H_2$ to be adsorbed on the catalyst surface.

• Analytical Science and Technology
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• v.15 no.3
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• pp.263-269
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• 2002

After porous filters were manufactured using cordierite powder whose mean particle size was 200 ${\mu}m$, they were loaded with catalysts such as Pt, Pd, Cu, Co, La, $V_2O_5$ by vacuum impregnation method. And we investigated the activity of catalysts used for catalytic oxidation of VOC by passing toluene through catalyst-loaded filters. The porous filters had the apparent porosity of 62%, the compressive strength of about 10 MPa and the pressure drop of 15 mmHg at the face velocity of 5 cm/sec. The loading of catalyst decreased the porosity of the filters and increased the pressure drop and the compressive strength of them. Among the catalysts, Pt had the highest activity for catalytic oxidation and could remove more than 90% of toluene at 250 $^{\circ}C$. Below 250 $^{\circ}C$, the content of Pt catalyst had an influence on the conversion of toluene but didn't show any influence above 250 $^{\circ}C$.

• Applied Chemistry for Engineering
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• v.24 no.1
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• pp.55-61
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• 2013

Heterogeneous metallocene catalysts supported on montmorillonite (MMT), [$Cp_2ZrCl_2$/MMT, $Cp_2ZrCl_2$/MAO/MMT, and $Cp_2ZrCl_2$ + MAO/MMT], were prepared with three different methods of immobilization and tested for ethylene polymerization. The heterogeneous catalysts immobilized on organo clay (30B-MMT) showed the higher metal loading and polymerization activity than those immobilized on natural clay $Na^+-MMT$. These results suggest that the hydroxyl groups of organo clay interlayers react with the MAO and catalyst through the chemical bond. The metallocene catalyst supported directly on MMT showed lower activity for ethylene polymerization compared to the homogeneous systems, while MMT/MAO/$Cp_2ZrCl_2$, catalysts treated with MAO before impregnation, showed a higher activity. The polymers obtained from MMT-supported catalysts have higher melting point, molecular weight and molecular weight distributions than those of homogeneous catalysts. The polymer particles with increasing significant size. Ethylene polymerization over 30B-MMT/MAO/$Cp_2ZrCl_2$ catalyst was also performed varying the process variables to optimize the process conditions.

• Journal of the Korean Geotechnical Society
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• v.28 no.11
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• pp.41-52
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• 2012

Suction drain method can directly apply vacuum pressure to the soft ground through vertical drains so it can make hardening zones around them. These hardening zones make steeply lower the discharge efficiency of the pore water with decreasing permeability. This paper considered a stepped vacuum pressure to minimize a hardening zone which is one of the important parameters that can decrease discharge efficiency. A series of laboratory tests were conducted in order to examine the effect of the hardening zones and to evaluate their effects to the ground improvements with varying durations which applied stepped vacuum pressures(-20kPa, -40kPa, -60kPa and -80kPa) with Busan marine clay. According to strength(CPT), water content test and theoretical investigation indicate a size of the hardening zone within 7cm and the decreasing ratio of permeability about 2.0~4.0. Also, the total settlements are larger for the stepped vacuum pressure than the instant vacuum loading. The application time with vacuum pressure is determined considering the geotechnical properties of the interested clays. Results of numerical analysis show that consolidation behavior is appropriate to measurement for considering hardening zones.

• Macromolecular Research
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• v.11 no.4
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• pp.207-223
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• 2003

For last five years, we are developing the novel local drug delivery devices using biodegradable polymers, especially polylactide (PLA) and poly(D,L-lactide-co-glycolide) (PLGA) due to its relatively good biocompatibility, easily controlled biodegradability, good processability and only FDA approved synthetic degradable polymers. The relationship between various kinds of drug [water soluble small molecule drugs: gentamicin sulfate (GS), fentanyl citrate (FC), BCNU, azidothymidine (AZT), pamidronate (ADP), $1,25(OH)_2$ vitamin $D_3$, water insoluble small molecule drugs: fentanyl, ipriflavone (IP) and nifedipine, and water soluble large peptide molecule drug: nerve growth factor (NGF), and Japanese encephalitis virus (JEV)], different types of geometrical devices [microspheres (MSs), microcapsule, nanoparticle, wafers, pellet, beads, multiple-layered beads, implants, fiber, scaffolds, and films], and pharmacological activity are proposed and discussed for the application of pharmaceutics and tissue engineering. Also, local drug delivery devices proposed in this work are introduced in view of preparation method, drug release behavior, biocompatibility, pharmacological effect, and animal studies. In conclusion, we can control the drug release profiles varying with the preparation, formulation and geometrical parameters. Moreover, any types of drug were successfully applicable to achieve linear sustained release from short period ($1{\sim}3$ days) to long period (over 2 months). It is very important to design a suitable formulation for the wanting period of bioactive molecules loaded in biodegradable polymers for the local delivery of drug. The drug release is affected by many factors such as hydrophilicity of drug, electric charge of drug, drug loading amount, polymer molecular weight, the monomer composition, the size of implants, the applied fabrication techniques, and so on. It is well known that the commercialization of new drug needs a lot of cost of money (average: over 10 million US dollar per one drug) and time (average: above 9 years) whereas the development of DDS and high effective generic drug might be need relatively low investment with a short time period. Also, one core technology of DDS can be applicable to many drugs for the market needs. From these reasons, the DDS research on potent generic drugs might be suitable for less risk and high return.