• Computers and Concrete
• /
• v.12 no.2
• /
• pp.131-149
• /
• 2013

Various types of reinforcement splicing methods have been developed and implemented in reinforced concrete construction projects for achieving the continuity of reinforcements. Due to the complicated reinforcement arrangements and the difficulties in securing bar spacing, the traditional lap splicing method, which has been widely used in reinforced concrete constructions, often shows low constructability and difficulties in quality control. Also, lap spliced regions are likely to be over-reinforced, which may not be desirable in seismic design. On the other hand, mechanical splicing methods can offer simple and clear arrangements of reinforcement. In order to utilize the couplers for the ribbed-deformed bars, however, additional screw processing at the ends of reinforcing bars is typically required, which often lead to performance degradations of reinforced concrete members due to the lack of workmanship in screw processing or in adjusting the length of reinforcing bars. On the contrary, the use of screw-ribbed reinforcements can easily solve these issues on the mechanical splicing methods, because it does not require the screw process on the bar. In this study, the mechanical coupler suitable for the screw-ribbed reinforcements has been developed, in which any gap between the reinforcements and sleeve device can be removed by grouting high-flow inorganic mortar. This study presents the uniaxial tension tests on the screw-ribbed reinforcement with the mechanical sleeve devices and the cyclic loading tests on RC columns with the developed coupler. The test results show that the mechanical sleeve connection developed in this study has an excellent splicing performance, and that it is applicable to reinforced concrete columns with a proper confinement by hoop reinforcement.

• Ocean and Polar Research
• /
• v.36 no.4
• /
• pp.423-435
• /
• 2014

Verifying the similarity of environmental characteristics between an artificial impact site and a preserved or reference site is necessary to quantitatively and qualitatively evaluate the environmental impact of mining activity. Although an impact site (BIS station) and a preserved site (called KOMO station) that have been selected in the Korea manganese nodule contract area may share similar environmental characteristics, similarities in terms of the water column environment between both sites has not been investigated. In this study, we compared the chemical properties of the water columns and sinking particle fluxes between BIS and KOMO stations through two observations (August 2011 and September 2012). Additionally, we observed particle fluxes at the KOMO station for five years (July 2003~July 2008) to understand long-term natural variability. Vertical distributions of water column properties such as dissolved oxygen, inorganic nutrients (N, P, Si), total organic carbon below surface layer (within the depth range of 200 m) were not considerably different between the two sites. Especially, values of water column parameters in the abyssopelagic zone from 4000 m to bottom layer (~5000 m) were very similar between the BIS and KOMO sites. Sinking particle fluxes from the two sites also showed similar seasonality. However, natural variation of particle flux at the KOMO site varied from 3.5 to $129.9mg\;m^{-2}day^{-1}$, with a distinct temporal variation originating from ENSO events (almost forty times higher than a minimum value). These results could provide valuable information to more exactly evaluate the environmental impact of mining activity on water columns.

• Elastomers and Composites
• /
• v.52 no.1
• /
• pp.22-26
• /
• 2017

The thermal conductivity and the adhesive properties were measured, after synthesis of thermal conductive composite which was obtained as a result of mixing alumina or graphite with acrylic adhesive synthesized by UV polymerization. The adhesive properties of the composite were evaluated measuring the peel strength at 180 degrees, the retention, and the initial tack;the thermal conductivity was estimated using laser flash analysis. As the filler contents increased, a decrease in peel strength and initial tack and an increase in retention and thermal conductivity were observed. When compared to alumina, the adhesion of graphite showed a dramatic decrease, whereas the thermal conductivity was further enhanced. It was found out that the small size of graphite increased the mechanical interlocking between the polymer and the filler, and it was easier for graphite to come into contact with other graphite in the matrix.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• v.37 no.5
• /
• pp.380-385
• /
• 2011

Introduction: Hydroxyapatite ($Ca_{10}(PO_4)_6(OH)_2$, HA) is the main inorganic phase of human hard tissue that is used widely as the repair material for bones. When HA is applied to a bony defect, however, it can be encapsulated with fibrous tissue and float in the implanted area due to a lack of consolidation. Bioceramics as allogenic graft materials are added to HA to improve the rate and bone healing capacity. Fluoridated hydroxyapatite ($Ca_{10}(PO_4)_6(OH,F)_2$, FHA), where F- partially replaces the OH- in hydroxyapatite, is considered a good alternative material for bone repair owing to its solubility and biocompatibility. Materials and Methods: This study was designed to determine the bone healing capacity of FHA newly produced as a nanoscale fiber in the laboratory. HA and FHA with bioglass was implanted in a rabbit cranium defect and the specimen was analysed histologically. Results: 1. At 4 weeks, fibrous connective tissue and little bone formation was observed around the materials of the experimental group I implanted HA and bioglass. Newly formed bone was observed around the materials in the experimental group II implanted FHA and bioglass. 2. At 8 weeks, the amount of newly formed and matured bone was higher in experimental group II than in experimental group I and the control group. Conclusion: These results suggest that FHA and bioglass is a relatively favorable bone substitute with biocompatibility and better bone healing capacity than pure HA and bioglass.

• The Journal of Engineering Geology
• /
• v.24 no.4
• /
• pp.583-595
• /
• 2014

The chemical properties and composition (pH, CaO, Fe, $HCO{_3}^-$, and $SO{_4}^{2-}$) of groundwater (GW) and surface water (SW) from the northern (non-carbonate bedrock) and southern (carbonate bedrock) sections of the Daedong River, Pyeongyang were analyzed and compared period of the 1930s. In the southern section, the GW and SW has a higher pH and $SO{_4}^{2-}$ concentration, but lower $HCO{_3}^-$ and Fe levels than in the north. This finding reflects a reaction that formed acid by replacing metal ions in inorganic salts by hydrogen, which resulted from the oxidation of organic material in a clay layer.

• Transactions of the Korean hydrogen and new energy society
• /
• v.22 no.1
• /
• pp.42-50
• /
• 2011

The Montmorillonite (MMT) in the polymer matrix is expected to reduce methanol permeability due to the tortous path formed by dispersed silicate layers. However, the polymer composite membranes containing non-proton conducting inorganic particle tend to show low proton conductivity. To solve this problem, we used an ion exchange method to prepare functionalized MMT with various silane coupling agents. The modified MMT was randomly dispersed in sulfonated poly (arylene ether sulfone) (SPAES) matrix to prepare SPAES/modified MMT composite membranes. The performances of hybrid membranes for DMFCs application were investigated. The SPAES/modified composite membrane showed increased proton conductivity compared with the non-modified MMT composite membrane. However, the methanol permeability of the SPAES/modified membrane was higher than that of the non-modified MMT.

• Korean Journal of Materials Research
• /
• v.24 no.8
• /
• pp.434-442
• /
• 2014

Serious environmental problems have been caused by the greenhouse effect due to carbon dioxide($CO_2$) or nitrogen oxides($NO_x$) generated by the use of fossil fuels, including oil and liquefied natural gas. Many countries, including our own, the United States, those of the European Union and other developed countries around the world; have shown growing interest in clean energy, and have been concentrating on the development of new energy-saving materials and devices. Typical non-fossil-fuel sources include solar cells, wind power, tidal power, nuclear power, and fuel cells. In particular, organic solar cells(OSCs) have relatively low power-conversion efficiency(PCE) in comparison with inorganic(silicon) based solar cells, compound semiconductor solar cells and the CIGS [$Cu(In_{1-x}Ga_x)Se_2$] thin film solar cells. Recently, organic cell efficiencies greater than 10 % have been obtained by means of the development of new organic semiconducting materials, which feature improvements in crystalline properties, as well as in the quantum-dot nano-structure of the active layers. In this paper, a brief overview of solar cells in general is presented. In particular, the current development status of the next-generation OSCs including their operation principle, device-manufacturing processes, and improvements in the PCE are described.

• Journal of Korean Society on Water Environment
• /
• v.32 no.5
• /
• pp.433-441
• /
• 2016

Many large dams have been constructed for water supply, irrigation, flood control and hydropower in Korea for the last century. Meanwhile, recent studies indicated that the artificial reservoirs impounded by these dams are major sources of carbon dioxide (CO₂) to the atmosphere and relevant to global budget of green house gases. However, limited information is available on the seasonal variations of CO₂ evasion from the reservoirs located in the temperate monsoon regions including Korea. The objectives of this study were to estimate daily Net Atmospheric Flux (NAF) of CO₂ in Daecheong Reservoir located in Geum River basin of Korea, and analyze the influencing parameters that characterize the variation of NAF. Daily pH and alkalinity (Alk) data collected in wet year (2012) and dry year (2013) were used for estimating the NAFs in the reservoir. The dissolved inorganic carbon (DIC) was computed using the pH and Alk measurements supposing an equilibrium state among the carbonate species. The results showed seasonal variations of NAF; negative NAFs from May to October when the primary production of the reservoir increased with water temperature increase, while positive NAF for the rest of the period. Overall the reservoir acted as sources of CO₂ to the atmosphere. The estimated NAFs were 2,590 and 771 mg CO₂ m^-2d^-1 in 2012 and 2013, respectively, indicating that the NAFs vary a large extent for different hydrological years. Statistical analysis indicated that the NAFs are negatively correlated to pH, water temperature, and Chl-a concentration of the reservoir.

• Membrane Journal
• /
• v.22 no.5
• /
• pp.318-325
• /
• 2012

PTMSP-PMMH-NaY zeolite composite membranes were prepared by the addition of 10, 20, 30, and 40 wt% NaY zeolite contents to PTMSP containing 20 wt% PMMH dendrimer. To investigate the physico-chemical characteristics of composite membranes, the analytical methods such as FT-IR, TGA, and SEM have been utilized, and the gas permeability and selectivity properties of hydrogen and nitrogen were evaluated. The permeability of the PTMSP-PMMH-NaY zeolite composite membranes increased as NaY zeolite content increased, the permeabilities of hydrogen and nitrogen gases were observed being 3,950~592,000 barrer and 1,550~143,000 barrer, respectively. Simultaneously, selectivity of hydrogen against nitrogen did not show a discernible difference at 0~30 wt% range of NaY zeolite contents and increased from 2.2 to 4.2 at 30~40 wt% range.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• v.33 no.5
• /
• pp.464-469
• /
• 2007

The bone graft materials are grossly divided into autogenous bone, allogenic bone, xenogenic bone, and alloplastic material. Among the various allogenic graft materials, hydroxyapatite($Ca_{10}(PO_4)_6(OH)_2$, HA), the main inorganic phase of human hard tissue, is widely used as a repair material for bones. When HA applied to bony defect, however, it may be encapsulated with fibrous tissue and floated in the implanted area by the lack of consolidation. Fluoridated hydroxyapatite($Ca_{10}(PO_4)_6(OH)_2$, FHA), where F- partially replaces the OH- in the hydroxyapatite, is considered as an alternative material for bone repair due to its solubility and biocompatibility. This study was designed to find out the bone healing capacity of FHA newly produced as a nanoscale fiber in the laboratory. We implanted HA and FHA in the rabbit cranium defect and histologically analysed the specimen. The results were as follows. 1. In the 4 weeks, fibrous connective tissue and little bone formation around materials of the experimental group I implanted HA were observed. In the experimental group II implanted FHA, newly formed bone around materials were observed. 2. In the 8 weeks, the amount of newly formed and matured bone of the experimental group II was more than the experimental group I and control group. From the results obtained, we suggest that FHA, newly synthesized, is relatively favorable bone substitute with bioconpatibility and has better bone healing capacity than pure HA.