• Structural Engineering and Mechanics
• /
• v.90 no.5
• /
• pp.481-492
• /
• 2024

This research examined the mechanical behavior of fiber-reinforced concrete at unstable environmental conditions. Concrete composites with varying percentages of steel and glass fibers were analyzed. Compressive, indirect tensile, and fracture toughness properties were evaluated using the Edge Notched Disc Bend (ENDB) test under freezing-thawing and acidic environments and the results were compared with normal conditions. Steel fibers decreased the strength in the specified cycles, while glass fibers showed a normal strength trend. The compressive, tensile and fracture toughness of the samples containing 1.5 vol.% fibers showed a 1.28-, 2.13- and 4.5-fold enhancement compared to samples without fibers, after 300 freezing-thawing cycles, respectively.

• Bulletin of the Korean Chemical Society
• /
• v.27 no.9
• /
• pp.1423-1428
• /
• 2006

In this study, we have prepared pitch binded AC (activated carbon)/$AC/TiO_2$ composites photocatalysts through carbon tetrachloride solvent method. The developed samples were characterized with surface properties, structural crystallinity between AC and $AC/TiO_2$, elemental identification and photocatalytic activity. The results of the textural surface properties demonstrate that there are slight increases in the BET surface area and adsorbed volume from adsorption isotherm of composite samples with increasing of the amount of AC. The SEM results present to the characterization of porous texture on the pitch/AC/$AC/TiO_2$ composites and homogenous compositions in the particle for all the materials used. From XRD data, a weak and broad carbon peak of graphene remained rutile peaks kept with anatase structure were observed in the X-ray diffraction patterns for the pitch/AC/$AC/TiO_2$ composites. The EDX spectra show the presence of C, O and S with strong Ti peaks. Most of these samples are richer in carbon and major Ti metal than any other elements. Finally, the excellent photocatalytic activity of the pitch/AC/$AC/TiO_2$ composites between relative concentration ($c/c_o$) of MB and UV irradiation time could be attributed to the both effects between photocatalysis of the supported $AC/TiO_2$ and adsorptivity of the two kinds of carbons.

• Proceedings of the Korean Society for Bioinformatics Conference
• /
• 2005.09a
• /
• pp.215-220
• /
• 2005

Generally, enzymes in the starch biosynthesis pathway exist in many isoforms, contributing to the difficulties in the dissection of their specific roles in controlling starch properties. In this study, we present an algorithm as an alternative method to classify isoforms of starch biosynthesis enzymes based on their conserved secondary structures. Analysis of the predicted secondary structure of plant soluble starch synthase I (SSI) and soluble starch synthase II (SSII) demonstrates that these two classes of isoform can be reclassified into three subsets, SS-A, SS-B and SS-C, according to the differences in the secondary structure of the protein at C-terminus. SS-A reveals unique structural features that are conserved only in cereal plants, while those of SS-B are found in all plants and SS-C is restricted to barley. These findings enable us to increase the accuracy in the estimation of evolutionary distance between isoforms of starch synthases. Moreover, it facilitates the elucidation of correlations between the functions of each enzyme isoforms and the properties of starches. Our secondary structure analysis tool can be applicable to study the functions of other plant enzyme isoforms of economical importance.

• Solar Energy
• /
• v.17 no.2
• /
• pp.55-66
• /
• 1997

The structural and optoelectronic properties of polycrystalline CdS films up to several microns in thickness, fabricated by three different methods, are compared to one another for the purpose of preparing CdTe/CdS solar cells. All films were deposited on an indium tin oxide on glass substrate. The three methods are: 1) alternated spraying of cation and anion solution at room temperature; 2) spray pyrolysis with substrate temperature up to $500^{\circ}C$; 3) chemical bath deposition (CBD). Deposited films were thermally treated in various ways. All films showed a well-developed wurtzite structure. Films grown by the alternated-spray method and the chemical bath method consist of randomly-oriented crystallites with dimensions <0.5 microns. Annealing at $400^{\circ}C$ increases the crystallite size slightly. Films which were grown by pyrolysis at substrate temperatures from $400^{\circ}C\;to\;500^{\cir\c}C$ were oriented in the <002> direction. For growth by pyrolysis at $500^{\circ}C$, the surface is rough on a lateral scale of 0.1 to 0.3 microns. The optical band gap and defect states are investigated by optical absorption, photoluminescene, Raman, and photothermal deflection spectroscopies.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.19 no.4
• /
• pp.165-171
• /
• 2009

In this study, ruby single crystals were successfully grown by flux method using an alumina crucible. The alumina crucible can be a substitute for the platinum crucible of high price. The ruby single crystals were grown in the temperature range of $915{\sim}1350^{\circ}C$ for 240 h, using $PbO-B_2O_3$ mixture. The grown ruby crystals with 9.02 ${\times}$ 6.36 mm in size exhibited red color and were transparent. The optical and structural properties were examined by UV-VIS spectrometry, FTIR and XRD. The optical properties of theses crystals were similar to those of the natural ruby and synthetic ruby grown by other methods.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.105-106
• /
• 2008

Structural, optical and electrical properties of CdS films deposited by chemical bath deposition (CBD), which are a very attractive method for low-cost and large-area solar cells, are presented. Cadmium sulfide (CdS) is II-VI semiconductor with a wide band gap of approximately 2.42 eV. CdS films have a great application potential such as solar cell, optical detector and optoelectronics device. In this paper, effects of Rapid Thermal Process (RTP) on the properties of CdS films were investigated. The CdS films were prepared on a glass by chemical bath deposition (CBD) and subsequently annealed at standard temperature $(400^{\circ}C)$ and treatment time (10 min) in various atmospheres (air, vacuum and $N_2$). The CdS films treated RTP in $N_2$ for to min were showed larger grain size and higher carrier density than the other samples.

• Journal of the Korea Concrete Institute
• /
• v.15 no.6
• /
• pp.811-819
• /
• 2003

The corrosion of steel reinforcing bar(re-bar) has been the major cause of the reinforced concrete deterioration. FRP(Fiber-reinforced polymer) reinforcing bar has emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. However, FRP re-bar is pone to deteriorate due to other degradation mechanisms than those for steel. The high alkalinity of concrete, for instance, is a possible degradation source. Other potentially FRP re-bar aggressive environments are sea water, acid solution and fresh water/moisture. In this study long-term durability performance of FRP re-bar were evaluated. The mechanical and durability properties of two type of CFRP-, GFRP re-bar and one type of AFRP re-bar were investigated; the FRP re-bars were subjected to alkaline solution acid solution, salt solution and deionized water. The mechanical and durability properties were investigated by performing tensile, compressive and short beam tests. Experimental results confirmed the desirable resistance of FRP re-bar to aggressive chemical environment.

• Korean Journal of Materials Research
• /
• v.8 no.11
• /
• pp.1061-1066
• /
• 1998

The synthesises of anion exchange resin from 4vinylpyridine-divinyIbenzene(4-VP-DVB) were intented to separate boron ion. The heterogeneous anion exchange membranes were prepared with polyethylene(PE) matrix bythe hot press method. The prepared exchange membranes were characterized by FT-IR, conductormeter and pH meter to confirm structural, mechanical and electrochemical properties. Their capacities were measured by changing floe rate and voltage. The best seperation capacity was appeared in the heterogeneous membrane which contains 50 wt % 4-VP-DVB resin within PE matrix. The heterogeneous membranes treated with acid were better than that treated with water. Results from this experiment were indicated that the optimal flow rate, voltage. and time in the seperation of boron ion were lOml/min, 18volts, and 4 hours respectively.

• 한국신재생에너지학회:학술대회논문집
• /
• 2011.11a
• /
• pp.47.1-47.1
• /
• 2011

We report on a direct measurement of two-dimensional chemical and electrical distribution on the surface of photovoltaic Cu(In,Ga)$Se_2$ thin-films using a nano-scale spectroscopic and electrical characterization, respectively. The Raman measurement reveals non-uniformed surface phonon vibration which comes from different compositional distribution and defects in the nature of polycrystalline thin-films. On the other hand, potential analysis by scanning Kelvin probe force microscopy shows a higher surface potential or a small work function on grain boundaries of the thin-films than on the grain surfaces. This demonstrates the grain boundary is positively charged and local built-in potential exist on grain boundary, which improve electron-hole separation on grain boundary. Local electrical transport measurements with scanning probe microscopy on the thin-films indicates that as external bias is increases, local current is started to flow from grain boundary and saturated over 0.3 V external bias. This accounts for carrier behavior in the vicinity of grain boundary with regard to defect states. We suggest that electron-hole separation at the grain boundary as well as chemical and electrical distribution of polycrystalline Cu(In,Ga)$Se_2$ thin-films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.11a
• /
• pp.533-538
• /
• 2003

It has been shown that ion implantation produces remarkable improvements in surface-sensitive physical and chemical properties as well as other mechanical properties, in polymers. In this study, ion implantation was performed onto polymer, PC(polycarbonate), in order to investigate surface hydrophilic property through contact angle measurement using distilled water. PC was irradiated with N, Ar, Xe ions at the irradiation energy of $20\;{\sim}\;50keV$ and the dose range of $5{\times}10^{15},\;1{\times}10^{16},\;7{\times}10^{16}\;ions/cm^2$. The contact angle of water has been reduced with increasing fluence and ion mass but increased with increasing implanted energy. The changes of chemical and structural property are discussed in view of infrared spectroscopy and FT-IR, XPS, which shows increasing C-O bonding and C-C bonding. The root mean square of surface roughness examined by means of AFM changed smoothly from 0.387nm to 0.207nm and the change of wettability was discussed with respect to elastic and inelastic collisions obtained as results of TRIM simulation. It was found that wettability of the modified PC surface was affected on change of functional group and nuclear stopping or linear energy transfer(LET, energy deposited per unit track length per ion) that causes chain scission by displacing atom from polymer chains, but was not greatly dependant on surface morphology.