• Polymer(Korea)
• /
• v.37 no.6
• /
• pp.694-701
• /
• 2013

A new copolymer named T-TI24T (poly((5,5-(2-butyl-5,6-bisdecyloxy-4,7-di-thiophen-2-yl-isoindole-1,3-dione))- alt-(2,5-thiophene))) based on phthalimide derivative and thiophene is synthesized by the Stille-coupling reaction. The polymer shows relatively high number average molecular weight of 86500 g/mol with good solubility in common organic solvents such as chloroform, 1,2-dichlorobenzene, and toluene and is thermally stable up to $380^{\circ}C$. Besides, it possesses a relatively low highest occupied molecular orbital (HOMO) energy level of -5.33 eV, promising the high open circuit voltage ($V_{oc}$) for photovoltaic applications. Active layer solution of polymer T-TI24T-as a donor and (6)-1-(3-(methoxycarbonyl)- {5}-1-phenyl[5,6]-fullerene (PCBM)-as an acceptor in different weight ratios is applied to fabricate the polymer solar cell devices. The ratio of polymer/PCBM affects the solar cell efficiency and the best performance exhibits in the device with polymer/PCBM = 1:3 (w/w), which shows a power conversion efficiency (PCE) of 0.199% and a $V_{oc}$ of 0.99 V, respectively. Even though the device shows the very low PCE, the $V_{oc}$ is higher than that of well known bulk heterojunction type solar cell based on P3HT:PC61BM (c.a. 0.5 V).

• FLOWER RESEARCH JOURNAL
• /
• v.16 no.2
• /
• pp.128-133
• /
• 2008

This study was conducted to select new variants with different characteristics in plant height, leaf color, and petal color of plantain lily (Hosta plantaginea) and Japanese farfugium (Farfugium japonicum). After 10-30Gy ${\gamma}-ray$ irradiation to seeds of both species, seed germination, variant induction, growth of variants, and survival ratios were estimated. Days required for seed germination were lengthened and % seed germination decreased as the dosage of ${\gamma}-ray$ increased over 20Gy. Lethal dose ($LD_{50}$) for plantain lily and Japanese farfugium were 30Gy and 25Gy, respectively. Plantain lily and Japanese farfugium treated by more than 20Gy ${\gamma}-ray$ showed dwarf characteristics in growth, and variations in leaf and petal colors. Total 166 variants in plantain lily were induced by ${\gamma}-ray$ irradiation in a $M_1$ generation, among which 12 promising variants were selected in a $M_2$ generation. Total 57 variants of Japanese farfugium were induced by ${\gamma}-ray$ irradiation in a $M_1$ generation, among which nine promising variants were selected in a $M_2$ generation.

• Structural Engineering and Mechanics
• /
• v.76 no.6
• /
• pp.687-708
• /
• 2020

Openings in steel plate shear walls (SPSWs) are usually used for decorative designs, crossing locations of multiple utilities and/or structural objectives. However, earlier studies showed that generating an opening in an SPSW has a negative effect on the cyclic performance of the SPSW. Therefore, this study proposes tripling or doubling the steel-sheet-plate (SSP) layer and stiffening the opening of the SPSW to provide a solution to undesirable opening effects, improve the SPSW performance and provide the infill option of potential strengthening measures after the construction stage. The study aims to investigate the impact of SSP doubling with a stiffened opening on the cyclic behaviour, expand the essential data required by structural designers and quantify the SPSW performance factors. Validated numerical models were adopted to identify the influence of the chosen parameters on the cyclic capacity, energy dissipation, ductility, seismic performance factors (SPF) and stiffness of the suggested method. A finite Element (FE) analysis was performed via Abaqus/CAE software on half-scale single-story models of SPSWs exposed to cyclic loading. The key parameters included the number of SSP layers, the opening size ratios corresponding to the net width of the SSP, and the opening shape. The findings showed that the proposed assembly method found a negligible influence in the shear capacity with opening sizes of 10, 15, 20%. However, a deterioration in the wall strength was observed for openings with sizes of 25% and 30%. The circular opening is preferable compared with the square opening. Moreover, for all the models, the average value of the obtained ductility did not show substantial changes and the ultimate shear resistance was achieved after reaching a drift ratio of 4.36%. Additionally, the equivalent sectional area of the SSP in the twin and triple configuration of the SPSWs demonstrated approximately similar results. Compared with the single SSP layer, the proposed configuration of the twin SSP layer with a stiffened opening suggest to more sufficiency create SSP openings in the SPSW compared to that of other configurations. Finally, a tabular SPF quantification is exhibited for SPSWs with openings.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.3
• /
• pp.40-47
• /
• 2021

This study investigates the influence of hooked-end steel fiber volume fraction and aspect ratio on the mechanical properties, such as compressive and flexural performance, of concrete with specified compressive strength of 30MPa. Three types of hooked-end steel fibers with aspect ratios of 64, 67 and 80 were selected. The flexural tests of steel fiber reinforced concrete (SFRC) prismatic specimens were conducted according to EN 14651. The compressive performance of SFRC with different volume fractions (0.25, 0.50 and 0.75%) were evaluated through standard compressive strength test method (KS F 2405). Experimental results indicated that the flexural strength, flexural toughness, fracture energy of concrete were improved as steel fiber volume fraction increases but there is no unique relationship between steel fiber volume fraction and compressive performance. The flexural and compressive properties of concrete incorporating hooked-end steel fiber with aspect ratio of 64 and 80 are a little better than those of SFRC with aspect ratio of 67. For each SFRC mixture used in the study, the residual flexural tensile strength ratio defined in Model Code 2010 was more than the limit value to be able to substitute rebar or welded mesh in structural members with the fiber reinforcement.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.24 no.5
• /
• pp.17-26
• /
• 2020

This study examined the structural effectiveness of the unbonded technique originally developed for seismic strengthening of unreinforced masonry walls on the basis of the prestressed steel bars and glass fiber (GF) grids. The masonry walls were strengthened by using individual steel bars or GF grids and their combination. Test results showed that the proposed technique was favorable in enhancing the strength, stiffness, and ductility of the masonry walls. When compared with the lateral load capacity, stiffness at the ascending branch of the lateral load-displacement curve, and energy dissipation capacity of the unstrengthened control wall, the increasing ratios were 110%, 120%, and 360%, respectively, for the walls strengthened with the individual GF grids, 140%, 130%, and 510%, respectively, for the walls strengthened with the individual steel bars, and 160%, 130%, and 840%, respectively, for the walls strengthened with the combination of steel bars and GF grids. The measured lateral load capacities of masonry walls strengthened with the developed technique were in relatively good agreement with the predictions by the equations proposed by Yang et al. Overall, the developed technique is quite promising in enhancing the seismic performance of unreinforced masonry walls.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.27 no.1
• /
• pp.145-152
• /
• 2021

The purpose of this study was to determine the optimal distances between pipes to minimize the pressure loss and turbulent intensity. This was accomplished by investigating the distances between sleeve-jointed pipes and the flow changes in pipes based on variations in the Reynolds (Re) number when installing adjusting pieces for the pipes. When the thickness tp of the sleeve-jointed piping was fixed at 5 mm and the pipe lengths Lp were 10, 50, 100, and 200 mm, the correlations with the velocity of the sleeve-jointed part, pressure distribution, length of the reattachment point in the recirculation area, and Re number were analyzed. The flow characteristic of the sleeve-jointed part from a laminar to a turbulent flow region was determined by setting the Re range to 200 ≤ Re ≤ 5,000. This was done by utilizing Ansys Fluent 18.1, which is a commercial program. The enlargement and contraction ratios of the sleeve-jointed part were 1.2 and 0.83, respectively, and the turbulent intensity of the sleeve downstream edge and pressure change both increased as the Re number increased while Lp remained constant. The fact that the flow on the sleeve wall surface was disturbed by tp resulted in losses in velocity energy. Therefore, the edge of the sleeve-jointed part was also effected. When Lp was 10 mm or less, the turbulent intensity of the edge part did not change significantly as the Re number increased. The reattachment point in the recirculation area did not appear at Lp of 10 mm or less and was not affected by the vortex. In the case of 3,000 ≤ Re, the reattachment length of the wall surface of the sleeve-jointed part was nearly constant as Lp increased.

• Journal of Soil and Groundwater Environment
• /
• v.27 no.2
• /
• pp.50-60
• /
• 2022

The concentration levels and distribution characteristics of 16 polycyclic aromatic hydrocarbons (PAHs) were investigated and evaluated for total 100 soil samples as a part of the survey on soil contamination in Gwangju. The results (median and range) of T-PAHs (sum of 16 PAH concentrations), C-PAHs (sum of carcinogenic PAH concentrations) and T-TEQs (sum of 16 TEQ concentrations) were 20.8 (7.6~1158.1), 2.2 (N.D~509.6), and 0.3 (N.D~424.6) ㎍/kg, respectively. There was a positive correlation between C-PAHs/T-PAHs and T-TEQs/T-PAHs except one point where the concentration of benzo(a)pyrene was high. The ratios of the C-PAHs/T-PAHs were 31.7% for low molecular weight-PAHs and 68.3% for high molecular weight-PAHs, suggesting that PAHs generation mainly arose from combustion sources. The ratio of isomers of individual PAHs, Phe/Ant, Flu/Pyr, Ant/(Ant+Phe), Flu/(Flu+Pyr), and BaA/(BaA+Chr), also confirmed the predominance of PAHs from combustion activities. Statistical tracing of the source of PAHs through principal component analysis indicated that the main sources of combustion were automobile fuel and coal. The overall results of this study suggested HMW-PAHs, T-PAHs, C-PAHs and T-TEQs should be separately evaluated to better assess the toxicity and environmental behavior of individual PAHs.

• Journal of the Korean Society of Earth Science Education
• /
• v.15 no.2
• /
• pp.224-234
• /
• 2022

The purpose of this study was to analyze STEAM elements and convergence types that appeared in the creative and convergent activities in elementary school science textbooks, which were converted from the national issuance system to the authorized system in 2022. For this study, 6 elementary school science textbooks for 3rd and 4th graders were selected. And STEAM elements in creative and convergent activities were analyzed by publishers, grade-semesters, and science fields, and the convergence type was analyzed for each publisher. The results of this study are as follows. First, the total frequencies of STEAM elements and the ratios of each element in the creative and convergent activities of textbooks were different for each publisher. However, among the four elements except for science (S) element in all publishers, the tendency to have a high proportion of art (A) element and a very low proportion of mathematics (M) element was common. Second, the higher the number of fused STEAM elements, the lower the rate of appearance in the textbooks in overall. Also the ratio of convergence types of STEAM elements varied by each publisher. Third, the ratio deviations of art (A), technology (T), and engineering (E) elements for each grade-semester were not large, but the ratio deviation of the mathematics (M) element was large. Fourth, technology (T) and engineering (E) elements appeared a lot in the fields of 'movement and energy' and 'material', while art (A) element appeared a lot in the fields of 'earth and universe', 'life', and 'integration'.

• Restorative Dentistry and Endodontics
• /
• v.48 no.1
• /
• pp.3.1-3.14
• /
• 2023

Objectives: This study evaluated the effect of different nanoparticulated zinc oxide (nano-ZnO) and conventional-ZnO ratios on the physicochemical properties of calcium aluminate cement (CAC). Materials and Methods: The conventional-ZnO and nano-ZnO were added to the cement powder in the following proportions: G1 (20% conventional-ZnO), G2 (15% conventional-ZnO + 5% nano-ZnO), G3 (12% conventional-ZnO + 3% nano-ZnO) and G4 (10% conventional-ZnO + 5% nano-ZnO). The radiopacity (R_ad), setting time (S_et), dimensional change (D_c), solubility (S_ol), compressive strength (C_st), and pH were evaluated. The nano-ZnO and CAC containing conventional-ZnO were also assessed using scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Radiopacity data were analyzed by the 1-way analysis of variance (ANOVA) and Bonferroni tests (p < 0.05). The data of the other properties were analyzed by the ANOVA, Tukey, and Fisher tests (p < 0.05). Results: The nano-ZnO and CAC containing conventional-ZnO powders presented particles with few impurities and nanometric and micrometric sizes, respectively. G1 had the highest Rad mean value (p < 0.05). When compared to G1, groups containing nano-ZnO had a significant reduction in the S_et (p < 0.05) and lower values of D_c at 24 hours (p < 0.05). The C_st was higher for G4, with a significant difference for the other groups (p < 0.05). The S_ol did not present significant differences among groups (p > 0.05). Conclusions: The addition of nano-ZnO to CAC improved its dimensional change, setting time, and compressive strength, which may be promising for the clinical performance of this cement.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.2D
• /
• pp.243-248
• /
• 2008

Moisture damage of asphalt pavements can usually occur because of the loss of adhesion and cohesion between the asphalt binder and aggregate in the asphalt mixture due to presence of water. And this is one of the causes that is effect on the main distress of asphalt pavement. The objective of this study is to find out moisture damage characteristics of asphalt pavement. Effects of this study changes of the material properties and resistance characteristics of moisture damage on the asphalt mixtures under various temperatures and repeated immersion using indirect tensile test and modify Lottman test were evaluated during this study. The asphalt mixtures were produced using straight asphalt binder, SBS modified asphalt binder and aggregates. The material properties (resilient modulus, indirect tensile strength, failure energy and $DCSE_f$) of the asphalt mixtures were generally decreased with increasing to moisture damage caused by the number of repeated immersion. The decrease ratios of material properties by repeated immersion on SBS modified asphalt mixtures were lower than those of straight asphalt mixtures at all three test temperatures. As a conclusion, current criterion for evaluation moisture damage of asphalt mixtures is difficult for using distinction standard because of the limited evaluation criterion with one time immersion and single material property. Based on this research, to evaluate long term moisture damage on asphalt mixtures, material property tests of various kinds with repeated immersion test are considered.