• Journal of the Korea Organic Resources Recycling Association
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• v.22 no.3
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• pp.41-52
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• 2014

In this study, to estimate the biodegradability of sewage discharged intermittently, field scale sampling and analysis was conducted and the results were obtained as follows. According to results of the biodegradability of sewage discharged intermittently, average concentration of TCODcr is 325.5mg/L and ratio of TCOD fraction resulted 100%. Also, average concentration of SCODcr resulted 135.9mg/L and ratio of TCOD fraction resulted 41.8%. Average concentration of Ss showed 74.1mg/L and ratio of TCOD fraction resulted 22.8%. Average concentration of $S_I$ was analyzed to be 61.8mg/L and ratio of TCOD fraction was calculated to 19.0%. Xs which is particulate matter was analyzed to show 27.8mg/L and ratio of TCOD fraction also showed 8.5%. Average concentration of $X_H$ is 103.4mg/L and ratio of TCOD fraction resulted 31.8%. Inert particulate matter showed that average concentration of $X_I$ is 58.5mg/L and ratio of TCOD fraction resulted 18.0%. Accordingly, dissolved biodegradable organic matter showed the ratio of 41.8%, and readily biodegradable matter among this showed 22.8%. Thus intermittent inflow is expected to have less effect with regards equalization by organic loading rate of influent.

• Education of Primary School Mathematics
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• v.25 no.2
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• pp.179-195
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• 2022

Mathematical communication competency, one of the six mathematical competencies emphasized in the latest mathematics curriculum, plays an important role both as a means and as a goal for students to learn mathematics. Therefore, it is meaningful to find instructional methods to improve students' mathematical communication competency and analyze their communication competency in detail. Given this background, this study analyzed 64 sixth graders' mathematical communication competency after they participated in the lessons of fraction division emphasizing mathematical communication. A written assessment for this study was developed with a focus on the four sub-elements of mathematical communication (i.e., understanding mathematical representations, developing and transforming mathematical representations, representing one's ideas, and understanding others' ideas). The results of this study showed that students could understand and represent the principle of fraction division in various mathematical representations. The students were more proficient in representing their ideas with mathematical expressions and solving them than doing with visual models. They could use appropriate mathematical terms and symbols in representing their ideas and understanding others' ideas. This paper closes with some implications on how to foster students' mathematical communication competency while teaching elementary mathematics.

• Journal of Powder Materials
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• v.17 no.4
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• pp.276-280
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• 2010

In the present work, ethylene glycol-based (EG) copper oxide nanofluids were synthesized by pulsed wire evaporation method. In order to explode the pure copper wire, high voltage of 23 kV was applied to the both ends of wire and argon/oxygen gas mixture was used as reactant gas. EG-based copper oxide nanofluids with different volume fraction were prepared by controlling explosion number of copper wire. From the transmission electron microscope (TEM) image, it was found that the copper oxide nanoparticles exhibited an average diameter about 100 nm with the oxide layer of 2~3 nm. The synthesized copper oxide consists of CuO/$Cu_2O$ phases and the Brunauer Emmett Teller (BET) surface area was estimated to be $6.86\;m^2\;g^{-1}$. From the analyses of thermal properties, it is suggested that viscosity and thermal conductivity of EG-based copper oxide nanofluids do not show temperature-dependent behavior over the range of 20 to $90^{\circ}C$. On the other hand, the viscosity and thermal conductivity of EG-based copper oxide nanofluids increase with volume fraction due to the active Brownian motion of the nanoparticles, i.e., nanoconvection.

• Korean Journal of Materials Research
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• v.12 no.4
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• pp.308-316
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• 2002

The cavitation erosion behavior of wear-resistant hardfacing alloys such as Co-base Stellite 6, Fe-base Norem 02 and new Fe-base alloy were investigated up to 50 hours by using a 20kHz vibratory cavitation erosion test equipment. The crack, initiated easily at the interfaces between matrix and hard second phase, was repressed effectively in Stellite 6 because the matrix was hardened by phase transformation. For this reason, Stellite 6 showed an excellent cavitation erosion resistance compared to Norem 02. The phase transformation also occurred in Norem 02, but the increase of volume fraction of the interfaces caused the crack to be initiated frequently, thus resulting in a 1arge material loss. The matrix of NewAlloy was hardened effectively by vlongrightarrow$\alpha$' phase transformation and the volume fraction of the interfaces was very small compared to Norem 02. This caused the propagation of crack to the matrix to be repressed effectively. Therefore, NewAlloy showed a very excellent cavitation erosion resistance. It wasn't considered that the cavitation erosion resistance of NewAlloy was influenced the temperature of the bath filled with a distilled water up to $80^{\circ}C$.

• Journal of Powder Materials
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• v.14 no.6
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• pp.348-353
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• 2007

In the present study, Zr-base metallic glass (MG) and Zr-base BMG/diamond composites were fabricated using a combination of gas atomization and spark plasma sintering (SPS). The microstructure, thermal stability and mechanical property of both the specimens as atomized and sintered were investigated. The experimental results showed that the SPSed specimens could be densified into nearly 100% and maintained the initial thermal stability at the sintering temperature of 630K. In addition, MG/diamond powder composites were successfully synthesised using SPS process. The composites, even a very low diamond volume fraction, generated a significant increase in compressive strength. With increasing the diamond volume fraction, the compressive strength was also increased due to the addition of hardest diamonds. It suggests that these composites would be potential candidates for a new cutting tool material.

• Journal of Powder Materials
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• v.25 no.2
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• pp.126-131
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• 2018

In the present study, we investigate the effects of milling time and the addition of a process control agent (PCA) on the austenite stability of a nanocrystalline Fe-7%Mn alloy by XRD analysis and micrograph observation. Nanocrystalline Fe-7%Mn alloys samples are successfully fabricated by spark plasma sintering. The crystallite size of ball-milled powder and the volume fraction of austenite in the sintered sample are calculated using XRD analysis. Changes in the shape and structure of alloyed powder according to milling conditions are observed through FE-SEM. It is found that the crystallite size is reduced with increasing milling time and amount of PCA addition due to the variation in the balance between the cold-welding and fracturing processes. As a result, the austenite stability increased, resulting in an exceptionally high volume fraction of austenite retained at room temperature.

• Nuclear Engineering and Technology
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• v.53 no.7
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• pp.2304-2311
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• 2021

The dislocation density in strain-hardened Alloy 690 was analyzed using scanning transmission electron microscopy (STEM) to study the relationship between the local plastic strain and susceptibility to primary water stress corrosion cracking (PWSCC) in nuclear power plants. The test material was cold-rolled at various thickness reduction ratios from 10% to 40% to simulate the strain-hardening condition of plant components. The dislocation densities were measured at grain boundaries (GB) and in grain interiors of strain-hardened specimens from STEM images. The dislocation density in the grain interior monotonically increased as the strain-hardening proceeded, while the dislocation density at the GB increased with strain-hardening up to 20% but slightly decreases upon further deformation to 40%. The decreased dislocation density at the GB was attributed to the formation of deformation twins. After the PWSCC growth test of strain-hardened Alloy 690, the fraction of intergranular (IG) fracture was obtained from fractography. In contrast to the change in the dislocation density with strain-hardening, the fraction of IG fracture increased remarkably when strain-hardened over 20%. From the results, it was suggested that the PWSCC growth behavior of strain-hardened Alloy 690 not only depends on the dislocation density, but also on the microstructural defects at the GB.

• Journal of Communications and Networks
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• v.15 no.1
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• pp.102-110
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• 2013

This paper considers a cooperative orthogonal frequency division multiple access (OFDMA)-based cognitive radio network where the primary system leases some of its subchannels to the secondary system for a fraction of time in exchange for the secondary users (SUs) assisting the transmission of primary users (PUs) as relays. Our aim is to determine the cooperation strategies among the primary and secondary systems so as to maximize the sum-rate of SUs while maintaining quality-of-service (QoS) requirements of PUs. We formulate a joint optimization problem of PU transmission mode selection, SU (or relay) selection, subcarrier assignment, power control, and time allocation. By applying dual method, this mixed integer programming problem is decomposed into parallel per-subcarrier subproblems, with each determining the cooperation strategy between one PU and one SU. We show that, on each leased subcarrier, the optimal strategy is to let a SU exclusively act as a relay or transmit for itself. This result is fundamentally different from the conventional spectrum leasing in single-channel systems where a SU must transmit a fraction of time for itself if it helps the PU's transmission. We then propose a subgradient-based algorithm to find the asymptotically optimal solution to the primal problem in polynomial time. Simulation results demonstrate that the proposed algorithm can significantly enhance the network performance.

• Fisheries and Aquatic Sciences
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• v.21 no.11
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• pp.35.1-35.7
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• 2018

Background: The aim of this study was to investigate the in vitro inhibitory effects of Fucofuroeckol-A isolated from Eisenia bicyclis against tyrosinase activity and 3-isobutyl-1-methylxanthine (IBMX)-induced melanin biosynthesis in B16F10 melanoma cells. Result: Among the ethanolic (EtOH) extract of E. bicyclis and its organic solvent fractions, the ethyl acetate (EtOAc) soluble fraction showed a noticeable inhibitory effect on mushroom tyrosinase with an $IC_{50}$ value of $37.6{\pm}0.1{\mu}g/mL$. Repeated column chromatography of the active EtOAc fraction resulted in the isolation of Fucofuroeckol-A. It evidenced more potent tyrosinase inhibitory effect with an $IC_{50}$ value of $11.4{\pm}1.4{\mu}M$ than arbutin ($IC_{50}=1076.6{\pm}44.3{\mu}M$), which was used as a positive control. Lineweaver-Burk plots suggest that Fucofuroeckol-A plays as a noncompetitive inhibitor against tyrosinase. Furthermore, we have evaluated the inhibitory effects of Fucofuroeckol-A on IBMX-induced melanin formation in B16F10 melanoma cells. Fucofuroeckol-A ($12.5-100{\mu}M$) exhibited a significant inhibition of melanin production in the melanoma cells. Conclusion: In the present study, we suggested that Fucofuroeckol-A might prove possibility as a novel inhibitor of melanin biosynthesis in cosmetic applications.

• Advances in Traditional Medicine
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• v.8 no.4
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• pp.339-348
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• 2008

Butea frondosa has been used traditionally as a topical formulation in the treatment of many diseases and disorders. Two compounds [BF-1 (crystalline flavonol quercetin) and BF-2 (tannin) from ethyl acetate fraction of ethanolic extract] were isolated from the bark of Butea frondosa. The stereostructures of the compounds were determined on the basis of chemical and physicochemical evidence. BF-1 and BF-2 were screened in vitro for possible antibacterial property against 112 bacteria comprising 3 genera of Gram-positive and 12 genera of Gram-negative types. It was found that both BF-1 and BF-2 exhibited inhibitory activity against several bacteria. Most of these strains were inhibited by BF-1 at $50-200\;{\mu}g/ml$, while BF-2 ($MIC_{50}$ $400\;{\mu}g/ml$) was much less active. The bacteria could be arranged in the decreasing order of sensitivity towards BF-1 in the following manner: S. aureus, Bacillus spp., Salmonella spp., Vibrio spp., Shigella spp., E. coli and Pseudomonas spp. The $MIC_{50}$ of the compound was $50\;{\mu}g/ml$ while the $MIC_{90}$ was $100\;{\mu}g/ml$. The decreasing order of sensitivity towards BF-2 was V. cholerae, Bacillus spp., S. aureus, V. parahaemolyticus, Salmonella spp. and Proteus spp. BF-1 was bactericidal in action. In vivo studies with this extract showed that it could offer statistically significant protection (p < 0.01) to mice challenged with a virulent bacterium. The inhibitory activity of Butea frondosa against Gram-positive and Gram-negative bacteria indicates its usefulness in the treatment of common bacterial infections. The potentiality of BF-1 as an antibacterial agent may be confirmed further by pharmacological studies.