• Journal of Ocean Engineering and Technology
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• v.26 no.5
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• pp.5-10
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• 2012

In this study, carbon steel (A53) is used as the material for the pipes in a marine plant and ship industry. Welds are necessary to join the carbon steel, and the effect of this welding on the properties of the carbon steel has been studied by many researchers. In this study, the dynamic behavior of welded carbon steel was studied using an acoustic emission (AE) technique, which is a nondestructive test. There are numerous AE parameters that can be used to analyze the damage behavior of carbon steel by external loading. The AE parameters of energy, cumulative count, amplitude, and AE event were used, and each parameter was differentiated according to the degree of damage to the carbon steel. The energy showed a high level at the elastic range of the load curve, while the amplitude had the highest value at the hardening region. The cumulative count showed a growth tendency similar to the loading curve. In addition, an ultrasonic technique and hardness test were applied to evaluate the mechanical properties according to the base zone, HAZ region, and weld zone of the weld specimen. The velocity and attenuation ratio showed little change between zones, and an evaluation of the ultrasonic waves on each zone of the specimen was found to be a useful method to clarify the mechanical properties of the carbon steel.

• Journal of Korean Society on Water Environment
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• v.39 no.6
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• pp.433-438
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• 2023

This study investigated the growth and metabolic characteristics of Arthrospira platensis (A. platensis) according to pH, which has an alkaline optimal pH. The intake of inorganic carbon was expected to be the highest at the optimum pH 9, but it was different from the expectation, so the cause of the excessive intake of inorganic carbon at pH 7 was investigated. We tried to verify the triacylglycerol (TAG) synthesis metabolic mechanism because it was assumedthat the inorganic carbon intake of A. platensis according to pH is closely related to lipid production inside the cell. To verify this, the effects of pH on inorganic carbon intake were examined through lipid analysis inthe cell of A. platensis according to pH. As a result, in the case of the effect of inorganic carbon intake of A. platensis according to pH on TAG content, pH 9 and pH 11 showed no significant difference in TAG content, but at pH 7, it was two times higher compared to pH 9 and pH 11. It was assumed that the reason why A. platensis excessively consumed inorganic carbon at pH 7 was because itincreased the TAG content in proportion to the intake of inorganic carbon to protect cells from external pH stress. In addition, it is considered that the TAG content produced in proportion to the intake of inorganic carbon is because acetyl-CoA produced in the Calvin cycle is required for the synthesis of TAG.

• Journal of Aquaculture
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• v.10 no.3
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• pp.335-346
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• 1997

Denitrification is one of the important processes of removing nitrate from in recirculating aquaculture systems. And this process is affected by many factors such as external organic carbon sources, hydraulic retention time (HRT), COD/NO3--N (C:N) ratio, etc. However, not many studies were done for the optimum conditions of denitrification in the recirculation system for aquaculture. Therefore, this study was conducted to find out the optimum removal condition of NO3--N using submerged denitrification biofilter. The combinations of two external organic carbon sources (glucose and methanol), two HRT (4 and 8-hour) and four differnent C : N ratios (3, 4, 5, 6) were tested. The removal efficiencies of NO3--N and total inorganic nitrogen (TIM) at 8-hour HRT were better than those at 4-hour's (P<0.05). The maximum removal efficiency of NO3--N by methanol (97.8%) was achieved at HRT and C : N ratio were 8-hour and 4.0 respectively. The efficiencies of methanol for the removal of NO3--N and TIN were always better than those of glucose (P<0.05). The maximum removal efficiencies of total inorgainc nitrogen (TIN) were gained at C : N ration of 5.0. The maximum removel efficiencies of TIN using methanol and glucose were 96.9% and 71.5% respectively. Anaerobic condition which is necessary for denitrification process was not made until the 8-hour HRT and higher C : N ratio (5.0). Removal of NO3--N at 4-hour HRT and C : N ration lower than 5.0 were inhibited by oxygen and/or low quantity of external organic carbon. Removal efficiencies of NO3--N were also inhibited by high C : N (6.0) ratio when HRT was 8-hour.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.8
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• pp.831-838
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• 2008

This study investigated the characteristics of nitrogen removal and microbial community in a lab-scale A$_2$O activated sludge process filled with the fluidized media at an aerebic basin. The change of microbial community was monitored based on quinone profiles of activated sludge according to feeding sewage with/without external carbon source. Low C/N ratio(COD$_{Cr}$/T-N of 1.24) sewage was fed. The obtained results from this study were as follows; Ubiquinone(UQ) in the influent was in the descending order of UQ-8, UQ-10 and UQ-9. Menaquinone(MK) was simpler and much less than UQ. The ratio of UQ/MK was less than 0.41 and the dissimilarity was below 0.26. Without an external carbon source, MK-8 was the dominant species and there were 3 kinds of quinone species and low DQ and EQ values in an anaerobic basin. The ratio of UQ/MK increased to 2.3 in an anoxic basin. In an oxic basin, UQ-7 and UQ-8 were the dominant species. UQ-7 was dominating in suspended microorganisms, while UQ-8 was in attached microorganisms. With an external carbon source addition, MK-8 decreased but UQ-8 increased in an anaerobic basin. So did quinone species, DQ and EQ values. There was also a change in an anoxic basin with the improvement of denitrification. UQ-8 decreased instead, MK-7 and MK-8 increased. UQ/MK ratio decreased 2.3 to 1.4. It means that the dominant species change from Pseudomonas sp. to Bacillus and Micrococcus species. etc. In an oxic basin, UQ-8 replaced UQ-7 in suspended microorganisms and UQ-10 replaced UQ-8 in attached microbials. This seemed related with the growth of Nitrosomonas and Nitrobactor species.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.3
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• pp.205-214
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• 2018

This paper deals with the experimental study on the hygrothermal ageing effect to the strength of Carbon Fiber Reinforced Plastics (CFRP) materials for marine leisure boat manufactured by vacuum assisted resin infusion method. The experiments performed consist of tensile, flexural and shear tests according to American Society for Testing and Materials (ASTM) and Korean Industrial Standards (KS) test methods. Test coupons are varied from uni-directional(UD, $0^{\circ}$, $90^{\circ}$), Bi-Directional (BD), and Double-Bias (DB) carbon fiber fabrics in conjunction with epoxy resin. The results of tensile test show that tensile strength reduces significantly while not the same degree of reduction is observed for elasticity modulus with respect to the existence of hygrothermal ageing effect. This implies that the tensile strain induced from external load holds steady values but ultimate strength values change widely under hygrothermal ageing effect. In case of the flexural test, $0^{\circ}$ UD shows more strength reduction than $90^{\circ}$ UD while BD has reduced values in both flexural strength and elasticity modulus under hygrothermal ageing effect. It is learned that the bending strain induced from external load and ultimate strength values are reduced with respect to hygrothermal ageing effect. Shear test performed only on DB materials, and the results show marginal reduction in ultimate strength and moderate reduction in elasticity modulus. This means that the shear strain varies more than ultimate shear strength with respect to hygrothermal ageing effect. The experiment conducted in this paper clearly demonstrates the differences in material properties of the CFRP for the consideration of hygrothermal ageing effect. Findings obtained from this experimental study can serve as a fundamental input data for the realistic structural responses of marine leisure boat built in CFRP materials.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.1
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• pp.95-102
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• 2002

The flexural behavior of the reinforced concrete (RC) structure upgraded by external reinforcements was examined in this study. It is well known that the incorporation of carbon fiber sheet (CFS) with concrete is one of the most effective ways to strengthen the RC structure. Complete bonding is required between CFS and concrete in order to make the RC structure provide its full function until the time the Re structures serve. Many studies have reported that construction deficiencies have caused the debonding of the CFS from concrete before the RC structure with CFS reaches its ultimate capacity. This research took a systematic look at the failure mechanism, macroscopic load-deformation characteristics, the maximum load applied, and maximum bending moment when construction deficiencies exist. The results of the experiment conducted were compared with theoretically derived values. In the future, the results of this investigation will help minimize the factors of construction deficiencies, which may occur when CFS is used to reinforce a RC structure. The experiment was manipulated with steel reinforcement ratio and piles of CFS on a total of 14 beams ($20cm{\times}30cm{\times}240cm$). The results showed that internal moment capacity increased even when construction deficiencies existed. However, RC structures with CFS in the field still contain a considerable level of potential risks.

• Environmental Engineering Research
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• v.21 no.3
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• pp.256-264
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• 2016

2-Methylisoborneol (2-MIB) is one of typical odorants in potable water sources, which is hardly removed by conventional water treatment process. In this study, three strains capable of removing 2-MIB singly from drinking water were isolated from activated carbon of sand filter. They were identified to be Shinella zoogloeoides, Bacillus idriensis and Chitinophagaceae bacterium based on 16S rRNA gene sequence analysis. In mineral salts medium without external carbon source, removal efficiencies of $20{\mu}g/L$ 2-MIB in three days were 23.3%, 32.9% and 17.0% for Shinella zoogloeoides, Bacillus idriensis and Chitinophagaceae bacterium, respectively. The biodegradation of 2-MIB was significantly improved with the presence of cometabolism carbon(glycerol, glucose, etc.). In the period of 20 days, Bacillus idriensis can remove 2 mg/L MIB to $368.2{\mu}g/L$ and $315.4{\mu}g/L$ in mineral salts medium without and with glycerol respectively. The removal of 2-MIB by Bacillus idriensis was from 2 mg/L to $958.4{\mu}g/L$ in Xiba river samples on 15 days.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.5
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• pp.551-558
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• 2007

From the view point of biological wastewater treatment, C/N ratio is one of the most important factor in biological nutrient removal process. However, municipal sewage in Korea is characterized by extremely low content of carbon source and relatively higher portion of N source. Accordingly, it is necessary to dose external carbon source in order to obtain higher degree of carbon source within the process. In this study, the effects of pH pretreatment as an alternative plan for increasing carbon source on the cell disruption and COD solubility of waste activated sludge were conducted under well defined experimental conditions. During 5 hours, the value of COD solubilization rate ($S_R$) at pH 11.5 is approximately 4.4 times higher than the value of $S_R$ at pH 9.5. It is expected that the level of SCOD increased due to the result from cell disruption. However, VSS/TSS ratio was not significantly changed after 5 hours. As Alkalinity changes gradually from less than 15, 30 and 60 meq NaOH/L, average RBCOD/SCOD fraction showed 34, 36 and 45%,respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.51-51
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• 2011

We have grown nanocrystalline graphite on sapphire substrate by using solid carbon source molecular beam epitaxy. Changes of structure from amorphous carbon to nanocrystalline graphite controlled by the growth temperature have been investigated by Raman spectroscopy. Raman spectra show D, G, and 2D peaks, whose intensities vary on the growth temperature. Atomic force microscopy reveals that the surface is very flat. Sapphire substrates of different cutting direction produce similar results. Simulations suggest that the interaction between carbon and oxygen causes disorders. Electrical transport measurements exhibit a Dirac-like peak, including a carrier type change by an external gate voltage bias.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.729-733
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• 1998

The surface structure and the pore size distribution of the activated carbon impregnated with silver have been investigated. It has been confirmed that the impregnants had an effect only on the external surface, not on the internal surface and that adsorption isotherms of both impregnated and non-impregnated activated carbons were classified as a typical BET type-I. As the amount of the impregnants increased, the amounts of adsorption, the specific surface area, and the micropore volume decreased and the window blocking was observed. The average pore diameter of the activated carbon impregnated with silver was observed to show the constant values regardless of the amount of the impregnants.