• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.4
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• pp.293-301
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• 2017

A Sub-kWe small-scale experimental test loop was manufactured to investigate characteristics of the supercritical carbon dioxide power cycle. A high-speed turbo-generator was also designed and manufactured. The designed rotational speed of this turbo-generator was 200,000 rpm. Because of the low expansion ratio through the turbine and low mass flowrate, the rotational speed of the turbo-generator was high. Therefore, it was difficult to select the rotating parts and design the turbine wheel, axial force balance and rotor dynamics in the lab-scale experimental test loop. Using only one channel of the nozzle, the partial admission method was adapted to reduce the rotational speed of the rotor. This was the world's first approach to the supercritical carbon dioxide turbo-generator. A cold-run test using nitrogen gas under an atmospheric condition was conducted to observe the effect of the partial admission nozzle on the rotor dynamics. The vibration level of the rotor was obtained using a gap sensor, and the results showed that the effect of the partial admission nozzle on the rotor dynamics was allowable.

• Korean Journal of Food Science and Technology
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• v.32 no.2
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• pp.396-401
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• 2000

The effect of gamma-irradiation on quality changes of Samjang, Korean traditional seasoned soy paste, was studied. Samjang was prepared, irradiated at 0, 2.5, 5, 10 kGy, and then stored at $25^{\circ}C$ and $37^{\circ}C$, respectively. Non-irradiated control, sample 2%- ethanol added and sample heated at $80^{\circ}C$ for 30 min were prepared with the same conditions to be compared. The results showed that yeasts were completely eliminated by gamma-irradiation with dose at 2.5 kGy or more, and total bacteria decreased by 5 log cycles with doses at 10 kGy, showing a significant decrease during storage. The gamma irradiation treatment showed repressive effect on the swelling by gas production and browning formation of Samjang during storage. Also, the indicators of enzyme activity, such as amino nitrogen, protease activity and pH change in the gamma irradiation treatment were more stable than control. The sensory evaluations showed that irradiated samples were more acceptable. Therefore, it was considered that gamma irradiation was effective for processing Samjang and for maintaining better quality during subsequent storage.

• Journal of Climate Change Research
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• v.3 no.2
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• pp.129-142
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• 2012

This study was carried out to evaluate carbon footprint during unhulled rice production and to compare mitigation technologies of methane, main carbon source during rice production, Carbon footprint of unhulled rice was a sum of $CO_2$ emission of agri-materials manufacture, rice cultivation and waste treatment. It was emitted 1.40 kg $CO_2$ during unhulled rice production, its distribution was 71.1% by $CH_4$ emission of rice cultivation, 11.8% of $N_2O$ emission by nitrogen application and 7.6% of complex fertilizer manufacture. $CH_4$ emission could be mitigated by some technologies; cultivation of the early maturing rice variety emitted lower by 44.4% than the mid maturing variety, intermittent drainage of submerged water by 43.8% than the continuous flooding condition, direct seeding by 32.0% than transplanting cultivation, no-ploughing by 20.9% than ploughing cultivation. It means that LCA on Global Warming Potential and the statistical data on innovated technical practice are key tools to systemize Measurable-Reportable-Verifiable (MRV) system for carbon footprint and carbon emission trade in the farm base.

• Journal of the Korean Institute of Gas
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• v.25 no.6
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• pp.66-73
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• 2021

In this study, The full load test and WHTC mode test were performed to examine the effect on a heavy duty natural gas engine according to the type of standard gas for certification to check engine performance and exhaust characteristics. Two types of standard gas (G_r, G₂₃) and commercially available natural gas were applied as the fuel used. As a result of the test results of three natural gases with different fuel compositions, G₂₃ with a high nitrogen content was inferior in torque, fuel consumption, and thermal efficiency conditions. In addition, when evaluated in the WHTC mode it was possible to obtain a result that satisfies the EURO VI regulation. However, compared to the other two fuels, the emission characteristics of G₂₃ decreased CO2 and CO, but increased CH4, NOx and PN emissions.

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.202-207
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• 2022

The study on electrode degradation of Proton Exchange Membrane Fuel Cell (PEMFC) was mainly studied on the particle growth and active area reduction of Pt on the electrode. The degradation of the electrode catalyst Pt in contact with the membrane affects the deterioration of the polymer membrane, but there are not many studies related to this. In this study, the phenomenon of the deposition of deteriorated Pt inside the polymer membrane during the accelerated electrode catalyst degradation test and its effects were studied. The voltage change (0.6 V ↔ 0.9 V) was repeated up to 30,000 cycles to accelerate the platinum degradation rate. When the voltage change cycle was repeated while oxygen was introduced into the cathode, the amount of Pt deposited inside the film was larger than when nitrogen was introduced. As the number of voltage change cycles increased, the amount of Pt deposited inside the membrane increased, and Pt dissolved in the cathode moved toward the anode, showing a uniform distribution throughout the membrane at 20,000 cycles. In the process of the accelerated electrode catalyst degradation test, the hydrogen crossover current density of the membrane did not change, and it was confirmed that the deposited Pt did not affect the durability of the membrane.

• Korean Chemical Engineering Research
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• v.62 no.3
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• pp.246-252
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• 2024

In this study, impurities such as Li and F were removed from waste graphite through citric acid treatment, and changes in structural properties, capacity, and cycle stability of regenerated graphite were observed accordingly. Regenerated graphite pretreated in a nitrogen atmosphere was treated with citric acid, and its structure and characteristics were analyzed through SEM (Scanning Electron Microscope), FT-IR (Fourier Transform Infrared spectroscopy), XRD (X-ray Diffraction), and XPS (X-ray Photoelectron Spectroscopy). Waste graphite that was not treated with acid had a rapid decrease in capacity before 70 cycles, but graphite that had been treated with citric acid showed a capacity of 302.9 mAh g^-1 and a capacity retention rate of 93.1% at 100 cycles. In addition, despite changes in current density in rate performance, samples treated with citric acid showed 340.2 mAh g^-1 performance at 1.0C without change in capacity. As a result, it was confirmed that citric acid treatment not only effectively removed impurities and showed a high capacity retention rate, but also showed stability even at high current densities.

• KSBB Journal
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• v.24 no.1
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• pp.30-40
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• 2009

Statistical optimization of the production medium was carried out in order to find an optimal medium composition in itaconic acid fermentation process. Itaconic acid utilized in the manufacture of various synthetic resins is a dicarboxylic acid biosynthesized by fungal cells of Aspergillus terreus in a branch of the TCA cycle via decarboxylation of cis-aconitate. Through OFAT (one factor at a time) experiments, six components (glucose, fructose, sucrose, soluble starch, soybean meal and cottonseed flour) were found to have significant effects on itaconic production among various carbon- and nitrogen-sources. Hence, using these six factors, interactive effects were investigated via fractional factorial design, showing that the initial concentrations of sucrose and cottonseed flour should be high for enhanced production of itaconic acid. Furthermore, through full factorial design (FFD) experiments, negative effects of $KH_2PO_4$ and $MgSO_4$ on itaconic acid biosynthesis were demonstrated, when excess amounts of the each component were initially added. Based on the FFD analysis, further statistical experiments were conducted along the steepest ascent path, followed by response surface method (RSM) in order to obtain optimal concentrations of the constituent nutrients. As a result, optimized concentrations of sucrose and cottonseed flour were found to be 90.4g/L and 53.8g/L respectively, with the corresponding production level of itaconic acid to be 4.36 g/L (about 7 fold higher productivity as compared to the previous production medium). From these experimental results, it was assumed that optimum ratio of the constituent carbon (sucrose) and nitrogen (cottonseed flour) sources was one of the most important factors for the enhanced production of itaconic acid.

• Microbiology and Biotechnology Letters
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• v.48 no.2
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• pp.205-214
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• 2020

Cyanobacteria are microorganisms which have important roles in the nitrogen cycle due to their ability to fix nitrogen in water and soil ecosystems. They also produce valuable materials that may be used in various industries. However, some species of cyanobacteria may limit the use of water resources by causing harmful algal blooms in water ecosystems. Many culture collection depositories provide cyanobacterial strains for research, but their systematic preservation is not well-developed in Korea. In this study, we developed a method for the cryopreservation of the cyanobacteria Trichormus variabilis (syn. Anabaena variabilis), using alginate microcapsules. Two approaches were used for the experiments and their outputs were compared. One of the methods involved the cryopreservation of cells using only a cryoprotectant and the other used the cryoprotectant within microcapsules. After cryopreservation for 35 days, cells preserved with both methods were successfully regenerated from the initial 1.0 × 10⁵ cells/ml to a final concentration of 6.7 × 10⁶ cells/ml and 1.1 × 10⁷ cells/ml. Irregular T. variabilis shapes were found after 14 days of regeneration. T. variabilis internal structures were observed by transmission electron microscopy (TEM), revealing that lipid droplets were reduced after cryopreservation. The expression of the mreB gene, known to be related to cell morphology, was downregulated (54.7%) after cryopreservation. Cryopreservation using cryoprotectant alone or with microcapsules is expected to be applicable to other filamentous cyanobacteria in the future.

• Korean Journal of Soil Science and Fertilizer
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• v.3 no.1
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• pp.55-59
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• 1970

In an effort to determine the bio-synthesis in the soybean as investigate to the variance of each substance: Glutamic acid, Aspartic acid and its amides during the growth of younger soybean plants. 1. The variance-curve of Gultamic acid and Aspartic acid as the acidic amino acids in the cotyledons was appeared the peak the first half period at Glutamic acid and the latter half at Aspartic acid in the growth of soybeans, and was received the symmetrical impression centering around the stage of adult leaf-development. But, in the embryonic organ, it appears the peak at both part, in the developmental stage of adult leaf and also appears near phenomena of increase and decrease in the variation-curve of metabolites. 2. It's amides-Gultamine and Asparagine-appears the peak at the developmental stage of adult leaf in the both cotyledons and embryonic organ, and rapid increase in the cotyledons were very impressed compare with the decrease at fallen stage of cotyledons in the embryonic organs. 3. In the relation of variance at Glutamic acid and Aspartic acid, both substance were discovered the fact of translocation from cotyledon to embryonic organ, and Glutamic acid could supposed that bear the charges of outrider substance in other amino acid as the Glutamic acid-self and major basic function for receiving the ammonia as the nitrogen contain constituent of plant. In the case of Glutamine, formation-mechanism of ammonia which develops due to its hydrolysis in the latter period of soybean growth, suggested that was forfeit its function till instance of fallen cotyledons. 4. In the relation the Aspartie acid and Asparagine, Aspartic acid which begins to decrease from seed-state was supposed that bear sufficiently the charge of outrider substance in the formation of Asparagine other than translocated to embryonic organ from cotyledon. And, formation-theory of Aspartic acid which suppose as formational substance from Kreb's cycle were recognized from latter period of soybean growth, and then, rapid accumulation of Asparagine's amounts were supposed that adapt to two theory: Theory which consider to transformation as Asparagine state for pressing to less than noxious weight the concentration of ammonia developing from the cells, and was formate and accumulate as ammonia or carbohydrates containing excess in the cotyledons.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.1
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• pp.31-48
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• 2019

The artificial ground freezing (AGF) method is a groundwater cutoff and/or ground reinforcement method suitable for constructing underground structures in soft ground and urban areas. The AGF method conducts a freezing process by employing a refrigerant circulating through a set of embedded freezing pipes to form frozen walls serving as excavation supports and/or cutoff walls. However, thermal expansion of the pore water during freezing may cause excessive deformation of the ground. On the other hand, as the frozen soil is thawed after completion of the construction, mechanical characteristics of the thawed soil are changed due to the plastic deformation of the ground and the rearrangement of soil fabric. This paper performed a field experiment to evaluate the freezing rate of marine clay in the application of the AGF method. The field experiment was carried out by circulating liquid nitrogen, which is a cryogenic refrigerant, through one freezing pipe installed at a depth of 3.2 m in the ground. Also, a piezo-cone penetration test (CPTu) and a lateral load test (LLT) were performed on the marine clay before and after application of the AGF method to evaluate a change in strength and stiffness of it, which was induced by freezing-thawing. The experimental results indicate that about 11.9 tons of liquid nitrogen were consumed for 3.5 days to form a cylindrical frozen body with a volume of about $2.12m^3$. In addition, the strength and stiffness of the ground were reduced by 48.5% and 22.7%, respectively, after a freezing-thawing cycle.