• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1095-1101
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• 2002

An experimental apparatus was prepared to investigate thermal and hydrodynamic characteristics of regenerator at cryogenic temperature under pulsating pressure condition. The regenerator was pressurized and depressurized by a compressor with various operating frequencies. Cold end of the regenerator was maintained around 100 K by means of a liquid nitrogen heat exchanger. Instantaneous gas temperature and mass flow rate were measured at both ends of the regenerator during the whole pressure cycle. Pulsating pressure drop across the regenerator was also measured to see if it could be predicted by a friction factor at steady flow condition. The operating frequency of pressure cycle was varied between 3 and 60 Hz, which are typical operating frequencies of Gifford-McMahon, pulse tube, and Stilting cryocoolers. First, the measured friction factor for typical wire screen mesh regenerator was nearly same as steady flow friction factor for maximum oscillating Reynolds number up to 100 at less than 9 Hz. For 60 Hz operations, however, the discrepancy between oscillating flow friction factor and steady flow one was noticeable if Reynolds number was higher than 50. Second, the ineffectiveness of regenerator was directly calculated from experimental data when the cold-end was maintained around 100 K and the warm-end around 293 K, which simulates an actual operating condition of cryogenic regenerator. Influence of the operating frequency on ineffectiveness was discussed at low frequency range.

• Atmosphere
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• v.27 no.3
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• pp.301-316
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• 2017

This study analyzes the spatio-temporal variability of terrestrial carbon flux and the response of land carbon sink with climate factors to improve of understanding of the variability of land-atmosphere carbon exchanges accurately. The coupled carbon-climate models of CMIP5 (the fifth phase of the Coupled Model Intercomparison Project) and CT (CarbonTracker) are used. The CMIP5 multi-model ensemble mean overestimated the NEP (Net Ecosystem Production) compares to CT and GCP (Global Carbon Project) estimates over the period 2001~2012. Variation of NEP in the CMIP5 ensemble mean is similar to CT, but a couple of models which have fire module without nitrogen cycle module strongly simulate carbon sink in the Africa, Southeast Asia, South America, and some areas of the United States. Result in comparison with climate factor, the NEP is highly affected by temperature and solar radiation in both of CT and CMIP5. Partial correlation between temperature and NEP indicates that the temperature is affecting NEP positively at higher than mid-latitudes in the Northern Hemisphere, but opposite correlation represents at other latitudes in CT and most CMIP5 models. The CMIP5 models except for few models show positive correlation with precipitation at $30^{\circ}N{\sim}90^{\circ}N$, but higher percentage of negative correlation represented at $60^{\circ}S{\sim}30^{\circ}N$ compare to CT. For each season, the correlation between temperature (solar radiation) and NEP in the CMIP5 ensemble mean is similar to that of CT, but overestimated.

• Journal of Environmental Science International
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• v.27 no.4
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• pp.233-240
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• 2018

The purpose of this study was to confirm the applicability of aerobic granular sludge (AGS) in the advanced sewage treatment process. Simulated influent was used in the operation of a laboratory scale reactor. The operation time of one cycle was 4 h and the reactor was operated for six cycles per day. The volume exchange ratio was 50%. The influent was injected in divisions of 25% to increase the removal efficiency of nitrogen in every cycle. As a result, the removal efficiencies of $COD_{Cr}$ and TN in this reactor were 98.2% and 76.7% respectively. During the operation period, the AGS/MLVSS concentration ratio increased from 70.0% to 86.7%, and the average $SVI_{30}$ was 67 mL/g. The SNR and SDNR were 0.073-0.161 kg $NH_4{^+}$-N/kg MLVSS/day and 0.071-0.196 kg $NO_3{^-}$-N/kg MLVSS/day respectively. These values were higher or similar to those reported in other studies. The operation time of the process using AGS is shorter than that of the conventional activated sludge process. Hence, this process can replace the activated sludge process.

• Membrane and Water Treatment
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• v.9 no.3
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• pp.181-188
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• 2018

A sidestream contains the filtrate or concentrate from the belt filter press, filter backwash and supernatant from sludge digesters. The sidestream flow, which heads back into the sewage treatment train, is about 1-3% less than the influent flow. However, the sidestream can increase the nutrient load since it contains high concentrations of phosphorus and nitrogen. In this study, the removal of PO4-P with organic matter characteristics and bacteriological changes during the sidestream treatment via ladle furnace (LF) slag was investigated. The sidestream used in this study consisted of 11-14% PO4-P and 3.2-3.6% soluble chemical oxygen demand in influent loading rates. LF slag, which had a relatively high $Ca^{2+}$ release compared to other slags, was used to remove $PO_4-P$ from the sidestream. The phosphate removal rates increased as the slag particle size decreased 19.1% (2.0-4.0 mm, 25.2% (1.0-2.0 mm) and 79.9% (0.5-1.0 mm). The removal rates of dissolved organic carbon, soluble chemical oxygen demand, color and aromatic organic matter ($UV_{254}$) were 17.6, 41.7, 90.2 and 77.3%, respectively. Fluorescence excitation-emission matrices and liquid chromatography-organic carbon detection demonstrated that the sidestream treatment via LF slag was effective in the removal of biopolymers. However, the removal of dissolved organic matter was not significant during the treatment. The intact bacterial biomass decreased from $1.64{\times}10^8cells/mL$ to $1.05{\times}10^8cells/mL$. The use of LF slag was effective for the removal of phosphate and the removal efficiency of phosphate was greater than 80% for up to 100 bed volumes.

• Applied Chemistry for Engineering
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• v.7 no.4
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• pp.653-660
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• 1996

For oxygen PSA process development, adsorbed amount of oxygen and nitrogen on various adsorbents were measured corresponding Langmuir isotherm parameters were measured. A reasonable adsorbent for oxygen process was selected based on the effective adsorbed amount. The PSA process consists of adsorption, desorption, pressurization, purging and pressure equilization steps. Adsorption pressure was about 2 atm and desorption pressure was between 120 torr to 400torr. Cycle time of 2-bed PSA process was 80 seconds and that of 3-bed oxygen PSA process was 180 seconds. In order to compare and analyze operation characteristics and economic feasibilities of 2-bed and 3-bed oxygen PSA processes, productivity, oxygen concentration and recovery were compared and the effect of purge and pressurization steps on the performance of PSA processes were analyzed. For the commercial scale oxygen PSA process, capital and electricity cost were estimated. In the range of $O_2$ production less than $700Nm^3/hr$, the 2-bed process is conformed more feasible in economic view point.

• The KSFM Journal of Fluid Machinery
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• v.13 no.1
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• pp.9-16
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• 2010

In the power generation industry, various efforts are needed to cope with tightening regulation on carbon dioxide emission. Integrated gasification combined cycle (IGCC) is a relatively environmentally friendly power generation method using coal. Moreover, pre-combustion $CO_2$ capture is possible in the IGCC system. Therefore, much effort is being made to develop advanced IGCC systems. However, removal of $CO_2$ prior to the gas turbine may affect the system performance and operation because the fuel flow, which is supplied to the gas turbine, is reduced in comparison with normal IGCC plants. This study predicts, through a parametric analysis, system performances of both an IGCC plant using normal syngas and a plant with $CO_2$ capture. Performance characteristics are compared and influence of $CO_2$ capture is discussed. By removing $CO_2$ from the syngas, the heating value of the fuel increases, and thus the required fuel flow to the gas turbine is reduced. The resulting reduction in turbine flow lowers the compressor pressure ratio, which alleviates the compressor surge problem. The performance of the bottoming cycle is not influenced much.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.1
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• pp.143-148
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• 2013

When the fault occurs in power system, the fault-current exceeds breaking capacity of the circuit breaker. So, reliablity of the power system is decreased sharply. Superconducting fault-current limiter (SFCL) is operated without impedance in normal state. The fault-current is limited by its impedance during the fault condition. However, the SFCL has several weak points such as huge size, high-price, liquid-nitrogen operation for the real power system. In this paper, We suggested the high-speed interrupter to limit the fault-current in case of the single line-to-ground fault. In addition, we compared the high-speed interrupter with the SFCL to ensure the operation reliability. The proposed interrupter detected the fault-current through the CT, and the power was supplied by operation of the SCR control system. In this experiment, the power of high-speed interrupter was applied after the 4.8[msec] from fault instant. The on-off operation of the interrupter was started after half-cycle from the fault. The fault-current was flowed into the impedance element by the switching operation of the high-speed interrupter. So, the fault current was limited within one cycle, and then it didnt exceed the capacity of a circuit breaker. We confirmed that there was slight difference between the SFCL with high-speed interrupter in terms of limiting-time of the fault-current and switching speed of the SCR. The high-speed interrupter was considered to be more efficient than the SFCL in size, cost or reliability.

• Journal of The Korean Society of Agricultural Engineers
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• v.63 no.3
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• pp.97-105
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• 2021

Most of the rural development projects for the welfare of residents are mainly new construction and remodeling projects for community buildings such as village halls and senior citizens. However, in the case of the construction industry, it has been studied that 23% of the total carbon dioxide emissions generated in Korea are generated in the building-related sector. (GGIC, 2015) In order to reduce the emission of environmental pollutants resulting from construction of rural community buildings, there is a need to establish a system for rural buildings by predicting the environmental impact. As a result of this study, the emissions of air pollutants from buildings in rural communities were analyzed by dividing into seven stages: material production, construction, operation, maintenance, demolition, recycling, and transportation activities related to disposal. As a result, 12 kg of carbon dioxide (CO), 0.06 kg of carbon monoxide (CO), 0.02 kg of methane (CH), 0.04 kg of nitrogen oxides (NO), 0.02 kg of sulfurous acid gas (SO), and non-methane volatile organics per 1m of buildings in rural communities It was analyzed that 0.02 kg of compound (NMVOC) and 0.00011 kg of nitrous oxide (NO) were released. This study proved that environmentally friendly design is possible with a quantitative methodology for the comparison of operating energy and air pollutant emissions through the design specification change based on the statement of the rural community building. It is considered that it can function as basic data for further research by collecting major structural changes and materials of rural community buildings.

• Journal of Climate Change Research
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• v.5 no.3
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• pp.189-197
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• 2014

Carbon footprint of apple was a sum of $CO_2$ emission in the step of manufacturing waste of agri-materials, and greenhouse gas emission during apple cultivation. Input amount of agri-materials was calculated on 2007 Income reference of Apple by Rural Development Administration. Emission factor of each agri- materials was based on domestic data and Ecoinvent data. $N_2O$ emission factor was based on 1996 IPCC guideline. Carbon dioxide was emitted 0.64 kg $CO_2$ to produce 1 kg apple fruit, and carbon dioxide was emitted 43.6% in the step of the manufacturing byproduct fertilizer, 1.3% in the step of the manufacturing single fertilizer, 4.7% in the step of the manufacturing composite fertilizer, 6.3% in the step of the manufacturing agri-chemicals, 14.6% in the step of the manufacturing fuel, 11.5% in the step of the fuel combustion, 17.7% of $N_2O$ emission by nitrogen application and 0.18% of disposal of agri-materials. It is needed for farmers to use fertilization recommendation based on soil testing (soil. rda.go.kr) because scientific fertilization is a major tools to reduce carbon dioxide of apple production. The fertilization recommendation could be also basic data in Measurable-ReporTablele-Verifiable (MRV) system for carbon footprint.

• Journal of Animal Reproduction and Biotechnology
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• v.36 no.4
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• pp.230-238
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• 2021

This study attempted to determine the characteristic features of postpartum dairy cows during their return to estrus. Moreover, it investigated the effects of abnormal ovarian cycles (AOC) on subsequent reproductive performance and the relationship between normal ovarian cycles (NOC) and the blood urea nitrogen (BUN) level postpartum. Incidentally, 56.3% of the Holstein cows and 66.7% of the Jersey cows had NOC, whereas the 43.7% and 33.3% of the Holstein and Jersey, respectively, had AOC. Within 100 days of calving, the cows with AOC had significantly lower rates of artificial insemination (AI) submission as well as pregnancy and a significantly longer interval to first AI, as compared to that in the cows with NOC. Additionally, the cows with NOC had a significantly higher first AI conception rate than that in the cows with AOC. In this study, of the 32 Holstein cows, 8 resumed their ovarian cycle within 20 days of calving, 10 resumed the cycle with 21-40 days of calving, 8 within 41-60 days of calving, while the remaining 6 did not resume their ovarian cycles until 60 days postpartum. Furthermore, the likelihood ratios of incidence of NOC are 0.93, 1.94, and 0.38, respectively, in the groups with BUN levels < 15, 15-19.9, and ≥ 20 mg/dl. In conclusion, AOC postpartum adversely affects reproductive performance such as AI submission rate, pregnancy rate, interval to first AI and first AI conception rate; moreover, an increase or decrease in the BUN levels beyond 15-19.9 mg/dL leads to the AOC postpartum.