• Microbiology and Biotechnology Letters
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• v.20 no.2
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• pp.196-202
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• 1992

Zoogloea ramigera 115 was selected for the production of viscous microbial polysaccharide for bioflocculants usage. Batch, fed-batch, and continuous culture processes were examined with regard to the high biopolymer production. Several carbon sources were tested, including glucose, lactose, molasses, and cheese whey. The C/N ratio of 90 was most effective for biopolymer production from glucose, while the C/N ratios of 30 for lactose and 60 for both molasses and cheese whey substrate gave a maximum production. Fed batch culture proved more effective to increase final biopolymer concentration than batch culture. Continuous fermentation with two stages modifying C/N ratio increased the productivity. The production rates were a maximum at dilution rate of 0.048 $hr^{-1}$ for molasses and at 0.096 $hr^{-1}$for cheese whey.

• Korean Journal of Veterinary Research
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• v.23 no.2
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• pp.173-178
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• 1983

This paper deals with the isolation of citrate-utilizing variants of Escherichia coli ($Cit^+$ E. coli) from the animals, their biochemical reactivity and antibiotic susceptibility, and whether the citrate utilizing ability is transmissible. One hundred arid twenty-three isolates of $Cit^+$ E. coli were obtained from cattle and pigs. but from other animals, no isolates were obtaied. Antibiotic susceptibility testing of $Cit^+$ E. coli was performed by the agar dilution method, using the following 9 antibiotics, chloramphenicol(CP), tetracycline(TC), streptomycine(SM), kanamycin(KM), colistin(CL), gentamicin(GM), cephaloridine(CR), aminobenzycillin and nalidixic acid(NA). All the variants tested were susceptible to KM, CL, GM, CR and NA. Of all the variants, 80(65%) were resistant to the drugs tested and resistance to TC and SM was most frequent. The transmission of the ability to utilize citrate on Simmons citrate agar at $37^{\circ}C$ was demonstrated in 78(67.8%) out of the 115 $Cit^+$ E. coli. There were no significant difference in the transfer rates of citrate utilizing ability between resistant and susceptible variants to above 9 drugs. Of 123 isolates, 8 were lost their citrate utilizing ability, spontaneously.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.1
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• pp.144-152
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• 2006

Split injection has been known to reduce total hydrocarbon (THC) emission level and increase engine performance under certain operating conditions 1, 2). Exhaust Gas Recirculation (EGR) is a common technique adopted for nirtric oxides (NOx) reduction by the dilution of intake air, despite a sacrifice of simultaneous increase in THC and decrease in engine performance3). Thus, using split injection with adequate EGR may improve the emission level of UBHC, NOx and the engine performance compared to that of single-injection with or without EGR cases. The purpose of this study is to investigate the engine performance and emission levels at various engine operating conditions and injection methods when it is applied with EGR. The characteristics of single-injection and split-injection were investigated with various engine loads and EGR rates. The engine speed is changed from 800rpm to 1200rpm to investigate how the combustion characteristics are changing with increasing engine speed.

• Korean Journal of Animal Reproduction
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• v.13 no.3
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• pp.141-148
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• 1989

The effects of seeding method and optimum time for freezing embryos according to the developmental stages on embryo survival rates after rapid freezing were determined using the FDA-test. The summarized results are as follows : 1. In the rapid freezing of embryos, the sucrose added medium together with Co-seeding or non-seeding showed the FDA scores of 4.67 and 4.20, respectively, but, raffinose addition obtained FDA scores of 4.27 and 3.97. 2. The developmental stage of embryos at freezing was most critical on the survival of embryos after thawing. Higher FDA scores were obtained in the order of blastocyst stage(4.94), morula stage(3.82) and ealy stage(2.65) in sucrose added medium. The same trend was observed in the raffinose added medium with an order or 4.91, 4.47 and 2.32. 3. Microscopic study of embryo before freezing and post-thawing indicated that the embryo showed shrinkage within 5 minutes after the embryo was transfer to the freezing medium. When thawed embryo was tranfered to the dilution medium, swelling of the embryo was observed and there after it reshrank indicating the removal of cryoprotectant from the embryo. The size of the embryo recovered to the original state when it was moved into a PBS-solution.

• Journal of the Korean Society of Combustion
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• v.20 no.4
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• pp.19-25
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• 2015

An experimental study was conducted to find the effect of a pilot flame on the flammability of inert-gas-diluted methane and propane. The diffusion pilot flame was formed with propane at the innermost nozzle of a concentric triple co-flow burner. The main diffusion flame was formed with nitrogen-diluted methane or propane at the outermost nozzle of the burner. An air flow was located in-between. The results showed that the existence of the pilot flame helped stabilizing the main flame even at the flammability limit concentration of nitrogen-diluted fuel. The co-flow burner generated re-circulation zones and local variation of equivalence ratio depending on the flow rates of the reactants, which are known to help flame stabilization. Hot-wire experiments confirmed that both heating of the reactants and supplying of active chemical species by the pilot flame contributed to stabilization of the main flame. The results of this study would suggest a design concept for an efficient SVRU system that minimizes the emission of unburned hydrocarbon fuel from ship fuel tanks.

• Journal of Microbiology and Biotechnology
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• v.27 no.7
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• pp.1316-1323
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• 2017

Geosmin and 2-methylisoborneol (2-MIB), responsible for earthy or musty smell, are a major concern for safe drinking water supplies. This study investigated the effects of environmental factors on odorous compound production and cell growth in cyanobacterial strains. Anabaena sp. FACHB-1384, a 2-MIB producer, was sensitive to low temperature (<$20^{\circ}C$). However, geosmin producers, Anabaena sp. Chusori and Anabaena sp. NIER, were sensitive to high light intensity (>$100{\mu}mol/m^2/sec$), but not to low temperature. Geosmin concentrations increased under higher nitrate concentrations, being linearly proportional to cell density. A P-limited chemostat showed that P-stress decreased the geosmin productivity and extracellular geosmin amount per cell in Anabaena sp. NIER. However, only 2-MIB productivity was reduced in Planktothrix sp. FACHB-1374 under P-limitation. The extracellular 2-MIB amount per cell remained constant at all dilution rates. In conclusion, high light intensity and P-stress can contribute to the lower incidence of geosmin, whereas 2-MIB reduction could be attainable at a lower temperature.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1763-1765
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• 2000

This paper presents deposition and characterizations of microcrystalline silicon ($\mu$ c-Si:H) films prepared by hot wire chemical vapor deposition at substrate temperature at 300$^{\circ}C$. The flow rates of $SiH_4$ gas are critical parameter for the formation of Si films with microcrystalline phase. We could obtain $\mu$ c-Si:H with columnar grain structure and volume fraction of 75% without H2 dilution. The electronic properties, hydrogen bonding configurations, and $H_2$ concentration inside the films are also strongly affected by $SiH_4$ flow rate, which is provided in this paper.

• Korean Journal of Microbiology
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• v.6 no.4
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• pp.107-112
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• 1968

Examining the microbial populations in the Han River estuary, we conducted this experiment at six sites of the estuarine area, Chollyu-ri, Cholsan-ri, Wolgon-ri, Chogi-ri, Inhwa-ri, and Oepo-ri for 5 months since May 1967. From the results obtained it could be summarized as follows. 1) The salinity of the estuarine water increased in order of the distances from the base point of the Old Han River Bridge to every site of the estuary, and pH of the water, which were between 7. 3 and 8. 1, showing little difference each other in both the sites and dates of experiment. 2) The populations of the general bacteria and coliform group bacteria were highest at the site of Chollyu-ri, and it decreased with the downstreaming of the river water toward Oepo-ri site. As for fungi which have comparatively high tolerance to the salinity, its population was shown hi hest at Chogi-ri. 3) The relationship between the salinity and the number of the general bacteria have indicated that the incresed salinity reduced the growth rates of the bacteria. By this it can be assumed that the fresh-water bacteria decreased due to the sea water as well as its dilution effects. 4) The high pollution of the esturarine water was caused by the increases of inhabitants and water thrown by industries in Seoul and Kyung-In Industrial District as well as the excrements fertilized to the farms.

• Journal of Environmental Health Sciences
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• v.23 no.4
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• pp.57-66
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• 1997

Successful energy conservation and good indcfor air quality (IAQ) are highly dependent on ventilation system. Air filtration is a primary solution of indoor air control strategies in terms of reducing energy consumption and improving ihdoor air quality. A conventional system with bypass filter, as it is called variable-air-volume/bypass filtration system (VAV/BPFS), is a variation of the conventional variable air volume (VAV) systems, which is designed to eliminate indoor air pollutant and to save energy. Bypass filtration system equipped with a high-efficiency particulate filter and carbon absorbent provides additional cleaned air into indoor environments and maintain good IAQ for human health. The objectives of this research were to compare the relative total decay rate of indoor air pollutant concentrations, and to develop a mathematical model simulating the performance of VAV/BPFS. All experiments were performed in chamber under the controlled conditions. The specific conclusions of this research are: 1. The VAV/BPFS system is more efficient than the VAV system in removing indoor air pollutant concentration. The total decay rates of aerosol, and total volatile organic compound (TVOC) for the VAV/BPFS system were higher than those of the conventional VAV system. 2. IAQ model predictions of each pollutant agree closely with the measured values. 3. According to IAQ model evaluation, reduction of outdoor supply air results in decreased dilution removal rate and on increased bypass filtration removal rate with the VAV/BPFS. As a results, we recommends the VAV/BPFS as an alternative to conventional VAV systems.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.58-64
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• 2006

Homogeneous charge compression ignition(HCCI) combustion is an advanced technique for reducing the hazardous nitrogen oxide(NOx) and particulate matter(PM) in a diesel engine. NOx could be reduced by achieving lean homogeneous mixture resulting in combustion temperature. PM could be also reduced by eliminating fuel-rich zones which exist in conventional diesel combustion. However previous researches have reported that power-output of HCCI engine is limited by the high intensive knock and misfiring. In an attempt to extend the upper load limit for HCCI operation, supercharging in combination with Exhaust Gas Recirculation(EGR) has been applied: supercharging to increase the power density and EGR to control the combustion phase. The test was performed in a single cylinder engine operated at 1200 rpm. Boost pressures of 1.1 and 1.2 bar were applied. High EGR rates up to 45% were supplied. Most of fuel was injected at early timing to make homogeneous mixture. Small amount of fuel injection was followed near TDC to assist ignition. Results showed increasing boost pressure resulted in much higher power-output. Optimal EGR rate influenced by longer ignition delay and charge dilution simultaneously was observed.