• 한국초전도ㆍ저온공학회논문지
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• 제5권2호
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• pp.58-65
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• 2003

The high temperature superconductivity(HTS) cable must be cooled below the nitrogen liquefaction temperature to applicate the cable in power generation and transmi-ssion system under the superconducting state. To obtain superconducting state. a reliable cryocooler system is required. Structural and thermal design have been performed to design cryocooler system operated with reverse Brayton cycle using gas neon as refrigerant. This cryocooler system consists of compressor. recuperator. coldbox. control valves and has 1 kW cooling capacity. Heat loss calculation was conducted for the given cryocooler system by considering the conduction and radiation through the multi-layer insulation(MLI) and high vacuum. The results can be summarized as: conduction heat loss is 7 W in valves and access port and radiation heat loss is 18 W through the surface of cryocooler. The full design specifications were discussed and the results were applied to construct in house HTS cable cooling system.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1998년도 제28회 추계학술대회
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• pp.91-99
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• 1998

A correlation between the low-cycle fatigue life and the scuffing-failure life is demonstrated using the plastic strain in boundary lubricated sliding. Loadings proportional to hardness with three different lubricated conditions were used to evaluate the plastic strain. As the results of scuffing tests using vacuum pump oils in nitrogen gas, plastic strain shows 0.0062, and In the mineral oils and commercial engine oils in air, plastic strain show 0.0042 and 0.00092. Those are very useful to describe quantitatively the real lubricated sliding conditions, and are very effective to find the relation between the low-cycle fatigue life and the scuffing life.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.181-185
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• 2008

The new concept for liquefaction of natural gas has been designed and simulated in this paper. Conventional liquefaction cycles are usually composed with Joule-Thomson valves at lower temperature refrigerant cycle. The new concept of natural gas liquefaction is discussed. The main difference with conventional liquefaction process is the presence of the turbine at low temperature of MR (mixed refrigerant) cycle. The turbine acts as expander but also as an energy generator. This generated energy is provided to the compressor which consumes energy to pressurize refrigerants. The composition of the mixed refrigerant is investigated in this study. Components of the refrigerant are methane, propane and nitrogen. Composition for new process is traced with Aspen HYSYS software. LNG heat exchangers are analyzed for the new process. Heating and cooling curves in heat exchangers were also analyzed.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제2권2호
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• pp.115-121
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• 1998

Train of chemical and biological processes was investigated to treat leachate from industrial waste landfill. Organics and nitrogen concentrations of landfill leachate studied in this research were high and their BOD/COD ratio was 0.3. Biological process should be combined with chemical process for optimum treatment of leachate. PAC(Polyaluminium chloride) was the best coagulant among three chemicals tested, and the optimum condition of PAC coagulation was pH 6 and 1,250 mg/L of dosage. When SBR was operated for simultaneous removal of organics and nitrogen, removal efficiency of COD and T-N reached over $82\%,\;71\%,$ respectively and time distribution of 2/4/2/1 was most effective for one cycle of anoxic/aerobic/anoxic/aerobic.

• Mycobiology
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• 제30권3호
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• pp.146-153
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• 2002

Two types of mycorrhizae, orchid(OM) and arbuscular mycorrhizae(AM), were observed in the cortical cells of Botrychium ternatum roots. The vesicles or arbuscules of AM fungi were examined and the fresh or digestive pelotons by other species of basidiomycetes were also observed in the roots under light microscope. These symbioses were, as the genomic DNAs extracted from roots of B. ternatum reacted with the specific primers, confirmed with PCR technique, being added to more strong evidences. These discoveries were rarely happened in the roots, especially a fern in nature. OM was observed in the roots of B. ternatum collected from the nationwide areas, whereas AM was only in the roots of B. ternatum collected from Chung-Buk areas. It is speculated that OM are associated with the nitrogen cycle in Islands and the growth of B. ternatum in the inland of Central Korea is related to both the phosphate and nitrogen cycle in the nature. The results suggest that B. ternatum is a typical species with two types of mycorrhizae under various growing conditions.

• Journal of Applied Biological Chemistry
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• 제42권1호
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• pp.1-6
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• 1999

Poly-${\beta}$-hydroxybutyrate (PHB) and enzymes related PHB metabolism have been measured in nitrogen-fixing symbiosis of chickpea and cowpea plants. Bacteroids from chickpea and cowpea contained PHB to 0.8% and 43% of their dry weight, respectively, whereas the free-living cells CC 1192 and I 16 produced $285{\pm}55mg$ and $157{\pm}18mg$ of PHB g (dry weight)$^{-1}$. To further understand why chickpea bacteroids contained little PHB, the enzyme activities of PHB metabolism (3-ketothiolase, acetoacetyl-CoA reductase, PHB depolymerase, and 3-hydroxybutyrate dehydrogenase), the TCA cycle (malate dehydrogenase, citrate synthase, and isocitrate dehydrogenase), and related reactions (malic enzyme, pyruvate dehydrogenase, and glutamate:2-oxoglutarate transaminase) were compared in extracts from chickpea and cowpea bacteroids and the respective free-living bacteria. Significant differences were observed between chickpea and cowpea bacteroids and between the bacteroid and free-living forms of CC 1192, with respect to the capacity for some of these reactions. It is indicated that a greater potential for oxidizing malate to oxaloacetate in chickpea bacteroids could be a factor that favors the utilization of acetyl-CoA in TCA cycle rather than for PHB synthesis.

• The Korean Journal of Ecology
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• 제11권2호
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• pp.55-64
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• 1988

The seasonal pattern of pool size and withdrawal from senescing or stroage organ, and the annual magintude of internal-and plant-soil cycles for nitrogen and phosphorus in a Glyceria leptolepis Ohwi population in a marsh of the Mt. Geumoh were investigared. The population pool changed from initial size of 6.8 to the maximum of 16.1gN$m^{-2}$ for N and from 1.7 to 3.9g Pm$m^{-2}$ for P, maintaining far higher relative pool size during the first half of the growth period as compared with that for biomass. A sharp increase in N and P pool was noticed in early spring before the biomass growth was recognized, The major process supplying the demand for N and P changed as the growth progressed showing the order; absorption-withdrwal-absorption-with-drawal. The annual magnitude of plant-soil cycle for N and P was 18.0-19.1 and 2.9-3.3gm$m^{-2}$, accounting for 3 and 5% of each nutrient pool in 0-20 cm humus layer, respectively. The higher exent of internal cycle and the lower rate of annual turnover for P(1.08) as compared with those for N may suggest that this population conserves and reuses P more efficiently than N.

• 대한환경공학회지
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• 제27권1호
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• pp.17-24
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• 2005

본 연구에서는 간헐적으로 포기되는 부직포 여과막 생물반응조에 하수를 연속적으로 주입하면서 수리학적 체류시간(HRT)을 12, 10 및 8시간으로 감소시키면서 17개월간 실험을 실시하였다. 먼저 각 HRT에서 질소 제거효율이 가장 좋은 포기/비포기 시간비를 찾기 위하여 포기/비포기 시간비 1에서 주기시간을 3, 2, 및 1시간으로 변화시키며 질소 제거효율을 비교한 후, 질소 제거효율이 가장 좋았던 2시간의 주기시간에서 포기/비포기 시간비를 다시 50분/70분, 40분/80분 그리고 30분/90분으로 변화시키면서 질소 제거효율을 비교하였다. 실험기간 동안 처리수의 SS농도는 항상 1.2 mg/L 미만으로 유지되었으며, BOD 제거효율은 95% 이상을 나타내었다. 모든 HRT에서 최대 질소 제거효율을 나타낸 포기/비포기 시간비는 40분/80분이었으며, HRT 10시간에서 질소 제거효율이 90.1%로 가장 높았다. 그리고 ORP가 반응조 내의 질산화 및 탈질 정도를 잘 나타냄을 알 수 있었다.

• 한국환경과학회지
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• 제16권1호
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• pp.45-53
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• 2007

This study was carried out to investigate the variation of organic, nitrogen and phosphorus in $(AO)_2$ SBBR process according to the variation of operating cycle at the high TOC concentration. The operation time in anoxic (anaerobic) time to oxic time was 1:1. Three lab-scale SBBRS were fed with synthetic wastewater based on glucose as carbon source, The variation of total TOC removal was similar each other irrespective of operation time, however, the TOC concentrations in SBBRs showed a little difference according to the operating condition. In SBBR, complete nitrification was not occurred at all reactors, however, R3 showed a higher nitrification than R2. And in SBBR, the variation of operating time more affected at phosphorus removal than nitrogen removal. R2 which had the shortest time at the 1st aeration time showed the lowest phosphorus release and uptake efficacy.

• Asian-Australasian Journal of Animal Sciences
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• 제13권5호
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• pp.698-701
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• 2000

To prevent surface and underground water pollution, wastewater treatment is essential. Four bench-scale activated sludge units (10 L operational volumes) were operated at 5, 10 and $20^{\circ}C$ for evaluation of treatment efficiencies with typical wastewater from swine housing. The units were set for a 24-hour cycle. As compared to the conventional process, high removal efficiencies for organic substances, nitrogen and phosphorus in swine wastewater were obtained simultaneously with an intermittent aeration process (lAP). The NOx-N produced during an aeration period was immediately reduced to nitrogen gas (e.g. $N_2$ or $N_2O$) in the subsequent non-aeration periods, and nitrification in aeration periods occurred smoothly. Under these conditions, phosphorus removal occurred with the release of phosphorus during the non-aeration periods followed by the excess uptake of phosphorus in the activated sludge during aeration periods. It was confirmed that the lAP had a better ability to remove pollutants under both low temperatures and high nitrogen loading conditions than the ordinary method did. In addition to that, the total emission of $N_2O$ from lAP was reduced to approximately 1/50 of the conventional process for the same loading. By adopting an adequate aeration programme for individual swine wastewater treatment, this system will provide a promising means for nitrogen and phosphorus control without pH control or addition of methanol.