• Biotechnology and Bioprocess Engineering:BBE
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• 제11권6호
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• pp.522-525
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• 2006

Biodiesel conversion from soybean oil reached a maximum of 70% at 18 h using immobilized 1,3-specific Rhizopus oryzae lipase alone. Biodiesel conversion failed to reach 20% after 30 h when immobilized nonspecific Candida rugosa lipase alone was used. To increase the biodiesel production yield, a mixture of immobilized 1,3-specific R. oryzae lipase and nonspecific C. rugosa lipase was used. Using this mixture a conversion of greater than 99% at 21 h was attained. When the stability of the immobilized lipases mixture was tested, biodiesel conversion was maintained at over 80% of its original conversion after 10 cycles.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권8호
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• pp.413-419
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• 2003

The paper presents a simulation model and analysis of a grid-connected variable speed wind energy conversion scheme (VSWECS) using the PSCAD/EMTDC software. The modeled system uses a variable speed drive, a fixed pitch angle, a synchronous generator as a wind generator and an AC-DC-AC conversion scheme, which facilitates the wind generation to efficiently operate under varying wind speed while connected to the distribution network. The power output of the WECS is controlled by the AC-DC-AC conversion scheme, the objective of which is to capture the maximum active power under varying wind conditions and to keep the voltage magnitude of the terminal bus at a specific level. Aerodynamic models are applied for a wind turbine model. An simulation analysis of the scheme in terms of its responding to wind variations is also presented.

• 한국물환경학회지
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• 제30권3호
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• pp.351-360
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• 2014

The allocation of margin of safety (MOS) at a uniform rate to all areas of the unit watershed makes it very difficult to keep the load allotment stable in the area for lack of reduction measures like forest land. This study developed an equation to calculate margin of safety differentially according to the regional characteristics. The equation was formulated on the basis of the regional characteristic factors such as a load contribution factor for land use type and a site conversion factor for the unit watershed. The load contribution factor represents a contribution of loads from a particular land use. The site conversion factor was derived from the site conversion ratio of a unit watershed. Margin of safety for the non-point pollution load in the land use sector decreased by 20~25% in three river basins. The margin of safety in the unit watersheds with low site occupation ratios decreased in high rate, while in the unit watersheds with large urban area decreased in low rate. With the application of the differential margin of safety considering regional characteristics, not only the reduction of pollution loads can become lighter but also it can be easier to develop plans for Total Maximum Daily Loads (TMDLs) even where the reduction measures are not available.

• 한국산업보건학회지
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• 제29권2호
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• pp.167-175
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• 2019

Objectives: The purpose of this study was to evaluate airborne radon and thoron levels and estimate the effective doses of workers who made household goods and mattresses using monazite. Methods: Airborne radon and thoron concentrations were measured using continuous monitors (Rad7, Durridge Company Inc., USA). Radon and thoron concentrations in the air were converted to radon doses using the dose conversion factor recommended by the Nuclear Safety and Security Commission in Korea. External exposure to gamma rays was measured at the chest height of a worker from the source using real-time radiation instruments, a survey meter (RadiagemTM 2000, Canberra Industries, Inc., USA), and an ion chamber (OD-01 Hx, STEP Co., Germany). Results: When using monazite, the average concentration range of radon was $13.1-97.8Bq/m^3$ and thoron was $210.1-841.4Bq/m^3$. When monazite was not used, the average concentration range of radon was $2.6-10.8Bq/m^3$ and the maximum was $1.7-66.2Bq/m^3$. Since monazite has a higher content of thorium than uranium, the effects of thoron should be considered. The effective doses of radon and thoron as calculated by the dose conversion factor based on ICRP 115 were 0.26 mSv/yr and 0.76 mSv/yr, respectively, at their maximum values. The external radiation dose rate was $6.7{\mu}Sv/hr$ at chest height and the effective dose was 4.3 mSv/yr at the maximum. Conclusions: Regardless of the use of monazite, the total annual effective doses due to internal and external exposure were 0.03-4.42 mSv/yr. Exposures to levels higher than this value are indicated if dose conversion factors based on the recently published ICRP 137 are applied.

• 조명전기설비학회논문지
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• 제23권12호
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• pp.217-223
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• 2009

계약전력 산정 방법에서 계약전력 환산율은 전력용변압기의 용량을 산정하는데 매우 중요한 기준이다. 본 연구에서는 AMR(자동검침시스템) 시스템에 의해 일반용전력사용고객(사무실, 상가, 호텔, 병원, 예식장, 기타)을 대상으로 각 수용가의 계약전력과 최근 5년 동안의 최대전력을 조사하였다. 조사된 자료의 전체 특징과 중심적인 경향을 알아 보기 위해서 평균값 등의 특징파라미터를 분석하였고, 회귀분석을 통한 선형적인 방법과 비선형적인 방법으로 그 경향을 분석하였다. 계약전력환산율과는 용도별로 다른 특성을 나타내고 있음을 확인하였으며, 전기사용고객의 특성을 고려한 계약종별 기준에 대한 체계적인 검토가 필요하다.

• 전력전자학회논문지
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• 제18권4호
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• pp.376-386
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• 2013

This paper proposes an improved Maximum Power Point Tracking method and design methods of unmanned solar vehicle system by parts of hardware, unmanned driving control and power conversion. The hardware design is offered on the weight reduction and structural reliability by using structural analysis software. The technique of curve fitting is applied to unmanned control system due to minimizing the vehicle's behavior. Furthermore, lateral controller applying actuator dynamics is robust enough to prevent performance degradation by measurement noise regarding position and heading angle. The power conversion system contains battery charger system and tapped-inductor boost converter. In the battery charger system, variable step-size MPPT is conducted for quick response of maximum power point tracking. The validity of the proposed algorithm are verified by simulations and experiments.

• 한국대기환경학회지
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• 제23권3호
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• pp.277-285
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• 2007

Porous cordierite beads, of which the average pore size was $130{\mu}m$ and porosity was about 80%, were prepared by the foaming method and then their application as support of the $Pt/{\gamma}-alumina$ catalyst for $NO_x$, reduction with propene was investigated. The pressure drop of a 2 mm porous beads filter was less than that of a 1 mm porous beads filter and the difference in pressure drop between these two increased as the flow rate increased. The catalytic activity of $Pt/{\gamma}-alumina$ washcoated on the porous bead was tested with varying Pt loading $(0.005{\sim}0.1g/cm^3),\;C_3H_6/NO$ mole ratio $(0.5{\sim}8)$, space velocity $(20,000{\sim}30,000h^{-1})$ and oxygen contents (1 and 8). Pt loading of $0.04g/cm^3$ showed the highest activity for $NO_x$ conversion. The $De-NO_x$, test was operated in the temperature range of $200{\sim}400^{\circ}C$ and the best operation temperature of the catalytic filter is about $250^{\circ}C$. As the C/N ratio increased, increase of the $NO_x$, conversion might result from the increase in exhaustion of the amount of oxygen by the reduction of hydrocarbon. $NO_x$ conversion at $20,000h^{-1}$ of space velocity shows a maximum 34% higher conversion than that at $30,000h^{-1}$. On condition that $O_2$ was 5%, space velocity was $20,000h^{-1}$ and the C/N ratio was 8, the $NO_x$ conversion exhibited a maximum of 40% at $250^{\circ}C$.

• Journal of Korean Society for Atmospheric Environment
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• 제18권E1호
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• pp.29-36
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• 2002

The selective catalytic reduction (SCR) reaction of promoter catalysts was investigated in this study. A pure anatase type of TiO$_2$ was used as support. Activation measurement of prepared catalysts was practiced on a fixed reactor packing by the glass bead after filling up catalysts in 1/4 inch stainless tube. The reaction temperature was measured by K-type thermocouple and catalyst was heated by electric furnace. The standard compositions of the simulated flue gas mixture in this study were as follows: NO 1,780ppm, NH$_3$1,780ppm, $O_2$1% and $N_2$ as balance gas. In this study, gas analyzer was used to measure the outgassing gas. Catalyst bed was handled for 1hr at 45$0^{\circ}C$, and the reactivity of the various catalyst was determined in a wide temperature range. Conversion of NH$_3$/NO ratio and of $O_2$ concentration was practiced at 1,1.5 and 2, respectively. The respective space velocity were as follows . 10,000, 15,000 and 17,000 hr-1. It was found that the maximum conversion temperature range was in a 5$0^{\circ}C$. It was also found toi be very sensitive at space velocity, $O_2$ concentration, and NH$_3$/NO ratio. We also noticed that the maximum conversion temperature of (W, Mo, Sn) -V$_2$O$_{5}$/TiO$_2$ catalysts was broad. Specially WO$_3$-V$_2$O$_{5}$TiO$_2$2 catalyst appeared nearly 100% conversion at not only above 30$0^{\circ}C$ ut also below 25$0^{\circ}C$. At over 30$0^{\circ}C$, NH$_3$ oxidation decreased with decrease of surface excess oxygen. In addition, WO$_3$-V$_2$O$_{5}$TiO$_2$ catalyst did not appear to affect space velocity, $O_2$ concentration, and NH$_3$/NO ratio.ratio.

• 한국물환경학회지
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• 제23권6호
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• pp.961-965
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• 2007

In this study, degradation of carbohydrates and composition of fermentative products were investigated in semi-continuous acid fermenter varying hydraulic retention time (HRT). Rice soup was used as a sole substrate for the acid fermentation. Solubilization efficiency of the substrate was higher than 70% for all HRT, however the gas conversion was ignorable implying that most of organic contents in the influent remained in the form of volatile fatty acids (VFAs) and ethanol after acid fermentation. The VFAs were the predominant product and the VFAs conversion increased as the HRT decreased. The VFAs conversion reached the maximum value at 12 hr HRT accounting for 70% of the influent COD. Similar to VFAs, ethanol conversion was increased with the decrease of HRT and the maximum ethanol conversion efficiency was 8% at the HRT of 12 hr. Composition of VFAs was markedly dependent on HRT. As HRT increased, the composition of acetic acid was increased as a product of acetogenesis from butyrate, valerate and ethanol. This study demonstrated that HRT affected acid fermentation of a carbohydrate containing organic wastes producing VFAs and ethanol which could be effectively used to compensate the lack of carbon in wastewater for biological nutrient removal.

• 대한의용생체공학회:의공학회지
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• 제39권6호
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• pp.243-249
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• 2018

The indoor radon concentration was measured in the lecture room of the university and the radon concentration was converted to the amount related to the radon exposure using the dose conversion convention and compared with the reference levels for the radon concentration control. The effect of indoor radon inhalation was evaluated by estimating the life effective dose and the risk of exposure. To measure the radon concentration, measurements were made with a radon meter and a dedicated analysis Capture Ver. 5.5 program in a university lecture room from January to February 2018. The radon concentration measurement was carried out for 5 consecutive hours for 24 hours after keeping the airtight condition for 12 hours before the measurement. Radon exposure risk was calculated using the radon dose and dose conversion factor. Indoor radon concentration, radon exposure risk, and annual effective dose were found within the 95% confidence interval as the minimum and maximum boundary ranges. The radon concentration in the lecture room was $43.1-79.1Bq/m^3$, and the maximum boundary range within the 95% confidence interval was $77.7Bq/m^3$. The annual effective dose was estimated to be 0.20-0.36 mSv/y (mean 0.28 mSv/y). The life-time effective dose was estimated to be 0.66-1.18 mSv (mean $0.93{\pm}0.08mSv$). Life effective doses were estimated to be 0.88-0.99 mSv and radon exposure risk was estimated to be 12.4 out of 10.9 per 100,000. Radon concentration was measured, dose effective dose was evaluated using dose conversion convention, and degree of health hazard by indoor radon exposure was evaluated by predicting radon exposure risk using nominal hazard coefficient. It was concluded that indoor living environment could be applied to other specific exposure situations.