• Proceedings of the Korea Water Resources Association Conference
• /
• 2017.05a
• /
• pp.1-1
• /
• 2017

녹조현상은 부영양화된 호수나 유속이 느린 하천에서 부유성의 조류(식물 플랑크톤)가 대량 증식하여 수면에 집적하게 되고 물의 색을 현저하게 녹색으로 변화시킴으로써 발생된다. 최근에는 이러한 녹조 현상이 광역화, 독성화, 장기화의 특성을 띠며 빈번히 발생되고 있다. 녹조현상은 독소를 발생시키는 남조류에 의해 수생식물에 악영향을 주는 것으로 알려져 있다. 예를 들면 독소에 의한 가축에의 영향, 생태계 파괴로 인한 생태학적인 문제, 산소결핍으로 인한 물고기 및 각종 수중생물 폐사 등의 심각한 문제를 야기한다. 또한 조류는 식수에서 맛과 냄새를 유발할 뿐 아니라 Microcystin-LR과 같은 유해한 독소를 배출하여 공중 보건을 위협한다. 이에 식수원으로 사용되는 하천의 조류 번식에 따른 대응방안 마련이 절실히 요구된다. 유입되는 조류로 부터의 정수처리 설비의 처리 부하를 줄이기 위해서는 취수시스템과 연계한 고속 전처리 조류 제거 시스템을 개발이 필요하다. 기존의 전기응집부상공정(Electro-Coagulation and Flotation, ECF)은 화학 약품(응집제) 투여량이 적은 이점이 있지만 비교적 긴 전기 분해 시간이 필요하여 기존 정수처리 시스템과 연계성에 있어 한계가 있다. 이에 본 연구는 전기 분해 시간을 줄여 유입된 조류를 수 초 내에 응집하여 1분 이내에 조류를 분리하는 초고속 조류 전처리 기술을 개발하였다. 개발된 기술의 현장적용 및 실험 결과, 응집과정이 없이도 Chlo-a는 약 45 %의 제거 효율을 나타났다. 또한 응집제의 투입 및 전극에 의한 부상시스템에 의해 Chlo-a가 약 80 %로 제거되는 것으로 나타나 빈번하게 발생되는 조류로부터 안정적인 물 공급을 위한 전처리 공정으로 활용이 가능할 것으로 판단된다.

• Korean Journal of Soil Science and Fertilizer
• /
• v.22 no.1
• /
• pp.18-24
• /
• 1989

The effect of soil physico-chemical properties of pre and post soil preparation and permanent bed period on growth and yield was analysed by two models of annual variation and percent annual change (PAC). 1. Aggregation, porosity, bulk density except moisture were significantly different in each year from preparation to the 6th year while all soil chemical properties except Mg were significantly different in each year. 2. Soil physical properties showed significant simple correlation with yield and negative with the missing plant rate in each year while the electroconductivity ($EC_5$) of the 4th year showed significant correlation with yield. 3. Yield showed significant positive correlation with the variation of aggregation in permanent bed period, and negative with variation and PAC of aggregation of preplanting soil and variation of moisture in permanent bed period. Missing plant rate was negatively correlated with porosity variation of preplanting soil and positively with PAC of aggregation in preplanting soil and of moisture in permanent bed period. 4. According to multiple regression between yield and soil physical properties, porosity of preplanting soil was in the greatest contribution. Among aggregations, the variation in permanent bed period was in the greatest contribution.

• The Korean Journal of Pesticide Science
• /
• v.2 no.1
• /
• pp.32-39
• /
• 1998

This study was performed to develop jumbo granules floated and spreaded on the water surface after application, having low production and formulation cost, and safe to environment for paddy herbicides and to establish the formulation recipe. The jumbo granules of azimsulfuron with molinate(0.075+7.5%) was formulated by KCl as water soluble carrier and paraffin oil as solvent to impose the floating and spreading force to granules. That showed 100% of total granules to be floated on and spreaded upto the water surface within 25 minutes after application. Change in carriers, surfactants and pH did not affected to improve the time-course degradation of azimsulfuron in jumbo granules, but salt formation of azimsulfuron added by 1.15M solution of NaOH a little. Addition of N-methyl acrylate and modification of formulation process affected decrease in degradation of azimsulfuron upto 1.2, 2.1, and 7.2% after 2, 6 and 12 weeks under storage at $40{\pm}2^{\circ}C$, respectively, which showed the establishment of formulation recipe of the jumbo granules.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.27 no.1
• /
• pp.1-8
• /
• 2023

A study was conducted to scrutinize the behavior of the ultrasonically-atomized kerosene lifted-flame according to the carrier gas flow-rate and position of ultrasonic standing wave (USW). The combustion region of the kerosene-aerosol generated through a slit-jet nozzle was visualized using a DSLR, ICCD, high-speed camera, and Schlieren technique, and the fuel consumption was measured by using a precision balance. As a result, the flame was confined within the region bounded by the USW-field, and the fuel consumption decreased as the position of the USW field increased.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.9
• /
• pp.1098-1105
• /
• 1999

A lifted laminar flame structure has been numerically analyzed. The present study employs the physical submodels including the detailed chemical kinetics and the variable transport properties. The validation cases Include a lifted laminar CH4/air flame with a central diluted fuel jet and a surrounding fuel-lean coflow. Numerical results indicate the present approach successfully simulate the detailed structure and mechanism of the triple flame in the lifted laminar methane flame.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1998.10a
• /
• pp.337-342
• /
• 1998

임계온도가 액체질소의 비등점(77K)보다 높은 산화물 고온 초전도체가 발견된 이후 초전도체를 여러분야에 응용하고자 하는 연구가 있어왔다. 이러한 연구중 초전도체의 자기부상특성을 이용한 마그네틱 베어링에 관한 연구가 시작되었다. 특히 최근에 임계전류밀도가 높은 덩어리형 고온 초전도체가 개발되어, 큰 부하지지력을 갖고 마찰계수가 작은 초전도 마그네틱 베어링이 가능하게 되었다. 고온 초전도체를 사용한 반발식 수동형 마그네틱 베어링은 마이스너 효과(Meissner effect)뿐 아니라 자속고정효과(Flux pinning effect)에 의해 자체적으로 외란에 대한 위치안정성을 가지며, 히스테리시스 손실에 의한 에너지 소산을 통해 외란에 대해 강한 감쇠능력을 가진다는 장점을 가지고 있으며, 대중량을 지지할 수 있다. 이러한 초전도체의 특성에 관한 정량적 수치해석은 초전도 베어링의 설계에 필수적이나 아직 국내에서는 그러한 시도가 없었다. 이러한 여건을 고려하여 본 연구에서는 Bulk형 초전도체와 자석간의 부상력 변화를 축대칭 모델로 수치해석하여 기존의 실험들과 정량적인 비교를 하여 수치해석 코드의 신뢰성을 확보하고 이를 기반으로 다양한 상황을 예측할 수 있음을 보이고자 한다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1997.10a
• /
• pp.167-172
• /
• 1997

초전도체를 기계요소중 하나인 베어링에 응용하기 위한 연구는 임계온도가 액체질소의 비등점(77K)보다 높은 산화물 고온 초전도체가 발견된 이후 시작되었으며, 특히 최근에는 $10^4A/cm^2$이상의 임계전류밀도를 갖는 덩어리형 고온 초전도체가 용융공정을 통해 개발되어, 큰 부하지지력을 갖고 10$^{-8}$ 이하의 마찰계수를 갖는 초전도 마그네틱 베어링으로서 플라이휠 같은 에너지 저장장치에 적용시키는 연구가 국내외적으로 진행되고 있다. 고온 초전도체를 사용한 반발식 수동형 미그네틱 베어링은 Meissner effect뿐 아니라 Fluxpinning effect에 의해 자체적으로 외란에 대한 위치안정성을 가지며, 히스테리시스 손실에 의한 에너지 소산을 통해 외란에 대해 강한 감쇠능력을 가진다는 장점을 가지고 있으며, 대중량을 지지할 수 있다. 이러한 초전도체의 특성에 관한 정량적 수치해석은 초전도 베어링의 설계에 필수적이나 아직 국내에서는 그러한 시도가 없었다. 이러한 여건을 고려하여 본 연구에서는 초전도체와 자석간의 부상력 변화를 2차원 Slab모델로 수치해석하여 히스테리시스라는 주요한 특성을 고찰하고자 한다.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.4 no.1
• /
• pp.30-35
• /
• 2000

The experimental study on the lift-off height of diffusion flames was conducted to investigate the damage of swirl-coaxial injector used in $GO_2$/kerosene rocket engine during initial stage of ignition. To investigate the causes of damage and to prevent further damage of the injector, experimental injector was designed and hot fire tests were performed with varying propellant momentum ratio($\frac{Momentum of {GO_2}}{Momentum of Kerosene}$) from 1 to 12. In experimental coaxial injector, kerosene is sprayed from the central nozzle with swirl and $GO_2$ sprayed around the kerosene nozzle in the direction parallel to the axis of combustion chamber. Chamber pressure are close to the atmospheric condition. Lift-off height was measured by still images from camcoder and average values were used as data.

• Weed & Turfgrass Science
• /
• v.5 no.4
• /
• pp.225-229
• /
• 2016

This study was conducted to investigate the herbicidal efficacy of up granule formula of benzobicyclon mixtures, benzobicyclon + azimsulfuron + oxaziclomefone up granule (BAO UG) and benzobicyclon + bensulfuron-methyl + fentrazamide up granule (BBF UG) to control annual and perennial weed species in a rice paddy field. Four annual weed species including Echinochloa crus-galli L. and three perennial weeds were dominated in the experimental field. Application of BAO UG and BBF UG was highly effective to control both annual and perennial weed species. No phytotoxic effect was observed in the rice based on the plant height, the number of tillers, and culm and panicle length. Finally, rice yield in the BAO UG and BBF UG treatment was as much as that in the hand weeding. This study indicates that self-dispersible floating formula of benzobicyclon mixtures can be applied to control both annual and perennial weed species in rice paddy fields and contribute to save labor costs.

• Journal of Ginseng Research
• /
• v.12 no.1
• /
• pp.1-10
• /
• 1988

Panax ginseng seedlings were grown at various temperature regimes from 15 to $30^{\circ}C$ for 19 days under dark and the linear relationship between various regrowth efficiencies and thermal stress indices, cumulative superoptimum temperatures corrected with factors. Gross growth efficiency(shoot weight l root weight loss) was 37.5 % at the optimum temperature $15^{\circ}C$/$15^{\circ}C$, and 12.3% at the highest temperature, $30^{\circ}C$/$30^{\circ}C$ while net growth efficiency (shoot weight + Sm)l(root loss-Rm), which corrected by maintenance respiration for shoot(Sm) and root(Rm) was 39.6% and 16.7 at optimum and highest temperature respectively. All growth efficiencies showed negative correlations (p = 0.001) with all thermal stress indices and negative(p = 0.001) with shoot growth(St). When growth temperature difference in a day was nil or above $15^{\circ}C$ growth efficiency decreased greatly. Thermal stress indices showed negative correlation with root dry matter loss(RDL) but positive with Rm. St showed positive correlation with RDL. Thermal stress appeared to inhibit substrate supply for shoot growth resulting in the extremely low growth efficiency comparing with other crops that seems to be main rate limiting factor of slow growth, Thus it is necessary that growth efficiency and thermal stress must be elucidated in terms of metabolic pathway.