• 환경생물
• /
• 제25권2호
• /
• pp.81-87
• /
• 2007

수화현상의 대표적 원인 생물인 남조류의 M. aeruginosa와 대조구로서 녹조류인 C. zofingiensis를 인공 배양하여 분말세라믹 투여에 따른 선택적 조류 제거 가능성에 대해 실험하였다. 0.05 mm의 분말세라믹을 투여에 따른 M. aeruginosa 및 C. zofingiensis의 침전효율은 각각 82와 63%였으며, 입자크기 0.1과 1 mm의 경우에서 는 M. aeruginosa는 각각 69와 34%, C. zofingiensis는 각각 52와 44%의 침전효율을 나타냄으로써, 분말세라믹 처리에 따른 침전효율의 차이를 나타내는 것을 확인하였다. 또한 Microcystis sp.에 의한 수화현상이 빈번한 수역의 현장시료를 대상으로 분말세라믹 처리에 따른 조류 제거효과를 실험한 결과 입자크기 0.05 mm, 투여농도 $1\;g\;L^{-1}$의 조건에서 24시간 후 약 67%의 Microcystis sp. 제거효과를 나타내었다. 분말세라믹의 수화현장에 적용가능성 여부를 확인하기 위하여 소규모 enclosure에서 분말세라믹 처리 농도에 따른 Microcystis sp. 제거효과 실험한 결과 입자크기 0.05 mm,투여농도 $1\;g\;L^{-1}$의 조건에서 24시간 후 약 69%의 Microcystis sp.의 제거효과를 나타내었으며, 이러한 연구결과로 보아 Microcystis sp.에 의해 수화가 발생한 현장에 분말세라믹을 적용하여 독성 남조류를 효율적으로 제거할 수 있을 것으로 기대된다.

• Bulletin of the Korean Chemical Society
• /
• 제26권11호
• /
• pp.1723-1727
• /
• 2005

A generalized fractional diffusion equation (FDE) is presented, which describes the time-evolution of the spatial distribution of a particle performing continuous time random walk (CTRW) on a fractal lattice. For a case corresponding to the CTRW with waiting time distribution that behaves as $\psi(t) \sim (t) ^{-(\alpha+1)}$, the FDE is solved to give analytic expressions for the Green’s function and the mean squared displacement (MSD). In agreement with the previous work of Blumen et al. [Phys. Rev. Lett. 1984, 53, 1301], the time-dependence of MSD is found to be given as < $r^2(t)$ > ~ $t ^{2\alpha/dw}$, where $d_w$ is the walk dimension of the given fractal. A Monte-Carlo simulation is also performed to evaluate the range of applicability of the proposed FDE.

• 한국세라믹학회지
• /
• 제25권4호
• /
• pp.415-423
• /
• 1988

Mixtures of carbon and silica (about 0.46${\mu}{\textrm}{m}$) which was synthesized by the hydrolysis of ethyl silicate, the molar ratio of silica/carbon was fixed as 1/10(weight ratio : 1/2), were nitrided in the temperature range 135$0^{\circ}C$~150$0^{\circ}C$. The phse of the product Si3N4 was $\alpha$ phase and the morphology was hexagnoal prism and the nitridation reaction was completed in 5 hrs at 150$0^{\circ}C$ or 7hrs at 145$0^{\circ}C$. The reaction rate above 150$0^{\circ}C$ was diffusion-controlled, following Jander equation. Activation energy Q was derived from the Arrhenius plot and the value was about 101kcal/mol. Axis ratio of Lattice constants(c/a) was 0.726 and unit volume was $\AA$3, the larger the molar ratio of carbon/Alkoxide was, the smaller the particle size of $\alpha$Si3N4 was.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.1162-1165
• /
• 2004

Size and crystalline phase changes of $Fe_{2}O_{3}$ nanoparticles formed in a $H_{2}/O_{2}$ flame have been investigated. At flame temperatures below $1350^{\circ}C$, the mean particle size increased monotonously with the distance from the burner edge; but in high-temperature flames above $1650^{\circ}C$, it suddenly decreased from 20 nm to ${\sim}3$ nm with the distance from the burner edge. The results of X-ray diffraction and HRTEM showed that this sudden reduction of the size of nanoparticles was accompanied by a partial phase transformation from ${\gamma}$-$Fe_{2}O_{3}$ into ${\alpha}$-$Fe_{2}O_{3}$. We suggest the structural instability due to ${\gamma}-$ to ${\alpha}-phase$ transformation as a mechanism for a rapid fragmentation of 20 nm particles into 3 nm ones.

• Nuclear Engineering and Technology
• /
• 제38권5호
• /
• pp.423-426
• /
• 2006

A developed neutron activation analysis(NAA) and gamma-spectrometry were applied to improve the analytical sensitivity and precision of impurities in electronic-circuit raw materials. It is well known that soft errors in high precision electronic circuits can be induced by alpha particles emitted from naturally occurring radioactive impurities such as U and Th. As electronic circuits have recently become smaller in dimension and higher in density, these alpha-particle emitting radioactive impurities must be strictly controlled. Therefore, new NAA methods have been established using a HTS(Hydraulic Transfer System) irradiation facility and a background reduction method. For eliminating or stabilizing fluctuated background caused by Rn-222 and its progeny nuclides in air, a nitrogen purging system is used. Using the developed NAA and gamma-spectrometry, ultra trace amounts of U(0.1ng/g) and Th(0.01ng/g) in an alumina ball and high purity silica used for an epoxy molding compound (EMC) could be determined.

• 한국세라믹학회지
• /
• 제24권2호
• /
• pp.147-154
• /
• 1987

Silicon nitride powders were prepared by the simultaneous reduction and nitridation from powder mixtures of Kim cheon quartzite and carbon (graphite or carbon black) at1400$^{\circ}C$ for 10 hours in nitrogen atmosphere. The effects of the reaction variables on the yield of products and on the ${\alpha}$/${\beta}$ ratio were examined. The average particle size, density, and the ${\alpha}$/${\beta}$ ratio of the obtained si3N4 were 1.0$\mu\textrm{m}$, 3.10g/㎤ and 90/10, respectively. It was found that the Si3N4 powders obtained in this work were comparable to the foreign commercial products.

• Nuclear Engineering and Technology
• /
• 제50권1호
• /
• pp.159-164
• /
• 2018

An evaluation of various radiometric methods to analyze $^{226}Ra$ in water has been employed on a set of 10 standard solutions of different concentrations in the range of $1-10Bq/L^{-1}$. The analysis was carried out using well-established procedures by means of gamma-ray, alpha-particle and liquid scintillation spectrometry. The feasibility of the various methods has been quantified in terms of relative standard error and percentage error. Correlations between the various methods have been presented and discussed. In general, good agreement was found in the results of various methodologies, which assures the accuracy of the methods and allows for the validation of instrumentation and procedures. Of the different methods adopted here, a combined procedure for the determination of $^{226}Ra$ along with $^{228}Ra$ using Quantulus 1220 ultra-low level background liquid scintillation counting gave the most accurate results.

• 동력기계공학회지
• /
• 제6권1호
• /
• pp.36-42
• /
• 2002

Two-dimensional natural convection in an inclined open cavity with bottom heated, two side insulated and the top open was investigated using PIV(Particle-Image-Velocimetry) measurement. Experimental results are presented for Prandtl number, Pr=6.62, cavity aspect ratio, A=1.0, Rayleigh number from $1.294{\times}10^6\;to\;3.8841{\times}10 ^6$, and inclination angles, ${\alpha}=0$, 30 and 60 deg to the horizontal. It was found that the fluid rises along both side walls in the boundary layer region at ${\alpha}=0\;deg$, and the inclination of the cavity induced flow entrainment. The experimental results are in good agreement with the numerical results.

• 방사성폐기물학회지
• /
• 제18권2_spc호
• /
• pp.227-235
• /
• 2020

우리는 실험과 MCNP 시뮬레이션을 통해 전알파 분석법의 한계를 설명하였다. 국내에서 중·저준위 방사성폐기물 인도 규정 관련, 전알파 분석법은 방사성폐기물을 처분하기 위해 반드시 규명해야 할 방사성 특성평가 인자이다. 전알파 분석법은 시료 준비 절차가 간단하고 신속한 분석 결과를 제공하지만, 정량분석 인자로 사용하는 것은 적절하지 않다. KCl과 ²⁴¹Am을 이용하여 시편 건조고형물 무게에 따른 전알파 계측효율을 평가하였다. 동일한 무게의 시편일지라도 계측효율의 차이가 20% 나는 것을 확인하였고, 이는 시편의 물리적 형태가 서로 다르기 때문인 것으로 보인다. 토양 중 우라늄을 화학분리 한 후, ICP-MS로 우라늄을 직접 측정한 결과와 전알파 농도를 비교하였다. 전알파는 실제 우라늄 농도에 비해 50% 과소평가되었다. 알파핵종별 전알파 계측효율이 최대 3배 차이 나기 때문에, 전알파 분석결과는 개별 알파핵종의 합과 비교하기 보다는 스크리닝 개념으로 사용하는 것이 적절하다.

• 한국주조공학회지
• /
• 제18권6호
• /
• pp.541-549
• /
• 1998

Microstructural characteristics of hypereutectic Al-Si alloys during reheating at semi-solid temperature have been investigated. The size and morphology of primary Si particles in wedge-type mold-cast ingot has been compared with hot-rolled sheet and Si particulate reinforced Al composite. Effects of P and Sr addition on the morphological changes of primary Si particles have been also investigated. Observation of the solidification microstructures of the wedge-type mold-cast ingot at different cooling rates showed that alloying elements such as P and Sr affect the morphology of Si particles, especially in the area solidified at a slow cooling rate. Negligible change in the size of primary crystals was observed after reheating experiment, but ${\alpha}-halo$ formed around the Si particles and fine particles of Si precipitated in the surrounding area of the Si particles. In addition, there seemed to be no coarsening with increasing of holding time and the region of ${\alpha}-halo$ being decreased. Nucleation and recrystallization was accelerated with addition of alloying elements during hot rolling resulting in a decrease of primary Si particle size. In the case of extruded specimens, morphological change of primary Si particles was not observed after reheating. No ${\alpha}-halo$ formation was observed in Si reinforced Al composite because of the oxide film formed on the Si particles which acted as a diffusion barrier between substrate and the primary Si particles.