• Nuclear Engineering and Technology
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• 제25권1호
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• pp.154-165
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• 1993

연속시간 마코프프로세스를 이용한 한 통계적 방법에 의한 일차원 지하 핵종이동 모델이 제시되었다. 지하매질은 보편적으로 지하수속도, 분산계수 또는 지연계수 등 물리화학적 변수 등의 비균질성을 보여 일반적인 결정론적 이류분산모델로는 잘 기술되지 않는다. 통계적 모델에서의 최종결과는 시간에 따른 함수로서의 기대값과 그 기대값의 분산도를 보여주는 분산치다. 매질이 균질하다고 생각될 정도로 나뉘어진 구획에 대한 핵종의 농도 분포를 구하여 결정론적인 해석해에 의한 농도분포와 비교하여 비균질 매질, 또는 현저하게 구분되는 다층매질의 경우에 대해서 유용 할 것이라는 결론을 얻었다. 매질을 나눈 구획수가 수치적 분산에 민감한 것으로 나타났지만 해석적 모델에 의해 분산계수가 보정될 수 있었다.

• Journal of Astronomy and Space Sciences
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• 제34권3호
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• pp.199-205
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• 2017

A high resolution spectroscopic observation of the red supergiant star RM_1-390 in the Large Magellanic Cloud was made from a 3.6 m telescope at the European Southern Observatory. Spectral resolving power was R=20,000, with a signal-to-noise ratio S/N > 100. We found the atmospheric parameters of RM_1-390 to be as follows: the effective temperature $T_{eff}=4,250{\pm}50K$, the surface gravity ${\log}\;g=0.16{\pm}0.1$, the microturbulent velocity $v_{micro}=2.5km/s$, the macroturbulence velocity $v_{macro}=9km/s$ and the iron abundance $[Fe/H]=-0.73{\pm}0.11$. The abundances of 18 chemical elements from silicon to thorium in the atmosphere of RM_1-390 were found using the spectrum synthesis method. The relative deficiencies of all elements are close to that of iron. The fit of abundance pattern by the solar system distribution of r- and s-element isotopes shows the importance of the s-process. The plot of relative abundances as a function of second ionization potentials of corresponding chemical elements allows us to find a possibility of convective energy transport in the photosphere of RM_1-390.

• 대한기계학회논문집B
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• 제28권6호
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• pp.688-696
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• 2004

Nonlinear dynamic behavior of diffusive-thermal instability in diluted CH$_4$/O$_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution, which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is net observed in this study, which is attributed to both convective flow and preferential diffusion effects.

• Korea-Australia Rheology Journal
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• 제18권2호
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• pp.51-65
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• 2006

Of concern in the present theoretical investigation is the study of blood flow and convection-dominated diffusion processes in a model bifurcated artery under stenotic conditions. The geometry of the bifurcated arterial segment having constrictions in both the parent and its daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is constructed mathematically with the introduction of suitable curvatures at the lateral junction and the flow divider. The streaming blood contained in the bifurcated artery is treated to be Newtonian. The flow dynamical analysis applies the two-dimensional unsteady incompressible nonlinear Wavier-Stokes equations for Newtonian fluid while the mass transport phenomenon is governed by the convection diffusion equation. The motion of the arterial wall and its effect on local fluid mechanics is, however, not ruled out from the present model. The main objective of this study is to demonstrate the effects of constricted flow characteristics and the wall motion on the wall shear stress, the concentration profile and on the mass transfer. The ultimate numerical solutions of the coupled flow and diffusion processes following a radial coordinate transformation are based on an appropriate finite difference technique which attain appreciable stability in both the flow phenomena and the convection-dominated diffusion processes.

• 한국농공학회지
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• 제39권2호
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• pp.62-73
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• 1997

The application of nutrients and pesticides to agricultural lands has been reported to contribute to groundwater contamination, which can be explained by preferential flow in lieu of convective-dispersive flow. An one-dimensional numerical model depicting preferential water and solute movement was modified to describe multi-layer flows. The model is based on a piecewise linear conductivity function. By combining conservation of mass and Darcy's law and using the method of characteristics a solution is obtained for water flow in which water moves at distinct velocities in different flow regions instead of an average velocity for the whole profile. The model allows transfer ofqr solutes between pore groups. The transfer is characterized by assuming mixing coefficients. The model was applied to undisturbed soil columns and an experiment site with structured sandy clay loam soil. Chloride, bromide, and 2, 4-D were used as tracers. Simulated solutes concentrations were in good agreement with the soil column data and field data in which preferential flow of solute is significant. The proposed model is capable of describing preferential solute transport under laboratory and field conditions.

• Asian Journal of Atmospheric Environment
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• 제5권3호
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• pp.172-180
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• 2011

The transfer of microorganisms is important process for ecosystems. Microorganisms in dryland can transport itself to wetland through atmospheric diffusion, but only few papers reported about the atmospheric bioaerosol present over dryland. We carried out the direct sampling using a tethered balloon over Dunhuang City, China's northwestern dryland. Bioaerosols were collected using a tethered balloon with a bioaerosol collector at 820 m above the ground (1,960 m above the sea level) around noon on August 17, 2007. The bioaerosols were cultured after the collection at Dunhuang Meteorological observatory. Two strains of molds were isolated using the Nutrient agar medium. About 400-bp 18S rRNA partial sequences were amplified by PCR and determined afterwards. The results of a homology search by 18S rRNA sequences of isolates in DNA databases (GenBank, DDBJ, and EMBL) and an observation of the form revealed that two bioaerosols in the convective mixed layer over Dunhuang City were Cladosporium sp. and Aspergillus sp.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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• pp.95-101
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• 2004

Dynamic behavior of diffusive-thermal instability in diluted $CH_4/O_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate. transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed Oil the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution. which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is not observed in this study, which is attributed to both convective flow and preferential diffusion effects.

• Nuclear Engineering and Technology
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• 제26권3호
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• pp.345-354
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• 1994

수치 해석을 통하여 이차유동을 포함한 핵연료봉 주위의 난류 유동장을 예측하였다. 등방성 난류와 점성계수 모델과 이차 유동을 모사하기 위해 단순화된 대수응력모델을 사용하여 난류 운동 에너지 (k)와 난류 에너지 소멸률($\varepsilon$)의 이 방정식 모델과 운동량 방정식을 유한 차분법으로 풀어 유동장내의 평균속도, 이차유동, 난류 운동 에너지, 난류 응력 분포 등을 구하였다. 수치해석 예측치를 실험데이타와 비교하여 만족할만한 결과를 얻었고 유동장내에서 이차유동의 영향을 확인하였다. 즉 이차유동이 절대 크기는 작더라도 대류 효과에 의해 큰 영향을 미치는 것을 본 연구를 통해 알 수 있었다.

• Nuclear Engineering and Technology
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• 제41권8호
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• pp.1045-1052
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• 2009

A calculation model is developed to predict the transient free surface flow on the containment floor following a loss-of-coolant accident (LOCA) of pressurized water reactors (PWR) for the use of debris transport evaluation. The model solves the two-dimensional Shallow Water Equation (SWE) using a finite volume method (FVM) with unstructured triangular meshes. The numerical scheme is based on a fully explicit predictor-corrector method to achieve a fast-running capability and numerical accuracy. The Harten-Lax-van Leer (HLL) scheme is used to reserve a shock-capturing capability in determining the convective flux term at the cell interface where the dry-to-wet changing proceeds. An experiment simulating a sudden break of a water reservoir with L-shape open channel is calculated for validation of the present model. It is shown that the present model agrees well with the experiment data, thus it can be justified for the free surface flow with accuracy. From the calculation of flow field over the simplified containment floor of APR1400, the important phenomena of free surface flow including propagations and interactions of waves generated by local water level distribution and reflection with a solid wall are found and the transient flow rates entering the Holdup Volume Tank (HVT) are obtained within a practical computational resource.

• 한국결정성장학회지
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• 제23권1호
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• pp.20-26
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• 2013

Special attention in the role of convection in vapor crystal growth has been paid since some single crystals under microgravity environments less than 1 $g_0$ exhibits a diffusive-convection mode and much uniformity in front of the crystal regions than a normal gravity acceleration of 1 $g_0$. The total molar fluxes show asymmetrical patterns in interfacial distribution, which indicates the occurrence of either one single or more than one convective cell. As the gravitational level decreases form 1 $g_0$ down to $1.0{\times}10^{-4}\;g_0$, the intensity of convection, indicative of the maximum molar fluxes, is reduced significantly for ${\Delta}T=30K$ and 90 K. The total molar fluxes decay first order exponentially with the partial pressure of component B, PB (Torr) for 20 Torr ${\leq}PB{\leq}$ 300 Torr, and two gravity accelerations of $g_y=1\;g_0$ and 0.1 $g_0$.