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Heewon Jung,Christof Meile 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10
Hydrological flow and transport properties of porous media may evolve over time as a result of biogeochemical reaction processes. Bioclogging, which is a widespread process both in natural and engineered systems, is of a particular interest because it determines the functioning of biogeochemical processes by changing flow and transport characteristics of subsurface environments. Here, we investigate the effect of bioclogging on porosity and permeability across a range of flow and reaction conditions using pore-scale reactive transport model in idealized porous media. The simulation results reveal preferential biofilm growth near the source of a growth-limiting substrate and depend strongly on flow and reaction conditions. This spatially non-uniform biofilm growth results in the rapid reduction in permeability without large changes in porosity deviating from empirical porosity-permeability relationships such as the Kozeny-Carman equation. The simulations considering various pore geometries and biofilm permeabilities highlight the importance of microscopic characteristics for macro-scale reactive transport in porous media.
Heewon Jung,Christof Meile 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10
Microbially-mediated biogeochemical reactions are at the center of shaping subsurface environments such as soils and aquifers, and determine the fate of many anthropogenic contaminants. Quantitative description of such biogeochemical processes typically relies on conventional rate formulations (e.g., Monod-type kinetics) with lumped and often ad hoc rate parameters. Here, we take recent advances in genome-scale characterization of microbial metabolic reactions into account for quantitative simulation of microbial growth and metabolic fluxes in heterogeneous porous media. Our novel pore-scale reactive transport model couples a Lattice-Boltzmann implementation of both flow and mass conservation equations with reaction descriptions of varying complexity, ranging from empirical rate expression to flux balance models. Our work therefore establishes a solid foundation for cross-disciplinary efforts that integrate bioinformatic approaches underlying cell models with descriptions suitable to resolve the dynamic nature of natural environments. This allows for the representation of microbial interactions, which is a major challenge to our current quantitative understanding of microbially mediated elemental cycling.
정희원(Heewon Jung),최민재(Minjae Choi),이재헌(Jaeheon Lee) 한국데이터정보과학회 2020 한국데이터정보과학회지 Vol.31 No.1
일반적인 관리도는 모니터링하는 대상의 분포가 모두 동일하다는 동일분포의 가정을 한다. 하지만 임상적 수술결과를 모니터링하기 위해서는 환자들의 수술전 위험상태가 모두 다르기 때문에 동일 분포의 가정을 할 수가 없다. 이러한 이유에서 환자들의 위험상태가 다름을 고려하는 위험조정의 개념이 도입되었고, 위험조정 베르누이 누적합 관리도 절차가 제안되었다. 그러나 위험조정 베르누이 누적합 관리도에서는 주어진 관리상태에서의 특성을 만족하는 관리한계의 설정이 쉽지 않다. 이 논문에서는 평균런길이에 대한 교정확산 (corrected diffusion) 근사를 이용하여 환자들의 위험상태에 따라 관리한계를 설정하는 방법을 제안하였다. 그리고 모의시험을 수행하여 이전에 연구된 방법과 관리 상태에서의 성능을 비교하였다. 이때 관리도의 성능을 판단하기 위해 런길이의 평균, 표준편차, 그리고 백분위수를 사용하였다. When using general control charts, we assume that quality characteristic monitored is identically distributed during the in-control period. However, when we monitor the surgical performance such as the surgical outcomes, this assumption is not satisfied because of variability in pre-operative risks of different patient populations. It was proposed that the risk-adjusted Bernoulli CUSUM chart that involves adjusting for each patient’s pre-operative risk of surgical failure using a logistic regression mode l and then applying a Bernoulli CUSUM chart. However, it is difficult to determine the control limits satisfying the specified in-control performance. In this paper, we propose the method for determining adaptive control limits of risk-adjusted Bernoulli CUSUM charts based on the corrected diffusion (CD) approximation. And we evaluate the in-control performance of the proposed method by using the average run length, the standard deviation of run length, and percentiles.