• Journal of Korean Society of Environmental Engineers
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• v.35 no.7
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• pp.457-463
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• 2013

The removal of sulfonamide antibiotics (SAs) by activated carbon was investigated by using granular activated carbon (GAC) tests and density functional theory (DFT) simulations. The GAC absorption tests show the removal efficiency of 68.4~90.7% and 99.0~99.9% in 1 and 24 hours, respectively. In both GAC tests, the removal efficiency of sulfamethazine (SMZ) was the highest followed by those of sulfathiazole (STZ) and sulfamethoxazole (SMTZ): SMZ > STZ > SMTZ. In DFT adsorption simulations, we found that the 4-aminobenzenesulfonamide parts of SMZ and STZ and the 3-methyl-1,2-oxazol-5-amine part of SMTZ are preferentially adsorbed on the edges of graphene model, provided that the adsorbates keep their structures without dissociation upon adsorption process. The adsorption energies of SMZ, STZ, and SMTZ are -4.91, -4.64, and -4.62 eV, respectively. This adsorption strength (SMZ > STZ > STMZ) agrees with the trend of the removal efficiency of SAs by GAC. In addition, dissociative adsorption configurations of SAs are discussed.

• Korean Chemical Engineering Research
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• v.55 no.5
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• pp.704-710
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• 2017

Although the desalination technique using gas hydrate formation is at a development stage compared to the commercially well-established reverse osmosis (RO), it still draws attention because of its simplicity and moderate operational conditions especially when using refrigerants for guest gases. In this study, DFT (density functional theory)-based molecular modeling was employed to explain the energetics of the gas hydrate formation using HFC (hydrofluorocarbon) and HCFC (hydrochlorofluorocarbon) refrigerants. For guest gases, R-134a, R-227ea, R-236fa, and R-141b were selected and three cavity structures ($5^{12}$, $5^{12}6^2$, and $5^{12}6^4$) composed of water molecules were constructed. The geometries of guest gas, cavity, and cavity encapsulating guest gas were optimized by molecular modeling respectively and their located energies were then used for the calculation of binding energy between the guest gas and cavity. Finally, the comparison of binding energies was used to propose which refrigerant is more favorable for the gas hydrate formation energetically. In conclusion, R-236fa was the best choice in terms of thermodynamic spontaneity, less toxicity, and low solubility in water.

• Journal of Wetlands Research
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• v.18 no.4
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• pp.404-412
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• 2016

This paper not only aims to establish a plan to acquire the water stage data in a constant and proper manner by using limited manpower and costs, but also establishes the fundamental technology for acquiring the water level observation data or the stage data. For this, this paper focuses on how to acquire the stage data, in a uniform manner, that can represent each basin by developing the technology for establishing the optimal observational network. For that, this paper identifies the current status of the stage gauge stations installed in the ChungJu dam including wetland basin mainly along the national rivers. Then, thus obtained factors are used to develop the representative unit hydrograph. After that, the data are converted into the probability density function. Then, the stations are calculated information transfer amount. As a last step, we establish the optimized stage gauge network by the location of the stage station and space impact that takes into account for the combinations of the number of the stations. In other words, we consider the combination of the stage gauge station with information transfer amount and spatial correlation analysis for estimation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.11-22
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• 1987

A plane buoyant jet discharged vertically upward into a crossflow is analyzed by numerical solution of the governing equations of continuity, momentum and constituent transport. The turbulent transport is modelled by the Prandtl's mixing length theory. In the numerical solution procedure, the governing equations are transformed by stream function and vorticity transport, non-dimensionalyzed by discharge velocity, slot width, and parameters representing flow characteristics, and solved by Gauss-Seidel iteration method with successive underrelaxation. The numerical experiments were performed for the region of established flow of buoyant jet in the range of discharge densimetric Froude number of 4 to 32 and in the range of velocity ratio of 8 to 15, which is the ratio of discharge velocity to crossflow velocity. Variations of velocities and temperatures, flow patterns and vorticity patterns of receiving water due to buoyant jet were investigated. Also investigated are the effects of velocity ratio and discharge densimetric Froude number on the trajectories of buoyant jet. Computed are velocities, temperatures and local densimetric Froude numbers along the trajectory of the buoyant jet. Spreading rate and dispersion ratio were analyzed in terms of discharge densimetric Froude number, local densimetric Froude number and distance from the source along the jet trajectory. It was noted that the similarity law holds in both the profiles of velocity and temperatures across the jet trajectory and the integral type analysis of Gaussian distribution is applicable.

• Journal of the Korean Vacuum Society
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• v.15 no.1
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• pp.50-56
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• 2006

We investigated the adsorption of benzene and pyridine on $Si(5\;5\;12)-2\times1$ at 80 K by using variable-low temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The benzene molecule most strongly binds to two adatoms on the D3 and D2 units in a tilted butterfly configuration, which consists of $di-\sigma$ bonds between C atoms and Si adatoms and two C=C double bonds in the benzene molecule Pyridine molecules interact with adatom(s) on the D2 and D3 units through both Si-N dative bonding and $di-\sigma$ bonds. The dative bonding through the lone pair electrons of N atom produces a vertical configuration (pyridine-like), which is more stable than $di-\sigma$ bonds $Di-\sigma$ bonds can be formed either through Si-N1 and Si-C4 or Si-C2 and Si-C5.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.211-211
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• 2011

지형은 강우에 의한 유역 유출응답을 결정하는 중요한 인자이다. 따라서 유역의 지형형태학적 인자를 수문해석에 이용하기 위한 시도는 긴 역사를 갖는다(Rodriguez-Itube and Valdes, 1979). 지형을 구성하는 대표적인 요소로 하천망과 사면을 들 수 있다. 당연히 이들이 어떤 방식으로 결합되는지에 따라 유출특성의 차이가 발생하게 된다(Zevenbergen and Thorne, 1987; Brierley and Fryirs, 2005). 이에 본 연구에서는 하천유역에서 사면과 하천망의 방향적 특성을 정량화하고, 그 둘 사이의 관계를 살펴보고자 한다. 만일 사면의 방향성과 하천의 방향성이 일정한 관계를 가지고 정량화될 수 있다면, 이러한 특성은 보다 간단히 강우-유출 모형에 고려될 수 있을 것이다. 일례로 확률밀도함수 형태로 제시되는 사면과 하천 방향성을 GIUH 이론에 근거하여 재해석할 수 있다. 궁극적으로는 호우 방향성에 의한 유출응답의 차이를 파악할 수 있게 된다. 본 연구에서는 내성천 유역을 대상으로 하였으며, 대상유역의 수치지형도를 수집하여 DEM을 구축하였다. 하천망 추출을 위해 ArcGIS의 Hydro Tool을 이용하였다. 이들 하천망의 방향성은 von Mises 분포에 적용하여 정량화하였으며, 이를 통해 하천유역에서 하천망의 방향적 특성을 살펴보았다. 추가로 하천망과 사면의 방향적 구조를 확인함으로써 이들 특성이 강우-유출 모형에 유연하게 고려될 수 있도록 하였다. 본 연구의 결과를 요약하면 다음과 같다. (1) 본 연구에서 고려한 von Mises 분포는 하천망의 방향적 특성을 적절히 표현할 수 있음을 확인하였다. 방위 기준으로 정리한 하천망의 방향성은 하나의 mode 특성이 뚜렷하고, 하천 합류점 하천을 기준으로 정리할 경우에는 두 개의 mode 특성이 뚜렷해짐을 알 수 있었다. (2) 하천망의 방향성은 사면의 방향성과 뚜렷한 관계를 갖는 것을 알 수 있었다. 하천망과 사면의 방향적 결합 구조는 유역의 특성을 보다 현실적으로 묘사할 수 있고, 이들 관계를 가정하고 하천망의 방향성이 정량화된다면, 강우-유출 모형에 이들 특성이 쉽게 반영될 수 있을 것으로 기대된다. (3) 하천망의 방향성은 고차 하천일수록 뚜렷한 mode 특성을 나타냄을 확인하였다. 이러한 결과는 고차 하천일수록 그 방향성이 한반도의 주구조선과 잘 일치하는 것으로 기존 연구성과와도 일치하는 것이다. (4) 하천망의 주방향은 하천연장에 대한 영향을 크게 받음을 알 수 있었다. 이는 대상 하천유역의 유역응답에서 하천유출이 사면유출보다 상대적으로 큰 영향력을 갖기 때문이다. 강우-유출 모형에 하천망 방향성을 고려하기 위해서도 하천연장을 고려하여 이들 방향성을 정량화하는 것이 호우 방향에 보다 뚜렷한 유출반응 특성을 나타낼 것으로 보인다. (5) 본 연구에서 고려한 하천망의 방향성 정량화 방안을 이용할 경우 이들 결과는 유출모형에 고려될 수 있을 뿐만 아니라 유출응답 특성을 정량적으로 파악하는데 이용될 수 있다. 방위 기준으로 정리한 하천망 방향성은 실제 유역에 대한 유출모형에 적용이 가능하며, 하천 합류점을 기준으로 정리한 결과는 호우의 방향성에 대한 유출응답의 반응을 정량적으로 살펴보는데 이용될 수 있다.

• Journal of the Korean Wood Science and Technology
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• v.46 no.5
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• pp.486-496
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• 2018

This study was conducted to confirm an effect of span length on bending properties of larch dimensional lumber in the four point bending test. The size of specimen in this study was 38 (width) ${\times}$ 89 (depth) ${\times}$ 3,600 (length) $mm^3$, and average air-dry density and moisture content of the specimens was $543.5kg/m^3$ and 10.5%, respectively. Visually graded No. 1 dimensional lumbers of 248 were divided by two groups to compare modulus of rupture (MOR) and modulus of elasticity (MOE). One group was tested in the four point bending test with span length of 1,650 mm, and other was tested with span length of 3,000 mm. While MOE was not different according to span length in 5% significance level, MOR was different in accordance with span lengths and was in inverse proportion to change of span length. Fifth percentiles of MOR in span length of 1,650 and 3,000 mm were 28.65 and 25.70 MPa, respectively. It was confirmed that the difference between MORs in each case increased as normalized rank increased. This is because of size effect in Weibull weakest link failure theory. Therefore, KS F 2150, in which there is only regulation about span to depth ratio of 15 or more, is needed to be revised to contain a method considering size effect for MOR. From the method, various results of bending test with different size of lumber could be used to determine design value of lumber.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.573-580
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• 2009

This paper presents the mix composition, production method, and curing condition applied to the extruded ECC(Engineered Cementitious Composite) panel which are able to exhibit multiple cracking and potential pseudo strain-hardening behavior. In addition to the production technique of extruded ECC panel, the effect of fiber distribution characteristics, which are uniquely created by applying extrusion process, on the flexural behavior of the panel is also focussed. In order to demonstrate fiber distribution, a series of experiments and analyses, including image processing/analysis and micro-mechanical analysis, was performed. The optimum mix composition of extruded ECC panel was determined in terms of water matrix ratio, the amount of cement, ECC powder, and silica powder. It was found that flexural behavior of extruded ECC panel was highly affected by the slight difference in mix composition of ECC panel. This is mainly because the difference in mix composition results in the change of micro-mechanical properties as well as fiber distribution characteristics, represented by fiber dispersion and orientation. In terms of the average fiber orientation, the fiber distribution was found to be similar to the assumption of two dimensional random distribution, irrespective of mix composition. In contrast, the probability density function for fiber orientation was measured to be quite different depending on the mix composition.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.2
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• pp.125-131
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• 2009

Reductive dechlorination of polychlorinated dibenzo-p-dioxins (PCDDs) and its toxicity change were predicted by the linear free energy relationship (LFER) model to assess the zero-valent iron (ZVI) and anaerobic dechlorinating bacteria (ADB) as electron donors in PCDDs dechlorination. Reductive dechlorination of PCDDs involves 256 reactions linking 76 congeners with highly variable toxicities, so is challenging to assess the overall effect of this process on the environmental impact of PCDD contamination. The Gibbs free energies of PCDDs in aqueous solution were updated to density functional theory (DFT) calculation level from thermodynamic results of literatures. All of dechlorination kinetics of PCDDs was evaluated from the linear correlation between the experimental dechlorination kinetics of PCDDs and the calculated thermodynamics of PCDDs. As a result, it was predicted that over 100 years would be taken for the complete dechlorination of octachlorinated dibenzo-p-dioxin (OCDD) to non-chlorinated compound (dibenzo-p-dioxin, DD), and the toxic equivalent quantity (TEQ) of PCDDs could increase to 10 times larger from initial TEQ with the dechlorination process. The results imply that the single reductive dechlorination using ZVI or ADB is not suitable for the treatment strategy of PCDDs contaminated soil, sediment and fly ash. This LFER approach is applicable for the prediction of dechlorination process for organohalogen compounds and for the assessment of electron donating system for treatment strategies.

• Journal of Korea Water Resources Association
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• v.36 no.2
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• pp.161-172
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• 2003

This study has evaluated the stream gauge network with the main emphasis on if the current stream gauge network can catch the runoff characteristics of the basin. As the evaluation of the stream gauge network in this study does not consider a special purpose of a stream gauge, nor the effect from a hydraulic structure, it becomes an optimization of current stream gauge network under the condition that each stream gauge measures the natural runoff volume. This study has been applied to the Nam-Han River Basin for the optimization of total 31 stream gauge stations using the entropy concept. Summarizing the results are as follows. (1) The unit hydrograph representing the basin response from rainfall can be transferred into a probability density function for the application of the entropy concept to optimize the stream gauge network. (2) Accurate derivation of unit hydrographs representing stream gauge sites was found the most important part for the evaluation of stream gauge network, which was assured in this research by comparing the measured and derived unit hydrographs. (3) The Nam-Han River Basin was found to need at least 28 stream gauge stations, which was derived by considering both the shape of the unit hydrograph and the runoff volume. If considering only the shape of the unit hydrograph, the number of stream gauges required decreases to 23.