X-ray micro-computed tomography (micro-CT) has been widely used in the non-destructive investigation of 3D microstructures of cementitious materials. Microstructures from micro-CT are reconstructed ...from the attenuated transmitted X-ray intensity through a sample or linear attenuation coefficient (LAC). Although uncertainties can be introduced during processes, such as data collection and microstructure reconstruction, the LAC values are determined based on the X-ray energy level and material composition so that they can be considered as almost absolute measures. In this study, the microstructural evolution of cement paste during hydration was investigated using microstructures with a 4.5 μm voxel size obtained from X-ray micro-CT. A new phase segmentation method based on the mean LAC values for the pore and unhydrated phases inside the binder was developed. The pore phase features were characterized by porosity, equivalent pore diameter, and two-point probability functions. The findings indicate that the proposed segmentation method is well adapted for micro-CT imaging to identify the characteristics of pores, hydrates, and clinkers.
•A phase segmentation method for X-ray micro-CT images is proposed based on the notable change of linear attenuation coefficient (LAC) value.•The pore and unhydrated phases are segmented well in terms of both morphological aspect and density-related values.•Pore and solid characteristics of cement paste according to the hydration periods are investigated using quantitative methods.•The change of microstructural characteristic for hydrating cement paste are confirmed.
갱생 옥내급수관 수돗물에서 비스페놀-A 분포 및 위해성 평가 정관조(Gwanjo Jeong); 손보영(Boyoung Son); 이인자(Inja Lee) ...
Daehan hwan'gyeong gonghag hoeji,
2016, Volume:
38, Issue:
7
Journal Article
Peer reviewed
Open access
In this study, the survey of bisphenol-A in indoor water service pipes rehabilitated with epoxy resin was conducted and the risk assessment was done to investigate the effect on the human health to ...drink tap water. Bisphenol-A in raw water was detected in a range of 50~118 ng/L in all samples, where the limit of quantification was 10 ng/L. This is caused by inflow of the sewage effluent or the tributaries of the surrounding area containing bisphenol-A. Bisphenol-A was not detected in finished water after the advanced water treatment process. It was achieved by its removal from the processes of flocculation-precipitation and oxidation of ozone and chlorine and by being changed to other by-product materials. For the indoor water service pipe, bisphenol-A was not detected in all cases which was not coated with epoxy resin. However, when epoxy resin is lined within the indoor water service pipe, bisphenol-A was identified at maximum level of 521 ng/L and was detected above the limit of quantitation at 68 percentages of all samples. The Hazard Quotient (HQ) at the maximum level (521 ng/L) of the detected bisphenol-A is 0.004, which is less than the reference value of 0.1 for the tap water intake. Therefore, it is considered that the detected levels of bisphenol-A in this study would be safe to drink tap water. 본 연구에서는 에폭시 수지 갱생 옥내급수관 수돗물에 대해 비스페놀-A 실태조사를 실시하였고, 비스페놀-A가 수돗물 음용에 있어 인체에 미치는 영향을 파악하기 위해 위해성 평가를 실시하였다. 원수 중 비스페놀-A는 50~118 ng/L로 채취된 모든 시료에서 정량한계 10 ng/L 이상으로 검출되었다. 이것은 주변지역의 하수 방류수나 지천에 의한 비스페놀-A 유입에 의한 것으로 판단된다. 정수에서의 비스페놀-A는 불검출되었으며, 고도정수처리 공정에서 모두 제거된 것으로 추정되었다. 응집-침전과정과 오존 및 염소에 의해 산화되어 제거되거나 다른 산화 부산물질로 변화한 것으로 판단된다. 옥내급수관 수돗물의 경우, 에폭시 갱생공사를 실시하지 않은 수돗물 모두에서 비스페놀-A는 검출되지 않았다. 그러나 에폭시 갱생공사를 실시한 옥내급수관 수돗물에서 비스페놀-A가 불검출에서 최대 521 ng/L로 범위로 검출되었으며, 채취된 시료의 68%가 정량한계 이상으로 검출되었다. 검출된 비스페놀-A의 최대값(521 ng/L)에 대한 위해도 지수 산정 결과, 위해도 지수(HQ)는 약 0.004로 수돗물 섭취에 의한 위해판단 기준값 0.1 이하로 나타나 음용에 안전한 것을 확인하였다.
In this paper, practical utilization of multiple distributed reconfigurable intelligent surfaces (RISs), which are able to conduct group-specific operations, for multi-group multicasting systems is ...investigated. To tackle the inter-group interference issue in the multi-group multicasting systems, the block diagonalization (BD)-based beamforming is considered first. Without any inter-group interference after the BD operation, the multiple distributed RISs are operated to maximize the minimum rate for each group. Since the computational complexity of the BD-based beamforming can be too high, a multicasting tailored zero-forcing (MTZF) beamforming technique is proposed to efficiently suppress the inter-group interference, and the novel design for the multiple RISs that makes up for the inevitable loss of MTZF beamforming is also described. Effective closed-form solutions for the loss minimizing RIS operations are obtained with basic linear operations, making the proposed MTZF beamforming-based RIS design highly practical. Numerical results show that the BD-based approach has ability to achieve high sum-rate, but it is useful only when the base station deploys large antenna arrays. Even with the small number of antennas, the MTZF beamforming-based approach outperforms the other schemes in terms of the sum-rate while the technique requires low computational complexity. The results also prove that the proposed techniques can work with the minimum rate requirement for each group.
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