Gongcheng Kexue Yu Jishu/Advanced Engineering Science

Saccharin (SAC) is an emerging contaminant, widely detected in the environment, with potential ecotoxicity risks to aqueous organisms and human beings. Wastewater treatment plants (WWTPs) are key sources and sinks of SAC, and play a vital role in eliminating SAC entering the environment. An overview is provided of the potential ecotoxicity of SAC, its occurrence in the aqueous environment, and its degradation performance in WWTPs. SAC treatments, including physical, chemical (mainly advanced oxidation processes AOPs), biological, and hybrid processes, and possible degradation mechanisms are also considered. Of the various SAC removal processes, we find that adsorption-based physical methods exhibit relatively poor performance in terms of SAC removal, whereas chemical methods, especially hydroxy radical-mediated oxidation processes, possess excellent capacities for SAC elimination. Although biological degradation can be efficient at removing SAC, its efficiency depends on oxygen supply and the presence of other co-existing pollutants. Hybrid aerobic biodegradation processes combined with other treatments including AOPs could achieve complete SAC reduction. Furthermore, novel adsorbents, sustainable chemical methods, and bioaugmentation technologies, informed by in-depth studies of degradation mechanisms and the metabolic toxicity of intermediates, are expected further to enhance SAC removal efficiency and enable comprehensive control of SAC potential risks

The dynamic characteristics of water and sediment in a meandering channel are more complex than that in a straight channel. The bed evolution and the characteristics of overbank floods in bend are affected by the changes of flood and sediment discharge. The laboratory experiment was carried out in a curved flume under several flow discharges and sediment supplies in this paper. The water surface elevation, bed topography, water level of bend and longitudinal velocities along the main channel and the floodplain were measured in detail, and the effects of flow discharges and sediment supplies on bed evolution and overbank floods in the meandering channel were discussed. The calculation results of Lan Yunchang formula, Zhang Hongwu formula and Mao Peiyu formula for the water surface superelevation of the curved channel were compared, Lanyunchang formula could better predict the water surface elevation of the curved reaches with stable bedform under different flow and sediment discharges. The sediment supply had little effect on bed evolution in bend with inbank flows, for that most of the sediment supply was deposited in the upstream straight reach or transported to the downstream reach and only a small amount of recharge sediment was deposited in the bend reach. More upstream sediment was transported to the curved reach and deposited by overbank flows. With the increase of sediment supply, the sediment deposition in the curved main channel increased, which however had little effect on the water level and flow velocity in bend. When the flood discharge increased, the water level in the bend and the flow velocity in the concave bank increased significantly. The results indicated that the flood discharge was the key factor affecting the water level in the bend and the flow velocity in floodplain, and the upstream sediment supply was the secondary influencing factor. The flow velocity in floodplain in the 30-60° of 90° bend reach was higher than that in the main channel and upstream reach. The maximum flow velocity in the floodplain occurred in section 50°, which could reach 1.3 times of the upstream flow velocity. The above results are of great significance for flood control and disaster reduction of meandering rivers

Vegetation restoration is one of the important reasons for the decrease of sediment yield in the Loess Plateau. To explore the effect of vegetation coverage on sediment transport, the relationship between vegetation coverage and sediment transport rate was analyzed by combining the theoretical analysis and the field plot experiment. Based on the Einstein's theory of sediment movement, the movement process of sediment particles on slope surface was analyzed theoretically from the perspective of sediment movement, and the relationship between slope relative sediment transport rate and vegetation coverage was established. Scour experiments were carried out to verify the formula. Six flow levels (flow range 0.14～1.40 L·s –1, including 0.14, 0.28, 0.56, 0.83, 1.11 and 1.40 L·s –1) and eight vegetation coverage levels (0, 20%, 30%, 40%, 50%, 60%, 80%, 100%) were set for 48 groups of experiments. The results showed that the calculated value was larger than the measured value; under the condition of large flow, the calculated value was in good agreement with the measured value; there was a certain deviation between the calculated value and the measured value under the condition of small flow. Based on the analyses of theory and test, The influence of vegetation on sediment transport capacity was related to vegetation coverage, plant diameter and sediment particle size. Under the same slope topography and vegetation coverage, the vegetation with smaller plant diameter was more beneficial to sediment reduction than the vegetation with larger plant diameter. In the area with coarser sediment particle size,the effect of slope vegetation on sediment reduction was more obvious, and the same planting only needed to reach a small coverage, then it could start to play an effective effect on sediment reduction. When the vegetation coverage was low, the coverage threshold for the effective The effect of sediment reduction was determined by the particle size of sediment and the plant diameter of vegetation.

A segmentation network of Tiny cracks (TCS-Net) is proposed to solve the problems of small cracks with few pixels, low contrast between cracks and background, much interferences from similar textures, and uneven illumination. TCS-Net has a coding-decoding structure similar to that of U-Net network. The soft Pooling was used in down-sampling process to preserve the basic features of original images while maintaining the amplification of high-response features, thus reducing information loss and preserving the details and location of crack edges. In the up-sampling process, a semantic compensation module combining channel attention and spatial attention was added at the decoding end to fuse the features of each layer at the coding end, which could enhance the multi-scale details of cracks.In view of the classification problem of unbalanced data in crack segmentation task, in order to avoid the training process being dominated by most classes (background pixels), the binary cross entropy loss and Dice coefficient were combined by TCS-Net model as the objective loss function to solve the problem of training instability caused by attention tendency of single loss. It can also optimize performance indicators such as accuracy, crossover ratio and recall rate. Compared with the existing mainstream semantic segmentation models, TCS-Net fracture segmentation model improves the intersection over union ratio index by 5%~9% and recall ratio index by 9%~13%,which demonstrates that the model achieves higher detection rate and detection accuracy. The proposed TCS-Net can be effectively applied to the fine crack segmentation task under the conditions of serious imbalance between target and background, complex background with many disturbances

Deep geotechnical engineering often faces complex variable temperature environments. The thermal cycle effect of rock mechanical properties is important for the stability evaluation of reservoir and surrounding rock and the rational utilization of rock materials. For fine grained dense granite geothermal reservoir, its mechanical properties are related to energy-efficient exploitation and engineering safety. Therefore, thermal cycling experiment, uniaxial compression experiment, and optical microscope observation experiment were carried out to study the failure characteristics, the changes in mechanical parameters, and the influence mechanism of fine grained dense structure on the mechanical properties of granite. The results showed that the changing trend of rock failure characteristics and mechanical properties with the temperature and times of thermal cycle was closely related to the structure. For the fine grained dense granite, the uniaxial compressive strength and elastic modulus gradually decreased with the increase of upper limit temperature and times of thermal cycle, and the reduction rate of compressive strength became slow after more than 10 thermal cycles. The increase of the upper limit temperature of the thermal cycle can improve the sensitivity of the mechanical properties of granite to the deterioration of the thermal cycle. Internal thermal cycling at 300 ℃ would not change the brittle failure characteristics of fine grained dense granite. The microscopic observation and analysis show that the thermal cycle could significantly promote the crack propagation of granite. After 20 thermal cycles at 20～300 ℃, the linear crack density was 1.69 mm–1, which was 1.5 times that of one thermal cycle. Due to the fine and dense structure, the expansion and compaction effect of granite mineral particles was constrained, resulting in the predominance of crack initiation and propagation evolution induced by thermal stress, and then the macro mechanical parameters decreased nonlinearly with the corresponding linear crack density. This study had a certain reference value for the exploration of deep geotechnical engineering mechanics problems in variable temperature environments