We aim to investigate variations in the resorption efficiencies of 10 mineral nutrients [i.e. nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), zinc (Zn), aluminum (Al), iron (Fe) and copper (Cu)] in leaves of desert shrubs and to explore effects of aridity on resorption efficiency of these nutrients. Plant samples were collected from 10 sites in northern Xinjiang Uygur Autonomous Region of China. Samples of green and senesced leaves were analysed to determine concentrations of N, P, K, Mg, Ca, Mn, Zn, Al, Fe and Cu and thus the nutrient resorption efficiency. The mean nutrient concentrations in the desert shrubs varied, with the stoichiometric ratio Ca:N (19.3 mg g⁻¹):K (10.5 mg g⁻¹):Mg:P (1.01 mg g⁻¹):Al:Fe:Mn:Zn:Cu (4.78 mg kg⁻¹) = 4038:2950:2199:1816:211:37:32:11:2:1 in green leaves; and Ca:N (12.6 mg g⁻¹):Mg:K (7.6 mg g⁻¹):P (0.56 mg g⁻¹):Fe:Al:Mn:Zn:Cu (2.85 mg kg⁻¹) = 5583:3710:2943:2523:178:133:119:19:3.7:1 in senesced leaves. Resorption generally occurred for six elements (N, P, K, Cu, Mg and Mn, with average resorption efficiency 47.8%, 52.0%, 38.6%, 41.0%, 12.7% and 7.89%, respectively) during leaf senescence, while the other four nutrients tended to accumulate in senesced leaves, showing averagely negative resorption efficiencies [Ca (–3.87%), Al (−57.1%), Zn (−62.6%), Fe (−89.6%)]. Aridity showed strikingly different effects on the resorption process of the 10 nutrients. Of the four elements with totally (N/P/K) or mostly (Cu) positive observations of resorption efficiency, their resorption generally decreased with aridity, suggesting that drought stress had negative effects on the resorption efficiencies of these elements. In contrast, with at least one-third observations of resorption efficiency being negative, the other elements (Mg/Mn/Ca/Zn/Al/Fe) showed generally increasing resorptive tendency with aridity, except for Zn. This research provided a systematic analysis on the large variation and contrasting responses of the resorption of multi-elements to aridity in typical desert shrubs. Our findings foster the understanding of nutrient resorption patterns of desert plants and enable us to better predict the contrastive effects of drought stress on the cycling of diverse nutrients and the consequent stoichiometric decoupling in plants of desert ecosystems.

To improve the stability of the bridge structure, we detect bolts in the bridge which cause the symmetry failure of the bridge center. For data acquisition, bolts are small-scale objects under complex background in images, and their feature expression ability is limited. Due to those questions, we propose a new bolt positioning detection based on improved YOLOv5 for bridge structural health monitoring. This paper makes three major contributions. Firstly, according to the calibration anchor boxes of bolts, the size and proportion parameters of the initial anchor boxes are optimized by K-means++ clustering algorithm to solve the initial clustering problem of anchor boxes in object detection. Second, the hypercolumn (HC) technique fuses the low-level global features of the trunk and the high-level local features of three different scales to solve the problem of the inefficient distribution of anchors and insufficient extraction of classification features. In this way, we improve the detection accuracy and speed of bolt detection. Finally, we establish a dataset of bridge bolts through network collection and public datasets, including 1494 images. We compare and verify the new method in the collected bolt dataset. The experimental results show that the precision (P) of the improved YOLOv5x is up to 87.3%, and the average precision (AP) is up to 86.3%, which are 6.5% and 5.9% higher than the original YOLOv5x, respectively.

The low-strain integrity testing of large-diameter piles has attracted more and more attention because of its wide application in offshore engineering, such as for wind turbines, etc. Body and Rayleigh waves generate on the top surface of large-diameter piles after the excitation load. The multi-reflections of these waves from the pile side result in the obvious three-dimensional effect at the pile top. Therefore, one-dimensional wave theory is no longer suitable for interpreting the wave propagation in the pile body under vertical excitation. In this paper, based on the “pile in pile” conception, both the pile and soil were simulated using a three-dimensional continuum model, considering the vertical displacement, to investigate the influence of the three-dimensional effect of the pile-soil system on the vertical dynamic response of large-diameter piles in low-strain integrity testing. The axisymmetric solution to the three-dimensional pile-soil system was obtained, and the rationality of the proposed solution was verified by comparing it with the results of the finite element method and the results of other existing solutions. Arithmetic examples were used to describe the influence of the three-dimensional effect of the pile-soil system on the vertical dynamic response of large-diameter piles.

Comprising a relatively large amount of industrial solid waste, the high-value utilization of phosphogypsum (PG) is closely related to the sustainable development of resource materials and the protection of the ecological environment. PG can improve some of the shortcomings of geopolymers, but there is a lack of systematic research on the specific influencing factors as well as the mechanism of the two in a hydration reaction. In this study, the effects of the Si/Al, Na/Al and Ca/Al ratios on the micropores as well as the hydration products of phosphogypsum-modified geopolymer material (PMGM) are systematically explored via macroscopic and microscopic tests from the molar ratios of the raw material’s target components. By changing the molar ratio, the generation of hydration products is affected, thereby altering the properties of the material. The effects of each molar ratio on paste workability, capillary water absorption, drying shrinkage and self shrinkage are systematically analyzed, while the types, productions, and micropores of hydration products are analyzed via XRD and SEM. This study provides a new idea for the large-scale recycling of PG and makes a systematic investigation of its hydration mechanism, which can provide a reference for the reaction principle of PG with geopolymers.

Due to its particularity and importance, long-distance oil and gas pipelines need to be well protected from damage by backfill materials. In this study, construction waste and expanded polystyrene (EPS) were used to replace conventional fine aggregate, and ethylene vinyl acetate-resin (EVA) was used to modify the surface of EPS to prepare lightweight controlled low strength materials (CLSM). Lightweight CLSM was tested in mechanics and physics and its microstructure was studied using microscopic analysis methods. The results revealed that the surface modification of EPS by EVA could greatly improve the compatibility of EPS with inorganic cementitious materials and prepare CLSM with a fluidity greater than 200 mm. EPS and cement content in cementitious materials play an important role in the development of material strength. When the volume ratio of EPS to construction waste was 2, and the content of cement in the cementitious materials was 35%, CLSM’s unconfined compressive strength at 28 days was only 0.48 MPa. In order to obtain the lightweight CLSM that meets the mechanical properties, the EPS content should not be too large. It can be concluded from the microscopic analysis that the increase of EPS content will lead to poor pore uniformity of the specimen, forming a loose mesh structure of defects, which is not conducive to the development of strength. In this study, EPS and construction waste are used to provide a green idea for preparing lightweight controlled low strength materials, which provides a reference for the backfill protection of the material in oil and gas pipelines in the future.