摘要 : Landfill gases can have numerous detrimental effects on the global climate and urban ecological environment. The protective efficacy of the final cover layer against landfill gases, following exposure to periodic natural meteorological changes during long-term service, remains unclear. This study conducted centrifuge tests and gas permeability tests on compacted loess. The experiments examined the impact and relationship of wetting-drying cycles and dry density on the soil water characteristic curve (SWCC) and gas permeability of compacted loess. Research findings reveal that during the dehumidification process of compacted loess, the gas permeability increases non-linearly, varying the gas permeability of soil with different densities to different extents under wetting-drying cycles. Two models were introduced to describe the impact of wetting-drying cycles on gas permeability of loess with various dry densities, where fitting parameters increased with the number of wetting-drying cycles. Sensitivity analysis of the parameters in the Parker-Van Genuchten-Mualem (P-VG-M) model suggests that parameter γ′s accuracy should be ensured in practical applications. Finally, from a microstructural perspective, wetting-drying cycles cause dispersed clay and other binding materials coalesce to fill minuscule pores, leading to an increase in the effective pores responsible for the gas permeability of the soil. These research results offer valuable guidance for designing water retention and gas permeability in compacted loess cover layers under wetting-drying cycles.

摘要 : Per- and polyfluoroalkyl substances (PFAS) have already drawn a lot of attention for their accumulation and reproductive toxicity in organisms. Perfluorooctanoic acid (PFOA) and perfluorooctanoic sulfonate (PFOS), two representative PFAS, are toxic to humans and animals. Due to their widespread use in environmental media with multiple toxicities, PFOA and PFOS have been banned in numerous countries, and many substitutes have been produced to meet market requirements. Unfortunately, most alternatives to PFOA and PFOS have proven to be cumulative and highly toxic. Of the reported multiple organ toxicities, reproductive toxicity deserves special attention. It has been confirmed through epidemiological studies that PFOS and PFOA are not only associated with reduced testosterone levels in humans, but also with an association with damage to the integrity of the blood testicular barrier. In addition, for women, PFOA and PFOS are correlated with abnormal sex hormone levels, and increase the risk of infertility and abnormal menstrual cycle. Nevertheless, there is controversial evidence on the epidemiological relationship that exists between PFOA and PFOS as well as sperm quality and reproductive hormones, while the evidence from animal studies is relatively consistent. Based on the published papers, the potential toxicity mechanisms for PFOA, PFOS and their substitutes were reviewed. For males, PFOA and PFOS may produce reproductive toxicity in the following five ways: (1) Apoptosis and autophagy in spermatogenic cells; (2) Apoptosis and differentiation disorders of Leydig cells; (3) Oxidative stress in sperm and disturbance of Ca 2+ channels in sperm membrane; (4) Degradation of delicate intercellular junctions between Sertoli cells; (5) Activation of brain nuclei and shift of hypothalamic metabolome. For females, PFOA and PFOS may produce reproductive toxicity in the following five ways: (1) Damage to oocytes through oxidative stress; (2) Inhibition of corpus luteum function; (3) Inhibition of steroid hormone synthesis; (4) Damage to follicles by affecting gap junction intercellular communication (GJIC); (5) Inhibition of placental function. Besides, PFAS substitutes show similar reproductive toxicity with PFOA and PFOS, and are even more toxic to the placenta. Finally, based on the existing knowledge, future developments and direction of efforts in this field are suggested.

摘要 : The Herglotz-type vakonomic dynamics of nonholonomic constrained systems with delayed arguments and its Noether theory are studied in this paper. First of all, the Herglotz-type equations of time-delayed vakonomic dynamics for nonholonomic systems are established, and the Herglotz-type local extremal equations are given. Secondly, on the basis of derivation of the variational formulas of Hamilton–Herglotz action with time delay, the Herglotz-type Noether symmetry criteria for time-delayed vakonomic dynamics are investigated. Thirdly, the Herglotz-type Noether's theorems and inverse theorems for time-delayed vakonomic dynamics of nonholonomic systems are deduced. Finally, an example is presented to demonstrate the application of the results.

摘要 : Recently, there has been a growing trend in utilizing waste rubber as a partial replacement for aggregates in concrete. This approach not only promotes the reuse of waste rubber but also addresses the shortage of natural aggregates. An issue arising from various compositions between rubber and the cement matrix is the accurate prediction and control of the mechanical properties of rubber concrete, which impedes the widespread application of rubber concrete because the indispensable on-site mechanical tests are time-consuming and labor-intensive. In response to this challenge, an integrated AI-based approach that enables the real-time prediction of the compressive strength of rubber concrete through mobile devices was proposed. Firstly, a U-Net-based semantic segmentation model is employed to identify different compositions within cross-section photos of rubber concrete. Subsequently, an artificial neural network (ANN) model is adopted to promptly and precisely predict the compressive strength of rubber concrete using the proportions of the semantic segmentation compositions. The proposed approach is validated through a database based on past experimental results. The U-Net-based component recognition model achieves an accuracy of 89.31 %, while the strength prediction model attains an accuracy of 82.08 %. Overall, this method effectively identifies various compositions and establishes a correlation between their proportions and the compressive strength of rubber concrete. This provides a partially explainable and efficient approach for the widespread on-site application of rubber concrete.

摘要 : Superhydrophilic-superoleophobic materials possess unique advantages in oil-water separation due to their water permeability and oil repellency. In this study, superhydrophilic-superoleophobic sand (CQS) was prepared using a facile and rapid mixing-drying coating method. Quartz sand was modified with polydopamine (PDA) as the hydrophilic binding agent, fluorosurfactant (FS-50) as the oleophobic agent, and CaCO 3 /SiO 2 to construct hierarchical surface roughness. The CQS exhibited a water contact angle of 0° and an oil contact angle of 154°, which resulted in a slightly increased water adhesion capacity and a significantly reduced oil adhesion capacity. Owing to its selective wettability towards oil and water, the CQS was capable of directly separating immiscible oil-water mixtures and oil-in-water emulsions with high separation efficiency (99.5 % and 98.5 %, respectively), driven by gravity. Moreover, immiscible oil/oil mixtures could be effectively separated by the CQS as well, expanding its application to separating immiscible organic liquids with different polarities. Additionally, the CQS demonstrated good reusability and superior stability against acid, alkali, salt, hot water and mechanical abrasion. These properties ensured its applicability in complex environments. The CQS, with exceptional separation capability and stability, holds promising prospects for future applications in related separation field.

摘要 : Thermal conductivity of soil is the key factor affecting utilization efficiency of ground source heat pumps (GSHPs). The microbially induced carbonate precipitation (MICP) technology has been proved to be an effective method to improve the thermal conductivity of soil. However, studies on using MICP treated soil as backfill to improve heat transfer performance of GSHP system is still rare. In this study, a small laboratory test device was developed to analyze the effects of different MICP treatment cycles on the heat transfer performance of GSHPs, taking into account four influencing factors: soil temperature, heat transfer and soil ultra-mild soil temperature recovery rate. The results show that MICP treated soil as backfill can improve heat transfer performance of GSHP to a certain extent, and the heat transfer amount in soil are 14.2 %, 34.9 % and 40.1 % corresponding to one to three MICP treatment cycles, which was higher than that of untreated soil. The longer the operation time, the more continuous heat dissipation or heat absorption of the system, the greater the heat transfer radius of the buried pipe temperature. For the influence of number of MICP treatment cycles, heat transfer effect of MICP-treated soil treated three times as backfill is the best. The temperature recovery rate of soil at the central test point of backfill area in summer is 73.15 %, followed by the temperature recovery rate of MICP-treated soil treated twice and treated once, which are 70.95 % and 69.6 % respectively. Considering heat transfer effect, treatment time and treatment cost, secondary MICP treated soil as backfill is the most cost-effective. Through scanning electron microscopy (SEM) image analyses, it is found that calcium carbonate acts as a "thermal bridge" between soil particles, increasing the contact surface between soil particles, resulting in improved heat transfer efficiency among soil particles, and thus improving the thermal conductivity of soil. The results provide good insight for the selection of GSHP layout, operation mode and environmental backfill in engineering practices.

摘要 : Simple SummaryThe research of this paper can be applied in the compaction parameter prediction of soil-filling materials, which can significantly reduce the amount of laboratory work and improve the efficiency of optimizing design for soil resource utilization in engineering construction. AbstractMaximum Dry Density (MDD) and Optimum Moisture Content (OMC) are two important parameters of soil filling, which affect the soil stability and bearing capacity, and thus the reliability and durability of facilities such as highways and bridges. Therefore, it is important to make reasonable predictions of OMC and MDD. Four machine learning algorithms, namely, Support Vector Machine (SVM), Artificial Neural Network (ANN), Random Forest (RF), and Extreme Gradient Boosting Tree (XGBoost), are adopted in this paper to establish MDD and OMC prediction models. After training and testing, the best models of the four algorithms are compared. The results show that, as an ensemble learning algorithm, XGBoost is the best model for predicting MDD and OMC, with an R2 of 0.9234 for OMC, and an R2 of 0.9098 for MDD. Finally, the feature importance analysis concludes that the plastic limit (PL) and the liquid limit (LL) are the two features that affect OMC and MDD the most. The prediction of soil compaction parameters using machine learning models, especially ensemble learning, can significantly reduce the amount of laboratory work and improve the efficiency of optimizing design for soil resource utilization in engineering construction.

摘要 : Bolts have been widely used in steel structures, and the resilience of the whole structural system under extreme loading conditions such as impact or blast, is closely related to the dynamic properties of the bolt materials. Bolted connections are possible to fail in modes different from the design expectations under high strain rate loading conditions due to the difference in strain rate sensitivity between bolts and the materials being connected. However, knowledge about their strain rate-dependent behaviour is still limited, and the effect of strain rates has been essentially disregarded in current standards and design codes. This paper presents tensile and compressive tests on grade 8.8 and grade 12.9 M12 high-strength steel bolts spanning quasi-static (2.5 × 10 −4 s −1 ) to high strain rates (10 3 s −1 ). The strain rate effect on the mechanical properties of the high-strength steel bolt material, in terms of the yield strength, tensile strength and the corresponding strain and elongation, was evaluated. A dynamic constitutive model was then developed based on the Cowper-Symonds model for predicting the stress-strain relationship of the two tested bolt materials at various strain rates and their dynamic strain energy absorption capacities were also compared. Both the deformation and energy absorption capacities of grade 12.9 bolts are weaker than those of grade 8.8 bolts, and the difference was found to increase with the increase in strain rate.

摘要 : The study of multi-time-delay dynamical systems has highlighted many challenges, especially regarding the solution and analysis of multi-time-delay equations. The symmetry and conserved quantity are two important and effective essential properties for understanding complex dynamical behavior. In this study, a multi-time-delay non-conservative mechanical system is investigated. Firstly, the multi-time-delay Hamilton principle is proposed. Then, multi-time-delay non-conservative dynamical equations are deduced. Secondly, depending on the infinitesimal group transformations, the invariance of the multi-time-delay Hamilton action is studied, and Noether symmetry, Noether quasi-symmetry, and generalized Noether quasi-symmetry are discussed. Finally, Noether-type conserved quantities for a multi-time-delay Lagrangian system and a multi-time-delay non-conservative mechanical system are obtained. Two examples in terms of a multi-time-delay non-conservative mechanical system and a multi-time-delay Lagrangian system are given.

摘要 : Hexafluoropropylene oxide dimer acid (GenX) is an alternative to perfluorooctanoic acid (PFOA), whose environmental concentration is close to its maximum allowable value established by the US Environmental Protection Agency, so its effects on human health are of great concern. The liver is one of the most crucial target organ for GenX, but whether GenX exposure induces liver cancer still unclear. In this research project, male C57 mice were disposed to GenX in drinking water at environmental concentrations (0.1 and 10 μg/L) and higher concentrations (1 and 100 mg/L) for 14 weeks to explore its effects on liver injury and potential carcinogenicity in mice. GenX was found to cause a dose-dependent increase in the serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total cholesterol (TC), and triglyceride (TG). As the content of GenX in drinking water increased, so did the concentrations of Glypican-3 (GPC-3) and detachment gamma-carboxyprothrombin (DCP), indicators of early hepatocellular cancer. GenX destroyed the boundaries and arrangements of hepatocytes, in which monocyte infiltration, balloon-like transformation, and obvious lipid vacuoles were observed between cells. Following exposure to GenX, Masson sections revealed a significant quantity of collagen deposition in the liver. Alpha-feto protein (AFP), vascular endothelial growth factor (VEGF), Ki67, matrix metalloproteinase 2 (MMP-2) and matrix metalloproteinase 9 (MMP-9) gene expression increased in a dose-dependent manner in the treatment group relative to the control group. In general, drinking water GenX exposure induced liver function impairment, elevated blood lipid level, caused liver pathological structure damage and liver fibrosis lesions, changed the liver inflammatory microenvironment, and increased the concentration of liver-related tumor indicator even in the environmental concentration, suggesting GenX is a potential carcinogen.