Abstract ：

This paper proposes a novel wall-type self-centering slip friction damper (WSCSFD), which mainly comprises of the grooved T-shape and L-shape plates that are combined by stacked disc springs. The damper resists shear forces arising from the inter-story drifts under earthquakes. By leveraging the variable friction mechanism and the pre-compressed disc springs, the WSCSFD can provide self-centering capability and energy dissipation capacity. The configuration and working mechanism of WSCSFD were first discussed. And then, the theoretical equations governing the force-displacement relationship were derived. One reduced-scale damper specimen was fabricated to conduct the proof-of-concept tests. The test results validated the deformation mode and cyclic behavior of the WSCSFD. The hysteretic parameters related to seismic applications were quantified and discussed. To complement the experimental observations and gain a further understanding of the local behavior, three-dimensional finite element (FE) models were established in ABAQUS. Finally, to address the deficiencies of the damper specimen, some potential improvement approaches were suggested and evaluated through the validated FE models.

Keyword ：

Experimental test Wall-type damper Numerical simulation Variable friction Self-centering

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Abstract ：

Frosting is a critical challenge that affects the energy efficiency of air source heat pumps (ASHPs). Defrosting periodically is the most widely used method to solve this problem. However, the rate of frosting varies considerably for ASHPs due to their configurations and operations (CICO) being different. This leads to the obvious differences in their defrosting initiating time. Defrosting too early or too late will both cause energy loss. To ensure the efficient operation of ASHPs, the variations of energy loss coefficient caused by frosting-defrosting (epsilon NL) and the defrosting initiating time for ASHPs with different CICO values were investigated. Based on the theory of optimal defrosting initiating time (Topt) and experimental results under different frosting durations, the Topt for different ASHPs is found. Then, a prediction model for ASHPs with different CICO values is established. Results show that there is a Topt for ASHPs with different CICO values, respectively. Under the frosting condition of 2/1 degrees C, the Topt increases with the rise of CICO values. When the CICO values increase from 3.14 to 22.44, the corresponding Topt increases from 22 min to 148 min. By fitting the Topt and CICO values, a cubic mathematical model for the prediction of the optimal defrosting time of ASHPs has been developed.

Keyword ：

Optimal defrosting initiating time Frosting energy loss Different configurations and operations Defrosting energy loss Air source heat pumps

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Abstract ：

This study investigates surface erosion wear caused by collision and friction between propellers and sand particles during the flight of propeller transport aircraft in harsh environments like deserts and plateaus, which are characterized by strong sand and wind conditions. Firstly, the erosion behavior of individual propeller blades is analyzed under various sand particle parameters using the commercial software FLUENT. Subsequently, dynamic simulations of the entire blade are conducted by the sliding mesh method to examine erosion patterns under different operational conditions, including rotation speed and climb angle. Finally, the impact of erosion on the aerodynamic characteristics of the propeller is obtained based on simulation results. This study delves into the erosion patterns observed in large aircraft propellers operating within sandy and dusty environments, as well as the consequential impact of propeller surface wear on aerodynamic performance. By elucidating these phenomena, this research provides valuable insights that can inform future endeavors aimed at optimizing propeller design.

Keyword ：

Erosive wear behavior Aircraft propellers Aerodynamic characteristics

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The present study develops a novel type of active joint node-bolt fasten wedge (BFW) active joints, aiming to investigate the loadbearing capacity of a BFW joint in a quantitative way and put forward precise formulas for its yield load and compression rigidity. To achieve this, indoor axial loading tests were conducted on two BFW joints, accompanied by a set of numerical simulations with the finite element approach implemented in ABAQUS. Parametric research was then conducted to assess the impact of various factors on the yield load and initial compression rigidity of BFW joints, leading to the derivation of precise calculation formulas for accurate prediction of these parameters. The key findings indicate that enhancing the bolt strength from 10.9 to 12.9 significantly improves mechanical performance. Under axial compression, the final bearing force, yield load, and initial compression rigidity increase by 0.86, 1.06, and 0.15 times, respectively. Numerical models accurately predict joint behavior under axial force, confirming their reliability. Parameter studies reveal that increasing web and eaves thickness, bolt strength, and diameter improves bearing capacity, while splint thickness has little effect. The fitting formulas introduced can precisely estimate yield load and rigidity, providing practical value for engineering applications.

Keyword ：

Finite element analysis (FEA) BFW Yield load Load-bearing capacity Compression rigidity Parametric analysis

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Retinal diseases such as age-related macular degeneration and diabetic macular edema will lead to irreversible blindness without timely diagnosis and treatment. Optical coherence tomography (OCT) has been widely utilized to detect retinal diseases because of its non-contact and non-invasive imaging peculiarities. Due to the lack of ophthalmic medical resources, automatic analyzing and diagnosing retinal OCT images is necessary with computer-aided diagnosis algorithms. In this study, we propose a lightweight retinal OCT image classification model integrating convolutional neural network (CNN) and Transformer to classify various retinal diseases with few parameters of the model. Local lesion features extracted by CNN can be encoded with the whole OCT image through the Transformer, which improves the classification ability. A convolutional block attention module is also integrated into our model to enhance the representational power. Compared with several classical models, our model achieves the best accuracy of 0.9800 and recall of 0.9799 with the least number of parameters and prediction time for an image on the OCT-C8 dataset. Moreover, on the OCT2017 dataset, our model outperforms the four state-of-the-art models except almost equal to another, achieving an average accuracy, precision, recall, specificity and F1-score of 0.9985, 0.9970, 0.9970, 0.9990, and 0.9970. Simultaneously, the number of parameters of our model has been reduced to just 1.28 M, and the average prediction time for an image is only 2.5 ms. © 2024 Elsevier Ltd

Keyword ：

Ophthalmology Optical coherence tomography Convolutional neural networks

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The primary challenge of applying partial denitrification/anammox (PD/A) to municipal wastewater treatment lied in the enrichment of functional bacteria with a considerable autotrophic nitrogen removal performance. The results showed influent NO3−-N: NH4+-N, reaction time and temperature would influence anammox nitrogen removal contribution. 15N isotopic tracing technology further revealed the average anammox contribution rate was up to 94.8 %. Extending reaction time was an effective measure to improve simultaneously PD and anammox activity. Microbial community indicated partial denitrifying bacteria (Bacillus) and anammox bacteria (Candidatus Brocadia) were enriched with abundance of 27.27 % and 7.09 % at NO3−-N: NH4+-N of 1:1. The correlation analysis showed that NO3−-N: NH4+-N ratio played the positive role for Bacillus enrichment, and low temperature was favorable to the enrichment of Thauera and Candidatus Jettenia. Overall, this study demonstrated the reasonable operational strategy would strengthen anammox contribution and facilitate enrichment of functional bacteria. © 2024

Keyword ：

Denitrification Wastewater treatment

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Abstract ：

The huge amount of leachate generated in landfills causes persistent pollution to soil and groundwater. Landfill cover is vital for reducing leachate generation through reducing rainwater infiltration. Yet, the traditional cover with capillary barrier effects (CCBE) is only applicable in reducing rainwater percolation at its base in arid or semi-arid region. To solve this problem, a novel capillary barrier cover is proposed, which adds multiple gravelsegments to the traditional CCBE to form the zipper-shape interface between fine- and coarse-grained soils. Hydraulic response of this zippered CCBE is numerically investigated considering different gravel-segment sizes, drainage-ditch widths and climate conditions. It is found that the zippered CCBE has a lower water percolation than the traditional one by up to 57 %. It is because the capillary barrier effects along the right side-wall of gravel-segment leads to water accumulation and hence water percolation near its base, facilitating reducing water percolation using drainage ditch below the gravel-segment. Moreover, water percolation increases when the gravel-segment height exceeds 0.3 times thickness of fine-grained soil or the gravel-segment width increases, due to reduction of water storage in fine-grained soil. Under the recorded annual precipitation of 1235 mm in the semi-humid region in China, the annual percolation of the traditional and zippered CCBEs are 84 mm/year and 36 mm/year, respectively. Thus, the zippered CCBE might extent the applicability of the traditional CCBE from arid or semi-arid region to semi-humid region.

Keyword ：

Finite element Zipper-shape interface Water movement Percolation Capillary barrier effects Landfill cover

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In cobalt-based catalyst/peroxymonosulfate (PMS) systems, the key issues are the leaching of metals and the stability of catalysts. In this study, a NH2-UiO-66 cladded CoZn/NC catalyst was synthesized for efficient degradation of sulfamethoxazole (SMX) using activated PMS. The removal efficiency of SMX could achieve 100% within 30 min. The leaching of Co2+ was inhibited to 0.05 ppm and the anti-interference and cyclic stability of the catalyst were enhanced by the NH2-UiO-66 shell. In addition, the quenching experiment, electron paramagnetic resonance (EPR) technique and probe experiment were used to analyze the reactive oxygen species (ROSs) qualitatively and quantitatively. The findings demonstrated that singlet oxygen (1O2) had the highest steady-state and cumulative concentration. However, 1O2 could only participate in the degradation of SMX through single electron transfer or addition reaction, resulting in a lower second-order rate constant of the SMX reaction with 1O2. Sulfate radical (SO4·-) contributed the most to the degradation of SMX due to the high reactivity of the sulfonamide structure in SMX to SO4·-. Finally, possible pathways for SMX degradation were proposed. The two primary mechanisms of SMX degradation were S-N cleavage and amino hydroxylation/oxidation. The toxicity of most of the intermediates was less than that of SMX through ecological structure–activity relationship analysis. Overall, a novel approach to synthesize low leaching and efficient cobalt based catalyst was put forward, and the activation mechanism of PMS was also revealed. © 2024 Elsevier B.V.

Keyword ：

Cobalt alloys Hydroxylation Paramagnetic resonance Zinc alloys Cobalt metallurgy Leaching Reaction intermediates Rate constants Activation analysis Electron spin resonance spectroscopy Bioremediation Cobalt Free radical reactions Degradation

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Offshore wind turbines (OWTs) are subjected to long-term cyclic loading, such as wind and wave loading, leading to axial-torsional bidirectional cyclic loading in the pile surrounding soil. This bidirectional cyclic loading results in the cumulative deformation of the pile foundation. The larger cumulative deformation endangers the operational safety of the wind turbine system. In China, offshore wind farms mainly consist of clay layers and their cyclic mechanical characteristics need to be examined. Therefore, a series of bidirectional cyclic loading tests are carried out by using a hollow cylindrical torsional shear apparatus to investigate the effect of different cyclic stress levels on the cumulative strain. The results revealed that cumulative strains stabilize as the cycles increase when the cyclic stress level is less than the critical cyclic stress level. An empirical model based on the test results is developed to reflect the cumulative deformation characteristic. In the bounding surface constitutive model, the plastic modulus interpolation function is improved by using the established empirical model,the effect of loading and unloading routes on the variation of plastic modulus is investigated. Furthermore, a modified constitutive model is used to predict the cumulative deformation of soil under the effect of bidirectional cyclic loading. The predicted results agree well with the findings achieved from the tests.

Keyword ：

Clay Bidirectional cyclic loading Hardening modulus Empirical model

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Abstract ：

Fiber-Reinforced Cementitious Composites (FRCC) have gained significant attention in engineering applications due to their superior mechanical properties and toughness, particularly under high strain rate conditions. This study performed dynamic tensile tests on FRCC at high strain rates (35–110 s⁻¹) using a Split Hopkinson Tensile Bar (SHTB) apparatus. Additionally, a novel Peridynamic (PD) model was developed for the SHTB and FRCC system, leveraging the advanced capabilities of the emerging PD theory. The study compared and analyzed dynamic tensile strength, ultimate tensile strain, strain rate effects, failure modes, and crack development in FRCC with different fiber ratios at various high strain rates, using both experimental data and PD simulations. The results show that the PD-SHTB-FRCC dynamic model developed in this study exhibits high consistency between numerical simulations and experimental findings, effectively capturing the processes of crack initiation, propagation, and complete failure in FRCC specimens. The dynamic tensile properties of FRCC improve significantly with increased strain rates, with polyethylene (PE) fibers providing superior reinforcement compared to steel fibers. Notably, the dynamic tensile strength, peak tensile stress, and ultimate tensile strain of FRCC increase significantly with rising strain rates, with specimens containing higher PE fiber content showing a more pronounced enhancement effect. For strain rates between 42.6 s⁻¹ and 76.1 s⁻¹, considering dynamic tensile strength, ultimate tensile strain, and peak tensile stress, the optimal combination for resisting dynamic tensile loads was 1.5 % PE fibers and 0.5 % steel fibers. At a strain rate of 99.8 s⁻¹, a 2 % PE fiber ratio alone provided the best performance. © 2024 Elsevier Ltd

Keyword ：

Tensile testing Fiber reinforced plastics Cracks Tensile stress Shear strain Strain rate Tensile strength Tensile strain

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