Search Results (1,279)

Auxetic metamaterials, characterized by negative Poisson’s ratio, have garnered significant interest due to their exceptional impact resistance. This study presents a type of auxetic metamaterial organized in re-entrant arrowhead lattices. The uniaxial impact behavior of a uniform auxetic lattice was first investigated through experiment and finite element simulation, which showed good agreement. Subsequently, two graded auxetic lattices with density-gradient profiles were proposed by varying the radius of the bars in the basic auxetic lattice. Numerical simulations demonstrate that, across various compression velocities, both graded architectures achieve higher plateau stresses and enhanced energy absorption compared to their uniform counterpart. Notably, the graded lattice with lower density at the impact end exhibited a reduced initial peak stress. An analytical framework was also established to characterize the compressive behavior of these auxetic lattices. Theoretical analyses elucidate the underlying mechanisms of impact energy dissipation and provide a solid basis for predicting dynamic compressive performance. Furthermore, a gradient-parametric study revealed that the stress–strain response is significantly influenced by both the density gradient and impact velocity, further demonstrating a high consistency between the theoretical predictions and the simulation results. This research is desirable to provide insights for designing graded auxetic metamaterials with tailored impact properties. Full article

To improve the seismic performance of semi-rigid steel frame beam–column joints connected by T-stubs, reinforced T-stubs formed via wedge-shaped and thickening modifications are proposed. Taking the middle column joints in steel frames as the research objects, three types of beam–column joints are designed by adopting ordinary, wedge-shaped, and thickened wedge-shaped T-stubs. To conduct a comparative analysis of the seismic performance of the test specimens, this study imposes low-cycle cyclic loads on the column ends of each specimen along their major-axis and minor-axis in-planes. This loading protocol is adopted to simulate the dynamic responses of the specimens under bidirectional seismic action. Comparing the macroscopic failure phenomena of the specimens, the influence of reinforced T-stubs on the plastic development mode of the joints is analyzed. Based on seismic indicators such as hysteresis characteristics, skeleton curves, stiffness degradation, and energy dissipation capacity, the energy dissipation capacity of the specimens along the major-axis is greater than that along the minor-axis, but their deformation capacity is slightly reduced. The bearing capacity, energy dissipation, and rotational stiffness could be improved by reinforced T-stubs, but the deformation capacity is reduced to varying degrees. The stiffness degradation rate of the specimen adopting wedge-shaped T-stubs shows a more obvious accelerating trend. Through the comparative analysis of the three specimens based on the energy damage index, the results indicate that wedge-shaped T-stubs significantly increase the damage degree of the specimens, but thickened wedge-shaped T-stubs have a relatively small impact on the evolution of joint damage. Full article

Generalized frosts have a significant impact on the Pampa Húmeda of Argentina, particularly those without persistence (0DP), defined as events that do not last more than one day, and are the most frequent generalized frosts. This study investigates the dynamical and physical mechanisms that sustain these events, emphasizing the nonlinear interactions represented by the Rossby Wave Source (RWS) equation. Composite analysis of pressure, temperature, wind and geopotential height fields were performed, showing that 0DP events are related to abrupt cold air intrusion linked to the enhancement of upper levels troughs over the eastern Pacific Ocean and transient surface anticyclones over South America. This linear analysis only showed a lack of persistent upper-level maintenance and did not explain the dynamics of the rapid weakening of the circulation. For this reason, a nonlinear analysis based on the decomposition of the RWS equation into its advective and divergent terms is performed. The advective term only acts as an initial trigger, deepening troughs and favoring meridional cold air advection, while the divergent term dominates the events, representing 63–67% of the affected area. This term reinforces ridges, promotes subsidence and favors clear sky conditions that enhance nocturnal radiative cooling and frost formation. Positive anomalies of the divergent RWS term strengthen the ridge and advect cold air over the Pampa Húmeda, whereas subsequent negative anomalies over the southwestern Atlantic act as sinks of wave activity, leading to the rapid dissipation of the synoptic configuration. Consequently, the same mechanism that generates favorable conditions for frost development also determines their lack of persistence. These findings demonstrate that the short-lived nature of 0DP frosts is not due to the absence of dynamical forcing, but rather to nonlinear processes that both enable and constrain frost occurrence. This highlights the importance of incorporating nonlinear diagnostics, such as the RWS, to improve the understanding of short-lived atmospheric extremes. Full article

Background: This study evaluates the impact of fibrinogen enrichment on the structural, mechanical, and bioactive properties of fibrin scaffold derived from balanced protein-concentrate plasma (BPCP), an autologous platelet-rich plasma (PRP) formulation with elevated extraplatelet content. Methods: A novel high-fibrinogen BPCP (HF-BPCP) scaffold was produced by combining BPCP platelet lysate with a concentrated fibrinogen solution at a 1:1 ratio, yielding nearly four-fold physiological fibrinogen levels. Comparative analyses between HF-BPCP and standard BPCP included platelet and fibrinogen quantification, scanning electron microscopy (SEM), rheology, indentation, adhesion testing, coagulation kinetics, retraction assays, biodegradation profiling, and growth factor (GF) release kinetics. Results: HF-BPCP displayed significantly denser fibrin networks with thinner fibers, higher porosity, and markedly faster coagulation times compared to BPCP. Mechanically, HF-BPCP exhibited greater stiffness, higher energy dissipation, and more stable adhesion, while almost eliminating scaffold retraction at 24 h. Despite improved early handling and structural integrity, HF-BPCP degraded more rapidly in vitro under tissue plasminogen activator exposure. GF release analysis showed reduced early peaks of platelet-derived factors (TGF-β1, PDGF-AB, VEGF) but sustained release thereafter, while extraplatelet factors (IGF-1, HGF) exhibited similar profiles between scaffolds. Conclusions: These results indicate that fibrinogen enrichment synergizes with the elevated extraplatelet protein profile of BPCP to enhance scaffold mechanical stability, handling properties, and controlled GF delivery. HF-BPCP combines the adhesive, structural, and bioactive features of fibrin sealants with the regenerative potential of PRP, offering a fully autologous alternative for clinical applications requiring rapid coagulation, high mechanical support, and sustained GF availability. Further preclinical and clinical studies are needed to evaluate therapeutic efficacy in the regenerative medicine field. Full article

Heavy-textured soils in monsoon-affected regions face challenges related to waterlogging and structural degradation, yet the long-term efficacy of biochar as a physical soil amendment under such conditions remains inadequately understood. This two-year field study (2018–2019) therefore evaluated the transient impacts of birch-derived biochar (360–380 °C pyrolysis; 0, 1, 3 kg/m²), subsurface drainage systems, and fertilizer regimes on key physical properties of Endoargic Anthrosols (clay loam) in coastal Primorsky Krai, Russia. Granulometric composition remained stable (silt loam: sand 42–48%, silt 38–44%, clay 12–16%), though drainage significantly increased the silt fraction by >7.5% (p < 0.05). Biochar induced short-term reductions in bulk density (ρ_b; max −12% at 3 kg/m², 2018) and aggregate density (ρ_a; max −9.3%, 2018), but these effects dissipated by 2019 due to tillage redistribution and monsoonal fragmentation, as verified by SEM. Total porosity fluctuated seasonally (0.50–0.65 cm³/cm³), peaking post-tillage but declining under monsoon saturation, with no significant sustained biochar contribution. Crucially, intra-aggregate pore architecture (2–50 nm) resisted amendment-induced changes; N₂ adsorption showed treatment-invariant mesopore dominance (65–75% volume; mean pore diameter 17–21 nm), attributable to biochar’s physical exclusion (>1 µm particles from sub-0.5 µm pores) and inert fragmentation. Drainage dominated structural dynamics, modulating pore volume seasonally (−15% in 2018; +18% in 2019), while organic fertilizer enhanced porosity through polysaccharide-stabilized microaggregation (+22%, 2019). We conclude that biochar’s physical benefits in clay loams under monsoon climates are transient and dose-dependent, operating primarily through inter-aggregate macroporosity rather than intra-aggregate modification, necessitating reapplication for sustained improvements. Full article

Based on the principle of re-centering with low prestress and energy dissipation through sloped friction (SF) energy dissipators, this study proposes a new hysteresis concept characterized by enhanced post-stiffness and energy dissipation for self-centering prestressed concrete (SCPC) frames. The focus of this research is to compare the seismic performance of SCPC frames utilizing both traditional and novel hysteresis concepts, aiming to provide critical evidence for the advancement of seismic-resilient structures. Nonlinear dynamic time history analyses were conducted under various seismic levels to investigate the impact of the novel hysteretic concept on seismic performance indicators, including inter-story drift, residual inter-story drift, and beam-column damage. Additionally, the influence of energy dissipator configuration and prestress level on the repair costs of structures subjected to the maximum considered earthquake (MCE) was analyzed to elucidate the structural functional recovery capacity. The results indicate that the combination of low prestress and sloped friction energy dissipators significantly reduces internal forces in beams and columns compared to traditional high prestress SCPC frames with conventional friction energy dissipators. The integration of sloped friction energy dissipators and the application of low prestress to post-tensioned (PT) strands effectively dissipate the energy transmitted to the frame during an earthquake, leading to a substantial reduction in structural damage within the SCPC frame utilizing the new hysteresis concept during large earthquakes, thereby facilitating post-earthquake repairs. Full article

In this work, we introduce a statistical framework for monitoring the performance of a breakwater structure in reducing wave impact. The proposed methodology aims to achieve diligent tracking of the underlying process and the swift detection of any potential malfunctions. The implementation of the new framework requires the construction of appropriate nonparametric Shewhart-type control charts, which rely on order statistics and scan-type decision criteria. The variance of the run length distribution of the proposed scheme is investigated, while the corresponding mean value is determined. For illustration purposes, we consider a real-life application, which aims at evaluating the effectiveness of a breakwater structure based on wave height reduction and wave energy dissipation. Full article

Since direct laser surface texturing of polymers is an emerging area, considerable attention is given to this technique with the aim of forming a basis for follow-up research that could open the way for potential technological ideas and optimization in novel applications. Laser pre-processing of ballistic textiles can raise surface roughness of smooth para-aramid fibres and as a result can improve the adhesion of functional coatings applied in following processing steps, thus opening new possibilities for material performance improvement. The impact resistance of ballistic fabric depends on the ability of its yarns in contact with the projectile absorb energy locally and disperse it to adjacent yarns without undergoing severe damage or failure. In addition to the yarn deformation and fracture, yarn resistance to pull-out contributes to the dissipation of impact energy significantly. The objective of this study is to optimize Kevlar^® KM2+ fabric surface topographies by adjusting the continuous wave (CW) CO₂ laser parameters in such a way that it increases the surface roughness and resistance to the yarn pull-out from the fabric without destroying the unique structure of the of Kevlar^® KM2+ fibres. Experimental research measured data show increase in surface roughness by 50–53% and set of laser parameter variants have been obtained that allow for an increase in KM2+ 440D woven fabric yarns pull out force from fabric in the range from 50% up to 99% compared to the untreated one. Full article

Surface-mounted devices (SMDs) are essential components that enable the miniaturization and enhanced performance in electronic products, significantly impacting both circuit performance and reliability. In this study, we propose a non-destructive evaluation method for cracks in SMD capacitors using the artificial intelligence of impedance spectra. To achieve this, cracks were induced in 132 specimens through incremental displacement using a shear module of a bond tester. At each crack level, frequency-domain spectra were acquired for 14 parameters using an impedance analyzer. Meaningful changes in parameter patterns corresponding to each crack stage were observed, confirming impedance spectroscopy as an effective tool for crack assessment. Through data augmentation, we generated 87,800 datasets representing various crack stages, which were used to train AI models that output crack stages from input impedance spectra. Based on this dataset, six AI models, ConvNeXt, LSTM, Transformer, Logistic Regression, SVM, and Random Forest, were developed to classify crack severity into nine stages. Model-wise, the Random Forest classifier consistently outperformed the other approaches. When trained with single parameters, it achieved its best performance using the dissipation factor, reaching 98.5% accuracy. Furthermore, when the dissipation factor was combined with any of the remaining impedance parameters, the Random Forest model achieved perfect diagnostic performance (100%) across all combinations, highlighting both its robustness and its suitability for multi-parameter learning. These results provide practical guidance for selecting effective parameters and model architectures for impedance spectrum-based crack diagnostics. Full article

Raindrop erosion of wind turbine blades’ leading edge is a critical degradation mechanism limiting wind turbine blade lifetime and aerodynamic efficiency. Protective coatings have been extensively studied to mitigate this damage. This review critically synthesises current knowledge on coating-based protection strategies against erosion, with emphasis on (i) the underlying mechanisms of erosion, (ii) advances in conventional and emerging coating technologies, and (iii) experimental approaches for testing and lifetime prediction. Across reported studies, nanofiller reinforcement (e.g., CNTs, graphene, CeO₂, Al₂O₃) enhances erosion resistance by 60–99%, primarily through improved toughness and stress-wave dissipation. Hybrid and multifunctional systems further combine mechanical durability with self-healing or anti-icing capabilities. Experimental results confirm that erosion rate follows a power-law dependence on impact velocity, with maximum damage occurring between 45° and 60° impact angles. Softer elastomeric coatings demonstrate longer incubation periods and superior viscoelastic recovery compared with rigid sol–gel systems. Persistent gaps include the lack of standardised testing, poor field–lab correlation, and limited long-term durability data. Future work should focus on coordinating multi-stressor testing with variable-frequency rain setups to replicate real field conditions and enable reliable lifetime prediction of next-generation erosion-resistant coatings. Full article

Accurate water hammer calculations are crucial for hydraulic safety and unit stability in hydropower systems with free-surface tailrace tunnels. However, existing models often neglect hydraulic variations in free-surface sections, while the commonly used method of characteristics tends to cause numerical instability and dissipation due to interpolation or wave speed adjustments, leading to significant computational errors. Aiming at the transient process of hydropower stations with free-surface tailrace tunnels and fully considering the influence between pressure and free-surface conditions, this study employs the second-order Godunov scheme to solve the governing flow equations for pressurized and free-surface flows. A generalized boundary of the regulating pool and a variable time step calculation method were proposed to solve the problem of real-time coupling calculation in the pressure–free-surface transition area. The results show that during the large fluctuation transient process, the hydraulic characteristics of the free-surface flow have little impact on the inlet pressure of the unit’s volute and the unit’s rotational speed but have a significant impact on the fluctuation period and extreme value of the inlet pressure of the draft tube. During the small fluctuation transient process, the hydraulic characteristics of open channel flow are beneficial for improving the unit’s regulation quality. This indicates that considering the hydraulic characteristics of free-surface flow is of great significance for realizing an accurate simulation of the transient process of hydropower stations. Full article

Reclaimed coastal areas are highly susceptible to uneven subsidence caused by the consolidation of soft marine deposits, which can induce differential settlement, structural deterioration, and systemic risks to urban infrastructure. Further, engineering activities, such as construction and loadings, exacerbate subsidence, impacting infrastructure stability. Therefore, monitoring the integrity and vulnerability of linear urban infrastructure after construction on reclaimed land is critical for understanding settlement dynamics, ensuring safe and reliable operation and minimizing cascading hazards. Subsequently, in the present study, to monitor deformation of the linear infrastructure constructed over decades-old reclaimed land in Mokpo city, South Korea (where 70% of urban and port infrastructure is built on reclaimed land), we analyzed 79 Sentinel-1A SLC ascending-orbit datasets (2017–2023) using the Persistent Scatterer Interferometry (PSInSAR) technique to quantify vertical land motion (VLM). Results reveal settlement rates ranging from −12.36 to 4.44 mm/year, with an average of −1.50 mm/year across 1869 persistent scatterers located along major roads and railways. To interpret the underlying causes of this deformation, Casagrande plasticity analysis of subsurface materials revealed that deep marine clays beneath the reclaimed zones have low permeability and high compressibility, leading to slow pore-pressure dissipation and prolonged consolidation under sustained loading. This geotechnical behavior accounts for the persistent and spatially variable subsidence observed through PSInSAR. Spatial pattern analysis using Anselin Local Moran’s I further identified statistically significant clusters and outliers of VLM, delineating critical infrastructure segments where concentrated settlement poses heightened risks to transportation stability. A hyperbolic settlement model was also applied to anticipate nonlinear consolidation trends at vulnerable sites, predicting persistent subsidence through 2030. Proxy-based validation, integrating long-term groundwater variations, lithostratigraphy, effective shear-wave velocity (V_s³⁰), and geomorphological conditions, exhibited the reliability of the InSAR-derived deformation fields. The findings highlight that Mokpo’s decades-old reclamation fills remain geotechnically unstable, highlighting the urgent need for proactive monitoring, targeted soil improvement, structural reinforcement, and integrated InSAR-GNSS monitoring frameworks to ensure the structural integrity of road and railway infrastructure and to support sustainable urban development in reclaimed coastal cities worldwide. Full article

This paper proposes an event-driven dynamic output feedback dissipative fuzzy (EDDOFDF) control strategy for direct current (DC) microgrids with nonlinear constant power loads (CPLs) subject to hybrid attacks and noises. Firstly, using the measurement output of the microgrid’s fuzzy model and information of hybrid attacks, a Zeno-free resilient event-triggered communication mechanism (RETM) is designed, which can save limited resources such as network bandwidth and actively exclude attack-induced packet dropouts. Secondly, by designing an EDDOFDF security controller, a closed-loop switched fuzzy system model is established, which presents a unified platform to study the impacts of hybrid attacks, RETM, noises, microgrid plant, and controllers. Thirdly, by introducing a piecewise Lyapunov functional, exponential stability conditions in mean square with guaranteed dissipative performance are obtained. Further, sufficient conditions for designing both the EDDOFDF controller and state-feedback switched fuzzy controller are derived. Examples illustrate the effectiveness of the proposed method. Full article

This study explores the comparative evaluation of PLA, carbon fiber-reinforced PLA (PLA-CF), and carbon fiber-reinforced high-temperature polyamide (PAHT-CF) for use in Fused Deposition Modeling (FDM) additive manufacturing. These materials were selected to examine how carbon fiber (CF) reinforcement affects PLA and PAHT, using virgin PLA as the baseline. Mechanical and thermal properties were tested to assess the influence of reinforcement on strength, toughness, and heat transfer. Tensile, impact, and thermal conductivity tests were conducted on all three materials. The results showed that PAHT-CF outperformed both PLA and PLA-CF in all categories, achieving an ultimate tensile strength of 57.5 MPa, an impact strength of 14.30 kJ/m², and thermal conductivity of 0.182 W/m·K. PLA-CF showed moderate improvements in strength over neat PLA but with increased brittleness and slight improvement in thermal conductivity. Notably, this is the first study to investigate the thermal conductivity and resistivity of PAHT-CF in the literature, offering new insights into its heat dissipation capabilities and suitability for high-temperature applications. These findings highlight the critical role of polymer selection and fiber reinforcement in optimizing material performance. The results offer guidance for material selection in additive manufacturing, especially for lightweight, strong, and thermally efficient parts in various industries. Full article

This paper addresses the optimization of traffic signal timing at urban intersections by introducing a dynamic green ratio allocation framework based on cycle-based delay classification. Conventional methods such as the Webster delay model often fail to capture the asymmetric delay characteristics and the impact of fluctuating flows across multiple cycles. We propose a novel approach that classifies cycles into undersaturated and oversaturated states and develops dedicated optimization models for each type. For undersaturated cycles, a new delay function is derived to accurately capture the interaction between queue dissipation and green time allocation, enabling multi-period minimization of total vehicle delay. For oversaturated cycles, queue minimization at the end of each phase is adopted to accelerate congestion dissipation. The framework is validated through simulation and compared with existing methods, demonstrating superior performance in congestion clearance and delay minimization. The results show improved adaptability to changing traffic conditions and enhanced practicality for real-time signal control in smart transportation systems. Full article