Search Results (1,655)

Background: Passive movement-based recovery strategies may support post-exercise recovery without additional metabolic demand. Objective: To examine the acute effects of passive foot flexions during recovery on isometric task performance after repeated exercise. Methods: Fourteen physically active men completed two randomized crossover sessions—passive rest and passive foot flexions—separated by a 7-day washout. Each session included a sustained static isometric plantar flexion task at 75% of maximal voluntary contraction (MVC), a 15 min recovery period, and a repeated isometric task. Work capacity was assessed as holding time. Cardiovascular, autonomic, and peripheral responses were recorded throughout the protocol. Results: Baseline holding time did not differ between the conditions. During the repeated isometric task, holding time was significantly longer following passive foot flexions compared to passive rest (67.7 ± 10.4 s vs. 52.9 ± 9.7 s; p < 0.05), with a large effect size (d ≈ 1.5). Passive foot flexions were associated with a greater increase in parasympathetic modulation, reflected by higher root mean square of successive differences (RMSSD) during recovery and altered muscle oxygenation dynamics, including faster post-exercise re-oxygenation. For both conditions, heart rate and systolic and diastolic blood pressure exhibited similar exercise–recovery patterns with no between-condition differences. Only minor changes in muscle stiffness were observed following the passive foot flexions. Conclusions: Passive foot flexions may support short-term recovery between repeated isometric efforts, particularly with respect to holding time and RMSSD. Full article

Wheeled multifunctional motorized crossing frames represent a new type of crossing equipment for high-voltage transmission line construction. The initial design is too conservative, having a large safety margin and high material redundancy. Therefore, it is necessary to study a lightweight design version. However, as the structure constitutes an assembly consisting of multiple components, it also exhibits relatively high complexity. In a lightweight design, optimizing multi-component and multi-size parameters can lead to structural interference and separation, seriously affecting the smooth progress of design optimization. Therefore, an optimization design method of a multi-parameter complex assembly structure is proposed to solve this problem. Firstly, the typical stress conditions of the wheeled multifunctional motorized crossing frame were analyzed using its structural model. Then, a finite element model of the beam was established in ANSYS 2021 R1 Workbench, and the mechanical characteristics were analyzed. The results show that the arm support is the key load-bearing component and has significant optimization potential. Subsequently, functional mapping relationships were established among the 14 dimension parameters of the arm support, reducing the number of design variables to six and successfully avoiding component separation or interference during optimization. Through global sensitivity analysis, the height, thickness, and length of the arm body were screened out as the core optimization parameters from six initial design variables. Then, 29 groups of sample points were generated via central composite design (CCD), and a response surface model reflecting the relationships among the arm body’s dimensional parameters, total mass, maximum stress, and maximum deformation was established using the Kriging method. Leave-one-out cross-validation (LOOCV) was performed, and the coefficients of determination (R²) for model fitting were all higher than 0.995, indicating extremely high prediction accuracy. Taking mass and deformation minimization as the optimization objectives, the MOGA algorithm was adopted to perform multi-objective optimization and determine the optimal engineering parameters. Simulation verification was conducted on the optimized arm support, and an eigenvalue buckling analysis was performed simultaneously to verify structural stability. Finally, the proposed optimization method was experimentally verified through mechanical performance tests of the full-scale prototype under symmetric and eccentric loads. The results show that the mass of the optimized arm support is reduced from 217.73 kg to 189.8 kg, with a weight reduction rate of 12.8%. Under an eccentric load of 70,000 N, the maximum deformation of the arm support is 8.9763 mm, the maximum equivalent stress is 314.86 MPa, and the buckling load factor is 6.08, all of which meet the requirements for structural stiffness, strength, and buckling stability. The maximum error between the experimental and finite element results is only 4.64%, verifying the accuracy and reliability of the proposed method. The proposed optimization methodology, validated on a wheeled multifunctional motorized crossing frame, serves as a transferable paradigm for the lightweight design of complex assemblies with coupled dimensional constraints, thereby offering a general reference for the structural optimization of multi-component transmission line equipment, construction machinery, and other multi-component engineering systems. Full article

Eringen’s integral constitutive relation is more general than its differential counterpart for modeling small-scale effects in micro- and nanostructures; however, it leads to integro-differential governing equations that are difficult to solve, which has limited the practical use of integral formulations. To directly address this gap, this paper introduces a novel symplectic-based numerical method that efficiently and accurately analyzes the free vibration of small-scale Kirchhoff plates governed by Eringen’s integral nonlocal model. The method discretizes the nonlocal integral operator by introducing inter-belt elements for long-range interactions and adopting a truncated influence domain, while balancing computational efficiency and accuracy. The effects of the nonlocal parameter, two-phase mixture parameter, mode numbers, kernel types, and geometric parameters on the natural frequencies are systematically investigated. The results indicate stiffness softening. For a simply supported square nanoplate with side length a = 10 nm, the first-order frequency parameter decreases by approximately 25% as the nonlocal parameter increases from 0 to 4 nm, and higher-order modes exhibit substantially greater sensitivity to nonlocal effects. Convergence and accuracy are validated against published continuum-level solutions and molecular dynamics simulations; relative deviations are below 2% in most cases, and the local limit (l_a = 0) yields errors on the order of 10⁻³. Full article

This paper will present a constant-force vibration isolator (CFVI), in which the isolated load is supported by two pulley-roller mechanisms, while the dynamic stiffness is modified by a cam mechanism with the piecewise profile redefined by the user. As a result, this model can generate the constant force-displacement response within the working region, thereby obtaining quasi-zero stiffness in this range. Because of the piecewise configuration of the cam, the system motion governed by the piecewise dynamic equation under base motion excitation will be analyzed and established. The approximate solution of the piecewise dynamic equation is derived by using the average method, from which the relative amplitude–frequency relation and the absolute amplitude transmissibility of the CFVI will be obtained. The effects of the key working parameters involving the damping coefficient, critical position, and excited amplitude on the dynamic behavior and isolation effectiveness of the CFVI are considered through numerical simulations. The simulation result reveals that the dynamic response of the CFVI offers two branches: resonance and isolation. The former is significantly affected by the working parameters, whereas the latter is weakly influenced. Furthermore, the isolation effectiveness of the CFVI will be compared with that of its linear counterpart and the quasi-zero stiffness vibration isolation model using a semicircle cam (QZSI). The results demonstrate that the CFVI outperforms the other models for base motion excitations. Full article

Thin-walled laminated cooling plates integrate internal channels and pin-fin cores, producing reduced and spatially non-uniform stiffness that changes welding restraint and distortion. This study investigates stiffness-controlled plastic-strain evolution in laser butt welding of GH3230 laminated plates, with geometrically identical solid plates as reference. A coupled heat-transfer and thermo-mechanical finite element model was developed in MSC Marc using a composite Gaussian surface–volumetric moving heat source and temperature-dependent properties. The thermal solution was validated against near-weld thermal cycles and fusion geometry; mechanical predictions were evaluated by CMM distortion and residual-stress measurements. Both structures show comparable residual-stress magnitudes and spatial trends, indicating that residual stress is governed mainly by the local weld thermal gradient. In contrast, the laminated plate exhibits larger angular/bending distortion. Simulations show that, although the plastic-strain pattern is similar, the laminated plate develops higher peak plastic strain confined to a narrower band near the weld, with the transverse plastic strain dominating. Plastic strain–temperature paths reveal continued transverse plastic-strain accumulation during cooling with limited recovery, consistent with restraint redistribution induced by stiffness non-uniformity. An equivalent restraint–stiffness spring model explains this “narrower-but-stronger” plastic zone and links stiffness to yielding and residual plastic-strain magnitude, supporting distortion prediction and stiffness-informed control of welded laminated cooling plates. Full article

Rigid internal fixation has long been the standard for fracture management; however, excessive construct stiffness can suppress interfragmentary strain, reduce callus formation, and impair secondary fracture healing. Low-elastic-modulus TiNbSn alloys have emerged as a promising alternative, offering mechanical behavior closer to that of cortical bone. This review synthesizes representative preclinical and computational evidence to clarify the mechanobiological rationale for TiNbSn alloy plates in fracture fixation. We summarize key biological requirements for secondary fracture healing, including controlled interfragmentary strain, preservation of vascularity, and effective load sharing, and contrast these with the limitations of conventional high-stiffness fixation plates, such as stress shielding and reduced callus formation. Finite element analyses from previously reported models illustrate qualitative trends toward increased axial displacement, favorable stress distribution, and within a biologically relevant range for endochondral ossification. Consistent findings from animal fracture models further indicate enhanced periosteal and intramedullary callus formation and more physiological healing patterns with TiNbSn plates compared with rigid fixation. Emerging clinical experience with TiNbSn femoral stems provides indirect support for the long-term potential of low-elastic-modulus titanium alloys to mitigate stress shielding; however, such findings should be interpreted only as indirect supportive evidence, as stem implantation and fracture plate fixation involve substantially different mechanical and biological contexts. Collectively, these observations provide preliminary support for the mechanobiological rationale of low-modulus TiNbSn plates and suggest their potential role as biologically informed fixation devices, while highlighting the need for further clinical validation. Full article

Background/Objectives: C1q/TNF-related protein 3 (CTRP3), progranulin (PGRN), and chemerin are adipokines that participate in systemic inflammation. This study systematically examined adipokine levels in cystic fibrosis patients of different ages to evaluate their role in inflammatory, metabolic, and hepatic processes. Thirty-seven pediatric and thirty-three adult CF patients were enrolled to assess the potential of these adipokines as biomarkers. Methods: Anthropometric and physiological data, pulmonary function (forced expiratory volume, FEV1; vital capacity, VC), and liver fibrosis score FIB-4 were assessed. Liver stiffness was measured by transient elastography. Serum samples from 40 healthy adult volunteers served as the control group. Serum concentrations of chemerin, CTRP3, and PGRN were quantified by enzyme-linked immunosorbent assay (ELISA). Results: Compared with healthy controls, adults with CF had markedly lower circulating CTRP3 levels, whereas PGRN concentrations were significantly higher. Among CF patients, both CTRP3 and PGRN were higher in the pediatric group than in adults, while chemerin did not vary with age. The presence of cystic fibrosis-related liver disease (CFLD) did not significantly alter adipokine levels relative to CF patients without liver disease. Receiver operator characteristic (ROC) analysis showed that circulating PGRN could reliably differentiate CF patients from controls; none of the three adipokines predicted the presence of CFLD. CTRP3 and PGRN were inversely correlated with age, BMI, and pulmonary function. Conclusions: Overall, our data support systemic PGRN as a potential biomarker for CF and indicate an age-dependent regulation of circulating CTRP3 and PGRN. Both proteins were inversely associated with BMI, inflammatory markers, liver fibrosis, and pulmonary capacity. Full article

Traditional virtual synchronous generator (VSG) control in photovoltaic–storage systems struggles with severe dynamic deterioration under high-impedance weak grid conditions. Through small-signal modeling, this paper analytically reveals that increased grid inductance forces the system’s dominant poles to migrate significantly toward the real axis, inducing a critical “overdamped hysteresis” that degrades transient tracking speed and oscillation attenuation. To break these physical constraints, an improved exponential synergistic adaptive control strategy is proposed. By establishing a synergistic optimization mechanism between the virtual inertia and damping coefficients via a square-root coupled exponential function, the proposed method achieves precise multi-parameter coordination. During the initial phase of disturbances, it triggers an explosive parameter surge to provide “stiff” transient support, strictly limiting frequency deviations and the rate of change of frequency (RoCoF). During the recovery phase, it drives a precipitous parameter decay to actively neutralize the overdamped coupling effect, forcibly pulling the migrated poles back to the ideal underdamped region. Rigorous switching-model simulations demonstrate that, compared to conventional fixed-parameter and power function-based adaptive methods, the proposed synergistic strategy significantly improves transient performance. Quantitatively, during load steps, it restricts the frequency nadir to 49.85 Hz (compared to 49.73 Hz for fixed parameters). During extreme grid stiffness transitions (SCR drops), it completely eliminates active power tracking hysteresis by reducing the settling time to just 0.26 s and aggressively clamps AC overcurrent peaks from 38 A down to 31 A. Supported by coordinated PV–storage energy management, the proposed method offers a highly robust grid-forming framework for renewable-dominated weak power grids. Supported by coordinated PV–storage energy management, the proposed method offers a highly robust grid-forming framework for renewable-dominated weak power grids. Full article

To address the inherent inaccuracies of the classical beam theory (which overestimates the flexural stiffness) and the “quasi-plane section method” (which neglects the shear deformation) in the deflection analysis of steel truss web–concrete composite beams, this study homogenizes discrete steel truss web members into a continuous steel web with equivalent thickness based on the strain energy equivalence principle. This homogenization is conducted under the assumption of fixed-end constraints for web members, thus establishing a sandwich laminated beam model. Incorporating the assumptions of zigzag axial displacement and layer-wise quadratic parabolic transverse shear stress, this study adopts the governing equations for static bending of composite beams derived via Hamilton’s mixed energy variational principle—this theory eliminates the need for an artificial shear correction factor, as the transverse shear stress naturally satisfies the zero boundary conditions at the upper and lower surfaces and the continuity condition at the interlayers. Analytical solutions for bending deflection under uniformly distributed loads are derived and validated against three-dimensional (3D) finite element (FE) models. The analysis results of a 45-meter-span beam demonstrate that the relative error in the maximum deflection of both simply supported beams and cantilever beams calculated by the proposed method is approximately 5%, which is significantly superior to the classical beam theory; the deflection induced by the zigzag effect at the mid-span of simply supported beams accounts for 15% of the total deflection, making it an indispensable key component in structural design. This method enables accurate deflection prediction and provides reliable technical guidance for the preliminary design of steel truss web–concrete composite beam bridges. Full article

Background: Opioid dependence treated with buprenorphine/naloxone is associated with increased cardiovascular risk; however, data regarding aortic elasticity and cardiac electrophysiological balance during long-term maintenance therapy remain limited. This study investigated aortic stiffness and distensibility in individuals receiving buprenorphine/naloxone (Suboxone), and examined their associations with echocardiographic and electrocardiographic parameters, including the index of cardiac electrophysiological balance (iCEB and iCEBc). Methods: A retrospective cohort analysis was conducted, including 130 intravenous opioid users receiving Suboxone and 150 age- and sex-matched healthy controls. All participants underwent clinical evaluation, transthoracic echocardiography, resting 12-lead electrocardiography, and 24-h ambulatory blood pressure monitoring. Results: Compared to controls, opioid users demonstrated significantly higher aortic distensibility (median 0.019 vs. 0.015, p < 0.001) and lower aortic stiffness (median 52.31 vs. 64.66, p < 0.001). Patients receiving Suboxone for more than 18 months exhibited higher diastolic blood pressure (p = 0.044), mean arterial pressure (p = 0.046), and pulmonary artery pressure (p = 0.022). Aortic elasticity indices showed strong correlations with blood pressure and echocardiographic parameters. In the overall cohort, Suboxone use duration was not significantly correlated with aortic stiffness or distensibility parameters, while a weak negative correlation was observed with ferritin levels (r = −0.231, p = 0.008). In subgroup analysis of long-term users (>18 months), a moderate positive correlation was observed between therapy duration and iCEB values (r = 0.367, p = 0.001). Conclusions: Chronic buprenorphine/naloxone therapy appears to be associated with changes in aortic elasticity, blood pressure, and mild electrophysiological alterations. These results support the use of non-invasive vascular and electrocardiographic evaluations for cardiovascular risk monitoring and stratification among patients receiving opioid maintenance therapy. Full article

Beam-to-column connections govern both seismic performance and post-earthquake repairability of steel moment-resisting frames. Yet direct, apples-to-apples comparisons among welded, bolted, and repair-oriented replaceable-fuse moment connections are still scarce, which hinders rational selection for resilient construction. This study conducts a unified finite-element comparison of three representative joint archetypes—W-RBS, Bolted, and Prefab-web-fuse—under monotonic and cyclic loading. Consistent moment-rotation definitions are adopted, and normalized indices are introduced to compare hysteresis shape, degradation, and energy dissipation across joint concepts with different strength scales. Component-wise plastic dissipation is also extracted to quantify damage localization and assess main-frame protection and replaceability. Results reveal clear trade-offs: W-RBS provides the highest strength and dissipation but degrades most in stiffness; the bolted joint shows pinching due to interface compliance; and the web-fuse concept concentrates inelastic demand in a replaceable segment, supporting repairability-oriented design. The proposed framework offers mechanism-based guidance for selecting steel moment connections toward resilient and repairable frames. Full article

To address the detuning sensitivity of conventional linear vibration absorbers under wide-frequency harmonic excitation and the limited effectiveness of nonlinear energy sinks (NESs) in low-energy regimes, this study investigates a bistable nonlinear energy sink (BNES) based on a negative-stiffness support. A coupled model of the primary system and the BNES is established, and the analytical steady-state amplitude–frequency relationship of the system is derived using the harmonic balance method. The accuracy of the analytical solutions is verified through numerical integration. Based on the first Lyapunov method, the instability regions of the system are identified, and the effects of system parameters on the amplitude–frequency response of the primary structure are analyzed. On this basis, a comprehensive performance index that accounts for both peak suppression and average vibration reduction over the frequency band is constructed, and an improved particle swarm optimization algorithm is employed for parameter optimization. The results demonstrate that the optimized BNES can effectively suppress isolated high-amplitude response branches and significantly reduce the response of the primary system within the resonance frequency band, exhibiting superior broadband vibration mitigation performance and enhanced stability. Full article

To overcome the limitations of conventional steel support systems in large-span concrete dome construction, this study proposes a novel prestressed modular aluminum alloy formwork system based on a radial–circumferential spatial truss configuration. A refined finite element model was established to simulate the staged construction process under the most unfavorable load combination (1.3G + 1.5Q), and the influences of prestress levels and concrete pouring sequences were systematically investigated. Results indicate that external prestressing significantly enhances structural stiffness and deformation control. Increasing the prestress level from 0.3fptk to 0.5fptk reduces the maximum vertical displacement by approximately 18%, while a prestress of 0.7fptk achieves a total reduction of about 31%. Radial support displacement decreases by up to 48%, demonstrating improved global stability. Considering both deformation control and material utilization efficiency, 0.5fptk is recommended as the optimal prestress level. Comparative analysis of construction schemes shows that the layered pouring method reduces maximum vertical displacement by approximately 15% compared with ring casting. Buckling analyses further confirm adequate stability reserve beyond code-required safety coefficients. These findings verify the feasibility and deformation control effectiveness of the proposed prestressed aluminum alloy dome formwork system for large-span construction applications. Full article

Bolted joints are extensively used in a wide range of industrial and commercial structures, making their condition monitoring essential for ensuring structural integrity and operational safety. Under the influence of vibration, cyclic loading, and environmental factors, bolts may gradually lose preload, which can degrade joint stiffness and eventually lead to structural failure. To address this issue, this study presents a smart percussion system developed on a Raspberry Pi platform that integrates acoustic signal acquisition, real-time signal processing, and visualization of diagnostic results. A bolt looseness detection strategy combining audio feature extraction with unsupervised learning is proposed. In contrast to traditional percussion-based approaches that depend on supervised learning and predefined baseline datasets, the proposed method does not require prior reference data, significantly improving its adaptability and ease of deployment across different structures, which shows essential practical significance. Experimental investigations demonstrate the effectiveness and advantages of the proposed system, indicating its strong potential to enhance percussion-based bolt looseness detection and to support real-time structural health monitoring, which are real-world engineering applications. Full article

Various types of turbine engines have been chosen as the primary power source of the long-endurance unmanned aerial vehicles (UAVs) because of their high propulsive efficiency and low specific fuel consumption. To ensure the healthy operation of UAV turbine engines, rotor unbalance should be monitored and constrained to a preset limit. This paper proposes an efficient and physically interpretable method to achieve rotor unbalance monitoring. This method enables the frequency response function (FRF) to inform the neural network design, bringing the physics-informed convolutional neural network (PICNN). Firstly, the FRF gives a qualitative judgment of the axial positions of dominant faulty parts. Then, the following subnet proceeds to achieve quantitative identification. This method is demonstrated on a series of numerical cases and on a twin-disk rotor-bearing-casing experimental setup with anisotropic supporting stiffness. This setup is representative of engine installation status on the UAV platform. The results show that the PICNN can achieve higher precision compared to pure data-driven or model-based benchmarks. The PI layer does not require a high-fidelity model that generates responses identical to the actual ones. The robustness against modeling errors in stiffness and damping ratios is demonstrated. The achieved relative errors are less than 1.5% under various experimental datasets. Full article