Search Results (1,506)

In this paper, we investigate the existence and positivity of solutions for a class of twelfth-order nonlinear boundary value problems that naturally arise in the mathematical modeling of elastic and micro-mechanical systems. The considered model incorporates higher-order derivatives to account for nonlocal and gradient effects that commonly appear in the analysis of micro- and nano-scale elastic structures. By employing the Leray–Schauder nonlinear alternative and fixed point theorems, we establish sufficient conditions for the existence of at least one positive solution. The analysis relies on the explicit construction and properties of the associated Green’s function, which plays a fundamental role in deriving upper and lower bounds for the nonlinear term. The obtained results extend and generalize earlier works on sixth, eighth and tenth-order problems to the twelfth-order case. Finally, numerical examples are presented to illustrate the applicability and accuracy of the theoretical findings. The results provide a rigorous analytical foundation for the study of high-order elastic models and micro-scale structural stability. Full article

Arid regions are ecologically fragile and occupy a substantial portion of the global terrestrial surface. In these regions, ecosystem services (ESs) are strongly constrained by water availability and, more importantly, by the balance between water supply and demand. However, the nonlinear responses and threshold mechanisms linking water supply–demand balance to ES dynamics remain unclear. Taking the Kubuqi Desert in the “Great Bend” of the Yellow River as the study area, this study quantified the Comprehensive Ecosystem Service Index (CESI) and the Water Supply–Demand Ratio (WSDR) by integrating the InVEST model, RWEQ model, the RUSLE model, Water Balance Method, and so on. The dual-constraint line method and elasticity coefficient approach were integrated to identify the constraint effects and critical thresholds of WSDR on CESI. Ecological management zones were further delineated by integrating the inflection-point intervals of the dual-constraint lines with the threshold intervals identified by elasticity coefficients. The results showed that CESI remained relatively low, with a maximum value of approximately 0.5, suggesting that the overall ES level was still limited, but exhibited a continuous increasing trend. The regional water supply–demand pattern gradually shifted from deficit toward relative balance, although agricultural water use still accounted for about three-quarters of total consumption. CESI showed a nonlinear threshold response to WSDR: mild water deficit suppressed CESI growth, whereas moderate water surplus promoted CESI recovery by alleviating water constraints and improving ecosystem functioning. Thresholds identified by elasticity coefficients mainly occurred near critical transitions between water deficit and surplus. Based on ES supply and threshold sensitivity, nine ecological management zones were identified, with priority enhancement areas accounting for approximately 75%. These findings provide a threshold-based basis for ecological zoning and differentiated restoration in arid regions. Full article

Achieving precise docking, reliable locking and damage-free emergency unlocking under complex ocean current conditions remains a key challenge for deep-water multi-way quick connectors (MQCs). This study proposes a novel MQC prototype characterised by a tiered tolerance guidance mechanism, an innovative L-shaped spatial helical cam locking system, and a real-time visual attitude indicator. Using Ansys 2023 R2 and its tools, the safe operating limits were determined through explicit non-linear finite element collision analysis. The results demonstrate that, under a controlled docking speed of 10 mm/s, the hierarchical guidance mechanism successfully accommodated extreme initial misalignments (25 mm lateral offset, 5° horizontal rotation and 15° axial rotation), whilst keeping the peak collision stress within the elastic limit. Furthermore, the L-shaped locking guide was analysed using a fifth-order polynomial motion law and a macro-micro elastoplastic Hertzian contact mechanics model, effectively eliminating rigid-flexible impact forces. Under extreme separation loads of 10,000 psi, the maximum equivalent plastic strain at the base of the locking shaft was strictly controlled at 0.00926. This is well below the failure threshold of 0.0865 specified by ASME, providing a substantial safety margin and completely preventing local yielding. Crucially, the emergency release strategy based on precision locating pins was validated through full-scale prototype testing. Destructive tests conducted under simulated severe jamming conditions demonstrated clean, damage-free disengagement under shear torques ranging from 2100 Nm to 2200 Nm. This threshold ensures that accidental triggering will absolutely not occur during routine operations (1400 Nm) and establishes a safe underwater robotic (ROV) operating speed of ≤4 r/min. This study provides a robust theoretical framework and empirical data for the future design of yield-resistant subsea connectors and safe emergency recovery. Full article

Aquaculture development increasingly faces the dual requirement of increasing economic output and reducing environmental pressure under limited aquatic resources. Existing studies have examined aquaculture efficiency, environmental performance, and production optimization separately, but region-specific strategies that jointly address economic improvement and environmental-emission mitigation remain insufficiently developed. This study proposes a data-driven modeling and computational framework to identify regional green modes of fishery production, with dual properties of higher economic output and lower environmental-emission intensity. In this framework, data-analysis techniques, including missing-value imputation, regional aquaculture classification, nonlinear variable reconstruction, and Lasso regression, are integrated with scenario-based optimization models under alternative management priorities. By applying the proposed framework to provincial fishery data from China during 2017–2024, the results reveal clear heterogeneity in green fishery production modes across different aquatic-resource systems. In particular, under the economic-priority scenario with emission-reduction constraints, the optimized outputs increase by 11.19% and 6.54% in Zone 1 (an inland freshwater system) and Zone 2 (a coastal-intensive system), respectively. Under the environmental-priority scenario with required economic-growth condition, moderate emission-reduction potential is identified in Zone 1, whereas substantial emission reduction is observed in Zone 2. Furthermore, in view of the determined green fishery strategy by our framework, the nearest-optimum province is identified for each zone. By elasticity analysis, it is further found that technology-extension funding and fishery medicine expenditure are two synergistic production investments in Zones 1 and 2, whereas seedling and feed-related investments display properties of region-specific coordination. Summarily, the proposed computational framework in this paper provides an efficient tool of analyzing the regional green fishery production strategies and the regional heterogeneity in virtue of data-driven modeling and advanced optimization techniques. Full article

Electric vehicle (EV) charging behaviors exhibit significant heterogeneity in terms of price sensitivity, time-of-day preference, and weekend charging habits, creating challenges for charging demand prediction and service management. To address this issue, this paper proposes a three-variable charging response framework that jointly considers electricity price, time-of-day preference, and weekend preference. Using real charging-order data from a public charging platform, four behavioral parameters, namely baseline charging demand (Q₀), price sensitivity (α), time preference (β), and weekend preference (γ), are estimated through nonlinear least squares (NLS). Based on the extracted parameter vectors, K-means clustering is employed to identify five representative user groups: Commuting-Dominant, elastic energy-saving, Weekend-Switching, Night-Preferential, and discount-sensitive users. The results reveal substantial behavioral heterogeneity among users. To validate the proposed framework, both parameter interpretability analysis and benchmark comparisons are conducted. Compared with the best baseline model, the proposed method reduces the test RMSE from 11.5 kWh to 8.3 kWh (27.8%), decreases the test MAPE from 25.3% to 18.7% (26.1%), and improves the test R² from 0.70 to 0.80. The proposed framework provides an interpretable approach for EV charging behavior modeling and user segmentation, offering practical support for differentiated pricing, charging demand management, and intelligent charging service operation. Full article

High intake tower structures exhibit significant time-varying characteristics in their seismic performance during service life due to environmental erosion and material deterioration. This paper establishes a time-varying seismic fragility analysis framework for intake towers over their full life cycle based on the incremental dynamic analysis (IDA) method. By introducing time parameters, time-varying probabilistic seismic demand models based on displacement and local damage indices are constructed, and five performance levels are defined. The research results indicate that with increasing service life, the probability of the structure reaching critical performance levels exhibits a nonlinear growth. After 40 years of service, material strength and elastic modulus begin to decline significantly, with evident degradation of seismic performance. At a seismic acceleration of 0.8 g, the probability of the 60-year-service structure reaching the slight damage limit state (LS₁) has reached 99%, while the probability of reaching the collapse limit state (LS₄) exceeds 25%. The local damage index results demonstrate that under the same seismic intensity, the exceedance probability of tower-side damage exceeding LS₁ for the 60-year-service structure has increased by approximately 10% compared to that of the new structure (0-year service). Therefore, in the seismic design and retrofitting decision-making for intake towers, the time-varying characteristics over the entire service life must be fully considered. Particularly when the service life exceeds 40 years, seismic fortification standards should be appropriately enhanced or targeted strengthening strategies should be developed based on time-dependent fragility curves, so as to avoid underestimating long-term seismic risks. This study provides a quantifiable scientific basis for whole-life safety assessment and resilience enhancement of high-rise intake towers. Full article

Background: Flattening of the medial longitudinal arch is traditionally attributed to excess body weight and Body Mass Index (BMI). However, controversy exists regarding whether adiposity or skeletal structure drives this biomechanical alteration, and which podometric index best detects it. Methods: A cross-sectional study evaluated 99 healthy university students (50 males, 49 females). Body composition was assessed via a four-component model. Plantar footprints were captured using 4K digital podoscopy and analyzed with five morphometric indices. Arch predictors were identified using multivariate regression models (Elastic Net regression) and Generalized Additive Models (GAMs). Results: Only Clarke’s Angle detected significant sexual dimorphism, showing structurally higher arches in females (50.28° ± 7.14) than in males (41.82° ± 11.20; p < 0.001). Multivariate analysis revealed bone mass as the dominant structural predictor, exerting a non-linear negative association with the arch profile, which stabilizes beyond 12 kg. BMI was not a significant predictor, whereas body fat percentage showed a modest positive association. Conclusions: Plantar arch morphology is strongly associated with skeletal load (anthropometrically estimated bone mass) rather than adiposity or BMI. Within this specific cohort, Clarke’s Angle emerged as a highly sensitive instrument for characterizing sexual dimorphism. Clinical assessments diagnosing functional flatfoot should prioritize underlying bone structure over BMI, particularly when evaluating a healthy and physically active university population. Future studies incorporating DXA or radiographic validation are needed to confirm these anthropometric findings. Full article

Historic masonry towers are iconic components of the world’s architectural heritage, yet their seismic vulnerability remains to be investigated, particularly regarding the influence of vertical ground motion. This study investigates the seismic response of the Roncole bell tower, a 35 m high slender masonry structure located in Emilia-Romagna, Italy, that experienced severe damage during the 2012 Emilia earthquake sequence, presumably related to the second shock of 29 May, the epicenter of which was within approximately 5 km of the tower. In the absence of direct site recordings, a simplified seismic scenario was reconstructed using accelerograms from two nearby stations and interpolation procedures based on logarithmic attenuation relationships. Nonlinear finite element analyses were performed in Abaqus using a detailed three-dimensional model comprising approximately 263,000 tetrahedral elements and a Concrete Damage Plasticity constitutive law for masonry. Four elastic moduli of the material and multiple seismic input scenarios were considered, with and without inclusion of the vertical seismic component. Modal analysis showed that the tower response is governed by the first two dominant horizontal bending modes and one significant vertical mode involving a high percentage of participating mass. Results indicate that while horizontal excitation controls global sway behavior, the vertical component strongly amplifies axial force fluctuations and vertical displacements located close the tower base and rules the bending capacity of the tower. Nonlinear time-history analyses also revealed residual drifts close to collapse thresholds drifts under most of the scenarios considered. Simulated crack patterns closely matched the actual earthquake damage, at the base of the tower, window openings, and the façade in the tilting side. The study demonstrates that three-component seismic analyses are essential for reliable assessment of historic slender masonry towers subjected to near-source earthquakes. Full article

This study investigates in situ hydrogel formation and its regulating effect on multiscale damage evolution in red sandstone subjected to chemical–wet–dry cycles. Uniaxial compression, X-ray diffraction, scanning electron microscopy coupled with energy-dispersive spectroscopy, mercury intrusion porosimetry, and inductively coupled plasma mass spectrometry tests were performed to characterize mechanical degradation, mineral alteration, pore-network evolution, ion migration, and gel micromorphology. By combining multiscale experimental characterization with a segmented statistical damage constitutive model, this study describes the hydrogel-mediated damage evolution of red sandstone under chemical–wet–dry cycles. The mechanical properties of red sandstone show nonlinear degradation, with a deterioration order of acidic > alkaline > neutral, and this effect intensifies with increasing cycle number. After 15 cycles at pH = 3, the compressive strength and elastic modulus decreased by 38.21% and 27.12%, respectively. Both acidic and alkaline environments promoted pore development in red sandstone. After 15 cycles at pH = 3, the porosity increased from 21.51% to 24.51%, and the most probable pore diameter shifted from 21.32 μm to 25.88 μm. The porosity increased by 2.86% at pH = 11, and in situ hydrogels formed under alkaline conditions partially filled pores and inhibited crack propagation. The developed model effectively reproduced the mechanical evolution of red sandstone, with all fitted results showing R² values no lower than 0.92. These findings provide a basis for evaluating hydrogel-regulated damage in red sandstone and support the application of in situ gel materials in geotechnical engineering. Full article

Foreign direct investment (FDI) is widely promoted as a driver of economic output through mechanisms such as technology transfer, capital accumulation, and productivity spillovers. However, the empirical literature shows highly inconsistent results known as the “FDI-output puzzle.” We argue that these inconsistencies arise because the output-level effects of FDI are non-linear and depend crucially on the host country’s absorptive capacity. By analyzing a global panel of 172 sovereign nations from 2000 to 2022, we demonstrate that FDI’s output impact depends on a country’s financial development and institutional quality. Our baseline fixed effects models yield a positive and significant within-country FDI-output elasticity of 0.019–0.047. Furthermore, interaction models reveal that deeper financial markets and stronger legal institutions amplify FDI’s effect on real GDP levels. Two-stage least squares estimation confirms these relationships are not due to reverse causality. Following I employ a levels specification—regressing the natural logarithm of real GDP on the natural logarithm of FDI—that directly estimates output-level elasticities, capturing the steady-state relationship between FDI and the level of economic output. This dual-specification design is complemented by dynamic panel GMM estimation, which confirms the positive FDI–output relationship in a dynamic setting. Our findings show that attracting FDI alone is insufficient for expanding output; countries must also develop robust financial infrastructure and effective governance to fully benefit from foreign capital. Full article

The present study deals with the nonlinear forced vibration of an axially functionally graded beam subjected to an electromagnetic actuator, moving load, and Casimir force, considering the curvature of the beam and it resting on a nonlinear elastic Winkler–Pasternak foundation. The presence of an electromagnetic actuator and Casimir force besides the presence of mechanical impact (moving load) and nonlinear elastic foundation is a characteristic of a real system, but this has not been studied in this form until now, currently representing a remaining gap. The governing differential equations of motion in the considered system are based on Euler–Bernoulli beam theory and von Kármán geometric nonlinearity. The material properties are expressed according to a power law function through the thickness direction. We point out that the present study is the first to consider the curvature in combination with electromagnetic actuation, Casimir force, an elastic foundation, and moving load. Unlike in other works, axial inertia is not assumed to be negligible in our investigation. The Optimal Homotopy Asymptotic Method is employed to obtain an approximate analytical expression for the nonlinear dynamic response and the nonlinear frequency. The solutions obtained are very accurate in comparison with numerical solutions, and our procedure is simple and easy to implement for nonlinear problems. The local stability near the primary resonance and internal resonance is analyzed by means of the variable expansion method, the homotopy perturbation method, equilibrium points, the Jacobian matrix, and the Routh–Hurwitz criterion. Full article

Slabbing failure of roadway-side backfill bodies critically threatens gob-side entry retaining stability. This study establishes an elastic thin-plate model with edge cracks, employing an innovative load transformation to reduce the three-dimensional in situ stress state to the combined action of roof–floor uniform load and equivalent axial bending moment. Based on fracture mechanics and elastic-plastic theory, the stress intensity factor $K_1$ and crack initiation load q are derived in closed form. Results show that q is positively correlated with plate thickness t and bending moment M and negatively with crack length a in the dominant range. Applying the nonlinear Hoek–Brown criterion, the failure zone width ${\mathrm{r}}_{\mathrm{p}}$ at the crack tip is shown to exhibit an approximately exponential relationship with $K_1$ for unbolted backfill. Introduction of tensioned bolts via a stress concentration factor $\mathsf{\eta }$ transforms the failure zone growth from exponential to asymptotic saturation, quantitatively confirming the crack-arresting effect. A sensitivity analysis identifies plate thickness as the dominant parameter. The model bridges the gap between initial slabbing and progressive V-shaped notch formation. Full article

This paper estimates an extended Cobb–Douglas production function for five major economies (China, the EU, India, the Russian Federation, and the USA) over the period of 1990–2023, incorporating electricity production from renewable, non-renewable, and nuclear sources as discrete production inputs. To capture complex properties in time series, a comprehensive econometric strategy is adopted, which combines linearity tests, multiple detection of structural changes, linear and nonlinear unit root tests, autoregressive distributed lag (ARDL) bounds testing for cointegration, error correction modelling, and error correction model (ECM)-based Granger causality. The results confirm the presence of mixed orders of integration, nonlinear dynamics, and structural instability across countries, justifying the use of the ARDL framework. The bounds test reveals a long-run cointegrating relationship between output, capital, labour, and energy inputs in all five economies. Long-run elasticities differ significantly across countries, highlighting strong structural heterogeneity. The short-term dynamics show that energy shocks have asymmetric and country-specific effects on output, while the error correction terms confirm convergence towards the long-run equilibrium, with the fastest adjustment observed in the EU and the slowest in the US. The causality results support the hypothesis of growth-led energy in China, India and the Russian Federation, while two-way feedback is observed in the EU and the US. These findings suggest that energy policy cannot be uniform across countries and must be aligned with domestic production structures, technological intensity, and energy transition stages. Full article

This study focuses on RCS frame structures and selects six different types of ground-motion intensity measures (IMs), including peak ground acceleration (PGA), spectral acceleration at the fundamental period Sa(T₁), the modified intensity measure S^* considering period elongation effects, IM₁₂ and IM₁₂₃ accounting for higher-mode effects, and Housner intensity (HI). Based on a set of near-fault pulse-like ground-motion records, a Bayesian seismic fragility analysis characterized by different IMs is conducted. This study reveals the influence of these IMs on the estimation of fragility parameters under three limit states—immediate occupancy (IO), life safety (LS), and collapse prevention (CP)—using both uniform non-informative priors and lognormal weakly informative priors. The results indicate that, in terms of the applicability of IMs across different limit states, all IMs exhibit highly stable fragility parameters in the elastic IO stage, where the results from maximum likelihood estimation (MLE), uniform priors, and lognormal priors are nearly identical, suggesting that sufficient sample information renders the influence of priors negligible. In contrast, in the CP stage, characterized by strong nonlinearity and collapse, the differences among IMs become most pronounced. HI consistently yields stable results across all methods with almost no variation. When the structure enters the CP stage with small samples and strong nonlinearity, the lognormal prior effectively promotes distribution convergence, suppresses over-dispersion, and corrects asymmetry, significantly improving the robustness of parameter estimation. Notably, different IMs exhibit varying sensitivity to Bayesian priors, among which S^* and HI are the least sensitive, demonstrating strong inherent stability and minimal dependence on prior constraints. Full article

Fractional derivatives introduce an effective mathematical structure to describe memory effects, long-range interactions, and anomalous transport processes that are not well represented by the traditional integer-order models. This paper presents the unidirectional fractional longitudinal wave equation as a governing equation where a model is proposed to explain the steady wave propagation of solitary waves in a magneto-electro-elastic circular rod. Magneto-electro-elastic substances are a groundbreaking category of advanced functional materials with tremendous nanotechnology and biomedical engineering prospects because of their effective multi-field energy conversion and temperature responsiveness. In order to solve this complicated fractional nonlinear equation, we introduce a new computation-analysis approach: the Riccati subequation neural network method. This hybrid solution is a synergistic combination of an analytical solution structure and a neural network structure consisting of input, hidden, and output layers, with interconnection between neurons through weighted connections and activation functions. It is important to note that every neuron in the first hidden layer is coupled to the solutions of the Riccati equation, and this allows the systematic use of the new trial functions. With the suggested method, analytical solutions are obtained for the spacetime fractional partial differential equations of the unidirectional fractional longitudinal wave equation in the exact form of trigonometric, hyperbolic, and rational functions. This paper is the first attempt to combine the Riccati subequation method with a neural network model, which has given rise to new types of solitary wave solutions. The three-dimensional, two-dimensional, and contour plots are used to visualize the dynamic nature of these solutions and to display the rich nonlinear wave behavior. The effectiveness and the robustness of the implemented technique is not only proven through our findings but also provides more profound information about the nonlinear wave phenomena in the advanced multifunctional materials, which can inform future developments in energy harvesting and the design of biomedical devices. Full article