Search Results (579)

This study focuses on a novel three-span hybrid continuous beam bridge, analyzing the force performance and key design parameters of the non-cellular post-support plate joint. A finite element model and parametric analysis were used to reveal the stress distribution patterns, the load-bearing characteristics of the connectors, and the load transfer path under negative bending moments. The study shows that the axial force within the joint is equitably shared among three load paths: the top slab concrete (20.7%), the bearing plate (40.1%), and the shear connectors (39.2%). Although interfacial friction contributes approximately 27.1% to the total shear resistance, it is conservatively recommended to neglect this effect in design due to inherent uncertainties. Parametric analysis reveals distinct marginal effects and efficiency thresholds: increasing the bearing plate thickness from 20 mm to 100 mm results in a mere 1.0 MPa reduction in the peak concrete stress, while extending the joint length beyond 1.0 times the beam height renders the central connectors ineffective. Furthermore, reducing the connector stiffness effectively lowers the non-uniformity coefficient from 2.3 to below 2.0. Notably, the first row of web PBLs carries 34.8% to 47.2% of the total shear force, with a stable non-uniformity coefficient of 1.05–1.06, establishing it as the critical control section for simplified design. These findings provide a theoretical basis and practical guidance for the design of similar joints in hybrid girder bridges. Full article

The pronounced heterogeneity of tight sandstone reservoirs in the Sulige Gas Field poses significant challenges to the uniform propagation of multi-cluster hydraulic fractures during horizontal well staged fracturing, often leading to uneven stimulation and compromised productivity. To address this issue, a coupled fluid–solid fracture propagation model based on the displacement discontinuity method (DDM) was developed, incorporating dynamic fluid distribution, rock deformation, and temporary plugging mechanisms. The model was validated against microseismic monitoring data from the Sulige field and subsequently employed to investigate the effects of reservoir heterogeneity—including porosity, permeability, and in situ stress—on multi-cluster fracture growth. Results indicate that permeability and stress heterogeneity exert the most significant influence on fracture non-uniformity, as reflected by increased coefficients of variation in fracture length. Engineering measures such as the use of high-viscosity guar gum fracturing fluids, variable perforation strategies (e.g., 6, 10, and 16 holes per cluster), and optimized temporary plugging parameters (timing of 0.5 with 12 balls) were shown to effectively mitigate these effects and promote more balanced fracture propagation. This study provides a quantitative framework for optimizing fracturing design in heterogeneous tight gas reservoirs and offers practical guidance for enhancing stimulation uniformity and gas recovery efficiency in the Sulige Gas Field. Full article

Wireless power transfer (WPT) is increasingly used in smart manufacturing, unmanned platforms, and contactless power-supply applications. However, weak coupling, load-dependent impedance drift, and spatial misalignment can shift the resonant condition, leading to unstable output voltage and reduced transfer efficiency. This paper proposes a constant-voltage WPT method that combines a non-uniform winding coupler, parasitic coils, and dynamic capacitor compensation. A composite magnetic coupler with dense outer windings, loose inner windings, and parasitic coils is first developed, and a region-based electromagnetic model is established to characterise self-inductance, mutual inductance, and coupling coefficients. An improved LCC-S compensation network with a dynamic capacitor compensation matrix is then derived to keep the system close to resonant operation at the nominal 85 kHz operating point under load variation and coil-displacement-induced coupling changes. A zero-voltage-switching-angle tracking method with mutual-inductance correction is further introduced to compensate for phase deviation and maintain soft-switching operation through limited switching-frequency adjustment. Experimental validation demonstrates that the system maintains a stable constant-voltage output across a load range of 20–50 Ω and under 5 cm lateral and longitudinal offsets. The measured efficiency remains above 89% and reaches 93.7% under the optimal coupling and load-matching condition. Full article

Friction at the cold rolling interface is affected jointly by the surface roughness, lubrication state, local pressure, and relative sliding. A constant friction coefficient is therefore insufficient to describe its non-uniform distribution along the contact arc. Accordingly, this study proposes a macro–micro two-scale mixed-lubrication and dynamic friction model based on the measured roll roughness. First, the measured roll roughness profile was represented within a finite effective scale interval by a scaled and truncated Weierstrass–Mandelbrot (W–M) function. The parameters D and G were obtained as finite-scale W–M roughness parameters and were introduced into a mixed-lubrication load-sharing model to calculate the local mixed-lubrication friction coefficient. The pressure distribution along the contact arc was calculated using the Karman equation, and the local macroscopic pressure was mapped to a representative microscopic contact load. Finally, the mixed-lubrication friction coefficient was used to calibrate the dynamic friction factor separately in the forward-slip and backward-slip zones, and the friction stress distribution along the contact arc was calculated. For the selected effective scale interval and preprocessing procedure, the fitted W–M roughness parameters were D = 1.528 and G = 9.15 × 10⁻⁸ m. The W–M parameter D had a more significant influence on the mixed-lubrication friction coefficient and load-sharing behavior than the scale parameter G. Increasing the rolling speed strengthened the oil-film load-carrying effect and reduced the equivalent interfacial friction coefficient. The friction stress was positive in the backward-slip zone and negative in the forward-slip zone, with a direction reversal near the neutral point. Field forward-slip inversion showed that both the simulated and measured equivalent friction coefficients decreased with increasing rolling speed, with a difference of approximately 0.009~0.017. The proposed model can capture the main trend of cold rolling interfacial friction with variations in the rolling speed and contact state. Full article

The tower with an attached vent stack is a special arrangement in chemical tower structures. Flow-induced vibration of this configuration directly affects the safe operation and structural fatigue life of the equipment. This paper investigates the vortex-induced vibration (VIV) characteristics of a two-cylinder system consisting of a tower and its attached vent stack. Through fluid–structure interaction (FSI) simulations of two unequally sized cylinders in a bundled arrangement, the vibration responses under first and second-mode critical wind speeds with a flow direction of 0° are analyzed. The analysis examines lift and drag coefficients, vibration displacements, and wake flow evolution to reveal the vibration response pattern under multi-parameter coupling. When the lift forces obtained from FSI are applied in a static calculation, the static results for both the first and second-mode critical wind speeds are approximately 250% larger than the FSI results, indicating a significant discrepancy. Further analysis shows that in the FSI simulations, a notable phase difference exists between the fluid excitation and the structural response, causing the lift force to do negative work during part of the vibration cycle, thereby limiting the net energy input. Under the second-mode critical wind speed, the lift distribution along the tower height is significantly non-uniform. The conventional static calculation method neglects both the phase difference and the non-uniform lift distribution along the height, leading to overly conservative predictions. Full article

Wastewater containing such inorganic contaminants, especially phosphate and nitrate ions, has to be treated thoroughly before disposal into natural environments. This is a precautionary measure to avoid adverse effects on public health, which are exacerbated when these two pollutants are present in an aqueous system. The present research investigated how the adsorption process is influenced by factors such as the effect of ion composition, contact time, temperature and competitive adsorption behavior in multi-anion systems using Ternary Biopolymer–Bentonite Beads. This study used five isotherms and four kinetic models to investigate phosphate ions removal on prepared natural Clay-Bio-polymer composite beads. The results indicate that the pseudo-second-order (PSO) kinetic model provides the most accurate description of the adsorption process. Moreover, the correlation coefficients (R²) obtained for both the Langmuir and Freundlich isotherm models are nearly equal to 1, confirming their strong reliability in fitting the experimental data. The strong fit of both the Langmuir and Freundlich models indicates that the adsorption process exhibits mixed behavior, with both monolayer adsorption on relatively homogeneous sites and multilayer adsorption on heterogeneous sites. This mixed-behavior system is typical of composite adsorbents with diverse surface properties. The Redlich-Peterson model, a hybrid of Langmuir and Freundlich, showed the best overall correlation (R² = 0.990 for H₂PO₄⁻ and 0.998 for NO₃⁻). The applicability of the Sips and Toth isotherm models, which account for both uniform and non-uniform adsorption behaviors, validated the experimental results. In the competitive binary system, the maximum adsorption capacities achieved by the composite were 121.844 mg/g for H₂PO₄⁻ and 27.979 mg/g for NO₃⁻. The results indicate strong competition between H₂PO₄⁻ and NO₃⁻ ions for the available active sites, reflecting an antagonistic adsorption. A positive value of ∆H° verifies that the adsorption process is endothermic and primarily physical, consistent with the experimental observations. The negative ∆G° values demonstrate that the adsorption occurs spontaneously, whereas the positive ∆S° indicates an increase in randomness at the solid–liquid interface during the uptake of phosphate ions. Full article

This study uses a comprehensive simulation to investigate the performance of bootstrap confidence intervals for the Pearson correlation coefficient and Xi correlation coefficient (XICOR). Different distributional settings (normal, lognormal, uniform, and $t\left(3\right)$), sample sizes ($n = 10, 30, 100, 1000$), and Gaussian copula dependence levels (${\rho }_0$ = 0.1, 0.3, 0.5, 0.8) were considered. For each scenario, the true population Pearson and XICOR values were separately estimated via a large-sample Monte Carlo reference. The coverage probability (CP), mean confidence interval width (MCIW) and absolute bias detection (BD) were used to evaluate the percentile, bias-corrected and accelerated (BCa) bootstrap methods. The results showed that bootstrap confidence intervals based on the Pearson correlation coefficient generally achieve coverage probabilities close to the nominal level across most scenarios, with some degradation observed under heavy-tailed distributions at large sample sizes. By contrast, confidence intervals based on XICOR showed a significant and systematic undercoverage problem across most sample sizes, especially for n ≥ 30, which worsened as sample size increased. Although XICOR tends to produce narrower intervals, these intervals were associated with low coverage and increased variability, indicating a false precision. The BCa method did not meaningfully improve XICOR’s coverage performance. In conclusion, reducing bias alone is insufficient for reliable inference when dealing with non-smooth dependence measures. Classical bootstrap methods may be inappropriate for XICOR since they do not provide accurate quantification of uncertainty. Full article

Understanding the structural characteristics of Pinus taiwanensis plantations in climatically transitional regions is essential for developing science-based management strategies under global change. This study investigated 23 plots in Huangbai Mountain Forest Farm, Henan Province, China, classified into low-, medium-, and high-density stands (n = 9, 9, and 5, respectively). Diameter distributions were fitted using six probability functions, and four spatial structure parameters—mixing degree (Mc), size ratio (U), uniform angle index (W), and forest layer index (S)—were quantified. In addition, five comprehensive spatial structure indices—average superiority coefficient index (SPV), spatial structure comprehensive index (Q), stand spatial structure distance index (FSI), Comprehensive Distance Evaluation (CDEV), and Comprehensive Assessment of Proximity Vector (CAPV)—were constructed using a combined analytic hierarchy process and entropy weight method. Given the unbalanced sample sizes, non-parametric Kruskal–Wallis tests were employed for comparisons, and bootstrap resampling (1000 iterations) was performed to assess the reliability of mean estimates. The results showed that both the Gamma and Weibull distributions were equally suitable for describing diameter distribution under different stand densities, as their AIC differences were below 2 for all density classes. Correlation analysis indicated that the relative importance of spatial parameters followed the order S > U > Mc > W. Medium-density stands exhibited the most optimal spatial structure, whereas low-density stands showed the poorest performance. These findings suggest that both overly dense and sparse stands negatively affect spatial organization. Appropriate management practices, such as thinning or enrichment planting, are recommended to optimize stand structure and enhance ecological resilience. Full article

Stream sediment geochemistry is a widely used reconnaissance tool in early-stage mineral exploration, particularly in regions where direct evidence of mineralisation is limited. Because stream sediment anomalies provide indirect geochemical signatures and are typically constrained by limited ground-truth information, labelled datasets are often scarce and spatially biased. This limitation restricts the applicability of supervised learning approaches and highlights the need for robust unsupervised methods. In this study, six unsupervised techniques, Principal Component Analysis (PCA), Non-negative Matrix Factorisation (NMF), Uniform Manifold Approximation and Projection (UMAP), Autoencoder (AE), Deep Embedded Clustering (DEC), and an Averaged Ensemble Index (AVE), were evaluated for integrating multivariate stream sediment geochemical data and delineating gold prospectivity zones. Eight gold-related elements (Au, As, Ag, B, Hg, Mo, Sb, and W) were selected based on regional metallogenic characteristics and previously reported geochemical associations. To facilitate direct comparison, all model outputs were normalised to a fuzzy membership scale ranging from 0 to 1. Model performance was quantitatively assessed using Receiver Operating Characteristic–Area Under the Curve (ROC–AUC) and Matthews Correlation Coefficient (MCC) metrics based on independently verified mineralised and non-mineralised locations. The results indicated that DEC and AE consistently outperformed the other methods investigated, achieving the highest ROC–AUC and MCC values, whereas UMAP exhibited comparatively weaker performance. The findings demonstrated that unsupervised representation learning approaches, particularly DEC and AE, provided a more effective framework for integrating multivariate geochemical data and delineating gold-related anomalies in data-limited exploration environments than conventional dimensionality reduction and heuristic integration methods. Full article

Post-rotation jacking is a critical construction stage for load-path reconstruction and alignment adjustment in rotation-constructed bridges, particularly for ultra-wide double-deck composite girder systems. Taking a two-span continuous steel truss–concrete composite girder bridge with spans of 2 × 85 m as the engineering background, this study investigates the mechanical behavior during post-rotation jacking through theoretical derivation, finite element simulation, and on-site monitoring. Based on the force method of structural mechanics, a linear relationship between vertical synchronous jacking force and displacement is derived, and an analytical formulation for bearing reaction redistribution under laterally asynchronous jacking is established by considering the coupling effects of vertical bending, torsion, and transverse multi-bearing support. A full-bridge spatial finite element model was developed in MIDAS Civil NX 2024 V1.1 to analyze the redistribution of bearing reactions and the stress response of the concrete crossbeam under different jacking conditions. The results show that, for the investigated bridge, the jacking force–displacement response remains highly linear during synchronous jacking. The B-axis middle bearing is more sensitive to jacking displacement than the two side bearings, with its fitted stiffness being approximately 2.19 times the average stiffness of the side bearings. Eccentric jacking causes reaction concentration at the jacked point and reaction reduction at adjacent supports, and the magnitude of reaction variation increases approximately linearly with jacking displacement. When the transverse non-uniform jacking magnitude reaches 20 mm, a tensile stress of 0.3 MPa appears at the bottom flange of the concrete crossbeam; therefore, a project-specific stroke-difference limit of 20 mm is recommended for this bridge, while the actual construction achieved a stroke control accuracy of ±0.5 mm and a transverse elevation difference within 1 mm. Field monitoring results validate the proposed analytical and numerical methods. The Pearson correlation coefficients of the measured jacking forces with the finite element and theoretical results are 0.9987 and 0.9988, respectively, and the corresponding mean relative errors are 3.84% and 4.23%. For stress responses, the measured and calculated values show a strong correlation, with a Pearson correlation coefficient of 0.9980 and a mean relative error of 12.77%; the critical mid-span monitoring point shows a relative error of only 0.65%. The final bridge alignment deviation is controlled within ±3 cm. The overall mean verification coefficient is 0.968, with a 95% empirical agreement range of [0.888, 1.048], indicating that the proposed mechanical analysis framework and combined force–displacement control strategy can provide a useful reference for refined construction control of similar ultra-wide double-deck composite girder bridges with comparable span arrangement and transverse bearing layout. Full article

Objectives: This study evaluated the utility of adaptive complex signal average (ACSA) diffusion-weighted imaging (DWI) specifically in breath-hold (BH) liver imaging, with a focus on signal intensity (SI) improvement, intrahepatic signal homogeneity, and apparent diffusion coefficient (ADC) behavior, and compared these findings with conventional non-ACSA DWI and free-breathing (FB) ACSA DWI. Methods: This retrospective study included 62 patients (mean age, 67.8 ± 13.6 years; 27 women) who underwent liver MRI with both FB and BH DWI on a 3-T system. Non-ACSA images were generated using conventional magnitude reconstruction, and ACSA images were reconstructed from identical raw data. SI, signal-to-noise ratio (SNR) and ADC were measured in the left lateral segment and right hepatic lobe. The signal intensity difference ratio (SIDR) between ACSA and non-ACSA, signal intensity ratio (SIR) and ADC ratio between right lobe and lateral segment were calculated. Results: In both FB and BH imaging, SI and SNR in both liver regions were significantly higher on ACSA DWI than on non-ACSA DWI (p < 0.01). ADC values were significantly lower with ACSA. SIDR was significantly higher in the left lateral segment (p < 0.01), indicating greater SI improvement in motion-prone regions. SIR and ADC ratios between lobes were significantly smaller with ACSA in both respiratory conditions (p < 0.01). FB-ACSA showed smaller SIR than BH-ACSA, while ADC ratios did not differ. Conclusions: ACSA DWI significantly improves SI, intrahepatic uniformity, and ADC reliability even under BH liver imaging. BH ACSA DWI may represent a potentially useful application complementary to FB ACSA DWI, supporting its consideration as a post-processing strategy for improving qualitative and quantitative liver DWI in future investigations. Full article

Airflow is widely used in grain cleaning and sorting processes to separate grains according to their aerodynamic properties. However, separation efficiency depends on airflow parameters and grain physical characteristics. The aim of this study was to evaluate the movement and sorting of wheat grains under different airflow conditions and to compare the effects of vertical and horizontal airflows on grain separation efficiency. A theoretical analysis was conducted to investigate grain motion in laminar and turbulent airflows by determining grain displacement and displacement differences. Theoretical calculations were used to predict the displacement behavior and separation potential of grains with different critical velocities under various airflow conditions. To evaluate these predictions, laboratory experiments were conducted in a horizontal airflow sorting chamber at grain feed rates of 1 and 2 kg min⁻¹. The experimentally observed grain distributions were then compared with the theoretical predictions, allowing comparison between predicted and experimentally observed grain movement patterns. The average critical velocity of wheat grains was found to be 10.35 m s⁻¹ at 14.2% moisture content, while the floating coefficient was approximately 0.092. The theoretical analysis showed that displacement differences between grains with different aerodynamic properties ranged from 0.103 to 0.185 m within 1 s, depending on airflow conditions. Experimental results revealed a non-uniform distribution of grains within the sorting chamber, with the majority of grains collected in the first boxes. Increasing the grain feed rate reduced separation efficiency to approximately 55%, indicating a significant influence of grain flow intensity on the separation process. The results demonstrate that efficient grain sorting requires the optimization of both airflow parameters and grain feeding conditions. The findings of this study may contribute to the design and improvement of grain cleaning and sorting equipment. Full article

Clamp band separation mechanisms are widely used in spacecraft interfaces, and the clamp band preload is a key factor governing both connection reliability and separation performance. The conventional torque-control method is susceptible to friction-induced preload non-uniformity in clamp band separation mechanisms. To overcome this limitation, thermal preloading has been proposed as an alternative installation method. In this paper, a thermo-mechanical analytical model is established for clamp band separation mechanisms during thermal preloading based on curved-beam and thin-shell theories. Theoretical analysis shows that the preload distribution can be divided into three characteristic zones: a stick zone, a slip zone, and a separation zone. In the stick zone, the preload remains constant and is mainly governed by thermal stress and structural relative stiffness. In the slip zone, friction dominates the load transfer, leading to a non-uniform preload distribution. In the separation zone, local disengagement occurs near the clamp band joint end due to the eccentricity-induced bending moment. The proposed model is validated by finite element simulations, and parametric studies are conducted to reveal the effects of friction coefficient and structural geometric parameters on preload distribution. Based on the theoretical model, a zoned-heating method is proposed to improve preload uniformity, providing a useful reference for optimizing the thermal preloading method. Full article

Extreme cyclic temperature fluctuations (−200 °C to 200 °C) and inherent clearance nonlinearity in deployment hinges severely threaten the on-orbit deployment accuracy and dynamic stability of large variable-geometry spacecraft antennas for geosynchronous Earth orbit applications. However, current modeling approaches suffer from three critical limitations: single-configuration models requiring manual switching, there are inherent geometric nonlinear errors from conventional floating frame formulations, and incomplete thermo-mechanical coupling neglects the temperature effects on contact stiffness and friction. To address these gaps, we propose a unified high-fidelity dynamic model based on the Absolute Nodal Coordinate Formulation (ANCF). This model eliminates geometric errors and mesh mismatch, enables seamless multi-configuration deployment without switching, and fully incorporates temperature-dependent material properties and nonlinear contact forces. An improved Hilber–Hughes–Taylor-$\alpha$ implicit integration algorithm with second-order accuracy and unconditional stability is adopted to solve the strongly nonlinear differential-algebraic equations. Numerical results demonstrate that the proposed model achieves a calculation error below 3% against experimental data, significantly outperforming the traditional floating frame of reference formulation with an error of 15–22%. Non-uniform temperature fields increase thermally induced vibration amplitudes by 32–45%, and every 0.1 increase in the friction coefficient raises the impact force at the clearance hinge by 15–20%. The proposed unified modeling framework provides a solid theoretical basis for deployment stability prediction and the on-orbit control optimization of large variable-geometry spacecraft antennas. Full article

The inverse problem under consideration concerns a one-dimensional parabolic equation whose thermal diffusivity takes the quadratic-in-space form $a_s\left(\tau \right){\kappa }^2+b_s\left(\tau \right)\kappa +c_s\left(\tau \right)$. The unknowns are three time-dependent coefficients $a_s\left(\tau \right),b_s\left(\tau \right),c_s\left(\tau \right)$ together with the temperature field $T(\kappa ,\tau )$. The direct problem supplies initial data, Neumann boundary conditions, and three over-determination conditions: two boundary temperatures and the spatial integral of T. We prove two theorems. The first theorem establishes the local-in-time existence of a solution under explicit regularity and sign conditions on the given data $\xi ,{\nu }_k,{\delta }_{\ell },\theta$ and compatibility at $\tau =0$. The second theorem guarantees the uniqueness of this solution. Despite uniqueness, the inverse reconstruction remains ill-posed: small perturbations in the over-specified data can cause large deviations in the recovered coefficients. For the forward model, we implement two numerical schemes: (i) a Crank–Nicolson finite difference methodology (CN-FDM) on a uniform grid and (ii) a semi-discretized Crank–Nicolson approach combined with Bell spectral collocation in space (CN–Bell). The inverse step minimizes a Tikhonov-regularized least-squares functional using MATLAB’s (R2026a) lsqnonlin. Two numerical examples (smooth and non-smooth), tested with both exact synthetic data and artificially added noise, demonstrate stable and accurate coefficient reconstructions. The framework applies directly to heat conduction and porous media flow where diffusivity varies quadratically in space. Full article