Search Results (428)

To meet the miniaturized cooling demands of high-heat-flux electronic devices, metal foams—featuring high specific surface area and multiscale porous structures—are considered promising candidates for enhancing flow boiling evaporation. However, pore density (PPI) and grooved geometry (channel aspect ratio, AR) jointly regulate vapor–liquid distribution, rewetting, and flow resistance, thereby constraining overall performance. Here, flow boiling experiments were conducted on nickel and copper foams with pore densities of 100, 500, and 1000 PPI and AR values of 0.7, 1.0, and 1.3. Heat transfer coefficient (HTC), wall superheat ($\mathsf{\Delta }T$), and pressure drop ($\mathsf{\Delta }p$) were systematically evaluated, complemented by transient two-phase simulations revealing vapor fraction, temperature, and pressure drop distributions. A pronounced non-monotonic pore-density dependence is observed: 500 PPI achieves an optimal balance between heat-transfer enhancement and flow resistance, whereas 100 PPI suffers from vapor accumulation and temperature non-uniformity, and 1000 PPI is penalized by excessive permeability resistance and pore-scale confinement. An optimal AR of 1.0 promotes efficient vapor venting and stable rewetting. Under the optimal configuration (500 PPI, AR $=1.0$), a limiting heat flux of 348.6 W/cm², corresponding to the HTC of 55.4 kW/(m² · K), and a limiting HTC of 130.3 kW/(m² · K) are achieved, providing quantitative design guidelines for metal-foam two-phase evaporators. Full article

The mechanical behavior of loess under varying moisture conditions plays a critical role in the stability of slopes and foundations in loess regions. Owing to its high porosity and metastable structure, loess is particularly sensitive to moisture-induced strength degradation. Although geogrid reinforcement has been widely adopted to improve soil stability, the combined influence of moisture condition, reinforcement characteristics, and confinement on the shear behavior of loess remains insufficiently understood. In this study, consolidated undrained (CU) triaxial tests were conducted on partially saturated loess reinforced with glass fiber geogrids (GFGs) and basalt fiber geogrids (BFGs) under different moisture contents (13–17%) and confining pressures (100–300 kPa). The effects of geogrid type, reinforcement configuration, and confinement on shear strength and deformation behavior were systematically examined. The results indicate that geogrid reinforcement significantly enhances the shear strength, stiffness, and ductility of loess, particularly under low to moderate confining pressures. Increasing the number of reinforcement layers resulted in peak strength improvements of up to approximately 25% and promoted a transition from brittle to ductile behavior. Distinct reinforcement responses were observed: GFG exhibited higher initial stiffness and more rapid mobilization, whereas BFG demonstrated progressive tensile mobilization and superior residual strength. Furthermore, a modified Unified Twin-Shear Strength Theory (UTSST) incorporating a strain-dependent reinforcement mobilization coefficient was proposed, which provided an empirical representation of the observed strength evolution with good agreement with the experimental results (R² > 0.96). Full article

Applying a constant external electric field to a semiconductor nanostructure with Wannier–Mott excitons, in which the electron and hole interact via a centrally symmetric Coulomb potential, alters the symmetry of the system. When the electric field is applied parallel to the z-axis, the system exhibits cylindrical symmetry; when the field lies in the $x-y$ plane, the symmetry is broken. These symmetry changes affect the optical properties of the system. We present a theoretical calculation that yields analytical expressions for the optical functions of CdSe Nanoplatelets—reflectivity, transmissivity, and the absorption coefficient—in an external homogeneous electric field. From these, we focus on the absorption coefficient. We consider various configurations, with the external field oriented perpendicular and parallel to the platelet planes. Using the real density matrix approach, we calculate the linear electro-optical functions of CdSe nanoplatelets, taking into account the effect of dielectric confinement on excitonic states. We also discuss the impact of platelet geometry (thickness and lateral dimensions) and applied field strength on the spectrum. Full article

This study examines the confined compressive strength (Fcc) of circular, square, and rectangular column geometries under varying confinement conditions. Results indicate that circular columns have the highest Fcc values, exceeding those of square and rectangular shapes. Increased confinement through clamps significantly enhances compressive strength. Five machine learning models, Linear Regression, Decision Tree, Random Forest, AdaBoost, and Gradient Boosting, were used to predict Fcc based on geometric and confinement parameters. Linear Regression and Decision Tree models achieved moderate predictive performance, with R² values of 0.84 and 0.83, respectively, and relatively higher error measures (RMSE, MAE, and MAPE), indicating limited ability to capture complex nonlinear relationships in the data. In contrast, ensemble-based methods demonstrated superior performance. The Random Forest model improved the coefficient of determination to 0.90 while substantially reducing all error metrics, reflecting enhanced generalization through bagging. The boosting-based approaches yielded the best results, with AdaBoost achieving the highest R² value of 0.99 and the lowest RMSE, MAE, and MAPE among all models, followed closely by Gradient Boosting with an R² of 0.98. These results confirm that ensemble learning techniques, particularly boosting algorithms, yield more accurate and robust predictions than single learners for the problem studied. Data visualization techniques, including Regression Error Characteristic curves (REC) and SHapley Additive exPlanations (SHAP) value analysis, highlighted model performance and feature importance, emphasizing the roles of confinement and geometry in compressive strength. This research demonstrates the potential of machine learning to optimize structural engineering design and suggests further exploration of alternative shapes and confinement strategies to enhance structural integrity. Full article

The accurate reconstruction of the internal temperature field in rotary kilns is critical for optimizing the clinker calcination process and ensuring energy efficiency. In this study, a rapid and high-fidelity surrogate modeling framework is proposed, utilizing snapshot ensembles generated by full-order Computational Fluid Dynamics (CFD) simulations to reconstruct the temperature field of the axial center section. The framework incorporates a symmetric Autoencoder (AE) coupled with a TabPFN network as its core components. Capitalizing on the kiln’s strong axial symmetry, this reduction–regression system efficiently maps the high-dimensional nonlinear thermodynamic topology of the central section into a compact low-dimensional latent manifold via AE, while utilizing TabPFN to establish a robust mapping between operating boundary conditions and these latent features. By leveraging the In-Context Learning (ICL) mechanism for prior-data fitting, TabPFN effectively overcomes the data scarcity inherent in high-cost CFD sampling. Predictive results demonstrate that the model achieves a coefficient of determination (R²) of 0.897 for latent feature regression, outperforming traditional algorithms by 6.53%. In terms of field reconstruction on the test set, the model yields an average temperature error of 15.31 K. Notably, 93.83% of the nodal errors are confined within a narrow range of 0–50 K, and the reconstructed distributions exhibit high consistency with the CFD benchmarks. Furthermore, compared to the hours required for full-scale simulations, the inference time is reduced to 0.45 s, representing a speedup of four orders of magnitude. Consequently, the predictive system demonstrates excellent accuracy and efficiency, serving as an effective substitute for traditional models to realize online monitoring and intelligent optimization. Full article

Calf rope-and-tie is a competitive rodeo event that has drawn criticism due to concerns around the potential for stress and injury of calves. While previous studies have utilised behavioural indicators to assess the welfare of rodeo calves in the arena, there are no published studies on rodeo calf behaviour during confinement in the chute prior to release into the arena. We analysed video footage of calves in the chute prior to release during two rodeo events. The footage was categorised into short duration (SD, 28–51 s, n = 17) and long duration (LD, 52–166 s, n = 14) based on the total length of the video clip of each calf in the chute. To enable comparison, the final 28 s from both SD and LD categories before calf release were reviewed, and an ethogram was developed to assess the frequency of observable calf behaviours. All calves expressed at least one behaviour indicative of a negative mental state, with ear and head movements being the most frequent. Behaviours observed in SD and LD clips were strongly correlated (Spearman’s rank correlation coefficient 0.875, p < 0.001). Longer confinement was associated with increased frequency of “red flag” behaviours indicating fear and/or stress (chi-square = 10.48, p = 0.0149), including mouth opening, tongue protrusion, rearing and escape attempts. We conclude that calves used in roping events experience fear and stress while held in the chute, especially during longer periods of confinement. Full article

The increasing demand for compact and high-performance thermal management systems in the industrial and energy sectors has renewed interest in plate-type heat exchangers for high heat-flux dissipation. These exchangers offer high surface-area-to-volume ratios, modular architecture, and scalable construction, making them suitable for applications requiring advanced cooling within restricted space. This study presents a structured thermo-hydraulic design framework for compact plate heat exchangers operating under fixed wall-temperature boundary conditions. The framework integrates geometric scaling, surface-morphology variation, and multi-parameter performance evaluation to assess the balance between convective enhancement and hydraulic losses. Water at 25 °C serves as the working fluid due to its favorable thermophysical properties and economic viability. A constant wall temperature of 100 °C is applied as a fixed boundary condition to provide a consistent thermal driving potential for comparing different geometries in a range of industrially relevant operating regimes. Three primary design variables are examined: (i) a baseline flat-plate configuration used to establish the fundamental flow–thermal response; (ii) systematic variation of inter-plate spacing to characterize the hydraulic–thermal tradeoff; and (iii) surface-morphology variation using chevron and sinusoidal corrugations to enhance convection through secondary flow generation and boundary-layer modulation. The key performance metrics include wall heat flux, overall heat-transfer coefficient, thermal resistance, and pressure-drop penalty. These indicators are evaluated to identify configurations that are thermally effective and hydraulically feasible. The results show that an inter-plate spacing of 7 mm provides a favorable balance between confinement and convective enhancement under the present operating conditions. Sinusoidal corrugations yield the most favorable thermo-hydraulic performance (PEC $\approx 1.30$) while maintaining low frictional losses. The proposed framework provides a transferable physics-based methodology for comparative assessment and early-stage design of compact heat exchangers under fixed pumping-power constraints. The approach is broadly applicable to renewable-energy systems and compact thermal management in industrial applications. Full article

Underground saturated jointed rock is prone to engineering geohazards under the combined effects of in situ stress and dynamic loading. A modified split Hopkinson pressure bar (SHPB) system was used to conduct dynamic loading tests on artificially fabricated saturated jointed rocks. The effects of joint matching coefficient (JMC) and confining pressure on the dynamic strength, deformation characteristics, energy evolution, and stress wave propagation of the specimens were investigated. The test results show that the dynamic compressive strength and stiffness of saturated jointed rocks increase with the increase in JMC, but the compressive strength is still lower than the typical dynamic strength range. Rock damage mainly occurs at the joint location, and the damage mode is dominated by tensile fracture. In terms of energy, the energy dissipation rate of the rock decreases with decreasing JMC and increasing confining pressure. The propagation of stress waves is mainly affected by the coupling of JMC and three-dimensional static stress, which is manifested as a transition from a rapidly changing phase to an unstable changing phase, a process accompanied by an energy distribution mechanism. These insights fill a gap in the mechanical response of saturated jointed rocks under complex loading conditions underground and help predict the risk of dynamic instability in underground engineering and mining operations. Full article

This study experimentally investigates the residual axial compression behavior of circular glass fiber-reinforced polymer (GFRP) tube-confined concrete short columns (CFGFT) after exposure to elevated temperatures. A total of 27 specimens were fabricated and tested under axial compression, with key parameters including GFRP tube wall thickness (5, 8, and 10 mm), exposure temperature (100, 150, 200, and 300 °C), and constant temperature duration (60 and 120 min). The results show that the load–displacement responses of CFGFT short columns after elevated temperature exposure exhibit distinct two-stage characteristics, culminating in brittle failure at the ultimate axial capacity. Wall thickness significantly influences the failure modes of the specimens, while elevated temperatures increase the occurrence of unfavorable failure modes. Temperature is identified as the primary factor governing the degradation of residual axial capacity and initial stiffness, with performance deterioration becoming more pronounced at temperatures exceeding 200 °C. In contrast, the effect of constant temperature duration within the range of 60–120 min is relatively limited. Based on the experimental results, a simplified binary quadratic regression model incorporating the coupled effects of temperature and wall thickness is proposed to predict the post-fire axial capacity reduction factor (Kr), with a coefficient of determination (R²) of 0.901. These findings provide experimental evidence and a practical predictive approach for the fire-resistant design and post-fire safety assessment of CFGFT members. Full article

Wear, a critical factor governing the performance and durability of mechanical systems, is typically characterized using point-contact and line-contact test configurations. However, it remains unclear whether the wear trends observed in one test configuration would be observed in the other configuration under the same nominal conditions. In this study, ball-on-disk (ASTM G99) and block-on-ring (ASTM G77) tests were conducted under an identical maximum Hertzian contact stress and sliding speed, using the same material pair and lubricating oil, to clarify which contact configuration exhibits more wear and why. The results show that, under the same Hertzian contact stress, the line-contact configuration exhibits a specific wear rate two orders of magnitude higher than the point-contact configuration, despite exhibiting a lower and more stable coefficient of friction. The disk wear is negligible and the ball shows only mild material loss, whereas the line-contact system displays wear rates several orders of magnitude higher, with the rotating ring contributing the dominant share of the total wear. White-light interferometry and scanning electron microscopy observations reveal directional, groove-dominated surface morphologies on the ball and disk, while wear on the block is confined to edge-localized regions and the worn ring surface has smooth, polished morphology. Energy-dispersive X-ray spectroscopy confirms that a Zn- and P-rich tribofilm forms exclusively on the ring surface. Finite element analysis shows stress amplification at the finite line-contact edges, explaining the observed wear severity. These results demonstrate that matching Hertzian contact stress alone is insufficient to ensure comparable wear behavior between point and line contacts. Full article

This paper presents a simulation of the heat exchange process in a solar dryer designed for corn cobs placed in flexible bulk containers (Big-Bag type). The distinctive feature of this drying system is the use of soft load-bearing containers, which simplify loading, unloading, and transportation, while also reducing mechanical damage to the corn cobs. The bottom of each container is perforated to allow the free flow of heated drying agent into the chamber. The study aims to improve the efficiency of the solar drying process to reduce the moisture content of corn cobs below 15%, thereby ensuring the required quality during storage and transport. To validate the drying regimes and parameters, heat and mass transfer processes were simulated using numerical modeling and experimental design methods based on a laboratory-scale physical model of the drying chamber. Numerical simulations were performed using the Reynolds-averaged equations coupled with the heat conduction equation for three porosity coefficients: 0.35, 0.45, and 0.55. The models provided contours of temperature and humidity distribution within the confined boundaries of the drying chamber and individual corn cobs, positioned both vertically and horizontally within the airflow zone, for varying drying durations. The core novelty of this research is the development of an optimized framework for solar drying corn in flexible containers, which integrates numerical simulation with experimental validation to establish key efficient parameters. Specifically, the study provides the following: (1) a validated regression model linking moisture content to airflow rate, drying time, and layer thickness at 45 °C; and (2) a detailed analysis of thermo-hydraulic contours within both the chamber and individual cobs for different porosities, offering practical insights for system design and operation. Full article

Bernsteinpolynomials on simplices provide a powerful framework for approximation, geometric modeling, and numerical analysis. A fundamental structural feature of their coefficients is the inclusion–isotone property: under subdivision of the domain simplex, the Bernstein coefficients over subsimplices remain confined within the bounds of the original coefficients. While this behavior has been established previously only for particular cases, a general and unified treatment has been lacking. In this paper, we present a dimension-independent proof of inclusion isotonicity for general simplicial Bernstein polynomials based on the positivity and stochasticity of the subdivision operator induced by barycentric refinement. We further show that the resulting Bernstein bounds over subsimplices are sharp, in the sense that they accurately represent the attainable range of the polynomial on the refined domain. In addition, we develop an optimized least-squares approximation in the Bernstein–Bezier basis, which improves numerical stability compared to monomial representations and admits an efficient computational implementation. Finally, nonlinear examples and applications to Lyapunov-based stability analysis of polynomial systems illustrate the contraction of coefficient bounds under subdivision and demonstrate the practical effectiveness of the proposed approach. Full article

Hollow-core microstructured optical fibres exhibit excellent properties, such as a low loss, tuneable high birefringence, and low nonlinearity, finding extensive applications across communications, industry, agriculture, medicine, military, and sensing technologies. This paper designs two types of asymmetric hollow-core photonic bandgap fibres featuring a high birefringence and low confinement loss. Both feature a cladding structure of rounded hexagonal honeycomb lattice, while the core structures comprise elliptical hollow cores and rounded rhombic hollow cores, respectively. By adjusting the radius of the cladding air holes and the core structure parameters, this study aims to maximise the birefringence coefficient and minimise the confinement loss. The control variable method is employed to optimise the parameters of two fibres. The simulation results indicate that, at a wavelength of 1.55 μm, the birefringence coefficient of the rhombic core, after parameter optimisation, reaches 1.4 × 10⁻⁴, with the confinement loss achieving 4.4 × 10⁻³ dB/km. Its bending loss remains at the order of 10⁻³ dB/km, indicating that this fibre maintains an exceptionally high transmission efficiency even when wound with a small curvature radius (such as within the resonant cavity of a compact fibre optic gyroscope). The elliptical core’s birefringence coefficient also reaches 3 × 10⁻⁴, with the confinement loss achieving 1.9 × 10⁻¹ dB/km. Specifically, this paper employs bismuth tellurite glass as the substrate material to simulate the performance of elliptical cores. Within a specific refractive index range, the elliptical-core fibre with a bismuth tellurite glass substrate exhibits a confinement loss comparable to quartz glass, whilst its birefringence coefficient reaches as high as 5.8 × 10⁻⁴. Therefore, the hollow-core photonic bandgap fibres designed in this thesis provide valuable reference and innovative significance, both in terms of the performance of two asymmetric core structures and in the exploration of polarisation-maintaining hollow-core photonic bandgap fibres on novel material substrates. Full article

The time–temperature curve serves as a fundamental input for calculating structural fire resistance. Accurate acquisition of this curve is essential for designing structures to withstand fire incidents effectively. In this study, fire test temperature variation data were analyzed to develop a comprehensive understanding of the temperature-rise curve, categorized into three primary phases: Confined Fire Phase, Reignition Phase, and Flashover to Fully Developed Fire. To address non-uniform temperature distribution, a temperature reduction coefficient was introduced into the temperature-rise curve formula. This coefficient was derived by fitting experimental temperature data from multiple fire tests, enhancing the formula’s applicability to compartment fires. Furthermore, accounting for non-uniform temperature distribution along compartment height is critical for accurate thermo-mechanical simulations of structural components. To simplify calculations, layer-specific reduction coefficients were proposed: top area (x ≥ 0.7H): 1.0; middle area (x < 0.7H): 0.73; bottom area (x ≤ 0.4H): 0.34. These coefficients, determined through numerical simulations, exhibit broad applicability. In conclusion, precise characterization of temperature-rise curves is vital for structural fire resistance assessment. The proposed methodology and reduction coefficients improve the robustness and generalizability of thermo-mechanical simulations in evaluating structural fire performance. Full article

Single-lane tunnels, characterized by narrow and high cross-sections with limited ventilation, present significantly higher fire hazards than conventional multi-lane tunnels. To investigate flame morphology and ceiling temperature evolution in such confined spaces, a comprehensive set of reduced-scale fire tests was conducted using a 1:10 scale tunnel model based on Froude similarity. The effects of the heat release rate (HRR), transverse fire location, and fire source height were systematically analyzed. The results indicate that the transverse fire location critically influences flame behavior: a centerline fire produces a stable, vertically symmetric flame, whereas a wall-attached fire exhibits a periodic oscillation of attachment, elongation, and detachment. The maximum ceiling temperature rise increases with both HRR and fire source height. Notably, compared to a centerline fire, a wall-attached fire can increase the maximum ceiling temperature rise by up to 39% due to sidewall confinement. Based on the experimental data, a predictive correlation for the maximum ceiling temperature rise under centerline fire conditions was established. Furthermore, a global prediction model incorporating a transverse position coefficient was proposed, which shows good agreement with the experimental results. Comparative analysis reveals that the temperature rise coefficient for the single-lane tunnel is approximately 13% higher than that of multi-lane tunnels. These findings provide a theoretical basis for fire risk assessment and safety design in single-lane tunnel infrastructure. Full article