Search Results (14,429)

Alkali-activated fly ash geopolymers are promising low-carbon binders, but their performance depends strongly on mix proportion design. This study investigated the effects of water-to-binder ratio, sand content, and NaOH concentration on fly ash-based geopolymer using an L25(5⁶) orthogonal design. Flexural and compressive strengths were evaluated through range analysis and Analysis of Variance (ANOVA), while Random Forest was used as an exploratory tool for factor-response interpretation. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were conducted to relate mechanical behavior to microstructural evolution. The optimal combination within the tested levels was a water-to-binder ratio of 0.30, sand content of 40%, and NaOH concentration of 12 mol/L. The maximum flexural and compressive strengths reached 3.65 MPa and 17.98 MPa, respectively. NaOH concentration dominated flexural strength, whereas water-to-binder ratio primarily controlled compressive strength. Model benchmarking and cross-validation showed that the machine-learning results had limited generalization capability under the small-sample condition and should be interpreted as candidate screening rather than independent predictive validation. Microstructural analyses indicated that strength development was associated with matrix densification, aluminosilicate network reorganization, and amorphous geopolymeric gel formation. Full article

Polylactic acid (PLA) remains poorly mineralized under mesophilic conditions relevant to home and decentralized composting. This study assessed whether bioaugmentation with Amycolatopsis orientalis, protein-based biostimulation with skimmed milk powder, or their combined application could enhance the mineralization of compression-molded amorphous PLA fragments at 28 °C in activated vermiculite. Closed respirometric bioreactors were monitored for 90 days, and the PLA mineralization extent was calculated from the cumulative CO₂ evolution after correction using treatment-specific blanks. The recovered PLA fragments were further analyzed by FTIR-ATR and DSC to provide complementary physicochemical monitoring. The final mineralization remained low, reaching 1.19 ± 1.88% for bioaugmentation, 3.49 ± 1.82% for biostimulation, and 8.75 ± 4.31% for the combined treatment. The combined treatment gave the highest mean value, which was significantly higher than bioaugmentation alone, but the individual biological replicates followed heterogeneous trajectories. In particular, BABS-3 reached 13.19% mineralization, indicating that higher responses can occur at the individual bioreactor level, although they were not consistently reproduced. FTIR-ATR and DSC revealed treatment- and replicate-dependent physicochemical changes but did not provide evidence of extensive bulk PLA transformation. These results contrast those of previous reports of higher PLA mineralization under warmer, mature compost conditions, emphasizing the complexity of the combined influence of temperature and matrix. Overall, the tested strategies were insufficient to achieve effective home compostability of PLA at 28 °C. Full article

Spurious correlations between time series are a persistent problem: simple, low-complexity patterns are abundant, so unrelated series can easily exhibit high Pearson correlation. We argue that Kolmogorov complexity—a series’ resistance to compression—provides a principled diagnostic for flagging such cases. We prove an algorithmic trilemma: a pair of binary sequences cannot simultaneously be algorithmically independent, highly correlated, and highly complex. This gives a deterministic complexity ceiling for independent correlated pairs and a probabilistic bound under which spurious correlations among independent high-complexity pairs are exponentially rare; we further bridge these results to an effective Hausdorff dimension obstruction. These guarantees hold for binary sequences under Hamming correlation; their extension to real-valued series via serialisation and LZ compression is empirically validated rather than proved, so the joint indicator $J_{\mathrm{LZ}}=min\{{\tilde{C}}_{\mathrm{LZ}}\left(x\right),{\tilde{C}}_{\mathrm{LZ}}\left(y\right)\}$ is a calibrated diagnostic, not a causal test. On two toy models—coupled logistic maps and multivariate fractional Brownian motion (${dim}_H=2-H$)—false positives are far more common among low-complexity series. Because noise inflates complexity and non-stationary processes can be both complex and spuriously correlated, we recommend a two-stage workflow: establish stationarity, then report $J_{\mathrm{LZ}}$ alongside $\rho$. Full article

Since the Kigali Amendment entered into force globally, propane (R290) has been regarded as one of the most promising next-generation alternative refrigerants for refrigeration and air conditioning. However, its flammability limits its maximum charge amount and leads to higher flow resistance loss. In this paper, a novel refrigeration cycle with an additional independent compression process was simulated and experimentally tested. The simulation error of capacity was less than 7.1%. The intermediate evaporation temperature was optimized. The results show that the new cycle delivers stable performance advantages over the conventional R290 heat pump in both cooling and heating modes, with average capacity and COP improvements of 4.8% and 7.8% for cooling, and 8.3% and 7.5% for heating. System flow resistance loss decreases by 33.0%, which raises the refrigerant mass flow rate by 12.5% and reduces the required compressor displacement by 6.6% at equivalent cooling capacity on average. Full article

Uniaxial compression tests were conducted on fly ash-based geopolymer concrete (FAG) with varying alkali-binder ratios (0.25, 0.35, 0.45, 0.55, 0.65) and curing ages (7 d, 28 d) to ascertain its mechanical performance parameters and stress–strain relationship curves. The formation mechanism of FAG multiscale strength is revealed through a systematic process that integrates statistical damage theory with microscopic testing techniques. This process involves the progression of microstructural state and the evolution of mesoscopic damage, providing a comprehensive understanding of the multiscale strength formation process. The results indicate that as the alkali-binder ratio increased, there was an initial rise and subsequent decline in microstructure density. At an alkali-binder ratio of 0.45, the alkaline activator can fully stimulate the fly ash to undergo depolymerization and polycondensation reactions. The result of this process is the formation of a continuous and dense cementitious matrix, thereby achieving the optimal improvement in macroscopic initial mechanical properties. Concurrent microstructural alterations further modify the morphology and path of microcrack initiation and propagation during uniaxial compression, as well as the effective force skeleton adjustment process. The characteristic parameters that are indicative of the evolution of microfracture and yield damage demonstrate regular changes in accordance with the alkali-binder ratio. The joint effect of these two factors determines the evolution characteristics of the macroscopic nonlinear stress–strain behavior of FAG, ultimately resulting in an increasing and then decreasing trend of FAG strength with the increase of alkali-binder ratio, while ductility shows a trend of decreasing first and then increasing. At an equivalent alkali-binder ratio, the porosity of the 7 d sample exhibited a decrease of 1.13% to 17.13%. Conversely, the strength of the 7 d sample increased by 39% to 312%. However, the deformation capacity of the 7 d sample decreased, with a peak strain reduction of 21% to 52% at 28 d. This research achievement has the potential to provide significant theoretical support for the practical engineering promotion and application of FAG. Full article

Nuclear infrastructure requires reliable gamma radiation shielding, for which heavyweight concrete offers a practical, structural solution. Conventional concrete provides poor gamma shielding and heat durability, demanding a denser alternative. Prior studies show that magnetite enhances attenuation and strength, while dolomite improves thermal/mechanical stability, yet findings are dispersed across materials and test conditions. Hybrid magnetite–dolomite concrete requires systematic evaluation for simultaneous optimal gamma shielding and mechanical performance under nuclear conditions. Two mixes were produced by partial replacement of coarse aggregate (Mix 1: 50% magnetite, 25% dolomite; Mix 2: 25% magnetite, 50% dolomite), casted and cured per standard practice with compressive strength measured at 7 and 28 days. Gamma attenuation was quantified using Cs-137 and Co-60. Mix 1 achieved 78.78% attenuation for Cs-137 and 76.86% for Co-60, while Mix 2 reached 77.65% and 74.68%, respectively. At 28 days, peak compressive strengths were 25.8 MPa (magnetite), 22.6 MPa (dolomite), and 20.6 MPa (control), with pre-peak energy capacity ranking as follows: magnetite > dolomite > control. Magnetite increased strength and attenuation but sharpened post-peak softening, whereas dolomite enhanced deformability and energy dissipation with minimal loss in shielding. Hybrid concrete satisfied shielding and strength targets and outperformed conventional concrete, with a magnetite-forward blend offering the best overall protection. Full article

This paper proposes a method for simulating freeze–thaw damage in water-rich sandstone using PFC3D (Particle Flow Code in three dimensions). Water-rich sandstone is idealized as a composite system consisting of rock particles, water particles, and three types of contact surface: rock–rock, rock–water, and water–water. The volume change in water particles is governed by temperature, unfrozen water content, and porosity. During thawing, the volume change in water particles is realized by increasing the porosity after each cycle because the expansion of water particles is reflected by pore enlargement and the accumulation of externally supplied water. The proposed approach is intended for saturated or highly water-rich sandstone under laboratory freeze–thaw conditions with external water replenishment. It represents freeze–thaw damage associated with pore water freezing expansion and porosity-controlled equivalent water replenishment, whereas ice segregation, cryogenic suction, moisture migration, and a moving freezing front are not explicitly considered. A comparison between simulation results and laboratory tests indicates that the proposed method can effectively reproduce the freeze–thaw cycling process in water-rich sandstone. The results show that the mechanical behavior of sandstone after freeze–thaw cycles, including uniaxial compressive strength and elastic modulus, deteriorates significantly. The failure mode changes from shear failure to splitting failure. Freeze–thaw cycling and subsequent uniaxial compression are dominated by tensile damage, with tensile cracks accounting for approximately 90% of the total cracks. The tensile damage rate, Rt, increases exponentially. Crack development induced by freeze–thaw cycling follows an S-shaped trend and can be divided into three stages: slow crack growth from 0 to 10 cycles, rapid crack growth from 10 to 32 cycles, and a reduced growth rate after 32 cycles. The results provide a reference for the freeze–thaw damage analysis of rocks in cold regions and numerical simulations of freeze–thaw cycling processes. Full article

Background/Objectives: Surgical repair of the rotator cuff tendons can lead to unsatisfactory results and the requirement for further surgical treatment. Development of repair techniques is limited by a lack of appropriate functional pre-clinical testing, especially over extended motion cycles. The purpose of this study was to demonstrate the efficacy of a novel shoulder simulator by assessing changes in internal muscle forces following a rotator cuff tear and double-row surgical repair. Methods: The developed shoulder simulator used motors to apply controlled movements/displacements to tendons (supraspinatus, infraspinatus, subscapularis, teres minor, anterior deltoid and middle deltoid) of a cadaveric human shoulder to produce cyclic abduction motion representative of normal shoulder function. The required displacement for each muscle was determined using a musculoskeletal model. The resultant force applied to each tendon during the cycles was measured using a compression load cell. Results: The developed simulator in this proof-of-concept study enabled the contribution of the different muscles involved in the shoulder during abduction to be assessed for the intact shoulder. The shoulder was also tested with a 50% supraspinatus tear and a double row surgical repair of the supraspinatus to assess the change in internal muscle forces. Conclusions: The study indicated that successful cyclic testing of cadaveric samples could be achieved using the simulator and changes in the internal muscle forces of the shoulder were identified following a supraspinatus tear and double-row surgical repair. Full article

Monitoring the activation of concealed water-conducting structures and predicting the evolution of mining-induced floor failure above a confined aquifer are critical for ensuring the safety and sustainability of deep coal mining. The present study formulates an optimized hydrophobic similar material, improves the bidirectional four-face stress-adjustable loading test platform, integrates water pressure-flow and excitation current monitoring systems, and innovatively introduces the electric current change rate (K value) as a core analytical indicator to systematically conduct physical simulation experiments on floor failure during coal seam mining above a confined aquifer containing concealed water-conducting structures. The results demonstrate the successful development of similar materials with tunable properties (density: 1605–1994 kg·m⁻³; uniaxial compressive strength: 0.07–0.41 MPa; water absorption: 0.2–3%; permeability: 6.8 × 10⁻⁶–7.68 × 10⁻⁴ cm·s⁻¹), effectively replicating the mechanical and seepage characteristics of the prototypical rock strata. The spatiotemporal evolution of the mining-induced fracture field was identified to occur in two distinct stages: “horizontal–vertical evolution” followed by “horizontal periodic evolution”, with a failure depth stabilizing above the No. 9 lower coal seam and a horizontal lag of 4.3–10.1 cm behind the working face. The K value parameter proves highly sensitive in dynamically characterizing the multi-field coupling process of stress–damage–seepage, enabling the clear delineation of the floor’s “six horizontal zones” and “three vertical zones” structure. Crucially, the K value analysis revealed the underlying mechanism of confined water conduction, showing a significant upward migration in the concealed structure area that approached, but did not breach, the key aquifuge layer. The present study provides a novel geophysical perspective and an effective technical parameter (K value) for deciphering the failure mechanism of mining-disturbed coal seam floors, thereby offering a diagnostic framework and a theoretical basis for water hazard early warning and the promotion of green and safe mining practices. Full article

Externally bonded reinforcement (EBR) using fiber reinforced polymer (FRP) is one of the most widely used techniques for strengthening reinforced concrete (RC) structures. However, early debonding of the concrete surface layer in the EBR method limits its structural performance. Recently, the externally bonded reinforcement on grooves (EBROG) method has emerged as a promising alternative. This study experimentally investigates the bond behavior between CFRP plates and concrete strengthened using the EBROG method. A total of 78 specimens were fabricated and evaluated using single-lap shear tests. The investigated parameters include groove dimensions, number of grooves, and concrete compressive strength. A digital image correlation (DIC) system was used to measure displacement. Unlike the EBR method, no debonding of the concrete surface layer occurred in the EBROG specimens, and the bond strength improved by 49.56–154.48% without additional surface treatment. Increased groove dimensions and a greater number of grooves significantly enhanced the bond performance. Higher concrete compressive strength and larger groove dimensions also delayed the onset of debonding. Based on the experimental results, a new effective strain model was proposed, and flexural capacity predictions using this model showed higher accuracy than those obtained from existing models. Full article

Accurate state of health (SOH) estimation of lithium-ion batteries (LIBs) is critical to ensuring the safety and reliability of battery management system (BMS). To achieve precise estimation, this study proposes a hybrid framework that integrates variational mode decomposition (VMD), kernel principal component analysis (KPCA), polar lights optimizer (PLO), and physics-informed neural network (PINN) for SOH estimation. First, multidimensional health features are extracted and decomposed by VMD into intrinsic mode functions (IMFs), which are then compressed into a one-dimensional principal component via KPCA, retaining over 95% of the original information. Subsequently, the PLO algorithm is used to adaptively optimize three key hyperparameters of the PINN-based model: the learning rate, the number of collocation points, and the regularization loss weight. Finally, the optimized PINN is deployed to predict the SOH of the Center for Advanced Life Cycle Engineering (CALCE) battery dataset. Experimental results demonstrate that the proposed VMD-KPCA-PLO-PINN exhibits high prediction accuracy under both 7:3 and 5:5 training-to-testing data partitions. For example, under the 5:5 partition, the proposed model achieves an average $R^2$ of 0.983 and an average RMSE of 0.0085 on the tested CALCE cells. Full article

To narrow spectral linewidth, stabilize longitudinal mode and improve output performance of a 1064 nm distributed feedback (DFB) semiconductor laser, we design and fabricate a laser module adopting fiber Bragg grating (FBG) external-cavity feedback and a butterfly packaging structure. The butterfly package effectively enhances heat dissipation and optical coupling reliability. Based on the classic Schawlow–Townes theory, we elaborate on how the narrowband filtering of FBG and the extended external cavity suppress mode hopping and reduce laser linewidth. A delayed self-heterodyne testing system is built to evaluate the photoelectric characteristics, spectral features and linewidth performance under varying driving currents and ambient temperatures. Experimental results show that the laser has a threshold current of 22.54 mA and a slope efficiency of 0.18 W/A, and its maximum output power reaches 80.8 mW at 480 mA. The side-mode suppression ratio (SMSR) reaches 58.2 dB at a temperature of 25 °C and driving current of 150 mA. Benefiting from FBG feedback, the laser linewidth is compressed from 485 kHz to 115 kHz, with lower noise and excellent wavelength stability. This compact all-fiber laser is well-suited for fiber sensing, coherent detection and LiDAR systems. Full article

Alkali-activated recycled aggregate concrete (AARAC) offers a sustainable alternative to traditional concrete but suffers from complex, non-linear mechanical behavior that challenges conventional prediction methods. This study develops and compares five machine learning models, linear regression (LR), M5P, Random Forest (RF), K-Nearest Neighbors (KNN) and XGBoost, for predicting the compressive strength (Cs), flexural strength (Fs), splitting tensile strength (Ss), pull-out bond strength (PT), and water absorption (Wa%) of AARAC. A dataset of 360 experimental samples, incorporating natural aggregate, recycled concrete aggregate (RCA), cement block aggregate (CBA), water-to-cement ratio (W/C), alkaline treatment status, and slump, was used. Models were evaluated via train/test split (80/20) and 10-fold cross-validation using R², MAE, RMSE, and MAPE. Random Forest achieved the highest test R² (0.8736) and lowest test MAPE (1.418%) and XGBoost (R² = 0.8605, MAPE = 1.557%). KNN and M5P performed moderately, while LR was the weakest (R² = 0.6958, MAPE = 2.147%). All tree-based models exhibited overfitting, with training R² up to 0.98. Scatter plot analysis revealed systematic underprediction by RF for Cs (constant offset of ~2 MPa) and increasing bias for PT, Ss, and Wa% at higher values. XGBoost gave perfect predictions for PT and Wa% but underpredicted Cs and Fs. K-fold cross-validation confirmed XGBoost as the most robust (mean R² = 0.9844). Correlation analysis showed W/C strongly increases Wa% (r = 0.80) and decreases PT (r = −0.73); RCA negatively affects mechanical properties, while CBA and alkaline treatment improve them. The study concludes that ensemble tree models, particularly Random Forest, are superior for AARAC prediction, but systematic bias requires post hoc calibration. Full article

The compressive strength of ultra-high-performance concrete (UHPC) is jointly influenced by multiple factors, including material composition, mixture proportion parameters, and curing regime. Conventional empirical methods are therefore insufficient to accurately characterize the highly nonlinear relationships involved. To improve the prediction accuracy of UHPC compressive strength and to achieve mixture proportion optimization that simultaneously considers mechanical performance, economic efficiency, and environmental impact, this study developed random forest (RF), artificial neural network (ANN), gradient boosting decision tree (GBDT), and extreme gradient boosting (XGBoost) models based on 810 publicly available UHPC experimental datasets. Model performance was evaluated using R², RMSE, MAE, and MAPE. To enhance the robustness of model validation, repeated K-fold cross-validation, sensitivity analysis with different random seed splits, and benchmark model comparisons were further introduced. The results indicate that the XGBoost model achieved superior predictive performance on both the test set and robustness validation, with test-set R², RMSE, MAE, and MAPE values of 0.9604, 7.77, 5.58, and 4.80, respectively. The model was further interpreted using SHAP, PDP, and ICE methods, and the results revealed that curing age, fiber content, silica fume content, and water-to-binder ratio were important variables affecting the compressive strength of UHPC. Furthermore, XGBoost was used as a surrogate model and coupled with NSGA-II and TOPSIS methods for multi-objective optimization. Under the constraints of compressive strength, water-to-binder ratio, superplasticizer-to-binder ratio, and absolute volume, a computationally recommended UHPC mixture proportion balancing strength, cost, and carbon emissions was obtained. This study provides a reproducible machine-learning-assisted approach for UHPC compressive strength prediction and low-carbon, cost-effective mixture proportion design. Full article

Circulating fluidized bed (CFB) fly ash exhibits immense potential as a supplementary cementitious material, yet its application is limited by volumetric instability related to delayed ettringite formation. This study investigates the effect of grinding and ultrafine grinding on hydration behavior, microstructure, and long-term volumetric stability of CFB fly ash–cement composites using isothermal calorimetry, XRD, SEM-EDS, TG-DSC, and MIP. Results show that increasing fineness shortens the induction period and advances the second hydration peak by ~6 h. The cumulative heat release of the UCFA system reaches 95.2% of plain cement (85 h). Ultrafine grinding improves hydration activity and reduces total pore volume by 7.32% compared with cement and 22.18% compared with RCFA, leading to denser microstructures and higher compressive strength. Mechanistically, grinding modifies the outer sulfate-bearing layer, accelerating sulfate dissolution and early ettringite formation, while promoting CaO exposure and pozzolanic reactions. Long-term tests up to 730 days confirm that UCFA significantly reduces linear expansion, indicating improved volumetric stability. These results demonstrate that ultrafine grinding simultaneously enhances hydration reactivity and long-term stability, providing a feasible route for high-value utilization of CFB fly ash in cementitious systems. Full article