Search Results (82)

Significant progress has been made in the low-temperature toughness and crack resistance of polypropylene fiber-reinforced composites. However, there is still a gap in the research on damage evolution under freeze–thaw cycles and complex stress ratios. To solve the problem of durability degradation of traditional rubble masonry in cold regions, this paper focuses on the study of polypropylene fiber-mortar-masonry blocks with different fiber contents. Using acoustic emission and digital image technology, the paper conducts a series of tests on the scaled-down polypropylene fiber-mortar-masonry structure, including uniaxial compressive tests, three-point bending tests, freeze–thaw cycle tests, and tests with different stress ratios. Based on the Kupfer criterion, a biaxial failure criterion for polypropylene fiber mortar-masonry stone (PPF-MMS) was established under different freeze–thaw cycles. A freeze–thaw damage evolution model was also developed under different stress ratios. The failure mechanism of PPF-MMS structures was analyzed using normalized average deviation (NAD), RA-AF, and other parameters. The results show that when the dosage of PPF is 0.9–1.1 kg/m³, it is the optimal content. The vertical stress shows a trend of increasing first and then decreasing with the increase in the stress ratio, and when α = 0.5, the degree of strength increase reaches the maximum. However, the freeze–thaw cycle has an adverse effect on the internal structure of the specimens. Under the same number of freeze–thaw cycles, the strength of the specimens without fiber addition decreases more rapidly than that with fiber addition. The NAD evolution rate exhibits significant fluctuations during the middle loading period and near the damage failure, which can be considered precursors to specimen cracking and failure. RA-AF results showed that the specimens mainly exhibited tensile failure, but the occurrence of tensile failure gradually decreased as the stress ratio increased. Full article

Ultra-high-performance concrete (UHPC) reinforced with recycled tire steel fibers (RTSFs) was studied to evaluate its mechanical properties and cracking behavior. Using acoustic emission (AE) monitoring, researchers tested various RTSF replacement rates in compression and flexural tests. Results revealed a clear trend: mechanical properties initially improved then declined with increasing RTSF content, peaking at 25% replacement. AE analysis showed distinct patterns in energy release and crack propagation. Signal timing for energy and ringing count followed a delayed-to-advanced sequence, while b-value and information entropy changes indicated optimal flexural performance at specific replacement rates. RA-AF classification demonstrated that shear failure reached its minimum (25% replacement), with shear cracks increasing at higher ratios. These findings demonstrate RTSFs’ dual benefits: enhancing UHPC performance while promoting sustainability. The 25% replacement ratio emerged as the optimal balance, improving strength while delaying crack formation. This study provides insights into the mechanism by which waste tire steel fibers enhance the performance of UHPC. This research provides valuable insights for developing eco-friendly UHPC formulations using recycled materials, offering both environmental and economic advantages for construction applications. Full article

Endurance training induces significant cardiac remodeling, with evidence suggesting that prolonged high-intensity exercise may increase the risk of atrial fibrillation (AF). However, physiological responses differ by event type. This review compares AF-related markers in marathon and ultramarathon runners, focusing on structural adaptations, inflammatory and endothelial biomarkers, and the incidence of arrhythmias. A systematic analysis of 29 studies revealed consistent left atrial (LA) enlargement in marathon runners linked to elevated AF risk and fibrosis markers such as Galectin-3 and PIIINP. In contrast, ultramarathon runners exhibited right atrial (RA) dilation and increased systemic inflammation, as indicated by elevated high-sensitivity C-reactive protein (hs-CRP) and soluble E-selectin levels. AF incidence in marathoners ranged from 0.43 per 100 person-years to 4.4%, while direct AF incidence data remain unavailable for ultramarathon populations, highlighting a critical evidence gap. These findings suggest distinct remodeling patterns and pathophysiological profiles between endurance disciplines, with implications for athlete screening and cardiovascular risk stratification. Full article

Acoustic emission (AE) signals exhibit a strong correlation with concrete damage. However, the relationship between column damage and AE signals under eccentric loading conditions, combined with the application of traditional RA-AF classification methods for crack characterization, demonstrates limitations. These approaches provide insufficient resolution to accurately identify damage types throughout the entire structural failure process. This study employed K-means clustering algorithm and Gaussian mixture models (GMMs) to analyze AE signal features from reinforced concrete (RC) columns undergoing failure under the eccentric compression loading of different eccentricity. Subsequently, a random forest model was used for automated damage stage classification. Experimental results demonstrate that the damage progression in eccentrically compressed columns comprises four distinct stages, each exhibiting unique AE signal characteristics. The integrated approach of clustering and random forest modeling demonstrates robust feasibility in identifying AE signal patterns associated with specific damage stages, achieving an 85% recognition rate for damage stage classification. These findings provide quantitatively validated evidence supporting the efficacy of machine learning-based methodologies for enabling stage-specific damage characterization in structural health monitoring applications. Full article

This study reveals the damage mechanisms and fracture evolution characteristics of deeply buried granite with prefabricated joints (inclinations of 0°, 30°, 45°, 60°, and 90°) using uniaxial compression tests monitored by Acoustic Emission (AE) technology. Three-dimensional X-CT technology was used to analyze post-damage fracture evolution in specimens with varying joint inclinations. The results show that the stress–strain curve of deeply buried jointed granite under uniaxial compression includes three stages: initial compaction, crack extension, and failure. AE characteristics align with these stages, showing clear stress responses and timing features. In the initial compaction stage, micro-crack closure dominates, with smaller joint inclinations showing stronger closure effects. In the crack extension stage, joint inclination determines the crack propagation mode. In the failure stage, joint inclination significantly affects the spatial distribution of the rupture network by altering stress concentration areas and crack types. The proportion of shear micro-cracks increases with joint inclination, and peak strength rises with increasing joint angle, potentially accelerating micro-crack evolution. These findings provide valuable insights for designing excavation and instability monitoring in deeply buried multi-jointed granite underground projects. Full article

Atrial fibrillation (AF) is the most common arrhythmia worldwide. AF is associated with a deficiency in nitric oxide (NO) production, which contributes to disturbances in the electrical and mechanical function of the atrial myocardium. NO donors are considered promising for the treatment and prevention of AF, but their effects on atrial contractility are unclear. This study examines the direct impact of a low-molecular-weight NO donor, spermine-NONOate (NOC-22), on the contractile function of atrial cardiomyocytes in paroxysmal AF. To study whether an NO donor-induced increase in NO level causes chamber-specific changes in atrial contractility, we measured sarcomere length (SL) dynamics in contracting single cardiomyocytes from the rat left and right atria (LA, RA) using a 7-day acetylcholine-CaCl₂-induced AF model. We showed that in control rats NOC-22 provoked alternans of sarcomere shortening in both LA and RA cardiomyocytes. In AF, NOC-22 decreased the sarcomere-shortening amplitudes and velocities of sarcomere shortening–relengthening and increased the magnitude of sarcomere-shortening alternans only in RA cardiomyocytes. The negative effects of NO donors on RA contractility warrant careful consideration of their use in AF treatment. Full article

Uniaxial compression tests were conducted on coal samples subjected to different dry–wet cycling treatments to investigate the damage and degradation mechanisms of coal samples under the dry–wet cyclic action of acidic, high-salinity solutions. The damage process of the coal samples was monitored in situ using acoustic emission (AE). The degradation evolution of the mechanical parameters and macroscopic failure modes with the number of cycles was analyzed. Based on the AE ringing parameters, the RA-AF distribution and the AE fractal dimension’s variation characteristics were studied. Additionally, scanning electron microscopy (SEM) was used to observe the microstructure of the coal samples. The results showed that with the increase in the number of dry–wet cycles, both the peak strength and elastic modulus of the coal samples exhibited varying degrees of degradation, and the failure mode gradually shifted from tensile failure to shear failure. AE ringing counts decreased progressively, while the proportion of shear cracks based on the RA-AF classification increased. At the same time, the mean AE fractal dimension of the coal samples increased, and the fractal dimension decreased with an increase in AE ringing counts. The sharp drop in fractal dimensions could serve as an early warning signal for a major failure in the coal samples. Furthermore, under the influence of dry–wet cycling in acidic, high-salinity solutions, defects such as pores and cracks in the microstructure of the coal samples became more pronounced, and the degradation effect continuously intensified. Full article

Tunnels frequently experience issues such as lining spalling and water leakage, making the stability of tunnel support critical for engineering safety. Given that tunnels are subjected to various ground stress disturbances and groundwater influences, it is essential to investigate the mechanical properties and damage mechanisms of tunnel support materials under different loading paths and saturation levels. Fiber-reinforced concrete (FRC) is widely used for tunnel support; in this study, uniaxial compression tests were conducted on FRC with different fiber contents (0%, 0.5%, 1.0%) under varying loading paths (monotonic, pre-peak cyclic loading, full cyclic loading). The stress–strain behavior, volumetric strain, and elastic modulus were analyzed. The results indicate that increasing fiber content enhances strength and stiffness, while higher water content leads to a significant water-weakening effect, reducing both parameters. To classify crack types, the logistic regression (LR) algorithm is employed based on the AF-RA features, identifying tensile damage (which accounts for 60–80%) as more dominant than shear damage. Using this classification, AE event distributions reveal the spatial characteristics of internal damage in FRC. Gaussian process regression (GPR) is further applied to predict the AE parameters, enabling the assessment of the tensile and shear damage responses in FRC. The location and magnitude of the predicted wave crest indicate extreme damage levels, which become more pronounced under a higher saturation condition. A damage constitutive model is proposed to characterize the post-peak softening behavior of FRC. The numerical verification demonstrates good agreement with the experimental results, confirming the model’s capability to describe the softening behavior of FRC under various fiber and water contents. Full article

Psoriasis is a chronic inflammatory skin disease characterized by dysregulation of the interleukin 17 (IL-17) signaling axis. Given that psoriasis development depends on keratinocyte stem cells and early progenitors’ sensitivity to differentiation, we analyzed IL-17 ligands and the expression and function of in a novel subset of keratinocyte subpopulations: keratinocyte stem cells (KSC) and early and late Transit Amplifying (ETA or LTA, respectively) cells. We found that all subpopulations expressed all IL-17 variants, predominantly in ETA and LTA. Conversely, IL-17 receptor expression resulted in more heterogeneity, with IL-17RA, -C, and -E being the most differentially regulated. Stimulus with IL-17A, IL-17-F, IL-17-A/F, and IL-17C promotes the upregulation of CXCL1, CXCL8, and DEFB4 mRNAs expression in both KSC and ETA. Moreover, IL-17A and IL-17A/F mainly decrease KSC proliferation and promote cell cycle block. Globally, IL-17A and IL-17A/F modulated the expression of proliferation, differentiation, and psoriasis-associated markers. Furthermore, KSC- and ETA-derived 3D reconstructions displayed increased epidermal thickness and upregulated KRT16 expression after treatment with IL-17A or IL-17A/F. Therefore, our data demonstrated that IL-17 family members perform distinctive functions in a specific keratinocyte subpopulation and define IL-17 signaling as a critical modulator of KSC behavior, proving its role in epidermal homeostasis dysregulation of psoriasis. Full article

To study the influence of the main roof period pressure on the instability mechanism of rock pillars with burst liability, the composite loading mode of “pre-cycling loading + continuous loading with a constant rate” was used to conduct compression experiments on rock samples. Meanwhile, the mechanical behaviour response characteristics of rock samples were discussed. Experiment results are shown as follows: (1) mechanical properties of rock samples were strengthened by closing primary pores under pre-cycling loading. The surface roughness and secondary crack number decreased gradually with the pre-cycling threshold; (2) the Kaiser effect of AE (Acoustic Emission) signals was significant in the second and third pre-cycling loading and unloading stages. The Kaiser effect disappeared in the continuous loading stage; (3) AF-RA (Average Frequency-Risetime Amplitude) signals were distributed in a dense-sparse-dense form. Low AF and high RA shear type cracks were more common. Shear failure was the dominant failure mode in rock samples. Full article

To investigate the stratification effect on rock splitting and Mode I fracture characteristics, standard Brazilian splitting disk specimens and straight-crack disk specimens were subjected to splitting loading tests, and a high-speed camera system and acoustic emission (AE) system were used to study the rocks’ mechanical properties, fracture parameters, and AE characteristics. The results demonstrate the following: (1) The tensile strength and fracture toughness of the layered rock exhibit significant stratification effects, gradually decreasing with the increase in the number of layers and the layer angle. (2) The different angles of the stratification planes lead to the diversity of failure modes in the disk specimens. (3) The S-value and the cumulative AE count curve of specimens without prefabricated cracks show two types of pattern during loading: fluctuating increase mode, and “gentle–steep” increase mode. (4) Layered rock specimens exhibit a low ratio of rise time to voltage amplitude (RA) value and high average frequency (AF) characteristics during fracture, and the shear failure mainly occurs during the stable propagation phase after the initiation of macroscopic cracks. (5) The fracture process zone (FPZ)’s length at the peak point of the specimens decreases exponentially with the increase in the number of layers, but this reduction does not go on indefinitely, and there exists a minimum value. Within the range of 0° to 60°, the FPZ length decreases linearly with increasing stratification angle. Full article

Indoor direct shear tests under different stress levels were conducted on sandstone–concrete samples to investigate the rock–concrete interfaces’ shear energy evolution features and fracture behaviors under different normal stresses, combined with acoustic emission (AE) and digital image correlation (DIC) techniques. The research results show that the growth of normal stress restricts the coalescence and failure of micro-cracks inside the sample and improves the bearing capacity. The shear strength of the sandstone–concrete cemented interface increases by 12.3–34.34% with increasing normal stress. The evolution behaviors of the total input energy, elastic strain energy and dissipated energy density are similar under different normal stress conditions, and the increase in normal stress raises the energy storage capacity of the sample, as well as the input external energy required for a sample’s failure, thereby enhancing the bearing capability of the sample. In addition, the AE count and b value characteristics indicate that crack propagation shows a three-stage variation trend. It can be seen from the RA (rise time/amplitude)-AF (AE count/duration time) curves that as the normal stress increases, the proportion of shear cracks in the sample progressively increases. When the final overall failure of the sample is imminent, the high-energy level fracture type changes from tensile fracture to shear fracture with increased normal stress, leading to an increasing percentage of shear fracture. Finally, the speckle results indicate that the nucleation and coalescence of tensile wing-shaped cracks are the main causes of sample failure. Under relatively high normal stress conditions, the damage degree of the serrated interface increases and the crack morphology becomes more intricate. Full article

Background/Objectives: The recurrence rate of atrial fibrillation (AF) after electrical cardioversion (ECV) appears to correlate with morpho-functional changes in both the left (LA) and right atria (RA). The present study focuses on identifying predictors for AF recurrence post-ECV. Methods: Sixty-one patients were included in the study following an elective ECV with a successful conversion to SR, and were subjected to cardiovascular assessment immediately after ECV. Results: At 6-month follow-up, 24 patients (39.3%) experienced AF recurrence. Patients without AF recurrence showed a lower right atrial valvular index (RAVi) (32 ± 8 vs. 40 ± 10 mL/m², p = 0.03), a higher LA strain S-R (15.8 ± 7.7 vs. 9.0 ± 4.2%, p = 0.003), and more pronounced lateral a’ wave (5 ± 3 vs. 3 ± 1 m/s, p = 0.01), tricuspid a’ wave (7 ± 3 vs. 4 ± 2 m/s, p = 0.02), average a’ wave (6 ± 2 vs. 3 ± 1, p = 0.005), and augmentation index corrected for 75 beats per minute (Aix75) (26 ± 13 vs. 37 ± 12, p = 0.01). Based on these results, patients were assigned one point for each of the following criteria: RAVi > 36 mL/m², average a’ wave > 4, LA strain S-R > 13%. The ROC curve analysis showed that a score of 3 had an AUC for AF recurrence of 0.81 (p < 0.001, CI 0.69–0.91), with a sensitivity of 96% and a specificity of 62%. Conclusions: LA strain, TDI Doppler, RAVi, and Aix75 measured immediately post-ECV were independent predictors of AF recurrence after ECV. Full article

Coal pillar dams are affected by mining disturbance, which threatens the efficient operation of the underground reservoir. To study the deformation behaviors and failure mechanism of coal pillars under mining disturbance, an acoustic emission (AE) system and a deformation field system were applied to conduct uniaxial compression tests at various displacement rates. The AE characteristics and deformation field evolution of coal were investigated, and the microfailure mechanism was identified. The result shows that the deformation field evolutions are the same under various displacement rates. The increment of accumulated absolute energy near the peak stress rises with the displacement rates. The increase rate of the mean vertical displacement is positively correlated with the displacement rate. The coefficient of variation (C_V) of the deformation field can be applied to identify the deformation behaviors of coal and shows the fluctuate–slow increase–rapid increase trend. The distribution ranges of AF (count/duration) and RA (rise time/amplitude) are mainly 0–750 kHz and 0–700 μs/dB. The microfailure mechanism is mainly tensile failure and is accompanied by some shear failure. The percentage of shear failure increases with the increase in the displacement rate. The result provides a reference for the design and stability evaluation of the underground reservoir. Full article

To investigate the fracture mechanism of rock–concrete (R–C) systems with an interface crack, Brazilian splitting tests were conducted, with a focus on understanding the influence of the interface crack angle on failure patterns, energy evolution, and RA/AF characteristics. The study addresses a critical issue in rock–concrete structures, particularly how crack propagation differs with varying crack angles, which has direct implications for structural integrity. The experimental results show that the failure paths in R–C disc specimens are highly dependent on the interface crack angle. For crack angles of 0°, 15°, 30°, and 45°, cracks initiate from the tips of the interface crack and propagate toward the loading ends. However, for angles of 60°, 75°, and 90°, crack initiation shifts away from the interface crack tips. The AE parameters RA (rise time/amplitude) and AF (average frequency) were used to characterize different failure patterns, while energy evolution analysis revealed that the highest percentage of energy consumption occurs at a crack angle of 45°, indicating intense microcrack activity. Moreover, a novel tensile strength prediction model, incorporating macro–micro damage interactions caused by both microcracks and macrocracks, was developed to explain the failure mechanisms in R–C specimens under radial compression. The model was validated through experimental results, demonstrating its potential for predicting failure behavior in R–C systems. This study offers insights into the fracture mechanics of R–C structures, advancing the understanding of their failure mechanisms and providing a reliable model for tensile strength prediction. Full article