Search Results (5,279)

Background: Lower airway diseases in children are one of the major causes of hospitalisation. This study aimed to evaluate the characteristics of children admitted to a tertiary pediatric hospital diagnosed with lower airway disease and to identify differences between age groups and the two years of the study. Methods: In this single-centre retrospective observational study, demographic and clinical information about children hospitalised in the emergency pediatric ward and diagnosed with lower respiratory disease from 1 June 2021 to 30 June 2023 were retrospectively reviewed. Results: A total of 410 episodes of hospitalisation for lower airway diseases were registered. In 83.9% of cases, the patient needed hospitalisation for respiratory failure, and children <1 year of age were at higher risk. Rhinovirus and respiratory syncytial virus (RSV) were the leading causes of lower respiratory tract infections. No death has been recorded. In 8.8% of cases, the patient was admitted to the Pediatric Intensive Care Unit. In 2021–2022, we recorded more hospitalisations for bronchiolitis with RSV as the primary pathogen detected and more patients were admitted to the hospital for respiratory failure. In 2022–2023, we registered more admissions for bacterial pneumonia and the need for intravenous therapy. Conclusions: Lower respiratory tract diseases are frequent in the pediatric population, and the risk of respiratory failure is higher. Analysing the differences between the two years of study, we underline how the COVID-19 pandemic has changed the epidemiology of acute respiratory infections in children. Full article

Icing significantly reduces the electrical performance of insulators, and grid failures caused by insulator icing are common. Currently, most research on the flashover characteristics of insulators under icing conditions focuses on artificially iced suspension insulators, with limited studies on post insulators under natural icing conditions. The shed spacing of post insulators is smaller, making them more prone to bridging by icicles in the same icing environment, which exacerbates insulation problems. Therefore, investigating the icing characteristics of post insulators is crucial. In this study, natural icing growth was observed on seven different types of post insulators at the Xuefeng Mountain Energy Equipment Safety National Observation and Research Station. The icing morphology and characteristics of these insulators were examined. The main conclusions are as follows: (1) the icing type and morphology of post insulators are influenced by meteorological conditions, with more severe icing observed on the windward side. (2) The icing mass and icicle length of the insulator increase nonlinearly with icing time. Specifically, during the glaze icing period from 0 to 8 h, the ice mass on the Type V composite post insulator was 3.89 times greater than that during the 13-to-18 h period. (3) Within the same icing cycle, the icing growth rate on composite post insulators is faster than on porcelain post insulators. (4) Compared to suspension insulators, the sheds of post insulators are more easily bridged by icicles. Notably, when the sheds of post insulators are bridged by icicles, the length of icicles on suspension insulators is only half of the gap size. Full article

Background: Current antibiotic regimens for infective endocarditis (IE) are effective but pose a high risk of delayed hypersensitivity reactions (DHR). Dose adjustments guided by therapeutic drug monitoring (TDM) could mitigate these risks while maintaining treatment efficacy. This study aimed to investigate the plasma concentration of benzylpenicillin and cloxacillin in patients with IE and explore associations between antibiotic concentrations and DHR. Methods: Plasma concentrations of benzylpenicillin and cloxacillin were measured as centre (midpoint concentrations between consecutive doses) and trough values during the first and third weeks of treatment in patients with IE. Patient characteristics and outcomes, including DHR, were documented. Results: A total of 55 patients were included, with 37 patients (67%) receiving benzylpenicillin and 18 (33%) receiving cloxacillin. The 90-day mortality rate was 3%. Both centre and trough concentration exhibited substantial interpatient variation for the two antibiotics, while intra-patient variability between weeks 1 and 3 remained low for most patients. Kidney function could explain, at best, 54% of the variation, and a multiple regression model including kidney function, body mass index, age, and albumin explained up to 68% of the variation for benzylpenicillin. There was no relation between high plasma concentration and the prevalence of DHR; conversely, we observed a tendency of low plasma concentrations in these patients. Conclusions: This study revealed significant interindividual variation in plasma concentrations for both studied penicillins. TDM might be useful in situations where concentrations are hard to predict, such as severe obesity or kidney failure. Additionally, we found no indication that high plasma concentrations are related to the prevalence of DHR. Full article

Trees are complex and dynamic living structures, where structural stability is essential for survival and for public safety in urban environments. Tree forks, as structural junctions, are key to tree integrity but are prone to failure under stress. The specific mechanical contributions of their internal conical structures remain largely unexplored. This study explores how conical structures optimize stress distribution, filling key gaps in the understanding of tree fork mechanics and supporting safety assessments. This study focused on the following factors: (1) external shape, (2) internal conical reinforcement, (3) interface of the conical connection, and (4) material changes within the conical structure. By analyzing physical samples to extract structural and morphological features, simulating these features in controlled variable models, and performing finite element analysis, we explored mechanical behavior, stress distribution, and performance characteristics, revealing the factors and mechanisms that strengthen tree forks. Insights from this study may facilitate safety assessments and inform pruning strategies for urban tree management. Full article

Structural fatigue can lead to catastrophic failures in various engineering applications and must be properly monitored and effectively managed. This paper provides a state-of-the-art review of recent developments in structural fatigue monitoring using piezoelectric-based sensors. Compared to alternative sensing technologies, piezoelectric sensors offer distinct advantages, including compact size, lightweight design, low cost, flexible formats, and high sensitivity to dynamic loads. The paper reviews the working principles and recent advancements in passive piezoelectric-based sensors, such as acoustic emission wave and strain measurements, and active piezoelectric-based sensors, including ultrasonic wave and dynamic characteristic measurements. These measurements, captured under in-service dynamic strain, can be correlated to the remaining structural fatigue life. Case studies are presented, highlighting applications of fatigue life monitoring in metals, polymeric composites, and reinforced concrete structures. The paper concludes by identifying challenges and opportunities for advancing piezoelectric-based sensors for fatigue life monitoring in engineering structures. Full article

To investigate the influencing factors of the shear failure behavior of rock joints, especially the shear instability characteristics, direct shear tests were performed on marble joints with various grain sizes under different constant normal loads (CNLs). The experimental results show that the grain size and CNL have significant effects on the shear mechanical properties of rock joints. The peak shear strength (τ_p), peak shear displacement (u_p), post-peak modulus (S), and stress drop (Δτ) of rock joints all increase first and then decrease with the increase in grain size, but they increase with the increase in CNL. The mineral composition and microstructure also have a certain influence on the shear mechanical properties of rock joints. In addition, the post-peak soften modulus (S_p) was proposed to describe the shear instability characteristics of rock joints, and its relationship with grain size and CNL was established. The mechanical model of the shear instability of rock joints was established, and the shear instability criterion of rock joints was proposed based on the stiffness criterion and the proposed post-peak soften modulus (S_p). This paper further reveals the shear instability mechanism of rock joints, which can provide a reference for the stability analysis of jointed rockmass. Full article

Rolling bearings, as critical components of rotating machinery, directly affect the reliability and efficiency of the system. Due to extended operation under high load, harsh environmental conditions, and continuous use, bearings become more susceptible to failure, leading to a higher likelihood of malfunction. To prevent sudden failures, reduce downtime, and optimize maintenance strategies, early and accurate diagnosis of rolling bearing faults is essential. Although existing methods have achieved certain success in processing acoustic and vibration signals, they still face challenges such as insufficient feature fusion, inflexible weight allocation, lack of effective feature selection mechanisms, and low computational efficiency. To address these challenges, we propose a dynamic weighted multimodal fault diagnosis model based on the fusion of acoustic and vibration information. This model aims to enhance feature fusion, dynamically adapt to signal characteristics, optimize feature selection, and reduce computational complexity. The model incorporates an adaptive fusion method based on a multi-branch convolutional structure, enabling unified processing of both acoustic and vibration signals. At the same time, a cross-modal dynamic weighted fusion mechanism is employed, allowing the real-time adjustment of weight distribution based on signal characteristics. By utilizing an attention mechanism for dynamic feature selection and weighting, the robustness of classification is further improved. Additionally, when processing acoustic signals, a depthwise separable convolutional network is used, effectively reducing computational complexity. Experimental results demonstrate that our method significantly outperforms other algorithms in terms of convergence speed and final performance. Additionally, the accuracy curve during training showed minimal fluctuation, reflecting higher robustness. The model achieved over 99% diagnostic accuracy under all signal-to-noise ratio (SNR) conditions, showcasing exceptional robustness and noise resistance in both noisy and high-SNR environments. Furthermore, its superiority across different data scales, especially in small-sample learning and stability, highlights its strong generalization capability. Full article

In this study, the mechanical performance and failure modes of cold-potted inserts within sandwich structures were examined, focusing on the influence of the potting radius, while maintaining constant insert radius and specimen characteristics. In this research, destructive testing was used to evaluate the pull out, load-carrying capacity, and failure mechanisms of the inserts. The methods of stiffness degradation and acoustic emissions (AE) were employed for structural health monitoring to capture real-time data on failure progression, including core buckling, core rupture, and skin delamination. The results indicated that increasing the potting radius significantly altered the failure modes and critical failure load of the insert system. A critical potting radius was identified where maximum stiffness was achieved. Beyond this point, insert fracture became the dominant failure mode, with minimal damage to the surrounding core and CFRP skins. Larger potting radii also led to reduced displacement at failure, increased ultimate loads, and elevated stiffness, which were maintained until sudden structural failure. Through detailed isolation and observation of each failure event and with the use of AE data, precise identification of system damage in real time was allowed, offering insights into the progression and causes of failure. Full article

The present research focuses on the mechanical properties and stress evolution of gas-bearing soft coal seams during drilling, which are affected by a multitude of complex factors such as high ground stress, gas pressure, and pre-existing fractures. In this study, a combination of PFC2D (Particle Flow Code in 2 Dimensions) numerical simulation and theoretical analysis is employed to investigate the borehole mechanics and fracture evolution characteristics under diverse complex conditions and to determine the factors influencing different forms of borehole failure in soft coal seams. The principal outcomes are as follows: (1) At a horizontal displacement of 0.1 m from the borehole orifice of the soft coal seam, a stress peak value of 13.9 MPa is attained; the peak value of the coal body contact force is 15.8 MPa; the peak value of the displacement is 0.008 m; and the porosity of the coal body around the borehole ranges from 0.14 to 0.35. (2) With an increase in the number of pre-existing fractures, the inclination progressively aligns with that of the pre-existing fractures. Maximum values of contact force (5.13–51.9 MPa), stress (3.19–37.2 MPa), shape dimension, and fracture angle (140–150°) are achieved under the highest lateral pressure coefficient and gas pressure (1.5 MPa). (3) The borehole energy is directly proportional to the number of pre-existing fractures, the lateral pressure coefficient, and gas pressure. The number of pre-existing fractures has the most significant impact on the damage degree, followed by the lateral pressure coefficient and then the gas pressure. (4) Two types of failure are identified: fracture-dominated failure, which is controlled by the geometric distribution of pre-existing fractures, and stress-dominated failure, wherein the failure zone gradually extends both upward and downward with an increasing lateral pressure coefficient. Full article

Titanium aluminides, particularly the Ti-48Al-2Cr-2Nb alloy, have drawn significant attention for their potential in high-temperature aerospace and automotive applications due to their exceptional performances and reduced density compared to nickel-based superalloys. However, their intermetallic nature poses challenges such as limited room-temperature ductility and fracture toughness, limiting their widespread application. Additive manufacturing, specifically Electron Beam Melting (EBM), has emerged as a promising method for producing complex-shaped components of titanium aluminides, overcoming challenges associated with conventional production methods. This work investigates the fracture behavior of Ti-48Al-2Cr-2Nb specimens with different microstructures, including duplex and equiaxed, under tensile and high-cycle fatigue at elevated temperatures. Fracture surfaces were analyzed to distinguish between static and dynamic fracture modes. A novel method, employing confocal microscopy acquisitions, is proposed to correlate surface roughness parameters with the causes of failure, offering new insights into the fracture mechanisms of titanium aluminides. The results reveal significant differences in roughness values between the propagation and fracture zones for all the temperatures and microstructure tested. At 650 °C, the crack propagation zone exhibits lower Sq values than the fracture zone, with the fracture zone showing more pronounced roughness, particularly for the equiaxed microstructure. However, at 760 °C, the difference in Sq values between the propagation and fracture zones becomes more pronounced, with a more substantial increase in Sq values in the fracture zone. These findings contribute to understanding fracture behavior in titanium aluminides and provide a predictive framework for assessing structural integrity based on surface characteristics. Full article

Acoustic emission (AE) is a powerful tool for investigating the intermittency of plastic flow by capturing elastic waves generated by dislocation rearrangements under load. This study explores the correlation between AE and plastic instabilities, such as Lüders bands, the Portevin–Le Chatelier (PLC) effect, and necking, each showing distinct AE signatures. Lüders and PLC bands generate significant AE during discontinuous yielding, with a sharp rise in AE levels and a shift in the spectrum to lower frequencies—characteristic of localized deformation. In contrast, necking exhibits limited AE activity, due to reduced strain hardening and dislocation mobility during late-stage deformation. A phenomenological model, based on dislocation dynamics and initially devised for uniform deformation, is discussed to explain the observed AE spectral features during localized plastic flow. This study underscores AE’s potential for non-destructive evaluation and failure prediction in structural metals, emphasizing its sensitivity to microstructural changes and instabilities. Understanding AE behavior across deformation stages offers valuable insights into improving material reliability and predicting failure. Full article

This paper aims to address the issue of hydraulic support crushing accidents or support failures in the retracement roadway (RR) that frequently occurs when a fully mechanized mining face is retraced during the end-mining stage. The deformation and instability mechanism of surrounding rock in the RR during the end mining of a fully mechanized mining face at the Hanjiawan Coal Mine located in the northern Shaanxi mining area is explored through field measurement, theoretical analysis, similar simulation, and numerical simulation. The results reveal that the stability of the remaining coal pillar (RCP) and the fracture position of the main roof are the main factors contributing to large-scale dynamic load pressure in the RR during the end-mining stage. The plastic zone width limit of the RCP is identified to be 5.5 m. Furthermore, the stress distribution within the RCP during the end-mining stage is determined, and the linear relationship between the load borne by the RCP and the strength of the coal pillar is quantified. A similar simulation experiment is conducted to examine the collapse and instability characteristics of the overlying rock structure during the end-mining stage. UDEC (v.5.0) software is utilized to optimize the roof support parameters of the RR. A surrounding rock control technology that integrates the anchor net cable and hydraulic chock is proposed to ensure RR stability. Meanwhile, a method involving ceasing mining operations and waiting pressure is adopted to ensure a safe and smooth connection between the working face and the RR. This study provides a reference for the surrounding rock control of the RR during end mining in shallow, closely-spaced coal seams under similar conditions. Full article

In view of the application status and technical challenges of steel–wood composite joints in architecture, this paper proposes an innovative connection technology to solve issues such as susceptibility to pry-out at beam–column joints and low load-bearing capacity and to provide various reinforcement methods in order to meet the different structural requirements and economic benefits. By designing and manufacturing four groups of beam–column joint specimens with different reinforcement methods, including no reinforcement, structural adhesive and angle steel reinforcement, 4 mm thick steel sleeve reinforcement, and 6 mm thick steel sleeve reinforcement, monotonic loading tests and finite element simulations were carried out, respectively. This research found that unreinforced specimens and structural adhesive angle steel-reinforced joints exhibited obvious mortise and tenon compression deformation and, moreover, tenon pulling phenomena at load values of approximately 2 kN and 2.6 kN, respectively. However, the joint reinforced by a steel sleeve showed a significant improvement in the tenon pulling phenomenon and demonstrated excellent initial stiffness characteristics. The failure mode of the steel sleeve-reinforced joints is primarily characterized by the propagation of cracks at the edges of the steel plate and the tearing of the wood, but the overall structure remains intact. The initial rotational stiffness of the joints reinforced with angle steel and self-tapping screws, the joints reinforced with 4 mm thick steel sleeves, and the joints reinforced with 6 mm thick steel sleeves are 3.96, 6.99, and 13.62 times that of the pure wooden joints, while the ultimate bending moments are 1.97, 7.11, and 7.39 times, respectively. Using finite element software to simulate four groups of joints to observe their stress changes, the areas with high stress in the joints without sleeve reinforcement are mainly located at the upper and lower ends of the tenon, where the compressive stress at the upper edge of the tenon and the tensile stress at the lower flange are both distributed along the grain direction of the beam. The stress on the column sleeve of the joints reinforced with steel sleeves and bolts is relatively low, while the areas with high strain in the beam sleeve are mainly concentrated on the side with the welded stiffeners and its surroundings; the strain around the bolt holes is also quite noticeable. Full article

This study investigates the design and mechanical evaluation of hydroxyapatite (HAp) scaffolds for bone tissue engineering, using stereolithography (SLA) to fabricate homogeneous and hollow elongated Voronoi structures. HAp, known for its biocompatibility and biodegradability, was selected to create scaffolds with a structure that supports cell growth. Both scaffold designs were tested under compression to measure key properties, including compressive strength, Young’s modulus, stiffness, and energy absorption. The homogeneous design demonstrated superior mechanical properties, achieving a maximum load of 913.6 N at a displacement of 0.166 mm and a stiffness of 5162.8 N/mm, indicating a higher load-bearing capacity and energy absorption compared to the hollow design. Despite these strengths, failure analysis revealed early fractures at strut junctions, particularly in slender areas, leading to fluctuations in the load–displacement curve and suggesting a risk to neighboring tissues in practical applications. These findings underscore the potential of Voronoi-based scaffolds for orthopedic use, while also highlighting the need for structural refinements to improve scaffold durability and clinical effectiveness. Full article

To thoroughly investigate the anchorage performance of a novel prefabricated concrete shear wall system assembled by anchoring closed-loop rebar, rebar pull-out tests were conducted. The effects of different rebar distribution forms, closed-loop rebar anchoring heights, and dowel rebar diameters on anchorage performance were considered. Strain measurements at key points were taken, and the failure modes and peak loads of shear walls with various closed-loop rebar assemblies were obtained. The results indicated that the rebars in all specimens fractured, with peak loads ranging from 90 kN to 100 kN, satisfying the anchorage requirements of the rebar. This demonstrates that even when the anchorage length of the rebar is less than specified, the method of assembling by anchoring closed-loop rebar can still provide good anchorage performance. Moreover, steel bars and concrete have different damage and failure characteristics under different load levels. This research also indicates that specimens with uniformly distributed closed-loop rebar exhibit superior anchorage performance compared to those with adjacent distribution. Furthermore, increasing the overlapping height of the closed-loop rebar contributed to enhancing the safety margin of the anchorage, while the diameter of the dowel rebar (similar to stirrups) had a relatively minor effect on the anchorage performance. These findings provide a scientific basis for the design and construction of prefabricated concrete shear walls with closed-loop rebar. Full article