Search Results (291)

The aim of the study was to determine correlations between performance of vertical jumps and dolphin kick sprints, and between the results of a dry-land butterfly arm pull test and butterfly arms-only swimming. The study recruited competitive junior male swimmers (15.9 (0.7) years, 179.3 (5.3) cm body height, 64.6 (4.3) kg body mass). On dry land, we measured jump height, lower-limb work and power, as well as peak velocity, power, and force in the butterfly arm pull test. In swimming tests, time, velocity, power, force, and work were assessed during the dolphin kick and butterfly arms-only trials. Pearson’s correlation coefficients and the coefficients of determination were calculated between measurements. The findings showed correlations between swimming velocity and power recorded during the dolphin kick test with jump height, work and power measured in the jump tests (maximum r = 0.90, r² = 0,81, p < 0.05). The best correlations between the results of the jump tests and swim variables were determined for the CJ30s test. The butterfly arm pull test was not associated with all parameters measured by the butterfly arms-only test. Our study demonstrates that targeted dry-land training programmes using exercises like vertical jumps can enhance competitive swimmers’ performance and offer coaches an accessible means of tracking athlete progress. Moreover, such simple drills may serve as a cost-effective approach for early evaluation of strength and power potential and for preventing musculoskeletal injuries, all without requiring pool access or specialized underwater equipment. However, the small and homogeneous sample (n = 12, junior males only) and the absence of reliability analyses limit the generalizability of the results. Full article

This study aimed to compare the anthropometric and performance characteristics of U16 and U18 male basketball players to better understand post-peak height velocity (PHV) developmental differences. A total of 31 athletes from the local international basketball academy participated in the research—15 from the U16 category (15.25 ± 0.86 years) and 16 from the U18 category (17.46 ± 0.34 years). Measurements included body composition, sprinting (with and without the ball), agility, and jump performance. The results revealed significant between-group differences in most anthropometric variables (p < 0.001), including body mass, BMI, skeletal muscle mass, fat-free mass, total body water, and segmental muscle mass. However, there were no significant differences in body height and body fat percentage. Performance comparisons showed that U18 players outperformed U16 players in agility (p = 0.026), 10 m and 20 m sprints (p = 0.045 and p = 0.016, respectively), and 20 m dribbling sprints (p = 0.011), while no significant differences were observed in jumping ability. These findings suggest that physical maturation strongly influences anthropometric parameters and partially affects performance characteristics. The results highlight the importance of age-appropriate training strategies that consider biological development stages in youth basketball. Full article

Gravity anomalies caused by tectonics are commonly assumed to be static, based on the argument that the motions are slow enough for the induced mass changes over time to be negligible. We exploit this concept in the context of rifting and subduction by showing that the horizontal motions of density contrasts occurring at active and passive margins are responsible for sizable amounts of gravity rate of change. These findings are obtained via 2D finite element modeling of the two tectonic mechanisms in a vertical cross-section perpendicular to the ocean–continent transition as well as through evaluating the time-dependent gravity disturbance at a reference height caused by mass readjustment underneath. This disturbance originates from deep-seated changing density anomalies and dynamic topography with respect to a reference normal Earth. The gravity rate of change is proven to scale linearly with extensional and trench migration velocity; the peak-to-peak values between the largest maxima and minima are 0.08 μGal/yr and 0.21 μGal/yr, for a velocity of 1 cm/yr. For both tectonic mechanisms, the dominant positive rate of change is due to the horizontal motion of a density contrast of about 300–400 kg/m³. We also consider the role of dynamic topography in comparison to that of deep-seated changing density anomalies. Full article

Introduction: Overuse injuries are a growing concern among adolescent soccer players, with the repetitive nature of the sport placing significant physical demands on young athletes. These injuries can have long-term implications for physical development, performance, and overall well-being. This narrative synthesis aimed to evaluate the existing literature on the epidemiology, risk factors, and management strategies for overuse injuries in adolescent soccer players. Methods: A comprehensive literature search was conducted using PubMed and Embase. A total of 123 articles were identified, 27 of which met the inclusion criteria after screening. Studies focusing on overuse injuries in adolescent soccer players aged 10–18 years were included, while those addressing acute injuries, non-soccer populations, or adult athletes were excluded. Relevant quantitative and qualitative data were extracted and evaluated. Due to heterogeneity in study designs and outcomes, findings were narratively synthesized rather than meta-analyzed. Results: The period around peak height velocity (PHV: 11.5 years in girls, 13.5 years in boys) was consistently identified as a high-risk window, with seven studies demonstrating a significantly increased incidence of overuse injuries. Additional risk factors included leg length asymmetry, truncal weakness, early sport specialization, high ratios of organized-to-free play, and increased body size. Injury burden was greatest for hamstring and groin injuries, often leading to prolonged time lost from play. Preventive interventions such as plyometric training, trunk stabilization, and structured load monitoring demonstrated reductions in injury incidence in several prospective studies, though protocols varied widely. Conclusion: This narrative synthesis highlights PHV as the most consistent risk factor for overuse injuries in adolescent soccer players, alongside modifiable contributors such as training load, sport specialization, and free play balance. Evidence supports neuromuscular training and structured monitoring as promising preventive strategies, but there remains a lack of standardized, evidence-based protocols. Future research should focus on optimizing and validating interventions, integrating growth and load monitoring, and leveraging emerging approaches such as machine learning-based risk prediction. Full article

Pedestrian wind comfort is a critical factor in the design of sustainable and livable dense urban areas. This study systematically investigates the effects of surrounding building height and wind incidence angle on pedestrian-level wind conditions, analyzing a nine-building arrangement through validated Computational Fluid Dynamics (CFD) simulations. Scenarios included neighborhood heights varying from 0L to 6L and wind angles from 0° to 45°. The results reveal that wind angles aligned with urban canyons (0° case) induce a strong Venturi effect, creating hazardous conditions with Mean Velocity Ratio (MVR) peaks reaching 3.42. Conversely, an oblique 45° angle mitigates high speeds by promoting flow recirculation. While increasing neighborhood height generally intensifies channeling, the study also highlights that even an isolated building (0L case) can generate hazardous localized velocities due to flow separation around its corners. The Overall Mean Velocity Ratio (OMVR) analysis identifies that, among the studied cases, a 2L neighborhood height is the most tolerable configuration, striking a balance between sheltering and channeling effects. Ultimately, these findings highlight for urban planners the importance of analyzing diverse geometric configurations and wind scenarios, reinforcing the value of CFD as an essential tool for designing safer and more comfortable public spaces. Full article

This study investigated countermovement jump (CMJ) strategies among NCAA Division 1 athletes and explored key variables associated with jump height. A total of 69 athletes (38 male, 31 female) from basketball and volleyball teams completed three or more CMJ trials on force plates during their regular neuromuscular monitoring. Using repeated-measures correlation analysis, we examined the relationships between various force–time variables and jump height across different sports and sexes. The results demonstrated very strong correlations between concentric peak velocity and jump height across all groups (r > 0.987). In addition, female athletes exhibited higher correlations between force-related parameters (concentric peak force, relative concentric peak force, and relative concentric mean force) and jump height compared to male athletes. Furthermore, no significant differences in force asymmetry were observed between sports or sexes. These findings indicate that concentric peak velocity serves as a key indicator of jump performance while emphasizing the importance of considering the interaction between force, time, and velocity, rather than focusing solely on peak force production. This research provides valuable insights for developing sport-specific training programs and monitoring jump performance in collegiate athletes, highlighting the necessity of individualized assessment and training approaches rather than assuming specific physical qualities are associated with particular populations. Full article

This study examines the ionospheric response to the intense geomagnetic storm of 9–12 October 2024 over the European sector. Digisonde data from mid-latitude European stations and in situ electron density measurements from Swarm A and B satellites were used to analyze variations in key ionospheric characteristics, including the critical frequency (foF2), peak height (hmF2) and plasma drift velocities. Significant uplift of the F2 layer and a corresponding reduction in foF2 were observed across latitudes, primarily driven by prompt penetration electric fields (PPEFs) and storm-induced thermospheric winds. Horizontal and vertical ion drifts showed large asymmetries and reversals, with zonal drift velocities exceeding 1000 m/s at some stations. Swarm observations confirmed plasma density enhancements during the main phase and notable depletions during recovery, particularly after 1:00 UT on 11 October. The midlatitude ionospheric trough (MIT) intensified during the recovery phase, as can be seen from Swarm B. These variations were shaped by electrodynamic forcing, compositional changes and disturbance dynamo electric fields (DDEFs). The results emphasize the role of solar wind drivers, latitude-dependent electrodynamic coupling and thermospheric dynamics in mid-latitude ionospheric variability during geomagnetic storms. Full article

The jet fan system is a widely adopted form of longitudinal ventilation due to its cost-effectiveness, operational flexibility, and high reliability. However, in large-section highway tunnels with a low height-to-span ratio, the limited clearance between the tunnel ceiling and surrounding structural boundaries imposes significant constraints on improving ventilation performance by adjusting the installation height or pitch angle of the jet fan. To address this limitation, this study proposes a deflector shield system to enhance the aerodynamic efficiency of jet fans. A total of thirteen test cases, including a control group, three deflector plate quantities, and four deflector pitch angles, were tested in a full-scale field test conducted in a large-section tunnel. The objective of this study was to evaluate the influence of the number and pitch angle of deflector plates on tunnel ventilation efficiency and to identify the optimal parameter combination for application in large-section tunnels. The results show that static pressure along the tunnel initially rises with distance from the fan, peaks, and then declines sharply. The pressure rise coefficient is significantly enhanced under several configurations, particularly with four deflector plates at 8° and 10° pitches, and with five plates at 4° to 10° pitches. When the number of deflector plates is five, a sharp drop in average wind speed is observed 15 m downstream of the fan, and extensive low-velocity regions appear further downstream. In contrast, the configurations with four deflector plates at 8° and 10° exhibit better wind speed uniformity in the downstream flow field. Considering both the pressure rise coefficient and wind speed uniformity, the optimal ventilation performance of the jet fan system is achieved with four deflector plates at a pitch angle of 8°. Full article

A novel honeycomb with gradient-thickness cell walls (HGTCWs) is fabricated through chemical etching to achieve progressive thickness reduction in the cell walls. This engineered honeycomb demonstrates superior energy absorption by effectively eliminating the peak load during the linear elastic stage of the load–displacement curve under impact loading, thereby preventing premature structural failure caused by excessive instantaneous loads. To systematically investigate the impact compression mechanics, energy absorption characteristics, and key influencing factors of aluminum HGTCWs, a three-factor orthogonal array of low-velocity impact experiments was designed. The design of experimental parameters for the impact test has taken into account the impact mass, impact velocity, and etching height. Comparative analysis assessed how these factors influence energy absorption performance. Results reveal that chemical etching-induced thickness gradient modification effectively suppresses peak load generation. Load–displacement curves exhibit distinct bilinear characteristics: an initial single linear phase when compression displacement is below the etching height, followed by a dual-linear phase with an inflection point at the gradient height. Time–velocity profiles during impact primarily consist of an initial nonlinear deceleration phase followed by a linear deceleration phase. Range analysis and analysis of variance identify impact velocity as the dominant factor influencing the energy absorption characteristics of HGTCWs. Full article

Background: Anterior cruciate ligament reconstruction (ACLr) often leads to asymmetries between limbs, with variable return-to-performance rates in athletes. The single-leg countermovement jump (SLCMJ) is commonly used to assess postoperative knee function. However, limited research has explored deficits specifically during the unweighting phase of the jump. Methods: This study assessed 53 recreational athletes (11 females, 42 males) between 6 and 9 months post-ACLr using a dual force plate system (1000 Hz). Each participant performed three maximal-effort SLCMJs per limb. Outcome measures included jump height, negative peak velocity, minimum force, and center of mass (COM) displacement. Paired t-tests and Wilcoxon tests were used to compare the ACLr limb with the contralateral limb. Results: Compared to the healthy limb, the ACLr limb showed significantly lower negative peak velocity (−0.80 ± 0.40 m/s vs. −0.94 ± 0.40 m/s, p < 0.001), higher minimum force (36.75 ± 17.88 kg vs. 32.05 ± 17.25 kg, p < 0.001), and reduced COM displacement (−17.62 ± 6.25 cm vs. −19.73 ± 5.34 cm, p = 0.014). Eccentric phase duration did not differ significantly. Conclusions: Athletes post-ACLr demonstrate altered neuromuscular control during the early SLCMJ phase. These findings highlight the importance of rehabilitation strategies targeting eccentric strength and symmetry restoration. Full article

The present study was motivated by the need to enhance indoor air quality and reduce airborne disease transmission in dense urban environments where high-rise residential buildings face challenges in achieving effective natural ventilation. The problem lies in the lack of scalable and convenient tools to optimize natural ventilation rate, particularly in urban settings with varying building heights. To address this, the scientific technique developed with an innovative metric, the urbanized natural ventilation effectiveness factor (uNVeF), integrates regression analysis of wind direction, velocity, air change rate per hour (ACH), window configurations, and building height to quantify ventilation efficiency. By employing a field measurement methodology, the measurements were conducted across 25 window-opening scenarios in a 13.9 m² residential unit on the 35/F of a Hong Kong public housing building, supplemented by the Hellman Exponential Law with a site-specific friction coefficient (0.2907, R² = 0.9232) to estimate the lower floor natural ventilation rate. The results confirm compliance with Hong Kong’s statutory 1.5 ACH requirement (Practice Note for Authorized Persons, Registered Structural Engineers, and Registered Geotechnical Engineers) and achieving a peak ACH at a uNVeF of 0.953 with 75% window opening. The results also revealed that lower floors can maintain 1.5 ACH with adjusted window configurations. Using the Wells–Riley model, the estimation results indicated significant airborne disease infection risk reductions of 96.1% at 35/F and 93.4% at 1/F compared to the 1.5 ACH baseline which demonstrates a strong correlation between ACH, uNVeF and infection risks. The uNVeF framework offers a practical approach to optimize natural ventilation and provides actionable guidelines, together with future research on the scope of validity to refine this technique for residents and developers. The implications in the building industry include setting up sustainable design standards, enhancing public health resilience, supporting policy frameworks for energy-efficient urban planning, and potentially driving innovation in high-rise residential construction and retrofitting globally. Full article

To compensate for the instability of renewable energy sources during China’s energy transition, large thermal power plants must provide critical operational flexibility, primarily through deep peaking. To investigate the combustion performance and wear and tear of a 600 MW pulverized coal boiler under deep peaking, the gas–solid flow characteristics and distributions of flue gas temperature, wall heat flux, and wall wear rate in a 600 MW tangentially fired pulverized coal boiler under variable loads (353 MW, 431 MW, 519 MW, and 600 MW) are investigated in this study employing computational fluid dynamics numerical simulation method. Results demonstrate that increasing the boiler load significantly amplifies gas velocity, wall heat flux, and wall wear rate. The maximum gas velocity in the furnace rises from 20.9 m·s⁻¹ (353 MW) to 37.6 m·s⁻¹ (600 MW), with tangential airflow forming a low-velocity central zone and high-velocity peripheral regions. Meanwhile, the tangential circle diameter expands by ~15% as the load increases. The flue gas temperature distribution exhibits a “low-high-low” profile along the furnace height. As the load increases from 353 MW to 600 MW, the primary combustion zone’s peak temperature rises from 1750 K to 1980 K, accompanied by a ~30% expansion in the coverage area of the high-temperature zone. Wall heat flux correlates strongly with temperature distribution, peaking at 2.29 × 10⁵ W·m⁻² (353 MW) and 2.75 × 10⁵ W·m⁻² (600 MW) in the primary combustion zone. Wear analysis highlights severe erosion in the economizer due to elevated flue gas velocities, with wall wear rates escalating from 3.29 × 10⁻⁷ kg·m⁻²·s⁻¹ (353 MW) to 1.23 × 10⁻⁵ kg·m⁻²·s⁻¹ (600 MW), representing a 40-fold increase under full-load conditions. Mitigation strategies, including ash removal optimization, anti-wear covers, and thermal spray coatings, are proposed to enhance operational safety. This work provides critical insights into flow field optimization and wear management for large-scale coal-fired boilers under flexible load operation. Full article

Accurate modeling of the power–cadence relationship is essential for assessing maximal anaerobic power (Pmax) of the lower limbs. Experimental data points from Force–Velocity tests during cycling do not always reflect the maximal and cadence-specific power individuals can produce. The quality of the models and the accuracy of Pmax estimation is potentially compromised by the inclusion of non-maximal data points. This study evaluated a novel residual-based filtering method that selects five strategically located, maximal data points to improve model fit and Pmax prediction. Twenty-three recreationally active male participants (age: 26 ± 5 years; height: 178 ± 5 cm; body mass: 73 ± 11 kg) completed a Force–Velocity test consisting of multiple maximal cycling efforts on a stationary ergometer. Power and cadence data were used to generate third-order polynomial models: from all data points (High Number, HN), from the highest power value in each 5-RPM interval (Moderate Number, MN), and from five selected data points (Low Number, LN). The LN model yielded the best goodness of fit (R² = 0.995 ± 0.008; SEE = 29 ± 15 W), the most accurate estimates of experimentally measured peak power (mean absolute percentage error = 1.45%), and the highest Pmax values (1220 ± 168 W). Selecting a limited number of maximal data points improves the modeling of individual power–cadence relationships and Pmax assessment. Full article

To address the challenges of inadequate adaptability, insufficient power, high ground clearance, and limited functionality in existing pineapple field machinery, this study proposes a height-adjustable pineapple field management platform based on previously established cultivation patterns and agronomic requirements. The structural configuration and operational principles of the platform’s power chassis are elucidated, with specific emphasis on the development of the traction power system and modular operational systems. Theoretical and experimental analyses of steering parameters, stability, and field performance were conducted. Finite element simulation analysis of the frame revealed that under full-load conditions, the equivalent elastic strains during descent and ascent phases were 0.000317 and 0.00125, respectively. Maximum equivalent stresses (48.27 MPa and 231.6 MPa for descent and ascent, respectively) were localized at the beam–plate junctions, while peak deformations of 1.14 mm (descent) and 4.31 mm (ascent) occurred at mid-frame and posterior–mid regions, respectively. Field validation demonstrated operational velocities of 0.16–1.77 m/s (forward) and 0.11–0.28 m/s (reverse), with a maximum gradability of 20°. The platform exhibited multifunctional capabilities including weeding, spraying, fertilization, flower induction, harvesting, and transportation, demonstrating its potential to fulfill the operational requirements for pineapple field management. Simultaneously, the overall work efficiency is increased by more than 50%, compared to manual labor. Full article

In this study, we present a comprehensive numerical investigation of alternating-current electrothermal (ACET) pumping strategies tailored for energy-efficient microfluidic applications. Using coupled electrokinetic and thermal multiphysics simulations in narrow microchannels, we systematically explore the effects of channel geometry, electrode asymmetry and external heating on flow performance and thermal management. A rigorous mesh convergence study confirms velocity deviations below ±0.006 µm/s across the entire operating envelope, ensuring reliable prediction of ACET-driven flows. We demonstrate that increasing channel height from 100 µm to 500 µm reduces peak temperatures by up to 79 K at a constant 2 W heat input, highlighting the critical role of channel dimensions in convective heat dissipation. Introducing a localized external heat source beneath asymmetric electrode pairs enhances convective circulations, while doubling the fluid’s electrical conductivity yields a ~29% increase in net flow rate. From these results, we derive practical design guidelines—combining asymmetric electrode layouts, tailored channel heights, and external heat bias—to realize self-regulating, low-power microfluidic pumps. Such devices hold significant promises for on-chip semiconductor cooling, lab-on-a-chip assays and real-time thermal control in high-performance microelectronic and analytical systems. Full article