Search Results (20)

Ferrite grain size strengthening makes the predominant contribution to the overall strength of ferrite–pearlite structural hollow section steel grades. A fine ferrite grain size is achieved through a two-stage controlled cooling process. First, the material is rapidly cooled with water. This provides a large undercooling, which is the driving force for ferrite to form. The second stage involves slow natural (air) cooling, where the cooling rates and the transition temperature from water to air cooling are carefully controlled. This is crucial to prevent the formation of bainite or martensite. Ferrite grain sizes can be predicted for continuous cooling and isothermal transformation based on the prior austenite grain size, composition and cooling rate/isothermal transformation temperature. However, predictions for multiple-cooling-stage transformations have not been reported. In this work, EN S355-grade steel was used to study ferrite grain size development during continuous cooling, isothermal holding and complex (two-stage or multi-stage) cooling. Dilatometry and microstructure assessment was used to study the relationship between the final ferrite grain size and undercooling at which 40% of the ferrite formed. It was found that any changes in cooling rate/temperature (including a possible ‘bounce back’ in temperature due to latent heat formation) after 40% of the ferrite had formed had a negligible effect on the final ferrite grain size, assuming that re-austenitization or bainite formation was avoided. Full article

The advent of digital mining has become a tangible reality in recent years. This digital evolution requires a predictive understanding of key elements, particularly considering the reliable communication infrastructures needed for autonomous machines. The LoRa technology and its underground propagation behavior can make an important contribution to this digitalization. Since LoRa operates with a high signal budget and long ranges in sub-GHz frequencies, its behavior is very promising for underground sensor networks. The aim of the development and series of measurements was to observe LoRa’s applicability and propagation behavior in active salt mines and to detect and identify effects arising from the special environment. The propagation of LoRa was measured via packet loss and signal strength in line-of-sight and non-line-of-sight configurations over entire mining sections. The aim was to analyze the performance of LoRa at the macroscopic level. LoRa operated at 868 MHz in the free band, and units were equipped with omni-directional antennas. The K+S Group’s active salt and potash mine Werra, Germany, was kindly opened as a distinctive experimental setting. The LoRa exhibited characteristics that were highly distinctive in this environment. The presence of the massive salt allowed the signal to bounce along drift edges with near-perfect reflection, which enabled travel over kilometers due to a waveguide-like effect. A packet loss of below $15\%$ showed that LoRa communication was possible over distances exceeding 1000 m with no line-of-sight in room-and-pillar structures. Measured differences of $\Delta 50\mathrm{dBm}$ values confirmed consistent path loss across different materials and tunnel geometries. This effect occurs due to the physical structure of the mining drifts, facilitating the containment and direction of signals, minimizing losses during propagation. Further modeling and measurements are of great interest, as they indicate that LoRa can achieve even better outcomes underground than in urban or indoor environments, as this waveguide effect has been consistently observed. Full article

Physical fitness is a key indicator of children’s health, yet amidst rising inactivity and obesity, data on Kenyan children are scarce. This study assessed health- and skill-related fitness differences between rural and urban Kenyan children while examining demographic influences. Cardiorespiratory fitness (CRF), BMI, strength, flexibility, speed, agility, and coordination were assessed in 1131 children aged 11.07 ± 0.9 years (52.7% girls) recruited using stratified cluster random sampling. Significant rural–urban disparities were observed. In urban areas, 16.6% were overweight and 2.8% obese, compared to 4% and 0.6% in rural areas (p < 0.001). Conversely, 44.5% of the rural cohort were underweight versus 13.7% urban cohort (p < 0.001). Multivariable regression revealed that rural children demonstrated superior CRF (β = −4.68 laps, p < 0.001) and lower back flexibility (β = −2.77 cm, p < 0.001), while urban children excelled in speed and coordination (β = 3.68 bounces, p < 0.001) and grip strength (β = 2.16 kg, p < 0.001). Boys outperformed girls in explosive leg power (β = −6.75 cm, p < 0.001) and CRF (β = −6.92 laps, p < 0.001). These findings highlight fitness inequities among Kenyan children, emphasising the need for equitable, targeted, and inclusive physical activity opportunities. Full article

Bubble–particle collisions in turbulent flows are fundamental to flotation processes, yet their complex dynamics remain challenging to characterize accurately. In this study, a comparison study of a particle–bubble collision system in homogeneous isotropic turbulence was performed using the particle-resolved method and point-particle method. Direct numerical simulations of turbulent flows were achieved using the lattice Boltzmann method (LBM). The effects of hydrodynamics on the collision particles were compared between Lagrangian tracking and directly resolving the disturbance flows around finite-size solid particles using an interpolated bounce-back scheme. The differences between point-particle and particle-resolved simulations are evaluated, highlighting their respective strengths and limitations. These findings enhance the understanding of turbulence-driven bubble–particle interactions and provide guidance for improving the accuracy of flotation modeling and process optimization. Full article

Large forgings are crucial in aerospace applications; however, the residual stresses generated during their forming and heat treatment seriously affect their serviceability. Therefore, the non-destructive detection of residual stresses in large forgings is of far-reaching significance for ensuring the quality of forgings and realising precision machining. Although a variety of detection methods are available, there is still a lack of a programme that can comprehensively, accurately and non-destructively measure the residual stresses in large forgings. This study is dedicated to exploring the application of the bouncing impact indentation method in the non-destructive testing of residual stresses in large forgings. Through in-depth finite element simulations and orthogonal scheme analyses, we found that the elastic modulus, yield strength and work hardening indexes have significant effects on the impact indentation process. Further, we establish the dimensionless function of residual stress and indentation parameters, and successfully obtain the inversion algorithm of residual stress. The relative error of the calculated values of the indentation curves hm and hr in the simulation with reference values is not more than 3%, and the relative error of the corrected Pm inversion values for most virtual materials is not more than 5%. The folding elastic modulus and apparent elastic modulus obtained by inversion are controlled within 10%, which demonstrates a high value for engineering applications. In addition, we innovatively express the research results in the form of 3D stress diagrams, realising the digital expression of 3D residual stresses in large forgings based on feature point measurements and contour surface configurations, which provides intuitive and comprehensive data support for engineering practice. Full article

Ice formation and accumulation on surfaces has a negative impact in many different sectors and can even represent a potential danger. In this review, the latest advances and trends in icephobic coatings focusing on the importance of their durability are discussed, in an attempt to pave the roadmap from the lab to engineering applications. An icephobic material is expected to lower the ice adhesion strength, delay freezing time or temperature, promote the bouncing of a supercooled drop at subzero temperatures and/or reduce the ice accretion rate. To better understand what is more important for specific icing conditions, the different types of ice that can be formed in nature are summarized. Similarly, the alternative methods to evaluate the durability are reviewed, as this is key to properly selecting the method and parameters to ensure the coating is durable enough for a given application. Finally, the different types of icephobic surfaces available to date are considered, highlighting the strategies to enhance their durability, as this is the factor limiting the commercial applicability of icephobic coatings. Full article

The research presented here demonstrates the practical aspects of the numerical correlation of the results of the compressive strength test. The destructive test (DT) in a hydraulic press and the non-destructive test (NDT) using a Schmidt hammer in several process variations were evaluated. The aim was to evaluate the real differences between the tool supplier’s curve and testing. Therefore, 150 concrete cube specimens with an edge length of 150 mm were produced using a mixture of three types of concrete classes: C30, C35, and C40. The test was carried out 7 and 28 days of age of the concrete. The Schmidt hammer test was carried out in horizontal (θ = 0) and vertical (θ = 90) directions and using a series of 10 measurements. Furthermore, the tests were performed in two sets: first, the sample was placed on the ground, and second, under a hydraulic jack with a load of 50% of the maximum bearing capacity of specific concrete. Then, regression analysis was performed on the data sets to establish linear mathematical relationships between compressive strength and number of bounces. The results showed that the correlation between the DT and NDT tests has a high value for each group, but the correlation equations are different and must be taken into account. Full article

Background: Plyometric jump training (PJT) encompasses a range of different exercises that may offer advantages over other training methods to improve human physical capabilities (HPC). However, no systematic scoping review has analyzed either the role of the type of PJT exercise as an independent prescription variable or the gaps in the literature regarding PJT exercises to maximize HPC. Objective: This systematic scoping review aims to summarize the published scientific literature and its gaps related to HPC adaptations (e.g., jumping) to PJT, focusing on the role of the type of PJT exercise as an independent prescription variable. Methods: Computerized literature searches were conducted in the PubMed, Web of Science, and SCOPUS electronic databases. Design (PICOS) framework: (P) Healthy participants of any age, sex, fitness level, or sports background; (I) Chronic interventions exclusively using any form of PJT exercise type (e.g., vertical, unilateral). Multimodal interventions (e.g., PJT + heavy load resistance training) will be considered only if studies included two experimental groups under the same multimodal intervention, with the only difference between groups being the type of PJT exercise. (C) Comparators include PJT exercises with different modes (e.g., vertical vs. horizontal; vertical vs. horizontal combined with vertical); (O) Considered outcomes (but not limited to): physiological, biomechanical, biochemical, psychological, performance-related outcomes/adaptations, or data on injury risk (from prevention-focused studies); (S) Single- or multi-arm, randomized (parallel, crossover, cluster, other) or non-randomized. Results: Through database searching, 10,546 records were initially identified, and 69 studies (154 study groups) were included in the qualitative synthesis. The DJ (counter, bounce, weighted, and modified) was the most studied type of jump, included in 43 study groups, followed by the CMJ (standard CMJ or modified) in 19 study groups, and the SJ (standard SJ or modified) in 17 study groups. Strength and vertical jump were the most analyzed HPC outcomes in 38 and 54 studies, respectively. The effects of vertical PJT versus horizontal PJT on different HPC were compared in 21 studies. The effects of bounce DJ versus counter DJ (or DJ from different box heights) on different HPC were compared in 26 studies. Conclusions: Although 69 studies analyzed the effects of PJT exercise type on different HPC, several gaps were identified in the literature. Indeed, the potential effect of the PJT exercise type on a considerable number of HPC outcomes (e.g., aerobic capacity, flexibility, asymmetries) are virtually unexplored. Future studies are needed, including greater number of participants, particularly in groups of females, senior athletes, and youths according to maturity. Moreover, long-term (e.g., >12 weeks) PJT interventions are needed Full article

The icing of glass insulators is likely to cause faults such as insulator flashover, which poses a serious threat to the power system. Traditional deicing techniques have the disadvantage of being costly and inefficient. Herein, polytetrafluoroethylenes (PTFEs) as nanoparticles and epoxy and fluorosilicone resins as binders were blended to construct an anti-icing coating. The superhydrophobic (SHP) epoxy/fluorosilicone/PTFE coatings for anti-icing were successfully prepared on glass slides through one-step spraying. The effect of PTFE mass fraction on the microstructure, on the wettability and on the anti-icing properties of the coatings was investigated. The results showed that the coatings with different PTFE mass fractions had different microstructures. When the PTFE mass fraction was 47.2%, the SHP coating exhibited a uniform rough structure with an apparent contact angle as high as 164.7° and a sliding angle as low as 3.2°. Moreover, the water droplets can bounce back five times with a contact time of only 9.5 ms and a rebound height of 4.58 mm. In the low-temperature environment (−10 °C), the SHP coating displayed good anti-frosting, anti-icing and icephobic properties. The delayed frosting time (1499 s) and delayed freezing time (1295.3 s) of the SHP coating were three and five times longer than those of the glass, respectively. The SHP coating presented an ice-adhesion strength (39.8 kPa) that was six times lower than that of glass. The prepared SHP coating demonstrated potential applications for the anti-icing of glass insulators. Full article

The aims of this study were to analyze the heart rate response, the game temporal structure (i.e., mean total time of the matches, real playing time, total rest time) and the stroke technique distribution and to describe its relations in the table tennis national category in simulated competitions. A cohort of 60 table tennis male players (22.06 ± 8.32 years) played 30 simulated matches. The obtained results show a mean heart rate (HR_mean) of 142.69 ± 14.10 bpm and a peak heart rate (HR_peak) of 167.26 ± 16.51 bpm. Total strokes were 7505, being the 57.88% and 42.12% forehand and backhand strokes, respectively. The most frequent forehand strokes were service (SERV) (33.13%) and forward spin technique (SPIN) (40.75%) stroke types, with the left quadrant of the table away from the net (Z_5) (25%) and right quadrant of the table away from the net (Z_6) (20.72%) being the most frequent ball bouncing placements. Meanwhile, the most frequent backhand strokes were backspin technique (PUSH) (42.74%) and SPIN (31.86%) stroke types, with the intermediate left quadrant of the table (Z_3) (17.21%), Z_5 (31.22%) and Z_6 (18.54%) being the most frequent ball placements. The mean total time of the matches was 15.74 ± 3.82 min, the mean real playing time was 4.14 ± 1.47 min and the total rest time was 11.60 ± 2.67 min. Heart rate variables did not correlate significantly with the different stroke types or the game temporal variables (p > 0.05). However, stroke types and game temporal structure variables were significantly correlated (p < 0.01). This information can be useful to reveal players’ strengths and weaknesses and prepare subsequent training sessions, adapting training sessions to the needs of the athletes. Full article

Mechanical properties, in particular, strength (tensile, shear, compressive) and porosity, are important parameters for understanding the evolution and activity of comets. However, they are notoriously difficult to measure. Unfortunately, neither Deep Impact nor other comet observations prior to Rosetta provided firm data on the strength of cometary material. This changed with the Rosetta mission and its detailed close observation data and with the landing(s) of Philae in 2014. There are already many articles and reviews in the literature that derive or compile many different strength values from various Rosetta and Philae data. In this paper, we attempt to provide an overview of the available direct and indirect data; we focus on comet Churyumov–Gerasimenko/67P but include a discussion on the Deep Impact strength results. As a prerequisite, we start by giving precise definitions of ‘strength’, discuss soil mechanics based on the Mohr–Coulomb ‘law’ of micro-gravity, and discuss bulk density and porosity, sintering, and the physics of the strength of a cohesive granular medium. We proceed by discussing the scaling of strength with the size and strain rate, which is needed to understand the observational data. We show how measured elastic properties and thermal (conductivity) data can be correlated with strength. Finally, a singular very high strength value is reviewed as well as some particularly small-strength values inferred from the bouncing motion of Philae, data from its collisions with the surface of the comet, and scratch marks it left, allegedly, on the surface close to its final resting site. The synthesis is presented as an overview figure of the tensile and compressive strength of cometary matter as a function of the size scale; conclusions about the size dependence and apparent natural variability of strength are drawn. Full article

The adhesion of water to the surfaces of unmanned aerial vehicles (UAVs) adversely affects the function. The proposed UAVs will have underwater as well as flight capability, and these aquatic UAVs must shed water to resume flight. The efficient separation of the adhering water from aquatic-UAV surfaces is a challenging problem; we investigated the application of hydrophobic surfaces as a potential solution. Using aquatic-UAV models, one with hydrophilic surfaces and the other with superhydrophobic anisotropic textured surfaces, the antiwetting mechanism of the hydrophobic surfaces was investigated using a simulated-precipitation system and instrumentation to measure the load of the water adhering to the aquatic UAV, and to measure the impact energies. When the model was stationary (passive antiwetting), no adhesion occurred on the superhydrophobic surfaces, while continuous asymmetric thick liquid films were observed on the hydrophilic surfaces. The superhydrophobic surfaces reduced the rain loading by 87.5%. The vibration and movement of the model (dynamic antiwetting, simulating flight motions) accelerated the separation process and reduced the contact time. The observed results were augmented by the use of computational fluid dynamics with lattice Boltzmann methods (LBM) to analyze the particle traces inside the droplets, the liquid phase velocity-field and pressure-field strengths, and the backward bouncing behavior of the derived droplet group induced by the moving surface. The synergy between the superhydrophobic surfaces and the kinetic energy of the droplets promotes the breakup of drops, which avoids the significant lateral unbalance observed with hydrophilic surfaces during simulated flight. Full article

The application of the traditional planar acoustics method is limited due to the low accuracy when computing the echo characteristics of underwater targets. Based on the concept of the shooting and bouncing ray which considers multiple reflections on the basic of the geometrics optics principle, this paper presents a more efficient GPU-accelerated multiresolution grid algorithm in the shooting and bouncing ray method (SBR) to quickly predict the target strength value of complex underwater targets. The procedure of the virtual aperture plane generation, ray tracing, scattered sound field integral and subdividing the divergent ray tubes are all implemented on the GPU. Particularly, stackless KD-tree traversal is adopted to effectively improve the ray-tracing efficiency. Experiments on the rigid sphere, cylinder and corner reflector model verify the accuracy of GPU-based multiresolution SBR. Besides, the GPU-based SBR is more than 750 times faster than the CPU version because of its tremendous computing capability. Further, the proposed accelerated GPU-based multiresolution SBR improves runtime performance at least 2.4 times that of the single resolution GPU-based SBR. Full article

This study examined the relations among burn stigma, quality of life, resilience, and life satisfaction, hypothesizing that higher stigma and lower burn-related quality of life would lead to lower life satisfaction; however, resilience would moderate this relation. A sample of 89 participants was recruited from an outpatient clinic of a burn center in a critical care hospital. Participants completed a battery of measures assessing these constructs. Results suggested that burn stigma was associated with reduced life satisfaction after accounting for other variables. Multiple regression models found that burn stigma predicted both affect and body image but not interpersonal relationship quality or sexuality. Interpersonal relationship quality, sexuality, affect, and body image all predicted life satisfaction. Both affect and body image partially accounted for the relation between stigma and life satisfaction, and resilience accounted for the relation between stigma and affect. Findings reinforce previous literature that has shown a relationship between stigma and life satisfaction but also emphasizes the role of resilience and burn-related quality of life. Individuals who experience a burn injury may have innate resilience abilities, which allow them to bounce back from stressors; thus, resilience can be a targeted strength to bootstrap in order to improve adjustment outcomes. Full article

The aim of the research was to implement an athletic program to improve the explosive force in order to optimize physical fitness at the level of elite football-tennis players and evaluate the progress made through specific tests using the Opto Jump. The research included 10 elite European and world-class players, on whom an experimental program was applied in order to improve the explosive force of the limbs in conditions of speed, endurance, and dynamic balance. Study tests: five vertical jumps on the spot, on the left/right leg; five back and forth jumps on the left/right leg; five left/right side jumps on the left/right leg; vertical jumps on both legs 60 s; BFS vertical jumps. For each test, the following parameters specific to the explosive force were statistically analyzed: contact time (s); flight time (s); jump height (cm), jump power (w/kg); RSI—Reactive Strength Index, defined as Height (m/s). In the study, the average value of the parameters specific to the jumps performed in each test was taken into account. During the study, the tests were performed and processed on the Opto Jump device and software. In all tests of the experiment monitored through Opto Jump, significant progress was made in the final test compared to the initial one, which demonstrates the efficiency of the physical training program implemented for the development of explosive force, with an impact on the sports performance of elite players. The most relevant results obtained for the left leg regarding the improvement of the explosive force of the lower limbs materialized in the jump height parameter was in the test of five vertical jumps on one leg on the spot, and for the right leg in the tests of: five back and forth jumps and five left/right side jumps. The most significant advances in the study were in the tests, in descending order of their weight: 60 s vertical jumps on both legs; five back-and-forth jumps and five left/right side jumps, five vertical jumps on one leg standing, and BFS vertical jumps. Full article