Search Results (533)

Pitching requires effective transfer of ground reaction force (GRF), and structural breakdown of the medial longitudinal arch (MLA) may influence glenohumeral internal rotation (IR) deficits. This study investigated whether changes in foot morphology of the stride leg and soft tissue characteristics are associated with loss of IR during repeated pitching. Fifteen male college pitchers completed 60 pitches in a simulated game. IR range of motion (IRROM) was assessed before and after pitching. The navicular height, mechanical properties of the abductor hallucis (AbH) and plantar fascia, and GRF were measured at multiple time points. Correlation analysis and a linear mixed model were used to identify predictors of IRROM change. The mean change in shoulder IRROM during pitching was −21.9° ± 8.4°. IRROM and navicular height decreased significantly over time. The AbH elasticity increased throughout the pitching sequence. Greater reductions in IRROM appeared related to a higher vertical GRF (p = 0.021) and increased AbH elasticity (p = 0.046). Vertical GRF was unrelated to fastball velocity (p = 0.260), whereas anteroposterior GRF correlated with fastball velocity (p = 0.038). Morphological and mechanical changes in the stride leg, particularly within the support of the MLA, can influence IRROM. Reducing vertical GRF and stress on the AbH may help preserve the IRROM without compromising performance. Full article

Microwave-Induced Hydrogen Plasma (MIHP) is introduced as a novel synthesis route for producing high-entropy carbides (HECs), offering an alternative to conventional mechanical alloying and/or sintering techniques. In this study, a representative HEC composition, ${\mathrm{MoNbTaVWC}}_5$, was successfully synthesized using MIHP processing at 200 Torr. The process employs microwave energy to generate hydrogen plasma to facilitate carbothermal reduction of metal oxide precursors. The plasma environment generates abundant reactive atomic hydrogen species, which enhance reaction spontaneity and promote efficient HEC formation. X-ray diffraction confirmed the formation of a single-phase rocksalt-type face-centered cubic structure. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy confirmed uniform elemental distribution within the synthesized microstructure. Nanoindentation measurements yielded hardness and elastic modulus values consistent with literature reports for similar compositions. X-ray photoelectron spectroscopy confirmed the chemical state of carbon to be primarily bonded with metals as carbides, with only minor oxygen present as metal-oxides. Raman spectroscopy performed over the 750–1900 ${\mathrm{cm}}^{-1}$ range yielded a featureless spectrum with no detectable D or G bands often observed for sp²-hybridized disordered carbon, graphite, or graphene materials. These results validate the structural and chemical purity of the synthesized HECs. This work aims to demonstrate the feasibility and reproducibility of MIHP as a synthesis method for HECs. Full article

Background/Objectives: This paper presents the results of predicting chronological age from psychophysiological tests using machine learning regressors. Methods: Subjects completed a series of psychological tests measuring various cognitive functions, including reaction time and cognitive conflict, short-term memory, verbal functions, and color and spatial perception. The sample included 99 subjects, 68 percent of whom were men and 32 percent were women. Based on the test results, 43 features were generated. To determine the optimal feature selection method, several approaches were tested alongside the regression models using MAE, $R^2$, and $CV\text{\_}{R}^2$ metrics. SHAP and Permutation Importance (via Random Forest) delivered the best performance with 10 features. Features selected through Permutation Importance were used in subsequent analyses. To predict participants’ age from psychophysiological test results, we evaluated several regression models, including Random Forest, Extra Trees, Gradient Boosting, SVR, Linear Regression, LassoCV, RidgeCV, ElasticNetCV, AdaBoost, and Bagging. Model performance was compared using the determination coefficient ($R^2$) and mean absolute error (MAE). Cross-validated performance ($CV\text{\_}{R}^2$) was estimated via 5-fold cross-validation. To assess metric stability and uncertainty, bootstrapping (1000 resamples) was applied to the test set, yielding distributions of MAE and RMSE from which mean values and 95% confidence intervals were derived. Results: The study identified RidgeCV with winsorization and standardization as the best model for predicting cognitive age, achieving a mean absolute error of 5.7 years and an $R^2$ of 0.60. Feature importance was evaluated using SHAP values and permutation importance. SHAP analysis showed that stroop_time_color and stroop_var_attempt_time were the strongest predictors, followed by several task-timing features with moderate contributions. Permutation importance confirmed this ranking, with these two features causing the largest performance drop when permuted. Partial dependence plots further indicated clear positive relationships between these key features and predicted age. Correlation analysis stratified by sex revealed that most features were significantly associated with age, with stronger effects generally observed in men. Conclusions: Feature selection revealed Stroop timing measures and task-related metrics from math and campimetry tests as the strongest predictors, reflecting core cognitive processes linked to aging. The results underscore the value of careful outlier handling, feature selection, and interpretable regularized models for analyzing psychophysiological data. Future work should include longitudinal studies and integration with biological markers to further improve clinical relevance. Full article

This paper discusses the phenomenon of concrete creep and its impact on bridge structures, with particular emphasis on the mechanical models used to describe it. Classical rheological models, such as the Maxwell and Kelvin–Voigt, along with their generalized and fractional extensions incorporating fractional-order derivatives, are presented. These models differ in their complexity and in the accuracy of fit to laboratory test results. The use of non-classical, fractional-order rheological models (the fractional Kelvin–Voigt model and the fractional Zener model) enables better model fitting. The paper further describes methods for estimating creep effects in bridge design. The most popular is the effective modulus method, which is easy to implement but does not account for the load application history. More accurate approaches (e.g., Trost, Bažant, incremental method according to linear elasticity theory) are based on iterative procedures and require advanced computer implementation. The consequences of creep in bridge structures are highlighted: geometric (changes in elevation) and static (redistribution of internal forces and support reactions, changes in sectional stresses). These effects are particularly important in structures erected in stages, such as bridges built using the balanced cantilever method. The analytical section presents the influence of various creep models on changes in static quantities for a three-span prestressed bridge constructed by the cantilever method. The importance of proper selection of the creep model for the accuracy of engineering calculations and for the correct assessment of the long-term behavior of the structure is emphasized. Full article

The elastic support structure is widely employed in rotor systems and has an important influence on the nonlinear vibration of such systems. Nevertheless, coupled motion between elastic supports and bearings has not been taken into account, and the coupling effect of these two components on rotor dynamics remains insufficiently elucidated. Therefore, this work presents a bearing force model considering the motion of the elastic support. Subsequently, this work presents a new rotor-bearing dynamics model, in which the coupled motion between elastic supports and bearings is explicitly accounted for. Moreover, the coupling effect of elastic supports and bearings is systematically investigated through analyses of frequency–amplitude responses, waterfall plots, contact loads of bearings, operational deflection shape, and bifurcation diagrams. To further reveal this coupling effect, the nonlinear vibration behaviors of the rotor-bearing system with elastic support are analyzed under different bearing initial clearances. Finally, the experiments on rotor test rigs with and without elastic supports are conducted to validate the accuracy of the proposed dynamic model. Both simulation and experimental results indicate that elastic supports mitigate the nonlinear vibration of the rotor-bearing system; additionally, elastic support could reduce the bearing reaction forces and contact loads. Moreover, elastic supports alter the operational deflection shape of the rotor-bearing system. Full article

An analytical method is proposed for determining the stress-strain state in an elastic layer with a cylindrical cavity supported by linear continuous supports perpendicular to the cavity. The need for such a development is due to the fact that in aerospace and mechanical engineering, structural elements are often affected by loads and supports described by infinite functions. This complicates the calculation for spatial bodies with complex geometry and stress concentrators. The methodology is based on the generalized Fourier method within the spatial problem of elasticity theory. The model is considered as a layer with specified stresses at the outer boundaries, where the reactions of the supports are represented as applied loads. A combined approach is used to describe the geometry using a Cartesian coordinate system for the layer and a cylindrical coordinate system for the cavity. The key idea is to decompose the original problem into two simpler ones using the principle of superposition. Auxiliary problem: the stresses in a solid layer (without a cavity) are calculated to determine the stress fields at its nominal location. Main problem: a layer with a cavity is considered, on the surface of which the stresses calculated in the first step are acting but taken with the opposite sign. The complete solution is the sum of the solutions of these two problems. Each of them is reduced to an infinite system of linear algebraic equations, which is solved by the method of reduction. This approach makes it possible to calculate the stress-strain state at any point of the body with high accuracy. Numerical analysis confirmed the correctness of satisfying the boundary conditions and showed the dependence of stresses on the nature of the distributed loads. The cylindrical cavity acts as a stress concentrator, which leads to a local increase in stresses σ_x and σ_z at the upper and lower boundaries of the layer to values that exceed both the applied load by and the calculated resistance of concrete of class C25/30. Full article

In the described studies, raw material from chemically recycled petrochemical foam and biobased polyurethane foams (100% of rapeseed oil polyol were used in polyol premix) were utilised in order to obtain viscoelastic foams. The recycled foams exhibited differences in chemical structure, resulting in the formation of four different repolyols. The obtained repolyols were employed as replacements for 10 to 30 wt.% of the petrochemical polyol in the mixture utilised to produce viscoelastic polyurethane foams. It was determined that the chemical structure of the polyol utilised for the foam’s initial production influences the properties of the repolyols obtained and thus also the properties of the viscoelastic foams obtained using them. It was found that foams obtained with the addition of 10 wt.% repolyols were characterized by the best properties among the obtained modified foams, comparable or even better than in the case of petrochemical reference foam. The apparent density of such foams was about 70 kg/m³. Depending on the type of repolyol used, the hardness of the foams ranged from 2 to 8 kPa, and the comfort factor was between 2.5 and 5.0. The foams obtained were characterised by their ability to absorb energy, as evidenced by a resilience of no more than 10% in most cases. However, increasing the percentage of repolyol in the reaction mixture caused too many changes in the structure of the polymer chains, disrupting the arrangement of rigid and elastic segments, which caused the hardness to increase significantly, and the foams were therefore more susceptible to permanent deformation. Full article

To explore new possibilities in topological materials, we designed a tetrafunctional crosslinker composed of a [c2]daisy-chain rotaxane framework. In this study, a novel topological network polymer was successfully synthesized via an addition reaction between 3,6-dioxa-1,8-octanedithiol (DODT) and a tetrafunctional crosslinker, a [c2]daisy-chain rotaxane constructed from dibenzo-24-crown-8 ether (DB24C8) units and bearing long-chain alkenes on its four benzene rings. The resulting network polymer exhibited both high stiffness and toughness, along with excellent shape-memory properties. These characteristics were governed by a balance between plastic and elastic deformation originating from the DODT and rotaxane domains, respectively, highlighting a new design strategy for the creation of advanced topological materials. Full article

This study aims to develop a modified starch with menthol (M) or sulfobetaine (S) using 1,6-hexamethyl diisocyanate (HMDI) as a linker to create biodegradable antibacterial materials for active packaging applications. The modification of potato starch is performed in a two-step reaction. First, the starch modifiers are synthesized through an equimolar reaction between HMDI and menthol or the sulfobetaine precursor. Next, the synthesized HMDI derivative is dissolved in a bio-based solvent (methyl-THF) with starch and K₂CO₃ (1:1 weight ratio) to chemically modify the starch. The chemical and thermal properties of the modified starch are analyzed. Starch films containing 25 wt.% glycerol and low amounts (0.5, 1, and 3% wt.) of M- or S-modified starch were successfully produced by extrusion. Although most film properties remain similar to the control, adding 3% of S-modified starch resulted in a 149% increase in Elastic Modulus and a 29% decrease in water vapor permeability. Additionally, just 0.5 wt.% of either M- or S-modified starch effectively inhibits S. aureus growth, indicating its potential as a bioactive compound for active packaging. Full article

This study presents a belt sanding robot for large convex surfaces together with a proportional–integral force control method. Sanding belt tension strongly affects area coverage and spatial normal-force uniformity on large curved surfaces; existing approaches typically use fixed tool positions or lack active tension regulation, which limits coverage and makes force distribution difficult to control. The mechanism consists of two series elastic actuator arms and an active re-tensioner that adjusts belt tension during contact. In contrast to a conventional belt sander, the series elastic configuration enables indirect estimation of the reaction force without load cells and provides compliant interaction with contact transients. The system is evaluated on curved steel plates using vertical scans with a belt width of 50 mm and a drive wheel speed of 300 rpm. Performance is reported for two target curvature values, namely 0.47 and 1.37, with five trials for each condition. The control objective is a constant normal force along the contact, achieved through proportional–integral control of the arms for normal-force tracking and the re-tensioner for belt tension regulation. To quantify spatial force uniformity, the distribution rate is defined as the ratio of the difference between the maximum and minimum normal forces to the maximum normal force measured across the belt–workpiece contact region. Compared with a simple belt sander baseline, the proposed system increased the sanded area coverage by 31.85%, from 62.20% to 94.05%, at the curvature value of 0.47, and by 8.49%, from 81.21% to 89.70%, at the curvature value of 1.37. The distribution rate improved by 113% at the curvature value of 0.47 and by 16.7% at the curvature value of 1.37. Under identical operating conditions of 50 mm belt width, 300 rpm, and five repeated trials, these results indicate higher area coverage and more uniform force distribution relative to the baseline. Full article

Polyacrylamide and polyacrylamide/polysaccharide hydrogels exhibiting high structural and mechanical properties, along with acceptable gelation times and gelant viscosity, are proposed for water shutoff applications in high-temperature reservoirs. The obtained polyacrylamide gels demonstrate an elastic modulus 1.6–2.7 times higher than that of the baseline polyacrylamide–resorcinol–paraform–sulfamic acid gel (17.2 Pa), reaching up to 46.3 Pa, while the polyacrylamide/polysaccharide gels surpass it by a factor of 2.3–5.2, reaching up to 89.9 Pa. The gelation time of the polyacrylamide/polysaccharide gels ranges from 3 to 7 h, with the gelant viscosity varying from 685 to 2098 mPa·s at a shear rate of 100 s⁻¹. Crosslinking of polyacrylamide with polysaccharides was achieved using paraform. Using the gel based on crosslinked polyacrylamide with xanthan as an example, spectral methods characterized the copolymer constituting the basis of the plugging material. Our analysis established that crosslinking occurs between the amide group of polyacrylamide and the hydroxyl group of the polysaccharide. Model reactions with low-molecular-weight analogs (glucose, acetamide, and formaldehyde), coupled with mass spectrometric confirmation of the structure of the resulting products, revealed possible reaction pathways. The crosslinking of polyacrylamide was investigated using a broad range of polysaccharides of plant and microbiological origin. The resulting series of hydrogels, possessing the suite of properties required for water shutoff in high-temperature formations, will enable oil companies (operators) and service firms to select a specific gel-forming system based on project objectives, logistics, and budget constraints. Full article

Rubber material with high elasticity and viscoelasticity has become the most widely used universal material, and the study of the aging failure mechanism of rubber has been meaningful research in the polymer materials field. Cis-polyisoprene was employed to analyze the mechanism of oxidative degradation under artificial UV irradiation, and the GQDs/g-C₃N₄ photocatalysis with a 2D layered structure prepared by the method of microwave-assisted polymerization enabled to accelerate the degradation procedure. The results showed that the oxidation of cis-polyisoprene occurred during the irradiation for 3 days and the structure of cis-polyisoprene changed. The α-H of the double bond was attacked by oxygen to form hydroperoxide. Then, aldehydes and ketones generated as the addition reaction of double bonds occurred. The content of the hydrogen of C=C reduced, and the oxidative degradation was dominant at the initial aging stage. The crosslinking reaction was dominant at the final aging stage and the average molecular weight decreased from 15.49 × 10⁴ to 8.78 × 10⁴. The GQDs could promote the charge transfer and the photodegradation efficiency and inhibit the electron–hole recombination. The light capture ability of GQDs was improved after compositing with g-C₃N₄. The free radicals ·O₂²⁻ generated after adding GQDs/g-C₃N₄ nanoparticles, and the molecular weight of cis-polyisoprene decreased to 5.79 × 10⁴, with the photocatalytic efficiency increasing by 20%. This work provided academic bases and reference values for the application of photocatalysts in the field of natural rubber degradation and rubber wastewater treatment. Full article

In this work, general purpose rubber composites were created based on a mixture of non-polar cis-1,4-isoprene rubber and cis-1,4-divinyl rubber as components. The main filler used was carbon black, while various graphite-like materials (graphite oxide, reduced graphite oxide, expanded graphite, and graphite nanoplatelets) served as additives. It was determined that the addition of these graphite-like materials resulted in a reduction in Mooney viscosity, with the introduction of graphene nanoplatelets having the most significant effect, contributing to a viscosity decrease of 8.5%. The relaxation rate increased, positively impacting elastic recovery and consequently reducing shrinkage. The introduction of graphite oxide, graphite nanoplatelets, and expanded graphite also increased the time to the onset of the vulcanization reaction; moreover, these additives lengthened the time needed to reach the optimum level of vulcanization. The addition of various graphite-like materials significantly affected the elongation at break, with the highest increase attributable to the addition of expanded graphite and reduced graphite oxide. It was found that the conditional tensile strength of these additives had little effect. Upon assessing the elastic-strength properties after aging, it was found that the inclusion of graphite-like materials reduced the elongation at break. Full article

Sports footwear is widely used across a range of physical activities. A key factor distinguishing running shoes from other types of footwear is the “drop,” the millimeter difference between the heel and the forefoot. This study aimed to analyze the influence of different drops (0, 5, and 10 mm) on ground reaction forces during walking and to examine the effects of sex and body mass index (BMI) under these conditions. An observational, descriptive, and cross-sectional study was conducted with 117 participants (56 men and 61 women). The Dinascan/IBV^® dynamometric platform (Instituto de Biomecánica de Valencia, Valencia, Spain) was used to measure ground reaction forces during walking (braking, take-off, propulsion, and swing forces), walking speed, and stance time. The descriptive analysis revealed comparable values for the left and right limbs, with slightly higher values observed in the right limb. Statistically significant differences were found in stance time, braking force, and swing force between the 0 mm and 10 mm drop conditions. Take-off force showed highly significant differences when comparing the 0–5 mm and 0–10 mm drop conditions. Sex-based differences were observed in all variables at the initial proposed drop condition of 0 mm, except for walking speed, possibly due to anatomical and physiological differences. Significant differences were found in stance time at 0 mm drop, braking force, and propulsion force. Highly significant values were obtained for take-off force and during the swing phase. A strong correlation was found between ground reaction forces and BMI with the different proposed drops in all forces studied, except for the support force, where a moderate correlation was obtained. Although shoe drop was found to influence ground reaction forces in this study, it is one of several factors that affect gait biomechanics. Other footwear characteristics, such as sole stiffness, material composition, weight, and elasticity, also play important roles in walking performance. Therefore, shoe drop should be considered an important but not exclusive parameter when selecting footwear. However, these results are limited to healthy young adults and may not be generalizable to other age groups or populations. Full article

The activation and dissociation of O₂ molecules play a key role in the oxidation of toxic gas molecules and the oxygen reduction reaction (ORR) in hydrogen–oxygen fuel cells. The interactions between O₂ molecules and the surfaces of Fe-doped γ-graphyne were systematically explored, mainly adopting the combined method of the density functional theory with dispersion correction (DFT-D3) and the climbing image nudged elastic band (CI-NEB) method. The order of the formation energy values of these defective systems is E_f(Fe_C2) < E_f(Fe_C1) < E_f(Fe_D1) < E_f(V_C1) < E_f(V_D1) < E_f(V_C2) < E_f(Fe_D2) < E_f(V_D2), which indicates that the process of Fe dopant atoms substituting single-carbon atoms/double-carbon atoms is relatively easier than the formation of vacancy-like defects. The results of ab initio molecular dynamics (AIMD) simulations confirm that the doped systems can maintain structural stability at room temperature conditions. Fe-doped atoms transfer a certain amount of electrons to the adsorbed O₂ molecules, thereby causing an increase in the O-O bond length of the adsorbed O₂ molecules. The electrons obtained by the anti-bonding 2π* orbitals of the adsorbed O₂ molecules are mainly derived from the 3d orbitals of Fe atoms. There is a competitive relationship between the substrate’s carbon atoms and the adsorbed O₂ molecules for the charges transferred from Fe atoms. In the C1 and C2 systems, O₂ molecules have a greater advantage in electron accepting ability compared to the substrate’s carbon atoms. The elongation of O-O bonds and the amount of charge transfer exhibit a positive relationship. More electrons are transferred from Fe-3d orbitals to adsorbed O₂ molecules, occupying the 2π* orbitals of adsorbed O₂ molecules, further elongating the O-O chemical bond until it breaks. The dissociation process of adsorbed O₂ molecules on the surfaces of GY-Fe systems (C2 and D2 sites) involves very low energy barriers (0.016 eV for C2 and 0.12 eV for D2). Thus, our studies may provide useful insights for designing catalyst materials for oxidation reactions and the oxygen reduction reaction. Full article