Search Results (19)

Metallic nanofoams with amorphous structures demonstrate exceptional properties and significant potential for diverse applications. However, their mechanical properties at different temperatures are still unclear. By using molecular dynamics simulation, this study investigates the mechanical responses of representative CuZr amorphous metallic nanofoam (AMNF) under uniaxial tension and compression at various temperatures. Our results reveal that the mechanical properties, such as Young’s modulus, yield stress, and maximum stress, exhibit notable temperature sensitivity and tension–compression asymmetry. Under tensile loading, the Young’s modulus, yield strength, and peak stress exhibit significant reductions of approximately 30.5%, 33.3%, and 32.9%, respectively, as the temperature increases from 100 K to 600 K. Similarly, under compressive loading, these mechanical properties experience even greater declines, with the Young’s modulus, yield strength, and peak stress decreasing by about 34.5%, 38.0%, and 41.7% over the same temperature range. The tension–compression asymmetry in yield strength is temperature independent. Interestingly, the tension–compression asymmetry in elastic modulus becomes more pronounced at elevated temperatures, which is attributed to the influence of surface energy effects. This phenomenon is further amplified by the increased disparity in surface-area-to-volume ratio variations between tensile and compressive loading at higher temperatures. Additionally, as the temperature rises, despite material softening, the structural resistance under large tensile strains improves due to delayed ligament degradation and more uniform deformation distribution, delaying global failure. Full article

The low-chirp operation of distributed feedback lasers is highly desirable in high-speed and high-bit rate optical transmission. In this article, we address this issue by theoretically investigating the possibility of further a reduction in the linewidth enhancement factor (LEF) of a quantum well (QW). The energy band structure of AlGaInAs quantum-well DFB lasers grown with a (110) crystal orientation in the active region of the L-band has been theoretically analyzed using multi-band k.p perturbation theory, by reducing the asymmetry of conduction bands and valence bands and thus the linewidth enhancement factor parameter, which is related to the frequency chirp. Simulation results show that the LEF of the directly modulated DFB laser is reduced from 2.434 to 1.408 by designing the (110)-oriented compression-strained Al_0.06Ga_0.24InAs multiple-quantum-well structure, and the eye diagram of the (110)-oriented quantum-well DFB laser with a digital signal transmission of 20 km is significantly better than the (001) crystal-oriented quantum-well DFB laser for the 10Gbps optical fiber communication system, thus achieving a longer distance and higher-quality optical signal transmission. Full article

Carbon staple fiber composites are materials reinforced with discrete-length carbon fibers processed using traditional textile technologies, offering moderate mechanical properties and flexibility in manufacturing. These composites can be produced from recycled carbon staple fibers, aligned into yarn and tape-like structures, providing a more sustainable alternative while balancing performance, cost-effectiveness, and environmental impact. Aligning staple fibers into tape-like structures enables similar applications to those of continuous-fiber-based products, while allowing control over fiber orientation distribution, fiber volume fraction, and length distribution, which are all critical factors influencing both mechanical and thermo-mechanical properties. This study focuses on the experimental characterization and numerical investigation of Coefficients of Thermal Expansion (CTEs) in aligned carbon staple fiber composites. The effects of fiber orientation and volume fraction on coefficients of thermal expansion under different fiber alignment parameters are analyzed, revealing distinct thermal expansion behavior compared to typical aligned unidirectional continuous carbon fiber composite laminates. Unlike continuous unidirectional laminates, which typically exhibit transversely isotropic behavior without tensile–shear coupling, staple fiber composites demonstrate different in-plane axial, transverse, and out-of-plane CTE characteristics. To explain these deviations, a modeling approach is introduced, incorporating detailed experimental information on fiber distributions and microstructural features rather than averaged fiber orientation values. This involves a multi-scale analysis based on a laminate analogy through which all composite thermo-elastic properties can be predicted, accounting for variations in fiber orientations, volume fractions, and tape thicknesses. It is shown that while the local variation of fiber volume fraction has a small effect on the homogenized value of the coefficients of thermal expansion, fiber misalignment, tape thickness, and asymmetry in fiber orientation distribution will significantly affect the measurements of CTEs. For the case of carbon staple fiber composites, the asymmetry in fiber orientation distribution significantly influences the measurements of axial CTE. Fiber orientation asymmetry causes tensile–shear coupling under mechanical and thermal loading, leading to an unbalanced laminate with in-plane shear–tensile deformation. This coupling disrupts uniform displacement, complicating strain measurements and the determination of composite properties. Full article

Background/Objectives: Thrombocytopenia–absent radius (TAR) syndrome is a rare genetic disorder characterized by the bilateral absence of the radius and thrombocytopenia, often leading to functional limitations and gait asymmetries. Prosthetic devices are sometimes employed to improve mobility and posture, but their impact on gait mechanics in pediatric patients remains poorly understood. Methods: The methodology used is based on a study that evaluated the gait parameters of a 10-year-old child with TAR syndrome under static and dynamic conditions, both with and without the use of a custom-designed upper limb prosthesis. The analysis focused on assessing the prosthesis’s impact on gait symmetry and biomechanics. A key aspect of the methodology involved studying the distribution of pressure forces on the ground during walking using the FreeMed EXTREME Maxi baropodometric platform. Results: Gait analysis demonstrated asymmetries between the left and right feet. In the absence of the prosthesis, the patient exhibited excessive forward loading and uneven pressure distributions. The use of a custom prosthesis, particularly with counterbalancing features, improved gait symmetry but led to increased reliance on the left foot. This foot experienced higher pressures (738–852 g/cm²) and longer ground contact times (690–865 ms) compared to the right foot (619–748 g/cm² and 673–771 ms). The left foot displayed elevated forefoot pressures (61–65%), while the right foot bore weight laterally (66–74%). Conclusions: The custom prosthesis influenced gait mechanics by redistributing plantar pressures and modifying ground contact times, partially improving gait symmetry. However, compensatory strategies, such as increased loading on the left foot, could contribute to musculoskeletal strain over time. Individualized rehabilitation programs and prosthetic designs are essential for optimizing gait mechanics, improving mobility, and minimizing long-term complications in TAR syndrome patients. Full article

This study investigates the mechanisms driving current generation, power output, and charge storage in carbon nanotube springs under mechanical strain, addressing the gap between experimental observations and theoretical modeling, particularly in asymmetric electrical responses. Leveraging the Dirac equation in curved spacetime, we analyze how curvature-induced scalar and pseudo-gauge potentials shape two-dimensional electron gases confined to carbon nanotube springs. We incorporate applied mechanical strain by introducing time-dependent variations in the Lamé coefficient and curvature parameters, enabling the analysis of mechanical deformation’s influence on electrical properties. Our model clarifies asymmetric electrical responses during stretching and compression cycles and explains how strain-dependent power outputs arise from the interplay between mechanical deformation and curvature effects. Additionally, we demonstrate mechanisms by which strain influences charge redistribution within the helically coiled structure. We develop a new equivalent circuit model linking mechanical deformation directly to electronic behavior, bridging theoretical physics with practical electromechanical applications. The analysis reveals asymmetric time-dependent currents, enhanced power output during stretching, and strain-dependent charge redistribution. Fourier analysis uncovers dominant frequency components (primary at $\Omega$, harmonic at $2\Omega$) explaining these asymmetries. Theoretical investigations explain the mechanisms behind the curvature-driven time-dependent current source, the frequency-dependent peak power, the characteristics of open-circuit voltage with strain, and the asymmetric electrical property response under applied strain as the generated current and the charge distribution within the carbon nanotube springs. These findings highlight carbon nanotube springs applied to energy harvesting, wearable electronics, and sensing technologies. Full article

Background: Postural symmetry ensures balanced alignment and equal weight distribution, promoting optimal function and minimizing stress on muscles and joints. This study aimed to evaluate lower limb movement symmetry in response to mechanical perturbations. Methods: Twelve healthy young women were subjected to mechanical perturbation tests while standing on the Motek GRAIL system treadmill. Maximum values of kinematic and kinetic parameters and symmetry indices were counted to compare the responses of dominant and non-dominant limbs. Results: The study identified symmetrical and asymmetrical features in lower limb dynamics. Symmetry nearness was observed in the ankle joint angle (SI = 0.03), the hip torque (SI = 0.03), and the vertical component of the ground reaction force (SI = 0.04). However, significant asymmetries were found in the medio-lateral component of the ground reaction force (SI = 1.84), ankle torque (SI = 0.23), knee torque (SI = 0.19), hip angle (SI = 0.15), and knee angle (SI = 0.08). The anterior–posterior component of the ground reaction force (SI = 0.14) showed asymmetry but was not statistically significant. Conclusions: Perturbations impact lower limb dynamics, revealing dominance- and joint-specific asymmetries. Bilateral assessment is crucial for understanding postural control, guiding rehabilitation to restore symmetry, and reducing the risk of injuries, falls, and musculoskeletal strain, particularly in athletes and older adults. These findings emphasize the value of symmetry indices in optimizing therapy and prevention strategies. Full article

The tension-compression yield asymmetry caused by the strengthening of Mg-Zn-Gd-Zr alloy due to extrusion deformation is an important issue that must be addressed in its application. In this study, the effects of loading direction on the tensile and compressive mechanical behaviors of Mg-5Zn-2Gd-0.2Zr alloy were systematically investigated. As the loading angle (the angle between the loading direction and the extrusion direction) increases from 0° to 30°, 45°, 60° and 90°, the tensile yield strength decreases more significantly than the compressive yield strength. Consequently, the tension-compression yield asymmetry is gradually improved. Additionally, the ultimate compressive strength decreases more markedly than the ultimate tensile strength with the increment of the loading angle. In tensile tests conducted at 0°, 30° and 45°, two distinct stages of decreasing strain hardening rates are typically observed. For the 60° and 90° tensile tests, one unusual ascending stage of strain hardening rate is observed. For all compressive tests, three stages of strain hardening are consistently noted; however, the increment in strain hardening rate caused by {10–12} extension twinning decreases with the increasing loading angle. A model combining loading angle and Schmid factor distribution was established. The calculated results indicate that the dominant deformation modes during the yielding process also vary significantly with the loading conditions. This clarification highlights the differences in yield strength variations between tension and compression. Finally, an analysis of the plane trace and crack propagation direction near the fracture surface reveals the fracture mechanisms associated with tensile and compressive tests at different loading directions. This study promotes understanding of the mechanical behaviors of Mg-5Zn-2Gd-0.2Zr alloy under different loading directions, and helps to thoroughly elucidate the anisotropic effects of texture on the mechanical properties of magnesium alloys. Full article

The temperature response of pavement is not only crucial for assessing the internal stresses within pavement structures but is also an essential parameter in pavement design. Investigating the temperature response of rubberized concrete pavements (RCP) can support the construction of large-scale rubber concrete pavements. This study constructed a pavement monitoring system based on fiber Bragg grating technology to investigate the temperature distribution, temperature strain, temperature effects, and temperature stress of RCP. The results show that the daily temperature–time history curves of concrete pavement exhibit a significant asymmetry, with the heating phase accounting for only one-third of the curve. The temperature at the middle of RCP is 1.8 °C higher than that of ordinary concrete pavement (OCP). The temperature distribution along the thickness of the pavement follows a “spindle-shaped” pattern, with higher temperatures in the center and lower temperatures at the ends. Additionally, the addition of rubber aggregates increases the temperature strain in the pavements, makes the temperature–strain hysteresis effect more pronounced, and increases the curvature of the pavement slab. However, the daily stress range at the bottom of RCP is approximately 0.7 times that of OCP. Full article

This study explores the dynamics of turbulent flow around a sphere at a Reynolds number of $\mathcal{R}e={10}^3$ using large-eddy simulation, focusing on the intricate connection between vortices and strain within the recirculation bubble of the wake. Employing a relatively new subgrid-scale modeling approach based on scale adaptivity, this research implements a functional relation to compute $k_{\mathrm{sgs}}$ that encompasses both vortex-stretching and strain rate mechanisms essential for the energy cascade process. The effectiveness of this approach is analyzed in the wake of the sphere, particularly in the recirculation bubble, at the specified Reynolds number. It is also evaluated in comparison with two different subgrid-scale models through detailed analysis of the coherent structures within the recirculation bubble. These models—scale-adaptive, k-Equation, and dynamic k-Equation—are assessed for their ability to capture the complex flow dynamics near the wake. The findings indicate that while all models proficiently simulate key turbulent wake features such as vortex formation and kinetic energy distribution, they exhibit unique strengths and limitations in depicting specific flow characteristics. The scale-adaptive model shows a good ability to dynamically adjust to local flow conditions, thereby enhancing the representation of turbulent structures and eddy viscosity. Similarly, the dKE model exhibits advantages in energy dissipation and vortex dynamics due to its capability to adjust coefficients dynamically based on local conditions. The comparative analysis and statistical evaluation of vortex stretching and strain across models deepen the understanding of turbulence asymmetries and intensities, providing crucial insights for advancing aerodynamic design and analysis in various engineering fields and laying the groundwork for further sophisticated turbulence modeling explorations. Full article

The present study investigated the effects of a series of 10 whole-body cryostimulation (WBC) sessions (3 min; −110 °C) on physiological and thermal responses to a submaximal exercise test in 17 elite athletes. Participants performed an exercise test twice at similar levels of intensity before and after a series of ten WBC sessions. Before and during the test, each participant’s oxygen uptake (VO₂), heart rate (HR), internal temperature (Ti), and skin temperature in selected areas of the skin were measured, and the mean arterial pressure (MAP), physiological strain index (PSI), and mean skin temperature (Tsk) were calculated. The results show that during exercise, increases in Ti and the PSI were significantly lower after the WBC sessions, and although there were no significant changes in HR or the MAP, the Tsk was significantly higher. Following exercise, an increase in skin temperature asymmetry over the lower-body muscles was detected. A series of WBC sessions induced a tendency toward a decrease in temperature asymmetry over the thigh muscles. In conclusion, a series of ten WBC sessions does not induce significant modifications in physiological variables but does influence the PSI and Ti during exercise. Moreover, a series of ten WBC sessions influences the distribution of skin temperature and the magnitude of temperature asymmetries in the early phase of recovery. Full article

The noctuid moth soybean looper (SBL), Chrysodeixis includens (Walker) is an economically important pest of soybeans (Glycine max (L.) Merr.) in the southeastern United States. It has characteristics that are of particular concern for pest mitigation that include a broad host range, the capacity for annual long-distance flight, and resistance in some populations to important pesticides such as pyrethroids and chitin synthesis inhibitor. The biology of SBL in the United States resembles that of the fellow noctuid fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), a major pest of corn and several other crops. FAW exhibits a population structure in that it can be divided into two groups (host strains) that differ in their host preferences but are broadly sympatric and exhibit incomplete reproductive isolation. In this paper, strategies used to characterize the FAW strains were applied to SBL to assess the likelihood of population structure in the United States. Evidence is presented for two SBL strains that were defined phylogenetically and display differences in the proportions of a small set of genetic markers. The populations exhibit evidence of reproductive barriers sufficient to allow persistent asymmetry in the distribution of mitochondrial haplotypes. The identified molecular markers will facilitate studies characterizing the behaviors of these two populations, with relevance to pest mitigation and efforts to prevent further dispersal of the resistance traits. Full article

The principle of symmetry is one of the general methodological principles of science. The effects of any external influences, such as deformation, stresses, temperature, etc., could lead to the anisotropy (asymmetry) of properties in constructional materials. During operation, metal structures and machine parts are exposed to time-varying external mechanical loads, which can cause changes in the metal structure, the initiation of cracks, and, as a result, the destruction of the product. The application of nondestructive testing methods prevents changes in the stress–strain state and, consequently, the destruction of the object. This article contains the results of studying the effects of elastic–plastic deformation by uniaxial tension and torsion on the change in the structure and magnetic parameters of low-alloy 13Cr-V pipe steel. Modern methods of metallography and magnetic nondestructive testing methods were used as part of this study. The results of the EBSD analysis showed that deformation during torsion, in contrast to uniaxial tension, is unevenly distributed over the sample cross section. In the cross section of the sample, the most severely deformed grains with a change in their geometry are observed near the surface; in the center, there is no change in geometry. During tension, the deformation over the cross section of the sample is uniformly distributed. Correlations between the applied normal and tangential stresses and magnetic characteristics of the 13Cr-V structural steel were determined. Informative parameters that could be used for the development of nondestructive testing methodologies for solving concrete tasks were determined. Different methods of deformation lead to diverse structural changes in grain structure. Full article

Three products hydrocyclone screen (TPHS) can be considered as the combination of a conventional hydrocyclone and a cylindrical screen. In this device, particles are separated based on size under the centrifugal classification coupling screening effect. The objective of this work is to explore the characteristics of fluid flow in TPHS using the computational fluid dynamics (CFD) simulation. The 2 million grid scheme, volume fraction model, and linear pressure–strain Reynolds stress model were utilized to generate the economical grid-independence solution. The pressure profile reveals that the distribution of static pressure was axisymmetric, and its value was reduced with the increasing axial depth. The maximum and minimum were located near the tangential inflection point of the feed inlet and the outlets, respectively. However, local asymmetry was created by the left tangential inlet and the right screen underflow outlet. Furthermore, at the same axial height, the static pressure gradually decreased along the wall to the center. Near the cylindrical screen, the pressure difference between the inside and the outside cylindrical screen dropped from positive to negative as the axial depth increased from −35 to −185 mm. Besides, TPHS shows similar distributions of turbulence intensity I, turbulence kinetic energy k, and turbulence dissipation rate ε; i.e., the values fell with the decrease in axial height. Meanwhile, from high to low, the pressure values are distributed in the feed chamber, the cylindrical screen, and conical vessel; the value inside the screen was higher than the outer value. Full article

Screw rolling of austenitic stainless-steel billets was conducted in two- and three-high mills. Statistical research results showed that, compared to heated but not rolled conditions, both screw rolling techniques provided a decrease of grain size, variance, grain size distribution asymmetry, and excess in the billet cross-section at the stationary stage of screw rolling. At that stage, grain size distribution after two-high screw rolling is closer to normal in terms of asymmetry and excess values compared to grain-size distribution after three-high screw rolling. A strong negative correlation between strain effective values and grain-size values for the cross-section of the rolled billets at the stationary stage was revealed for both two- and three-high screw rolling. Full article

To reveal the relationship between grain size and twinning deformation of magnesium alloys under cyclic strain, this study carried out a group of strain-controlled low-cycle fatigue experiments and statistical analysis of microstructures. Experimental results show that the shape of the hysteresis loop exhibits significant asymmetry at different strain amplitudes, and the accumulation of residual twins plays an important role in subsequent cyclic deformation. For the different strain amplitudes, the statistical distribution of the grain size of magnesium alloy approximately follows the Weibull probability function distribution, while the statistical distribution of twin thickness is closer to that of Gaussian probability function. The twin nucleation number (TNN) increases with the increase of grain size, but there is no obvious function relationship between twin thickness and grain size. Twin volume fraction (TVF) increases with the increase of grain size, which is mainly due to the increase of TNN. This work can provide experimental evidence for a more accurate description of the twinning deformation mechanism. Full article