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Background: The bulk of relevant studies compare individual or very few sports and on small samples of athletes. This requires extensive analysing postural stability in various sports.Research Question: The main objective of our study was to identify the features of postural stability in a normal vertical stance in athletes of various kinds.Methods: This study compares postural stability in a normal bipedal stance with eyes open (EO) and eyes closed (EC) conditions among athletes (n = 936, age: 6-47 years) from different sports and performance level. Postural stability was measured through the center of pressure (COP) sway area (AS) and velocity (VCP) while standing quietly in a normal bipedal position with EO and EC on a stabiloplatform (50 Hz).Results: The order of VCP-EO increase in athletes compared to Control was as follows: Shooting (-11.3 %, p < .0001) < Football (-10.4 %, p < .0001) < Boxing (-8.7 %, p < .0001) < Cross-Country Skiing (-7.2 %, p < .0001) < Gymnastics (-7.0 %, p < .0001) < Running (-6.9 %, p < .0001) < Team Games Played with Hands (-6.8 %, p < .0001) < Wrestling (-6.3 %, p < .0001) < Tennis (-5.5 %, p = .0004) < Alpine Skiing (-5.4 %, p = .002) < Rowing (-5.0 %, p = .194) < Speed Skating (-4.7 %, p = .004) < Figure Skating (-3.6 %, p = .034) < Control.Significance: Practicing any kind of sport was associated with increased postural stability in normal bipedal stance. This is the first study that provides reference values of COP sway and velocity with and without visual control on a stable force platform for different sport groups. [ABSTRACT FROM AUTHOR]

The theory of superimposed incremental elastic deformations is applied to a deformed configuration of a residually-stressed circular cylindrical tube. The tube is subject to internal or external pressure and an axial load that maintain its circular cylindrical shape, and then bifurcations from this shape are analysed. Detailed governing equations and boundary conditions are provided for axisymmetric, prismatic and asymmetric bifurcations for a general form of strain–energy function that incorporates radial and circumferential residual stress components. The theory is applied to a simple model strain–energy function with two material parameters and a parameter that reflects the magnitude of the residual stress. Numerical computations are used to illustrate the dependence of the results of the bifurcation analysis on these parameters and the axial and radial underlying deformation. It is shown that in general the presence of residual stress has a significant effect compared with the corresponding results without residual stress. [ABSTRACT FROM AUTHOR]

This paper is concerned with the bifurcation analysis of a pressurized electroelastic spherical shell with compliant electrodes on its inner and outer boundaries. The theory of small incremental electroelastic deformations superimposed on a radially finitely deformed electroelastic thick-walled spherical shell is used to determine those underlying configurations for which the superimposed deformations do not maintain the perfect spherical shape of the shell. Specifically, axisymmetric bifurcations are analyzed, and results are obtained for three different electroelastic energy functions, namely electroelastic counterparts of the neo-Hookean, Gent and Ogden elastic energy functions. For the neo-Hookean energy function it was reported previously that for the purely mechanical case axisymmetric bifurcations are possible under external pressure only, no bifurcation solutions being possible for internally pressurized spherical shells. In the case of an electroelastic neo-Hookean model bifurcation under internal pressure becomes possible when the potential difference between the electrodes exceeds a certain value, which depends on the ratio of inner to outer undeformed radii. Results obtained for the three classes of model are significantly different and are illustrated for a range of fixed values of the potential difference. Although of less practical significance, results are also shown for fixed charges, and these are both different between the models and different from the case of fixed potential difference. • Detailed bifurcation analysis of a pressurized spherical electroelastic shell. • Compliant electrodes on the inner and outer spherical surfaces. • Results for different energy functions compared, extending those for the purely elastic case. [ABSTRACT FROM AUTHOR]

The paper presents the results of theoretical study for the influence of an additional magnetostatic field applied to the radio-frequency discharge region on the operating parameters of radio-frequency ion injector, taking into account the shape of its discharge chamber. The integral characteristics are calculated for three injector configurations: with a cylindrical, conical, and hemispherical discharge chamber. For calculations, we used a mathematical model, in which the charged particle behavior in plasma is described by relations close to magnetohydrodynamic, while the neutral particle distribution is determined using an approximate analytical solution obtained when considering a one-dimensional problem of gas flow in a tube. Simulation was carried out in the COMSOL Multiphysics software package. According to the calculation results, an additional magnetostatic field can improve the ion injector performance with any discharge chamber configuration. The greatest operation efficiency increase was observed with a cylindrical discharge chamber. However, according to calculations, the best performance can be obtained if a hemispherical chamber is used. • An additional magnetostatic field can increase the efficiency of RF ion injector. • Positive effect can be expected with any shape of the ion injector discharge chamber. • Optimal induction of an additional magnetostatic field for RF ion injector. [ABSTRACT FROM AUTHOR]

Freeze-thaw weathering can alter the geometry of soil minerals and severely damage the Earth's surface. This has significant implications for the global geological environment. To investigate the process of morphological development and show the morphological trends and evolution of quartz minerals under freeze-thaw cycle (FTC) action, researchers conducted many freeze-thaw weathering experiments. We collected the surface morphology of quartz under different freeze-thaw cycles (FTCs) using a particle image processor. The results showed that: (1) Grain-size morphology became increasingly heterogeneous geometrically as the number of FTCs increased. (2) Freeze-thaw weathering caused the breakage of soil minerals. For longer FTCs, the ratio of the corresponding elliptical axis to the rectangular axis fluctuated. The fluctuation in the equivalent elliptical perimeter exhibited the same trend as the texture and angle values of the particles. (3) During freeze-thaw weathering, the surface geometrical characteristics of quartz minerals resembled those of quartz crystals. Extensive morphological characterization data played a crucial role in determining the morphological evolution of quartz mineral grains during freeze-thaw weathering. Researchers made a novel discovery of self-similarity between the macro- and micro-morphology of quartz minerals during weathering denudation, which has significant implications for advancing our understanding of underlying geomorphological changes. [Display omitted] • The use of freeze-thaw cycles to simulate environmental weathering in the monsoonal freeze zone is a feasible approach. • Sand soil particles break apart and the grain class level changes due to the environment's freeze-thaw weathering. • Macroscopic and microscopic morphology of quartz minerals are self-similar after freeze-thaw weathering. [ABSTRACT FROM AUTHOR]

Non-frost susceptible soils (e.g., gravel) are typically used as embankment fill to minimize the frost heave problem on the highways in the Arctic. However, accesses to the non-frost susceptible soils are limited in the remote regions, and the transportation costs for it are very high, thereby resulting that frost susceptible soils have to be used to fill the embankments. In this study, nano-ZnO was added to two types of frost susceptible soils, namely silty clay and clay, to reduce the frost susceptibility of soils and to mitigate the frost heave. Firstly, the unconfined compressive strengths of the soil samples whose the mass ratios of the nano-ZnO to the silty clays were 1.5 wt%, 3.0 wt%, 4.5 wt% and 6.0 wt% were tested. A series of isotropic freezing tests were then conducted to study the temperatures and frost heave deformations of the soil samples with the nano-ZnO of 0.0 wt%, 1.5 wt%, 3.0 wt% and 4.5 wt%, thereby verifying the effectiveness of the nano-ZnO in reducing the frost susceptibility of the soils. The optimal mass percentage of the nano-ZnO was determined by the mechanical and freezing tests. Finally, a clay embankment model with the nano-ZnO of the optimal mass percentage (defined as the nano-ZnO embankment model) during freezing-thawing cycles under various artificial rainfall conditions in the Arctic environment was tested. A clay embankment model without nano-ZnO was the control case, and defined as the control embankment model. Experimental results revealed that 1) with the increased nano-ZnO, the unconfined compressive strengths of the soil samples initially increased and subsequently decreased, and the maximum value corresponded to the mass percentage of 4.5 wt%; 2) the usage of the nano-ZnO can considerably reduce the freezing point and the frost heave deformations of the soil samples; 3) the optimal mass percentage of the nano-ZnO was 4.5 wt%. Compared with the soil sample without the nano-ZnO, the frost heave deformation of the soil sample with the nano-ZnO of 4.5 wt% was reduced by 71.98% and 78.44% using the rapidly cooling and step by step cooling method, respectively; 4) the usage of 4.5 wt% nano-ZnO was reduced the frost heave deformation of the clay embankment model by a maximum value of 74.06% under artificial rainfall, whereas the frost heave deformation of the embankment model reduced by a maximum value of 31.94% without artificial rainfall. Moreover, the mechanisms of the increase in the compressive strength and the decrease in the frost heave were analyzed. This study can provide considerable insights for mitigating the frost heave problems in highways in the Arctic when frost susceptible soil is used as embankment fill. [Display omitted] • Usage of nano-ZnO can increase unconfined compressive strength and mitigate frost heave of silty clay. • With 4.5 wt% nano-ZnO, the silty clay become a non-frost susceptible soil. • 4.5 wt% nano-ZnO can mitigate the frost heave of clay embankment by 74.06%. • The mechanisms mitigating the frost heave are analyzed and discussed. [ABSTRACT FROM AUTHOR]

H-alpha and visible spectroscopy (HA&VS) diagnostic in ITER is aimed at the measurements of the intensity of hydrogen isotopes and of impurity lines in the SOL emission. It is based on the endoscope scheme with the first mirror unit (FMU) containing two mirrors (flat and aspheric) located behind a small entrance pupil and a discharge cleaning system. A primary candidate material for the FMU mirror is a single-crystal molybdenum (SC-Mo). A sandwich-like design is proposed, in which few small-sized SC-Mo plates are bound by a diffusive welding to a large-size polycrystalline Mo substrate. An acceptable welding regime is presented. A recent progress is discussed on the polishing of SC-Mo focusing mirrors up to 150 mm diameter. Thermal tests of the molybdenum FMU mock-up had been performed. The FMU was heated up to 200 °C whereas the mirror temperature was up to 300 °C under the pressure of 8–9 Pa. A technique for the quantitative assessment of the image quality (contrast and resolution) at the elevated temperatures has been suggested. As a result, a sub-mm shift of an image plane along the optical axis had been observed with no significant degradation of the image quality. [ABSTRACT FROM AUTHOR]

• The multi-scale experiments and micro-scale numerical simulation were carried out. • The optimum content of nano-silica to be added to concrete is 2%. • 2% nano-silica improves the mechanical properties of ITZ and mortar. In this study, multi-scale experiments and micro-scale numerical simulation were used to comprehensively analyze the influencing mechanism of nano-silica (NS) on the concrete performances. With the NS content increases, the results indicate that the concrete performances are improved first and then deteriorated, and the optimum NS content is 2%. By improving the physical and mechanical properties of cement paste and meliorating the interface transition zone (ITZ) structure, 2% NS increases the compressive strength of the concrete sample cured for 28 days by 23.04%. Meanwhile, it can be found that 2% NS makes the pore structure the most refined and maximizes the compactness of concrete through the nuclear magnetic resonance technology, making concrete the best resistance to chloride ion penetration. Through numerical simulation, it can be found that the concrete added with 2% NS has the better resistance to external force than the concrete without NS, and the reason for the improvement is that 2% NS enhances the mechanical properties of ITZ and mortar. Although 5% NS meliorates the ITZ structure, it deteriorates the physical and mechanical properties of cement paste, which makes the compressive strength of concrete sample cured for 28 days decrease by 7.91%. [ABSTRACT FROM AUTHOR]