Limb Differences in Unipedal Balance Performance in Young Male Soccer Players with Different Ages

In soccer, the dominant leg is frequently used for passing and kicking while standing on the non-dominant leg. Consequently, postural control in the standing leg might be superior compared to the kicking leg and is further enhanced with increasing age (i.e., level of playing experience). Unfortunately, leg differences in postural control are associated with an increased risk of injuries. Thus, we examined differences between limbs in unipedal balance performance in young soccer players at different ages. Performance in the Lower Quarter Y Balance Test (YBT-LQ) of the dominant and non-dominant leg and anthropometry was assessed in 76 young male soccer players (under-13 years [U13]: n = 19, U15: n = 14, U17: n = 21, U19: n = 22). Maximal reach distances (% leg length) and the composite scores were used for further analyses. Statistical analyses yielded no statistically significant main effects of leg or significant Leg × Age interactions, irrespective of the measure investigated. However, limb differences in the anterior reach direction were above the proposed cut-off value of >4 cm, which is indicative of increased injury risk. Further, statistically significant main effects of age were found for all investigated parameters, indicating larger reach distances in older (U19) compared to younger (U13) players (except for U15 players). Although reach differences between legs were non-significant, the value in the anterior reach direction was higher than the cut-off value of >4 cm in all age groups. This is indicative of an increased injury risk, and thus injury prevention programs should be part of the training of young soccer players

Effect of Arm Movement and Task Difficulty on Balance Performance in Children, Adolescents, and Young Adults

BACKGROUND: Studies have shown that restricted compared to free arm movement negatively affects balance performance during balance assessment and this is reinforced when the level of task difficulty (e.g., varying stance/walk conditions, sensory manipulations) is increased. However, it remains unclear whether these findings apply to individuals with differences in the development of the postural control system. Thus, we examined the influence of arm movement and task difficulty on balance performance in children, adolescents, and young adults. METHODS: Static, dynamic, and proactive balance performance were assessed in 40 children (11.5 ± 0.6 years), 30 adolescents (14.0 ± 1.1 years), and 41 young adults (24.7 ± 3.0 years) using the same standardized balance tests [i.e., one-legged stance (OLS) time with eyes opened/closed and/or on firm/foam ground, 3-m beam (width: 6, 4.5, or 3 cm) walking backward step number, Lower Quarter Y-Balance test (YBT-LQ) reach distance] with various difficulty levels under free vs. restricted arm movement conditions. RESULTS: In all but one test, balance performance was significantly better during free compared to restricted arm movement. Arm by age interactions were only observed for the YBT-LQ and post hoc analyses revealed significantly greater performance differences between free and restricted arm movement, especially, in young adults. Arm by age by task difficulty interactions were found for the OLS and the 3-m beam walking backward test. Post hoc analyses showed significantly greater performance differences between free and restricted arm movement during high vs. low levels of task difficulty and this was more pronounced in children and adolescents. CONCLUSIONS: Regardless of age, static, dynamic, and proactive balance performance benefited from arm movements and this was especially noted for youth performing difficult balance tasks

Chemical imaging of mixed metal oxide catalysts for propylene oxidation: from model binary systems to complex multicomponent systems

Industrially-applied mixed metal oxide catalysts often possess an ensemble of structural components with complementary functions. Characterisation of these hierarchical systems is challenging, particularly moving from binary to quaternary systems. Here a quaternary Bi−Mo−Co−Fe oxide catalyst showing significantly greater activity than binary Bi−Mo oxides for selective propylene oxidation to acrolein was studied with chemical imaging techniques from the microscale to nanoscale. Conventional techniques like XRD and Raman spectroscopy could only distinguish a small number of components. Spatially-resolved characterisation provided a clearer picture of metal oxide phase composition, starting from elemental distribution by SEM-EDX and spatially-resolved mapping of metal oxide components by 2D Raman spectroscopy. This was extended to 3D using multiscale hard X-ray tomography with fluorescence, phase, and diffraction contrast. The identification and co-localisation of phases in 2D and 3D can assist in rationalising catalytic performance during propylene oxidation, based on studies of model, binary, or ternary catalyst systems in literature. This approach is generally applicable and attractive for characterisation of complex mixed metal oxide systems. © 2021 The Authors. ChemCatChem published by Wiley-VCH Gmb

An Observational Overview of Solar Flares

We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era. Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections. We also discuss flare soft X-ray spectroscopy and the energetics of the process. The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory. The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations.Comment: This is an article for a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011

Effects of Single Compared to Dual Task Practice on Learning a Dynamic Balance Task in Young Adults

Background: In everyday life, people engage in situations involving the concurrent processing of motor (balance) and cognitive tasks (i.e., “dual task situations”) that result in performance declines in at least one of the given tasks. The concurrent practice of both the motor and cognitive task may counteract these performance decrements. The purpose of this study was to examine the effects of single task (ST) compared to dual task (DT) practice on learning a dynamic balance task.Methods: Forty-eight young adults were randomly assigned to either a ST (i.e., motor or cognitive task training only) or a DT (i.e., motor-cognitive training) practice condition. The motor task required participants to stand on a platform and keeping the platform as close to horizontal as possible. In the cognitive task, participants were asked to recite serial subtractions of three. For 2 days, participants of the ST groups practiced the motor or cognitive task only, while the participants of the DT group concurrently performed both. Root-mean-square error (RMSE) for the motor and total number of correct calculations for the cognitive task were computed.Results: During practice, all groups improved their respective balance and/or cognitive task performance. With regard to the assessment of learning on day 3, we found significantly smaller RMSE values for the ST motor (d = 1.31) and the DT motor-cognitive (d = 0.76) practice group compared to the ST cognitive practice group but not between the ST motor and the DT motor-cognitive practice group under DT test condition. Further, we detected significantly larger total numbers of correct calculations under DT test condition for the ST cognitive (d = 2.19) and the DT motor-cognitive (d = 1.55) practice group compared to the ST motor practice group but not between the ST cognitive and the DT motor-cognitive practice group.Conclusion: We conclude that ST practice resulted in an effective modulation of the trained domain (i.e., motor or cognitive) while only DT practice resulted in an effective modulation of both domains (i.e., motor and cognitive). Thus, particularly DT practice frees up central resources that were used for an effective modulation of motor and cognitive processing mechanisms

Nanotomography on Fuel Catalyst Particles with Structural and Elemental Contrast

Aim of this thesis was to study the pore structure of and elemental distributions in a fuel catalyst particle by means of X-ray nanotomography. The experiment was performed using an X-raybeam with a size of about 278 x 351 nm$^2$ FWHM at an energy of 11.8 keV. Elemental contrast in the tomogram was achieved by scanning X-ray fluorescence spectroscopy and structural contrast by ptychography. Tomographic reconstruction of 202 fluorescence projections yielded slices displaying the elemental distribution of Fe, Ti, Ni, V, Cu as well as Pt in the particle with a pixel size of 200 nm and a resolution of at least 610 nm. As a result it was found that Fe and Ni are mostly located on the surface of the sample. However, in areas with little or no Fe, Ni tends to spread further into the particle compared with areas with high amount of Fe. The fluorescence analysis of Ti and V was not possible, because of a flawed fit of the fluorescence spectra. Cu was found in small regions on the surface of the sample and the distribution of Pt, which was used as a marker, was limited to the marked area.The tomographic reconstruction of 161 ptychographic projections yielded slices displaying the structure of the particle with a pixel size of 40.7 nm and a resolution of at least 164 nm. Poreswith sizes between hundred nanometers and multiple microns were found. Furthermore, it was observed that the pore size tends to decrease near the surface of the sample. Volume analysis by image segmentation showed that the volume of all pores amounts to about 12.2 % of the total volume of the observed sample. In addition, it was found that 65.4 % of all pores belong to a main pore network, which is mainly located near the center of the sample. Because the fluorecence and ptychographic datasets were recorded simultaneously during the same experiment, combining the elemental and the structural information was simplified to an upscaling of the fluorescence data and aligning it to the ptychographic slices. By analyzing thiscombined data, the distribution of multiple elements could be correlated to different structural components of the sample

Self-Absorption Corrected X-Ray Microtomography with Structural and Elemental Contrast

X-ray fluorescence tomograms of large or highly absorbing samples often suffer from self-absorption effects. For qualitative and quantitative results, it is necessary to correct these effects.In this thesis, a fully 3D self-absorption corrected reconstruction algorithm for X-ray fluorescence tomography datasets is presented. As an extension of the tomographic maximum-likelihood expectation-maximization algorithm, it is an iterative algorithm that reconstructs the density volumes of all measured elements in parallel. The algorithm includes multiple optional parts to aid its convergence, including density and background constraints. Noise may be reduced by using a priori information of the sample to introduce a weighted penalty term. All calibration parameters are derived from experimental measurements and small inconsistencies in those values may be corrected by a rudimentary adaptive calibration. Parallel calculations on CPU and GPU as well as downscaling approximations are used to assure high performance of the algorithm and to allow for online reconstruction during experiments.Numerical simulations of multi-element phantoms without and with added noise confirmed the qualitative as well as quantitative properties of the self-absorption correction. Additionally, tomographic STXM and XRF measurements of a barred olivine micrometeorite were performed at beamline P06 of the PETRA III synchrotron storage ring at DESY in Hamburg, Germany. Although the algorithm was able to correct parts of the self-absorption effects in the micrometeorite data, the qualitative and quantitative properties of the final reconstructions were severely limited by inconsistencies in the experimental calibration, mainly the deadtime and pile-up corrections