Introduction & Purpose: Small-sided games (SSGs) are widely used in soccer training to recreate the physical, technical and tactical demands of official matches within controlled environments (Morgans et al., 2014). Manipulating pitch size, player numbers, and rules, allows SSGs to develop these demands, especially physical performance (Bujalance-Moreno et al., 2019). The interaction of pitch size and player numbers can be quantified through the relative pitch area (RPA; m2*player-1) (Hill-Haas et al., 2011; Olthof et al., 2019). A larger RPA elicits greater total distance, high-speed running, and sprinting demands (Riboli et al., 2020). However, limited evidence exists on age-related differences in physical demands among late-stage academy players. Therefore, this study investigated age-related differences in physical performance between U18 and U21 elite academy players across SSG formats defined by RPA. Methods: Thirty-seven male elite academy players (U18: n=17; U21: n=20) from one club performed SSGs over 9 weeks. Formats were classified by RPA as small (>125 m2*player-1), medium (125-225 m2*player-1), and large (>225 m2*player-1). Physical performance was measured via 10 Hz GPS with embedded inertial sensors. Outcome measures (per minute) were total distance (TD), high-speed running distance (HSRD; >20 km*h-2), sprinting distance (SD; >25km*h-1), accelerations (>2 m*s-2), and decelerations (>2m*s-2). Two-level mixed-effects models (measurements nested within players) tested effects of age category and SSG format (p<0.05). Results: Multilevel analysis showed significant effects of both age category and SSG format on all physical variables (p<0.05). U21 players covered greater high-speed running (HSRD: 2.2 m*min-1, p=0.003) and sprinting distances (SD: 1.0 m*min-1, p=0.005) compared to U18 players. Whereas U18 players performed more accelerations (0.44*min-1, p=0.014) and decelerations (0.44*min-1, p=0.017). No significant difference was observed in total distance (TD: p=0.326). Across formats, large-sided games elicited the highest TD (129 m*min-1), HSRD (10.0 m*min-1), and SD (2.3 m*min-1), followed by medium (122, 6,0, and 1.0 m*min-1) and small formats (105, 1.9 and 0.1 m*min-1). In contrast, small-sided games induced the most accelerations (3.6*min-1) and decelerations (3.4*min-1). All pairwise comparisons between formats were significant (p<0.05). Discussion: The findings highlight age-related disparities in the physical demands of SSGs among late-stage academy players. Older players (U21) covered more distances at higher speeds, reflecting greater physical performance in larger available spaces. In contrast, younger players (U18) executed higher accelerations and decelerations, indicating a more intermittent movement profile. These findings align with previous work showing that older players show a greater physical performance, possibly influenced by differences in biological maturation and tactical behaviour (Buchheit et al., 2010; Radnor et al., 2021; Olthof et al., 2015). Furthermore, the progressive increase in external load across SSG formats confirms that RPA is a key determinant of physical demands, supporting the use of larger RPAs to replicate match demands (Riboli et al., 2022). Conclusion: This study gives a better understanding of physical performance differences in elite late-stage academy soccer, highlighting the influence of age category and game format. Manipulating RPA provides a practical strategy for coaches to optimise training design and support the physical transition from late-stage academy levels. References Buchheit, M., Méndez-Villanueva, A., Simpson, B.M., & Bourdon, P.C. (2010). Match running performance and fitness in young soccer players. International journal of sports medicine, 31(11), 818-825. https://doi.org/10.1055/s-0030-1262838 Bujalance-Moreno, P., Latorre-Roman, P.A., & Garcia-Pinillos, F. (2019). A systematic review on small-sided games in football players: Acute and chronic adaptations. Journal of Sports Sciences, 37(8), 921-949. https://doi.org/10.1080/02640414.2018.1535821 Hill-Haas, S.V., Coutts, A.J., Rowsell, G., et al. (2009). Generic versus small-sided game training in soccer. Int J Sports Med., 30(9), 636-42. https://doi.org/10.1055/s-0029-1220730 Morgans, R., Orme, P., Anderson, L., & Drust, B. (2014). Principles and practices of training for soccer. J Sport Health Sci., 3(4), 251-257. https://doi.org/10.1016/j.jshs.2014.07.002 Olthof, S.B.H., Frencken, W.G.P., & Lemmink, K. (2015). The older, the wider: On-field tactical behavior of elite-standard youth soccer players in small-sided games. Human Movement Science, 41, 92-102. https://doi.org/10.1016/j.humov.2015.02.004 Olthof, S.B.H., Frencken, W.G.P., & Lemmink, K. (2019). A Match-Derived Relative Pitch Area Facilitates the Tactical Representativeness of Small-Sided Games for the Official Match. J Strength Cond Res., 33(2), 523-530. https://doi.org/10.1519/JSC.0000000000002978 Radnor, J.M., Staines, J., Bevan, J., Cumming, S.P., Kelly, A.L., Lloyd, R.S., & Oliver, J.L. (2021). Maturity Has a Greater Association than Relative Age with Physical Performance in English Male Academy Soccer Players. Sports (Basel), 9(12), 171. https://doi.org/10.3390/sports9120171 Riboli, A., Coratella, G., Rampichini, S. et al. (2020). Area per player in small-sided games to replicate the external load and estimated physiological match demands in elite soccer players. PLoS One, 15(9), e0229194. https://doi.org/10.1371/journal.pone.0229194 Riboli, A., B.H. Olthof, S., Esposito, F., & Coratella, G. (2022). Training elite youth soccer players: area per player in small-sided games to replicate the match demands. Biology of Sport, 39(3), 579–598. https://doi.org/10.5114/biolsport.2022.106388
Flag Football is the fastest growing format of American Football and is a recent addition to the 2028 Olympics. The Flag format is a non-contact version of American Football, where tackles are made by removing flags from players hips. Activity profiles in the NFL (Sanchez et al., 2013, App Sci, 13:9278; Wellman et al., 2016, J Strength Cond Res, 30, 11–19) have highlighted the need for high levels of strength, power, and speed. Given the similarities within Flag, these physical capabilities may be equally applicable to Flag players. However, a lack of literature on the Flag format, and the paucity of research in female football, irrespective of format, exists. Therefore, the aim of this study was to explore the physical fitness capabilities of a national league Women’s Flag Football team. Fourteen participants (age 28 ± 5 years; stature 166 ± 8 cm; mass 79 ± 29 kg) from a national league Women’s Flag team took part in a physical fitness testing battery comprising; countermovement jump (CMJ), squat jump (SJ), broad jump (BJ), 20-yard sprint and shuttle, and the Isometric mid-thigh pull (IMTP). Participants were familiarised with testing procedures and initially completed a standardised warm-up. Mean and SD results from the jump assessments were as follows; CMJ jump height 25.1 ± 5.9 cm, peak power 39.1 ± 7.1 w/kg; SJ jump height 24.6 ± 6.3 cm, peak power 39.3 ± 6.6 w/kg; broad jump 1.89 ± 0.28 m. Absolute and relative peak force in the IMTP was 2201 ± 422 N and 30.1 ± 4.1 N/kg respectively. The Dynamic Strength Index (DSI) calculated from CMJ and IMTP peak force was 0.76 ± 0.12. Lastly, 20-yard sprint and shuttle times were 3.43 ± 0.28 and 5.36 ± 0.38 s respectively. Significant correlations were found between mean CMJ jump height and mean sprint time (p 0.001; r = −0.780), between mean CMJ jump height and mean shuttle time (p <.001; r −0.857), between mean BJ distance and mean shuttle time (p <0.01; r = 0.870) and between mean BJ distance and CMJ jump height (p <.001; r = −0.911). This study is the first of its kind to report the physical capabilities of female flag football players. The findings of this study may help develop the understanding of a growing and soon to be Olympic sport.
For fitness professionals delivering strength and conditioning programmes and recreational athletes designing their own programmes, exercise selection and an appropriate loading stimulus over time are the cornerstones of an effective resistance training programme. The conventional deadlift (CD), a compound, closed-chain movement, is prescribed to increase the strength of the posterior chain and the quadriceps. The Romanian Deadlift (RDL) is an isolated knee variation of the CD, whereby the knee angle is stable throughout the movement (Lee et al., 2018, J Exer Sci Fit, 16, 87-93). The RDL is a key movement in weightlifting training and is a commonly used developer of posterior chain muscles (Weaver and Kerksick, 2017, Strength Cond J, 39, 85-90). Studies comparing the CD and RDL are limited. Using surface EMG 2D motion analysis of the lower limb, we aim to determine if (i) biceps femoris activation is greater than the vastus lateralis during the RDL, (ii) there is a higher activation of both vastus lateralis and biceps femoris during the CD, and (ii) whether an injury is more likely to occur during a CD or RDL using the angles and range of motion (ROM) of the hip, knee, and ankle. 15 recreationally active adults with experience with the CD and RDL were recruited. Surface EMG sensors were placed on the vastus lateralis and biceps femoris, and markers were placed for 2D motion analysis in the sagittal plane. MVC data were collected for three repetitions of both lifts at 70% RDL 1RM. Five repetitions at 50% RDL 1RM were used for analysis. Statistical analysis was conducted using a paired t-test and Wilcoxon signed-rank test. The results show greater activation of the vastus lateralis in the CD than the RDL (P < 0.05) but no difference in the biceps femoris. No differences were found in hip angles during ascent or descent at mid-thigh and knee height (P = 0.343), but there were differences at the bottom position. Knee angles during ascent and descent at the mid-thigh were different (P = 0.027) but not at knee height. No differences at the ankle joint were found at the mid-thigh (P = 0.12), but differences were found at knee height and bottom position. Finally, ROM at the hip, knee, and ankle during ascent and descent were significantly different (P = 0.002). The findings may help fitness professionals and recreational athletes make decisions such as exercise selection, load management, and injury prevention strategies based on the comparative effectiveness and risks of the CD and RDL.
The first experience of virtual free-radical copolymerization (FRCP) of vinyl monomers with stable radicals in the framework of the digital twins (DTs) concept (arXiv:2309.11616 [physics.chem-ph] and arXiv:2311.02752 [cond-mat.mtrl-sci]) is extended to N-isopropylacrylamide (NIPA). The virtualization of the chemical process is based on the concept of a chain reaction that covers a set of elementary reactions (ERs) and is the most suitable for quantum chemical treatment. The calculations were performed using a semi-empirical version of the unrestricted Hartree-Fock approximation. Once input in the chemical reactor, providing free-radical polymerization of NIPA, the fullerene C60 inhibits capturing the formed monomer-radicals and terminates the polymerization. The obtained virtual kinetic data, providing the appearance of an induction period at the initial stage of the NIPA polymerization, are in a full agreement with experimental reality.
We modify a theory of flow stress introduced in [arXiv:1803.08247[cond-mat.mtrl-sci]], [arXiv:1809.03628[cond-mat.mes-hall]], [arXiv:1908.09338[cond-mat.mtrl-sci]] for a class of polycrystalline materials with equilibrium and quasy-equilibrium defect structure under quasi-static plastic deformations. We suggest, in addition to modified Bose-Einstein distribution, Maxwell-like distribution law for defects (within dislocation-disclination mechanism) in the grains of polycrystalline samples with respect to grain's diameter. Polycrystalline aggregates are considered within single- and two-phase models that correspond to the presence of crystalline and grain-boundary (porous) phases. The scalar dislocation density is derived. Analytic and graphic forms of the generalized Hall-Petch relations for yield strength are produced for single-mode samples with BCC ($\alpha$-Fe), FCC (Cu, Al, Ni) and HCP ($\alpha$-Ti, Zr) crystal lattices at T=300 K with different values of the grain-boundary phase. We derived new form of the temperature-dimensional effect. The values of extremal grain and maximum of yield strength are decreased with raising the temperature in accordance with experiments up to NC region.
Configurations of the molecules on the wall of a vacancy, formed by removing a central and its first and second nearest-neighbor (NN) molecules in solid CO2 with the Pa3 structure, were calculated by the Monte Carlo simulation technique at T = 0, 100, and 200 K and a nominal pressure of P = 1 bar. It was found that the deviations of both the center-of-mass and the orientational coordinates of the molecules from the unperturbed coordinates had a three-fold symmetry about a body diagonal axis of the crystal. It was also found that a single CO2 molecule, initially placed in the center of the vacancy, was stabilized at a position close to the vacancy wall. This paper is a continuation of arXiv:1711.04976 [cond-mat.mtrl-sci] (2017) and arXiv:1809.04291 [cond-mat.mtrl-sci] (2018).
Native surface oxide turns alloyed silicon membranes into nanophononic metamaterials with ultra-low thermal conductivity Shiyun Xiong 1,2 , ∗ Daniele Selli 2 , Sanghamitra Neogi 3 , and Davide Donadio 4† arXiv:1705.03143v1 [cond-mat.mtrl-sci] 9 May 2017 1 Functional Nano and Soft Materials Laboratory (FUNSOM) and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, Jiangsu 215123 , P.R. China 2 Max Planck Institute for Polymer Research, Ackermannweg 10, 55218 Mainz, Germany 3 Department of Aerospace Engineering Sciences, University of Colorado Boulder, Boulder, Colorado 80309, USA 4 Department of Chemistry, University of California Davis, One Shields Ave. Davis, 95616, CA A detailed understanding of the relation between microscopic structure and phonon propagation at the nanoscale is essential to design materials with desired phononic and thermal properties. Here we uncover a new mechanism of phonon interaction in surface oxidized membranes, i.e., native oxide layers interact with phonons in ultra-thin silicon membranes through local resonances. The local resonances reduce the low frequency phonon group velocities and shorten their mean free path. This effect opens up a new strategy for ultralow thermal conductivity design as it complements the scattering mechanism which scatters higher frequency modes effectively. The combination of native oxide layer and alloying with germanium in concentration as small as 5% reduces the thermal conductivity of silicon membranes to 100 time lower than the bulk. In addition, the resonance mechanism produced by native oxide surface layers is particularly effective for thermal condutivity reduction even at very low temperatures, at which only low frequency modes are populated. Controlling terahertz vibrations and heat transport in nanostructures has a broad impact on several ap- plications, such as thermal management in micro- and nano-electronics, renewable energies harvesting, sensing, biomedical imaging and information and communication technologies [1–8]. Significant efforts have been made to understand and engineer heat transport in nanoscale silicon due to its natural abundance and technological relevance [9–12]. In the past decade researchers ex- plored strategies to obtain silicon based materials with low thermal conductivity (TC) and unaltered electronic transport coefficients, so to achieve high thermoelectric figure of merit and enable silicon-based thermoelectric technology[11–18]. From the earlier studies it was recognized that low- dimensional silicon nanostructures, such as nanowires, thin films and nano membranes feature a largely re- duced TC, up to 50 times lower than that of bulk at room temperature. TC reduction becomes more promi- nent with the reduction of the characteristic dimension of the nanostructures [19–22]. Theory and experiments consistently show that surface disorder and the pres- ence of disordered material at surfaces play a major role in determining the TC of nanostructures [12, 23–25]. However, a comprehensive understanding of the physi- cal mechanisms underlying so large TC reduction is lack- ing. The effect of surface roughness and surface disor- der on phonons has been so far interpreted in terms of phonon scattering [26–30], but scattering would not ac- count for mean free path reduction of long-wavelength low-frequency modes. Recent theoretical work demon- strated that surface nanostructures, such as nanopillars at the surface of thin films or nanowires, can efficiently reduce TC through resonances, a mechanism that is in- trinsically different from scattering [31, 32]. Surface res- onances alter directly phonon dispersion relations by hy- bridizing with propagating modes in the nanostructures, thus hampering their group velocity. In this Communication we unravel the effect of native oxide surface layers on thermal transport in ultra-thin silicon membrane models that closely resemble experi- ments, by atomistic molecular dynamics simulations. We show that the observed low TC in these systems, and plausibly in other oxide coated silicon nanostructures, is predominantly due to resonances analogous to those occurring in nanophononic metamaterials. It is worth stressing that surface oxide layers in low dimensional Si materials grow spontaneously at atmospheric conditions, and do not require any specific processing. Our simu- lations ascertain the occurrence of low frequency reso- nant modes that hybridize with the acoustic branches (ω . 4 THz) of the membrane, effectively suppressing their mean free path (MFP). This discovery opens up the possibility to further optimize the TC of ultra-thin silicon membranes by combining resonances with mass scattering, which affects phonons with higher frequency (ω & 4 THz). We show that alloying the crystalline core of ultra-thin membranes with a small percentage of sub- stitutional germanium atoms brings forth ultra-low TC in silicon membranes with technologically viable thick- ness [33]. All TCs are calculated with equilibrium molecular dy- namics (EMD) simulations at 300 K using LAMMPS [34] with interatomic interactions described by the widely used Tersoff potential [35–37]. The equations of mo- tion are integrated with the velocity Verlet algorithm
In the framework of the suggested in [arxiv:1803.08247 [cond-mat.mtrl-sci]] statistical theory of the equilibrium flow stress, including yield strength, ${\sigma}_y$, of polycrystalline materials under quasi-static (in case of tensile strain) plastic deformation in dependence on average size, d, of the crystallites (grains) in the range, $10^{-8}$ m - $10^{-2}$ m. it is found the coincidences of the theoretical and experimental data of ${\sigma}_y$ for the materials with BCC (${\alpha}$- Fe), FCC (Cu, Al, Ni) and HCP (${\alpha}$-Ti, Zr) crystal lattice at T=300K. The temperature dependence of the strength characteristics is studied. It is shown on the example of Al, that the yield strength grows with decreasing of the temperature for all grains with d greater than $3*d_0$ (with $d_0$ being extremal size of the grain for maximal ${\sigma}_y$) and then ${\sigma}_y$ decreases in the nano-crystalline region, thus determining a temperature-dimension effect. Stress-strain curves, ${\sigma}={\sigma}({\epsilon})$, are constructed for the pure crystalline phase of ${\alpha}$-Fe with Backofen-Consid\'ere fracture criterion validity. The single-phase model of polycrystalline material is augmented by means of inclusion of a softening grain boundary phase.
The statistical theory of flow stress, including yield strength, for polycrystalline materials under quasi-static plastic deformation suggested in [arxiv:1803.08247[cond-mat.mtr-sci], arxiv:1805.08623[cond-mat.mtr-sci]] is developed in the framework of a two-phase model. Analytic and graphic forms of the generalized Hall-Petch relations are obtained for samples with BCC (\alpha-phase Fe), FCC (Cu, Al, Ni) and HCP (\alpha-Ti, Zr) crystalline lattices at T=300K with different values of grain-boundary (second) phase. The maximum of yield strength and respective extremal grain size of the samples are shifted by changing of the second phase. Temperature dependence in the range 100-350K for yield strength (using the example of Al) revealed its increase for closely packed nano-crystalline samples with the growth of temperature. An enlargement of the second phase in a sample neutralizes this property.
The configurations of the molecules nearest to a single vacancy in solid CO2 were studied by the Metropolis Monte Carlo (MC) simulation at temperatures T = 0, 100, and 200 K. It was found that distorted orientational configurations at T = 0 and 100 K became uniform at 200 K. The MC simulation was useful to study the local configurations around the vacancy. This work is a continuation of a precedent paper, arXiv:1711.04976 [cond-mat.mtrl-sci] (2017).
Electronic structure of fully epitaxial Co 2 TiSn thin films Markus Meinert, ∗ Jan Schmalhorst, Hendrik Wulfmeier, and G¨ nter Reiss u Thin Films and Physics of Nanostructures, Department of Physics, Bielefeld University, 33501 Bielefeld, Germany Elke Arenholz Advanced Light Source, Lawrence Berkeley National Laboratory, CA 94720, USA Tanja Graf and Claudia Felser arXiv:1010.5754v1 [cond-mat.mtrl-sci] 27 Oct 2010 Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg University, 55128 Mainz, Germany (Dated: October 28, 2010) In this article we report on the properties of thin films of the full Heusler compound Co 2 TiSn prepared by DC magnetron co-sputtering. Fully epitaxial, stoichiometric films were obtained by deposition on MgO (001) substrates at substrate temperatures above 600 ◦ C. The films are well ordered in the L2 1 structure, and the Curie temperature exceeds slightly the bulk value. They show a significant, isotropic magnetoresistance and the resistivity becomes strongly anomalous in the paramagnetic state. The films are weakly ferrimagnetic, with nearly 1 µ B on the Co atoms, and a small antiparallel Ti moment, in agreement with theoretical expectations. From comparison of x-ray absorption spectra on the Co L 3,2 edges, including circular and linear magnetic dichroism, with ab initio calculations of the x-ray absorption and circular dichroism spectra we infer that the electronic structure of Co 2 TiSn has essentially non-localized character. Spectral features that have not been explained in detail before, are explained here in terms of the final state band structure. PACS numbers: 75.70.-i, 78.70.Dm, 73.61.At, 81.15.Cd I. INTRODUCTION The materials class of Co 2 YZ Heusler compounds (with Y a transition metal and Z an sp element) has been the subject of extensive studies in the context of spintronics during the last decade. They are of interest because many of them are predicted as half-metallic fer- romagnets with full spin polarization at the Fermi edge. The Heusler compound Co 2 TiSn (CTS) is of partic- ular interest for applications. It is predicted to be a half-metallic ferromagnet with a magnetic moment of 2 µ B /f.u. and it has a high formation energy of the Co- Ti site-swap defect. 1,2 Making use of Heusler compounds which exhibit low disorder or high tolerance of the ground state properties against disorder is highly desired. Co 2 TiSn has been the subject of many experimental and theoretical studies. The ground state properties ob- tained by density functional theory (DFT) depend sensi- tively on the choice of the DFT method. 1–8 The poten- tial has strong non-spherical components and thus only a full-potential treatment in connection with the general- ized gradient approximation (GGA) to the density yields a half-metallic ground state. 1,4 Experiments conducted on bulk CTS find a lat- tice parameter of 6.07 ˚ , a magnetic moment of about A 1.95 µ B /f.u. and a Curie temperature (T C ) around 355 K. 1,9,10 Further, it is found to have a strongly anoma- lous temperature dependence of resistivity, the temper- ature coefficient becomes negative above the Curie tem- perature. A large negative magnetoresistance reveals the importance of spin fluctuations in the compound. 11 A rather new development aims at the magnetocaloric properties of Co 2 TiSn, which has a large and constant Seebeck coefficient of −50 µV/K above T C in the bulk. 10 There have been some efforts to understand the unusual transport properties of CTS by ab initio band structure and semi-classical transport theory. 10,12 These properties make CTS interesting for a possible application in spin caloritronics, which attempt to make use of the interac- tions between heat and spin. An implementation into thin films is of particular importance for such applica- tions. Only two studies on thin films of CTS are available as far as we know. Gupta et al. applied pulsed laser ablation to grow CTS on Si (001) substrates from a stoichiometric target at growth temperatures up to 200 ◦ C. 13 The au- thors found off-stoichiometric, polycrystalline films with (022) texture. Suharyadi et al. utilized an atomically controlled alternate deposition technique based on elec- tron beam evaporation. 14 They have grown (001) ori- ented, L2 1 ordered films on Cr buffered MgO (001) sub- strates at growth temperatures up to 600 ◦ C and investi- gated them by nuclear resonant scattering. In this paper we present a successful preparation tech- nique based on DC magnetron co-sputtering. We present data on the structural and magnetic properties of our films. Further, we characterize the electronic transport properties which make CTS a particularly interesting compound. Finally we discuss the electronic structure of our CTS films based on soft x-ray absorption spec- troscopy and ab initio electronic structure calculations.