Polynomial decay of correlations in linked-twist maps

Linked-twist maps are area-preserving, piece-wise diffeomorphisms, defined on a subset of the torus. They are non-uniformly hyperbolic generalisations of the well-known Arnold Cat Map. We show that a class of canonical examples have polynomial decay of correlations for \alpha-H\"{o}lder observables, of order 1/n

Topological entropy and secondary folding

A convenient measure of a map or flow's chaotic action is the topological entropy. In many cases, the entropy has a homological origin: it is forced by the topology of the space. For example, in simple toral maps, the topological entropy is exactly equal to the growth induced by the map on the fundamental group of the torus. However, in many situations the numerically-computed topological entropy is greater than the bound implied by this action. We associate this gap between the bound and the true entropy with 'secondary folding': material lines undergo folding which is not homologically forced. We examine this phenomenon both for physical rod-stirring devices and toral linked twist maps, and show rigorously that for the latter secondary folds occur.Comment: 13 pages, 8 figures. pdfLaTeX with RevTeX4 macro

Prior workload has moderate effects on high-intensity match performance in elite-level professional football players when controlling for situational and contextual variables

This investigation examined the effect of prior workload on high-intensity football match performance. Player load variables were recorded using a global positioning system and converted into composite variables: rolling season accumulated load (AL), exponentially weighted moving average acute, chronic and acute:chronic workload ratio (A:C). Match-play high-intensity performance-per-minute: accelerations (ACC), sprints, high-speed running (HSR) and high metabolic load (HMLd) distances; and situational and contextual variables were recorded for all games. Partial least squares modelling, and backward stepwise selection determined the most parsimonious model for each performance variable. Quadratic relationships of small to moderate effect sizes were identified for sprint AL and sprint performance, HSR AL and HSR performance, acute HMLd and HMLd performance, acute sprint load and ACC performance and A:C sprint load and ACC performance. Match performance was typically greatest between the mean and +1SD. High chronic HMLd, and combined acceleration and deceleration (ACC+DEC) load exerted small beneficial effects on HMLd and HSR performance, whereas high acute load exerted trivial to moderate negative effects. High sprint A:C exerted a small beneficial effect on sprint performance and playing position exerted small effects on HSR and HMLd performance. Prior workload has trivial to moderate effects on high-intensity match performance in professional players

Lithium-Doped Two-Dimensional Perovskite Scintillator for Wide-Range Radiation Detection

Two-dimensional lead halide perovskites have demonstrated their potential as high-performance scintillators for X- and gamma-ray detection, while also being low-cost. Here we adopt lithium chemical doping in two-dimensional phenethylammonium lead bromide (PEA)2PbBr4 perovskite crystals to improve the properties and add functionalities with other radiation detections. Li doping is confirmed by X-ray photoemission spectroscopy and the scintillation mechanisms are explored via temperature dependent X-ray and thermoluminescence measurements. Our 1:1 Li-doped (PEA)2PbBr4 demonstrates a fast decay time of 11 ns (80%), a clear photopeak with an energy resolution of 12.4%, and a scintillation yield of 11,000 photons per MeV under 662 keV gamma-ray radiation. Additionally, our Li-doped crystal shows a clear alpha particle/gamma-ray discrimination and promising thermal neutron detection through 6Li enrichment. X-ray imaging pictures with (PEA)2PbBr4 are also presented. All results demonstrate the potential of Li-doped (PEA)2PbBr4 as a versatile scintillator covering a wide radiation energy range for various applications

The moderating effects of speed, strength and endurance capacities on match induced neuromuscular fatigue in U-18 English premier league academy football players: A hypothesis-generating case report

Purpose: To identify new hypotheses relating to the moderating effects of speed, strength and endurance capacities on match-induced neuromuscular fatigue. Methods 14 U-18 outfield players from one EPL academy team completed countermovement jump (CMJ) and isometric adductor (IADS) and posterior chain (IPCS) strength tests one day before match day (MD) (i.e., MD-1) and on MD + 2 around 8 competitive games. Explosive strength (CMJ), reactive strength (30 cm drop jump (DJ)), speed (10 m and 30 m), maximal strength (isometric mid-thigh pull (IMTP)) and endurance (1 km Time Trial (TT)) were measured at 4 time points across the season. Relationships between the average match induced change to each NMF measure and the average of each physical capacity measure were examined using Pearson's R ( r ) (when normally distributed) or Spearman's rank ( rho ) (when not normally distributed) correlation coefficients. Results: Moderate positive relationships were observed between CMJ-JH change ( δ ) and DJ-RSI ( rho = 0.36; p = 0.16) and IMPT ( r = 0.46; p = 0.06). Small negative relationships were observed between IADS-PF δ and 10 m speed ( rho = 0.27; p = 0.29), 30 m speed ( r = 0.22; p = 0.41), CMJ-JH ( rho = 0.29; p = 0.26) and DJ-RSI ( rho = 0.36; p = 0.16), and between IPCS-PF δ and 10 m speed ( rho = 0.20; p = 0.45) and 1kmTT ( rho = 0.26; p = 0.33). Conclusions: These results generate important hypotheses relating to the potential mitigating effects that reactive strength, maximal strength and endurance capacities might exert on match induced NMF in U-18 academy football players. These relationships warrant further investigation in larger research designs spanning both older and younger player age groups (i.e., across other youth development and professional development phase players) and competition levels (i.e., elite and sub-elite players)

Differences in physical and technical performance characteristics between 11 v 11 chronological and bio-banded soccer match-play in youth soccer

Objectives: Bio-banding groups athletes by maturity rather than chronological age, to promote more equitable competition and development opportunities. We investigated whether physical and technical performance differed between chronological and bio-banded 11v11 match-play formats in youth soccer. A secondary aim was to examine whether these differences varied by maturity status and timing. Design: Twelve Junior Premier League teams (N = 139 players) from the U13, U14, and U15 age groups participated. Each team played six, 20-minute matches: three in chronological age and three in bio-banded formats. Bio-banding was based on the percentage of predicted adult height: pre-peak height velocity (< 90 %), mid-peak height velocity (90–96 %) and post-peak height velocity (> 96 %). Methods: Players wore foot-mounted inertial measurement units to record physical (distance covered, high-speed running > 4 m/s, sprinting > 5.5 m/s, and accelerations/decelerations ± 2.6 m/s/s) and technical (total touches, possessions, time on ball and one-touch/short/long possession counts) performance characteristics. Data were analysed using t-tests and analysis of variance with Bonferroni correction. Significance was set at p < 0.05, and effect sizes (Cohen's d) were calculated. A multivariate analysis was also conducted. Results: Whole sample analysis showed significantly more time on the ball per possession (d = 0.17), and fewer one-touch actions (d = 0.25) in bio-banded matches. Post-peak height velocity players covered significantly more high-intensity distance (d = 0.63) but recorded fewer total touches (d = 0.60), total possessions (d = 0.65) and one-touch possessions (d = 0.71) in the bio-banded format. There were significant differences between pre- and mid-peak height velocity players for all physical metrics across both chronological and bio-banded matches (d = 0.48–72), and between maturity groups (pre-post-peak height velocity, mid-post-peak height velocity) for technical actions in chronological format but not mirrored in bio-banding matches. Conclusions: Bio-banding was associated with altered physical and technical demands, especially for post-peak height velocity players. Findings suggest bio-banding may provide an appropriate competition format, exposing players to different developmental challenges, which may support more equitable and balanced experiences

The moderating effects of speed, strength and endurance capacities on match induced neuromuscular fatigue in U-18 English Premier League academy football players: a hypothesis-generating case report.

Purpose: To identify new hypotheses relating to the moderating effects of speed, strength and endurance capacities on match-induced neuromuscular fatigue. Methods: 14 U-18 outfield players from one EPL academy team completed countermovement jump (CMJ) and isometric adductor (IADS) and posterior chain (IPCS) strength tests one day before match day (MD) (i.e., MD-1) and on MD+2 around 8 competitive games. Explosive strength (CMJ), reactive strength (30 cm drop jump (DJ)), speed (10m and 30m), maximal strength (isometric mid-thigh pull (IMTP)) and endurance (1 km Time Trial (TT)) were measured at 4 time points across the season. Relationships between the average match induced change to each NMF measure and the average of each physical capacity measure were examined using Pearson’s R (r) (when normally distributed) or Spearman’s rank (rho) (when not normally distributed) correlation coefficients. Results: Moderate positive relationships were observed between CMJ-JH change () and DJ-RSI (rho=0.36;p=0.16) and IMPT (r=0.46;p=0.06). Small negative relationships were observed between IADS-PF and 10m speed (rho=0.27;p=0.29), 30m speed (r=0.22;p=0.41), CMJ-JH (rho= 0.29;p=0.26) and DJ-RSI (rho=0.36;p=0.16), and between IPCS-PF and 10m speed (rho=0.20;p=0.45) and 1kmTT (rho=0.26;p=0.33). Conclusions: These results generate important hypotheses relating to the potential mitigating effects that reactive strength, maximal strength and endurance capacities might exert on match induced NMF in U-18 academy football players. These relationships warrant further investigation in larger research designs spanning both older and younger player age groups (i.e., across other youth development and professional development phase players) and competition levels (i.e., elite and sub-elite players)

Bio-banding influences talent experts' ratings of psycho-social behaviours during 11 v 11 soccer match-play.

Selection into talent programmes is determined by perceptions of talent experts (i.e. professional academy scouts or coaches). Biological maturity status and/or timing can influence psycho-social behaviours in match-play. This study examined whether bio-banding (i.e. grouping players by biological maturity) influences talent experts' ratings of psycho-social behaviours. Using the Hull Soccer Behavioural Scoring Tool (HSBST), 14 talent experts rated 118 trained/developmental, male, adolescent (age: 13.7 ± 0.8 years) soccer players during six 20-minute, chronological age and bio-banded 11v11 matches. Players were bio-banded using percentage of predicted adult height (%PAH) using modified band thresholds relevant to peak height velocity (PHV; 96%PAH, post-PHV). Dependent sample t-tests between the whole group ratings identified significant differences ( < 0.05) between formats. Decision-making and composure ratings increased in pre-PHV, with X-factor improving for circa-PHV players. Perceptions of resilience, competitiveness and confidence had to ( = 0.26-0.65) reductions for early maturers. Bio-banding significantly enhanced perceptions of competitiveness, confidence, composure and X-factor in on-time maturers ( = 0.011-0.049). Data indicates bio-banding positively influences perceptions of composure, competitiveness, decision-making and X-factor by talent experts, particularly for less biologically advanced players. Bio-banding may alter talent experts' observations of psycho-social behaviours, potentially improving (de)selection accuracy by assessing talent more holistically

(gamma,np) reactions in ¹²C , ⁶Li and ^3,4He

The emission of neutron-proton pairs is the most probable outcome of photon absorbtion in the energy region above the giant resonance at least up to the pion threshold, but little detailed information on the process has been obtained due to experimental difficulties. Two nucleon emission following photon absorbtion by a correlated pair is favoured compared to direct knockout of a single nucleon, which is suppressed by the large momentum mismatch between the ingoing photon and a single outgoing fast nucleon. Studies of the (gamma,np) process seek firstly to obtain a quantitative understanding of the photon interaction mechanism, and through this to open the door to investigations of nucleon correlations in nuclei [1], information about which is long sought but not readily obtainable

Countermovement Jump and Isometric Strength Test-Retest Reliability in English Premier League Academy Football Players.

To examine the test-retest reliability of countermovement jump (CMJ) and isometric strength testing measures in elite-level under-18 and under-23 academy football players. A total of 36 players performed 3 maximal CMJs and isometric abductor (IABS), adductor (IADS), and posterior chain (IPCS) strength tests on 2 separate test days using dual force plates (CMJ and IPCS) and a portable strength testing device (IABS and IADS). Relative (intraclass correlation coefficient) and absolute (coefficient of variation, standard error of the measurement, and minimal detectable change [MDC%]) reliabilities for 34 CMJ, 10 IABS, 10 IADS, and 11 IPCS measures were analyzed using between-sessions best, mean, and within-session methods. For all methods, relative reliability was good to excellent for all CMJ and all IADS measures and poor to good for all IABS and IPCS measures. Absolute reliability was good (ie, coefficient of variation < 10%) for 27 (best) and 28 (mean) CMJ variables and for 6 (IABS and IADS) and 2 (IPCS) isometric measures. Commonly used CMJ measures (jump height, eccentric duration, and flight-time:contraction-time ratio) had good to excellent relative reliability and an MDC% range of 14.6% to 23.7%. Likewise, commonly used isometric peak force measures for IABS, IADS, and IPCS had good to excellent relative reliability and an MDC% range of 22.2% to 26.4%. Commonly used CMJ and isometric strength measures had good test-retest reliability but might be limited by their MDC%. Rate-of-force-development measures (for all isometric tests) and impulse measures (IPCS) are limited by poor relative and absolute reliability and high MDC%. MDC% statistics should be considered in the context of typical responsiveness