The hypothesis that sport-specific skill learning is correlated with earlier childhood multi-sport practice experiences was empirically studied among youth soccer players. Fourteen youth soccer coaches (38.1 ± 12.0 years) evaluated 100 youth players (11.8 ± 0.7 years) regarding their progress in soccer-specific skill learning through the course of a one-year season. The players completed a questionnaire recording their earlier and current participation in coach-led practice and youth-led play in soccer and in other sports. Reliability of the coach rating and of players’ reported sport activities ranged 0.83 ≤  rtt ≤ 1.00. Analyses revealed that the progress of the youth players in soccer-specific skill learning was not significantly correlated with their earlier or current amounts of coach-led soccer practice (–0.07 ≤  rs ≤ 0.07), youth-led soccer play (0.01 ≤  rs ≤ 0.08), or youth-led play in other sports (0.13 ≤  rs ≤ 0.22). Progress in soccer-specific skill learning was significantly correlated with the accumulated years and hours of earlier (but not current) coach-led practice in other sports (0.54 ≤  rs ≤ 0.57). A binary logistic regression accurately classified 83% of players with better and poorer learning progress based on earlier years and hours of practice in other sports. The observations suggest that earlier practice experiences in other sports had a lagged effect in interaction with later soccer practice and facilitated skill learning in soccer-specific practice.

We present 3D calculations for dielectric haloscopes such as the currently envisioned MADMAX experiment. For ideal systems with perfectly flat, parallel and isotropic dielectric disks of finite diameter, we find that a geometrical form factor reduces the emitted power by up to 30 % compared to earlier 1D calculations. We derive the emitted beam shape, which is important for antenna design. We show that realistic dark matter axion velocities of 10 −3 c and inhomogeneities of the external magnetic field at the scale of 10 % have negligible impact on the sensitivity of MADMAX. We investigate design requirements for which the emitted power changes by less than 20 % for a benchmark boost factor with a bandwidth of 50 MHz at 22 GHz, corresponding to an axion mass of 90 µeV. We find that the maximum allowed disk tilt is 100 µm divided by the disk diameter, the required disk planarity is 20 µm (min-to-max) or better, and the maximum allowed surface roughness is 100 µm (min-to-max). We show how using tiled dielectric disks glued together from multiple smaller patches can affect the beam shape and antenna coupling.

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