No abstract

Purpose. the playing formation of football teams influences how players interact with each other via passing. the aim of this study was to use network analysis to determine the passing characteristics of playing positions within a professional a professional football team across two consecutive competitive seasons, when playing two different formations. Methods. In season one (2016/2017) the team played 1-4-2-2-2 in 21 matches, and in season two (2017/2018) the team played 1-4-2-3-1 in 21 matches. Network analysis was applied to calculate the individual centrality metrics of indegree centrality (IDC), outdegree centrality (ODC), closeness centrality (CC), and betweenness centrality (BC) for the playing positions, using the Social Network Visualizer (SocNetV). the centrality metrics were compared across the playing formations and as a function of match outcome. Results. the forward positions in 1-4-2-2-2 had significantly (p < 0.05) more outgoing passes compared with 1-4-2-3-1. the defensive midfield positions in 1-4-2-3-1 had a significantly (p < 0.05) higher %BC compared with 1-4-2-2-2. the forward positions had increased %IDC and %ODC when playing 1-4-2-2-2 in matches drawn compared with 1-4-2-3-1. Conclusions. the current study shows that subtle changes to playing formation elicit differences in the passing contributions of the players. the results suggest that coaches may adopt the playing formation 1-4-2-2-2 compared with 1-4-2-3-1 owing to the increased passing involvement from the forwards.

The drop weight impact or drop hammer test has been a staple of energetic material small-scale sensitivity testing for over 100 years, but the link between material properties and sensitivity has proven difficult to evaluate, especially for composite materials. In this study, the work of adhesion and elastic modulus of the binder were varied to assess their impact on the sensitivity of a family of plastic bonded explosive composite energetic materials. Drop weight impact tests performed using the German Bundesanstalt für Materialprufung impact test demonstrated significant decreases in sensitivity as the elastic modulus and the work of adhesion decrease. It was determined that the elastic modulus of the binder was the most significant contributor to the corresponding changes in sensitivity.

Polymer bonded explosives (PBXs) have exhibited localized heating and, in some cases, subsequent reactions in response to ultrasonic excitation. The objectives of this work are to investigate the conditions for, and locations of, hot spot initiation of energetic crystals embedded within a polymer binder subjected to periodic mechanical excitation from a contacting transducer operating at 210.5 kHz. Crystal and binder interactions and events such as delamination, solid-solid phase change, and gas production were observed in real time via optical microscopy. We conclude that there are two main pathways of heat generation which are capable of driving an explosive to decomposition in the systems of interest: frictional heating from a delaminated and moving binder interface and viscoelastic heating in the binder near an embedded crystal. Formulations that address the vibration initiation sensitivity of PBX composites require knowledge of the key internal heat generation mechanisms. The results included here indicate that improving binder adhesion to energetic crystals or improving crystal morphology to reduce heating during cyclic loading may only address one of the available pathways of energy dissipation and that binder and crystal selection should be done concurrently. Furthermore, the results presented herein appear to indicate that rounded particles, in contrast to faceted crystals, with strong adhesion to the binder are expected to result in decreased heating rates under ultrasonic excitation.