网球裁判员临场注意力特征及影响因素分析

网球比赛中,网球裁判员的判罚是最重要的,要想保证判罚的准确率,减少误判、错判、漏判情况的发生,需要裁判员提高自身的临场注意力;网球裁判一直都是网球比赛的守护神,维护着场上的公平,也默默操持着场下各个环节;网球裁判员是确保网球比赛顺利进行的执法者,而在比赛过程中,网球裁判员的临场注意力直接影响了赛场判罚的准确率,因此,对影响裁判员临场注意力的因素进行仔细的分析,以提高裁判员的临场注意力;指出网球裁判员要明确主裁以及司线员的临场注意力特征,并对判罚过程中的难点进行重点训练,通过多参加比赛,多总结影响裁判员临场注意力的原因而有针对性地进行训练,可克服影响因素。     

Coherence incoherence and dimensional crossover in layered strongly correlated metals

The properties of an interacting electron system depend on the electron correlations and the effective dimensionality. For example, Coulomb repulsion between electrons may inhibit, or completely block, conduction by intersite electron hopping, thereby determining whether a material is a metal or an insulator. Furthermore, correlation effects increase as the number of effective dimensions decreases; in three-dimensional systems, the low-energy electronic states behave as quasiparticles, whereas in one-dimensional systems, even weak interactions break the quasiparticles into collective excitations. Dimensionality is particularly important for exotic low-dimensional materials where one- or two-dimensional building blocks are loosely connected into a three-dimensional whole. Here we examine two such layered metallic systems with angle-resolved photoemission spectroscopy and electronic transport measurements, and we find a crossover in the number of effective dimensions from two to three with decreasing temperature. This is apparent from the observation that, in the direction perpendicular to the layers, the materials have an insulating character at high temperatures but become metal-like at low temperatures, whereas transport within the layers remains metallic over the whole temperature range. We propose that this change in effective dimensionality correlates with the presence of coherent quasiparticles within the layers.