We study an air-fluidized granular monolayer, composed in this case of plastic spheres, which roll on a metallic grid. The air current is adjusted so that the spheres never loose contact with the grid, so that the dynamics may be regarded as pseudo two-dimensional (or two-dimensional, if the effects of sphere rolling are not taken into account). We find two surprising continuous transitions, both of them displaying two coexisting phases. Moreover, in all cases, we found the coexisting phases display strong energy non-equipartition. In the first transition, at weak fludization, a glassy phase coexists with a disordered fluid-like phase. In the second transition, a hexagonal crystal coexists with the fluid phase. We analyze, for these two-phase systems, the specific diffusive properties of each phase, as well as the velocity correlations. Surprisingly, we find a glass phase at very low packing fraction and for a wide range of granular temperatures. Both phases are characterized also by a strong anti-correlated velocities upon collision. Thus, the dynamics observed for this quasi two-dimensional system unveils phase transitions with peculiar properties, very different from the predicted behavior in well know theories for their equilibrium counterparts.

中文翻译：

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宏观滚球系统中相变的扩散和速度相关性

我们研究了一种空气流化的粒状单层，在这种情况下由塑料球组成，在金属网格上滚动。调整气流，使球体永远不会与网格松散接触，因此动力学可以被视为伪二维（或二维，如果不考虑球体滚动的影响）。我们发现了两个令人惊讶的连续转变，它们都显示了两个共存的阶段。此外，在所有情况下，我们发现共存相显示出强烈的能量非均分。在第一个转变中，在弱流态化时，玻璃相与无序流体状相共存。在第二次转变中，六方晶体与流体相共存。对于这些两相系统，我们分析了每个相的特定扩散特性，以及速度相关性。令人惊讶的是，我们发现了在非常低的填充率和宽范围的颗粒温度下的玻璃相。两个阶段的特征还在于碰撞时具有强烈的反相关速度。因此，对这种准二维系统观察到的动力学揭示了具有特殊性质的相变，这与众所周知的平衡对应物理论中的预测行为非常不同。