【摘要】 文章作者系统地研究了垂直振动颗粒床中 ,在不同气压、颗粒尺寸以及密度情况下大球的运动规律 .实验发现 ,系统处于真空状态或低气压时 ,大球总是向上运动 .然而 ,当在通常大气压下 ,大球则会出现上升和下降两种运动状态 .大球下降这种运动状态 ,只在大球的密度和颗粒床中颗粒尺寸足够小时才会出现 ,颗粒床中的负气压梯度导致大球下降 .更多还原

【Abstract】 The effects of interstitial air on t he motions of a large intruder in a shaken granular bed are studied experimental ly as a function of ambient air pressure, particle size of the bed, and the dens ity of the intruder. It is found that the intruder always rises from the granula r bed in the absence of air. However, the intruder can acquire both positive and negative buoyancy in the presence of air. Negative buoyancy can be observed onl y when both the density of the intruder and the particle size of the bed are sma ll enough. This negative buoyancy can be explained by the unusual air pressure d istribution found in the bed.更多还原