A new method for computing the expected hitting time between arbitrary   different configurations of the multiple-urn Ehrenfest model
  We study a multiple-urn version of the Ehrenfest model. In this setting, we denote the n urns by Urn 1 to Urn n, where n>=2. Initially, M balls are randomly placed in the n urns. At each subsequent step, a ball is selected and put into the other n-1 urns with equal probability. The expected hitting time leading to a change of the M balls' status is computed using the method of stopping times. As a corollary, we obtain the expected hitting time of moving all the M balls from Urn 1 to Urn 2. This proves a conjecture which was recently made in Chen et al.(2017). 
Sai Song, Qiang Yao
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