世界十大最古老树木

据国外媒体报道，在古巴比伦王国开始记录时间之前，一些最古老的树已经存活了数百年。不仅如此。它们还见证了希腊和罗马帝国的兴衰、基督教和伊斯兰教等宗教的诞生，并一直持续到现在。以下是世界上的十大古树。     

Mean waiting time approximation for a real time polling system

This paper considers a novel polling system with two classes of message which can experience an upper bounded time before being served. The station serves these two classes with mixed service discipline, one class with exhaustive service discipline, and the other with gated service discipline. Using iterative method, we have developed an approximation method to obtain the mean waiting time for each message class. The performance of approximation has been compared with the simulation results. The expression for the upper bound of waiting time is given too.