Age is one of the factors which influnce foreign language learning, but not the most important one. Comparision on the effect of foreign language learning between adults and children cannot rely merely on age. So the ...Age is one of the factors which influnce foreign language learning, but not the most important one. Comparision on the effect of foreign language learning between adults and children cannot rely merely on age. So the question of an optimum age for foreign language learning is not a simple one which is only related to age. There are different optimum ages for different aims and demands of learning foreign language.展开更多
文摘Age is one of the factors which influnce foreign language learning, but not the most important one. Comparision on the effect of foreign language learning between adults and children cannot rely merely on age. So the question of an optimum age for foreign language learning is not a simple one which is only related to age. There are different optimum ages for different aims and demands of learning foreign language.
文摘作为网络传输控制机制的核心,拥塞控制关注如何在异构网络环境中最优化特定传输性能目标。已有拥塞控制机制忽略了不同应用的性能偏好在吞吐量-时延两个维度上的帕累托最优前沿(Pareto optimal frontier,POF)分布,难以满足差异化应用的性能需求。针对上述问题,本文提出了一种面向应用性能偏好的帕累托最优拥塞控制机制pBBR(ParetooptimalBBR),结合离线网络场景学习和在线控制参数优化的思想,最大程度满足应用的差异化性能偏好。实验结果表明,pBBR能够在一个采集-识别周期内判断出网络场景的切换,从而快速选择当前网络场景的最优控制参数。每个网络场景下,pBBR都能够最大化满足不同的应用性能偏好:针对吞吐量敏感业务,pBBR可以达到Cubic(吞吐优先)的97%,且时延只有Cubic的52%;针对时延敏感业务,pBBR的时延可以达到Sprout(时延优先)的95%,同时吞吐量损失只有1%。此外,多参数优化可进一步提升pBBR性能,例如在高铁长期演进技术(long term evolution,LTE)通信场景下,单参数pBBR的吞吐量、时延分别是Cubic的94%和99%,而三参数pBBR则分别提升到Cubic的101%和93%(优于Cubic)。
