A Flexible Improvement for Ping-Pong Protocol

A deterministic quantum communication protocol, called the ping-pong protocol, has been represented by Bostr6m and Felbinger [Phys. Rev. Lett. 89 （2002） 187902]. Based on an entangled pair of photons, it allows asymptotically secure key distribution and quasi-secure direct communication. However, it was concluded from our previous research that the experiment realization of this protocol requires two optic paths strictly equivalent for interferometry. Here we propose an improved protocol, which is more flexible and secure for conceivable applications. Its feasibility and security are also discussed.     

QUASI-STATIONARY DISTRIBUTIONS FOR THE RADIAL ORNSTEIN-UHLENBECK PROCESSES

The purpose of this article is to obtain the quasi-stationary distributions of the δ（δ 〈 2）-dimensional radial Ornstein-Uhlenbeck process with parameter -λ by using the methods of Martinez and San Martin （2001）. It is described that the law of this process conditioned on first hitting 0 is just the probability measure induced by a （4 - δ）- dimensional radial Ornstein-Uhlenbeck process with parameter -λ. Moreover, it is shown that the law of the conditioned process associated with the left eigenfunction of the process conditioned on first hitting 0 is induced by a one-parameter diffusion.     

近接基坑施工对既有隧道气囊桩的保护效果研究

为研究高压气囊桩的布设方式对既有隧道的保护效果,以JD08地块基坑施工对宁波轨道交通3号线区间隧道的影响为例,通过建立基坑开挖对隧道影响的二维计算模型,计算分析了气囊桩与隧道距离、气囊桩埋深、气囊桩加载压力对隧道水平和竖向位移以及其整体结构的影响,并与实测结果进行对比.结果表明:计算结果与实测结果较为接近,基坑设计方案满足地铁保护要求;气囊桩加载后,隧道出现挤压回弹,基坑开挖引起的隧道水平位移有所减小;随着气囊桩长度的增加,挤压作用更为明显,隧道水平位移减小,隆起增大,横向收敛增大;气囊桩与隧道间距以3 m为宜,气囊压力以800 kPa为宜.