Scintillation reduction using multi-beam propagating technique in atmospheric WOCDMA system

We propose employing multi-beam propagating technology to mitigate the influence of atmospheric scintillation to the wireless optical code division multiple access (WOCDMA) system and then deduce the bit error rate (BER) formulas of systems in weak and strong scintillations,respectively.According to simulation experiment results,multi-beam propagation can improve the system performance very well compared with single-beam propagating technique.Moreover,the more beams we use,the better the performance we get.When the received optical power is-30 dBm,the BER of the system employing four beams is 5 and 1 dB lower than that of using single-beam propagating technique in weak and strong scintillations,respectively.     

氧族氢化物的压致金属化与奇异超导电性

富氢化合物在目前实验所能达到的压力范围内有望实现金属化,是潜在的具有高超导临界温度的材料。实验和理论研究均发现高压下S-H化合物的超导临界温度高达203 K,创造了高温超导的新纪录,掀起了新一轮富氢化合物超导电性研究的热潮。本文主要介绍近年来关于氧族氢化物的压致金属化和奇异超导电性研究,对比分析氧族富氢化合物高压行为的异同。氧族元素的最外层电子排布相同,但原子质量和电负性的差异巨大,导致形成的富氢化合物在化学配比、结构、化学成键以及超导电性来源上存在较大差别。S-H和Se-H化合物的超导电性主要源自与氢原子拉伸振动模式相关的强电子-声子耦合,而Te-H和Po-H化合物中对超导电性贡献最大的是氢原子的切向振动模式。     

固体氢在极端压强下的超导性能

氢元素在常压下具有最简单的晶体结构和物理性质。随着压强增加,氢单质发生相变,由绝缘体转变为金属,被称为金属氢。数值模拟表明,金属氢具有高温超导电性,因此,金属氢研究也被称为高压物理领域的“圣杯”课题。利用基于密度泛函理论的第一性原理计算方法,对固体氢在极端高压(0.5～5.0 TPa)下的结构和超导电性开展了系统研究。研究结果表明：固体氢的高压相变序列为I4₁/amd→oC12→cI16;对于同一种结构,随着压强增加,电声耦合系数减小,费米面处电子态密度减小,特征振动频率增加,超导转变温度发生小幅变化;在2.0 TPa压强下,固体氢的超导转变温度高达418 K(库伦赝势经验值μ^*=0.10)。研究工作将为金属氢及其超导电性的后续理论和实验研究提供参考。     

Dynamic manipulation of probe pulse and coherent generation of beating signals based on tunneling-induced inference in triangular quantum dot molecules

We investigate the dynamic propagation of a probe field via the tunneling-induced interference effect in a triple model of quantum dot molecules. By theoretical analysis and numerical simulation, we find that the number of transparency window relate to the energy splitting and the group velocity of probe field can be effectively controlled by the tunneling coupling intensity. In addition, in the process of light storage and retrieval, when the excited states have no energy splitting in the storage stage but opposite values of the energy splitting in the retrieval stage, the beating signals can be generated.