采用投影光学估计弱起伏条件下的大气闪烁指数

在远场散斑投影成像系统上整合大气闪烁指数测量功能,有助于全面分析激光大气传输特性及其对光电系统性能的影响。但是在大口径接收时,大气闪烁会因孔径平滑效应而变得微弱,光源稳定性引起的强度起伏会更为明显。针对这一问题,基于光源强度起伏和大气闪烁的乘性调制假设,建立了考虑光源强度起伏的大气闪烁指数的测量模型。利用光源强度起伏不随孔径变化而大气闪烁随孔径变化这一差异性,通过投影光学在同一时刻测量两个不同接收孔径上的光强闪烁,结合弱起伏条件下的孔径平滑因子来求解测量模型,从而分别估计大气闪烁指数和光源强度闪烁指数。实验结果表明,在孔径0.05 m至0.4 m之间,实测值和理论估计值的最大相对误差小于9.685%,理论模型与实验符合度较高。采用该方法可以在投影光学上实现弱起伏条件下的大气闪烁指数估计。     

混沌专题系列研究性实验介绍

介绍了北京邮电大学物理实验中心在教学内容改革中开发的混沌专题系列实验.通过简单的、易于实现的力学和电路系统介绍混沌,将复杂的学术问题转化成了可以为不同层次学生所接受的研究性实验课题,激发了学生的实验兴趣,将科研成果直接转化为了教学实践.     

声、光、电转换演示仪的设计和制作

介绍了声光电转换的原理,设计和制作了演示声光电转换的实验装置。     

开环全光混沌通信系统中的光纤信道结构

根据外光反馈半导体激光器及光纤传输方程,构建了基于光纤信道的开环全光混沌通信系统.考虑混沌调制和混沌键控两种信息加密方法,采用先进的校正相减解调法恢复信息,并且通过解调Q因子衡量系统性能.以不同次序排列单模光纤和色散补偿光纤构成4种结构的光纤信道,通过数值仿真分析信道结构对系统通信性能的影响.结果表明,为光纤信道保留少量的负累积色散有利于改善远程传输性能;两端补偿和中间补偿这两种对称结构的性能一致,对称结构优于非对称结构即预补偿和后补偿,适用于远程高速开环全光混沌通信.另外,无论光纤信道结构怎样,在远程高速激光混沌通信中混沌调制方法总是优于混沌键控方法.     

High‐performance direct algorithms for computing the sign function of triangular matrices

Algorithms and implementations for computing the sign function of a triangular matrix are fundamental building blocks for computing the sign of arbitrary square real or complex matrices. We present novel recursive and cache‐efficient algorithms that are based on Higham's stabilized specialization of Parlett's substitution algorithm for computing the sign of a triangular matrix. We show that the new recursive algorithms are asymptotically optimal in terms of the number of cache misses that they generate. One algorithm that we present performs more arithmetic than the nonrecursive version, but this allows it to benefit from calling highly optimized matrix multiplication routines; the other performs the same number of operations as the nonrecursive version, suing custom computational kernels instead. We present implementations of both, as well as a cache‐efficient implementation of a block version of Parlett's algorithm. Our experiments demonstrate that the blocked and recursive versions are much faster than the previous algorithms and that the inertia strongly influences their relative performance, as predicted by our analysis.     

用于扩频通信的声光循环平稳信号处理技术

传统的基于声光技术的信号处理模型被建模为平稳随机过程,而在扩频通信中,信号是被伪码调制的循环(周期)平稳信号。因此,扩频信号应被建模为循环平稳随机过程。基于声光信号处理技术和循环平稳随机过程理论,建立了声光循环平稳信号处理模型,并应用于扩频通信中,理论分析和仿真表明,声光循环平稳信号处理技术在扩频通信领域的信号分析中是十分有用的。     

载流子复合机制对InGaN多量子阱蓝光LED调制带宽的影响

通过设计InGaN多量子阱LED有源区的不同结构,研究了载流子复合机制对LED调制速度的影响。结果显示,由于窄量子阱LED的载流子空间波函数重叠几率更高,且电子泄露效应更显著,所以复合速率更快,调制带宽更高。In组分为1%的InGaN量子垒LED可提高辐射复合的权重,使得调制带宽高于GaN量子垒LED;In组分为5%时,电子泄露和俄歇复合占据主导地位,且由于这两种复合机制复合速率很快,所以调制带宽显著提高。     

Controlled Secure Quantum Communication Using Pure Entangled W Class States

We present a controlled secure quantum communication protocol using non-maximally （pure） entangled W states first, and then discuss the basic requirements for a real quantum communication. We show that the authorized two users can exchange their secret messages with the help of the controller after purifying the non-maximally entangled states quantum channel unconditionally securely and simultaneously. Our quantum communication protocol seems even more feasible within present technologies.     

Oxidative Coupling of Anionic Abnormal N‐Heterocyclic Carbenes: Efficient Access to Janus‐Type 4,4′‐Bis(2H‐imidazol‐2‐ylidene)s

The oxidative coupling of anionic imidazol‐4‐ylidenes protected at the C2 position with [MnCp(CO)₂] or BH₃ led to the corresponding 4,4′‐bis(2H‐imidazol‐2‐ylidene) complexes or adducts, in which the two carbene moieties are connected through a single C?C bond. Subsequent acidic treatment of the later species led to the corresponding 4,4′‐bis(imidazolium) salts in good yields. The overall procedure offers practical access to a novel class of Janus‐type bis(NHC)s. Strikingly, the coplanarity of the two NHC rings within the mesityl derivative 4,4′‐bis(IMes), favored by steric hindrance along with stabilizing intramolecular C?H???π aryl interactions, allows the alignment of the π‐systems and, as a direct consequence, significant electron communication through the bis(carbene) scaffold.     

近10年中国作者在Journal of Chemical Education发表论文概述

对2007-2016年中国作者在美国Journal of Chemical Education上发表论文的数量、作者人数、发文地区、作者单位及合作情况、论文内容等进行了统计与分析,揭示了近年来我国化学教育研究成果的特点,旨在为我国化学化工人才培养工作提供一些参考,并促进中国化学教育的国际交流。