相位调制对双泵浦光参量放大器增益的影响

双泵浦波在光纤中的传输可以用耦合非线性薛定谔方程来描述，在群速度失配不能忽略和可以忽略两种情况下进行增益计算，并采用升余弦滚降信号作为相位调制信号，从理论上得到了双泵浦光参量放大器增益的解析解与数值解，并由此得到增益曲线。得到采用不同波长的泵浦波，也就是在群速度失配的情况下，增益要比群速度匹配的情况下大些。采用不同波长的泵浦波有利于提高光参量放大器的增益。且在相位调制的上升和下降时间段，增益有起伏的特点。     

Spectral characteristics of periodic tunnelling of chirped soliton in nonautonomous system with external potentials

We present an exact chirped soliton solution for a nonautonomous system with external potentials and periodic nonlinear barriers/wells (NBs/NWs). Based on the soliton solution, we disclose the interesting spectral features of the chirped solitons through periodic NBs and NWs. In addition to the spectrum being broadened through NBs and being compressed through NWs, we find that distinct spectral characteristics of the chirped soliton appear at the centre, leading and trailing edges of NBs and NWs, which are related to the chirp of the solitons, the period of NBs/NWs and external potentials. When the period of NBs/NWs decreases and the soliton chirp increases, the spectrum appears additional broadening near the leading and trailing edges of both NBs and NWs, but the spectral widths at the centre of both NBs and NWs remain unchanged. Moreover, the linear potential affects the trajectory and the frequency shift of the chirped soliton.     

Adenovirus Terminal Protein Contains a Bipartite Nuclear Localisation Signal Essential for Its Import into the Nucleus

Adenoviruses contain dsDNA covalently linked to a terminal protein (TP) at the 5′end. TP plays a pivotal role in replication and long-lasting infectivity. TP has been reported to contain a nuclear localisation signal (NLS) that facilitates its import into the nucleus. We studied the potential NLS motifs within TP using molecular and cellular biology techniques to identify the motifs needed for optimum nuclear import. We used confocal imaging microscopy to monitor the localisation and nuclear association of GFP fusion proteins. We identified two nuclear localisation signals, PV(R)6VP and MRRRR, that are essential for fully efficient TP nuclear entry in transfected cells. To study TP–host interactions further, we expressed TP in Escherichia coli (E. coli). Nuclear uptake of purified protein was determined in digitonin-permeabilised cells. The data confirmed that nuclear uptake of TP requires active transport using energy and shuttling factors. This mechanism of nuclear transport was confirmed when expressed TP was microinjected into living cells. Finally, we uncovered the nature of TP binding to host nuclear shuttling proteins, revealing selective binding to Imp β, and a complex of Imp α/β but not Imp α alone. TP translocation to the nucleus could be inhibited using selective inhibitors of importins. Our results show that the bipartite NLS is required for fully efficient TP entry into the nucleus and suggest that this translocation can be carried out by binding to Imp β or Imp α/β. This work forms the biochemical foundation for future work determining the involvement of TP in nuclear delivery of adenovirus DNA.     

Dark solitons in nonlinear-optical fibers

Opticalsolitonsinfibersarepulsesthatpropagatepreservingtheirshapeorintensityundercertainconditions,becausetheeffectsofintensity--dependentrefractiveindexofthefiberexactlycompensateforthepulse--spreadingeffectsofgroup--velocitydispersion(GVD)[lj.Intheanomalous--dispersionregimeofthefiber,brightsolitonscanbeobtainedandhavebeenstudiedextensively.Inthenormal--dispersionregion,darksolitonscanbeobtained.Theexistenceofdark--pulsesolitonshasbeenverifiedinexperiments.Thepropertiesofdarksolitonshavebe…     

光孤子传输及其系统的关键技术

光孤子具有传输不变形的特性,是光纤通信系统中最理想的信息载体。简要阐述了光孤子的成形机制及其传输理论,并介绍了光孤子传输系统构成与其所涉及到的关键技术,最后探讨了光孤子传输系统的研究现状及发展前景。     

ZNF 219基因核定位信号序列的确定

ZNF2 19是新发现定位在人 14号染色体 q11带上的特异性锌指基因 .本实验对其核定位信号的识别说明其中有两组核定位序列存在 ,因此通过将ZNF2 19的核定位序列(NLS)与N -端增强绿色荧光蛋白载体 (pEGFP N1)构建成质粒 (pEGFP ZNF2 19NLS) ,然后瞬时转染到COS靶细胞 ,实验结果表明 :绿色荧光蛋白 (GFP)进入细胞核区     

Text-making practices beyond the classroom context: Private instant messaging in Hong Kong

This article explores the ways in which instant messaging (IM) texts are produced by a group of university students in Hong Kong. Even though there exists a body of research on linguistic issues of computer-mediated communication (CMC) in non-Western contexts, much emphasis has been placed on the features of CMC English used by ESL learners. Instead of focusing on one particular language, this article reports on a number of language-related issues that are specific to the Hong Kong CMC context such as the use of Chinese and English, invented Cantonese spellings, and code-mixing. Drawing upon qualitative data such as observational notes and interviews, my study analyzes the text-making practices associated with the use of IM (ICQ and MSN Messenger) within the New Literacy Studies (NLS) framework [Gee, James Paul. (1996). Social linguistics and literacies. London: Routledge; Barton, David, Hamilton, Mary, & Ivani?, Roz (Eds.). (2000). Situated literacies, London: Routledge; Street, Brian V. (1998). New literacies in theory and practice: What are the implications for language in education? Linguistics and Education, 10(1), 1-24], which is a social practice approach to the study of reading and writing in real-life contexts. This article concludes by arguing that learning to produce texts in IM involves an entirely different process from that of formal language learning in the classroom. In a multilingual society like Hong Kong, teachers and educators need to be aware of such differences so as to bridge the gap between actual uses of language in students’ private lives and the form of language used in the formal classroom context.     

Parallel Split-Step Fourier Methods for the Coupled Nonlinear Schrödinger Type Equations

The nonlinear Schrödinger type equations are of tremendous interest in both theory and applications. Various regimes of pulse propagation in optical fibers are modeled by some form of the nonlinear Schrödinger equation.In this paper we introduce parallel split-step Fourier methods for the numerical simulations of the coupled nonlinear Schrödinger equation that describes the propagation of two orthogonally polarized pulses in a monomode birefringent fibers. These methods are implemented on the Origin 2000 multiprocessor computer. Our numerical experiments have shown that these methods give accurate results and considerable speedup.     

基于NLS-RELAX的空中多机动目标参数估计

针对机载雷达在环境复杂的高空飞行时检测空中多机动目标难度大的问题,提出了一种基于NLS-RELAX的空中多机动目标参数估计方法。本方法借鉴了RELAX算法的思想,可对多个机动目标进行有效分离,并利用非线性最小二乘(Nonlinear Least Squares, NLS)对分离后的每个机动目标信号进行参数估计。仿真实验表明,在目标信号严重被强杂波淹没且脉冲数有限的情况下,本方法可以获得较为精确的参数估计结果,且由于加入了RELAX的分离思想,在待检测距离单元内存在多个机动目标时本方法同样适用。     

基于非线性最小二乘的双基地声纳定位优化算法

双基地声纳定位是一种重要的定位方法,采用优化算法来提高定位精度是其重要的研究内容。本文采用了将双基地声纳定位方程转化为非线性最小二乘(NLS)问题的技术方法,并后置最优化方法LMF算法,研究了基于多基地接收源的目标定位性能和定位精度的几何稀释(GDOP),给出了定位误差分布。通过数值仿真,研究了不同基线长度时双基地声纳的定位精度,并将NLS拟和算法的多接收源定位性能与纯时间估计定位性能进行了比较。研究表明,本文的基于多基地接收源的目标定位方法相对于纯时间估计定位方法提高了定位精度,特别是在相对短的基线(7.4 km基线长度)情况下,可提高30%的精度。该研究为最优化方法在水声定位中的应用提供了依据。