梯度折射率激光准直器的原理与设计

本文研究用单块抛理型梯度折射率棒透镜作激光准直器的原理、特性和设计。     

硫化物光纤及其功能器件的应用

本文概述了９０年代初兴起的硫化物光纤的独特性能、目前的发展状况及可能的应用前景;针对硫化物光纤实用化中的关键技术进行了分析,并对硫化纤的光敏机理作了一定的探讨。由于具有优于石英光纤的特点,硫化物光纤及其人器件具有广阔的应用前景。     

ATM视频传输中信元丢失的分析与对策

ＡＴＭ的出现使得我们能够实时地,高效地传输视频信号,但同时在传输过程中ＡＴＭ的信元丢失将是导致解压缩后的图像质量严重下降。文章首先基于ＭＰＥＧ－２标准,给出了一个基本的视频通信系统框架及各部分的码流格式,然后分析了系统中信元丢失的原因,特点和影响。文中给出了现有的各种减少信元丢失的方法及其如何隐藏信元丢失对图像质量造成的影响,分析其优质和适用场合,并讨论了以后的研究方向。     

被动直升机声信号波达方向估计

在分析直升机声信号和背景噪声特点的基础上,提出了1种适合于被动单直升机 目标声信号波达方向(DOA)估计的方法。首先在1帧时间内利用傅立叶变换估计直升机声信 号基频,然后用查表获得的投影矩阵滤除不需要的频率成分,最后用波束形成估计到达角。方 法运算量适中,精度较高,通过对采录的1架某型号直升机声信号的分析验证了该算法的有效 性。     

一种基于交换机的彩铃业务实现方案

首先介绍了在GSM移动网络中实现彩铃业务的原理，然后提出一种基于交换机实现彩铃业务的技术方案，分析了此方案中媒体设备的物理结构和内部信令的交互过程，最后将该方案与基于智能网的方案进行了对比。     

基于嵌入式Web服务器的数字视频监控的解决方案

本文提供了在 ARMS3C2410芯片上基于嵌入式 Web 服务器的网络视频监控的一种解决方案。在压缩方面采用了以 WIS G700SB 为核心的 MPEG-4采集压缩模块。先叙述总体设计思想，然后分软件和硬件两部分进行详细探讨。     

Surface State Mediated NIR Two‐Photon Fluorescence of Iron Oxides for Nonlinear Optical Microscopy

The development of fluorescent iron oxide nanomaterials is highly desired for multimodal molecular imaging. Instead of incorporating fluorescent dyes on the surface of iron oxides, a ligand‐assisted synthesis approach is developed to allow near‐infrared (NIR) fluorescence in Fe₃O₄ nanostructures. Using a trimesic acid (TMA)/citrate‐mediated synthesis, fabricated Fe₃O₄ nanostructures can generate a NIR two‐photon florescence (TPF) peak around 700 nm under the excitation by a 1230‐nm femtosecond laser. By tailoring the absorption of Fe₃O₄ nanostructures toward NIR band, the NIR‐TPF efficiency can be greatly increased. Through internal etching, surface peeling, and ligand replacement, spectroscopic results validated that such resonantly enhanced NIR‐TPF is mediated by surface states with strong NIR‐IR absorption. This TPF signal evolution can be generalized to other iron oxide nanomaterials like magnetite nanoparticles and α‐Fe₂O₃ nanoplates. Using the developed fluorescent Fe₃O₄ nanostructures, it is demonstrated that their TPF and third harmonic generation (THG) contrast in the nonlinear optical microscopy of live cells. It is anticipated that the synthesized NIR photofunctional Fe₃O₄ will serve as a versatile platform for dual‐modality magnetic resonance imaging (MRI) as well as a magnet‐guided theranostic agent.     

Noise limit in heterodyne Interferometer demodulator for FBG-based sensors

This paper reports the results of a recent investigation on the noise-limited performance in heterodyne interferometric demodulation systems for fiber Bragg grating strain sensors. Theoretical and simulation results are presented and compared with experimental results.     

Boosting Piezo-Catalytic Activity of KNN-Based Materials with Phase Boundary and Defect Engineering

Although the piezo-catalysis is promising for the environmental remediation and biomedicine, the piezo-catalytic properties of various piezoelectric materials are limited by low carrier concentrations and mobility, and rapid electron-hole pair recombination, and reported regulating strategies are quite complex and difficult. Herein, a new and simple strategy, integrating phase boundary engineering and defect engineering, to boost the piezo-catalytic activity of potassium sodium niobate ((K, Na)NbO₃, KNN) based materials is innovatively proposed. Tur strategy is validated by exampling 0.96(K_0.48Na_0.52)Nb_0.955Sb_0.045O₃-0.04(Bi_xNa_4-3x)_0.5ZrO₃-0.3%Fe₂O₃ material having phase boundary engineering and conducted the defect engineering via the high-energy sand-grinding. A high reaction rate constant k of 92.49 × 10⁻³ min⁻¹ in the sand-grinding sample is obtained, which is 2.40 times than that of non-sand-grinding one and superior to those of other representative lead-free perovskite piezoelectric materials. Meanwhile, the sand-grinding sample has remarkable bactericidal properties against Escherichia coli and Staphylococcus aureus. Superior piezo-catalytic activities originate from the enhanced electron-hole pair separation and the increased carrier concentration. This study provides a novel method for improving the piezo-catalytic activities of lead-free piezoelectric materials and holds great promise for harnessing natural energy and disease treatment.     

Indirect Control of Donor/Acceptor Interactions for Highly Efficient Space-Confined Thermally Activated Delayed Fluorescence Emitters

Conformational engineering is essential to further reinforce the luminescent properties of thermally activated delayed fluorescence (TADF) materials featuring through-space charge transfer (TSCT) characteristics. Herein, two TSCT-TADF emitters (8MeDM-B and 8FDM-B) with the methyl and fluorine moieties substituted at the C8 site of the rigid spiro-fluorene bridge is reported. Derivation of the C8 site is first proposed to control the molecular configuration with the ability to indirectly tune the intramolecular interaction between donor and acceptor groups. As a result, 8MeDM-B and 8FDM-B both present small singlet-triplet energy gaps, fast reverse intersystem crossing rates, and high photoluminescence quantum yields. Interestingly, the smaller fluorine atom not the bigger methyl group exhibits more evident electrostatic repulsive force onto the central donor and thus rectifies the central spiro structure. Consequently, the high external quantum efficiency values of 28.8% and 31.7% for 8MeDM-B and 8FDM-B-based electroluminescence devices are achieved, respectively. This study offers a measure for enhancing TSCT-TADF emitters without directly modifying the donor or acceptor.