基于双检波积分器的脉冲信号被动检测算法

提出了背景变化较大场合下脉冲信号检测的新算法,该算法基于双检波积分器,分别对背景噪声和脉冲信号进行检波处理,可实时跟踪背景的变化,自适应调整检测门限,适用于噪声背景变化较大的应用场合.指数加权积分算法的使用,解决了积分时间大的问题,适用于存储空间有限且又需要大积分时间的系统.经过TMS320C5502 DSP处理,该方...     

基于信号分离估计理论的GPS多径抑制算法

信号多径效应是全球卫星定位系统(Global Positioning System,GPS)定位误差的主要来源之一.虽然差分技术可以提高导航系统的定位精度,但由于参考站和用户所处的地理环境不同,因此差分GPS系统仍然不能消除由于卫星信号多径所引起的定位误差.根据GPS多径信号模型的特点,本文提出了一种基于信号分离估计理论的GPS时延估计算法.该算法在信号时延未知情况下,先估计出信号的载波频率,然后根据估计得到频率,利用信号分离估计理论估计信号时延.仿真结果表明,该方法具有很好的估计精度,能够准确的估计出信号时延和频率,有效地抑制信号多径.当存在多径时,本文方法效果明显好于常规方法,并在大多数情况下优于常用的窄带相关算法.     

基于MAX274的滤波器设计与实现

针对通信与信号处理系统中对滤波器多样性的需求,分析了MAXIM公司推出的能灵活设计各种类、各频段滤波器的连续时间、有源滤波器芯片MAX274,并对其设计滤波器的原理进行了推导。以设计一个中心频率为125 kHz的八阶Bessel有源带通滤波器为例,给出了滤波器软件设计方法。最后为检验基于MAX274滤波器的性能,将该设计做成电路板,并用滤波器特性检测系统检验其频谱特性,实际测试结果表明该滤波器的设计频率具有精确度高、成本低等特性。     

删余Turbo乘积码的编译码算法分析

基于现有的Turbo乘积码的编译码方法,提出一种附加删余的Turbo乘积码编译码算法,介绍其编码器的构造方法,阐述了译码算法及实现框图,分析了删余信息对传输帧长的影响,仿真了其误码性能,并与未删余的Turbo乘积码做比较。分析和仿真结果表明,附加删余的Turbo乘积码可满足特定系统传输速率及帧长的需要,在相同的信噪比下,删余Turbo乘积码的误码性能优于未加删余的误码性能。     

预烧温度对0.363BiScO3-0.637PbTiO3高温压电陶瓷性能的影响

研究了不同预烧温度对反应烧结0.363BiScO3-0.637PbTi O3陶瓷的微观结构及压电介电性能的影响。根据0.363BiScO3-0.637PbTi O3的配方,通过热失重-差热分析判断Sc2O3、Bi2O3、Pb3O4、Ti O2粉末混合物分解、化合反应点和预烧温度范围;运用XRD、SEM研究了不同预烧温度下制备陶瓷样品的微观结构;通过压电介电性能测试,确定出最佳预烧工艺条件。结果表明,最佳的预烧条件为740℃保温2 h。经1 080℃、2 h烧成陶瓷的压电常数d33=308 pC/N,机电耦合系数kp=0.437,介电常数ε3T3/ε0=1 560,介电损耗tanδ=0.021,退极化温度TD=460℃。在此工艺条件下,该陶瓷性能优良、制备重复性好,在高温压电陶瓷传感器、换能器等方面显示出实用化前景。     

长周期光纤光栅对结构参数的敏感特性

基于模式耦合理论,对影响长周期光纤光栅（LPFG）光谱特性的各种物理结构参数进行了研究,得到LPFG光谱特性响应的一系列定量或定性的规律。利用紫外线,通过振幅掩模法曝光H载掺Ge光纤制作了两根LPFG,写入的光栅长度分别为3.0 cm和4.5 cm,测得温度灵敏度分别为0.044 6 nm/℃和0.059 4 nm/℃...     

基于PMV控制目标的舒适性空调应用研究

与传统的空调系统控制方式相比,基于PMV(预测平均投票指标--Predicted Mean Vote)热舒适控制系统的作用点由室内空气转移到了人体上.以热舒适指标PMV作为空调控制系统的控制目标,分析了各环境因素对PMV的影响,提出了空调系统的优化控制方案,不仅改善了舒适度,而且节能效果明显,具有良好的适用性.     

双梳型共聚物在莠去津颗粒表面吸附的X射线光电子能谱分析

采用X射线光电子能谱(XPS)研究了双梳型共聚物吸附于莠去津颗粒样品表面的电子状态,计算了吸附厚度.结果表明:吸附后,莠去津颗粒界面的N 1s和Cl 2p谱峰强度明显减弱,Cl 2s几乎消失,而C 1s和O1s谱峰强度则明显增强,这主要是双梳型共聚物中C和O的贡献,且吸附后能在莠去津颗粒界面形成良好的吸附保护膜,其厚度...     

Aggregation and pH responsive disassembly of a new acid-labile surfactant synthesized by thiol-acrylate Michael addition reaction

Nucleophilic thiol-acrylate Michael reaction between a hydrophobic thiol and hydrophilic acrylate derivative generated a nonionic surfactant with acid-labile β-thiopropionate linker. Micellization of the surfactant, its ability to encapsulate hydrophobic dye, acid-induced disruption of the aggregate and pH-selective dye release profile have been revealed in this report. The micellar aggregates were found to be stable under neutral conditions, but they could be disrupted in acidic pH (5.3), and thus the encapsulated hydrophobic dye molecules could be selectively released. Appropriate control experiments revealed that the sulfur atom in the β-position is essential for acidic hydrolysis of the ester functionality of the surfactant.     

Spectrometric study on the interaction of dodecyltrimethylammonium bromide with curcumin

The interaction between dodecyltrimethylammonium bromide (DTAB) and curcumin has been studied in pH 5.0 sodium phosphate buffer using absorption and fluorescence measurements. With increasing DTAB concentration (C(DTAB)) from 0 to 20 mM, the absorption peak of curcumin at 430 nm, corresponding to the conjugated structure of curcumin, first weakens gradually into a shoulder but increases back into one peak with much higher absorption intensity. On the contrary, as C(DTAB) increases, the initial small absorption shoulder of curcumin at 355 nm, corresponding to the feruloyl unit of curcumin, first increases gradually into a clear peak but decreases back into one shoulder until almost disappeared finally. By remaining at nearly the same wavelength, the fluorescence of curcumin first decreases at C(DTAB) lower than 5 mM and then increases gradually up to C(DTAB) = 10 mM, which is followed by sharp increases of fluorescence intensity with marked blue-shifts at higher C(DTAB). The values of anisotropy and microviscosity of curcumin obtained from the fluorescence polarization technique also showed pronounced changes at different surfactant concentrations. The interaction mechanisms of DTAB with curcumin have been presented at low, intermediate, and high surfactant concentrations, which is relating to interaction forces, surfactant aggregations, as well as structural alterations of curcumin.