PPM-PAM联合调制UWB系统介绍及性能分析

UWB(Ultra-Wide Band)作为一种具有强大商业价值和发展前景的通信传输技术,业界对于超宽带发射与接收系统的研究也相当重视.文中提出了一种新的UWB混合调制方式,在信道条件较好的情况下可以成倍提高信息的传输速率.该方法将传统的幅度调制与跳时调制相结合,对传输信号进行2次调制,以携带更多的信息.     

S波段800kW同轴磁控管的研制

对S波段同轴磁控管的谐振系统、同轴谐振腔、阻抗变换器的设计进行了分析,重点论述结合国内材料及工艺水平所做的一系列工艺改进,通过这些改进,使得该管研制能顺利完成。     

GMSK中频数字化非相干接收机的设计与实现

针对突发模式下的GMSK信号,设计并实现了一种非相干数字化接收机,并且提出了一种更容易硬件实现而且频谱更好的GMSK信号产生方式。该接收机为了降低系统的复杂度,接收机采用2bit差分的方式按样点先进行信号解调,然后利用提出的基于引导码的位定时算法,在8个符号之内实现了位定时的快速捕获。最后在FPGA上的实现证明了接收机的可行性和优越性。     

调制信号的解调算法与基于LABVIEW的实现

介绍了调幅、调频的解调算法,对比了相干解调和非相干解调算法,并在相干解调算法的基础上,提出了正交解调算法和正切解调算法。利用LabVIEW数据流图的编程方式,编程得到二次正交解调算法,实现复合调制信号的数字化解调。通过仿真与实验结果可以得知,采用二次正交解调算法对复合调制信号进行数字解调能够得到较好的解调效果。     

脑fMRI特征重建的分层快速聚类方法

在对大脑fMRI感兴趣区域的分析中,利用特征选择所得到的筛选属性进行特征重建问题上,提出了分层快速聚类的分析方法,同已有K-均值聚类方法相比,在聚类有效性得到提高的前提下,总体降低了聚类的时间代价,并为后续的回归分析处理提供了精确保证。     

Silica-coated nanocrystalline TiO2 with improved thermal stability

Deposition of a SiO₂ coating on anatase TiO₂ nanocrystals is shown to improve their thermal stability. As low as 0.5% Si was shown to preserve the small anatase crystallite size after calcination at 600?°C. Such treatment led to considerable sintering of TiO₂ nanocrystals without the silica with the average particle size growth from 9 to 50?nm, surface area decrease from 135 to 22?m²/g and partial anatase conversion to rutile. The phase composition, crystallite size, and surface area of 5%Si-TiO₂ samples were largely preserved till the temperatures as high as 800?°C whereas the anatase phase was mostly stably even after calcination at 1000?°C. The phase transformation from anatase to rutile in xerogel TiO₂ and TiO₂@SiO₂ samples apparently did not occur until the crystallites grew larger than the critical size about 50?nm. Electron-acceptor sites capable of ionizing perylene to its radical cations were observed on all samples with anatase crystalline structure. So, the silica shell deposition improves the TiO₂ thermal stability without limiting access to the surface active sites.     

Isomer Identification of Monohydroxylated Polycyclic Aromatic Hydrocarbon Metabolites by Gas Chromatography/Fourier Transform Infrared Spectroscopy and Carbon-13 Nuclear Magnetic Resonance Spectroscopy

The foundation for a systematic approach utilizing spectral/structural correlations was established for unambiguous identification of monohydroxylated polyaromatic hydrocarbon metabolite (PAHm) isomers. Using elements of a theoretical/empirical valence-bond model developed earlier in our laboratory for isomer identification of chlorinated dibenzo- p -dioxin isomers, both gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR) and carbon-13 nuclear magnetic resonance ( 13 C NMR) spectroscopy were employed for PAHm isomer identification. Results indicate that PAHm isomers also can be systematically identified by these techniques. However, many of the parameters leading to the success of the dioxin analysis (high symmetry of the parent dioxin molecule and laterally stabilized delocalization from chlorine substituents through ether linkage oxonium ions) are not generally present in the PAHm ring systems under investigation. The observed infrared parameters in PAH metabolites are C--O stretch, O--H stretching and bending vibrations, along with C=C skeletal stretching vibrations. In addition, 13 C NMR parameters such as chemical shift perturbations for carbons adjacent to functional groups have been observed.     

鱼雷电磁引信的水中目标高精度实时识别方法

鱼雷武器系统的主动电磁引信回波信号中蕴含着雷目交会过程重要特征信息。针对回波信号能量比较法受到直达场耦合成分和噪声影响的问题,提出了基于数字信号处理技术的目标特征提取算法。对接收天线的回波信号进行全相位二次补偿处理;采用短时傅里叶变换对目标回波信号进行包络解调;再利用改进的三次多项式最小二乘拟合方法,以抑制数据波动影响并提高计算效率;提出一种基于钟型脉冲的参数识别算法对回波包络极大值点进行估计。仿真和试验数据验证表明所提出方法具有一定的工程实用性。     

水下磁感应无线通信模块设计

为了解决海洋观测系统中传感器节点与主机之间的无缆信息传输问题,设计了一种基于磁场耦合的低功耗水下半双工无线通信模块。通过线圈之间的电磁感应进行信息传输,采用二进制频移键控(Binary Frequency Shift Keying,BFSK)调制方式对基带信号进行调制。选用超低功耗单片机MSP430F5338作为主控单元。通过内部定时器的输出模块产生调制载波,在外部中断中进行频率切换,实现信号调制;采用专用解调芯片XR2211实现信号解调。模块由通信总线上的信号唤醒,设计了一种通过软件检测载波信号的方法,降低误触发概率。实验结果表明,模块在水下间隔2米时,通信成功率达到100%。该模块实现方案简单,成本和功耗较低,满足海洋观测系统中的应用需求。     

Cation vacancies in perovskites doped with La and Gd

Abstract

Whereas doping CaTiO₃ or SrTiO₃ with ～0·05 formula units (f.u.) of trivalent rare earth ions substituted for Ca can yield majority positron annihilation lifetime τ₁ increases of up to 30% due to the presence of cation vacancies, similar doping of BaTiO₃ produces increases of only ～10%. The difference is attributed to hole trapping around cation vacancies in BaTiO₃. The absence of significant changes to τ₁ for La doped CaTiO₃ when oxidised samples are reduced by sintering in a hydrogenous atmosphere is attributed to the formation of oxygen vacancies that co-exist with the original cation vacancies. Solid state nuclear magnetic resonance showed that a significant fraction of the La ions in BaTiO₃ containing 0·04 f.u. of La were in cubic coordination, irrespective of the charge compensation scheme employed. Doping of sintered SrTiO₃ with La to produce up to 0·2 f.u. of Sr cation vacancies had no significant effect on Sr leaching in deionised water at 90°C.