一种基于麦克风阵列的声源定位算法研究

麦克风阵列声源定位广泛应用于视音频会议系统及枪声定位系统等领域。提出了一种基于最小熵值（ME）的麦克风阵列声源定位新方法,其特点在于利用最小熵值方法对麦克风阵列进行时延估计,并与离散网格方法相结合,对声源进行空间搜索。实验结果表明,在同等混响或噪声条件下,该方法定位优于广义互相关-相位变换方法（GCC-PHAT）。     

A model order selection criterion with applications to cardio-respiratory-renal systems

We introduce a model order selection criterion called signal prediction error (SPE) for the identification of a linear regression model, which can be an adequate representation of a resting physiologic system. SPE is an estimate of the prediction error variance due only to model estimation error and not unobserved noise, which distinguishes it from the widely used final prediction error (FPE). We then present a theoretical analysis of SPE, which predicts that its ability to select correctly the model order is more dependent on the signal-to-noise ratio (SNR) and less dependent on the number of data samples available for analysis. We next propose a heuristic procedure based on SPE (called SPE(D)) to improve its robustness to SNR levels. We then demonstrate, through simulated physiologic data at high SNR levels, that SPE will be equivalent to consistent model order selection criteria for long data records but will become superior to FPE and other model order selection criteria as the size of the data record decreases. The simulated data results also show that SPE(D) is indeed a significant improvement over SPE in terms of robustness to SNR. Finally, we demonstrate the applicability of SPE and SPE(D) to actual cardio-respiratory-renal data.     

DSSS/QPSK信号盲检测方法仿真

采用功率谱检测法,自相关检测法和高阶累计量检测法对低信噪比下DSSS/QPSK信号进行检测方法。计算机仿真表明,功率谱检测法在信噪比较低时失去了检测能力,而充分利用了伪随机码周期特性的自相关检测法和高阶累计量检测法的检测性能较优,高阶累计量法由于其更好的抑制噪声特性显示出更好的性能。同时,文中比较了DSSS/BPSK信号和DSSS/QPSK信号在相同检测方法下的性能差异。由于调制方式不同,相同的方法对DSSS/QPSK信号的检测性能略低于DSSS/BPSK信号。     

弹道目标平动补偿与微多普勒特征提取方法

针对传统逆合成孔径雷达(ISAR)成像中的平动补偿方法并不适用于弹道目标平动补偿的问题,该文提出了一种弹道目标平动补偿与微多普勒(m-D)特征提取方法。在分析有翼弹道目标未完成平动补偿时的m-D效应的基础上,首先采用形态学中的骨架提取方法抑制1维距离像旁瓣,再在快时间频率(距离)-慢时间平面上搜索分离各散射点的m-D特征曲线,然后对其进行经验模式分解(EMD)分解,利用分解结果中的趋势项分量完成目标回波的平动补偿,并通过分析EMD分解结果获得了目标的自旋频率、锥旋频率等特征信息。仿真实验验证了所提方法的有效性与鲁棒性。     

海面流场的三种雷达体制成像仿真

监测海面流场是微波遥感重要应用之一,它对民用和军用领域都有非常重要的意义。微波传感器主要包括早期的真实孔径雷达、高分辨率合成孔径雷达和新兴的双站合成孔径雷达。文中提出一种对海面弱流场和波浪进行真实孔径雷达/合成孔径雷达/双站合成孔径雷达成像的仿真方法。该方法根据给定的海面流场数据、海况条件和雷达参数,考虑倾斜、流体动力和速度聚束调制作用,并利用海面微波散射模型和雷达回波信号模型生成雷达仿真图像,得到的雷达图像可为后续的海洋目标检测等算法提供仿真数据源。     

Switching on Fluorescent Emission by Molecular Recognition and Aggregation Dissociation

A generic and effective approach to “switch on” and enhance the two‐photon fluorescence (TPF) emission of quenched TPF molecules, i.e., fluorene derivatives, is reported in terms of molecular recognition with a decoupling medium. Such a medium, in this case Bombyx mori silk, can recognize TPF molecules and inhibit the aggregation of the TPF molecules. The designed TPF molecules are 2,7‐bis[2‐(4‐nitrophenyl)ethenyl]‐9,9‐dibutylfluorene ( 4NF ) and 2,7‐bis[2‐(4‐nitrophenyl)ethenyl]‐9,9‐dioctylfluorene ( 8NF ), which exhibit suppressed TPF emission owing to molecular‐stacking‐led aggregation in the solid form. Due to the specific recognition between –NO₂ in the quenched fluorescent molecules and –NH groups in silk fibroin molecules, the aggregated molecules of 4NF / 8NF molecules are decoupled. This decoupling gives rise to a significant increase in TPF quantum yields. The mechanism is further confirmed by replacing the terminal group –NO₂ in 8NF with –CH₃ (in 2,7‐bis[2‐(4‐methylphenyl)ethenyl]‐9,9‐dioctylfluorene; 8MF ) to eliminate the possibility of molecular recognition. As predicted, in the case of 8MF the switching‐on effect is eliminated. Completely new TPF silk fibers can additionally be applied in real‐time 3D high‐resolution TPF scaffold bioimaging.     

Joint optimization of power allocation and relay location for regenerative relaying with multi‐antenna reception at destination

We consider joint power allocation (PA) and relay positioning in a dual‐hop regenerative relay system with multiple antennas equipped at the destination. With a fixed relay location, an adaptive PA strategy at the source and relay under a sum power constraint that minimizes the system outage probability is presented. With a fixed PA strategy, the optimal relay location is derived. We then propose to jointly optimize PA and relay location. It is shown that employing more destination antennas and/or choosing an appropriate relay location can significantly save the power needed at the relay. Numerical results are presented to demonstrate the performance of the proposed PA and relay positioning algorithms. Copyright © 2011 John Wiley & Sons, Ltd.     

A Novel Approach to BaTiO3-based X8R Ceramics by Calcium Borosilicate Glass Ceramic Doping

High-performance X8R dielectric materials could be sintered at 1150°C by doping calcium borosilicate (CBS) glass ceramic into the BaTiO₃-Nb₂O₅-ZnO system, with a dielectric constant greater than 1800 and a dielectric loss lower than 1.0%. The effects of CBS, Nb₂O₅, and ZnO on the dielectric properties were discussed in this article. The X8R specification was achieved with the content of CBS ≥ 4 wt.%, Nb₂O₅ ≥ 1.0 mol%, and ZnO ≤ 2.0 mol%. The sample doped with 4 wt.% CBS exhibited the highest density and lowest dielectric loss in our experiment. A reduction in grain size was observed in the specimens with 4 and 7 wt.% CBS as compared with CBS-free specimen, whereas the abnormal growth of rectangle-shaped grains took place in the 10 wt.% CBS-doped specimen. The Curie point progressively moved to higher temperatures with CBS content up to 7 wt.%. However, T _c of the sample decreased slightly in the case when 10 wt.% CBS was doped. X-ray diffraction (XRD) analysis indicated that the crystal structure of sintered ceramics changed from tetragonal to pseudocubic symmetry as increasing CBS content.     

舰船可视化指挥调度通信系统设想

本文结合当前舰船指挥调度通信系统的大趋势，设想了一个指挥调度系统可视化方案，组建了一个有线／无线混合的可视化指挥调度系统，说明了此系统的功能及关键技术，并在理论上阐述了方案的可行性。