基于PC机的断层图象序列3-D表面重建

由断层图象序列重建三维物体模型及其可见表面显示是目前国际上十分活跃的研究课题。本文对X射线CT图象序列重建三维对象模型,以及可见表面3-D显示进行了研究。提出一种给定分段点数的轮廓多边形近似方法,继而提出一种快速断面图象间轮廊插值方法。对重建出的人体肝脏体元阵列,用深度和梯度明暗显示方法进行显示,肝脏可见表面的3-D显示结果令人满意。全部软件都是在以PC/AT为主机,配以PC-VISION图象处理板的微机图象处理系统上,用C语言编程实现的。     

多芯片组件的热三维有限元模拟与分析

以ATMEL公司生产的MCM的内部结构、尺寸和材料为基础,在有限元分析软件ANSYS的环境下建立了该MCM的三维模型。对该MCM在典型工作模式下内部和封装表面温度场分布情况进行了模拟,并分析了该MCM工作时各部分散热比例情况和MCM各部分材料的热导率对内部温度的影响。MCM表面温度的模拟结果和用红外热像仪测得的结果基本一致,有限元模型和分析方法能够比较精确地反映MCM温度场分布。     

基于改进的2-D Otsu方法和YCgCr空间的肤色分割

为了弥补基于固定阈值的肤色分割方法存在的缺陷,在对多种彩色空间和肤色模型进行分析的基础上,提出采用改进的2-D Otsu方法和YCgCr彩色空间进行肤色分割。首先将光照补偿之后的肤色样本图像从RGB彩色空间转换到YCgCr彩色空间,并利用样本图像上的179221个肤色点建立2维高斯模型;进而将待分割的图像进行光照补偿并转换到YCgCr彩色空间,利用已经建立的高斯模型计算图像的肤色相似度,得到肤色相似度图像;最后,结合像素的空间邻域信息,使用改进的2-D Otsu方法对肤色相似度图像进行2值化处理。对这种方法进行了理论分析和实验验证。结果表明,该肤色分割算法有效地克服了使用固定阈值法进行图像分割时缺乏针对性和抗噪性的缺陷,该算法是可行的。     

三维建模对学习机械知识的能力的培养研究

三维建模即利用三维绘图软件,把给出的二维平面图绘制成三维空间立体模型,再进一步的话,可以将拟建好的三维模型生成二维平面图。这种操作,可以大大提高学生绘制二维平面图、阅读二维平面图和三维空间想象能力,了解机械结构及其作用。这对高职学生后续课程学习及以后工作打下良好基础。     

用最小二乘支持向量机的可见-近红外光谱测定蜂花粉贮存时间

为了探索一种快速有效的蜂花粉新鲜程度检测方法,利用可见近红外光谱技术结合最小二乘支持向量机（LSSVM）对蜂花粉的贮存时间进行了检测.选择常温环境中贮存时间为4~50天（共计47天）的茶花蜂花粉作为研究对象,将全光谱数据作为输入变量建立了LSSVM模型.结果显示,该LSSVM模型预测效果较好,预测相关系数rp达到了0.996,预测标准误差（SEP）和预测均方根误差（RMSEP）的值分别为1.310和1.308,优于偏最小二乘法（PLS）和主成分回归（PCR）的预测结果,说明基于LSSVM的可见近红外光谱技术能够很好地对花粉贮存时间进行检测.同时对不同贮存时间段花粉的预测效果进行了比较,发现该LSSVM模型适用于对第11~50天范围的贮存时间进行检测.     

超级电容器的阻抗特性及其复空间建模

以阻抗平面图分析法研究超级电容器的阻抗特性,揭示了该特性的典型区域:45°斜率的Warburg阻抗线和接近于垂直斜率的低频阻抗线,以此建立了四参数(Rs,R,C,p)表示的超级电容器复空间模型。试验结果表明,该模型预测的充电过程端电压变化历程与试验数据有着良好的一致性和适应性。     

Okumura-Hata模型在城市环境LoRa网络中的应用

对城市建设的LoRa网络的道路覆盖性能进行拉远测试,并将实测结果与Okumura-Hata模型进行比较,发现该模型不能较为准确地反应城市环境下LoRa网络的路径损耗。考虑到当今城市发展的速度和规模已远超传统无线电传播模型建立时的预期,所以在Okumura-Hata模型的基础上,基于实测数据对该模型利用最小二乘法进行校正,然后使用RMSE(标准误差)法计算校正后的模型预测值与实测数据的标准误差,结果在允许的误差范围之内。最后在实验室搭建一个LoRa网关,对该网关的拉远测试结果与修正后的路径损耗模型的预测值相符。     

海上编队雷达网空间优化部署方法

在分析海上编队雷达网作战效能的基础上,建立了海上编队雷达网空间优化部署模型.海上编队雷达网在有/无威胁条件下,经过空间优化部署模型的解算,编队成员机动到较优阵位,使编队雷达网实现无缝连接且无盲区,从而获得较好的作战效能.文中在该条件下进行了仿真,并对仿真结果进行分析对比,验证了所建立模型的可行性和正确性.该模型对于未来海战场复杂电磁环境下对更好地发挥编队雷达网探测和预警能力具有重要意义.     

DVD伺服控制芯片的系统级仿真环境的构造

文章介绍了DVD伺服控制芯片的系统级仿真环境的构造，包括仿真模型的建立和采用的仿真管理方法。仿真结果显示，该系统级仿真环境能准确地模拟各功能模块之间的交互，在该仿真环境下能快速地对RTL源代码进行调试。     

三维网格模型的预测压缩算法研究

通过遍历顶点的位置信息和3-D网格中的角度信息,提出了一种顶点邻域预测和角度预测相结合的3-D网格模型顶点位置预测压缩算法。采用Hausdorff距离测量预测误差,试验的结果表明,提出的算法在不同的测试模型上都优于MPEG-4标准中的三维网格模型编码(3-DMC)算法,较好地减少了3-D网格顶点预测的几何失真。     

An effective focusing approach for azimuth invariant bistatic SAR processing

This paper proposes a processing method to extend monostatic imaging algorithms for the azimuth invariant bistatic SAR (BISAR) data where the transmitter and the receiver move on parallel tracks with equal velocities. The bistatic range history is approached by a polynomial of the azimuth time. Based on this model, an analytic 2-D signal spectrum derived by the method of series reversion is utilized and a simple one-to-one mapping between the transmitter and the receiver closest ranges is established. In this way, efficient monostatic imaging algorithms which operate in the 2-D frequency domain or the range-Doppler domain are easily modified to handle the BISAR data. In this paper, a chirp scaling algorithm for the BISAR is developed as an application of the new method. By implementing two key operations, range cell migration correction by a chirp scaling, and azimuth compression by a curve fitting technique, this algorithm is able to process the azimuth invariant BISAR data. Simulation results are presented to demonstrate the validity and the efficiency of the proposed algorithm.     

机载平行等速双基SAR的极坐标格式成像算法

平行等速双基SAR是指收发平台速度大小和方向均相同的双基SAR系统,该构型具有广阔的应用前景。在此将传统适用于单基地SAR成像的极坐标格式算法（PFA）加以改进,使之适用于平行等速双基SAR成像处理。由于收发异置,回波信号在接收平面和发射平面的斜距几何关系比较复杂。为了便于后续的二维插值操作,用一个新的几何模型来描述收发平面上斜距的关系。该算法具有传统PFA算法的操作简单,易于实现的特点。最后通过仿真数据的成像处理对该方法进行了验证。     

孔径匹配对中继镜系统上行传输影响的模拟与分析

利用激光大气传输四维程序,建立了双望远镜中继镜系统上行传输模型,研究了孔径匹配对中继镜系统上行传输的影响。选择去除畸变相位后的接收光场的远场峰值功率密度作为中继镜系统上行传输的性能指标,通过光束在真空中传输的计算,得到了接收口径一定时不同发射口径对应的最优发射焦距,并对不同发射功率激光在大气中上行传输的情况进行了模拟计算。结果表明,当接收孔径一定时,随着发射孔径的增大,最优发射焦距减小;增大发射孔径,可以增大临界发射功率;当发射功率较小时,在一定发射口径范围内,发射口径的变化对中继镜系统上行传输的性能指标影响不大,当发射功率较大时,增大发射口径可以有效提高中继镜系统上行传输的性能指标。     

Three-Dimensional Urban EM Wave Propagation Model for Radio Network Planning and Optimization Over Large Areas

A new 3-D urban electromagnetic wave propagation model is presented. It provides fast 3-D deterministic predictions in urban radio configurations and over large areas. The various techniques to make it suitable to the network planning and optimization of large wireless networks are described. The resulting radio propagation maps exhibit seamless coverage between the various environments (dense urban, urban, and suburban). The model efficiently addresses all types of outdoor transmitter configurations (macrocells, minicells, microcells, and picocells) and all types of receiver locations (at ground level, over the rooftop, and at high building floors). It predicts the field strength as well as the dominant specular contributions of the impulse responses to build ray spectra (including delays and angles). Thus, the model may also be used to estimate the performances of new radio systems [diversity and multiple-input–multiple-output (MIMO)]. The narrowband power prediction of the model is evaluated by comparison with microcell measurements. The evaluation stresses the advantage of 3-D modeling compared with the vertical-plane approach or 2-D ray tracing. Finally, the ability of the model to simulate radio wideband characteristics in a complex environment is demonstrated by comparing delay-spread estimates to measurements collected from a high-macrocell transmitter in a hilly city and to arrival angles collected in a suburban macrocell area.      

A Two-Dimensional Spectrum Model for General Bistatic SAR

This paper derives a 2-D spectrum model for general bistatic synthetic aperture radar (SAR). By introducing some new parameters such as equivalent monostatic parameters, bistatic factor, and weighted-equivalent range, the 2-D spectrum of general bistatic SAR can be expressed in the form of monostatic SAR even when the transmitter and receiver move along unparallel trajectories with different velocities. The result formulates bistatic SAR into an equivalent monostatic SAR model and would be useful for developing efficient bistatic SAR algorithms in frequency-domain or hybrid-domain processing. Simulation results are given to validate the performance of the model. For special bistatic SAR configurations, the model can be simplified. Compared to other similar models, the proposed model is clearer and much more concise.      

Complex Envelope Second-Order Statistics in High-Altitude Platforms Communication Channels

High-altitude platforms are one of the most promising alternative infrastructures for realizing next generation high data rate wireless networks. This paper presents a three-dimensional (3-D) scattering model for land mobile stratospheric multipath-fading channel with its complex faded envelope. From the scattering model and the complex envelope second-order statistics are derived for a 3-D non-isotropic scattering environment. When we discuss on the second-order statistics we refer to the level crossing rate and the average fade duration, whichare two main parameters in describing the fading severity over time and are very important in assess system characteristics such as hand off, velocities of the transmitter and receiver and fading rate. Numerical calculations have been carried out to demonstrate theoretical derivations and the utility of the proposed model.     

Markov-jump-system-based secure chaotic communication

In this paper, a new Markov-jump-system (MJS)-based secure chaotic communication technique is proposed. An MJS evolves by switching from one state evolution model to another according to a finite state Markov chain. The transmitter in the proposed communication system is an MJS consisting of multiple transmission maps, that is, the transmitter switches from one chaotic map to another during the transmission of data. This switching feature makes it difficult to identify and follow the transmission without knowing the transmitter parameters, i.e., to eavesdrop, thereby increasing the security offered by the inherently secure chaotic communication system. If the chaotic maps used at the transmitter, and the corresponding Markov transition probability matrix of the MJS are known to the (authorized) receiver, then a multiple model estimator can be used to track the MJS transmitter. In this paper, the use of the interacting multiple model (IMM) estimator is proposed as part of the receiver to follow the switching transmitter. The effectiveness of the IMM-estimator-based receiver to follow the switching transmitter is evaluated by means of simulations. A new modulation technique that uses the MJS transmitter is also introduced. Further, it is shown that the same receiver framework, when used as a receiver for chaotic parameter modulation, provides significant performance improvement in terms of bit-error rate compared to a receiver that uses extended Kalman filter. In addition, the seemingly more complex IMM-estimator-based receiver is shown to significantly reduce the computational complexity per transmitted bit, thus resulting in increased data rate.     

Theoretical Performance Analysis of Sliding Window Flow Control

A transmitter breaks a message up into packets and transmits the packets to a receiver over a single virtual circuit within a local area network. The receiver has a finite amount of storage capacity for buffering messages. A sliding window protocol turns the transmitter on and off to ensure there is always storage room in the receiver for packets. Mean throughput rate and delay statistics are studied as a function of model parameters.     

基于角度和多普勒频率的外辐射源定位系统的接收器最优航迹分析

该文提出了一种利用角度和多普勒频率的一发一收外辐射源定位体制,针对运动目标,给出了接收站的最优航迹规划。该文采用定位的位置误差(Geometrical Dilution Of Precision, GDOP)作为优化对象,具体分析2维目标定位的优化问题,通过一边估计目标一边优化接收站运动的方法,使用无迹卡尔曼滤波 (Unscented Kalman Filter, UKF)估计目标的位置和速度,以达到在定位的各个时刻能够得到最优的定位精度。仿真实验验证了该方法的有效性。      

Clock synchronization using a linear process model

In this paper, we present a clock synchronization scheme based on a simple linear process model which describes the behaviors of clocks at a transmitter and a receiver. In the clock synchronization scheme, a transmitter sends explicit time indications or timestamps to a receiver, which uses them to synchronize its local clock to that of the transmitter. Here, it is assumed that there is no common network clock available to the transmitter and the receiver and, instead, the receiver relies on locking its clock to the arrival of the timestamps sent by the transmitter. The clock synchronization algorithm used by the receiver is based on a weighted least‐squares criterion. Using this algorithm, the receiver observes and processes several consecutive clock samples (timestamps) to generate accurate timing signals. This algorithm is very efficient computationally, and requires the storage of only a small number of clock samples in order to generate accurate timing signals. Copyright © 2006 John Wiley & Sons, Ltd.