Microwave tomography for breast cancer detection on Cell broadband engine processors

Microwave tomography (MT) is a safe screening modality that can be used for breast cancer detection. The technique uses the dielectric property contrasts between different breast tissues at microwave frequencies to determine the existence of abnormalities. Our proposed MT approach is an iterative process that involves two algorithms: Finite-Difference Time-Domain (FDTD) and Genetic Algorithm (GA). It is a compute intensive problem: (i) the number of iterations can be quite large to detect small tumors; (ii) many fine-grained computations and discretizations of the object under screening are required for accuracy. In our earlier work, we developed a parallel algorithm for microwave tomography on CPU-based homogeneous, multi-core, distributed memory machines. The performance improvement was limited due to communication and synchronization latencies inherent in the algorithm. In this paper, we exploit the parallelism of microwave tomography on the Cell BE processor. Since FDTD is a numerical technique with regular memory accesses, intensive floating point operations and SIMD type operations, the algorithm can be efficiently mapped on the Cell processor achieving significant performance. The initial implementation of FDTD on Cell BE with 8 SPEs is 2.9 times faster than an eight node shared memory machine and 1.45 times faster than an eight node distributed memory machine. In this work, we modify the FDTD algorithm by overlapping computations with communications during asynchronous DMA transfers. The modified algorithm also orchestrates the computations to fully use data between DMA transfers to increase the computation-to-communication ratio. We see 54% improvement on 8 SPEs (27.9% on 1 SPE) for the modified FDTD in comparison to our original FDTD algorithm on Cell BE. We further reduce the synchronization latency between GA and FDTD by using mechanisms such as double buffering. We also propose a performance prediction model based on DMA transfers, number of instructions and operations, the processor frequency and DMA bandwidth. We show that the execution time from our prediction model is comparable (within 0.5 s difference) with the execution time of the experimental results on one SPE.     

开口谐振环结构负折射率材料对电磁波偏振特性的影响研究

电磁波在经过负折射率材料以后,偏振状态会有所改变.对开口谐振环电磁响应特性了解的基础上,采用时域有限积分方法,分别研究了方形、六边形和圆形开口谐振环负折射率材料在不同频率处以及斜入射时对电磁波偏振特性的影响.仿真结果表明,不同的结构、频率和入射角度,电磁波偏振翻转的程度有所不同.研究结果可为电磁波偏振状态的调控提供一定的理论依据和借鉴.     

线性最优励磁控制器的设计与仿真

在线性控制理论的基础上设计同步发电机的最优励磁控制器,基于Matlab编程的时域仿真验证,表明:设计的系统有良好的动态响应速度和阻尼特性,具备良好的静态和暂态稳定性.通过对最优励磁控制系统暂态稳定性的分析,验证增大强励倍数对提高电力系统暂态稳定性起到的积极作用;对于单机无穷大系统短路点距线路首端越远,该线路的极限切除时间越大.     

Adjustable transmission properties through ring-shaped nanotube arrays using finite-difference time-domain method

Metallic ring-shaped nanotube arrays are proposed and its optical transmission properties are studied by using finite-difference time-domain （FDTD） method. Compared with the transmission spectra of conventional circular nanotube arrays, two photonic band gaps are emerged in the transmission spectra offing-shaped nanotube arrays, the two band gaps and transmission spectra are adjusted by the length, inner radius, intertube spacing and the dielectric constants of the core and embedding medium, and magnitude modification, redshift and blueshift of the resonance modes are observed. A metallic ring-shaped nanotube arrays for subwavelength band-stop filter in the range of visible light can be achieved. To understand its physical origin, field-interference mechanism was suggested by the field distributions. The proposed nanostructures and results may have great potential applications in subwavelength near-field optics.     

THz-TDS signal analysis and substance identification via the conformal split

A terahertz time-domain spectroscopy(THz-TDS)imaging system can obtain high-dimensional signals with substance fingerprint information.By introducing geometric algebra,a novel signal analysis approach to THz-TDS signals is developed based on an optical physical mechanism.Using this approach,signals are represented with vectors in the high-dimensional real vector space.Geometric distribution properties and algebraic relationships of THz-TDS signals are deduced.It is proved that every complex refractive index of substances relates to a unique 2-blade,the vectors corresponding to the samples of the same substance are collinear and belong to the intrinsic 2-blade of the substance.When decomposed through the conformal split with respect to a 2-blade,THz-TDS signals of high dimensionality can be related to vectors in a 2-dimensional subspace.Based on the conformal split properties we deduced,two criteria for substance identification on the basis of THz-TDS signals are proposed.Accordingly,a novel substance identification method via the conformal split is presented.In the method,the 2-blade related to each "known" substance is calculated with two vectors corresponding to THz-TDS signals measured from samples of the substance but with dierent thicknesses.Using the conformal split with respect to those 2-blades,an identified vector corresponding to a THz-TDS signal is linearly related to the vector in a 2-dimensional subspace.The substance of a sample can be identified using criteria on the projected vectors in the subspaces.This method can contribute to accurate classification and identification.Finally,two experiments are presented that show the feasibility and accuracy of this method.     

基于时域Neal-Smith准则的人机控制系统设计多目标优化研究

为了获得驾驶员和飞机良好的匹配特性,使用基于人机闭环参考模型的方法将飞行品质的要求引入优化算法,进行飞行控制系统设计。首先使用CAP准则建立飞机等效系统模型。然后,基于时域Neal-Smith准则,通过多目标优化算法一次性得到在不同任务条件下的最优驾驶员模型。根据需要选择相应的驾驶员模型,并与飞机等效系统模型组成人机闭环参考模型,进行飞行控制设计多目标优化。仿真结果显示,文中的算法不仅可以整定控制器参数,根据任务需求选取最优驾驶员模型,还可以利用优化结果进行PIO易感性的分析。     

基于分布式光纤技术的煤矿巷道顶板监测系统

当前巷道顶板变形监测方式为基于井下工业环网的在线实时监测,采用电子式和光纤光栅式的位移传感器并以无线方式连接,存在有较多监测盲点、误差较大、依靠连续供电等问题。针对上述问题,设计了一种基于分布式光纤技术的煤矿巷道顶板监测系统。该系统以布里渊光时域反射计(BOTDR)作为数据采集和分析的核心监测工具,采用5 mm钢绞线光纤作为感测光纤,以锚杆、锚索为固定点布设光缆,通过顶板光纤的应变变化来监测顶板变形状况,实现了对煤矿巷道顶板的实时在线分布式监测。现场应用结果表明,光纤应变变化能够实时准确地反映顶板变形情况,基于光纤应变的顶板监测结果与顶板离层仪监测结果、十字法观测结果一致。用光纤应变表征顶板变形程度消除了人为因素和断电等影响,保证了监测结果的客观性,这种长距离、耐腐蚀、抗干扰、无需供电的分布式光纤应变监测方式为煤矿提供了一种全新的巷道监测手段。     

新型光子晶体四通道滤波器研究与设计

基于光子晶体环形腔缺陷与线缺陷波导之间的共 振耦合原理,设计了一种由新型环形腔和主波导组 成的四通道二维三角晶格光子晶体滤波器。运用平面波展开法和时域有限差分法分析了光波 在整合结构中 的传输特性,并进一步讨论环形滤波器内的内部介质柱半径大小对滤波器传输特性的影响。 结果表明:新 改进环形的滤波器传输效率达到80%左右。通过实验,选取内部 介质 柱半径在0.44R~0.53R时,其传输效 率达到85%以上,并进一步选取内部介质柱半径为0.46R,0.47R,0.52R 制作四通道滤波器,实现 了波长为1646.9nm,1647.7 nm, 1648.5 nm,1652.3 nm四信道波分复用,其传输效率均在92%以上,半峰宽 高小于6.0 nm。由于滤波器传输效率高,窄带特性良好,所以适用于 光器件集成。     

辛时域多分辨率算法在波导结构仿真中的应用

文中基于Daubechies紧支撑尺度函数的辛时域多分辨率(symplectic multiresolution time-domain, S-MRTD)算法,在时间方向上采用优化的3级3阶的辛算子进行离散,以减少时间步的迭代次数,在空间方向上采用小波尺度函数展开算法进行离散. 给出了S-MRTD算法的三维迭代公式,并将其应用到波导结构相关特征参数的数值计算和分析中. 数值计算结果表明,与传统的MRTD算法相比,S-MRTD算法在使用粗网格和较高的稳定性常数时,仍能得到精确计算结果,且具有内存使用少、计算效率高的特点.     

基于异构加速的Φ-OTDR实时信号处理系统

针对相位敏感光时域反射计(Φ-OTDR)信号处理复杂、计算量大、实时性要求高的特点,提出一种基于现场可编程门阵列(FPGA)异构加速计算技术的Φ-OTDR实时信号处理系统。对外差探测式Φ-OTDR信号处理流程进行分析与分解,提出基于FPGA的滑动窗数据帧分割、多通道并行快速傅里叶变换(FFT)计算、频域滤波、短时能量求和等一系列加速计算方法。该系统最终实现在40 km光纤传感距离、2 kHz重复频率与1 m采样间隔下的长时间、实时扰动信号解调与显示,并且具有80%的帧重叠率。该FPGA系统作为异构加速器,能够减轻计算机数据处理压力,保证传感系统高重复频率下的运算实时性,为系统可靠性和稳定性提供了有效保障。