48V/500A全数字交流调速控制器主电路及保护电路的设计

随着电力电子技术及大规模集成电路的发展,基于集成SPWM电路构成的变频调速系统以其结构简单、运行可靠、节能效果显著等突出优点以及先进的IGBT技术得到广泛应用。本文介绍48 V/500 A全数字交流调速控制器主电路及其保护电路的设计。     

Spectral resolution in conjunction with polar plots improves the accuracy and reliability of FLIM measurements and estimates of FRET efficiency

A spectrograph with continuous wavelength resolution has been integrated into a frequency‐domain fluorescence lifetime‐resolved imaging microscope (FLIM). The spectral information assists in the separation of multiple lifetime components, and helps resolve signal cross‐talking that can interfere with an accurate analysis of multiple lifetime processes. This extends the number of different dyes that can be measured simultaneously in a FLIM measurement. Spectrally resolved FLIM (spectral‐FLIM) also provides a means to measure more accurately the lifetime of a dim fluorescence component (as low as 2% of the total intensity) in the presence of another fluorescence component with a much higher intensity. A more reliable separation of the donor and acceptor fluorescence signals are possible for Förster resonance energy transfer (FRET) measurements; this allows more accurate determinations of both donor and acceptor lifetimes. By combining the polar plot analysis with spectral‐FLIM data, the spectral dispersion of the acceptor signal can be used to derive the donor lifetime – and thereby the FRET efficiency – without iterative fitting. The lifetime relation between the donor and acceptor, in conjunction with spectral dispersion, is also used to separate the FRET pair signals from the donor alone signal. This method can be applied further to quantify the signals from separate FRET pairs, and provide information on the dynamics of the FRET pair between different states.     

脉冲调频法测距在机载PD雷达中的应用研究

文中对机载脉冲多普勒雷达在HPRF（高脉冲重复频率）状态下,使用PRF转换法和线性调频测距的优缺点进行了比较分析,提出了采用二者综合运用的测距方法。结果表明,该方法能够在HPR．F工作模式下完成远距离目标速度测量的同时,获得精度较高的距离测量值。     

Performance of a gradient‐based shift estimator in a spatially sparse data environment: tracking the sub‐pixel motion of fluorescent particles

Through a series of numerical simulations, we investigate the suitability of a relatively new gradient‐based particle‐tracking algorithm for efficiently quantifying sub‐pixel shifts of fluorescently labelled cells or particles from a sequence of video microscopy images. The algorithm excels at estimating sub‐0.5 pixel per frame shifts in both data‐dense (e.g. laser speckle imaging) and data‐sparse (e.g. fluorescence imaging) applications. No upsampling (i.e. interpolation) is required to achieve the sub‐pixel shift resolution, and thus the approach avoids the complexity and potential errors associated with the interpolation process. An efficient matlab sub‐routine is provided for implementing the algorithm.     

Direct modulation of the effective sensitivity of a CCD detector: a new approach to time-resolved fluorescence imaging

In this paper a novel approach to frequency‐domain fluorescence lifetime imaging (FLIM) is described. In a CCD camera a single pixel is defined by a charge pattern on a group of electrodes. By modulation of the pattern of voltages defining the pixel structure it is possible to modulate the sensitivity of the CCD at radio frequency. The modulation enhances the noise performance of the CCD, in contrast to the deterioration in performance seen when an intensifier stage is similarly modulated. The new technology has potential applications to a wide range of assays as well as in conventional FLIM applications. Unlike intensifier‐based systems, the directly modulated CCD is physically small, inexpensive, robust and offers superior resolution and noise performance.     

Using cross‐correlation for automated stitching of two‐dimensional multi‐tile electron backscatter diffraction data

A method for automatically aligning consecutive data sets of large, two‐dimensional multi‐tile electron backscatter diffraction (EBSD) scans with high accuracy was developed. The method involved first locating grain and phase boundaries within search regions containing overlapping data in adjacent scan tiles, and subsequently using cross‐correlation algorithms to determine the relative position of the individual scan tiles which maximizes the fraction of overlapping boundaries. Savitzky‐Golay filtering in two dimensions was used to estimate the background, which was then subtracted from the cross‐correlation to enhance the peak signal in samples with a high density of interfaces. The technique was demonstrated on data sets with a range of interface densities. The equations were implemented as enhancements to a recently published open source code for stitching of multi‐tile EBSD data sets.     

用于调频式电感传感器的高稳定性LC振荡电路

提出以具有零温度系数的场效应晶体管代替普通晶体管作为LC振荡器的有源器件。理论和实验证明，该振荡电路具有更高的频率稳定度。     

Experiments and quantitative analysis of frequency division multiplexing confocal fluorescence microscopy with UV excitation

In this paper, we experimentally demonstrated a two-channel frequency division multiplexing confocal fluorescence microscopy system using a UV laser as the excitation source. In our two-channel frequency division multiplexing confocal fluorescence system, the incoming laser beam was divided into two beams and each beam was modulated with an individual carrier frequency. These two laser beams were then spatially combined with a small angle and focused into two diffraction-limited spots on the targeted cell (rat neural cell) surface to generate fluorescent signal. As a result, the fluorescent signals from two spots of the rat neural cell surface can be demodulated and distinguished during data processing. Furthermore, a quantitative analysis on the cross-talk among different frequencies was provided as well. The experimental results confirm that the two-channel frequency division multiplexing confocal fluorescence technology can not only maintain the high spatial resolution, but also realize the multiple points detection simultaneously with high temporal resolution (within millisecond level range), which benefits the dynamic studies of living biological cells.     

浅剖仪垂直探测分辨力分析

文章推导了PCW浅剖仪和Chirp信号浅剖仪垂直地层分辨力的公式，对影响浅剖仪垂直地层分辨力的各个因素给出了详细分析。比较了两种典型浅剖仪垂直地层分辨力指标。     

基于DSP的直流伺服电机的双闭环控制系统

作为数字阀的电一转换器,电机的频率响应对数字阀的性能有非常直接的影响。为提高数字阀的动态响应,设计了直流伺服电机双闭环系统。该系统采用TMS320LF2812为控制核心,在脉宽调制（PWM）方法的基础上,加入了超前补偿网络提高电流环的带宽;采用PI控制算法实现了电机转子的精确定位。简述了实现该控制系统的硬件设计方案和软件控制策略。实验结果表明,该系统能够实现直流伺服电机的电流和位置控制,显著提高了电流环的频率响应。     

空间调制型偏振成像的滤波器带宽优化方法研究

针对空间调制型全偏振成像系统在不同目标场景下成像效果不稳定的问题,使其在多目标场景均能保持最佳性能,提出了一种基于仿真干涉水印条纹的滤波器带宽优化计算方法,实现了对系统成像透镜的选型理论指导。 通过在强度图像上叠加不同稀疏程度仿真干涉水印条纹的二维正弦函数得到仿真干涉图像,应用快速傅里叶变换和频域低通滤波算法对仿真干涉图解调得到全偏振图像,再对与强度图像结构相似度最高的偏振图像进行求解。 提出了基于改进粒子群优化算法的最优滤波器带宽计算方法,通过引入疫苗提取选择策略和模拟退火机制实现了最优滤波器带宽的自适应选取,再结合不同目标场景下选定的图像分辨率、入射光波长及 Savart 偏光镜单束光偏移量等系统参数,计算得到成像透镜最优焦距,从而完成理论选型。 实验部分对比分析了基于最优滤波器带宽选型与传统的自行经验选型的空间调制型全偏振成像系统稳定性,实验结果表明,基于最优滤波器带宽搭建的空间调制型全偏振成像系统性能较好,所提出的基于最优滤波器带宽选型相比于自行经验选型的频谱图反演面积增大 4. 16 倍、图像结构相似度提高了 63% ,显著提高了系统的偏振成像质量。     

相关信道中光多输入多输出系统的误码率

多输入多输出(MIMO)技术可以在不额外增加频谱资源和发射功率的条件下成倍提高通信系统的信道容量,但子信道间存在的空间相关性会影响光MIMO无线通信系统(OWC)的性能。本文研究了对数衰落信道中空间相关性对光MIMO系统误码率的影响。针对脉冲位置调制(PPM)方式,采用指数相关模型推导出了光MIMO通信系统在不同相关机制下的对数振幅衰落系数矩阵和最大似然检测准则。然后,采用Wilkinson近似方法推导出了该条件下光MIMO系统误码率的上界。最后,利用仿真实验进一步分析了空间相关性对OWC MIMO系统误码率的影响。结果表明:空间相关性的存在使得OWC MIMO系统的性能恶化,且随着收发天线数量的增加,空间相关性会导致系统误码率恶化加剧。因此在实际工程应用中要合理放置天线,尽量减小天线之间的相关性,以便更好地发挥MIMO系统的优势。     

Spectra and lifetimes of fluorescence resonance energy transfer fluorophores under two-photon excitation

We show two-photon spectra and lifetimes acquired using conventional confocal microscopes equipped with an ultra-short pulsed laser and a time-gated intensified charge coupled device. We report on the two-photon spectra and lifetimes of Alexa350, enhanced green fluorescent protein (EGFP), EGFP-CD46, and Cy3 labelled antibodies. Cellular and extracellular EGFP two-photon spectra and lifetimes are compared.     

TMS320LF2407在电机变频控制中的应用

介绍了电机变频控制原理,采用LF2407作为系统控制的核心部件,辅助以智能功率驱动模块和其他外部器件,设计出了一种通用变频器。讨论了系统的硬件设计,给出了硬件的设计方案。软件采用汇编语言和C语言相结合的方式,实现了正弦脉宽调制波形及系统各部分的集成。该系统具有一定的实际应用价值,可用于多种工业控制场合。     

步进电机步距角细分单片机控制系统设计与研究

对步进电机步懈细分单片机控制系统进行了设计研究,并且对软件程度进行了周试与试验分析。由于步进电机具有快速启停、精确步进、直接接收数字量等特点,所以在数控系统中得到广泛与试验分析。由于步进电机具有快速启停、精确步进、直接接收数字量等特点,所以在数摈系统中得广泛应用。但是由于步进电机存在步距角罗大及低速振动等问题,限制了它在高精度场合下的应用。为解决此问题,有必要进行步距角细分。本文采单片机控制系统实