Recent progress in exact and reduced-order modeling of light-scattering properties of complex structures

An emerging research area in biophotonics with potentially near-term clinical applications in early stage cancer detection involves the investigation of possible correlations of the elastic light scattering properties of tissues with alterations in their cellular composition and nanostructure. Until recently, exploring these correlations has been impeded by a lack of robust and accurate mathematical models of the light scattering properties of complex structures. In this paper, we review recent progress in this area. Topics include: 1) development of accurate reduced-order expressions for the total scattering cross section spectra of a wide range of nonspherical and inhomogeneous particles; 2) rigorous finite-difference time-domain modeling results showing how the backscattering of light can be sensitive to nanometer scale features embedded within micrometer-scale particles; and 3) development of accurate reduced-order expressions for the backscattering depolarization properties of a wide range of inhomogeneous particles. These advances provide an improved science base for cellular level biophotonics, and have promise to accelerate the development of novel corresponding clinical technologies.     

宽带扫频RCS自动测量系统

传统的微波暗室远场雷达散射截面积(RCS)测量方法采用点频测试。对低RCS目标,点频RCS测量系统精度差,信息量少。为克服这些缺点,文中运用宽带扫频测量RCS的原理和方法,构建基于该方法的自动测量系统,以得到较高的精度。该系统利用矢量网络分析仪所具有的时域功能,把目标的频率响应变换到时域中进行分析,再通过软件上的背景回波消除技术,进一步降低背景回波的干扰,最后得到目标的RCS。实验证明,该方法系统测量精度高、结果准确,值得深入研究和推广。     

LED单边侧入式导光板的网点设计

单边侧入式导光板可降低其设计成本和制作成本,为了获得均匀的表面照度,本文介绍了LED为光源的单边侧入式导光板散射网点设计方法。建立了相应模型,得到这种导光板散射网点的一种排布公式和计算方法,并用TracePro软件进行模拟仿真,验证了网点设计方法的正确性。模拟和实验结果表明通过这种网点设计方法可获得均匀度优于90%的表面照度分布。     

35MnB 合金淬硬层深度的超声无损测量

针对过渡层较大的感应淬火零件用超声法测量淬硬层深度时,极限硬度点难以准确定位的问题,开展35MnB合金淬硬件的淬硬层深度超声测量实验。用小波多分辨率分析(MRA)研究信号在不同分解尺度下的时频特征,分析信号在各频带的能量分布,并探求提取背散射信号的趋势特征计算淬硬层深度的方法。结果表明,背散射信号中的高频振动成分明显,分布无规律且能量较低;趋势特征项随信号振动幅值包络缓慢变化,能量占比高达96.73%,显著高于其他分解项,高尺度分解下的MRA过程实质上滤除了多数与淬硬层深度信息无关的杂波噪声项。基于趋势特征项的实测结果最大平均误差为0.123 mm,最大重复误差为6.24%,测量精度以及重复可靠性均显著高于常规超声测量模型,相比于金相法和显微硬度法具有更高效、无损等优势,在工程机械零件的实际测量中具有较好的应用前景。     

Optical coherence tomography for ophthalmic imaging: new techniquedelivers micron-scale resolution

The authors have developed a new technique for micron scale resolution cross-sectional imaging of ocular and other biological tissue, called optical coherence tomography (OCT). OCT is similar to B-scan ultrasonic imaging, except that image contrast relies on differences in optical rather than acoustic backscattering characteristics of tissue. In contrast to ultrasound and nonlinear optical gating techniques, low-coherence interferometry is used to resolve the position of reflective or optical backscattering sites within a sample. Two-dimensional tomographic images of a thin, optical slice of tissue may be obtained with 10 μm longitudinal and lateral resolution. Optical heterodyne detection and the application of noise-reduction techniques originally developed for optical communication achieve sensitivity to reflected light as small as 10^-10 of the incident optical power. OCT is non-contact, non-invasive, and has superior resolution to conventional clinical ultrasound. Unlike scanning laser ophthalmoscopy and scanning laser tomography, the optical sectioning capability of OCT is not limited by the pupil aperture and ocular aberrations. OCT may be implemented in a compact, low-cost, fiber-optic based interferometer that is easily coupled to existing ophthalmic instrumentation. Here, the authors demonstrate high-speed in vivo OCT imaging in both the anterior and posterior eye, and highlight the system's potential usefulness for the early diagnosis and quantitative monitoring of a variety of ocular diseases and treatments     

Determination of epithelial tissue scattering coefficient using confocal microscopy

Most models of light propagation through tissue assume the scattering properties of the various tissue layers are the same. The authors present evidence that the scattering coefficient of normal cervical epithelium is significantly lower than values previously reported for bulk epithelial tissue. They estimated the scattering coefficient of normal and precancerous cervical epithelium using measurements of the reflectance as a function of depth from confocal images. Reflectance measurements were taken from ex vivo cervical biopsies and fit to an exponential function based upon Beer's law attenuation. The mean scattering coefficients derived were 22 cm/sup -1/ for normal tissue and 69 cm/sup -1/ for precancerous tissue. These values are significantly lower than previously reported for bulk epithelial tissues and suggest that scattering of bulk tissue is dominated by the stroma. They also suggest that computational models to describe light propagation in epithelial tissue must incorporate different scattering coefficients for the epithelium and stroma. Further, the lower scattering of the epithelium suggests greater probing depths for fiber optic probes used by optical diagnostic devices which measure reflectance and fluorescence in epithelial tissue. The difference in scattering between normal and precancerous tissue is attributed to increased nuclear size, optical density, and chromatin texture. The scattering coefficients measured here are consistent with predictions of numerical solutions to Maxwell's equations for epithelial cell scattering.     

Three-dimensional computation of light scattering from cells

Using the finite-difference time-domain method, three-dimensional scattering patterns are computed for cells containing multiple organelles. The scattering cross section and average cosine of the scattering angle are computed for cells as a function of volume fraction of melanin granules and mitochondria. Results show that small organelles play a significant role in light scattering from cells, and the volume fraction of organelles affects both the total amount of scattered light and the angular distribution of scattered light     

模糊单神经元混合控制的轧机扭振抑制研究

在轧机轧制过程中,运行工况的变化可能诱发扭振,严重影响轧机轴系的安全.通过分析轧机扭振产生的原因,针对传统PI控制方式对轧机扭振抑制的不足,提出采用模糊单神经元混合控制的方法,在误差较大的情况下采用模糊控制,加快系统的动态响应速度,在误差较小的情况下采用单神经元控制,提高系统的稳态精度,从而达到对轴系扭振进行抑制的目的.     

Road-Condition Recognition Using 24-GHz Automotive Radar

This paper studies 24-GHz automotive radar technology for detecting low-friction spots caused by water, ice, or snow on asphalt. The backscattering properties of asphalt in different conditions are studied in both laboratory and field experiments. In addition, the effect of water on the backscattering properties of asphalt is studied with a surface scattering model. The results suggest that low-friction spots could be detected with a radar by comparing backscattered signals at different polarizations. The requirements for the radar are considered, and a 24-GHz radar for road-condition recognition is found to be feasible.      

基于多光谱图像融合的光学表面疵病检测

为了实现对精密光学元件表面疵病的高精度测量,提出了一种基于多光谱图像融合的光学元件表面疵病检测方法。通过使用不同波长的光源入射到光学表面,在显微暗场成像系统中获得了450nm,532nm,650nm单波长光源照明时光学表面疵病的检测结果,并将采集到的图片通过加权平均法、拉普拉斯金字塔变换法和小波变换法三种方法进行图像融合后,再进行图像处理获取疵病尺寸信息。由实验结果对比可知,相较于单波长原始图像的疵病检测结果,多光谱融合图像的检测结果更加精确,并且通过对比三种融合方法结果,其中以拉普拉斯金字塔变换融合的效果最佳。     

基于单线图的配电网GIS应用系统

介绍了基于单线图的配电网GIS地理情息系统（以下简称DDM／GIS系统)的设计思想、主要功能、特点及应用开发体会,提出了一种电力GIS系统开发的新思路,即从单线图入手．“先绘制单线图．再向地理图映射,最后形成完整的配网GIS系统”的技术路线,具有一定的参考和实用价值。     

太阳能电池自动跟踪系统的研究与改进

对太阳能电池自动跟踪系统进行分析,提出改进的新方案。新方案通过光敏传感器的合理放置,利用比较电路处理不同位置的光强信号,进而产生控制信号,达到用纯粹的硬件组成电路,做到光源的准确跟踪。其反应速度快,自动跟踪迅速,对光源跟踪效率提高有很大帮助,大大改进太阳能电池的转换效率。尤其是该方案较高的性价比,加上并不复杂的应用电路,具有广泛的应用潜力和相关方面的扩展空间。     

基于ZigBee的无线传感器供电电源优化设计

提出了利用单晶硅太阳能电池结合半导体温差发电技术为ZigBee无线传感器持续提供电能的新方法,实现了变电站运行设备中大电流回路连接点发热温度的实时采集。对比分析了在不同光线强度下,单晶硅太阳能电池对超级电容充电性能的影响。通过对电源的优化设计,解决了在连续阴雨天太阳能电池效率下降时,利用半导体温差发电模块提供电能,及时传输故障信息的问题。     

喷雾法制备FeS_2薄膜材料及其在热电池中的性能

采用喷雾法薄膜化工艺制备了FeS_2薄膜正极,研究了薄膜正极中导电剂(超导炭黑)的添加量对热电池单体电池放电性能的影响。以异丙醇为溶剂,适量的超导炭黑为导电剂,采用喷雾法制备热电池FeS_2薄膜正极。与传统的压片制备FeS_2阴极相比,喷雾法合成的黄铁矿薄膜厚度小,在放电过程中有较高的放电比容量。在500℃,相对湿度RH1%的条件下,测试了单体电池的放电性能。测试结果表明,5%XC-72R掺杂FeS_2材料的单体电池的放电比容量最高。     

Emission and absorption of optical phonons in Multigate Silicon Nanowire MOSFETs

In this paper we study the influence of emission/absorption processes due to optical phonons on the electrical properties of multigate silicon nanowire transistors. We show that low-energy phonons reduce drain current through backscattering of carriers by emission/absorption processes while high-energy phonons redistribute the current energy spectrum along the nanowire channel through phonon emission without significantly reducing the drain current drive. The influence of emission/absorption is investigated in different multigate silicon FET structures with uniform channel, single impurity, random doping atom distribution and oxide tunnel barriers. A three-dimensional quantum mechanical device simulator based on the NEGF formalism in coupled mode-space approach is used to model electron transport in the presence of optical phonon scattering mechanism. Electron-phonon scattering is accounted for by adopting the self-consistent Born approximation and using the deformation potential theory.     

A high-resolution MACROscope with differential phase contrast, transmitted light, confocal fluorescence, and hyperspectral capabilities for large-area tissue imaging

Recent advances in imaging technology have contributed greatly to biological science. Confocal fluorescence microscopes can acquire two-dimensional and three-dimensional images of biological samples such as live or fixed cells and tissues. Specimens that are large (e.g., a 10 mm/spl times/10 mm tissue section) and overfill the field of view (FOV) of typical microscope objectives require the use of image tiling to cover the entire specimen. This can be time consuming and cause artifacts in the composite image. The MACROscope system (Biomedical Photometrics Inc., Waterloo, ON, Canada) is a confocal device with a 22 mm/spl times/70 mm FOV designed for imaging large tissue sections in a single frame. The prototype demonstrated here can obtain images in reflected, transmitted, fluorescence, phase contrast, and hyperspectral modes. The new spectral imaging mode is characterized with a series of test targets, and sampled spectra are compared to a commercial spectrometer. Fluorescence images of human SiHa tumor xenografts stained with CD31-Cy3, showing blood vessel location, and EF5-Cy5, showing areas of tissue hypoxia, were collected. Differential phase contrast images of the same section, as well as human epithelial cells, were recorded to assess the phase contrast mode. Additionally, fluorescence images of Cytokeratin-Cy3 stained squamous cell carcinoma tissue sections were captured. Finally, red, green, blue transmitted light images of human tongue were obtained. This new device avoids the need for image tiling and provides simultaneous imaging of multiple fluorescently labeled tissue-specific markers in large biological samples. This enables time- and cost-efficient imaging of (immuno)histopathological samples. This device may also serve in the imaging of high-throughput DNA and tissue arrays.     

Investigation of electron device based low dimensional nano structures

ABSTRACT

Nanowire is an important low dimensional semiconductor nano-material which can be used in field effect transistors, photovoltaic cells, field emission nanodevices, and chemical and gas sensors. In this paper, CuO nanowires are synthesized by heating copper substrates in air, and the CuO nanowire is assembled on two opposite microelectrodes to fabricate a single CuO nanowire nanodevice by dielectrophoresis (DEP). In experiment, suitable parameters are chosen, such as concentration of the CuO nanowire solution, applied voltage and frequency on the microelectrodes, time of DEP duration, to assemble a single CuO nanowire on the microelectrode. Using this single nanowire nanodevice, this paper measured FET effect and photoconductivity of the single CuO nanowire. The results show that the single CuO nanowire nanodevice can work as a FET and it also has novel sensitivity to light intensity.     

基于微脉冲激光雷达的能见度反演算法

在基于后向散射原理的大气能见度测量过程中,大气消光系数边界值的选取对反演精度具有较大影响。提出一种基于弦截法的大气消光系数边界值的确定方法,并利用迭代的思想对边界值的选取结果进行修正。通过理论仿真和实地测量对本方法的可行性进行验证,结果表明,弦截法具有较快的收敛速度,且迭代次数较少,经过比对迭代修正之后的消光系数边界值可以更准确的反演出大气消光系数,进而实现大气能见度的高精度测量,具有较强的实际应用价值。     

Compensation for light intensity variation by superposing AC magnetic field in optical measurement of DC current

Optical voltage and current measurement generally necessitates the compensation of light intensity variation which occurs in the optical measuring system, because it is possible the light intensity variation may give rise to a measuring error. Therefore, such compensation methods as dividing the ac component by the dc component of the light intensity are usefully introduced in optical ac voltage and current measurement, but those methods are not useful exactly for the optical measurement of the quantities including dc components. This paper deals with a new useful compensation method for light intensity variation in the optical dc current measurement. Linearly polarized light passes through two kinds of Faraday sensors, in which one detects dc magnetic field caused by dc current and the other detects externally applied constant ac magnetic field. Then, the compensation of the light intensity variation is carried out by measuring the dc and ac components of the beam. The principle of the compensation method using the ac component is described in the paper. Experimental results of this method using flint glass as the Faraday effect cells are reported and it is clarified that this method can decrease the measuring error of the modulation depth for dc current and compensate light intensity variation validity.     

Influence of rapid thermal annealing on pyrochlore/perovskite phase formation in laser ablated Pb(Zr,Ti)O3 thin films

Abstract

Pb(Zr,Ti)O₃ thin films were prepared by ArF excimer laser deposition on silicon and Pt-coated silicon substrates, and then were treated by rapid thermal annealing. The dependence of perovskite/pyrochlore phase formation on annealing conditions was investigated. The results show that the formation of perovskite phase or pyrochlore phase in the films was not only dependent on the heat treatment temperature, but also dependent on the heat treatment time. A wide range operational window of heat treatment time and temperature for obtaining single phase perovskite Pb(Zr,Ti)O₃ thin films was given, and the films were analyzed by Rutherford backscattering spectroscopy to explain this phase transition.