Automated detection of ocular alignment with binocular retinal birefringence scanning

We previously developed a retinal birefingence scanning (RBS) device to detect eye fixation. The purpose of this study was to determine whether a new binocular RBS (BRBS) instrument can detect simultaneous fixation of both eyes. Control (nonmyopic and myopic) and strabismic subjects were studied by use of BRBS at a fixation distance of 45 cm. Binocularity (the percentage of measurements with bilateral fixation) was determined from the BRBS output. All nonstrabismic subjects with good quality signals had binocularity >75%. Binocularity averaged 5% in four subjects with strabismus (range of 0-20%). BRBS may potentially be used to screen individuals for abnormal eye alignment.     

二色调相式双折射系统的设计及其应用

以二色氩离子激光作光源,采用相调制技术设计了用于同时实时测量流场双折射及取向角的二色调相式流动双折射实验装置。由于采用了二色光源,避免了在计算过程中运用二阶贝塞尔函数以及在信号处理时分析二次谐波,简化了实验装置及结果计算。装置通过低通滤波电路和锁相放大器分别测量入射光和出射光中基频成分的光强度,并把它们转换成数字信号,由此计算出待测流场的双折射和取向角。实验证明,应用该装置同步测量了双折射及取向角,最大测量误差控制在0.5%~1%。     

Birefringence in gradient-index rod lenses: a direct measurement method and interferometric polarization effects

Gradient-index (GRIN) media can contain stress birefringence resulting from the variation in material composition. Anisotropy in a GRIN rod lens affects ray propagation and can degrade image quality. A technique, believed to be new, for measuring birefringence in GRIN rod lenses has been developed. The change in optical path difference (OPD) for orthogonal polarizations is measured directly. With this method, effects on OPD from standard imaging aberrations are excluded. Birefringence measurements for various GRIN rod samples are presented. The data are compared with results obtained previously by use of a Twyman-Green measurement method. Also, the polarization effects on tilt fringes observed with the direct measurement method and the Twyman-Green method are presented and modeled theoretically. Tilt fringes for large birefringence test cases are also modeled.     

分析薄膜厚度与成分的卢瑟福背散射技术

对卢瑟福背散射分析技术的基本原理、试验设备、样品要求及数据处理方法进行了介绍,并举例分析了硅衬底上钛膜厚度的测定,以及钼衬底上钛钼合金膜的实际组分以及氦离子注入杂质的分布范围和实际剂量测定。讨论了卢瑟福背散射技术的发展和应用,介绍了弹性反冲、高能非卢瑟福散射和沟道技术三种分析方法。     

Accuracy of energy dispersive x-ray composition analysis of YBCO films on yttrium-containing substrates as compared to Rutherford backscattering spectroscopy

We address the accuracy of Energy Dispersive X-ray Spectroscopy (EDS) composition analysis of YBa₂Cu₃O (YBCO) thin films. YBCO films deposited on yttrium stabilized zirconia (YSZ) and strontium titanate (STO) substrates were analyzed by EDS and Rutherford Backscattering Spectrometry (RBS) to determine their compositions. The YSZ substrates used in this work contained a common element, yttrium; therefore, EDS intensities of yttrium signals resulting from the film alone were calculated using EDS results of blank YSZ substrates. The EDS compositions of all the elements were obtained using the proportionality factor, k calculated from RBS data from a standard film deposited on silicon and the intensity ratios of the respective standard obtained from EDS. The film thickness was found to be an important factor to consider when choosing the optimum accelerating voltage for the EDS analysis. For films having comparable thickness to that of the standard (0.8 m), we found 25 kV was the optimum accelerating voltage for the EDS analysis that obtained compositions in good agreement with the RBS data. For films having half the thickness of the standard film, EDS composition analyses were unreliable quantitatively and were best qualitatively at 15 kV.     

Design considerations of form birefringent microstructures

Diffraction characteristics of high-spatial-frequency (HSF) gratings are evaluated for application to polarization-selective computer-generated holograms by the use of two different approaches: second-order effective-medium theory (EMT) and rigorous coupled-wave analysis (RCWA). The reflectivities and the phase differences for TE- and TM-polarized waves are investigated in terms of various input parameters, and results obtained with second-order EMT and RCWA are compared. It is shown that although the reflection characteristics can be accurately modeled with the second-order EMT, the phase difference created by form birefringence for TE- and TM-polarized waves requires the use of a more rigorous, RCWA approach. The design of HSF gratings in terms of their form birefringence and reflectivity properties is discussed in conjunction with polarization-selective computer-generated holograms. A specific design optimization example furnishes a grating profile that provides a trade-off between the largest form birefrin gence and the lowest reflectivities.     

Ammonia plasma treatment of ultra-high strength polyethylene fibres for improved adhesion to epoxy resin

A study of the effect of plasma treatments on the mechanical properties and adhesion of ultra-high strength polyethylene fibres to epoxy resin is reported. Fibres were treated with ammonia plasma under various time and power conditions. The fibre/matrix interfacial shear strength was measured using load and fibre pull-out data obtained in a single-fibre pull-out test. The debonding was optically as well as acoustically monitored. Optical birefringence patterns were visible at the fibre debond region. Acoustic emission signals generated from debonding and stick-slip processes were also detected. A more than four-fold increase in the interfacial shear strength was achieved by plasma treating the fibres at the discharging condition of 30 W and 0.5 torr for 1 min. The birefringence patterns showed, qualitatively, that the shear in the matrix around the fibres increased for treated fibres and extended further into the matrix material. Surface topography of the pulled out fibres showed that the failure mode was unchanged by the treatment.     

Light scattering and form birefringence of parallel cylindrical arrays that represent cellular organelles of the retinal nerve fiber layer

The retinal nerve fiber layer (RNFL) comprises bundles of unmyelinated axons that run across the surface of the retina. The cylindrical organelles of the RNFL (axonal membranes, microtubules, neurofilaments, and mitochondria) as seen by electron microscopy were modeled as parallel cylindrical arrays in order to gain insight into their optical properties. Arrays of thin fibrils were used to represent organelles that are thin relative to wavelength, and the model took into account interference effects that may arise from spatial order. Angular and spectral light-scattering functions were calculated for the backscattering hemisphere. Scattering was much larger from axonal membranes than from microtubules or neurofilaments. Spectra from 400 to 700 nm show that scattering increases at shorter wavelengths for both axonal membranes and microtubules. At 560 nm, scattering from mitochondria modeled as thick cylinders was approximately the same as that from microtubules but showed little wavelength dependence. The model reveals differences in backscattered polarization ratios that may permit experimental discrimination between microtubule and membrane mechanisms for the RNFL reflectance. Calculated backscattering exceeds measured values by at least 1 order of magnitude, but calculated form birefringence for microtubule arrays is approximately the same as measured birefringence.     

Dispersion effects in elliptical-core highly birefringent fibers

Modal birefringence and its sensitivity to temperature and hydrostatic pressure were measured versus wavelength in three elliptical-core fibers and one fiber with stress-induced birefringence. We carried out the measurements in the spectral range from 633 to 843 nm by using interferometric methods. In fibers with elliptical cores all the measured parameters showed high chromatic dependence, whereas in fibers with stress-induced birefringence this dependence was weak. We modeled the dispersion characteristics of two elliptical-core fibers by using the modified perturbation approach first proposed by Kumar. The modification consists of introducing into the expression for the normalized propagation constants an additional perturbation term that contains information about stress-induced birefringence. The results of modeling show that the temperature and pressure sensitivity of elliptical-core fiber are associated primarily with variations in stress induced by these parameters. The agreement between measured and calculated values of sensitivity in the worst case was equal to 20% for modal birefringence and temperature sensitivity and 50% for pressure sensitivity. Lower agreement between measured and calculated values of pressure sensitivity is most probably associated with uncertainties in the material constants used in modeling.     

Characterization of Cast Iron Microstructure Through Fluctuation and Fractal Analyses of Ultrasonic Backscattered Signals Combined with Classification Techniques

This work aims at evaluating the performance of pattern recognition methods in the identification of different microstructures presented by cast iron, namely, lamellar, vermicular and nodular microstructures, through the statistical fluctuation and fractal analyses of backscattered ultrasonic signals. The signals were obtained with a broad band ultrasonic probe with a central frequency of 5 MHz. The statistical fluctuations of the ultrasonic signals were analyzed by means of Hurst (RSA) and detrended-fluctuation analyses (DFA), and the fractal analyses were carried out by applying the minimal cover and box-counting techniques to the signals. The curves obtained from the statistical fluctuations and fractal analyses, as functions of the time window, were processed by using four pattern classification techniques, namely, principal-component analysis (PCA), Karhunen-Loève transformation (KLT), neural networks and Gaussian classifier. The best results were obtained by Karhunen-Loève expansion and neural networks, where an approximately 100% success rate has been reached for the classification of the different microstructures as well as for the training and the testing sets of events. The results presented correspond to an average taken over 100 randomly chosen sets of events. These results indicate that, within the techniques used, the Karhunen-Loève transformation and neural network associated with the statistical fluctuation analyses (RSA and DFA) are the best tools for the recognition of the different cast iron microstructures. It is worthwhile pointing out that the microstructure classification was made by using backscattering signals acquired during pulse echo ultrasonic nondestructive testing only. Therefore, that approach is a promising method for material characterization.     

Directional eye fixation sensor using birefringence-based foveal detection

We recently developed and reported an eye fixation monitor that detects the fovea by its radial orientation of birefringent nerve fibers. The instrument used a four-quadrant photodetector and a normalized difference function to check for a best match between the detector quadrants and the arms of the bow-tie pattern of polarization states surrounding the fovea. This function had a maximum during central fixation but could not tell where the subject was looking relative to the center. We propose a linear transformation to obtain horizontal and vertical eye position coordinates from the four photodetector signals, followed by correction based on a priori calibration information. The method was verified on both a computer model and on human eyes. The major advantage of this new eye-tracking method is that it uses true information coming from the fovea, rather than reflections from other structures, to identify the direction of foveal gaze.     

Optimized birefringence changes during isolated nerve activation

Single trial, birefringence signals associated with action potentials from isolated lobster nerves were optimized with high-intensity light-emitting diodes (LEDs) and glass polarizers. The narrow spectral output of the LEDs allowed us to select specific wavelengths, increasing the effectiveness of the polarizers and minimizing the stray light in the system. The LEDs produced intensity profiles equivalent to narrowband filtered 100-W halogen light, and birefringence signals were comparable or superior in size and clarity to halogen lamp recordings. The results support a direct correlation between signal size and polarizer extinction coefficient. Increasing the sensitivity of birefringence detection through the use of LED light sources could ameliorate noninvasive brain imaging techniques that employ fast optical consequences associated with action potential propagation.     

The study of polystyrene surface swelling by quartz crystal microbalance and Rutherford backscattering techniques

A quartz crystal microbalance technique (QCM) was used to measure the mass gain of a glassy polystyrene film as 1 -iodo-n-hexane (IOH) was diffused into it. We present a technique by whichØ _s(t), the time dependent volume fraction of IOH at the surface of the PS film, can be obtained from the QCM data. The surface swelling data thus obtained are shown to be in good agreement with values ofØ _s(t) measured independently by Rutherford backscattering spectrometry (RBS). The QCM method has the advantage that the data are obtained continuously from one sample rather than requiring the tedious exposure and analysis of the multiple samples that the RBS method does; it is, however, sensitive to small errors in determining the mass gain rate.     

On the validity of the reduced bending stiffness method for laminated composite plate analysis

The ‘reduced bending stiffness’ (RBS) method has been used on occasions in the past as a means of simplifying the analysis of the flexural behavior of unsymmetrically laminated composite plates. However, the validity of the method has never been established. This paper makes direct comparisons between relatively simple, exact solutions for the static deflections, buckling loads and vibration frequencies of simply-supported plates and those arising from the RBS method. Extensive calculations are made for wide ranges of the physical parameters involved (aspect ratio, moduli ratio, lamination orientation angle, numbers of plies). The RBS method is found to yield sufficient accuracy for cross-ply plates, but errors up to 29% are obtained for angle-ply plates constructed with materials currently under development.     

翼缘削弱型钢梁的整体稳定性分析

针对钢框架梁翼缘削弱式(RBS)节点梁的整体稳定性能进行了分析。采用能量法研究了不同荷载作用下RBS 梁的整体稳定性能, 将梁翼缘削弱段刚度采用等效折减刚度进行分析, 得到RBS 梁侧向弯扭失稳的临界荷载, 并与等截面梁临界荷载进行对比。讨论了不同削弱参数下RBS 梁的临界弯矩变化规律, 并通过有限元数值计算验证了削弱参数对RBS 梁弯扭失稳临界弯矩的影响。研究结果表明:RBS 梁削弱参数整体对侧向弯扭失稳影响明显, 其临界弯矩值较同尺寸的普通钢梁明显降低, 工程设计中应考虑其不利影响;RBS随梁跨度的增加, 削弱段局部刚度对整段梁的刚度影响作用减弱, 当RBS梁的高跨比较小时, 可以忽略削弱参数对临界弯矩的影响。     

基于FPGA的偏振OCT双路信号处理系统

针对目前基于计算机的偏振OCT具有系统数据处理速度慢、不能实时显示等问题,设计了基于FPGA的偏振OCT双路信号处理系统.FPGA设计包含同步时序控制、正交解调和CORDIC运算三个模块.同步时序控制模块为系统的各器件提供同步控制信号,实现数据的实时处理和同步显示.正交解调和CORDIC运算模块对预处理后的干涉信号进行振幅解调和相位解调,获取反射率和双折射率数据,经USB接口送入计算机进行实时显示.对玻片、云母片和生物组织进行偏振OCT系统成像,对成像结果的分析验证了系统具有实时探测生物组织反射率和双折射率的能力.     

High birefringence photonic crystal fiber with a complex unit cell of asymmetric elliptical air hole cladding

High birefringence induced by elliptical air hole photonic crystal fibers (EHPCFs) is analyzed numerically using the finite-element method. Statistical correlations between the birefringence and the various parameters are obtained. We found that the complex elliptical air hole is better than that of a circular one to obtain high birefringence in photonic crystal fibers. Our suggested structures can considerably enhance the birefringence in EHPCFs and show that the birefringence can be as high as 1.1294 x 10(-2), which is higher than the birefringence obtained from conventional step-index fiber (5 x 10(-4)), circular air holes PCF (3.7 x 10(-3)), and elliptical hollow PCF (2.35 x 10(-3)).     

Detection of general yielding in a516 steel by acoustic emission

A study of the acoustic emission behaviour of A516-70 steel has shown that acoustic emission is well suited to the detection of general yielding. The acoustic emission parameters studied were the count rate and the total count as well as a quantitative analysis of the frequency spectrum of acoustic emission signals obtained during the fracture tests. It was found that the major acoustic emission activity occurs during the process of formation of the plastic zone and ends at the load corresponding to general yielding of the untorn ligament. The frequency analysis of the acoustic signals, however, was found to overestimate the onset of unstable crack growth. Ductile crack propagation mechanisms for this material did not exhibit a high activity of acoustic emission.     

Study of process parameters on optical qualities for injection-molded plastic lenses

Numerical simulations for mold-flow analysis and experimental measurements of injection-molded plastic lenses have been conducted for investigation of optical qualities, residual birefringence, and form accuracy resulting from various pertinent process conditions. First, residual birefringence distributions on the lens have been predicted and verified experimentally. Furthermore, full-scale factorial design of experiments was conducted to comprehend the influences of qualities, such as shear stresses, form accuracy, and volumetric deviation, on the measured primary or Seidel aberrations. In conclusion, residual birefringence induced by stresses represented by photoelasticity measurements agrees well with the numerical predictions and the experimental results indicate that the residual birefringence is mainly generated during the mold-filling stage. In addition, spherical aberration of the injection-molded plastic lenses is more sensitive to the pertinent qualities as compared to coma and astigmatism.     

钇硅化物的合成及相变研究

利用离子注入的方法在Si（111）衬底上制备出了具有六方结构的稀土硅化物YSi₂埋层,并对其进行了结构及电学特性的研究.钇注入剂量为1×10¹⁸Y⁺cm^-2,注入能量为100keV.利用X射线衍射（XRD）及卢瑟福背散射技术（RBS）得到了注入样品的结构相.结果显示,在对衬底Si进行Y离子注入的过程中就已经形成了YSi₂相,在随后的红外光辐照退火过程中,样品呈现出了取向生长的趋势.利用RBS的测量分析了注入层中的Y离子在样品不同深度处的浓度分布.利用四探针法对刚注入的样品进行了红外光辐照过程中的原位方块电阻测量,结果显示,当退火温度升到160℃时,样品中形成了斜方的YSi亚稳相;而240℃则对应着YSi-YSi₂的相转变点。