Cylindrical diameters method for calibrating section thickness in serial electron microscopy

An estimate of section thickness is required for measuring structures in serial section microscopy. Mean section thickness is estimated reliably by averaging the ratios of the diameters of cylindrical objects, such as mitochondria, to the number of sections they span. This cylindrical diameters method improves the accuracy of section thickness as inferred from the colour of sections floating in water. The cylindrical diameters method gives the same answer as that obtained by the minimal folds method. It is preferable because it can be done in a series that has no folds that can distort and obscure the objects that are being measured.     

Estimation of the section thickness and optical disector height with a simple calibration method

The distance between the upper and lower surfaces of a section (i.e. the section thickness) can be measured with a microcator or a shaft encoder. In the present report, an alternative simple method is described for estimating the section thickness where such equipment is not available. The basic principle of the method is based on a calibration method already described in the literature. The main difference is that it enables one to make more precise measurements. Provided that the calibration and measurements are made properly, this method can be used in estimating the section thickness, optical disector heights, and in particular in the determination of the thickness sampling fraction for the optical fractionator.     

Three-dimensional reconstruction of a periodic specimen from a single view of an oblique section

Methods are described for producing a three-dimensional reconstruction from a single view of an oblique section through a two- or three-dimensional crystal. The image produced by the electron microscope corresponds to a projection through the thickness of the section, which smears out the details of the structure. This projection operation can be described mathematically by sets of linear projection equations or equivalently by convolution of the density in the unit cell with the section thickness. Solution of the projection equations or other methods of deconvolution reduces the smearing and gives a three-dimensional map of the density within the crystal superior to that obtained by direct inspection of the image. The degree of improvement attainable depends on the noise level in the image but computational experiments indicate that a factor of at least four should be achievable. The method, which is most powerful when the section thickness is small, has the advantage over conventional methods involving tilted that it is not affected by changes in section thickness on electron irradiation.     

叶切面最大厚度的数值计算方法

叶切面最大厚度计算是螺旋曲面加工准备过程中必要的环节.探讨适合于叶切面最大厚度的数值计算方法.详细介绍叶切面厚度数值计算所包括的叶切面最大厚度区域搜索、叶切面最大厚度精确计算过程.     

3D reconstruction from the Fourier transform of a single superlattice image of an oblique section.

An image of a thin oblique section through a 3D crystal exhibits superlattice periods much larger than the unit cell dimensions of the crystal. Within a superlattice period the contents of the unit cell of the 3D crystal are sampled at different levels, so that a 2D image of the section contains 3D information about the crystal. The 2D Fourier transform of an electron micrograph of such an oblique section thus exhibits superlattice spots, which provide an estimate of the 3D transform of the original crystal. The strengths of the observed spots are reduced from their true values by convolution with a weighting function that depends on section thickness. A method is described that uses phase relationships among symmetry-related structure factors to determine the section thickness and hence the weighting function. Wiener filter deconvolution of the section thickness is performed, in which the filter level is set by the ratio of diffraction spot intensity to background intensity. From the deconvoluted set of structure factors a 3D map of the unit cell can be computed by a standard crystallographic Fourier program. The approach is illustrated with images of oblique sections through rigor insect flight muscle.     

Estimation of the average section thickness in ribbons of ultra-thin sections

A simple procedure for estimating the depth to which a ribbon of ultra-thin sections cuts into a block is described. The average section increment is obtained by dividing the depth by the number of sections in the ribbon. Comparison with measurements of individual sections made using interference microscopy suggests: (a) that loss of resin brought about by the cutting process is insignificant, i.e. that the average section increment equals the average section thickness, and (b) that there can be considerable variation in section thickness along a ribbon. Provided that such variation is taken into account, the method based on measurements of the block face is simple, avoids time-consuming alternative procedures, and is appropriate when seeking to determine the depth dimension to be used in making three-dimensional reconstructions from long sequences of sections.     

Mass thickness determination by electron energy loss for quantitative X-ray microanalysis in biology

As is well known, electron energy loss spectroscopy can be used to determine the relative sample thickness in the electron microscope. This paper considers how such measurements can be applied to biological samples in order to obtain the mass thickness for quantitative X-ray microanalysis. The important quantity in estimating the mass thickness from an unknown sample is the total inelastic cross section per unit mass. Models for the cross section suggest that this quantity is constant to within ±20% for most biological compounds. This is comparable with the approximation made in the continuum method for measuring mass thickness. The linearity of the energy loss technique is established by some measurements on evaporated films and quantitation is demonstrated by measurements on thin calcium standards. A significant advantage of the method is that the energy loss spectrum can be recorded at very low dose, so that mass thickness determination can be made before even the most sensitive samples suffer damage resulting in mass loss. The energy loss measurements avoid the necessity to correct the continuum measurement for stray radiation produced in the vicinity of the sample holder. Unlike the continuum method the energy loss technique requires uniform mass thickness across the probe area, but this is not usually a problem when small probes (<100 nm diameter) are used.     

A simple calibration for routine section thickness measurements using current density ratios

A method to calibrate current density ratios for the determination of specimen thickness is presented. This method uses a tilt series from a single noncrystalline specimen to create different thicknesses; these are used to generate data points to establish the relationship between specimen thickness and current density ratio. The actual specimen thickness at 0° tilt was determined to an accuracy of 5 nm by a parallax method. From the calibration curves obtained, we observed that the current density ratio was sensitive to relative thickness changes on the same section of less than 1 nm when a 50-μm objective aperture was used.     

中空吹塑型坯壁厚多点控制研究

中空吹塑成型突出的缺点是中空吹塑成型产品壁厚均匀性不易控制,尤其是形状复杂的大型制品,其受型坯自重的影响,导致在型坯上发生减薄和缩颈现象。为了实现对大型中空吹塑件的壁厚进行均匀控制,设计了以多点控制来控制壁厚的计算方法,并借助于制造参数的调整,得到壁厚的理想厚度分布;设计了多点控制曲线,通过控制机头套与模芯构成的模唇间隙,达到最终控制中空吹塑产品壁厚的目的。研究结果表明,中空吹塑型坯壁厚控制精度为±1mm左右,能够满足实际生产要求。     

A protocol for 3D image reconstruction from a single image of an oblique section.

Oblique section 3D reconstruction can produce a 3D image of a sectioned crystal from a single electron micrograph. We describe here in detail a reconstruction protocol applicable to an electron micrograph of an oblique section through a 3D crystal. The protocol is described in six steps: (1) selection criteria for images, (2) preprocessing steps to correct for image defects, (3) determination of unit cell coordinates, (4) interpolation of strip images with correction for image distortions and crystal disorder, (5) production of a crystallographic serial section reconstruction, (6) correction for skewed sampling to produce an oblique section reconstruction. In addition, we explore Wiener filter deconvolution of the section thickness. We describe a method for determining the section thickness by comparing data from projections of the oblique section reconstruction with corresponding data from a thick longitudinal section. Several schemes for Wiener filter deconvolution are described that differ in the way information on the signal-to-noise ratio is used in the filter.     

门槛梁抗弯性能影响因素研究

以某微型车门槛梁为研究对象,分析在侧面碰撞过程中的变形模式,确定薄弱截面。为便于对抗弯性能影响因素研究,将其等效简化为单帽梁。设计三点弯曲准静态试验,采用单一变量的方法,分析单帽梁的厚度、截面长宽比和材料对抗弯性能的影响规律。结果表明:薄壁梁内板厚度对抵抗弯曲所起的作用较小,薄壁梁的抗弯性能主要由外板厚度来体现,厚度越大,薄壁梁的抗弯性能越好。截面长宽比越小,所用材料的屈服强度越高,薄壁梁的抗弯性能越好。对后期门槛梁结构设计提供参考。     

内压及扭矩载荷下无缺陷弯管的应力分析

分析在内压或扭矩载荷作用下非均匀壁厚椭圆弯管的应力分布，结果表明内压引起的最大应力随着弯管的截面不均匀度而变化，由此解释了工程实际中弯管失效的原因，同时也为求解弯管的塑性极限载荷奠定了基础。     

基于MATLAB的高速磨削电主轴单元定子冷却管道的优化设计

针对电主轴单元定子表面的散热问题,研究了冷却管道的截面形状尺寸及管道的疏密程度对传热的影响。提出了确定冷却管道的最优截面形状尺寸及壁体厚度的优化设计方法,运用Matlab软件进行了优化计算,并用有限元软件Nastran对优化结果进行了仿真分析,得到了较为理想的温度分布,为实践中定子表面冷却管道的设计提供了理论依据。运用薄壁圆筒模型的相关理论,从管壁因承受冷却液内压力而产生的应力应变方面着手,通过定量分析壁厚的最小范围,优化设计高速主轴单元定子表面冷却管道的截面大小与形状,提高表面对流换热系数,增加换热面积,从而达到增强换热的目的。     

基于Lamb波的平尾大轴裂纹扩展监测

平尾大轴作为在役飞机的主承力构件,其轴内变厚度截面处存在应力集中现象,是疲劳断裂高发的关键部位。针对平尾大轴变截面处裂纹损伤,研究其基于主动Lamb波的裂纹深度在线监测方法。首先,通过线切割制造真实损伤,对压电传感器采集的监测信号进行Shannon连续复数小波变换,去噪提取Lamb波信号;其次,重点研究了不同模式Lamb波的4种损伤因子对大轴裂纹深度的表征能力,结果表明,基于A_0模式的互相关损伤因子对裂纹深度的表征效果最佳;最后,利用A_0模式的互相关损伤因子实现了平尾大轴裂纹萌生及裂纹尺寸的定量化监测,为平尾大轴的在线监测提供了方法基础。     

变截面柔性铰链变形分析计算方法

柔性铰链的几何结构对其性能有着直接的影响。文中分析了变截面柔性铰链的变形特性,给出了变截面柔性铰链的特征厚度比和等效截面厚度的概念。定义了平均截面厚度的修正系数,通过算例给出了不同特征厚度比对应的修正系数值,以此对变截面柔性铰链的平均截面厚度进行修正得到等效截面厚度,进而采用伪刚体模型法分析变截面柔性铰链的变形。实例计算结果表明,经过修正计算得到的变形结果与有限元法的分析结果具有很好的一致性,表明了修正系数的合理性。     

基于中弧线的空心涡轮叶片壁厚计算方法研究

针对高精度复杂空心涡轮叶片壁厚测量问题,提出了一种基于中弧线的壁厚计算方法。通过对空心叶片CT切片数据的处理,建立了相应的点云数据测量模型,并与叶片CAD模型进行配准,实现了各截面数据点的提取与拟合,从而计算出了中弧线;在此基础上,运用UG二次开发平台求出了叶片各点的壁厚。实测结果表明:通过该方法能够精确计算复杂空心涡轮叶片的壁厚,提高空心叶片壁厚精度及其可靠性。     

多层厚度电涡流检测技术及实验研究

研究了多层厚度的电涡流检测原理和有限截面线圈置于多层结构上其各种参数与阻抗变化关系的数学模型；建立了用于多层厚度检测的涡流检测系统，对两层厚度的检测进行了几种检测电压值--厚度回归模型实验研究，并对反演计算结果进行了比较分析，给出了最佳的拟合模型和多层厚度反演算法。     

An interference technique for measuring the thickness of semi-thin and thick sections

An interference method is described for measuring section thickness in the range 0·3–45 μm. An incident illumination objective incorporating a beam splitter and adjustable reference mirror is used to generate interference fringes by reflection from the upper surfaces of sections on glass slides. Sections do not require a reflective coating. The lateral displacement of the zero-order fringe generated using white light is measured in terms of sodium light fringes and photographic enlargement of the fringes allows measurement to ± 30 nm. The method is simple in operation and allows rapid assessment of any local distortions over the entire section area.     

叶切面最大厚度数值计算与应用

以叶切面最大厚度的数值计算方法为基础,探讨叶切面最大厚度计算的计算机实现,介绍叶切面厚度数值计算法的应用实例.     

磁巴克豪森噪音(MBN)法对产品厚度测量的影响

本文试图说明通过变化被测产品横截面和标定试块的厚度做出依据巴克豪森噪音法测量产品残余应力的结论。将测量和比较不同试块厚度获取的RMS值和巴克豪森脉冲的整体数目作为巴克豪森噪音参数,间接有效地反映了试块各种横截面厚度对巴克豪森噪音电平的影响。文中还分析了磁化频率和磁化电流对灵敏度的影响。