An electron tomography algorithm for reconstructing 3D morphology using surface tangents of projected scattering interfaces

Upon discerning the mere shape of an imaged object, as portrayed by projected perimeters, the full three-dimensional scattering density may not be of particular interest. In this situation considerable simplifications to the reconstruction problem are possible, allowing calculations based upon geometric principles. Here we describe and provide an algorithm which reconstructs the three-dimensional morphology of specimens from tilt series of images for application to electron tomography. Our algorithm uses a differential approach to infer the intersection of projected tangent lines with surfaces which define boundaries between regions of different scattering densities within and around the perimeters of specimens. Details of the algorithm implementation are given and explained using reconstruction calculations from simulations, which are built into the code. An experimental application of the algorithm to a nano-sized Aluminium tip is also presented to demonstrate practical analysis for a real specimen.

Program summary

Program title: STOMO version 1.0Catalogue identifier: AEFS_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFS_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 2988No. of bytes in distributed program, including test data, etc.: 191 605Distribution format: tar.gzProgramming language: C/C++Computer: PCOperating system: Windows XPRAM: Depends upon the size of experimental data as input, ranging from 200 Mb to 1.5 GbSupplementary material: Sample output files, for the test run provided, are available.Classification: 7.4, 14External routines: Dev-C++ (http://www.bloodshed.net/devcpp.html)Nature of problem: Electron tomography of specimens for which conventional back projection may fail and/or data for which there is a limited angular range. The algorithm does not solve the tomographic back-projection problem but rather reconstructs the local 3D morphology of surfaces defined by varied scattering densities.Solution method: Reconstruction using differential geometry applied to image analysis computations.Restrictions: The code has only been tested with square images and has been developed for only single-axis tilting.Running time: For high quality reconstruction, 5-15 min     

身份认证技术

本文简要描述了身份认证的概念和身份认证机制,主要介绍了身份认证的密码技术,电子钥匙和生物辨别技术,最后提出了异地漫游问题的解决方案。     

Image reconstruction from in-line Fresnel holograms by using coherent background elimination

Image reconstruction from in-line Fresnel holograms by eliminating a coherent background is studied by computer simulation. The coherent background is calculated by averaging an intensity of a recorded hologram. The quality of the reconstructed image is measured by using a ratio of peak signal to noise. In comparison with the conventional reconstruction method, the results show that the background elimination can improve significantly the quality of the reconstructed images. The text was submitted by the authors in English.     

基于声场空间变换方法的轿车加速行驶车外噪声预测

采用近场声全息和声场空间变换方法对轿车车外噪声进行了预测。阐述了声场空间变换的基本原理,构建了近场声全息测量系统,并对声全息测量系统的误差进行了校准。在试验工况为2档、55km/h匀速行驶条件下,在消声室内转鼓试验台上对轿车左右两侧近场声全息数据进行了测试。根据声场空间变换的基本理论,编制了声场空间变换的计算程序,对被试轿车左右两侧变换面的声场进行了重建。根据车外噪声测试标准GB1495—2002中的测量位置对车外噪声进行了预测,并与车外噪声试验结果进行了对比。对比结果表明:左右两侧误差均在1.0dB(A)以内,而相对误差均小于5%,满足工程精度要求。     

电子束选区熔化成形技术及在模具中的应用

基于电子束的选区熔化成形技术利用电子束能量密度高、无反射及真空加工环境无污染等优点，将电子束加工与快速原型制造技术相结合，可以制备传统模具制造技术无法制造的具有内流道和材料梯度的模具。本文结合自行研制的国内第一台电子束选区熔化成形设备的构成及技术路线，阐述了该技术在模具行业中的应用前景，并且采用该技术制备了完全致密的金属三维零件。     

Solution route synthesis of dendrite Cu6Sn5 powders, anode material for lithium-ion batteries

Intermetallic dendrite particles, such as Cu₆Sn₅ compound, possible anode materials for high power lithium-ion batteries, can be synthesized by using solution technique. Solution route method can induce the formation of the compound by performing a redox reaction between metal chloride salts and metallic reducing powder in a suitable solvent. The morphological features and single-phase formation corresponding to different processing conditions including solvent type, reducing agent particle size, and reaction temperature, were determined. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) results illustrate the dendritic morphology of Cu₆Sn₅ particles with small amount of impurities, which can be synthesized by using ethylene glycol as solvent and zinc powder as reducing agent. Reducing agent particle size and reaction temperature have a very small effect on the formation of the Cu₆Sn₅ dendrite powder.     

Photoinduced phenomena in nanostructured porous silicon

In this work we study the evolution of porous silicon photoluminescence under illumination. Samples were obtained by electrochemical etching of crystalline silicon wafers of different types. For the p-type samples the evolution of the spectra is explained in terms of photoinduced oxidation of nanostructures, which in turns leads to a discrete change in the photoluminescence spectra, as we reported in previous works. For the n-type material, a progressive decrease of the luminescence intensity is observed, which is attributed to the photoinduced generation of dangling bond related defect states at the surface layer surrounding the nanostructures. This model explains qualitatively well the kinetics of the evolution of the measured photoluminescence. Preliminary results of electronic paramagnetic resonance spectroscopy agree with this model.     

Corrosion-resistant analogue of Hadfield steel

The concept of alloying austenitic steels with carbon + nitrogen is used for the development of a corrosion-resistant austenitic CrMn steel having an impact wear resistance close to that of the Hadfield steel. A higher stabilization of the austenitic phase by C + N, as compared to carbon or nitrogen alone, is substantiated by ab initio calculation of the electron structure, measurements of the concentration of free electrons and calculations of the phase equilibrium. Based on these results, the compositions (mass%) Cr18Mn18C0.34N0.61 and Cr18Mn18C0.49N0.58 were melted and tested along with Hadfield steel Mn12C1.2. Mechanical tests have shown that, as compared to the Hadfield steel, the experimental steels possess a higher strength, plasticity, hardness and the same resistance to impact wear. TEM studies of the surface layer after impact treatment revealed a mixture of the amorphous phase, nanocrystals and fine-twinned austenite. At the same time, using Mössbauer spectroscopy of conversion electrons, the ferromagnetic ordering was found in the surface layer of up to 10 μm in depth, which is the sign of the strain-induced martensitic phase. The hypothesis of a transition from the low-spin to the high-spin state of the iron atoms within the thin twins in austenite was proposed in order to interpret the discrepancy between TEM and Mössbauer studies. Potentiodynamic measurements and immersion tests show that the CrMnCN steels possess a significantly higher pitting potential and resistance to general corrosion in comparison with Hadfield steel.     

Control of 0.2CaTiO3-0.8Li0.5Nd0.5TiO3 microwave dielectric ceramics by additions of Bi2Ti2O7

Ceramics of 0.2CaTiO₃-0.8Li_0.5Nd_0.5TiO₃) have been prepared by the mixed oxide route using additions of Bi₂O₃-2TiO₂ (up to 15 wt%). Powders were calcined 1100^∘C; cylindrical specimens were fired at temperatures in the range 1250–1325^∘C. Sintered products were typically 95% dense. The microstructures were dominated by angular grains 1–2 μm in size. With increasing levels of Bi₂O₃-2TiO₂ additions, needle and lath shaped second phases developed. For Bi₂Ti₂O₇ additions up to 5 wt%, the relative permittivity increased from 95 to 131, the product of dielectric Q value and measurement frequency increased from 2150 to 2450 GHz and the temperature coefficient of resonant frequency (τ _f ) increased from −28pp/^∘C to +22pp/^∘C. A product with temperature stable τ _f could be obtained at ∼2 wt% Bi₂Ti₂O₇ additions. For high levels of additives, there is minimal change in relative permittivity, the Qxf values degrade and τ _f becomes increasingly negative.     

Electron beam evaporated carbon nanotube dispersed SnO2 thin film gas sensor

Carbon nanotube (CNT) is a useful material for gas-sensing applications because of its high surface to volume ratio structure. In this work, multi-wall CNTs are incorporated into tin oxide thin film by means of powder mixing and electron beam evaporation and the enhancement of gas-sensing properties is presented. The CNTs were combined with SnO₂powder with varying concentration in the range of 0.25–5% by weight and electron beam evaporated onto glass substrates. From AFM and TEM characterization, CNT inclusion in SnO₂thin film results in the production of circular cone protrusions of CNT clusters or single tube coated with SnO₂layer. Experimental results indicate that the sensitivity to ethanol of SnO₂thin film increases by the factors of 3 to 7, and the response time and recovery time were reduced by the factors of 2 or more with CNT inclusion. However, if the CNT concentration is too high, the sensitivity is decreased. Moreover, the CNT doped film can operate with good sensitivity and stability at a relatively low temperature of 250–300^∘C. The improved gas-sensing properties should be attributed to the increasing of surface adsorption area of metal oxide produced by CNT protrusion.