不锈钢微裂纹形核扩展的TEM原位观察

３１０奥氏体不锈钢在透射电镜中的原位拉伸观察表明，如在裂尖发射位错后保持恒位移，则在裂尖能形成无位错区，这个弹性的ＤＦＺ不均匀减薄，其应力集中可等于原子键合力，从而导致纳米微裂纹在ＤＦＺ中形核，并很快钝化成空洞，如果裂尖发射位错后继续拉伸，则上述基本过程被掩盖，仅看到交滑移使裂尖区减薄，从而导致微米给空洞或裂纹的形核和连接。如稍稍卸载，则可观察到裂尖前反塞积位错群的逆返现象。     

WAVE FIELD EXTRAPOLATION IN VISCOELASTIC MEDIUM AND VARIABLE FOCUS METHOD TO SEPARATE SEISMIC COMPOUND WAVE

ＷＡＶＥＦＩＥＬＤＥＸＴＲＡＰＯＬＡＴＩＯＮＩＮＶＩＳＣＯＥＬＡＳＴＩＣＭＥＤＩＵＭＡＮＤＶＡＲＩＡＢＬＥＦＯＣＵＳＭＥＴＨＯＤＴＯＳＥＰＡＲＡＴＥＳＥＩＳＭＩＣＣＯＭＰＯＵＮＤＷＡＶＥ￥ＳｏｎｇＳｈｏｕｇｅｎ；ＹｕａｎＸｉｕｇｕｉ；ＨｅＪｉｓｈａｎ...     

Features of ultrasonic wave propagation to identify defects in composite materials modelled by finite element method

A two-dimensional plane strain finite element model with absorbing boundary condition has been developed to investigate the ultrasonic wave propagation in isotropic and orthotropic media. It is capable of simulating the experimental pulse echo technique to obtain A-scan data, when a short duration pulse is transmitted into a domain with or without a flaw. The flaw can either be a crack or an inclusion of different material such as a Teflon insert or a resin rich zone. After performing FFT on the A-scan data, frequency domain feature analysis is done. The study provides a guideline regarding the suitability of certain harmonics sensitive to certain types of flaw. The simulation shows other important artifacts of wave propagation such as mode conversion and scattering due to the presence of flaws.     

IGBT逆变式波形控制CO2弧焊电源的研究

本文针对ＩＧＢＴ弧焊逆变器，提出并实现了适于短路过渡ＣＯ_２气体保护焊的输出波形控制方法。对焊接电弧参数实时采样以及工艺试验均表明，所研制的逆变式波控ＣＯ_２弧焊电源对减小金属飞溅和改善焊缝成型均有明显效果。     

铝电解槽TiB2涂层阴极技术

将含有ＴｉＢ２、碳纤维和热固性粘结剂的涂料，涂敷到铝电解槽的阴极基体上，制备出可润湿的阴极表面。经固化和碳化后，涂层和碳质基体材料的粘结力强，热膨胀匹配性好。每台硼化钛涂层阴极试验槽能节省ＮａＦ２５０～３００ｋｇ，试验槽的电流效率高出对比槽１．４４％，能耗降低１７５～２１１ｋＷ·ｈ／ｔＡ     

In-situ TEM on (de)hydrogenation of Pd at 0.5-4.5 bar hydrogen pressure and 20-400°C

We have developed a nanoreactor, sample holder and gas system for in-situ transmission electron microscopy (TEM) of hydrogen storage materials up to at least 4.5 bar. The MEMS-based nanoreactor has a microheater, two electron-transparent windows and a gas inlet and outlet. The holder contains various O-rings to have leak-tight connections with the nanoreactor. The system was tested with the (de)hydrogenation of Pd at pressures up to 4.5 bar. The Pd film consisted of islands being 15 nm thick and 50-500 nm wide. In electron diffraction mode we observed reproducibly a crystal lattice expansion and shrinkage owing to hydrogenation and dehydrogenation, respectively. In selected-area electron diffraction and bright/dark-field modes the (de)hydrogenation of individual Pd particles was followed. Some Pd islands are consistently hydrogenated faster than others. When thermally cycled, thermal hysteresis of about 10-16 °C between hydrogen absorption and desorption was observed for hydrogen pressures of 0.5-4.5 bar. Experiments at 0.8 bar and 3.2 bar showed that the (de)hydrogenation temperature is not affected by the electron beam. This result shows that this is a fast method to investigate hydrogen storage materials with information at the nanometer scale.     

Preparation of high-quality ultrathin transmission electron microscopy specimens of a nanocrystalline metallic powder

This article explores the achievable transmission electron microscopy specimen thickness and quality by using three different preparation methods in the case of a high-strength nanocrystalline Cu-Nb powder alloy. Low specimen thickness is essential for spatially resolved analyses of the grains in nanocrystalline materials. We have found that single-sided as well as double-sided low-angle Ar ion milling of the Cu-Nb powders embedded into epoxy resin produced wedge-shaped particles of very low thickness (<10 nm) near the edge. By means of a modified focused ion beam lift-out technique generating holes in the lamella interior large micrometer-sized electron-transparent regions were obtained. However, this lamella displayed a higher thickness at the rim of ≥30 nm. Limiting factors for the observed thicknesses are discussed including ion damage depths, backscattering, and surface roughness, which depend on ion type, energy, current density, and specimen motion. Finally, sections cut by ultramicrotomy at low stroke rate and low set thickness offered vast, several tens of square micrometers uniformly thin regions of ～10-nm minimum thickness. As major drawbacks, we have detected a thin coating on the sections consisting of epoxy deployed as the embedding material and considerable nanoscale thickness variations.     

TEM image analysis and modelling: application to boehmite nanoparticles

Boehmite occurs in the form of nanoparticles. Upon drying, it can form the alumina that is common in catalyst support used in refining and petrochemicals. The topotactic transformation of boehmite alumina led to an interest in the precise shape and size of these nanoparticles which is highly linked to the catalyst activity. Boehmite nanoparticles can be observed by transmission electron microscopy. Although they are highly aggregated, the analysis of transmission electron microscopy images with a specific random model approach, here a dilution model, can give an accurate estimate of their size. To use this approach, electronic noise and diffraction artefacts on the edges of the nanoparticles have to be removed. Covariance measurements on micrographs can be performed. They can be used to fit a model. The fitting uses a novel numerical method to estimate the covariogram of grains. The model can take into account the specific orientations of the nanoparticles. The influence of noise, image filters used to remove noise and diffraction artefacts, as well as all the parameters of the model are all studied in this paper. We propose nanoparticle size estimations procedures based on both single and mixture-of-two particle models.     

Long-term monitoring of live cell proliferation in presence of PVP-Hypericin: a new strategy using ms pulses of LED and the fluorescent dye CFSE

During fluorescent live cell imaging it is critical to keep excitation light dose as low as possible, especially in the presence of photosensitizer drugs, which generate free radicals upon photobleaching. During fluorescent imaging, stress by excitation and free radicals induces serious cell damages that may arrest the cell cycle. This limits the usefulness of the technique for drug discovery, when prolonged live cell imaging is necessary. This paper presents a strategy to provide gentle experimental conditions for dynamic monitoring of the proliferation of human lung epithelial carcinoma cells (A549) in the presence of the photosensitizer Polyvinylpyrrolidone-Hypericin. The distinctive strategy of this paper is based on the stringent environmental control and optimizing the excitation light dose by (i) using a low-power pulsed blue light-emitting diode with short pulse duration of 1.29 ms and (ii) adding a nontoxic fluorescent dye called carboxyfluorescein-diacetate-succinimidyl-ester (CFSE) to improve the fluorescence signals. To demonstrate the usefulness of the strategy, fluorescence signals and proliferation of dual-marked cells, during 5-h fluorescence imaging under pulsed excitation, were compared with those kept under continuous excitation and nonmarked reference cells. The results demonstrated 3% cell division and 2% apoptosis due to pulsed excitation compared to no division and 85% apoptosis under the continuous irradiation. Therefore, our strategy allows live cell imaging to be performed over longer time scales than with conventional continuous excitation.     

Assessment of collagen fibril spacing in relation to selected region of interest (ROI) on electron micrographs--application to the mammalian corneal stroma

AIMS: To evaluate measurements of collagen fibril spacing using different shaped regions of interest (ROI) on transmission electron micrograph (TEM) images of rabbit corneal stroma. METHODS: Following glutaraldehyde fixation and phosphotungstic acid staining, TEM images of collagen fibrils in cross section were projected at a final magnification close to 250,000 × to obtain overlays. Interfibril distances (IFDs; center‐to‐center spacing) were measured within different ROIs of the same nominal area (0.25 μm²) but different shape (with the length to width, L:W, ratio from 1:1 to 6:1). The IFD distribution was analyzed, and the 2D organization assessed using a radial distribution analysis. RESULTS: The fibrils had an average diameter of 35.3 ± 3.8 (SD) nm, packing density of 393 ± 4 fibrils / μm² and a fibril volume fraction of 0.39 ± 0.02. IFDs ranged from 29 to 1400 nm depending on the shape of the ROI, with average values ranging from 263 to 443 nm. By artificially selecting IFD data only to a radial distance of 250 nm, the average IFDs were just 145–157 nm. The radial distributions, to 250 nm, all showed a nearest neighbors first peak which shifted slightly from predominantly at 45–54 nm with more rectangular ROIs. The radial distribution profiles could be shown to be statistically different if the ROI L:W ratio was 2:1 or greater. CONCLUSION: Selection of an ROI for assessment of packing density and interfibril distances should be standardized for comparative assessments of TEMs of collagen fibrils. Microsc. Res. Tech., 2011. © 2011 Wiley‐Liss, Inc.