Color cathodoluminescence display in the scanning electron microscope of deep relief surfaces

A scanning electron microscope (SEM) is a multifunctional instrument for the measurement of topographic relief on the surface of bulk specimen images. This instrument is also available to detect the physical effects induced by an electron beam into subsurface layers. Space distribution of the physical properties of measured effects in the relative microrelief is a very important problem in the SEM. We describe a method of displaying specimen information in the SEM using the color cathodoluminescence (CCL-SEM) technique nondistorted by relief influence and CCL-SEM images with composite (color and black / white ) contrast using CCL+BSEmode.     

Theoretical explanation of the relationship between backscattered electron and x-ray linear attenuation coefficients in calcified tissues

X-ray absorption and backscattered electron (BSE) microscopies are two commonly used techniques for estimating mineral contents in calcified tissues. The resolution in BSE images is usually higher than in x-ray images, but due to the previous lack of good standards to quantify the grey levels in BSE images of bones and teeth, x-ray microtomog-raphy (XMT) images of the same specimens have been used for calibration. However, the physics of these two techniques is different: for a specimen with a given composition, the x-ray linear attenuation coefficient is proportional to density, but there is no such relation with the BSE coefficient. To understand the reason that this calibration appears to be valid, the behaviour of simulated bone samples was investigated. In this, the bone samples were modelled as having three phases: hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂), protein, and void (either empty or completely filled with polymethylmethacrylate (PMMA), a resin which is usually used for embedding bones and teeth in microscopic studies). The x-ray linear attenuation coefficients (calculated using published data) and the BSE coefficients (calculated using Monte Carlo simulation) were compared for samples of various phase proportions. It was found that the BSE coefficient correlated only with the x-ray attenuation coefficient for samples with PMMA infiltration. This was attributed to the properties of PMMA (density and mean atomic number) being very similar to those of the protein; therefore, the sample behaves like a two-phase system which allows the establishment of a monotonic relation between density and BSE coefficient. With the newly developed standards (brominated and iodinated dimethacrylate esters) for BSE microscopy of bone, grey levels can be converted to absolute BSE coefficients by linear interpolation, from which equivalent densities can be determined.     

混凝土中低合金钢筋腐蚀产物的微结构分析

通过电迁移法加速了混凝土中钢筋的锈蚀进程,并利用背散射电子(BSE)图像和X射线能谱(EDS)对比研究了钢筋-混凝土界面区低合金钢筋和普通低碳钢筋腐蚀产物的微观形貌与分布规律.此外,分析了钢筋的表面状态(含氧化皮和无氧化皮)对其耐蚀性能的影响.结果表明:在加速腐蚀作用下,钢筋-混凝土界面区均由腐蚀层、局部点蚀区及腐蚀填充浆体组成;其中,含氧化皮的低碳钢筋腐蚀最严重,表现为生成更厚且分布更广的腐蚀层;而无氧化皮的低合金钢筋的腐蚀层较薄且结构更致密,并在点蚀区出现局部Cr元素富集现象,证实其具有最好的耐蚀性能.     

Detection and survival of prion agents in aquatic environments

Environmental contamination is considered a potential mechanism of transmission of prion diseases. Sheep scrapie and cervid chronic wasting diseases (CWD) epizootics are thought to be maintained by natural horizontal transmission through the environment. Here, we describe a method for the detection of prion proteins (PrPres) in aquatic environments. The procedure is based on a glycine buffer-mediated extraction, sonication, and an ultracentrifugation step. The detection limit of the method was estimated to be over 5-10 microg of infected tissue. In order to determine the inactivation of these agents, we spiked infected brain tissue in urban sewage, seawater and a buffered solution (final concentrations of 0.1-0.2% brain in matrix), and studied the decay of BSE- and scrapie-associated PrPres over time (up to 265 days). Densitometric data from Western blots were plotted in logarithmic scale against time. Reduction of PrPres titer in sewage was quantified in one logarithm after 13.5 days for BSE, 27.9 days for mouse-passaged scrapie and 32.6 days for sheep scrapie. In the buffered solution, a logarithm of BSE-associated PrPres also disappeared earlier than that of scrapie (113.9 and 214.3 days, respectively). By means of the covariance analysis, these differences in the inactivation patterns were shown to be statistically significant. According to the data, prions may be stable for extended periods of time in buffered solutions like PBS, but would show limited survival in aquatic environmental matrices.     

SEraMic: A semi-automatic method for the segmentation of grain boundaries

The SEraMic method, implemented in the SEraMic plugin for Fiji or ImageJ software, was developed to calculate a segmented image of a ceramic cross section that shows the grain boundaries. This method was used to accurately and automatically determine grain boundary positions and further assess the grain size distribution of monophasic ceramics, metals, and alloys. The only required sample preparation is polishing the cross section to a mirror-like finish. The SEraMic method is based on at least six backscattered electron scanning electron microscopy images of a unique region of interest with various tilt angles ranging from -5° to +5°, which emphasises the orientation contrasts of the grains. Because the orientation contrast varies with the incident beam angle on the sample, the set of images contains information related to all the grain boundaries. The SEraMic plugin automatically calculates and builds a segmented image of the grain boundaries from the set of tilted images. The SEraMic method was compared with classical thermal etching methods, and it was applied to determine the grain boundaries in various types of materials (oxides, phosphates, carbides, and alloys). The method remains easy to use and accurate when the average grain diameter is greater than or equal to 0.25 μm.     

Risk assessment for prion protein reduction under the conditions of the biodiesel production process

Due to the increased demand for biofuels, all different feedstocks from oils and fats have to be considered for biodiesel production. Animal fats have proved to be excellent sources for biodiesel due to their high cetane number and good stability. Large amounts of fat from so‐called high‐risk material, possibly contaminated with infectious prions, are available for biodiesel production. In this paper, the grade of destruction of prions during the biodiesel production process, including pre‐esterification with conc. sulfuric acid followed by KOH‐catalyzed transesterification, was studied. The starting material of the different production steps was spiked with purified and highly infectious prion rods, and the destruction of these prions was determined by gel electrophoresis (SDS‐PAGE) and Western blot. The pre‐esterification step led to a destruction factor of at least 100, the transesterification led to a factor of at least 250, and the distillation of the final biodiesel showed a destruction factor of at least 1000. During all experiments, no traces of prions could be detected after the different reaction steps. Based on these data, a complete and unequivocal risk assessment regarding the industrial process of biodiesel production was carried out, leading to a calculated overall risk of 5.8×10^?15 ID₅₀ units/person and year, which means that a hypothetical BSE contamination from biodiesel is more than 10⁹ times lower than the background risk.     

Backscattered electron imaging of titanium dioxide in frozen hydrated preparations

Backscattered electron (BSE) imaging was used to study ultrafine TiO₂ crystals distribution in a test cream. The cream was fast frozen, cryofractured and observed uncoated at low temperature. The BSE detector was a microchannel plate. The results demonstrate that up-to-date photoprotective preparations can be investigated by this technique.