摘要:

SUMMARYThe performance of many electron optical instruments is fundamentally limited by the dimensions of the focused probe. This is true of the scanning electron microscope and the scanning transmission electron microscope and, by inference, it may affect the transmission electron microscope. There has been very little improvement over the past few years and it seems reasonable to look for the explanation. It is possible to arrive at some simple expressions for the limiting performances of conventional instruments in a way that is independent of the design details and depends upon practical limits of field strength. Experiment and theory also appear to be in agreement with the fact that the limit for high‐voltage instruments has been reached, although there is still room for improvement for low voltage

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03584.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARYMarine aggregates were examined for the first time in the hydrated state using an environmental scanning electron microscope (ESEM). Sample preparation consisted of fixation followed by rinsing with distilled water to remove excess salts and fixative. Aggregates were continuously observed at resolutions comparable to conventional scanning electron microscopy through stages of hydration, from completely immersed to desiccated. Because no metallic coating is required, energy‐dispersive X‐ray spectroscopy (EDXS) can be used to analyse rapidly constituent elements occurring at low concentrations with no spectral interference. Subtle differences in mineral particles were seen in both EDXS spectra and in direct observation of relative hydration, reflecting apparent differences in mineralogy. ESEM enabled examination of effects of desiccation and rehydration on individual particles composed primarily of hydrated polymer and eliminated dehydration artefacts in delicate organi

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03585.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARYWith increasing frequency, cellular organelles and nuclear structures are being investigated at high resolution using electron microscopic tomography of thick sections (0·3–1·0 μm). In order to reconstruct the structures in three dimensions accurately from the observed image intensities, it is essential to understand the relationship between the image intensity and the specimen mass density. The imaging of thick specimens is complicated by the large fraction of multiple scattering which gives rise to incoherent and partially coherent image components. Here we investigate the mechanism of image formation for thick biological specimens at 200 and 300 keV in order to resolve the coherent scattering component from the incoherent (multiple scattering) components.Two techniques were used: electron energy‐loss spectroscopic imaging (ESI) and exit wavefront reconstruction using a through‐focus series. Although it is commonly assumed that image formation of thick specimens is dominated by amplitude (absorption) contrast, we have found that for conventionally stained biological specimens phase contrast contributes significantly, and that at resolutions better than ∼10 nm, superposed phase contrast dominates. It is shown that the decrease in coherent scattering with specimen thickness is directly related to the increase in multiple scattering. It is further shown that exit wavefront reconstruction can exclude the microscope aberrations as well as the multiple scattering component from the image formation. Since most of the inelastic scattering with these thick specimens is actually multiple inelastic scattering, it is demonstrated that exit wavefront reconstruction can act as a partial energy filter. By virtue of excluding the multiple scattering, the ‘restored’ images display enhanced contrast and resolution.These findings have direct implications for the three‐dimensional reconstruction of thick biological specimens, where a simple direct relationship between image intensity and mass density was assumed, and the aberrations were

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03586.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARYDifferent fractions of a mixture of protein–pigment complexes have been separated from one another by non‐denaturing gel electrophoresis. These complexes were prepared for observation by inserting electron microscope grids directly into the focused bands of the pigment–protein complexes and resuming electrophoresis for a brief time, so that the complexes were deposited onto the grids. It was found that complexes deposited from each band exhibited distinctly different appearances. It was also found that the exact conditions of electrophoretic deposition onto the grids affected the appearance of the complexes. The protein–pigment complexes were characterized additionally by spectroscopy and denaturing gel electrop

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03587.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARYInformation about the properties of materials in acoustic microscopy can be obtained in the form of theV(Z) curves. The purpose of this paper is to present the theoretical and experimental study of theV(Z) curve formation for solid spheres. It is shown that an investigation of the position of different peaks in theV(Z) curves is useful to determine the size and acoustical properties of a spherical particle.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03588.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARYThe chemical microstructure of Ni‐base superalloy/Al2O3metal‐matrix composites (MMCs) has been studied by scanning ion microprobe microanalysis, using the secondary ion mass spectrometry (SIMS) technique. The MMCs were fabricated using the transient‐liquid‐phase bonding (TLP) process, with B‐doped superalloy powder as an interlayer. Boron was found to diffuse rapidly throughout the matrix to form boride phases, mostly at the grain boundaries in the matrix. These borides contain excess Cr (also Mo, Si, W) in comparison with the Ni alloy‐matrix, but are depleted in Ni (also in Al and Co). Carbides form at the grain boundaries as thin platelets and inside the grains as fine particles. Chemical reaction occurs between the sapphire fibre and the matrix; formation of NiAl2O4spinel at the interface is suggested. This interface reaction layer is friable and parts of it peel off during consolidation to become inclusions in the matrix near the fibre/matri

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03589.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARYThe area of an individual bounded surface (e.g. the boundary of a properly sampled cell) can be estimated from an isotropic uniform random stack of parallel sections, or of non‐invasive planar scans, using the well‐known spatial grid. A standing problem was to estimate the area of an individual bounded surface with an arbitrary degree of accuracy from a vertical (i.e. not isotropic) stack of sections or scans. A new tool to do this, called the ‘vertical spatial grid’, is pr

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03590.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARYPrevious stereological approaches to estimate feature length include isotropic sections, which tend to be inefficient for highly anisotropic structures such as skeletal muscle capillaries, and semiparametric model‐based methods, which require transverse and longitudinal sections only, but are biased to a variable, unknown degree. The recent method of vertical slices combines the advantages of both approaches, namely it is unbiased, efficient and convenient. This study illustrates for the first time how to apply the vertical slices method in biology by direct light microscopy and intersection counting with a properly orientated cycloid test system. Neither image processing nor confocal microscopy are used. The purpose of the study was to estimate capillary length in the left ventricle of rat heart. Beyond this, a novel histochemical method enables the staining of the venular capillary region in red and the arteriolar capillary region in blue, and hence estimates their separate lengths. The vertical slices method to estimate feature length seems to be a promising approach for biolog

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03591.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARYThree‐dimensional reconstructions of biological structures can be obtained by the use of serial sections, tomography, confocal microscopy techniques and X‐ray crystallography. The earliest reconstructions were achieved manually, but semi‐automatic and automatic techniques are now available. Tissue studied by microscopy contains structures of greatly varying dimensions. When producing a three‐dimensional reconstruction of the contours of the spinal cord and its white and grey matter, greater magnification of the fine nerve endings may provide additional information. However, reconstruction at different magnifications of the structures of interest cannot be achieved automatically, but requires manual delineation of the structures. A method is described in which a commercial program was used to provide a wire‐frame reconstruction which had been drawn by hand. The data were processed further to obtain a realistic image which could be rotated to provide details of the three‐dimensional relationships of the spinal cord structures. This technique is useful when relationships and details are otherwise difficult to comprehend due to large size

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03592.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARYQuantitative studies of three‐dimensional (3‐D) structure of microscopic objects have been made possible through the introduction of microscopic volume imaging techniques, most notably the confocal fluorescence microscope (CFM). Although the CFM is a true volume imager, its specific imaging properties give rise to distortions in the images and hamper subsequent quantitative analysis. Therefore, it is a prerequisite that confocal images are restored prior to analysis. The distortions can be divided into several categories: attenuation of areas in the image due to self‐absorption, bleaching effects, geometrical effects and distortions due to diffraction effects. Of these, absorption and diffraction effects are the most important. This paper describes a method aimed at the correction of diffraction‐induced distortions. All the steps necessary in restoring confocal images are discussed, including a novel method to measure instrumental properties on a routine basis. To test the restoration procedure an image of a fluorescent planar object was restored. The results show a considerable improvement in the z‐resolution and no ringing artefacts. The relevance of the method for image analysis is demonstrated by a comparison of results of applying 3‐D texture analysis to restored and unrestored images of a synthetic object. Furthermore, the method can be successfully applied to noisy fluorescence images of biological objects, such as interphase

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1995.tb03593.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY