ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03411.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryA compact Schwarzschild soft X‐ray microscope using a laser‐produced plasma soft X‐ray source has been developed. The laser‐produced plasma source, which is small but of high brilliance, has made it possible to use the soft X‐ray microscope in a small laboratory. The microscope is composed of a Schwarzschild objective and a grazing incidence mirror condenser. Image contrast for biological specimens in soft X‐ray regions is investigated briefly. It is possible to observe the fine structures of a thin specimen at a wavelength of 15 nm; at this wavelength high‐contrast images of biological specimens have been obtained with a single laser shot of pulse width of 8 ns at a resolution of 0·3 μm. The resolution of the system is limited

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03412.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryCertain liquids with a very low vapour pressure, such as glycerol or triethylene glycol, can be used to infiltrate biological specimens so that they may be observed in the scanning electron microscope (SEM) without drying. The conductive properties of the fluids allow specimens to be examined either uncoated or with very thin coatings. The advantages of liquid substitution include the retention of lipids, waxes, loose particles, and surface contaminants. Since the procedure does not require expensive equipment, it offers an alternative to critical point drying or cryo‐preparation. For certain types of specimens, liquid substitution may represent the best preparation procedure. In addition, the fluids themselves may be imaged directly in the SEM, or indirectly by cathodoluminescence following labelling with fluorochrome

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03413.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryOptimized fixation conditions were determined for protein‐protein and protein‐DNA crosslinking within calf‐thymus nucleosomes in low monovalent salt concentrations. Nucleosomes were examined without heavy‐atom staining by darkfield electron microscopy. The dimensions of these macromolecular complexes and those of HeLa core particles optimally fixed in divalent salt were analysed using principal component analysis. According to this analysis the structure of the calf‐thymus nucleosomes was best presented by a prolate ellipsoid. Particle images had average major and minor axis lengths of 14·1 and 10·5 nm, respectively. In contrast, the HeLa nucleosomes were best modelled by an oblate ellipsoid from the analysis of their images, which had average major and minor axes of 13·3 and 11·5 nm. The applicability of this multivariate statistical analysis to the interpretation of macromolecular images is illustrated

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03414.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryScanning tunnelling microscopy is developing as an important biophysical tool for the molecular imaging of biological material. In this study, the effect of sample deposition technique and substrate employed on the resultant images of a microbial polysaccharide is investigated. Scanning tunnelling microscopy topographs of xanthan gum, pipette deposited and spray deposited onto highly orientated pyrolytic graphite and mica substrates are presented. The use of pipette deposition of the aqueous sample solution is shown to result in a xanthan network. In contrast, images of isolated xanthan molecules are obtained when spray deposition with glycerol is employed. The effect of these deposition techniques on the macroscopic distribution of sample material across substrates is shown using confocal fluorescence microscopy.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03415.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryA study of the quality and accuracy of the methods based on frequency analysis for the fractal characterization of surfaces as measured by scanning tunnelling microscopy (or profilometry) is made. The study is based on computer simulation of images of fractal surfaces. A discussion of the mathematical algorithms used for computer generation of fractal surfaces then follows. The main conclusion is that studies of fractal characterization by frequency analysis reported in previous papers in the STM field, as well as conclusions about the performance of the various methods, are doubtful. New methods for frequency analysis that in some cases produce more reliable results are proposed.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03416.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryA new frequency analysis method, fractal analysis by circular average (FACA), and an image replication procedure are proposed that together produce accurate measurements of the fractal dimension of surfaces and profiles, eliminating Fourier transform artefacts which arise from the lack of periodic continuity in real surfaces and profiles.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03417.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryMeasurement of the fractal dimension of surfaces imaged by the scanning tunnelling microscope, atomic force microscope or similar instruments can be performed using several different algorithms. Dimensional analysis—plots of log (perimeter) vs. log (area)—are compared to Korcak and slit‐island methods, which also employ a horizontal plane section, and to Fourier analysis of the two‐dimensional array of elevation values. The effects of surface anisotropy and instrument noise on each of these measurement techniques is inves

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03418.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummarySystematic sampling designs are widely used in stereology. When an estimator of the total amount,Q, of the sampled variable is evaluated by such a procedure, the coefficient of error can be predicted by applying Matheron's theory of regionalized variables. To evaluate the accuracy of the estimate ofQ, it is necessary to study the behaviour of the regionalized variable and to model its covariogram. Histological data with a low short‐range variability and agronomic data with a pronounced nugget effect provided the biological material for extreme case studies. Results show that the short‐range variability, if present, cannot be detected when only small samples are available. An underestimation of the coefficient of error is then to be expected. We propose several models of the covariogram, which can be used to test for the presence of a nugget effect. If a nugget effect is present, these models will provide better estimates of the coefficient of error. If there is no nugget effect a simplified method can be used and will provide reliable estimates of the coefficient of er

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03419.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThis paper discusses the problem of determining suitable roses of intersections for systems of planar thick fibres which cross and overlap. A planar Boolean model with long rectangular (or similar) grains is suggested as an appropriate mathematical model. It leads to a statistical estimator for the rose of intersections of the system of fibre spines. The method is used to analyse the microstructure of the outer layer of two samples of cardboard.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1993.tb03420.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY