ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03830.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYMethods of analysing electron micrographs are reviewed, with special reference to the needs of the practising electron microscopist. It is concluded that a simplified optical diffractometer and a projection ‘Periodograph’ can be particularly helpful, especially in biological investigations, to which extensive reference is made in the bibliogra

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03831.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYA systematic account is given, in relation to amorphous and paracrystalline (especially biological) material, of electron scattering and image formation for the range of electron energy from 50 to 100 keV. Contrast mechanisms in both elastic and inelastic scattering are discussed and image formation is considered under both scattering contrast and phase contrast conditions.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03832.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYFor the practical biologist applying electron microscopy to the study of biological macromolecules, there are serious problems in obtaining high resolution images showing detail below 2.5–3.0 nm. The limitation in resolution from biological specimens can be attributed to support film thickness and granularity, specimen preparation, irradiation damage, focusing effects and possible contamination in the electron beam. Specimens possessing repeating features can be analysed and averaged by optical diffraction and image reconstruction methods which offer some improvement to the signal to noise ratio. The above problems, with particular reference to irradiation damage, still impose the basic limitation for high resolution applications. When considered together they offer formidable difficulties in practical terms in attempting to make full use of the potential resolving power of modern electron microscope

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03833.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe properties of two electron microscope phase contrast imaging methods are compared. The first is the conventional bright‐field method in which dark phase contrast is created by defocusing; the second is a phase plate method in which bright phase contrast is created by means of a suitably shaped electric field.Using some negatively stained biological specimens which have a well‐known repeating structure as the test object, it is shown that the phase plate method has some important advantages over the bright‐field method. Its contrast transfer characteristics are such that it can provide a more faithful representation of the high resolution detail in the object. Moreover, by producing bright, rather than the normal dark, phase contrast it is able to simultaneously enhance the detail in the specimen and weaken the detail in the stain; this latter property enables the method to display information about the specimen that it would not be possible to detect with the bright‐field

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03834.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe theory of defocusing phase contrast is presented in terms of Scherzer's (1949) ‘integrated‐ray’ and Heidenreich's (1964) ‘single‐ray’ approach to spherical aberration; contrast transfer theory in terms of the Scherzer expression is included. Fine structure in transverse sections, negative stain and carbon film is shown to be the result of defocusing phase contrast. Examples of interpretative confusion are given for various macromolecular systems and quantitative support is found for a simplified ‘rule‐of‐thumb’ approach to phase‐contrast enhancement. High‐resolution studies of carbon‐fibre lattices demonstrate contrast reversal, hence it is possible to show that a practical expression for the phase change due to spherical aberration falls between the Scherzer and the Heidenreich terms; the defocus term is also found t

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03835.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYA review of electron diffraction studies of polypeptide structures is given together with a discussion of the methods for obtaining diffraction patterns without serious specimen damage by electrons. Electron diffraction studies of poly‐β‐benzyl‐L‐aspartate show that diffraction intensities can be used quantitatively to determine polypeptide structures and the advantages of these studies in observing high angle meridional reflections are shown up by the observation of a novel structure in the unheated left handed helical form of the polypeptide. A large catalogue of techniques for preparing orientated films of polypeptides suitable for electron diffraction investigations makes the technique a powerful one for studying these structures. Polypeptides are shown to be useful for studying electron beam damage in protein‐like

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03836.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYIn the last few years some promising images of biological specimens have been obtained using the high contrast and resolution of dark‐field electron microscopy. However, important problems of image interpretation and difficulties in specimen preparation limit at the present time, the usefulness of this mode of image formation. The destruction of the sample by the electron beam, is of utmost importance. Some possibilities of partly overcoming it are discusse

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03837.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe techniques whereby an electron microscope may be used to observe the low angle electron diffraction pattern from crystallized macromolecules are described. A discussion is then presented of the advantages and disadvantages of the technique relative to X‐ray diffraction, high resolution electron microscopy and optical diffraction or computer analysis of electron micrograph

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03838.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThis paper endeavours to give all the necessary practical information to operate with the contrast‐stop method as far as fairly thick objects (from 10 to 100 nm) are concerned; including working diagrams, practical operation out of the stops and also to define the range of application of this method. It is shown that false detail is not to be feared in these rather thick specimens, which is not at variance with the results obtained by Hanszen (1967, 1969) and Thon (1966) as far as very thin specimens are concerne

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03839.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY