摘要:

AbstractElectron diffraction patterns generated from phases that have low crystallographic symmetry are difficult and tedious to analyze by conventional techniques. This paper describes a computation scheme that can index electron diffraction patterns efficiently and quickly and be easily implemented on a personal computer. The technique is based on sorting and searching and is especially useful when rapid analyses of electron diffraction patterns are necessary and the crystalline phase under study has a low symmetry.

ISSN:0741-0581    

DOI:10.1002/jemt.1060030203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractA method for the measurement of electron probe beam diameter by digital image processing has recently been published. The purpose of the present report is to describe the development of an automatic system for beam diameter measurement. To complete this system, a method based on a theory which combines automation and high‐resolution conditions is proposed. In practice, the beam diameter is measured from the STEM image of a crystalline hole in a gold thin film, utilizing an on‐line computer system equipped with newly developed digital processing programs linked to a SEM in the transmission mode. The functions of the programs include statistical processing, matching, noise removal, interpolation, selection, and rotation. By combining these functions, the scanning beam diameter is accurately measured, in spite of difficulties, under most electron microscope operating conditions. The user simply appoints the edge included in the STEM im

ISSN:0741-0581    

DOI:10.1002/jemt.1060030204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractThis work employs a Fortran program to simulate rotary shadowing, that is, metal evaporation deposits in which the substrate is rotating during the deposition process. The results are compared with computer simulations of unidirectional shadowing published in a previous paper. (See Colquhoun et al., 1985). The analysis shows that a substantial improvement in resolution is possible with rotary shadowing. The improved information retrieval amounts to ∼15% with a shadow angle of 33° and ∼37% with a shadow angle of 8°. Unidirectional shadowing results in a grain linearity; the computer simulations show that this undesirable effect is eliminated by the rotary process.These advantages of rotary shadowing are discussed along with the more straight forward interpretability of the rotary shadowed images. These advantages are weighed against the higher contrast generated by the unidirectional shadowing pr

ISSN:0741-0581    

DOI:10.1002/jemt.1060030205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractMost of our current knowledge of cellular ultrastructure is derived from studies of chemically fixed and chemically cryoprotected preparations. In the first part of this review, we document the many artifacts associated with chemical techniques that render them unsuitable for further refinement of our understanding of cellular ultrastructure. The best method currently available for the preservation of cellular ultrastructure is ultrarapid freezing. The second part of this review is a consideration of the physics of ice crystal formation in biological systems, which suggests that ice crystals will be present in any frozen, uncryoprotected specimen. We define an ultrarapidly frozen preparation as one in which the ice crystals are so small as to be invisible at the electron microscopic level. Improvements in the ease of application and reliability of ultrarapid freezing techniques have reached the point that these techniques can be used by anyone requiring the best achievable preservation of cellular ultrastructure. In the third part of this review, we describe and critique the five methods of ultrarapid freezing in current use.

ISSN:0741-0581    

DOI:10.1002/jemt.1060030206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractGlutaraldehyde‐fixed insects were embedded in Tissue‐TekRand sectioned on a liquid‐nitrogen‐cooled stage. The sections were sandwiched between two layers of microscope lens paper and all postsectioning treatments were carried out on this sandwich, including dehydration and critical‐point drying. In some cases, the sections were placed on filter membranes and lyophilized. These procedures produced intact specimens which maintained internal morphology as well as inter‐ and intracellular integrity without expensive or specialize

ISSN:0741-0581    

DOI:10.1002/jemt.1060030207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractEase of cutting thin sections with glass knives is markedly improved if the embedding resin contains a surfactant such as lecithin. With lecithin, it is possible to cut 50–100 thin sections from the same place on the knife edge even after facing off the block with 1–2‐μm‐thick sections. Image quality is similar to that of the unmodified resin if the resin formula is optimized. If not, some chatter or a “mottled” appearance of the tissue image may be present. Lecithin does not significantly affect sectioning with a diamond knife or the appearance of the section in the microscope. The increased ease of sectioning with glass presumably will be translated to diamond knives in the form of an increased useful life of the

ISSN:0741-0581    

DOI:10.1002/jemt.1060030208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractMicrotubules and associated structures are among the more difficult samples studied by 3D reconstruction techniques because of their size, complexity, and lability. Nevertheless, their importance in many cellular functions often justifies efforts to acquire 3D information up to the resolution limit of negatively stained specimens or beyond. A combined approach which utilizes methods appropriate to both helical symmetry and 2D crystal lattices seems to provide the surest route to 3D reconstruction. Images of unstained specimens obtained by newer techniques of microscopy present challenging problems in data analysis, but potentially offer higher‐resolution informatio

ISSN:0741-0581    

DOI:10.1002/jemt.1060030209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractIn conventional freeze‐fracture replicas produced from tissue cryoprotected with glycerol, the hydrophobic inner surfaces of membranes are revealed, but hydrophillic structures are obscured in the surrounding ice. Quick‐freezing of tissue obviates the need for glycerol, which prevents the removal of this ice by etching or freeze‐drying, but the major problem in freezing without glycerol cryoprotection is ice crystal formation. We describe here a simple method for quick‐freezing tissue, in the absence of glycerol, on a nitrogen‐cooled copper block with a hand‐held specimen holder. This method freezes samples well enough to preserve molecular detail that can be revealed by subsequent etching. We show some examples of the quality of this freezing with respect to the visualization of molecular detail in isolated protein molecules such as ferritin and catalase. Furthermore, we show examples of in situ cellular structures that are revealed by this method, and we compare the structure seen in these replicas with structures preserved by quick‐freezing at liquid helium

ISSN:0741-0581    

DOI:10.1002/jemt.1060030210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060030202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY