摘要:

SUMMARYTo reach the 0·2 nm point‐to‐point resolution possible with some high voltage electron microscopes, the astigmatism of the objective lens must be compensated to within 5 nm. Due to a number of factors the resolution of the image seen on the viewing screen of the high voltage microscope is, however, quite poor and does not permit compensation of such accuracy.We describe a technique for evaluating and correcting the astigmatism that starts from a recorded micrograph of a thin amorphous specimen. The astigmatism is determined from the optical diffraction pattern using a variation of the Thon method. This variation avoids any direct measurement of the radii of the contrast transfer zones, and is extremely rapid and convenient. Adjusting the stigmator coil currents, calibrated in terms of their stigmating power, for zero astigmatism completes the correction in less than 10 min after the recording of the microg

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1977.tb00068.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARYDifferent spacing factors and various orientation efficiency factors, applied to characterize the spatial distribution of the (steel) fibres in fibre reinforced cementitious materials, cannot constitute a sound basis for a mutual comparison of experiments or for an evaluation of experiments in a fracture mechanical sense.This paper therefore presents a complete framework, based on geometrical probability theory, providing the investigator with methods to obtain three‐dimensional information from two‐dimensional images produced by X‐ray radiography. In this approach the fibres are assumed to be disposed in such a way that on the average a partially planar‐oriented structure is obtained. In addition, because of their high aspect ratio, the fibres are considered to be lineal features.Two methods are elaborated, i.e. the feature counting technique and the method of directed secants. These operations have to be performed in the projection plane. Both methods yield data on the degree of inhomogeneity (segregation) and the degree of orientation (anisometry), as well as on spacing and orientation efficiency. By substituting design data in the presented formulae, this framework can also serve to characterize the spatial properties of the fibre structure in the designed mix.The application of the theory is illustrated with the help of data that confirm the occurrence of segregation and preferred orientation effects due to vibration of the sp

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1977.tb00069.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARYMyocardial tissue was quickly quench‐frozen by letting the specimen fall either into liquid nitrogen (LN2) or into LN2‐slush, or, by drill‐propelling the specimen into LN2at a speed of 1·5 m/s. The preservation of the tissues was studied in ultra‐thin, dry‐cut and freeze‐dried cryo‐sections. Shock‐freezing by propelling into LN2yields extensive areas of well preserved tissue without hole damage. Quenching into LN2‐slush shows variable results, while a maximum of hole damage is obtained by letting the specimen fall into LN2. Replicas of freeze‐fractured tissue which had been quench‐frozen by the same methods confirmed these observations. By the drill‐propelling, areas 2000–5000 μm2wide reveal good preservation without visible ice crystals. Such areas occur within a superficial band of tissue to a depth ofc.20 μm. Even at 35 μm and 50 μm depth good preservation may be registered at the periphery of the replicas.Description is given of modifications in accessories and methods in order to make the LKB CryoKit more suitable as a routine instrument. These modifications cover replacement of the knife coolant container by a coolant brass container in open connection with three copper tubes, replacement of one of the LKB Dewar flasks by a 25 litre Dewar equipped with a Balzers filling device, and replacement of the LKB plastic sleeve fixed to the back of the specimen coolant container, by two perspex‐glass discs mounted in the slit between the Ultrotome base and the cryo‐chamber. In addition, modified constructions are presented of the grid‐carrier, the press‐assembly as well as of the container for freeze‐dryi

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1977.tb00070.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARYA resistance monitor with sensors and automatic power cut‐off has been developed to control the thickness of Pt‐C shadow and C replica films in freeze‐etching and related techniques. The monitor and sensors, in conjunction with newly modified evaporators, should considerably reduce the amount of C and Pt required and should prove useful in other applications employing vacuum evaporation of thin films of Pt, C, or other conducting mate

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1977.tb00071.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARYA catalogue of the Schlegel graphs of all the three‐valent tetrakaidecahedra with faces having at least four edges and at most six edges is presented. These fifty‐nine polyhedra can be used for all purposes in stereology, either as morphological models of grains in microscopic studies of all kinds of materials where the unit cells are supposed in equilibrium, for the experimental and theoretical study of three‐dimensional packing and non‐packing problems or as a conceptual basis for the theoretical frequency computation of occurrences of the different types of polygons in materials observed in slides or polished s

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1977.tb00072.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARYThe oil emulsion technique has been applied to rat brain and liver tissue for freeze‐etching preparation without antifreeze pretreatment. It has been demonstrated that the dispersed tissue exhibits a high degree of vitrification throughout the mostly globular fragments up to at least 30 μm in diameter. Signs of insignificant ice crystal formation of 50 nm and less could only rarely be detected. Although the dispersion process seriously affects the tissue organization as a whole, most cellular organelles and the plasma membrane show satisfactory preservation of structure. In larger tissue drops, a local overall structural preservation of the original cellular organization is recognizable. The results obtained demonstrate the applicability of this method to various biological objects for realizing sufficient cryofixation in the absence of cryoprotectan

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1977.tb00073.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARYA simple low‐cost critical point dryer with continuous flow dehydration attachment is described. By using the critical point pressure chamber for all fluid exchanges, loss of material and air‐drying artefacts due to specimen handling are reduced. An operating schedule that allows the optimum path around the critical point process to be followed is propo

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1977.tb00074.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARYBased on the idea of a spring‐loaded microscope objective, a boring attachment has been designed and constructed to fit a standard revolving multi‐objective holder. It enables many small specific areas of a slide embedded specimen to be selected, ringed and bored out without removing the slide from the microscope st

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1977.tb00075.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY