bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and assessment of frozen‐hydrated sections of mammalian tissue for electron microscopy and X‐ray microprobe analysis
Authors: Ross A. , Sumner A. T. , Ross A. R. 
Published: August 2011

SUMMARYA system is described for preparing and examining frozen‐hydrated sections of mammalian tissue, using commercially available equipment. An essential part of the system is a liquid nitrogen cooled vacuum transfer system. Minor modifications were required to interface the various manufacturers' equipment, and also to facilitate handling of specimens in the cryoultramicrotome. A variety of criteria indicates that our sections are truly frozen‐hydrated, but negligible image contrast in the sections is a serious problem both for morphological work and X‐ray microanalysis.
The microscopes of Antoni van Leeuwenhoek
Authors: van Zuylen J. 
Published: August 2011

SUMMARYThe seventeenth‐century Dutch microscopist, Antoni van Leeuwenhoek, was the first man to make a protracted study of microscopical objects, and, unlike his contemporary Robert Hooke, he viewed by transmitted light. Leeuwenhoek made over 500 of his own, curious, simple microscopes, but now only nine are known to exist. The exact nature of the lenses Leeuwenhoek made, has for long been a puzzle. The existing microscopes have now been examined in detail, and their optical characteristics measured and tabulated. It is proposed that the lens of highest magnification, x 266, was made using a special blown bubble technique.
An integrated electron and optical metallographic procedure for the identification of precipitate phases in type 316 stainless steel
Authors: Slattery G. F. , O'Riordan P. , Lambert M. E. , Green S. M. 
Published: August 2011

SUMMARYA sequential and integrated metallographic procedure has been developed and successfully employed to differentiate between carbide, sigma, chi, Laves and ferrite phases which are commonly encountered in type 316 austenitic steel. The experimental techniques of optical and electron microscopy to identify these phases have been outlined and provide a rapid and convenient method of characterizing the microstructure of the steel. The techniques sequence involves selective metallographic etching, Nomarski interference microscopy, scanning electron microscopy, energy dispersive microanalysis, transmission electron microscopy and electron diffraction.
Distribution curves of sectional areas through some families of convex particles
Authors: Paul J. Lawrence 
Published: August 2011

SUMMARYWe outline the results of a computer program which calculates frequency distributions of functions of cross‐sectional regions of convex planar‐faced polyhedra, ‘sphero‐polyhedra’, and populations of perturbed polyhedra. This is done by ‘cutting’ a computer representation of the figure by a large number of random planes. The procedure is applied to cubes, dodecahedra, truncated octahedra, and approximate β‐tetrakaidecahedra. Certain aspects of the shape of the object, e.g. sharpness of corners, angularity, compactness, and degree of symmetry are related to aspects of the shape of the distribution curves, e.g. beginning and ending points of the curves, rate of rise of the peak, relative location of the peak, and height and width of the peak.
Preparation of P‐47 scintillators for STEM
Authors: Baumann W. , Niemietz A. , Reimer L. , Volbert B. 
Published: August 2011

SUMMARYUniform P‐47 powder scintillators can be prepared with reproducible mass thicknesses by sedimenting the powder in an 0·01% solution of formvar in chloroform. A reflecting coating can be glued by floating a 60 nm aluminium film on the scintillation layer in an 0·1% solution of gelatine in water. The optimum thickness of P‐47 for 20–100 keV electrons increases slower than the electron range due to the absorption and scattering of light with increasing thickness. An aluminium coating increases the light output by a factor 1·85 for 20 keV and 1·4 for 100 keV electrons. The noise of the emitted light quanta and the photomultiplier detection system shows a minimum for the optimum thickness of largest light output and is only a factor 1·3–1·6 larger than the calculated shot noise of the incident electron beam.
Excitation under the scanning electron microscope of DNA‐associated fluorescence from chicken erythrocyte nuclei, polytene chromosomes and adenovirus 2 virions
Authors: Hough Paul V. C. , McKinney Wayne R. 
Published: August 2011

Biological structures not seen by conventional light microscopy, such as longitudinal striations in polytene chromosomes, and, at the limit of sensitivity, virions of adenovirus 2, have been detected via DNA‐associated fluorescence excited under the scanning electron microscope. The maximum sensitivity realized, about 1 detected photon per 700 base pairs, falls short by about an order of magnitude of that required to achieve, in unreplicated specimens, the 2 nm intrinsic resolution of the method. A combination of D2O‐H2O substitution with freeze‐drying provides the best unquenching procedure found for in situ DNA.DNA‐associated fluorescence for light microscopy can be created by moderate exposure of the specimen in the electron microscope.
The characterization of periodic dislocation arrays from the fine structure of electron diffraction patterns
Authors: Morton A. J. 
Published: August 2011

SUMMARYThe accuracy of the technique of using the fine‐structure observed in electron diffraction patterns to determine the periodicity and characteristic direction associated with a periodic strain field is assessed. This is done by applying the technique to dislocation multipoles which have a strain field with only a single periodic component and which can be well characterized by other means. It is shown that, for such a single‐component strain field, precision measurement of the diffraction patterns combined with numerical analysis of the data allows the determination of the direction and spacing characterizing the strain field with an accuracy of about 0.25° to 1.0° in direction (depending upon periodicity) and ± 2% in spacing. This is better than can usually be achieved from measurements of corresponding features in the electron micrographs.
Sampling designs for stereology*
Authors: Cruz‐Orive Luis‐M. , Weibel Ewald R. 
Published: August 2011

SUMMARYThe purpose of this paper is to propose the necessary sampling techniques for estimating a global parameter defined in a solid opaque specimen (e.g. the total volume of mitochondria in a given liver, the total capillary surface area in a given lung, etc.). The geometry of the specimen often suggests a multi‐level or cascade sampling design at different magnifications, whereby the object phase at one level becomes the reference phase in the next level. The final parameter is then estimated as the product of the intermediate ratios with the volume of the specimen, which is estimated independently. Each level can be regarded as an independent sampling design; a given stereological project may be planned in terms of one or more of these designs.Our development is a blend of practical experience and recent theoretical advances on sampling for stereology with well‐known sampling techniques previously developed with different purposes in mind.
Spatial resolution and detection sensitivity in microanalysis by electron energy loss selected imaging
Authors: Adamson‐Sharpe K. M. , Ottensmeyer F. P. 
Published: August 2011

SUMMARYAn electron energy filter of the Castaing‐Henry type in a high resolution transmission electron microscope was tested for sensitivity and spatial resolution at a specific electron energy loss in energy selected images of a murine leukaemia virus. Electron spectroscopic images of phosphorus within the virus membrane bilayer demonstrated a best spatial resolution between 0·3 and 0·5 nm and a sensitivity of 2 × 10−21 g.
In situ liquid propane jet‐freezing and freeze‐etching of monolayer cell cultures
Authors: Espevik Terje , Elgsaeter Arnljot 
Published: August 2011

SUMMARYA procedure for in situ liquid propane jet‐freezing of unfixed and unglycerinated monolayer cell cultures is described. We have used the method to study monolayer cultures of rat Sertoli cells and human monocytes. The described procedure gives a cooling rate during specimen freezing high enough to yield adequately frozen specimens even in the absence of any cryo‐protectant. Use of the procedure therefore eliminates artefacts usually caused by cell fixation and addition of cryoprotectives.
Scanning electron microscopy, autolysis, and irradiation as techniques for studying small intestinal morphology
Authors: Carr K. E. , Hamlet R. , Watt C. 
Published: August 2011

SUMMARYExamination of autolysed control mouse small intestine using scanning electron microscopy has revealed details of the connective tissue components of the mucosa. The cores of the villi are seen collapsed across the intervillous basin. Crypts of Lieberkuhn are seen as tubular channels stretching down from the intervillous basin. Sometimes the crypts are split in two by a connective tissue septum. The mouths of the crypts of Lieberkuhn are, in general, arranged in double rows between the single rows of villi. The ratio of number of crypts to numbers of villi was calculated as 5.01:1. This is close to the figure of 4.53:1, as quoted by Smith & Jarvis (1980) who used differential interference contrast microscopy to investigate the crypt to villus ratio. After radiation, the severe drop in the number of crypt mouths can be clearly seen by the combination of autolysis and scanning electron microscopy: the rows of crypt mouths between the villi have been lost, and many crypt mouths have been occluded by stromal tissue. The arrangement of the crypt mouths and the observation of mucosal abnormalities after irradiation have led to the postulation that cells leaving the crypt mouths move in a spiral manner towards and then up the villous surface: this postulated movement might imply an asymmetry in some properties of enterocytes. The use of scanning electron microscopy in conjugation with autolysis and irradiation has thus forced a critical re‐examination of the relationships between crypts and villi.
Cell surface distribution of fibronectin in cultures of fibroblasts and bladder derived epithelium: SEM‐immunogold localization compared to immunoperoxidase and immunofluorescence
Authors: Trejdosiewicz L. K. , Smolira M. A. , Hodges G. M. , Goodman S. L. , Livingston D. C. 
Published: August 2011

SUMMARYExpression of cell surface fibronectin in cultures of untransformed fibroblasts is well documented, but little is known of its presence and distribution in cultured epithelial cells. Using species monospecific anti‐fibronectin antibodies, the distribution of fibronectin in untransformed fibroblasts and in normal and neoplastic bladder epithelial cells was characterized by indirect labelling experiments using immunogold scanning electron microscopy (SEM). The surface matrix of fibronectin expressed in rodent and human fibroblast cell lines was demonstrated with ease by SEM of gold‐tagged second antibodies. However, no fibronectin could be detected on any of the mouse and human bladder epithelium‐derived cells studied in single or in mixed epithelial‐fibroblast cultures. These SEM‐immunogold observations were compared to and confirmed by immunofluorescence and immunoperoxidase microscopy. Immunofluorescence and SEM localization of the fibronectin in the extracellular matrix presented similar distribution patterns but the higher resolution of the SEM provided a more detailed analysis.
The effect of chromium and nickel on the γ→α phase transformation in steels and iron‐base alloys
Authors: Ricks R. A. , Southwick P. D. , Howell P. R. 
Published: August 2011

SUMMARYSTEM X‐ray microanalysis has been used to determine the redistribution of chromium and nickel during the austenite to ferrite and reverse ferrite to austenite transformation. This paper reports results concerning three particular systems which are representative of a large number of alloy steels and iron‐base alloys. It is shown that, in general, no partitioning of the substitutional solute is observed in the transformable alloy steel or the carbon‐free iron‐base alloy such that during the austenite to ferrite transformation the austenite maintains the same chemical composition. Conversely, for the duplex stainless steel, partitioning of the solute does occur within certain temperature ranges.The results also suggest that solute enrichment may occur at the austenite/ferrite interface which can be interpreted in terms of the existence of a ‘solute drag’ effect.
Crazes in osmium tetroxide stained styrene polymers
Authors: Kruse Robert L. 
Published: August 2011

SUMMARYCrazes in polystyrene and rubber modified polystyrene became opaque in the electron microscope after films of the polymers are exposed to osmium tetroxide. The osmium tetroxide with the polystyrene in the crazes is shown to form a flexible insoluble material that is easily folded and twisted without breaking.
Uranyl sulphate: A new negative stain for electron microscopy
Authors: Estis Leonard F. , Haschemeyer Rudy H. , Wall Joseph S. 
Published: August 2011

SUMMARYUranyl sulphate is a negative stain of high quality for electron microscopy of macromolecules below their isoelectric point. The stain results in good contrast and high resolution as demonstrated by optical diffraction of periodic structure. Analysis of scanning transmission electron microscopic data reveals that uranyl sulphate is lower in background noise level than uranyl acetate and is dramatically more resistant toward granularization upon continued exposure to electron irradiation.Electron microscopic images of most macromolecules contrasted with uranyl sulphate were indistinguishable from those obtained with uranyl acetate. However, electron microscopic images of Reo virus contrasted with uranyl sulphate are always readily distinguished from those obtained with uranyl acetate.
Stereological ratio estimation based on counts from integral test systems
Authors: Jensen E. B. , Gundersen H. J. G. 
Published: August 2011

SUMMARYThe stereological practice of using integral test systems in the estimation of the fundamental stereological ratios is studied in the light of recent theoretical developments in sampling. The estimation of a ratio is based on counts only, obtained from two, in general different, test sets constituting the integral test system. The ordinary ratio‐of‐sums estimator based on counts from uniformly positioned integral test systems is compared with two estimators based on non‐uniform, weighted sampling. It is shown that the estimators based on weighted sampling are not, in general, unbiased. Furthermore, it is pointed out that the mean‐of‐ratios estimator based on replicated weighted sampling needs not have smaller MSE than the ordinary ratio‐of‐sums estimator based on replicated uniform sampling.The fact that the estimation is based on counts as opposed to complete 2‐d observations does not necessarily mean a reduction in information. For certain types of stereological ratios, the ordinary ratio‐of‐sums estimator based on complete observation is shown, counter to intuition, to be less accurate than that based on simple and fast counting.
Improved spatial and temporal resolution in an apparatus for time‐lapse phase contrast ciné light micrography of cells in vitro
Authors: Veselý P. , Malý M. , ČUmpelík J. , Pluta M. , Tůma V. 
Published: August 2011

SUMMARYAn apparatus for time‐lapse cinemicrography of living animal cells in vitro is described. It has an increased information capacity in comparison with conventional types of equipment in that successful combination of the highest possible spatial resolution with phase contrast microscopy and an improved temporal resolution provided by flash light illumination has been achieved. The interval between exposures of 1/200 s approximately can be reduced to 1/4 s using a negative phase‐contrast objective of NA 1·3. Negative phase‐contrast also appeared to be the best technique for imaging of tiny cell surface structures. Thus the new apparatus is suitable for the study of the patterns of cell surface motility in vitro.
The use of quadrats and test systems in stereology, including magnification corrections
Authors: Cruz‐Orive Luis‐M. 
Published: August 2011

SUMMARYAt present a model‐free, design‐based theory of unbiased estimation, and a model‐based one of linear unbiased estimation of minimum variance, are available for stereology. The main developments rest upon the nested scheme {section (quadrat)}, whence the raw data are expressible in terms of area, length and number. The main aim of this paper is to complete the available model‐based theory by introducing the step in which sections are analysed by point‐counting via coherent test systems (CTSs). Using this development, the stereologist should be able to handle raw point and intersection counts optimally, in order to find the best estimator of a ratio R in a given specimen in a wide range of circumstances. The latter include, for instance, the use of different CTSs on different sections and of double CTSs on each section, as well as the case—(not uncommon in electron microscopy)—in which different sections from the same sample are observed at slightly different magnifications but analysed by quadrats (via automatic or semi‐automatic image analysers, for instance), or CTSs of fixed sizes. The main conclusion pertaining to the latter case is that the estimators obtained via section‐wise magnification corrections are in general superior to those corrected via a global, average magnification.In order to illustrate the methodology, a synthetic numerical example, and a real one, are given.
Experiments on freezing damage with freeze substitution using moth antennae as test objects
Authors: Steinbrecht Rudolf Alexander 
Published: August 2011

SUMMARYInsect antennae can be easily frozen by immersion into propane at 90 K, freeze substituted at 194 K and, after warming up, embedded and sectioned at room temperature. Freezing damage (f.d.) may occur during cooling the specimen down (primary f.d.) or due to re‐crystallization, during warming up, if substitution was not complete (secondary f.d.). Experimental evidence suggests that secondary freezing damage is not likely to occur with freeze substitution, provided the acetone is water free (by adding molecular sieve) and the rate of warming up is low. All freezing damage observed in the specimens therefore most probably is due to primary freezing damage during cooling. Propelling the specimen with high speed into the coolant, instead of merely dropping it in, does not improve the quality of preservation obtainable but increases the yield of well‐frozen specimens.
Thermal and radiation damage to frozen hydrated specimens
Authors: Talmon Yeshayahu 
Published: August 2011

SUMMARYAlthough low temperature fixation seems to be superior to chemical fixation with respect to structure preservation, complex interactions between the electron beam and frozen hydrated specimens can limit its applications. A review is given of the present knowledge of beam heating and radiation damage with emphasis on recent developments in the field.Beam heating is found not to be a major limitation to cold stage microscopy. But radiolysis of ice and the formation of free radicals that subsequently attack organic matter in contact with ice can severely alter the specimen structure before a useful image is recorded. Use of low dose techniques may help in some cases, but the problem cannot be overcome in X‐ray microanalysis of very small regions, when high beam doses must be used. The use of liquid helium stages operating near 4 K may reduce damage also in frozen hydrated specimens.
Mercuric chloride in alcohol and chloroform used as a rapidly acting fixative for contracting muscle fibres
Authors: Brown L. M. , Hill L. 
Published: August 2011

SUMMARYA fixative which preserves the correct alignment of the filaments in actively contracting muscle fibres must prevent sliding during fixation. Glutaraldehyde is unsuitable because the fibres are capable of relaxation and contraction for several seconds. A modification of Carnoy's fixative rapidly fixes tetanized fibres without relaxation or further activity.The fixative contained ethanol and chloroform saturated with mercuric chloride. Fibres were thereby fixed and dehydrated at the same time. They were then stained with uranyl acetate, embedded, and stained with lead in the usual way.Isolated fibres from R. temporaria were tetanized with low voltage pulses in air, and normal tetanic tensions were recorded prior to fixation. At least 50% of the tension remained after fixation. Unstimulated fibres were activated by the fixative, but fibres depolarized with K+ developed no tension.Embedded fibres were examined intact in polarized light and closely resembled fresh fibres.Electron micrographs showed that, although the membranes were disrupted, the myofibrils were well preserved to 15 μm below the surface and the band pattern was maintained throughout the fibre. There was some local variability in the width of the overlap zone, especially where myofibrils branched. The fine structure of the filaments was similar to that seen after conventional fixation. The cross‐bridges were visible, but the alcoholic dehydration probably interfered with their orientation.Measurements of filament length, and of troponin and cross‐bridge periods by optical diffraction of calibrated electron micrographs, indicated differential shrinkage between the I‐band, overlap zone and H‐zone similar to that seen with other fixatives.Criteria for satisfactory fixation of contracting muscle are discussed. The fixative is considered to be suitable for examining the longitudinal alignment of the filaments, and also for periodicity measurements if the small shrinkage artefact is allowed for. It is unsuitable for studying the reticulum, or for measuring the volume ratio of the myofibrils.
Quantitative low temperature optical microscopy of biological systems
Authors: Diller Kenneth R. 
Published: August 2011

SUMMARYA comprehensive review is presented of low temperature optical microscopy techniques as applied to the study of freezing processes in biological systems. Emphasis is placed on analysis of physical and physiological parameters which were measured and/or controlled and the procedures for effecting such operations. Quantitative analysis of photomicrographs by digital computer processing is also discussed.
Organic mass loss at 100 K and 300 K
Authors: Egerton R. F. 
Published: August 2011

SUMMARYElectron energy‐loss spectroscopy has been used to measure the loss of light elements from thin organic samples during exposure to 80 keV electrons. Cooling the specimen from 300 to 100 K is found to reduce the rate of removal of carbon, nitrogen and oxygen by factors up to 100.
Understanding the artefact problem in freeze‐fracture replication: a review
Authors: Sleytr U. B. , Robards A. W. 
Published: August 2011

SUMMARYFreeze‐fracture and freeze‐etching techniques do not provide artefact‐free images of native in vivo or in vitro cells and tissues. Each preparation stage can produce specific artefacts which must be recognized and understood if these methods are to contribute meaningful information to cell biology. This paper reviews the latest information available on artefacts in freeze‐fracture replication (and etching) methods and points to possibilities for avoiding some of them. Different specimens show different sensitivity to artefactual changes and the final images must be interpreted carefully with regard to the multi‐event process that has led to their production.