bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plastic deformation during freeze‐cleavage: a review
Authors: Sleytr U. B. , Robards A. W. 
Published: August 2011

SUMMARYExamples of plastic deformation are illustrated from a wide range of specimens that have been prepared for electron microscopic examination by fracturing at low temperature prior to replication of the frozen surface. Deformation has been shown to occur in some specimens when fractured at temperatures as low as 4 K.Plastic deformation is recognized in non‐biological polymers such as polystyrene and polyacrylate latex spheres, as well as in similar biological molecules such as poly‐β‐hydroxybutyrate (PHB). However, it is also demonstrated that plastic deformation occurs widely in more complex biological systems, including membranes and protein macromolecules.The interpretation of the structure of fracture faces of frozen membranes, and particularly the lack of complementarity on opposing fracture faces, is discussed in relation to deformation artifacts.It is concluded that very considerable energy must be dissipated as heat during the cleavage process. In the case of some of the latex spheres, the glass transition temperature (Tg) of the bulk polymer can be more than 200 K above the cleavage temperature, and yet plastic deformation still occurs.Once a molecule has deformed, its appearance in the final replica may be significantly changed by heating during evaporation of the replica. An empirical attempt has been made to define the factors leading to the ‘survival’ of a deformed particle.Although the evidence in this review has been drawn from freeze‐fracture and freeze‐etching studies, it is emphasized that the process of cleaving at low temperature—whether in freeze‐fracture techniques or in cryoultramicrotomy—is essentially the same. Therefore the interpretation of structure in ultra‐thin frozen sections will also need to allow for the possibility of deformation artefacts.
On the choice of quadrats in stereology
Authors: Miles R. E. , Davy Pamela 
Published: August 2011

SUMMARYIt is described how inference concerning the geometrical structure of a two‐phase specimen may be carried out on the basis of sampling subregions or ‘quadrats’. Two basically different situations are considered—firstly when the specimen itself is the centre of interest, and secondly when the specimen is only part of a larger body of interest Weighted random quadrats are shown to be useful in the first case. Serial and multistage sectioning, and the incorporation of supplementary information via Monte Carlo techniques, are also discussed.
Relative frequencies of random intercepts through convex bodies
Authors: Warren R. , Naumovich N. 
Published: August 2011

SUMMARYA computer simulation of the random linear intersecting process has been used to derive the relative frequency distributions of random intercepts through selected convex shapes. The classes of shapes chosen for investigation were ellipsoids, rounded cubes, orthogonally‐faceted spheres, rectangular prisms and triangular prisms. Certain shape‐related characteristics of the distributions are pointed out.
Ponceau 2R staining on semi‐thin sections of tissues fixed in glutaraldehyde‐osmium tetroxide and embedded in epoxy resins
Authors: Gori Paolo 
Published: August 2011

SUMMARYProteins were stained (brilliant red) by using 0·5% Ponceau 2R (C.I. 16150) in sulphuric acid (pH 2) at 40°C on sections 1–2 μm thick of tissues fixed in glutaraldehyde‐osmium tetroxide and embedded in epoxy resins. The staining is free from precipitates and does not require the removal of the embedding media.Section bleaching with 1–2% periodic acid at 40°C for 30–90 min was also carried out in order to obtain a more brilliant colour of the proteins which may be photographed using black and white films.
Polymeric cryoproteetants in the preservation of biological ultrastructure
Authors: Echlin Patrick , Skaer Helen le B. , Gardiner B. O. C. , Franks Felix , Asquith M. H. 
Published: August 2011

SUMMARYA study has been made of the physiological effects of three non‐penetrating polymeric cryoprotective agents on sixteen different plant and animal cells and tissues. The cryoproteetants, when used at concentrations at which they are effective in preventing ice‐crystal formation, generally have a lower toxicity to cells and tissue than similar concentrations of glycerol. The relatively low toxicity of these substances suggests that they would be more suitable as cryoproteetants for morphological and analytical studies than the commonly used low molecular weight compounds.
A resistance monitor with power cut‐off for automatic regulation of shadow and support film thickness in freeze‐etching and related techniques
Authors: Steere Russell L. , Erbe Eric F. , Moseley J. Michael 
Published: August 2011

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 materials.
Optical character of thermally metamorphosed coals of northern England
Authors: Jones J. M. , Creaney S. 
Published: August 2011

SUMMARYThe Carboniferous sediments of northern England have formed the context for an optical study of the effects of differing geothermal history on the included organic material. In the north of the area, the Northumbrian Trough contains 5000 m of cyclothemic Carboniferous sediments with frequent coals and is probably underlain by Old Red Sandstone rocks. To the south, the Alston Block comprises 1500 m of basically similar Carboniferous sediments underlain by highly metamorphosed Silurian slates and a Caledonoid granite. The contrasting nature of the basements has produced variable geothermal gradients and consequently varying coal rank throughout the Carboniferous succession.Alteration of the coals and dispersed organic matter in the sediments by the intrusion of a quartz dolerite sill, the Whin Sill, during Stephanian times has been closely examined. The optical changes induced by the thermal metamorphism depend on the initial rank of the sediments. It has been possible to deduce rank profiles through the succession at the time of intrusion; these can be closely related to the character of the basement. The area was subsequently subjected to hydrothermal (lead, zinc) mineralization.
Quantitative analysis of particle growth in TiC‐Ni alloys*
Authors: Chermant J. L. , Coster M. 
Published: August 2011

SUMMARYThe methods of quantitative metallography and stereology have been used to determine the distribution of the diameter of equivalent spheres and hence study the change in particle size of titanium carbide undergoing growth/coarsening in a nickel matrix. The distribution obtained, using the Saltykov method, is in agreement with that proposed theoretically by Hanitzsch for the kinetics of growth controlled by an interface reaction. The change in the Smith shape factor shows that growth of titanium carbide is isotropic.This is thus an example of the possibilities offered by stereology. The crystal size distribution in three dimensions is closest to the theoretical models.
The use of PIPES buffer in the fixation of mammalian and marine tissues for electron microscopy
Authors: Baur P. S. , Stacey T. R. 
Published: August 2011

SUMMARYPIPES, an organic based buffer, was used in the preparation of a variety of marine and mammalian tissues for electron microscopic study. The ultrastructural results demonstrate that this buffer renders superior ultrastructural details to those obtained with some of the more common inorganic buffers especially when long fixation times are required. Furthermore, this buffer system does not appear to contribute extraneous anions or cations to the tissues and thus permits accurate elemental determinations to be performed on thin sections of the plastic embedded specimens by means of energy dispersive X‐ray analysis.
Estimation of the average section thickness in ribbons of ultra‐thin sections
Authors: Gunning B. E. S. , Hardham A. R. 
Published: August 2011

SUMMARYA simple procedure for estimating the depth to which a ribbon of ultra‐thin sections cuts into a block is described. The average section increment is obtained by dividing the depth by the number of sections in the ribbon. Comparison with measurements of individual sections made using interference microscopy suggests: (a) that loss of resin brought about by the cutting process is insignificant, i.e. that the average section increment equals the average section thickness, and (b) that there can be considerable variation in section thickness along a ribbon. Provided that such variation is taken into account, the method based on measurements of the block face is simple, avoids time‐consuming alternative procedures, and is appropriate when seeking to determine the depth dimension to be used in making three‐dimensional reconstructions from long sequences of sections.
Microanalysis of Grain Boundary Segregation in Embrittled Iron‐3wt% Nickel Alloys Using STEM
Authors: Doig P. , Flewitt P. E. J. 
Published: August 2011

SUMMARYThe segregation of minor embrittling additions of tin and phosphorus to the grain boundaries of an Fe‐3wt%Ni alloy after ageing at 823 K has been measured on thin foils using a Scanning Transmission Electron Microscope (STEM) interfaced with an energy dispersive X‐ray spectrometer. The microanalysis technique is discussed and shown to be useful for measuring grain boundary solute segregations.
Fixation of Senescing Plant Tissues: Sclerenchymatous Fibre Cells From the Flowering Stem of A Grass
Authors: Lawton June R. , Harris P. J. 
Published: August 2011

SUMMARYThe quality of fixation for transmission electron microscopy of young and older sclerenchymatous fibre cells from the flowering stem of a grass, Lolium temulentum L., was judged by their ultrastructure. In preliminary studies using glutaraldehyde buffered with sodium phosphate as the primary fixative the tonoplast was not complete even in many of the young fibre cells. This was thought to be an artefact of fixation and not due to natural senescence. Much improved fixation was obtained using NaOH‐PIPES to buffer the glutaraldehyde; the tonoplast was complete and there was a sharp demarcation between the cytoplasm and the central vacuole even in older cells with thick lignified cell walls. At all stages of development of fibre cells the tonoplast appears to be extremely fragile and sensitive to fixation conditions and can thus form a useful criterion for evaluating the quality of fixation.The use of permanganate as a fixative led to improvement in the retention of the tonoplast and other membrane systems. Some improvement in fixation was obtained by the addition of formaldehyde to the sodium phosphate buffered glutaraldehyde and also when the glutaraldehyde was buffered with sodium cacodylate. More consistent results were obtained using glutaraldehyde purified by vacuum distillation.
Distribution of Membrane Thickness Determined By Lineal Analysis
Authors: Gundersen H. J. G. , Jensen T. B. , Østerby R. 
Published: August 2011

SUMMARYThe expected statistical distributions of intercept length are derived in terms of geometrical probability density functions pertaining to plates with known thickness penetrated by lines with random orientation. These expressions provide arithmetic and graphical solutions for obtaining distributions of membrane thickness and reciprocal membrane thickness from empirical distributions of intercept lengths. Furthermore, general relationships between probability density functions of distributions of intercept length and membrane thickness are derived as well as those between their moments.Examples of the application of the method to biological samples are given, and estimated distributions of glomerular basement membrane thickness are compared to those obtained by an independent, direct method.Various sources of bias, which in practice may occur due to departures from the sample model, are discussed and the influence of some of them is estimated. The knowledge of the probability density function of reciprocal intercepts makes it possible to perform a correction of the distributions of measured intercept length, which to some extent eliminates bias.
High Resolution Scanning Electron Microscopy in Biology: Artefacts Caused By the Nature and Mode of Application of the Coating Material
Authors: Bråten Trond 
Published: August 2011

SUMMARYResults of high resolution secondary electron observations of the haemocyanin molecule from the marine whelk Buccinum undatum are given.The choice of metal used for surface coating of the sample (gold, gold‐palladium or carbon/gold‐palladium) and the mode of application of this metal (thermal vacuum evaporation or diode sputtering) were both found to be of utmost importance when working at high magnifications in the scanning electron microscope.Sputter coating with gold gives poor results because of a granular and cracked appearance of the surface film. The haemocyanin molecules were difficult to recognize in these preparations. Best results were obtained by a thermal vacuum evaporation of gold‐palladium.It is suggested that the inferior results seen after sputter coating may be due to the high temperatures which the specimen experiences during the sputtering, even when cooling of the specimen stage is carried out.Other specimens (diatom valves and latex spheres) were also studied at high magnification giving the same results as the haemocyanin molecules.
Critical point drying for scanning electron microscopy: a semi‐automatic method of preparing biological specimens
Authors: Hall D. J. , Skerrett E. J. , Thomas W. D. E. 
Published: August 2011

SUMMARYSlow, controlled, rates of critical point bomb heating and of gas venting have been shown to improve the preservation of biological specimens in critical point drying. A procedure that represents a balance between avoidance of specimen damage and speed of operation has been developed for use with CO2 as the transitional fluid. Bomb heating is automated and controlled electronically, and manual venting of the gaseous CO2 is monitored using a gas flow meter.
A simple technique for the direct SEM observation of the interior of a small capsular organ
Authors: Cross R. H. M. 
Published: August 2011

SUMMARYThe direct SEM observation of the interior of closed or semi‐closed capsular organs has presented difficulties in cases where the organ is small and not suitable for accurate dissection. Descriptions of such organs have usually been based upon reconstruction from serial sections cut for optical microscopy or TEM. A method is described whereby the established techniques of epoxy removal from embedded material are used to permit direct SEM observation of the interior of a small capsular organ.
Observations of silicon carbide by high resolution transmission electron microscopy
Authors: Smith David J. , Jepps N. W. , Page T. F. 
Published: August 2011

SUMMARYHigh resolution transmission electron microscopy techniques, principally involving direct lattice imaging, have been used as part of a study of the crystallography and phase transformation mechanics of silicon carbide polytypes. In particular, the 3C (cubic) and 6H (hexagonal) polytypes have been examined together with partially transformed structural mixtures. Although direct observation of two‐dimensional atomic structures was not possible at an operating voltage of 100 kV, considerable microstructural information has been obtained by careful choice of the experimental conditions. In particular, tilted beam observations of the 0·25 nm lattice fringes have been made in the 3C polytype for two different {111} plane arrays in order to study the dimensions and coherency of finely‐twinned regions together with {0006} and lattice images in the 6H polytype which allow the detailed stacking operations to be resolved. Lower resolution lattice images formed with axial illumination have also been used to study the nature of the 3C → 6H transformation and results are presented showing that the transformation interface may originate with fine twinning of the 3C structure followed by growth of the resultant 6H regions. Observations have been made of the detailed stepped structure of this interface together with the stacking fault distribution in the resultant 6H material. The images obtained suggest that tilted beam techniques will be useful for studying the one‐dimensional disorder in other SiC polytypes and related ceramic materials. Some of the possible advantages of future observations with high voltage, high resolution instruments are considered.
Monitoring of the course of fixation of plant cells
Authors: Mersey Brent , Mccully M. E. 
Published: August 2011

SUMMARYThe fixation of cells of petiolar hairs of tomato was monitored by phase contrast and Nomarski interference contrast microscopy. Because the cuticle covering these hairs is relatively impermeable some fixatives enter only the base of the hair so that a ‘fixation front’ can be followed through a single cell. The basal end of such a cell may be immobilized by the fixative while the apical end is still streaming. A variety of fixatives were tested at room temperature and at 273–278 K. All procedures tested failed to stabilize a pleomorphic canalicular system that is a dominant feature of these cells so that no clue to the presence of this system can be seen in sectioned material. It is therefore very desirable that images of fixed cells be compared to the structure of similar cells which are still alive.
Extraction of glycoproteins during tissue preparation for electron microscopy
Authors: Sturgess J. M. , Mitranic M. M. , Moscarello M. A. 
Published: August 2011

SUMMARYThe extraction of glycoproteins labelled with 3H or 14C precursors: fucose and glucosamine, has been compared during processing of rat liver for transmission electron microscopy.Using 14C labelled fucose, approximately 6% of labelled macromolecules were extracted during processing including 3% during glutaraldehyde fixation, 1% during post‐fixation and 2% during dehydration. Greater extraction (8%) occurs with glucosamine as a precursor, which may be attributed to hydrolysis of the more labile sialic acid residues of the glycoprotein molecules.Tritium labelled glycoproteins were more susceptible to extraction than 14C‐labelled glycoproteins. The extraction of 3H‐labelled glycoproteins as measured by liquid scintillation counting may prove difficult to interpret owing to the quenching from processing solutions.
A photoelastic substrate technique for dynamic measurements of forces exerted by moving organisms
Authors: Harris Jack K. 
Published: August 2011

SUMMARYThe forces produced by small moving organisms have been quantitatively measured by having the organisms move on a polymeric substrate which transduces the applied stress into an optical birefringence signal (photoelastic effect). The optical signal can be rigorously interpreted to give static force measurements, and by calibrating the substrate empirically, dynamic measurements are obtained. The technique measures stresses, forces applied to an area, so it is not possible to determine ultimate sensitivity of the technique for measurements of forces without regard to area. The technique is especially useful when small forces are exerted over very small areas as, for example, may be the situation with moving tissue cells. The technique is noninvasive, requires minimal equipment, and is easily performed on microscopes adapted for polarized light measurements. Gelatin has the highest sensitivity and adaptability as a photoelastic substrate.
The rôle of optical microscopy in refractories development within the iron and steel industry*
Authors: Warman M. O. 
Published: August 2011

SUMMARYUntil comparatively recently the optical microscope was used infrequently in many refractories laboratories. It was regarded by many as a device which provided interesting information but had little application in solving real refractories problems. A number of distinguished people in the industry realized that this attitude was wrong and actively promoted the use of the microscope as a tool of practical importance. Since then the microscope has become indispensable in refractories research and plant investigations. The paper describes a number of the many investigations carried out by one laboratory over the last 10 years. They illustrate the importance of the microscope in problem solving and in understanding the wear mechanisms of refractories, so that furnace and vessel lining configurations can be modified to give optimum performance.
Radiation damage relative to transmission electron microscopy of biological specimens at low temperature: a review
Authors: Glaeser Robert M. , Taylor Kenneth A. 
Published: August 2011

SUMMARYWhen biological specimens are irradiated by the electron beam in the electron microscope, the specimen structure is damaged as a result of molecular excitation, ionization, and subsequent chemical reactions. The radiation damage that occurs in the normal process of electron microscopy is known to present severe limitations for imaging high resolution detail in biological specimens. The question of radiation damage at low temperatures has therefore been investigated with the view in mind of reducing somewhat the rate at which damage occurs. The radiation damage protection found for small molecule (anhydrous) organic compounds is generally rather limited or even non‐existent. However, large molecule, hydrated materials show as much as a 10‐fold reduction at low temperature in the rate at which radiation damage occurs, relative to the damage rate at room temperature. In the case of hydrated specimens, therefore, low temperature electron microscopy offers an important advantage as part of the overall effort required in obtaining high resolution images of complex biological structures.
Radiation damage in the high resolution electron microscopy of biological materials: A review*
Authors: Cosslett V. E. 
Published: August 2011

SUMMARYRadiation damage to a biological specimen arises from a variety of interactions between the illuminating electrons and the atoms in it. The relative probabilities of these events, and the amount of energy transferred, can be calculated from basic physical theory. The microscopic damage caused in a particular specimen in given operating conditions is more difficult to predict, but it can be measured by a number of macroscopic indicators, the chief of which are loss of mass and changes in the energy loss spectrum (or electron diffraction pattern, if any). For most biological material the observed rate of damage is such as to set a limit to the intensity of illumination, the maximum magnification and the minimum size of detail that can be made visible. Several techniques have been devised and tested for reducing the radiation sensitivity of a specimen, of which cooling to a very low temperature and encasing it in an inert medium are the most effective. If the various protective measures act cooperatively, they could increase the effective resolution of sensitive material by an order of magnitude, making possible electron microscopy of the atomic structure of, for instance, the nucleic acid bases and other macromolecules. The prospects for observing living cells at a resolution better than that of the best optical microscopes would remain very small.
An image reversal process for electron microscope film
Authors: Brandt Curtis R. , Davis Ronald 
Published: August 2011

SUMMARYAn improved technique has been developed to produce a positive image directly on some standard electron microscope films (Kodak 4489, SO 163, and Ilford Electron Microscope Film). This technique has been useful for processing micrographs of freeze‐etched and shadowed specimens, and eliminates the need for producing positive image transparencies before printing.