bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recognition and classification of structure by means of stereological methods in neurobiology
Authors: Bernroider Gustav 
Published: August 2011

SUMMARYThe problem of measuring fine structure of individual particles without losing information on largescale characteristics of particle arrangement is discussed. With the help of stereological and pattern recognition methods a possible solution of this important problem is introduced. The domain specimen for which the brain serves as an example is characterized by two main properties. One of them being the position dependent ‘aggregate characteristics’ (distribution of neurons within the specimen), the other position invariant ‘single cell characteristics’ (structural properties of single neurons). It is shown that by simultaneous observation both properties together cannot be detected with sufficient accuracy by conventional methods. This is the decisive problem of ‘correlation microscopy’. The method described in this paper is based on selection of the most informative variables and selection of subdomains (e.g. sections and reference planes). This results in a very general probabilistic concept in modern stereology, offering solutions to complex structure classification problems in biology.
Quantitative characterization of wood microstructure
Authors: Steele James H. , Ifju Geza , Johnson Jay A. 
Published: August 2011

SUMMARYStereological countings were applied to transverse sections of closely related and widely different species of hardwoods for quantitative characterization. Anatomical elements, such as the wall and lumen of vessels, fibres, and ray cells, were distinguished. Volume fraction, average size, average spacing, aspect ratios for oriented features, and size distribution parameters were then calculated. Sampling fields were strategically and systematically located within growth rings for characterization of the spatial distribution of the anatomical elements.Initially five species: paper birch, yellow birch, sugar maple, aspen, and sassafras cross‐sections were subjected to quantitative stereological analysis. The two birch species were anatomically very similar, and somewhat similar to the sugar maple. Sassafras was very different in structure from the other three species studied. Aspen was typical diffuse‐porous wood.The initial results were promising, and revealed certain subtle distribution patterns never before recognized. Second, all species including those which were very similar, were recognized by quantitative expression of their structural elements. Third, the method provided quantitative descriptions of the structural characteristics. It is expected that stereological analysis of wood structure will be used for prediction of properties and utilization potentials of the various species, as well as for their identification.
Ultrastructural effects of performic acid oxidation of epoxy‐embedded tissue with and without early uranyl staining
Authors: Heath Everett 
Published: August 2011

SUMMARYEpoxy‐embedded blocks of glutaradehyde and OsO4 fixed adenohypophyseal tissue were immersed in performic acid, rinsed and sectioned for electron microscopy. Sections exhibited a general image intensity equivalent to control sections but their stainability with both uranyl acetate and lead citrate stains was increased. It was concluded that osmium was not removed by performic acid oxidation.Membranes of endoplasmic reticulum and the Golgi apparatus were not visible, and other components (acidophil granules, in particular) were markedly distorted in shape after oxidation. Such changes, however, were not evident in specimens previously exposed to uranyl acetate during ethanol dehydration.
Using simultaneous three colour X‐ray mapping and digital‐scan‐stop for rapid elemental characterization of coal combustion by‐products
Authors: Pawley James B. , Fisher Gerald L. 
Published: August 2011

SUMMARYA system is described for rapid, simultaneous three colour elemental mapping with a scanning electron microscope (SEM) and an energy dispersive X‐ray analyser. The technique, which uses a SEM scanning at TV rate, minimizes the disadvantages of long scan times such as inefficient use of linear amplifier and observable dead‐time shadowing. The system also employs a digital scan‐stop assembly utilizing a light pen to rapidly and reproducibly direct the beam to an object of choice for spot‐mode analysis. Application of the system to analysis of fine particulates with emphasis on fly ash derived from coal‐fired electric power plants is discussed. Chemical heterogeneity of fine particles in standard reference material fly ash and in phagocytized fly ash within pulmonary macrophages is demonstrated.This system combines the morphologic capability of the SEM with X‐ray multielement mapping to provide a needed tool for particulate source identification.
Reduction of background due to backscattered electrons in energy‐dispersive X‐ray microanalysis
Authors: Hall T. A. 
Published: August 2011

SUMMARYWhen energy‐dispersive X‐ray microanalysis is practised in a scanning electron microscope, most of the spectral background may come from electrons entering the detector. This background can be eliminated by deflecting magnets. Alternatively, the electrons can be blocked by a plastic film but only at the cost of suppression of the low‐energy end of the X‐ray spectrum.
A specimen carrier, storage disc system for scanning electron microscopy (SEM): evaluation of stainless steel as a substratum for cell culture in vitro
Authors: Yeger Herman , Lea Peter J. 
Published: August 2011

SUMMARYA method of sample preparation for scanning electron microscopy (SEM) studies based on the use of stainless steel discs as a cell culture substratum is described in detail. A number of different cell lines were grown on stainless steel, and the growth patterns and biocompatibility of cells cultured on stainless steel were compared to identical cells cultured on aluminium, glass and plastic substrata. Stainless steel provides cells with an excellent growth surface which allows these cells to retain their normal growth characteristics and appearance. The non‐toxic stainless steel discs can be manipulated through any combination of fixatives and organic solvents. The discs have been incorporated into a versatile system of sample preparation for SEM.
A simple electron beam gun for platinum evaporation
Authors: Hagler Herbert K. , Schulz Werner W. , Reynolds Rolland C. 
Published: August 2011

SUMMARYA simple electron beam gun for platinum shadowing of freeze‐fractured or freeze‐etched surfaces is described. In the Steere‐Denton freeze‐etch instrument, this inexpensive device consistently yielded high quality replicas. The compact design possibly renders this gun operable in most freeze‐etch instruments.
On the methodology of the thyroid epithelial cell thickness determination
Authors: Kališnik Miroslav , Jakopin Primož , ŠUštaršič Janez 
Published: August 2011

SUMMARYThe average thickness of the thyroid epithelial cells may be determined either directly or indirectly. By the direct or caliper method, this thickness is overestimated as a result of which its empirical value must be divided by a correction factor Kd. By the indirect method, on the other hand, the thickness of the thyroid gland epithelium is calculated as the ratio of the double volume density of the epithelium to the sum of the inner and the outer surface density of the epithelium; in this case the sought for thickness value is underestimated and must consequently be multiplied by a factor Ki.Both correction factors are algebraically defined. Their values are calculated and graphically represented as a function of the thyroid activation index (the ratio between the volume density of the epithelium and the colloid) for the range from 0·1 to 100.The validity of the theoretical interpretation of the discrepancy between the values obtained for the average thickness of the thyroid epithelium by the direct and the corresponding values obtained by the indirect method, is empirically tested. It is shown that by the introduction of appropriate correction factors the difference between the results obtained by each method can be reduced. These improved direct and indirect methods for determining the wall thickness of a hollow sphere seem to lend themselves to being used in the stereological analysis of other biological, perhaps even non‐biological materials of similar structure.
A simple method for holding electron microscope grids during autoradiography of serial sections
Authors: Heywood Peter , Hodge Lon , Davis Frances , Simmons Tobianne 
Published: August 2011

SUMMARYA simple, reliable, and inexpensive method is described for holding electron microscope grids during the application of photographic emulsion and during subsequent storage and processing. This method has proved to be especially useful in autoradiographic studies using serial sections.
Visualization of vesicles in semi‐thin sections by the heat removal of epoxy resins
Authors: Uhrík B. , Zacharová D. 
Published: August 2011

SUMMARYA partial removal of the embedding medium from sections of tissue with hollow structures results in the formation of a phase object. The removal of epoxy resin by the heat of a gas‐burner flame is a simple method which does not lead to shifts and losses of sections from glass slides.
Polymeric cryoproteetants in the preservation of biological ultrastructure
Authors: Franks Felix , Asquith M. H. , Hammond Catherine C. , Skaer Helen le B. , Echlin Patrick 
Published: August 2011

SUMMARYThe solid states formed by vitrified and frozen aqueous solutions of some hydrophilic polymers, able to act as biological cryoproteetants, have been studied by differential scanning calorimetry and freeze fracture electron microscopy. Glass transitions, devitrification, recrystallization and melting behaviour of aqueous solutions of polyvinylpyrrolidone, hydroxyethyl starch and dextran have been established. The vitrified polymer solutions exhibit a characteristic microspherical morphology which is not induced by the quench cooling process but is an inherent feature of the solutions themselves.
Polymeric cryoproteetants in the preservation of biological ultrastructure
Authors: Skaer Helen le B. , Franks Felix , Asquith M. H. , Echlin Patrick 
Published: August 2011

SUMMARYTwo high molecular weight polymers, polyvinylpyrrolidone (PVP) and hydroxyethyl starch (HES), have been used as cryoproteetants for preparing specimens to be freeze fractured. Solutions of 25% (w/w) suppress the formation of intracellular ice in single cells and tissue blocks from both plants and animals to the extent that fine structural details of the cell can be elucidated. The mode of action of these cryoproteetants, together with the structures they reveal and the peculiar advantages attached to their use, is discussed.
Ultrastructure of unfixed plasma membranes in ultrathin frozen sections
Authors: Vogel Frank 
Published: August 2011

SUMMARYUltrathin sections of unfixed kidney tubular cells were obtained by cryo‐ultramicrotomy using the ‘wet’ method. The results showed that extremely thin sections permit high resolution studies on unfixed plasma membranes. Structural units on the inner surface of the plasma membrane could be detected.
Preparation of thin cryo‐sections for electron probe analysis of calcifying cartilage
Authors: Ali S. Y. , Gray J. Craig , Wisby Angela , Phillips M. 
Published: August 2011

SUMMARYConventional methods of fixation, dehydration, embedding and wet‐sectioning can produce artefacts in the chemical composition of mineralizing tissues. Cryoultramicrotomy was adopted for a more reliable approach to electron probe analysis of initial apatite formation in calcifying cartilage. Fresh rabbit epiphyseal cartilage was mounted on silver pins, frozen by immersion in liquid nitrogen, and sectioned with the specimen temperature at 133 K and the knife temperature at 273 K. Dry cryo‐sections (30–70 nm in thickness) were manipulated on to coated grids and examined the same day. These cryo‐sections showed good morphological and cytoplasmic detail, with large areas relatively free of ice‐crystal damage. Sections stained either with osmium vapour or negatively stained with silicotungstic acid showed areas with well‐preserved mitochondria with granules and endoplasmic reticulum. Unstained sections also showed dense granules (50–120 nm in diameter) in the mitochondria of chondrocytes and preliminary electron probe analysis of these has indicated a Ca/P mass ratio of approximately 1·14. In the longitudinal septa, about 2 μm away from the chondrocytes, matrix‐vesicle‐like particles could be seen with crystal needles inside them. Micro‐analysis of two of these gave a Ca/P mass ratio of 1·73 and 2·68. Cryo‐ultramicrotomy appears to confirm a number of conclusions derived from conventional ultrastructural study of growth cartilage and suggests for the first time how amorphous calcium phosphate and crystalline apatite can be shown to exist in different organelles in the same cryo‐section of the tissue.
Freeze‐fracturing: a review of methods and results
Authors: Sleytr U. B. , Robards A. W. 
Published: August 2011

SUMMARYFreeze‐fracturing may be accomplished either under vacuum, or at atmospheric pressure. The devices available for freeze‐cleaving are discussed in relation to the vacuum and temperature conditions prevailing during cleaving, etching and replication. It is concluded that most specimens can be satisfactorily cleaved (even at 4 K), and processed using simple cleavage devices and systems that provide ample cold‐trapping protection for the specimen. Only for special purposes are microtome assemblies or ultra‐high vacuum units essential.The fracturing process may produce artefacts by plastic deformation. Such artefacts have been noted in both non‐biological and biological polymers cleaved at temperatures as low as 4 K. Contamination of the frozen surface need not be a problem provided that the specimen is transferred under ‘safe’ conditions, and is protected by well‐designed cold traps.Freeze‐cleavage and freeze‐sectioning are compared. It is considered that there will be a temperature range for most heterogeneous specimens within which both cleavage and fracturing may occur, depending upon the nature of the molecules in the cleavage/sectioning plane. Local heating during freeze‐sectioning will produce deformation artifacts as in freeze‐cleavage, and may also lead to more general surface ‘flow’. The relationships between sectioning and fracturing biological specimens at low temperature require further clarification.
Evaluation of membrane structure facts and artefacts produced during freeze‐fracturing
Authors: Bullivant S. 
Published: August 2011

SUMMARYThe freeze‐fracture technique is now widely used in the study of membranes, but it should be stressed that it shows internal hydrophobic planes of membranes, prepared under physical conditions far removed from those prevailingin vivo.Hence there is considerable potential for artefact. Work on the membrane lipid component, the intramembrane particles, and their aggregation under certain conditions, is reviewed in the context of fact versus artefact. Particular attention is paid to the results of complementary replica experiments, performed in the author's laboratory and elsewhere, which indicate that lipid collapse and protein particle deformation contribute to the appearance of the membrane fracture face seen in the final replica. A model, showing the effects of freeze‐fracturing on membranes, is presented.
Interpreting the results of freeze‐etching
Authors: Branton Daniel , Kirchanski Stefan 
Published: August 2011

SUMMARYMorphological data obtained by freeze‐fracturing and other low temperature techniques must be interpreted in terms of molecular organization and function. Interpretation is aided by physical and biochemical approaches. Physical approaches such as rotary replication and ultralow temperature fracturing can improve resolution and preserve molecular arrangements which are difficult or impossible to observe with standard freeze‐etching techniques. Biochemical approaches such as dissociation‐reconstitution experiments can establish the molecular parameters underlying electron‐microscopically visible forms. Both approaches are illustrated by investigations of the human erythrocyte membrane.
Freeze‐drying process of biological specimens observed with a scanning electron microscope
Authors: Nei Tokio , Fujikawa Seizo 
Published: August 2011

SUMMARYA pit membrane was observed with a cryo‐SEM during the course of dehydration at low temperatures. The freeze‐drying process of sea‐urchin eggs and parenchyma cells of higher plants was also examined with this microscope. Conditions for observation of frozen specimens in the native state were discussed on the basis of morphological studies of alterations such as shrinkage or deformation which appeared during the freeze‐drying process.
Contrast and quantitation in uniform regions of thin sections using transmission electron microscopy
Authors: Edie John W. , Karlsson Ulf L. 
Published: August 2011

SUMMARYA direct approach to quantitative measurements of uniform regions in thin sections is described. Accelerating voltages around 80 kV and objective aperture angles of about 9·3 mrad will provide conditions where contrast is directly proportional to specimen mass thickness. An extensive treatment of electron scattering in Formvar films for wide ranges of electron microscopic operating conditions is summarized in a simple, empirical equation. The extent to which Formvar results may be generalized to other materials, both embedding media and structures within the thin section, is treated. Using these results, precise measurements of local section thickness and of specimen density and/or dry mass of regions which penetrate the entire section thickness are possible, with the accuracy dependent upon irradiation effects and specimen makeup.
Accurate stigmating of a high voltage electron microscope
Authors: Krivanek O. L. , Isoda S. , Kobayashi K. 
Published: August 2011

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 micrograph.
Preservation of shock‐frozen myocardial tissue as shown by cryo‐ultramicrotomy and freeze‐fracture studies
Authors: Sætersdal T. S. , Røli J. , Myklebust R. , Engedal H. 
Published: August 2011

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 LN2 at 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 LN2 yields 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 μm2 wide reveal good preservation without visible ice crystals. Such areas occur within a superficial band of tissue to a depth of c. 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‐drying and warming up of the frozen sections.
Freeze‐etching of unglycerinated tissue dispersions by application of the oil emulsion technique
Authors: Buchheim W. , Welsch U. 
Published: August 2011

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 cryoprotectants.
Developments in automated reflectance microscopy of coal
Authors: Davis Alan , Vastola Francis J. 
Published: August 2011

SUMMARYAutomated reflectance microscopy (ARM) systems employ a microscope photometer in conjunction with a computer which controls a motor‐driven stage drive and records and categorizes the photomultiplier output. In a system being developed at The Pennsylvania State University, the object stage moves continuously under the microscope objective at a constant speed and in a predetermined raster. With a scan speed of 1600 μm/s and the computer recording the photo‐multiplier output every 1.25 ms, each recording represents a scan of 2 μm. An aperture below the photomultiplier is set to give an effective area of measurement of 2 μm square, so that a continuous series of readings is obtained on adjacent fields of this size. The difference in reflectance between coal and pyrite particles in polished coal pellets enables pyrite chord‐size distributions to be measured; consecutive recordings on pyrite grains are summed to give a measure of chord length. Size distributions determined by ARM compare well with values measured by visual microscopy. In the course of analysis of a single coal pellet, approximately 400,000 individual readings are recorded, the entire operation of scanning and printout of data taking approximately 18 min. Coal reflectograms obtained by ARM may be used for rank measurements and to indicate petrographic compositions.
The standardization of petrographic analysis of coal
Authors: Juckes L. M. , Pitt G. J. 
Published: August 2011

SUMMARYPetrographic analysis is used to characterize coals in terms of the maceral group composition and the reflectance of the vitrinite. Interchangeability of results and applicability of prediction methods have been hampered up to now through differences between the methods used by different petrographers. Some aspects of a proposed standard method being developed in this country are described.