bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of resin embedded unicellular organisms without the use of fixatives and dehydration media
Authors: Pfaller Walter , Rovan Erwin 
Published: August 2011

SUMMARYA method is presented for processing single cells for conventional ultrathin sectioning without the use of fixatives and dehydration media.The cells were fixed by a physical method— spray freezing— which provides extremely high cooling rates, needs no pretreatment with cryoprotective agents and is therefore assumed to maintain the in vivo morphology of the cell. Hitherto cells prepared in this way have been investigated exclusively by freeze etching. To combine the advantages of this method with those of conventional ultrathin sectioning we have processed spray frozen cells with widely varying water contents (spermatozoa and lymphocytes) by freeze drying at 188 K and vacuum embedding.When compared to conventional chemical fixation the differences found in ultra‐structural preservation of spermatozoa using this kind of preparation were confined to the arrangement of spermhead membranes and middlepiece structures. Lymphocyte structure was much closer to that known from chemical preparation, the only differences being a denser cytoplasm, denser mitochondrial matrices and thicker plasma membranes. These differences are probably due to the absence of eluating and dissolving effects present in conventional chemical preparations.The ultrastructural preservation of spray frozen cells is not different after freeze etching or after freeze‐drying and vacuum embedding. This indicates clearly that drying and resin embedding does not produce artefacts and that structural preservation is therefore limited by the quality of cryofixation.Therefore this method is considered a contribution to the problem of preservation of the in vivo assembly of cellular substructure. Furthermore it seems to be a potential basis for preparation of soluble or diffusible substances or cellular compounds which would be influenced by fixatives and dehydrating agents.
The direct measurement of temperature changes within freeze‐fracture specimens during rapid quenching in liquid coolants
Authors: Costello M. J. , Corless J. M. 
Published: August 2011

SUMMARYWe have evaluated the cooling rates of specimens mounted in a variety of freeze‐fracture holders when plunged into a series of liquid coolants. These rates were measured using miniature thermocouples placed within the mounted specimens. The most rapid cooling rates were obtained using propane at 83 K as the coolant. When mounted on a newly devised ‘copper sandwich’ holder, specimen cooling rates in excess of 4500 K/s have been recorded.A simple guillotine‐like device for quenching freeze‐fracture specimens under reproducible conditions is presented.
Low temperature scanning electron microscopy: a review
Authors: Echlin Patrick 
Published: August 2011

SUMMARYLow temperature scanning electron microscopy is useful for morphological and analytical studies both in situations where low temperature techniques are used during specimen preparation and where low temperature stages are used for specimen examination and analysis. Examples are given of different low temperature specimen preparation techniques and how they may be applied to different types of specimen. There are still a number of problems associated with morphological identification in fully frozen‐hydrated samples and it is important to carry out parallel studies using more conventional transmission electron microscopy and light microscopy preparation techniques. A number of criteria are presented, some or all of which may be used to establish the existence of the frozen‐hydrated state.
Quantitative X‐ray microanalysis of diffusible ions in the skeletal muscle bulk specimen
Authors: Zierold K. , Schäfer D. 
Published: August 2011

SUMMARYX‐ray microanalysis in the scanning electron microscope (SEM) is used to obtain information about the distribution and mobility of electrolyte ions in the skeletal muscle tissue. In order to localize the diffusible ions in their physiological state, so far as possible, any chemical fixative is avoided. A special ‘cooling chain’ preparation method is applied which enables studies on cryofractured bulk specimens at low temperatures.Quantitation of the obtained X‐ray spectra is done by the use of glycerol‐treated tissue specimens which are incubated with electrolyte solutions of defined ion concentration.
Low temperature microspectrofluorometry: design of a ‘cold chamber‘
Authors: Giordano P. , Bottiroli G. , Prenna G. , Doglia S. , Balnini G. 
Published: August 2011

SUMMARYLow temperature microspectrofluorometry allows an improvement of spectral resolution and an increase of fluorescence intensity. Suppression of fluorescence fading, or at least a marked reduction, is also obtained. A cooling chamber for microspectrofluorometric measurement is described which allows the cooling, under a microscope, of a biological sample down to liquid nitrogen temperature. Objectives with numerical apertures better than 1.0 and a magnification power up to 100 × can be used. Low temperature measurements on a histological sample are presented and discussed.
Structure determination of frozen, hydrated, crystalline biological specimens
Authors: Taylor Kenneth A. 
Published: August 2011

SUMMARYLow temperature transmission electron microscopy can be used to study the structure of biological materials in the hydrated state. Spatial averaging techniques are necessary to overcome the radiation damage problems, and for this reason the techniques described are most applicable to crystalline objects. However, with thin, crystalline biological specimens there are no difficulties with preserving periodicity during the freezing process. Improved specimen preparation methods are described which achieve the production of very thin aqueous films with the hydrated specimen embedded in them. Defocused bright field images of frozen, hydrated protein crystals possess a surprisingly high contrast, presumably due to the difference in density of the protein and the aqueous phase. The techniques described have been used to study the crystal structure of hydrated catalase and the outermost cell wall of Spirillum serpens.
Particle size‐shape distributions: the general spheroid problem: II. Stochastic model and practical guide
Authors: Orive Luis‐M. Cruz 
Published: August 2011

SUMMARYMathematical relationships linking the size‐shape probability density function (pdf) of an infinite population of variable spheroids uniformly and isotropically scattered in space on the one hand, with the size‐shape pdf of the ellipses produced by a plane of section on the other, have recently been published (Cruz Orive, 1976). In the present paper, an independent model is developed for estimating the size‐shape bivariate histogram of a finite population of variable spheroids (either prolate, or oblate) uniformly and isotropically scattered within an arbitrary specimen, from the corresponding histogram of the elliptical profiles produced by an arbitrary section (or sections) through the whole specimen. The approach is stochastic, allowing the estimation of the variance‐covariance matrix of the ‘unfolded’ size‐shape spheroid frequencies.The numerical reliability of the methods is checked by means of an example, whereas a practical guide illustrates and summarizes the unfolding procedure.Natural ways of estimating spheroid properties, alternative to those found in Cruz Orive (1976), are presented.
Structure and function of frozen cells: freezing patterns and post‐thaw survival
Authors: Nei Tokio 
Published: August 2011

SUMMARYFreezing patterns and post‐thaw survival of cells varies with different cooling rates. The optimal cooling rates, indicating the highest percentage survival, were different in yeast and red blood cells. A difference of freezing patterns was also noticed in preparations frozen above and below the optimal cooling rate for each cell, namely, cell shrinkage at lower rates and intracellular ice formation at higher rates, which showed similar trends in both the cells, even though there was some shifting of the optimum.Ultra‐rapid freezing and addition of cryoprotectants are useful ways to minimize ice crystal formation and to cause such ice formations to approach the vitreous state. Ice crystals are hardly detectable in yeast cells as well as in erythrocytes, when these cells are frozen ultra‐rapidly in the presence of cryoprotective agents in moderate concentration.
Description and comparison of a new cleaning method of diatom frustules for light and electron microscope studies
Authors: Ma Josten C. W. , Jeffrey Lela M. 
Published: August 2011

SUMMARYA general review is made of some of the methods commonly used by phyto‐planktologists in preparing and cleaning siliceous diatom frustules for light and electron microscopy. A comparatively simple and safe method using potassium persulphate and oven heating is described. Procedures for rinsing and mounting field samples are also included.
Signal to noise enhancement in a study of cell wall structure of Bacillus subtilis by interactive computation
Authors: Barrett A. N. , Burdett I. D. J. , Paton K. A. 
Published: August 2011

SUMMARYThis paper describes a technique for obtaining values of the width and variation in optical density of sectioned bacterial cell walls by interactive computational methods. Background ‘noise’ prevents accurate determination of cell wall boundaries from the data in a single scan line but the noise may be suppressed by averaging several consecutive scan lines. Although application of the technique is explained for sectioned bacterial cell walls, it is equally valid for similar situations where single line scans of electron micrographs are inadequate for precise determination of measurement.
Determination of membrane thickness distribution from orthogonal intercepts
Authors: Jensen E. B. , Gundersen H. J. G. , Østerby R. 
Published: August 2011

SUMMARYThis report deals with the reconstruction of the distribution of membrane thickness T from that of orthogonal intercept length L0, measured in random section planes. In such planes the membrane appears as a band and the linear distance from one of its boundaries perpendicular to the opposite one is the length of the orthogonal intercept. Using a membrane model, an integral equation relating the probability density functions of orthogonal intercept length f(l0) and membrane thickness g(τ) is derived. Relations between moments are derived and the analytic solution to the problem of reconstructing g(τ) from f(l0) is given. The parametric approach by which it is assumed that g(τ) has some known analytic form with unknown parameters is considered, and the use of a suggested analytic form for describing the thickness distribution of the human glomerular basement membrane is discussed.
Measurement by Quantimet 720 of the proportion of actively growing cells in tissue cultures of human lymphocytes
Authors: Brown R. A. , Mcwalter R. , Slidders W. , Gibbs J. , Beck J. Swanson 
Published: August 2011

SUMMARYThe size‐distribution of normal human lymphocytes growing in tissue culture was measured with a Quantimet 720 image‐analysing computer. The proportion of cells undergoing volumetric growth after phytohaemagglutinin (PHA) stimulation was derived from a simple mathematical model describing the growth patterns of the cells up to the first mitotic division. The approach may have general application in biology as a method for measuring the proportion of growing cells by microscopy.
Modification of an EM6G electron microscope for X‐ray microanalysis
Authors: Fitzgerald A. G. , Storey B. E. 
Published: August 2011

SUMMARYA dual purpose stage has been constructed for an EM6G 100 kV transmission electron microscope. With this stage the composition of thin films and bulk specimens can be determined by X‐ray microanalysis. With thin films a change of specimen cartridge then enables a full analysis of crystal defects in the film to be made using tilt controls incorporated in the stage. Modifications to the stage to reduce background effects in X‐ray microanalysis spectra are also described.The alternative use of this system in the bulk analysis of specimens by an X‐ray fluorescence technique is also discussed.
Freeze substitution for preservation of ciliated surfaces for scanning electron microscopy
Authors: Barlow D. I. , Sleigh M. A. 
Published: August 2011

SUMMARYA technique is described for arresting rapid movement of living cells and preserving their fine surface structures for scanning electron microscopy. Rapid freezing is recommended as the method of immobilization and freeze substitution has been employed to fix and dehydrate the specimens; this technique is more reliable than osmium fixation, both in terms of obtaining a much higher proportion of good results and in the improved preservation of detail. Various techniques of substitution have been investigated for best preservation, and the roles of the constituents of the substitution mixture have been discussed.
A Rapid Method For Estimating Volume Ratios
Authors: Orive L. M. Cruz , Myking A. O. 
Published: August 2011

SUMMARYA rapid stereological method is proposed for estimating the volume ratio V(K2)/V(K1) of two bodies K1, K2 such that K2 is embedded in K1. If K1, K2 fit approximately into a ‘star specimen’ model, then a single section, taken at a certain level through K1, provides a rather accurate estimate of V(K2)/V(K1). For a population of moderately similar star specimens, a constant sectioning level can be estimated from a sample using a least squares criterion.A pilot experiment involving mouse lymph nodes, aimed at estimating the mean and the variance of the individual fractions V(paracortex)/V(node), indicates a fair robustness against deviations from the model.
Microscopical Image Analysis: Problems And Approaches*
Authors: Bradbury S. 
Published: August 2011

SUMMARYThis article reviews some of the problems which have been encountered in the application of automatic image analysis to problems in biology. Some of the questions involved in the actual formulation of such a problem for this approach are considered as well as the difficulties in the analysis due to lack of specific contrast in the image and to its complexity.Various practical methods which have been successful in overcoming these problems are outlined, and the question of the desirability of an opto‐manual or semiautomatic system as opposed to a fully automatic version is considered.
A New Method For Scanning Electron Microscopic Visualization Of Dermal Elastic Fibres
Authors: Tsuji Takuo , Lavker Robert M. , Kligman Albert M. 
Published: August 2011

SUMMARYAutoclaving sections of dermis for 8 h followed by fixation, dehydration and xylol‐air drying yields a pure preparation of elastic fibres for scanning electron microscopy which retains the native architecture of this component. Elastic fibres were intertwined in a complex fashion with numerous branches. Fibres were predominantly cylindrical in the upper dermis and became larger and more elliptical in the deeper dermis. This method produces a means to study the organization of elastic fibres in a variety of disorders in which dermal changes are prominent.
Histologie Investigation Of Glycol Methacrylate Embedded Chick Embryonic Tissue
Authors: Swartz William J. , Nusbickel Fred R. 
Published: August 2011

SUMMARYSpecific light microscopic investigations (i.e. histochemical) of early embryonic material have always been beset by difficulties in processing and obtaining tissue sections of good quality. The advent of glycol methacrylate (GMA) as an embedding medium now provides a means to overcome these inherent problems with this tissue. Investigations were carried out to assess the histological results produced by different fixatives and times of fixation of GMA embedded 5‐day chick embryonic tissue. Optimum cellular preservation of all tissues occurred following fixation in a mixture of acetic acid, 95% ethanol and neutral buffered formalin (AAF). With the procedures described in this study, a new method is available for more comprehensive examination of all types of early embryonic material.
Visibility Of Diffraction Patterns And Bend Contours In Thick Composite Amorphous‐Crystalline Specimens Observed In Stem And Ctem
Authors: Craven A. J. , Valdreè U. 
Published: August 2011

SUMMARYFor a number of reasons, the specimens used to try to correlate the electrical and structural properties of commercial semiconductor devices often consist of a thick amorphous layer (e.g. silicon oxide) and a thinned layer of crystalline material (e.g. silicon) containing the p‐n junctions. Diffraction patterns and diffraction contrast images from such specimens recorded in conventional and scanning transmission electron microscopes at 80 and 500 kV are shown. The visibility of these diffraction patterns and images depends on the mode of operation, the aperture sizes and the side on which the electrons enter the specimen. The interpretation of these results is discussed and the practical implications for imaging of such specimens are pointed out.
A Double Embedding Technique For The Electron Microscopic Analysis Of The Liver Acinus
Authors: Miller Deborah L. , Gumucio Jorge J. 
Published: August 2011

SUMMARYA double embedding technique allowing accurate and systematic sampling of zones of the hepatic acinus by electron microscopy was developed. The method involved the primary embedding of large (10 mm × 30 mm × 0·5 mm) liver slices and the preparation of 10 μm thick tissue sections by means of a rotary microtome with a steel knife. Veins 20–40 μm in diameter, the landmarks of the hepatic acinus, were localized by light microscopy, dissected from surrounding tissue and re‐embedded for ultramicrotomy. The method facilitated the systematic evaluation of hepatocyte ultrastructure in each zone of the microcirculatory unit of the liver, the hepatic acinus.
A Modified Levanol Fast Cyanine 5Rn Staining Method For Myoepithelial Cells
Authors: Van Bogaert Louis‐Jacques , Quinones Jorge Abarca , Maldague Paul 
Published: August 2011

SUMMARYThe specificity of the tannic acid‐phosphomolybdic acid‐Levanol Fast Cyanine 5RN procedure for myosin‐like proteins in myoepithelial cells is hampered by the affinity of the dye for other structures. The selectivity of myoepithelial cell staining is enhanced by oxidation of sections, nuclear staining by Safranin‐O, and differentiation with Tartrazine.
A Microscopic Examination Of Void Formation In Superplastic Materials
Authors: Langdon Terence G. 
Published: August 2011

SUMMARYThere are two distinct groups of superplastic materials, depending on whether the final fracture surface has a large cross‐sectional area at optimum ductility or the specimen gradually pulls down to a very fine point. Experiments on a commercial superplastic copper alloy and the Zn‐22% Al eutectoid indicate that the formation of internal voids is important in materials of both groups. In addition, the results show that the size and shape of the internal voids is dependent both on the material and the testing conditions.
Irregular Helium Bubbles In Niobium Alloys
Authors: Tyler S. K. , Goodhew P. J. 
Published: August 2011

SUMMARYHelium bubbles have been produced in niobium‐1% Zr by ion implantation and their growth has been studied by transmission electron microscopy of annealed specimens. Bubbles are normally faceted and develop from tetrakaidodecahedra at short times to cuboids bounded by {100} faces after long annealing periods. This behaviour, together with the observation of steps on the faces of many bubbles, is accounted for in terms of competition between the conditions necessary for thermodynamic equilibrium and the kinetics of bubble motion. The larger bubbles must contain an excess gas pressure.
Tem Study Of Amorphous Alloys Produced By Ion Implantation
Authors: Johnson E. , Wohlenberg T. , Grant W. A. , Hansen P. , Chadderton L. T. 
Published: August 2011

SUMMARYIon implantation is a technique for introducing foreign elements into surface layers of solids. Ions, as a suitably accelerated beam penetrate the surface, slow down by collisions with target atoms to produce a doped layer. This non‐equilibrium technique can provide a wide range of alloys without the restrictions imposed by equilibrium phase diagrams.This paper reports on the production of some amorphous transition metal‐metalloid alloys by implantation. Thinned foils of Ni, Fe and stainless steel were implanted at room temperature with Dy+ and P+ ions at doses between 1018 and 1021 ions m−2 at energies of 20 and 40 keV respectively. Transmission electron microscopy and selected area diffraction analysis were used to investigate the implanted specimens.Radial diffracted intensity measurements confirmed the presence of an amorphous implanted layer. The peak positions of the maxima are in good agreement with data for similar alloys produced by conventional techniques. Only certain ion/target combinations produce these amorphous layers. Implantations at doses lower than those needed for amorphization often result in formation of new crystalline phases such as an h.c.p. phase in nickel and a b.c.c. phase in stainless steel.
The Imaging Of Surface Step Structures By Dark Field Electron Microscopy
Authors: Levitt J. P. F. , Howie A. 
Published: August 2011

SUMMARYThe dark field imaging of monatomic surface steps is studied by weak beam electron microscopy using reflections in higher order Laue zones. Dynamical theory calculations of the step intensities and of the diffuse background intensity in various diffracting conditions are in moderately good agreement with experimental observation on (111) thin films of gold. From grooving effects visible at incoherent twin boundaries, the boundary energy is estimated to be about one‐third of the surface energy. The extension of the method to other crystal surfaces or other materials is discussed.
The Measurement Of Excess Volume At Grain Boundaries Using Transmission Electron Microscopy
Authors: Pond R. C. 
Published: August 2011

SUMMARYA technique enabling accurate measurements of relative displacements between adjacent coincidence related crystals has been described previously. The technique depends on intensity measurements of stacking‐fault‐like fringes by comparison of experimental and theoretically simulated fringe profiles. This matching procedure is illustrated in the present work for a (l̄2l̄) boundary between twin related aluminium crystals. The main part of the paper describes the application of the technique for measuring excess volume at certain coincidence boundaries, and considers in detail the measurement for (l̄2l̄) boundaries. The excess volume per unit area at (l̄2l̄) boundaries is found to be 0·02 nm.
Interaction Of Grain Boundary Dislocations With Precipitates During High Temperature Creep
Authors: Dunlop G. L. , Nilsson J.‐O. , Howell P. R. 
Published: August 2011

SUMMARYThe interactions between grain boundary dislocations (GBDs) and intergranular TiC precipitates in an austenitic stainless steel (Alloy 800) have been investigated after creep at very low stresses at 800°C. The absence of Orowan looping suggests that the GBDs by‐pass the precipitates by glide/climb in the particle/matrix interfaces. An approximate calculation shows that the stress for bowing of GBDs between TiC precipitates is consistent with a measured value of the threshold stress for diffusion creep. However, it is suggested that an additional factor may be present in the threshold stress due to attractive forces between the precipitates and the GBDs.
The Austenite/Ferrite Interface In A Duplex Alloy Steel: Structure And Associated Diffraction Effects
Authors: Howell P. R. , Southwick P. D. , Honeycombe R. W. K. 
Published: August 2011

SUMMARYThis paper describes the structure of the austenite/ferrite interface in a duplex alloy steel. Specifically, it is shown that a single periodic set of dislocations exists in this interface. This dislocation array can act as a diffraction grating, and the extra reflections observed in selected area diffraction patterns are shown to be consistent with the dislocation structure observed in the image mode.