bluuebunny/crossref_metadata_2025_split huggingface dataset:
The correlation averaging of a regularly arranged bacterial cell envelope protein
Authors: Saxton W. O. , Baumeister W. 
Published: August 2011

SUMMARYAn adaptation of the ‘correlation averaging’ method is described which allows reliable and almost fully automatic image averaging in the case of near‐periodic structures notwithstanding the presence of substantial crystal imperfections; methods for assessing resolution and symmetry without reliance on crystallinity are also discussed. Electron micrographs of negatively stained and rotary shadowed preparations of the HPI‐layer protein from the cell envelope of Micrococcus radiodurans have been averaged using the method, and the projected structure is described to a resolution of about 1·9 nm.
An automatic focusing and astigmatism correction system for the SEM and CTEM
Authors: Erasmus S. J. , Smith K. C. A. 
Published: August 2011

SUMMARYFocusing and correcting the astigmatism of an electron microscope can be time consuming and difficult to achieve accurately. An automatic method of performing these tasks using an on‐line computer system and a digital framestore has been developed. The method is applicable to noisy images in both scanning and conventional transmission electron microscopes. It is capable of setting focus and correcting astigmatism at least as accurately as can be achieved by an experienced operator.
An improved specimen table for the Balzers freeze etching system BAF 400
Authors: Wisse D. M. , Spies F. 
Published: August 2011

SUMMARYA time saving, simple and inexpensive adaptation of a Balzers specimen table is described. This specimen table is used in combination with the small specimen holders originally developed for the Denton Freeze‐etching module. They are in particular suited for cell suspensions, and are easy to handle for freezing procedures. Ten replicas are produced routinely per freeze fracture run, with the aid of this combined system.
A new technique for perfusion fixation and contrast enhancement of foetal lamb myocardium for electron microscopy
Authors: Dae Michael W. , Heymann Michael A. , Jones Albert L. 
Published: August 2011

SUMMARYA technique of perfusion fixation following elective diastolic cardiac arrest was developed to obtain excellent preservation of foetal lamb hearts for morphological studies with electron microscopy. A technique was developed to markedly enhance the contrast of embedded material by treating thin sections with tannic acid prior to lead staining. This technique has been particularly useful for quantitative morphometric analysis.
On‐line image processing in high resolution electron microscopy
Authors: Boyes E. D. , Muggridge B. J. , Goringe M. J. 
Published: August 2011

SUMMARYOn‐line processing and analysis of high resolution electron microscope (HREM) images has been implemented using a software controlled image processor based on a commercial digital video framestore. It directly digitizes the output from the low light TV camera on the HREM and applies any processing necessary. The conditions under which images from amorphous specimens are being obtained can be established on‐line. The fast fourier transforms (FFTs) of 256 times 256 pixels produced in 15 s with the system off‐line are comparable to those from diffraction analysis of the same data on a laser optical bench. The precision of analysis of defocus, aberrations and astigmatism on‐line is discussed, together with possible approaches to routine analysis of crystalline specimens and for interactive control.
Resolution and contrast in the electron microscope: an historical review
Authors: Cosslett V. E. 
Published: August 2011

SUMMARYThe development of quantitative interpretation of electron micrographs, in respect of contrast as well as resolution, has followed similar lines to those in optical microscopy, though on a faster time scale. A thorough understanding of phase contrast came relatively late in both disciplines. The definition of resolution is more complicated in the case of the electron image on account of the severe effect of lens aberrations, especially spherical aberration. Experimental measurement of the performance of an electron microscope requires an operational definition of resolving power, which must include contrast considerations as well as the limitations imposed by lack of spatial and temporal coherence of the electron source. Agreement on suitable test procedures is now being reached, at least for a very thin specimen.
The contribution of electron microscopic cytochemistry to an understanding of the biogenesis of the endoplasmic reticulum of rat hepatocytes
Authors: Higgins Joan A. 
Published: August 2011

SUMMARYThe endoplasmic reticulum has the enzymic machinery for the synthesis of both protein and phospholipid and hence plays a central role in its own biogenesis and that of other cellular membranes. The evidence available concerning the biogenesis of the phospholipid bilayer of the endoplasmic reticulum, particularly from the application of fine structural cytochemical methods for the localization of acyltransferases, is reviewed. The observations are consistent with a model in which phospholipid is synthesized in situ at the site of membrane growth. Synthesis is asymmetric, with most enzymes located at the cytoplasmic side of the membrane, and controlled transmembrane movement of phospholipid results in an asymmetric bilayer.
Quantitative light and electron microscopical studies of the epithelial‐connective tissue junction in intraoral mucosae
Authors: Bale Elizabeth , White F. H. 
Published: August 2011

SUMMARYThe present study was designed to clarify the morphological nature of epithelial‐connective tissue attachment by quantitative comparison of palatal and buccal mucosae. Tissue samples were obtained from ferrets and, following a strict sampling regime, sections were obtained for quantitative light and electron microscopy. Electron micrographs from the epithelial‐connective tissue junction were subjected to analysis by stereological intersection counting. Quantitative results show that palatal epithelium has a comparatively convoluted interface, and is twice as thick as buccal epithelium. Stereological data are presented for relative surface area of basal plasma membrane occupied by hemidesmosomes, mean hemidesmosomal diameter and numerical density of hemidesmosomes per unit area of basal plasma membrane. Larger hemidesmosomes are found in the palatal epithelium. Results suggest that a prominent rete‐ridge pattern, as seen in the palatal epithelium, along with a greater specialized surface for adhesion, may be responsible for providing epithelial‐connective tissue stability in regions subjected to high mechanical stress.
Specificity of stain distribution in electron micrographs of protein molecules contrasted with uranyl acetate
Authors: Steven Alasdair C. , Navia Manuel A. 
Published: August 2011

SUMMARYThe mechanism of contrast enhancement of protein molecules by negative staining with uranyl acetate has been investigated by analysing electron micrographs of microcrystals of the human immunoglobulin Dob. Digitally filtered micrographs were compared systematically with idealized reference images which were constructed computationally, starting from knowledge of the primary sequence and three‐dimensional crystal structure of this IgG molecule. By separately modelling negative staining as bulk exclusion of heavy metals, and positive staining as the specific decoration of charged amino acid residues, and then combining these simulated images, we were able to assess quantitatively the amount of positive staining present in micrographs of ostensibly ‘negatively stained’ proteins. At a resolution of 2 nm, we find that the experimental images do indeed exhibit predominantly negative staining, the best matches being obtained by simulations which also include a minor contribution (10–40%) of positive staining. We have also compared two independent measures for the significant resolution present in images of periodic biological specimens: (i) the outermost visible orders of optical diffraction patterns, and (ii) the band‐limited resolutions of the idealized simulations when they most closely match the experimental images. These criteria observe close correspondence, thus vindicating the traditional practice of inferring resolution from the optical diffraction spectra of indirectly represented (stained) objects.
Electron scattering in ice and organic materials
Authors: Eusemann R. , Rose H. , Dubochet J. 
Published: August 2011

SUMMARYScattering cross‐sections for the interpretation of the scattering‐absorption contrast of microscopical images of amorphous biological specimens are calculated. The constituent atoms are treated as independent particles and their atomic potential is approximated by a modified Lenz‐Wentzel potential. Both elastic and inelastic scattering processes are considered. Formulas of the effective elastic and inelastic atom scattering cross‐sections are derived for both a CTEM with hollow‐cone illumination and a STEM using an annular detector. The scattering‐absorption contrast is plotted as a function of the atomic number for a CTEM applying parallel illumination and a STEM using a dark‐field detector with maximum collection efficiency. The presented results are valid for acceleration voltages U in the range 20 kV<U<150 kV. Employing these data the ‘angular mass thicknesses’ of representative constituents of biological materials are determined. The application of the listed data is demonstrated by means of a special example.
The evaluation of autofluorescence emission spectra derived from neuronal lipopigment
Authors: Dowson J. H. 
Published: August 2011

SUMMARYA method for measuring the emission spectra from regions of neuronal lipopigment in tissue sections is described and illustrated. Each emission spectrum was derived from the means of six sets of readings, from either six regions of lipopigment from six neurones which were presumed to be from a homogeneous cell population, or from one region of one neurone. Characteristics of the emission spectra from lipopigment in various forms of neuronal ceroid‐lipofusinoses (NCLs) and in brains without evidence of NCL are presented and discussed. The results indicate that the classification of lipopigments should not be restricted to the two categories of ‘lipofuscin’ and ‘ceroid’.This method may aid the identification of various pathogenic mechanisms in neurones, and provide another means of investigating the effects of certain drugs on cerebral function.
Low temperature techniques applied for CTEM and STEM analysis of cellular components at a molecular level
Authors: Sjöstrand Fritiof S. 
Published: August 2011

SUMMARYOne of the most important problems in tissue preparation for electron microscopic analysis at a molecular level involves the preservation of the tissue without introducing extensive denaturation of the proteins. Low temperature is a most efficient condition for the inhibition of protein denaturation and freeze‐drying offers favourable conditions for transferring proteins to a dry state with minimal denaturation of the proteins. However, the embedding of the dried tissue in a plastic leads to extensive denaturation of the proteins when performed in the conventional way. This eliminates very efficiently the advantages of the method. The situation becomes even worse when subjecting the tissue to freeze‐substitution. To eliminate as far as possible the denaturing effect of plastic embedding, freeze‐drying can be combined with low temperature embedding in a plastic.Freeze‐fracturing allows a most efficient use of low temperature to reduce conformation changes in proteins. The value of the freeze‐fracturing technique depends entirely on a precise knowledge of the location of the fracture planes. Since this location is not known, it must be determined on the basis of a deduction. If this deduction is wrong, the method becomes misleading. Two methods which allow a certain testing of the correctness of the deduced location of the fracture planes are mentioned.
Imaging of outer segment periodicities in unstained cryoultramicrotomy sections of the frog retina
Authors: Kretzer Frank , Cohen Harold 
Published: August 2011

SUMMARYFrog retinas were examined following cryoultramicrotomy. The extent of glutaraldehyde cross‐linking ranged from maximally 2% for 2 h to no cross‐linking. When the tissue was cryo‐protected, the effects of hypotonic, isotonic and hypertonic media on outer segment banding periodicities were studied. The specimen was cryosectioned at 193 K to 113 K with sections collected on a dry knife (213 K to 123 K). The sections were freeze‐dried and only rehydrated with phosphotungstic acid section stain when transmission electron microscopy was used to establish the extent of gross retinal morphology for each fixation protocol employed. As the extreme of no cross‐linking and no cryoprotection was approached and reached, conventional sections which displayed extensive retinal morphology were not obtained. Instead, fragments of retinal tissue resulted which showed periodicities of alternating light and dark bands. These periodicities are interpreted as photoreceptor outer segment discs with contrast formation depending upon an interplay between three factors: mass density differences between disc and interdisc space, section cutting angle, and section thickness.
A polychrome stain for conventionally fixed paraffin‐embedded woody plant tissues
Authors: Sam Sterling J. 
Published: August 2011

SUMMARYA method for the differential staining of conventionally fixed paraffin‐embedded woody plant tissue is described. A five‐component stain combination is used with Bismarck Brown, included to avoid the stain variability, precipitation, and overstaining problems often encountered when using safranin.
Holographic methods in microscopy
Authors: Smith R. W. 
Published: August 2011

SUMMARYHolography can be used to record, on a flat photographic plate, information about a three‐dimensional object. In conventional microscopy a thin slice of an object is observed in focus and recorded. By combining microscopy and holography it is possible to encode, on the same flat record, all the depth information in a three‐dimensional microscopic object, not just a single infocus section. Any section of the three‐dimensional object may be subsequently reconstructed and brought into focus by using a suitable viewing system to decode the hologram. Arrangements for doing this are described. It is shown that in order to achieve the highest resolution imagery of a three‐dimensional object, reversed wave reconstruction is necessary.As holograms are made and reconstructed using a coherent laser light source, holographic microscopes are easily adapted for interferometry and an example of this is described. The differences between coherent and conventional imagery are briefly considered. The coherence of the illumination gives rise to the problems of coherent noise and speckle. Coherent noise is due to stray reflections in the optical system and can be reduced by using as few surfaces as possible or by using holographic lenses. A speckle reduction technique employing a new type of holographic optical element is described and its application to the stereomicroscopy of fossil ostracods considered.
Some improvements in the phase contrast microscope
Authors: Yamamoto K. , Taira A. 
Published: August 2011

SUMMARYSome considerations on the improvement of the image quality of the phase contrast microscope are presented. The significance of glare and image fidelity discussed theoretically and the dependence of image fidelity and contrast on the phase plate characteristics are investigated on the basis of images calculated for different parameters of the annular phase plate. This paper also describes an anti‐reflection technique for the phase plate and demonstrates its effectiveness in the elimination of glare.
An evaluation of methods for preparing easily damaged cuticular surfaces of plants for scanning electron microscopy
Authors: Eveling D. W. , McCall R. D. 
Published: August 2011

SUMMARYTechniques were tested to ascertain the best method for preparing the surfaces of delicate plant cuticles for microscopic examination at magnifications not exceeding 10,000. Using scanning electron microscopy, comparative examinations were made of cuticles of fresh material, ambient dried, freeze dried, critical point dried, and frozen material kept at low temperature. Micrographs were compared with material examined using light microscopy which acted as a control at low magnification. Cuticles of the leaves of runner bean, Coleus and the petals of Nicotiana, showed best surface preservation and least wrinkling when frozen, held at low temperature, and examined on a cryostage.
Vascular reactions to perfusion fixation
Authors: Thorball N. , Tranum‐Jensen J. 
Published: August 2011

SUMMARYVascular reactions to fixation with a 2·5% w/v glutaraldehyde fixative were studied in a constant flow perfusion system on isolated rabbit intestines and hind limb preparations. Reactions induced by the fixative were compared to reactions induced by noradrenaline in each single preparation. Changes in vascular resistance were assessed from continuous recordings of arterial and venous pressures and perfusion flow. Changes in vascular filtration and macro‐molecular permeability during fixation were approximated from recordings of flow and measurements of concentrations of dextran in the perfusate at the arterial inlet and at the venous outlet.Our results indicate that the vascular bed of the preparations studied can be reliably fixed in a high resistance state of smooth muscle activity induced by noradrenaline as well as in a low resistance state in the absence of noradrenaline, provided that hydrodynamic parameters are strictly controlled. The vascular filtration decreases during fixation. In optimally perfused preparations 5–10 min are required to fully saturate the binding capacity of the tissue for glutaraldehyde.Data on viscosity and colloid osmotic pressure of Tyrode solution containing dextran T‐70 in various concentrations, and of various aldehyde‐containing fixatives in 0·1 M sodium phosphate buffer with and without dextran added, are given.
Fractal analysis and stereological evaluation of microstructures
Authors: Wright K. , Karlsson B. 
Published: August 2011

SUMMARYFractal properties and the concept of fractal dimension has been studied. Emphasis is given to the applicability in structure analysis. Comparison between different measurement procedures, analyses of mathematically defined lines and surfaces as well as measurements on real surfaces have been performed. The stereological consequences have been considered.A restrictive use of the fractal analysis results as an indicator of size, shape and self‐similarity is recommended. If results obtained by quantitative microscopy at different magnification‐resolution levels are to be compared, fractal analysis may be of advantage. The actual choice of resolution should yet be determined from the physical relevance of the geometrical details.
Extraction of membrane lipids during fixation, dehydration and embedding of Acholeplasma laidlawii‐cells for electron microscopy
Authors: Weibull C. , Christiansson A. , Carlemalm E. 
Published: August 2011

SUMMARYThe aim of the present investigation was to study the extent to which lipids are extracted from biological membranes during dehydration and embedding procedures carried out at high or low temperatures. Cells of Acholeplasma laidlawii were used as experimental material, since the lipids of this bacterium easily can be radioactively labelled without labelling the rest of the cell, and the lipids are almost entirely located in the cytoplasmic membrane. The cells were fixed at 277 K with glutaraldehyde, sequentially with this reagent and osmium tetroxide, or with glutaraldehyde, osmium tetroxide and uranyl acetate in that order. Loss of lipid during these procedures was negligible.When cells fixed with glutaraldehyde and osmium tetroxide were dehydrated with ethanol at room temperature and embedded in Epon at 333 K, i.e. subjected to a conventional treatment, about 90% of the lipid content of the cells was extracted. The loss was reduced to c. 20% when treatment with uranyl acetate was included in the procedure and the non‐polar methacrylate resin Lowicryl HM20 was substituted for Epon. When cells fixed with glutaraldehyde and osmium tetroxide were dehydrated with ethanol at 238 K and embedded in Lowicryl HM20 at room temperature, practically no lipid was extracted. Substitution of the polar methacrylate‐acrylate resin Lowicryl K4M for Lowicryl HM20 resulted in the loss of about half of the lipid content of the cells. The use of ethanediol as dehydrating agent instead of ethanol did not diminish the extraction. Cells fixed solely with glutaraldehyde lost about half of their lipid content, even when both dehydration and embedding was performed at 238 K.The lipid material extracted from glutaraldehyde‐fixed cells contained slightly more saturated fatty acids than that remaining in the cells. The reverse was true for osmium tetroxide‐fixed cells. With respect to lipid species, the extractions were generally rather unspecific.
High resolution and conventional electron microscopy studies of repeated wedge microtwins in monoclinic rare earth sesquioxides
Authors: Boulesteix C. , Yangui B. , Nihoul G. , Bourret A. 
Published: August 2011

SummaryHigh resolution and conventional studies have been made on the inclined twin boundaries occurring near the tip of wedge microtwins in the case of repeated wedge microtwins occurring at twin intersections. These inclined boundaries appear to be continuous and all the atomic planes are also continuous so that we suggest the use of the term ‘inclined coherent boundaries’ instead of ‘incoherent’ which one generally employs, in analogy to the case of precipitates in a matrix. This is different from what occurs in the case of isolated wedge microtwins for the same material and for the same kind of twins where the inclined twin boundary is really not coherent, being made of non‐inclined coherent regions separated by steps containing a dislocation.The coherent inclined boundaries of repeated wedge microtwins appear to be rotated about two perpendicular axes of the habit plane (tilt and twist) giving rise to a distribution of microdislocations whose role has been studied. The values of the tilt and twist angles are related to a minimization of the total energy by a mechanism that is likely to appear only in the case of thin foils. A comparative study of the different roles related to the different structures of inclined twin boundaries for isolated and repeated wedge microtwins has been made, and also a comparative study of the mechanisms of stress relaxation in each case. The studies have been made on (313) twins of a monoclinic samarium sesquioxide.
Coherency strain fields: magnitude and symmetry
Authors: Porter A. J. , Ecob R. C. , Ricks R. A. 
Published: August 2011

SummaryThis paper considers the various methods available for the measurement of small values of in‐situ lattice misfit between a coherent particle and the matrix. Examination of such misfits by Asby‐Brown contrast imaging, moiré fringe measurements, lattice fringe imaging and convergent beam electron diffraction (C.B.E.D.) is considered, and the results obtained by these techniques are compared. In addition the nature of the strain fields in the matrix adjacent to a coherent misfitting particle is examined using C.B.E.D.
Topographic quantification of non‐planar localized surfaces
Authors: Wright K. , Karlsson B. 
Published: August 2011

SUMMARYThe topography of non‐planar localized surfaces can be quantified by roughness indices as well as by height and angular distributions of the surface elements. For the roughness indices general relationships between the profile and spatial quantities including overlapping have been established. Some measurement methods are briefly considered. The profile analysis has proved to be a reliable, easy and fast way to characterize the topography of surfaces.