bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxygen ordering and twinning in YBa2Cu3O7−x
Authors: Barry J. C. 
Published: February 2005

AbstractDirect structure images of the YBa2Cu3O7−x high Tc superconducting ceramic (also called the 1–2–3 compound) at 1.7 Å resolution have been obtained for the [100] and [001] orientations. It was found that for the purposes of studying oxygen ordering in this compound it is better to use lattice images of lower resolution. The oxygen ordering was studied via the measurement of the bending of (100) and (110) lattice planes on crossing the (110) twin boundaries in crystals oriented in the [001] zone. Significant variations were found in the b/a ratios, owning to a variation in oxygen ordering, between different crystal grains, and between different regions in the same grain. For the three different 1–2–2 samples studied, the average b/a ration was 1.016, the same value as was found in neutron diffraction studies. The twin boundaries in the orthorhombic 1–2–3 phase are sharp and planar. It seems likely that the transformation from the high‐temperature tetragonal phase to the lower‐temperature orthorhombic phase is martensitic in nature. A new phase has been discovered on some of the twin boundaries. The new phase can be indexed as tetragonal with a = 7.5 ± 0.2 Å, and c = 6.8 ± 0.2 Å. It is possible that the new phase is stabilized by the stress which occurs at the twin boundaries.
Backscattered electron imaging of lectin binding sites in tissues following freeze‐fracture cytochemistry
Authors: Kan Frederick W. K. , Nanci Antonio 
Published: February 2005

AbstractRecently, cytochemical techniques have been applied for localizing membrane components; however, transmission electron microscopy only provides two‐dimensional information about their distribution. Scanning electron microscopy, on the other hand, offers the possibility of examining the three‐dimensional architecture of biological samples. The fracture‐label cytochemical technique was combined with the backscattered electron imaging (BEI) mode of the scanning electron microscope to visualize the in vivo distribution of lectin binding sites on freeze‐fractured biological membranes in tissues and cells. Pancreatic and testicular tissues, fixed with glutaraldehyde, were freeze‐fractured and labeled with Helix pomatialectin‐gold or Ricinus communis I‐gold complexes. The labeled specimens were then critical‐point dried and replicated with platinum‐carbon for routine transmission electron microscopy or with carbon alone for BEL. Lectin‐gold labeling of fractured plasma and intracellular membranes observed with BEI showed a labeling pattern similar to that seen by the replica method. However, BEI‐fracturelabel provided additional information about the distribution of the labeling with respect to three‐dimensional organization of tissues and cells. Large sample areas could be examined, making this technique particularly useful as a survey method for specimens that are either differentially labeled or composed of heterogenous cell populations.
Introduction to X‐ray microanalysis in biology
Authors: Roomans Godfried M. 
Published: February 2005

AbstractThis paper gives an introduction to X‐ray microanalysis for biologists. The physical principles of X‐ray microanalysis and the instrumentation used in wavelength‐dispersive and energy‐dispersive analysis are reviewed. A special problem in biological microanalysis is the adequate preparation of the specimen: The preparative method must retain the localization of the element(s) of interest and allow identification of morphological features at the level of analytical resolution. Conventional preparation methods for electron microscopy have only a limited applicability in biological X‐ray microanalysis, and often cryomethods have to be used. Methods for qualitative analysis and some common pitfalls and artefacts are discussed. The possibilities and limitations of electron‐probe X‐ray microanalysis with regard to biological specimens are compared to those of other microanalytical techniques.
Low temperature techniques for X‐ray microanalysis in pathology: Alternatives to cryoultramicrotomy
Authors: Wroblewski Joanna , Wróblewski Romuald , Roomans Godfried M. 
Published: February 2005

AbstractMany diseases are associated with a change in the distribution of diffusible ions at the cell or tissue level. These diseases can profitably be studied by X‐ray microanalysis. This technique for the study of ion distribution requires the use of cryoprepared specimens. Analysis at low or medium resolution can be carried out on thick or semi‐thick cryosections, or on frozenhydrated or freeze‐dried embedded bulk samples. Such analyses are particularly useful in the initial stages of an investigation or when data from a large number of samples have to be acquired. Also X‐ray microanalysis of cultured or single cells prepared by freeze‐drying can be used to rapidly collect information on a large number of cells. Analysis at high resolution has to be carried out on thin sections: Cryosections or sections of freeze‐substituted or freeze‐dried embedded tissue. For the latter type of specimens, the use of low‐temperature embedding methods may have important advantages.
Reflection high resolution analytical electron microscopy: A technique for studying crystal surfaces
Authors: Wang Z. L. 
Published: February 2005

AbstractReflection electron microscopy (REM), reflection high energy electron diffraction (RHEED), reflection electron energy‐loss spectroscopy (REELS), and energy dispersion x‐ray spectroscopy (EDX) have been comprehensively used as a technique, termed reflection high resolution analytical electron microscopy (RHRAEM), for studying the structures of the bulk crystal GaAs (110) surfaces by transmission electron microscopy (TEM). The simultaneous observations of surface topography imaging, the surface diffraction mechanism with RHEED, surface atomic inner‐shell excitations with REELS, and surface chemical compositions with EDX provide a systematic description of the atomic structure and chemical structure of the surface. The surface channelling effect has been observed in GaAs (110) with REELS, which may provide a basis for localizing surface foreign atoms with ALCHEMI. The theoretically predicted surface‐resonance wave has been observed directly in the RHEED pattern; the surface‐captured Bragg reflection wave have been identified. It is shown that surface chemical compositions can be determined by analyzing the EDX spectra obtained in the REM case. Finally, the surface monolayer resonance characteristic of the RHRAEM has been confirmed by calculations with dynamical RHEED theory.
Controlled environment vitrification system: An improved sample preparation technique
Authors: Bellare J. R. , Davis H. T. , Scriven L. E. , Talmon Y. 
Published: February 2005

AbstractThe controlled environment vitrification system (CEVS) permits cryofixation of hydrated biological and colloidal dispersions and aggregates from a temperature‐ and saturation‐controlled environment. Otherwise, specimens prepared in an uncontrolled laboratory atmosphere are subject to evaporation and heat transfer, which may introduce artifacts caused by concentration, pH, ionic strength, and temperature changes. Moreover, it is difficult to fix and examine the microstructure of systems at temperatures other than ambient (e.g., biological systems at in vivo conditions and colloidal systems above room temperature). A system has been developed that ensures that a liquid or partially liquid specimen is maintained in its original state while it is being prepared before vitrification and, once prepared, is vitrified with little alteration of its microstructure. A controlled environment is provided within a chamber where temperature and chemical activity of volatile components can be controlled while the specimen is being prepared. The specimen grid is mounted on a plunger, and a synchronous shutter is opened almost simultaneously with the release of the plunger, so that the specimen is propelled abruptly through the shutter opening into a cryogenic bath. We describe the system and its use and illustrate the value of the technique with TEM micrographs of surfactant microstructures in which specimen preparation artifacts were avoided. We also discuss applications to other instruments like SEM, to other techniques like freeze‐fracture, and to novel “on the grid” experiments that make it possible to freeze successive instants of dynamic processes such as membrane fusion, chemical reactions, and phase transitions.
Membrane and cytoplasmic structure at synaptic junctions in the mammalian central nervous system
Authors: Landis Dennis M. D. 
Published: February 2005

AbstractApplication of rapid freezing, freeze substitution fixation, and freeze fracture techniques to the study of synaptic junctions in the mammalian central nervous system has revealed new aspects of synaptic structure that are consistent with and partially explicate advances in synaptic biochemistry and physiology. In the axoplasm adjacent to the presynaptic active zone, synaptic vesicles are linked to large spectrin‐like filamentous proteins by shorter proteins that resemble synapsin I in morphology. This mesh of presynaptic filamentous proteins serves to concentrate synaptic vesicles in the vicinity of the active zone. The affinity with which the vesicles are bound by the mesh is probably modulated by the extent of phosphorylation at specific sites on the constituent filamentous proteins, and changes in the binding affinity result in changes in transmitter release.The structural organization of the postsynaptic density in Purkinje cell dendritic spines consists of very fine strands with adherent, heterogeneous globular proteins. Some of these globular proteins probably correspond to protein kinases and their substrates. The postsynaptic density, positioned at the site of the maximal depolarization caused by synaptic currents, apparently serves as a supporting framework for a variety of proteins, which respond to and transduce postsynaptic depolarization.At least two classes of filamentous protein fill the cytoplasm of spines with a complex mesh, which presumably contributes to maintenance of the spine shape. Membrane bound cisterns are a ubiquitous feature of Purkinje cell dendritic spines. Studies of rapidly frozen tissue with electron probe microanalysis and elemental imaging reveal that these cisterns take up and sequester calcium, which is derived from the extracellular space, and which probably enters the spine as part of the synaptic current.
A review of recent observations concerning the synaptic organization of the basilar pontine nuclei
Authors: Mihailoff G. A. , Kosinski R. J. , Border B. G. , Lee H. S. 
Published: February 2005

AbstractUltrastructural studies are described that have identified in the basilar pontine nuclei (BPN), the synaptic boutons formed by the corticopontine, cerebellopontine, tectopontine, and dorsal column nucleipontine afferent projection systems. In addition, immunocytochemical studies visualized neuronal somata, dendrites, and synaptic boutons that contain immunoreactivity for GABA or the synthesizing enzyme glutamic acid decarboxylase (GAD).Based upon differences in the mode of degeneration and postsynaptic locus of degenerative synaptic boutons in the BPN, it is suggested that two types of cortical neurons and three classes of deep cerebellar nuclear cells project to the BPN. For similar reasons, it appears that two types of neurons in the dorsal column nuclei project to the BPN while only one type of afferent synaptic bouton takes origin from the superior colliculus. Furthermore it appears that the population of BPN neurons projecting to the paramedian lobule receives convergent inputs from the cutaneous periphery and the corresponding region of sensorimotor cortex. Studies employing GAD immunohistochemistry indicate that GABA‐ergic neurons and axon terminals are present in the BPN and thus support the suggestion that a local inhibitory interneuron is present within the BPN. Taken together these observations suggest that basilar pontine neurons might play a more active role in the integration of various types of information destined for the cerebellar cortex than has previously been recognized.
Synaptic organization of the thalamic reticular nucleus
Authors: Ohara P. T. 
Published: February 2005

AbstractThis study describes the synaptic organization of the thalamic reticular nucleus (TRN) in the rat, cat, and monkey using electron microscopy combined with immunocytochemistry, degeneration, or horseradish peroxidase (HRP) tracing methods. Three morphological types of terminals are described in the TRN of the rat: a small terminal with densely packed spherical vesicles (D‐terminal), which originates from the cortex; a large terminal with loosely packed spherical vesicles (L‐terminal), which originates in the dorsal thalamus; and a terminal containing flattened synaptic vesicles (F‐terminal) that is probably a TRN recurrent collateral. The cortical input to the TRN has been shown by double‐labeling studies to terminate directly upon TRN projection neurons. Similar classes of terminals are found in the TRN of cat and monkey, but there is in addition a large terminal with spherical synaptic vesicles that is invaginated by dendritic spines. Also present in the cat and monkey, but not in the rat, are vesicle‐containing dendrites and dendritic appendages.In the rat, degeneration experiments indicate that the terminals of TRN projection neurons in the dorsal thalamus are F‐terminals. These terminals contain flattened synaptic vesicles and exhibit GABA immunoreactivity.
High‐resolution electron microscopy image simulation on a Cray 1S/2300 computer
Authors: Spycher R. , Stadelmann P. , Buffat P. , Flueli M. 
Published: February 2005

AbstractHigh‐resolution electron microscopy (HREM) image simulation by the multislice method has been implemented on a Cray 1S/2300 computer, allowing accurate full nonlinear image intensity calculations with possible sampling up to 2n × 2m samples of the transmission function (n + m = 20). As examples of applications, images have been obtained from an interface in PbTiO3 and of a small gold aggregate. HREM image simulation of perfect or faulted crystals can now be applied with reasonable computing times to problems involving a large number of atoms and thick or large supercells.
Image analysis of electron micrographs relating to mineralization in calcifying cartilage: Theoretical considerations
Authors: Hunziker E. B. , Herrmann W. , Cruz‐Orive L. M. , Arsenault A. L. 
Published: February 2005

AbstractBiological mineralization is a cell‐mediated process which is believed to be triggered by a “nucleating agent.” Various matrix structures, such as matrix vesicles, collagen fibrils and macromolecules, have been claimed to be the source of this substance, since these components have been found by transmission electron microscopy (TEM) of thin sections to be associated with early mineral crystals. Systematic image analysis of the relationships revealed in electron micrographs between specific matrix components and early mineral deposits has shown that unequivocal image interpretation is not possible. This is due principally to the problems posed by overprojection and truncation phenomena, since the structures being analyzed lie within the same dimensional range as thin section thickness. Various examples are illustrated and discussed. The site at which mineral crystals are initially laid down thus cannot be identified with any matrix structure using thin section TEM. Possible technical approaches to resolve this problem of image analysis are discussed.
Optimum specimen positioning in the electron microscope using a double‐tilt stage
Authors: Turner J. N. , Rieder C. L. , Collins D. N. , Chang B. B. 
Published: February 2005

AbstractOptimal imaging of complex structures requires proper alignment relative to the optic axis of the electron microscope. This is especially important for high‐voltage and intermediatevoltage microscopes, which form an in‐focus image throughout the entire thickness of the object. As a result, structures at different specimen heights form overlapping and confused images that severely curtail the usefulness of these instruments.The work described here provides a generalized, flexible method for optimizing specimen orientation and eliminating or limiting image overlap by means of a commonly used double‐tilt stage. Analysis of the motion about the two axes provides accurate tilting for any azimuthal direction whether or not it corresponds to a mechanical axis of the stage. An object can be positioned to minimize image overlap, to record stereopairs for any parallax axis, and to record three‐dimensional data sets by the conical collection geometry.Images of muscle paracrystals are shown after tilting about an axis perpendicular to a symmetry direction. The tilted image displays higher‐order symmetry, which is altered by changes of one degree. Precision double‐tilting for optimizing stereopairs is shown for a desmosome recorded using different parallax axes and pretilts. A tomographic conical data‐collection scheme is demonstrated by imaging a microtubule axoneme for a specific cone half‐angle and arbitrary azimuthal angles.
Preparation of cross‐sectional transmission electron microscopy samples by electron beam lithography and reactive ion etching
Authors: Wetzel J. T. 
Published: February 2005

AbstractA cross‐sectional sample preparation technique is described that relies on lithographic and dry‐etching processing, thus avoiding metallographic polishing and ion milling. The method is capable of producing cross‐sectional transmission electron microscopy samples with a large amount of transparent area (1 μm × 2.5 mm) which allows the examination of many patterned test sites on the same sample from the same chip of a silicon wafer. An example of the application of the technique is given for localized oxidation through a mask.
Experimental conditions for surface microanalysis with reflection electron energy‐loss spectroscopy
Authors: Wang Z. L. 
Published: February 2005

AbstractExperimental conditions for obtaining the optimum signal‐to‐background (S/B) ratio in reflection electron energy‐loss spectroscopy (REELS) are investigated. It is shown that the S/ B ratio can be improved by lowering the incident energy of the electrons. The spectra taken from the GaAs (660) specular reflection spot under the surface resonance condition is demonstrated to have the best S/B ratio and lowest surface plasma excitation, which is capable of providing structural information on the top few atomic layers.
Removal of background label in immunocytochemistry with the apolar lowicryls by using washed protein A–gold‐precoupled antibodies in a one‐step procedure
Authors: Dürrenberger Markus B. 
Published: February 2005

AbstractAntiserum mixed with protein A–gold produces aggregates that can be washed by centrifugation and redissociated by ultrasonication. These precoupled antibodies are used for immunocytochemical labeling in a one‐step procedure and reveal a very low background on sections of material embedded in polar and apolar Lowicryls. Controls have shown that the background label stems from serum components with only one protein A binding site and is discarded during the wash steps of the precoupling procedure.
Quantitative analytical electron microscopy of multiphase alloys
Authors: Prybylowski J. , Ballinger R. , Elliott C. 
Published: February 2005

AbstractIn this paper, we present a technique for analysis of composition gradients, using an analytical electron microscope, within the primary phase of a two‐phase alloy for the case where the second‐phase particle size is similar to the size of the irradiated volume. If the composition difference between the two phases is large, the detected compositional fluctuations associated with varying phase fractions may mask any underlying composition gradient of the primary phase. The analysis technique was used to determine grain boundary chromium concentration gradients in a nickel‐base superalloy, alloy X‐750. The technique may also be of use in other alloy systems.
Study of airway epithelial permeability with dextran
Authors: Hulbert W. C. , Forster B. B. , Mehta J. G. , Man S. F. P. , Molday R. S. , Walker B. A. , Walker D. C. , Hogg J. C. 
Published: February 2005

AbstractWe studied the penetration of fluorescein isothiocyanate (FITC) T‐40 dextran into the paracellular spaces in the tracheal mucosa and its appearance in the blood plasma of guinea pigs exposed to cigarette smoke or (controls) breathing room air. Under general anesthesia, the dextran solution was instilled onto the tracheal surface via a tracheotomy tube, arterial blood was sampled serially for 40 min, and then the trachea was fixed by perfusion or immersion. Examination of the tracheal mucosa with light microscopy, with and without epifluorescence, and transmission electron microscopy, revealed dextran in the paracellular spaces in mucosa from experimental animals but not controls. In all control animals, the levels of the dextran in plasma was below the sensitivity of the assay. By contrast, dextran levels in the plasma from the experimental animals fell within the sensitivity range of the assay and increased in blood at a rate of 0.00125 ± 0.00023 (SE) expressed as a percentage of the instilled dose/min. We conclude that FITC T‐40 dextran provides a reliable, fairly simple, fast method for assessing major, but not subtle, changes in paracellular permeability of the tracheal mucosa.
Observation of microdiffraction patterns with a dedicated STEM instrument
Authors: Cowley J. M. , Ou H.‐J. 
Published: February 2005

AbstractA two‐dimensional detector system, designed for the observation and recording of microdiffraction patterns formed in an HB 5 scanning transmission electron microscope (STEM) is described and discussed. Possibilities are described and demonstrated for the simultaneous or successive recording of microdiffraction patterns from regions of diameter 3 å or more, bright‐ or dark‐field STEM images, EELS spectra, secondary electron images, and in‐line holograms. Applications of the system have been made to studies of catalyst particles, reflection‐mode imaging of bulk surfaces, and image reconstruction from microdiffraction patterns obtained from each point of a STEM image.
Extraction of carbon 14‐labeled compounds from plant tissue during processing for electron microscopy
Authors: Coetzee J. , van der Merwe C. F. 
Published: February 2005

AbstractLoss of 14C‐labeled compounds from bean leaf tissue was monitored during all the stages of routine specimen preparation. No significant differences in extraction were associated with the use of acetone, ethanol, or dioxane as dehydration fluids. Fixation at low temperature increased the loss of label. Prolonged fixation in glutaraldehyde increased the loss, but fixation in osmium solutions for periods as long as 4 hr had no influence on extraction. Buffer rinses and dehydration fluids caused appreciable amounts of label to be extracted. The use of propylene oxide as transition fluid resulted in low extraction. Some embedding media caused the loss of small amounts of labeled compounds, but one of the media tested (LR‐white) extracted significant amounts of label.