bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiation Damage in Vanadium
Authors: Rau Robert C. , Ladd Robert L. , Moteff John 
Published: June 2020

Transmission electron microscopy has been used to study the microstructure of vanadium irradiated at reactor ambient temperature (∼ 70°C) to a fast (E > 1 MeV) neutron fluence of 5 x 1019 n/cm2. Observations were made of the as-irradiated material, and after one-hour vacuum annealing at various temperatures ranging from 330°C to 1175°C.In the as-irradiated condition, shown in Fig. 1, a very high density of small defect clusters was present. These clusters appeared as black dots averaging approximately 25-50 Å in diameter, and were estimated to be present in quantities of 1016 to 1017 per cm3. Post-irradiation annealing caused the clusters to increase in average size and decrease in number, as shown in Figs. 2 and 3, until after the highest temperature anneal, 1175°C, the cluster density was legs than 1014 per cm3 and the average cluster size was approximately 500Å. After annealing at temperatures of 510°C or above, many of the clusters were seen to be resolvable as dislocation loops. Tilting experiments indicated that these loops were probably interstitial in nature.
Optical Image-Reconstruction From Fraunhofer Electron-Hologram
Authors: Tonomura A. , Fukuhara A. , Watanabe H. , Komoda T. 
Published: June 2020

Since the principle of holography was discussed by Gabor in the intention of improving the quality of electron-microscopic images, several authors have tried electron beam holography of in-line Fresnel type. However, the reconstructed images are seriously disturbed by a virtual image, i.e. accompanied with Fresnel fringes. Meanwhile, in the field of light optics various types of the holography technique and their applications have been proposed and developed under the decisive influence of growing laser technology.This paper deals with electron-beam version of Thompson's in-line Fraunhofer holography, which was already mentioned in Gabor's work but has not yet been tried in electron-optics. The principle of the method is as follows. A beam of quasimonochromatic electrons is collimated by two lenses and illuminates a small object on a plane S as shown in Fig. 1(a). Diffraction fringes produced on a plane A in a far-field region from S are magnified and recorded on a photographic film at H. This film, which is just a Fraunhofer hologram, is inserted in a collimated light beam from a laser as in Fig. 1(b) and an image of the object is reconstructed onto a plane B.
Applications of Scanning Microscopy in Biomedical Research
Authors: Hayes T. L. 
Published: June 2020

Biomedical applications of the scanning electron microscope (SEM) have increased in number quite rapidly over the last several years. Studies have been made of cells, whole mount tissue, sectioned tissue, particles, human chromosomes, microorganisms, dental enamel and skeletal material. Many of the advantages of using this instrument for such investigations come from its ability to produce images that are high in information content. Information about the chemical make-up of the specimen, its electrical properties and its three dimensional architecture all may be represented in such images. Since the biological system is distinctive in its chemistry and often spatially scaled to the resolving power of the SEM, these images are particularly useful in biomedical research.In any form of microscopy there are two parameters that together determine the usefulness of the image. One parameter is the size of the volume being studied or resolving power of the instrument and the other is the amount of information about this volume that is displayed in the image. Both parameters are important in describing the performance of a microscope. The light microscope image, for example, is rich in information content (chemical, spatial, living specimen, etc.) but is very limited in resolving power.
A Combined Scanning Electron Microscope/Electron Microprobe Analyzer
Authors: Macres V.G. , Preston O. , Yew N.C. , Buchanan R. 
Published: June 2020

The instrument described here is the Materials Analysis Company Model 400S combined scanning electron microscope/electron micro-probe analyzer. It was designed specifically to incorporate the most advanced features of a high performance electron microprobe analyzer with those of a medium resolution (1000A°) scanning electron microscope. The high effective x-ray take-off angle of the instrument (38.5°) offers low x-ray absorption, and thus allows the analysis of fairly rough specimens. The large depth of focus of the scanned electron images further enhances the capability of examining rough specimens.The electron-optical column comprises a triode electron gun, double condenser lens and objective lens. The electron gun uses a conventional hairpin filament, autobiased Wehnelt cylinder and anode. An externally controlled filament/Wehnelt cylinder height adjustment is provided for optimizing gun performance at all operating potentials. The double condenser lens is unitized and has two lens regions and a common energizing coil.
Annealing Effects in Ten Films of Thoria
Authors: Bronisz S. E. , Douglass Dana L. 
Published: June 2020

Thin films of thoria, either cleaved from air-fired material or vacuum deposited on polished copper substrates, were examined by transmission electron microscopy. As prepared, the two types of samples were considerably different, but after being heated in the electron microscope they were closely similar.The cleaved samples were obtained by means of extraction replication of fracture surfaces of polycrystalline thoria. The thin flakes ranged from about 0.1 to 20 μm in diameter. Most of them were single crystals exhibiting the diffraction effects expected of crystalline materials and containing many long dislocations. Upon heating with the unapertured electron beam the dislocations disappeared, the crystals became more electron transparent, and the striated microstructure shown in Fig. 1 developed. The orientations of most of the cleaved crystals were equally divided among ﹛110﹜, ﹛111﹜, and ﹛112﹜. The striae were usually parallel to <110> or <135>.
A Method For Determining The Anomalous Absorption Parameter of a Crystal
Authors: Bell W. L. , Thomas G. 
Published: June 2020

The two-beam dynamical theory gives the intensity diffracted by a perfect wedge-shaped, absorbing crystal at the Bragg angle for diffraction as:where and are all dimensionless parameters of absorption and thickness. In common notation and are the mean and anomalous absorption distances, to is the extinction distance and z is the thickness of the foil; all are generally expressed in Angstroms.Values for the absorption parameters are obtained using the extrema values from an intensity profile and determining the envelope for the intensity variations.
Electron Microscopy of Diamond Synthesized by Explosive Shock
Authors: Trueb Lucien F. 
Published: June 2020

The microstructure of early shock-synthesized diamond was discussed in a previous report; this paper is concerned with the characterization of improved material which is now available from E. I. du Pont de Nemours & Company in various size ranges suitable for lapping and polishing.This new type of synthetic industrial diamond is produced by shocking dense graphite-metal mixtures at high explosive pressures. It consists of two types of particles which are shown in Figure 1; polycrystalline aggregates which are rounded and have a mottled surface, and single crystals or fragments thereof which have straight edges and flat surfaces. Figure 2 shows the two types of particles in transmission; they both partly consist of the hexagonal modification of diamond. Single crystals have either a cubic or a hexagonal habit and they often contain large numbers of stacking faults. Polycrystalline particles consist of densely aggregated bundles of acicular crystallites having an average width of 150 A and a length varying between 0.05 and 0.3 p.; a strong preferred orientation is invariably present (Figure 3).
High-resolution scanning electron microscopy (HRSEM) of mitochondria from various rat tissues
Authors: Lea P.J. , Hollenberg M.J. 
Published: June 2020

Our current understanding of mitochondrial ultrastructure has been derived primarily from thin sections using transmission electron microscopy (TEM). This information has been extrapolated into three dimensions by artist's impressions (1) or serial sectioning techniques in combination with computer processing (2). The resolution of serial reconstruction methods is limited by section thickness whereas artist's impressions have obvious disadvantages.In contrast, the new techniques of HRSEM used in this study (3) offer the opportunity to view simultaneously both the internal and external structure of mitochondria directly in three dimensions and in detail.The tridimensional ultrastructure of mitochondria from rat hepatocytes, retinal (retinal pigment epithelium), renal (proximal convoluted tubule) and adrenal cortex cells were studied by HRSEM. The specimens were prepared by aldehyde-osmium fixation in combination with freeze cleavage followed by partial extraction of cytosol with a weak solution of osmium tetroxide (4). The specimens were examined with a Hitachi S-570 scanning electron microscope, resolution better than 30 nm, where the secondary electron detector is located in the column directly above the specimen inserted within the objective lens.
Determination of connections between cellular structures using 3-d reconstruction from multiple-view stereopair images of thick sections
Authors: Marko M. , Leith A. , Parsons D. 
Published: June 2020

An important application for serial section reconstruction is determining whether a structure is composed of separate parts, or is continuous. Structures which are apparently separate on random sections may actually be continuous within the 3-D volume. The presence of connections between different types of organelle compartments within a cell should give important information about metabolic control of the cell. The determination of whether an organelle type is composed of multiple compartments, or actually exists as one or a few complexes, should also be of metabolic significance. The metabolic importance of some connections, such as gap junctions, between adjacent cells has already been well established.One method to prove that two membrane-bound structures connect is to trace the membrane continuously from one structure to the other. This is difficult when using thick sections because the membranes may be nearly invisible if they are at an oblique angle to the direction of view.
Measurement of [Ca] in single cells and pH in single organelles by fluorescence microscopy
Authors: Maxfield F.R. , Shelanski M.L. 
Published: June 2020

Microscope spectrofluorometry and digital image processing provide the ability to study changes in ion concentrations in living cells with high temporal and spatial resolution. We have used fluorescein labeled macromolecules to measure the pH of specific endosomal compartments (1-3). The ratio of fluorescence intensities at 450 nm and 490 nm excitation provides a measure of the pH (4). The acidification of endosomes detected by this technique provide an explanation for endosome functions including intracellular sorting of ligands and receptors, release of iron from transferrin, and penetration of viruses and toxins into the cytosol (3).Using the tetracarboxylate calcium indicator dyes synthesized by R. Tsien and his colleagues (5), the same instruments can be used for measuring intracellular free calcium, [Ca2+]i, in single cells. We have used the system to measure [Ca2+]i changes associated with cell motility (6-9).Cells are examined using a Leitz Diavert microscope with a computer-controlled illumination and photometry system.
Enhancement of outer cell layers of a methanotrophic bacterium using uranyl acetate en bloc
Authors: Putzer K. , Fassel T.A. , Remsen C.C. 
Published: June 2020

Obligate methanotrophic bacteria are autotrophic microorganisms capable of oxidizing methane to supply both their carbon and energy requirements. Methanotrophs are placed in one of two groups based on certain biochemical features and the arrangement of intracytoplasmic membranes (ICM). Type I methanotrophs contain ICM arranged as bundles of disc-like vessicles in the interior of the cell, while Type II methanotrophs display paired peripheral ICM. The organism used in this study, Methylosinus trichosporium OB3b, is a Type II methanotroph and has a capsular structure surrounding the cell as well as several complex cell wall structures described as cup-like, filamentous, and spike-shaped. This study examines the external surface of M. trichosporium OB3b following en bloc staining with uranyl acetate.Cells were harvested in mid-log phase, fixed in 0.5% glutaraldehyde and postfixed in 1% OsO4. Cells were enrobed in 4% agar prior to dehydration in a graded ethanol series.
Quantitative x-ray elemental imaging in stimulated single intact skeletal muscle fibers: The fate of calcium in the presence of ryanodine
Authors: Sommer J. , Ingram P. , LeFurgey A. , Nassar R. , High T. 
Published: June 2020

We are involved in a continuing series of experiments aimed at a complete description,in terms of morphology and quantitative topochemistry, of the time course of spatial distributions of physiologically important elements during excitation-contraction coupling (ECC) at different time intervals (fractions of msec) following electrical stimulation of single, intact frog skeletal muscle fibers. In this present study wg report such distributions for Ca after 1,2 and 3 min of electrical stimulation in the presence of 2x10-4 M ryanodine, an alkaloid that, in time, causes irreversible muscle contractures.Single, intact frog skeletal muscle fibers were quick-frozen, cryosectioned, freeze-substituted and in one case freeze-fractured. The freeze-dried cryosections were subjected to electron probe X-ray microanalysis (EPXMA) in a JEOL 1200EX analytical electron microscope equipped with a Tracor Northern X-ray detector and a fully quantitative imaging system. Both, 64/64 pixel images (ambient temp.), and small raster probes (cold stage,-115 °C) for better statistics, were obtained, each from the same section.
Reversibility of Action of Clostridium Difficile Toxin a on Cho Cells and Intermediate Filaments in Nuclei
Authors: Kushnaryov V.M. , Sedmak J.J. , Lyerly D.M. , Wilkins T.D. 
Published: June 2020

C. difficile, produces 2 potent cytopathic enterotoxins, A and B; their mechanism of action is poorly understood. We studied effects of enterotoxin A (EA) on cultured Chinese Hamster Ovary (CHO) cells employing light microscopy and TEM. Cells grown to 75% confluency were exposed to EA (2.5 μg/ml) at 37°C. Within 1-3 hrs cytoplasm became more retractile and contracted with thin protrusions from the cell (Fig. B). The cells were washed after 2 or 3 hr and incubation continued for 48 hrs. If EA was removed within 2 hrs cells returned to normal in 24-48 hr; if EA was removed after 3 hrs it did not affect rounding of the cells which remained firmly attached and not permeable to erythrosin B implying that they were viable.TEM employing monoclonal Abs and colloidal gold-protein A conjugate showed that at 4°C EA was randomly distributed on plasma membrane (PM). At 37°C EA was located in pinocytotic invaginations and in coated pits (Figs. E-H) suggesting EA internalization by both the bulk and receptor-mediated endocytosis.
A Novel Reconstitution Method for Inducing the Formation of Regular 2-Dimensional Arrays of Membrane Proteins and Lipids
Authors: Engel A. , Holzenburg A. , Stauffer K. , Rosenbusch J. , Aebi U. 
Published: June 2020

Reconstitution of solubilized and purified membrane proteins in the presence of phospholipids into vesicles allows their functions to be studied by simple bulk measurements (e.g. diffusion of differently sized solutes) or by conductance measurements after transformation into planar membranes. On the other hand, reconstitution into regular protein-lipid arrays, usually forming at a specific lipid-to-protein ratio, provides the basis for determining the 3-dimensional structure of membrane proteins employing the tools of electron crystallography.To refine reconstitution conditions for reproducibly inducing formation of large and highly ordered protein-lipid membranes that are suitable for both electron crystallography and patch clamping experiments aimed at their functional characterization, we built a flow-dialysis device that allows precise control of temperature and flow-rate (Fig. 1). The flow rate is generated by a peristaltic pump and can be adjusted from 1 to 500 ml/h. The dialysis buffer is brought to a preselected temperature during its travel through a meandering path before it enters the dialysis reservoir. A Z-80 based computer controls a Peltier element allowing the temperature profile to be programmed as function of time.
Analysis of Molluscan Hemocyanins by Scanning Transmission Electron Microscopy and Light Scattering
Authors: Furcinitti P. S. , Wall J. S. , Hamilton M. G. , Herskovits T. T. 
Published: June 2020

Hemocyanins are copper containing, oxygen binding proteins found in many invertebrate species of the phyla Arthropoda and Mollusca. Molluscan hemocyanins are cylindrical macromolecular assemblies of a basic decameric unit. The hemocyanins of two chitons, Stenonlax conspicua and Mopalia muscosa. are decamers, while those of two gastropods, Fasciolaria tulipa and Pleuroplora gieantea. are di-decamers. The hemocyanins of a third gastropod species, Busvcon contrarium can exist in a spectrum of multi-decameric forms. Molecular weights of the various types of molluscan hemocyanins were measured by absolute light scattering and Scanning Transmission Electron Microscopy (STEM) as a first step in understanding multi-decamer formation in some types of hemocyanins.Hemocyanins were prepared as previously described, dialyzed into 1M HEPES buffer, pH 7.4, containing 0.05M MgCl and freeze-dried or negatively stained for STEM analysis. Specimens were examined at the Brookhaven STEM Biotechnology Resource, which was operated at 40 kV using a -140°C cold stage. The elastically scattered electron signal from the STEM large angle annular detector was used to form the images.
Diameter Determination of Frozen-Hydrated Virions Using Polyoma Virus as a Calibration Standard
Authors: Olson N. H. , Baker T. S. 
Published: June 2020

Accurate determination of particle dimensions requires both a reliable measure of the instrumental magnification and reproducible, non-distorting specimen preparation procedures. Typical calibration standards for measuring microscope magnification include replica gratings, polystyrene spheres, and negatively-stained catalase crystals. Polystyrene spheres and catalase crystals may be used as internal standards but both are highly sensitive to beam damage. Calibrations with replica gratings are subject to greater inaccuracies at magnifications exceeding 10,000-20,000 X. Furthermore, for negatively-stained biological specimens, the object of interest as well as the standard (e.g. catalase) are susceptible to significant distortions produced when the stained sample dries on the grid. The stain itself also moves during the initial stages of irradiation.1.2Large discrepancies are often found between diameter measurements from particle images with circular profiles (e.g. spherical viruses) made in the microscope and from those measurements determined by x-ray solution scattering or other x-ray diffraction techniques. Measurements from virions embedded in negative-stain, suspended over holes in a carbon substrate, are typically much lower than the corresponding measurements by x-ray techniques, reflecting a probable shrinkage of virions in the stain.
High-Resolution Scanning Electron Microscopy of Biological Specimens
Authors: Müller M. , Hermann R. 
Published: June 2020

Three major factors must be concomitantly assessed in order to extract relevant structural information from the surface of biological material at high resolution (2-3nm).Procedures based on chemical fixation and dehydration in graded solvent series seem inappropriate when aiming for TEM-like resolution. Cells inevitably shrink up to 30-70% of their initial volume during gehydration; important surface components e.g. glycoproteins may be lost. These problems may be circumvented by preparation techniques based on cryofixation. Freezedrying and freeze-substitution followed by critical point drying yields improved structural preservation in TEM. An appropriate preservation of dimensional integrity may be achieved by freeze-drying at - 85° C. The sample shrinks and may partially collapse as it is warmed to room temperature for subsequent SEM study. Observations at low temperatures are therefore a necessary prerequisite for high fidelity SEM. Compromises however have been unavoidable up until now. Aldehyde prefixation is frequently needed prior to freeze drying, rendering the sample resistant to treatment with distilled water.
The Formation of Cartilage Extracellular Matrix
Authors: Vertel B.M. 
Published: June 2020

Normal cartilage function is dependent upon the unique structural properties of the extensive extracellular matrix (ECM). In final assembled form, the ECM of hyaline cartilage is composed of abundant amounts of proteoglycan (PG) and type II collagen. Additional collagens and glycoproteins may be important structural components as well. Through their concentration of negative charges, PGs confer upon the cartilage ECM the ability to retain high levels of hydration and thereby resist compression. Type II collagen fibers contribute to the tensile strength of cartilage.In the cartilage ECM, PG monomers associate with hyaluronic acid and link protein to form large aggregates. In turn, PG aggregates are associated with the fibrous meshwork of type II collagen. Interactions with other ECM molecules may occur as well. The cartilage matrix constituents are themselves large and complex. For example, the PG monomer is 1-5 x 106 daltons in size and contains a core protein of Mr >300K (comprising only 8-10% of the complete monomer).
Collagen fibril and matrix assembly during morphogenesis
Authors: Birk David E. , Zycband Emanuel , Trelstad Robert L. 
Published: June 2020

The morphogenesis of the extracellular matrix requires the synthesis, assembly and deposition of collagen in a tissue specific manner. Collagen synthesis and molecular assembly occur within a series of well defined cytoplasmic compartments, while the assembly and deposition of collagen fibrils, fibril bundles and collagen macroaggregates occurs within a series of extracellular compartments. In the studies described here we focus our attention on the assembly of collagen molecules into fibrils, bundles and tissue specific macroaggregates.The fibroblast has a complex topography which serves to partition the extracellular space into distinct domains where the hierarchical stages in matrix assembly occur. The first recognizable extracytoplasmic domain is a narrow channel which originates deep within the cytoplasm and is open to the extracellular space. These narrow spaces contain single or sometimes 2-3 collagen fibrils and are intimately associated with secretory vacuoles. These channels fuse with each other and with the cell surface giving rise to the second level of compartmentalization and matrix hierarchy where fibrils coalesce to form bundles.