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At least 109 records · Page 6Linked to original sources
PubMed2005

Diagnosis of aberrations from crystalline samples in scanning transmission electron microscopy.

The Ronchigrams, or shadow images, observed from a thin crystalline sample in a scanning transmission electron microscope characteristically present many sets of fringes, which appear thanks to the coherent interference between the various Bragg-diffracted discs as they overlap in the diffraction plane. A particular region of such patterns can be shown to be independent of the defocus at which they are recorded. The intensity along this so-called achromatic ring depends on the microscope aberrations and can be used to diagnose the wave aberration coefficients, a crucial first step in the operation of an aberration-corrected microscope. A new algorithm is presented that allows the accurate determination of all non-cylindrically symmetric aberrations up to fourth-order from a crystalline sample using this property of the Ronchigram. An experimental procedure for determining the position of and intensity along the achromatic lines, as well as examples of diagnosis from two different crystalline structures, are detailed.

Journal Article↗
PubMed1983

A scanning transmission electron microscopy study of two dental amalgams.

Two fully aged amalgam alloys were examined using a scanning transmission electron microscope both in the transmission and scanning mode. The dispersed type amalgam containing a distribution of silver-copper spheres in addition to the Ag3Sn powder showed a markedly reduced gamma 1 grain size compared to a conventional Ag3Sn type amalgam. It is suggested that the increased compressive creep strength of the dispersed type material is a direct result of the reduced gamma 1 grain size and not due to a dispersion hardening effect from the cores of the remaining Ag-Cu spheres. Similarly, the formation of complex Cu-Sn intermediate phases at the Ag-Cu sphere surfaces are unlikely to lead to a dispersion strengthening effect. It is postulated that the reduced grain size in high copper amalgams is a consequence of the enhanced nucleating effect of a copper based phase on gamma 1.

Biomechanical Phenomena↗
PubMed1999

The reaction center complex from the green sulfur bacterium Chlorobium tepidum: a structural analysis by scanning transmission electron microscopy.

The three-dimensional (3D) structure of the reaction center (RC) complex isolated from the green sulfur bacterium Chlorobium tepidum was determined from projections of negatively stained preparations by angular reconstitution. The purified complex contained the PscA, PscC, PscB, PscD subunits and the Fenna-Matthews-Olson (FMO) protein. Its mass was found to be 454 kDa by scanning transmission electron microscopy (STEM), indicating the presence of two copies of the PscA subunit, one copy of the PscB and PscD subunits, three FMO proteins and at least one copy of the PscC subunit. An additional mass peak at 183 kDa suggested that FMO trimers copurify with the RC complexes. Images of negatively stained RC complexes were recorded by STEM and aligned and classified by multivariate statistical analysis. Averages of the major classes indicated that different morphologies of the elongated particles (length=19 nm, width=8 nm) resulted from a rotation around the long axis. The 3D map reconstructed from these projections allowed visualization of the RC complex associated with one FMO trimer. A second FMO trimer could be correspondingly accommodated to yield a symmetric complex, a structure observed in a small number of side views and proposed to be the intact form of the RC complex.

Bacterial Proteins↗
PubMed1999

Mass determination of rous sarcoma virus virions by scanning transmission electron microscopy.

The internal structural protein of retroviruses, Gag, comprises most of the mass of the virion, and Gag itself can give rise to virus-like particles when expressed in appropriate cells. Previously the stoichiometry of Gag in virions was inferred from indirect measurements carried out 2 decades ago. We now have directly determined the masses of individual particles of the prototypic avian retrovirus, Rous sarcoma virus (RSV), by using scanning transmission electron microscopy. In this technique, the number of scattered electrons in the dark-field image integrated over an individual freeze-dried virus particle on a grid is directly proportional to its mass. The RSV virions had a mean mass of 2.5 x 10(8) Da, corresponding to about 1,500 Gag molecules per virion. The population of virions was not homogeneous, with about one-third to two-thirds of the virions deviating from the mean by more than 10% of the mass in two respective preparations. The mean masses for virions carrying genomes of 7.4 or 9.3 kb were indistinguishable, suggesting that mass variability is not due to differences in RNA incorporation.

Animals↗
PubMed2006

New method for analysis of nanoparticle geometry in supported fcc metal catalysts with scanning transmission electron microscopy.

To apply the knowledge of reaction mechanisms of heterogeneously catalyzed reactions on the atomic scale to supported catalyst systems, a detailed description of the structure of active particles on the atomic scale is required. In this article, a method is developed to construct atomic-scale geometric models for supported active fcc metal nanoparticles, based on a measurement of particle sizes and particle volumes by Scanning Transmission Electron Microscopy (STEM) and the M-M coordination number determined from EXAFS. The method is applied to supported Au/TiO(2), Au/MgAl(2)O(4)(-), and Au/Al(2)O(3) catalysts. These geometric models allow for estimation of geometric properties, such as specific Au surface area, metal-support contact perimeter, metal-support contact surface area, edge length, and number of Au atoms located at the corners of the particles, with an error on the order of 20%. In the three catalysts studied here we find that the Au particles in the Al(2)O(3) supported catalyst are small. The Au particles in the Au/TiO(2) catalyst are smaller in diameter than those for the Au/MgAl(2)O(4), but also thicker. The differences in particle size and shape seem to reflect the differences in the metal-support interface energy in the three catalyst systems.

Journal Article↗
PubMed1991

Morphologic changes in the human amnion epithelium that accompany labor as seen with scanning and transmission electron microscopy.

Scanning and transmission electron microscopy were used to assess the influence of normal, active labor on the ultrastructure of the human amnion epithelial membrane. Amnion membranes (reflected and placental portions) were obtained from patients either in active labor who were delivered vaginally or by cesarean section after 6 to 12 hours of labor or from patients who underwent elective cesarean section before clinical signs of overt labor. Scanning electron microscopy revealed that reflected amnion membranes that were obtained from patients who were not in labor consisted of a uniform single layer of epithelial cells with numerous microvilli on the apical surface and closely associated cellular borders. In contrast, amnion membranes that were obtained from patients who were in labor consisted of a single layer of epithelial cells, which was interrupted by wide intercellular gaps and extracellular extrusions. Transmission electron microscopy showed that intercellular junctions tended to be less complex in patients who were in labor versus patients who were not in labor. Although lipid droplets were prevalent in both patient groups, specimens that were obtained from patients who were in labor had more lipid droplets per cell than specimens from patients who were not in labor. These results support the theory that the complex biochemical events that culminate in parturition are accompanied and/or preceded by demonstrable morphologic changes in the amnion membrane.

Amnion↗
PubMed2006

Interfacial reactions of glasses for biomedical application by scanning transmission electron microscopy and microanalysis.

Short-term physico-chemical reactions at the interface between bioactive glass particles and biological fluids are studied for three glasses with different bioactive properties; these glasses are in the SiO(2)-Na(2)O-CaO-P(2)O(5)-K(2)O-Al(2)O(3)-MgO system. Our aim is to show the difference between the mechanisms of their surface reactions. The relation between the composition and the bioactive properties of these glasses is also discussed. The elemental analysis is performed at the submicrometer scale by scanning transmission electron microscopy associated with energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. After different immersion times (ranging from 0 to 96 h) of bioactive glass particles in a simulated biological solution, results show the formation of different surface layers at the glass periphery in the case of two bioactive glasses (A9 and BVA). For the third glass (BVH) we do not observe any surface layer formation or any modification of the glass composition. For the two other glasses (A9 and BVA), we observe the presence of different layers: an already observed (Si, O, Al) rich layer at the periphery, a previously demonstrated thin (Si, O) layer formed on top of the (Si, O, Al) layer and a (Ca, P) layer. We determine the different steps of the mechanisms of the surface reactions, which appear to be similar in these glasses, and compare the physico-chemical reactions and kinetics using the different immersion times. The A9 glass permits the observation of all important steps of the surface reactions which lead to bioactivity. This study shows the important relationship between composition and bioactivity which can determine the medical applicability of the glass.

Aluminum Oxide↗
PubMed1975

Electron microscopic studies of the lung of the frog. II. Topography of the inner surface by scanning and transmission electron microscopy.

Scanning and transmission electron microscopy were used to study the inner architecture of the frog lung. In some specimens the alveolar surface mucus layer was removed to permit the examination of underlying features. The inner surface of the frog's lung is covered by a layer of microvilli belonging to only one type of epithelial cells. The boundaries of these epithelial cells are demarcated by small ridges. Different degrees of lung expansion cause variations of the surface topography. The morphology of certain surface features is examined in detail. Several methods of drying the specimens are compared.

Animals↗
PubMed2004

Low-voltage electron microscopy of polymer and organic molecular thin films.

We have demonstrated the capabilities of a novel low-voltage electron microscope (LVEM) for imaging polymer and organic molecular thin films. The LVEM can operate in transmission electron microscopy, scanning transmission electron microscopy, scanning electron microscopy, and electron diffraction modes. The microscope operates at a nominal accelerating voltage of 5 kV and fits on a tabletop. A detailed discussion of the electron-sample interaction processes is presented, and the mean free path for total electron scattering was calculated to be 15 nm for organic samples at 5 kV. The total end point dose for the destruction of crystallinity at 5 kV was estimated at 5 x 10(-4) and 3.5 x 10(-2) C/cm2 for polyethylene and pentacene, respectively. These values are significantly lower than those measured at voltages greater than 100 kV. A defocus series of colloidal gold particles allowed us to estimate the experimental contrast transfer function of the microscope. Images taken of several organic materials have shown high contrast for low atomic number elements and a resolution of 2.5 nm. The materials studied here include thin films of the organic semiconductor pentacene, triblock copolymer films, single-molecule dendrimers, electrospun polymer fibers and gold nanoparticles.

Electrons↗
PubMed1985

Quaternary structure of pyruvate dehydrogenase complex from Escherichia coli.

The pyruvate dehydrogenase complex of Escherichia coli and subcomplexes derived from it by selective removal of component enzymes have been subjected to quaternary structural analysis by scanning transmission electron microscopy. Scanning transmission electron microscopic images of the intact complex (E1E2E3), the dihydrolipoyl transacetylase-dihydrolipoyl dehydrogenase (E2E3) subcomplex, and the E2 core enzyme appear as cubic particles in various orientations. Mass distributions within this complex and its subcomplexes have been determined by radial mass analysis of similarly oriented scanning transmission electron microscopic images of each type. The data show that mass attributable to dihydrolipoyl dehydrogenase (E3) is well integrated into the structural framework of the E2 core, dihydrolipoyl transacetylase, whereas mass attributable to pyruvate dehydrogenase (E1) is located about the periphery of the core enzyme. The mass distributions are fully consistent with a structural model in which 6 E3 dimers are integrated into the six faces of the cubic E2 core, and 12 E1 dimers are associated along the 12 edges of the core enzyme.

Escherichia coli↗
PubMed1983

Acute toxicity of lead particulates on pulmonary alveolar macrophages. Ultrastructural and microanalytical studies.

Although it is well established that respiratory uptake of lead-containing particles plays a substantial role in the epidemiology of plumbism, relatively little is known about the role of the pulmonary alveolar macrophage in lead poisoning. An in vitro system was designed to investigate the effects of lead oxide particles of respirable size on the rabbit alveolar macrophage. The studies were concerned with the intracellular solubility of PbO and Pb3O4 and changes in fine structure attributable to lead toxicity. The distribution of phagocytosed lead and its intracellular reprecipitation complexes was established by electron microprobe analysis and secondary ion mass spectroscopy in conjunction with transmission electron microscopy, scanning electron microscopy, scanning transmission electron microscopy, and backscatter imaging. It was found that Pb3O4, PbO and PbO-coated particles were ingested by the rabbit alveolar macrophages and that each of these lead oxide compounds produced similar damage to the fine structure of the cell. Swelling of the mitochondria, nuclear membrane, and endoplasmic reticulum was common, as well as were characteristic reprecipitation complexes of lead, phosphorous, and calcium within the nuclear heterochromatin and cytoplasm of the cell. The precipitation complexes were not seen in cells incubated with the particles if phagocytosis was blocked by 0.22-microns, membrane filters. It was concluded that phagocytosis of these lead oxide particles was necessary to produce the cytopathic changes. It is suggested that solubilization of lead from the ingested particles in phagosomes of macrophages results in the liberation of intracellular lead with the resultant formation of reprecipitation complexes.

Animals↗
PubMed1995

At least one of the protofilaments in flagellar microtubules is not composed of tubulin.

BACKGROUND: The core of the eukaryotic flagellum is the axoneme, a complex motile organelle composed of approximately 200 different polypeptides. The most prominent components of the axoneme are the central pair and nine outer doublet microtubules. Each doublet microtubule contains an A and a B tubule; these are composed, respectively, of 13 and 10-11 protofilaments, all of which are thought to be made of tubulin. The mechanisms that control the assembly of the doublet microtubules and establish the periodic spacings of associated proteins, such as dynein arms and radial spokes, are unknown. Tektins, a set of microtubule-associated proteins, are present in the axoneme as stable filaments that remain after the extraction of doublet microtubules; they are localized near to where the B tubule attaches to the A tubule and near to the binding sites for radial spokes, inner dynein arms and nexin links. Tektin filaments may contribute in an interesting way to the structural properties of axonemes. RESULTS: We have fractionated doublet microtubules from sea urchin sperm flagella into ribbons of stable protofilaments, which can be shown to originate from the A tubule. Using cryo-electron microscopy, conventional electron microscopy, scanning transmission electron microscopy, three-dimensional reconstruction and kinesin decoration, we have found that one protofilament in the ribbon is not composed of tubulin. This protofilament is an integral protofilament of the A tubule wall, has less mass per unit length than tubulin and does not bind kinesin. CONCLUSION: Contrary to what is generally assumed, at least one protofilament in the wall of the A tubule is not composed of tubulin. Our data suggest that this nontubulin protofilament is primarily composed of tektins, proteins that show some structural similarity to intermediate filament proteins. A 480 A axial periodicity within these ribbons, revealed by scanning transmission electron microscopy, can be related to the structure of tektin, and may determine the large-scale structure of the axoneme in terms of the binding of dynein, nexin and radial spokes to the doublet microtubule.

Animals↗
PubMedDate not supplied

Cryo-electron microscopy of trichocyte (hard alpha-keratin) intermediate filaments reveals a low-density core.

Trichocyte intermediate filaments (IF) are the principal components of epidermal appendages such as hair and nail. Based on studies by a variety of techniques, it has been inferred that trichocyte IF are structurally similar to other kinds of IF. However, some basic structural attributes have yet to be established: in particular, it has remained unclear whether IF are hollow. We have examined trichocyte IF isolated from rat vibrissae and human hair follicles by electron microscopy. Scanning transmission electron microscopy of freeze-dried specimens yielded mass-per-unit-length values of approximately 32 kDa/nm, with the human preparations also containing filaments at half this density, corresponding to two rather than four protofibrils. Radial density profiles calculated from cryo-electron micrographs of vitrified specimens preserved in a near-native state revealed a low-density region of approximately 3 nm diameter around the filament axis. A minor species of filament with the same internal structure was surface-decorated with material arranged with a helical pitch length of 9.3 nm. These filaments appear to represent IF coated with associated proteins-perhaps, "high-sulfur" proteins-readied for incorporation into the filament-matrix biocomposite of the mature hair.

Animals↗
PubMed1985

A study of endometrial adenocarcinoma treated with tamoxifen by scanning and transmission electron microscopy.

By scanning and transmission electron microscopy the Authors studied four cases of endometrial adenocarcinoma (stage I, G1) after 15-days treatment with Tamoxifen (20 mg X 2) before surgery. The ultrastructural findings, similar to those observed in untreated adenocarcinomas but quite different from those obtained in MAP-responsive cases - as other Authors reported too - seem to indicate an almost complete absence of secretory or cytotoxic induction at least as far as 15-days treatment is concerned. According to the Authors this study raises many doubts about the usefulness of a first-instance therapeutical protocol based on Tamoxifen alone. However they believe that Tamoxifen can be utilized combined with a progestational agent in a simultaneous or sequence treatment.

Adenocarcinoma↗
PubMed2004

HAADF-STEM study on the early stage of precipitation in aged Al-Ag alloys.

We report on the structure of Ag precipitates in aged Al-Ag alloys using transmission electron microscopy and high-angle annular detector darkfield scanning transmission electron microscopy (HAADF-STEM). Irregularly shaped small Ag particles of 1-2 nm dominate the alloy annealed at 140 degrees C for 10 h. These particles are present also within large precipitates (10-50 nm), which are often characterized by their {100} and {110} facets. In addition, atomic-resolution HAADF-STEM images revealed that Ag atoms tend to form {111} planar clusters, which criss-cross a colony of the irregularly shaped small Ag precipitates.

Alloys↗
PubMedDate not supplied

Filling single-wall carbon nanotubes with d- and f-metal chloride and metal nanowires.

Nanowires of magnetic metals (Fe, Co, Ho, Gd) have been synthesized inside the hollow interiors of single-wall carbon nanotubes (SWNTs) by filling SWNTs with precursor metal chlorides and subsequent reduction. SWNTs have been filled by either the melt-phase sealed-tube reaction or a solution-phase method. Among the metal chlorides investigated in this study, HoCl3 and GdCl3 filled the SWNTs to a significantly higher extent. The nanowires have been imaged by transmission electron microscopy (TEM), high-resolution transmission electron microscopy, and scanning transmission electron microscopy (STEM). X-ray energy dispersive spectroscopy carried out in conjunction with TEM and STEM confirmed the presence of metal chloride and metal nanowires.

Chlorides↗
PubMedDate not supplied

Localization of bacteria on the rat tongue with scanning and transmission electron microscopy.

Scanning microscopy of rat tongue showed that bacterial habitation of the tongue was almost completely localized to the middle third of the anterior surface of the filiform papillae. Transmission microscopy showed coccal forms attached to the surface of the epithelium by means of fibrillar strands and present up to four cell layers deep within the epithelium.

Animals↗