bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phagocytosis of tumor cells by activated liver macrophages.
Authors: Wasserman Arthur J. , Gardner Carol R. , Laskin Debra L. 
Published: June 2020

Kupffer cells (KC) are fixed macrophages (Mø) that line the hepatic sinusoids. In response to antigenic or tumor cell challange KC become “activated” and display enhanced biochemical and functional reactivity including increased chemotaxis, phagocytosis, oxidative metabolism and tumor cell killing. We have observed that lipopolysaccharide (LPS)-activated liver Mø phagocytize certain tumor cell targets depending on their tissue origin. This was unusual as Mø typically do not kill tumor targets by phagocytosis. The present studies were designed to study the mechanism involved in liver mø mediated phagocytosis of tumor targets.Mø were isolated from rat livers 48 hr following treatment with LPS (5mg/kg IV) by combined pronase/collagenase perfusion, selective digestion and differential centrifugation. Mø were coincubated on glass coverslips or slides with tumor cells for 48 hr. For both scanning and transmission electron microscopy (SEM,TEM), cells were fixed for 60 min at 4°C in 236 glutaraldehyde buffered by 0.1M cacodylate containing 0.1M sucrose and 1.5mM CaCl2 (pH 7.4).
Morphometric analysis of normal canine Leydig cells and their organelles in sexually mature beagles
Authors: Argentieri G. J. , Visscher G. E. , Robison R. L. 
Published: June 2020

It was our goal to obtain quantitative baseline information on canine Leydig cells and their organelles. Little quantitative baseline data on canine Leydig cells exists in the literature which gives a comprehensive light microscopic (LM) and transmission electron microscopic (TEM) overview. Information is available for various species which correlates testicular physiological and morphometric data. Morphometric data on canine Leydig cells and their organelles becomes important when evaluating naturally occurring and experimentally induced changes during research and development.Four control adult male beagles (14 to 20 months old) were used in this study. A reliable in vitro vascular perfusion fixation method for the testis was developed. Initial buffer rinsing of the vasculature was accomplished using a vasodilator and an anticoagulant. Primary fixation was with 1% paraformaldehyde, 1.5% glutaraldehyde in a 0.1 M cacodylate buffered solution, followed by a second, doubly concentrated aldehyde fixative solution.
The structure of the gills of the axolotl, Ambystoma mexicanum
Authors: Jarial Mohinder S. 
Published: June 2020

The axolotl is a strictly aquatic salamander in which the larval external gills are retained throughout life. The external gills of the adult axolotl have been studied by light and electron microscopy for ultrastructural evidence of ionic transport. The thin epidermis of the gill filaments and gill stems is composed of 3 cell types: granular cells, the basal cells and a sparce population of intervening Leydig cells. The gill epidermis is devoid of muscles, and no mitotic figures were observed in any of its cells.The granular cells cover the gill surface as a continuous layer (Fig. 1, G) and contain secretory granules of different forms, located apically (Figs.1, 2, SG). Some granules are found intimately associated with the apical membrane while others fuse with it and release their contents onto the external surface (Fig. 3). The apical membranes of the granular cells exhibit microvilli which are covered by a PAS+ fuzzy coat, termed “glycocalyx” (Fig. 2, MV).
Paired helical filaments (PHF) in rats: An experimental animal model for Alzheimer's disease
Authors: Montpetit V.J.A. , Dancea S. , French S.W. , Clapin D.F. 
Published: June 2020

A continuing problem in Alzheimer research is the lack of a suitable animal model for the disease. The absence of neurofibrillary tangles of paired helical filaments is the most critical difference in the processes by which the central nervous system ages in most species other than man. However, restricting consideration to single phenomena, one may identify animal models for specific aspects of Alzheimer's disease. Abnormal fibers resembling PHF have been observed in dorsal root ganglia (DRG) neurons of rats in a study of chronic ethanol intoxication and spontaneously in aged rats. We present in this report evidence that PHF-like filaments occur in ethanol-treated rats of young age. In control animals lesions similar in some respects to our observations of cytoskeletal pathology in pyridoxine induced neurotoxicity were observed.Male Wistar BR rats (Charles River Labs) weighing 350 to 400 g, were implanted with a single gastrostomy cannula and infused with a liquid diet containing 30% of total calories as fat plus ethanol or isocaloric dextrose.
Identification and localization of avian leukosis/sarcoma virus P-27 antigen by Immunogold technique
Authors: Steffens W.L. , Goodwin Mark 
Published: June 2020

The leukosis/sarcoma viruses (L/SV) induce benign and malignant neoplasms in chickens and other birds. By sexual maturity, most birds in all chicken flocks have been infected, with losses as high as 25% in commercial breeder flocks attributed to L/SV-induced neoplasms. Prevention and control of L/SV infection depends on sanitation and disinfection programs coupled with genetic selection for host resistance to viral infection, however tests to detect L/SV infection must first be developed and perfected before these programs can be implemented.Adult chickens from a flock suspected of harboring avian leukosis virus were used to evaluate the efficiacy of the immunogold technique in aiding in the diagnosis of the disease in samples submitted for routine microscopy. A commercial monospecific polyclonal antiserum to P-27 protein, an L/SV group-specific protein was utilized for immunolabelling. Samples were taken of myocardium and kidney from chickens killed at necropsy. Tissues were processed for indirect immunogold labelling as described elsewhere. Controls were performed by utilizing non-immune serum and by using immune serum pre-adsorbed with P-27 protein.
Utilization of replicas to show gold-probe binding to sperm cells for SEM and TEM
Authors: Battjes C. J. , Adams J. L. , Buthala D. A. 
Published: June 2020

The introduction of gold particles bound to various probes has facilitated studies of cell surface and intracellular tracing. One problem has been the inability to show surface binding of small gold particles without embedding and thin-sectioning the sample. Our work has shown that small gold probes of 10-15 nm diameter attached to lectins can be detected at surface sites by the use of replicas. The replica retains the three-dimensional aspect of the cell surface while fixing the gold-probe in place. Murine spermatazoa labelled with gold-Con A were replicated directly or replicated following a silver intensification. Results showed that the probes remained at their binding sites and were clearly visible at the ultrastructural level.Murine epididymal and caudal sperm were collected in PBS pH=7.4. Sperm were sedimented twice through PBS, then spread onto clean glass slides and fixed with 3% glutaraldehyde in Millonig's buffer.
Application of slow-scan CCD cameras in routine biological TEM
Authors: Mooney P.E. , Krivanek O.L. , Ray D.A. , Charlesworth J. 
Published: June 2020

Slow scan CCD (charge-coupled device) cameras (SSCs) are based on image detection technology introduced in the seventies and first used in astronomy in the eighties. When they are properly configured for the detection of medium energy electrons rather than photons, they are able to capture images whose quality exceeds the quality of images recorded on photographic film. Here we discuss aspects of their operation pertinent to routine biological TEM.Compared to the TV-rate CCD sensors that have become ubiquitous in miniature camcorders, scientific (astronomy-grade) CCDs have several unique characteristics: 1) their pixels are typically 20-27 μm in size rather than the 6 μm typical of TV rate CCDs, 2) their read-out amplifiers are optimized for low noise at read out rates of 1/10 to 1/100 of TV rate, 3) they do not have a separate frame-transfer buffer for CCD read-out, and 4) they are available in large total sizes (up to 2048 × 2048 pixels).
The identification of magnetic minerals and other selfassembled structures within magnetotactic bacteria using Electron Microscopy and related micro-techniques
Authors: Bazylinski Dennis A. , Garratt-Reed Anthony J. , Frankel Richard B. 
Published: June 2020

Magnetotactic bacteria are a diverse group of procaryotes whose direction of motility is influenced by magnetic fields. These organisms are ubiquitous in aquatic habitats and contain unique intracellular iron-rich membrane-bounded inclusions called magnetosomes that are responsible for the cells’ magnetic behavior. The composition, size (40-100 nm), morphology, position, and orientation of the particles appear to be highly controlled by these bacteria. Ferrimagnetic magnetite (Fe3O4), greigite (Fe3S4), and pyrrhotite (Fe7S8) and nonmagnetic pyrite (FeS2) have been identified as the mineral phases of the magnetosomes in different bacteria. These organisms also contain other intracellular structures that reflect aspects of their physiology, metabolism, and ecology. In order to determine the external structural features of cells and the composition and structure of their intracellular inclusions, transmission electron microscopy (TEM), scanning-transmission electron microscopy (STEM), energy-dispersive x-ray detection (EDXA), and selected area electron diffraction (SAED) techniques were employed.The results of a typical electron microscope (EM) and microanalytical study of a Fe3O4-producing magnetotactic bacterium is shown in Figures 1-4. This unidentified organism, designated strain MV-4, was isolated from sulfide-rich water and sediment collected from a salt marsh.
Design and calibration of an IVEM for general 3-dimensional imaging of non-diffracting materials
Authors: Rowlands Neil , Price Jeff , Kersker Michael , Suzuki Seichi , Young Steve , Ellisman Mark 
Published: June 2020

Three-dimensional (3D) microstructure visualization on the electron microscope requires that the sample be tilted to different positions to collect a series of projections. This tilting should be performed rapidly for on-line stereo viewing and precisely for off-line tomographic reconstruction. Usually a projection series is collected using mechanical stage tilt alone. The stereo pairs must be viewed off-line and the 60 to 120 tomographic projections must be aligned with fiduciary markers or digital correlation methods. The delay in viewing stereo pairs and the alignment problems in tomographic reconstruction could be eliminated or improved by tilting the beam if such tilt could be accomplished without image translation.A microscope capable of beam tilt with simultaneous image shift to eliminate tilt-induced translation has been investigated for 3D imaging of thick (1 μm) biologic specimens. By tilting the beam above and through the specimen and bringing it back below the specimen, a brightfield image with a projection angle corresponding to the beam tilt angle can be recorded (Fig. 1a).
Three-dimensional reconstruction from dark-field electron micrographs of macromolecules at random unknown angles
Authors: Ottensmeyer F.P. , Farrow N.A. 
Published: June 2020

Electron microscopy produces 2D images of 3D objects with resolutions generally from about 2-5 nm for stained or shadowed specimens, to as good as 0.3-0.5 nm for unstained specimens using bright field or dark field techniques. Many groups have worked on methods that attempt to recover the 3D information that is lost in the 2D representation. We have built on and extended previous techniques, and report here the development and application of a robust, unbiased quaternion-based alignment procedure to facilitate 3D reconstruction of molecules imaged at random unknown orientations. The approach is demonstrated using dark field electron micrographs of the Klenow fragment of DNA polymerase.Many procedures for 3D structure determination using electron microscopy have been reported. For fairly simple, small proteins it has been possible to derive a correct high resolution 3D structure by folding the known amino acid chain using dark field electron micrographs as geometric constraintse.g.. However, in general the reconstruction of a 3D density distribution requires knowledge of the relative orientation of different projection images of the object. To determine such orientations a variety of techniques have been employed, frequently adapted to the specimen of interest.
The discovery of the glass knife
Authors: Latta Harrison 
Published: June 2020

We celebrate 500 years of development of the new world following its discovery by Columbus. We also celebrate 50 years of the Electron Microscope Society of America and the exploration of the new world of electron microscopy. A major part of this exploration was the development of techniques for the preparation and sectioning or biologic materials for electron microscopy, which depended on improvements in fixation, staining, embedding, microtomes, and microtome knives.The story of the glass knife involves serendipity and a Japanese sword. It begins in 1949 when a group of research fellows at the Massachusetts Institute of Technology (MIT) were trying to section tissue for electron microscopy with conventional microtome knives sharpened by hand. One day I had to park my car at the far end of the MIT lot and walk back through several buildings. On my way I passed a metallurgy exhibit which displayed a Samurai sword.
Atomic AEM - poissonian problems from gaussian probes!
Authors: Cliff Graham , Kenway Peter B. 
Published: June 2020

In a previous paper, the authors have described the engineering requirements needed to detect one atom in the analytical electron microscope (AEM) by using x-ray microanalyis. Whilst the requirements to achieve this goal cannot be specified at present for a particular instrument, the specification for machines being developed by Vacuum Generators have a calculated minimum detection limit (MDL) of fewer than 4 atoms. At these detection limits the usual Gaussian statistics which have applied in AEM give way to Poissonian statistics. This paper will look at some of the interesting consequences of AEM at the atomic level.The energy dispersive x-ray spectrometers (EDS) used in AEM have percentage detection limits usually quoted as about 0.1 wt. %. For this to equal 1 atom as the MDL, the analysed volume, defined by the probe diameter and the specimen thickness, must contain about 1000 atoms. For a field emission gun (FEG) on an AEM, sufficient current (1nA) can be obtained in a small enough probe (1nm FWHM) to allow analysis from a volume containing 1000 atoms (assuming adequate x-ray detection sensitivity) if the sample is about 20 atoms thick.
Core-Shell Excitation EELS of High-Angle Phonon-Scattered Electrons
Authors: Wang Z. L. , Fisher A. T. 
Published: June 2020

A new technique, thermal-diffuse-scattered electron energy-loss spectroscopy (TDS-EELS), has been demonstrated to be useful for measurement of atomic mean vibration amplitude aA. This technique is performed in the dark-field image mode with a large-angle, annular objective aperture in a conventional transmission electron microscope (TEM) (Figs. 1 and 2). TDS-EELS is based on high-angle phonon - atomic inner-shell double inelastic (rather than high-angle atomic inner-shell single inelastic) scattering processes, and has shown significant temperature dependence (Fig. 3), which may arise from the variation of aA with temperature.Signals in TDS-EELS could be generated by the following scattering mechanisms. One is the “coherent” double-inelastic scattering process, in which TDS and core-shell excitations occur “simultaneously” during scattering by the same atom. The other is “incoherent” double-inelastic scattering, in which TDS and core-shell excitations occur separately during scattering by different atoms. If the incoherent double scattering is the dominant process in TDS-EELS and if the collection angular range of the annular objective aperture is large (>30 mrad), the ratio of the integrated ionization edge intensities would be expected to be independent of temperature and similar to the intensity ratio of the corresponding ionization edges acquired in bright-field (BF-EELS) mode, where I(A)/I(B) ≈ nA/nB·σ(A)/σ(B), σ is the integrated ionization cross-section and n is the atomic concentration.
Predicting resolution in backscattered electron SEM images from monte carlo calculations of the interaction volume
Authors: Newbury Dale E. 
Published: June 2020

Calculations of spatial resolution in scanning electron microscopy are typically based on estimates of the beam size from considerations of the electron optics. The gaussian beam diameter, dg, which is determined from the brightness equation, the contributions of the aberrations (spherical, dS and chromatic, dC), and aperture diffraction (dD) are added in quadrature to give the diameter of the focused probe, dp:(1)This formula can predict the size of the unscattered probe outside of the specimen but to predict image resolution, it is necessary to include a description of the beam interaction with the target. Monte Carlo electron trajectory simulation provides a good description of the complex, multiple scattering situation that exists and the distribution of signals emitted, but the simulation is too slow to be used for on-line calculations, except for a few laboratories with direct access to a parallel-processing computer environment. Monte Carlo studies show that the distribution of emitted signals is dominated by the scattering processes and not by the beam size, at least for high resolution conditions.
Gas-flow field in the environmental SEM
Authors: Danilatos G. D. 
Published: June 2020

The study of the gas flow in the environmental SEM (ESEM) is important both for the instrument design and for determining the environmental conditions around the specimen. Some results from such a study were published previously and the present report is a continuation from the same work. The Monte Carlo simulation method for the gas flow was used. Of particular importance is the question on the flow field contours as the specimen approaches the pressure limiting aperture (PLA) and the question on the mass density of the supersonic jet formed above the plane of the PLA and on the mass density immediately below the aperture.A conically shaped PLA is preferred for several reasons; one such reason is that it allows the preservation of a stagnation pressure environment over the specimen surface for a short distance down to one PLA diameter (D): In Fig. 1 the specimen is placed 1.2 mm (i.e. 3 PLA diameters) below the aperture, and from the number density contours no effect is observed over the specimen surface.
Environmental Scanning Electron Microscope Applications in Agricultural Chemistry Research
Authors: Campbell S. M. , Kohls C. L. 
Published: June 2020

The environmental scanning electron microscope (ESEM) can be used to examine hydrated biological samples and observe dynamic processes in the SEM chamber. We have used the ESEM to explore solvent/sample interactions in a number of agricultural products. Two examples are given below.Unidentified crystals were observed by SEM on the surface of a pelletized pesticide. The identity of these crystals was sought. EDS revealed the presence of copper, sulfur and phosphorus, but did not allow positive identification. The ESEM was used to identify a solvent that could extract the crystals for identification by other analytical techniques. Figure 1 shows the uncoated pellet surface at low magnification. Figure 2 shows the surface of a pellet after a drop of methylene chloride was applied to the sample and pumped away with the ESEM vacuum. Figures 3 and 4 are the same surface of a single pellet before and after chloroform was used to briefly extract the surface. Of several solvents investigated in this way, chloroform appeared to extract the crystals with the least disruption of the pellet's surface.
Principles of Low-Vacuum SEM
Authors: Peters Klaus-Ruediger 
Published: June 2020

Only recently it became possible to expand scanning electron microscopy to low vacuum and atmospheric pressure through the introduction of several new technologies. In principle, only the specimen is provided with a controlled gaseous environment while the optical microscope column is kept at high vacuum. In the specimen chamber, the gas can generate new interactions with i) the probe electrons, ii) the specimen surface, and iii) the specimen-specific signal electrons. The results of these interactions yield new information about specimen surfaces not accessible to conventional high vacuum SEM. Several microscope types are available differing from each other by the maximum available gas pressure and the types of signals which can be used for investigation of specimen properties.Electrical non-conductors can be easily imaged despite charge accumulations at and beneath their surface. At high gas pressures between 10-2 and 2 torr, gas molecules are ionized in the electrical field between the specimen surface and the surrounding microscope parts through signal electrons and, to a certain extent, probe electrons. The gas provides a stable ion flux for a surface charge equalization if sufficient gas ions are provided.
Slow-Scan CCD Observation of Backscattering Patterns in SEM
Authors: Ouyang F. , Ray D. A. , Krivanek O. L. 
Published: June 2020

Electron backscattering Kikuchi diffraction patterns (BKDP) reveal useful information about the structure and orientation of crystals under study. With the well focused electron beam in a scanning electron microscope (SEM), one can use BKDP as a microanalysis tool. BKDPs have been recorded in SEMs using a phosphor screen coupled to an intensified TV camera through a lens system, and by photographic negatives. With the development of fiber-optically coupled slow scan CCD (SSC) cameras for electron beam imaging, one can take advantage of their high sensitivity and wide dynamic range for observing BKDP in SEM.We have used the Gatan 690 SSC camera to observe backscattering patterns in a JEOL JSM-840A SEM. The CCD sensor has an active area of 13.25 mm × 8.83 mm and 576 × 384 pixels. The camera head, which consists of a single crystal YAG scintillator fiber optically coupled to the CCD chip, is located inside the SEM specimen chamber. The whole camera head is cooled to about -30°C by a Peltier cooler, which permits long integration times (up to 100 seconds).
Analysis of SEM Electron Backscattered Kikuchi Patterns Using a CCD Detector and a Macintosh Computer
Authors: Goehner Raymond P. , Michael Joseph R. , Hills Charles R. , Carr Martin J. 
Published: June 2020

The existence of electron backscattered (Kikuchi) patterns (EBSP) in the scanning electron microscope (SEM) is well known. The principal application of EBSP has been to determine the crystallographic orientation of bulk samples from materials with cubic symmetry. More recently the technique has being used to study crystallographic distortions and make space group determinations. An unexploited application of EBSP is that of phase identification, for example in metallographically prepared cross sections of solders and brazes.We have adapted EBSP to the general problem of crystallographic analysis of materials in an SEM though the development of high quality imaging hardware and interactive analysis software. Though visually complex, EBSP patterns exhibit interplanar spacing data comparable to Selected Area Diffraction (SAD) in TEM. After correcting for projection distortion, the angular information in a typical EBSP pattern is also comparable in precision to SAD (∼±1°), but, significantly, includes a much larger solid angle (∼60°) of reciprocal space which typically includes several crystallographic zones simultaneously.