bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum molecular dynamics simulation of Σ13 grain boundary in Si
Authors: Kim M.J. , Ma H. , Carpenter R.W. , Lin S.H. , Sankey O.F.
Published: June 2020

Grain boundary (GB) structure determination at an atomic level by HREM had received increasing attention in recent years. However, models of grain boundary structure deduced from the experiment results are usually not unique, and they do not necessarily represent the equilibrium structure. A newly developed quantum-molecular-dynamics (QMD) method, which does not depend on any empirical potentials, can be used to test these models and find the equilibrium atomic structure through simulated quenching. The method employs an electronic structure tight-binding model based on density functional theory within the local density approximation and the nonlocal pseudopotential scheme, and is used to compute the total energy and atomic forces for a variety of covalent materials. In the present study, this QMD method, coupled with image simulation, was used to predict the relaxed atomic configuration for the Σ=13 (510), [001] tilt grain boundary in Si.
Off-axis electron holography applied to the study of interfaces
Authors: Weiss J.K. , Gajdardziska-Josifovska M. , McCartney M. R. , Smith David J.
Published: June 2020

Interfacial structure is a controlling parameter in the behavior of many materials. Electron microscopy methods are widely used for characterizing such features as interface abruptness and chemical segregation at interfaces. The problem for high resolution microscopy is to establish optimum imaging conditions for extracting this information. We have found that off-axis electron holography can provide useful information for the study of interfaces that is not easily obtained by other techniques.

Electron holography permits the recovery of both the amplitude and the phase of the image wave. Recent studies have applied the information obtained from electron holograms to characterizing magnetic and electric fields in materials and also to atomic-scale resolution enhancement. The phase of an electron wave passing through a specimen is shifted by an amount which is proportional to the product of the specimen thickness and the projected electrostatic potential (ignoring magnetic fields and diffraction effects). If atomic-scale variations are ignored, the potential in the specimen is described by the mean inner potential, a bulk property sensitive to both composition and structure. For the study of interfaces, the specimen thickness is assumed to be approximately constant across the interface, so that the phase of the image wave will give a picture of mean inner potential across the interface.
HREM study in Ti/6H-SiC interface
Authors: Bow J.S. , Spellman L.M. , Kim M.J. , Carpenter R.W. , Davis R.F.
Published: June 2020

A semiconductor of Ti/6H-SiC with rectifying characteristics was reported recendy. That its electrical properties were degraded for 20 min. anneal at 700°C but improved again with subsequent 20 min. and longer anneal was considered to be caused by phase transformation during annealing. The purpose of this study is to identify those phases formed in the annealing process, and to identify those responsible for changing the electrical properties.

A 100 nm Ti thin film was deposited on 6H-SiC by electron beam evaporation in UHV, and subsequent annealing was also done in UHV at 700°C. Cross section TEM specimens were prepared by bonding wafers with Ti-films face to face, grinding, polishing, and then ion milling in a Gatan 600. All TEM observations were performed in an ISI 002B with a 0.18nm resolution at 200KV. HREM images were analyzed by using die SEMPER program.
Intensity measurement of surface diffraction spots by EELS
Authors: Xu P. , Marks L. D.
Published: June 2020

With the development of the modern ultra-high vacuum (UHV) transmission electron microscopes, it has become possible to study the surfaces of various materials in a clean environment. Transmission electron diffraction in a plan view geometry is particularly powerful in solving the surface atomic structures, for example Si(111)-7x7. Surface diffraction spots in such a pattern are usually quite strong, readily apparent on a phosphor screen. In addition, these spots are much clearer in an off zone diffraction pattern. This paper presents the absolute intensity measurement of the surface spots intensity using an electron energy loss spectrometer.
EM of surface dynamics
Authors: Tromp R.M.
Published: June 2020

A proper understanding of the structure and properties of surfaces and interfaces can only be obtained by consideration of the dynamic aspects of their formation and further evolution. In the last few years we have designed and built a Low Energy Electron Microscope (LEEM) for the study of surface dynamics. With an electron energy of only a few eV at the sample a lateral resolution of ∼150Å can be obtained, and single height atomic steps can be resolved by phase contrast. Images are obtained at videorate. In this talk I will present results of studies of Ge/Si heteroepitaxial growth, both with and without surfactants, phase transitions on Si(111), 2-D island nucleation and ripening on Si(001), and new step shape phase transitions on Si(001). I will briefly discuss our progress in establishing a new UHV-TEM experiment with in situ surface preparation and diagnostics, such as Molecular Beam Epitaxy, Reflection High Energy Electron Diffraction, Scanning Electron Microscopy, and Auger Electron Spectroscopy.
Characterization of iron-implanted silicon carbide
Authors: Bentley J. , Romana L. J. , Horton L. L. , McHargue C. J.
Published: June 2020

As part of extensive fundamental studies of ion-implanted ceramics, analytical electron microscopy (AEM) has been used to characterize [0001] single crystal 6H α-silicon carbide implanted at room temperature with 160 keV 57Fe ions to fluences of 1,3, and 6 x 1016 ions/cm2. AEM was performed at 100 kV with a Philips EM400T equipped with a field emission gun, a 6585 STEM unit, an EDAX 9100/70 energy dispersive X-ray spectrometer (EDS), and a Gatan 666 parallel-detection electron energy loss spectrometer (PEELS).

A micrograph of a cross-sectioned specimen implanted with 6 × 1016 ions/cm2 is shown in Fig. 1. The implanted region extending to 195 nm from the surface is amorphous, as confirmed by convergent beam electron diffraction (CBED) patterns (insets), and contains iron at levels easily detectable by EDS (Fig. 2). The 15 nm lattice fringes of the edge-on 6H basal planes in the substrate provide an unambiguous depth calibration scale. The transition layer at the end of the ion range exhibits the expected strain contrast. The depth profile of the implanted iron was measured by EDS line scans perpendicular to the implant surface; the mean of three of these scans is shown by the filled symbols in Fig. 3. The integrated iron profile agrees with the expected 6.0 × 1016 ions/cm2 only if the density of the amorphous SiC is equal to that of its crystalline forms, rather than the 20% lower density reported earlier.
Use of backscattered electron image intensity signals to calculate the water/cement ratio of concrete
Authors: Lee R. J. , Schwoeble A. J. , Jie Yuan
Published: June 2020

Water/Cement (W/C) ratio is a very important parameter affecting the strength and durability of concrete. At the present time, there are no ASTM methods for determining W/C ratio of concrete structures after the production period. Existing techniques involving thin section standard density comparative associations using light optical microscopy and rely on visual comparisons using standards and require highly trained personnel to produce reliable data. This has led to the exploration of other methods utilizing automated procedures which can offer a precise and rapid measurement of W/C ratio. This paper discusses methods of determining W/C ratio using a scanning electron microscope (SEM) backscattered electron image (BEI) intensity signal and x-ray computer tomography.
HRTEM observations on electron irradiation damage in F-apatite
Authors: Cameron M. , Wang L.M. , Crowley K.D. , Ewing R.C.
Published: June 2020

Radiation damage in crystalline phases with the apatite structure is of interest in the biomedical, geoscience, and materials science communities. Phases close to hydroxyl apatite [Ca5(PO4)3OH] in composition are volumetrically the most significant in dental enamel and bone. Natural apatites with variable halogen compositions [Ca5(PO4)3(F,OH,Cl)] are used by geoscientists to place constraints on the thermochronologic conditions under which portions of the Earth evolved. Rare-earth-silicate isomorphs of these naturally occurring apatites are also of interest because they may be actinide hosts in ceramic nuclear waste forms.
Effects of argon ion sputtering on zirconium and titanium
Authors: Carpenter G.J.C. , Jackman J.A. , McCaffrey J.
Published: June 2020

Argon ion sputtering is widely used in the final thinning stage for the preparation of thin foils for transmission electron microscopy. During a recent study of a titanium alloy, we observed that ion-beam thinning resulted in specimens that appeared in the electron microscope to have become severely damaged. Similar microstructures had been observed previously in zirconium, thinned in this manner. Because ion-beam sputtering takes place on the atomic scale, it seemed unlikely that gross distortion of a thin foil could have been caused directly by the sputtering process. A more detailed study has therefore been made of this phenomenon.
High-resolution video-enhanced light microscopy
Authors: Salmon E. D.
Published: June 2020

Video-enhanced differential interference contrast (VE-DIC) methods can produce high contrast images of isolated macromolecular complexes and cellular fine structures invisible by eye or photographic recording methods through the light microscope. Objects 10 nm - 20 nm wide, much smaller than the wavelength of green light, can be seen at high contrast, although lateral resolution is limited by the Abbe diffraction limit (about 200 nm for 550 green light through objective NA = 1.4). In addition, VE-DIC microscopy can produce thin optical sections through transparent thick specimens with z-axis resolution less than 200 nm. We have been developing this technology to provide video assays (30 frames per sec) of the dynamics of individual molecular complexes. Applications include measurement of the polymerization kinetics of individual 25 nm diameter microtubules in living cells and in reconstituted preparations, the assembly of individual polymers of sickle cell hemoglobin in vitro, the translation of mechanochemical enzymes like dynein and kinesin along individual microtubules in vitro and the movements of individual sister kinetochores during mitosis. Lateral movements of diffraction limited images of spherical particles can be tracked with 1 nm precision. We have used a semi-automatic version of the Gelles tracking algorithm to measure the movements of individual kinetochores and centrosomes in living cells at 1 sec intervals with 100-200 nm precision.
Video microscopic measurements of diffusion and flow in cultured kidney cells
Authors: Spring Kenneth R. , Bungay Peter M. , Chatton Jean-Yves , Flamion Bruno , Gibson Carter C. , Harrist Peter J.
Published: June 2020

New, optical microscopic techniques were developed to study the composition, fluid flow patterns and restrictions to diffusion in the fluid filled spaces surrounding renal epithelial cells. The prevailing theoretical model for the mechanism of isosmotic fluid transport by epithelia, the standing osmotic gradient hypothesis, predicts gradients in ion composition as well as significant restrictions to the diffusion of small solutes within the lateral intercellular spaces separating epithelial cells. Key questions about the validity of the model arise from uncertainties about the values for the hydraulic water permeability of the cell membranes and the lack of data about the composition of the fluid filling the lateral intercellular spaces. This presentation will describe measurements of the local composition, geometry and diffusion coefficients within lateral intercellular spaces of cultured renal epithelia and in the lumen of isolated, perfused renal tubules.
Optical tweezers as a tool to study cellular function
Authors: Block Steven M.
Published: June 2020

A single beam gradient force optical trap1-3, or “optical tweezers”, exerts forces on microscopic dielectric particles using a highly focused beam of laser light, and can achieve stable, three-dimensional trapping of such particles (for a review, see ref. 4). Using an infrared laser, calibratable forces in the piconewton (pN) range can be easily generated without causing significant damage to living biological specimens. Optical tweezers work through the microscope, without mechanical intrusion within sealed preparations, and can even reach directly inside transparent cells or organelles. Because it is formed by light, an optical trap can be controlled with very high spatial and temporal precision. Its characteristic size (i.e., its “grasp”) is approximately equal to the wavelength of light, but it can be used to capture and/or manipulate objects ranging in size from ∼20 nm to ∼100 mm. Biological preparations (e.g., cells, vesicles, organelles) or small particles (e.g., latex or silica microspheres, perhaps carrying reagents coupled to their surfaces) can be held, maneuvered, or released at will. Already, researchers have begun to contemplate experiments that were practically impossible just a few years ago. Some possibilities include: (1) the sorting and isolation of cells, vesicles, organelles, chromosomes, etc.; (2) the direct measurement of the mechanical properties of cytoskeletal assemblies, membranes, or membrane-bound elements; (3) measurement of the tiny forces produced by mechanoenzymes; (4) establishing cell-cell contacts, or measuring receptor-ligand interactions; (5) studying cellular rheology on the micrometer scale; (6) doing cellular microsurgery, membrane fusion, and building novel cellular (or noncellular) structures; (7) capturing and maintaining fragile biological structures away from vessel surfaces, in order to study them in isolation under optimal viewing conditions; (8) and much more! The principles by which optical tweezers work will be explained, and a videotape illustrating a number of experimental uses will be shown.
The structure of membranes and membrane proteins embedded in amorphous ice
Authors: Lücken Uwe , Jäger Joachim
Published: June 2020

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.

Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.
Diversity in gap junction structures
Authors: Sosinsky Gina E.
Published: June 2020

Gap junctions are the specialized regions between two adjoining cells responsible for regulated communication. The morphological unit of the gap junction is composed of 12 copies of the connexin molecule. Six connexins form a hexamer in each cell membrane called a connexon and two connexons pair across the two cell membranes of coupled cells to form gated channels. Although other proteins are found in enriched gap junction preparations, it is generally accepted that the gap junction structures are formed from a family of connexin proteins. The connexins are named according to their DNA deduced molecular weights, e.g. Cx32 for the 32kDa liver major connexin and Cx26 for the 26 kDa liver minor connexin. Within a given tissue, several connexins are often found and different connexins are often found within the same junctional plaque. These connexins contain both conserved and variable domains in their primary amino acid sequences, with the major differences occuring in the sequence and size of the cytoplasmic C terminus. The most conserved regions of the compared sequences are in the transmembrane and gap portions of the proteins. Determination of the sequences of the connexin proteins and correlation of information on antibody binding, proteolytic cleavage and chemical reactivity have led to a model where the C- and N- termini are located at the cytoplasmc surface and four α-helical segments of the protein cross the membrane.
Visualisation of E. coli ribosomal RNA in situ by electron spectroscopic imaging and image averaging
Authors: Beniac Daniel , Harauz George
Published: June 2020

The structures of E. coli ribosomes have been extensively probed by electron microscopy of negatively stained and frozen hydrated preparations. Coupled with quantitative image analysis and three dimensional reconstruction, such approaches are worthwhile in defining size, shape, and quaternary organisation. The important question of how the nucleic acid and protein components are arranged with respect to each other remains difficult to answer, however. A microscopical technique that has been proposed to answer this query is electron spectroscopic imaging (ESI), in which scattered electrons with energy losses characteristic of inner shell ionisations are used to form specific elemental maps. Here, we report the use of image sorting and averaging techniques to determine the extent to which a phosphorus map of isolated ribosomal subunits can define the ribosomal RNA (rRNA) distribution within them.
HRSEM of the nuclear envelope (NE): Nuclear pore substructure; baskets and fibrous components
Authors: Goldberg Martin W. , Allen Terence D.
Published: June 2020

The nuclear envelope (NE) of eukaryotic cells has been studied for many years by a variety of em techniques yielding a three dimensional model of the nuclear pore complex (NPC) consisting of two rings (∼120nm diameter), one at the outer NE and one at the inner NE. Between the rings are eight spoke structures and a central plug. The cytoplasmic ring may be decorated with up to eight particles. The NPCs are embedded in a proteinaceous network: the nuclear lamina. Recently, low voltage HRSEM was used to show the existence of a basket-like structure attached to the nucleoplasmic ring. SEM is an ideal technique for the study of membrane surfaces. High resolution can be achieved in SEMs by the use of a field emission source which produces a high brightness probe of less than lnm diameter and a specimen stage within the objective lens, reducing chromatic abberations and production of SEIII electrons. Resolution of biological specimens can be further enhanced by coating with thin, continuous films of refractory metals such as chromium or tantalum which allows the use of higher accelerating voltages and magnifications. The NEs of Xenopus oocyte germinal vesicles have been prepared as previously described for HRSEM without detergent except they have been coated nominally with 3nm of tantalum by magnetron sputtering instead of ion beam sputtered platinum. NEs have then been examined at 30kV. The ring, plug/spoke complex and particles can all be seen at the cytoplasmic surface as well as details of the outer membrane structure and particles associated with it (Fig. 1). On the nucleoplasmic surface (Fig. 2) the inner ring is observed. It has a subunit appearance with eight filaments extending from between the subunits to a third ring structure: these make up the basket-like structure. When ‘baskets’ are close together they are joined by fibres at the ‘basket ring’ (Fig. 2). When several baskets are in close proximity these fibres form a network like a canopy over the baskets (Fig. 3). Other fibres are present on the inner membrane surface which may be membrane associated fibres or canopy fibres that have collapsed. It is uncertain which, if any, of these fibres are lamins as a further level of fibres is observed at the level of the nucleoplasmic ring when the membrane is removed with detergent (Fig. 4). These fibres are consistent with previously described lamina.
Use of human autoantibodies and immunoelectron microscopy to study structure and function of the nucleolus and nuclear bodies
Authors: Ochs Robert L.
Published: June 2020

By conventional electron microscopy, the formed elements of the nuclear interior include the nucleolus, chromatin, interchromatin granules, perichromatin granules, perichromatin fibrils, and various types of nuclear bodies (Figs. 1a-c). Of these structures, all have been reasonably well characterized structurally and functionally except for nuclear bodies. The most common types of nuclear bodies are simple nuclear bodies and coiled bodies (Figs. 1a,c). Since nuclear bodies are small in size (0.2-1.0 μm in diameter) and infrequent in number, they are often overlooked or simply not observed in any random thin section. The rat liver hepatocyte in Fig. 1b is a case in point. Historically, nuclear bodies are more prominent in hyperactive cells, they often occur in proximity to nucleoli (Fig. 1c), and sometimes they are observed to “bud off” from the nucleolar surface.
Electron Microscopy and image reconstruction reveal the structural basis for spectrin's elastic properties
Authors: McGough Amy M. , Josephs Robert
Published: June 2020

The remarkable deformability of the erythrocyte derives in large part from the elastic properties of spectrin, the major component of the membrane skeleton. It is generally accepted that spectrin's elasticity arises from marked conformational changes which include variations in its overall length (1). In this work the structure of spectrin in partially expanded membrane skeletons was studied by electron microscopy to determine the molecular basis for spectrin's elastic properties. Spectrin molecules were analysed with respect to three features: length, conformation, and quaternary structure. The results of these studies lead to a model of how spectrin mediates the elastic deformation of the erythrocyte.

Membrane skeletons were isolated from erythrocyte membrane ghosts, negatively stained, and examined by transmission electron microscopy (2). Particle lengths and end-to-end distances were measured from enlarged prints using the computer program MACMEASURE. Spectrin conformation (straightness) was assessed by calculating the particles’ correlation length by iterative approximation (3). Digitised spectrin images were correlation averaged or Fourier filtered to improve their signal-to-noise ratios. Three-dimensional reconstructions were performed using a suite of programs which were based on the filtered back-projection algorithm and executed on a cluster of Microvax 3200 workstations (4).
Cooling-induced wrinkling of thin crystals of biological macromolecules can be prevented by using molybdenum grids
Authors: Glaeser Robert M.
Published: June 2020

It is an important requirement of high resolution electron diffraction and electron microscopy of thin crystals of biological macromolecules that the specimen be flat (i.e. planar) to one degree or less over distances of one micrometer or more. This high degree of specimen flatness is required in order to collect diffraction patterns and images at high tilt angles and high resolution. Imperfect flatness causes the diffraction spots which are perpendicular to the tilt axis to become streaked or blurred, while the spots parallel to the tilt axis remain sharp. If the specimen wrinkling, or mosaic angular spread, is too severe, the diffraction spots overlap one another to make a continuum, and data retrieval becomes impossible (see Figure 3, for an example). Even before that point is reached, the broadening of the diffraction spots makes it increasingly difficult to obtain accurate background-subtracted diffraction intensities, and the signal-to-noise ratio in the computed Fourier transform of high resolution images is severely decreased. In some preparations of thin protein crystals the stringent requirements for specimen flatness can be met with a reasonable rate of success. In the case of bacteriorhodopsin, prepared as large singlecrystal sheets by detergent-induced fusion of the native purple membrane of Halobacterium halobium, the frequency of success is normally very low.
What happens to the normal cytoplasmic features of fish erythrophores when, under identical conditions of culture, the erythrophores are fused with normal rat kidney cells?
Authors: Porter Keith R. , Anderson Karen L.
Published: June 2020

We have shown that a small population of normal cells can be cultured from the scales of the squirrel fish, Holocentrus rufus. They can be grown directly on Formvar-carbon-coated gold grids and, while still on the grids they can be fixed, stained and dehydrated for high voltage electron microscopy. One of the cell types (epidermal) spreads out on the carbon-coated surface and is thin enough in most parts for conventional (100kV) electron microscopy. The aspect of wholeness represented in these qells should not be overlooked for it provides information that might be missed in a series of thin sections where the sample is obviously smaller. Furthermore, if experimental studies are contemplated, they can be made while the cells are still alive and available for light microscopy.
New views inside cells with the digital imaging microscope
Authors: Fay F.S. , Moore E.D.W. , Elliot D. , Rosbash M. , Carter K. , Lawrence J. , Lynch R. , Lifshitz L. , Fogarty K.
Published: June 2020

The digital imaging microscope has been developed as a tool for understanding changes in molecular distribution underlying changes in cell function. It has evolved principally to meet the needs and opportunities afforded cell biologists to analyze molecular distribution in single cells with an ever increasing range of bright fluorescent indicators having a high degree of molecular specificity. The operation of the digital imaging microscope usually involves four basic steps: 1. image acquisition; 2) image restoration, to reverse the distortion introduced by the optics; 3) image feature extraction, to identify and isolate important characteristic features of an image, and; 4) visualization and interactive analysis of the image. These procedures differ depending on the nature of the specimen and the questions being asked. It is this malleability of the digital imaging microscope that makes it such a powerful and versatile tool.
Cell-matrix interactions in the early mouse embryo
Authors: Sutherland A.E. , Calarco P.G. , Damsky C.H.
Published: June 2020

Cell-extracellular matrix (ECM) interactions mediated by the integrin family of receptors are critical for morphogenesis and may also play a regulatory role in differentiation during early development. We have examined the onset of expression of individual integrin subunit proteins in the early mouse embryo, and their roles in early morphogenetic events. As detected by immunoprecipitation, the α6, αV, β1, and β3 subunits are detected as early as the 4-cell stage, α5 at the hatched blastocyst stage and αl and α3 following blastocyst attachment. We tested the role of these integrins in the attachment and migratory activity of two cell populations of the early mouse embryo: the trophoblast giant cells, which invade the uterine stroma and ultimately contribute to the chorio-allantoic placenta, and the parietal endoderm, which migrates over the inner surface of the trophoblast and ultimately forms Reichert's membrane and the parietal yolk sac. Experiments were done in serum-free medium on substrates coated with laminin (Ln) and fibronectin (Fn). Trophoblast outgrowth occurs on Ln and its E8 fragment (long arm), but not on the E1’ fragment (cross region) (Figs. 1, 2 ). This outgrowth is inhibited by anti-E8, anti-Ln, and by the anti-β1 family antiserum anti-ECMR, but not by anti-αV or the function-perturbing GoH3 antibody that recognizes the α6/β1 integrin, a major Ln (E8) receptor. This suggests that trophoblast outgrowth on Ln or E8 is mediated by a different β1 integrin such as α3/β1. Early stages of trophoblast outgrowth (up to 48 hours) on Fn are inhibited by anti-Fn and by function-perturbing anti-αV antibodies, whereas at later times outgrowth becomes insensitive to anti-αV but remains sensitive to the anti-β1 family antiserum anti-ECMr, indicating that trophoblast cells modulate their interaction with Fn during outgrowth. Trophoblast outgrowth on vitronectin (Vn) is sensitive to anti-αV antibodies throughout the 5-day period examined.
Human mast cells but not human basophils coculture with mouse 3T3 fibroblasts
Authors: Goff J. P. , Kirshenbaum A. S. , Albert J. P. , Kessler S. W. , Metcalfe D. D.
Published: June 2020

Human mast cells and basophils have been shown to arise from CD34+ pluripotent progenitor cells in the presence of rhIL-3 (1). Two different culture systems using CD34+ cells, the agarose interphase culture and 3T3 fibroblast/CD34 + coculture, give rise to mast cells and basophils but with markedly different results. (1,2). By 3 weeks in interphase agarose cultures, CD34+ cells give rise to approximately 25-45% basophils and 1-5% tryptase positive mast cells. These mast cells have homogeneous granule patterns that resemble immature mast cells. With the addition of stem cell factor (rhSCF) (3) to rhIL-3, total cell number increases and mast cell maturation is promoted without altering the percentages of mast cells and basophils (4). These mast cells have tryptase-positive granules, with characteristic patterns seen in mature mast cells. In contrast, CD34+ cells cocultured with mouse 3T3 fibroblasts give rise by 6 weeks to approximately 50% tryptase positive mast cells which adher to the monolayer and possess granule scroll patterns. No basophils are ever identified by six weeks in cocultures.
Ultrastructural features of prognostic significance in human oral cancer
Authors: Ahluwalia Karvita B. , Sharma Nidhi
Published: June 2020

It is common knowledge that apparently similar tumors often show different responses to therapy. This experience has generated the idea that histologically similar tumors could have biologically distinct behaviour. The development of effective therapy therefore, has the explicit challenge of understanding biological behaviour of a tumor. The question is which parameters in a tumor could relate to its biological behaviour ? It is now recognised that the development of malignancy requires an alteration in the program of terminal differentiation in addition to aberrant growth control. In this study therefore, ultrastructural markers that relate to defective terminal differentiation and possibly invasive potential of cells have been identified in human oral leukoplakias, erythroleukoplakias and squamous cell carcinomas of the tongue.
Kearns-Sayre syndrome, a mitochondrial myopathy: First diagnosed case in Oman
Authors: Buhl Line , Muirhead David , Doyle David
Published: June 2020

Mitochondrial myopathy of the Kearns-Sayres Syndrome is described as a severe disorder which is progressive with CNS involvement, has metabolic acidotic crisis and is eventually fatal. The proportion of muscle fibres containing abnormal mitochondria maybe as low as 5-10% in cases presenting with severe clinical symptoms. There is no recognised treatment for this degenerative disease.

An 11 year old Omani girl well until the age of 5 years, showed increasing symptoms of external ophthalmoplegia, ptosis, tubular vision and retinitis pigmentosa. CT scan showed atrophy of the brain. Biochemistry revealed an elevated creatinine kinase. A muscle biopsy was performed at the age of 11 years. The patient had no known family history.
Influences of low and high dietary vitamin A on rat liver ultrastructure in a two-stage hepatocarcinogenesis model
Authors: Wasserman A. J. , Robertson L.W. , Megill J. R. , Bahia I.M. , Durham S.K.
Published: June 2020

Polychlorinated biphenyls (PCBs) were used extensively in industrial processes and subsequently contaminated the ecosystem resulting in their accumulation in biological systems including man (Wassermann, 1979). Specific PCB congeners induce different microsomal enzymes. 3,3′,4,4′-tetrachlorobiphenyl (TCB) is a 3-methylcholanthrene-like inducer, whereas 2,2′,4,4′,5,5′-hexachlorobiphenyl (HCB) is a phenobarbitol-like inducer. A previous study documented that both PCBs are tumor promotors in DEN-initiated rats (Buchmann, 1986). High levels of vitamin A have been demonstrated to be protective against the development of chemically-induced injury and neoplasia (Sporn, 1976; Lotan, 1980). The effects of different concentrations of vitamin A on hepatocellular injury was examined in an established two-stage hepatocarcinogenesis model.
Hexachlorobenzene toxicity in the rat ovary: II. Ultrastructure induced by medium (10 mg/kg) dose exposure
Authors: Singh Amreek , Foster Warren G. , Dykeman Anna , Villeneuve David C.
Published: June 2020

Hexachlorobenzene (HCB) is a known toxicant that is found in the environment as a by-product during manufacture of certain pesticides. This chlorinated chemical has been isolated from many tissues including ovary. When administered in high doses, HCB causes degeneration of primordial germ cells and ovary surface epithelium in sub-human primates. A purpose of this experiment was to determine a no-effect dose of the chemical on the rat ovary. The study is part of a comprehensive investigation on the effects of the compound on the biochemical, hematological, and morphological parameters in the monkey and rat.
The use of SEM to study the effect of bacteriostatic properties of sponges on bacterial attachment and growth
Authors: Pontefract R.D , Bergeron G.
Published: June 2020

Many bacteria possess the ability to adhere and grow on solid surfaces. The existence of bacterial biofilms in food processing plants and in or on food processing equipment can have serious consequences, and various cleaning and sanitizing procedures are employed to deal with such contamination. Bacteriological monitoring methods are employed to test the efficiency of these cleaning procedures, and the most widely used technique is the swab rinse method whereby a moistened sterile sv/ab is rubbed over the surface of the area to be sampled. One difficulty with this procedure is that the surface contact area of the swab is quite small, so that evenly swabbing a defined area can be difficult. To correct this problem, square sponges have been tried as substitutes to provide a much greater contact area. However, recent studies have shown that some sponges may contain bacteriostatic substances which can hinder test results. To determine whether some makes of sponges may contain bacteriostatic agents, SEM was used to examine samples which had been exposed to conditions to promote bacterial attachment and growth on their surface. The results of these observations were correlated with microbial tests to determine bacteriostatic activity of duplicate sponge samples.
Immunogold study of the differentiation of malignant human hematopoietic cells
Authors: de Harven Etienne , Christensen Hilary
Published: June 2020

The sequential steps in the differentiation of hematopoietic cells may be characterized from several viewpoints, i.e. the appearance of specific ultrastructural features, of enzymes and/or of surface antigens. Megakaryocyte(MKC) progenitors develop alpha granules, surface protrusions and demarcation membranes even before reaching the polyploid stage. They also express on their surfaces a platelet glycoprotein usually referred to as the 2b/3a complex. Monoclonal antibodies (mAbs) which recognize this glycoprotein are commercially available. Moreover, a monoclonal antibody against the 3a part of the complex (CD61) is, reportedly, expressed early in megakaryocytic differentiation.
Macromolecular specializations that mediate lateral interactions between microfilaments and the membrane at focal contacts
Authors: Samuelsson Steven J. , Luther Paul W. , Pumplin David W. , Bloch Robert J.
Published: June 2020

Focal contacts are membrane specializations of cultured cells where stress fibers terminate and where the cell is most closely applied to the substrate. The organization of this cytoskeletal-membrane-extracellular matrix assembly has been well characterized. Immunofluorescence microscopy has shown that two focal contact-specific proteins, vinculin and talin, colocalize with microfilaments for several microns before the stress fiber terminates. This result raises the question of whether microfilament-membrane interactions are limited to the ends of microfilaments, or if lateral interactions also occur. We addressed this question by examining the cytoplasmic surface of isolated focal contacts in detail.
Use of lanthanum as a conductive material in secondary electron imaging
Authors: Gupta P. D. , Relia Shashi B.
Published: June 2020

The use of colloidal lanthanum (La) as a conductive material in preparatory procedures for scanning electron microscopy of dehydrated non-conductive biological specimens has been explored for the present study. The ability of La to bind certain moities of the plasma membrane has been successfully employed to impart conductivity to a wide variety of biological material. LaNO3 solution (2%) in 0.1M cacodylate buffer (CB) was treated with 0.01 N NaOH with vigorous shaking. At pH 7.5 – 7.8 faint flocculent material appeared which indicated the formation of colloidal La. This solution was used for incubation of fresh and/or fixed biological specimen as described. Specimens were incubated in 1% La solution (final concentration) for 3h and 6h followed by fixation in 2.5% glutaraldehyde (glu) for 15 min on specimens were incubated and fixed simultaneously in 1% La and 2.5 glu (final concentration) in 0.1M CB for 3h. Then washed and post fixed in 1% OsO4 in 0.1M CB for 30 min. Tissues were dehydrated in ascending grades of acetone and dried by the CPD technique. After mounting on metallic stubs, the specimens were examined in JEOL 100 CX electron microscope with scanning attachment in the voltage range 20-40 kV and beam current of 50 μA and also in SEM Hitachi S 520 in the voltage range of 1-30 kV and beam current 10-100 μA. It has been shown that La generates enough secondary electrons to form an optimal image having a good contrast. The resolution achieved in this preparation is as good as that obtained in metal-coated samples (Figs. 1,2). In contrast to metal-coated samples, masking of topographical features is not observed in La incubated samples. The later samples are transparent (Fig. 2). The technique is applicable to a variety of specimens such as lipid vesicles (Fig.3), algae (Fig.4), ciliates, single cell suspensions (Fig.2), various tissues of rat (Fig. 5) and radical of germinating beans (Fig.6). La was also used for the preparation of biological material for back-scattered imaging mode. To study the process of phagocytosis, yeast cells were coated with La and incubated with cultures of macrophage tumor AK-5 cells. The engulfed yeast cells could be detected inside the cell as dark bodies (Figs.7,8).
PRO’s for a multiple/repeated use and safe disposal with recovery of osmiumtetroxide solution(s) in routine EM
Authors: Muss Wolfgang H.
Published: June 2020

Double fixation with an/aldehyde(s) and osmiumtetroxide is most commonly employed to process tissues for electron microscopy. The metal Os is precious and recycling would keep a toxic substance out of the environment and conserves a non-renewable resource. Since the pure substance is expensive, the handling of crystals & solutions is critical if not hazardous, disposal of used working solutions seems to be problematic (waste or recovery?; How to do it properly/safely according to new regulations concerning disposal of harmful and toxic lab-chemicals?..) one looks out for solutions. Searching for a routine and standard method which works satisfyingly concerning preservation of ultrastructure in human tissue, a method which is reliable and reproducible, low in cost as well as simple in handling, disposal and recovery of OsO2 precipitate over a period of now 4 years – a schedule sufficient also for higher demands was developed: after a fixation routine ( PRE: 0.5% formaldehyde + 1.5% glutaraldehyde=GA in 0.1M phosphate buffer; MASTER: 4% GA in 0.1M phosphate buffer; fix.at room temperature (RT) 10 min and up to 3 hours, respectively; rinsing) followed by POSTFIXATION (1-1.5 hrs, at RT) with the solution according to modified as:
Immunohistochemical localization of gene expression in Onchocerca volvulus using latex spheres as an SEM marker
Authors: Kreitzer David , Tuan Rocky S. , Shipley Kenneth J.
Published: June 2020

Onchocerca volvulus, the filarial parasite responsible for river blindness, is being studied for identification of sera reactive antigens. In an attempt to localize these reactive antigens, scanning electron microscopy is being utilized as a correlative technique with light microscopic observations.

Worm material is obtained by nodulectomy. The nodules were fixed in a modified Camoy’s fixative, dehydrated through graded ethanol and embedded in paraplast. Sections were cut at 8um, mounted onto glass slides and baked to dryness. Prior to immunohistochemical treatment, sections were deparaffinized with histoclear and xylene, and rehydrated through graded ethanols to water.
Acetylcholinesterase (AChE) demonstrated by a vascular perfusion incubation technique
Authors: Luo Zhongrong , Whitter Ernest F. , Manoonkitiwongsa Panya S. , Schultz Robert L.
Published: June 2020

For the cytochemical demonstration of enzymes, the commonly employed procedures involve using chopped small cubes or sections of tissue incubated in a proper medium. With the chopped tissue, penetration of substrate and capturing agents is very slow. When using frozen sections artifacts are difficult to avoid. Also proper vibratome sections are hard to achieve with small organs such as the pineal gland. In order to overcome these disadvantages, we have developed a vascular perfusion incubation technique for the demonstration of AChE.

With this technique, a simple gravity flow apparatus for vascular perfusion with two glass containers for fixative and Tyrode solution was used. A needle (19g) with a 32 cm long vinyl tube was connected to the apparatus by a three-way valve. Adult Djungarian hamsters were anesthetized with 1.5 g/kg urethane. The needle was inserted into the ascending aorta through the left ventricle. The following solutions were then perfused for the times indicated: Tyrode, 1 min; fixative (1% purified glutaraldehyde and 2% formaldehyde, 0.05 M cacodylate buffer, pH 7.2), 5 min; Tyrode, 10 min; substrate-free incubation medium, 10 min; complete incubation medium, 20 min; pause for 10 min; repeat of the last two steps four times; isotonic sodium sulphate, 10 min; buffered sulphide, 30 min; isotonic sodium sulphate, 10 min; fixative (3% glutaraldehyde and 2% formaldehyde, 0.05 M cacodylate buffer), 5 min. The entire pineal gland and pieces of the tongue were taken. After osmium postfixation standard electron microscopic procedures were used.
SEM observations of bloom-forming toxic diatoms from Monterey Bay, California
Authors: Hale E. A. , Krupp J. M. , Garrison D. L.
Published: June 2020

In the late summer of 1991, large numbers of seabirds in northern Monterey Bay, California died after showing unusual neurological symptoms. The first suspects were dinoflagellates, planktonic algae known to produce the toxins responsible for paralytic shellfish poisoning (PSP). Although toxic dinoflagellates were found, no evidence for PSP was present. Subsequent chemical analysis of tissue and stomach contents from affected birds and from locally collected northern anchovy showed high concentrations of domoic acid. During the seabird kill in Monterey Bay, the plankton was dominated by Pseudonitzschia australis (=Nitzschia pseudoseriata) a diatom not previously known to produce domoic acid.
Sample preparation for immunocytochemical localization of small soluble organic molecules in plant cells
Authors: Echlin Patrick , Monaghan Paul , Robertson David
Published: June 2020

Highly soluble organic molecules, such as alkaloids, sugars, amino acids, plant growth substances and secondary metabolites, play an important role in the growth and development of plants. Although a great deal is known about the metabolism of these chemicals, there is only fragmentary evidence as to where precisely in the plant body many of these materials are synthesized, how they are transported and where they are either utilized or stored. Recent developments in histochemical and immunocytochemical procedures coupled with both invasive and non-invasive imaging methods offer techniques which can be used to establish the spatial location of these substances, provided they remain in their natural place in the cells and tissue during the processes of sample preparation. This paper considers the current state in the development of such procedures with particular reference to the alkaloid nicotine.
Space-exposed seed experiment developed for students
Authors: Leeper Donna , Bridgers Kelvin , Hammond Ernest C.
Published: June 2020

The SEEDS project was flown in orbit aboard the Long Duration Exposure (LDEF) for nearly six years. During this time in space, the tomato seeds received an enormously abundant supply of cosmic radiation. Upon the return of the LDEF to earth, the SEEDS project was distributed throughout the United States and 30 foreign countries for analysis. The purpose of the experiment was to determine the long term effects of cosmic rays on living tissue. At Morgan, the analysis performed varied from germination and growth rates to electron microscopy and x ray analysis.

In analyzing the seeds under the electron microscope, usual observations were performed on the nutritional and epidermic layers of the seed. These layers appeared to be more porous in the space-exposed seeds than in the Earth-based control seeds. This unusual characteristic may explain the increase in the space seeds’ growth pattern. (Several test results show that the space-exposed seeds germinate sooner than the Earth-based seeds. Also, the space exposed seeds are growing at a faster rate.) The porous nutritional region may allow the the seeds to receive necessary nutrients and liquids more readily. Thus, enabling the plant to grow at a much faster rate.
Ultrastructural and chlorophyll content changes of leaves in peanut plant caused by iron deficiency
Authors: Tsai Yang-Zenq , Lai Kwan-Long , Lee Chau-Yunn
Published: June 2020

Yield of peanut is significantly low at Hua-lien area where is Fe-deficiency because of high pH value in soil. In order to understand the effect of iron ion on the growth and development in peanut plant, a series of experiments were conducted . First, two peanut cultivars namely Tainan Sel. 9 and Tainan 11 were used as excised root and embryo culture in vitro with Fe-proficiency or Fe-deficiency treatment. The result showed that the growth of excised root or embryo was significantly inhibited and the symptom of chlorosis appeared on the leaves caused by Fe-deficiency.
Human-hair analysis
Authors: Lambert Brenda E. , Hammond Ernest C.
Published: June 2020

The purpose of this study was to examine the external structure of four human hair shaft samples with the scanning Electron Microscope (SEM) and to obtain information regarding the chemical composition of hair by using the attached x ray microanalysis unit.

The hair samples were obtained from two female subjects. Sample A was taken from a black female and had not undergone any type of chemical processing. Sample B, C, D were taken from a white female, and were natural, processed, and unpigmented, i.e. “gray”, respectively. Sample C had been bleached, tinted, and chemically altered using a permanent wave technique.