bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microscopic examinations of toxic marine microalgae
Authors: O’Neil David , Leggiadro Cynthia , Kim Gwang Hoon , Fritz Lawrence 
Published: June 2020

A number of microalgae have been implicated in toxicity episodes in cultured shellfish in Eastern Canada. Nitzschia pungens f. multiseries and Prorocentrum lima are two organisms that have been shown to produce the toxins associated with poisonous shellfish. The present study examines these organisms by light microscopy (DIC and fluorescence), and SEM.The pennate marine diatom, N. pungens(fig. 2), has been shown to produce a potent neurotoxin, domoic acid, in pure culture. The distinctive features of this pennate diatom are illustrated in Fig. 1. The silica covering (frustule) consists of parallel rows of costa with multiple rows of minute pores (poroids). P. lima (fig. 5) is a dinoflagellate that has been found to produce a toxin known as okadaic acid. This toxin has been associated with ciguatera, a fish poison, and was implicated in a recent toxic shellfish event in Eastern Canada. The cellulosic thecal plates are adorned with regular, distinctive pattern of pores (fig. 4).
Ultrastructure and Senescence in an Achloroplastic Mutant of Hordeum vulgare L. cv. Dyan
Authors: Cross R.H.M. , Botha C.E.J. , Cowan A.K. , Hartley B.J. 
Published: June 2020

Senescence is an ordered degenerative process leading to death of individual cells, organs and organisms. The detection of a conditional lethal mutant (achloroplastic) of Hordeum vulgare has enabled us to investigate ultrastructural changes occurring in leaf tissue during foliar senescence.Examination of the tonoplast structure in six and 14 day-old mutant tissue revealed a progressive degeneration and disappearance of the membrane, apparently starting by day six in the vicinity of the mitochondria associated with the degenerating proplastid (Fig. 1.) where neither of the plastid membrane leaflets is evident (arrows, Fig. 1.). At this stage there was evidence that the mitochondrial membranes were undergoing retrogressive changes, coupled with disorganization of cristae (Fig. 2.). Proplastids (P) lack definitive prolamellar bodies. The cytoplasmic matrix is largely agranular, with few endoplasmic reticulum (ER) cisternae or polyribosomal aggregates. Interestingly, large numbers of actively-budding dictysomes, associated with pinocytotic vesicles, were observed in close proximity to the plasmalemma of mesophyll cells (Fig. 3.). By day 14 however, mesophyll cells showed almost complete breakdown of subcellular organelle structure (Fig. 4.), and further evidence for the breakdown of the tonoplast. The final stage of senescence is characterized by the solubilization of the cell wall due to expression and activity of polygalacturonase and/or cellulose. The presence of dictyosomes with associated pinocytotic vesicles formed from the mature face, in close proximity to both the plasmalemma and the cell wall, would appear to support the model proposed by Christopherson for the secretion of cellulase. This pathway of synthesis is typical for secretory glycoproteins.
A transmission electron microscopic study of structural transitions in fast ionic conductors
Authors: Queenan R. B. , Davies P. K. 
Published: June 2020

Na ß“-alumina (Na1.67Mg67Al10.33O17) is a non-stoichiometric sodium aluminate which exhibits fast ionic conduction of the Na+ ions in two dimensions. The Na+ ions can be exchanged with a variety of mono-, di-, and trivalent cations. The resulting exchanged materials also show high ionic conductivities.Considerable interest in the Na+-Nd3+-ß“-aluminas has been generated as a result of the recent observation of lasing in the pulsed and cw modes. A recent TEM investigation on a 100% exchanged Nd ß“-alumina sample found evidence for the intergrowth of two different structure types. Microdiffraction revealed an ordered phase coexisting with an apparently disordered phase, in which the cations are completely randomized in two dimensions. If an order-disorder transition is present then the cooling rates would be expected to affect the microstructures of these materials which may in turn affect the optical properties. The purpose of this work was to investigate the affect of thermal treatments upon the micro-structural and optical properties of these materials.
Grain boundary composition in silicon nitride
Authors: Bradley S. A. , Karasek K. R. 
Published: June 2020

Since one of the major factors for controlling creep properties in silicon nitride components is the addition of sintering aids, determination of the composition of the resulting intergranular second phases becomes very important. High resolution electron microscopy has been used to investigate the crystalline or non-crystalline character of the grain boundary while analytical electron microscopy studies have focused on the composition of the grain boundary pockets. As sintering aid additions and processing become more complex, multiple second phases are produced. Ascertaining the composition of the grain boundaries and grain boundary pockets is necessary for correlating the microstructure with the creep properties.A dedicated VG HB-5 scanning transmission electron microscope was used to measure the composition of grain boundaries and grain boundary pockets of silicon nitride.
Influence of W additions in rapidly solidified nial
Authors: Locci I. E. , Nathal M. V. 
Published: June 2020

The B2 aluminide NiAl has potential as a high temperature structural material, although its lack of low temperature toughness is a major obstacle. One strategy for improving low temperature toughness is by grain refinement. Fortunately, fine grained intermetallics appear to retain their strengths to much higher fractions of their melting point than do pure metals and alloys. The purpose of this study was to investigate the effects of melt spinning and small W additions on the grain size and stability of NiAl.Two alloys of the same matrix composition, equiatomic NiAl, were examined. One also contained 0.5 W at% (NiAl+W). The alloys were cast as ribbon ∼45 pm thick by ∼2.5 mm wide using a free jet melt spinning apparatus. To simulate consolidation conditions, sections of ribbon were annealed for 1 hour at either 1273 or 1573 °K in purified argon. Optical, X-ray and electron analyses of the as-spun and annealed ribbons were performed.
Rutherford backscattering & TEM studies of nitrogen, oxygen & argon incorporation in sputter-deposited titanium nitride films
Authors: Brown J.M. , Baiocchi F.A. , Williams D.S. , Beairsto R.C. , Knoell R.V. , Murarka S.P. 
Published: June 2020

Titanium nitride films are incorporated into semiconductor device fabrication to form both contacts and diffusion barriers. These films are often deposited by means of reactive sputtering of a titanium nitride target in an argon atmosphere. During the course of the deposition process, gaseous components may be incorporated into the films resulting in changes in their physical and electrical properties.The stress and resistivity of titanium nitride films have been measured as a function of several processing variables: i) target power, ii) substrate bias, iii) pressure and iv) N2/Ar ratio. The concentration of oxygen, nitrogen and argon and their distribution throughout the films were measured using Rutherford Backscattering Spectroscopy of 2.12MeV helium ions generated in a General Ionex 1.7MV accelerator.
Faceted antiphase boundaries in GaAs grown on Ge
Authors: Cho N.-H. , McKernan S. , Carter C.B. , Wagner K. 
Published: June 2020

Interest has recently increased in the possibility of growing III-V compounds epitactically on non-polar substrates to produce device quality material. Antiphase boundaries (APBs) may then develop in the GaAs epilayer because it has sphalerite structure (face-centered cubic with a two-atom basis). This planar defect may then influence the electrical behavior of the GaAs epilayer. The orientation of APBs and their propagation into GaAs epilayers have been investigated experimentally using both flat-on and cross-section transmission electron microscope techniques. APBs parallel to (110) plane have been viewed at the atomic resolution and compared to simulated images.Antiphase boundaries were observed in GaAs epilayers grown on (001) Ge substrates. In the image shown in Fig.1, which was obtained from a flat-on sample, the (110) APB planes can be seen end-on; the faceted APB is visible because of the stacking fault-like fringes arising from a lattice translation at this interface.
Structure-property relationships of PE/PP sandwiched films
Authors: Petermann J. , Broza G. , Rieck U. , Jaballah A. , Kawaguchi A. 
Published: June 2020

Oriented overgrowth of polymer materials onto ionic crystals is well known and recently it was demonstrated that this epitaxial crystallisation can also occur in polymer/polymer systems, under certain conditions. The morphologies and the resulting physical properties of such systems will be presented, especially the influence of epitaxial interfaces on the adhesion of polymer laminates and the mechanical properties of epitaxially crystallized sandwiched layers.Materials used were polyethylene, PE, Lupolen 6021 DX (HDPE) and 1810 D (LDPE) from BASF AG; polypropylene, PP, (PPN) provided by Höchst AG and polybutene-1, PB-1, Vestolen BT from Chemische Werke Hüls. Thin oriented films were prepared according to the method of Petermann and Gohil, by winding up two different polymer films from two separately heated glass-plates simultaneously with the help of a motor driven cylinder. One double layer was used for TEM investigations, while about 1000 sandwiched layers were taken for mechanical tests.
High-resolution scanning electron microscopy
Authors: Nagatani T. 
Published: June 2020

Although the main development of scanning electron microscopy (SEM) has been accomplished mostly by the Cambridge group and it has not been changed so much for about two decades, it should be noted that there have been two important developments to pursuing high resolution of better than 1nm.Most notably, use of a field emission gun developed by Crewe et al for the scanning transmission electron microscope (STEM) to form a fine electron beam has been most effective in SEMs due to its high brightness and low energy spread. Thus, several models of field emission (FE) SEMs have been developed in the early ’70s and commercialized with a resolution of 2∼3nm at around 30kV.The second development is to use a highly excited objective lens. The specimen has to be set inside the pole-pieces (so-called “in-lens” type).
What does the biologist want from the physical scientist?
Authors: Beer Michael 
Published: June 2020

The Biologist is interested in discovering and then understanding the chemical processes in organisms. Crucial in his analysis is a knowledge of the structure of the system at various levels. At the level of the cell he must recognize the positions of particular macromolecules. For proteins or nucleoproteins this is best done with labeled antibodies. Inorganic ions like calcium or sodium can be localized by X-ray microprobe or EELS. From the designer he requires instruments in which the distribution of these species is not altered by the data collection. Specimen stability is favored by low temperature and efficient collection of data. That means simultaneous detection of all possible scattering events. Rapid display of the results as abundances requires computers of sufficient capability.Similar procedures look promising in the analysis of the structure of nucleic acid-protein complexes. Nucleic acids can be traced through phosphorus and protein through sulphur or perhaps carbon to nitrogen ratio.
Nonspecific structures seen in diagnostic muscle biopsies
Authors: Caughey R. C. , Kalyan-Raman U. P. 
Published: June 2020

In a period of two years we have analyzed 50 muscle biopsies using the transmission electron microscope. Six nonspecific structures consisting of filamentous bodies, tubular aggregates, paracrystalline mitochondrial inclusions, honeycomb arrays, concentric laminated bodies, and finger print profiles were observed in 47 of 50 cases. In order to know the significance of these structures in muscle biopsies, we correlated their occurrence with their clinical history, histological findings, and histochemistry.The biopsies were initially fixed in 2.5% glutaraldehyde (pH. 7.5, 500 mOsm), then randomly minced and post fixed in 1% osmium tetroxide. All biopsies were processed with and without uranyl acetate en bloc staining in Walpole's buffer before ethanol dehydration. They were embedded in Epon 812 epoxy resin, sectioned, and stained with uranyl acetate and lead citrate before evaluation with a JEOL, JEM 100 C Transmission Electron Microscope. All grid squares of six different blocks were scanned to evaluate the ultra-structural pathology.
Effects of Zn deficiency on thymus of growing rats
Authors: Yamashiro S. , Bast T. , Bray T.M. , Bettger W.J. 
Published: June 2020

Zinc (Zn) deficiency is thought to cause depressed immune function in both the cell mediated and humoral aspects of the system. Alteration of lymphocyte maturation and migration has been observed in Zn-deficiency and marked reduction of the lymphocyte number was noted in the thymus of the pups fed Zn-deficient diet. Other alterations include parakeratosis of the squamous epithelia of digestive system and skin.Three groups of seven, weanling, male Wistar rats each were fed diets containing either 1.1 ppm Zn (deficient) or supplemented with 100 ppm Zn ad libitum (control) or the Zn supplemented diet limited to the amount consumed by those on the deficient diet (pair-fed) for 3 weeks. Details of the diet compositions have been reported previously (7). The animals were weighed at the onset and end of the experiment. The organ was weighed after it was fixed in Karnovsky's fixative and small pieces of the tissue were post-fixed in 2.0%, OsO4 for electron microscopy.
Calcium phosphate cements as binders for hydroxylapatite particles for bone repair
Authors: Hanker J. S. , Giammara B. L. , Lupton C. R. , Chow L. C. 
Published: June 2020

Calcium phosphate cements (CPCs) are under study for dental applications such as root canal filling or sealing and pulp capping. Upon setting they are converted principally to hydroxyapatite, the mineral constituent of bone. The presence of a small amount of fluoride or hydroxyapatite in the cement mixture hastens the setting time. Nevertheless, the CPCs set much more slowly than plaster of Paris (calcium sulfate hemihydrate) when moistened with water or dilute phosphoric acid.Hydroxylapatite (HA) is hydroxyapatite which has been processed either by sintering or firing into a dense ceramic or made into porous particles. Plaster has been found very useful as a binder to prevent the scatter of HA particles implanted for jawbone reconstruction. The composite HA/plaster implants can be tailored to fit the site during surgery or preformed and sterilized prior to surgery.
Immunoelectron microscopic localization of α2u-globulin in the male rat kidney after gasoline administration
Authors: Garg B.D. , Olson M.J. , Li L. , Mancini M.A. , Roy A.K. 
Published: June 2020

Exposure of male rats to unleaded gasoline and other volatile hydrocarbons causes acute nephrotoxicity with accumulation of hyalin droplets (HD) in epithelial cells of the proximal convoluted tubules (PCT). We have shown that HD accumulated after gasoline intoxication are partially composed of α2u-globulin, a protein found exclusively in adult male rats. Ultrastructural examination revealed HD to be enlarged phagolysosomes (secondary lysosomes). Metabolites of gasoline hydrocarbons are hypothesized to bind reversibly to α2u-globulin, perhaps limiting lysosomal degradation of this protein. α2u-Globulin accumulation may also result from hydrocarbon-mediated inhibition of lysosomal proteolytic enzyme activity. These studies were conducted to determine the distribution of α2u-globulin within epithelial cells of PCT during gasoline intoxication.Male F-344 rats were administered unleaded gasoline or 0.9% NaCl solution (2.0 mL/Kg, p.o., once daily, nine days) and 2 mm slices of saline-perfused kidney were fixed by immersion in 2.5% glutaraldehyde, 0.1 M sodium cacodylate (pH 7.4).
Fibrinogen binding to activated thrombocytes
Authors: O'Toole E. T. 
Published: June 2020

Avian thrombocytes (TC) are involved in hemostasis through a fibrinogen (Fib) mediated process. Although Fib acts to bridge cells, the localization of Fib binding sites on cells has not been characterized. Described is Fib binding to TC activated either for aggregation while in suspension or following adhesion to formvar. Use of colloidal gold both conjugated to the ligand, Fib, and indirectly as an immuno-gold probe against an antibody specific for the Fib receptor, enabled visualization of the binding regions. Fib receptor 3-D organization was revealed by serial reconstructions of TC aggregates and by whole cell mount stereo microscopy.Pigeon TC, obtained from citrated (1:9) blood by differential centrifugation, were washed in Ca++ free Puck's saline G (pH 6.5). Pigeon Fib was conjugated to 15 nm gold by vortexing and used to facilitate TC aggregation to 0.5 U/ml thrombin and 3 mM Ca++.
Effects of dasheen mosaic virus and a large bacilliform particle on the anatomy and ultrastructure of Colocasia esculenta (L.) Schott (Araceae)
Authors: Stein B. D. , Strauss M. S. 
Published: June 2020

Taro, Colocasia esculenta (L.) Schott (Araceae) is a monocot grown as a starchy root crop in much of the tropics and subtropics. It is subject to a number of fungal, bacterial, and viral diseases. Viral diseases have inhibited the cultivation of taro in parts of New Guinea and the Solomon Islands where taro is an integral part of the culture. Two different viruses, a Rhabdovirus, the Large Bacilliform Particle (LBP), and a smaller bacilliform virus, are the cause. Dasheen Mosaic Virus, a Potyvirus, has been found wherever taro is cultivated and produces a leaf mottle but is not lethal to plants.Colocasia esculenta cv K268 corms, infected with virus, were obtained from Michael Pearson, Department of Botany, University of Papua New Guinea, Port Moresby, New Guinea. Upon planting some of the corms produced leaves with virus symptoms. Others were symptomless but symptoms could be induced by stress.
Protein electron crystallography by 400kV cryo-microscopy
Authors: Chiu Wah , Brink Jaap , Soejima Toshinori , Schmid Michael F. 
Published: June 2020

Protein electron crystallography can provide a reconstruction detailed enough for the polypeptide chain of a membrane protein to be traced (1). However, there remain a number of technical problems associated with this technique that must be overcome before it can become a routine tool for high resolution three-dimensional structural analysis of protein crystals. A 400 kV electron microscope has been demonstrated to be advantageous for enhancement of resolution and contrast in images of protein crystals (1,2) because of a reduction in chromatic aberration effects. This paper addresses the question of experimental strategy in data collection for thin protein crystals with a 400 kV cryo-microscope. We will use crotoxin complex and T4 DNA helix destabilizing protein as examples of thin crystals to illustrate our approach.Crotoxin complex forms highly ordered crystals with different thicknesses among different crystals. In order to simplify sorting out data from the various crystals for 3-dimensional merging, it is desirable to collect as much data as possible from a single crystal.
Embedding resins: An historical perspective
Authors: Mollenhauer Hilton H. 
Published: June 2020

There are several factors that were requisites for the biological applications of electron microscopy. One of these was, clearly, the development of a matrix substance that could infiltrate biological material and encapsulate tissue components so that they could be thin sectioned and examined under an electron beam. Without such matrix substances, examination of tissue as we know it today, would not be possible.Perhaps the start of practical electron microscopy in the context stated above was the application of methacrylate resins for tissue embedment. Methacrylates have a very low viscosity and maintain this viscosity until polymerization is initiated (for days or weeks if one should wish). The two most commonly used methacrylates were n-butyl (soft) and n-methyl (hard) which could be mixed in various proportions to yield almost any block hardness. Methacrylates can be cross-linked with divinyl benzene to improve stability but this was not commonly done. Methacrylates are very easy to section which was an important aspect at the time since sectioning had to be done with glass knives.
Difference mode EXELFS with parallel-detection EELS
Authors: Kundmann Michael K. , Krivanek Ondrej L. 
Published: June 2020

Parallel detection has greatly improved the elemental detection sensitivities attainable with EELS. An important element of this advance has been the development of differencing techniques which circumvent limitations imposed by the channel-to-channel gain variation of parallel detectors. The gain variation problem is particularly severe for detection of the subtle post-threshold structure comprising the EXELFS signal. Although correction techniques such as gain averaging or normalization can yield useful EXELFS signals, these are not ideal solutions. The former is a partial throwback to serial detection and the latter can only achieve partial correction because of detector cell inhomogeneities. We consider here the feasibility of using the difference method to efficiently and accurately measure the EXELFS signal.An important distinction between the edge-detection and EXELFS cases lies in the energy-space periodicities which comprise the two signals. Edge detection involves the near-edge structure and its well-defined, shortperiod (5-10 eV) oscillations. On the other hand, EXELFS has continuously changing long-period oscillations (∼10-100 eV).
Ultra-high resolution backscattered imaging
Authors: Joy David C 
Published: June 2020

A recent paper by Ogura displays backscattered electron (BSE) images from a bulk, layered structure of AlAs/GaAs with repeat spacings of the order of 10nm. Typically BSE images are thought of as being inherently limited in resolution to a level which is of the order of a fraction of the Bethe range of the incident electrons, which for the beam energy and specimen used in these experiments would be of the order of 5 μm. The purpose of this paper is, therefore, to examine the conditions required for the nanometer level resolution achieved in this case.Backscattered electrons can be grouped into two classes, the BSI which are backscattered by a single high angle event soon after their entry into the specimen, and the BSII which are produced as the cumulative result of plural scattering. There is no sharp division between these groups but the two classes can be separated experimentally by energy filtering, since the BSI will have lost little energy in their short transit through the sample.