bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of fractals to describe microstructures of porous thick-film platinum electrodes
Authors: Toteda Steven D.
Published: June 2020

Zirconia oxygen sensors, in such applications as power plants and automobiles, generally utilize platinum electrodes for the catalytic reaction of dissociating O2 at the surface. The microstructure of the platinum electrode defines the resulting electrical response. The electrode must be porous enough to allow the oxygen to reach the zirconia surface while still remaining electrically continuous. At low sintering temperatures, the platinum is highly porous and fine grained. The platinum particles sinter together as the firing temperatures are increased. As the sintering temperatures are raised even further, the surface of the platinum begins to facet with lower energy surfaces. These microstructural changes can be seen in Figures 1 and 2, but the goal of the work is to characterize the microstructure by its fractal dimension and then relate the fractal dimension to the electrical response. The sensors were fabricated from zirconia powder stabilized in the cubic phase with 8 mol% percent yttria. Each substrate was sintered for 14 hours at 1200°C. The resulting zirconia pellets, 13mm in diameter and 2mm in thickness, were roughly 97 to 98 percent of theoretical density. The Engelhard #6082 platinum paste was applied to the zirconia disks after they were mechanically polished ( diamond). The electrodes were then sintered at temperatures ranging from 600°C to 1000°C. Each sensor was tested to determine the impedance response from 1Hz to 5,000Hz. These frequencies correspond to the electrode at the test temperature of 600°C.
Microstructures of cavity surfaces in silicon
Authors: Follstaedt D.M. , Myers S. M. , Wampler W. R. , Stein H. J.
Published: June 2020

Helium is insoluble in most materials and forms “bubbles” when it is ion implanted into them. The microstructures of the cavities formed when Si is implanted with He and annealed are of interest for several basic materials science investigations: luminescence of porous structures, stabilities of atomic surfaces and H attachment to Si bonds on the internal cavity surfaces. Such cavities can allow new “surface-science”-type investigations to be conducted, such as the recent determination of the Si-H bond strength (2.5±0.2 eV). We have used cross-section TEM at 200 kV to characterize the cavities formed when (001) Si is implanted with l×1017 He/cm2, 30 keV, at room temperature and then annealed at 700 or 800 °C. The enhancement of internal surface area relative to the wafer surface is quantified, and faceting of the cavities is used to infer the relative stabilities of Si surfaces.
The crystallization of thin-film ceramics
Authors: Schwartz J.M. , Francis L.F. , Schmidt L.D. , Schabes-Retchkiman P.S.
Published: June 2020

Ceramic thin films and coatings are of interest for electrical, optical, magnetic and thermal barrier applications. Critical for improved properties in thin films is the development of specific microstructures during processing. To this end, the sol-gel method is advantageous as a versatile processing route. The sol-gel process involves depositing a solution containing metalorganic or colloidal ceramic precursors onto a substrate and heating the deposited layer to form a crystalline or non-crystalline ceramic coating. This route has several advantages, including the ability to create tailored microstructures and properties, to coat large or small areas, simple or complex shapes, and to more easily prepare multicomponent ceramics. Sol-gel derived coatings are amorphous in the as-deposited state and develop their crystalline structure and microstructure during heat-treatment. We are particularly interested in studying the amorphous to crystalline transformation, because many key features of the microstructure such as grain size and grain size distribution may be linked to this transformation.
Structure of stacking faults in pyrite using TEM techniques
Authors: Subramanian Raja , Vecchio Kenneth S.
Published: June 2020

The structure of stacking faults and partial dislocations in iron pyrite (FeS2) have been studied using transmission electron microscopy. Pyrite has the NaCl structure in which the sodium ions are replaced by iron and chlorine ions by covalently-bonded pairs of sulfur ions. These sulfur pairs are oriented along the <111> direction. This covalent bond between sulfur atoms is the strongest bond in pyrite with Pa3 space group symmetry. These sulfur pairs are believed to move as a whole during dislocation glide. The lattice structure across these stacking faults is of interest as the presence of these stacking faults has been preliminarily linked to a higher sulfur reactivity in pyrite. Conventional TEM contrast analysis and high resolution lattice imaging of the faulted area in the TEM specimen has been carried out.
Identification of polymer phases in elastomer blends
Authors: Sadhukhan P.
Published: June 2020

Elastomers are composed of natural rubber and synthetic polymers. They are generally blended to produce rubbers with certain “designing properties” Shaffer, et al., 1985), including high resilience, tensile strength and elongation, resistance to tear, flexing, freezing and abrasion and low permanent set. The analytical procedures used for the identification and characterization of these polymer blends range from a simple color or flame test to more sophisticated technique like electron microscopy. Over the years, transmission electron microscopy has become the principal technique of direct visualization and subsequent characterization of phase separation and domains in polymer blends. The standard specimen preparation has been to perform cryo-ultramicrotomy on solid blend materials at liquid nitrogen temperature (Andrews et al., 1967) followed by staining with osmium tetroxide (Kato, 1966) to enhance differential contrast between the polymers in these blends. Without prior knowledge of the chemistry between the polymers and osmium, it is difficult to identify them under the TEM.
Preparation and examination of Y-Ba-Cu-O wire sections
Authors: Zanota A. , Perry D. , Kvam E.P. , Balkin D. , McGinnt P.
Published: June 2020

The electrical properties of directionally solidified YBa2Cu3O7 wires have been shown to be as good as or better than any other bulk-form materials in many situations. However, the microstructural defects, including subgrain, stacking fault, and dislocation contents of these materials have not been well-characterized, in part because of the difficulty of preparing specimens for TEM examination.

A new technique has been developed to prepare these wires for TEM examination. The wires were less then .7mm in diameter, making handling of cross-sections difficult. Further, adhesion of evaporated films, electroplated films,and epoxies to the wires was so poor that the wire sections would either shed the films completely, or fall out of the epoxy even when several hundred microns thick. To avoid this problem, a coating technique which adhered tightly to the wire surface was needed.
Organized packing of RNA inside viruses as revealed by cryo-electron microscopy and x-ray diffraction analysis
Authors: Baker T. S. , Cheng R. H. , Johnson J. E. , Olson N. H. , Wang G. J. , Schmidt T. J.
Published: June 2020

The development of modern electron microscopy techniques to visualize the hydrated structures of biological macromolecules has stimulated many new studies, especially with viruses and virus-macromolecule complexes that are too large to study with current x-ray crystallographic methods, Cryo-electron microscopy (cryoEM) in conjunction with three-dimensional reconstruction procedures is capable of revealing both external and internal features of these structures.
Neuronal transplantation in the CNS: Preclinical and clinical studies
Authors: Fine Alan
Published: June 2020

Embryonic central nervous system neurons can survive transplantation to the adult brain and spinal cord in diverse mammalian species. Such transplanted cells can differentiate anatomically, neurochemically and physiologically, extending processes, establishing synaptic connections with host CNS neurons, and influencing host behavior. Neuronal grafts can thus serve as useful tools for the study of factors influencing aspects of differentiation, for the analysis of function of particular brain pathways, and for the development of new therapeutic strategies for the treatment of traumatic or neurodegenerative disorders.
DNA sequence mapping in interphase and metaphase chromosomes by fluorescence in situ hybridization
Authors: Trask Barbara , Allen Susan , Bergmann Anne , Christensen Mari , Fertitta Anne , Massa Hillary , Sachs Rainer , van den Engh Ger
Published: June 2020

Using fluorescence in situ hybridization (FISH), the positions of DNA sequences can be discretely marked with a fluorescent spot. The efficiency of marking DNA sequences of the size cloned in cosmids is 90-95%, and the fluorescent spots produced after FISH are ≈0.3 μm in diameter. Sites of two sequences can be distinguished using two-color FISH. Different reporter molecules, such as biotin or digoxigenin, are incorporated into DNA sequence probes by nick translation. These reporter molecules are labeled after hybridization with different fluorochromes, e.g., FITC and Texas Red. The development of dual band pass filters (Chromatechnology) allows these fluorochromes to be photographed simultaneously without registration shift.
New methods for the analysis of helical objects: Application of cross-correlation techniques
Authors: Morgan D.G. , Owen C. , Melanson L. , DeRosier D.J.
Published: June 2020

Electron microscopy coupled with image analysis has recently been used to solve the structure of several membrane proteins to used to solve the structure of several membrane proteins to near atomic resolution (1,2). Helical objects have also been examined using similar techniques, but in general, the resulting structures have been limited to relatively low resolution. A major factor contributing to this limitation is that helical structures are inherently weak diffractors compared to the same amount of material arranged in a planar crystal. The diffracting power of a helical object may be two orders of magnitude weaker. It is possible to compensate for this effect by averaging the data from many identical particles. However, it has been impractical to analyze sufficiently large data sets to recover reliable weak diffraction data at high resolution. We have recently developed image processing programs which will make the analysis of such large data sets possible.
1.4nm gold cluster labeling of tRNA and pyruvate dehydrogenase complex
Authors: Hainfeld James F. , Furuya Frederic R. , Carbone Kyra
Published: June 2020

A new 1.4 nm gold cluster that is stable, water soluble, and can be covalently linked to specific sites has recently been described. Previous applications have coupled this gold to Fab’ fragments to make one of the smallest EM immunolabels yet developed. This gold differs from colloidal gold significantly: it does not aggregate proteins by non-specific binding; binding is covalent and to a specific residue (e.g., thiol, amine, or carboxyl); it is very uniform in size; its small size makes it a high resolution marker.
Effects of radiation damage on frozen hydrated capsids of HSV-1
Authors: Conway James F. , Trus Benes L. , Booy Frank P. , Newcomb William W. , Brown Jay C. , Steven Alasdair C.
Published: June 2020

Radiation damage imposes severe limitations on the information content of frozen hydrated specimens, In this context we have investigated the effects of electron radiation damage on three dimensional density maps calculated from cryo-electron micrographs, using capsids of herpes simplex virus type-1 (HSV-1) as a model system. These studies investigated the “moderate” dose regime, ie prior to the onset of severe and conspicuous structural defects such as “bubbling”.
Fluorescence microscopy of molecular organization and dynamics in cultured cells
Authors: Wang Yu-li
Published: June 2020

Over the past ten years various technical advances have allowed the direct study of molecular activities in cultured cells under a fluorescence microscope. Fluorescent probes are well known for their high sensitivity, specificity and amenability to various spectroscopic analyses. When used in conjunction with low-light-level detectors and image processing computers, high resolution images of weak signals from single cells can be successfully acquired. In addition, the availability of digitized images has greatly facilitated the extraction of photometric and morphometric information.

We use Zeiss inverted microscopes equipped with epi-illuminators and Dage-MTI ISIT video cameras or Photometrics cooled CCD cameras. Custom incubator systems built on the microscope stages allow the maintenance of live cells for up to several days. The signals are processed with image processing systems (Imaging Technologies) interfaced with graphics workstations (Silicon Graphics, Model 3130 or 4D/20) or personal computers (386/33). All images are acquired by frame averaging/signal integration, followed by subtraction of the dark noise, and storage as computer files. A variation of this simple processing strategy has allowed the detection of extremely weak signals that are essentially invisible on unprocessed ISIT images. Computer programs are then used to display sequences or images as motion pictures, to measure the linear dimension and angular orientation, and to integrate intensities over defined areas.
EM of associated spermatozoa of squirrel (Funambulus pennanti)
Authors: Bawa S. R. , Bains H. K.
Published: June 2020

Associations amongst spermatozoa have been reported in a variety of vertebrate and invertebrate animals. Spermatozoa come together and are attached to each other only in the region of the head, their tails are free – required to steer the spermatozoa. We have studied sperm-sperm association in squirrel using electron microscopy.

Small pieces of epididymides of adult squirrels (Funambulus pennanti) were fixed in cacodylate buffered glutaraldehyde and processed in a conventional manner for transmission and scanning electron microscopy Ultrathin sections and freeze-fracture replicas were examined with JEOL 1200 EX electron microscope.
Cytochemical methods for the rapid demonstration of infection at the tissue-biomaterial interface
Authors: Hanker J. , Dobbins J.J. , Yates P.E. , Giammara B.L.
Published: June 2020

Infection can be an extensive problem developing during implantation of an autogenous or prosthetic (biomaterial) device or graft. Although culture techniques are invaluable in identifying the responsible microorganisms, the times required frequently emphasize the need for rapid staining methods which can reduce the classification times from days to hours. Studies in our laboratories over the past few years have resulted in microwave-accelerated stains and in methods developed by Giammara, which enable the rapid study of glass slides and coverslips by electron as well as light microscopy.
Ultrastructural localization of DNA topoisomerase II in oral squamous cell carcinoma utilizing immunogold EM
Authors: D'Andrea M , Farber P , Foglesong D
Published: June 2020

DNA topoisomerases are enzymes which insert transient breaks into duplex DNA and are important in DNA replication, transcription and recombination. There are two forms of the enzyme, Topoisomerase I which breaks and rejoins only one of the two strands of DNA and Topoisomerase II (Topo II) which breaks and rejoins both of the DNA duplex strands. The essential role of Topo II in cell proliferation is reflected in its abundance in dividing cells, including normal and neoplastic cells.
Effects of azithromycin in tapetal and atapetal dogs
Authors: Jakowski A.B. , Fortner J.H. , Milisen W.B. , Marsh P.M. , Carver J.M. , Lundeen G.R.
Published: June 2020

The tapetum lucidum is a reflective layer that lies beneath part of the retina in the eyes of many animals. It is believed to enhance night vision by reflecting light onto the sensory cells of the retina. Primates, including humans, do not have a tapetum. Routine safety studies have revealed that treatment of Beagle dogs with high doses of azithromycin, a novel macrolide antibiotic, causes changes in the color and reflectivity of the tapetal fundus. In order to determine whether the change is due to a direct effect on the tapetum as opposed to a change in transparency of the retina, a study was conducted that compared the effects of azithromycin treatment in normal versus congenitally atapetal dogs.
Ultrastructural anomalies of the flagellum in relation with abnormal motility in hybrid mice (C57BL x CDI)F1, treated with a mutagen: Ethyl methane sulphonate (EMS)
Authors: Ríos B. C. , Cantú M.G. , Gallegos L. , Ramírez B. E.
Published: June 2020

In 1975, the effect of EMS on the dismorphic sperm fraction, was reported (1). Since then, the action of this drug at different levels on the seminiferous epithelium and over the spermatogenic process has been studied (2,3).

Modifications in relation to the finding of morphologically abnormal sperms have been described too (6). Likewise the lowering of the count and of the sperm motility have been used as evidence of genetic damage caused by drugs (5). Recently it has been described that EMS not only affects the morphology of sperm but also their concentration and their motility (6). The present study has been done to determine if the effect of EMS on sperm motility has a morphological cause. Hybrid mice were administred a dose of 200 mg/Kg. of EMS intraperitoneally, for five consecutive days. The epididimary and deferens ducts content was studied four weeks later. They were fixed in 2.5% glutaraldehyde and 1 % osmium tetroxide; the material was included in epoxy-resin by the conventional method, sectioned and studied with a Zeiss EM 109 electron microscope.
Defective sperm cells in two captive cheetahs: analysis by TEM and SEM
Authors: Gray Lynn D. , Simmons Robert Shane , Thedford Louisa Schmid , Holiday David B. , Marsh Cathey
Published: June 2020

Captive breeding of cheetahs (Acinortyx jubatus) is of great interest to zoological parks and preserves. Semen quality is a major factor in successful reproduction and ultrastructural assessment can be helpful in choosing suitable males. There is, however, relatively little ultrastructural data on cheetah spermatozoa as compared with other species. Studies using both light and electron microscopy have indicated a high percentage of defective spermatozoa in cheetahs and have noted a number of specific defects including coiled tails, acrosomal malformations and basal plate “pouches”.
Formation of spermatophore in ejaculatory duct of yellow mealworm beetle, Tenebrio molitor: SEM study
Authors: Weyda Frantíšek , Happ George M.
Published: June 2020

Main role of the accessory glands of Tenebrio molitor male is to facilitate transfer of sperm to the females. They produce heterogeneous secretions. Two anatomically distinct glands are present. While the tubular accessory glands (TAG) are composed of the secretory cells of one type only, the bean-shaped accessory glands (BAG) consist of eight cellular types. Low viscosity secretion of the TAG mix with sperms forming seminal fluid while high viscosity secretions (spermatophorins) of the BAG are largely transformed into the insoluble wall and core of the spermatophore. The prespermatophoric mass is transferred to the ejaculatory duct (EJD) where solidify and forms the complex spermatophore. Immunocytochemical experiments with monoclonal antibodies based on the colloidal gold technique were used in order to understand exact composition of individual layers of the spermatophore. In the recent study we have used SEM to observe the whole process of the formation of spermatophore in the ejaculatory duct.
Rapid demonstration of septic or infectious arthritis due to Gram-negative bacteria
Authors: Hanker Jacob S. , Gross Paul R. , Giammara Beverly L.
Published: June 2020

Blood cultures are positive in approximately only 50 per cent of the patients with nongonococcal bacterial infectious arthritis and about 20 per cent of those with gonococcal arthritis. But the concept that gram-negative bacteria could be involved even in chronic arthritis is well-supported. Gram stains are more definitive in staphylococcal arthritis caused by gram-positive bacteria than in bacterial arthritis due to gram-negative bacteria. In the latter situation where gram-negativebacilliare the problem, Gram stains are helpful for 50% of the patients; they are only helpful for 25% of the patients, however, where gram-negativegonococciare the problem. In arthritis due to gram-positiveStaphylococci. Gramstained smears are positive for 75% of the patients.
Hemolysis of erythrocytes by the hemolytic system from the blood-feeding stable fly, Stomoxys calcitrans
Authors: Kirch H. J. , Spates G. , Droleskey R. , Kloft W.J. , DeLoach J.R.
Published: June 2020

Blood feeding insects have to rely on the protein content of mammalian blood to insure reproduction. A substantial quantity of protein is provided by hemoglobin present in erythrocytes. Access to hemoglobin is accomplished only via erythrocyte lysis. It has been shown that midgut homogenates from the blood feeding stable fly, Stomoxys calcitrans, contain free fatty acids and it was proposed that these detergent-like compounds play a major role as hemolysins in the digestive physiology of this species. More recently sphingomyelinase activity was detected in midgut preparations of this fly, which would provide a potential tool for the enzymatic cleavage of the erythrocyte's membrane sphingomyelin. The action of specific hemolytic factors should affect the erythrocyte's morphology. The shape of bovine erythrocytes undergoing in vitro hemolysis by crude midgut homogenates from the stable fly was examined by scanning and transmission electron microscopy.
Encapsulation by hypotonic dialysis: The role of endocytosis
Authors: Droleskey Robert E. , Andrews Kathleen , Chiarantini Laura , DeLoach John R.
Published: June 2020

Encapsulation of compounds by hypotonic dialysis is thought to occur via diffusion in which pores appear in the erythrocyte membrane when they are subjected to reduced osmotic pressure. Under certain conditions encapsulation may also occur to some degree via endocytosis. It has recently been reported that the drug methotrexate may be entrapped primarily by endocytosis and secondarily by passive diffusion when erythrocytes were prepared via hypotonic dialysis. The objective of this study was to determine to what extent endocytic vesicles appear at specific stages of the hypotonic dialysis process.
Freeze-fracture electron microscopy and enzyme activity of reconstituted cytochrome oxidase
Authors: Tihova M. , Tattrie B. , Nicholls P.
Published: June 2020

Eukaryotic cytochrome oxidase (CO) is a multisubunit enzyme spanning the inner mitochondrial membrane. As the terminal component in the respiratory assembly it catalyzes the reduction of oxygen to water. The size, shape and other gross features of the 3-dimensional structure of this protein have been obtained only for its 2-dimensional crystal form. The enzyme can be incorporated into liposomes of a defined lipid composition. Freeze-fracture electron microscopy of cytochrome oxidase vesicles (COV) has been combined with kinetic and spectroscopic measurements to study the phospholipid requirements for enzyme activity and protein orientation within the bilayers.
Cryofixation of various biological samples by high pressure freezing
Authors: YIN LUCY RU-SIU
Published: June 2020

The ultimate aim of ultrastructural fixation of biological specimen is to preserve all the compartments in their native state. Cryofixation is a superior method than conventional chemical fixation in reaching this goal. However, ice crystal formation during cryofixation often damages the structures. High pressure (2100 bar) freezing provides a way to alter freezing properties while cool down the specimen at a relatively high rate, minimizing the ice crystal formation. Nearly vitrified samples(up to 500 um) have been obtained with this method. Samples in suspension tend to get lost during high pressure freezing. The low percentage (∼30%) of successfully cryofixed specimens can be improved if the sample completely fills the cavity of the metal specimen carriers in which the specimen is frozen. Various methods to overcome sample loss are reported in this study.
Discerning water contamination during freeze—fracturing on stearic acid crystal sheets
Authors: Müller Theo , Gross Heinz
Published: June 2020

In high vacuum (HV) systems, as well as in ultra high vacuum (UHV) systems that have not been sufficiently baked out, the main component of the residual gas atmosphere is water. Adsorbed water is present on all surfaces of the vacuum chamber. Whether or not ice introduced into such a vacuum system sublimes depends on its saturation pressure (at the surface, as a function of the specimen temperature )and on the surrounding partial pressure of water (pH2O). These facts must be considered when fracturing frozen biological material in vacuum systems. Thus the critical condensation temperature ( 162, 144.5, 130 K for 10−6, 10−8, 10-10 mbar, respectively) is an important factor in discussions of specimen fracture face contamination. Possibilities to reduce the rate of water condensation include the use of UHV (p < 10 —9 mbar) and/or surrounding the specimen with a cold, optically dense shroud system. When such a shroud is used, water molecules originating outside the shroud can only reach the specimen surface if they condense on and reevaporate from the shroud surface at least once (probability at T < 123 K is less than 10 4).
Simple desiccation method for SEM using dimethoxypropane
Authors: Weyda Frantíšek
Published: June 2020

A number of techniques such as critical point drying (the most commonly used method of drying cells and tissues), freeze-drying or freeze-substitution are available to process various tissues preparations for scanning electron microscopy (SEM). Those techniques are more or less complicated (depending also on expensive equipments) and time consuming. While more simple air-drying from aqueous suspension or organic solvents can be used for some rigid biological specimen, it is generally not satisfactory for most tissues and biological objects. On the opposite, rapid and simple procedure using hexamethyldisilazane (HMDS) and air drying has been successfully applied to insect and mite tissues without observable artifacts. We have developed similar simple and rapid method using dimethoxypropane (DMP) and air drying. DMP has previously been used for chemical dehydration of tissues.
Xeroxographic-assisted location of areas or structures on clinical slides for EM examination
Authors: Giammara Beverly L. , Hanker Jacob S.
Published: June 2020

Recent studies in our laboratories have resulted in the development of microwave-accelerated silver stains for the demonstration of basement membranes and fungi, gram-negative bacteria, type III collagen, endoneurium, perineurium, DNA, and DAB or PPD-PC cytochemical or immunocytochemical reaction products. We have also found that the very structure in a specimen that raised a question by light microscopy can be mapped with a Micro-Locator Slide and then located and examined by the SEI and BEI modes of SEM by the techniques collated in this summary.
SEM study of cytoskeleton of osteoblasts immobilized on HA-ceramic during biocompatibility testing
Authors: Fratssinet P. , Delga C. , Conte P. , Rouquet N. , Nadal M.
Published: June 2020

Some standards for biocompatibility testing of biomaterials requires the determination of the cytoskeleton aspect of differentiated cells in contact with the material. It is usually determined by indirect immunofluorescence staining of cytoskeleton proteins and examination with a light microscope.

This examination is difficult on non transparent material and the resolution is very poor. In order to study the interaction of osteoblast cytoskeleton with HA-macroporous ceramics, we grew chicken embryo osteoblasts on the material then we extracted cell membranes to expose the cytoskeleton proteins. They were then examined in SEM.
Immunoelectron microscopic detection of mannan-antigen on yeast cells of Candida albicans
Authors: Edwards Mercedes , Trimble Robert , Samsonoff William
Published: June 2020

Candida albicans (Ca) is an opportunistic fungal pathogen of worldwide distribution. In recent years, infections by this fungus have received increased attention due to their prevalence in immunocomproimsed hosts (e.g. AIDS patients). However, Ca infection mechanisms are still to be ascertained. Investigations on the antigenicity of this organism have found that mannan, a component of its cell wall, is a major circulating antigen in systemic candidiasis. A few previous reports using electron microscopy, have indicated that mannan is located at the cell wall, but the resolution of the published micrographs did not afford a conclusive determination of the antigen distribution.
The leaf mesophyll of coyotillo (Karwinskia humboldtiana Zucc.) morphological characterization
Authors: Ordóñez J. Ruiz , Torres Cepeda T.E. , López A. Piñeyro
Published: June 2020

Karwinskia humboldtiana, a semi arid shrub of México known by the ccmnon names cqyotillo or tullidora produces several toxins with high toxicity against humans and ruminants. These toxins are present in different organs the plant. In relation to morphology, with the exception of the histological stucty of Lux and Earl, we have little information applicable in defining kind of tissue, internal secretory structures or cells are involved in the production, storing or distribution of these toxins. The aim of this work is to offer sane structural description of coyotillo mesophyll especially the features of the internal secretory structures,

Fresh leaves in physiological mature stage were obtained fran the field, and processed by routine techniques of light microscopy and transmission and scanning electron microscopy.
Generative cell mitosis in pollen tubes ofNicotiana tabacum: Ultrastructure and 3-D reconstruction
Authors: Yu Hong-Shi , Russell S. D.
Published: June 2020

In bicellular pollen, the two sperm cells are formed by mitotic division of the generative cell (GC) in the pollen tube. This division is characterized by several unique features, including: lack of a preprophase band (PPB), absence of a metaphase plate, absence of normal spindle formation, and irregular patterns of cytokinesis. Purportedly, this is the result of spatial constraints within the pollen tube, whichin vivomay be as narrow as 3 μm (as inNicotiana) and slightly widerin vitro.Immunofluorescence studies of GC mitosis have been published in the last five years2−7, but only one incomplete ultrastructural report on GC divisionin vitrois available. This study is the first using three-dimensional (3-D) techniques to reconstruct the mitotic apparatus of the GCin vivo.
Secondary-wall development in the cotton fiber
Authors: Goynes W.R. , Ingber B. F. , Triplett B.A.
Published: June 2020

Secondary wall thickness is considered to be a function of maturity in cotton fibers. Normal fibers are formed from a single epidermal cell of a fertilized ovule. Development of these cells into fibers occurs in two, possibly overlapping, stages. Fibers begin to elongate at anthesis, and elongation continues for approximately 20 days postanthesis (DPA). As this elongation period ends, deposition of secondary wall begins, and continues for 25-30 days until the boll “matures” and opens. The exact period of elongation and secondary thickening is dependent on factors such as variety, growing temperature, and light level. Between six and nine weeks, wall thickening terminates as bolls begin to open.
An ultrastructural analysis of the sympathetic innervation of the rabbit ear artery and middle cerebral artery and their branches
Authors: Dodge John T. , Bevan John A.
Published: June 2020

Unlike many peripheral vascular beds, the sympathetic nervous system exerts little control on cerebral blood flow. The contractile response of isolated rabbit middle cerebral artery (MCA) segments to electrical field stimulation of its intramural nerves is less than in a similar-sized artery from the ear. This study was undertaken to characterize and compare the perivascular neuromuscular relationships and innervation density of similar-sized arteries varying in diameter from these two different regional arterial beds to see if there were structural correlates for these functional differences.
The ultimate reliability of high-resolution electron imaging
Authors: Saxton W. O.
Published: June 2020

High resolution electron microscopy is patently an experimental science; yet what we do with high resolution microscopes does not always deserve the designation of ‘experimenting’ at all. Good experiments involve the observation of one set of (’dependent’ - preferably strongly dependent) quantities while another set (the ‘independent’ quantities) is varied systematically. We have however quite insufficient control of most of the independent variables in our experiments: a specimen prepared in a more or less brutal fashion, with an inaccurately known thickness, is placed under a highly damaging beam, and examined through an optical system whose adjustment, though known to be critical, is still rather more of an art than a science, yielding a micrograph covered with bright and dark lines and/or spots; while some of us then suppose that these directly reveal atomic column positions to within 5pm, others are so cautious about the various possible complicating factors that we are unable to draw the simplest inferences from the image with confidence.
convergent-beam diffraction from surfaces
Authors: Eades J. A. , Smith A. E. , Lynch D. F.
Published: June 2020

It is quite simple (in the transmission electron microscope) to obtain convergent-beam patterns from the surface of a bulk crystal. The beam is focussed onto the surface at near grazing incidence (figure 1) and if the surface is flat the appropriate pattern is obtained in the diffraction plane (figure 2). Such patterns are potentially valuable for the characterization of surfaces just as normal convergent-beam patterns are valuable for the characterization of crystals.

There are, however, several important ways in which reflection diffraction from surfaces differs from the more familiar electron diffraction in transmission.

Geometry

In reflection diffraction, because of the surface, it is not possible to describe the specimen as periodic in three dimensions, nor is it possible to associate diffraction with a conventional three-dimensional reciprocal lattice.
Effects of surface stress relaxation on reflection electron microscopy images of normal emerging edge dislocations
Authors: Peng L.-M. , Cowley J.M. , Hsu Tung
Published: June 2020

It has been well established that, due to the termination of the bulk periodic potential at the surface, the forces acting on the surface atoms are no longer symmetrical but the surface atoms are displaced from their ideal lattice positions. Similarly, additional surface relaxation due to the loss of periodicity is expected to occur at the points where some kinds of bulk defects, like dislocations, intersect the surface. There are experimental indications that the rather more pronounced contrast observed in TEM at these intersection points may be contributed to by the additional stress relaxation.

The REM technique is sensitive to crystal orientation and provides an ideal method of detecting the surface strain relaxation. The diffraction contrast effects arise from the changes of the angle between the incident beam and the local surface reciprocal lattice resulting from the strain field on the surface.
Automated high-resolution microscopy: the approaches so far
Authors: Saxton W. O.
Published: June 2020

Recent commercial microscopes with internal microprocessor control of all major functions have already demonstrated some of the benefits anticipated from such systems, such as continuous magnification, rotation-free diffraction and magnification, automatic recording of mutually registered focal series, and fewer control knobs. Complete automation of the focusing, stigmating and alignment of a high resolution microscope, allowing focal series to be recorded at preselected focus values as well, is still imminent rather than accomplished, however; some kind of image pick-up and analysis system, fed with the electron image via a TV camera, is clearly essential for this, but several alternative systems and algorithms are still being explored. This paper reviews the options critically in turn, and stresses the need to consider alignment and focusing at an early stage, and not merely as an optional extension to a basic proposal.
Analysis of computer-simulated tilted-beam images of grain boundaries
Authors: Krakow William , Wetzel Jeffrey T.
Published: June 2020

It is well known for perfect crystals, that tilting the beam can lead to an improvement in resolution, over axial illumination lattice images, particularly when the direct and diffracted beam are equally inclined to the microscope optical axis. The origin of the fringe structures observed in tilted beam electron micrographs of amorphous materials can also be explained in terms of phase contrast imaging theory which likewise applies to tilted beam images of crystalline materials. The present author has described a system of interactive computer programs used in conjunction with a digital television frame store which can, amongst other capabilities, compute tilted beam electron micrographs of any structure model seen in projection, i.e. weak phase objects. Separate multislice computations of (001) tilt boundaries for the Σ = 41, (910) and Σ = 5, (210) misorientations in Au have also been presented where the resolution required to form good lattice images was dealt with for both 200 and 400 keV microscopes under axial illumination conditions.
Electron energy loss spectroscopy and energy filtered electron microscopy
Authors: Shuman H.
Published: June 2020

The distribution of elements in thin biological specimens can be determined at high resolution with electron energy loss spectroscopy (EELS). The advantage of EELS is that the signal is large, since roughly 50% of the characteristic ionization events can be observed, but this is accompanied by difficulties related to the generally large background and the more stringent requirements for ultrathin specimens in EELS than in electron probe X-ray microanalysis. Therefore it is generally necessary to use signal processing methods to extract absorption edge information in EELS.

EELS can be used in two ways: to produce line spectra with a stationary or rastered probe, or to directly form energy-filtered electron microscope (EFEM) images representative of the elemental distribution.
Making optimum use of the signal in image digitization
Authors: Christenson K. K.
Published: June 2020

The detectors on modern electron microscopes often have a very high bandwidth which makes their outputs appear noisy on a short time scale. This noise is not a problem when photographing an image because the film integrates the signal. But it causes an annoying blurring of the trace in slow y-modulated line scans and can result in large errors if the signal is measured with a fast analog to digital converter (ADC)(Figs, 1,2).

The noise in digital measurements can be reduced by reading the detector may times and taking the numerical average of the readings. This requires no extra hardware but it increases the time required to acquire a linescan or image and ignores the fundamental problem that the ADC wastes most of the information available in the signal by only sampling for a very small portion of its total cycle time.
Calculations of oxygen electron energy loss near edge structure
Authors: Weng Xudong , Rez Peter
Published: June 2020

Most analytical microscopes are equipped with energy loss spectrometers capable of giving spectra showing 1-2 eV resolution for inner shell edges. The relatively weak modulation starting 30-50 eV from threshold due to Extended X-ray Edge Energy Loss Fine Structure (EXELFS) which is analogous to EXAFS in X-ray absorption has been studied in some detail. Although the theory is, in principle, straightforward the technique using energy loss in the electron microscope to determine nearest neighbour distances has not attracted widespread interest. This is partly due to the long counting times involved. The near edge structure (NES) within 20-30 eV of threshold is characterized by a very strong modulation and is clearly visible even when small amounts of the element are present. Interpretation of the features is very much more difficult and except in those cases in which peaks can be clearly assigned to transitions to antibonding orbitals the main form of analysis has been limited to simple comparisons or fingerprinting.
Multislice Simulation of Adf Stem Images
Authors: Kirkland E. J. , Loane R. F. , Silcox J.
Published: June 2020

The multislice method (e.g. Goodman and Moodie) of simulating bright field conventional transmission electron microscope (BF-CTEM) images of crystalline specimens can be extended to simulation of scanning transmission electron microscope (STEM) images of similar specimens in the annular dark field (ADF) mode. According to the reciprocity theorem (Pogany and Turner and Cowley) BF-CTEM would be equivalent to BF STEM with a point detector. Such a detector (STEM) however would yield an exceedingly small signal to noise ratio. Thus, STEM has found more use in the ADF mode (e.g. Crewe et al.) exploiting the large contrast arising from heavy atoms. In BF imaging (CTEM and STEM) the constrast is roughly proportional to the scattering amplitude f α Z3/4 whereas in DF (CTEM and STEM) imaging it is roughly proportional to the scattering cross σ α Z3/2 where Z is atomic number, a form that is advantageous foatom discrimination.
Ordering in Ni4Mo by TEM and APFIM
Authors: Kenik E.A. , Zagula T.A. , Miller M.K. , Bentley J.
Published: June 2020

The state of long-range order (LRO) and short-range order (SRO) in Ni4Mo has been a topic of interest for a considerable time (see Brooks et al.). The SRO is often referred to as 1½0 order from the apparent position of the diffuse maxima in diffraction patterns, which differs from the positions of the LRO (D1a) structure. Various studies have shown that a fully disordered state cannot be retained by quenching, as the atomic arrangements responsible for the 1½0 maxima are present at temperatures above the critical ordering temperature for LRO. Over 20 studies have attempted to identify the atomic arrangements associated with this state of order. A variety of models have been proposed, but no consensus has been reached. It has also been shown that 1 MeV electron irradiation at low temperatures (∼100 K) can produce the disordered phase in Ni4Mo. Transmission electron microscopy (TEM), atom probe field ion microscopy (APFIM), and electron irradiation disordering have been applied in the current study to further the understanding of the ordering processes in Ni4Mo.
Silicon near-surface damage induced by reactive ion etching
Authors: Jeng S. J. , Oehrlein G. S.
Published: June 2020

Reactive ion etching (RIE) is an anisotropic etching process which has been used to etch silicon oxide, silicon nitride and polysilicon films. Due to the nonuniformities of etch rate and film thickness, overetching is often required to ensure the complete removal of these films. Previous X-ray photoemission spectroscopy (XPS), He ion channeling, nuclear reaction profiling, Raman scattering and ellipsometry studies have indicated the presence of a fluorocarbon film (30-40 Å) on Si, a heavily disordered layer (∼30 Å) and the etching gas related impurity implantation region (∼250 Å) underneath the Si surface caused by CF4/x% H2 (0≤x≤40) reactive ion etching. In the present investigation, high resolution electron microscopy (HREM) is used to study the structures and distribution of lattice defects in the heavily disordered region. Particular attention is paid to the effects of overetch time and hydrogen addition to CF4 etching gas on Si near-surface damage structures.
Tem analysis of multiple-energy arsenic implanted and Rta'd silicon
Authors: Herring R.A.
Published: June 2020

Rapid thermal annealing (RTA) of ion-implanted Si is important for device fabrication. The defect structures of 2.5, 4.0, and 6.0 MeV As-implanted silicon irradiated to fluences of 2E14, 4E14, and 6E14, respectively, have been analyzed by electron diffraction both before and after RTA at 1100°C for 10 seconds. At such high fluences and energies the implanted As ions change the Si from crystalline to amorphous. Three distinct amorphous regions emerge due to the three implantation energies used (Fig. 1). The amorphous regions are separated from each other by crystalline Si (marked L1, L2, and L3 in Fig. 1) which contains a high concentration of small defect clusters. The small defect clusters were similar to what had been determined earlier as being amorphous zones since their contrast was principally of the structure-factor type that arises due to the difference in extinction distance between the matrix and damage regions.
Growth of spinel into alumina
Authors: Kouh Simpson Y. , Carter C. B.
Published: June 2020

The structure of spinel/alumina phase boundaries has recently been studied using the selected- area diffraction technique. It has been found that there exist several dominant topotactic relationships; of these, the two most common situations are when the {111} plane of spinel is parallel to either the (0001) plane or the {1120} plane of alumina. In both of these cases, it has been found that there is often a small rotation from exact topotaxy (typically 0° to 2° but with larger rotations possible) which partially eliminates the need for misfit dislocations. This rotation is a special phenomenon that may be unique to non-metallic interfaces such as phase boundaries in ceramics. In this report, a special spinel/alumina interface in which a large rotation from the exact topotaxy exists between the (111) plane of spinel and the (OOOl) plane of alumina is discussed.
Heteroepitaxy of stable metallic phases on GaAs: identification of candidate phases by TEM
Authors: Sands T.
Published: June 2020

The structural perfection and thermal stability of epitaxical silicide contacts provides silicon technology with the potential for three-dimensional device integration as well as novel discrete device structures. Furthermore, the detrimental effects of grain boundaries on film resistivity and interdiffusion are eliminated in these epitaxical contact structures. Similar benefits for GaAs technology may be expected if stable metallic phases that grow epitaxically on GaAs can be identified. Such structures would also represent the ideal configuration for understanding the relationship between interface structure and electronic transport properties of metal/compound semiconductor systems.

The search for candidate metallic phases can be simplified by considering only those phases that are cubic with lattice parameters compatible with aо (GaAs) = 0.565 nm. Of the many cubic structure types, the CsCl structure is the most common among the transition metal MGa phases.
Microstructural Characterization of Au-Ge-Ni based ohmic contacts to GaAs/AlGaAs modfet device
Authors: Rai A.K. , Petford-Long A.K. , Ezis A. , Langer D.W.
Published: June 2020

Considerable amount of work has been done in studying the relationship between the contact resistance and the microstructure of the Au-Ge-Ni based ohmic contacts to n-GaAs. It has been found that the lower contact resistivity is due to the presence of Ge rich and Au free regions (good contact area) in contact with GaAs. Thus in order to obtain an ohmic contact with lower contact resistance one should obtain a uniformly alloyed region of good contact areas almost everywhere. This can possibly be accomplished by utilizing various alloying schemes. In this work microstructural characterization, employing TEM techniques, of the sequentially deposited Au-Ge-Ni based ohmic contact to the MODFET device is presented.

The substrate used in the present work consists of 1 μm thick buffer layer of GaAs grown on a semi-insulating GaAs substrate followed by a 25 Å spacer layer of undoped AlGaAs.