bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural and fractographic characterization of B4C-Al cermets tested under dynamic and static loading
Authors: Kim Gyeung Ho , Sarikaya Mehmet , Milius D. L. , Aksay I. A.
Published: June 2020

Cermets are designed to optimize the mechanical properties of ceramics (hard and strong component) and metals (ductile and tough component) into one system. However, the processing of such systems is a problem in obtaining fully dense composite without deleterious reaction products. In the lightweight (2.65 g/cc) B4C-Al cermet, many of the processing problems have been circumvented. It is now possible to process fully dense B4C-Al cermet with tailored microstructures and achieve unique combination of mechanical properties (fracture strength of over 600 MPa and fracture toughness of 12 MPa-m1/2). In this paper, microstructure and fractography of B4C-Al cermets, tested under dynamic and static loading conditions, are described.

The cermet is prepared by infiltration of Al at 1150°C into partially sintered B4C compact under vacuum to full density. Fracture surface replicas were prepared by using cellulose acetate and thin-film carbon deposition. Samples were observed with a Philips 3000 at 100 kV.
Grain boundaries in zinc oxide-based varistor ceramics
Authors: Sung Gun Yong , McKernan Stuart , Carter C. Barry
Published: June 2020

Since the development of the zinc oxide-based varistor with highly nonlinear current-voltage characteristics and high energy absorption capabilities [1], the electro-physical behavior of non-ohmic ZnO varistors has been studied and related to the microstructure of the material, the conduction and degradation mechanisms, the dielectric properties, and the high pressure memory. An extensive research effort has been aimed at characterizing ZnO/ZnO grain boundary regions in order to explain the origin of the nonlinear current/voltage characteristics of these materials [2-4]. A typical ZnO-varistor material contains small concentrations of several metal oxides (e.g., Bi2O3, CoO, MnO, Sb2O3, and Cr2O3). Co and Mn are contained within the ZnO grains, while the other “impurities are present as several polymorphic forms of Bi2O3, the spinel, Zn7Sb2O12, and the pyrochlore Zn2Bi3Sb3O14, are present as intergranular phases [1,5-7]. The breakdown voltage depends on the number of grain boundaries between the electrodes of the ZnO varistor device [8]. Therefore, the breakdown voltage is influenced by the presence and form of these intergranular phases, and the size, shape and distribution of the ZnO grains. In ZnO-Bi2O3-MnO-TiO2-based varistor materials, the morphology of the ZnO grains is strongly influenced by their tendency to grow preferentially along the directions perpendicular to the prism planes [9] (i.e., the basal plane becomes a common grain boundary facet plane). The aim of the present study is to advance the understanding of the role of the special grain boundaries which are found in air-quenched Zn0-Bi2O3-MnO-TiO2-based varistor materials.
Defect reduction in oxygen implanted silicon-on-insulator material during high-temperature annealing
Authors: Roitman P. , Cordts B. , Visitserngtrakul S. , Krause S.J.
Published: June 2020

Synthesis of a thin, buried dielectric layer to form a silicon-on-insulator (SOI) material by high dose oxygen implantation (SIMOX – Separation by IMplanted Oxygen) is becoming an important technology due to the advent of high current (200 mA) oxygen implanters. Recently, reductions in defect densities from 109 cm−2 down to 107 cm−2 or less have been reported. They were achieved with a final high temperature annealing step (1300°C – 1400°C) in conjunction with: a) high temperature implantation or; b) channeling implantation or; c) multiple cycle implantation. However, the processes and conditions for reduction and elimination of precipitates and defects during high temperature annealing are not well understood. In this work we have studied the effect of annealing temperature on defect and precipitate reduction for SIMOX samples which were processed first with high temperature, high current implantation followed by high temperature annealing.
Hydrogen embrittlement
Authors: Birnbaum H. K. , Robertson I. M.
Published: June 2020

The effects of hydrogen on the fracture of metals will be reviewed using a selection of observations based on the use of in situ environmental cell experiments. These were developed to allow understanding of the mechanisms of the failure process. The in situ technique, combined with use of the environmental cell, is well suited to mechanistic studies of environmental fracture as it allows observation of crack tip processes at high resolution and in a relatively high fugacity aggressive environment. These methods have been applied to studies of the behavior of several systems. Selected examples will be discussed and a general pattern of behavior will be developed.

A clear distinction will be made between the kinetics of hydrogen related fracture and the mechanisms by which fracture occurs. The rate at which hydrogen related fractures propagate depends on the factors which control the mobility and transfer of hydrogen across surfaces, on the fugacity of the hydrogen source, on the metallurgical properties of the alloys and on the stress intensities.
Irradiation-induced grain growth in gold and copper: In situ HVEM studies at 75-300 K
Authors: Allen Charles W.
Published: June 2020

When thin polycrystalline films of Au, Cu and various other materials are subjected to energetic ion irradiation, the average grain size increases even at cryogenic temperatures. As is the case with many ion beam processes, this phenomenon of ion irradiation induced grain growth exhibits only a very mild temperature dependence. This contribution is based on in situ experiments, performed at the HVEM-Tandem User Facility at Argonne National Laboratory. This Facility interfaces a 2 MV Tandem ion accelerator and a 0.6 MV ion implanter to a 1.2 MV AEI high voltage electron microscope, which allows a wide variety of in situ ion beam experiments to be performed with simultaneous irradiation and electron microscopy or diffraction. A series of in situ ion and/or electron irradiation experiments is being performed at the HVEM-Tandem Facility at Argonne which have shown clearly for fine grained Au films that two mechanisms for growth are operative for the ion beam case: grain boundary migration as in normal thermal grain growth and grain coalescence which is similar in appearance to recrystallization by subgrain coalescence. Especially in the case of Au for which ion-induced growth is relatively rapid, such in situ experiments also demonstrate the importance of dislocation activity which is a consequence of the collision cascade damage associated with ion irradiation. Existing theories for irradiation-induced grain growth assume that growth occurs by boundary migration and that only point defects generated at grain boundaries are responsible for the growth phenomenon.
TEM study of ball-milled Ni-Ta alloy containing WC inclusions
Authors: Merk N. , Tanner L. E.
Published: June 2020

High energy ball-milling of metallic powders is used extensively to achieve structural refinement. In recent years it has been found that cold-milling can induce transformations to highly metastable phases.In particular, the elemental mixing at the atomic-scale in certain systems may eventually lead to solid-state amorphization reactions (SSAR) after short periods of time. A problem that often arises in using this technique is contamination of the product from the grinding balls and container material.

In this note we describe such a development in the microstructures that evolve during SSAR of a mixture of 75 atm% Ni and 25 atm% Ta high-purity powders processed for 17h in a planetary mill using WC + Co balls and container. The average composition of the ball-milled powders determined by EDS-analysis in a SEM was Ni75Ta25. X-ray diffraction confirmed the formation of an amorphous phase and also revealed the presence of sharp crystalline peaks identified as WC hexagonal phase (a=0.291 nm and c=0.283 nm); no detectable crystalline peaks from the initial Ni or Ta powders were observed. For TEM observations, small quantities of the ball-milled powders were embedded in epoxy and subsequently sectioned with a diamond knife using a Dupont-6000 ultramicrotome.
Stereoscopic analyses of surfaces on polystyrene foam
Authors: Lindsey E.F. , Price C. W. , Franks R. M. , Lane M. A.
Published: June 2020

Analysis of surface finishes on machined polystyrene foam presents a unique challenge when the cell size of the foam is of the order of or larger than desired surface finishes. Ideally, the surface could be defined as the geometric surface formed by the locus of the severed edges of the cell walls. However, both machining and grinding tend to rip and fracture cell walls and leave asperities formed by agglomerations of fragmented cell walls. Machined geometric surfaces can be defined as the locus of the tips of the asperities, but the surface in between asperities can extend several cell layers below the asperities. The severe nature of this problem is emphasized by stereoscopic examinations of fractured, machined and ground, and cryo-vibratomed polystyrene surfaces in the SEM.

Since coating does not seriously distort low-density polystyrene foam, the specimens were gold-palladium coated for examination in a Hitachi S-800 FESEM at 5 kV. Stereo pairs were obtained using tilts of + and − 3 1/2 degrees. The polystyrene foam had a cell size that varied between 2 to 11 μm.
Microtomy applications for materials science
Authors: Omlor R.E. , Lloyd P. F.
Published: June 2020

Standard sample preparation techniques of various metals, composites, ceramics and polymer specimens can be very time consuming (such as dimpling and ion milling etc.), yet still introroduce artifacts during specimen preparation. With many of these materials numerous hours and sometimes even days can be spent preparing samples for TEM studies. In the past, ultramicrotomy has been used primarily for biological applications, but over the years has been tried on various polymers, metal and ceramic powders, oxide layers, etc. The main concern has been deformation introduced to the specimen while cutting. This study will demonstrate successful ultramicrotomy over a variety of non-biological specimens.

Materials chosen for this experiment consist of Rapidly Solidified (RS) Al-V powders, P-120 Carbon fibers, Silicon Carbide (MMC) fibers, Kevlar and an IC semiconductor chip. Routine SEM micrographs were taken of all material as-received. All the specimens were embedded using a low viscoscity resin, L. R. White (hard grade). They were microtomed with a diamond knife at a 55-60° cutting angle using an AO/Reichert Ultracut Ultramicrotome with a slow cutting speed of 0.4 mm/sec which obtained the best results. All sections were picked up on Hex 700TB Ni grids.
A technique for preparing semiconductor cross sections for both TEM and SEM analysis
Authors: Klepeis Stanley J. , Benedict J.P. , Anderson R.M
Published: June 2020

The ability to prepare a cross-section of a specific semiconductor structure for both SEM and TEM analysis is vital in characterizing the smaller, more complex devices that are now being designed and manufactured. In the past, a unique sample was prepared for either SEM or TEM analysis of a structure. In choosing to do SEM, valuable and unique information was lost to TEM analysis. An alternative, the SEM examination of thinned TEM samples, was frequently made difficult by topographical artifacts introduced by mechanical polishing and lengthy ion-milling. Thus, the need to produce a TEM sample from a unique,cross-sectioned SEM sample has produced this sample preparation technique.

The technique is divided into an SEM and a TEM sample preparation phase. The first four steps in the SEM phase: bulk reduction, cleaning, gluing and trimming produces a reinforced sample with the area of interest in the center of the sample. This sample is then mounted on a special SEM stud. The stud is inserted into an L-shaped holder and this holder is attached to the Klepeis polisher (see figs. 1 and 2). An SEM cross-section of the sample is then prepared by mechanically polishing the sample to the area of interest using the Klepeis polisher. The polished cross-section is cleaned and the SEM stud with the attached sample, is removed from the L-shaped holder. The stud is then inserted into the ion-miller and the sample is briefly milled (less than 2 minutes) on the polished side. The sample on the stud may then be carbon coated and placed in the SEM for analysis.
Techniques in preparing TEM specimens of diamond thin films
Authors: Chiou W. A. , Wong M. S. , Chen F. R. , Li D. X. , Chang R. P. H. , Meshii M.
Published: June 2020

Diamond, with its unique combination of optical, physical, mechanical, and electrical properties, has provided a superior potential for industrial and military applications. It has caught the attention of a growing number of researchers over the past decade. The recent development of low-pressure vapor deposition of diamond film has greatly increased the prospects for the practical utilization of diamond. To use a diamond film, the nature of the interface between diamond film and substrate must be understood. This paper presents three different techniques in preparing diamond thin films specimens for TEM study of the interfacial structure between diamond and substrate as well as the internal structure of diamond crystals.

Diamond crystallites and films produced by radio frequency (RF) and microwave (MW) plasma enhanced chemical vapor deposition (PECVD) techniques were deposited on Si (100), polycrystalline Mo, and Cu substrates (925°C) at 40 mbar, with 0.5% methane and 0.2% oxygen in hydrogen gas at a total flow rate of 200 seem for MWPECVD and 2000 seem for RFPECVD. To examine the internal and interfacial structures of the diamond film on different substrates, three techniques were employed: (1) the chemical etching technique, which removes substrates then the substrate-free diamond film was supported on a Cu grid, (2) the conventional epoxy-embedding technique for cross-section study, and (3) the direct deposition of diamond crystallites on metal grids.
Solid-state reaction of Ru and Al in molten Bi
Authors: Garland C. M. , Johnson R. W.
Published: June 2020

There has been much recent interest in the reactions that occur when two crystalline metals inter-diffuse at low temperatures. Metastable phase formation can occur when structural relaxation into equilibrium crystalline phases is kinetically inhibittedf. These reactions are typically studied in thin—film diffusion couples formed by sequentially depositing two elemental crystalline metals. In this paper we describe a novel low—temperature reaction sequence for the formation of very fine-grain Alx Ru,1-xalloys that allows a further extension of these techniques. This reaction regime uses molten Bi as a medium for the transfer of Al solute atoms to the surface of Ru powder where reaction occurs with the formation Alx Ru1-x,intermetallic phases. The low melting point and ease of handling of Bi, its solvent ability towards Al and Ru, the absence of equilibrium phases of Bi with Al and Ru, and previous experience in our laboratory with equilibrium and metastable phase formation in this system made it attractive as a prototype for this initial study.

Ru powder and Al pellets were separatedly prereacted in molten Bi at 500 C for several hours to ensure wetting of the solid surfaces. This Ru and Al and additional excess Bi were then sealed together in a fused silica tube and reacted in a vertical tube furnace. Separate such reactions were carried out at temperatures ranging from 300 to 600 C. After reaction samples were broken free from the fused silica tube and the Bi transfer medium was etched away in concentrated HNO3.
A digital processing method for obtaining dark-field HREM image
Authors: Liu Yang , Huiming Tang
Published: June 2020

The contrast of images can be increased by use of dark-field HREM. But in comparison with bright-field imaging, the increased exposure times required will result in more serious radiation damage effects on the specimen. This work is to develop a method to obtain computing dark-field images from bright-field images by use of computer processing, which can overcome the shortcome above.

For A weak phase object,σϕ≤1, the transmission function can be written as[1].

(1)

Assuming that the amplitude of an incident wave is unity, the distribution of amplitude on the back focal plane of an ideal lens is

(2)

Cowley [2] demonstrated that a reasonable approximation to the ideal imaging condition, sinχ = 1, can be achieved for an optimum defocus, then we have

(3)

The image amplitude can be given by Fourier transform of (3) as the following:

(4)
Apical poiarity of glycosyl-phosphatidylinositol anchored proteins in epithelial cells
Authors: Lisanti P. , Le Bivic A. , Saltiel A. , Rodriguez-Boulan E.
Published: June 2020

Epithelial cells are characterized by a polarized distribution of structural features and functions between two plasma membrane domains, apical and basolateral. The molecular mechanisms responsible for this surface polarization are currently under intensive investigation. Studies on the biogenesis of viral envelope glycoproteins in the kidney cell line MDCK have demonstrated that sorting occurs in the distal cisternae of the Golgi apparatus (trans Golgi network) by incorporation into different populations of transport vesicles that fuse with the corresponding plasma membrane domain. Recombinant DNA technology has been utilized to localize the “sorting signal” to a specific glycoprotein domain, namely, extracellular, transmembrane or cytoplasmic. These studies have not been conclusive, but it appears that the exoplasmic domain appears to be sufficient for targeting to the apical surface.

In order to understand the mechanisms responsible for sorting, we have recently characterized the polarized distribution of a group of plasma membrane proteins that are linked to the plasma membrane via a glycolipid, glycosyl-phosphatidylinositol (GPI). Proteins belonging to this class are attached via the C-terminal aminoacid to ethanolamine which, in turn is linked to an oligosaccharide chain, linked to the inositol ring of phosphatidylinositol (PI). The precise function of this mode of membrane attachment is still unknown. We explored the possibility that either the protein or the GPI anchor carry the sorting information.
Cryomicroscopy of crotoxin complex crystals at 400 KV
Authors: Brink Jaap , Chiu Wah
Published: June 2020

The crotoxin complex is a potent neurotoxin composed of a basic subunit (Mr = 12,000) and an acidic subunit (M = 10,000). The basic subunit possesses phospholipase activity whereas the acidic subunit shows no enzymatic activity at all. The complex's toxocity is expressed both pre- and post-synaptically. The crotoxin complex forms thin crystals suitable for electron crystallography. The crystals diffract up to 0.16 nm in the microscope, whereas images show reflections out to 0.39 nm2. Ultimate goal in this study is to obtain a three-dimensional (3D-) structure map of the protein around 0.3 nm resolution. Use of 100 keV electrons in this is limited; the unit cell's height c of 25.6 nm causes problems associated with multiple scattering, radiation damage, limited depth of field and a more pronounced Ewald sphere curvature. In general, they lead to projections of the unit cell, which at the desired resolution, cannot be interpreted following the weak-phase approximation. Circumventing this problem is possible through the use of 400 keV electrons. Although the overall contrast is lowered due to a smaller scattering cross-section, the signal-to-noise ratio of especially higher order reflections will improve due to a smaller contribution of inelastic scattering. We report here our preliminary results demonstrating the feasability of the data collection procedure at 400 kV.

Crystals of crotoxin complex were prepared on carbon-covered holey-carbon films, quench frozen in liquid ethane, inserted into a Gatan 626 holder, transferred into a JEOL 4000EX electron microscope equipped with a pair of anticontaminators operating at −184°C and examined under low-dose conditions. Selected area electron diffraction patterns (EDP's) and images of the crystals were recorded at 400 kV and −167°C with dose levels of 5 and 9.5 electrons/Å, respectively.
Imaging sub-micron objects with light microscopy: Visualization of the T-4 bacteriophage
Authors: Brown Malcolm , Delgado Reynolds M. , Fink Michael J.
Published: June 2020

While light microscopy has been used to image sub-micron objects, numerous problems with diffraction-limitations often preclude extraction of useful information. Using conventional dark-field and phase contrast light microscopy coupled with image processing, we have studied the following objects: (a) polystyrene beads (88nm, 264nm, and 557mn); (b) frustules of the diatom, Pleurosigma angulatum, and the T-4 bacteriophage attached to its host, E. coli or free in the medium. Equivalent images of the same areas of polystyrene beads and T-4 bacteriophages were produced using transmission electron microscopy.

For light microscopy, we used a Zeiss universal microscope. For phase contrast observations a 100X Neofluar objective (N.A.=1.3) was applied. With dark-field, a 100X planachromat objective (N.A.=1.25) in combination with an ultra-condenser (N.A.=1.25) was employed. An intermediate magnifier (Optivar) was available to conveniently give magnification settings of 1.25, 1.6, and 2.0. The image was projected onto the back focal plane of a film or television camera with a Carl Zeiss Jena 18X Compens ocular.
Cytotoxic mechanisms and disorders associated with natural killer (NK) cells
Authors: Payne Claire M. , Cromey Douglas W.
Published: June 2020

Natural killer (NK) cells represent a first line of defense in the immune system, and are capable of spontaneous cytotoxicity against a variety of malignant cells, virally-infected cells and certain microorganisms. NK cytotoxicity is not dependent on prior sensitization by antigens, since target killing is not restricted to recognition of the major histocompatibility complex (MHC), in contrast to the need for MHC recognition by cytotoxic T-lymphocytes (CTLs). The mechanisms of target cell recognition by NK cells are largely unknown, although the glycolipid asialo GM2, the transferrin receptor and the laminin receptor, known to be present on sensitive target surfaces, have been implicated. NK cells share surface markers with T-lymphocytes and monocytes, and may represent a third mononuclear cell type with a distinct cell lineage.

Previous work from our laboratory indicated that, like monocytes, NK cells bear an Fc-receptor for cytophilic antibody , and are capable of phagocytosis. NK cells, however, morphologically resemble lymphoid cells, since the cell surface is covered with microvilli, not surface folds. NK cells are also responsible (after monocyte depletion) for the majority of antibody-dependent cytotoxicity (K cells), since enrichment for K cells also enriches for functional NK cells, and vice-versa. NK cells have the morphologic appearance of large granular lymphocytes (LGLs). The cytoplasmic granules are azurophilic using Wright’s stain, have a substructure that has the appearance of parallel tubular arrays (PTAs) at the ultra-structural level , and biochemically contain a 70 kD protein called cytolysin (similar to the perforin lytic molecules of CTL granules).
Correlative histochemical and immunocytochemical techniques for the study of classical transmitters and neuropeptides
Authors: Pelto-Huikko M.T.
Published: June 2020

A growing number of small biologically active peptides has been discovered in the nervous system and the endocrine organs of different mammalian species. These so-called neuro- or regulatory peptides may function as neurotransmitters, hormones or trophic factors. In many cases neuropeptides are colocalized in the same neurons and endocrine cells with classical transmitters and hormones. To understand the functions of neuropeptides it is important to determine the exact localization of neuropeptides in tissues and to clarify their relations to classical transmitters. In this paper a method for correlative visualization of epinephrine and norepinephrine with formaldehyde-glutaraldehyde (Faglu) fluorescence and subsequent demonstration of neuropeptides at light and electron microscopic level with pre-embedding immunocytochemistry in the same Vibratome section is described. A method for correlative demonstration of acetylcholinesterase (AChE) and neuropeptides at light microscopic level is also presented.

Adrenal glands were fixed with a mixture of 4% paraformaldehyde and 0.2% glutaraldehyde in 0.1M phosphate buffer, pH = 7.3. The adrenals of small rodents such as rat and hamster were fixed by immersion fixation for 6 h. The adrenals of larger species like cats and guinea pigs were fixed by perfusion for 20 min and further fixed by immersion for 1 hr. After fixation the tissues were rinsed several times in phosphate buffer and 7- to 10-um-thick sections were cut with a Vibratome. Sections are embedded in 0.5M Tris-saline buffer, pH = 7.6, which contained 20% glycerol and the catecholamine fluorescence was photographed (Fig. 1). After photography the coverslip was removed and the sections were processed free-floating through the steps of the pre-embedding modification of the PAP-method. After immunocytochemical staining the sections were post-fixed with 2% aqueous osmiumtetroxide for 1 h and dehydrated in graded ethanol series and flat-embedded in Epon under plastic coverslip. The areas photographed for catecholamine fluorescence were identified and photographed (Fig. 2). Desired areas were processed for electron microscopic examination. Human sympathetic ganglia were obtained from surgery and fixed with 4% paraformaldehyde for 6 h. Tissues were cryoprotected with 10% sucrose and 5 um frozen sections were cut on glass slides. Immunocytochemistry was carried out with indirect immunofluorescence method. After immunocytochemistry the sections were reacted for AChE according to the method of Karnovsky and Roots. Rhodamine-fluorescence and AChE were photographed using appropriate filters.
Immunolabelling of glomerular deposits in kidney biopsies routinely fixed in glutaraldehyde
Authors: Lhoták Ś , Alexopoulou I. , Simon G. T.
Published: June 2020

Various kidney diseases are characterized by the presence of dense deposits in the glomeruli. The type(s) of immunoglobulins (Igs) present in the dense deposits are characteristic of the disease. The accurate Identification of the deposits is therefore of utmost diagnostic and prognostic importance. Immunofluorescence (IF) used routinely at the light microscopical level is unable to detect and characterize small deposits found in early stages of glomerulonephritis. Although conventional TEM is able to localize such deposits, it is not capable of determining their nature. It was therefore attempted to immunolabel at EM level IgG, IgA IgM, C3, fibrinogen and kappa and lambda Ig light chains commonly found in glomerular deposits on routinely fixed ( 2% glutaraldehyde (GA) in 0.1M cacodylate buffer) kidney biopsies.

The unosmicated tissue was embedded in LR White resin polymerized by UV light at -10°C. A postembedding immunogold technique was employed
Digestion techniques for exposure of smooth muscle cells in cerebral arterioles
Authors: Ghoneim S. , Baumbach G.
Published: June 2020

Scanning electron microscopy has proven to be a useful tool for the quantitation of three- dimensional characteristics of vascular smooth muscle. A major impediment to obtaining useful preparations of cerebral blood vessels for scanning electron microscopy is that smooth muscle in the tunica media is covered by a thin layer of basement membrane and by arachnoid tissue which contains collagen. The goal of this study was to develop a reliable, reproducible method for removing basement membrane and arachnoid tissue from cerebral arterioles, while at the same time leaving the smooth muscle intact.

We compared several methods of tissue digestion in pial arterioles in adult Sprague-Dawley rats. The cerebral circulation was perfused with glutaraldehyde (2.5%) in cacodylate buffer (0.1 M) via the ascending aorta and then reinfused with packed red blood cells. In one group of rats, whole brains were immersed in osmium tetroxide (2%) for 2 hours (1 hr at 5°C and 1 hr at 40°C), followed by immersion in HC1 (8 N at 60°C) for 20-25 minutes. In another group, whole brains were dipped briefly in HC1 (8 N at 60°C) and then immersed in collagenase type II (2 mg/ml at 37° C; Sigma) for 12 hours. In a third group of rats, individual arterioles were dissected from the brain with a microsurgical knife, dipped briefly in HC1 (5-10 seconds) or KOH (5M at 60°C for 2-3minutes), and immersed in collagenase type II alone (12 hours), or in combination with collagenase type IV (2 mg/ml; 6-12 hours) and/or pepsin (2 mg/ml; 6-12 hours).
EM studies of the structural basis of tactile learning and memory
Authors: Robertson J. David , Lee Psyche
Published: June 2020

It has long been speculated that a rearrangement of neurites might occur in learning neuropils to provide a structural basis of learning and memory. However, this has never been proven definitively, even though there is evidence that new synapses are formed in response to cortical activity in mammals and birds [see(l)] We are studying this problem using Octopus vulgaris. The nervous system of octopus is the most advanced of all invertebrates. It can readily learn and remember a training paradigm whereby it is taught to associate food with touching a smooth plastic ball (positive stimulus) and a 10 VAC electric shock with touching a plastic ball roughened by cutting grooves into its surface (negative stimulus). Touch learning occurs primarily in the inferior frontal system. The brain of the animal can be split sagittaly into two halves and one half brain shown to control the ipsilateral half of the body. Four arms can be taught to respond positively to touching a smooth ball and the other four negatively to touching the same ball. If the posterior buccal (PB) lobe on one side is removed surgically that side of the animal cannot learn the paradigm, while the other half does. We postulate that learning involves formation of new synapses forming as in development or in tissue culture, via growth cones. We have tested this proposition in one way (1-2). It is known that the drug cytochalasin B (CB) interferes with the polymerization of actin monomers in growth cones and that this results in the reversible collapse of their filopodia. If our theory is correct, injecting CB into the PB lobe should block learning without having any effect on memory or overall functioning of the PB lobe neuropil. We have found that this is true. However, since CB has other effects, it is necessary to demonstrate directly that filopodia are involved. We report here on preliminary electron microscopic (EM) studies of the PB lobe neuropil directed to this problem.
Ultrastructure of superficial neuromasts in the mottled sculpin, Cottus bairdi
Authors: Jones W.R. , Coombs S. , Janssen J.
Published: June 2020

The lateral line system of the mottled sculpin, like that of most bony fish, has both canal (CNM) and superficial (SNM) sensory end organs, neuromasts, which are distributed on the head and trunk in discrete, readily identifiable groupings (Fig. 1). CNM and SNM differ grossly in location and in overall size and shape. The former are located in subdermal canals and are larger and asymmetric in shape, The latter are located directly on the surface of the skin and are much smaller and more symmetrical It has been suggested that the two may differ at a more fundamental level in such functionally related parameters as extent of myelination of innervating fibers and the absence of efferent innervation in SNM. The present study addresses the validity of these last two features as distinguishing criteria by examining the structure of those SNM populations indicated in Fig. 1 at both the light and electron microscopic levels.

All of the populations of SNM examined conform in general to previously published descriptions, consisting of a neuroepithelium composed of sensory hair cells, support cells and mantle cells, Several significant differences from these accounts have, however, emerged. Firstly, the structural composition of the innervating fibers is heterogeneous with respect to the extent of myelination. All SNM groups, with the possible exception of the TRrs and CFLs, possess both myelinated and unmyelinated fibers within the neuroepithelium proper (Fig. 2), just as do CNM. The extent of myelina- tion is quite variable, with some fibers sheath terminating just before crossing the neuroepithelial basal lamina, some just after and a few retaining their myelination all the way to the base of the hair cells in the upper third of the neuroepithelium. Secondly, all SNMs possess fibers that may, on the basis of ultrastructural criteria, be identified as efferent. Such fibers contained numerous cytoplasmic vesicles, both clear and with dense cores. In regions where such fibers closely apposed hair cells, subsynaptic cisternae were observed in the hair cell (Fig. 3).
Ultrastructural analysis of “Sensory” surface nerve endings and “putative” neurotransmitter sites in Schistosoma mansoni Miracidia
Authors: Jones Betty Ruth , Pan Steve Chi-Tang
Published: June 2020

INTRODUCTION: Schistosomiasis has been described as “one of the most devastating diseases of mankind, second only to malaria in its deleterious effects on the social and economic development of populations in many warm areas of the world.” The disease is worldwide and is probably spreading faster and becoming more intense than the overall research efforts designed to provide the basis for countering it. Moreover, there are indications that the development of water resources and the demands for increasing cultivation and food in developing countries may prevent adequate control of the disease and thus the number of infections are increasing.

Our knowledge of the basic biology of the parasites causing the disease is far from adequate. Such knowledge is essential if we are to develop a rational approach to the effective control of human schistosomiasis. The miracidium is the first infective stage in the complex life cycle of schistosomes. The future of the entire life cycle depends on the capacity and ability of this organism to locate and enter a suitable snail host for further development, Little is known about the nervous system of the miracidium of Schistosoma mansoni and of other trematodes. Studies indicate that miracidia contain a well developed and complex nervous system that may aid the larvae in locating and entering a susceptible snail host (Wilson, 1970; Brooker, 1972; Chernin, 1974; Pan, 1980; Mehlhorn, 1988; and Jones, 1987-1988).
Morphology of sensilla of adult Pachypsylla celtids-mamma (Homoptera: Psyllidae) and of the gall formed on leaves of Celtis occidentalis (Urticales: Ulmaceae)
Authors: Beisler J. M.
Published: June 2020

In comparison to other insects, very little Homoptera, and available information mainly location and type of sensory sens ilia of the psyllid Pachypsy1la celtidis-mamma and the morphology of the gall it forms on leaves of Celtis occidentalis were characterized by conventional scanning electron microscopy.

Adult insects were fixed in buffered 4% glutaraldehyde (pH 7.2), postfixed in OsO4, dehydrated in ethanol, critical-point dried with CO2, and sputter-coated with goId-paHadium. For light microscopy (LM) insects were silver stained to identify porous chemosensilla. For SEM, whole or broken galls were fixed in 2.5% glutaraldehyde and processed as described above, except after dehydration whole galls were cryofractured in LN2. For LM, frozen sections of fresh galls were stained for lipids with Sudan Black B; PAS stain for carbohydrates was used on resin embedded galIs. SEM specimens were examined at 20 kV with a Hitachi HHS-2R or a JEOL 35CF.
Thin filament structure and activation
Authors: Whittaker M. , Milligan R.
Published: June 2020

Skeletal muscle contraction is triggered by the release of calcium ions from the sarcoplasmic reticulum of the myofibrils. Troponin and tropomyosin in the thin (actin-containing) filaments act together as the transducer of this signal. Evidence from reconstruction of electron images of negatively stained samples and from x-ray diffraction studies of intact myofibrils (e.g. 2) have led to the steric blocking model of regulation by the tropomyosin troponin complex. In this model, tropomyosin is believed to occupy a defined location on the myosin binding site in the absence of calcium. When calcium binds to the regulatory complex, tropomyosin is thought to change its location on actin, moving to occupy a second site adjacent to the myosin binding site. Time resolved x-ray diffraction studies on muscle during activation show that movement of tropomyosin precedes crossbridge attachment by 12-17ms, suggesting that it is a prerequisite for myosin binding. In contrast, biochemical experiments suggest that tropomyosin may not affect the ability of the myosin head to bind to actin but rather may interfere with a subsequent kinetic step in the crossbridge cycle.
Combined high-voltage and scanning electron microscopy on the same brain tissue samples for the study of blood-brain barrier injury
Authors: Lossinsky A.S. , Song M. J. , Pluta R. , Moretz R. C. , Wisniewski H. M.
Published: June 2020

The application of combined techniques utilizing both scanning electron microscopy (SEM) with conventional transmission electron microscopy (CTEM) has a decided advantage because it permits analysis of identical tissue areas. If one is interested in analyzing of endothelial cell (EC) tight junctions, for example, although SEM offers unlimited topographical information, it is of critical importance to concomitantly assess EC junctions by CTEM from adjacent tissue blocks in order to visualize whether or not the junctional complexes are open only at the surface, for example, while deeper regions of this junctional complex may actually be occluded. Generally, three dimensional reconstruction is required employing either serial thin section analysis or high-voltage electron microscopic (HVEM) analysis of thick (0.25-1.0 μm) sections in order to obtain this information.

Micro blood vessels (veins and venules) from the thalamus of SJL mice subjected to chronic relapsing experimental allergic encephalomyelitis were used in the present studies for examining EC junctional complexes and perivascular infiltration of inflammatory cells. Animals were perfused, fixed with standards buffered aldehydes, prepared for SEM, and blood vessels were identified and analyzed with an ISI-40 SEM. The same tissue blocks were trimmed to the targeted micro blood vessels, rinsed three times in propylene oxide (p.o.) for 20 min. each and flat-embedded in Spurr plastic following 1 hr. in 1:1 p.o.:Spurr. Thick (0.5 μm) sections were collected on Formvar-coated slot grids, stained with uranyl and lead salts and examined with an AEl HVEM (Albany, NY) at 1000 KV.
Structure of ribosomes from a thermophilic bacterium
Authors: Dickie Janet , Kyle Karen , Flannigan Derrick , Harauz George
Published: June 2020

The most direct and informative probe of ribosome structure is electron microscopy (EM), of negatively stained and antibody-labelled specimens. Ribosomes from Escherichia coli have been the most intensively studied, although those from other prokaryotes and eukaryotes have also been imaged [e.g., 3, 4, 5],

The amount of structural information obtained from electron images can be significantly increased using multivariate statistical analysis and classification techniques [e.g., 6]. Noisy electron micrographs of single particles are sorted according to their principal features, and average images formed with an enhanced signal-to-noise ratio and better reproducible resolution. The class averages represent projections from which a three-dimensional reconstruction can be computed.

Thermus aguaticus is a species of extremely thermophilic bacteria isolated from environments such as hot springs. This species possesses macromolecular enzyme complexes with a great thermostability which must be reflected somehow instructural differences. In this study, we investigate the structures of ribosomes and ribosomal subunits from this bacterium.
Two dimensional crystals of botulinum toxin, serotype B
Authors: Morgan D.G. , DasGupta B.R. , Stubbs G. , Robinson J.P.
Published: June 2020

Botulinum toxin is a powerful, protein neurotoxin produced by Clostridium botulinum which exerts its toxic action by inhibiting the release of acetyl choline. There are several immunologically distinguishable types of botulinum toxin and most of these have been shown to bind the ganglioside GTlb. The ganglioside binding property of these neurotoxins has allowed us to prepare two dimensional crystals of serotypes A, B, and E. We report here our preliminary observations of two dimensional crystals of serotype B.

Type B botulinum toxin was purified by methods reported by DasGupta and Woody. The two dimensional crystals were prepared by slightly modified procedures used previously to prepare similar crystals of tetanus and cholera toxins. Purified toxin was dialyzed into citric acid-sodium phosphate buffer at pH 4.0 to 6.5 and ionic strength of about 0.04. Dialyzed toxin was placed into the wells of microtiter dishes in 20 μl volumes at a concentration of fifty to one hundred μgm per ml. The toxin solutions were then layered with one to two μl of a solution of one to two mg per ml of egg lecithin (Sigma Cat. No. P- 2772) in chloroform containing five to ten percent by weight of the ganglioside GT1B (Supelco Cat. No. 4-6035). The microtiter dishes were then placed in the cold and crystallization was allowed to proceed for one to four days at 4°C. The crystals were then picked up on carbon coated electron microscope grids, negatively stained with one to two percent uranium acetate and examined in the electron microscope.
Correlation between myocardial glutathione content and extent of ischemia-reperfusion injury
Authors: Lee C. Y. , Singh Amar , Lee Kevin J. , Goldfarb Roy D. , Tsan Min-Fu
Published: June 2020

Considerable evidence suggests that myocardial injury may occur during reperfusion of the ischemic myocardium. Reactive oxygen species are generated during reperfusion which may play an important role in the genesis of myocardial reperfusion injury. Glutathione (GSH) is an important antioxidant in the heart. A decrease in myocardial GSH content has been observed during ischemia and reperfusion of the ischemic myocardiijm. We hypothesized that this depletion of GSH may be detrimental to the ability of the ischemic myocardium to protect itself against reactive oxygen species during reperfusion.

In this study, anesthetized open chest pigs were subjected to coronary occlusion for 45 minutes and 2 hours reperfusion. Myocardial GSH was experimentally depleted by pretreatment with buthionine sulfoximine (BSO), a potent inhibitor of cellular GSH synthesis, and was augmented by intravenous administration of GSH. For ultrastructural study multiple subepicardial biopsies 3 mm deep were taken from myocardium supplied by the occluded artery. The biopsies were processed by routine procedures. Thin sections were stained with uranyl acetate and lead citrate and examined with a Philip EM 300 electron microscope.
Correlative electron microscopic study of metallic particle contaminants in tissue adjacent to dental implants: Part II. 12 months
Authors: Krizan K. E. , Zeiller D. L. , Dogan A. U. , Laffoon J. E. , Madison S.
Published: June 2020

This research is a follow up of the study reported last year Part I-3 months. The purpose of this study Part II-12 months is to evaluate titanium (Ti) and vitallium (Vi, an alloy composed of Co, Cr, Ni, and Fe) endodontic endosseous implants (EEI) and the tissue surrounding them, one year after insertion. In humans this type of implant is sometimes used to stabilize compromised teeth. An adult primate model was employed using comparable techniques during implantation. Various clinical and research methodologies were used to investigate EEI and adjacent tissue in subapical bone of the maxillae (Mx) and mandibles (Md). Under general anesthesia four cynomolgus monkeys received EEI in all central incisors, a total of eight Ti and eight Vi. Placement followed a pulpectomy and hand drilling with dental files to the proper depth and size for the solid EEI rods to use the root canal as a pathway to supporting bone. During the procedure radiographs were made to insure that the EEI exited the root apex and extended 2-5 mm into Mx & Md bone. As controls, 3-5 mm long samples of implant material were placed intraosseously in the region of the Mx between a lateral incisor and canine. One year after the procedures the animals were sacrificed and perfused with a fixative. Jaws were retrieved, decalcified, the EEI were separated from the tissue, and both processed routinely for electron microscopy (EM). The EEI along with the instruments used in the operations were examined with scanning EM (SEM)[Amray 1820D(Fig. .1), JEOL JSM-35C(Fig. 2), Hitachi S-570], and backscattered electron imaging (BSE)[G. W. Electronics]. Tissues were embedded into plastic, one μm sections made and viewed with a light microscope (LM)[Zeiss TP 111(F i g.3)] for morphological evaluation & orientation. Blocks were then trimmed to appropriate areas for thinning. Four one nm sections were cut with a diamond knife [Diatome A310] and viewed with transmission EM (TEM) [Zeiss IOC(Fig.4), Hitachi H-600]. Every fifth section was cut 3-4 nm thick and viewed with scanning transmission EM (STEM)[Hitachi H-6010]. Dense particulates (DP) in STEM sections were analyzed with energy dispersive spectroscopy (EDS) [Kevex 7000]. EEI, instruments & materials were further analyzed with EDS [EDAX 9900(Fig.5)], wavelength dispersive spectroscopy (WDS)[Microspec WDX-3PC], and x-ray fluorescence (XRF)[Tracor 431(Fig.6)] to determine elemental composition and probable origins of DP. In general these data are consistent with the findings in Part I. This study Part II demonstrates that the tissue around the EEI is more vascular, cells of fibrous encapsulation are more mature, there are more multinucleated giant cells present, and DP is more extensive, especially in the Md.
Ultra-high resolution cinematic digital 3-D imaging of the cell surface by field-emission scanning electron microscopy
Authors: Peters Klaus-Ruediger , Fox Martin D.
Published: June 2020

Field emission scanning electron microscopes (FSEM) establish high resolution on rugged bulk surfaces. However, often visualization and recognition of image details are hindered by low contrasts. Retrieval of such obscured image information is possible with three-dimensional (3-D) imaging.

3-D information can be accessed in several ways. At low magnifications direct TV-rate imaging is possible allowing continuous relocation of the specimen and deduction of 3-D information from dynamic changes of perspectives and parallax. Additionally, two images from different stereo perspectives can be simultaniously produced and 3-D information can directly be displayed through optical or electronic devices (stereo imaging). The combination of dynamic perspective changes and stereo-presentation matches the 3-D information input of the human visual system and provides an optimal tool for visual 3-D pattern recognition.

At higher magnifications (>~10,000-20,000x) real time stereo imaging is not possible. 3-D information display becomes limited to stationary perspective displays generated with long frame times.