bluuebunny/crossref_metadata_2025 huggingface dataset:
Cryo-TEM of CTAB micelles and microemulsions
Authors: Vinson Phillip K.
Published: June 2020

Single-tailed surfactant molecules in aqueous solutions can associate into several different microstructural forms within a one-phase region of the phase diagram (Fig. 1). The molecules associate into globular aggregates called spherical micelles above a surfactant concentration called the critical micelle concentration, or cmc. At higher surfactant concentrations some surfactants will associate into rod-like micelles called cylindrical micelles. In systems containing ionic surfactants the transition from spherical to cylindrical micelles can be brought about at lower surfactant concentrations by adding an electrolyte. The electrolyte screens the electrostatic repulsion between surfactant head groups and allows formation of the lower mean curvature cylindrical microstructures. Micellar aggregates are equilibrium microstructures in which the nonpolar (often hydrocarbon or fluorocarbon) moieties of the surfactant molecules are shielded from the aqueous medium by the water-soluble moieties of the surfactant molecules. The solubilization of oil into the nonpolar micelle interior produces an aqueous solution of oil swollen micelles, i.e., a microemulsion.
Reversibility of Action of Clostridium Difficile Toxin a on Cho Cells and Intermediate Filaments in Nuclei
Authors: Kushnaryov V.M. , Sedmak J.J. , Lyerly D.M. , Wilkins T.D.
Published: June 2020

C. difficile, produces 2 potent cytopathic enterotoxins, A and B; their mechanism of action is poorly understood. We studied effects of enterotoxin A (EA) on cultured Chinese Hamster Ovary (CHO) cells employing light microscopy and TEM. Cells grown to 75% confluency were exposed to EA (2.5 μg/ml) at 37°C. Within 1-3 hrs cytoplasm became more retractile and contracted with thin protrusions from the cell (Fig. B). The cells were washed after 2 or 3 hr and incubation continued for 48 hrs. If EA was removed within 2 hrs cells returned to normal in 24-48 hr; if EA was removed after 3 hrs it did not affect rounding of the cells which remained firmly attached and not permeable to erythrosin B implying that they were viable.

TEM employing monoclonal Abs and colloidal gold-protein A conjugate showed that at 4°C EA was randomly distributed on plasma membrane (PM). At 37°C EA was located in pinocytotic invaginations and in coated pits (Figs. E-H) suggesting EA internalization by both the bulk and receptor-mediated endocytosis.
A Novel Reconstitution Method for Inducing the Formation of Regular 2-Dimensional Arrays of Membrane Proteins and Lipids
Authors: Engel A. , Holzenburg A. , Stauffer K. , Rosenbusch J. , Aebi U.
Published: June 2020

Reconstitution of solubilized and purified membrane proteins in the presence of phospholipids into vesicles allows their functions to be studied by simple bulk measurements (e.g. diffusion of differently sized solutes) or by conductance measurements after transformation into planar membranes. On the other hand, reconstitution into regular protein-lipid arrays, usually forming at a specific lipid-to-protein ratio, provides the basis for determining the 3-dimensional structure of membrane proteins employing the tools of electron crystallography.

To refine reconstitution conditions for reproducibly inducing formation of large and highly ordered protein-lipid membranes that are suitable for both electron crystallography and patch clamping experiments aimed at their functional characterization, we built a flow-dialysis device that allows precise control of temperature and flow-rate (Fig. 1). The flow rate is generated by a peristaltic pump and can be adjusted from 1 to 500 ml/h. The dialysis buffer is brought to a preselected temperature during its travel through a meandering path before it enters the dialysis reservoir. A Z-80 based computer controls a Peltier element allowing the temperature profile to be programmed as function of time.
Analysis of Molluscan Hemocyanins by Scanning Transmission Electron Microscopy and Light Scattering
Authors: Furcinitti P. S. , Wall J. S. , Hamilton M. G. , Herskovits T. T.
Published: June 2020

Hemocyanins are copper containing, oxygen binding proteins found in many invertebrate species of the phyla Arthropoda and Mollusca. Molluscan hemocyanins are cylindrical macromolecular assemblies of a basic decameric unit. The hemocyanins of two chitons, Stenonlax conspicua and Mopalia muscosa. are decamers, while those of two gastropods, Fasciolaria tulipa and Pleuroplora gieantea. are di-decamers. The hemocyanins of a third gastropod species, Busvcon contrarium can exist in a spectrum of multi-decameric forms. Molecular weights of the various types of molluscan hemocyanins were measured by absolute light scattering and Scanning Transmission Electron Microscopy (STEM) as a first step in understanding multi-decamer formation in some types of hemocyanins.

Hemocyanins were prepared as previously described, dialyzed into 1M HEPES buffer, pH 7.4, containing 0.05M MgCl and freeze-dried or negatively stained for STEM analysis. Specimens were examined at the Brookhaven STEM Biotechnology Resource, which was operated at 40 kV using a -140°C cold stage. The elastically scattered electron signal from the STEM large angle annular detector was used to form the images.
Diameter Determination of Frozen-Hydrated Virions Using Polyoma Virus as a Calibration Standard
Authors: Olson N. H. , Baker T. S.
Published: June 2020

Accurate determination of particle dimensions requires both a reliable measure of the instrumental magnification and reproducible, non-distorting specimen preparation procedures. Typical calibration standards for measuring microscope magnification include replica gratings, polystyrene spheres, and negatively-stained catalase crystals. Polystyrene spheres and catalase crystals may be used as internal standards but both are highly sensitive to beam damage. Calibrations with replica gratings are subject to greater inaccuracies at magnifications exceeding 10,000-20,000 X. Furthermore, for negatively-stained biological specimens, the object of interest as well as the standard (e.g. catalase) are susceptible to significant distortions produced when the stained sample dries on the grid. The stain itself also moves during the initial stages of irradiation.1.2

Large discrepancies are often found between diameter measurements from particle images with circular profiles (e.g. spherical viruses) made in the microscope and from those measurements determined by x-ray solution scattering or other x-ray diffraction techniques. Measurements from virions embedded in negative-stain, suspended over holes in a carbon substrate, are typically much lower than the corresponding measurements by x-ray techniques, reflecting a probable shrinkage of virions in the stain.
Electron mimcroscopic imaging of theE. ColiRNA polymerase during transcription
Authors: Bear David G. , Andrews Christopher L.
Published: June 2020

RNA polymerase is an enzyme found in all cellular organisms, and functions to direct the synthesis of RNA using double stranded DNA as a template. The best characterized form of the enzyme is from the enteric gram-negative bacterium, E. coli. Like other RNA polymerases, theE. colienzyme contains several tightly associated subunits; these include two large subunits, β' (155 kDA) and β (150 kDa) , two copies of a smaller subunit, α (35 kDA), and up to two copies of another small subunit, ω (11 kDA). Another more loosely associated subunit, the a factor (70 kDa), is bound to the polymerase only at the initiation step of RNA biosynthesis, and is involved in promoter recognition. The goal of this study was to gain an understanding of the structural organization of the transcribing RNA polymerase, using high resolution electron microscopic imaging and digital image processing, as well as chemical cross-linking methods.
High-Resolution Scanning Electron Microscopy of Biological Specimens
Authors: Müller M. , Hermann R.
Published: June 2020

Three major factors must be concomitantly assessed in order to extract relevant structural information from the surface of biological material at high resolution (2-3nm).

Procedures based on chemical fixation and dehydration in graded solvent series seem inappropriate when aiming for TEM-like resolution. Cells inevitably shrink up to 30-70% of their initial volume during gehydration; important surface components e.g. glycoproteins may be lost. These problems may be circumvented by preparation techniques based on cryofixation. Freezedrying and freeze-substitution followed by critical point drying yields improved structural preservation in TEM. An appropriate preservation of dimensional integrity may be achieved by freeze-drying at - 85° C. The sample shrinks and may partially collapse as it is warmed to room temperature for subsequent SEM study. Observations at low temperatures are therefore a necessary prerequisite for high fidelity SEM. Compromises however have been unavoidable up until now. Aldehyde prefixation is frequently needed prior to freeze drying, rendering the sample resistant to treatment with distilled water.
An Efficient Annular Dark-Field Detector Capable of Single-Electron Counting Adapted to a High-Resolution Field-Emission SEM
Authors: Reichelt R. , Aebi U. , Engel A.
Published: June 2020

Various high resolution scanning electron microscopes (HRSEM) are now commercially available providing probe sizes in the range of 0.5 to 1.5 nm at 30 keV due to their field emission gun 1.2. Equipped with efficient detector systems (which collect different signals and applied to specifically prepared samples) HRSEM challenge the conventional transmission electron microscope (TEM) with high resolution surface images of biological specimens collecting secondary (SE) or backscattered (BSE) electrons. However, the yield of (SE) carrying high resolution information is rather small, i.e. the SE-I yield at 20 keV primary electron energy amounts to < 1% for the major elements (H; C; N; O; P) constituting biological matter. The yield of BSE is greater than the corresponding total SE yield (electron energy >15 keV), but BSE emerge due to high angle elastic scattering from a surface area with a diameter of typically 30% of the deepest electron penetration R (e.g. R≈10 μm for elements mentioned above at 30 keV).
Nuclear Envelope Dynamics During Mitosis
Authors: Burke Brian
Published: June 2020

The nuclear envelope is a complex membrane structure that forms the boundary of the nuclear compartment in eukaryotes. It regulates the passage of macromolecules between the two compartments and may be important for organizing interphase chromosome architecture. In interphase animal cells it forms a remarkably stable structure consisting of a double membrane ouerlying a protein meshwork or lamina and penetrated by nuclear pore complexes. The latter form the channels for nucleocytoplasmic exchange of macromolecules, At the onset of mitosis, however, it rapidly disassembles, the membranes fragment to yield small vesicles and the lamina, which is composed of predominantly three polypeptides, lamins R, B and C (MW approx. 74, 68 and 65 kDa respectiuely), breaks down. Lamins B and C are dispersed as monomers throughout the mitotic cytoplasm, while lamin B remains associated with the nuclear membrane vesicles.
The Formation of Cartilage Extracellular Matrix
Authors: Vertel B.M.
Published: June 2020

Normal cartilage function is dependent upon the unique structural properties of the extensive extracellular matrix (ECM). In final assembled form, the ECM of hyaline cartilage is composed of abundant amounts of proteoglycan (PG) and type II collagen. Additional collagens and glycoproteins may be important structural components as well. Through their concentration of negative charges, PGs confer upon the cartilage ECM the ability to retain high levels of hydration and thereby resist compression. Type II collagen fibers contribute to the tensile strength of cartilage.

In the cartilage ECM, PG monomers associate with hyaluronic acid and link protein to form large aggregates. In turn, PG aggregates are associated with the fibrous meshwork of type II collagen. Interactions with other ECM molecules may occur as well. The cartilage matrix constituents are themselves large and complex. For example, the PG monomer is 1-5 x 106 daltons in size and contains a core protein of Mr >300K (comprising only 8-10% of the complete monomer).
Collagen fibril and matrix assembly during morphogenesis
Authors: Birk David E. , Zycband Emanuel , Trelstad Robert L.
Published: June 2020

The morphogenesis of the extracellular matrix requires the synthesis, assembly and deposition of collagen in a tissue specific manner. Collagen synthesis and molecular assembly occur within a series of well defined cytoplasmic compartments, while the assembly and deposition of collagen fibrils, fibril bundles and collagen macroaggregates occurs within a series of extracellular compartments. In the studies described here we focus our attention on the assembly of collagen molecules into fibrils, bundles and tissue specific macroaggregates.

The fibroblast has a complex topography which serves to partition the extracellular space into distinct domains where the hierarchical stages in matrix assembly occur. The first recognizable extracytoplasmic domain is a narrow channel which originates deep within the cytoplasm and is open to the extracellular space. These narrow spaces contain single or sometimes 2-3 collagen fibrils and are intimately associated with secretory vacuoles. These channels fuse with each other and with the cell surface giving rise to the second level of compartmentalization and matrix hierarchy where fibrils coalesce to form bundles.
Computer-Assisted Three-Dimensional Reconstruction of Aortic Endothelium: Elucidation of its Transport Pathways for Macromolecules
Authors: Ogawa K. S. , Watabe T. , Aita S. , Matsuo T. , Ogawa K.
Published: June 2020

The control of vascular permeability is regarded as one of the important endothelial functions. Recently, a number of possible transport pathways in endothelium come to be illustrated with regard to various kinds of capillaries. In continuous-type capillaries, it is postulated that the major routes for macromolecules across the endothelial layer exist in the ones via the intercellular junction and the cytoplasmic vesicles. According to the published physiological data, arterial endothelium has not a few resemblances to the wall of continuous capillaries in its transport properties. We have demonstrated the existence of transendothelial channels composed of fused vesicles in the aortic endothelium. However, in the arterial endothelium, there have been not enough morphological and cytochemical studies to grasp its transport properties for macromolecules in detail. The major purpose of the present study lies in the elucidation of the three-dimensional (3-D) organization of the aortic endothelial cell transport pathways using the ultrathin serial sections which are labeled with Horseradish peroxidase (HRP) as tracer molecules.
Characterization of Phospholipid Vesicles with Freeze Fracture, Negative Staining, and Nuclear Magnetic Resonance Spectroscopy
Authors: Anderson W.H. , Kumar V.V. , Baumann W.J. , Thompson E.W.
Published: June 2020

Phospholipid vesicles are used as models of biological membranes in which the constituent lipids can be defined and interactions among them can be studied without interference from other membrane components. Phospholipid vesicles are also attracting interest as drug carriers. Entrapment of drugs in liposomes reduces toxicity and improves targeting to specific tissue sites. Small unilamellar vesicles are easily prepared by sonication and are usually stable and uniform in size. However, because of their small size and high curvature, these vesicles poorly mimic natural membranes and their entrapment capacity is quite limited. It is therefore often desirable to prepare larger unilamellar liposomes by other techniques, such as extrusion through polycarbonate filters.

We have investigated the utility of routine electron microscopic procedures for the examination and analysis of vesicles of different sizes. Samples of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was dissolved, dried, and dispersed as described previously. Vesicles were prepared either by sonication or by extrusion at nitrogen pressures of 200-800 psi through polycarbonate filters with pore sizes ranging from 30 to 200 nm.
Preliminary Report of a Comparative Study of Seminiferous Tubular Epithelium from Rats Flown on Cosmos 1887 and SL3
Authors: Sapp Walter J. , Philpott D.E. , Williams C.S. , Kato K. , Stevenson J. , Serova L.V.
Published: June 2020

Space flight, with its unique environmental constraints such as immobilization, decreased and increased pressures, and radiation, is known to affect testicular morphology and spermatogenesis. Selye, summarized the manifestations of physiological response to nonspecific stress and he pointed out that atrophy of the gonads always occurred. Reports of data collected from two dogs flown in space for 22 days (Cosmos 110) indicate that there was an increase of 30 to 70% atypical spermatozoa when compared to ground based controls. Seventy-five days after the flight the abnormalities had decreased to the high normal value of 30% and mating of these dogs after this period produced normal offspring, suggesting complete recovery. Effects of immobilization and increased gravity were investigated by spinning rats and mice at 2x g for 8-9 weeks. A decrease in testicular weight was noted in spun animals when compared to controls. Immobilization has been show to cause arrest of spermatogenesis in Macaca meminstrins.
A scanning electron microscopic study of the veliger larvae of the scallop argopecten purpuratus
Authors: Bellolio G.C. , Lohrmann K.S. , Dupré E.M.
Published: June 2020

Argopecten purpuratus is a scallop distributed in the Pacific coast of Chile and Peru. Although this species is mass cultured in both countries there is no morphological description available of the development of this bivalve except for few characterizations of some larval stages described for culture purposes. In this work veliger larvae (app. 140 pm length) were examined by the scanning electron microscope (SEM) in order to study some aspects of the organogenesis of this species.

Veliger larvae were obtained from hatchery cultures, relaxed with a solution of MgCl2 and killed by slow addition of 21 glutaraldehyde (GA) in seawater (SW). They were fixed in 2% GA in calcium free artificial SW (pH 8.3), rinsed 3 times in calcium free SW, and dehydrated in a graded ethanol series. The larvae were critical point dried and mounted on double scotch tape (DST). To permit internal view, some valves were removed by slightly pressing and lifting the tip of a cactus spine wrapped with DST, The samples were coated with 20 nm gold and examined with a JEOL JSM T-300 operated at 15 KV.
Immuno-electron microscopy of surface antigens of Bordetella pertussis
Authors: Bisher M. E. , Brennan M. J. , Li Z. M. , Steven A. C.
Published: June 2020

Bordetella pertussis is the Gram-negative bacterium responsible for whooping-cough. To develop a better understanding of the interactions between B. pertussis and the cells of colonized tissues, as well as for purposes of vaccine design, much effort has been devoted to characterizing the antigenic molecules exposed at its outer surface. A set of six U.S. Reference Factor Antisera raised by Eldering recognize agglutinogens that are specific to B. pertussis. Since each strain exhibits a particular subset of these antigens, the antisera provide a convenient means of classifying different strains of this bacterium. Several of these antigens have been identified at the molecular level. Serotype 1 agglutinogen is associated with a lipo-oligosaccharide, and those of serotypes 2 and 6 are fimbriae of two morphologically similar but antigenically distinct kinds. Recently, it has been demonstrated serotype 3 antiserum recognizes a 69kDa protein. To characterize the distribution of this antigen in and around B. pertussis cells, we have performed immuno-gold electron microscopy, using monoclonal antibodies raised against the 69kDa protein.
Direct stereoscopic visualization of icosahedral capsid geometry in bacteriophage T4 freeze-fractured, deep-etched replicas
Authors: Ruben George C. , Marx Kenneth A. , Benbasat Julyet
Published: June 2020

Bacteriophage T4 is one of the most complex of the tailed bacteriophage. Its DNA is packaged inside a protein capsid whose structure has long been the subject of study. All T-even bacteriophage appear to have a capsid structure based upon an icosahedral geometry. This has been established indirectly by a combination of symmetry considerations and physical and biochemical experiments, including some electron microscopy. Perhaps the most persuasive demonstration of the icosahedral capsid geometry in bacteriophage T2 is not based on a direct visualisation of the T2 capsid. Instead, the argument relies critically on the authors' ability to accurately count protein capsomers on the T2 capsid replica of a freeze-fractured, etched sample. Moreover, the icosahedral geometry of T4 capsids is simply inferred from results on T2. In the present study, we visualize directly the prolate icosahedral capsid geometry of T4 bacteriophage from stereopairs of micrographs of replicas produced by the freeze-fracture, deep-etch technique utilizing vertical replication to identify the triangular faces comprising the icosahedral T4 capsid.
Alterations of type II cell microvilli following ozone-induced alveolar injury
Authors: Haller E. M. , Paterson J. F. , Lundh J. M. , Balis J. U.
Published: June 2020

Ozone is a major oxidizing constituent in photochemical smog, and it is known to cause, at high concentrations, bronchiolo-al veoar injury with early loss of cilia and desquamation of alveolar type I cells, followed by proliferation of type II cells. In the present study, we investigated the sequential sur face alterations of alveolar type II cells using an established model for ozone-induced alveolar injury and repair.

Fisher 344 male rats weighing 260±10g were exposed to 3 ppm ozone for 8 h. The animals were killed at various time intervals, inclduing zero time, 24, 48, and 96 h after termination of ozone exposure. The lungs were inflated at 20cm pressure with 2.5% glutaraldehyde in 0.1M Sorensen's phosphate buffer, ph 7.2, at 37 C for 4 h. Lung slices, 10 x 4 mm x 500 μm, were obtained by random selection from the left lobe, osmicated in 1% phosphate buffered OsO4, for 1 h at 4 C, dehydrated in a graded series of acetone, infiltrated with Freon 113, and critical-point dried using carbon dioxide.
Optimal sampling of liver parenchyma for electron microscopy
Authors: Buschmann R. J. , Ryoo J. W.
Published: June 2020

We have been studying cirrhosis by morphometric analysis of human and rat liver. Our studies, like most electron microscopic studies, use a tissue sampling scheme that is hierarchical or nested with the number of primary sample units, i.e. the number of human subjects or experimental rats, subsampled by a number of tissue blocks per animal and by a number of micrographs per block. For each study, time and effort is a factorial function of the number of samples at each level. More importantly, the final standard error of the mean is also a function of the number of samples at each level. Thus, optimal sampling is of substantial import.

A statistical method, the nested analysis of variance, has been promoted for estimating the optimal number of samples at each level. We have produced a computer program designed to facilitate the use of the nested analysis of variance in determining an efficient sampling strategy.
Identification of knife cutmarks in bone: An sem and light microscope study
Authors: Houck Max M.
Published: June 2020

The goal of toolmark analysis is to individualize marks made by a specific tool involved in the commission of a crime. This involves the recognition and matching of class and individual characteristics of the striations imparted by a suspected tool with the markings found at the crime scene. Identifying tool- marks as having been made by a particular tool requires a significant correspondence between the suspected tool and the toolmark from the crime scene. Individual characteristics are random in generation and generally result from manufacturing devices, grinding and finishing processes, and normal wear and usage. These processes produce surface phenomena called striations that are characteristic of only that tool; that is, each tool's particular developmental and usage history places it in a category of one.

The most common method of identifying toolmarks is by comparing test marks made with the suspected item with the markings from the crime scene.
Morphometric evaluation of astrocyte perivascular process swelling in cerebral cortical tissue of fasted rats following incomplete ischemia
Authors: Dimlich R.V.W. , Kern L.M.
Published: June 2020

The swelling of astrocytes is a frequently observed response to numerous pathogenic stimuli including ischemia. Previously we noted that astrocyte processes adjacent to necrotic neurons primarily in layers 3 and 5 of the cerebral cortex of ischemic rats appeared enlarged (1). In that tissue, perivascular processes of astrocytes also evidenced swelling without compromising the vascular lumen (2). The goal of the present study was to quantify this apparent difference in the area occupied by perivascular processes of astrocytes between ischemic rats and sham ischemic controls.

Ischemia was achieved by bilateral carotid ligation and bleeding to a mean arterial blood pressure of 50 Torr. Fasted adult male Wistar rats were anesthetized and assigned to either a sham ischemic control (n = 4) or an ischemic experimental (n = 4) group. After 30 min of ischemia and 30 min for recirculation, rats were perfused through the heart with 2% glutaraldehyde and 2.8% paraformaldehyde in a 90 mM K oxalate, 1.4% sucrose buffer (pH 7.4) at 40 C.
Ultrastructural response of cultured heart cells to calcium depletion and repletion
Authors: LeFurgey A. , Wagenknecht B. , Schreiner P.J. , Hawkey L.A. , Lieberman M.
Published: June 2020

Calcium-free incubation followed by exposure to Ca produces ultrastructural damage in the intact myocardium—a phenomenon known as the Ca paradox. Controversy exists as to whether the observed Ca overload during Ca repletion is a primary cause for, or a secondary consequence of, sarcolemmal disruption and cell injury. In these experiments cultured embryonic chick heart cells have been subjected to Ca depletion/repletion to explore the structural, transport and metabolic mechanisms by which cells may be irreversibly damaged.

Monolayer muscle enriched cell cultures were prepared by serial trypsin-disaggregation of 11-day old chick embryo hearts. Cells were incubated for 10 or 120 min in Ca-free (1 mM EGTA) Hepes-buffered salt solution (pH 7.4) followed by incubation for 60 or 180 min in the same solution containing 1 mM Ca. In another series of experiments, the mitochondrial uncoupling agent carbonyl cyanide chlorophenylhydrazone (CCCP, 10 μM ) was added during depletion and repletion.
Use of SEM, X-ray analysis and TEM to localize Fe3+ reduction in roots
Authors: Wergin William P. , Bell P. F. , Chaney Rufus L.
Published: June 2020

In dicotyledons, Fe3+ must be reduced to Fe2+ before uptake and transport of this essential macronutrient can occur. Ambler et al demonstrated that reduction along the root could be observed by the formation of a stain, Prussian blue (PB), Fe4 [Fe(CN)6]3 n H2O (where n = 14-16). This stain, which is an insoluble precipitate, forms at the reduction site when the nutrient solution contains Fe3+ and ferricyanide. In 1972, Chaney et al proposed a model which suggested that the Fe3+ reduction site occurred outside the cell membrane; however, no physical evidence to support the model was presented at that time. A more recent study using the PB stain indicates that rapid reduction of Fe3+ occurs in a region of the root containing young root hairs. Furthermore the most pronounced activity occurs in plants that are deficient in Fe. To more precisely localize the site of Fe3+ reduction, scanning electron microscopy (SEM), x-ray analysis, and transmission electron microscopy (TEM) were utilized to examine the distribution of the PB precipitate that was induced to form in roots.
The role of 2-Row laminae in sickle hemoglobin crystallization
Authors: Gabriel Barbra L. , Josephs Robert
Published: June 2020

Deoxygenated solutions of sickle hemoglobin (HbS) exhibit a sequential development of structural intermediates that crystallize. Different crystallization intermediates form under different solution conditions. One such intermediate is the macrofiber, a structure which closely resembles a twisted section of the crystal. Macrofibers are composed of rows of antiparallel double strands that are twisted about the particle axis with a pitch of 10,000 Å.

Under appropriate conditions a layer consisting of two rows can “peel” from a macrofiber. As shown in Figure 1, this results in a six-row macrofiber forming a four row particle and a layer containing two rows. These peeling segments retain the helical twist of their parent particle, even when completely separated from the parent particle (Figure 1b and c). The narrow region of the 2-row layer provides an edge-on view of the particle. It is 190 Å ± 20 Å in diameter, and corresponds to the known width of 185 Å for a layer of antiparallel double strands.
Simultaneous demonstration of matrix lipid and proteoglycan in rat growth plate through selective preservation: A new technique
Authors: Shepard Nora , Mitchell Nelson
Published: June 2020

The presence of lipid in cartilage has been determined through biochemical analysis and associated with mineralization (1,2,3), as is proteoglycan (4,5). However, unlike proteoglycan, an ultrastructural technique does not exist for cartilage lipid stabilization.

Nile blue sulphate, a dye used in fluorescence microscopy to study lipids, when added to the initial glutaraldehyde fixation and followed by potassium ferrocyanide reduced osmium and en bloc, uranyl acetate, retained lipids in the cartilage matrix. In addition to the lipid stabilization, matrix proteoglycan was also rendered insoluable, two matrix components that have not been observed simultaneously before.

Slices of growth plate cartilage from Sprague Dawley rats were fixed in 2% glutaraldehyde/0.1M Na phosphate (pH 7.4) containing 0.1% nile blue (min.2 hrs.), rinsed (15 min.) with 0.1M Na phosphate buffer containing 0.2M sucrose and 0.1% nile blue,post fixed with 1% aqueous OSO4 containing 1.5% potassium ferrocyanide, briefly washed in 0.1M Na acetate buffer (pH 6.3) then stained with 0.25% uranyl acetate in 0.1M Na acetate for one hour.
Effects of a freeze substitution method and chemical fixation techniques on the ultrastructure of campylobacter pylori
Authors: Crooker A. R. , Myers M. C. , Beard T. L. , Freedman R.
Published: June 2020

Campylobacter pylori is a newly recognized microaerophilic, gram-negative spiral bacterium. The role of this organism in the pathogenesis of human gastritis and ulceration is currently being widely investigated. Published reports of the ultrastructure of C. pylori exhibit poor preservation of subcellular detail indicating that certain conventional fixation procedures may not be appropriate for optimal results. Consequently, we utilized freeze substitution and conventional methods to examine the influence of fixation technique on the preservation of ultrastructural detail.

C. pylori strain NCTC 11638 was grown for 24 h in liquid media. Conventional fixation was performed with (1) the Ryter-Kellenberger procedure, (2) to 3% glutaraldehyde with secondary fixation in 2% OsO4 (3) combinations of formaldehyde (F) and glutaraldehyde (G) ranging from 10% F/0.5% G to 2% F/1% G with secondary fixation in 2% OsO4 and (4) fixation at 0°C. For all fixatives, pH was 7.2-7.4; osmolarity varied between 300 and 2000 mOsM depending on the fixative.
Low-voltage field-emission scanning electron microscopy applications in nematology
Authors: Wergin William P. , Sayre Richard M. , Reilly Terrence W.
Published: June 2020

Conventional scanning electron microscopy (CSEM) has long been used to gain structural information on the taxonomy, morphology, host-parasite relationships and predators of plant parasitic nematodes. Although a significant amount of new information has accumulated during the past few years, further gains in structural detail will be hampered because CSEMs have resolutions of 40-70A, 5-20kV accelerating voltages are normally required to excite adequate secondary electrons, and current preparation techniques require specimen coatings of 200-300A.

Recently a new SEM, the Hitachi S900, combined a condensor-objective lens system with a field emission electron source. This instrument, known as a field emission (FE) SEM, has a resolution of about 5A or 10 times greater than that of CSEMs, can be used to observe specimens with little or no coating and operates at accelerating voltages as low as 1 or 2 kV while producing electron densities nearly 1000 times brighter than those of CSEMs.
A scanning tunneling microscope for use in the philips EM400 electron microscope in the reflection mode
Authors: Spence J.C.H. , Kuwabara M. , Lo W.
Published: June 2020

A scanning tunneling microscope (STM) has been built in the form of a side-entry specimen holder for the Philips EM400T (9mm pole piece gap). The instrument is intended to provide STM and Reflection Electron Microscope (REM) images of the same region, possibly simultaneously (STM operation with tunneling gaps of up to l.5nm is possible while REM resolution is about 0.9nm). The purpose is to study the basic physics of the STM. The great sensitivity of REM diffraction-contrast imaging to strain will be used to determine if strains, or other surface modifications, accompany tunneling on graphite and gold. Figure 1 shows a typical REM image of the GaP[110] surface obtained on the EM400.

Figure 2 shows a schematic diagram of the STM while figure 3 shows the completed device, now undergoing trials. A single tube scanner is used5, as in certain stereo record- player cartridges.
Glass — amorphous?
Authors: Tazaki Kazue , Fyfe W. S.
Published: June 2020

Glass, amorphous, and noncrystalline materials are important constituents of rocks, soils, marine sediments, and nuclear waste. It has long been recognized that many clay minerals crystallize from noncrystalline precursors, the paracrystalline allophane, and saprolite passing through adsorption and deposition in solution.

Three glass materials were examined with a JEOL-JEM 100C at 100 KV and JEOL-JEM 400 EX, TEM-STEM analytical electron microscope at 400 KV. The <2 μm sized fractions were concentrated by the sedimentation technique and pipetted on grids for TEM. Specimens were collected from Michipicoten Island, Canada, and Ilha Bela, Brazil, and compared with a waste form glass.

High-resolution transmission electron microscopy clearly shows the rearrangement of the glass framework of 3Å domain structure and growth of the transitional products, primitive clay precursors and 14Å clays.

The crystallization may be induced by the domain structure on the substrate surface already existing prior to deposition.
Precipitation processes in materials synthesis by high-dose ion implantation of semiconductors
Authors: Krause S. J. , Jung C. O. , Ravi T.S. , Wilson S.R.
Published: June 2020

High dose ion implantation for materials synthesis in semiconductors is receiving increasing attention with the commercialization of medium and high current ion implanters. Surface and buried dielectric layers in silicon are being fabricated by high-dose implantation of oxygen, nitrogen, and carbon. Metallic silicides are being synthesized by implantation of metals such as cobalt and nickel. The evolution of a new phase or phases from a supersaturated solid solution during implantation occurs in a zone with increasing concentration which is also in a concentration gradient. Because of this, and the dynamic phenomena occurring, the whole process is quite complex. Additionally, a final, high temperature anneal to remove damage and to consolidate and stabilize the new phase(s) further complicates any analysis. There is no standard approach to analyze structural changes during high dose implantation and subsequent annealing, but it should be possible to approximate the phenomena based on traditional models for precipitation processes in solids. These processes include precipitate nucleation, growth, coarsening, coalescence, and dissolution. The most heavily studied process of materials synthesis by implantation is formation of a buried oxide layer in silicon (often referred to as SIMOX material).
Plasmon lineshape analysis in EELS of semiconductors
Authors: Kundmann Michael K. , Ronald Gronsky
Published: June 2020

Many materials display plasmon peaks in their low-loss EELS spectra. The plasmon peak shape, energy, and linewidth are characteristic of each material and are sensitive to the outer-shell electron density and details of the electronic band and energy-level structures. As these properties are a function not only of the composition but also the structure and chemistry of a sample, plasmon spectroscopy can potentially become a materials characterization tool which goes beyond the elemental analyses provided by EDXS and ionization-edge EELS. However, analysis of plasmon spectra requires considerably more sophistication than either of the aforementioned techniques due to the possibility of overlapping spectrum features, the prevalence of plural scattering, and the difficulty in detecting and characterizing the often subtle differences between the plasmon spectra of similar materials. As yet, no systematic approach to plasmon analysis analogous to that available commercially for EDXS or EELS core-edge analysis has been developed. We present here an approach which, for the simple case of semiconductors, makes some progress in this direction.
Absolute inner-shell cross section determination for EELS analysis
Authors: Crozier P.A.
Published: June 2020

Absolute inelastic scattering cross sections or mean free paths are often used in EELS analysis for determining elemental concentrations and specimen thickness. In most instances, theoretical values must be used because there have been few attempts to determine experimental scattering cross sections from solids under the conditions of interest to electron microscopist. In addition to providing data for spectral quantitation, absolute cross section measurements yields useful information on many of the approximations which are frequently involved in EELS analysis procedures. In this paper, experimental cross sections are presented for some inner-shell edges of Al, Cu, Ag and Au.

Uniform thin films of the previously mentioned materials were prepared by vacuum evaporation onto microscope cover slips. The cover slips were weighed before and after evaporation to determine the mass thickness of the films. The estimated error in this method of determining mass thickness was ±7 x 107g/cm2. The films were floated off in water and mounted on Cu grids.
In situ oxidation of Ni3Al Alloys
Authors: Lawless K. R. , Cathcart J. V. , Kenik E. A.
Published: June 2020

Ni3Al is subject to dynamic embrittlement when tested in an oxidizing environment; whereas pre-oxidation under stress does not embrittle the alloy. In situ HVEM oxidation studies of several ordered intermetallic (LI2 structure) Ni3Al alloys with small additions of boron and hafnium are reported. AEM studies of the oxidized specimens were also made to fully characterize the microstructure. Specimens were annealed and then electropolished to penetration just prior to insertion in the hot stage of the HVEM. Oxidations were carried out at an oxygen pressure of 13-60 mPa at 750°C. Gas pressure and composition were monitored with a residual gas analyzer. Specimens raised to the operating temperature in the base vacuum (∼0.2 mPa) showed no indication of oxide in the diffraction pattern and were almost entirely free of dislocations.

Many of the features of different stages of the oxidation process are shown in Fig. 1. After two minutes exposure to oxygen, a thin, fine-grained, oriented, polycrystalline region of primarily γ-Al2O3 developed at the thinnest regions of the foil (Region A in Fig. 1 and Fig. 2).
TEM study of boron additions to cobalt aluminide
Authors: Feldewerth Gerald B.
Published: June 2020

In recent years an increasing emphasis has been placed on the study of high temperature intermetallic compounds for possible aerospace applications. One group of interest is the B2 aiuminides. This group of intermetaliics has a very high melting temperature, good high temperature, and excellent specific strength. These qualities make it a candidate for applications such as turbine engines. The B2 aiuminides exist over a wide range of compositions and also have a large solubility for third element substitutional additions, which may allow alloying additions to overcome their major drawback, their brittle nature.

One B2 aluminide currently being studied is cobalt aluminide. Optical microscopy of CoAl alloys produced at the University of Missouri-Rolla showed a dramatic decrease in the grain size which affects the yield strength and flow stress of long range ordered alloys, and a change in the grain shape with the addition of 0.5 % boron.
Defect structures induced by inert-gases in rapidly solidified type 304 stainless steel
Authors: Chan Bae Jung
Published: June 2020

Defects-are formed in most plastically deformed, quenched, and radiation damaged materials, and their type and distribution depend on the experimental conditions. Extensive research on radiation damage has shown that inert gases accumulate in materials and cause significant alterations of the microstructure and mechanical properties. In the centrifugal atomization process, the exposure of Type 304 stainless steel droplets to inert gas environments presents opportunities for their entrapment. The observation of large number density defects such as vacancy type dislocation loops and stacking faults in as-solidified Type 304 stainless steel powder is attributed to the inert gas/vacancy interaction.

The purpose of this work is to examine the defect microstructure of extruded powder metallurgy (P/M) Type 304 stainless steel after preconditioning heat treatments at 900, 1000,1100, and 1200C for 1 hour followed by water quenching. Also, ingot metallurgy (l/M) Type 304 stainless steel (remnants of the feed stock for the powders) was heat treated at 1000 and 1100C for 1 hour followed by water quenching for comparison.
Microstructural characterization of laser-melted/roller-quenched dicalcium silicate
Authors: Chan C. J. , Venkatachari K. R. , Kriven W. M. , Young J. F.
Published: June 2020

Dicalcium silicate (Ca2SiO4) is a major component of Portland cement. It has also been investigated as a potential transformation toughener alternative to zirconia. It has five polymorphs: α, α'H, α'L, β and γ. Of interest is the β-to-γ transformation on cooling at about 490°C. This transformation, accompanied by a 12% volume increase and a 4.6° unit cell shape change, is analogous to the tetragonal-to-monoclinic transformation in zirconia. Due to the processing methods used, previous studies into the particle size effect were limited by a wide range of particle size distribution. In an attempt to obtain a more uniform size, a fast quench rate involving a laser-melting/roller-quenching technique was investigated.

The laser-melting/roller-quenching experiment used precompacted bars of stoichiometric γ-Ca2SiO4 powder, which were synthesized from AR grade CaCO3 and SiO2xH2O. The raw materials were mixed by conventional ceramic processing techniques, and sintered at 1450°C. The dusted γ-Ca2SiO4 powder was uniaxially pressed into 0.4 cm x 0.4 cm x 4 cm bars under 34 MPa and cold isostatically pressed under 172 MPa. The γ-Ca2SiO4 bars were melted by a 10 KW-CO2 laser.
Structural multiplicity in a tilt boundary in germanium
Authors: Smith D.A. , Elgat Z. , Krakow W. , Levi A.A. , Carter C.B.
Published: June 2020

There has been considerable progress made recently in understanding the atomic structure of grain boundaries in metals, semiconductors and ceramics. There is still, however, some dispute over whether a given grain boundary can exist with more than one non-symmetry-related structure. This has been shown experimentally to be the case in Ge for the first-order twin boundary lying parallel to the lateral {112} plane. In the present paper, it will be shown that a similar result holds for a more general grain boundary (actually Σ=137) lying close to the Σ=19 orientation; the Σ=19 boundary is formed by a rotation of 26.5° about a common <110> direction and lies along a common {31} plane. It is thus likely that a similar result will hold for other grain boundaries.

Since it is essential to know that the different structures are not due to impurity segregation effects, bicrystals were grown from the melt with pre-oriented seeds using the Czochralski method following the approach of Bacmann as modified at Cornell by Skrotzki et al.
Grain boundary dislocation networks in YBa2Cu3O7-δ
Authors: Babcock S.E.
Published: June 2020

The crystallography, morphology, and structure of typical grain boundaries in sintered samples of the high temperature superconducting oxide YBa2Cu3O7-δ(123) have been investigated by transmission electron microscopy using two-beam diffraction contrast imaging and selected area diffraction techniques.

Since most of the grains present in sintered samples of 123 are plate shaped with the plate normal parallel to the c-axis of the crystal, the grain boundaries can be divided into two classes: (a) those for which the boundary plane normal is nearly parallel to the c-axis of one of the abutting grains (basal-plane-faced boundaries), and (b) those which are not basal-planefaced. Regular networks of grain boundary dislocations have been observed in high-angle grain boundaries of both types. These networks extend the length of the imagable portion (i.e., sufficiently thin) of the boundary without changing their basic geometry. The line contrast produced by the networks shows several of the key characteristics of dislocation images.
Application of parallel recorded EELS to analysis of beam-sensitive organic compounds
Authors: Leapman R.D.
Published: June 2020

Electron energy loss spectroscopy (EELS) is the optimum technique for studying specific mass loss of light elements from organic compounds under irradiation in the electron microscope. The recent availability of parallel detection systems has provided a factor of approximately 1000 improvement in detection efficiency compared with serial detection. This implies a corresponding reduction in recording time or a reduction in the electron dose needed to obtain sufficient counting statistics for elemental detection. In addition, parallel detection allows us to perform “real-time” EELS, i.e. to observe the actual decay of characteristic peaks in the spectrum.

EELS spectra have been recorded with a Gatan model 607 spectrometer fitted with a Gatan model 666 parallel detector based on a 1024 channel photodiode array. Data were transfered to a Tracor Northern TN5500 analysis system for display and processing. Samples were examined at 100 keV beam energy in a Hitachi H700H electron microscope operated in the TEM mode at 1000X to 10000X magnification and with a 30 mrad collection semi-angle defined by the objective aperture.