bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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&#x0027;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 &#x03BC;M ) was added during depletion and repletion.
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.
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.