bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Point Defect Clusters by 2-1/2-D TEM
Authors: Mitchell B. , Bell W. L.
Published: June 2020

Many of the TEM studies of radiation damage in crystalline materials have been directed toward illucidating the nature, number density, and size distributions of the primary structural defects resulting from the displacement of atoms from their normal lattice sites, i.e., "black spots." The "black spots" have been identified as either nonresolvable dislocation loops or planar clusters of self interstitials or vacancies by TEM techniques and diffraction contrast theories that are described in the book by Hirsch, et al. and the reviews by Ruhle and Eyre. An indispensable part of the studies of point defect clusters is the identification of their character (vacancy or interstitial).
Structure of Deformed Iron: Irradiation Softening and Orientation Dependence
Authors: Nagakawa Johsei , Sato A. , Meshii M.
Published: June 2020

Solid solution softening and the orientation dependence of yield stress can be regarded as the two most important phenomena characterizing the low temperature plastic deformation of b.c.c. metals. Recently, the orientation dependence of solid solution softening was reported in electron irradiated pure iron in which self-interstitial atoms simulate the solid solution effect. Single crystals oriented for the hard (112) slip showed the largest softening effect and became the softest crystals after irradiation (Fig. 1). Also, the shape of the stress-strain curve for the irradiation-softened crystal suggests that the irradiation may have influenced the dislocation structure at an early stage of deformation. Specimens oriented for the soft (211) slip showed hardly any effect. In this study, the dislocation structure was investigated to determine the mechanism responsible for the softening effect and the orientation dependence.
Effect of Thermomechanical Treatment on the Grain Boundary Structure in Pure Aluminum
Authors: Venkatesh Eswarahalli , Murr L.E.
Published: June 2020

In recent years, many researchers have shown great interest in understanding the structure of grain boundaries and their influence on the mechanical properties in metals and alloys. In recent years, the structure of grain boundaries and their control have been considered as a means of understanding the strengthening mechanisms in metals and alloys. There are many ways by which the grain boundary structure can be changed both in pure metals and alloys. One such means considered here is the thermomechanical treatment of pure metals.

In the present work, high purity (99.9999%) aluminum sheet, mill rolled to 0.004 in. thick, is used. The as-received condition of the sample was flash-annealed at 903°K in an argon atmosphere. Batch specimens from this stock were cold rolled to 50% reduction in thickness and annealed in air at 903°K followed by either furnace cooling or air cooling to room temperature.
On the Contrast of High Resolution Backscattered Electron Images
Authors: Lin P. S. D.
Published: June 2020

When the angle θ between the incident electron and the normal to a surface changes, the yield of secondary electrons Y varies approximately as secθ. The topographic contrast thus produced renders secondary electrons useful for surface studies. On the other hand, as the atomic number Z increases, the backscattering coefficient η increases more rapidly than Y. Therefore, backscattered electrons should be collected as signal when atomic number contrast is desired. Figs. 1 and 2 exemplify the increase of atomic number contrast as one switches from secondary to backscattered electron mode.

Backscattering is not a localized process, since both single and plural/ multiple scattering are involved. In Everhart's model, incident electrons are retarded by the inelastic scattering and scattered backwards by large angle Rutherford scattering.
Ribosomal Associations with Glycogen Bodies in Rabbit Extraocular Muscle
Authors: Davidowitz Jacob , Philips Gloria H. , Pachter Bruce R. , Breinin Goodwin M.
Published: June 2020

Membrane-glycogen arrays composed of double membranes in alternation with glycogen layers (Figs. 1,4) have been described in many kinds of tissue and were recently observed in extraocular muscle of apparently normal adult rabbits. These systematically organized glycogen bodies are often seen to be continuous with the intermyofibrillar sarcoplasmic reticulum, as well as with randomly disposed membrane-glycogen complexes which form extensive structures that are independent of the myofibrils. Often seen in close association with these complexes are groupings of 10-20 mu particles which are typically discriminable from the 30-40 mu β-glycogen particles. These small particles may appear at the periphery of arrays, either unbounded or enclosed within rounded cisternae; they may also occur between the cisternal lamellae well within the arrays, either as short layers or in small clusters (Figs. 1,4). Histochemical EM procedures were employed to test whether the 10-20 mu particles are polysaccharide entities such as have been proposed to be the structural subunits of particulate glycogen, and which may also occur as independent populations of small particles under certain conditions.
Detection of Reovirus-Like Particles in HeLa Cells
Authors: Holder Walter D. , Peer Gary W.
Published: June 2020

The HeLa cervical carcinoma cell line was established in 1951 by George Gey at the Johns Hopkins Hospital in Baltimore, Maryland. HeLa cells have been subsequently used throughout the world in numerous laboratories. One of the subsequent cultures, designated the Hela D line has been found to contain virus morphologically and antigenically related to the Mason-Pfizer monkey virus (MPMV). The HeLa D line, containing virus, was originally derived from Dr. W.A.K. Schmidt in Dusseldorf, Germany.

In the present study we examined HeLa D cells by transmission electron microscopy to morphologically evaluate the virus produced by this line. Cells were grown in RPMI-1640 medium with 10% v/v heat-inactivated fetal calf serum in a 5% C02/95% air incubator at 37° C. Cultures were fed twice weekly and submitted for electrormicroscopy when approximately 70% confluent 24 hours after feeding. Cells were scraped from the flasks, pelleted, fixed in 2.5% Millonig's buffered glutaraldehyde, post fixed in 1% osmium tetroxide and embedded in Epon.
Ultrastructural Variations in the Congenital Hair Defect Monilethrix
Authors: West H.
Published: June 2020

The hair of Monilethrix is characterized by a noded appearance with the internode being very susceptible to breakage resulting in hair loss at the scalp. Freshly epilated hairs from a moderately affected male Caucasian having light brown hair were used.

Histological examination of the bulb indicates the presence of vacuoles in the cortical prekeratinized area of the zone of cellular differentiation. Fig. 1 shows a morphological defect in the cells of the precortical region of the germinal matrix. The nuclei of several of these cells have become elongated and in some cases, string-like, with the nuclei becoming pyknotic. It is possible that the lack of a functioning nucleus early in cell growth results in large open areas or vacuoles. Gross structural analysis indicates that the internode region of the shaft has less cortical area than does the node.
Fine Structural Classification of Chromophobe Adenomas of the Human Pituitary Gland
Authors: Kovacs K. , Horvath E.
Published: June 2020

Chromophobe pituitary adenomas arise from adenohypophysial cells and fail to exhibit cytoplasmic staining with conventional acid or basic dyes by light microscopy. The aim of the present work was to study the electron microscopic features of these tumors, to separate them into distinct entities and to correlate their fine structural appearances with secretory activity.

Among 48 surgically removed various pituitary adenomas 30 tumors were found which, based on the tinctorial characteristics of the cytoplasm, corresponded to chromophobe adenomas. For electron microscopic investigation pieces of these tumors were fixed in 2.5 per cent glutaraldehyde in Sorensen's buffer, post fixed in 1 per cent osmium tetroxide in Millonig's buffer, dehydrated in graded ethanol and embedded in Epon 812. Ultrathin sections were stained with uranyl acetate and lead citrate.

By electron microscopy it was possible to separate chromophobe adenomas into 3 distinct entities: 1) adenomas consisting of sparsely granulated growth hormone cells (7 cases).
Pericytic Alterations in Cerebral Infarction
Authors: Dodson Ronald F. , Tagashira Yukio , Chu Lena W. F. , Scates Ronald W.
Published: June 2020

The pericyte is a nonendothelial cell type which is in close association with the capillary bed and is surrounded by basement membrane. Earlier concepts based on light microscopy lead to the hypothesis that this cell type formed a type of investment around the vessel. Ultra structural investigations have shown this concept to be invalid but the function of this cell type is yet to be determined.

Earlier work from our laboratory compared the ultra structural characteristics of pericytes from various areas in normal animal brain; our present aim is to define pericytic response in acute cerebral infarction.

The adult baboons utilized in this experiment were subjected to a transorbital occlusion of the right middle cerebral artery for respective periods of 2, 3, 4, 5 and 24 hrs. At the end of the period of occlusion the clip was removed and the animals were perfused (intra-cardiac) with a 500 ml solution of 3% glutaraldehyde in 0.1 M phosphate buffer.
Aspects of Myocardial Regeneration in Notoopthalmus Viridescens
Authors: Philpott D. , Corbett R. , Person P. , Becker R.
Published: June 2020

While obtaining blood samples from the common newt, Notoopthalmus viridescens, it was observed that at least one-third of the heart could be excised and the animal would still survive. Up to fifty per cent of the blood is lost resulting in circulatory stasis which lasts about an hour. Following this circulatory pulsations and capillary flow are slowly reestablished.

Heart samples were obtained five minutes, one hour, two hours, three hours, and twenty-four hours after heart resection. Fixation was in gluteraldehyde followed by osmium tetroxide and embedded in vestopal. Samples were also taken at seven, fifteen, and thirty minutes and counterstained with ruthenium red to obtain information on possible polysaccharide alterations.

Erythrocytes are trapped in the clot formation and those adjacent to the myocardial tissue appear to become attached and undergo extensive modification (Fig. 1-3). Pseudopods are sent out from the erythrocytes and extend into and onto, the surface of the myocardium increasing muscular-RBC contact (Fig. 2-3).
Initial Light Effects on Chloroplast Ultrastructure in Soybeans
Authors: Crang Richard E. , Colin Budd G. , Ashbaugh Patrick H. , Noble Reginald D.
Published: June 2020

Light induced changes in chloroplast volume and thylakoid membranes have been documented in a few plants by light and electron microscopy, as well as with the use of a Coulter counter. We wish to demonstrate that significant structural changes occur in soybean chloroplasts mediated both by genetically dictated levels of photosynthetic pigments, and by light intensity and duration as examined by TEM and an electronic image analyzer.

A comparison was made of a field variety (Harasoy) with strain T219 soybeans which genetically segregate into three phenotypes: dark green (DG), light green (LG), and a lethal yellow (LY). All plants in mineral nutrient media were maintained under 12 hr. photoperiods for six weeks prior to sampling. LY plants were grafted to DG at 3-5 days postgermination. Interveinal leaf discs were stamped from sixth node trifoliate leaves prior to illumination and fixed for TEM as were samples at varying time intervals up to 1 hr.
Invasion of Soybean Root Cells in Culture by Rhizobium japonicum.
Authors: Dan Raveed  , Minocher Reporter  , Grace Norris
Published: June 2020

The initiation of association between cultured soybean root cells and Rhizobia shows specificity under proper conditions of culture. The establishment of these culture conditions for symbiotic association have been described previously. The compatible plant cells produced a filamentous extracellular material which was capable of trapping Rhizobia. Non-compatible cells did not produce extracellular material and were not invaded. In this presentation we have followed the effect of Rhizobial invasion on the wall morphology of the soybean root cells in suspension cultures. Changes in the morphology of the soybean cell walls were then examined as follows.

Harosoy root cells were grown in liquid culture in Gamborg's B-5 medium for two weeks. Rhizobium japonicum strain 138 was added to the culture for another 3 days. For this purpose, fixation was carried out by adding glutaraldehyde to the medium to a final concentration of 2%. The cell clumps were fixed 1 hr.
Virus-Like Particles in Spirometra Sp. from a Case of Human Sparganosis
Authors: Sun C.N. , Daly J.J. , White H.J. , Barron A.L.
Published: June 2020

Mueller and Strano have reported finding virus-like particles lining the walls of excretory ducts in plerocercoid (sparganum) larvae of the pseudophyllidean tapeworms, Sparganum proliferum, from a human host, and Spirometra mansonoides and Spirometra mansoni, from animal hosts. Although human sparganosis caused by these species is distributed world-wide, only 50 cases have been officially reported in the United States. A sparganum in a nodule from the outer aspect of the right thigh of a 30 year-old male in Arkansas has recently been described which is believed to be either S. mansonoides or S. mansoni. Since the previously studied material of these two species were from non-human hosts, this worm afforded the opportunity to examine a non-proliferating sparganum from a human host for the presence of virus particles.

The worm, which was 90 mm long and 1 mm wide, was fixed in neutral buffered formalin and post-fixed with buffered 2% osmium tetroxide.
Dynamic Compaction of Rapidly Solidified Al-6%Si Powder
Authors: Allen Robert M. , Smugeresky John E.
Published: June 2020

The production of alloy powders by processes involving rapid solidification can yield powder particles which exhibit highly-refined microstructures desireable from a mechanical properties standpoint. Unfortunately, traditional methods for compacting powders into parts often cause significant coarsening of the starting powder microstructure. Alternative methods such as dynamic compaction (the shock-loading of the powder under high stresses) are under study as means of preserving the fine-scale of the starting microstructure throughout the manufacturing of a fully-dense bulk part.

The purpose of the present work was to examine the microstructures developed by the dynamic compaction of rapidly-solidified Al-6%Si alloy powders. The powder was prepared from cast alloy using an ultrasonic gas atomizer. Particles < 250 μm in diameter were sieved to produce uniform size splits for the compaction study. Dynamic compaction was carried out with a gas gun device which imposed a shock stress of ∼4 GPa on a powder sample, producing a fully-dense compact 30 mm in diameter and 5 to 6 mm thick. Microstructural characterization was carried out using a JEOL 35CF SEM and a 200CX STEM, both equipped with energy-dispersive x-ray spectrometry systems.
Applications of CCEM to Environmental Health Problems
Authors: Lee R. J. , Walker J. S.
Published: June 2020

Electron microscopy (EM), with the advent of computer control and image analysis techniques, is rapidly evolving from an interpretative science into a quantitative technique. Electron microscopy is potentially of value in two general aspects of environmental health: exposure and diagnosis.

In diagnosis, electron microscopy is essentially an extension of optical microscopy. The goal is to characterize cellular changes induced by external agents. The external agent could be any foreign material, chemicals, or even stress. The use of electron microscopy as a diagnostic tool is well- developed, but computer-controlled electron microscopy (CCEM) has had only limited impact, mainly because it is fairly new and many institutions lack the resources to acquire the capability. In addition, major contributions to diagnosis will come from CCEM only when image analysis (IA) and processing algorithms are developed which allow the morphological and textural changes recognized by experienced medical practioners to be quantified. The application of IA techniques to compare cellular structure is still in a primitive state.
Microstructure Development in a High Current Density NbTi Superconducting Composite
Authors: Lee P. J. , Larbalestier D. C.
Published: June 2020

Several features of the metallurgy of superconducting composites of Nb-Ti in a Cu matrix are of interest. The cold drawing strains are generally of order 8-10, producing a very fine grain structure of diameter 30-50 nm. Heat treatments of as little as 3 hours at 300 C (∼ 0.27 TM) produce a thin (1-3 nm) Ti-rich grain boundary film, the precipitate later growing out at triple points to 50-100 nm dia. Further plastic deformation of these larger a-Ti precipitates by strains of 3-4 produces an elongated ribbon morphology (of order 3 x 50 nm in transverse section) and it is the thickness and separation of these precipitates which are believed to control the superconducting properties. The present paper describes initial attempts to put our understanding of the metallurgy of these heavily cold-worked composites on a quantitative basis. The composite studied was fabricated in our own laboratory, using six intermediate heat treatments. This process enabled very high critical current density (Jc) values to be obtained. Samples were cut from the composite at many processing stages and a report of the structure of a number of these samples is made here.
High-Temperature Oxidation of 310 Stainless Steel
Authors: Roy Tapan
Published: June 2020

Austenitic stainless steels find application in heat exchangers, furnace parts, exhaust systems and other such high temperature applications because of their good corrosion resistance at elevated temperatures. This is believed to be because of a passive film of α-Cr2O3 that forms on the surface. Silicon is usually added to afford better scaling resistance. The steel under investigation (AISI # 31000) has minor alloying additions of manganese, silicon and titanium in addition to chromium(25 wt%) and nickel(20 wt%).

Annealed and polished 3 mm discs as well as bulk specimens were oxidized at temperatures between 700°C and 900°C in dry oxygen at low pressure. Kinetic studies were performed using a CAHN 1000 microbalance. The 3 mm discs were back-thinned for TEM studies while the bulk specimens were used for SEM observations.
Analysis of Silicon-On-Insulator Structures Formed By Oxygen Ion Implantation
Authors: Lewis N. , Hall E. L. , Mogro-Campero A. , Love R. P.
Published: June 2020

The formation of buried oxide structures in single crystal silicon by high-dose oxygen ion implantation has received considerable attention recently for applications in advanced electronic device fabrication. This process is performed in a vacuum, and under the proper implantation conditions results in a silicon-on-insulator (SOI) structure with a top single crystal silicon layer on an amorphous silicon dioxide layer. The top Si layer has the same orientation as the silicon substrate. The quality of the outermost portion of the Si top layer is important in device fabrication since it either can be used directly to build devices, or epitaxial Si may be grown on this layer. Therefore, careful characterization of the results of the ion implantation process is essential.
Real-Space Reconstructions of Non-Ideal Helical Models
Authors: Bluemke David A. , Carragher Bridget , Potel Michael J.
Published: June 2020

We have studied the effects of variable pitch, particle flattening, particle curvature, imaging noise and variable negative stain on two dimensional (2D) real-space reconstructions using electron density models of the sickle cell hemoglobin (HbS) macrofiber. The HbS macrofiber, a 500 A diameter helical particle with a pitch of about 10,000 A, is formed in vitro at pH < 7.1. The Fourier transform of the particle is extremely complex due to disorder, large particle size, and variable pitch, making the indexing required for Fourier-Bessel reconstructions very difficult. However, real-space techniques require fewer assumptions about the particle order. Preliminary particle reconstructions have led us to consider the effect of non-ideal particle imaging on the reconstruction result.
Routine Determination of X-Ray Detector Efficiencies Using Submicron Spheres of Pure Materials
Authors: Kelly Thomas F.
Published: June 2020

The purpose of this paper is to outline an approach to routine determination of x-ray detector efficiencies over the entire applicable energy range that may be used on any transmission electron microscope.

BACKGROUND

The quantification of x-ray intensities using the ratio technique can be accomplished [see, for example, 1] using a relation of the form:

Here, for element A, CA is the composition in the sample as a weight fraction, kA is the x-ray generation constant (see below) which contains only sample-dependent information, eA is the detector efficiency for characteristic x-rays which contains only detector-dependent information, and lA is the measured x-ray intensity in a characteristic line.
The Application of Protein A-Gold Immunocytochemistry to Studies of Protein Secretion
Authors: Herbener George H. , Nanci Antonio , Bendayan Moise
Published: June 2020

Protein A-gold immunocytochemistry is a two-step, post-embedding labeling procedure which may be applied to tissue sections to localize intra- and extracellular proteins. The key requisite for immunocytochemistry is the availability of the appropriate antibody to react in an immune response with the antigenic sites on the protein of interest. During the second step, protein A-gold complex is reacted with the antibody. This is a non- specific reaction in that protein A will combine with most IgG antibodies. The ‘label’ visualized in the electron microscope is colloidal gold. Since labeling is restricted to the surface of the tissue section and since colloidal gold is particulate, labeling density, i.e., the number of gold particles per unit area of tissue section, may be quantitated with ease and accuracy.
The Fine Structure of Phloem Cells
Authors: Cronshaw James
Published: June 2020

Long distance transport in plants takes place in phloem tissue which has characteristic cells, the sieve elements. At maturity these cells have sieve areas in their end walls with specialized perforations. They are associated with companion cells, parenchyma cells, and in some species, with transfer cells. The protoplast of the functioning sieve element contains a high concentration of sugar, and consequently a high hydrostatic pressure, which makes it extremely difficult to fix mature sieve elements for electron microscopical observation without the formation of surge artifacts. Despite many structural studies which have attempted to prevent surge artifacts, several features of mature sieve elements, such as the distribution of P-protein and the nature of the contents of the sieve area pores, remain controversial.
Scanning Electron Microscope Evaluation of Hair Dye Effects on the Cuticle Cells of Canine Hair
Authors: Al-Bagdadi F. , Ruhr L. , Archibald L. , Titkemeyer C.
Published: June 2020

Skin and hair are exposed to environmental factors such as pollutants sun & water(Garcia et al 1978). Hair care products are designed to reduce the damage of environmental influences and for cosmetic reasons. Hair dye products are brought into contact with the hair shaft and the scalp, and on occasions, may penetrate as deeply as the hair roots (Stuttgen 1981). Some of the constituents of hair dyes have been related to skin allergies, nervousness and toxicity (Stuttgen 1981).

Only in recent years, in part due to the rising demands for scientific documentation of advertising claims has interest been focused on the development of reliable measurements for the safety of hair dye products.

The hair cuticle cells are critical to the preservation of the physical integrity of the hair fibers of the cortex (Wolfram 1972). The scant and controversial information on the effects of hair dye products on the hair shaft and on the epidermis led to this investigation. This study, was conducted by the use of scanning electron microscopy, of mixed-breed dogs subjected to intensive usage of hair dye products reports the changes of the cuticle of the hair shaft and the epidermis.
Probing the spatial organization of nucleic acids within cells by nonisotopic in situ hybridization
Authors: Lawrence Jeanne Bentley
Published: June 2020

In situ hybridization is a powerful experimental approach that directly couples molecular and cytological information in a visual context. Advances in hybridization procedures over recent years, coupled with previously described non-isotopic labelling methods developed in a number of laboratories, now provide a way to detect nucleic acids within cells with a high degree of resolution and sensitivity. Adaptations of this technology allow either DNA or RNA to be detected and visualized either with the light microscope, using fluorescence or colorimetric methods, or with the electron microscope using antibodies conjugated to gold or peroxidase. The potential applications of this technology are relevant to numerous areas of biomedical research and range from the more straightforward study of differential gene expression in single cells within a population to the precise localization of individual genes or RNAs within the cytoplasm or nucleus of a cell.
TEM characterization of a new chromium hydride phase
Authors: Pan Y. , Takeo M. , Dash J.
Published: June 2020

Single crystal, body centered cubic (bcc) Cr thin films were prepared by epitaxial growth on newly cleaved optical grade rock salt substrates (Figure 1). With a vacuum of 6-8 x 10-7 torr and the substrate at about 500 °C, the deposition of the thin film was almost instantaneously completed by rapidly evaporating Cr powder (99.996%) in a tungsten basket. These films were exposed to hydrogen gas (99.999%) at high temperature (close to the melting point of Cr) and 550 atm pressure in a ballistic compressor (BC) for about 1 millisecond. The cooling rate of the compressed gas is higher than 105°C/s. This process was repeated several times to enhance the interaction of Cr with H2.
Identification of T1 phase in Al-Li-Cu alloy (2090)
Authors: Kim J.S. , Baek S. S. , Kim G. H. , Chun C. H.
Published: June 2020

In Al-Li-Cu alloy(2090) the extra spots in the Selected Area Diffraction Pattern (SADP) of [112]α zone axis have been argued. Huang and Ardell described that the extra spots were originated from T1 variants tilted to electron beam. Rioja and Ludwiczak, however, presented that die precursor of T1 termed T1' was present in alloy(2090) and generated the extra spots. Rioja and Ludwiczak explained die existence of extra spots as making the simulated SADP diagrams and analyzing x ray diffraction lines of T1'. The existence of T1' has been inconsistent with the other papers. Huang and Ardell's model has been well recognized in present. The investigations on the extra spots had mainly been restricted in [112]α SADP. In the present paper, the extra spots from [110]αand [100]α zone axes were investigated using High Resolution Electron Microscope (HREM) and optical laser diffractometer.
The role TEM in a government laboratory serving industrial clients
Authors: Malis Tom
Published: June 2020

The challenge of meeting demands for enhanced performance while maintaining a competitive price has become the norm for industries producing engineering materials. A government laboratory intending to assist such industries in a formal manner must adapt its policies, structure and capabilities as the needs of its clients change. TEM would come under close scrutiny in this process because of the relatively high financial and intellectual investment required to produce good results. The following project examples illustrate secondary, but quite important aspects of the prime goal of solving the client's problem(s). They include judicious facility/methodolgy upgrading (including in-house development and external networking), fruitful interactions with project scientists (including accurate prediction of resource usage) internal and external marketing, and dealing creatively with personnel shortages, all while producing what is hopefully the ‘good science’ needed for institutional and individual recognition!

Fig 1 shows typical precipitates in a pipeline steel for which the distribution and composition vis-a-vis various microalloying elements were crucial to the mechanical behavior of the product (via austenite grain size control). Before acquisition of a suitable in-house TEM, university work was funded which demonstrated the complex nature of coprecipitation in these steels, a fact not then appreciated by the steel industry. Subsequent in-house work built upon these findings to the point where characterization of such precipitates has become a most useful component of formalized collaborations with steel companies in that both resource usage and delivery of useful information have become quite predictable.
TEM characterization of the α' and β phases in polycrystalline distrontium silicate (Sr2SiO4)
Authors: Kim Y. J. , Shull J. L. , Kriven W. M.
Published: June 2020

Two polymorphs, α' and β, are known to be major phases in pure distrontium silicate (Sr2SiO4) at atmospheric pressure. Fully dense pellets were fabricated by sintering chemically prepared powders in the temperature range of 900° to 1400°C for 1 to 5 hours. Their phases and microstructures were studied by TEM. At lower sintering temperatures such as 900°C, the major phase was orthorhombic α' (space group, Pmnb). The euhedral α' grains had a size of about 1 μm diameter (Fig. la). As the sintering temperature increased, the amount of monoclinic β phase (space group, P21/n) tended to increase. These β grains were usually irregular and twinned on {100}β or {001}β planes. Concentration of the electron beam on the grains gave rise to a disappearance of twins (Fig. lb).
Morphological studies of linear (AB)n multiblock copolymers and their blends
Authors: Spontak Richard J. , Smith Steven D. , Ashraf Arman
Published: June 2020

Block copolymers are composed of sequences of dissimilar chemical moieties covalently bonded together. If the block lengths of each component are sufficiently long and the blocks are thermodynamically incompatible, these materials are capable of undergoing microphase separation, a weak first-order phase transition which results in the formation of an ordered microstructural network. Most efforts designed to elucidate the phase and configurational behavior in these copolymers have focused on the simple AB and ABA designs. Few studies have thus far targeted the perfectly-alternating multiblock (AB)n architecture. In this work, two series of neat (AB)n copolymers have been synthesized from styrene and isoprene monomers at a composition of 50 wt% polystyrene (PS). In Set I, the total molecular weight is held constant while the number of AB block pairs (n) is increased from one to four (which results in shorter blocks). Set II consists of materials in which the block lengths are held constant and n is varied again from one to four (which results in longer chains). Transmission electron microscopy (TEM) has been employed here to investigate the morphologies and phase behavior of these materials and their blends.
Prospecting for gold in a VG STEM
Authors: Shoemaker G. L , Sherman W. M. , Duff R. H. , Rothbard D. R.
Published: June 2020

A calcined pyritic gold ore concentrate was examined using both ion–milled and ultramicrotomed samples to determine the distribution of gold and the porosity of the matrix supporting the gold. Examinations of the same specimen prepared by different techniques yielded complementary information about the overall characteristics of the material.

Figure 1 is a secondary electron image (SEI) of a piece of roasted pyritic ore. The particles are highly porous with morphology suggesting that the iron pyrite (FeS2) particles virtually exploded when labile sulfur was released during oxidative calcination. The particles produced by this process are not large enough to permit ordinary solid specimen preparation techniques. Therefore, a compacted bar of material was made by compressing the powder with a binder to form a disk which was subsequently impregnated with epoxy in a PARR bomb under isostatic pressure of a few thousand psi. From this dense material two types of specimen were prepared, one by diamond knife ultramicrotomy and the other by standard thin foil techniques. For the latter, the sample was sliced with a diamond saw, core–drilled into 3mm disks, polished to about 100μm, dimple ground, and Argon ion milled to perforation. This yielded specimens which show the porosity and connectivity of the iron oxide frameworks formed during calcination. Figure 2 is a 10,000X annular dark field (ADF) image of an ion–milled particle taken with a VG HB501 STEM. The channel structures evident in this image are easily related to the SEI image in Figure 1. Figure 3 is a 200,000X ADF image which illustrates the connectivity of individual iron oxide crystallites that form the skeletal structure. This sample was electron transparent only near the central perforation and did not have a large usable area. Also, the outer surfaces ot the particles may have been milled away during specimen preparation and therefore it is not easy to determine where the remaining structures were located in the original particles.
High-resolution three-dimensional Coulomb potential map of PhoE porin
Authors: Jap Bing K. , Earnest Thomas N. , Walian Peter , Gehring Kalle
Published: June 2020

PhoE porin is an outer membrane, pore-forming channel with selectivity for the transport of phosphate-containing compounds and negatively charged solutes. We have reconstituted this membrane protein with lipids to form highly coherent, 2-dimensional crystalline patches. Diffraction patterns and images of trehalose embedded crystalline patches were recorded using a JEOL 100B electron microscope, which is equipped with a field emission gun and a cold stage that was operated at about −120° C. A complete 3-dimensional (3-D) diffraction data set to a resolution of 2.8Å and a number of high resolution images at tilt angles ranging from 0 to 60 degrees were collected. A high resolution projection map at 3.5Å resolution and a 3-D map at 6Å , showing the detailed structural architecture of this protein, have been published.
Three-dimensional organization of chromatin fibers in situ examined by EM tomography
Authors: Woodcock C.L. , Horowitz R.A. , Agard D.A.
Published: June 2020

Electron tomography is being used to understand the 3D organization of chromatin in situ. As demonstrated previously, the nuclei of Patiria miniata (starfish) sperm contain particularly well-defined chromatin fibers. These studies are being extended through the analysis of 3D reconstructions of material embedded at low temperature in Lowicryl K11M and contrasted with osmium ammine-B, which preferentially stains nucleic acids. Tilt series of sections were recorded at 150KV, over an angular range of +/−75° and tilt increment of 2.5° using a Philips EM430. Image data were collected directly using a 1024x1024 CCD array with 2x2 binning to give a final pixel size of 1.3nm. Gold beads deposited on the sections were used for alignment, and reconstruction was by weighted back projection. Six volumes totalling 0.48um and containing numerous chromatin fibers have been examined utilizing Voxel View (Vital Images, Fairfield Iowa) software running on a Silicon Graphics Iris 4D workstation.
Chromosome structure and dynamics as revealed by 3-D and 4-D imaging
Authors: Agard David A. , Swedlow Jason R. , Hiraoka Yasushi , Paddy Michael R. , Sedat John W.
Published: June 2020

Cellular DNA is packaged into chromosomes through complex processes whereby the DNA becomes compacted up to 10,000-fold by assembly into higher-order structures. In spite of many decades of intense study, the details of this process are not known. In addition, there is little information describing the dynamics of these higher-order structures during DNA replication, transcription, and mitosis. The goal of our laboratory is to use state-of-the-art 3-D imaging methods to understand how DNA is arranged into chromosomes and how chromosomes are spatially and temporally organized in the nucleus.
Role of freeze-fracture technique in tumour pathology
Authors: Mukherjee T. M. , Swift J. G.
Published: June 2020

The freeze-fracture technique is unique in its ability to expose extensive face views of the interior of the cell membranes. This feature is particularly useful for studies of events occurring at the plasma membrane, such as exocytosis of secretory granules and of structural components within the membrane such as the intercellular junctions. We have used freeze-fracture preparations in conjunction with conventional thin sections to study the intercellular junctions in a variety of human tumours.
Errors and distortion induced under some operating conditions in a confocal laser scanning microscope (CLSM)
Authors: Leung Harry , Jeun Gwendolyn
Published: June 2020

Fluorescent beads have been recommended and used frequently as calibration standards for fluorescent microscopy. However, during our work with a CLSM we observed that images of these beads varied in diameter with dianges in illumination level, detector aperture diameter, and signal amplification (gain). In addition, XZ images showed distortion in proportion to such changes.

Images from 9 μm fluorescent beads (Excitation Max. @ 458 nm) were collected with a BIORAD MRC600 CLSM attached to a Nikon Diaphot-TMD inverted microscope. A Nikon Planapo 60x (NA=1.4) oil immersion objective was used in all experiments. The beads were embedded in 5 % gelatin to prevent drifting. Using an illuminating wavelength of 488 nm, the beads were optically sectioned at their equators under varying conditions of laser illumination, detector aperture diameter and gain. To eliminate image variations due to size differences among the beads, all images in Fig 1 were collected from the same bead. Those in Fig 2 were from another similar sized bead.
Microscopic examinations of toxic marine microalgae
Authors: O’Neil David , Leggiadro Cynthia , Kim Gwang Hoon , Fritz Lawrence
Published: June 2020

A number of microalgae have been implicated in toxicity episodes in cultured shellfish in Eastern Canada. Nitzschia pungens f. multiseries and Prorocentrum lima are two organisms that have been shown to produce the toxins associated with poisonous shellfish. The present study examines these organisms by light microscopy (DIC and fluorescence), and SEM.

The pennate marine diatom, N. pungens(fig. 2), has been shown to produce a potent neurotoxin, domoic acid, in pure culture. The distinctive features of this pennate diatom are illustrated in Fig. 1. The silica covering (frustule) consists of parallel rows of costa with multiple rows of minute pores (poroids). P. lima (fig. 5) is a dinoflagellate that has been found to produce a toxin known as okadaic acid. This toxin has been associated with ciguatera, a fish poison, and was implicated in a recent toxic shellfish event in Eastern Canada. The cellulosic thecal plates are adorned with regular, distinctive pattern of pores (fig. 4).
An investigation into the ultrastructure and histochemistry of glandular trichomes of johnsongrass [Sorghum halepense (L.) Pers.] leaves
Authors: Paul R. N. , McWhorter C. G. , Ouzts J.C.
Published: June 2020

Secretory trichomes have been described on johnsongrass leaves previously, but there is little knowledge of their ultrastructure or the nature of their secretion. Since johnsongrass is a pernicious weed, there is much interest in the nature of compounds found on its foliar surface, and the possible effect of these extrusions on herbicide efficiency. This report describes the results of an investigation into the ultrastructure of the secretory apparatus, and into the nature of the secretion.
Ultrastructure and Senescence in an Achloroplastic Mutant of Hordeum vulgare L. cv. Dyan
Authors: Cross R.H.M. , Botha C.E.J. , Cowan A.K. , Hartley B.J.
Published: June 2020

Senescence is an ordered degenerative process leading to death of individual cells, organs and organisms. The detection of a conditional lethal mutant (achloroplastic) of Hordeum vulgare has enabled us to investigate ultrastructural changes occurring in leaf tissue during foliar senescence.

Examination of the tonoplast structure in six and 14 day-old mutant tissue revealed a progressive degeneration and disappearance of the membrane, apparently starting by day six in the vicinity of the mitochondria associated with the degenerating proplastid (Fig. 1.) where neither of the plastid membrane leaflets is evident (arrows, Fig. 1.). At this stage there was evidence that the mitochondrial membranes were undergoing retrogressive changes, coupled with disorganization of cristae (Fig. 2.). Proplastids (P) lack definitive prolamellar bodies. The cytoplasmic matrix is largely agranular, with few endoplasmic reticulum (ER) cisternae or polyribosomal aggregates. Interestingly, large numbers of actively-budding dictysomes, associated with pinocytotic vesicles, were observed in close proximity to the plasmalemma of mesophyll cells (Fig. 3.). By day 14 however, mesophyll cells showed almost complete breakdown of subcellular organelle structure (Fig. 4.), and further evidence for the breakdown of the tonoplast. The final stage of senescence is characterized by the solubilization of the cell wall due to expression and activity of polygalacturonase and/or cellulose. The presence of dictyosomes with associated pinocytotic vesicles formed from the mature face, in close proximity to both the plasmalemma and the cell wall, would appear to support the model proposed by Christopherson for the secretion of cellulase. This pathway of synthesis is typical for secretory glycoproteins.
UV absorption microspectrophotometry of plant cell walls in relation to biodegradation
Authors: Akin D.E. , Rigsby L.L. , Borneman W.S. , Hartley R.D.
Published: June 2020

A major limitation to the biodegradation of plant cell walls is the presence of phenolic compounds, which covalently link to carbohydrates and render these potentially digestible components unavailable for microbial utilization. A more detailed understanding of phenolic compounds and their association within specific cell types is required for development of strategies to enhance biodegradation of plant fiber for efficient utilization of foods and feeds. UV absorption microspectrophotometry was employed to characterize the phenolics within cell walls of a series of plants with different biodegradabilities. Scanning electron microscopy was used to assess the degradation of specific cell types incubated with fiber-digesting microorganisms from the rumen ecosystem.
Three-dimensional reconstruction of large subcellular structures: A method for combining axial tilt tomography with serial reconstruction of thick sections
Authors: Soto Gabriel E. , Martone Maryann E. , Lamont Stephan , Carragher Bridget O. , Deerinck Thomas J. , Young Stephen J. , Ellisman Mark H.
Published: June 2020

The study of subcellular structures requires the resolution afforded by the electron microscope. However, cellular organelle systems can extend for tens of microns and therefore cannot be encompassed in a single thin section required for conventional electron microscopic observation. Even with the use of high voltage electron microscopy, section thickness is limited to no more than a few microns. Visualization of 3-dimensional cellular structure in large volumes of tissue can be achieved by using 3-dimensional reconstructions based on serial sections. This approach is often tedious, requiring an extremely large series of thin sections in order to encompass the structure of interest. This method also suffers from technical difficulties in obtaining, processing and maintaining adequate registration over large numbers of sections. We have been exploring a method in which the number of sections is reduced by employing a series of thick sections in which the structures of interest are selectively stained. Three-dimensional information is extracted from each section using axial tilt tomography. The resulting serial volumes are then aligned and linked to form a single volume which is displayed using volume rendering techniques.
Practical experience with computer-controlled high-resolution electron microscopy
Authors: Smith David J. , Higgs A. , Perkes P.
Published: June 2020

The recent proliferation of the so-called intermediate-voltage HREMs has led to a vast expansion in the ranges of materials which are nowadays being examined on the atomic scale. Impressive-looking micrographs containing detail as fine as 1A are comparatively easy to obtain. However, relating this image information in a quantitative manner to particular features of the object can be tedious and time-consuming even when the imaging conditions (eg. objective lens focus, illumination angle, focal spread) and the specimen parameters (eg. thickness, orientation, composition) are well-known. The presence of residual astigmatism and/or incident beam misalignment leads to spurious image features which can seriously compromise this process of interpretation, but it is difficult, even for skilled operators, to adjust these variables with sufficient precision that their effects are negligible.
Applications of the Van Cappellen technique for thin-foil microanalysis to the measurement of x-ray calibration factors
Authors: Carpenter G.J.C. , Woo O.T.
Published: June 2020

The Cliff-Lorimer technique for thin foil microanalysis using X-rays is widely used in materials science applications of analytical electron microscopy. However, the corrections for absorption and (less commonly) fluorescence that may be necessary to obtain quantitative data are inconvenient to perform and can be prone to errors. Recently, a methodology has been developed by Van Cappellan that overcomes these difficulties. Termed “parameterless”, because no external measurements are necessary apart from the X-ray intensities, the technique requires spectra to be collected from areas of different thickness of the phase of interest. The characteristic X-ray intensities are used to obtain uncorrected concentration ratios for the elements of interest, using the Cliff-Lorimer equation. The absolute X-ray intensities give an indirect measure of mass thickness. However, calculations of absolute mass thickness are avoided, simply by plotting the concentration ratios against intensity and extrapolating to zero intensity, which corresponds to zero mass thickness.
A transmission electron microscopic study of structural transitions in fast ionic conductors
Authors: Queenan R. B. , Davies P. K.
Published: June 2020

Na ß“-alumina (Na1.67Mg67Al10.33O17) is a non-stoichiometric sodium aluminate which exhibits fast ionic conduction of the Na+ ions in two dimensions. The Na+ ions can be exchanged with a variety of mono-, di-, and trivalent cations. The resulting exchanged materials also show high ionic conductivities.

Considerable interest in the Na+-Nd3+-ß“-aluminas has been generated as a result of the recent observation of lasing in the pulsed and cw modes. A recent TEM investigation on a 100% exchanged Nd ß“-alumina sample found evidence for the intergrowth of two different structure types. Microdiffraction revealed an ordered phase coexisting with an apparently disordered phase, in which the cations are completely randomized in two dimensions. If an order-disorder transition is present then the cooling rates would be expected to affect the microstructures of these materials which may in turn affect the optical properties. The purpose of this work was to investigate the affect of thermal treatments upon the micro-structural and optical properties of these materials.