bluuebunny/crossref_metadata_2025_split huggingface dataset:
The evolution of dislocation structure in the creep of hot-isostatically pressed niobium carbide
Authors: Nixon R. D. 
Published: June 2020

The kinetics and mechanisms of creep in transition metal carbides are evaluated in order to design engineering structures which incorporate creep behavior. The mechanisms of creep in hot isostatically pressed niobium carbide involves the generation and movement of dislocations which were examined in this material by transmission electron microscopy.Constant uniaxial compressive stress experiments in the temperature and stress ranges of 1730K to 2100K and 16 MN/m2 to 70 MN/m2 were performed on right circular cylindrical samples of hot isostatically pressed NbC0.74 of average height and diameter 7.6 x 10-3 m and 4.4 x 10-3 m, respectively. These experiments were performed by either applying a single constant stress to the sample at four different temperatures to determine the activation energy of creep or by keeping the sample at one constant temperature and applying four different constant stresses to determine the stress exponent of creep.
Transmission Electron Microscope characterization of a slip propagation event in alpha brass
Authors: Bamford T.A. , Clark W.A.T. , Wagoner R.H. 
Published: June 2020

Slip propagation through grain boundaries is a process which is, in part, responsible for grain size strengthening. TEM characterization of a slip propagation event combined with quantitative stress analysis allows determination of the critical stress and micromechanism for the event. Such an analysis is presented here.Commercially pure alpha brass(30 w/o Zn) was rolled to 125um and was then annealed in a dry hydrogen atmosphere at 800°C for one hour. The material was lightly deformed, and samples prepared using standard electopolishing techniques. This was then examined in a JEOL 200CX operating at 200keV.
ESEM - A multipurpose surface Electron Microscope
Authors: Danilatos G.D. 
Published: June 2020

Over recent years a new type of electron microscope - the environmental scanning electron microscope (ESEM) - has been developed for the examination of specimen surfaces in the presence of gases. A detailed series of reports on the system has appeared elsewhere. A review summary of the current state and potential of the system is presented here.The gas composition, temperature and pressure can be varied in the specimen chamber of the ESEM. With air, the pressure can be up to one atmosphere (about 1000 mbar). Environments with fully saturated water vapor only at room temperature (20-30 mbar) can be easily maintained whilst liquid water or other solutions, together with uncoated specimens, can be imaged routinely during various applications.
Chromium deposition by sputtering
Authors: Specht R. C. , Lutz G. J. 
Published: June 2020

Previous works have shown the benefits of depositing ultrathin films (0.5-3.0 nm) of chromium onto SEM specimens to permit improved resolution at higher magnification. The finer grain structure of the chromium permits closer replication of the specimen surface topography than is possible with the conventional 10 nm of gold. This paper presents the results of an ongoing program at Denton Vacuum to develop guidelines for successful, repeatable deposition of ultrathin chromium films by sputtering.Chromium can be deposited using a high vacuum evaporator by either evaporation of chips from baskets or sputtering. Sputtering is the more desirable method since it has the potential for better rate control, coverage, repeatability and least specimen exposure to radiant heat.
The use of convergent-beam electron diffraction to determine the influence of anodization of a metal substrate
Authors: Bowman Keith J. 
Published: June 2020

Research by Gibala and co-workers has revealed that the application of thin oxide films can substantially reduce the flow stresses of bcc metals at low temperatures. Because the extent of this change in flow stress has been related to the stresses generated at the oxide/metal interface, the sign and magnitude of these stresses are of interest. The experiment described in this paper was used to ascertain the potential of using center-disk HOLZ lines from CBED experiments to measure elastic stresses induced by anodic film formation. The power of CBED for measuring small changes in lattice parameter has been discussed by Steeds.An electron beam zone refined and vacuum annealed [110] tungsten single crystal was diamond sectioned to 200 μm. The foil was hand polished to about 100 μm and electrothinned in a Tenupol twin jet polisher with a 2% NaOH solution at 25°C.
EDA and ELS in the AEM - A biological perspective
Authors: Johnson D. E. 
Published: June 2020

The purpose of this symposium/tutorial presentation will be to assess the current state and future prospects of both energy dispersive x-ray analysis and electron energy loss analysis in the submicron spectroscopy of biological systems.In the successful use of any analytical technique in a biological study, the specimen preparative steps are crucial to the ultimate validity of the results. Nowhere is this more true, than in the analytical electron microscope. Fortunately, current techniques of cryofixation, cryosectioning and analysis, including freeze drying, have developed such that morphology and elemental distributions are typically preserved to a spatial resolution at least as good as the analytical and electron optical instrumentation allow.
Use of a protective film to assure the integrity of asbestos samples collected for TEM analysis
Authors: Lentzen D. E. , Dunmyre G. R. 
Published: June 2020

Air samples which have been collected on a Nuclepore™ filter for TEM asbestos and other particulate analysis may lose fibers or other particulate during normal transport and handling conditions. Various reports and observations confirm that the distribution of collected particulates may be altered due to static electricity charge effects, physical dislocation, and even some subsequent analytical proceduresA method to help assure particulate sample integrity during transport is presented here. It involves enveloping the freshly taken sample between two electron transparent films. The first film is evaporated onto a Nuclepore™ filter of the chosen diameter and pore size. Vacuum deposit about 40 nm of carbon onto the collection side of the filter without polymerizing the polycarbonate by overheating. Load this filter in the sampling cassette under clean room conditions and store for transport to the field. Next, cast an electron transparent film of collodion in amyl acetate on a clean water surface. Select a portion of the cured film that is even, colorless, and flawless to pick up on the base end of the middle piece of a second cassette.
The crystalline-amorphous-crystalline transformations in the formation of FeSi2
Authors: Vanderwalker D. M. 
Published: June 2020

The crystalline to amorphous transformation which occurs as a result of interdiffusion of Au and La was first observed by Schwarz and Johnson. This study will examine the crystalline-amorphous-crystalline transformations in the formation of FeSi2.A layer of Fe was evaporated on Si wafers when the chamber pressure was below 10-6 torr. The samples were prepared for TEM by mechanical and chemical thinning with 6/7 nitric acid 1/7 hydrofluoric acid solution. The TEM was performed on the JEM 200 CX at Stony Brook.
Morphology of as-precipitated and dried powders in the PLZT system
Authors: Schwartz R. W. , Payne D. A. 
Published: June 2020

High quality ceramic products, such as transparent electro-optic materials, require better control of chemical composition, powder particle size and morphology, than is offered by conventional mixed-oxide ceramic processing methods. Chemical preparation procedures can be used to prepare powders with the required characteristics of controlled size and morphology.Precipitated hydroxides in the PLZT system (lead lanthanum zirconium titanate) were prepared in a constant volume continuous reactor, following a procedure suggested by Murata, which uses nitrate and chloride precursors, and ammonium hydroxide for pH control. After washing with deionized water, the powders were dried by either spray-drying or freeze-drying in liquid nitrogen.
Molecular cytochemistry of freeze-fractured cells
Authors: da Silva Pedro Pinto 
Published: June 2020

I will describe four approaches that combine cytochemistry with freeze-fracture: 1) FREEZE-ETCHING; 2) FRACTURE-LABEL; 3) FRACTURE-PERMEATION; and 4) LABEL-FRACTURE. These techniques, in particular fracture-label, involve delicate points of interpretation and numerous validating controls. In the publications listed at the end, these issues have been addressed in detail.1. FREEZE-ETCHING. I developed freeze-etching as a cytochemical approach to prove that membranes were split by freeze-fracture and to show that biological membranes were comprised of a bilayer membrane continuum interrupted by integral membrane proteins.1 - 4 In freeze-etching, the distribution of the marker over the membrane surface exposed by sublimation is compared to that of the intramembrane particles exposed by fracture. It is often required to aggregate the particles into domains larger than the labeling molecules (Fig. 1). This, and the need for freezing in distilled water, severely limits the application of freeze-etching.
Criteria for the evaluation of low-temperature Scanning Electron Microscopy
Authors: Beckett Alan 
Published: June 2020

Low temperature scanning electron microscopy (LTSEM) has been evaluated with special reference to its application to the study of morphology and development in microorganisms. A number of criteria have been considered and have proved valuable in assessing the standard of results achieved. To further aid our understanding of these results, it has been necessary to compare those obtained by LTSEM with those from more conventional preparatory procedures such as 1) chemical fixation, dehydration and critical point-drying; 2) freeze-drying with or without chemical vapour fixation before hand.The criteria used for assessing LTSEM for the above purposes are as follows:
1)Specimen immobilization and stabilization2)General preservation of external morphology3)General preservation of internal morphology4)Exposure to solvents5)Overall dimensional changes6)Cell surface texture7)Differential conformational changes8)Etching frozen-hydrated material9)Beam damage10)Specimen resolution11)Specimen life
Ultrastructural diagnosis of a thyrotroph cell adenoma of the pituitary
Authors: Siew Shirley , Mueller Willys F. , Fratkin Jonathan D. 
Published: June 2020

Thyrotroph cell adenoma is an extremely rare neoplasm, comprising less than 1% of pituitary tumors.We report a case of a 42 year old woman, who had presented first at the age of 33 with the chief complaint of blurred vision in the left half of her visual field. Examination showed the presence of bitemporal homonymous hemianopsia and optic atrophy in the left eye. CT scan, skull x-ray and tomograms showed expansion of the sella turcica with an intrasellar and suprasellar mass. Pancerebral angiogram showed vascular displacement secondary to an avascular sellar and suprasellar mass. There was also a history of secondary amenorrhoea. The follicle stimulating and luteinizing hormone levels were low. Thyroid function tests were within normal limits. A transsphenoidal radical excision of a pituitary adenoma was performed and the pathological diagnosis was a chromophobe adenoma. The patient was followed with periodic CT scans. The present admission followed the finding of a large recurrent pituitary adenoma with recurrence of loss of visual fields. The serum prolactin was normal, T4 was low and TSH was normal.
Freeze etch replication of extracellular bacterial polymers adsorbed onto kaolinite
Authors: Barker William W. , Hurst Vernon J. 
Published: June 2020

Freeze etch replication of experimental mixtures of euhedral kaolinite and pure cultures of polysaccharide and protein-producing bacteria reveals that surface textures formed by adsorption of extracellular bacterial polymers onto kaolinite surfaces resemble structures observed in natural estuarine clay rich sediments, where anhedral 0.1 micrometer clay surfaces are covered by anhedral masses and fibrous elements of organic material.All samples, were cryofixed in a Balzers QFD101 propane jet and replicated in a Balzers 360M freeze etch device. Etching occurred at −100°C for 45 sec. and replicas were created with 15 nm Pt @ 45 °, 15 sec. C @ 90°. Following 24 h digestion in cone. HF, replicas were mounted on Formvar-coated 100 mesh Cu grids, carbon-coated for thermal stability, and examined in a Philips STEM 400.Anionic mucopolysaccharide produced by pure cultures of encapsulated Klebsiella pneumoniae (ATCC 8044) readily adsorbed to both the basal (negative charge) and edge (positive charge) surfaces of kaolinite (Fig. 1).
Visualizing replicas of molecules made in a fully automated freeze-fracture machine
Authors: Branton Daniel 
Published: June 2020

We have designed and constructed an automated, computer driven freeze-etch apparatus that optimizes all of the standard operating procedures through which biological samples are normally processed to create a replica suitable for electron microscopy. Although designed for automated freeze-etching, manual intervention is possible at any step and the apparatus may be used to facilitate any or several sequences of computer driven or manual steps (Figure 1) that render a high resolution replica of a frozen or dried biological specimen.The gradual evolution and improvement of scientific apparatus are commonplace, but there are some specific reasons why we sought to automate the freeze-etch process:1) Many are dissuaded from using standard freeze-etch machines because operator training is time-consuming and using the apparatus is laborious;2) Reproducible results are difficult to obtain and require conscientious attention to a mire of trivial details that are easily remembered by computers;3) Numerous sub processes, e.g. the speed of fracturing, have not been systematically optimized because formidable record keeping is required to encompass the many subtle variations of conditions sustained by the specimens in a single freeze-etch run;
Molecular features of heterochromatin condensation
Authors: Hamkalo B.A. , Lundgren K. , Parseghian M.H. , Radic M.Z. , Saghbini M. 
Published: June 2020

Eukaryotic chromosomes are nonuniformly condensed in both interphase and metaphase. This difference is most apparent in mitotic chromosomes in which centromeric heterochromatin is distinguishable from euchromatic arms because of a higher degree of condensation. This difference prevails in interphase and has led to the designation of this type of heterochromatin as “constitutive”. Differences in condensation presumably are a consequence of differential stability of higher order chromatin structure. Since higher order structure is likely to be due to distinctive DNA-protein and protein-protein interactions, our goal is to identify components of such interactions as a first step in understanding the molecular basis for differential chromatin condensation.Analysis of the structure of the mouse major centromeric satellite DNA revealed the presence of stable DNA curvature which could be reversed if certain small ligands which recognize a sequence motif common to this highly repeated DNA were bound to the DNA. In addition, growth of cells in the presence of these ligands prevented complete condensation of centromere regions of metaphase chromosomes (Fig.1).
Video-light microscopic analyses of centrosome separation in vivo during mitosis in vertebrate cells
Authors: Rieder Conly L. , Waters Jennifer , Cole Richard W. 
Published: June 2020

The major microtubule (MT) organizing center of the vertebrate interphase cell is the centrosome. After replication near DNA synthesis it functions as a single unit until mitosis. At the onset of mitosis the cytoplasmic MT complex is resorbed and the replicated centrosomes separate to form the spindle poles. During this time each nucleates a radial array of dynamically unstable MTs known as an aster. After spindle formation the centrosomes separate again during anaphase B to elongate the spindle. The mechanism(s) by which the centrosomes separate during these two mitotic stages remain unknown. The most popular hypothesis is that interacting MTs of opposite polarity, derived from opposing asters, elongate and slide relative to one another through the action of MT plus-end directed motor proteins. Unfortunately, this hypothesis does not explain why centrosomes continue to separate in vertebrate cells when their MT arrays no longer overlap, as in anaphase-like prometaphase (ALP).Both centrosomes are clearly visible in vivo during mitosis in newt lung cells. The goal of our study was to compare, with high spatial and temporal resolution, the behavior of centrosomes as they separate when their MT arrays overlap during prophase (Fig. 1) and anaphase B (Fig. 3), with when they no longer overlap during ALP (Fig. 2).
Cryo-enhancement of ultrastructural, immunological, cytochemical, and low-voltage SEM characterization of fungal growth and morphogenesis
Authors: Howard Richard J. , Bourett Timothy M. 
Published: June 2020

Cells of filamentous fungi exhibit a characteristic somatic form, organized as a linear file of individual cells, known as the hypha. Growth of the fungus occurs primarily through expansion at the apex of the hyphal tip cell, where highly organized and localized exocytosis is thought to be responsible for the deposition of new cell wall. In pathogenic fungi, changes in the pattern of tip growth are the means by which specialized infection structures develop, enabling the fungus to adhere to and penetrate the host surface, establish infection and cause disease. The use of cryo techniques has provided a vastly expanded knowledge of the cellular bases underlying these important morphogenetic events.Hyphae are easily grown as a monolayer in culture, on pieces of cellophane overlying nutrient agar. These cell monolayers are easily manipulated for plunge freezing with minimal perturbation and no treatment necessary prior to quenching. In this sense, plunge freezing is superior to other cryo-fixation techniques that require pre-treatment or mounting of live specimens onto holders, hats or pistons.
Low-temperature evaluation of high-pressure frozen biological samples by TEM cryosections and high-resolution SEM
Authors: Müller Martin 
Published: June 2020

The unique ability of electron microscopy in biology is its power to describe and integrate structural details down to molecular dimensions within the context of a complex living system.Structural information closely related to the living state may be achieved by cryoimmobilisation techniques that vitrify the cellular water and, at the same time rapidly arrest all physiological processes.High-pressure freezing (Müller and Moor 198, Moor 1987) is at present the only practical way of cryofixing larger non-pretreated samples up to a thickness of 500 μm. A very high yield of adequately frozen specimens was demonstrated in TEM using suspensions of microorganisms as well as plant and animal tissue (i. e. no detectable effects of ice crystal damage are visible after freeze substitution) (Studer et al. 1989). High-pressure freezing can vitrify biological samples sometimes up to a thickness of 200μm, as extrapolated from electron diffraction of cryosections (Michel et al 1991) The actual thickness that can be vitrified depends on the specimen, particularly on the presence of substances that exhibit cryoprotectant activity and also depends on the optimum transfer of pressure and cold to the sample and on the sample geometry (thickness and shape of the aquous layer, and the mass of the specimen planchettes necessery to protect the biological sample from direct pressure effects).
Microtubule organization in the siphonous green alga bryopsis: An ultrastructural observation with Electron Spectroscopic Imaging (ESI)
Authors: Wei Sheng Jun , Bishop Kyle 
Published: June 2020

Transmission electron microscopy (TEM) has been routinely used to study the ultrastructure of microtubules (MT). However, we found that some MTs in the filamentous green alga we examined could not be easily recognized using conventional brightfield imaging, because of low contrast. Electronspectroscopic imaging (ESI) microscopy using the imaging electron energy filter solves many problems involving low contrast and feature resolution. By ESI, the contrast can be tuned and optimized so that images with higher resolution can be produced. In the present study we used ESI to improve the image quality in order to clearly resolve the MTs.A specimen of the giant marine green alga Bryopsis sp. was prepared following a new modified double fixation procedure of our own to preserve cell structures (Fig. 1). In brief, the branched alga was cut into small segments of about 1 cm in length in 2% glutaraldehyde in 0.1 M phosphate at pH 7.2.
UV absorption microspectroscopy and alkali extraction to characterize aromatic constituents in plant cell walls
Authors: Akin D. E. , Morrison W. H. , Rigsby L. L. 
Published: June 2020

Aromatic compounds bound to structural carbohydrates in plant cell walls limit the microbial utilization of otherwise biodegradable polysaccharides. Such limitations have important consequences in conversion of plant biomass to useful products and in carbon recycling. These aromatic constituents are chemically diverse, with further variations occurring in chemical linkages. Microspectroscopy and chemical analysis of alkali-treated plant walls was used to investigate aromatics.Pearl millet (Pennisetum glaucum) stems (Fig. 1) were separated into pith parenchyma, pith vascular bundles, and rind (vascular and sclerenchyma cells combined). A normal (N) line and a counterpart brown midrib (bmr) mutant line, which has modified lignins, were both sampled. Ground (~ 1 mm) walls of these cell types were sequentially treated with 1M NaOH at 25°C for 20 h to remove ester-linked phenolic acids, and the residues were then treated with 4M NaOH in Teflon polyfluoroalkoxy copolymer vials which were placed in stainless steel vessels at 170°C for 2 h to remove more resistant ether-linked and polymerized aromatics.
Meiotic spindle assembly in cytoplasmic extracts of Spisula solidissima oocytes
Authors: Palazzo Robert E. , Vaisberg Eugeni , Cole Richard W. , Rieder Conly L. 
Published: June 2020

Critical for karyokinesis in animal cells, is the assembly of a spindle-chromosome-aster complex which serves as the force-generation system for chromosome segregation. Spisula solidissima oocytes offer a unique system for the study of spindle assembly since they can be obtained in large quantities, are naturally synchronized in the cell cycle and can be induced to assemble meiotic spindles within 15 min after parthenogenetic activation. Oocytes contain a large nucleus [germinal vesicle (GV)] and are arrested at the G2/M border of meiosis I. No centrosomes or asters have been observed in oocytes at this stage by either electron microscopy or fluorescence microscopy using anti-tubulin antibodies. Observation of live oocytes with polarized light microscopy revealed that within 4-6 min after parthenogenetic activation, asters appeared and invaded the GV as it breaks down (GVBD). 15 min after activation a complete bipolar meiotic spindle was observed.As a first step towards the development of an in vitro biochemical reconstitution system for the study of spindle assembly, concentrated lysates were prepared at various times following parthenogenetic activation and analyzed by phase-contrast microscopy.