bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Voltage Fesem Examinations of the Structure of Silica Aerogel
Authors: Price C. W. , McCarthy P. L.
Published: June 2020

Silica aerogel is a low-density material with a loose porous structure. The structure revealed by early TEM studies was found to be composed of fibrous chains of globular particles. Iler showed that measurements of the specific surface area obtained by the Brunauer-Emmett-Teller (BET) technique correlated reasonably well with calculations based on the surface area of spheres with the average diameter of the globular particles revealed by TEM. The structure of aerogel also is conducive to calculations of specific surface area based on data generated by small-angle x-ray scattering (SAXS) using synchrotron radiation, and the SAXS data correlates well with the BET measurements. Since the delicate structure of silica aerogel is highly susceptible to beam damage in the TEM, the agreement of surface-area estimates based on TEM particle-size measurements with the SAXS and BET data provides important support for the significance of the TEM results.
Aem analysis of defects in processed Si wafers
Authors: Lewis Nathan , Hall Ernest L. , Hall Robert N.
Published: June 2020

The analytical electron microscope is particularly well suited for the characterization of many types of defects observed in semiconductor materials. One type of common defect which has been shown to occur in some devices is an electrically-active rod defect which has a detrimental effect on some properties. In the present AEM investigation Si devices which exhibited a significant degradation in certain electrical properties (excess junction leakage) were examined in order to ascertain the cause of this phenomenon.

The starting material in the process was n-type (100) silicon wafers. The initial processing step was the growth of 200nm of LPCVD SiO2. During the processing sequences wafers were subjected to temperatures up to 900°C.
A new method for preparing tilt grain boundaries in thin vapor-deposited films
Authors: Krakow William , Castaño Victor
Published: June 2020

In the past the electron microscope samples used to study tilt grain boundaries and interfaces were prepared from bulk samples grown from the melt which were then cut, polished and thinned by ion milling or chemical jet etching. This technique is also employed routinely in preparing crossectional semiconductor materials and metals. Another technique to prepare tilt boundaries in metals is to fuse two thin single crystal films each on substrates by heating and forming twist boundaries (e.g. Au (100)). Then, the boundary which forms at the composite film midplane, migrates to one of the two films surfaces having many island grains separated by tilt boundaries perpendicular to the foils’ surface. One of the present authors has carried this technique further by being able to perform this process directly in the microscope and observe the boundary migration when the total film thickness, in the case of Au, was ∼250Å. The technique is limited to this composite thickness because small holes develop in thinner films which thin rapidly become discontinuous when heated in-situ.
Glide of extended dislocation in III-V compounds
Authors: De Cooman B.C. , Carter C.B.
Published: June 2020

The study of dislocation dynamics has until recently been restricted to relatively high temperatures and low stresses due to the the brittle nature of most semiconductors. Although much is already known for this deformation regime, there is little information from controlled deformation at the low temperatures (i.e., T< 0.5Tm) and high stresses (τ≫ 10 MPa). Deformation of III-V compounds under such conditions has shown the following characteristics:

a. High-stress deformation experiments give rise to well-defined dislocation configurations, which makes the study of doping effects on dislocation mobility directly visible. In addition, individual partial dislocations can be observed using weak-beam microscopy.
Cathodoluminescence for characterization of quantum wires and discs
Authors: Lin P. S. D. , Dobisz E. A. , Kash K. , Scherer A. , Craighead H. G. , Tell B. , Harbison J. P.
Published: June 2020

Detection of cathodoluminescence(CL) in an scanning electron microscope(SEM) is a powerful technique in the study of novel nanometer size structures in semiconductors. In the SEM, the electrons can be focused into a nanometer probe and one can choose to excite either a single structure or multiple structures. Geometric parameters can be measured in-situ from the secondary(or transmitted) electron image. The carrier injection level is uniform and insensitive to adsorbed surface contamination. We demonstrate in this report the potential of CL in the study of nanometer size quantum-well wires and discs.

The experimental setup (Fig. 1) includes a scanning electron microscope, a liquid helium cooled cryostat (from Oxford Instruments) which cools both the ellipsoidal mirror and the sample, and an optical spectrometer equipped with a silicon diode array detector controlled by a multi-channel analyzer (TN 1710).
The microstructure of ionized cluster beam aluminum deposited on (100) silicon and (111) silicon
Authors: Madden Michael C. , Tracy Bryan M.
Published: June 2020

Ionized cluster beam (ICB) is a novel method of depositing thin films. The apparatus consists of a graphite crucible containing the material to be deposited, in this case aluminum, with a small hole in its top. The crucible is heated under vacuum. The atomic clusters that emerge from the hole are showered with electrons, then accelerated through a potential of several kilovolts before striking a substrate. Aluminum films prepared in this manner have been reported to have several interesting properties, including improved spiking resistance and improved electromigration resistance.

Aluminum samples were prepared on (100) and (111) silicon substrates. 3mm discs were cut uItrasonicaIly, mechanically thinned to 100 μm, chemically etched with HF-HNO3 (1:3), and ion milled to perforation. All thinning was done from the substrate side of the sample. Samples were then examined in a JEOL 1200EX TEM operated at 120 kV.
The observation of nano-voids in Au thin films
Authors: Krakow William
Published: June 2020

It has long been known that defects such as stacking faults and voids can be quenched from various alloyed metals heated to near their melting point. Today it is common practice to irradiate samples with various ionic species of rare gases which also form voids containing solidified phases of the same atomic species, e.g. ref. 3. Equivalently, electron irradiation has been used to produce damage events, e.g. ref. 4. Generally all of the above mentioned studies have relied on diffraction contrast to observe the defects produced down to a dimension of perhaps 10 to 20Å. Also all these studies have used ions or electrons which exceeded the damage threshold for knockon events. In the case of higher resolution studies the present author has identified vacancy and interstitial type chain defects in ion irradiated Si and was able to identify both di-interstitial and di-vacancy chains running through the foil.
Generation of surface plasmons in a supported metal particle with an external electron beam: I. quantum theory
Authors: Wang Z.L. , Cowley J.M.
Published: June 2020

The theoretical prediction of surface plasmon frquencies for a supported metal particle system is based on the model as shown in fig. 1. A spherical particle covered with a thin shell of oxide is half embedded in the support. Two surface plasmons (ωH, ωLO) and four surface plasmons (ω1 to ω4) have been predicted by using dielectric theory for the cases of a metal particle sitting on (A) a dielectric insulator and (B) a metal plate, respectively[l-2]. The relative excitation probabilities of those predicted surface plasmons have been calculated using the so-called coherent-state theory[3-4]. Two directions of incidence for the external electron beam are assumed as indicated in fig. 1, P(||) and P(⊥) one is parallel to the Z axis and the other is perpindicular to it. The curves marked with H and L are the calculated excitation probabilities for ωH and WLO as predicted in [1-2]
A method of asbestos fiber counting using transmission electron microscopy
Authors: Ghosh A. , Jenniss S. W. , Shahiea S. I.
Published: June 2020

As the health hazard posed by small asbestos fibers in ambient air has become increasingly evident in recent years, so too has the need increased for a means to accurately and precisely measure the concentration of these fibers (1,2,3,4). The goal of this study was to develop a standard procedure for sample preparation and estimation of asbestos fiber mass using Transmission Electron Microscope (TEM) which would yield highly precise and accurate data.

The proposed method under evaluation required air samples be taken on membrane filters and carbon coated in a vacuum evaporator. Three randomly punched 3 x 3 mm sections of the coated filters were placed on 200 mesh carbon-coated EM grids and washed with acetone vapor in a condensation washer, carefully controlling the solvent reflux height at 4 - 5 mm above the cold finger, to remove the filter material. The processed samples were then analyzed by TEM.
Energy-dispersive spectroscopy of melanosomes in horse hair follicles
Authors: Swafford J. R. , Woolf C. M.
Published: June 2020

As part of a study on the genetics of coat color in the Arabian horse, we initiated studies on the ultrastructure of melanosomes produced by melanocytes in the hair follicles at the base of black and reddish-colored hairs. The purpose was to determine if a correlation exists between hair color and the presence of specific types of melanosomes.

Melanosomes can be characterized by shape and chemical composition. The biochemical pathway from tyrosine to melanin is branched with different paths leading to the production of eumelanin (black pigment) and pheomelanin (yellowish-red pigment). The major isomer of eumelanin is dopaquinone and that of pheomelanin is 5-S-cysteinyldopa. Hence, sulfur is absent in eumelanin but present in pheomelanin. Eumelanogenesis leads to ellipsoidal melanosomes; pheomelanogenesis leads to spherical melanosomes. However, classification of melanosomes solely on the basis of their shape may be misleading under certain conditions.
A comparative STM and TEM study of polycarbonate substrates
Authors: Reifenberger R. , Baro A. M. , Vazquez L. , Bartolami A. , Garcia N. , Goldberg H. A. , Kohn R. , Chen R. T. , Sawyer L. C.
Published: June 2020

Scanning tunneling microscopy (STM) is the newest method that allows real space imaging of surfaces on a scale extending to atomic dimensions. The STM technique was developed by C. Binnig, H. Rohrer, and co-workers at IBM Zurich laboratories and is notable for its ability to image a wide range of materials under a variety of different conditions. The technique has received considerable attention for its ability to provide information about postions of individual surface atoms with unprecendented three-dimensional resolution.

The physical basis for the STM is a quantum mechanical electron tunneling from a sharp tip to a conducting substrate. The exponential dependence of the tunneling current with the tip-to-sample separation allows a measurement of vertical position differences smaller than ca. 0.01 nm often with a lateral resolution of better than ca. 0.2 nm. By rastering the tip across a sample surface while monitoring the tunneling current, a three dimensional topographic image of the surface can be obtained.
Direct visualization of microstructure deformation processes in polyethylene
Authors: Adams W.W. , Yang D. , Thomas E.L.
Published: June 2020

Deformation processes of semicrystalline polymers are highly dependent on microstructure and its orientation, as for example in the different zones of spherulites. The elucidation of the deformation mechanisms is a complex problem, primarily due to the hierarchy of structural features present. Our approach to the determination of the important morphological processes occuring during deformation is to simplify both the sample morphology and the applied stress. The production of near single-crystal texture thin polyethylene (PE) film was made possible by modification of Petermann's method to prepare highly chain axis oriented and planar textured films of high density (HD) PE, in both as-drawn (AD) and annealed (AN) forms. These single crystal texture films were ideal for in situ microscopic deformation studies.

HDPE (Marlex 6003 from Phillips Chemical) was melt-drawn from a glass slide at 120°C to form AD films, some of which were then annealed on glycerol at 128°C for two hours.
Grain boundary imaging by digital reconstruction of HREM lattice images of poly(P-phenylene benzobisthiazole) fibers
Authors: Martin David C. , Boudet Alain , Thomas Edwin L.
Published: June 2020

Poly(p-phenylene benzobisthiazole) (PBT) is a rigid-rod polymer of interest for high-strength fibers and other applications including nonlinear optical behavior. PBT fibers are formed by coagulation into water from solutions of the molecule in strong acid. Because of the high orientation and strength of these fibers, the nature of boundaries and defects between crystalline regions is of particular scientific and technical concern.

The crystal structure of PBT fibers has been investigated by electron and X-ray diffraction. It has been found that the unit cell is monoclinic with a =.59 nm, b =.36 nm, c =1.249 nm, gamma =95.5 degrees. The molecules are oriented along the c axis of the unit cell and exhibit axial translational disorder in both the [100] and [010] directions.

PBT is resistant to electron beam damage, having a critical dose of 1.6 Coulombs/cm2 at 100 kV and room temperature.
Electron crystallography of imperfect crystals: Melting and polydispersity
Authors: Dorset Douglas L.
Published: June 2020

The phase behavior of linear chain molecules has been of great interest to researchers in areas as diverse as membrane biophysics and polymer physics. Two aspects of this behavior are possibly related, i.e. the conformational requirements of linear chains undergoing mesomorphic transitions and the packing requirements for components of a polydisperse solid to form a solid solution. Generally, calorimetric studies of linear chain crystals are accompanied by powder x-ray diffraction measurements to interpret the phase diagram in terms of molecular packing. From such studies, structural models have been proposed for higher energy conformers of linear chains and, in polydisperse systems, rules have been given for the formation of solid solutions (2). However, such structural models remain somewhat ambiguous due to the disadvantages of Debye-Scherrer x-ray measurements, which include uncertainties of indexing (hence, symmetry assignment and intensity measurement) of diffraction reflections from a randomly oriented polycrystalline sample.
The morphology and deformation behavior of poly(butylene terephthalate) blends
Authors: Hobbs S.Y. , Dekkers M.E.J. , Watkins V.H.
Published: June 2020

Impact-modified blends of BPA polycarbonate (BPAPC) and poly(butylene terephthalate) (PBT) are being used to an increasing extent in engineering applications requiring superior low temperature toughness (e.g., automotive bumpers). In order to optimize the performance of these materials in such demanding situations, it is essential to develop a thorough understanding of the factors affecting their microstructure and deformation behavior. To be successful in this endeavor, an interdisciplinary effort involving detailed microscopic characterization, sophisticated mechanical testing, and careful analytical studies is required. Although some work of this type has appeared in the literature (1,2) together with more fundamental research on BPAPC/PBT miscibility (3-6), major questions with respect to phase segregation, distribution of blend components, and morphological changes which occur during deformation remain.

In response to these issues, a more complete investigation of the microstructure and deformation characteristics of several PBT blends containing various combinations of polycarbonate and impact modifier was recently carried out in our laboratory.
Resolution and measurement in the scanning electron microscope
Authors: Postek Michael T.
Published: June 2020

The term ultimate resolution or resolving power is the very best performance that can be obtained from a scanning electron microscope (SEM) given the optimum instrumental conditions and sample. However, as it relates to SEM users, the conventional definitions of this figure are ambiguous. The numbers quoted for the resolution of an instrument are not only theoretically derived, but are also verified through the direct measurement of images on micrographs. However, the samples commonly used for this purpose are specifically optimized for the measurement of instrument resolution and are most often not typical of the sample used in practical applications.

SEM RESOLUTION. Some instruments resolve better than others either due to engineering design or other reasons. There is no definitively accurate definition of how to quantify instrument resolution and its measurement in the SEM.
The SEM interpretation of fractal surfaces
Authors: Christian Russ J. , Russ John C.
Published: June 2020

The concept of a fractal dimension, a non-integer value greater than the traditional 1 (for a line) or 2 (for a surface) that we are accustomed to in Euclidean geometry, was first popularized by B. B. Mandelbrot. From its beginning as a mathematical construct and curiosity, it quickly developed some very practical uses, and now in several branches of science there are fractal interpretations of data that show much promise.

Briefly, a fractal line (which has a dimension greater than 1 and less than 2) is not straight, but “crinkly” so that its length exceeds the distance between its endpoints. Further, for an ideal fractal this same degree of irregularity is present at any magnification, so that as we zoom in closer to the line, it continues to reveal more detail (as a function of the resolution of our instrument) but there is no internal way to judge the magnification.
Condenser-objective lens SE microscopy: application for high - resolution imaging of cell membranes
Authors: Apkarian R.P.
Published: June 2020

Recent developments in high brightness field emission (FE) and LaB6 electron sources for scanning electron microscopes (SEM) equipped with condenser-objective lens specimen stages has resulted in the collection of secondary electron (SE) signals that contain unsurpassed high resolution topographic contrasts. High resolution low loss images were described for a condenser-objective lens SEM when SE contrasts were first being scrutinized. The low energy SE-I imaging mode contains contrasts generated by only specimen specific SE-I and II. The SE-I signal is produced by the primary electron beam interaction with the specimen surface before a scattering event occurs and can be best collected when SE-IIIs are eliminated and SE-IIs are suppressed. High resolution SE-I topographic contrasts include particle contrast (resolution of particles < 10 nm), relief contrast (imaging of very small contours), and edge brightness contrast (sum of beam diameter and SE range).
Ultrastructural analysis of human tumors with immunohistochemical correlations
Authors: Erlandson Robert A.
Published: June 2020

Transmission electron microscopic (TEM) studies and, more recently, immuno-histochemical (IHC) procedures using newly developed monoclonal antibodies have made significant contributions to the diagnosis of poorly differentiated tumors and to the histogenetic analysis of cytologically complex neoplasms. In this report we will show how TEM and IHC studies confirm a suspected diagnosis of amelanotic malignant melanoma and reveal that the so-called “mesenchymal” cells found in benign pleomorphic adenomas are actually metaplastic myoepithelial cells. Epithelial differentiation of mesenchymal tissues is exemplified by TEM and IHC evaluation of synovial and epithelioid sarcomas, respectively.

The ultrastructural diagnosis of amelanotic malignant melanoma requires the recognition of premelanosomal organelles or aberrant melanosomes in the cytoplasm of the neoplastic cells. Ovoid or ellipsoidal vesicles with a characteristic internal inclusion consisting of rigid parallel fibrils (pseudo-crystalline substructure) or coiled or pleated (zig-zag) fibrils (Figs. 1&2) also known as stage II melanosomes are diagnostic.
Clq nepropathy: A case report of a newly described glomerularopathy
Authors: Price George , Cerezo Lizardo
Published: June 2020

A distinctly new pathologic entity that causes steroid resistant nephrotic syndrome has been described by Jennette and Hipp. Clq nephropathy gets its name from the strong positivity of Clq localized by immunofluorescence. Reactions for C3, IgG and IgM are present, with a mild reaction for IgA occuring in some cases.

The ultrastructural features of Clq glomerular nephropathy (Clq GN) and systemic lupus erythmatosis glomerular nephropathy (SLE GN) are strikingly similar in that they both demonstrate mesangial cell proliferative activity, mesangial dense deposits, and subendothelial or subepithelial dense deposits. One ultrastructural difference between Clq GN and SLE GN is the lack of endothelial tubuloreticular inclusions in Clq GN.

The most interesting aspect of Clq GN is that although the glomerular changes resemble SLE GN by light microscopy and electron microscopy, these patients lack clinical or serological evidence for SLE. Specifically, serological tests for ANA, anti-DNA, and LE are all negative in Clq GN patients.
Computer graphics 3-D reconstruction of intracytoplasmic lumina in breast carcinoma
Authors: Song M.J. , Hussain M. , Marko M. , Song C.Y. , Parsons D.F.
Published: June 2020

Intracytoplasmic lumina occur mainly in infiltrating lobular carcinoma. Their identification in large number provides additional support for the breast origin of a metastatic tumor. Although intracytoplasmic lumuina were originally characterized with the electron microscope, they can be identified by light microscopy. Recently their usefulness in histopathologic diagnosis has received attention. However, their role in cell physiology or pathology remains unknown. It is not known whether they communicate with the exterior of the cell. This information might suggest a possible function. In attempting to seek communicating channels, we have studied infiltrating lobular carcinoma of signet-ring cell type in two patients.

All tumor biopsy specimens from the breast and associated lymph nodes were taken under local anesthesia. Specimens for LM were fixed in phosphate-buffered 10% formaldehyde and processed by paraffin embedding, hematoxylin-eosin stains, and mucicarmine stain.
Eponate 12, a new epoxy resin: Comparisons with EPON 812 and observations on its use for general biological electron microscopy
Authors: Mascorro J.A. , Kirby G.S.
Published: June 2020

Many epoxy resins have been introduced during the last several years as replacements for Epon 812 since the Shell Chemical Company discontinued production of this popular embedding resin. In a past study, the present investigators examined several of the “replacement” resins for physical characteristics such as viscosity, flow rate, density, mass weight, and hardness of the polymerized medium. In addition, other equally important parameters including sectioning and infiltrating character as well as stain-ability and section strength subsequent to beam and vacuum conditions also were evaluated. The present work follows a similar rationale and seeks to determine this same information for Eponate 12, an epoxy resin designated as a true generic replacement for the formerly available Epon 812 product.

For purposes of physical comparisons, Eponate 12 was tested against a sample of original Shell Epon 812 still maintained in our laboratory.
Three Dimensional structure and organization of diploid chromosomes by optical section microscopy
Authors: Agard David A. , Hiraoka Yasushi , Sedat John W.
Published: June 2020

In an effort to understand the complex relationship between structure and biological function within the nucleus, we have embarked on a program to examine the three-dimensional structure and organization of Drosophila melanogaster embryonic chromosomes. Our overall goal is to determine how DNA and proteins are organized into complex and highly dynamic structures (chromosomes) and how these chromosomes are arranged in three dimensional space within the cell nucleus. Futher, we hope to be able to correlate structual data with such fundamental biological properties as stage in the mitotic cell cycle, developmental state and transcription at specific gene loci.

Towards this end, we have been developing methodologies for the three-dimensional analysis of non-crystalline biological specimens using optical and electron microscopy. We feel that the combination of these two complementary techniques allows an unprecedented look at the structural organization of cellular components ranging in size from 100A to 100 microns.
A rotatable 3-D computer reconstruction of paper from light microscopic images of serial-sections
Authors: Neal R. J. , Telljohann M.
Published: June 2020

The utilization of images from serial-sections to build 3-D models has always been a desirable goal of microscopists. This has been a formidable task because of the tedious effort required to obtain suitable microscopic images from properly registered serial-sections, and to build 3-D models from these images. With the advent of computerized imaging capabilities, 3-D modeling has been simplified considerably. It seemed likely, then, that by combining serial-sectioning techniques with computerized processing, a rotatable 3-D model of paper could be generated. Such a model could yield considerable insight into void structure and fiber relationships that relate to the strength and absorption qualities of paper. This data could lead to novel ways of manufacturing paper of improved quality.

Small pieces of paper hand-sheets were embedded in plastic and polymerized at 60° overnight. Registration holes (50 μm Dia.) were burned into the block with an Ar laser.
Ultrastructural comparison of cynomolgus monkey liver samples following immersion fixation in different primary fixatives
Authors: Egy M. A.
Published: June 2020

This study was undertaken to find an optimal primary fixative for the assessment of ultrastructural morphology of hepatic tissue from cynomolgus monkeys under common constraints in a pathology laboratory. No single fixative for electron microscopy is suitable for every organ, species or application. Immersion fixation is prescribed when a limited amount of tissue is available from biopsies or when tissues must be shared with other investigators. In addition, tissues are often collected at another location and then sent to the electron microscopist so a delay is incurred before processing is completed. The ultrastructural effects of eight fixatives and two designed delays were evaluated in this study.

Fresh hepatic tissue was excised from the left lateral hepatic lobe of normal control young adult male cynomolgus monkeys and fixed by immersion according to 8 protocols.
Phagocytosis of tumor cells by activated liver macrophages.
Authors: Wasserman Arthur J. , Gardner Carol R. , Laskin Debra L.
Published: June 2020

Kupffer cells (KC) are fixed macrophages (Mø) that line the hepatic sinusoids. In response to antigenic or tumor cell challange KC become “activated” and display enhanced biochemical and functional reactivity including increased chemotaxis, phagocytosis, oxidative metabolism and tumor cell killing. We have observed that lipopolysaccharide (LPS)-activated liver Mø phagocytize certain tumor cell targets depending on their tissue origin. This was unusual as Mø typically do not kill tumor targets by phagocytosis. The present studies were designed to study the mechanism involved in liver mø mediated phagocytosis of tumor targets.

Mø were isolated from rat livers 48 hr following treatment with LPS (5mg/kg IV) by combined pronase/collagenase perfusion, selective digestion and differential centrifugation. Mø were coincubated on glass coverslips or slides with tumor cells for 48 hr. For both scanning and transmission electron microscopy (SEM,TEM), cells were fixed for 60 min at 4°C in 236 glutaraldehyde buffered by 0.1M cacodylate containing 0.1M sucrose and 1.5mM CaCl2 (pH 7.4).
The light and electron microscopic demonstration of B-lymphocytes with a new Mg++/ATPase method
Authors: Hanker J. , Strauss G. , Yates P. , Giammara B.
Published: June 2020

Helper T-lymphocytes are readily demonstrated for light microscopy by an enzyme cytochemical method for nonspecific esterase with the substrate α-naphthyl butyrate acetate. It was recently shown that a modification of this esterase method also demonstrates immature and cultured helper T cells. Although Harigaya et al. were able to demonstrate B-cells in B lymphomas and in some smears of whole blood, they were unable to demonstrate B lymphocytes in enriched leukocyte preparations. Studies in our laboratories have shown that a new method for the demonstration of myofibrillar ATPase could be also used to show B cells as long as the fixative contained ATP and the cobalt sulfide end product was intensified and stabilized by very brief treatment with silver methenamine solution in a microwave oven.
Microtubule dynamics in the mitotic spindle
Authors: Richard McIntosh J. , Vigers Guy P. A.
Published: June 2020

Six lines of evidence suggest that the mitotic spindle is highly labile in vivo: the spindle forms for division and disassembles as it finishes its job; the spindle dissolves under most conditions of cell lysis; the spindle disappears when a living cell is treated with temperatures near 0°C or high hydrostatic pressure; the spindle quickly disassembles when drugs that block tubulin polymerization are put on or injected into a cell; labeled tubulin, injected into a mitotic cell, is incorporated into the spindle within seconds of injection; and the spindle of a living cell, equilibrated with injected fluorescent tubulin, may be photobleached with a laser microbeam, and the spindle fluorescence redistributes with a half time of 15 - 20 sec. These data suggest that spindle microtubules (MTs) are in rapidly exchanging equilibrium with a pool of soluble tubulin subunits (Reviewed in 1 - 3).
Morphometric analysis of normal canine Leydig cells and their organelles in sexually mature beagles
Authors: Argentieri G. J. , Visscher G. E. , Robison R. L.
Published: June 2020

It was our goal to obtain quantitative baseline information on canine Leydig cells and their organelles. Little quantitative baseline data on canine Leydig cells exists in the literature which gives a comprehensive light microscopic (LM) and transmission electron microscopic (TEM) overview. Information is available for various species which correlates testicular physiological and morphometric data. Morphometric data on canine Leydig cells and their organelles becomes important when evaluating naturally occurring and experimentally induced changes during research and development.

Four control adult male beagles (14 to 20 months old) were used in this study. A reliable in vitro vascular perfusion fixation method for the testis was developed. Initial buffer rinsing of the vasculature was accomplished using a vasodilator and an anticoagulant. Primary fixation was with 1% paraformaldehyde, 1.5% glutaraldehyde in a 0.1 M cacodylate buffered solution, followed by a second, doubly concentrated aldehyde fixative solution.
The structure of the gills of the axolotl, Ambystoma mexicanum
Authors: Jarial Mohinder S.
Published: June 2020

The axolotl is a strictly aquatic salamander in which the larval external gills are retained throughout life. The external gills of the adult axolotl have been studied by light and electron microscopy for ultrastructural evidence of ionic transport. The thin epidermis of the gill filaments and gill stems is composed of 3 cell types: granular cells, the basal cells and a sparce population of intervening Leydig cells. The gill epidermis is devoid of muscles, and no mitotic figures were observed in any of its cells.

The granular cells cover the gill surface as a continuous layer (Fig. 1, G) and contain secretory granules of different forms, located apically (Figs.1, 2, SG). Some granules are found intimately associated with the apical membrane while others fuse with it and release their contents onto the external surface (Fig. 3). The apical membranes of the granular cells exhibit microvilli which are covered by a PAS+ fuzzy coat, termed “glycocalyx” (Fig. 2, MV).
Paired helical filaments (PHF) in rats: An experimental animal model for Alzheimer's disease
Authors: Montpetit V.J.A. , Dancea S. , French S.W. , Clapin D.F.
Published: June 2020

A continuing problem in Alzheimer research is the lack of a suitable animal model for the disease. The absence of neurofibrillary tangles of paired helical filaments is the most critical difference in the processes by which the central nervous system ages in most species other than man. However, restricting consideration to single phenomena, one may identify animal models for specific aspects of Alzheimer's disease. Abnormal fibers resembling PHF have been observed in dorsal root ganglia (DRG) neurons of rats in a study of chronic ethanol intoxication and spontaneously in aged rats. We present in this report evidence that PHF-like filaments occur in ethanol-treated rats of young age. In control animals lesions similar in some respects to our observations of cytoskeletal pathology in pyridoxine induced neurotoxicity were observed.

Male Wistar BR rats (Charles River Labs) weighing 350 to 400 g, were implanted with a single gastrostomy cannula and infused with a liquid diet containing 30% of total calories as fat plus ethanol or isocaloric dextrose.
Dermal nerves in monzygotic twins discordant for diabetes: Morphometric study of perineurial cell basement membrane
Authors: Beggs J. L. , Johnson P. C. , Watkins C. J. , Olafsen A. G. , Jones C. P.
Published: June 2020

Nerves in the dermal layer of skin are typically composed of several myelinated and unmyelinated nerve fibers surrounded by a perineurial sheath. Generally, this sheath is composed of one to two perineurial cell layers. The perineurial sheath helps to maintain a suitable environment for proper nerve function (1) and morphological changes in the sheath may cause nerve dysfunction (2). Perineurial cell basement membrane (PCBM) becomes thickened in diabetics and this phenomenon has been viewed as a diagnostic aid in the detection of diabetes (3). Since other factors (e.g. genetics, aging, vascular disease) may play a role in basement membrane morphology, we undertook this study of dermal nerves from identical twins discordant for diabetes to determine the effects of diabetic dysmetabolism on morphological changes in the PCBM. Since monozygotic twins have an identical genetic composition, it is likely that any significant differences in the dermal nerve would be due to factors related to diabetes.
Identification and localization of avian leukosis/sarcoma virus P-27 antigen by Immunogold technique
Authors: Steffens W.L. , Goodwin Mark
Published: June 2020

The leukosis/sarcoma viruses (L/SV) induce benign and malignant neoplasms in chickens and other birds. By sexual maturity, most birds in all chicken flocks have been infected, with losses as high as 25% in commercial breeder flocks attributed to L/SV-induced neoplasms. Prevention and control of L/SV infection depends on sanitation and disinfection programs coupled with genetic selection for host resistance to viral infection, however tests to detect L/SV infection must first be developed and perfected before these programs can be implemented.

Adult chickens from a flock suspected of harboring avian leukosis virus were used to evaluate the efficiacy of the immunogold technique in aiding in the diagnosis of the disease in samples submitted for routine microscopy. A commercial monospecific polyclonal antiserum to P-27 protein, an L/SV group-specific protein was utilized for immunolabelling. Samples were taken of myocardium and kidney from chickens killed at necropsy. Tissues were processed for indirect immunogold labelling as described elsewhere. Controls were performed by utilizing non-immune serum and by using immune serum pre-adsorbed with P-27 protein.
Utilization of replicas to show gold-probe binding to sperm cells for SEM and TEM
Authors: Battjes C. J. , Adams J. L. , Buthala D. A.
Published: June 2020

The introduction of gold particles bound to various probes has facilitated studies of cell surface and intracellular tracing. One problem has been the inability to show surface binding of small gold particles without embedding and thin-sectioning the sample. Our work has shown that small gold probes of 10-15 nm diameter attached to lectins can be detected at surface sites by the use of replicas. The replica retains the three-dimensional aspect of the cell surface while fixing the gold-probe in place. Murine spermatazoa labelled with gold-Con A were replicated directly or replicated following a silver intensification. Results showed that the probes remained at their binding sites and were clearly visible at the ultrastructural level.

Murine epididymal and caudal sperm were collected in PBS pH=7.4. Sperm were sedimented twice through PBS, then spread onto clean glass slides and fixed with 3% glutaraldehyde in Millonig's buffer.
Evidence for lateral associations in the Type IV collagen network from freeze-dried platinum-carbon replicated amniotic basement membrane
Authors: Ruben George C. , Yurchenco Peter D.
Published: June 2020

The structural scaffolding of basement membrane (BM) is formed by a polymerized and covalently cross-linked network of type IV collagen whose molecular structurein situhas eluded detailed analysis. The monomeric unit of assembly of this collagen is a 424nm linear protein which, compared to other interstitial collagens, is longer, more flexible, contains frequent interruptions by non-collagenous type sequences, and possesses distinct end-region domains. Type IV collagen, unlike the interstitial collagens I, II & III, does not assemble into long bundled fibers. Our present knowledge of collagen IV's intermole- cular associations comes from biochemical characterizations correlated with low angle rotary shadowed glycerol spreads of proteolytically extracted fragments’ and reconstituted collagen IV oligomeric complexes and networks Earlier work led to the identification of an amino(N)-terminal 30nm region that binds three other N-termini in an overlapping fashion to produce a four-armed tetramer (7s domain) and a carboxyl(C)-terminal globular domain (NC-1) of a given monomer which attaches to the same domain of another monomer to form a linear dimer.
Application of slow-scan CCD cameras in routine biological TEM
Authors: Mooney P.E. , Krivanek O.L. , Ray D.A. , Charlesworth J.
Published: June 2020

Slow scan CCD (charge-coupled device) cameras (SSCs) are based on image detection technology introduced in the seventies and first used in astronomy in the eighties. When they are properly configured for the detection of medium energy electrons rather than photons, they are able to capture images whose quality exceeds the quality of images recorded on photographic film. Here we discuss aspects of their operation pertinent to routine biological TEM.

Compared to the TV-rate CCD sensors that have become ubiquitous in miniature camcorders, scientific (astronomy-grade) CCDs have several unique characteristics: 1) their pixels are typically 20-27 μm in size rather than the 6 μm typical of TV rate CCDs, 2) their read-out amplifiers are optimized for low noise at read out rates of 1/10 to 1/100 of TV rate, 3) they do not have a separate frame-transfer buffer for CCD read-out, and 4) they are available in large total sizes (up to 2048 × 2048 pixels).
Biomimetic materials: An introduction
Authors: Sarikaya M. , Staley J. T. , Aksay I. A.
Published: June 2020

Biomimetics is an area of research in which the analysis of structures and functions of natural materials provide a source of inspiration for design and processing concepts for novel synthetic materials. Through biomimetics, it may be possible to establish structural control on a continuous length scale, resulting in superior structures able to withstand the requirements placed upon advanced materials. It is well recognized that biological systems efficiently produce complex and hierarchical structures on the molecular, micrometer, and macro scales with unique properties, and with greater structural control than is possible with synthetic materials. The dynamism of these systems allows the collection and transport of constituents; the nucleation, configuration, and growth of new structures by self-assembly; and the repair and replacement of old and damaged components. These materials include all-organic components such as spider webs and insect cuticles (Fig. 1); inorganic-organic composites, such as seashells (Fig. 2) and bones; all-ceramic composites, such as sea urchin teeth, spines, and other skeletal units (Fig. 3); and inorganic ultrafine magnetic and semiconducting particles produced by bacteria and algae, respectively (Fig. 4).
The identification of magnetic minerals and other selfassembled structures within magnetotactic bacteria using Electron Microscopy and related micro-techniques
Authors: Bazylinski Dennis A. , Garratt-Reed Anthony J. , Frankel Richard B.
Published: June 2020

Magnetotactic bacteria are a diverse group of procaryotes whose direction of motility is influenced by magnetic fields. These organisms are ubiquitous in aquatic habitats and contain unique intracellular iron-rich membrane-bounded inclusions called magnetosomes that are responsible for the cells’ magnetic behavior. The composition, size (40-100 nm), morphology, position, and orientation of the particles appear to be highly controlled by these bacteria. Ferrimagnetic magnetite (Fe3O4), greigite (Fe3S4), and pyrrhotite (Fe7S8) and nonmagnetic pyrite (FeS2) have been identified as the mineral phases of the magnetosomes in different bacteria. These organisms also contain other intracellular structures that reflect aspects of their physiology, metabolism, and ecology. In order to determine the external structural features of cells and the composition and structure of their intracellular inclusions, transmission electron microscopy (TEM), scanning-transmission electron microscopy (STEM), energy-dispersive x-ray detection (EDXA), and selected area electron diffraction (SAED) techniques were employed.

The results of a typical electron microscope (EM) and microanalytical study of a Fe3O4-producing magnetotactic bacterium is shown in Figures 1-4. This unidentified organism, designated strain MV-4, was isolated from sulfide-rich water and sediment collected from a salt marsh.
Design and calibration of an IVEM for general 3-dimensional imaging of non-diffracting materials
Authors: Rowlands Neil , Price Jeff , Kersker Michael , Suzuki Seichi , Young Steve , Ellisman Mark
Published: June 2020

Three-dimensional (3D) microstructure visualization on the electron microscope requires that the sample be tilted to different positions to collect a series of projections. This tilting should be performed rapidly for on-line stereo viewing and precisely for off-line tomographic reconstruction. Usually a projection series is collected using mechanical stage tilt alone. The stereo pairs must be viewed off-line and the 60 to 120 tomographic projections must be aligned with fiduciary markers or digital correlation methods. The delay in viewing stereo pairs and the alignment problems in tomographic reconstruction could be eliminated or improved by tilting the beam if such tilt could be accomplished without image translation.

A microscope capable of beam tilt with simultaneous image shift to eliminate tilt-induced translation has been investigated for 3D imaging of thick (1 μm) biologic specimens. By tilting the beam above and through the specimen and bringing it back below the specimen, a brightfield image with a projection angle corresponding to the beam tilt angle can be recorded (Fig. 1a).
Three-dimensional reconstruction from dark-field electron micrographs of macromolecules at random unknown angles
Authors: Ottensmeyer F.P. , Farrow N.A.
Published: June 2020

Electron microscopy produces 2D images of 3D objects with resolutions generally from about 2-5 nm for stained or shadowed specimens, to as good as 0.3-0.5 nm for unstained specimens using bright field or dark field techniques. Many groups have worked on methods that attempt to recover the 3D information that is lost in the 2D representation. We have built on and extended previous techniques, and report here the development and application of a robust, unbiased quaternion-based alignment procedure to facilitate 3D reconstruction of molecules imaged at random unknown orientations. The approach is demonstrated using dark field electron micrographs of the Klenow fragment of DNA polymerase.

Many procedures for 3D structure determination using electron microscopy have been reported. For fairly simple, small proteins it has been possible to derive a correct high resolution 3D structure by folding the known amino acid chain using dark field electron micrographs as geometric constraintse.g.. However, in general the reconstruction of a 3D density distribution requires knowledge of the relative orientation of different projection images of the object. To determine such orientations a variety of techniques have been employed, frequently adapted to the specimen of interest.
The discovery of the glass knife
Authors: Latta Harrison
Published: June 2020

We celebrate 500 years of development of the new world following its discovery by Columbus. We also celebrate 50 years of the Electron Microscope Society of America and the exploration of the new world of electron microscopy. A major part of this exploration was the development of techniques for the preparation and sectioning or biologic materials for electron microscopy, which depended on improvements in fixation, staining, embedding, microtomes, and microtome knives.

The story of the glass knife involves serendipity and a Japanese sword. It begins in 1949 when a group of research fellows at the Massachusetts Institute of Technology (MIT) were trying to section tissue for electron microscopy with conventional microtome knives sharpened by hand. One day I had to park my car at the far end of the MIT lot and walk back through several buildings. On my way I passed a metallurgy exhibit which displayed a Samurai sword.
Her garter snapped: Old problems, unique solutions
Authors: Philpott Delbert E.
Published: June 2020

Indiana U. purchased an electron microscope sight unseen for $600, deciding it was an E.M. on the basis of weight. Seeing Dr. Fischer's ad for an assistant, I wondered what an E.M. was. I dashed upstairs to find his office. Having come directly from the airport where I was a pilot, I was dirty and needed a shave. I planned to come back when I had cleaned up. I put my nose against the door to read his small handwriting and office hours. Out he came. We hung together nose to nose as he asked, “Did you want something?” “Poor time to tell you no,” I responded. I got the job in spite of my appearance because, as he told me, I knew photography, could learn the panel on an airplane and wasn't afraid of work. We put the microscope together and it ran ! We set up a summer lab course, but he asked me to teach it when he got a sabbatical. Having signed up, I gave myself an A. I was starting at the top. I felt there was a great future if we could just learn to cut sections. The chairman warned me not to make it my career as it was only one instrument, could go away and I wouldn't be able to make a living at it. To show him, I quit with my Master's Degree and took a job at the U. of Il. Med. School. I learned to cut sections with a tongue depressor (published) and designed an ultramicrotome (published). He was right. At $300/month, I could barely eat hamburger, but I was showing him.