bluuebunny/crossref_metadata_2025 huggingface dataset:
Envelope structure of semliki forest virus reconstructed from projections of randomly oriented single particles visualized by cryo-electron microscopy
Authors: Vogel R.H. , Provencher S.W. , Bonsdorff C.-H. von , Adrian M. , Dubochet J.
Published: June 2020

The basic principles of the architecture of many viral protein shells are now well established and the structure of several viruses have been elucidated to atomic resolution. Enveloped viruses, like Semliki Forest virus (SFV), have been more difficult to study because they resist crystallization and are easily deformed when prepared for electron microscopy. The latter limitation has been coped with by using a cryo-electron microscopy method in which unfixed and unstained viruses are observed in an unsupported thin layer of vitrified suspension. The appearance of the virus depends strongly on the focus (Fig. 1), because, unlike in conventionally stained specimens, the contrast is essentially due to phase contrast. The focus values of the four micrographs in the series, which were used for the reconstruction, have been chosen to give an optimal coverage of the information contained in the specimen (Fig. 2).
Quantitative analysis of freeze fracture morphology of mouse embryo cells treated with retinoids and phorbol esters
Authors: Fassel Theresa A. , Hui Sek-Wen
Published: June 2020

Phenotypic changes in C3H/10T mouse embryo fibroblast cells, induced by retinyl acetate (RAC) or 12-0-tetradecanoylphorbol-13-acetate (TPA) treatments, were studied by freeze fracture electron microscopy. TPA accelerates transformation while RAC suppresses transformation in these cells.

Unfixed cells on glass substrates were rapidly frozen in liquid propane by the sandwich method. Freeze fracture was carried out at -120°C and vacuum better than 5x10-7torr in a Polaron unit equipped with a Perkin-Elmer Ultek ion pump and Cressi ngton electron guns. Intramembraneous particle (IMP) detection and quantitation was done using a Cambridge Instrument Quantimet 920 image analyzer with a macroviewer attachment.
Probing the surface of cultured endothelial cells grown on dextran beads
Authors: Hogan Margaret E.
Published: June 2020

Primary cultures of endothelial cells were grown on cross-linked dextran beads to allow electron microscopic observation of Antithrombin III (ATIII) binding.

Busch and Owen demonstrated a heparin-like, stationary ATIII cofactor on the surface of bovine aorta endothelial cells. This stationary cofactor was found to have several functional properties in common with the anticoagulant glycosaminoglycans (GAGS) heparin and heparitin sulfate. The purpose of this study was to characterize this cofactor and try to determine more about its function.
Effect of osmium vapor on calcium loss during sectioning of freeze-dried, embedded tissue
Authors: McGuffee L. J. , Little S. A.
Published: June 2020

Our laboratory has been using electron microscopic autoradiography to localize 45Ca in smooth muscle. We prepare the tissue for these studies by quick freezing against a copper mirror, freeze-drying at low temperature, exposing the dry tissue to osmium tetroxide vapors in vacuo, and infiltrating and embedding in Spurr resin.

Two requirements must be met before one can examine the distribution of a soluble ion, such as calcium, using this, or any morphological technique. First, morphological perservation of the tissue must be sufficient to identify cellular organelles and membranes. This requirement can be met in smooth muscle by using freeze-dried Spurr embedded tissue. Second, the distribution of calcium must be representative of the in vivo distribution.
Ultrastructure of neuromuscular relationships in the canine heartworm (dirofilaria immitis)
Authors: Steffens W. L. , Roberts Nancy B. , Bowen J. M.
Published: June 2020

The canine heartworm is a common and serious nematode parasite of domestic dogs in many parts of the world. Although nematode neuroanatomy is fairly well documented, the emphasis has been on sensory anatomy and primarily in free-living soil species and ascarids. Lee and Miller reported on the muscular anatomy in the heartworm, but provided little insight into the peripheral nervous system or myoneural relationships. The classical fine-structural description of nematode muscle innervation is Rosenbluth's earlier work in Ascaris. Since the pharmacological effects of some nematacides currently being developed are neuromuscular in nature, a better understanding of heartworm myoneural anatomy, particularly in reference to the synaptic region is warranted.
Fecal peritonitis: Microbial colonization of the serosal mesothelium following cecal ligation and puncture
Authors: Edmiston Charles E. , Jones Frank E. , Kornhall Sven , Goheen Michael P. , Condon Robert E.
Published: June 2020

Intrusion of colonic flora within the peritoneal cavity is a serious and potentially life threatening event. In spite of the available arsenal of antimicrobial agents mortality ranges from 10 to 20%. In the present study the cecal ligation and puncture (CLP) model of fecal peritonitis was used to investigate: (A) Microbial colonization of the serosal surfaces following bowel perforation and (B) The utility of peritoneal lavage to reduce the microbial populations which reside on the serosal mesothelium.
Structure and chemistry of silicon carbide whisker surfaces
Authors: Allard L. F. , Pendleton P. , Brinen J. S.
Published: June 2020

Silicon carbide whiskers are of interest as dispersed phase strengthened in metals, ceramics, and polymer composites. Characterization of whisker structure, including surface morphology, crystallography and chemistry, is important so that whisker models can be devised on which calculations of surface energetics controlling wetting/bonding phenomena can be accurately based. In current work, the microstructures of several commercially-available SiC whisker types have been characterized by high resolution TEM and surface analysis techniques. Results of the characterization of one manufacturer's whiskers, Tateho Chemical Industries, are described in this paper.
Breakaway oxidation in Fe-9Cr: Chemical or mechanical initiation?
Authors: Newcomb S.B. , Stobbs W.M.
Published: June 2020

Fe-9Cr alloys are used in the power generation industry and are subject to oxidation in carbon dioxide based environments. Here protective duplex oxides are generally formed though after long periods of exposure accelerated oxidation may occur with the formation of “breakaway” scales. The primary question is whether breakaway occurs as a result of simple mechanical rupturing of the pre-existing oxide or alternatively, whether it derives from inherent chemical instabilities within the scale. While a variety of models have been proposed for breakaway behaviour, it is generally assumed that a build up of stresses as well as significant deposition of carbon occurs within the scale during the oxidation process. Accordingly, we have attempted to characterize the microstructures involved in order to clarify the evidence for the variety of assumptions made. We have therefore used transmission electron microscopy to examine in cross-section both a breakaway and a pre-breakaway scale, as formed on Fe-9Cr in 1%Co-CO2 at 600°C. Our results indicate that different parts of the scales may be in various stress, and sometimes stress cycled, states at different times. More interestingly, we also present evidence to suggest that breakaway may be initiated by purely chemical processes.
Electron microscopy of alpha-plutonium
Authors: Staudhammer K. P. , Johnson K. A. , Stevens M. , Medina W. J.
Published: June 2020

During the past several decades metallurgists world-wide have sought for a reliable and reasonable method to characterize plutonium and its alloys via transmission electron microscopy. Metallurgically, plutonium (Pu) represents one of the most fascinating metals; it has six solid phases and contracts when melted.

A number of workers over the years have tried to produce thin foils of plutonium, but the foils were later shown to have been completely converted to oxide. The primary problem has been in the preparation of electron transparent thin foils of a material having one of the highest atomic numbers that is highly oxidation prone, in addition to being radioactive. Advances in Pu metallography in the late 70's and early 80's produced a new series of electro-chemical thinning solutions modified for plutonium.
NbCN precipitation during solidification of HSLA steels
Authors: Burke M.G. , Pottore N.S. , DeArdo A.J.
Published: June 2020

A TEM/STEM investigation has been directed towards improving the quality of continuously cast HSLA steels. The considerable economic advantages to be derived from continuous casting of HSLA steels is being arrested by the greatly reduced hot-ductility of the con-cast structures. Therefore, to determine the cause of this reduction in ductility, a microstructura1 investigation was conducted using unidirectiona11y solidified ingots to simulate the continuous casting process. This is part of an ongoing research program on Nb-bearing HSLA steels.
Electron diffraction analysis of the pentagonal arrangement of grains found in CVD Pure Ni films
Authors: Campbell Ann N. , Carr Martin J. , VanderSandet John B.
Published: June 2020

The microstructure of 25-500 μm-thick, pure-Ni films formed by chemical vapor deposition on copper substrates at 180°C is complex, consisting of areas of a fine, heavily faulted structure and of relatively larger grains, 1-3 μm in diameter. The large grains have a <110> axis parallel to the growth direction and are frequently twinned. Pentagonal arrangements of the large grains, Figure 1, were commonly observed by transmission electron microscopy. Similar microstructural features have been reported to form during vapor deposition of other FCC metals, and have been shown to possess a true five-fold axis developed by twinning and distorting small crystals.
Quadrupole/YAG Coupling of a parallel-recording system to a commercial energy-loss spectrometer
Authors: Egerton R.F. , Crozier P.A.
Published: June 2020

We have interfaced a Tracor DARSS detector head to a Gatan 607 energy-loss spectrometer to produce a parallel-recording system operating in the indirect-exposure mode. Magnetic quadrupole lenses were used to increase the electron-optical dispersion by a factor of at least 20. These quadrupoles had a large bore (2 cm) and were mounted outside the vacuum (see Fig.1) to allow easy relocation so that various electron-optical arrangements could be investigated.

The most economical scheme requires only a single quadrupole, placed close to the spectrometer exit, operating from a virtual object and forming a non-inverted spectrum at the conversion screen.
A side-entry high-precision tilt stage for a high-voltage Electron Microscope
Authors: Turner J.N. , Barnard D.P. , Matuszek G. , See C.W.
Published: June 2020

A high precision specimen stage is essential for the accurate recording of images for three-dimensional reconstruction. The efficient calculation and resolution of a “tomographic type” three-dimensional reconstruction is influenced by the precision of the angular tilt settings. The ability to identify structures at low magnification and later return to them for detailed study at high magnification is crucial to the efficient study of structures by serial section reconstruction, and is greatly aided by a precise, repeatable translation stage. To study such problems, we have designed and fabricated a single-tilt specimen stage for our high-voltage electron microscope (HVEM), which represents a different design philosophy to that usually employed in side entry stages for transmission electron microscopes.
Experiments with a scanning tunneling microscope (STM) mounted in a scanning electron microscope (SEM)
Authors: Wells Oliver C. , Welland Mark E.
Published: June 2020

Scanning tunneling microscopes (STM) exist in two versions. In both of these, a pointed metal tip is scanned in close proximity to the specimen surface by means of three piezos. The distance of the tip from the sample is controlled by a feedback system to give a constant tunneling current between the tip and the sample. In the low-end STM, the system has a mechanical stability and a noise level to give a vertical resolution of between 0.1 nm and 1.0 nm. The atomic resolution STM can show individual atoms on the surface of the specimen.

A low-end STM has been put into the specimen chamber of a scanning electron microscope (SEM). The first objective was to investigate technological problems such as surface profiling. The second objective was for exploratory studies. This second objective has already been achieved by showing that the STM can be used to study trapping sites in SiO2.
Near-field scanning optical microscopy
Authors: Betzig E. , Harootunian A. , Isaacson M. , Lewis A.
Published: June 2020

In general, conventional methods of optical imaging are limited in spatial resolution by either the wavelength of the radiation used or by the aberrations of the optical elements. This is true whether one uses a scanning probe or a fixed beam method. The reason for the wavelength limit of resolution is due to the far field methods of producing or detecting the radiation. If one resorts to restricting our probes to the near field optical region, then the possibility exists of obtaining spatial resolutions more than an order of magnitude smaller than the optical wavelength of the radiation used. In this paper, we will describe the principles underlying such "near field" imaging and present some preliminary results from a near field scanning optical microscope (NS0M) that uses visible radiation and is capable of resolutions comparable to an SEM. The advantage of such a technique is the possibility of completely nondestructive imaging in air at spatial resolutions of about 50nm.
High-resolution signal detection of specimen-specific secondary electrons in an analytical SEM
Authors: Apkarian R.P.
Published: June 2020

Field emission scanning electron microscopy (SEM) has produced high resolution images of secondary electron-I (SE-I) edge brightness contrast on small particles by the elimination of SE-III produced from backscattered electrons (BSE) within the microscope (SE-I image mode). The resolution of surface fine structure at high magnification is dependent upon signal type and collection efficiency, beam diameter and current, acceleration voltage, and the topography of the specimen. In an analytical SEM, an efficient detector placed above the objective lens specimen stage and a high brightness LaB6 emitter create a collection condition of specimen specific SE useful for imaging SE-I contrast. In the present study a test specimen of uncoated colloidal gold, ferritin and Tobacco Mosiac Virus (TMV) deposited onto silicon was used to determine conditions required for imaging edge brightness contrasts on the gold particles.
A Scanning Electron Microscopic study of hematite inclusions in cordierite porphyroblasts
Authors: Mitchell J.N.
Published: June 2020

Porphyroblasts are monocrystalline to polycrystalline mineral grains in metamorphic rocks that are distinctly larger than the matrix grain surrounding them. Their presence reflects the metamorphic release and rapid diffusion of their chemical components, with subsequent crystallization at limited nucleation sites. Small inclusions of other minerals are often present in porphyroblasts, especially in members of the garnet group, staurolite, and cordierite. Various hypotheses may be suggested to explain such inclusions: (1) they are relics of earlier grains, either of the protolith or of a stage of metamorphism prior to porphyroblast growth; (2) they are reaction residues of the mineral grains that decomposed to form the porphyroblasts; or (3) they are decomposition products produced from the porphyroblasts by secondary or retrograde metamorphism.
A library of convergent-beam electron diffraction patterns
Authors: Mansfield John F.
Published: June 2020

One of the most important advancements of the transmission electron microscopy (TEM) in recent years has been the development of the analytical electron microscope (AEM). The microanalytical capabilities of AEMs are based on the three major techniques that have been refined in the last decade or so, namely, Convergent Beam Electron Diffraction (CBED), X-ray Energy Dispersive Spectroscopy (XEDS) and Electron Energy Loss Spectroscopy (EELS). Each of these techniques can yield information on the specimen under study that is not obtainable by any other means. However, it is when they are used in concert that they are most powerful. The application of CBED in materials science is not restricted to microanalysis. However, this is the area where it is most frequently employed. It is used specifically to the identification of the lattice-type, point and space group of phases present within a sample. The addition of chemical/elemental information from XEDS or EELS spectra to the diffraction data usually allows unique identification of a phase.
Convergent-beam diffraction and x-ray analysis of the lamellar structure in the Dayton meteorite
Authors: Kowalik J. A.
Published: June 2020

The phase transformation resulting in a lamellar morphology found in the iron meteorite Dayton (18 wt% Ni-Fe) has been investigated using analytical electron microscopy (AEM). The transformation is unique to the Dayton meteorite since in other iron meteorites of similar composition and cooling history, only the classical Widmanstätten structure is present consisting of ferritic (α-BCC) plates precipitating on the (111) planes of the prior austenite (γ-FCC). However, in some areas of Dayton, the structure changes from the classical Widmanstätten pattern to a lamellar morphology. As a first step in understanding the mechanisms of the precipitation reactions, convergent beam electron diffraction (CBED) and x-ray energy dispersive spectrometry (XEDS) have been used to examine the crystallographic orientation and composition of the α/γ interface of the Widmanstätten and lamellar morphology.
A technique to prepare cross-sectional TEM specimens of semiconducting devices
Authors: Rai A. K. , Pronko P. P.
Published: June 2020

Several techniques have been reported in the past to prepare cross(x)-sectional TEM specimen. These methods are applicable when the sample surface is uniform. Examples of samples having uniform surfaces are ion implanted samples, thin films deposited on substrates and epilayers grown on substrates. Once device structures are fabricated on the surfaces of appropriate materials these surfaces will no longer remain uniform. For samples with uniform surfaces it does not matter which part of the surface region remains in the thin sections of the x-sectional TEM specimen since it is similar everywhere. However, in order to study a specific region of a device employing x-sectional TEM, one has to make sure that the desired region is thinned. In the present work a simple way to obtain thin sections of desired device region is described.
Scanning Electron Microscopy-based sub-micron spectroscopies
Authors: Russell Phillip E.
Published: June 2020

The scanning electron microscope provides a convenient mechanism for utilizing a sub-micron focused electron probe as a basis for many diverse spectroscopies. While the main use of an SEM is high resolution and/or large depth of field imaging of topographical features, the same system can be used to locate an electron probe, with spot size as small as 1 nm, on a region of interest, and with approiate spectrometers and detectors, sub-micron spectroscopies of the many signals produced by the interaction of the electron beam with the solid sample can be performed. Of the many signals produced in a typical SEM, the following is a review of the ones which have been utilized as the basis of a sub-micron spectroscopy.
Atomic Spectroscopy in the FIM
Authors: Hren J. J. , Walck S. D.
Published: June 2020

The field ion microscope (FIM) has had the ability to routinely image the surface atoms of metals since Mueller perfected it in 1956. Since 1967, the TOF Atom Probe has had single atom sensitivity in conjunction with the FIM. “Why then hasn't the FIM enjoyed the success of the electron microscope?” The answer is closely related to the evolution of FIM/Atom Probe techniques and the available technology. This paper will review this evolution from Mueller's early discoveries, to the development of a viable commercial instrument. It will touch upon some important contributions of individuals and groups, but will not attempt to be all inclusive. Variations in instrumentation that define the class of problems for which the FIM/AP is uniquely suited and those for which it is not will be described. The influence of high electric fields inherent to the technique on the specimens studied will also be discussed. The specimen geometry as it relates to preparation, statistical sampling and compatibility with the TEM will be examined.
SbC15 intercalated graphite
Authors: Mittleman R. K. , Parker N. W.
Published: June 2020

SbC15 intercalated graphite is one of the most widely studied of the graphite intercalated compounds. The reasons for this are that upon intercalation SbC15 undergoes the dissociation reaction:

3SbC15 + 2e- ⇒ 2SbC16- + SbCl31

consequently the physical properties of the compound are not merely a superposition of the parent material. SbC15-graphite compounds are also among the most stable of the graphite intercalants.
Electron microscopy of a triblock copolymer molecular composite
Authors: Haddock T. , Krause S. J. , Adams W. W.
Published: June 2020

Molecular composites are a new class of structural polymers which are high-strength, high-modulus, thermally stable, and environmentally resistant. A rigid-rod, extended chain polymer component is used to reinforce a matrix of flexible, coil-like polymer component with the intent of achieving a composite on the molecular level. The critical factor in processing a molecular composite is that the rod-like reinforcing component be well dispersed and not phase separate from the matrix component. We previously reported on the morphology of a molecular composite from a physical blend of rigid-rod and flexible-coil homopolymers. In this paper we are reporting on the morphology of a rigid-rod, flexible-coil, triblock copolymer processed by vacuum casting or fiber spinning from a dilute solution.
Electron microscopy of dilute solutions of emulsifier
Authors: Shaffer O.L. , El-Aasser M.S. , Vanderhoff J.W.
Published: June 2020

Emulsion polymerization is usually carried out using a mixture of monomer(s) into an aqueous solution of emulsifier(s) of the type suitable for making an oil-in-water emulsion. The monomer is then polymerized using a free-radical initiator. The final product is a colloidal dispersion of polymer spheres in water, i.e. a latex stabilized by the adsorbed emulsifier molecules. An emulsifier such as an alkyl sulfate dissolved in water will form micelles at a critical concentration (CMC). Because of unfavorable alkyl chain-water interactions, the interior of the micelle would be similar to a liquid hydrocarbon and the head group therefore must be at the alkyl chain-water interface. Several techniques have provided information about the size and shape of micelles in particular quasi-elastic light scattering (QELS).
The formation of hydrogen phases on twin boundaries in Si
Authors: Vanderwalker D. M.
Published: June 2020

When a Si crystal is placed in a hydrogen plasma, H ions diffuse into the crystal and passify dangling bonds at point defects, dislocations, and grain boundaries. The H passivation changes the electrical properties of silicon. The nucleation of H-Si solid second phases was not discussed before this experiment, although H-Si complexes were thought to form. This study is of the formation of H phases on twins in silicon.

A Si sample, which was compressed along a <231> axis at 420°C and cooled under a high stress, was placed in a closed gas discharge tube between Pt electrodes. The pressure of the H gas was less than one torr. A hydrogen plasma was produced when 440 volts were applied at 180°C and maintained for 90 minutes.
Charging microscopy and cathodoluminescence imaging of semi-insulating gallium arsenide
Authors: Sheu T.C. , Myhajlenko S. , Davito D. , Edwards J.L. , Roedel R. , Krause S.J.
Published: June 2020

Liquid encapsulated Czochralski (LEC) semi-insulating (SI) GaAs has applications in integrated optics and integrated circuits. Yield and device performance is dependent on the homogeniety of the wafers. Therefore, it is important to characterise the uniformity of the GaAs substrates. In this respect, cathodoluminescence (CL) has been used to detect the presence of crystal defects and growth striations. However, when SI GaAs is examined in a scanning electron microscope (SEM), there will be a tendency for the surface to charge up. The surface charging affects the backscattered and secondary electron (SE) yield. Local variations in the surface charge will give rise to contrast (effectively voltage contrast) in the SE image. This may be associated with non-uniformities in the spatial distribution of resistivity. Wakefield et al have made use of “charging microscopy” to reveal resistivity variations across a SI GaAs wafer. In this work we report on CL imaging, the conditions used to obtain “charged” SE images and some aspects of the contrast behaviour.
Scanning Electron Microscopy of PLZT powders precipitated from nitrate solutions, and confirmation of population balance studies
Authors: Eichorst D. J. , Payne D. A.
Published: June 2020

Lead lanthanum zirconium titanate (PLZT) ceramics are used in many electrooptic devices which require optical transparency and uniform microstructure. In order to obtain the required chemical homogeneity, purity, stoichiometry, particle/grain sizes, chemical precipitation techniques are used. However, the relationship between precipitation parameters, powder morphology and microstructure are poorly understood. For a continuous precipitator, a population balance may be carried out relating size, initial quantity and growth rate for crystallites, clusters and agglomerates for residence time in the reactor. In this terminology, clusters are groups of primary crystallites, and agglomerates are groups of clusters or clusters with added crystallites. The purpose of this investigation was to evaluate the suitability of population balance studies for the characterization of PLZT powders produced by chemical precipitation methods.
Microstructural examination of tetragonal - YTTRIA stabilized zirconia
Authors: Baskaran S. , Buchanan R. C.
Published: June 2020

Solid solutions of ZrO2 with small amounts of Y2O3 can stabilize the tetragonal and cubic phases which are formed at high temperature. Fullystabilized cubic ZrO2, owing to its high oxygen-ion mobility, is commonly used as solid-state electrolytes in oxygen monitors. Partially-stabilized ZrO2, containing metastable tetragonal particles in a cubic matrix, has good mechanical and thermomechanical properties. Tetragonal-Yttria-Stabilized Zirconia containing 2-3 mol% Y2O3 with sub-micron grain structures exhibits even higher strengths of the order of 1 GPa and good ionic conductivity. The tetragonal phase stability at low to moderate temperatures (<400°C) as well as mechanical and electrical properties are closely related to the microstructure, particularly grain size and distribution and the nature of the intergranular phase. In this study, heat-treatment effects on microstructure and phase stability in 2 mol% YSZ were investigated.
Coprecipitation between binary carbonates of alkaline earth elements at 90 C
Authors: Takiyama K.
Published: June 2020

The coprecipitation of two compounds in the aqueous solution has been studied by means of electron microscopy and X-ray diffraction techniques and the morphological and crystallographic properties of the coprecipitated particles were discussed from the viewpoint of crystal chemistry. In the present investigation the coprecipitation of binary carbonates such as CaCO3-SrCO3, SrCO3-BaCO3 and BaCO3-CaCO3 was studied. Calcium carbonate precipitated as aragonite at high temperature in aqueous solution. Strontium and barium. carbonates precipitated as aragonite type crystals regardless of the reaction temperature. The particles of CaCO3, SrCO3 and BaCO3 produced at 90°C were generally rod-shaped and the sizes were related to the solubilities of the precipitates (Fig. 1). The solubility products of CaCO3, SrCO3 and BaCO3 at 90 C were 7x10-11, 2.1x1011 and 2.9x10-8 respectively.
A Scanning Electron Microscopic evaluation of tensile fracture in a heavily filled epoxide-matrix particulate composite
Authors: Montes-G G. M. , Draughn R. A.
Published: June 2020

Particle reinforcement of glassy amorphous polymers with rigid fillers increases the stiffness and fracture resistance measured by the critical stress intensity factor for crack propagation (K1c). The tensile strength and fatigue properties, however, decrease with increasing concentrations of fillers and strongly depend on the degree of filler/matrix adhesion. Treatment of filler surfaces with coupling agents, typically organo-silane compounds, serves to increase the fracture resistance of the materials in aqueous environments. The objective of this study is to define tensile fracture processes as a part of work to improve the properties of the materials in an aggressive environment.
Magnetic sandwiches: Adjustment between gold and cobalt layers
Authors: Cesari C. , Renard D. , Nihoul G.
Published: June 2020

The behaviour of thin films of ferromagnetic metals have received a lot of attention recently new properties induced by the quasi-bidimensionality of the lattice can be exhibited. Here we have performed some studies on thin Cobalt layers protected from oxidation by 2 Gold films orientated with their surfaces roughly parallel to (111) planes Details about the preparation and characterization of these "sandwiches" are given in: the hexagonal structure of the Cobalt layer has been proved and this can be related to the existence of an easy magnetization axis perpendicular to the film (ie parallel to the c axis) and of a large magnetic anisotropy constant.
Resolution vs specimen thickness comparison of 100kV, 200kV, and 1000kV electron microscopes using semithick sections
Authors: Cole R. W. , Marko M.
Published: June 2020

We have found that micrographs of conventional epoxy sections up to 0.25 μm in thickness taken at either 200 kV or 1000 kV are of equally good quality, although at some thickness beyond 0.25 μm there is a rapid divergence in quality. We note that even lOOkV microscopes can be used with sections up to about 0.5 μm for prescreening grids to be viewed on higher voltage instruments.

Although several papers have been published dealing with resolution at different specimen thicknesses and/or different accelerating voltages, we are not aware of data relating to the maximum useful specimen thickness for biological work at 200 kV. Only one paper involved biological specimens using acclerating voltages lower than 400 kV.
Characterization of magnetic microstructure at high spatial resolution
Authors: Scheinfein M.R.
Published: June 2020

Advances in metal epitaxial growth techniques have produced renewed interest in magnetic materials through the unique properties of novel atomically engineered structures. Ultrathin layered and nanocrystalline, textured composites possess unique magnetic properties which are intimately connected to the physical microstructure on both the atomic and nanometer length scales. The length scales present in magnetic interactions span several orders of magnitude from the atomic length scales of the exchange interaction, to the mesoscopic length scales important in anti-ferromagnetic RKKY coupling between thin ferromagnetic films and small particles, to the macroscopic length scales determined by the long range magnetostatic interactions which are responsible for the formation of magnetic domains.

Special characterization and computation techniques are required to analyze the micromagnetic and microstructural properties of these novel, low dimensional systems. In order to correlate the structure with the magnetic properties of any system, in-situ growth, structural, chemical and magnetic characterization is desirable.

Most methods used for the observation of micromagnetic structure rely on a contrast mechanism derived from the magnetic fields present in ferromagnetic systems. We have implemented the conventional Fresnel, and less conventional Differential Phase Contrast modes of imaging magnetic microstructure in an HB5 STEM.
Ultrastructural effects of manganese in cultured heart cells
Authors: Winter Kerri
Published: June 2020

Manganese (e.g. Mn2+, Mn gluconate, Mn-DPDP) has been used as a contrast reagent for magnetic resonance imaging of liver and myocardial perfusion. In addition, Mn has been used to block the voltage-dependent calcium channel, interfere with excitation-contraction coupling, and inhibit Na/Ca exchange. Although Mn has proved useful in both clinical and research settings, little information is available about its effects on cell structure. Therefore, we examined the effects of Mn on ultrastructure in a model system of cultured embryonic chicken heart cells.

Free-floating cardiac myocyte aggregates were cultured from 11 day-old chick embryos. Aggregates were incubated with a HEPES/TRIS-buffered salt solution containing various concentrations of MnCl2 (0, 1, 20 mM) for 5 min at 37°C. Following incubation, buffer solution was removed, aggregates were chemically fixed in glutaraldehyde and processed for routine electron microscopic analysis. Parallel studies on confluent myocytes were conducted to assess the Mn uptake by atomic absorption spectroscopy.
Distribution and modulation of ion channel and receptor topography on nerve cell surfaces
Authors: Angelides Kimon J. , Hicks Barry
Published: June 2020

The distribution of ion channels and receptors over the neuronal surface is important for the receipt of incoming synaptic inputs and for the integration of these inputs. Most voltage-gated and ligand-gated ion channels have non-homogeneous distributions in the neuronal membrane, many being restricted to either dendritic, axonal or somatic domains and further localized within these domains to regions such as dendritic spines, nodes of Ranvier or synaptic junctions (1-3). For example voltage-dependent calcium channels are localized and immobilized on dendrites (4), while voltage-dependent sodium channel are localized on axon hillocks (5) and nodes of Ranvier. Determining where and how ion channels are distributed and maintained is important for a variety of reasons. Ion channels in growth cones have a role in neurite outgrowth mechanisms (6), they are obligatory for synaptic transmission and they are required for amplification of neurotransmitter signals in the post synaptic membrane (7). Changes in ion channel distributions are an important aspect in development and plasticity (8,9).
Reflections on the life and science of Russell L. Steere
Authors: Erbe Eric F. , Wergin William P.
Published: June 2020

During the early years of electron microscopy a variety of techniques were developed to visualize biological samples. Nearly forty years ago Dr. Russell L. Steere conceived and developed a method, which became widely known as “freeze-etching”, that could be used to image virus crystals. Since this technique was first demonstrated, further refinements, developments and applications have advanced our knowledge of biological ultrastructure to the macromolecular level. Until recently, use of freeze-etching was confined to TEM observations; however, today variations of the technique are being combined with the use of cryostages on SEMs to observe replicas or coating films on the surface of frozen hydrated specimens. Scanning probe microscopies are also utilizing the freeze-etch replicas to image ultrastructural detail. Not only is freeze-etching an effective preparative technique for the various forms of microscopy that are currently pushing the limits of resolution but it provides an excellent tool for advancements in the future as well.
Jet freezing of cells and tissues with and without cryoprotectants
Authors: Parthasarathy M.V. , Daugherty Carole , Müller T.
Published: June 2020

For the past several years cryofixation/freeze-substitution techniques have become valuable alternatives to chemical fixation of biological specimens. The superiority of cryofixation in preserving labile cell structures has been documented in several studies. Commercially available jet freezers and the BAL-TEC HPM010 high pressure freezer have extended high quality cryofixation from monolayer cells to cells relatively deep inside tissues. High pressure freezing can theoretically freeze biological materials of 0.5 mm thickness without the use of cryoprotectants and propane jet freezing is reported to freeze biological samples up to 40 μm in thickness without cryoprotection. Although high pressure freezing is the obvious method of choice for freezing large biological samples, its high cost combined with its apparent inability to consistently preserve microfilaments in some plant cells has prompted us to explore the capability of jet freezing to yield well frozen samples with and without cryoprotectants.

We used the commercially available jet freezer JFD 030 (BAL-TEC) to obtain our results. Tightly pelleted cells sandwiched between 0.1 mm thick copper specimen carriers normally froze well without any cryoprotectants, after propane jet freezing (Figs. 1-2).
High-pressure freezing improves quantitative and qualitative structural data in the actinomycete microsymbiont frankia
Authors: Howard Berg R.
Published: June 2020

Symbiotic plant root nodules containing the nitrogen-fixing bacterium Frankia occur on a variety of woody shrubs and trees. Ever since the first micrographs of freeze substituted cells of Frankia in culture were published there has been impetus to see if freeze substitued nodule tissue will improve imaging of Frankia in vivo. High pressure freezing/freeze substitution (HPFS) accomplishes this.

Frankia is an actinomycete that fixes N2 in a specialized multicellular, spherical structure termed the “symbiotic vesicle” that is surrounded by a multilamellate envelope (MLE) comprised of lipids. Early work based on MLE birefringence suggested the MLE was a O2 diffusion barrier, thereby protecting nitrogenase from O2- inactivation. Recently this has been challenged by freeze fracture data. Traditionally it has been assumed that the MLE is electrontranslucent because the lamina of the MLE are extracted by dehydration solvents, producing the “void space”--an extraction artifact hindering TEM analysis of MLE structure.

En bloc staining with chromic acid stains the MLE, showing that the MLE is present after exposure to dehydration solvents and that the void space results from tissue shrinkage in the symbiotic vesicle (Figure 1).
Electron Microscopy immunocytochemistry following cryofixation by high-pressure freezing and Low-temperature embedding
Authors: McDonald Kent , Morphew Mary K. , McIntosh J.R.
Published: June 2020

A look at recent journals publishing cell and developmental biology papers shows that localization of antigens by immunoEM techniques is becoming increasingly popular. One can also see that a wide variety of immunoEM methods are being applied: pre-embed and post-embed labelling, cryofixation and room temperature fixation, cryosections and resin sections, LR White and Lowicryl resins, 5 - 10 nm gold and silver-enhanced 1 nm gold, and so on. This array of choices can be confusing to investigators unfamiliar with EM techniques but wanting to do EM immunolocalization of their antibodies. A very helpful overview of the problems can be found in the article by Kellenberger and Hayat and in the series of books on colloidal gold methods edited by Hayat. In this presentation, we will consider the different ways to fix cells for immunoEM and our experience with LR White and Lowicryl K4M resins.
Use of platinum shadowing and magnetron sputter coating in an Oxford Cryotrans system to increase low temperature resolution of biological samples in a Hitachi field-emission Scanning Electron Microscope
Authors: Wergin William P. , Erbe Eric F. , Robins Alan
Published: June 2020

Previous studies in this laboratory have shown that the resolution of biological specimens could be increased at least two fold in a conventional as well as a field emission SEM by substituting high vacuum evaporation of Pt for standard sputter coating. Because the EMscope SP2000A Sputter Cryo System and the Oxford CT 1500 Cryotrans System, which were used in these experiments, employed standard sputter coating, Pt shadowing and C evaporation were carried out in a modified Denton DFE-3 freeze-etch module on a DV-503 high vacuum evaporator and the coated specimens were transferred to the cryostage (EMscope) or the prechamber (Oxford) of the cryosystem. Not only did this procedure require a high vacuum evaporator but as a result of a through air transfer into LN2, considerable contamination condensed on the surface of the specimen. Most of this contamination consisted of water ice that could be easily sublimed; however, other unidentifiable contaminants remained. To increase the versatility of the cryosystem, reduce surface contamination of the specimen and evaluate alternative coating procedures, Oxford Cryotrans Systems were equipped and tested with a Pt evaporator and a high resolution magnetron sputter head. Low temperature observation and evaluation of the coated specimens were performed in a Hitachi S4100 field emission scanning electron microscope.
The influence of confocal microscope design on imaging performance
Authors: Sheppard C J R
Published: June 2020

The confocal microscope is now widely used in both biomedical and industrial applications for imaging, in three dimensions, objects with appreciable depth. There are now a range of different microscopes on the market, which have adopted a variety of different designs. The aim of this paper is to explore the effects on imaging performance of design parameters including the method of scanning, the type of detector, and the size and shape of the confocal aperture.

It is becoming apparent that there is no such thing as an ideal confocal microscope: all systems have limitations and the best compromise depends on what the microscope is used for and how it is used. The most important compromise at present is between image quality and speed of scanning, which is particularly apparent when imaging with very weak signals. If great speed is not of importance, then the fundamental limitation for fluorescence imaging is the detection of sufficient numbers of photons before the fluorochrome bleaches.
Three-dimensional image reconstruction of fluorescence micrographs without knowing the point spread function
Authors: Holmes Timothy J. , Krishnamurthi Vijaykumar , Liu Yi-Hwa
Published: June 2020

The term blind deconvolution refers to the deconvolution, or deblurring, of a signal (optical, sound, or other) without explicit knowledge of the point spread function (PSF). The PSF is, instead, reconstructed concurrently with the deblurred signal from the collected, noisy data. Blind deconvolution methodologies have been under study for general signal processing applications, such as in restoring phonographs, as early as 1968. Ayers and Dainty have performed pioneering blind deconvolution research for deblurring 2D images, which has been applied to astronomy. Inspired by this earlier blind deconvolution research, we have taken a new approach which is based on maximum likelihood estimation (MLE). Our approach is extended from previous research in applying MLE to positron-emission tomography (PET). A novelty of our research is in the application of MLE and blind deconvolution to 2D and 3D fluorescence microscopy.

The fundamental advantage of the MLE approach over some of the other blind deconvolution approaches is that it is a mathematical optimization approach, wherein the likelihood functional of the collected image data, the fluorescence probe concentration and the PSF is maximized.
Real-time confocal microscopy of the human in vivo cornea
Authors: Masters Barry R. , Thaer Andreas A.
Published: June 2020

A new confocal microscope has several unique features which differentiates it from other in vivo confocal imaging systems.is described. • The light source is a halogen lamp. This source has many advantages over the mercury or xenon arc lamps used in other confocal designs. The mercury or xenon arc lamps have the problem of arc jitter which results in changing illumination intensity. Filters are inserted in the lamp housing to remove both short ultraviolet and infrared light. • The microscope uses standard microscope objectives which are readily interchangeable. Other in vivo confocal systems are limited to a built in objective which is not removable. In these studies we used a Leitz 50X, NA 1.0 water immersion objective.• The detection system consists of an intensitified video camera with video output to a Sony U-matic tape recorder. In parallel with the video recording there is a video monitor in order that the operator can observe in real-time the confocal images of the subject's eye.
Three-Dimensional reconstruction of the synaptonemal complex from pachytene maize meiocytes using Electron Microscopy tomography
Authors: Fung Jennifer C. , Scalettar Bethe A. , Agard David A. , Sedat John W.
Published: June 2020

The synaptonemal complex (SC) is a structure involved in the synapsis of homologous chromosomes during the prophase I stage of meiosis. Although the exact function of the complex is unknown, it has been suggested that one possible role might be to promote recombination by ensuring close synapsis of the homologous chromosomes. In addition, it is thought that the SC may also be required to convert the resulting recombination events into functional chiasmata to provide for proper chromosome segregation at the end of the first stage of meiosis.

The SC structure itself is highly conserved across a variety of species. The organization of the SC is tripartite consisting of lateral, central and transverse elements. Two-dimensional cytological observations have been made to characterize the general features of these SC components. The lateral elements are 300 - 500 Å wide proteinaceous structures which flank the synapsed regions of the chromosome bivalent. Between the two lateral elements is a central region containing the central element commonly characterized as a less dense amorphous structure.
Subcellular distribution of an ethidium bromide/poly r(A-U) complex
Authors: Jamison J.M. , Summers J.L. , Gilloteaux J.
Published: June 2020

Previous results have shown that drug uptake by cells is enhanced when the drug is bound to DNA. Chick embryo fibroblasts (CEF) treated with ethidium bromide (EB) exhibit inhibited cell multiplication, mitochondrial swelling and nucleolar segregation. However, EB-DNA treated CEF cells exhibit a much lower cytotoxicity than the EB-treated CEF cells and the mitochondrial and nucleolar alterations are reversible. Conversely, in Ehrlich ascites tumor cells exposed to EB or EB-DNA complexes, the toxicity of the DNA bound EB (as measured by inhibition of cell multiplication, nucleolar segregation, mitochondrial swelling and intramitochondrial inclusions) is more pronounced and appears earlier after treatment than the EB induced cytotoxicity. More recent results have shown that when EB was combined with double stranded RNA (poly r(A-U)) and then added to human foreskin fibroblasts (HSF), the 50% effective dose of the poly r(A-U) was 154-fold lower. The results of additional studies demonstrated that the enhanced antiviral activity was not due to superinduction of interferon, direct viral inactivation, or host cell cytotoxicity.