bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructures and compositions of oxide films formed on CoCrAlY and Y-ion-implanted CoCrAl alloys
Authors: Sprague J. A , Johnston G. R.
Published: June 2020

Hot stage components in many gas turbine engines require surface coatings to protect them from aggressive atmospheres at elevated temperatures. The most commonly employed protection scheme is to modify the surface composition of the components so that high temperature exposure in an oxidizing atmosphere will produce a dense, slow-growing, and adherent aluminum and/or chromium oxide film. Alloys of the MCrAlX-type, where M = Co, Ni, Fe, or combinations thereof, and X = a highly oxygen-active element such as Y, Hf, or Ce, are widely employed as overlay coatings in these applications. In the present investigation, several microanalytical techniques were applied to examine the mechanisms by which the microstructure and microchemistry of a CoCrAlY coating alloy affects the growth and adherence of protective oxide scales.

Two cast alloy compositions were examined: Co-22Cr-llAl, and Co-22Cr-l1A1- 0.5Y (nominal compositions, wt. %). Selected specimens of the CoCrAl alloy were implanted with 2 × 1016 Y+/cm2 or 5 × 1016 Co+/cm2 at 150 keV.
Radiation damage and phase instability in irradiated stainless steel
Authors: Kenik Edward A. , Lee Eal H.
Published: June 2020

The radiation response of metallic alloys can be strongly dependent on specific solute elements. Void swelling and phase instability of the matrix are two primary concerns in the design of nuclear reactors. A 316 stainless steel, LS1A, with greater than nominal levels of silicon and titanium has been developed which exhibits high resistance to swelling under ion irradiation. The origin of this swelling resistance and the roles of silicon and titanium have been investigated in the current study.

Figure 1 illustrates the evolution of the damage structure in LS1A under nickel ion irradiation at 625°C. At low dose [∽1 dpa, Fig. 1(a)], faulted interstitial dislocation loops (43-nm-av diam) are observed. We have previously reported that significant solute silicon segregation (approaching 7.0 at. %) in the vicinity of the loop fault plane occurs at such doses in LS1A. Below 10 dpa, precipitates appear to replace the loops in similar sizes and densities. At 70 dpa [Fig. 1(b)] there is no swelling and the matrix phase instability has produced ∽5% volume fraction precipitate.
Detection of new co phase morphologies in β-III Ti using transmission electron microscopy
Authors: Pande C. S. , Fatemi M.
Published: June 2020

The to phase transformation in titanium and other alloys has been extensively studied1. This phase has an hep structure with three atoms per cell located at (000), (1/3, 2/3, 1/2) and (2/3, 1/3, 1/2). ‘Isothermal’ ω phase precipitates are oriented in the bec β matrix such that [lll]β ‖ [0001]ω and [110]β ‖ω. In fact four varients of such an ω phase exist oriented in all four [111] directions. Isothermal ω phase has been studied as a displacement controlled growth as distinct from another type of ω phase (as quenched) which is produced by a dif fusionless transformation resulting from a very rapid cooling rate.

Using transmission electron microscopy (TEM) and small angle neutron scattering (SANS) we have detected and identified two previously unreported morphologies in β-III Ti (Ti-11.0 Mo-6.0 Zr-4.5 Sn-0.15 O2). Fig. 1 shows a TEM micrograph of a conventional ‘isothermal’ ω precipitate (obtained by annealing β-III Ti 20 hours at 400°C) imaged in bright field with its diffraction pattern showing hep spots as well as the brighter spots of the bec matrix. The long axis of the precipitates is oriented along a [111] direction.
The microstructure of electrodeposited chromium
Authors: Szirmae A. , Fisher R. M.
Published: June 2020

Electrodeposition of chromium, i.e., chrome plating, is widely used to provide corrosion protection or wear resistance to other materials following fabrication to their finished dimensions and shape. Chrome plate is characterized by hardness as high as 1200 KHN and initially large internal tensile, i.e., contractile, stresses that result in extensive cracking and partial relaxation of the stresses although further electroplating may result in the generation of compressive stresses. These, and other properties of electrodeposited chromium, depend on plating conditions such as current density and bath temperature. Scanning and transmission electron microscopy have been utilized to determine the effects of plating conditions on microstructure.

Chromium was electrodeposited on 4340 steel to a thickness of 100 μm, with a conventional chromic acid solution under the following conditions: Sample A, 30 amp/Dm2 at 55°C, resulting in a bright hard (1150 KHN) coating; Sample B, 120 amp/Dm2 at 85°C, resulting in a dull and softer (650 KHN) coating.
On crystal symmetry and crystal structure determination from high-resolution electron micrographs
Authors: Wood G.J. , Smith David J.
Published: June 2020

Despite the widespread use of high-resolution electron microscopy for characterizing crystalline defects down to the atomic level, the determination of crystal structures ab initio from electron micrographs remains far from straightforward. This is partly because, as well as being focus‐ and thickness‐dependent, images are generally sensitive to both beam and crystal tilt, with 1mrad. of the former typically being sufficient to cause considerable spurious image detail even in very thin (<25Å) crystalline regions. Whilst careful attention to alignment can normally correct for loss of symmetry, the absence of dynamically‐allowed reflections in certain projections due to systematic cancellation results in extreme image sensitivity; these reflections quickly increase in amplitude with any slight relative misalignment. Under these conditions, tilt correction becomes virtually impossible and erroneous conclusions about crystal symmetry are well‐nigh inevitable. Crystal symmetry operators associated with tilt sensitivity are (a) a glide plane normal, and/or (b) a screw axis, perpendicular to the electron beam. All except a few of the lowest symmetry space groups have at least one zone satisfying one, or both of these criteria.
The extinction role for forbidden 200 diffraction spots in silicon and spinel
Authors: Ling P.
Published: June 2020

The conditions for dynamical extinction have been discussed by Cowley, Moodie, Miyake, Takagi, and Fujimoto and by Gjønnes and Moodie. We will extend the analysis used by Gønnes and Moodie for axial glide planes to explain dynamical extinction in crystals with diamond glide planes.

Both the diamond glide plane and the four-fold screw axis are present in crystals which have the Fd3m structure, of which silicon, germanium, and spinel are examples. The diamond glide plane is perpendicular to the x-y plane, passing through (0,⅛,0) as shown by the broken line in Fig. 1.
Stage cooling rates and specimen-transfer facilities of the Duke University cryomicroscope
Authors: Lamvik M.K. , Worsham R.E. , Kopf D.A. , Robertson J.D.
Published: June 2020

A liquid helium cold stage offers unique advantages for biological electron microscopy, including a five-fold reduction in radiation damage, higher ultimate specimen resolution and greater stability for frozen hydrated specimens. Ultra-high vacuum and reduced surface diffusion also reduce specimen contamination to negligible levels. To make efficient use of these advantages in biological studies, however, the microscope must be able to handle a variety of specimens while quickly achieving low temperature.

The cryomicroscope that is currently in operation at Duke University (Fig. 1) was originally designed and built at Oak Ridge National Laboratory as a high-resolution electron microscope with a superconducting objective lens. The well-shielded cryostat for the objective lens assures a low specimen temperature. There are two thermal shields surrounding the liquid helium vessel, each cooled by the venting cold helium gas. The inner shield is at its nominal value, 20°K, at the end of the helium transfer when gas is actively venting from the system; later during routine operation, the inner shield temperature is about 30°K.
Instrumentation at the National Center for Electron Microscopy: The atomic resolution microscope
Authors: Gronsky R. , Thomas G.
Published: June 2020

The Atomic Resolution Microscope (ARM) is one of two unique high voltage electron microscopes at the Lawrence Berkeley Laboratory's National Center for Electron Microscopy (NCEM). This paper reports on the latest results from this new instrument which was manufactured by JEOL, Ltd. to the performance specifications of the NCEM, delivered in January of 1983, and soon to be open to access by the entire microscopy community. Details of its history and development are given in reference 1; its performance specifications are reviewed below.

Adopting as a design definition for resolution the first zero crossover of th% phase contrast transfer function at Scherzer defocus, the ARM (Fig. 1) maintains 1.7Å point-to-point resolution over its 400kV to 1000kV operating range. Consequently the microscope can be tuned to a voltage which is below the threshold for knock-on damage in a specimen and used to directly image its contiguous-atom structure. The key to this variable-voltage, high-resolution performance is a top-entry objective stage, which, in addition to ± 40° biaxial tilting, incorporates a height (Z)-control to alter specimen position within the objective lens.
Analysis of electron-diffraction intensity profiles using a photodiode-array detection system
Authors: Warren J. B.
Published: June 2020

Electron diffraction intensity profiles have been used extensively in studies of polycrystalline and amorphous thin films. In previous work, diffraction intensity profiles were quantitized either by mechanically scanning the photographic emulsion with a densitometer or by using deflection coils to scan the diffraction pattern over a stationary detector. Such methods tend to be slow, and the intensities must still be converted from analog to digital form for quantitative analysis. The Instrumentation Division at Brookhaven has designed and constructed a electron diffractometer, based on a silicon photodiode array, that overcomes these disadvantages. The instrument is compact (Fig. 1), can be used with any unmodified electron microscope, and acquires the data in a form immediately accessible by microcomputer.

Major components include a RETICON 1024 element photodiode array for the de tector, an Analog Devices MAS-1202 analog digital converter and a Digital Equipment LSI 11/2 microcomputer. The photodiode array cannot detect high energy electrons without damage so an f/1.4 lens is used to focus the phosphor screen image of the diffraction pattern on to the photodiode array.
Simultaneous TEM thin foil preparation and SIMS analysis of multi-layered photovoltaic devices
Authors: Jones Kim M.
Published: June 2020

Ion etching of multi-layered photovoltaic devices is commonly used in thin foil preparation for transmission electron microscopy studies. A technique by which a particular intermediate layer of interest can be retained for examination has been developed. By combining a secondary ion tthss spectrometer (SIMS), with an ion etching instrument, we have a powerful means of controlling sanple preparation. Figure 1 is a schematic of the type of thin film photovoltaic device for which these techniques were developed. This device is representative of the generic problans that are associated with the polycrystalline low cost photovoltaic approaches. The limitations on ultimate cell performance can be directly related to defects occuring at interfaces and within the crystallites, nultiple phase formation at Junctions, crystallographic integrity of the grains, impurity segregation and accunulation at intergrain regions, and enhanced diffusion down grain boundaries.

Isolating a particular layer of 1-10 μm thickness in multi-layered devices is at best time consuming and inefficient using the conventional methods of pre-polishing chanical etching, or ion etching alone.
Slow-scan imaging applications of a digital video framestore system
Authors: Boyes E. D. , Goringe M. J. , Gill J. J. , Muggridge B. J. , Northover J. p. , Salter C. J.
Published: June 2020

Conversion of slow scan signals with a continuously updated image display or video recording at TV rate is one of the functions available using a digital video framestore system in conjunction with a scanning electron microscope (SEM, STEM, AEM etc.) or other types of electron probe equipment e.g. EPMA, AES etc. Acceptable inputs are standard TV format; digital sampling of a range of analogue slow scans or directly coupled digital scans.

Routines for noise reduction by spatially resolved time averaging during acquisition are under software control with direct operator involvement in selecting the appropriate conditions via a soft-key redesignation of the VDU numeric pad functions (Fig.l) and within the possibilities of the hardware; making TV rate more useable e.g. to reduce specimen charging and as an essential prerequisite to more sophisticated signal/image processing. Both running average (RVP, 8-bit) and straight integration (16-bit) modes are possible with the Microconsultants Intellect systems in use in our laboratory.
Production and STEM examination of controlled-size silver clusters
Authors: Listvan M. A. , Andres R. P.
Published: June 2020

Knowledge of the function and structure of small metal clusters is one goal of research in catalysis. One important experimental parameter is cluster size. Ideally, one would like to produce metal clusters of regulated size in order to characterize size-dependent cluster properties.

A source has been developed which is capable of producing microscopic metal clusters of controllable size (in the range 5-500 atoms) This source, the Multiple Expansion Cluster Source, with a Free Jet Deceleration Filter (MECS/FJDF) operates as follows. The bulk metal is heated in an oven to give controlled concentrations of monomer and dimer which were expanded sonically. These metal species were quenched and condensed in He and filtered to produce areosol particles of a controlled size as verified by mass spectrometer measurements. The clusters were caught on pre-mounted, clean carbon films. The grids were then transferred in air for microscopic examination. MECS/FJDF was used to produce two different sizes of silver clusters for this study: nominally Ag6 and Ag50.
Direct observations of radiation-enhanced transformations in glass
Authors: DeNatale J. F. , Howitt D. G.
Published: June 2020

The electron irradiation of silicate glasses containing metal cations produces various types of phase separation and decomposition which includes oxygen bubble formation at intermediate temperatures figure I. The kinetics of bubble formation are too rapid to be accounted for by oxygen diffusion but the behavior is consistent with a cation diffusion mechanism if the amount of oxygen in the bubble is not significantly different from that in the same volume of silicate glass. The formation of oxygen bubbles is often accompanied by precipitation of crystalline phases and/or amorphous phase decomposition in the regions between the bubbles and the detection of differences in oxygen concentration between the bubble and matrix by electron energy loss spectroscopy cannot be discerned (figure 2) even when the bubble occupies the majority of the foil depth.

The oxygen bubbles are stable, even in the thin foils, months after irradiation and if van der Waals behavior of the interior gas is assumed an oxygen pressure of about 4000 atmospheres must be sustained for a 100 bubble if the surface tension with the glass matrix is to balance against it at intermediate temperatures.
Radiation-induced surface decomposition
Authors: Knotek M. L.
Published: June 2020

Modern surface analysis is based largely upon the use of ionizing radiation to probe the electronic and atomic structure of the surfaces physical and chemical makeup. In many of these studies the ionizing radiation used as the primary probe is found to induce changes in the structure and makeup of the surface, especially when electrons are employed. A number of techniques employ the phenomenon of radiation induced desorption as a means of probing the nature of the surface bond. These include Electron- and Photon-Stimulated Desorption (ESD and PSD) which measure desorbed ionic and neutral species as they leave the surface after the surface has been excited by some incident ionizing particle. There has recently been a great deal of activity in determining the relationship between the nature of chemical bonding and its susceptibility to radiation damage.
The effect of particle height on the analysis of precipitates in alloy foils
Authors: Allen Robert M.
Published: June 2020

The relative height of small second-phase particles within a thin alloy foil can have a significant effect on the characteristic x-ray signal obtained from the particle during microanalysis in a STEM. Figure 1 illustrates this for the case where the energy dispersive x-ray detector attached to the STEM views the sample on the side entered by the incident electron beam. If the particle is located below the top foil surface, as in Fig. 1a, beam spreading may reduce the total current striking the particle, thereby reducing the generated signal. The x-ray spectrun of the particle may be further reduced and distorted by matrix absorption en route to the detector. Clearly the optimal position for microanalysis is shown in Fig. 1b: The particle to be analyzed should be on the sample surface facing the beam and x-ray detector.

These considerations were demonstrated in an experiment performed on a sample of Alloy 800, a high-allqy austenitic steel. The STEM used was a JEQL 200CX operated at 200kV. The second phase particles (Ti-carbides in this case) in the Alloy 800 electropolished at different rates from the matrix during sample preparation. Those particles located at the surface of the foil after thinning therefore produced surface relief and could be imaged using the secondary electron detector on the STEM. Figure 2 shows a mixed secondary electron/transmitted electron image of the TiC particles analyzed for this experiment.
Very-high spatial resolution analysis in STEM
Authors: Garratt-Reed A.J.
Published: June 2020

When analyzing a composition profile in a thin foil using a Scanning Transmission Electron Microscope, the measured profile is a convolution of the electron probe diameter, the actual profile and the degree of beam spreading in the sample. While it is possible to show that fractions of a monolayer of segregant are detectable in foils 100 nm thick, similar calculations indicate that if a probe 0.8 nm in diameter is incident upon a foil 20 nm thick, then broadening is insignificant. For example, fig. 1 is a computation (using the method of Hall, et.al) of the predicted measured profile resulting from a real gaussian distribution of chromium in iron, 2.5 nm wide, measured in the conditions just mentioned. Such results indicate that distributions of solutes well under 10 nm in separation should be readily distinguishable from each other.

In some pearlitic steels, alloy elements are incompletely partitioned during the pearlite reaction, and subsequently diffuse from the ferrite into the cementite, where they form very narrow (∿ 2 nm wide) enriched zones either side of the cementite plate, which is itself around 10 nm thick.
The role of radiation damage to the analysis of composition in electron microscopes
Authors: McElfresh D. K. , Howitt D. G.
Published: June 2020

The effect of the illuminating electron beam on the local composition of beam sensitive specimens is an important consideration when applying the techniques of analytical electron microscopy (AEM). The decrease in the signal from certain elements is often attributed to their volitalization under beam heating, however, radiation damage to the material by the electron beam is another mechanism which can contribute to compositional changes.

The ionization and displacement processes that occur within the region of the specimen irradiated by the electron beam can lead to relatively high concentrations of interstitials. The surrounding material is virtually devoid of these species and so these elements will diffuse down the concentration gradient that is generated and so reduce the X-ray or electron loss signal as the region within the probe is depleted.

The radiation damage process will continue as long as the electron beam impinges on the specimen and the presence of high vacancy concentration could induce the displacement of other species as the local binding energies are reduced. In the extreme case one might expect to observe tunnels of condensed vacancies arising from the diffusion process.
Electron energy loss spectroscopy in glancing reflection and other recent EELS developments
Authors: Krivanek O.L. , Tanishiro Y. , Yagi K. , Burgner R.P.
Published: June 2020

Surface reflection images have recently revealed surface steps, surface- intersecting dislocations, and even the nature of a surface reconstruction process. While a large fraction of electrons incident on a crystal at a low angle penetrate into the bulk where they excite X-rays thus rendering glancing reflection EDXS surface insensitive, the electrons which emerge eventually penetrate typically only 10 to 30Å into the crystal, and should thus be highly sensitive as a surface probe. We have therefore investigated the suitability of glancing reflection EELS as a surface-sensitive chemical analysis technique complementary to glancing reflection imaging.

The experiments were performed in a JEM 100B electron microscope modified for ultra-high vacuum (UHV) performance by the addition of liquid He cryo- pumping around the specimen, using a Gatan 607 electron energy loss spectrometer. Fig. 1 shows a series of spectra recorded for various glancing reflection conditions on clean (111) Si. It is clear that most electrons with which REM images are formed have been scattered inelastically at least once.
Application of computer control to STEM
Authors: Clark L. D. , Garratt-Reed A. J.
Published: June 2020

The current trend in instrumentation of all types is towards computer control. Major increases in system utility are often achieved, and it is frequently also possible to digest and display, in a useful fashion, quantities of data that would be quite unmanageable without the aid of the computer.

As the owners of a VG HB5 STEM, for which no commercial computer control package currently is available, our only option was to build a system. This paper describes the reasons we chose to proceed, the type of system we designed, and the results we have obtained so far.

The bulk of the work performed on our HB5 consists either of generating composition profiles across grain or phase boundaries, or of particle identification and analysis. In these cases, the work involves much tedium, and the performance of quite simple operations. We decided initially to provide computer-control of the beam position and x-ray analysis, to allow automation of these tasks.
Some applications of a computer-interfaced TEMSCAN
Authors: Nash James W. , Kokubo Yasushi
Published: June 2020

An electron microscope, interfaced to a computer and image processor becomes a powerful analytic tool. With a simple general interface, applications are defined entirely in software and are thus very flexible.

Our system consists of a 100CX TEMSCAN and PDP-11/23 (figure 1). Two selected SEM/STEM signals are converted to digital using Voltage to Frequency convertors (VFC) and counters. The use of VFC's insures capturing an integrated signal over the sample period. Acquired images are stored in a Recognition Concept Inc. "Trapix" image processor. The Trapix consists of memory organized as six 512 x 512 x 8 bit images, and a Pipeline Image Processor with which we can rapidly perform many of transformations useful to disk storage, analysis and presentation of images.

The Trapix is able to scroll one image relative to another and combine them in 1/30th second. Hence, stereo pairs can be aligned and combined to display red/green stereo images in real time. The data is stored as 512 x 512 x 4 bits showing some contouring or as 512 x 256 x 7 bits having decreased resolution.
Frozen hydration of protein crystals
Authors: Chiu Wah , Cohen Harold A. , Grant Robert A. , Jeng Tzyy-Wen
Published: June 2020

The choice of medium for maintaining the protein crystal hydrated on an electron microscopic investigation is made by taking into account its effectiveness in keeping the crystal wet and its scattering density relative to protein molecules. The frozen hydration method first introduced by Taylor and Glaeser seems to be an attractive procedure. They obtained electron diffraction patterns of catalase crystals with reflections beyond 3 Å resolution, and low resolution images with remarkable contrast. This paper deals with our recent experience in applying this technique to the structural studies of the thin crystals of crotoxin complex from rattlesnake venom, T4 DNA helix destabilizing protein, and Fc fragment from IgG of rabbit serum.

The most difficult part of the frozen hydration technique is the preparation of a proper amount of ice embedding the protein crystals. We have adopted the method of using double carbon films to sandwich the protein crystals and ice. A visual judgement of the water thickness is made prior to its being frozen in liquid nitrogen
The native structure of the eukaryotic ribosome
Authors: Milligan R.A. , Unwin P.N.T.
Published: June 2020

A detailed understanding of the mechanism of protein synthesis will ultimately depend on knowledge of the native structure of the ribosome. Towards this end we have investigated the low resolution structure of the eukaryotic ribosome embedded in frozen buffer, making use of a system in which the ribosomes crystallize naturally.

The ribosomes in the cells of early chicken embryos form crystalline arrays when the embryos are cooled at 4°C. We have developed methods to isolate the stable unit of these arrays, the ribosome tetramer, and have determined conditions for the growth of two-dimensional crystals in vitro, Analysis of the proteins in the crystals by 2-D gel electrophoresis demonstrates the presence of all ribosomal proteins normally found in polysomes. There are in addition, four proteins which may facilitate crystallization. The crystals are built from two oppositely facing P4 layers and the predominant crystal form, accounting for >80% of the crystals, has the tetragonal space group P4212, X-ray diffraction of crystal pellets demonstrates that crystalline order extends to ~ 60Å.
Three-dimensional structure of a regular bacterial surface layer: The HPI-layer of Deinococcus radiodurans
Authors: Baumeister W. , Hahn M. , Saxton W.O.
Published: June 2020

Regularly organized surface (RS) layers are a feature common to many bacterial species; they are clearly more abundant than was anticipated even a few years ago. The RS-layers are believed to fulfil a variety of functions in the interaction between the cell and its environment (see e.g. [1]). The so-called HPI-layer of the radiotolerant bacterium Deinococcus radiodurans is a typical example of such a layer: It is composed of a single polypeptide species (Mr 105 kDa) arranged on a hexagonal lattice to form a network that covers the entire surface of the bacterium; it is associated with the outer membrane via hydrophobic protein-protein interactions.

Isolated HPI-layer sheets, released from the outer membrane by detergent treatment, have been studied in the electron microscope making extensive use of the present arsenal of preparation techniques: negative staining, (auro- thio)glucose embedding, freeze-dried/unstained, freeze-dried/metal shadowed etc.

Because of the notorious problem of lattice imperfections image processing usually followed the strategy of correlation averaging as outlined in some detail elsewhere.
Image reconstruction of polymorphic tubulin aggregates and relationship with microtubule assembly
Authors: Mandelkow Eckhard , Mandelkow Eva-Maria , Schultheiss Reiner
Published: June 2020

Tubulin is capable of assembling into a remarkably large number of polymorphic aggregates. Besides microtubules one observes rings, hoops, sheets, helical ribbons and others. They are often seen transiently during microtubule assembly, and for this reason some of them have been considered as assembly intermediates in various assembly models. We will discuss an alternative view: polymorphic forms represent side branches of assembly which result from kinetic overshoot. The overshoot aggregates are metastable, and they disappear again with prolonged incubation in assembly conditions so that their protein subunits are liberated for assembly into more stable structures, i.e. microtubules. This process may be analysed within the framework of Oosawa's nucleation-condensation mechanism of protein selfassembly. The type and extent of overshoot is determined largely by the nucleation conditions, while the transition from polymorphic forms to microtubules takes place during the redistribution phase. With simple helical polymers (e.g. actin filaments) kinetic overshoot results only in a non-equilibrium length distribution.
High-voltage electron microscopy of capillary endothelial vesicles
Authors: Wagner Roger C. , Robinson Candy S.
Published: June 2020

The three dimensional association of endothelial vesicles must be a determinant in their role in transcapillary transport: Vesicles which shuttle materials across the capillary wall would constitute a discontinuous and nonhydraulically-conductive pathway. Transendothelial channels of fused vesicles would be true pores conducting materials in response to hydrostatic and osmotic pressure gradients across the capillary wall. Sessile, fused clusters of vesicles attached to the plasma membrane but not communicating across the endothelial cell would be inconsequential in transcapillary transport. In order to discern the three dimensional association of vesicles, we have employed high voltage electron microscopy to obtain stereopairs of thick sections through blood capillaries.

Whole rats were perfuse-fixed with glutaraldehyde-tannic acid (both 1% w/v) via the left ventricle of the heart. The diaphragm muscle was removed and cut into small strips parallel to the muscle fibers. These were osmicated, dehydrated and embedded in Spurr's medium in an orientation such that cross sections of the capillaries could be taken.
Differentiation of the airways epithelium of fetal rat tracheal organ explants in serum-free culture: SEM observations
Authors: McAteer J.A. , Cavanagh T.J.
Published: June 2020

This report describes SEM observations on the maturation of airways epithelial surface features in organ explants of fetal rat trachea. Tracheal explants were prepared from fetuses of timed pregnant Sprague-Dawley rats (16 days postcoitum). Tracheas were isolated intact, each was cut into two segments and the explants transferred to submersion culture (unsupported) in 3.5 ml culture medium within 60 mm Petri dishes (5% CO2 in air, humidified). Cultures were maintained in a component defined, serum-free, hormone supplemented medium patterned after medium K-l of Taub et al. Nutrient medium F12K was prepared with sodium bicarbonate (2.0 mg/ml), 10 mM HEPES, 10 nM Na2SeO3-5H2O, BSA (0.1%) and antibiotics (penicillin G, 100 U/ml; gentamicin sulfate, 10 ug/ml), pH 7.35. The medium was supplemented with five hormones including; bovine insulin, 5 ug/ml; human transferrin, 5 ug/ml; corticosterone 10-7M; PGE1, 25 ng/ml; and T3, 5xl0-12M. The medium was replaced every other day. Explants were processed for SEM by routine methods (2) at various time points throughout an 8 day culture period.
Remarks on the application of backscattered electron imaging (BEI) to the scanning electron microscopy (SEM) of biological structures
Authors: de Harven Etienne
Published: June 2020

Biological ultrastructures have been extensively studied with the scanning electron microscope (SEM) for the past 12 years mainly because this instrument offers accurate and reproducible high resolution images of cell shapes, provided the cells are dried in ways which will spare them the damage which would be caused by air drying. This can be achieved by several techniques among which the critical point drying technique of T. Anderson has been, by far, the most reproducibly successful. Many biologists, however, have been interpreting SEM micrographs in terms of an exclusive secondary electron imaging (SEI) process in which the resolution is primarily limited by the spot size of the primary incident beam. in fact, this is not the case since it appears that high resolution, even on uncoated samples, is probably compromised by the emission of secondary electrons of much more complex origin.

When an incident primary electron beam interacts with the surface of most biological samples, a large percentage of the electrons penetrate below the surface of the exposed cells.
Last second twitch-response test of single intact skeletal muscle fibers prior to quick-freezing after various stimulation intervals
Authors: Sommer J.R. , Nassar R. , Taylor I.
Published: June 2020

Conventional chemical fixation of muscle fibers is not suited to disclose morphological changes occurring with a time course of only a few msec, e.g.during excitation-contraction-coupling. We have taken advantage of a quick-freeze method to be able to study single intact frog skeletal muscle fibers (r.temporaria) after various time intervals following electrical stimulation. The electronics were designed to permit any time interval from 0 to more than 1 sec between stimulation and impact of the specimen on a liquid He-cooled copper block. It is important to monitor the twitch-response to stimulation. Given the geometry of the freezing device ("Slammer", Polaron), and the fact that the device does not operate vibration-free, it is quite difficult to design and built an effective monitor able to record the actual twitch-response following the stimulation of an isolated single muscle fiber during its descent prior to freezing. We have built a simple device that allows visual observation of the twitch-response within a few seconds prior to the definitive stimulation during the specimen drop.
Determination of the 'true' width of the actin filament
Authors: Fowler Walter E. , Aebi Ueli
Published: June 2020

Although the structure of the actin filament has been studied extensively both, by X-ray diffraction analysis and by electron microscopy and structure reconstruction, molecular models of actin have been obtained only recently. However none of the crystalline forms used in these latter studies are made directly from filaments. Since the resolution of current filament models is insufficient to allow unambiguous tracing of the actin subunits within them [e.g.2], the orientation of molecular models within such filament models is speculative. A primary constraint on the overall orientation of the elongated and polar actin subunit model within the actin filament is the 'true' width of the filament: reported values as obtained by electron microscopy range from 6 to 8nm for negatively stained specimens and to 9.5nm or more for rotary shadowed filaments [reviewed in 3]. Furthermore, X-ray solution scattering of actin filaments has revealed an average width of 7nm. Using a variety of different specimen preparation methods, we have endeavoured to set realistic upper and lower limits for this crucial parameter.
Filaments and membranes in the mitotic apparatus
Authors: McDonald Kent
Published: June 2020

At the light microscope level the recent developments and interest in antibody technology have permitted the localization of certain non-microtubule proteins within the mitotic spindle, e.g., calmodulin, actin, intermediate filaments, protein kinases and various microtubule associated proteins. Also, the use of fluorescent probes like chlorotetracycline suggest the presence of membranes in the spindle. Localization of non-microtubule structures in the spindle at the EM level has been less rewarding. Some mitosis researchers, e.g., Rarer, have maintained that actin is involved in mitosis movements though the bulk of evidence argues against this interpretation. Others suggest that a microtrabecular network such as found in chromatophore granule movement might be a possible force generator but there is little evidence for or against this view. At the level of regulation of spindle function, Harris and more recently Hepler have argued for the importance of studying spindle membranes. Hepler also believes that membranes might play a structural or mechanical role in moving chromosomes.
An immunogold study of protein synthesis in plant tissue
Authors: Craig Stuart , Goodchild D.J.
Published: June 2020

Two reserve proteins, legumin and vicilin, account for ∽70% of the total protein in mature pea seed cotyledons, where they are restricted to small membrane bound organelles, the protein bodies. These protein bodies are formed by fragmentation of the cell vacuoles during seed development. The reserve proteins were first detected by immunofluorescence in isolated deposits within such vacuoles.

On-grid immunogold labelling of fixed and embedded cotyledons offered the possibility of detecting ultrastructurally the site of synthesis and subsequent stages in the relocation of the protein to the vacuoles. Biochemical data indicate that synthesis takes place on ER-bound polysomes, but has not been able to establish subsequent steps in the transport pathway (5). Immunocytochemical localisation was carried out on glutaraldehyde-osmium fixed tissue embedded in Spurr's resin, sectioned and then treated on-grid with NaIO4. and HCl. This chemical treatment unmasks protein antigenicity, probably by removing protein-bound osmium and aldehyde.
Use of LR white embedding medium for routine transmission electron microscopy
Authors: Murphy Judith A. , Price Robert L.
Published: June 2020

Most current EM embedding media require component mixing prior to use. Also, many epoxy resins are carcinogenic and can present significant health hazards in the unpolymerized form. LR White acrylic embedding resin(by London Resin Co.; available Fullam, Pelco, Polaron etc.) is a one component, extremely low viscosity resin. The resin, according to Mfr. has a very low toxicity both in monomeric and polymerized states. We have found no skin sensitivity specifically known to be related to the resin over a period of 1 yr routine resin use. The cold cure accelerator does have some toxic risk, and contact with skin and eyes should be avoided. Accelerator, however, is not used for thermal curing. Because of resin advantages, the purpose of this study was to determine routine TEM methods consistent with LR White resin use for a variety of sample types(fungal, plant, and animal).
Two types of lipidic particles
Authors: Hui S.W. , Stewart T. P. , Boni L.T.
Published: June 2020

The molecular arrangements in lipidic particles (LIP) seen on freeze fracture faces of liposomes have been a subject of much discussion. Miller and Hui proposed that these particles were intermembrane attachment sites, while Cullis and de Kruijff favored a model consisting of inverted micelles between bilayer leaflets.

In our study of polymorphic phase transitions in mixtures of unsaturated phosphatidylethanolamine (PE) and phosphatidylcholine (PC), We have found evidence of two distinct types of LIP. In most PE/PC mixtures such as soybean PE and egg PC, the LIP have a dimple-like appearance and are definitely conical in cross fracture (fig. 1). Both concave and convex forms are commonly found on the same fracture face (fig. 2). In mixtures of dilinoleoyl-PE and palmitoyl-oleoyl-PC, the LIP are larger and have a round, bead-like appearance. These LIP often align in rows between entrapped water space (fig. 3), or stack in a cubic arrangement (fig. 4). In less ordered areas, conical and spherical LIP can be viewed as complementary lattice.
Nexuses in cultured heart cells: Response to oxygen/substrate deprivation
Authors: Odegarden S. , LeFurgey A. , Sommer J. , Murphy E. , Lieberman M.
Published: June 2020

Synchronously contracting cultures of embryonic chick heart cells have been developed as a model for evaluating biochemical and structural parameters of functional significance in the intact myocardium during normal or pathophysiological states. Of particular importance in these cells is the morphology of the gap junction or nexus, the structure often associated with cell-to-cell communication (e.g. ionic translocation, electrical coupling). The aims of the present study are [a] to ascertain the presence and describe the morphology of gap junctions in this model system of cardiac cells using freeze fracture electron microscopy and [b] to evaluate changes in the structure of the nexus associated with experimental conditions that alter or disrupt cell metabolism and electrical coupling.

For control preparations muscle-enriched monolayer cultures of heart cells from 11-day old chick embryos were grown and maintained in a 5% CO2/95% oxygen atmosphere at 37°C with or without substrate (glucose) as previously described.
An ultrastructural study of hairy-cell leukemia: Report of one case in a Chinese
Authors: Chew E. C. , Li C. L. , Lee K. W. , Chow C. H. , Huang D. P. , Saw D. , Ho J. H. C.
Published: June 2020

Hairy cell leukemia is a rather rare malignant lymphoreticular disorder. In U.S.A. Bouroncle gave a case incidence of approximately 2% of all leukemias. In China only a few cases have been reported according to a monograph entitled 'Leukemia' written in Chinese by a grout) of authors working in the Haematology Laboratory of the First Hospital affiliated to the Medical University of Wuhan. Recently, a case has been discovered in a Chinese in Singapore (Shannugaratnam*) and probably another in Taiwan (Huang*). We report here a case in whom the hairy cells have been studied by scanning and transmission electron microscopies.

For TEM, lymphoid cells isolated from peripheral blood by ficoll solution and centrifugation were fixed in 2.5% glutaraldehyde for 1 hour. Routine procedures were followed for dehydration and embedding in Spon 812. The stained sections were examined with a Philips EM 300 at 60 kV. For SSM, the pre-fixed specimens were dehydrated, critically dried, coated with goldpalladium and examined with a Cambridge Stereoscan 150 EM at 20 kV.
Deep-etched, replicated DNA toruses held on edge in ice demonstrate a complex 3-D substructure by extensive tilting along shadowing direction
Authors: Ruben George C. , Marx Kenneth A.
Published: June 2020

Torus shaped spermidine-DNA structures formed in vitro are thought to have a DNA organization similar to certain double stranded DNA bacteriophage and viruses. For this reason we have used freeze-etch low Pt-C metal replica TEM to visualize toruses formed from a variety of condensed DNAs. Both Calf Thymus DNA and circular and linear ϕX-174 RFII DNA freeze-etch TEM and biochemical data support a circumferential DNA winding model for hydrated spermidine-condensed DNA toruses. Heretofore, we utilized stereoscopic measurements from tilt views of thin replicas (60-90 Å) of toruses to yield information about the DNA topology and thickness of these objects. In a companion paper in these proceedings we examine the precision of such stereoscopic measurements on tilt micrographs of a torus. In our attempts to visualize DNA toruses we have noted that deep-etched toruses are generally suspended above the surface by virtue of a residual attachment to the ice.
Effect of trypsin in the presence or absence of Ca2+ on tight junction in an epithelial cell line
Authors: Polak-Charcon Sylvie , Pitelka Dorothy R.
Published: June 2020

Recent studies indicate that adhesion between cells is mediated by at least two different surface sites, one Ca2+-dependent and one Ca2+-independent. The first is highly sensitive to trypsin in the absence of Ca2+ but resistant in the presence of Ca2+, whereas inactivation of the second requires higher trypsin concentrations and Ca2+ has no effect on proteolysis.

Tight junctions (TJ) in vertebrate epithelia provide a transepithelial permeability barrier, help to maintain cell polarity, and also are strongly adhesive. Trypsin and other proteases are often used in cell dissociation protocols but are known in several epithelia to induce TJ proliferation. Our previous study of LA7, a rat mammary epithelial cell line, showed as demonstrated by others that withdrawal of Ca2+ leads to disruption of TJ. The effect of trypsin on LA7 cells in the absence or presence of Ca2+ was studied to determine whether TJ are related to the Ca2+-dependent mechanism of cell adhesion in epithelia.
Electron microscopy of T4 DNA helix destabilizing protein (GP32*I) crystal
Authors: Cohen H.A. , Chiu W. , Hosoda J.
Published: June 2020

The DNA helix destabilizing protein of T4 phage, gp32, may be enzymatically cleaved to produce the major fragment gp32*I, which crystallizes as thin platelets suitable for electron diffraction and imaging. The low resolution three-dimensional structure of gp32*I was previously determined. That model, based on the exclusion of negative stain showed that the protein crystallizes as dimers about 90 Å high, with each monomer about 20 Å in diameter. Since negative stain limits possible resolution to about 15 Å, glucose embedding was used to maintain the long range order of the crystal. A projected mass density map was reconstructed to 7.6 Å which resolved five masses in each dimer. The map was difficult to interpret since the average density of the protein was only slightly less than that of the embedding media. As a consequence, regions of protein that are denser than average (e.g. alpha helices running perpendicular to the surface of the crystal) approach the mass density of the embedding glucose and thus are invisible.
Examination of lysozyme CH crystals by low-dose electron microscopy
Authors: Robinson J.P. , Jeng T.W. , Chiu W. , Hash J.H.
Published: June 2020

Lysozyme Ch is an extracellular bacteriolytic enzyme produced by a species of fungus that has been provisionally classified as Chalaropsis. This enzyme has been isolated in pure form with a combination of ion-exchange chromatography and salt fractionation and has been physically characterized and completely sequenced. Circular dichroic measurements indicate a high content of beta-structure. It has a molecular weight of 22415 and contains a single disulfide bond. Lysozyme Ch is distinctly different from the lysozymes of avian egg whites, bacteriophages, plants, and invertebrates. Part of the interest in lysozyme Ch stems from its specificity. In addition to having β-1,4-N-acetylmuramidase activity in common with other lysozymes, it also has β-l,4-N,6-0-diacetylmuramidase activity. It is therefore active against bacterial species that have 6-0-acetylmuramic acid in their cell wall peptidoglycans; e.g., Staphylococcus aureus.

Lysozyme Ch crystallizes from 45% ammonium sulfate solution and to date crystals in habits suitable for X-ray crystallography have not been obtained. Therefore the available crystals have been examined by electron microscopy. The ammonium sulfate in which the crystals are formed is replaced with ammonium acetate which is more volatile for specimen preparation.
Two-dimensional arrays of membrane-bound (Na+, K+) - ATPase
Authors: Mohraz M. , Kivisild K.L. , Simpson M.V. , Rinder C.A. , Smith P.R.
Published: June 2020

(Na+, K+) - ATPase is a trans-membrane protein which utilizes energy from ATP hydrolysis to transport K+ into the cell and Na+ out of the cell against the concentration gradient of both of these ions. It consists of a catalytic subunit (α, M.W. 100,000) and a glycoprotein chain (β, M.W. 40,000). It is however, uncertain if the B structure or an oligomeric (αβ)2 structure forms the minimum active unit. The sequence information on the α and β-subunits is also incomplete. Therefore information about the structure of the enzyme should prove helpful in answering some of the outstanding questions about its function.

(Na+, K+) - ATPase was purified in membrane-bound form from the outer medulla of pig and dog kidneys according to the procedure of P.L. Jorgensen. The activity measurements and polyacrylamide gel electrophoresis indicated that the preparations were 75-85% pure.