bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic structure of CdTe dislocations studied by HREM
Authors: Lu P. , Glaisher R.W. , Smith David J.
Published: June 2020

The determination of the atomic core of dislocations in semiconductors is a challenging problem for high-resolution electron microscopy(HREM). In previous studies, various defects in elemental semiconductors, III-V and II-VI compound semiconductors have been reported. In particular, the core structure of the 30° partial dislocations in silicon, which are dissociated from a perfect 60° dislocation, have been deduced. present study, various CdTe dislocations have been imaged at 400keV. and their core structures have been analyzed with assistance from multi-slice image simulations. Sections of CdTe single crystal were cut normal to the [110] direction, followed by mechanically polishing to a thickness of ˜ 20 microns and finally argon ion-beam milling to perforation for electron microscopy. The crystals were examined with a JEM-4000EX. having a structure resolution limit of ˜ 1.7Å at 400keV.
Precipitation and dislocation decoration via extrinsic gettering of Co, Au and Pt by misfit dislocations in Si/Si-2%Ge epitaxy
Authors: Lee D. M.
Published: June 2020

Previous work on the gettering activity of a well defined array of buried interfacial misfit dislocations (MDs) showed that the amount of nickel gettered by MD is dominated by the strong temperature-dependent solubility. Precipitation occurs on or in the immediate vicinity of MDs due to nucleation enhancement by strain effects. High temperature 〈1000°C〉 diffusion of gold resulted in the planar colony precipitates on two {111} planes associated with stacking fault formation. In this contribution, we discuss our continuing research pertaining to cobalt, gold (at low temperature), and platinum gettering by MDs which involves studying the nature of dislocation decoration and impurity precipitation in the Si/Si-2%Ge epitaxial system.

All the samples used in this study have a buried Si-2%Ge epitaxial layer of ∼ 2 μm thickness.Co, Au and Pt were deliberately diffused into the wafer. The details of the sample structure and preparation are described in a preceding paper. Two-beam bright field and weak-beam dark field imaging techniques were performed on cross-section TEM specimens.
SEM-based nanolithography for quantum dot research
Authors: Moore T. M. , Randall J. N.
Published: June 2020

Devices based on quantum-mechanical effects offer the potential of a reduction in size of two orders of magnitude and a reduction in cost per function of four orders of magnitude over present integrated circuit technology. Such a dramatic reduction in size will require an entirely new approach to process technology. As part of a research program in quantum effect devices, nanolithography in an automated scanning electron microscope (SEM) is used to augment conventional optical lithography for the production of “quantum dot” devices. A quantum dot is a form of resonant tunnelling diode in which a thin GaAs or AlGaAs double-barrier quantum well is further confined by Fermi-level pinning at a vertical cylindrical surface created by reactive ion etching (RIE). In the resulting zero-dimensional quantum dot, the conduction band for confined carriers is split into discrete energy levels. Conduction through the quantum dot demonstrates maxima at bias potentials where these discrete energy levels align with the conduction band outside the barrier layers. At these maxima, resonant tunnelling occurs through the double-barrier heterostructure.
In Situ Electron Microscopy in catalysis research and related surface reactions
Authors: Gai Pratibha L.
Published: June 2020

Catalysis plays a major role in the modern oil and chemical industries. Solid state catalysts are most common, whilst the reactants are commodity gases and liquids. The performance of the catalysts depends strongly on their microstructure, chemistry and surface structures on a fine (nanometer) scale and electron microscopy (EM) plays an increasingly important role in the characterization. In-situ EM with an environmental cell permits direct observations of chemical reactions under near operating conditions and in conjunction with HREM and AEM can provide in favorable cases, significant atomic level information about the surface/microstructural changes and about possible reaction with substrates. In this paper, examples of catalyst materials in chemical technology and the nature of catalysis in alloy steels with applications in nuclear reactors are shown to elucidate this.

A variety of supported metallic catalysts were examined: Ni/carbon, Cu/alumina and bimetallic Cu-Pd/C (both of interest in methanol synthesis), Cu-Ru/C (incyclohexane conversions) and Cu-Ni/alumina.
The decomposition of praseodymium carbonate, carbonate hydrate, and hydroxy carbonate: An in situ study by High-Resolution Electron Microscopy
Authors: Sharma R. , Hinode H. , Eyring L.
Published: June 2020

High resolution electron microscopy (HREM) has been successfully used to study electron-induced chemical decompositions in the past few years. With HREM having near-atomic resolution, atomic-level details can provide insight into the mechanisms of solid state reaction. In this work the in situ decomposition of Pr2(CO3)3, Pr2(CO3)3·8H2O and PrCO3OH has been studied.

The starting materials were prepared as described elsewhere. Samples for HREM were prepared by crushing the crystal fragments in an agate mortar and placing a drop of the suspended powder in absolute alcohol on a holey carbon film supported on a copper grid to provide a distribution of fine crystal flakes. The samples were then studied by using a JEOL 4000EX microscope operated at 400KV and fitted with double-tilt-lift stage. The current density on the specimen was varied by changing the size of condenser aperture and spot providing various amounts of irradiation and heat transfer.

The decomposition reaction was rapid, hence it was not possible to get good HREM images of the starting material. Fig. 1a shows the diffraction pattern of the starting materials. Fig. 1b presents a sequence of images showing crystallization of (PrO)2CO3 (type II), growing from the edge inward.
Transmission Electron Microscopical studies of chemical rearrangements in bismuth uranium oxide
Authors: Parkinson G M , Billyard P D , Goringe M J , Long N J
Published: June 2020

Electron beam induced transformations in metal oxides have been the subject of a number of TEM studies, including, recently, transition metals (eg 1), lanthanides and actinides (eg 2). In this paper we present preliminary results of a high resolution TEM study of bismuth uranium oxide (Bi2UO6), in which several unusual electron beam induced phenomena have been observed. Samples exhibit one of four different types of behaviour in the electron beam. Although in each case the onset of the phenomena is dose-rate dependent, differences in dose-rate do not seem to be solely responsible for the observed differences in behaviour. Although all the samples are nominally of the same chemical stoichiometry, microscopic inhomogeneities in composition may result in differing decomposition behaviour. In this respect, the known ability of Bi2UO6 to give up large proportions of its lattice oxygens (3) without apparently changing crystal structure may be directly relevant.

The observed types of behaviour are as follows:
a) The sample remains unchanged, apparently indefinitely, under periods of continous electron irradiation.
b) The sample remains unchanged for a period, after which it suddenly “explodes”, depositing crystalline material on the surrounding carbon support film.
Directional disordering prior to amortization in electron-irradiated Cu-Ti intermetallic compounds
Authors: Luzzi D.E.
Published: June 2020

At temperatures below approximately 265 K, intermetallic compounds in the Cu-Ti binary alloy system undergo an amorphizat ion transformation when irradiated by high energy electrons. Previous in-situ experimental studies revealed that the irradiation first induces chemical disordering in the compound (seen as a reduction in superlattice reflection intensity) which is followed by the crystalline-amorphous (C-A) transition. However, the actual structural evolution of the material during the C-A transition was not addressed in the previous study.

In the present study, the structural evolution of the compound Cu4Ti3 was studied by ex-situ diffraction experiments in irradiated material that had not received a sufficient electron dose for amorphization. Cu4Ti3 has a Frank-Kasper-type tetragonal crystal structure composed of seven stacked body-centeredtetragonal sublattices.

In Fig. 1, a diffraction pattern of the (017) systematic reflections is shown prior to complete amorphization. The double arrows mark the location of intersections of the first-order amorphous halo with the second-order halo arising from the (017) reflections and the Ewald sphere.
Observation of tweed microstructures in Ni-Al-Fe alloys
Authors: Munroe P. R. , Baker I.
Published: June 2020

Ni-Fe-Al alloys are currently being considered for structural applications in the aerospace industry. Two compositions in particular Ni-30Al-20Fe and Ni-20Al-30Fe (in at. %) have generated the most interest. The former alloy is a single phase ordered body-centered cubic or B2 structure and the latter alloy has a B2 + Ll2 (ordered face-centered cubic) two-phase microstructure. X-ray microanalysis performed on Ni-20Al-30Fe has shown that the compostion of the B2 phase is Ni-30Al-20Fe, the same composition as the single phase alloy, and the compostion of the Ll2 phase is Ni-12Al-40Fe. This paper reports upon the observation of tweed microstructures in both alloys.

The alloys were cast, canned in mild steel, extruded to rod at 1000°C and then cooled in sand. Details of thin foil preparation conditions have been reported before . Foils were examined in a JEOL 100CX operating at 100kV.

Selected area diffraction (SAD) patterns from the B2 phase in Ni-20Al-30Fe(fig.1) exhibited streaking <110> directions, similar to the SAD patterns obtained from the B2 phase in Ni-37at%Al where a tweed microstructure was also observed.
X-ray image analysis: An application to petrographic modal analysis
Authors: Liang Long-Cheng
Published: June 2020

Image analysis is a fast and accurate technique for measuring the relative amounts of various mineral components of a rock. In a routine scanning electron microscope (SEM) based modal analysis, backscattered electrons (BSE) are used to generate average atomic number contrast to determine the presence of the various minerals. The minerals are then identified with the use of an energy dispersive (EDS) or a wavelength dispersive spectrometer (WDS). Once a mineral is identified, its modal percent can be calculated by comparing the area of pixels which the mineral occupies with the total area scanned. This BSE/EDS method works well in most cases except where samples contain minerals with similar average atomic numbers or backscattering coefficients, thus producing ambiguity in mineral identification. In an attempt to eliminate this ambiguity and to enhance the analytical capabilities of image analysis, the present study will evaluate a superimposed x-ray map method which utilizes the logical operation of conjunction (AND) to combine multiple x-ray maps of characteristic elements to complete the modal analysis.
The effect of embedding resins on ultramicrotomed polymer membrane morphology
Authors: Dietz N. L.
Published: June 2020

A variety of microporous polymeric membranes are used in separation processes. Because the unique chemical and physical properties of these membranes affect performance, determining the membrane ultrastructure is essential to understanding how the structure and performance are related.

TEM examination of ultramicrotomed membrane cross-sections is the most appropriate means of observing the thin active edge where the critical separation process occurs. Observation and interpretation of the image, however, is often difficult due to the low electron scattering of the polymer and alteration of the ultra-structure by the embedding resin. To solve the problem of low contrast in polymer thin sections, heavy metal stains such as osmium tetroxide and ruthenium tetroxide are used to selectively increase mass at specific locations. These stains, however, have limited application and carry the potential for creating artifacts. When staining is effective or unnecessary, there is the other concern of how the embedding resin has effected polymer morphology. Previous work with biological material has shown the effect of different epoxies on contrast and the correlation between the mechanical properties of various resins and sectioning dynamics, but the potential alteration of polymer ultrastructure has largely been ignored.
Artifacts of preparation in polymer microscopy
Authors: Cieslinski R.C. , Dineen M. T. , Marshall J. G. , Blackson J. H. , Mizer D. , Garrett H. L.
Published: June 2020

The interpretation of, and information available from a transmission electron photomicrograph, frequently depend upon specimen preparation. A major consideration in the selection of a preparation method is the potential for preparation artifacts. The goal of this work is to illustrate some sectioning and staining artifacts found in the preparation of a variety of polymer specimens. The following artifacts, in addition to several others, will be presented during the poster session.
High-resolution scanning electron microscopy of carbon fiber
Authors: Vezie Deborah L.
Published: June 2020

As part of an extensive study of polyacrylonitrile (PAN) and mesophase pitch-based carbon fibers, high resolution scanning electron microscopy (HRSEM) is shown to provide additional insight into understanding and modelling microstructural origins of mechanical properties of carbon fiber. Although carbon fiber has been studied extensively, no sufficiently clear relationship between structure and mechanical properties such as elastic modulus and compressive strength has yet been developed from quantitative TEM and WAXS investigations.In this study, HRSEM data of selected carbon fibers is used to illustrate the power of HRSEM to elucidate structural differences likely accounting for changes in mechanical properties not sensitively probed either by TEM or WAXS. The three-dimensional nature of SEM imaging with accompanying high resolution permits a clearer visualization and more detailed examination of regional structures within carbon fiber over two-dimensional TEM and globally averaged WAXS data.

The design of the high resolution, field emission SEM permits low voltage imaging of poorly conducting samples with resolution an order of magnitude greater than a conventional tungsten hairpin filament SEM under the same operating voltage and sample preparation conditions. Although carbon fiber is a relatively conductive material, charging effects can be seen in uncoated PAN fibers above 3.0 keV in a conventional SEM. Lower accelerating voltages are necessary for uncoated imaging of these fibers, but become impractical due to degradation of conventional SEM performance at these voltages. Uncoated sample imaging is preferred to prevent conventional evaporation or sputter coating techniques from obscuring or altering the sample surface, although charging effects may then be a problem. The high resolution, field emission SEM solves these competing voltage/ charging/ resolution issues for poorly conducting materials with the very nature of its design; the high brightness of the electron gun at low voltage coupled with the “in lens” sample placement and above the objective lens detector dramatically improve the resolution of these instruments, especially at low voltage.
Preparation of BiCaSrCuO specimens for High-Resolution Transmission Electron Microscopy
Authors: Fortunati K. , Fendorf M. , Powers M. , Burmester C.P. , Gronsky R.
Published: June 2020

Transmission electron microscopy, in particular high-resolution TEM, is proving to be a valuable tool in the continuing effort to characterize and understand the “high-Tc” superconducting oxides. Since specimen quality is of critical importance in high-resolution studies, care must be taken to choose the most appropriate specimen preparation technique for the material under study. The BiCaSrCuO material investigated here was in the form of small, sintered pellets with a porous microstructure which consists of small, randomly oriented, poorly connected, plate-like grains (see Figure 1). We have found that this morphology can significantly effect the production of suitable TEM specimens.

The simplest and most rapid specimen preparation method employed consists of crushing a small amount of the starting material to a fine powder in an agate mortar and suspending the powder in pure ethanol or propanol. An eye dropper or syringe is then used to transfer 4-6 drops of the suspension onto a holey carbon film supported on a mesh grid, thus effectively dispersing the powder across the grid. A strong tendency for the crystal to cleave along (001) planes, due to the weak bonding between BiO layers, results in flake-like particles which exhibit a preferred [001] orientation on the grid. A high-resolution image of a specimen prepared using this method is shown in Figure 2. We have observed that some specimens produced in this manner are unstable under a 200kV beam (with LaB6 filament), with heavy damage occurring within the time that a through-focus series of micrographs can be exposed. It is also important to note that since separation along grain boundaries occurs during crushing, this method is not an appropriate choice for imaging grain boundary structures.
A temperature-jump technique for time-resolved cryo-transmission Electron Microscopy
Authors: Chestnut H. , Siegel D. P. , Burns J. L. , Talmon Y.
Published: June 2020

Transmission electron microscopy of rapidly-frozen, hydrated specimens (cryo-TEM) is a powerful way of examining labile microstructures. This technique avoids some artifacts associated with conventional preparative methods. Use of a controlled environment vitrification system (CEVS) for specimen preparation reduces the risk of unwanted sample changes due to evaporation, and permits the examination of specimens vitrified from a defined temperature. Studies of dynamic processes with time resolution on the order of seconds, in which the process was initiated by changes in sample pH, have been conducted. We now report the development of an optical method for increasing specimen temperature immediately before vitrification. Using our method, processes that are regulated by temperature can be initiated in less than 500 msec on the specimen grid. The ensuing events can then be captured by plunge-freezing within an additional 200 msec.

Dimyristoylphosphatidylcholine (DMPC) liposomes, produced by extrusion, were used as test specimens. DMPC undergoes a gel/liquid crystalline transition at 24°C, inducing a change in liposome morphology from polyhedral to spherical. Five-μl aliquots of DMPC dispersions were placed on holey-carbon-filmed copper grids mounted in the CEVS environmental chamber, and maintained at 6-8°C and 80% relative humidity. Immediately before the temperature jump most of the sample was blotted away with filter paper, leaving a thin specimen film on the grid. Upon pressing the trigger, an electronic control circuit generated this timed sequence of events. First, a solenoid-activated shutter was opened to heat the specimen by exposing it for a variable time to the focused beam of a 75W Xenon arc lamp. Simultaneously, a solenoid-activated cryogen shutter in the bottom of the CEVS was opened. Next, the lamp shutter was closed after the desired heating interval. Finally, a solenoid-activated cable release was used to trigger a spring-loaded plunger in the CEVS, propelling the sample into a reservoir of liquid ethane. Vitrified samples were subsequently transferred to a Zeiss EM902 TEM, operated in zero-loss brightfield mode, for examination at −163°C.
Mechanisms of cytoplasmic inheritance in western white pine
Authors: Bruns Darla , Owens John N.
Published: June 2020

The chloroplast genome is predominantly paternally-inherited in conifers whereas mitochondria may be maternally-inherited. Molecular approaches do not reveal the mechanisms by which this is achieved. A recent study of mechanisms of organelle inheritance in Pseudotsuga menziesii has complimented earlier work on fertilization in conifers by demonstrating that, in the archegonium prior to syngamy, maternal plastids are transformed into large inclusions and mitochondria concentrate in a perinuclear zone. Paternal plastids and mitochondria are transferred with the male gametes and contribute to proembryo formation. In the present study, male and female gametophyte development, fertilization and proembryo development were examined inPinus monticola to determine mechanisms of plastid and mitochondrial inheritance.

Second year female cones were collected from mid-April to mid-June in 1987 and 1988 from trees growing in Victoria, B.C., Canada. Ovules were removed and median portions dissected out and fixed under vacuum for 2h-overnight in cold 2.5% glutaraldehyde and 2% formaldehyde in 50 mM P-buffer, pH 7.2. Tissues were buffer-washed for lh, post-fixed in 1% buffered OsO4 for lh and buffer-washed overnight. Dehydration in a graded acetone series preceded infiltration in low viscosity resin and then 60-70 nm sections were cut on a Sorvall MT5000 ultramicrotome using a diamond knife. Sections were collected on uncoated mesh or formvar-coated notchdot grids, stained with uranyl acetate and lead citrate and examined on a Phillips EM300 at 60 kV or JOEL JEM-1200EX at 60 kV.
Structural aspects of tracheary element differentiation in suspension cultures of Zinnia elegans
Authors: Haigler C. H. , Roberts A. W.
Published: June 2020

Tracheary elements, the water-conducting cells in plants, are characterized by their reinforced walls that became thickened in localized patterns during differentiation (Fig. 1). The synthesis of this localized wall involves abundant secretion of Golgi vesicles that export preformed matrix polysaccharides and putative proteins involved in cellulose synthesis. Since the cells are not growing, some kind of endocytotic process must also occur. Many researchers have commented on where exocytosis occurs in relation to the thickenings (for example, see), but they based their interpretations on chemical fixation techniques that are not likely to provide reliable information about rapid processes such as vesicle fusion. We have used rapid freezing to more accurately assess patterns of vesicle fusion in tracheary elements. We have also determined the localization of calcium, which is known to regulate vesicle fusion in plant and animal cells.

Mesophyll cells were obtained from immature first leaves of Zinnia elegans var. Envy (Park Seed Co., Greenwood, S.C.) and cultured as described previously with the following exceptions: (a) concentration of benzylaminopurine in the culture medium was reduced to 0.2 mg/l and myoinositol was eliminated; and (b) 1.75ml cultures were incubated in 22 x 90mm shell vials with 112rpm rotary shaking. Cells that were actively involved in differentiation were harvested and frozen in solidifying Freon as described previously. Fractures occurred preferentially at the cell/planchet interface, which allowed us to find some excellently-preserved cells in the replicas. Other differentiating cells were incubated for 20-30 min in 10(μM CTC (Sigma), an antibiotic that fluoresces in the presence of membrane-sequestered calcium. They were observed in an Olympus BH-2 microscope equipped for epi-fluorescence (violet filter package and additional Zeiss KP560 barrier filter to block chlorophyll autofluorescence).
Progress in understanding the biosynthesis and degradation of cellulose: The roles of light and Electron Microscopy
Authors: Brown Malcolm
Published: June 2020

Cellulose is the most abundant macromolecule on earth. It is a homopolymer of ß-1,4 linked glucose residues. The glucan chains have a degree of polymerization (=dp) ranging from several hundred to more than 20,000 glucose residues. The glucan chains typically associate with their neighbors to form crystalline rod-like structures known as microfibrils. Specific intermolecular associations of glucan chains (usually via H-bonding) result in several crystyalline polymorphs of cellulose such as Cellulose I (with parallel glucan chain orientation), or Cellulose II (absolute chain orientation not established). Cellulose is synthesized by many different organisms, including prokaryotic cells (Acetobacter, Rhizobium, Agrobacterium, Sarcina) and eukaryotic cells and organisms (many algae, fungi, mosses, ferns, vascular plants, Ascidians, and possibly humans).

Electron microscopy has been very important in elucidating the site of cellulose synthesis. Using conventional ultrathin sections and specific cytochemical localization combined with negative staining of isolated scales, the site of cellulose synthesis was confirmed in the Golgi apparatus (Cellulose synthesis is localized in the Golgi apparatus of a few specialized algae such as Pleurochrysis. More commonly, cellulose synthesis occurs in association with the plasma membrane. Freeze fracture was instrumental in first visualizing terminal complexes (=TCs) associated with elongating microfibrils. TCs are presently known to exist either as rosettes (in all vascular plants so far examined, or in certain zygnematalean algae or linear arrays, largely confined to certain algae. The subunits of the TCs may be either transmembrane as in Valonia and Boergesenia or confined to one leaflet as in Oocystis or Vaucheria.
An Electron Microscope study of the production of wax filaments by specialized epidermal cells of johnsongrass [Sorghum halepense(L.) Pers.]
Authors: Paul R. N. , McWhorter C. G.
Published: June 2020

Deposition of wax on the surface of johnsongrass occurs through two means: A. secretion through the cuticle of epidermal cells, resulting in an amorphous base layer and, then, as deposition continues, in flaky wax crystals; and B. wax filaments on the leaf surface produced by silica cell-cork cell associations . The latter process results in smooth overlay wax whose effects are seen as the glossy surface of the mature leaf. The sequence of initial wax deposition resulting in the formation of wax crystals, but not wax filaments can be duplicated in vitro. The purpose of this study is to delineate internal and external structures in cork cells that may be involved in wax filament production.

Greenhouse-grown johnsongrass leaves of varying ages were used in this study. For SEM, leaf tissue was air-dried (AD) in a desiccator (for optimum wax preservation) or critical point dried (CPD). Leaf tissue for CPD was fixed overnight in 5% glutaraldehyde in 0.1M cacodylate acid pH 7.0, dehydrated in ethanol, then dried in a Balzers CPD 020 critical point drier. Some tissue was dewaxed by dipping in chloroform for 1 min before immersion in fixative, then further washed in chloroform overnight on a rotator at the end of the dehydration series. After coating with 10 nm of AuPd, the specimens were viewed in a JEOL JSM 840 scanning electron microscope. Material for TEM was fixed in 3% w/v glutaraldehyde, post-fixed in 1% w/v OsO4, then dehydrated and embedded in Spurr’s Medium. Thin sections were observed in a Zeiss EM1OCR transmission electron microscope.
Enhanced membrane turnover in response to stimuli in the primate taste bud
Authors: Farbman Albert I. , Hellekant Göran
Published: June 2020

The presence of membrane-enclosed vesicles, 50-100 nm in diameter (cf. Fig. 1), has been observed in the taste pores of rats, mice, and rabbits, although little attention has been devoted to their importance. Murray has noted that fungiform papilla taste pores contained more vesicles than foliate papilla pores. In a recent paper we showed that thaumatin, an intensely sweet, basic protein (pl = 12), binds to the vesicles and to microvilli in taste pores. We suggested that the vesicles were shed from the microvilli as a kind of apocrine secretion, and proposed that the shedding of these vesicles may be an important means by which taste bud cells rid themselves of certain stimulus/receptor complexes, particularly when the stimulus is a large and/or highly charged molecule, such as thaumatin. To investigate this hypothesis further, we used electron microscopy to examine taste pores of both vallate and foliate papillae from Rhesus monkeys, before and after stimulation with thaumatin. We also recorded neural activity from the glossopharyngeal and chorda tympani nerves during stimulation with thaumatin and other tastants.

Rhesus monkeys were anesthetized with ketamine and given glycopyrrolate to inhibit salivary secretion. Tongues were thoroughly rinsed and the region of the foliate or vallate papilla treated with thaumatin (33 mg/1) or sucrose (0.3M) for 5-10 min. After a brief rinse, papillae were removed surgically. Control papillae were biopsied with no stimulation. Specimens were fixed for 2 h in: 2% paraformaldehyde, 2% glutaraldehyde in phosphate buffer, pH 7.2, rinsed and post-fixed in phosphate-buffered 1% OsO4,dehydrated in ethanols, and embedded in Epon-Araldite. Thin sections were examined in a JEOL-100 CX electron microscope with particular attention to the contents of the taste pores. For neurophysiology, the glossopharyngeal or chorda tympani nerve was exposed, in anesthetized monkeys, by dissection, and electrodes were placed on the nerve. Impulse activity was recorded with a PAR 113 amplifier, monitored over a loudspeaker and an oscilloscope, and fed into a recorder together with the output from an integrator which indicated the type and time of stimulation. The tongue was stimulated with a system that delivers solutions at programmed intervals under conditions of constant flow and temperature. Each stimulation lasted 10 sec, followed by a 30 or 50 sec rinse before the next stimulus. Stimuli were 0.02M citric acid, 0.1 M NaCl, 0.3M sucrose and 33 mg/l thaumatin.
Cell biology of retinal photoreceptors and pigment epithelium
Authors: Bok Dean
Published: June 2020

Retinal photoreceptors (rods and cones) and retinal pigment epithelium (RPE) are highly-polarized cells that reside in close association within the eye. They carry out their interactions from a time early in embryologic life until the demise of the organism. RPE cells position their basal surfaces on an elaborate membrane (Bruch's membrane) which is intercalated between this epithelial monolayer and the photoreceptor blood supply. Their apical surfaces face the light-sensitive organelles (outer segments) of the photoreceptors. Interactions between photoreceptors and RPE take place at this interface.

Mechanisms underlying photoreceptor phototransduction are now understood to a significant degree. When a photon is absorbed by a rod or cone photopigment, its chromophore, 11-cis retinaldehyde (11-cis retinal), isomerizes to the all trans form (t-retinol) and the protein undergoes a conformational change as well. The latter event activates a retina-specific GTPase (a G-protein called transducin) which, in turn, activates a retina-specific cGMP phosphodiesterase (cGMP-PDE). This cGMP-PDE then reduces the intracellular levels of cGMP which results in the closure of Na+/Ca++channels in the photoreceptor outer segment plasma membrane. The cell hyperpolarizes as a result and release of neurotransmitter at the synaptic terminal is diminished.
Immunological approaches to gap junctions: Studies of immuno-localization, membrane protein topology, and function
Authors: Johnson Ross G. , Lu Tze-Hong , Klukas Kathleen , Takemoto Larry , Yancey S. Barbara
Published: June 2020

It is now widely accepted that the plasma membranes of epithelial cells display a marked degree of polarity. This polarity is reflected in a number of parameters, e.g. the localization of certain proteins to basolateral membranes. Polarity is also illustrated by the presence of discrete membrane specializations, including desmosomes, tight junctions and gap junctions. These specializations provide strong support for the idea of membrane "domains" within the polarized membrane of the epithelial cell. This presentation relates to the proteins found in gap junction membranes. The issues include a clear identification of these proteins in different cells and an analysis of how a cell-to-cell channel is constructed by these proteins.

The plasma membranes of most animal cells contain cell-to-cell channels, which provide for the direct, passive exchange of small molecules between cells. Collections of these channels are identified as "gap junctions." This form of intercellular communication is thought to be important in a wide variety of biological processes, including cellular differentiation, proliferation, and tissue homeostasis.
Electron Microscopy of stained and unstained bovine papilloma virus: Comparison with polyoma virus
Authors: Baker T.S. , Olson N. H. , Newcomb W. W. , Brown J. C. , Olson C.
Published: June 2020

Bovine papilloma virus type 1 (BPV-1) is a member of the papillomavirus genus, one of two in the Papovaviridae family. Papovaviruses are characterized by similarities in their capsid structure, genetics, biochemical composition and role in the formation of benign and cancerous tumors. The discoveries that the capsid structures of polyoma and simian virus 40 (SV40) (members of the genus polyomavirus) consist of 72 pentameric capsomeres raises the fundamental question of whether or not the capsids of the larger and more complex papilloma viruses have a similar, unexpected arrangement of the capsid subunits. The recent development of cryo-electron microscopy techniques, which facilitate direct visualization of the “native” morphology of biological specimens at moderate resolution (1-4 nm), provides an opportunity to critically examine the structure of BPV-1.

The BPV-1 used in this study was originally isolated from a calf in 1965, passaged again in 1986, and stored in 50% glycerin and phosphate buffered saline. Virus was extracted and purified following the protocol of Cowsert et al. (1987): epithelial tissue rich in BPV-1 was mixed with an equal volume of buffer (1M NaCl, 20mM Tris, pH 7.5) and disrupted in a Waring blender. After high speed clarification, the supernatant fraction was mixed with an equal volume of Freon 113 and centrifuged at low speed. Virus from the aqueous phase was pelleted, resuspended in CsCl (ρ=l.33 g/cm3), density banded, pelleted and finally resuspended in 30 mM KCl and 6 mM Tris (pH 7.5) to a protein concentration of ˜3 mg/ml.
Scanning transmission x-ray microscopy of cultured cells
Authors: Pine J. , Gilbert John
Published: June 2020

Soft x-rays provide an interesting possibility for imaging thick specimens at resolution better than that of the light microscope. Because of the way these x-rays interact with matter, a transmission image is formed essentially entirely by absorption, and suffers negligible blurring due to scattering. The only serious effect of sample thickness is to attenuate the x-ray beam. At x-ray wavelengths between 2.3 and 4.4 nm, the absorption is particularly appropriate for examining thick biological specimens. In this region water is weakly absorbing while carbon is strongly absorbing. As a result, absorption by a whole live cell is dominated by biological molecules. The magnitude of the absorption is such that cells up to ten microns thick can be imaged. Finally, these x-rays can traverse up to a millimater of air without serious attenuation. Transmission microscopy of live cells in air is thus possible.

The technology for producing high resolution x-ray images has only recently become available. Zone-plate focussing has been perfected to the point where an x-ray beam spot 40 nm in diameter can be formed. This spot can be raster-scanned over a specimen and the transmitted x-rays detected, to form a scanning transmission x-ray microscope (STXM) image. The spot size, and resolution, are expected to improve to about 20 nm in the next few years. A very intense source of nearly monochromatic soft x-rays is also needed, at present only available at synchrotron light sources. We are working with a group from SUNY Stony Brook, IBM Watson Laboratories, and the Center for X-Ray Optics who have just finished building a microscope at the National Synchrotron Light Source. Two other microscopes are now being built, at Daresbury in England, and in Berlin.
Evidence that a secretory component of the sea urchin egg is routed to yolk platelets after fertilization
Authors: Valdizan M. C. , Decker G. L.
Published: June 2020

During fertilization the sea urchin egg undergoes a global wave of secretion (the cortical reaction) followed by a period of endocytotic activity involved in membrane retrieval. Using a monoclonal antibody (MAb 1223) that recognizes a 130-kDa glycoprotein found in both the egg and embryo of Strongylocentrotus purpuratus, we recently suggested that glycoproteins bearing the 1223 epitope are stored in the cortical vesicles of the egg, secreted during fertilization, and subsequently endocytosed and routed to yolk platelets, a possible site of degradation.

In the current study, to determine whether fertilized eggs could internalize an antibody probe directed at the cell surface, we coupled MAb 1223 to colloidal gold and presented it to eggs that had been stripped of fertilization envelopes and hyaline layers. Gold-conjugated mouse IgG (preimmune), bovine serum albumin (BSA), and goat-antimouse IgG served as controls. Colloidal gold (8 and 15 nm) was prepared and conjugated to BSA or antibody as previously described. For localization of the 1223 antigen in unfertilized eggs MAb 1223-gold was diluted 1:20 in buffer and applied to sections of eggs embedded in Lowicryl K4M. To remove the envelopes and hyaline layers, 20-30 seconds after addition of sperm the eggs were suspended in ice-cold artificial sea water containing 25 mM EGTA and passed through a nylon screen (64 μm mesh). Subsequently, 1 ml aliquots of the denuded eggs [10% suspension (vol/vol)] were gravity settled, removed from the Ca2+-chelator and resuspended in complete sea water. After a second wash, 20 μl aliquots of the eggs were transferred to fresh 1.0 ml volumes of sea water equilibrated at 14°C in the presence of the individual gold probes. The final dilution of the gold probes in sea water was 1:100. After gentle mixing of the eggs and gold probes, at time points 5,15,30 and 60 minutes specimens were fixed and embedded in Spurr resin as previously described.
Tritiated thymidine in the chick embryo inner ear
Authors: Fermin Cesar D.
Published: June 2020

Development of the chick (Gallus domesticus) inner ear has been studied, and the maturation of cells that detect sound has been analyzed at the E.M. level [1,2,3]. Other workers showed correspondence between ultrastructural maturation and behavioral responses [4,5]. In mammals [6] hair cells mature after ceasation of mitosis {Fig.l}, in a pattern so that older cells are in the base of the cochlea while younger cells are in the apex [7]. But, electrophysiology indicates that cells at the base do not function first. Chicks are precocious with well developed sensory organs at birth, and their embryonic development follows, on a very short time span, a sequence that resembles that of the human ear. This study was undertaken to standarize tritiated thymidine (TT) because resolution of TT in avian embryos differs significantly from mammals [6]. Embryos were injected with 100 μl of TT, and sacrificed 1 or 2 hours later in order to label only those cells that were actively dividing cells at the time of the injection. Specimens were fixed and processed for autoradiography [6].

Actively dividing cells incorporate TT after short exposure, with minimal background. It seems that vestibular sensory epithelia {Fig.2} have more dividing cells than the auditory sensory epithelia {Fig.3}, even though the vestibule develop before the cochlea. The ratio between the number of labeled cells over the length of the sensory epithelia is lower in the auditory basilar papilla (0.098 cell/(μm) than in the vestibular utricle (0.77 cell/μm) and saccule (1.66 cell/ μm). When dividing cells were analyzed in the basilar papilla alone, and their distribution displayed along the length of the cochlea over time, older cells were opposite to the VIIIth nerve fibers that innervate those hair cells. A lateral and a longitudinal gradient has been established and hair cells closer to the nerve in the mid-basal area mature earlier than hair cells at both ends of the cochlea [2]. This finding, if occuring in mammals, may explain why mid-frequency are the first to appear [5]. The first 1/3 of the chick cochlea contains mainly short hair cells and are innervated primarily by efferent nerve fibers, which arrive in the cochlea almost a week after the afferent do. Moreover, tall hair cells extend 2/3 of the cochlear length from apex to mid-base and show mature innervation patterns before the short hair cells do. In the short embryonic cochlea, frequencies may be produced first in the what will later be the mid-region because, early in development, that area contains more mature receptors [1,2,3].
Electron Microscopic investigation of crooke’s change in the pituitaries of patients with hypercorticism
Authors: Horvath E. , Kovacs K. , Stefaneanu L. , Losinski N.
Published: June 2020

Human pituitary corticotropins have unique morphologic markers: bundles of type-1 filaments, measuring approximately 70 A in width and representing cytokeratin. The extreme ring-like accumulation of type-1 filaments, known as Crooke's hyalinization, signals functional suppression of the corticotropins and occurs in endogenous and exogenous glucocorticoid excess, caused by ACTH-secreting pituitary adenoma, glucocorticoid secreting adrenocortical tumor, ectopic ACTH-syndrome and administration of pharmacologic doses of glucocorticoids. Cells of autonomous corticotroph adenomas usually do not show Crooke's hyalin change. A minority of these tumors, however, retains sensitivity to the negative feed-back effect of elevated blood glucocorticoid levels and display typical Crooke’s change.

In the present study pituitary corticotropins in various phases of Crooke's hyalinization were investigated in patients with glucocorticoid excess of various origin, applying histology, immunocytochemistry, count of argyrophilic nucleolar organizer regions (AgNOR), and transmission electron microscopy.
Correlation of γ-radioactivity and Scanning Electron Microscopy in measurement of retention of 111Indium-labeled canine endothelial cells on synthetic vascular grafts
Authors: Prendiville E.J. , Verdon S. Laliberté , Gould K. E. , Ramberg K. , Connolly R. J. , Callow A. D.
Published: June 2020

Endothelial cell (EC) seeding is postulated as a mechanism of improving patency in small caliber vascular grafts. However the majority of seeded EC are lost within 24 hours of restoration of blood flow in previous canine studies . We postulate that the cells have insufficient time to fully develop their attachment to the graft surface prior to exposure to hemodynamic stress. We allowed EC to incubate on fibronectin-coated ePTFE grafts for four different time periods after seeding and measured EC retention after perfusion in a canine ex vivo shunt circuit.

Autologous canine EC, were enzymatically harvested, grown to confluence, and labeled with 30 μCi 111 Indium-oxine/80 cm 2 flask. Four groups of 5 cm x 4 mm ID ePTFE vascular prostheses were coated with 1.5 μg/cm.2 human fibronectin, and seeded with 1.5 x 105 EC/ cm.2. After seeding grafts in Group 1 were incubated in complete growth medium for 90 minutes, Group 2 were incubated for 24 hours, Group 3 for 72 hours and Group 4 for 6 days. Grafts were then placed in the canine ex vivo circuit, constructed between femoral artery and vein, and subjected to blood flow of 75 ml per minute for 6 hours. Continuous counting of γ-activity was made possible by placing the seeded graft inside the γ-counter detection crystal for the duration of perfusion. EC retention data after 30 minutes, 2 hours and 6 hours of flow are shown in the table.
Same-section correlative light and electron microscopy
Authors: Rieder C.L. , Alexander S.P. , Bowser S.S.
Published: June 2020

Epoxy embedded biological material, sectioned for conventional, intermediate or high-voltage electron microscopy (EM), can be visualized within the section with good contrast and detail by phase-contrast or dark-field light microscopy (LM). The contrast of such material is not substantially influenced by the type of embedding resin or section support substrate. It is, however, influenced by the type of fixation (glutaraldehyde with and without osmium postfixation), by heavy metal (uranyl and lead) staining, and by the section thickness. The ability to examine the specimen with the LM, within a section cut for EM, allows each section to be rapidly screened for content prior to examination in the EM. We have found this approach to be particularly useful for studies requiring the ultrastructural examination of a selected area or structure which is large enough to be visualized with the LM but which comprises only a small volume of the embedded material (e.g., centrosomes and nuclei within oocytes; specific regions of large protists.)

Same section LM-EM can also be extended to sections cut from cells stained prior to embedding for the immunofluorescent localization of antigens using fluorescein, rhodamine or Texas red-conjugated antibodies. Under these conditions the sections show high resolution patterns of antigen-specific fluorescence against a background void of autoflouorescence. The fidelity in the correlation between the distribution of immunofluorescently labeled antigens and the ultrastructure in the same section can be extended to structures as small as a single microtubule or just a few actin filaments . This approach of same section correlative fluorescence microscopy (FLM) and EM can eliminate the need, in many instances, to employ more complex procedures such as immunoferritin or immunogold for labeling antigens for ultrastructural detection.
Correlative microscopy and microprobe analysis in pathology
Authors: Shelburne J.D. , Estrada H. , Hale M. , Ingram P. , Tucker J.A.
Published: June 2020

In performing transmission electron microscopic (TEM) studies of biopsies, pathologists must be extremely careful to “aim” the TEM at features of the tumor or pathologic process which are important at the light microscopic (LM) level. Fine structural data devoid of such correlations are generally of no clinical value. For example, a TEM study of a tumor must focus primarily on the tumor cells. Care must be taken not to misidentify stromal cells (e.g., capillaries, fibroblasts) as tumor cells, or else serious errors can occur.

Likewise, in performing electron microprobe analysis (EPMA) on biopsies, it is extremely important that the pathologist be able to interpret the spectral findings in light of the H&E section appearance. Like it or not, the current “gold standard” in surgical pathology labs around the world is the H&E stained paraffin section. Accordingly, as in TEM studies, electron microprobe results must be obtained in such a manner that one can relate the findings to the appearance of the biopsy as viewed by light microscopy in an H&E section. If one cannot make that correlation, then one has obtained data that generally will be of little interest to most pathologists and clinicians. Accordingly, our group has stressed the importance of correlative microscopy, and has developed several regimens for analyzing histologic sections. Last year in these proceedings we published a schematic overview of that regimen.