bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure/property relations in YBa2Cu3O7-x powders
Authors: Thiel B.L. , Sarikaya M. , Javadpour J. , Han C. , Aksay I.A.
Published: June 2020

We have studied several samples of YBa2Cu3O7-x superconductor with substantially differing electromagnetic characteristics in an effort to relate microstructure with superconducting properties. It is has been shown that the bulk oxygen content of the material can be related to the difference in the a and b lattice parameters which has a linear relationship with the bulk Tc value. Bulk measurements of electronic properties may be misleading as they are complicated by the presence of weak-links in the forms of inter- or intra- granular phases or even oxygen poor regions within a single grain.

The samples used were all prepared with the same starting materials but subject to heat treatments which varied the 950°C sintering time and the partial pressure of oxygen in the furnace atmosphere. All of the samples had nominally identical x-ray diffraction patterns (e.g., equivalent bulk Δa/a values as measured by the (103)-(013)/(110) peak splitting) but showed markedly different superconducting properties as measured by the inductance-flux exclusion technique.
UHV microscopy of surfaces: Recent results
Authors: Bonevich J.E. , Zhang J.P. , Jacoby M. , Ai R. , Dunn D. , Stair P.C. , Marks L.D.
Published: June 2020

In order to examine surfaces of materials, a prerequisite is a microscope which combines ultra-high vacuum (UHV) with surface science cleaning and characterization techniques such as ion beam sputtering, annealing, and Auger spectroscopy. In order to achieve this, we have mounted onto the side of a UHV-H9000 microscope LEED/Auger, an ion gun, and optical heating; in the transfer chamber specimens can be cleaned at a base pressure of 2×10-10 torr and transferred into the microscope which operates at pressures better than 2×10-10 torr. With this marriage, it is relatively simple to prepare and characterize clean surfaces.

As an example, thin gold film specimens, textured with the [111] normal to the film, were made in a standard vacuum evaporator and floated onto a gold grid. The transfer chamber was then baked-out at 250°C for about 12 hours to achieve UHV conditions. Figure 1 shows an image taken from the gold film after bakeout.
Characterization of interfaces in CVD-coated nicalon fiber-reinforced SiC
Authors: More K.L. , Lowden R.A.
Published: June 2020

The mechanical properties of fiber-reinforced composites are directly related to the nature of the fiber-matrix bond. Fracture toughness is improved when debonding, crack deflection, and fiber pull-out occur which in turn depend on a weak interfacial bond. The interfacial characteristics of fiber-reinforced ceramics can be altered by applying thin coatings to the fibers prior to composite fabrication. In a previous study, Lowden and co-workers coated Nicalon fibers (Nippon Carbon Company) with silicon and carbon prior to chemical vapor infiltration with SiC and determined the influence of interfacial frictional stress on fracture phenomena. They found that the silicon-coated Nicalon fiber-reinforced SiC had low flexure strengths and brittle fracture whereas the composites containing carbon coated fibers exhibited improved strength and fracture toughness. In this study, coatings of boron or BN were applied to Nicalon fibers via chemical vapor deposition (CVD) and the fibers were subsequently incorporated in a SiC matrix. The fiber-matrix interfaces were characterized using transmission and scanning electron microscopy (TEM and SEM). Mechanical properties were determined and compared to those obtained for uncoated Nicalon fiber-reinforced SiC.
Quantification of submicron magnetisation structures in thin films using DPC
Authors: McFadycn Ian R.
Published: June 2020

Differential phase contrast Lorentz. microscopy has been shown to be a powerful technique for studying submicron magnetisation distributions in thin magnetic films. However, the technique has not found wide spread use, perhaps because it is thought to require either a dedicated STEM with a field emission gun, or extensive modifications to the electron optics of a conventional TEM. In this work we have demonstrated that DPC can be implemented on a conventional TEM, in our case a JEOL JEM 2000FX, without recourse to modifications ofthe electron optics ofthe microscope. Some of the controls of the microscope have been modified, but this was for convenience rather than necessity and in no way affects the normal operation ofthe microscope.

Figure I illustrates the principle behind DPC. A focused electron probe, of half angle α is scanned across the sample and at each point in the scan, the denection (β1) due to the sample is measured by means of a quadrant detector as follows. Any deflection of the beam can he split into an x-component and a y-component.
Multiply faulted defects in high-current oxygen-implanted silicon-on-insulator
Authors: Visitserngtrakul S.
Published: June 2020

High-dose oxygen implantation into silicon, SIMOX (separation by implantation of oxygen), is a leading technique for producing silicon-on-insulator (SOI) material. Most studies have examined SIMOX prepared with a traditional implanter, which has beam currents of 100 to 400 μA. Since the formation of SIMOX requires a very high dose of oxygen, typically one hundred times larger than the standard dopant implant doses, the process takes many hours. Recently, a high-current implanter has been developed for SIMOX fabrication, which produces a 40 mA beam current. However, the higher current density has not only shortened the implantation time, but also produced features not routinely observed in samples implanted at much lower currents. The study reported here used conventional transmission and high resolution electron microscopy (CTEM,HREM) to characterize microstructure and defects in SIMOX implanted at high currents.
In situ TEM studies of deformation and fracture
Authors: Robertson I.M. , Lee T.C. , Dewald D.K. , Birnbaum H.K.
Published: June 2020

The in-situ TEM straining technique has been used to investigate the micromechanisms of deformation and fracture in several ductile and semi-brittle systems. Attention has been focussed on the dislocation structures ahead of advancing cracks and on the interaction between lattice dislocations and grain boundaries.

The deformation experiments were performed in-situ in a transmission electron microscope equipped with a video camera system. The dynamic events were recorded on video tape with a time resolution of l/30th of a second. Static interactions were recorded using the regular microscope plate system. The straining stage deforms the samples in Mode I and can operate at a displacement rate of 4 in sec-1.

An example of one of the possible interactions between lattice dislocations and a ∑- 3 ([ll)/60°) grain boundary in 310 stainless steel is shown in the micrograph in Figure 1. The dislocations on slip systems A (a/2[110)1 (ll) 1 ) and B (a/2[101] (11) 1 ) impinge on the grain boundary, generating slip systems C (a/2[l0) 2/(111) 2) and D (a/2[l0) 2/(111) 2). To understand this effect three conditions were considered:
High-resolution hot-stage experiments
Authors: Boyes E.D.
Published: June 2020

High resolution electron microscopy provides a powerful method for studying controlled dynamic reaction sequences and the development of microstructures on the atomic scale. Temperatures can be controlled with reasonable accuracy using a standard hot-stage, but at elevated temperatures there is some reduction in the contrast, and stability, of images. It is, of course, essential to minimise the effects, including additional heating, of irradiating the sample with a high voltage electron beam in a high vacuum environment, and to take into account the close proximity of two specimen surfaces in designing experiments. TV imaging techniques, in-situ, relocatable ex-situ and environmental methods are being developed for use with two medium voltage side-entry high resolution TEMs, equipped with complementary chemical and structural microanalytical STEM facilities.

TV imaging techniques
Dynamic reaction sequences are now mostly viewed with a low-light level TV camera (LLTV) using a thin YAG or YAP pickup screen and recorded on U-matic videotape to facilitate subsequent processing. The results can be improved substantially by using a digital framestore based image processor to enhance the signal to noise ratio of the video signal in realtime. A major element in the SNR is the shot noise statistics of the TEM electron beam.
Quantitative surface damage studies by H.R.E.M.
Authors: Singh S. R. , Fan H. J. , Marks L. D.
Published: June 2020

Since the original observation that the surfaces of materials undergo radiation damage in the electron microscope similar to that observed by more conventional surface science techniques there has been substantial interest in understanding these phenomena in more detail; for a review see. For instance, surface damage in a microscope mimics damage in the space environment due to the solar wind and electron beam lithographic operations.

However, purely qualitative experiments that have been done in the past are inadequate. In addition, many experiments performed in conventional microscopes may be inaccurate. What is needed is careful quantitative analysis including comparisons of the behavior in UHV versus that in a conventional microscope. In this paper we will present results of quantitative analysis which clearly demonstrate that the phenomena of importance are diffusion controlled; more detailed presentations of the data have been published elsewhere.

As an illustration of the results, Figure 1 shows a plot of the shrinkage of a single, roughly spherical particle of WO3 versus time (dose) driven by oxygen desorption from the surface.
Electron-beam damage of oxides at high current densities
Authors: McCartney M. R. , Weiss J. K. , Smith David J.
Published: June 2020

It is well-known that electron-beam irradiation within the electron microscope can induce a variety of surface reactions. In the particular case of maximally-valent transition-metal oxides (TMO), which are susceptible to electron-stimulated desorption (ESD) of oxygen, it is apparent that the final reduced product depends, amongst other things, upon the ionicity of the original oxide, the energy and current density of the incident electrons, and the residual microscope vacuum. For example, when TMO are irradiated in a high-resolution electron microscope (HREM) at current densities of 5-50 A/cm2, epitaxial layers of the monoxide phase are found. In contrast, when these oxides are exposed to the extreme current density probe of an EM equipped with a field emission gun (FEG), the irradiated area has been reported to develop either holes or regions almost completely depleted of oxygen. ’ In this paper, we describe the responses of three TMO (WO3, V2O5 and TiO2) when irradiated by the focussed probe of a Philips 400ST FEG TEM, also equipped with a Gatan 666 Parallel Electron Energy Loss Spectrometer (P-EELS). The multi-channel analyzer of the spectrometer was modified to take advantage of the extremely rapid acquisition capabilities of the P-EELS to obtain time-resolved spectra of the oxides during the irradiation period. After irradiation, the specimens were immediately removed to a JEM-4000EX HREM for imaging of the damaged regions.
Crystal structure and stacking faults of myristyl stearate identified by electron diffraction
Authors: Zhang W.P. , Dorset D.L. , Hanlon J.
Published: June 2020

Although a few X-ray crystal structures of normal-chain esters of long chain acids and short chain alcohols have been carried out, attention has been paid mostly to the long-spacings of waxes synthesized from longer chain alcohols. We have been interested in exploring the crystal structures of the more symmetric waxes via electron diffraction studies.

Myristyl stearate thin crystals were epitaxially grown on benzoic acid by the method developed by Wittmann et al. Some samples with or without the presence of the nucleating substrates were annealed at 45°C for 4 hours on a Met tier FP82 hot stage. The thin crystals before or after annealing were examined with a JEOL JEM-100CX electron microscope operated at 100 kV, and selected area electron diffraction patterns from [100] and [110] directions were recorded on Kodak DEF-5 X-ray film. The calibration of the camera length was carried out with a gold Debye-Scherrer diagram. Models of molecular packing were scanned with an Optronics P-1000, and their Fourier transforms were calculated with a program in IMAGIC.
Wavefunction and CBED results of the STEM multislice calculation
Authors: Loane R. F. , Kirkland E. J. , Silcox J.
Published: June 2020

The multislice algorithm has been used to simulate ADF STEM images. Examination of the evolution of the electron wavefunction as it propagates through the specimen, can provide insight into the sources of contrast in the STEM image. Plots of the wavefunction intensity as a function of position and as a convergent beam electron diffraction (CBED) pattern are two complementary views of the diffraction process. Examples from the large number of these plots that are calculated during the ADF STEM calculations will be presented.

The simulated specimen consists of multiples of 47 Å (15 slices) of silicon (111). The slices are 65 Å × 66 Å(512 × 512 pixels) in size, setting the maximum included scattering angle to 95 mrad. The incident probe models a 100 keV VG-HB501 STEM at Scherzer focus with either the low resolution pole piece (Cs=3.3 mm, Δf=1100 Å, αap = 8.2 mrad) or the high resolution pole piece (Cs = 0.7 mm, Δf=510 Å, αap=12.1 mrad). The beam and specimen are aligned exactly along the (111) zone axis (no tilt).
Secondary electron imaging of YBa2Cu3O7-x high-Tc superconductors in Scanning Transmission Electron Microscope
Authors: Liu D. R. , Williams D. B.
Published: June 2020

The secondary electron imaging technique in a scanning electron microscope (SEM) has been used first by Millman et al. in 1987 to distinguish between the superconducting phase and the non-superconducting phase of the YBa2Cu3O7-x superconductors. They observed that, if the sample was cooled down below the transition temperature Tc and imaged with secondary electrons, some regions in the image would show dark contrast whereas others show bright contrast. In general, the contrast variation of a SEM image is the variation of the secondary electron yield over a specimen, which in turn results from the change of topography and conductivity over the specimen. Nevertheless, Millman et al. were able to demonstrate with their experimental results that the dominant contrast mechanism should be the conductivity variation and that the regions of dark contrast were the superconducting phase whereas the regions of bright contrast were the non-superconducting phase, because the latter was a poor conductor and consequently, the charge building-up resulted in high secondary electron emission. This observation has since aroused much interest amoung the people in electron microscopy and high Tc superconductivity. The present paper is the preliminary report of our attempt to carry out the secondary electron imaging of this material in a scanning transmission electron microscope (STEM) rather than in a SEM. The advantage of performing secondary electron imaging in a TEM is obvious that, in a TEM, the spatial resolution is higher and many more complementary techniques, e.g, diffraction contrast imaging, phase contrast imaging, electron diffraction and various microanalysis techniques, are available.
TEM characterization of III-V semiconductors heteroepitaxially grown on Si substrates
Authors: Jones K.M. , Al-Jassim M.M.
Published: June 2020

There has been considerable improvement over the last two years in the growth of III-V semiconductors on Si substrates, and some majority carrier devices such as FETs were reported using this technology. However, there are still a number of formidable problems to overcome in order to obtain high quality layers for minority carrier devices. Not excluding serious problems such as the large difference in thermal expansion coefficients, the effects of interface contamination and lattice mismatch were recognized by many workers to be the most adverse. In this work, these effects were investigated using conventional, analytical and high resolution TEM in an attempt to produce better quality epilayers. All layers were grown by MOCVD on (100) Si substrates misoriented by 2° towards (110). The TEM foils were prepared by a combination of mechanical polishing and I/Ar ion beam milling. This mixture of iodine and argon proved to be particularly valuable for milling InP/Si layers. To avoid the incongruent evaporation of phosphorous, the latter was performed at liquid nitrogen temperature using 15-20 μA beam current, 5KeV beam voltage and 12° incidence.
Low-temperature Scanning Electron Microscope constructed with high-excitation objective lens
Authors: Koike H. , Inoué T.
Published: June 2020

Low temperature microscope technology can be traced back to the last century including the time of light microscope, and its history is over a hundred years. In the field of electron microscopy, low temperature techniques such as the freeze-fracture replica, freeze-sectioning, freeze-substitution, etc. were tested up to early 1960s. According to the progress of the rapid-freezing method, the freeze-substitution and freeze-etching replica methods have provided great successful results.

The low temperature scanning electron microscope (LTSEM) was also tested by Echlin et al. in 1970, and thereafter, a number of LTSEM constructions were attempted. These LTSEMs are generally classified into two groups: the type with fracturing and coating facilities directly attached to the SEM column, and the group having a separated preparation chamber and a transfer device. The LTSEM so far constructed were reviewed comprehensively in greater detail. Some such instruments were designed taking account of stringent requirements of low temperature techniques. These systems, however, seemed to be too comprehensive, involving complex procedures as compared withe their resolutions. In comparison with the conspicuous results obtained by other low temperature techniques, the LTSEM can be regarded as still in the stage prior to practical application from the viewpoint of the high resolution. In consideration of these circumstances, the present paper aims at providing a new LTSEM to realize simple operation retaining the advantage of the ultrastructural preservation by the rapid-freezing and the high resolution by introducing the high-excitation objective lens.
Anatomy and cytochemistry of abscission zones by microscopical examination of nitrocellulose tissue prints
Authors: Reid Philip D. , del Campillo Elena
Published: June 2020

Tissue printing on nitrocellulose membranes has been used to localize extensin in soybean seeds and as a matrix for histochemical localization of enzymes in bean abscission zones. Pressing hand cut sections of abscission zones into nitrocellulose membranes results in a tissue print which is seen as a three dimensional image when viewed with side illumination and shows the characteristic morphology and anatomical organization of the tissues in these segments. Changes in the cells of the abscission layer can be observed on the tissue prints as the process of abscission proceeds, and treatment of the tissue prints with antibodies to abscission specific enzymes identifies the cells in the abscission layer.

Ten day old explants of Phaseolus vulgaris c.v. red kidney were induced to abscise by removing the leaf blades. Tissue prints were made on dry nitrocellulose membranes (0.45 μm pore size) at zero time, 24, 48 and 53 h and observed using either transmitted or side illumination at 10X magnification. Some tissue prints were incubated with rabbit 9.5 cellulase antibody followed by exposure to an alkaline phosphatase conjugated-goat antirabbit antibody. Color was then developed using standard alkaline phosphatase substrates. The 9.5 cellulase is an abscission specific form of the enzyme.
Changes in microtubule arrays during cotton fiber development
Authors: Seagull Robert W.
Published: June 2020

Developing cotton fiber provides an excellent model system for the study of microtubule (MT) arrays and their involvement in cell wall deposition. The secondary wall of the cotton fiber is arranged in layers of parallel microfibrils, to produce a polylamellate configuration. Cortical MTs parallel microfibrils and undergo re-orientations which predicted new microfibril orientations. Previous studies describe the general relationship between MTs and microfibrils but provided no quantitative analysis of MT arrays. In this paper quantitative measurements of MT arrays were done during primary and secondary wall synthesis. Changes in the MT array accompany the shift from primary to secondary wall deposition.

Fibers of cotton (Gossypium hirsutum, variety Acala SJ-2) were grown using ovule culture techniques. At various stages of development (days post anthesis, DPA) ovules with attached fibers were fixed in 0.1M phosphate buffered (pH 6.9) 1% glutaraldehyde for 1 h. After a 1 h wash, the fibers were post-fixed in phosphate buffered 1% OsO4. After rapid dehydration with 2,2 dimethoxypropane, cells were infiltrated with Spurr's resin. At this point fibers were removed from ovules and flat embedded between teflon coated microscope slides. Serial section reconstruction analysis of microtubule arrays was done as previously described.
Development and self-repair in hair cell epithelia
Authors: Corwin Jeffrey T.
Published: June 2020

This presentation will attempt to explain current understanding of the cellular mechanisms of normal hair cell development and the mechanisms of hair cell regeneration. Hair cells are the mechanoreceptors that transduce sound and balance stimulation of the ear and water current stimulation of the lateral line organs into electrical activity that is transmitted to the brain. Hair cells have one true cilium, the kinocilium, and 30 to 200 or more stereocilia which are modified, actin-filled microvilli, that project from the flat apical surfaces of the cells. The stereocilia are arrayed across each cell in an “organ pipe” arrangement, with a row of short stereocilia at one end and rows of increasingly taller stereocilia proceeding from that row toward the single eccentrically positioned kinocilium. That asymmetrical surface structure defines the functional polarity of each hair cell, because stimuli that mechanically bend the stereocilia array in the direction of its tall end cause a decrease in the transmembrane potential of the hair cell and increased exocytotic release of neurotransmitter from vesicles at tonically active synaptic sites in the subnuclear region. In that way the appropriately directed bending of the stereocilia causes excitation of neurons that conduct action potentials to the brain. Bending of the stereocilia in the opposite direction causes hyperpolarization of the hair cell, reduction in the exocytosis of neurotransmitter, and a resulting decrease in the frequency of action potentials conducted to the brain.

In most mature organs the orientations of the stereocilia arrays of the hair cells are aligned throughout the epithelia. However, during early development of these cells their cilia bundles are oriented in a nearly random distribution. As the cells differentiate their cilia arrays grow taller and reorient, so that neighbors come into alignment. In some epithelia, such as the auditory epithelium in the cochlea of the chicken, both the number and the maximum length of the stereocilia on hair cells vary systematically along gradients related to cell position in the epithelium. This pattern of sensory cell ultrastructure correlates with the high to low pitch tuning of the basilar membrane that supports the epithelium and with the tuning of the neurons that contact the individual cells. Cells at the distal end of the chicken cochlea have less than 50 stereocilia; cells at the proximal end have over 200. The stereocilia on proximal hair cells are short (<2 microns); those on distal hair cells are long (>5 microns). The reorientation of the stereocilia arrays and their location-specific differences in stereocilia number and length all become recognizable at approximately the time when synapses form between these cells and their neurons, but experiments have shown that these processes of hair cell differentiation can occur in the absence of neurons. Several hypotheses that attempt to explain the control of differentiation in hair cells will be covered
Cytoskeletal functions in sensory receptors
Authors: Burnside Beth
Published: June 2020

Since the shapes of sensory receptors are so exquisitely specialized for mediating their unique functions, the cytoskeletons of sensory cells are deployed for morphogenetic and motile objectives in particularly interesting ways. Receptors erect cytoskeletal scaffolding to support two basic sorts of surface elaborations: 1) those designed to achieve the most effective presentation of specialized membrane laden with receptor proteins (photoreceptors, olfactory receptors, taste cells, and chemoreceptors), and 2) those designed to respond directly to mechanical perturbations in the cell's environment (auditory hair cells, mechanoreceptors). Each of these receptor types has specific structural requirements.

Sensory receptors have built their surface elaborations upon either microtubule- or actin-based scaffoldings. Microtubule-based scaffoldings have evolved from motile cilia, and the axoneme has been modified to various ends. All ciliary-derived receptors so far described, except (curiously) those from the worm Caenorhabdites elegans, are associated with basal bodies which nucleate the assembly of surface specializations. The mechanisms for elaborating the myriad membrane specializations associated with ciliary receptors are not yet understood. Recently it has been shown that in vertebrate photoreceptors, actin is not required for the addition of membrane to the outer segment, but it is required for the proper assembly of new disks .
Mechanisms for establishing and reversing epithelial cell polarity
Authors: Nelson W. James , Wang Allan Z.
Published: June 2020

Polarized epithelial cells play fundamental roles in the ontogeny and function of a variety of tissues and organs. However, the mechanisms involved in the morphogenesis of this important cell type are poorly understood. When epithelial cells, such as Madin-Darby Canine Kidney (MDCK) cells, are induced to develop polarity structurally and functionally different plasma membrane domains (apical and basal-lateral) must be established and maintained (ref. 1). This requires the sorting of constituent proteins to the correct membrane domain and the removal of incorrectly localized proteins. To understand how these domains are formed we designed an experimental situation in which cells that have established membrane polarity in one orientation are forced to reverse this orientation; by observing this reversal we should gain new insight into the mechanisms of membrane domain assembly and disassembly (Figure 1).

We have now established this experimental situation in vitro. Under appropriate growth conditions in suspension culture or in a collagen gel MDCK cells are induced to form multicellular cysts. These multicellular cysts comprise a closed monolayer of cells of defined polarity (see below) that surrounds a fluid-filled lumen. We have begun to analyze morphologically the state of cell polarity of these structures using electron microscopy and immunocytochemistry with antibodies specific for marker proteins of the apical (gpl35) and basal-lateral (Na+,K+-ATPase) plasma membranes, and the tight junction (ZO-1) (Figure 2).
The organization of cell surface membrane domains
Authors: Edidin Michael
Published: June 2020

Cell surface membranes are based on a fluid lipid bilayer and models of the membranes' organization have emphasised the possibilities for lateral motion of membrane lipids and proteins within the bilayer. Two recent trends in cell and membrane biology make us consider ways in which membrane organization works against its inherent fluidity, localizing both lipids and proteins into discrete domains. There is evidence for such domains, even in cells without obvious morphological polarity and organization [Table 1]. Cells that are morphologically polarised, for example epithelial cells, raise the issue of membrane domains in an accute form.

The technique of fluorescence photobleaching and recovery, FPR, was developed to measure lateral diffusion of membrane components. It has also proven to be a powerful tool for the analysis of constraints to lateral mobility. FPR resolves several sorts of membrane domains, all on the micrometer scale, in several different cell types.
Import of proteins into chloroplasts and mitochondria
Authors: Pain D. , Murakami H. , Schnell D. J. , Blobel G.
Published: June 2020

Although both chloroplasts and mitochondria are capable of nucleic acid and protein synthesis, their biogenesis requires the import of a large number of nuclear-encoded proteins that are synthesized on cytoplasmic ribosomes. In the case of both organelles the transfer is post-translational and energy dependent. Most of the nuclear-encoded proteins are synthesized as precursors with an amino-terminal extension known as the signal, transit or pre-sequence. Like proteins destined for the secretory pathway, targeting of nuclear-encoded chloroplast and mitochondrial proteins to the proper cellular location is mediated by these N-terminal topogenic sequences. As is the case for protein translocation across the endoplasmic reticulum or prokaryotic plasma membrane, our data suggest dual recognition of signal sequences for protein import into mitochondria or chloroplasts; first by a soluble recognition system and then by a membrane bound one. The latter has been localised to distinct regions where the inner and outer membrane of these organelles are in close contact.

The in vitro import of cytoplasmically synthesized precursors into chloroplasts has been previously described. We have transcribed mRNA from a cDNA clone coding for a cytoplasmically synthesized polypeptide of the chloroplast stroma, the small subunit of ribulose 1,5,-bisphosphate carboxylase. Translation of the specific mRNA in a wheat germ cell-free system yielded a large precursor (pS), and post-translational incubation with isolated pea chloroplasts resulted in import of pS into the chloroplast stroma accompanied by conversion of pS into the mature form (S) by means of cleavage of an NH2-terminal transit sequence. Import was an energy-dependent process and required ATP hydrolysis. Nonpenetrating ATP-consuming systems had no effect on import when chloroplasts were allowed to synthesize ATP in the stroma in the dark, suggesting that the ATP exerts its effect on import within the stroma and not in the cytosol. Studies with various ionophores demonstrated that ATP hydrolysis within the stroma was not used to generate a membrane potential across membranes.
Image of PhoE Porin in projection at 3.5Å resolution
Authors: Jap B.K. , Walian P. J. , Downing K. H.
Published: June 2020

The outer membrane of Gram-negative bacteria, such as E. coli, contains a high density of a family of pore-forming proteins, which are often called porins. One member of the family, PhoE porin, is expressed under conditions of phosphate starvation, and has been shown to favor the transport of phosphate-containing compounds and negatively charged molecules. The three-dimensional (3-D) structure of PhoE porin obtained from two-dimensional crystals, negatively stained with uranyl acetate, has been determined to a resolution of about 18Å. The projected structure of glucose-embedded PhoE porin has also been obtained to a resolution of about 6.5Å. Based on these results and previous spectroscopic studies, a 3-D model of PhoE porin has been proposed, consisting of a trimer of extended funnel-like structures. Each funnel-like structure comprises a large water filled vestibule leading into a narrower extension. The vestibule wall is formed by β-sheet which has a large fraction of the β-strands oriented perpendicular to the membrane plane. In this report, we present an extension of the resolution to 3.5Å in the projection map of PhoE porin. At this resolution we can confirm that the β-strands of the vestibule are predominantly normal to the membrane plane.

We have recorded high resolution images of trehalose-embedded PhoE porin using both the conventional flood illumination technique and the spot scan illumination method. Images with high quality as judged from optical diffraction were digitized and processed to correct for crystal distortions, lens aberrations and illumination tilt. Phases obtained from several high quality images were used to determine the phases of the reflections used in reconstructing the projected map. The amplitudes of the reflections needed to generate the reconstruction were obtained from the 3-D diffraction data set of PhoE porin, which has been determined to a resolution of about 2.8Å. A typical electron diffraction pattern of PhoE porin at zero tilt angle is shown in Figure 1.
Cryo-electron microscopy of cauliflower mosaic virus
Authors: Cheng R. H. , Olson N. H. , Baker T. S.
Published: June 2020

Cauliflower mosaic virus (CaMV), the type member of the Caulimovirus family, is one of the most extensively studied plant viruses since it was one of the first plant viruses shown to encapsidate a genome of double stranded DNA. This virus has served as a model system for studying plant gene organization, expression and replication and is potentially useful as a gene vector for the genetic manipulation of higher plants. Despite being well characterized in terms of its molecular biology, little is known about the structure, organization and assembly of mature CaMV virions.

CaMV virions have a molecular mass of ˜22.8x106 daltons and a sedimentation coefficient of 208S.2 In negatively-stained samples, the diameter of the virus was determined to be 50.3±1.4 nm. The capsid consists of multiple copies of a single, phosphorylated polypeptide (37-42 kDa) which is presumed to be post-translationally modified from the 58kDa primary product of gene IV. The sizes of the virion and mass of the capsid protein indicate that there may be 420 copies of the polypeptide, arranged with T=7 icosahedral lattice symmetry, although no direct evidence exists to support this model. Projected images of CaMV particles, examined by conventional electron microscopy procedures, are difficult to interpret since the details are relatively smooth and featureless. The organization of the circular doubled-stranded DNA molecule (˜4.9xl06 daltons) is unknown: neutron diffraction experiments indicate that it is mainly confined to the region between radii 15.0-21.5 nm. The current study is aimed at obtaining a reliable three-dimensional structural determination of CaMV by examining purified virus samples using recently developed cryo-electron microscopy techniques and image analysis procedures.
The hyaline layer in early development of the sea urchin: Cell-extracellular matrix interactions
Authors: McClay David R. , Alliegro Mark C. , Black Steven D
Published: June 2020

The hyaline layer is released by the sea urchin zygote starting about 30 seconds after fertilization. This layer is elevated above the surface of the zygote where it serves as a protective layer, a barrier to polyspermy, and as an adhesive substrate for the early stages of development. We have been interested in learning how the hyaline layer is stored in the egg, how it is released after fertilization, and how it functions as an extracellular matrix during early development. The layer contains about fifteen abundant proteins plus a number of others that may be present or may contaminate preparations of the layer during isolation procedures. Our goal was to identify the major components of the hyaline membrane, to follow assembly of the structure after fertilization, and to identify molecules that are active as adhesive substrates for cells.

Using double-label immunofluorescence and ultrastructural immunogold localization of polyclonal and monoclonal antibodies, the components of the hyaline layer have been localized to four vesicle classes in the unfertilized egg. Centrifugation studies on unfertilized eggs and double-label immunofluorescent studies have shown that the four classes each contain a distinct group of proteins. The four vesicles were followed through oogenesis to learn when proteins of each class were synthesized by the oocyte. Each of the four classes (cortical granules, basal lamina vesicles, apical vesicles and echinonectin vesicles) were synthesized, localized, and relocalized in the oocyte by unique spatial and temporal pathways.
Ultrastructure of colonic biopsies in gardner's syndrome
Authors: Siew S. , Lev R. , Lebenthal E. , Rossi T.
Published: June 2020

Gardner's Syndrome is a familial condition which is inherited as an autosomal Mendelian dominant with a high degree of penetrance. It is characterized by the development of multiple adenomatous polyps in the gastrointestinal tract with a particular predilection for the colon. This multiple polyposis is associated with desmoid tumors. The condition carries a high malignant potential and carcinoma of the colon may develop by the age of forty. The gross and histologic features of the polyps have been defined. We undertook a blind study of 19 colonic endoscopic biopsies by means of transmission electron microscopy (TEM) in order to elucidate the applications of this technique in the investigation and diagnosis of Gardner's Syndrome.

Endoscopy of the colon was performed on 8 patients; 6 males and 2 females. Their ages ranged from 2-17 years with a mean of 9.1. Two of the cases were siblings from a family with Gardner's Syndrome, who showed evidence of the disease, another two were siblings from a family with Gardner's Syndrome, who did not manifest the disease. The remaining 4 patients were normal controls. Biopsies obtained by means of endoscopy were fixed immediately either for histologic examination or TEM. The tissue was processed in the conventional manner.
TEM studies of primitive neuroectodermal tumors with neuronal and glial differentiation
Authors: Harb Joseph M.
Published: June 2020

The term primitive neuroectodermal tumor (PNET) was originally applied in 1973 by Hart and Earle to refer to a group of undifferentiated cerebral neoplasms in children. Since that report, few studies have utilized the transmission electron microscope (TEM) to establish the identity of the tumor cells and to clarify the propensity of the PNETs for pluripotential differentiation. Of particular interest are reports which suggest the possibility of simultaneous neuronal and glial differentiation within the same cell. It would be of significant interest to know if the propensity to divergent differentiation can be explained by a single population of neoplastic cells that have the potential to differentiate in multiple directions. We will present a small series of cases with ultrastructural evidence that some of the cells in the tumors express both neuronal and glial features.

The first case is a primary cerebral neuroblastoma which was associated with a population of neoplastic glial cells. At the ultrastructural level neuroblast and glial cell populations were identified. We also recognized a population of cells which displayed a continuous basal lamina and rare, poorly developed junctional complexes. Of particular interest was yet another, smaller, population of cells which displayed both dense-core granules and microtubules typical of neuroblasts and abundant cytoplasmic filaments typical of glial cells (Figure 1). In two other cases, the astrocytic nature of the cells was confirmed at the ultrastructural level on the basis of prominent glial filaments in the cytoplasm. However, some of the astrocytes in one of the cases were invested partially by a distinct basal lamina (Figure 2), and there were dense-core granules in the cytoplasm (Figure 2, inset).
Alteration in vitreal structure following C3F8 injection
Authors: Panessa-Warren Barbara J. , Maisel James , Warren John B.
Published: June 2020

Although the use of intraocular perfluorocarbon gases has been demonstrated to be a clinically useful procedure for retinal compression and diagnostic procedures, the effect of the gas expansion to 90% ocular volume causes the displacement of the vitreous. This investigation examines the morphological changes in the vitreous of 36 rabbit eyes following C3F8 intravitreal gas injection, by light (LM), transmission (TEM) and scanning (SEM) electron microscopy. Lincoff et al have demonstrated that C3F8gas exhibits a fourfold expansion of its volume at 3-4 days after injection into the vitreous. Following expansion the gases disappear logarithmically with the volume of the bubble following first order decay kinetics. For the rabbit, the C3F8 half-life is six days, with the total reabsorption of the gas in 40 days. To determine whether initial structural changes following gas injection eventually resolved, eyes were studied at 3, 6, 8, 16, 41 and 64 days post injection.

Four pigmented and 14 albino mature (3-4 Kg) rabbits were anesthetized and given topical proparacaine anesthetic prior to injection into the inferior vitreous cavity with 0.1, 0.3 or 0.4 cc filtered C3F8. An indirect ophthalmoscope was used to direct the 30 gauge needle to a position 2-3 mm posterior to the limbus. In each case, the contralateral eye was used as the normal control. Animals were euthanized with intravenous T61 solution and the eyes immediately enucleated and frozen in liquid nitrogen. While still submerged in liquid nitrogen the tissue was placed in a deep freeze and allowed to equilibrate to −80°C for 24 hrs. Eyes were cryosectioned at −20°C and the sections placed on prechilled glass slides, cover slips, sapphire wafers or pyrolytic graphite planchets. For LM histochemistry, the frozen sections were placed in 95% ethanol 10 min and stained using a Papanicolaou method. To identify collagen, Van Gieson's picric acid fuchsin and 2.5% aniline blue were used. Proteoglycans were stained with pH 1 or pH 1.5 alcian blue or 0.5% ruthenium red. Some cryosections were freeze dried or fixed in 3% glutaraldehyde, dehydrated and dried by the critical point method (CO2) for SEM examination of an AMRay 1000A equipped with a lanthanum hexaboride gun at Brookhaven National Laboratory, Upton, NY. Tissue for routine TEM was fixed immediately following enucleation in 3% glutaraldehyde in 0.1 M cacodylate buffer (pH 7.4), post fixed in 1% aqueous OsO4, dehydrated in acetone and embedded in Epon 812. To identify and retain proteoglycans, some eyes were fixed in 2% glutaraldehyde in 0.1 M cacodylate containing 0.01% ruthenium red. Both unstained and stained (Ur-acetate and Pb-citrate) plastic thin sections were examined at 80 kV on a Philips 300.
Identification of viruses causing gastroenteritis in central florida: A one-year survey
Authors: Price G. , Franklin R. , Cerezo L.
Published: June 2020

Acute gastroenteritis is known to cause millions of deaths worldwide, many of which are attributable to viral agents. Death is caused by cardiac arrest as a result of dehydration and electrolytic imbalance brought on by vomiting and diarrhea. The majority of these deaths occur in developing countries where public sanitation and health care is at a minimum. Deaths from gastroenteritis in the United States have dropped considerably since the 1900's because of improvements in health care.

Viruses may be identified as the pathological agent of gastroenteritis by a variety of methods, one of which is morphological identification by electron microscopy (EM). Electron microscopy offers a rapid method for identifying viruses regardless of serotype, but requires a concentration of viral particles of between 105- 106/ml to be effective. This concentration problem can be overcome by ultracentrifu-gation, although detection of Norwalk Agent requires immuno-electron microscopy.
Neutrophil pseudoplatelets in subgingival plaque and crevicular fluid samples from periodontal diseased sites
Authors: Hanker J , Burkes E.J. , Greco G. , Scruggs R. , Giammara B.
Published: June 2020

The mature neutrophil with a segmented nucleus (usually having 3 or 4 lobes) is generally considered to be the end-stage cell of the neutrophil series. It is usually found as such in the bone marrow and peripheral blood where it normally is the most abundant leukocyte. Neutrophils, however, must frequently leave the peripheral blood and migrate into areas of infection to combat microorganisms. It is in such areas that neutrophils were first observed to fragment to form platelet-size particles some of which have a nuclear lobe. These neutrophil pseudoplatelets (NPP) can readily be distinguished from true platelets because they stain for neutrophil myeloperoxidase. True platelets are not positive in this staining reaction because their peroxidase Is inhibited by glutaraldehyde. Neutrophil pseudoplatelets, as well as neutrophils budding to form NPP, could frequently be observed in peripheral blood or bone marrow samples of leukemia patients. They are much more prominent, however, in smears of inflammatory exudates that contain gram-negative bacteria and in gingival crevicular fluid samples from periodontal disease sites. In some of these samples macrophages ingesting, or which contained, pseudoplatelets could be observed. The myeloperoxidase in the ingested pseudoplatelets was frequently active. Despite these earlier observations we did not expect to find many NPP in subgingival plaque smears from diseased sites. They were first seen by light microscopy (Figs. 1, 3-5) in smears on coverslips stained with the PATS reaction, a variation of the PAS reaction which deposits silver for light and electron microscopy. After drying replicate PATS-stained coverslips with hexamethyldisilazane, they were sputter coated with gold and then examined by the SEI and BEI modes of scanning electron microscopy (Fig. 2). Unstained replicate coverslips were fixed, and stained for the demonstration of myeloperoxidase in budding neutrophils and NPP. Neutrophils, activated macrophages and spirochetes as well as other gram-negative bacteria were also prominent in the PATS stained samples. In replicate subgingival plaque smears stained with our procedure for granulocyte peroxidases only neutrophils, budding neutrophils or NPP were readily observed (Fig. 6).
Neotendon formation using a collagen fiber tendon prosthesis
Authors: Wasserman Arthur J. , Kato Y. Pedro , Ganim Don , Dunn Michael G. , Silver Frederick H.
Published: June 2020

Damage to tendons occurs commonly during physical activity. Tendons can be repaired using natural and synthetic materials. The purpose of a tendon prosthesis is to provide support while allowing a new tendon to form. The newly formed tendon should have morphological and mechanical properties identical to the normal tissue. Neotendon formation can be assessed ultrastructurally to compare its morphology with that of mature tendon. The extent of cell ingrowth, collagen fibril diameter, proteoglycan (PG)/collagen interactions and collagen fibril bundle formation are all morphological criteria to evaluate the status of tendon repair. The purpose of this study is to ultrastructurally evaluate the mechanism by which a reconstituted collagen fiber tow is replaced by neotendon.

Collagen fibers of the tow were prepared from insoluble type I collagen derived from bovine corium and crosslinked by severe dehydration followed by treatment with cyanamide, as previously described. A tow of 250 fibers was coated with a 1% type I collagen dispersion to form a thin ribbon prosthesis. Mature New Zealand white rabbits weighing 6-7 lbs were anesthetized and the Achilles tendon was removed and replaced with a sterile collagen fiber tow. At 3 and 10 weeks postoperatively the explants were fixed for conventional TEM and SEM as previously described.