bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.