Electron Photomicrographs Research Articles

Sorption of Heavy Metals on a Coal BeneficiationTailing Material. I: Characterization and Mechanisms Involved

A Brazilian coal jigging refuse was studied as a sorbing material for heavy metal ions such as copper, zinc and nickel. This refuse was characterized in terms of its petrographic composition and surface properties. Metal ions uptake mechanism involved was studied through sorption isotherms, scanning electron photomicrographs scanning electron spectral analysis and zeta potential measurements. Sorption isotherms showed saturation values of the order of 2.2 mEq · g−1 at optimal pH of 9.5. Main compounds responsible for the sorption were found to be kaolinite, vitrinite and less quartz and pyrite. Probable mechanisms involved in the sorption were found to be the interfacial complexation between the hydrolyzed species and the negatively charged silicate or carboxylic (at the vitrinite surface) and surface precipitation of the metal hydroxide. Ion exchange was found to have a minor role in this system. It is concluded that because of the affinity and high sorption values for metal ions, this coal jigging refuse has a high potential as sorbing material at a very low cost.

Two New <I>Allocapnia</I> from Eastern North America (Plecoptera: Capniidae)

Two new species of Allocapnia in the recta complex are described, Allocapnia sequatchie n. sp. and A. starki n. sp. from Tennessee and Mississippi, respectively. Descriptions are supported by illustrations and scanning electron photomicrographs. Additionally, scanning electron photomicrographs of an A. recta × loshada hybrid from southwestern Virginia are presented.

The Effect of Ultrasonic Vibration on the Compaction Characteristics of Paracetamol

An ultrasonic (US) compaction rig has been developed that is capable of providing compaction pressure together with high‐power ultrasonic vibrations of 20 kHz to a powder or granular material in a die. The rig has been used to investigate the effect of US on the compaction properties of paracetamol, a drug that produces tablets that are weak and frequently exhibit capping. It was found that coherent paracetamol tablets could be prepared by US‐assisted compaction at pressures as low as 20 to 30 MPa. Application of US before and after compaction was not found to be as effective as US applied during compaction. The breaking forces of the tablets produced with US applied during compaction were found to be consistently significantly higher than when compaction was performed conventionally or with US applied before or after compaction. The application of US during compaction made it possible to increase tablet breaking force, typically by a factor of 2 to 5. It was concluded that pressure should be applied together with US to achieve a better acoustical contact, which is required to transmit vibrations from the horn to the material and also to bond the surfaces of the particles.US application during compaction also resulted in an increase in apparent density, in relation to the apparent density of conventionally prepared paracetamol tablets, of up to 12.8%. US appears to improve particle rearrangement and provide energy for partial melting of particle asperities and subsequent fusion of particle surfaces, thus increasing interparticulate bonding. Development of solid bridges between the particles during US‐assisted compaction was observed on scanning electron photomicrographs. Solid bridge formation was thought to result in a reduction of void space, which in turn reduced the rate of water penetration into the compacts and consequently increased tablet disintegration and drug dissolution times.It was found that the results of US‐assisted compaction are influenced by formulation and US time. An increase in binder (polyvinylpyrrolidone) concentration and/or US time resulted in a significant increase in the breaking forces of paracetamol tablets produced with US. When paracetamol was mixed with a second material, such as dicalcium phosphate dihydrate and microcrystalline cellulose, stronger compacts were prepared by US‐assisted compaction compared with the tablets containing no filler. Positive interactions were considered to have occurred as a result of US‐induced bonding between the two materials.Overall, the application of US was found to significantly improve the compaction properties of paracetamol. © 2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89:705–723, 2000

A note on the possible electrostatic disruption of bacteria

Recently published scanning electron and transmission electron photomicrographs of cells of the bacterium Escherichia coli exposed to plasma glow discharges at atmospheric pressure indicate physical disruption of their outer cell membranes. However, the mechanism of cell disruption was unclear. Here, we propose and model an electrophysical mechanism for this phenomenon, namely, the electrostatic disruption of the cell membrane, which takes place when it has acquired a sufficient electrostatic charge that the outward electrostatic stress exceeds its tensile strength. It also appears that surface roughness or irregularity would render it more sensitive to electrostatic disruption.

Digital imaging analysis for the study of endotoxin-induced mitochondrial ultrastructure injury.

Primary defects in mitochondrial function have been implicated in over 100 diverse diseases. In situ, mitochondria possess unique and well-defined morphology in normal healthy cells, but diseases linked to defective mitochondrial function are characterized by the presence of morphologically abnormal and swollen mitochondria with distorted cristae. In situ study of mitochondrial morphology is established as an indicator of mitochondrial health but thus far assessments have been via subjective evaluations by trained observers using discontinuous scoring systems. Here we investigated the value of digital imaging analysis to provide for unbiased, reproducible, and convenient evaluations of mitochondrial ultrastructure. Electron photomicrographs of ileal mucosal mitochondria were investigated using a scoring system previously described by us, and also analyzed digitally by using six digital parameters which define size, shape, and electron density characteristics of over 700 individual mitochondria. Statistically significant changes in mitochondrial morphology were detected in LPS treated animals relative to vehicle control using both the subjective scoring system and digital imaging parameters (p < 0:05). However, the imaging approach provided convenient and high throughput capabilities and was easily automated to remove investigator influences. These results illustrate significant changes in ileal mucosal mitochondrial ultrastructure during sepsis and demonstrate the value of digital imaging technology for routine assessments in this setting.

Analysis of Spatial Distribution of Vesicles in Presynaptic Terminals of the Hippocampus in vivo and in vitro

A comparative morphometric analysis of electron photomicrographs of the presynaptic terminals in cultured in vitro for 7 days CA1 hippocampal slices from 7-day-old rats and in the hippocampi of 14-day-old rats was conducted. As compared with the terminals of intact neurons, the terminals of cultured cells were larger and contained a greater amount of synaptic vesicles, which, however, to a lesser extent were united in clusters. Distributions of the vesicle profiles in cultured slices were characterized by a greater distance to the nearest neighbor. Obviously, such structural features should be taken into account when interpreting data obtained in electrophysiological studies on hippocampal slice cultures.

Study of P(AM-NVP-DMDA) hydrophobically associating water-soluble terpolymer

A new kind of hydrophobically associating water-soluble terpolymer P(AM-NVP-DMDA) was synthesized by free radical terpolymerization. Compared with micellar terpolymerization, this terpolymerization can be conducted in aqueous solution in absence of external surfactant, because the hydrophobic monomer is surface active. Synthesis, structure, and solution properties of P(AM-NVP-DMDA) terpolymer were studied, including its electrolyte effect, rheological behavior, temperature dependence of viscosity, dilute solution property, and the polymer-alkali, polymer-surfactant interaction. The terpolymer shows strong hydrophobic effect, and the terpolymer aqueous brine solution exhibits high viscosity at low polymer concentration. Incorporation of N-vinyl-pyrrolidone into the terpolymer causes an improvement in thermal stability of the terpolymer. The transmission electron photomicrograph analysis of the terpolymer indicates that the presence of the microphase separation of the terpolymer in aqueous solution plays an important role in the viscosification efficiency of the terpolymer.

Effect of different types of maltodextrin and drying methods on physico-chemical and sensory properties of encapsulated durian flavour

A study on durian (Durio zibethinus Murr) flavour encapsulation was conducted using three types of maltodextrin – glucose syrup solid (GSS), fieldose PHS-15 and pasilli – and two drying methods: spray and freeze drying. Results showed that the three types of maltodextrin used in this study proved to be suitable for use in the preparation of durian flavour encapsulation. GSS, however, was shown to be the most suitable encapsulating agent in maintaining the original aroma of durian. For both physico-chemical and sensory analyses, durian powder dried using the freeze drying method was better in terms of moisture, water activity, fat, total sugar, colour, bulk density, degree of lump, scanning electron photomicrograph microstructure and sensory attributes, including aroma, appearance and colour, compared to the durian powder dried using the spray drying method. © 1999 Society of Chemical Industry

Effect of different types of maltodextrin and drying methods on physico‐chemical and sensory properties of encapsulated durian flavour

A study on durian (Durio zibethinus Murr) flavour encapsulation was conducted using three types of maltodextrin – glucose syrup solid (GSS), fieldose PHS-15 and pasilli – and two drying methods: spray and freeze drying. Results showed that the three types of maltodextrin used in this study proved to be suitable for use in the preparation of durian flavour encapsulation. GSS, however, was shown to be the most suitable encapsulating agent in maintaining the original aroma of durian. For both physico-chemical and sensory analyses, durian powder dried using the freeze drying method was better in terms of moisture, water activity, fat, total sugar, colour, bulk density, degree of lump, scanning electron photomicrograph microstructure and sensory attributes, including aroma, appearance and colour, compared to the durian powder dried using the spray drying method. © 1999 Society of Chemical Industry

A new method for preparing electron microscopic specimens of Helicobacter pylori.

Abstract A new method for preparing electron microscopic specimens of Helicobacter pylori was developed and used to examine the ultrastructure of this bacterium. We have also investigated the morphological changes in the bacterium when exposed to amoxicillin using our new method. Bacterial specimens for electron microscopy are usually prepared by collecting the bacteria by centrifugation during the fixation and dehydration processes. In our new method the bacteria are filtered through and adsorbed onto a filter before fixation, and the entire filter containing the adhered bacteria is fixed and dehydrated. Using this method we were able to obtain electron photomicrographs in which the external appearances or internal structures of the bacteria were well conserved. The advantages of this method are that it uses only a small amount of bacterial suspension, shortens the time required for the dehydration procedure, and keeps the artifacts to the minimum. Amoxicillin treatment resulted in coccoid form with blebs in the bacterial surface and the appearance of vacuoles, granules, and an area of low electron density in the cytoplasm at one and four minimum inhibitory concentrations. These changes were consistent with results previously reported in the literature.

Distribution of carboxyl groups in carboxymethylated cotton fibers

Cotton cellulose was partially carboxymethylated by a one-bath method using monochloroacetic acid and sodium hydroxide. A method was developed to study the extent of the carboxymethylation of cellulose within the cotton fibers using scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Uranyl nitrate was used as a stain. Scanning electron photomicrographs revealed that the carboxymethylation of cellulose occurred throughout the cotton fiber cross section. However, the X-ray microanalysis data indicated a variation in the extent of the reaction among the morphological regions that have different chemical accessibility. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 203–207, 1999

Subnuclear organization of the rat habenular complexes.

The habenular complexes represent phylogenetically constant structures in the diencephalon of all vertebrates. Available evidence suggests that this area is engaged in a variety of important biological functions, such as reproductive behaviors, central pain processing, nutrition, sleep-wake cycles, stress responses, and learning. Based on Nissl-stained sections, one medial nucleus and two lateral nuclei (divisions) have been widely accepted in the rat. Cytochemical, hodologic, and functional studies suggest a considerably more complex subnuclear structure. To improve our knowledge of the precise structural composition of the habenular complexes, we have systematically investigated their fine ultrastructure in the rat. Based on the detailed analysis of complete series of large, semithin sections supplemented with electron photomicrographs of selected fields, clear criteria for the delineation of five distinct subnuclei of the medial and ten subnuclei of the lateral habenular complexes were elaborated for the first time. All 15 subnuclei were reconstructed, and their dimensions were determined. A medial and lateral stria medullaris were described. Different roots of the fasciculus retroflexus were differentiated within the medial and lateral habenular complexes. The topographical relationships with respect to the adjacent habenular areas as well as to the neighboring thalamic nuclei were identified and demonstrated. The new understanding of the subnuclear organization of the habenular complexes certainly will facilitate further functional investigations. Whether the newly identified subnuclei finally will be recognized as functionally distinct awaits ongoing immunocytochemical, hodologic, and functional studies.

Morfologia dos tricomas em Tibouchina sect. Pleroma (D. Don) cogn. (melastomataceae)

Melastomataceae é a família que apresenta a maior diversidade de tricomas. Dr. Wurdack em seu "Atlas of hairs" reconheceu 46 tipos de tricomas para as Melastomataceae neotropicais com o uso de MEV, e referiu 17 destes para o gênero Tibouchina. Em Melastomataceae a morfologia dos tricomas tem sido extensivamente usada na delimitação dos táxons, assim como em estudos que antecederam ao trabalho de Cogniaux, a monografia das Melastomataceae brasileiras publicada em 1885. Em Tibouchina sect. Pleroma a morfologia dos tricomas foi substancial para a circunscrição de várias espécies. O uso da MEV permitiu uma caracterização dos 15 tipos diferentes de tricomas observados nas 41 espécies examinadas. Os diferentes tipos são descritos com base no aspecto morfológico tanto em MO como em MEV e ilustrados através de eletromicrografias de varredura e fotomicrografias.

Spatial and Temporal Distribution of Foraminifera in Sediments off the Central West Coast of India and Use of Their Test Morphologies for the Reconstruction of Paleomonsoonal Precipitation

From the shallow region off the central west coast of India, 21 samples of surface sediments (ranging in depth from 22 to 52 m) along with two sediment cores of 4.80 m and 4.00 m (surface/subsurface) have been analyzed for foraminiferal composition and diversity. A total of 177 species have been identified and illustrated by scanning electron photo micrographs. Seventy-two genera, 47 families, 26 super families and 5 sub orders are represented. In order to have insight into paleoclimatic changes in this region, quantitative spatial distribution data was generated for morpho-groups (angular-asymmetrical and rounded-symmetrical). The distribution revealed less abundance of angular-asymmetrical forms at the river mouth thus indicating an inverse relationship of angular-asymmetrical morpho-groups with river discharge (low salinity water). The reverse is true for rounded-symmetrical forms. The down core profiles of these parameters revealed major wet periods at around 3200 years BP and 1000 AD separated by a dry spell at around 2000 years BP. Our inference is in agreement with the climatic conditions reported elsewhere in the world.

Sister‐group relationships of the Platygastroidea and Chalcidoidea (Hymenoptera) — an alternate hypothesis to Rasnitsyn (1988)

Evidence for the hypothesis that Platygastroidea and (Chalcidoidea + Mymarommatoidea) are sister groups is reviewed and an alternate hypothesis of relationships is proposed for Platygastroidea. Platygastroidea is postulated to form a monophyletic group with Pelecinidae, Proctotrupoidea and Vanhorniidae based on common possession of an annular pronotum and a mesopleural‐mesotrochanteral muscle. Hypotheses of character‐state transformation are illustrated diagrammatically to explain distribution of the mesotrochanteral depressor muscle and relative structure of the pronotum, mesothoracic spiracle, prepectus, and pronotal‐mesepisternal attachment throughout the nonaculeate Apocrita. The states of 16 characters are defined in one table and another table summarises the distribution of the states in Orussidae and Apocrita. Retention of an independent prepectus and a mesotergal‐mesotrochanteral depressor muscle indicates that Chalcidoidea + Mymarommatoidea are a relatively early clade of Apocrita but does not indicate exact relationships. Chalcidoidea + Mymarommatoidea are indicated as possibly being more closely related to Diapriidae or Ceraphronoidea based on other characters. It is postulated that structure of the mesocoxal articulation of taxa assigned to the Evaniomorpha may represent a retained symplesiomorphy rather than a synapomorphy. Mesocoxal articulatory structure is illustrated by scanning electron photomicrographs.

Three-dimensional analysis of vacuoles and surface invaginations of capillary endothelia in the eel rete mirabile

One layer of attenuated endothelia of continuous capillaries provides a partially selective diffusion barrier between the blood and the interstitium. Ultrastructures of membrane specialization without the known physiologic functions have been found in blood vessel endothelia. The vacuolar profiles or vacuole-like, membrane-bound structures, which are larger than plasmalemmal vesicles, have been observed routinely in normal endothelial cytoplasm or in blood vessels challenged by insults in electron microscopic studies. Three-dimensional information from serial sections is required to understand the organization and functions of vacuole-like structures in capillary endothelium. The capillaries in eel retia mirabile were perfused with electron-dense tracers, glutaraldehyde in buffer, and were processed for transmission electron microscopy. Ribbons of serial thin sections without counterstaining were examined under a transmission electron microscope. The vacuolar profiles inside endothelial cytoplasm were investigated with the techniques of serial section analysis and three-dimensional reconstruction from serial sections. The vacuole-like structures inside endothelial cytoplasm either were connected to extracellular (luminal, abluminal) compartments or existed as isolated vacuoles from serial section analysis. In the eight series examined in this study, six of ten vacuole-like structures were classified as isolated vacuoles inside endothelia, and their diameters ranged between 186 nm and 266 nm. Two of ten vacuole-like structures were found to extend to the luminal surface of capillaries as luminal, pocket-like invaginations. One of ten vacuole-like structures was found to be connected to the albuminal compartment, and another one existed as an extracellular compartment surrounded by endothelia. Three-dimensional projection of the vacuolar compartments from serial sections showed that endothelial cytoplasm of sheet shape protruded and folded over adjacent endothelium. Three-dimensional information from serial sections reveals the organization of vacuolar profiles and pocket-like invaginations from the cell surfaces in capillary endothelium. The vacuolar profiles in capillary endothelia in two-dimensional electron photomicrographs may represent the extracellular compartments surrounded by the endothelial finger-like extensions. The results indicate that the luminal and abluminal surfaces of the capillary lumen are not smooth or static, and endothelia may change their shape in three dimensions through cytoplasmic protrusions when the tissue environment changes.

Petrologic evidence for K-feldspar metasomatism in granulite facies rocks

We present evidence for K-feldspar metasomatism in charnockitic granulites from two well-known terranes: the Shevaroy Hills Massif, S. India (750°C, 8 kbars) and the Bamble Sector, S.E. Norway (790°C, 7.5 kbars) in the form of K-feldspar veins principally along plagioclase and quartz grain boundaries and in the form of highly variable antiperthitic patches of K-feldspar in an uneven scattering of plagioclase grains. With one exception, orthopyroxene or amphibole grains in contact with these K-feldspar veins show no alteration to secondary biotite, indicating that the H 2O activity of the fluids responsible for these veins must have been relatively low. A high Ba concentration in these veins also suggests a metasomatic origin. Point counted, back-scattered electron photomicrographs, along with microprobe analyses, provide reintegrated K-feldspar and plagioclase compositions for 8 to 12 predetermined random areas per thin section for three samples from Bamble and three samples from the Shevaroy Hills. These reintegrated feldspar compositions plot over a range of temperatures on the feldspar ternary for each sample, and indicate saturation temperatures above the mean temperature for either region with a few reintegrated compositions above the 1000°C isotherm and with the lower cut-off temperatures at 700°C and 600°C for the Shevaroy and Bamble samples, respectively. These patterns suggest that exsolution alone could not have been responsible for the formation of the K-feldspar veins and patches in these rocks. We suggest that these veins are due to the influx of complex, supercritical, low H 2O activity brines shortly after peak metamorphic conditions, that this influx continued during the initial phases of post-peak metamorphic uplift and that these fluids represent the first stage in a series of fluid influxes in which the H 2O activity increased as uplift continued. Reaction of these brines with potassium-undersaturated plagioclase grains formed K-feldspar veins along grain boundaries and fractures, as well as diffusing into the plagioclase, which became supersaturated, and exsolved K-feldspar as antiperthite patches during uplift and cooling. Formation of secondary biotite halos around orthopyroxene in one sample associated with these K-feldspar veins can be explained by heightened H 2O activity in the brines due to enrichment in H 2O, emplacement of the veins at lower pressure during uplift or both compared to the other Shevaroy and Bamble samples.

Fibronectin: structure, assembly, and cardiovascular implications.

In the past 2 decades, it has been appreciated that the functions of the extracellular matrix (ECM) are not entirely structural. ECM components interact with specific adhesion receptors on cell surfaces and regulate various cellular functions, including differentiation, proliferation, migration, and apoptosis. Fibronectin (FN) is a paradigm adhesive protein, nonreactive with adhesion receptors in its soluble state but highly adhesive when insoluble. Polymerization of FN into the ECM must be tightly regulated to ensure that the adhesive information in the ECM is appropriate. FN exists in a soluble protomeric form in micromolar concentration in blood plasma and in an insoluble multimeric form in the ECM.1 2 Unlike fibrillar or basement membrane collagens, laminins, actin, and tubulin, circulating FN does not self-polymerize in physiologically relevant solutions. Furthermore, there is little passive accumulation of FN in preexisting ECM. Rather, assembly of FN takes place at specialized areas on the cell surface.3 FN is especially abundant in the ECM of embryonic and regenerating or injured tissues, although it can be found in most ECMs, including basement membranes. FN interacts with cells through integrins, heterodimeric transmembrane receptors linking the ECM to the intracellular cytoskeleton and signaling pathways. The aim of this review is to describe the mechanisms and consequences of FN deposition and give a brief overview of the significance of FN for selected areas of cardiovascular research. In the first section we describe important features of the FN molecule that account for its multiple functions. Next, we focus on the assembly process, ie, the conversion of soluble FN to its active, adhesive, insoluble form. Finally, we discuss several areas of cardiovascular research in which FN may have an important role, exemplifying how the adhesive information of FN can drive pathophysiological processes. Soluble FN is a dimeric glycoprotein. Each subunit is a …

Influence of quench medium on the structure and gas permeation properties of cellulose acetate membranes

Integrally skinned asymmetric cellulose acetate membranes made by the wet phase inversion for removal of CO2 from natural gas were investigated. The membrane was cast with the membrane-forming systems of cellulose acetate–acetone and quench media, such as methanol, ethanol and isopropanol, respectively, without heat-treating and multistage exchange process. By means of evaluation on separating characteristics of the membrane for CO2/CH4, observation of morphologies by scanning electron photomicrographs and analysis of the phase diagrams on the membrane-forming systems, it has shown that the membrane-forming system of cellulose acetate–acetone–methanol is quite suitable to prepare integrally skinned asymmetric cellulose acetate membranes for gas separation with good selectivity CO2/CH4 = 30 and flux coefficient = 2.4 × 10−5 cm3/cm2 − s − cm Hg. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1269–1276, 1998

Effect of Formation and Growth of Dislocation Loops and Cavities on Low-Temperature Swelling of Irradiated Uranium-Molybdenum Alloys

AbstractScanning electron photomicrographs of U–10 wt.% Mo irradiated at low temperature in the Advanced Test Reactor (ATR) to about 40 at.% burnup show the presence of cavities. We have used a rate-theory-based model to investigate the nucleation and growth of cavities during low-temperature irradiation of uranium-molybdenum alloys in the presence of irradiation-induced interstitial-loop formation and growth. Our calculations indicate that the swelling mechanism in the U–10 wt.% Mo alloy at low irradiation temperatures is fission-gas driven. The calculations also indicate that the observed bubbles must be associated with a subgrain structure. Calculated bubble-size-distributions are compared with irradiation data.