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At least 1,315 records · Page 73Linked to original sources
PubMed1991

Grain boundary character distributions in Ni-16Cr-9Fe using selected area channeling patterns: methodology and results.

Selected area channeling patterns imaged on an SEM are digitized and displayed on the screen of a Macintosh computer, on which the user selects channeling bands that are measured to determine orientation. Grain boundary misorientations are found using the orientation information for pairs of grains adjacent at grain boundaries, and the boundaries are classified as low angle boundaries (LABs), coincident site lattice boundaries (CSLBs), or general boundaries (GHABs) based on the misorientation information. The technique was implemented to analyze the grain boundary character distributions (GBCDs) in Ni-16Cr-9Fe. The GBCDs of solution annealed material were similar to those expected in an aggregate of randomly oriented polycrystals. However, sequential thermomechanical treatments (5% tensile strain + 945 degrees C:75 min + 2% tensile strain + 890 degrees C:15 h + 3% tensile strain + 890 degrees C:20 h or 9% compressive strain + 890 degrees C:20 h + 9% compressive strain + 890 degrees C:20 h + 3% compressive strain + 890 degrees C:15 h) applied after the solution anneal lowered the proportions of GHABs in the GBCDs from 76-79% to 47-64%. The CSL-enhanced GBCDs of both the tensile-deformed samples and the compression-deformed sample appear to have evolved mainly through impingement of twin and twin-related boundaries during recrystallization; the CSL-enhanced GBCD of a compression-deformed sample appears to have been influenced by grain rotation processes to a greater degree than were the tensile-deformed samples The CSL boundaries in the CSL-enhanced GBCDs were, in general, closer to the exact CSL misorientations than were those in the near-random GBCDs of the solution annealed material. An analysis of the distribution of misorientation axes did not indicate any correlation between grain misorientation texture and GBCD evolution.

Alloys↗
PubMed1990

Theophylline tablets coated with aqueous latexes containing dispersed pore formers.

Constant drug release was achieved from theophylline tablets coated with a multiporous membrane in an aqueous environment. The tablets were coated with an aqueous acrylic latex containing a dispersed pore-forming agent with pH-dependent solubility characteristics. The pore former, dibasic calcium phosphate, was insoluble in the latex but leached out rapidly in 0.1 M HCl. Theophylline was then released at a constant rate through the multiporous membrane. The drug release was a function of the level of the pore-forming agent and the membrane thickness, but independent of the pH of the dissolution medium and the degree of agitation.

Chemistry, Pharmaceutical↗
PubMed1999

Dispersed polyphosphate in fungal vacuoles in Eucalyptus pilularis/Pisolithus tinctorius ectomycorrhizas.

Ectomycorrhizas produced between Pisolithus tinctorius and Eucalyptus pilularis under axenic conditions were rapidly frozen, freeze-substituted in tetrahydrofuran and embedded anhydrously, and dry-sectioned for X-ray microanalysis. The vacuoles of the sheath and Hartig net hyphae were rich in phosphorus and potassium. They also contained sulfur and variable amounts of chlorine. In anhydrously processed freeze-substituted mycorrhizas, dispersed electron-opaque material filled the fungal vacuoles. X-ray maps indicated that P was distributed evenly throughout the entire vacuole profile and was not concentrated in spherical bodies or subregions of the vacuole. There were no electron-opaque granules surrounded by electron-lucent areas, such as are commonly seen in chemically fixed material. The fungal vacuoles were also rich in K, which similarly gave a signal from the entire vacuolar profile. Such P-rich vacuoles occurred in both the mycorrhizal sheath and Hartig net hyphae. Stained sections of ether-acrolein freeze-substituted mycorrhizas also showed only dispersed material in the fungal vacuoles as, in most cases, did acetone-osmium freeze-substituted material. Precipitation of metachromatic granules by ethanol suggested that large amounts of polyphosphate are stored in these regions under the conditions of our experiments, as well as in the tips of actively growing hyphae of the same fungus. The higher plant vacuoles of ectomycorrhizas gave a much lower signal for K, and P was barely detectable. Much more K was located in the vacuoles of the root exodermal cells than in epidermal cells. The analysis of element distribution between the vacuole and cytoplasm in root cells agrees well with that found for other plant species using other techniques. We conclude that polyphosphate is indeed present in the vacuoles of the fungal cells of these ectomycorrhizas, but that in vivo it is in a dispersed form, not in granules.

Basidiomycota↗
PubMed1993

Effects of acrylamide on subcellular distribution of elements in rat sciatic nerve myelinated axons and Schwann cells.

Electron probe X-ray microanalysis was used to determine whether experimental acrylamide (ACR) neuropathy involves deregulation of subcellular elements (Na, P, S, Cl, K, Ca and Mg) and water in Schwann cells and small, medium and large diameter myelinated axons of rat sciatic nerve. Results show that in proximal but not distal sciatic nerve, ACR treatment (2.8 mM in drinking water) was associated with an early (15 days of exposure), moderate increase in mean axoplasmic K concentrations (mmol/kg) of medium and small diameter fibers. However, all axons in proximal and distal nerve regions displayed small increases in dry and wet weight contents of axoplasmic Na and P. As ACR treatment progressed (up to 60 days of exposure), Na and P changes persisted whereas proximal axonal K levels returned to control values or below. Alterations in mitochondrial elemental content paralleled those occurring in axoplasm. Schwann cells in distal sciatic nerve exhibited a progressive loss of K, Mg and P and an increase in Na, Cl and Ca. Proximal glia displayed less extensive elemental modifications. Elemental changes observed in axons are not typical of those associated with cell injury and might reflect compensatory or secondary responses. In contrast, distal Schwann cell alterations are consistent with injury, but whether these changes represent primary or secondary mechanisms remains to be determined.

Acrylamides↗
PubMed1987

Studies of the ocular compatibility of hydrogels. White spot deposits--chemical composition and geological arrangement of components.

Light, SEM and histochemical techniques were used to determine the architecture and composition of elevated deposits on a variety of commercial lenses of differing bulk and surface chemistries and wear protocols. Spoilt lenses were derived from controlled lens wear trials and additional clinical sources. Elevated deposits display a complex multilayered structure, unaffected by variations in wear protocol or bulk and surface chemistries. These deposits are predominantly composed of tear-derived lipids laid down in a well-defined fashion. The primary layer is composed of unsaturated lipids, whilst the secondary and tertiary layers are dominated by cholesterol and cholesterol esters. The composition and location of deposit components is unaffected by variations in, wear protocol, chemistry of the lens matrix, or tear composition of lens wearers. These findings suggest that unsaturated lipids are responsible for the biological interfacial conversion of hydrogel lenses, reducing their compatibility with the ocular environment.

Biocompatible Materials↗
PubMed1994

Effects of sandblasting and silica-coating procedures on pure titanium.

Silica coating titanium improves chemomechanical bonding. Sandblasting is recommended as a pretreatment to thermal silica coating (Silicoater MD) or as part of a tribochemical silica coating process (Rocatec). This study evaluated the effects of sandblasting and coating techniques on volume loss, surface morphology and composition changes in pure titanium. Volume loss of titanium was similar to values reported for base alloys and does not seem to be critical for the clinical fit of restorations. Embedded alumina particles were found in the titanium after sandblasting and the alumina content increased to a range of 27.5-39.3 wt% as measured by EDS. Following tribochemical silica coating, a layer of small silica particles remained on the surface, increasing the silica content to a range of 17.9-19.5 wt%. Ultrasonic cleaning removed loose alumina or silica particles from the surface, resulting in only slight decreases in alumina or silica contents, suggesting firm attachment of most of the alumina and silica to the titanium surface. Silica content following thermal silica coating treatment increased only slightly from the sandblasted specimen to 1.4 wt%. The silica layer employed by these silica coating methods differs widely in both morphology and thickness. These results provide a basis for explanation of adhesive failure modes in bond strength tests and for developing methods to optimize resin bonding. Clinically, ultrasonic cleaning of sandblasted and tribochemically silica coated titanium should improve resin bonding as loose surface particles are removed without relevant changes in composition.

Aluminum Oxide↗
PubMed1996

Effects of hexafluorosilicate on the precipitate composition and dentine tubule occlusion by calcium phosphate.

OBJECTIVES: To improve the calcium phosphate precipitation (CPP) method for the occlusion of dentine tubules with calcium phosphate, the addition of calcium hexafluorosilicate (CaSiF6) to CPP solution was evaluated in vitro with respect to its occluding capacity and the composition of the precipitate. METHODS: The occlusion of dentine tubules was evaluated by SEM observations and by measurements of dentine permeability. The composition of the precipitate was determined by measuring the calcium to phosphorus (Ca/P) ratio of the precipitate in dentine tubules by energy dispersive X-ray spectroscopy (EDS). RESULTS: The addition of CaSiF6 to the CPP solution resulted in an increase of the Ca/P ratio in the precipitate not only on the dentine surface but also inside the dentine tubules; indicating that the precipitate became more apatitic in nature. The addition of CaSiF6 had no effect on occluding capacity in terms of measurements of dentine permeability or SEM observations. Dentine permeability decreased to approximately 4% of pretreatment values and the dentine tubules were occluded for approximately 10-15 microns from the dentine surface. CONCLUSION: It is concluded that the addition of CaSiF6 to CPP solution was desirable, since it provided a more apatitic precipitate in the dentine tubules, not only on the dentine surface but also inside the tubules, and there were no drawbacks with respect to its occluding capacity.

Apatites↗
PubMed1983

Mass determination of thin biological specimens using backscattered electrons. Application in quantitative X-ray microanalysis on an automated STEM system.

The capabilities of modern computerized X-ray analysis systems can be expanded to the acquisition of various signals available in the electron probe microanalyzer, in parallel with the X-rays. These facilities allow the use of backscattered electrons for the measurement of the total specimen mass thickness, which can be used in mass fraction calculations, up to a (biological) specimen thickness of 10 micron. A mass measurement procedure based on the use of backscattered electrons may become an alternative for the X-ray continuum normalization method, often used in electron probe X-ray microanalysis. A mass measurement procedure using backscattered electrons is described, and preliminary results are given.

Animals↗
PubMedDate not supplied

Optimization of quantitative electron energy loss spectroscopy in the low loss region: phosphorus L-edge.

The purpose of this study was to optimize quantitative electron energy loss spectroscopy (EELS) of elements that have characteristic edges in the low energy loss region and are components of organic matrices. The optimum parameters for phosphorus L2,3-edge (at 135 eV) detection were determined by numerical analysis of computer-generated, Poisson-noisy spectra and by experimental measurements (at 80 keV) of films of the phosphoprotein, phosvitin. When the first, second and third valence electron/plasmon scatterings are included in the multiple least-squares (MLS) fit, the background subtraction of (first-difference) spectra is significantly more accurate than that obtained with the "inverse power law" method, even for a specimen thickness of only 0.25 lambda. Taking into account the effects of plural scattering, the optimal thickness for P quantitation is approximately 0.3 lambda. Signal-to-noise (S/N) ratio decreases rapidly with thickness, and at 1.0 lambda, it is only about 60% of the optimum S/N. The combined effects of the statistical uncertainty of measurements and of the systematic error due to gain variations of the parallel detector were evaluated, and the relative sensitivities of the no-difference (raw spectrum), first-difference and second-difference methods were compared. For channel-to-channel gain variations greater than 0.1% and up to 0.8%, the first-difference method results in the lowest uncertainty of P measurements. In the absence of gain variations, direct fitting provides the greatest sensitivity (least uncertainty), whereas at larger gain variations it may be necessary to use the second-difference method. The optimum energy shift for collecting a first-difference spectrum, approximately 15 eV, did not show any great variation between 5 and 25 eV, and is, in general, specimen dependent. Quantitation with EELS showed excellent correlation with simultaneous electron probe X-ray microanalysis, but, for the detection of P in a 0.25 lambda thick specimen, EELS was approximately five to six times more sensitive than X-ray. The minimal detectable P concentration, with 0.5 nA beam current for 100 s in a 0.25 lambda thick specimen, was 8.4 mmol/kg (0.01 at%) at the 99% confidence level, equivalent to 34 phosphorus atoms for a 15 nm probe. This value is close to the theoretical prediction of 7.5 mmol/kg, and can be improved only by further reducing the gain variation and directly fitting the non-difference spectrum. Appropriate reduction of the gain variations to less than 0.1% would result in a further, approximately two-fold, improvement in the parallel EELS detection system.(ABSTRACT TRUNCATED AT 400 WORDS)

Computer Simulation↗
PubMed2006

Effect of mineral elements on phosphorus release from heated sewage sludge.

The aim of this work was to examine the influence of mineral elements on phosphorus (P) release from heated waste sludges. Energy dispersive X-ray microanalysis suggested that P was associated with Al, Ca, and Mg on the surface of waste sludge biomass obtained from six wastewater treatment plants. The extent of P release decreased with increasing the total concentrations of Al, Mg, and Ca in waste sludges. The addition of Al2(SO4)3, Ca(OH)2, CaCl2, MgSO4, or NaAlO2 to activated sludges, which were taken from a bench-scale EBPR process, reduced the P release significantly.

Electron Probe Microanalysis↗
PubMed2002

Different trends in modulation of NMDAR1 and NMDAR2B gene expression in cultured cortical and hippocampal neurons after lead exposure.

Exposure to heavy metal lead (Pb(2+)) has been reported to cause problems in cognitive functions of the brain, e.g. memory loss and difficulties in mental development. N-Methyl-D-aspartate receptors (NRs) are important molecules that are known to be involved in mediation of learning and memory. In order to investigate the effects of Pb(2+) on the gene expression of NR1 and NR2B subunits in neurons, primary cell cultures of rat cortical and hippocampal neurons were employed. After treatments with different concentrations of Pb(2+) ions in culture medium (0, 5, 10, 25 and 50 microM), the cellular localization of Pb(2+) in neurons was evaluated by laser scan confocal microscopy by using a Pb(2+) ion specific fluorescence probe. In addition, the gene expression of NR1 and NR2B subunits was determined by reverse transcriptase-polymerase chain reaction, immunofluorescence and Western blotting. The results of the present study showed that both cortical and hippocampal neurons accumulated intracellular Pb(2+) in accordance with the concentrations of Pb(2+) ions present in the culture medium. After Pb(2+) treatments, levels of NR1 mRNA, immunoreactivity and protein were found to be unchanged but levels of NR2B mRNA, immunoreactivity and protein were found to be significantly increased in cortical neurons. In contrast, both NR1 and NR2B mRNAs, immunoreactivity and proteins were found to be significantly decreased in hippocampal neurons. The changes in gene expression were found to be dose dependent in accordance with the Pb(2+) concentrations. The present results indicate that Pb(2+) has a differential effect on the expression of NR1 and NR2B subunits in cortical and hippocampal neurons, respectively. It is likely that the toxic effects of Pb(2+) may cause differential damage to different types of memory that are mediated by cortical and hippocampal neurons, respectively.

Animals↗
PubMed1999

Dental diamond burs made with a new technology.

STATEMENT OF PROBLEM: Conventional diamond burs show several limitations such as the heterogeneity of grain shapes, the difficulty of automation during fabrication, the decrease of cutting effectiveness due to repeated sterilization, and short lifetime. An additional shortcoming may be represented by the potential release of Ni+2 ions from the metallic binder into the body fluids. PURPOSE: This study investigated a new diamond rotative instrument made of a continuous diamond film obtained by chemical vapor deposition (CVD). This bur, characterized by a pure diamond cutting surface without metallic binder between crystals, was compared with a conventional diamond bur. MATERIAL AND METHODS: Cutting tests were followed by SEM examination and electron microprobe analysis (EMA) to trace metallic residues both at the surface of the bur and the substrate. RESULTS: EMA demonstrated that the metals Ni, Cr, Si, and Fe were present in the metallic binder matrix of the conventional bur and could be smeared on the surface of the substrate during cutting. SEM showed that significant loss of diamond particles occurred during cutting. On the other hand, no discrete particles sheared off the CVD bur. The smearing of the metallic binder cannot occur using the new bur. CONCLUSION: The new CVD bur not only proves to be more efficient in its cutting ability and longevity, but also excludes the risk of metal contamination. This last aspect concerns both the pollution of the oral environment and the contamination of the ceramic during the laboratory manufacturing of dental restorations.

Dental Instruments↗
PubMed2003

Microcystin-LR causes the collapse of actin filaments in primary human hepatocytes.

Microcystin-LR (MCLR) is a potent inhibitor of protein phosphatases 1 and 2A and causes alterations in cytoskeletal filaments and morphological changes that underlie apoptosis in rat hepatocytes. It has also been reported that it caused several cases of human deaths and illness. As no study on the effect of microcystins on human hepatocytes was done, yet, the aim of the study is to evaluate the toxicity of MCLR on primary human hepatocytes. The hepatocytes were incubated in 12.5-50 nM MCLR for 3, 6 and 9 h, fixed and stained with fluorescent probes for actin filaments and nuclei. Spectral laser-scanning confocal microscopy revealed that in the MCLR-treated primary human hepatocytes the actin mesh collapsed into the center of the cell, similarly as it has been described for rat hepatocytes. Cells were blebbing, fragmenting, and separated from each other. The nuclei in the affected cells condensed. In conclusion, this study confirms that MCLR is toxic to primary human hepatocytes, and it may be responsible for the liver failure cases observed after acute cyanobacterial poisoning.

Actin Cytoskeleton↗
PubMedDate not supplied

Study on tip-substrate interactions by STM and APFIM.

Processes occurring at the interface of two materials coming in contact, separating or moving with respect to each other have been studied with the scanning tunnelling microscope (STM) and atom-probe (AP) field ion microscopy (APFIM). STM probe tips have been first characterised by field ion microscopy (FIM), brought into well-defined contact in the STM and afterwards inspected by time-of-flight AP. The results from mechanical contact and indentation experiments, showing material transfer and neck formation, are in reasonable good agreement with computer-based simulations on metal tip-surface interactions.

Journal Article↗