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Transmission Electron Microscopy Observations (transmission + electron_microscopy_observation)
Selected AbstractsSuper-silicic garnet microstructures from an orogenic garnet peridotite, evidence for an ultra-deep (>6 GPa) originJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2000Van Roermund We report the field, petrographic and mineral chemical characteristics of relict super-silicic (=majoritic) garnet microstructures from the Otrøy peridotites in the Western Gneiss Region, Norway. The evidence for the former existence of super-silicic garnet consists of two-pyroxene exsolution microstructures from garnet. Estimates of the initial composition of the super-silicic garnet imply pressures of 6,6.5 GPa, indicating that the Otrøy garnet peridotites were derived from depths >185 km. The garnet peridotites consist of inter-banded variable compositions with c. 50% garnet peridotite and 50% garnet-free peridotite. Two distinct garnet types were identified: (a) normal matrix garnet, grain-size ,4 mm, and (b) large isolated single garnet crystals and/or (polycrystalline) garnet nodules up to 10 cm in size. Large garnet nodules occur only within limited bands within the garnet peridotites. The relicts of super-silicic garnet were exclusively found in some (not all) of the larger garnet nodules. Petrographic observations revealed that the microstructure of nodular garnet consists of the following four characteristic elements. (1) Individual garnet nodules are polycrystalline, with grain sizes of 2,8 mm. Garnet grain boundaries are straight with well-defined triple junctions. (2) Some garnet triple junctions and garnet grain boundaries are decorated by interstitial orthopyroxene. (3) Cores of larger polycrystalline garnet contain two-pyroxene exsolution microstructures. (4) Precipitation-free rims (2 mm thick) surround garnet cores containing the exsolved pyroxene microstructure. Pyroxene exsolution from super-silicic garnet was subsequently followed by brittle,ductile deformation of garnet. Both exsolved pyroxene needles and laths become undulous or truncated by fractures. Simultaneous garnet plasticity is indicated by the occurrence of high densities of naturally decorated dislocations. Transmission electron microscopy observations indicate that decoration is due to Ti-oxide precipitation. Estimates of the P,T conditions for mineral chemical equilibration were obtained from geothermobarometry. The mineral compositions equilibrated at mantle conditions around 805±40 °C and 3.2±0.2 GPa. These P,T estimates correspond to cold continental lithosphere conditions at depths of around 105 km. From a combination of both depth estimates it can be concluded that the microstructural memory of the rock extends backwards to twice as great a depth range as obtained by thermobarometric methods. Available geochronological and geochemical data of Norwegian garnet peridotites suggest a multi-stage, multi-orogenic exhumation history. [source] Novel features of Equisetum arvense spermatozoids: insights into pteridophyte evolutionNEW PHYTOLOGIST, Issue 1 2002K. S. Renzaglia Summary ,,To characterize structural diversity within Equisetum and among pteridophytes, architectural features of the sperm cell are described here in a second subgenus of Equisetum, a divergent basal group in the fern clade. ,,Transmission electron microscopy observations of prereleased spermatozoids of Equisetum arvense were correlated with three-dimensional scanning electron microscopy images of swimming cells. ,,The mature spermatozoid completes a helix of approximately 2.5 revolutions. At the cell anterior is a complex multilayered locomotory apparatus with staggered flagella. Mitochondria (elongated,rounded) are aggregated near the locomotory apparatus and organelles extend along the cell length. The spline contains up to 300 microtubules and wraps in part around the long cylindrical nucleus. In swimming sperm cells, the anterior of the cell remains tightly coiled while the posterior relaxes and extends in a trailing fashion. ,,Spermatozoids of Equisetum arvense are smaller than those of Equisetum hyemale but structurally similar, except for nuclear shape. Conservation of cellular features suggests recent radiation of the genus. Equisetum spermatozoids share several critical features with ferns, including Psilotum, and support monophyly of a fern,Equisetum assemblage. Entry of the male gametes of Equisetum in their entirety into the archegonial venters indicates possible biparental inheritance of chloroplast and mitochondrial genomes. [source] Photoluminescence from Boron-Doped Titanium Nitride Nanocomposite Thin Films Prepared by the Magnetron Sputtering MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Sheng-Guo Lu Boron-doped titanium nitride (TiBN) thin films with nanosized grains were prepared by a magnetron sputtering method. X-ray diffraction and transmission electron microscopy observation indicated that TiBN thin films have a cubic structure with grains ,5 nm in size. The photoluminescence (PL) of the films was investigated as a function of temperature over a wavelength range of 350,900 nm. Two PL peaks near 3.20 and 2.38 eV were conisdered to have resulted from the recombination of the donor-bound excitons and deep-trap defects with the holes in the valence band, respectively. An energy transfer from bound electrons to deep-trap defects was observed in the nanocomposite thin film. [source] High-quality InN grown on KOH wet etched N-polar InN template by RF-MBEPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006D. Muto Abstract We have succeeded in dramatically decreasing the density of dislocations in InN by regrowing InN films on micro-facetted N-polar InN templates. The micro-facetted N-polar InN templates were formed by wet etching in a 10 mol/l KOH solution. InN films were regrown on the micro-facetted N-polar InN templates and on flat surface N-polar InN templates for comparison by radio-frequency plasma-assisted molecular beam epitaxy. InN regrown on micro-facetted InN had considerably smaller twist distribution than that grown on the flat InN templates. From transmission electron microscopy observation, it was confirmed that the InN grown on the micro-facetted InN template had much lower density of dislocations than that grown on the flat InN template, and moreover the propagation of edge dislocations was almost completely terminated at the interface between the regrown InN and the micro-facetted InN template. Based on the results, we propose that regrowth of InN on micro-facetted InN templates is an effective way to obtain high-quality InN films. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of melt-blending conditions on structural, rheological, and interfacial properties of polyamide-12 layered silicate nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 8 2006Pascal Médéric The influence of the melt-blending conditions on the structural, rheological, and interfacial properties of modified montmorillonite/Polyamide-12 nanocomposites has been studied performing transmission electron microscopy observation combined with X-Ray diffraction and rheological experiments. In the dilute regime, for short mixing times, the apparent aspect ratio of primary clay entities, determined from intrinsic viscosity measurements, is shown to increase with rotational speed. At high blade rotational speeds, the viscometric results suggest an almost achieved exfoliation, as confirmed by transmission electron microscopy micrographs. For longer mixing times, a significant drop of viscous dissipation is observed, which is very marked at high blade rotational speeds and attributed to a modification of the particle/matrix interface. In the concentrated regime, the rheological behavior of nanocomposites is attributed to the formation of a network of mesoscopic domains, composed of correlated clay entities. Upon increasing strain during mixing, the clay aggregates within these domains break into intercalated stacks and finally exfoliated layers, as shown by transmission electron microscopy micrographs and wide-angle X-ray diffraction patterns. The melt state elastic and viscous properties of the nanocomposites are mainly governed by the networked domains, and not by the nature and properties of the structure within the domains. POLYM. ENG. SCI. 46:986,994, 2006. © 2006 Society of Plastics Engineers. [source] Effects of tributyltin(IV) chloride on the gametes and fertilization of Ascidia malaca (Ascidiacea: Tunicata)APPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2003L. Villa Abstract Ascidia malaca gametes before fertilization incubated in 10,5 or 10,7,M solutions of tributyltin(IV) chloride, TBTCl, for 3,h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd. [source] Evidence for plant viruses in the region of Argentina Islands, AntarcticaFEMS MICROBIOLOGY ECOLOGY, Issue 2 2007Valery Polischuk Abstract This work focused on the assessment of plant virus occurrence among primitive and higher plants in the Antarctic region. Sampling occurred during two seasons (2004/5 and 2005/6) at the Ukrainian Antarctic Station ,Academician Vernadskiy' positioned on Argentina Islands. Collected plant samples of four moss genera (Polytrichum, Plagiatecium, Sanionia and Barbilophozia) and one higher monocot plant species, Deschampsia antarctica, were further subjected to enzyme-linked immunosorbent assay to test for the presence of common plant viruses. Surprisingly, samples of Barbilophozia and Polytrichum mosses were found to contain antigens of viruses from the genus Tobamovirus, Tobacco mosaic virus and Cucumber green mottle mosaic virus, which normally parasitize angiosperms. By contrast, samples of the monocot Deschampsia antarctica were positive for viruses typically infecting dicots: Cucumber green mottle mosaic virus, Cucumber mosaic virus and Tomato spotted wilt virus. Serological data for Deschampsia antarctica were supported in part by transmission electron microscopy observations and bioassay results. The results demonstrate comparatively high diversity of plant viruses detected in Antarctica; the results also raise questions of virus specificity and host susceptibility, as the detected viruses normally infect dicotyledonous plants. However, the means of plant virus emergence in the region remain elusive and are discussed. [source] Microstructure-Lattice Thermal Conductivity Correlation in Nanostructured PbTe0.7S0.3 Thermoelectric MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Jiaqing He Abstract The reduction of thermal conductivity, and a comprehensive understanding of the microstructural constituents that cause this reduction, represent some of the important challenges for the further development of thermoelectric materials with improved figure of merit. Model PbTe-based thermoelectric materials that exhibit very low lattice thermal conductivity have been chosen for this microstructure,thermal conductivity correlation study. The nominal PbTe0.7S0.3 composition spinodally decomposes into two phases: PbTe and PbS. Orderly misfit dislocations, incomplete relaxed strain, and structure-modulated contrast rather than composition-modulated contrast are observed at the boundaries between the two phases. Furthermore, the samples also contain regularly shaped nanometer-scale precipitates. The theoretical calculations of the lattice thermal conductivity of the PbTe0.7S0.3 material, based on transmission electron microscopy observations, closely aligns with experimental measurements of the thermal conductivity of a very low value, ,0.8,W,m,1,K,1 at room temperature, approximately 35% and 30% of the value of the lattice thermal conductivity of either PbTe and PbS, respectively. It is shown that phase boundaries, interfacial dislocations, and nanometer-scale precipitates play an important role in enhancing phonon scattering and, therefore, in reducing the lattice thermal conductivity. [source] Encapsulation and Ostwald Ripening of Au and Au,Cl Complex Nanostructures in Silica Shells,ADVANCED FUNCTIONAL MATERIALS, Issue 13 2006W. Lou Abstract We report a general template strategy for rational fabrication of a new class of nanostructured materials consisting of multicore shell particles. Our approach is demonstrated by encapsulating Au or Pt nanoparticles in silica shells. Other superstructures of these hollow shells, like dimers, trimers, and tetramers can also be formed by nanoparticle-mediated self-assembly. We have also used the as-prepared multicore Au,silica hollow particles to perform the first studies of Ostwald ripening in confined microspace, in which chloride was found to be an efficient mediating ligand. After treatment with aqua regia, Au,Cl complex is formed inside the shell, and is found to be very active under in,situ transmission electron microscopy observations while confined in a microcell. This aspect of the work is expected to motivate further in,situ studies of confined crystal growth. [source] Preparation and properties of polyhedral oligosilsequioxane tethered aromatic polyamide nanocomposites through Michael addition between maleimide-containing polyamides and an amino-functionalized polyhedral oligosilsequioxaneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2006Ying-Ling Liu Abstract Polyhedral oligosilsequioxane (POSS) tethered aromatic polyamide nanocomposites with various POSS fractions were prepared through Michael addition between maleimide-containing polyamides and amino-functionalized POSS. The chemical structures of the polyamide,POSS nanocomposites were characterized with Fourier transform infrared and 1H NMR. The polyamide,POSS nanocomposites exhibited good homogeneity in scanning electron microscopy and transmission electron microscopy observations. POSS modification increased the storage modulus and Young's modulus of the polyamides, slightly decreased their glass-transition temperatures from 312 to 305 °C, and significantly lowered their dielectric constants from 4.45 to 3.35. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4632,4643, 2006 [source] Fabrication and Luminescent Properties of Nd3+ -Doped Lu2O3 Transparent Ceramics by Pressureless SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Ding Zhou The fabrication of transparent Nd3+ ion-doped Lu2O3 ceramics is investigated by pressureless sintering under a flowing H2 atmosphere. The starting Nd-doped Lu2O3 nanocrystalline powder is synthesized by a modified coprecipitant processing using a NH4OH+NH4HCO3 mixed solution as the precipitant. The thermal decomposition behavior of the precipitate precursor is studied by thermogravimetric analysis and differential thermal analysis. After calcination at 1000°C for 2 h, monodispersed Nd3+:Lu2O3 powder is obtained with a primary particle size of about 40 nm and a specific surface area of 13.7 m2/g. Green compacts, free of additives, are formed from the as-synthesized powder by dry pressing followed by cold isostatic pressing. Highly transparent Nd3+:Lu2O3 ceramics are obtained after being sintered under a dry H2 atmosphere at 1880°C for 8 h. The linear optical transmittance of the polished transparent samples with a 1.4 mm thickness reaches 75.5% at the wavelength of 1080 nm. High-resolution transmission electron microscopy observations demonstrate a "clear" grain boundary between adjacent grains. The luminescent spectra showed that the absorption coefficient of the 3 at.% Nd-doped Lu2O3 ceramic at 807 nm reached 14 cm,1, while the emission cross section at 1079 nm was 6.5 × 10,20 cm2. [source] Verhalten laserschockverfestigter und festgewalzter Randschichten der Ti-Legierung Ti-6Al-4V bei schwingender Beanspruchung unter erhöhten TemperaturenMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 6 2003I. Altenberger Laser Shock Peening; Deep Rolling; Residual Stresses; Ti-6-4 Abstract Es ist seit langem bekannt, dass mechanische Oberflächenbehandlungen wie etwa Festwalzen, Kugelstrahlen oder Laserschockoberflächenbehandlungen, um nur einige zu nennen, das Ermüdungsverhalten hochbeanspruchter metallischer Bauteile entscheidend verbessern können. Insbesondere Festwalzen und Laserschockoberflächenbehandlungen haben sich als besonders wirksam herausgestellt, da sie tiefe Druckeigenspannungs- und Verfestigungsprofile sowie eine vergleichsweise glatte Oberflächentopographie erzeugen. Tatsächlich wird z.,B. das Festwalzen bereits serienmässig zur Erhöhung der Schwingfestigkeit von Stählen, wie etwa beim Festwalzen von Kurbelwellen, eingesetzt. Obwohl die meisten Arbeiten zum Festwalzen sich mit Stählen beschäftigen, wurde dieses Verfahren in jüngerer Zeit auch auf eine Reihe von Titanwerkstoffen erfolgreich angewendet. Die vorliegenden Untersuchungen beschäftigen sich mit dem Einfluss von Festwalzbehandlungen auf das Niedrig- und Hochlastwechselermüdungsverhalten der wichtigsten kommerziellen Titanlegierung Ti-6Al-4V, wobei besonderes Augenmerk auf die thermische und mechanische Stabilität randnaher Eigenspannungszustände und Mikrostrukturen gerichtet wurde. Zusätzlich werden erste Ergebnisse zum Eigenspannungszustand und zur Schwingfestigkeit lasergeschockter Ti-6Al-4V-Proben präsentiert und mit Resultaten festgewalzter Zustände verglichen. Ausserdem wird untersucht, ob die Oberflächenbehandlungen auch bei erhöhten Temperaturen (bis 450,°C) ihre Wirksamkeit zur Verbesserung der Schwingfestigkeit behalten. Basierend auf Wechselverformungs- und Lebensdaueruntersuchungen, in Kombination mit Röntgendiffraktometrie und In-situ -Transmissionselektronenmikroskopie, lässt sich feststellen, dass Laserschockoberflächenbehandlungen und insbesondere Festwalzen die Rissbildung und Ausbreitung in hochtemperaturschwingbeanspruchtem Ti-6Al-4V trotz eines fast völligen Druckeigenspannungsabbaus wirkungsvoll hemmt. Daraus lässt sich ableiten, dass zusätzlich zu Eigenspannungen vor allem randnahe Mikrostrukturen, welche im Falle von mechanisch randschichtverfestigtem Ti-6Al-4V durch sehr hohe Versetzungsdichten und Nanokristallite gekennzeichnet ist, einen wesentlichen Einfluss bei der Lebensdauererhöhung durch Randschichtverfestigung haben. Residual stress stability and near-surface microstructures in high temperature fatigued mechanically surface treated Ti-6Al-4V It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly-stressed metallic components. Deep rolling is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In the present investigation, the effect of deep rolling on the low-cycle and high-cycle fatigue behavior of a Ti-6Al-4V alloy is examined, with particular emphasis on the thermal and mechanical stability of the residual stress states and the near-surface microstructures. Preliminary results on laser shock peened Ti-6Al-4V are also presented for comparison. Particular emphasis is devoted to the question of whether such surface treatments are effective for improving the fatigue properties at elevated temperatures up to ,450,°C, i.e., at an homologous temperature of ,0.4 T/Tm (where Tm is the melting temperature). Based on cyclic deformation and stress/life (S/N) fatigue behavior, together with the X-ray diffraction and in situ transmission electron microscopy observations of the microstructure, it was found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti-6Al-4V at such higher temperatures, despite the almost complete relaxation of the near-surface residual stresses. In the absence of such stresses, it is shown that the near-surface microstructures, which in Ti-6Al-4V consist of a layer of work hardened nanoscale grains, play a critical role in the enhancement of fatigue life by mechanical surface treatment. [source] Ultrastructural characterization of the new NG97ht human-derived glioma cell line using two different electron microscopy technical proceduresMICROSCOPY RESEARCH AND TECHNIQUE, Issue 4 2009Camila Maria Longo Machado Abstract On the basis of transmission electron microscopy observations in tumor cell lines, oncologists have made innumerous diagnostic and therapeutical progresses. Following this path, the UNICAMP immunopathologies laboratory established the NG97 cell line derived from a human astrocytoma grade III, which when injected to the athymic nude mouse flank developed a grade IV astrocytoma. In this study, we focused on ultrastructural characterization of the NG97 cells after being recovered from xenotransplant (NG97ht). These cells in culture were assayed by two different electron microscopy procedures to characterize ultrastructures related to grade IV astrocytomas and to observe their structures through cell subcultivation. Additionally, comparative morphological descriptions of different cell passages in these technical procedures could be a useful tool for improving electron microscopy cell lineage protocols. Results from many cell passage observations showed ultrastructural similarities, which suggest malignant and glioblastoma phenotypes. In the first procedure, NG97ht cells were harvested and then incorporated into agarose before subjecting them to electron microscopy protocols, whereas in the second one, monolayer cells grew first on cover slides. Comparison among protocols revealed that organelles, cytoplasmatic extensions, spatial conformation of filopodia, and cell attachment to substrate were more preserved in the second procedure. Furthermore, in this latter procedure, a unique ellipsoidal structure was observed, which was already described when dealing with gliosarcoma cell line elsewhere. Therefore, these analyses demonstrated a morphological characterization of a new NG97ht cell line using electron transmission microscopy. Moreover, it has been shown that the second procedure provides more detailed information compared with the first. Microsc. Res. Tech, 2009. © 2008 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||