Home About us Contact
|
Home About us Contact | ||
|
|
||
Dense Material (dense + material)
Selected AbstractsMicrostructure and Properties of Pressureless Sintered HfB2 -Based Composites with Additions of ZrB2 or HfC,ADVANCED ENGINEERING MATERIALS, Issue 10 2007L. Silvestroni Ternary HfB2 -ZrB2 and HfB2 -HfC composites (see figure) with 20,vol.-% MoSi2 were produced from commercial powder and densified through pressureless sintering. Dense materials with fine microstructures were obtained at 1900,1950,°C. Flexural strength at 1500,°C confirmed the excellent stability of the composites at high temperature. [source] Ultrastructural characteristics of the process of cornification in developing claws of the brushtail possum (Trichosurus vulpecula)ACTA ZOOLOGICA, Issue 3 2009Lorenzo Alibardi Abstract Cornification of developing claws in the brush possum has been analysed by electron microscopy and compared with the process in other tetrapods. Newborns from 3 to 60 days postparturition were studied. After formation of symmetric and round outgrowth in digits the epidermis becomes thicker in the dorsal with respect to the ventral digit tip. The claw elongates forming the unguis and a shorter subunguis. Spinosus keratinocytes in both unguis and subunguis accumulate tonofilaments that fill their cytoplasm. Keratohyaline-like granules are formed in early stages of differentiation in both unguis and subunguis but they later disappear in highly cornified corneocytes. Tonofilaments become electron-dense in keratinocytes of the precorneous layer in the large corneocytes of the unguis and in narrow corneocytes of the subunguis. Keratin bundles transform into an amorphous corneous material that embeds or masks the original keratin intermediate filaments. Nucleated corneocytes are accumulated in the unguis while thinner corneocytes are present in the subunguis. The latter contain a dense material, possibly containing high sulphur keratin associated proteins, as occurs during cornifcation of the cortex and cuticle hair cells and in the nail. The process of cornification of mammalian claws is compared with that of reptilian and avian claws. [source] Humic acid metal cation interaction studied by spectromicroscopy techniques in combination with quantum chemical calculationsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2010M. Plaschke Humic acids (HA) have a high binding capacity towards traces of toxic metal cations, thus affecting their transport in aquatic systems. Eu(III),HA aggregates are studied by synchrotron-based scanning transmission X-ray microscopy (STXM) at the carbon K -edge and laser scanning luminescence microscopy (LSLM) at the 5D0,7F1,2 fluorescence emission lines. Both methods provide the necessary spatial resolution in the sub-micrometre range to resolve characteristic aggregate morphologies: optically dense zones embedded in a matrix of less dense material in STXM images correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. In the C 1s -NEXAFS of metal-loaded polyacrylic acid (PAA), used as a HA model compound, a distinct complexation effect is identified. This effect is similar to trends observed in the dense fraction of HA/metal cation aggregates. The strongest complexation effect is observed for the Zr(IV),HA/PAA system. This effect is confirmed by quantum chemical calculations performed at the ab initio level for model complexes with different metal centres and complex geometries. Without the high spatial resolution of STXM and LSLM and without the combination of molecular modelling with experimental results, the different zones indicating a `pseudo'-phase separation into strong complexing domains and weaker complexing domains of HA would never have been identified. This type of strategy can be used to study metal interaction with other organic material. [source] Spark Plasma Sintering of an Infrared-Transparent Y2O3,MgO NanocompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010DongTao Jiang A novel optically transparent ceramic nanocomposite Y2O3,MgO was produced using spark plasma sintering technique. Sintering parameters was optimized to obtain fully dense material while maintaining nanoscale grain size. The sintered nanocomposite has an excellent infrared transmission as a result of small grain size and homogeneous microstructure. Postsinter annealing can significantly improve the transmission. Overly larger grain size severely degrades the transmittance. [source] Light and Electron Microscopy of the Spore of Myxobolus heckelii n. sp. (Myxozoa), Parasite from the Brazilian Fish Centromochlus heckelii (Teleostei, Auchenipteridae)THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 6 2009CARLOS AZEVEDO ABSTRACT. A myxosporean parasitizing the gill filaments of the freshwater teleost fish Centromochlus heckelii collected in the Tocantins River (Lower Amazonian Region, Brazil) is described using light and electron microscopy. This parasite produces spherical to ellipsoidal cyst-like plasmodia up to 250 ,m in diameter, with a thick wall strengthened by several stratified juxtaposed crossed collagen layers, whose thickness varies according to the number of the layers. Several compressed fibroblasts are observed among the collagen fibrils. Deposits of spherical dense material are scattered at the internal periphery of the cysts. Plasmodia and different developmental stages, including immature and mature spores, filled the central region of the cysts. The spore body is ellipsoidal in valvar view and biconvex in sutural view. It is formed by two equal-sized and symmetric valves measuring 12.7 ,m long (12.2,13.1) (n=50), 6.6 ,m wide (6.3,6.9) (n=25), and 4.0 ,m (3.7,4.4) (n=20) thick. A thin layer formed by fine and anastomosed microfibrils is observed at the spore surface. Two equal, elongated pyriform polar capsules measure 2.9 ,m (2.7,3.3) × 1.7 ,m (1.4,2.0) (n=25), each containing four or five oblique polar filament coils. The binucleated sporoplasm contains numerous spherical sporoplasmosomes, glycogen particles, and a large vacuole with fine granular matrix. Based on the morphological and ultrastructural differences and specificity of the host, we describe this isolate as a new myxosporidian, Myxobolus heckelii n. sp. (Myxozoa, Myxosporea). [source] A New Species of Myxozoa, Henneguya rondoni n. sp. (Myxozoa), from the Peripheral Nervous System of the Amazonian Fish, Gymnorhamphichthys rondoni (Teleostei)THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 3 2008CARLOS AZEVEDO ABSTRACT. Henneguya rondoni n. sp. found in the peripheral lateral nerves located below the two lateral lines of the fish Gymnorhamphichthys rondoni (Teleostei, Rhamphichthyidae) from the Amazon river is described using light and electron microscopy. Spherical to ellipsoid cysts measuring up to 110 ,m in length contained only immature and mature spores located in close contact with the myelin sheaths of the nervous fibres. Ellipsoidal spores measured 17.7 (16.9,18.1)-,m long, 3.6 (3.0,3.9)-,m wide, and 2.5 (2.2,2.8)-,m (n=25) thick. The spore body measuring 7.0 (6.8,7.3)-,m long was formed by two equal symmetric valves, each with an equal tapering tail 10.7 (10.3,11.0) ,m in length. The tails were composed of an internal dense material surrounded by an external homogeneous sheath of hyaline substance. The valves surrounded two equal pyriform polar capsules measuring 2.5 (2.2,2.8)-,m long and 0.85 (0.79,0.88)-,m (n=25) wide and a binucleated sporoplasm cell containing globular sporoplasmosomes 0.38 (0.33,0.42) ,m (n=25) in diam. with an internal eccentric dense structure with half-crescent section. Each polar capsule contains an anisofilar polar filament with 6,7 turns obliquely to the long axis. The matrix of the polar capsule was dense and the wall filled with a hyaline substance. The spores differed from those of previously described species. Based on the ultrastructural morphology of the spore and specificity to the host species, we propose a new species name H. rondoni n. sp. [source] Structure of the Lining Epithelium of the Cauda Epididymis of the Golden HamsterANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 1 2009C. C. L. Beu Summary The ductus epididymis has roles in the maturation and storage of spermatozoa. The main function of the cauda epididymis is the storage of spermatozoa; however, this region exerts other morphophysiological roles. So, this study was aimed at investigating structural features of the cauda epididymis epithelium, which could indicate roles other than the storage. The relative percentages of the cell types in the epithelium were 74.9, 6.9, 12.5 and 5.6% of principal, clear, basal and halo cells respectively. Large intercellular spaces were seen among the lateral plasmatic membranes of adjacent principal cells or among these cells and others cell types. These spaces were found to be filled with multivesicular bodies, myelin figures, scrolls and debris of membranes or flocculent dense material. Clear cells had the cytoplasms filled with lysosomes (¾ of basal cytoplasm), and vacuoles and vesicles (¼ of apical cytoplasm). The observations allowed us to infer that clear cells could act in the process of endocytosis and also in water transfer from the lumen to the interstitium through the epithelium compartment. Moreover, transcytosis may occur at the cauda epididymis of Golden hamster. [source] Barium Non-Stoichiometry Role on the Properties of Ba1+xCe0.65Zr0.20Y0.15O3,, Proton Conductors for IT-SOFCsFUEL CELLS, Issue 5 2008S. Barison Abstract Proton conducting perovskite oxides have been widely investigated because of their potential as electrolytes for intermediate temperature solid oxide fuel cells. Among them, BaCeO3 - based materials exhibit good proton conductivity under a humidified hydrogen-containing atmosphere, but rather poor chemical stability in CO2 atmosphere. The substitution with Zr for Ce improves the chemical stability but reduces proton conductivity due to difficulties in fabricating dense materials. In the present work, single phase nanostructured powders of Ba1+xCe0.65Zr0.20Y0.15O3,, (x,=,0, 0.05, 0.10) solid solutions have been prepared by a modified sol,gel Pechini method with the final aim of evaluating the role of barium on their chemical and electrical properties. A significant influence of barium excess on the preparation and on properties of these materials has been demonstrated. In fact, density measurements evidenced that a 5 or 10,mol% nominal barium excess sensibly favoured the sintering process. Impedance analyses of sintered pellets confirmed the necessity of barium excess in order to avoid the lowering of proton conductivity, which has been evidenced for samples having stoichiometric barium content. Moreover, an unforeseen increase in chemical stability in CO2 -containing atmosphere with the growth of the barium excess was detected by thermogravimetric analyses. [source] Reactive Processing in Ceramic-Based SystemsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2006William G. Fahrenholtz Reactive hot pressing is discussed as a processing method to form ceramic-based materials. Fundamental aspects of thermodynamics such as favorable Gibbs'-free energy changes, phase equilibria, and adiabatic temperature are presented as criteria for determining whether the desired reactions can be used to form dense materials. Two case studies are presented as examples to describe control of microstructure and properties. The fabrication of Al2O3,Nb and ZrB2 are discussed with respect to the three thermodynamic criteria as well as the microstructure and properties of the materials that are produced. [source] Alumina/Silicon Carbide Laminated Composites by Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009Vincenzo M. Sglavo Ceramic laminates composed of alumina/silicon carbide composite layers were produced by spark plasma sintering (SPS). Monolithic composite disks containing up to 30 vol% of silicon carbide were fabricated by stacking together and cosintering by SPS green layers prepared by tape casting water-based suspensions. An engineered laminate with a specific layer combination that is able to promote the stable growth of surface defects before final failure was also designed and produced. Fully dense materials with an optimum adhesion between the constituting layers and a homogeneous distribution of the two phases were obtained after SPS. Monolithic composites showed an increasing strength with SiC load, and biaxial strength values as high as 700 MPa were observed for a SiC content of 30 vol%. The engineered laminate showed a peculiar crack propagation that is responsible for the high strength value of about 600 MPa and for the evident insensitivity to surface defects. [source] Ion-Exchange Plasma Membranes for Fuel Cells on a Micrometer Scale,CHEMICAL VAPOR DEPOSITION, Issue 6-7 2007S. Roualdès Abstract Recent advances in,miniaturization technology make polymer electrolyte membrane fuel cells very attractive as power sources for portable devices. Ion-exchange membranes for microscale fuel cells are synthesized by plasma polymerization (using a precursor containing ion-exchange groups) and intensively characterized. Ion-exchange plasma membranes are thin, amorphous, and dense materials with no defects. Spectroscopic analyses reveal a polymer-type matrix containing a rather high concentration of ion-exchange groups. Under the best synthesis conditions, membranes show a satisfying ionic conduction level and a high compatibility with other active layers of fuel cells, making them suitable for insertion in such power-supply devices. [source] | ||||||||||||||||||||||||||||