Search results for "quartz"
showing 10 items of 239 documents
The formation of large quartz veins by rapid ascent of fluids in mobile hydrofractures
2001
Abstract This paper aims to resolve two main problems related to the formation of quartz veins: (1) the predominance of quartz veins at shallow crustal levels and not deeper in the crust, close to the source of metamorphic fluids where the temperature sensitivity of quartz solubility is much higher than at lower, upper-crustal temperatures and (2) the formation of very large 100–1000 m scale quartz veins that would require huge amounts of fluid flow in current models of vein formation. It is proposed here that these problems are resolved by the recognition of very fast (m/s) mobile hydrofracture ascent of batches of fluid. Mobile hydrofractures are fluid-filled fractures that propagate at t…
Review of the relationship between aggregates geology and Los Angeles and micro-Deval tests
2021
Rock aggregates constitute the enormous volume of inert construction material used around the globe. The petrologic description as igneous, sedimentary, and metamorphic types establishes the intrinsic formation pattern of the parent rock. The engineering properties of these rocks vary due to the differences in the transformation process (e.g. hydrothermal deposits) and weathering effect. The two most common mechanical tests used to investigate the performance of aggregates are the Los Angeles (LA) and micro-Deval (MD) tests. This study reviewed the geological parameters (including mineralogy, grain and crystal size, grain shape, and porosity) and the relationship to Los Angeles and micro-De…
530Ma syntectonic syenites and granites in NW Namibia — Their relation with collision along the junction of the Damara and Kaoko belts
2012
Abstract The Lower Ugab and Goantagab structural domains are located at the junction between the N–S trending Kaoko and the E–W trending Damara belts (NW Namibia), where Neoproterozoic metavolcano-sedimentary sequences were intruded by several syenitic/granitic plutons. We present here new U–Pb ages on zircon grains from the Voetspoor and Doros plutons. Together with petrological, geochemical and structural data we evaluate the timing of the deformation and relation to the geodynamics during the final stage of Gondwana amalgamation. The plutons are composed of three main rock types: hornblende quartz-syenite, syenodiorite and biotite granite. The two former are predominant and show genetic …
Authigenic phase formation and microbial activity control Zr, Hf, and rare earth element distributions in deep-sea brine sediments
2014
Abstract. Sediments collected from hypersaline and anoxic deep-sea basins in the eastern Mediterranean (Thetis, Kryos, Medee, and Tyro) were characterised in terms of their mineralogical composition, the distributions of rare earth elements (REE), Zr, and Hf and their content of microbial DNA. We identified two major mineralogical fractions: one fraction of detritic origin was composed of quartz, gypsum, and low-Mg calcite bioclasts (with 0 < Mg < 0.07%) and another fraction of authigenic origin constituted of halite, dolomite, high-Mg calcite (with a Mg content of up to 22%) and rare bischofite and showed a textural evidence of microbial assemblages. We found that in the Medee and Ty…
Obtaining of nanostructured ZnO coatings using mechanoactivated oxidation
2007
The concept to use nanostructured state of metal at the instant of destruction in air environment was used to obtain nanostructured Zn-ZnO coatings on glass and quartz by mechanical method. Subsequent annealing in the ambient atmosphere, annealing in vacuum and irradiation with 532-nm YAG:Nd laser were used to obtain completely oxidized, transparent ZnO coatings. The saturated with oxygen nanostructured coatings were transformed into nanostructured ZnO coatings after annealing above 773K or irradiation with laser (allowing to reach 673K) in ambient atmosphere. AFM and SEM images show that after annealing ZnO coatings have multi-shaped structure. The formation of ZnO need-like whiskers (d = …
EQCM and EIS studies of Znaq2++2e−⇄Zn0 electrochemical reaction in moderated acid medium
2003
The zinc electrodissolution and electrodeposition have been studied by means of electrochemical quartz crystal microbalance and electrochemical impedance spectroscopy. Relevant information on the mechanism of these electrochemical processes is provided by the analysis of experimental data. The zinc electrodeposition takes place with an important participation of hydrogen ions while the zinc electrodissolution occurs, in these experimental conditions, by a mechanism in two steps. Besides, it is proved that the presence of molecular oxygen in the solution contributes to the formation of a passive layer on the metallic zinc deposit.
Synthesis of tumor-associated MUC1-glycopeptides and their multivalent presentation by functionalized gold colloids
2014
The mucin MUC1 is a glycoprotein involved in fundamental biological processes, which can be found over-expressed and with a distinctly altered glycan pattern on epithelial tumor cells; thus it is a promising target structure in the quest for effective carbohydrate-based cancer vaccines and immunotherapeutics. Natural glycopeptide antigens indicate only a low immunogenicity and a T-cell independent immune response; however, this major drawback can be overcome by coupling of glycopeptide antigens multivalently to immunostimulating carrier platforms. In particular, gold nanoparticles are well suited as templates for the multivalent presentation of glycopeptide antigens, due to their remarkably…
Photoactivatable caged cyclic RGD peptide for triggering integrin binding and cell adhesion to surfaces.
2011
We report the synthesis and properties of a photoactivatable caged RGD peptide and its application for phototriggering integrin- and cell-binding to surfaces. We analysed in detail 1) the differences in the integrin-binding affinity of the caged and uncaged forms by quartz crystal microbalance (QCM) studies, 2) the efficiency and yield of the photolytic uncaging reaction, 3) the biocompatibility of the photolysis by-products and irradiation conditions, 4) the possibility of site, temporal and density control of integrin-binding and therefore human cell attachment, and 5) the possibility of in situ generation of cell patterns and cell gradients by controlling the UV exposure. These studies p…
Enhanced light scattering in Si nanostructures produced by pulsed laser irradiation
2013
An innovative method for Si nanostructures (NS) fabrication is proposed, through nanosecond laser irradiation (lambda = 532 nm) of thin Si film (120 nm) on quartz. Varying the laser energy fluences (425-1130 mJ/cm(2)) distinct morphologies of Si NS appear, going from interconnected structures to isolated clusters. Film breaking occurs through a laser-induced dewetting process. Raman scattering is enhanced in all the obtained Si NS, with the largest enhancement in interconnected Si structures, pointing out an increased trapping of light due to multiple scattering. The reported method is fast, scalable and cheap, and can be applied for light management in photovoltaics. (C) 2013 AIP Publishin…
Ionic and Free Solvent Motion in Poly(azure A) Studied by ac-Electrogravimetry
2011
International audience; This work is focused on the mechanistic aspects of the redox behavior of poly(azure A) taking advantage of the controlled modulation of their oxidation states by ac-electrogravimetry. The originality of this technique is its ability to discriminate between cation and anion involved in the charge compensation process and the accompanying free solvent transfer, directly or indirectly. Two processes were proposed where the faster ionic exchange is considered to be the participation of the anion species acting as counterions whereas the slower one is related to the proton transfer. The proton is implied as reactants for the two electroactive sites identified in the polym…