1,720,977 research outputs found
Reactivity of some vanadium oxides: An EPR and XRD study
No full textV2O5, VO2 and V2O3 fresh samples and at different times after purchase or preparation (aged samples) were investigated by chemical analysis, redox treatments, XRD and EPR. The ageing process through a reaction with water and oxygen slowly oxidize crystalline VO2 and V2O3, leading to a quasi-amorphous phase with bariandite structure (V10O24 (.) 12H(2)O). The role of water is the progressive demolition of the compact structures and formation of hydrated phase. Kinetic study of VO2 oxidation by O-2 and O-2 + H2O mixture indicates that increasing the temperature LIP to 723 K the effect of water becomes less important. The reaction leads to partially oxidized products with decreasing water content: bariandite at room temperature, V3O7 (.) H2O at 383 K and V3O7 at 723 K. Kinetic investigation of V2O5 reduction by CO at 633-723 K showed that the reduction process proceeds trough the formation of V4+ and of electrons delocalized in the conduction band. © 2005 Elsevier Inc. All rights reserved
Intrinsic and extrinsic paramagnetic centers in zirconia
No full textIn the literature two intrinsic paramagnetic centers have been identified by EPR in pure zirconia: Zr3+ ions, yielding an axial signal (g(parallel to) = 1.958 and g(perpendicular to) = 1.979) and electrons trapped in oxygen vacancies (V (o) over circle). In this study we investigated by quantitative-EPR pure and doped ZrO2 heated in air and redox treated at various temperatures. In pure and in doped zirconia the axial signal has similar spectral features, including the satellite line due to the most intense component of Cr-53 hyperfine structure, and the signal intensity yielded the same redox trend. In doped zirconia the concentration of the species yielding the axial signal was a constant fraction (about 50%) of the total chromium content. In pure zirconia samples, the concentration determined by EPR was also about 50% of the Cr impurity level determined by GFAAS. These findings attribute this signal to the extrinsic center, Cr5+ ion, arising from chromium impurity. In reduced zirconia a signal of Lorentzian shape (g = 2.002; DeltaH(pp) = 4-5 G) arises from the only intrinsic defect detected by EPR in zirconia bulk, namely V (o) over circle center. This signal could easily be confused with another having the same g value, but a different line width (DeltaH(pp) = 0.5-1 G) and line shape that forms in some vacuum-activated zirconia samples and arises from an extrinsic center, carbon paramagnetic impurity
Determination of oxygen permeability of food wrapping films by an amperometric sensor
No full textA new method for measuring the oxygen permeability (Dk) of common polymer membranes based on an amperometric sensor was developed. The system was successfully applied to food wrapping and storing films. The method is based on measurement of oxygen concentration variations in time, by means of an amperometric oxygen sensor (Clark electrode), covered with the polymer film and secured with a proper cap. Measurements were carried out under a constant flow of oxygen in order to be independent of initial oxygen concentration. The oxygen permeability of various commercially available food wrapping films was determined according to Fick's first law of diffusion. The method was tested using a reference material of different thickness, Hydrofilcon-43, with a known permeability value. This method gave more reproducible results compared with the ISO measurement systems. The influence of time, use and hydration degree of oxygen permeability was also tested by exposing the tested films for 36h to UV radiation and keeping them for 50 days in a dryer under vacuum. Results showed that oxygen permeability is proportional to the degree of hydration of the film
Development and in-house validation of biosensor-based transferable techniques for the low-cost toxicity quantification in agro-zootechnical foodstuffs
No full textElectrochemical determination of pharmaceuticals in spiked water samples
No full textThe electrochemical behaviour of acidic and neutral pharmaceutical active compounds (PhACs) was studied by cyclic voltammetry and pulse voltammetric techniques on mercury, carbon nanotube paste, carbon paste and gold electrodes. The best results, in terms of sensitivity, linearity range and detection limits, were obtained by differential pulse voltammetry (DPV) for ofloxacin (LOD 5.2 mu M), differential pulse polarography (DPP) for clofibric acid (LOD 4.7 mu M) and normal pulse voltammetry (NPV) for diclofenac (LOD 0.8 mu M) and propranolol (LOD 0.5 mu M). An enrichment step of approximately two orders of magnitude was performed by a solid-phase extraction procedure (SPE) in order to concentrate the samples. The developed method was optimized and tested on spiked river water samples. (c) 2005 Elsevier B.V. All rights reserved
Functional toxicity and tolerance patterns of bioavailable Pd(II), Pt(II), and Rh(III) on suspended Saccharomyces cerevisiae cells assayed in tandem by a respirometric biosensor
No full textToxicological implications of exposure to bioavailable platinum group metals, here Pd, Pt, and Rh, are still to be clarified. This study obtained by a biosensor-based method preliminary information on potential effects on cellular metabolism as well as on possible tolerance mechanisms. Aerobic respiration was taken as the toxicological end point to perform tandem tests, namely functional toxicity test and tolerance test. Cells were suspended in the absence of essential constituents for growth. The dose-response curves obtained by exposure (2 h) to the metals (nanogram per gram range) suggested the same mechanisms of action, with Rh showing the greatest curve steepness and the lowest EC 50 value. Conservative (95% lower confidence interval) EC 10 values were 187, 85 and 51 ng g-1 for Pt, Pd, and Rh respectively. Tolerance patterns were tested during the same runs. The full tolerance obtained after 12 h of exposure to each metal suggested mitochondrial inhibition of aerobic respiration as a target effect. The hazard rating of the metals in the tolerance test changed in the Rh EC50 range, where Rh showed the lowest toxicity. The observed tolerance might suggest a protective mechanism such as metallothionein induction at concentrations around the EC 50 values. The performance of the bioassay was satisfactory, in terms of the limit of detection, repeatability, reproducibility, roboustness, sensibility, and stability; the method's critical uncertainty sources were identified for improvements. [Figure not available: see fulltext.] © 2007 Springer-Verlag
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
"Nickel oxide-Zirconium oxide: Ni2+ incorporation and its influence on the phase transition and sintering of zirconia"
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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