139,382 research outputs found
Spectroscopic analysis of the structure of amorphous nitrogenated carbon films after wear tests
No full textThe effects of wear tests on the electronic structure of amorphous nitrogenated carbon (a-C:H:N) films prepared in a radiofrequency plasma-enhanced chemical vapor deposition system from a mixture of methane and nitrogen have been investigated. The tribological properties were investigated with a tribometer in a ball-on-disk configuration. For different N-2 fractions, film structure and chemical composition were examined using conventional Raman and X-ray photoelectron spectroscopy, and also by means of high-lateral-resolution soft X-ray photoemission microscopy using synchrotron radiation. Nitrogen incorporation into the as-deposited amorphous carbon network results in an increase in the number of N-sp(2)-C bonded sites with respect to the films grown in a nitrogen-free atmosphere. The wear stability of the films was analyzed as a function of the nitrogen fraction, and a thorough description of the electronic structure was obtained in the as-deposited state and after wear testing. High-lateral-resolution photoemission microscopy reveals for the first time that inhomogeneities within the film after wear testing are correlated to nitrogen incorporation. The study of energy distribution curves and high-lateral-resolution images on the nitrogenated samples shows that a modification of the surface chemistry occurs by mechanical action. (C) 2002 Elsevier Science B.V. All rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-201
Influence of grain size and film composition on wear resistance of ultra fine AISI 304 stainless steel coated with amorphous carbon films
No full textWear Resistance of a High Nitrogen Austenitic Stainless Steel Coated with Amorphous Carbon Films: Influence of Grain Size and Film Composition
No full textInfluence of grain size and film composition on the wear resistance of a structural stainless steel coated with amorphous carbon films
No full textFluorinated amorphous carbon thin films: Analysis of the role of the plasma excitation mode on the structural and mechanical properties
No full textStructure and mechanical properties of argon assisted carbon nitride films
No full textThis paper reports on the effects of Ar dilution on the structure, bonding and tribological properties of nitrogen-doped amorphous carbon films (a-C:H:N) deposited by r.f. glow discharge from CH4-N-2 and CH4-N-2-Al mixtures on silicon substrates. For different N-2 fractions, film structure and chemical composition were examined using Raman spectroscopy, X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS). The mechanical and tribological properties were investigated by scratch testing and a tribometer in a ball-on-disk configuration. Results indicate that, as argon is introduced in the gas mixture, progressive graphitization of the films occurs and the mass density decreases. The behavior of the adhesive strength, as a function of nitrogen content, achieved with Ar addition is of the same order as those reported for CN, films. However, at a fixed nitrogen partial pressure, films obtained without Ar dilution show better adhesion and a denser sp(3) bonded carbon network. (C) 2001 Elsevier Science B.V All rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-201
Wear resistance of fine-grained high nitrogen austenitic stainless steel coated with amorphous carbon films: The soft X-ray spectroscopy approach
No full textThe wear resistance dependence on grain size of a high-nitrogen-alloyed austenitic stainless steels (HN) is investigated and compared to measurements for the same samples coated with amorphous carbon (a-C : H) and nitrogenated amorphous carbon (a-C : H(N)) films, deposited by means of plasma-enhanced chemical vapour deposition. A synergic effect between the grain re. ning and the film in the case of nitride amorphous carbon overcoats is observed in terms of increased low-friction performance duration. The temperature dependence of the wear resistance of a micro crystalline HN stainless steel coated with carbon films is also investigated. An overall decrease of the films' wear resistance is found with increasing temperature. Furthermore, a higher wear resistance is found in the a-C : H coated steel with respect to the a-C : H: N material. High-lateral-resolution photoemission microscopy reveals that inhomogeneities within the film after wear testing are correlated to an increase of the number of N-sp(2) C-bonded sites. The study of energy-distribution curves and high-lateral-resolution images on the nitrogenated samples shows that a modi. cation of the surface chemistry occurs by mechanical action; in particular this implies that existing N-sp(2) C sites are beginning to cluster as temperature increases. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-201
Spatially-localized time dependent solutions including turbulence and their interactions in 2D Kolmogorov flow
No full textIn 2D Kolmogorov flow in small aspect ratio domains, spatially-localized solutions such as kink, traveling or time-dependent kink-antikink pars coexist. However, the conservation of the flow rate in the y direction strongly restrict combination of localized solutions and their positioning. We find that by adding a homogeneous flow U y their positioning is controlled and each of localized solutions including a spatially-localized chaos is isolated. Numerical results suggest that these isolated solutions can be elements constructing a whole flow
Characteristics of overlap region in high-Reynolds number turbulent channel flow
No full textDirect numerical simulation of the fully developed turbulent channel flows have been carried out at the Reynolds number based on the friction velocity and the channel half width, 2000, 4000 and 8000. A hybrid 10th order accurate finite difference scheme in the stream and spanwise directions, and a second-order scheme in the wall-normal direction is adapted as the spatial discretization method. We observed the plateau profiles in the indicator function corresponded to the von Karman constant. Furthermore, second peak of streamwise pre-multiplied spectra were appeared in the same wall normal height, 300 < y+ < 600, in case of Re = 4000. Nevertheless, the effects of the lager than the channel half height scale on the streamwise turbulent intensity are fixed contributions without dependence on Reynolds number. These results suggested that the new streamwise vortexes are formed between buffer layer and outer layer with increasing of Reynolds number
La 'circunstancia' de 'Herederos y Pretendientes
No full textIn June 2010, the Ortega y Gasset Foundation hosted a Conference about the “Spanish Philosophical Transition” in order to debate the book of Francisco Vázquez, La filosofía española. Herederos y Pretendientes. Una lectura sociológica (1963-1990), recently published. This paper is the author’s response to criticism raised in the Conference and to published reviews received by this book. First, the author summarized the argument of Herederos y pretendientes. Secondly he responds and takes into account the most important objections against the book’s hypothesis and methodology. Finally the author evaluates the favorable judgments received by the book and suggests the limits of the historian’s task.Fundación Ortega y Gasset-Marañó
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