El espíritu de la enseñanza superior

Alcanzáronme el otro día, las claridades de la aurora con un libro en la mano. Su simple título bastará para darle el secreto de esta lectura fuera de hora para la mayoría de los mortales. Era «L’athéisme» de Le Dantec, el conocido profesor de la Sorbona. Como en todas sus obras, el autor ha pasado á las páginas las profundas convicciones de su espíritu, madurado por el constante cultivo de las ciencias naturales, sin preocuparse en lo más mínimo de si ellas hieren ó no el estado de cosas establecido, la situación creada por otros sistemas. El piensa así. y escribe así, obedeciendo á esa imperiosa tendencia á la exteriorización, radicación activa de los profundamente convencidos. En esto se halla gran parte del secreto de las llamadas obras maestras; hacen vivir al autor á través de las páginas escritas.Facultad de Ciencias Jurídicas y Sociale

Ti3SiC2-Cf composites by spark plasma sintering: Processing, microstructure and thermo-mechanical properties

MAX phases, and particularly Ti3SiC2, are interesting for high temperature applications. The addition of carbon fibers can be used to reduce the density and to modify the properties of the matrix. This work presents the densification and characterization of Ti3SiC2 based composites with short carbon fibers using a fast and simple fabrication approach: dry mixing and densification by Spark Plasma Sintering. Good densification level was obtained below 1400 °C even with a high amount of fibers. The reaction of the fibers with the matrix is limited thanks to the fast processing time and depends on the amount of fibers in the composite. Bending strength at room temperature, between 437 and 120 MPa, is in the range of conventional CMCs with short fibers and according to the resistance of the matrix and the presence of residual porosity. Thermo-mechanical properties of the composites up to 1500 °C are also presented.This work has received funding from the European Union’s Horizon2020 “Research and innovation programme” under grant agreement No 685594 (C3HARME

Redescripción del concepto clásico de modernidad

Este trabajo recupera el concepto clásico de modernidad como punto de partidadesde el cual abordar los recientes debates que hoy lo renuevan. Se trata devolver la mirada sobre la cuestionada modernidad europea e ilustrada con elpropósito de recuperar algunas claves todavía útiles para comprender nuestropropio tiempo. Tal revisión parte de la naturaleza ambivalente y contingente dela modernidad para explorarla en tres dimensiones fundamentales: modernidadcomo actitud (o experiencia), como época y como proyecto.La modernidad como actitud refleja una determinada manera de obrar, pensar ysentir implícita en la autonomía del sujeto, en su libertad, y definida, encontraste con la actitud premoderna, por su carácter contingente, su predilecciónpor lo novedoso y por el ejercicio de la crítica. La modernidad como época serefiere a una nueva conciencia del tiempo y a la cronología empleada paradesignar y clasificar los fenómenos económicos, políticos y sociales más visiblesque han dado pie a la caracterización retrospectiva de la modernidad. Lamodernidad como proyecto trata de orientar una determinada construcción delpresente en virtud de un ideal moral situado en el futuro que constituye elhorizonte moral de validez universal hacia el cual se ha de encaminar elpresente, una utopía de emancipación ambivalente que la crítica postmodernadesvalorizó especialmente

Operando Spectroscopic Studies of Cu–SSZ-13 for NH3–SCR deNOx Investigates the Role of NH3 in Observed Cu(II) Reduction at High NO Conversions

The small pore zeolite chabazite (SSZ-13) in the copper exchanged form is a very efficient material for the selective catalytic reduction by ammonia (NH 3 ) of nitrogen oxides (NOx) from the exhaust of lean burn engines, typically diesel powered vehicles. The full mechanism occurring during the NH 3 –SCR process is currently debated with outstanding questions including the nature and role of the catalytically active sites. Time-resolved operando spectroscopic techniques have been used to provide new level of insights in to the mechanism of NH 3 –SCR, to show that the origin of stable Cu(I) species under SCR conditions is potentially caused by an interaction between NH 3 and the Cu cations located in eight ring sites of the bulk of the zeolite and is independent of the NH 3 –SCR of NOx occurring at Cu six ring sites within the zeolite

In Vivo insulin-dependent glucose uptake of specific tissues is decreased during aging of mature wistar rats

Copyright (1997) The Endocrine Society .The paper can be found at the following URL on the website http://endo.endojournals.org

In situ X-ray Diffraction Computed Tomography studies examining the thermal and chemical stabilities of working Ba0.5Sr0.5Co0.8Fe0.2O3-δ membranes during oxidative coupling of methane

In this study we present the results from two in situ X-ray diffraction computed tomography experiments of catalytic membrane reactors (CMRs) using Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) hollow fibre membranes and Na-Mn-W/SiO2 catalyst during the oxidative coupling of methane (OCM) reaction. The negative impact of CO2, when added to the inlet gas stream, is seen to be mainly related to the C2+ yield, while no evidence of carbonate phase(s) formation is found during the OCM experiments. The main degradation mechanism of the CMR is suggested to be primarily associated with the solid-state evolution of the BSCF phase rather than the presence of CO2. Specifically, in situ XRD-CT and post-mortem SEM/EDX measurements revealed a collapse of the cubic BSCF phase, formation of secondary phases, which include needle-like structures and hexagonal Ba6Co4O12, and formation of a BaWO4 layer, the latter being a result of chemical interaction between the membrane and catalyst materials at high temperatures

Detection of Key Transient Cu Intermediates in SSZ-13 During NH₃-SCR deNOₓ by Modulation Excitation IR spectroscopy

The small pore zeolite Cu-SSZ-13 is an efficient material for the standard selective catalytic reduction of nitrogen oxides (NOₓ) by ammonia (NH₃). In this work, Cu-SSZ-13 has been studied at 250 °C under high conversion using a modulation excitation approach and analysed with phase sensitive detection (PSD). While the complementary X-ray absorption near edge structure (XANES) spectroscopy measurements showed that the experiments were performed under cyclic Cu^{+}/Cu^{2+} redox, Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments provide spectroscopic evidence for previously postulated intermediates Cu–N([double bond, length as m-dash]O)–NH_{2} and Cu–NO_{3} in the NH_{3}-SCR deNO_{x} mechanism and for the role of [Cu^{2+}(OH^{−})]^{+}

Implications of the Molybdenum Coordination Environment in MFI Zeolites on Methane Dehydroaromatisation Performance

The structure and activity of Mo/Silicalite‐1 (MFI, Si/Al=∞) were compared to Mo/H‐ZSM‐5 (MFI, Si/Al=15), a widely studied catalyst for methane dehydroaromatisation (MDA). The anchoring mode of Mo was evaluated by in situ X‐ray absorption spectroscopy (XAS) and density functional theory (DFT). The results showed that in Mo/Silicalite‐1, calcination leads to dispersion of MoO3 precursor into tetrahedral Mo‐oxo species in close proximity to the microporous framework. A weaker interaction of the Mo‐oxo species with the Silicalite‐1 was determined by XAS and DFT. While both catalysts are active for MDA, Mo/Silicalite‐1 undergoes rapid deactivation which was attributed to a faster sintering of Mo species leading to the accumulation of carbon deposits on the zeolite outer surface. The results shed light onto the nature of the Mo structure(s) while evidencing the importance of framework Al in stabilising active Mo species under MDA conditions

Understanding the Deactivation Phenomena of Small-Pore Mo/H-SSZ-13 during Methane Dehydroaromatisation

Small pore zeolites have shown great potential in a number of catalytic reactions. While Mo-containing medium pore zeolites have been widely studied for methane dehydroaromatisation (MDA), the use of small pore supports has drawn limited attention due to the fast deactivation of the catalyst. This work investigates the structure of the small pore Mo/H-SSZ-13 during catalyst preparation and reaction by operando X-ray absorption spectroscopy (XAS), in situ synchrotron powder diffraction (SPD), and electron microscopy; then, the results are compared with the medium pore Mo/H-ZSM-5. While SPD suggests that during catalyst preparation, part of the MoOx anchors inside the pores, Mo dispersion and subsequent ion exchange was less effective in the small pore catalyst, resulting in the formation of mesopores and Al2(MOO4)3 particles. Unlike Mo/H-ZSM-5, part of the Mo species in Mo/H-SSZ-13 undergoes full reduction to Mo0 during MDA, whereas characterisation of the spent catalyst indicates that differences also exist in the nature of the formed carbon deposits. Hence, the different Mo speciation and the low performance on small pore zeolites can be attributed to mesopores formation during calcination and the ineffective ion exchange into well dispersed Mo-oxo sites. The results open the scope for the optimisation of synthetic routes to explore the potential of small pore topologies