1,723,085 research outputs found
[Telegrama de Sucesores de José María Serra e Hijo a Germán Gamazo (21 de diciembre de 1888)]
Full text linkRemitentes: Sucesores de José María Serra e Hijo et al. Referencia: Pi y CompañíaFuente de la fecha: matasellosCopia digital. España : Ministerio de Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 202
Catalytic combustion of methane by perovskite-type oxide nanoparticles as pollution prevention strategy
No full textThe transition from the existing brown economy towards the desired green economy drives the research efforts to the development of advanced technologies promoting the efficient utilization of energy sources. Catalysis science offers to combustion technology significant opportunity to increase the fuel efficiency by lowering the internal temperature gradients and reduce the environmental impact by lowering local peak temperature and, consequently, thermodynamically inhibiting the nitrogen oxides formation. Alternative catalytic materials are transition metals oxide, including complex oxides with perovskite crystalline structure. The aim of this work is to synthetize lanthanum ferrite perovskites with lanthanum ions partially substituted by strontium ions in order to study the substitution effects on structural properties and redox activity of the original oxide. Lanthanum ferrite oxides partially substituted with different Strontium amount were synthesized by solution combustion method. The perovskite nanopowders obtained were characterized by XRD, SEM, TPR analyses for defining crystalline structure, morphology and redox properties. Finally, the catalytic activity for methane combustion was tested. The most performing catalysts was La0.6Sr0.4FeO3 having the highest oxygen vacancy concentration as revealed by TPR analysis. © 2016 Author(s)
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
Active feedback cooling of a SiN membrane resonator by electrostatic actuation
No full textFeedback-based control techniques are useful tools in precision measurements as they allow us to actively shape the mechanical response of high quality factor oscillators used in force detection measurements. In this paper, we implement a feedback technique on a high-stress low-loss SiN membrane resonator, exploiting the charges trapped on the dielectric membrane. A properly delayed feedback force (dissipative feedback) enables the narrowing of the thermomechanical displacement variance in a similar manner to the cooling of the normal mechanical mode down to an effective temperature Teff. In the experiment reported here, we started from room temperature and gradually increasing the feedback gain, we were able to cool down the first normal mode of the resonator to a minimum temperature of about 124mK. This limit is imposed by our experimental setup and, in particular, by the injection of the read-out noise into the feedback. We discuss the implementation details and possible improvements to the technique.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and MaterialsEKL Equipmen
Gas sensors for sustainable and safe bioenergy production from an integrated gasification-FC system
No full textCombustion synthesis of LaFeO3 sensing nanomaterial
No full textSince industrial revolution, human activities drive towards unsustainable global economy due to the overexploitation of natural resources and the unacceptable emissions of pollution and greenhouse gases. In order to address that issue, engineering research has been focusing on gas sensors development for monitoring gas emissions and controlling the combustion process sustainability. Semiconductors metal oxides sensors are attractive technology because they require simple design and fabrication, involving high accessibility, small size and low cost. Perovskite oxides are the most promising sensing materials because sensitivity, selectivity, stability and speed-response can be modulated and optimized by changing the chemical composition. One of the most convenient synthesis process of perovskite is the citrate-nitrate auto-combustion method, in which nitrate is the oxidizing agent and citrate is the fuel and the chelating argent in the same time. Since the sensibility of perovskite oxides depends on the defective crystallographic structure and the nanomorphology, the experimental was designed in order to study the dependence of powder properties on the synthesis conditions, such as the solution acidity and the relative amount of metals, nitrates and citric acid. Crystalline structure was studied in depth for defining the effects of synthesis conditions on size, morphology and crystallographic structure of nanopowders of LaFeO3. © 2015 AIP Publishing LLC
Quality by design approach for SrTiO3 perovskite nanomaterials synthesis
No full textThe current environmental and energy concerns at global level drive toward politics of sustainable development for a green economy growth. In this scenario, chemical sensors play an important role in regulating energetic, ecological, and productive efficiency because of their excellent potential to develop technology for online gas emissions monitoring and feedback system control. Since sensor performances are affected by size, morphology, crystalline structure, and stoichiometry of the sensing materials, the aim of this work is to study how the synthesis conditions affect the properties of sensing nanoparticles of strontium titanate perovskite oxide and develop mathematical models with predictive ability for the design of materials. The investigated ranges of operating conditions were pH levels from 2 to 12; CA/NO3 molar ratio from 0.09 to 0.17; CA/M molar ratio from 0.63 to 2.00, where CA, NO3, and M terms are related to citric acid, nitrate ions, and the total metals, including strontium and titanium. The results confirm that fuel-to-oxidizer molar ratio of the initial solution affects the properties of the synthesized nanopowder because of its significant effects on flame temperature, burning rate, and reaction time. Depending on the synthesis conditions, the crystallite size changes from 10 to 30 nm and the grain size from 20 to 50 nm. From reacting solution with stoichiometric amounts of fuels and oxidizers, it was obtained more crystalline, pure, and nanosized perovskite oxide powder. In addition, the solution acidity and the complexing agent amount affects the dissolution of metal ions, reflecting upon the homogeneity of the dried gel and the characteristics of the final products in turn. Finally, a quality by design approach, using multiple regression analysis, was successfully used to study the combustion synthesis process by defining the direct and indirect effects of pH, CA/NO3, and CA/M on synthesized nanomaterial properties. © 2016, Springer Science+Business Media New York
Mechanical properties and corrosion behaviour of 316l stainless steel honeycomb cellular cores manufactured by selective laser melting
No full textSelective laser technology is an additive technology that can allow for the manufacture of cellular structures using different types of metallic powder with complex applications in industries such as aerospace, automotive and medical implant industries. This paper presents the effect of climate and mechanical stresses on some honeycomb cellular cores, used in sandwich structures made of 316L stainless steel powder by applying the selective laser melting technology. The honeycomb cellular cores have undergone the microhardness testing and the resulting variation obtained from the analyzed samples was 225 ± 15 HV0.3. The compressive strength and the modulus of elasticity of the cellular structures were determined for flatwise and edgewise compressive stresses. Also, the cellular structures were subjected to accelerated corrosion tests in order to determine their mean life in application use conditions similar to those near seas and oceans. Also, a microstructural evaluation of salt deposits was carried out on the cellular structures subjected to accelerated corrosion tests using a salt spray test chamber. © 2017 Transactions of Famena. All Rights Reserved
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