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Valverde de Leganés, Spain

Sierra-Fernandez A.,Complutense University of Madrid | Sierra-Fernandez A.,Charles III University of Madrid | Gomez-Villalba L.S.,Complutense University of Madrid | Rabanal M.E.,Charles III University of Madrid | And 3 more authors.
RSC Advances | Year: 2016

Paper aging and protection are of crucial interest for improving the preservations of library collections and archives. Highly aging-resistant cellulose fiber sheets were obtained by treatment with magnesium hydroxide nanoparticles (Mg(OH)2). The procedure was tested on the sheets made of bleached (B) and refined unbleached (UB) pine cellulose fibers as well as their 50%/50% mixture (M). The mor and structural properties of the obtained sheets were studied by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) methods. Stress-strain, smoothness and pH measurements were employed to determine the changes in physical-chemical characteristics of the sheets after mixing two types of the fibers and subsequent treatment with Mg(OH)2. It has been shown that the sheets made of the fiber mixture show a higher tensile index and smoothness. The modification with Mg(OH)2 nanoparticles induces an increase in the pH of the sheets to slightly basic values (around pH 8), facilitates the inter-fiber bonding and additionally enhances the smoothness of the sheets. Finally, by exposing the sheets to thermo-hygrometric accelerated artificial ageing, it was found that the physical properties of the treated sheets were not significantly dependent on the environmental factors. © 2016 The Royal Society of Chemistry. Source

Valdivia V.,Charles III University of Madrid | Lazaro A.,Charles III University of Madrid | Barrado A.,Charles III University of Madrid | Barrado A.,Avda University 30 | And 3 more authors.
SAE Technical Papers | Year: 2011

Modeling and simulation are powerful tools to design power distribution systems made up by multiple converters and loads, such as the system of the more-electric-aircraft. However, the system designer usually has no access to detailed data of the power converters, due to confidentiality of manufacturers. Therefore, a behavioral black-box modeling approach is necessary. These models can be used to evaluate the response of power electronics systems which are composed of commercial converters, since they can be fully parameterized from the actual converter response and only reproduce the signals required for a system-level analysis: input-output voltage and currents. In this paper a behavioral black-box modeling method of three-phase DC-AC converters is proposed. The identification of the model is based on the analysis of the converter transient response, which is obtained by means of a set of simple experiments and easily usable fitting algorithms. An experimental validation of the proposed method has been carried out on a 5 kVA three-phase DC-AC converter implemented in an aircraft power system test bench. Copyright © 2011 SAE International. Source

Parra-Cerrada A.,Technical University of Madrid | Jimenez-Martin J.L.,Technical University of Madrid | Segovia-Vargas D.,Avda University 30 | Gonzalez-Posadas V.,Technical University of Madrid
Journal of Electromagnetic Waves and Applications | Year: 2016

This paper shows one active patch antenna with a Negative Impedance Converters (NIC) and other one without it. The NIC works as negative admittance to increase the Q of the antenna. These circuits can be analysed using classic methods, but classic methods require the verification of the appropriated provisos. The chosen classic method depends on the oscillator topology, while the Normalized Determinant Function (NDF) is independent of topologies and it does not require any provisos. The NDF is suitable for Q estimation and noise optimization during linear analysis of any topology. The oscillators are designed using the NDF and the Admittance; then the phase noise is evaluated using the NDF. The Harmonic Balance (HB) analysis and the measurements of the prototypes confirm, in favour of NDF, the stability discrepancies between classic methods and NDF. The linear approximation of the improvements introduced by a NIC is questioned by the risk of instabilities and the introduction of new noise sources. © 2015 Taylor and Francis. Source

Gomez-Villalba L.S.,Complutense University of Madrid | Sierra-Fernandez A.,Complutense University of Madrid | Sierra-Fernandez A.,Charles III University of Madrid | Rabanal M.E.,Charles III University of Madrid | And 2 more authors.
Ceramics International | Year: 2016

The dehydration process from Mg0.97Ca0.03 (OH)2 nanoparticles (brucite type hexagonal structure) to Mg0.97Ca0.03O (periclase type cubic structure) was studied by Transmission Electron Microscopy (TEM-HRTEM), Electron Diffraction (SAED), Electron Energy Loss Spectroscopy (EELS) and image analysis. The transformation process was monitored in function of the reaction time applying 200 and 300 KV. Changes in porosity were possible to observe only during the irradiation with 200KV. Depending on the irradiation time, the changes were gradual, producing an increase from the particle's edge towards the inner region. Different stages were observed, corresponding to the amount of water extracted from the particle, until finally a decrease in porosity and particle shrinkage occurs, coinciding with the formation of the Mg-Ca oxide. However, when samples were exposed to 300KV, the dehydration process was much faster, and the pores structure was destroyed in a shorter time in comparison with lower doses of radiation. High resolution electron microscopy (HRTEM) applying 300kV allowed identifying the progressive changes from brucite to periclase, including the formation of an intermediate dehydrated phase. The transformation along [0001]brucite and [101-0] brucite orientations was monitored determining differences in the kinetic of reaction related to the presence of point defects affecting the atomic lattice. © 2016. Source

Castrillo P.D.,Avda University 30 | Olmos D.,Avda University 30 | Sue H.-J.,Texas A&M University | Gonzalez-Benito J.,Avda University 30
Composite Structures | Year: 2015

In this work the mechanical behavior of composite materials formed by a diepoxy-diamine (epoxy) thermosetting matrix filled with kaolin intercalated with ethylenediamine (K-EDA) was studied. Fracture toughness experiments showed that an addition of 2. wt% K-EDA to the epoxy matrix causes an approximately 24% increase in the critical stress intensity factor (KIC). The study of fracture mechanisms was completed using the double-notch four-point-bending test. The presence of kaolin particles in the matrix induces crack branching and deflection mechanisms. Furthermore, observation of the fracture surface revealed the presence of tails near kaolin particles, which is consistent with crack-pinning. The present study indicates that kaolin clay can be effective in toughening epoxy at small quantities if it is reasonably well dispersed. © 2015 Elsevier Ltd. Source

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