Nanocrystalline cathodes for PC-SOFCs

Ceramic proton conductors are of great interest for the development of solid oxide fuel cells (PC-SOFC) operating at relatively low temperatures between 400 and 700 ºC. Perovskites based on BaCeO3-δ exhibit the highest proton conductivity among this class of materials, however, they are susceptible to hydra-tion and carbonation in presence of water vapor and CO2 [1]. In contrast, the chemical stability of BaZrO3-based protonic conductors is better, but they require sintering temperatures as high as 1700 ºC and usually suffer from high intrinsic grain boundary resistance, limiting the final performance. Partial substitution of Zr for Ce in Ba(Ce0.9-xZrx)Y0.2O3-δ allows obtaining electrolytes with both high proton conductivity and good chemical stability. The performance of a PC-SOFC at low tempe-ratures depends significantly on the ohmic resis-tance of the electrolyte, although it can be lowered by reducing the electrolyte thickness. Another im-portant limiting factor is the increase of the cathode polarization resistance due to the thermally activated nature of the oxygen reduction reaction. For this reason, it is essential to obtain high efficiency cathodes operating at reduced temperatures. In this work, BaCe0.6Zr0.2Y0.2O3-δ (BCZY) powders were prepared by freeze-drying precursor method. These powders were mixed with a Zn-containing solution as sintering additive in order to obtain dense pellets with submicrometric grain size at only 1200 ºC. After that, La0.6Sr0.4Co0.8Fe0.2O3 nanocrystalline electrodes were deposited symmet-rically onto dense pellets BCZY by conventional spray-pyrolysis [3]. The structure, microstructure and electrochemical properties of these electrodes have been examined by XRD, FE-SEM and im-pedance spectroscopy. The stability of these elec-trodes at intermediate temperatures was evaluated as a function of time. These nanocrystalline cathodes exhibit a sub-stantial improvement of the electrode polarization resistance with respect to the same materials pre-pared by screen-printing method at high sintering temperatures, e.g. 0.7 and 3.2 cm2 at 600ºC for LSCF cathodes prepared by spray-pyrolysis and screen-printing method respectively (Fig. 1). An anode supported cell with composition LSCF/BCZY/NiO-BCZY was also prepared to test the electrochemical performance.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Plasmons and near-field amplification in double-layer graphene

We study the optical properties of double-layer graphene for linearly polarized evanescent modes and discuss the in-phase and out-of-phase plasmon modes for both, longitudinal and transverse polarization. We find a energy for which reflection is zero, leading to exponentially amplified transmitted modes similar to what happens in left-handed materials. For layers with equal densities $n=10^{12}$cm$^{-2}$, we find a typical layer separation of $d\approx500\mu$m to detect this amplification for transverse polarization which may serve as an indirect observation of transverse plasmons. When the two graphene layers lie on different chemical potentials, the exponential amplification either follows the in-phase or out-of-phase plasmon mode depending on the order of the low- and high-density layer. This opens up the possibility of a tunable near-field amplifier or switch.Comment: 9 pages, 8 figure

Universal Features of the Time Evolution of Evanescent Modes in a Left-Handed Perfect Lens

The time evolution of evanescent modes in Pendry's perfect lens proposal for ideally lossless and homogeneous, left-handed materials is analyzed. We show that time development of sub-wavelength resolution exhibits universal features, independent of model details. This is due to the unavoidable near-degeneracy of surface electromagnetic modes in the deep sub-wavelength region. By means of a mechanical analog, it is shown that an intrinsic time scale (missed in stationary studies) has to be associated with any desired lateral resolution. A time-dependent cut-off length emerges, removing the problem of divergences claimed to invalidate Pendry's proposal.Comment: 4 pages, 3 figures, title slightly changed, reference added, minor correction

Plasmonics in topological insulators: Spin-charge separation, the influence of the inversion layer, and phonon-plasmon coupling

We demonstrate via three examples that topological insulators (TI) offer a new platform for plasmonics. First, we show that the collective excitations of a thin slab of a TI display spin-charge separation. This gives rise to purely charge-like optical and purely spin-like acoustic plasmons, respectively. Second, we argue that the depletion layer mixes Dirac and Schr\"odinger electrons which can lead to novel features such as high modulation depths and interband plasmons. The analysis is based on an extension of the usual formula for optical plasmons that depends on the slab width and on the dielectric constant of the TI. Third, we discuss the coupling of the TI surface phonons to the plasmons and find strong hybridisation especially for samples with large slab widths.Comment: 37 pages, 7 figure

Spin-charge separation of plasmonic excitations in thin topological insulators

We discuss plasmonic excitations in a thin slab of a topological insulators. In the limit of no hybridization of the surface states and same electronic density of the two layers, the electrostatic coupling between the top and bottom layers leads to optical and acoustic plasmons which are purely charge and spin collective oscillations. We then argue that a recent experiment on the plasmonic excitations of Bi2Se3 [Di Pietro et al, Nat. Nanotechnol. 8, 556 (2013)] must be explained by including the charge response of the two-dimensional electron gas of the depletion layer underneath the two surfaces. We also present an analytic formula to fit their data.Comment: 7 pages, 5 figure

Lesiones severas de las rodillas producto de los accidentes escolares en el Hospital San Pablo de Coquimbo, Chile

21 páginas.Trabajo Fin de Máster Universitario en Patología de la Rodilla (2017/18). Tutor: Gabriel Domecq Fernández de Bobadilla ; INTRODUCCION. El programa de seguro escolar es un derecho constitucional en Chile desde 1972, en el cual el estudiante de todos los niveles de educación tiene acceso gratuitamente. Las lesiones severas de las rodillas productos de estos accidentes escolares, requieren altos recursos económicos y tratamientos técnicos de avanzada para su resolución, los cuales no están disponibles en todas las regiones de chile. METODOLOGIA. se realizará un estudio observacional prospectivo longitudinal, desde el 01 enero del 2019 hasta el 31 de diciembre del 2019, con una población de influencia para el estudio de 43.166 estudiantes provenientes de los 75 colegios de la comuna de Coquimbo. La muestra será todos los estudiantes con lesiones graves en la rodilla que ingresen a la urgencia del Hospital San Pablo de Coquimbo; teniendo como objetivo determinar la incidencia y conducta terapéutica de las lesiones severas de las rodillas producto de los accidentes escolares que son atendidos en el Hospital San Pablo de Coquimbo. RESULTADOS. La data de los resultados se analizará tomando en cuenta las diferentes variables cualitativas y cuantitativas, siendo la P <0,05 estadísticamente significativa, la cual va a ser realizada por el departamento de bioestadística de la Universidad Católica del Norte con sede en Coquimbo. DISCUSION. Mediante este estudio se espera aclarar todas las incógnitas para poder aplicar las medidas correctivas respectivas basadas en la prevención de estos accidentes y también orientar adecuadamente los recursos profesionales y económicos para mejorar la resolución quirúrgica de estas lesiones que son altamente incapacitantes para paciente jóvenes.Introduction. The school insurance Program is a constitutional right in Chile since 1972, in which the student of all levels of education has access free of charge. Severe knee injuries products from these school accidents require high economic resources and advanced technical treatments for resolution, which are not available in all regions of Chile. Methodology. There will be a longitudinal prospective observational study, from January 01, 2019 to December 31, 2019, with a population of influence for the study of 43,166 students from the 75 schools in the municipality of Coquimbo. The sample will be all students with serious knee injuries entering the urgency of the San Pablo Hospital in Coquimbo; Aiming to determine the incidence and therapeutic behavior of severe injuries to the knees resulting from school accidents that are attended at the San Pablo Hospital in Coquimbo. Results. The data of the results will be analyzed considering the different qualitative and quantitative variables, being the P < 0.05 statistically significant, which will be carried out by the Department of Biostatistics of the Catholic University of the North with Headquarter in Coquimbo. Discussion. This study is expected to clarify all the unknowns in order to apply the respective corrective measures based on the prevention of these accidents and adequately orient the professional and economic resources to improve the resolution Surgical lesions that are highly disabling for young patients

Las sargas y otros modos de temple: estudio comparativo experimental

La pintura al temple sobre lienzo ha recibido diversas denominaciones en los tratados artísticos. Entre éstas, figura sencillamente el término temple, pero también el vocablo sarga, pintura aguazo y aguadas de colores. Referencias a cada uno de estos tipos de temples aparecen en tratados de diferentes épocas y la metodología y materiales empleados en ellos es similar, si bien pueden establecerse algunas desemejanzas. El presente estudio trata de configurar un estudio comparativo experimental de tal manera puedan establecerse ciertas diferencias, sencillamente mediante su apreciación visual. Para ello, se han realizado siete probetas que corresponden a diversos modos de temple. Se han seguido las indicaciones de los tratados artísticos y antiguas ordenanzas a fin de configurarlos. Se constata, dentro de los temples estudiados, que la pintura aguazo, debido a la metodología empleada en su ejecución, es la que más impregna el soporte, lo que se refleja de su observación por su cara posterior, y resulta, por tanto, especialmente adecuada si se persigue la estabilidad de la pintura entre las fibras textiles cuando el lienzo es utilizado para fines que impliquen su movimiento o pliegue. Esta impregnación del soporte deriva de la ausencia de preparación así como del mantenimiento del soporte húmedo mientras se pinta. Caso aparte son las aguadas de colores, que difieren notoriamente de otros modos de temple, ya que se ejecutan sobre raso. En ellas también se aprecia una intensa impregnación del soporte