Hyperbolic character of the angular moment equations of radiative transfer and numerical methods

We study the mathematical character of the angular moment equations of radiative transfer in spherical symmetry and conclude that the system is hyperbolic for general forms of the closure relation found in the literature. Hyperbolicity and causality preservation lead to mathematical conditions allowing to establish a useful characterization of the closure relations. We apply numerical methods specifically designed to solve hyperbolic systems of conservation laws (the so-called Godunov-type methods), to calculate numerical solutions of the radiation transport equations in a static background. The feasibility of the method in any kind of regime, from diffusion to free-streaming, is demonstrated by a number of numerical tests and the effect of the choice of the closure relation on the results is discussed.Comment: 37 pags, 12 figures, accepted for publication in MNRA

Rheology of acid suspensions containing cassava bagasse: Effect of biomass loading, acid content and temperature

[EN] Understanding the characterization and rheological behavior of acid suspensions of cassava bagasse provides essential information for the design of conversion processes. Samples with different cassava bagasse concentrations (0-10% w.w-1), phosphoric acid (0-10% w.w(-1)) at temperatures between 278.13 and 318.13 K were submitted to steady-state flow over a wide range of shear rates (1-265 s(-1)). The biomass particles had considerable residual starch (similar to 50% db), low lignin content and adequate particle size (<200 mu m) for the conversion process. Flow curves were well-fitted to the Herschel-Bulkley model, presenting a Newtonian domain at low solids and acid content and a non-Newtonian behavior with noticeable yield stress and shear-thinning characteristic (n < 1) at above 6% of cassava bagasse. Resistance to flow increased as the solids loading and acid content increased. Temperature dependence could be expressed as a function of an Arrhenius-type equation with good accuracy of fit. (C) 2019 Elsevier B.V. All rights reserved.The authors would like to thank Prof. Rosiane Lopes Cunha and Prof. Ana Carla Kawazoe Sato from University of Campinas (UNICAMP) for their support with particle size analyses. The authors also acknowledge the Sao Paulo Research Foundation - FAPESP (Grant number 2017/06518-2) and the Coordination for the Improvement of Higher Education Personnel -CAPES (Grant number 88881.132626/2016-01) for their financial support.Carregari-Polachini, T.; Mulet Pons, A.; Carcel, JA.; Telis Romero, J. (2019). Rheology of acid suspensions containing cassava bagasse: Effect of biomass loading, acid content and temperature. Powder Technology. 354:271-280. https://doi.org/10.1016/j.powtec.2019.05.086S27128035

Evidencias del incremento en la movilidad de dunas costeras en el último medio siglo como respuesta a la intervención humana

Given the risk of two roads being buried by the sand of two highly mobile coastal dunes (Valdevaqueros and Bolonia, SW Spain), several measures have been taken over the last half century in order to stabilize them or at least slow their progress: installation of several rows of 1-m-high concrete structures, planting of species such as Pinus pinea, Retama monosperma and Ammophila arenaria, wicker and wooden fencing, and sand mining (only performed on the Valdevaqueros dunefield). The evolution of the two dunes was investigated through the interpretation of intensive topographical monitoring and aerial photography. Average migration rates of approximately 10 m yr–1 were detected and the burial of anthropic structures has eventually occurred. This process has caused a serious regional problem, making dune management of these areas a difficult challenge. The comparison of the evolution of these two dunes has been of great importance in assessing the effect of historical human intervention and has provided a new perspective for future dune management strategies. The results obtained show that management measures based on sand removal have been proven to be unsustainable. Moreover, the monitoring methodology presented herein has proven very useful in predicting dune advance rates. For instance, the Bolonia dune could reach the nearest road in approximately 12 years.Se han tomado diferentes medidas a lo largo del último medio siglo tratando de estabilizar o al menos ralentizar el progreso de dos dunas costeras de alta movilidad (Valdevaqueros y Bolonia, SW España) dado el riesgo de enterramiento de sendas carreteras: Entre las medidas tomadas cabe destacar la instalación de filas de estructuras de hormigón de 1 m de altura, la plantación de diferentes especies (como el Pinus pinea, la Retama monosperma o la Ammophila arenaria), vallas de madera y brezo, y la extracción de arena (sólo en la duna de Valdevaqueros). La evolución de ambas dunas se ha investigado a través de la comparación de levantamientos topográficos y fotografías aéreas. Se han detectado tasas medias de avance de aproximadamente 10 m/año hasta que, finalmente, se han enterrado estructuras antrópicas. Este proceso ha causado graves problemas convirtiendo en un difícil reto la gestión de dunas de estas áreas. La comparación de la evolución de estas dos dunas ha resultado de gran importancia a la hora de evaluar el efecto de la intervención humana, y ha proporcionado una nueva perspectiva para las futuras estrategias de gestión. Entre los resultados obtenidos, debería destacarse el que la gestión basada en la retirada de arena ha resultado insostenible. Además, la metodología de seguimiento aquí presentada ha probado ser de gran utilidad al predecir las tasas de avance de las dunas. Por ejemplo, la duna de Bolonia podría alcanzar la carretera próxima en unos 12 años

Evidence of coastal dune mobility increases over the last half century in response to historical human intervention

Given the risk of two roads being buried by the sand of two highly mobile coastal dunes (Valdevaqueros and Bolonia, SW Spain), several measures have been taken over the last half century in order to stabilize them or at least slow their progress: installation of several rows of 1-m-high concrete structures, planting of species such as Pinus pinea, Retama monosperma and Ammophila arenaria, wicker and wooden fencing, and sand mining (only performed on the Valdevaqueros dunefield). The evolution of the two dunes was investigated through the interpretation of intensive topographical monitoring and aerial photography. Average migration rates of approximately 10 m yr–1 were detected and the burial of anthropic structures has eventually occurred. This process has caused a serious regional problem, making dune management of these areas a difficult challenge. The comparison of the evolution of these two dunes has been of great importance in assessing the effect of historical human intervention and has provided a new perspective for future dune management strategies. The results obtained show that management measures based on sand removal have been proven to be unsustainable. Moreover, the monitoring methodology presented herein has proven very useful in predicting dune advance rates. For instance, the Bolonia dune could reach the nearest road in approximately 12 years

Diffraction by electronic components of everyday use

[EN] We demonstrate the use of CCD image sensors and LCD screens from discarded electronic devices as elements for performing simple optical diffraction experiments. The experiments can determine the spatial structure of these components by analyzing diffraction patterns generated by their interaction with monochromatic light. This article presents the design and results of such experiments. (C) 2014 American Association of Physics Teachers.The authors would like to thank the financial support of the Ministerio de Economía y Competitividad (Projects: DPI2012-32994 and FIS2011-23175), the Generalitat Valenciana (Project: PROMETEO2009-077), Universitat Polite`cnica de Vale`ncia (PAID-05-11). This work has been developed by the teaching innovation groups GCID35/2009 and MoMa from the Universitat de Vale`ncia and Universitat Polite`cnica de Vale`ncia, respectively. The authors would also like to thank Dr. Michael Devereux for kindly revising the manuscript as a native English-speaking person.Barreiro, JJ.; Pons, A.; Barreiro, JC.; Castro-Palacio, JC.; Monsoriu Serra, JA. (2014). Diffraction by electronic components of everyday use. American Journal of Physics. 82(3):257-261. https://doi.org/10.1119/1.4830043S25726182

Harmonic balance algorithms for the nonlinear simulation of HTS devices

This paper describes the application of Harmonic Balance algorithms to predict nonlinear effects in planar High Temperature Superconductors (HTS) microwave circuits. The resulting algorithms are fast and efficient and can be used both for the characterization of the nonlinearities in the HTS material, and for the prediction of the behavior of an HTS circuit given the parameters of these nonlinearities (such as a dependence of the surface impedance on the current density). Most previously published nonlinear HTS models can be used, because the algorithms are not restricted to a specific model of HTS nonlinearities. Two different types of algorithms are described: (1) algorithms specific for one-dimensional resonators (transmission lines and TM010 disk resonators) and (2) an algorithm based on the combination of Method of Moments and Harmonic Balance, applicable to 2D planar structures with few restrictions in their shape. Several cross-checks with theory and measurements are presented.Peer Reviewe

Evidence for Heating of Neutron Stars by Magnetic Field Decay

We show the existence of a strong trend between neutron star surface temperature and the dipolar component of the magnetic field extending through three orders of field magnitude, a range that includes magnetars, radio-quiet isolated neutron stars, and many ordinary radio pulsars. We suggest that this trend can be explained by the decay of currents in the crust over a time scale of few Myr. We estimate the minimum temperature that a NS with a given magnetic field can reach in this interpretation.Comment: 4 pages, 1 figures, version accepted for publication in Phys. Rev. Let

La enseñanza universitaria apoyada en plataformas virtuales. Cambios en las prácticas docentes: el caso de la Universidad de Sevilla

El estudio de los usos de las plataformas virtuales en la enseñanza universitaria constituye hoy un referente de interés para la docencia. El objetivo de esta investigación es explorar los usos pedagógicos de estas herramientas, con la finalidad de identificar factores condicionantes y sus variables asociadas. Esta investigación, que analiza el caso de la Universidad de Sevilla, se basa en un estudio descriptivo, tipo encuesta. Los resultados obtenidos permiten establecer como conclusiones relevantes que las prácticas de enseñanza online están mediadas por las concepciones y creencias pedagógicas del profesorado; pero a su vez los usos tecnológicos influyen y transforman dichas concepcione

Numerical 3+1 general relativistic magnetohydrodynamics: a local characteristic approach

We present a general procedure to solve numerically the general relativistic magnetohydrodynamics (GRMHD) equations within the framework of the 3+1 formalism. The work reported here extends our previous investigation in general relativistic hydrodynamics (Banyuls et al. 1997) where magnetic fields were not considered. The GRMHD equations are written in conservative form to exploit their hyperbolic character in the solution procedure. All theoretical ingredients necessary to build up high-resolution shock-capturing schemes based on the solution of local Riemann problems (i.e. Godunov-type schemes) are described. In particular, we use a renormalized set of regular eigenvectors of the flux Jacobians of the relativistic magnetohydrodynamics equations. In addition, the paper describes a procedure based on the equivalence principle of general relativity that allows the use of Riemann solvers designed for special relativistic magnetohydrodynamics in GRMHD. Our formulation and numerical methodology are assessed by performing various test simulations recently considered by different authors. These include magnetized shock tubes, spherical accretion onto a Schwarzschild black hole, equatorial accretion onto a Kerr black hole, and magnetized thick accretion disks around a black hole prone to the magnetorotational instability.Comment: 18 pages, 8 figures, submitted to Ap

La representación innovadora de una arquitectura museística. La línea Guggenheim

[ES] Sin resumenPuebla Pons, J.; Falcón Meraz, JM. (2009). La representación innovadora de una arquitectura museística. La línea Guggenheim. EGA. Revista de Expresión Gráfica Arquitectónica. (14):74-81. https://doi.org/10.4995/ega.2009.10239SWORD748114DAI Co, F. Il tempo e l'architetto. Frank L/oyd Wright e il Guggenheim Museum, 2004, Roma: Mondadori Electa.DAVIS, D., The museum transformed. Design and culture in the post-Pompidou age, 1990, New York: Abbeville Press Publishers.DAVIS, J, The Guggenheims, 1848-1988: An American Epic, 1988, New York Shapolsky Publishers.ROCCA, A., "Guggenheim - Gehry, Gwathmey & Siegel, lsozaki, Wright Dalla spirale alla rete. From the spiral to the Web". Lotus, 1995(85): p. 47-52.VAN BRUGGEN, C., El museo Guggenheim Bilbao, 1997, Nueva York: Guggenheim Foundation