The Gauss map of surfaces in PSL˜2(R)

We define a Gauss map for surfaces in the universal cover of the Lie group PSL2(R) endowed with a left-invariant Riemannian metric having a 4-dimensional isometry group. This Gauss map is not related to the Lie group structure. We prove that the Gauss map of a nowhere vertical surface of critical constant mean curvature is harmonic into the hyperbolic plane H2 and we obtain a Weierstrass-type representation formula. This extends results in H2 ×R and the Heisenberg group Nil3, and completes the proof of existence of harmonic Gauss maps for surfaces of critical constant mean curvature in any homogeneous manifold diffeomorphic to R3 with isometry group of dimension at least 4.Ministerio de Ciencia y Tecnología MTM2010-19821Junta de Andalucía P09-FQM-508

Comparison results for the Stokes equations

This paper enfolds a medius analysis for the Stokes equations and compares different finite element methods (FEMs). A first result is a best approximation result for a P1 non-conforming FEM. The main comparison result is that the error of the P2-P0-FEM is a lower bound to the error of the Bernardi-Raugel (or reduced P2-P0) FEM, which is a lower bound to the error of the P1 non-conforming FEM, and this is a lower bound to the error of the MINI-FEM. The paper discusses the converse direction, as well as other methods such as the discontinuous Galerkin and pseudostress FEMs. Furthermore this paper provides counterexamples for equivalent convergence when different pressure approximations are considered. The mathematical arguments are various conforming companions as well as the discrete inf-sup condition

ARE THE DYNAMICS OF KNOWLEDGE-BASED INDUSTRIES ANY DIFFERENT?

The concept of «knowledge-based industries» (KBIs) has been widely used both in the academy and in policy-making over the last decade, due to the increasing role those industries play – both in terms of value added and employment – in contemporary, advanced economies. In this paper we discuss the extent to which KBIs differ from other industries in what concerns some of the stylised facts and regularities of industry dynamics usually found in the literature. In particular, we analyse the patterns and the determinants of firm entry and post-entry performance (measured in terms of survival of new firms), comparing KBIs groups with the remaining industries, using data for the Portuguese economy in the second half of the 1990s. We find that KBIs and the firms within them show some signs of distinctiveness in their dynamics as compared to the general case. In particular, on average, KBIs firms have higher survival chances, and entry within the KBIs groups is less responsive to incentives.knowledge-based industries; market entry; firm survival

Análisis de un nuevo sensor de radiación solar para su uso en aplicaciones de sistemas fotovoltaicos integrados en edificios

[EN] The solar radiation assessment is a key factor for this growth as it is the critical variable for all solar energy generation systems. EKO instruments has developed a sensor that integrates six photodiodes to measure solar irradiance upwards (global horizontal), downwards (ground reflected) and irradiance in all four cardinal directions for vertical surfaces. It is believed that the extra data would reduce uncertainty in prediction of PV outputs during the design phase and performance verification during the PV plant operation. This could therefore enhance the investment in vertical PV systems such as BIPV or east-west BF plants. In the first place, an investigation on the optimal transposition model for BIPV facades with GHI as the only input was carried out. A decomposition model fitted for the studied region was created. Two different study cases were conducted with the intention of identifying the optimal transposition model among the five studied and to account for the inaccuracies that the new decomposition model might introduced to the process. The results validated the use of the new decomposition model for south facing surfaces. Nevertheless, its use for non south-facing surfaces did not show the same accuracy, which was increased when the uncertainties of the GHI sensor were taken into account. None of the anisotropic studied models can be declared as the best performing, nor does any particular model demonstrate clear advantages over the others for the location and scenarios studied here. The measurements from the vertical sensors in the MDPD within a five month period were compared to the transposed irradiance from a PD installed nearby. The inherent errors that project developers of vertical PV systems should account for in the choice between the use of measured (MDPD) or transposed data (and the associated transposition model choice) were accurately quantified. For north facing surfaces, the average error of each predicted irradiance value over the measured one (RMSE) can be up to 11.2 W/m2 , overestimating the solar irradiance by 6 W/m2 should they choose to not use measured data, or the optimal transposition model. In the case of a south-facing surface those errors can be up to 45.5 W/m2 and 12.8 W/m2 respectively. The east and west facing surfaces could show RMSE of 26.5 W/m2 and 24.2 W/m2 , and MBE of -4.5 W/m2 and 4.6 W/m2 respectively[ES] En este proyecto, el alumno trabajará con mediciones tomadas por un sensor de fotodiodo multidireccional (MDPD) desarrollado por EKO Instruments. El MDPD consta de seis fotodiodos de silicio independientes que pueden enfrentar las cuatro direcciones cardinales (N-E-S-W), hacia arriba (horizontal global) y hacia abajo (reflejada del suelo). Las posibles aplicaciones fotovoltaicas (PV) para este sensor incluyen la construcción de sistemas fotovoltaicos integrados en edificios (BIPV) donde los paneles PV a menudo se montan verticalmente y en superficies no orientadas al sur y fotovoltaica bifacial (FV BF) donde la radiación reflejada del suelo (albedo) es de gran interés. La mayoría de las estaciones meteorológicas y las bases de datos solo proporcionan datos de irradiación horizontal global (GHI), por lo que el objetivo de este proyecto es demostrar los beneficios de los datos adicionales de un MDPD. Este proyecto es una colaboración entre DTU Fotonik y EKO Instruments B.V. para validar el sensor MDPD. El estudiante puede esperar trabajar en estrecha colaboración con estos dos socios. El sensor MDPD se instalará próximo a los sensores de radiación solar de Clase A de DTU Fotonik, que se utilizarán para la validación del MDPD. Durante el proyecto, el alumno se familiarizará con las diferencias inherentes entre los sensores de Clase A y MDPD, varios modelos de transposición y modelos de rendimiento BIPV. Objetivos: - Identificar el modelo de transposición óptimo (por ejemplo, Pérez, Reindl, Hay & Davies, etc.) para estimar la irradiación en fachadas BIPV utilizando solo irradiación global en el plano horizontal. - Utilizar los datos del MDPD para estimar la producción solar en un sistema BIPV en Dinamarca. - Estimar el error sistemático al que se arriesgan los desarrolladores de proyectos BIPV si no utilizan el modelo de transposición apropiado, o si no usan el MDPD para su evaluación de los recursos solares.Álvarez Mira, D. (2020). Análisis de un nuevo sensor de radiación solar para su uso en aplicaciones de sistemas fotovoltaicos integrados en edificios. http://hdl.handle.net/10251/145354TFG

Thermo-optical interactions in a dye-microcavity photon Bose-Einstein condensate

Superfluidity and Bose-Einstein condensation are usually considered as two closely related phenomena. Indeed, in most macroscopic quantum systems, like liquid helium, ultracold atomic Bose gases, and exciton-polaritons, condensation and superfluidity occur in parallel. In photon Bose-Einstein condensates realized in the dye microcavity system, thermalization does not occur by direct interaction of the condensate particles as in the above described systems, i.e. photon-photon interactions, but by absorption and re-emission processes on the dye molecules, which act as a heat reservoir. Currently, there is no experimental evidence for superfluidity in the dye microcavity system, though effective photon interactions have been observed from thermo-optic effects in the dye medium. In this work, we theoretically investigate the implications of effective thermo-optic photon interactions, a temporally delayed and spatially non-local effect, on the photon condensate, and derive the resulting Bogoliubov excitation spectrum. The calculations suggest a linear photon dispersion at low momenta, fulfilling the Landau's criterion of superfluidity . We envision that the temporally delayed and long-range nature of the thermo-optic photon interaction offer perspectives for novel quantum fluid phenomena.Comment: 21 pages, 5 figure

Heat loss prediction of a confined premixed jet flame using a conjugate heat transfer approach

The presented work addresses the investigation of the heat loss of a confined turbulent jet flame in a lab-scale combustor using a conjugate-heat transfer approach and large-eddy simulation. The analysis includes the assessment of the principal mechanisms of heat transfer in this combustion chamber: radiation, convection and conduction of heat over walls. A staggered approach is used to couple the reactive flow field to the heat conduction through the solid and both domains are solved using two implementations of the same code. Numerical results are compared against experimental data and an assessment of thermal boundary conditions to improve the prediction of the reactive flow field is given.The research leading to these results has received funding through the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7, 2007–2013) under the Grant agreement No. FP7-290042 for the project COPA-GT as well as the European Union’s Horizon 2020 Programme (2014–2020) and from Brazilian Ministry of Science, Technology and Innovation through Rede Nacional de Pesquisa (RNP) under the HPC4E Project, Grant agreement No. 689772. The authors thankfully acknowledge the computer resources, technical expertise and assistance provided by the Red Española de Supercomputación (RES). Finally, the authors would like to thank O. Lammel for the useful discussions and kindly providing the data for the comparison.Peer ReviewedPostprint (published version

Study of the Wall Thermal Condition Effect in a Lean-Premixed Downscaled Can Combustor Using Large-Eddy Simulation

The primary purpose of this study is to evaluate the ability of LES, with a turbulent combustion model based on steady flamelets, to predict the flame stabilization mechanisms in an industrial can combustor at full load conditions. The test case corresponds to the downscaled Siemens can combustor tested in the high pressure rig at the DLR. The effects of the wall temperature on the prediction capabilities of the codes is investigated by imposing several heat transfer conditions at the pilot and chamber walls. The codes used for this work are Alya and OpenFOAM, which are well established CFD codes in the fluid mechanics community. Prior to the simulation, results for 1-D laminar flames at the operating conditions of the combustor are compared with the detailed solutions. Subsequently, results from both codes at the mid-plane are compared against the experimental data available. Acceptable results are obtained for the axial velocity, while discrepancies are more evident for the mixture fraction and the temperature, particularly with Alya. However, both codes showed that the heat losses influence the size and length of the pilot and main flame.The research leading to these results has received funding through the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7, 2007-2013) under the grant agreement No. FP7-290042 for the project COPA-GT and the European Union’s Horizon 2020 Programme (2014-2020) and from Brazilian Ministry of Science, Technology and Innovation through Rede Nacional de Pesquisa (RNP) under the HPC4E Project, grant agreement No. 689772. The authors thankfully acknowledge the computer resources, technical expertise and assistance provided by the Red Española de Supercomputación (RES).Peer ReviewedPostprint (author's final draft

Paying It Forward: A Gift Economy of Poetry and Visual Art Images

As our world has changed rapidly and ineluctably with the COVID-19 pandemic, many are advocating an ethos of generosity and a gift economy, based on generative, creative offerings, as an alternative or balance to the excesses of a mainstream neoliberal exchange economy. What is the gift economy, and how does it entangle us in a fabric of mutual responsibility, obligation, creative practices and love, within the human and greater-than-human world? A Pay-It-Forward New Year\u27s gift game amongst a group of artist/ educators, ongoing since 2014, gives rise to this meditation on the gift economy, based on Mauss, Hyde, Kimmerer, Vaughan and Jordan\u27s work and contemplation of intergenerational, inter-being webs of mutuality. Visual artwork (photography and painting), and poetry and song that inspired and arose from the Pay-It-Forward engagement are part of this piece