Metamaterials for radiactive cooling

The increasing pressure of society to decrease energy consumption and to enhance energetic efficiency has lead to search novel technologies to accomplish it. Notwithstanding the increasing electricity production of renewable energies, it is a fact that the energy expenses can be drastically reduced in most areas. Among these areas, cooling systems stand out for being energetically inefficient. Furthermore, both economical and energy cost of such systems are increasing due to the global warming, which is aggravated by the energy production for them, making a loop that is increasingly damaging the environment. A solution to this problem has emerged under the name of radiative cooling, which is a physical phenomenon by which any terrestrial object losses heat in form of radiation that is sent to outer space. This process can be explained by black body radiation theory and the atmospheric window. The former states that any object at some temperature above 0 K radiates energy at all wavelengths, with its radiation peak and spectral location modulated by its temperature. The latter is a frequency band in which the atmosphere is transparent to radiation, making possible for waves at certain frequencies to cross freely. These phenomena allows a direct heat transmission between earth and space, which is cold and almost infinite, making a great storage for excess warmth without wasting energy in the process. In this work, it has been studied one of the main technologies that can implement radiative cooling in practice, metamaterials, with the aim to understand how to improve its associated problems of manufacturing and design for radiative cooling applications. In Chapter 1, the fundamentals of radiative cooling are introduced along with the state of the art. Then, Chapter 2 presents the materials used in the literature and in this work to develop later analytical models for thin film multilayered metamaterials and a possible way to automatically design them. To better understand the analytical developments, two appendices introducing the underlying theory and equations are included. Also, the software used in this work is presented. Finally, the performance and analysis of three different radiative cooling devices is exposed in Chapter 3, one of them using the materials and methods of Chapter 2.Máster Universitario en Ingeniería de Telecomunicación por la Universidad Pública de NavarraNafarroako Unibertsitate Publikoko Unibertsitate Masterra Telekomunikazio Ingeniaritza

Max Bill a través de cinco conceptos

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Dilatometric characterization of pearlite dissolution in 0.1c-0.5mn low carbon low manganese steel

The authors acknowledge financial support from the European Coal and Steel Community (ECSC- 7210. EC/939) and the Spanish Comisio´n Interministerial de Ciencia y Tecnologı´a (CICYT-MAT95-1192-CE)Peer reviewe

Kinetics Model of Isothermal Pearlite Formation in a 0.4C-1.6Mn Steel

The present article is concerned with a theoretical and experimental study of the growth kinetics of pearlite in a 0.4C-1.6Mn medium carbon steels. Factors controlling the isothermal formation of this microconstituent are explored in this work. In this sense, the transition temperature between local equilibrium (LE) and no partition local equilibrium (NPLE) growth mechanisms is theoretically determined. Moreover, the nucleation of pearlite has been considered as a cementite precipitation process on a moving austenite-ferrite interface. Finally, a theoretical model is presented in this work to calculate the evolution of austenite-to-pearlite transformation with time at a very wide temperature range.The authors acknowledge financial support from Spanish Ministerio de Ciencia y Tecnologı´a (MAT2001-1617). C. Capdevila would like to express his gratitude to the Consejo Superior de Investigaciones Cientifı´cas for financial support as a Post-Doctoral contract (I3P PC-2001-1). F.G. Caballero would like to thank the Consejerı´a de Educacio´n. D.G. de Investigacio´n de la Comunidad Auto´noma de Madrid (CAM) for the financial support in the form of a Postdoctoral Research GrantPeer reviewe

Kinetics Model of Isothermal Pearlite Formation in a 0.4C-1.6Mn Steel

The present article is concerned with a theoretical and experimental study of the growth kinetics of pearlite in a 0.4C-1.6Mn medium carbon steels. Factors controlling the isothermal formation of this microconstituent are explored in this work. In this sense, the transition temperature between local equilibrium (LE) and no partition local equilibrium (NPLE) growth mechanisms is theoretically determined. Moreover, the nucleation of pearlite has been considered as a cementite precipitation process on a moving austenite-ferrite interface. Finally, a theoretical model is presented in this work to calculate the evolution of austenite-to-pearlite transformation with time at a very wide temperature range.The authors acknowledge financial support from Spanish Ministerio de Ciencia y Tecnologı´a (MAT2001-1617). C. Capdevila would like to express his gratitude to the Consejo Superior de Investigaciones Cientifı´cas for financial support as a Post-Doctoral contract (I3P PC-2001-1). F.G. Caballero would like to thank the Consejerı´a de Educacio´n. D.G. de Investigacio´n de la Comunidad Auto´noma de Madrid (CAM) for the financial support in the form of a Postdoctoral Research GrantPeer reviewe

Incubation time of isothermally transformed allotriomorphic ferrite in medium carbon steels

The authors acknowledge financial support from the Spanish Comisio´n Interministerial de Ciencia y Tecnologı´a (CICYT) (project-PETRI 95-0089-OP). GSB Acero S.A. and CEIT are thanked for providing the steel and their collaboration in this projectPeer reviewe

Modeling of the interlamellar spacing of isothermally formed pearlite in a eutectoid steel

The authors acknowledge financial support from the European Coal and Steel Community (ECSC-7210. EC/939) and the Spanish Comisio´n Interministerial de Ciencia y Tecnologı´a (CICYT-MAT95-1192-CE)Peer reviewe

Estimation of dislocation density in bainitic microstructures using high-resolution dilatometry

It is possible by means of high resolution dilatometry together with a model based on isotropic dilatation and atomic volumes, to estimate the dislocation density introduced in the microstructure as a consequence of the isothermal decomposition of austenite into bainitic ferrite. The relatively high dislocation density associated with this microstructure is attributed to the fact that the shape deformation accompanying this displacive transformation is accommodated by plastic relaxationThe authors gratefully acknowledge the financial support of the Spanish MCYT. Plan Nacional deI+D (Programa I3 2007–2009) Ref. 200760I013 and the RFCS Programme for 2007 (Commission of the European Communities) Ref. RFSR-CT-2008-00022Peer reviewe

Influence of V Precipitates on Acicular Ferrite Transformation. Part 1: The Role of Nitrogen

6 pages, 8 figures, 1 table.-- This is Part I of paper "Influence of V Precipitates on Acicular Ferrite Transformation", Part II available at: http://hdl.handle.net/10261/17758Vanadium Award 2009-Council of the Institute of Materials, Minerals and Mining-UK for the most outstanding paper in the metallurgy and technology of vanadium and its alloys. Sponsored and selected by the Vanadium International Technical Committee (Vanitec).This paper (part 1 of a two part study) deals with the influence of N in its combination with V, as V(C, N) precipitates, on the decomposition of austenite into acicular ferrite. Likewise, the intragranular nucleation potency of V(C, N) precipitates is analyzed through the continuous cooling transformation diagrams (CCT) of two C–Mn–V steels with different contents of N under two different austenitising temperatures, i.e. different austenite grain sizes. The results clearly show that for austenite to decompose into acicular ferrite is necessary, first to have a representative fraction of V(C, N) precipitates within austenite, and second to decorate the austenite grain boundaries with proeutectoid ferrite so bainite can not form. Part 2 of the study concerns with the influence that those precipitates have on the kinetics of acicular ferrite formation during austenite isothermal decomposition.The authors would like to acknowledge the Commission of the European Communities for the financial support in the frame of the RFCS Programme for 2004 (RFS-PR-03136). Also to the Spanish MCYT through the project MAT2005-24485-E.Peer reviewe

Estilo de vida y rendimiento académico en adolescentes: comparación entre deportistas y no-deportistas

In this research we wanted to clear some doubts about the use of adolescent athletes’s leisure in comparison with non-athletes, and how it could influence in their academic performance. The sample consisted of 313 adolescent subjects from 3rd and 4th ESO grade, 181 men and 132 women, from 12 Secondary Schools; 124 were athletes and 189 non-athletes. The instruments used were questionnaires CHTE (habits and study skills) and PFYTL (physical practice and use of leisure). The variables analyzed were academic performance, study habits, sedentary leisure and sleep. The main results showed that athletes had better academic performance, better study habits and spent less time in sedentary leisure than non-athletes. In addition, related to study habits, athletes had a better attitude and a better study planning than non-athletes.Con esta investigación se quiso esclarecer algunas dudas respecto al uso que hacen del tiempo libre los sujetos deportistas adolescentes en comparación con sus iguales no-deportistas y de qué forma podía influir esto en su rendimiento académico. La muestra estaba formada por 313 sujetos adolescentes de 3º y 4º de ESO, 181 hombres y 132 mujeres, de 12 Centros de Castellón de la Plana; 124 eran deportistas y 189 no-deportistas. Los instrumentos utilizados fueron los cuestionarios CHTE (Cuestionario de Hábitos y Técnicas de Estudio), PFYTL (Práctica Física Y uso del Tiempo Libre). Las variables analizadas fueron el rendimiento académico, los hábitos de estudio, el ocio sedentario y el sueño. Los principales resultados muestran que los sujetos deportistas tienen mejor rendimiento académico, mejores hábitos de estudio y dedican menos tiempo al ocio sedentario; además, dentro de los hábitos de estudio, los sujetos deportistas planifican mejor su tiempo libre y presentan mejor actitud frente a los estudios