Scattering of surface plasmons by one-dimensional periodic nanoindented surfaces

In this work, the scattering of surface plasmons by a finite periodic array of one-dimensional grooves is theoretically analyzed by means of a modal expansion technique. We have found that the geometrical parameters of the array can be properly tuned to achieve optimal performance of the structure either as a Bragg reflector or as a converter of surface plasmons into light. In this last case, the emitted light is collimated within a few degrees cone. Importantly, we also show that a small number of indentations in the array are sufficient to fully achieve its functional capabilities.Comment: 5 pages, 5 figures; changed sign convention in some definition

On the transmission of light through a single rectangular hole

In this Letter we show that a single rectangular hole exhibits transmission resonances that appear near the cutoff wavelength of the hole waveguide. For light polarized with the electric field pointing along the short axis, it is shown that the normalized-to-area transmittance at resonance is proportional to the ratio between the long and short sides, and to the dielectric constant inside the hole. Importantly, this resonant transmission process is accompanied by a huge enhancement of the electric field at both entrance and exit interfaces of the hole. These findings open the possibility of using rectangular holes for spectroscopic purposes or for exploring non-linear effects.Comment: Submitted to PRL on Feb. 9th, 200

Terahertz surface plasmon polariton propagation and focusing on periodically corrugated metal wires

In this letter we show how the dispersion relation of surface plasmon polaritons (SPPs) propagating along a perfectly conducting wire can be tailored by corrugating its surface with a periodic array of radial grooves. In this way, highly localized SPPs can be sustained in the terahertz region of the electromagnetic spectrum. Importantly, the propagation characteristics of these spoof SPPs can be controlled by the surface geometry, opening the way to important applications such as energy concentration on cylindrical wires and superfocusing using conical structures.Comment: accepted at PRL, submitted 29th May 200

Optical bistability in subwavelength apertures containing nonlinear media

We develop a self-consistent method to study the optical response of metallic gratings with nonlinear media embedded within their subwavelength slits. An optical Kerr nonlinearity is considered. Due to the large E-fields associated with the excitation of the transmission resonances appearing in this type of structures, moderate incoming fluxes result in drastic changes in the transmission spectra. Importantly, optical bistability is obtained for certain ranges of both flux and wavelength.Comment: 4 pages, 4 figure

Environment and citizenship: Education for the participation as a base for a global citizenship education

Ciudadanía y medio ambiente se plantean como dos de los grandes retos a abordar en el siglo XXI en el ámbito de la educación. Esta investigación pretende aportar resultados acerca de la relevancia que los programas de participación ciudadana tienen en el alumnado en orden a fomentar las competencias relacionadas con la ciudadanía activa. Proponemos un marco teórico conjunto de la educación ambiental y la educación para la ciudadanía asumiendo una perspectiva de educación ciudadana planetaria o educación global. La investigación se desarrolla sobre varios casos de programas de educación para la participación ciudadana (Ecoescuela, Parlamento joven, Seguro que te mueves) en Andalucía y utiliza una metodología cualitativa de triangulación de datos con cuestionarios, entrevistas y grupos de discusión, utilizándose el software Atlas.ti para el tratamiento de los datos. Pretendemos así identificar las potencialidades y limitaciones de dichos programas, que han ido surgiendo de la necesidad de dar respuesta a valores considerados como deseables para la ciudadanía del siglo XXI. Entre los resultados obtenidos destacamos la potencialidad de estos programas educativos para formar ciudadanos comprometidos con los problemas sociales y ambientales desde una perspectiva de ciudadanía planetaria.Citizenship and environment are presented as two of the big challenges to be faced in the 21st century in the area of education. This research aims to provide results about the relevance that citizen participation programs have on students in order to foster the skills related to active citizenship. A theoretical framework of environmental education and education for citizenship is set assuming a perspective of planetary or global citizenship education. The research is based on several cases of education programs for citizen participation (Eco-Shool, Parlamento Joven, Seguro que te mueves) in Andalusia and uses a qualitative methodology of triangulation data through questionnaires, interviews and focus groups, using the software Atlas.ti for the data processing. We intend to identify the potentials and limitations of these programs, which have arisen from the need to provide responses to what are considered desirable values for 21st century citizenship. Among the results we highlight the potential of these educational programs to educate citizens involved in social and environmental problems from the perspective of global citizenship.Ministerio de Educación y Ciencia y por Fondos FEDE

Escuela y desarrollo comunitario: educación ambiental y ciudadanía en las aulas de secundaria

La finalidad básica de la investigación que aquí se presenta es analizar la potencialidad educativa del programa Seguro que te mueves, cuyo objetivo es favorecer la participación activa del alumnado en su entorno inmediato, generando actitudes de compromiso con las problemáticas de su localidad. Se han analizado las propuestas llevadas a cabo en dos institutos de enseñanza secundaria de la provincia de Sevilla (España). Para el análisis se ha diseñado una metodología de carácter cualitativo que ha permitido establecer las dificultades pero, sobre todo, las posibilidades del programa para construir un modelo deseable de ciudadanía participativa y comprometida con el entorno. En cuanto a las conclusiones, se percibe una carencia de actividades específicas que permitan entender las cuestiones detectadas desde un enfoque más amplio, conectando así los problemas locales con los globales.The basic end of the research presented in this article is to analyze the educational potential of the “Move Already!” program, which is aimed at encouraging students’ active participation in their immediate surroundings, while generating attitudes of commitment toward local problems. An analysis was made of the actions carried out in two secondary schools in Seville, Spain. Qualitative methodology has allowed a definition of difficulties, as well as a program’s possibilities in constructing a desirable model of participative citizens committed to their environment. In conclusion, a lack of specific activities prevents understanding issues from a broader perspective that would connect local and global problems

Educating for participation from a planetary perspective. Analysis of educational experiences in Andalusia

Las finalidades básicas de la Educación Ambiental y de la Educación para la Ciudadanía pueden confluir en una perspectiva de “educación ciudadana planetaria”, que tenga como eje central la educación para la participación como ciudadanos en relación con los problemas sociales y ambientales, a escala local y a escala global. Desde este marco se analizan varios programas de educación para la participación ciudadana desarrollados en Andalucía: “Ecoescuela”, “Parlamento Joven” y “Seguro que te mueves”, valorando sus potencialidades y sus dificultades, con especial atención a las concepciones del profesorado y del alumnado implicados en los mismos.The basic aims of Environmental Education and Education for Citizenship can converge in a perspective of “global citizenship education”, which has as its central axis education for participation as citizens in relation to social and environmental issues, in a local and global scale. From this framework several education programs for citizen participation developed in Andalusia are analyzed: “Eco-School”, “Youths’ Parliament” and “Sure You Move”, assessing their strengths and their difficulties, with particular attention to the conceptions of teachers and students involved therein

Treatment of end-of-life concrete in an innovative heating-air classification system for circular cement-based products

A stronger commitment towards Green Building and circular economy, in response to environmental concerns and economic trends, is evident in modern industrial cement and concrete production processes. The critical demand for an overall reduction in the environmental impact of the construction sector can be met through the consumption of high-grade supplementary raw materials. Advanced solutions are under development in current research activities that will be capable of up-cycling larger quantities of valuable raw materials from the fine fractions of End-of-Life (EoL) concrete waste. New technology, in particular the Heating-Air classification System (HAS), simultaneously applies a combination of heating and separation processes within a fluidized bed-like chamber under controlled temperatures (±600 °C) and treatment times (25–40 s). In that process, moisture and contaminants are removed from the EoL fine concrete aggregates (0–4 mm), yielding improved fine fractions, and ultrafine recycled concrete particles (<0.125 mm), consisting mainly of hydrated cement, thereby adding value to finer EoL concrete fractions. In this study, two types of ultrafine recycled concrete (either siliceous or limestone EoL concrete waste) are treated in a pilot HAS technology for their conversion into Supplementary Cementitious Material (SCM). The physico-chemical effect of the ultrafine recycled concrete particles and their potential use as SCM in new cement-based products is assessed by employing substitutions of up to 10% of the conventional binder. The environmental viability of their use as SCM is then evaluated in a Life Cycle Assessment (LCA). The results demonstrated accelerated hydration kinetics of the mortars that incorporated these SCMs at early ages and higher mechanical strengths at all curing ages. Optimal substitutions were established at 5%. The results suggested that the overall environmental impact could be reduced by up to 5% when employing the ultrafine recycled concrete particles as SCM in circular cement-based products, reducing greenhouse gas emissions by as much as 41 kg CO2 eq./ton of cement (i.e. 80 million tons CO2 eq./year). Finally, the environmental impacts were reduced even further by running the HAS on biofuel rather than fossil fuel.The authors of the present paper, prepared in the framework ofthe Project VEEP "Cost-Effective Recycling of C&DW in High AddedValue Energy Efficient Prefabricated Concrete Components forMassive Retrofitting of our Built Environment", wish to acknowl-edge the European Commission for its support. This project hasreceived funding from the European Union’s Horizon 2020 researchand innovation programme under grant agreement No 723582.This paper reflects only the author’s view and the European Com-mission is not responsible for any use that may be made of theinformation it contains.The authors are also grateful to the Spanish Ministry of Science,Innovation and Universities (MICIU) and the European RegionalDevelopment Fund (FEDER) for funding this line of research(RTI2018-097074-B-C21)

Transmission properties of a single metallic slit: From the subwavelength regime to the geometrical-optics limit

In this work we explore the transmission properties of a single slit in a metallic screen. We analyze the dependence of these properties on both slit width and angle of incident radiation. We study in detail the crossover between the subwavelength regime and the geometrical-optics limit. In the subwavelength regime, resonant transmission linked to the excitation of waveguide resonances is analyzed. Linewidth of these resonances and their associated electric field intensities are controlled by just the width of the slit. More complex transmission spectra appear when the wavelength of light is comparable to the slit width. Rapid oscillations associated to the emergence of different propagating modes inside the slit are the main features appearing in this regime.Comment: Accepted for publication in Phys. Rev.