Metal nanoparticles-PDMS nanocomposites for tunable optical filters and sensors

The peculiar optical response of polydimethylsiloxane (PDMS) doped with metallic nanoparticles can be employed to develop optical sensing materials. These nanocomposites may work in an ample range of temperatures, showing good linearity and high sensitivity. Plasmon resonances of the metallic nanoparticles produce interesting effects on the optical response by affecting the effective refractive index of PDMS. The high resonant response leads to a number of different configurations of optical filters and phase devices whose resonant frequency depends on the chosen nanoparticle. Moreover, the wavelength can be tuned up by external manufacturing conditions such as nanoparticle size or fill factor, and by working parameters such as temperature. This work develops the theoretical background required for the design of these structures, and evaluates the adequate dimensional and doping ranges for device optimization.This work was supported by Spanish Government RETOS Program grant no. TEC2013-47342-C2-R and no. TEC2013-50138-EXP, the R&D Program SINFOTON S2013/MIT-2790 of the Comunidad de Madrid, and the European COST Action IC1208

Ecología y distribución de Senecio pterophorus (Compositae) en la Península Ibérica

Field survey in Catalonia (Spain) has increased the known distribution and the number of populations of the South African daisy Senecio pterophorus DC. in the Iberian Peninsula and mainland Europe. The species colonizes relatively disturbed habitats such as river beds, road borders and disturbed helm-oak communities with no limitation in light and water. The analysis of population structure related to habitat type has revealed that in riparian and ruderal areas populations are large and well-established, with a large number of members per age class. However, in disturbed forests populations have only a few scattered adults. Senecio pterophorus also shows great morphological plasticity related with habitat type: in open environments plants are shorter, adopt a spherical habit, and have smaller leaves than in forests, where they are taller and have leaves twice in size. This species may be considered as invasive in the Iberian Peninsula and mainland Europe, where it has rapidly spread in recent years. Furthermore, we suggest that S. pterophorus may be a threat to native species and habitat diversity as occurs in Australia, where the species displaces the native plants and hybridizes with some native Senecio species.En este trabajo se describen el área de distribución y el número de poblaciones de la especie sudafricana Senecio pterophorus DC. en Cataluña, única área de la Europa continental de donde hasta ahora se conoce. Esta especie coloniza ambientes perturbados, como lechos de ríos, márgenes de carreteras y áreas forestales perturbadas, siempre que no haya limitación por la luz y la humedad. En los hábitats riparios y ruderales las poblaciones son más estables y densas, con un gran número de individuos de diversas clases de edad, mientras que en ambientes forestales las poblaciones suelen contar con pocos individuos adultos distribuidos de forma dispersa. Senecio pterophorus presenta, además, una acusada plasticidad morfológica en relación con el hábitat, de modo que en ambientes riparios y ruderales los individuos desarrollan un porte esférico, de menor tamaño, y unas hojas más pequeñas que en ambientes forestales, donde el porte de las plantas es más alargado y el tamaño de las hojas mucho mayor. Esta especie, en creciente expansión, debe ser considerada una planta invasora en la Península Ibérica, ya que ha aumentado considerablemente el número de sus poblaciones en un período relativamente corto. Además, se sugiere que S. pterophorus puede llegar a ser una amenaza para la conservación de la diversidad de especies y de hábitats naturales autóctonos, como ocurre en Australia, donde desplaza a las especies nativas e incluso se hibrida con otras especies de Senecio

Ecologia y distribucion de Senecio pterophorus (Compositae) en la Peninsula Iberica.

En este trabajo se describen el área de distribución y el número de poblaciones de la especie sudafricana Senecio pterophorus DC. en Cataluña, única área de la Europa continental de donde hasta ahora se conoce. Esta especie coloniza ambientes perturbados, como lechos de ríos, márgenes de carreteras y áreas forestales perturbadas, siempre que no haya limitación por la luz y la humedad. En los hábitats riparios y ruderales las poblaciones son más estables y densas, con un gran número de individuos de diversas clases de edad, mientras que en ambientes forestales las poblaciones suelen contar con pocos individuos adultos distribuidos de forma dispersa. Senecio pterophorus presenta, además, una acusada plasticidad morfológica en relación con el hábitat, de modo que en ambientes riparios y ruderales los individuos desarrollan un porte esférico, de menor tamaño, y unas hojas más pequeñas que en ambientes forestales, donde el porte de las plantas es más alargado y el tamaño de las hojas mucho mayor. Esta especie, en creciente expansión, debe ser considerada una planta invasora en la Península Ibérica, ya que ha aumentado considerablemente el número de sus poblaciones en un período relativamente corto. Además, se sugiere que S. pterophorus puede llegar a ser una amenaza para la conservación de la diversidad de especies y de hábitats naturales autóctonos, como ocurre en Australia, donde desplaza a las especies nativas e incluso se hibrida con otras especies de Senecio

Tecnologías de materiales con aplicaciones en fusión y su desarrollo en la instalación TechnoFusión

El futuro Centro Nacional de Tecnologías para la Fusión, TechnoFusión, tiene como objetivo desarrollar aquellas tecnologías, relacionadas con materiales, metales líquidos, manipulación remota y simulación, que permitan avanzar en los actuales retos que supone el uso de la fusión nuclear. Sus instalaciones, abiertas al servicio de la comunidad científica externa, garantizarán una destacada participación de empresas y grupos de investigación españoles. En esta contribución se describirán y analizarán las instalaciones que TechnoFusión construirá con capacidad para abordar: la fabricación y procesado de nuevas aleaciones a escala semiindustrial; el comportamiento de materiales, simulando las condiciones durante operación mediante una instalación de triple irradiación (iones pesados, hidrógeno y helio), generadores de plasma lineal (continuo y pulsado) y un circuito de litio líquido; y la caracterización del efecto que las severas condiciones de experimentación producen en las propiedades, en la composición y en la microestructura de materiales estructurales y funcionales (técnicas convencionales e in-situ)

Nanostructured tungsten as a first wall material for the future nuclear fusion reactors

The lack of materials able to withstand the severe radiation conditions (high thermal loads and atomistic damage) expected in fusion reactors is the actual bottle neck for fusion to become a reality. The main requisite for plasma facing materials (PFM) is to have excellent structural stability since severe cracking or mass loss would hamper their protection role which turns out to be unacceptable. Additional practical requirements for plasma facing materials are among others: (i) high thermal shock resistance, (ii) high thermal conductivity (iii) high melting point (iv) low physical and chemical sputtering, and (v) low tritium retention

Capabilities of Nanostructured Tungsten for Plasma Facing Material

One of the bottle necks for fusion to become a reality is the lack of materials able to withstand the harsh conditions taken place in a reactor environment. In particular, plasma facing materials (PFM) have to resist large radiation fluxes and thermal loads. Nowadays, tungsten is one of the most attractive materials proposed for PFM. However, it is known that the irradiation of tungsten with H leads to surface blistering and subsequent cracking and exfoliation which is unacceptable. In particular, these effects have been observed to be more severe when W is subjected to pulse irradiation

Oscillator Finite-Difference Time-Domain (O-FDTD) electric field propagation model: integrated photonics and networks

The recently developed Lorentz Oscillator Model-inspired Oscillator Finite-Difference Time-Domain (O-FDTD) is one of the simplest FDTD models ever proposed, using a single field equation for electric field propagation. We demonstrate its versatility on various scales and benchmark its simulation performance against theory, conventional FDTD simulations, and experimental observations. The model’s broad applicability is demonstrated for (but not limited to) three contrasting realms: integrated photonics components on the nano- and micrometer scale, city-wide propagating radiofrequency signals reaching into the hundreds of meters scale, and for the first time, in support of 3D optical waveguide design that may play a key role in neuromorphic photonic computational devices

Modifying light propagation in planar waveguides with cladding liquid crystals

Liquid crystal devices are increasingly being used in non-display applications to manufacture small devices that can be driven by low voltage electronics. LCs are low cost, light weight and avoid using mechanical components. A wide number of interesting applications involve the use of LCs for phase modulation of light. This can be done with light propagating through the LC itself or rather with light propagating in a waveguide (WG) where sections of its cladding are filled with LC that interacts with the light?s evanescent field. Several device families based on this general outline are being tested in our group. The devices can be roughly classified into two categories. The first group consists of WGs having a width much larger than the light wavelength (Fig. 1), therefore behaving as 1D waveguides. In these structures, effective beam steering can be achieved using pixelated electrodes having specific shapes. Beam steering has been demonstrated in IR beams [1] using silicon substrates. In our laboratory, steering of visible light is tested employing, besides silicon substrates, ITO-coated glass substrates with a high-index guiding layer of SU-8

Polymer selective laser curing for integrated optical switches

A simple in-layer electro optical switch has been prepared by selectively curing a photocurable optical polymer with a UV laser. The core of the device is a NOA-81 multimode waveguide grown by selective laser curing. The cladding is a positive calamitic liquid crystal, which allows tunability and switching of the waveguide by external driving electric signals. The effective refractive index in the guide changes upon switching the liquid crystal. Depending on the geometry, this setup leads to an electrooptical modulator or a switch between two levels of transmitted ligh

Electrical Behavior of Liquid Crystal Devices with Dielectric Nanoparticles

Nowadays, the development of new devices based on liquid crystal (LC) materials requires improved tuning characteristics according to the application. One approach for this improvement is the use of nanomaterials with the capability of modifying the effective properties of the doped LC mixture. In this work, we analyze the electrical behavior of a titanium dioxide (TiO2) nanoparticle-doped liquid crystal cell using an equivalent circuit. The circuit parameters have been obtained using the impedance spectroscopy technique and time response measurements. The particularity of the samples designed is that the nanoparticles are not dispersed in the LC. Instead of that, nanoparticles are randomly deposited on one of the electrodes. Measurements show that the presence of the nanoparticles increases the temperature sensitivity of the equivalent cell capacitance and the capacitance difference between switched and nonswitched states. These results could be quite useful in the design of novel liquid crystal electronic devices and sensors