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

Optimal light harvesting structures at optical and infrared frequencies

One-dimensional light harvesting structures with a realistic geometry nano-patterned on an opaque metallic film are optimized to render high transmission efficiencies at optical and infrared frequencies. Simple design rules are developed for the particular case of a slit-groove array with a given number of grooves that are symmetrically distributed with respect to a central slit. These rules take advantage of the hybridization of Fabry-Perot modes in the slit and surface modes of the corrugated metal surface. Same design rules apply for optical and infrared frequencies. The parameter space of the groove array is also examined with a conjugate gradient optimization algorithm that used as a seed the geometries optimized following physical intuition. Both uniform and nonuniform groove arrays are considered. The largest transmission enhancement, with respect to a uniform array, is obtained for a chirped groove profile. Such enhancement is a function of the wavelength. It decreases from 39% in the optical part of the spectrum to 15% at the long wavelength infrared.Comment: 13 pages, 5 figure

An automated design methodology of RF circuits by using Pareto-optimal fronts of EMsimulated inductors

A new design methodology for radiofrequency circuits is presented that includes electromagnetic (EM) simulation of the inductors into the optimization flow. This is achieved by previously generating the Pareto-optimal front (POF) of the inductors using EM simulation. Inductors are selected from the Pareto front and their S-parameter matrix is included in the circuit netlist that is simulated using an RF simulator. Generating the EM-simulated POF of inductors is computationally expensive, but once generated, it can be used for any circuit design. The methodology is illustrated both for a singleobjective and a multiobjective optimization of a low noise amplifierMinisterio de Economía y Competitividad TEC2013-45638-C3-3-R, TEC2013-40430-RJunta de Andalucía PIC12-TIC-1481Consejo Superior de Investigaciones Científicas 201350E05

Surface shape resonances in lamellar metallic gratings

The specular reflectivity of lamellar gratings of gold with grooves 0.5 microns wide separated by a distance of 3.5 microns was measured on the 2000 cm$^{-1}$ - 7000 cm$^{-1}$ spectral range for p-polarized light. For the first time, experimental evidence of the excitation of electromagnetic surface shape resonances for optical frequencies is given. In these resonances the electric field is highly localized inside the grooves and is almost zero in all other regions. For grooves of depth equal to 0.6 microns, we have analyzed one of these modes whose wavelength (3.3 microns) is much greater than the lateral dimension of the grooves.Comment: 4 pages (LaTex), 5 postscript figures, to be published in Physical Review Letter

Phase transitions with finite atom number in the Dicke Model

Two-level atoms interacting with a one mode cavity field at zero temperature have order parameters which reflect the presence of a quantum phase transition at a critical value of the atom-cavity coupling strength. Two popular examples are the number of photons inside the cavity and the number of excited atoms. Coherent states provide a mean field description, which becomes exact in the thermodynamic limit. Employing symmetry adapted (SA) SU(2) coherent states (SACS) the critical behavior can be described for a finite number of atoms. A variation after projection treatment, involving a numerical minimization of the SA energy surface, associates the finite number phase transition with a discontinuity in the order parameters, which originates from a competition between two local minima in the SA energy surface.Comment: 8 pages, 10 figures, Conference Proceedings of CEWQO-2012, to be published as a Topical Issue of the journal Physica Script

Obtention of Antimicrobial Fibers Type Core/Shell PLA/PVOH-LAE by Coaxial Electrospinning

Coaxial electrospinning (EC) is a technology that allows the encapsulation of active compounds, as ethyl lauroyl arginate (LAE), in shell/core structures, in order to develop new antimicrobial food packaging materials with slowdown of active compound´s release with the purpose of extending food shelf life. For this reason, the objective of this study consisted in developing antimicrobial fibers shell/core type by EC. Two polymers with different hydrophilic character as poly (lactic acid) (PLA) to the shell and poly (vinyl alcohol) (PVOH) and LAE to the core were used to obtain PLA/PVOH-LAE fibers, and slowdown the release of antimicrobial compound. The morphology of fibers was evaluated by optical microscopy and the thermal properties through thermogravimetric analyses (TGA). Release studies were carried out in fatty (ETOH 95%) food simulant and was compared with the minimum inhibitory concentration (MIC) values of LAE against Listeria innnocua. The optical micrographs evidenced the obtention of shell/core structure with an average diameter of 0,6 µm approximately, and the TGA analyses demonstrated the thermal protection of LAE by shell of fibers. Released LAE reached the equilibrium state in ETOH 95% during the first 3 hours, maintaining a higher concentration than MIC value obtained in L. innnocua (10 ppm). The results demonstrate that new packaging materials with antimicrobial activity as PLA/PVOH-LAE polymeric fibers with shell/core structure can be obtained through coaxial electrospinning technique. Keywords: coaxial electrospinning, ethyl lauroyl arginate, fibers, shell/core, food packaging. Resumen El electrohilado coaxial (EC) es una tecnología que permite encapsular compuestos activos como el etil lauroil arginato (LAE) en estructuras tipo pared/núcleo con la finalidad de desarrollar nuevos materiales antimicrobianos para el envasado de alimentos que ralenticen la liberación del compuesto y extiendan la vida útil del alimento. Por tal razón, el objetivo de este estudio consistió en desarrollar fibras antimicrobianas tipo pared/núcleo mediante EC. Dos polímeros con distinto carácter hidrofílico como el poli (ácido láctico) (PLA) para la pared y poli (alcohol vinílico) (PVOH) y LAE para el núcleo se utilizaron para obtener las fibras PLA/PVOH-LAE, y ralentizar la liberación del compuesto antimicrobiano. La morfología de las fibras se evaluó mediante microscopía óptica y sus propiedades térmicas mediante análisis termogravimétricos (TGA). Se realizaron estudios de liberación del LAE en un simulante de alimentos graso (ETOH 95%), y se comparó con la concentración mínima inhibitoria (MIC) hacia una bacteria Gram positiva Listeria innnocua. Las micrografías ópticas evidenciaron la obtención de la estructura pared/núcleo con un diámetro promedio de 0,6 µm aproximadamente, y el análisis TGA demostró la protección térmica del LAE por la pared de las fibras. El LAE liberado alcanzó el estado de equilibrio en ETOH 95% durante las 3 hr iniciales, manteniendo una concentración superior a la MIC obtenida para L. innnocua (10 ppm). Los resultados demuestran que nuevos materiales de envase con actividad antimicrobiana como fibras poliméricas PLA/PVOH-LAE con estructura pared/núcleo pueden ser obtenidos mediante la técnica de electrohilado coaxial. Palabras clave: electrohilado coaxial, etil lauroil arginato, fibras, pared/núcleo, envase de alimentos

Parallel Two-Stage Least Squares algorithms for Simultaneous Equations Models on GPU

Today it is usual to have computational systems formed by a multicore together with one or more GPUs. These systems are heterogeneous, due to the di erent types of memory in the GPUs and to the di erent speeds of computation of the cores in the CPU and the GPU. To accelerate the solution of complex problems it is necessary to combine the two basic components (CPU and GPU) in the heterogeneous system. This paper analyzes the use of a multicore+multiGPU system for solving Simultaneous Equations Models by the Two-Stage Least Squares method with QR decomposition. The combination of CPU and GPU allows us to reduce the execution time in the solution of large SEM.Ramiro Sánchez, C.; López-Espín, JJ.; Giménez, D.; Vidal, AM. (2012). Parallel Two-Stage Least Squares algorithms for Simultaneous Equations Models on GPU. http://hdl.handle.net/10251/1496

Obtention of Antimicrobial Fibers Type Core/Shell Pla/Pvoh-Lae By Coaxial Electrospinning

Coaxial electrospinning (EC) is a technology that allows the encapsulation of active compounds, such as ethyl lauroyl arginate (LAE), in shell/core structures, in order to develop new antimicrobial materials for food packaging that slow down the release of active compounds and extend the food’s shelf life. For this reason, the objective of this study was to develop antimicrobial fibers shell/core type by EC. Two polymers with different hydrophilic character, polylactic acid (PLA) for the shell and polyvinyl alcohol (PVOH) and LAE for the core, were used to obtain PLA/PVOH-LAE fibers and slow the release of the antimicrobial compound. The morphology of fibers was evaluated by optical microscopy and their thermal properties through thermogravimetric analyses (TGA). LAE release studies were carried out in a fatty food simulant (ETOH 95%), and was compared with the minimum inhibitory concentration (MIC) values of LAE against a gram-positive bacteria, Listeria innnocua. The optical micrographs showed the obtaining of the shell/core structure with an average diameter of approximately 0.6 µm, and the TGA analyses demonstrated the thermal protection of LAE by the shell of the fibers. Released LAE reached the equilibrium state in ETOH 95% during the first 3 hours, maintaining a higher concentration than the MIC value obtained in L. innnocua (10 ppm). The results demonstrate that new packaging materials with antimicrobial activity such as PLA/PVOH-LAE polymeric fibers with a shell/core structure can be obtained through the coaxial electrospinning technique. Keywords: coaxial electrospinning, ethyl lauroyl arginate, fibers, shell/core, food packaging. Resumen El electrohilado coaxial (EC) es una tecnología que permite encapsular compuestos activos como el etil lauroil arginato (LAE) en estructuras tipo pared/núcleo con la finalidad de desarrollar nuevos materiales antimicrobianos para el envasado de alimentos que ralenticen la liberación del compuesto y extiendan la vida útil del alimento. Por tal razón, el objetivo de este estudio consistió en desarrollar fibras antimicrobianas tipo pared/núcleo mediante EC. Dos polímeros con distinto carácter hidrofílico como el poli (ácido láctico) (PLA) para la pared y poli (alcohol vinílico) (PVOH) y LAE para el núcleo se utilizaron para obtener las fibras PLA/PVOH-LAE, y ralentizar la liberación del compuesto antimicrobiano. La morfología de las fibras se evaluó mediante microscopía óptica y sus propiedades térmicas mediante análisis termogravimétricos (TGA). Se realizaron estudios de liberación del LAE en un simulante de alimentos graso (ETOH 95%), y se comparó con la concentración mínima inhibitoria (MIC) hacia una bacteria Gram positiva Listeria innnocua. Las micrografías ópticas evidenciaron la obtención de la estructura pared/núcleo con un diámetro promedio de 0,6 µm aproximadamente, y el análisis TGA demostró la protección térmica del LAE por la pared de las fibras. El LAE liberado alcanzó el estado de equilibrio en ETOH 95% durante las 3 hr iniciales, manteniendo una concentración superior a la MIC obtenida para L. innnocua (10 ppm). Los resultados demuestran que nuevos materiales de envase con actividad antimicrobiana como fibras poliméricas PLA/PVOH-LAE con estructura pared/núcleo pueden ser obtenidos mediante la técnica de electrohilado coaxial. Palabras clave: electrohilado coaxial, etil lauroil arginato, fibras, pared/núcleo, envase de alimentos