Pensar la economía en tiempos de crisis

.Fundación Universitaria Los Libertadore

Surface plasmon resonance sensors based on uniform-waist tapered fibers in a reflective configuration

We present a configuration for surface plasmon resonance sensors based on uniform-waist tapered optical fibers and reflective elements. Once the fiber is tapered fulfilling the adiabatic criterion, a multilayer including a metallic medium is asymmetrically deposited on the uniform waist of the fiber. This feature provides the resonant excitation of multiple surface plasma waves. In addition, a mirror is produced at the fiber tip by a chemical Tollens reaction. In this way, the sensor operates in a reflective mode, more convenient for dip probes. When these sensors are spectrally interrogated, a high sensitivity of 10^4 refractive index units per nanometer is attained. These devices can be advantageously used for any kind of chemical sensing and biosensing

Adherencia a las recomendaciones nutricionales entre adolescentes Españoles e inmigrantes residentes en España: Estudio AFINOS

Objectives: This study compares the adherence of immigrant and Spanish adolescents residing in the Madrid region (Spain) to national dietary recommendations. The factors compared were the consumption of items from the eight basic food groups (vegetables, fruits, bread/cereals, meat, eggs, fish, legumes and milk/dairy products), including the excessive or deficient consumption of eggs, meat and fish. In addition, the evaluation of excessive sweet foods or soft drinks in the diet was also considered. Subsequently, the influence of length of residence on dietary habits was examined. Materials and methods: Self-reported data were co - llected in a cross-sectional survey conducted over the period November 2007 to February 2008. The study participants were a representative sample of adolescents aged 13 to 17 years (n = 2,081, 1,055 girls) living in the Madrid region. Participants were recruited from secondary schools (grades 7th to 10th) randomly selected according to the geographic distribution of adolescents in the region. Results: Immigrant adolescents showed a greater likelihood of not fulfilling recommendations for the consumption of meat, fish, eggs, legumes, bread/cereals, and milk/dairy products. Their diets were also more likely to lack sufficient fish and they also consumed more eggs and more sweet foods and soft drinks than their native counterparts. Spanish adolescents were more likely not to meet recommendations for the intake of vegetables. Length of residence weakly affected dietary habits, with both negative and positive effects observed. Conclusion: The likelihood of not fulfilling dietary recommendations was higher among the immigrant adolescents with the exception of the intake of fruits and vegetables.Objetivos: Este estudio compara la adherencia a las recomendaciones nutricionales de adolescentes inmigrantes y españoles residentes en la Comunidad de Madrid, España. Se comparó el consumo de ocho grupos principales de alimentos (verduras, frutas, pan/cereales, carne, huevos, pescado, legumbres, leche/derivados lácteos) incluyendo el consumo excesivo y deficiente de huevos, carne y pescado. También fue valorado el consumo excesivo de dulces y bebidas azucaradas. Posteriormente se analizó la influencia del tiempo de residencia en España sobre los mencionados hábitos de dieta. Material y método: Se llevó a cabo un estudio transversal en el que fueron recogidos datos auto-reportados durante el periodo comprendido entre noviembre 2007 y febrero 2008. Se obtuvo una muestra representativa de adolescentes con edades comprendidas entre 13 y 17 años (n = 2.081, 1.055 mujeres) residentes en la Comunidad de Madrid. Los participantes pertenecían a centros de enseñanza secundaria seleccionados aleatoriamente según la distribución geográfica de los adolescentes en la región. Resultados: Los inmigrantes adolescentes presentaron una mayor probabilidad de no cumplir las recomendaciones nutricionales para el consume de carne, pescado, legumbres, pan/cereales y leche/derivados, de consumir una cantidad insuficiente de pescado y más dulces y bebidas azucaradas que sus compañeros españoles. Los adolescentes españoles mostraron una mayor probabilidad de no cumplir con la recomendación establecida para verduras. El tiempo de residencia afectó débilmente los hábitos de dieta, asociando aspectos tanto positivos como negativos. Conclusiones: La probabilidad de no cumplir las recomendaciones nutricionales fue mayor entre los adolescentes inmigrantes con excepción del consumo de frutas y verduras.The AFINOS Study was supported by grant DEP2006- 56184-C03-01-02-03/PREV from the Spanish Ministry of Education and Science and co-funded by FEDER funds from the European Unio

Surface plasmon excitation in fiber-optics sensors: a novel theoretical approach.

A theoretical method for the study of surface plasmon excitation in metallic layers, as used in fiber-optics sensors, is presented. It is based in the calculation of the propagated fields in the waveguide structure and allows us to compute the loss of optical power in the fiber (which is the measured parameter) from energy conservation considerations. The agreement with experimental data obtained with real sensors is good. The method is conceptually simple and can be adapted to different configurations of the sensors

Simple model of compound waveguide structures used as fiber-optic sensors

In this work we present an application of a simple quasi-geometrical model to analyze the behavior of compound waveguide structures used as fiber-optic sensors. This theoretical model is based on the adjustment of the parameters of the structure from the experimental measures to predict the observed behavior of the device. It also takes into account the non-monocromaticity of the used source. In this way, it can be used as a design criterion for this kind of structures. It is applied to a refractive index fiber-optic sensor based on the excitation of surface plasmon in a metal layer by the light guided by a monomode fiber

Effective index model as a reliable tool for the design of nanostructured thin-film solar cells

Nanostructured anti-reflection coatings (ARC) are used to reduce the reflectivity of the front surface of solar cells. Computational electromagnetism helps to evaluate the spectral reflectivity of of this type of ARC using several approaches. They typically require large computational resources both in time and hardware elements (memory allocation, speed of processors, etc.). Long computational times may jeopardize optimization processes based on the iterative evaluation of a given merit function that depends on several parameters. Then, simplified analytic methods can speed up this evaluation with moderate computational resources. In this contribution we adapt an Effective Index Model (EIM) to the case of the design of an ARC made with nanoparticles (NP) embedded in a medium at the front surface of a thin-film silicon solar cell. Our approach modifies the discrete dipole approximation method to adapt it to the geometric and material properties of the NPs. The results obtained from the analytic method are compared with those evaluated through a Finite Element Method (FEM) for several cases involving variations in the size and geometry of the NP arrangement, obtaining reflectances that differ less than 10% for the worst case analyzed but bieng about 100 times faster than the FEM.Sección Deptal. de Óptica (Óptica)Fac. de Óptica y OptometríaTRUEMinisterio de Ciencia e Innovación de EspañaComunidad de Madrid (España)Agencia Estatal de Investigación (AEI) (España) - Fondos FEDERpu

Theoretical method for the study of plasmon generation in hybrid multilayer-optical fiber structures

A theoretical method is presented for the determination of the behavior of devices based on the deposition of multilayer structures on polished optical fibers. Plasmon generation in metallic layers is modeled. The method is based on the Rayleigh expansion of the electric fields and permits us to determine their distribution over the whole structure by an application of boundary conditions. Once the distribution is known, the power transmitted by the fiber can be computed as a function of the geometrical and refractive parameters of the device. The method is versatile and can be used as a theoretical tool for the design of devices of that type used for many different purposes. We present real experimental results obtained with an operative sensor that agree with the theoretical predictions of our technique and prove its suitability

On-Chip Solar Energy Harvester and PMU With Cold Start-Up and Regulated Output Voltage for Biomedical Applications

This paper presents experimental results from a system that comprises a fully autonomous energy harvester with a solar cell of 1 mm 2 as energy transducer and a Power Management Unit (PMU) on the same silicon substrate, and an output voltage regulator. Both chips are implemented in standard 0.18 μm CMOS technology with total layout areas of 1.575 mm 2 and 0.0126 mm 2 , respectively. The system also contains an off-the-shelf 3.2 mm × 2.5 mm × 0.9 mm supercapacitor working as an off-chip battery or energy reservoir between the PMU and the voltage regulator. Experimental results show that the fast energy recovery of the on-chip solar cell and PMU permits the system to replenish the supercapacitor with enough charge as to sustain Bluetooth Low Energy (BLE) communications even with input light powers of 510 nW. The whole system is able to self-start-up without external mechanisms at 340 nW. This work is the first step towards a self-supplied sensor node with processing and communication capabilities. The small form factor and ultra-low power consumption of the system components is in compliance with biomedical applications requirementsThis work was supported in part by the Spanish Government (Ministerio de Ciencia, Innovación y Universidades) under Project RTI2018-097088-B-C32 and Project RTI2018-095994-B-I00 (MICINN/FEDER), in part by the Xunta de Galicia, in part by the Consellería de Cultura, Educación e Ordenación Universitaria (accreditation 2016-2019, ED431G/08 and reference competitive group 2017-2020, ED431C 2017/69) and European Regional Development Fund (ERDF), and in part by the Junta de Extremadura and the ERDF, under Grant IB 18079S

A fibre-optic temperature sensor based on the deposition of a thermochromic material on an adiabatic taper

A fibre-optic sensor has been developed for the measurement of temperature, especially of liquids. The device is conceived as part of an all-optical CTD probe for the control of the physical parameters of a marine medium. The dependence on temperature of the optical properties (specifically, absorbance) of a thermochromic material, namely lophine (2,4,5-triphenylimidazole), is the basis of the sensor. The sensor presents some significant differences with respect to other similar sensors proposed in the literature: the use of adiabatic, long, tapered optical fibres with adjustable geometric parameters; the use of LED illumination in the 800 nm range; improvements in the deposition technique, etc. The sensors show a linear behaviour over the desired temperature range, and their sensitivity is high. Also, the dependence of the response of the sensor with variations of the geometry of the tapers is discussed. Specifically, we have performed measurements with different diameters of the taper waist, and we show the dependence of the slope of the response curve with that parameter

Surface plasmon resonance in the visible region in sensors based on tapered optical fibers

Doubly deposited uniform-waist tapered optical fibers (DLUWTs) have shown their versatility and good performance as basis for surface plasmon resonance (SPR) sensors for a variety of wavelength ranges. In this work we experimentally show how these devices can be employed to extend the technology of SPR fiber sensors to the visible region, down to about 530 nm, with remarkable results in terms of sensitivity, plasmon definition and the availability of multiple plasmon resonances for each configuration. In this way, DLUWTs can be used to cover a range of more than 1000 nm for aqueous media only by changing the thickness of the deposits. Also, it is shown how these results can be used with the so-called absorption method to make selective the response of the sensors and a study is made on the influence of the taper waist in the performance of the devices. The number of SPR fiber sensors working in the visible region, of great interest in biological research, that have been depicted in the literature is very small, and the sensors that we present here notably improve their performance