Light trapping properties of cylindrical well diffraction gratings in solar cells: Computational calculations

Light trapping using diffraction gratings is a promising approach to increasing absorption in solar cells. In this paper, the computationally calculated absorption enhancement expected from a diffraction grating consisting of a triangular array of cylindrical wells is presented. Angle-extended polychromatic illumination is considered, and special attention is paid to absorption of sub-bandgap photons in an intermediate band solar cell. Results are compared to the absorption enhancement expected from an ideal Lambertian (randomizing) scatterer, which is considered as a baseline. It is found that for cells which absorb very weakly, the diffraction grating provides absorption enhancement above that of the ideal Lambertian scatterer over a wide wavelength range. For cells which absorb more strongly, the grating underperforms the ideal Lambertian scatterer over almost all wavelengths. Finally, the grating period, well height and well radius are optimised. Keywords: Light Trapping, Diffraction Grating, Intermediate Band Solar Cel

Sliding mode control for Antilock Brake System

A Sliding Mode (SM) Block Control is proposed to control an Antilock Brake System (ABS). The control problem is to achieve reference tracking for the slip rate, such that, the friction between tyre and road surface is good enough to control the car. The closed-loop system is robust in presence of matched and unmatched perturbations. To show the performance of the proposed control strategy, a simulation study is carried on, where results show good behavior of the ABS under variations in the road friction.CINVESTAVUniversidad de Guadalajar

Una aproximación para resolución de ambigüedad estructural empleando tres mecanismos diferentes

La ambigüedad estructural es uno de los problemas más difíciles de resolver en sistemas de procesamiento de lenguaje natural. Consideramos dos tipos de resolución de ambigüedad estructural que pueden emplearse en el análisis de textos sin restricciones: conocimiento léxico y cierta clase de contexto. En este trabajo, proponemos un modelo basado en tres diferentes mecanismos para revelar la estructura sintáctica correcta y un módulo de clasificación para obtener las estructuras más probables para la oración analizada. Nuestro modelo está dirigido al análisis de textos sin restricciones y las herramientas desarrolladas no requieren ninguna desambiguación de marcas morfológicas ni ningún tipo de marcas sintácticas.Trabajo hecho con apoyo parcial del CONACyT, SNI y CGEPI-IPN, México

ABS design and active suspension control based on HOSM

This paper tackles the control of a brake assisted with an active suspension. The goal of the paper is ensure an effective braking process improving the vehicle safety in adverse driving conditions. To address this, the wheel slip ratio is kept to a desired value reducing the effective braking distance by designing of a robust tracking controller based on high order sliding modes algorithms, imposing the anti-lock brake system feature. On the other hand, the active suspension problem is carried with a nested backward sliding surface design. The purpose of this control is to improve the driving comfort. To this aim, the designed controller compensate the effects of the unmatched perturbation coming from the road. This controller exploits a high order sliding modes observer, which guarantees theoretically exact state and perturbation estimation. In both cases, a continuous control action drives the state trajectories to the designed sliding manifolds and keeps them there in spite of the matched and unmatched perturbations. The feasibility of the proposed scheme has been exposed via simulations.Consejo Nacional de Ciencia y TecnologíaUniversity of Bordeau

Integral Nested Sliding Mode Control for Antilock Brake System

An integral nested Sliding Mode (SM) Control is proposed for an Antilock Brake System (ABS) control problem by employing integral SM and nested SM concepts. This controller has robustness against matched and unmatched perturbations, and the capability to reduce the sliding functions gains. Application to an ABS is presented as a simulationConsejo Nacional de Ciencia y TecnologíaLomonosov Moscow State UniversityUniversidad Autónoma Metropolitana-AzcapotzalcoUniversidad de Guadalajar

A numerical study into the influence of quantum dot size on the sub-bandgap interband photocurrent in intermediate band solar cells

A numerical study is presented of the sub-bandgap interband photon absorption in quantum dot intermediate band solar cells. Absorption coefficients and photocurrent densities are calculated for the valence band to intermediate band transitions using a four-band k · p method. It is found that reducing the quantum dot width in the plane perpendicular to the growth direction increases the photocurrent from the valence band to the intermediate-band ground state if the fractional surface coverage of quantum dots is conserved. This provides a path to increase the sub-bandgap photocurrent in intermediate band solar cells

The feasibility of high-efficiency InAs/GaAs quantum dot intermediate band solar cells

In recent years, all the operating principles of intermediate band behaviour have been demonstrated in InAs/GaAs quantum dot (QD) solar cells. Having passed this hurdle, a new stage of research is underway, whose goal is to deliver QD solar cells with efficiencies above those of state-of-the-art single-gap devices. In this work, we demonstrate that this is possible, using the present InAs/GaAs QD system, if the QDs are made to be radiatively dominated, and if absorption enhancements are achieved by a combination of increasing the number of QDs and light trapping. A quantitative prediction is also made of the absorption enhancements required, suggesting that a 30 fold increase in the number of QDs and a light trapping enhancement of 10 are sufficient. Finally, insight is given into the relative merits of absorption enhancement via increasing QD numbers and via light trapping

Determinantes de la competitividad regional en el Distrito Federal: un análisis del índice de competitividad estatal (2008-2012)

Entre los problemas del crecimiento económico se presenta la interrogante sobre por qué existen territorios que pueden mantener tasas constantes de crecimiento con mejoría en las condiciones de vida de sus ciudadanos y otras no. Esto ha llevado en los últimos años al auge del estudio de la competitividad y en particular de la competitividad regional. El objetivo de esta investigación es identificar los indicadores que han favorecido la competitividad del Distrito Federal, en el contexto de las diversas teorías del crecimiento económico, a través del índice de competitividad estatal (ice) elaborado por el imco en el periodo 2008-2012. Se concluye que los subíndices sectores precursores, sociedad incluyente, preparada y sana, aprovechamiento de las relaciones internacionales e innovación contienen indicadores que impulsan la competitividad del Distrito Federal, sustentados por las teorías que promueven los modelos del desarrollo endógeno.

Upper limits to absorption enhancement in thick solar cells using diffraction gratings

The application of diffraction gratings to solar cells is a promising approach to superseding the light trapping limits of conventional Lambertian structures. In this paper a mathematical formalism is derived for calculating the absorption that can be expected in a solar cell equipped with a diffraction grating, which can be applied to any lattice geometry and grating profile. Furthermore, the formalism is used to calculate the upper limit of total absorption that can theoretically be achieved using a diffraction grating. The derived formalism and limits are valid when the solar cell thickness is greater than the coherence length of the illuminating solar spectrum. Comparison is made to the upper limit achievable using an angularly selective Rugate filter, which is also calculated. Both limits are found to be considerably higher than the Lambertian limit within the range of sunlight concentration factors practically employed in photovoltaic systems (1–1000×). The upper limit of absorption using the diffraction grating is shown to be equal to the thermodynamic limit for all absorbances and concentration factors. The limit for the Rugate filter is generally lower, but tends to the thermodynamic limit for lower cell absorbance

Why and How Physical Activity Promotes Experience-Induced Brain Plasticity

Adult hippocampal neurogenesis is an unusual case of brain plasticity, since new neurons (and not just neurites and synapses) are added to the network in an activity-dependent way. At the behavioral level the plasticity-inducing stimuli include both physical and cognitive activity. In reductionistic animal studies these types of activity can be studied separately in paradigms like voluntary wheel running and environmental enrichment. In both of these, adult neurogenesis is increased but the net effect is primarily due to different mechanisms at the cellular level. Locomotion appears to stimulate the precursor cells, from which adult neurogenesis originates, to increased proliferation and maintenance over time, whereas environmental enrichment, as well as learning, predominantly promotes survival of immature neurons, that is the progeny of the proliferating precursor cells. Surprisingly, these effects are additive: boosting the potential for adult neurogenesis by physical activity increases the recruitment of cells following cognitive stimulation in an enriched environment. Why is that? We argue that locomotion actually serves as an intrinsic feedback mechanism, signaling to the brain, including its neural precursor cells, increasing the likelihood of cognitive challenges. In the wild (other than in front of a TV), no separation of physical and cognitive activity occurs. Physical activity might thus be much more than a generally healthy garnish to leading “an active life” but an evolutionarily fundamental aspect of “activity,” which is needed to provide the brain and its systems of plastic adaptation with the appropriate regulatory input and feedback