Triple-Junction Solar Cells for Ultra-High Concentrator Applications

After the successful implementation of a record performing dual-junction solar cell at ultra high concentration, in this paper we present the transition to a triple-junction device. The semiconductor structure of the solar cells is presented and the main changes in respect to a dual-junction design are briefly discussed. Cross-sectional TEM analysis of samples confirms that the quality of the triple-junction structures grown by MOVPE is good, revealing no trace of antiphase disorder, and showing flat, sharp and clear interfaces between the layers. Triple-junction solar cells manufactured on these structures have shown a peak efficiency of 36.2% at 700X, maintaining the efficiency over 35% from 300 to 1200 suns. With some changes in the structure and a fine tuning of its processing, efficiencies close to 40% at 1000 suns are envisaged.

Self-validating technique for the measurement of the linewidth enhancement factor in semiconductor lasers

A new method for measuring the linewidth enhancement factor (α-parameter) of semiconductor lasers is proposed and discussed. The method itself provides an estimation of the measurement error, thus self-validating the entire procedure. The α-parameter is obtained from the temporal profile and the instantaneous frequency (chirp) of the pulses generated by gain switching. The time resolved chirp is measured with a polarization based optical differentiator. The accuracy of the obtained values of the α-parameter is estimated from the comparison between the directly measured pulse spectrum and the spectrum reconstructed from the chirp and the temporal profile of the pulse. The method is applied to a VCSEL and to a DFB laser emitting around 1550 nm at different temperatures, obtaining a measurement error lower than ± 8%.

Using the Journalistic Metaphor to Design User Interfaces That Explain Sensor Data

Facilitating general access to data from sensor networks (including traffic, hydrology and other domains) increases their utility. In this paper we argue that the journalistic metaphor can be effectively used to automatically generate multimedia presentations that help non-expert users analyze and understand sensor data. The journalistic layout and style are familiar to most users. Furthermore, the journalistic approach of ordering information from most general to most specific helps users obtain a high-level understanding while providing them the freedom to choose the depth of analysis to which they want to go. We describe the general characteristics and architectural requirements for an interactive intelligent user interface for exploring sensor data that uses the journalistic metaphor. We also describe our experience in developing this interface in real-world domains (e.g., hydrology).

A User Centered Design Approach for Patient Interfaces to a Diabetes IT Platform

Improving patient self-management can have a greater impact than improving any clinical treatment (WHO). We propose here a systematic and comprehensive user centered design approach for delivering a technological platform for diabetes disease management. The system was developed under the METABO research project framework, involving patients from 3 different clinical centers in Parma, Modena and Madrid.

Using SCXML to integrate semantic sensor information into context-aware user interfaces

This paper describes a novel architecture to introduce automatic annotation and processing of semantic sensor data within context-aware applications. Based on the well-known state-charts technologies, and represented using W3C SCXML language combined with Semantic Web technologies, our architecture is able to provide enriched higher-level semantic representations of user’s context. This capability to detect and model relevant user situations allows a seamless modeling of the actual interaction situation, which can be integrated during the design of multimodal user interfaces (also based on SCXML) for them to be adequately adapted. Therefore, the final result of this contribution can be described as a flexible context-aware SCXML-based architecture, suitable for both designing a wide range of multimodal context-aware user interfaces, and implementing the automatic enrichment of sensor data, making it available to the entire Semantic Sensor Web

Generador de interfaces de usuario como periódicos gráficos interactivos

El proyecto se encuadra en el ámbito de la generación automática de interfaces de usuario, orientados a entornos web y con contenido multimedia, por otro lado dicha generación de interfaces, encaja en la disciplina de simulación del periodismo de datos, concretamente en el área de presentación y difusión. Sobre la generación automática de interfaces de usuario, en este proyecto se considera un tipo de interfaz de usuario a modo de periódico virtual, que permita al usuario visualizar de forma clara la información de diferentes noticias y permita la interacción entre los diferentes elementos de dicha presentación. Dicho interfaz de usuario se diseña usando la metáfora periodística, es decir, con un esquema de organización similar al del periódico clásico, para así facilitar la comprensión de las noticias, gracias a un interfaz sencillo y claro. OBJETIVOS El objetivo principal de este proyecto consiste en dar solución a la problemática de generar presentaciones multimedia de manera automática. Dichas presentaciones deben mostrar de una manera clara y sencilla la información a partir de planes de presentación de noticias y un sistema de base de datos. Para dicho fin se pretende desarrollar una herramienta, que genere presentaciones, a modo de periódico virtual. Las presentaciones de las noticias permiten al usuario interactuar de manera directa con los diferentes elementos de la presentación, ya sean texto, imágenes, animaciones, gráficos, mapas, etc. lo que facilita la comprensión de la información que se quiere ofrecer al usuario. De manera más detallada se presentan los objetivos concretos para el desarrollo del presente proyecto fin de carrera: • Análisis del problema. Se realiza un estudio de la problemática que se pretende solucionar con el sistema. Se revisan las técnicas y estado de la técnica en el campo Generador de interfaces de usuario como periódicos gráficos interactivos 4 de la generación automática de interfaces de usuario y su adaptación para ofrecer la difusión de la información a través de internet mediante aplicaciones web. Se identifica y estudia el contexto del sistema, el cual se orienta a la simulación del periodismo de datos. • Diseño del sistema. Se pretende diseñar un sistema informático completo, desde la capa de datos hasta la capa de presentación, que cumpla con los objetivos o requisitos propuestos. El diseño es general dado que un objetivo es permitir que el sistema pueda operar en dominios de naturaleza variada. • Implementación. Se aborda la fase de implementación con el objetivo de realizar un código modular, que sea fácil de mantener y aumentar, ya que esta herramienta pretende ofrecer servicio a diferentes sistemas de dominios variados y por lo tanto pueden surgir nuevas necesidades según el ámbito donde opere. Otro objetivo en esta parte del desarrollo, es que el sistema sea eficiente y capaz de manejar grandes volúmenes de datos así como realizar una adecuada generación automática de la presentación multimedia con texto y gráficos. • Validación. Para verificar el buen funcionamiento del sistema se desarrollan pruebas específicas que prueban las funcionalidades del sistema de manera unitaria. Para probar la generalidad del sistema se plantean diversos ejemplos de noticias en diferentes escenarios o dominios de datos, lo que nos permite comprobar la versatilidad del sistema. Para probar la robustez y solidez del sistema se pretende introducir este generador de interfaces de usuario dentro de un sistema generador automático de noticias de información hidrológica en tiempo real. El sistema generador de interfaces de usuario debe recoger cada plan de noticia, realizar automáticamente la presentación de cada noticia y organizar toda la colección de dichas noticias en un periódico virtual adaptado a las noticias que va a presentar. ORGANIZACIÓN DE LA MEMORIA La memoria se estructura de la siguiente manera; en primer lugar se presenta el estado de la técnica, con los avances y últimos desarrollos en la temática de la generación automática de interfaces de usuario, las aplicaciones web como solución de interfaz de usuario y de difusión a través de internet y los avances en simulación de periodismo dirigido por datos. Seguidamente se presenta la descripción del software, con una explicación de las diferentes fases del proceso de desarrollo software, como análisis, diseño e implementación, así como la ubicación que ocupa este sistema en un sistema de simulación de periodismo de datos. En esta parte se muestran los detalles concretos a tecnologías, lenguajes y bibliotecas utilizadas. En el siguiente capítulo se trata la validación del producto, se detallan las características del sistema automático de información hidrológica (SAIH), con el cual se ha podido probar completamente el sistema de generación automática de interfaces de usuario. Seguidamente se detallan las conclusiones a las que se ha llegado después de la realización de este proyecto, haciendo un repaso de los objetivos planteados así como las líneas futuras sobre estas técnicas. Por último se adjunta el manual de usuario de la herramienta y una colección de ejemplos mostrando las entradas y salidas procesadas por el software.

Computational study of ligand binding in lipid transfer proteins: Structures, interfaces, and free energies of protein-lipid complexes

Plant nonspecific lipid transfer proteins (nsLTPs) bind a wide variety of lipids, which allows them to perform disparate functions. Recent reports on their multifunctionality in plant growth processes have posed new questions on the versatile binding abilities of these proteins. The lack of binding specificity has been customarily explained in qualitative terms on the basis of a supposed structural flexibility and nonspecificity of hydrophobic protein-ligand interactions. We present here a computational study of protein-ligand complexes formed between five nsLTPs and seven lipids bound in two different ways in every receptor protein. After optimizing geometries inmolecular dynamics calculations, we computed Poisson- Boltzmann electrostatic potentials, solvation energies, properties of the protein-ligand interfaces, and estimates of binding free energies of the resulting complexes. Our results provide the first quantitative information on the ligand abilities of nsLTPs, shed new light into protein-lipid interactions, and reveal new features which supplement commonly held assumptions on their lack of binding specificity.

Critical Role of Two-Dimensional Island-Mediated Growth on the Formation of Semiconductor Heterointerfaces

We experimentally demonstrate a sigmoidal variation of the composition profile across semiconductor heterointerfaces. The wide range of material systems (III-arsenides, III-antimonides, III-V quaternary compounds, III-nitrides) exhibiting such a profile suggests a universal behavior. We show that sigmoidal profiles emerge from a simple model of cooperative growth mediated by twodimensional island formation, wherein cooperative effects are described by a specific functional dependence of the sticking coefficient on the surface coverage. Experimental results confirm that, except in the very early stages, island growth prevails over nucleation as the mechanism governing the interface development and ultimately determines the sigmoidal shape of the chemical profile in these two-dimensional grown layers. In agreement with our experimental findings, the model also predicts a minimum value of the interfacial width, with the minimum attainable value depending on the chemical identity of the species.

Application of photoreflectance to advanced multilayer structures for photovoltaics

Photoreflectance (PR) is a convenient characterization tool able to reveal optoelectronic properties of semiconductor materials and structures. It is a simple non-destructive and contactless technique which can be used in air at room temperature. We will present experimental results of the characterization carried out by means of PR on different types of advanced photovoltaic (PV) structures, including quantum-dot-based prototypes of intermediate band solar cells, quantum-well structures, highly mismatched alloys, and III?V-based multi-junction devices, thereby demonstrating the suitability of PR as a powerful diagnostic tool. Examples will be given to illustrate the value of this spectroscopic technique for PV including (i) the analysis of the PR spectra in search of critical points associated to absorption onsets; (ii) distinguishing signatures related to quantum confinement from those originating from delocalized band states; (iii) determining the intensity of the electric field related to built-in potentials at interfaces according to the Franz?Keldysh (FK) theory; and (v) determining the nature of different oscillatory PR signals among those ascribed to FK-oscillations, interferometric and photorefractive effects. The aim is to attract the interest of researchers in the field of PV to modulation spectroscopies, as they can be helpful in the analysis of their devices.

Pulse shortening of gain switched single mode semiconductor lasers using a variable delay interferometer

We propose a pulse shaping and shortening technique for pulses generated from gain switched single mode semiconductor lasers, based on a Mach Zehnder interferometer with variable delay. The spectral and temporal characteristics of the pulses obtained with the proposed technique are investigated with numerical simulations. Experiments are performed with a Distributed Feedback laser and a Vertical Cavity Surface Emitting Laser, emitting at 1.5 µm, obtaining pulse duration reduction of 25-30%. The main asset of the proposed technique is that it can be applied to different devices and pulses, taking advantage of the flexibility of the gain switching technique.

Análisis de interfaces basadas en movimientos de iris y de cabeza para personas con parálisis cerebral

Este documento es la memoria final del trabajo de fin de Máster para optar al título de Máster en Ingeniería de Sistemas Electrónicos. El trabajo lleva por nombre “Análisis de interfaces basadas en movimientos de iris y de cabeza para personas con parálisis cerebral”. Ha sido desarrollado por el Ing. Alejandro Clemotte bajo la supervisión del Dr. Rafael Raya, Dr. Ramón Ceres y el Dr. Ricardo de Cordoba en el periodo 2011-2013. El trabajo ha sido desarrollado en las instalaciones del grupo de bioingeniería del Consejo Superior de Investigaciones Científicas (GBIO-CSIC) [1] en el marco de desarrollo del Máster en Ingeniería de Sistemas Electrónicos de la Universidad Politécnica de Madrid. Los avances tecnológicos permiten mejorar la calidad de vida de las personas. Sin embargo en ocasiones, la tecnología no se encuentra al alcance de todos los seres humanos ya que quienes padecen de limitaciones motrices, auditivas, del habla, etc., no pueden acceder a estos beneficios por la falta de interfaces adaptadas a las capacidades de estos colectivos menores. En particular el ordenador es una herramienta tecnológica que permite realizar infinitud de tareas, tanto sociales, de rehabilitación, del tipo lúdicas, etc. [2], difícilmente accesible para personas con capacidades limitadas. Es por ello importante el desarrollo de esfuerzos que permitan la construcción de herramientas de acceso universal. El trabajo realizado consiste en estudiar de forma práctica el desempeño de personas con parálisis cerebral y sin discapacidad mientras que estas realizan tareas de alcance al objetivo. Las tareas serán realizadas con dos interfaces alternativas al ordenador. Se analizaran las limitaciones técnicas de cada una de ellas mediante la definición de métricas especiales y se realizará una propuesta conceptual para la reducción de tales limitaciones, con el fin de mejorar la accesibilidad del computador para el grupo de personas con discapacidad. Calificación del tribunal: 10 con matrícula de honor

Using clustering techniques for intelligent camera-based user interfaces

The area of Human-Machine Interface is growing fast due to its high importance in all technological systems. The basic idea behind designing human-machine interfaces is to enrich the communication with the technology in a natural and easy way. Gesture interfaces are a good example of transparent interfaces. Such interfaces must identify properly the action the user wants to perform, so the proper gesture recognition is of the highest importance. However, most of the systems based on gesture recognition use complex methods requiring high-resource devices. In this work, we propose to model gestures capturing their temporal properties, which significantly reduce storage requirements, and use clustering techniques, namely self-organizing maps and unsupervised genetic algorithm, for their classification. We further propose to train a certain number of algorithms with different parameters and combine their decision using majority voting in order to decrease the false positive rate. The main advantage of the approach is its simplicity, which enables the implementation using devices with limited resources, and therefore low cost. The testing results demonstrate its high potential.

Sound of lasers (SOL) - An audiovisual approach to semiconductor laser dynamics

We present an educational software addressed to the students of optical communication courses, for a simple visualization of the basic dynamic processes of semiconductor lasers. The graphic interface allows the user to choose the laser and the modulation parameters and it plots the laser power output and instantaneous frequency versus time. Additionally, the optical frequency variations are numerically shifted into the audible frequency range in order to produce a sound wave from the computer loudspeakers. Using the proposed software, the student can simultaneously see and hear how the laser intensity and frequency change, depending on the modulation and device parameters.

Interaction between a laser beam and semiconductor nanowires: application to the raman spectrum of Si nanowires

One presents in this work the study of the interaction between a focused laser beam and Si nanowires (NWs). The NWs heating induced by the laser beam is studied by solving the heat transfer equation by finite element methods (fem). This analysis permits to establish the temperature distribution inside the NW when it is excited by the laser beam. The overheating is dependent on the dimensions of the NW, both the diameter and the length. When performing optical characterization of the NWs using focused laser beams, one has to consider the temperature increase introduced by the laser beam. An important issue concerns the fact that the NWs diameter has subwavelength dimensions, and is also smaller than the focused laser beam. The analysis of the thermal behaviour of the NWs under the excitation with the laser beam permits the interpretation of the Raman spectra of Si NWs, where it is demonstrated that temperature induced by the laser beam play a major role in shaping the Raman spectrum of Si NWs

Two-wavelength switching with a distributed-feed back semiconductor optical amplifier (DFBSOA)

Switching of a signal beam by another control beam at different wavelength is demonstrated experimentally using the optical bistability occurring in a 1.55 mm-distributed feedback semiconductor optical amplifier (DFBSOA) working in reflection. Counterclockwise (S-shaped) and reverse (clockwise) bistability are observed in the output of the control and the signal beam respectively, as the power of the input control signal is increased. With this technique an optical signal can be set in either of the optical input wavelengths by appropriate choice of the powers of the input signals. The switching properties of the DFBSOA are studied experimentally as the applied bias current is increased from below to above threshold and for different levels of optical power in the signal beam and different wavelength detunings between both input signals. Higher on-off extinction ratios, wider bistable loops and lower input power requirements for switching are obtained when the DFBSOA is operated slightly above its threshold value.