Propagation losses by tunnelling in barrier optical waveguides

An analytical model is proposed in order to estimate the optical propagation losses due to tunnelling in barrier waveguides. The results are validated by means of a beam propagation method (BPM) simulations for different waveguides conditions

Optoelectronic tweezers under arbitrary illumination patterns: theoretical simulations and comparison to experiment

Photovoltaic tweezers are a promising tool to place and move particles on the surface of a photovoltaic material in a controlled way. To exploit this new technique it is necessary to accurately know the electric field created by a specific illumination on the surface of the crystal and above it. This paper describes a numerical algorithm to obtain this electric field generated by several relevant light patterns, and uses them to calculate the electrophoretic potential acting over neutral, polarizable particles in the proximity of the crystal. The results are compared to experiments carried out in LiNbO3 with good overall agreement

Development of a computing application for the dimensioning of deployment mechanisms in artificial satellites - Desarrollo de una Aplicación Informática para el Dimensionado de Mecanismos de Despliegue en Satélites Artificiales

Los satélites artificiales a menudo deben desplegar instrumentos una vez puestos en órbita. El diseño de los mecanismos encargados de llevar a cabo este cometido es crítico, ya que un despliegue incorrecto implicaría en muchos casos la pérdida del satélite. En el caso de las antenas, un despliegue incorrecto o descontrolado podría tener como consecuencia impactos excesivamente altos que podrían producir daños estructurales, cambios de actitud del satélite, des alineamiento de las mismas, etc. Los mecanismos encargados de desplegar las antenas usualmente están compuestos por un muelle pretensado que aporta el par necesario para desplegar la misma y un sistema de amortiguación encargado de evitar que desarrolle velocidades excesivamente altas. Basándose en este contexto, se han desarrollado dos aplicaciones informáticas que, partiendo de las características de un despliegue definido por el usuario, son capaces de realizar simulaciones del mismo utilizando distintos mecanismos de despliegue, obtenidos al variar las características del muelle o el sistema de amortiguación, aportando información del comportamiento cinemático y dinámico del elemento a desplegar en cada caso, y clasificando cada uno de los posibles mecanismos de acuerdo con los requisitos de diseño impuestos por las normas ECSS, que son de obligado cumplimiento para la Agencia Espacial Europea

Migration to an a on-line laboatory in mechanical engineering. The case of a cam-follower design practice.

The European Higher Education Area (EHEA) has leaded to a change in the way the subjects are taught. One of the more important aspects of the EHEA is to support the autonomous study of the students. Taking into account this new approach, the virtual laboratory of the subject Mechanisms of the Aeronautical studies at the Technical University of Madrid is being migrated to an on-line scheme. This virtual laboratory consist on two practices: the design of cam-follower mechanisms and the design of trains of gears. Both practices are software applications that, in the current situation, need to be installed on each computer and the students carry out the practice at the computer classroom of the school under the supervision of a teacher. During this year the design of cam-follower mechanisms practice has been moved to a web application using Java and the Google Development Toolkit. In this practice the students has to design and study the running of a cam to perform a specific displacement diagram with a selected follower taking into account that the mechanism must be able to work properly at high speed regime. The practice has maintained its objectives in the new platform but to take advantage of the new methodology and try to avoid the inconveniences that the previous version had shown. Once the new practice has been ready, a pilot study has been carried out to compare both approaches: on-line and in-lab. This paper shows the adaptation of the cam and follower practice to an on-line methodology. Both practices are described and the changes that has been done to the initial one are shown. They are compared and the weak and strong points of each one are analyzed. Finally we explain the pilot study carried out, the students impression and the results obtained

Calculation of dielectrophoretic potential generated under illumination patterns on x- and z-cut LiNbO3 : application to photovoltaic particle trapping

The dielectrophoretic potential generated near the surface of a z-cut LiNbO3 by photovoltaic charge transport has been calculated for first time. The procedure and results are compared with the ones corresponding to x-cut. Diferences in the position, sharpness and time evolution are reported, and their implication on particle trapping are discussed

Metodologias Activas en la Asignatura de Mecánica, Resultados de Tres Años de Experiencia.

La asignatura de Mecánica I forma parte de las experiencias piloto de curso completo que la EUIT Aeronáutica viene desarrollando desde 2005 con el fin de adaptar sus enseñanzas al EEES. En todos los casos, la experiencia se ha dirigido a un colectivo de alumnos de nuevo ingreso (Grupo Piloto), pero con tamaños de grupos y notas de corte muy diferentes. La Mecánica I es una asignatura troncal de primer curso que se imparte durante el segundo semestre y, desde 2006, también se ofrece durante el primer semestre con la nueva metodología a un grupo de alumnos repetidores en la modalidad de Docencia complementaria. En este trabajo se presenta, mediante una revisión histórica, la nueva metodología basada en el aprendizaje cooperativo, la evaluación continua y la incorporación de las Tecnologías de la Información y la Comunicación (TIC). Se muestran los resultados académicos obtenidos por los alumnos del Grupo Piloto comparados mediante los indicadores ANECA con los obtenidos por el Grupo de Control constituido por los alumnos de nuevo ingreso de las mismas carreras, y los resultados alcanzados por el grupo de Docencia complementaria. También se expone la valoración cualitativa de los alumnos de disponer de objetos digitales de aprendizaje

Comparative theoretical analysis between parallel and perpendicular geometries for 2D particle patterning in photovoltaic ferroelectric substrates

This paper describes the dielectrophoretic potential created by the evanescent electric field acting on a particle near a photovoltaic crystal surface depending on the crystal cut. This electric field is obtained from the steady state solution of the Kukhtarev equations for the photovoltaic effect, where the diffusion term has been disregarded. First, the space charge field generated by a small, square, light spot where d < l (being d a side of the square and l the crystal thickness) is studied. The surface charge density generated in both geometries is calculated and compared as their relation determines the different properties of the dielectrophoretic potential for both cuts. The shape of the dielectrophoretic potential is obtained and compared for several distances to the sample. Afterwards other light patterns are studied by the superposition of square spots, and the resulting trapping profiles are analysed. Finally the surface charge densities and trapping profiles for different d/l relations are studied

Photorefractive nonlinear propagation of single beams in undoped LiNbO3: Self-defocusing and beam break-up

Beam propagation in photorefractive LiNbO3 planar waveguides has been studied at different beam intensities and propagation lengths. Self-defocusing and beam break-up have been observed and explained using BPM simulations under a 2-centre band transport model

Particle Patterning on Lithium Niobate waveguides via photovoltaic tweezers

Successful micro and nano-particle patterning on iron doped lithium niobate waveguides using photovoltaic fields is reported. This technique previously used in bulk crystals is here applied to waveguide configuration. Well defined particle patterns are obtained using two types of planar waveguides (by proton exchanged and swift heavy ion irradiation) and metallic and dielectric neutral particles. The use of waveguide configuration has allowed a reduction of the light exposure time until 3 s, two orders of magnitude smaller than typical values used in bulk

Calculation of the spatial distribution of photovoltaic field by arbitrary 2D ilumination patterns en LiNbO3; application to photovoltaic particle trapping.

Patterns of evanescent photovoltaic field induced by illumination on a surface of lithium niobate (LN) have been calculated and compared with the experimental patterns of nano- and microparticles trapped by dielectrophoretic forces. A tool for this calculation has been developed. Calculo de distribución espacial de campo por efecto fotovoltaico con patrones arbitrarios de iluminación, en LiNbO