Highly conductive p++-AlGaAs/n++-GaInP tunnel junctions for operation up to 15,000 suns in concentrator solar cells

In the last few decades there has been great interest in III-V multijunction solar cells (MJSC) for concentrator applications due to their promise to significantly reduce the cost of electricity. Being formed by series connection of several solar cells with different bandgaps, a key role in a MJSC structure is played by the tunnel junctions (TJ) aimed to implement such series connection. Essentially, tunnel junctions (tunnel diodes or Esaki diodes) are thin, heavily doped p-n junctions where quantum tunneling plays a key role as a conduction mechanism. Such devices were discovered by Nobel laureate Leo Esaki at the end of 1950. The key feature of tunnel junctions for their application in MJSC is that, as long as quantum tunneling is the dominant conduction mechanism, they exhibit a linear I-V dependence until the peak tunneling current (Jp) is reached. This initial ohmic region in the I-V curve is ideal for implementing low-loss interconnections between the subcells with different energy bandgaps that constitute a MJSC.

Proyecto de construcción de un túnel por el sistema "Cut and cover" para el acceso ferroviario del cercanías a Marbella

El proyecto describe el diseño de un túnel ferroviario en la zona sur de España, entre las localidades de Fuengirola y Marbella en la provincia de Málaga. La ejecución de las obras incluidas en este proyecto permitirá conectar mediante una nueva línea ferroviaria dicha Estación con la población de Marbella y en un futuro con más poblaciones del Corredor Ferroviario de la Costa del Sol que en este momento no cuenta con ninguna conexión ferroviaria. En la geometría se concreta la sección del túnel que se va a ejecutar. Se utiliza como referencia el estudio geológico y geotécnico con el fin de caracterizar los materiales que se van a encontrar en la excavación del túnel. Una vez concluida esta fase se determinan los sostenimientos de acuerdo con las clasificaciones geomecánicas. Realizando el tramo elegido por el Método “Cut and Cover”, y siendo objeto de este proyecto todo el proceso constructivo del mismo así como otras obras complementarias que se tendrán que llevar a cabo debido al paso de dicho túnel por zonas transitadas o habitadas actualmente. Abstract Project describes the design of a high speed railway tunnel in the sur of Spain, between the villages of Fuengirola and Marbella (Málaga). The execution of the constructions incluyed in this proyect will allow the conection, by a neww railway line, this station with Marbella and,in the future, with more village of the “Corredor Ferroviario of Costa del Sol”, witcth al presente hasn´t gotany rail connection.It be can observed in the section of the tunnel that is going to be performed. Geological and geotechnical studies are taken into account in order to classify the rock mass materials involved in the construction process. Afterwards, supports are defined according to geomechanical classifications, specifying four different sections. Making the stretch chosen by “Cut and Cover” method and being the main goal of this proyect all the constructive process of this, as well as other complementary works that will be executed of the crossing of this tunnel by accessible or inhabited areas currently.

Contribution to Load-Frequency Regulation of a Hydropower Plant with Long Tail-Race Tunnel

In this paper, a hydroelectric power plant with long tail-race tunnel has been modelled for assessing its contribution to secondary regulation reserve. Cavitation problems, caused by the discharge conduit length, are expected downstream the turbine where low pressure appears during regulation manoeuvres. Therefore, governor's gains should be selected taking into account these phenomena. On the other hand, regulation services bidden by the plant operator should fulfil TSO (Transmission System Operator) quality requirements. A methodology for tuning governor PI gains is proposed and applied to a Hydro power plant in pre-design phase in northwest area of Spain. The PI gains adjustment proposed provides a proper plant response, according to some established indexes, while avoiding cavitation phenomena.

Estudio sobre un sistema de radiocomunicaciones ferroviarias de acuerdo al paradigma 4G

No hay duda de que el ferrocarril es uno de los símbolos del avance tecnológico y social de la humanidad, y su imparable avance desde el primer tercio del Siglo XIX así lo atestigua. No obstante, a lo largo de gran parte de su historia se ha mostrado algo renuente a abrazar ciertas tecnologías, lo que le ha causado ser tachado de conservador. Sin embargo, en los últimos años, coincidiendo con el auge masivo de los trenes de alta velocidad, los metropolitanos y los tranvías, muchas tecnologías han ido penetrando en el mundo del ferrocarril. La que hoy nos ocupa es una de las que mayor valor añadido le ha proporcionado (y que probablemente le proporcionará también en el futuro): las comunicaciones móviles. Actualmente el uso de este tipo de tecnologías en el entorno ferroviario puede calificarse como de inicial o, por seguir la nomenclatura de las comunicaciones móviles públicas, de segunda generación. El GSM-R en las líneas de alta velocidad es un caso (aunque de éxito al fin y al cabo) que define perfectamente el estado del arte de las comunicaciones móviles en este entorno, ya que proporcionó un gran valor añadido a costa de un gran esfuerzo de estandarización; ha supuesto un importante salto adelante en el campo de la fiabilidad de este tipo de sistemas, aunque tiene unas grandes limitaciones de capacidad y graves problemas de escalabilidad. Todo hace pensar que en 2025 el sustituto de GSM-R deberá estar en el mercado. En cualquier caso, se debería abandonar la filosofía de crear productos de nicho, que son extraordinariamente caros, y abrazar las filosofías abiertas de las redes de comunicaciones públicas. Aquí es donde LTE, la última gran estrella de esta familia de estándares, puede aportar mucho valor. La idea subyacente detrás de esta Tesis es que LTE puede ser una tecnología que aporte gran valor a las necesidades actuales (y probablemente futuras) del sector del ferrocarril, no solamente en las líneas y trenes de alta velocidad, sino en las denominadas líneas convencionales y en los metros y tranvías. Dado que es un campo aún a día de hoy que dista bastante de estar completamente estudiado, se ha explorado la problemática de la propagación electromagnética en los diferentes entornos ferroviarios, como pueden ser los túneles de metro y la influencia de las estructuras de los trenes. En este sentido, se ha medido de forma bastante exhaustiva en ambos entornos. Por otro lado, dado que los sistemas multiantena son uno de los pilares fundamentales de los modernos sistemas de comunicaciones, se ha verificado de forma experimental la viabilidad de esta tecnología a la hora de implementar un sistema de comunicaciones trentierra en un túnel. Asimismo, de resultas de estas medidas, se ha comprobado la existencia de ciertos fenómenos físicos que pueden suponer una merma en la eficiencia de este tipo de sistemas. En tercer lugar, y dado que uno de los grandes desafíos de las líneas de alta velocidad está provocado por la gran celeridad a la que se desplazan los trenes, se ha explorado la influencia de este parámetro en la eficiencia global de una red completa de comunicaciones móviles. Por supuesto, se ha hecho especial hincapié en los aspectos relacionados con la gestión de la movilidad (traspasos o handovers Por último, a modo de cierre de la Tesis, se ha tratado de identificar los futuros servicios de comunicaciones que aportarán más valor a las explotaciones ferroviarias, así como los requisitos que supondrán para las redes de comunicaciones móviles. Para los casos antes enunciados (propagación, sistemas multiantena, movilidad y desafíos futuros) se proporcionan las contribuciones ya publicadas en revistas y congresos internacionales, así como las que están enviadas para su revisión. ABSTRACT There is almost no doubt that railways are one of the symbols of the technological and social progress of humanity. However, most of the time railways have been somewhat reluctant to embrace new technologies, gaining some reputation of being conservative. But in the last years, together with the massive boom of high speed lines, subways and trams all over the world, some technologies have broken through these conservative resistance. The one which concerns us now is one of the most value-added (both today and in the future): mobile communications. The state-of-the-art of these technologies in the railway field could be called as incipient, or (following the mobile communications’ notation) ‘second generation’. GSM-R, the best example of mobile communications in railways is a success story that shows perfectly the state-of-the-art of this field: it provided a noticeable mark-up but also required a great standardization effort; it also meant a huge step forward in the reliability of these systems but it also needs to face some scalability issues and some capacity problems. It looks more than feasible that in 2025 the alternative to GSM-R should be already available. Anyway, the vision here should be forgetting about expensive niche products, and embracing open standards like public mobile communications do. The main idea behind this Thesis is that LTE could be a technology that provides a lot of added value to the necessities of the railways of today and the future. And not only to highspeed lines, but also to the so-called conventional rail, subways and tramways. Due to the fact that even today, propagation in tunnels and influence of car bodies is far from being full-studied, we measured in a very exhaustive way the EM propagation in these two environments. Also, multiantenna systems are one of the basic foundations of the modern communications systems, so we experimentally verified the feasibility of using such a system in a train-towayside in a tunnel. Moreover, from the measurements carried out we proved the existence of some physical phenomena that could imply a decrease in the performance of these multiantenna systems. In third place, we have explored the influence of high-speed in the whole performance of the network, from the mobility management point-of-view. This high-speed movement is one of the most relevant challenges for the mobile communications networks. The emphasis was placed on the mobility aspects of the radio resource management. Finally, the Thesis closure is an identification of the future communication services that could provide a bigger addition of value to railways, and also the requirements that imply to mobile communications networks. For all the previous for scenarios depicted before (propagation, multiantenna systems, mobility and challenges) we provide some contributions already published (or submitted for revision or still in progress) on publications and international conferences.

Tridimensional simulation of the speed, pressure and turbulence fields of the air flow on the geometry of a freight truck inside a wind tunnel

This study shows the air flow behavior through the geometry of a freight truck inside a AF6109 wind tunnel with the purpose to predict the speed, pressure and turbulence fields made by the air flow, to decrease the aerodynamic resistance, to calculate the dragging coefficient, to evaluate the aerodynamics of the geometry of the prototype using the CFD technique and to compare the results of the simulation with the results obtained experimentally with the “PETER 739 HAULER” scaled freight truck model located on the floor of the test chamber. The Geometry went through a numerical simulation process using the CFX 5,7. The obtained results showed the behavior of the air flow through the test chamber, and also it showed the variations of speed and pressure at the exit of the chamber and the calculations of the coefficient and the dragging force on the geometry of the freight truck. The evaluation of the aerodynamics showed that the aerodynamic deflector is a device that helped the reduction the dragging produced in a significant way by the air. Furthermore, the dragging coefficient and force on the prototype freight truck could be estimated establishing an incomplete similarity.

Frequency control support of a wind-solar isolated system by a hydropower plant with long tail-race tunnel

Pumped storage hydro plants (PSHP) can provide adequate energy storage and frequency regulation capacities in isolated power systems having significant renewable energy resources. Due to its high wind and solar potential, several plans have been developed for La Palma Island in the Canary archipelago, aimed at increasing the penetration of these energy sources. In this paper, the performance of the frequency control of La Palma power system is assessed, when the demand is supplied by the available wind and solar generation with the support of a PSHP which has been predesigned for this purpose. The frequency regulation is provided exclusively by the PSHP. Due to topographic and environmental constraints, this plant has a long tail-race tunnel without a surge tank. In this configuration, the effects of pressure waves cannot be neglected and, therefore, usual recommendations for PID governor tuning provide poor performance. A PI governor tuning criterion is proposed for the hydro plant and compared with other criteria according to several performance indices. Several scenarios considering solar and wind energy penetration have been simulated to check the plant response using the proposed criterion. This tuning of the PI governor maintains La Palma system frequency within grid code requirements.

Gust wind tunnel study on ballast pick-up by high-speed trains

This paper describes the experimental setup, procedure, and results obtained, concerning the dynamics of a body lying on a floor, attached to a hinge, and exposed to an unsteady flow, which is a model of the initiation of rotational motion of ballast stones due to the wind generated by the passing of a high-speed train. The idea is to obtain experimental data to support the theoretical model developed in Sanz-Andres and Navarro-Medina (J Wind Eng Ind Aerodyn 98, 772–783, (2010), aimed at analyzing the initial phase of the ballast train-induced-wind erosion (BATIWE) phenomenon. The experimental setup is based on an open circuit, closed test section, low-speed wind tunnel, with a new sinusoidal gust generator mechanism concept, designed and built at the IDR/UPM. The tunnel’s main characteristic is the ability to generate a flow with a uniform velocity profile and sinusoidal time fluctuation of the speed. Experimental results and theoretical model predictions are in good agreement.

Analysis of the behavior of multijunction solar cells under high irradiance Gaussian light profiles showing chromatic aberration with emphasis on tunnel junction performance

In this work, we explain the behavior of multijunction solar cells under non-uniform (spatially and in spectral content) light profiles in general and in particular when Gaussian light profiles cause a photo-generated current density, which exceeds locally the peak current density of the tunnel junction. We have analyzed the implications on the tunnel junction's limitation, that is, in the loss of efficiency due to the appearance of a dip in the I–V curve. For that, we have carried out simulations with our three-dimensional distributed model for multijunction solar cells, which contemplates a full description of the tunnel junction and also takes into account the lateral resistances in the tunnel junction. The main findings are that the current density photo-generated spreads out through the lateral resistances of the device, mainly through the tunnel junction layers and the back contact. Therefore, under non-uniform light profiles these resistances are determinant not only to avoid the tunnel junction's limitation but also for mitigating losses in the fill factor. Therefore, taking into account these lateral resistances could be the key for jointly optimizing the concentrator photovoltaic system (concentrator optics, front grid layout and semiconductor structure)

Ultrasound treatment for treating the carpal tunnel syndrome: randomised “sham” controlled trial

Objective: To assess the efficacy of ultrasound treatment for mild to moderate idiopathic carpal tunnel syndrome.

Tunnel magnetoresistance in GaMnAs: going beyond Jullière formula

The relation between tunnel magnetoresistance (TMR) and spin polarization is explored for GaMnAs∕GaAlAs∕GaMnAs structures where the carriers experience strong spin–orbit interactions. TMR is calculated using the Landauer approach. The materials are described in the 6 band k⋅p model which includes spin–orbit interaction. Ferromagnetism is described in the virtual crystal mean field approximations. Our results indicate that TMR is a function of spin polarization and barrier thickness. As a result of the stong spin–orbit interactions, TMR also depends on the the angle between current flow direction and the electrode magnetization. These results compromise the validity of Julliere formula.

Intrinsic spin noise in MgO magnetic tunnel junctions

We consider two intrinsic sources of noise in ultra-sensitive magnetic field sensors based on MgO magnetic tunnel junctions, coming both from 25 Mg nuclear spins (I = 5/2, 10% natural abundance) and S = 1 Mg-vacancies. While nuclear spins induce noise peaked in the MHz frequency range, the vacancies noise peaks in the GHz range. We find that the nuclear noise in submicron devices has a similar magnitude than the 1/f noise, while the vacancy-induced noise dominates in the GHz range. Interestingly, the noise spectrum under a finite magnetic field gradient may provide spatial information about the spins in the MgO layer.

High Speed Rail Passenger Profile in Sun and Beach Tourism Destinations: The Case of Alicante (Spain)

This paper aims to study and highlight the profile of the high speed rail (HSR) passenger in the case of the well-known sun and beach destination of Alicante, located in the Southeast of Spain. This region, which is directly connected with Madrid, differs from others because of its warm and sunny weather. The province is a tourist destination for both Spanish citizens and foreigners. However, the studies on the dynamics of the corridor towards Madrid and Alicante regarding HSR are quite recent and it is not possible to draw final conclusions about its impact on tourist mobility.

Thames Tunnel, London, England, 1827 (Raster Image)

This layer is a georeferenced raster image of the historic paper map entitled: Plan of the roads and main objects on the eastern part of London : as connected with the tunnel excavating under the Thames from Rotherhithe to Wapping, projected by M.I. Brunel, C.E. F.R.S., 1827. It was published by H. Teape & Son in 1827. Scale [ca. 1:48,000]. The image inside the map neatline is georeferenced to the surface of the earth and fit to the British National Grid coordinate system (British National Grid, Airy Spheroid OSGB (1936) Datum). All map collar and inset information is also available as part of the raster image, including any inset maps, profiles, statistical tables, directories, text, illustrations, index maps, legends, or other information associated with the principal map. This map shows features such as roads, docks, drainage, canals, selected buildings, and more. Includes text, advertisement, and engravings: View of the Thames River -- View of the Interior of the Thames Tunnel -- View of the iron shield compartments for workers. This layer is part of a selection of digitally scanned and georeferenced historic maps from The Harvard Map Collection as part of the Imaging the Urban Environment project. Maps selected for this project represent major urban areas and cities of the world, at various time periods. These maps typically portray both natural and manmade features at a large scale. The selection represents a range of regions, originators, ground condition dates, scales, and purposes.

Stress Inversion Using LiDAR Tunnel Deformation Measurements

Far-field stresses are those present in a volume of rock prior to excavations being created. Estimates of the orientation and magnitude of far-field stresses, often used in mine design, are generally obtained by single-point measurements of stress, or large-scale, regional trends. Point measurements can be a poor representation of far-field stresses as a result of excavation-induced stresses and geological structures. For these reasons, far-field stress estimates can be associated with high levels of uncertainty. The purpose of this thesis is to investigate the practical feasibility, applications, and limitations of calibrating far-field stress estimates through tunnel deformation measurements captured using LiDAR imaging. A method that estimates the orientation and magnitude of excavation-induced principal stress changes through back-analysis of deformation measurements from LiDAR imaged tunnels was developed and tested using synthetic data. If excavation-induced stress change orientations and magnitudes can be accurately estimated, they can be used in the calibration of far-field stress input to numerical models. LiDAR point clouds have been proven to have a number of underground applications, thus it is desired to explore their use in numerical model calibration. The back-analysis method is founded on the superposition of stresses and requires a two-dimensional numerical model of the deforming tunnel. Principal stress changes of known orientation and magnitude are applied to the model to create calibration curves. Estimation can then be performed by minimizing squared differences between the measured tunnel and sets of calibration curve deformations. In addition to the back-analysis estimation method, a procedure consisting of previously existing techniques to measure tunnel deformation using LiDAR imaging was documented. Under ideal conditions, the back-analysis method estimated principal stress change orientations within ±5° and magnitudes within ±2 MPa. Results were comparable for four different tunnel profile shapes. Preliminary testing using plastic deformation, a rough tunnel profile, and profile occlusions suggests that the method can work under more realistic conditions. The results from this thesis set the groundwork for the continued development of a new, inexpensive, and efficient far-field stress estimate calibration method.