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Estrategia Avanzada de Modelo Subrogado para la Cuantificación de la Incertidumbre en Pelotones de Vehículos Heterogéneos
No full textEl uso de pelotones de vehículos autónomos es una solución efectiva para reducir la congestión y el riesgo de colisiones, ya que permite que los vehículos circulen en formaciones estrechamente coordinadas, con velocidades sincronizadas y un espaciamiento optimizado. El objetivo de esta estrategia de transporte es ofrecer sistemas de movilidad por carretera que sean seguros, eficientes y sostenibles. Por tanto, es fundamental comprobar el grado de fiabilidad de los modelos de pelotón de vehículos para garantizar su correcto funcionamiento en escenarios reales.
La variabilidad en la respuesta de uno de los vehículos puede alterar la eficacia prevista del pelotón, provocando ciclos de conducción de parada y arranque que pueden afectar a la estabilidad de la cadena de vehículos. Por tanto, es esencial comprobar el rendimiento del modelo de pelotón de vehículos autónomos en diferentes escenarios inciertos que incluyan incertidumbres internas y externas, como diferentes tipos de carreteras, condiciones meteorológicas y pesos de los vehículos.
En entornos reales, puede ser difícil determinar cómo cambian los parámetros que afectan al modelo de pelotón, por lo que las simulaciones computacionales son una alternativa viable. Un método eficaz para ello es el método de Montecarlo, que permite generar muestras aleatorias a partir de parámetros inciertos para evaluar el comportamiento del pelotón de vehículos. Sin embargo, dependiendo de la complejidad del modelo, puede resultar costoso desde el punto de vista computacional ejecutar un gran número de reiteraciones. En este contexto, los modelos subrogados o metamodelos son la opción más adecuada, ya que permiten realizar un mayor número de simulaciones y garantizar que los resultados sean significativos y fiables.
Este trabajo destaca la necesidad de realizar verificaciones rigurosas de los modelos heterogéneos de pelotones de vehículos para garantizar su solidez y eficacia en entornos inciertos. Para ello, se propone una estrategia basada en modelos subrogados que combina los modelos MISO (Multiple Input Single Output), NARX (Nonlinear Autoregressive Exogenous) e interpolación espacial Kriging. El modelo MISO-NARX permite relacionar la posición, velocidad y aceleración del vehículo líder con los errores de separación entre vehículos. Por otro lado, el interpolador de Kriging captura la variabilidad de los coeficientes MISO-NARX debido a la incertidumbre de los parámetros del modelo del pelotón de vehículos. La estrategia propuesta permite representar de manera eficiente y precisa las posibles respuestas dinámicas del sistema de pelotón de vehículos, lo que facilita un análisis exhaustivo y fiable de su incertidumbre.El trabajo ha sido financiado por la subvención PID2022-136468OB-I00], otorgada por el Ministerio de Ciencia e Innovación (MCIN) y la Agencia Estatal de Investigación (AEI), con la referencia 10.13039/501100011033, así como por el Fondo Europeo de Desarrollo Regional (FEDER), dentro del programa ``Una manera de hacer Europa
Designing a Capacitive Sensor to Detect Series Arcs in Aircraft HVDC Electrical Systems
No full textThe transition toward more electric aircraft (MEA) and all-electric aircraft (AEA) has driven the adoption of high-voltage DC (HVDC) electrical architectures to meet increasing power demands while reducing weight and enhancing overall efficiency. However, HVDC systems introduce new challenges, particularly concerning insulation reliability and the detection of in-flight series arc faults. This paper presents the design and evaluation of a capacitive sensor specifically developed to detect series arc faults in HVDC electrical systems for aerospace applications. A model of the sensor is proposed and validated through both simulations and experimental measurements using a step response test. The results show excellent agreement between the model and the physical setup. After validating the capacitive coupling value and its response to high-frequency signals, series arcs were generated in the laboratory to evaluate the sensor's performance under realistic operating conditions, which involve different signal dynamics. The results are highly satisfactory and confirm the feasibility of using capacitive sensing for early arc detection, particularly aligned with the stringent requirements of more electric aircraft (MEA) and all-electric aircraft (AEA). The proposed sensor thus enables non-intrusive detection of series arc faults in compact, lightweight, and safety-critical environments.The authors would like to thank to HECATE Project, funded by the European Union (EU) under GA no 101101961—HECAT
Chromatic aberration compensation using thin, transparent, large aperture, wide focal range, adaptive liquid crystal lens
No full textIn this paper large area flat transparent reconfigurable liquid crystal (LC) spiral diffractive lenses (SDL) are employed. These SDLs are assembled back-to-back emulating a varifocal Fresnel lens with an optical power range of 7 diopters. The designed lens can be tuned for any desired wavelength within the visible light spectrum. The tunability of the developed lenses has been employed to generate dynamic chromatic aberration compensation. The manufactured 25.4 mm diameter active area SDLs consist of 24 independently driven spiral shaped electrodes, separated using laser ablation on Indium-Tin Oxide (ITO) coated glass substrates, leading to a fill factor exceeding 98 % and allowing for a simple low voltage (<3.75 VRMS) direct drive addressing scheme.This research was funded by the Comunidad de Madrid through the “Programa de Actividades de I+D” (“SINFOTON2-CM”—S2018/NMT-4326), “PANTOMIME” APOYO-JOVENES-21-9FOMOQ-22-0CNGFM, “DISEÑO Y FABRICACIÓN DE DISPOSITIVOS FOTÓNICOS” (BEAGALINDO-21-QU81R4-7-0QQBF3) and the “Ayudas para la realización de Doctorados Industriales de la Comunidad de Madrid” (IND2020/TIC-17424). The financial support to this study has also come from the Spanish Government, “ENHANCE-5G” (PID2020-114172RB-C22), “LC-LENS” (PDC2021-121370-C21), “DISRADIO” (TSI-063000-2021-83) and WOW-2D (PLEC2022-009381), as well as the Attract-IALL EU project G.A 101004462 and the CONCEPT-2D - G.A 101062995 financed by the European Union. In addition, authors are grateful to the European Space Agency (ESA) for the financial support received with the “Smart Heaters” project (4000133048/20/NL/KML). MCG is grateful to Spanish government grant (BG20/00136)
Control de seguimiento de trayectoria durante maniobras evasivas de un vehículo usando MPC-offline y vectorización de par
No full textEl desarrollo de sistemas de automatización de la conducción ha aumentado considerablemente en los últimos años, buscando soluciones enfocadas principalmente en reducir el número y la gravedad de los accidentes de tráfico y disminuir el impacto medioambiental en el sector del transporte. Uno de los aspectos que más afectan al comportamiento del vehículo es cómo se realiza el control longitudinal y lateral del mismo para realizar el seguimiento de una trayectoria preplanificada. La mayoría de trabajos en este ámbito se enfocan en el diseño de controladores que trabajan en condiciones normales de conducción. Sin embargo, en el caso de situaciones de emergencia como maniobras evasivas, es necesario tener en cuenta la alta no-linealidad y el acoplamiento de las dinámicas longitudinal y lateral del vehículo, lo que transforma el problema de control en un reto complejo.
El control predictivo basado en modelo, o “Model Predictive Control” (MPC), es una de las estrategias de control más usadas para el seguimiento de trayectoria de vehículos. Sin embargo, a medida que se requiere mayor fiabilidad en situaciones de conducción críticas, la complejidad de los modelos de vehículo aumenta junto con el tiempo de procesamiento “online”. Esto último puede comprometer la seguridad del vehículo en situaciones donde se requiere una respuesta muy rápida del controlador. Además, en maniobras evasivas de emergencia el vehículo se mueve cerca del límite de la estabilidad. Las acciones de control que se aplican en cada momento (giro de volante y par total aplicado en las ruedas) deben asegurar el mínimo error de seguimiento a la vez que se mantiene el vehículo dentro del límite de adherencia.
En vista de las anteriores razones, se propone el diseño de un controlador MPC “offline” de seguimiento de trayectoria con vectorización de par para su aplicación en maniobras evasivas de emergencia. La estabilidad del sistema en bucle cerrado se ha asegurado mediante un análisis de¡ estabilidad usando funciones de Lyapunov y basado en la teoría de las elipses robustamente invariantes, obteniendo ganancias de control para un amplio rango de estados del vehículo. En tiempo real, el control se realiza en dos etapas. En primer lugar, se lleva a cabo una programación de ganancias en función de las mediciones y estimaciones de los estados del vehículo para generar el giro de las ruedas delanteras y el par necesarios para seguir la trayectoria y la velocidad de referencia. En la segunda etapa, se calcula el momento de guiñada necesario para reducir el error con la trayectoria de referencia sin que el vehículo sobrepase el límite de manejo mediante un control combinado de la velocidad de guiñada y el ángulo de deriva del vehículo. Por último, el par total calculado en la primera etapa se distribuye entre las cuatro ruedas para generar el momento de guiñada deseado. Se han realizado simulaciones en el software de simulación de dinámica vehicular Carsim donde se ha podido comprobar la superioridad del sistema de control propuesto en maniobras evasivas (doble cambio de carril) con asfalto húmedo frente a un control de seguimiento de trayectoria sin vectorización de par.Este trabajo es parte de la subvención PID2022-136468OB-I00 financiada por MICIU/AEI/ 10.13039/501100011033 y por ERDF, EU
Simulator and hardware emulator of a short electrodynamic tether system
No full textA simulator and a hardware-in-the-loop (HIL) setup for the study of the electric system made by a short electrodynamic tether (EDT), an Electric Power Module (EPM) and a heaterless Hollow Cathode (HC) are presented. In the simulator, the EDT is modeled by the current-voltage (IV) characteristic of a bare EDT, the EPM involves a power supply and a variable resistor, and the IV curves of the emitter and the keeper of the HC are given by the linear fittings of the experimental curves obtained in the laboratory. The simulator was used to study an important problem for short EDT: the minimum power required by the power supply to reach an electric current at the cathode above the critical threshold to keep the plasma discharge as a function of ambient variables (the motional electric field and plasma density). Regarding the HIL, it emulates the EDT with a programmable power supply and a resistor, the EPM with a power supply and a set of resistors, and the HC by a set of Zener diodes. Additionally, the emulator has a computer and a microcontroller that allow to measure key electrical variables and command in real time and in closed-loop the programmable power supply to ensure that the EDT emulator satisfy the bare EDT IV curve. The three elements of the HIL were tested and compared with the theoretical model to validate its correct implementation and operation. Finally, the HIL was used to test and verify the electronic boards of the device of the E.T.PACK-F project.This work was supported by the European Union’s Horizon Europe Research and Innovation Programme (No 101058166, E.T.PACK-F project). Authors are grateful to the partners of the project for fruitful discussions and support, in particular with Technische Universität Dresden (TUD) for its assistance with the hollow cathode emulation
NLP-Driven Approaches to Measuring Online Polarization and Radicalization
No full textThe growing popularity of social media has coincided with a massive number of real-world issues and crises that are controversial and polarizing. Recent issues such as Russo-Ukrainian and Israeli-Palestinian topics, alongside classic issues such as abortion-ban and gun-control, have raised heated debates offline and online. Throughout the past two decades, Computational Social Scientists have been introducing methods of modeling and measuring online polarization and radicalization. Yet, most of the proposed methods rely on traditional tools such as graph analysis and classic NLP models. These tools are accompanied by limitations in terms of computational efficiency, accuracy, granularity, and availability of data (e.g., follow network is no longer publicly available on Twitter). Fortunately, in the past few years, thanks to the invention of the transformers architecture, the world has witnessed massive breakthroughs in the field of Natural Language Processing (NLP). Especially, Large Language Models (LLMs) have grasped the attention of both public and scientific communities. These breakthroughs have also created unprecedented opportunities for advancing classic techniques in various domains of Computational Social Sciences, including polarization detection and opinion mining. This thesis aims to propose novel approaches using state-of-the-art NLP techniques to model and track polarization on social media. It introduces a scalable method for quantifying echo chambers with sentence transformers, revealing asymmetries in discourse diversity across political ideologies. Furthermore, it applies LLMs to analyze the content of cross-partisan interactions, showing that cross-party engagement does not necessarily lead to productive discourse. The thesis also investigates radicalization in gender-based communities and compares the spread of radical content across platforms like Reddit and Discord. Lastly, it addresses the limitations of existing language models in detecting stance polarity by fine-tuning a sentence transformer to become stance-aware, enabling more accurate detection of opposing viewpoints on similar topics. Together, these contributions offer Computational Social Scientists new tools for understanding polarization, radicalization, and bias in online environments.This work has been supported by IMDEA Networks InstitutePrograma de Doctorado en Ingeniería Telemática por la Universidad Carlos III de MadridPresidente: Dong Nguyen.- Secretario: Rubén Cuevas Rumín.- Vocal: Walid Magd
Bare Photovoltaic Tether characteristics for ISS reboost
No full textThis study focuses on designing a bare photovoltaic tether (BPT) for maintaining the International Space Station (ISS) orbit using a zig-zag strategy that was conceptually introduced in a recent previous work. This strategy involves alternating reboost maneuvers and natural decays due to atmospheric drag. The BPT characteristics, including total length, photovoltaic cell coverage of the tether/tape, and cell efficiency are crucial for an effective system operation. These characteristics are determined by an optimization process and the system effectiveness is evaluated by using FLEXSIM, a simulation software package capable of modeling ISS orbital dynamics during BPT operations. The simulations consider the semimajor axes for starting and ending BPT operations and incorporate the Lorentz Force generated by the tether/tape during reboost maneuvers. During the decay phases, the BPT is not operational, it is retrieved back and only gravity and neutral drag are acting on the system. The numerical simulations are used to validate the BPT system design for the ISS station-keeping maneuvers. Consequently, the goal of this paper is to showcase the feasibility of implementing this novel, sustainable, and environmentally friendly use of BPT technology to benefit the ISS station keeping, creating a fully autonomous system capable of independently generating the necessary input power to produce the Lorentz force necessary to carry out that task.This work was supported by the following programs: Horizon Europe EIC Pathfinder Programme under Grant Agreement No. 101161603 (E.T.COMPACT), and Horizon Europe EIC Transition Programme under Grant Agreement No. 101058166 (E.T.PACK-F)
La salud de las mujeres: un enfoque desde el género y los Objetivos de Desarrollo Sostenible. El caso de Ruanda
Get PDFPrograma de Doctorado en Estudios Avanzados en Derechos Humanos por la Universidad Carlos III de MadridPresidente: Carlos Lema Añón.- Secretario: Ramiro , Miguel Ángel.- Vocal: Dalli Almiñana, María Amparo.
Synthesis of ternary and quaternary MAX phases in Ti/Cr/Nb/V-Al-C system by high energy ball milling and pressureless spark plasma sintering
Get PDFThe search for MAX phase synthesis methods that allow good energy efficiency and phase purity remains ongoing. In this work, high energy ball milling and pressureless spark plasma sintering were used to synthesize ternary and quaternary MAX phases from Ti/Nb/V/Cr-Al-C system in a powder form. The powders were densified in a separate spark plasma sintering process. Synthesized powders and bulks structure were studied using scanning electron microscope and X-ray diffraction. Chemical composition was determined using energy dispersive X-ray spectroscopy and carbon and oxygen analyzers. Thermal oxidation and mechanical properties were assessed using thermogravimetry and nanoindentation. The high energy ball milling and pressureless spark plasma sintering route allowed fabrication of both ternary and quaternary MAX phase systems, except TiCrAlC and NbCrAlC. The synthesized MAX phases purity was in the range of 92¿98 %, according to Rietveld refinement. Secondary phases consisted of M-X carbides and M-A intermetallics, as well as aluminum oxide. The highest hardness and elastic modulus values were observed for Nb2AlC and NbVAlC MAX phases. Thermogravimetric tests showed limited oxidation rate of MAX phases within 20–900◦C range, except for Ti2AlC, which could be attributed to increased oxygen content before test. This work presents a beneficial method for fabrication of relatively phase-pure MAX phases using different M-type elements as precursor materials.The research work was carried out as part of Applied Doctorate programme funded by Ministry of Education and Science (currently Ministry of Science and Higher Education) Project Agreement No. DWD/5/0214/2021. This work was supported by the European Union through the Horizon Europe programme under GA number 101135965
Experimental characterization of turbulent boundary layers around a NACA 4412 wing profile
Get PDFAn experimental characterization of the turbulent boundary layers developing around a NACA 4412 wing profile is carried out in the Minimum Turbulence Level (MTL) wind tunnel located at KTH Royal Institute of Technology. The campaign included collecting wall-pressure data via built-in pressure taps, capturing velocity signals in the turbulent boundary layers (TBLs) using hot-wire anemometry (HWA), and conducting direct skin-friction measurements with oil-film interferometry (OFI). The research spanned two chord-based Reynolds numbers ( = 4 × 105 and 106) and four angles of attack (5◦, 8◦, 11◦ and 14◦), encompassing a broad spectrum of flow conditions, from mild to strong adverse-pressure gradients (APGs), including scenarios where the TBL detaches from the wing surface. This dataset offers crucial insights into TBL behavior under varied flow conditions, particularly in the context of APGs. Key features include the quasi-independence of the pressure coefficient distributions from Reynolds number, which aids in distinguishing Reynolds-number effects from those due to APG strengths. The study also reveals changes in TBL dynamics as separation approaches, with energy shifting from the inner to the outer region and the eventual transition to a free-shear flow state post-separation. Additionally, the diagnostic scaling in the outer region under spatial-resolution effects is considered, showing further evidence for its applicability for small +, however with inconsistent results for larger +. The findings and database resulting from this campaign may be of special relevance for the development and validation of turbulence models, especially in the context of aeronautical applications.This research is funded by the Knut and Alice Wallenberg (KAW) Foundation through the Academy Fellow Programme of PS. The high-resolution LES used for the validation in this work were performed on resources provided by the National Academic Infrastructure for Supercomputing in Sweden (NAISS) at the PDC Center for High-Performance Computing in KTH (Stockholm), by the PRACE, Belgium project nr. 2021250090 on HAWK (Stuttgart) and by the European High-Performance Computing Joint Undertaking (EuroHPC JU) project EHPC-REG-2021R0088 in LUMI (Finland)