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Full-domain POD modes from PIV asynchronous patches
Get PDFA method is proposed to obtain full-domain spatial modes based on proper orthogonal decomposition (POD) of particle image velocimetry (PIV) measurements taken at different (overlapping) spatial locations. This situation occurs when large domains are covered by multiple non-simultaneous measurements and yet the large-scale flow field organization is to be captured. The proposed methodology leverages the definition of POD spatial modes as eigenvectors of the spatial correlation matrix, where local measurements, even when not obtained simultaneously, provide each a portion of the latter, which is then analyzed to synthesize the full-domain spatial modes. The measurement domain coverage is found to require regions overlapping by 50–75% to yield a smooth distribution of the modes. The procedure identifies structures twice as large as each measurement patch. The technique, referred to as Patch POD, is applied to planar PIV data of a submerged jet flow where the effect of patching is simulated by splitting the original PIV data. Patch POD is then extended to 3D robotic measurement around a wall-mounted cube. The results show that the patching technique enables global modal analysis over a domain covered with a multitude of non-simultaneous measurements.This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No 949085)
Sharing Heterogeneous Computing Resources in Virtualized Open Radio Access Networks
Get PDFMención Internacional en el título de doctorVirtualization has recently become a fundamental paradigm in the implementation of 5G Networks, specifically in the context of Radio Access Networks (RANs). RAN virtualization enables baseband processing on general-purpose computing platforms, thus overcoming the coupling of RAN functions with dedicated hardware of traditional hardwired RANs. This approach allows RAN operators to disrupt traditional hardware vendor lock-ins and enable sharing and multiplexing of the available computing resources, as the RAN Base Station (BS) is disaggregated into minimal Radio Unit (RU) hardware connected to cloud-oriented computing platforms that run in software virtual signal processing tasks of the Distributed Unit (DU) and Centralized Unit (CU).
However, the execution of such tasks in a timely manner at high probabilities (reliably) is challenging due to their computationally intensive nature, especially at DU level. For this purpose, carrier-grade virtualized RANs (vRANs) today rely on general-purpose computing platforms equipped with Hardware Accelerators (HAs), which are generally energy-hungry and monetarily expensive but can guarantee DU processing reliability. Traditional HAs include Application-Specific Integrated Circuits (ASICs) and Field Programmable Gate Arrays (FPGAs). Recently, Graphics Processing Units (GPUs) have also been considered as HAs, hinging on their unique capability to be easily programmable in software and to efficiently process Machine Learning (ML) workloads, whose algorithms can be used to automate and optimize DU operations.
HAs also significantly increase the energy and monetary costs of vRANs, which puts at stake the environmental and economic sustainability of next-generation mobile networks. Therefore, deploying reliable hardware accelerated vRANs with the lowest possible energy toll while reducing deployment costs has become a challenging problem for operators. Indeed, current industrial solutions fail to provide energy and cost efficiency in vRAN, as respectively (i) more energy-efficient processors are shunned for DU tasks processing and (ii) dedicated HAs are assigned to individual DUs following an overprovisioned approach.
This thesis investigates the deployment of energy- and cost-effective yet reliable vRANs in order to close the gap with respect to the aforementioned standard solutions. The vision set forth by this thesis is twofold: (i) increasing the energy-efficiency of traditional hardware accelerated vRANs by opportunistically complementing HAs with less energy-hungry computing processors like Central Processing Units (CPUs) to process DU tasks; (ii) improving the cost-efficiency by means of DU centralization, that allows to amortize the cost of each expensive HA by sharing the same HA across multiple DUs.
In line with this vision, the first solution proposed in this thesis is ECORAN, an efficient multi-agent contextual bandit ML algorithm operating in the O-RAN Near-Real-Time RAN Intelligent Controller (Near-RT-RIC). ECORAN configures policies to opportunistically offload DU workloads to either a GPU-based HA or CPUs in the OCloud to save energy while preserving the reliability of the vRAN. To address costefficiency, instead, ECORAN applies concepts from mean field theory to be fully scalable and thus deal with an arbitrarily large and dynamic number of DUs, that are centralized in the same shared and HA-powered computing platform. Using traffic traces from a production mobile network, ECORAN can provide up to 40% energy savings and roughly up to 60x cost gains with respect to the standard approach used today by the industry.
As with many other studies on RAN control in the literature, the offloading policy used in ECORAN is determined by an ML model that requires GPU resources for efficient training and execution in production. However, dedicating a GPU to each ML model that automates a specific RAN control function and reserving a GPU-based HA solely for DU processing is not a cost-efficient approach. Conversely, indiscriminately co-locating DU workloads and multiple ML services can compromise the processing reliability of the former and the throughput performance of the latter. Under this perspective, this thesis explores reliable multiplexing opportunities of the resources of a single GPU to further squeeze cost-efficiency in vRANs. To this end, this thesis proposes YinYangRAN, an innovative system operating in the Non-Real-Time-RIC that supervises the multiplexing of the computing resources of a GPU-based HA as to ensure reliability in processing DU tasks while maximizing the throughput of a concurrent ML service running in the same GPU. Experiments performed with workloads collected in real RANs show that YinYangRAN can potentially reduce the deployment cost by a factor of N compared to the solution using N dedicated GPUs per process, and improve vRAN reliability by over 50% compared to hardware-accelerated vRANs using conventional GPU multiplexing methods, with minimal impact on co-located ML workloads.
Based on insights from tracking workload dynamics in real-world cells, it is observed that traffic exhibits burstiness at the Transmission Time Interval (TTI) level, i.e. with a timescale of 1 ms. However, YinYangRAN operates in Non-Real-Time (timescale≥ 1 s), and ECORAN operates in Near-Real-Time (timescale ∼ 10 − 100 ms). Consequently, to ensure reliability in the vRAN, both solutions adopt a conservative approach by configuring resources for the highest expected peak over the entire decision period, that is significantly longer than 1 ms. This approach leads to wasting resources for most of the decision period due to overprovisioning. Thus, additional gains in energy and cost efficiency can potentially be achieved by exploiting a heterogeneous O-Cloud infrastructure with both HAs and CPUs through a real-time controller capable of responding to TTI-level traffic fluctuations. To address this, this thesis introduces CloudRIC, a real-time brokering system powered by lightweight data-driven models that jointly coordinates a centralized access for multiple DUs to a heterogeneous pool of computing processors, including HAs and CPUs, and assists DUs with compute-aware radio policies while meeting vRAN-specific reliability targets. Extensive experimental evaluations on GPU-accelerated vRANs demonstrate that CloudRIC can achieve, respectively, 3x and 15x average gains in energy and cost efficiency under real and even dense RAN workloads compared to the industry-standard solution that assigns dedicated HAs to individual DUs, while maintaining the same 99.999% target reliability.
At the time of writing this thesis, the proposed solutions are, to the best of our knowledge, the only approaches aimed at reliably deploying energy- and cost-efficient hardware-accelerated vRANs through both DU centralization and the combined use of HAs and CPUs for DU processing.This work has been supported by IMDEA Networks InstitutePrograma de Doctorado en Ingeniería Telemática por la Universidad Carlos III de MadridPresidente: Claudio Fiandrino.- Secretaria: Carla Fabiana Chiasserini.- Vocal: Eduardo Baena Martíne
Spatially Controlled All-Optical Switching of Liquid-Crystal-Empowered Metasurfaces
Get PDFEmbedding metasurfaces in liquid crystal (LC) cells is a promising technique for realizing tunable optical functionalities. Here, we demonstrate spatially controlled all-optical switching of the optical response of a homogeneous silicon nanocylinder metasurface featuring various Mie-type resonances in the spectral range between 670 and 720 nm integrated in a nematic LC cell. The initial alignment of the LC molecules is controlled by photoalignment layers, where the alignment direction is defined by homogeneous exposure with linearly polarized light at a 450 nm wavelength. Exposure of the photoalignment layer with the same light, whose polarization is rotated by 90 degrees , induces a local change in the direction of the LC alignment and modulates the optical response of the metasurface. The resulting spatially dependent optical properties of the metasurface system are characterized by hyperspectral imaging. The described technique allows the nonvolatile creation of complex spatio-spectral response functions with a spatial resolution of 20 ¿m. Moreover, we demonstrate that the response of the LC-integrated metasurface can be switched multiple times by subsequent exposures with alternating orthogonal polarizations. Finally, we show that the images can be temporarily erased by heating the sample above the critical LC transition temperature, where the LC transitions to its isotropic phase. The demonstrated approach represents the controlling-light-by-light concept, an alternative to electro-optical or electromechanical control methods, which require complicated electronic architectures for spatially resolved modulation. Our results hold significant potential for applications such as next-generation displays or spatial light modulators that require spatial control of a tunable, tailored optical response.This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), Project-ID: 437527638 – IRTG 2675 (Meta-Active). This project was made possible by funding from the Carl Zeiss Foundation. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the H2020-FETOPEN-2018–2020 grant agreement no. [899673]“Metafast”. This work reflects only the author view, and the European Commission is not responsible for any use that may be made of the information it contains. A.B. gratefully acknowledges financial support from Spanish national project No. PID2022–137857NA-I00. A.B. thanks MICINN for the Ramon y Cajal Fellowship (grant No. RYC2021–030880-I). S.L.W. acknowledges funding from the Zukunfts Fellowship as part of the Jena Excellence Fellowship Program
Análisis de herramientas, algoritmos y servicios para el desarrollo e implementación de un asistente digital interactivo
Get PDFEl presente Trabajo de Fin de Grado se centra en el análisis, diseño e implementación parcial de un avatar digital. Para ello, se han empleado conocimientos de diversos campos como la Inteligencia Artificial, Ingeniería del Software y prácticas DevOps. La finalidad del trabajo es presentar una propuesta de una solución viable para la implementación de un avatar digital orientado a la atención al cliente.
En una primera etapa, se realiza un estudio comparativo de la estructura del avatar y las tecnologías que lo componen para poder evaluar y seleccionar las herramientas, algoritmos, y servicios que formarán parte de la solución propuesta, priorizando una interacción natural, fluida y de baja latencia. A partir del análisis, se plantean los requisitos funcionales, no funcionales, y técnicos con los que debería de cumplir el avatar para el caso de uso establecido. Se propone una arquitectura modular y escalable, SOA dirigida con eventos, ofreciendo una alta cohesión y bajo acoplamiento. Seguidamente, se realiza una implementación parcial centrada en el despliegue del flujo de trabajo Tokkio de NVIDIA sobre Microsoft Azure como proveedor cloud, con automatización de la infraestructura mediante Terraform y recursos DevOps.
El trabajo no plantea la implementación total de una aplicación final, sino demostrar la viabilidad técnica de la solución, documentar los principales retos encontrados durante su desarrollo, y establecer una base sólida para futuras líneas de trabajo que busquen incorporar asistentes digitales basados en avatares, contribuyendo a la transformación digitalDoble Grado en Ingeniería Informática y Administración de Empresa
Entre antiguos y modernos: obras comentadas de Jaime Alvar Ezquerra
Get PDFGeneraciones de estudiantes, doctorandos e investigadores han hallado en Jaime Alvar un maestro exigente y cercano, un investigador brillante y pionero, y un amigo siempre dispuesto a acompañar en los retos académicos y personales. Su jubilación — más formalidad que realidad — brinda la ocasión de rendirle homenaje con aquello que más le apasiona: la investigación.
Este volumen reúne una selección de los trabajos más significativos de Jaime Alvar, comentados por especialistas que sitúan cada aportación en su contexto y resaltan sus logros. El resultado es un recorrido por una obra que ha renovado el estudio de la Historia Antigua, de la Historia de las Religiones y de la historiografía, reflejando la evolución de un pensamiento siempre inquieto e inquisitivo. Organizados cronológicamente, estos textos abarcan desde la colonización fenicia y griega en el Mediterráneo hasta las religiones mistéricas del Imperio Romano, pasando por la Protohistoria ibérica, el Próximo Oriente o la transición de la Edad del Bronce a la del Hierro.
Este libro es, a la vez, tributo y testimonio: una invitación a descubrir el alcance del pensamiento de Jaime Alvar y a celebrar la pasión por el conocimiento que siempre ha compartido con generosidad
Mejora de la Seguridad y el Confort en Vehículos Autónomos mediante Control Combinado de Seguimiento de Trayectoria y Balanceo
Get PDFGracias a los recientes avances en tecnologías de computación y comunicación, los sistemas de conducción automatizada han pasado de ser un concepto futurista a una realidad concreta. Entre las ventajas de los vehículos inteligentes destacan mejoras significativas en la seguridad y comodidad de los pasajeros, así como una mayor eficiencia energética. Por estas razones, la tecnología de vehículos sin conductor ha captado el interés de la comunidad académica y la industria, quienes ven en ella un área de gran potencial.
Uno de los aspectos críticos en los sistemas de automatización de la conducción es el control de seguimiento de trayectoria, un tema central en la investigación actual. Este se enfoca en desarrollar leyes de control de dirección que permitan guiar al vehículo a lo largo de una trayectoria de referencia, asegurando que se alcancen puntos sin comprometer la estabilidad y la seguridad durante la conducción.
Dado que los accidentes por vuelco tienen una tasa de mortalidad aproximadamente diez veces mayor que otros tipos de colisiones, es importante considerar la estabilidad de balanceo al diseñar controladores que afecten la dinámica lateral del vehículo. Para lograrlo, se pueden incorporar suspensiones activas o semiactivas, así como barras estabilizadoras activas, que generan un momento antivuelco para reducir el balanceo del vehículo y mejorar su estabilidad.
Aunque existen estudios que abordan por separado el control de seguimiento de trayectoria y la estabilidad de balanceo, es común que ambos sistemas se diseñen sin considerar su acoplamiento mecánico, lo cual puede comprometer la seguridad general del vehículo. Además, la naturaleza no lineal de la dinámica del vehículo presenta desafíos adicionales para el diseño de una ley de control que garantice un comportamiento robusto del sistema, lo que hace necesaria la implementación de técnicas avanzadas, como el control con ganancias de parámetros variables lineales.
En este trabajo, se propone un sistema de control de múltiples entradas y múltiples salidas (MIMO, multiple-input multiple-output) y variante en el tiempo, diseñado “offline” y que integra el control de seguimiento de trayectoria y la estabilidad de balanceo en un marco unificado. Este enfoque permite abordar ambos aspectos de manera conjunta para mejorar tanto el rendimiento como la seguridad del vehículo autónomo en condiciones de operación complejas.Este trabajo ha sido financiado por FEDER/Ministerio de Ciencia e Innovación - Agencia Estatal de Investigacion (AEI) del Gobierno de España a través del proyecto PID2022-136468OB-I00, y por el Programa Propio de Investigación de la Universidad Carlos III de Madrid a través del programa Proyectos Jóvenes PPIT2024, con el proyecto “Planificación y control de seguimiento de trayectorias para un sistema de conducción automatizada en intersecciones no semaforizadas considerando dinámica vehicular heterogénea”
Nudging state-space models for Bayesian filtering under misspecified dynamics
Get PDFNudging is a popular algorithmic strategy in numerical filtering to deal with the problem of inference in high-dimensional dynamical systems. We demonstrate in this paper that general nudging techniques can also tackle another crucial statistical problem in filtering, namely the misspecification of the transition kernel. Specifically, we rely on the formulation of nudging as a general operation increasing the likelihood and prove analytically that, when applied carefully, nudging techniques implicitly define state-space models that have higher marginal likelihoods for a given (fixed) sequence of observations. This provides a theoretical justification of nudging techniques as data-informed algorithmic modifications of state-space models to obtain robust models under misspecified dynamics. To demonstrate the use of nudging, we provide numerical experiments on linear Gaussian state-space models and a stochastic Lorenz 63 model with misspecified dynamics and show that nudging offers a robust filtering strategy for these cases.JM and FG acknowledge the support of the Office of Naval Research (award N00014-22-1-2647) and Spain’s Agencia Estatal de Investigación (ref. PID2021-125159NB-I00 TYCHE) funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”. The work of DC has been partially supported by European Research Council (ERC) Synergy grant STUODDLV-856408
Crashworthiness assessment of a composite fuselage stanchion employing a strain rate dependent damage model
No full textNumerical testing is crucial for the design of composite fuselages, which have strict crashworthiness regulations. However, the majority of studies on numerical fuselage impacts do not account for the effects of strain rate in simulations. A damage model considering strain rate dependence has been implemented to accurately predict the impact behaviour of a composite fuselage structure. This model enhances the existing three-dimensional Hashin criterion by incorporating strain rate effects and its implemented numerically using a VUMAT subroutine in ABAQUS/explicit. Validation of the model is done through a low-velocity impact problem, showing a better correlation with experimental data compared to previous numerical analyses available in the literature. The study focuses on high-energy impact on a composite stanchion in the lower lobe of an aircraft fuselage. Results demonstrate that the newly proposed model effectively predicts failure zones and modes, indicating its potential in addressing dynamic composite problems typical of impact scenarios
Instrumental Variables and Omitted Migrant Flows: Immigration and Emigration in Peru
No full textInstrumental variables are often used to identify the causal effect of immigration on labor market outcomes of natives. In this paper, I investigate the sensitivity of 2SLS estimators in the (common) case where a simultaneous shock occurs to the unit of interest and we do not explicitly account for it. For this purpose, I estimate the effects of both the Venezuelan immigration shock and the Peruvian emigration during the last decades on the labor market outcomes of Peruvian native stayers. Using shift-share instruments, I document positive effects of both immigration and emigration on employment rates, household income, and household expenditure (with emigration effects being about eight times larger). Reassuringly for the literature, even in a context of instruments correlated with the omitted flow the point estimates are shown to be robust to the inclusion of the omitted variable
Numerical integration of the KPZ and related equations on networks: the case of the Cayley tree
No full textThe numerical integration of stochastic growth equations on non-Euclidean networks presents unique challenges due to the nonlinearities that occur in many relevant models and to the structural constraints of the networks. In this study, we integrate the Kardar-Parisi-Zhang (KPZ), Edwards-Wilkinson and tensionless KPZ equations on Cayley trees using different numerical schemes and compare their behavior with previous results obtained for discrete growth models. By assessing the stability and accuracy of these methods, we explore how network topology influences interface growth and how boundary effects shape the observed scaling properties. Our results show good agreement with previous studies on discrete models, reinforcing key scaling behaviors while highlighting some differences. These findings contribute to a better understanding of surface growth on networked substrates and provide a computational framework for studying nonlinear stochastic processes beyond Euclidean lattices.This work was partially supported by Ministerio de Ciencia, Innovación y Universidades (Spain), Agencia Estatal de Investigación (AEI, Spain, 10.13039/501100011033), and European Regional Development Fund (ERDF, A way of making Europe) through Grants No. PID2020-112936GB-I00 and No. PID2021-123969NB-I00, and by the Junta de Extremadura (Spain) and Fondo Europeo de Desarrollo Regional (FEDER, EU) through Grants No. GR21014 and No. IB20079. J. M. Marcos is grateful to the Spanish Ministerio de Universidades for a predoctoral fellowship No. FPU2021-01334. We have run oursimulations in the computing facilities of the Instituto de Computacion Científica Avanzada de Extremadura (ICCAEx). The authors thank Alejandro Ortega for discussions about numerical integration techniques for differential equations defined on networks