6,584 research outputs found

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Reinforcement learning in large state action spaces

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    Reinforcement learning (RL) is a promising framework for training intelligent agents which learn to optimize long term utility by directly interacting with the environment. Creating RL methods which scale to large state-action spaces is a critical problem towards ensuring real world deployment of RL systems. However, several challenges limit the applicability of RL to large scale settings. These include difficulties with exploration, low sample efficiency, computational intractability, task constraints like decentralization and lack of guarantees about important properties like performance, generalization and robustness in potentially unseen scenarios. This thesis is motivated towards bridging the aforementioned gap. We propose several principled algorithms and frameworks for studying and addressing the above challenges RL. The proposed methods cover a wide range of RL settings (single and multi-agent systems (MAS) with all the variations in the latter, prediction and control, model-based and model-free methods, value-based and policy-based methods). In this work we propose the first results on several different problems: e.g. tensorization of the Bellman equation which allows exponential sample efficiency gains (Chapter 4), provable suboptimality arising from structural constraints in MAS(Chapter 3), combinatorial generalization results in cooperative MAS(Chapter 5), generalization results on observation shifts(Chapter 7), learning deterministic policies in a probabilistic RL framework(Chapter 6). Our algorithms exhibit provably enhanced performance and sample efficiency along with better scalability. Additionally, we also shed light on generalization aspects of the agents under different frameworks. These properties have been been driven by the use of several advanced tools (e.g. statistical machine learning, state abstraction, variational inference, tensor theory). In summary, the contributions in this thesis significantly advance progress towards making RL agents ready for large scale, real world applications

    An empirical investigation of the relationship between integration, dynamic capabilities and performance in supply chains

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    This research aimed to develop an empirical understanding of the relationships between integration, dynamic capabilities and performance in the supply chain domain, based on which, two conceptual frameworks were constructed to advance the field. The core motivation for the research was that, at the stage of writing the thesis, the combined relationship between the three concepts had not yet been examined, although their interrelationships have been studied individually. To achieve this aim, deductive and inductive reasoning logics were utilised to guide the qualitative study, which was undertaken via multiple case studies to investigate lines of enquiry that would address the research questions formulated. This is consistent with the author’s philosophical adoption of the ontology of relativism and the epistemology of constructionism, which was considered appropriate to address the research questions. Empirical data and evidence were collected, and various triangulation techniques were employed to ensure their credibility. Some key features of grounded theory coding techniques were drawn upon for data coding and analysis, generating two levels of findings. These revealed that whilst integration and dynamic capabilities were crucial in improving performance, the performance also informed the former. This reflects a cyclical and iterative approach rather than one purely based on linearity. Adopting a holistic approach towards the relationship was key in producing complementary strategies that can deliver sustainable supply chain performance. The research makes theoretical, methodological and practical contributions to the field of supply chain management. The theoretical contribution includes the development of two emerging conceptual frameworks at the micro and macro levels. The former provides greater specificity, as it allows meta-analytic evaluation of the three concepts and their dimensions, providing a detailed insight into their correlations. The latter gives a holistic view of their relationships and how they are connected, reflecting a middle-range theory that bridges theory and practice. The methodological contribution lies in presenting models that address gaps associated with the inconsistent use of terminologies in philosophical assumptions, and lack of rigor in deploying case study research methods. In terms of its practical contribution, this research offers insights that practitioners could adopt to enhance their performance. They can do so without necessarily having to forgo certain desired outcomes using targeted integrative strategies and drawing on their dynamic capabilities

    Meso-scale FDM material layout design strategies under manufacturability constraints and fracture conditions

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    In the manufacturability-driven design (MDD) perspective, manufacturability of the product or system is the most important of the design requirements. In addition to being able to ensure that complex designs (e.g., topology optimization) are manufacturable with a given process or process family, MDD also helps mechanical designers to take advantage of unique process-material effects generated during manufacturing. One of the most recognizable examples of this comes from the scanning-type family of additive manufacturing (AM) processes; the most notable and familiar member of this family is the fused deposition modeling (FDM) or fused filament fabrication (FFF) process. This process works by selectively depositing uniform, approximately isotropic beads or elements of molten thermoplastic material (typically structural engineering plastics) in a series of pre-specified traces to build each layer of the part. There are many interesting 2-D and 3-D mechanical design problems that can be explored by designing the layout of these elements. The resulting structured, hierarchical material (which is both manufacturable and customized layer-by-layer within the limits of the process and material) can be defined as a manufacturing process-driven structured material (MPDSM). This dissertation explores several practical methods for designing these element layouts for 2-D and 3-D meso-scale mechanical problems, focusing ultimately on design-for-fracture. Three different fracture conditions are explored: (1) cases where a crack must be prevented or stopped, (2) cases where the crack must be encouraged or accelerated, and (3) cases where cracks must grow in a simple pre-determined pattern. Several new design tools, including a mapping method for the FDM manufacturability constraints, three major literature reviews, the collection, organization, and analysis of several large (qualitative and quantitative) multi-scale datasets on the fracture behavior of FDM-processed materials, some new experimental equipment, and the refinement of a fast and simple g-code generator based on commercially-available software, were developed and refined to support the design of MPDSMs under fracture conditions. The refined design method and rules were experimentally validated using a series of case studies (involving both design and physical testing of the designs) at the end of the dissertation. Finally, a simple design guide for practicing engineers who are not experts in advanced solid mechanics nor process-tailored materials was developed from the results of this project.U of I OnlyAuthor's request

    k-Means

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    Operatic Pasticcios in 18th-Century Europe

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    In Early Modern times, techniques of assembling, compiling and arranging pre-existing material were part of the established working methods in many arts. In the world of 18th-century opera, such practices ensured that operas could become a commercial success because the substitution or compilation of arias fitting the singer's abilities proved the best recipe for fulfilling the expectations of audiences. Known as »pasticcios« since the 18th-century, these operas have long been considered inferior patchwork. The volume collects essays that reconsider the pasticcio, contextualize it, define its preconditions, look at its material aspects and uncover its aesthetical principles

    Land Use and Land Cover Mapping in a Changing World

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    It is increasingly being recognized that land use and land cover changes driven by anthropogenic pressures are impacting terrestrial and aquatic ecosystems and their services, human society, and human livelihoods and well-being. This Special Issue contains 12 original papers covering various issues related to land use and land use changes in various parts of the world (see references), with the purpose of providing a forum to exchange ideas and progress in related areas. Research topics include land use targets, dynamic modelling and mapping using satellite images, pressures from energy production, deforestation, impacts on ecosystem services, aboveground biomass evaluation, and investigations on libraries of legends and classification systems

    Islands at Risk - Analyzing Resource-use Dynamics from a Socio-metabolic Research Perspective

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    Our resource-use dynamics have contributed significantly to the improvement in global material standards of living through the provisioning of essential societal services. Nonetheless, these dynamics have also impacted on the already limited natural resource-base of the Earth system on which we depend. Moreover, the characteristics of a global self-perpetuating resource-use linearity, the growing demand for finite raw materials, the high waste generation that remains unrecovered, and the increasing negative effects of climate change further exacerbate the Earth system’s vulnerabilities and exposure to risks. As such, the resource-use dynamics is posited as an important example of complex systems in need for better understanding, particularly in advancing towards sustainability and build system’s resilience. For resource-stressed settings like small island nations, the analysis of these complex systems is not only crucial, but urgent. Small Island Developing States are often characterized by sustainability challenges like limited resource-bases, reduced waste absorption capacity, a strong dependency on external resources to meet their basic needs, geographic isolation from markets which impact connectivity and resource supply, and natural and built environment that is progressively been threatened by the negative effects of climate change, which amplify the pre-existing vulnerabilities and risks for these territories. Thus, dealing with sustainability would require a deeper understanding of the interactions and trade-offs between the resource-use dynamics and the influences that internal/external factors like climate change have over these. By doing so, the system will have the ability to both contribute to global environment change, but also determine their own vulnerability or resilience to those changes. This thesis analyzes resource-use dynamics from a socio-metabolic research perspective in the context of small islands to enhance resource security and build system’s resilience, by looking into the way in which natural resources are interconnected, influenced, and managed. The analysis is spread across three main empirical Chapters, each of which contribute to advancing the arguments that arise from this work. First, in Chapter 3, the thesis analyzes the shifting resource-baselines of water, energy, and food, emphasizing the intra- and interconnected nature between essential resources and socio-metabolic risk, which builds the foundations for deeper analysis on current and future sustainability in small islands. Then, in Chapter 4, the thesis analyzes and identifies the size and make-up of material and energy flows specific to an individual case study, bringing important quantitative and qualitative insights on the potentials that reconfigured resource-use patterns may offer to minimizing or reducing socio-metabolic risk in small islands. Next, in Chapter 5, the thesis analyzes the role that critical material stocks play in driving resource-use and in furthering sustainable development, emphasizing climate change adaptation strategies to build system’s resilience. The overall framework of this thesis has demonstrated how a better understanding of resource-use dynamics may offer an opportunity to achieve resource security and self-reliance as a resilience building measure in the island context. Finally, this thesis encourages for the development and application of holistic and long-term resource management strategies through inclusive, climate and nature-based solutions that consider the trade-offs and synergies between different resource-use dynamics

    Recuperación de polifenoles de efluentes de almazara mediante procesos de membrana y tratamiento biológico de las corrientes de rechazo

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    Tesis por compendio[ES] Toneladas de aceite de oliva son producidas cada año en el área mediterránea, generando aguas residuales con elevada carga orgánica (COD) y polifenoles (TPhs). Los TPhs son compuestos fitotóxicos, sin embargo, poseen una alta actividad antioxidante, siendo valiosos para su comercialización. La Tesis Doctoral pretende implementar la economía circular para el tratamiento de estas aguas residuales. Para ello, varias combinaciones de procesos fueron estudiados, para recuperar TPhs y reincorporar estas aguas en el proceso productivo. El agua estudiada corresponde a agua de lavado de aceite de oliva (OOWW, "olive oil washing wastewater"), obtenida a la salida de la centrifugación vertical (lavado del aceite), generada en la elaboración de aceite de oliva mediante centrifugación de dos fases. El estudio contempla la utilización de procesos de membrana, resinas de adsorción y tratamiento biológico. Primero se realizó un pretratamiento (flotación, sedimentación y filtración con cartucho) eliminando 89% de grasas y aceites y 40% de color, turbidez y sólidos en suspensión. Luego fue alimentada al proceso de Ultrafiltración (UF) para obtener un permeado rico en TPhs con baja COD. Diferentes membranas, condiciones operacionales (presión transmembranal (TMP) y velocidad tangencial (CFV)) y protocolos de limpieza fueron estudiados. Modelos matemáticos semi-empíricos, método de superficies de respuesta (RSM) y redes neuronales artificiales (ANN) fueron utilizados para predecir el comportamiento de la densidad de flujo de permeado y analizar el tipo de ensuciamiento predominante. La membrana UP005 a TMP de 2 bar y CFV de 2.5m/s fue seleccionada, con una densidad de flujo de permeado estable de 40L/h·m2, bajo rechazo de TPhs (8%) y alto rechazo de COD (61%). Los modelos matemáticos indicaron que más de un proceso de ensuciamiento contribuyeron al ensuciamiento de las membranas. El análisis estadístico ANOVA de RSM mostró que la CFV como la TMP afectan a la densidad de flujo de permeado. Mediante ANN fue posible predecir los datos experimentales de variación de densidad de flujo de permeado con el tiempo. La nanofiltración (NF) y la ósmosis directa (FO) se estudiaron para concentrar los TPhs presentes en el permeado de UF. En la NF se analizaron varias membranas bajo diferentes condiciones operacionales para obtener el mayor rechazo de TPhs. La membrana NF270 a CFV de 1m/s y TMP de 10 bar, logró una densidad de flujo de permeado estable de 74L/h·m2, rechazo de TPhs del 94% y rechazo de COD del 83%. Para el estudio del ensuciamiento de las membranas se utilizaron dos técnicas espectroscópicas, fluorescencia 2D y FTIR, obteniendo información sobre la adsorción de algunos compuestos sobre la superficie de las membranas, y evaluar la eficiencia del protocolo de limpieza. En la FO dos membranas fueron analizadas para la concentración de TPhs. También se estudió el uso de aguas residuales procedentes de la etapa de fermentación en la elaboración de aceitunas de mesa (FTOP) como disolución de arrastre debido a su alta salinidad. Con la membrana HFFO6 (caudal de 30 L/h) se logró la concentración de TPhs en un 79% y la dilución de la FTOP. Cuatro resinas de adsorción fueron estudiadas para recuperar los TPhs presentes en los concentrados de la FO y de la NF. Se estudiaron diferentes concentraciones de resina, tiempos de contacto y disolventes de desorción para la obtención de un concentrado puro, rico en TPhs. Los mejores resultados se obtuvieron con 40 g/L de resina MN200 y una disolución 50% etanol/agua como disolvente. Finalmente, las aguas resultantes (concentrado de FO y rechazos de NF y UF) fueron sometidas a tratamientos biológicos. Primero se realizaron estudios para evaluar la concentración inicial de los reactores biológicos. Mediante tratamiento biológico SBR se logró eliminar en gran medida la COD y los TPhs (rechazo de UF) presentes, logrando obtener efluentes con características aptas para ser utilizadas como agua de limpieza de maquinaria.[CA] Tones d'oli d'oliva són produïdes cada any a l'àrea mediterrània, generant aigües residuals amb càrrega orgànica elevada (COD) i polifenols (TPhs). Els TPhs són compostos fitotòxics, no obstant això, tenen una alta activitat antioxidant, sent valuosos per a la seva comercialització. La Tesi Doctoral pretén implementar l¿economia circular per al tractament d¿aquestes aigües residuals. Per això, diverses combinacions de processos van ser estudiats, per recuperar TPhs i reincorporar aquestes aigües al procés productiu. L'aigua estudiada correspon a aigua de rentat d'oli d'oliva (OOWW, olive oil washing wastewater), obtinguda a la sortida de la centrifugació vertical (rentat de l'oli), generada en l'elaboració d'oli d'oliva mitjançant centrifugació de dues fases. L'estudi contempla la utilització de processos de membrana, resines d'adsorció i tractament biològic. Primer es va realitzar un pretractament (flotació, sedimentació i filtració amb cartutx) eliminant 89% de greixos i olis i 40% de color, terbolesa i sòlids en suspensió. Després va ser alimentada al procés d'Ultrafiltració (UF) per obtenir un permeat ric en TPhs amb baixa COD. Diferents membranes, condicions operacionals (pressió transmembranal (TMP) i velocitat tangencial (CFV)) i protocols de neteja van ser estudiats. Models matemàtics semi-empírics, mètode de superfícies de resposta (RSM) i xarxes neuronals artificials (ANN) van ser utilitzats per predir el comportament de la densitat de flux de permeat i analitzar el tipus d'embrutament predominant. La membrana UP005 a TMP de 2 bar i CFV de 2.5m/s va ser seleccionada, amb una densitat de flux de permeat estable de 40L/h·m2, baix rebuig de TPhs (8%) i alt rebuig de COD (61%) . Els models matemàtics van indicar que més d'un procés d'embrutament van contribuir a embrutar les membranes. L'anàlisi estadística ANOVA de RSM va mostrar que la CFV com la TMP afecten la densitat de flux de permeat. Mitjançant ANN va ser possible predir les dades experimentals de variació de densitat de flux de permeat amb el temps. La nanofiltració (NF) i l'osmosi directa (FO) es van estudiar per concentrar els TPhs presents al permeat d'UF. A la NF es van analitzar diverses membranes sota diferents condicions operacionals per obtenir el major rebuig de TPhs. La membrana NF270 a CFV de 1m/s i TMP de 10 bar, va aconseguir una densitat de flux de permeat estable de 74L/h·m2, rebuig de TPhs del 94% i rebuig de COD del 83%. Per estudiar l'embrutament de les membranes es van utilitzar dues tècniques espectroscòpiques, fluorescència 2D i FTIR, obtenint informació sobre l'adsorció d'alguns compostos sobre la superfície de les membranes, i avaluar l'eficiència del protocol de neteja. A la FO dues membranes van ser analitzades per a la concentració de TPhs. També es va estudiar l'ús d'aigües residuals procedents de l'etapa de fermentació en l'elaboració d'olives de taula (FTOP) com a dissolució d'arrossegament per la seva alta salinitat. Amb la membrana HFFO6 (cabal de 30 L/h) es va aconseguir la concentració de TPhs en un 79% i la dilució de la FTOP. Quatre resines d'adsorció van ser estudiades per recuperar els TPhs presents als concentrats de la FO i de la NF. Es van estudiar diferents concentracions de resina, temps de contacte i dissolvents de desorció per obtenir un concentrat pur, ric en TPhs. Els millors resultats es van obtenir amb 40 g/L de resina MN200 i una dissolució 50% etanol/aigua com a dissolvent. Finalment, les aigües resultants (concentrat de FO i rebutjos de NF i UF) van ser sotmeses a tractaments biològics. Primer es van fer estudis per avaluar la concentració inicial dels reactors biològics. Mitjançant tractament biològic SBR es va aconseguir eliminar en gran mesura la COD i els TPhs (rebuig d'UF) presents, aconseguint obtenir efluents amb característiques aptes per ser utilitzades com a aigua de neteja de maquinària.[EN] Tons of olive oil are produced each year in the Mediterranean area, generating wastewater with a high organic load (COD) and polyphenols (TPhs). TPhs are phytotoxic compounds, however, they have a high antioxidant activity, being valuable for their commercialization. The Doctoral Thesis aims to implement the circular economy for the treatment of these wastewaters. For this, various combinations of processes were studied to recover TPhs and reincorporate these waters into the production process. The water studied corresponds to olive oil washing water (OOWW), obtained at the outlet of the vertical centrifugation (oil washing), generated in the production of olive oil by means of two-phase centrifugation. The study contemplates the use of membrane processes, adsorption resins and biological treatment. First, a pretreatment (flotation, sedimentation and cartridge filtration) was carried out, eliminating 89% of fats and oils and 40% of colour, turbidity and suspended solids. Then it was fed to the Ultrafiltration (UF) process to obtain a permeate rich in TPhs with low COD. Different membranes, operational conditions (transmembrane pressure (TMP) and cross low velocity (CFV)) and cleaning protocols were studied. Semi-empirical mathematical models, the response surface method (RSM) and artificial neural networks (ANN) were used to predict the behavior of the permeate flux density and to analyze the predominant type of fouling. The UP005 membrane at 2 bar TMP and 2.5m/s CFV was selected, with a stable permeate flux density of 40L/h·m2, low TPhs rejection (8%) and high COD rejection (61%). Mathematical models indicated that more than one fouling process contributed to the fouling of the membranes. Statistical analysis ANOVA of RSM showed that both CFV and TMP affect permeate flux density. Through ANN it was possible to predict the experimental data of permeate flux density variation over time. Nanofiltration (NF) and forward osmosis (FO) were studied to concentrate the TPhs present in the UF permeate. In the NF several membranes were analyzed under different operational conditions to obtain the highest rejection of TPhs. The NF270 membrane at CFV of 1m/s and TMP of 10 bar, achieved a stable permeate flux density of 74L/h·m2, TPhs rejection of 94% and COD rejection of 83%. To study the fouling of the membranes, two spectroscopic techniques were used, 2D fluorescence and FTIR, obtaining information on the adsorption of some compounds on the surface of the membranes, and evaluating the efficiency of the cleaning protocol. In the FO two membranes were analyzed for the concentration of TPhs. The use of wastewater from the fermentation stage in the production of table olives (FTOP) as a stripping solution due to its high salinity was also studied. With the HFFO6 membrane (flow rate of 30 L/h) the concentration of TPhs was achieved by 79% and the dilution of the FTOP. Four adsorption resins were studied to recover the TPhs present in the FO and NF concentrates. Different resin concentrations, contact times and desorption solvents were studied to obtain a pure concentrate, rich in TPhs. The best results were obtained with 40 g/L of MN200 resin and a 50% ethanol/water solution as solvent. Finally, the resulting waters (FO concentrate and NF and UF rejections) were subjected to biological treatments. First, studies were carried out to evaluate the initial concentration of the biological reactors. Using SBR biological treatment, it was possible to largely eliminate the COD and the TPhs (rejection of UF) present, managing to obtain effluents with suitable characteristics to be used as machinery cleaning water.The authors acknowledge the financial support from the Spanish Ministry of Economy, Industry and Competitiveness through the project CTM2017-88645-R and The European Union through the Operational Program of the Social Fund (FSE) of the Comunitat Valenciana 2014-2020, ACIF-2018 and BEFPI-2021, and the Associate Laboratory for Green Chemistry-LAQV which is financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020).Cifuentes Cabezas, MS. (2022). Recuperación de polifenoles de efluentes de almazara mediante procesos de membrana y tratamiento biológico de las corrientes de rechazo [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/191508Compendi

    Inclusive Intelligent Learning Management System Framework - Application of Data Science in Inclusive Education

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    Dissertation presented as the partial requirement for obtaining a Master's degree in Data Science and Advanced Analytics, specialization in Data ScienceBeing a disabled student the author faced higher education with a handicap which as experience studying during COVID 19 confinement periods matched the findings in recent research about the importance of digital accessibility through more e-learning intensive academic experiences. Narrative and systematic literature reviews enabled providing context in World Health Organization’s International Classification of Functioning, Disability and Health, legal and standards framework and information technology and communication state-of-the art. Assessing Portuguese higher education institutions’ web sites alerted to the fact that only outlying institutions implemented near perfect, accessibility-wise, websites. Therefore a gap was identified in how accessible the Portuguese higher education websites are, the needs of all students, including those with disabilities, and even the accessibility minimum legal requirements for digital products and the services provided by public or publicly funded organizations. Having identified a problem in society and exploring the scientific base of knowledge for context and state of the art was a first stage in the Design Science Research methodology, to which followed development and validation cycles of an Inclusive Intelligent Learning Management System Framework. The framework blends various Data Science study fields contributions with accessibility guidelines compliant interface design and content upload accessibility compliance assessment. Validation was provided by a focus group whose inputs were considered for the version presented in this dissertation. Not being the purpose of the research to deliver a complete implementation of the framework and lacking consistent data to put all the modules interacting with each other, the most relevant modules were tested with open data as proof of concept. The rigor cycle of DSR started with the inclusion of the previous thesis on Atlântica University Institute Scientific Repository and is to be completed with the publication of this thesis and the already started PhD’s findings in relevant journals and conferences
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