This thesis consists of a thermodynamically based kinetic model that more accurately predicts grain boundary mobility (GBM) over a large range of thermodynamic states including changes in temperature, pressure and shear stress. The form of the model was validated against calculated GBM values for Al bicrystals via molecular dynamics (MD) simulations. A total of 98,786 simulations were performed (164 different GBs, each with a minimum of 250 different thermodynamic states, and 2 different driving forces). Methodology for the computation of the GBM via MD simulations is provided. The model parameters are directly linked to extensive thermodynamic quantities and suggest potential mechanisms for GBM under combined thermal and triaxial loads. This thesis also discusses the influence of GB character on the thermodynamic mobility parameters. The resulting insights about GB character and thermodynamic state on GBM suggest an opportunity to achieve designed microstructures by controlling thermodynamic state during microstructure evolution.

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Die neuen 3D-Entwurfs-, Berechnungs- und Fertigungsverfahren in Kombination mit dem Werkstoff ultrahochfester Beton (UHPC) bieten das Potenzial, den Beton-Leichtbau zu revolutionieren [1]. Die Herausforderung bei der Herstellung von geometrisch komplexen und hochpräzisen UHPC-Bauteilen liegt dabei im Schalungsbau. Da bisher keine verfügbaren abfallfreien und somit nachhaltigen alternativen Schalungsmaterialien bzw. -systeme identifiziert werden konnten, wurde der Forschungsansatz entwickelt, frei geformte Schalungen für Betonbauteile unter Verwendung von CNC-gefrästen recycelbaren Industriewachsen zu verwenden. Die Erforschung dieses Ansatzes hin zu einer anwendbaren Non-Waste-Schalungstechnologie wurde in einem gemeinsamen Forschungsprojekt des Instituts für Werkzeugmaschinen und Fertigungstechnik (IWF) und des Instituts für Tragwerksentwurf (ITE) der TU Braunschweig durchgeführt. Im Folgenden werden die wesentlichen Inhalte des Vorhabens, ausgehend von der Auswahl geeigneter Wachse, über die Untersuchung der Zerspanbarkeit bis hin zur Betonierung und anschließenden Analyse der Schalungen und Abgüsse, vorgestellt und diskutiert. Grundlegende Erkenntnisse wurden u. a. bereits 2016 in [2]–[5] veröffentlicht. Diese werden hier teilweise wiedergegeben und zudem mit zusätzlichen Informationen ergänzt. Die wesentlichen Erkenntnisse aus dem Forschungsvorhaben werden zusammengefasst. Ausführliche Informationen zur Entwicklung der Non-Waste-Wachsschalungstechnologie finden sich in der 2019 veröffentlichten Dissertation von Jeldrik Mainka [6]. / The new 3D design, calculation and manufacturing methods in combination with ultra-high strength concrete (UHPC) off er the potential to revolutionise lightweight concrete construction [1]. The challenge in the production of geometrically complex and high-precision UHPC components lies in formwork construction. As no available waste-free and thus sustainable alternative formwork materials or systems have been identified so far, the research approach was developed to use freely shaped formwork for concrete components using CNC-milled recyclable industrial waxes. The research of this approach towards an applicable non-waste formwork technology was carried out in a joint research project of the Institute for Machine Tools and Production Engineering (IWF) and the Institute of Structural Design (ITE) of the Technical University of Braunschweig. In the following, the main contents of the project, starting with the selection of suitable waxes, the investigation of machinability up to the concreting and subsequent analysis of the formwork and castings are presented and discussed. Basic findings have already been published in 2016 in [2]–[5]. These are partly reproduced here and supplemented with additional information. The main findings of the research project are summarised. Detailed information on the development of non-waste wax formwork technology can be found in the dissertation by Jeldrik Mainka [6], published in 2019.

The strain capacity of structures depends on the plastic hinge behaviour. There are different proposals in the scientific literature in order to improve this behaviour in reinforced concrete structures such as the following ones: proposals include the use of fiber reinforced concrete, very high performance concrete or replacing in the critical structure zone, the steel reinforcement with shape memory alloy and superelasticity bars (from this point forward SMA), among other solutions. However, the strain capacity of hinges is dependent on the compressed reinforcement buckling, which means a drastic diminishing in the bearing capacity and ductility. This phenomenon happens due to the cover spalling or degradation, or due to an insufficient transverse reinforcement arrangement. The design codes propose requirements related to the diameter of longitudinal bars and to the transverse reinforcement separation to assure the bearing capacity or to assure the hinge rotation without the compressed reinforcements buckle. Nevertheless, the aforementioned requirements are not valid in compressed elements made of new materials (fiber reinforced concrete, very high performance concrete or SMA bars). This doctoral thesis analyzes the compressed steel or NiTi - SMA bars behaviour in elements made of conventional, high strength or very high performance concrete, with or without fibres. Therefore, an experimental research has been carried out to study the local instability of the compressed bars (steel and NITI) in concrete elements. 32 columns subject to a bending-compression load have been analyzed. An analytic model has been proposed to analyze the buckling critical stress and length in the compressed bars in concrete elements. This model has been calibrated based on experimental tests. It has been performed an experimental and numerical research to analyze the behaviour of the NITI bars as isolated bars. It has been proposed an analytic model to calculate the relationship stress-strain of the compressed bars that includes the buckling effect. This model has been verified by both experimental and numerical results. Finally, it has been proposed an expression to calculate the maximum separation of the transverse reinforcement according to the required limited stress, for both steel and SMA bars. In order to define that stress, two criteria have been proposed: one of them is based on stresses and the other one on strains. With respect to the concrete without fibres case, the proposed expression has been compared with the current code. / La capacidad de deformación de las estructuras depende del comportamiento de las rótulas plásticas. Para mejorar dicho comportamiento en estructuras de hormigón armado, en la literatura técnica se propone utilizar hormigón con fibras de acero en su masa, hormigón de muy altas prestaciones o sustituir en la zona crítica de la estructura las armaduras de acero por barras de aleación con memoria de forma y superelasticidad (en adelante SMA) entre otras soluciones. Sin embargo, la capacidad de deformación de las rótulas está condicionada por el pandeo de la armadura comprimida, lo que supone una disminución drástica de la capacidad resistente y de la ductilidad. Este fenómeno se produce porque el recubrimiento del hormigón salta o se degrada, o por una insuficiente disposición de armadura transversal. En las normativas de diseño se proponen requisitos acerca del diámetro y de la separación de la armadura transversal para asegurar la capacidad resistente o la deformación de la rótula sin que las armaduras comprimidas pandeen. Sin embargo, dichas expresiones no son válidas en elementos comprimidos fabricados con nuevos materiales (hormigón con fibras en su masa, hormigones de muy altas prestaciones o barras de SMA). En esta tesis doctoral se analiza el comportamiento de barras comprimidas, de acero o de SMA en base NiTi, en elementos fabricados con hormigones convencionales, de alta resistencia o de muy altas prestaciones, con o sin fibras en su masa. A tal efecto, se ha ejecutado un programa experimental para estudiar la inestabilidad local de las barras comprimidas (acero y NiTi) en elementos de hormigón. Se han analizado un total de 32 soportes sometidos a una solicitación de flexo-compresión. Se ha propuesto un modelo analítico para determinar la tensión y la longitud crítica de pandeo de barras comprimidas en elementos de hormigón. Este modelo ha sido calibrado con los ensayos experimentales. Se ha realizado un estudio experimental y numérico para analizar el comportamiento de las barras de NiTi como barras aisladas. Se ha propuesto un modelo analítico para calcular la relación tensión - deformación de barras comprimidas que incluye el efecto del pandeo. Este modelo ha sido verificado tanto con los resultados experimentales como numéricos. Finalmente, se ha propuesto una expresión para el cálculo de la separación máxima de la armadura transversal en función de la tensión límite requerida, tanto para barras de acero como de SMA. Para la definición de dicha tensión se proponen dos criterios: uno basado en tensiones y otro en deformaciones. En el caso de hormigón sin fibras, la expresión propuesta se ha comparado con la normativa actual. / La capacitat de deformació de les estructures depén del comportament de les ròtules plàstiques. Per a millorar dit comportament en estructures de formigó armat, en la literatura tècnica es proposa utilitzar formigó amb fibres d'acer en la seua massa, formigó de molt altes prestacions o substituir en la zona crítica de l'estructura les armadures d'acer per barres d'aliatge amb memòria de forma i superelasticitat (d'ara endavant SMA) entre d'altres solucions. No obstant això, la capacitat de deformació de les ròtules està condicionada pel vinclament de l'armadura comprimida, la qual cosa suposa una disminució dràstica de la capacitat resistent i de la ductilitat. Este fenomen es produeix perquè el recobriment del formigó salta o es degrada, o per una insuficient disposició de l'armadura transversal. En les normatives de disseny es proposen requisits quant al diàmetre i a la separació de l'armadura transversal per assegurar la capacitat resistent o la deformació de la ròtula sense que les armadures comprimides vinclen. No obstant això, estes expressions no son vàlides en elements comprimits fabricats amb nous materiales (formigó amb fibres en la seua massa, formigons de molt altes prestacions o barres de SMA). En esta tesis doctoral s'analitza el comportament de barres comprimides, d'acer o de SMA compost per NiTi, en elements fabricats amb formigons convencionals, d'alta resistència o de molt altes prestacions, amb o sense fibres en la seua massa. A tal efecte, s'ha executat un programa experimental per estudiar la inestabilitat local de les barres comprimides (acer i NiTi) en elements de formigó. S'han analitzat un total de 32 soports somesos a una solicitació de flexo-compressió. S'ha proposat un model analític per determinar la tensió i longitud crítica de vinclament de barres comprimides en elements de formigó. Este model ha sigut calibrat amb els assajos experimentals. S'ha realitzat un estudi experimental i numéric per analitzar el comportament de les barres de NiTi com barres aïllades. S'ha proposat un model analític per calcular la relació tensió-deformació de barres comprimides que inclou l'efecte del vinclament. Este model ha sigut verificat tant amb els resultats experimentals com numérics. Finalment, s'ha proposat una expressió per al càlcul de la separació màxima de l'armadura transversal en funció de la tensió límit requerida., tant per a barres d'acer com de SMA. Per a la definició de dita tensió es proposen dos criteris: uno basat en tensions i l'altre en deformacions. En el cas del formigó amb fibres, l'expressió proposada s'ha comparat amb la normativa actual. / Pereiro Barceló, J. (2017). INESTABILIDAD DE BARRAS COMPRIMIDAS DE ACERO Y DE SMA EN ELEMENTOS DE HORMIGÓN FABRICADOS CON NUEVOS MATERIALES. RECOMENDACIONES DE DISEÑO [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90650

[pt] Conforme entramos na era de precisão da astronomia multimensageira, novas janelas se abrem para compreendermos melhor o Universo, desde a escala quântica até a escala cósmica. Em particular, o estudo de fenômenos astrofísicos de altas energias tem nos permitido acessar os ambientes mais extremos conhecidos pela humanidade, bem como obter avanços sem precedentes no domínio da física de partículas. Esta tese resume as descobertas importantes da astrofísica multi-mensageira ao longo dos anos, e, em seguida, foca a sua atenção em três tópicos relevantes que estão atualmente sendo investigados neste campo. Primeiramente, abordamos o problema da propagação de raios gama no espaço. Interações durante este processo levam à formação de cascatas eletromagnéticas que se desenvolvem ao longo de distâncias cosmológicas. Apresentaremos um código semi-analítico chamado “γ-Cascade”, que calcula os fluxos na Terra resultantes de tais cascatas. Também exploramos a possibilidade de se produzir neutrinos em cascatas ocorrendo a energias ultra-altas. Em segundo lugar, estabeleceremos uma relação multimensageira nova e original entre os fluxos medidos de neutrinos astrofísicos entre TeV–PeV e raios cósmicos ultra-energéticos. Para isso, utilizaremos nossas observações precisas de raios gama em energias abaixo de TeV, demonstrando o poder de uma análise multimensageira. Finalmente, estudaremos a evolução da composição de sabor de neutrinos produzidos em supernovas. Nosso novo método permite previsões genéricas sobre os possíveis sabores de neutrinos medidos na Terra. São levados em consideração os efeitos de matéria dentro dos ambientes densos de supernovas, enquanto permanecemos completamente agnósticos em relação ao resultado das conversões auto-induzidas de sabor em seus núcleos. / [en] As we enter the precision era of multi-messenger astronomy, new windows are opened for us to better understand the Universe, from quantum to cosmic scales. In particular, the study of high-energy astrophysical phenomena has allowed us to probe the most extreme environments known to mankind, as well as obtain unprecedented breakthroughs within the realm of particle physics. This thesis summarizes the important findings of multi-messenger astrophysics over the years, before focusing its attention to three relevant topics currently being investigated in the field. Firstly, we tackle the problem of γ-ray propagation in space. High center-of-momenta interactions during this process leads to the formation of electromagnetic cascades that develop over cosmological distances. We describe a semi-analytical code called “γ-Cascade, which calculates the fluxes at the Earth resulting from such cascades. We also explore the possibility of producing neutrinos in ultra-high-energy cascades. Secondly, we establish a new, original multi-messenger connection between the measured fluxes of TeV–PeV astrophysical neutrinos and ultra-high-energy cosmic rays. This is done by taking advantage of our precise γ-ray observations at sub-TeV energies, demonstrating the power of multi-messenger analyses. Finally, we study the evolution of the flavor composition of supernova neutrinos in a model-independent way. Our novel method allows for predictions of the neutrino flavor content measured at the Earth from supernovae, accounting for matter effects within its dense environment, while remaining completely agnostic about the outcome of self-induced flavor conversions in its core.

A near-field technique known as evanescent interferometric lithography allows for high resolution imaging. However its primary limitation is that the image exponentially decays within the photoresist due to physical limits. This thesis aims to overcome this limitation and presents a method to considerably enhance the depth of focus of images created using evanescent interferometric lithography by using a material underlay beneath the photoresist. A key enabler of this is the understanding that evanescent fields couple to surface states and operating within proximity of a resonance, the strength of the coupling allows for considerable energy extraction from the incident beam and redistribution of this energy in a photoresist cavity. This led to the analysis of the Fresnel equations, which suggested that such coupling was in fact the result of an enhanced reflectance that takes place at boundaries of carefully chosen materials. While it is known that metals and lossy dielectrics result in surface plasmon polaritons (SPP) and surface exciton polaritons (SEP) as conventional solutions to the Fresnel reflection equations for the TM polarization of light, there is no such naturally occurring surface state that allows evanescent wave enhancement with the TE polarization of light. Further investigation of the Fresnel reflection equations revealed both for TM and TE that in fact another solution exists that is but unconventional to enhance the reflectivity. This solution requires that one of the media have a negative loss. This is a new type of surface resonance that requires that one of the media be a gain medium; not one in the optical pumped sense but one that would naturally supply energy to a wave to make it grow. This new surface resonance is also a key result of this thesis. Clearly, however this is only a hypothetical solution as a real gain medium would violate the conservation of energy. However, as it is only the reflectance of this gain medium that is useful for evanescent wave enhancement, in fact a multilayered stack consisting of naturally occurring materials is one way to achieve the desired reflectivity. This would of course be only an emulation of the reflectivity aspect of the gain medium. This multilayered stack is then an effective gain medium for the reflectivity purposes when imaging is carried out at a particular NA at a particular wavelength. This proposal is also a key idea of this thesis. At λ = 193 nm, this method was used to propose a feasible design to image high resolution structures, NA = 1.85 at an aspect ratio of ~3.2. To experimentally demonstrate the enhancements, a new type of solid immersion test bed, the solid immersion Lloyd's mirror interference lithography test-bed was constructed. High quality line and space patterns with a half-pitch of 55.5 nm were created using λ = 405 nm, corresponding to a NA of 1.824, that is well in the evanescent regime of light. Image depths of 33-40 nm were seen. Next, the evanescent image was coupled to an effective gain medium made up of a thin layer of hafnium oxide (HfO) upon silicon dioxide (SiO2). This resulted in a considerable depth enhancement, and 105 nm tall structures were imaged. The work in this thesis details the construction of the solid immersion lithography test-bed, describes the implementation of the modeling tools, details the theory and analysis required to achieve the relevant solutions and understanding of the physical mechanism and finally experimentally demonstrates an enhancement that allows evanescent interferometric lithography beyond conventional limits.

The availability of ultra high-frequency (UHF) data on transactions has revolutionised data processing and statistical modelling techniques in finance. The unique characteristics of such data, e.g. discrete structure of price change, unequally spaced time intervals and multiple transactions have introduced new theoretical and computational challenges. In this study, we develop a Bayesian framework for modelling integer-valued variables to capture the fundamental properties of price change. We propose the application of the zero inflated Poisson difference (ZPD) distribution for modelling UHF data and assess the effect of covariates on the behaviour of price change. For this purpose, we present two modelling schemes; the first one is based on the analysis of the data after the market closes for the day and is referred to as off-line data processing. In this case, the Bayesian interpretation and analysis are undertaken using Markov chain Monte Carlo methods. The second modelling scheme introduces the dynamic ZPD model which is implemented through Sequential Monte Carlo methods (also known as particle filters). This procedure enables us to update our inference from data as new transactions take place and is known as online data processing. We apply our models to a set of FTSE100 index changes. Based on the probability integral transform, modified for the case of integer-valued random variables, we show that our models are capable of explaining well the observed distribution of price change. We then apply the deviance information criterion and introduce its sequential version for the purpose of model comparison for off-line and online modelling, respectively. Moreover, in order to add more flexibility to the tails of the ZPD distribution, we introduce the zero inflated generalised Poisson difference distribution and outline its possible application for modelling UHF data.

Ce travail de thèse porte sur l’étude de nouveaux phénomènes vibratoires dans les systèmes Nano-électromécaniques (NEMS) conçus à partir de nanofils (NFs) SiC ou de nanotubes de carbone (NCs) résonants. La configuration encastré-libre permet d'effectuer l'émission de champ (EC) pour caractériser nos échantillons et notamment mesurer le module de Young et le facteur de qualité (Q) de nos NEMS. Le chauffage du résonateur permet d'accroître fortement la valeur de Q des nanofils SiC (Qmax = 159 000). Les auto-oscillations observées sous EC sont obtenues seulement par l'application d'une tension continue et permettent un taux de conversion AC/DC de l'ordre de 50%. L'utilisation de NFs très résistifs couplée au courant d'EC est indispensable pour engendrer ces oscillations spontanées. La réalisation d'une nanoradio sous EC permet la démodulation d'un signal AM ou FM grâce à la résonance d'un NC. Nous décrivons une méthode originale pour exciter les vibrations d'un NF à partir du faisceau d'électrons d'un microscope électronique. L'évolution de la charge au bout du NF est la principale cause de ces auto-oscillations. La configuration encastré-encastré consiste à obtenir un transistor à base de NCs suspendus. Les composants sont caractérisés électriquement et mécaniquement dans un testeur sous pointe sous ultra vide à partir de techniques dites de mixing. La fréquence de résonance de ces échantillons est de l'ordre de 100 MHz et la démodulation d'un signal FM est réalisée pour la première fois dans cette configuration de NEMS. Pour l'ensemble des phénomènes découverts et traités dans ce manuscrit, un modèle et les simulations qui en découlent sont présentés et commentés / This thesis focuses on new phenomena in the mechanical resonances of SiC nanowires (NWs) and carbon nanotubes (CNs) of interest for the emerging field of nano-electro-mechanical systems (NEMS). The clamped-free confiuration allowed the study of our nanowire and nanotube samples by field emission (FE), including measuring the Young's modulus and the quality factor (Q). Heating NW resonators significantly increased their Q factor (Qmax = 159 000). Self-oscillations were observed during FE where only a DC voltage was applied, thus allowing DC/AC conversion with a rate of up to » 50%. Using highly resistive NWs coupled with FE current was required to generate these spontaneous oscillations. Achieving a nanoradio under FE allowed the demodulation of AM or FM signals through the mechanical resonance of CNs. We describe a new method to excite vibrations of a NW from the electron beam of an electron microscope. The evolution of the charge at the end of NW is the main source of these self-oscillations. The clamped-clamped configuration consists of a transistor based on suspended CNs. The devices are characterized electrically and mechanically in a probe station under ultrahigh vacuum with mixing techniques. The resonance frequencies of these samples was around 100 MHz. The demodulation of an FM signal was achieved for the first time in this NEMS configuration. For all the phenomena discovered and treated in this manuscript, a model and derived simulations are described and discussed