Systems of magnetic nanowires are considered strong candidates in many technological applications as microwave filters, sensors or devices for data storage. Because of their strong potential as candidates in such applications they became lately the object of many studies. However, due to the very complicated nature of the interwire interactions, their magnetic behavior is very difficult to be interpreted. The main parameter controlling the response of magnetic nanowires assemblies is the aspect ratio of the nanowires that is defined as the ratio of the length to the wire's diameter. In our study we choose to modify the aspect ratio by keeping a constant length of nanowires and modifying the wire's diameter while keeping the same interwire distance. The samples were studied at room temperature, using vibrating sample magnetometer and X-band ferromagnetic resonance experiments. The results are explained taking into account the effects of the magnetostatic interactions and shape anisotropy.

O trabalho trata da formulação, implementação e aplicação de um modelo para análise não-linear de estruturas reticuladas planas em concreto armado, baseado no conceito simplificado de localização dos processos físicos irreversíveis (dano, plasticidade e histerese) em zonas previamente definidas denominadas rótulas que se localizam nas extremidades de um elemento finito de barra. O modelo proposto tem por objetivo reproduzir os deslocamentos residuais relacionados tanto ao comportamento plástico do concreto danificado quanto ao escoamento do aço, além de possibilitar a reprodução de laços de histerese observados experimentalmente em diagramas momento-rotação, ou equivalentemente força-deslocamento, quando a história de carregamento incluir ciclos de descarregamento e recarregamento. A formulação termodinâmica é desenvolvida fazendo-se referência as variáveis de tensão e deformação generalizadas em razão de sua aplicação no âmbito da teoria clássica de flexão de barras. Neste modelo a não-linearidade do elemento estrutural é totalmente decorrente da dissipação de energia localizada nas rótulas e é representada por três variáveis escalares a elas associadas: a variável adimensional de dano, a rotação plástica e a rotação por escorregamento, que representa o fenômeno físico do escorregamento entre as faces das microfissuras no concreto (encaixe e desencaixe dos agregados). Na fase de aplicações as respostas numéricas obtidas com a utilização do modelo proposto foram avaliadas mediante o confronto com diversos resultados experimentais disponíveis na literatura para estruturas de concreto armado sob solicitações estáticas e dinâmicas. Os resultados obtidos evidenciam o bom funcionamento do modelo no caso das solicitações estáticas, tendo sido obtidos resultados limitadamente satisfatórios no caso das solicitações dinâmicas. / This work deals with the formulation, implementation and application of a model for nonlinear analysis of reinforced concrete planed frame structures, based on the simplified concept of localization of the irreversible physical processes (damage, plasticity and hysteresis) in zones previously defined called hinges which are located in the extremities of a bar finite element. The proposed model has as objective to reproduce the residual displacements related to the plastic behavior of the damaged concrete as well as to the steel yielding, moreover making possible the reproduction of hysteresis loops experimentally observed in moment-rotation diagrams, or equivalently force-displacement, when the loading history includes unloading and reloading cycles. The thermodynamic formulation is developed referring to generalized stress and deformation variables due to their application in the scope of the classic theory of bars bending. In this model the nonlinearity of the structural element is totally due to the energy dissipation in the hinges and is represented by three scalar variables associated to them: the non-dimensional damage variable, the plastic rotation and the sliding rotation, which represents the physical phenomenon of sliding between the microcracks faces in the concrete (aggregate interlocking). In the applications phase, the numerical solutions obtained with the use of the proposed model had been evaluated by confrontation with various experimental results available in the literature of reinforced concrete structures under static and dynamic solicitations. The obtained results evidence the good performance of the model in the case of static solicitations, having been obtained limited satisfactory results in the case of dynamic solicitations.

Estômatos são poros responsáveis pela troca gasosa entre a folha e o meio externo. A partir da década de 80, experimentos revelaram um complexo padrão espaço temporal na abertura e fechamento dos estômatos. As experiências apontam para uma possível coordenação entre estômatos em algumas áreas da folha chamada de patches. Esse fenômeno é conhecido na literatura como patchy stomatal conductance. Frequentemente a coordenação dinâmica dos estômatos está associada à oscilações temporais na condutãncia estomática (média especial da abertura dos estômatos). Em 1997 Haefner, Buckley e Mott (HBM) publicaram uma análise numérica de um modelo dinâmico para explorar o comportamento complexo dos estômatos. O modelo é baseado em algumas características conhecidas dos estômatos e assume transporte hídrico em uma rede definida por uma geometria simples e bastante restritiva. De acordo com os autores, o modelo reproduz qualitativamente os dados experimentais. Recentemente, Ferraz e Prado mostraram que esse modelo não é capaz de reproduzir os resultados experimentais. Usando ingredientes do modelo sugerido por HBM, Ferraz e Prado sugeriram uma geometria realística de distribuição reservatórios hídricos. Embora essa configuração reproduza os patches, eles permanecem estáticos e nenhuma oscilação é observada. Sem explorar detalhes significativos, Ferraz e Prado afirmaram que a histerese na abertura estomatal poderia explicar vários aspectos dos resultados experimentais. No presente estudo comprovamos, através de uma abordagem computacional baseada em transdutores histeréticos, que a hipótese de histerese na abertura dos estômatos de fato reproduz qualitativamente os dados experimentais. Em nossa abordagem a histerese na abertura dos estômatos é emulada através de operadores chamados de histerons. A robustez da hipótese é testada usando diferentes tipos de histerons. Analisamos a correlação entre os estômatos na rede que simula a superfície da folha. Observamos que a correlação entre estômatos depende da geometria da veia. Uma análise detalhada dos parâmetros envolvidos revela uma dependência entre o período de oscilação na condutância estomática e o déficit de vapor d\'água entre a folha e o meio ambiente. Esta característica subjacente ao modelo pode inspirar novas experiências para testar a hipótese da histerese na abertura dos estômatos. / Stomata are pores on the surface of leaves responsible for controlling the exchange of gas between the plant and the environment. Experiments revealed a complex spatial-temporal pattern in the opening and closing mechanism of stomata. The main feature of the phenomenon is that stomata appear to be synchronized into clusters, known as patches. The dynamical coordination of stomata often involves oscillations in stomatal conductance. In 1997 Haefner, Buckley, and Mott (HBM) published a numerical analysis of a dynamic model to explore the complex behavior of stomata. The model is based on some known features of the stomata, and assumes that water diffuses within the leaves according to a simple geometric arrangement. According to the authors, the model reproduces qualitatively the experimental data. Recently, Ferraz and Prado showed that the computational approach of HBM is not able to reproduce the experimental results. Inspired by this model, Ferraz and Prado introduced a new geometric features that leads to static patches of stomata; however no oscillation was observed and the patches remained static. The authors suggested that hysteresis in stomatal aperture could explain several experimental aspects. We now report a further investigation of the changes suggested by Ferraz and Prado in the original model of HBM. The theoretical approach confirmed that hysteresis in the aperture mechanism of pores reproduces a variety of behaviors of stomatal conductance described in experiments. We explore the hysteresis feature through the formalism of hysteretic transducer. The robustness of the hysteretic assumption is tested by different kinds of hysteresis operators. We analyzed the correlation among stomata in the lattice. We observed that the correlation depends on the geometry of the veins. Finally, the analysis of the model reveals a dependence between the period of oscillation in the stomatal conductance time series and water vapor pressure deficits Δω - an external parameter. Further experiments might explore this underlying feature of the model.

Respiratory motion causes artifacts and blurring of cardiac structures in reconstructed images of SPECT and PET cardiac studies. Hysteresis in respiratory motion causes the organs to move in distinct paths during inspiration and expiration. Current respiratory motion correction methods use a signal generated by tracking the motion of the abdomen during respiration to bin list- mode data as a function of the magnitude of this respiratory signal. They thereby fail to account for hysteretic motion. The goal of this research was to demonstrate the effects of hysteretic respiratory motion and the importance of its correction for different medical imaging techniques particularly SPECT and PET. This study describes a novel approach for detecting and correcting hysteresis in clinical SPECT and PET studies. From the combined use of MRI and a synchronized Visual Tracking System (VTS) in volunteers we developed hysteretic modeling using the Bouc-Wen model with inputs from measurements of both chest and abdomen respiratory motion. With the MRI determined heart motion as the truth in the volunteer studies we determined the Bouc Wen model could match the behavior over a range of hysteretic cycles. The proposed approach was validated through phantom simulations and applied to clinical SPECT studies.

This work focuses on the development of a highly accurate energy-based hysteresismodel for the modeling of magnetic hysteresis phenomena. The model relies on anexplicit representation of the magnetic pinning effect as a dry friction-like force actingon the magnetic polarization. Unlike Preisach and Jiles-Atherton models, this modelis vectorial from the beginning and derives from thermodynamic first principles.Three approaches are considered: the first one, called vector play model, relies on asimplification that allows an explicit, and thus fast, update rule, while the two others,called the variational and the differential approaches, avoid this simplification,but require a non-linear equation to be solved iteratively. The vector play model andthe variational approach were already used by other researchers, whereas the differentialapproach introduced in this thesis, is a new, more efficient, exact implementation,which combines the efficiency of the vector play model with the accuracy of the variationalapproach. The three hysteresis implementations lead to the same result forpurely unidirectional or rotational excitation cases, and give a rather good approximationin all situations in-between, at least in isotropic material conditions.These hysteresis modeling approaches are incorporated into a finite-element code asa local constitutive relation with memory effect. The inclusion is investigated in detailfor two complementary finite-element formulations, magnetic field h or flux densityb conforming, the latter requiring the inversion of the vector hysteresis model,naturally driven by h, for which the Newton-Raphson method is used. Then, at thefinite-element level, once again, the Newton-Raphson technique is adopted to solvethe nonlinear finite-element equations, leading to the emergence of discontinuous differentialreluctivity and permeability tensors, requiring a relaxation technique in theNewton-Raphson scheme. To the best of the author’s knowledge, the inclusion of anenergy-based hysteresis model has never been successfully achieved in a b-conformfinite-element formulation before. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

The electrochemical double layer (EDL) at the solid–liquid interface is the near surface region where important electrochemical processes (e.g., electrodeposition, corrosion, and heterogeneous catalysis) take place. Subtle changes in the electrode surface material/topography and the nature of the fluid medium can drastically alter interactions between liquid molecules and the solid surface. A better understanding of this interfacial region can help advance numerous applied fields, such as battery technologies, solar cells, double layer capacitors, and carbon dioxide capture/conversion. Ionic liquids (IL) are an emerging class of solvents that could replace traditional aqueous/non-aqueous solvents due to their advantageous physiochemical properties (e.g., wide solvent window, high thermal stability, and excellent solvating power). However, our understanding of the near-surface structure of ILs in the EDL is still being developed. This thesis focuses on the fundamental electrochemical behavior of ILs to help understand its interfacial behavior in three main areas: 1) the nature of capacitance-potential relationships in neat ILs, 2) the role of ‘user-defined’ experimental variables on capacitive electrochemical measurements, and 3) the impact of IL + water mixtures on experimental data. The general shape of capacitance-potential curves can suggest at the broad architecture of the EDL region. Fundamental capacitive studies of the IL EDL show a wide range of results, even for similar electrochemical systems. Theoretical predictions suggest the capacitance-potential curve should exhibit bell- or camel-shaped curvature depending on the nature of the IL. Experimental observations have demonstrated several functional shapes such as U-shaped, bell-shaped, camel-shaped, and relatively featureless responses. Much of the work in this thesis starkly contrasts theoretical expectations by demonstrating capacitive behavior that is analogous to high temperature molten salts and dilute aqueous electrolytes with metallic and non-metallic electrode materials. However, our systematic studies of a model IL electrochemical system reveal that there are several ‘user-defined’ experimental variables (i.e. potential scan direction, data acquisition protocol, experimental technique, and potential range probed) which in some instances can significantly impact the resulting capacitance curvature. Some of these variables are often overlooked in the literature and our efforts are aimed at uniting the scientific community in this area to help better compare and understand results. An additional experimental variable of importance is the sorption of water into ILs, which is nearly impossible to prevent due to their hygroscopic nature. The presence of water is known to have a significant effect on the resulting mixtures’ bulk and interfacial properties. While the interaction between ILs and water can significantly vary depending on the nature of the IL, this thesis demonstrates that within small quantities (e.g., < 5000 ppm) of sorbed water there are only minor changes in spectroscopic and electrochemical responses. Collectively, the work outlined in this thesis helps the scientific community better understand electrochemical measurements in IL solvents by examining key analytical variables associated with capacitive measurements. The fundamental electrochemical studies described in this thesis demonstrate that the solid-liquid interface for IL solvents is response to even subtle changes in surface chemistries. These governing interfacial properties have ramifications in myriad applications from energy storage to lubrication.

This treatise is a recapitulation of the theoretical and experimental study of hysteresis in atmospheric kinetics. The original problem arose from a theoretical study of a series of reactions for clean air. Upon evaluation a bistable equilibrium was predicted. The steady-state analysis had delineated a metastable region for the set of reactions. This bounded region is the hysteresis that this research project evaluated.

Ratings curves are conventional means to continuously provide estimates of discharges in rivers. Among the most-often adopted assumptions in building these curves are the steady and uniform flow conditions for the open-channel flow that in turn provide a one-to-one relationships between the variables involved in discharge estimation. The steady flow assumption is not applicable during propagation of storm-generated waves hence the question on the validity of the steady rating curves during unsteady flow is of both scientific and practical interest. Scarce experimental evidence and analytical inferences substantiate that during unsteady flows the relationship between some of the variables is not unique leading to looped rating curves (also labeled hysteresis). Neglecting the unsteadiness of the flow when this is large can significantly affect the accuracy of the flow estimation. Currently, the literature does not offer criteria for a comprehensive evaluation of the methods for estimation of the departure of the looped rating curves from the steady ones nor for identifying the most appropriate means to dynamically capturing hysteresis for different possible river flow conditions. Therefore, the overarching goal of this study was to explore the uncertainty of the conventional approaches for constructing stage-discharge rating curves (hQRCs) and to evaluate methodologies for accurate and continuous discharge monitoring in unsteady open channel flows using analytical inference, index velocity rating curves (VQRCs), and continuous slope area method (CSA) with considerations on discharge measurement uncertainty. The study will demonstrate conceptual and experimental evidences to illustrate some of the unsteady flow impacts on rating curves and suggest the development of a uniform end-to-end methodology to enhance the accuracy of the current protocols for continuous stream flow estimation for both steady and unsteady river conditions. Moreover, hysteresis diagnostic method will be presented to provide the way to conveniently evaluate when and where the hysteresis becomes significant as a function of the site and storm event characteristics. The measurement techniques and analysis methodologies proposed herein will allow to dynamically tracking both the flood wave propagation and the associated uncertainty in the conventional RCs.

Anti-control of chaos has attracted a lot of attention recently due to its potential applications in science and engineering. How to generate useful chaos that is also practically implementable and useful is a current focus of research. This research aims at developing new chaos generation schemes which demonstrate complex dynamical behaviours using simple linear systems with hysteresis function series. A continuous-time linear unstable second-order system with a feedback of hysteresis function is first proposed for generating chaos. The design for chaos generation is studied theoretically. A Poincaré map is used to demonstrate the dynamical behaviour of the system. The existence and the analytic solution of the limit cycle that bounds the basin of attraction of the chaotic attractor are derived. Conditions for the existence of chaotic attractors are studied. A hysteresis based system with a maximum chaotic stability margin is designed. Second, systematic methods for generating 1D n-scroll chaotic attractors in the directions of the state variables and 2D nxm-grid scroll chaotic attractors in the phase plane via continuous-time linear unstable second-order systems with a feedback of hysteresis function series are proposed. Furthermore, systematic methods for generating 1D n-scroll, 2D nxm-grid scroll and 3D nxmxl-space scroll chaotic attractors via continuous-time linear unstable third-order systems using hysteresis function series feedback are also presented in this thesis. Simulation results are presented to demonstrate effectiveness of the schemes. It is shown that the multi-scroll chaos generation systems can be represented in Lur'e form, and as a result it may be used within synchronization schemes for secure communication. Third, the limit cycle that bounds the basin of attraction in the multi-scroll chaos generation with second-order systems case is studied. The relationship of the size of the basin of attraction with the numbers of hysteresis function series is studied. The multi-scroll chaos generation mechanism is then further explored by analyzing the system trajectories; the switching boundaries, switching rules and the trajectories on each subspace. The chaotic behaviours are confirmed theoretically and it is proved that a non-ordinary attractor exists in the multi-scroll chaotic attractor of the second-order systems case. The abundant dynamical behaviour of the multi-scroll chaos generation systems using different hysteresis feedback are demonstrated. A double-hysteresis function, which is the superimposition of two basic hysteresis functions, is proposed for the implementation of the hysteresis based chaotic system. In this design, the double-hysteresis block and its series are constructed via a systematic method. The ideal hysteresis function series can be implemented easily with the proposed double-hysteresis function. The number of scroll attractors can be designed arbitrarily, and the multi-scroll chaotic attractors can be located anywhere and cover any chosen area of the phase plane. The circuitry implementation for generating 1D n-scroll, 2D nxm-grid scroll chaotic attractors with linear second-order systems and hysteresis function series is given. And the oscilloscope illustrated waveforms which included as many as 9x9=81 scrolls chaotic attractor are presented. The experimental results confirmed the theoretical analysis very well and validated the effectiveness as well as the feasibility of the proposed multi-scroll chaos generation schemes. This research may find potential engineering applications in areas such as digital coding and image processing, etc.

Abstract There is a need in medicine and research for noninvasive, painless, safe and simple bed-side techniques to measure physiological processes associated with muscle function and activity. Bioelectrical Impedance Analysis (BIA) is a widely used, noninvasive, painless, safe and simple procedure for the measurement of body composition. However, although capable of producing accurate and reproducible data, it is known to be prone to movement artifacts. This poses the interesting question “Could impedance changes be used to monitor movement and, consequently, be related to muscle function or activity?” This project investigated the utility of impedance change as a monitoring technique for physiological processes that involve movement such as muscular contraction, the calf muscle pump, and swallowing. The impedance of leg muscle segments during locomotion, whilst riding a stationary exercise cycle, was measured at discrete frequencies and by bioimpedance spectroscopy to monitor muscle function or activity. Impedance traces were compared to information obtained by electromyography (EMG). Impedance, at a discrete frequency, was able to measure the cadence of cycling and its magnitude was related to the position of the pedal during the pedal cycle. When the cycling action was measured by bioimpedance spectroscopy, R0 and Zc showed a statistically significant difference, (p<0.05), between all angles of the pedal crank cycle while R∞ showed a statistically significant difference between angles in the lower hemisphere of the pedal crank cycle. The cyclical changes in impedance during cycling may be attributed to changes in shape and volume of the muscle during contraction as well as a volume change due to blood and lymph being pumped from the limb by the action of the calf muscle pump. Based on procedures used in the cycling studies, an impedance-based method for the measurement of calf muscle pump function during an exercise protocol, originally designed for use with air plethysmography, was developed. It was shown that impedance measured at 5 kHz provides a simple, non-invasive method for the measurement of the ejection fraction and ejection volume of the calf muscle pump as well as other haemodynamic variables. The impedance-based method was less technically challenging than accepted volumetric methods, such as air plethysmography and strain gauge plethysmography, and non-invasive c.f. ambulatory venous pressure, enabling it to be used repeatedly. Muscle function and activity is not confined to the legs so impedance changes in the arm and forearm during exercise were measured. Impedance measurements, at discrete frequencies and using bioimpedance spectroscopy, of the forearm during contractions of the hand were able to distinguish the difference between a ramp and a pulse contraction. When the impedance of the arm and forearm were plotted against the angle of the forearm to the horizontal during a bicep curl, there was an hysteresis effect. Impedance traces of a bicep curl were compared to an EMG trace of the same action. The larynx is a hollow muscular organ situated in the front of the neck above the trachea consisting of a framework of cartilages bound together by muscles and ligaments. The two major functions of the larynx are deglutition and phonation. Dysphagia, which is becoming more prevalent as the population ages, is defined as difficulty in swallowing thin liquids such as water or juices which splash into the trachea because the patient is unable to control the thin liquid bolus. Aspiration pneumonia and dehydration can be prevented by using thickened liquids which allow patients to achieve a safer swallowing response, but it is difficult to assess this response without interfering with the swallowing process. Impedance pharynography (IPG) is a technique using BIA to monitor an impedance waveform of the swallowing process that presents no radiation hazard to the patient, is non-invasive and does not require specialist trained personnel to operate it. Resistance changes across the neck were measured while subjects swallowed solutions of different viscosities. The resistance changes were distinctive and reproducible for each of the solutions of different viscosities which were swallowed. Measuring the function of the larynx by this method could be useful in the diagnosis and treatment of dysphagia. In conclusion, the studies described in this thesis demonstrate the potential usefulness of the measurement of change in impedance as a measure of muscle activity. Impedance-based methods can measure volume changes associated with changes in cross-sectional area of the muscles involved in contraction as well as compartmental fluid changes caused by the force of the contraction on the surrounding tissues including the vasculature. In particular, measuring the ejection fraction and other haemodynamic variables of the calf muscle pump by impedance has the potential to become the method of choice in the future because it is easy to use, inexpensive, non-invasive, safe, and hygenic. Measuring resistance changes across the neck during swallowing yields distinctive waveforms with features corresponding to the physiological phases of the swallowing process as well as identifying distinctive swallowing patterns associated with the different viscosities of liquids swallowed. Function of the larynx and the associated diseases of the larynx will potentially be easier to diagnose and treat with a safe, non-invasive, inexpensive, portable bed-side method of assessment such as BIA.