L’archipel du Cap Vert constitue de 10 iles volcaniques appartient a la zone sahelienne qui s’etend de l’atlantique jusqu’a la mer rouge. Depuis, plusieurs decennies le Cap Vert est affecte par la desertification causee en grande partie par la recession climatique et l’erosion des sols. Ces facteurs, associes a la forte pression anthropique sur les ressources, a l’orographie accidentee et a des pluies tropicales parfois diluviennes, provoquent de serieuses pertes du patrimoine foncier. Cependant, depuis son Independance en 1975, le Gouvernement a mene un vaste programme d’arborisation, de restauration des terres et d’amenagement des cours d’eau. Pourtant, tres peu de recherches ont ete menees pour evaluer les actions de protection et de conservation des sols et des eaux. Par consequent, il n’existe quasiment pas de donnees sur la problematique de la degradation des terres ni de bilans. Dans le cadre de ce travail, nous avons etudie les differents facteurs qui controlent l’erosion hydrique des sols. Nous avons plus particulierement cherche a differencier les effets des activites humaines, notamment agricoles, de ceux des facteurs climatiques comme les precipitations et la generation des ecoulements. Nous avons egalement etabli les premiers bilans d’exportations de matieres en suspension et en solution dans le contexte de l’archipel du Cap Vert. L’etude a ete menee a l’echelle de trois bassins versants de l’ile de Santiago Cap-Vert. Ces trois bassins versant (Longueira, Grande et Godim) sont localises dans la partie centrale de l’ile de Santiago et representatifs des divers modes d’occupation du sol et des differents climats de l’ile. Il existe un gradient climatique entre les trois bassins versants. En effet, Longueira qui presente une superficie de 4,18 km2, une pente moyenne de 47 %, se localise dans une zone humide couverte a 69 % par une foret et une surface agricole de 17 %. Grande avec une superficie de 1,87 km2, se localise en zone sub humide pour une pente moyenne de 50 %, il est essentiellement agricole. Godim, avec une superficie de 2,0 km2, se localise en zone semi aride, il est particulierement agricole et sa pente moyenne est de 32 %. Pour ces trois bassins versants, les ecoulements de crue a l’exutoire ont ete mesures et echantillonnes de 2004 a 2009. Le bassin versant de Longueira a fait l’objet d’un suivi plus pousse, notamment en termes de frequence d’echantillonnage et de suivi des ecoulements hors crue. Sur chaque echantillon nous avons procede a la determination de la concentration des matieres en suspension ainsi qu’a l’analyse des elements majeurs. Les resultats obtenus montrent que l’erosion mecanique dans les 3 bassins versants est caracterisee par une forte variabilite spatiale et temporelle. Sur la periode 2005-2009, le bilan moyen annuel pour les bassins versants de Longueira, Grande et Godim est de : 4266, 157 et 10,1 t.km2.an-1 respectivement. La saison humide 2006 a ete la plus erosive pour l’ensemble des trois bassins versants et particulierement dans Longueira avec 2 crues exceptionnelles qui ont genere une concentration moyenne de matieres en suspension superieure a 100 g/l. En revanche, les saisons 2005 et 2008 ont ete dans l’ensemble peu erosives car les concentrations moyennes ne depasserent pas 20 g/l. Par ailleurs, il n’y a pas eu de lames d’eau ecoulees pour les saisons 2005 et 2007 pour le bassin de Godim. Sur le bassin de Longueira, l’etude des phenomenes d’hysteresis permet de caracteriser chaque crue et de montrer que l’evolution temporelle des exportations de matieres en suspension au cours de la saison est fortement influencee par les activites agricoles. En effet, la premiere crue provoque l’exportation massive des sediments disponibles et localises dans le lit du cours d’eau. En consequence, la seconde est moins exportatrice de sediments. etc / The archipelago of Cape Verde comprises 10 volcanic islands and belongs to the Sahelian zone stretching from the Atlantic to the Red Sea. Since several decades, Cape Verde is affected by desertification caused largely by climatic recession and soil erosion. These factors, coupled with high population pressure on resources, rugged topography and torrential tropical rains, cause serious losses of lands. However, since its independence in 1975, the Government conducted an extensive program of afforestation, soil and water conservation. Nevertheless very little research has been conducted to evaluate the actions of protection and conservation of soil and water. Therefore, there is no data on the problem of land degradation or budget. As part of this work, we studied the various factors that control soil erosion by water. Specifically, we sought to differentiate the effects of human activities including agriculture, those climatic factors such as rainfall and runoff generation. We also established the first mass budget of suspended and dissolved load in the context of the archipelago of Cape Verde. The study was conducted across three watersheds of the Santiago Island, Cape Verde. These three watersheds (Longueira, Grande and Godim) are located in the central part of the island and are representative of various types of land use and of the different climates of the island. There is a climatic gradient between the three watersheds. Indeed, Longueira which covers an area of 4.18 km2, an average slope of 47 % is localized in a humid zone and covered to 69 % by forest and the agricultural area is 17 %. Grande with an area of 1.87 km2, is localized in sub humid zone for an average slope of 50 %, it is mainly agricultural. Godim, with an area of 2.0 km2, is localized in semi arid, it is particularly agriculture and its average slope is 32 %. For these three watersheds, flood flows at the outlet were measured and sampled from 2004 to 2009. Watershed Longueira has been further monitoring, particularly in terms of sampling and monitoring of flood flows out. On each sample we determined the concentration of suspended sediment and we analyzed dissolved major elements. The results show that mechanical erosion in the three watersheds is characterized by high spatial and temporal variability. Over the period 2005-2009, the average annual budget for Longueira, Grande and Godim watersheds is: 4266, 157 and 10.1 t.km2.an-1 respectively. The wet season 2006 was the most erosive for all three watersheds, particularly in Longueira with 2 exceptional floods that have generated an average concentration of suspended sediment exceeding 100 g/l. In contrast, the seasons 2005 and 2008 have been generally low erosive because mean concentrations did not exceed 20 g/l. Moreover, there was no runoff for the seasons 2005 and 2007 for the watershed of Godim. In Longueira watershed, the study of hysteresis phenomena can characterize each flood and show that the temporal evolution of suspended sediment yield during the season is strongly influenced by agricultural activities. Indeed, the first flood caused the massive export of sediment available and located in the bed of the watercourse. Accordingly, the second exported less sediment. One month after the first rains, weeding activities decreased the density of vegetation cover and deconstruct the superficial soil, which again caused a very strong export of sediments during the third run off. The results of the chemical erosion in the watershed of Longueira indicate that the budget of chemical erosion rate is 45 t.km-2.an-1 with a strong temporal variability. Indeed, the wettest seasons of 2006 and 2007 are the most export of dissolved load, whereas 2005 had a low export. The use of model mixtures EMMA (End-Members Mixing Analysis) shows that the interflow and deep, feeding the streams in dissolved elements are the main factors of chemical erosion. etc

The thesis deals with analysis of conceptual-methodological issues examined in the framework of post-keynesian economics. The author´s goal is to supply a solution to the problem of a definition of determinism/non-determinism for both deterministic and stochastic systems and also to the problem of the prevailing confusion which surrounds the notion of reversibility/irreversibility in both path-dependent and traditional-equilibrist systems. The author regards the determinism/non-determinism problem as essentially linked to the problem of a definition of fundamental uncertainty. The key issues are being identified in the "problem of a generator of endogenous shocks" and the "selection - creation problem". Finding solutions to these enables us to take a stand on the validity/invalidity of the classical dichotomy, in the eyes of the author. Davidson´s interpretation of ergodicity and O´Donnell´s critique of this are being presented and, drawing on the latter, along with Álvarez-Ehnts´ critique, the author rejects a simplifying pattern of Davidson´s, according to which neoclassical economics is based on the ergodic axiom. The author suggests a solution to the "selection - creation problem" consisting in distinguishing epistemological determinism from ontological determinism on the one hand, and epistemological determinism from epistemological non-determinism on the other hand. While selection is a characteristic feature of epistemological determinism and, in effect, the realm of "fundamental certainty", creation is referred to by the author as a characteristic feature of epistemological non-determinism, i. e., in effect, the realm of fundamental uncertainty. The author regards the "problem of a generator of endogenous shocks" a self-contradictory notion, based on the principle of causality and the law of non-contradiction, and suggests a solution to the problem consisting in rejection of the concept of shock endogeneity. At the same time, the author rejects Davidson´s "fundamental neoclassical article of faith" rhetoric, based on the first cause argument implied by the principle of causality. In opposition to Davidson, the author regards fundamental uncertainty being of a basically epistemological nature, consisting in our ignorance of the "ultimate law of change", the "Devine formula". Unlike O´Donnell, however, who puts stress on the element of epistemological uncertainty in his epistemological approach to uncertainty, the author also puts stress on the element of ontological certainty, consisting in our knowledge of the existence of the "Devine formula", apart from our epistemological uncertainty.

Orientador: Flávio César Guimarães Gandra / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-30T17:33:36Z (GMT). No. of bitstreams: 1 Monteiro_JoseCarlosBotelho_D.pdf: 10216375 bytes, checksum: 06d25402d8c5828939f2e7fa0710efbe (MD5) Previous issue date: 2016 / Resumo: Esta tese tem como principal objetivo desenvolver, apresentar e justificar a utilização de uma metodologia experimental que permita avaliar o efeito magnetocalórico (EMC), em qualquer tipo de material, de modo que as medidas reflitam a resposta real que a amostra fornece ao ser submetida a ciclos de magnetização similares àqueles que ocorrem em sistemas de refrigeração magnética. Para tal, construímos sistemas de medidas que utilizam dispositivos Peltier como sensores de fluxo de calor, capazes de realizar medidas diretas da quantidade de calor que a amostra absorve ou libera em situações aonde há variação de temperatura, campo magnético ou do ângulo entre direção do cristal e o campo aplicado. Na primeira parte do trabalho, foram realizadas medidas no sistema com dispositivos Peltier desenvolvido para uso no equipamento comercial PPMS - Physical Property Measurement System (Sistema de medidas de propriedades físicas) da Quantum Design. Utilizamos os métodos indiretos de medida do EMC mais comuns na literatura (medidas via curvas de magnetização e calor específico) para comparação com as medidas diretas de fluxo de calor através de varredura de campo obtidas pelo nosso sistema. Esta análise foi feita inicialmente em duas amostras com transições magnéticas de primeira e segunda ordem, consideradas como amostras padrão na área do EMC: Gadolínio e a liga Gd5Ge2Si2. Discutimos as diferenças encontradas e definimos aquele que acreditamos ser o protocolo de medidas mais correto para a avaliação do EMC para fins práticos. A partir desta conclusão, analisamos três outras amostras que apresentam comportamentos não usuais e alto potencial magnetocalórico e discutimos as diferenças. Perdas do EMC por histerese foram obtidas experimentalmente. Na segunda parte, com o auxílio de um calorímetro com o elemento Peltier capaz de realizar um giro de até 80° sob campo constante de até 1,9 T, realizamos o estudo do efeito magnetocalórico anisotrópico (EMC-ani) em amostras monocristalinas da família RAl2, obtidas pelo processo de Czochralski. Primeiramente medidas de calor específico e do EMC convencional foram realizadas nos monocristais, através do protocolo definido como ideal na primeira parte do trabalho, utilizando o sistema Peltier do PPMS. A partir desses dados, fomos capazes de obter o EMC-ani, de modo indireto, pela subtração das curvas obtidas. Por fim utilizamos o sistema Peltier de giro para realizar medidas diretas do EMC-ani em monocristais de DyAl2. Os resultados das medidas indiretas e diretas foram comparados com cálculos obtidos através de um modelo autoconsistente / Abstract: This thesis aimed to develop, present and justify the use of a methodology that allows one to evaluate the magnetocaloric effect (MCE), for any kind of material, such that the results reflects the real behavior of the sample submitted to magnetization cycles similar to those of magnetic refrigeration systems. To do so, we built measurement systems that uses Peltier devices as heat flux sensors to determine the heat absorbed or released by the sample in situations where the temperature, magnetic field, or angle between a given crystal direction and field changes. In the first part of the work, we report measurements using a Peltier device system developed for use with the Quantum Design PPMS (Physical Property Measurement System). We evaluated the indirect MCE measurements by using the most common techniques found in literature (through magnetization or specific heat curves) and compared to the direct heat flux measurements obtained through field sweep scans with our system. This analysis was initially made with two samples that present a first and a second order magnetic transition, considered as standard samples at MCE research area: Gadolinium and the Gd5Ge2Si2 alloy. We discussed the differences found and defined the measurement protocol that we believe to be correct to the practical evaluation of the MCE. From this conclusion, we analyzed three other samples that present uncommon behavior and high magnetocaloric potential and discussed their differences. MCE hysteresis losses were experimentally obtained. In the second part, with the aid of a calorimeter built with Peltier devices capable of perform an 80° rotation under constant magnetic field up to 1,9 T, we made the study of the Anisotropic Magnetocaloric Effect (MCE-ani) in monocrystalline samples of the RAl2 family grown by the Czochralski method. First, we made specific heat and conventional MCE measurements with the ideal protocol that was defined in the first part of the work, using the PPMS Peltier system. From these data, we were able to calculate indirectly the MCE-ani by subtracting the acquired curves. Finally, we used the Peltier rotation system to perform direct measurements of the MCE-ani in DyAl2 single crystals. The results of the indirect and direct measurements were compared with calculations achieved using a self-consistent process / Doutorado / Física / Doutor em Ciências / 1060137/2011 / CAPES

Dans un contexte de réchauffement climatique et de fin programmée des énergies fossiles, le secteur du bâtiment vise à réduire de 38% sa consommation d’énergie et à atteindre 10% de matériaux bio-sourcés utilisés dans la construction à l’horizon 2020. Ainsi, le béton de chanvre peut jouer un rôle majeur grâce à son bilan environnemental et à ses propriétés hygrothermiques qui lui permettent d’assurer un rôle d’amortisseur thermique et de stabilisateur de confort. Or le comportement hygrothermique du béton de chanvre à l’échelle du bâtiment est peu abordé dans la littérature et jamais pour les bâtiments tertiaires. L’objectif principal de ce projet est de combler ce vide en étudiant et en optimisant les performances énergétiques d’un bâtiment en béton de chanvre destiné à usage de bureaux et/ou de salles d’enseignement. Afin d’assurer le confort thermique intérieur différentes solutions techniques seront couplées au bâtiment et comparées entre elles : - une ventilation double flux thermodynamique associant une pompe à chaleur à une centrale double flux. - Une ventilation simple flux associé à un puits canadien qui récupère la chaleur du sous-sol pour préchauffer l’air de ventilation en hiver ou le rafraîchir en été. - Une ventilation double flux associé à un puits canadien. Par le biais de la simulation numérique et de mesures faites d’abord à l’échelle des composants, il sera ainsi possible d’évaluer le potentiel de chaque composant sur l’énergétique et le confort hygrothermique de bâtiments tertiaires intégrant principalement le périmètre du projet Grand Campus de Reims mais également pouvant être élargi à la spécificité d’autres climats français. / In a context of global warming and planned end of fossil fuels, the construction industry aims to reduce by 38% its energy consumption and to achieve 10% of bio-based materials used in construction in 2020. Thus, the hemp concrete can play a major role thanks to its positive environmental impact and its hygrothermal properties that allow it to ensure a role of heat damper and comfort stabilizer. Or hygrothermal behavior of hemp concrete throughout the building is little discussed in the literature and never for commercial buildings. The main objective of this project is to fill this gap by studying and optimizing the energy performance of a hemp concrete building designed for offices and / or classrooms. To ensure inside thermal comfort, different technical solutions will be coupled to the building and compared with each other: - A double flow thermodynamical ventilation combining a heat pump with a double flow central. - A simple flow ventilation associated to a pipe system which recovers heat from the basement to preheat ventilation air in winter and cool in the summer. - A double flow ventilation associated to a Canadian well. Through computer simulation and measurements made initially at the level of components, it will be possible to evaluate the potential of each component on the energy and hygrothermal comfort of commercial buildings mainly integrating the project boundary Grand Campus Reims but also can be extended to other French specificity climates.

We report the experimental observation of hysteresis-free negative capacitance (NC) in thin ferroelectric Hf₀.₅Zr₀.₅O₂ (HZO) films through high-speed pulsed charge-voltage measurements. Hysteretic switching is suppressed by the addition of thin Al₂O₃ layers on top of the HZO to prevent the screening of the polarization. We observe an S-shaped polarization-electric field dependence without hysteresis in agreement with Landau theory, which enables direct extraction of NC modeling parameters for ferroelectric HZO. Hysteresis-free NC is demonstrated down to 100 ns pulse widths limited only by our measurement setup. These results give critical insights into the physics of ferroelectric NC and practical NC device design using ferroelectric HZO.

The diploma thesis is structured with regard to the design and use of artificial muscle in robotics. The thesis starts with a theoretical section where different types of artificial muscles are described with their advantages and disadvantages. After considering all the types of described muscles, one species was selected for further processing. Vacuum-controlled origami muscles were chosen for use in a small manipulation device. After the design of the whole machine, the risk analysis and the economic evaluation of the whole design were carried out.

This thesis deals with computer modeling of temperature hysteresis during phase change, namely complete and partial phase change. There is performed a review of methods for modeling temperature hysteresis based on the enthalpy method and the effective heat capacity method. In the case of complete phase change, there are several methods that use the effective heat capacity method, as well as the heat source method, which, on the contrary, is a certain analogy of the enthalpy method. The following are works dealing with modelling of partial phase change, the most interesting of which is due to the validation method of static hysteresis and the method designed by Bony and Citherlet. The second part of this thesis deals with the hysteresis behavior of the material with phase change, which is organic paraffin RT 27. The input data obtained by differential scanning calorimetry was converted to the dependence of the enthalpy on temperature. These curves was represented by piecewise linear function. In the case of partial phase transformations, a modeling method based on the methods proposed by Bonym and Citherlet was designed. An one-dimensional model enabling thermal simulation of the material was implemented in the MATLAB software environment. The results obtained with this simulation are finally compared with a model that does not consider thermal hysteresis.

<div>We propose an order parameter theory of the quantum Hall nematic in high fractional Landau levels in terms of an Ising description. This new model solves a couple of extant problems in the literature: (1) The low-temperature behavior of the measured resistivity anisotropy is captured better by our model than previous theoretical treatments based on the electron nematic having XY symmetry. (2) Our model allows for the development of true long-range order at low temperature, consistent with the observation of anisotropic low-temperature transport.<br></div><div><div> We furthermore propose new experimental tests based on hysteresis that can distinguish whether any two-dimensional electron nematic is in the XY universality class (as previously proposed in high fractional Landau levels), or in the Ising universality class (as we propose). Given the growing interest in electron nematics in many materials, we expect our proposed test of universality class to be of broad interest.</div><div> </div><div> Whereas the XY model in two dimensions does not have a long-range ordered phase, the addition of uniaxial random field disorder induces a long-range ordered phase in which the spontaneous magnetization points perpendicular to the random field direction, via an order-by-disorder transition. We have shown that this spontaneous magnetization is robust against a rotating driving field, up to a critical driving field amplitude. Thus we have found evidence for a new non-equilibrium phase transition that was unknown before in this model. Moreover, we have discovered an incredible anomaly at this nonequilibrium phase transition: the critical region is accompanied by a cascade of period multiplication events. This physics is reminiscent of the period bifurcation cascade signaling the transition to chaos in nonlinear systems, and of the approach to the irreversibility transition in models of yield in amorphous solids~\cite{reichhardt-dahmen,leishangthem_yielding_2017}. This period multiplication cascade is surprising to be present in a statistical mechanics model, and suggests that the non-equilibrium transition as a function of driving field amplitude is part of a larger class of transitions in dynamical systems.</div><div> Moreover, we show that this multi-period behavior represents a new emergent classical discrete time-crystal, since the new period is robust against changes to initial conditions and low-temperature fluctuations over hundreds of driving period cycles.</div><div><br></div><div> We expect this work to be of broad interest, further encouraging cross-fertilization between the rapidly growing field of time-crystals with the well-established fields of nonequilibrium phase transitions and dynamical systems.</div><div> </div><div> Geometrical configurations gave us a better understanding of the multi-period behavior of the limit-cycles.</div><div> Moreover, surface probes are continually evolving and generating vast amounts of spatially resolved data of quantum materials, which reveal a lot of detail about the microscopic and macroscopic properties of the system. <br></div><div> Materials undergoing a transition between two distinct states, phase separate.</div><div> These phase-separated regions form intricate patterns on the observable surface, which can encode model-specific information, including interaction, dimensionality, and disorder. </div><div> While there are rigorous methods for understanding these patterns, they turn out to be time-consuming as well as requiring expertise. </div><div> We show that a well-tuned machine learning framework can decipher this information with minimal effort from the user.</div><div> We expect this to be widely used by the scientific community to fast-track comprehension of the underlying physics in these materials.</div><div><br></div></div>

Na-ion batteries (NIBs) are expected to revolutionise the battery sector by promising an affordable technology while capitalising on sustainable development. To compete with Li-ion batteries, however, electrode materials with higher capacities need to be developed. Transition metal nitroprussides (TM-NPs), NaxM[Fe(CN)5NO]1-y ·zH2O, is a material class derived from one of the most popular positive electrode materials for NIBs, Prussian blue analogues (PBAs), where one of the cyano ligands have been replaced by an electroactive nitrosyl (NO) ligand. Thus, in theory TM-NPs should be able to reach higher capacities than PBAs and therefore be attractive candidates for high-capacity electrodes. However, if the nitrosyl is redox active in NIBs and how the cycling behaviour may be affected by the M cation is unknown. The focus in this thesis is therefore to explore the charge-discharge behaviour of four different TM-NPs (M=Fe, Ni, Mn, and Cu) in Na-ion half-cell batteries to gain an initial understanding of their electrochemical behaviour and to set up research questions to be pursued in the future. Based on our observations and previous studies, we propose that the nitrosyl is electrochemically active in all four TM-NPs, and that it contributes with a considerable amount of capacity, although with a large voltage hysteresis. It is further concluded that all M cations apart from Ni were redox active, but to varying degrees on charging and discharging. We argue that both the redox and the voltage hysteresis is caused by anisotropic charge transfer within the materials, and that it needs to be understood before commercialisation of TM-NPs can be realised. Though there are challenges to overcome, the many interesting attributes of TM-NPs, including anionic redox, anisotropic charge transfer and structural diversity, makes them promising as a new type of cheap and sustainable electrode material for NIBs.

To overcome the fundamental limit of the transistor subthreshold swing of 60 mV/dec at room temperature, the use of negative capacitance (NC) in ferroelectric materials was proposed [1]. Due to the recent discovery of ferroelectricity in CMOS compatible HfO₂ and ZrO₂ based thin films [2], [3], the promise of ultra-low power steep-slope devices seems within reach. However, concerns have been raised about switching-speed limitations and unavoidable hysteresis in NC devices [4], [5]. Nevertheless, it was shown that NC effects without hysteresis can be observed in fast pulsed voltage measurements on ferroelectric/dielectric capacitors [6], which was recently confirmed using ferroelectric Hf₀.₅ Zr₀.₅ O₂[7], [8]. While in these works only the integrated charge after each pulse was studied, here we investigate for the first time if the transient voltage and charge characteristics are also hysteresis-free.