Située à l'interface entre les eaux de surface et les eaux souterraines, la zone hyporhéique (ZH) est depuis maintenant plusieurs décennies considérée comme une zone cruciale pour la préservation des milieux aquatiques. Elle constitue souvent un indicateur fiable de la bonne qualité des eaux et une niche écologique primordiale pour de nombreuses espèces. Mais elle est aussi le lieu d'interaction entre deux masses d'eau de signature différente, ce qui conduit à la formation d'un milieu extrêmement fragile et siège d'un grand nombre de réactions biogéochimiques. L'objectif principal de cette thèse est de parvenir à une meilleure compréhension de la dynamique des échanges au sein de la zone hyporhéique. L'approche de cette problématique s'est faite sous un aspect innovant en couplant une démarche hydrogéologique "classique" à l'aide de mesures hydrodynamiques et géochimiques, et l'utilisation de la tomographie de résistivité électrique (ERT). Plusieurs campagnes de terrain ont été menées sur la rivière Essonne, choisie comme lieu d'expérimentation. Différents outils de prélèvement et/ou de mesure ont été mis en place et un grand nombre de mesures à différentes périodes de l'année ont été réalisées. Des expériences assez techniques et innovantes de suivi d'un abaissement et relèvement de barrage, ainsi qu'un traçage artificiel au sel ont pu être effectués grâce à la collaboration avec le syndicat chargé de la gestion et l'aménagement d'une partie du réseau hydrographique de l'Essonne (SIARCE). En parallèle avec cette étude expérimentale, une maquette numérique 3D de la zone d'étude a été réalisée à l'aide du logiciel HydroGeoSphere. Des tests de sensibilité ont permis d'identifier les paramètres hydrodynamiques les plus importants et de quantifier leur impact sur la formation et l'évolution de la zone hyporhéique. Finalement, les premières simulations des expériences menées sur le terrain ont permis de confronter l'approche expérimentale et l'approche théorique. / The Hyporheic Zone (HZ) is located at the interface between surface water and groundwater. For several decades it is considered as a hotspot for the development of a rich aquatic environment in rivers. Its system is often considered as a reliable indicator for water quality and a primary ecological niche for many species. From a hydrological point of view, it is also the place of interaction between two distinct water bodies with different geochemical signatures. This place of mixing forms a very fragile equilibrium where many biogeochemical reactions can occur. The objective of this thesis is to reach a better understanding of mixing and water fluxes in a dynamic context within the hyporheic zone. An innovative method was used by coupling a "classic" hydrogeological approach with hydrodynamic and geochemical measurements with Electrical Resistivity Tomography (ERT). Several field campaigns were done on the Essonne river as experimental site. A large number of measurements were done at various periods of the year and field equipment for water sampling and measurements were installed during these three years. Technical and innovative experiments were conducted such as a dam lowering and rising and an artificial salt tracer test in collaboration with the federation in charge of organization and management of the Essonne network. Finally, a 3D-model of the studied area was built with the HydroGeosphere software. The main hydrodynamic parameters have been tested in order to understand their impact and their variation in a static or dynamic environment on the hyporheic system and its development. In addition, field experiments were reproduced to compare the experimental and theoretical approach.

Orientador: Cesar Augusto Moreira / Resumo: Uma barragem de rejeitos é constituída por uma barreira física, cuja função é a acumulação de produtos residuais do processo industrial de beneficiamento mineiro. Os métodos de projeto para barragens de rejeitos diferem das barragens de retenção de água pela construção do barramento em diferentes etapas. Deste modo, os problemas de estabilidade em uma barragem são de grande importância, principalmente quando se trata de barragens construídas para armazenamento destes rejeitos de mineração, uma vez que a possibilidade de falhas não apenas ameaça a segurança das pessoas e da propriedade industrial, mas também pode causar impactos ambientais substanciais. No Estado de Minas Gerais, aproximadamente 30 km a sudoeste do município de Caldas, está localizada a Mina Osamu Utsumi de responsabilidade das Indústrias Nucleares do Brasil (INB), a qual tem um sistema para contenção de rejeitos provenientes da exploração e processamento de urânio, atualmente desativado. O Sistema consiste em uma barragem de rocha e terra a qual apresenta a existência de surgências no maciço rochoso à jusante do barramento, cujo fluxo ocorre em sistema fraturado. O objetivo do trabalho é reconhecer possíveis zonas de fluxo no interior e na base da barragem por meio de um conjunto de ensaios geofísicos de eletrorresistividade adquiridos com a técnica de tomografia elétrica através de modelos de inversão 2D e modelamento 3D. Foram adquiridas 5 linhas de tomografia elétrica com espaçamento entre eletrodos de 6 m... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: A tailings dam is constituted by a barrier, whose function is the accumulation of residual products from the mining beneficiation industrial process. Project methods for tailings dams differ from water retention dams by the construction of the dam in different stages. Thus, the stability problems in a dam are of great importance, especially when it comes to dams built for the storage of these mining waste, since the possibility of failures not only threatens the safety of people and industrial property, but also cause negative and substantial effects to the local environment. The Osamu Utsumi uranium mine, administrated by the state company Industrias Nucleares do Brasil (INB), is located 30 km southwest of Caldas, in the State of Minas Gerais, and its contention system of tailings, generated by the exploration and processing of uranium ore, is currently out of operation. The system is composed of a rock-soil dam, which presents the existence of water upwellings downstream in the bedrock, with water flux confined in fractures. This research aims the recognition of possible flux zones into the base of the dam through geophysical surveys applying DC Resistivity, in addition to Electrical Resistivity Tomography technique in the generation of 2D inversion models and 3D modeling. The acquisition was composed of five lines of electrical resistivity tomography with 6 m of spacing between electrodes, using Schlumberger array. The results are presented by 2D and 3D geophysical models ... (Complete abstract click electronic access below) / Mestre

Title: The magnetocrystalline anizotropy in the TbTX compounds Author: Milan Klicpera Department: Department of Condensed Matter Physics Supervisor: doc. Mgr. Pavel Javorský, Dr. Supervisor's e-mail address: javor@mag.mff.cuni.cz Abstract: The subject of this work is the study of structural, magnetic and trans- port properties of the TbNi(Al,In) series to finding connections between magne- tocrystalline anisotropy and lattice parameters of the structure of the TbTX com- pounds. Polycrystalline TbNiAl1−xInx samples were prepared by melting. The phase and crystal structure analysis were provided on samples. We performed the measurements of the magnetization, susceptibility, specific heat, resistivity, low temperature X-ray diffraction and powder neutron diffraction. From the neutron diffraction data we refined lattice parameters and propagation vectors of the series. The main propagation is (000) and second weaker component has the propagation vector (1 2 0 1 2 ). The change of the magnetocrystalline anisotropy from uniaxial to planar type occurs for compounds with x between 0.4 and 0.5. Keywords: magnetization, X-ray and neutron diffraction, electrical resistivity.

Title: Defects limiting charge collection in semiinsulated CdZnTe Author: Vít Zajac Department: Institute of Physics of Charles University Supervisor: doc. Ing. Jan Franc, DrSc., Institute of Physics of Charles University Abstract: We achieved to detect photoluminescence transitions deep in the band gap in 4 samples cut from 2 different crystals of semiinsulating Cd1-xZnxTe (x = 0,02 - 0,18) in a row of points along the growth axis. The spectral peaks give evidence of the presence of deep levels in the sample and the intensity of the photoluminescence peaks is to a certain extent proportional to the concentration of these levels. A comparison between resistivity and photoconductivity that were measured by a contact-less method showed that the change of photoluminescence intensity of deep levels does not bring about an unambigous change of neither resistivity nor photoconductivity. Correlation analysis of resistivity and photoconductivity of 6 samples from 4 different crystals confirmed the following model: A shift of the Fermi level within the band gap induced by a change of donor-acceptor compensation is accompanied by an unambigous change of resistivity and results in a change in occupation of the deep levels. This causes a change in the photoconductivity of the crystal because the occupation factor of...

Masters of Science / Rare-earth (RE) compounds have been an attractive subject, based on the unique electronic structures of the rare-earth elements. In particular, the RETX (RE = rare-earth, T = 3d/4d/5d, transition metals, and X = p – block elements) series is a large family of intermetallic compounds which crystallizes in different crystal structure depending on the constituents. Most of these compounds crystalize in the hexagonal, orthorhombic, and tetragonal crystal structure. On the other hand, the family of compounds RET2X2 adopted the tetragonal crystal structure of the ThCr2Si2 or the CaBe2Be2 with different space groups. Owing to the different crystal structure, these compounds show versatile magnetic and electrical properties such as Kondo effect, complex magnetic behaviour, valence fluctuation, unconventional and conventional superconductivity, heavy fermion behaviour, Fermi and non – Fermi liquid behaviour, metamagnetism, spin – glass, memory effect, crystal electric field (CEF), magnetoresistance and magnetocaloric effect. The history of magnetism reveals that it is closely related to practical applications and magnetic materials from the most vital components in many applications. These are memory devices, permanent magnets, transformer cores, magneto-mechanical devices and magneto-electronic devices. Recent additions to this list include magnetic refrigeration through the studies of magnetocaloric effect as well as spintronics. Magnetic refrigeration (MR) is an emerging technology and shows real potential to enter conventional markets and the principles of MR obeys the magnetocaloric effect (MCE), which is based on the effect caused by a magnetic field on the materials that accept the property of varying the magnetic entropy, as well as its temperature when varying the magnetic field. In this thesis, we report giant magnetocaloric effect and magnetic properties of NdPd2Al2 and RECuGa (RE = Nd, Dy, and Ho) compounds. These investigations were done through measurements of X – ray diffraction (XRD), magnetic susceptibility, ((T)), magnetization, (M(H)), isothermal magnetization, (M(H, T)), heat capacity, (Cp(T)) and electrical resistivity, ((T)). MCE has been studied from the isothermal magnetization and heat capacity measurements.The first chapter of the thesis describes the theoretical background from which the experimental results have been analyzed and interpreted. This is followed by the chapter which presents experimental details and methodology carried out in this thesis. Chapter three presents the results and discussion of the transport, magnetic and magnetocaloric properties of NdPd2Al2 compounds. XRD studies confirm the tetragonal CaBe2Ge2 – type structure with space group P4/nmm (No. 129). The results of (T), (T) and Cp(T) indicate a putative antiferromagnetic (AFM) phase transition at low temperature at, TN = 3 K. On the other hand, (T) data at high temperatures follow the Curie – Weiss relationship giving an effective magnetic moment close to that expected for the trivalent Nd3+ ion. The magnetization results indicate metamagnetic – like transition at a low field that bears a first-order character which corroborates with the Below – Arrott plots. Giant MCE was obtained for the NdPd2Al2 compound similar to those reported for potential magnetic refrigerant materials. Chapter four discusses the magnetic and thermodynamic properties of the series of compounds RECuGa where RE = Nd, Dy, and Ho. XRD studies indicate the orthorhombic CeCu2 – type crystal structure with space group Imma (No. 74) for all three compounds. Magnetic measurements indicate a putative AFM phase transition below 𝑇𝑁 = 7.1, 8.5, and 3.7 K for Nd, Dy, and Ho compounds, respectively. The high-temperature (T) data for all three compounds follow the Curie – Weiss relationship giving an effective magnetic moment close to that expected for the trivalent rare-earth ion. Again, large MCE were obtained for all three compounds similar to those reported for materials that can be used as magnetic refrigerant materials.

Transportation is a large and growing part of the world’s energy consumption. This drives a need for reduced weight of rail vehicles, just as it does for road vehicles. In spite of weight reductions, the vehicle still has to provide the same level of acoustic comfort for the passengers. Porous materials, with more than 90% air, are often included in multi-layer vehicle panels, contributing to acoustic performance without adding much weight. Here the acoustic performance of open cell porous materials, with focus on flow resistivity, is evaluated based on simplified micro-structure models to investigate the effect of anisotropy on the performance In order to evaluate how the redistribution of material affects the flow resistivity, the porosity of the material is kept constant. Two micro-geometries are analysed and compared: the hexahedral model and the tetrakaidecahedron (Kelvin cell). For flow resistivity calculations the solid frame is assumed to be rigid. The models are elongated in one direction to study the influence of micro-structural anisotropy on the macro level flow resistivity. To keep porosity constant, two different approaches are investigated. The first approach is to let strut thickness be uniform and adjust the volume of the cell to a constant ratio compared to the isotropic case. The second approach is to let the strut volume, and cell volume, be constant. For an anisotropic hexahedral cell with uniform strut thickness, the flow resistivity increases substantially with increasing height to width ratio for the hexahedral model, while the flow resistivity for the tetrakaidecahedron model with uniform strut thickness decreases with increasing height to width ratio. For both geometries and constant strut volume, the average flow resistivity is close to the same constant value. For uniform strut thickness the relative volume of anisotropic to isotropic volume is very important. / <p>The work has been carried out within the Centre for ECO² Vehicle Design.</p><p></p><p>QC 20160523</p>

The investigation of environmental impacts of 16 different contaminants originating from the E18 Highway (17 000 AADT) were carried out over the first six months of the highway‘s operational life. Investigative methods used include electrical resistivity surveying, water chemistry analyses, soil analyses, distribution modelling and transportation modelling. The investigation shows conclusively a year round infiltration due to melting of the snowpack from road salt, and a strong preferential anthropogenic pathway due to in-creased hydraulic conductivities of the road building materials relative to the natural soils. The resistivity surveys show values well below the expected values for the highway materials, indicating increased ionic content of the unsaturated zone. Time lapse resistivity modelling shows a clear downwards spreading of contamination from the roadway to subsurface distances greater than 5 m. Elevated concentrations of nearly every contaminant relative to baseline values were observed, with many concentrations of metals in the snow pack averaging values in excess of Swedish EPA groundwater limitations. Distribution modelling demonstrated a potential offset of peak values from the road surface due to ploughing and splash transport processes, but otherwise conformed to established distribution patterns. One dimensional transport modelling demonstrated the importance of adsorption and other retentive factors to the migration of contaminants to the water table, and provided an estimate for potential long term contaminant concentrations.

This thesis is a study of tailoring amorphous Fe-B-Si based alloy to produce bulk glassy rods by adding Nb. We have prepared rapid quenched thin ribbons (thickness ~12 µm) by melt spinning, and glassy rods of diameter ~1mm by Cu-mold casting based on compositions (Fe0.78B0.13Si0.9)100-xNbx (x=0, 4, 8, 12), and studied their different physical properties. The melt-spun ribbons are found to be X-ray amorphous, whereas some nano-crystallinity is observed in the case of rods. All the ribbons show high saturation magnetization and low coercivity, which are the desirable characteristics of a soft ferromagnet. These ribbons are thus suitable for designing high frequency transformers, and sensors from an applications point of view. With increasing Nb content their saturation magnetization, ferromagnetic Curie temperature, and resistivity are found to decrease as expected. The temperature dependence of electrical resistivity shows small positive temperature co-efficient that is expected for a metallic disordered material. We have also studied the modification of the properties on thermal annealing the (Fe0.78B0.13Si0.9)96 Nb4 ribbon at different temperatures in a neutral atmosphere.

A dimensionality controlled metal insulator transition in epitaxial [LaNiO3 (d nm)/LaAlO3(2nm)]10 (100) superlattices (thereafter [d/2]10 SLs) is demonstrated for decreasing LaNiO3 single layer thickness from 4nm down to 1.2 nm. The [4/2]10 SL shows metallic behavior with positive resistivity temperature coefficient, while the [2/2]10 SL shows a metal-insulator transition with crossover from 3D to two-dimensional single-layer dimensionality. Strong localization appears for the [1.2/2]10 SL with the resistivity being dominated by two-dimensional variable range hopping with a localization length of about 0.035 nm.

Recently, topological conductivity has been predicted theoretically in LaNiO3(111)-based superlattices. Here we report high-quality epitaxial LaNiO3/LaAlO3 superlattices on (111)-oriented SrTiO3 and LaAlO3 single crystals. For both substrates a metal-insulator transition with decreasing number of LaNiO3 monolayers is found. While the electrical transport is dominated by twodimensional variable range hopping for superlattices grown on polar mismatched SrTiO3(111), it switches to a thermally activated single gap behavior on polar matched LaAlO3(111). The gap energy of the polar double-layer LaNiO3 superlattices can be tuned via the thickness of the insulating LaAlO3 layers.