To see the other types of publications on this topic, follow the link: Electric susceptibility.
Dissertations / Theses on the topic 'Electric susceptibility'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Electric susceptibility.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Ritchie, Porter. "The Susceptibility of Electric Resistance Welded Line Pipe to Selective Seam Weld Corrosion." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586336007742949.
Full text
2
Lewin, William. "The Sound Of Silence : Applying Disruptive Innovation in the Electric Motorcycle Industry." Thesis, Uppsala universitet, Industriell teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-445540.
Full textAbstract:
The motorcycle industry is experiencing a paradigm shift. Alternatives to fossil fuels and changing customer preferences have slowly begun phasing out parts of the traditional motorcycle market. As a result of this, electric motorcycles are growing in popularity. A theory which discusses and theorizes regarding these types of industrial paradigm shifts is the theory of disruptive innovation. Disruptive innovation was introduced by scholar Clayton Christensen and has received a lot of attention since. The aim with this degree project was to contribute to our collective understanding of the innovation process by examining the electric motorcycle industry from the perspective of disruptive innovation. This was accomplished by compiling an industrial history of electric motorcycles which was analyzed using the concepts introduced by Christensen and further developed by his critics. This study used secondary information compiled in an industrial history using the narrative approach to historical analysis. The results showed that Christensen’s version of disruption was the most suited to explain the early attempts at electric motorcycles. The versions of disruption proposed by Christensen’s critics provided insight into how customer needs and the motorcycle market developed disruptive susceptibility over the years. The results of the study suggest that producers of electric motorcycles are adapting their products to the mainstream market instead of considering low-end markets with disruptive potential, which indicates that the actors are not expecting disruption as Christensen describes it.
3
Bracanovic, Darko. "Ac susceptibility and resistivity studies of YBaâ†2Cuâ†3Oâ†7â†-â†#delta# high-temperature superconductors." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302027.
Full text
4
Saxena, Siddharth Shanker. "Magnetic and superconducting phases of heavy fermion compounds." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323011.
Full text
5
Kaiser, Vojtech. "The Wien Effect in Electric and Magnetic Coulomb systems - from Electrolytes to Spin Ice." Thesis, Lyon, École normale supérieure, 2014. http://www.theses.fr/2014ENSL0942/document.
Full textAbstract:
Les gaz ou fluides de Coulomb sont composés de particules chargées couplées entre elles par interaction coulombienne à longue portée. De part la nature de ces interactions, la physique du gaz de Coulomb est très riche, comme par exemple dans des électrolytes plus ou moins complexes, mais aussi à travers l'émergence de monopôles magnétiques dans la glace de spin. Dans cette thèse nous nous intéressons au comportement hors d'équilibre des gaz de Coulomb et de la glace de spin. Au centre de cette étude se trouve le deuxième effet de Wien, qui est une croissance linéaire de la conductivité en fonction du champ électrique appliqué à un électrolyte faible. Ce phénomène est une conséquence directe de l'interaction coulombienne qui pousse les charges à se lier par paires ; le champ électrique va alors aider à dissocier ces paires et créer des charges mobiles qui amplifient la conductivité. Le deuxième effet de Wien est un processus hors-équilibre non-linéaire, remarquablement décrit par la théorie de Onsager. Nos simulations sur réseau permettent de découvrir le rôle de l'environnement ionique qui agit contre le deuxième effet de Wien, ainsi que de caractériser la mobilité du système et sa dépendance en fonction du champ externe. Les simulations nous ont aussi donné accès aux corrélations de charges qui décrivent le processus microscopique à la base de l'effet Wien. Enfin, nous regardons plus précisément le gaz émergent de monopôles dans la glace de spin, aussi appelé « magnétolyte », capable de décrire de manière remarquable les propriétés magnétiques de glace de spin. Nous décrivons la dynamique complète hors-équilibre de cette magnétolyte soumise à une forçage périodique ou une trempe dans un champ magnétique en incluant à la fois le deuxième effet de Wien et la réponse du réseau de spins qui est à la base de l'émergence des monopôles magnétiques. Tout au long, nous utilisons une simple extension des simulations de gaz de Coulomb sur réseau pour préciser nos prédictions. Il est très rare de trouver une théorie analytique du comportement hors-équilibre d'un système hautement frustré au-delà de la réponse linéaireA Coulomb gas or fluid comprises charged particles that interact via the Coulomb interaction. Examples of a Coulombic systems include simple and complex electrolytes together with magnetic monopoles in spin ice. The long-range nature of the Coulomb interaction leads to a rich array of phenomena.This thesis is devoted to the study of the non-equilibrium behaviour of lattice based Coulomb gases and of the quasi-particle excitations in the materials known as spin ice which constitute a Coulomb gas of magnetic charges. At the centre of this study lies the second Wien effect which describes the linear increase in conductivity when an electric field is applied to a weak electrolyte. The conductivity increases due to the generation of additional mobile charges via a field-enhanced dissociation from Coulombically bound pairs.The seminal theory of Onsager gave a detailed analysis of the Wien effect. We use numerical simulations not only to confirm its validity in a lattice Coulomb gas for the first time but mainly to study its extensions due to the role of the ionic atmosphere and field-dependent mobility. The simulations also allow us to observe the microscopic correlations underlying the Wien effect.Finally, we look more closely at the emergent gas of monopoles in spin ice—the magnetolyte. The magnetic behaviour of spin ice reflects the properties of the Coulomb gas contained within. We verify the presence of the Wien effect in model spin ice and in the process predict the non-linear response when exposed to a periodic driving field, or to a field quench using Wien effect theory. We use a straightforward extension of the lattice Coulomb gas simulations to refine our predictions. It is a highly unusual result to find an analytic theory for the non-equilibrium behaviour of a highly frustrated system beyond linear response
6
Fenn, Michael. "Electrical resistivity of thin metal films and multilayers." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325924.
Full text
7
Combes, Frédéric. "Thermodynamique de la réponse électrique dans les isolants de bande - Synchronisation et écho de spin dans une horloge atomique." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS540/document.
Full textAbstract:
Le travail présenté dans ce manuscrit porte sur deux sujets distincts. Le premier concerne la réponse d'un diélectrique cristallin à un champ électrique uniforme ; il s'ancre sur la théorie moderne de la polarisation développée par King-Smith, Vanderbilt et Resta. En nous restreignant d'abord au cas unidimensionnel, nous décrivons de manière perturbative à faible champ électrique le spectre de Wannier-Stark d'un modèle de bande. Nous utilisons ensuite ce développement dans une approche thermodynamique que nous modifions pour palier aux problèmes posés par le caractère non-borné du spectre de Wannier-Stark : nous introduisons en particulier un potentiel chimique local assurant la neutralité électrique locale au sein du cristal. Cette approche permet d'accéder à la polarisation et à la susceptibilité électrique des cristaux diélectriques. Finalement, nous étendons le travail effectué au cas bidimensionnel où de nouvelles caractéristiques associé aux isolants topologiques apparaissent.Le deuxième sujet porte sur la synchronisation de spin dans les gaz d'atomes froids. Nous étudions la compétition entre le mécanisme d'écho de spin et le phénomène d'auto-synchronisation lié à l'effet de rotation des spins identiques (emph{ISRE}). La méthode de l'écho de spin permet de compenser certains déphasage apparaissant dans une gaz d'atomes ultra-froid piégé, et accroît ainsi le temps de cohérence de l'ensemble. L'emph{ISRE} apparaît dans les gaz denses via les collisions entre atomes et conduit également à un accroissement du temps de cohérence. Nous montrons que ces deux mécanismes ne sont pas systématiquement compatibles. En particulier, leur compatibilité est lié à la relation entre les échelles de temps propres à chacun des phénomènesThe work exposed in this manuscript covers two distinct topics. The first is about the response of crystalline dielectrics to an external static electric field; it is based on King-Smith, Vanderbilt and Resta modern theory of polarisation. Restricting ourselves to the 1D case, we first describe the Wannier-Stark ladder of a band model with a low-field perturbative approach. We then use this development to derive the thermodynamical response of the band model. We have to modify the usual thermodynamics to account for the unboundedness of the Wannier-Stark spectrum, through the introduction of a local chemical potentiel which ensures local electric neutrality in the crystal. In a last step, we extend our approch to the 2D cas, where new characteristics related to the topic of topological insulators appear.The second topic tackles synchronization and spin-echo in cold atom gases. We study the competition between the spin-echo mechanism and the self-synchronization mechanism which emerges from the identical spin rotation effet (emph{ISRE}). The spin-echo thechnique was built to compensate for some the of dephasing that appears in trapped ultra-cold gases, leading to an increased coherence time for the ensemble. The emph{ISRE} appears in dense atomic clouds where collisions also lead to an increased coherence time. We show that these two mechanism are not always compatible, in particular, their compatibility is based on the relation between the time scales associated to both phenomena
8
Leigh, Nigel Royston. "Specific heat measurements on chevrel phase materials exhibiting coexistence of superconductivity and magnetism." Thesis, Durham University, 2001. http://etheses.dur.ac.uk/3849/.
Full textAbstract:
A probe for measuring the specific heat of superconductors at low temperatures and in high magnetic fields has been built and commissioned. The probe has been tested using the relaxation method on samples of copper and the accuracy of the data is 1.3 % between 5 K and 30 K, data taken using the long range pulse method has a resolution of 10 mK. Specific heat measurements have been performed on members of the series (Pb(_1)-(_x))Cu(_1.8x)Mo(_6)S(_8), (Sn(_1-x))Eu(_x)Mo(_6)S(_8) and (Pb(_1-x)M(_x))Mo(_6)S(_8) where M = Gd and Eu, from 3 K up to 30 K and in magnetic fields up to 15 T. Additional results from resistivity, susceptibility, magnetisation. X-ray diffraction, transmission electron microscopy and electron dispersive-ray measurements are also presented. These data have been compared to results from other authors and are analysed in terms of the BCS and GLAG theories of superconductivity and the magnetic properties of these materials. The mean field model has been used to calculate numerically the magnetic contribution to the specific heat (cm) of both ferromagnetic and antiferromagnetic systems as a function of temperature and applied field both above and below the ordering temperature. In addition an approximate analytic form for the magnetisation has been used to calculate Cm above the ordering temperature. Expressions have been derived for the saturation value of the peak in C(_m): C(^sat)(_m) = 1.1245n(_cell)RJI(J+1) and the temperature dependence of the peak with applied field ȡ(μ(_o)H(_ext))/ȡT(_peak)=6.540/g(_J)(J+1). They allow the simple calculation of the values of J and g(_J)(J + 1) from specific heat data. The magnetic contribution to the specific heat of the samples (Sn(_0.65)Eu(0.35)Mo(_6)S(_8)) and (Sn(0.50)Eu(_0.50)Mo(_6)S(_8)) have been modelled using these calculations and excellent agreement is found by considering the magnetic ions as free ions. The sample is accurately modelled by including an additional minority phase (Gd(_2)S(_3)). The approximate expressions have also been used to analyse data on high temperature superconductors producing values of J and g(_J)}{J + 1) consistent with a doublet ground state. The properties of Chevrel phase materials have been determined as a function of doping level. The critical temperature is degraded by doping but an increase in the critical current density is observed in the series (Pb(_1-x)Cu(_1-8x)Mo(_6)S(_8) for very low levels of doping. Increases of up to 28 % in the upper critical field, that are probably due to the compensation effect and an increase in the normal state resistivity, are also observed in the series (Sn(_1-x)Eu(_x)Mo(_6)S(_8)) at high levels of doping and in the series (Pb(_1-x)Gd(_x)Mo(_6)s(_8) for low levels of doping.
9
Diver, Andrew James. "The strongly correlated electron systems CeNiâ†2Geâ†2 and Srâ†2RuOâ†4." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364543.
Full text
10
Le, Poul Nicolas. "Charge transfer at the high-temperature superconductor/liquid electrolyte interface." Thesis, University of Exeter, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391279.
Full text
11
Naik, Meghana. "Automating the process of antibiotic susceptibility testing." Thesis, California State University, Long Beach, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10253001.
Full textAbstract:
The proposed project presents a methodology to detect how susceptible or resistant certain bacteria are to an applied antibiotic. This detection is achieved by calculating the area of Zone of Inhibition (ZOI) regions present in the petri dish and comparing the results to the prescribed standards. The ZOI regions are empty areas formed around an antibiotic disc when placed on a petri dish containing a sample of the bacterial culture. Digital image processing techniques are employed to automate the process of ZOI detection. Experimental results show that the proposed project is successful in detecting ZOI regions of various shapes, such as perfectly circular, irregular, and overlapping. The experimental results also show that the accuracy of detection is typically over 95%, and it remains above 90%, even when the image is degraded by additive Gaussian noise.
12
Pouant, Clovis. "Caractérisation de la susceptibilité électromagnétique des étages d'entrée de composants électroniques." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS064/document.
Full textAbstract:
Le travail de recherche présenté dans ce manuscrit contribue à une étude générale de la susceptibilité électromagnétique (EM) d'un transistor MOS (Metal Oxide Semiconductor) dans une gamme de fréquences allant de 10 MHz à 1 GHz. Ce composant est destiné à un usage général pour des applications analogiques et numériques. Le but principal de ce travail est d'apporter une compréhension fine des mécanismes physiques mis en jeu au sein du composant lorsque ce dernier est soumis à une agression EM injectée en mode conduit au niveau de sa grille. Notre étude porte sur l'élaboration d'un modèle physique, essentiellement basé sur les variations de charges au sein du composant électronique. Cette approche permet à la fois de comprendre le fonctionnement nominal du transistor et la modification de son comportement lors d'un dysfonctionnement. En effet, la compréhension des mécanismes physiques mis en jeu est la base de la compréhension de la susceptibilité EM. Pour mettre en œuvre ce type d'approche, nous avons choisi d'étudier un type de susceptibilité correspondant à la modification de son point de fonctionnement sous agression EM. Cette modification du point de fonctionnement peut induire un dysfonctionnement du circuit dans lequel est implanté le transistor. Le phénomène physique à l'origine duquel les signaux parasites EM modifient le point de fonctionnement d'un composant électronique est le phénomène de redressement. Ce phénomène apparaît lorsqu'une distorsion est créée au sein du composant. C'est aussi pourquoi les non-linéarités du dispositif sont directement responsables de son observation. Ainsi, pour comprendre finement et physiquement l'effet induit par une agression EM, il est nécessaire de mettre en place une méthode d'étude. Celle-ci est basée sur une mesure des formes d'onde des courants à tous les accès du transistor. En effet, la visualisation de ces courants renseigne sur l'évolution des charges au sein de la structure. De plus, une telle mesure donne accès à une large palette d'observables (valeurs moyennes des courants, distorsions des courants, valeurs crêtes des courants, etc..). Dans un premier temps, les différentes mesures des formes d'onde des courants ont été réalisées lorsqu'une impulsion de tension était appliquée sur la grille du composant avec des temps de montée variables et choisis par rapport au temps de réponse du transistor. Cela nous a permis d'approfondir la compréhension du fonctionnement transitoire fort signal du MOSFET. Dans un second temps, nous avons mesuré les courants lors de l'application d'un signal EM à la grille du composant. En support à ces mesures nous avons utilisé deux outils de calcul : analytique et numérique. La méthode analytique permet la prédiction et l'identification des grandeurs du composant mises en jeu dans le mécanisme de la modification du comportement du transistor. La méthode numérique par simulation électrique permet, quant à elle, de prédire les effets de l'agression EM. Une étape de caractérisation statique et dynamique du composant a également été nécessaire pour enrichir la compréhension des phénomènes observés et fournir les entrées au modèleThe research work presented here contributes to an overall study of the electromagnetic (EM) susceptibility of Metal Oxide Semiconductor Field Effect Transistors (MOSFET's), in a frequency range from 10 MHz to 1 GHz. This device is used for general purpose: analog and digital applications. The main aim of this study is to provide a detailed understanding of the physical mechanisms involved in the device when the Radio-Frequency (RF) interference is superimposed on the gate terminal. Our study focuses on the development of a physical model, based essentially on the charge variations within the electronic device. This approach allows to understand its behavior with and without the RF interference. Indeed, the knowledge of the involved physical mechanisms is the basic understanding of EM susceptibility. When RF interference is superimposed on the MOSFET terminals, various susceptibility effects take place depending on RF power level, frequency and the transistor operation region. Due to the nonlinearity of the MOS current-voltage characteristics, RF excitations cause distorted drain current waveform which leads to a bias point shift. This modification of the average drain current is called rectification effect. So we developed a method to clearly understand the effect induced by the EM interference. This method is based on the measurement of the currents waveforms to all of the transistor access. In fact, these currents waveforms measurements give us information on the charge variations within the electronic device. Moreover, such a measurement provides access to a wide range of current information (average values, distortion, peak values, etc.). Initially, the different currents waveforms measurements were made when a voltage ramp was applied to the device gate with variable rise time in respect to the transistor response time. This allowed us to understand the large signal transient response of the MOSFET. Secondly, we measured the currents waveforms when an EM interference was injected to the gate terminal. In support of these measurements we used two computation tools: analytical and numerical. The analytical method allows prediction and identification of the quantities of the device involved in the modification of transistor's behavior. The numerical method allows electrical simulation to predict the effects of EM aggression. A static and dynamic characterization of the component was also necessary to understand the observed phenomenon and provide data to the electrical model
13
Nakamine, Genki. "Superconducting Spin Susceptibility of Ute₂." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263450.
Full text
14
Svensson, Lucas, and Gustaf Ljungné. "Feasibility of an Electrically Tuneable EMC Susceptibility Antenna for 26-150 MHz." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-73163.
Full textAbstract:
Electromagnetic compatibility (EMC) is an essential part in today’s society and there are more products around us that emit electromagnetic waves than ever before. To make sure that all these products function properly under all circumstances EMC testing is needed. One test that is conducted is radiated immunity testing. A susceptibility antenna is needed to perform immunity testing. This thesis aims to show that a tuneable antenna could be used for immunity testing in the frequency band 26-150 MHz and in the future replace the current antenna, which is not tuneable, used at SAAB Support and Services EMC in Östersund. A simulation program called EZNEC+ was used to simulate different antennas that were tested in the semi-anechoic chamber at SAAB. Two antenna types showed better efficiency and reached lower in frequency than SAAB’s current antenna. These antennas were a bowtie antenna and an x-shaped antenna, both extending in only two spacial directions instead of the normal three. Their drawback was a less uniform E-field at the lowest frequencies, where the E-field was much stronger to the sides compared to straight in front of the antenna. This results in a narrow lobe width, but if this drawback could be accepted or mitigated both antennas are possible replacements for the current antenna at SAAB and should be further investigated.
15
Fan, Audrey Peiwen. "Development, testing, and application of quantitative oxygenation imaging from magnetic susceptibility by MRI." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/89990.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 101-133).
The healthy brain consumes 20% of total oxygen used by the body under normal conditions. Continuous oxygen delivery to neural tissue is needed to maintain normal brain function and viability. Reliable measurements of brain oxygenation can provide critical information to diagnose and manage diseases in which this oxygen supply is disturbed, including stroke and tumor. In acute stroke, for instance, metabolic biomarkers such as local oxygen extraction fraction (OEF) have been shown to identify tissue at risk of infarction by positron emission tomography. This knowledge can then be used to identify patients who are candidates for reperfusion therapies or to avoid thrombolytic therapy in futile situations. Unfortunately, there is currently no clinically feasible method for radiologists to assess brain oxygenation in patients. My thesis aims to address this need through development of a clinically viable tool to examine regional OEF in the brain with magnetic resonance imaging (MRI). We have designed a novel imaging and analysis method to quantify oxygenation in cerebral veins. MRI phase images are sensitive to local, oxygenation-dependent magnetic field variations in brain vessels, due to the presence of paramagnetic deoxyhemoglobin molecules in venous blood. Our method was developed on a 3 Tesla MRI scanner and tested in 10 healthy volunteers during hypercapnia, i.e. breathing of low levels of CO₂. This respiratory challenge changes the baseline oxygenation state of the brain, enabling us to test whether our MRI method can detect different levels of OEF in vivo. We also show that OEF is reduced in 23 patients with multiple sclerosis, an autoimmune disease of the central nervous disease, and relates to their performance on cognitive tasks.
by Audrey P. Fan.
Ph. D.
16
俞大風 and Tai-fung Yu. "An analysis of electrical transport and magnetic susceptibility properties of YBa2Cu3O7-[delta] and La2-xSrxCuO4 high Tcsuperconductors." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31238014.
Full text
17
Watkins, James Robert. "Evaluating the susceptibility of electronic components assembled with leaded solder to flexural failures, with high rate considerations." College Park, Md.: University of Maryland, 2008. http://hdl.handle.net/1903/8861.
Full textAbstract:
Thesis (Ph. D.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
18
Colbert, Benjamin Anthony. "Susceptibility of Venting Systems in Post-Tensioned Bridges to Chloride Intrusion." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563197826745693.
Full text
19
Yu, Tai-fung. "An analysis of electrical transport and magnetic susceptibility properties of YBa2Cu3O7-[delta] and La2-xSrxCuO4 high Tc superconductors /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19036607.
Full text
20
Negodaev, Igor. "The calculation of the thermal dependency of the magnetic susceptibility in extended systems with ab initio electronic structure parameters." Doctoral thesis, Universitat Rovira i Virgili, 2011. http://hdl.handle.net/10803/31934.
Full textAbstract:
La tesi estudia l'acoblament magnètic en sistemes de diferent dimensionalitat amb mètodes multireferencials. L’objectiu principal del treball és calcular propietats macroscòpiques, com la dependència de la susceptibilitat magnètica amb la temperatura, a partir de la constant d'intercanvi magnètic calculada, J. Aquest paràmetre microscòpic quantifica la interacció magnètica entre dos centres i es pot extreure per ajust de la corba de susceptibilitat experimental en sistemes finits però això no és possible en sistemes magnètics infinits com cadenes o capes 2D.
L’estratègia del treball és calcular J en petits clusters i simular els sistemes estesos utilitzant aquesta J en l’Hamiltonià de Heisenberg en models de 8 a 16 centres. Amb l’espectre obtingut es construeixen les corbes de dependència tèrmica de la susceptibilitat magnètica que, comparades amb les experimentals, donen la possibilitat de quantificar les interaccions magnètiques dels materials estudiats a nivell microscòpic.
S'han estudiat diferents tipus de sistemes estesos com cadenes i xarxes hexagonals, on els centres magnètics són ions de metalls de transició.The thesis studies the magnetic coupling in systems of different dimensionality, by using multireference methods. The aim of the work is to determine macroscopic properties such as the thermal dependency of magnetic susceptibility, from the calculated magnetic exchange constant J. This microscopic parameter quantifies the magnetic interaction between two magnetic sites and can be extracted from the experimental susceptibility curve in finite systems. However this extraction is not possible in extended magnetic systems such as chains or 2D-layers. The strategy followed consists in calculating J in small clusters and in simulating the extended systems by introducing the calculated J in the Heisenberg Hamiltonian of 8 to 16 site models. From the spectrum, the thermal dependency of the magnetic susceptibility is the calculated. When compared to the experimental one, this curve gives a quantification of the magnetic interactions of the studied materials at the microscopic level. We have studied different types of extended systems such as chains and hexagonal lattices, where the magnetic sites are transition metal ions.
21
Martorell, Alexandre. "Détection à distance d’électroniques par l’intermodulation." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS019/document.
Full textAbstract:
Électromagnétisme, sécurité et guerre électronique sont étroitement liés depuis des décennies. Leur association rassemble des applications de surveillance radar, de neutralisation de systèmes électroniques ou de détection d’électroniques cachées. Aujourd’hui, la multiplication des EEI (Engins Explosifs Improvisés) aussi bien sur les théâtres d’opération que dans les milieux urbains conduit à la nécessité de leur détection. Les travaux de cette thèse peuvent entrer dans cette thématique et proposent une nouvelle alternative qui permet de mettre en évidence la présence de récepteurs RF cachés. Le radar non-linéaire est particulièrement adapté à la détection de dispositifs contenant des métaux et des semi-conducteurs (électroniques). Une technique populaire consiste à transmettre une seule fréquence f1 et à recevoir la seconde harmonique générée par la cible. Une autre technique, moins courante, consiste à transmettre deux fréquences, f1 et f2, et à recevoir les produits d'intermodulation d’ordre 3 (2f1 - f2 et 2f2 - f1). Un état de l’art approfondi des systèmes radars non-linéaires est effectué dans un premier chapitre avec une comparaison de leurs caractéristiques. Dans un second chapitre, un banc de test en mode conduit est développé permettant la mesure de l’IM3 réfléchi d’une cible RF. Ainsi des analyses et des ordres de grandeurs seront connus aidant au développement du radar. Dans le chapitre 3, Le démonstrateur du radar à IM3 est développé. Un large panel de systèmes RF, commerciaux ou non, susceptibles d’être trouvé dans des milieux opérationnels est mis sous test. Leur détection va permettre de valider la technique de récupération de l’IM3. Un nouveau bilan de liaison réaliste du radar IM3 est mis en place afin d’estimer la portée de détection réelle du radar, pour différentes cibles RF. Dans le dernier chapitre les travaux s’orientent sur l’identification et la classification d’une cible RF. L’étude porte sur la possibilité d’extraire tous paramètres pouvant aider à une classification (évaluation du danger) de récepteurs RF dans un milieu opérationnel. Le travail de recherche présenté dans ce manuscrit contribue à l’amélioration des techniques de détection d’électroniques cachées. Un protocole de détection a été proposé décrivant les faits et gestes du radar IM3. Il inclut un balayage en fréquence puis en puissance. Les premiers tests ont été effectués sur un Talkie-Walkie démontrant la possibilité de détecter sa bande passante via la réémission d’IM3, à plus de 2 m. La répétabilité des tests sur un panel élargi de récepteurs RF valide le protocole de détection et l’intérêt du radar IM3. Une puissance d’émission du radar IM3 de 40 dBm, à une fréquence d’IM3 de 400 MHz, peut potentiellement détecter un récepteur à 80 m. Enfin dans un dernier travail exploratoire nous avons démontré que, par l’observation de la réponse de l’IM3 réfléchi suite à un balayage en puissance, le radar IM3 peut ajouter de nouveaux critères d’identification discriminant les récepteurs détectés entre euxElectromagnetism, security and electronic warfare have been closely linked for decades. Their association gathers applications of radar surveillance, neutralization of electronic systems or detection of hidden electronics. Today, the multiplication of IEDs (Improvised Explosive Devices) both in theatres of operation and in urban environments leads to the need for their detection. The works of this thesis can enter into this theme and propose a new alternative that allows to highlight the presence of hidden RF receivers. The nonlinear radar is particularly suitable for detecting devices containing metals and (electronic) semiconductors. A popular technique is to transmit a single frequency f1 and receive the second harmonic generated by the target. Another less common technique consists of transmitting two frequencies, f1 and f2, and receiving intermodulation products of order 3 (2f1 - f2 and 2f2 - f1). An in-depth state of the art of nonlinear radar systems is made in a first chapter with a comparison of their characteristics. In a second chapter, an inductive test bench is developed to measure the reflected IM3 of an RF target. Thus analyses and orders of magnitude will be known helping the development of radar. In chapter 3, the IM3 radar demonstrator is developed. A wide range of RF systems, commercial and non-commercial, that may be found in operational environments are being tested. Their detection will validate the IM3 recovery technique. A new realistic IM3 radar link budget is implemented to estimate the actual radar detection range for different RF targets. In the last chapter the work focuses on the identification and classification of an RF target. The study focuses on the possibility of extracting all parameters to assist in a classification (hazard assessment) of RF receptors in an operational environment. The research work presented in this manuscript contributes to the improvement of hidden electronic detection techniques. A detection protocol was proposed describing the actions of the IM3 radar. It includes a frequency scan and then a power scan. The first tests were carried out on a walkie-talkie demonstrating the possibility of detecting its bandwidth via IM3 retransmission, at more than 2 m. The repeatability of the tests on an extended panel of RF receivers validates the detection protocol and the interest of the IM3 radar. An IM3 radar transmission power of 40 dBm, at an IM3 frequency of 400 MHz, can potentially detect a receiver at 80 m. Finally in a final exploratory work, we demonstrated that by observing the IM3 response reflected following a power scan the IM3 radar can add new identification criteria that discriminate the hidden receivers detected between them
22
McDaniel, Patrick Christopher. "Improved accuracy in susceptibility-based OEF measurements by mitigation of partial-volume effects via combined magnitude and phase reconstruction." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100637.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Title as it appears in MIT Commencement Exercises program, June 5, 2015: Improved accuracy in susceptibility-based MRI oxygenation measurements by mitigation of partial-volume effects via combined magnitude and phase reconstruction. Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Regional quantitative Oxygen Extraction Fraction (OEF) values can only be reliable obtained from blood vessels larger than the acquisition voxel size. Blood vessels beyond this limit produce unreliable measurements due to partial-volume effects. We demonstrate a method for obtaining more reliable OEF measurements beyond this limit by performing a joint reconstruction using both the magnitude and phase of the complex-valued MRI signal. This method is validated both in numerical simulations and on in vivo data. The ability to perform high-quality fetal brain imaging is hampered by motion of the fetus, which can severely degrade image quality. Previously, low-resolution volumetric navigator (vNav) acquisitions have been shown to accurately track motion in human adults and prospectively correct for it. Here, a technique for using vNavs to measure fetal head motion in utero is developed and validated on in vivo data. Parallel Transmission (pTx) improves image quality and patient safety in high-field MRI. Unlike in single-channel MR excitation, an array of multiple excitation coils is used in pTx. However, coupling between these independent coils significantly degrades the power efficiency of the pTx array. Previously, it a decoupling matrix was proposed to solve this inefficiency. In this work, a physical realization of a 4-channel decoupling matrix was constructed and tested.
by Patrick C. McDaniel.
M. Eng.
23
Craig, Samantha L. "Rubidium Oscillator Error Model for Specific Force and Magnetic Field Susceptibility." Ohio University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1398126124.
Full text
24
Guibert, Laurent Christian Jean. "Etude des effets non linéaires et de la susceptibilité des systèmes électroniques embarqués." Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0054/document.
Full textAbstract:
Dans le domaine de la Compatibilité ElectroMagnétique (CEM), la connaissance du niveau d’immunité ou de susceptibilité d’un équipement embarqué est un paramètre important à contrôler et à gérer tout au long de sa durée de vie. En particulier,lors des opérations de maintenance de cet équipement, il est important de veiller au maintien de son niveau de susceptibilité pour garantir son fonctionnement. Pour répondre à ce besoin, les travaux de cette thèse proposent une méthode expérimentale originale de contrôle rapide et facile à mettre en œuvre dans le cas d’essais de susceptibilité rayonnée en haute fréquence. Cette méthode est basée sur l’observation de fréquences harmoniques rayonnées par un équipement lorsque celui-ci est soumis une illumination parfaitement monochromatique en haute fréquence. Pour cela, on fait l’hypothèse que l’amplitude de ces fréquences est d’autant plus grande que l’équipement électronique est en dysfonctionnement. Pour vérifier cette hypothèse, un dispositif expérimental adapté à une illumination en CRBM a tout d’abord été développé et étudié afin de mettre en œuvre cette méthode. Ensuite, après avoir mis en évidence sur plusieurs configurations de cartes électronique l’observation d’harmoniques, nous nous sommes intéressés à une modélisation du phénomène physique pour vérifier celui-ci par la simulation. Ace titre, une modélisation FDTD des expériences a été réalisée en 3D et une comparaison mesures/calcul a été effectuée. Ce travail a permis de montrer qu’à partir du des équations de Maxwell, des harmoniques identiques à celles mesurées étaient rayonnées et que la méthode de contrôle de susceptibilité rayonnée que nous proposions était donc tout à fait viable. Concernant la phase de modélisation, nous nous sommes intéressés essentiellement à représenter le fonctionnement du circuit logique et non à entrer finement dans le détail de chaque composant électronique le constituant. Pour les applications retenues, nous avons donc porté notre effort sur la prise en compte d’un signal numérique représenté sous forme d’une suite de bits, ainsi que sur l’introduction dans le modèle FDTD de Maxwell de quelques composants non linéaires comme la diode et un inverseur CMOS. La généralisation du modèle d’inverseur peut s’appliquer sans difficultés à d’autres composants CMOS, comme les mémoires de type SRAM que nous avons étudiées expérimentalementIn the frame of ElectroMagnetic Compatibility (EMC), the knowledge of EM immunity or susceptibility levels of on-board equipment is an important parameter to control and manage throughout the whole life of equipment. In fact, during maintenance phases of this equipment, it is important to ensure that these levels are maintained in order to guarantee its operation. To meet this need, this thesis proposes to focus on a novel and easy-to-implement experimental method for a quick diagnosis of equipment EM radiated susceptibility at high frequency.. This method is based on the observation of the harmonic frequencies radiated by an equipment device when this one is summited to a perfectly monochromatic illumination at high frequency. We make the hypothesis that the amplitude of those frequencies increases when the electronic equipment is in a dysfunction state. For this, a experimental method suitable for MSRCs has first been developed and studied to highlight the principle of this method. Then, having observed experimentally the radiation phenomenon of harmonic frequencies on several configurations of electronic cards, we have developed a 3D FDTD model to simulate the phenomenon. With this model, a modeling of the experiments was carried out and comparisons between measurements and calculations were performed. Calculation results coming from FDTD Maxwell’s equation models showed trends and functional behaviors identical to those observed in measurements which demonstrated that the proposed control method was fully viable. Regarding the modeling phase, we concentrated on models describing the operation of the logic circuit but we did not to enter into the physical description of each electronic component. Our selected applications have therefore focused on the inclusion in the Maxwell FDTD model of a digital signal represented as a series of bits, as well as the introduction of some components such as a diode and a CMOS inverter. The generalization of the proposed inverter model can be easily extended to other CMOS components such as the SRAM memories we studied in experimental tests
25
Marin, Córdoba Roberto. "Chromium carcinogenesis characterization of DNA damaging intermediates by EPR ³¹P NMR, HPLC, ESI-MS and magnetic susceptibility /." Ohio : Ohio University, 2010. http://www.ohiolink.edu/etd/view.cgi?ohiou1261417590.
Full text
26
Mainini, Kevin. "Reducing Radio Frequency Susceptibilities in Commercial-Off-the-Shelf Camera Equipment for use in Electromagnetic Compatibility Testing." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etd/2484.
Full textAbstract:
The Technical Testing and Analysis Center (TTAC) Group at Oak Ridge National Laboratory performs electromagnetic compatibility testing on various radiation detection units. These tests require remote viewing of the equipment’s display to monitor its compliance with national and international standards. The Commercial-Off-the-Shelf (COTS) camera equipment that is used to monitor the displays exhibits radio frequency susceptibilities causing issues when determining the actual susceptibilities of the device under test. In order to mitigate this issue, a COTS camera was placed in two common test positions and cycled through three angled orientations with various radio frequency shielding methods applied. The development of these shielding methods was investigated in this thesis. The goal was to reduce the number of susceptible frequencies. The reduction of susceptibilities would greatly increase the viewing capacity of the cameras during testing. The techniques discovered have allowed for other COTS camera equipment to be modified and used effectively during electromagnetic compatibility testing.
27
Mbulunge, Masevhe Hamisi. "Giant Magnetocaloric effect and Magnetic Properties of selected Rare-Earth compounds." University of the Western Cape, 2021. http://hdl.handle.net/11394/7926.
Full textAbstract:
Masters of ScienceRare-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.
28
Shabsogh, Nisrein Mohammad Ahmad. "Impact of eWOM source characteristics on the purchasing intention." Thesis, University of Bradford, 2013. http://hdl.handle.net/10454/7518.
Full textAbstract:
The use of e-mail communication between consumers has been growing and companies are seeking to increase their understanding of this type of private communication medium between consumers. The privacy and cost-effectiveness characteristics of e-mail make it an important communication medium for consumers. Consumers use e-mail to exchange a variety of information including electronic word of mouth (eWOM) about products, services and organisations. The travel industry, the context of this study, is increasingly being delivered online. Understanding what influences consumers and how consumers evaluate eWOM will increase the travel industry’s knowledge about its consumer base. This study aims to contribute to existing knowledge on the impact of eWOM on consumer purchase intention. Its focus is on an interpersonal context where eWOM is sent from the source to the receiver in an e-mail about holiday destination. The study, which was undertaken from a positivist perspective, used qualitative and quantitative research techniques to better understand the influence of eWOM on purchase intention. The literature on word of mouth (WOM) and eWOM was initially examined to identify the major factors that have an influence on the receiver of eWOM. Consistent with previous studies, both perceived expertise and similarity were identified as source characteristics that have an influence on the receiver’s purchase intention. The literature also indicated that trustworthiness belief would have a key effect on the influence of eWOM on the attitude of the receiver. Consequently, this study examined each trustworthiness dimension – ability, benevolence, and integrity – with respect to its role in the influence of eWOM on purchase intention. The literature review also revealed that certain receiver characteristics were important in the process of influence, especially consumer susceptibility to interpersonal influence. The relationships between the variables identified were further developed into the research model, which has its roots in the theory of reasoned-action (Fishbein and Ajzen, 1975) and the dual process theory of influence (Deutsch and Gerard, 1955). Methodologically, a scenario-building approach to developing authentic e-mail was used. The qualitative data gathered from eight focus group discussions were analysed using “framework analysis” (Ritchie and Spencer, 1994) to develop eight scenarios. This was then used to manipulate the moderating variables in the scenario. Three manipulations, each with two levels, were included: eWOM direction “positive and negative”; source characteristic of “expert/non-expert”; and source characteristic of “similar/non-similar”. These scenarios formed part of a questionnaire. The questionnaire was used to collect data from a sample of University of Bradford students. The final number of usable questionnaires was 477. Structural equation modelling was used to determine the validity of the conceptual model and test the hypotheses. In particular, multiple group analysis was used to assess both the measurement and structural models, and to identify the impact of the eWOM direction. The theoretical model that describes the relationships between the exogenous variables (source’s and receiver’s characteristics) and the endogenous variables (trustworthiness dimensions, interpersonal influence and purchase intention) was accepted. The research findings provided empirical evidence on the difference in the impact of positive and negative eWOM on purchase intention. The source’s and receiver’s characteristics and related trustworthiness beliefs, (i.e. ability, benevolence, and integrity) are influenced by the direction of eWOM. The findings show that positive and negative eWOM differ with respect to how they impact on consumers’ attitudes and intentions. For instance, consumers have more belief in the credibility of a source who provides negative eWOM. However, the overall influence of the source’s characteristics tends to be stronger with positive than with negative eWOM. The findings of this study provide insights for both academics and practitioners to understand the potential of eWOM. This might be tailored to help develop more private relationships with customers through e-mail marketing strategies that incorporate eWOM. Negative eWOM is more credible but less directly useful to marketers. Nevertheless, it is important for marketers to realise the significance of managing dissatisfaction and to harness the power of negative eWOM. Similarly, positive eWOM is effective especially when the source is both expert and similar. This might be translated into online marketing campaigns that use consumer-to-consumer discussions in addition to viral marketing. Future research might test the model in different contexts, (e.g. financial services), to provide a more comprehensive picture of the influence of eWOM on purchase intention.
29
Favillier, Nathalie. "Caracterisation electrique et magnetique des manganites de nickel : application aux thermistances." Toulouse 3, 1988. http://www.theses.fr/1988TOU30066.
Full textAbstract:
Etablissement des correlations entre la composition, la stoechiometrie et la structure des composes par mesures de rpe (bande x et q), de susceptibilite magnetique et de conductivite electrique. Mise en evidence du caractere polyphasique des manganites de nickel et necessite d'un controle precis de l'atmosphere de synthese pour une bonne qualite d'echantillons
30
Ammarguellat, Chafika. "Contribution à l'étude des propriétés des composés ternaires intermétalliques de type TM2Si2." Paris 6, 1986. http://www.theses.fr/1986PA066007.
Full textAbstract:
Etude du phénomène de valence intermédiaire dans les composés du type CeM2Si2 (m=métal de transition 3d). Mise en évidence d'anomalies lors de l'absorption x ainsi que dans les propriétés magnétiques et de transport. Mesure des seuils d'absorption l(i)ii et classification des composes sur une échelle de valeurs de la valence. Etude des variations thermiques de la valence. L'instabilité de valence a également été mise en évidence qualitativement par des mesures des paramètres de maille.
31
Ahmed, Adam Saied. "Skyrmions and Novel Spin Textures in FeGe Thin Films and Artificial B20 Heterostructures." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492686407034025.
Full text
32
Druaux, Fabrice. "Etude de la relation entre la cristallisation et l'évolution du magnétisme dans des couches minces désordonnées Ni-Ag riches en Ag." Rouen, 1986. http://www.theses.fr/1986ROUES039.
Full textAbstract:
Evolution du magnétisme et de l'effet Hall dans les alliages Ni(x)Ag(1-x) riches en argent obtenus dans un état désordonné puis cristallisés par recuit. Polarisation magnétique, susceptibilité en champ fort et coefficients de Hall. Interprétation des résultats par des considérations de structure
33
Cavalcante, Geane Carolina Gonçalves. "Evolução tectônica e reologia de uma crosta orogênica quente: o caso do Anatexito Carlos Chagas, Faixa Araçuaí (Leste do Brasil)." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/44/44141/tde-11022014-143756/.
Full textAbstract:
A Faixa Araçuaí foi formada no Neoproterozóico a partir da colisão E-W entre os continentes Sul-Americano e Africano. Sua porção leste compreende uma extensa área migmatítica (~300 km de comprimento por 50-100 km de largura) onde afloram anatexitos e leucogranitos (unidade Carlos Chagas), kinzigitos e granulitos migmatizados, que provavelmente são o registro de uma ampla fusão parcial da crosta intermediária a inferior. Observações de campo associadas com evidências micro-estruturais indicam que a deformação ocorreu quando as rochas estavam incompletamente solidificadas. Estimativas de temperaturas sincinemáticas realizadas a partir do geotermômetro TitaniQ (titânio-em-quartzo) indicam que a temperatura mínima para a cristalização de cristais de quartzo é ~750°C. Tais temperaturas combinadas com composição química de leucossomas dos anatexitos sugerem que a viscosidade das rochas crustais foi reduzida para pelo menos 108 Pa s. Baixo valor de viscosidade associado às evidências de campo e de micro-estruturas são consistentes com a geração de no mínimo 30% de volume de magma durante a orogênese. Grandes quantidades de magma promovem um drástico enfraquecimento da resistência mecânica das rochas à deformação, e atestam que a crosta anatética do extremo leste da Faixa Araçuaí representa um análogo de litosferas quentes (hot orogen), tal como a Himalaiana. Investigação mineralógica detalhada permitiu caracterizar um comportamento dominantemente paramagnético para os anatexitos e ferromagnético para os granulitos. Medidas de orientação preferencial cristalográfica (OPC) a partir da técnica de EBSD (electron backscatter diffraction) revelam que a foliação magnética surge, sobretudo, a partir da orientação preferencial dos eixos [001] da biotita orientados perpendicularmente ao plano de fluxo. Contudo, dada a fraca anisotropia linear desse mineral, apenas uma secundária contribuição de sua subtrama foi observada para a origem da lineação magnética (k1). A correspondência entre os eixos [001] de feldspatos e k1 ocorre devido a OPC de pequenas inclusões de ilmenita que imitam a OPC de seus minerais hospedeiros. Correlação entre k1 da Anisotropia de Remanência Anistéretica (ARA) e k1 da Anisotropia de Suscetibilidade Magnética (ASM) demonstra que, na escala do espécime, a lineação magnética tem uma contribuição da anisotropia dos minerais ferromagnéticos. Assim sendo, a lineação magnética nos anatexitos é o resultado da combinação da trama cristalográfica de feldspatos e de biotita com o alinhamento preferencial de grãos ferromagnéticos. Medidas de ASM realizadas para recuperar a trama mineral e investigar o fluxo nos migmatitos revela um padrão de deformação complexo, no qual, em função das direções de lineação, especialmente, é possível caracterizar três setores estruturais. A porção norte (região estrutural 1) com foliações dominantemente sub-horizontais e lineação fortemente orientada na direção NW-SE representa uma região de escape tectônico que ocorre através de um fluxo horizontal de canal (channel flow). Fluxos de canais possivelmente resultam da atuação de forças gravitacionais (gravity-driven flow). O setor sul (regiões estruturais 2 e 3) com variadas direções de foliação (NE-SW, E-W e NW-SE) e lineações com caimentos para Norte e Oeste, provavelmente refletem um regime de fluxo influenciado, sobretudo, pela tectônica de convergência E-W (collision-driven flow). Ambos os setores sugerem que na escala regional o fluxo crustal registrado pelos migmatitos resulta de um regime de deformação que envolve forças gravitacionais, devido a carga topográfica da crosta superior sobreposta à crosta intermediária parcialmente fundida, com viscosidade baixa, e forças tectônicas, associadas à colisão entre os continentes Sul-Americano e Africano.The Araçuaí belt was formed by the collision between South American and African protocontinents during the Neoproterozoic. Its eastern part consists of an extensive migmatitic area (~300 km long x 50-100 km wide) where crop out anatexites and leucogranites (Carlos Chagas unit), migmatitic kinzigites and granulites that probably are the record of a widespread partial melting of the middle to lower crust. Field observations associated with microstructural evidences indicate that the deformation occurred when the rocks were incompletely solidified. Synkinematic temperature estimates realized using the TitaniQ (titaniun-in-quartz) geotermomether suggest that the minimum temperature for the quartz crystallization is ~750°C. Such temperatures combined with bulk rock composition of leucosome in the anatexites suggest that the viscosity of crustal rocks was dropped to at least 108 Pa s. Low viscosity values associated with field and microstructural evidences are consistent with the generation of at least 30% volume of melt during the orogeny. The presence of large volumes of melt promotes a drastic weakening of the mechanical strength of rocks and suggests that the anatectic crust of the eastern Araçuaí belt represents an analogue of present day hot orogen such the Himalayas. Detailed mineralogy investigation permitted to characterize the paramagnetic behaviour of the anatexites and the ferromagnetic behaviour of the granulites. Crystallographic preferred orientation (CPO) measurements using the EBSD (Electron Backscatter Diffraction) technique reveal that the magnetic foliation results from the preferred orientation of the biotite [001] oriented normal to the flow plane. However, given the feeble linear anisotropy of this mineral, only a subsidiary contribution of its subfabric to the origin of the magnetic lineation (k1) was observed. Correspondence between [001] of feldspars and k1 is due to the CPO of small inclusions of ilmenite that mimic the CPO of their host minerals. Correlation between k1 of the Anisotropy of Anhysteretic Remanent Magnetization (AARM) and k1 of the Anisotropy of Magnetic Susceptibility (AMS) demonstrate that, at the specimen scale, the magnetic lineation has a contribution of the anisotropy of the ferromagnetic minerals. AMS measurements realized to recover the mineral fabric and investigate the migmatitic flow field revealed a complex strain pattern in which, considering the lineation trends, especially, it is possible to characterize three structural sectors. The north region (structural sector 1) with foliations dominantly sub-horizontal and lineation trending NW-SE is interpreted as a region of tectonic escape that may represent a horizontal channel flow. This oblique tectonic escape probably results from gravity forces (gravity-driven flow). The Southern region (structural sectors 2 and 3) with variable trending foliations (NE-SW, E-W and NW-SE) and lineation plunging to North and West, probably reflect a flow regime dominantly influenced by the E-W convergence of the African and South-American continents (collision-driven flow). Altogether, the characteristics of the various domains suggest that the deformation of the partially molten middle crust of the Araçuaí belt was the result of the combination of gravity forces due to the topographic load and tectonic forces due to the convergence between the African and South-American continents.
34
Maly, Mascimiliano de Los Santos. "Avaliação da técnica de eletrorresistividade no mapeamento de sedimentos rasos associados a ocorrência de gás no Saco do Mamanguá e na Enseada de Paraty-Mirim." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/21/21136/tde-10102017-174424/.
Full textAbstract:
A constante pressão exercida sobre os ambientes costeiros por parte das diferentes atividades humanas, em conjunto com novas necessidades relacionadas a estudos ambientais particularmente no que diz respeito à geração de gases de efeito estufa em sedimentos marinhos, têm gerado uma crescente demanda por conhecimento dos processos de geração, acúmulo e liberação desses gases. Dado esse desafio, torna-se necessário o desenvolvimento de novas aplicações de ferramentas geofísicas que forneçam informações além das propriedades acústicas do meio. Dessa forma, o presente trabalho tem como objetivo a avaliação do método eletrorresistivo no mapeamento estratigráfico e na detecção de feições geoelétricas indicativas da presença de gás em sedimentos rasos. Para isso, foram analisadas seções geoelétricas adquiridas no Saco do Mamanguá e na Enseada de Paraty-Mirim por meio da comparação com perfis sísmicos de alta resolução e da medição de resistividade em amostras de sedimentos. Nessas amostras foi simulada a presença de bolhas de gás e analisada a variação da resistividade com a diminuição da salinidade da água intersticial. Observou-se que um volume de bolhas de 0,20% do volume total é suficiente para aumentar em um fator de 1,8 a resistividade de uma amostra saturada em água do mar. Também verificou-se que a resistividade medida é dependente da resistividade da água intersticial. Medidas de susceptibilidade magnética mostraram, neste local, que a variação da resistividade não é devida a variações mineralógicas. As seções geoelétricas mostraram boa correlação com os perfis sísmicos até 9 m de profundidade a partir da superfície da água, onde ocorre uma camada geoelétrica de resistividade <0,35 Ohm.m. Nessa profundidade, observa-se uma interface entre camadas de resistividade elétrica possivelmente causada por uma mudança no teor de água ou de matéria orgânica. Essa interface coincide com o topo da turbidez acústica produzida pela presença de gás.Given the constant pressure exerted over coastal environments by different human activities, in addition to the need for more knowledge concerning environmental issues, particularly with respect to greenhouse gases generation in marine sediments have generated an increasing demand for more information regarding the generation, accumulation and seepage of these gases. Faced with this challenge, there is a necessity to develop new applications to geophysical tools that provide more information than merely the acoustic properties of the medium. This work aims to the evaluation of the geoelectric method in stratigraphic mapping and the detection of geoelectric features of shallow gas. For that purpose, geoelectric sections acquired in the ria of Saco do Mamanguá and Paraty-Mirim were compared with high resolution seismic profiles and resistivity measurements in sediment samples. Presence of gas bubbles inside the sedimentary matrix was simulated and resistivity variation analyzed against the decrease of interstitial water salinity. It was observed that a bubble volume of 0.20% of the total volume is sufficient to increase the resistivity by a factor of 1.8. It was also confirmed that the sample resistivity is dependent on interstitial water resistivity. Magnetic susceptibility measurements showed that resistivity variation is not due to mineralogical variations. The geoelectric sections showed good correlation with the seismic profiles up to 9 m depth from the water surface, where occurs a geoelectric layer of resistivity <0.35 Ohm.m. At this depth, it is observed an interface between resistivity layers possibly caused by a change in water or organic matter content. This interface matches the top of the acoustic turbidity produced by shallow gas occurrences.
35
Ramdani, Hamdane. "Contribution à l'étude d'aimants samarium-cobalt : relation entre les propriétés magnétiques et la microstructure." Rouen, 1987. http://www.theses.fr/1987ROUES034.
Full textAbstract:
Etude d'aimants frittés Sm (Co, Fe, Cu, Zr)(7,29) ayant subi des traitements thermiques différents. Mesure de la coercivité et observation de la microstructure par microscopie électronique en transmission. Corrélation entre les microstructures avant et après recuit a 830°C et les propriétés magnétiques, à partir d'un modèle basé sur la répartition des éléments d'addition
36
Berger, Claire. "Propriétés électroniques des alliages quasicristallins AlMn." Grenoble 1, 1987. http://www.theses.fr/1987GRE10067.
Full text
37
Vermeulen, Jean-Luc. "Elaboration par pulvérisation ionique et caractérisation de couches minces ferromagnétiques à forte perméabilité." Grenoble 1, 1993. http://www.theses.fr/1993GRE10071.
Full textAbstract:
Dans le cadre des applications employant des materiaux ferromagnetiques aux hyperfrequences, nous avons etudie les proprietes magnetiques et electriques de couches minces ferromagnetiques metalliques et dielectriques deposees par pulverisation ionique. Le premier volet de ce memoire se rapporte a l'installation de depot. Des parametres cles tels que l'orientation de la cible et la temperature du substrat font l'objet d'une analyse approfondie. Cette etude a permis ainsi d'aboutir a l'obtention de couches denses de qualite maitrisee. Sur la base de ces preliminaires, des films minces microcristallises de co-fe-si-b ont ete elabores et caracterises. L'analyse des proprietes magnetiques statiques et dynamiques en fonction des conditions experimentales montre qu'elles sont particulierement sensibles aux deux parametres: temperature de depot et bombardement ionique. Leur controle a permis ainsi de realiser des couches presentant a la fois des permeabilites elevees a basse frequence et de fortes pertes a des frequences plus hautes. En dernier lieu, l'accent est mis sur la realisation et l'etude de couches resistives de b-n et de fe-b-n. Nous montrons qu'il est possible d'obtenir, grace a un bombardement simultane d'ions azote de la couche en croissance, des depots nitrures de concentration en azote variable dans l'intervalle 0-50 pour cent. Concernant les depots de fe-b-n, une forte dependance des caracteristiques electromagnetiques vis-a-vis de la composition a ete observee. Selon la concentration de fer, les proprietes du compose evoluent d'un caractere fortement ferromagnetique et conducteur, a un comportement tres resistif mais a faible induction a saturation
38
Gottlieb, Ulrich. "Quelques propriétés physiques intrinsèques des siliciures métalliques et semiconducteurs." Grenoble INPG, 1994. http://www.theses.fr/1994INPG0008.
Full textAbstract:
Dans la premiere partie nous decrivons la mise au point d'une experience de mesures de transport a basses temperatures. Nous avons construit un dispositif experimental qui permet de piloter la rotation de l'echantillon a basse temperature sous fort champ magnetique a partir de l'exterieur du cryostat. La deuxieme partie de la these est consacree a l'etude systematique des siliciures isostructuraux et isoelectroniques vsi#2, nbsi#2 et tasi#2. Les echantillons sont monocristallins. Les trois composes sont metalliques et leur resistivite a haute temperature est anisotrope. Des mesures de magnetoresistance nous ont permis d'explorer la surface de fermi de nbsi#2. Des mesures de chaleur specifique a tres basse temperature revelent que la densite d'etats electronique au niveau de fermi est deux fois plus elevee pour vsi#2 que pour les deux autres siliciures. Les temperatures de debye des trois composes varient en fonction de m##1#/#2 (m: masse molaire) indiquant que les forces interatomiques sont identiques. Nbsi#2 et tasi#2 sont supraconducteurs en dessous respectivement 130 mk et 353 mk. Des mesures de susceptibilite montrent que vsi#2 est paramagnetique, nbsi#2 et tasi#2 sont diamagnetiques. Les spectres de phonons obtenus par des mesures de spectroscopie de pointes sont en bon accord avec les temperatures de debye obtenues par les autres methodes. Des etudes sur les proprietes de transport des siliciures semiconducteurs crsi#2, resi#1#,#7#5 et ru#2si#3 sont decrites dans le troisieme chapitre. La preparation de monocristaux de ces materiaux est plus difficile que celle des siliciures metalliques. La resistivite des trois composes est anisotrope. Ru#2si#3 et resi#1#,#7#5 se comportent comme des semiconducteurs dopes en regime extrinseque. Crsi#2 montre plutot le comportement d'un mauvais metal. La magnetoresistance de ru#2si#3 a basse temperature peut s'interpreter dans un modele de localisation faible ou les interactions electron-electron sont dominantes
39
Brunet, Laurence. "Repartition spatiale de la densite electronique moleculaire en composantes atomiques in situ." Paris 6, 1987. http://www.theses.fr/1987PA066042.
Full textAbstract:
Modelisation originale de la densite electronique moleculaire par la superposition de densites atomiques spheriques, centrees sur les noyaux a partir de calculs d'orbitales moleculaires, avec trois invariants : la charge totale, le potentiel electrons-noyaux, le moment dipolaire. Description de la methode numerique pour determiner les densites associes aux atomes dans une base d'orbitales gaussiennes. Renseignements obtenus sur les modifications spatiales de la charge electronique par formation de liaisons, sur les facteurs de structure atomiques effectifs, apres transformation de fourier, en tenant compte de l'effet de l'environnement. Extension de la methode a la decomposition de la densite electronique moleculaire en densites composantes, autres qu'atomiques et non necessairement centrees sur les noyaux. Outre les applications a l'etude de la structure et des proprietes electroniques des molecules, proposition d'utilisation au calcul des polarisabilites optiques (lineaires ou non), a l'analyse des donnees cristallographiques obtenues par diffraction de rayon x et a la prevision de la structure des cristaux moleculaires
40
Kitaura, R., H. Okimoto, H. Shinohara, T. Nakamura, and H. Osawa. "Magnetism of the endohedral metallofullerenes M@C_82 (M=Gd,Dy) and the corresponding nanoscale peapods: Synchrotron soft x-ray magnetic circular dichroism and density-functional theory calculations." American Physical Society, 2007. http://hdl.handle.net/2237/11305.
Full text
41
Ben, Salem Azzedine. "Synthese et caracterisation physique et structurale des conducteurs unidimensionnels de type fe : :(1+x)nb::(3-x)se::(10)." Nantes, 1987. http://www.theses.fr/1987NANT2018.
Full textAbstract:
Ce compose est le prototype d'une serie de formulation (mm')nb::(2)s::(10)(mm' = fe,v,cr,nb,ta) presentant une chaine trigonale prismatique |nbse::(3)| et une double chaine oelaedrique |(mm')se::(6)|. Ces composes ont une transition metal isolant vers 140 k. L'observation d'une onde de densite de charge aux caracteristiques identiques a celles de nbse::(3) indique que la chaine conductrice est la chaine trigonale prismatique |nbse::(3)|. La variation de la conductivite au voisinage de la transition indique un mecanisme de localisation d'anderson. Les proprietes physiques du compose ou se a ete substitue par s ont ete etudiees. L'etude de l'insertion par li a ete effectuee
42
Najib, Abdelkrim. "Etude de quelques composés de cérium du type fermions lourds : corrélations, cohérence, diagrammes de phases sous pression." Grenoble 1, 1988. http://www.theses.fr/1988GRE10064.
Full textAbstract:
Etude des composes ce in cu::(2), ce mg et ce cu::(6). Les etudes de susceptibilite magnetique, resistivite electrique et chaleur specifique sur les solutions solides(ce-y)incu::(2) et (ce-la)incu::(2) mettent en evidence des correlations antiferromagnetiques dans le compose ceincu::(2). Influnce des impuretes sur la coherence du reseau. Determination pour ce compose du coefficient de grueneisen a partir des proprietes de transport sous pression hydrostatique. Etude pour les autres composes des diagrammes de phase sous pression hydrostatique jusqu'a 130 kbar
43
Aka, Gérard. "Alumino-gallates de sodium-lanthanide de type alumine beta, magnetoplombite ou mixte : cristallochimie, etude spectroscopique et proprietes physiques." Paris 6, 1988. http://www.theses.fr/1988PA066008.
Full textAbstract:
Obtention des composes a structure mixte par echange ionique en sel fondu d'ions lanthanides trivalents sur les cristaux d'aluminogallate de sodium, na::(1+y)(al::(1-x)ga::(x))::(11) o::(17+(y/2)), obtenus par la methode du fondant, avec 0,5y1 et 0x0,5. Caracterisation par des mesures de susceptibilite magnetique et conductivite electrique. Analyse des spectres rpe pour localiser les ions lanthanides dans les structures de type alumine beta ou mixte, pour lesquelles les etudes d'absorption optique, de fluorescence et de declin de fluorescence indiquent des proprietes optiques differentes des ions ce**(3+), nd**(3+), eu**(2+) et eu**(3+)
44
MONDOLONI, CHRISTIAN. "Contribution a l'etude de la valence anormale de l'ytterbium et du thulium dans yb : :(1-x)tm::(x)se et yb::(1-y)tm::(y)s." Paris 7, 1988. http://www.theses.fr/1988PA077122.
Full textAbstract:
Etude experimentale de l'instabilite de la valence des atomes de tm en fonction de la concentration dans les composes du titre. On mesure la valence des atomes de tm par susceptibilite magnetique et absorption rx, et on met en evidence une divergence de resultats par ces deux methodes. On met en evidence une transition metal-semiconducteur pour x=0,84, un ordre antiferromagnetique a 1,5 k, une magnetoresistivite negative. L'etude des sulfures amene a interpreter les proprietes de transport dans le domaine y >ou= 0,08 pour t>15 k par l'effet kondo
45
Guyot, Hervé. "Etude des transitions d'onde de densité de charge et des propriétés de transport des oxydes de molybdène [êta]-Mo4O11 et [gamma]-Mo4O11." Grenoble 1, 1986. http://www.theses.fr/1986GRE10122.
Full text
46
Marreto, Lais Carneiro Naziasene Lima. "Identificação das espécies de Candida, avaliação da ultraestrutura e perfil de suscetibilidade de biofilmes aos antifúngicos." Universidade Federal de Goiás, 2014. http://repositorio.bc.ufg.br/tede/handle/tede/4233.
Full textAbstract:
Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2015-03-04T15:47:31Z
No. of bitstreams: 2
Dissertação - Laís Carneiro Naziasene Lima - 2014.pdf: 3242345 bytes, checksum: d0ace95b026350f2bf41251459258252 (MD5)
license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5)Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-03-05T10:40:24Z (GMT) No. of bitstreams: 2 Dissertação - Laís Carneiro Naziasene Lima - 2014.pdf: 3242345 bytes, checksum: d0ace95b026350f2bf41251459258252 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5)
Made available in DSpace on 2015-03-05T10:40:24Z (GMT). No. of bitstreams: 2 Dissertação - Laís Carneiro Naziasene Lima - 2014.pdf: 3242345 bytes, checksum: d0ace95b026350f2bf41251459258252 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2014-05-08
Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG
The increase in the number of fungal infections by Candida species, as a result of the significant increase of immunocompromised patients emphasizes the importance of studies associated to this genre. The resistance of these strains to antifungal drugs is observe in specific isolates, as well as infections associated with biofilm formation (BF). The aim of this study was to compare the susceptibility profile of sessile and planktonic cells of different Candida isolates, differentiating species by multiplex qPCR and scanning electron microscopy. The sample consisted of 10 C. albicans, 10 C. parapsilosis and 1 C. tropicalis. The genetic material was extracted by phenolchloroform extraction of the sample C. tropicalis, ATCC 28367 (C. albicans) and ATCC 22019 (C. parapsilosis) for use in a species-specific multiplex qPCR assay with analysis of differences in the curve fusion. Microdilution plate test and reduction of the tetrazolium salt for 21 isolates were performed for the susceptibility of sessile and free cells, respectively. The evaluation of the ultrastructure of the biofilm was performed on strips of polyurethane with visualization by scanning electron microscopy. The amplified products from C. albicans obtained three melting peaks with values of 75,2 °C, 76,8 °C and 79,8 °C, while C. tropicalis and C. parapsilosis showed one peak with values 73,5 °C and 78,5 °C, respectively. The identification test showed to be reliable for the identification of the most common species in the study. All of Candida yeasts were able to form biofilm with own organization of each specie. The in vitro susceptibility test of planktonic cells demonstrated that amphotericin B and caspofungin showed better activity compared to fluconazole and voriconazole who obtained 19% of resistant strains, all C. albicans. In assessing of the CIMs50% and CIMs80% of sessile cells, we observed an increase of at least 60 times the values of planktonic cells. It was observed a high percentage of BF that demonstrates the need for diagnosis and combat against this biomass formed by Candida species. The BF is a virulence factor determinant for decrease of susceptibility to antifungal agents thus compromising antifungal therapy.
O aumento no número de infecções fúngicas por espécies de Candida, como resultado do expressivo aumento de pacientes imunocomprometidos destaca a importância de estudos relacionados a esse gênero. A resistência destas leveduras aos fármacos antifúngicos é observada em isolados específicos, assim como em infecções associadas com a formação de biofilme (FB). O objetivo deste estudo foi comparar o perfil de suscetibilidade in vitro de células sésseis e planctônicas de diferentes isolados de Candida, diferenciando as espécies por qPCR multiplex e microscopia eletrônica de varredura. A amostra foi composta de 10 C. albicans, 10 C. parapsilosis e 1 C. tropicalis. O material genético foi extraído pelo método de extração fenol-clorofórmio da amostra de C. tropicalis, ATCC 28367 (C. albicans) e ATCC 22019 (C. parapsilosis) para utilização no ensaio espécie-específico qPCR multiplex com avaliação das diferenças na curva de fusão. Foram realizados teste de microdiluição em placa e redução do sal tetrazólio para 21 isolados a fim de determinar a suscetibilidade de células livres e sésseis, respectivamente. A avaliação da ultraestrutura do biofilme foi realizada em tiras de poliuretano com visualização por microscopia eletrônica de varredura. Os produtos amplificados de C. albicans, obtiveram três picos de fusão com valores de 75,2°C, 76,8°C e 79,8°C, enquanto C. parapsilosis e C. tropicalis mostraram um pico de valores 73,5°C e 78,5°C, respectivamente. O teste de identificação apresentou-se confiável para a identificação das espécies mais comuns no estudo. Todas as leveduras de Candida foram capazes de formar biofilme com organização própria de cada espécie. O teste de suscetibilidade in vitro das células planctônicas demonstrou que anfotericina B e caspofungina apresentaram melhor atividade em comparação com o fluconazol e voriconazol que obtiveram 19% das amostras resistentes, sendo todas C. albicans. Na avaliação da CIMs50% e CIMs80% das células sésseis, observou-se um aumento de pelo menos 60 vezes dos valores das células planctônicas. Foi observada porcentagem elevada de FB que demonstra a necessidade do diagnóstico e combate à essa biomassa formada pelas espécies de Candida, pois é um fator de virulência determinante para a diminuição da suscetibilidade aos antifúngicos comprometendo assim a terapêutica antifúngica.
47
Westerkamp, Tanja. "Quantenphasenübergänge in den Schwere-Fermionen-Systemen Yb(Rh_{1-x}M_x)_2Si_2 und CePd_{1-x}Rh_x." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244202394324-81635.
Full textAbstract:
Die Betrachtung von Schwere-Fermionen-Systemen stellt ein wichtiges Themengebiet im Bereich der Festkörperphysik dar. Das Verhalten von Schwere-Fermionen-Systemen wird durch die starken Korrelationen der magnetischen Momente der ungepaarten Spins der f-Elektronen bestimmt. Experimentell zugängliche Messgrößen sind dadurch bei tiefen Temperaturen stark erhöht, so dass sich diese Systeme besonders gut zur Untersuchung von Grundzustandseigenschaften eignen. Zentrales Thema dieser Arbeit ist die Untersuchung zweier intermetallischer Seltenerd-Verbindungen in Bezug auf Quantenphasenübergänge. Diese treten am absoluten Nullpunkt der Temperatur als Funktion eines anderen Parameters wie Magnetfeld, Druck oder chemischer Substitution auf und sind bei endlicher Temperatur durch Abweichungen physikalischer Messgrößen von der durch L. D. Landau aufgestellten Theorie der Fermi-Flüssigkeiten nachzuweisen. Zu diesem Zweck wurden Tieftemperaturexperimente bis hinab zu 20mK und in Magnetfeldern bis zu 18T durchgeführt. Es wurden elektrischer Widerstand, magnetische Wechselfeldsuszeptibilität, Magnetostriktion und thermische Ausdehnung gemessenThe investigation of heavy-fermion systems marks an important subject in the research field of solid state physics. The behaviour of heavy-fermion systems is dominated by the strong correlations of the magnetic moments of the unpaired f-electron spins. At low temperatures, experimentally accessible variables are strongly enhanced so that these systems are especially suited to analyse ground state properties. The central topic of this thesis is the investigation of two intermetallic rare-earth compounds with regard to quantum phase transitions. The latter occur at zero temperature as a function of parameters such as magnetic field, pressure or chemical substitution. They are traceable at finite temperature due to deviations of physical variables from the theory of Fermi liquids established by L. D. Landau. For this purpose, low-temperature experiments were performed down to 20mK and in magnetic fields up to 18T. Electrical resistivity, magnetic ac susceptibility, magnetostriction and thermal expansion were measured
48
Er-Rakho, Lahcen. "Oxydes de cuivre a valence mixte : perovskites deficitaires en oxygene." Caen, 1987. http://www.theses.fr/1987CAEN2036.
Full textAbstract:
Mise en evidence et etude de deux grandes familles de composes dans le systeme la::(2)o::(3)-ao-cuo(a=ca,ba,sr) : la::(2-x)ba::(1-x)cu::(1-x/2)o::(5-x)(ln=la,nd) ou cu est essentiellement au degre d'oxydation 2 et une seconde famille caracterisee par la valence mixte du cuivre, les quantites de cuivre 3 pouvant atteindre dans certains cas 40%. Tous ces oxydes ont en commum leur appartenance a la structure perovskite. Proprietes electriques et magnetiques
49
PETIT, PIERRE. "Magnetisme et proprietes de conduction des derives cristallins et liquides cristallins de la bisphtalocyanine de lutecium : effet de dimensionnalite." Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13163.
Full textAbstract:
Etude parrpe et par des mesures de la conductivite dc et de la reponse dielectrique ac hyperfrequence. Mise en evidence de la nature radicalaire de type pi du systeme, a l'etat cristallin comme en solution; effet du solvant et de la temperature; observation de sauts de l'electron non apparie d'un macrocycle a l'autre a une frequence voisine de 1 mhz. Mise en evidence de la possibilite de formation de deux systemes cristallins (empilement de chaines ou de plans paralleles) et de leur caractere 1d ou 2d au moyen du modele de richards. La susceptibilite du systeme mesomorphe indique un desordre magnetique comparable a celui de la phase liquide; la conductivite est celle des systemes desordonnes. Les cristaux solvates sont des semiconducteurs moleculaires intrinseques
50
Westerkamp, Tanja. "Quantenphasenübergänge in den Schwere-Fermionen-Systemen Yb(Rh_{1-x}M_x)_2Si_2 und CePd_{1-x}Rh_x." Doctoral thesis, Technische Universität Dresden, 2008. https://tud.qucosa.de/id/qucosa%3A23821.
Full textAbstract:
Die Betrachtung von Schwere-Fermionen-Systemen stellt ein wichtiges Themengebiet im Bereich der Festkörperphysik dar. Das Verhalten von Schwere-Fermionen-Systemen wird durch die starken Korrelationen der magnetischen Momente der ungepaarten Spins der f-Elektronen bestimmt. Experimentell zugängliche Messgrößen sind dadurch bei tiefen Temperaturen stark erhöht, so dass sich diese Systeme besonders gut zur Untersuchung von Grundzustandseigenschaften eignen. Zentrales Thema dieser Arbeit ist die Untersuchung zweier intermetallischer Seltenerd-Verbindungen in Bezug auf Quantenphasenübergänge. Diese treten am absoluten Nullpunkt der Temperatur als Funktion eines anderen Parameters wie Magnetfeld, Druck oder chemischer Substitution auf und sind bei endlicher Temperatur durch Abweichungen physikalischer Messgrößen von der durch L. D. Landau aufgestellten Theorie der Fermi-Flüssigkeiten nachzuweisen. Zu diesem Zweck wurden Tieftemperaturexperimente bis hinab zu 20mK und in Magnetfeldern bis zu 18T durchgeführt. Es wurden elektrischer Widerstand, magnetische Wechselfeldsuszeptibilität, Magnetostriktion und thermische Ausdehnung gemessen.The investigation of heavy-fermion systems marks an important subject in the research field of solid state physics. The behaviour of heavy-fermion systems is dominated by the strong correlations of the magnetic moments of the unpaired f-electron spins. At low temperatures, experimentally accessible variables are strongly enhanced so that these systems are especially suited to analyse ground state properties. The central topic of this thesis is the investigation of two intermetallic rare-earth compounds with regard to quantum phase transitions. The latter occur at zero temperature as a function of parameters such as magnetic field, pressure or chemical substitution. They are traceable at finite temperature due to deviations of physical variables from the theory of Fermi liquids established by L. D. Landau. For this purpose, low-temperature experiments were performed down to 20mK and in magnetic fields up to 18T. Electrical resistivity, magnetic ac susceptibility, magnetostriction and thermal expansion were measured.