Dissertations / Theses on the topic 'Théorie des champs théoriques'
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Chamma, Didier. "Les résonances de Fermi en liaison hydrogène X-H. . . Y : profils théoriques du spectre infrarouge de l'élongation X-H." Perpignan, 1999. http://www.theses.fr/1999PERP0337.
Colle, Stéphane. "Modélisation des champs diffus en acoustique urbaine par la théorie des transports : développements théoriques et mise en forme numérique." Le Mans, 2006. http://cyberdoc.univ-lemans.fr/theses/2006/2006LEMA1031.pdf.
This work has contributed to the development of a new propagation model of diffuse sound fields in urban acoustics, making it possible to take analytically into account the whole phenomena involved in the propagation (i. E. The diffuse reflection and, at least, on the principle, other phenomena such as the atmospheric attenuation, the micrometeorological effect. . . ). Based on an energetic and probabilistic approach, this model consista in decomposing the sound wave into a sum of sound particles (or phonons) in the propagation medium (i. E. A street). The distribution function of the phonons then follows a transport equation, whose boundary conditions consider the absorption coefficients and the reflection law (specular and/or diffuse) of the façades. In its most general form, the problem does not admit an analytical solution. For narrow streets, the use of an asymptotic approach makes it nevertheless possible to express the distribution and the deerease of sound energy through a diffusion equation. The problem is then reduced to the determination of the diffusion coefficient (function of the street characteristics), and to the calculation of an exchange coefficient modelling the absorption by the openings of the street. This approach, initially developed by Le Pollès, was generalized for streets made up of non-absorbing walls, characterized by A\w\n (n > 2) reflection laws on both sides of the street. Under these conditions, the analytical developments show that the diffusion coefficient depends on the street width, on the reflection laws and on the façades accommodation coefficient. This last coefficient represents the ratio between the specular and diffuse reflection. In addition, this development shows that in the case of a narrow street, the diffusion process only occurs in the median plane of the street, the density of sound energv being uniform on a transverse line of the street. The mathematical solutions were successfully compared to numerical simulations using the SPPS code, which is the direct application of the particles model. Due to the inability of the asymptotic development to take into account the acoustic absorption of the façades, a new approach inducing a damping in the propagation medium was proposed. This development was analytically performed, but its practical use requires numerical resolutions of integrals. Finally a numerical application of the diffusion model was proposed using a finite elements software (and the theoretical results of the above-mentioned diffusion model). This numerical approach makes it possible to model easily and quickly the sound propagation in complex urban areas, in multi-sources environments. Several examples are proposed and show the general interest of our work for the development of a simple and fast software, making it possible to carry out acoustic predictions in complex urban configurations
Duret, Quentin. "Contribution à l’étude des Fermions et de leurs angles de mélange en Théorie Quantique des Champs." Paris 6, 2008. http://www.theses.fr/2008PA066301.
Achard, Franck. "Argumentation et thèmes méthodologiques dans les publications théoriques de James Clerk Maxwell sur l'électricité et le magnétisme (1856-1879)." Paris, EHESS, 2002. http://www.theses.fr/2002EHES0054.
This study analyses how Maxwell defined and justified his scientific undertaking in his main theoretical publications on electromagnetism. It describes the function of some methodological themes to define the relationship between the uniqueness of his theory and its conformity with the knowledge produced by the contemporary mathematical physics. It stresses the high significance of a distinction between the “mathematical laws”, produced empirically, and the “physical hypothesis”, imagined afterwards to “explain” the phenomena. This theoretical framework, stemming from an article published by William Thomson in 1845, helps to illuminate the traditional picture of Maxwell's theory as a “mathematical translation” of Faraday's heterodox views and methods, Maxwell's use of mechanical “analogies” and “models” and the internal inconsistencies in some of his texts
Maurat, Emmanuel. "Étude théorique de la dynamique de charge et de spin de structures électroniques confinées." Strasbourg, 2009. https://publication-theses.unistra.fr/public/theses_doctorat/2009/MAURAT_Emmanuel_2009.pdf.
In this first approach, the dynamic aspects are modeled using concepts of statistical mechanics at the thermodynamic equilibrium. By using the Local Spin Density Functional Theory (LSDA-DFT) at finite temperature and within the grand canonical ensemble, we have studied the magnetic properties of small metal particles with open-shell structures made up of elements which are no magnetic in the bulk (like the noble metals Ag, Au or Pt). As for ferromagnetic bulk materials, these nano objects present a ferromagnetic-paramagnetic second order phase transition at a critical temperature which depends heavily on their size and on the electronic correlations. We have shown that the magnetic susceptibility obeys the Curie-Weiss law. This result is due to the finite size of the system implying a discrete spectrum of electronic levels and is consistent with recent measurements on aggregates of platinum sorted by mass [109]. Thus, when the electron temperature increases sharply, the magnetization decreases. Then, through the electron-phonon coupling the thermal energy is distributed over the lattice, which in turn decreases the electron temperature and allows the resurgence of the magnetization. This analysis is supported by some experimental results as the fact that the demagnetization is more or less pronounced according to the Curie temperature of the material [130]. Thanks to the linear response theory for LSDA-DFT that we developed, we were also able to find the features of a such demagetization on optical spectrums. However, this model is only qualitative. Indeed, the mechanisms that are causing the phenomenon of demagnetization are hidden by the statistical treatment of the problem. The spin magnetic moment (which, for metals, is essential to the magnetization of the system) may be redistributed on the orbital moment via spin-orbit coupling. The latter is of relativistic origin and must be added to the non-relativistic Hamiltonian describing the usual light-matter interaction. A few years ago, this hypothesis had already been discussed by G. P. Zhang and W. Hübner [149] to explain the demagnetization in ferromagnetic films. However, it was later refuted by B. Koopmans [131] ; the parameters used in [149] are not compatible with those used in experiments. First, in order to make us our own ideas on the subject and second, to extend to finite systems the studies conducted for the bulk, we have investigated the effect of spin-orbit coupling on the spin dynamics in nanoparticles. To this end, still using the jellium model (assuming a purely electronic processus), we choosed the TDDFT approach (Time Dependent Density Functionnal Theory) which have been completed by the introduction of the spin-orbit coupling term. We have thus observed that the spin-orbit coupling is a good mechanism for demagnetization, but it is not sufficient to explain the experimental observations. Indeed, as confirmed by a recent publication [? ], the quantity of orbital angular momentum is not a good reservoir to absorb the amount of spin angular momentum coming from the demagnetization. However, if the mechanism induced by the spin-orbit coupling is not sufficient to explain the full demagnetization, it is necessary as explained in the last part. In addition, we were able to highlight the important role played by the polarization of the laser pulse in the demagnetization process. This last aspect has been recently confirmed experimentally [138]. In the very last part of the manuscript, we propose a microscopic mechanism allowing to go beyond mean field which involves jointly the electron-electron collisions, the spin-orbit coupling and the conservation of total angular momentum. A diagram of the algorithmic model is proposed to allow its implementation in a standard TDDFT approach. Indeed, we believe that a redistribution of angular momentum induced by electron collisions must play a crucial role in the demagnetization phenomenon and all the more so that (i) the electronic temperatures, because of the interaction with the laser, are very high, and (ii) the highly nonlinear processes of electron collisions
Demarty, Sylvain. "Contribution à l'étude électromagnétique théorique et expérimentale des cartes de circuit imprimé." Limoges, 2006. http://aurore.unilim.fr/theses/nxfile/default/21c7910e-cd16-4aaf-a075-3639b658bc3f/blobholder:0/2006LIMO0042.pdf.
This thesis document presents a theoretical and experimental printed circuit boards analysis to understand their electromagnetic behaviour. In particular, the work completed during this research project is related to electromagnetic compatibility (EMC). In that field, the study was split in two themes : design of an electromagnetic near field measurement bench and its associated probes, and a development of numerical analysis software for the calculation of coupling between PCB strips. The first axis was the subject of a development phase, passive probes calibration, and a validation of the bench. The second research axis is based on the theory of the lines which was used to develop a software dedicated to the engineers. The theoretical results were validated with an experimental real case and a parametric study was undertaken to show its provisions
Zein, Samir. "Études théoriques des composés à transition de spin mono- et bi- nucléaires." Lyon 1, 2005. http://www.theses.fr/2005LYO10174.
Oblak, Blagoje. "BMS Particles in Three Dimensions." Doctoral thesis, Universite Libre de Bruxelles, 2006. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/231882.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Oblak, Blagoje. "BMS Particles in Three Dimensions." Doctoral thesis, Universite Libre de Bruxelles, 2016. https://dipot.ulb.ac.be/dspace/bitstream/2013/231882/4/Thesis.pdf.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Weitz, Eamonn. "Theoretical developments for jets in heavy-ion collisions." Electronic Thesis or Diss., Nantes Université, 2023. http://www.theses.fr/2023NANU4063.
The quark-gluon plasma (QGP) is an exotic phase of matter, composed of deconfined quarks and gluons and is briefly created in heavy-ion collisions (HIC) at the LHC and at the RHIC. High-energy, self-collimated structures of final-state particles also created in HIC, called jets, probe the QGP, piercing through it on their way to the particle detector. In particular, as the jet propagates, it is quenched, shedding its energy through its interaction with the QGP. Quantum field theory at finite temperature – thermal field theory, is then an extremely powerful tool, capable of analytically quantifying how such a high-energy object interacts with a weakly coupled thermal bath. In this thesis, we work towards the computation of corrections (in the expansion of the strong coupling constant) to two quantities, which dictate how jets are quenched by the QGP. The first being the transverse momentum broadening coefficient, which describes how the jet diffuses in transverse momentum space through its interaction with the medium. We focus on the computation of logarithmically enhanced corrections, carefully showing how the thermal scale affects the logarithmic phase space. The second is the asymptotic mass, which can be thought of as a shift in the jet’s dispersion relation as it undergoes forward scattering with the medium’s constituents. We complete a matching calculation, which rids the mass’ classical corrections of any unphysical divergences, while also beginning the completion of its full two-loop, quantum corrections
Brugeas, Isabelle. "Analyse théorique des effets de perturbations electromagnétiques sur un aéronef dans la gamme 500 MHz-5GHz." Limoges, 1993. http://www.theses.fr/1993LIMO0185.
Saporta, Albert. "Phenomenological analysis of charged lepton flavour changes." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1110/document.
In this doctoral thesis, we investigate charged lepton flavour violating processes in effective field theory, in which possible new physics effects can be parametrized by higher dimensional gauge invariant operators built from Standard Model fields. The discovery of neutrino oscillations is a clear evidence that lepton flavour violation can occur and that neutrinos are massive. In the Standard Model extended with massive neutrinos, charged lepton flavour violating processes are strongly suppressed, and the discovery of such processes would be a clear signal of physics beyond the Standard Model. After a general introduction on the Standard Model of particle physics and beyond, this manuscript contains two introductory chapters. The first one introduce the theoretical and experimental context for the searches of charged lepton flavour violating processes, and their huge potential to constrain new physics model. We make a review of many processes and the current experiments, then we discuss the prospects for the upcoming experiments. The second chapter describe the formalism of the effective field theory approach. We discuss the principles of renormalization and loop integrals calculations with dimensional regularization. We also discuss the renormalization group equations that describe the running and the mixing of the coefficients with the energy scale. Finally, we discuss two different approaches in effective field theories. After introducing the experimental context and the effective field theory formalism, we study the μ → e conversion on nuclei in a top-down approach and charged lepton flavour violating two and three body decays of pseudoscalar mesons in a bottom-up approach. We first list all the operators and their associated coefficients that contribute to the processes. In our work, we mostly focus on dimension six operators. We compute the branching ratios for each processes as a function of the operator coefficients at the experimental scale, and use the experimental upper limit to constrain the coefficients. We also use the renormalization group equations to compute the running and the mixing of the coefficients with energy scale in both top-down and bottom-up approaches. The results discussed in this thesis are based on two publications [1, 2]
Riffet, Vanessa. "Interactions non-covalentes et propriétés physico-chimiques de petits systèmes biologiques : approches théoriques." Palaiseau, Ecole polytechnique, 2014. https://tel.archives-ouvertes.fr/tel-01084858/document.
The three-dimensional structure and physico-chemical properties of biomolecules such as peptides are not only governed by their elementary composition but also various non-covalent intra-and inter-molecular interactions. The characterization, measurement and effects of these interactions are currently at the center of many researches at the interface between biology and physical chemistry. In this context, the aim of our thesis is a better understanding of these interactions in biomolecules and aggregates using the tools of quantum chemistry and molecular modeling. In this regard, due to the complexity and size of the real biological systems, chemical models have been developed. These have allowed us to study and understand the nature and effects of these interactions taken "individually" on the geometric and electronic structure of molecular systems such as small peptides and aggregates of glycine betaine. The role of non-covalent interactions on the reactivity of various physico-chemical conditions (electronic reduction, gas phase, microsolvation) is also one of the several approaches of our work. Among the systems examined, many of them included at least one ammonium, guanidinium or imidazolium charged groups, which are founded in the side chains of the amino acids lysine, arginine and histidine. We have shown that the chemical environment of these electronic charges greatly influences the structure and reactivity of the molecules that contain these groups. Eventually, we both performed a calibration of modeling methods for the study of the electronic properties of radical peptides and developed new protocols for the potential energy surface exploration starting from the AMOEBA polarizable force field, in order to optimize the conformational searches exhaustivity for flexible biological systems
Delpueyo, Didier. "Étude théorique et expérimentale des microstructures martensitiques dans les alliages à mémoire de forme." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2011. http://tel.archives-ouvertes.fr/tel-00626616.
Abendshein, Andreas. "Hamiltoniens effectifs pour des aimants quantiques sous champ magnétique." Toulouse 3, 2008. http://thesesups.ups-tlse.fr/452/.
This thesis deals with the physics of one-and two-dimensional quantum magnets in a magnetic field. Using numerical methods, we consider coupled dimer systems which are described with models of strongly correlated electrons: namely, the spin ladder and the orthogonal dimer chain in one dimension as well as the Heisenberg bilayer and the Shastry-Sutherland lattice in two dimensions. In order to derive effective hamiltonians, we apply the method of ”Contractor Renormalization (CORE)” which is a non-perturbative real-space renormalization technique capable of reproducing the low-energy physics of a system while reducing its complexity. The analysis of the effective model – either with analytical means or numerically by solving effective systems with exact diagonalisation – allows us to conclude on the physics of the system and in particular on the existence of magnetization plateaux. We compare our results both with exact numerical studies of the microscopic model and with other theoretical approaches. Since we study models characterizing real compounds, we also discuss our results in the light of experimental data. For example, we suggest the stability of new magnetization plateaux for the Shastry-Sutherland lattice which asks for experimental clarification
Lasseri, Raphaël-David. "Distribution spatiale de fermions fortement corrélés en interaction forte : formalisme, méthodes et phénoménologie en structure nucléaire." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS248/document.
The atomic nucleus is intrinsically a complex system, composed of strongly correlated non-elementary fermions, sensitive to strong and electroweak interaction. The description of its internal structure is a major challenge of modern physics. In fact the complexity of the nucleon-nucleon interaction generates correlations which are responsible of the diversity of shapes that the nuclei can adopt. Indeed the nuclei can adopt either quasi-homogeneous shapes when nucleons are delocalized or shapes where spatially localized structure can emerge, namely nuclear clusters. This work is an extension of relativistic mean-fields approach (RMF), which allows an universal treatment of nuclear phenomenology. In a first time we will present the necessary formalism to construct such an approach starting with the fundamental interactions underlying nucleons dynamics within the nucleus. However this approach doesn't allow an accurate reproduction of experimental properties: a purely mean-field approach neglects to many correlations. Existing methods to treat both particle-hole (deformation), particle-particle (pairing) correlations will be discussed. First we will propose a new diagrammatic method, which take correlation into account in a perturbative way, the implementation of this approach using combinatory theory will be discussed. Then we will get back to a phenomenological treatment of particle-hole correlations, to focus on the impact of particle-particle. Formation of nucleonic pair will be discussed in the language of graph theory, allowing several formal simplifications and shed a different light on pairing. Pairing correlations will be at first treated using a relativistic Hartree-Bogolioubov approach. Nevertheless this formalism doesn't conserve particle number, and thus we will present a projective approach to restore it. The effect of this restoration will also be studied. Then to describe general nuclear deformation, several implementations and optimizations developed during this PhD will be presented. With this tools, clusterisation will be investigated as phenomenon emerging for certain class of correlations. Localization measure will be derived allowing a clearer understanding of cluster physics. The analysis of theses quantities makes possible a first unified description of cluster formation both for light nuclei (Neon) or for heavy alpha emitters (Polonium). Cluster emergence will be described as a quantum phase transition, an order parameter will be displayed and this formation will be characterized as a Mott transition. The influence of pairing correlations on cluster formation is studied and a detailed study of pairs spatial properties is performed for nuclei from several mass regions. Lastly a method allowing treatment of 4-body correlations (quartteting) is proposed to explain cluster emergence as alpha particle preformation
Megi, Fabien. "Étude théorique d'agrégats soumis à des champs laser intenses." Phd thesis, Université Paul Sabatier - Toulouse III, 2005. http://tel.archives-ouvertes.fr/tel-00011994.
Premièrement nous proposons d'ajouter un terme d'amortissement avec la surface au modèle nanoplasma original de T.Ditmire et al. (1996). Nous comparons diverses observables expérimentales (xénon) et étudions l'évolution des états de charge avec la taille ou l'éclairement.
Deuxièmement nous proposons un modèle microscopique de dynamique moléculaire à trois dimensions robuste en l'absence d'excitation. L'émission électronique à 10^11 W/cm^2 (sodium) se compare à celle obtenue par d'autres modèles tels que le modèle VUU-LDA. Les électrons de coeur sont émis à partir de 5 10^15 W/cm^2. Les événements rares sont accessibles et nous montrons que l'explosion ionique de type coulombien est autosimilaire (10^16 W/cm^2). Enfin, l'émission électronique (gaz rare) est comparée avec le modèle nanoplasma.
Megi, Fabien. "Etude théorique d'agrégats soumis à des champs lasers intenses." Toulouse 3, 2005. http://www.theses.fr/2005TOU30110.
During this PhD thesis we have been studying by two models the interaction of lasers (intensity 10^11 to 10^17 W/cm^2) with big size clusters (100 atoms to a few thousand). We propose to add a term of damping with the surface to the original nanoplasma model of T. Ditmire et al. (1996). We get good agreement with experimental evidences (xenon) and study the evolution of charge states with size or intensity. We propose a robust, three dimensional and microscopic, molecular dynamics model, stable in the absence of excitation. The soft Coulomb potential is parameterized to mimic the atomic energy levels. The electronic emission at 10^11 W/cm^2 (sodium) is comparable to the one obtained by other models such as VUU-LDA model. Core electrons are emitted from 5 10^15 W/cm^2. We show that rare events are accessible and that ionic explosion is Coulomb like and self-similar (10^16 W/cm^2). Eventually, electronic emission (rare gaz) is compared with the nanoplasma model
Zhang, Wenxing. "Études théoriques de l'effet de couplage électron-phonon sur les propriétés de transport dans les nanofils de silicium." Thesis, Lille 1, 2009. http://www.theses.fr/2009LIL10016/document.
In this thesis, the electronic structure, the phonon spectrum, and the electron-phonon (e-p) coupling effect in transport properties of Silicon Nanowires (SiNW) have been studied systematically based on Tight-Binding (TB) model and Valence-Force-Field (VFF) model. The electronic structure of SiNW is strongly dependent on the orientation and the diameter, even changing from direct gap to indirect gap, and the gap of SiNWs decreases and tends to the bulk value as the diameter increases. The phonon spectra are also dependent on the orientation and the diameter. It’s a character of nanowires that there are four acoustic phonon modes. Based on the calculation of both low field mobility and lifetime of electrons in SiNWs along [110], it’s confirmed that at room temperature the transport of carriers in SiNWs strongly depends on the phonon scattering, involving both optical phonons and acoustic phonons. The mobility increases and tends to the bulk value when the diameter increases. The mobility decreases in power law when the temperature increases from 77K to 300K. The relationship between the mobility and the density of carrier is more complicated. For low density of carrier (<10 19/cm3), the mobility is almost constant because it is approximately independent on the Fermi level at low concentration. For higher concentration, the mobility is strongly dependent on the density of carrier because the Fermi level is high enough to cross the conduction band edge (CBE) and multi-band transport becomes important. In a second study undertaken in this thesis, TB model and Nonequilibrium Green's Function (NEGF) are used to calculate the ballistic transport properties of carbon nanotube (CNT) heterojunctions (n1,m1)/(n2,m2)/(n1,m1). The conductance of semiconducting junctions decreases exponentially when the length of the middle CNT (n2,m2) increases. However, the conductance of (12,0)/(9,0)/(12,0) increases when the length of the CNT (9,0) increases. This anomalous increase of conductance is explained and reproduced very well by an exponentially dropped potential. Furthermore, the relationship between the conductance and the rotation symmetry in metallic jonctions is studied. The conductance spectra change periodically, and there are three different spectra at most for a special type of jonction. This universal behavior of conductance can be well understood by the phase difference of electrons, which travel through two interfaces of a junction. Finally, the ballistic conductance of multi-Iead junctions is studied and the possibility of making pure CNT electronic device is revealed
Zhang, Wenxing. "Études théoriques de l'effet de couplage électron-phonon sur les propriétés de transport dans les nanofils de silicium." Electronic Thesis or Diss., Lille 1, 2009. http://www.theses.fr/2009LIL10016.
In this thesis, the electronic structure, the phonon spectrum, and the electron-phonon (e-p) coupling effect in transport properties of Silicon Nanowires (SiNW) have been studied systematically based on Tight-Binding (TB) model and Valence-Force-Field (VFF) model. The electronic structure of SiNW is strongly dependent on the orientation and the diameter, even changing from direct gap to indirect gap, and the gap of SiNWs decreases and tends to the bulk value as the diameter increases. The phonon spectra are also dependent on the orientation and the diameter. It’s a character of nanowires that there are four acoustic phonon modes. Based on the calculation of both low field mobility and lifetime of electrons in SiNWs along [110], it’s confirmed that at room temperature the transport of carriers in SiNWs strongly depends on the phonon scattering, involving both optical phonons and acoustic phonons. The mobility increases and tends to the bulk value when the diameter increases. The mobility decreases in power law when the temperature increases from 77K to 300K. The relationship between the mobility and the density of carrier is more complicated. For low density of carrier (<10 19/cm3), the mobility is almost constant because it is approximately independent on the Fermi level at low concentration. For higher concentration, the mobility is strongly dependent on the density of carrier because the Fermi level is high enough to cross the conduction band edge (CBE) and multi-band transport becomes important. In a second study undertaken in this thesis, TB model and Nonequilibrium Green's Function (NEGF) are used to calculate the ballistic transport properties of carbon nanotube (CNT) heterojunctions (n1,m1)/(n2,m2)/(n1,m1). The conductance of semiconducting junctions decreases exponentially when the length of the middle CNT (n2,m2) increases. However, the conductance of (12,0)/(9,0)/(12,0) increases when the length of the CNT (9,0) increases. This anomalous increase of conductance is explained and reproduced very well by an exponentially dropped potential. Furthermore, the relationship between the conductance and the rotation symmetry in metallic jonctions is studied. The conductance spectra change periodically, and there are three different spectra at most for a special type of jonction. This universal behavior of conductance can be well understood by the phase difference of electrons, which travel through two interfaces of a junction. Finally, the ballistic conductance of multi-Iead junctions is studied and the possibility of making pure CNT electronic device is revealed
Latinne, Olivier. "Etude théorique de l'ionisation multiphotonique d'atomes en champs lasers intenses." Doctoral thesis, Universite Libre de Bruxelles, 1995. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212590.
Ngome, Abiaga Juste Jean-Paul. "(Super) symétries des modèles semi-classiques en physique théorique et de la matière condensée." Phd thesis, Tours, 2011. http://tel.archives-ouvertes.fr/tel-00622874.
Kimmoun, Olivier. "Etude théorique et expérimentale des champs de vagues à courtes crêtes." Aix-Marseille 2, 1997. http://www.theses.fr/1997AIX22108.
Niro, Pierluigi. "Strong coupling in 2+1 dimensions from dualities, holography, and large N." Doctoral thesis, Universite Libre de Bruxelles, 2021. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/327659.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Makhoute, Abdelkader. "Etude théorique des collisions électrons-hélium en présence de champs laser intenses." Doctoral thesis, Universite Libre de Bruxelles, 1991. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/213048.
de, Franckenberg Jean Henri. "Etude théorique des collisions électrons-atomes en présence de champs laser intenses." Doctoral thesis, Universite Libre de Bruxelles, 1988. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/213356.
Perrot, Olivier. "Étude théorique des propriétés statistiques de la lumière dans les dispositifs optiques à deux modes couples : génération d'états comprimés." Paris 11, 1986. http://www.theses.fr/1986PA112050.
In this work we present two approaches in order to estimate the evolution of quantum fluctuations on the components of a field coupled with its second harmonic. In the first approach, the numerical calculation is performed by integrating all the components of the matrix-density of the two modes-field, while in the second one, we expand Taylor series of the observables, on a computer using the symbolic language REDUCE. Then, these series are estimate with quadratic Pade approximants. From this study, we take out the mains properties of this device: Whatever input fields, the maximum reduction of fluctuations is reached for one optimal time interaction. This device can squeeze thermal fields. In all the cases, the squeezing increases with the intensity of inpùt-fields. Squeezing appears as a quantum macroscopic effect
Krief, Hervé. "Sémiotique et communication : incidences d'un champ théorique sur la pratique réelle." Perpignan, 1997. http://www.theses.fr/1997PERP0232.
Seck, Baye N'dialou. "Sillages M. H. D. En champ aligné : contribution théorique et expérimentale." Grenoble INPG, 1992. http://www.theses.fr/1992INPG0097.
Maître, Claire. "La réforme cistercienne du plain-chant : étude d'un traité théorique." Paris 1, 1992. http://www.theses.fr/1992PA010613.
This thesis is divided into three volumes : 1) an historical study of the reform of plain-chant within the cister cian order, during the twelfth century. 2) edition and translation of the treatise which formalized this reform. This treatise is now preserved in just one faulty copy, from the thirteenth century : ms Paris, Bibliothèque Sainte-Geneviève, 2284 3) Musical commentary of this treatise
Pillon, François. "Étude de la brisure de symétries dans des théories de cordes et de supergravité." Paris 7, 1995. http://www.theses.fr/1995PA077070.
Rabah, Hassan. "Étude théorique et expérimentale de faisabilité d'une stimulation électrique par champs électrique et ultrasonore simultanés." Nancy 1, 1993. http://www.theses.fr/1993NAN10022.
Gomes, Jean-Marie. "Etude expérimentale et théorique de la genèse des potentiels de champs locaux par les neurones corticaux." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066409/document.
Local field potentials (LFPs) are low-frequency (< 200-500 Hz) events resulting from brain activity. Their meaning and the mechanisms shaping them have been highly debated for decades. The existence and importance of a frequency-dependant filtering of ionic currents by brain tissue is controversial. Some authors conclude that the medium is resistive, while others suggest that brain tissue may exert significative low-pass filtering on electrical currents. A new measurement method is presented here, relying on the concept of natural impedance, which is measured using a neuron as an ''electrode''. This allows to obtain the most relevant impedance from a physiological point of view, in terms of electrode-medium interface, current intensity and spatial scale. The measured impedance is stable, reproducible, stronger than what is traditionally measured, and has a 1/\√f frequency dependance. A physical model, taking into account ionic diffusion in the medium, is able to reproduce this impedance. A similar method allows to compute the transfer function between the intra- and extracellular potentials of a neuron. Models are proposed to explain its structure, predict LFPs from cell activity and vice-versa. These results may help interpreting LFP and electroencephalography signals, yielding a deeper understanding of the physiological and pathological brain function
Versnaeyen, Christophe. "Étude théorique et experimentale du transistor à effet de champ à hétérojonction AlGaAs/GaAs." Lille 1, 1985. http://www.theses.fr/1985LIL10074.
Bollaert, Sylvain. "Etude théorique et expérimentale de transistors à effet de champ à canaux quasi-unidimentionnels." Lille 1, 1994. http://www.theses.fr/1994LIL10032.
Odry, Dominique. "Logiques et discours de l'évaluateur : contribution à une définition du champ théorique de l'évaluation." Paris 8, 1994. http://www.theses.fr/1994PA080892.
The notion of evaluation is attracting increasing attention in the field of education. Is it possible to bring out the different systems of ideas at work both at the discourse level as well as at the practical level ? our study is an epistemological one, and is built on the analysis of classroom based research as well as on the study of a corpus of texts. Discourse analysis reveals the overwhelming presence of three differents types of utterance : explanations, descriptions of actions and utterances of implication. These three utterance types reveal the different systems of ideas that evaluative discourse attempts to bring together. A phenomenological approach allows us to show that this type of discourse rests on the ambiguous nature of the relationship between meaning, signification and value. A methodological analysis of the notions of referent, criterion, and indicator is made. In the field of evaluation, the term indicator condenses several aspects of the sign. A particular paradigm is put forward. Evaluation as a form of discourse in the field of education is seen as emanating from a divided subject. To apprehend it, it is necessary to construct a model analagous to the trilogy of personel pronouns 'i you he'
Mouis, Mireille. "Étude théorique du fonctionnement des dispositifs à effet de champ haute mobilité à hétérojonction." Paris 11, 1988. http://www.theses.fr/1988PA112053.
Toen, Bertrand. "K-théorie et cohomologie des champs algébriques." Phd thesis, Université Paul Sabatier - Toulouse III, 1999. http://tel.archives-ouvertes.fr/tel-00773086.
Faquir, Mohamed. "Aux frontières de la théorie des champs." Montpellier 2, 2006. http://www.theses.fr/2006MON20163.
I. The equation describing short waves dynamics on th surface of a fluid after a Green-Naghdi type reduction of Euler equations is found to be a new integrable system that exhibits very interesting properties. Indeed, an unexpected relation with the sine-Gordon model, through transformations involving a conserved quantity, leads to singular and multivalued solutions for the new equation and allows to build a description in terms of the Lagrangien of a relativistic field. The existence of cases very similar to this one leads us to investigate general condition for this kind of relations to appear and to study a model not explicitely Lorentz-invariant which mix two of the equations we obtained earlier. The last point we focus on is the effects on low-order quantum corrections due to those transformations. II. In order to find a consistent theory for higher-spin fields, we have studied a new way to build gauge groups and fields based on string field theory and mixing all levels of spin. We first calculate elements of the group and the composition law thanks to hermiticity constraints. We then choose the gauge fields to belong to the adjoint representation of the group and modify them to get closer to usual definitions. Eventually, the study of the spin 3 needs us to introduce auxiliary fields which can be used to build a Lagrangian for the massive spin 2, analogous to what Veltman did in the Yang-Mills case
Reynaud, Damien. "Développement perturbatif variationnel en théorie des champs." Montpellier 2, 2001. http://www.theses.fr/2001MON20216.
Métivet, Thibaut. "Lattice QCD at the physical point : pion-pion scattering and structure of the nucleon." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112243/document.
The formalism of Quantum Chromodynamics on the lattice (or Lattice QCD) allows to perform ab-initio non-perturbative studies of strong-interaction driven processes, as it provides both a covariant regularisation of the theory of QCD and a natural framework for numerical computations. In this work, after a review of the main features of QCD and a step-by-step presentation of our discretization of QCD on a lattice, we undertake detailed studies of two problems of hadronic physics: the phenomenon of resonant scattering and the structure of the nucleon. The lattice calculations are performed with the Budapest-Marseille-Wuppertal Collaboration's 2+1-flavour gauge configurations, which give access to a wide range of lattice spacings, volumes and quarks masses, thereby allowing to study the sensibility of our results on these parameters, and to perform a complete continuum extrapolation. These configurations include dynamical quarks, and use a clover-improved Wilson QCD action. To investigate the scattering of particles on the lattice, we set up a Lüscher analysis for the emblematic case of pion-pion scattering in the channel of the rho meson resonance. We analyse our data with a variational generalized eigenvalue method, and give an in-depth calculation of the scattering phase-shifts and the corresponding resonance parameters, with a full control of the systematic errors. Our results provide an important step for lattice studies of scattering states, as they are the first to be performed at the physical pion mass, where one can see the actual decay of the rho into two pions. The obtained rho meson parameters are in good agreement with the experimental values, and consistent with a weak pion mass dependence of the coupling between the rho and two pions. As for our probe of the structure of the nucleon, we present a complete extraction of the electroweak isovector form factors, with a comprehensive study of the electric charge squared radius and of the axial charge. Our analysis also feature data at the physical pion mass, which turns out to be crucial in order to perform safe extrapolations to the physical point, as the chiral perturbation theory predicts violent variations of these quantities near the massless-quarks point. Our calculation includes source and sink projections onto the nucleon state, as well as a combined fit method between the two-point and three-point correlation functions to control the contamination of our data by excited states. Although one would need more data to perform a high-accuracy determination of the nucleon radius and axial charge at the physical point with a relevant estimation of the systematic errors, the results we obtain are in good agreement with the experiment and suggest that the excited-state effects are under control. Our analysis also highlights that gauge configurations ensembles near the physical pion mass and with large volumes must be used in order to extract accurate information about the nucleon structure from lattice calculations
Chqondi, Soumia. "Etude théorique de petits systèmes quantiques en champ laser intenses (infrarouges et/ou hautes fréquences)." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066546/document.
The interaction between laser radiation and atomic system, can lead to various physical processes such as photoionization, multiphoton ionization, tunneling ionization, High Order Harmonic Generation ... The importance of each of these processes is in fact dependent on the intensity and frequency of the laser field. In this thesis, we describe the interaction of a laser field (Infrared and / or high frequencie) with hydrogen (arche-type of a system with one active electron). We first developed numerical methods for solving the time-dependant Schrödinger equation of time describing the hydrogen atom laser system. These methods allowed us to write a numerical code for the simulation of solutions of this equation. We then used, after the verification of the numerical convergence of our program to present the results on the single-photon photoionization on multiphoton ionization. We also concentrate on another phenomenon resulting from the ionization process, it is absorption of photons above the ionization threshold, named process ATI (above threshold ionization). Then, we will apply this numerical code to the photoionization hydrogen combining two photons, infrared (low frequency) and one of its harmonics (high frequency). Finally, a calculation of the angular distribution of the emitted electron was carried out numerically
Hussein, Yasser. "Analyse de champs de vitesse par FTLE à partir de la méthode des moments : validation théorique et expérimentale." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2016. http://www.theses.fr/2016ESMA0009/document.
With the development of technology, instantaneous flow fields coming from experiments or numerical simulation are available now. It has been followed by a rise of interest for the Lagrangian analysis of such data. One central tool to analyze the flow fields is the Finite Time Lyapunov Exponent (FTLE). It allows to the identify of the Lagrangian Coherent Structures (LCS) which appear as ridges in the FTLE fields. The LCS are quasi transport bareers and separatte the fluid domain into regions which have different dynamic properties. However, the computation methodology currently used in order to obtain the FTLE requires numerical evalution of a large number of fluid particle trajectories on cartesian or adaptive meshes that are superimposed on the original data grid.In this thesis, we propose a new method for calculating the Finite Time Lyapunov Exponent FTLE fields. For this, we use the method of second-order moments which allows to evaluate over time the dispersion of particles uniformly distributed in a circular or elliptical domain. We call this new scalar field, the M-FTLE field. We validate this approach theoretically, at every point of the fluid domain by comparing FTLE and M-FTLE and also by the comparison of the classic examples (linear velocity field, circular and hyperbolic) and a numerical example (velocity field of double gyre). This method is then applied on experimental measurements of tidal bore velocity fields, obtained within the institute 'Pprime' by using a measurement technique called particle image velocimetry (PIV)
Katrib, Juliano. "Etude théorique et expérimentale des implants médicaux actifs en environnement électromagnétique : application aux défibrillateurs implantables en champ magnétique basse fréquence dans la bande 50Hz - 50kHz." Electronic Thesis or Diss., Nancy 1, 2011. http://www.theses.fr/2011NAN10134.
This thesis was conducted under a contract between the "Electronic Measurements" Research Group within the Electronic Instrumentation Laboratory of Nancy and the Research Department of EDF. The focus of this thesis is the behavior of implantable defibrillators in low frequency (50 Hz-50 kHz) magnetic environments. The first chapter introduces the principles and summarizes the basics of the interactions between electromagnetic fields and active medical implants. General and specific data concerning implantable medical devices are also presented. The main aim of the second chapter is to determine the fields and/or electric currents induced in a human body by a magnetic source at low frequency (50 Hz to 50 kHz). The calculations are based on a finite integral method elements model using CST software. In the third chapter, a virtual phantom is described, based on 77 different organs. It is constructed using the Virtual Family. Based on the above results, an implantable defibrillator is inserted into the virtual model to calculate the voltages induced at the end of the probe. These voltages are compared with threshold values obtained from the Standards to demonstrate their very low values regardless of the frequency of the magnetic field. The fourth and final chapter presents the results obtained for experimental validation with in vitro tests in an electromagnetic phantom made of gelatin, placed within a Faraday cage. A cardiac signal is generated as an artificial lure. The experimental set up is configured and managed by virtual instrumentation (GPIB HPVEE). It controls the power source and collects telemetry signals via the defibrillator. Some reversible episodes were observed at 50 Hz showing the sensitivity of the electronics (input filter) according to the ICD models destined for Europe (50 Hz) and the USA (60 Hz). These are normal values for heart rate. The series of measurements showed no failure for four defibrillators tested in electromagnetic fields up to 3.44 mT
Harrivel, Dikanaina. "Théorie des champs : approche multisymplectique de la quantification, théorie perturbative et application." Phd thesis, Université d'Angers, 2005. http://tel.archives-ouvertes.fr/tel-00011761.
Nous nous interessons tout d'abord à l'équation linéaire et nous proposons une description multisymplectique de la quantification canonique par le biais d'une representation des symétries, de la quantification par deformation et enfin nous introduisons la notion de quatification par déformation multisymplectique.
Ensuite nous traitons le champ en interaction. Nous construisons dans un premier temps des observables sous la forme de séries sur les arbres plans puis nous montrons comment elles peuvent être reliées aux séries de Butcher. Enfin nous voyons comment appliquer nos résultats à la théorie du contrôle.
Harrivel, Ramiaramanana Dikanaina. "Théorie des champs : approche multisymplectique de la quantification, théorie perturbative et application." Angers, 2005. http://www.theses.fr/2005ANGE0027.
The main subject of this thesis is the study of the Klein-Gordon equation together with an interaction term and the quantization of this theory from the multisymplectic point of view. Multisymplectic geometry provides a general framework for a covariant finite dimensional Hamiltonian formulation of variational problems with several variables. In the first part we study the linear Klein-Gordon equation (free fields). We propose a description of the canonical quantization of free fiels from the multisymplectic point of view. We investigate three approachs : the algebraic approach by giving a representation of the Lie algebra of the symetries, the deformation point of view and finally we introduce a notion of multisymplectic geometric quantization. In the second part we study the classical Øp-theory. First we define explicitely a conserved quantity using a perturbative expansion based on planar trees and a kind of Feynman rule. Then we link this expansion with Butcher series which describe the perturbative expansion of the solutions of some PDE and we show how Butcher series can be related to perturbative quantum theory. Finally we see how we can apply our result in order to solve problems from control theory
Allard, Denis. "Détection des rayons cosmiques ultra-énergétiques avec l'observatoire Pierre Auger et étude théorique de leur propagation dans le milieu extragalactique." Paris 6, 2004. http://www.theses.fr/2004PA066350.
Bégin, Luc. "Règles de fusion en théorie des champs conformes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0021/NQ48526.pdf.
Iacomi, Marius. "Calculs non-perturbatifs en théorie des champs bidimensionnelle." Montpellier 2, 1997. http://www.theses.fr/1997MON20240.
Arvanitis, Christos. "Méthodes variationnelles-perturbatives en théorie quantique des champs." Aix-Marseille 2, 1993. http://www.theses.fr/1993AIX22059.