Ce travail porte sur les techniques de mesure des champs en cavité électromagnétique et plus précisément en chambre réverbérante. En raison de la perturbation induite sur la distribution du champ au sein d'une cavité résonante par la présence d'un objet, les techniques de mesure de champ classiques utilisant une antenne souffrent d'une précision limitée. Par conséquent, nous proposons une nouvelle technique de mesure de la distribution du champ électrique basée sur la théorie des perturbations. Elle consiste à mesurer les variations de la fréquence de résonance de la cavité pour chaque position de l'élément perturbateur introduit dans la cavité, puis à en déduire la variation de l'amplitude du champ électrique. Le choix de la forme de l'objet perturbateur, de ses dimensions et de son matériau constitutif est effectué à partir des résultats des simulations et des mesures dans un cas canonique, de façon à adapter le banc de mesure au cas étudié. Cette technique de mesure est ensuite appliquée avec succès au cas d'une chambre réverbérante équipée d'un brasseur de modes, ainsi qu'à des mesures de champ à l'intérieur d'un boitier inséré dans la cavité. Cette approche a permis, via un post-traitement basé sur l'utilisation de l'algorithme MUSIC, de déterminer avec une grande précision les directions d'arrivée des champs dans la chambre réverbérante / This work deals with field measurement techniques in large electromagnetic enclosures namely reverberation chambers. Due to the perturbation of the field distribution within a resonant cavity due to the presence of an introduced object, conventional field measurement techniques employing an antenna suffer from a limited accuracy. Therefore we propose a new measurement technique of the electric field distribution based on the perturbation theory; it consists of a measure of the cavity resonant frequency variation when displacing a small perturbing object within the cavity, and leads to the electric field distribution. The choice of the perturbing object shape, dimension and material is discussed with the help of simulation and measurement results in a canonical case in order to adapt the measurement setup to the studied case. This technique is then successfully employed in a reverberation chamber equipped with a mode stirrer, as well as to measure the field within a metallic box placed in the cavity. Using a post-processing based on MUSIC algorithm, this approach has permitted to determine accurately the field directions-of-arrival in the reverberation chamber

The need for reliable, high-throughput, mobile wireless communication technologies has never been greater as increases in the demand for on-the-go access to information, entertainment, and other electronic services continues. Two such technologies, which are at the forefront of current research efforts, are orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output (MIMO) systems, their union being known simply as MIMO-OFDM. The successful performance of these technologies depends upon the availability of accurate information concerning the wireless communication channel. In this dissertation, several issues related to quality of this channel state information (CSI) are studied. Specifically, the first part of this dissertation considers the design of optimal pilot signals for OFDM systems. The optimization is addressed via lower bounds on the estimation error variance, which bounds are given by formulations of the Cram'{e}r-Rao bound (CRB). The second part of this dissertation uses the CRB once again, this time as a tool for evaluating the potential performance of MIMO-OFDM channel estimation and prediction. Bounds are found for several parametric time-varying wideband MIMO-OFDM channel models, and numerical evaluations of these bounds are used to illuminate several interesting features regarding the estimation and prediction of MIMO-OFDM channels. The final part of this dissertation considers the problem of MIMO multiplexing using SVD-based methods when only imperfect CSI is available. For this purpose, general per-MIMO-subchannel signal and interference-plus-noise power expressions are derived to quantify the effects of CSI imperfections, and these expressions are then used to find robust MIMO-SVD power and bit allocations which maintain good overall performance in spite of imperfect CSI.

Not so long ago, the value of the branching ratio of a neutral pion decay to an electron-positron pair (π0 → e− e+ ) has been updated and became more accurate thanks to the fact, that new measurements were performed at KTeV experiment at Fermilab. In this context it has been showed, that the Standard Model theoretical prediction is not precise enough. The resulting discrepancy was not explained yet. In presented work, there are summarized preceding results, al- ready computed correction were taken into account and newly the Bremsstrahlung contribution was thoroughly calculated. Besides, the contribution of π-loop cor- rections in terms of double-logarithms is estimated. In the end, because of the persisting disagreement of the accepted theory with the experiment, an additional contribution is suggested from beyond the Standard Model on the basis of models describing the dark matter. The latter mentioned is a hot candidate to explain many phenomena, for example the mysterious source of a great amount of γ-rays coming from the center of our galaxy and having the origin in the annihilation of electron-positron pairs. 1

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Conductivity of semicoductor nanostructures has its maximum in terahertz spectral range. Linear response is described in reasonable detail. With high intensity light sources it is also needed to be concerned with nonlinear response. In this thesis, there is firstly described already existing quantum model of linear conductivity which is using perturbation theory. This model is then extended by adding another perturbations, getting us quantum model for calculating nonlinear conductivity of arbitrary order. Model is then applied for calculation of third order nonlinear conductivity spectra for cubic nanocrystal. There is described spectra for varying parametres, such as tempera- ture, volume, electron density or scattering rate. In the end it is compared with semiclassical compuptation using Monte-Carlo simu- lation. 1

This thesis familiarizes the reader with the process behind the construction of ππ scattering amplitudes. Several representations and transformations nec- essary to pass from one to another are introduced. Then known solutions of Roy equations are employed to extract values of subthreshold parameters αππ and βππ from recent experimental data. As a second goal three-flavour chiral perturbation theory(χPT), which is a low energy effective field theory of quan- tum chromodynamics, is used to obtain theoretical predictions for αππ and βππ by applying a technique called resummed approach. A large statistical ensemble of predictions is numerically generated. Subsequently, Bayesian statistics is uti- lized to get more information about spontaneous symmetry breaking parameters X(3), Y (3), Z(3), which are related to the leading order low energy coupling constants of three-flavour χPT. These results are then compared to several other recent determinations. Significant shifts in probability distributions compared to Descotes-Genon et al. [2004] are observed. The new results are more consistent with theoretical expectations. 1 Bibliography S. Descotes-Genon, N. H. Fuchs, L. Girlanda, and J. Stern. Resumming qcd vac- uum fluctuations in three-flavor chiral perturbation theory. The European Phys- ical Journal C,...

Scope and Content stated in the place of the abstract. / The principal methods of calculating nuclear spin coupling constants by applying perturbation theory to molecular orbital wavefunctions for the electronic structure of molecules are discussed. A new method employing a self-consistent-field perturbation theory (SCFPT) is then presented and compared with the earlier methods. In self-consistent-field (SCF) methods, the interaction of an electron with other electrons in a molecule is accounted for by treating the other electrons as an average distribution of negative charge. However, this charge distribution cannot be calculated until the electron-electron interactions themselves are known. In the SCF method, an initial charge distribution is assumed and then modified in an iterative calculation until the desired degree of self-consistency is attained. In most previous perturbation methods, these electron interactions are not taken into account in a self consistent manner in calculating the perturbed wavefunction even when SCF wavefunctions are used to describe the unperturbed molecule. The main advantage of the new SCFPT approach is that it treats the interactions between electrons with the same degree of self-consistency in the perturbed wavefunction as in the unperturbed wavefunction. The SCFPT method offers additional advantages due to its computational efficiency and the direct manner in which it treats the perturbations. This permits the theory to be developed for the orbital and dipolar contributions to nuclear spin coupling as well as for the more commonly treated contact interaction. In this study, the SCFPT theory is used with the Intermediate Neglect of Differential Overlap (INDO) molecular orbital approximation to calculate a number of coupling constants involving 13c and 19F. The usually neglected orbital and dipolar terms are found to be very important in FF and CF coupling. They can play a decisive role in explaining the experimental trend of JCF among a series of compounds. The orbital interaction is found to play a significant role in certain CC couplings. Generally good agreement is obtained between theory and experiment except for JCF and JFF in oxalyl fluoride and the incorrect signs obtained for cis JFF in fluorinated ethylenes. The nature of the theory permits the latter discrepancy to be rationalized in terms of computational details. The value of JFF in difluoracetjc acid is predicted to be -235 Hz. The SCFPT method is used with a theory of dπ - pπ bonding to predict in agreement with experiment that JCH in acetylene will decrease when that molecule is bound in a transition metal complex. / Thesis / Doctor of Philosophy (PhD)

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