Accretion discs efficiently transport angular momentum by a wide variety of as yet imperfectly understood mechanisms, with profound implications for the disc lifetime and planet formation. We discuss two different methods of angular momentum transport: first, generation of acoustic waves by mixing of inertial waves, and second, the generation of a self-sustaining magnetic field via the magnetorotational instability (MRI) which would be a source of dissipative turbulence. Previous local simulations of the MRI have shown that the dynamo changes character on addition of vertical stratification. We investigate numerically 3D hydrodynamic shearing waves with a conserved Hermitian form in an isothermal disc with vertical gravity, and describe the associated symplectic structure. We continue with a numerical investigation into the linear evolution of the MRI and the undular magnetic buoyancy instability in isolated flux regions and characterise the resultant quasi-linear EMFs as a function of height above the midplane. We combine this with an analytic description of the linear modes under an assumption of a poloidal-toroidal scale separation. Finally, we use RAMSES to perform full MHD simulations in a zero net flux shearing box, followed by spatial and a novel temporal averaging to reveal the essential structure of the dynamo. We find that inertial modes may be efficiently converted into acoustic modes for "bending waves", despite a fundamental ambiguity in the inertial mode structure. With our linear MRI and the undular magnetic buoyancy modes we find the localisation of the instability high in the atmosphere becomes determined by magnetic buoyancy rather than field strength for small enough azimuthal wavenumber, and that the critical Alfven speed below which the dynamo can operate increases with increasing distance from the midplane. We calculate analytically quasi-linear EMFs which predict both a vertical propagation of toroidal field and a method for creation of radial field. From our fully nonlinear calculations we find an electromotive force in phase with the toroidal field, which is itself 3π/2 out of phase with the radial (sheared) field at the midplane, and good agreement with our quasi-linear analytics. We have identified an efficient mechanism for generating acoustic waves in a disc. In our investigation of the accretion disc dynamo, we have reproduced analytically the EMFs calculated in our simulations, given arguments based on the phase of relevant quantities, several correlation integrals and the scalings suggested by our analytic work. Our analysis contributes significantly to an explanation for the dynamo in an accretion disc.

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La représentation du mouvement – Representational Momentum (Freyd & Finke, 1984) – est la tendance qu’a un observateur à se souvenir de la position spatiale d’une cible en mouvement plus loin dans la direction du mouvement qu'elle ne l'est en réalité. La conséquence de la représentation du mouvement (RM) est donc une anticipation. La question de recherche qui traverse l’ensemble de cette thèse concerne l’impact des connaissances acquises ontogénétiquement sur la RM. Les recherches expérimentales réalisées abordent la RM en se focalisant sur la familiarité ou l’expertise de l’observateur vis-à-vis de situations dynamiques naturelles dans lesquelles il est immergé. Cette thèse comprend quatre articles : une revue de question et trois articles expérimentaux. Les résultats expérimentaux obtenus dans ces travaux montrent que les connaissances spécifiques développées par l’observateur sont décisives pour élaborer une RM efficace. En effet, moins ces connaissances sont disponibles moins l’anticipation est importante. Cependant, les connaissances spécifiques n'ont une influence sur la RM que si les scènes dynamiques sont suffisamment proches des situations qui en ont permis le développement. Enfin, ces connaissances spécifiques apparaissent en partie liées à l’action, car plus l'observateur est impliqué dans l’action, plus il anticipe la dynamique des scènes perçues. L’ensemble de ces travaux suggère que la RM est composée, non seulement de processus génériques, mais aussi de processus spécifiques élaborés à partir des situations qui sont régulièrement rencontrées. / Representational Momentum (RM) refers to the tendency of participants to "remember" the stopping point of an event as being farther along in the direction of movement than it was in reality (Freyd & Finke, 1984). The consequence of RM is anticipation. The research question that runs through this thesis concerns the impact of knowledge ontogenetically acquired on RM. The experimental research undertaken in this thesis addresses the RM focusing on the observers' familiarity or expertise about natural dynamic situations in which they are immersed. This thesis includes four articles: a review of literature and three experimental papers. The experimental results obtained show that specific knowledge developed by the observers is crucial for developing an efficient RM. The more specific knowledge is available, the stronger the anticipation. However, specific knowledge has an influence on RM only if the dynamic scenes are sufficiently similar to the situations that have led to its development. Finally, specific knowledge seems partly linked to action because the more the observer is involved in action, the more he anticipates the dynamics of the scenes. As a whole this work suggests that RM is composed of generic processes, as well as specific ones that are built up from the situations regularly encountered.

In the search for natural orbital angular momentum (OAM) effects, some of the first incoherent scatter experiments with twisted radar beams during aurora were conducted at Poker Flat Incoherent Scatter Radar (PFISR), Alaska, USA, in October 2012. Experimental data of scatter from beam configurations with opposite twists were investigated. By the use of hypothesis tests in combination with Monte Carlo simulations together with traditional estimations of the mean and confidence interval, asymmetries between scatter of radar beams with opposite twists were identified for an integration time of at least 30 minutes. Asymmetries were detected in the internal radar noise too, but not necessarily with the same signs as for the asymmetries from the ionospheric signals. The asymmetries identified could be due to amplified noise for signals coming from intense aurora or perhaps the rectangular-shaped antenna array used at PFISR. These two possible causes need to be ruled out before suggesting that the asymmetries identified are an outcome of OAM effects present in the ionosphere.

This thesis presents phenomenological studies of a state-of-the-art NNLL+NLO theoretical calculation of a novel collider observable known as 'phi star'. In these studies the 'phi star' observable, a measure of azimuthal decorrelation, is applied directly to the leptons in the production of massive lepton pairs in hadron collisions (the Drell-Yan process). This provides an alternate measure of the recoil of the massive vector boson (Z/gamma) against initial state QCD radiation, but with distinct experimental advantages over the traditional boson transverse momentum. Attention is focused on the small-'phi star' regime (the quasi-back-to-back regime) where the infrared dynamics of soft/collinear gluon emissions become important. These phenomenological studies are followed up with the presentation of a measurement of 'phi star' in 'Z to mu mu' events using 20.3 fb^-1 of collision data collected by the ATLAS experiment in 2012. Finally, studies directly related to the ATLAS absolute luminosity calibration by the van der Meer (vdM) method are presented, with the objective of elucidating the role of transverse linear beam correlation. In particular, I present studies using an analytical method I have developed in order to precisely extract individual beam information by way of studying phenomena pertaining to the luminous region during vdM scans. In addition, a dedicated study of the long- and short-term stabilities of the principal detectors for luminosity monitoring is also presented, along with an appropriate recalibration of these detectors.

This thesis deals with the description and testing of the capital market models. It consists of an analysis of the most famous models such as the CAPM, the three-factor Fama-French model, the four-factor Fama-French-Carhart model and an alternative multi-factor model that includes the current relevant risk factors. In the first part, one can find the introduction to the capital market theory that is essential for the definition of model assumptions. The second part is dedicated to the description and construction of the models in reference to the relevant research papers. The last part of this thesis contains the regression model estimates, taking into account the data set of the fifteen most profitable IT companies. A portfolio of these firms is expected to exhibit a positive and statistically significant alpha. Daily portfolio returns in the period 1990 -- 2014 are regressed on risk factors of particular models. The aim of this thesis is to test whether the capital market models are valid for the long-term portfolio returns composed of the selected shares.

The aim of this research is to develop a method for expanding the Jost functions as a Taylor-type power series on the complex angular momentum plane. From this method in conjunction with the Watson transformation, we were able to express the scattering amplitude as a sum of the background and pole terms, furthermore, this method propose a way of evaluating, numerically, the pole term. To demonstrate how this method may be applied, we considered the Born approximation. We found out that the developed method improved the Born approximation at large scattering angles. Therefore, this method is useful when the di fferential cross section of the background term fails to converge to that of the exact diff erential cross section at large scattering angles. / Dissertation (MSc)--University of Pretoria, 2016. / National Research Foundation (NRF) / Physics / MSc

The inverse eigenvalue problem for a given operator is to determine the coefficients by using knowledge of its eigenfunctions and eigenvalues. These are determined by the behavior of the solutions on the domain boundaries. In our problem, the Schrödinger operator acting on functions defined on the unit ball of $\mathbb{R}^3$ has a radial potential taken from $L^2_{\mathbb{R}}[0,1].$ Hence the set of the eigenvalues of this problem is the union of the eigenvalues of infinitely many Sturm-Liouville operators on $[0,1]$ with the Dirichlet boundary conditions. Each Sturm-Liouville operator corresponds to an angular momentum $l =0,1,2....$. In this research we focus on the uniqueness property. This is, if two potentials $p,q \in L^2_{\mathbb{R}}[0,1]$ have the same set of eigenvalues then $p=q.$ An early result of P\"oschel and Trubowitz is that the uniqueness of the potential holds when the potentials are restricted to the subspace of the even functions of $L_{\mathbb{R}}^2[0,1]$ in the $l=0$ case. Similarly when $l=0$, by using their method we proved that two potentials $p,q \in L^2_{\mathbb{R}}[0,1]$ are equal if their even extension on $[-1,1]$ have the same eigenvalues. Also we expect to prove the uniqueness if $p$ and $q$ have the same eigenvalues for finitely many $l.$ For this idea we handle the problem by focusing on some geometric properties of the isospectral sets and trying to use these properties to prove the uniqueness of the radial potential by using finitely many of the angular momentum.

Le moment angulaire est une quantité essentielle pour l'étude d'objets en interaction. Tout comme la matière, un rayonnement porte du moment angulaire. Il se décompose en deux composantes, moment angulaire de spin (MAS) et moment angulaire orbital (MAO). Chacune de ces composantes a des propriétés spécifiques et ont donné lieu à de nombreuses applications en utilisant de la lumière dans le domaine visible et infrarouge. Dans cette thèse, nous nous proposons d'étudier le comportement des deux types de moment angulaire de la lumière dans un processus très non-linéaire appelé génération d'harmoniques d'ordre élevé (GHOE). Dans ce processus physique connu depuis 1987, un laser infrarouge intense est focalisé dans un jet d'atomes ou de molécules, ce qui dans le bon régime d'intensité permet de générer un rayonnement à courte longueur d'onde (domaine extrême ultraviolet) et extrêmement bref (attoseconde, 1 as = 10⁻¹⁸ s). Nous commençons par décrire théoriquement ce processus, ainsi que définir de manière approfondie la notion de moment angulaire de la lumière. Nous étudions ensuite la GHOE à partir d'un faisceau infrarouge portant du MAO, ce qui nous permet d'obtenir une source unique, générant des impulsions lumineuses ultrabrève de moment angulaire orbital contrôlé et de longueur d'onde de l'ordre de 10nm. Nous étudions étudions la GHOE à partir de faisceaux portant du MAS. En utilisant une résonance du gaz de génération, nous parvenons à transmettre ce moment angulaire au rayonnement extrême ultraviolet. Ce rayonnement est ensuite utilisé pour mesurer des dichroïsmes circulaires de photoionisation dans des molécules chirales, mesures auparavant réservées aux sources synchrotrons. Ceci ouvre la voie à des mesures chirotpiques résolues en temps à l'échelle femto/attoseconde. / Angular momentum is an ubiquitous quantity in all areas of physics. Just like matter, radiation carries angular momentum. It can be decomposed in two parts, namely the spin angular momentum (SAM) and the orbital angular momentum (OAM). Each one of these components has very specific properties and lead to numerous applications using visible and infrared light. In this thesis, we study the behavior of these two types of light angular momentum in a very non-linear process called high harmonic generation (HHG). In this physical process known since 1987, an intense infrared laser is focused into an atomic or molecular gas jet, which in the right intensity regime allows to generate a radiation which has a short wavelength (extreme ultraviolet domain) and is extremely brief (attosecond, 1 as = 10⁻¹⁸ s).We begin by describing theoretically this process, as well as defining in depth the notion of light angular momentum. We then study HHG from an infrared laser carrying OAM. This allows to obtain an unique light source, generating ultrashort light pulses of controlled orbital angular momentum with a wavelength of the order of 10 nm. We then study GHOE from beams carrying MAS. Using a resonance from the generation gas, we manage to transfer this angular momentum to the emitted extreme ultraviolet radiation. This radiation is finally used to measure photoionisation circular dichroisms in chiral molecules, measurements previously restricted to synchrotron sources. This paves the way towards chiroptic time resolved measurement on a femto/attosecond timescale.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22756号 / 工博第4755号 / 新制||工||1744(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 細田 尚, 教授 戸田 圭一, 准教授 音田 慎一郎 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM