ATLAS, LHC, quark b, quark top, étiquetage des jets issus de quark b, calibration des algorithmes d'étiquetage des jets issus de quark b, quarks top-antitop, section efficace, section efficace différentielle des paires top-antitop, masse du top, rapidité du top, nouvelle physique.

Les lasers de puissance permettent depuis une dizaine d'années de produire des faisceaux de particules accélérées dans lesquels quelques 1012 électrons, protons sont accélérés en quelques ps. Nous avons simulé et développé des diagnostiques, utilisant l'activation nucléaire, pour qualifier les distributions angulaire et en énergie des faisceaux de particules générés. Les techniques de caractérisation sont présentées et illustrées à l'aide des résultats obtenus dans différentes expériences réalisées auprès des lasers de puissance. Nous envisageons d'utiliser ces faisceaux pour exciter des états nucléaires dans des environnements plasma. Celui-ci peut en effet influencer des caractéristiques intrinsèques du noyau comme la durée de vie de certains états isomériques. Dans le cadre de la préparation de telles expériences, nous avons mesuré la section efficace de la réaction (g,n) permettant de produire l'état isomérique du 84Rb à 463 keV d'énergie d'excitation, à l'aide de l'accélérateur ELSA du CEA/DIF de Bruyères-le-Châtel.

Mid-ocean ridge hydrothermal systems are known to extend to deep levels of the oceanic crust, including the plutonic section, but little is known about the timing and nature of fluid-rock interactions at these levels. To investigate the temporal and spatial characteristics of hydrothermal alteration in the lower crust, this study investigates a suite of hydrothermally altered (<5 to >20% hydrous alteration) gabbroic rocks recovered from the Hess Deep Rift, where 1.2 Ma fast-spreading East Pacific Rise crust is well-exposed. These samples were altered to amphibole-dominated assemblages with chlorite-rich samples occurring in a restricted region of the field area. Hornfels, indicative of reheated, previously altered rocks, are clustered in the central part of the field area. The entire sample suite has elevated 87Sr/86Sr (mean: 0.70257±0.00007 (2σ), n=16) with respect to fresh rock (0.7024). Bulk rock 87Sr/86Sr is strongly correlated with percentage of hydrous alteration and weakly correlated with bulk rock Sr content. The distribution of Sr in igneous and metamorphic minerals suggests that greenshist-facies alteration assemblages (chlorite, actinolitic amphibole, albitic plagioclase) lose Sr to the fluid while amphibolite-facies secondary assemblages (secondary hornblende, anorthitic plagioclase) take up Sr. The temperature-dependent mobilization of Sr in hydrothermal systems has implications for the 87Sr/86Sr and ultimately fluid/rock ratio calculations based on the assessed 87Sr/86Sr systematics. Considering Sr behaviour, minimum fluid/rock ratios of ~1 were calculated for the plutonic section. Due to the large uncertainty regarding fluid Sr composition at depth and the sensitivity of fluid/rock ratio calculations on this parameter, a model combining the sheeted dike complex and the plutonic section to one hydrothermal system is introduced, yielding a fluid/rock ratio of 0.5. This value may be more realistic since the fluid composition entering and exiting the sheeted dike complex is better constrained. The regional distribution of hornfelsed material with elevated 87Sr/86Sr suggests that fluid ingress into the upper plutonics at Hess Deep occurred on-axis in a dynamic interface of a vertically migrating axial magma chamber (AMC) and the base of the hydrothermal system. / Graduate

Le travail présenté dans cette thèse concerne la mise en oeuvre numérique de techniques temporelles pour des applications en compatibilité électromagnétique (CEM) impulsionnelle, essentiellement pour des études en chambre réverbérante à brassage de modes (CRBM). Prenant le contre-pied des approches fréquentielles, adaptées par nature aux études de cavités résonantes, l’idée directrice de ce mémoire a été d’étudier des moyens temporels originaux d’investigation de CRBM en vue de proposer de nouveaux paradigmes pour la caractérisation d’équipements. Originellement développé en acoustique, le processus de retournement temporel (RT) récemment appliqué aux ondes électromagnétiques permet une focalisation spatiale et temporelle de ces dernières d’autant meilleur que le milieu de propagation est réverbérant. Les chambres réverbérantes (CR) sont ainsi des endroits idéaux pour l’application du processus de RT. Après une nécessaire étude des nombreux paramètres qui gouvernent ce dernier couplée à la définition de méthodologies numériques spécifiques, les applications du RT en CRBM sont exposées. En particulier, l’intérêt d’une focalisation sélective pour des tests en susceptibilité rayonnée est démontré. L’importance des coefficients d’absorption et de diffraction des équipements en CRBM justifie leur caractérisation précise et efficace. À cette fin, la mise en oeuvre d’un calcul temporel de section efficace totale de diffraction (TSCS en anglais) est détaillée. L’application de cette nouvelle technique à différentes formes de brasseurs de modes permet au final de confronter ces résultats avec ceux obtenus à l’aide de tests normatifs CEM. / The work presented in this thesis concerns the use of time techniques for impulsive ElectroMagnetic Compatibility (EMC) applications, mainly for Modes Stirred Reverberation Chamber (MSRC) studies. Contrary to approaches from frequency domain, obviously well-fitted for studies in resonant cavities, the main idea of this thesis was to study an original time method for MSRC investigation to propose new paradigms for equipment characterization. Originally developed in acoustics, the Time Reversal (TR) process recently applied to electromagnetic waves allows focusing it both in time and space. The process quality is even higher if the propagation environment is reverberant. Thus, the Reverberation Chambers (RC) are an ideal locations for TR implementation. After a study of parameters involved in the TR process coupled with the definition of specific numerical methods, the applications of TR in MSRC are exposed. In particular, the interest of selective focusing for radiated susceptibility tests is demonstrated. The importance of absorption and diffraction coefficients for MSRC equipment justifies their accurate and efficient characterization. To this end, the implementation of a temporal calculation of the Total Scattering Cross Section (TSCS) in RC is detailed. The application of this new technique to different forms of stirrers allows finally to face these results with those obtained from standard EMC test.

This diploma thesis deals with the validation of spectral average cross-sections (SACS) of 55 Mn(n,2n)54 Mn, 90 Zr(n,2n)89 Zr, 127 I(n,2n)126 I reactions in well-defined LR-0 reactor spectrum. The measurement of SACS for selected reactions is of high interest because they are used for the practical reactor dosimetry. Various experiments for description of neutron field in reactor and detector characterization, which are necessary for validation, are described. The spectral average cross-sections are derived from Net Peak Areas of irradiated samples measured using a semiconductor high purity germanium detector. Obtained result were compared with MCNP6 calculations using ENDF/B-VII.0, ENDF/B-VII.1, JEFF-3.1, JEFF-3.2, JENDL-3.3, JENDL-4, ROSFOND-2010, CENDL-3.1 and IRDFF nuclear data libraries. Notable discrepancies were found in 90 Zr(n,2n)89 Zr and 127 I(n,2n)126 I reactions. This thesis also contains a theoretical basis for the interaction of neutrons with matter.

The Companies Act of 71 of 2008 makes a number of important changes to the rules relating to capital maintenance. In line with the objectives of the Companies Act of 71 of 2008, section 44 of the Act has removed the prohibition on the provision of financial assistance by a company which was contained under the previous section 38 of the Companies Act 61 of 1973. Despite the repeal of the prohibition, a transaction which involves the provision of financial assistance by a company for the acquisition of or subscription of its own securities still needs to be effected in accordance with the requirements and conditions that are provided under the Act and Memorandum of Incorporation. To explore the new developments, within this study, the provision of financial assistance in terms of section 44 of the Companies Act of 2008 is, therefore, analysed in detail. On the other hand, the UK Companies Act of 2006 repealed the prohibition on the giving of financial assistance by private companies in most circumstances. It, however, retained the prohibition to public companies only because of the requirements of the Second Company Law Directive (77/91/EEC). This study also explores the rules of financial assistance by a company under the UK Companies Acts in detail. Though the source of financial assistance by a company both in South Africa and in English Company laws is rooted in the English decision of the Trevor v Whitworth case, currently these countries have adopted what is deemed appropriate and significant in their own countries. This study, therefore, examines and compares the rules governing the provision of financial assistance by a company in the company laws of these two countries. / Mercantile Law / LL.M. (Commercial law)

The Regulation of Gatherings Act 205 of 1993 is a old order piece of legislation, but gives full recognition to the right to freedom of assembly and expression. These rights are entrenched in sections 16 and 17 of the Bill of Rights and enjoy a generous interpretation. Section 5 of the Act creates limitations on these rights, as the responsible officer of a local authority is allowed to prohibit a gathering when he has reasonable grounds to believe that the police will not be able to prevent traffic disruption, injury or substantial damage to property. Given the fact that this limitation serves to protect a compelling state interest, it constitutes a reasonable and justifiable limitation in terms of section section 36 of the Bill of Rights. / Law / LL.M.

The constitutionality of affirmative action in terms of section 8 of Act 200 of 1993 is investigated. The study contends that in constitutional interpretation it is permissible to have recourse to ethical precepts as long as these are anchored within the four corners of the Constitution. It is contended that the •equality clause• does not prescribe equality of outcome in favour of substantive equality of opportunity. It is asserted that group-based affirmative action may justifiably be attacked as being unconstitutional; either on the basis that it infringes the nonbeneficiary's equality rights in terms of sections 8(1) and 8(2) or that it falls beyond the constitutional protection afforded to affirmative action in terms of section 8(3). Furthermore, group-based modalities of affirmative action may also not constitute a permissible limitation on the fundamental right to equality, if compared to an individual-based socio-economic affirmative action model. / Jurisprudence / LL. M.

Text in Afrikaans, abstract in English / Writer investigates the constitutionality of section 18(4)(d) of the Child Care Act 74 of 1983 against the backdrop of the South African common law and the common law of comparative legal systems. In the South Africa law the mother of an illegitimate child has guardianship. The natural father does not have parental power which weakens his legal position. In analysing the judgement of the Constitutional Court, writer criticises the court for stating that in the case of a newborn baby the kind of discrimination which section 18( 4 )( d) authorises against a natural father may be justifiable in the initial period after the child is born. The constitutional position of the natural father in American jurisprudence is discussed at length. Writer concludes that the natural father has to take positive steps to vest a right to be heard in an adoption application. Proposals for legal reform are also made. / Private Law / LL. M. (Law)

Section 33(1)(b) is fraught with borrowed provisions. The end-product marries German and Canadian features. The failure of the German Constitutional Courts to interpret the "essential content of a right" precipitated the adopted infant's bumpy landing in South Africa. That the sibling still lacks identity is evidenced by our Constitutional Court's evasive and superficial treatment of the clause. Section 33(1)(a) - proportionality prong enables judges to justify their neglect of Section 33(1)(b). The opinion is expressed that Section 33(1){b) demands interpretation but to date it has been shrouded in vagueness. After all without demarcating boundaries with sufficient precision and highlighting where the State may not tread the State may trespass. Alternatively the limitable nature of human rights could become a myth as Section 33(1)(b) could be transformed into an insurmountable hurdle for the State, rendering every right absolute in practice. A workable conceptual framework proposes an inverted, porous and value imbibing solution. / Law / LL.M.