Advances in the knowledge of chemical structure of coal and development of high performance computational techniques led to more than hundred and thirty four proposed molecular level representations (models) of coal between 1942 and 2010. These models were virtually on the carboniferous coals from the northern hemisphere. There are only two molecular models based on the inertinite- and vitrinite-rich coals from the southern hemisphere. The current investigation is based on the chars derived from the Permian-aged coals in two major South African coalfields, Witbank #4 seam and Waterberg Upper Ecca. The two coals were upgraded to 85 and 93% inertinite- and vitrinite-rich concentrates, on visible mineral matter free basis. The coals were slow heated in inert atmosphere at 20 ℃ min-1 to 450, 700 and 1000 ℃ and held at that temperature for an hour. After the HCl-HF treatment technique at ambient temperatures, the characteristics of the coals and chars were examined with proximate, ultimate, helium density, porosity, surface area, petrographic, solid-state 13C NMR, XRD and HRTEM analytical techniques. The results largely showed that substantial transitions occurred at 700-1000 ℃, where the chars became physically different but chemically similar. Consequently, the chars at the highest temperature (1000 ℃) drew attention to the detailed study of the atomistic properties that may give rise to different reactivity behaviours with CO2 gas. The H/C atomic ratios for the inertinite- and vitrinite-rich chars were respectively 0.31 and 0.49 at 450 ℃ and 0.10 and 0.12 at 1000 ℃. The true density was respectively 1.48 and 1.38 g.cm-3 at 450 ℃ and 1.87 and 1.81 g.cm-3 at 1000 ℃. The char form results from the petrographic analysis technique indicated that the 700-1000 ℃ inertinite-rich chars have lower proportions of thick-walled isotropic coke derived from pure vitrinites (5-8%) compared with the vitrinite-rich chars (91-95%). This property leads to the creation of pores and increases of volume and surface area as the softening walls expand. It was found that the average crystallite diameter, La, and the mean length of the aromatic carbon fringes from the XRD and HRTEM techniques, respectively, were in good agreement and made a definite distinction between the 1000 ℃ inertinite- and vitrinite-rich chars. The crystallite diameter on peak (10) approximations, La(10), of 37.6Å for the 1000 ℃ inertinite-rich chars fell within the HRTEM’s range of minimummaximum length boundary of 11x11 aromatic fringes (27-45Å). The La (10) of 30.7Å for the vitrinite-rich chars fell nearly on the minimum-maximum length range of 7x7 aromatic fringes (17-28Å.) The HRTEM results showed that the 1000 ℃ inertinite-rich chars comprised a higher distribution of larger aromatic fringes (11x11 parallelogram catenations) compared with a higher distribution of smaller aromatic fringes (7x7 parallelogram catenations). The mechanism for the similarity between the 700-1000 ℃ inertinite- and vitrinite-rich chars was the greater transition occurring in the vitrinite-rich coal to match the more resistant inertinite-rich coal. This emphasised that the transitions in the properties of vitrinite-rich coals were more thermally accelerated than those of the inertinite-rich coals. The similarity between the inertinite- and vitrinite-rich chars was shown by the total maceral reflectance, proximate, ultimate, skeletal density and aromaticity results. Evidence for this was the carbon content by mass for the inertinite- and vitrinite-rich chars of respectively 90.5 and 85.3% at 450 ℃ and 95.9 and 94.1% at 1000 ℃. The aromaticity from the XRD technique was respectively 87 and 77% at 450 ℃ and 98 and 96% at 1000 ℃. A similar pattern was found in the hydrogen and oxygen contents, the atomic O/C ratios and the aromaticity from the NMR technique. The subsequent construction of large-scale molecular structures for the 1000 ℃ inertinite-rich chars comprised 106 molecules constructed from a total of 42929 atoms, while the vitrinite-rich char model was made up of 185 molecules consisting of a total of 44315 atoms. The difference between the number of molecules was due to the inertinite-rich char model comprising a higher distribution of larger molecules compared with the vitrinite-rich char model, in agreement with the XRD and HRTEM results. These char structures were used to examine the behaviour on the basis of gasification reactivity with CO2. The density functional theory (DFT) was used to evaluate the interactions between CO2 and the atomistic representations of coal char derived from the inertinite- and vitrinite rich South African coals. The construction of char models used the modal aromatic fringes (fringes of highest frequencies in size distributions) from the HRTEM, for the inertinite- and vitrinite-rich chars, respectively (11x11 and 7x7 parallelogram-shaped aromatic carbon rings). The structures were DFT geometrically optimized and used to measure reactivity with the Fukui function, f+(r) and to depict a representative reactive carbon edge for the simulations of coal gasification reaction mechanism with CO2 gas. The f+(r) reactivity indices of the reactive edge follows the sequence: zigzag C remote from the tip C (Czi = 0.266) > first armchair C (Cr1 = 0.087) > tip C (Ct = 0.075) > second armchair C (Cr2 = 0.029) > zigzag C proximate to the tip C (Cz = 0.027). The DFT simulated mean activation energy, ΔEb, for the gasification reaction mechanism (formation of second CO gas molecule) was 233 kJ mol-1. The reaction for the formation of second CO molecule is defines gasification in essence. The experimental activation energy determined with the TGA and random pore model to account essentially for the pore variation in addition to the gasification chemical reaction were found to be very similar: 191 ± 25 kJ mol-1 and 210 ± 8 kJ mol-1; and in good agreement with the atomistic results. The investigation gave promise towards the utility of molecular representations of coal char within the context of fundamental coal gasification reaction mechanism with CO2. / PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

L'habitat de la fin du premier âge du Fer ne bénéficiait pas jusqu'à présent d'une approche globale et synthétique des productions métalliques découvertes en son sein. Pour quelques établissements situés de l'Allemagne du Sud Ouest à la France centrale, nous proposons une définition générale de la diversité de ces mobiliers au travers de leurs aspects qualitatif et quantitatif. Nous avons eu l'occasion de constater, quels avaient été les choix de consommation du fer ou des alliages cuivreux. Des évolutions sont aussi notables avec l'apparition, ou le développement au cours du temps des mobiliers fabriqués en fer. Une pénétration de celui-ci dans les milieux domestiques est un fait important dans l'évaluation de sa diffusion au cours de la période hallstattienne. Par ailleurs, l'étude précise des assemblages a permis de mettre en évidence des changements liés à la consommation du métal en général. L'accumulation de ce matériau par les milieux privilégiés est avérée pour les phases les plus anciennes, alors qu'ensuite au Ha D2, Ha D3 et à LTA, il se propage dans les milieux domestiques et artisanaux. En définitive, à la fin du premier âge du Fer, le métal est consommé en plus grande quantité sur les sites de hauteurs ou à proximité. Il faut attendre le début de LTA pour observer d'autres cas de figures, liés aux transformations des formes de l'habitat mais aussi très probablement à une certaine diffusion du métal. En outre, certains objets semblent avoir parcouru de longues distances, retrouvés très éloignés de leur zone de productions. Ils évoquent ainsi un monde en mouvement où les contacts établis : commerciaux, aristocratiques ou cultuel (?) attestent du dynamisme et de l'intégration de la plupart des sites abordés dans de vastes réseaux. Enfin, si le monde artisanal, les femmes et les élites ressortent tout particulièrement au travers du métal, ce dernier a permis aussi de préciser la caractérisation du statut de quelques-uns des établissements étudiés, notamment ceux dont le niveau de structuration était le plus élevé.

La passion des Romains pour les jeux du cirque, et surtout pour les courses de chars, apparaît comme un topos dans la littérature ancienne. Si les auteurs anciens ont maintes fois évoqué l’état d’excitation du public, les jugements moraux et les stéréotypes l’emportent sur toute tentative d’analyse et très peu d’amateurs de courses ont laissé de témoignage, comme la première partie de cette thèse le met en évidence. Il nous a donc fallu dépasser ces préjugés afin d’expliquer les raisons d’un tel engouement. La confrontation des données issues des sources textuelles aux résultats de travaux récents en psychologie des émotions et en sociologie du sport nous a permis de démontrer, dans la seconde partie, le lien entre la passion des jeux et les émotions provoquées par ces spectacles. En effet, cette passion se nourrissait largement des émotions intenses éprouvées par les spectateurs, elles-mêmes conséquence d’un phénomène d’hyperstimulation sensorielle auquel ils étaient soumis depuis leur arrivée aux abords du bâtiment jusqu’à la fin des jeux. Cet engouement pour les ludi circenses avait donc des causes intrinsèques aux spectacles. Face à ce constat et à l’intérêt croissant du pouvoir pour les circenses dès la fin de la République, la troisième partie de cette thèse examine la question de l’instrumentalisation de ces jeux à des fins politiques. Si des chefs d’armées, comme Pompée ou Jules César, comprirent tout le bénéfice qu’ils pouvaient en retirer en terme de popularité et si, à partir d’Auguste, les circenses font partie intégrante de la politique impériale, il serait néanmoins erroné de percevoir les spectateurs du cirque comme une foule manipulée par le pouvoir. Ils jouissaient en ce lieu d’une autorité considérable, non seulement sur le déroulement des jeux, mais aussi à l’égard de l’empereur, à tel point que le rapport de force avec ce dernier pouvait même éventuellement s’inverser. Le cirque a été en effet parfois le cadre de manifestations d’hostilité de la foule à l’encontre de l’empereur ou de ses proches et dans la plupart des cas les manifestants ont obtenu gain de cause. La clémence du prince semble donc avoir été l’usage en ce lieu. Cependant, il convient de ne pas réduire les acteurs de ces mouvements de protestation à la plèbe. Ces manifestations étaient vraisemblablement souvent orchestrées et soigneusement préparées à l’avance, or il nous est apparu que seuls des membres de l’ordre sénatorial ou équestre avaient les moyens humains et logistiques d’y parvenir. / Passion for Roman circus games, and especially for chariot races, appears as a topos in ancient literature. Even if ancient authors frequently evoke the excitement of the audience, this excitement often attracts moral condemnations and stereotypes rather than critical analysis and there are very few testimonies coming from chariot races enthusiasts, as it may be noted in the first part of the thesis. This study aims to overcome these prejudices in order to explain the reasons for such an enthusiasm. In the second part, after confronting data coming from textual sources with what recent works in psychology of emotion and sociology of sport can teach us, we demonstrate the link between passion for the games and the emotions provoked by those spectacles. This passion, indeed, was mainly entertained by the intensity of the emotions, resulting themselves from the sensory overload which the spectators experienced, from the moment they were reaching the circus to the end of the games. This passion may be due to factors intrinsic to the show. Considering this aspect as well as the growing interest of the power for circenses at the end of the Republic, the third part examines the exploitation of the games for political purposes. Even if army leaders, such as Pompey and Caesar, well understood all the benefits they could derive in terms of popularity, and even if the circenses started to be, from Augustus on, an integral part of imperial policy, it would be a mistake to see the spectators simply as a crowd manipulated by political power. It appears that the spectators enjoyed considerable authority over this place, not only in relation to the conduct of the games, but also even in relation to the emperor, insomuch as the power struggle between the emperor and his subjects could sometimes be reversed. On several occasions, indeed, the circus was the scene of the crowd’s hostility against the emperor or his relatives, and in many such cases, the demonstrators were successful. It seems that it was customary for the emperor to show clemency within the circus. However, it is important not to generalise about the participants of protests and not to consider them simply as a plebeian mob. Such protests were in all likelihood often carefully orchestrated and planned in advance; it seems clear that only members of the senatorial or equestrian orders had the human resources and logistical capacity to achieve that.