Les carottes de glace sont des archive climatiques sans équivalents : les gaz contenus dans la glace de la région aride de l'Antarctique de l'Est permettent de reconstruire les compositions atmosphériques au cours des derniers 800 000 ans. Les gaz sont piégés pendant la compaction de la neige tombée sur l'inlandsis. Dans la neige en surface, aussi appelée névé, le réseau poreux interstitiel diminue jusqu'au pincement des pores qui piègent définitivement les gaz dans la glace. Cependant, le processus même de piégeage des gaz impacte l'enregistrement des signaux mesurés dans les carottes. L'interprétation de ces signaux demande de caractériser en quoi ils diffèrent de l'atmosphère passée. Le but de cette thèse est d'étudier deux effets altérant les enregistrements gaz des carottes, le piégeage par couches qui crée des irrégularités stratigraphiques et le lissage qui retire la variabilité rapide de l’enregistrement. Une attention particulière est portée sur les glaces de l'Antarctique de l'Est.Ce travail démarre avec l'étude multi-traceurs d'une carotte de névé forée au site de Lock-In en Antarctique de l'Est. Les résultats montrent que le bas du névé est un empilement hétérogène de strates se densifiant suivant une même évolution de leur réseau poreux. La stratification reflète simplement que certaines strates sont en avance (ou retard) dans leur densification, mais la fermeture des pores est similaire dans toutes les strates. Notamment, les strates contiennent toutes des quantités similaires de gaz, comme le montrent des mesures directes. Des mesures de chimie à haute-résolution montrent que les strates denses ont une haute conductivité liquide, suggérant que la stratification profonde du névé est due à une densification préférentielle induite par des impuretés.Ces connaissances sont appliquées pour étudier des variations centimétriques mesurées dans les signaux méthane des carottes de glace. Pour cette thèse, nous utilisons 6 nouveaux signaux méthane à haute résolution, mesurés dans des carottes d'Antarctique de l'Est à l'IGE. On montre que ces variations sont des artefacts dus aux irrégularités stratigraphiques causées par des strates denses se fermant en avance. Un modèle est proposé pour simuler la présence irrégulière de ces artefacts.Une nouvelle méthode est proposée pour estimer la distribution en âge des gaz dans les carottes, qui à l'origine du lissage des variations atmosphériques rapides. Elle peut être appliquée aux carottes de la dernière période glaciaire, et donne pour la première fois des indications quantitatives sur le lissage des signaux dans les carottes à très faible accumulation. Nos résultats montrent qu'en Antarctique de l'Est, le lissage est peu sensible au taux d'accumulation, et que plus d'information que prévu est préservée lors du piégeage.Enfin, nous présentons le développement d'un nouveau type de modèle micro-mécanique du névé. Son but est de simuler l'évolution des pores dans une strate de névé. Un tel modèle pourrait être utilisé pour contraindre le piégeage des gaz dans la glace, dans des conditions de période glaciaire. / As they contain air from past atmospheres, ice cores are unparalleled climate paleo-archives. The study of the gases enclosed in ice cores from the arid region of East Antarctica allows to infer the past compositions of the atmosphere back to 800,000 years ago. Gases are trapped during the compaction of the snow deposited on top of the ice sheet. In the near-surface snow, also referred to as firn, the interstitial porous network shrinks until it eventually pinches and traps gases in the ice. However, the very process of gas trapping has impacts on the gas signals recorded in ice cores. The interpretation of gas records requires to characterize how ice core and atmospheric signals differ. The aim of this PhD is to study two effects altering ice core gas records, namely gas layered trapping that creates stratigraphic irregularities and firn smoothing that removes fast variability from the record. A specific focus is put on low-accumulation East Antarctic ice cores.This inquiry starts with the multi-tracer study of a firn core drilled at the Lock-In site, East Antarctica. The results show that the bottom of the firn can be seen as a stack of heterogeneous strata that densify following the same porous network evolution with density. In this vision, the stratification simply reflects the fact that some strata are in advance (or late) in their densification, but that pore closure happens in a similar fashion in all strata. This notably means that all strata contain nearly similar amounts of gases, as supported by direct measurements. High-resolution chemistry data indicate that denser strata are characterized by a high liquid conductivity, suggesting that deep firn stratification is due the impurity-induced preferential densification.This knowledge is then used to explain abrupt spikes observed in ice core methane records. For this PhD we rely on 6 new high-resolution methane records, measured in several East Antarctic ice cores at IGE. We show that the abrupt variations are layering artifacts due to stratigraphic irregularities caused by dense firn strata closing in advance. A simple model is developed to simulate the irregular occurrence of layering artifacts.A novel technique is proposed to estimate the age distributions of gases in ice cores, that are responsible for the smoothing of fast atmospheric variations. It can notably be applied to glacial records, and for the first time provides quantitative insights on the smoothing of very low-accumulation records. Our results show that in East Antarctica, the firn smoothing is weakly sensitive to the accumulation rate, meaning that more information than previously thought is preserved.Finally, we present the development of a new type of micro-mechanical firn model. Its ambition is to simulate the evolution of the porous network of a firn stratum. Such a model could be used to better constrain the enclosure of gases in polar ice under glacial conditions.

The spatial structure of Cape Town is characterised by segregated low density development patterns and urban sprawling. With a high population growth rate and urbanisation, these patterns are becoming more prominent. Due to the spatial nature of Cape Town, a large proportion of economic activities and employment opportunities are concentrated in patches across the city. In order to combat low-density sprawl and integrate spatially separated areas the key concept ?city densification? and the various elements thereof emerged. The segregated low density city structure, the concentrated nature of economic and employment opportunities along with an ever increasing population and inadequate public transport system resulted in issues such as long average travel lengths, low accessibility by poorer communities, greater use of private vehicles, and a sharp rise in traffic congestion. With the implementation of the Integrated Rapid Transport System (IRT), an initiative to transform the public transport sector to integrate all modal options, the opportunity is rendered to address these environmental, social and economical issues. The purpose of this study was to determine whether the City of Cape Town (CoCT) is utilising the full potential of the new Integrated Transport System currently being developed and implemented in Cape Town, namely the MyCiTi BRT System. It was determined that in terms of potential environmental benefits the CoCT, is utilising its full potential. Furthermore, although the potential social benefits were being utilised, the urgency of addressing social inequality is not reflected in the phased timeframe set out for the system. In terms of economic benefits, the options of using land-value add and environmental finance currently not sufficiently utilised and should be used to encourage a more sustainable public transport system. / Thesis (M.Art. et Scien. (Town and Regional planning))--North-West University, Potchefstroom Campus, 2011.

The spatial structure of Cape Town is characterised by segregated low density development patterns and urban sprawling. With a high population growth rate and urbanisation, these patterns are becoming more prominent. Due to the spatial nature of Cape Town, a large proportion of economic activities and employment opportunities are concentrated in patches across the city. In order to combat low-density sprawl and integrate spatially separated areas the key concept ?city densification? and the various elements thereof emerged. The segregated low density city structure, the concentrated nature of economic and employment opportunities along with an ever increasing population and inadequate public transport system resulted in issues such as long average travel lengths, low accessibility by poorer communities, greater use of private vehicles, and a sharp rise in traffic congestion. With the implementation of the Integrated Rapid Transport System (IRT), an initiative to transform the public transport sector to integrate all modal options, the opportunity is rendered to address these environmental, social and economical issues. The purpose of this study was to determine whether the City of Cape Town (CoCT) is utilising the full potential of the new Integrated Transport System currently being developed and implemented in Cape Town, namely the MyCiTi BRT System. It was determined that in terms of potential environmental benefits the CoCT, is utilising its full potential. Furthermore, although the potential social benefits were being utilised, the urgency of addressing social inequality is not reflected in the phased timeframe set out for the system. In terms of economic benefits, the options of using land-value add and environmental finance currently not sufficiently utilised and should be used to encourage a more sustainable public transport system. / Thesis (M.Art. et Scien. (Town and Regional planning))--North-West University, Potchefstroom Campus, 2011.

Face au contexte particulier du territoire réunionnais, avec un climat tropical cyclonique, une surface habitable réduite de plus en plus en proie à un étalement urbain grandissant, un foncier rare et cher, des matériaux pour la plupart importés, une main d'œuvre peu qualifiée, une dépendance énergétique extérieure, une demande croissante de logements, des revenus plus bas que la moyenne nationale ainsi qu'une population qui ne cesse d'augmenter, le défi architectural à relever est de proposer de nouvelles formes d'habitat économique et écologique qui soient différentes de la kaz créole traditionnelle consommatrice d'espace tout en étant respectueuses des us et coutumes réunionnaises. / Facing the context of the territory of Reunion island, with its tropical and cyclonic climate, a restricted inhabiting surface that is more and more exposed to a growing urban spreading out, a rare and costly land property, building material which are mainly imported, a low-qualified man power, an outer energetic dependence, a growing demand for housing, wages that are lower than the national average and a population which never get up increasing, the architectural challenge consists in proposing new shapes of low-cost and ecological habitat that could be different from the traditional Creole cabin very consuming of space while being respectful of the ways and customs of inhabitants of Reunion.

Le but de cette étude est d’explorer la possibilité d’utiliser trois argiles dans l’industrie céramique locale au Sénégal. Une argile rouge (NM) et deux argiles grises (MN1) et (MN2) proviennent respectivement de la région de Ziguinchor à Néma et de Tambacounda à Malème Niani. L'étude concernant les caractéristiques physico-chimiques des argiles, indique que les compositions chimique et minéralogique contiennent la présence de quartz, de kaolinite, d’illite, de montmorillonite et de goethite. Leurs caractéristiques structurales et leurs surfaces spécifiques sont similaires. Leur caractéristiques minéralogiques mènent à un classement dans les groupes des argiles kaolino-illite ou kaolino-smectique. Par des analyses thermiques, les températures de transformations thermiques caractéristiques des phases ont été bien identifiéesLa mise en forme par pressage uniaxial des poudres humidifiées et granulées de ces argiles a été optimisée. Les propriétés d’usage des produits frittés ont été mesurées indiquant que les propriétés mécaniques sont limitées, bien que la mullite et la cristobalite constituent les phases minérales majoritaires des microstructures. La porosité a été mesurée après frittage à différentes températures (1000°C, 1100°C et 1200°C), variant de 25% à 30% et diminuant peu avec l’augmentation de la température de frittage. Dans l’ensemble, les résultats révèlent que ces argiles prises à l’état brut nepossèdent pas toutes les caractéristiques satisfaisantes pour la production de briques et tuiles. Pour améliorer les propriétés mécaniques, une substance éco-durable organique, le Cola Cordifolia, a été ajoutée aux argiles. Cet additif induit une augmentation de 28% de la résistance mécanique de l’argile rouge (NM) après cuisson à 1000°C, atteignant la valeur minimale de la norme concernant les briques. Finalement, d’autres pistes d’amélioration des propriétés d’usage ont été explorées telles que l’ajout de l’urée et de fondants potassique et sodique. Ces ajouts ont permis d’accentuer la densification des matériaux de terre cuite pour la production de briques. / The aim of this study is to explore the possibility of using three clays for the local ceramic industry in Senegal. We used a red clay (NM) and two gray clays (MN1) and (MN 2) from the region of Ziguinchor in Nema and Tambacounda in Niani Maleme, respectively. The study of the physicochemical characteristics of clays indicates that the chemical and mineralogicalcompositions contain the presence of quartz, kaolinite, illite, montmorillonite and goethite. Their structural characteristics and their surface areas are similar. Their mineralogical characteristics lead to a classification in groups of Kaolino-illite clays or Kaolino-smectite. By thermal analysis, typical phase transformation temperatures were well identified. The shaping by uniaxial pressing of moistened and granulated powders of clays was optimized. The properties in use of the sintered products were measured indicating that the mechanical properties are limited, although cristobalite and mullite constitute the major mineral phases in microstructures. Porosity was measured after sintering at different temperatures (1000°C, 1100°C and 1200°C), ranging from 25% to 30% and with a little lowering with increasing the sintering temperature. Overall,results indicate that these clays do not attain satisfactory characteristics for the production of bricks. To improve the mechanical properties, an organic eco-sustainable substance, the Cola Cordifolia, has been added to clays. This additive induces a 28% increase of the mechanical strength of the red clay (NM) after firing at 1000°C, reaching the minimum value of the standard for bricks. Finally, other areas for improvement of properties in use were explored such as the addition of urea and potassium or sodium fluxes. These additions have helped the increase of densification of clay materials for the production of bricks.

Le comportement à haute pression du verre de silice a été largement étudié dansde différents domaines pour ses propriétés mécanique et physiques, tels que la mécaniquenon-linéaire, laphysiquede haute pression, laphysiquenon-cristallins, laphysique appliquée, lagéophysique, etc. La densification permanente est la propriété la plus fondamentale obtenue à partir de la haute pression. Nous discutons un modèle constitutif décrivant le mécanisme de déformation permanente par la densification sous haute pressionde verre de silice. La loi de comportement proposée dans cette étude considère que la pression est hydrostatique pure. Elle est composée d’une partieélastique et d’autre partie un écoulement décrivant l'évolution des déformations permanentes après l’initiation de ladensification. Dans cette loi, trois critères d’écrouissage sont discutés à l'égard de la dépendance de la densification incrémentale (progressive)aux niveaux de contraintes appliquées. Les mesuresexpérimentales ex-situ et in-situ sont utilisées pour évaluer notre modèle. En misant en œuvre de notre modèle dans Abaqus et SiDoLo(corotational logiciel), l’analyse inverse est utilisée pour déterminer le seuil de la pression de densification, la pression à la saturation et le taux de densification saturée. Les calculs numériques montrent un excellent accord avec les données expérimentales. Il est à noter que notre modèle non seulement réussit à déterminer les propriétés de densification, mais aussi pour prédire les changements de propriétés élastiques, telles que le module de compressibilité, le module de cisaillement, module d’élasticité et le coefficient de Poisson, sous la pression hydrostatique. Dans les perspectives, notre modèle fournit une nouvelle loi pour analyser le comportement à la déformation de silice sous l’état de contraintes complexes. / High-pressure behavior of SiO2 glass has been studied extensively because it has attracted considerable attention in various fields of mechanical and physical sciences, such as non-linear mechanics, high-pressure physics, noncrystalline physics, applied physics, geophysics, etc. Permanent densification is the most fundamental property obtained from very high pressure. We discuss a constitutive model describing the permanent densification induced deformation mechanism of silica. The constitutive law is assumed to be pure hydrostatic pressure, and uses a yield function and a flow rule describing the evolution of permanent strains after initial densification, and three hardening rules discussing the dependence of the incremental densification on the levels of applied stresses. Ex-situ and in-situ experiments are both considered to evaluate our model. Implementing our model to a finite software Abaqus and a corotational framework software SiDoLo, inverse analysis is used to determine the threshold densification pressure, the saturate densification pressure and the saturate value of densification. Numerical results show an excellent agreement to experimental data. It should be noted that our model not only succeeding in determine the densification properties, but also in predicting the changes of elastic properties, such as Bulk modulus, Shear modulus, Young’s modulus and Poisson’s ratio, under hydrostatic pressure. Seen in perspective, our model provides a new rule to analyze the deformation behavior of silica under complex stress states.

Le déphasage entre augmentation de température et augmentation de gaz à effet de serre (GES) dans l'atmosphère lors des grandes transitions climatiques passées est estimé grâce aux mesures effectuées dans les carottes de glace polaires dans la phase glace pour la température et dans la phase gaz (bulles d’air piégées) pour la concentration en GES. Ce déphasage est encore mal contraint et, pour résoudre ce problème, il est nécessaire de mieux comprendre le processus mécanique de transformation de neige en glace près de la surface de la calotte (centaine de mètres supérieurs, le névé). En l'absence de fusion, la transformation de la neige (matériau à porosité ouverte en contact avec l'atmosphère) en glace (matériau contenant des bulles d'air isolées) s'effectue progressivement sous l'action des gradients de température près de la surface, puis sous l'action du poids des couches de neige situées au-dessus. Selon les conditions de température et précipitation, ce processus peut prendre quelques décennies à plusieurs millénaires et s'étend sur une centaine de mètres de profondeur. Il contrôle la différence d'âge entre la glace et les gaz qu'elle renferme. La prédiction de la profondeur de piégeage des gaz représente un enjeu majeur pour la paléoclimatologie en particulier sur la séquence des changements relatifs de température et de concentration en gaz à effet de serre.Un modèle thermo-mécanique de densification de la neige a été conçu et développé au LGGE en intégrant la formulation des processus mécaniques, des propriétés thermiques, et des critères de piégeage des gaz. Les performances de ce modèle peuvent être testées et améliorées grâce à des études de structure de névés actuels (densité, rapport porosité ouverte/fermée, …). Pour les périodes plus anciennes, des mesures d’isotopes des gaz inertes d15N et d40Ar) dans l’air piégé dans les carottes de glace polaire permettent d’obtenir des informations directes sur les variations passées de la structure du névé (e.g. épaisseur de la zone diffusive). Les larges divergences observées en Antarctique entre les sorties de modèle de densification et les mesures isotopiques de gaz piégé dans la glace génèrent une grande incertitude sur les reconstructions climatiques passées et comprendre ce désaccord est un défi majeur de la paleoclimatologie actuelle.Dans le cadre de cette thèse, nous avons pris en compte les influences de la dépendance à la température des énergies d'activation et des impuretés (poussières) sur la vitesse de densification. Cela a permis de concilier les données et le modèle. Les résultats du modèle modifié sont globalement cohérents avec les profils de densité mesurés pour des névés actuels et les données d'isotopes de gaz inertes pour les déglaciations (aussi appelées terminaisons). Nous avons également présenté de nouvelles mesures à haute résolution de d15N et d40Ar pour les terminaisons 2 (129-138ka) et 3 (243-251ka) des carottes antarctiques de Dôme C et Vostok. Nous avons montré que les différentes évolutions de d15N entre les différents sites et différentes déglaciations s’expliquaient largement par les différences de taux d’accumulation qui contrôlent la profondeur de transition neige-glace. Nous avons aussi montré que l’utilisation des isotopes de l’air était un complément important à l’utilisation des isotopes de l’eau pour contraindre la dynamique climatique locale en Antarctique de l’Est lors des déglaciations. / The phasing between increases in temperature and greenhouse gas concentrations during large climatic variations in the past is classically estimated using analyses in polar ice cores, in the ice phase for the temperature and in the gas phase (trapped air bubbles) for the concentration of greenhouse gases. This phasing is still insufficiently constrained and solving this problem requires a better understanding of the mechanical process of snow to ice metamorphism near to the top of the ice sheet (i.e. the firn, about 100 m deep). In the absence of melting, the transformation of snow (a material with open porosity in contact with the atmosphere) into ice (a material containing isolated bubbles) occurs progressively as a response to temperature gradients near the surface, and the weight of overlying snow in deeper layers. Depending on temperature and precipitation conditions, this process occurs in a few decades to several millennia and a ~100 meters depth range. It controls the age difference between the ice and the entrapped gases. Predicting the gas trapping depth is a major issue in paleoclimatology, especially in order to understand the phasing between temperature changes and changes in greenhouse gas concentrations.A thermo-mechanical model of snow densification has been developed at LGGE, it includes the main mechanical processes, the thermal properties of ice, and gas trapping criteria. The model performances can be tested and improved using experimental studies of modern firns (density, open/closed porosity ratio, etc). For firnification under ancient climates, measurements of isotopes of inert gases (d15N et d40Ar) in the air trapped in ice cores provide direct informations about past variations of firn structure (e.g. diffusive zone thickness). Large differences between firn densification model outputs and gas isotopic data are obtained in Antarctica, and imply a large uncertainty on past climatic reconstructions. Understanding this discrepancy is a major issue in paleoclimatology.As part of this thesis work, we took into account the effects of the temperature dependence of activation energies and impurities (dust) on the firn densification speed. It allowed to reconcile the model results with available data. The modified model results show an overall consistency with measured density profiles of present-day polar firns and isotopes of inert gases over deglaciations (also called terminations). We also analyze new high resolution measurements of d15N and d40Ar over Terminations 2 (129-138ka) and 3 (243-251ka) on the Dome C and Vostok ice cores. We have shown that the different evolutions of d15N between different sites and different deglaciations are largely explained by differences in accumulation rates that control the snow/ice transition depth. We also showed that the use of air isotopes was an important complement to the use of water isotopes to constrain local climatic dynamics in eastern Antarctica during deglaciations.

This study aims to describe and analyze changes over time in the degree of relative crowding in preschools within the urban area of a medium-sized city in the northern part of Sweden – and does so by examining the size of the available open space per child. Further, this work explores the spatial variation of open space dimensioning in relation to the urban center in order to decide whether shrinking of children’s open space should be considered to be limited to the major metropolitan areas of Sweden. With the basis in an assumption of increasing competition over land as a consequence of neoliberal governance and densification as strategies to promote urban growth, it’s hypothesized from recent literature that these ambitions increasingly risk confining children’s right to adequate areas of open space for outdoor play. Using a combination of quantitative approaches of analysis, with the use of regression analysis the study concluded that the coefficient of the independent variable Building age is positive, and therefore matches the expected direction. However, no statistically significant linear relationship was observed even with the use of relevant variables – highlighting a complex relationship surrounding the understanding and prediction of land use in general and urban open space in particular. A comparison of mean values using grouping based on both the aspect of time and centrality found that preschools built after 1998 generally contains 0,85 m2 larger open space per child than those built before 1987, whereas preschools within the urban center had 6,18 m2 larger open space per child than those located in more peripheral locations. When controlling for the share of preschools that undercuts and exceeds the recommendations related to dimensioning of open space communicated by the Swedish National Board of Housing, Building and Planning, units within the city center was found to meet these recommendations to a greater extent. Preschools built after 1998 seem to be more prevalent among units that undercuts the said recommendations. The results call for further research within this field of study in order to determine whether or not children’s shrinking open space can be limited to be a phenomenon encompassing solely major metropolitan areas.

Urban greenspace has the potential to bring a lot of positive effects to the urban environment. Better health for its residents, increased biodiversity as well as helping the city adapt to the changing climate, to name a few examples. At the same time, the current planning paradigm in Sweden values the creation of dense urban environments. This, coupled with the current housing shortage, creates a situation where urban greenspace is being put under a lot of pressure and on the risk of being exploited in densification processes. This thesis has explored how urban greenspace is valued, as well as which strategies are being employed, in comprehensive municipal planning documents. Through the use of a documentary content analysis, comprehensive planning documents from three Swedish municipalities have been analyzed: Umeå, Uppsala and Helsingborg. The results shows that the analyzed municipalities have a fairly balanced valuation of its urban greenspace in their comprehensive planning documents. No one aspect of the sustainable development is given a significantly higher value compared to the other. At the same time, different patterns emerges when looking at themes underlying the different aspects of the sustainable development, with themes such as recreation being discussed to a higher degree in comprehensive planning documents from Umeå and Uppsala, compared to Helsingborg. The strategies employed by the studied municipalities are also quite similar, although the details vary. All three municipalities are vague in describing their strategies for urban greenspace, but Umeå and Helsingborg goes further with working with quantifiable goals, compared to Uppsala.

Planners in Norrköping municipality today facing a challenge to meet Norrköping'sneeds in the housing market, while at the same time achieving demand for public places and areas such as parks, squares and nature areas. When existing areas within the city's borders are built, so-called densification takes place in the city, whichcan have both positive and negative consequences. The aim of this study is to investigatehow the densification has affected Norrköping's inner city from a social and ecologicalperspective with a focus on free space, and present proposals for measures forbetter management of the densification in central Norrköping. This study has mainly been carried out using a qualitative research method.A qualitative study is based on soft data such as interviews, document analysis and literature studies. The interviews have been conducted with respondents from Norrköpings municipality and the document analysis consists of steering documents obtained from Norrköpings municipality and Pontarius AB. Some data is obtained from documents and studies where results are presented in the form of tables, diagrams, figures and GIS analysis, which means that quantitative methods are also applied. To perform a safer densification, it is important that the municipality establishes safe guidelines and steering documents to relate to. These control documents should be used as a framework for efficient exploitation and ensure that the city's freeareas are developed from a sustainable perspective and that a good quality is includedin the development. It is advantageous that the development of the densification takes placeaccording to guidelines and documentation prepared by the municipality. To ensure maximum efficiency in exploitation, these guidelines should be followed at an early stage. It is also important that there is a balance of free space size and their quality. Too small a surface leads to a higher load and larger surfaces can be perceived as superfluousand a feeling of unsecure. It is recommended to study how the densification developsin connection with the infrastructure and how it will affect free and green areas in the long run. This study is limited to only the inner city of Norrköping. The study also delimits economic and political factors that can influence the planning of the densification and the development of the city’s infrastructure and public transport.