Educational Fiscal Policy and Its Effects on How our Children Learn: Comparing Minnesota and Illinois

The study compares Illinois’ and Minnesota’s education fiscal policies. Illinois funds it’s education system mainly from the local level, whereas Minnesota funds it’s mainly from the state level. Thus, in Illinois, if there are discrepancies between household incomes in wealthier and poorer areas, the schools in wealthier areas would receive more money than those in poorer areas. Test scores are then compared. Illinois typically has lower scores than Minnesota. The conclusion is that Illinois’ policies are hindering their students’ learning, compared to Minnesota students, with some mixed results

Experimental study of Perovskite / post-Perovskite phase transformation mechanism and its kinetics in the earth mantle

Aux conditions de pression et température de la couche D'', située à 2700 km de profondeur sous la surface terrestre, la Bridgmanite (Pv), le minéral le plus abondant dans le manteau profond, se transforme en sa phase de haute pression, (Mg,Fe)SiO3 post-perovskite (pPv). Cette transformation de phase est souvent évoquée pour expliquer les différentes anomalies et discontinuités des ondes sismiques au sein de la couche D''. Toutefois, nous manquons d'information sur les détails de cette transformation. L'objectif de cette thèse fut d'améliorer notre compréhension du mécanisme de transformation Pv / pPv et d'en étudier la cinétique. Pour cela, j'ai utilisé la cristallographie multigrains, une méthode qui permet de caractériser des centaines de cristaux in situ dans un matériau polycristallin. Le manuscrit commence par une démonstration de la fiabilité de cette méthode pour des expériences aux conditions extrêmes de pression. Je décris ensuite l'étude expérimentale du mécanisme de transformation Pv/pPv avec l'analogue structural NaCoF3. Je trouve que ce mécanisme est martensitique pour le sens Pv vers pPv et reconstructif au retour. Je discute également leurs impacts sur la microstructure au sein de la couche D''. Par la suite, je présente l'étude cinétique de cette transformation dans la composition (Mg0,86,Fe0,14)SiO3 et j'extrapole nos données afin de contraindre la dynamique et la cinétique de cette transformation aux conditions P/T de la couche D'', en tenant compte de la pression, de la température, et de la taille de grains.The radial seismic structure of the earth is marked by a sharp transition about 200 km above the core-mantle boundary. This defines the top of the region called the D'' layer. Moreover, at these P/T conditions, Bridgmanite (Pv), the main lower mantle mineral, transforms into its high-pressure phase, (Mg,Fe)SiO3 post-perovskite (pPv). This phase transition has received considerable interest due to its thermodynamic properties, the induced textures and microstructures that seem to explain many of the seismic anomalies of the D'' layer. However, its thermodynamic properties and transformation mechanisms are not very well known. The main purpose of this thesis was to investigate the Pv/pPv phase transition and its kinetics. To do so, we used a novel method, called Multigrain Crystallography, to characterize in-situ hundreds of crystals in a polycrystalline material. The reliability of the method for experiments under extreme conditions is tested in the first part of this manuscript. I then focus on the Pv/pPv phase transition mechanism on a structural analog of composition NaCoF3. I determine that the Pv to pPv transformation is martensitic and that the reverse transformation is reconstructive. Their impacts on the D'' layer microstructure are also discussed. Finally, I explore the kinetics of the (Mg0,86,Fe0,14)SiO3 Pv to pPv transition by time-series experiments. Moreover, based on our data, I present two possible kinetic models that include the effect of pressure, temperature, and grain size. These models have important implications to constrain the dynamics and kinetics of the Bridgmanite to pPv transition at the D'' layer P/T conditions

3D-XRD Study of Phase Transformation Microstructures in Deep Earth Minerals

International audienc

Etude expérimentale des interfaces dans le manteau profond

National audienc

Perovskite / Post-Perovskite Phase Transformation : Effect on Grain Sizes and Orientations

International audienc

Kinetics and detectability of the bridgmanite to post-perovskite transformation in the Earth's D″ layer

International audienceBridgmanite, the dominant mineral in the Earth’s lower mantle, crystallizes in the perovskite structure and transforms into post-perovskite at conditions relevant for the D′′ layer. This transformation affects the dynamics of the Earth’s lowermost mantle and can explain a range of seismic observations. The thickness over which the two phases coexist, however, can extend over 100 km, casting doubt on the assignment of the observed seismic boundaries. Here, experiments show that the bridgmanite to post-perovskite transition in (Mg0.86,Fe0.14)SiO3 is fast on geological timescales. The transformation kinetics, however, affects reflection coefficients of P and S waves by more than one order of magnitude. Thick layers of coexisting bridgmanite and post-perovskite can hence be detected using seismic reflections. Morever, the detection and wave period dependence of D′′ reflections can be used to constrain significant features of the Earth’s lowermost mantle, such as the thickness of the coexistence layer, and obtain information on temperature and grain sizes

Deformation of NaCoF3_ 3 perovskite and post-perovskite up to 30 GPa and 1013 K: implications for plastic deformation and transformation mechanism

Texture, plastic deformation, and phase transformation mechanisms in perovskite and post-perovskite are of general interest for our understanding of the Earth's mantle. Here, the perovskite analogue NaCoF$_3$ is deformed in a resistive-heated diamond anvil cell (DAC) up to 30 GPa and 1013 K. The in situ state of the sample, including crystal structure, stress, and texture, is monitored using X-ray diffraction. A phase transformation from a perovskite to a post-perovskite structure is observed between 20.1 and 26.1 GPa. Normalized stress drops by a factor of 3 during transformation as a result of transient weakening during the transformation. The perovskite phase initially develops a texture with a maximum at 100 and a strong 010 minimum in the inverse pole figure of the compression direction. Additionally, a secondary weaker 001 maximum is observed later during compression. Texture simulations indicate that the initial deformation of perovskite requires slip along (100) planes with significant contributions of {110} twins. Following the phase transition to post-perovskite, we observe a 010 maximum, which later evolves with compression. The transformation follows orientation relationships previously suggested where the c axis is preserved between phases and hh0 vectors in reciprocal space of post-perovskite are parallel to [010] in perovskite, which indicates a martensitic-like transition mechanism. A comparison between past experiments on bridgmanite and current results indicates that NaCoF$_3$ is a good analogue to understand the development of microstructures within the Earth's mantle

Phase transformation microstructures and their effect on seismic signals from the Earth's mantle

International audienc

High-pressure deformation experiments at ID06-LVP: in-situ measurements of stress partitioning within two-phases aggregates for understanding strain localisation in rocks

International audienc