No description available.

The use of predictive analysis is becoming more commonplace with each passing day, which lends increased credence to the fact that even governmental institutions should adopt it. Kronofogden is in the middle of a digitization process and is therefore in a unique position to implement predictive analysis into the core of their operations. This project aims to study if methods from predictive analysis can predict how many debts will be received for a first-time debtor, through the use of uplift modeling. The difference between uplift modeling and conventional modeling is that it aims to measure the difference in behavior after a treatment, in this case guidance from Kronofogden. Another aim of the project is to examine whether the scarce literature about uplift modeling have it right about how the conventional two-model approach fails to perform well in practical situations. The project shows similar results as Kronofogden’s internal evaluations. Three models were compared: random forests, gradient-boosted models and neural networks, the last performing the best. Positive uplift could be found for 1-5% of the debtors, meaning the current cutoff level of 15% is too high. The models have several potential sources of error, however: modeling choices, that the data might not be informative enough or that the actual expected uplift for new data is equal to zero.

Les reliefs continentaux sont des interfaces dynamiques entre la lithosphère et l'atmosphère où interagissent une grande diversité de processus en lien avec la géodynamique interne et la géodynamique externe. Ils sont au cœur de la problématique des interactions entre le climat et la tectonique, dont une meilleure compréhension passe nécessairement par une meilleure appréhension des effets du climat et de ses variations sur la morphologie des reliefs et leur érosion. Nous présentons dans ce travail les résultats d'une étude expérimentale, en laboratoire, de la dynamique des reliefs, sous l'effet de forçages tectoniques (taux de surrection) et climatiques (taux de précipitations). A partir de l'élaboration d'une base de données conséquente d'expériences réalisées sous des conditions de surrection et de précipitations différentes, nous montrons que les hauteurs moyennes d'équilibre des reliefs, que leur temps de mise à l'équilibre et que leur morphologie déduite d'analyses de type pente-aire drainée sont des fonctions non- linéaires de la surrection, avec un effet des précipitations qui reste à préciser. Nous montrons que l'altitude moyenne d'équilibre des reliefs expérimentaux est contrôlée par le rapport entre taux de précipitation et de surrection (" water-to-rock ratio ") selon une loi non linéaire bien contrainte par plus de 80 données expérimentales. Le problème de la réponse des reliefs aux variations climatiques a été abordé en considérant l'effet d'une chute de pluviométrie sur un relief initialement à l'équilibre, en considérant différentes durées de chute, à taux de surrection constant. Nous montrons que plus la durée de chute de pluviométrie n'est importante, plus la réponse érosive (chute de vitesse d'érosion) est décalée dans le temps et amoindrie en amplitude. Ce résultat implique que sur les très longues échelles de temps (> quelques Ma), les variations climatiques n'ont probablement que très peu d'impact sur les vitesses d'érosion. Nous montrons également que cette réponse est contrôlée dans nos expériences par un seuil d'érosion. Nous avons également abordé l'impact de variations spatiales de précipitation sur la mobilité des réseaux de rivières et de crêtes. Nous montrons que de telles variations sont à l'origine d'une dissymétrie des vallées et d'une migration des réseaux de drainage qui peuvent aboutir à des captures entre bassins versants. Ces phénomènes observés dans les expériences sont tout à fait cohérents avec les caractéristiques géomorphologiques des vallées du piedmont nord-pyrénéen. Ces différents résultats mettent en évidence le rôle du climat, en l'occurrence les précipitations, sur la dynamique à long-terme des surfaces topographiques. / Continental reliefs are dynamic interfaces between the lithosphere and the atmosphere here a great diversity of processes interact with internal geodynamics and external geodynamics. They are at the essence of the problem of interactions between climate and tectonics. A better understanding of this interactions suggests a better understanding of effects of climate and its variations on the morphology of the landforms and their erosion. We present in this work the results of an experimental study in laboratory of the dynamics of the reliefs, under the effect of tectonic forcing (uplift rate) and climatic (rainfall rate). From the development of a consistent database of experiments carried out under different conditions of uplift and precipitation, we show that the mean steady-state of the reliefs, their update time and their morphology, deduced from slope-area analyzis, are non-linear functions of the uplift, with a rainfall effect that needs to be specified. We show that the mean equilibrium altitude of the experimental landscape is controlled by the ratio between rainfall and uplift "water-to-rock ratio", according to a nonlinear law constrained by more than 80 experimental data. The problem of the response of reliefs to climatic variations was approached by considering the effect of a decrease of rainfall rate on a landscape initially at steady-state, considering different durations of the decrease, with constant rate of rise. We show that more the deacreasing of rainfall asts in time, more the erosive response (erosion rate) is shifted in time and decreases in amplitude. This result implies that over very long-time scales (> a few Ma), climatic variations probably have very little impact on erosion rates. We also show that this response is controlled in our experiments by an erosion threshold. We also discussed the impact of spatial rainfall variations on the mobility of river and ridge networks. We show that such variations lead to a dissymmetry of the valleys and a migration of the drainage networks, which can cause catches between catchments. These phenomena observed in the experiments are in agreement with the geomorphological characteristics of the valleys of the north-Pyrenean piedmont. These results highlight the role of climate, in this case precipitation, in the long-term dynamics of topographic surfaces.

No description available.

No description available.

No description available.

In 1908 Jack Johnson became the first black heavyweight boxing champion of the world. His reign would be rife with controversy, leading to widespread racial violence and draconian government intervention. Lester Walton, theater critic for the New York Age, became obsessed with Johnson; his extensive writing on the boxer powerfully reveals not just Walton’s own struggle with issues of race in America, but sheds light on the difficulties the black community at large faced in trying to make sense of a figure who simultaneously represented hope for the positive change Reconstruction failed to produce and, ironically, also threatened to intensify the hardships of Jim Crow era oppression.

acase@tulane.edu / 1 / Qi Li

I have studied syntectonic veins from shales and coarse calcareous sands of the Ordovician Womble Shale, Benton uplift, Arkansas. All veins are composed of calcite with minor quartz and trace feldspar and dolomite or high-Mg calcite in the coarser veins. All host lithologies have a pressure-solution cleavage, more closely spaced in the fine-grained shale beds. The vein internal fabrics are coarsely to finely fibered, with a strong host-rock grain size control on fiber width. The finest fibers are in veins with shale host and the coarsest in the coarse-grained calcareous sandstone. Fiber aspect ratio is inversely proportional to host grain size; more equant vein grains are found in the veins hosted in the coarse host fraction. Within one outcrop, the δ13C and δ18O compositions of the host lithologies range from 1.5 to -3.0 per mil and 7.5 to -14.0 per mil (VPDB), respectively. By contrast, the δ18O composition of the veins is remarkably constant (-13.5 per mil) among veins of starkly different fabrics. This composition is identical to that of the coarse calcareous sandstone lithology in the outcrop. No cathodoluminescence or stable isotope zoning was observed in the veins. In addition, there were no gradients in Ca or Si in the vicinity of the veins, suggesting either that the host did not contribute these elements or that diffusion was not the rate-limiting step to vein formation. In any case, the wide variety of veins was probably formed from meter-scale migration of fluid derived from local calcite-rich layers in calcareous sandstone.

This dissertation contains studies that use various geochronometric and thermochronometric techniques to better understand the post-magmatic evolution of Sierra Nevada, California. (U-Th)/He ages in apatite and zircon from Sierran batholithic rocks are used to constrain the Cenozoic exhumation of the northern part of the range. Zircon and apatite ages determined from the same samples revealed relatively rapid cooling and exhumation rates (0.2 - 0.8 km/My) from ~ 90 to 60 Ma, followed by tectonic quiescence and slow exhumation (0.02 - 0.04 km/My) from the late Paleocene to present. In addition to the thermochronology of basement lithologies, the detrital zircon geochronology of grains from preserved Eocene fluvial sediments in the central and northern Sierra Nevada was performed. U-Pb ages of detrital zircons from the deposits were found to have distributions closely matching age-area estimates of Mesozoic plutons in the Sierra Nevada, suggesting that Eocene river systems were draining local Sierran catchments and likely had steeper axial gradients than has been proposed. Provenance analysis of the Eocene sediments is used to provide constraints on the paleotopography of the Sierra Nevada and inferred range-wide Cenozoic uplift.In addition to the Sierra Nevada work, this dissertation also contains studies that focus on the development of the K-Ca system as a geochronometric technique suitable for dating the deposition of sedimentary sequences. We present a new method for measuring Ca isotopic ratios using a multi-collector ICP-MS equipped with a hexapole collision cell. Isobaric argon interferences are minimized via gas phase reactions in the collision cell. The reproducibility of Ca ratio measurements is found to be ~ 0.02 % (RSD), which is comparable to high precision TIMS techniques and an order of magnitude improvement over single collector ICP-MS techniques using a similar reaction cell method. K-Ca ages of glauconite and K-rich evaporites are determined in order to evaluate the usefulness of the K-Ca system as a sedimentary geochronometer. K-Ca ages in both glauconite and K-salts are found to be variable and significantly younger than documented depositional ages. Reported ages, however, are thought to be recording important basinal thermal histories and recrystallization events.