Examination of the seepage face boundary condition in subsurface and coupled surface/subsurface hydrological models

A seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions, water table fluctuations, and flow patterns. Its handling in hydrological models, especially under complex conditions such as heterogeneity and coupled surface/subsurface flow, has not been extensively studied. In this paper, we compare the treatment of the seepage face as a static (Dirichlet) versus dynamic boundary condition, we assess its resolution under conditions of layered heterogeneity, we examine its interaction with a catchment outlet boundary, and we investigate the effects of surface/subsurface exchanges on seepage faces forming at the land surface. The analyses are carried out with an integrated catchment hydrological model. Numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the Landscape Evolution Observatory. The results show that the static boundary condition is not always an adequate stand-in for a dynamic seepage face boundary condition, especially under conditions of high rainfall, steep slope, or heterogeneity; that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic; that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role; and that seepage faces at the land surface are not always controlled by subsurface flow. The paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way, is applicable to unstructured grids, and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models

A Computational Framework for Formalizing Rules and Managing Changes in Normative Systems

Legal texts are typically written in a natural language. However, a legal text that is written in a formal language has the advantage of being subject to automation, at least partially. Such a translation is not easy, and the matter is even more complex because the law changes with time, so if we formalized a legal text that was originally written in natural language, there is a need to keep track of the change. This thesis proposes original developments on these subjects. In order to formalize a legal document, we provide a pipeline for the translation of a legal text from natural to formal language and we apply it to the case of natural resources contracts. In general, adjectives play an important role in a text and they allow to characterize it: for this reason we developed a logical system aimed at reasoning with gradable adjectives. Regarding norm change, we provide an ontology to represent change in a normative system, some basic mechanisms by which an agent may acquire new norms, and a study on the problem of revising a defeasible theory by only changing its facts. Another contribution of this thesis is a general framework for revision that includes the previous points as specific cases

Reduced Order Models and Data Assimilation for Hydrological Applications

The present thesis work concerns the study of Monte Carlo (MC)-based data assimilation methods applied to the numerical simulation of complex hydrological models with stochastic parameters. The ensemble Kalman filter (EnKF) and the sequential importance resampling (SIR) are implemented in the CATHY model, a solver that couples the subsurface water flow in porous media with the surface water dynamics. A detailed comparison of the results given by the two filters in a synthetic test case highlights the main benefits and drawbacks associated to these techniques. A modification of the SIR update is suggested to improve the performance of the filter in case of small ensemble sizes and small variances of the measurement errors. With this modification, both filters are able to assimilate pressure head and streamflow measurements and correct model errors, such as biased initial and boundary conditions. SIR technique seems to be better suited for the simulations at hand as they do not make use of the Gaussian approximation inherent the EnKF method. Further research is needed, however, to assess the robustness of the particle filters methods in particular to ensure accuracy of the results even when relatively small ensemble sizes are employed. In the second part of the thesis the focus is shifted to reducing the computational burden associated with the construction of the MC realizations (which constitutes the core of the EnKF and SIR). With this goal, we analyze the computational saving associated to the use of reduced order models (RM) for the generation of the ensemble of solutions. The proper orthogonal decomposition (POD) is applied to the linear equations of the groundwater flow in saturated porous media with a randomly distributed recharge and random heterogeneous hydraulic conductivity. Several test cases are used to assess the errors on the ensemble statistics caused by the RM approximation. Particular attention is given to the efficient computation of the principal components that are needed to project the model equations in the reduced space. The greedy algorithm selects the snapshots in the set of the MC realizations in such a way that the final principal components are parameter independent. An innovative residual-based estimation of the error associated to the RM solution is used to assess the precision of the RM and to stop the iterations of the greedy algorithm. By way of numerical applications in synthetic and real scenarios, we demonstrate that this modified greedy algorithm determines the minimum number of principal components to use in the reduction and, thus, leads to important computational savings

Statistical Inference in the Duffing System with the Unscented Kalman Filter

We investigate the accuracy of inference in a chaotic dynamical sys- tem (Duffing oscillator) with the Unscented Kalman Filter, and quantify the dependence on the sample size, the signal to noise ratio and the initialization

Environmental effects on star formation in dwarf galaxies and star clusters

We develop a simple analytical criterion to investigate the role of the environment on the onset of star formation. We will consider the main external agents that influence the star formation (i.e. ram pressure, tidal interaction, Rayleigh-Taylor and Kelvin-Helmholtz instabilities) in a spherical galaxy moving through an external environment. The theoretical framework developed here has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy. We develop an analytic formalism to solve the fluid dynamics equations in a non-inertial reference frame mapped with spherical coordinates. The two-fluids instability at the interface between a stellar system and its surrounding hotter and less dense environment is related to the star formation processes through a set of differential equations. The solution presented here is quite general, allowing us to investigate most kinds of orbits allowed in a gravitationally bound system of stars in interaction with a major massive companion. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system (as a dwarf galaxy or a globular cluster) on its surrounding environment useful in theoretical interpretations of numerical results as well as observational applications. We show how spherical coordinates naturally enlighten the interpretation of the two-fluids instability in a geometry that directly applies to astrophysical case. This criterion predicts the threshold value for the onset of star formation in a mass vs. size space for any orbit of interest. Moreover, we show for the first time the theoretical dependencies of the different instability phenomena acting on a system in a fully analytical way.Comment: ACCEPTED in A&A the 09/09/2014. Changes from ver 1: the non-inertial linear-response theory for gas instabilities in spherical coordinates is moved to the Appenidx and will be available only on-lin

Orbital evolution of the Carina dwarf galaxy and self-consistent star formation history determination

We present a new study of the evolution of the Carina dwarf galaxy that includes a simultaneous derivation of its orbit and star formation history. The structure of the galaxy is constrained through orbital parameters derived from the observed distance, proper motions, radial velocity and star formation history. The different orbits admitted by the large proper motion errors are investigated in relation to the tidal force exerted by an external potential representing the Milky Way (MW). Our analysis is performed with the aid of fully consistent N-body simulations that are able to follow the dynamics and the stellar evolution of the dwarf system in order to determine self-consistently the star formation history of Carina. We find a star formation history characterized by several bursts, partially matching the observational expectation. We find also compatible results between dynamical projected quantities and the observational constraints. The possibility of a past interaction between Carina and the Magellanic Clouds is also separately considered and deemed unlikely.Comment: Accepted in A&

Étude et développement d'un procédé de traitement des odeurs par oxydation à l'ozone : application aux effluents gazeux d'usines de production de superphosphate

Dans le procédé de production d’engrais à base de superphosphate, l’attaque de la roche phosphatée par l’acide sulfurique génère des sous-produits gazeux odorants. Bien que leurs émissions se situent dans les limites réglementaires, les usines d’engrais à base de superphosphate sont susceptibles de causer des nuisances olfactives pour les riverains. Cette thèse propose d’étudier la faisabilité d’un procédé de traitement des odeurs par l’ozonation en phase gazeuse homogène. Une première étape de priorisation des composés chimiques ayant le potentiel odorant le plus important a été réalisée. Ce classement a été effectué à partir d’un rapport technique fourni par notre partenaire industriel basé sur une campagne de mesure olfactométrique et de caractérisation chimique des gaz émis par la cheminée d’une usine de production des engrais superphosphate. À partir du calcul de la valeur d’activité odorante (OAV), deux familles de composés ont été ciblées : les composés soufrés – représentés par le sulfure d’hydrogène (H2S), le sulfure d’éthylméthyle (MES) et le disulfure de diméthyle (DMDS) – et les aldéhydes (représentés par le propanal et le butanal). Deux techniques analytiques (GC/FID et SIFT/MS) ont été mises en œuvre afin d’évaluer les performances d’élimination de ces composés, la difficulté d'analyser une matrice gazeuse contenant de l'ozone ayant été mise en évidence. Ainsi, une interférence de l'ozone sur l'analyse des aldéhydes par GC/FID a été identifiée. La technique SIFT/MS a, quant à elle, nécessité un développement important. L’ozonation d’effluents gazeux modèles a été réalisée en suivant l’élimination des composés cibles dans différentes conditions de fonctionnement (temps de résidence, température du réacteur, concentration en ozone et taux d’humidité) dans un domaine expérimental compatible avec les contraintes industrielles. Les composés soufrés ont présenté des taux d’élimination élevés, particulièrement dans le cas de H2S, dont les conversions ont atteint environ 80%. Les monosulfures (MES) et disulfures organiques (DMDS) se sont montrés moins réactifs à l’ozone, puisque les conversions sont restées assez faibles (de l’ordre de 30% pour un ratio O3/soufrés similaire). Dans la gamme de conditions opératoires utilisées, ni l'humidité, ni le temps de résidence dans le réacteur n’ont montré d'influence considérable. La concentration d'ozone s’avère être le paramètre du procédé le plus influant, ayant un effet positif sur les taux de conversion des trois composés soufrés étudiés. Parallèlement, pour le DMDS, une augmentation de la température du réacteur a aussi amélioré la conversion. De manière globale, les taux de conversion les plus importants ont été obtenus pour les ratio O3/soufrés et la température du réacteur les plus élevés. A l’inverse, même lorsque les conditions de réaction les plus favorables ont été appliquées (température et concentration d’ozone les plus élevées), les aldéhydes se sont montrés non réactifs vis-à-vis de l’ozone. Malgré les faibles conversions obtenues, l’utilisation du SIFT/MS a permis d’identifier les principaux sousproduits de la réaction ozone-composés soufrés en phase gazeuse comme étant le méthyléthylsulfoxyde (MESO), le méthyléthylsulfone (MESO2), le diméthyl thiosulfinate (DMSOS), les isomères de diméthyl thiosulfonate (DMSO2S), le diméthyldisulfoxyde (DM(SO)2) et également le dioxyde (SO2) et le trioxyde de soufre (SO3). Le procédé de traitement des odeurs par ozonation directe des gaz en sortie de cheminée industrielle apparaît donc difficilement envisageable en raison de la faible efficacité d’élimination des composés malodorants démontrée dans nos essais. En revanche, cette technique couplée avec une absorption chimique pourrait s’avérer intéressante pour éliminer les nuisances olfactives avec une bonne efficacit

Exploring the environment of high Rotation Measure Active Galactic Nuclei through wide-band radio spectropolarimetry observations

In this Thesis I present an observational study of a sample of radio AGN sources. I study their radio polarization properties in a wide frequency range by observing with the 100-m Effelsberg telescope and the Very Large Array (VLA) interferometer. The aim was 1) to define a sample of candidates to contain an extreme environment around the SMBH and, 2) to study their environment by modeling of the polarization properties within a wide frequency range. I select sources with no detectable flux polarization at 1.4GHz in the NVSS survey, characteristic of strong depolarization due to a high value of Rotation Measure (RM) and thus, of an extreme medium in these sources. I performed single dish observations at 10.45 GHz using the 100-m Effelsberg telescope. At this high frequency, I detected polarized flux density on 30 sources, which became our high-RM candidates. Single dish follow-up in the 2 to 15 GHz frequency range, were performed to characterize their radio spectra and to determine their RMs. The polarization angle behavior deviates significantly from the lambda^2 law, suggesting that several Faraday screens are present in the intervening medium. I studied the most interesting high-RM cases through wide-band high sensitive observations at C and X bands using the JVLA. I modeled the polarization properties constructing a set of models which are combinations of simple internal and the external Faraday screens. This new approach of polarization study allows to spectrally resolve multiple polarized components of unresolved AGN with the result to trace some clumpy and dense region surrounding them. This new spectropolarimetry approach can be adopted as a new way to trace clumpy and dense regions surrounding the AGN

Fatigue performance of recycled hot mix asphalt: A laboratory study

The paper introduces and analyses the results of an experimental trial on the fatigue resistance of recycled hot mix asphalt for road pavements. Based on the gyratory compaction and the indirect tensile strength test, the mix design procedure has optimized nine different mixes, considering both conventional limestone and Reclaimed Asphalt Pavement (RAP), the latter used at different quantities, up to 40% by weight of the aggregate. A standard bitumen and two polymer modified binders were used for the production of the mixes. The fatigue study was carried out with four-point bending tests, each one performed at 20\ub0C and 10 Hz. The empirical stiffness reduction method, along with the energy ratio approach, based on the dissipated energy concept, was adopted to elaborate the experimental data. Unaged and aged specimens were checked, to analyse the ageing effects on the fatigue performance. In comparison with the control mixes, produced only with limestone, improved fatigue performance was noticed for the mixtures prepared with RAP, especially when made with polymer modified binders, under both aged and unaged conditions. Both the approaches adopted for the experimental data analysis have outlined the same ranking of the mixes