Thesis (Ph. D.)--California Institute of Technology, 1985. / Typescript (photocopy). Includes bibliographical references (leaves 183-189).

Thesis (Ph. D.)--California Institute of Technology, 1984. / Includes bibliographical references (leaves 213-230).

L'inversion des formes d'onde (full waveform inversion, FWI) a suscité un intérêt dans le monde entier pour sa capacité à estimer de manière précise et détaillée les propriétés physiques du sous-sol. La FWI est généralement formulée sous la forme d'un problème d'ajustement des données par moindres carrés et résolus par une approche linéarisée utilisant des méthodes d'optimisation locales. Cependant, la FWI est bien connue de souffrir du problème de saut de phase rendant les résultats fortement dépendant de la qualité des modèles initiaux. L'inversion des formes d'ondes des arrivées réfléchies (reflection waveform inversion, RWI) a récemment été proposée pour atténuer ce problème en supposant une séparation d'échelle entre le modèle de vitesse lisse et le modèle de réflectivité à haut nombre d'onde. La formulation de RWI considère explicitement les ondes réfléchies afin d'extraire de ces ondes une information sur les variations lisses de vitesse des zones profondes. Cependant, la méthode néglige les ondes transmises qui contraignant les informations lisses de vitesse en proche surface.Dans cette thèse, une étude de la sensibilité en nombre d'ondes des méthodes de FWI et RWI a d'abord été revisitée dans le cadre de la tomographie en diffraction et des décompositions orthogonales. A partir de cette analyse, je propose une nouvelle méthode, à savoir l'inversion jointe des formes d'ondes transmises et réfléchies (joint full waveform inversion, JFWI). La méthode propose une formulation unifiée pour combiner la FWI des transmissions et la RWI pour les réflexions, donnant naturellement une sensibilité commune aux petits nombres d'onde venant des arrivées grand-angle et réfléchies. Les composantes à hauts nombres d'onde sont naturellement atténuées par la formulation. Pour satisfaire l'hypothèse de séparation d'échelle, j'utilise une paramétrisation du sous-sol basée sur la vitesse des ondes de compression et l'impédance acoustique. La complexité temporelle de cette approche est le double de la méthode de FWI classique et la requête mémoire reste la même.Une procédure d'inversion est ensuite proposée, permettant d'estimer alternativement le modèle de la vitesse du sous-sol par JFWI et l'impédance inversion de formes d'ondes réfléchies. Un exemple synthétique réaliste du modèle de Valhall est d'abord utilisé avec des données de streamer et à partir d'un modèle initial très lisse. Dans ce cadre, alors que la FWI converge vers un minimum local, la JFWI réussit à reconstruire un modèle de vitesse lisse de bonne qualité. La prise en compte des ondes tournante par la JFWI montre un fort intérêt pour la qualité de reconstruction superficielle, comparée à la méthode RWI seule. Cela se traduit ensuite par une reconstruction améliorée en profondeur. Le modèle de vitesse lisse construit par JFWI peut ensuite être considéré comme modèle initial pour la FWI classique, afin d'injecter le contenu en haut nombres d'onde tout en évitant le problème de saut de phase.Les avantages et limites de l'approche de JFWI sont ensuite étudiés dans une application sur données réelles, venant d'un profil 2D de données de fond de mer (OBC) recoupant un nuage de gaz au dessus d'un réservoir. Plusieurs modèles initiaux et stratégies d'inversion sont testés afin de minimiser le problème de saut de phase, tout en construisant des modèles de sous-sol avec une résolution suffisante. Sous réserve de mettre en œuvre des stratégies limitant le problème de saut de phase, la JFWI montre qu'elle peut produire un modèle de vitesse acceptable, injectant les bas nombres d'onde dans le modèle de vitesse. L'amélioration de l'éclairage en angles de diffraction fournie par des acquisitions 3D devrait permettre de pouvoir commencer l'inversion par JFWI à partir de modèle encore moins bien définis. / Full waveform inversion (FWI) has attracted worldwide interest for its capacity to estimate the physical properties of the subsurface in details. It is often formulated as a least-squares data-fitting procedure and routinely solved by linearized optimization methods. However, FWI is well known to suffer from cycle skipping problem making the final estimations strongly depend on the user-defined initial models. Reflection waveform inversion (RWI) is recently proposed to mitigate such cycle skipping problem by assuming a scale separation between the background velocity and high-wavenumber reflectivity. It explicitly considers reflected waves such that large-wavelength variations of deep zones can be extracted at the early stage of inversion. Yet, the large-wavelength information of the near surface carried by transmitted waves is neglected.In this thesis, the sensitivity of FWI and RWI to subsurface wavenumbers is revisited in the frame of diffraction tomography and orthogonal decompositions. Based on this analysis, I propose a new method, namely joint full waveform inversion (JFWI), which combines the transmission-oriented FWI and RWI in a unified formulation for a joint sensitivity to low wavenumbers from wide-angle arrivals and short-spread reflections. High-wavenumber components are naturally attenuated during the computation of model updates. To meet the scale separation assumption, I also use a subsurface parameterization based on compressional velocity and acoustic impedance. The temporal complexity of this approach is twice of FWI and the memory requirement is the same.An integrated workflow is then proposed to build the subsurface velocity and impedance models in an alternate way by JFWI and waveform inversion of the reflection data, respectively. In the synthetic example, JFWI is applied to a streamer seismic data set computed in the synthetic Valhall model, the large-wavelength characteristics of which are missing in the initial 1D model. While FWI converges to a local minimum, JFWI succeeds in building a reliable velocity macromodel. Compared with RWI, the involvement of diving waves in JFWI improves the reconstruction of shallow velocities, which translates into an improved imaging at greater depths. The smooth velocity model built by JFWI can be subsequently taken as the initial model for conventional FWI to inject high-wavenumber content without obvious cycle skipping problems.The main promises and limitations of the approach are also reviewed in the real-data application on the 2D OBC profile cross-cutting gas cloud.Several initial models and offset-driven strategies are tested with the aim to manage cycle skipping while building subsurface models with sufficient resolution. JFWI can produce an acceptable velocity model provided that the cycle skipping problem is mitigated and sufficient low-wavenumber content is recovered at the early stage of inversion. Improved scattering-angle illumination provided by 3D acquisitions would allow me to start from cruder initial models.

Knowledge of the geoacoustic properties of the ocean bottom is essential for accurate modeling of acoustic propagation in shallow-water environments. Estimates of these properties can be obtained through geoacoustic inversion. Among the various inversion methods, the ones based on matched-field processing (MFP) have been increasingly used due to their relatively easy implementation and their good performance. In matched-field inversion (MFI), the objective is to maximize the match between the measured acoustic pressure field and the modeled field calculated for trial sets of geoacoustic parameters characterizing the environment. This thesis investigates the technique of matched-field tomographic inversion, a recent application of MFI that takes advantage of a multiple array-multiple source configuration to estimate range-dependent geoacoustic parameters. A two-stage inversion method based on the ray approach adopted to calculate the modeled pressure fields is developed to increase the efficiency of the estimation. The first stage consists of matching measured and modeled amplitudes of waterborne rays propagating between each source-array pair to estimate the parameters at the seafloor. The second stage consists of matching measured and replica pressure fields corresponding to rays that penetrate the sediment to estimate deeper parameters. In the first stage, the match is quantified using a least-squares function whereas in the second stage the robust pairwise processor is used. Both stages use a simplex genetic algorithm to guide the search over the parameter space. The inversion method is first applied to the two-dimensional (2-D) problem of vertical-slice tomography where four sets (2 sources x 2 vertical line arrays) of multi-tone pressure fields are used to estimate the depth and range variations of geoacoustic parameters. The method is validated via simulation studies that show its good performance in the ideal case where every model parameter except the ones to be estimated are exactly known, and quantify its limitations in non-ideal cases where noise in the data or errors in the array positions are present. The inversion results show that the parameters to which the pressure field is the most sensitive are well estimated for signal-to-noise ratios greater than or equal to 5 dB or for array position uncertainties less than two wavelengths of the source wavelet. The inversion method is then applied to a 3-D environment problem. From the different array configurations studied, it is found that the accuracy of the parameter estimates increases with decreasing propagation range. Finally, the method is applied to experimental data for a vertical-slice configuration. The relatively poor match obtained between the replica and measured data is attributed to the large uncertainty in the array position and the simplistic parameterization of the environment. / Graduate

The interconversion of sugars in nature has for long been a source of interest and speculation. Many attempts were made to postulate a mechanism for the smooth and facile transformations but until 1933 the theories were unsupported by any experimental evidence. The first direct conversion of one aldose to another by means of changes involving a Walden inversion was achieved by Irvine and Hynd who obtained either d-glucose or d-mannose from d-glucosamine, according to the experimental procedure. It was obvious that in one case Walden inversion took place on C₂, but an interpretation of reaction was complicated by the removal of the nitrogen atom. Later, by the action of ammonia on methylglucoside-2-bromohydrin, Fischer et al. obtained “methylepiglucosamine” which was later shewn to be 2-amino-methylaltroside. The research which is now to be described was undertaken with a view to extending to the pentose series the application of the general principles which had been worked out for the hexoses. Although the research was incomplete, in the sense that no interconversion was achieved, many interesting facts emerged in the course of the work and some important derivatives of arabinose were prepared for the first time.

Este trabalho apresenta um procedimento de inversão magnética de três etapas no qual quantidades invariantes em relação à fonte magnética são sequencialmente invertidas para recuperar i) a geometria da fonte no substrato, ii) sua intensidade de magnetização e iii) a inclinação da magnetização da fonte. A primeira quantidade invertida (chamada função geométrica) é obtida pela razão entre a intensidade do gradiente da anomalia magnética e a intensidade do campo magnético anômalo. Para fontes homogêneas, a função geométrica depende apenas da geometria da fonte, o que permite a reconstrução da forma do corpo usando valores arbitrários para a magnetização. Na segunda etapa, a forma da fonte é fixa e a intensidade de magnetização é estimada ajustando o módulo do gradiente da anomalia magnética, uma quantidade invariante com a direção da magnetização e equivalente à amplitude do sinal analítico. Na última etapa, a forma da fonte e a intensidade da magnetização são fixas e a inclinação da magnetização é determinada ajustando a anomalia magnética. Além de recuperar a forma e a magnetização de fontes homogêneas, esta técnica permite, em alguns casos, verificar se as fontes magnéticas são homogêneas. Isto é possível pois a função geométrica de fontes heterogêneas pode ser ajustada por um modelo homogêneo, mas o modelo assim obtido não permite o ajuste da amplitude do sinal analítico nem da anomalia magnética. Esse é um critério que parece efetivo no reconhecimento de fontes fortemente heterogêneas. O método de inversão por etapas é testado em experimentos numéricos de computador e utilizado para interpretar uma anomalia magnética gerada por rochas básicas intrusivas da Bacia do Paraná. / This work presents a three step magnetic inversion procedure in which invariant quantities related to source parameters are sequentially inverted to provide i) cross-section of two-dimensional sources; ii)intensity of source magnetization, and iii) inclination of source magnetization. The first inverted quantity (called geometrical function) is obtained by rationing intensity gradient of total field anomaly and intensity of vector anomalous field. For homogenous sources, geometrical function depends only on source geometry thus allowing shape reconstruction by using arbitrary values for source magnetization. In the second step, source shape is fixed and magnetization intensity is estimated by fitting intensity gradient of total field anomaly, an invariant quantity with magnetization direction and equivalent to amplitude of the analytical signal. In the last step, source shape and magnetization intensity are fixed and magnetization inclination is determined by fitting magnetic anomaly. Besides furnishing shape and magnetization of homogeneous two-dimensional sources, this technique allows to check in some cases if causative sources are homogeneous. It is possible because geometrical function from inhomogeneous sources can be fitted by a homogeneous model but a model thus obtained does not fit the amplitude of analytical signal nor magnetic anomaly itself. This is a criterion that seems efective in recognizing strongly inhomogeneous sources. The proposed technique is tested with numerical experiments, and used to model a magnetic anomaly from intrusive basic rocks of Paraná Basin, Brazil.

Les émulsions de Pickering ont suscité un intérêt croissant dans de nombreux domaines de la recherche en raison de leur grande stabilité et versatilité. Une attention particulière a été accordée à la fabrication des systèmes complexes et originaux qui peuvent être obtenus avec différentes particules. Cette étude a consisté dans l'analyse des différents paramètres physico-chimiques des particules, des milieux liquides et des systèmes dispersées, et leur relation avec le comportement mécanique et la structure des émulsions afin de prédire et de moduler les caractéristiques de ces dernières. Nous avons étudié plus particulièrement pour la première fois, le diagramme de phase concernant les inversions de phase du type catastrophique et transitionnelle des émulsions de Pickering. Nous avons utilisé des particules de silice avec des structures et hydrophobicités différentes. En particulier, nous avons montré que le mélange de particules de différente hydrophobicités peut moduler finement l'inversion de phase aussi bien que les propriétés rhéologiques et structurales des émulsions. La fabrication de membranes à partir des émulsions de Pickering précédentes a été proposée comme un exemple de l'utilisation de ces systèmes modèles pour la conception de matériaux complexes. / Pickering emulsions have gained interest in many fields of research due their properties like higher stability and versatility. Special attention has been given to the processing of complex and original systems which can be obtained by using different particles. This study consists in the analysis of the different physicochemical parameters of particles, liquid media as well dispersion systems, and their relationship with emulsions structural and mechanical behavior in order to predict and modulate the emulsions characteristics. We studied extensively for the first time the phase diagram of catastrophic and transitional phase inversion of Pickering emulsions. We used silica particles with different structure and hydrophobicity. In particular we showed that mixing particles with different hydrophobicity can finely modulate the phase inversion as well the rheological and structural properties of the emulsions. The manufacturing of emulsified membranes based on previous Pickering emulsions was proposed as an example of the use of these systems as templates for the design of complex materials.

Pour mieux comprendre les résultats géophysiques en termes de géologie, il est important d’utiliser différents types de données acquises par plusieurs méthodes. Une seule méthode géophysique n’a pas nécessairement la résolution suffisante pour expliquer la géologie. Avec une seule méthode, il peut être difficile de donner un sens géologique aux anomalies observées dans les modèles. L’inversion coopérative, en revanche, est une approche permettant de combiner des données de différentes natures. L’inversion conjointe peut être réalisée de deux façons : structurale ou petrophysique. On peut subdiviser les inversions conjointes en deux groupes : l’inversion conjointe de méthodes sensibles au même paramètre physique, et l’inversion coopérative de méthodes sensibles aux paramètres de natures différentes, comme l’électrique et la sismique. Dans ce travail de thèse, on propose de combiner une inversion coopérative par zonation et une méthode Gauss-Newton de minimisation de la fonction coût. L’inversion coopérative par zonation consiste à utiliser séquentiellement une approche de classification non-hiérarchique fuzzy c-means (FCM) et un algorithme d’inversion séparée. Dans un processus itératif, l’algorithme de classification non-hiérarchique est appliqué sur les résultats obtenus par inversion séparée pour générer des modèles composés de plusieurs zones homogènes représentant chacune une certaine lithologie du milieu investigué. Les modèles ainsi construits sont ensuite utilisés comme modèles a priori dans l’expression du terme de covariance a priori sur l’espace des modèles dans une nouvelle étape d’inversion séparée. La solution obtenue par une telle approche peut être biaisé vers le modèle a priori qui est fonction du nombre de classes dans l’algorithme de classification non-hiérarchique. Pour résoudre ce problème, nous proposons l’utilisation d’un paramètre de régularisation choisi par une méthode dérivée de la méthode L-curve qui permet de pondérer l’impact du modèle a priori sur la solution dans le cas où la géologie ne se prête pas à une segmentation des modèles et de réduire l’effet du biais que pourrait introduire un mauvais a priori. Le choix du nombre de classes pour la construction du modèle a priori est ainsi également rendu moins crucial. La méthodologie développée durant cette thèse est testée et validée sur deux modèles synthétiques. Une application est réalisée sur des données réelles acquises dans le cadre d’un projet de recherche de l’agence nationale pour la gestion des déchets radioactifs (Andra) pour la caractérisation d’un site d’intérêt. Au vu des résultats de cette application, l’utilisation d’une approche coopérative pour l’inversion des données électrique et sismique permet l’obtention d’un modèle géologique (structure et propriétés) plus robuste et cohérent avec toutes les données. Les variations de paramètres en profondeur sont définies de manière plus précise avec cette approche. / Understanding geology from geophysical investigation is better when information is obtained from different kinds of data. A single method may not have sufficient resolution to provide the expected information. Joint inversion is a step forward to quantitatively combine data of different nature. Joint inversion may be considered in two different ways, petrophysical or structural. We may subdivide a joint inversion into two categories, joint inversion of data function of the same physical parameter, and cooperative inversion of data of different nature such as electrical and seismic data. In this work, we propose to combine a zonal cooperative inversion scheme with a Gauss-Newton method for minimizing the cost function. The basic idea of zonal cooperative inversion is to use cooperatively fuzzy c-means (FCM) classe analysis and separate inversion algorithm. For each iteration classe analysis of separate inversion results is used to construct models composed by several classes that contain the parameter characteristics of dominant subsurface structures. These constructed models are then used in the expression of the model space a priori covariance term in a new stage of separate inversion. The resulting models are then possibly biased to a priori models which depend on the number of classes. To overcome this problem, we formulate the inverse problem using a regularization parameter selected by an adapted L-curve method to weigh the impact of the a priori model on the solution when geology cannot be described by segmented models. The advantage of such a formulation is to avoid undesirable bias towards the starting model and leads to significantly improved spatial resolution for consistent prior information. Hence, the choice of the number of classe to create the a priori model is although less important. The developed methodology is tested and validated on two synthetic models. An experimental application is performed on real data acquired as part of a research survey of the National Agency for Radioactive Waste Management (Andra) for the characterization of a site of interest. Given the results of this application, the use of a cooperative approach for the inversion of electrical and seismic data allows the reconstruction of a more robust geological model, consistent with all the data. The variations of the parameters with depth are more precisely described using this approach.

The aim of this work is to fabricate nanostructured membranes from polysulfone-based block copolymers through self-assembly and non-solvent induced phase separation. Block copolymers containing polysulfone are novel materials for this purpose providing better mechanical and thermal stability to membranes than polystyrene-based copolymers, which have been exclusively used now. Firstly, we synthesized a triblock copolymer, poly(tert-butyl acrylate)-b-polsulfone-b-poly(tert-butyl acrylate) through polycondensation and reversible addition-fragmentation chain-transfer polymerization. The obtained membrane has a highly porous interconnected skin layer composed of elongated micelles with a flower-like arrangement, on top of the graded finger-like macrovoids. Membrane surface hydrolysis was carried out in a combination with metal complexation to obtain metal-chelated membranes. The copper-containing membrane showed improved antibacterial capability. Secondly, a poly(acrylic acid)-b-polysulfone-b-poly(acrylic acid) triblock copolymer obtained by hydrolyzing poly(tert-butyl acrylate)-b-polsulfone-b-poly(tert-butyl acrylate) formed a thin film with cylindrical poly(acrylic acid) microdomains in polysulfone matrix through thermal annealing. A phase inversion membrane was prepared from the same polymer via self-assembly and chelation-assisted non-solvent induced phase separation. The spherical micelles pre-formed in a selective solvent mixture packed into an ordered lattice in aid of metal-poly(acrylic acid) complexation. The space between micelles was filled with poly(acrylic acid)-metal complexes acting as potential water channels. The silver0 nanoparticle-decorated membrane was obtained by surface reduction, having three distinct layers with different particle sizes. Other amphiphilic copolymers containing polysulfone and water-soluble segments such as poly(ethylene glycol) and poly(N-isopropylacrylamide) were also synthesized through coupling reaction and copper0-mediated reversible-deactivation radical polymerization. Finally, phase inversion membranes were prepared from polytriazole-polysulfone random copolymers, which were obtained by “clicking” 1,2,3-triazole ring substituents bearing OH groups onto the polysulfone backbone via copperI-catalyzed azide-alkyne cycloaddition. The increased hydrophilicity of membranes imparted the higher water permeability and fouling resistance to the ultrafiltration membranes. Polytriazole-b-polysulfone-b-polytriazole triblock copolymer was synthesized by RAFT and post-polymerization click modification. Hydrogen bond-mediated self-assembly induced the formation of a nanostructured polytriazole-b-polysulfone-b-polytriazole / poly(acrylic acid)-b-polysulfone-b-poly(acrylic acid) blend membrane with a 1: 1 stoichiometric ratio of triazole and acid. String-like fused micelles with polytriazole/poly(acrylic acid) corona were present on the membrane surface, after immersion in a coagulation bath of copper2+ aqueous solution.

Abstract From the very beginning of modern ionospheric science, different radar applications have been utilised in ionospheric measurements. The most sophisticated ionospheric radars are the incoherent scatter radars, which detect the extremely weak scattering of radio waves from thermal fluctuations in the ionospheric plasma. Besides the low signal level, the stochastic nature of the scattering process causes further complications to the measurements. The scattering produces a zero-mean random signal, whose autocorrelation function contains the information of the ionospheric plasma parameters. Incoherent scatter radars have been used for about half a century, but the demanding task of developing transmission modulation and data analysis is still in progress. In this thesis, a statistical inversion based method for removing range ambiguities from the autocorrelation functions, lag profile inversion, is applied to incoherent scatter radar data. The data have been recorded with the EISCAT incoherent scatter radars, located in Northern Fennoscandia. The method is first applied to standard EISCAT experiments, the results giving strong evidence that the method is applicable for the purpose, and it provides results of at least equal quality with the present standard methods. In subsequent studies, new radar modulation methods are developed, which may provide significant improvements to the present incoherent scatter radar experiments. All the methods have been tested with a real radar, and lag profile inversion has been successfully applied to the recorded data. The methods are also put to use in order to measure the predicted effects of artificial heating of the free electrons in the D-region of the ionosphere.