51 research outputs found
Viscoacoustic Frequency-Domain Full-Waveform Inversion – Application to Numerical VSP Data
No full textInternational audienceC029 Viscoacoustic Frequency-Domain Full-Waveform Inversion – Application to Numerical VSP Data A. Ribodetti* (Geosciences Azur) R.E. Plessix (Shell) S. Operto (Geosciences Azur - CNRS) & J.M. Virieux (Geosciences Azur) SUMMARY This work presents numerical tests to show that viscoacoustic frequency-domain full waveform tomographic inversion can be a useful tool for velocity and attenuation Q factor estimates from Vertical Seismic Profiles data. EAGE 69 th Conference & Exhibition — London UK 11 - 14 June 2007 EAGE 69 th Conference & Exhibition — London UK 11 - 14 June 2007 EAGE 69 th Conference & Exhibition — London UK 11 - ..
Viscoacoustic Frequency-Domain Full-Waveform Inversion – Application to Numerical VSP Data
No full textInternational audienceC029 Viscoacoustic Frequency-Domain Full-Waveform Inversion – Application to Numerical VSP Data A. Ribodetti* (Geosciences Azur) R.E. Plessix (Shell) S. Operto (Geosciences Azur - CNRS) & J.M. Virieux (Geosciences Azur) SUMMARY This work presents numerical tests to show that viscoacoustic frequency-domain full waveform tomographic inversion can be a useful tool for velocity and attenuation Q factor estimates from Vertical Seismic Profiles data. EAGE 69 th Conference & Exhibition — London UK 11 - 14 June 2007 EAGE 69 th Conference & Exhibition — London UK 11 - 14 June 2007 EAGE 69 th Conference & Exhibition — London UK 11 - ..
L'aire d'attraction des petites villes, étude comparée dans la France du Nord et du Nord-Ouest (Anjou, Artois, Maine, Basse-Normandie et Perche) au XIXe siècle
No full textRené Plessix, The Area of Attraction of the Smaller Cities, a Comparative Study of North and North-West France (Anjou, Artois, Maine, Lower Normandy and Perche) in the XIXth Century.
The renewal of the urban populations through migration currents intensifies in the XIXth century. This invites us to try and assess this phenomenon and to raise the question : can that help to measure the areas of attraction of the smaller cities ? The investigation, limited in time and in space and carried out on eight smaller cities of the Pas-de-Calais, the Maine-et-Loire, the Orne and the Sarthe, that have various administrative status, different socio-professional structures and with fairly similar demographic levels, brings us some information. Three specific professional groups — government employees, the professions, including the members of the congregations, and the servants, essentially female — account for the intensity of the migration movements. These latter shape for every city a demographic basin or area of strong attraction, a larger but also more diffuse area of recruiting stretching over the rest of the department and to the neighbouring departments, and a nebula covering a varying number of departments. In there, there appears a migration current from Paris to most of these smaller cities that must not be under-rated.Le renouvellement des populations urbaines par les courants migratoires s'intensifie au XIXe siècle. Ceci invite à prendre la mesure du phénomène et à s'interroger : peut-il permettre de mesurer l'aire d'attraction des petites villes ? L'enquête entreprise, limitée dans le temps et dans l'espace à huit petites villes du Pas-de-Calais, du Maine-et-Loire, de l'Orne et de la Sarthe aux statuts administratifs variés, aux structures socioprofessionnelles différentes et aux niveaux démographiques assez voisins apporte quelques enseignements. Trois groupes professionnels spécifiques : les fonctionnaires, les professions libérales en y incluant les congréganistes et la domesticité notamment féminine rendent compte de l'intensité des courants migratoires. Ceux-ci dessinent pour chaque villle un bassin démographique ou zone de forte attraction, une aire de recrutement plus large mais aussi plus diffuse s 'étendant au reste du département et aux départements voisins, une nébuleuse couvrant un nombre variable de départements. Là apparaît un flux migratoire non négligeable de Paris vers la plupart de ces petites cités.René Plessix, De aantrekkingkracht van kleinere steden. Vergelijkend onderzoek in noordfrankrijk en noorwestfrankrijk (Anjou, Artois, Maine, Besse-Normandie en Perche), in de XIXde eeuw.
In de XIXde eeuw versterken migratiestromen de vernieuwing van de stadsbevolking. Kan men daaraan de invloedssfeer van kleinere steden meten ? Ons onderzoek over 8 kleinere steden in Pas-de-Calais, Maine-et-Loire, Orne en Sarthe, met verschillend administratief statuut en socioprofessioneel profïel maar op demografisch gebied ver- want, brengt enkele elementen aan het licht. Drie beroepsgroepen, ambtenaren, libérale beroepen (waarbij de congreganisten) en de huisbedienden (vooral vrouwelijke) weers- piegelen de intensiteit van de migratie. Daarmee kan men voor elke stad een zone van sterke aantrekkingskracht tekenen, een veel ruimer maar minder sterk recruteringsgebied over het hele département en een wazig gebied over meerdere departementen. Daaruit blijkt een niet te verwaarlozen migratie vanuit Parijs naar de kleinere steden.Plessix René. L'aire d'attraction des petites villes, étude comparée dans la France du Nord et du Nord-Ouest (Anjou, Artois, Maine, Basse-Normandie et Perche) au XIXe siècle. In: Revue du Nord, tome 82, n°335-336, Avril-septembre 2000. pp. 367-391
Resistivity imaging with controlled-source electromagnetic data: Depth and data weighting
No full textWe discuss some computational aspects of resistivity imaging by inversion of offshore controlled-source electromagnetic data. We adopt the classic approach to imaging by formulating it as an inverse problem. A weighted least-squares functional measures the misfit between synthetic and observed data. Its minimization by a quasi-Newton algorithm requires the gradient of the functional with respect to the model parameters. We compute the gradient with the adjoint-state technique. Preconditioners can improve the convergence of the inversion. Diagonal preconditioner based on a Born approximation are commonly used. In the context of CSEM inversion, the Born approximation is not really accurate, this limits the possibility of estimating a correct approximation of the Hessian in a smooth medium or, in fact, in any reference background that does not roughly account for the resistors. We hence rely on the limited memory BFGS approximation of the inverse of the Hessian and we improve the inversion convergence with the help of a heuristic data and depth weighting. Based on a numerical example, we show that a simple exponential depth weighting combined with an offset or frequency data weighting significantly improves the convergence rate of a deep-water controlled-source electromagnetic data inversion.Geoscience & EngineeringCivil Engineering and Geoscience
An Helmholtz iterative solver for the three-dimensional seismic imaging problem?
No full textDuring the last three decades high-frequency approximations or paraxial (one-way) approximations of the wave equation have been successfully used to process seismic data in two-dimensional or three-dimensional spaces. With the increase of computer power and the need to take into account complex geological structures, solutions of the exact wave equation either in time domain or in frequency domain are required. The time-domain wave equation can be solved with a marching approach in time and an explicit scheme. Currently three-dimensional imaging algorithms, so-called reverse time migrations, are developed based on time-domain solutions. The frequency-domain wave equation, namely the Helmholtz equation in the acoustic case with constant density, leads to a large sparse linear solver. In a two-dimensional space a direct solver, based on a LU decomposition, can be used. This leads to attractive and efficient imaging methods faster than the time-domain imaging methods. In a three-dimensional space, due to the size of the matrix, an iterative solver is required. In practice three-dimensional frequency-domain solutions are not used because most of the iterative solvers are not robust at seismic frequency or are too expensive. The difficulty arises because the matrix of the linear system is not definite and because the model size generally corresponds to several hundreds of wavelength in the three space directions. A new preconditioner based on a heavily damped wave equation and a multi-grid solver has been proposed by Erlangga et al.. The iterative solver is a preconditioned bicgstab. The preconditioner corresponds to the approximated inverse of the heavily damped wave-equation after one multigrid cycle. Numerical results have shown that this new iterative solver is robust. However does a frequency-domain imaging algorithm based on this solver compete with a time-domain imaging algorithm? To handle realistic three-dimensional geophysical problem the multigrid solver is implemented with a standard full-weighting coarsening, a tri-linear interpolation, a matrix-free approach, and an 8th order scheme in space. Three-dimensional numerical results indicate that the number of bicgstab iterations linearly increase with frequency. Based on this result, the number of the floating point operations needed for the time-domain and the frequency-domain imaging algorithms is roughly estimated. It is then shown that the migration algorithm is about one order of magnitude faster in the time domain and that the velocity modeling building algorithm based on a least-squares formulation and a scale separation is about three time faster in the frequency domain
Impossible Appetites : Nine Stories
No full textThe collection of nine stories which won the 1980 Short Fiction Award is woven in a pattern so subtle that reading it is like writing your own nine-part novel. The author allows brief glimpses into the tormented journals of Joseph Quaile, a man of acute compassions and consuming hungers; then juxtaposes them with the fiction Quaile writes to scourge his demons and come to terms with himself and the people he loves. This is a dispassionate intelligence in passionate pursuit of freedom and reconciliation.—Front flap.https://ir.uiowa.edu/uipress_isfa/1008/thumbnail.jp
Le contentieux d'un rescrit fiscal
No full textInternational audienceConseil d'État, 2 décembre 2016, Ministre des finances et des comptes publics c/ Société Export Press, n° 387613, Lebon ; AJDA 2016. 2354 ; AJ fam. 2017. 94, obs. S. Paillar
Le contentieux d'un rescrit fiscal
No full textInternational audienceConseil d'État, 2 décembre 2016, Ministre des finances et des comptes publics c/ Société Export Press, n° 387613, Lebon ; AJDA 2016. 2354 ; AJ fam. 2017. 94, obs. S. Paillar
Le transfert des cimetières des petites villes de l’Anjou et du Maine (XVIIIe-XIXe siècle)
No full textMaine-et-Loire, Mayenne et Sarthe, assimilés aux provinces du Maine et de l'Anjou, comptent trente-sept petites villes. Sur les vingt-huit en observation, quatre échappent à l'obligation – imposée par les lois de 1776 et du 23 prairial an XII – de déplacer leurs cimetières. Dans les vingt-quatre autres les transferts s''échelonnent sur près d'un siècle, le plus grand nombre intervenant entre 1820 et 1869. C'est que municipalités et collectivités mettent un certain temps à prendre conscience du problème puis à trouver un emplacement convenable. Le transfert effectué, les espaces libérés, vendus, disparaissent dans le tissu urbain ou, le plus souvent, deviennent des places publiques dont certaines accueillent le marché hebdomadaire. Deux municipalités en profitent pour y élever de nouvelles constructions : mairie à Chalonnes-sur-Loire, presbytère à Mamers, ce dernier servant à différents usages après la loi de Séparation.Plessix René. Le transfert des cimetières des petites villes de l’Anjou et du Maine (XVIIIe-XIXe siècle). In: Ordonner et régénérer la ville : entre modernités et révolutions. Actes du 137e Congrès national des sociétés historiques et scientifiques, « Composition(s) urbaine(s) », Tours, 2012. Paris : Editions du CTHS, 2014. pp. 69-80. (Actes des congrès nationaux des sociétés historiques et scientifiques, 137-5
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