Éditeur(s) : HAL CCSD
Résumé : In an earlier paper, we developed an efficient incremental unknowns (IU) preconditioner for solving the two-dimensional (2D) Helmholtz problem in both high and low frequency (wavenumber) regimes. The multilevel preconditioning scheme involves separation of each grid into a coarser grid of the following level and a complementary grid on which the IUs are defined by interpolation. This approach is efficient as long as the mesh size of the coarsest grid is sufficiently small compared to the wavelength. In order to overcome this restriction, the authors introduced recently a modified IU method combining the conventional interpolation with the Helmholtz equation based interpolation (EBI). The EBI coefficients are derived numerically using a sufficiently large set of analytic solutions of the Helmholtz equation on a special hierarchy of stencils. The modified IUs using Helmholtz EBI are shown to provide improved preconditioning on the coarse scales where the conventional interpolation can not be employed. This study deals with the extension of this idea for solving the three-dimensional (3D) Helmholtz equation.
https://hal.univ-antilles.fr/hal-00763930

Droits : info:eu-repo/semantics/OpenAccess
hal-00763930
https://hal.univ-antilles.fr/hal-00763930
https://hal.univ-antilles.fr/hal-00763930/document
https://hal.univ-antilles.fr/hal-00763930/file/eci3D_3d.pdf

Éditeur(s) : HAL CCSD
Résumé : poster presentation, 22nd European Meeting on Hypertension and Cardiovascular protection, London,26-29 April 2012
OBJECTIVE: Several studies demonstrate that the perception of overweight is associated with attempts at weight control in overweight subjects. Our objective is to describe the factors associated with the perception of overweight in an adult Caribbean population, and in particular, to assess the relationship between the perception of overweight and previous medical diagnosis of overweight. METHOD AND DESIGN: Consant was a cross-sectional study carried out in 2007 on a representative sample of the adult Guadeloupean population. Included were 1,005 subjects aged 25-74 years, drawn from stratified random sampling, and interviewed at home. The perception of overweight was evaluated by the question: "Do you consider yourself to be overweight?" with a binary response. RESULTS: Among overweight subjects (Body Mass Index ≥ 25 kg/m2, n = 576), 38.6% provided an incorrect assessment of their weight status. This proportion falls to 17.4% in those who stated to have previously received a medical diagnosis of overweight. However, only 48.8% of overweight subjects stated to have received such a diagnosis. A logistic regression shows that the underestimation of weight status is associated with the absence of previous diagnosis for overweight (OR: 5.35 - p < 10-3), as well as an age greater than or equal to 55 years (OR: 2.91 - p < 10-3), a BMI of less than 30 kg/m² (OR: 2.26 - p: 0.001), the male sex (OR: 1.86 - p: 0.004), and a low income level (OR: 1.62 - p: 0.030), but not a lack of awareness regarding the role of weight control in the prevention of cardiovascular diseases. Similar results are observed if waist circumference is taken as a factor instead of BMI. CONCLUSION: In this population, the lack of medical diagnosis of overweight was the leading factor associated with misperception of overweight. Screening for overweight therefore appears to be one of the preconditions to weight management, and remains a fundamental but often unused element in the fight against obesity.
https://hal.univ-antilles.fr/hal-00739785

Droits : info:eu-repo/semantics/OpenAccess
hal-00739785
https://hal.univ-antilles.fr/hal-00739785
https://hal.univ-antilles.fr/hal-00739785/document
https://hal.univ-antilles.fr/hal-00739785/file/The_lacksur screening_is_the_leading_factor_associated_with_the_misperceptionsur overweight_cor.pdf

Éditeur(s) : HAL CCSD Institute for Scientific Computing and Information
Résumé : International audience
In this paper, we solve a problem describing the mechanical deformations of a porous medium in the presence of a monophasic linear flow or a two phase nonlinear flow with the purpose of modelizing subsidence of hydrocarbon reservoirs. An essential characteristics of this problem is that the mechanical deformation and the flow have different time scales. In petroleum industry, one uses different very efficient simulators for the flow problem and the mechanical deformations, which enables to handle complex models. Therefore it is necessary to be able to combine as efficiently as possible the exploitation of these simulators. We propose two alternative splitting approaches. The first one is the staggered algorithm used by engineers, which amounts to a Gauss-Seidel method in the one phase linear case. The second approach is based upon the preconditioned conjugate gradient method. We use a numerical multi-scale method in both of these algorithms. We compare these two approaches and we show that the preconditioned conjugate gradient algorithm is faster and more robust than the staggered algorithm. Applying the preconditioned conjugate gradient algorithm therefore seems to compensate for the fact that the inf-sup condition for the mixed discretization method is not satisfied when combining the simulators for the mechanical deformations and for the flow computations.
ISSN: 1705-5105

Droits : http://creativecommons.org/licenses/by/
hal-01449039
https://hal.archives-ouvertes.fr/hal-01449039
https://hal.archives-ouvertes.fr/hal-01449039/document
https://hal.archives-ouvertes.fr/hal-01449039/file/DHLE.pdf

Éditeur(s) : HAL CCSD Institute for Scientific Computing and Information
Résumé : International audience
The production of oil in soft highly compacted reservoirs produces a significant reduction in the pore space which in turn causes the surface to subside. The authors couple two simulators to model the mechanical deformations in the presence of a Darcy flow, both one- and two-phase. The simulators solve for flow in a porous medium using a finite volume method, and solve for the mechanical deformation of the porous media using a finite element method. The flow equations and the deformation equations are coupled using Biot's law. The authors use two different methods for the coupling: the first uses a staggered algorithm; the second is based on a preconditioned conjugate method. The authors use a multiscale method in both approaches. The authors show that the inf-sup condition is not satisfied, because of the mixed discretization which is done by using two separate simulators. The authors give convergence comparisons for the two methods for several examples. Two of the examples are for the linear problem (one-phase) where they know the exact solution and one is for the nonlinear problem (two-phase). In all cases, the preconditioned conjugate algorithm is faster and more robust, in particular when the inf-sup condition is not satisfied. In the nonlinear problem the authors state that the results agree with physical predictions but do not give actual empirical data. Finally, they show the effects of grid orientation on the nonlinear problem.
ISSN: 1705-5105

hal-00730673
https://hal.archives-ouvertes.fr/hal-00730673

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
ISSN: 0168-9274

hal-00530819
https://hal.archives-ouvertes.fr/hal-00530819
DOI : 10.1016/j.apnum.2009.12.006

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
We describe the simulation of an exterior problem using a magnetic field deriving from magnetostatics, with a numerical method mixing the approaches of C. I. Goldstein and L.-A. Ying. This method is based on the use of a graded mesh obtained by gluing homothetic layers in the exterior domain. On this mesh, we use an edge elements discretization and a recently proposed mixed formulation. In this paper, we provide both a theoretical and numerical study of the method. We establish an error estimate, describe the implementation, propose some preconditioning techniques and show the numerical results. We also compare these results with those obtained from an equivalent boundary elements approach. In this way, we retain that our method leads to a practical numerical implementation, a saving of storage, and turns out to be an alternative to the classical boundary elements method.
ISSN: 0749-159X

hal-00730196
https://hal.archives-ouvertes.fr/hal-00730196
DOI : 10.1002/num.10064

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In a previous work, one of the authors has studied a numerical treatment (by fully implicit discretizations) of a two-dimensional Navier-Stokes-like problem and has proved existence and convergence results for the resulting discretized systems with homogeneous Dirichlet boundary conditions. In this work, we propose some new preconditioned multilevel versions of inexact-Newton algorithms to solve these equations. We also develop another multilevel preconditioner for a nonlinear GMRES algorithm. All of the preconditioners are based on incremental unknowns formulations.
ISSN: 0096-3003

hal-00770269
https://hal.univ-antilles.fr/hal-00770269
DOI : 10.1016/S0096-3003(96)00304-9

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : La compétitivité touristique est un concept dont l’importance est aujourd’hui largement reconnue. La plupart des travaux consacrés à ce thème l’ont abordé jusqu’ici sous différents aspects, mais sans qu’aucun modèle théorique n’ait réussi à notre connaissance à établir les liens empiriques qui existent entre tourisme et compétitivité. Cette étude tente de combler cette lacune, en proposant d’explorer, à l’aide de la technique de cointégration et du modèle à correction d’erreur, dans un contexte bivarié, la relation empirique qui existe entre tourisme et compétitivité, comme condition préalable à l’application du test de causalité de Granger. Cette procédure est adoptée et appliquée au cas des Antilles françaises (Guadeloupe et Martinique) sur la période 1990-2010. Les résultats révèlent l’existence d’une relation de cointégration entre compétitivité et activité touristique. Cependant, les tests de causalité de Granger, basés sur un modèle à correction d’erreurs indiquent qu’il n’existe pas de causalité ou d’impact unidirectionnel ou bidirectionnel entre variation de la recette touristique/PIB (proxy du développement touristique) et variation du PIB réel par habitant (proxy de la compétitivité). Par conséquent, l’hypothèse de la croissance tirée par le tourisme ne peut être inférée pour la Guadeloupe et la Martinique. Il s’agit d’enseignements majeurs dont devraient tenir compte les autorités responsables de cette activité.
The tourism competitiveness is an important concept today. The most studies investigate this theme from different ways. However, there are few studies about empirical link between tourism and competitiveness. This paper, thus attempts to examine the empirical relationship between these two variables. It uses the cointegration and error correction model (ECM) in a bivariate context as a precondition to apply Granger causality tests. This procedure was carried out in the case of French West Indies’s tourism industry during 1990-2010. The results show that there is a long-term relationship between tourism and competitiveness. In addition, Granger causality tests reveal no one-directional or bi-directional impact in the case of tourism receipts and GDP. Therefore, tourism-led growth hypothesis (TLG) cannot be inferred for French West Indies’s economy as a major concern of destination managers.
Guadeloupe
Martinique

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.6316
http://journals.openedition.org/etudescaribeennes/6316

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This article is devoted to the presentation of a multilevel method using finite differences that is well adapted for solving Stokes and Navier-Stokes problems in primitive variables. We use Uzawa type algorithms to solve the saddle point problems arising from spatial discretization by staggered grids and a semi-explicit temporal scheme. By means of a new change of basis operator, the two-dimensional velocity and pressure fields of an M.A.C mesh are gathered in a hierarchical order, into several grids preserving the M.A.C property on each of them. These new hierarchical unknowns, called Staggered Incremental Unknowns (SIU), allow us to develop techniques which reduce the cost of the resolution of either Stokes or generalized Stokes problems. An experimental estimation of the condition number of the inner matrix is given, and justifies the preconditioning effect of the staggered incremental unknowns.
ISSN: 0168-9274

hal-00770268
https://hal.univ-antilles.fr/hal-00770268
DOI : 10.1016/S0168-9274(99)00044-6

Éditeur(s) : HAL CCSD
Résumé : Taiwan is a young mountain belt, known as one of the most active area in the world. Since the beginning of the 20th century more than twenty _ Mw 7 earthquakes have struck the island. However, the occurrence of larger events (_Mw 8) is still a matter of debate. In this framework it is of key importance to obtain longer record in order to evaluate the occurrence of large past earthquakes. The sub-aqueous paleoseismology, based on the record of the sedimentary gravity deposits, appears as a serious alternative to approach this thematic and is a rapidly advancing field that has the potential to illuminate the long-term history of seismicity.The first part of this work was to investigate the present sedimentary systems off east Taiwan, essential to understand the morphosedimentary features, sedimentary facies and processes governing the evolution of the submarine slope, and the controlling factors of the recent sedimentation. Our results showed that the offshore slope east Taiwan is affected by a variety of sedimentary systems and processes, and that turbidity currents appear as the main erosional processes covering nearly 60% of the sedimentary record. Turbidity currents are generated by distinct controlling factors such as tectonic and climatic activity that enabled us to define twoend-members relative to turbidity currents initiation: Turbidity currents preconditioned by tectonic activity and triggered by earthquakes shaking and likely deposited into intra-slope basin and turbidity currents driven by climatic activity such as extreme floods or typhoons, generated in basin directly connected with onland rivers.The second part consisted to apply a paleoseismic approach, based on turbidites record, at two time-scales. First, we tested and validated the method by correlating turbidites deposits with instrumental earthquakes. Then, once calibrated we extended the time-series back in time. We dated the three most recent turbidites layers circa 2001 ± 3 AD, 1950 ± 5 AD and 1928 ± 10 AD. Using empirical relationship that link peakground acceleration, distance and magnitude to calibrate the seismic sources, we correlate these three turbidites with instrumental earthquakes: the Chengkong Earthquake 12/10/2003 (Mw 6.8), the 11/24/1951 Taitung Earthquake (Mw 7.1) and the 9/4/1935 Lutao Earthquake (Mw 7.0) respectively. Applying criteria to discriminating the different triggering mechanisms for turbidity current generation, we propose that earthquakes are the main triggering mechanisms. Dating and age modeling provided a part of the chronology of extreme events since the last 3000 years and allowed us to estimate return time for earthquakes Mw _ 6.8.This work represents a good starting-point for future investigations in order to better assess Holocene time series of extreme events.
La chaine de Taïwan représente l’une des zones les plus actives au monde. Depuis le début du XXe siècle, plus d’une vingtaine de séismes _Mw 7 ont affecté l’île. Cependant la probabilité d’occurrence de séismes plus importants (_Mw 8) est toujours matière à débat. Dans un tel contexte, il apparait donc important d’obtenir des enregistrements plus anciens pour évaluer l’occurrence de tels évènements. La paléosismologie marine, basée sur l’enregistrement des dépôts issus de la sédimentation gravitaire, apparait comme une alternative sérieuse afin d’illuminer l’histoire de la sismicité sur des périodes anciennes. Ce travail de thèse apporte de nouvelles contraintes sur l’histoire sismique au large, à l’est de Taïwan, au cours des derniers 3000 ans.La première partie de ce travail consiste à caractériser les systèmes sédimentaires récents. Cette étape fut essentielle pour la compréhension des processus, faciès sédimentaires et les facteurs de contrôle de la sédimentation qui régissent l’évolution de la pente sous-marine. Ces résultats ont montré que l’Est de Taïwan est caractérisé par une grande variabilité de processus et que les courants de turbidité dominent l’enregistrement sédimentaire.Les courants de turbidité sont générés par deux facteurs distincts : l’activité tectonique/sismique et l’activité climatique. La deuxième partie de ce travail est consacrée à l’approche paléosismique en utilisant les dépôts de turbidités comme marqueurs des paléoséismes. Pour ce faire, nous avons dans un premier temps testé et validé l’approche à l’échelle du siècle dernier. Ensuite une fois calibré, nous avons pu étendre les séries temporelles à l’échelle de l’Holocène. Nous avons daté les trois plus récents évènements turbiditiques autour de 2001 ± 3 AD, 1950 ± 5 AD et 1928 ± 10 AD. En utilisant des relations empiriques intégrant magnitude, distance et valeur du "peak ground acceleration", nous avons pu calibrer la source sismique et ainsi corréler ces trois turbidites à trois séismes instrumentaux : le séisme de Chengkong (12/10/2003) (Mw 6.8), le séisme de Taitung (11/24/1951) (Mw 7.1) et le séisme de Lutao (9/4/1935) (Mw 7.0). Au-delà du siècle dernier, les datations et modèles d’âges nous permettent d’établir une partie de la chronologie des évènements extrêmes sur une période de 3000 ans et d’estimer un temps de retour pour des évènements de l’ordre _Mw 7. Les résultats ont toutefois montré que ces temps de retour sont nettement supérieurs à ceux connus sur le siècle dernier, ce qui suggère que tous les séismes ne sont pas enregistrés par les dépôts sédimentaires marins. Ce travail de thèse a donc permis de montrer que les dépôts issus de la sédimentation évènementielle peuvent être considérés comme marqueurs de la sismicité et que cette approche peut constituer un outil complémentaire pour les études portant sur le risque sismique.
https://tel.archives-ouvertes.fr/tel-01661529

NNT : 2014MON20133
tel-01661529
https://tel.archives-ouvertes.fr/tel-01661529
https://tel.archives-ouvertes.fr/tel-01661529/document
https://tel.archives-ouvertes.fr/tel-01661529/file/55796_LEHU_2014_archivage_cor.pdf