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Inversion of multi-temporal geoelectrical field data sets: insights on noise characterization and regularization Nguyen, Frédéric ; ; Robert, Tanguy et al Poster (2012, July 11) Inversion of geoelectrical time-lapse data sets is increasingly growing as monitoring systems are being used in more applications such as seawater intrusion, landslides, remediation of contaminated sites ... [more ▼] Inversion of geoelectrical time-lapse data sets is increasingly growing as monitoring systems are being used in more applications such as seawater intrusion, landslides, remediation of contaminated sites, landfill operation, shallow geothermal systems, or management of water resources. To date, several inversion strategies exist for taking into account the temporal dimension of the data. The most used nowadays are the independent inversion of multi-temporal data sets, the difference inversion, the temporally-constrained inversion, and the more recent process-based inversion. However, difference inversion schemes generally assume that part of the noise contained in the data cancels out when working with temporal data differences. Temporally-constrained inversion on the other hand assumes that the changes are localized and minor. Process-based inversion requires a more advanced knowledge of the system prior the inversion. In this study we demonstrate that the resolution of the time-lapse inversion scheme is mostly dependent on the quantification of the temporal behavior of the data error, on the resolution of the model-dependent pattern of the survey, and not on the regularization strategy. Our study is based on the imaging results of different data sets with different time and spatial scales, and with different degrees of geological complexity and resistivity contrast, The considered sites are a shallow sandy aquifer and a fractured hard rock aquifer where tracer experiments were performed and monitored using surface arrays. The two studied transport processes are advection, with velocities on the order of 10 m/hour and slower advection/diffusion processes. The strongest improvements were brought by using the data difference and a quantitative estimation of the data error. We found in particular a dependence of the time-lapse data error to the measured resistance (i.e., signal-to-noise-ratio), permitting to formulate an error model to describe the data error present in time-lapse data sets. We used minimum gradient support regularization to invert for model changes with enhanced contrast and found this technique more suited to time-lapse studies than for static images. Noise characterization and error models appear therefore as essential and the most impacting for a successful inversion both for static and time-lapse data whereas different spatio-temporal regularization techniques allowed to decrease artefacts but needs to be coherent with the process. [less ▲] Detailed reference viewed: 70 (10 ULg)Inversion of probabilistic models of structures using measured transfer functions Arnst, Maarten Doctoral thesis (2007) The aim of this thesis is to develop a methodology for the experimental identification of probabilistic models for the dynamical behaviour of structures. The inversion of probabilistic structural models ... [more ▼] The aim of this thesis is to develop a methodology for the experimental identification of probabilistic models for the dynamical behaviour of structures. The inversion of probabilistic structural models with minimal parameterization, introduced by Soize, from measured transfer functions is in particular considered. It is first shown that the classical methods of estimation from the theory of mathematical statistics, such as the method of maximum likelihood, are not well-adapted to formulate and solve this inverse problem. In particular, numerical difficulties and conceptual problems due to model misspecification are shown to prohibit the application of the classical methods. The inversion of probabilistic structural models is then formulated alternatively as the minimization, with respect to the parameters to be identified, of an objective function measuring a distance between the experimental data and the probabilistic model. Two principles of construction for the definition of this distance are proposed, based on either the loglikelihood function, or the relative entropy. The limitation of the distance to low-order marginal laws is demonstrated to allow to circumvent the aforementioned difficulties. The methodology is applied to examples featuring simulated data and to a civil and environmental engineering case history featuring real experimental data. [less ▲] Detailed reference viewed: 77 (14 ULg)Inversion of probabilistic structural models using measured transfer functions Arnst, Maarten ; ; in Computer Methods in Applied Mechanics & Engineering (2008), 197(6-8), 589-608 This paper addresses the inversion of probabilistic models for the dynamical behaviour of structures using experimental data sets of measured frequency-domain transfer functions. The inversion is ... [more ▼] This paper addresses the inversion of probabilistic models for the dynamical behaviour of structures using experimental data sets of measured frequency-domain transfer functions. The inversion is formulated as the minimization, with respect to the unknown parameters to be identified, of an objective function that measures a distance between the data and the model. Two such distances are proposed, based on either the loglikelihood function, or the relative entropy. As a comprehensive example, a probabilistic model for the dynamical behaviour of a slender beam is inverted using simulated data. The methodology is then applied to a civil and environmental engineering case history involving the identification of a probabilistic model for ground-borne vibrations from real experimental data. [less ▲] Detailed reference viewed: 24 (3 ULg)Inversion of the Biot-Savart Law: an approach based on discrete sine and cosine transforms ; Denis, Samuel ; Vanderheyden, Benoît et al in Johansen, T. H.; Shantsev, D. V. (Eds.) Magneto-Optical Imaging, Proceedings of the NATO Advanced Research Workshop, held in Øystese, Norway, 28-30 August 2003 (2004) Detailed reference viewed: 89 (14 ULg)Inversion of Venus NO nightglow limb profiles Stiepen, Arnaud ; Soret, Lauriane ; Gérard, Jean-Claude et al Conference (2012, July) Detailed reference viewed: 23 (9 ULg)Inversions Estrangeres Directes i Innovació a Catalunya Artige, Lionel ; in Busom, Isabel (Ed.) La situació de la innovació a Catalunya (2006) Detailed reference viewed: 18 (1 ULg)Les invertébrés des carrières souterraines de craie de la Montagne Saint-Pierre (Province de Liège, Belgique). Note préliminaire ; Willems, Luc in Notes Fauniques de Gembloux (2005), 57 During the 1930’s, Leruth collected 145 species in the underground chalk quarries at the Montagne Saint-Pierre. None was troglobitic. To evaluate the biological interest of the sites and the faunal drift ... [more ▼] During the 1930’s, Leruth collected 145 species in the underground chalk quarries at the Montagne Saint-Pierre. None was troglobitic. To evaluate the biological interest of the sites and the faunal drift 70 years after, we have undertaken in 2004 a new faunistic survey. [less ▲] Detailed reference viewed: 15 (0 ULg)Inverted patterns of genetic diversity in continental and island populations of the heather Erica scoparia s.l. Desamore, Aurélie ; Laenen, Benjamin ; et al in Journal of Biogeography (2012), 39(3), 574--584 Aim Using the heather Erica scoparia s.l. as a model, this paper aims to test theoretical predictions that island populations are genetically less diverse than continental ones and to determine the ... [more ▼] Aim Using the heather Erica scoparia s.l. as a model, this paper aims to test theoretical predictions that island populations are genetically less diverse than continental ones and to determine the extent to which island and continental populations are connected by pollen- and seed-mediated gene flow.Location Macaronesia, Mediterranean, Atlantic fringe of Europe.Methods Patterns of genetic diversity are described based on variation at two chloroplast DNA (cpDNA) loci and one nuclear DNA (nDNA) locus for 109 accessions across the entire distribution range of the species. Global patterns of genetic differentiation were investigated using principal coordinates analysis. Genetic differentiation between island and continental areas, estimations of pollen- and seed-mediated gene flow, and the presence of phylogeographical signal were assessed by means of Fst/NST (continental scale) and Fij/Nij (local scale). Extant and past distribution ranges of the species were inferred from niche modelling using layers describing present and Last Glacial Maximum (LGM) macroclimatic conditions.Results The Azores exhibited a significantly higher genetic diversity than the continent. The lowest levels of genetic differentiation were observed between the Azores and the western Mediterranean, and the diversity observed in the Azores resulted from at least two colonization waves. Within the Azores, kinship coefficients showed a significant and much steeper decrease with geographical distance in the cpDNA than in the nDNA. The distribution predicted by LGM models was markedly different from the current potential distribution, particularly in western Europe, where no suitable areas were predicted by LGM models, and along the Atlantic coast of the African continent, where LGM models predicted highly suitable climatic conditions.Main conclusions The higher diversity observed in Azorean than in continental populations is inconsistent with MacArthur and Wilson’s equilibrium model and derived theoretical population genetic expectations. This inverted pattern may be the result of extinction on the continent coupled with multiple island colonization events and subsequent allopatric diversification and lineage hybridization in the Azores. The results highlight the role of allopatric diversification in explaining diversification on islands and suggest that this process has played a much more significant role in shaping Azorean biodiversity than previously thought. [less ▲] Detailed reference viewed: 41 (7 ULg)Inverting Hydraulic Heads In An Alluvial Aquifer Constrained With Electrical Resistivity Tomography Data Through Multiple-Point Statistics And Probability Perturbation Method: A Case Study Hermans, Thomas ; ; et al Conference (2014, July) Solving spatial inverse problems in the Earth Sciences remains a considerable challenge given the large number of parameters to invert for, the non-linearity of forward models and as a result the ill ... [more ▼] Solving spatial inverse problems in the Earth Sciences remains a considerable challenge given the large number of parameters to invert for, the non-linearity of forward models and as a result the ill-posedness of the problem. Geostatistics is therefore needed to specify prior models, more particularly, information to control the spatial features of the inverse solutions. We used multiple-point statistics (MPS) to build models of pre-defined hydrofacies: clay, sand and gravel facies constrained to geological data (hard data) and geophysical data (soft data). The electrical resistivity tomography method was chosen to bring relevant spatially distributed information on the presence of the facies, given its sensitivity to variations in lithology and porosity. The comparison of the geophysical signature of the deposits with direct observations in boreholes enables to derive the conditional probability of observing a facies given its electrical resistivity. This is used to produce probability maps for each facies and constrain stochastic simulations of the alluvial aquifer. Then, the probability perturbation method (PPM) is used to integrate hydraulic heads data, using MPS to generate models. This process enables us to obtain calibrated models of the aquifer. The PPM algorithm will automatically seek solutions fitting both hydrogeological data and training-image based geostatistical constraints. Only geometrical features of the model are affected by the perturbation, i.e. we do not attempt to directly find the optimal value of hydrogeological parameters (chosen a priori), but the optimal spatial distribution of facies whose prior distribution is quantified in a training image. The methodology is first tested with a synthetic benchmark. The tests performed show that the choice of the training image is a major source of uncertainty. Therefore, one first needs to select those training images consistent with the geophysical data (and hence reject the inconsistent ones). Then, we proceed with them to hydrogeological inversions. Geophysical data (soft constraints) acts as an accelerator of convergence by reducing prior uncertainty. The hydraulic conductivity of each facies is a sensitive parameter, but it can be easily optimized prior to the PPM process. The stochastic method is then successfully applied within the context of an alluvial aquifer submitted to a pumping experiment. We show how the integration of various sources of data (borehole logs, geophysics, hydraulic heads) aids in calibrating hydrogeological models, locating high hydraulic conductivity zones and reducing uncertainty. The developed methodology proposes a common framework (multiple-point statistics) to integrate various information sources with variable resolutions relevant for hydrogeology: geological, geophysical and hydrogeological data. The method can be extended to integrate tracer tests to enable the calibration of transport parameters as well. The originality of the method is to use geophysical data both to refine the choice of the training image and to constrain the inversion of hydrogeological models. [less ▲] Detailed reference viewed: 76 (16 ULg)A Investigacao Sociologica os "pragamatic" americanos Stassart, Pierre M Scientific conference (2011) Detailed reference viewed: 13 (0 ULg)La investigación experimental en educación De Landsheere, Gilbert Book published by UNESCO (1982) Detailed reference viewed: 106 (4 ULg)La investigación pedagógica de Landsheere, Gilbert ; Book published by Angel Estrada - 1ère éd. (1971) Detailed reference viewed: 19 (1 ULg)Investigación y Desarrollo más Innovación Artige, Lionel ; Book published by Consejo Económico y Social de España (2008) Detailed reference viewed: 31 (5 ULg)Investigaciones sobre el aceite de Mauritia flexuosa L. Lognay, Georges ; ; et al in Grasas Y Aceites (1987), 38(5), 303-307 Detailed reference viewed: 47 (0 ULg)Investigating a bottom-up approach for extracting domain ontologies from urban databases ; Teller, Jacques ; Billen, Roland in Proceedings of the 1st Workshop of COST Action C21 Towntology (2006) Detailed reference viewed: 36 (4 ULg)Investigating a Bottom-up Approach for Extracting Ontologies from Urban Databases ; Billen, Roland ; Teller, Jacques in Teller, Jacques; Lee, John; Roussey, Catherine (Eds.) Ontologies for Urban Development (2007) Detailed reference viewed: 53 (10 ULg)Investigating a two-level dynamic estimation algorithm for large-scale electric power systems Rousseaux, Patricia ; Van Cutsem, Thierry ; in Proceedings of the 1st European Workshop on the Real Time Control of Large Scale Systems (1984) Detailed reference viewed: 15 (0 ULg)Investigating apical adverse effects of four endocrine active substances in the freshwater gastropod Lymnaea stagnalis Giusti, Arnaud ; ; et al in Science of the Total Environment (2014), 493 The hermaphroditic gastropod Lymnaea stagnalis is proposed as a candidate species for the development of OECD guidelines for testing of the reprotoxicity of chemicals, including endocrine active ... [more ▼] The hermaphroditic gastropod Lymnaea stagnalis is proposed as a candidate species for the development of OECD guidelines for testing of the reprotoxicity of chemicals, including endocrine active substances (EASs). Up to now, only a few putative EASs have been tested for their reproductive toxicity in this species. In this study, we investigate the effects of four EASs with different affinities to the vertebrate estrogen and androgen receptors (chlordecone as an estrogen; cyproterone acetate, fenitrothion and vinclozolin as anti-androgens) on the reproduction of L. stagnalis in a 21-day semi-static test. Testosterone and 17α-ethinylestradiol (EE2) were used as the reference compounds. The tested EASs had no significant effect on growth and survival at the tested concentration ranges (ng to μg/L). Classical reproduction endpoints (i.e., oviposition and fecundity) were not responsive to the tested chemicals, except for chlordecone and 17α-ethinylestradiol, which hampered reproduction from 19.6 μg/L and 17.6 μg/L, respectively. The frequency of polyembryonic eggs, used as an additional endpoint, demonstrated the effects of all compounds except EE2. The molecular pathways, which are involved in such reproduction impairments, remain unknown. Our results suggest that egg quality is a more sensitive endpoint as compared to other reproductive endpoints commonly assessed in mollusk toxicity tests. [less ▲] Detailed reference viewed: 30 (13 ULg)Investigating Circumferential Non-Uniformities in Throughflow Calculations using an Harmonic Reconstruction Thomas, Jean-Philippe ; Léonard, Olivier in Proceedings of the ASME Turbo Expo 2008 (2008, June) The ﬂow ﬁeld in a multistage turbomachine is very complex. It is 3D, unsteady and turbulent. Even if modern simulation tools can describe most of the ﬂow features, the computation time needed and the ... [more ▼] The ﬂow ﬁeld in a multistage turbomachine is very complex. It is 3D, unsteady and turbulent. Even if modern simulation tools can describe most of the ﬂow features, the computation time needed and the extraction of useful information remain severe drawbacks to systematic use of URANS codes in a design procedure. In this context the throughﬂow simulation proved to be more convenient. Nevertheless the need for empiricism limits the potential of throughﬂow solvers. As an alternative, Admaczyck (1984) proposed three averaging operators (ensemble, time and passage) that lead to the average-passage model, linking the unsteady turbulent ﬂow ﬁeld to a steady ﬂow ﬁeld in a typical blade passage. This model involves additional terms that respectively bring back the mean effect of turbulence, deterministic unsteadiness and aperiodicity on the mean periodic ﬂow. These terms need to be modelled; it is the closure problem. Harmonic closure, which consists in solving a linearized perturbation system in the frequency domain, revealed to be an efficient method to approximate deterministic stresses (He and Ning, 1998, Stridh, 2005, Vilmin, 2006). A fourth averaging can be performed, a circumferential averaging, giving rise to the throughﬂow model. Additional terms appear: the so-called circumferential stresses. It has been proven that these terms play an important role in the description of the ﬂow (Jennions, 1986, Perrin, 1995), being at least as considerable as deterministic stresses. Introducing these terms in a throughﬂow simulation allows to reproduce the averaged 3D steady ﬂow ﬁeld (Simon, 2007). The aim of the present contribution is to prove that harmonic method can potentially be used to reconstruct circumferential stresses. The importance of circumferential stresses in a throughﬂow simulation is ﬁrst highlighted on a single stage low speed compressor testcase, for viscous and non-viscous ﬂow ﬁelds. The second step is the characterization of the frequency spectrum of the circumferential perturbation ﬁeld. Next are compared the stresses associated to a Fourier reconstruction of the perturbation ﬁeld with the real ones. Finally the approximated circumferential stresses are injected into a throughﬂow simulation tool to analyse and demonstrate their capability to reproduce a 3D averaged ﬂow ﬁeld. [less ▲] Detailed reference viewed: 79 (18 ULg)Investigating Depth-Fanout Trade-Off in WiMAX Mesh Networks ; ; Donnet, Benoît et al in 1st WEIRD Workshop on WiMAX, Wireless and Mobility (2007, May) In the last years, Wireless Mesh Networks (WMNs) have been an emerging technology for providing cost/effective broadband Internet access. The research done insofar usually assumes that the wireless ... [more ▼] In the last years, Wireless Mesh Networks (WMNs) have been an emerging technology for providing cost/effective broadband Internet access. The research done insofar usually assumes that the wireless backbone of a WMN is built using IEEE 802.11 technologies. Such an approach has the drawback of leading to dense and sub-optimal deployments, due to the short transmission range of this standard. Recently standardized, the WiMAX technology is supposed to transcend this limitation by a transmission range of several miles. In particular, the mesh mode of the WiMAX standard enables direct communications between subscriber stations and, hence, reduces dead zones while increasing the global throughput. In this paper, we investigate the throughput capacity of a WiMAX mesh tree. More specifically, we are interested in balancing the impact of the depth of the tree with its fanout. We provide a traffic model and evaluate the WiMAX mesh tree by simulations. 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