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See detailOn the use of adhesion parameters to validate models specified using systems of affine differential equations
Jaeger, Jonathan ULg; Lambert, Philippe ULg

E-print/Working paper (2012)

A strategy for the selection of system of differential equations is proposed based on Bayesian ODE-penalized B-spline approach. It estimates the ODE parameters, approximates the solution of the ODE model ... [more ▼]

A strategy for the selection of system of differential equations is proposed based on Bayesian ODE-penalized B-spline approach. It estimates the ODE parameters, approximates the solution of the ODE model and quantifies the suitability of the proposed differential equations to model the dynamics of the observed state functions. Simulation study confirms that these ODE-adhesion parameters are able to question a system of differential equations as a descriptor of the dynamics in the state functions. This methodology is illustrated on a pharmacokinetic study. [less ▲]

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See detailOn the Use of Automata-based Techniques in Symbolic Model Checking: invited address
Legay, Axel; Wolper, Pierre ULg

in Electronic Notes in Theoretical Computer Science (2006, March 09), 150(1), 3-8

Checking infinite-state systems is frequently done by encoding infinite sets of states as regular languages. Computing such a regular representation of, say, the reachable set of states of a system ... [more ▼]

Checking infinite-state systems is frequently done by encoding infinite sets of states as regular languages. Computing such a regular representation of, say, the reachable set of states of a system requires acceleration techniques that can finitely compute the effect of an unbounded number of transitions. Among the acceleration techniques that have been proposed, one finds both specific and generic techniques. Specific techniques exploit the particular type of system being analyzed, e.g. a system manipulating queues or integers, whereas generic techniques only assume that the transition relation is represented by a finite-state transducer, which has to be iterated. In this paper, we survey two generic techniques that have been presented in [B. Boigelot and A. Legay and P. Wolper, Iterating Transducers in the Large, Proc. 15th Int. Conf. on Computer Aided Verification, Boulder, USA, Lecture Notes in Computer Science, volume 2725, year 2003, pages 223–235] and [B. Boigelot and A. Legay and P. Wolper, Omega-Regular Model Checking, Proc. 10th Int. Conf. on Tools and and Algorithms for the Construction and Analysis of Systems, Barcelona, Spain, Lecture Notes in Computer Science, volume 2988, year 2004, pages 561–575]. Those techniques build on earlier work, but exploits a number of new conceptual and algorithmic ideas, often induced with the help of experiments, that give it a broad scope, as well as good performance. [less ▲]

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See detailOn the use of Belgian Soil Map to predict risk of nitrate and pesticide lixiviation
Bah, Boubacar Billo ULg; Vandenberghe, Christophe ULg; Deneufbourg, Mathieu ULg et al

Poster (2014, February 26)

Pollution by nitrate and pesticides has impacts on drinking water reserves and aquatic systems. Nowadays, this problem is the key point of the European Policy with the implementation of the Water ... [more ▼]

Pollution by nitrate and pesticides has impacts on drinking water reserves and aquatic systems. Nowadays, this problem is the key point of the European Policy with the implementation of the Water Framework Directive (Directive 2000/60/EC). According to these legislations, Member States are supposed to take measures to limit environmental and toxicological effects caused by nitrate and pesticides use. This paper presents three different approaches allowing assessment of diffuse (non-point sources) pollution risks of water resources by nitrate and pesticides. The first approach consists on the interpretation of the geomorphopedological information (geologic substratum type, presence of karst phenomena, soil texture, natural drainage, profile development, type and percent of stoniness, soil thickness, …) provided by the Digital Soil Map of Wallonia. Soil physical characteristics are assessed in terms of soil water percolation/infiltration, runoff, pollutants retention, mineralization, and erosion. Second approach consists on the use of spatially distributed mechanistic models. Nitrate lixiviation from agricultural land to groundwater has been simulated from the SWAT model. Pesticide lixiviation from soil to groundwater has been predicted from the one-dimensional, dynamic, multi-layered model named PEARL (Pesticide Emission Assessment at Regional and Local scales). Model input parameters are mainly extracted from the existing soil physical and physico-chemical, crop and pesticides properties databases. Relevant soil parameters not directly available in existing databases, such as bulk density, hydraulic conductivity, potential evapotranspiration… have been derived from pedotransfers functions. Third approach consists on in situ lixiviation studies by the way of lysimeters. Concentrations measured at the bottom (2 m deep) of lysimeters represent a straight “index of risk” for groundwater and, on the other hand, allow the validation of simulation models used to predict nitrate and pesticides lixiviation risk under different scenarios. The Digital Soil Map of Wallonia, one of the core data source, allows the spatialisation of the predicted lixiviation risk at regional level, providing to the local authorities and the decision makers a tool for the identification of the areas at risk of pollution, where specific monitoring actions and prevention measures for the protection of waters can be implemented. [less ▲]

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See detailOn the use of control surface excitation in flutter testing
Wright, Jan R; Wong, Jerry; Cooper, Jonathan E et al

in Proceedings of the Institution of Mechanical Engineers - Part G - Journal of Aerospace Engineering (2003), 217(6), 317-332

Flutter testing is aimed at demonstrating that the aircraft flight envelope is flutter free. Response measurements from deliberate excitation of the structure are used to identify and track frequency and ... [more ▼]

Flutter testing is aimed at demonstrating that the aircraft flight envelope is flutter free. Response measurements from deliberate excitation of the structure are used to identify and track frequency and damping values against velocity. In this paper, the common approach of using a flight control surface to provide the excitation is examined using a mathematical model of a wing and control surface whose rotation is restrained by a simple actuator. In particular, it is shown that it is essential to use the demand signal to the actuator as a reference signal for data processing. Use of the actuator force (or strain) or control angle (or actuator displacement) as a reference signal is bad practice because these signals contain response information. It may also be dangerous in that the onset of flutter may not be seen in the test results. [less ▲]

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See detailOn the use of control surface excitation in flutter testing
Wright, Jan R; Wong, Jerry; Cooper, Jonathan Edward et al

in Proceedings of the 2003 International Forum on Aeroelasticity and Structural Dynamics (2003, June)

Flutter testing is used to demonstrate that the aircraft flight envelope is flutter free. Response measurements from deliberate excitation of the structure are used to identify and track frequency and ... [more ▼]

Flutter testing is used to demonstrate that the aircraft flight envelope is flutter free. Response measurements from deliberate excitation of the structure are used to identify and track frequency and damping values against velocity. In this paper, the common approach of using a flight control surface to provide the excitation is examined us ing a mathematical model of a wing and control surface whose rotation is restrained by a simple actuator. In particular, it is shown that it is essential to use the demand signal to the actuator as a reference signal for data processing. Use of the actuator force (or strain) or control angle (or actuator displacement) as a reference signal is bad practice because these signals contain response information. It may also be dangerous in that the onset of flutter may not be seen in the test results. Control sur face flutter is of particular concern. [less ▲]

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See detailOn the use of Cowan Code for Atomic Structure Calculations in Singly Ionized Lanthanides
Quinet, Pascal ULg; Palmeri, P.; Biémont, Emile ULg

Conference (1998, August)

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See detailOn the use of diffusion equations to model the acoustics of coupled rooms
Billon, Alexis ULg; Valeau, Vincent; Picaut, Judicaël et al

in Journal of the Acoustical Society of America (2008), 123(5), 3910-3910

he acoustics of coupled rooms are characterized by energy exchanges through apertures and/or partition walls. The use of systems of diffusion equations allows to predict the temporal and spatial energy ... [more ▼]

he acoustics of coupled rooms are characterized by energy exchanges through apertures and/or partition walls. The use of systems of diffusion equations allows to predict the temporal and spatial energy distributions in these configurations quite accurately. In this presentation, the diffusion formalism for room acoustics-prediction is summarized. The systems of equations to be solved in the case of coupling through an aperture and through a partition wall are presented. For two rooms coupled through an aperture (two classrooms connected through an open door), the results obtained with the diffusion model are compared to experimental data, in terms of sound pressure levels and sound decays. On the other hand, for the case of two classrooms connected through a partition wall, the diffusion model is compared to experimental data in terms of sound pressure level difference only. Finally, an engineering application is presented in the configuration involving a workroom including multiple sound sources (e.g., machines) connected to offices through open and closed doors. [less ▲]

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See detailOn the Use of Distance in the Taxonomic Study of Critical Plant Groups-Case Studies of Western European Orchidaceae
Tyteca, D.; Dufrêne, Marc ULg

in Annals of Botany (1993), 71(3), 257-277

Four distance coefficients are compared on four data sets composed of samples coming from western European populations of the genera Dactylorhiza, Orchis and Epipactis (Orchidaceae). The performance of ... [more ▼]

Four distance coefficients are compared on four data sets composed of samples coming from western European populations of the genera Dactylorhiza, Orchis and Epipactis (Orchidaceae). The performance of the distance coefficients is evaluated through: (a) the quality of clusters obtained by five classical methods (as compared to a priori classification), (b) the Mantel statistic with respect to an a priori distance matrix resulting from previous knowledge, (c) the result obtained with the k-means method, and (d) principal coordinate diagrams. It appears that: (a) the Mahalanobis distance based on the pooled dispersion matrix performs best on the whole; (b) a distance based on the recently developed Common Principal Component model, used with a log transformation, also provides useful information and performs best on the largest data set; (c) the Gölz and Reinhard taxonomic distance, widely used among orchidologists, is attractive for its simplicity, yet good performance and the valuable information it provides, despite its theoretical shortcomings. A brief taxonomic discussion is made on the results obtained for the Dactylorhiza samples, especially about samples whose identification was in doubt. [less ▲]

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See detailOn the Use of DNA Fingerprints for Linkage Studies in Cattle
Georges, Michel ULg; Lathrop, M.; Hilbert, P. et al

in Genomics (1990), 6(3), 461-474

To find a marker for the bovine "muscular hypertrophy" gene and for the "roan" locus, we have typed six cattle pedigrees totaling 540 animals for nine blood group systems, for 12 biochemical markers, for ... [more ▼]

To find a marker for the bovine "muscular hypertrophy" gene and for the "roan" locus, we have typed six cattle pedigrees totaling 540 animals for nine blood group systems, for 12 biochemical markers, for RFLPs at four loci, and with five probes revealing multilocus DNA fingerprints. Segregation analysis of the fingerprint bands showed that, in cattle, a fingerprint probe will reveal a mean of 7.6 clearly resolvable bands, behaving as simple, highly informative Mendelian entities characterized by a mean mutation rate of +/- 1/4500 gametes. For one of the bands, we observed a "mutation burst" generating germline mosaicism. Because some of the fingerprint bands were allelic or corresponded to clustered minisatellites, a mean of only 5.7 independent loci is explored per probe. Fingerprint bands revealed by different probes also show a clear propensity for close linkage, pointing toward nonrandom distribution of minisatellite sequences or the existence of minisatellite clusters. Although this reduces the power of fingerprints for linkage analysis substantially, we were able to demonstrate genetic linkage between fingerprint bands and at least three of the classical markers, to exclude the roan locus from 4.5 Morgans of the bovine genome with the DNA fingerprints and for an additional 2.5 Morgans with the classical markers, and to identify a solid candidate marker for the bovine muscular hypertrophy gene, yielding a lod score greater than or equal to 2.84 without any obliged recombinant. [less ▲]

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See detailOn the use of Fourier averages to compute the global isochrons of (quasi)periodic dynamics
Mauroy, Alexandre ULg; Mezić, Igor

in Chaos (2012), 22(3),

The concept of isochrons is crucial for the analysis of asymptotically periodic systems. Roughly, isochrons are sets of points that partition the basin of attraction of a limit cycle according to the ... [more ▼]

The concept of isochrons is crucial for the analysis of asymptotically periodic systems. Roughly, isochrons are sets of points that partition the basin of attraction of a limit cycle according to the asymptotic behavior of the trajectories. The computation of global isochrons (in the whole basin of attraction) is however difficult, and the existing methods are inefficient in high-dimensional spaces. In this context, we present a novel (forward integration) algorithm for computing the global isochrons of high-dimensional dynamics, which is based on the notion of Fourier time averages evaluated along the trajectories. Such Fourier averages in fact produce eigenfunctions of the Koopman semigroup associated with the system, and isochrons are obtained as level sets of those eigenfunctions. The method is supported by theoretical results and validated by several examples of increasing complexity, including the 4-dimensional Hodgkin-Huxley model. In addition, the framework is naturally extended to the study of quasiperiodic systems and motivates the definition of generalized isochrons of the torus. This situation is illustrated in the case of two coupled Van der Pol oscillators. © 2012 American Institute of Physics. [less ▲]

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See detailOn the use of Galerkin-Eckhaus method to study the nonlinear regime of Marangoni-Benard instabilities in an evaporating liquid layer
Margerit, Jonathan; Dondlinger, Mireille; Dauby, Pierre ULg

in European Physical Journal B -- Condensed Matter (2006), 54(4), 485-492

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See detailOn the use of gender-marked personal pronouns: the emergence of a new system in southern Dutch?
De Vos, Lien ULg

Scientific conference (2011, May 30)

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See detailOn the use of gender-marked personal pronouns: towards a semantic system
De Vos, Lien ULg

Conference (2011, June 30)

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See detailOn the use of HF as a reference for the comparison of stratospheric observations and models
Chipperfield, M. P.; Burton, M.; Bell, W. et al

in Journal of Geophysical Research (1997), 102(11D), 12901-12919

Hydrogen fluoride (HF) is often used as a simple reference for other column observations of chemically active stratospheric species. However, seasonal and shorter timescale variations in column HF make ... [more ▼]

Hydrogen fluoride (HF) is often used as a simple reference for other column observations of chemically active stratospheric species. However, seasonal and shorter timescale variations in column HF make its use as a reference more complicated. In this paper we characterize the expected magnitude of these variations in HF, and variations of ratio quantities involving HF, using a two-dimensional (2-D) photochemical model and two versions of a three-dimensional (3-D) transport model. The 2-D model predicts that the column ratios HNO3/HF and HCl/HF increase from midlatitudes to the tropics, although this is very sensitive to HCl and HNO3 abundances in the tropical upper troposphere. Seasonal variations in vertical motion modifys the predicted ratios; for example, wintertime descent at high latitudes decreases HCl/HF. The ratio HNO3/HF at high latitudes is strongly modified by seasonal variations in the chemical partitioning of the odd nitrogen (NOy) species. We compare these model predictions with ground-based Fourier transform infrared spectroscopy (FTIR) observations of HF along with HCl, ClONO2 and HNO3 obtained at eight northern hemisphere sites between October 1994 and July 1995. We investigate quantitatively how HF can be used as a tracer to follow the evolution of observations at a single station and to intercompare results from different stations or with photochemical models. The magnitude of the 3-D model HF column agrees well with the observations, except on some occasions at high latitudes, giving indirect support for the important role of COF2 in the stratospheric inorganic fluorine budget. The observed day-to-day variability in the column ratios HCl/HF and HNO3/HF is much larger at high latitudes. This variability is reproduced in the 3-D models and is due to horizontal motion. Short timescale vertical displacement of the species profiles is estimated to have a small effect on the column ratios. In particular, we analyze the usefulness of the observed column ratio (ClONO2 + HCl)/HF as an indicator for chlorine activation. Current measurement uncertainties limit the degree of activation which can be unambiguously detected using this observed quantity, but we can determine that chlorine-activated air was observed above Aberdeen (58 degrees N) on 6 days in late January 1995. [less ▲]

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See detailOn the use of IMAGE FUV for estimating the latitude of the open/closed magnetic field line boundary in the ionosphere
Boakes, P. D.; Milan, S. E.; Abel, G. A. et al

in Annales Geophysicae (2008), 26

A statistical comparison of the latitude of the open/closed magnetic field line boundary (OCB) as estimated from the three far ultraviolet (FUV) detectors onboard the IMAGE spacecraft (the Wideband ... [more ▼]

A statistical comparison of the latitude of the open/closed magnetic field line boundary (OCB) as estimated from the three far ultraviolet (FUV) detectors onboard the IMAGE spacecraft (the Wideband Imaging camera, WIC, and the Spectrographic Imagers, SI-12 and SI-13) has been carried out over all magnetic local times. A total of over 400 000 OCB estimations were compared from December 2000 and January and December of 2001 2002. The modal latitude difference between the FUV OCB proxies from the three detectors is small, <1°, except in the predawn and evening sectors, where the SI-12 OCB proxy is found to be displaced from both the SI-13 and WIC OCB proxies by up to 2° poleward in the predawn sector and by up to 2° equatorward in the evening sector. Comparing the IMAGE FUV OCB proxies with that determined from particle precipitation measurements by the Defense Meteorological Satellites Program (DMSP) also shows systematic differences. The SI-12 OCB proxy is found to be at higher latitude in the predawn sector, in better agreement with the DMSP OCB proxy. The WIC and SI-13 OCB proxies are found to be in better agreement with the DMSP OCB proxy at most other magnetic local times. These systematic offsets may be used to correct FUV OCB proxies to give a more accurate estimate of the OCB latitude. [less ▲]

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See detailOn the use of large time steps with an energy momentum conserving algorithm for non-linear hypoelastic constitutive models
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in International Journal of Solids and Structures (2004), 41(3-4), 663693

This paper presents an extension of the energy momentum conserving algorithm, developed by the authors for hypoelastic constitutive models. For such a material, contrarily to hyperelastic models, no ... [more ▼]

This paper presents an extension of the energy momentum conserving algorithm, developed by the authors for hypoelastic constitutive models. For such a material, contrarily to hyperelastic models, no potential can be defined, and thus the conservation of the energy is ensured only if the elastic work of deformation can be restored by the scheme. In a previous paper, we proposed a new expression of internal forces at the finite element level which is shown to verify this property. We also demonstrated that the work of plastic deformation is positive and consistent with the material model. In this paper, the second order terms that were neglected in the previous work are now taken into account. Several numerical applications are presented to demonstrate the necessity of taking these terms into account once large time step sizes are used. The limitations of the Newmark algorithm in the non-linear range are also illustrated. (C) 2003 Elsevier Ltd. All rights reserved. [less ▲]

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See detailOn the use of Lie group time integrators in multibody dynamics
Bruls, Olivier ULg; Cardona, Alberto

in Journal of Computational and Nonlinear Dynamics (2010), 5(3), 031002

This paper proposes a family of Lie group time integrators for the simulation of flexible multibody systems. The method provides an elegant solution to the rotation parameterization problem. As an ... [more ▼]

This paper proposes a family of Lie group time integrators for the simulation of flexible multibody systems. The method provides an elegant solution to the rotation parameterization problem. As an extension of the classical generalized-alpha method for dynamic systems, it can deal with constrained equations of motion. Second-order accuracy is demonstrated in the unconstrained case. The performance is illustrated on several critical benchmarks of rigid body systems with high rotation speeds and second order accuracy is evidenced in all of them, even for constrained cases. The remarkable simplicity of the new algorithms opens some interesting perspectives for real-time applications, model-based control and optimization of multibody systems. [less ▲]

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See detailOn the use of locally composite columns to improve the seismic robustness of reinforced concrete frames
Degée, Hervé ULg; Plumier, André ULg

in Proceedings of the 8th Sismica Conference (2010)

Detailed reference viewed: 22 (6 ULg)
See detailOn the use of magnetic susceptibility on different carbonate systems
Da Silva, Anne-Christine ULg; Boulvain, Frédéric ULg; Mabille, Cedric

in Abstract book 13th Bathurst meeting of carbonate sedimentologists (2007)

Detailed reference viewed: 6 (1 ULg)
See detailOn the use of O2/Ar and O2/N2 to estimate the biological carbon uptake in landfast sea ice
Zhou, Jiayun ULg; Delille, Bruno ULg; Brabant, F. et al

Poster (2014, March)

Sea ice is one of the largest biomes on Earth. The net community production (NCP) of the microorganisms living in sea ice impacts the dynamics of pCO2 in sea ice, and therefore the CO2 exchanges at the ... [more ▼]

Sea ice is one of the largest biomes on Earth. The net community production (NCP) of the microorganisms living in sea ice impacts the dynamics of pCO2 in sea ice, and therefore the CO2 exchanges at the air-ice-sea interfaces. As oxygen O2 and carbon C are both involved in the photosynthetic and respiration processes, one can theoretically assess NCP (in terms of C uptake) from O2 measurements. However, the concentration of O2 in sea ice depends not only on biological processes (i.e., NCP) but also on physical processes. We present a technique for assessing NCP in sea ice, based on the use of the O2/Ar ratio, which should correct for the physical contribution in O2 variations. We also compare the use of O2/Ar and O2/N2 for deriving NCP, and demonstrate that O2/Ar is more suitable, as it is more sensitive and less affected by gas diffusion and gas bubble formation during sea ice growth and decay than O2/N2. Using O2/Ar, we then provide conservative estimates of NCP in landfast sea ice, from ice cores collected in Barrow, from January through June 2009. The minimum estimate of the NCP in the whole ice cover reached 229 mg C.m-².d-1 in late spring. This is about 20 times higher than the atmospheric C uptake at that time identified from CO2 fluxes measurements at the ice-air interface, and therefore indicates that the main source of C used in the NCP was from the under-ice water. [less ▲]

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