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See detailOn the modelling of contact problems with friction by the finite element method.
Charlier, Robert ULg; Godinas, André; Cescotto, Serge ULg

in Proc. 8th Conf. on SMIRT (1985, August)

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See detailOn the modelling of tridimensional contact with friction problems in context of large displacements problems
Charlier, Robert ULg; Habraken, Anne ULg

in Proc. of the 2nd Int. Conf. on Numerical Methods in Industrial Forming Processes (1986, August)

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See detailOn the Motion of Trapped Particles in the Vicinity of Corotation Centers
Beaugé, C.; Lemaitre, Anne; Jancart, Sylvie ULg

in Celestial Mechanics and Dynamical Astronomy (1999), 73

In the present paper we analyse the motion of a massless particle during the capture process in an exterior mean-motion resonance under the effects of an external dissipative force. In particular, we ... [more ▼]

In the present paper we analyse the motion of a massless particle during the capture process in an exterior mean-motion resonance under the effects of an external dissipative force. In particular, we study the orbital evolution from its initial approach to the commensurability up to the final nesting place in the periodic orbit around the equilibrium solution. [less ▲]

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See detailOn the motion of trapped particles in the vicinity of corotation centers
Beaugé, C.; Lemaitre, Anne; Jancart, Sylvie ULg

in Ferraz-Mello, S. (Ed.) Impact of Modern Dynamics in Astronomy (1999)

In this presentation we revisit the analytical determination of the corotation solutions of the restricted planar three-body problem under the effects of a Stokes drag. Previous calculations by different ... [more ▼]

In this presentation we revisit the analytical determination of the corotation solutions of the restricted planar three-body problem under the effects of a Stokes drag. Previous calculations by different authors, and using different external dissipative forces, have always shown significant quantitative errors of the models with respect to the numerical values. Up to date no concrete explanation has been obtained for this discrepancy. We show that the origin of these errors lies not only in the modelization of the gravitational forces (i.e. disturbing function) but in the averaging process of the variational equations. A second-order averaging is developed based on a Lie transform method (Kamel, 1969). With it we can calculate new equilibrium solutions with a greatly improved accuracy. In a second part, this same perturbation method is applied to study the periodic orbits (i.e. limit cycles) which describe the motion of the particles around the averaged corotational solutions. We show how analytical approximations of these cycles can be obtained through the inverse transformation of the averaging process itself. In all cases, we present comparisons with numerical simulations of the exact equations. [less ▲]

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See detailOn the mtDNA restriction patterns variation of the Iberian wood mouse (Apodemus sylvaticus). Comparison with other west Mediterranean populations.
Michaux, Johan ULg; Libois, Roland ULg; Ramalhinho, M. G. et al

in Hereditas (1998), 129(3), 187-94

In previous studies, the presence of three main lineages of wood mice mtDNA was described in western Europe: a first one distributed from the Pyrenees to Scandinavia. a Thyrrenian one occurring in ... [more ▼]

In previous studies, the presence of three main lineages of wood mice mtDNA was described in western Europe: a first one distributed from the Pyrenees to Scandinavia. a Thyrrenian one occurring in peninsular Italy, Elba, Corsica and Sardinia and a third one restricted to Sicily and Marettimo. Do the Iberian wood mice belong to one of these lineages? In order to answer this question, animals were trapped all over the Iberian peninsula (11 sites) as well as in three of the Balearic islands. Comparisons with specimens from the above mentioned lineages were made. From 158 animals trapped in 30 sites, 78 different mtDNA restriction patterns were obtained and compared using the NEI and LI index ((Nei M and Li WH, (1979). Mathematical model for studying genetic variation in terms of restriction endonucleases. Proc. Natl. Acad. Sci. USA 76: 5269-5273) of nucleotide divergence. A neighbour-joining tree, with a specimen of Apodemus flavicollis as outgroup, was then computed from the similarity matrix. Apodemus flavicollis is well separated from all the A. sylvaticus and all the Iberian restriction patterns are clustered with those of continental France, showing a great similarity level between the Iberian and north-west European animals. This group is well separated from the Sicilian and from the Tyrrhenian ones. These results suggest that the Pyrenees are not a biogeographic barrier for the wood mouse and that the postglacial recolonisation of western Europe by that species has its origin in populations which, during the latest Ice age, were living in refuges situated in southern France or in the Iberian peninsula. Because the Balearic restriction patterns are clustered in a lineage joining Iberian pattern at a low divergence level, we suggest that their origin is continental Spain or southern France. [less ▲]

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See detailOn the multiplicity of the non-thermal radio emitters 9 Sgr and HD 168112
Rauw, Grégor ULg; Sana, H.; Gosset, Eric ULg et al

in Massive Stars and High-Energy Emission in OB Associations (2005, November)

We discuss the first results of our ongoing optical spectroscopic monitoring campaign of the two O-type stars 9 Sgr and HD 168112. Both objects display a non-thermal radio emission and were considered as ... [more ▼]

We discuss the first results of our ongoing optical spectroscopic monitoring campaign of the two O-type stars 9 Sgr and HD 168112. Both objects display a non-thermal radio emission and were considered as single stars. Based on a large set of high-resolution spectra, we find that 9 Sgr is clearly an eccentric SB2 binary with an orbital period of several years. On the other hand, no evidence for radial velocity variations attributable to binary motion is found in our spectra of HD 168112. [less ▲]

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See detailOn the multiplicity of the O-star Cyg OB2#8a and its contribution to the gamma-ray source 3EG J2033+4118
De Becker, Michaël ULg; Rauw, Grégor ULg; Swings, Jean-Pierre ULg

in Astrophysics & Space Science (2005), 297(1-4), 291-298

We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 # 8A is an O6+ O5.5 binary system with a period of about 21.9 days. Cyg OB2 # 8A is a bright X ... [more ▼]

We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 # 8A is an O6+ O5.5 binary system with a period of about 21.9 days. Cyg OB2 # 8A is a bright X-ray source, as well as a non-thermal radio emitter. We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the radio waveband to gamma-rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for a putative gamma-ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified EGRET source 3EG J2033+ 4118. [less ▲]

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See detailOn the multivariate nature of brain metabolic impairment in Alzheimer’s disease
Salmon, Eric ULg; Kerrouche, Nacer; Perani, Daniela et al

in Neurobiology of Aging (2009), 30

We used principal component analysis to decompose functional images of patients with AD in orthogonal ensembles of brain regions with maximal metabolic covariance. Three principal components explained 38 ... [more ▼]

We used principal component analysis to decompose functional images of patients with AD in orthogonal ensembles of brain regions with maximal metabolic covariance. Three principal components explained 38% of the total variance in a large sample of FDG-PET images obtained in 225 AD patients. One functional ensemble (PC2) included limbic structures from Papez's circuit (medial temporal regions, posterior and anterior cingulate cortex, thalamus); its disruption in AD patients was related to episodic memory impairment. Another principal component (PC1) illustrated major metabolic variance in posterior cerebral cortices, and patients' scores were correlated to instrumental functions (language and visuospatial abilities). PC3 comprised frontal, parietal, temporal and posteromedial (posterior cingulate and precuneus) cortices, and patients' scores were related to executive dysfunction and global cognitive impairment. The three main metabolic covariance networks converged in the posterior cingulate area that showed complex relationships with medial temporal structures within each PC. Individual AD scores were distributed as a continuum along PC axes: an individual combination of scores would determine specific clinical symptoms in each patient. [less ▲]

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See detailOn the nature of the hard X-ray source IGR J2018+4043
Bykov, Andrei Mikhailovich; Krassilchtchikov, Alexandre Mikhailovich; Uvarov, Yuri Alexandrovich et al

in Astrophysical Journal (2006), 649(1, Part 2), 21-24

We found a very likely counterpart to the recently discovered hard X-ray source IGR J2018 + 4043 in the multiwavelength observations of the source field. The source, originally discovered in the 20-40 keV ... [more ▼]

We found a very likely counterpart to the recently discovered hard X-ray source IGR J2018 + 4043 in the multiwavelength observations of the source field. The source, originally discovered in the 20-40 keV band, is now confidently detected also in the 40-80 keV band, with a flux of (1.4 +/- 0.4) x 10(-11) ergs cm(-2) s(-1). A 5 ks Swift observation of the IGR J2018 + 4043 field revealed a hard pointlike source with an observed 0.5-10 keV flux of 3.4(-0.8)(+0.7) x 10(-12) ergs cm(-2) s(-1) (90% confidence level) at alpha = 20(h)18(m)38(s).55, delta = +40 degrees 41'00.4" (with a 4".2 uncertainty). The combined Swift-INTEGRAL spectrum can be described by an absorbed power-law model with photon index Gamma = 1.3 +/- 0.2 and N-H = 6.1(-2.2)(+3.3) x 10(22) cm(-2). In archival optical and infrared data we found a slightly extended and highly absorbed object at the Swift source position. There is also an extended VLA 1.4 GHz source peaked at a beamwidth distance from the optical and X-ray positions. The observed morphology and multiwavelength spectra of IGR J2018 + 4043 are consistent with those expected for an obscured accreting object, i.e., an AGN or a Galactic X-ray binary. The identification suggests possible connection of IGR J2018 + 4043 to the bright gamma-ray source GEV J2020 + 4023 detected by COS B and CGRO EGRET. [less ▲]

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See detailOn the nature of the spectral and photometric periodic variability of apparently single Wolf-Rayet stars
Morel, Thierry ULg

in The Observatory (1999), 119

Not Available

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See detailOn the necessity to consider varying parameters in the land subsidence computations
Dassargues, Alain ULg

in Barends, F. B. J.; Brouwer, F. J. J.; Schröder, F. H. (Eds.) Land Subsidence (Proc. of the Vth Int. Symp.) (1995)

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See detailOn the necessity to use three-dimensional groundwater models for describing impact of drought conditions on streamflow regimes
Dassargues, Alain ULg; Maréchal, J. C.; Carabin, Guy et al

in Hydrological Extremes : Understanding, Predicting, Mitigating (1999)

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See detailOn the Number of Abelian Bordered Words
Rampersad, Narad; Rigo, Michel ULg; Salimov, Pavel ULg

in Lecture Notes in Computer Science (2013), 7907

In the literature, many bijections between (labeled) Motzkin paths and various other combinatorial objects are studied. We consider abelian (un)bordered words and show the connection with irreducible ... [more ▼]

In the literature, many bijections between (labeled) Motzkin paths and various other combinatorial objects are studied. We consider abelian (un)bordered words and show the connection with irreducible symmetric Motzkin paths and paths in Z not returning to the origin. This study can be extended to abelian unbordered words over an arbitrary alphabet and we derive expressions to compute the number of these words. In particular, over a 3-letter alphabet, the connection with paths in the triangular lattice is made. Finally, we study the lengths of the abelian unbordered factors occurring in the Thue--Morse word. [less ▲]

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See detailOn the numerical damping of time integrators for coupled mechatronic systems
Bruls, Olivier ULg; Golinval, Jean-Claude ULg

in Computer Methods in Applied Mechanics & Engineering (2008), 197(6-8), 577-588

The generalized-alpha time integrator is considered for the simulation of mechatronic systems. In this context, the fundamental concept of numerical damping is analysed for coupled sets of first and ... [more ▼]

The generalized-alpha time integrator is considered for the simulation of mechatronic systems. In this context, the fundamental concept of numerical damping is analysed for coupled sets of first and second-order differential-algebraic equations. First, it appears that the algebraic variables do not influence the spectral properties of the dynamic variables. Second, we demonstrate that the coupling between the dynamic variables does not influence the high-frequency spectral response, so that the numerical damping can be determined as usual from elementary characteristic polynomials. Those results are exploited to assess the stability properties of the scheme and to select an algorithm with optimal damping properties. [less ▲]

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See detailOn the numerical integration of an advanced Gurson model
Ben Bettaieb, Mohamed ULg; Lemoine, Xavier; Duchene, Laurent ULg et al

in International Journal for Numerical Methods in Engineering (2011), 85(8), 1049-1072

This article is focused on a new extended version of Gurson's model (J. Eng. Mater. Technol. 1977; 99:2–15), its numerical integration scheme and its consistent tangent matrix being within an FE code ... [more ▼]

This article is focused on a new extended version of Gurson's model (J. Eng. Mater. Technol. 1977; 99:2–15), its numerical integration scheme and its consistent tangent matrix being within an FE code. First, this new advanced Gurson model is proposed, which is an extension of the original to take into account plastic anisotropy and mixed (isotropic+kinematic) hardening. In this paper, only the growth phase of cavities is considered (the nucleation of new voids is ignored). Second, a new numerical algorithm for the integration of this new Gurson model is presented. The algorithm is implicit in all variables and is unconditionally stable. This algorithm is generic and could be used for other anisotropic yield functions and other hardening laws. Third, the consistent tangent matrix is computed in an explicit way by exact linearization of the constitutive equations. To check its efficiency and robustness, the proposed integration algorithm is compared, under some simplified assumptions and choices, with the algorithms of Aravas (Int. J. Numer. Meth. Engng 1987; 24:1395–1416) and Kojic (Int. J. Numer. Meth. Engng 2002; 53(12):2701–2720). The performance of the developed consistent modulus, compared to other techniques for the computation of the tangent matrix is assessed. The paper ends with numerical simulations of tensile tests on homogeneous and notched specimens. [less ▲]

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See detailOn the numerical integration of rate independent single crystal behavior at large strain
Ben Bettaieb, Mohamed; Débordes, Olivier; Dogui, Abdelwaheb et al

in International Journal of Plasticity (2012), 32-33

This paper presents a new numerical algorithm for the integration of the constitutive equations of a single crystal for finite rate-independent elastoplastic strains. The algorithm addressed in this paper ... [more ▼]

This paper presents a new numerical algorithm for the integration of the constitutive equations of a single crystal for finite rate-independent elastoplastic strains. The algorithm addressed in this paper is dedicated to face-centered-cubic (FCC) crystal structures. Its first feature is a much more efficient and more accurate integration scheme of the constitutive equations compared to previous attempts. This scheme is based on a fully implicit integration procedure, yet it may be transformed easily into an explicit scheme. Determining the set of active slip systems is performed by the use of a combinatorial search procedure, and the determination of the slip rates of the different active slip systems is based on the fixed point method. The second feature of this algorithm stems from the original method used to solve the ambiguity of the possible non-uniqueness of the set of active slip systems. A robust method, based on a small positive perturbation of the critical shear stresses, is proposed to overcome this difficulty. It is worth mentioning that the algorithm developed in this paper is not limited to one particular hardening law or to FCC crystal structures. Rather, it can be used and extended to various hardening laws and crystal structures (e.g. BCC or HCP. . .) in a straightforward manner. The authors demonstrate the performance of the proposed algorithm and illustrate its accuracy and efficiency through various numerical simulations at the single crystal and polycrystal scales. The predicted results obtained from those simulations were compared with those obtained using other numerical techniques and algorithms (i.e., a pseudo-inversion technique and an explicit algorithm). Our numerical predictions are also compared with some numerical and experimental results from other papers. The response of the polycrystal was computed by using the proposed algorithm combined with Taylor’s homogenization scheme, which is used to compute the overall polycrystalline behavior. The paper ends with a statistical study of the influence of the perturbation technique on the response prediction for a single crystal and a polycrystal. [less ▲]

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See detailOn the numerical modeling of shear banding around an excavation
Collin, Frédéric ULg; Li, Xiang Ling; Lambarki, A. et al

Conference (2005)

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See detailOn the numerical modelling of shear banding around an excavation
Collin, Frédéric ULg; Li, X.L.; Lambarki, A. et al

Conference (2005)

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See detailOn the numerical modelling of shear banding around an excavation
Collin, Frédéric ULg; Lambarki, A.; Charlier, Robert ULg et al

Conference (2005)

For an underground storage of nuclear waste, it is necessary to minimize the excavation damage zone (EDZ) that could be a higher permeability zone. This paper deals with the FE modelling of the EDZ extent ... [more ▼]

For an underground storage of nuclear waste, it is necessary to minimize the excavation damage zone (EDZ) that could be a higher permeability zone. This paper deals with the FE modelling of the EDZ extent during tunnelling. A Drucker – Prager law with cohesion strain softening is used. Results show a shear banding around the excavation. Its extent and the tunnel convergence are highly dependent on the hydraulic boundary condition within the tunnel (imposed pore pressure – suction or unilateral flow condition). [less ▲]

Detailed reference viewed: 31 (4 ULg)