Publications ORBi OA
Bookmark and Share    
Full Text
See detailQuadratic reformulations of nonlinear binary optimization problems
Anthony, Martin; Boros, Endre; Crama, Yves ULg et al

E-print/Working paper (2015)

Very large nonlinear unconstrained binary optimization problems arise in a broad array of applications. Several exact or heuristic techniques have proved quite successful for solving many of these ... [more ▼]

Very large nonlinear unconstrained binary optimization problems arise in a broad array of applications. Several exact or heuristic techniques have proved quite successful for solving many of these problems when the objective function is a quadratic polynomial. However, no similarly efficient methods are available for the higher degree case. Since high degree objectives are becoming increasingly important in certain application areas, such as computer vision, various techniques have been recently developed to reduce the general case to the quadratic one, at the cost of increasing the number of variables. In this paper we initiate a systematic study of these quadratization approaches. We provide tight lower and upper bounds on the number of auxiliary variables needed in the worst-case for general objective functions, for bounded-degree functions, and for a restricted class of quadratizations. Our upper bounds are constructive, thus yielding new quadratization procedures. Finally, we completely characterize all ``minimal'' quadratizations of negative monomials. [less ▲]

Detailed reference viewed: 34 (1 ULg)
Full Text
See detailA next-generation approach to assess the cyanobacterial diversity and biogeography in the High Arctic (Svalbard)
Laughinghouse, Haywood Dail; Stelmach Pessi, Igor ULg; Velazquez, David et al

Poster (2015, August 03)

Polar ecosystems are extremely sensitive to global climate changes and human activities. Cyanobacteria are key photosynthetic organisms in these latitudes, due to their roles in soil aggregation, nitrogen ... [more ▼]

Polar ecosystems are extremely sensitive to global climate changes and human activities. Cyanobacteria are key photosynthetic organisms in these latitudes, due to their roles in soil aggregation, nitrogen fixation, carbon cycles, and secondary metabolite production, among others. Previous works indicate that different cyanobacterial taxa/communities have different impacts on the environment, in both biogeochemical cycles and bioactive compound productions. Furthermore, the presence of biogeographical patterns in microorganisms, as found in macroorganisms, is an ongoing debate. In this study, during the 2013 MicroFun expedition, we sampled 72 locations around Svalbard including diverse biotopes such as glacial forefields, tundra soils, hot springs, soil crusts, microbial mats, wet walls, cryoconites, plankton and periphyton, in order to (1) assess the biodiversity of cyanobacteria around Svalbard, (2) verify the existence of biogeographical trends around the archipelago, and (3) compare these data with other polar (cold) areas, especially Antarctica. We used a pyrosequencing approach targeting cyanobacteria-specific 16S rRNA gene sequences to deeply study the cyanobacterial communities. [less ▲]

Detailed reference viewed: 22 (0 ULg)
Full Text
See detailDevelopment of cryopreservation methods for long-term preservation of cyanobacterial strains in the BCCM/ULC collection
Crahay, Charlotte ULg; Renard, Marine ULg; Mari, Maud et al

Poster (2015, August 03)

Long-term genetic and functional stability is a fundamental requirement for the maintenance of microorganisms and cryopreservation is the preferred method for the long-term storage of many micro-organisms ... [more ▼]

Long-term genetic and functional stability is a fundamental requirement for the maintenance of microorganisms and cryopreservation is the preferred method for the long-term storage of many micro-organisms, including cyanobacteria. The BCCM/ULC collection currently holds 200 cyanobacterial strains, but only 62 are cryo-preserved. The main limiting factors are the low levels of survival of some strains and the long periods required to recover from cryopreservation, and thus the inability to deliver rapidly cryopreserved strains to the user community. The devel-opment of improved cryopreservation protocols is therefore required for the future expansion and valorization of the collection. The BRAIN-be project PRESPHOTO (preservation of photosynthetic micro-algae in the BCCM collections) (www.presphoto.ulg.ac.be) aims to improve the preservation of cyanobacterial and diatoms in the BCCM/ULC and BCCM/DCG collections, respectively. [less ▲]

Detailed reference viewed: 11 (1 ULg)
Full Text
See detailContribution of cyanobacteria to the building of travertines in a calcareous stream
Wilmotte, Annick ULg; Golubic, Stjepko; Kleinteich, Julia et al

Poster (2015, August 03)

The ambient temperature travertine deposits of the calcareous Hoyoux River (Modave, Belgium) and several tributaries are organized and promoted by the filamentous cyanobacterium identified by its ... [more ▼]

The ambient temperature travertine deposits of the calcareous Hoyoux River (Modave, Belgium) and several tributaries are organized and promoted by the filamentous cyanobacterium identified by its morphotype and ecological properties as Phormidium cf. incrustatum. A combination of techniques was used to study this biotope: physico-chemical parameters and CO2 measurements, Scanning and Transmission Electron Microscopy, RAMAN microspectroscopy. A molecular diversity study with pyrosequencing of the cyanobacterial 16S rRNA is in progress. A potential candidate was isolated in culture. [less ▲]

Detailed reference viewed: 24 (1 ULg)
Full Text
See detailA propos des fonctions continues qui ne sont dérivables en aucun point
Esser, Céline ULg

Conference (2015, August 03)

En 1872, Karl Weierstrass présenta non seulement une, mais toute une famille de fonctions continues et nulle part dérivables. Après la publication de ce résultat, beaucoup d'autres mathématiciens ... [more ▼]

En 1872, Karl Weierstrass présenta non seulement une, mais toute une famille de fonctions continues et nulle part dérivables. Après la publication de ce résultat, beaucoup d'autres mathématiciens apportèrent leur propre contribution en construisant d'autres fonctions continues et nulle part dérivables. Dans cet exposé, nous présenterons les fonctions de Weierstrass et nous montrerons que le théorème de Baire permet d'affirmer que l'ensemble des fonctions nulle part dérivables est dense dans l'ensemble des fonctions continues. Nous étudierons également la régularité ponctuelle des fonctions de Weierstrass en introduisant la notion d'exposant de Hölder. [less ▲]

Detailed reference viewed: 16 (4 ULg)
Full Text
Peer Reviewed
See detailTime series of high-resolution spectra of SN 2014J observed with the TIGRE telescope
Jack, D.; Mittag, M.; Schröder, K.-P. et al

in Monthly Notices of the Royal Astronomical Society (2015), 451

We present a time series of high-resolution spectra of the Type Ia supernova 2014J, which exploded in the nearby galaxy M82. The spectra were obtained with the HEROS échelle spectrograph installed at the ... [more ▼]

We present a time series of high-resolution spectra of the Type Ia supernova 2014J, which exploded in the nearby galaxy M82. The spectra were obtained with the HEROS échelle spectrograph installed at the 1.2-m TIGRE telescope. We present a series of 33 spectra with a resolution of R ≈ 20 000, which covers the important bright phases in the evolution of SN 2014J during the period from 2014 January 24 to April 1. The spectral evolution of SN 2014J is derived empirically. The expansion velocities of the Si II P-Cygni features were measured and show the expected decreasing behaviour, beginning with a high velocity of 14 000 km s[SUP]-1[/SUP] on January 24. The Ca II infrared triplet feature shows a high-velocity component with expansion velocities of >20 000 km s[SUP]-1[/SUP] during the early evolution apart from the normal component showing similar velocities as Si II. Further broad P-Cygni profiles are exhibited by the principal lines of Ca II, Mg II and Fe II. The TIGRE SN 2014J spectra also resolve several very sharp Na I D doublet absorption components. Our analysis suggests interesting substructures in the interstellar medium of the host galaxy M82, as well as in our Milky Way, confirming other work on this SN. We were able to identify the interstellar absorption of M82 in the lines of Ca II H & K at 3933 and 3968 Å as well as K I at 7664 and 7698 Å. Furthermore, we confirm several diffuse interstellar bands, at wavelengths of 6196, 6283, 6376, 6379and 6613 Å and give their measured equivalent widths. [less ▲]

Detailed reference viewed: 15 (0 ULg)
Full Text
Peer Reviewed
See detailSystematic analysis of site-specific yield distributions resulting from nitrogen management and climatic variability interactions
Dumont, Benjamin ULg; Basso, Bruno; Leemans, Vincent ULg et al

in Precision Agriculture (2015), 16(4), 361-384

At the plot level, crop simulation models such as STICS have the potential to evaluate risk associated with management practices. In nitrogen (N) management, however, the decision-making process is ... [more ▼]

At the plot level, crop simulation models such as STICS have the potential to evaluate risk associated with management practices. In nitrogen (N) management, however, the decision-making process is complex because the decision has to be taken without any knowledge of future weather conditions. The objective of this paper is to present a general methodology for assessing yield variability linked to climatic uncertainty and variable N rate strategies. The STICS model was coupled with the LARS-Weather Generator. The Pearson system and coefficients were used to characterise the shape of yield distribution. Alternatives to classical statistical tests were proposed for assessing the normality of distributions and conducting comparisons (namely, the Jarque-Bera and Wilcoxon tests, respectively). Finally, the focus was put on the probability risk assessment, which remains a key point within the decision process. The simulation results showed that, based on current N application practice among Belgian farmers (60 60 60 kgN ha-1), yield distribution was very highly significantly non normal, with the highest degree of asymmetry characterised by a skewness value of -1.02. They showed that this strategy gave the greatest probability (60%) of achieving yields that were superior to the mean (10.5 t ha-1) of the distribution. [less ▲]

Detailed reference viewed: 48 (18 ULg)
Full Text
Peer Reviewed
See detailLayman versus Professional Musician: Who Makes the Better Judge?
Larrouy, Pauline ULg; Magis, David ULg; Grabenhorst, Matthias et al

in PLoS ONE (2015)

The increasing number of casting shows and talent contests in the media over the past years suggests a public interest in rating the quality of vocal performances. In many of these formats, laymen ... [more ▼]

The increasing number of casting shows and talent contests in the media over the past years suggests a public interest in rating the quality of vocal performances. In many of these formats, laymen alongside music experts act as judges. Whereas experts' judgments are considered objective and reliable when it comes to evaluating singing voice, little is known about laymen’s ability to evaluate peers. On the one hand, layman listeners–who by definition did not have any formal training or regular musical practice–are known to have internalized the musical rules on which singing accuracy is based. On the other hand, lay- man listeners’ judgment of their own vocal skills is highly inaccurate. Also, when compared with that of music experts, their level of competence in pitch perception has proven limited. The present study investigates laypersons' ability to objectively evaluate melodies per- formed by untrained singers. For this purpose, laymen listeners were asked to judge sung melodies. The results were compared with those of music experts who had performed the same task in a previous study. Interestingly, the findings show a high objectivity and reliabil- ity in layman listeners. Whereas both the laymen's and experts' definition of pitch accuracy overlap, differences regarding the musical criteria employed in the rating task were evident. The findings suggest that the effect of expertise is circumscribed and limited and supports the view that laypersons make trustworthy judges when evaluating the pitch accuracy of untrained singers. [less ▲]

Detailed reference viewed: 14 (0 ULg)
Full Text
See detailOpérations militaires : entre prise de risque, solidarité, souveraineté et "entrée en premier"
Dumoulin, André ULg

in Sécurité & Stratégie (2015), (201),

Detailed reference viewed: 18 (0 ULg)
Full Text
Peer Reviewed
See detailShort-term responses of glass eels transported from UK to small Belgian streams
Ovidio, Michaël ULg; Tarrago-Bes, Frédérique; Nzau Matondo, Billy ULg

in Annales de Limnologie = International Journal of Limnology (2015), 51(3), 219-226

Restocking of inland waters with glass eels is one of the recovery options to prevent the decline of European eel Anguilla anguilla (L.) populations. We studied the growth, dispersion, density and habitat ... [more ▼]

Restocking of inland waters with glass eels is one of the recovery options to prevent the decline of European eel Anguilla anguilla (L.) populations. We studied the growth, dispersion, density and habitat preferences in the imported glass eels from United-Kingdom and stocked in three typologically different small Belgian streams, using electrofishing surveys around the single release point, 1 year following stocking. Our results clearly support that the recaptured individuals stocked in our streams farther from the sea, survived, grew, dispersed upstream and downstream. Elvers exploited the complete transversal section of stream, with preference for the sheltered microhabitats near the banks with slower water velocity and low depth. Length-weight relationship was different between streams in terms of allometric coefficient (b). We assume that microhabitats and food availabilities lead to contrasted results in terms of growth and absolute occurrence. Restocking of glass eels in small middle-land streams was found to be an interesting and unconventional option that requires adequate stream and habitat selection. [less ▲]

Detailed reference viewed: 42 (6 ULg)
Full Text
See detailReduced Order Modeling Techniques in Experimental Dynamic Substructuring
Roettgen, Dan; Dossogne, Tilàn ULg; Seeger, Benjamin et al

Poster (2015, August)

Detailed reference viewed: 17 (1 ULg)
Full Text
Peer Reviewed
See detailBifurcation Analysis of a Spacecraft Structure Using the Harmonic Balance Method
Detroux, Thibaut ULg; Renson, Ludovic ULg; Masset, Luc ULg et al

in Proceedings of the ASME 2015 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE 2015) (2015, August)

The harmonic balance (HB) method has been widely used in the past few years, as a numerical tool for the study of nonlinear models. However, in its classical formulation the HB method is limited to the ... [more ▼]

The harmonic balance (HB) method has been widely used in the past few years, as a numerical tool for the study of nonlinear models. However, in its classical formulation the HB method is limited to the approximation of periodic solutions. The present paper proposes to extend the method to the detection and tracking of bifurcations in the codimension-2 system parameters space. To validate the methodology, the forced response of a real spacecraft is examined. The paper first provides some numerical evidence of the presence of quasiperiodic oscillations and isolated solutions. It then demonstrates how the tracking of Neimark-Sacker and fold bifurcations can help get a deeper understanding of these attractors. [less ▲]

Detailed reference viewed: 15 (2 ULg)
Full Text
See detailGouvy Jazz & Blues Festival Août 2015
Sacré, Robert ULg

E-print/Working paper (2015)

Compte rendu du festival BLUES avec photos

Detailed reference viewed: 27 (0 ULg)
Full Text
Peer Reviewed
See detailLe Parc National Sahamalaza - Iles Radama serait-il l’ultime refuge pour certaines espèces de lémuriens du nord-ouest de Madagascar ?
Wilmet, Leslie ULg; Beudels-Jamar, Roseline C.; Schwitzer, Christoph et al

in Tropicultura (2015)

Depuis des millions d’années, la faune et la flore terrestre de Madagascar ont évolué dans un espace isolé. Suite à cette situation, le niveau d’endémisme y est très élevé et l’ensemble de l’île ... [more ▼]

Depuis des millions d’années, la faune et la flore terrestre de Madagascar ont évolué dans un espace isolé. Suite à cette situation, le niveau d’endémisme y est très élevé et l’ensemble de l’île représente un des plus importants hotspot de biodiversité. Madagascar fait aussi partie des pays les plus touchés en termes de destruction des habitats naturels ; 90 % de la végétation d’origine est aujourd’hui perdue. La déforestation et la fragmentation des habitats forestiers menace particulièrement les primates de l’île, les lémuriens. L’île est considérée par de nombreuses organisations internationales comme une priorité pour la conservation de la nature, autant dans le domaine zoologique que botanique. Les premières aires protégées de Madagascar ont été établies en 1927 et l’île en compte aujourd’hui 47. Cet article reprend l’historique et fait l’état des lieux du parc national Sahamalaza-Ile Radama, situé au nord-ouest de Madagascar. Nous nous intéressons spécifiquement à deux espèces de lémuriens emblématiques du parc ; Eulemur flavifrons et Lepilemur sahamalazensis ainsi qu’aux menaces qui pèsent sur leur écosystème. Différentes mesures ont été proposées dans le cadre d’un Plan d’Action de Conservation afin d’en améliorer la gestion et assurer la survie de ces espèces. [less ▲]

Detailed reference viewed: 16 (0 ULg)
Full Text
See detailAtmospheric circulation changes identified thanks to ground-based FTIR monitoring of hydrogen chloride (HCl)
Mahieu, Emmanuel ULg; Chipperfield, Martyn. P.; Notholt, Justus et al

Article for general public (2015)

Detailed reference viewed: 9 (3 ULg)
Full Text
Peer Reviewed
See detailA study of composite laminates failure using an anisotropic gradient-enhanced damage mean-field homogenization model
Wu, Ling ULg; Sket, Federico; Molina-Aldareguia, Jon M et al

in Composite Structures (2015), 126

The failure of carbon fiber reinforced epoxy laminates is studied using an anisotropic gradient-enhanced continuum damage model embedded in a mean-field homogenization scheme. In each ply, a homogenized ... [more ▼]

The failure of carbon fiber reinforced epoxy laminates is studied using an anisotropic gradient-enhanced continuum damage model embedded in a mean-field homogenization scheme. In each ply, a homogenized material law is used to capture the intra-laminar failure. The anisotropy of the homogenized material model results from the homogenization method and from the reformulation of the non-local continuum damage theory to account for the material anisotropy. As a result the damage propagation direction in each ply is predicted with accuracy as compared to the experimental results, while the problems of losing uniqueness and strain localization, which occur in classical finite element simulations when strain softening of materials is involved, can be avoided. To model the delamination process, the hybrid discontinuous Galerkin/extrinsic cohesive law method is introduced at the ply interfaces. This hybrid method avoids the need to propagate topological changes in the mesh with the propagation of the delamination while it preserves the consistency and stability in the un-cracked interfaces. As a demonstration, open-hole coupons with different stacking sequences are studied numerically and experimentally. Both the intra- and inter-laminar failure patterns are shown to be well captured by the computational framework. [less ▲]

Detailed reference viewed: 92 (29 ULg)
Full Text
Peer Reviewed
See detailOptimization of composite structures with curved fiber trajectories
Lemaire, Etienne; Zein, Samih; Bruyneel, Michaël ULg

in Composite Structures (2015), 131

Detailed reference viewed: 17 (0 ULg)
Full Text
See detailGeophysical Investigation of the Pb-Zn deposit of Plombières, Belgium
Evrard, Maxime ULg; Pirard, Eric ULg; Nguyen, Frédéric ULg

in André-mayer, anne-Sylvie; Cathelineau, Michel; Muchez, Philippe (Eds.) et al Mineral resources in a sustainable worl, proceeding, volume 5 (2015, August)

Full Text
See detailMeeting farmers who sowed wildflower strips - The survey methodology
Méhu, Marie; Hatt, Séverin ULg; Brédart, David ULg et al

Scientific conference (2015, July 31)

Detailed reference viewed: 19 (2 ULg)