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See detailMars Topography Investigated Through the Wavelet Leaders Method: a Multidimensional Study of its Fractal Structure
Deliège, Adrien ULg; Kleyntssens, Thomas ULg; Nicolay, Samuel ULg

in Planetary and Space Science (2017), 136C

This work examines the scaling properties of Mars topography through a wavelet-based formalism. We conduct exhaustive one-dimensional (both longitudinal and latitudinal) and two-dimensional studies based ... [more ▼]

This work examines the scaling properties of Mars topography through a wavelet-based formalism. We conduct exhaustive one-dimensional (both longitudinal and latitudinal) and two-dimensional studies based on Mars Orbiter Laser Altimeter (MOLA) data using the multifractal formalism called Wavelet Leaders Method (WLM). This approach shows that a scale break occurs at approximately 15 km, giving two scaling regimes in both 1D and 2D cases. At small scales, these topographic profiles mostly display a monofractal behavior while a switch to multifractality is observed in several areas at larger scales. The scaling exponents extracted from this framework tend to be greater at small scales. In the 1D context, these observations are in agreement with previous works and thus suggest that the WLM is well-suited for examining scaling properties of topographic fields. Moreover, the 2D analysis is the first such complete study to our knowledge. It gives both a local and global insight on the scaling regimes of the surface of Mars and allows to exhibit the link between the scaling exponents and several famous features of the Martian topography. These results may be used as a solid basis for further investigations of the scaling laws of the Red planet and show that the WLM could be used to perform systematic analyses of the surface roughness of other celestial bodies. [less ▲]

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See detailStagnation of Saturn's auroral emission at noon
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2017)

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See detailApplication of a 3D unsteady surface panel method with flow separation model to horizontal axis wind turbines
Prasad, Chandra Shekhar; Dimitriadis, Grigorios ULg

in Journal of Wind Engineering & Industrial Aerodynamics (2017), 166

This work describes the development and application of a 3D unsteady surface panel method with a separation model to the problem of simulating the flow around the blades of a horizontal axis wind turbine ... [more ▼]

This work describes the development and application of a 3D unsteady surface panel method with a separation model to the problem of simulating the flow around the blades of a horizontal axis wind turbine. The present method is intended as a design tool to capture the 3D time-dependent characteristics of both attached and separated flow conditions and is an extension of previous 2D approaches. Flow separation is modelled using a loose coupling procedure between the inviscid panel method and a quasi-3D viscous boundary layer solution. A separated wake is shed at the predicted separation points and propagated at the local flow velocity, just like the trailing edge wake. The methodology is demonstrated on the NREL phase-VI wind turbine test case and the model predictions are compared to experimental measurements. [less ▲]

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See detailCan regional blocs (still) talk with each other? The Euro-Mercosur relationship
Santander, Sébastian ULg

in World Affairs (2016), 2/33 (459)

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See detailA poetic of parody
Saint-Amand, Denis ULg

Scientific conference (2016, November 25)

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See detailShear banding simulation in clay rock around an underground opening, and its contact mechanism with the gallery’s lining
Charlier, Robert ULg; Salehnia, Fatemeh ULg

in Proc. 5th International conference on geotechnical engineering and soil mechanics (2016, November 15)

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See detailSpeech style manipulations in dysarthria in French-speaking children: Acoustic findings.
Ancelle, Josephine; Moya Gale, G.; Hetrick, B et al

Poster (2016, November)

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See detailMeasurements of reference ISO nozzles by high-speed imaging
De Cock, Nicolas ULg; Massinon, Mathieu ULg; Nuyttens, David et al

in Crop Protection (2016), 89

Agricultural spray characteristics determine the efficiency of a pesticide application because size and velocity affect droplet trajectory and impact behavior. At present, the relevance of different ... [more ▼]

Agricultural spray characteristics determine the efficiency of a pesticide application because size and velocity affect droplet trajectory and impact behavior. At present, the relevance of different characterization techniques remains controversial since discrepancies may be significant between measurements performed in different laboratories. A digital image acquisition technique and analysis algorithm is proposed for droplet size and velocimetry measurements as an alternative to well-established techniques such as the Phase Doppler Particle Analyzer (PDPA) or laser diffraction spectrometry (LDS). The algorithm requires double exposed shadow images acquired in a back-lighted arrangement with a Particle Image Velocimetry (PIV) camera and a pulsed light emitting diode (LED). Spatial illumination heterogeneities are corrected by subtracting from each image a mean background acquired on several images without any particle. The algorithm accuracy is ensured by the rejection of out-of-focus particles using a focus parameter depending on gradient intensity at the particle edges. Thresholds for focus particle selection were determined by studying the evolution of the focus parameter and the error on particle size measurements from images containing droplets with uniform size at various distance of the object plane. Selected droplets were identified on both pairs of images to determine their size and velocity. Droplet size distributions were corrected to account for the uneven sampling probability caused by the volumetric method. Droplet size distributions of a set of reference nozzle/pressure combinations defined in the ISO/DIS 25358 were measured. The image technique was able to distinguish each of the reference sprays well. Comparison with PDPA measurements showed that the imaging technique tends to measure an equivalent Dv50, a lower Dv10 and a higher Dv90 leading therefore to a higher relative span factor. Velocity measurements showed good agreement between both techniques except for one nozzle/pressure combination. [less ▲]

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See detailLa médiation, un "quasi-concept"
Servais, Christine ULg

in Servais, Christine (Ed.) La médiation. Théorie et terrains (2016)

Il s'agit d'une présentation des problématiques qui traversent l'ouvrage à partir du constat d'un écart entre l'approche théorique de la médiation et son approche par les pratiques.

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See detailBounding surface plasticity model for natural clays
Ahayan, Sanae ULg; Yin, Zhen-Yu; Kotronis, Panagiotis et al

Conference (2016, October 26)

Natural soft clay exhibits a considerable degree of anisotropy as a result of its past sedimentation and consolidation history. It also tends to have significant inter-particle bonding, which affects its ... [more ▼]

Natural soft clay exhibits a considerable degree of anisotropy as a result of its past sedimentation and consolidation history. It also tends to have significant inter-particle bonding, which affects its mechanical behavior. The natural structure of in-situ soils makes their behavior different from that of a reconstituted material. In fact, most clays lose a proportion of their strength when remoulded. Various authors proposed anisotropic elastoplastic soil models allowing the yield surface to rotate with the stress history. These models have a “rotational hardening law" which relates the change of the inclination of the yield surface to the current soil state and to the increments of the plastic volumetric and/or shear strain, [Sekiguchi and Otha (1977)], [Hashiguchi and Chen (1998)], [Wheeller et al (2003)]… Other authors combine the plastic anisotropy with destructuration effects observed in soft sensitive soils by assuming that the size and /or the position of the center of the yield surface depends on the amount of the structural soil degradation. These models use an additional isotropic hardening law that relates the size and/or the position of the yield surface of the intact sample to that of the reconstituted one [Nova et al (2003)]. The previous models provide little or no flexibility when it comes to describe the change of the plastic modulus with the loading direction as they are unable to produce a smooth degradation of the stiffness, being single yield surface models. A way to improve this behavior is to introduce the “bounding surface plasticity” theory, initially developed by Dafalias [Dafalias and Herrmann 1986]. Unlike a single yield surface model, the bounding surface theory allows a smooth transition of stresses within and on the bounding surface. The mean feature of this concept is that the actual stress is mapped to the imaginary stress on the bounding surface. The distance between the real and imaginary stress, which is called the “ function distance ”, is used to specify the plastic modulus. This work presents a bounding surface plasticity model for natural and structured clays based on the critical state theory. A novel rotational hardening rule for clays is presented, and a hardening function distance is introduced to describe the evolution of the bounding surface. Validation of the model is provided by drained and undrained tests of Scottish and Finnish intact and reconstituted clays [Kastunnen 2008]. Finally, finite element simulations of a foundation considering the formulated constitutive law are presented. [less ▲]

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See detailFolie et Corps chez Hegel
Rizzo, Rémy ULg

Conference (2016, October 24)

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See detailA Stochastic Multi-Scale Approach for the Modeling of Thermo-Elastic Damping in Micro-Resonators
Wu, Ling ULg; Lucas, Vincent ULg; Nguyen, Van Dung ULg et al

in Computer Methods in Applied Mechanics & Engineering (2016), 310

The aim of this work is to study the thermo-elastic quality factor (Q) of micro-resonators with a stochastic multi-scale approach. In the design of high-Q micro-resonators, thermo-elastic damping is one ... [more ▼]

The aim of this work is to study the thermo-elastic quality factor (Q) of micro-resonators with a stochastic multi-scale approach. In the design of high-Q micro-resonators, thermo-elastic damping is one of the major dissipation mechanisms, which may have detrimental effects on the quality factor, and has to be predicted accurately. Since material uncertainties are inherent to and unavoidable in micro-electromechanical systems (MEMS), the effects of those variations have to be considered in the modeling in order to ensure the required MEMS performance. To this end, a coupled thermo-mechanical stochastic multi-scale approach is developed in this paper. Thermo-mechanical micro-models of polycrystalline materials are used to represent micro-structure realizations. A computational homogenization procedure is then applied on these statistical volume elements to obtain the stochastic characterizations of the elasticity tensor, thermal expansion, and conductivity tensors at the meso-scale. Spatially correlated meso-scale random fields can thus be generated to represent the stochastic behavior of the homogenized material properties. Finally, the distribution of the thermo-elastic quality factor of MEMS resonators is studied through a stochastic finite element method using as input the generated stochastic random field. [less ▲]

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See detailUsing PCB signatures and enantiomer fractions for source identification and to age date exposure
Megson, D; Focant, Jean-François ULg; Patterson, D et al

Conference (2016, October)

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See detailLa viande des uns, la faune des autres. Analyse anthropologique de la conservation de la faune dans trois villages Badjoué de la zone forestière de l'Est-Cameroun
Dieudonné, Mélodie ULg

Doctoral thesis (2016)

The Cameroonian forestry and environmental policies adopted in 1994 come within the scope of a will to manage forests sustainably and to involve local populations in the management of their environment ... [more ▼]

The Cameroonian forestry and environmental policies adopted in 1994 come within the scope of a will to manage forests sustainably and to involve local populations in the management of their environment. The aim of this doctoral thesis is to take an anthropological look at the wildlife conservation at the “microsociological” level of three Badjoué villages from the East region while putting these observations in the larger context of Cameroonian forest governance. In what way are wildlife community management measures appropriated, transformed and distorted by the actors? How do interactions between local populations and conservation organizations help transform local contexts and relations to wildlife? By applying an approach at the crossroads of the anthropology of conservation, the anthropology of development and an anthropology of nature which considers human-animal relations in an interactive and dynamic perspective, this thesis aims at paying a particular attention to the relations that the Badjoué of the Dja entertain with their environment, the intertwining of these relations in the local social, economic and political dynamics as well as to the evolution of these problems in the context of the community management of forest resources in Cameroon. The thesis so allows a reflection on the place of participation and local community autonomy in the management of natural resources and a questioning of the impact of coercive models on the environmental practices and conceptions. It finally raises the question of the intertwining between global environmental issues and the necessary consideration of peoples’ right to self-determination. [less ▲]

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See detailMécanismes moléculaires associés à l’induction de la pathogénicité chez Streptomyces scabies
Jourdan, Samuel ULg

Doctoral thesis (2016)

Streptomyces are filamentous soil-dwelling bacteria that actively participate in the mineralization of dead organic matter. Members of this bacterial genus are commonly known for the plethora of secondary ... [more ▼]

Streptomyces are filamentous soil-dwelling bacteria that actively participate in the mineralization of dead organic matter. Members of this bacterial genus are commonly known for the plethora of secondary metabolites of interest they secrete. Predominantly saprophytes, some Streptomyces species have been proved to be phytopathogenic. The most widespread and best characterized of these species is Streptomyces scabies which is the causative agent of the common scab disease that affects the underground organs of many plants with a preference for storage organs such as potato tubers or pivot roots (beet, turnip, carrot, etc.). Common scab is characterized by brown and corky lesions on the infected organs and causes significant economic losses around the world. The pathogenicity of S. scabies is directly related to its ability to produce the phytotoxin thaxtomin. Unveiling when, how and why S. scabies triggers the production of its phytotoxin is therefore of major interest to understand phytopathogenicity and the virulence associated with this bacteria. Previous works identified cellobiose as the main elicitor of thaxtomin production. However, no signaling pathway from the sensing of the eliciting signal to the biosynthesis of thaxtomin has been proposed so far. The aim of this work is to elucidate the molecular mechanisms involved in the onset of thaxtomin production in the model species S. scabies. In this work we highlighted the central role of the cellulose utilization transcriptional repressor CebR in S. scabies pathogenicity. Indeed, we showed that this regulator directly controls the expression of thaxtomin biosynthesis genes, but also the expression of genes involved in sensing, transport and catabolism of cellooligosaccharides. Together, our results allow to propose a first signaling pathway from cellooligosaccharide transport to the production of thaxtomin in S. scabies, with each step of the cascade controlled by CebR. The results obtained in the course of this thesis extended well beyond the fundamental research scope of elucidating the mechanisms associated with the onset of virulence of S. scabies. Indeed, assessed if/how our findings could propose solutions to current industrial biotechnology iapplications, i.e. i) to provide a mutant that constitutively produce thaxtomine could improve the production yields of this promising bioherbicide, and ii) to assess the enzymatic characteristics of a Beta-glucosidase of S. scabies as possible candidate in lignocellulose saccharification processes. [less ▲]

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See detailHydrodynamics and bed stability at smooth-to-rough transitions. Experiments based on acoustic flow measurements
Duma, Diana ULg

Doctoral thesis (2016)

As reflected in the scale of large contemporary hydropower schemes, flowing water may carry huge amounts of energy. If not mastered properly, this energy may cause impressive channel erosion and local ... [more ▼]

As reflected in the scale of large contemporary hydropower schemes, flowing water may carry huge amounts of energy. If not mastered properly, this energy may cause impressive channel erosion and local scour. Therefore, one lasting concern in hydraulic engineering has been the stability of structures, riverbeds and riverbanks against flow erosion. Two main limitations of current understanding of riverbed and riverbank stability are highlighted: the first one is directly linked to the evaluation of the flow action, while the second one relates to the conceptual framework in which stone stability is evaluated. Since the standard approaches use the mean bed shear stress to quantify the flow forces, they may only apply under uniform flow conditions, for which the ratio of turbulence intensity to the bed shear stress remains almost constant and the influence of turbulence is therefore implicitly incorporated. For non-uniform flow, correction factors have been conventionally applied to account for the turbulence fluctuations; but this approach does not reproduce the physical influence of turbulence higher in the water column and can only be used as a rule of thumb. A new approach was initiated recently in literature. Instead of using the standard Shields parameter, it quantifies the flow forces by means of a new set of parameters which combine explicitly the velocity and turbulence distributions over a certain water depth above the riverbed, while remaining reasonably accessible for engineering applications. Next, this quantity is related to a mobility parameter, which describes the bed damage. This new approach requires additional high quality experimental data to confirm its validity for a wider range of non-uniform flow. In this research, the focus was set on a single canonical configuration, namely a smooth-to-rough transition. We take a preventive perspective by focusing on the flow and bed stability conditions before a scour hole starts to develop and we are interested in characterising the flow conditions to ensure bed stability, i.e. prevent the dislodging of bed material downstream of the structure. As a second specific objective of the thesis, we aimed at evaluating the feasibility of using acoustic techniques to properly estimate the new bed stability parameters proposed in literature in the last decade and draw conclusions on stone mobility at smooth-to-rough transitions. The experimental tests were conducted in two laboratory flumes, a horizontal bottom flume (6 m long and 15 cm wide) and a tilting flume (up to 4% slope, 20 m long and 50 cm wide), in which we measured the flow velocity at a 100 Hz frequency, using two different acoustic instruments: an Ultrasound Velocity Profiler (UVP) and a 3D Acoustic Doppler Velocity Profiler (ADVP). The measurements were done immediately downstream of the transition from smooth-to-rough. Two types of tests were undertaken. In the first type, the stones were glued with silicone on the flume bottom and velocity measurements were performed without stone motion. This enables measurements of the flow characteristics both below and above the threshold for inception of sediment motion, without perturbations induced by stone displacements. In the second type, the stones in the measurement area were laid on the bottom of the flume (i.e. not glued) and the number of entrained stones was recorded. The tests were conducted by varying (i) the grain size of the bed material (8 mm, 15 mm and 30 mm), (ii) the flow velocity (between 0.74 m/s and 1.16 m/s), (iii) the sediments density (1410 kg/m³, 1690 kg/m³ and 2650 kg/m³) and (iv) the configuration (quasi-uniform vs. smooth-to-rough transition). Indeed, for the purpose of comparison, a uniform rough bed (quasi-uniform configuration) was considered also, by replacing the smooth part of the bed with similar sediments as in the measurement area. After a specific signal processing, flow variables were derived from the measurements and were next exploited to evaluate several bed stability parameters, with the aim of correlating them with bed damage data obtained from dedicated experiments. The results showed no correlation between the bed damage and the bed shear stress or between the bed damage and flow turbulent kinetic energy. In contrast, when the flow action is described by both mean velocity and turbulence characteristics, a relative good correlation with the bed damage was observed. Nonetheless, these correlations appear only per subset of points corresponding to the same grain size and/or same material density or flume geometry. With a total of 45 hydraulic configurations for which the flow characteristics were measured and 66 (times four repetitions) tests in which the bed damage was observed, the present research ends up with a unique dataset, which may prove useful in various research such as for the validation of 2D-vertical and 3D turbulent flow and morphodynamic simulations. Another key outcome of the present doctoral research is a systematic comparison between measurements conducted with the UVP and the ADVP. The ADVP is deemed generally more accurate and reliable. Nonetheless, both instruments remain somehow complementary. We showed that, under certain conditions, the considered instruments have the potential to contribute to the assessment of bed stability in the considered configurations. [less ▲]

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See detailWhat’s with the hyphens? A social studies perspective on science-technology-society
Van Oudheusden, Michiel ULg

Scientific conference (2016, September 13)

This presentation highlights the roles social scientists (notably in the field of science and technology studies) can/should play in nuclear research and development. Three cases are briefly described and ... [more ▼]

This presentation highlights the roles social scientists (notably in the field of science and technology studies) can/should play in nuclear research and development. Three cases are briefly described and assessed: citizen science after Fukushima, incident reporting at the Belgian Nuclear Research Centre SCK-CEN, and the "microbiologization" of radioactive waste management. [less ▲]

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