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See detailCooperative spontaneous emission with quantized atomic motion
Damanet, François ULg

Doctoral thesis (2016)

In this thesis, we present investigations on the cooperative dynamics of (ultra)cold atoms coupled to the electromagnetic field in vacuum. The main objective is to identify the consequences of the ... [more ▼]

In this thesis, we present investigations on the cooperative dynamics of (ultra)cold atoms coupled to the electromagnetic field in vacuum. The main objective is to identify the consequences of the quantization of the atomic center-of-mass motion on the atoms-field dynamics, more particularly the atomic \emph{internal} dynamics including dipole-dipole interactions and cooperative spontaneous emission processes. For this purpose, we derive a Markovian master equation for the internal state of a collection of two-level atoms coupled to vacuum accounting for all effects related to the quantization of their motion. These effects depend on three characteristic lengths that can be tuned experimentally: the interatomic distance $r$, the wavelength $\lambda$ of the emitted radiation, and the typical size $\ell$ of the atomic wave packets. This leads to a rich panel of phenomena depending on the hierarchy between these characteristic lengths. Our master equation provides a unifying picture of the consequences of recoil and quantum statistics (bosonic or fermionic) on both the internal dissipative and conservative dynamics, and applies equally well to distinguishable and indistinguishable atoms. It is valid even beyond the Lamb-Dicke regime, i.e.\ for large recoil effects. We give general expressions for the decay rates and the dipole-dipole shifts entering the master equation for arbitrary motional states, and we find closed-form formulas for a number of relevant states (Gaussian states, harmonic oscillator eigenstates, Bose-Einstein condensates motional states). In particular, we show they can be strongly influenced by the motional state of the atoms, which suggests the possibility to quantum program their internal dynamics through motional state engineering. Based on the derived master equation, we investigate in full detail the super- and subradiance phenomena arising from a collection of indistinguishable atoms. Due to the symmetry (for bosons) or antisymmetry (for fermions) of the global state under exchange of atoms, the internal dynamics is restricted to the permutation invariant subspace whose dimension grows as $N^2$ with $N$ the number of atoms. In this particular case, the master equation involves only three rates: a single-atom decay rate $\gamma_0$, a cooperative decay rate $\gamma$ and a collective dipole-dipole shift $\Delta_\mathrm{dd}$. We solve the dynamics exactly for $2$ atoms, numerically for up to $30$ atoms, and obtain the large-$N$ limit by a mean-field approach. We show that a superradiant enhancement of the radiated intensity is always observed for a sufficiently large number of atoms. As regards subradiance, we show that exact decoherence free subspaces that protect against spontaneous emission through destructive interference of individual spontaneous emission amplitudes exist only in the limit of classically localized atoms, i.e.\ for atoms in infinitely steep traps. We assess the validity of our master equation in the optical domain through the study of the exact atoms-field dynamics. Among others, this complementary approach gives access to the vibrational state populations of the atoms after a photon emission and to the angular dependence of the emission spectrum. It also highlights the complex interplay between the atomic internal and motional states, such as the entanglement transfer that can occur during the collective decay of the atoms. Moreover, it opens the door for the study of the non-Markovianity of the internal dynamics. In conclusion, our thesis provides a comprehensive picture of the consequences of the quantization of the atomic motion on cooperative spontaneous emission processes and contributes to the development of theoretical tools for the study of the internal dynamics of (ultra)cold atoms. [less ▲]

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See detailFrom Silenced Nature to Worldness in American Literature
Lombard, David ULg

Conference (2016, December 02)

As Christopher Manes writes, ‘[n]ature is silent in our culture […] in the sense that the status of being a speaking subject is jealously guarded as an exclusively human prerogative’ (Manes, 1996 ... [more ▼]

As Christopher Manes writes, ‘[n]ature is silent in our culture […] in the sense that the status of being a speaking subject is jealously guarded as an exclusively human prerogative’ (Manes, 1996). According to this view, nature is less silent than silenced, the difference lying in a refusal to have a relationship with the natural world because of the lack of adequate language to describe our relationship with our natural environment. Human faculties promoted by the Enlightenment have led humans to believe that our language ‘ha[s] no analogues in the natural world’. I will show that American authors such as Henry David Thoreau, John Muir, Aldo Leopold or Edward Abbey accounted for a multi-sensorial experience of nature that betrays an attempt to find a form of language that would relate humans to natural elements. Although nature does not ‘speak’, I will argue that humans were provided with their sensory perception that allows them to appreciate worldness and to develop a harmonious relationship with the rest of the world. I will also stress that our alienation from the natural world is as much a cultural problem as it is a consequence of Western consumer capitalism and supermodernity, as suggested, for example, in Don DeLillo’s White Noise (1985). Adopting an ecocritical approach, I will examine the ways in which we tend to perceive worldness as silent and how literary texts may revive worldness and world as essential concepts in the study of the relationship between literature and our physical environment. [less ▲]

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See detailInfectious disease of the eye: how to improve the microbiological diagnosis?
DESCY, Julie ULg

Conference given outside the academic context (2016)

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See detailSchizophrénie et hyperconscience : Une étude en première personne
Englebert, Jérôme ULg; Valentiny, Caroline

Conference (2016, December 02)

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See detailDevelopment and analysis of low-order models of frame structures under blast loads
Hamra, Lotfi ULg

Doctoral thesis (2016)

The main aim of this thesis is to propose an easy-to-apply tool to assess the level of damage of a structure in which one compartment is subjected to blast loading. This compartment is extracted from the ... [more ▼]

The main aim of this thesis is to propose an easy-to-apply tool to assess the level of damage of a structure in which one compartment is subjected to blast loading. This compartment is extracted from the structure accounting for the interaction with the part of the structure surrounding the loaded compartment, which is assumed to be elastic. Before studying the whole frame structure, the structural elements (i.e. the beam and its adjacent columns) are firstly studied separately taking into account the lateral restraint and mass offered by the indirectly affected part (IAP) of the structure. Secondly, the dynamic behaviour of a simple compartment made of pinned members and laterally braced is investigated. The material laws are assumed to be elastic-perfectly plastic, neglecting the effect of strain rate on the yield strength. The out-of-plane instabilities of the structural members are disregarded. • To explain the context of this study + final aim of this research Two analytical models are developed to predict the dynamic response of the frame beam subjected to blast loading, including the elastic lateral restraint and inertia offered by the IAP of the structure, the development of nonlinear membrane action (P-\delta effect) and also, the interaction between bending moment and axial force in the plastic hinges. The first model is based on a single degree of freedom (SDOF model) which is the transverse mid-span deflection of the beam while the second model is a two-degree-of-freedom (2-DOF) model which also includes the axial elongation of the beam. The accuracy of these two low-order models is assessed with finite element simulations. This validation stage shows that the proposed low-order models capture the physics of the problem in most cases of practical interest. A dimensional analysis of the problem reveals that, under the considered assumptions, four dimensionless parameters mainly influence the required ductility of the beam. Two of them are related to the behavior of the indirectly affected part (the lateral restraint and mass). Another one is related to the mechanical properties of the investigated beam (i.e. the ratio of the bending to axial resistance). The last parameter incorporates scales of the geometry and of the deformed configuration at the onset of the plastic mechanism. Concerning the columns, an analytical model is proposed to assess its dynamic response under constant axial compressive load and lateral blast loading. It accounts for large displacement (P-\delta effect), bending moment-axial force (M-N) plastic interaction as well as its interaction with the indirectly affected part (IAP) of the structure. This model is non-smooth piecewise linear and involves two degrees of freedoms (2 DOFs) in each regime of the motion of the column (related to the possibilities of development of plastic hinges). The dimensional analysis of the problem reveals that, under the considered assumptions, four dimensionless parameters mainly influence the dynamic stability of the beam-column. Two of them are related to the behavior of the indirectly affected part (the lateral restraint and mass). Another one is related to the critical load multiplier (i.e. the ratio of the axial compressive load to Euler elastic buckling resistance). The last parameter is the reduced slenderness of the beam-column. Subsequent to a parametric study, it is demonstrated that a good correlation is found between the results provided by the analytical model and a richer FEM model, despite some little discrepancies observed for some intermediate values of stiffness of the lateral restraint and lateral mass. As a possible improvement, adjustments to the analytical model are suggested. Finally, the dynamic behaviour of a simple frame under constant compressive loads and lateral blast loading is studied with a last 2-DOF analytical model. A multi-layer model of the cross-section of the beam is used to derive the bending moment-axial force (M-N) plastic interaction instead of the Lescouarc'h formula and normality rule. The coupling between the beam and the adjacent columns is ensured through appropriate boundary conditions. For the studied frame, two blast scenarios are contemplated, the first one corresponds to a quasi-static blast loading while the second one refers to a dynamic blast loading. The first case study shows that a very good agreement is achieved between the deflections predicted by the analytical and numerical models although a discrepancy is observed in the assessment of the axial force in the column due to the shape of the inertial force distribution of the beam assumed in the model. The second case study illustrates that, in both analytical and numerical models, the columns are predicted to fail by buckling due to the P-\delta effect although the axial force in the column is again inaccurately captured by the analytical model for the same reason. [less ▲]

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See detailLa nostra «avvelenata» (Guccini non ne ha colpa)
Curreri, Luciano ULg; Belletti, Gabriele

Article for general public (2016)

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See detailLarge neighborhood search for multi-trip vehicle routing
François, Véronique ULg; Arda, Yasemin ULg; Crama, Yves ULg et al

in European Journal of Operational Research (2016), 255(2), 422-441

We consider the multi-trip vehicle routing problem, in which each vehicle can perform several routes during the same working shift to serve a set of customers. The problem arises when customers are close ... [more ▼]

We consider the multi-trip vehicle routing problem, in which each vehicle can perform several routes during the same working shift to serve a set of customers. The problem arises when customers are close to each other or when their demands are large. A common approach consists of solving this problem by combining vehicle routing heuristics with bin packing routines in order to assign routes to vehicles. We compare this approach with a heuristic that makes use of specific operators designed to tackle the routing and the assignment aspects of the problem simultaneously. Two large neighborhood search heuristics are proposed to perform the comparison. We provide insights into the configuration of the proposed algorithms by analyzing the behavior of several of their components. In particular, we question the impact of the roulette wheel mechanism. We also observe that guiding the search with an objective function designed for the multi-trip case is crucial even when exploring the solution space of the vehicle routing problem. We provide several best known solutions for benchmark instances. [less ▲]

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See detailASSURANCE QUALITE et RECHERCHE …
Hubert, Philippe ULg

Scientific conference (2016, December 01)

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See detailL'art de gouverner les déchets hautement radioactifs. Analyse comparée de la Belgique, la France et le Canada
Parotte, Céline ULg

Doctoral thesis (2016)

Comment l'art de gouverner les déchets hautement radioactifs, tel qu'il a évolué au cours des deux dernières décennies, a-t-il redéfini les enjeux sociotechniques du programme de gestion des déchets ... [more ▼]

Comment l'art de gouverner les déchets hautement radioactifs, tel qu'il a évolué au cours des deux dernières décennies, a-t-il redéfini les enjeux sociotechniques du programme de gestion des déchets hautement radioactifs et réciproquement? Telle est la question qui traverse cette thèse. Combinant l'analytique de gouvernement (Dean 2010) à une approche co-productionniste forte (Joly 2015), trois régimes de pratiques de gouvernement, en France, en Belgique et au Canada sont scrutés et comparés. Cet écrit propose de suivre l'objet, en cinq chapitres, depuis sa définition (au travers des systèmes de classification), en passant par l’élaboration, la mise en oeuvre territoriale et l'évaluation régulière de son programme de gestion. Chemin faisant, nous cherchons à comprendre comment le dépôt géologique est resté l’option de référence clef pour la catégorie "déchet hautement radioactif". Différentes co-productions seront mises à jour révélant l'asymétrie de pouvoir entre les acteurs, la trajectoire (dis)continue du programme et le caractère expérimental de l’art de gouverner les déchets hautement radioactifs. Un art expérimental, dont nous soutenons que les formes peuvent varier, entre autres, selon l'attitude des expérimentateurs. [less ▲]

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See detailReplication Errors Made During Oogenesis Lead to Detectable De Novo mtDNA Mutations in Zebrafish Oocytes with a Low mtDNA Copy Number.
Otten, Auke B. C.; Stassen, Alphons P. M.; Adriaens, Michiel et al

in Genetics (2016), 204(4), 1423-1431

Of all pathogenic mitochondrial DNA (mtDNA) mutations in humans, ~25% is de novo, although the occurrence in oocytes has never been directly assessed. We used next generation sequencing to detect point ... [more ▼]

Of all pathogenic mitochondrial DNA (mtDNA) mutations in humans, ~25% is de novo, although the occurrence in oocytes has never been directly assessed. We used next generation sequencing to detect point mutations directly in the mtDNA of 3-15 individual mature oocytes and three somatic tissues from eight zebrafish females. Various statistical and biological filters allowed reliable detection of de novo variants with heteroplasmy >/=1.5%. In total, we detected 38 de novo base substitutions, but no insertions or deletions. These 38 de novo mutations were present in 19 of 103 mature oocytes, indicating that ~20% of the mature oocytes carry at least one de novo mutation with heteroplasmy >/=1.5%. This frequency of de novo mutations is close to that deducted from the reported error rate of polymerase gamma, the mitochondrial replication enzyme, implying that mtDNA replication errors made during oogenesis are a likely explanation. Substantial variation in the mutation prevalence among mature oocytes can be explained by the highly variable mtDNA copy number, since we previously reported that ~20% of the primordial germ cells have a mtDNA copy number of </=73 and would lead to detectable mutation loads. In conclusion, replication errors made during oogenesis are an important source of de novo mtDNA base substitutions and their location and heteroplasmy level determine their significance. [less ▲]

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See detailAspects du bilinguisme à Rome
Rochette, Bruno ULg

Conference (2016, December 01)

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See detailHidden Hunger: Seeking Solutions with Staple Crops
Vanderschuren, Hervé ULg

Scientific conference (2016, December 01)

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See detailKilling it Softly: Girdling as an Efficient Eco-friendly Method to Locally Remove the Invasive Acer negundo
Merceron, Nastasia ULg

in Ecological Restoration (2016), 34(4), 297-305

Acer negundo (boxelder maple) is a North American native tree species that currently invades riparian and disturbed areas in Europe, affecting both bank stability and ecosystem biodiversity. As a response ... [more ▼]

Acer negundo (boxelder maple) is a North American native tree species that currently invades riparian and disturbed areas in Europe, affecting both bank stability and ecosystem biodiversity. As a response to managers’ requests, we aimed at finding an eco-friendly method which would locally remove this species and help habitat restoration. Four control methods were tested on A. negundo adults and saplings from stands located in three experimental sites along different watercourses in Southwestern France: girdling, low cutting, high cutting, and cutting followed by the application of juglone (a natural allelopathic substance from walnut tree leaves). Mortality and resprout production on the treated A. negundo individuals were assessed during two years following the application of the control methods. Girdling was the most efficient method as it significantly induced higher mortality rates compared to the others (65 vs 15% of dead A. negundo two years after treatment administration). When healing emerged on trunks, yearly repeated girdling was required to reach full success. None of the control methods significantly reduced resprout production; not even the application of juglone. Girdling is the most recommended method to kill and remove A. negundo at a local scale in invaded natural habitats. Considering that A. negundo benefits from increases in light availability to outcompete native species, we further recommend removing seedlings from understories when applying girdling on adult and sapling individuals in order to optimize restoration conditions in natural stands and improve native species re-establishment. [less ▲]

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See detailLe profil en fibres alimentaires de légume modifie leur fermentation intestinale et la production d’acides gras à chaine courte dans modèle in vitro humain
Kalala Bolokango, Gaetan ULg; Kambashi Mutiaka, Bienvenu ULg; Njeumen, Patrick et al

Poster (2016, December 01)

La modulation du microbiote intestinal induite par les fibres alimentaires (DF)a des conséquences positives sur la santé, notamment sur l’obésité et ses comorbidités. La nature et l’ampleur des ... [more ▼]

La modulation du microbiote intestinal induite par les fibres alimentaires (DF)a des conséquences positives sur la santé, notamment sur l’obésité et ses comorbidités. La nature et l’ampleur des changements dépendent du type de fibres.Les légumes sont des sources privilégiées de DF, certaines espèces et variétés fournissant davantage de DF solubles (SDF), d’autres étant plus riches en DF insolubles (IDF). Contrairement aux SDF, les IDF sont souvent considérées comme peu fermentescibles, ne contribuant que faiblement à une modulation de l’écophysiologie intestinale. En opposition à cette hypothèse, pour explorer si l’impact potentiel sur la santé intestinale des légumes varie suivant leur nature, des légumes présentant des teneurs et des profils en DF différents ont été comparés dans un modèle in vitro de fermentation colique. [less ▲]

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See detailIn-depth study of 16CygB using inversion techniques
Buldgen, Gaël ULg; Salmon, Sébastien ULg; Reese, D. R. et al

in Astronomy and Astrophysics (2016), 596

Context. The 16Cyg binary system hosts the solar-like Kepler targets with the most stringent observational constraints. Indeed, we benefit from very high quality oscillation spectra, as well as ... [more ▼]

Context. The 16Cyg binary system hosts the solar-like Kepler targets with the most stringent observational constraints. Indeed, we benefit from very high quality oscillation spectra, as well as spectroscopic and interferometric observations. Moreover, this system is particularly interesting since both stars are very similar in mass but the A component is orbited by a red dwarf, whereas the B component is orbited by a Jovian planet and thus could have formed a more complex planetary system. In our previous study, we showed that seismic inversions of integrated quantities could be used to constrain microscopic diffusion in the A component. In this study, we analyse the B component in the light of a more regularised inversion. <BR /> Aims: We wish to analyse independently the B component of the 16Cyg binary system using the inversion of an indicator dedicated to analyse core conditions, denoted t[SUB]u[/SUB]. Using this independent determination, we wish to analyse any differences between both stars due to the potential influence of planetary formation on stellar structure and/or their respective evolution. <BR /> Methods: First, we recall the observational constraints for 16CygB and the method we used to generate reference stellar models of this star. We then describe how we improved the inversion and how this approach could be used for future targets with a sufficient number of observed frequencies. The inversion results were then used to analyse the differences between the A and B components. <BR /> Results: The inversion of the t[SUB]u[/SUB] indicator for 16CygB shows a disagreement with models including microscopic diffusion and sharing the chemical composition previously derived for 16CygA. We show that small changes in chemical composition are insufficient to solve the problem but that extra mixing can account for the differences seen between both stars. We use a parametric approach to analyse the impact of extra mixing in the form of turbulent diffusion on the behaviour of the t[SUB]u[/SUB] values. We conclude on the necessity of further investigations using models with a physically motivated implementation of extra mixing processes including additional constraints to further improve the accuracy with which the fundamental parameters of this system are determined. [less ▲]

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See detailGeneralized Pascal triangles and binomial coefficients of words
Stipulanti, Manon ULg

Poster (2016, December 01)

We introduce a generalization of Pascal triangle based on binomial coefficients of finite words. These coefficients count the number of times a word appears as a subsequence of another finite word ... [more ▼]

We introduce a generalization of Pascal triangle based on binomial coefficients of finite words. These coefficients count the number of times a word appears as a subsequence of another finite word. Similarly to the Sierpinski gasket that can be built as the limit set, for the Hausdorff distance, of a convergent sequence of normalized compact blocks extracted from Pascal triangle modulo 2, we describe and study the first properties of the subset of [0, 1] × [0, 1] associated with this extended Pascal triangle modulo a prime p. From the extended Pascal triangle obtained when p is equal to 2, we derive a sequence of which we study the regularity and the asymptotic behavior of the summatory function. Inspired from this regularity, we extend our results to another famous numeration systems, namely the Zeckendorff numeration system. [less ▲]

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See detailWASP-92b, WASP-93b and WASP-118b: Three new transiting close-in giant planets
Hay, K. L.; Collier-Cameron, A.; Doyle, A. P. et al

in Monthly Notices of the Royal Astronomical Society (2016), 463

We present the discovery of three new transiting giant planets, first detected with the WASP telescopes, and establish their planetary nature with follow up spectroscopy and ground-based photometric ... [more ▼]

We present the discovery of three new transiting giant planets, first detected with the WASP telescopes, and establish their planetary nature with follow up spectroscopy and ground-based photometric lightcurves. WASP-92 is an F7 star, with a moderately inflated planet orbiting with a period of 2.17 days, which has R[SUB]p[/SUB] = 1.461 ± 0.077R[SUB]J[/SUB] and M[SUB]p[/SUB] = 0.805 ± 0.068M[SUB]J[/SUB]. WASP-93b orbits its F4 host star every 2.73 days and has R[SUB]p[/SUB] = 1.597 ± 0.077R[SUB]J[/SUB] and M[SUB]p[/SUB] = 1.47 ± 0.029M[SUB]J[/SUB]. WASP-118b also has a hot host star (F6) and is moderately inflated, where R[SUB]p[/SUB] = 1.440 ± 0.036R[SUB]J[/SUB] and M[SUB]p[/SUB] = 0.514 ± 0.020M[SUB]J[/SUB] and the planet has an orbital period of 4.05 days. They are bright targets (V = 13.18, 10.97 and 11.07 respectively) ideal for further characterisation work, particularly WASP-118b, which is being observed by K2 as part of campaign 8. The WASP-93 system has sufficient angular momentum to be tidally migrating outwards if the system is near spin-orbit alignment, which is divergent from the tidal behaviour of the majority of hot Jupiters discovered. [less ▲]

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See detailSpider-Man. Corps spectaculaire pour éthique ordinaire.
Tomasovic, Dick ULg

Scientific conference (2016, December 01)

Analyse des principaux motifs et structures des récits sériels de Spider-Man en comics et au cinéma.

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See detailWASP-157b, a Transiting Hot Jupiter Observed with K2
Močnik, T.; Anderson, D. R.; Brown, D. J. A. et al

in Publications of the Astronomical Society of the Pacific (2016), 970

We announce the discovery of the transiting hot Jupiter WASP-157b in a 3.95-d orbit around a V = 12.9 G2 main-sequence star. This moderately inflated planet has a Saturn-like density with a mass of $0.57 ... [more ▼]

We announce the discovery of the transiting hot Jupiter WASP-157b in a 3.95-d orbit around a V = 12.9 G2 main-sequence star. This moderately inflated planet has a Saturn-like density with a mass of $0.57 \pm 0.10$ M$_{\rm Jup}$ and a radius of $1.06 \pm 0.05$ R$_{\rm Jup}$. We do not detect any rotational or phase-curve modulations, nor the secondary eclipse, with conservative semi-amplitude upper limits of 250 and 20 ppm, respectively. [less ▲]

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