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See detailMeasurements on magnetized GdBCO pellets subjected to small transverse ac magnetic fields at very low frequency: Evidence for a slowdown of the magnetization decay
Fagnard, Jean-François ULg; Kirsch, Sébastien; Morita, Mitsuru et al

in Physica C: Superconductivity (2015), 512

Due to their ability to trap large magnetic inductions, superconducting bulk materials can be used as powerful permanent magnets. The permanent magnetization of such materials, however, can be ... [more ▼]

Due to their ability to trap large magnetic inductions, superconducting bulk materials can be used as powerful permanent magnets. The permanent magnetization of such materials, however, can be significantly affected by the application of several cycles of a transverse variable magnetic field. In this work, we study, at T = 77 K, the long term influence of transverse ac magnetic fields of small amplitudes (i.e. much smaller than the full penetration field) on the axial magnetization of a bulk single grain superconducting GdBCO pellet over a wide range of low frequencies (1 mHz–20 Hz). Thermocouples are placed against the pellet surface to probe possible self-heating of the material during the experiments. A high sensitivity cryogenic Hall probe is placed close to the surface to record the local magnetic induction normal to the surface. The results show first that, for a given number of applied triangular transverse cycles, higher values of dBapp/dt induce smaller magnetization decays. An important feature of practical interest is that, after a very large number of cycles which cause the loss of a substantial amount of magnetization (depending on the amplitude and the frequency of the field), the rate of the magnetization decay goes back to its initial value, corresponding to the relaxation of the superconducting currents due to flux creep only. In the amplitude and frequency range investigated, the thermocouples measurements and a 2D magneto-thermal modelling show no evidence of sufficient self-heating to affect the magnetization so that the effect of the transverse magnetic field cycles on the trapped magnetic moment is only attributed to a redistribution of superconducting currents in the volume of the sample and not to a thermal effect. [less ▲]

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See detailWhy are flux avalanches deflected by a metallic layer?
Brisbois, Jérémy ULg

Conference (2015, May 15)

Sudden avalanches of magnetic flux bursting into a superconducting sample are deflected from their trajectories when they encounter a conductive layer deposited on top of the superconductor. Remarkably ... [more ▼]

Sudden avalanches of magnetic flux bursting into a superconducting sample are deflected from their trajectories when they encounter a conductive layer deposited on top of the superconductor. Remarkably, in some cases the flux is totally excluded from the area covered by the conductive layer. Even if this phenomenon has been known for a few years, there is currently no theoretical model describing it. Moreover, the question whether the deflection would also be observed for a single vortex entering the region covered by a metallic layer is still unanswered. In this work we use the magneto-optical imaging (MOI) technique, based on the Faraday effect, to show that a conductive layer (Cu) can repel flux avalanches triggered in an underlying superconducting film (Nb) (see figure). We present a simple classical model that accounts for the deflection of a single vortex and considers a magnetic monopole approaching a semi-infinite conductive plane. This model suggests the important role played in the avalanche deflection by electromagnetic braking, arising from the eddy currents induced by the moving vortex in the metal. Moreover, we have found a decrease of the vortex damping coefficient due to the metallic sheet at large vortex velocities, correcting early theoretical descriptions where a linear behaviour was proposed. [less ▲]

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See detailWhat makes the invasive Harmonia axyridis so successful? Six years of research in Gembloux provide additional answers
Fassotte, Bérénice ULg; Durieux, Delphine ULg; Vandereycken, Axel ULg et al

Conference (2015, May 14)

Following the introduction of the invasive species Harmonia axyridis (Pallas) in Europe, many research works were conducted on its ecological, economic and social impacts. Recently, our team has been ... [more ▼]

Following the introduction of the invasive species Harmonia axyridis (Pallas) in Europe, many research works were conducted on its ecological, economic and social impacts. Recently, our team has been involved in the characterization of the behavioral traits making this lady beetle species so successful. The main conclusions of two PhD works will be shortly presented: (1) Through a six-year inventory performed in Belgian agroecosystems, we have demonstrated that H. axyridis has become well established and was among the most abundant aphidophagous predatory species, causing a severe depression of biodiversity, even if communities of aphid predators are still quite diversified. (2) The social issues associated with the establishment of overwintering aggregations in human constructions were also carefully investigated. We have demonstrated the importance of social interactions on the establishment and cohesion of the aggregates. Finally, we have demonstrated that the deposition of a set of saturated and non-saturated hydrocarbons on the surfaces where the lady beetles were settling on, allowed their conspecifics to follow their markings and join the group. [less ▲]

Detailed reference viewed: 27 (5 ULg)
See detailChristianisme et paideia dans l'Égypte byzatine : l'apport des papyrus scolaires grecs à contenu composite profane et chrétien (fin du IIIe-début du VIIIe s.)
Carlig, Nathan ULg

Conference (2015, May 14)

Documentée par des milliers de papyrus, restes de livres ou de documents, dont les plus anciens remontent à la fin du IIe siècle de notre ère, la christianisation de l’Égypte a profondément modifié le ... [more ▼]

Documentée par des milliers de papyrus, restes de livres ou de documents, dont les plus anciens remontent à la fin du IIe siècle de notre ère, la christianisation de l’Égypte a profondément modifié le rapport des populations à la paideia hellénique, sans pour autant se substituer à elle. L’examen du matériau, de la forme, de la mise en page, du contenu, ainsi que de la provenance des papyrus scolaires grecs à contenu composite profane et chrétien (fin IIIe – 1e moitié VIIIe s.), permettra d'illustrer cette problématique en relevant les continuités et les ruptures dans les stratégies d'enseignement par rapport à la paideia de tradition hellénique. [less ▲]

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See detailMasculinités et migrations chinoises
Florence, Eric ULg

in La vie des idées.fr (2015)

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See detailAuroral emissions at Jupiter and Saturn, at the crossroads of Astrophysics Geophysics and Plasma Physics
Grodent, Denis ULg

Conference (2015, May 13)

Auroral physics is at the intersection of more general fields of physics such as Astrophysics, Geophysics and Plasma Physics. In particular, the giant planets Jupiter and Saturn may be seen as slow ... [more ▼]

Auroral physics is at the intersection of more general fields of physics such as Astrophysics, Geophysics and Plasma Physics. In particular, the giant planets Jupiter and Saturn may be seen as slow rotating pulsars. For these two planets, there is a direct link between this pulsar-like behaviour and the auroral processes that are taking place in their atmosphere. We will take the example of Jupiter to illustrate haw the aurora is generated in the magnetosphere as a result of the volcanic activity of the moon Io. [less ▲]

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See detailFirst experimental realization of an Iron Magneto-Optical Trap
Bastin, Thierry ULg; Crauwels, Justine ULg; Huet, Nicolas ULg et al

Conference (2015, May 13)

Detailed reference viewed: 23 (2 ULg)
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See detailFirst evidence of a volatile sex pheromone in Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)
Fassotte, Bérénice ULg; Fischer, Christophe ULg; Durieux, Delphine ULg et al

Conference (2015, May 13)

To date, volatile sex pheromones have not been identified in the Coccinellidae family; yet, various studies have suggested that such semiochemicals exist. Here, we collected volatile chemicals released by ... [more ▼]

To date, volatile sex pheromones have not been identified in the Coccinellidae family; yet, various studies have suggested that such semiochemicals exist. Here, we collected volatile chemicals released by virgin females of the multicolored Asian lady beetle, Harmonia axyridis (Pallas), which were either allowed or not allowed to feed on aphids. Virgin females in the presence of aphids, exhibited “calling behavior”, which is commonly associated with the emission of a sex pheromone in several Coleoptera species. These calling females were found to release a blend of volatile compounds that is involved in the remote attraction (i.e., from a distance) of males. Gas Chromatography Mass Spectrometry (GC-MS) analyses revealed that (–)-β-caryophyllene was the major constituent of the volatile blend (ranging from 80 to 86%), with four other chemical components also being present; β-elemene, methyl-eugenol, α-humulene, and α-bulnesene. In a second set of experiments, the emission of the five constituents identified from the blend was quantified daily over a 9-day period after exposure to aphids. We found that the quantity of all five chemicals significantly increased across the experimental period. Finally, we evaluated the activity of a synthetic blend of these chemicals by performing bioassays which demonstrated the same attractive effect in males only. The results confirm that female H. axyridis produce a volatile sex pheromone. These findings have potential in the development of more specific and efficient biological pest-control management methods aimed at manipulating the behavior of this invasive lady beetle. [less ▲]

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See detailTowards the identification of cis-elements responsible for the high expression of HMA4, an essential gene for zinc hyperaccumulation in Arabidopsis halleri.
Spielmann, Julien ULg; Nouet, Cécile ULg; Scheepers, Maxime ULg et al

Poster (2015, May 13)

A. halleri is a Zn and Cd hypertolerant and hyperaccumulator plant which stores metals in shoot vacuoles. One key step for hyperaccumulation is a highly efficient root-to-shoot translocation of metals ... [more ▼]

A. halleri is a Zn and Cd hypertolerant and hyperaccumulator plant which stores metals in shoot vacuoles. One key step for hyperaccumulation is a highly efficient root-to-shoot translocation of metals. The Zn/Cd plasmamembrane pump HMA4 (heavy metal ATPase 4) plays a central role in this process and is involved in xylem loading/unloading. Moreover, HMA4 is overexpressed in A. halleri compare to its non-tolerant and non-hyperaccumulator sister, Arabidopsis thaliana. The HMA4 overexpression is determined by a combination of gene triplication and cis-regulatory changes increasing transcription levels of each three HMA4 copies. In this study, we are focusing on the two most active HMA4 promoters and we aim to identify the cis-elements underlying high expression of HMA4 in A. halleri using promoter-reporter constructs. Through deletion analysis, two important regions for a high expression have been identified. Ongoing analysis of more detailed deletions will be presented. [less ▲]

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See detailCheckpoints modulation by the human T-lymphotropic virus type 1 (HTLV-1) Tax protein : towards new therapeutic approaches
Carpentier, Alexandre ULg; Barez, Pierre-Yves ULg; Boxus, Mathieu et al

Poster (2015, May 13)

HTLV-1 infects approximately 15 million people worldwide and causes several diseases. This virus is responsible for the adult T-cell leukemia (ATL) and for a chronic neuropathology (TSP/HAM). There is ... [more ▼]

HTLV-1 infects approximately 15 million people worldwide and causes several diseases. This virus is responsible for the adult T-cell leukemia (ATL) and for a chronic neuropathology (TSP/HAM). There is currently no satisfactory treatment for these diseases. Among the proteins encoded by HTLV-1, Tax appears to play an important role in the mechanisms leading to pathogenicity. We are interested in the mechanisms of cell transformation by the Tax viral oncoprotein. In particular, we aim at understanding the interplay between Tax and the DNA damage response (DDR). We show that transient expression of Tax results in DNA damage, cell cycle arrest and activation of the DDR. In fibroblasts, cell cycle arrest occurs at the G1 and G2 phases depending on the p53 background. In contrast, HTLV-1 infected lymphocytes proliferate continuously and appear to be adapted to the checkpoints. This mechanism of checkpoint adaptation thus allows ongoing proliferation despite the presence of genomic lesions. Quantification of the rates of NHEJ and homologous recombination indicates that HTLV-1 infected cells require very efficient DNA repair for survival. Therefore, we propose a novel therapeutic approach based on the principle of synthetic lethality using inhibitors of DNA repair. [less ▲]

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See detailOn the nature of cosmological time
Hauret, Clémentine ULg

Conference (2015, May 13)

Detailed reference viewed: 9 (4 ULg)
See detailPartenariats entre services publics de l'emploi et opérateurs privés. Une question de confiance?
Remy, Céline ULg

Scientific conference (2015, May 13)

À l’heure des politiques d’activation des demandeurs d’emploi et d’un taux de chômage élevé, il semble tout particulièrement intéressant d’interroger les réformes institutionnelles des services publics de ... [more ▼]

À l’heure des politiques d’activation des demandeurs d’emploi et d’un taux de chômage élevé, il semble tout particulièrement intéressant d’interroger les réformes institutionnelles des services publics de l’emploi (SPE), notamment en matière de partenariats. Fin des années 90, la Commission européenne invite les SPE à établir des collaborations avec des organismes d’insertion socioprofessionnelle. Les SPE doivent déléguer une partie de leur mission d’accompagnement des demandeurs d’emploi à des opérateurs privés marchands et non-marchands. Des partenariats publics-privés voient progressivement le jour. Leur objectif est la mise en place de projets de formation et d’accompagnement à destination des demandeurs d’emploi en vue de la réinsertion de ceux-ci dans un emploi stable et de qualité. Perdant leur monopole en matière d’accompagnement, les SPE se repositionnent sur le marché de l’emploi en tant qu’« institution régulatrice » de ce marché. Déléguer leur mission aux opérateurs privés engendre nécessairement la question de la confiance. Comment les SPE accordent-ils leur confiance à ces organismes ? Une étude menée auprès de trois services publics de l’emploi, situés en Belgique et en Suisse, nous a permis d’analyser en profondeur les collaborations entre l’Office de l’Emploi et ses prestataires de service. La recherche porte tout particulièrement sur la construction, la vie et les effets du partenariat en termes de confiance. [less ▲]

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See detailMultiscale model of the human cardiovascular system: healthy and pathological behaviours
Kosta, Sarah ULg; Negroni, Jorge; Lascano, Elena et al

Poster (2015, May 13)

Detailed reference viewed: 23 (4 ULg)
See detailSurfactin: a receptor-independent bacterial elicitor of plant immunity?
Luzuriaga Loaiza, Walter ULg; Legras, Aurelien; Crowet, Jean-Marc ULg et al

Scientific conference (2015, May 13)

Detailed reference viewed: 21 (3 ULg)
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See detailTransport of Bose-Einstein Condensates through Aharonov-Bohm rings
Chrétien, Renaud ULg; Dujardin, Julien ULg; Petitjean, Cyril ULg et al

Poster (2015, May 13)

We study the one-dimensional (1D) transport properties of an ultracold gas of Bose-Einstein condensed atoms through Aharonov-Bohm (AB) rings. Our system consists of a Bose-Einstein condensate (BEC) that ... [more ▼]

We study the one-dimensional (1D) transport properties of an ultracold gas of Bose-Einstein condensed atoms through Aharonov-Bohm (AB) rings. Our system consists of a Bose-Einstein condensate (BEC) that is outcoupled from a magnetic trap into a 1D waveguide which is made of two semi-infinite leads that join a ring geometry exposed to a magnetic flux φ. We specifically investigate the effects of a small atom-atom contact interaction strength on the AB oscillations. The main numerical tools that we use for this purpose are a mean-field Gross-Pitaevskii (GP) description and the truncated Wigner (tW) method. The latter allows for the description of incoherent transport and corresponds to a classical sampling of the evolution of the quantum bosonic many-body state through effective GP trajectories. We find that resonant transmission peaks move with an increasing interaction strength and can be suppressed for sufficiently strong interaction. We also observe that the coherent transmission blockade due to destructive interference at the AB flux φ = π is very robust with respect to the interaction strength. [less ▲]

Detailed reference viewed: 62 (15 ULg)
See detailJupiter's equatorward auroral features
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2015, May 13)

Detailed reference viewed: 19 (3 ULg)
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See detailGravitational lensing search for dark matter haloes (2)
Biernaux, Judith ULg

Scientific conference (2015, May 13)

Detailed reference viewed: 8 (1 ULg)
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See detailInvestigation on a hydrogen maser cavity in the TE111 mode : first results
Van Der Beken, Emeline ULg; Léonard, Daniel; Counet, Arnaud et al

Poster (2015, May 13)

Results of our preliminary investigation on a hydrogen maser cavity in the unusual TE111 mode are presented. Hydrogen masers use the transition at 1420.405MHz between the two hyperfine levels F = 0 and F ... [more ▼]

Results of our preliminary investigation on a hydrogen maser cavity in the unusual TE111 mode are presented. Hydrogen masers use the transition at 1420.405MHz between the two hyperfine levels F = 0 and F = 1 of the 1s1/2 ground state of the hydrogen atom. In contrast to standard hydrogen maser that exploits the TE011 mode, the TE111 mode allows one to design hydrogen masers with significant reduced dimensions, which represents a huge benefit for space applications and in particular for the global positioning system. In view of a future development of a hydrogen maser in the TE111 mode we performed a thorough analysis of the maser physics for this mode. Different simulations carried out are compared with first measurement results obtained for such a cavity. [less ▲]

Detailed reference viewed: 24 (2 ULg)
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See detailChaotic Bohmian trajectories for the hydrogen atom
Cesa, Alexandre ULg; Struyve, Ward ULg; Martin, John ULg

Poster (2015, May 13)

In Bohmian mechanics, a single-particle quantum system is described in part by its wave function and in part by the actual position of the particle. The trajectory of the latter can be computed using the ... [more ▼]

In Bohmian mechanics, a single-particle quantum system is described in part by its wave function and in part by the actual position of the particle. The trajectory of the latter can be computed using the guiding equation. This equation states that the velocity of the particle is proportional to the usual probability current associated with its wave function. In this work, we study the quantum trajectory of a single particle in a Coulomb potential whose eigenstates are the well known eigenstates of the hydrogen atom. More precisely, we focus on the relation between chaotic Bohmian trajectories and the motion of wave function nodes. At wave function nodes i.e., where the wave function vanishes, the velocity is not defined which generically induces vorticity. In order to probe chaos, we compute Poincaré map and we numerically evaluate Lyapounov exponents, which characterize the divergence of close trajectories as time increases. For the 2d Coulomb potential, although the superposition of two eigenstates with different energies can lead to an arbitrary high number of moving nodes of the wave function, the Bohmian trajectories display no trace of chaos. This absence of chaotic behaviour originates from the existence of a constant of motion. Therefore, the motion and the number of nodes do not constitute a sufficient condition for the emergence of chaos in Bohmian mechanics. For superpositions of more than two eigenstates, there is no constant of motion, there are moving nodes and we find that the Bohmian trajectories are chaotic. [less ▲]

Detailed reference viewed: 22 (4 ULg)