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Peer Reviewed
See detailNon-stationnarite et aspects fonctionnels du comportement agonistique chez Tilapia macrochir (Boulenger 1912) (Piscer: Cichlidae)
Balthazart, Jacques ULg

in Acta Zoologica et Pathologica Antverpiensia (1974), 58(0), 29-40

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See detailNon-symbiotic hemoglobin-2 leads to an elevated energy state and to a combined increase in polyunsaturated fatty acids and total oil content when over-expressed in developing seeds of transgenic Arabidopsis plants.
Vigeolas, Hélène ULg; Huhn, D.; Geigenberger, P.

in Plant Physiology (2011)

Non-symbiotic hemoglobins are ubiquitously expressed in plants and divided into two different classes based on gene-expression pattern and oxygen binding-properties. Most of the published research has ... [more ▼]

Non-symbiotic hemoglobins are ubiquitously expressed in plants and divided into two different classes based on gene-expression pattern and oxygen binding-properties. Most of the published research has been on the function of class-1 hemoglobins. To investigate the role of class-2 hemoglobins, transgenic Arabidopsis plants were generated over-expressing Arabidopsis hemoglobin-2 (AHb2) under the control of a seed-specific promoter. Over-expression of AHb2 led to a 40% increase in the total fatty acid content of developing and mature seeds in three subsequent generations. This was mainly due to an increase in the poly-unsaturated C18:2 (omega-6) linoleic and C18:3 (omega-3) alpha-linolenic acids. Moreover, AHb2 over-expression led to an increase in the C18:2/C18:1 and C18:3/C18:2 ratios as well as in the C18:3 content in mol% of total fatty acids and in the unsaturation/saturation index of total seed lipids. The increase in fatty-acid content was mainly due to a stimulation of the rate of triacylglycerol synthesis which was attributable to a 3-fold higher energy state and a 2-fold higher sucrose content of the seeds. Under low external oxygen, AHb2 over-expression maintained an up to 5-fold higher energy state and prevented fermentation. This is consistent with AHb2 over-expression results in improved oxygen availability within developing seeds. In contrast to this, over-expression of class-1 hemoglobin did not lead to any significant increase in the metabolic performance of the seeds. Results provide evidence for a specific function of class-2 hemoglobin in seed oil production and in promoting the accumulation of poly-unsaturated fatty acids by facilitating oxygen supply in developing seeds. [less ▲]

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See detailNon-symmetrically substituted phenoxazinones from laccase-mediated oxidative cross-coupling of aminophenols: an experimental and theoretical insight
Bruyneel, Frédéric; Dive, Georges ULg; Marchand-Brynaert, Jacqueline

in Organic & Biomolecular Chemistry (2012), 10

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See detailNon-synoptic versus pseudo-synoptic data sets: an assimilation experiment
Rixen, Michel; Allen, J. T.; Beckers, Jean-Marie ULg

in Journal of Marine Systems (2001), 29(1-4), 313-333

Several first-order correction methods are implemented to compute pseudo-synoptic data sets from non-synoptic raw data sets. These include a geostrophic relocation method, a linear and a quadratic ... [more ▼]

Several first-order correction methods are implemented to compute pseudo-synoptic data sets from non-synoptic raw data sets. These include a geostrophic relocation method, a linear and a quadratic interpolation method, and a method using spatio-temporal correlation functions. The relocation method involves analyses and geostrophic velocity computations to allow the relocation of stations in time and space to a particular analysis time. Interpolation methods involve several almost identical and consecutive surveys interpolated in time. Temporal weighting methods are based upon a spatio-temporal function modifying the weight on data with respect to the time at which they have been sampled. These techniques are tested on the OMEGA data set and are validated by simple nudging assimilation into a 3D primitive equation model (PE). It is shown that, under certain hypothesis, these methods are able to correct the lack of synopticity in hydrographic data sets, and improve the diagnosis of vertical velocities computed from the Omega equation. These methods are of particular interest for the scientific community. They might be used together with diagnostic models. They might provide suitable pseudo-synoptic fields required by 3D PE models as initial conditions, boundary conditions or assimilation data sets. They may also be useful in the design of mesoscale samplings. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailNon-thermal emission from early-type binaries
Rauw, Grégor ULg

in Cosmic Gamma-Ray Sources (2004)

Not Available

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See detailNon-thermal emission processes in massive binaries
De Becker, Michaël ULg

in Astronomy and Astrophysics Review (2007), 14(3-4), 171-216

In this paper, I present a general discussion of several astrophysical processes likely to play a role in the production of non-thermal emission in massive stars, with emphasis on massive binaries. Even ... [more ▼]

In this paper, I present a general discussion of several astrophysical processes likely to play a role in the production of non-thermal emission in massive stars, with emphasis on massive binaries. Even though the discussion will start in the radio domain where the non-thermal emission was first detected, the census of physical processes involved in the non-thermal emission from massive stars shows that many spectral domains are concerned, from the radio to the very high energies. First, the theoretical aspects of the non-thermal emission from early-type stars will be addressed. The main topics that will be discussed are respectively the physics of individual stellar winds and their interaction in binary systems, the acceleration of relativistic electrons, the magnetic field of massive stars, and finally the non-thermal emission processes relevant to the case of massive stars. Second, this general qualitative discussion will be followed by a more quantitative one, devoted to the most probable scenario where non-thermal radio emitters are massive binaries. I will show how several stellar, wind and orbital parameters can be combined in order to make some semi-quantitative predictions on the high-energy counterpart to the non-thermal emission detected in the radio domain. These theoretical considerations will be followed by a census of results obtained so far, and related to this topic. These results concern the radio, the visible, the X-ray and the gamma-ray domains. Prospects for the very high energy gamma-ray emission from massive stars will also be addressed. Two particularly interesting examples-one O-type and one Wolf-Rayet binary-will be considered in details. Finally, strategies for future developments in this field will be discussed. [less ▲]

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See detailNon-thermal Hard X-ray Emission from Colliding Wind Binary Systems
Khangulyan, Dmitry; Bosch-Ramon, Valenti; De Becker, Michaël ULg

Poster (2012, July)

Colliding-wind massive star binaries are known to produce strong shocks in their wind-wind interaction regions. The interaction region is the scenario of several physical processes, including strong ... [more ▼]

Colliding-wind massive star binaries are known to produce strong shocks in their wind-wind interaction regions. The interaction region is the scenario of several physical processes, including strong thermal X-ray emission and in several cases particle acceleration up to relativistic energies. The latter process is still poorly understood in these environments, and deserves a particular attention in stellar astrophysics. The investigation of particle acceleration is a critical aspect of high-energy astrophysics, especially at energies above 10 keV where non-thermal emission processes dominate. We discuss the possibility to detect the hard X-ray emission from WR147, a well-known particle accelerator, using Astro-H Hard X-ray Telescope (HXT) and Soft Gamma-Ray Detector (SGD), and to probe the particle acceleration process at work in its colliding-wind region. [less ▲]

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See detailNon-thermal processes in colliding-wind massive binaries: the contribution of Simbol-X to a multiwavelength investigation
De Becker, Michaël ULg; Blomme, Ronny; Micela, Giusi et al

in AIP Conference Proceedings (2009, May), 1126

Several colliding-wind massive binaries are known to be non-thermal emitters in the radio domain. This constitutes strong evidence for the fact that an efficient particle acceleration process is at work ... [more ▼]

Several colliding-wind massive binaries are known to be non-thermal emitters in the radio domain. This constitutes strong evidence for the fact that an efficient particle acceleration process is at work in these objects. The acceleration mechanism is most probably the Diffusive Shock Acceleration (DSA) process in the presence of strong hydrodynamic shocks due to the colliding-winds. In order to investigate the physics of this particle acceleration, we initiated a multiwavelength campaign covering a large part of the electromagnetic spectrum. In this context, the detailed study of the hard X-ray emission from these sources in the SIMBOL-X bandpass constitutes a crucial element in order to probe this still poorly known topic of astrophysics. It should be noted that colliding-wind massive binaries should be considered as very valuable targets for the investigation of particle acceleration in a similar way as supernova remnants, but in a different region of the parameter space. [less ▲]

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See detailNon-thermal radiation from a runaway early-type star
del Valle, M.; Romero, G.E.; De Becker, Michaël ULg

in AIP Conference Proceedings (2012, December), 1505

HD 195592 is an O-type supergiant star, known as a well-established runaway. Recently, a Fermi γ-ray source (2FGL J2030.7+4417) with a position compatible with that of HD 195592 has been reported. Our ... [more ▼]

HD 195592 is an O-type supergiant star, known as a well-established runaway. Recently, a Fermi γ-ray source (2FGL J2030.7+4417) with a position compatible with that of HD 195592 has been reported. Our goal is to explore a scenario where HD 195592 is the counterpart of the Fermi γ-ray source. The high-energy emission would be inverse Compton radiation produced in the bowshock of the runaway star. We calculate relativistic particle energy losses and the resulting radiation from the bowshock of HD 195592 and show that the latter is compatible with the detected γ-ray emission. We conclude that the Fermi source 2FGL J2030.7+4417 might be produced, under some energetic assumptions, by inverse Compton up-scattering of infrared photons from locally heated dust. HD 195592 might therefore be the very first object detected belonging to the category of γ-ray emitting runaway massive stars, whose existence has been recently predicted. [less ▲]

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See detailNon-thermal radio emission from colliding-wind binaries: modelling Cyg OB2 No. 8A and No. 9
Volpi, Delia; Blomme, Ronny; De Becker, Michaël ULg et al

in Neiner, Coralie; Wade, G.; Meynet, G. (Eds.) et al Active OB stars: structure, evolution, mass loss and critical limits (2011, July 01)

Some OB stars show variable non-thermal radio emission. The non-thermal emission is due to synchrotron radiation that is emitted by electrons accelerated to high energies. The electron acceleration occurs ... [more ▼]

Some OB stars show variable non-thermal radio emission. The non-thermal emission is due to synchrotron radiation that is emitted by electrons accelerated to high energies. The electron acceleration occurs at strong shocks created by the collision of radiatively-driven stellar winds in binary systems. Here we present results of our modelling of two colliding wind systems: Cyg OB2 No. 8A and Cyg OB2 No. 9. [less ▲]

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See detailNon-thermal radio emission from O-type stars. I. HD168112
Blomme, Ronny; Van Loo, S.; De Becker, Michaël ULg et al

in Astronomy and Astrophysics (2005), 436(3), 1033-1040

We present a radio lightcurve of the O5.5 III(f(+)) star HD 168112, based on archive data from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). The fluxes show considerable ... [more ▼]

We present a radio lightcurve of the O5.5 III(f(+)) star HD 168112, based on archive data from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). The fluxes show considerable variability and a negative spectral index, thereby confirming that HD 168112 is a non-thermal radio emitter. The non-thermal radio emission is believed to be due to synchrotron radiation from relativistic electrons that have been Fermi accelerated in shocks. For HD 168112, it is not known whether these shocks are due to a wind-wind collision in a binary system or to the intrinsic instability of the stellar wind driving mechanism. Assuming HD 168112 to be a single star, our synchrotron model shows that the velocity jump of the shocks should be very high, or there should be a very large number of shocks in the wind. Neither of these is compatible with time-dependent hydrodynamical calculations of O star winds. If, on the other hand, we assume that HD 168112 is a binary, the high velocity jump is easily explained by ascribing it to the wind-wind collision. By further assuming the star to be an eccentric binary, we can explain the observed radio variability by the colliding-wind region moving in and out of the region where free-free absorption is important. The radio data presented here show that the binary has a period of between one and two years. By combining the radio data with X-ray data, we find that the most likely period is similar to 1.4 yr. [less ▲]

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See detailNon-thermal radio emission from O-type stars. II. HD167971
Blomme, Ronny; De Becker, Michaël ULg; Runacres, M. C. et al

in Astronomy and Astrophysics (2007), 464(2), 701-148

HD 167971 is a triple system consisting of a 3.3-day eclipsing binary (O5- 8 V + O5- 8 V) and an O8 supergiant. It is also a well known non-thermal radio emitter. We observed the radio emission of HD ... [more ▼]

HD 167971 is a triple system consisting of a 3.3-day eclipsing binary (O5- 8 V + O5- 8 V) and an O8 supergiant. It is also a well known non-thermal radio emitter. We observed the radio emission of HD 167971 with the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). By combining these data with VLA archive observations we constructed a radio lightcurve covering a 20-yr time-range. We searched for, but failed to find, the 3.3-day spectroscopic period of the binary in the radio data. This could be due to the absence of intrinsic synchrotron radiation in the colliding-wind region between the two components of the eclipsing binary, or due to the large amount of free-free absorption that blocks the synchrotron radiation. We are able to explain many of the observed characteristics of the radio data if the non-thermal emission is produced in a colliding-wind region between the supergiant and the combined winds of the binary. Furthermore, if the system is gravitationally bound, the orbital motion occurs over a period of similar to 20 years or longer, as suggested by the long-term variability in the radio data. We argue that the variability is due to the free-free absorption that changes with orbital phase or may also in part be due to changes in separation, should the orbit be eccentric. [less ▲]

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See detailNon-thermal radio emission from O-type stars. IV. Cygnus OB2 No. 8A
Blomme, R.; De Becker, Michaël ULg; Volpi, D. et al

in Astronomy and Astrophysics (2010), 519

Context. Several early-type colliding-wind binaries are known to emit synchrotron radiation due to relativistic electrons, which are most probably accelerated by the Fermi mechanism. By studying such ... [more ▼]

Context. Several early-type colliding-wind binaries are known to emit synchrotron radiation due to relativistic electrons, which are most probably accelerated by the Fermi mechanism. By studying such systems we can learn more about this mechanism, which is also relevant in other astrophysical contexts. Colliding-wind binaries are furthermore important for binary frequency determination in clusters and for understanding clumping and porosity in stellar winds. Aims: We study the non-thermal radio emission of the binary Cyg OB2 No. 8A, to see if it is variable and if that variability is locked to the orbital phase. We investigate if the synchrotron emission generated in the colliding-wind region of this binary can explain the observations and we verify that our proposed model is compatible with the X-ray data. Methods: We use both new and archive radio data from the Very Large Array (VLA) to construct a light curve as a function of orbital phase. We also present new X-ray data that allow us to improve the X-ray light curve. We develop a numerical model for the colliding-wind region and the synchrotron emission it generates. The model also includes free-free absorption and emission due to the stellar winds of both stars. In this way we construct artificial radio light curves and compare them with the observed one. Results: The observed radio fluxes show phase-locked variability. Our model can explain this variability because the synchrotron emitting region is not completely hidden by the free-free absorption. In order to obtain a better agreement for the phases of minimum and maximum flux we need to use stellar wind parameters for the binary components which are somewhat different from typical values for single stars. We verify that the change in stellar parameters does not influence the interpretation of the X-ray light curve. Our model has trouble explaining the observed radio spectral index. This could indicate the presence of clumping or porosity in the stellar wind, which - through its influence on both the Razin effect and the free-free absorption - can considerably influence the spectral index. Non-thermal radio emitters could therefore open a valuable pathway to investigate the difficult issue of clumping in stellar winds. [less ▲]

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See detailThe Non-thermal Radio Emitter HD 93250 Resolved by Long Baseline Interferometry
Sana, H.; Le Bouquin, J.-B.; De Becker, Michaël ULg et al

in Astrophysical Journal Letters (2011), 740

As the brightest O-type X-ray source in the Carina nebula, HD 93250 (O4 III(fc)) is X-ray overluminous for its spectral type and has an unusually hard X-ray spectrum. Two different scenarios have been ... [more ▼]

As the brightest O-type X-ray source in the Carina nebula, HD 93250 (O4 III(fc)) is X-ray overluminous for its spectral type and has an unusually hard X-ray spectrum. Two different scenarios have been invoked to explain its X-ray properties: wind-wind interaction and magnetic wind confinement. Yet, HD 93250 shows absolutely constant radial velocities over timescales of years suggesting either a single star, a binary system seen pole-on view or a very long period, and/or highly eccentric system. Using the ESO Very Large Telescope Interferometer, we resolved HD 93250 as a close pair with similar components. We measured a near-infrared flux ratio of 0.8 ± 0.1 and a separation of (1.5 ± 0.2) × 10-3 arcsec. At the distance of Carina, this corresponds to a projected physical distance of 3.5 AU. While a quantitative investigation would require a full characterization of the orbit, the binary nature of HD 93250 allows us to qualitatively explain both its X-ray flux and hardness and its non-thermal radio emission in the framework of a colliding wind scenario. We also discuss various observational biases. We show that, due to line blending of two similar spectral components, HD 93250 could have a period as short as 1 to several years despite the lack of measurable radial velocity variations. [less ▲]

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See detailA non-traumatic case of intracranial haemorrhage in a horse
Verwilghen, Denis ULg; Van Galen, Gaby ULg; Peters, Fabrice et al

Poster (2006, August)

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See detailThe non-trivial dispersion of Y2BaCuO5 particles trapped in the YBa2Cu3O7-x crystal matrix
Vandewalle, Nicolas ULg; Pirard, E.; Cloots, Rudi ULg et al

in Philosophical Magazine Letters (1998), 77(5), 301-306

Micrographs of melt-textured YBa2Cu3O7-x/Y2BaCuO5 (123/211) have been digitized. Through image analysis, we point out that the dispersion of the 211 particles is highly inhomogeneous in the melt and in ... [more ▼]

Micrographs of melt-textured YBa2Cu3O7-x/Y2BaCuO5 (123/211) have been digitized. Through image analysis, we point out that the dispersion of the 211 particles is highly inhomogeneous in the melt and in the 123 crystal matrix. Indeed, free 211 particle regions and 211 aggregates are observed. The distribution laws are given. Moreover, the dispersions of 211 particles in the melt and those trapped in the crystal matrix are quite different. We point out that this difference cannot be explained solely by the partial dissolution of the 211 particles during the growth process. [less ▲]

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See detailNon-uniform adaptive vertical grids for 3D numerical ocean models
Hofmeister, R.; Burchard, H.; Beckers, Jean-Marie ULg

in Ocean Modelling (2010), 33

A new strategy for the vertical gridding in terrain-following 3D ocean models is presented here. The vertical grid adaptivity is partially given by a vertical diffusion equation for the vertical layer ... [more ▼]

A new strategy for the vertical gridding in terrain-following 3D ocean models is presented here. The vertical grid adaptivity is partially given by a vertical diffusion equation for the vertical layer positions, with diffusivities being proportional to shear, stratification and distance from the boundaries. In the horizontal, the grid can be smoothed with respect to z-levels, grid layer slope and density. Lagrangian tendency of the grid movement is supported. The adaptive terrain-following grid can be set to be an Eulerian–Lagrangian grid, a hybrid r–q or r–z grid and combinations of these with great flexibility. With this, internal flow structures such as thermoclines can be well resolved and followed by the grid. A set of idealised examples is presented in the paper, which show that the introduced adaptive grid strategy reduces pressure gradient errors and numerical mixing significantly. The grid adaption strategy is easy to implement in various types of terrain-following ocean models. The idealised examples give evidence that the adaptive grids can improve realistic, long-term simulations of stratified seas while keeping the advantages of terrain-following coordinates. [less ▲]

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See detailNon-uniform adaptive vertical grids in one-dimensional numerical ocean models
Burchard, Hans; Beckers, Jean-Marie ULg

in Ocean Modelling (2004), 6(1), 51-81

It is demonstrated in this paper how the concept of general vertical coordinates can be exploited for constructing adaptive grids in primitive equation ocean models. The term adaptive is used here in the ... [more ▼]

It is demonstrated in this paper how the concept of general vertical coordinates can be exploited for constructing adaptive grids in primitive equation ocean models. The term adaptive is used here in the sense of coordinate iso-surfaces which follow certain internal structures of the flow in such a way that higher vertical resolution is obtained in locations where vertical gradients are large. The internal structures considered here are shear and stratification. In this paper, one-dimensional models are applied in order to demonstrate the ability of such grid adaptation methods to follow internal structures even in flow situations dominated by vertical mixing processes. Here, a variational approach is considered for the generation of grids which results in a diffusion equation for the vertical coordinate. The method is tested for five different idealised and realistic scenarios with the result that the discretisation error can be significantly reduced in comparison to equidistant Cartesian grids. Some recommendations for extending these methods for three-dimensional models are given at the end of this paper. (C) 2003 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailNon-uniqueness of the natural and projectively equivariant quantization
Radoux, Fabian ULg

in Journal of Geometry & Physics (2008), 58

In [C. Duval, V. Ovsienko, Projectively equivariant quantization and symbol calculus: Noncommutative hypergeometric functions, Lett. Math. Phys. 57 (1) (2001) 61–67], the authors showed the existence and ... [more ▼]

In [C. Duval, V. Ovsienko, Projectively equivariant quantization and symbol calculus: Noncommutative hypergeometric functions, Lett. Math. Phys. 57 (1) (2001) 61–67], the authors showed the existence and the uniqueness of a sl(m+1,R)-equivariant quantization in non-critical situations. The curved generalization of the sl(m+1,R)-equivariant quantization is the natural and projectively equivariant quantization. In [M. Bordemann, Sur l’existence d’une prescription d’ordre naturelle projectivement invariante (submitted for publication). math.DG/0208171] and [Pierre Mathonet, Fabian Radoux, Natural and projectively equivariant quantizations by means of Cartan connections, Lett. Math. Phys. 72 (3) (2005) 183–196], the existence of such a quantization was proved in two different ways. In this paper, we show that this quantization is not unique. [less ▲]

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See detailNon-visual brain sensitivity to light in aging
Daneault, V; Vandewalle, Gilles ULg; Hébert, M et al

Poster (2011, March)

Detailed reference viewed: 7 (2 ULg)