Studying debris disks with near‐infrared interferometry

Conference (2011, April 13)

In this talk, I will describe and illustrate two different ways in which near-infrared stellar interferometry can be used to constrain the nature and physics of debris disks, and help understand the ... [more ▼]

In this talk, I will describe and illustrate two different ways in which near-infrared stellar interferometry can be used to constrain the nature and physics of debris disks, and help understand the global architecture of planetary systems in general. In the first part of the talk, I will review the on-going efforts to detect bright exozodiacal disks with precision near-infrared interferometry. I will describe the results of the exozodi survey that we are currently carrying out at the CHARA array, and briefly discuss our first results and perspectives with the new PIONIER instrument at the VLTI (including the identification of previously unknown low-mass companions). Preliminary statistical trends on the occurrence of bright exozodi around nearby main sequence stars will be presented, and I will discuss how this information could be used to constrain the global architecture and evolution of debris disks. In the second part of the talk, I will focus on our on-going project to characterize the “spin-orbit” alignment of resolved debris disks with the rotation axis of their (rapidly rotating) host star. Our first result obtained with the VLTI/AMBER spectro-interferometer on Fomalhaut will be presented, as well as its possible consequences on the dynamics of the planetary system and on the physics of the grains composing the Fomalhaut dust ring. I will then briefly describe the status and perspectives of this project. [less ▲]

Studying massive stars with the International X-ray Observatory

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

Chandra and XMM-Newton have deeply changed our view of the X-ray emission of massive stars. However, the majority of the massive stars being rather faint sources, the number of high-resolution X-ray ... [more ▼]

Chandra and XMM-Newton have deeply changed our view of the X-ray emission of massive stars. However, the majority of the massive stars being rather faint sources, the number of high-resolution X-ray spectra of massive stars remains rather limited and obtaining these spectra requires rather long exposure times. ESA, NASA and JAXA are currently designing the International X-ray Observatory (IXO) that will provide a quantum leap in collecting area compared to the current missions. In this contribution, we highlight the capabilities of IXO and its instrumentation for the study of massive stars in our Galaxy and beyond. [less ▲]

Studying RNA-Protein Interactions In Vivo By RNA Immunoprecipitation

in Methods in Molecular Biology (Clifton, N.J.) (2011), 791

The crucial roles played by RNA-binding proteins in all aspects of RNA metabolism, particularly in the regulation of transcription, have become increasingly evident. Moreover, other factors that do not ... [more ▼]

The crucial roles played by RNA-binding proteins in all aspects of RNA metabolism, particularly in the regulation of transcription, have become increasingly evident. Moreover, other factors that do not directly interact with RNA molecules can nevertheless function proximally to RNA polymerases and have significant effects on gene expression. RNA immunoprecipitation (RIP) is a powerful technique used to detect direct and indirect interactions between individual proteins and specific RNA molecules in vivo. Here, we describe RIP methods for both yeast and mammalian cells. [less ▲]

Studying the Fomalhaut debris disk with infrared interferometry

Scientific conference (2011, July 15)

In this talk, I will describe two recent studies carried out with infrared interferometry to characterise the planetary system around Fomalhaut, and its debris disk in particular. In the first study, we ... [more ▼]

In this talk, I will describe two recent studies carried out with infrared interferometry to characterise the planetary system around Fomalhaut, and its debris disk in particular. In the first study, we aimed to determine whether the debris disk is located within the equatorial plane of the stellar photosphere, in an attempt to improve our understanding of spin-orbit misalignements in planetary systems in general. We measured the orientation of the rotationnally-distorted stellar photosphere using micro-arcsecond precision VLTI/AMBER spectro-astrometry within the Br-gamma line. The derived poition angle is in perfect agreement with the position angle of the cold debris disk measured in visible and sub-millimeter images. We discuss the implications of this result on our understanding of the dust grain properties in the Fomalhaut disk. In the second study, we aimed at characterising the dust content of the innermost part of the debris disk. We used archival high-precision K-band visibility measurements with VLTI/VINCI and obtained N-band nulling observations with the Keck Interferometer Nuller. We report a significant excess emission at K band, and a marginal excess emission at N band, that we attempt to reproduce with a 2D debris disk model. A comprehensive Bayesian analysis of the main disk parameters is performed to derive most-probable values. Our analysis points towards a very compact ring of hot dust close to the sublimation radius as the origin of the reported excess emission. [less ▲]

Studying the Magnetic Properties of Upper Main-sequence Stars with FORS1

in The Messenger (2009), 135

We summarise the results of our recent magnetic field studies in upper main-sequence stars, which have exploited the spectropolarimetric capability of FORS1 at the VLT extensively.

Studying the Topology and Dynamics of Elasto-inertial Channel Flow Turbulence Using the Invariants of the Velocity Gradient Tensor and Dynamic Mode Decomposition

Conference (2012, November 20)

Direct numerical simulations (DNS) of the transition to and fully developed elasto-inertial turbulence (EIT) of a polymer solution in a channel flow has been used as a basis for the study of the topology ... [more ▼]

Direct numerical simulations (DNS) of the transition to and fully developed elasto-inertial turbulence (EIT) of a polymer solution in a channel flow has been used as a basis for the study of the topology and dynamics of these flows. The Reynolds number in these DNS ranged from 500 to 5000. The topology of these flows was studied through the joint probability density functions (JPDFs) of the second and third invariants of the velocity gradient tensor (VGT), $Q_A$ and $R_A$ respectively and the JPDFs of the second invariants of the rate-of-strain tensor and the rate-of-rotation tensor, $Q_S$ and $Q_W$ respectively. The results suggest that these transitional and fully developed EIT flows are predominantly made up of vortex sheets. Dynamic mode decomposition has been undertaken on the second invariant of the VGT, $Q_A$, which reveals that the most amplified mode is a two-dimensional structure located in the near-wall region. A ``discontinuity'' is observed close to the wall, which corresponds closely to the location of extrema of the mean polymer extension and is hypothesized to be a critical layer. [less ▲]

Stunting may determine the severity of malaria-associated anemia in African children.

in Pediatrics (2002), 110(4), 48

OBJECTIVE: Evidence from previous studies that malnourished children are protected against malaria is controversial. In individuals repeatedly exposed to malaria, immunity may develop first against severe ... [more ▼]

OBJECTIVE: Evidence from previous studies that malnourished children are protected against malaria is controversial. In individuals repeatedly exposed to malaria, immunity may develop first against severe disease, then against pyrogens, and last, against parasites. If this is true, this would suggest that reduced immune function that may exist in stunted children exacerbates the severity of malarial signs and symptoms, rather than the occurrence of parasitemia. On the other hand, several studies have suggested that malnourished children are protected to some degree against malaria. Our aim was to evaluate whether observational data support the hypothesis that nutritional inadequacies that cause stunting modify the associations between malaria and hematologic indicators such as hemoglobin concentration and serum concentrations of C-reactive protein and soluble transferrin receptor (sTfR). We showed earlier that increased serum concentrations of these receptors in asymptomatic malaria may be explained, at least in part, by increased erythropoiesis to compensate for malaria-induced hemolysis. METHODOLOGY: Community-based cluster survey among Kenyan children aged 2 to 36 months asymptomatic for malaria or anemia (n = 318). RESULTS: When adjusted for age and wasting, the malaria-associated decrease in mean hemoglobin concentration was 8.5 g/L and 15.8 g/L in nonstunted and stunted children, respectively. The malaria-associated increase in geometric mean serum concentrations of sTfR was 1.1-fold and 1.8-fold in nonstunted and stunted children, respectively. The malaria-associated increase in geometric mean serum concentrations of C-reactive protein was 1.4-fold and 2.3-fold in nonstunted and stunted children, respectively. Thus, children with malaria and those who were stunted suffered from more severe anemia and had higher serum concentrations of C-reactive protein and sTfR than would be expected from the combined effect of the 2 working independently. CONCLUSIONS: Our results are consistent with the notion that the nutritional inadequacies causing stunting also impair host immunity, thus increasing the degree to which malaria is associated with decreased concentrations of hemoglobin, with increased inflammation, and with increased iron demand in developing erythroblasts. Increased intake of micronutrients may not only reduce stunting and nutritional anemia, but also reduce malaria-associated anemia. [less ▲]

Les stupéfiants

Conference given outside the academic context (2008)

The Sturtian 'snowball' glaciation: fire and ice

in Earth And Planetary Science Letters (2003), 211(1-2), 1-12

The Sturtian 'snowball' glaciation (730 Ma) is contemporary with the dislocation of the Rodinia supercontinent. This dislocation is heralded and accompanied by intense magmatic events, including the onset ... [more ▼]

The Sturtian 'snowball' glaciation (730 Ma) is contemporary with the dislocation of the Rodinia supercontinent. This dislocation is heralded and accompanied by intense magmatic events, including the onset of large basaltic provinces between 825 and 755 Ma. Among these magmatic events, the most important one is the onset of a Laurentian magmatic province at 780 Ma around a latitude of 30degreesN. The presence of these fresh basaltic provinces increases the weatherability of the continental surfaces, resulting in an enhanced consumption of atmospheric CO2 through weathering, inducing a global long-term climatic cooling. Based on recent weathering laws for basaltic lithology and on climatic model results, we show that the weathering of a 6 x 10(6) km(2) basaltic province located within the equatorial region (where weathering of the province and consumption of CO2 are boosted by optimal climatic conditions) is sufficient to trigger a snowball glaciation, assuming a pre-perturbation PCO2 value of 280 ppmv. We show that the Laurentian magmatic province might be the main culprit for the initiation of the Sturtian 'snowball' glaciation, since the Laurentian magmatic province had drifted within the equatorial region by the time of the glaciation. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

Style beyond Borders: Language in Recent Nigerian Fiction

Doctoral thesis (2008)