Parasitic interference in nulling interferometry

in Monthly Notices of the Royal Astronomical Society (2013), 431(2), 1286-1295

Nulling interferometry aims to detect faint objects close to bright stars. Its principle is to produce a destructive interference along the line of sight so that the stellar flux is rejected, while the ... [more ▼]

Nulling interferometry aims to detect faint objects close to bright stars. Its principle is to produce a destructive interference along the line of sight so that the stellar flux is rejected, while the flux of the off-axis source can be transmitted. In practice, various instrumental perturbations can degrade the nulling performance. Any imperfection in phase, amplitude or polarization produces a spurious flux that leaks to the interferometer output and corrupts the transmitted off-axis flux. One of these instrumental perturbations is the crosstalk phenomenon, which occurs because of multiple parasitic reflections inside transmitting optics, and/or diffraction effects related to beam propagation along finite size optics. It can include a crosstalk of a beam with itself, and a mutual crosstalk between different beams. This can create a parasitic interference pattern, which degrades the intrinsic transmission map - or intensity response - of the interferometer. In this context, we describe how this instrumental effect impairs the performance of a Bracewell interferometer. A simple formalism is developed to derive the corresponding modified intensity response of the interferometer, as a function of the two parameters of interest: the crosstalk level (or contamination rate) and the phase shift between the primary and secondary - parasitic - beams. We then apply our mathematical approach to a few scientific cases, both analytically and using the GENIESIM simulation software, adapted to handle coherent crosstalk. Our results show that a coherent crosstalk level of about 1 per cent implies a 20 per cent drop of the signal-to-noise ratio at most. Careful attention should thus be paid to reduce the crosstalk level inside an interferometric instrument and ensure an instrumental stability that provides the necessary sensitivity through calibration procedures. [less ▲]

Durabilité (s) des matériaux de construction : un challenge pour l’ingénieur

Conference (2013, May 10)

Le choix des matériaux utilisés dans la construction repose sur des critères techniques identifiables et quantifiables tels la résistance mécanique, le comportement chimique ou le transfert de chaleur ... [more ▼]

Le choix des matériaux utilisés dans la construction repose sur des critères techniques identifiables et quantifiables tels la résistance mécanique, le comportement chimique ou le transfert de chaleur, paramètres qui permettent non seulement de satisfaire les exigences opérationnelles de l'ouvrage, mais aussi d'en garantir la durabilité et la durée de vie utile attendues. Quoi qu'il en soit, ces critères ne sont aujourd’hui plus suffisants: énergie grise, analyse de cycle de vie, incidence sur l’environnement, qualité environnementale des constructions, etc. sont de nouveaux facteurs qui interviennent dans le caractère « durable » des constructions. L’ingénieur se doit désormais d'intégrer ces considérations dans le dimensionnement et la réalisation des ouvrages, ce qui constitue un réel challenge pour l’avenir. [less ▲]

Of ‘Cyber-Coolies’ and Globalized India: Representing the Cosmos of Call-Centers in Films from the Subcontinent and Abroad

Conference (2013, May 09)

In today’s globalized India, not only has the outsourcing sector generated employment for some two million people, but it has also promoted the mesmerizing idea of a ‘new India’ of foreign investment ... [more ▼]

In today’s globalized India, not only has the outsourcing sector generated employment for some two million people, but it has also promoted the mesmerizing idea of a ‘new India’ of foreign investment, global markets, economic growth and expanding middle class. Drawing its workforce from an urban, college-educated Indian youth who receive training in ‘accent neutralization,’ the call centre industry offers the hope of rapid upward mobility, even if this involves working grinding shifts and faking an American name, accent, location, and time-zone. As against the somewhat cultish belief that ‘pretend-Nancy’ or ‘pretend-Bill’ (Susan Sontag) can reap the benefits of the corporate search for cut-rate labor, critics such as Harish Trivedi and Siddhartha Deb have proved highly critical of the ways in which the call centre industry results in creating a generation of ‘cyber-coolies’ and cultural emulators. A “public spectacle,” in Shehzad Nadeem’s words, outsourcing can be seen to promote an Indian fantasy landscape of high tech, virtual lives, and consumer culture that is reproduced and/or resisted in a growing number of cultural productions. Investigating TV series (Outsourced, Mumbai Calling), blockbusters (Slumdog Millionaire, The Best Exotic Marigold Hotel), and documentaries (John and Jane Toll-Free, Bombay Calling), this paper will explore the cosmos of call centres from a cross-cultural perspective. [less ▲]

Transformer les pratiques des enseignants d'histoire au secondaire en modifiant leurs outils ?

Scientific conference (2013, May 08)

Hydraulic modelling in civil and environmental engineering

Scientific conference (2013, May 08)

Preclinical radiation dosimetry for the novel SV2A radiotracer [18F]UCB-H

in European Journal of Nuclear Medicine and Molecular Imaging Research (2013), 3(1), 35

Background: [18F]UCB-H was developed as a novel radiotracer with a high affinity for synaptic vesicle protein 2A, the binding site for the antiepileptic levetiracetam. The objectives of this study were to ... [more ▼]

Background: [18F]UCB-H was developed as a novel radiotracer with a high affinity for synaptic vesicle protein 2A, the binding site for the antiepileptic levetiracetam. The objectives of this study were to evaluate the radiation dosimetry of [18F]UCB-H in a preclinical trial and to determine the maximum injectable dose according to guidelines for human biomedical research. The radiation dosimetry was derived by organ harvesting and dynamic micro positron emission tomography (PET) imaging in mice, and the results of both methods were compared. Methods: Twenty-four male C57BL-6 mice were injected with 6.96 ± 0.81 MBq of [18F]UCB-H, and the biodistribution was determined by organ harvesting at 2, 5, 10, 30, 60, and 120 min (n = 4 for each time point). Dynamic microPET imaging was performed on five male C57BL-6 mice after the injection of 9.19 ± 3.40 MBq of [18F]UCB-H. A theoretical dynamic bladder model was applied to simulate urinary excretion. Human radiation dose estimates were derived from animal data using the International Commission on Radiological Protection 103 tissue weighting factors. Results: Based on organ harvesting, the urinary bladder wall, liver and brain received the highest radiation dose with a resulting effective dose of 1.88E-02 mSv/MBq. Based on dynamic imaging an effective dose of 1.86E-02 mSv/MBq was calculated, with the urinary bladder wall and liver (brain was not in the imaging field of view) receiving the highest radiation. Conclusions: This first preclinical dosimetry study of [18F]UCB-H showed that the tracer meets the standard criteria for radiation exposure in clinical studies. The dose-limiting organ based on US Food and Drug Administration (FDA) and European guidelines was the urinary bladder wall for FDA and the effective dose for Europe with a maximum injectable single dose of approximately 325 MBq was calculated. Although microPET imaging showed significant deviations from organ harvesting, the Pearson’s correlation coefficient between radiation dosimetry derived by either method was 0.9666. [less ▲]

Evaluation of gross primary production, community respiration, and net community production in various benthic communities (Posidonia oceanica seagrass meadow, Posidonia oceanica litter, epilithic macro-algae) in the Bay of Revellata (Corsica) using optodes

Poster (2013, May 07)

La santé des indépendants : qui s'en préoccupe vraiment ? "L'enquête et ses principaux résultats"

Speech (2013)

Autre jeunesse ou autre engagement ? Etudier l'engagement des jeunes à travers l'offre disponible

Conference (2013, May 07)

Approximation Algorithms for Multi-Dimensional Vector Assignment Problems

E-print/Working paper (2013)

We consider a special class of axial multi-dimensional assignment problems called multi-dimensional vector assignment (MVA) problems. An instance of the MVA problem is defined by $m$ disjoint sets, each ... [more ▼]

We consider a special class of axial multi-dimensional assignment problems called multi-dimensional vector assignment (MVA) problems. An instance of the MVA problem is defined by $m$ disjoint sets, each of which contains the same number $n$ of $p$-dimensional vectors with nonnegative integral components, and a cost function defined on vectors. The cost of an $m$-tuple of vectors is defined as the cost of their component-wise maximum. The problem is now to partition the $m$ sets of vectors into $n$ $m$-tuples so that no two vectors from the same set are in the same $m$-tuple and so that the total cost of the $m$-tuples is minimized. The main motivation comes from a yield optimization problem in semi-conductor manufacturing. We consider two classes of polynomial-time heuristics for MVA, namely, hub heuristics and sequential heuristics, and we study their approximation ratio. In particular, we show that when the cost function is monotone and subadditive, hub heuristics, as well as sequential heuristics, have finite approximation ratio for every fixed $m$. Moreover, we establish better approximation ratios for certain variants of hub heuristics and sequential heuristics when the cost function is monotone and submodular, or when it is additive. We provide examples to illustrate the tightness of our analysis. Furthermore, we show that the MVA problem is APX-hard even for the case $m=3$ and for binary input vectors. Finally, we show that the problem can be solved in polynomial time in the special case of binary vectors with fixed dimension $p$. [less ▲]