Synthèse et caractérisation de polymères organométalliques luminescents de cuivre(I) et d'argent(I) à base de diphosphines et diisocyanures

La première approche fut de synthétiser les unités de base et de les caractériser cristallographiquement afin de connaître l'arrangement spatial du polymère. Les unités de base étaient constituées du métal, d'une bis(diphénylphosphine)alcane et d'un ligand monodentate, le (tert -butylisonitrile) t-BuNC ayant approximativement le même encombrement stérique que le dmb. Étant donné que l'obtention de cristaux favorables à l'analyse cristallographique n'est pas toujours facile, d'autres analyses comme la RMN 31 P, l'ATG et la DRX de poudre ont dû être effectuées dans le but d'obtenir des informations sur la structure moléculaire du matériau. À la suite de l'étude de la conformation des unités de base et des polymères, l'étude des propriétés photophysiques de ces nouveaux matériaux a été faite. L'effet des groupements phényles sur les diphénylphosphines compliquait les données photophysiques. Nous avons donc décidé de remplacer les diphénylphosphines par des diméthylphosphines. Cette nouvelle approche a été étudiée en profondeur (structures cristallographiques, analyses photophysiques à l'état solide, en solution et à 77K)."--Résumé abrégé par UMI

Les photographies des ruines de Paris en 1871 ou les faux-semblants de l’image

Ce dossier iconographique présente quelques images – essentiellement des photographies – des ruines de Paris après la « semaine sanglante » de 1871. Considérée comme un œil-témoin mécanique indépendant de la volonté du photographe, la photographie participe en fait à des pratiques et des stratégies photographiques précises, élaborées depuis le milieu du dix-neuvième siècle. Les photographes professionnels participent à l’élaboration d’un Paris en ruines tout en se définissant comme des auxiliaires de l’autorité témoignant des crimes communards. Mais, une fois décryptée, cette production photographique reste, faute de mieux, le meilleur moyen de restituer le paysage sensible qui s’est offert aux Parisiens amateurs de ruines.The following iconographic file presents a few pictures, especially photographs, of the ruins of Paris after the “bloody week” in 1871. Almost seen as a mechanical eye independent of the photographer’s will, photography is in fact involved in precise practices and strategies elaborated from the second half of the 19th century onwards. In 1871, photographers were involved in the creation of the image of a destroyed Paris and characterized themselves as the auxiliaries of the authorities, since they supplied testimony of the communards’ crimes. However, these photographs, once decrypted, remain, for want of a better alternative, the best path towards reconstituting the sensitive landscape which Parisians keen on ruins could contemplate

Empereurs et évêques à Trèves, Milan et Sirmium (285-402) : l'impact religieux de la présence impériale

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

Inverse problem approach for particle digital holography: accurate location

International audienceOptical holography allows to record tridimensionnal informations of a scene using only one 2D sensor. Physical optics allows to analyticaly modelise hologram formation according to objects parameters (position, size, shape...). In simple objects case (e.g. spherical particles), the model is reduced to few parameters (four per particles: x,y,z,radius). Using inverse problem approach, it is possible to determine these parameters resolving a global optimization problem. This new approach is more efficient than classical method : particle parameters estimation is far more precise and it is possible to localize particles outside of the camera field of view. The presented method achieves to detect particles in an area sixteenth times wider than the CCD field of view with equal precision on both simulated and real digital holograms. Moreover strong improvements in the precision of the localization of the particles were noticed, particularly along the depth dimension

Inline hologram reconstruction with sparsity constraints

International audienceInline digital holograms are classically reconstructed using linear operators to model diffraction. It has long been recognized that such reconstruction operators do not invert the hologram formation operator. Classical linear reconstructions yield images with artifacts such as distortions near the field-of-view boundaries or twin-images. When objects located at different depths are reconstructed from a hologram, in-focus and out-of-focus images of all objects superimpose upon each other. Additional processing, such as maximum-of-focus detection, is thus unavoidable for any successful use of the reconstructed volume. In this letter, we consider inverting the hologram formation model in Bayesian framework. We suggest the use of a sparsity-promoting prior, intrinsically verified due to inline holography requirements, and present a simple iterative algorithm for 3D object reconstruction under sparsity and positivity constraints. Preliminary results with both simulated and experimental holograms are highly promising

Inverse problem approach for particle digital holography: accurate location based on local optimisation

The definitive version is available at http://www.opticsinfobase.org/abstract.cfm?URI=josaa-24-4-1164International audienceThis paper proposes a new micro-particles localization scheme in digital holography. Most conventionnal digital holography methods, are based on Fresnel transform and have several issues such as twin-image, border effects... To avoid these difficulties, we propose an inverse problem approach, which yields the optimal particles set which best models the observed hologram image. We resolve this global optimization problem by conventional particle detection followed by a local refinement for each particle. Results on both simulated and real digital holograms show strong improvements in the localization of the particles, in particular along the depth dimension. In our simulations, the position precision is about or better than 1 µm rms. Our results also show that the localization precision does not deteriorate for particles near the edges of the field of view

Inverse problem approach in Particle Digital Holography : out-of-field particle detection made possible

The definitive version is available at http://www.opticsinfobase.org/abstract.cfm?URI=josaa-24-12-3708International audienceWe propose a microparticle detection scheme in digital holography. In our inverse problem approach, we estimate the optimal particles set that best models the observed hologram image. Such a method can deal with data that have missing pixels. By considering the camera as a truncated version of a wider sensor, it becomes possible to detect particles even out of the camera field of view. We tested the performance of our algorithm against simulated and experimental data for diluted particle conditions. With real data, our algorithm can detect particles far from the detector edges in a working area as large as 16 times the camera field of view. A study based on simulated data shows that, compared with classical methods, our algorithm greatly improves the precision of the estimated particle positions and radii. This precision does not depend on the particle's size or location (i.e., whether inside or outside the detector field of view)

Digital holography of particles: benefits of the “inverse problem” approach

This paper was published in Measurement Science and Technology and is made available as an electronic reprint with the permission of IOP. The paper can be found at the following URL on the IOP website: http://www.iop.org/EJ/journal/MSTInternational audienceThe potential of in-line digital holography to locate and measure the size of particles distributed throughout a volume (in one shot) has been established. These measurements are fundamental for the study of particle trajectories in fluid flow. The most important issues in digital holography today are poor depth positioning accuracy, transverse field-of-view limitations, border artifacts and computational burdens. We recently suggested an ‘inverse problem' approach to address some of these issues for the processing of particle digital holograms. The described algorithm improves axial positioning accuracy, gives particle diameters with sub-micrometer accuracy, eliminates border effects and increases the size of the studied volume. This approach for processing particle holograms pushes back some classical constraints. For example, the Nyquist criterion is no longer a restriction for the recording step and the studied volume is no longer confined to the field of view delimited by the sensor borders. In this paper we present a review of the limitations commonly found in digital holography. We then discuss the benefits of the ‘inverse problem' approach and the influence of some experimental parameters in this framework

Le XIXe siècle et l’histoire scolaire

On se plaint souvent des barrières qui séparent l’histoire universitaire et l’histoire scolaire. Les renouvellements des problématiques des chercheurs peinent à passer dans les connaissances enseignées en cours (sauf à l’initiative de l’enseignant lui-même), et les grands débats qui touchent à l’histoire scolaire, pourtant vifs et majeurs, arrivent feutrés dans les laboratoires de recherche. Ce tableau est sans doute un peu caricatural ; un regain d’intérêt pour de tels échanges se manifeste ..

Draft Genome Sequence of a Necrotoxigenic Escherichia coli Isolate

Here, we present the draft genome sequence of a necrotoxigenic Escherichia coli strain isolated from a patient following a very rapidly evolving, lethal necrotizing fasciitis