Lasers à fibre Fabry-Perot distribués multilongueurs d'onde : modélisation, fabrication et caractérisation

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2010-2011Cette thèse traite de lasers à fibre multilongueurs d'onde fabriqués en inscrivant des réseaux de Bragg superstructurés de type "Fabry-Perot distribué" dans une fibre photosensible codopée à l'erbium et à l'ytterbium. Ce type de laser multilongueur d'onde se distingue des autres approches proposées dans la littérature par sa simplicité : en plus du réseau de Bragg superstructuré inscrit à même la fibre de gain, seuls une diode laser de pompe et un coupleur d'injection de pompe sont requis pour produire un peigne formé de plusieurs raies laser monomodes espacées de 50 GHz ou de 100 GHz. Ces lasers multilongueurs d'onde pourraient éventuellement être utilisés pour certaines applications de tests et mesures dans le domaine des télécommunications optiques en plus d'avoir un potentiel pour l'interrogation de capteurs à fibre optique requérant des lasers à faible largeur de raie. Cette thèse comporte plusieurs volets. Premièrement, les lasers multilongueurs d'onde sont étudiés en utilisant un modèle théorique combinant un modèle de gain d'une fibre codopée à l'erbium et à l'ytterbium avec un modèle de réseau de Bragg utilisant la théorie des modes couplés. Cette modélisation a permis de démontrer que ces lasers sont en fait des cascades ultra-compactes de courtes cavités laser monomodes. Par la suite, nous présentons les détails de la fabrication des lasers. Nous démontrons que l'uniformité en puissance et en fréquence des lignes du laser est limitée principalement par l'uniformité du profil d'indice effectif moyen photoinscrit le long du réseau. Nous avons aussi effectué une caractérisation détaillée des fluctuations de puissance des lignes laser. Ces fluctuations sont non corrélées, ce qui peut être expliqué par le fait que les cavités laser correspondant à chacune des lignes sont spatialement réparties. En outre, nous avons montré qu'il est possible d'éteindre temporairement certaines lignes du laser au moyen de fils chauffants placés contre la fibre et ainsi obtenir un laser reconfigurable. Finalement, l'étude détaillée de la fabrication des réseaux de Bragg superstructurés a permis d'identifier qu'il était nécessaire de tenir compte de la dynamique de la diffusion du deuterium afin de décrire la croissance de réseaux de Bragg à fort changement d'indice

Developmental regulation of the neuroinflammatory responses to LPS and/or hypoxia-ischemia between preterm and term neonates: An experimental study

<p>Abstract</p> <p>Background</p> <p>Preterm and term newborns are at high risk of brain damage as well as subsequent cerebral palsy and learning disabilities. Indeed, hypoxia-ischemia (HI), pathogen exposures, and associated intracerebral increase of pro-inflammatory cytokines have all been linked to perinatal brain damage. However, the developmental effects of potential variations of pro- and anti-inflammatory cytokine ratios remain unknown.</p> <p>Methods</p> <p>Using rat models of perinatal brain damage induced by exposures to lipopolysaccharide (LPS) and/or HI at distinct levels of maturity, we compared cytokine expression at stages of cerebral development equivalent to either preterm (postnatal day 1, P1) or term (P12) newborns.</p> <p>Results</p> <p>At P1, expression of anti-inflammatory cytokine within the brain was either not modulated (IL-6, IL-10) or down-regulated (IL-1ra, TGF-β1) by HI, LPS or LPS+HI. In contrast, there was at P12 an up-regulation of all anti-inflammatory cytokines studied in HI or LPS+HI condition, but not after LPS exposure. Interestingly, IL-1β was the main pro-inflammatory cytokine up-regulated moderately at P1, and strongly at P12, with a weak co-expression of TNF-α observed mainly at P12. These age-dependant inflammatory reactions were also accompanied, under HI and LPS+HI conditions, at P12 only, by combined: (i) expression of chemokines CINC-1 and MCP-1, (ii) blood-brain barrier (BBB) leakage, and (iii) intracerebral recruitment of systemic immune cells such as neutrophils. In contrast, sole LPS induced IL-1β responses mainly within white matter at P1 and mainly within gray matter at P12, that were only associated with early MCP-1 (but no CINC-1) induction at both ages, without any recruitment of neutrophils and CD68+ cells.</p> <p>Conclusion</p> <p>HI and LPS+HI induce pro-inflammatory oriented immune responses in both preterm and term like brains, with a maximal inflammatory response triggered by the combination of LPS+HI. The profile of these neuroinflammatory responses presented striking variations according to age: no or down-regulated anti-inflammatory responses associated with mainly IL-1β release in preterm-like brains (P1), in sharp contrast to term-like brains (P12) presenting stronger anti-and pro-inflammatory responses, including both IL-1β and TNF-α releases, and BBB leakage. These developmental-dependant variations of neuroinflammatory response could contribute to the differential pattern of brain lesions observed across gestational ages in humans. This also highlights the necessity to take into consideration the maturation stage, of both brain and immune systems, in order to develop new anti-inflammatory neuroprotective strategies.</p

Variants of a genomic island in Aeromonas salmonicida subsp. salmonicida link isolates with their geographical origins

Aeromonas salmonicida subsp. salmonicida is a fish pathogen. Analysis of its genomic characteristics is required to determine the worldwide distribution of the various populations of this bacterium. Genomic alignments between the 01-B526 pathogenic strain and the A449 reference strain have revealed a 51-kb chromosomal insertion in 01-B526. This insertion (AsaGEI1a) has been identified as a new genomic island (GEI) bearing prophage genes. PCR assays were used to detect this GEI in a collection of 139 A. salmonicida subsp. salmonicida isolates. Three forms of this GEI (AsaGEI1a, AsaGEI1b, AsaGEI2a) are now known based on this analysis and the sequencing of the genomes of seven additional isolates. A new prophage (prophage 3) associated with AsaGEI2a was also discovered. Each GEI appeared to be strongly associated with a specific geographic region. AsaGEI1a and AsaGEI2a were exclusively found in North American isolates, except for one European isolate bearing AsaGEI2a. The majority of the isolates bearing AsaGEI1b or no GEI were from Europe. Prophage 3 has also a particular geographic distribution and was found only in North American isolates. We demonstrated that A. salmonicida subsp. salmonicida possesses unsuspected elements of genomic heterogeneity that could be used as indicators to determine the geographic origins of isolates of this bacterium.Keywords : Bacteria, Genomics-functional genomics-comparative genomics; Furunculosis; Aeromonas salmonicida; Fish pathogen; Genomic island; Geographical distributio

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements