Application of the multiple-scattering method to analysis of systems with semi-infinite photonic waveguides

We propose a technique of compensating the spurious reflections implied by the multiple-scattering (MS) method, commonly used for analyzing finite photonic crystal (PC) systems, to obtain exact values of characteristic parameters, such as reflection and transmission coefficients, of PC functional elements. Rather than a modification of the MS computational algorithm, our approach involves postprocessing of results obtained by the MS method. We derive analytical formulas for the fields excited in a finite system, taking explicitly into account the spurious reflections occurring at the artificial system boundaries. The intrinsic parameters of the investigated functional element are found by fitting the results of MS simulations to those obtained from the formulas derived. Devices linked with one and two semi-infinite waveguides are analyzed explicitly; possible extensions of the formalism to more complex circuits are discussed as well. The accuracy of the proposed method is tested in a number of systems; the results of our calculations prove to be in good agreement with those obtained independently by other authors.Comment: 8 pages, 5 figure

Mise au point d'outils portables de spectrométrie dans le proche infrarouge (SPIR) pour évaluer la qualité des fourrages à la ferme

L'évaluation de la qualité nutritive des ressources fourragères ainsi que leur variation saisonnière sont indispensables pour la gestion raisonnée de l'alimentation des ruminants. L'analyse de la qualité des fourrages est généralement réalisée à l'aide de méthodes conventionnelles (analyses chimiques en laboratoire). Néanmoins, ces méthodes coûteuses en temps, en argent et en matériel ne permettent pas d'évaluer dans un intervalle suffisamment court la qualité des fourrages (Bruno-Soares et al., 1998). La spectrométrie dans le proche infrarouge (SPIR), méthode physique basée sur la capacité des composés organiques à absorber le rayonnement infrarouge, permet d'estimer la composition chimique de l'échantillon dans un intervalle de temps beaucoup plus raisonnable. Par ailleurs, elle présente l'avantage d'être une méthode non destructive, multi-composant, sans recours aux solvants et peu onéreuse par rapport aux méthodes analytiques conventionnelles. Depuis les années 90, la méthode développée sur les fourrages a gagné en précision et en fiabilité (Dardenne et al., 1991 ; Aufrère et al., 2006 ; Tran et al., 2010). L'avancée technologique a permis le développement d'appareils SPIR portatifs tels que le LabSpec 5000 (ASD Inc., USA) ou le PhazIR TM (Polychromix, USA). Il devient aujourd'hui possible d'accompagner en temps réel les agriculteurs dans leurs pratiques, afin de pérenniser leur activité de productions végétale et animale. Depuis une dizaine d'années, la SPIR (en version laboratoire à poste fixe ; Foss NIR System 5000 monochromator) est disponible au CIRAD pour la prédiction de la qualité des fourrages produits à la Réunion. L'Association Réunionnaise du Pastoralisme (ARP), associée au CIRAD, mène depuis deux ans un programme de recherche-développement destiné à mettre au point des outils SPIR portatifs pour gérer, en temps réel, les systèmes fourragers des élevages de ruminants. La rapidité d'obtention des résultats, obtenus in situ et directement restitués aux éleveurs, ainsi que le faible coût des analyses font de ces appareils portatifs des outils d'aide à la décision particulièrement intéressants pour optimiser la gestion raisonnée des prairies en temps réel et améliorer la qualité de la ration des ruminants. La restitution des résultats en temps réel et in situ aux éleveurs a permis une excellente réactivité des professionnels vis-à-vis de la valorisation précise de ses ressources et l'ajustement des compléments de production pour le troupeau (diminution du gaspillage). Ceci contribue de manière directe à mieux maitriser les coûts de production afin d'être plus compétitifs et en garantissant le maintien des revenus. L'objectif de la présente étude est de développer les étalonnages des appareils portatifs pour estimer directement en exploitation la valeur nutritive des ressources fourragères

Bayesian modelling of an absolute chronology for Egypt's 18th Dynasty by astrophysical and radiocarbon methods

Only a few astrophysical points and synchronisms listed in texts provide anchor points for the absolute chronology of Ancient Egypt. At first we will show how we can re-calculate some of these anchor points by using Sothic dating based on the arcus visionis method, and modelling lunar dates using a Bayesian approach. Then, we will discuss two radiocarbon studies carried out on short-lived Egyptian materials held at the Louvre Museum that could be attributed to particular reigns or other precise periods. Using a Bayesian approach, these dates were combined with the known order of succession and the lengths of reigns. Sothic and lunar dates were integrated as priors in the model. This approach has led to a new proposal for the absolute chronology of Egypt's 18th Dynasty

Use of fluorescence expression tools for the comparative analysis of the interactions of Mycoplasma mycoides and Mycoplasma bovis with bovine cells

Background: Fluorescence expression systems adapted to the analysis of host-mycoplasma interactions were recently developed. The aim of this work was to apply them to study the colonisation and persistence capabilities of the bovine pathogens Mycoplasma mycoides subsp. mycoides (Mmm) and Mycoplasma bovis in bovine cells. Methods. Mini-transposons affording high-level expression of GFP2, mCherry, mKO2 and mNeonGreen were used to mark Mmm and M. bovis strains. The resulting fluorescent mutants were characterised by epifluorescence microscopy and fluorimetry and the sites of transposon insertion were identified by sequencing. Interactions of mNeonGreen mutants with bovine cells were analysed using flow cytometry and confocal microscopy. Results: The production, selection and characterisation of fluorescent clones were straightforward and compatible with the production of fluorescent mutant banks. M. bovis presented much higher adhesion, invasion and proliferation capacities than Mmm in culture with non-phagocytic cells and showed increased resistance to elimination by macrophages. Conclusion: The remarkable differences in the invasion and persistence capabilities of Mmm and M. bovis observed here are in agreement with the pathogenesis of the infections caused by these mycoplasmas. mNeonGreen fluorescent mutants have proven extremely useful for analysis of mycoplasma-host cell interactions. Furthermore, the fluorescence expression tools used in this study offer innumerable perspectives for the functional analysis of a wide range of mycoplasma species both in vitro and in vivo

Use of fluorescence expression tools for the comparative analysis of the interactions of Mycoplasma mycoides and Mycoplasma bovis with bovine cells

Background: Fluorescence expression systems adapted to the analysis of host-mycoplasma interactions were recently developed. The aim of this work was to apply them to study the colonisation and persistence capabilities of the bovine pathogens Mycoplasma mycoides subsp. mycoides (Mmm) and Mycoplasma bovis in bovine cells. Methods. Mini-transposons affording high-level expression of GFP2, mCherry, mKO2 and mNeonGreen were used to mark Mmm and M. bovis strains. The resulting fluorescent mutants were characterised by epifluorescence microscopy and fluorimetry and the sites of transposon insertion were identified by sequencing. Interactions of mNeonGreen mutants with bovine cells were analysed using flow cytometry and confocal microscopy. Results: The production, selection and characterisation of fluorescent clones were straightforward and compatible with the production of fluorescent mutant banks. M. bovis presented much higher adhesion, invasion and proliferation capacities than Mmm in culture with non-phagocytic cells and showed increased resistance to elimination by macrophages. Conclusion: The remarkable differences in the invasion and persistence capabilities of Mmm and M. bovis observed here are in agreement with the pathogenesis of the infections caused by these mycoplasmas. mNeonGreen fluorescent mutants have proven extremely useful for analysis of mycoplasma-host cell interactions. Furthermore, the fluorescence expression tools used in this study offer innumerable perspectives for the functional analysis of a wide range of mycoplasma species both in vitro and in vivo

Focal plane wavefront sensing on SUBARU/SCExAO

Focal plane wavefront sensing is an elegant solution for wavefront sensing since near-focal images of any source taken by a detector show distortions in the presence of aberrations. Non-Common Path Aberrations and the Low Wind Effect both have the ability to limit the achievable contrast of the finest coronagraphs coupled with the best extreme adaptive optics systems. To correct for these aberrations, the Subaru Coronagraphic Extreme Adaptive Optics instrument hosts many focal plane wavefront sensors using detectors as close to the science detector as possible. We present seven of them and compare their implementation and efficiency on SCExAO. This work will be critical for wavefront sensing on next generation of extremely large telescopes that might present similar limitations

Recent advances in radiation-hardened fiber-based technologies for space applications

International audience; In this topical review, the recent progress on radiation-hardened fiber-based technologies is detailed, focusing on examples for space applications. In the first part of the review, we introduce the operational principles of the various fiber-based technologies considered for use in radiation environments: passive optical fibers for data links, diagnostics, active optical fibers for amplifiers and laser sources as well as the different classes of point and distributed fiber sensors: gyroscopes, Bragg gratings, Rayleigh, Raman or Brillouin-based distributed sensors. Second, we describe the state of the art regarding our knowledge of radiation effects on the performance of these devices, from the microscopic effects observed in the amorphous silica glass used to design fiber cores and cladding, to the macroscopic response of fiber-based devices and systems. Third, we present the recent advances regarding the hardening (improvement of the radiation tolerance) of these technologies acting on the material, device or system levels. From the review, the potential of fiber-based technologies for operation in radiation environments is demonstrated and the future challenges to be overcome in the coming years are presented