Monitoring à long terme d'une liaison optique aérienne cohérente à 40 Gbit/s

Le développement des formats de modulation à multiplexage en polarisation a suscité un regain d'intérêt pour l'étude des effets de polarisation dans les liaisons optiques cohérentes, qui pourraient engendrer des pannes de système. L'étude de ces effets de polarisation pourrait permettre de dimensionner les modules de traitement de signal, qui sont utilisés dans les transpondeurs cohérents, et dont le rôle est notamment de compenser les effets de polarisation tels que la dispersion modale de polarisation (PMD). Ce mémoire présente l'analyse des mesures de paramètres de performance et d'activité de polarisation effectuées sur une liaison optique cohérente à 40 Gbit/s déployée principalement sur un câble de garde à fibre optique (OPGW). Les mesures ont été faites durant plus de deux ans au moyen d'un transpondeur cohérent à double polarisation et à modulation de phase différentielle décalée en quadrature (DP-QPSK) et d'un polarimètre. La première partie concerne l’étude de l’évolution temporelle des différents paramètres caractérisant le système de transmission, tels que le taux d’erreur sur les bits (BER), le délai de groupe différentiel (DGD) ou encore la dispersion modale de polarisation (PMD). Ces paramètres ont été mesurés par un transpondeur cohérent DP-QPSK à 40 Gbit/s, avec un taux d’échantillonnage de 1 kHz, durant plusieurs saisons afin de déterminer les caractéristiques de la liaison et ont ensuite été analysés avec des outils de traitement développés sous Matlab. La seconde partie concerne l’analyse des variations rapides de polarisation à l’aide d’un polarimètre Agilent N7786B. Les paramètres de Stokes ont été mesurés avec un taux d’échantillonnage de 20 kHz durant 182 jours couvrant une période de 22 mois. La vitesse de rotation du vecteur de Stokes a été calculée pour l’ensemble des mesures et il a été possible d’étudier les changements rapides de polarisation sur l’ensemble des mesures à l’aide d’un outil développé sous Matlab. Une analyse harmonique des états de polarisation a été effectuée et enfin, une étude du bruit du polarimètre a été proposée au moyen d'un outil de simulation développé sous Matlab

Line transect sampling of primates : can animal-to-observer distance methods work?

An erratum to this article can be found at http://dx.doi.org/10.1007/s10764-010-9469-4Line transect sampling is widely used for estimating abundance of primate populations. Animal-to-observer distances (AODs) are commonly used in analysis, in preference to perpendicular distances from the line. This is in marked contrast with standard practice for other applications of line transect sampling. We formalize the mathematical shortcomings of approaches based on AODs, and show that they are likely to give strongly biased estimates of density. We review papers that claim good performance for the method, and explore this performance through simulations. These confirm strong bias in estimates of density using AODs. We conclude that AOD methods are conceptually flawed, and that they cannot in general provide valid estimates of density.PostprintPeer reviewe

Population status of Pan troglodytes verus in Lagoas de Cufada Natural Park, Guinea-Bissau

The western chimpanzee, Pan troglodytes verus, has been classified as Endangered on the IUCN Red List since 1988. Intensive agriculture, commercial plantations, logging, and mining have eliminated or degraded the habitats suitable for P. t. verus over a large part of its range. In this study we assessed the effect of land-use change on the population size and density of chimpanzees at Lagoas de Cufada Natural Park (LCNP), Guinea-Bissau. We further explored chimpanzee distribution in relation to landscape-level proxies of human disturbance. Nest count and distance-sampling methods were employed along 11 systematically placed linear transects in 2010 and 2011. Estimated nest decay rate was 293.9 days (%CV = 58.8). Based on this estimate of decay time and using the Standing-Crop Nest Count Method, we obtained a habitat-weighted average chimpanzee density estimate for 2011 of 0.22 nest building chimpanzees/km2 (95% CI 0.08–0.62), corresponding to 137 (95% CI 51.0–390.0) chimpanzees for LCNP. Human disturbance had a negative influence on chimpanzee distribution as nests were built farther away from human settlements, roads, and rivers than if they were randomly distributed, coinciding with the distribution of the remaining patches of dense canopy forest. We conclude that the continuous disappearance of suitable habitat (e.g. the replacement of LCNP's dense forests by monocultures of cashew plantations) may be compromising the future of one of the most threatened Guinean coastal chimpanzee populations. We discuss strategies to ensure long-term conservation in this important refuge for this chimpanzee subspecies at its westernmost margin of geographic distribution.Publisher PDFPeer reviewe

Ultrasmall particles for Gd-MRI and Ga-68-PET dual imaging

Nanoparticles made of a polysiloxane matrix and surrounded by 1,4,7,10-tetraazacyclododecane-1-glutaric anhydride-4,7,10-triacetic acid (DOTAGA)[Gd3+] and 2,2’-(7-(1-carboxy-4-((2,5-dioxopyrrolidin-1-yl)oxy)-4-oxobutyl)-1,4,7-t riazonane-1,4-diyl)diacetic acid) NODAGA[Ga-68(3+)] have been synthesized for positron emission tomography/magnetic resonance (PET/MRI) dual imaging. Characterizations were carried out in order to determine the nature of the ligands available for radiolabelling and to quantify them. High radiolabelling purity (>95%) after Ga-68 labelling was obtained. The MR and PET images demonstrate the possibility of using the nanoparticles for a combined PET/MR imaging scanner. The images show fast renal elimination of the nanoparticles after intravenous injection.Copyright (C) 2014 John Wiley & Sons, Ltd

Thymus and mediastinal node involvement in childhood Langerhans cell histiocytosis: long-term follow-up from the French national cohort

International audienceBACKGROUND: Mediastinal involvement (MI) in Langerhans cell histiocytosis (LCH) has been rarely reported. Here, we describe the clinical, radiological, and biological presentation, and the outcome of childhood LCH with MI. METHOD: From the French LCH register, which includes 1,423 patients aged less than 18 years, we retrieved the medical charts of patients with mediastinal enlargement detected on chest X-rays. RESULTS: Thirty-seven patients were retrieved, including 18 males; median age of diagnosis was 0.7 years, and median follow-up time was 6.2 years. The prevalence of MI varied with the age at diagnosis, ranging from 7% below 1 year old to less than 1% at \textgreater5 years. Thirteen cases (35%) were diagnosed because of MI-related symptoms, including respiratory distress (N = 4), superior venous cava syndrome (N = 2), and/or cough and polypnea (N = 10). CT scans performed in 32 cases at diagnosis showed tracheal compression (N = 5), cava thrombosis (N = 2), and/or calcification (N = 16). All patients presented multi-system disease at LCH diagnosis, and 35/37 were initially treated with vinblastine and corticosteroids. Death occurred in five cases, due to MI (N = 1) or hematological refractory involvement (N = 4). The overall 5-year survival was 87.1%, and immunodeficiency was not detected as a sequel. CONCLUSIONS: MI in LCH mainly occurs in young children, and diagnosis was based on CT showing thymus enlargement and calcifications