Performance Evaluation of the Labelled OBS Architecture

A comparison of three different Optical Burst Switching (OBS) architectures is made, in terms of performance criteria, control and hardware complexity, fairness, resource utilization, and burst loss probability. Regarding burst losses, we distinguish the losses due to burst contentions from those due to contentions of Burst Control Packets (BCP). The simulation results show that as a counterpart of an its additional hardware complexity, the labelled OBS (L-OBS) is an efficient OBS architecture compared to a Conventional OBS (C-OBS) as well as in comparison with Offset Time-Emulated OBS (E-OBS)

Etude de l'interaction modale rotor/stator dans un moteur d'avion

International audienceIn modern turbo machines such as aircraft jet engines, contact between the casing and bladed disk may occur through avariety of mechanisms : coincidence of vibration modes, thermal deformation of the casing, rotor imbalance, etc. Thesenonlinear interactions may result in severe damage to both structures and it is important to understand the physicalmechanisms that cause them and the circumstances under which they occur. In this study, we focus on the phenomenonof interaction caused by modal coincidence. A simple two-dimensional model of the casing and bladed disk structures isintroduced in order to predict the occurrence of the interaction phenomenon in terms of the rotation speed of the rotor.Each structure is represented in terms of its two $n_ d$ -nodal diameter vibration modes, which are characteristic of axi-symmetric structures and allow for travelling wave motions that may interact through direct contact. The equations ofmotion are solved first using an explicit time integration scheme in conjunction with the Lagrange multiplier method, andthen by the Harmonic Balance Method. Both methods generally agree well and exhibit two distinct zones of completelydifferent behaviors of the system. Finally, a second planar model is introduced in order to achieve a deeper understandingof the interaction phenomenon.Dans le domaine des turbo-machines comme les moteurs d’avion par exemple, les contacts structurels entre le carter etla roue aubagée peuvent avoir plusieurs origines : coïncidence vibratoire entre des modes, déformation thermique ducarter, apparition d’un balourd au niveau du rotor, etc. Ces interactions non linéaires peuvent fortement endommagerles structures et il est important de comprendre l’origine de ces mécanismes. Dans ce travail, nous nous concentronssur le phénomène d’interaction modale. Un premier modèle planaire du carter et de la roue aubagée est développé pourprédire les vitesses de rotation du moteur pour lesquelles le phénomène d’interaction peut exister. Chaque structure estdiscrétisée sur ses deux modes à $n_ d$ diamètres nodaux, caractéristiques des structures à symétrie cyclique et qui, combinés, permettent de construire des ondes de propagation qui interagissent par l’intermédiaire du contact. Les équations sont résolues grâce à un schéma d’intégration explicite couplé à la méthode des multiplicateurs de Lagrange, puis par la méthode de l’équilibrage harmonique. Les deux méthodes sont en accord et montrent qu’il y a deux zones distinctes de fonctionnement. Finalement, un deuxième modèle planaire est présenté pour comprendre plus en détail le phénomène d’interaction

Fertilisation des céréales en agriculture biologique

En agriculture biologique, la gestion de la fertilisation repose essentiellement sur un raisonnement à long terme basé sur la fertilité du sol (rotation, légumineuses, apports de matières organiques). La spécialisation d’un nombre croissant de fermes bio en grandes cultures avec peu ou pas de bétail rend cette gestion de la fertilité du sol encore plus compliquée, en raison du manque d’engrais de ferme directement disponible sur l’exploitation et de l’absence de prairies dans la rotation. Dans le cas particulier des céréales, les besoins en azote aux stades tallage et début redressement sont importants, à une période où la minéralisation de l'azote du sol est encore faible (faible température du sol et faible activité des bactéries nitrifiantes). Ce manque d'azote minéralisé se marque dès le début du développement de la végétation et se poursuit pendant tout le cycle végétatif des céréales. Cela impacte les rendements et explique notamment les faibles teneurs en protéines des céréales cultivées en agriculture biologique en Wallonie ou en France. De surcroît, le retard de développement de la culture entraîne un manque de concurrence vis-à-vis des adventices. C’est pourquoi le recours aux engrais organiques du commerce (ou à certains engrais de ferme si disponibles) est fréquent afin de compenser le déficit en fourniture d’azote par le sol et répondre à des besoins en azote à des moments clés de la croissance

Pharmacokinetic modelling and development of Bayesian estimators for therapeutic drug monitoring of mycophenolate mofetil in reduced-intensity haematopoietic stem cell transplantation.

International audienceBACKGROUND: Mycophenolate mofetil, a prodrug of mycophenolic acid (MPA), is used during non-myeloablative and reduced-intensity conditioning haematopoetic stem cell transplantation (HCT) to improve engraftment and reduce graft-versus-host disease (GVHD). However, information about MPA pharmacokinetics is sparse in this context and its use is still empirical. OBJECTIVES: To perform a pilot pharmacokinetic study and to develop maximum a posteriori Bayesian estimators (MAP-BEs) for the estimation of MPA exposure in HCT. PATIENTS AND METHODS: Fourteen patients administered oral mycophenolate mofetil 15 g/kg three times daily were included. Two consecutive 8-hour pharmacokinetic profiles were performed on the same day, 3 days before and 4 days after the HCT. One 8-hour pharmacokinetic profile was performed on day 27 after transplantation. For these 8-hour pharmacokinetic profiles, blood samples were collected predose and 20, 40, 60, 90 minutes and 2, 4, 6 and 8 hours post-dose. Using the iterative two-stage (ITS) method, two different one-compartment open pharmacokinetic models with first-order elimination were developed to describe the data: one with two gamma laws and one with three gamma laws to describe the absorption phase. For each pharmacokinetic profile, the Akaike information criterion (AIC) was calculated to evaluate model fitting. On the basis of the population pharmacokinetic parameters, MAP-BEs were developed for the estimation of MPA pharmacokinetics and area under the plasma concentration-time curve (AUC) from 0 to 8 hours at the different studied periods using a limited-sampling strategy. These MAP-BEs were then validated using a data-splitting method. RESULTS: The ITS approach allowed the development of MAP-BEs based either on 'double-gamma' or 'triple-gamma' models, the combination of which allowed correct estimation of MPA pharmacokinetics and AUC on the basis of a 20 minute-90 minute-240 minute sampling schedule. The mean bias of the Bayesian versus reference (trapezoidal) AUCs was 20%. AIC was systematically calculated for the choice of the most appropriate model fitting the data. CONCLUSION: Pharmacokinetic models and MAP-BEs for mycophenolate mofetil when administered to HCT patients have been developed. In the studied population, they allowed the estimation of MPA exposure based on three blood samples, which could be helpful in conducting clinical trials for the optimization of MPA in reduced-intensity HCT. However, prior studies will be needed to validate them in larger populations

Mid Infrared Properties of Low Metallicity Blue Compact Dwarf Galaxies From Spitzer/IRS

We present a {\em Spitzer}-based mid-infrared study of a large sample of Blue Compact Dwarf galaxies (BCD) using the Infrared Spectrograph (IRS), including the first mid-IR spectrum of IZw18, the archetype for the BCD class and among the most metal poor galaxies known. We show the spectra of Polycyclic Aromatic Hydrocarbon (PAH) emission in low-metallicity environment. We find that the equivalent widths (EW) of PAHs at 6.2, 7.7, 8.6 and 11.2 $\mu$m are generally weaker in BCDs than in typical starburst galaxies and that the fine structure line ratio, [NeIII]/[NeII], has a weak anti-correlation with the PAH EW. A much stronger anti-correlation is shown between the PAH EW and the product of the [NeIII]/[NeII] ratio and the UV luminosity density divided by the metallicity. We conclude that PAH EW in metal-poor high-excitation environments is determined by a combination of PAH formation and destruction effects.Comment: 41 pages, 14 figure