Evaluation of Error Correcting Code performances of a free space optical communication system between LEO satellite and Ground Station

Optical communication between LEO satellite and optical ground station creates the opportunity to highly increase the transmitted data rate. The propagation channel has specificities that imply the potential use of error correcting code (ECC) and interleaving at physical and higher layer. A physical layer simulator designed to investigate the performance of the combination of ECC and interleaving in presence of various channel scenarios and receiver architectures is presented here. The simulator emulates signal generation, propagation impairments by the use of dedicated optical attenuation time series provided by state of the art wave optics results and the effect of receiver front-ends with various detection methods. Mutual information (MI) is computed in order to approximate ECC performances. Various receiver architectures and channel scenarios were studied. Among others, direct coupling of the received signal into the photo-detector (PD) or the use of pre-amplified receiver with single mode fiber (SSMF) coupling and optical amplification prior to the detection were considered. Several receiver architectures were considered: the use of a wide field-of-view detector, SSMF coupling with a single tip/tilt correction or with higher order adaptive optics correction. Two modulations of OOK and DBPSK along with various detection methods were examined. The tuning of ECC parameters was studied through the computation of mutual information. Additionally, the two cases of physical and higher layer interleaving were implemented providing an excellent diversity to the channel seen by the codeword of ECC

Performance evaluation of coded transmission for adaptive-optics corrected satellite-to-ground laser links

Performance estimation of coded LEO satellite-to ground laser transmissions partially corrected by adaptive-optics are presented. Through numerical simulations, the conjugation of adaptive-optics with a cross-layering optimization of data reliability mechanisms is investigated. The emphasis is put on the minimization of the data memories required at both the transmitter and the receiver in order to guarantee an error-free downlink

Cross layer optimisation for adaptive-optics corrected satellite to Ground laser links

For future satellite-to-ground communications link, very high throughput might be achievable at a reasonable cost assuming the use of existing single mode components developed for fiber technologies (optical detectors and amplifiers, MUX/DEMUX...). The influence of atmospheric turbulence degrades the injection efficiency of the incoming wave into single mode components. This leads to signal fading and channel impairments. Several mitigation strategies are considered to prevent them. The use of adaptive optics (AO) should contribute to reduce substantially the criticality of the fading at the expense of potentially complex and expensive systems if very high stability of the injection is requested. The use of appropriate numerical mitigation techniques (coding+interleaving) can help to relax the specifications and cost of AO systems but could lead among others to unmanageable buffer size. Thus the specification of AO correction and interleavers/forward error codes should be addressed jointly. A model to evaluate the channel capacity in terms of outage probability and packet error rate has been developed that jointly takes into account partial correction by AO and channel interleaving. It includes the capability to evaluate coded transmission performance over the correlated FSO channel in satellite-to-ground scenarios. This model is presented here and confronted to numerical simulations for several distinct correction cases. The interdependence of AO correction with numerical mitigation techniques is investigated

Statistical properties of single-mode fiber coupling of satellite-to-ground laser links partially corrected by adaptive optics

In the framework of satellite-to-ground laser downlinks, an analytical model describing the variations of the instantaneous coupled flux into a single-mode fiber after correction of the incoming wavefront by partial adaptive optics (AO) is presented. Expressions for the probability density function and the cumulative distribution function as well as for the average fading duration and fading duration distribution of the corrected coupled flux are given. These results are of prime interest for the computation of metrics related to coded transmissions over correlated channels, and they are confronted by end-to-end wave-optics simulations in the case of a geosynchronous satellite (GEO)-to-ground and a low earth orbit satellite (LEO)-to-ground scenario. Eventually, the impact of different AO performances on the aforementioned fading duration distribution is analytically investigated for both scenarios

The myofibroblast, multiple origins for major roles in normal and pathological tissue repair

Myofibroblasts differentiate, invade and repair injured tissues by secreting and organizing the extracellular matrix and by developing contractile forces. When tissues are damaged, tissue homeostasis must be re-established, and repair mechanisms have to rapidly provide harmonious mechanical tissue organization, a process essentially supported by (myo)fibroblasts. Under physiological conditions, the secretory and contractile activities of myofibroblasts are terminated when the repair is complete (scar formation) but the functionality of the tissue is only rarely perfectly restored. At the end of the normal repair process, myofibroblasts disappear by apoptosis but in pathological situations, myofibroblasts likely remain leading to excessive scarring. Myofibroblasts originate from different precursor cells, the major contribution being from local recruitment of connective tissue fibroblasts. However, local mesenchymal stem cells, bone marrow-derived mesenchymal stem cells and cells derived from an epithelial-mesenchymal transition process, may represent alternative sources of myofibroblasts when local fibroblasts are not able to satisfy the requirement for these cells during repair. These diverse cell types probably contribute to the appearance of myofibroblast subpopulations which show specific biological properties and which are important to understand in order to develop new therapeutic strategies for treatment of fibrotic and scarring diseases

OSBPL10, a novel candidate gene for high triglyceride trait in dyslipidemic Finnish subjects, regulates cellular lipid metabolism

Analysis of variants in three genes encoding oxysterol-binding protein (OSBP) homologues (OSBPL2, OSBPL9, OSBPL10) in Finnish families with familial low high-density lipoprotein (HDL) levels (N = 426) or familial combined hyperlipidemia (N = 684) revealed suggestive linkage of OSBPL10 single-nucleotide polymorphisms (SNPs) with extreme end high triglyceride (TG; >90th percentile) trait. Prompted by this initial finding, we carried out association analysis in a metabolic syndrome subcohort (Genmets) of Health2000 examination survey (N = 2,138), revealing association of multiple OSBPL10 SNPs with high serum TG levels (>95th percentile). To investigate whether OSBPL10 could be the gene underlying the observed linkage and association, we carried out functional experiments in the human hepatoma cell line Huh7. Silencing of OSBPL10 increased the incorporation of [3H]acetate into cholesterol and both [3H]acetate and [3H]oleate into triglycerides and enhanced the accumulation of secreted apolipoprotein B100 in growth medium, suggesting that the encoded protein ORP10 suppresses hepatic lipogenesis and very-low-density lipoprotein production. ORP10 was shown to associate dynamically with microtubules, consistent with its involvement in intracellular transport or organelle positioning. The data introduces OSBPL10 as a gene whose variation may contribute to high triglyceride levels in dyslipidemic Finnish subjects and provides evidence for ORP10 as a regulator of cellular lipid metabolism

A MAP6-Related Protein Is Present in Protozoa and Is Involved in Flagellum Motility

In vertebrates the microtubule-associated proteins MAP6 and MAP6d1 stabilize cold-resistant microtubules. Cilia and flagella have cold-stable microtubules but MAP6 proteins have not been identified in these organelles. Here, we describe TbSAXO as the first MAP6-related protein to be identified in a protozoan, Trypanosoma brucei. Using a heterologous expression system, we show that TbSAXO is a microtubule stabilizing protein. Furthermore we identify the domains of the protein responsible for microtubule binding and stabilizing and show that they share homologies with the microtubule-stabilizing Mn domains of the MAP6 proteins. We demonstrate, in the flagellated parasite, that TbSAXO is an axonemal protein that plays a role in flagellum motility. Lastly we provide evidence that TbSAXO belongs to a group of MAP6-related proteins (SAXO proteins) present only in ciliated or flagellated organisms ranging from protozoa to mammals. We discuss the potential roles of the SAXO proteins in cilia and flagella function

Propagation optique et correction en forte turbulence

L optique adaptative multi-conjuguée (OAMC) a été proposée en astronomie pour augmenter le champ de correction de l optique adaptative. En imagerie terrestre, les effets de la turbulence atmosphérique sont plus importants : le champ de correction est encore plus faible et les effets diffractifs de la propagation ne peuvent être négligés. L objectif de cette thèse est de déterminer les performances et les limites de l OAMC lorsque les effets de la propagation sont pris en compte. Pour cette étude, nous nous sommes placés dans une configuration idéale où les effets de la turbulence sont simulés par deux couches parfaitement conjuguées avec deux miroirs déformables. Nous avons montré que l OAMC pourrait permettre d apporter une correction satisfaisante même dans les cas de très fortes perturbations. La limitation ultime de la correction est due à la troncature de la pupille qui provoque en particulier des fluctuations d intensité dans le plan image de la pupille. Nous avons proposé un modèle de réponse impulsionnelle prenant en compte ces effets. Nous avons montré que ces fluctuations représentent un problème majeur pour la mise en œuvre d une OAMC en perturbant la mesure de front d onde. Parallèlement, en se plaçant dans le cadre des faibles perturbations, nous avons évalué analytiquement les corrélations des mesures de l analyseur de Shack-Hartmann (pentes et intensités) en fonction du profil de Cn2. Nous avons utilisé ce formalisme pour étudier l erreur d anisoplanétisme sur les mesures de front d onde par Shack-Hartmann avec un objet étendu. Nous avons ensuite montré qu il était possible de l appliquer à la détermination du profil de Cn2 par inversion des mesures.Multi-conjugate Adaptive Optics (MCAO) has been suggested in astronomy to increase the correction field of adaptive optics. The effects of atmospheric turbulence are stronger in case of near to ground observations: the correction field is smaller and diffractive effects of the propagation can no longer be neglected. The main purpose of this work is to study MCAO performances and limitations when the diffractive effects of the propagation are taken into account. We have considered an ideal configuration of two layers and two exactly conjugated dynamical mirrors. We show that MCAO may provide a good correction even if perturbations are strong. We observe that the limitation to a perfect correction comes from pupil truncation effects. They cause intensity fluctuations in the conjugated plane of the pupil. We propose a model of the point spread function which takes into account those effects. Concerning intensity fluctuations, we demonstrate that they can strongly affect wavefront measurement and therefore jeopardise MCAO systems operation. Finally, in the framework of the small perturbations approximation, we have expressed analytically the correlations between Shack-Hartmann data (slopes and intensities) as functions of the Cn profile. This formalism is used to study anisoplanatism effects on wavefront measurement with a Shack-Hartmann operating on extended sources. We also demonstrate that it can be used to recover the Cn profile by data inversion.NICE-BU Sciences (060882101) / SudocSudocFranceF

The effect of incubation conditions on the laboratory measurement of the methane producing capacity of livestock wastes

International audienceThe effects of incubations conditions (dilution, mixing, incubation time and inoculum amount and origin) on the determination of the maximum methane producing capacity (B0) from various livestock slurries were evaluated. For this purpose, the methane yields of different livestock slurries were determined using batch anaerobic incubations performed at 30 [degree sign]C as regard these different conditions. The B0 and the methane (CH4) generation as a function of time were used to study the processes and to determine the best incubation conditions. Methanogenesis was identified as the major rate-limiting step during the anaerobic degradation of slurries, probably due to inhibition by volatile fatty acids. In some cases, high free NH3 concentrations were suspected to inhibit the hydrolysis process. The addition of inoculum and/or the dilution of the substrate reduced the inhibition and allowed to reach the B0 more rapidly. However, the addition of inoculum must be minimized to reduce the possible errors made by considering a similar production by the inoculum with and without the substrate. All experiments performed during this study allowed to define the incubation conditions required for the determination of the B0 from livestock slurries. Applying these conditions, the B0 values determined for swine slurries varied from 244 to 343 L , from 204 to 296 L for dairy cattle slurries and equalled 386 and 319 L respectively for calves and duck slurries