Adaptive density estimation for general ARCH models

We consider a model $Y\_t=\sigma\_t\eta\_t$ in which $(\sigma\_t)$ is not independent of the noise process $(\eta\_t)$, but $\sigma\_t$ is independent of $\eta\_t$ for each $t$. We assume that $(\sigma\_t)$ is stationary and we propose an adaptive estimator of the density of $\ln(\sigma^2\_t)$ based on the observations $Y\_t$. Under various dependence structures, the rates of this nonparametric estimator coincide with the minimax rates obtained in the i.i.d. case when $(\sigma\_t)$ and $(\eta\_t)$ are independent, in all cases where these minimax rates are known. The results apply to various linear and non linear ARCH processes

Adaptive density deconvolution with dependent inputs

In the convolution model $Z\_i=X\_i+ \epsilon\_i$, we give a model selection procedure to estimate the density of the unobserved variables $(X\_i)\_{1 \leq i \leq n}$, when the sequence $(X\_i)\_{i \geq 1}$ is strictly stationary but not necessarily independent. This procedure depends on wether the density of $\epsilon\_i$ is super smooth or ordinary smooth. The rates of convergence of the penalized contrast estimators are the same as in the independent framework, and are minimax over most classes of regularity on ${\mathbb R}$. Our results apply to mixing sequences, but also to many other dependent sequences. When the errors are super smooth, the condition on the dependence coefficients is the minimal condition of that type ensuring that the sequence $(X\_i)\_{i \geq 1}$ is not a long-memory process

Liens entre la structure et la performance métabolique des communautés bactériennes aquatiques en réponse aux gradients de l'environnement

Les communautés bactériennes aquatiques sont extrêmement sensibles et réactives aux gradients environnementaux. Il a été proposé que leur réponse résultent de changements dans leur structure, tels que la composition, la fonction ct la structure physiologique. L'objectif de cette thèse est de décrire les processus qui déterminent la réponse métabolique des communautés bactériennes face à des gradients dans les principales ressources, avec un intérêt particulier pour le rôle de la composition dans cette réponse. Les chapitres de cette thèse explorent dans un contexte de métacommunauté: Dans quelle mesure les ressources déterminent le métabolisme bactérien et leur structure, comment les composantes de la structure sont liées les unes aux autres, avec les ressources et la performance de la communauté, comment la composition des communautés est liée à la fonction, comment la plasticité métabolique et la redondance fonctionnelle influencent le rôle de la composition dans la réponse de la communauté. Ces différents aspects ont été explorés in situ dans divers écotones dans un bassin versant et par des expériences de transplantations en laboratoire. Spécifiquement, les objectifs sont (1) d'examiner si les patrons en termes du métabolisme et des composantes de la structure de la communauté présentent une certaine spécificité écosystémique (2) d'étudier le lien entre la composition et la fonction des communautés, (3) de décrire la séquence des relations entre les composantes de la structure des communautés qui médient la réponse de la communauté aux changements des ressources, (4) d'évaluer l'influence de la plasticité métabolique et redondance fonctionnelle sur le métabolisme en réponse aux changements environnementaux. Les résultats indiquent que la régulation du métabolisme bactérien par les ressources est médiée par des changements dans les composantes de la structure qui peuvent être soit directionnels, spécifiques aux écosystèmes, ou aléatoire. En fait, les résultats montrent que la réponse peut être médiée d'une part, par des ajustements physiologiques des phylotypes dominants ou par le remplacement même des phylotypes dominants. Le type de réponse n'apparaît pas être déterminé par le type, ni l'intensité des gradients, mais par la plasticité métabolique de la communauté, qui à son tour semble être déterminée par des facteurs indépendants des gradients eux-mêmes. Les résultats montrent que la composition et la fonction des communautés sont liées l'une à l'autre d'une manière très dynamique, tel que leurs patrons absolus ne sont pas corrélés. La force et la forme de la relation varient en fonction du type et de l'intensité des gradients, suggérant un haut niveau de redondance fonctionnelle tant au sein de la communauté, qu'au sein de la métacommunauté, à partir de laquelle les phylotypes sont sélectionnés pour occuper les nouvelles niches créées le long des écotones. Les résultats des expériences de transplantations indiquent: L'existence d'un seuil environnemental qui détermine le niveau de redondance fonctionnelle, et une spécificité écosystémique dans la plasticité métabolique. Collectivement, les résultats de cette thèse montrent que les conditions environnementales locales ont une plus grande influence sur la structure de la communauté que la dispersion, et que la composition des communautés bactériennes joue toujours un rôle dans cette réponse en déterminant le niveau de plasticité de la communauté, mais que ce rôle n'est qu'apparent lorsque la réponse implique un remplacement des phylotypes dans les communautés qui sont intrinsèquement moins plastiques. \ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : bactérioplancton, gradients environnementaux, métabolisme du carbone, structure des communautés, métacommunauté

Chlorovirus and myovirus diversity in permafrost thaw ponds

Permafrost thaw ponds occur in high abundance across the northern landscape of Canada and are sites of intense microbial activity, resulting in carbon dioxide and methane emissions to the atmosphere. In this study, we focused on viruses as largely unstudied agents of top-down control in these high-latitude microbial ecosystems. Specifically, we compared the diversity of myovirus, chlorovirus and host microbial communities in an organic soil palsa valley pond and a mineral soil lithalsa valley pond. These 2 subarctic permafrost landscapes are both common in northern Québec, Canada. Sequence analysis of ribosomal small subunit RNA genes showed that the community structure of bacteria and microbial eukaryotes differed significantly between the 2 ponds, which both differed from microbial communities in a rock-basin lake (whose formation was not related to permafrost thawing and which we used as a reference pond) in the same region. The viral assemblages included 439 OTUs in the uncultured Myoviridae category and 41 OTUs in the family Phycodnaviridae. Phylogenetic analysis of the latter based on an amino acid sequence alignment revealed a single large clade related to chloroviruses, consistent with the abundant presence of chlorophytes in these waters. As there was for the bacterial and eukaryotic communi-ties, there were also significant differences in the community structure of these viral groups among the 3 ponds. These results suggest that host community composition is influenced by environmental filtering, which in turn contributes to driving viral diversity across landscape types

Rapid on-site detection of harmful algal blooms: real-time cyanobacteria identification using Oxford Nanopore sequencing

With the increasing occurrence and severity of cyanobacterial harmful algal blooms (cHAB) at the global scale, there is an urgent need for rapid, accurate, accessible, and cost-effective detection tools. Here, we detail the RosHAB workflow, an innovative, in-the-field applicable genomics approach for real-time, early detection of cHAB outbreaks. We present how the proposed workflow offers consistent taxonomic identification of water samples in comparison to traditional microscopic analyses in a few hours and discuss how the generated data can be used to deepen our understanding on cyanobacteria ecology and forecast HABs events. In parallel, processed water samples will be used to iteratively build the International cyanobacterial toxin database (ICYATOX; http://icyatox.ibis.ulaval.ca) containing the analysis of novel cyanobacterial genomes, including phenomics and genomics metadata. Ultimately, RosHAB will (1) improve the accuracy of on-site rapid diagnostics, (2) standardize genomic procedures in the field, (3) facilitate these genomics procedures for non-scientific personnel, and (4) identify prognostic markers for evidence-based decisions in HABs surveillance

Bilateral optic neuropathy related to severe anemia in a patient with alcoholic cirrhosis: A case report and review of the literature

Anemia appears frequently in patients with alcoholic liver disease (ALD) but has never been linked to bilateral nonarteritic anterior ischemic optic neuropathy (NAION). A 65-year-old woman with a medical history of alcoholic cirrhosis was admitted for bilateral NAION. On admission, she was found to have a low arterial pressure and severe normocytic anemia (48 g/L). The anemia was related to chronic bleeding due to antral gastritis along with other factors associated with ALD. The applied treatment consisted of urgent transfusion followed by high doses of proton-pump inhibitors, iron and vitamin supplementation, and support in lifestyle measures. Her hemoglobin levels remained stable after 2 years but the patient still suffered from visual loss. This case highlights the link between anemia and bilateral NAION in ALD patients. The optic nerve head is prone to infarction in this context due to the vascularization characteristics of ALD. Hemoglobin levels should be monitored in ALD patients to avoid the severe complication of NAION

Spatio-temporal connectivity of the aquatic microbiome associated with cyanobacterial blooms along a Great Lake riverine-lacustrine continuum

Lake Erie is subject to recurring events of cyanobacterial harmful algal blooms (cHABs), but measures of nutrients and total phytoplankton biomass seem to be poor predictors of cHABs when taken individually. A more integrated approach at the watershed scale may improve our understanding of the conditions that lead to bloom formation, such as assessing the physico-chemical and biological factors that influence the lake microbial community, as well as identifying the linkages between Lake Erie and the surrounding watershed. Within the scope of the Government of Canada’s Genomics Research and Development Initiative (GRDI) Ecobiomics project, we used high-throughput sequencing of the 16S rRNA gene to characterize the spatio-temporal variability of the aquatic microbiome in the Thames River–Lake St. Clair-Detroit River–Lake Erie aquatic corridor. We found that the aquatic microbiome was structured along the flow path and influenced mainly by higher nutrient concentrations in the Thames River, and higher temperature and pH downstream in Lake St. Clair and Lake Erie. The same dominant bacterial phyla were detected along the water continuum, changing only in relative abundance. At finer taxonomical level, however, there was a clear shift in the cyanobacterial community, with Planktothrix dominating in the Thames River and Microcystis and Synechococcus in Lake St. Clair and Lake Erie. Mantel correlations highlighted the importance of geographic distance in shaping the microbial community structure. The fact that a high proportion of microbial sequences found in the Western Basin of Lake Erie were also identified in the Thames River, indicated a high degree of connectivity and dispersal within the system, where mass effect induced by passive transport play an important role in microbial community assembly. Nevertheless, some cyanobacterial amplicon sequence variants (ASVs) related to Microcystis, representing less than 0.1% of relative abundance in the upstream Thames River, became dominant in Lake St. Clair and Erie, suggesting selection of those ASVs based on the lake conditions. Their extremely low relative abundances in the Thames suggest additional sources are likely to contribute to the rapid development of summer and fall blooms in the Western Basin of Lake Erie. Collectively, these results, which can be applied to other watersheds, improve our understanding of the factors influencing aquatic microbial community assembly and provide new perspectives on how to better understand the occurrence of cHABs in Lake Erie and elsewhere

Composition Influences the Pathway but not the Outcome of the Metabolic Response of Bacterioplankton to Resource Shifts

Bacterioplankton community metabolism is central to the functioning of aquatic ecosystems, and strongly reactive to changes in the environment, yet the processes underlying this response remain unclear. Here we explore the role that community composition plays in shaping the bacterial metabolic response to resource gradients that occur along aquatic ecotones in a complex watershed in Québec. Our results show that the response is mediated by complex shifts in community structure, and structural equation analysis confirmed two main pathways, one involving adjustments in the level of activity of existing phylotypes, and the other the replacement of the dominant phylotypes. These contrasting response pathways were not determined by the type or the intensity of the gradients involved, as we had hypothesized, but rather it would appear that some compositional configurations may be intrinsically more plastic than others. Our results suggest that community composition determines this overall level of community plasticity, but that composition itself may be driven by factors independent of the environmental gradients themselves, such that the response of bacterial communities to a given type of gradient may alternate between the adjustment and replacement pathways. We conclude that community composition influences the pathways of response in these bacterial communities, but not the metabolic outcome itself, which is driven by the environment, and which can be attained through multiple alternative configurations

Dosage des radionucléides à vie longue 79Se et 126Sn dans les solutions de produits de fission issues du traitement des combustibles nucléaires

La détermination des radionucléides dans les déchets de traitement des combustibles nucléaires est indispensable pour assurer une gestion optimale de ces déchets. Cette thèse concerne le développement de méthodes de dosage de deux radionucléides à vie longue: 79Se et 126Sn, dans des solutions de produits de fission (PF) issues du traitement des combustibles nucléaires usés. Leurs déterminations, par des techniques radiochimiques ou par spectrométrie de masse, exigent des séparations chimiques sélectives vis à vis des principaux radionucléides responsables de l'activité et des interférents de mesure. Pour le 79Se, émetteur b- de période environ 10 puissance 6 ans, deux techniques : la précipitation par l'iodure de potassium et la séparation sur résines échangeuses d'ions ont été appliquées sur une solution de PF à COGEMA La Hague. Les résultats montrent que seule la méthode par échange d'ions permet d'obtenir des fractions suffisamment décontaminées et avec un rendement important en sélénium...The quantification of radionuclides present in waste resulting from the nuclear fuel reprocessing is essential to ensure an optimal management of this waste. This thesis deals with the development of analytical methods for the determination of two long-lived radionuclides: 79Se and 126Sn, in a solution of fission products (FP) exit from nuclear fuel reprocessing. Their determination, by radiochemical method or mass spectrometry, involves selective chemical separations from the others b/g emitters and from the interfering elements. For 79 Se, a b emitter with a half-life estimated to 10 power 6 years, two techniques , i.e. precipitation by potassium iodine and separation on ion exchange resins were applied to a solution of FP at COGEMA La Hague. The results showed that only the ion exchange method allows us to obtain a solution sufficiently decontaminated with a significant selenium yield. This separation allows the measurement of the 79Se by electrothermal vaporisation coupled with inductively coupled plasma mass spectrometry...ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

High cycle fatigue damage mechanisms in cast aluminium subject to complex loads

Lien vers la version éditeur: http://www.sciencedirect.com/science/article/pii/S0142112312002356This article is dedicated to the high cycle fatigue behaviour of cast hypo-eutectic Al–Si alloys. In particular, the AlSi7Cu05Mg03 alloy is investigated. It presents the results of a vast experimental campaign undertaken to investigate the fatigue behaviour, and more specifically the fatigue damage mechanisms observed under complex loading conditions: plane bending with different load ratios, fully reversed torsion and equibiaxial bending with a load ratio of R = 0.1. A specific test set-up has been designed to create an equibiaxial stress state using disk shaped specimens. A tomographic analysis is also presented with the aim of characterising the micro-shrinkage pore population of the material. It is shown that two distinct and coexisting fatigue damage mechanisms occur in this material, depending on the presence of different microstructural heterogeneities (i.e. micro-shrinkage pores, Silicon particles in the eutectic zones, Fe-rich intermetallic phases, etc.). Furthermore, it is concluded that the effect of an equibiaxial tensile stress state is not detrimental in terms of high cycle fatigue. It is also shown that the Dang Van criterion is not able to simultaneously predict the multiaxial effect (i.e. torsion and equibiaxial tension) and the mean stress effect for this material