Créer une exposition virtuelle

La fiche propose un cheminement pour créer des expositions virtuelles : les questions à se poser en amont et les étapes de la création, ainsi que de nombreux exemples d\u27expositions virtuelles

Un algorithme de débruitage Non-Local means espace-fréquence

National audienceThe efficiency of the Non-Local means (NLM) image denoising algorithm relies on the identification of similar original pixels from noisy similar patches. Hence fine details and low-contrasted structures are badly recovered after the application of NLM. But as these structures tend to correspond to redundant ones in the Fourier domain, NLM filtering in this domain allows one to better denoise them. A mixed space-frequency approach improves the denoising performances of NLM because it ensures that the information is redundant enough, in the spatial domain or in the frequency domain. Our approach is simple : it consists in running two times the NLM algorithm (firstly in the frequency domain and secondly in the spatial domain). For fine textures and isolated points we get a better visual reconstruction than with the original NLM. In terms of PSNR, the improvement can be over 1 dB. Our approach gives intermediate results between the original NLM and state-of-the-art methods while at the same time having moderate complexity and leading to few visual artifacts

Non-Local means est un algorithme de débruitage local

National audienceThe Non-Local Means (NLM) image denoising algorithm pushed the limits of denoising. But it introduced a new paradigm, according to which one could capture the similarity of images with the NLM weights. We show that, contrary to the prevailing opinion, the NLM weights do not allow to get a reliable measure of the similarity in a noisy image, unless one add a locality constraint. As an image denoising method, the Non-Local Means prove to be local. Some works had already pointed out that to get the best denoising performances with the NLM algorithm, one should run it locally. But no general conclusion has been yet proposed and the only explanation that was proposed to justify the experimental results is not sufficient. Our study based on experimental evidence proves that, on average on natural images, the bias of the NLM estimator is an increasing function of the radius of the similarity searching zone. The reason for this phenomenon is that noise disrupts the order of similarity between patches. Hence the mean squared error between the original image and the NLM estimation, which is the sum of the bias, the variance and the covariance of the estimator, has an absolute minimum for a disk of radius 3 to 4 pixels

Continuous enrichment cultures: insights into prokaryotic diversity and metabolic interactions in deep-sea vent chimneys

The prokaryotic diversity of culturable thermophilic communities of deep-sea hydrothermal chimneys was analysed using a continuous enrichment culture performed in a gas-lift bioreactor, and compared to classical batch enrichment cultures in vials. Cultures were conducted at 60°C and pH6.5 using a complex medium containing carbohydrates, peptides and sulphur, and inoculated with a sample of a hydrothermal black chimney collected at the Rainbow field, Mid-Atlantic Ridge, at 2,275m depth. To assess the relevance of both culture methods, bacterial and archaeal diversity was studied using cloning and sequencing, DGGE, and whole-cell hybridisation of 16S rRNA genes. Sequences of heterotrophic microorganisms belonging to the genera Marinitoga, Thermosipho, Caminicella (Bacteria) and Thermococcus (Archaea) were obtained from both batch and continuous enrichment cultures while sequences of the autotrophic bacterial genera Deferribacter and Thermodesulfatator were only detected in the continuous bioreactor culture. It is presumed that over time constant metabolite exchanges will have occurred in the continuous enrichment culture enabling the development of a more diverse prokaryotic community. In particular, CO2 and H2 produced by the heterotrophic population would support the growth of autotrophic populations. Therefore, continuous enrichment culture is a useful technique to grow over time environmentally representative microbial communities and obtain insights into prokaryotic species interactions that play a crucial role in deep hydrothermal environment

Thermodesulfatator atlanticus sp. nov., a thermophilic, chemolithoautotrophic, sulfate-reducing bacterium isolated from a Mid-Atlantic Ridge hydrothermal vent.

International audienceA novel, strictly anaerobic, thermophilic, sulfate-reducing bacterium, designated strain AT1325(T), was isolated from a deep-sea hydrothermal vent at the Rainbow site on the Mid-Atlantic Ridge. This strain was subjected to a polyphasic taxonomic analysis. Cells were Gram-negative motile rods (approximately 2.4 x 0.6 microm) with a single polar flagellum. Strain AT1325(T) grew at 55-75 degrees C (optimum, 65-70 degrees C), at pH 5.5-8.0 (optimum, 6.5-7.5) and in the presence of 1.5-4.5 % (w/v) NaCl (optimum, 2.5 %). Cells grew chemolithoautotrophically with H2 as an energy source and SO4(2-) as an electron acceptor. Alternatively, the novel isolate was able to use methylamine, peptone or yeast extract as carbon sources. The dominant fatty acids (>5 % of the total) were C(16 : 0), C(18 : 1)omega7c, C(18 : 0) and C(19 : 0) cyclo omega8c. The G+C content of the genomic DNA of strain AT1325(T) was 45.6 mol%. Phylogenetic analyses based on 16S rRNA gene sequences placed strain AT1325(T) within the family Thermodesulfobacteriaceae, in the bacterial domain. Comparative 16S rRNA gene sequence analysis indicated that strain AT1325(T) belonged to the genus Thermodesulfatator, sharing 97.8 % similarity with the type strain of Thermodesulfatator indicus, the unique representative species of this genus. On the basis of the data presented, it is suggested that strain AT1325(T) represents a novel species of the genus Thermodesulfatator, for which the name Thermodesulfatator atlanticus sp. nov. is proposed. The type strain is AT1325(T) (=DSM 21156(T)=JCM 15391(T))

Isolation and physiological characterization of two novel, piezophilic, thermophilic chemolithoautotrophs from a deep-sea hydrothermal vent chimney

The definitive version is available at ww3.interscience.wiley.com. En libre-accès sur Archimer : http://archimer.ifremer.fr/doc/2009/publication-6652.pdfInternational audienceTwo novel, thermophilic piezophiles, capable of chemolithoautotrophic growth, are successfully cultivated and isolated from a black smoker chimney at the TAG field (Mid Atlantic Ridge: MAR) by using a piezophilic cultivation technique. Both strains (strains 106 and 108) represent dominant cultivated populations of the microbial communities in the chimney surface habitat. Strain 106 represents typically thin, long spiral cells under the piezophilic growth condition but short bent cells under the non-piezophilic condition. It is a strictly chemolithoautotrophic gammaproteobacterium using reduced sulfur compounds as the electron donors, and nitrate and O(2) as the electron acceptors. Based on the 16S rRNA gene sequence, strain 106 would represent a novel genus of the previously uncultivated group (Symbiont Group I; a potentially novel family) within the Gammaproteobacteria, and 'Thioprofundum lithotrophica' gen. nov., sp. nov. is proposed. Strain 108 is a short, oval rod at any of the growth pressures. It is a facultative chemoautotroph, capable of both chemolithoautotrophic growth with H(2) and S oxidations and organotrophic growth with complex organics or organic acids using nitrate and O(2) as the electron acceptors. The chemolithoautotrophic growth is strictly piezophilic and under the organotrophic growth condition, it grows at conventional pressures (0.1 MPa). Strain 108 is phylogenetically distinctive from any of the previously described genera of the family Rhodobacteraceae within the Alphaproteobacteria, and 'Piezobacter thermophilus' gen. nov., sp. nov. is proposed. The piezophilic cultivation technique can be a powerful tool to isolate and characterize the previously uncultivated phylotypes in the deep-sea hydrothermal vent environments

Metabolic challenges and key players in serpentinite-hosted microbial ecosystems

Serpentinite-hosted systems are amongst the most challenging environments for life on Earth. Serpentinization, a geochemical alteration of exposed ultramafic rock, produces hydrothermal fluids enriched in abiotically derived hydrogen (H2), methane (CH4), and small organic molecules. The hyperalkaline pH of these fluids poses a great challenge for metabolic energy and nutrient acquisition, curbing the cellular membrane potential and limiting electron acceptor, carbon, and phosphorous availability. Nevertheless, serpentinization supports the growth of diverse microbial communities whose metabolic make-up might shed light on the beginning of life on Earth and potentially elsewhere. Here, we outline current hypotheses on metabolic energy production, carbon fixation, and nutrient acquisition in serpentinizing environments. A taxonomic survey is performed for each important metabolic function, highlighting potential key players such as H2 and CH4 cycling Serpentinimonas, Hydrogenophaga, Methanobacteriales, Methanosarcinales, and novel candidate phyla. Methodological biases of the available data and future approaches are discussed

Onderzoek en restauratie van twaalf schilderijen met het leven van de heilige Rochus uit de Sint-Jacobskerk in Antwerpen (1517)

À la suite de la campagne de conservation-restauration des peintures illustrant la Vie de saint Roch (1517) provenant de l’église Saint-Jacques d’Anvers, l’IRPA a mené une étude interdisciplinaire ayant livré de nouvelles données intéressantes. Les douze panneaux peuvent fonctionner en un polyptyque structuré en trois registres de quatre panneaux chacun. Il faut certes tenir compte des différences manifestes entre les panneaux du registre supérieur et ceux du registre inférieur. Les épisodes de la vie du saint sont représentés sur les panneaux intérieurs selon le texte d’un incunable de 1482-1488. Les figures aux revers témoignent de la dévotion aux saints antipesteux et aux saints patrons locaux. C’est probablement la Confrérie de Saint-Roch qui en fit la commande, sous l’impulsion ou non de la famille Imhoff de Nuremberg, du moins avec son soutien. Au début du XXe siècle, la série fut d’abord attribuée à Bernard van Orley, puis à Valentin et Everard van Orley. Récemment, on mentionna aussi le nom du peintre Hendrik van Wueluwe, doyen de la guilde de Saint-Luc et concepteur de l’autel de Saint-Roch, mais des éléments de comparaison manquent encore pour ce dernier. Des détails iconographiques permettent d’établir un lien avec le Maître de Saint Michel, issu de l’entourage de Van Orley, ainsi qu’avec les tapisseries de Notre-Dame du Sablon. L’église du Sablon apparaît d’ailleurs en évidence dans un des tableaux. Enfin, l’article démontre l’influence du protestantisme naissant, auquel les Van Orley se sont montrés sensibles.Naar aanleiding van de conservatie-restauratie van de schilderijen met het Leven van de H. Rochus (1517) uit de Sint-Jacobskerk te Antwerpen voerde het KIK een multidisciplinair onderzoek dat interessante nieuwe gegevens opleverde. De twaalf panelen kunnen als veelluik in drie registers van telkens vier panelen functioneren; wel moet rekening worden gehouden met afwijkingen tussen de panelen van de twee bovenste registers en die van het onderste register. De episodes van het heiligenleven worden op de binnenzijde voorgesteld volgens de tekst van een incunabel van 14821488. De figuren op de keerzijde getuigen van de devotie tot pestheiligen en lokale patroonheiligen. Waarschijnlijk gaf de Broederschap van de H. Rochus de opdracht om het werk te realiseren, al dan niet onder impuls en met de steun van de Nürnbergse familie Imhoff. In de vroege twintigste eeuw werd de reeks eerst toegeschreven aan Bernard van Orley, later aan Valentijn en Everaert van Orley. Recent werd ook schilder Hendrik van Wueluwe, deken van het Sint-Lucasgilde en tevens bestuurder van het Rochusaltaar, genoemd, maar ook voor hem ontbreekt elk vergelijkingsmateriaal. Iconografische details leggen wel een link met de Meester van de H. Michaël uit de entourage van Van Orley, en met de wandtapijten van de O.-L.-Vrouw van de Zavel. Op één schilderij is de kerk van de Zavel zelfs prominent aanwezig. Ten slotte wordt de invloed aangetoond van het opkomende protestantisme waar de Van Orleys gevoelig voor waren.Following the conservation-restoration of the paintings of the Life of Saint Roch (1517) from the Sint-Jacobskerk in Antwerp, KIK-IRPA conducted a multidisciplinary study that yielded interesting new data. The 12 panels can function as a polyptych in three registers of four panels each; but with due account taken of the differences between the panels of the two upper and those of the lower register. The episodes of the saints’ life are depicted on the insides, based on the text of an incunable dating from 1482-1488. The figures on the reverse of the panels witness to a devotion to plague and local patron saints. It was probably the Brotherhood of St. Rochus that commissioned the work, possibly at the instigation and with the financial support of the Imhoff family from Nuremberg. In the early 20th century, the series was first attributed to Bernard van Orley, and later to Valentijn and Everaert van Orley. Recently, painter Hendrik van Wueluwe, dean of the Guild of Saint Luke and also warden of the Rochus altar, has been named as the possible painter, but in the absence of any material for comparison. Iconographic details do establish a link with the Master of St. Michael from Van Orley’s entourage, and with the tapestries of Our Lady of the Sablon. In one painting the church of the Sablon is even prominently shown. Finally, the influence of the emerging Protestantism to which the Van Orleys were attracted is demonstrated