Ours blanc

Résumé

L'ours blanc (Ursus maritimus), aussi connu sous le nom d'ours polaire, est un grand mammifère omnivore (à prédominance carnivore) originaire de l'Arctique. C'est, avec l'ours kodiak et l'éléphant de mer, l'un des plus grands carnivores terrestres et il figure au sommet de sa pyramide alimentaire. Parfaitement adapté à son habitat, l'ours blanc possède une épaisse couche de graisse ainsi qu'une fourrure qui l'isolent du froid. La couleur blanche de son pelage lui assure un camouflage idéal sur la banquise et sa peau noire lui permet de mieux conserver sa chaleur corporelle. Pourvu d'une courte queue et de petites oreilles, il possède une tête relativement petite et fuselée ainsi qu'un corps allongé, caractéristiques de son adaptation à la natation. L'ours blanc est parfois considéré comme un mammifère marin semi-aquatique, dont la survie dépend essentiellement de la banquise et de la productivité marine. Il chasse aussi bien sur terre que dans l'eau. Son espérance de vie est de . C

Source officielle

https://fr.wikipedia.org/wiki/Ours_blanc

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In the South, you can't talk just about global warming

Nathalie Jollien, Arindam Roy

Alongside his postdoc research at EPFL, Arindam Roy works hard to communicate about climate change in his native language of Bengali. The workshops he runs don’t focus on polar bears on ice caps, but rather on concrete solutions to the very real problems faced by people in the Global South.

2021

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In this study, the fission yeast Schizosaccharomyces pombe was used as a model system to study the cellular signaling that underlies cell cycle progression. Phosphorylation plays an important part in the regulation of this process. Kinases catalyze the transfer of a phosphate group to a substrate, which may regulate its activity. Protein phosphatases oppose the activity of protein kinases; the balance of their activities regulates signaling flux in many signaling pathways. The Septation Initiation Network (SIN) is a signaling cascade that regulates cytokinesis in fission yeast. SIN signaling is triggered by a GTPase and is transduced by three protein kinases; phosphorylation plays an important role in controlling SIN signalling. Numerous genetic screens and biochemical analyses have identified phosphatases and kinases that regulate the SIN. The protein phosphatases Calcineurin/Protein Phosphatase 2B (PP2B) and Flp1p promote SIN signaling, while PP2A is a SIN inhibitor. PP2A is conserved and is activated by the chaperone Phosphatase Two A Phosphatase Activator (PTPA). S. pombe has two PTPA-related genes, ypa1 and ypa2; the deletion mutant of the latter rescues SIN mutants which cannot undergo cytokinesis, consistent with PP2A opposing SIN signaling. The phenotype of the deletion mutant of ypa2, indicates that it is involved in the control of cell polarity, cell growth, mitotic commitment and cytokinesis. In this study, we characterized the hypomorphic allele ypa2-S2 which rescues SIN mutants, but is otherwise largely normal. ypa2-s2 was used as bait in a synthetic genetic array screen, to identify genes whose products compensate for reduced function of Ypa2p. A large number of hits were identified, of which approximately ninety percent are novel genetic interactors of ypa2. Validation studies indicated that eighty percent of the interactions seen in the high-throughput screen can be reconstructed. The identified genes regulate several biological processes, including signal transduction and protein phosphorylation. This prompted us to further characterize the roles of Ckb1p and Flp1p, in regulating cytokinesis signaling. Ckb1p is a regulatory subunit for Casein Kinase II (CK II), which was previously implicated in polar growth. The phenotype of the mutant ypa2-S2 ckb1-â indicates that Ckb1p, similar to Ypa2p, contributes to the regulation of mitotic commitment and cytokinesis signaling. Furthermore, ckb1-â showed negative genetic interaction with PP2A and SIN mutants. Flp1p is a protein phosphatase that was reported to regulate mitotic commitment and to promote SIN signaling. The double mutant between ypa2-S2 and flp1-â showed cell separation defects and phenotypic analysis of double mutants between flp1-â and PP2A mutants indicates that these phosphatases cooperate in cell separation. Overall, this work has uncovered novel facets of the regulation of cytokinesis in S. pombe, implicating CK II in controlling SIN signaling, and uncovering cooperative interactions between different phosphatases in controlling cytokinesis.

EPFL2016

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Elastic, dielectric, and piezoelectric anomalies and Raman spectroscopy of 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3

Leili Batooli, Alberto Biancoli, Dragan Damjanovic, Amirhossein Vahabzadeh

The solid solution 0.5Ba(Ti0.8Zr0.2)O-3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) is a promising lead-free piezoelectric material with exceptionally high piezoelectric coefficients. The strong response is related to structural instabilities close to ambient temperature. We report here on temperature-induced anomalies in the dielectric, piezoelectric, and elastic coefficients and Raman spectroscopy of ceramic BCZT. The data indicate ferroelectric-ferroelectric structural phase transitions in this material in addition to those previously reported. An anomaly is also observed above the Curie temperature T-C and is associated with the loss of polar structure that persists thirty degrees above T-C. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4714703]

American Institute of Physics2012

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EPFL2016