144 research outputs found
AccĂ©lĂ©romĂštre atomique double espĂšce 87Rb/39K aĂ©roportĂ© pour un test du principe dâĂ©quivalence
During the last two decades, new techniques to cool and manipulate atoms has enabled the development of inertial sensors based on atom interferometry. The ICE project aims to verify the weak equivalence principle (WEP) using a compact and transportable dual-species atom interferometer. To make precise tests of the WEP, this experiment is performed in a micro-gravity environment during parabolic flights onboard the Novespace zero-g aircraft. The interferometer is composed of two atomic species (87Rb et 39K) with similar transition wavelengths (780 nm and 767 nm), which are derived from frequency-doubled telecom lasers. This ultra-stable laser source is able to withst and the parabolic flight and their rough conditions.In previous work, we have demonstrated measurements from a cold rubidium interferometer during the 1g and 0g phases during flights. Recently, we manage to carry out one of the first gravimeter with 39K in a new titanium vacuum system. This is a huge achievement because this atom is hard to cool down and to manipulate. I will present in this thesis, the results with Rubidium and Potassium on the newset-up, I we will report on recent progress toward a double species 87Rb/39K interferometer.Lors de ces vingt derniĂšres annĂ©es, de nouvelles techniques de refroidissement et de manipulation des atomes ont permis le dĂ©veloppement de senseurs inertiels basĂ©s sur lâinterfĂ©romĂ©trie atomique. Le projet ICE est un interfĂ©romĂštre atomique double espĂšce qui a pour objectif de tester le principe dâĂ©quivalence faible. Afin dâaugmenter la sensibilitĂ© de lâinstrument, lâexpĂ©rience est rĂ©alisĂ©e en micro-gravitĂ© lors de vols paraboliques Ă borde lâAirbus A300 zero-g de Novespace. LâinterfĂ©romĂštre est composĂ© de deux espĂšces atomiques (87Rb et 39K) ayant des transitions atomiques trĂšs proches (780 et 767nm). Ces longueurs dâondes sont gĂ©nĂ©rĂ©es par une source laser bi-frĂ©quence ultra-stable. Issue des technologies telecom et ensuite doublĂ©es en frĂ©quence, elle est capable de rĂ©sister aux contraintes des vols paraboliques. PrĂ©cĂ©demment, des mesures dâaccĂ©lĂ©rations furent rĂ©alisĂ©es par un interfĂ©romĂštre Rubidiumen 1g et 0g en vol. RĂ©cemment, Ă lâaide dâun nouveau dispositif expĂ©rimental reposant sur une nouvelle enceinte Ă vide en titane, nous avons rĂ©alisĂ© un des premiers accĂ©lĂ©romĂštres Potassium. Cet atome prĂ©sente en effet certaines difficultĂ©s Ă refroidir et Ă manipuler et demande un excellent contrĂŽle des diffĂ©rents paramĂštres expĂ©rimentaux.Je prĂ©sente ainsi dans ce manuscrit, les rĂ©sultats obtenus avec le Rubidium et le Potassium sur le nouveau dispositif expĂ©rimental, et les rĂ©cents progrĂšs rĂ©alisĂ©s en vue dâun accĂ©lĂ©romĂštre double espĂšce Rb/K
The PlcR Virulence Regulon of Bacillus cereus
PlcR is a Bacillus cereus transcriptional regulator, which activates gene expression by binding to a nucleotidic sequence called the âPlcR boxâ. To build a list of all genes included in the PlcR regulon, a consensus sequence was identified by directed mutagenesis. The reference strain ATCC14579 sequenced genome was searched for occurrences of this consensus sequence to produce a virtual regulon. PlcR control of these genes was confirmed by comparing gene expression in the reference strain and its isogenic Î-plcR strain using DNA microarrays, lacZ fusions and proteomics methods. The resulting list included 45 genes controlled by 28 PlcR boxes. Forty of the PlcR controlled proteins were exported, of which 22 were secreted in the extracellular medium and 18 were bound or attached to cell wall structures (membrane or peptidoglycan layer). The functions of these proteins were related to food supply (phospholipases, proteases, toxins), cell protection (bacteriocins, toxins, transporters, cell wall biogenesis) and environment-sensing (two-component sensors, chemotaxis proteins, GGDEF family regulators). Four genes coded for cytoplasmic regulators. The PlcR regulon appears to integrate a large range of environmental signals, including food deprivation and self cell-density, and regulate the transcription of genes designed to overcome obstacles that hinder B. cereus growth within the host: food supply, host barriers, host immune defenses, and competition with other bacterial species. PlcR appears to be a key component in the efficient adaptation of B. cereus to its host environment
Molecular basis for group-specific activation of the virulence regulator PlcR by PapR heptapeptides
The transcriptional regulator PlcR and its cognate cellâcell signalling peptide PapR form a quorum-sensing system that controls the expression of extra-cellular virulence factors in various species of the Bacillus cereus group. PlcR and PapR alleles are clustered into four groups defining four pherotypes. However, the molecular basis for group specificity remains elusive, largely because the biologically relevant PapR form is not known. Here, we show that the in vivo active form of PapR is the C-terminal heptapeptide of the precursor, and not the pentapeptide, as previously suggested. Combining genetic complementation, anisotropy assays and structural analysis we provide a detailed functional and structural explanation for the group specificity of the PlcRâPapR quorum-sensing system. We further show that the C-terminal helix of the PlcR regulatory domain, specifically the 278 residue, in conjunction with the N-terminal residues of the PapR heptapeptide determines this system specificity. Variability in the specificity-encoding regions of plcR and papR genes suggests that selection and evolution of quorum-sensing systems play a major role in adaptation and ecology of Bacilli
Necrotrophism Is a Quorum-Sensing-Regulated Lifestyle in Bacillus thuringiensis
How pathogenic bacteria infect and kill their host is currently widely investigated. In comparison, the fate of pathogens after the death of their host receives less attention. We studied Bacillus thuringiensis (Bt) infection of an insect host, and show that NprR, a quorum sensor, is active after death of the insect and allows Bt to survive in the cadavers as vegetative cells. Transcriptomic analysis revealed that NprR regulates at least 41 genes, including many encoding degradative enzymes or proteins involved in the synthesis of a nonribosomal peptide named kurstakin. These degradative enzymes are essential in vitro to degrade several substrates and are specifically expressed after host death suggesting that Bt has an active necrotrophic lifestyle in the cadaver. We show that kurstakin is essential for Bt survival during necrotrophic development. It is required for swarming mobility and biofilm formation, presumably through a pore forming activity. A nprR deficient mutant does not develop necrotrophically and does not sporulate efficiently in the cadaver. We report that necrotrophism is a highly regulated mechanism essential for the Bt infectious cycle, contributing to spore spreading
Une curieuse invention du PĂšre Mersenne La psophologie et la musique du cĆur
National audienceLâimportance de lâĆuvre musicale du PĂšre Mersenne nâest plus Ă dĂ©montrer : ses travaux en acoustique ont fait date dans lâhistoire des sciences. En 1634, il publie lâacte de baptĂȘme dâune curieuse invention, la psophologie. Cette nouvelle « science des sons » est lâenfant dâun homme dont les recherches sâinscrivent dans une dĂ©marche de foi. MĂ©ditation joyeuse sur les beautĂ©s dâun monde qui ne cesse de chanter la gloire de son CrĂ©ateur, ce texte est lâexpression dâune spiritualitĂ© qui se chante autant quâelle se dit
Compte-rendu d'ouvrage : Frédérique Aït-Touati et Stephen Gaukroger, Le Monde en image : Voir, représenter, savoir, de Descartes à Leibniz
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An airborne, dual species atom interferometer 87Rb/39K for an Equivalence Principle test
Lors de ces vingt derniĂšres annĂ©es, de nouvelles techniques de refroidissement et de manipulation des atomes ont permis le dĂ©veloppement de senseurs inertiels basĂ©s sur lâinterfĂ©romĂ©trie atomique. Le projet ICE est un interfĂ©romĂštre atomique double espĂšce qui a pour objectif de tester le principe dâĂ©quivalence faible. Afin dâaugmenter la sensibilitĂ© de lâinstrument, lâexpĂ©rience est rĂ©alisĂ©e en micro-gravitĂ© lors de vols paraboliques Ă borde lâAirbus A300 zero-g de Novespace. LâinterfĂ©romĂštre est composĂ© de deux espĂšces atomiques (87Rb et 39K) ayant des transitions atomiques trĂšs proches (780 et 767nm). Ces longueurs dâondes sont gĂ©nĂ©rĂ©es par une source laser bi-frĂ©quence ultra-stable. Issue des technologies telecom et ensuite doublĂ©es en frĂ©quence, elle est capable de rĂ©sister aux contraintes des vols paraboliques. PrĂ©cĂ©demment, des mesures dâaccĂ©lĂ©rations furent rĂ©alisĂ©es par un interfĂ©romĂštre Rubidiumen 1g et 0g en vol. RĂ©cemment, Ă lâaide dâun nouveau dispositif expĂ©rimental reposant sur une nouvelle enceinte Ă vide en titane, nous avons rĂ©alisĂ© un des premiers accĂ©lĂ©romĂštres Potassium. Cet atome prĂ©sente en effet certaines difficultĂ©s Ă refroidir et Ă manipuler et demande un excellent contrĂŽle des diffĂ©rents paramĂštres expĂ©rimentaux.Je prĂ©sente ainsi dans ce manuscrit, les rĂ©sultats obtenus avec le Rubidium et le Potassium sur le nouveau dispositif expĂ©rimental, et les rĂ©cents progrĂšs rĂ©alisĂ©s en vue dâun accĂ©lĂ©romĂštre double espĂšce Rb/K.During the last two decades, new techniques to cool and manipulate atoms has enabled the development of inertial sensors based on atom interferometry. The ICE project aims to verify the weak equivalence principle (WEP) using a compact and transportable dual-species atom interferometer. To make precise tests of the WEP, this experiment is performed in a micro-gravity environment during parabolic flights onboard the Novespace zero-g aircraft. The interferometer is composed of two atomic species (87Rb et 39K) with similar transition wavelengths (780 nm and 767 nm), which are derived from frequency-doubled telecom lasers. This ultra-stable laser source is able to withst and the parabolic flight and their rough conditions.In previous work, we have demonstrated measurements from a cold rubidium interferometer during the 1g and 0g phases during flights. Recently, we manage to carry out one of the first gravimeter with 39K in a new titanium vacuum system. This is a huge achievement because this atom is hard to cool down and to manipulate. I will present in this thesis, the results with Rubidium and Potassium on the newset-up, I we will report on recent progress toward a double species 87Rb/39K interferometer
Father Marin Mersenne's Harmonie universelle : music & theology in XVIIth century
Musique et religion ont partie liĂ©e pour Marin Mersenne. Dans lâHarmonie universelle, le savant minime Ă©labore lâune des grandes sommes de la musicographie baroque. Il y dĂ©voile Ă©galement les plans dâune thĂ©orie artistique inspirĂ©e par les leçons du mouvement tridentin. Il sâagit dans ce travail dâen comprendre les enjeux en reconstituant la trame dâune doctrine dissĂ©minĂ©e dans tout le traitĂ©. Oeuvre composite, lâHarmonie est en effet constituĂ©e de quatre opus qui forment autant dâĂ©tapes dans la rĂ©alisation du projet final : le TraitĂ© de l'harmonie universelle (1627), les Questions harmoniques, Les PrĂ©ludes de l'harmonie universelle (1634), et l'Harmonie universelle (1636). Notre corpus embrasse ainsi un ensemble Ă©ditorial conçu par son auteur comme un tout indivisible. Si son Ćuvre est aujourd'hui apprĂ©ciĂ©e des musicologues ainsi que des historiens de la philosophie qui reconnaissent en elle l'un des grands manifestes de la science moderne, l'Harmonie n'a en revanche fait jusqu'ici l'objet d'aucune Ă©tude littĂ©raire approfondie. A travers ce travail de thĂšse, nous proposons ainsi de rendre Ă l'oeuvre du minime son unitĂ© en Ă©tudiant la portĂ©e religieuse d'un ouvrage qui a trop souvent Ă©tĂ© occultĂ©e par la critique. Nous en retracerons lâhistoire et interrogerons le sens dâune telle rĂ©alisation. Ce travail nous conduira Ă©galement Ă questionner les enjeux littĂ©raires de lâĂ©criture du minime. Offert Ă lâinstigation du lecteur, lâouvrage entend aussi lâĂ©difier et le retourner vers Dieu. Dans un esprit cher Ă son temps, lâĂ©crivain nâoublie jamais de convertir en enseignant, et de prier en raisonnant. A la croisĂ©e des lettres et de la musique, lâHarmonie accomplit ainsi le grand oeuvre littĂ©raire de lâĂ©poque baroque.Music and religion are closely united according to Marin Mersenne. In LâHarmonie universelle, the scholar elaborates one of the great encyclopedias of baroque musicography. He also exposes an artistic theory inspired by the ideas of the Tridentine movement. This work is about understanding the issues by reconstructing a doctrine set out throughout the book. LâHarmonie is in fact made up of four opuses which form as many stages in the realisation of the final project : Le TraitĂ© de l'harmonie universelle (1627), Les Questions harmoniques, Les PrĂ©ludes de l'harmonie universelle (1634), and L'Harmonie universelle (1636). Those four books are linked between them. They are also complementary. His book is now known by musicologists and historians in human sciences. Harmonie universelle is for them recognised as an important book of modern science. Nevertheless, the book was never studied in literature. We want to popularise his work and highlight his religious studies. In the first part named « Ecrire la musique », we will analyse cultural issues and rhetoric strategies of LâHarmonie universelle. In the second part named « Musique et thĂ©ologie », we will study religious intensions precisely. Finally, in the last part named « La PoĂ©tique de lâHarmonie », we will see the literary structure of the treaty. We also will retrace its history and analyse the meaning of such a presentation. This work will also lead us to question the literary issues of Mersenne's writing. In a traditional way, the writer never forgets to edify his reader, and to pray while reasoning. At the crossroads of letters and music, LâHarmonie universelle thus accomplishes the great literary work of the Baroque period
La correspondance savante au XVIIe siĂšcle : l'exemple de Descartes et Mersenne
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