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Physique Théorique
(81) Production(s) de l'année 2019
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Bi-gravity with a single graviton
Auteur(s): Alexandrov S., Speziale Simone
(Article) Publié:
Journal Of High Energy Physics, vol. p.070 (2019)
Texte intégral en Openaccess :
Ref HAL: hal-02114493_v1
Ref Arxiv: 1904.11906
DOI: 10.1007/JHEP08(2019)070
WoS: WOS:000483191300001
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
1 Citation
Résumé: We analyze a bi-gravity model based on the first order formalism, having as fundamental variables two tetrads but only one Lorentz connection. We show that on a large class of backgrounds its linearization agrees with general relativity. At the non-linear level, additional degrees of freedom appear, and we reveal the mechanism hiding them around the special backgrounds. We further argue that they do not contain a massive graviton, nor the Boulware-Deser ghost. The model thus propagates only one graviton, whereas the nature of the additional degrees of freedom remains to be investigated. We also present a foliation-preserving deformation of the model, which keeps all symmetries except time diffeomorphisms and has three degrees of freedom.
Commentaires: 29 pages
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Looping and Clustering: a statistical physics approach to protein-DNA complexes in bacteria
Auteur(s): Walliser N.-O.
Conference: APS March Meeting 2019 (Boston, US, 2019-03-04)
Texte intégral en Openaccess :
Ref HAL: hal-02106612_v1
Exporter : BibTex | endNote
Résumé: The DNA shows a high degree of spatial and dynamical organization over a broad range of length scales. It interacts with different populations of proteins and can form protein-DNA complexes that underlie various biological processes, including chromosome segregation. A prominent example is the large ParB-DNA complex, an essential component of a widely spread mechanism for DNA segregation in bacteria. Recent studies suggest that DNA-bound ParB proteins interact with each other and condense into large clusters with multiple extruding DNA-loops. In my talk, I present the Looping and Clustering model [1], a simple statistical physics approach to describe how proteins assemble into a protein-DNA cluster with multiple loops. Our analytic model predicts binding profiles of ParB proteins in good agreement with data from high precision ChIP-sequencing – a biochemical technique to analyze the interaction between DNA and proteins at the level of the genome. The Looping and Clustering framework provides a quantitative tool that could be exploited to interpret further experimental results of ParB-like protein complexes and gain some new insights into the organization of DNA.[1] Walter, J.-C., Walliser, N.-O., ... & Broedersz, C. P., New J. Phys. 20, 035002 (2018).
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Low-frequency phonon dynamics and related thermal properties of axially stressed single-walled carbon nanotubes
Auteur(s): Chalin Dmitrii, Avramenko Marina v., Parmeggiani A., Rochal S.B.
(Article) Publié:
Journal Of Physics: Condensed Matter, vol. 31 p.425302 (2019)
Ref HAL: hal-02106171_v1
DOI: 10.1088/1361-648X/ab285c
WoS: WOS:000476903200001
Exporter : BibTex | endNote
Résumé: Synthesis temperatures of composite materials are usually far less than the ones of their use, thus carbon nanotubes (CNTs) embedded into a polymer matrix undergo significant axial stress. We develop a continuous theory, which describes the dynamics of stressed single-walled (SW-) CNTs and predicts their low-frequency phonon spectra. The changes in dispersion laws of SWCNT low-frequency phonon modes due to the axial stress of different signs are discussed. Then, the results obtained are used to analyze low-temperature (T<70 K) heat capacity and thermal conductivity of individual nanotubes. We demonstrate that compressive stress leads to increase in heat capacity CV of an individual SWCNT, while tensile stress causes CV to decrease. In the latter case at T→0 heat capacity diminishes according to a linear law ~T instead of a power one ~T1/2.Nevertheless, according to our results, axial stress hardly affects low-temperature thermal conductance of SWCNTs.Influence of investigated effects on the corresponding macroscopic properties of CNT-based composite materials are discussed as well.
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Macrophage plasticity is Rac signalling and MMP9 dependant
Auteur(s): Travnickova Jana, Nhim Sandra, Abdellaoui Naoill, Djouad Farida, Nguyen-Chi Mai, Parmeggiani A., Kissa Karima
(Document sans référence bibliographique) 2019-04-19Texte intégral en Openaccess :
Ref HAL: hal-02106150_v1
DOI: 10.1101/614388
Exporter : BibTex | endNote
Résumé: In vitro, depending on extracellular matrix (ECM) architecture, macrophages migrate either in amoeboid or mesenchymal mode; while the first is a general trait of leukocytes, the latter is associated with tissue remodelling via Matrix Metalloproteinases (MMPs). To assess whether these stereotyped migrations could be also observed in a physiological context, we used the zebrafish embryo and monitored macrophage morphology, behaviour and capacity to mobilisation haematopoietic stem/progenitor cells (HSPCs), as a final functional readout. Morphometric analysis identified 4 different cell shapes. Live imaging revealed that macrophages successively adopt all four shapes as they migrate through ECM. Treatment with inhibitors of MMPs or Rac GTPase to abolish mesenchymal migration, suppresses both ECM degradation and HSPC mobilisation while differently affecting macrophage behaviour. This study depicts real time macrophage behaviour in a physiological context and reveals extreme reactivity of these cells constantly adapting and switching migratory shapes to achieve HSPCs proper mobilisation.
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