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Scaling limits for a population model with growth, division and cross-diffusion
No full textInternational audienceOriginally motivated by the morphogenesis of bacterial microcolonies, the aim of this article is to explore models through different scales for a spatial population of interacting, growing and dividing particles. We start from a microscopic stochastic model, write the corresponding stochastic differential equation satisfied by the empirical measure, and rigorously derive its mesoscopic (mean-field) limit. Under smoothness and symmetry assumptions for the interaction kernel, we then obtain entropy estimates, which provide us with a localization limit at the macroscopic level. Finally, we perform a thorough numerical study in order to compare the three modeling scales
A categorical and logical framework for iterated protocols
No full textIn this article, we show that the now classical protocol complex approach to distributed task solvability of Herlihy et al. [1] can be understood in standard categorical terms. First, protocol complexes are functors, from chromatic (semi-) simplicial sets to chromatic simplicial sets, that naturally give rise to algebras. These algebras describe the next state operator for the corresponding distributed systems. This is constructed for semi-synchronous distributed systems with general patterns of communication for which we show that these functors are always Yoneda extensions of simpler functors, implying a number of interesting properties. Furthermore, for these protocol complex functors, we prove the existence of a free algebra on any initial chromatic simplicial complex, modeling iterated protocol complexes. Under this categorical formalization, protocol complexes are seen as transition systems, where states are structured as chromatic simplicial sets. We exploit the epistemic interpretation of chromatic simplicial sets [2] and the underlying transition system (or algebra) structure to introduce a temporal-epistemic logic and its semantics on all free algebras on chromatic simplicial sets. We end up by giving hints on how to extend this framework to more general dynamic network graphs and state-dependent protocols, and give example in fault-tolerant distributed systems and mobile robotics
Étude de la reconnexion magnétique du côté jour en présence d'ions froids et de champ guide
No full textDepending on the orientation of the interplanetary magnetic field (IMF) transported by the solar wind, the magnetic field lines of the Earth's magnetic field can reconnect with those of the IMF at the dayside magnetopause, the boundary between the solar wind and the Earth's magnetic field. As the plasma conditions on each side of the magnetopause are different, the magnetic reconnection is called asymmetric. The reconnection process starts in a diffusion region at electron scales and generates fast diverging electron and ion jets. The boundaries separating the plasma flowing into the reconnection region from the outflow plasma are called the separatrices. This PhD thesis investigates in detail the structure of the magnetospheric separatrix far from the diffusion region in the presence of magnetospheric cold ions, a high density gradient and a moderate guide field. Using in-situ measurements of the NASA Magnetospheric Multiscale(MMS) mission and fully kinetic 2D Particle-In-Cell (PIC) simulations obtained from the open source SMILEI code, the current densities, electric and magnetic signatures as well as energy conversion processes are investigated. From in-situ measurements at the separatrix, the current density is found dominated by the ion diamagnetic current and the normal electric field sustained by the drift of the cold ions in agreement with the simulations. The energy conversion in the fluid frame is ensured by the parallel current and the electric field produced by the parallel electron pressure term. The partitioning of the energy between ions and electrons is discussed based on the pressure strain calculations. From the kinetic simulations performed with and without cold ions, and with and without guide field, it is found that with a guide field, the presence of cold ions reinforces the electron pressure gradient reducing the normal electric field and increasing the motion of the reconnection region. All these effects modify the energy and plasma exchanges between the solar wind and the Earth's magnetosphere.En fonction de l'orientation du champ magnétique interplanétaire (CMI) transporté par le vent solaire, les lignes du champ magnétique terrestre peuvent se reconnecter à celles du CMI sur le côté jour de la magnétopause, la frontière entre le vent solaire et le magnétique terrestre. Les conditions de plasma étant différentes de chaque côté de la magnétopause, la reconnexion magnétique est dite asymétrique. Le processus de reconnexion débute dans une région de diffusion aux échelles électroniques et produit des jets d'électrons et d'ions divergents. Les frontières séparant le plasma qui s'écoule vers la région de reconnexion de celui qui s'en éloigne sont appelées séparatrices. Cette thèse de doctorat étudie en détail la structure la séparatrice magnétosphérique loin de la région de diffusion en présence d'ions froids magnétosphériques, d'un fort gradient et d'un champ guide modéré. A partir des mesures in situ de la mission Magnetospheric Multiscale (MMS) de la NASA et de simulations 2D complètement cinétiques de type "Particle-In-Cell" (PIC) obtenues à partir du code en accès libre SMILEI, les densités de courant, les signatures électriques et magnétiques ainsi que les processus de conversion d'énergie sont étudiés. A partir des mesures in situ à la séparatrice, il est trouvé que la densité de courant est dominée par le courant diamagnétique des ions et que le champ électrique normal est soutenu par le mouvement des ions froids en accord avec les simulations. La conversion d'énergie dans le repère du plasma est assurée par le courant parallèle et le champ électrique parallèle produit par le terme de gradient parallèle de la pression des électrons. La partition de l'énergie entre les ions et les électrons est discutée à l'aide du calcul du terme de contrainte de pression. A partir des simulations cinétiques réalisées avec ou sans ions froids et avec ou sans champ guide, il est montré que la présence des ions froids renforce le gradient de pression des électrons réduisant le champ électrique normal et augmentant la vitesse de déplacement de la région de reconnexion. L'ensemble de ces effets modifie les échanges d'énergie et de plasma entre le vent solaire et la magnétosphère terrestre
Joint Simulation Study of Chiral Symmetry Recovery and Transport Response in QCD at Finite Temperature and Chemical Potentials
No full textInternational audienceWe investigate QCD matter using the two-flavor PNJL model and find that the shear viscosity to entropy density ratio η/s reaches a minimum while the bulk viscosity ζ/s peaks near the chiral crossover line, particularly at large baryon chemical potential, indicating sensitivity to critical dynamics and offering potential signatures for the QCD critical endpoint in heavy-ion collisions
On discrete X-ray transform
No full textWe consider a discrete version of X-ray transform going back, in particular, to Strichartz (1982). We suggest non-overdetermined reconstruction for this discrete transform. Extensions to weighted (attenuated) analogues are given. Connections to the continuous case are presented
Design, synthesis, biophysical and biological evaluation of original condensed pyrrolopyrimidine and pyrrolopyridine ligands as anti-SARS-CoV-2 agents targeting G4
No full textInternational audienceThe design and synthesis of novel bis[(substituted-aminomethyl)phenyl]phenyl pyrrolopyrimidines, pyrrolopyridines, pyrazolopyrimidines, imidazopyrimidines, and tris[(substituted-aminomethyl)phenyl]phenyl pyrrolopyrimidines are reported here. These original G-quadruplex (G4) ligands have been then subjected to a screening on SARS-CoV-2 using a competition HTRF assay by targeting the SUD-NM/TRF2 RNA G4 interaction. The more promising derivatives have been evaluated in vitro to determine their potential antiviral effect on two different cell lines infected by two SARS-CoV-2 strains. This study revealed a clear correlation between their antiviral property and their efficacy to prevent the SUD/G4 interaction. This correlation supports the choice of SUD/RNA G4 complexes formed during SARS-CoV-2 infection as new antiviral target
Search for heavy neutral resonances decaying to tau lepton pairs in proton-proton collisions at = 13 TeV
No full textInternational audienceA search for heavy neutral gauge bosons (Z') decaying into a pair of tau leptons is performed in proton-proton collisions at = 13 TeV at the CERN LHC. The data were collected with the CMS detector and correspond to an integrated luminosity of 138 fb. The observations are found to be in agreement with the expectation from standard model processes. Limits at 95% confidence level are set on the product of the Z' production cross section and its branching fraction to tau lepton pairs for a range of Z' boson masses. For a narrow resonance in the sequential standard model scenario, a Z' boson with a mass below 3.5 TeV is excluded. This is the most stringent limit to date from this type of search
Observation of hyperon local polarization in pPb collisions at = 8.16 TeV
No full textInternational audienceThe polarization of the and hyperons along the beam direction has been measured in proton-lead (pPb) collisions at a center-of-mass energy per nucleon pair of 8.16 TeV. The data were obtained with the CMS detector at the LHC and correspond to an integrated luminosity of 186.0 6.5 nb. A significant azimuthal dependence of the hyperon polarization, characterized by the second-order Fourier sine coefficient , is observed. The values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the pPb results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies
Search for new physics in jet scaling patterns of multilepton events at = 13 TeV
No full textInternational audienceA first search for beyond the standard model physics in jet scaling patterns of multilepton events is presented, using a data sample corresponding to an integrated luminosity of 138 fb of 13 TeV proton-proton collisions recorded by the CMS detector at the LHC. The search uses observed jet multiplicity distributions in one-, two-, and four-lepton events to explore possible enhancements in jet production rate in three-lepton events with and without bottom quarks. The data are found to be consistent with the standard model expectation. The results are interpreted in terms of supersymmetric production of electroweak chargino-neutralino superpartners with cascade decays terminating in prompt hadronic -parity violating interactions
Laguerre–Gaussian laser filamentation in ambient air
No full textInternational audienceThe filamentation of ultrashort laser pulses in air with Laguerre–Gaussian beams opens up numerous possibilities for atmospheric applications. In this work, we demonstrate a novel method to measure the critical power for self-focusing of structured laser beam based on the acoustic detection of laser ionization. Using this method, we determine the critical power of different Laguerre–Gaussian beams at 800 nm with ultrashort (50 fs) and sub-picosecond (500 fs) pulse durations. We also discuss the effect of the numerical aperture of the beam on the critical power and present the first measurements of the energy deposited by Laguerre–Gaussian filaments in the air. Our results reveal an unexpected influence of the laser pulse duration on the filamentation of vortex beams