- Accueil

[hal-01768084] On the Schrodinger-Poisson--Vlasov-Poisson correspondence (23/04/18)

The Schr\"odinger-Poisson equations describe the behavior of a superfluid Bose-Einstein condensate under self-gravity with a 3D wave function. As $\hbar/m\to 0$, $m$ being the boson mass, the equations have been postulated to approximate the collisionless Vlasov-Poisson equations also known as the collisionless Boltzmann-Poisson equations. The latter describe collisionless matter with a 6D classical distribution function. We investigate the nature of this correspondence with a suite of numerical test problems in 1D, 2D, and 3D along with analytic treatments when possible. We demonstrate that, while the density field of the superfluid always shows order unity oscillations as $\hbar/m\to 0$ due to interference and the uncertainty principle, the potential field converges to the classical answer as $(\hbar/m)^{2}$. Thus, any dynamics coupled to the superfluid potential is expected to recover the classical collisionless limit as $\hbar/m\to 0$. The quantum superfluid is able to capture rich phenomena such as multiple phase-sheets, shell-crossings, and warm distributions. Additionally, the quantum pressure tensor acts as a regularizer of caustics and singularities in classical solutions. This suggests the exciting prospect of using the Schr\"odinger-Poisson equations as a low-memory method for approximating the high-dimensional evolution of the Vlasov-Poisson equations. As a particular example we consider dark matter composed of ultra-light axions, which in the classical limit ($\hbar/m\to 0$) is expected to manifest itself as collisionless cold dark matter.

[hal-01743602] How does temperature impact the conformation of single DNA molecules below melting temperature? (27/03/18)

[...]

[hal-01743510] Disentangling and modeling interactions in fish with burst-and-coast swimming reveal distinct alignment and attraction behaviors (28/03/18)

[...]

[hal-01725109] Phase transitions in distributed control systems with multiplicative noise (08/03/18)

[...]

[tel-01720712] Statistical Mechanics of Self-Gravitating Systems in General Relativity JURY (07/03/18)

The statistical mechanics of self-gravitating systems constitutes one of the most fascinating and puzzling fields of research. Due to the long-range nature of the gravitational force, the usual notion of statistical equilibrium is modified, making of this study an out-of-equilibrium problem. As a consequence, these systems exhibit some peculiar features such as the occurrence of phase transitions associated with a gravitational collapse. The work presented in this thesis aims at providing a detailed description of the phase transitions in a general relativistic framework by considering, in particular, the case of self-gravitating fermions. The thesis is conceptually divided in three parts, according to the degeneracy level of the system. We firstly focus our attention on the case of degenerate fermions (T = 0), by studying in detail the gravitational equilibrium. Successively, considering the high temperature limit (T >> 1), we show the existence of two kinds of gravitational collapse in the series of equilibria. Finally, we explore the general case, by illustrating the occurrence of the gravitational phase transitions, in both microcanonical and canonical ensembles.

[hal-01709075] The Wiskott-Aldrich Syndrome Protein Contributes to the Assembly of the LFA-1 Nanocluster Belt at the Lytic Synapse (15/02/18)

[...]

[hal-01696373] Ionic Transport through Uncharged Nanopores (24/04/18)

In the area of nanopore technology, detection methods are based on the recorded electrical signal induced by ionic transport through the nanopore. This signal also is often used to determine the nanopore diameter. Thus fundamental understanding of ionic transport at the nanoscale is essential, because ions do not in general exhibit bulk-like behavior. Indeed, at low salt concentration, the conductance-concentration relation does not follow a bulk-like linear law. In addition, for small nanopores, surface effects can prevail over bulk transport. In order to illustrate this phenomenon, we have tailored high aspect ratio (conical and cylindrical), putatively uncharged nanopores using tracketching on PET Film and atomic layer deposition technique. Starting from experimental results, we will discuss different approaches to fitting the data, including a simple phenomenological model, commonly used to determine nanopore diameter, and a more sophisticated mesoscopic model based on the space charge model. Application of the mesoscopic model leads us to conclude that, surprisingly, a weak surface charge density is needed to fit the transport model to the experimental data. To go further, molecular dynamic simulations were also performed on a system modeled to resemble as closely as possible the experimental one. From different nanopore geometries and the adsorption of hydrophibic polypeptides, we will attempt to explain the origin of the weak surface charge.

[hal-01695582] The secular evolution of discrete quasi-Keplerian systems II. Application to a multi-mass axisymmetric disc around a supermassive black hole (21/03/18)

[...]

[hal-01691955] Nearly Deconfined Spinon Excitations in the Square-Lattice Spin-1/2 Heisenberg Antiferromagnet (25/01/18)

[...]

[hal-01690943] How social information can improve estimation accuracy in human groups (02/03/18)

[...]

[hal-01669848] Hydrodynamic representation of a cosmic scalar field (24/01/18)

We derive the fluid equations governing the evolution of a cosmic scalar field (e.g. an axion field) described by the Klein-Gordon-Einstein equations in an expanding universe. We consider the nonrelativistic limit where the Klein-Gordon-Einstein equations reduce to the Schrödinger-Poisson or to the Gross-Pitaevskii-Poisson equations. Our quantum hydrodynamic equations generalize the classical hydrodynamic equations of the cold dark matter model by including a quantum force and a pressure force due to the self-interaction of the scalar field. We derive the equation for the density contrast, solve it in the linear regime of small perturbations, and discuss the differences with the cold dark matter model.

[hal-01669607] Anisotropic fermionic matter in a general relativistic framework and dynamic stability of anisotropic systems (24/01/18)

In this paper we study nonrotating, spherical, gravitational equilibrium configurations of a semidegenerate collisionless Fermi gas, in a general relativistic framework. We consider a modified Fermi-Dirac distribution function, including an energy cutoff term to ensure solutions with finite mass and radius, as well as a second term taking into account the effect of the anisotropy with prevalence of transverse component of velocity. The problem of the dynamical stability is also considered in Newtonian regime by introducing a general criterion, for the anisotropic systems, in terms of adiabatic indexes.

[hal-01669606] Are dark matter halos described by the fermionic King model? (24/01/18)

We consider the possibility that dark matter halos are made of massive neutrinos (e.g., sterile neutrinos) described by the fermionic King model. This model takes into account the Pauli exclusion principle and the escape of high energy particles. It has a finite mass. Dwarf halos are in a quantum (degenerate) condensed phase. Intermediate size halos are partially degenerate. Large halos are in a classical (nondegenerate) gaseous phase. Because of collisions and evaporation their central density increases until the gravothermal catastrophe sets in. The marginal King profile can be approximated by the modified Hubble profile which is similar to the Burkert profile that provides a good fit of dark matter halos. Some halos may undergo core collapse. For large halos, this leads to the formation of a central black hole. For small halos, the collapse is stopped by quantum degeneracy. This leads to a condensed object and to the expulsion of a massive atmosphere. We argue that large dark matter halos should not contain fermion balls because these nucleus-halo structures are saddle points of entropy.

Game theory Dynamical friction Coarsening Diffusion Baseball Statistical Mechanics Théorème du viriel Self-gravitating systems Chemotaxis Colloids Statistical mechanics Evaporation Classical phase transitions theory Brownian Dynamics 0510Gg AQUEOUS-SOLUTION Mouvement brownien Colliqionless stellar-systems Polytrope Violent relaxation Bethe ansatz Smoluchowski equation Dissipationless galaxy formation Catastrophe Keller-Segel Asymptotic expansion Collapse Long-range interactions DNA Chemotactic aggregation Bose Einstein condensation Dwarf galaxies ADN DYNAMICS SIMULATIONS AQUEOUS-SOLUTIONS Smoluchowski-Poisson Phase transition Dark matter Persistence AIR/WATER INTERFACE Bending Critical exponent Black hole Cyclodextrin COMPOSITE POLYAMIDE RO Adsorption COATING LAYER Collective behaviour Axion Disordered systems Interacting agents Chemotaxie Glass transition Brownian motion Absorption Collisionless stellar-systems Ions close to interfaces Dark matter halo Drag forces Membrane transport Effondrement gravitationnel Euler-Maclaurin Nanofiltration Competition Transition vitreuse Gravitational collapse Scalar field CARBON NANOTUBE MEMBRANES Fokker-Planck Barotropic stars Physique statistique Crossings Dipole Angle-action variables Marcheur aléatoire Thermodynamics Processus stochastique COMPUTER-SIMULATION Generalized thermodynamics Random walker Atmosphere TASEP 7722Ej Turbulence Random tilings Dynamical scaling Entropy Current fluctuations Virial theorem Dynamic transition Metastable states Automatic Keywords BEHAVIOR Denaturation Brisure de symétrie Catastrophe theory Density Brisure de symétrie des répliques Random process Computational modelling