Search results for "fluid"

Incoherent dispersive shocks in the spectral evolution of random waves

2013

We predict theoretically and numerically the existence of incoherent dispersive shock waves. They manifest themselves as an unstable singular behavior of the spectrum of incoherent waves that evolve in a noninstantaneous nonlinear environment. This phenomenon of "spectral wave breaking" develops in the weakly nonlinear regime of the random wave. We elaborate a general theoretical formulation of these incoherent objects on the basis of a weakly nonlinear statistical approach: a family of singular integro-differential kinetic equations is derived, which provides a detailed deterministic description of the incoherent dispersive shock wave phenomenon.

Shock-induced complex phase-space dynamics of strongly turbulent flows

2017

Shock waves have been thoroughly investigated during the last century in many different branches of physics. In conservative (Hamiltonian) systems the shock singularity is regularized by weak wave dispersion, thus leading to the formation of a rapidly and regular oscillating structure, usually termed in the literature dispersive shock wave (DSW), see e.g. [1]. Here, we show that this fundamental singular process of DSW formation can break down in a system of incoherent nonlinear waves. We consider the strong turbulent regime of a system of nonlocal nonlinear optical waves. We report theoretically and experimentally a characteristic transition: Strengthening the nonlocal character of the non…

Radiative Shocks in Rotating Accretion Flows around Black Holes

2004

It is well known that the rotating inviscid accretion flows with adequate injection parameters around black holes could form shock waves close to the black holes, after the flow passes through the outer sonic point and can be virtually stopped by the centrifugal force. We examine numerically such shock waves in 1D and 2D accretion flows, taking account of cooling and heating of the gas and radiation transport. The numerical results show that the shock location shifts outward compared with that in the adiabatic solutions and that the more rarefied ambient density leads to the more outward shock location. In the 2D-flow, we find an intermediate frequency QPO behavior of the shock location as …

Metastable oxygen atom velocity and temperature in supersonic CO2plasma expansions

2008

Radial and axial velocity distribution functions of metastable oxygen atoms were obtained by way of resonant laser induced fluorescence spectroscopy at 777.19 nm in rarefied supersonic plasma jets produced from pure CO2 and CO2–N2 gas mixtures. The N2 seeded fraction is 3% in volume in order to mimic the Martian atmosphere composition. The measured lineshapes allow computation of the mean radial velocity and the perpendicular temperature, with respect to the jet axis, as well as the mean axial velocity and the parallel temperature. With an arcjet plasma source input power of 6.5 kW, the metastable O(5S) atom axial velocity is around 4500 m s−1 and the atom perpendicular temperature reaches …

Spectral long-range interaction of temporal incoherent solitons.

2014

We study the interaction of temporal incoherent solitons sustained by a highly noninstantaneous (Raman-like) nonlinear response. The incoherent solitons exhibit a nonmutual interaction, which can be either attractive or repulsive depending on their relative initial distance. The analysis reveals that incoherent solitons exhibit a long-range interaction in frequency space, which is in contrast with the expected spectral short-range interaction described by the usual approach based on the Raman-like spectral gain curve. Both phenomena of anomalous interaction and spectral long-range behavior of incoherent solitons are described in detail by a long-range Vlasov equation.

High-order regularization in lattice-Boltzmann equations

2017

A lattice-Boltzmann equation (LBE) is the discrete counterpart of a continuous kinetic model. It can be derived using a Hermite polynomial expansion for the velocity distribution function. Since LBEs are characterized by discrete, finite representations of the microscopic velocity space, the expansion must be truncated and the appropriate order of truncation depends on the hydrodynamic problem under investigation. Here we consider a particular truncation where the non-equilibrium distribution is expanded on a par with the equilibrium distribution, except that the diffusive parts of high-order nonequilibrium moments are filtered, i.e., only the corresponding advective parts are retained afte…

Impact of self-steepening on incoherent dispersive spectral shocks and collapse-like spectral singularities

2014

International audience; Incoherent dispersive shock waves and collapselike singularities have been recently predicted to occur in the spectral evolution of an incoherent optical wave that propagates in a noninstantaneous nonlinear medium. Here we extend this work by considering the generalized nonlinear Schrödinger equation. We show that self-steepening significantly affects these incoherent spectral singularities: (i) It leads to a delay in the development of incoherent dispersive shocks, and (ii) it arrests the incoherent collapse singularity. Furthermore, we show that the spectral collapselike behavior can be exploited to achieve a significant enhancement (by two orders of magnitudes) of…

Apolipoprotein A1 in Cerebrospinal Fluid Is Insufficient to Distinguish Alzheimer's Disease from Other Dementias in a Naturalistic, Clinical Setting.

2020

Apolipoprotein A1 (ApoA1) is the major protein component of the high-density lipoprotein and involved in cholesterol transport. Disruption of cholesterol homeostasis has been identified as a contributing factor for Alzheimer's disease (AD). Moreover, polymorphisms of ApoA1 have been associated with higher risk of disease onset and cognitive decline. Therefore, ApoA1 has been suggested as a biomarker in AD. Here, we tested a small cohort of AD and non-AD dementia patients and measured levels of ApoA1 in cerebrospinal fluid. Our results indicate that ApoA1 might not be applicable to distinguish AD from other forms of dementia.

Sida. Un défi anthropologique

2013

The classical two-dimensional Heisenberg model revisited: An $SU(2)$-symmetric tensor network study

2021

The classical Heisenberg model in two spatial dimensions constitutes one of the most paradigmatic spin models, taking an important role in statistical and condensed matter physics to understand magnetism. Still, despite its paradigmatic character and the widely accepted ban of a (continuous) spontaneous symmetry breaking, controversies remain whether the model exhibits a phase transition at finite temperature. Importantly, the model can be interpreted as a lattice discretization of the $O(3)$ non-linear sigma model in $1+1$ dimensions, one of the simplest quantum field theories encompassing crucial features of celebrated higher-dimensional ones (like quantum chromodynamics in $3+1$ dimensio…