Search results for "fluid"
showing 10 items of 5513 documents
Vortex density waves and high-frequency second sound in superfluid turbulence hydrodynamics
2010
In this paper we show that a recent hydrodynamical model of superfluid turbulence describes vortex density waves and their effects on the speed of high-frequency second sound. In this frequency regime, the vortex dynamics is not purely diffusive, as for low frequencies, but exhibits ondulatory features, whose influence on the second sound is here explored.
A Fractional Approach to Non-Newtonian Blood Rheology in Capillary Vessels
2019
In small arterial vessels, fluid mechanics involving linear viscous fluid does not reproduce experimental results that correspond to non-parabolic profiles of velocity across the vessel diameter. In this paper, an alternative approach is pursued introducing long-range interactions that describe the interactions of non-adjacent fluid volume elements due to the presence of red blood cells and other dispersed cells in plasma. These non-local forces are defined as linearly dependent on the product of the volumes of the considered elements and on their relative velocity. Moreover, as the distance between two volume elements increases, the non-local forces decay with a material distance-decaying …
IMEX Finite Volume Methods for Cloud Simulation
2017
We present new implicit-explicit (IMEX) finite volume schemes for numerical simulation of cloud dynamics. We use weakly compressible equations to describe fluid dynamics and a system of advection-diffusion-reaction equations to model cloud dynamics. In order to efficiently resolve slow dynamics we split the whole nonlinear system in a stiff linear part governing the acoustic and gravitational waves as well as diffusive effects and a non-stiff nonlinear part that models nonlinear advection effects. We use a stiffly accurate second order IMEX scheme for time discretization to approximate the stiff linear operator implicitly and the non-stiff nonlinear operator explicitly. Fast microscale clou…
SINGLET NEUTRINOS AS HOT DARK MATTER
1993
A model is presented that generates mass and magnetic moment matrices for singlet neutrinos radiatively at one-loop level. It allows the singlet neutrinos to account for the hot dark matter and the anomalous ionization of interstellar hydrogen.
Numerical Analysis of a Transposed Multiwired Armature in Electromagnetic Rail Launchers
2020
Solid armatures in electromagnetic rail launchers have to undergo severe electromagnetic, mechanical, and thermal stresses. These stresses are unevenly distributed in the armature mainly due to the velocity skin effect. Contrasting this effect reduces the peak to average ratio of the stresses and allows better performance of the device. In this article, the behavior of a transposed multiconductor solid armature is numerically investigated by the research code electric network for electromagnetics (EN4EM) developed at the Department of Energy, System, Territory and Construction Engineering (DESTEC), University of Pisa, Pisa, Italy. The code is based on an integral formulation that reduces th…
Wellentypen in Helium II-Schichten
1968
In liquid helium two wave modes are possible. Their properties may be analysed by solving the thermohydrodynamical equations under the condition that the tangential component of the normal fluid velocity is vanishing on the walls. In the present paper, these two types of wave propagation are determined for a plane-parallel capillary with the heat conduction and the thermal expansion being neglected and with the width of the capillary being much smaller than the penetration depth of a viscous wave. In particular, the dispersion relations of both, the so called fourth sound and an overdamped mode are calculated. (This overdamped mode may be called fifth wave mode.) The velocity fields can be …
Biases on cosmological parameters by general relativity effects
2012
General relativistic corrections to the galaxy power spectrum appearing at the horizon scale, if neglected, may induce biases on the measured values of the cosmological parameters. In this paper, we study the impact of general relativistic effects on non standard cosmologies such as scenarios with a time dependent dark energy equation of state, with a coupling between the dark energy and the dark matter fluids or with non-Gaussianities. We then explore whether general relativistic corrections affect future constraints on cosmological parameters in the case of a constant dark energy equation of state and of non-Gaussianities. We find that relativistic corrections on the power spectrum are no…
Current constraints on early and stressed dark energy models and future 21 cm perspectives
2014
Despite the great progress of current cosmological measurements, the nature of the dominant component of the universe, coined dark energy, is still an open question. Early Dark Energy is a possible candidate which may also alleviate some fine tuning issues of the standard paradigm. Using the latest available cosmological data, we find that the 95% CL upper bound on the early dark energy density parameter is $\Omega_{\textrm{eDE}}$. On the other hand, the dark energy component may be a stressed and inhomogeneous fluid. If this is the case, the effective sound speed and the viscosity parameters are unconstrained by current data. Future omniscope-like $21$cm surveys, combined with present CMB …
Future weak lensing constraints in a dark coupled universe
2011
Coupled cosmologies can predict values for the cosmological parameters at low redshifts which may differ substantially from the parameters values within non-interacting cosmologies. Therefore, low redshift probes, as the growth of structure and the dark matter distribution via galaxy and weak lensing surveys constitute a unique tool to constrain interacting dark sector models. We focus here on weak lensing forecasts from future Euclid and LSST-like surveys combined with the ongoing Planck cosmic microwave background experiment. We find that these future data could constrain the dimensionless coupling to be smaller than a few $\times 10^{-2}$. The coupling parameter $\xi$ is strongly degener…
Constraints from $v_2$ fluctuations for the initial state geometry of heavy-ion collisions
2014
The ability to accurately compute the series of coefficients $v_n$ characterizing the momentum space anisotropies of particle production in ultrarelativistic heavy ion collisions as a function of centrality is widely regarded as a triumph of fluid dynamics as description of the bulk matter evolution. A key ingredient to fluid dynamical modeling is however the initial spatial distribution of matter as created by a yet not completely understood equilibration process. A measurement directly sensitive to this initial state geometry is therefore of high value for constraining models of pre-equilibrium dynamics. Recently, it has been shown that such a measurement is indeed possible in terms of th…