Influence Of Bulk Viscosity Research Articles

Dynamical system method of viscous fluid in f(T) gravity theory

In this paper, using the recently introduced f(T) gravity framework, we have analyzed the viscous fluid cosmological model in FLRW cosmological model by assuming a specific form of the bulk viscosity coefficient as, ζ=ζ0+ζ1H+ζ2ḢH+H and a non-linear f(T) model particularly, f(T)=T−α−T where α is the model parameter. The bulk viscosity coefficients are estimated by using Hubble 31 data set. Using the phase space technique, we examine the asymptotic behaviour of our cosmological bulk viscous model. We found one stable critical point. Phase space analysis and the geometrical interpretations are given. We discover that according to our model, the Universe evolved from a matter-dominated decelerated phase (a past attractor) to a stable de-Sitter accelerated epoch (a future attractor). The evolution of EoS parameter shows the acceleration phase of the cosmic expansion whereas the negative behavior of viscosity-induced pressure indicates the accelerated expansion of the Universe. Additionally, the cosmic matter-energy density exhibits positive behavior. We look into how statefinder parameters behave for our model . We discover that the trajectory of our model starts at the quintessence and ends at the ΛCDM region. We use the Om diagnostic test, which reveals that our model displays quintessence behaviour. The energy condition criteria are analyzed, and we discover that SEC has been violated, whereas WEC, NEC and DEC satisfy the positivity criteria. Our f(T) cosmological model, with the influence of bulk viscosity successfully describes the expansion history of the Universe and provides a good fit to recent observational data.

A Study on the Various Aspects of Bounce Realisation for Some Choices of Scale Factors

The current study examines the realisation of cosmic bounce in two situations involving two distinct scale factor selections, one of which is a scale factor already developed for bouncing and the other of which is a scale factor created by truncating a series expansion of a de Sitter scale factor. Generalized Chaplygin gas (GCG) is assumed to be the background fluid in both situations. When the scale factor is set to the first kind, the pre-bounce scenario’s GCG energy density decreases due to contraction, reaches its lowest point at t=0 during the bounce, and then rises as a result of expansion following the bounce. However, it is noted that the truncation has an impact on the density evolution from pre-bounce in the other scale factor scenario. The influence of bulk viscosity is shown in all circumstances, in addition to the influence of non-viscosity, and the test for stability makes use of the squared speed of sound. At the turn-around places, the null energy criterion is also violated. The final stage of the study includes a cosmographic analysis and a demonstration of the Hubble flow dynamics. In conclusion, we find that inflationary cosmology can also be realized with GCG as the background fluid for two-scale factor options. When the equivalent cosmic parameter is examined for pre-bounce and post-bounce scenarios, a symmetry is frequently seen. The symmetry occurs near the point of bouncing or turning.

Extended continuum models for shock waves in CO2

Three continuum models extending the conventional Navier–Stokes–Fourier approach for modeling the shock wave structure in carbon dioxide are developed using the generalized Chapman–Enskog method. Multi-temperature models are based on splitting multiple vibrational relaxation mechanisms into fast and slow processes and introducing vibrational temperatures of various CO2 modes. The one-temperature model takes into account relaxation processes through bulk viscosity and internal thermal conductivity. All developed models are free of limitations introduced by the assumptions of a calorically perfect gas and constant Prandtl number; thermodynamic properties and all transport coefficients are calculated rigorously in each cell of the grid. Simulations are carried out for Mach numbers 3–7; the results are compared with solutions obtained in the frame of other approaches: multi-temperature Euler equations, model kinetic equations, and models with constant Prandtl numbers. The influence of bulk viscosity and Prandtl number on the fluid-dynamic variables, viscous stress, heat flux, and total enthalpy is studied. Bulk viscosity plays an important role in sufficiently rarefied gases under weak deviations from equilibrium; in multi-temperature models, non-equilibrium effects are associated with slow relaxation processes rather than with bulk viscosity. Using a constant Prandtl number yields over-predicted values of the heat flux. Contributions of various energy modes to the total heat flux are evaluated, with emphasis on the compensation of translational–rotational and vibrational energy fluxes.

Bulk viscosity and cavitation in heavy ion collisions

Relativistic heavy ion collisions generate nuclear-sized droplets of quark-gluon plasma (QGP) that exhibit nearly inviscid hydrodynamic expansion. Smaller collision systems such as $p+\mathrm{Au}, d+\mathrm{Au}$, and $^{3}\mathrm{He}+\mathrm{Au}$ at the BNL Relativistic Heavy Ion Collider, as well as $p+\mathrm{Pb}$ and high-multiplicity $p+p$ at the CERN Large Hadron Collider may create even smaller droplets of QGP. If so, the standard time evolution paradigm of heavy ion collisions may be extended to these smaller systems. These small systems present a unique opportunity to examine pre-hydrodynamic physics and extract properties of the QGP, such as the bulk viscosity, where the short lifetimes of the small droplets make them more sensitive to these contributions. Here, we focus on the influence of bulk viscosity, its temperature dependence, and the implications of negative pressure and potential cavitation effects on the dynamics in small and large systems using the publicly available hydrodynamic codes sonic and music. We also discuss pre-hydrodynamic physics in different frameworks including anti--de Sitter/conformal field theory strong coupling, ip-glasma weak coupling, and free streaming.

Modified Chaplygin gas equation of state on viscous dissipative extended holographic Ricci dark energy and the cosmological consequences

The present paper reports a study on modified Chaplygin gas (MCG)-based reconstruction scheme for extended holographic Ricci dark energy (EHRDE) in the presence of viscous type dissipative term. The dissipative effect has been described by using Eckart approach. Under the assumption that the universe is filled with MCG–EHRDE under the influence of bulk viscosity we have studied the cosmological dynamics, where the bulk viscosity coefficient has been chosen in a particular time varying form [Formula: see text], where [Formula: see text] and [Formula: see text] are constant coefficients and [Formula: see text] is the Hubble parameter. Furthermore, we have reconstructed the potential and dynamics of viscous MCG–EHRDE as scalar field. Thereafter we have studied the statefinder trajectories to discern its departure from [Formula: see text] cold dark matter ([Formula: see text]CDM) and finally investigated validity of the generalized second law (GSL) of thermodynamics considering event horizon as the enveloping horizon of the universe.

Israel-Stewart Approach to Viscous Dissipative Extended Holographic Ricci Dark Energy Dominated Universe

This paper reports a study on the truncated Israel-Stewart formalism for bulk viscosity using the extended holographic Ricci dark energy (EHRDE). Under the consideration that the universe is dominated by EHRDE, the evolution equation for the bulk viscous pressureΠin the framework of the truncated Israel-Stewart theory has been taken asτΠ˙+Π=-3ξH, whereτis the relaxation time andξis the bulk viscosity coefficient. Considering effective pressure as a sum of thermodynamic pressure of EHRDE and bulk viscous pressure, it has been observed that under the influence of bulk viscosity the EoS parameterwDEis behaving like phantom, that is,wDE≤-1. It has been observed that the magnitude of the effective pressurepeff=p+Πis decaying with time. We also investigated the case for a specific choice of scale factor; namely,a(t)=(t-t0)β/(1-α). For this choice we have observed that a transition from quintessence to phantom is possible for the equation of state parameter. However, theΛCDM phase is not attainable by the state-finder trajectories for this choice. Finally it has been observed that in both of the cases the generalized second law of thermodynamics is valid for the viscous EHRDE dominated universe enveloped by the apparent horizon.

Evidence for ball-bearing mechanism of microparticulated whey protein as fat replacer in liquid and semi-solid multi-component model foods

The current understanding of the mechanisms underlying the fat mimicking properties of fat replacers, such as microparticulated whey protein (MWP), is limited. MWP is known to provide fat-related mouth-feel in specific foods, such as yoghurts and cheeses.Tribological and rheological properties are well known to contribute to the perception of fat related sensory attributes. This study investigated the tribological and rheological properties of MWP in liquid and semi-solid model foods to reveal the mechanisms underlying the fat mimicking properties of MWP.In liquids, addition of MWP reduced the friction coefficient effectively. After scaling out the impact of viscosity on lubrication, results provide strong evidence that the reduction of friction of MWP in liquids is mainly due to ball-bearing lubrication. In semi-solid gels, addition of MWP also decreased the friction, but to a smaller extent compared to liquid model foods. The mechanism underlying the lubrication behavior of multi-component semi-solid foods that contain fat droplets, emulsifier, fat replacers such as MWP embedded in a gel matrix is complex. We conclude that different components affect the lubrication properties of the composite food through different mechanisms. Fat droplets reduce friction due to the formation of a fat film following a plate-out mechanism. We suggest that emulsifiers influence the formation of a fat or emulsifier film, whereas MWP is suggested to reduce friction due to a ball-bearing mechanism. In addition, the influence of bulk viscosity, gel fracture behavior, and the interactions between the MWP and its surrounding matrix and emulsifiers, need to be accounted for.

On the theory of bulk viscosity and relaxation pressure

A general theory of bulk viscosity and relaxation pressure, based on the generalized Chapman-Enskog method, is given, and also simple qualitative theories of them. Problems associated with the definition of temperature are discussed. Formulae are given for the bulk viscosity coefficient and the thermal conductivity of a gas possessing rotational degrees of freedom. The influence of bulk viscosity on the absorption and dispersion of sound and on the structure of a shock wave in nitrogen is investigated.