Charged Fluid Research Articles

Charged anisotropic compact stars in Logarithmic-Corrected R2 gravity

We consider [Formula: see text] corrected model, i.e. [Formula: see text], where [Formula: see text] is the Ricci scalar and [Formula: see text], [Formula: see text] are arbitrary constant values, to investigate some of the interior configurations of static anisotropic spherical charged stellar structures. The existence of electric charge and a strong electric field confirms due to the higher values of pressure distribution and energy density of the matter inside the stars. Furthermore, for compact star configurations, we also consider the simplified MIT bag model equation of state (EoS) given by [Formula: see text], where [Formula: see text] is radial pressure, [Formula: see text] is energy density and [Formula: see text] is bag constant. This approach allows to find electric charge from the Einstein–Maxwell field equations. We have extensively discussed the behavior of the electric charge and anisotropic fluid distribution factor for five different values of [Formula: see text]. Interestingly, it is noticed during this study, for smaller values of [Formula: see text] we get intensity in electric charge. The Tolman–Oppenheimer–Volkoff equation (TOV), is modified in order to carry electric charge. In particular, we model the compact star candidates SAXJ 1808.4–3658 and Vela X-1 and give graphical representation of some important properties such as equilibrium condition, mass-radius ratio and surface redshift. In the end, our calculated solutions provide strong evidences for more realistic and viable charged stellar model.

Impact of generalized polytropic equation of state on charged anisotropic polytropes

In this paper, generalized polytropic equation of state is used to get new classes of polytropic models from the solution of Einstein-Maxwell field equations for charged anisotropic fluid configuration. The models are developed for different values of polytropic index n=1,~frac{1}{2},~2. Masses and radii of eight different stars have been regained with the help of developed models. The speed of sound technique and graphical analysis of model parameters is used for the viability of developed models. The analysis of models indicates they are well behaved and physically viable.

Novel Undamped Gapless Plasmon Mode in a Tilted Type-II Dirac Semimetal.

We predict the existence of a novel long-lived gapless plasmon mode in a type-II Dirac semimetal (DSM). This gapless mode arises from the out-of-phase oscillations of the density fluctuations in the electron and the hole pockets of a type-II DSM. It originates beyond a critical wave vector along the direction of the tilt axis, owing to the momentum separation of the electron and hole pockets. A similar out-of-phase plasmon mode arises in other multicomponent charged fluids as well, but generally, it is Landau damped and lies within the particle-hole continuum. In the case of a type-II DSM, the open Fermi surface prohibits low-energy finite momentum single-particle excitations, creating a "gap" in the particle-hole continuum. The gapless plasmon mode lies within this particle-hole continuum gap and, thus, it is protected from Landau damping.

Electro-magneto-hydrodynamics of non-linear viscoelastic fluids

A combined mechanical, electrical and magnetic field driven flow of a charged viscoelastic fluid is analyzed here. Body forces on the fluid are exerted due to the multifold interactions between electrical charges in the electrical double layer (EDL), the electric field, the magnetic field as well as the electrical currents. The fluid is assumed to obey the non-linear Phan-Thein-Tanner (PTT) constitutive behavior. We analyze combined electroosmotic and pressure driven flows, along with the streaming potential resulting from a purely pressure driven flow in presence of a magnetic field. The analysis is carried out for a slit type channel closed along the width. Flows in confinements open sideways, may be treated as a special case of our analysis. Our results reveal that, while viscoelasticity tends to augment the flow rate, the magnetic field can both aid and oppose the flow through its interactions with the electrical currents, depending on the actuating mechanism. We argue that the electro-magneto-hydrodynamic (EMHD) flow of viscoelastic fluids (or, any fluids, for that matter) is inherently multi-dimensional, because of the 3-dimensional nature of the Lorentz forces and this introduces an element of anisotropy in the fluid motion as well as the induced streaming potentials. We demonstrate that presence of non-linear viscoelasticity generally augments the streaming potential, whereas, the influence of magnetic field is more complex and depends on the primary driving factor behind the induced electric field. The anisotropy, on the other hand, mainly depends on the strength of the applied magnetic field and is largely independent of the fluid properties.

Symmetry actuated closed-loop Hamiltonian systems

This paper extends the theory of controlled Hamiltonian systems with symmetries due to [9, 10, 6, 7, 11] to the case of non-abelian symmetry groups $G$. The notion of symmetry actuating forces is introduced and it is shown, that Hamiltonian systems subject to such forces permit a conservation law, which arises as a controlled perturbation of the $G$-momentum map. Necessary and sufficient matching conditions are given to relate the closed-loop dynamics, associated to the forced Hamiltonian system, to an unforced Hamiltonian system. These matching conditions are then applied to general Lie-Poisson systems, to the example of ideal charged fluids in the presence of an external magnetic field ([20]), and to the satellite with a rotor example ([9, 10]).

Transverse Magnetosonic Waves and Viscoelastic Resonance in a Two-Dimensional Highly Viscous Electron Fluid

In high-mobility materials, conduction electrons can form a viscous fluid at low temperatures. We demonstrate that in a high-frequency flow of a two-dimensional electron fluid in a magnetic field the two types of excitations can coexist: those of the shear stress (previously unknown transverse magnetosound) and those associated with the charge density (conventional magnetoplasmons). The dispersion law and the damping coefficient of transverse magnetosound originate from the time dispersion of the viscosity of the fluid. Both the viscoelastic and the plasmonic components of the flow exhibit the recently proposed viscoelastic resonance that is related to the own dynamics of shear stress of charged fluids in a magnetic field. We argue that the generation of transverse magnetosound, manifesting itself by the viscoelastic resonance, is apparently responsible for the peak in photoresistance and peculiarities in photovoltage observed in ultrahigh-mobility GaAs quantum wells.

Noncommutative dynamical variables in magnetohydrodynamics algebraic structure

Magnetohydrodynamics (MHD) describes the behavior of a charged fluid in a strong magnetic field. One way to analyze noncommutativity in MHD is by considering the result of an eternal magnetic field on noncommutative (NC) photon dynamics. In this paper we have introduced a new MHD Lagrangian and we have obtained the Navier-Stokes MHD equation. We have constructed a NC algebra for the dynamical MHD variables and analyzed the mechanical energy variation rate together with the coupling between the vortex and magnetic field. We have calculated the rate of variation of circulation and analyzed each term. We have seen that these terms are connected to noncommutativity which can act as a source of vorticity.

Origin of the reservoir quality difference between Chang 8 and Chang 9 Member sandstones in the Honghe Oil Field of the Southern Ordos Basin, China

Understanding the reservoir quality and heterogeneity of tight oil sandstone reservoirs is essential for their exploration and production. An integration of lithological, diagenetic and hydrocarbon emplacement factors was analyzed to understand the reservoir quality difference in Chang 8 and Chang 9 sandstones of Yanchang Formation, Honghe Oil Field, Ordos Basin, using core, well logs, casting thin sections, SEM, cathode luminescence images and x-ray diffraction data. The results show that Chang 8 and Chang 9 sandstones are mainly fine to medium-grained feldspathic litharenites and lithic arkose with moderately well to well sorting, from braided-delta front subaqueous distributary channel facies. The average porosity and permeability of Chang 8 and Chang 9 sandstones are 8.52%, 0.27mD and 12.96%, 2.86mD, respectively. The main diagenesis types are mechanical compaction, authigenic chlorite, calcite cement, and dissolution. The Chang 8 and Chang 9 sandstone reservoir quality difference is mainly a result of the oil charging and diagenetic environment change. The Chang 8 sandstones that close to the source rock have a high content of feldspar and lithic dissolution and grain collapse from the acidic fluids injection, which dramatically decrease porosity and permeability. Whereas, the Chang 9 sandstones far from the NW-SE direction faults have a small amount of oil charging and acidic fluid injection, which result in high content of chlorite that narrow the throats and reduce permeability, but slightly reduce porosity. Only the sandstones at the bottom of Chang 8 or close to the NW-SE direction faults in Chang 9 Member have a small amount of acidic dissolution, medium content of chlorite, which lead to the relatively high porosity and permeability. High calcite cement contents are mainly observed at the top or bottom of the sandbody, which is not the main factor that leads to the Chang 8 and Chang 9 sandstone reservoir quality difference.

Effect of excess charge carriers and fluid medium on the magnitude and sign of the Casimir-Lifshitz torque

Last year, we reported a perturbative theory of the Casimir-Lifshitz torque between planar biaxially anisotropic materials in the retarded limit [Phys. Rev. Lett. {\bf 120}, 131601 (2018)], which is applied here to study the change of sign and magnitude of the torque with separation distance in biaxial black phosphorus having excess charge carriers. The study is carried out both in vacuum as well as in a background fluid medium. The presence of extra charge carriers and that of an intervening fluid medium are both found to promote enhancement of the magnitude of the torque between identical slabs. The degree of enhancement of the magnitude of torque increases not only with an increased carrier concentration but also with separation distance. In the non-identical case when different planes of anisotropic black phosphorus face each other, owing to the non-monotonic characteristic of the sign-reversal effect of the torque, the enhancement by carrier addition and intervening medium also becomes non-monotonic with distance. In the presence of a background medium, the non-monotonic degree of enhancement of the torque with distance is observed even between identical slabs.

Relativistic charged spheres: compact stars, compactness and stable configurations

This paper aims to explore a class of static stellar equilibrium configuration of relativistic charged spheres made of a charged perfect fluid. For solving the Einstein-Maxwell field equations, we consider a particularized metric potential, Buchdahl ansatz [1] and then by using a simple transformation. The study is developed by matching the interior region with Riessner-Nordström metric as an exterior solution. The matter content the charged sphere satisfies all the energy conditions and hydrostatic equilibrium equation, i.e. the modified Tolman-Oppenheimer-Volkoff (TOV) equation for the charged case is maintained. In addition to this, we also discuss some important properties of the charged sphere such as total electric charge, mass-radius relation, surface redshift, and the speed of sound. Obtained solutions are presented by the graphical representation that provides strong evidence for a more realistic and viable stellar structure. Obtained results are compared with analogue objects with similar mass and radii, such as SAX J1808.4-3658, 4U 1538-52, PSR J1903+327, Vela X-1, and 4U1608-52. It is also noted that the Buchdahl ansatz for a given transformation provides a physically viable solution only for the charged case when 0 < K < 1, where density and pressure are maximum at the center and monotonically decreasing towards the boundary. Obtained results are also quite important both from theoretical and astrophysical scale to analyze other compact objects such as white dwarfs, neutron stars, boson stars, and quark stars.

Analytical studies on the hoop conjecture in charged curved spacetimes

Recently, with numerical methods, Hod clarified the validity of Thorne hoop conjecture for spatially regular static charged fluid spheres, which were considered as counterexamples against the hoop conjecture. In this work, we provide an analytical proof on Thorne hoop conjecture in the spatially regular static charged fluid sphere spacetimes.

Local Grand Canonical Monte Carlo Simulation Method for Confined Fluids.

We describe a new local grand canonical Monte Carlo method to treat fluids in pores in chemical equilibrium with a reference bulk. The method is applied to Lennard-Jones particles in pores of different geometry and is shown to be much more accurate and efficient than other techniques such as traditional grand canonical simulations or Widom's particle insertion method. It utilizes a penalty potential to create a gas phase, which is in equilibrium with a more dense liquid component in the pore. Grand canonical Monte Carlo moves are employed in the gas phase, and the system then maintains chemical equilibrium by "diffusion" of particles. This creates an interface, which means that the confined fluid needs to occupy a large enough volume so that this is not an issue. We also applied the method to confined charged fluids and show how it can be used to determine local electrostatic potentials in the confined fluid, which are properly referenced to the bulk. This precludes the need to determine the Donnan potential (which controls electrochemical equilibrium) explicitly. Prior approaches have used explicit bulk simulations to measure this potential difference, which are significantly costly from a computational point of view. One outcome of our analysis is that pores of finite cross-section create a potential difference with the bulk via a small but nonzero linear charge density, which diminishes as ∼1/ln(L), where L is the pore length.

Obliquely propagating ion-acoustic solitary and shock waves in magnetized quantum degenerate multi-ions plasma in the presence of trapped electrons

The properties of obliquely propagating ion-acoustic waves have been investigated in multi-ions magnetized plasma comprising of inertial, positively and negatively charged ion fluids, trapped electrons, and negatively charged stationary heavy ions. The propagation of the waves is oblique to the ambient magnetic field which is along the z-direction. Only fast type of modes exists in the linear regime. The reductive perturbation method was adopted to derive the Korteweg– de Vries (KdV) and Burger equations, as well as the solitary and shock wave solutions of the evolved equations, have been used to analyze the properties of the small but finite amplitude waves. The effects of the constituent plasma parameters, namely, the trapping effect of electrons, the electron degenerate temperature and the viscosity coefficient on the dynamics of the small amplitude solitary and shock waves have been examined. The influence of the magnetic field and the obliquity parameter on the propagation characteristics of ion-acoustic waves are discussed.

Charged perfect fluid sphere in higher-dimensional spacetime

In the present paper, a new model for perfect fluid sphere filled with charge, in higher-dimensional spacetime, admitting conformal symmetry has been investigated. We have considered a linear equation of state, with coefficients fixed by the matching conditions, at the boundary of the source corresponding to the exterior Reissner–Nordström higher-dimensional spacetime. Several physical features for different dimensions, starting from four up to eleven, have been briefly discussed. It has been shown that all the features as obtained from the present model are physically desirable.

The importance of lithofacies control on fluid migration in heterogeneous aeolian formations for geological CO2 storage: Lessons from observational evidence and modelling of bleached palaeoreservoirs at Salt Wash Graben, Utah

Exhumed bleached palaeoreservoirs provide a means of understanding fluid flow processes in geological media because the former movement of fluids is preserved as visible geochemical changes (grey bleaching of continental red-beds). The bleached palaeoreservoirs of the Jurassic Entrada Sandstone occur in a region (Utah) where there are high fluxes of naturally-occurring CO2 and form outcrop analogues for processes related to geological storage of CO2. In this paper a bleached palaeoreservoir now exposed at outcrop is used to test the importance of geological heterogeneity on fluid flow. The bleached palaeoreservoir is developed in ‘wet aeolian’ lithofacies composed of alternating layers of sandstone and cemented muddy sandstone that range across three or more orders of magnitude in permeability. Despite these permeability contrasts the bleaching shows a remarkably uniform distribution within the palaeoreservoir that crosses lithofacies boundaries. Evidence from bleaching therefore suggests that geological heterogeneity within the range 1–103 millidarcies should not greatly impede the relatively uniform distribution of low-viscosity CO2 charged fluids throughout a reservoir: a conclusion that has been substantiated here by flow modelling. Residence time is an important factor and where flows are transient the distribution of bleaching and modelling shows that flows are confined to high-permeability lithofacies.

Self-similar solutions and critical behavior in Einstein-Maxwell-dilaton theory sourced by charged null fluids

We investigate continuously self-similar solutions of four-dimensional Einstein-Maxwell-dilaton theory supported by charged null fluids. We work under the assumption of spherical symmetry and the dilaton coupling parameter a is allowed to be arbitrary. First, it is proved that the only such vacuum solutions with a time-independent asymptotic value of the dilaton necessarily have vanishing electric field, and thus reduce to Roberts’ solution of the Einstein-dilaton system. Allowing for additional sources, we then obtain Vaidya-like families of self-similar solutions supported by charged null fluids. By continuously matching these solutions to flat spacetime along a null hypersurface one can study gravitational collapse analytically. Capitalizing on this idea, we compute the critical exponent defining the power-law behavior of the mass contained within the apparent horizon near the threshold of black hole formation. For the heterotic dilaton coupling a = 1 the critical exponent takes the value 1/2 typically observed in similar analytic studies, but more generally it is given by γ = a2(1 + a2)−1. The analysis is complemented by an assessment of the classical energy conditions. Finally, and on a different note, we report on a novel dyonic black hole spacetime, which is a time-dependent vacuum solution of this theory. In this case, the presence of constant electric and magnetic charges naturally breaks self-similarity.

Charged compact star model in Einstein-Maxwell-Gauss-Bonnet gravity

In this paper we present a model of a static charged anisotropic fluid sphere in the Einstein-Maxwell-Gauss-Bonnet (EMGB) theory of gravitation. We utilize the Krori-Barua (KB) ansatz together with a linear equation of state of the form \(p_{r}=\beta \rho -\gamma \) to generate exact solutions of the EMGB field equations describing compact objects. The model obtained here is found to satisfy the elementary physical requirements necessary for a physically realizable stellar object. We demonstrate that contributions from the Gauss-Bonnet terms have a nonzero impact on the density, pressure and anisotropy profiles. The vanishing of the electromagnetic field at the center of the stellar configuration leads to a relation between the equation of state parameter and the Gauss-Bonnet term. Our model reveals a direct connection between the nature of the matter configuration and higher dimensional effects.

New classes of spherically symmetric, inhomogeneous cosmological models

We present two classes of inhomogeneous, spherically symmetric solutions of the Einstein-Maxwell-Perfect Fluid field equations with cosmological constant generalizing the Vaidya-Shah solution. Some special limits of our solution reduce to the known inhomogeneous charged perfect fluid solutions of the Einstein field equations and under some other limits we obtain new charged and uncharged solutions with cosmological constant. Uncharged solutions in particular represent cosmological models where the universe may undergo a topology change and in between is a mixture of two different Friedmann-Robertson-Walker universes with different spatial curvatures. We show that there exist some spacelike surfaces where the Ricci scalar and pressure of the fluid diverge but the mass density of the fluid distribution remains finite. Such spacelike surfaces are known as (sudden) cosmological singularities. We study the behavior of our new solutions in their general form as the radial distance goes to zero and infinity. Finally, we briefly address the null geodesics and apparent horizons associated to the obtained solutions.

Comparison among three types of relativistic charged anisotropic fluid spheres for self-bound stars

The number of exact solutions for spherically symmetric anisotropic fluid spheres is derived. And the relativistic model of an electrically charged compact star whose energy density associated with the electric fields is on the same order of magnitude as the energy density of fluid matter itself, such as electrically charged bare strange stars is also investigated. Among the three models, Heintzmann and Durgapal IV, and V permit a simple method that provide bounds on the maximum possible mass of compact electrically charged self-bound stars, and numerically exhibit that the maximum compactness and mass increase in the presence of an electric field and anisotropic pressure. Based on analytic models developed in this work, it has been compared to investigate which one is better than the others; the values of some pertinent physical quantities have been considered by assuming the estimated masses and radii of some well-known potential strange star candidates like Vela X-1, Cen X-3, PSR J1903+327 and EXO 1785-248. This analysis depends on several mathematical assumptions.

Toward a Full MHD Jet Model of Spinning Black Holes. I. Framework and a Split Monopole Example

Abstract In this paper, we construct a framework for investigating the magnetohydrodynamical jet structure of spinning black holes (BHs), where electromagnetic fields and fluid motion are governed by the Grad–Shafranov equation and the Bernoulli equation, respectively. Assuming steady and axisymmetric jet structure, we can self-consistently obtain electromagnetic fields, fluid energy density, and velocity within the jet, given proper plasma loading and boundary conditions. Specifically, we structure the two coupled governing equations as two eigenvalue problems, and develop full numerical techniques for solving them. As an example, we explicitly solve the governing equations for the split monopole magnetic field configuration and simplified plasma loading on the stagnation surface where the poloidal fluid velocity vanishes. As expected, we find the rotation of magnetic field lines is dragged down by fluid inertia, and the fluid as a whole does not contribute to energy extraction from the central BH, i.e., the magnetic Penrose process is not working. However, if we decompose the charged fluid as two oppositely charged components, we find the magnetic Penrose process does work for one of the two components when the plasma loading is low enough.