Computational Algorithms for the Study of Distributions with Electric Charge and Radiation Flux in General Relativity

The following research contributes to the understanding of how electric charge influences the unwrapping of spherically symmetric distributions using a relativistic approach. With the recent detection of gravitational waves and the location of black holes, where a strong emission of electromagnetic radiation prevails, interest has arisen to consider the existence of compact charged objects. Thus, the appearance of charge in small quantities during gravitational collapse, the process by which black holes originate, is not ruled out; this also includes the emission of electromagnetic waves from them. This article intends to establish algorithms and write field equations for a charged fluid as those corresponding to an anisotropic fluid with radiation flux. Using an appropriate definition of the mass function, considering self-similar symmetry and Bondian observers, dynamical results are obtained for the Einstein–Maxwell electromagnetic system with added gravity. Imposing an additional homothetic symmetry, the field equations are solved, and the most relevant conclusions are drawn about the influence of the electric charge during the collapse and subsequent changes in the physical variables.

Chiral torsional effects in anomalous fluids in thermal equilibrium

Using the similarity between spacetime torsion and axial gauge couplings, we study torsional contributions to the equilibrium partition function in a stationary background. In the case of a charged fluid minimally coupled to torsion, we spot the existence of linear torsional magnetic and vortical effects, while the axial-vector current and the spin energy potential do not receive corrections in the torsion at linear order. The covariant energy-momentum tensor, on the other hand, does contain terms linear in the torsion tensor. The case of a two-flavor hadronic superfluid is also analyzed, and the torsional contributions to the constitutive relations computed. Our results show the existence of a torsional electric chiral effect mediated by the charged pions.

An isotropic analytical model for charged stars

In this investigation report, we present a perfect charged fluid solution for a static and spherically symmetric spacetime; for its construction, we suppose a metric potential, [Formula: see text], and a specific form of the electric field’s intensity, [Formula: see text], in such a manner that the resulting stellar model is physically acceptable and stable. The model presented depends on two parameters [Formula: see text] related to the compactness and the magnitude of the electric field and these same parameters will generate different possibilities for the behavior of the speed of sound. For the particular case in which [Formula: see text], we obtain once more a chargeless model constructed previously, the compactness for the charged model case is greater than in the chargeless case. As an effect of the charge, the model admits two regions for the parameter [Formula: see text], in one of these the speed of sound is a monotonic decreasing function and in the other it is a monotonic increasing function. By means of a numerical analysis, it is shown that the orders of magnitude associated to the pressure and density are characteristic of the compact stars. In particular for [Formula: see text], the range of [Formula: see text], which implies that the radius of an object with mass [Formula: see text] is found between 6554.620 m and 7672.702 m with a maximum central density of [Formula: see text].

Gravitational and Electromagnetic Perturbations of a Charged Black Hole in a General Gauge Condition

We derive a set of coupled equations for the gravitational and electromagnetic perturbation in the Reissner–Nordström geometry using the Newman–Penrose formalism. We show that the information of the physical gravitational signal is contained in the Weyl scalar function Ψ4, as is well known, but for the electromagnetic signal, the information is encoded in the function χ, which relates the perturbations of the radiative Maxwell scalars φ2 and the Weyl scalar Ψ3. In deriving the perturbation equations, we do not impose any gauge condition and as a limiting case, our analysis contains previously obtained results, for instance, those from Chandrashekhar’s book. In our analysis, we also include the sources for the perturbations and focus on a dust-like charged fluid distribution falling radially into the black hole. Finally, by writing the functions on the basis of spin-weighted spherical harmonics and the Reissner–Nordström spacetime in Kerr–Schild type coordinates, a hyperbolic system of coupled partial differential equations is presented and numerically solved. In this way, we completely solve a system that generates a gravitational signal as well as an electromagnetic/gravitational one, which sets the basis to find correlations between them and thus facilitates gravitational wave detection via electromagnetic signals.

Investigating the effect of outer layer of magnetic particles on cervical cancer cells HeLa by magnetic fluid hyperthermia

Background Magnetic fluid hyperthermia (MFH) is a successful nanotechnology application in recent decade where a biocompatible magnetic fluid is used to kill cancer cells in a controlled heating using AC magnetic field. In the present study, two ferrite-based magnetic fluids, with and without surfactant coating, were synthesized to study the effect of the outer layer of magnetic nanoparticles on cervical cancer cells. The magnetic fluid without surfactant coating (MFWI) was made stable by providing negative charge on the surface of each particle. On the other hand, lauric acid was used as a surfactant to have a stable dispersion of particles in aqueous media (MFWL). Methods The structural, magnetic properties and induction heating response of both the fluids were investigated using XRD, VSM, DLS, TGA, FTIR, and a high-frequency induction heater. The in vitro cytotoxicity of the synthesized fluids was observed on HeLa cells by performing MTT assay, and the effect of magnetic fluid hyperthermia was examined using Trypan blue assay. Results The crystallite size of surfactant stabilized particles was higher (11.0 ± 0.5 nm) compared to the charge stabilized particles (8.3 ± 0.5 nm). Induction heating experiments showed that the specific absorption rate of the surfactant-coated particles was almost double compared to ionic particle fluid. Magnetic fluid hyperthermia up to 1 hour at a concentration of 0.25 mg/mL of surfactant-coated magnetic fluid and 0.2 mg/mL concentration of charged fluid resulted in approximately 66 and 80% cell death, respectively, compared to untreated control cells. Conclusion The preliminary analysis of this study shows significant cell death due to hyperthermia, wherein MFWI revealed higher cytotoxicity compared to MFWL. Additional analysis into the role of the outer stabilizing layer on nanoparticle’s surface, concentration of nanoparticles, and hyperthermic duration is desirable to utilize MFH as a futuristic anti-cancer therapeutic tool.

Suppression of dendrite growth by cross-flow in microfluidics

Formation of rough, dendritic deposits is a critical problem in metal electrodeposition processes and could occur in next-generation, rechargeable batteries that use metallic electrodes. Electroconvection, which originates from the coupling of the imposed electric field and a charged fluid near an electrode surface, is believed to be responsible for dendrite growth. However, few studies are performed at the scale of fidelity where root causes and effective strategies for controlling electroconvection and dendrite growth can be investigated in tandem. Using microfluidics, we showed that forced convection across the electrode surface (cross-flow) during electrodeposition reduced metal dendrite growth (97.7 to 99.4%) and delayed the onset of electroconvective instabilities. Our results highlighted the roles of forced convection in reducing dendrite growth and electroconvective instabilities and provided a route toward effective strategies for managing the consequences of instability in electrokinetics-based processes where electromigration dominates ion diffusion near electrodes.

An electromagnetic extension of the Schwarzschild interior solution and the corresponding Buchdahl limit

We wish to construct a model for charged star as a generalization of the uniform density Schwarzschild interior solution. We employ the Vaidya and Tikekar ansatz (Astrophys Astron 3:325, 1982) for one of the metric potentials and electric field is chosen in such a way that when it is switched off the metric reduces to the Schwarzschild. This relates charge distribution to the Vaidya–Tikekar parameter, k, indicating deviation from sphericity of three dimensional space when embedded into four dimensional Euclidean space. The model is examined against all the physical conditions required for a relativistic charged fluid sphere as an interior to a charged star. We also obtain and discuss charged analogue of the Buchdahl compactness bound.

DC conductivities and Stokes flows in Dirac semimetals influenced by hidden sector

In the holographic model of Dirac semimetals, the Einstein–Maxwell scalar gravity with the auxiliary U(1)-gauge field, coupled to the ordinary Maxwell one by a kinetic mixing term, the black brane response to the electric fields and temperature gradient has been elaborated. Using the foliation by hypersurfaces of constant radial coordinate we derive the exact form of the Hamiltonian and equations of motion in the phase space considered. Examination of the Hamiltonian constraints enables us, to the leading order expansion of the linearised perturbations at the black brane event horizon, to derive the Stokes equations for an incompressible doubly charged fluid. Solving the aforementioned equations, one arrives at the DC conductivities for the holographic Dirac semimetals.

Causality and stability conditions of a conformal charged fluid

In this paper, I study the conditions imposed on a normal charged fluid so that the causality and stability criteria hold for this fluid. I adopt the newly developed General Frame (GF) notion in the relativistic hydrodynamics framework which states that hydrodynamic frames have to be fixed after applying the stability and causality conditions. To do this, I take a charged conformal matter in the flat and 3 + 1 dimension to analyze better these conditions. The causality condition is applied by looking to the asymptotic velocity of sound hydro modes at the large wave number limit and stability conditions are imposed by looking to the imaginary parts of hydro modes as well as the Routh-Hurwitz criteria. By fixing some of the transports, the suitable spaces for other ones are derived. I observe that in a dense medium having a finite U(1) charge with chemical potential μ0, negative values for transports appear and the second law of thermodynamics has not ruled out the existence of such values. Sign of scalar transports are not limited by any constraints and just a combination of vector transports is limited by the second law of thermodynamic. Also numerically it is proved that the most favorable region for transports $$ {\tilde{\upgamma}}_{1,2}, $$ γ ˜ 1 , 2 , coefficients of the dissipative terms of the current, is of negative values.

Charged stellar structure in Tolman–Kuchowicz spacetime

In this paper, we have presented the Einstein–Maxwell equations which are described by the spherically symmetric spacetime in the presence of charge by exploiting the Tolman–Kuchowicz spacetime. The corresponding field equations are constructed and the form of charge distribution is chosen to be [Formula: see text], where [Formula: see text] is a constant quantity. We also find the values of unknown constants from junction conditions and discuss the behavior of effective energy density, effective radial and tangential pressure and anisotropic factor with two viable [Formula: see text] models. We examine the physical stability of charged stellar structure through energy conditions, causality and stability condition. We use modified form of TOV equation for anisotropic charged fluid sphere to analyze the equilibrium condition. In this work, we model the compact star candidate SAXJ 1808.4 – 3658 and study the compactness level and anisotropic behavior corresponding to the variation of physical parameters which are involved in [Formula: see text] models. Further, we evaluate some important properties such as mass-radius ratio compactness factor and surface redshift. It is depicted from this study that the obtained solutions provide strong evidences for more realistic and viable stellar model.