Tidal-charge effects on the superradiance of rotating black holes

The changes a (negative) tidal charge causes at the phenomenon of superradiance which occurs around rotating black holes are investigated. This is made by computing the amplification factors of massless scalar waves being scattered by the black hole. It is shown that the increase of the tidal-charge intensity leads to a considerable enhancement of energy extraction from near-extreme black holes. Such improvement results from the fact that extreme black holes with more negative tidal charges spin faster. Maximum amplification decreases with the increase of the tidal charge intensity if the angular momentum of the black hole per unit mass is fixed. The tidal charge may also change crucially the superradiance phenomenon of massless scalar waves causing maximum amplification to occur for $$m > 1$$ m > 1 differently from the case of Kerr black holes.

Anisotropic charged realistic models in f(R) gravity under Durgapal transformation

In this paper, we investigate the charged static spherically symmetric models in [Formula: see text] theory of gravity. We consider a linear equation of state (EoS) in the background of anisotropic matter configuration. We formulate the modified field equations and implement Durgapal transformation to examine the gravitational nature of compact stellar objects. For this purpose, we choose a specific gravitational potential and electric charge intensity to analytically solve the set of field equations. We generate three special cases of solutions for specific parametric values of [Formula: see text] appearing in the expression of gravitational potential. The evolution of physical observables, such as energy density, anisotropy parameter, radial and tangential pressures and electric field intensity, are presented in all cases. Via physical analysis, it is observed that the solution of charged compact spheres satisfies acceptability criteria, models are well behaved, and depict stability and consistency in accordance with [Formula: see text] gravity for generated models.

Analysis and Measurement of the Charge Intensity of the Selected Electrospinning Electrodes

Polymer solutions due to their chemical and physical properties requires for efficient spinning with different intensity of the charge. This corresponds to the geometry of the design of the spinning electrode. The electrode may have geometry in the shape of a smooth cylinder to obtain a less intense charge. Contrary barbed roll or roll with strings produces locally extremely intensive charge. For selected geometry of electrodes FEM models describing the intensity and the potential of the electrostatic field have been established and the results were compared with the experimentally determined results. From a comparison of the results it is evident that on the basis of the FE model can be formed with a certain accuracy to design suitably shaped electrodes to obtain the most efficient process of production of nanofibers. Key words: Electrodes, electrospinning, charge, intensity, FEM