Temperature Profile of Black Hole Accretion Disc with Magnetic Coupling

Two new mapping relations between the angular coordinate on the black hole (BH) horizon and radialcoordinate on the disc are given according to the requirement of general relativity and Maxwell‘s equations, and theeffects of magnetic coupling (MC) on temperature of accretion disc are investigated by comparing with pure accretion.It is shown that the MC effects on the temperature profile are related intimately to the BH spin, and the influenceon the peak value of disc temperature based on the modified mapping relations is not as great as that based on thelinear mapping.The peak value and the corresponding radius of peak value ring of disc temperature do not increasemonotonically as the increasing spin of BH, each containing a maximum for the fast-spinning BH. The value ranges ofthe bolometric luminosity and color temperature of the disc are both extended by the MC effects.     

Coexistence of Two Mechanisms for Extracting Energy from a Rotating Black Hole

Evolution characteristics of a rotating black hole (BH) are discussed in coexistence of the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process in the parameter space consisting of the BH spin and the power-law index of the magnetic field on the disc. The condition for the coexistence of the two energy mechanisms are derived by using the mapping relation between the angular coordinate on the BH horizon and the radial coordinate on the disc. It is shown that not only the two mechanisms can coexist, but also the power and the rate of change of BH entropy in the BZ process will dominate over those in the MC process, provided that the BH spin and the power-law index are great enough.     

Parameter Space for Evolution of Black Hole Systems and Gamma—Ray Bursts

An analytical model of black hole(BH) evolution is proposed by considering the Blandford-Znajek process with a tansient magnetized accretion disc,which is used as a central engine for powering gamma ray bursts(GRBs),The state of BH evolution can be described by the representative points in the corresponding sub-regions of a parameter space.It is shown that the BH spin might be spun up rather than slowed down.provided that the ratio of the angular velocity of the magnetic field lines to that of the BH horizon is greater than a critical value.In addition,the effects of some initial values of the BH system on the evolution terminals and the output energy for GRBs are discussed in the parameter space.     

Cycle of Black Hole Spin due to Disc Accretion Alternating with Magnetic Transfer

The cycle of black hole (BH) spin proposed by Li and Paczynski (henceforth CYCLP) is compared with a more naturad model (henceforth CYC03), in which energy and angular momentum are transferred from a rotating BH to a region of some widths by the closed magnetic field fines. It turns out that the efficiency of converting theaccreted mass into the radiation energy in the CYC03 is less than that estimated in the CYCLP, while the BH mass and entropy in the CYC03 are greater than those in the CYCLP. It is shown that the features of the CYC03 are insensitive to the power-law index indicating the variation of the magnetic field in the disc.     

Two Kinds of Magnetic Connection in Black-Hole Accretion Disc

We discuss two kinds of magnetic connection （MC） in the black hole （BH） accretion disc： the magnetic connection between the BH and the disc （MCHD） and that between the plunging region and the disc （MCPD）. The magnetic field configuration is produced by an electric current flowing at the inner edge of the disc. It turns out that the transfer direction of energy and angular momentum depends on the BH spin and a parameter λ for adjusting the angular velocities of the plunging matter, which corresponds to at most five regions in the disc. The effect of MCPD results in a much steeper emissivity than a standard accretion disc in the inner disc, however it fails to reach the observation range 4.3-5.5 in several objects, such as Seyfert 1 galaxy MCG-6-30-15, microquasars XTE J1650-500 and GX 399-4.     

Iron Kα Emission in Seyfert（—Like） Active Galactic Nuclei：Revelation of a Rapidly Spinning Central Black Hole

Fe Kα lines are superimposed upon the x-ray continuum in most Seyfert(-like) active galactic nuclei(AGNs).By a data-fitting study,previous authors have claimed that the central black hole(BH)is either rotating or non-rotating according to the thin disc model.We develop the disc model to the torus model to determine the real spin of the BH.With formulations of the motion of both torus particles and photons near a BH in Kerr metric,we simulate iron emission lines from a thin luminous torus,It is found that only spinning BH galaxies can radiate observable profiles.The data-fitting to Fe lines of four AGNs observed by ASCA predicts that the cenrral BH is spinning rapidly with the dimensionless specific angular monentum approaching the maximal value of 1.     

Effects of Screw Instability on Extracting Energy from a Rotating Black Hole

Magnetic extraction of energy from a rotating black hole (BH) is discussed in the coexistence of the BlandfordZnajek (BZ) process and the magnetic coupling (MC) process by considering the effects of the screw instability of the magnetic field. It is shown that the screw instability affects the configuration of the magnetosphere and the evolution characteristics of the BH, augmenting the energy extracted in the BZ and MC processes. In addition, the observed energy and duration of several gamma-ray bursts can be fitted well by virtue of our model.     

Effects of Magnetic Coupling on Profile of Emission Lines and Images of an Accretion Disc Around a Black Hole

The profiles of emission lines and images of an accretion disc around a black hole (13tt) are simulated by considering the effects of the magnetic coupling (MC) of a central BH with the disc. The MC effects are discussed for both slow- and fast-spinning BHs, and the following results are obtained. Firstly, the width of the emission lines and the brightness of the disc are reduced and augmented for slow- and fast-spinning BHs, respectively. Secondly,the image of the disc becomes dimmer and brighter near the inner edge of the disc for slow- and fast-spinning BHs, respectively. It turns out that all these results arise from the MC effects on the position of the dominant emission region of the accretion disc.     

Magnetic Extraction of Energy from Accretion Disc Around a Rotating Black Hole

An analytical expression for the jet power extracted from the disc (JPEFD) is derived based on an equivalent circuit in black hole magnetosphere with a mapping relation between the radial coordinate of the disc and that of unknown astrophysical load. It turns out that this JPEFD is comparable with two other JPEFDs derived in the Poynting flux and hydrodynamic regimes, respectively. In addition, the relative importance of this JPEFD relative to the Blandford-Znajek power is discussed. It is shown that the BZ power is generally dominated by the JPEFD except in some extreme cases. Furthermore, we show that the JPEFD derived in our model can be well fitted with the jet power of 3C 273.     

Screw Instability in Black Hole Magnetosphere and kHz QPOs in X-Ray Binaries

Screw instability of the magnetic field connecting a rotating black hole (BH) with its surrounding disc is discussed in coexistence with the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process. A scenario for kilohertz quasi-periodic oscillations (kHz QPOs) in x-ray binaries is proposed by introducing inductance components in the equivalent circuit for BH magnetosphere. It turns out that the period related to the screw instability is consistent with the observations of kHz QPO x-ray binaries.     

Connection of Screw Instability with Electric Current in an Accretion Disc around a Black Hole

The screw instability of the magnetic field is discussed based on its poloidal configuration generated by a single toroidal electric current flowing in the equatorial plane of a Kerr black hole （BH）. The rotation of the BH relative to the disc induces an electromotive force, which in turn results in a poloidal electric current. By using Ampere＇s law, we calculate the toroidal component of the magnetic field and derive a criterion for the screw instability of the magnetic field connecting the rotating BH with its surrounding disc. It is determined that the screw instability is related to two parameters： the radius of the disc and the BH spin. The occurrence of screw instability is depicted in a parameter space. In addition, we discuss the effect of the screw instability on magnetic extraction of energy from the rotating BH.     

A Unified Model of Magnetic Extraction of Spin Energy from a Black Hole

A unified model of magnetic extraction of spin energy from a black hole in discussed based on the theory of black hole magnetosphere.The magnetic extracting power is expressed by a unified formula,which is applicable to bloth the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process.The strength and characteristics of the BZ power and the MC power are compared in detail.In addition,the impedance matching condition for the BZ power is extended to the more general case.     

Thermodynamic behaviour of Rashba quantum dot in the presence of magnetic field

The thermodynamic properties of an In Sb quantum dot have been investigated in the presence of Rashba spin–orbit interaction and a static magnetic field. The energy spectrum and wave-functions for the system are obtained by solving the Schrodinger wave-equation analytically. These energy levels are employed to calculate the specific heat, entropy,magnetization and susceptibility of the quantum dot system using canonical formalism. It is observed that the system is susceptible to maximum heat absorption at a particular value of magnetic field which depends on the Rashba coupling parameter as well as the temperature. The variation of specific heat shows a Schottky-like anomaly in the low temperature limit and rapidly converges to the value of 2kB with the further increase in temperature. The entropy of the quantum dot is found to be inversely proportional to the magnetic field but has a direct variation with temperature. The substantial effect of Rashba spin–orbit interaction on the magnetic properties of quantum dot is observed at low values of magnetic field and temperature.     

Hawking Radiation of Grumiller Black Hole

In this paper, we consider the relativistic Harnilton-Jacobi （HJ） equation and study Hawking radiation （HR） of scalar particles from uncharged Grumiller black hole （GBH） which is affordable for testing in astrophysics. It is a/so known as Rindler modified Schwarzschild BH. Our aim is not only to investigate the effect of the Rindler parameter a on the Hawking temperature （TH ）, but to examine whether there is any discrepancy between the computed horizon temperature and the standard TH as well. For this purpose, in addition to its naive coordinate system, we study on the three regular coordinate systems, which are Painlevd--Gullstrand （PG）, ingoing Edding~on-Finkelstein （IEF）, and Kruskal-Szekeres （KS） coordinates. In o21 coordinate systems, we calculate the tunneling probabilities of incoming and outgoing scalar particles from the event horizon by using the HJ equation. It has been shown in detail that the considered HJ method is concluded with the conventional T~ in all these coordinate systems without giving rise to the famous factor-2 problem. Filrthermore, in the PG coordinates Parikh-Wilczek＇s tunneling （PWT） method is employed in order to show how one can integrate the quantum gravity （QG） corrections to the semiclassical tunneling rate by including the effects of self-gravitation and back reaction. We then show how this yields a modification in the TH.     

Correlations of Active Galactic Nuclei with Microquasars

Correlations of active galactic nuclei （AGNs） with microquasars are discussed based on the coexistence of the Blandford-Znajek （BZ） and magnetic coupling （MC） processes （CEBZMC） in black hole （BH） accretion disk. The proportions of several quantities of BH systems for both AGNs and microquasars are derived by combining the observational data with CEBZMC. It is shown that the square of the magnetic field at the BH horizon is inversely proportional to the BH mass, while the accretion rate of the disk is proportional to the BH mass. In addition, the very steep emissivity indexes from the recent XMM-Newton observations of the nearby bright Seyfert 1 galaxy MCG-6-30-15 and the microquasars XTE J1650-500 are well fitted by considering the MC effects on the disk radiation. These results suggest strongly the correlations of A GNs with microquasars.     

A New Approach to Black hole Spin in X-Ray Binaries

A new approach of detecting the black hole spin in x-ray binaries is proposed based on the model of the coexistence of the Blandford-Znajek （BZ） and magnetic coupling （MC） processes, in which the BZ process is used to power the jet emissions from x-ray binaries, and high frequency quasi-periodic oscillations （QPOs） are explained by a rotating hotspot in the inner region of the accretion disc surrounding a fast-spinning black hole. It is shown that the black hole spins of several x-ray binaries （XTE J1550-564, GRO d1665-40 and GRS 1915＋105） can be constrained in a rather narrow range, provided that QPOs and jets coexist in these sources.     

Impact of melting heat transfer in the time-dependent squeezing nanofluid flow containing carbon nanotubes in a Darcy-Forchheimer porous media with Cattaneo-Christov heat flux

This study aims to investigate the time-dependent squeezing of nanofluid flow, comprising carbon nanotubes of dual nature, e.g. single-walled carbon nanotubes, and multi-walled carbon nanotubes,between two parallel disks. Numerical simulations of the proposed novel model are conducted,accompanied by Cattaneo-Christov heat flux in a Darcy-Forchheimer permeable media. Additional impacts of homogeneous–heterogeneous reactions are also noted, including melting heat. A relevant transformation procedure is implemented for the transition of partial differential equations to the ordinary variety. A computer software-based MATLAB function, bvp4c, is implemented to handle the envisioned mathematical model. Sketches portraying impacts on radial velocity, temperature, and concentration of the included parameters are given, and deliberated upon. Skin friction coefficient and local Nusselt number are evaluated via graphical illustrations. It is observed that the local inertia coefficient has an opposite impact on radial velocity and temperature field. It is further perceived that melting and radiation parameters demonstrate a retarding effect on temperature profile.     

Pressure effects on magnetic properties and martensitic transformation of Ni–Mn–Sn magnetic shape memory alloys

The mechanism for the effects of pressure on the magnetic properties and the martensitic transformation of Ni-Mn- Sn shape memory alloys is revealed by first-principles calculations. It is found that the total energy difference between paramagnetic and ferromagnetic austenite states plays an important role in the magnetic transition of Ni-Mn-Sn under pressure. The pressure increases the relative stability of the martensite with respect to the anstenite, leading to an increase of the martensitic transformation temperature. Moreover, the effects of pressure on the magnetic properties and the martensitic transformation are discussed based on the electronic structure.     

The eccentricity enhancement effect of intermediate-mass-ratio-inspirals: dark matter and black hole mass

It was found that dark matter(DM) in an intermediate-mass-ratio-inspiral(IMRI) system has a significant enhancement effect on the orbital eccentricity of a stellar massive compact object, such as a black hole(BH),which may be tested by space-based gravitational wave(GW) detectors, including LISA, Taiji, and Tianqin in future observations. In this paper, we study the enhancement effect of the eccentricity for an IMRI under different DM density profiles and center BH masses. Our results are as follows:(1) in terms of the general DM spike distribution,the enhancement of the eccentricity is basically consistent with the power-law profile, which indicates that it is reasonable to adopt the power-law profile;(2) in the presence of a DM spike, the different masses of the center BH will affect the eccentricity, which provides a new way for us to detect the BH’s mass;and(3) considering the change in the eccentricity in the presence and absence of a DM spike, we find that it is possible to distinguish DM models by measuring the eccentricity at a scale of approximately 105 GM/c2.     

Electric and magnetic screenings of gluons in a model with a dimension-2 gluon condensate

Electric and magnetic screenings of thermal gluons are studied using the background expansion method in a gluodynamic model with a gauge invariant dimension-2 gluon condensate at zero momentum. At low temperature, the electric and magnetic gluons are degenerate. With the increase of temperature, it is found that the electric and magnetic gluons start to split at a certain temperature T₀ . The electric screening mass changes rapidly with temperature when T >T₀ , and the Polyakov loop expectation value rises sharply around T₀ from zero in the vacuum to a value around 0.8 at a high temperature. This suggests that the color electric deconfinement phase transition is driven by electric gluons. It is also observed that the magnetic screening mass remains almost the same as its vacuum value, which manifests that the magnetic gluons remain confined. Both the screening masses and the Polyakov loop results are qualitatively in agreement with the Lattice calculations.