Motion of charged particles in a spacetime of a five dimensional rotating black hole in a magnetic field

We study the effect of an external magnetic field on the stability of circular motion around a five dimensional Myers–Perry metric. Using the Hamilton–Jacobi formalism we derive the effective potential for the radial motion of charged particles around a five dimensional rotating black hole in a uniform magnetic field. We show that there are stable circular orbits around a five dimensional rotating black hole immersed in a uniform magnetic field.     

Accretion onto a Kerr black hole in the presence of a dipole magnetic field

We analyze the accretion of charged matter onto a rotating black hole immersed in an aligned dipolar magnetic field. We specialize to motion in the equatorial plane and calculate the ‘Keplerian’ angular momentum distribution, the marginally stable and marginally bound orbits, and the efficiency of mass-to-energy conversion as functions of the angular momentum of the black hole and of the product of the dipole moment and the charge of the infalling matter. Although the detailed results are quite different from those previously obtained in the case of an uniform magnetic field, the astrophysically relevant results are very similar; when hydrodynamical accretion is considered, these effects of the magnetic field are always very small. But for test particles the efficiency can be significantly increased for limited ranges of the parameters.     

Magnetic support near a charged rotating black hole

Three equilibrium conditions for magnetic trapping are applied to a charged black hole whose axis of rotation is aligned with an asymptotically uniform weak magnetic field.     

Magnetopolaron state of particles in quantum rings of finite width

The energies of the electron and hole weak-coupling polarons are determined in quantum rings of finite width in a uniform magnetic field. It is shown that polaron corrections exhibit oscillatory behavior as a function of a magnetic field. The effect of polaron corrections on the absorption and emission spectra of light by excitons in a quantum ring is considered.     

Orbital and epicyclic motion of charged test particles around non-rotating Einstein-Æther black holes

The study of charged test particle dynamics in the combined black hole gravitational field and magnetic field around it could provide important theoretical insight into astrophysical processes around such compact object. We have explored the orbital and epicyclic motion of charged test particles in the background of non-rotating Einstein-Æther black holes in the presence of external uniform magnetic field. We numerically integrate the equations of motion and analyze the trajectories of the charged test particles. We examined the stability of circular orbits using effective potential technique and study the characteristics of innermost stable circular orbits. We analyze the key features of quasi-harmonic oscillations of charged test particles nearby the stable circular orbits in an equatorial plane of the black hole, and investigate the radial profiles of the frequencies of latitudinal as well as radial harmonic oscillations in dependence on the strength of magnetic field, mass of the black hole and dimensionless coupling constants of the theory. We demonstrate that the magnetic field and dimensionless parameters of the theory have strong influence on charged particle motion around Einstein-Æther black holes.     

The electromagnetic energy with the truncation method for a five-dimensional rotating black hole in a uniform magnetic field

We consider a charged five-dimensional Myers–Perry black hole in a uniform magnetic (test) field. Using the Komar mass formula, we calculate the total energy of the electromagnetic field within the truncation three-sphere for a five-dimensional rotating black hole with two equal-rotation parameters and two equal-magnetic field strengths. We show that the total electromagnetic energy takes the minimum value when the five-dimensional rotating black hole acquires a non-zero net electric charge Q.     

Superradiant instability for black holes immersed in a magnetic field

We consider the bound states of the massive scalar field around a rotating black hole immersed in the asymptotically uniform magnetic field. In the regime of slow black hole rotation, the Klein–Gordon equation allows separation of variables. We show that the growth rate of the instability can be amplified a few times by the magnetic field. The effect occurs because the magnetic field adds the “effective mass” term B|m|$B|m|$ to the scalar field potential for a Kerr black hole. In addition, and as a by-product, we discuss the behavior of the quasinormal modes for the magnetized rotating black holes.     

Magnetised black hole as a gravitational lens

We use the Ernst–Schwarzschild solution for a black hole immersed in a uniform magnetic field to estimate corrections to the bending angle and time delay due-to presence of weak magnetic fields in galaxies and between galaxies, and also due-to influence of strong magnetic field near super-massive black holes. The magnetic field creates a kind of confinement in space, that leads to increasing of the bending angle and time delay for a ray of light propagating in the equatorial plane.     

Coupled magnetoplasma and phonon systems

A long-wavelength Hamiltonian approach for coupled plasmons and polar phonons in a degenerate semiconductor with and without a uniform d.c. magnetic field is presented. Neglecting ionic motion, and with a uniform magnetic field present, a Hamiltonian is formulated for the magnetoplasma oscillations and a Hamiltonian is presented which includes the coupling between longitudinal optical phonons and collective hybrid-cyclotron plasma resonances. Canonical transformations, which put the latter Hamiltonian into second quantized diagonal form, are given. The normal modes, obtained by diagonalizing the appropriate Hamiltonian, correspond to the zeros and the infinities of the appropriate dielectric function. In analogy with the electron-phonon case, the resonances for a compensated system of coupled electrons and holes, in the presence of a uniform magnetic field, are treated by means of a Hamiltonian. The coupling in the above problems is represented by a product of two sets of plasma frequencies, the electron and ion or the electron and hole in the latter case. In all cases the coupling is independent of the magnetic field.     

Electronic states of the icosahedral quasiperiodic systems in magnetic fields

The electronic properties of the icosahedral quasiperiodic system in a tile-dependent or uniform magnetic field is studied by quasi-Bloch scheme and the general solutions are obtained for the electronic states. The behavior of the three-dimensional (3D) non-interacting electrons in an icosahedral quasiperiodic system may be treated as the projection of that of the non-interacting pseudo-electrons in 6D. In the presence of the tile-dependent magnetic field, the non-interacting electrons are quasi-Bloch electrons, while they are partial quasi-Bloch electrons when the magnetic field is uniform.     

Analytical Ground-State of an Exciton Trapped in a Circular Parabolic Quantum Dot in the Presence of a Magnetic Field

The quasi-exact properties of an exciton are investigated theoretically in the presence of an external magnetic field using the effective-mass approach in GaAs parabolic quantum dot. The energy spectrum is obtained analytically as a function of the dot radius, interaction strength and magnetic field. It is established that, a steady bound state of an exciton in the ground state exists under the effect of a strong magnetic field; also I noticed that the exciton binding energy decreases by increasing both the radius of the dot and the magnetic field strength and the reduction becomes pronounced for larger dots. As expected, it has been found that the exciton total energy decreases with increasing the size of the dot and it enhances by increasing the magnetic field. It appears that the exciton total energy strongly depends on the magnetic field for dots with big size. The magnetic field effect on the exciton size also has been studied. It is shown that the increase in the magnetic field leads to a reduction in the exciton size; due to magnetic field confinement, while the size of an exciton reach its bulk limit as the dot size increases. Moreover, it is shown that, if the dot radius is sufficiently large the oscillator strength saturates and it becomes insensitive to the magnetic field while the increase in the magnetic field gradually weakened the oscillator strength. I have calculated the ground-state distribution for both the electron and the hole. It is found that the localization of the electron/hole increases in the presence of a magnetic field. Moreover, the ground-state optical-absorption intensity is investigated. Finally, the dependence of the lowest five states of an exciton on both the dot radius and the magnetic field are discussed.

     

Dynamics of Particles Around a Regular Black Hole with Nonlinear Electrodynamics

We investigate the dynamics of a charged particle being kicked off from its circular orbit around a regular black hole by an incoming massive particle in the presence of magnetic field. The resulting escape velocity, escape energy and the effective potential are analyzed. It is shown that the presence of even a very weak magnetic field helps the charged particles in escaping the gravitational field of the black hole. Moreover the effective force acting on the particle visibly reduces with distance. Thus particle near the black hole will experience higher effective force as compared to when it is far away.     

Cyclotron resonance in the InAs/GaSb heterostructure in an inclined magnetic field

The mechanism of cyclotron resonance line splitting in the InAs/GaSb heterostructure in an inclined magnetic field has been studied experimentally and theoretically. It is shown that the admixing of electron and hole states leads to anticrossing of the Landau levels and, hence, to splitting of the cyclotron resonance line. In the case of an inclined magnetic field, the splitting is not observed, which is explained by the suppression of the admixing of electron and hole states due to the occurrence of an additional barrier for electrons and holes given a longitudinal magnetic field component.     

Biological effects of magnetic fields: chronic exposure of the nematode Panagrellus redivivus

The Panagrellus redivivus bioassay, an established monitor of adverse toxic effects of different environments, has been used to study the biological effects of exposure to static and time-varying uniform and gradient magnetic fields, and to time-varying magnetic field gradients superimposed on a static uniform magnetic field of 2.35 Tesla. Temporally stationary magnetic fields have no effect on the fitness of the test animals. Time-varying magnetic fields cause some inhibition of growth and maturation in the test populations. The combination of pulsed magnetic field gradients in a static uniform magnetic field also has a small detrimental effect on the fitness of the test animals.     

Gravitational energy of a magnetized Schwarzschild black hole: a teleparallel approach

We investigate the distribution of gravitational energy in the spacetime of a Schwarzschild black hole immersed in a cosmic magnetic field. This is done in the context of the teleparallel equivalent of general relativity, which is an alternative geometrical formulation of general relativity, where gravity is described by a spacetime endowed with torsion rather than curvature, whose fundamental field variables are tetrad fields. We calculate the energy enclosed by a two-surface of constant radius—in particular, the energy enclosed by the event horizon of the black hole. In this case we find that the magnetic field has the effect of increasing the gravitational energy as compared to the vacuum Schwarzschild case. We also compute the energy (i) in the weak magnetic field limit, (ii) in the limit of vanishing magnetic field, and (iii) in the absence of the black hole. In all cases our results are consistent with what should be expected on physical grounds.     

Quasinormal modes and absorption of a massless scalar field for the magnetic Gauss–Bonnet black hole

We study the massless scalar quasinormal frequencies of an asymptotically flat static and spherically symmetric black hole with a nonzero magnetic charge in four-dimensional extended scalar-tensor-Gauss–Bonnet theory. The results show that the real part of the quasinormal frequency becomes larger and the imaginary part becomes smaller with increasing the magnetic charge or the angular harmonic index. The existence of magnetic charges will reduce the damping of scalar perturbation, but increase the frequency. We also study the absorption cross-section of the scalar field in this black hole. We find that its curve will become lower as the magnetic charge increases, i.e. the magnetic charge will weaken the absorption capacity of the black hole. Meanwhile, the high-frequency limit of the total absorption cross-section is just the area of black hole shadow.     

Properties of a two-dimensional semimetal in a strong magnetic field

A system of two-dimensional electrons and holes ha s been investigated in a strong magnetic field, when it is sufficient to take into account only the ground Landau level. It has been shown that the interaction of electrons and holes can lead to an ordered state. In this problem, the exchange interaction in electron and hole subsystems is significant. The following two cases have been considered: (a) there are one electron and one hole valleys, and at some magnetic field strength, there exists an ordered state, as in an excitonic insulator; and (b) there exist one electron and two equivalent hole valleys (as in the experiment performed by Kvon et al. [1]), and the hole system has an ordered state of the Stoner ferromagnetic type in a specific range of magnetic field strengths. The spectra of elementary excitations of the Bose and Fermi types have been obtained. The Fermi excitations have a gap in the energy spectrum, whereas the Bose excitations in the ordered states begin with zero (to these excitations there corresponds an electric dipole moment). The self-consistent field approximation has been used, which is exact when the numbers of electrons and holes are equal to each other.     

环形磁场金属等离子体源冷却流场的数值模拟与优化

环形磁场金属等离子体源作为一种全新的等离子体源结构,可用于产生高度离化、无大颗粒、高密度的离子束流,但传统流道结构不能保证其高效、均匀散热,大功率工作时可能引起密封胶圈的烧蚀失效,需对其冷却流场进行优化设计.利用Solidworks Flow Simulation软件对等离子体源冷却流道进行模拟,分析出入水孔分布角度、孔数、孔径以及入水孔高度对冷却效果的影响规律,并对流道结构参数进行优化.结果表明,增大水孔的周向分布范围,有利于提高散热的均匀性;入水孔设置在结构上层有利于减少冷却水的温度分层现象,使铜套和密封胶圈都处于较好的冷却状态;适当减小孔径有利于增大冷却水射流速度,增大湍流程度强化传热,提高换热效率.优化后的流场结构可以提高冷却水的利用率,在相同流量条件下获得更好的冷却效果,改善等离子体源的放电稳定性,为环形磁场金属等离子体源的冷却结构设计提供理论依据.     

Principles of Adaptive Optics, 3rd edn., by Robert K. Tyson

A review is made of the quantum effects which are observed in the transport coefficients of semiconductors. Quantization of the free carriers in semiconductors is produced whenever an external potential acts on an otherwise uniform and perfect crystal. Typical examples are a magnetic field, an electric field or the physical boundaries of the sample. A magnetic field quantizes the electron and hole states into a ladder of equally spaced Landau levels. This gives rise to the Shubnikov–de Haas, magnetophonon and magneto-impurity effects, where the positions of the Landau levels resonate with the Fermi, phonon, or impurity energies present in the sample. A series of oscillations in the magneto-resistance of many different types of materials results. Electric fields applied to the surface of metal oxide semiconductor (MOS) devices result in a set of quantum levels for motion perpendicular to the surface. At low temperatures the charge carriers are bound to the surface and behave as if they were two-dimensional. This is shown to give rise to very dramatic oscillatory metal–insulator behaviour in high magnetic fields. Quantization is also shown to occur in very thin layers of semiconductors which act like a simple square well potential, the energy levels of which can be studied as a function of layer thickness. The carriers are confined within the layers, and also show two-dimensional behaviour.     

Periodic structure of acicular magnetic clusters in a magnetic liquid

The behavior of magnetic clusters in a magnetic liquid placed in a circular capillary is considered. When a uniform magnetic field is applied to the system, acicular clusters grow from the sediment, being aligned with the field. The interaction of the clusters as magnetic dipoles with one another and with an external gradient magnetic field is considered theoretically. In a nonuniform symmetric magnetic field with a peak, the cluster distribution is uniform near the peak. Such a distribution is fairly stable when the magnetic field gradient is varied over certain limits. The ordered (periodic) cluster configuration is realized experimentally, and it is shown that its period can be controlled. As the magnetic field gradient exceeds a certain threshold, the clusters are redistributed, forming a multirow hexagonal array.