11,789 research outputs found
Making Clean Energy with a Kerr Black Hole: a Tokamak Model for Gamma-Ray Bursts
In this paper we present a model for making clean energy with a Kerr black
hole. Consider a Kerr black hole with a dense plasma torus spinning around it.
A toroidal electric current flows on the surface of the torus, which generates
a poloidal magnetic field outside the torus. On the surface of the tours the
magnetic field is parallel to the surface. The closed magnetic field lines
winding around the torus compress and confine the plasma in the torus, as in
the case of tokamaks. Though it is unclear if such a model is stable, we look
into the consequences if the model is stable. If the magnetic field is strong
enough, the baryonic contamination from the plasma in the torus is greatly
suppressed by the magnetic confinement and a clean magnetosphere of
electron-positron pairs is built up around the black hole. Since there are no
open magnetic field lines threading the torus and no accretion, the power of
the torus is zero. If some magnetic field lines threading the black hole are
open and connect with loads, clean energy can be extracted from the Kerr black
hole by the Blandford-Znajek mechanism.
The model may be relevant to gamma-ray bursts. The energy in the Poynting
flux produced by the Blandford-Znajek mechanism is converted into the kinetic
energy of the electron-positron pairs in the magnetosphere around the black
hole, which generates two oppositely directed jets of electron-positron pairs
with super-high bulk Lorentz factors. The jets collide and interact with the
interstellar medium, which may produce gamma-ray bursts and the afterglows.Comment: 14 pages, 1 figure, accepted by Ap
Formal Relation among Various Hermitian and non-Hermitian Effective Interactions
A general definition of the model-space effective interaction is given. The
energy-independent effective hamiltonians derived in a time-independent way are
classified systematically.Comment: To appear in IJMPE; Proceedings of "Blueprints for the Nucleus,"
Istanbul, Turkey, May 200
Tuning the spin dynamics of kagome systems
Despite the conceptional importance of realizing spin liquids in solid states
only few compounds are known. On the other side the effect of lattice
distortions and anisotropies on the magnetic exchange topology and the
fluctuation spectrum are an interesting problem. We compare the excitation
spectra of the two s=1/2 kagome lattice compounds volborthite and vesignieite
using Raman scattering. We demonstrate that even small modifications of the
crystal structure may have a huge effect on the phonon spectrum and low
temperature properties.Comment: 3 pages, 2 figure
A -anaolg of the sixth Painlev\'e equation
A -difference analog of the sixth Painlev\'e equation is presented. It
arises as the condition for preserving the connection matrix of linear
-difference equations, in close analogy with the monodromy preserving
deformation of linear differential equations. The continuous limit and special
solutions in terms of -hypergeometric functions are also discussed.Comment: 8 pages, LaTeX file (Two misprints corrected
Stochastic Model and Equivalent Ferromagnetic Spin Chain with Alternation
We investigate a non-equilibrium reaction-diffusion model and equivalent
ferromagnetic spin 1/2 XY spin chain with alternating coupling constant. The
exact energy spectrum and the n-point hole correlations are considered with the
help of the Jordan-Wigner fermionization and the inter-particle distribution
function method. Although the Hamiltonian has no explicit translational
symmetry, the translational invariance is recovered after long time due to the
diffusion. We see the scaling relations for the concentration and the two-point
function in finite size analysis.Comment: 7 pages, LaTeX file, to appear in J. Phys. A: Math. and Ge
Noncommutative Field Theory and Lorentz Violation
The role of Lorentz symmetry in noncommutative field theory is considered.
Any realistic noncommutative theory is found to be physically equivalent to a
subset of a general Lorentz-violating standard-model extension involving
ordinary fields. Some theoretical consequences are discussed. Existing
experiments bound the scale of the noncommutativity parameter to (10 TeV)^{-2}.Comment: 4 page
Electron-lattice coupling, orbital stability and the phase diagram of CaSrRuO
Hartree-Fock calculations are presented of a theoretical model describing the
Sr/CaRuO family of compounds. Both commensurate and incommensurate magnetic
states are considered, along with orbital ordering and the effect of lattice
distortions. For reasonable parameter values, interactions disfavor orbital
disproportionation. A coherent description of the observed phase diagram is
obtained.Comment: Changed content, and added a new referenc
From antiferromagnetism to superconductivity in Fe 1+y(Te1-x,Sex) (0 < x < 0.20): a neutron powder diffraction analysis
The nuclear and magnetic structure of Fe1+y(Te1-x,Sex) (0 < x < 0.20)
compounds was analyzed between 2 K and 300 K by means of Rietveld refinement of
neutron powder diffraction data. Samples with x < 0.075 undergo a tetragonal to
monoclinic phase transition at low temperature, whose critical temperature
decreases with increasing Se content; this structural transition is strictly
coupled to a long range antiferromagnetic ordering at the Fe site. Both the
transition to a monoclinic phase and the long range antiferromagnetism are
suppressed for 0.10 < x < 0.20. The onset of the structural and of the magnetic
transition remains coincident with the increase of Se substitution. The low
temperature monoclinic crystal structure has been revised. Superconductivity
arises for x > 0.05, therefore a significant region where superconductivity and
long range antiferromagnetism coexist is present in the pseudo-binary FeTe -
FeSe phase diagram.Comment: 33 pages, 4 tables, 13 figure
Magnetized Accretion Inside the Marginally Stable Orbit around a Black Hole
Qualitative arguments are presented to demonstrate that the energy density of
magnetic fields in matter accreting onto a black hole inside the marginally
stable orbit is automatically comparable to the rest-mass energy density of the
accretion flow. Several consequences follow: magnetic effects must be
dynamically significant, but cannot be so strong as to dominate; outward energy
transport in Alfven waves may alter the effective efficiency of energy
liberation; and vertical magnetic stresses in this region may contribute to
"coronal" activity.Comment: to appear in Ap. J. Letter
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