56,078 research outputs found
Thermodynamical Bethe Ansatz and Condensed Matter
The basics of the thermodynamic Bethe ansatz equation are given. The simplest
case is repulsive delta function bosons, the thermodynamic equation contains
only one unknown function. We also treat the XXX model with spin 1/2 and the
XXZ model and the XYZ model. This method is very useful for the investigation
of the low temperature thermodynamics of solvable systems.Comment: 52 pages, 6 figures, latex, lamuphys.st
Takahashi Integral Equation and High-Temperature Expansion of the Heisenberg Chain
Recently a new integral equation describing the thermodynamics of the 1D
Heisenberg model was discovered by Takahashi. Using the integral equation we
have succeeded in obtaining the high temperature expansion of the specific heat
and the magnetic susceptibility up to O((J/T)^{100}). This is much higher than
those obtained so far by the standard methods such as the linked-cluster
algorithm. Our results will be useful to examine various approximation methods
to extrapolate the high temperature expansion to the low temperature region.Comment: 5 pages, 4 figures, 2 table
Trans-Magnetosonic Accretion in a Black Hole Magnetosphere
We present the critical conditions for hot trans-fast magnetohydrodynamical
(MHD) flows in a stationary and axisymmetric black-hole magnetosphere. To
accrete onto the black hole, the MHD flow injected from a plasma source with
low velocity must pass through the fast magnetosonic point after passing
through the ``inner'' or ``outer'' Alfven point. We find that a trans-fast MHD
accretion solution related to the inner Alfven point is invalid when the
hydrodynamical effects on the MHD flow dominate at the magnetosonic point,
while the other accretion solution related to the outer Alfven point is invalid
when the total angular momentum of the MHD flow is seriously large. When both
regimes of the accretion solutions are valid in the black hole magnetosphere,
we can expect the transition between the two regimes. The variety of these
solutions would be important in many highly energetic astrophysical situations.Comment: 27 pages, 12 figures, accepted to Ap
Boltzmann expansion in a radiofrequency conical helicon thruster operating in xenon and argon
A low pressure (~ 0.5 mTorr in xenon and ~ 1 mTorr in argon) Boltzmann expansion is
experimentally observed on axis within a magnetized (60 to 180 G) radiofrequency (13.56 MHz)
conical helicon thruster for input powers up to 900 W using plasma parameters measured with a
Langmuir probe. The axial forces, respectively, resulting from the electron and magnetic field
pressures are directly measured using a thrust balance for constant maximum plasma pressure
and show a higher fuel efficiency for argon compared to xenon
Anisotropic radiation field and trapped photons around the Kerr black hole
Aims. In order to understand the anisotropic properties of local radiation
field in the curved spacetime around a rotating black hole, we investigate the
appearance of a black hole seen by an observer located near the black hole.
When the black hole is in front of a source of illumination the black hole cast
shadow in the illumination. Accordingly, the appearance of the black hole is
called the black hole shadow.
Methods. We first analytically describe the shape of the shadow in terms of
constants of motion for a photon seen by the observer in the locally
non-rotating reference frame (LNRF). Then, we newly derive the useful equation
for the solid angle of the shadow. In a third step, we can easily plot the
apparent image of the black hole shadow. Finally, we also calculate the ratio
of the photon trapped by the hole and the escape photon to the distant region
for photons emitted near the black hole.
Results. From the shape and the size of the black hole shadow, we can
understand the signatures of the curved spacetime; i.e., the mass and spin of
the black hole. Our equations for the solid angle of the shadow has technical
advantages in calculating the photon trapping ratio. That is, this equation is
computationally very easy, and gives extremely precise results. This is because
this equation is described by the one-parameter integration with given values
of the spin and location for the black hole considered. After this, the solid
angle can be obtained without numerical calculations of the null geodesics for
photons.Comment: Accepted for publication in A&
- …