2,062 research outputs found
Explanation of the Tao effect
In a series of experiments Tao and coworkers\cite{tao1,tao2,tao3} found that
superconducting microparticles in the presence of a strong electrostatic field
aggregate into balls of macroscopic dimensions. No explanation of this
phenomenon exists within the conventional theory of superconductivity. We show
that this effect can be understood within an alternative electrodynamic
description of superconductors recently proposed that follows from an
unconventional theory of superconductivity. Experiments to test the theory are
discussed.Comment: Submitted to Science January 2nd, declined January 6th; to Nature
January 7th, declined January 13th; to PRL January 14th, declined February
25t
Capture of non-relativistic particles in eccentric orbits by a Kerr black hole
We obtain approximate analytic expressions for the critical value of the
total angular momentum of a non-relativistic test particle moving in the Kerr
geometry, such that it will be captured by the black hole. The expressions
apply to arbitrary orbital inclinations, and are accurate over the entire range
of angular momentum for the Kerr black hole. The expressions can be easily
implemented in N-body simulations of the evolution of star clusters around
massive galactic black holes, where such captures play an important role.Comment: 8 pages, 1 figure, published versio
Absence of Dipole Transitions in Vortices of Type II Superconductors
The response of a single vortex to a time dependent field is examined
microscopically and an equation of motion for vortex motion at non-zero
frequencies is derived. Of interest are frequencies near ,
where is the bulk energy gap and is the fermi energy. The low
temperature, clean, extreme type II limit and maintaining of equilibrium with
the lattice are assumed. A simplification occurs for large planar mass
anisotropy. Thus the results may be pertinent to materials such as and
high temperature superconductors. The expected dipole transition between core
states is hidden because of the self consistent nature of the vortex potential.
Instead the vortex itself moves and has a resonance at the frequency of the
transition.Comment: 12 pages, no figure
Schwarzschild Tests of the Wahlquist-Estabrook-Buchman-Bardeen Tetrad Formulation for Numerical Relativity
A first order symmetric hyperbolic tetrad formulation of the Einstein
equations developed by Estabrook and Wahlquist and put into a form suitable for
numerical relativity by Buchman and Bardeen (the WEBB formulation) is adapted
to explicit spherical symmetry and tested for accuracy and stability in the
evolution of spherically symmetric black holes (the Schwarzschild geometry).
The lapse and shift which specify the evolution of the coordinates relative to
the tetrad congruence are reset at frequent time intervals to keep the
constant-time hypersurfaces nearly orthogonal to the tetrad congruence and the
spatial coordinate satisfying a kind of minimal rate of strain condition. By
arranging through initial conditions that the constant-time hypersurfaces are
asymptotically hyperbolic, we simplify the boundary value problem and improve
stability of the evolution. Results are obtained for both tetrad gauges
(``Nester'' and ``Lorentz'') of the WEBB formalism using finite difference
numerical methods. We are able to obtain stable unconstrained evolution with
the Nester gauge for certain initial conditions, but not with the Lorentz
gauge.Comment: (accepted by Phys. Rev. D) minor changes; typos correcte
Gravitational energy
Observers at rest in a stationary spacetime flat at infinity can measure
small amounts of rest-mass+internal energies+kinetic energies+pressure energy
in a small volume of fluid attached to a local inertial frame. The sum of these
small amounts is the total "matter energy" for those observers. The total
mass-energy minus the matter energy is the binding gravitational energy.
Misner, Thorne and Wheeler evaluated the gravitational energy of a
spherically symmetric static spacetime. Here we show how to calculate
gravitational energy in any static and stationary spacetime for isolated
sources with a set of observers at rest.
The result of MTW is recovered and we find that electromagnetic and
gravitational 3-covariant energy densities in conformastatic spacetimes are of
opposite signs. Various examples suggest that gravitational energy is negative
in spacetimes with special symmetries or when the energy-momentum tensor
satisfies usual energy conditions.Comment: 12 pages. Accepted for publication in Class. Quantum Gra
The Extreme Kerr Throat Geometry: A Vacuum Analog of AdS_2 x S^2
We study the near horizon limit of a four dimensional extreme rotating black
hole. The limiting metric is a completely nonsingular vacuum solution, with an
enhanced symmetry group SL(2,R) x U(1). We show that many of the properties of
this solution are similar to the AdS_2 x S^2 geometry arising in the near
horizon limit of extreme charged black holes. In particular, the boundary at
infinity is a timelike surface. This suggests the possibility of a dual quantum
mechanical description. A five dimensional generalization is also discussed.Comment: 21 page
Towards a Singularity-Proof Scheme in Numerical Relativity
Progress in numerical relativity has been hindered for 30 years because of
the difficulties of avoiding spacetime singularities in numerical evolution. We
propose a scheme which excises a region inside an apparent horizon containing
the singularity. Two major ingredients of the scheme are the use of a
horizon-locking coordinate and a finite differencing which respects the causal
structure of the spacetime. Encouraging results of the scheme in the spherical
collapse case are given.Comment: 9 page
The Transition from Inspiral to Plunge for a Compact Body in a Circular Equatorial Orbit Around a Massive, Spinning Black Hole
There are three regimes of gravitational-radiation-reaction-induced inspiral
for a compact body with mass mu, in a circular, equatorial orbit around a Kerr
black hole with mass M>>mu: (i) The "adiabatic inspiral regime", in which the
body gradually descends through a sequence of circular, geodesic orbits. (ii) A
"transition regime", near the innermost stable circular orbit (isco). (iii) The
"plunge regime", in which the body travels on a geodesic from slightly below
the isco into the hole's horizon. This paper gives an analytic treatment of the
transition regime and shows that, with some luck, gravitational waves from the
transition might be measurable by the space-based LISA mission.Comment: 8 Pages and 3 Figures; RevTeX; submitted to Physical Review
Manifestly Gauge Covariant Treatment of Lattice Chiral Fermion
We propose a lattice formulation of the chiral fermion which maximally
respects the gauge symmetry and simultaneously is free of the unwanted species
doublers. The formulation is based on the lattice fermion propagator and
composite operators, rather than on the lattice fermion action. The fermionic
determinant is defined as a functional integral of an expectation value of the
gauge current operator with respect to the background gauge field: The gauge
anomaly is characterized as the non-integrability. We perform some perturbative
test to confirm the gauge covariance and an absence of the doublers. The
formulation can be applied rather straightforwardly to numerical simulations in
the quenched approximation.Comment: 11 pages, phyzzx, The final version to appear in Phys. Rev.
Boron Isotope Effect in Superconducting MgB
We report the preparation method of, and boron isotope effect for MgB, a
new binary intermetallic superconductor with a remarkably high superconducting
transition temperature (B) = 40.2 K. Measurements of both
temperature dependent magnetization and specific heat reveal a 1.0 K shift in
between MgB and MgB. Whereas such a high transition
temperature might imply exotic coupling mechanisms, the boron isotope effect in
MgB is consistent with the material being a phonon-mediated BCS
superconductor.Comment: One figure and related discussion adde
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