1,265 research outputs found
On the origin of exponential growth in induced earthquakes in Groningen
The Groningen gas field shows exponential growth in earthquakes event counts
around a magnitude M1 with a doubling time of 6-9 years since 2001. This
behavior is identified with dimensionless curvature in land subsidence, which
has been evolving at a constant rate over the last few decades {essentially
uncorrelated to gas production.} We demonstrate our mechanism by a tabletop
crack formation experiment. The observed skewed distribution of event
magnitudes is matched by that of maxima of event clusters with a normal
distribution. It predicts about one event \,M5 per day in 2025, pointing to
increasing stress to human living conditions.Comment: 12 pages, 7 figures, to appear in Earthquakes and Structure
Uniqueness in MHD in divergence form: right nullvectors and well-posedness
Magnetohydrodynamics in divergence form describes a hyperbolic system of
covariant and constraint-free equations. It comprises a linear combination of
an algebraic constraint and Faraday's equations. Here, we study the problem of
well-posedness, and identify a preferred linear combination in this divergence
formulation. The limit of weak magnetic fields shows the slow magnetosonic and
Alfven waves to bifurcate from the contact discontinuity (entropy waves), while
the fast magnetosonic wave is a regular perturbation of the hydrodynamical
sound speed. These results are further reported as a starting point for
characteristic based shock capturing schemes for simulations with
ultra-relativistic shocks in magnetized relativistic fluids.Comment: To appear in J Math Phy
On the detectability of gravitational waves background produced by gamma ray bursts
In this paper we discuss a new strategy for the detection of gravitational
radiation likely emitted by cosmological gamma ray burst. Robust and
conservative estimates lead to the conclusion that the uncorrelated
superimposition of bursts of gravitational waves can be detected by
interferometric detectors like VIRGO or LIGO. The expected signal is predicted
to carry two very distinctive signatures: the cosmological dipole anisotropy
and a characteristic time scale in the auto correlation spectrum, which might
be exploited, perhaps with ad hoc modifications and/or upgrading of the planned
experiments, to confirm the non-instrumental origin of the signal.Comment: 9 pages, 2 figures, LATEX2e, Accepted for pubblications as a Letter
to the Editor in Journal of Physics G: Nuclear and Particle Physic
Gravitational radiation from gamma-ray bursts as observational opportunities for LIGO and VIRGO
Gamma-ray bursts are believed to originate in core-collapse of massive stars.
This produces an active nucleus containing a rapidly rotating Kerr black hole
surrounded by a uniformly magnetized torus represented by two counter-oriented
current rings. We quantify black hole spin-interactions with the torus and
charged particles along open magnetic flux-tubes subtended by the event
horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of
frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with
GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii)
aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich
et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al.
2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating
LIGO/Virgo detectors enables searches for nearby events and their spectral
closure density 6e-9 around 250Hz in the stochastic background radiation in
gravitational waves. At current sensitivity, LIGO-Hanford may place an upper
bound around 150MSolar in GRB030329. Detection of Egw thus provides a method
for identifying Kerr black holes by calorimetry.Comment: to appear in PRD, 49
Electron-positron outflow from black holes
Gamma-ray bursts (GRBs) appear as the brightest transient phenomena in the
Universe. The nature of the central engine in GRBs is a missing link in the
theory of fireballs to their stellar mass progenitors. Here it is shown that
rotating black holes produce electron-positron outflow when brought into
contact with a strong magnetic field. The outflow is produced by a coupling of
the spin of the black hole to the orbit of the particles. For a nearly extreme
Kerr black hole, particle outflow from an initial state of electrostatic
equilibrium has a normalized isotropic emission of erg/s, where B is the
external magnetic field strength, B_c=4.4 x 10^{13}G, and M is the mass of the
black hole. This initial outflow has a half-opening angle
. A connection with fireballs in -ray bursts is
given.Comment: 10 pages LaTe
Causal propagation of geometrical fields in relativistic cosmology
We employ the extended 1+3 orthonormal frame formalism for fluid spacetime
geometries , which contains the Bianchi field
equations for the Weyl curvature, to derive a 44-D evolution system of
first-order symmetric hyperbolic form for a set of geometrically defined
dynamical field variables. Describing the matter source fields
phenomenologically in terms of a barotropic perfect fluid, the propagation
velocities (with respect to matter-comoving observers that Fermi-propagate
their spatial reference frames) of disturbances in the matter and the
gravitational field, represented as wavefronts by the characteristic 3-surfaces
of the system, are obtained. In particular, the Weyl curvature is found to
account for two (non-Lorentz-invariant) Coulomb-like characteristic eigenfields
propagating with and four transverse characteristic eigenfields
propagating with , which are well known, and four
(non-Lorentz-invariant) longitudinal characteristic eigenfields propagating
with |v| = \sfrac{1}{2}. The implications of this result are discussed in
some detail and a parallel is drawn to the propagation of irregularities in the
matter distribution. In a worked example, we specialise the equations to
cosmological models in locally rotationally symmetric class II and include the
constraints into the set of causally propagating dynamical variables.Comment: 25 pages, RevTeX (10pt), accepted for publication by Physical Review
Reduced EPO receptor expression may contribute to limited pleiotropic effects of EPO during critical illness
Hyperbolic Equations for Vacuum Gravity Using Special Orthonormal Frames
By adopting Nester's higher dimensional special orthonormal frames (HSOF) the
tetrad equations for vacuum gravity are put into first order symmetric
hyperbolic (FOSH) form with constant coefficients, independent of any time
slicing or coordinate specialization.Comment: 14 pages, 3 figures, LaTeX, 13 macros. CQG 14 (1997) 1237-1247 has
algebraic errors. +/- signs in Equations (2), (4) and (5) are here corrected,
and factors of 2 added to Eqs. (18) and (19
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