3,768 research outputs found
Geometric transport along circular orbits in stationary axisymmetric spacetimes
Parallel transport along circular orbits in orthogonally transitive
stationary axisymmetric spacetimes is described explicitly relative to Lie
transport in terms of the electric and magnetic parts of the induced
connection. The influence of both the gravitoelectromagnetic fields associated
with the zero angular momentum observers and of the Frenet-Serret parameters of
these orbits as a function of their angular velocity is seen on the behavior of
parallel transport through its representation as a parameter-dependent Lorentz
transformation between these two inner-product preserving transports which is
generated by the induced connection. This extends the analysis of parallel
transport in the equatorial plane of the Kerr spacetime to the entire spacetime
outside the black hole horizon, and helps give an intuitive picture of how
competing "central attraction forces" and centripetal accelerations contribute
with gravitomagnetic effects to explain the behavior of the 4-acceleration of
circular orbits in that spacetime.Comment: 33 pages ijmpd latex article with 24 eps figure
Kerr metric, static observers and Fermi coordinates
The coordinate transformation which maps the Kerr metric written in standard
Boyer-Lindquist coordinates to its corresponding form adapted to the natural
local coordinates of an observer at rest at a fixed position in the equatorial
plane, i.e., Fermi coordinates for the neighborhood of a static observer world
line, is derived and discussed in a way which extends to any uniformly
circularly orbiting observer there.Comment: 15 page latex iopart class documen
Circular holonomy in the Taub-NUT spacetime
Parallel transport around closed circular orbits in the equatorial plane of
the Taub-NUT spacetime is analyzed to reveal the effect of the gravitomagnetic
monopole parameter on circular holonomy transformations. Investigating the
boost/rotation decomposition of the connection 1-form matrix evaluated along
these orbits, one finds a situation that reflects the behavior of the general
orthogonally transitive stationary axisymmetric case and indeed along Killing
trajectories in general.Comment: 9 pages, LaTeX iopart class, no figure
Spacetime Slices and Surfaces of Revolution
Under certain conditions, a -dimensional slice of a
spherically symmetric black hole spacetime can be equivariantly embedded in
-dimensional Minkowski space. The embedding depends on a real parameter
that corresponds physically to the surface gravity of the black hole
horizon.
Under conditions that turn out to be closely related, a real surface that
possesses rotational symmetry can be equivariantly embedded in 3-dimensional
Euclidean space. The embedding does not obviously depend on a parameter.
However, the Gaussian curvature is given by a simple formula: If the metric is
written , then
\K_g=-{1/2}\phi''(r).
This note shows that metrics and occur in dual pairs, and that
the embeddings described above are orthogonal facets of a single phenomenon. In
particular, the metrics and their respective embeddings differ by a Wick
rotation that preserves the ambient symmetry.
Consequently, the embedding of depends on a real parameter. The ambient
space is not smooth, and is inversely proportional to the cone angle
at the axis of rotation. Further, the Gaussian curvature of is given
by a simple formula that seems not to be widely known.Comment: 15 pages, added reference
Electrocardiogram of the Mixmaster Universe
The Mixmaster dynamics is revisited in a new light as revealing a series of
transitions in the complex scale invariant scalar invariant of the Weyl
curvature tensor best represented by the speciality index , which
gives a 4-dimensional measure of the evolution of the spacetime independent of
all the 3-dimensional gauge-dependent variables except for the time used to
parametrize it. Its graph versus time characterized by correlated isolated
pulses in its real and imaginary parts corresponding to curvature wall
collisions serves as a sort of electrocardiogram of the Mixmaster universe,
with each such pulse pair arising from a single circuit or ``complex pulse''
around the origin in the complex plane. These pulses in the speciality index
and their limiting points on the real axis seem to invariantly characterize
some of the so called spike solutions in inhomogeneous cosmology and should
play an important role as a gauge invariant lens through which to view current
investigations of inhomogeneous Mixmaster dynamics.Comment: version 3: 20 pages iopart style, 19 eps figure files for 8 latex
figures; added example of a transient true spike to contrast with the
permanent true spike example from the Lim family of true spike solutions;
remarks in introduction and conclusion adjusted and toned down; minor
adjustments to the remaining tex
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Wearable activity sensors and early pain after total joint arthroplasty.
A prospective observational cohort of 20 primary total hip arthroplasty (n = 12) and total knee arthroplasty (n = 8) patients (mean age: 63 ± 6 years) was passively monitored with a consumer-level wearable activity sensor before and 6 weeks after surgery. Patients were clustered by minimal change or decreased activity using sensor data. Decreased postoperative activity was associated with greater pain reduction (-5.5 vs -2.0, P = .03). All patients surpassed minimal clinical benefit thresholds of total joint arthroplasty (TJA) (Hip Disability and Osteoarthritis Score Junior 30.5 vs 20.8, P = .23; Knee Injury and Osteoarthritis Outcome Score Junior 23.3 vs 18.2, P = .77) within 6 weeks. Patients who objectively "take it easy" after TJA may experience less pain with no difference in early subjective outcome. Remote, passive analysis of outpatient wearable sensor data may permit real-time detection of early problems after TJA
Gravitomagnetism in the Kerr-Newman-Taub-NUT spacetime
We study the motion of test particles and electromagnetic waves in the
Kerr-Newman-Taub-NUT spacetime in order to elucidate some of the effects
associated with the gravitomagnetic monopole moment of the source. In
particular, we determine in the linear approximation the contribution of this
monopole to the gravitational time delay and the rotation of the plane of the
polarization of electromagnetic waves. Moreover, we consider "spherical" orbits
of uncharged test particles in the Kerr-Taub-NUT spacetime and discuss the
modification of the Wilkins orbits due to the presence of the gravitomagnetic
monopole.Comment: 12 pages LaTeX iopart style, uses PicTex for 1 Figur
The general relativistic Poynting-Robertson effect
The general relativistic version is developed for Robertson's discussion of
the Poynting-Robertson effect that he based on special relativity and Newtonian
gravity for point radiation sources like stars. The general relativistic model
uses a test radiation field of photons in outward radial motion with zero
angular momentum in the equatorial plane of the exterior Schwarzschild or Kerr
spacetime.Comment: 19 pages iop style, 8 eps figure files for 5 figure
Loop variables in the geometry of a rotating black string
In this paper we analyze in the Wilson loop context the parallel transport of
vectors and spinors around a closed loop in the background space-time of a
rotating black string in order to classify its global properties. We also
examine particular closed orbits in this space-time and verify the Mandelstam
relations.Comment: 14 pages, iopart styl
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