11,127 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
Chandra X-ray Observations of the Two Brightest Unidentified High Galactic Latitude Fermi-LAT gamma-ray Sources
We present Chandra ACIS-I X-ray observations of 0FGL J1311.9-3419 and 0FGL
J1653.4-0200, the two brightest high Galactic latitude (|b|>10 deg) gamma-ray
sources from the 3 month Fermi-LAT bright source list that are still
unidentified. Both were also detected previously by EGRET, and despite
dedicated multi-wavelength follow-up, they are still not associated with
established classes of gamma-ray emitters like pulsars or radio-loud active
galactic nuclei. X-ray sources found in the ACIS-I fields of view are
catalogued, and their basic properties are determined. These are discussed as
candidate counterparts to 0FGL J1311.9-3419 and 0FGL J1653.4-0200, with
particular emphasis on the brightest of the 9 and 13 Chandra sources detected
within their respective Fermi-LAT 95% confidence regions. Further follow-up
studies, including optical photometric and spectroscopic observations are
necessary to identify these X-ray candidate counterparts in order to ultimately
reveal the nature of these enigmatic gamma-ray objects.Comment: ApJ, accepted. 18 pages, 5 figure
Efficacy and toxicity of bevacizumab in recurrent ovarian disease: an update meta-analysis on phase III trials
Background: To analyze the efficacy and toxicity of bevacizumab on survival outcomes in recurrent ovarian cancer.
Results: Bevacizumab was associated with significant improvement of PFS and OS compared with standard treatment with HRs of 0.53 (95% CI 0.44 - 0.63; p < 0.00001) and 0.87 (95% CI, 0.77 to 0.99; p = 0.03), respectively.
Bevacizumab increased the incidence of G3/G4 hypertension (RR 19.01, 95% CI 7.77 - 46.55; p < 0.00001), proteinuria (RR 17.31, 95% CI 5.42 - 55.25; p < 0.00001), arterial thromboembolic events (ATE) (RR 4.99, 95% CI 1.29 - 19.27; p = 0.02) and bleeding (RR 3.14, 95% CI 1.35 - 7.32; p = 0.008).
Materials and Methods: Three randomized phase III trials representing 1502 patients were identified.
Pooled hazard ratio (HR), odd ratio (OR), risk ratio (RR) with 95% confidence interval (CI) were calculated using fixed or random effects model.
Conclusions: Adding bevacizumab to standard chemotherapy improved ORR, PFS and OS, and it had a higher, but manageable, incidence of toxicities graded 3 to 4
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
Spin precession in the Schwarzschild spacetime: circular orbits
We study the behavior of nonzero rest mass spinning test particles moving
along circular orbits in the Schwarzschild spacetime in the case in which the
components of the spin tensor are allowed to vary along the orbit, generalizing
some previous work.Comment: To appear on Classical and Quantum Gravity, 200
Discovery of an unidentified Fermi object as a black widow-like millisecond pulsar
The Fermi Gamma-ray Space Telescope has revolutionized our knowledge of the
gamma-ray pulsar population, leading to the discovery of almost 100 gamma-ray
pulsars and dozens of gamma-ray millisecond pulsars (MSPs). Although the
outer-gap model predicts different sites of emission for the radio and
gamma-ray pulsars, until now all of the known gamma-ray MSPs have been visible
in the radio. Here we report the discovery of a "radio-quiet" gamma-ray
emitting MSP candidate by using Fermi, Chandra, Swift, and optical
observations. The X-ray and gamma-ray properties of the source are consistent
with known gamma-ray pulsars. We also found a 4.63-hr orbital period in optical
and X-ray data. We suggest that the source is a black widow-like MSP with a
~0.1 solar-mass late-type companion star. Based on the profile of the optical
and X-ray light-curves, the companion star is believed to be heated by the
pulsar while the X-ray emissions originate from pulsar magnetosphere and/or
from intra-binary shock. No radio detection of the source has been reported yet
and although no gamma-ray/radio pulsation has been found, we estimated that the
spin period of the MSP is ~3-5 ms based on the inferred gamma-ray luminosity.Comment: 6 pages, 2 figures; accepted for publication in ApJ
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
- …