1,361,521 research outputs found
Bayesian model selection for testing the no-hair theorem with black hole ringdowns
General relativity predicts that a black hole that results from the merger of
two compact stars (either black holes or neutron stars) is initially highly
deformed but soon settles down to a quiescent state by emitting a superposition
of quasi-normal modes (QNMs). The QNMs are damped sinusoids with characteristic
frequencies and decay times that depend only on the mass and spin of the black
hole and no other parameter - a statement of the no-hair theorem. In this paper
we have examined the extent to which QNMs could be used to test the no-hair
theorem with future ground- and space-based gravitational-wave detectors. We
model departures from general relativity (GR) by introducing extra parameters
which change the mode frequencies or decay times from their general
relativistic values. With the aid of numerical simulations and Bayesian model
selection, we assess the extent to which the presence of such a parameter could
be inferred, and its value estimated. We find that it is harder to decipher the
departure of decay times from their GR value than it is with the mode
frequencies. Einstein Telescope (ET, a third generation ground-based detector)
could detect departures of <1% in the frequency of the dominant QNM mode of a
500 Msun black hole, out to a maximum range of 4 Gpc. In contrast, the New
Gravitational Observatory (NGO, an ESA space mission to detect gravitational
waves) can detect departures of ~ 0.1% in a 10^8 Msun black hole to a
luminosity distance of 30 Gpc (z = 3.5).Comment: 9 pages, 5 figure
GA-tuning of nonlinear observers for sensorless control of automotive power steering IPMSMs
The paper considers two observer-based rotor position estimation schemes for sensorless control of interior permanent magnet synchronous motors (IPMSMs) for use in future automotive power steering systems. Specifically, emphasis is given to techniques based on feedback-linearisation followed by classical Luenberger observer design, and direct design of non-linear observers. Genetic algorithms (GAs), using the principles of evolution, natural selection and genetic mutation, are introduced to address difficulties in selecting correction gains for the observers, since no analytical tuning mechanisms yet exist. Experimental measurements from an automotive power steering test-facility are included, to demonstrate the enhanced performance attributes offered by tuning the proposed observer schemes, online, in this manner
Galactic cosmic ray heavy primary secondary doses
Results of a calculation which estimates the heavy primary secondary doses from cosmic ray interaction data are reported. The incident galactic cosmic ray heavy primary spectrum is represented as the sum of helium, nitrogen, magnesium, and iron components. The incident iron nuclei are allowed to fragment into lesser Z secondaries, which are assumed to travel in the same direction and start with the same energy per nucleon as the interacting primary. The total emergent particle energy spectra and dose are then presented for the galactic heavy primary spectrum incident on aluminum and tissue slabs. The importance of the fragmentation parameters assumed is also evaluated. The total dose from the heavy primaries and their secondaries is found to be reduced by only a factor of two in 20 g/sq cm of shielding
A study of radiation environment in space and its biological effects
Biological effects on man in space resulting from galactic and solar cosmic radiation are discussed. Importance of secondary ions which contribute to galactic cosmic radiation hazards is analyzed. Mathematical model to show rate of production of secondary ions of given atomic number at various points in absorber is presented
Point Charge Self-Energy in the General Relativity
Singularities in the metric of the classical solutions to the Einstein
equations (Schwarzschild, Kerr, Reissner -- Nordstr\"om and Kerr -- Newman
solutions) lead to appearance of generalized functions in the Einstein tensor
that are not usually taken into consideration. The generalized functions can be
of a more complex nature than the Dirac \d-function. To study them, a
technique has been used based on a limiting solution sequence. The solutions
are shown to satisfy the Einstein equations everywhere, if the energy-momentum
tensor has a relevant singular addition of non-electromagnetic origin. When the
addition is included, the total energy proves finite and equal to , while
for the Kerr and Kerr--Newman solutions the angular momentum is .
As the Reissner--Nordstr\"om and Kerr--Newman solutions correspond to the point
charge in the classical electrodynamics, the result obtained allows us to view
the point charge self-energy divergence problem in a new fashion.Comment: VI Fridmann Seminar, France, Corsica, Corgeze, 2004, LaTeX, 6 pages,
2 fige
SkyMapper and the Southern Sky Survey - a resource for the southern sky
SkyMapper is amongst the first of a new generation of dedicated, wide-field
survey telescopes. The 1.3m SkyMapper telescope features a 5.7 square degree
field-of-view Cassegrain imager and will see first light in late 2007. The
primary goal of the facility is to conduct the Southern Sky Survey a six
colour, six epoch survey of the southern sky. The survey will provide
photometry for objects between 8th and 23rd magnitude with global photometric
accuracy of 0.03 magnitudes and astrometry to 50 mas. This will represent a
valuable scientific resource for the southern sky and in addition provide a
basis for photometric and astrometric calibration of imaging data.Comment: 6 pages, 4 figures, proceedings of ESO Calibration Workshop 200
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