8,381 research outputs found
Constraining neutron star tidal Love numbers with gravitational wave detectors
Ground-based gravitational wave detectors may be able to constrain the
nuclear equation of state using the early, low frequency portion of the signal
of detected neutron star - neutron star inspirals. In this early adiabatic
regime, the influence of a neutron star's internal structure on the phase of
the waveform depends only on a single parameter lambda of the star related to
its tidal Love number, namely the ratio of the induced quadrupole moment to the
perturbing tidal gravitational field. We analyze the information obtainable
from gravitational wave frequencies smaller than a cutoff frequency of 400 Hz,
where corrections to the internal-structure signal are less than 10 percent.
For an inspiral of two non-spinning 1.4 solar mass neutron stars at a distance
of 50 Mpc, LIGO II detectors will be able to constrain lambda to lambda < 2.0
10^{37} g cm^2 s^2 with 90% confidence. Fully relativistic stellar models show
that the corresponding constraint on radius R for 1.4 solar mass neutron stars
would be R < 13.6 km (15.3 km) for a n=0.5 (n=1.0) polytrope.Comment: 4 pages, 2 figures, minor correction
Ionization Structure and the Reverse Shock in E0102-72
The young oxygen-rich supernova remnant E0102-72 in the Small Magellanic
Cloud has been observed with the High Energy Transmission Grating Spectrometer
of Chandra. The high resolution X-ray spectrum reveals images of the remnant in
the light of individual emission lines of oxygen, neon, magnesium and silicon.
The peak emission region for hydrogen-like ions lies at larger radial distance
from the SNR center than the corresponding helium-like ions, suggesting passage
of the ejecta through the "reverse shock". We examine models which test this
interpretation, and we discuss the implications.Comment: 4 pages, 6 figures; To appear in "Young Supernova Remnants" (11th
Annual Astrophysics Conference in Maryland), S. S. Holt & U. Hwang (eds),
AIP, New York (2001
Shuttle flight pressure instrumentation: Experience and lessons for the future
Flight data obtained from the Space Transportation System orbiter entries are processed and analyzed to assess the accuracy and performance of the Development Flight Instrumentation (DFI) pressure measurement system. Selected pressure measurements are compared with available wind tunnel and computational data and are further used to perform air data analyses using the Shuttle Entry Air Data System (SEADS) computation technique. The results are compared to air data from other sources. These comparisons isolate and demonstrate the effects of the various limitations of the DFI pressure measurement system. The effects of these limitations on orbiter performance analyses are addressed, and instrumentation modifications are recommended to improve the accuracy of similar fight data systems in the future
A Nonsingular Brans Wormhole: An Analogue to Naked Black Holes
In a recent paper, we showed the Jordan frame vacuum Brans Class I solution
provided a wormhole analogue to Horowitz-Ross naked black hole in the wormhole
range -3/2<{\omega}<-4/3. Thereafter, the solution has been criticized by some
authors that, because of the presence of singularity in that solution within
this range, a wormhole interpretation of it is untenable. While the criticism
is correct, we show here that (i) a singularity-free wormhole can actually be
obtained from Class I solution by performing a kind of Wick rotation on it,
resulting into what Brans listed as his independent Class II solution (ii) the
Class II solution has all the necessary properties of a regular wormhole in a
revised range -2<{\omega}<-3/2 and finally, (iii) naked black holes, as
described by Horowitz and Ross, are spacetimes where the tidal forces attain
their maxima above the black hole horizon. We show that in the non-singular
Class II spacetime this maxima is attained above the throat and thus can be
treated as a wormhole analogue. Some related issues are also addressed.Comment: 20 pages, 4 figure
Abstract Interpretation with Unfoldings
We present and evaluate a technique for computing path-sensitive interference
conditions during abstract interpretation of concurrent programs. In lieu of
fixed point computation, we use prime event structures to compactly represent
causal dependence and interference between sequences of transformers. Our main
contribution is an unfolding algorithm that uses a new notion of independence
to avoid redundant transformer application, thread-local fixed points to reduce
the size of the unfolding, and a novel cutoff criterion based on subsumption to
guarantee termination of the analysis. Our experiments show that the abstract
unfolding produces an order of magnitude fewer false alarms than a mature
abstract interpreter, while being several orders of magnitude faster than
solver-based tools that have the same precision.Comment: Extended version of the paper (with the same title and authors) to
appear at CAV 201
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