12,470 research outputs found
Variability Abstractions: Trading Precision for Speed in Family-Based Analyses (Extended Version)
Family-based (lifted) data-flow analysis for Software Product Lines (SPLs) is
capable of analyzing all valid products (variants) without generating any of
them explicitly. It takes as input only the common code base, which encodes all
variants of a SPL, and produces analysis results corresponding to all variants.
However, the computational cost of the lifted analysis still depends inherently
on the number of variants (which is exponential in the number of features, in
the worst case). For a large number of features, the lifted analysis may be too
costly or even infeasible. In this paper, we introduce variability abstractions
defined as Galois connections and use abstract interpretation as a formal
method for the calculational-based derivation of approximate (abstracted)
lifted analyses of SPL programs, which are sound by construction. Moreover,
given an abstraction we define a syntactic transformation that translates any
SPL program into an abstracted version of it, such that the analysis of the
abstracted SPL coincides with the corresponding abstracted analysis of the
original SPL. We implement the transformation in a tool, reconfigurator that
works on Object-Oriented Java program families, and evaluate the practicality
of this approach on three Java SPL benchmarks.Comment: 50 pages, 10 figure
De Sitter Stability and Coarse Graining
We present a 4-dimensional back reaction analysis of de Sitter space for a
conformally coupled scalar field in the presence of vacuum energy initialized
in the Bunch-Davies vacuum. In contrast to the usual semi-classical
prescription, as the source term in the Friedmann equations we use expectation
values where the unobservable information hidden by the cosmological event
horizon has been neglected i.e. coarse grained over. It is shown that in this
approach the energy-momentum is precisely thermal with constant temperature
despite the dilution from the expansion of space due to a flux of energy
radiated from the horizon. This leads to a self-consistent solution for the
Hubble rate, which is gradually evolving and at late times deviates
significantly from de Sitter. Our results hence imply de Sitter space to be
unstable in this prescription. The solution also suggests dynamical vacuum
energy: the continuous flux of energy is balanced by the generation of negative
vacuum energy, which accumulatively decreases the overall contribution.
Finally, we show that our results admit a thermodynamic interpretation which
provides a simple alternate derivation of the mechanism. For very long times
the solutions coincide with flat space.Comment: v6: added an appendix giving details on mode normalizatio
Holographic bounds on the UV cutoff scale in inflationary cosmology
We discuss how holographic bounds can be applied to the quantum fluctuations
of the inflaton. In general the holographic principle will lead to a bound on
the UV cutoff scale of the effective theory of inflation, but it will depend on
the coarse-graining prescription involved in calculating the entropy. We
propose that the entanglement entropy is a natural measure of the entropy of
the quantum perturbations, and show which kind of bound on the cutoff it leads
to. Such bounds are related to whether the effects of new physics will show up
in the CMB.Comment: 19 pages, 2 figures;(V3):Comments and references adde
Static and Dynamic Properties of Inhomogeneous Elastic Media on Disordered Substrate
The pinning of an inhomogeneous elastic medium by a disordered substrate is
studied analytically and numerically. The static and dynamic properties of a
-dimensional system are shown to be equivalent to those of the well known
problem of a -dimensional random manifold embedded in -dimensions.
The analogy is found to be very robust, applicable to a wide range of elastic
media, including those which are amorphous or nearly-periodic, with local or
nonlocal elasticity. Also demonstrated explicitly is the equivalence between
the dynamic depinning transition obtained at a constant driving force, and the
self-organized, near-critical behavior obtained by a (small) constant velocity
drive.Comment: 20 pages, RevTeX. Related (p)reprints also available at
http://matisse.ucsd.edu/~hwa/pub.htm
Schwarzchild Black Holes in Matrix Theory II
We present a crude Matrix Theory model for Schwarzchild black holes in
uncompactified dimension greater than . The model accounts for the size,
entropy, and long range state interactions of black holes. The key feature of
the model is a Boltzmann gas of D0 branes, a concept which depends on certain
qualitative features of Matrix Theory which have not previously been utilized
in studies of black holes.Comment: 20 pages,harvmac,big, Some Typos corrected, 1 reference adde
Towards optical intensity interferometry for high angular resolution stellar astrophysics
Most neighboring stars are still detected as point sources and are beyond the
angular resolution reach of current observatories. Methods to improve our
understanding of stars at high angular resolution are investigated. Air
Cherenkov telescopes (ACTs), primarily used for Gamma-ray astronomy, enable us
to increase our understanding of the circumstellar environment of a particular
system. When used as optical intensity interferometers, future ACT arrays will
allow us to detect stars as extended objects and image their surfaces at high
angular resolution.
Optical stellar intensity interferometry (SII) with ACT arrays, composed of
nearly 100 telescopes, will provide means to measure fundamental stellar
parameters and also open the possibility of model-independent imaging. A data
analysis algorithm is developed and permits the reconstruction of high angular
resolution images from simulated SII data. The capabilities and limitations of
future ACT arrays used for high angular resolution imaging are investigated via
Monte-Carlo simulations. Simple stellar objects as well as stellar surfaces
with localized hot or cool regions can be accurately imaged.
Finally, experimental efforts to measure intensity correlations are
expounded. The functionality of analog and digital correlators is demonstrated.
Intensity correlations have been measured for a simulated star emitting
pseudo-thermal light, resulting in angular diameter measurements. The StarBase
observatory, consisting of a pair of 3 m telescopes separated by 23 m, is
described.Comment: PhD dissertatio
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