55,690 research outputs found
Automata and rational expressions
This text is an extended version of the chapter 'Automata and rational
expressions' in the AutoMathA Handbook that will appear soon, published by the
European Science Foundation and edited by JeanEricPin
Simple nonlinear models suggest variable star universality
Dramatically improved data from observatories like the CoRoT and Kepler
spacecraft have recently facilitated nonlinear time series analysis and
phenomenological modeling of variable stars, including the search for strange
(aka fractal) or chaotic dynamics. We recently argued [Lindner et al., Phys.
Rev. Lett. 114 (2015) 054101] that the Kepler data includes "golden" stars,
whose luminosities vary quasiperiodically with two frequencies nearly in the
golden ratio, and whose secondary frequencies exhibit power-law scaling with
exponent near -1.5, suggesting strange nonchaotic dynamics and singular
spectra. Here we use a series of phenomenological models to make plausible the
connection between golden stars and fractal spectra. We thereby suggest that at
least some features of variable star dynamics reflect universal nonlinear
phenomena common to even simple systems.Comment: 9 pages, 9 figures, accepted for publication in Physica
The set of realizations of a max-plus linear sequence is semi-polyhedral
We show that the set of realizations of a given dimension of a max-plus
linear sequence is a finite union of polyhedral sets, which can be computed
from any realization of the sequence. This yields an (expensive) algorithm to
solve the max-plus minimal realization problem. These results are derived from
general facts on rational expressions over idempotent commutative semirings: we
show more generally that the set of values of the coefficients of a commutative
rational expression in one letter that yield a given max-plus linear sequence
is a semi-algebraic set in the max-plus sense. In particular, it is a finite
union of polyhedral sets
Enhanced Gauge Symmetry in Type II and F-Theory Compactifications: Dynkin Diagrams from Polyhedra
We explain the observation by Candelas and Font that the Dynkin diagrams of
nonabelian gauge groups occurring in type IIA and F-theory can be read off from
the polyhedron that provides the toric description of the Calabi-Yau
manifold used for compacification. We show how the intersection pattern of
toric divisors corresponding to the degeneration of elliptic fibers follows the
ADE classification of singularities and the Kodaira classification of
degenerations. We treat in detail the cases of elliptic K3 surfaces and K3
fibered threefolds where the fiber is again elliptic. We also explain how even
the occurrence of monodromy and non-simply laced groups in the latter case is
visible in the toric picture. These methods also work in the fourfold case.Comment: 26 pages, LaTeX2e, 17 figures, references adde
Constraining Exoplanet Mass from Transmission Spectroscopy
Determination of an exoplanet's mass is a key to understanding its basic
properties, including its potential for supporting life. To date, mass
constraints for exoplanets are predominantly based on radial velocity (RV)
measurements, which are not suited for planets with low masses, large
semi-major axes, or those orbiting faint or active stars. Here, we present a
method to extract an exoplanet's mass solely from its transmission spectrum. We
find good agreement between the mass retrieved for the hot Jupiter HD189733b
from transmission spectroscopy with that from RV measurements. Our method will
be able to retrieve the masses of Earth-sized and super-Earth planets using
data from future space telescopes that were initially designed for atmospheric
characterization.Comment: 66 pages, 25 figures, published in the December 20, 2013 edition of
Science Magazine. Includes supplementary material
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