32,229 research outputs found
On Semantic Word Cloud Representation
We study the problem of computing semantic-preserving word clouds in which
semantically related words are close to each other. While several heuristic
approaches have been described in the literature, we formalize the underlying
geometric algorithm problem: Word Rectangle Adjacency Contact (WRAC). In this
model each word is associated with rectangle with fixed dimensions, and the
goal is to represent semantically related words by ensuring that the two
corresponding rectangles touch. We design and analyze efficient polynomial-time
algorithms for some variants of the WRAC problem, show that several general
variants are NP-hard, and describe a number of approximation algorithms.
Finally, we experimentally demonstrate that our theoretically-sound algorithms
outperform the early heuristics
Regular Cost Functions, Part I: Logic and Algebra over Words
The theory of regular cost functions is a quantitative extension to the
classical notion of regularity. A cost function associates to each input a
non-negative integer value (or infinity), as opposed to languages which only
associate to each input the two values "inside" and "outside". This theory is a
continuation of the works on distance automata and similar models. These models
of automata have been successfully used for solving the star-height problem,
the finite power property, the finite substitution problem, the relative
inclusion star-height problem and the boundedness problem for monadic-second
order logic over words. Our notion of regularity can be -- as in the classical
theory of regular languages -- equivalently defined in terms of automata,
expressions, algebraic recognisability, and by a variant of the monadic
second-order logic. These equivalences are strict extensions of the
corresponding classical results. The present paper introduces the cost monadic
logic, the quantitative extension to the notion of monadic second-order logic
we use, and show that some problems of existence of bounds are decidable for
this logic. This is achieved by introducing the corresponding algebraic
formalism: stabilisation monoids.Comment: 47 page
From Finite Automata to Regular Expressions and Back--A Summary on Descriptional Complexity
The equivalence of finite automata and regular expressions dates back to the
seminal paper of Kleene on events in nerve nets and finite automata from 1956.
In the present paper we tour a fragment of the literature and summarize results
on upper and lower bounds on the conversion of finite automata to regular
expressions and vice versa. We also briefly recall the known bounds for the
removal of spontaneous transitions (epsilon-transitions) on non-epsilon-free
nondeterministic devices. Moreover, we report on recent results on the average
case descriptional complexity bounds for the conversion of regular expressions
to finite automata and brand new developments on the state elimination
algorithm that converts finite automata to regular expressions.Comment: In Proceedings AFL 2014, arXiv:1405.527
The Physics of the FIR-Radio Correlation: II. Synchrotron Emission as a Star-Formation Tracer in High-Redshift Galaxies
We construct one-zone steady-state models of cosmic ray (CR) injection,
cooling, and escape over the entire dynamic range of the FIR-radio correlation
(FRC), from normal galaxies to starbursts, over the redshift interval 0 <= z <=
10. Normal galaxies with low star-formation rates become radio-faint at high z,
because Inverse Compton (IC) losses off the CMB cool CR electrons and positrons
rapidly, suppressing their nonthermal radio emission. However, we find that
this effect occurs at higher redshifts than previously expected, because
escape, bremsstrahlung, ionization, and starlight IC losses act to counter this
effect and preserve the radio luminosity of galaxies. The radio dimming of
star-forming galaxies at high z is not just a simple competition between
magnetic field energy density and the CMB energy density; the CMB must also
compete with every other loss process. We predict relations for the critical
redshift when radio emission is significantly suppressed compared to the z ~ 0
FRC as a function of star-formation rate per unit area. Additionally, we
provide a quantitative explanation for the relative radio brightness of some
high-z submillimeter galaxies. We show that at fixed star formation rate
surface density, galaxies with larger CR scale heights are radio bright with
respect to the FRC, because of weaker bremsstrahlung and ionization losses
compared to compact starbursts. We predict that these "puffy starbursts" should
have steeper radio spectra than compact galaxies with the same star-formation
rate surface density. We find that radio bright submillimeter galaxies alone
cannot explain the excess radio emission reported by ARCADE2, but they may
significantly enhance the diffuse radio background with respect to a naive
application of the z ~ 0 FRC.Comment: Published in Ap
STAR: A Concise Deep Learning Framework for Citywide Human Mobility Prediction
Human mobility forecasting in a city is of utmost importance to
transportation and public safety, but with the process of urbanization and the
generation of big data, intensive computing and determination of mobility
pattern have become challenging. This study focuses on how to improve the
accuracy and efficiency of predicting citywide human mobility via a simpler
solution. A spatio-temporal mobility event prediction framework based on a
single fully-convolutional residual network (STAR) is proposed. STAR is a
highly simple, general and effective method for learning a single tensor
representing the mobility event. Residual learning is utilized for training the
deep network to derive the detailed result for scenarios of citywide
prediction. Extensive benchmark evaluation results on real-world data
demonstrate that STAR outperforms state-of-the-art approaches in single- and
multi-step prediction while utilizing fewer parameters and achieving higher
efficiency.Comment: Accepted by MDM 201
Neutrino oscillations and gamma-ray bursts
If the ordinary neutrinos oscillate into a sterile flavor in a manner
consistent with the Super-Kamiokande data on the zenith-angle dependence of
atmospheric mu-neutrino flux, an energy sufficient to power a typical cosmic
gamma-ray burst (GRB) (about 10^{52} erg) can be carried by sterile neutrinos
away from the source and deposited in a region relatively free of baryons.
Hence, ultra-relativistic bulk motion (required by the theory of and
observations of GRBs and their afterglows) can easily be achieved in the
vicinity of plausible sources of GRBs. Oscillations between sterile and
ordinary neutrinos would thus provide a solution to the ``baryon-loading
problem'' in the theory of GRBs
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