1,021 research outputs found
Using ACL2 to Verify Loop Pipelining in Behavioral Synthesis
Behavioral synthesis involves compiling an Electronic System-Level (ESL)
design into its Register-Transfer Level (RTL) implementation. Loop pipelining
is one of the most critical and complex transformations employed in behavioral
synthesis. Certifying the loop pipelining algorithm is challenging because
there is a huge semantic gap between the input sequential design and the output
pipelined implementation making it infeasible to verify their equivalence with
automated sequential equivalence checking techniques. We discuss our ongoing
effort using ACL2 to certify loop pipelining transformation. The completion of
the proof is work in progress. However, some of the insights developed so far
may already be of value to the ACL2 community. In particular, we discuss the
key invariant we formalized, which is very different from that used in most
pipeline proofs. We discuss the needs for this invariant, its formalization in
ACL2, and our envisioned proof using the invariant. We also discuss some
trade-offs, challenges, and insights developed in course of the project.Comment: In Proceedings ACL2 2014, arXiv:1406.123
Cosmology with gamma-ray bursts: II Cosmography challenges and cosmological scenarios for the accelerated Universe
Context. Explaining the accelerated expansion of the Universe is one of the
fundamental challenges in physics today. Cosmography provides information about
the evolution of the universe derived from measured distances, assuming only
that the space time ge- ometry is described by the
Friedman-Lemaitre-Robertson-Walker metric, and adopting an approach that
effectively uses only Taylor expansions of basic observables. Aims. We perform
a high-redshift analysis to constrain the cosmographic expansion up to the
fifth order. It is based on the Union2 type Ia supernovae data set, the
gamma-ray burst Hubble diagram, a data set of 28 independent measurements of
the Hubble param- eter, baryon acoustic oscillations measurements from galaxy
clustering and the Lyman-{\alpha} forest in the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS), and some Gaussian priors on h and {\Omega}M .
Methods. We performed a statistical analysis and explored the probability
distributions of the cosmographic parameters. By building up their regions of
confidence, we maximized our likelihood function using the Markov chain Monte
Carlo method. Results. Our high-redshift analysis confirms that the expansion
of the Universe currently accelerates; the estimation of the jerk parameter
indicates a possible deviation from the standard {\Lambda}CDM cosmological
model. Moreover, we investigate implications of our results for the
reconstruction of the dark energy equation of state (EOS) by comparing the
standard technique of cosmography with an alternative approach based on
generalized Pad\'e approximations of the same observables. Because these
expansions converge better, is possible to improve the constraints on the
cosmographic parameters and also on the dark matter EOS. Conclusions. The
estimation of the jerk and the DE parameters indicates at 1{\sigma} a possible
deviation from the {\Lambda}CDM cosmological model.Comment: 10 pages, 7 figures, accepted for publication in A &
Slacktivists or Activists?: Identity Work in the Virtual Disability March
Protests are important social forms of activism, but can be inaccessible to people with disabilities. Online activism, like the 2017 Disability March, has provided alternative venues for involvement in accessible protesting and social movements. In this study, we use identity theory as a lens to understand why and how disabled activists engaged in an online movement, and its impact on their self-concepts. We interviewed 18 disabled activists about their experiences with online protesting during the Disability March. Respondents' identities (as both disabled individuals and as activists) led them to organize or join the March, evolved alongside the group's actions, and were reprioritized or strained as a result of their involvement. Our findings describe the values and limitations of this activism to our respondents, highlight the tensions they perceived about their activist identities, and present opportunities to support further accessibility and identity changes by integrating technology into their activist experiences
Cosmology with gamma-ray bursts: I. The Hubble diagram through the calibrated - correlation
Gamma-ray bursts are the most energetic explosions in the Universe. They are
detectable up to very high redshifts, therefore can be used to study the
expansion rate of the Universe and to investigate the observational properties
of dark energy, provided that empirical correlations between spectral and
intensity properties are appropriately calibrated. We used the type Ia
supernova luminosity distances to calibrate the correlation between the peak
photon energy, , and the isotropic equivalent radiated energy, in GRBs. With this correlation, we tested the reliability of applying
GRBs to measure cosmological parameters and to obtain indications on the basic
properties and evolution of dark energy. Using 162 GRBs with measured redshifts
and spectra, we applied a local regression technique to calibrate the - correlation against the type Ia SN data to build a calibrated GRB
Hubble diagram. We tested the possible redshift dependence of the correlation
and its effect on the Hubble diagram. Finally, we used the GRB Hubble diagram
to investigate the dark energy EOS. For this, we focused on the so-called
Chevalier-Polarski-Linder (CPL) parametrization of the dark energy EOS and
implemented the Markov chain Monte Carlo (MCMC) method to efficiently sample
the space of cosmological parameters. Our analysis shows once more that the
- correlation has no significant redshift dependence.
Therefore the high-redshift GRBs can be used as a cosmological tool to
determine the basic cosmological parameters and to test different models of
dark energy in the redshift region (), which is unexplored by the
SNIa and baryonic acoustic oscillations data. Our updated calibrated Hubble
diagram of GRBs provides some marginal indication (at level) of an
evolving dark energy EOS.Comment: 12 pages, 11 figure
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