1,998 research outputs found
Decidability of the Clark's Completion Semantics for Monadic Programs and Queries
There are many different semantics for general logic programs (i.e. programs
that use negation in the bodies of clauses). Most of these semantics are Turing
complete (in a sense that can be made precise), implying that they are
undecidable. To obtain decidability one needs to put additional restrictions on
programs and queries. In logic programming it is natural to put restrictions on
the underlying first-order language. In this note we show the decidability of
the Clark's completion semantics for monadic general programs and queries.
To appear in Theory and Practice of Logic Programming (TPLP
Searching for primordial magnetism with multi-frequency CMB experiments
Bounds on the amplitude of a scale-invariant stochastic primordial magnetic
field (PMF) can be significantly improved by measurements of the Faraday
Rotation (FR) of CMB polarization. The mode-coupling correlations induced by FR
make it possible to extract it from cross-correlations of the B-mode
polarization with the E-mode and the temperature anisotropy. In this paper, we
construct an estimator of the rotation measure that appropriately combines
measurements of the FR from multiple frequency channels. We study the
dependence of the signal-to-noise in the PMF detection on the resolution and
the noise of the detectors, as well as the removal of the weak lensing
contribution and the galactic FR. We show that a recently proposed space-based
experiment PRISM can detect magnetic fields of 0.1 nano-Gauss strength at a 2
sigma level. Higher detection levels can be achieved by reducing the detector
noise and improving the resolution or increasing the number of channels in the
30-70 GHz frequency range.Comment: 6 pages, 1 figure, 1 table; references added, Figure and the caption
improved; matches the version accepted to MNRA
Categoricity in Quasiminimal Pregeometry Classes
Quasiminimal pregeometry classes were introduces by Zilber [2005a] to isolate
the model theoretical core of several interesting examples. He proves that a
quasiminimal pregeometry class satisfying an additional axiom, called
excellence, is categorical in all uncountable cardinalities. Recently Bays et
al. [2014] showed that excellence follows from the rest of axioms. In this
paper we present a direct proof of the categoricity result without using
excellence
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