8,774 research outputs found
Reachability analysis of first-order definable pushdown systems
We study pushdown systems where control states, stack alphabet, and
transition relation, instead of being finite, are first-order definable in a
fixed countably-infinite structure. We show that the reachability analysis can
be addressed with the well-known saturation technique for the wide class of
oligomorphic structures. Moreover, for the more restrictive homogeneous
structures, we are able to give concrete complexity upper bounds. We show ample
applicability of our technique by presenting several concrete examples of
homogeneous structures, subsuming, with optimal complexity, known results from
the literature. We show that infinitely many such examples of homogeneous
structures can be obtained with the classical wreath product construction.Comment: to appear in CSL'1
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
Slow Conductance Relaxation in Insulating Granular Al: Evidence for Screening Effects
It is shown that the conductance relaxations observed in electrical field
effect measurements on granular Al films are the sum of two contributions. One
is sensitive to gate voltage changes and gives the already reported anomalous
electrical field effect. The other one is independent of the gate voltage
history and starts when the films are cooled down to low temperature. Their
relative amplitude is strongly thickness dependent which demonstrates the
existence of a finite screening length in our insulating films and allows its
quantitative estimate (about 10nm at 4K). This metallic-like screening should
be taken into account in the electron glass models of disordered insulators
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