10,631 research outputs found
Graded change of ring
We investigate scalar restriction, scalar extension, and scalar coextension
functors for graded modules, including their interplay with coarsening
functors, graded tensor products, and graded Hom functors. This leads to
several characterisations of epimorphisms of graded rings.Comment: To appear in Quaestiones Mathematica
Quasicoherent sheaves on toric schemes
Let X be the toric scheme over a ring R associated with a fan Sigma. It is
shown that there are a group B, a B-graded R-algebra S and a graded ideal I of
S such that there is an essentially surjective, exact functor ~ from the
category of B-graded S-modules to the category of quasicoherent O_X-modules
that vanishes on I-torsion modules and that induces for every B-graded S-module
F a surjection Xi_F from the set of I-saturated graded sub-S-modules of F onto
the set of quasicoherent sub-O_X-modules of ~F. If Sigma is simplicial, the
above data can be chosen such that ~ vanishes precisely on I-torsion modules
and that Xi_F is bijective for every F. In case R is noetherian, a toric
version of the Serre-Grothendieck correspondence is proven, relating sheaf
cohomology on X with B-graded local cohomology with support in I.Comment: To appear in Expositiones Mathematicae; corrected typo
Geographic Centroid Routing for Vehicular Networks
A number of geolocation-based Delay Tolerant Networking (DTN) routing
protocols have been shown to perform well in selected simulation and mobility
scenarios. However, the suitability of these mechanisms for vehicular networks
utilizing widely-available inexpensive Global Positioning System (GPS) hardware
has not been evaluated. We propose a novel geolocation-based routing primitive
(Centroid Routing) that is resilient to the measurement errors commonly present
in low-cost GPS devices. Using this notion of Centroids, we construct two novel
routing protocols and evaluate their performance with respect to positional
errors as well as traditional DTN routing metrics. We show that they outperform
existing approaches by a significant margin.Comment: 6 page
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