42,392 research outputs found
Rediscovery and redescription of Ceradryops punctatus Hinton, 1937 (Coleoptera: Dryopidae)
Ceradryops punctatus Hinton from Sri Lanka is redescribed and illustrated. Notes are made on the habitat of the species
Why Water Markets Are Not Quick Fixes for Droughts in the Western United States
Water in the western United States can be bought and sold, but the transactions will always be complicated. Transfers of water will always be expensive and time consuming because of the hydrologic and institutional interconnections inherent to water. Our data show that most of the water rights in the West are messy. Therefore, markets cannot be quick fixes, and using markets for future water allocation, even if it is economically efficient, will take time and resources to set up. Untangling serial uses and negotiating multiple ownership claims are hurdles, not barriers, and they can be overcome in time but will require both time and money. Buying existing water rights may be less costly than building infrastructure to transport available water from long distances or desalinating seawater, but the transactions will come at a price. Municipalities may purchase water from farmers and thus bear the transaction costs directly, or the private sector may purchase agricultural water (e.g., Two Rivers Water and Farming, Colorado (Landry 2012)), bear the associated risk and transaction costs, and sell it on to municipalities. In either case, the end users will inevitably pay higher prices for water. Markets can and will be part of western U.S. water allocation, but they do not provide quick solutions. Droughts can focus public attention on the value of water and potentially increase the willingness-to-pay prices that reflect the transaction costs of tangled western water markets
Three new species of Hexanchorus Sharp, 1882 (Coleoptera: Elmidae: Larainae) from South America
Three new species of Hexanchorus Sharp, H. dimorphus and H. shannoni from Argentina, and H. mcdiarmidi from Venezuela, are described and illustrated
Luchoelmis : a new genus of Elmidae (Coleoptera) from Chile and Argentina
Luchoelmis New Genus is described with four new species: aequalis, magallanensis, and penai from Chile and cekalovici from Argentina and Chile. Luchoelmis penai is designated as the type species of the genus. A key to the four species is presented
Second order splitting of a class of fourth order PDEs with point constraints
We formulate a well-posedness and approximation theory for a class of generalised saddle point problems with a specific form of constraints. In this way we develop an approach to a class of fourth order elliptic partial differential equations with point constraints using the idea of splitting into coupled second order equations. An approach is formulated using a penalty method to impose the constraints. Our main motivation is to treat certain fourth order equations involving the biharmonic operator and point Dirichlet constraints for example arising in the modelling of biomembranes on curved and flat surfaces but the approach may be applied more generally. The theory for well-posedness and approximation is presented in an abstract setting. Several examples are described together with some numerical experiments
X-ray irradiation in low mass binary systems
We calculate self-consistent models of X-ray irradiated accretion discs in
close binary systems. We show that a point X-ray source powered by accretion
and located in the disc plane cannot modify the disc structure, mainly because
of the self-screening by the disc of its outer regions. Since observations show
that the emission of the outer disc regions in low mass X-ray binaries is
dominated by the reprocessed X-ray flux, accretion discs in these systems must
be either warped or irradiated by a source above the disc plane, or both. We
analyse the thermal-viscous stability of irradiated accretion discs and derive
the stability criteria of such systems. We find that, contrary to the usual
assumptions, the critical accretion rate below which a disc is unstable is
rather uncertain since the correct formula describing irradiation is not well
known.Comment: to be published in MNRAS, uses epsfig.st
Task-based Augmented Contour Trees with Fibonacci Heaps
This paper presents a new algorithm for the fast, shared memory, multi-core
computation of augmented contour trees on triangulations. In contrast to most
existing parallel algorithms our technique computes augmented trees, enabling
the full extent of contour tree based applications including data segmentation.
Our approach completely revisits the traditional, sequential contour tree
algorithm to re-formulate all the steps of the computation as a set of
independent local tasks. This includes a new computation procedure based on
Fibonacci heaps for the join and split trees, two intermediate data structures
used to compute the contour tree, whose constructions are efficiently carried
out concurrently thanks to the dynamic scheduling of task parallelism. We also
introduce a new parallel algorithm for the combination of these two trees into
the output global contour tree. Overall, this results in superior time
performance in practice, both in sequential and in parallel thanks to the
OpenMP task runtime. We report performance numbers that compare our approach to
reference sequential and multi-threaded implementations for the computation of
augmented merge and contour trees. These experiments demonstrate the run-time
efficiency of our approach and its scalability on common workstations. We
demonstrate the utility of our approach in data segmentation applications
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