6,816 research outputs found
Agri-Environmental Schemes and Grassland Biodiversity: Another Side of the Coin
In this paper part of the existing Agri-Environmental Schemes (AES) of the European Union are evaluated by using data on county level instead of applying field studies. The attempt is made to disentangle the effects of AES on land management practice as well as land use on biodiversity. It is argued that subsidies as AES should promote environmental-friendly land use which, in turn, should lead to biodiversity conservation. First results show that AES promotes ecological land use rather than extensive agricultural practice. Furthermore, AES is predominantly allocated in biodiversity rich counties and not in counties with low biodiversity which should be enhanced. Furthermore, no clear evidence is so far found, that land use practice is improving the biodiversity status.AES effectiveness, biodiversity, policy evaluation
About least-squares type approach to address direct and controllability problems
- We discuss the approximation of distributed null controls for partial
differential equations. The main purpose is to determine an approximation of
controls that drives the solution from a prescribed initial state at the
initial time to the zero target at a prescribed final time. As a non trivial
example, we mainly focus on the Stokes system for which the existence of
square-integrable controls have been obtained in [Fursikov \& Imanuvilov,
Controllability of Evolution Equations, 1996]) via Carleman type estimates. We
introduce a least-squares formulation of the controllability problem, and we
show that it allows the construction of strong convergent sequences of
functions toward null controls for the Stokes system. The approach consists
first in introducing a class of functions satisfying a priori the boundary
conditions in space and time-in particular the null controllability condition
at time T-, and then finding among this class one element satisfying the
system. This second step is done by minimizing a quadratic functional, among
the admissible corrector functions of the Stokes system. We also discuss
briefly the direct problem for the steady Navier-Stokes system. The method does
not make use of any duality arguments and therefore avoid the ill-posedness of
dual methods, when parabolic type equation are considered
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