We study a geometric hitting set problem involving unirectional rays and curves in the plane. We show that this problem is hard to approximate within a logarithmic factor even when the curves are convex polygonal x-monotone chains. Additionally, it is hard to approximate within a factor of 76 even when the curves are line segments with bounded slopes. Lastly, we demonstrate that the problem is ...

Despite the dynamic nature of annual cropping systems, few studies have investigated how structure predator communities and their interactions with prey corresponds crop seasonality. Adding winter habitat, such as cover crops, improves soil health likely contributes seasonal habitat availability for arthropod communities. Stable may lead to functionally diverse predatory associated ecosystem se...

Seedling emergence, survival and early growth of the Mediterranean conifer P. pinaster were studied under closed canopy and open canopy (gaps) cover conditions in a Mediterranean forest of central Spain during two consecutive years (March 2008 to January 2010). Our main objective was to understand how overstorey structure, shrubs and soil properties influence recruitment in this species. Natura...

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Weyl’s theorem for an operator says that the complement in the spectrum of the Weyl spectrum coincides with the isolated points of the spectrum which are eigenvalues of finite multiplicity. H. Weyl ([22]) discovered that this property holds for hermitian operators and it has been extended from hermitian operators to hyponormal operators and to Toeplitz operators by L. Coburn ([5]), and to sever...

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