منابع مشابه
Sunflowers in Lattices
A Sunflower is a subset S of a lattice, with the property that the meet of any two elements in S coincides with the meet of all of S. The Sunflower Lemma of Erdös and Rado [2] asserts that a set of size at least 1 + k!(t − 1)k of elements of rank k in a Boolean Lattice contains a sunflower of size t. We develop counterparts of the Sunflower Lemma for distributive lattices, graphic matroids, and...
متن کاملWilliam Pickles lecture 1989. Seeing sunflowers.
THE clearest memory I have from my first year as a medical student is of a botany practical. We had the task, one sunny Thursday afternoon, of cutting a very thin slice of a sunflower stem, putting it under the microscope and drawing what we saw. In the textbook there was an illustration of what we should expect to see: as I remember, it showed regular, neatly-'packed cells with several smaller...
متن کاملRapid hybrid speciation in wild sunflowers.
Hybrid or "recombinational" speciation refers to the origin of a new homoploid species via hybridization between chromosomally or genetically divergent parental species. Theory predicts that this mode of speciation is punctuated, but there has been little empirical evidence to support this claim. Here, we test the hypothesis of rapid hybrid speciation by estimating the sizes of parental species...
متن کاملMajor ecological transitions in wild sunflowers facilitated by hybridization.
Hybridization is frequent in many organismal groups, but its role in adaptation is poorly understood. In sunflowers, species found in the most extreme habitats are ancient hybrids, and new gene combinations generated by hybridization are speculated to have contributed to ecological divergence. This possibility was tested through phenotypic and genomic comparisons of ancient and synthetic hybrid...
متن کاملSeed size variation and predation of seeds produced by wild and crop-wild sunflowers.
The movement of pollen between crop and wild sunflowers (both Helianthus annuus) has led to concerns about the possible introduction of crop transgenes into wild populations. The persistence of crop traits in wild populations will depend in part on the relative fitness of crop-wild hybrid vs. wild plants. Using seeds from two large experimental field plots, we found that seeds produced by crop-...
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ژورنال
عنوان ژورنال: American Journal of Psychiatry Residents' Journal
سال: 2019
ISSN: 2474-4662
DOI: 10.1176/appi.ajp-rj.2019.150211