Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

Breeding systems in a montane tropical cloud forest in Venezuela

Abstract: The breeding systems, reproductive efficacies and population densities of 75 species of trees, shrubs, perennial herbs and vines in a montane tropical cloud forest in Venezuela are investigated. 56.96% and 44.32% of the trees, versus the other life forms considered, respectively possess obligate outbreeding mechanisms. Two shrubs are non-pseudogamous apomicts. The percentage of dioecy among tree species (31%) is among the highest recorded in tropical forests. Reproductive efficacy is similar under all breeding systems in the forest interior. Obligately outbred taxa are slower recolonizers of a disturbed border as compared with non-obligate outbreeders. Explanations are advanced for the high incidence of dioecy combined with a low level of self-incompatibility among hermaphroditic species. It is concluded that the breeding system spectrum reflects an unpredictable pollination pattern, rather than insufficient pollinator servicing.

Precise predictions for Z -boson + 4 jet production at hadron colliders

Abstract: We present the cross section for production of a $Z$ boson in association with four jets at the Large Hadron Collider, at next-to-leading order in the QCD coupling. When the $Z$ decays to neutrinos, this process is a key irreducible background to many searches for new physics. Its computation has been made feasible through the development of the on-shell approach to perturbative quantum field theory. We present the total cross section for $pp$ collisions at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$, after folding in the decay of the $Z$ boson, or virtual photon, to a charged-lepton pair. We also provide distributions of the transverse momenta of the four jets, and we compare cross sections and distributions to the corresponding ones for the production of a $W$ boson with accompanying jets.