1,738,781 research outputs found
Il mondo fino a ieri
No full textLa prerogativa di Homo sapiens è la capacità di sopravvivere negli ambienti più diversi, di trasformarli ai propri fini, di riadattarsi molto rapidamente a nuove nicchie ecologiche, ben prima che i geni abbiano il tempo di adeguarsi al cambiamento. L’apprendimento individuale e sociale, la diversità fra popolazioni e la cultura fanno tutti parte di questa strategia evolutiva indubbiamente di successo.La prerogativa di Homo sapiens è la capacità di sopravvivere negli ambienti più diversi, di trasformarli ai propri fini, di riadattarsi molto rapidamente a nuove nicchie ecologiche, ben prima che i geni abbiano il tempo di adeguarsi al cambiamento. L’apprendimento individuale e sociale, la diversità fra popolazioni e la cultura fanno tutti parte di questa strategia evolutiva indubbiamente di successo
Calabi-Yau cones from contact reduction
No full textWe consider a generalization of Einstein-Sasaki manifolds, which we characterize in terms both of spinors and differential forms, that in the real analytic case corresponds to contact manifolds whose symplectic cone is Calabi-Yau. We construct solvable examples in seven dimensions. Then, we consider circle actions that preserve the structure, and determine conditions for the contact reduction to carry an induced structure of the same type. We apply this construction to obtain a new hypo-contact structure on S^2\times T^3
Some remarks on Hermitian manifolds satisfying Kähler-like conditions
Full text linkWe study Hermitian metrics whose Bismut connection ∇ B satisfies the first Bianchi identity in relation to the SKT condition and the parallelism of the torsion of the Bimut connection. We obtain a characterization of complex surfaces admitting Hermitian metrics whose Bismut connection satisfy the first Bianchi identity and the condition RB(x, y, z, w) = RB(Jx, Jy, z, w) , for every tangent vectors x, y, z, w, in terms of Vaisman metrics. These conditions, also called Bismut Kähler-like, have been recently studied in Angella et al. (Commun Anal Geom, to appear, 2018), Yau et al. (2019) and Zhao and Zheng (2019). Using the characterization of SKT almost abelian Lie groups in Arroyo and Lafuente (Proc Lond Math Soc (3) 119:266–289, 2019), we construct new examples of Hermitian manifolds satisfying the Bismut Kähler-like condition. Moreover, we prove some results in relation to the pluriclosed flow on complex surfaces and on almost abelian Lie groups. In particular, we show that, if the initial metric has constant scalar curvature, then the pluriclosed flow preserves the Vaisman condition on complex surfaces
Pluriclosed and Strominger Kähler–like metrics compatible with abelian complex structures
No full textWe show that the existence of a left-invariant pluriclosed Hermitian metric on a unimodular Lie group with a left-invariant abelian complex structure forces the group to be 2-step nilpotent. Moreover, we prove that the pluriclosed flow starting from a left-invariant Hermitian metric on a 2-step nilpotent Lie group preserves the Strominger Kahler-like condition
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