48,943 research outputs found
Foliations invariant by rational maps
We give a classification of pairs (F, f) where F is a holomorphic foliation
on a projective surface and f is a non-invertible dominant rational map
preserving F. We prove that both the map and the foliation are integrable in a
suitable sense.Comment: 17 pages. To appear in Math. Zeitshrift
Probing the Effects of Lorentz-Symmetry Violating Chern-Simons and Ricci-Cotton Terms in Higher Derivative Gravity
The combined effects of the Lorentz-symmetry violating Chern-Simons and
Ricci-Cotton actions are investigated for the Einstein-Hilbert gravity in the
second order formalism modified by higher derivative terms, and their
consequences on the spectrum of excitations are analyzed. We follow the lines
of previous works and build up an orthonormal basis of operators that splits
the fundamental fields according to their individual degrees of freedom. With
this new basis, the attainment of the propagators is remarkably simplified and
the identification of the physical and unphysical modes gets a new insight. Our
conclusion is that the only tachyon- and ghost-free model is the
Einstein-Hilbert action added up by the Chern-Simons term with a time-like
vector of the type . Spectral consistency imposes taht
the Ricci-Cotton term must be switched off. We then infer that gravity with
Lorentz-symmetry violation imposes a drastically different constraint on the
background if compared to usual gauge theories whenever conditions for
suppression of tachyons and ghosts are required.Comment: 15 pages. It coincides with the version published in Phys. Rev.
Resonant tunneling through protected quantum dots at phosphorene edges
We theoretically investigate phosphorene zigzag nanorribons as a platform for
constriction engineering. In the presence of a constriction at the upper edge,
quantum confinement of edge protected states reveals resonant tunnelling
Breit-Wigner transmission peaks, if the upper edge is uncoupled to the lower
edge. Coupling between edges in thin constrictions gives rise to Fano-like and
anti-resonances in the transmission spectrum of the system.Comment: 8 pages,7 figure
Interações entre as populações de actinomicetos e outros organismos na rizosfera.
Interações das populações de actinomicetos com as demais populações bacterianas e com as populações fungicas na rizosfera. Interações com as bactérias em geral. Interações com micorrizas. Interações com fitopatógenos. Interações das populações de actinomicetos com vegetais superiores. Actinomicetos fitopatógenos. Actinorrizas.bitstream/CNPAB-2010/27377/1/doc118.pd
Conformal and gauge invariant spin-2 field equations
Using an approach based on the Casimir operators of the de Sitter group, the
conformal invariant equations for a fundamental spin-2 field are obtained, and
their consistency discussed. It is shown that, only when the spin-2 field is
interpreted as a 1-form assuming values in the Lie algebra of the translation
group, rather than a symmetric second-rank tensor, the field equation is both
conformal and gauge invariant.Comment: 12 pages, no figures; accepted for publication in Gravitation &
Cosmolog
BRS Vitória: nova cultivar de bananeira do subgrupo prata para o agronegócio no Estado do Amazonas.
Características fitotécnicas da cultivar BRS Vitória. Reação da cultivar Vitória às principais doenças e pragas.bitstream/item/64259/1/ComTec-34-2005.pd
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