22,577 research outputs found
Structure of fish assemblages on coastal rocky shores of the Azores
Bol. Mus. Mun. Funchal, Sup. N.Âş 6: 127-138, 2001The structure of fish assemblages was investigated from the surface down to 25 m depth on Azorean rocky shores. A total of 57 fish species was recorded by visual censuses, most species (66%) occurring in the whole depth range studied. Fish abundance was dominated by 11 species, mainly sparids, labrids, carangids and pomacentrids, which constituted over 88% of the total number of individuals recorded. The trophic structure of the fish assemblages studied in the Azores was characterized by the dominance of benthic mesocarnivores and high proportions of herbivores and pelagic macrocarnivores.A estrutura das comunidades ictiolĂłgicas dos fundos rochosos dos Açores foi estudada desde a superfĂcie atĂ© aos 25 m de profundidade. Um total de 57 espĂ©cies de peixes foi identificado com recurso a censos visuais. A maioria das espĂ©cies (66%) ocorreu em toda a gama de profundidades estudada. A fauna ictiolĂłgica era dominada, em termos de abundância, por 11 espĂ©cies, principalmente pertencentes Ă s famĂlias Sparidae, Labridae, Carangidae e Pomacentridae, os quais constituĂram mais de 88% do nĂşmero total de indivĂduos observados. A estrutura trĂłfica das comunidades ictiolĂłgicas estudadas nos Açores apresentouse dominada por meso-carnĂvoros bentĂłnicos e proporções elevadas de herbĂvoros e macro-carnĂvoros pelágico
DMRG study of the Bond Alternating \textbf{S}=1/2 Heisenberg ladder with Ferro-Antiferromagnetic couplings
We obtain the phase diagram in the parameter space and an
accurate estimate of the critical line separating the different phases. We show
several measuments of the magnetization, dimerization, nearest neighbours
correlation, and density of energy in the different zones of the phase diagram,
as well as a measurement of the string order parameter proposed as the non
vanishing phase order parameter characterizing Haldane phases. All these
results will be compared in the limit with the behaviour of the
Bond Alternated Heisenberg Chain (BAHC). The analysis of our
data supports the existence of a dimer phase separated by a critical line from
a Haldane one, which has exactly the same nature as the Haldane phase in the
BAHC.Comment: Version 4. 8 pages, 15 figures (12 figures in document
Radiative corrections in bumblebee electrodynamics
We investigate some quantum features of the bumblebee electrodynamics in flat
spacetimes. The bumblebee field is a vector field that leads to a spontaneous
Lorentz symmetry breaking. For a smooth quadratic potential, the massless
excitation (Nambu-Goldstone boson) can be identified as the photon, transversal
to the vacuum expectation value of the bumblebee field. Besides, there is a
massive excitation associated with the longitudinal mode and whose presence
leads to instability in the spectrum of the theory. By using the
principal-value prescription, we show that no one-loop radiative corrections to
the mass term is generated. Moreover, the bumblebee self-energy is not
transverse, showing that the propagation of the longitudinal mode can not be
excluded from the effective theory.Comment: Revised version: contains some more elaborated interpretation of the
results. Conclusions improve
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