4,081 research outputs found
Hamiltonian embedding of the massive noncommutative U(1) theory
We show that the massive noncommutative U(1) can be embedded in a gauge
theory by using the BFFT Hamiltonian formalism. By virtue of the peculiar
non-Abelian algebraic structure of the noncommutative massive U(1) theory,
several specific identities involving Moyal commutators had to be used in order
to make the embedding possible. This leads to an infinite number of steps in
the iterative process of obtaining first-class constraints. We also shown that
the involutive Hamiltonian can be constructed.Comment: 8 pages, Revtex (multicol
Noncommutative Particles in Curved Spaces
We present a formulation in a curved background of noncommutative mechanics,
where the object of noncommutativity is considered as an
independent quantity having a canonical conjugate momentum. We introduced a
noncommutative first-order action in D=10 curved spacetime and the covariant
equations of motions were computed. This model, invariant under diffeomorphism,
generalizes recent relativistic results.Comment: 1+15 pages. Latex. New comments and results adde
Sistema de produção usando o rejeito da dessalinização de água salobra no semi-árido brasileiro.
Objetivando reduzir os impactos causados pelo rejeito da dessalinização de água salobra, no trópico semi-árido brasileiro, três alternativas de aproveitamento de água com alta salinidade, subproduto da dessalinização foram avaliadas nos campos da Estação Experimental da Embrapa Semi-Árido, em Petrolina-PE. As alternativas foram: (a) produção de tilápia rosa (Oreochromis sp); (b) produção de feno da erva-sal (Atriplex nummularia) irrigado; e (c) engorda de caprino/ovino com feno de erva-sal. A salinidade média da água usada foi de 11,38 ds/m. A tilápia atingiu o peso de 518,72 gramas em 153 dias de cultivo; o rendimento do feno da erva-sal foi de 14.900kg de matéria seca por hectare, e o ganho de peso de ovino/caprino, quando alimentado com 1,5 kg de feno da erva-sal, foi de 138 gramas/dia. Em função dos resultados obtidos com estes estudos, é possível a viabilização do uso do rejeito da dessalinização de água de poços no cristalino do semi-árido brasileiro para a geração de renda
Exciton-polariton mediated interaction between two nitrogen-vacancy color centers in diamond using two-dimensional transition metal dichalcogenides
In this paper, starting from a quantum master equation, we discuss the interaction between two negatively charged nitrogen-vacancy color centers in diamond via exciton-polaritons propagating in a two-dimensional transition metal dichalcogenide layer in close proximity to a diamond crystal. We focus on the optical 1.945 eV transition and model the nitrogen-vacancy color centers as two-level (artificial) atoms. We find that the interaction parameters and the energy-level renormalization constants are extremely sensitive to the distance of the nitrogen-vacancy centers to the transition-metal dichalcogenide layer. Analytical expressions are obtained for the spectrum of the exciton-polaritons and for the damping constants entering the Lindblad equation. The conditions for occurrence of exciton mediated superradiance are discussed.- B.A. and N.M.R.P acknowledge support by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020. B.A. further acknowledges support from FCT through Grant No. CEECIND/02936/2017. N.M.R.P. acknowledges support from the European Commission through the project Graphene-Driven Revolutions in ICT and Beyond (Ref. No. 881603, CORE 3), COMPETE 2020, PORTUGAL 2020, FEDER and the FCT through Project No. POCI-01-0145-FEDER-028114
Two limit cases of twisted hBN bilayers and their excitonic response
In this paper, we discuss the optical response due to the excitonic effect of two types of hBN bilayers: AB and AA′. Understanding the properties of these bilayers is of great utility to the study of twisted bilayers at arbitrary angles since these two configurations correspond to the limit cases of 0∘ and 60∘ rotation. To obtain the excitonic response, we present a method to solve a four-band Bethe-Salpeter equation by casting it into a one-dimensional problem, thus greatly reducing the numerical burden of the calculation when compared with strictly two-dimensional methods. We find results in good agreement with ab initio calculations already published in the literature for the AA′ bilayer, and predict the excitonic conductivity of the AB bilayer, which remains largely unstudied. The main difference in the conductivity of these two types of bilayers is the appearance of a small, yet well-resolved resonance between two larger ones in the AB configuration. This resonance is due to a mainly interlayer exciton, and is absent in the AA′ bilayer. Also, the conductivity of the AB bilayer is due to both intralayer and interlayer excitons and is dominated by p-states, while intralayer s-states are the relevant ones for the AA′ configuration, like in a monolayer. The effect of introducing a bias in the AA′ bilayer is also discussed.B.A., R.M.R and N.M.R.P acknowledge support by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020. J.C.G.H. acknowledges the Center of Physics for a grant funded by the UIDB/04650/2020 strategic project. B.A. and N.M.R.P acknowledge support from FCT-Portugal through Project EXPL/FIS-MAC/0953/2021. B.A. further acknowledges funding from FCT-Portugal via Grant CEECIND/02936/2017. R.M.R. and N.M.R.P. also acknowledge support from the European Commis sion through the project GrapheneDriven Revolutions in ICT and Beyond (Ref. No. 881603, CORE 3)
and the project PTDC/FIS-MAC/2045/2021. N.M.R.P. further acknowledges COMPETE 2020, PORTUGAL
2020, FEDER and the FCT through projects POCI-01-0145-FEDER-028114, POCI-01-0145-FEDER-02888 and PTDC/NAN-OPT/29265/2017
The spatially resolved star formation history of CALIFA galaxies: Cosmic time scales
This paper presents the mass assembly time scales of nearby galaxies observed
by CALIFA at the 3.5m telescope in Calar Alto. We apply the fossil record
method of the stellar populations to the complete sample of the 3rd CALIFA data
release, with a total of 661 galaxies, covering stellar masses from 10
to 10 M and a wide range of Hubble types. We apply spectral
synthesis techniques to the datacubes and process the results to produce the
mass growth time scales and mass weighted ages, from which we obtain temporal
and spatially resolved information in seven bins of galaxy morphology and six
bins of stellar mass (M) and stellar mass surface density
(). We use three different tracers of the spatially resolved
star formation history (mass assembly curves, ratio of half mass to half light
radii, and mass-weighted age gradients) to test if galaxies grow inside-out,
and its dependence with galaxy stellar mass, , and morphology.
Our main results are as follows: (a) The innermost regions of galaxies assemble
their mass at an earlier time than regions located in the outer parts; this
happens at any given M, , or Hubble type, including
the lowest mass systems. (b) Galaxies present a significant diversity in their
characteristic formation epochs for lower-mass systems. This diversity shows a
strong dependence of the mass assembly time scales on and
Hubble type in the lower-mass range (10 to 10), but a very
mild dependence in higher-mass bins. (c) All galaxies show negative
log age gradients in the inner 1 HLR. The profile
flattens with increasing values of . There is no significant
dependence on M within a particular bin, except for
the lowest bin, where the gradients becomes steeper.Comment: 15 pages, 13 figures, 3 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
The spatially-resolved star formation histories of CALIFA galaxies: Implications for galaxy formation
This paper presents the spatially resolved star formation history (SFH) of
nearby galaxies with the aim of furthering our understanding of the different
processes involved in the formation and evolution of galaxies. To this end, we
apply the fossil record method of stellar population synthesis to a rich and
diverse data set of 436 galaxies observed with integral field spectroscopy in
the CALIFA survey. The sample covers a wide range of Hubble types, with stellar
masses ranging from to . Spectral
synthesis techniques are applied to the datacubes to retrieve the spatially
resolved time evolution of the star formation rate (SFR), its intensity
(), and other descriptors of the 2D-SFH in seven bins of
galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd), and five bins of stellar
mass. Our main results are: a) Galaxies form very fast independently of their
current stellar mass, with the peak of star formation at high redshift (). Subsequent star formation is driven by and morphology, with less
massive and later type spirals showing more prolonged periods of star
formation. b) At any epoch in the past the SFR is proportional to ,
with most massive galaxies having the highest absolute (but lowest specific)
SFRs. c) While nowadays is similar for all spirals, and
significantly lower in early type galaxies (ETG), in the past scales well with morphology. The central regions of today's ETGs are
where reached the highest values (Gyrpc), similar to those measured in high redshift
star forming galaxies. d) The evolution of in Sbc systems
matches that of models for Milky-Way-like galaxies, suggesting that the
formation of a thick disk may be a common phase in spirals at early epochs.Comment: 21 pages, 11 figures, 1 table, accepted for publication in Astronomy
& Astrophysics, abstract abridged for arXiv submissio
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