798 research outputs found
Revealing the large nuclear dust structures in NGC 1068 with MIDI/VLTI
To understand the relation between the small "obscuring torus" and dusty
structures at larger scales (5-10 pc) in NGC 1068, we use ESO's Mid-Infrared
Interferometer (MIDI) with the 1.8 m Auxiliary Telescopes to achieve the
necessary spatial resolution (~ 20-100 millarcsec). We use the chromatic phases
in the data to improve the spatial fidelity of the analysis. We present
interferometric data for NGC 1068 obtained in 2007 and 2012. We find no
evidence of source variability. Many (u,v) points show non-zero chromatic
phases indicating significant asymmetries. Gaussian model fitting of the
correlated fluxes and chromatic phases provides a 3-component best fit with
estimates of sizes, temperatures and positions of the components. A large,
warm, off-center component is required at a distance approximately 90 mas to
the north-west at a PA ~ -18 deg. The dust at 5-10 pc in the polar region
contributes 4 times more to the mid-infrared flux at 12 um than the dust
located at the center. This dust may represent the inner wall of a dusty cone.
If similar regions are heated by the direct radiation from the nucleus, then
they will contribute substantially to the classification of many Seyfert
galaxies as Type 2. Such a region is also consistent in other Seyfert galaxies
(the Circinus galaxy, NGC 3783 and NGC 424).Comment: 21 pages, 10 figures; Accepted for publication on A&
Topological mass generation to antisymmetric tensor matter field
We propose a mechanism to give mass to tensor matter field which preserve the
U(1) symmetry. We introduce a complex vector field that couples with the tensor
in a topological term. We also analyze the influence of the kinetic terms of
the complex vector in our mechanism.Comment: 5 pages, to appear in Europhysics Letter
Controle da cochonilha Ortézia Orthezia praelonga (Hemiptera: Ortheziidae), em aceroleira, medidas culturais e calda sulfocálcica, no Vale do São Francisco.
Objetivando-se o controle da praga, realizou-se experimento em área comercial, no Projeto de Irrigação Senador Nilo Coelho, em Petrolina-PE.1 CD-ROM
NGC 1068: No change in the mid-IR torus structure despite X-ray variability
Context. Recent NuSTAR observations revealed a somewhat unexpected increase
in the X-ray flux of the nucleus of NGC 1068. We expect the infrared emission
of the dusty torus to react on the intrinsic changes of the accretion disk.
Aims. We aim to investigate the origin of the X-ray variation by
investigating the response of the mid-infrared environment.
Methods. We obtained single-aperture and interferometric mid-infrared
measurements and directly compared the measurements observed before and
immediately after the X-ray variations. The average correlated and
single-aperture fluxes as well as the differential phases were directly
compared to detect a possible change in the structure of the nuclear emission
on scales of 2 pc.
Results. The flux densities and differential phases of the observations
before and during the X-ray variation show no significant change over a period
of ten years. Possible minor variations in the infrared emission are
8 %.
Conclusions. Our results suggest that the mid-infrared environment of NGC
1068 has remained unchanged for a decade. The recent transient change in the
X-rays did not cause a significant variation in the infrared emission. This
independent study supports previous conclusions that stated that the X-ray
variation detected by NuSTAR observations is due to X-ray emission piercing
through a patchy section of the dusty region.Comment: 6 pages, 5 figures, 3 tables. Accepted for publication on A&
Manejo e controle da Cochonilha Ortézia (Orthezia praelonga), em plantios irrigados de acerola, no Submédio São Francisco.
O cultivo da acerola é uma importante alternativa econômica para a Região Nordeste do Brasil. No Submédio São Francisco, há cerca de mil hectares cultivados e a expansão do cultivo deve-se, basicamente, ao apreciado sabor da fruta e ao alto teor de ácido ascórbico (vitamina C), que, em algumas variedades, alcança até 5.000 miligramas por 100 gramas de polpa.bitstream/CPATSA/37176/1/CTE83.pd
Novel Graph-based Adaptive Triangular Mesh Refinement for Finite-volume Discretizations
A novel graph-based adaptive mesh refinement technique for triangular finite-volume discretizations in order to solve second-order partial differential equations is described. Adaptive refined meshes are built in order to solve time-dependent problems aiming low computational costs. In the approach proposed, flexibility to link and traverse nodes among neighbors in different levels of refinement is admitted; and volumes are refined using an approach that allows straightforward and strictly local update of the data structure. In addition, linear equation system solvers based on the minimization of functionals can be easily used; specifically, the Conjugate Gradient Method. Numerical and analytical tests were carried out in order to study the required execution time and the data storage cost. These tests confirmed the advantages of the approach proposed in elliptic and parabolic problems
Utilização de herbicidas no controle de plantas indesejáveis em pastagem natural.
A aplicação de herbicidas sob a pastagem natural, tanto para o estabelecimento de pastagens cultivadas através do plantio direto, como no controle de plantas indesejáveis tem crescido nos últimos anos. A pesquisa, até o presente momento não dispõe de informações seguras para recomendar tal procedimento. O efeito de herbicidas sobre uma vegetação natural tão diversificada e rica em espécies forrageiras tem sido uma das maiores interrogantes neste processo.bitstream/item/55664/1/ct24-1999.pd
A Systematic Review of Algorithms with Linear-time Behaviour to Generate Delaunay and Voronoi Tessellations
Triangulations and tetrahedrizations are important geometrical discretization procedures applied to several areas, such as the reconstruction of surfaces and data visualization. Delaunay and Voronoi tessellations are discretization structures of domains with desirable geometrical properties. In this work, a systematic review of algorithms with linear-time behaviour to generate 2D/3D Delaunay and/or Voronoi tessellations is presented
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