A new model for gravitational potential perturbations in disks of spiral galaxies. An application to our Galaxy

We propose a new, more realistic, description of the perturbed gravitational potential of spiral galaxies, with spiral arms having Gaussian-shaped groove profiles. We investigate the stable stellar orbits in galactic disks, using the new perturbed potential. The influence of the bulge mass on the stellar orbits in the inner regions of a disk is also investigated. The new description offers the advantage of easy control of the parameters of the Gaussian profile of its potential. We find a range of values for the perturbation amplitude from 400 to 800 km^2 s^{-2} kpc^{-1} which implies a maximum ratio of the tangential force to the axisymmetric force between 3% and 6%, approximately. Good self-consistency of arm shapes is obtained between the Inner Lindblad resonance (ILR) and the 4:1 resonance. Near the 4:1 resonance the response density starts to deviate from the imposed logarithmic spiral form. This creates bifurcations that appear as short arms. Therefore the deviation from a perfect logarithmic spiral in galaxies can be understood as a natural effect of the 4:1 resonance. Beyond the 4:1 resonance we find closed orbits which have similarities with the arms observed in our Galaxy. In regions near the center, in the presence of a massive bulge, elongated stellar orbits appear naturally, without imposing any bar-shaped potential, but only extending the spiral perturbation a little inward of the ILR. This suggests that a bar is formed with a half-size around 3 kpc by a mechanism similar to that of the spiral arms. The potential energy perturbation that we adopted represents an important step in the direction of self-consistency, compared to previous sine function descriptions of the potential. Our model produces a realistic description of the spiral structure, able to explain several details that were not yet understood.Comment: 12 pag., 11 fig. Accepted for publication in A&A, 2012 December 1

Dengue disease, basic reproduction number and control

Dengue is one of the major international public health concerns. Although progress is underway, developing a vaccine against the disease is challenging. Thus, the main approach to fight the disease is vector control. A model for the transmission of Dengue disease is presented. It consists of eight mutually exclusive compartments representing the human and vector dynamics. It also includes a control parameter (insecticide) in order to fight the mosquito. The model presents three possible equilibria: two disease-free equilibria (DFE) and another endemic equilibrium. It has been proved that a DFE is locally asymptotically stable, whenever a certain epidemiological threshold, known as the basic reproduction number, is less than one. We show that if we apply a minimum level of insecticide, it is possible to maintain the basic reproduction number below unity. A case study, using data of the outbreak that occurred in 2009 in Cape Verde, is presented.Comment: This is a preprint of a paper whose final and definitive form has appeared in International Journal of Computer Mathematics (2011), DOI: 10.1080/00207160.2011.55454

Viabilidade de pupas de Thelosia camina schaus coletadas em plantios de erva-mate.

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Discovery of optical pulsations in V2116 Ophiuchi/GX 1+4

We report the detection of pulsations with $\sim 124$ s period in V2116 Oph, the optical counterpart of the low-mass X-ray binary GX 1+4. The pulsations are sinusoidal with modulation amplitude of up to 4% in blue light and were observed in ten different observing sessions during 1996 April-August using a CCD photometer at the 1.6-m and 0.6-m telescopes of Laborat\'orio Nacional de Astrof\'{\i}sica, in Brazil. The pulsations were also observed with the $UBVRI$ fast photometer. With only one exception the observed optical periods are consistent with those observed by the BATSE instrument on board the Compton Gamma Ray Observatory at the same epoch. There is a definite correlation between the observability of pulsations and the optical brightness of the system: V2116~Oph had $R$ magnitude in the range $15.3-15.5$ when the pulsed signal was detected, and $R = 16.0-17.7$ when no pulsations were present. The discovery makes GX 1+4 only the third of $\sim 35$ accretion-powered X-ray pulsars to be firmly detected as a pulsating source in the optical. The presence of flickering and pulsations in V2116 Oph adds strong evidence for an accretion disk scenario in this system. The absolute magnitude of the pulsed component on 1996 May 27 is estimated to be $M_V \sim -1.5$. The implied dimensions for the emitting region are 1.1 R_{\sun}, 3.2 R_{\sun}, and 7.0 R_{\sun}, for black-body spectral distributions with $T = 10^5$ K, $2 \times 10^4$ K, and $1 \times 10^4$ K, respectively.Comment: 9 pages, 3 figures in PostScript, latex, accepted for publication on the Astrophysical Journal Letter

Insetos associados às sementes e frutos de espécies da arborização de Curitiba, PR.

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Total hair mercury in children from a coastal population in Cananéia, São Paulo State, Brazil

Os níveis de mercúrio (Hg) total em cabelos estão diretamente relacionados à alimentação, particularmente ao consumo de peixes por populações costeiras com grande representação caiçara. No presente estudo foram avaliados os níveis de mercúrio total em cabelos de crianças com idade entre 4 e 12 anos, pertencente a três escolas públicas da cidade de Cananéia, São Paulo, Brasil. Os resultados obtidos (mediana e intervalo) para mercúrio total foram de: 0,04mg.kg-1 (0,01-0,77mg.kg-1), 0,39mg.kg-1 (< 0,01-3,33mg.kg-1) e 0,39mg.kg-1 (< 0,01-2,81mg.kg-1) considerando as escolas ES1, ES2 e ES3, respectivamente. Em geral, os valores encontrados estiveram bem abaixo do valor preconizado pela Organização Mundial da Saúde para uma população adulta não exposta ao mercúrio (2,0mg.kg-1). Os baixos valores observados e a inexistência de valores de referência para mercúrio total em cabelos de crianças brasileiras possibilitam a consideração desses valores como possível referência nacional em cabelos de populações costeiras, uma vez que foram obtidos em região de baixo impacto ambiental.Mercury (Hg) levels in hair are directly related to eating habits, especially fish consumption by coastal populations with a large contingent of traditional fishing families. This study assessed total Hg levels in children's hair. The study group was selected from three public elementary schools in Cananéia, São Paulo State, Brazil (ages 4 to 12 years). The results (median and range) for total Hg levels in children's hair were: 0.04mg.kg-1 (0.01-0.77mg.kg-1), 0.39mg.kg-1 (< 0.01-3.33mg.kg-1), and 0.39mg.kg-1 (< 0.01-2.81mg.kg-1) for schools ES1, ES2, and ES3, respectively. The values were well below the level set by World Health Organization for an adult population unexposed to Hg (2.0mg.kg-1). However, since there are no existing reference values for total Hg in children's hair, these results can be used as a contribution to establishing reference values for total hair Hg in Brazilian children living in coastal areas.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq