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

Intense CIII] 1907,1909 emission from a strong Lyman continuum emitting galaxy

We have obtained the first complete ultraviolet (UV) spectrum of a strong Lyman continuum(LyC) emitter at low redshift -- the compact, low-metallicity, star-forming galaxy J1154+2443 -- with a Lyman continuum escape fraction of 46% discovered recently. The Space Telescope Imaging Spectrograph spectrum shows strong Lya and CIII] 1909 emission, as well as OIII] 1666. Our observations show that strong LyC emitters can have UV emission lines with a high equivalent width (e.g. EW(CIII])$=11.7 \pm 2.9 \AA$ rest-frame), although their equivalent widths should be reduced due to the loss of ionizing photons. The intrinsic ionizing photon production efficiency of J1154+2443 is high, $\log(\xi_{\rm ion}^0)=25.56$ erg$^{-1}$ Hz, comparable to that of other recently discovered $z \sim 0.3-0.4$ LyC emitters. Combining our measurements and earlier determinations from the literature, we find a trend of increasing $\xi_{\rm ion}^0$ with increasing CIII] 1909 equivalent width, which can be understood by a combination of decreasing stellar population age and metallicity. Simple ionization and density-bounded photoionization models can explain the main observational features including the UV spectrum of J1154+2443.Comment: 5 pages, 4 figures. Accepted for publication in A&A Letter

Recomendações para prevenção e controle de bicheiras em bezerros no Pantanal.

Com quase 50 milhões de cabeças, os estados de Mato Grosso do Sul e Mato Grosso possuem os maiores rebanhos bovinos do país. Embora a maior parte destes animais esteja distribuída no planalto, cerca de 3,5milhões de cabeças são mantidas na planície pantaneira. A bovinocultura tradicional no Pantanal se caracteriza por uma pecuária de corte extensiva, calcada em pastagens nativas e com ênfase na fase de cria e, secundariamente, de recria. Este artigo apresenta uma breve revisão sobre o problema das bicheiras (miíases) e recomendações técnicas enfocando a prevenção e tratamento de miíases umbilicais em bezerros recém-nascidos.bitstream/item/79511/1/COT35.pd

What doubts, concerns and fears about COVID-19 emerged during the first wave of the pandemic?

Objectives: The control of the COVID-19 pandemic depends strongly on effective communication, which must be grounded on the population’s perceptions and knowledge. We aimed to analyse the doubts, concerns and fears expressed by the Portuguese population about COVID-19. Methods: We performed a content analysis of 293 questions submitted to online, radio, newspaper and TV channel forums during the first month of the pandemic in Portugal. Results: Most questions contained doubts (n = 230), especially on how to prevent person-to-person transmission (n = 40) and how to proceed in case of symptoms (n = 37). Concerns and fears were also very commonly expressed (n = 144), mostly about which persons could be considered vulnerable (n = 53) and how to prevent transmission during daily life or normal activities (n = 37). Conclusion: As the pandemic evolved and suppression measures were put in place, doubts moved to concerns of vulnerability, quarantine and social isolation, and to doubts about transmission, transmission prevention, and on how to proceed in case of symptoms. Practice implications: These results may inform future communication strategies for a more adequate response in the next phases of the COVID-19 pandemic, as well as in future pandemics.This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors

Perceptions of secondary school teachers towards school expulsion of pregnant adolescents at Igunga District, Tanzania—a qualitative study

Background:In Tanzania, adolescent pregnancy results in a denial of the girl’s fundamental right to education. School expulsion of pregnant adolescents is a common practice exercised by teachers in this country for decades. This study aimed to explore the perceptions and feelings of secondary school teachers towards this practice. Methods: The study used a qualitative approach comprising focus groups and individual semistructured interviews with a purposive sample of sixteen teachers and nine headmasters (n=25) from nine secondary schools of the rural Igunga district, in Tabora region, Tanzania. Data was collected in March to June 2017 and submitted to thematic analysis. Results: Though most participants were not satisfied with the practice, their role on the expulsion of pregnant students was perceived as mandatory by law and regulations. Main argument in favor was its deterrent effect, yet the review of schools’ registries did not sustain that perception. Stigma and fear of contamination added a relevant contribution to its implementation. Conflicting feelings among teachers were also disclosed. Conclusion: This study was of most value to understand current perceptions and feelings of those who exercise the practice of banning pregnant adolescents from school in Tanzania, while having identified some of the cultural and social believes acting as influential factors in its pervasiveness. International and national human rights organizations should increase their efforts and campaigns in order to strength social awareness of the benefit of females’ education to society as a whole and of adopting policies and practices in support of their equal right to education.info:eu-repo/semantics/publishedVersio

Group Theory analysis of phonons in two-dimensional Transition Metal Dichalcogenides

Transition metal dichalcogenides (TMDCs) have emerged as a new two dimensional materials field since the monolayer and few-layer limits show different properties when compared to each other and to their respective bulk materials. For example, in some cases when the bulk material is exfoliated down to a monolayer, an indirect-to-direct band gap in the visible range is observed. The number of layers $N$ ($N$ even or odd) drives changes in space group symmetry that are reflected in the optical properties. The understanding of the space group symmetry as a function of the number of layers is therefore important for the correct interpretation of the experimental data. Here we present a thorough group theory study of the symmetry aspects relevant to optical and spectroscopic analysis, for the most common polytypes of TMDCs, i.e. $2Ha$, $2Hc$ and $1T$, as a function of the number of layers. Real space symmetries, the group of the wave vectors, the relevance of inversion symmetry, irreducible representations of the vibrational modes, optical selection rules and Raman tensors are discussed.Comment: 32 pages, 4 figure

An integrated approach for analysing and assessing the performance of virtual learning groups

Collaborative distance learning involves a variety of elements and factors that have to be considered and measured in order to analyse and assess group and individual performance more effectively and objectively. This paper presents an approach that integrates qualitative, social network analysis (SNA) and quantitative techniques for evaluating online collaborative learning interactions. Integration of various different data sources, tools and techniques provides a more complete and robust framework for group modelling and guarantees a more efficient evaluation of group effectiveness and individual competence. Our research relies on the analysis of a real, long-term, complex collaborative experience, which is initially evaluated in terms of principled criteria and a basic qualitative process. At the end of the experience, the coded student interactions are further analysed through the SNA technique to assess participatory aspects, identify the most effective groups and the most prominent actors. Finally, the approach is contrasted and completed through a statistical technique which sheds more light on the results obtained that far. The proposal draws a well-founded line toward the development of a principled framework for the monitoring and analysis of group interaction and group scaffolding which can be considered a major issue towards the actual application of the CSCL proposals to real classrooms.Peer ReviewedPostprint (author's final draft

Mutucas (Diptera: Tabanidae) do Pantanal: abundância relativa e sazonalidade na sub-região da Nhecolândia.

De junho/92 a maio/94, capturas de mutucas foram realizadas mensalmente em eqüino e utilizando armadilhas do tipo ?canopy?, na fazenda Nhumirim, subregião da Nhecolândia, Pantanal sul-mato-grossense. Capturas no eqüino foram realizadas do crepúsculo matutino ao vespertino, com o auxílio de redes entomológicas, em ambientes de campo e cerradão (1 dia/ambiente/mês), durante o primeiro ano do estudo. Capturas com armadilhas foram realizadas nos mesmos ambientes (10 dias/ambiente/mês), por dois anos. Foram capturadas 6.274 mutucas ao longo do estudo, pertencentes a 25 espécies, 13 gêneros e 3 subfamílias. A espécies mais abundantes foram Tabanus importunus (44,04%), Tabanus occidentalis (15,95%), Tabanus claripennis (9,98%) e Lepiselaga crassipes (7,60%). Apesar do menor esforço de captura, as coletas no eqüino foram mais eficientes que as realizadas com armadilhas, totalizando 3.442 (54,9%) e 2.832 (45,1%) mutucas, respectivamente. Picos populacionais foram observados próximos ao início do período chuvoso, geralmente entre setembro e novembro (primavera). Entretanto, as mutucas foram relativamente abundantes também durante parte do verão. Os resultados obtidos nestes estudos indicam que mutucas são mais abundantes durante a época chuvosa, particularmente na primavera, considerada a época de maior risco de transmissão mecânica de patógenos por estes vetores.bitstream/item/37402/1/BP48.pd