Rodrigues H.,Federal University of Rio de Janeiro |
Duarte S.B.,Brazilian Center for Research in Physics (CBPF) |
De Oliveira J.C.T.,Federal University of Roraima
Astrophysical Journal | Year: 2011
High-mass compact stars have been reported recently in the literature, providing strong constraints on the properties of the ultra dense matter beyond the saturation nuclear density. In view of these results, the calculations of quark star or hybrid star equilibrium structure must be compatible with the provided observational data. But since the equations of state used in describing quark matter are in general too soft in comparison with the equation of states used to describe the hadronic or nuclear matter, the calculated quark star models presented in the literature are in general not suitable to explain the stability of highly-compact massive objects. In this work, we present the calculations of a spherically symmetric quark star structure by using an equation of state that takes into account the superconducting color-flavor locked phase of the strange quark matter. In addition, some fundamental aspects of QCD (asymptotic freedom and confinement) are considered by means of a phenomenological description of the deconfined quark phase, the density-dependent quark mass model. The quark matter behavior introduced by this model stiffens the corresponding equation of state. We thus investigate the influence of this model on the mass-radius diagram of quark stars. We obtain massive quark stars due to the stiffness of the equation of state, when a reasonable parameterization of the color superconducting gap is used. Models of quark stars enveloped by a nucleonic crust composed of a nuclear lattice embedded in an electron gas, with nuclei close to neutron drip line, are also discussed. © 2011. The American Astronomical Society. All rights reserved.
Naka L.N.,Louisiana State University |
Naka L.N.,Federal University of Roraima |
Bechtoldt C.L.,National Institute of Amazonian Research |
Magalli Pinto Henriques L.,National Institute of Amazonian Research |
Brumfield R.T.,Louisiana State University
American Naturalist | Year: 2012
Suture zones represent natural forums in which to examine the role of geography and ecology in the speciation process. Here, we conduct a comparative analysis designed to investigate the location of avian phylogeographic breaks and contact zones in the Guiana Shield, northern Amazonia.We use distributional and genetic data from 78 pairs of avian taxa to address whether phylogeographic breaks and contact zones are associated with contemporary landscape features. Using spatially explicit statistical models, we found that phylogeographic breaks and contact zones are not randomly distributed throughout the landscape. In general, geographic breaks cluster along physical barriers (rivers, nonforested habitats, and small mountain ranges), whereas contact zones aggregate where these barriers either break down or are easier to overcome, such as around rivers' headwaters. Our results indicate that although major Amazonian rivers are often key determinants of taxon boundaries, the "riverine barrier effect" is a synergistic consequence of the wide lower reaches of some rivers, coupled with nonriverine landscape features at the headwaters. Our data suggest that ancestral refugia are not necessary to explain current distribution patterns and that pairs of codistributed taxa do not seem to be the result of simultaneous diversification processes. © 2012 by The University of Chicago.
Campos M.,University of Sao Paulo |
Campos M.,Federal University of Roraima |
Lima J.A.S.,University of Sao Paulo
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012
We discuss the gravitational collapse of a spherically symmetric massive core of a star in which the fluid component is interacting with a growing vacuum energy density. The influence of the variable vacuum in the collapsing core is quantified by a phenomenological β parameter as predicted by dimensional arguments and the renormalization group approach. For all reasonable values of this free parameter, we find that the vacuum energy density increases the collapsing time, but it cannot prevent the formation of a singular point. However, the nature of the singularity depends on the value of β. In the radiation case, a trapped surface is formed for β≤1/2, whereas for β1/2, a naked singularity is developed. In general, the critical value is β=1-2/3(1+ω), where ω is the parameter describing the equation of state of the fluid component. © 2012 American Physical Society.
De Lima M.M.,Coronel Mota Hospital |
Granja F.,Federal University of Roraima
BMC Urology | Year: 2015
Background: Genital warts caused by human papillomavirus (HPV) infection are the most common sexually transmitted disease leading to anogential lesions. Although the laser therapy has been shown to be effective in a number of conditions, the use of laser diode vaporization in urological applications and the understanding on its effectiveness as a treatment for various urological conditions is limited. Therefore, the aim of this study was to evaluate the efficacy of diode laser vaporization as a treatment for genital lesions. Methods: Patients presenting with genital lesions at the urology outpatient clinic at Coronel Mota Hospital, between March 2008 and October 2014, were enrolled into the study. Data collected included age, gender, duration of the lesion, site of the lesion and numbers of the lesions, length of follow-up, recurrence of lesions after treatment and whether there were any complications. Results: A total of 92 patients were enrolled in the study; 92.4% (n = 85) male; mean age (± SD) 27.92 ± 8.272 years. The patients presented with a total of 296 lesions, with a median of 3 lesions each, including penis (n = 78), urethra (n = 4) lesions, and scrotum (n = 2) lesions. Lesions ranged in size from 0.1 to 0.5 cm2, most commonly 0.3 cm2 (n = 38; 41.3%), 0.4 cm2 (n = 21; 22.8%) or 0.5 cm2 (n = 20; 21.7%). Patients most commonly reported that they had their lesions for a duration of 12 (n = 29; 31.5%) or 6 months (n = 23; 25.0%). Eighteen patients (19.6%) had a recurrence after their 1st/conventional treatment. There were no incidences of post-operative infection or complications from the laser diode vaporization. Conclusions: Laser diode vaporization can be considered as an alternative method for treating genital lesions in urology, with satisfactory results in terms of pain, aesthetic and minimal recurrence. © 2015 de Lima et al.; licensee BioMed Central.
Pinto V.M.,Federal University of Roraima |
Hartmann L.A.,Federal University of Rio Grande do Sul |
Santos J.O.S.,University of Western Australia |
McNaughton N.J.,Curtin University Australia |
Wildner W.,Companhia de Pesquisa de Recursos Minerais
Chemical Geology | Year: 2011
Ion microprobe U-Pb isotopic data on zircons from the Paraná magmatic province are presented from one tholeiitic (high-Ti Pitanga type) and three felsic volcanic rocks from the low-Ti Palmas and high-Ti Chapecó types. Igneous zircons from the four volcanic rocks yield volcanism ages within error: i.e. 134.4 ± 1.1. Ma (basalt), 134.6 ± 1.4. Ma (rhyodacite), 134.8 ± 1.4 (quartz latite) and 135.6 ± 1.8. Ma (quartz latite). The age of Paraná magmatism based on previous Ar-Ar geochronology has two divergent ranges: 1) 1 to 2. million years with magmatic peak at 131-133. Ma, and 2) over ~. 10. m.y. between 137 and 127. Ma. Our results show that the bimodal volcanics of the province, at least to the south of the Piquiri lineament, have very high effusion rates over a brief period with a main pulse at ~. 135. Ma, about 2% older than proposal 1, more akin to a short period of magmatism. These results are most significant for the understanding of time relations in this large intraplate magmatic province. © 2010 Elsevier B.V.
Campos M.,Federal University of Roraima
Journal of Physics: Conference Series | Year: 2014
To explain the accelerated expansion of the universe, models with interacting dark components (dark energy and dark matter) have been considered recently in the literature. Generally, the dark energy component is physically interpreted as the vacuum energy of the all fields that fill the universe. As the other side of the same coin, the influence of the vacuum energy on the gravitational collapse is of great interest. We study such collapse adopting different parameterizations for the evolution of the vacuum energy. We discuss the homogeneous collapsing star fluid, that interacts with a vacuum energy component, using the stiff matter case as example. We conclude this work with a discussion of the Cahill-McVittie mass for the collapsed object. © Published under licence by IOP Publishing Ltd.
Miguel Kanai J.,University of Miami |
Oliveira R.S.,Federal University of Roraima
Environment and Planning A | Year: 2014
This paper examines the neoliberal reshaping of infrastructure provision in Brazil's extreme north since the mid-1990s, when roadway investments resulted in unprecedented regional connectivity. The BR-174 upgrade, the era's most important project, marked a transition from resource-based developmentalism to free-market transnationalism. Primarily concerned with urban competitiveness, the federal government funded the trunk roadway's paving to facilitate manufacturing exports from Manaus. While an effort was made to minimize deforestation, planners sidelined development implications in adjacent Roraima. The state's urban system has thus experienced reperipheralization and intensified primacy. Market-led growth now compounds the inheritance of hierarchical centralism and ongoing governmental neglect. Our study shows a vast territory dependent on primate cities for basic goods and services. Travelling with Roraimans from bypassed towns, we detected long-distance passenger transportation and surface logistics with selective routes. Heterogeneous Roraiman (im)mobilities comprise middle-class tourism and heightened consumerism as well as informal mobility tactics and transnational circulations of precarious labor. The paper exhorts neoliberal urbanism research to look beyond both EuroAmerica's metropoles and their Global South counterparts. Urbanization dynamics in Brazil's extreme north demonstrate that market-disciplined investments to globalize cities produce far-reaching spatial effects. These are felt even by functionally-articulatedyet- marginalized peripheries in ostensibly remote locations.
De Campos M.,Federal University of Roraima
International Journal of Geometric Methods in Modern Physics | Year: 2016
In this work, we study a particle creation mechanism at the expense of the energy stored in an extra dimension with the respective process of compactification, and hence the emergence of 4D space. The spacetime resulting can be the Friedmann-Robertson-Walker (FRW) type, but also can be the cosmological term plus cold dark matter (CDM) type, depending on the model's parameters. Concurrent with the compactification process we have also the homogenization process, since initially the spacetime is anisotropic. © 2016 World Scientific Publishing Company.
Flores A.S.,Fundacao Estadual do Meio Ambiente |
Rodrigues R.S.,Federal University of Roraima
Acta Botanica Brasilica | Year: 2010
(Leguminosae diversity in a savanna area of Roraima, Brazil). Leguminosae is the most diverse family in the savannas of Roraima, which are the largest savanna areas in the Brazilian Amazon. This paper presents a floristic survey and an analysis of the geographic distribution patterns of Leguminosae taxa in a savanna area at Boa Vista, Roraima (02°52′07″N; 60°43′03″W). The survey identified 80 taxa belonging to 38 genera. Six taxa are new records for the flora of Roraima. The best-represented genera were Aeschynomene and Chamaecrista, both with seven species each. Leguminosae- Papilionoideae was the most diverse subfamily based on the number of genera (24) and infrageneric taxa (53). The phytogeographical analysis revealed predominance of taxa with a Neotropical distribution. The savanna site analyzed represents a legume diverse area, because it concentrates 87% of legume diversity referred for the savannas of Roraima.
Rodrigues R.S.,Federal University of Roraima |
Flores A.S.,Museu Integrado de Roraima
Phytotaxa | Year: 2012
Entada simplicata, formerly recognized as a variety of E. polystachya, is reinterpreted as a distinct legume species, based on consistent differences regarding their leaves (number of pairs and width of leaflets), and fruits (mesocarp presence, stipe and funiculus length). Illustrations and a distribution map are provided for E. simplicata, which is endemic to Roraima State, northern Amazonia, Brazil. © 2012 Magnolia Press.