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Federal University of Roraima

Education
About: Federal University of Roraima is a based out in . It is known for research contribution in the topics: Population & Thermogravimetry. The organization has 981 authors who have published 1218 publications receiving 7849 citations. The organization is also known as: Federal University of Roraima.


Papers
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Journal ArticleDOI
TL;DR: In this article, it was shown that the used equations of state describing quark matter are in general too soft, in comparison with the equation of states used to describe the hadronic or nuclear matter, to explain the stability of high compact massive objects.
Abstract: High massive compact stars have been reported recently in the literature, providing strong constraints on the properties of the ultradense 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 used equations of state 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 high compact massive objects.

26 citations

Journal ArticleDOI
TL;DR: Leaf litter quality (chemical and structural components) is a main factor affecting leaf breakdown in Amazonian streams and is related to different chemical characteristics among the five studied species.
Abstract: Our objective was to assess the relative importance of leaf litter quality, and the microbial and aquatic invertebrate communities involved in leaf litter breakdown in Amazonian streams. We test the hypothesis that leaf litter quality is the driving force of leaf breakdown rates, rather than the microbial or invertebrate community, independent of stream characteristics. We incubated 3 g of Eucalyptus camaldulensis (EC), Baccharis platypoda, Symphonia globulifera, Mabea speciosa (MS), and Eperua duckeana (ED) leaves in five streams for 75, 56, 46, 26, 14, or 7 days. In all of the streams, leaf litter breakdown was higher for EC and lower in ED. This result may be related to different chemical characteristics among the five studied species. We observed higher frequency of shredders in MS and stream 4, and scrapers in streams 1 and 2. The concentration of ergosterol was higher in MS and lower in EC when adenosine triphosphate differed significantly among streams. Our data indicated that leaf litter quality (chemical and structural components) is a main factor affecting leaf breakdown in Amazonian streams.

26 citations

Journal ArticleDOI
TL;DR: Chemical analysis, hematoxylin staining and energy dispersive X-ray spectrometry showed greater Al accumulation in the root tips of the UFVM-200 genotype, indicative of possible precipitation and/or immobilization of Al in theroot tip apoplast of this genotypes, which contributes to symplastic detoxification.
Abstract: The objective of this study was to evaluate the effects of toxic levels of aluminum (Al) on the growth and external morphology of root tips in two maize genotypes with differential Al tolerance. The maize genotypes UFVM-100 (Al-sensitive) and UFVM-200 (Al-tolerant) were treated with 0 and 50 mM Al in a 0.5 mM CaCl2 solution at pH 4.5; root elongation, Al content and the external morphology of the root tips were evaluated. Chemical analysis, hematoxylin staining and energy dispersive X-ray spectrometry (EDS) showed greater Al accumulation in the root tips of the UFVM-200 genotype. The inhibition of root elongation in the UFVM-100 genotype, however, was much stronger than in the UFVM-200 genotype. Both maize genotypes exhibited visible and intense alterations in external micromorphology of the root tip, especially the Al-sensitive UFVM-100 genotype. Scanning electron micrographs showed intense cell disorganization and transverse ruptures of the protodermic and outer cortex layers of the cells in both genotypes. The ruptures were deeper and wider and reached the inner cortex layers in the UFVM-100 genotype. The EDS analysis showed that, in addition to Al accumulation, there was a proportional increase in the P concentration in the root tips of the UFVM-200 genotype. This is indicative of possible precipitation and/or immobilization of Al in the root tip apoplast of this genotype, which contributes to symplastic detoxification.

26 citations

Journal ArticleDOI
TL;DR: In this article, a bisadduct was prepared in a water medium and the monoadducts were isolated with water or water-ethanol mixtures as solvents, and the kinetic parameters, activation energy (Ea), frequency factor (A) and order of reaction (n), were calculated.

26 citations

Journal ArticleDOI
TL;DR: In this article, the authors 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.
Abstract: 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.

26 citations


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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20232
20222
2021125
2020183
201992
201899