Showing papers by "Federal University of Roraima published in 2001"
TL;DR: The presence of this variety in a virgin environment without either anthropic action or introduced vegetation is discussed with regard to the common knowledge of Cr.
Abstract: Cryptococcus neoformans var. gattii was isolated for the first time from decaying wood in a hollow of a native jungle tree Guettarda acreana, in a wild area of an Amazon rainforest island, in Brazil. The presence of this variety in a virgin environment without either anthropic action or introduced vegetation is discussed with regard to the common knowledge of Cr. neoformans ecology.
99 citations
TL;DR: A series of titanates and niobates, K2Ti4O9, Na2Ti3O7, KNb3O8, K4Nb6O17, and their respective acid forms were prepared and characterized by X-ray diffraction, thermogravimetry and scanning electron microscopy as discussed by the authors.
39 citations
TL;DR: In this paper, the Brans-Dicke solution of a stationary circular cosmic string loop is investigated in the weak field approximation of the field equations, and the solution is quasi-conformally related to the corresponding solution in Einstein's General Relativity (GR) and goes over to the equivalent solution in GR when the BRD parameter w becomes infinitely large.
Abstract: The gravitational field of a stationary circular cosmic string loop, externally supported against collapse, is investigated in the context of Brans-Dicke theory in the weak field approximation of the field equations. The solution is quasi-conformally related to the corresponding solution in Einstein's General Relativity(GR) and goes over to the corresponding solution in GR when the Brans-Dicke parameter w becomes infinitely large.
30 citations
TL;DR: In this article, it was shown that the anatase phase can be obtained independently on any previous or further treatment of the synthesized powder, such as hydrothermal or heat treatment, providing a new, simple, quick, and inexpensive route to synthesize anatase powders.
16 citations
TL;DR: In this article, a silicon-titanium inorganic-organic hybrid is used as substrate to study the adsorption and spectroscopy of a europium luminescent complex: Eu(fod)3.
16 citations
TL;DR: In this article, the title compounds were synthesized by using an alternative solid state route, and characterized by elemental analysis, infrared spectroscopy and thermogravimetry, and the IR data are in agreement with a coordination through oxygen for ethyleneurea (EU) and propyleneUREa (PU) and through nitrogen for ethylenethiourea (ETU).
13 citations
TL;DR: In this paper, six adducts of general formula MCl2·4L (M = Cu and Co; L = ethyleneurea, eu, ethylenethiourea, etu; and propyleneureas, pu) were prepared and characterized by elemental analysis, i.r. spectroscopy and by thermogravimetry (t.g.).
Abstract: Six adducts of general formula MCl2·4L (M = Cu and Co; L = ethyleneurea, eu; ethylenethiourea, etu; and propyleneurea, pu) were prepared and characterized by elemental analysis, i.r. spectroscopy and by thermogravimetry (t.g.). Using the non-isothermal Coats–Redfern method, the kinetic parameters for the non-isothermal degradation of the adducts were calculated using thermogravimetric data. The i.r. results show that, for eu and pu adducts, coordination occurs through oxygen, whereas for etu nitrogen is the donor atom. All the adducts exhibited a single mass loss step in the t.g. curve, related to the release of ligand molecules. For eu, etu and pu adducts, the associated activation energies for the degradation process are: 36.4; 68.07 and 103.07 kJ mol−1; 67.15; 80.86 and 121.06 kJ mol−1 for copper and cobalt adducts, respectively.
12 citations
TL;DR: In this article, an inorganic-organic intercalation hybrid of formula MoO3·0.54apdc was synthesized, which was characterized by CHN elemental analysis, infrared spectroscopy, X-ray diffraction and SEM microscopy.
12 citations
TL;DR: In this paper, the synthesis, characterization and thermal behavior of 18 adducts of general formula CdX 2 · n L (where X=Cl, Br and I, n =1 and 2, and L=ethyleneurea (eu), ethylenethiourea (etu), and propyleneurea(pu)) were reported.
11 citations
TL;DR: In this paper, the same authors used infrared spectroscopy and reaction-solution calorimetry to characterize CdCl 2 · n L [ n = 1 and 2; L=ethyleneurea (eu), ethylenethiourea (etu), and propyleneurea(pu), and showed that eu and pu coordinate through carbonylic oxygen atoms, whereas etu uses the nitrogen as coordinating site.
11 citations
TL;DR: In this paper, the authors used infrared spectroscopy, thermogravimetry and calorimetry to characterize the properties of adducts of the general formula CuCl 2 ·4L (L: ethyleneurea (eu), ethylenethiourea (etu) and propyleneureas (pu), and obtained the following values: −4250±092; −4876±066 and −4364±051 ǫ −1 for eu, etu, and pu, respectively.
TL;DR: In this paper, a series of six oxides, Si-Al, Ti, Zr, Al-Zr and Al-Ti, were obtained by using tetraethylortosilicate, titanium and zirconium tetrabutoxide, and aluminum sec-butoxide, as well as neutral 1,10 and 1,12 alkyldiamines or dodecyltrimethylammonium bromide as precursors.
TL;DR: In this paper, an Si-Ti-Zr oxide nanocomposite was synthesized through sol-gel process and characterized by thermogravimetry, scanning electron microscopy and X-ray diffraction patterns.
TL;DR: In this paper, the role of the scalar field as a weakener agent of the strength of gravitational forces due to pressure terms is discussed. And the nature of the gravitational forces exerted by topological defects on surrounding matter in the frame of Brans-Dicke theory of gravity (BD) is investigated.
Abstract: The nature of gravitational forces exerted by topological defects on surrounding matter in the frame of Brans–Dicke theory of gravity (BD) is investigated. Comparison is made with the corresponding cases in General Relativity (GR). The role of the scalar field as a weakener agent of the strength of gravitational forces due to pressure terms is discussed.
TL;DR: A series of titanates and niobates, K2Ti4O9, Na2Ti3O7, KNb3O8, K4Nb6O17, and their respective acid forms were prepared and characterized by X-ray diffraction, thermogravimetry and scanning electron microscopy as mentioned in this paper.
Abstract: A series of titanates and niobates, K2Ti4O9, Na2Ti3O7, KNb3O8, K4Nb6O17, and their respective acid forms were prepared and characterized by X-ray diffraction, thermogravimetry and scanning electron microscopy. The ion exchange capacity of the alkaline and acid forms towards Cu(II) was studied and it is concluded that, as general behavior, the alkaline titanates and niobates have a higher ion exchange capacity towards copper cations than their respective acid forms. Furthermore, the sodium matrix Na2Ti3O7 exhibits the highest ion exchange capacity of 3.00 mmol g−1. Based on the thermogravimetric results, the Cu(II) cation is coordinated to two water molecules when adsorbed on the titanate and niobate matrices.