Optical properties of polydisperse submicrometer aggregates of sulfur-containing zinc oxide consisting of spherical nanocrystallites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Morfologia e cristalinidade de hidroxicarbonato de zinco obtido via precipitação homogênea: influência dos ânions cloreto e nitrato

The effects of chloride and nitrate anions and their respective concentrations, as well as urea presence, on solid phase morphologies were investigated. Zinc hydroxide carbonate was prepared by aging diluted zinc salt solution in presence of urea at 90ºC. Samples were identified by X-ray powder diffractograms showing the characteristic patterns of hydrozincite. The crystallinity was correlated with the concentrations of reagents. Spherulitic-type aggregates and single acicular particles were obtained from diluted chloride and nitrate solutions while porous aggregates of uniform size were formed from solutions with high chloride and urea concentrations.

Identificação de regiões pluviometricamente homogêneas no Estado do Rio de Janeiro, utilizando-se valores mensais

O objetivo deste trabalho é dar uma contribuição ao estudo das condições climáticas do Estado do Rio de Janeiro, visando a uma melhor Classificação Climática por meio da identificação de regiões homogêneas em precipitação. Para isto foram utilizadas médias mensais da precipitação de 48 estações meteorológicas, em um período de 30 anos (1971-2000). A análise hierárquica de agrupamento, a orografia e a proximidade do mar, mostraram que o Estado do Rio de Janeiro pode ser dividido, quanto à precipitação, em seis regiões pluviometricamente homogêneas o que possibilitou classificar as estações meteorológicas pelo método de classificação não hierárquica k-means. A região norte do Estado, com precipitações anuais em torno de 870 mm é a mais seca, e a região da encosta sul da Serra do Mar, com 2020 mm, é a mais chuvosa. Mas, em ambas as regiões, os valores da precipitação da estação chuvosa representam em torno de 70% dos totais anuais.

Study of crystallite size and strain as a function of morphological evolution in zinc oxide powder obtained from hydroxycarbonate precursor

In this work, zinc oxide samples were obtained from hydroxycarbonate by thermal decomposition at 300°C. Zinc hydroxycarbonate samples were produced by homogeneous precipitation over different periods of time. The method used to obtain zinc oxide produces different morphologies as a function of the precursor precipitation time. Among the obtained particle shapes were porous spherical aggregates, spherulitic needle aggregates, and single acicular particles. This work investigated spherulitic needle-aggregate formation and the correlation among morphology, domain size, and microstrain. Transmission electron microscopy data revealed that the acicular particles that form the spherulitic needle aggregates consist of nanometer crystallites. Apparent crystallite size and microstrain in the directions perpendicular to (h00), (h0l), (hk0), and (00l) planes were invariable as a function of precursor precipitation time. From the results, it was possible to conclude that the precursor precipitation period directly influenced the morphology of the zinc oxide but did not influence average crystallite size and microstrain for ZnO samples. Therefore, using this route, it was possible to prepare zinc oxide with different morphologies without microstructural alterations. © 2001 International Centre for Diffraction Data.

Efeito da microestrutura na cintilação de nanopartículas de Y2O3 : EU3+

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Hidroxicarbonato de gadolínio ativado com európio ou térbio trivalentes como precursor de óxidos, oxissulfetos e silicatos luminescentes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermal behaviour of the basic carbonates of lanthanum-europium

The basic carbonates of lanthanum with 10%, 20%, 50% and 80% of europium were prepared by precipitation from homogeneous solutions via the hydrolysis of urea, without the addition of an auxiliary anion, at two different temperatures. Elemental analysis, complexometric methods, X-ray diffraction patterns, solid state IR absorption, thermogravimetry/derivative thermogravimetry (TG/DTG) and differential thermal analysis (DTA) were used to characterise the compounds and study their thermal behaviour.

Thermal behavior of Ca2+ and Cu2+ oxalates obtained by precipitation in homogeneous solution from dimethyl oxalate hydrolysis

Mixed calcium and copper oxalates, with different proportions of Ca2+ and Cu2+ ions, were precipitated by dimethyl oxalate hydrolysis in homogeneous solution. The compounds were evaluated by means of scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetry (TG), and differential thermal analysis (DTA). The results suggested quantitative precipitation without solid solution formation. From the TG and DTA curves, it was possible to evaluate the Ca2+ ion proportion in the solid phase and to confirm the precipitation of the individual species.

Reversibility properties of semigroup actions on homogeneous spaces

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A Model for Bundled Conductors considering a Non-Homogeneous Distribution of the Current through Subconductors

This paper describes an alternative procedure to obtain an equivalent conductor from a bundled conductor, taking into account the distribution of the current in subcondutors of the bundle. Firstly, it is introduced a brief background about the concept of Geometric Mean Radius (GMR) and how this methodology is applied to define an equivalent conductor and its electric parameters. Emphasizing that the classical procedure, using GMR, is limited to premise which the current is equally distributed through subconductors. Afterwards, it is described the development of proposed method and applications for an equivalent conductor obtained from a conventional transmission line bundled conductor and from an equivalent conductor based on a bundle with compressed SF(6) insulation system, where the current is unequally distributed through subconductors.

Effect of Iron II on Hydroxyapatite Dissolution and Precipitation in vitro

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Curves in homogeneous spaces and their contact with 1-dimensional orbits

Let alpha be a C(infinity) curve in a homogeneous space G/H. For each point x on the curve, we consider the subspace S(k)(alpha) of the Lie algebra G of G consisting of the vectors generating a one parameter subgroup whose orbit through x has contact of order k with alpha. In this paper, we give various important properties of the sequence of subspaces G superset of S(1)(alpha) superset of S(2)(alpha) superset of S(3)(alpha) superset of ... In particular, we give a stabilization property for certain well-behaved curves. We also describe its relationship to the isotropy subgroup with respect to the contact element of order k associated with alpha.

Lower bounds on blow up solutions of the three-dimensional Navier-Stokes equations in homogeneous Sobolev spaces

Suppose that u(t) is a solution of the three-dimensional Navier-Stokes equations, either on the whole space or with periodic boundary conditions, that has a singularity at time T. In this paper we show that the norm of u(T - t) in the homogeneous Sobolev space (H)over dot(s) must be bounded below by c(s)t(-(2s-1)/4) for 1/2 < s < 5/2 (s not equal 3/2), where c(s) is an absolute constant depending only on s; and by c(s)parallel to u(0)parallel to((5-2s)/5)(L2)t(-2s/5) for s > 5/2. (The result for 1/2 < s < 3/2 follows from well-known lower bounds on blowup in Lp spaces.) We show in particular that the local existence time in (H)over dot(s)(R-3) depends only on the (H)over dot(s)-norm for 1/2 < s < 5/2, s not equal 3/2. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4762841]

Ag precipitation and dissolution reactions in the Cu-3 wt.% Al-4 wt.% Ag alloy

The Ag precipitation and dissolution reactions in the Cu-3 wt.% Al-4 wt.% Ag alloy were studied using isothermal and non-isothermal analyses. The activation energy values, obtained for the Ag precipitation reaction indicated that, when the Kissinger, Ozawa and Johnson-MehI-Avrami methods are compared, the Kissinger method is the most appropriate. Although the Johnson-Mehl-Avrami equation often does not fit precipitation data, the energy values obtained for Ag precipitation kinetics are in agreement with what was experimentally observed. For the dissolution reaction of Ag precipitates the activation energy values obtained from the Kissinger and Ozawa methods are higher than that found in the literature for the Ag dissolution in Cu. This discrepancy seems to be related to the fact that the activation energy is influenced by the heating rate. (c) 2006 Elsevier B.V. All rights reserved.