São Cristóvão, Brazil
São Cristóvão, Brazil

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Montes P.J.R.,Instituto Federal Of Sergipe | Teixeira V.C.,Brazilian Synchrotron Light Laboratory (LNLS) | Barbosa D.A.B.,Federal University of Maranhão | Paschoal C.W.A.,Federal University of Ceará | Rezende M.V.D.S.,Federal University of Sergipe
Journal of Alloys and Compounds | Year: 2017

SrAl2O4 is one of the most investigated phosphors for long lasting phosphorescence, mainly when activated with Eu2+ ions. Usually Eu2+ is obtained by the Eu3+ reduction during the material synthesis under a reducing atmosphere, such as H2 for example. In this paper, we investigated the effect of substituting Sr for Ba on the SrAl2O4:Eu2+ phosphor obtained by sol-gel route based on polyvinyl alcohol (PVA). Our results showed that SrAl2O4:Eu2+ phosphor obtained by this method presents higher Eu3+→Eu2+ conversion degree than samples obtained by the proteic sol-gel route, which was based on coconut water. Also, we observed that Ba-substitution does not change the temperature in which Eu3+ starts converting into Eu2+, which occurs between 700 and 800 °C. However, the Ba inclusion reduces the Eu3+→Eu2+ conversion. © 2017 Elsevier B.V.


Macieira R.M.,Federal University of Pernambuco | Lisboa E.B.,Instituto Federal Of Sergipe | Barros E.N.S.,Federal University of Pernambuco
Proceedings - 2011 Brazilian Symposium on Computing System Engineering, SBESC 2011 | Year: 2011

Optimizing time and effort in embedded systems design is essential nowadays. The increased productivity gap together with the reduced time to market make the design of some components of the system the main design bottleneck. Taking into account the natural complexity of HdS design, a software checking technique helps finding bugs. However the increasing complexity of HdS makes the development and use of checking techniques a challenge. Reducing the time spent to build the checking environment can be a solution for this kind of problem. This can be accomplished by automating the generation of the checking environment from a device specification. The use of virtual platforms also represents an advantage since it supports to start the HdS development in an initial design phase. This paper proposes an approach for checking errors during the development of a very error prone Hardware dependent Software, that is device drivers. The proposed checking mechanism can be generated from a device specification using a language called Temporal DevC. Taking a device description in TDevC, the proposed approach generates a driver checking mechanism based on state machines. Experiments show the efficiency and effectiveness of the proposed mechanism, enabling its use for the detection of unwanted flows in the device driver simulation as well. © 2011 IEEE.


Rezende M.V.D.S.,Instituto Federal Of Sergipe | Arrouvel C.,Federal University of Sergipe | Parker S.C.,University of Bath | Rey J.F.Q.,Federal University of ABC | Valerio M.E.G.,Federal University of Sergipe
Materials Chemistry and Physics | Year: 2012

BaAl 2O 4 nanoparticles samples were prepared by sol-gel proteic route. The preparation of the precursor mixture and the formation of the ceramic product were monitored using TG/DTA, X-ray diffraction (XRD), electron microscopy (SEM, TEM). The results show that sol-gel proteic route is a reliable method for the synthesis of pure BaAl 2O 4 powders and that irregular hexagonal facetted nanoparticles are observed. Atomistic modeling was used to calculate the structures and energies of 24 (hkl) surfaces and to evaluate morphologies of BaAl 2O 4 at the thermodynamic and pseudo-kinetic equilibrium. The calculations show that the two most stable surfaces are the (001) and (011) with a surface energy of 1.33 J m -2 and 1.36 J m -2 respectively and that the predicted morphologies are in accord with experiment. © 2012 Elsevier B.V. All rights reserved.


Dos S. Rezende M.V.,Instituto Federal Of Sergipe | Montes P.J.R.,Instituto Federal Of Sergipe Ifs | Soares F.M.D.S.,Federal University of Sergipe | Santos C.D.,Federal University of Sergipe | Valerio M.E.G.,Federal University of Sergipe
Journal of Synchrotron Radiation | Year: 2014

Xerogels of strontium chlorate and aluminium chlorate doped with europium (un-co-doped) and co-doped with rare earth ions (Ln = Gd, Dy, Er and Y) were prepared using the proteic sol-gel route. Synchrotron radiation was used to investigate the effect of different co-dopants on the Eu3+ → Eu2+ reduction process during the synthesis of the samples. Samples were excited at the Eu L III-edge and the XANES regions were analyzed. The results suggest that some of the Eu ions can be stabilized in the divalent state and that it is difficult to completely reduce Eu3+ to Eu 2+ during thermal treatment. The mechanisms of the Eu reduction processes are explained by a proposed model based on the incorporation of charge-compensation defects.© 2014 International Union of Crystallography.


Montes P.J.R.,Instituto Federal Of Sergipe Ifs | Valerio M.E.G.,Federal University of Sergipe | Rezende M.V.D.S.,Instituto Federal Of Sergipe
Journal of Electron Spectroscopy and Related Phenomena | Year: 2013

Pure and rare earth doped SrAl2O4 and Ca 12Al14O33 have been synthesized by a new sol-gel proteic methodology. Photoluminescence (PL) and radioluminescence (RL) spectra show different behavior when excited with either UV light or X-ray radiation. Such behavior may be connected to the X-ray absorption/reduction of Eu ions process in samples. X-ray absorption spectroscopy (XAS) was carried out simultaneously with X-ray excited optical luminescence (XEOL) and the analysis indicates that are depends on the energy of excitation and the kind of excited species. Dispersive X-ray absorption spectroscopy (DXAS) was carried out to follow the kinetic of reduction process in the samples during the irradiation. The reduction process does not produce stable Eu2+ species. An overall analysis of the results makes possible to build the mechanisms of radioluminescence of rare earths doped SrAl2O4 and Ca 12Al14O33 systems. © 2013 Elsevier B.V. All rights reserved.


Freitas A.S.,Instituto Federal Of Sergipe | De Albuquerque D.F.,Federal University of Sergipe
Solid State Communications | Year: 2016

We describe the phase diagram of binary and ternary disordered alloys using the mixed-bond Ising model, via effective field theory (EFT). For example, we describe the Fe-Al alloy as a mixed-bond system instead of as diluted alloy. In our approach, we obtain the percolation threshold for some lattices and describe the lines of ferro-paramagnetic transition of Fe-Al, Fe-Mn, Fe-Mn-Al and Fe-Ni-Mn alloys and we obtain good agreement with the experimental data. © 2015 Elsevier Ltd


Lobo J.S.,Instituto Federal Of Sergipe | Medina R.D.,Federal University of Santa Maria
UBICOMM 2013 - 7th International Conference on Mobile Ubiquitous Computing, Systems, Services and Technologies | Year: 2013

This paper presents a customization of a service desk tool inserting some context-aware computing elements based on location, temporal and expertise awareness. As main result, a context-aware service desk system, that also allows access from mobile devices and improves technical calls distribution based on professional expertise and geographical location, was concept.


Freitas A.S.,Instituto Federal Of Sergipe
Solid State Communications | Year: 2016

In this paper I present a Quantum Monte Carlo (QMC) study of the magnetic properties of an antiferromagnetic spin ladder (C5H12N)2CuBr4. This compound is the prototype of the Heisenberg model for a two leg spin ladder in the presence of an external magnetic field. The susceptibility phase diagram has a rounded peak in the vicinity of T=7.4 K, obeys Troyer's law for low temperatures, and Curie's law for high temperatures. I also study the susceptibility diagram in low temperatures and I found the spin gap Δ=9.26 K, in good concordance with the experimental value, 9.5 K. In high field, I present a diagram of magnetization as a function of temperature. In the vicinity of a critical field, Hci, the magnetization scales with T1/2 and this result was found also in the QMC simulation. In all the results, there is a very good concordance with the experimental data. I also show in this paper that the spin gap is null and the susceptibility is proportional to T for low temperatures when relatively high values of the ladders' coupling is taken in account. © 2016 Elsevier Ltd.


Passos A.L.,Federal University of Sergipe | De Albuquerque D.F.,Federal University of Sergipe | Filho J.B.S.,Instituto Federal Of Sergipe
Physica A: Statistical Mechanics and its Applications | Year: 2016

This work presents a representation of the Kagome and pyrochlore lattices using Monte Carlo simulation as well as some results of the critical properties. These lattices are composed corner sharing triangles and tetrahedrons respectively. The simulation was performed employing the Cluster Wolf Algorithm for the spin updates through the standard ferromagnetic Ising Model. The determination of the critical temperature and exponents was based on the Histogram Technique and the Finite-Size Scaling Theory. © 2016 Elsevier B.V. All rights reserved.


Freitas A.S.,Federal University of Sergipe | Freitas A.S.,Instituto Federal Of Sergipe | De Albuquerque D.F.,Federal University of Sergipe
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

We study the phase diagram in the H-T plane of the potassium jarosite compound KFe3(OH)6(SO4)2 for the antiferromagnetic XY model with Dzyaloshinskii-Moriya (DM) interaction using the mean-field theory for different values of DM. In our approach, we obtain the tricritical point in the H-T plane and the adjustment has a strong correlation with experimental data. © 2015 American Physical Society.

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