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Recife, Brazil

Guedes M.A.,University of Sao Paulo | Paolini T.B.,University of Sao Paulo | Felinto M.C.F.C.,Brazilian National Nuclear Energy Commission | Kai J.,University of Sao Paulo | And 4 more authors.
Journal of Luminescence | Year: 2011

In this work a series of tetrakis complexes C[Tm(acac)4], where C=Li, Na and K countercations and acac=acetylacetonate ligand, were synthesized and characterized for photoluminescence investigation. The relevant aspect is that these complexes are water-free in the first coordination sphere. The emission spectra of the tetrakis Tm3-complexes present narrow bands characteristic of the 1G4→3H6 (479 nm), 1G4→3F4 (650 nm) and 1G4→3H5 (779 nm) transitions of the Tm3 ion, with the blue emission color at 479 nm as the most prominent one. The lifetime values (τ) of the emitting 1G 4 level of the C[Tm(acac)4] complexes were 344, 360 and 400 ns for the Li, Na and K countercations, respectively, showing an increasing linear behavior versus the ionic radius of the alkaline ion. An efficient intramolecular energy transfer process from the triplet state (T) of the ligands to the emitting 1G4 state of the Tm3 ion is observed. This fact, together with the absence of water molecules in first coordination sphere, allows these tetrakis Tm3-complexes to act as efficient blue light conversion molecular devices. © 2010 Elsevier B.V. Source

Pianto D.M.,Campus Universitrio Darcy Ribeiro | Cribari-Neto F.,Cidade Universitria
Computational Statistics and Data Analysis | Year: 2011

In this paper we study maximum likelihood estimation (MLE) of the roughness parameter of the GA0 distribution for speckled imagery (Frery et al., 1997). We discover that when a certain criterion is satisfied by the sample moments, the likelihood function is monotone and MLE estimates are infinite, implying an extremely homogeneous region. We implement three corrected estimators in an attempt to obtain finite parameter estimates. Two of the estimators are taken from the literature on monotone likelihood (Firth, 1993; Jeffreys, 1946) and one, based on resampling, is proposed by the authors. We perform Monte Carlo experiments to compare the three estimators. We find the estimator based on the Jeffreys prior to be the worst. The choice between Firth's estimator and the Bootstrap estimator depends on the value of the number of looks (which is given before estimation) and the specific needs of the user. We also apply the estimators to real data obtained from synthetic aperture radar (SAR). These results corroborate the Monte Carlo findings. Further clarification of the choice between the Firth and Bootstrap estimators will be obtained through future studies of the classification properties of these estimators. © 2010 Elsevier B.V. All rights reserved. Source

Da Costa Mattos H.S.,Federal University of Fluminense | Sampaio E.M.,State University of Rio de Janeiro | Monteiro A.H.,Cidade Universitria
International Journal of Adhesion and Adhesives | Year: 2010

The present work is concerned with the study of the influence of adhesive layer thickness on the mechanical strength of axially loaded aluminiumepoxy butt joints. The main goal is to predict the rupture force using model equations that combine enough mathematical simplicity to allow their usage in engineering problems with the capability of describing a complex non-linear mechanical behaviour (three-dimensional state of stress; possibility of cohesive failure, of adhesive failure or mixed failure, depending on the geometry of the joint, on the adhesive strength and on the interaction between surfaces). The predicted values of the rupture force for different values of the thickness of the adhesive layer are compared with experimental data, showing a good agreement. © 2010 Elsevier Ltd. Source

Franca B.W.,Cidade Universitria | Aredes M.,Federal University of Rio de Janeiro
IECON Proceedings (Industrial Electronics Conference) | Year: 2011

In this paper the Unified Power Quality conditioner is studied with conventional operation mode (UPQC) and with its dual topology (iUPQC). The iUPQC is presented as solution to improve the dynamic response in power quality disturbance mitigation. Comparisons in steady-state and dynamic response are provided. Simulations and experimental results are shown to verify the iUPQC behavior for power quality safety and several load change issues. © 2011 IEEE. Source

Rocha A.B.,Cidade Universitria | De Moura C.E.V.,Cidade Universitria
Journal of Chemical Physics | Year: 2011

Potential energy curves for inner-shell states of nitrogen and carbon dioxide molecules are calculated by inner-shell complete active space self-consistent field (CASSCF) method, which is a protocol, recently proposed, to obtain specifically converged inner-shell states at multiconfigurational level. This is possible since the collapse of the wave function to a low-lying state is avoided by a sequence of constrained optimization in the orbital mixing step. The problem of localization of K-shell states is revisited by calculating their energies at CASSCF level based on both localized and delocalized orbitals. The localized basis presents the best results at this level of calculation. Transition energies are also calculated by perturbation theory, by taking the above mentioned MCSCF function as zeroth order wave function. Values for transition energy are in fairly good agreement with experimental ones. Bond dissociation energies for N 2 are considerably high, which means that these states are strongly bound. Potential curves along ground state normal modes of CO 2 indicate the occurrence of Renner-Teller effect in inner-shell states. © 2011 American Institute of Physics. Source

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