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Petrolina de Goias, Brazil

Rakov N.,Federal University of Vale do Sao Francisco | Maciel G.S.,Federal University of Fluminense
Dalton Transactions | Year: 2014

Er3+ doped nanocrystalline powders are extensively used for thermometry based on luminescence spectral analysis. The luminescence from Er3+ is produced by a nonlinear (two-photon) absorption process which may generate strong internal heat by activation of nonradiative relaxation channels. If the heat dissipation is not efficient, as is the case for compact powders, there will be inaccurate readings of the temperature. Our proposed solution is to cool down Er3+ by transferring part of its accumulated energy to another rare-earth element in the lattice. Here, we show our results for Er3+-Tm3+ co-doped yttrium silicate powders prepared by combustion synthesis. This journal is © the Partner Organisations 2014. Source

Amaral T.M.,Federal University of Pernambuco | Amaral T.M.,Federal University of Vale do Sao Francisco | Costa A.P.C.,Federal University of Pernambuco
Operations Research for Health Care | Year: 2014

An Emergency Department (ED) is considered the heart of a hospital and in many cities around the world, and especially in developing countries such as Brazil, it is very often the sole source of medical care. Making decisions about hospital resource management is not a trivial activity and incorrect decision-making can have serious consequences on the quality of health care services provided to the community. This paper describes the application of the PROMETHEE II method to support decision-making and resource management in an ED. Multiple Criteria Decision Analysis (MCDA) is especially useful in systems in which decision-making is complex and involves different considerations. PROMETHEE II was chosen for this study because its outranking approach is considered appropriate for the decision context of hospital services. This method was tested and validated with experimental data from a Brazilian public hospital. The ranking showed the best alternatives to be implemented to improve the throughput of patients in the "Blue Room". Six months after implementing the best alternatives, the waiting time during periods of overcrowding had been reduced by around 70%. The PROMETHEE II method proved to be a rational tool to support the Decision Maker (DM) to choose the best alternative to solve bottlenecks related to overcrowding in an ED. Improving decision-making in hospital departments means taking actions to increase the throughput of patients and reducing the number of patients-in-process. © 2013 Elsevier Ltd. Source

Maciel G.S.,Federal University of Fluminense | Rakov N.,Federal University of Vale do Sao Francisco
Journal of Materials Chemistry C | Year: 2013

We performed up-conversion (UC) experiments in rare-earth (Er3+, Tm3+, Nd3+) doped yttrium oxide (Y2O 3) powders using a high power (1.6 W) near-infrared (808 nm) diode laser modulated at 20 Hz as the excitation source. Below the threshold for incandescence, the analysis of the dynamics of the UC luminescence showed the presence of an unusual depletion of the luminescence signal. This anomalous effect could be controlled by the laser excitation power or the modulation frequency or the combination of rare-earth species doped in the samples. The phenomenon was associated with a thermo-optical effect generated by strong laser absorption, poor thermal dissipation of the powder and energy transfer (ET) between different rare-earth species. The experimental results also led us to believe that the ET mechanism cools down the rare-earth donor, Tm3+, and heats up the rare-earth acceptor, Er3+. © 2013 The Royal Society of Chemistry. Source

Rakov N.,Federal University of Vale do Sao Francisco | Maciel G.S.,Federal University of Fluminense
Optics Letters | Year: 2014

Er3+ doped powders are generally used for fluorescence-based temperature sensing application when near-infrared lasers are the excitation sources of choice. The fluorescence of Er3+ is produced by nonlinear (upconversion) processes, which generate strong internal heat. Lowering the excitation power causes drastic reduction of the fluorescence signal, and as a consequence the sensor applicability of Er3+ doped powders becomes compromised. Here we propose the use of the downconverted fluorescence of Yb3+ produced by efficient energy transfer from Nd3+ as an alternative temperature sensing system. Our results are presented for yttrium silicate powders prepared by combustion synthesis. © 2014 Optical Society of America. Source

De Oliveira H.P.,Massachusetts Institute of Technology | De Oliveira H.P.,Federal University of Vale do Sao Francisco | Sydlik S.A.,Massachusetts Institute of Technology | Swager T.M.,Massachusetts Institute of Technology
Journal of Physical Chemistry C | Year: 2013

Interfacial/in situ oxidative polymerization of polypyrrole in the presence of functionalized graphene sheets produces high-quality composites for supercapacitors, as analyzed by electrochemical impedance spectroscopy and cyclic voltammetry analysis. The synergistic interaction induced by the growth of p-type polypyrrole on the surface of negatively charged carboxylate functionalized graphene sheets results in higher storage capacity than graphene-only or polymer-only films. The high conductivity of p-doped polypyrrole and high surface area of graphene promote high charge accumulation in capacitors. We report the optimization of the relative concentrations of carboxylate functionalized graphene in the polypyrrole matrix to maximize the composition's capacitance to 277.8 F/g. © 2013 American Chemical Society. Source

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