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Moura G.M.,Federal University of Maranhao | Moura G.M.,Federal University of Para | Carvalho J.O.,Federal University of Maranhao | Carvalho J.O.,Instituto Federal do Tocantins | And 3 more authors.
Materials Chemistry and Physics | Year: 2015

l-Histidinium bromide monohydrate (LHBr) single crystal is a nonlinear optical material. In this work the high temperature phase transformation and the thermal stability of single crystals of LHBr was investigated by X-ray diffraction, thermogravimetric analysis, differential thermal analysis, differential scanning calorimetry and Raman spectroscopy. The results showed the LHBr phase transformation of orthorhombic (P2 1 2 1 2 1 ) to monoclinic system (P 1 2 1) at 120°C, with the lattice parameters a=12.162(1)Å, b=16.821(2)Å, c=19.477(2)Å and β=108.56(2)°. These techniques are complementary and confirm the structural phase transformation due to loss water of crystallization. © 2015 Elsevier B.V. Source

Cardoso S.R.S.,Sao Paulo State University | Cardoso S.R.S.,Instituto Federal do Tocantins | Forti L.C.,Sao Paulo State University | Nagamoto N.S.,Sao Paulo State University | Camargo R.S.,Sao Paulo State University
Sociobiology | Year: 2014

Most ants, as leaf cutting ants, construct nests underground to maintain environmental conditions favorable to the development of immature and adult individuals. But there was little works about this, especially doing comparison of nest growth among leafcutting ant species. Thus, we studied the growth of nests of the leaf-cutting ants Atta bisphaerica and Ata sexdens rubropilosa from nest foundation until the appearance of a second chamber. To this end, we verified the measurements of the chamber recently constructed by the queen and monitored its growth in the initial phase of nest development. The nests were marked immediately after nuptial flight, with 40 nests of each species being dug at 45, 90, 135, 180, and 225 days afterwards. As a result, it was found a first time statistical demonstration that an ellipsoid chamber shape was verified in both species in the initial chamber at 45 days, and that, after, these chamber became spherical. In general, chamber size increased and format change was found in both species. The depth of the first chamber was found to increase significantly only in A. bisphaerica; this result means that this chamber growths downside rather than upside. The occurrence of a second chamber was verified from six months after nest foundation, in both species. Our study contributes to knowledge of the colony development for up to 1 year, by performing comparison of two leaf-cutting ants species. Source

Silva S.B.,Instituto Federal do Tocantins | Silva S.B.,University of Brasilia | Severino M.M.,University of Brasilia | De Oliveira M.A.G.,University of Brasilia
Renewable Energy | Year: 2013

Abstract: This paper aimed to evaluate the use of a photovoltaic-fuel cell-battery system to supply electric power in an isolated community in the Amazon region. The study focused on technical and cost issues of a pilot-project set up in an environmental protection area, located in the state of Tocantins, Brazil. A comparative analysis of the costs of the hybrid system after optimization was made with the aid of the HOMER© (Hybrid Optimization Model for Electric Renewables) program. The analysis shows that the optimal system's initial cost, net present cost, and electricity cost with the hydrogen storage system is US$ 87,138; US$102,323; and US$ 1.351/kWh, respectively. Components are costly (fuel cell and electrolyzer), with the photovoltaic modules and the electrolyzer presenting the main cost of system. Based on the results, the study confirmed that the best option for storing energy from photovoltaic systems is still the use of batteries. In the short term, implementation of hybrid photovoltaic-fuel cell-battery system in the region remains prohibitive due to the high cost of its components. © 2013 Elsevier Ltd. Source

Victor V.F.,Instituto Federal do Tocantins | Quintaes F.O.,Federal University of Rio Grande do Norte | Lopes J.S.B.,Federal University of Rio Grande do Norte | Junior L.D.S.,Federal University of Rio Grande do Norte | And 2 more authors.
IEEE Transactions on Magnetics | Year: 2012

This paper shows the analysis and study of a bearingless ac Motor type divided winding for a conventional squirrel cage induction motor, (IM). The conventional IM is used as a bearingless motor for artificial-lift oil proposes, allowing a reduction in maintenance and operation costs. The goal of this paper is improving electromagnetic forces performance, such as the Lorentz and Maxwell forces, allowing rotor positioning at the rotation axis. It was used a simulator based on the finite element method for acquiring load results for a 3,75 kW, 380 V, 4-poles, 60 Hz, 1.04 Nm, IM motor. Experimental results show that is possible to use a conventional IM as a bearingless motor, achieving a 80% efficiency. This paper presents simulated and experimental results that demonstrated the operation of the IM bearingless-type split coil built from a conventional induction motor. © 2012 IEEE. Source

Carvalho J.O.,Federal University of Maranhao | Carvalho J.O.,Instituto Federal do Tocantins | Moura G.M.,Federal University of Maranhao | Moura G.M.,Federal University of Para | And 4 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2016

Single crystal of monoglycine nitrate has been studied by Raman spectroscopy under high pressures up to 5.5 GPa. The results show changes in lattice modes in the pressure ranges of 1.1-1.6 GPa and 4.0-4.6 GPa. The first change occurs with appearance of bands related to the lattice modes as well as discontinuity in the slope of dΩ/dP of these modes. Moreover, bands associated with the skeleton of glycine suggest that the molecule undergoes conformational modifications. The appearance of a strong band at 55 cm- 1 point to a second phase transition associated with the lattice modes, while the internal modes remain unchanged. These anomalies are probably due to rearrangement of hydrogen bonds. Additionally, decompression to ambient pressure shows that the phase transitions are reversible. Finally, the results show that the nitrate anions play an important role on the stability of the monoglycine nitrate crystal. © 2016 Elsevier B.V. All rights reserved. Source

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