ECT - Artigos publicados em periódicos

URI Permanente para esta coleçãohttps://repositorio.ufrn.br/handle/1/2969

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α Function for a series of hydrocarbons to peng−robinson and van der waals equations of state
(ACS Publications, 2001) Chiavone Filho, Osvaldo; Amaral Filho, Pedro G.; Silva, Douglas do Nascimento; Terron, Luiz Roberto
This paper reports estimated coefficients for the α function based on vapor pressure data to a series of 438 components, mainly hydrocarbons, for both van der Waals and Peng−Robinson equations of state (EoS). The α function utilized for the attractive term is the one proposed by Mathias and Copeman in 1983, and it improves the cubic EoS calculations. Accurate vapor-pressure correlations and critical data required for the estimation of the constants were retrieved from two databases, i.e., AIChE DIPPR and the Reid et al. (The Properties of Gases and Liquids; McGraw-Hill: New York, 1987) reference book. The method of calculation is described, and the constants are tested with respect of their representation of thermodynamic properties, mainly in terms of the vapor-pressure deviations. The behavior of density and enthalpy EoS predictions is also evaluated. The estimated coefficients for the α function are reported in the Supporting Information and may be applied as a data bank in a simulator, providing more accurate thermodynamic property calculations in the recommended temperature range, as demonstrated
Experimental results for the extraction of essential oil from Lippia sidoides cham. using pressurized carbon dioxide
(Scielo, 2002-04) Chiavone Filho, Osvaldo; Sousa, E. M. B. D.; Moreno, M. T.; Silva, Douglas do Nascimento; Marques, M. O. M.; Meireles, M. A. A.
The odoriferous species Lippia sidoides Cham. is abundant in the Brazilian Northeast. Its essential oil possesses antiseptic activity due to the presence of thymol. In this work, thermodynamic and kinetic data were experimentally determined for the CO2 + L. sidoides system. Solubility was determined using the dynamic method at pressures of 66.7 and 78.5 bar and temperatures of 283.15, 288.15, 293.15, 295.15, and 298.15 K. SFE kinetic data were obtained at 288.15 K and 66.7 bar. The composition of the multicomponent solute mixture was determined by GC-MS and compared to the composition of both the volatile oil obtained by steam distillation and the oleoresin obtained using ethanol. The SFE process yield was higher than the yield of either the steam distillation or the ethanol extraction. The solubilities were correlated using the Peng-Robinson equation of state with one binary interaction parameter for the attractive term, considering the essential oil as a pseudo-component. Sovov·ís model quantitatively described the overall extraction curve
Treatment of saline wastewater contaminated with hydrocarbons by the photo-fenton process
(ACS Publications, 2004-01-03) Chiavone Filho, Osvaldo; Moraes, José Ermírio Ferreira de; Quina, Frank H.; Nascimento, Cláudio Augusto Oller do; Silva, Douglas do Nascimento
The application of the photo-Fenton process to the treatment of saline wastewater contaminated with hydrocarbons is investigated. Aqueous saline solutions containing raw gasoline were used as a model oil-field-produced water. The dependence on concentrations of the following reagents has been appropriately evaluated: hydrogen peroxide (100−200 mM), iron ions (0.5−1 mM), and sodium chloride (200−2000 ppm). The reactions were monitored by measurement of the absorption spectra and total organic carbon (TOC). Experimental results demonstrate that the photo-Fenton process is feasible for the treatment of wastewaters containing hydrocarbons, even in the presence of high concentrations of salt. The effect of the salt in this process is described through a series of reactions. A simple feedforward neural network model was found to correlate well the observed data for the degradation process
Utilization of solar energy in the photodegradation of gasoline in water and of oil-field-produced water
(ACS Publications, 2004-05-28) Chiavone Filho, Osvaldo; Moraes, José Ermírio Ferreira de; Silva, Douglas do Nascimento; Quina, Frank H.; Nascimento, Cláudio Augusto Oller do
The photo-Fenton process utilizes ferrous ions (Fe2+), hydrogen peroxide (H2O2), and ultraviolet (UV) irradiation as a source of hydroxyl radicals for the oxidation of organic matter present in aqueous effluents. The cost associated with the use of artificial irradiation sources has hindered industrial application of this process. In this work, the applicability of solar radiation for the photodegradation of raw gasoline in water has been studied. The photo-Fenton process was also applied to a real effluent, i.e., oil-field-produced water, and the experimental results demonstrate the feasibility of employing solar irradiation to degrade this complex saturated-hydrocarbon-containing system
Magnetostatic modes in metamagnetic superlattices
(Elsevier, 2005-09) Vasconcelos, Manoel Silva de; Anselmo, Dory Hélio Aires de Lima; Bezerra, Claudionor Gomes
A detailed analysis of the spin wave modes propagating in magnetic superlattices made up of two metamagnetic materials is carried out in the magnetostatic regime, for the antiferromagnetic phase. Our model takes into account the presence of an external applied magnetic field, which is perpendicular to the interfaces of the superlattice, as well as the crystalline anisotropic contribution to the inner magnetic field. The magnetostatic bulk and surface modes are obtained by using the transfer matrix technique. The metamagnetic material considered here is FeBr2, however, our results can be extended to other materials. Our numerical results show the presence of a striking behavior of these modes, for small frequencies of the energy spectra. The results reported here can be experimentally observed by light scattering techniques
XAFS characterization of La1−xSrxMnO3±δ catalysts prepared by Pechini’s method
(Elsevier, 2006-03-20) Melo, Dulce Maria de Araújo; Borges, Filipe Martel de Magalhães; Ambrósio, Renato Canha; Pimentel, Patricia Mendonça; Silva Júnior, Carlos Neco da; Melo, Marcus Antônio de Freitas
XAFS experiments at the Mn and Sr K-edges were carried out in order to investigate the short-range arrangement of Mn and Sr sites on La1−xSrxMnO3±δ highly doped perovskites (x = 0, 0.2, 0.4 and 0.6). The Mn K-edge EXAFS spectra show a static Jahn–Teller distortion of the MnO6 for x = 0 and 0.2, which is drastically reduced as x increases. The distortion of perovskite, characterized by the Mn–O–Mn tilt angle, progressively decreases with increasing Sr contents. Sr K-edge results indicated a decrease on the Sr–Mn coordination number upon Sr doping. Based on this and TPD results, a charge compensating mechanism is proposed suggesting a partial Mn oxidation and formation of Mn defect vacancies due to the introduction of Sr.
Specific heat spectra for quasiperiodic ladder sequences
(Springer Verlag, 2007-01-05) Moreira, Darlan Araújo; Albuquerque, Eudenilson Lins de; Bezerra, Claudionor Gomes
We performed a theoretical study of the specific heat C(T) as a function of the temperature for double-strand quasiperiodic sequences. To mimic DNA molecules, the sequences are made up from the nucleotides guanine G, adenine A, cytosine C and thymine T, arranged according to the Fibonacci and Rudin-Shapiro quasiperiodic sequences. The energy spectra are calculated using the two-dimensional Schrödinger equation, in a tight-binding approximation, with the on-site energy exhibiting long-range disorder and non-random hopping amplitudes. We compare the specific heat features of these quasiperiodic artificial sequences to the spectra considering a segment of the first sequenced human chromosome 22 (Ch22), a real genomic DNA sequence
Specific heat spectra of non-interacting fermions in a quasiperiodic ladder sequence
(Elsevier BV, 2008-06-11) Anselmo, Dory Hélio Aires de Lima; Moreira, Darlan Araújo; Albuquerque, Eudenilson Lins de
We compute the specific heat spectra of non-interacting fermions whose energy spectrum was obtained from a quasiperiodic ladder sequence (Fibonacci and Rudin–Shapiro type), mimicking a DNA molecule model. The specific heat is calculated from their underlying multi-fractal energy spectrum, considering several values of energy densities. Comparisons are made with a real DNA sequence, namely the human chromosome 22 (Ch22)
Thermal radiation in quasiperiodic photonic crystals
(Elsevier, 2009) Mauriz, P. W.; Vasconcelos, Manoel Silva de; Medeiros, F. F. de; Albuquerque, Eudenilson Lins de
In this work we investigated the thermal power spectrum of the electromagnetic radiation through onedimensional stacks of alternating negative and positive refractive index layers, arranged as truncated quasiperiodic photonic structures obeying the Fibonacci (FB), Thue–Morse (TM), and double-period (DP) sequences. The thermal radiation power spectra are determined by means of a theoretical model based on a transfer matrix formalism for both normal and oblique incidence geometries, together with Kirchoff’s second law. We studied the radiation spectra by considering the case where both refractive indices of layers A and B are assumed to be a constant, as well as a more realistic case which takes into account the frequency-dependent electric permittivity and magnetic permeability m to characterize the negative refractive index n in layer B
Optical transmission spectra in symmetrical Fibonacci photonic multilayers
(Elsevier, 2009) Mauriz, P. W.; Vasconcelos, Manoel Silva de; Albuquerque, Eudenilson Lins de
We study the transmission properties of light through the symmetric Fibonacci photonic multilayers, i.e, a binary one-dimensional quasiperiodic structure, made up of both positive (SiO2) and negative refractive index materials with a mirror symmetry. These spectra are calculated by using a theoretical model based on the transfer matrix approach for normal incidence geometry, in which many perfect transmission peaks (the transmission coefficients are equal to the unity) are numerically obtained. Besides, the transmission coefficient exhibits a six-cycle self-similar behavior with respect to the generation number of the Fibonacci sequence
Optical filters based in quasiperiodic photonic crystal
(Elsevier, 2009) Vasconcelos, Manoel Silva de; Mauriz, P. W.; Albuquerque, Eudenilson Lins de
In this work we investigate theoretically the behavior of a light beam incident on a wð2Þ nonlinear quasiperiodic photonic crystal (or quasiperiodic S˘olc filter), in which each building block containing a pair LiNbO3 layers with antiparallel poled domains, arranged in a quasiperiodical fashion which follows the Pell, Fibonacci, Thue–Morse, and double-period substitutional sequences. The transmittances at filtering wavelengths can be modulated from 0 to 1 by applying an external voltage but the filtering wavelengths are unchanged. We show that the filtering wavelengths tuned by varying voltage around 0.9 kV, indicate that quasiperiodic S˘olc filter based in Pell and Thue–Morse sequences are so efficient as the Fibonacci S˘olc filter, while the double-period sequence have a low efficiency
Detecção automática de movimentos utilizando visão computacional para monitoramento seguro de áreas supervisionadas
(Unisal, 2009-01) Valentim, Ricardo Alexsandro de Medeiros; Araújo, Bruno Gomes; Lacerda, João Marcos Teixeira; Florentino, Gustavo Henrique Pereira; Leite, Cicília Raquel Maia; Brandão, Gláucio Bezerra
Este artigo apresenta um sistema de segurança que realiza detecção automática de movimentos através de um dispositivo de captura de vídeo. A detecção automática de movimentos permite que o usuário seja notificado através de eventos de segurança sem que seja necessária a observação contínua do vídeo do local supervisionado. Neste trabalho também é apresentada a modelagem computacional do sistema fazendo-se uso do Java Media Framework da Sun Microsystems
Phase conversion in a weakly first-order quark-hadron transition
(American Physical Society, 2009-02-12) Moreira, André Bessa; Fraga, Eduardo Souza; Mintz, Bruno Werneck
We investigate the process of phase conversion in a thermally driven weakly first-order quark-hadron transition. This scenario is physically appealing even if the nature of this transition in equilibrium proves to be a smooth crossover for vanishing baryonic chemical potential. We construct an effective potential by combining the equation of state obtained within lattice QCD for the partonic sector with that of a gas of resonances in the hadronic phase, and present numerical results on bubble profiles, nucleation rates, and time evolution, including the effects from reheating on the dynamics for different expansion scenarios. Our findings confirm the standard picture of a cosmological first-order transition, in which the process of phase conversion is entirely dominated by nucleation, also in the case of a weakly first-order transition. On the other hand, we show that, even for expansion rates much lower than those expected in high-energy heavy-ion collisions, nucleation is very unlikely, indicating that the main mechanism of phase conversion is spinodal decomposition. Our results are compared to those obtained for a strongly first-order transition, as the one provided by the MIT bag model
Influence of soybean biodiesel content on basic properties of biodiesel–diesel blends
(Elsevier BV, 2009-04) Bicudo, Tatiana de Campos; Candeia, R. A.; Silva, M. C. D.; Carvalho Filho, J. R.; Brasilino, M. G. A.; Santos, I. M. G.; Souza, A. G.
The world tendency in last years is to restrict the use of fossil fuels and replace them partially or totally by renewable fuels. Accordingly, biodiesel is being studied as one of the main alternatives and the production and consumption of this pure biofuel and its binary blends with fossil diesel have been markedly grown. Thus, the present work evaluated the influence of biodiesel concentration on such blends when mixed to diesel in 5, 15, 25 and 50 volume percentages. For each blend, both methanol and ethanol biodiesels were investigated. The biodiesel samples were physicochemically characterized. Their rheological behavior was analyzed. It was observed that the biodiesel enrichment leads to an acceptable increase in the viscosity and to a decrease in the volatilization of the binary blends. The viscosity was also shown to be temperature-dependent, as well as the fatty acids chain length and unsaturation
On the nucleation of hadronic domains in the quark-hadron transition
(Elsevier, 2009-04-01) Mintz, Bruno Werneck; Moreira, André Bessa; Fraga, Eduardo Souza
We present numerical results on bubble profiles, nucleation rates and time evolution for a weakly first-order quark-hadron phase transition in different expansion scenarios. We confirm the standard picture of a cosmological first-order phase transition, in which the phase transition is entirely dominated by nucleation. We also show that, even for expansion rates much lower than those expected in heavy-ion collisions nucleation is very unlikely, indicating that the main phase conversion mechanism is spinodal decomposition
Semiclassical calculation of decay rates
(Elsevier, 2009-04-01) Moreira, André Bessa; Carvalho Filho, Carlos Alberto Aragão de; Fraga, Eduardo Souza
Several relevant aspects of quantum-field processes can be well described by semiclassical methods. In particular, the knowledge of non-trivial classical solutions of the field equations, and the thermal and quantum fluctuations around them, provide non-perturbative information about the theory. In this work, we discuss the calculation of the one-loop effective action from the semiclasssical viewpoint. We intend to use this formalism to obtain an accurate expression for the decay rate of non-static metastable states
Antioxidative properties of hydrogenated cardanol for cotton biodiesel by PDSC and UV/VIS
(Springer, 2009-04-27) Bicudo, Tatiana de Campos; Rodrigues Filho, M. G.; Souza, A. G.; Santos, I. M. G.; Silva, M. C. D.; Sinfrônio, F. S. M.; Vasconcelos, A. F. F.
Biodiesel is a non-toxic biodegradable fuel that consists of alkyl esters produced from renewable sources, vegetal oils and animal fats, and low molecular mass alcohols, and it is a potential substitute for petroleum-derived diesel. Depending on the raw materials used, the amount of unsaturated fatty acids can vary in the biodiesel composition. Those substances are widely susceptible to oxidation processes, yielding polymeric compounds, which are harmful to the engines. Based on such difficulty, this work aims to evaluate the antioxidant activity of cashew nut shell liquid (cardanol), as additive for cotton biodiesel. The oxidative stability was investigated by the pressure differential scanning calorimetry (PDSC) and UV/Vis spectrophotometer techniques. The evaluated samples were: as-synthesized biodiesel – Bio T0, additivated and heated biodiesel – Bio A (800 ppm L –1 of hydrogenated cardanol, 150°C for 1 h), and a heated biodiesel – Bio B (150°C, 1 h). The oxidative induction time (OIT) analyses were carried out employing the constant volume operation mode (203 psi oxygen) at isothermal temperatures of 80, 85, 90, 100°C. The high pressure OIT (HPOIT) were: 7.6, 15.7, 22.7, 64.6, 124.0 min for Bio T0; 41.5, 77.0, 98.6, 106.6, 171.9 min for Bio A and 1.7, 8.2, 14.8, 28.3, 56.3 min for Bio B. The activation energy (E) values for oxidative processes were 150.0 1.6 (Bio T0), 583.8 1.5 (Bio A) and 140.6 0.1 kJ mol –1 (Bio B). For all samples, the intensities of the band around 230 nm were proportional to the inverse of E, indicating small formation of hyper conjugated compounds. As observed, cardanol has improved approximately four times the cotton biodiesel oxidative stability, even after the heating process
Themo-oxidative stability ald cold flow properties of babassu biodiesel by PDSC ans TMDSC techniques
(Springer, 2009-04-27) Bicudo, Tatiana de Campos; Santos, N. A.; Santos, J. R. J.; Sinfrônio, F. S. M.; Santos, I. M. G.; Antoniosi Filho, N. R.; Fernandes Jr, V. J.; Souza, A. G.
The babassu (Orbignya PhalerataMart.) biodiesel has lauric esters as main constituents, resulting in high oxidative stability and low cloud and freezing points. In order to reduce these side effects, the saturated ethyl esters content was reduced by means of winterization process. The TMDSC and PDSC techniques were used to verify the thermal and oxidative stabilities of the ethyl babassu biodiesel. During the heating stage, the winterized solid phase of ethyl esters presented an endothermic transition associated to the solidification process. This behavior was not observed for the liquid winterized FAEE, confirming the efficiency of the winterization process
Detecção de faltas evolutivas e múltiplos distúrbios em registros oscilográficos baseada na transformada wavelet discreta
(Sociedade Brasileira de Automática (SBA), 2009-05-11) Costa, Flávio Bezerra; Brito, Núbia Silva Dantas; Souza, Benemar Alencar de
Apresenta-se neste artigo um método de detecção automática de faltas baseado na análise da energia janelada dos coeficientes wavelet das tensões e correntes de fase. O método é capaz de detectar faltas evolutivas e de múltiplos distúrbios transitórios, a exemplo de uma falta seguida por um religamento automático, capturados no mesmo registro oscilográfico. O método também consegue distinguir faltas de algumas ocorrências relacionadas à qualidade da energia elétrica, tais como afundamento de tensão e transitórios de chaveamento.O método é eficaz na identificação dos instantes inicial e final da falta, além de conseguir analisar sinais referentes a linhas de transmissão de diferentes classes de tensão e que tenham sido registrados com frequências de amostragem diversas. Em avaliação de desempenho com registros oscilográficos simulados e reais, o método apresentou bons resultados
The H-N2N framework: towards providing interperception in massive applications
(Springer, 2009-05-23) Burlamaqui, Aquiles Medeiros Filgueira; Azevedo, Samuel Oliveira de; Dantas, Rummenigge Rudson; Schneider, Claúdio Alexandre; Xavier, Josivan; Melo, Julio Cesar Paulino de; Goncalves, Luiz Marcos Garcia; Souza Filho, Guido Lemos de; Oliveira, Jauvane Cavalcante de
We propose a framework with a flexible architecture that have been designed and implemented for collaborative interaction of users, to be applied in massive applications through the Web. We introduce the concept of interperception and use technologies as massive virtual environments and teleoperation for the creation of environments (mixing virtual and real ones) in order to promote accessibility and transparency in the interaction between people, and between people and animate devices (such as robots) through the Web. Experiments with massive games, with interactive applications in digital television, with users and robots interacting in virtual and real versions of museums and cultural centers are presented to validate our proposal

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