Artigos Científicos - FEE/ITEC
URI Permanente para esta coleçãohttp://10.7.2.76:4000/handle/2011/2516
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Item Acesso aberto (Open Access) Nanoelectronic Devices Based on Carbon Nanotubes(Universidade Federal do Pará, 2015-03) DMITRIEV, Victor Alexandrovich; GOMES, Fernando Antonio Pinheiro; NASCIMENTO, Clerisson Monte doCarbon nanotubes are possible building blocks in the development of new generation of electronic devices. The carbon nanotubes allow one fabrication of devices using nanometric scales. They can be used in projects of a wide range of electronic and optoelectronic components such as diodes, transistors and interconnection elements, among others. This paper presents the state-of-the-art of this area, emphasizing the influence of quantum effects on the characteristics of such components.Item Acesso aberto (Open Access) Analysis of modified bowtie nanoantennas in the excitation and emission regimes(2011-06) COSTA, Karlo Queiroz da; DMITRIEV, Victor AlexandrovichIn this work, we analyze modified bowtie nanoantennas with polynomial sides in the excitation and emission regimes. In the excitation regime, the antennas are illuminated by an incident plane wave, and in the emission regime, the excitation is fulfilled by infinitesimal electric dipole positioned in the gap of the nanoantennas. Several antennas with different sizes and polynomial order were numerically analyzed by method of moments. The results show that these novel antennas possess a controllable resonance by the polynomial order and good characteristics of near field enhancement and confinement for applications in enhancement of spontaneous emission of a single molecule.Item Acesso aberto (Open Access) Analysis of electronic structure of boron nitride nanotubes with different positions of intrinsic impurities(2014-12) GOMES, Fernando Antonio Pinheiro; DMITRIEV, Victor Alexandrovich; NASCIMENTO, Clerisson Monte doThe pristine boron nitride nanotubes have a large direct band gap around 5 eV. This band gap can be engineered by doping. We investigate electronic structure of the doped hexagonal boron nitride (5,5) nanotubes using the linearized augmented cylindrical wave method. In particular, this work focuses on systematical study of the band gap and the density of states around the Fermi-level when the nanotubes are doped by intrinsic impurities of two substitutional boron atoms in a super cell and a comparative analysis of the relative stability of three structures studied here. This corresponds to 3.3% of impurity concentration. We calculate 29 configurations of the nanotubes with different positions of the intrinsic impurities in the nanotube. The band gap and density of states around the Fermi level show strong dependence on the relative positions of the impurity atoms. The two defect sub bands called D∏(B) appear in the band gap of the pristine nanotube. The doped nanotubes possess p-type semiconductor properties with the band gap of 1.3-1.9 eV.Item Acesso aberto (Open Access) QoS management in smart grids: a Markovian approach(2014-12) SILVA, Marcelino Silva da; FRANCÊS, Carlos Renato Lisboa; COSTA, João Crisóstomo Weyl Albuquerque; CARDOSO, Diego Lisboa; VIJAYKUMAR, Nandamudi Lankalapalli; CARVALHO, Solon Venâncio deIn Smart Grids, a variety of new applications are available to users of the electrical system (from consumers to the electric system operators and market operators). Some applications such as the SCADA systems, which control generators or substations, have consequences, for example, with a communication delay. The result of a failure to deliver a control message due to noncompliance of the time constraint can be catastrophic. On the other hand, applications such as smart metering of consumption have fewer restrictions. Since each type of application has different quality of service requirements (importance, delay, and amount of data to transmit) to transmit its messages, the policy to control and share the resources of the data communication network must consider them. In this paper Markov Decision Process Theory is employed to determine optimal policies to explore as much as possible the availability of throughput in order to transmit all kinds of messages, considering the quality of service requirements defined to each kind of message. First a non-preemptive model is formulated and after that a preemptive model is derived. Numerical results are used to compare FIFO, non-preemptive and preemptive policies.Item Acesso aberto (Open Access) Microwave switchable frequency selective surface with high quality factor resonance and low polarization sensitivity(2012-12) KAWAKATSU, Marcelo Nobuyuki; DMITRIEV, Victor AlexandrovichWe present a microwave switchable frequency selective surface with high quality factor transmission resonance. The high quality resonance is achieved by excitation of the trapped-mode in array with two concentric metal rings in a cell on a silicon substrate. Optical activation of the silicon substrate permits to switch off the transmission band.Item Acesso aberto (Open Access) Development of computational 3D MoM algorithm for nanoplasmonics(2013-12) SOUZA, Nadson Welkson Pereira de; COSTA, Karlo Queiroz da; DMITRIEV, Victor AlexandrovichIn this paper, we present an algorithm for full-wave electromagnetic analysis of nanoplasmonic structures. We use the three-dimensional Method of Moments to solve the electric field integral equation. The computational algorithm is developed in the language C. As examples of application of the code, the problems of scattering from a nanosphere and a rectangular nanorod are analyzed. The calculated characteristics are the near field distribution and the spectral response of these nanoparticles. The convergence of the method for different discretization sizes is also discussed.Item Acesso aberto (Open Access) Resonant properties, of modified triangular plasmonic nanoparticles with higher field concentration(2013-12) COSTA, Karlo Queiroz da; DMITRIEV, Victor AlexandrovichIn this paper, we present an analysis of the resonant response of modified triangular metallic nanoparticles with polynomial sides. The particles are illuminated by an incident plane wave and the method of moments is used to solve numerically the electromagnetic scattering problem. We investigate spectral response and near field distribution in function of the length and polynomial order of the nanoparticles. Our results show that in the analyzed wavelength range (0.5-1.8) µm these particles possess smaller number of resonances and their resonant wavelengths, near field enhancement and field confinement are higher than those of the conventional triangular particle with linear sides.Item Acesso aberto (Open Access) Comparative analysis of circular and triangular gold nanodisks for field enhancement applications(2010-12) COSTA, Karlo Queiroz da; DMITRIEV, Victor AlexandrovichIn this paper, we present a quantitative comparison of circular and triangular gold nanodisks with the same length and thickness. The method of moments is used to solve numerically the scattering problem. With this model, we investigate the spatial near field distribution, spectral response, far field diagrams, and bandwidth wavelength of these particles. Our results show that the resonant wavelength and the near field enhancement and confinement of the triangular particle are larger than those for the circular particle, but the resonance bandwidth and scattering cross section of the triangular particle are smaller.Item Acesso aberto (Open Access) Controladores fuzzy aplicados ao conversor de geradores de indução duplamente excitados em sistemas eólicos integrados a sistemas de potência(2007-03) VIEIRA, João Paulo Abreu; BEZERRA, Ubiratan Holanda; BARRA JUNIOR, Walter; NUNES, Marcus Vinícius Alves; NASCIMENTO, André Cavalcante doThis paper presents new fuzzy control strategies for application on the control of the static converter that connects the doubly fed induction generator into the electrical grid in variable speed wind generation systems. The proposed control strategies are of the type "look-up- table" with supervision. The performance of these intelligent regulators is compared with those obtained with constant gain PI's controllers, when the electrical power systems is submitted to faults. The fuzzy controllers are intended to ensure the continous operation of the static converter, even during the fault period, and at the same time to improve the transient performance of the electrical system as compared with the case of using PI conventional controllers. The results presented confirm the efficiency of the proposed control strategies. The mathematical models that represent the dynamics of the wind turbines and generators were implemented using computacional programs developed in MATLABTM.Item Acesso aberto (Open Access) Comparison between known propagation models using least squares tuning algorithm on 5.8 GHz in Amazon region cities(2011-06) CASTRO, Bruno Souza Lyra; PINHEIRO, Márcio Rodrigues; CAVALCANTE, Gervásio Protásio dos Santos; GOMES, Igor Ruiz; CARNEIRO, Oziel de OliveiraThis paper presents a performance comparison between known propagation Models through least squares tuning algorithm for 5.8 GHz frequency band. The studied environment is based on the 12 cities located in Amazon Region. After adjustments and simulations, SUI Model showed the smaller RMS error and standard deviation when compared with COST231-Hata and ECC-33 models.Item Acesso aberto (Open Access) Estratégias de identificação paramétrica aplicadas à modelagem dinâmica de um servidor web Apache(2012-02) ABREU, Thiago Wanderley Matos de; BARRA JUNIOR, Walter; BARREIROS, José Augusto Lima; COSTA JÚNIOR, Carlos Tavares daThis article presents an experimental study about parametric identification techniques applied to the modeling of an Apache webserver. In order to simulate load variations at the server, an experimental arrangement was developed, which is composed of two personal computers, one used to run the Apache server and the other to generate workload by requesting services to the Apache. Auto-regressive (AR) parametric models were estimated at different operating points and workload conditions. The mean values of the MaxClients input (a parameter which is used to set the maximum number of the server's active processes) were used to define the operating points, in order to obtain the Apache server CPU utilization (in %) as output. 600 samples were collected at each operating point every 5 seconds. To proceed with the system identification, half of the data set was used for parameter estimation while the other half was used for model validation, at each operating point. A study of the most adequate system order showed that a 7th order model could be satisfactorily used for MaxClients low values operating points. However, the results showed that higher order models are needed for MaxClients higher values, due to system inherent non-linearities.Item Acesso aberto (Open Access) Avaliação da estabilidade de tensão do sistema brasileiro: um caso de estudo(2008-09) AFFONSO, Carolina de Mattos; SILVA, Luciano José da; SILVA, Luiz Carlos Pereira daThis paper presents results of a study of the Brazilian system operation in respect to voltage stability criteria. The analyses are applied using real-life data from the operation and planning. The system is divided in 4 regions: North, Northeast, South and Southeast/West Center. System stability margin is evaluated for each one of these areas. The results show that Brazilian system has stability margin much lower than the existing voltage stability criteria, limited by the Southeast/West Center region. A detailed analysis of this critical area is performed. This paper also presents the stability margin behavior during a typical weekday curve and a contingency analysis. The contingency severity is verified by using the modal analysis technique assessing each contingency impact classifying as local, area or systemic.Item Acesso aberto (Open Access) Estabilizador neural não-linear para sistemas de potência treinado por rede de controladores lineares(2006-06) BARREIROS, José Augusto Lima; FERREIRA, André Maurício Damasceno; BARRA JUNIOR, Walter; COSTA JÚNIOR, Carlos Tavares da; BAYMA, Rafael SuzukiPower System Stabilizers (PSS) have been applied as the most common solution to damp small magnitude and low frequency oscillations in modern electric power systems. Conventional Stabilizers, with fixed structure and parameters, have been used with this objective for several decades, but there are some system operation conditions where the performance of these linear stabilizers may deteriorate, especially when compared with that of stabilizers designed using modern control techniques. A Neural PSS, trained with a set of local linear controllers, is applied to establish the regions where a Conventional PSS shows low performance. Using non-linear digital simulations of a synchronous machine connected to an infinite-bus system and a multi-machine power system the Neural PSS is assessed showing superiority in those regions.