Comparative analysis of circular and triangular gold nanodisks for field enhancement applications

ABSTRACT: In 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.

An automatic methodology for obtaining optimum shape factors for the radial point interpolation method

In this letter, a methodology is proposed for automatically (and locally) obtaining the shape factor c for the Gaussian basis functions, for each support domain, in order to increase numerical precision and mainly to avoid matrix inversion impossibilities. The concept of calibration function is introduced, which is used for obtaining c. The methodology developed was applied for a 2-D numerical experiment, which results are compared to analytical solution. This comparison revels that the results associated to the developed methodology are very close to the analytical solution for the entire bandwidth of the excitation pulse. The proposed methodology is called in this work Local Shape Factor Calibration Method (LSFCM).

Physicochemical properties of three sugary cassava landraces

Neste trabalho, foram avaliadas propriedades físicas e físico-químicas das raízes de três acessos de mandiocaba (Manihot esculenta Crantz): São Francisco Bag 3, Manicueira 62 e Castanhal Iracema. Os três acessos apresentaram elevada produtividade estimada (≥3,93kg planta^-1) e as suas raízes apresentaram altos teores de açúcares (≥3,92g 100g^-1 de raiz), apresentando-se como uma alternativa para a produção de xarope, particularmente o acesso São Francisco Bag 3 (4,76g 100g^-1). O acesso Manicueira 62 foi o que apresentou o maior conteúdo de amido (4,40g 100^-1). As três raízes estudadas apresentaram altos níveis de cianeto total (>195mg kg^-1), o que indica que elas também necessitam ser processadas antes de serem consumidas.

Resonant properties, of modified triangular plasmonic nanoparticles with higher field concentration

In 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.

Development of computational 3D MoM algorithm for nanoplasmonics

In 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.

Microwave switchable frequency selective surface with high quality factor resonance and low polarization sensitivity

We 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.

QoS management in smart grids: a Markovian approach

In 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.

New strategies for planning and performance evaluation of wireless networks: case studies based on the cross-layer approach

The use of wireless local area networks, called WLANs, as well as the proliferation of the use of multimedia applications have grown rapidly in recent years. Some factors affect the quality of service (QoS) received by the user and interference is one of them. This work presents strategies for planning and performance evaluation through an empirical study of the QoS parameters of a voice over Internet Protocol (VoIP) application in an interference network, as well as the relevance in the design of wireless networks to determine the coverage area of an access point, taking into account several parameters such as power, jitter, packet loss, delay, and PMOS. Another strategy is based on a hybrid approach that considers measuring and Bayesian inference applied to wireless networks, taking into consideration QoS parameters. The models take into account a cross layer vision of networks, correlating aspects of the physical environment, on the signal propagation (power or distance) with aspects of VoIP applications (e.g., jitter and packet loss). Case studies were carried out for two indoor environments and two outdoor environments, one of them displaying main characteristics of the Amazon region (e.g., densely arboreous environments). This last test bed was carried out in a real system because the Government of the State of Pará has a digital inclusion program called NAVEGAPARÁ.

Wavelength assignment using a hybrid evolutionary computation to reduce cross-phase modulation

In this paper, we propose a hybrid methodology based on Graph-Coloring and Genetic Algorithm (GA) to solve the Wavelength Assignment (WA) problem in optical networks, impaired by physical layer effects. Our proposal was developed for a static scenario where the physical topology and traffic matrix are known a priori. First, we used fixed shortest-path routing to attend demand requests over the physical topology and the graph-coloring algorithm to minimize the number of necessary wavelengths. Then, we applied the genetic algorithm to solve WA. The GA finds the wavelength activation order on the wavelengths grid with the aim of reducing the Cross-Phase Modulation (XPM) effect; the variance due to the XPM was used as a function of fitness to evaluate the feasibility of the selected WA solution. Its performance is compared with the First-Fit algorithm in two different scenarios, and has shown a reduction in blocking probability up to 37.14% when considered both XPM and residual dispersion effects and up to 71.42% when only considered XPM effect. Moreover, it was possible to reduce by 57.14% the number of wavelengths.

Proveniência e idade do metamorfismo das rochas da Faixa Brasília, na Região de Tapira (SW de Minas Gerais)

A Faixa Brasília na região de Tapira, no SW do estado de Minas Gerais, exibe quatro domínios litotectônicos diferentes, imbricados através de falhas de empurrão, com vergência para o Cráton do São Francisco. Foram conduzidos estudos isotópicos através do método Sm/Nd, que revelam diferentes idades modelo e de metamorfismo para estas escamas. As rochas da escama inferior apresentam idade de metamorfismo de 543 Ma, enquanto a escama que a superpõem, apresentam idade de metamorfismo de 581 Ma. As idades modelo (TDM) são similares para as duas escamas, variando entre 1,7 e 2,2 Ga. Em função das características litológicas essas escamas são interpretadas como derivadas de rochas depositadas em plataforma continental distal, que tiveram como fonte principal rochas de idades paleoproterozóicas do Cráton do São Francisco. As rochas da escama superior apresentam idade de metamorfismo de 612 Ma e uma distribuição bimodal das idades modelo (TDM), 1,3 e 1,9 - 2,0 Ga. Em função das características litológicas e isotópicas as rochas dessas escamas são interpretadas como depositadas em ambiente de talude continental ou assoalho oceânico, tendo os sedimentos fonte mista, de idades paleo- e mesoproterozóicas do Cráton do São Francisco. Embora, com as limitações impostas tanto pelo pequeno número de amostras analisadas, quanto pelas incertezas do método Sm/Nd, interpreta-se que o metamorfismo não foi síncrono nas diferentes escamas. Isto é esperado em um sistema de cavalgamento, no qual as escamas mais metamórficas justapõem-se às escamas menos metamórficas.

Estradas, alagados antrópicos, peixes e a fragmentação de redes fluviais em uma paisagem agrícola do Nordeste do Pará

Estradas cruzando riachos (ou igarapés) por estruturas mal planejadas podem ocasionar alagamentos em segmentos do canal à montante do cruzamento, transformando este trecho de um ambiente lótico em um lêntico. O presente trabalho teve como objetivo estudar a diversidade e a estrutura trófica funcional de comunidades de peixes em alagados de origem antrópica na região nordeste do Pará. Estes alagados são formados pelo cruzamento de estradas sobre a rede fluvial, com maiores ou menores impactos sobre sua conectividade hidrológica, assunto que é largamente ignorado em sistemas lóticos neotropicais. Foram amostrados dezoito trechos de canais em sete igarapés nas bacias dos rios Maracanã e Marapanim, sendo seis deles cruzados por estradas, e um não, como referência. Todos igarapés estão localizados na região nordeste do estado do Pará, sendo cinco nos municípios de Igarapé-Açu e Marapanim, inseridos em uma paisagem agrícola, e dois no município de São Francisco do Pará, inseridos em uma matriz florestal. Dos seis igarapés cruzados por estradas, cinco apresentaram a formação de amplas áreas alagadas. Nestes locais, foram selecionados três trechos do sistema fluvial para amostragem de peixes: um à montante do alagamento, um no próprio alagamento e outro à jusante. No igarapé que não apresentava alagamento, selecionou-se, apenas dois trechos: montante e jusante do cruzamento da estrada sobre o canal. Os ambientes selecionados foram amostrados uma vez, entre junho e novembro de 2010, por técnicas de censo visual, em segmentos de 200 metros de extensão. Foram registradas 73 espécies distribuídas em seis ordens, 26 famílias e 63 gêneros. Characiformes (38,4%) e Siluriformes (31,5%) foram as ordens mais representativas em números de espécies. Characidae, com 15 espécies (20,5%), e Cichlidae, com 10 (13,7%) foram as famílias mais representativas em número de espécies. Estas espécies foram organizadas em 18 grupos tróficos funcionais (GTF), formados de acordo com a tática alimentar observada com maior frequência para cada espécie e sua distribuição espacial observada durante as sessões de mergulho ad libitum. Os alagamentos impuseram modificações na estrutura biótica e física dos igarapés. Estes ambientes apresentaram menor número de espécies, maior abundância e menor diversidade de espécies e de GTF em relação aos trechos à jusante e à montante. Os alagamentos apresentaram maior largura, profundidade e temperatura; e menor velocidade e oxigênio de dissolvido quando comparados aos trechos de igarapés à montante e à jusante. O uso da abordagem de grupos tróficos funcionais facilitou na inferência de como o processo de fragmentação da rede fluvial interfere na estrutura da assembleia de peixes estudada.

Analysis of electronic structure of boron nitride nanotubes with different positions of intrinsic impurities

The 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.

Inversion method for obtaining electrical parameters for soil in the rural region in Brazil

This paper presents an inversion methodology through weighted least squares to obtain the electrical parameters for the soil of a typical mid-western region in Brazil using the model based in the formalism of the parabolic equations to calculate the electric field intensity received. To validate this methodology, the results of the radio signal measurement campaign conducted in six radial routes leaving the city of Brasilia, Federal District, where the transmitter was located, were used. The measurements were compared to computer simulations and, thus, the optimal values for the electric conductivity and relative permittivity for the soil of the region could be estimated. Finally, a quantitative analysis of these parameters was performed with the values found in the literature, which demonstrated the effectiveness of the proposed methodology.

Radio-wave propagation model for UHF band in different climatic conditions with dyadic green’s function

This article proposes a deterministic radio propagation model using dyadic Green's function to predict the value of the electric field. Dyadic is offered as an efficient mathematical tool which has symbolic simplicity and robustness, as well as taking account of the anisotropy of the medium. The proposed model is an important contribution for the UHF band because it considers climatic conditions by changing the constants of the medium. Most models and recommendations that include an approach for climatic conditions, are designed for satellite links, mainly Ku and Ka bands. The results obtained by simulation are compared and validated with data from a Digital Television Station measurement campaigns conducted in the Belém city in Amazon region during two seasons. The proposed model was able to provide satisfactory results by differentiating between the curves for dry and wet soil and these corroborate the measured data, (the RMS errors are between 2-5 dB in the case under study).

Novel technique for locating an intruder in 3D environments by using a cooperative system of multistatic radars

The aim of this work is to present a new methodology, based on vector and geometrical techniques, for determining the position of an intruder in a residence (3D problem). Initially, modifications in the electromagnetic responses of the environment, caused by movements of the trespasser, are detected. It is worth mentioning that slight movements are detected by high frequency components of the used pulse. The differences between the signals (before and after any movement) are used to define a sphere and ellipsoids, which are used for estimating the position of the invader. In this work, multiple radars are used in a cooperative manner. The multiple estimates obtained are used to determine a mean position and its standard deviation, introducing the concept of sphere of estimates. The electromagnetic simulations were performed by using the FDTD method. Results were obtained for single and double floor residences.