Abstract Using a local atmospheric electric field sensor network (Field Mill), an electromagnetic link model was proposed considering a free space electric field and a theoretical electric field calculated from an atmospheric discharge. With this, it was possible to compare the theoretical value of this electric field with the experimental value of the local atmospheric electric field (estimated by the Field Mill sensor network). The results are initially analyzed considering wavelengths in the EHF spectrum (λ ~ 10-5m) and the VLF spectrum (λ ~ 104m). As assumed before, admitting that the lightning channel acts as an isotropic irradiator and a Field Mill sensor acts as a receiving antenna for the spectrum emitted by the lightning, a irradiated power model of the electromagnetic waves reaching the Field Mill sensor, according to the ITU-R P.873.4 standard, was calculated, thus allowing a correlation with a satellite radio link, in which the Field Mill sensor acts as a ground receiving antenna and the main channel of the lightning strikes acts as a transmitting antenna. Also, a model of the power irradiated by each lightning discharge, recorded by the Field Mill sensor network, was proposed, and the Equivalent Isotropically Radiated Power - EIRP was calculated for different values of effective electric field (Eef) and then compared with the model of the power irradiated by the antenna (lightning). This makes it possible to do an analysis and determine if the lightning discharge can be approximated to an isotropically irradiated antenna model.

O modelo de tight-binding é um dos pilares da Física da Matéria Condensada, permitindo descrever de forma bastante simples uma ampla gama de fenômenos de interesse, como por exemplo a estrutura de bandas dos materiais e o transporte eletrônico. Nesse trabalho, o Hamiltoniano de tight-binding, escrito em linguagem de segunda quantização, é utilizado na modelagem das densidades de estados de energia em polímeros orgânicos. O procedimento de segunda quantização permite obter as expressões para a determinação dos parâmetros de hopping de forma natural. No âmbito do modelo de tight-binding são analisadas a cadeia atômica infinita e as moléculas do benzeno, do ciclopentadieno e do tiofeno.

The tight-binding model is a cornerstone of Condensed Matter Physics, describing in a simple way a wide range of phenomena, such as the band structure of materials and the electronic transport. In this paper, the referred model, written in the language of second quantization, is used to describe the density of states in organic polymers. Using the second quantization method the expressions for the hopping parameters emerge quite naturally. The infinite atomic chain, the benzene, cyclopentadiene and tyophene molecules are analyzed within the tight-binding model.

Abstract: The global atmospheric electric circuit is based on a model of electrical connection between the earth and the ionosphere (waveguide), capable of representing the flow of electric current in this waveguide. In the proposed model, a storm acts as a generator, allowing the ionosphere to maintain its highest electrical potential (approximately 300kV) in relation to Earth. When a storm forms, the bottom of the cloud becomes negatively charged. This study is focused on modeling this specific part of the global atmospheric electric circuit, which is renamed local atmospheric electric circuit. In the methodology, we use an RLC circuit to calculate the effects of electrified clouds in a 375kV transmission line considering an electrical coupling between them (an RLC circuit is an electrical circuit consisting of a resistor (R), an inductor (L), and to capacitor (C). The mathematical formulation was developed using transmission line theory considering a connection with the top of the storm cloud. Then, a model simulation using GNU Octave was performed, and the results demonstrated how this coupling affects voltage drop and phase shift in a 375kV transmission line. Thus, a local atmospheric electric circuit model, considering the particularities of the environment immersed in a real transmission line model, configures an important model in the perspective of project management of electric energy transmission networks.

Abstract During the last year the Group of Atmospheric Electricity Phenomena (FEA/UFPR) developed a short range lightning location network based on a sensor device called Storm Detector Network (SDN), along with a set of algorithms that enables to track storms, determining the Wide Area Probability (WAP) of lightning occurrence, risk level of lightning and Density Extension of the Flashes (DEF), using the geo-located lightning information as input data. These algorithms compose a Dashboard called Tracking Storm Interface (TSI), which is the visualization tool for an experimental short range Storm Detector network prototype in use on the region of Curitiba-Paraná, Brazil. The algorithms make use of Geopandas and clustering algorithms to locate storms, estimate centroids, determine dynamic storm displacement and compute parameters of thunderstorms like velocity, head edge of electrified cloud, Mean Stroke Rate, and tracking information, which are important parameters to improve the alert system which is subject of this research. To validate these algorithms we made use of a simple storm simulation, which enabled to test the system with huge amounts of data. We found that, for long duration storms, the tracking results, velocity and directions of the storms are coherent with the values of simulation and can be used to improve an alert system for the Storm Detector network. WAP can reach at least 75% of prediction efficiency when used 6 past WAP data, but can reach 98.86% efficiency when more data is available. We use storm dynamics to make improved alert predictions, reaching an efficiency of ~87%.

Resumo A conversão fotovoltaica de energia é uma área de pesquisa muito ativa devido à necessidade de ampliar a participação das fontes de energia renováveis na matriz energética global. Os esforços de pesquisa vão desde a modelagem de dispositivos fotovoltaicos a partir de princípios físicos fundamentais ou fenomenologias, passando pelo desenvolvimento e caracterização de novos materiais e dispositivos aplicáveis na conversão fotovoltaica e indo até os estudos de impacto ambiental e aspectos econômicos. No presente trabalho, utilizando-se do modelo de sistema de dois níveis acoplado a um campo de fótons, apresentam-se os princípios físicos da conversão fotovoltaica de energia. Com isso, além de servir de rápido guia para os pesquisadores e estudantes no campo da conversão fotovoltaica, o problema spin-bóson é utilizado de forma pedagógica para servir como um exercício contextualizado de mecânica quântica e física dos semicondutores.

Abstract Photovoltaic energy conversion is an extraordinarily active research field, mainly due to the need for increasing the participation of renewable energy sources in the world energy matrix. Research efforts range from the photovoltaic devices modelling from first principles or using phenomenology and the development and characterization of novel photovoltaic materials and devices to environmental and economical aspects of photovoltaic energy. The present work presents the physical aspects of photovoltaic energy conversion, using in a pedagogical way a two system level coupled to a photon field as a toy model to discuss the main ideas, serving as a quick guide for researchers and students in the field.

Resumo A geometria fractal fascina pela capacidade de descrever formas geométricas complexas e que usualmente estão presentes no mundo real . A dimensão fractal ou de Hausdorff d é utilizada para descrever leis de invariância de escala, em que as funções autossimilares seguem uma lei da forma f ( s x ) = s d f ( x ), sendo s o fator de escala. Intimamente relacionado ao problema da invariância de escala está o problema da determinação dos pontos fixos de um sistema, que matematicamente correspondem aos pontos que mapeiam o domínio de uma função para ele mesmo. Em sistemas dinâmicos correspondem ao valor para o qual a resposta do sistema usualmente converge e permanece estável. Na presente contribuição são apresentados os conceitos gerais associados à invariância de escala e ponto fixo, para prontamente empregá-los no problema de associação de impedâncias complexas em série e em topologia de escada. São discutidos em detalhes o problema da função de transferência de linhas de transmissão e o estudo de alguns gráficos de fluxo (flow graphs) de convergência das equações de recursividade.

Abstract Fractal geometry is fascinating due to its ability to describe the complex geometries naturally occurring in real world. The fractal or Hausdorff dimension d is used to describe the laws of scale invariance, which are exemplified by functions satisfying a mathematical law of the form f ( s x ) = s d f ( x ), being s the scale factor. Closely related is the problem of determining the fixed point of physical systems. Mathematically, the fixed point corresponds to a point in the domain of a function which is mapped to itself. In dynamical systems, it typically corresponds to the value to which the response of the system converge and stabilize. The present contribution aims to present the general concepts of scale invariance and fixed or critical points, employing such aspects to the problem of complex impedance association, both in series and in ladder configuration. The complex impedance, and transfer function of transmission lines and flow graphs related to the convergence the iterative equations to a fixed points are discussed in more details.

Dá-se o nome difração a um conjunto de fenômenos de natureza inerentemente ondulatória caracterizado pelo encurvamento, alargamento espacial e interferência de ondas que podem ser ondas mecânicas (som, ondas de água), eletromagnéticas ou ondas de matéria no caso da mecânica quântica. Neste trabalho a difração é abordada sob o ponto de vista de um princípio de incerteza e da superposição e interferência de soluções de ondas planas.

Diffraction is a set of inherently wave-like phenomena characterized by the bending, spreading and interference of waves which can be mechanical (sound included), electromagnetic or matter waves in quantum mechanics. In this paper we address the problem of diffraction under the viewpoint of uncertainty principle and superposition of plane waves and interference.