Investigation of electrical properties with medium and heavy Brazilian crude oils by electrochemical impedance spectroscopy

Objetivando conhecer como as atividades experimentais estao sendo abordadas na literatura especializada, realizamos uma revisao bibliografica que abarcou todos os artigos publicados na Revista Brasileira de Ensino de Fisica no periodo compreendido entre os anos de 2002 e 2017. Os 138 artigos encontrados versando sobre essa tematica foram classificados em relacao ao nivel de ensino a que foram destinados e quanto aos seus aspectos metodologicos em: i) Funcao Didatica: Atividades de Demonstracao, Verificacao e Investigacao; ii) Promocao de Conteudos Procedimentais; iii) Processo de Construcao do Aparato Experimental: Enfase no uso de tecnologia, de material de baixo custo e na montagem de equipamentos. No estudo realizado, verificamos que a maioria das publicacoes refere-se ao processo de construcao e aperfeicoamento de atividades experimentais e sao destinadas ao ensino superior . https://doi.org/10.33871/23594381.2020.18.1.136-166

/pdf/panorama-dos-artigos-sobre-atividades-experimentais-3g9wrm34hv.pdf

Panorama dos artigos sobre Atividades Experimentais publicados na Revista Brasileira de Ensino de Física no período compreendido entre 2002 e 2017

Honey is a natural product produced by honey bees whose composition depends on factors such as climate, soil and floral source. It is one of the foods naturally produced, with a characteristic taste and considerable nutritional value. Due to the worldwide demand for large-scale production and seasonality, adulteration has become increasingly frequent. Minas Gerais is the fourth largest Brazilian state producer of honey. Considering that there are few studies on the characterization of honeys in this state and none related to its mesoregions, the objective of this study was to evaluate the physical-chemical, electrical and rheological characteristics of 48 honeys collected in 6 mesoregions of Minas Gerais, corresponding to 75% of its production area. The present study focused on characterization, investigation of the possibility of adulteration and the influence of blossom and regions on the physical-chemical, rheological and electrical properties. Statistical characterization using principal component analysis and clustering were also used. The results suggested that the samples were compatible with the identity and quality standards recommended by Brazilian legislation. Furthermore, the results from rheological analysis and impedance spectroscopy showed that there was a profile specific for each type of blossom. The use of statistical methods on physical-chemical results was a useful tool to characterize different types of honey based on the variables of each group in relation to the similarity between the samples.

Physical-chemical characterization of commercial honeys from Minas Gerais, Brazil

Solid State Lighting technologies based on Organic Light Emitting Diodes, became an interesting focus due to their unique properties. The use of a unique RGB active layer for white emission, although simple in theory, shows difficulty to stabilize both CIE coordinates and color modulation. In this work, a WOLED using a simple RGB layer, was developed achieving a high color stability and shade modulation. The RGB matrix comprises a blue host material NPB, doped with two guests, a green (Coumarin 153) and a red (DCM1) in low concentrations. The RGB layer carrier dynamics allows for the white emission in low device complexity and high stability. This was also shown independent of the white shade, obtained through small changes in the red dopant resulting in devices ranging from warm to cool white i.e. an easy color tuning. A detailed analysis of the opto-electrical behavior is made.

/pdf/control-of-a-white-organic-light-emitting-diode-s-emission-4foqw061lc.pdf

Control of a white organic light emitting diode’s emission parameters using a single doped RGB active layer

spectroscopy (EIS) is a powerful tool for investigating material properties and the reactions that take place at the electrode interface. EIS has some advantages when compared to other electrochemical techniques, such as: (i) the use of sligth signals that do not change the electrode properties, (ii) the possibility of studying corrosion reactions, as well as measuring corrosion rates in low conductivity and (iii) determination of the electrical double layer capacitance and charge transfer resistance in a single measurement. Although there are numerous works in the literature that report the advantages of the EIS technique, there is a need for detailed work on the mathematical tooling, as well as some simple applications. In this sense, this bibliographic review work presents the historical context of the EIS technique, the basic principles and some applications in the areas of corrosion of metallic materials, supercapacitors and lithium-ion batteries.

/pdf/electrochemical-impedance-spectroscopy-basic-principles-and-11qo0ccd.pdf

Electrochemical Impedance Spectroscopy: Basic Principles and Some Applications

Neste trabalho, mostramos que uma configuracao desconhecida de um circuito montado com resistores e capacitores no interior de uma "caixa preta", pode ser determinada atraves de uma tecnica, conhecida como espectroscopia de impedância, largamente utilizada em varias areas da ciencia. Como essa tecnica faz uso da impedância complexa, apresentamos tambem uma introducao aos circuitos AC do ponto de vista do formalismo de numeros complexos. O arranjo experimental utiliza um gerador de audio como fonte AC para alimentar a caixa e um osciloscopio de duplo canal para medir tanto a parte real como a imaginaria da impedância complexa do circuito desconhecido em funcao da frequencia do gerador. A partir do espectro de impedância obtido, identifica-se nao so a configuracao do circuito no interior da caixa como tambem os valores das resistencias e capacitâncias utilizadas para monta-lo.

/pdf/espectroscopia-de-impedancia-no-laboratorio-de-ensino-ae5rdrdfra.pdf

Espectroscopia de impedância no laboratório de ensino

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Espectroscopia de impedância no laboratório de ensino