D. Francisco Manuel de Melo, historiador

Oliveira, António de

doi:10.14195/978-989-26-0245-5_11

Cited by 3 publications

(7 citation statements)

References 2 publications

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“…The frequency independent part corresponds to the free charge carrier transport and the frequencydispersed portion reflects the response of the bound charges. Now as the temperature increases, the thermally activated charge carriers participate more and more to the transport and as a result the frequency up to which the limiting dc value prevails extends along with decrease in the impedance of the nanocomposites [24,61,62]. The presence of two regions is also manifested in the Z 00 versus f graphs where a broad relaxation peak appears which shifts towards higher frequencies with increase in temperature.…”

Section: Resultsmentioning

confidence: 99%

“…Dielectric characteristics of Methyl orange (MO)/polyvinyl alcohol films were studied by Oliveira and de Melo [24] in the temperature range 294 K to 370 K and they observed that incorporation of the methyl orange aggregation in the matrix enhances the effective charge transport and affects the dielectric properties significantly. They have found that electrical properties of the polymeric films can also be altered by incident light, based on which they had proposed that this PVA composite can be considered in designing solid state memory devices.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of the dielectric relaxation and ac conductivity behavior of polyvinyl alcohol‐cadmium selenide nanocomposite films

et al. 2015

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We adopt an analytical approach to study the dielectric relaxation and ac conductivity behavior of the polyvinyl alcohol (PVA) -Cadmium Selenide (CdSe) nanocomposite films in the frequency range 100 Hz £ f £ 1 MHz and in the temperature range 298 K £ T £ 420 K. The CdSe nanoparticles are synthesized via a simple wet chemical route and are then impregnated into the polyvinyl alcohol matrix by 0.5 wt%, 1 wt%, and 4 wt%. About 1.7 times increase in effective permittivity (at 100 KHz) for the 4 wt% nanoparticle impregnated sample is observed from the analysis of the dielectric reinforcement function, which is attributed to the occurrence of interfacial polarization. It is found that the Cole-Cole model with a dc conductivity correction term can well fit the permittivity data. We have found that the dielectric relaxation time increases with increase in nanoinclusion into the matrix but decreases with increase in temperature. However, the space charge carrier conductivity and free charge carrier conductivity increase either with increase in nano inclusions or with increase in temperature. AC conductivity behavior have been analyzed considering the Jonscher power law and Dyre's random free energy barrier model, which reveals lowering of the maximum barrier height and correlated barrier hopping as the prevalent charge transport mechanism for the nanocomposites. Electric modulus study indicates similar conductivity relaxation dynamics for the nanocomposites but the responses deviate appreciably from the simulated ideal Debye responses. POLYM. COMPOS., 00:000-000, 2015.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Analysis of the dielectric relaxation and ac conductivity behavior of polyvinyl alcohol‐cadmium selenide nanocomposite films

et al. 2015

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“…Eqs. (85)(86)(87)(88)(89)(90)(91)(92)(93)(94)(95)(96) constitute non-perturbative constraints on the fermion-photon vertex: for every Ansatz for the Yfunctions, the resulting function W is restricted to guarantee the integral constraint (85), so that the MR of the fermion propagator is ensured. To bring out the applicability and scope of the integral constraint on the massless Y -functions, Eq.…”

Section: Mr Constraintsmentioning

confidence: 99%

“…Therefore, physically meaningful truncations of QCD's SDEs demand incorporation of DCSB through the relevant Green functions, in particular the quark propagator and the quark-gluon vertex. Regarding the latter, valuable progress has been made both in lattice, [85][86][87][88][89][90][91] and continuum studies. However, due to the non-abelian nature of QCD, investigating the impact of DCSB on the quark-gluon vertex, and vice versa, from the first principles, is still a theoretical challenge.…”

Section: Introductionmentioning

confidence: 99%

Transverse Takahashi identities and their implications for gauge independent dynamical chiral symmetry breaking

et al. 2019

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In this article, we employ transverse Takahashi identities to impose valuable non-perturbative constraints on the transverse part of the fermion-photon vertex in terms of new form factors, the so called Yi functions. We show that the implementation of these identities is crucial in ensuring the correct local gauge transformation of the fermion propagator and its multiplicative renormalizability. Our construction incorporates the correct symmetry properties of the Yi under charge conjugation operation as well as their well-known one-loop expansion in the asymptotic configuration of incoming and outgoing momenta. Furthermore, we make an explicit analysis of various existing constructions of this vertex against the demands of transverse Takahashi identities and the previously established key features of quantum electrodynamics, such as gauge invariance of the critical coupling above which chiral symmetry is dynamically broken. We construct a simple example in its quenched version and compute the mass function as we vary the coupling strength and also calculate the corresponding anomalous dimensions γm. There is an excellent fit to the Miransky scalling law and we find γm = 1 rather naturally in accordance with some earlier results in literature, using arguments based on Cornwall-Jackiw-Tomboulis effective potential technique. Moreover, we numerically confirm the gauge invariance of this critical coupling.

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“…1. Observou-se uma perda de massa contínua entre a temperatura ambiente e 900 ºC, atribuída à eliminação de água adsorvida e à decomposição dos aminoácidos presentes na estrutura orgânica da gelatina [17]. As amostras apresentaram pequenas quantidades de perda de massa, sendo 5,3% e 5% para os pós CoCr 2 O 4 e Co x Zn 1-x Cr 2 O 4 , respectivamente.…”

Section: Resultsunclassified

Pigmentos à base de cobalto para aplicação em revestimentos cerâmicos

et al. 2020

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ResumoPigmentos inorgânicos foram preparados com estrutura espinélio para aplicações em revestimentos cerâmicos. Pigmentos com composição CoCr 2 O 4 e Co 0,8 Zn 0,2 Cr 2 O 4 foram sintetizados por uma rota química usando gelatina de uso farmacêutico como precursor orgânico. Foram investigadas a influência da dopagem e a temperatura de tratamento térmico na coloração dos pigmentos e dos esmaltes cerâmicos. Os materiais foram caracterizados por análise termogravimétrica, difração de raios X, microscopia eletrônica de varredura, espectroscopia por energia dispersiva, espectroscopia na região do UV-visível e colorimetria. Os pós apresentaram estrutura espinélio a partir de 500 °C, com formação de fase secundária residual de Cr 2 O 3 nas amostras Co 0,8 Zn 0,2 Cr 2 O 4 tratadas termicamente a 500 e 1000 °C. Os pigmentos e os esmaltes preparados apresentaram cores em tons de azul esverdeado para as amostras CoCr 2 O 4 e verde para a amostra Co 0,8 Zn 0,2 Cr 2 O 4 . Os resultados confirmaram a efetividade da rota de síntese utilizada para produzir óxidos com estrutura espinélio. Palavras-chave: síntese de espinélios, pigmentos cerâmicos, gelatina. AbstractInorganic pigments were prepared with spinel structure for applications in ceramic tiles. Pigments with composition CoCr 2 O 4 and Co 0.8 Zn 0.2 Cr 2 O 4 were synthesized by a chemical route using gelatin for pharmaceutical use as an organic precursor. The influences of doping and thermal treatment temperature on pigment and ceramic glaze color were investigated. The materials were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, dispersive energy spectroscopy, spectroscopy in the UV-visible region and colorimetry. The powders treated at 500 °C presented spinel structure, with the formation of residual secondary phase of Cr 2 O 3 in samples Co 0.8 Zn 0.2 Cr 2 O 4 heat-treated at 500 and 1000 °C. The prepared pigments and glazes presented blue-green colors for the samples CoCr 2 O 4 and green color for the sample Co 0.8 Zn 0.2 Cr 2 O 4 . The results confirmed the effectiveness of the synthesis route used to produce oxides with a spinel structure.

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D. Francisco Manuel de Melo, historiador

Cited by 3 publications

References 2 publications

Analysis of the dielectric relaxation and ac conductivity behavior of polyvinyl alcohol‐cadmium selenide nanocomposite films

Analysis of the dielectric relaxation and ac conductivity behavior of polyvinyl alcohol‐cadmium selenide nanocomposite films

Transverse Takahashi identities and their implications for gauge independent dynamical chiral symmetry breaking

Pigmentos à base de cobalto para aplicação em revestimentos cerâmicos

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