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Your search keyword '"Pereira, Marcelo B."' showing total 118 results
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118 results on '"Pereira, Marcelo B."'

5. The compound class of extended Weibull power series distributions

Author

Silva, Rodrigo B., Pereira, Marcelo B., Dias, Cícero R. B., and Cordeiro, Gauss M.

Subjects
Statistics - Methodology
Abstract

In this paper, we introduce a new class of distributions which is obtained by compounding the extended Weibull and power series distributions. The compounding procedure follows the same set-up carried out by Adamidis and Loukas (1998) and defines at least new 68 sub-models. This class includes some well-known mixing distributions, such as the Weibull power series (Morais and Barreto-Souza, 2010) and exponential power series (Chahkandi and Ganjali, 2009) distributions. Some mathematical properties of the new class are studied including moments and generating function. We provide the density function of the order statistics and obtain their moments. The method of maximum likelihood is used for estimating the model parameters and an EM algorithm is proposed for computing the estimates. Special distributions are investigated in some detail. An application to a real data set is given to show the flexibility and potentiality of the new class of distributions.

Published
2012

6. The Kumaraswamy Pareto distribution

Author

Pereira, Marcelo B., Silva, Rodrigo B., Zea, Luz M., and Cordeiro, Gauss M.

Subjects
Statistics - Methodology
Abstract

The modeling and analysis of lifetimes is an important aspect of statistical work in a wide variety of scientific and technological fields. For the first time, the called Kumaraswamy Pareto distribution is introduced and studied. The new distribution can have a decreasing and upside-down bathtub failure rate function depending on the values of its parameters. It includes as special sub-models the Pareto and exponentiated Pareto (Gupta et al. [12]) distributions. Some structural properties of the proposed distribution are studied including explicit expressions for the moments and generating function. We provide the density function of the order statistics and obtain their moments. The method of maximum likelihood is used for estimating the model parameters and the observed information matrix is derived. A real data set is used to compare the new model with widely known distributions.

Published
2012

8. Eucalyptus globulus essential oil thin film polymerized by cold plasma on Ti6Al4V: Sterilization effect, antibacterial activity, adhesion, and viability of mesenchymal stem cells

Author

da Silva Bullmann, Matheus, primary, de Castro, Victor Velho, additional, Coutinho, Daniel Augusto Krieger, additional, Lopes, Fernanda Cortez, additional, Maurmann, Natasha, additional, Pereira, Marcelo B., additional, Rodrigues, Miguel, additional, Pranke, Patricia, additional, Ferraz, Maria Pia, additional, Lopes, Maria Ascensão, additional, Arenas, Leliz Ticona, additional, and Malfatti, Célia de Fraga, additional

Published
2023
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22. Simple polarimetric approach to direct measurement of the near-surface refractive index in graded-index films

Author

Pereira, Marcelo B. and Horowitz, Flavio

Subjects
Astronomy, Physics
Abstract

In the standard M-line method for the characterization of graded-index films, an analytical curve is fitted to the waveguide mode measurements and extrapolated to provide the refractive index in the zero-depth limit. Here we review our polarimetric approach to a direct near-surface measurement, which complements the M-line method. Also, we present its new and more straightforward version, which is applicable to existing samples and does not require masking before ion exchange. OCIS codes: 310.6860, 120.5410.

Published
2003

25. Photosensitised Degradation of Organic Dyes by Visible Light Using Riboflavin Adsorbed on the Surface of TiO2 Nanotubes

Author

Backes, Claudio W., Scheffer, Francine R., Pereira, Marcelo B., Teixeira, Sérgio R., and Weibel, Daniel E.

Subjects
titanium dioxide, sensitiser, riboflavin, visible light, nanotubes
Abstract

Visible light-assisted degradation of indigo carmine (IC), methylene blue (MB) and methyl orange (MO) aqueous solutions has been achieved on the surface of TiO2 nanotube (NT) arrays impregnated with riboflavin (RF). Diluted RF water solutions in the presence of RF-TiO2 NTs irradiated with UV light produced O2, CO and CO2 as main gas products. On the contrary, the same solutions irradiated with visible light evolved O2 as a main product. This in situ O2 generation under visible light absorption allows the degradation of the dyes without the necessity to bubble air or oxygen in the reaction system The photocatalytic degradation of MO, MB and IC can be described by a pseudo-first-order kinetic model obtaining ca. 100% degradation of MB, MO and IC in less than 3 h of visible light illumination. The results provided here are highly promising in view of various photocatalytic applications of the prepared RF-TiO2 NTs catalysts by two environmentally friendly compounds in the degradation of pollutants using solar radiation. A degradação de soluções aquosas de índigo carmim (IC), azul de metileno (MB) e laranja de metilo (MO) assistida pela luz visível foi conseguida sobre a superfície de nanotubos (NTs) de TiO2 impregnados com riboflavina (RF). Soluções aquosas diluídas de RF na presença de RF-NTs TiO2 irradiados com luz UV produziram O2, CO e CO2 como principais produtos gasosos. As mesmas soluções quando irradiadas com luz visível mostraram que o O2 foi o produto principal obtido. Esta geração de O2 in situ com luz visível permite a degradação dos corantes, sem a necessidade de borbulhar ar ou oxigênio no sistema de reação. A degradação fotocatalítica de MO, MB e IC pode ser descrita por um modelo de cinética de pseudo-primeira ordem obtendo ca. 100% de degradação de MB, MO e IC em menos de 3 h de iluminação de luz visível. Os resultados aqui apresentados são altamente promissores em vista da potencial aplicação dos catalisadores RF‑TiO2 NTs preparados com dois compostos ambientalmente corretos na degradação de poluentes utilizando radiação solar.

Published
2014

26. Effects of the large distribution of CdS quantum dot sizes on the charge transfer interactions into TiO2 nanotubes for photocatalytic hydrogen generation

Author

Gonzalez-Moya, Johan R., Garcia-Basabe, Yunier, Rocco, Maria Luiza M., Pereira, Marcelo B., Princival, Jefferson L., Almeida, Luciano C., Araujo, Carlos M., David, Denis G. F., da Silva, Antonio Ferreira, Machado, Giovanna, Gonzalez-Moya, Johan R., Garcia-Basabe, Yunier, Rocco, Maria Luiza M., Pereira, Marcelo B., Princival, Jefferson L., Almeida, Luciano C., Araujo, Carlos M., David, Denis G. F., da Silva, Antonio Ferreira, and Machado, Giovanna

Abstract

Hydrogen fuels generated by water splitting using a photocatalyst and solar irradiation are currently gaining the strength to diversify the world energy matrix in a green way. CdS quantum dots have revealed a hydrogen generation improvement when added to TiO2 materials under visible-light irradiation. In the present paper, we investigated the performance of TiO2 nanotubes coupled with CdS quantum dots, by a molecular bifunctional linker, on photocatalytic hydrogen generation. TiO2 nanotubes were obtained by anodization of Ti foil, followed by annealing to crystallize the nanotubes into the anatase phase. Afterwards, the samples were sensitized with CdS quantum dots via an in situ hydrothermal route using 3-mercaptopropionic acid as the capping agent. This sensitization technique permits high loading and uniform distribution of CdS quantum dots onto TiO2 nanotubes. The XPS depth profile showed that CdS concentration remains almost unchanged (homogeneous), while the concentration relative to the sulfate anion decreases by more than 80% with respect to the initial value after similar to 100 nm in depth. The presence of sulfate anions is due to the oxidation of sulfide and occurs in greater proportion in the material surface. This protection for air oxidation inside the nanotubular matrix seemingly protected the CdS for photocorrosion in sacrificial solution leading to good stability properties proved by long duration, stable photocurrent measurements. The effect of the size and the distribution of sizes of CdS quantum dots attached to TiO2 nanotubes on the photocatalytic hydrogen generation were investigated. The experimental results showed three different behaviors when the reaction time of CdS synthesis was increased in the sensitized samples, i.e. similar, deactivation and activation effects on the hydrogen production with regard to TiO2 nanotubes. The deactivation effect was related to two populations of sizes of CdS, where the population with a shorter band gap ac

Published
2016
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27. Effects of the large distribution of CdS quantum dot sizes on the charge transfer interactions into TiO2 nanotubes for photocatalytic hydrogen generation

Author

González-Moya, Johan R, Garcia-Basabe, Yunier, Rocco, Maria Luiza M, Pereira, Marcelo B, Princival, Jefferson L, Almeida, Luciano C, Araujo, C Moyses, David, Denis G F, da Silva, Antonio Ferreira, Machado,, Giovanna, González-Moya, Johan R, Garcia-Basabe, Yunier, Rocco, Maria Luiza M, Pereira, Marcelo B, Princival, Jefferson L, Almeida, Luciano C, Araujo, C Moyses, David, Denis G F, da Silva, Antonio Ferreira, and Machado,, Giovanna

Abstract

Hydrogen fuels generated by water splitting using a photocatalyst and solar irradiation are currently gaining the strength to diversify the world energy matrix in a green way. CdS quantum dots have revealed a hydrogen generation improvement when added to TiO2 materials under visible-light irradiation. In the present paper, we investigated the performance of TiO2 nanotubes coupled with CdS quantum dots, by a molecular bifunctional linker, on photocatalytic hydrogen generation. TiO2 nanotubes were obtained by anodization of Ti foil, followed by annealing to crystallize the nanotubes into the anatase phase. Afterwards, the samples were sensitized with CdS quantum dots via an in situ hydrothermal route using 3-mercaptopropionic acid as the capping agent. This sensitization technique permits high loading and uniform distribution of CdS quantum dots onto TiO2 nanotubes. The XPS depth profile showed that CdS concentration remains almost unchanged (homogeneous), while the concentration relative to the sulfate anion decreases by more than 80% with respect to the initial value after ~100 nm in depth. The presence of sulfate anions is due to the oxidation of sulfide and occurs in greater proportion in the material surface. This protection for air oxidation inside the nanotubular matrix seemingly protected the CdS for photocorrosion in sacrificial solution leading to good stability properties proved by long duration, stable photocurrent measurements. The effect of the size and the distribution of sizes of CdS quantum dots attached to TiO2 nanotubes on the photocatalytic hydrogen generation were investigated. The experimental results showed three different behaviors when the reaction time of CdS synthesis was increased in the sensitized samples, i.e. similar, deactivation and activation effects on the hydrogen production with regard to TiO2 nanotubes. The deactivation effect was related to two populations of sizes of CdS, where the population with a shorter band gap acts as a tr

Published
2016

29. Effects of the large distribution of CdS quantum dot sizes on the charge transfer interactions into TiO2nanotubes for photocatalytic hydrogen generation

Author

González-Moya, Johan R, primary, Garcia-Basabe, Yunier, additional, Rocco, Maria Luiza M, additional, Pereira, Marcelo B, additional, Princival, Jefferson L, additional, Almeida, Luciano C, additional, Araújo, Carlos M, additional, David, Denis G F, additional, da Silva, Antonio Ferreira, additional, and Machado, Giovanna, additional

Published
2016
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33. Silver Nanoparticle Thin Films Deposited on Glass Surface Using an Ionic Silsesquioxane as Stabilizer and as Crosslinking Agent

Author

Schneid, Andressa C., primary, Pereira, Marcelo B., additional, Horowitz, Flavio, additional, Mauler, Raquel S., additional, Matte, Carla R., additional, Klein, Manuela P., additional, Hertz, Plinho F., additional, Costa, Tania M. H., additional, Menezes, Eliana W. de, additional, and Benvenutti, Edilson V., additional

Published
2015
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