47 results on '"Chaves, Anderson"'
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2. Magnesium whitlockite nanoparticles: Hydrothermal synthesis, anti-inflammatory and anti-cancer potential
- Author
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Maximiano, Laila Véras, Correa, Luana Barbosa, Gomes-da-Silva, Natália Cristina, da Costa, Luelc Souza, Da Silva, Maria Graciele Pereira, Chaves, Anderson Valério, Franco, Michel Lopes, Fechine, Pierre Basílio Almeida, de Menezes, Alan Silva, Santos-Oliveira, Ralph, and Andrade Neto, Davino Machado
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- 2024
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3. Microbiological, physicomechanical, and surface evaluation of an experimental self-curing acrylic resin containing halloysite nanotubes doped with chlorhexidine
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Timbó, Isabelle C.G., Oliveira, Mayara S.C.S., Lima, Ramille A., Chaves, Anderson V., Pereira, Vanessa de A., Fechine, Pierre B.A., and Regis, Romulo R.
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- 2024
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4. CALANGO: A phylogeny-aware comparative genomics tool for discovering quantitative genotype-phenotype associations across species
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Hongo, Jorge Augusto, de Castro, Giovanni Marques, Albuquerque Menezes, Alison Pelri, Rios Picorelli, Agnello César, Martins da Silva, Thieres Tayroni, Imada, Eddie Luidy, Marchionni, Luigi, Del-Bem, Luiz-Eduardo, Vieira Chaves, Anderson, Almeida, Gabriel Magno de Freitas, Campelo, Felipe, and Lobo, Francisco Pereira
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- 2023
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5. Chemical modification of clay nanocomposites for the improvement of the catalytic properties of Lipase A from Candida antarctica
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Cavalcante, Antônio Luthierre Gama, Chaves, Anderson Valério, Fechine, Pierre Basílio Almeida, Holanda Alexandre, Jeferson Yves Nunes, Freire, Tiago Melo, Davi, Dalila Maria Barbosa, Neto, Francisco Simão, de Sousa, Isamayra Germano, da Silva Moreira, Katerine, de Oliveira, André Luiz Barros, de Mattos, Marcos Carlos, Oliveira, Maria Conceição Ferreira, de Brito, Maria Vieira, Ballereau, Stéphanie, Bernardes-Génisson, Vania, da Fonseca, Aluísio Marques, and dos Santos, José C.S.
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- 2022
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6. Taguchi design-assisted co-immobilization of lipase A and B from Candida antarctica onto chitosan: Characterization, kinetic resolution application, and docking studies
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da S. Moreira, Katerine, Barros de Oliveira, André Luiz, Saraiva de Moura Júnior, Lourembergue, Germano de Sousa, Isamayra, Luthierre Gama Cavalcante, Antonio, Simão Neto, Francisco, Bussons Rodrigues Valério, Roberta, Valério Chaves, Anderson, de Sousa Fonseca, Thiago, Morais Vieira Cruz, Daniel, Vieira Lima, Gledson, de Oliveira, Gabriel Paixão, de Souza, Maria Cristiane Martins, Basílio Almeida Fechine, Pierre, de Mattos, Marcos Carlos, Marques da Fonseca, Aluísio, and dos Santos, José C.S.
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- 2022
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7. A novel hybrid biocatalyst from immobilized Eversa® Transform 2.0 lipase and its application in biolubricant synthesis.
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Germano de Sousa, Isamayra, Valério Chaves, Anderson, de Oliveira, André Luiz Barros, da Silva Moreira, Katerine, Gonçalves de Sousa Junior, Paulo, Simão Neto, Francisco, Cristina Freitas de Carvalho, Simone, Bussons Rodrigues Valério, Roberta, Vieira Lima, Gledson, Sanders Lopes, Ada Amélia, Martins de Souza, Maria Cristiane, da Fonseca, Aluísio Marques, Fechine, Pierre Basílio Almeida, de Mattos, Marcos Carlos, and dos Santos, José C. S.
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LIPASES , *GLUTARALDEHYDE , *ENZYMES , *FOURIER transform infrared spectroscopy , *ORGANIC solvents , *IONIC strength - Abstract
In this study, a Taguchi experimental design was used for optimzing the immobilization of the lipase Eversa® Transform 2.0 (EVS) onto a hybrid support consisting of chitosan (CHI) and agarose (AGA), with glutaraldehyde (GLU) used as the support activator. The biocatalyst obtained was characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetry (TGA), Energy Dispersive Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). The optimized reaction conditions (60 min, 5 mM ionic strength, 1% GLU concentration, and 5 mg protein load per g of support) resulted in a highly active biocatalyst (74.39 ± 0.48 U/g) and delivered an immobilization yield of 74.20 ± 0.28%. The biocatalyst produced was observed to lose only 15.3% of its activity after 61 days of storage. The activity was also observed to increase by 96.70% ± 0.76, 27.34% ± 2.34, and 84.35% ± 1.68 in the presence of the organic solvents hexane, cyclohexane, and methanol, respectively. Additionally, the byocatalist showed more pronounced activity at temperatures above 50 °C and was still able to retain approximately 30% of it at 70 °C. These values were found to be higher at alkaline pHs, as the activity of Eversa® 2.0 Transform saw an increase of up to 140% at pH 9. The desorption tests performed did not reveal any enzymatic detachment from the support. The novel biocatalyst also showed promising ester-lubricating properties. Furthermore, the in silico study revealed a binding affinity of −5.1 kcal/mol between oleic acid and the enzyme, suggesting that the combination of the substrate and the lipase was more stable and therefore, suitable for esterification. [ABSTRACT FROM AUTHOR]
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- 2024
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8. Computational prediction of high thermoelectric performance in As2Se3 by engineering out-of-equilibrium defects.
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Chaves, Anderson Silva, Silva, Murilo Aguiar, and Antonelli, Alex
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We employed first-principles calculations to investigate the thermoelectric transport properties of the compound As
2 Se3 . Early experiments and calculations have indicated that these properties are controlled by a kind of native defect called antisites. Our calculations using the linearized Boltzmann transport equation within the relaxation time approximation show good agreement with the experiments for defect concentrations of the order of 1019 cm−3 . Based on our total energy calculations, we estimated the equilibrium concentration of antisite defects to be about 1014 cm−3 . These results suggest that the large concentration of defects in the experiments is due to kinetic and/or off-stoichiometry effects and in principle it could be lowered, yielding relaxation times similar to those found in other chalcogenide compounds. In this case, for relaxation time higher than 10 fs, we obtained high thermoelectric figures of merit of 3 for the p-type material and 2 for the n-type one. [ABSTRACT FROM AUTHOR]- Published
- 2024
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9. Spatial ecology and conservation of the microendemic ovenbird Cipo Cinclodes (Cinclodes espinbacensis) from the Brazilian highlands
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Freitas, Guilherme H. S., Costa, Lílian M., Silva, Pedro H. V. B. P., Chaves, Anderson V., Ribeiro, Leonardo C., and Rodrigues, Marcos
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- 2019
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10. Augmenting the algebraic connectivity for certain families of graphs
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Justel, Claudia, Rocha, Carlos, Chaves, Emanuelle, Chaves, Anderson, and Avelino, Geraldo
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- 2019
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11. Trade-offs and resource breadth processes as drivers of performance and specificity in a host–parasite system: a new integrative hypothesis
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Pinheiro, Rafael B.P., Félix, Gabriel M.F., Chaves, Anderson V., Lacorte, Gustavo A., Santos, Fabrício R., Braga, Érika M., and Mello, Marco A.R.
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- 2016
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12. Outstanding thermoelectric performance predicted for out-of-plane p-doped GeSe
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Chaves, Anderson S., Larson, Daniel T., Kaxiras, Efthimios, and Antonelli, Alex
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Condensed Matter - Materials Science ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
The record-breaking thermoelectric performance of tin selenide (SnSe) has motivated the investigation of analogue compounds with the same structure. A promising candidate that emerged recently is germanium selenide (GeSe). Here, using extensive first-principles calculations of the hole-phonon and hole-impurity scattering, we investigate the thermoelectric transport properties of the orthorhombic phase of p-doped GeSe. We predict outstanding thermoelectric performance for GeSe over a broad range of temperatures due to its high Seebeck coefficients, extremely low Lorenz numbers, ultralow total thermal conductivity, and relatively large band gap. In particular, the out-of-plane direction in GeSe presents equivalent or even higher performance than SnSe for temperatures above 500 K. By extending the analysis to 900 K, we obtained an ultrahigh value for the thermoelectric figure of merit (zT = 3.2) at the optimal hole density of 4x10^19 cm^-3. Our work provides strong motivation for continued experimental work focusing on improving the GeSe doping efficiency in order to achieve this optimal hole density., 13 pages, 7 figures
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- 2022
13. Chitosan-Based Nanoparticles for Cardanol-Sustained Delivery System.
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Valério, Roberta Bussons Rodrigues, da Silva, Nilvan Alves, Junior, José Ribamar Paiva, Chaves, Anderson Valério, de Oliveira, Bruno Peixoto, Souza, Nágila Freitas, de Morais, Selene Maia, Santos, José Cleiton Sousa dos, and Abreu, Flávia Oliveira Monteiro da Silva
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CASHEW nuts ,POLYSACCHARIDES ,INFRARED spectra ,NANOPARTICLES ,ALGINATES ,SODIUM alginate ,FREE radicals ,CHITOSAN - Abstract
Cardanol, principal constituent of the technical cashew nut shell liquid, has applications as antioxidant and antibacterial, and these properties may be enhanced through encapsulation. In the present study, we isolated and purified cardanol, and nanoparticles (NPs) were produced by polyelectrolyte complexation using polysaccharide systems with chitosan, sodium alginate, and non-toxic Arabic gum, because they are biocompatible, biodegradable, and stable. We characterized the NPs for morphological, physicochemical, and antioxidant activity. The micrographs obtained revealed spherical and nanometric morphology, with 70% of the distribution ranging from 34 to 300 nm, presenting a bimodal distribution. The study of the spectra in the infrared region suggested the existence of physicochemical interactions and cross-links between the biopolymers involved in the encapsulated NPs. Furthermore, the NPs showed better antioxidant potential when compared to pure cardanol. Thus, the encapsulation of cardanol may be an effective method to maintain its properties, promote better protection of the active ingredient, minimize side effects, and can target its activities in specific locations, by inhibiting free radicals in various sectors such as pharmaceutical, nutraceutical, and biomedical. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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14. Microscopic origin of the excellent thermoelectric performance in n-doped SnSe
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Chaves, Anderson S., Larson, Daniel T., Kaxiras, Efthimios, and Antonelli, Alex
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Condensed Matter - Materials Science ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
Excellent thermoelectric performance in the out-of-layer n-doped SnSe has been observed experimentally (Chang et al., Science 360, 778-783 (2018)). However, a first-principles investigation of the dominant scattering mechanisms governing all thermoelectric transport properties is lacking. In the present work, by applying extensive first-principles calculations of electron-phonon coupling associated with the calculation of the scattering by ionized impurities, we investigate the reasons behind the superior figure of merit as well as the enhancement of zT above 600 K in n-doped out-of-layer SnSe, as compared to p-doped SnSe with similar carrier densities. For the n-doped case, the relaxation time is dominated by ionized impurity scattering and increases with temperature, a feature that maintains the power factor at high values at higher temperatures and simultaneously causes the carrier thermal conductivity at zero electric current (k_el) to decrease faster for higher temperatures, leading to an ultrahigh-zT = 3.1 at 807 K. We rationalize the roles played by k_el and k^0 (the thermal conductivity due to carrier transport under isoelectrochemical conditions) in the determination of zT. Our results show the ratio between k^0 and the lattice thermal conductivity indeed corresponds to the upper limit for zT, whereas the difference between calculated zT and the upper limit is proportional to k_el., 12 pages, 5 figures
- Published
- 2021
15. DJEnsemble: On the Selection of a Disjoint Ensemble of Deep Learning Black-Box Spatio-Temporal Models
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Souto, Yania Molina, Pereira, Rafael, Zorrilla, Roc��o, Chaves, Anderson, Tsan, Brian, Rusu, Florin, Ogasawara, Eduardo, Ziviani, Artur, and Porto, Fabio
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FOS: Computer and information sciences ,Computer Science - Machine Learning ,Artificial Intelligence (cs.AI) ,Computer Science - Artificial Intelligence ,Machine Learning (cs.LG) - Abstract
In this paper, we present a cost-based approach for the automatic selection and allocation of a disjoint ensemble of black-box predictors to answer predictive spatio-temporal queries. Our approach is divided into two parts -- offline and online. During the offline part, we preprocess the predictive domain data -- transforming it into a regular grid -- and the black-box models -- computing their spatio-temporal learning function. In the online part, we compute a DJEnsemble plan which minimizes a multivariate cost function based on estimates for the prediction error and the execution cost -- producing a model spatial allocation matrix -- and run the optimal ensemble plan. We conduct a set of extensive experiments that evaluate the DJEnsemble approach and highlight its efficiency. We show that our cost model produces plans with performance close to the actual best plan. When compared against the traditional ensemble approach, DJEnsemble achieves up to $4X$ improvement in execution time and almost $9X$ improvement in prediction accuracy. To the best of our knowledge, this is the first work to solve the problem of optimizing the allocation of black-box models to answer predictive spatio-temporal queries.
- Published
- 2020
16. Density functional investigation of the adsorption effects of PH3 and SH2 on the structure stability of the Au55 and Pt55 nanoclusters.
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Guedes-Sobrinho, Diego, Chaves, Anderson S., Piotrowski, Maurício J., and Da Silva, Juarez L. F.
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METAL clusters , *DENSITY functional theory , *ADSORBATES , *ADSORPTION (Chemistry) , *ICOSAHEDRA - Abstract
Although several studies have been reported for Pt55 and Au55 nanoclusters, our atomistic understanding of the interplay between the adsorbate-surface interactions and the mechanisms that lead to the formation of the distorted reduced core (DRC) structures, instead of the icosahedron (ICO) structure in gas phase, is still far from satisfactory. Here, we report a density functional theory (DFT) investigation of the role of the adsorption effects of PH3 (one lone pair of electrons) and SH2 (two lone pairs) on the relative stability of the Pt55 and Au55 nanoclusters. In gas phase, we found that the DRC structures with 7 and 9 atoms in the core region are about 5.34 eV (Pt55) and 2.20 eV (Au55) lower in energy than the ICO model with Ih symmetry and 13 atoms in the core region. However, the stability of the ICO structure increases by increasing the number of adsorbed molecules from 1 to 18, in which both DRC and ICO structures are nearly degenerate in energy at the limit of 18 ligands, which can be explained as follows. In gas phase, there is a strong compression of the cationic core region by the anionic surface atoms induced by the attractive Coulomb interactions (core+-surface-), and hence, the strain release is obtained by reducing the number of atoms in the cationic core region, which leads to the 55 atoms distorted reduced core structures. Thus, the Coulomb interactions between the core+ and surface- contribute to break the symmetry in the ICO55 structure. On the other hand, the addition of ligands on the anionic surface reduces the charge transfer between the core and surface, which contributes to decrease the Coulomb interactions and the strain on the core region of the ICO structure, and hence, it stabilizes a compact ICO structure. The same conclusion is obtained by adding van der Waals corrections to the plain DFT calculations. Similar results are obtained by the addition of steric effects, which are considered through the adsorption of triphenylphosphine (PPh3) molecules on Au55, in which the relative stability between ICO and DRC is the same as for PH3 and SH2. However, for Pt55, we found an inversion of stability due to the PPh3 ligand effects, where ICO has higher stability than DRC by 2.40 eV. Our insights are supported by several structural, electronic, and energetic analyses. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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17. A theoretical investigation of the structural and electronic properties of 55-atom nanoclusters: The examples of Y-Tc and Pt.
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Batista, Krys E. A., Piotrowski, Maurício J., Chaves, Anderson S., and Da Silva, Juarez L. F.
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ATOMIC clusters ,ELECTRIC properties ,SURFACE chemistry ,TRANSITION metals ,DENSITY functional theory ,POLAR effects (Chemistry) - Abstract
Several studies have found that the Pt55 nanocluster adopts a distorted reduced core structure, DRC
55 , in which there are 8-11 atoms in the core and 47-44 atoms in the surface, instead of the compact and high-symmetry icosahedron structure, ICO55 , with 13 and 42 atoms in the core and surface, respectively. The DRC structure has also been obtained as the putative global minimum configuration (GMC) for the Zn55 (3d), Cd55 (4d), and Au55 (5d) systems. Thus, the DRC55 structure has been reported only for systems with a large occupation of the d-states, where the effects of the occupation of the valence anti-bonding d-states might play an important role. Can we observe the DRC structure for 55-atom transition-metal systems with non-occupation of the anti-bonding d-states? To address this question, we performed a theoretical investigation of the Y55 , Zr55 , Nb55 , Mo55 , Tc55 , and Pt55 nanoclusters, employing density functional theory calculations. For the putative GMCs, we found that the Y55 adopts the ICO55 structure, while Nb55 and Mo55 adopt a bulk-like fragment based on the hexagonal close-packed structure and Tc55 adopts a face-centered cubic fragment; however, Zr55 adopts a DRC55 structure, like Zn55 , Cd55 , Pt55 , and Au55 . Thus we can conclude that the preference for DRC55 structure is not related to the occupation of the anti-bonding d-states, but to a different effect, in fact, a combination of structural and electronic effects. Furthermore, we obtained that the binding energy per atom follows the occupation of the bonding and anti-bonding model, i.e., the stability of the studied systems increases from Y to Tc with a small oscillation for Mo, which also explains the equilibrium bond lengths. We obtained a larger magnetic moment for Y55 (31 μB) which can be explained by the localization of the d-states in Y at nanoscale, which is not observed for the remaining systems (0-1 μB). [ABSTRACT FROM AUTHOR]- Published
- 2016
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18. Hydroxyapatite-Based Magnetic Bionanocomposite as Pharmaceuticals Carriers in Chitosan Scaffolds.
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Chaves, Anderson Valério, Freire, Rafael Melo, Feitosa, Victor Pinheiro, Pontes Silva Ricardo, Nágila Maria, Denardin, Juliano Casagrande, Andrade Neto, Davino Machado, and Almeida Fechine, Pierre Basílio
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HYDROXYAPATITE ,MAGNETIC nanoparticles ,CHITOSAN ,BIOCERAMICS ,OSTEOBLASTS - Abstract
Hydroxyapatite (HA) is a bioceramic very similar to the mineral component of bones and teeth. It is well established that osteoblasts grow better onto HA-coated metals than on metals alone. Herein, the preparation of a new system consisting of magnetite (Fe3O4 ) and HA functionalized with oleic acid and simvastatin (SIMV), and incorporated in chitosan (CHI) scaffolds, was undertaken. HA was synthesized by the hydrothermal method, while Fe3O4 was synthesized by co-precipitation. The polymer matrix was obtained using a 2% CHI solution, and allowed to stir for 2 h. The final material was freeze-dried to produce scaffolds. The magnetic properties remained unchanged after the formation of the composite, as well as after the preparation of the scaffolds, maintaining the superparamagnetism. CHI scaffolds were analyzed by scanning electronic spectroscopy (SEM) and showed a high porosity, with very evident cavities, which provides the functionality of bone growth support during the remineralization process in possible regions affected by bone tissue losses. The synthesized composite showed an average particle size between 15 and 23 nm for particles (HA and Fe3O4 ). The scaffolds showed considerable porosity, which is important for the performance of various functions of the tissue structure. Moreover, the addition of simvastatin in the system can promote bone formation. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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19. Investigating charge carrier scattering processes in anisotropic semiconductors through first-principles calculations: the case of p-type SnSe.
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Chaves, Anderson S., González-Romero, Robert Luis, Meléndez, Juan J., and Antonelli, Alex
- Abstract
Efficient ab initio computational methods for the calculation of the thermoelectric transport properties of materials are of great interest for energy harvesting technologies. The constant relaxation time approximation (CRTA) has been largely used to efficiently calculate thermoelectric coefficients. However, CRTA usually does not hold for real materials. Here we go beyond the CRTA by incorporating realistic k-dependent relaxation time models of the temperature dependence of the main scattering processes, namely, screened polar and nonpolar scattering by optical phonons, scattering by acoustic phonons, and scattering by ionized impurities with screening. Our relaxation time models are based on a smooth Fourier interpolation of Kohn–Sham eigenvalues and its derivatives, taking into account non-parabolicity (beyond the parabolic or Kane models), degeneracy and multiplicity of the energy bands on the same footing, within very low computational cost. In order to test our methodology, we calculated the anisotropic thermoelectric transport properties of the low temperature phase (Pnma) of intrinsic p-type and hole-doped tin selenide (SnSe). Our results are in quantitative agreement with experimental data, regarding the evolution of the anisotropic thermoelectric coefficients with both temperature and chemical potential. Hence, from this picture, we also obtained the evolution and understanding of the main scattering processes of the overall thermoelectric transport in p-type SnSe. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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20. Geographic range and conservation of the Cipo Canastero Asthenes luizae , an endemic furnariid of Brazilian sky islands.
- Author
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FREITAS, GUILHERME H. S., COSTA, LÍLIAN M., CHAVES, ANDERSON V., VASCONCELOS, MARCELO F., RIBEIRO, LEONARDO C., SILVA, JULIANO C., SOUZA, RONEY A., SANTOS, FABRÍCIO R., and RODRIGUES, MARCOS
- Abstract
Summary: Cipo Canastero Asthenes luizae is a relict ovenbird restricted to rocky outcrops at high elevations within the campo rupestre vegetation of the Espinhaço Range in the state of Minas Gerais, south-eastern Brazil. This poorly known species is considered 'Near Threatened', but recent studies have suggested that it should be listed under a higher category of threat. To contribute to the knowledge of this species and its conservation assessment and related planning, we compiled all literature records of the species distribution (n = 16 locations), collected new data on its occurrence (n = 72 locations), and calculated its geographic range using four different approaches. First, we defined the sky islands where the species occurs (nine units) using the lowest elevation value recorded (1,100 m asl) as a cut-off. Second, we performed species distribution modelling (SDM) across the sky islands and identified an area of 2,225.21 km
2 . Third, we measured the species' extent of occurrence (EOO = 24,555.85 km2 ) and used SDM to estimate its upper limit (EOOup = 30,697.58 km2 ). Fourth, we measured the area of occupancy (AOO = 228 km2 ) and used SDM to estimate its upper limit (AOOup = 1,827.39 km2 ). We analysed the Cipo Canastero sky islands in terms of landscape metrics including size, isolation, protected area coverage, shape index, core area index, and proportion covered by SDM. We observed a very fragmented distribution, especially in the North sector of the species distribution, composed of small and isolated populations (separated by up to 112 km); the South sector is the core of its distribution and is composed of larger, more connected patches with differences in shape complexity that are not strongly influenced by an edge effect. The range sizes calculated, along with other reported information regarding population and habitat trends, justifies the inclusion of the species in at least the 'Vulnerable' category. [ABSTRACT FROM AUTHOR]- Published
- 2020
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21. Vicariant events in the montane hummingbird genera Augastes and Schistes in South America.
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Chaves, Anderson V., Vasconcelos, Marcelo F., Freitas, Guilherme H. S., and Santos, Fabrício R.
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HUMMINGBIRDS ,MITOCHONDRIAL DNA ,NUCLEAR DNA ,CLIMATE change ,NUCLEOTIDE sequence ,FEATHERS - Abstract
We assessed the evolutionary histories of two hummingbirds, Augastes scutatus and Augastes lumachella, endemic to the highlands of the Espinhaço Range in Brazil. These hummingbirds are considered relictual taxa with phylogenetic affinities to members of the genus Schistes from the Andean region. We reconstructed phylogenetic relationships of Augastes through the use of mitochondrial DNA and nuclear sequences within the Polytminae hummingbird clade, and found that the inferred phylogenetic reconstructions placed A. scutatus as the sister species of A. lumachella and Augastes as sister to Schistes geoffroyi from the northern Andes, as previously suggested by similarities found in plumage and morphology. Our results are consistent with an initial divergence of Augastes and Schistes lineages in the Late Miocene, associated with geological and climatic changes across the South American landscape. A Late Pliocene vicariant event between A. scutatus and A. lumachella may be associated with climatically distinct environmental conditions influencing the local differentiation and adaptation of ancestral Augastes populations. Our findings represent additional important evidence of vicariant events between east and west in southern South America, and between north and south within the Espinhaço Range of Brazil. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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22. Past vicariance promoting deep genetic divergence in an endemic frog species of the Espinhaço Range in Brazil: The historical biogeography of Bokermannohyla saxicola (Hylidae).
- Author
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Nascimento, Augusto César, Chaves, Anderson Vieira, Leite, Felipe Sá Fortes, Eterovick, Paula Cabral, and Santos, Fabrício Rodrigues dos
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FROGS , *ENDEMIC animals , *HABITATS , *PLEISTOCENE Epoch , *ANIMAL diversity - Abstract
The highland endemic frog Bokermannohyla saxicola occurs within the Espinhaço Range, the most extensive and continuous orogenic belt of the Brazilian territory, located in southeastern Brazil. We used mitochondrial DNA markers to test for spatial structure, to investigate the likely influence of past vicariant events, to evaluate demographic dynamics along the species range, and to understand the role of habitat discontinuities in promoting connectivity and diversity along the range. We found four major monophyletic lineages, each one associated with distinct mountain tops. The divergence time found between the four main clades clearly pre-dated the Pleistocene, except for the most recent separation. We observed no signs of population expansion for most of the sampling sites along the range, and a higher genetic diversity in the most continuous and central highland plateau, compared to smaller marginal regions. The Espinhaço Range harbors four deeply divergent lineages of B. saxicola within areas restricted by barriers for millions of years. These relatively isolated populations were kept apart by discontinuities represented by lowland habitats between mountain tops. Most of the lineage divergences occurred earlier than the Pleistocene, thus they cannot be solely explained by climatic oscillations of this epoch. However, within-lineage divergence times were all dated from the Pleistocene, suggesting an important effect in population dynamics. We also suggest that some marginal populations like those from Serra Negra and Serra de Itacambira can be the result of recent colonization events. Finally, in the southern Espinhaço region, the most continuous central highland area shows greater genetic diversity than the marginal discontinuous areas, where we have also observed a significant correlation between genetic and geographic distances. Bokermannohyla saxicola is a good model to study the biogeography of the Espinhaço Range because its high genetic structure reflects ancient as well as recent geological/climatic events, with important implications for conservation. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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23. The striking polyphyly of <italic>Suiriri</italic>: Convergent evolution and social mimicry in two cryptic Neotropical birds.
- Author
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Lopes, Leonardo Esteves, Chaves, Anderson Vieira, de Aquino, Marla Mendes, Silveira, Luís Fábio, and dos Santos, Fabrício Rodrigues
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FLYCATCHERS , *TYRANNIDAE , *BIRD phylogeny , *BIRD morphology , *COLOR of birds , *BIRD behavior , *MIMICRY (Biology) - Abstract
Abstract: Two species of
Suiriri (Aves: Tyrannidae) inhabit semi‐open habitats in South America: the polytypic Suiriri Flycatcher (S. suiriri ) and the monotypic Chapada Flycatcher (S. affinis ). The phylogenetic relationship between these congeneric species has never been investigated in detail. Here we used molecular tools—three nuclear introns and two mitochondrial genes—to investigate the systematic position of the Chapada Flycatcher, comparing the results found with morphological and behavioral data. We found that the polytypic Suiriri Flycatcher to be monophyletic and that it is included in a clade of Elaeniini flycatchers includingPhyllomyias, Phaeomyias, andCapsiempis among other genera. The Chapada Flycatcher, on the other hand, is a member of the Fluvicolini, sister toSublegatus , and should be allocated on its own monospecific genus, which we herein describe. We suggest that social mimicry is responsible for the remarkable convergence in size, shape, plumage coloration, and behavior in the adults of the Suiriri Flycatcher and the Chapada Flycatcher. [ABSTRACT FROM AUTHOR]- Published
- 2018
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24. Ultralow and anisotropic thermal conductivity in semiconductor As2Se3.
- Author
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González-Romero, Robert L., Antonelli, Alex, Chaves, Anderson S., and Meléndez, Juan J.
- Abstract
An ultralow lattice thermal conductivity of 0.14 W m
−1 K−1 along the b axis of As2 Se3 single crystals was obtained at 300 K using first-principles calculations involving density functional theory and the resolution of the Boltzmann transport equation. This ultralow lattice thermal conductivity arises from the combination of two mechanisms: (1) a cascade-like fall of the low-lying optical modes, which results in avoided crossings of these with the acoustic modes, low sound velocities and increased scattering rates of the acoustic phonons; and (2) the repulsion between the lone-pair electrons of the As cations and the valence p orbitals of the Se anions, which leads to an increase in the anharmonicity of the bonds. The physical origins of these mechanisms lie in the nature of the chemical bonding in the material and its strong anisotropy. These results, whose validity has been addressed by comparison with SnSe, for which excellent agreement between the theoretical predictions and the experiments is achieved, point out that As2 Se3 could exhibit improved thermoelectric properties. [ABSTRACT FROM AUTHOR]- Published
- 2018
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25. Evolution of the structural, energetic, and electronic properties of the 3d, 4d, and 5d transition-metal clusters (30 TMn systems for n = 2–15): a density functional theory investigation.
- Author
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Chaves, Anderson S., Piotrowski, Maurício J., and Da Silva, Juarez L. F.
- Abstract
Subnanometric transition-metal (TM) clusters have attracted great attention due to their unexpected physical and chemical properties, leastwise compared to their bulk counterparts. An in-depth understanding of the evolution of the properties as a function of the number of atoms for such systems is a basic prerequisite to leverage countless applications, from catalysis to magnetic storage, as well as to answer fundamental questions related to their intrinsic stability. Here, we reported a systematic density functional study to investigate the structural, electronic properties and stability of all TM
n (30 elements) unary clusters as a function of the number of atoms (n = 2–15). We provided the complete structural patterns for all TM periodic table groups, considering the growth evolution as well as the main trends of the structural and electronic properties. The combination of the occupation of the bonding/anti-bonding d-states and the s–d hybridization is found to be the main stabilization mechanism, helping in the understanding of the structural patterns. Most TMn clusters have a magic number of atoms, for which there are peaks in s–d hybridization and null electric dipole moments. Thus, our extensive and comparative study addresses size effects along with the evolution of d-orbital occupation for the TMn gas-phase cluster properties. [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
- View/download PDF
26. Theoretical Study of the Structural, Energetic, and Electronic Properties of 55-Atom Metal Nanoclusters: A DFT Investigation within van der Waals Corrections, Spin-Orbit Coupling, and PBE+U of 42 Metal Systems.
- Author
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Piotrowski, Maurício J., Ungureanu, Crina G., Tereshchuk, Polina, Batista, Krys E. A., Chaves, Anderson S., Guedes-Sobrinho, Diego, and Da Silva, Juarez L. F.
- Published
- 2016
- Full Text
- View/download PDF
27. The patchy distribution of the Pale-throated Serra-Finch Embernagra longicauda (Aves: Thraupidae) in the eastern Brazilian mountaintops: the overlooked campos rupestres of the Rio Doce valley.
- Author
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Esteves LOPES, Leonardo, de Freitas MARÇAL, Bráulio, and Vieira CHAVES, Anderson
- Subjects
FINCHES ,ZOOGEOGRAPHY - Abstract
The Pale-throated Serra-Finch lives in the unique vegetation types known as campos rupestres, campos gerais and campos de altitude, which are found on the mountaintops of Eastern Brazil. In this paper, we present the first records of disjunct populations of the Pale-throated Serra-Finch in the Rio Doce valley, municipality of Alvarenga, Minas Gerais, Brazil. The Atlantic Forest formerly covered this region, with open grasslands floristically related to the campos rupestres vegetation found at higher elevations. We highlight the importance of conducting botanical and faunal inventories on these mountaintops, which are currently not granted legal protection and might harbor other threatened and/or undescribed endemic species. [ABSTRACT FROM AUTHOR]
- Published
- 2016
28. Ethanol and Water Adsorption on Transition-Metal 13-Atom Clusters: A Density Functional Theory Investigation within van der Waals Corrections.
- Author
-
Zibordi-Besse, Larissa, Tereshchuk, Polina, Chaves, Anderson S., and Da Silva, Juarez L. F.
- Published
- 2016
- Full Text
- View/download PDF
29. New and reconfirmed birds from Bertioga, coastal São Paulo state, with a catalogue of an overlooked and important bird collection made by Emílio Dente.
- Author
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Ferreira de Vasconcelos, Marcelo, Vieira Chaves, Anderson, Tahuyta Tonini, Annanda, and de Figueiredo Felix, Cleverson
- Subjects
- *
ORNITHOLOGY , *OWLS , *SPECIES - Abstract
The article offers information on the new and reconfirmed birds from Bertioga, coastal São Paulo state in Brazil. It presents a catalogue of an overlooked and important bird collection prepared by Emílio Dente. The species discussed include Ferruginous Pygmy-Owl Glaucidium brasilianum, Hooded Berryeater Carpornis cucullata, and Sooty Tyrannulet Serpophaga nigricans.
- Published
- 2016
30. Theoretical Investigation of the Adsorption Properties of CO, NO, and OH on Monometallic and Bimetallic 13-Atom Clusters: The Example of Cu13, Pt7Cu6, and Pt13.
- Author
-
Chaves, Anderson S., Piotrowski, Maurício J., Guedes-Sobrinho, Diego, and Da Silva, Juarez L. F.
- Subjects
- *
PHYSICAL & theoretical chemistry , *METAL clusters , *ADSORPTION (Chemistry) , *DENSITY functional theory , *BINDING energy - Abstract
We report a density functional theory investigation of the adsorption properties of CO, NO, and OH on the Cu13, Pt7Cu6, and Pt13 clusters in the cationic, neutral, and anionic states with the aim to improve our atomistic understanding of the adsorption properties on bimetallic clusters compared with monometallic clusters. The adsorption energy of CO and NO are substantially stronger on Pt13 than on Cu13, and hence, CO and NO bind preferentially on Pt sites on Pt7Cu6. Thus, it can contribute to drive the migration of the Pt atoms from the core to the surface region in large PtCu nanoalloys. The CO and NO adsorption energies on the bimetallic cluster are enhanced by a few percent compared with the energies of the monometallic clusters, which shows that the Pt-Cu interaction can contribute to an increase in the adsorption energy. In contrast with CO and NO trends, the OH adsorption energies on Cu13, Pt7Cu6, and Pt13 deviates only up to 0.31 eV, and hence, there is no clear preference for Cu or Pt sites on Pt7Cu6 or an enhancement of the adsorption energy on the bimetallic systems. We found a reduction of the CO and NO vibrational frequencies upon adsorption, which indicates a weakening of the CO and NO binding energies, and it is supported by a slight increase in the bond lengths. However, the OH vibrational frequency increases upon adsorption, which indicates an enhancement of the OH binding energy, which is supported by a slight decrease in the bond length by about 0.01 Å. It can be explained by the large charge transfer from the clusters to the O atom, which enhances the electrostatic interaction in the O-H bonding. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
31. Theoretical Investigation of the Adsorption Properties of CO, NO, and OH on Monometallic and Bimetallic 13-Atom Clusters: The Example of Cu13, Pt7Cu6, and Pt13.
- Author
-
Chaves, Anderson S., Piotrowski, Maurício J., Guedes-Sobrinho, Diego, and Da Silva, Juarez L. F.
- Published
- 2015
- Full Text
- View/download PDF
32. Barcoding Neotropical birds: assessing the impact of nonmonophyly in a highly diverse group.
- Author
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Chaves, Bárbara R. N., Chaves, Anderson V., Nascimento, Augusto C. A., Chevitarese, Juliana, Vasconcelos, Marcelo F., and Santos, Fabrício R.
- Subjects
- *
BIRDS , *GENETIC barcoding , *BAYESIAN analysis , *PASSERIFORMES , *BIRD phylogeny - Abstract
In this study, we verified the power of DNA barcodes to discriminate Neotropical birds using Bayesian tree reconstructions of a total of 7404 COI sequences from 1521 species, including 55 Brazilian species with no previous barcode data. We found that 10.4% of species were nonmonophyletic, most likely due to inaccurate taxonomy, incomplete lineage sorting or hybridization. At least 0.5% of the sequences (2.5% of the sampled species) retrieved from GenBank were associated with database errors (poor-quality sequences, Nu MTs, misidentification or unnoticed hybridization). Paraphyletic species (5.8% of the total) can be related to rapid speciation events leading to nonreciprocal monophyly between recently diverged sister species, or to absence of synapomorphies in the small COI region analysed. We also performed two series of genetic distance calculations under the K2P model for intraspecific and interspecific comparisons: the first included all COI sequences, and the second included only monophyletic taxa observed in the Bayesian trees. As expected, the mean and median pairwise distances were smaller for intraspecific than for interspecific comparisons. However, there was no precise 'barcode gap', which was shown to be larger in the monophyletic taxon data set than for the data from all species, as expected. Our results indicated that although database errors may explain some of the difficulties in the species discrimination of Neotropical birds, distance-based barcode assignment may also be compromised because of the high diversity of bird species and more complex speciation events in the Neotropics. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
33. Genetic Structure Is Associated with Phenotypic Divergence in Floral Traits and Reproductive Investment in a High-Altitude Orchid from the Iron Quadrangle, Southeastern Brazil.
- Author
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Leles, Bruno, Chaves, Anderson V., Russo, Philip, Batista, João A. N., and Lovato, Maria Bernadete
- Subjects
- *
ORCHIDS , *BIOLOGICAL evolution , *MICROSATELLITE repeats , *BIOMARKERS , *BAYESIAN analysis , *PRINCIPAL components analysis - Abstract
Knowledge of the role of Neotropical montane landscapes in shaping genetic connectivity and local adaptation is essential for understanding the evolutionary processes that have shaped the extraordinary species diversity in these regions. In the present study, we examined the landscape genetics, estimated genetic diversity, and explored genetic relationships with morphological variability and reproductive strategies in seven natural populations of Cattleya liliputana (Orchidaceae). Nuclear microsatellite markers were used for genetic analyses. Spatial Bayesian clustering and population-based analyses revealed significant genetic structuring and high genetic diversity (He = 0.733 ± 0.03). Strong differentiation was found between populations over short spatial scales (FST = 0.138, p < 0.001), reflecting the landscape discontinuity and isolation. Monmonier´s maximum difference algorithm, Bayesian analysis on STRUCTURE and principal component analysis identified one major genetic discontinuity between populations. Divergent genetic groups showed phenotypic divergence in flower traits and reproductive strategies. Increased sexual reproductive effort was associated with rock outcrop type and may be a response to adverse conditions for growth and vegetative reproduction. Here we discuss the effect of restricted gene flow, local adaptation and phenotypic plasticity as drivers of population differentiation in Neotropical montane rock outcrops. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
34. Structural formation of binary PtCu clusters: A density functional theory investigation.
- Author
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Chaves, Anderson S., Rondina, Gustavo G., Piotrowski, Maurício J., and Da Silva, Juarez L.F.
- Subjects
- *
MOLECULAR structure , *BINARY metallic systems , *METAL clusters , *DENSITY functional theory , *TRANSITION metals , *CENTER of mass - Abstract
Binary transition-metal clusters have attracted great attention and a large number of studies have been reported, however, our atomistic understanding of the structural formation mechanisms of those clusters is still far from satisfactory. In this paper, we report a systematic study of the Pt n Cu m − n clusters ( m = 2 , 3 , … , 14 , n = 0 , 1 , … , m ) employing Ab-Initio density functional theory calculations within the Perdew–Burke–Ernzerhof functional. Using a set of structural design principles, we obtained a hierarchical set of atomic configurations from which the structural formation mechanisms are discussed in details. We found a negative excess energy for m > 2 , providing strong evidence favouring the formation of binary PtCu clusters. In general, the Cu atoms tend to form agglomerates located near the center of gravity of the clusters while the Pt atoms tend to lie further away from the center of gravity and separated from each other. Therefore, this behaviour tends to reduce the number of Pt–Pt bonds whereas the number of Cu–Cu and Pt–Cu bonds tends to be maximized. These mechanisms help to release strain energy by means of relaxation of the gas-phase clusters, and the locations of the Cu and Pt atoms suggest that the formation of core–shell like structures starts already in this small size regime. Furthermore, the formation of the PtCu alloy does not lead to changes in the magnetic properties of the clusters in comparison with the parent Pt and Cu clusters. The systematic work presented here provides a basis to understand and tailor the properties of binary cluster. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
35. Biogeographic patterns, origin and speciation of the endemic birds from eastern Brazilian mountaintops: a review.
- Author
-
Chaves, Anderson V., Freitas, Guilherme H. S., Vasconcelos, Marcelo F., and Santos, Fabrício R.
- Subjects
- *
ENDEMIC birds , *GENETIC speciation , *BIRD phylogeny , *BIRD classification , *BIOGEOGRAPHY , *VICARIANCE , *ZOOGEOGRAPHY - Abstract
We review the main biogeographic and phylogenetic hypotheses about the origin and distribution of the endemic birds from Brazilian mountaintops, a heterogeneous group composed of hummingbirds and passerines living in high-altitude open habitats ofcampos rupestres,campos de altitudeandcampos sulinosfrom southern to north-eastern Brazilian mountaintops (Espinhaço Range, Serra do Mar, Serra da Mantiqueira and Serra Geral). Some authors consider that these birds are probably closely related to other species distributed in cooler areas of South America. We used ranges of these birds, spatial pattern and discontinuities in the distribution of phytophysiognomies to determine potential geographic barriers to dispersal and centres of origin and speciation. We reanalysed biogeographical hypotheses regarding the evolution of the endemic birds from Brazilian mountaintops and their habitats in the light of recent phylogenetic reconstructions that included some of these species. The evolutionary histories of the speciesAugastes scutatus,Augastes lumachella,Formicivora grantsaui,Polystictus superciliarisandEmbernagra longicaudaare difficult to assess due to lack of phylogenies that establish their systematic position. ForAsthenes luizae,Asthenes moreirae,Cinclodes pabstiandC. espinhacensis, the phylogenies estimate also their lineage divergence times, which allows for inferences concerning connections between the biota of eastern Brazil, southern South America and the Andean mountains. We also identified 26 lowland regions between the mountains that were potentially barriers to dispersal. Phylogenetic relationships strongly highlight the importance of connecting paths and speciation through the south, especially in the cooler areas in South America. These patterns show that eastern Brazil, southern South America and the central and northern Andes are four important centres of origin and radiation for the endemic birds from the eastern Brazilian mountains. [ABSTRACT FROM PUBLISHER]
- Published
- 2015
- Full Text
- View/download PDF
36. Bacteria and Genes Involved in Arsenic Speciation in Sediment Impacted by Long-Term Gold Mining.
- Author
-
Costa, Patrícia S., Scholte, Larissa L. S., Reis, Mariana P., Chaves, Anderson V., Oliveira, Pollyanna L., Itabayana, Luiza B., Suhadolnik, Maria Luiza S., Barbosa, Francisco A. R., Chartone-Souza, Edmar, and Nascimento, Andréa M. A.
- Subjects
GOLD mining ,SEDIMENTS ,ARSENIC ,BACTERIAL population ,METAGENOMICS ,PHYLOGENY - Abstract
The bacterial community and genes involved in geobiocycling of arsenic (As) from sediment impacted by long-term gold mining were characterized through culture-based analysis of As-transforming bacteria and metagenomic studies of the arsC, arrA, and aioA genes. Sediment was collected from the historically gold mining impacted Mina stream, located in one of the world’s largest mining regions known as the “Iron Quadrangle”. A total of 123 As-resistant bacteria were recovered from the enrichment cultures, which were phenotypically and genotypically characterized for As-transformation. A diverse As-resistant bacteria community was found through phylogenetic analyses of the 16S rRNA gene. Bacterial isolates were affiliated with Proteobacteria, Firmicutes, and Actinobacteria and were represented by 20 genera. Most were AsV-reducing (72%), whereas AsIII-oxidizing accounted for 20%. Bacteria harboring the arsC gene predominated (85%), followed by aioA (20%) and arrA (7%). Additionally, we identified two novel As-transforming genera, Thermomonas and Pannonibacter. Metagenomic analysis of arsC, aioA, and arrA sequences confirmed the presence of these genes, with arrA sequences being more closely related to uncultured organisms. Evolutionary analyses revealed high genetic similarity between some arsC and aioA sequences obtained from isolates and clone libraries, suggesting that those isolates may represent environmentally important bacteria acting in As speciation. In addition, our findings show that the diversity of arrA genes is wider than earlier described, once none arrA-OTUs were affiliated with known reference strains. Therefore, the molecular diversity of arrA genes is far from being fully explored deserving further attention. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
37. Exploring the Diversity and Distribution of Neotropical Avian Malaria Parasites – A Molecular Survey from Southeast Brazil.
- Author
-
Lacorte, Gustavo A., Félix, Gabriel M. F., Pinheiro, Rafael R. B., Chaves, Anderson V., Almeida-Neto, Gilberto, Neves, Frederico S., Leite, Lemuel O., Santos, Fabrício R., and Braga, Érika M.
- Subjects
PLASMODIUM ,HABITATS ,MOUNTAINS ,PARASITIC diseases ,BIRD classification ,HAPLOTYPES - Abstract
Southeast Brazil is a neotropical region composed of a mosaic of different tropical habitats and mountain chains, which allowed for the formation of bird-rich communities with distinct ecological niches. Although this region has the potential to harbor a remarkable variety of avian parasites, there is a lack of information about the diversity of malarial parasites. We used molecular approaches to characterize the lineage diversity of Plasmodium and Haemoproteus in bird communities from three different habitats in southeast Brazil based on the prevalence, richness and composition of lineages. We observed an overall prevalence of 35.3%, with a local prevalence ranging from 17.2% to 54.8%. Moreover, no significant association between prevalence and habitat type could be verified (p>0.05). We identified 89 Plasmodium and 22 Haemoproteus lineages, with 86% of them described for the first time here, including an unusual infection of a non-columbiform host by a Haemoproteus (Haemoproteus) parasite. The composition analyses of the parasite communities showed that the lineage composition from Brazilian savannah and tropical dry forest was similar, but it was different from the lineage composition of Atlantic rainforest, reflecting the greater likeness of the former habitats with respect to seasonality and forest density. No significant effects of habitat type on lineage richness were observed based on GLM analyses. We also found that sites whose samples had a greater diversity of bird species showed a greater diversity of parasite lineages, providing evidence that areas with high bird richness also have high parasite richness. Our findings point to the importance of the neotropical region (southeast Brazil) as a major reservoir of new haemosporidian lineages. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
38. A new species of Cinclodes from the Espinhaço Range, southeastern Brazil: insights into the biogeographical history of the South American highlands.
- Author
-
Freitas, Guilherme H. S., Chaves, Anderson V., Costa, Lílian M., Santos, Fabrício R., Rodrigues, Marcos, and Collinson, Martin
- Subjects
FURNARIIDAE ,BIOGEOGRAPHY ,UPLANDS ,VICARIANCE - Abstract
We describe Cinclodes espinhacensis (Furnariidae) , a new species discovered at high elevation in the southern portion of the Espinhaço Range, in the state of Minas Gerais, southeastern Brazil. This new taxon is closely related to the Long-tailed Cinclodes Cinclodes pabsti, endemic to Serra Geral, southern Brazil. We present diagnostic morphological, genetic and vocal characters that support the rank of species for this allopatric taxon. It is readily distinguishable from C. pabsti by its much darker back, chest and flanks, lower body mass, shorter tarsus-length, lower frequency of vocalizations, and longer duration of calls. DNA sequence data estimate that the divergence time between this new species and Cinclodes pabsti occurred c. 220 000 years ago, during the late Pleistocene. This discovery illustrates remarkable biogeographical connections among the cold regions of South America. The new species has a restricted range and we suggest it meets the criteria of the IUCN Red List category of Endangered. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
39. Inaccuracy of Enzyme-Linked Immunosorbent Assay Using Soluble and Recombinant Antigens to Detect Asymptomatic Infection by Leishmania infantum.
- Author
-
Moreno, Elizabeth Castro, Gonçalves, Andréa Vieira, Chaves, Anderson Vieira, Melo, Maria Norma, Lambertucci, José Roberto, Andrade, Antero Silva Ribeiro, Negrão-Corrêa, Deborah, Antunes, Carlos Mauricio de Figueiredo, and Carneiro, Mariângela
- Subjects
ENZYME-linked immunosorbent assay ,LEISHMANIA infantum ,VISCERAL leishmaniasis ,MOLECULAR biology ,ANTIGENS ,THEILERIA ,LEISHMANIA mexicana - Abstract
Background: One of the most important drawbacks in visceral leishmaniasis (VL) population studies is the difficulty of diagnosing asymptomatic carriers. The aim of this study, conducted in an urban area in the Southeast of Brazil, was to evaluate the performance of serology to identify asymptomatic VL infection in participants selected from a cohort with a two-year follow-up period. Methodology: Blood samples were collected in 2001 from 136 cohort participants (97 positive and 39 negatives, PCR/hybridization carried out in 1999). They were clinically evaluated and none had progressed to disease from their asymptomatic state. As controls, blood samples from 22 control individuals and 8 patients with kala-azar were collected. Two molecular biology techniques (reference tests) were performed: PCR with Leishmania-generic primer followed by hybridization using L. infantum probe, and PCR with specific primer to L. donovani complex. Plasma samples were tested by ELISA using three different antigens: L. infantum and L. amazonensis crude antigens, and rK39 recombinant protein. Accuracy of the serological tests was evaluated using sensitivity, specificity, likelihood ratio and ROC curve. Findings: The presence of Leishmania was confirmed, by molecular techniques, in all kala-azar patients and in 117 (86%) of the 136 cohort participants. Kala-azar patients showed high reactivity in ELISAs, whereas asymptomatic individuals presented low reactivity against the antigens tested. When compared to molecular techniques, the L. amazonensis and L. infantum antigens showed higher sensitivity (49.6% and 41.0%, respectively) than rK39 (26.5%); however, the specificity of rK39 was higher (73.7%) than L. amazonensis (52.6%) and L. infantum antigens (36.8%). Moreover, there was low agreement among the different antigens used (kappa<0.10). Conclusions: Serological tests were inaccurate for diagnosing asymptomatic infections compared to molecular methods; this could lead to misclassification bias in population studies. Therefore, studies which have used serological assays to estimate prevalence, to evaluate intervention programs or to identify risk factors for Leishmania infection, may have had their results compromised. Author Summary: Visceral leishmaniasis or kala-azar in Brazil, caused by a parasite protozoon, is transmitted to humans by sandflies and has wild and domestic dogs as reservoirs. The disease can become chronic, characterized by fever, weight loss, and enlargement of the liver and spleen. However, the infection in humans can be asymptomatic, and the importance of this phase is unknown. The low levels of immune response and the small number of circulating parasites in the blood are the main problems in identifying the asymptomatic phase. In this study we evaluated the performance of the serology tests compared with molecular tests to identify asymptomatic infection in individuals identified in an urban area of Brazil. Also included were non-infected individuals (healthy controls) and patients (diseased controls). Blood was collected and examined by different serological methods and compared with molecular techniques. The presence of the parasite was confirmed by all molecular techniques and should be the method used to identify true infection. The serology methods showed low sensitivity in detecting the infection. We concluded that the serologic methods are inaccurate in identifying asymptomatic infection when compared to molecular techniques and could underestimate the infection in population studies. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
40. MICROSATELLITE MARKERS FOR VELLOZIA GIGANTEA (VELLOZIACEAE), A NARROWLY ENDEMIC SPECIES TO THE BRAZILIAN CAMPOS RUPESTRES.
- Author
-
Martins, Ana Paula V., Proite, Karina, Kalapothakis, Evanguedes, Santos, Fabrício R., Chaves, Anderson V., and Borba, Eduardo L.
- Subjects
MICROSATELLITE repeats in plants ,MICROSATELLITE repeats ,VELLOZIACEAE ,PLANT population genetics ,PLANT populations - Abstract
Premise of the study: Microsatellite primers were developed for the first time in Velloziaceae, in the endangered species Vellozia gigantea. Methods and Results: Using two different protocols, seven primer sets were characterized in three populations of V. gigantea. The primers amplified di- and trinucleotide repeats with six to 12 alleles per locus. These revealed high levels of genetic variation, presenting an average observed heterozygosity of 0.508 in V. gigantea. The seven primers were tested for cross-amplification in three Vellozia species. All primers successfully amplified in V. auriculata. Six primers amplified in V. compacta and three in V. hirsuta. Conclusions: The new marker set described here will be useful for studies of population genetics of V. gigantea. The cross-amplification results indicate the utility of primers for studies in other Vellozia species. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
41. Parrot Genomes and the Evolution of Heightened Longevity and Cognition.
- Author
-
Wirthlin, Morgan, Lima, Nicholas C.B., Guedes, Rafael Lucas Muniz, Soares, André E.R., Almeida, Luiz Gonzaga P., Cavaleiro, Nathalia P., Loss de Morais, Guilherme, Chaves, Anderson V., Howard, Jason T., Teixeira, Marcus de Melo, Schneider, Patricia N., Santos, Fabrício R., Schatz, Michael C., Felipe, Maria Sueli, Miyaki, Cristina Y., Aleixo, Alexandre, Schneider, Maria P.C., Jarvis, Erich D., Vasconcelos, Ana Tereza R., and Prosdocimi, Francisco
- Subjects
- *
PARROTS , *GENOMES , *DNA damage , *CELL proliferation , *TELOMERASE - Abstract
Summary Parrots are one of the most distinct and intriguing groups of birds, with highly expanded brains [ 1 ], highly developed cognitive [ 2 ] and vocal communication [ 3 ] skills, and a long lifespan compared to other similar-sized birds [ 4 ]. Yet the genetic basis of these traits remains largely unidentified. To address this question, we have generated a high-coverage, annotated assembly of the genome of the blue-fronted Amazon (Amazona aestiva) and carried out extensive comparative analyses with 30 other avian species, including 4 additional parrots. We identified several genomic features unique to parrots, including parrot-specific novel genes and parrot-specific modifications to coding and regulatory sequences of existing genes. We also discovered genomic features under strong selection in parrots and other long-lived birds, including genes previously associated with lifespan determination as well as several hundred new candidate genes. These genes support a range of cellular functions, including telomerase activity; DNA damage repair; control of cell proliferation, cancer, and immunity; and anti-oxidative mechanisms. We also identified brain-expressed, parrot-specific paralogs with known functions in neural development or vocal-learning brain circuits. Intriguingly, parrot-specific changes in conserved regulatory sequences were overwhelmingly associated with genes that are linked to cognitive abilities and have undergone similar selection in the human lineage, suggesting convergent evolution. These findings bring novel insights into the genetics and evolution of longevity and cognition, as well as provide novel targets for exploring the mechanistic basis of these traits. Highlights • The blue-fronted Amazon, Amazona aestiva, and other parrots share unique novel genes • Convergent selection in long-lived birds suggests new lifespan-influencing genes • Parrot genomes share genetic changes related to genes critical for brain function • Similar changes in parrot and human genomes suggest convergent evolution of cognition The genetic basis for the complex traits that characterize parrots, including extreme longevity and advanced cognition, remains unknown. Wirthlin et al. present the genome of the blue-fronted Amazon, Amazona aestiva. Comparisons with other birds and humans reveal genomic similarities, suggesting convergent mechanisms in the evolution of these traits. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
42. Computational prediction of high thermoelectric performance in As 2 Se 3 by engineering out-of-equilibrium defects.
- Author
-
Chaves AS, Silva MA, and Antonelli A
- Abstract
We employed first-principles calculations to investigate the thermoelectric transport properties of the compound As
2 Se3 . Early experiments and calculations have indicated that these properties are controlled by a kind of native defect called antisites. Our calculations using the linearized Boltzmann transport equation within the relaxation time approximation show good agreement with the experiments for defect concentrations of the order of 1019 cm-3 . Based on our total energy calculations, we estimated the equilibrium concentration of antisite defects to be about 1014 cm-3 . These results suggest that the large concentration of defects in the experiments is due to kinetic and/or off-stoichiometry effects and in principle it could be lowered, yielding relaxation times similar to those found in other chalcogenide compounds. In this case, for relaxation time higher than 10 fs, we obtained high thermoelectric figures of merit of 3 for the p-type material and 2 for the n-type one.- Published
- 2024
- Full Text
- View/download PDF
43. Ultralow and anisotropic thermal conductivity in semiconductor As 2 Se 3 .
- Author
-
González-Romero RL, Antonelli A, Chaves AS, and Meléndez JJ
- Abstract
An ultralow lattice thermal conductivity of 0.14 W m
-1 K-1 along the b[combining right harpoon above] axis of As2 Se3 single crystals was obtained at 300 K using first-principles calculations involving density functional theory and the resolution of the Boltzmann transport equation. This ultralow lattice thermal conductivity arises from the combination of two mechanisms: (1) a cascade-like fall of the low-lying optical modes, which results in avoided crossings of these with the acoustic modes, low sound velocities and increased scattering rates of the acoustic phonons; and (2) the repulsion between the lone-pair electrons of the As cations and the valence p orbitals of the Se anions, which leads to an increase in the anharmonicity of the bonds. The physical origins of these mechanisms lie in the nature of the chemical bonding in the material and its strong anisotropy. These results, whose validity has been addressed by comparison with SnSe, for which excellent agreement between the theoretical predictions and the experiments is achieved, point out that As2 Se3 could exhibit improved thermoelectric properties.- Published
- 2018
- Full Text
- View/download PDF
44. Evolution of the structural, energetic, and electronic properties of the 3d, 4d, and 5d transition-metal clusters (30 TM n systems for n = 2-15): a density functional theory investigation.
- Author
-
Chaves AS, Piotrowski MJ, and Da Silva JLF
- Abstract
Subnanometric transition-metal (TM) clusters have attracted great attention due to their unexpected physical and chemical properties, leastwise compared to their bulk counterparts. An in-depth understanding of the evolution of the properties as a function of the number of atoms for such systems is a basic prerequisite to leverage countless applications, from catalysis to magnetic storage, as well as to answer fundamental questions related to their intrinsic stability. Here, we reported a systematic density functional study to investigate the structural, electronic properties and stability of all TM
n (30 elements) unary clusters as a function of the number of atoms (n = 2-15). We provided the complete structural patterns for all TM periodic table groups, considering the growth evolution as well as the main trends of the structural and electronic properties. The combination of the occupation of the bonding/anti-bonding d-states and the s-d hybridization is found to be the main stabilization mechanism, helping in the understanding of the structural patterns. Most TMn clusters have a magic number of atoms, for which there are peaks in s-d hybridization and null electric dipole moments. Thus, our extensive and comparative study addresses size effects along with the evolution of d-orbital occupation for the TMn gas-phase cluster properties.- Published
- 2017
- Full Text
- View/download PDF
45. Density functional investigation of the adsorption effects of PH 3 and SH 2 on the structure stability of the Au 55 and Pt 55 nanoclusters.
- Author
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Guedes-Sobrinho D, Chaves AS, Piotrowski MJ, and Da Silva JLF
- Abstract
Although several studies have been reported for Pt
55 and Au55 nanoclusters, our atomistic understanding of the interplay between the adsorbate-surface interactions and the mechanisms that lead to the formation of the distorted reduced core (DRC) structures, instead of the icosahedron (ICO) structure in gas phase, is still far from satisfactory. Here, we report a density functional theory (DFT) investigation of the role of the adsorption effects of PH3 (one lone pair of electrons) and SH2 (two lone pairs) on the relative stability of the Pt55 and Au55 nanoclusters. In gas phase, we found that the DRC structures with 7 and 9 atoms in the core region are about 5.34 eV (Pt55 ) and 2.20 eV (Au55 ) lower in energy than the ICO model with Ih symmetry and 13 atoms in the core region. However, the stability of the ICO structure increases by increasing the number of adsorbed molecules from 1 to 18, in which both DRC and ICO structures are nearly degenerate in energy at the limit of 18 ligands, which can be explained as follows. In gas phase, there is a strong compression of the cationic core region by the anionic surface atoms induced by the attractive Coulomb interactions (core+ -surface- ), and hence, the strain release is obtained by reducing the number of atoms in the cationic core region, which leads to the 55 atoms distorted reduced core structures. Thus, the Coulomb interactions between the core+ and surface- contribute to break the symmetry in the ICO55 structure. On the other hand, the addition of ligands on the anionic surface reduces the charge transfer between the core and surface, which contributes to decrease the Coulomb interactions and the strain on the core region of the ICO structure, and hence, it stabilizes a compact ICO structure. The same conclusion is obtained by adding van der Waals corrections to the plain DFT calculations. Similar results are obtained by the addition of steric effects, which are considered through the adsorption of triphenylphosphine (PPh3 ) molecules on Au55 , in which the relative stability between ICO and DRC is the same as for PH3 and SH2 . However, for Pt55 , we found an inversion of stability due to the PPh3 ligand effects, where ICO has higher stability than DRC by 2.40 eV. Our insights are supported by several structural, electronic, and energetic analyses.- Published
- 2017
- Full Text
- View/download PDF
46. Theoretical Investigation of the Adsorption Properties of CO, NO, and OH on Monometallic and Bimetallic 13-Atom Clusters: The Example of Cu13, Pt7Cu6, and Pt13.
- Author
-
Chaves AS, Piotrowski MJ, Guedes-Sobrinho D, and Da Silva JL
- Abstract
We report a density functional theory investigation of the adsorption properties of CO, NO, and OH on the Cu13, Pt7Cu6, and Pt13 clusters in the cationic, neutral, and anionic states with the aim to improve our atomistic understanding of the adsorption properties on bimetallic clusters compared with monometallic clusters. The adsorption energy of CO and NO are substantially stronger on Pt13 than on Cu13, and hence, CO and NO bind preferentially on Pt sites on Pt7Cu6. Thus, it can contribute to drive the migration of the Pt atoms from the core to the surface region in large PtCu nanoalloys. The CO and NO adsorption energies on the bimetallic cluster are enhanced by a few percent compared with the energies of the monometallic clusters, which shows that the Pt-Cu interaction can contribute to an increase in the adsorption energy. In contrast with CO and NO trends, the OH adsorption energies on Cu13, Pt7Cu6, and Pt13 deviates only up to 0.31 eV, and hence, there is no clear preference for Cu or Pt sites on Pt7Cu6 or an enhancement of the adsorption energy on the bimetallic systems. We found a reduction of the CO and NO vibrational frequencies upon adsorption, which indicates a weakening of the CO and NO binding energies, and it is supported by a slight increase in the bond lengths. However, the OH vibrational frequency increases upon adsorption, which indicates an enhancement of the OH binding energy, which is supported by a slight decrease in the bond length by about 0.01 Å. It can be explained by the large charge transfer from the clusters to the O atom, which enhances the electrostatic interaction in the O-H bonding.
- Published
- 2015
- Full Text
- View/download PDF
47. The role of charge states in the atomic structure of Cu(n) and Pt(n) (n = 2-14 atoms) clusters: a DFT investigation.
- Author
-
Chaves AS, Rondina GG, Piotrowski MJ, Tereshchuk P, and Da Silva JL
- Abstract
In general, because of the high computational demand, most theoretical studies addressing cationic and anionic clusters assume structural relaxation from the ground state neutral geometries. Such approach has its limits as some clusters could undergo a drastic structural deformation upon gaining or losing one electron. By engaging symmetry-unrestricted density functional calculations with an extensive search among various structures for each size and state of charge, we addressed the investigation of the technologically relevant Cu(n) and Pt(n) clusters for n = 2-14 atoms in the cationic, neutral, and anionic states to analyze the behavior of the structural, electronic, and energetic properties as a function of size and charge state. Moreover, we considered potentially high-energy isomers allowing foresight comparison with experimental results. Considering fixed cluster sizes, we found that distinct charge states lead to different structural geometries, revealing a clear tendency of decreasing average coordination as the electron density is increased. This behavior prompts significant changes in all considered properties, namely, energy gaps between occupied and unoccupied states, magnetic moment, detachment energy, ionization potential, center of gravity and "bandwidth" of occupied d-states, stability function, binding energy, electric dipole moment and sd hybridization. Furthermore, we identified a strong correlation between magic Pt clusters with peaks in sd hybridization index, allowing us to conclude that sd hybridization is one of the mechanisms for stabilization for Pt(n) clusters. Our results form a well-established basis upon which a deeper understanding of the stability and reactivity of metal clusters can be built, as well as the possibility to tune and exploit cluster properties as a function of size and charge.
- Published
- 2014
- Full Text
- View/download PDF
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