Publications

We employed PBE and BLYP semi-local functionals and the van der Waals density functional of Dion et al. (2004) (vdW-DF) to investigate structural properties of liquid acetonitrile and methanol. Among those functionals the vdW-DF is the only one that correctly predicts energy minima in inter-molecular interactions between acetonitrile molecules. We found that van der Waals interactions have a negligible effect on H-bonds in methanol chains. However, it significantly increases chain packing resulting in a more dense liquid in comparison to the other two functionals. The overall trend is that the vdW-DF tends to overestimate density and bulk modulus, meanwhile the semi-local functionals tend to underestimate density. Thus, van der Waals interactions play an important role in the properties of liquids in which much stronger dipole-dipole interactions are present.

We employed PBE and BLYP semi-local functionals and the van der Waals density functional of Dion et al. (2004) (vdW-DF) to investigate structural properties of liquid acetonitrile and methanol. Among those functionals the vdW-DF is the only one that correctly predicts energy minima in inter-molecular interactions between acetonitrile molecules. We found that van der Waals interactions have a negligible effect on H-bonds in methanol chains. However, it significantly increases chain packing resulting in a more dense liquid in comparison to the other two functionals. The overall trend is that the vdW-DF tends to overestimate density and bulk modulus, meanwhile the semi-local functionals tend to underestimate density. Thus, van der Waals interactions play an important role in the properties of liquids in which much stronger dipole-dipole interactions are present.

Calcium phosphates are suggested as a CO2 adsorbent via pressure swing adsorption. Amorphous calcium phosphate (ACP) and biphasic calcium phosphate (BCP) (composed of hydroxyapatite and beta-tricalcium phosphate) were investigated for the capture/immobilization of the gas. A fluidized bed was set up to assess the levels of CO2 adsorption by ACP and BCP. A gaseous mixture was synthesized, mimicking the conditions for possible industrial use. The results show a significant reduction in CO2 concentrations. Using DFT calculations, we show that CO2 adsorption increases the stability by reducing the surface energy. The energies involved and preferential adsorption sites were also theoretically predicted.

O presente artigo aborda o problema de cobertura máxima de p-eixos não capacitados com alocação simples (Uncapacitated Single Allocation p-hub Maximal Covering Problem - USApHMCP), que objetiva maximizar a cobertura de um conjunto de nós de uma rede através de p-eixos. Uma heurística baseada na estratégia de busca em descida com vizinhança variável (Variable Neighborhood Descent - VND) foi desenvolvida para o problema. Dois diferentes conjuntos de instâncias, Civil Aeronautics Board (CAB) e Australian Post (AP), são utilizados para avaliar e comparar o desempenho do VND à metaheurística Busca Tabu (Tabu Search - TS) encontrada na literatura. Como resultado, o VND apresentou limites superiores melhores para instâncias de grande porte (AP), bem como um desempenho médio ligeiramente superior em tempo computacional de resolução para as instâncias CAB, de menor porte.

A infraestrutura inadequada e o intenso fluxo de pessoas e veı́culos resultam em problemas associados às vias urbanas no mundo. O Problema de Orientação de Redes Fortemente Conexas (Strong Network Orientation Problem – SNOP) é uma alternativa para amenizar esse cenário na medida em que objetiva minimizar a soma das distâncias percorridas a partir de cada ponto de interseção entre vias, tendo em vista os custos associados à rede urbana. Classificado como NP-Difı́cil, algoritmos heurı́sticos são eficazes para atingir soluções de qualidade, uma vez que obter a melhor solução exige grande esforço computacional. Este artigo apresenta o algoritmo de pesquisa em vizinhança variável General Variable Neighborhood Search (GVNS) para a resolução do SNOP, bem como as estratégias utilizadas. Os resultados obtidos indicam que o GVNS é eficiente em tempo e qualidade de solução quando comparado com outras abordagens aproximadas e exata para o problema.

The reduction by hydrogen and the thermal decomposition of a siliceous nickel laterite ore in the presence of NaCl were studied using thermogravimetric analysis (TGA). Reduction tests on H2 atmosphere in rotary kiln were performed in the presence of NaCl and the product of the reaction was leached in ammoniacal solution. The presence of only 1 pct of NaCl in the furnace increased the nickel extraction values from ≈ 3 to ≈ 90 pct when the experiment was carried out at 850 °C. According to the results of X-ray diffractometry and TGA, the presence of NaCl in the system and the reducing atmosphere of H2 promote the segregation of nickel according to the following steps: (1) Nickel oxide reduction by hydrogen: NiO + H2(g) → Ni + H2O(g). (2) Formation of HCl: Al2SiO5 + 2NaCl + SiO2 + H2O → 2HCl(g) + 2NaAlSiO4. (3) Chlorination of metallic nickel by HCl: Ni + 2HCl(g) → NiCl2 + H2(g). (4) Reduction of nickel chloride by hydrogen: NiCl2 + H2(g) → Ni + 2HCl(g).

A oxidação do concentrado de esfalerita (ZnS) por oxigênio gasoso foi realizada por meio de análise termogravimétrica (TGA). Os produtos de oxidação foram analisados por difratometria de raios X e microscopia eletrônica de varredura (MEV/EDS) e a formação de sulfato de zinco foi detectada durante o processo de oxidação. A pirita presente no concentrado foi aquecida a uma temperatura mais baixa do que a esfalerita e o mecanismo de oxidação estava de acordo com o mecanismo proposto por Dunn J. G. et. al. (1989). A cinética da oxidação da esfalerita foi avaliada por meio do método de isoconversão de Linhas de Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS) e não-linear (MNL) e os resultados sugerem que o processo de oxidação segue um mecanismo complexo. Os valores de energia de ativação encontrados foram superiores a 40kJ/mol na gama completa de conversão sugerindo que a etapa de controle ocorre por meio de reação química.

We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes with different degrees of eccentricity at 300 K. We found a water structural transition between tubular-like to single-file for (7,7) nanotubes associated with change from a high to low mobility regimes. Water is frozen when confined in a perfect (9,9) nanotube and it becomes liquid if such a nanotube is deformed above a certain threshold. Water diffusion enhancement (suppression) is related to a reduction (increase) in the number of hydrogen bonds. This suggests that the shape of the nanotube is an important ingredient when considering the dynamical and structural properties of confined water.

Phenazine derivative molecules were studied using steady state and time resolved fluorescence techniques and demonstrated to lead to strong formation of aggregated species, identified as dimers by time dependent density functional theory calculations. Blended films in a matrix of Zeonex®, produced at different concentrations, showed different contributions of dimer and monomer emissions in a prompt time frame, e.g. less than 50 ns. In contrast, the phosphorescence (e.g. emission from the triplet state) shows no significant effect on dimer formation, although strong dependence of the phosphorescence intensity on concentration is observed, leading to phosphorescence being quenched at higher concentration.

Tin telluride (SnTe) ultrathin films were deposited electrochemically on polycrystalline and monocrystalline gold substrates using the electrochemical atomic layer epitaxy (ECALE) method. The electrochemical behaviors of Sn and Te were studied systematically by means of cyclic voltammetry. Cyclic voltammetry curves for Sn displayed a broad peak in the region between -0.15 V and -0.35 V, which was related to the under-potential deposition (UPD), while the curves for Te displayed a peak at 0.3 V for Te UPD. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) were employed for the characterization of the ultrathin SnTe films. XRD and Raman spectroscopy confirmed the deposition of a single SnTe phase, while SEM revealed that the deposits were composed of nanocrystallites.

We report on an experimental investigation of serpentine, an abundant phyllosilicate, as an alternative source of two-dimensional (2D) nanomaterials. We show, through scanning probe microscopy (SPM) measurements, that natural serpentine mineral can be mechanically exfoliated down to few-layer flakes, where monolayers can be easily resolved. The parent serpentine bulk material was initially characterized via conventional techniques like XRD, XPS, FTIR and Raman spectroscopies and the results show that it is predominantly constituted by the antigorite mineral. From ab initio calculations using density functional theory, we also determine the geometry and electronic structure of antigorite, the observed structural form of serpentine. Additionally, we further characterized electrical and mechanical properties of the obtained 2D material flakes using SPM and broadband synchrotron infrared nanospectroscopy. Wavelength tuning of the serpentine vibrational resonances, assigned to in- and out-of-plane molecular vibrations, are observed and compared with the FTIR characterization of the parent bulk material. They show that there is no degradation of serpentine’s structural properties during its mechanical exfoliation down to nanometer-thin sheets. Therefore, our results introduce the serpentine mineral as an attractive low-cost candidate in 2D materials applications.

We report on an experimental investigation of serpentine, an abundant phyllosilicate, as an alternative source of two-dimensional (2D) nanomaterials. We show, through scanning probe microscopy (SPM) measurements, that natural serpentine mineral can be mechanically exfoliated down to few-layer flakes, where monolayers can be easily resolved. The parent serpentine bulk material was initially characterized via conventional techniques like XRD, XPS, FTIR and Raman spectroscopies and the results show that it is predominantly constituted by the antigorite mineral. From ab initio calculations using DFT, we also determine the geometry and electronic structure of antigorite, the observed structural form of serpentine. Additionally, we further characterized electrical and mechanical properties of the obtained 2D material flakes using SPM and broadband synchrotron infrared nanospectroscopy. Wavelength tuning of the serpentine vibrational resonances, assigned to in- and out-of-plane molecular vibrations, are observed and compared with the FTIR characterization of the parent bulk material. They show that there is no degradation of serpentine`s structural properties during its mechanical exfoliation down to nanometer-thin sheets. Therefore, our results introduce the serpentine mineral as an attractive low-cost candidate in 2D materials applications.

Discute-se, no presente trabalho, a reconstrução da identidade, por meio de processos desencadeados pela memória do vivido, mas, tendo como elemento central de análise, a produção do discurso formulado de um lugar discursivo que é do “Outro”, do colonizador. A análise da tensão de re-estruturação do “Eu”, a partir da língua desse Outro, é desenvolvida na perspectiva comparada de dois romances: “O outro pé da sereia”, de Mia Couto, e “Bom dia Camaradas”, de Ondjaki, considerando, em ambos, o processo de construção da identidade do narrador. Para tanto, utiliza-se como categoria teórica privilegiada os trabalhos localizados na interface da teoria da literatura, que trabalham com a temática do tempo e os estudos culturais.

The goal of this article is to analyse the musical preferences of Brazilian students by considering the variables of gender and religion. Using random sampling, a class was selected from each high school year group of 10 public schools in the city of São Luís (Brazil).The total study sample consisted of 658 students: 358 females (54.4%) and 300 males (45.6%). Of these, 343 (52.1%) were Protestants and 315 (47.9%) were Catholics, and their ages ranged from 14 to 19 years (M = 16.24 years old, SD = 1.14). For the data collection, a version of the Questionnaire on Musical Style Preferences by Lorenzo, Herrera, and Cremades (2008) was used; however, it was shortened and culturally adapted to the Brazilian context. The participants were asked to evaluate how often they listened to 19 different styles of music. The overall results indicated that the participants’ musical preferences were heavily influenced by mass media. However, ANOVA results indicated significant differences and a variety of size effects in the frequency of musical listening based on gender and religion. Females had a greater preference for styles with emotional content, dance music and music with a strong connection to mass culture, while males preferred more vigorous styles. Regarding religion, Protestants had a stronger preference for gospel music, while Catholic preferences were more diverse.

Scanning probe microscopy and ab initio calculations reveal modifications on the electronic and structural properties of graphene/h-BN heterostructures induced by compression. Using AFM and EFM techniques, with charge injection being made in the heterostructures at different pressures, the charge injection efficiency monotonically decreases with increasing pressure for monolayer-graphene (MLG)+BN heterostructures, indicative of a conductor-insulator electronic transition. Bilayer-graphene (BLG)+BN and trilayer-graphene (TLG)+BN heterostructures show a non-monotonic behavior of charge injection versus pressure, indicative of competing electronic structure modifications. First-principle calculations of these systems indicate a pressure-induced van der Waals-to-covalent interlayer transition, where such interlayer covalent binding, in the presence of water molecules, results in a disordered insulating structure for the MLG + BN case, while it leads to an ordered conducting structure for both BLG + BN and TLG + BN heterostructures. These opposing effects may have a strong influence on graphene/h-BN-based electronic devices and their physics under pressurized environments.

The cementation of copper and cadmium by zinc powder was investigated in order to assess the influence of different parameters in the process. The results showed that the process follows a first order reaction with two stages in both systems. In the system Cu/Zn, the second stage is faster than the first while in the system Cd/Zn the second stage is slower than the first. In the system Cu/Zn, the variation on the surface area of copper cement followed a power law and a straight line was obtained by plotting –ln([Cu2+]/[Cu2+] 0 ) against t3/2, the activation energy was calculated as 16.3kJ. In the system Zn/Cd the surface area available for reaction decreased as a result of the cement agglomeration. On the experiments carried out with ions Cu2+ and Cd2+ in solution, purer copper cement was obtained when the experiments were carried out in the presence of less than stoichiometric amount of zinc powder and longer reaction times.

Os consumidores de bens e serviços de um determinado mercado são atraídos por um conjunto de atributos de valor que direta ou indiretamente os qualificam em relação aos seus concorrentes. Por outro lado, embora o “preço” seja apenas um dentre os vários atributos, ele muitas vezes é interpretado como uma variável resposta que reúne os demais, justamente pelo seu grau de relevância quanto à restrição orçamentária dos consumidores. Esse artigo objetiva entender o grau de influência e correlação de um conjunto de variáveis explicativas nos preços de imóveis residenciais ofertados para locação e venda na cidade de João Monlevade-MG, via modelos de regressão linear multivariada. A metodologia proposta se baseia em informações reais referentes aos preços ofertados na cidade e suas características estruturais e locacionais, a citar: quantidade de quartos e vagas na garagem; quantitativo de ocorrências policiais; proximidade com o centro comercial, postos de saúde e escolas estaduais mais próximas. Como resultado, foi possível obter um conjunto de equações matemática capazes de explicar o preço em função das variáveis preditoras, bem como entender a relação entre estas variáveis.

Energetics and electronic properties of three-layered hBN nanoribbons, with reconstructed edges, were investigated, using density functional theory. Such edges present lines of pentagonal and heptagonal rings, where homopolar B-B and N-N bonds exist. The homopolar bonds and their distribution, determine the energetic stability of hBN nanoribbons. The structures with the lowest amount of homopolar bonds presents a value of formation energy smaller than the single hBN layer, which suggests that such kind of reconstruction may indeed occur in real three-layered hBN systems. In addition, our results suggest that reconstructed edges on hBN nanoribbons are more stable than their carbon counterparts.