Publications

The current Universe is composed by a mixture of relativistic species, baryonic matter, dark matter and dark energy which evolve in a non-trivial way at perturbative level. An advanced description of the cosmological dynamics should include non-standard features beyond the simplistic approach idealized by the standard cosmology in which cosmic components do not interact, are adiabatic and dissipationless. We promote a full perturbative analysis of linear scalar perturbations of a non-interacting cosmological model containing baryons, dark matter (both pressureless) and a scalar field allowing for the presence of relative entropic perturbations between the three fluids. Assuming an effective scalar-field sound speed equal to one and neglecting anisotropic stresses we establish a new set of equations for the scalar cosmological perturbations. As a consequence of this new approach, we show that tiny departures from a constant scalar field equation of state wS=−1 damage structure formation in a non-acceptable manner. Hence, by strongly constraining wS our results provide compelling evidence in favor of the standard cosmological model and rule out a large class of dynamical dark energy models.

Hydroxyapatite nanoparticles have been investigated as biological agents for the treatment and diagnosis of bone diseases due to their properties, providing high affinity to bone tissues and also due to the possibility to chemically modify the surfaces of these nanoparticles to provide active targeting to bone tumors or other bone disorders. In this work, synthetic hydroxyapatite nanoparticles and their surface modifications with folic and medronic acid were studied. Copper-64 was produced by neutron irradiation in a TRIGA MARK I nuclear reactor, and the functionalized nanoparticles radiolabeled with this radioisotope. The multi-technique characterization includes FTIR, PXRD, TGA, DSC, CHN, Zeta potential, XPS, SEM, TEM, and Gamma spectroscopy. Furthermore, the evaluation of the chemical interaction stability was through leaching tested for efficiency. The results indicate that folic and medronic acids can be covalently bonded to HA surface, producing a new material not yet described in the literature, been stably attached to hydroxyapatite nanoparticle surfaces, able to provide active targeting for bone disorders. The complexation of copper-64 provides high radiochemistry purity, although the specific activity must be improved.

The mixed crystals of the Tutton’s salt doped with Li following the empirical formula K2LiyNixCo1-x (SO4)2.6H2O, were synthesized from the slow evaporation of the solvent at constant temperature. The presence of K, S, Ni, Co and O elements in the studied crystalline structure was confirmed by EDS spectroscopy using a scanning electron microscope and their quantification including Li was carried out with the help of ICP-OES technique. Raman spectroscopy in the range 100−3600 cm−1, confirmed the presence of tetrahedral (SO4), octahedral complexes Ni(H2O)6, Co(H2O)6, and H2O molecules in the crystal structure. Our UV–vis studies have shown that the mixed crystals have good optical transparency in the ultraviolet (200−350 nm) and infrared (750−1000 nm) region. The direct and indirect optical energy gap of the synthesized crystals were determined from the Tauc’s plot. XRD diffractograms of the sample crystals do not show any specific changes due to the presence of Li ion in the crystalline network.

Background We investigated a likely scenario of COVID-19 spreading in Brazil through the complex airport network of the country, for the 90 days after the first national occurrence of the disease. After the confirmation of the first imported cases, the lack of a proper airport entrance control resulted in the infection spreading in a manner directly proportional to the amount of flights reaching each city, following the first occurrence of the virus coming from abroad. Methodology We developed a Susceptible-Infected-Recovered model divided in a metapopulation structure, where cities with airports were demes connected by the number of flights. Subsequently, we further explored the role of the Manaus airport for a rapid entrance of the pandemic into indigenous territories situated in remote places of the Amazon region. Results The expansion of the SARS-CoV-2 virus between cities was fast, directly proportional to the city closeness centrality within the Brazilian air transportation network. There was a clear pattern in the expansion of the pandemic, with a stiff exponential expansion of cases for all the cities. The more a city showed closeness centrality, the greater was its vulnerability to SARS-CoV-2. Conclusions We discussed the weak pandemic control performance of Brazil in comparison with other tropical, developing countries, namely India and Nigeria. Finally, we proposed measures for containing virus spreading taking into consideration the scenario of high poverty.

Propolis is a natural, non-toxic resin produced by honey bees that has been used for hundreds of years for its biological activities, such as antimicrobial, anti-inflammatory, anesthetic, cytostatic, and cariostatic properties. Currently, it is used in food, pharmaceutical, and cosmetic industries. The aim of this work was to evaluate the antioxidant activity, sun protection factor, and photostability of different hydroalcoholic extracts of green propolis. All extracts prepared presented high absorption in the UVB region. The extract of 70% green propolis (high temperature) was incorporated into Gel Permulen TR-1. This new formulation presented a higher value of sun protection factor. Besides that, the formulation developed with Gel Permulen TR-1 and the hydroalcoholic extract of 70% green propolis (high temperature) showed good photostability and it was safe to be applied on the skin according the HET-CAM test. These results indicated the potential of hydroalcoholic extracts of 70% green propolis (high temperature) for use in sunscreen.

ABSTRACT The use of polyaniline (PANI) as a conductive material has steadily increased in recent years due to its interesting physicochemical properties, low manufacturing cost, and easy processing. This conductive material, associated with the diffraction properties of organized nanostructures in thin films, has excellent application potential in microelectronics and photonic devices. Initially, this work presents improvement routes for the breath figure method (a nanopatterning technique) in polystyrene (PS) films through the control of film deposition parameters and the presence of water in the polymer solution. Such improvements are then extended to the production of PANI nanostructures, in the form of pores, from patterned porous PS films. Consequently, PANI films with a partially ordered pore structure (mean pore diameter of  100 nm) are produced in a facile and easily scalable method. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48597.

Low-dimensionality materials are highly susceptible to interfaces. Indeed, intercalation of different chemical species in between epitaxial graphene and silicon carbide (SiC), for instance, may decouple the graphene with respect to the substrate due to the conversion of the buffer layer into a graphene layer. O-intercalation is known to release the strain of such 2D material and to lead to the formation of high structural quality AB-stacked bilayer graphene. Nonetheless, this interface transformation concomitantly degrades graphene electronic transport properties. In this work we employed different techniques in order to better understand the structure of the graphene/SiC interface generated by O-intercalation and to elucidate the origin of the poor electronic properties of graphene. Experimental results revealed the formation of a SiO2 rich layer with a defective transition layer in between it and the SiC, which is characterized by the existence of silicon oxycarbide structures. Scanning tunneling spectroscopy measurements revealed an extensive presence of electronic states just around the Fermi level all over the sample surface, which may suppress the charge carriers mobility around this region. According to theoretical calculations, such states are mainly due to the formation of silicon oxicarbides within the interfacial layer.

Molecular Dynamics simulations of water confined in carbon nanotubes subjected to external electric fields show that water mobility strongly depends on the confining geometry, the intensity and directionality of the electric field. While fields forming angles of 0° and 45° slow down the water dynamics by increasing organization, perpendicular fields can enhance water diffusion by decreasing hydrogen bond formation. For 1.2 diameter long nanotubes, the parallel field destroys the ice-like water structure increasing mobility. These results indicate that the structure and dynamics of confined water are extremely sensitive to external fields and can be used to facilitate filtration processes.

Herein, we report the synthesis and characterization of fluorophores containing a 2,1,3-benzoxadiazole unit associated with a π-conjugated system (D-π-A-π-D). These new fluorophores in solution exhibited an absorption maximum at around  419 nm (visible region), as expected for electronic transitions of the π-π^* type (ε  2.7 × 10⁷ L mol⁻¹ cm⁻¹), and strong solvent-dependent fluorescence emission (Φ_FL  0.5) located in the bluish-green region. The Stokes' shift of these compounds is ca. 3,779 cm⁻¹, which was attributed to an intramolecular charge transfer (ICT) state. In CHCl₃ solution, the compounds exhibited longer and shorter lifetimes, which was attributed to the emission of monomeric and aggregated molecules, respectively. Density functional theory was used to model the electronic structure of the compounds 9a–d in their excited and ground electronic states. The simulated emission spectra are consistent with the experimental results, with different solvents leading to a shift in the emission peak and the attribution of a π-π^* state with the characteristics of a charge transfer excitation. The thermal properties were analyzed by thermogravimetric analysis, and a high maximum degradation rate occurred at around 300°C. Electrochemical studies were also performed in order to determine the band gaps of the molecules. The electrochemical band gaps (2.48–2.70 eV) showed strong correlations with the optical band gaps (2.64–2.67 eV).

Background. We investigated a likely scenario of COVID-19 spreading in Brazil through the complex airport network of the country, for the 90 days after the first national occurrence of the disease. After the confirmation of the first imported cases, the lack of a proper airport entrance control resulted in the infection spreading in a manner directly proportional to the amount of flights reaching each city, following first occurrence of the virus coming from abroad. Methodology. We developed a SIR (Susceptible-Infected-Recovered) model divided in a metapopulation structure, where cities with airports were demes connected by the number of flights. Subsequently, we further explored the role of Manaus airport for a rapid entrance of the pandemic into indigenous territories situated in remote places of the Amazon region. Results. The expansion of the SARS-CoV-2 virus between cities was fast, directly proportional to the airport closeness centrality within the Brazilian air transportation network. There was a clear pattern in the expansion of the pandemic, with a stiff exponential expansion of cases for all cities. The more an airport showed closeness centrality, the greater was its vulnerability to SARS-CoV-2. Conclusions. We discussed the weak pandemic control performance of Brazil in comparison with other tropical, developing countries, namely India and Nigeria. Finally, we proposed measures for containing virus spreading taking into consideration the scenario of high poverty.Competing Interest StatementThe authors have declared no competing interest.Funding StatementFunding by CNPqAuthor DeclarationsAll relevant ethical guidelines have been followed; any necessary IRB and/or ethics committee approvals have been obtained and details of the IRB/oversight body are included in the manuscript.YesAll necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived.YesI understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.YesI state all data will be available in submission material

Viscous properties are attributed to the dark sector of the Universe. They contribute to the accelerated expansion phase of the Universe and can alleviate existing tensions in the ΛCDM model at small scales. We provide a short review of recent efforts on this topic. Different viscous models for the dark sector are analysed both from theoretical and observational point of view.

The control of geometric structure is a key aspect in the interplay between theoretical predictions and experimental realization in the science and applications of nanomaterials. This is particularly important in one-dimensional structures such as nanoribbons, in which the edge morphology dictates most of the electronic behavior in low energy scale. In the present work we demonstrate by means of first principles calculations that the oxidation of few-layer antimonene may lead to an atomic restructuring with formation of ordered multilayer zig-zag nanoribbons. The widths are uniquely determined by the number of layers of the initial structure, allowing the synthesis of ultranarrow ribbons and chains. We also show that the process may be extended to other compounds based on group V elements, such as arsenene. The characterization of the electronic structure of the resulting ribbons shows an important effect of stacking on band gaps and on modulation of electronic behavior.

v. 13, n. 4 (2019): Especial: Física p.63-69

Extensions of the gravity theory in order to obtain traceless field equations have been widely considered in the literature. The leading example of such class of theories is the unimodular gravity, but there are other possibilities like the mimetic gravity and the Rastall gravity with a coupling parameter λ = 1/2. The unimodular gravity proposal is a very interesting approach in order to address the cosmological constant problem. When coupled to matter, such theories may imply that the energy–momentum tensor is not divergence free anymore. In this paper, a unimodular type theory will be developed by evading the conservation T;μμν = 0. The cosmological consequences of the later, both at background as well as for scalar and tensor perturbations, are explored. Possible further extensions of this approach are discussed as well as its connection with the traditional unimodular gravity.