Publications

A Newtonian-like theory inspired by the Brans–Dicke gravitational Lagrangian has been recently proposed by us. For static configurations, the gravitational coupling acquires an intrinsic spatial dependence within the matter distribution. Therefore, the interior of astrophysical configurations may provide a testable environment for this approach as long as no screening mechanism is evoked. In this work, we focus on the stellar hydrostatic equilibrium structure in such a varying Newtonian gravitational coupling G scenario. A modified Lane–Emden equation is presented and its solutions for various values of the polytropic index are discussed. The role played by the theory parameter ω, the analogue of the Brans–Dicke parameter, in the physical properties of stars is discussed.

Hundred years after the flu pandemic of 1918, the world faces an outbreak of a new severe acute respiratory syndrome, caused by a novel coronavirus. With a high transmissibility, the pandemic spreads worldwide, creating a scenario of devastation in many countries. By the middle of 2021, about 3% of the world population has been infected and more than 4 million people have died. Different from the H1N1 pandemic, which had a deadly wave and cessed, the new disease is maintained by successive waves, mainly produced by new virus variants, and the small number of vaccinated people. In the present work, we create a version of the SIR model with spatial localization of persons, their movements, and taking into account social isolation probabilities. We discuss the effects of virus variants, and the role of vaccination rate in the pandemic dynamics. We show that, unless a global vaccination is implemented, we will have continuous waves of infections.HighlightsThe COVID-19 has infected more than 200 millions and has killed more than 4 million persons.WHO has not been successful in defining a global vaccination policy.Many epidemic scenarios arise when different countries apply different vaccination strategies.Present model can show some insights on how vaccination programs can be managed.Competing Interest StatementThe authors have declared no competing interest.Funding StatementThis research did not receive any specific grant from funding agencies in the commercial, or non-profit sectors. SPR acknowledges grant from Conselho Nacional de Desenvolvimento Cientifico e Tecnologico - CNPq, through proccess 306572/2019-2.Author DeclarationsI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.YesThe details of the IRB/oversight body that provided approval or exemption for the research described are given below:The manuscript is a modeling paper, there was no clinical trial of any kind.All 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).YesI 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.YesThe code of model is included in manuscript files.

In this work we apply first principles calculations to investigate the flat band phenomenology in twisted antimonene bilayer. We show that the relatively strong interlayer interactions which characterize this compound have profound effects in the emergence and properties of the flat bands. Specifically, when the moiré length becomes large enough to create well defined stacking patterns along the structure, out-of-plane displacements take place and are stabilized in the regions dominated by the AB stacking, leading to the emergence of flat bands. The interplay between structural and electronic properties allows for detection of flat bands in higher twist angles comparable to other two-dimensional materials. We also show that their energy position may be modulated by noncovalent functionalization with electron acceptor molecules.

Economic viability and eco-friendliness are important characteristics that make implants available to the population in a sustainable way. In this work, we evaluate the performance of a low-cost, widely available, and eco-friendly material (talc from soapstone) relative to reduced graphene oxide as reinforcement to brittle hydroxyapatite coatings. We employ a low-cost and straightforward technique, electrodeposition, to deposit the composite coatings on the titanium substrate. Corrosion, wear, and biocompatibility tests indicate that the reduced graphene oxide can be effectively replaced by talc without reducing the mechanical, anticorrosion, and biocompatible composite coatings properties. Our results indicate that talc from soapstone is a promising material for biomedical applications.

Co-, Ni-, and Mn-doped BiFeO3 (BFO) ceramics were synthesized herein through a solid-state reaction. All doped BFO samples exhibit visible-light response, and the Co- and Ni-doped BFO samples present enhanced ferromagnetic order at room temperature. All doped samples show secondary phases in minor quantities. Optical spectra reveal two absorptions bands, indicating multiple electron transitions for BFO and its secondary phases. M − H hysteresis loops suggest enhanced ferromagnetism in the Co- and Ni-doped BFO samples because of magnetic spinel CFP and NFO phases, respectively, whereas changes in oxygen vacancies and Fe–O–Fe bond angle play minor roles in the ferromagnetic behavior.

The world’s population suffers a COVID-19 pandemic. By September 2020 nearly 1 million people had died. These are official numbers. The real cases might be much higher, due to under-reporting in many countries. Different strategies were adopted by national governments. Neglecting what was defined by sanitarian authorities, some politicians, at the beginning of the pandemic, declared that it would be a little flu, without consequences, lighter than seasonal flues. Some politicians propagated medicines with no scientific support. In many countries and regions, people became confused. The population’s reactions to these political positions may facilitate or block the virus spread. In this paper, we propose a model connecting the spreading of opinions with the propagation of a pandemic. We discuss how conflicting opinions can diffuse in the pandemic environment and the influence it has on the population’s behavior; how it may cause a greater or smaller number of infected individuals.