Publications

2019
Boriero D, Schwarz DJ, Velten H. Flavour Composition and Entropy Increase of Cosmological Neutrinos After Decoherence. Universe [Internet]. 2019;5 (10). Publisher's VersionAbstract
We propose that gravitational interactions of cosmic neutrinos with the statistically homogeneous and isotropic fluctuations of space-time lead to decoherence. This working hypothesis, which we describe by means of a Lindblad operator, is applied to the system of two- and three-flavour neutrinos undergoing vacuum oscillations and the consequences are investigated. As a result of this decoherence we find that the neutrino entropy would increase as a function of initial spectral distortions, mixing angles and charge-parity (CP)-violation phase. Subsequently we discuss the chances to discover such an increase observationally (in principle). We also present the expected flavour composition of the cosmic neutrino background after decoherence is completed. The physics of two- or three-flavour oscillation of cosmological neutrinos resembles in many aspects two- or three-level systems in atomic clocks, which were recently proposed by Weinberg for the study of decoherence phenomena.
Calheiro DS, Bianchi RF. Tuning the detection limit in hybrid organic-inorganic materials for improving electrical performance of sensing devices. Sensors and Actuators A: Physical [Internet]. 2019;298 :111480. Publisher's VersionAbstract
Research in hybrid electronics has included advances in materials, devices and architectures. However, in practice, controversy still exists on some details which limit hybrid materials to high-performance applications, such as processing–structure–design–property relations. This paper describes a practical approach to enhancing the sensing performance of a prototype ammonia gas sensor based on electrical conductivity changes, percolation theory and current limitation to a semiconducting polymer-metal oxide medium. This device is based on fully-gravure printed polyaniline/indium - tin oxide nanocomposites, Pani100−xITOx [0 ≤ x≤ 100% (wt/wt)], layers on a freestanding high-density polyethylene substrate. We find that the electrical current of the device decreases and tends to saturate as the gas concentration increases, and the value of this electrical current limit (IL) depends on x: the higher the value of x, the smaller the IL, when the current that flows through the electronic device was dominated by the ITO-nanoparticle filled PAni, which increase the concentration of hopping carriers and contribute to the desired electrical response of a heterogeneous gas sensor. In this regime, we find a good linear relationship between x and ammonia concentration. These findings suggest new directions for future research on the development and investigation of organic-inorganic devices in which the electrical current variation is desired for enhanced sensitivity and stability of hybrid sensors.
Nascimento R, Moraes EE, Matos MJS, Prendergast D, Manhabosco TM, de Oliveira AB, Chacham H, Batista RJC. Graphene/h-BN In-Plane Heterostructures: Stability and Electronic and Transport Properties. The Journal of Physical Chemistry C [Internet]. 2019;123 (30) :18600-18608. Publisher's Version
Santos J, Barboza A, Matos MJS, Barcelos ID, Fernandes TFD, Soares EA, Moreira RL, Almeida Neves BR. Exfoliation and characterization of a two-dimensional serpentine-based material. Nanotechnology [Internet]. 2019. Publisher's VersionAbstract
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.
Zimdahl W, Velten HES, Algoner WC. Matter growth in extended $Łambda$CDM cosmology. Int. J. Mod. Phys. 2019;D28 (06) :1950086.
Fabris JC, Velten H, Wojnar A. Existence of static spherically-symmetric objects in action-dependent Lagrangian theories. Phys. Rev. D [Internet]. 2019;99 :124031. Publisher's Version
Perenon L, Velten H. The Effective Field Theory of Dark Energy Diagnostic of Linear Horndeski Theories After GW170817 and GRB170817A. Universe [Internet]. 2019;5 (6). Publisher's VersionAbstract
We summarize the effective field theory of dark energy construction to explore observable predictions of linear Horndeski theories. We review the diagnostic of these theories on the correlation of the large-scale structure phenomenological functions: the effective Newton constant, the light deflection parameter, and the growth function of matter perturbations. We take this opportunity to discuss the evolution of the bounds the propagation speed of gravitational waves has undergone and use the most restrictive one to update the diagnostic.
Salla CAM, Teixeira dos Santos J, Farias G, Bortoluzi AJ, Curcio SF, Cazati T, Izsák R, Neese F, de Souza B, Bechtold IH. New Boron(III) Blue Emitters for All-Solution Processed OLEDs: Molecular Design Assisted by Theoretical Modeling. European Journal of Inorganic Chemistry [Internet]. 2019;2019 (17) :2247-2257. Publisher's VersionAbstract
Luminescent boron(III) complexes have recently been employed as emitters in organic light-emitting diodes (OLEDs) with reasonable success. They are easy to prepare and sufficiently stable to be used in such devices, being of great interest as a simple molecular emissive layer. Although emitters for this class with all colors have already been reported, highly efficient and stable blue emitters for applications in solution processed devices still pose a challenge. Here, we report the design, synthesis, and characterization of new boron complexes based on the 2-(benzothiazol-2-yl)phenol ligand (HBT), with different donor and acceptor groups responsible for modulating the emission properties, from blue to red. The molecular design was assisted by calculations using our newly developed formalism, where we demonstrate that the absorption and fluorescence spectra can be successfully predicted, which is a powerful technique to evaluate molecular photophysical properties prior to synthesis. In addition, density functional theory (DFT) enables us to understand the molecular and electronic structure of the molecules in greater detail. The molecules studied here presented fluorescence efficiencies as high as Φ = 0.88 and all solution processed OLEDs were prepared and characterized under an ambient atmosphere, after dispersion in the emitting layer. Surprisingly, even considering these rather simple experimental conditions, the blue emitters displayed superior properties compared to those in the present literature, in particular with respect to the stability of the current efficiency.
Zimdahl W, Velten HES, Algoner WC. Matter Growth in Imperfect Fluid Cosmology. Universe [Internet]. 2019;5 (3). Publisher's VersionAbstract
Extensions of Einstein’s General Relativity (GR) can formally be given a GR structure in which additional geometric degrees of freedom are mapped on an effective energy-momentum tensor. The corresponding effective cosmic medium can then be modeled as an imperfect fluid within GR. The imperfect fluid structure allows us to include, on a phenomenological basis, anisotropic stresses and energy fluxes which are considered as potential signatures for deviations from the cosmological standard Λ -cold-dark-matter ( Λ CDM) model. As an example, we consider the dynamics of a scalar-tensor extension of the standard model, the e Φ Λ CDM model. We constrain the magnitudes of anisotropic pressure and energy flux with the help of redshift-space distortion (RSD) data for the matter growth function f σ 8 .
Dias RF, da Costa CC, Manhabosco TM, de Oliveira AB, Matos MJS, Soares JS, Batista RJC. Ab initio molecular dynamics simulation of methanol and acetonitrile: The effect of van der Waals interactions. Chemical Physics Letters [Internet]. 2019;714 :172 - 177. Publisher's VersionAbstract
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.
Souza FS, Matos MJS, Galvão BRL, Arapiraca AFC, da Silva SN, Pinheiro IP. Adsorption of CO2 on biphasic and amorphous calcium phosphates: An experimental and theoretical analysis. Chemical Physics Letters [Internet]. 2019;714 :143 - 148. Publisher's VersionAbstract
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.
dos Santos PL, Silveira OJ, Huang R, Jardim GAM, Matos MJS, da Silva Júnior EN, Monkman AP, Dias FB, Cury LA. Dynamics of aggregated states resolved by gated fluorescence in films of room temperature phosphorescent emitters. Phys. Chem. Chem. Phys. [Internet]. 2019;21 :3814-3821. Publisher's VersionAbstract
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.
2018
da Costa Junior E, da Fernandes BS, da Lima GS, de Siqueira AJ, Paiva JNM, e Santos MG, Tavares JP, de Souza TV, Gomes TMF. Divulgacão e ensino de Astronomia e Física por meio de abordagens informais. Revista Brasileira de Ensino de FÃ\-sica [Internet]. 2018;40. Publisher's Version
Silva Nunes ME, de Silva ÉM, Martins PHL, Plascak JA, Florencio J. Effects of a magnetic field on the dynamics of the one-dimensional Heisenberg model with Dzyaloshinskii-Moriya interactions Phys. Rev. E. PHYSICAL REVIEW E [Internet]. 2018 :null. Publisher's Version
da C. Gonçalves M, Taylor J, Rossoni Júnior J, Carolina S. Rabelo A, Costa D, Cazati T, M. R. dos Santos V. Preliminary Studies of the Cytotoxicity and Photoprotective Properties of Benzophenone and Lactone Derivatives. Revista Virtual de Química. 2018;10 :600-608.
Barboza APM, Matos MJS, Chacham H, Batista RJC, de Oliveira AB, Mazzoni MSC, Neves BRA. Compression-Induced Modification of Boron Nitride Layers: A Conductive Two-Dimensional BN Compound. ACS Nano [Internet]. 2018 :null. Publisher's Version
de Sousa TASL, Fernandes TFD, Matos MJS, Araujo END, Mazzoni MSC, Neves BRA, Plentz F. Thionine Self-Assembled Structures on Graphene: Formation, Organization, and Doping. Langmuir [Internet]. 2018;34 (23) :6903-6911. Publisher's Version
Colla T, Mohanty PS, Nöjd S, Bialik E, Riede A, Schurtenberger P, Likos CN. Self-Assembly of Ionic Microgels Driven by an Alternating Electric Field: Theory, Simulations, and Experiments. ACS Nano [Internet]. 2018 :null. Publisher's Version
Alencar TV, von Dreifus D, Moreira MGC, Eliel GSN, Yeh C-H, Chiu P-W, Pimenta MA, Malard LM, de Paula AM. Twisted bilayer graphene photoluminescence emission peaks at van Hove singularities. Journal of Physics: Condensed Matter [Internet]. 2018;30 (17) :175302. Publisher's VersionAbstract
We report on photoluminescence emission imaging by femtosecond laser excitation on twisted bilayer graphene samples. The emission images are obtained by tuning the excitation laser energies in the near infrared region. We demonstrate an increase of the photoluminescence emission at excitation energies that depends on the bilayer twist angle. The results show a peak for the light emission when the excitation is in resonance with transitions at the van Hove singularities in the electronic density of states. We measured the photoluminescence excitation peak position and width for samples with various twist angles showing resonances in the energy range of 1.2 to 1.7 eV.
Cariglia M, Galajinsky A, Gibbons GW, Horvathy PA. Cosmological aspects of the Eisenhart–Duval lift. The European Physical Journal C [Internet]. 2018;78 (4) :314. Publisher's VersionAbstract
A cosmological extension of the Eisenhart–Duval metric is constructed by incorporating a cosmic scale factor and the energy-momentum tensor into the scheme. The dynamics of the spacetime is governed by the Ermakov–Milne–Pinney equation. Killing isometries include spatial translations and rotations, Newton–Hooke boosts and translation in the null direction. Geodesic motion in Ermakov–Milne–Pinney cosmoi is analyzed. The derivation of the Ermakov–Lewis invariant, the Friedmann equations and the Dmitriev–Zel'dovich equations within the Eisenhart–Duval framework is presented.

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