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Disertaciones |
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1
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CELSO ALVES DO NASCIMENTO JÚNIOR
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Entanglement of Valley Excitonic Qubits in the New Two-Dimensional Systems Integrated into a Nanocavity
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Líder : QU FANYAO
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MIEMBROS DE LA BANCA :
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DAVID LIMA AZEVEDO
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ALEXANDRE CAVALHEIRO DIAS
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ANDRÉ JORGE CARVALHO CHAVES
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MARCOS RAFAEL GUASSI
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Data: 20-ene-2023
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Resumen Espectáculo
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In this work, the qubit-excitonic dynamics in three different quantum systems will be analyzed which will allow us to extract various relevant information, such as the concurrence, which it is the means by which it is possible to calculate how entangled a quantum system is. First we study the open quantum system composed by two valleys populated by bright excitons, where it was shown that competition as a function of time always decays, that is, it always reached zero steady states. In the second study, we introduced to the first system a bimodal microcavity, where two initial states di- ferents: The first with the qubit-excitons in an uncorrelated state (non-correlated state). entangled) and the cavity photons in a Bell state (maximally entangled state). in the second initial state, we leave the qubit-excitons in a Bell state and the cavity photons in an uncorrelated state. Calculations were then carried out post-dynamics, such as the separation of the density matrices of the composite system, and finally we calculated the concurrence for the excitonic system. This analysis showed that the concurrence presented satisfactory stationary values for its use in Computing Quantum, showing that the cavity introduced to the system benefited entanglement of qubit-excitons. In the third, we worked with a system of three levels located in a single valley, populated by bright and dark qubit-excitons, where the objective was to find analytical stationary solutions, as well as comparing the equations of motion obtained through the Linblad Master Equation with the equations obtained using the formalism of the rate equations.
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2
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Guilherme Carlos Carvalho de Jesus
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Electronic and dynamic properties of non-covalent diatomic aggregates formed by helium with neutral and ionic lithium and beryllium.
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Líder : RICARDO GARGANO
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MIEMBROS DE LA BANCA :
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Cassius Marcellus Costa Carvalho
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FERNANDO MARQUES CARVALHO
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LUIZ ANTONIO RIBEIRO JUNIOR
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RICARDO GARGANO
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Data: 24-feb-2023
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Resumen Espectáculo
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This work aims to study the influence of the absence and presence of permanent charges on the electronic and dynamical properties of the non-covalent bound diatomic systems involving He and Li, Be as neutral and ionic partners. More precisely, by advanced theoretical methods, it was determined the potential energy curves describing the stability of the HeLi, HeLi+, HeBe, HeBe+, and HeBe2+ systems, the charge displacement within the formed adducts, the decomposition of their total interaction energy, the topological analysis of their bonds, their rovibrational energies, their spectroscopic constants and lifetimes. The charge displacement results suggest that in the formation of HeLi+, HeBe+, and HeBe2+, the neutral He atom undergoes, in the electric field of the ion, a pronounced electronic polarization, and the natural bond order theoretical approach indicates that in the formation of the molecular orbital He acts as a weak electron donor. The energy decomposition analysis provides the dispersion and induction components as the attractive leading terms controlling the stability of all systems, confirming that the formed bond substantially maintains a non-covalent nature which is also supported by the Quantum Theory of Atoms in Molecules (QTAIM) analysis. Finally, it was found that the HeLi and HeBe neutral systems are unstable under any condition, HeLi+ and HeBe+ ionic systems are stable below 317K and 138K, respectively, while the HeBe2+ system becomes unstable only after 3045K.
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3
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Amanda Queiroz Sena
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Vibrational and Long-Range Corrections in the Reorganization Energy of Photosynthetic Molecules
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Líder : PEDRO HENRIQUE DE OLIVEIRA NETO
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MIEMBROS DE LA BANCA :
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DEMETRIO ANTONIO DA SILVA FILHO
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LEONARDO EVARISTO DE SOUSA
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PEDRO HENRIQUE DE OLIVEIRA NETO
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WILIAM FERREIRA DA CUNHA
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Data: 30-mar-2023
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Resumen Espectáculo
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Photosynthetic organisms are responsible for the most abundant form of energy con- version in nature. Therefore, it is important to understand how charge transport between the mo- lecules involved in this process works. According to Marcus theory, this transport depends on certain properties of these molecules, such as reorganization energy (λ) and Gibbs free energy. These properties can be quantitatively estimated by applying density functional theory (DFT). However, most pigments in photosynthesis have conjugated bonds. Thus, the alternation of single and double bonds increases the overlap of electronic orbitals. Therefore, orbital deloca- lization and vibrational effects are even more relevant for these molecules. Here, we calculated the reorganization energies of 15 important molecules for photosynthesis using a reliable DFT- based approach. The fitting of the long-range parameter of the functional reduces the effects of orbital delocalization, while molecular vibrations are accounted for by the method of nu- clear ensembles. The results show that the functional fitting reduces the reorganization energy, while the vibrational effects produce distributions of this quantity, affecting charge transfer rates between the molecules involved by up to an order of magnitude.
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4
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Miguel Citeli de Freitas
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Squeezing and non-Gaussianity of coherent phase states
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Líder : VIKTOR DODONOV
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MIEMBROS DE LA BANCA :
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CAIO CESAR HOLANDA RIBEIRO
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MATHEUS BARBOSA DE ALCÂNTARA HOROVITS
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SERGIO COSTA ULHOA
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VIKTOR DODONOV
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Data: 14-sep-2023
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Resumen Espectáculo
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One of the main attempts to describe the phase of quantum systems was proposed by Lerner, Huang and Walters in 1970 with the introduction of coherent phase states |ε⟩ = p 1 − |ε| 2 P∞ n=0 ε n |n⟩, where |n⟩ are the Fock states and ε = |ε|e iφ, with |ε| < 1 and φ ∈ [0, 2π). The states |ε⟩ were named by Shapiro, Shepard and Wong in 1990 due to their similarity with the Glauber-Sudarshan coherent state, differing only in the absence of the factor 1/ √ n! in its definition, |α⟩ = exp − 1 2 |α| 2 P∞ n=0 α n √ n! |n⟩. Since most works on phase are dedicated to studying properties of the number and phase operators (ˆn, φˆ), we chose to focus our research on the characteristics associated with the position and moment operators (ˆx, pˆ), initially calculating mean values and variances. We observe that there is a strong squeezing of the position (momentum) when the phase is equal to π/2 (0), although this is still smaller than the squeezing suffered by the squeezed vacuum state. We noticed that the mixed analogue of the pure state |ε⟩, described by the statistical operator ˆρ = (1 − |ε| 2 ) P∞ n=0 |ε| 2n|n⟩⟨n|, has a Gaussian density matrix ⟨x|ρˆ|x⟩, even though the probability density |ψε(x)| 2 is not. For this reason, we investigated in detail different measures of non-Gaussianity of coherent phase states. Finally, we calculated the Wigner function of |ε⟩ and saw how Gaussianity is easily lost with small variations of φ when ε is close to 1.
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5
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Matheus de Souza Lucena Trindade
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Isotopic "catalysts" and anti-Arrhenius behaviors in chiral transitions of non-covalent complexes.
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Líder : RICARDO GARGANO
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MIEMBROS DE LA BANCA :
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ALEXANDRE NAVES DE BRITO
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DAVID LIMA AZEVEDO
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RICARDO GARGANO
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Railson da Conceição Vasconcelos
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Data: 18-dic-2023
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Resumen Espectáculo
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This study reports on the isotopic effect controlling the conformation rearrangement rates, as a function of the temperature, of isolated hydrogen peroxide (H2O2), the simplest chiral molecule exhibiting enantiomeric configurations, and of the same molecule in weakly bound complexes formed with noble gases (He, Ne, Ar, Kr, Xe, and Rn), as both H atoms are replaced by the muonium (the lightest isotope of the hydrogen atom), deuterium, and tritium (the heaviest isotopes of the hydrogen atom). The thermal chiral rate calculations, with and without tunneling corrections, were performed exploiting the theory of transition state by using geometries, energies, and frequencies of relevance calculated at MP2(full)/aug-cc-pVTZ level and with Counterpoise correction of basis set superposition error. Through this study, we understood how isotopes and noble gases affect the transition rates between chiral conformations of hydrogen peroxide. The findings indicate that muonium acts as a ”catalyst” for chiral transition, providing an important anti-Arrhenius behavior controlled by the tunneling through barriers, whereas deuterium and tritium have a preserving effect, that is their rates follow the canonical Arrhenius behavior. Furthermore, heavier noble gases significantly alter the chiral conformational rate.
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6
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LUIGI LUCAS DE CARVALHO SILVA
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Angular power spectrum of galaxies and cosmic microwave background lensing: validation of the CCL and NumCosmo libraries.
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Líder : MARIANA PENNA LIMA VITENTI
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MIEMBROS DE LA BANCA :
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BRUNO AZEVEDO LEMOS MORAES
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CAMILA PAIVA NOVAES
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MARIANA PENNA LIMA VITENTI
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VANESSA CARVALHO DE ANDRADE
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Data: 21-dic-2023
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Resumen Espectáculo
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With the increase in the volume of observational data obtained from astronomical surveys and the improvement in the accuracy of these data, statistical errors in the estimates of cosmological and astrophysical parameters are being surpassed by systematic errors. To better constrain these parameters and minimize the impact of systematic errors on analyses, in addition to calculating the angular power spectrum of a certain cosmological probe, another tool is gaining importance: the cross-angular power spectrum between probes of different natures. Furthermore, with the improved precision of the data, it is also necessary for numerical calculations to have sufficient precision so that numerical errors do not interfere with data analyses. Therefore, the comparison and validation of different computational libraries are essential to ensure such precision. In this work, we focus on the theoretical calculation of auto- and cross-angular power spectra of galaxies and the gravitational lensing of the cosmic microwave background (CMB). To do this, we conduct a literature review of the standard cosmological model to obtain the linear matter power spectrum. Next, we address the calculation of the two-point correlation and, consequently, the angular power spectrum. We then discuss two matter tracers: the distribution of galaxies and CMB lensing. Finally, we perform the numerical calculation of auto- and cross- power spectra using the programming libraries Core Cosmology Library (CCL) and Numerical Cosmology (NumCosmo), which are used by the Dark Energy Science Collaboration of the Legacy Survey of Space and Time (DESC/LSST). We calculate the relative difference between the results of both libraries and discuss the numerical accuracy of these calculations.
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7
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Bruna Cristina Corcino Carneiro
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Studies of cyclic structures: nanobelts of boron nitride and double nanorings.
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Líder : DAVID LIMA AZEVEDO
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MIEMBROS DE LA BANCA :
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DAVID LIMA AZEVEDO
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EDVAN MOREIRA
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FERNANDO ALBUQUERQUE DE OLIVEIRA
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RICARDO GARGANO
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Data: 21-dic-2023
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Resumen Espectáculo
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Since the 1950s, theoretical researchers in the field of nanomaterials have focused their attention on developing computational methods capable of creating nanotube structures that can be recreated in nature with the aim of contributing to the technological market. From this perspective, this research proposes the creation and analysis of nanoring and nanobelt structures that can contribute to the construction and physical characterization of nanotubes. In this work, 19 nanoring structures were developed, theorized and calculated using Density Functional Theory (DFT), which proved to be stable and promising to be synthesized. Their computational calculations presented relevant results based on the analysis of convergence criteria, such as: analysis of structural, electronic and optical properties. However, some of these structures showed significant results electronically: three of them showed superconducting properties and one structure showed insulating properties. All of these electronic properties have promising applications in the cosmetic and energy industries, which means that this research can indirectly contribute to the well-being of society. Furthermore, a nanobelt structure was developed, the Boron Nitride nanobelts. It was calculated using DFT and Time-Dependent Density Functional Theory (TDFT) and it was identified that it could be a possible replacement for [12]cyclofenacene as it is more stable and less energetic, which contributes to the detection of ultraviolet radiation (UV).
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Tesis |
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1
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FUJUN LIU
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Estudo das Propriedades Topológicas, Elétricas e Ópticas, e a Dinâmica de Portadores de Materiais 2D
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Líder : QU FANYAO
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MIEMBROS DE LA BANCA :
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ALEXANDRE CAVALHEIRO DIAS
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DAVID LIMA AZEVEDO
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MARIANA MALARD SALES ANDRADE
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DIEGO RABELO DA COSTA
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SABRINA MENDONÇA RUFO
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Data: 03-mar-2023
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Resumen Espectáculo
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First, we propose an simple and general method to create robust topological nodal line semi-metal, by introducing periodic vacancies into the lattice. Normally the nodal lines are suppressed in the presence of spin orbit coupling, unless they are protected by some topological symetries. In this section, we turn a 2D material into a lattice with nonsymmorphic symmetry, by periotically removing selected atoms. As a case study, we investigate borophene (a honeycomb-like boron sheet). Pristine borophene is employed as the reference. While the Dirac cones of pristine borophene are gapped out by spin orbit coupling and magnetic exchange, robust nodal lines emerge in the energy spectrum of borophene with nonsymmorphic symmetry. We propose an effective 2D model and a symmetry analysis to demonstrate that these nodal lines are topological and protected by a nonsymmorphic glide plane. Our findings offer a paradigm shift to the design of nodal line semi-metals: instead of searching for nonsymmorphic materials, robust nodal line semi-metals may be realized simply by removing atoms from ordinary symmorphic crystals.
Next, we study the the excitonic spectrum of 2D material and the heterostructure derivatives. Our approach takes into account the anomalous screening in two dimensions and the presence of a magnetic substrate. The Bethe-Salpeter equation is solved for a DFT-based tight-binding description of the single particle spectrum. We obtain the main features of the optical spectrum analyzing the localization in light zone of the excitonic peaks. We study the effect of different stacking forms on the main optical features of heterostructures, namely, the contributions of interlayer interaction, and the validity of valley polorizations. We compare the absolute magnitude of the linear optical conductivity.
Finally, we investigate the inter-/intra- valley scattering of carriers in 2D transition metal dichalcogenide monolayers. A detailed analysis of the electron-phonon and exciton-phonon inter-/intra- valley scattering is described. The scattering of electrons at conduction bands are studied by several teams, but the scattering of holes at valence bands is never reported yet, due to the big energy difference induced by spin-orbit coupling. To solve this issue, we study the scattering possibility by exciton exchange effect between different valleys.
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2
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Carlos Xavier de Oliveira
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Study of the Electronic Structure of Neutral and Ionized Organic Molecules, in the search for fragmentation routes.
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Líder : DAVID LIMA AZEVEDO
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MIEMBROS DE LA BANCA :
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DAVID LIMA AZEVEDO
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ALEXANDRE CAVALHEIRO DIAS
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RICARDO GARGANO
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GUNAR VINGRE DA SILVA MOTA
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ANTÔNIO MAIA DE JESUS CHAVES NETO
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Data: 24-abr-2023
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Resumen Espectáculo
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The study presented in this doctoral thesis work is important for us to understand the elec-tronic properties of a group of organic molecules, such as the amino acid cysteine and aromatic molecules (benzene, aniline, and o-, m-, and p-nitroaniline), in their forms of neutral and singly charged ions, which has great interest in the field of atomic molecular physics, quantum chemistry, pharmacy, biochemistry, and industrial chemistry. Five conformations of the cysteine amino acid (Cys01, Cys02, Cys03, Cys04, and Cys05) were calculated, with five neutral molecules and from these structures, five cationic conformations were calculated. The calculation results showed that there are structural modifications in the cysteine amino acid conformations, which are evident in the lengths of chemical bonds, bond orders (BOs), and charge distribution, when comparing the differ-ent singly charged conformations with the neutral ones. Our results indicate that the alpha carbon is the most favorable fragmentation point for the CH2SH and COOH radicals, after a single ionization of the cysteine molecule. The possibility of finding fragmentation routes, by theoretical methods, led us to compare molecular ions between neutral benzene, aniline, and o-, m-, and p-nitroaniline molecules, using Density Functional Theory (DFT), under an aug-cc-pVDZ basis set and a B3LYP ex-change correlation functional. After determining the structure and electronic energy of the neutral and doubly charged species, we also used the same methods used for the cysteine amino acid cal-culations such as: Wiberg bond indices and Bader's quantum theory of atoms in molecules (QTAIM). Where it was possible to observe the charge transfer and electronic distribution in each monomer, making it possible to observe possible locations for fragment formation in at least two pairs of car-bon-carbon (CC) atoms of the aromatic ring, which indicates the possible loss of the -CNH2 and -NO2 groups in the doubly charged aniline and nitroaniline molecules.
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3
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Alexandre Silva Santos
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Use of vibrational spectroscopy in the characterization of nanocarriers based on lipid and metallic nanoparticles loaded with bioactive molecules.
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Líder : SEBASTIAO WILLIAM DA SILVA
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MIEMBROS DE LA BANCA :
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SEBASTIAO WILLIAM DA SILVA
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JORLANDIO FRANCISCO FELIX
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PAULO EDUARDO NARCIZO DE SOUZA
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ANIELLE CHRISTINE ALMEIDA SILVA
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GUSTAVO OLIVEIRA DE MEIRA GUSMÃO
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Data: 01-jun-2023
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Resumen Espectáculo
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In this thesis, Raman spectroscopy and Fourier transform infrared (FTIR) techniques were used to study nanocarriers based on lipidic and metallic nanoparticles loaded with bioactive molecules. The temporal stability regarding the oxidation state of the nanoemulsion based on fish oil (FO), rich in docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) was evaluated over time after prepa-ration, at 0, 365 and 730 days. The FTIR data evidenced the presence of several chemical markers that showed a continuous oxidation of the FO nanoemulsion with the course of the preparation time. The results showed that due to their unsaturated characteristics, lipids are subject to molecular changes, which begin with the isomerization of double bonds cis to trans. These changes lead to oxidation processes and cleavages with the generation of by-products. The interaction between dif-ferent of [Fe(phen)3]2+ complex contents and solid lipid nanoparticles were investigated. The results showed the formation of a bidentate chelating bond between the carboxylate group from sodium ole-ate, present on lipid nanoparticle, and the Fe2+ ion of the [Fe(phen)3]2+ complex. Finally, the suc-cessful functionalization of the anti-SARS-CoV-2 antibody onto Au nanoparticles surface, precoated with 3,3'-dithiobis (Sulphosuccinimidyl Propionate-DTSSP) was demonstrated. The data showed that the primary amine groups of the antibody are covalently bound to the terminal succinimidyl ester group, forming a secondary amide bond by the nucleophilic attack of the amine to the ester carbonyl carbon present on the Au nanoparticle surface.
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4
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YESSICA ACOSTA URIAN
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Study of the surface properties and particle-particle interactions in oleic acid and oleic acid/essential oilcoated Fe3O4 nanoparticles
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Líder : JOSE ANTONIO HUAMANI COAQUIRA
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MIEMBROS DE LA BANCA :
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JOSE ANTONIO HUAMANI COAQUIRA
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PAULO EDUARDO NARCIZO DE SOUZA
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MARCELO HENRIQUE SOUSA
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ANTÔNIO OLIVEIRA DE SOUZA
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ANSELMO FORTUNATO RUIZ RODRIGUEZ
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Data: 01-jun-2023
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Resumen Espectáculo
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Magnetite (Fe3O4) nanoparticles coated with organic material are of considerable importance in various areas of engineering, as well as in biomedicine. Several papers show drastic changes in the magnetic properties related to the surface effects and the particle-particle interactions strength. However, there is no consensus about the origin or mechanisms that produce these changes, which could be different depending on the particle size and shape, coating efficiency and particle-particle interaction strength. Aiming to shed light on these issues, oleic acid (OA) coated Fe3O4 nanoparticles with sizes 4, 6 and 9 nm were synthesized by a thermal decomposition method using phenyl ether, benzyl ether and octadecene as organic solvents. These samples were additionally coated with essential oil ((Fe3O4@AO/OE). Structural and microscopic Fe3O4@AO nanoparticles results revealed Fe3O4 nanoparticles with good crystallinity and almostspherical or polyhedral shapes depending on the solvent used for the synthesis. Infrared (FTIR) spectroscopy indicated OA molecules attached to the surface of Fe3O4 NPs via bidentate (chelating and/or bridging) bonds. Thermogravimetric analysis (TGA) confirmed the presence of weakly and strongly bound AO molecules in the Fe3O4@AO samples, suggesting a successful coating of the Fe3O NPs. Magnetization (M) vs. magnetic field (H) curves are consistent with a core/shell structure formed by magnetite/maghemite phases, in consistency with FTIR spectroscopy. Lower than expected saturation magnetization values were determined for bulk magnetite, which was attributed to the probable presence of a fraction of low-spin (LS) iron ions in the maghemite layer on the surface of the particles. In that regard, the analysis by Mössbauer spectroscopy confirmed these results, as well as the better crystalline quality in the samples synthesized with benzyl ether used as the synthesis solvent. The magnetic results show that depending on the amount of AO coating, it is possible to adjust the particleparticle separation distance, avoiding nanoparticle agglomeration and particle-particle interactions. Dependence of magnetization on temperature reveals the presence of interacting and non-interacting NPs. AC magnetic susceptibility measurements are consistent with these results and confirm a superparamagnetic behavior (SPM), attributed to non-interacting NPs, and interacting SPM, attributed to interacting NPs and whose interaction strength is not sufficient to lead to behavior similar to that of spin glass. On the other hand, the FTIR results of the Fe3O4@AO/EO samples indicate the presence of EO without direct connection with the AO or with the metal ions on the surface of the Fe3O4 NPs. These results are consistent with those obtained from the analysis of thermogravimetric curves, where the intermediate-sized sample showed a higher amount of EO. Also, the EO coating had changes in the magnetic response. A reduction in the saturation magnetization and variation in the ZFC and FC curves was observed with lower blocking temperatures and lower activation energies in relation to Fe3O4@AO samples. These results were confirmed by measurements of AC susceptibility as a function of temperature. This suggests a lower degree of particle agglomeration and the weakening of particle-particle interactions as a function of the amount of EO in the Fe3O4@AO/EO samples.
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5
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Ravi Jayantibhai Mistry
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On the temperature of a causal diamond in algebraic quantum field theory.
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Líder : ALEKSANDR NIKOLAIEVICH PINZUL
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MIEMBROS DE LA BANCA :
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ALEKSANDR NIKOLAIEVICH PINZUL
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ARSEN ROBERT MELIKYAN
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CAROLINA MATTE GREGORY
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ANDRÉS FERNANDO REYES LEGA
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CHRISTIAN DIETER JAKEL
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Data: 01-jun-2023
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Resumen Espectáculo
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In this thesis, we study the temperature of an abstract spacetime region called a double cone, which is also referred to as a diamond. The framework under consideration is free massless scalar field theory treated within the algebraic quantum field theory approach. Before discussing the main result we review, somewhat rigorously, the von Neumann algebras, their type classification, the Tomita-Takesaki (TT) modular theory and KMS condition, which are indispensable parts of the model used in our analysis. We also provide an extensive discussion on some known results, in particular, geometrical transformations and the corresponding modular operators for interconnected spacetime regions: a right wedge, a forward lightcone and a diamond. This review serves as a stepping stone of our studies. As a main result, we present an intrinsic definition of temperature in terms of an inverse temperature vector field that can be computed without referring to a particular TT trajectory. This vector field reproduces the Unruh temperature for a right wedge. Later it is applied to compute the temperature of a diamond. We also consider some counterintuitive limits in which the modular flow of a diamond resembles that of Minkowski spacetime or a wedge. While in the former case the stipulated behavior is found in the center of a diamond, away from the boundaries, in the latter case it is close to the boundaries, more specifically, close to left and right corners.
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6
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David de Sousa Brandão
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Excitonic behavior and topological properties in low-dimensional systems
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Líder : QU FANYAO
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MIEMBROS DE LA BANCA :
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PEDRO PAULO DE MELLO VENEZUELA
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ALEXANDRE CAVALHEIRO DIAS
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MARIANA MALARD SALES ANDRADE
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PAULO EDUARDO DE BRITO
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WEI CHEN
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Data: 07-jun-2023
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Resumen Espectáculo
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This thesis aims to address new properties and behaviors in low-dimensional systems, which can be divided into two branches: (i) new topological properties found in a one-dimensional electron system with Rashba and Dresselhaus spinorbit interaction, periodically modulated in space, and (ii) manipulation of the valley degree of freedom in two-dimensional materials with inversion asymmetry and potential use as a carrier of quantum information. In the first work we have investigated the phase diagram of a one-dimensional band insulator with spin-orbit coupled electrons, supporting trivial, and topological gapped phases separated by intersecting critical surfaces. The intersections define multicritical lines across which the ground-state energy becomes nonanalytical, concurrent with a closing of the band gap, but with no phase transition taking place. This finding challenges the standard theory of quantum phase transitions according to which a nonanalyticity in the ground-state energy implies a quantum phase transition. Regarding quantum information, we studied a two-level exciton qubit that takes into account the valley degree of freedom. In this scenario, the two valley states are mixed by the intervalley exchange Coulomb interaction and can be tuned by an external magnetic field. We observed that the intensity and sign of the external magnetic field affect the valley pseudospin for different exciton momentum. Finally, We have worked with optical excitonic and valleytronics in two dimensional (2D) materials. We have so far obtained results for the dynamics and scatterings of excitons between excitonic states in 2D van der Walls transition metal dichalchogenides heterostructures MoS2/WS2. We have also investigated the magnetic proximity effect by tuning the valley polarization, as well as the photoluminescence of interlayer excitons, singlets, and long-living triplets. We found that crossing their energies for certain exchange field values gives rise to a photoluminescence peak signature near this critical field. The large valleysplitting energy plays an important role in the valley polarization.
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7
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Railson da Conceição Vasconcelos
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Theoretical Modeling of Magnesium Dichloride Monolayers and Nanoribbons for Applications in Spintronics: A Study of Doping, passivation, and quantum transport.
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Líder : RICARDO GARGANO
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MIEMBROS DE LA BANCA :
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CECILIA COLETTI
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IGO TORRES LIMA
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LUIZ ANTONIO RIBEIRO JUNIOR
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PAULO EDUARDO NARCIZO DE SOUZA
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RICARDO GARGANO
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Data: 14-ago-2023
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Resumen Espectáculo
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Our recent breakthroughs in manipulating matter at the atomic scale have opened up new possibilities for creating and designing highly efficient electronic devices. With this goal in mind, this study utilizes first-principles techniques to investigate the control of magnesium dichloride monolayers (MgCl2) for technological applications. We begin by examining the effects of substitutional doping in monolayers and then advance to the study of quantum transport in nanoribbons of the same material. Our results indicate that both the monolayers and nanoribbons of MgCl2 exhibit ideal properties for spintronic applications. Substitutional doping of the MgCl2 monolayers with different dopant groups proves efficient in inducing magnetism in the material. All pristine MgCl2 nanoribbons with different edge terminations are stable. Depending on the atoms at the zigzag edge of the nanoribbons, it is possible to induce the half-metallic state and achieve perfect spin filtering. The passivation of the MgCl2 nanoribbons is not only effective in increasing the system’s stability but also in modulating its electronic and magnetic properties, enabling the creation of perfect spin filters and spin bipolar diodes with dual rectification. Therefore, this work highlights the remarkable potential of MgCl2 crystals for applications in nanoelectronics and spintronics.
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8
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LEONARDO DE SOUZA BARBOSA
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Viability of inorganic nanobelts: a study on their electronic, optical and thermodynamic properties.
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Líder : DAVID LIMA AZEVEDO
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MIEMBROS DE LA BANCA :
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ALEXANDRE CAVALHEIRO DIAS
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DAVID LIMA AZEVEDO
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EDVAN MOREIRA
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NILTON FERREIRA FRAZÃO
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RICARDO GARGANO
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Data: 27-sep-2023
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Resumen Espectáculo
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In recent years, organic molecules known as carbon nanobelts have been the subject of much research. Recently, one of these molecules - called (12)cyclophenacene - was synthesized. This synthesis marked a great advance in synthesis technologies since this molecule has been studied since the 1950s. In this work, two new molecules derived from (12)cyclophenacene are proposed, which are called silicon carbide nanobelt or SiC-nanobelt (C24Si24H24) and boron nitride nanobelt or BN-nanobelt (B24N24H24). To verify stability and possible applications of these molecules, the electronic, optical, and thermodynamic properties of SiC and BN-nanobelts were determined. These properties were calculated using the DFT method with the PWC and PBE functionals, with the Double Numerical Plus Polarization (DNP) basis set. It was verified, through electronic structure calculations, that the BN-nanobelt is more stable (-14.11 hartrees) than the SiC-nanobelt (-12.21 hartrees). It was also observed that the SiC-nanobelt has characteristics of a semiconductor (GAP estimated at 2.13 eV), and the BN-nanobelt has characteristics of an insulator (GAP estimated at 4.62 eV). Optical properties revealed that SiC-nanobelt absorbs in the visible region, while BNnanobelt absorbs in the ultraviolet region. From the point of view of thermodynamic properties, it was observed through the Gibbs free energy that for a temperature above 718 K a spontaneous reaction occurs for SiC-nanobelt. Furthermore, quantum dynamics calculations showed that both proposed nanobelts are thermally stable, with the bonds of BN-nanobelt and SiC-nanobelt breaking at temperatures of 3000 K and 2500 K respectively. Based on the results obtained for the electronic, optical, thermodynamic, and dynamic properties, it is possible to infer that the new inorganic nanobelts are stable systems (their syntheses are viable) and have potential technological applications
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9
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Breytner Ribeiro Morais
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On the Gravitational Thermodynamics in the FLRW Universe.
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Líder : SERGIO COSTA ULHOA
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MIEMBROS DE LA BANCA :
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ALESANDRO FERREIRA DOS SANTOS
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EDNARDO PAULO SPANIOL
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RONNI GERALDO GOMES DE AMORIM
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SERGIO COSTA ULHOA
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TARCISIO MARCIANO DA ROCHA FILHO
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Data: 28-sep-2023
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Resumen Espectáculo
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The Friedmann-Lemaître-Robertson-Walker (FLRW) solution is the suggestion of a metric applicable to Einstein's equations and that describes an isotropic and homogeneous universe that may be expanding or contracting in an accelerated way. Recent observational data suggests that the present universe is approximately flat and that it is expanding accelerated. In this work, in the context of the Teleparallelism Equivalent of General Relativity (TEGR), we will try to understand the cause on which the universe, based in the FLRW model, is expanding in an accelerated way. We also present a relation to the first law of thermodynamics to the apparent horizon of the FLRW model, and from this relation we will obtain a expression to the temperature at the apparent horizon. And, based on a model of a primordial and empty universe where the Weyl quantization procedure is applied, obtaining values for the energy discretization, a study of the thermodynamics of this system will be carried out with the properties of a canonical ensemble.
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