Mestrado em Física (IF)

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Estudos de materiais dopados com íons lantanídeos para aplicações em nanotermometria
(Universidade Federal de Goiás, 2023-10-31) Silva, Daniel Lopo da; Maia, Lauro June Queiroz; http://lattes.cnpq.br/9454054374479016; Maia, Lauro June Queiroz; Poirier, Gaël Yves; Santana, Ricardo Costa de
Optical phenomena such as luminescence of materials depend on several characteristics such as temperature, dopants, crystalline structure, etc. Electromagnetic emissions from materials doped with rare-earth ions can provide thermal information regarding the environment where these materials are inserted. Materials with good thermal sensitivity are considered promising for the development of technologies for nanoscale temperature measurements. In this work, nine samples previously prepared through different synthesis routes such as sol-gel process and modified Pechini were analyzed. The samples studied have matrices of several compounds such as aluminum borates (Al4B2O9) monophasic and embedded in silica, aluminum germanates (Al6Ge2O13) monophasic and embedded in silica, yttrium borates (YBO3) and yttrium aluminum silicates (YAS). Altogether, five trivalent lanthanide ions were used as dopants of the samples: Nd, Eu, Er, Tb and Yb. The emission spectra of the samples were analyzed at seven different temperatures from 25 °C to 55 °C with a variation of 5 °C. Diffuse reflectance spectra were studied to confirm the presence of ions in the matrix and enable the calculation of the energy gap for each sample. From the emission spectrum, photoluminescent intensity ratios (RIFs) were calculated for the calculation of relative thermal sensitivities. The sample that showed the highest value for relative thermal sensitivity (Sr) was the one with the composition YBO3 : Nd3+, Eu3+, Er3+, Yb3+, Tb3+ synthesized at 900°C, presenting a value of Sr = (1,52 ± 0,20) %.K-1 in the temperature range of 35°C and 55°C.
Estudo das interações dos surfactantes iônicos SDS, CTAC e HPS e miltefosina com membranas de leishmania, macrófagos e eritrócitos
(Universidade Federal de Goiás, 2023-09-18) Cardoso, Éder Jéferson Souza; Alonso, Antônio; http://lattes.cnpq.br/5013069863616789; Alonso, Antônio; Mendanha Neto, Sebastião Antônio; Silva, Kleber Santiago Freitas e
Miltefosine (MT) is an internationally approved oral drug for the treatment of leishmaniasis, however, its mechanism of action is not yet well established. Understanding the mechanism of action of compounds with leishmanicidal activity is important to help in the search for new drug prototypes with greater activity and fewer side effects. Surfactants are compounds widely used in the industry in the manufacture of soap, shampoos and other cosmetics. They are usually classified according to the molecular charge, and may be nonionic, anionic, cationic or zwitterionic (or amphoteric) when they have a positive and negative charge in the same compound. Electron Paramagnetic Resonance (RPE) spectroscopy associated with the spin-label method was used to compare the interactions of MT and the surfactants Sodium Dodecyl Sulfate (SDS, anionic), Cetyl Trimethyl Ammonium Chloride (CTAC, cationic) and N, N-dimethyl-3-ammonio-1-propanesulfonate (HPS, zwitterionic) with the membranes of Leishmania (L.) amazonensis, erythrocyte and macrophage. All compounds increased the molecular dynamics of membrane proteins; however, SDS caused the smallest increase in parasite and erythrocyte membrane dynamics and was also the least effective in antileishmanial activity, cytotoxicity in macrophages J774.A1 and hemolytic potential in both PBS and whole blood. It was detected, in blood plasma, the albumin stiffness caused by 2.5 mM SDS due to the electrostatic and hydrophobic interactions of the compound with the protein. CTAC did not show significant differences in relation to the other compounds, but at higher cell concentrations (>1x109 cells/mL), it showed high activity against the L. amazonensis promastigotes, besides being the most cytotoxic to macrophages J774.A1. For all the experiments, the zwitterionic molecules HPS and MT did not present significant differences between them. The data suggest the possibility of using cationic or zwitterionic surfactants in formulations containing leishmanicides, aiming at the treatment of cutaneous leishmaniasis.
Landauer principle in the context of relativistic communication theory
(Universidade Federal de Goiás, 2023-04-25) Alvim, Yuri de Jesus; Céleri, Lucas Chibebe; http://lattes.cnpq.br/6630683190018665; Céleri, Lucas Chibebe; Vanzela, Daniel Augusto Turolla; Pereira, Rômulo Cesar Rougemont
This monograph aims to investigate Landauer's principle for a quantum system in a relativistic context. Specifically, we consider a communication channel described by a mode of a quantum field in a curved spacetime. In order to accomplish that, an introduction to Shannon's theorems, as well as some very important concepts in information theory, will be first presented. The relativistic spacetime structure will be described in the sequence, such that the quantum field theory can be used, in this context, to describe the communication channel. Lastly, the calculation of the channel capacity and the energy contributions for the transmission of information over such a channel will be done. Such calculations provide three different contributions to the total energy variation of the system: one due to the change in the spacetime, one associated with the work necessary to switch on or off the interaction between the detectors ---qubits employed to read and codify the information--- with the field and, finally, the last one which is due to the communication process itself. This third contribution vanishes for the considered communication channel, so that no extra energy cost is needed to transmit information once the states of the qubits are settled. The original contribution of this work enters here by considering the cyclical conversion of the transmitted information into work. Since no energy is transferred from the sender to the receiver, this engine apparently violates the second law of thermodynamics. By employing Landauer principle we find the energy contribution which allows the receiver to convert information into work without contradictions with thermodynamics.
Quantum thermodynamics: a modified otto engine
(Universidade Federal de Goiás, 2023-03-02) Matos, Richard Quintiliano; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes de; Moraes Neto, Gentil Dias de; Gomes, Rafael de Morais
Quantum thermodynamics is an emerging area that arouses the interest of many scientists and engineers. Although it is a new and incomplete theory, it comes with surprising results. We propose to study a quantum engine that utilizes thermal reservoirs as baths but an unusual system as working fluid, a squeezed harmonic oscillator. The fluid was chosen as an educated guess to study if an engine working solely with a quantum resource could surpass Carnot’s limit. The problem was solved analytically and then simulated using the qutip library to python, we showed that this engine is capable of working in Carnot’s regime. Furthermore, we calculated the Shortcut to adiabaticity to the evolving hamiltonian so we could improve the system’s power without losing efficiency. This kind of machine serves the purpose of showing that one cannot surpass Carnot’s limit if one is using thermal reservoirs.
Modelagem teórica para melhoramento da eficiência energética em supercapacitores
(Universidade Federal de Goiás, 2023-03-01) Chagas, Henrique de Araujo; Oliveira, Guilherme Colherinhas de; http://lattes.cnpq.br/0171051425848743; Oliveira, Guilherme Colherinhas de; Castro, Marcos Antonio de; Andrade, Douglas Xavier de
Two-dimensional carbon materials, such as graphene and graphyne, have stood out in energy storage applications due to their unique physical, chemical, and electronic properties. Graphyne, in particular, presents even more remarkable properties, such as higher specific area, electronic mobility, and intrinsic energy band. Furthermore, biocompatible ionic liquids (ILs), such as those formed by choline and glycine, are increasingly being studied as a less toxic alternative for the environment. This work performed molecular dynamics simulations to investigate the properties of electrolytes based on aqueous mixtures of the biodegradable IL [Ch][Gly] with the IL [Bmim][PF6] as electrolytes in graphyne supercapacitors. Through energetic, structural, and electrostatic analyses, it was possible to describe the Electric Double Layer (EDL) formed near the electrodes. It was found that, although the structure and formation of the EDL are governed by a complex network of electrostatic and van der Waals (vdW) interactions, their interaction with the electrode is dominated by vdW interactions. It was observed that choline-based electrolytes can perform as well as most conventional ILs, but with the advantage of low toxicity. The comparison between graphyne and graphene supercapacitors for the IL mixture revealed a higher capacitance for graphyne, even when comparing similar values for the potential drop. Subsequently, an extensive comparison of electrode performances in energy storage applications under thermodynamic conditions was performed. The electrostatic properties of eight different supercapacitors, four made of graphene and four made of graphyne, in different electrolytes were investigated. A detailed analysis of the energy and organization of the electric charges of these systems is reported for all systems. The results indicate the superiority of the graphyne electrode over the graphene electrodes, confirming previous findings and making graphyne a promising candidate for electrochemical energy storage systems. Thus, this study contributes to the understanding of the properties of two-dimensional carbon materials and their application in energy storage devices.
Modelagem de membranas peptídicas formadas por arginina e fenilalanina usando dinâmica molecular
(Universidade Federal de Goiás, 2023-03-08) Soares, Karinna Mendanha; Oliveira, Guilherme Colherinhas de; http://lattes.cnpq.br/0171051425848743; Oliveira, Guilherme Colherinhas De; Almeida, Agnaldo Rosa de; Cardoso, Wesley Bueno
The use of computational resources for modeling organic nanostructures from peptides has a potential to elucidate fundamental characteristics that guide molecular interactions and that collaborate with the understanding of the selfassembly process of these materials. In this study, we describe a structural and energetic study of a membrane using molecular dynamics. Our simulations were carried out by exploring three ways of juxtaposition between the peptides that shape the organic nanostructure. The simulations also shows that the three forms of organization are viable during the self-assembly process leading to similar structures. Our studies reinforce the importance of hydrogen bond and the correct modeling of the hydrophobic and hydrophilic structure of the peptide in the nanomembrane idealization process (especially bola-amphiphilic peptide). For membrane thickness, our results obtained from the mass density profile were 2,28; 2,25 and 2,22 nm. From the surface mapping we found the results 2,47; 2,14 and 2,32 nm, that differs by up to 2,36 nm from the experimental result of 3,2 – 4,5 nm. This led us to adopt a bilayer model in which the results highlight an average thickness of 3,95 nm indicating that the experimental results may be indicate the presence of structures bilayers model and not monolayers.
Propriedades ópticas não lineares de um novo derivado de quinolinona
(Universidade Federal de Goiás, 2022-09-23) Vinhal, Rafael de Siqueira; Osório, Francisco Aparecido Pinto; http://lattes.cnpq.br/1354763162575957; Osório, Francisco Aparecido Pinto; Torres, Elber Magalhães; Fonseca, Tertius Lima da
In this work we have studied the linear and nonlinear optical properties of a quinolinone derivative4(1H)-quinolinone-(E)-4-bromobenzylidene-4-chlorophenyl-phenylsulfonyl (QBCP) with formula C28H19BrClNO3S. The theoretical calculations of the electrical properties of the QBCP crystal were performed at the Density Functional Theory (DFT) level with the CAM-B3LYP functional and the 6-311++G (d,p) basis function, both in the static and dynamic regime. To better understand the optical properties of the QBCP molecule, we obtained the HOMO-LUMO boundary orbitals and through their energies we calculated the global reactivity parameters such as the gap energy, the ionization energy, the electronic affinity, the global hardness, among others. We also calculated using the TD-DFT theory the absorption and emission spectrum in the ultraviolet (UV-Vis) of QBCP, making it possible to calculate the Stokes shift, we also studied the absorption spectrum in the infrared (IR) of the QBCP molecule. And the intermolecular interactions of QBCP were studied through the Hirshfeld Surface analysis. The results obtained for the optical properties of the QBCP molecule were very good when compared with the results obtained for other organic crystals, suggesting that it can be studied as a possible nonlinear optical material.
Quantum refrigerators operating under effective negative temperatures
(Universidade Federal de Goiás, 2023-02-24) Damas, Gabriella Gonçalves; Assis, Rogério Jorge de; http://lattes.cnpq.br/7703787869253387; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes De; Souza, Alexandre Martins de; Maia, Leonardo Paulo
Ao longo das últimas décadas, uma nova teoria tem sido desenvolvida com o intuito de descrever a termodinâmica de sistemas quânticos microscópicos, a qual ficou conhecida como termodinâmica quântica. Uma aplicação interessante dessa teoria está no desenvolvimento de motores térmicos nos quais a substância de trabalho é um sistema quântico microscópico, esses dispositivos passaram a ser conhecidos como motores térmicos quânticos. Dentro desse contexto, o estudo de refrigeradores quânticos tem atraído bastante atenção especialmente para sua aplicação potencial em sistemas nanoscópicos. Nesse contexto, a presente dissertação apresenta dois estudos relacionados a um refrigerador quântico autônomo. No primeiro estudo, abordamos um refrigerador autônomo composto por três qubits operando com um dos reservatórios com temperaturas negativas, que tem como finalidade resfriar um dos qubits. Encontramos os valores da temperatura mais baixa possível que o qubit de interesse atinge ao fixar os parâmetros relevantes e também analisamos o limite para resfriar o qubit arbitrariamente próximo ao zero absoluto. Procedemos assim a um estudo comparativo mostrando que reservatórios com temperaturas negativas efetivas são mais poderosos do que aqueles em temperaturas positivas para resfriar o qubit de interesse. No segundo estudo, realizamos um estudo de caso de um refrigerador quântico operando na presença de reservatórios térmicos bosônicos ou fermiônicos, e mostramos que os banhos fermiônicos apresentam vantagens sobre os bosônicos. Por fim, é feita uma discussão sobre o uso de reservatórios com população invertida e a medida de eficiência utilizada para esses sistemas.
Propriedades estatísticas de fótons de micro-ondas gerados por uma junção túnel
(Universidade Federal de Goiás, 2022-10-30) Campos, Maikon Bruno Alves; Mendes, Udson Cabral; https://lattes.cnpq.br/2549501479254454; Mendes, Udson Cabral; Almeida, Norton Gomes de; Silva, Cláudio José da
In this dissertation, we investigate the statistical properties of microwave photons generated by a tunnel junction coupled to a microwave resonator. For that, we developed the master equation formalism to calculate the statistical properties of (i) an electromagnetic field mode coupled to a thermal reservoir and (ii) to a squeezed vacuum reservoir. Furthermore, we derived the Hamiltonian of the tunnel junction coupled to a microwave resonator. This allows us to derive the master equation for the tunnel junction coupled to a microwave resonator and Confirm that (i) in the absence of ac voltage, the junction behaves as a thermal reservoir and (ii) in the presence of an ac voltage oscillating at a frequency equal to twice the frequency of the resonator, the junction behaves as a squeezed reservoir. Also we studied the tunnel junction coupled to a microwave resonator subjected to ac voltage with a frequency equal to three times the resonator frequency, theoretically demonstrating the possibility of generating photon trios, which has already been explored experimentally, but which has yet to be has no theoretical explanation for these experiments.
Structural and electronic properties of functionalized germanene
(Universidade Federal de Goiás, 2020-06-09) Oliveira, Flávio Bento de; Rosa, Andreia Luísa da; http://lattes.cnpq.br/1038061895538870; Rosa, Andreia Luísa da; Lima, Erika Nascimento; Bufaiçal, Leandro Felix de Sousa
The study of two-dimensional (2D) materials has increasing interest after the discovery of graphene whose property differed surprisingly from its three-dimensional form. 2D materials have electrical properties of great interest for technological applications, and play a role in the reduction of the dimensions of the electronic devices that are currently produced as well. Graphene in its honeycomb structure has a zero gap, with conducing and valence bands being degenerate at K and K’ points, forming cones. However, difficulties in carrying out and adjusting a reasonable sizeable band gap in graphene is attracting increasing interest to other two-dimensional materials. One of the promising material is a single layer of germanium, the so-called germanene. Recent investigations suggest that germanium layers react rapidly with the environment. This may affect not only their electronic structure, but also their reactivity and optical properties. Therefore one may search for ways of tuning the electronic properties of these twodimensional layers. A promising route for tuning the electronic structure of bare layered materials is the adsorption of organic molecules or functional groups. Recently, germanene has been synthesized to create hybrid layers upon adsorption of organic ligands. In this work, band gap tuning of organic ligands adsorbed on bidimensional germanium monolayers have been investigated using first-principles calculations. We show that the adsorption of these small groups retains the initially stable free-standing pristine buckled germanium nanostructures. We claim that the stability of these structures stem from both strain induced by the adsorption of this organic group and ligand-ligand interactions. Our studies of a finite band gap form the way for a rational design of germanium nanostructures, which can find applications in electronic devices.
Redução dimensional para condensados de Bose-Einstein em forma de “tubo” e “anilha plana”
(Universidade Federal de Goiás, 2019-02-28) Santos, Mateus Calixto Pereira dos; Cardoso, Wesley Bueno; http://lattes.cnpq.br/6845416823133684; Cardoso, Wesley Bueno; Avelar, Ardiley Torres; Santana, Ademir Eugênio de
The study of nonlinear dynamics represents a challenge of contemporary physics. In particular, the investigation of Bose Einstein condensates proved to be a hard task due to the large number of interacting particles. Therefore, given the difficulty of modeling these systems, approximations were introduced, which promoted the description of the Bose-Einstein condensation state in interacting atomic gases as a three-dimensional nonlinear Schrödinger equation, known as the Gross-Pitaevskii equation. In this work we review the dimensional reduction method, which use a variational treatment with the goal of derive effective one-dimensional (1D) and two-dimensional (2D) equations in cigar-shaped and pancake-shaped Bose-Einstein condensates, where we show that these equations describe almost exactly the dynamics of their respective models. Thus, we studied the ground-state solutions in tube-shaped and flat washer-shaped Bose-Einstein condensates by means of effectives non-polynomials equations, derived from the dimensional reduction method. The results produced by this equations were in very good agreement with those obtained from the corresponding full 3D Gross-Pitaevskii equation.
Relativistic symmetry in quantum information theory
(Universidade Federal de Goiás, 2022-04-04) Bidinotto, Alexandre Borges; Taillebois, Emile Raymond Ferreira; Avelar, Ardiley Torres; http://lattes.cnpq.br/5732286631137637; Avelar, Ardiley Torres; Santana, Ademir Eugênio de; Cardoso, Wesley Bueno
This dissertation begins with a succinct introduction to group theory to enable the understanding of special relativity theory from a symmetrical point of view. From this perspective, the notion of hierarchy of dynamical variables, which is present in relativity, is introduced to quantum mechanical formalism in order to construct the irreducible unitary representations of the Poincaré group for secondary variables. Given this discussion, the questions regarding the existence of a subset of transformations in which the Wigner rotations associated do not depend on the momenta. In sequence, the relativistic Stern-Gerlach observable is presented. This observable also depends on the momenta, so the initial problem on the density matrices for spin remains unsolved. The open question on the Stern-Gerlach observable is what is the minimum number of measurements in order to fully determine a relativistic density matrix. Both questionings on this dissertation can lead to the determination of the quantum state tomography of relativistic particles, which is the further goal of this document.
Strong magnetic field corrections to the NJL coupling constant from vacuum polarization
(Universidade Federal de Goiás, 2022-01-28) Moreira, Thiago Henrique; Braghin, Fábio Luis; http://lattes.cnpq.br/9375085677737347; Braghin, Fábio Luis; Shovkovy, Igor; Markó, Gergely
In this work we calculate corrections to the NJL model coupling constant in the presence of a uniform magnetic field. Starting with the Nambu-Jona-Lasinio Lagrangian coupled with an external magnetic field, we separate the quark field into two components: one corresponding to the condensed quarks and the other corresponding to the interacting quasiparticle quarks. By integrating out the former, an effective action in terms of the interacting quarks is obtained. We then expand the quark determinant in terms of the quark currents and show that the first-order term provides a correction to the quark masses given by the gap equation. The values obtained for the constituent quark masses increase with the magnetic field, which signals the enhancement of chiral symmetry breaking by the external field and therefore showing that the system exhibits magnetic catalysis. The second-order term of the quark determinant expansion provides a correction to the NJL coupling constant, which decreases with increasing magnetic field for the scalar interactions and increases with increasing magnetic field for the pseudoscalar ones. We then consider a NJL model with the flavor- and B-dependent couplings obtained from vacuum polarization and compute quark and meson masses. While the scalar couplings seem to improve the conciliation with lattice results for the quark masses, the same cannot be said about the pseudoscalar couplings which alters the pseudoscalar meson masses in a different way than what is known in the literature due to its behavior with the applied field.
On the controversies of the Unruh effect
(Universidade Federal de Goiás, 2021-08-16) Diniz, João Vítor Barnez Pignata Leal; Taillebois, Emile Raymond Ferreira; http://lattes.cnpq.br/1212175267808857; Avelar, Ardiley Torres; http://lattes.cnpq.br/5732286631137637; Avelar, Ardiley Torres; Céleri, Lucas Chibebe; Matsas, George Emanuel Avraam
In the 50 years since it was first proposed, the Unruh effect has been discussed extensively in literature, with many theoretical results supporting its existence and some questioning whether it is actually observed. The Unruh effect states that observers with constant proper acceleration in Minkowski spacetime will respond as if interacting with a thermal bath at a temperature proportional to the acceleration. For common accelerations this temperature is very low, so experimental confirmation has been challenging. To understand the effect and the discussion around it, we review some important results from quantum field theory and work out a detailed derivation of the Unruh effect for massless and massive fields, including the calculation of the Bogoliubov coefficients for these problems. Furthermore, we follow a discussion on the role that the boundary conditions play in this effect, showing that they may lead to an incomplete description of the field in Minkowski spacetime when written in terms of the modes in Rindler spacetime.
Investigação da influência da estrutura cristalina no efeito exchange bias espontâneo da série La1,5(Sr0,5-xBax)CoMnO6
(Universidade Federal de Goiás, 2021-03-18) Belluzi, Marlon Boldrin; Bufaiçal, Leandro Felix de Sousa; http://lattes.cnpq.br/1392206843733548; Bufaiçal, Leandro Felix de Sousa; Ferreira, Letície Mendonça; Franco Júnior, Adolfo
The exchange bias (EB) effect is of great academic interest due to its potential applications in spintronics. Recently there were discovered some material exhibiting the EB effect spontaneously, i.e., even after being cooled in the absence of an external magnetic field. The main focus of this work is to investigate the influence of crystalline and electronic structures on the spontaneous EB effect. Therefore, here we describe the synthesis and structural, electronic and magnetic characterizations of polycrystalline samples of the La1.5(Sr0.5-xBax)CoMnO6 series. The main objective was to investigate the evolution of the magnetization of the system when Sr is gradually substituted by Ba. Polycrystalline samples were synthesized by conventional solid state reaction, and their structural properties were characterized by powder X-ray diffraction and the Rietveld Refinement. The magnetic properties were investigated by means of magnetization as a function of temperature [M(T)] and magnetization as a function of magnetic field [M(H)] measurements. The compounds were formed in a single phase, in the rhombohedral space group 𝑅3̅c. In addition, it was observed that the lattice parameters increase as the Ba concentration increases. The M(T) measurements indicate that all compounds have ferromagnetic (FM) and antiferromagnetic (AFM) ordering, where an increase in the proportion of the AFM phase was observed as the Ba concentration increases. Also, a trend of change is observed in the average spin state of the Co3+ ions, which varies from the low spin (LS) configuration to the high spin (HS) configuration as the Ba concentration increases. The M(H) measurements performed after cooling the samples in zero field showed a robust spontaneous EB effect, with the concentration x = 0.25 having the greatest effect ever observed. M(H) measurements taken after cooling the materials in the presence of an external field showed a qualitative behavior similar to those taken after cooling in zero field. The variations in the exchange bias effect observed throughout the series can be explained by the variations in the AFM phase and in the spin state of Co3+.
A possible inadequacy of a recent proposal for redefining heat and work in quantum thermodynamics
(Universidade Federal de Goiás, 2021-03-15) Bottosso, Eduardo Borges; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Moussa, Miled Hassan Youssef; Céleri, Lucas Chibebe; Almeida, Norton Gomes de
A primeira identificação de um sistema quântico aberto como um modelo para um motor térmico quântico data de 1959. Desde então, a física não tem um conjunto concreto de fórmulas para definir, com precisão, como lidar com o calor e trabalhar no contexto de conjuntos quânticos . Uma das propostas mais proeminentes, que foi afirmada pelo artigo de R. Alicki de 1979, tem um regime de validade limitado e pode levar a algumas inconsistências com relação à primeira lei da termodinâmica. Várias abordagens para o problema foram propostas, levando a um novo conjunto de definições para calor e trabalho em termodinâmica quântica. Particularmente, novas redefinições para calor e trabalho foram introduzidas, as quais são baseadas na entropia de von Neumann. Nosso objetivo aqui é apresentar essa nova formulação, bem como sua motivação e investigar as consequências dessas fórmulas. Estudamos alguns modelos simples que empregam esse novo conjunto de definições. Nossa análise mostra um comportamento peculiar dos sistemas quânticos quando esse novo formalismo é dado como certo, possivelmente indicando uma inadequação dessas novas definições.
Caracterização estrutural e investigação do efeito exchange bias espontâneo na perovskita dupla La1,5Sr0,5CoMn0,5Fe0,5O6
(Universidade Federal de Goiás, 2021-02-26) Silva, Arthur Garcia; Bufaiçal, Leandro Felix de Sousa; http://lattes.cnpq.br/1392206843733548; Bufaiçal, Leandro Felix de Sousa; Bittar, Eduardo Matzenbacher; Santana, Ricardo Costa de
In this work we describe the synthesis and characterization of the structural, eletronic and magnetic properties of La1.5Sr0.5CoMn0.5Fe0.5O6 compound. Our main focus was on the investigation of 50% of Mn to Fe substitution in La1.5Sr0.5CoMnO6, with a particular interest in the spontaneous exchange bias effect, a phenomena characterized by the shift in the magnetic hysteresis curves taken after the system bein cooled in zero magnetic field. The polycrystalline sample here investigated was syntesized by conventional solid state reaction technique and investigated by means of X-ray powder diffraction, magnetization as a function of temperature [M(T)] and magnetization as a function of magnetic field [M(H)]. The La1.5Sr0.5CoMn0.5Fe0.5O6 crystal forms in rhombohedral symmetry, space group, in agreement with results observed for similar compounds. The M(T) measurements have revealed a ferromagnetic-like transition at TC ≈ 150 K, and also indicated the presence of competing magnetic phases, which leads to the formation of ferromagnetics clusters embedded in a paramagnetic matrix at high temperature. This is a hallmark of the Griffiths Phase, here occurring in the 150 K < T < 205 K range. The M(H) curves carried after cooling the system in zero field have showed that La1.5Sr0.5CoMn0.5Fe0.5O6 exhibits the spontaneous Exchange Bias effect at low temperatures, while for the measurements carried after cooling the system in the presence of a external magnetic field it is observed a significant enhancement of the shift in the M(H) curve.
Thermodynamics and the Unruh effect
(Universidade Federal de Goiás, 2020-04-13) Borges, Lucas Aurélio de Oliveira; Céleri, Lucas Chibebe; http://lattes.cnpq.br/6630683190018665; Céleri, Lucas Chibebe; Braghin, Fábio Luis; Vanzela, Daniel Augusto Turolla
A uniformly accelerated detector perceives the Minkowski vacuum as a thermal state. In particular, for a massless scalar field, one cannot distinguish these two scenarios -accelerated detector in the vacuum and an inertial detector in contact with a thermal reservoir- just by using a point-like detector. In this work we show that one can probe the existence of acceleration by using an extended detector with dimension perpendicular to the acceleration direction. Also, we verify that the internal degrees of freedom of the detector may get entangled by a process of spontaneous emission, and as such is dependent on the initial state of the detector. It is found that the entropy production and entropy fluxes from out the detector also allow one to tell the two scenarios apart: more internal entangled detectors produce less entropy and vice-versa; the wavelength of the sought particle is the critical length at which the behavior of the two system is inverted.
Sensitivities to neutrino non-standard interactions from the disappearance of muon (anti)neutrinos at the NOvA experiment
(Universidade Federal de Goiás, 2020-10-13) Prais, Luiz Ricardo; Gomes, Ricardo Avelino; http://lattes.cnpq.br/6538341799051577; Gomes, Ricardo Avelino; Moura Junior, Celio Adrega de; Motta Filho, Hélio da
The experimental confirmation of the phenomenon of neutrino oscillations provided evidence for a non-zero value for the mass of neutrinos, a property not initially predicted by the Standard Model of Physics. Investigations of the existence of the so called Physics Beyond the Standard Model is a subject of growing interest and effort in the field of particle physics. Interactions of neutrinos with matter are well described by the Standard Model, however in the presence of new Physics, additional phenomena regarding neutrino properties would be possible, including non-standard interactions of neutrinos with matter. The NOvA experiment, at Fermilab, has been investigating neutrino oscillations through studies of νμ produced at the Fermilab accelerator facilities, and also comprise a suitable environment for investigation of additional phenomena taking part in the neutrino oscillation framework. We show in this thesis the results of the sensitivity studies to neutrino non-standard interactions in the NOvA experiment through investigation of the disappearance of muon (anti)neutrinos during their evolution in the NOvA 810 km baseline. We investigate the effect of the NSI parameters, |εεμτ|ε and δμτ, on the determination of the standard oscillation parameters sin2(θ23) and Δm2 32 , as well as the relation between each parameter, for both neutrino mass hierarchies. This study makes use of an exposure of 9.48 × 1020 POT for neutrino beam (FHC), and 12.33 × 1020 POT for antineutrino beam (RHC). No deviations from the standard oscillation scenario is found at the 90% CL limit. The joint neutrino and antineutrino fit yields a limit of |εεμτ|ε ≤ 0.086 (0.085) for a fixed value of δμτ = 0, and |εεμτ|ε ≤ 1.054 (1.053) for the case where both NSI parameters are fitted, for the normal (inverted) neutrino mass hierarchy, at the 90% CL. In the current sensitivity, all values of δμτ are found to be allowed. The 90% CL interval for the standard oscillation parameters are Δm2 32 ∈ [2.379, 2.580] and [2.379, 2.580] and sin2(θ23) ∈ [2.379, 2.580] and [0.420, 0.602] for the normal hierarchy scenario, and Δm2 32 ∈ [2.379, 2.580] and [−2.639, − 2.438] and sin2(θ23) ∈ [2.379, 2.580] and [0.418, 0.602] for the inverted hierarchy scenario.
Frustração magnética em um modelo de ising triangular com anisotropia rotacional
(Universidade Federal de Goiás, 2020-03-16) Nascimento, Ricardo Mayckon Lopes; Silva, Cláudio José da; http://lattes.cnpq.br/1361379226289069; Caparica, Álvaro de Almeida; http://lattes.cnpq.br/4726638254587108; Caparica, Álvaro de Almeida; Silva, Hermann Freire Ferreira Lima e; Branquinho, Luis Cesar
In this work, we present a new model for the study of frustrated magnetic systems proposed for a triangular lattice equipped with Ising type spins that takes into account not only the interaction between the spins but also the interaction due to the symmetry of a given substrate that corresponds to a host lattice of the magnetic system. This last interaction is related to a phenomenological parameter that is responsible for controlling the intensity of this interaction and that is proportional to a function representative of the symmetry of the host material in question. The interest behind this study seeks to characterize the influence of this interaction on the behavior of the spins through the evaluation of their main thermodynamic properties associated with a phase transition that imply a new way of modeling these systems pointing to a complementary view of what can promote frustration in magnetic systems in general. For the development of this research, we adopted entropic sampling simulations based on the Wang-Landau method, where a random walk in the energy space is performed, allowing to estimate the density of states g(E) while the energy distribution is generated in the histogram. Through this methodology, we calculated some thermodynamic properties of interest and managed to represent a phase diagram that illustrates the various forms that the system takes in function of a control parameter that is responsible for adjusting the different magnetic phases of the model. We also adopted the finite-size scale theory that allowed us to estimate the critical exponents corresponding to a certain class of universality that the system may belong to. As a result of this, we were able to establish the proper conclusions regarding the dynamics of the system and we became able to formulate the possible developments resulting from this work.

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