Programa de Pós-graduação em Física

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Estudo teórico sobre membranas peptídicas e lipídicas: uma análise via dinâmica molecular
(Universidade Federal de Goiás, 2021-08-10) Alves, Eyber Domingos; Oliveira, Guilherme Colherinhas de; http://lattes.cnpq.br/0171051425848743; Oliveira, Guilherme Colherinhas de; Castro, Marcos Antonio de; Almeida, Norton Gomes de; Ludwig, Valdemir Eneias; Fileti, Eudes Eterno
In this work, the molecular dynamics formalism was used to study the physicochemical properties of peptide and lipid membranes when immersed in solution. Concerningpeptide membranes, the energetic and structural properties were evaluated in the situations in which these membranes were immersed in the Ionic Liquid (IL) formed by the choline (COL) and glycine (GLY) pair. The results indicate the existence of energetic and structural stability of these membranes when in IL, with potential application in energy storage in biodegradable supercapacitors. For lipid membranes, we used the umbrella sampling technique to proceed with a series of 150 insertions of the Fullerene-C 60 molecule in four lipid membranes composed of DOPC (Dipalmitoylphosphatidylcholine) at a ratio of 00% (pure membrane), 10%, 20% and 30% of cholesterol molecules, evaluating the average behavior of molecular insertion energies. The results showed that the presence of cholesterol molecules makes the inclusion process of Fullerene-C 60 energetically unfavorable. Under the computational pathway, we evaluated the pharmacological characteristics associated with monomers constructed based on peptides. For this purpose, we interact the lipid membranes composed of DOPC (Dipalmitoylphosphatidylcholine) at a proportion of 00% (pure membrane), 10% and 30% of cholesterol molecules with the peptide drug L-GL13K. The results reveal that the hydrogen bonds between the compound L-GL13K and the DOPC molecules promote membrane destabilization and increasing the infiltration of water molecules.
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.
Versatilidade estrutural de aminoácidos agregados: design de nanomateriais orgânicos via dinâmica molecular
(Universidade Federal de Goiás, 2022-02-25) Andrade, Douglas Xavier de; Oliveira, Guilherme Colherinhas de; http://lattes.cnpq.br/0171051425848743; Oliveira, Guilherme Colherinhas de; Cruzeiro, Vinícius Wilian dias; Fonseca, Tertius Lima da; Ludwig, Valdemir Eneias; Georg, Herbert de Castro
In this work, we carried out structural and energetic characterization of nine nanomembranes and two nanofibers composed of surfactant-like peptides (SLPs), using Molecular Dynamics (MD) simulations with atomistic resolution. The nanomembranes [nanofibers] studied are formed by the peptides I3V3A3G3K3 and K3G3A3V3I3 [G3A3V3I3K3 and K3I3V3A3G3]; A6Hε and A6Hδ; and I3XGK (X = Q, S, N, G or L). The nanomembranes I3V3A3G3K3 and K3G3A3V3I3 are formed by the same amino acids, but linked in inverted primary sequences, which changes torsions, the side chains, and the C and N peptide terminals, affecting the hydration and stability of the nanomembranes. The A6Hε and A6Hδ nanomembranes are differentiated by the position of the hydrogen atom attached to the aromatic ring of histidine (H) residues, alterning the way that this residue is exposed to water, and consequently, the lateral attachment of alanine residues (A). By studying the I3XGK (X = Q, S, N, G or L) nanomembranes, we realized that the peptides with polar residues (X = Q, S, or N) present properties of polar zippers connecting β-sheets laterally. Therefore, this work aims at elucidating and characterizing the formation of polar zippers that, recently, have attracted significant scientific and technological interest. The nanofibers G3A3V3I3K3 and K3I3V3A3G3 are formed by peptides with the same amino acids, but linked in inverted primary sequences, similar to the case of the nanomembranes I3V3A3G3K3 and K3G3A3V3. This way, by studying nanomembranes and nanofibers composed with the same amino acids, this work allows us to understand how changes in the disposition of the peptide side chains lead to the formation of distinct nanostructures, evidencing the structural versatility of aggregate amino acids. The analyses performed are based on the mass density profiles, on nanomembrane thicknesses, on the radial distribution functions, g(r), on the average number of Hydrogen Bonds (HBs) between amino acids and between each amino acid and water molecules - for a better characterization of HBs between peptides and consequently the nanomembranes’ hydration, HB’s time correlation functions are presented - and in the Coulombic and vdW energetic interactions which together with the HBs play a fundamental role in the organization of the peptides forming the nanostructures. Our results indicate that the C-terminal attached to the charged lysine (K) leads to the formation of more hydrated nanomembranes; the A6Hε and A6Hδ are nanostructures with a high degree of organization and with features of crystalline structures; the polar zippers present an interesting route for the design of robust and stable nanostructures, by joining neighboring β-sheets; the peptide nanostructures presented in this work have interesting characteristics suggesting that they can be used to encapsulate and transport drugs, as hydrogels and as an antimicrobial agent. Our MD results show excellent agreement with experimental data reported in the literature. In addition, we show that the CHARMM36 force field could be recommended for the study of the peptide nanomembranes and nanofibers presented. This validation is important because it allows the prediction from the theoretical point of view of new features of peptide structures of this species, providing advances in the development of organic nanostructures.
Eficiência de um motor térmico de Otto quântico baseado em um sistema de dois níveis
(Universidade Federal de Goiás, 2021-12-09) Assis, Rogério Jorge de; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes de; Serra, Roberto Menezes; Cardoso, Wesley Bueno; Brito, Frederico Borges de; Pinto, Diogo de Oliveira Soares
Classical thermodynamics, also called equilibrium thermodynamics, is a theory that deals with macroscopic systems in equilibrium. After its development, other theories emerged to encompass macroscopic out-of-equilibrium systems. Over the past few decades, researchers have developed a new theory to describe also the thermodynamics of microscopic quantum systems, which became known as quantum thermodynamics. An important application of this theory is in the development of heat engines in which the working substance (the substance responsible for transforming heat into work) is a microscopic quantum system. Due to their composition, these devices came to be commonly called quantum heat engines. Notably, recent studies have shown that using an out-of-equilibrium reservoir as a heat source can improve the performance of quantum heat engines, compared to the usual case where the heat source is an equilibrium reservoir (a thermal reservoir). In this context, this thesis presents two studies related to a quantum Otto heat engine whose working substance is a two-level system: in the first study, the engine has a squeezed thermal reservoir as the heat source, while in the second study, the heat source is a reservoir with a negative temperature. Both studies explore the finite-time regime of the expansion and compression stages of the heat engine. The first study shows that the engine efficiency can be greater than the Carnot efficiency in both the quasi-static and finite-time regimes. However, as in the usual case, decreasing the time of the expansion and compression stages degrades the engine efficiency. In its turn, the second study shows that the engine efficiency can surpass the Otto efficiency in the finite-time regime. Here, different from the usual case, decreasing the time of the expansion and compression stages can increase the engine's efficiency. Finally, the present thesis shows an experimental scheme in the nuclear magnetic resonance context able to provide a proof of concept for the engine in the different situations studied.
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+.
Estudo das interações de porfirinas com sistemas de interesse biológico: potencial uso no transporte de fármacos e aplicação fotodinâmica
(Universidade Federal de Goiás, 2019-08-23) Bezerra, Fábio de Castro; Gonçalves, Pablo José; http://lattes.cnpq.br/0515343409614452; Gonçalves, Pablo José; De Boni, Leonardo; Iglesias, Bernardo Almeida; Borissevitch, Iouri; Alonso, Antonio
The purpose of this work was to study the interactions of porphyrins in systems of biological interest aiming at drug transport and photodynamic applications. Interactions of anionic meso-tetrakis(p-sulphonatephenyl) porphyrin (TPPS4) and cationic meso-tetrakis (4- methyl-pyridyl) porphyrin (TMPyP) porphyrins with bovine serum albumin (BSA), antibodies, DNA and biocompatible nanoparticles of maghemite were evaluated. To obtain the binding constants and thermodynamic parameters, spectroscopic UV/Vis absorption and fluorescence techniques were used. Binding constants indicate a higher affinity of porphyrin TPPS4 for proteins compared to TMPyP. Thermodynamic parameters showed that electrostatic and hydrophobic interactions mediated the BSA interactions with the porphyrins TPPS4 and TMPyP, respectively. On the other hand, the nature of porphyrin-antibody interactions shows a behavior opposite to that observed for BSA (electrostatic for TMPyP and hydrophobic for TPPS4), indicating that the binding site of porphyrin TMPyP in the antibodies is likely to have a net negative charge. In the porphyrin TPPS4 interaction with maghemite nanoparticles, besides obtaining the binding parameters of the interaction, it was possible to estimate the number of 21 porphyrins coupled in each nanoparticle. Regarding the interaction of DNA with the porphyrins TPPS4, TMPyP and its complexes with zinc, it was observed that ZnTMPyP has higher affinity for DNA than TMPyP, whereas TPPS4 and ZnTPPS4 do not bind to DNA, which explains the results of photodegradation of DNA by these porphyrins. Keywords: Photodynamic
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.
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.
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.
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.
Markov monogamy inequalities
(Universidade Federal de Goiás, 2022-03-09) Capela, Matheus; Araújo, Rafael Chaves Souto; ttp://lattes.cnpq.br/1509277905143351; Céleri, Lucas Chibebe; http://lattes.cnpq.br/6630683190018665; Celeri, Lucas Chibebe; Avelar, Ardiley Torres; Oliveira, Thiago Rodrigues de; Santos, Marcelo Paleologo Elefteriadis de Franca; Pinto, Diogo de Oliveira Soares
O estudo dos limites na comunicação com canais ruidosos é um problema central na teoria de informação. Data processing inequalities são de fundamental importância sob esta perspectiva. Entretanto, estas não são as as únicas condições existentes sob o processamento de informação. Neste trabalho, apresentamos uma nova categoria de condições chamadas Markov monogamy inequalities. Estes novos resultados são aplicados ao estudo e caracterização de processos não-Markovianos clássicos e quânticos. De grande importância, as condições Markov monogamy inequalities revelam-se serem mais eficientes que as data processing inequalities na certificação de processos não-Markovianos em determinados exemplos.
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.
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.
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.
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.
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.
Quebra de simetria em condensados de Bose-Einstein confinados por um potencial funil
(Universidade Federal de Goiás, 2021-04-09) Miranda, Bruno Martins; Cardoso, Wesley Bueno; http://lattes.cnpq.br/6845416823133684; Cardoso, Wesley Bueno; Malbouisson, Jorge Mário Carvalho; Almeida, Norton Gomes de
Theoretically predicted in 1923-1924 by Bose and Einstein and experimentally obtained only in 1995, the Bose-Einstein condensate became an important laboratory for the investigation of various quantum phenomena, such as the Josepshon oscillations, the study of vortex, use as interferometers, etc. Using mean-field theory to include the effects of the average interaction between particles, in the 1960s, Gross and Pitaevskii obtained an equation capable of describing the dynamics of a diluted gas at a temperature of 0 K. Dimensional reduction models for the Gross-Pitaevskii equation were developed for several types of confining potentials in order to simplify numerical calculations and reproduce accurate results. For condensates with a strong attractive strength, confined by doublewell potentials, it is known that the phenomenon of spontaneous symmetry breaking occurs. In this state, the particle population between wells becomes asymmetrical, in contrast with the symmetry of the confining potential. In this work, we consider a condensate in the self-focusing regime, confined transversely by a funnel-like potential and axially by a double well formed by the combination of two inverted Pöschl-Teller potentials. We used an effective equation, obtained by means of a variational method for the Gross-Pitaevskii equation, to analyze the symmetry break of the probability density of the wave function that describes the condensate. This symmetry break was observed for several interaction strength values as a function of the minimum potential well. A quantum phase diagram was obtained, in which it is possible to recognize the three phases of the system: symmetric phase (Josepshon), asymmetric phase (spontaneous symmetry breaking - SSB), and collapsed states, i.e., when the solution becomes singular, which does not represent the physical system, showing a validity limit for the model under consideration. We analyzed our symmetric and asymmetric solutions using the real-time evolution method, in which it was possible to confirm the stability of the results. Finally, a comparison with the cubic nonlinear Schrödinger equation in one dimension and the Gross-Pitaevskii equation in three dimensions is performed for the purpose of analyzing the accuracy of the effective equation used here.
Stability and aromaticity of small neutral and charged boron clusters: a quantum Monte Carlo study
(Universidade Federal de Goiás, 2019-07-26) Moreira, Emanuel Melo Isaac; Silva, Ladir Cândido da; http://lattes.cnpq.br/7442411485710574; Silva, Ladir Cândido da; Oliveira, Marcos Cesar de; Oliveira, Heibbe Cristhian Benedito de; Oliveira, Guilherme Colherinhas de; Vale, Renato Pessoa
Neste trabalho, investigamos as energias de ligação eletrônica dos clusters de boro neutros Bn, com n = 3 até n = 13, seus ânions e cátions, usando uma combinação dos métodos, Monte Carlo quântico na aproximação dos nós fixos (FN-DMC), teoria do funcional da densidade e Hartree-Fock. As energias de ligação eletrônica como adiabatic detachment energy, vertical detachment energy, adiabatic ionization potential e vertical ionization potential foram examinadas para diferentes isômeros, e os valores obtidos estão em excelente concordância com resultados disponíveis na literatura, indicando que as geometrias dos clusters de boro, obtidas neste trabalho, estão corretas. A decomposição dessas energias de ligação eletrônica em três componentes físicas como, o potencial eletrostático e a interação de exchange, a energia de relaxação, a qual inclui a relaxação da geometria e dos orbitais, e a correlação eletrônica, nos permitiu determinar que os clusters de boro neutros são estabilizados pelas interações eletrostática e de exchange, enquanto os clusters aniônicos são estabilizados pela energia eletrostática e exchange, energia de relaxação e efeitos de correlação eletrônica. Também investigamos a aromaticidade de pequenos clusters de boro com três e quatro átomos através de princípios de estrutura eletrônica e energia de ressonância. Os resultados FN-DMC aplicados aos princípios de estrutura eletrônica para a energia, hardness e electrophilicity suportam a aromaticidade dos clusters B3-, B4- e B4 , e parcialmente suportam a aromaticidade dos clusters B3 , B3+ e B4+. Os valores obtidos para a energia de ressonância dos clusters B3, B3-, B3+, B4, B4- e B4+ foram: 55.1(7), 54.2(8), 33.9(7), 84(1), 67(1), and 58(1) kcal/mol, respectivamente. Então, a ordem decrescente de estabilidade do trímero é B3- > B3 > B3+, enquanto que paro o tetrâmero é B4 > B4+ > B4- , o que está de acordo com resultados de análise de orbitais.
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.
Development and investigation of lanthanide-doped oxide nanocrystals for nanothermometry
(Universidade Federal de Goiás, 2024-11-14) Nogueira, Camila Tsuchida; Ibanez, Alain; Maia, Lauro June Queiroz; http://lattes.cnpq.br/9454054374479016; Carvalho, Jesiel Freitas; http://lattes.cnpq.br/5841291496427516; Carvalho, Jesiel Freitas; Maia, Lauro June Queiroz; Araújo, Eudes Borges de; Gomes, Danielle Cangussu de Castro
Temperature sensing with accuracy and good spectral resolution is highly sought in research and industry, especially in biomedicine and microelectronics, where conventional thermal probes are unsuitable for remote measurements below 10 μm. In biology, thermal monitoring can indicate inflammatory areas, diseases, and tumors. Previous studies suggest temperature monitoring is promising for early diagnosis and assisting disease treatments, such as hyperthermia for cancer treatment. In this regard, luminescent nanoprobes made of inorganic materials doped with rare-earth ions have emerged as an effective means to measure local temperature precisely and remotely. The thermal readout is obtained by tracking the Luminescence Intensity Ratio (LIR) between two photoluminescence (PL) emission lines, which evolves with temperature. A calibration curve between LIR and temperature can then be extracted from experimental data in the laboratory. Nonetheless, developing adequate luminescent nanothermometers for biological applications continues to be a major hurdle. These thermal sensors must be small, stable and well-dispersed in physiological solutions, nontoxic, and exhibit strong PL emissions within the biological windows (BWs) ¾ the wavelength ranges where light penetrates tissues deeply. This work focuses on oxides doped with rare-earth ions for nanothermometry in future biological applications, comprising the synthesis, characterization, and analysis of thermal sensing performance using PL emissions in the BWs of Y3Al5O12 (YAG), Y2O3, and Y4Al2O9 (YAM) co-doped with Nd3+ and Yb3+. The first two host matrices were synthesized via the modified Pechini method for co-doping engineering to optimize the concentrations of Nd3+ and Yb3+ for ideal PL emission. To obtain well-dispersed individual nanocrystals (NCs), YAG: Nd3+- Yb3+ and Y2O3: Nd3+-Yb3+ were synthesized by the solvothermal route and the two-step urea-based route, respectively, with conditions systematically optimized to fulfill the requirements of this thesis. The third host matrix, YAM, was also studied using the modified Pechini synthesis to investigate its thermal response when single-doped with Nd3+ and co-doped with Nd3+ and Yb3+. Lastly, a new synthesis method for YAM was explored. The findings showed that YAG: Nd3+-Yb3+ exhibited great potential, particularly after applying a silica coating around the NCs synthesized by the solvothermal route. This coating allowed annealing at 850°C to enhance the PL emission without agglomerating the NCs. The resulting YAG: Nd3+-Yb3+@SiO2 nanoparticles (NPs) had a final size of 87 ± 20 nm, a relative thermal sensitivity (Sr) of 0.60%.K-1, and thermal resolution (δT) of 0.2 K at physiological temperature. Y2O3: Nd3+-Yb3+ NCs of 22 ± 10 nm had Sr of ~ 0.50%.K-1, but δT ~ 0.4 K due to a lower signal-to-noise ratio. YAM, when single-doped with Nd3+, revealed competitive thermal response with Sr = 0.50%.K-1 and δT = 0.3 K at body temperature. However, co-doping YAM with both Nd3+ and Yb3+ ions hampers the thermal sensing efficiency to less than 0.40%.K-1 of Sr at physiological temperature, with δT fluctuating between 0.2 and 0.7 K across the temperature range. Thus, this study paves the way for improving the synthesis and applications of the oxides in nanothermometry and highlights promising prospects of Nd3+-Yb3+ co-doped YAG nanothermometers thanks to their decreased size, good thermal sensing features, and intense PL emission within the BWs.

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