Programação

O fenômeno da supercondutividade é conhecido há mais de 100 anos. Materiais supercondutores apresentam resistência elétrica próxima de zero e, portanto, são capazes de transportar altos valores de corrente elétrica. Esses materiais são principalmente divididos em supercondutores de baixa e alta temperatura. Os supercondutores de alta temperatura operam em temperaturas próximas à do nitrogênio líquido (T = 77K). Os fatores que limitam o estado supercondutor desses materiais são a temperatura crítica (Tc), a densidade de corrente crítica (Jc) e a intensidade crítica do campo magnético externo (Hc). Esses parâmetros críticos também estão relacionados a dois parâmetros espaciais: o comprimento de coerência (ξ) e o comprimento de penetração de London (λ). Dependendo da relação λ/ξ, os supercondutores se classificam como Tipo I e Tipo II. O parâmetro ξ refere-se ao comprimento característico associado à coerência quântica dos pares de Cooper, sendo também uma medida da extensão espacial dos pares de Cooper e está relacionado à estabilidade do estado supercondutor. Por outro lado, λ está associado à capacidade de um supercondutor de repelir campos magnéticos, mesmo quando está em um estado supercondutor. Essa medida determina até que ponto um campo magnético pode penetrar no interior do supercondutor sem destruir o estado supercondutor. Entre os supercondutores de alta temperatura, a maior atenção está nos chamados cupratos supercondutores, e aqueles com composições YBCO (YBa2Cu3O7-y) e BiSCCO ((Bi,Pb)2Sr2Ca2Cu10+y) (Bi-2223) são os mais estudados e amplamente utilizados em aplicações. Na apresentação, mostramos um estudo sistemático do efeito de tamanho nas propriedades supercondutoras de amostras nanoestruturadas de Bi-2223. O trabalho envolve dois tipos de amostras, algumas na forma de pó e outras na forma de pastilhas. As primeiras foram obtidas por moagem de alta energia por diferentes períodos de tempo. As pastilhas foram conformadas, partindo dos pós obtidos, mediante uma sinterização rápida, com o objetivo de preservar o tamanho das partículas na ordem dos nanômetros. De forma geral, discutirei sobre supercondutividade, medição de propriedades supercondutoras e como estas mudam quando o tamanho das partículas começa a ser da ordem dos parâmetros λ e ξ.

The use of lithium-ion batteries (LIBs) has become increasingly prevalent in daily life, both in portable electronic devices and electric vehicles, as well as in energy storage systems. However, these batteries face safety issues due to the use of organic liquid electrolytes that are toxic and highly flammable. To address these concerns, one solution is to replace liquid electrolytes with solid electrolytes, which are safer due to their higher thermal stability and ability to operate at higher temperatures. In this seminar, we will provide an overview of lithium-ion batteries and demonstrate how the use of Li3NbO4-based materials can enhance the performance and safety of these batteries.

This work presents a theoretical study on the effects of rotation on the nonrelativistic quantum motion of a charged particle confined to a 2D ring in the presence of the Aharonov-Bohm effect and a uniform magnetic field. We formulate the Schrödinger equation with minimal coupling, incorporating the gauge field for the rotating frame and the potential vector of the electromagnetic field. By solving the equation of motion, we determine the eigenvalues and eigenfunctions of the particle. We analyze the probability distribution as a function of varying rotating parameter values and observe a perceptible shift in the distribution. This shift indicates a higher probability of locating the electron at the edges of the ring. The second part of our study focuses on the investigation of rotation effects on the linear and nonlinear optical properties of the system. Specifically, we examine the linear, nonlinear, and total refractive index changes, as well as the optical absorption coefficients. Through numerical analysis, we demonstrate significant rotating effects on energy levels and optical properties. Our findings indicate that, for the considered physical parameters, the impact of rotation on the optical properties becomes prominent at values on the order of a few terahertz.

Depending on thermodynamic conditions, molybdates can adopt new structural arrangements, potentially resulting in distinct physical and chemical properties. This characteristic renders them an attractive model for obtaining and exploring novel properties. In this study, we present the temperature-dependent behavior of hexagonal silver molybdate using in situ Raman scattering and X-ray diffraction (XRD). The samples were synthesized using the conventional hydrothermal method at 413 K and pH 1 for 12 h. The resulting samples exhibited a microrod morphology with well-defined facets and a hexagonal cross-section. The material crystallized in the hexagonal structure with space group P63/m. This structure consists of interconnected octahedra forming one-dimensional tunnels interspersed with silver atoms. Polarized Raman spectroscopy was employed to assist in identifying vibrational modes. Hexagonal silver molybdate undergoes dehydration when subjected to a vacuum. The temperature dependencies of the unit cell parameters were determined, and the thermal expansion coefficients were calculated. No structural phase transitions were observed between 300 K and 12 K during the Raman scattering and XRD experiments. However, structural phase transformations were noted at higher temperatures. The material showed uniaxial negative thermal expansion (NTE) at low temperatures and NTE in three directions at high temperatures. This study presents the initial findings on the temperature-dependent structural and vibrational in situ characterization of hexagonal silver molybdate rods.

In this study, we delve into the structural, magnetic, and vibrational characteristics of hexagonal ErMnO_3 (h-ErMnO_3) manganite employing X-ray Diffraction (XRD), Magnetometry, and Raman Spectroscopy techniques. The structural and vibrational data obtained through XRD and Raman analyses exhibit consistency with hexagonal symmetries, specifically the P63cm space group (C_6v^3-185). The XRD data, monitored with respect to temperature, unveil deviations in the monotonic behaviors of lattice parameters and interatomic distances. This outcome not only elucidates the origin of robust phonon frequency renormalizations but also brings to light isostructural transitions. Furthermore, the Raman data, studied across varying temperatures, illuminate the role of deformation in the magneto-electric effect. This occurs through the intricate coupling between order parameters and their interaction with optically active phonons in Raman spectroscopy.

The growing interest in two-dimensional materials has spurred the development of new nanostructured materials. Bismuth Tungstate (Bi2WO6) has distinguished itself with its diverse synthesis routes and remarkable versatility in photocatalytic applications under visible light. These applications include the environmental sector, where it contributes to the development of new photocatalysts for pollutant degradation, as well as in the creation of devices for solar energy conversion. Moreover, it finds application in the field of biomedicine due to its ease of forming reactive oxygen species and exhibiting antibacterial actions. The physical properties of Bi2WO6 are influenced by the synthesis method and particle morphology. In this study, the synthesis of Bi2WO6 monolayers was achieved through the hydrothermal method and structurally characterized using X-Ray Powder Diffraction (XRD) and Raman spectroscopy. Morphological characterization was conducted with Atomic Force Microscopy (AFM). Additionally, the surface potential distribution for the monolayers was investigated using the Kelvin Probe Force Microscopy (KPFM) technique. Nanomechanical analysis conducted by AFM revealed that the topography of the Bi2WO6 monolayers had a height of ≈1.60 nm, corresponding to the thickness of a single unit cell along the [001] direction. The adhesion forces between the probe and the sample were found to be smaller than the interaction between the probe and the substrate (cleaved mica). KPFM results showed a higher surface potential at the edges compared to the inner region of the monolayers. In this scenario, the study aims to gain a better understanding of the physical and chemical aspects associated with the reduced dimensions of the material and its effectiveness in photocatalytic activities.

We consider a restricted baby Skyrme-Maxwell scenario enlarged via the inclusion of a nontrivial magnetic permeability. We then proceed with the minimization of its total energy by means of the Bogomol'nyi-Prasad-Sommerfield (BPS) prescription, from which we get that the self-dual potential is now defined in terms of a differential constraint which involves both the superpotential and the magnetic permeability itself. As a result, we obtain not only the lower bound of energy, but also the first-order BPS equations whose solutions saturate the bound. In this context, we focus our attention on those time-independent gauged skyrmions with radial symmetry and no electric charge. We then investigate some basic aspects of our generalization theory and compare them with the standard case.

This work aims to develop the Hamiltonian formulation for an effective model of modified gravity that incorporates a dynamical scalar background field called u(x) in the minimal gravitational sector of the Standard-Model Extension (SME). The presence of such a scalar field spontaneously breaks one of the fundamental symmetries of General Relativity (GR), namely diffeomorphism symmetry. To construct the Hamiltonian associated with this model, we use the (3+1) decomposition developed by Arnowitt, Deser, and Misner, which consists of foliating the four-dimensional spacetime into a continuous family of three-dimensional hypersurfaces of constant time. This foliation is governed by the lapse function N and components N^i of the shift vector, representing gauge degrees of freedom. On each hypersurface, a set of canonical variables is defined, to which we associate a set of conjugate momenta, leading to the derivation of the canonical Hamiltonian through the Legendre transformation. This allows for a description of the gravitational phase space. As does GR, our model contains constraints. Current investigations aim to determine if the latter are of first or second class. This result will permit obtaining the number of degrees of freedom of our gravitational model. Moreover, the constraints act as generators of spacetime diffeomorphisms and spatial diffeomorphisms in the hypersurfaces, respectively, leading to the field equations of our model. These equations provide indications on the dynamics of spacetime in the presence of u(x).

We investigate the existence of self-dual configurations in the restricted gauged baby Skyrme model enlarged with a Z2-symmetry, which introduces a real scalar field. For such a purpose, we implement the Bogomol'nyi procedure that provides a lower bound for the energy and the respective self-dual equations whose solutions saturate such a bound. Aiming to solve the self-dual equations, we specifically focused on a class of topological structures called compacton. We obtain the corresponding numerical solutions within two distinct scenarios, each defined by a scalar field, allowing us to describe different magnetic media. Finally, we analyze how the compacton profiles change when immersed in each medium.

We have demonstrated the existence of compact self-dual solitons in a gauged baby Skyrme model in the presence of a magnetic impurity. The consistent implementation of the Bogomol'nyi-Prasad-Sommerfield formalism depends on the type of magnetic impurity. These impurities can have radii lesser or greater than the compacton's radius, and we will study them in detail. Consequently, for all cases, we have obtained a Bogomol'nyi bound for the energy and the respective self-dual equations satisfied by the fields that saturate that bound. The Bogomol'nyi bound is proportional to the topological charge of the Skyrme field, which is quantized, whereas the total magnetic flux is not. After solving the self-dual equations numerically, we present the compacton's profiles and comment on their main characteristics.

Máquinas térmicas quânticas são ótimas plataformas teóricas e experimentais para testar a termodinâmica em escalas onde efeitos quânticos são relevantes. Um destes efeitos é a coerência quântica, presente em muitos modelos de ciclos termodinâmicos operando em regime de tempo finito. Este regime é desejável para qualquer modelo de máquina térmica, pois permite obter uma potência diferente de zero. Nesta apresentação, mostrarei inicialmente que para um ciclo de Otto com um sistema quântico como substância de trabalho e com reservatórios térmicos clássicos, a coerência sempre degrada a performance do ciclo. Então, comentarei dois trabalhos em que utilizamos protocolos diferentes para diminuir a degradação causada pela coerência em ciclos de Otto. O primeiro envolve realizar termalização incompleta com o reservatório térmico quente, enquanto o segundo consiste em substituir o reservatório térmico quente por um protocolo de medidas projetivas.

In this presentation, we will highlight several scientific applications of advanced synchrotron-based X-ray diffraction employed at the Brazilian Synchrotron Light Laboratory (LNLS), situated in Campinas, São Paulo. The laboratory hosts multi-user facilities that are accessible to both the Brazilian and international scientific communities. It is responsible for operating Sirius, a fourth-generation synchrotron light source. Firstly, we will present the results of high-quality X-ray diffraction measurements, enabling us to elucidate the impact of elevated temperatures on the crystal network of L-asparagine monohydrate. Notably, this crystal exhibits a fascinating effect -- negative thermal expansion along the a axis within the temperature range of 311 to 358 K. In the second scientific case, in situ synchrotron X-ray powder diffraction is employed to clarify the formation mechanism of multiferroic BiFeO3 nanoparticles during moderate heat treatment at ambient pressure from an amorphous precursor. Additionally, we will explore the structural behavior of the bis(L-alaninate)copper(II) crystal in response to varying pressure conditions. The stability of the complex is influenced by metal-ligand bonds, coordination geometry around the metal atom, and hydrogen bonds. To conclude, we will briefly mention other examples, providing a comprehensive overview of the diverse applications of synchrotron-based techniques in our research endeavors.

Nesse seminário irei apresentar a entropia de buracos negros em cenário de gravidade modificada bem como a complexidade holográfica. A complexidade holográfica para buracos negros foi uma proposta elaborada por Leonard Susskind e Adam Brown, os quais mostraram que o buraco negro ainda continua emitindo informação após sua morte.

Os agrotóxicos são largamente utilizados em todo o mundo, sendo um dos principais responsáveis pela manutenção e desenvolvimento da agricultura. Apesar de atuar na eliminação de insetos em plantações, acabam se infiltrando no solo atingindo as águas subterrâneas trazendo riscos aos seres aquáticos e também à saúde humana. Seus efeitos tóxicos podem causar alterações no sistema nervoso central, além de gerar mutações genéticas de graus elevados e que podem ter como consequência neoplasias. Dentre os agrotóxicos mais utilizados encontra-se glifosato, inseticida altamente tóxico e quando consumido em excesso pode causar efeitos neurológicos. Por conta disso, é necessário, por meio de recursos tecnológicos, identificar e remover este e muitos outros agrotóxicos da natureza. O presente trabalho, tem como objetivo analisar através de simulações computacionais baseadas na teoria do funcional da densidade as propriedades eletrônicas, estruturais e energéticas da interação do agrotóxico glifosato com o grafeno em diferentes configurações. Os resultados mostram que a interação entre o glifosato e o grafeno ocorre via processo físico. A análise das propriedades eletrônicas e energéticas mostram que o grafeno é sensível a presença da molécula de glifosato, assim inferimos que o grafeno pode ser utilizado sensor ou filtro para esse perigoso agrotóxico.

We have studied the existence of self-dual configurations in a nonminimal CPT-odd and Lorentz-violating Podolsky-Higgs model. The Bogomol’nyi-Prasad-Sommerfield formalism reveals that self-dual equations become non-local and contain derivative couplings. Despite this, the CPT-odd self-dual equations describe electrically neutral configurations with finite total energy proportional to the total magnetic flux; this way, they maintain the characteristic of the case without the Podolsky term. In particular, we show that the model also supports Abrikosov-Nielsen-Olesen’s vortices.

Nosso estudo se concentra no movimento de uma partícula carregada não relativística dentro do espaço-tempo de um monopolo global. Utilizamos a equação de Schrödinger para descrever esse movimento, considerando dois potenciais distintos: (a) o potencial de Kratzer e (b) sua versão modificada. As autofunções e autovalores desse problema são determinados pela resolução da equação radial de movimento. O potencial efetivo do sistema é expresso em termos do potencial de auto interação eletrostática e do potencial Kratzer, resultando em soluções para estados ligados. Durante nossa análise do espectro de energia, destacamos a sua sensibilidade aos parâmetros físicos do sistema. Tanto o potencial de Kratzer modificado quanto o potencial de autointeração desempenham um papel crucial no perfil do potencial efetivo e do espectro de energia. Eles também permitem a existência de estados ligados para certas escolhas dos parâmetros físicos envolvidos. Nossa investigação é acompanhada por gráficos ilustrativos e uma discussão detalhada, que evidenciam os diferentes comportamentos mencionados.

O inseticida acefato, com fórmula química C4H10NO3PS, é utilizado para controle de insetos em casas ou plantações. O Brasil, por ser considerado um dos grandes produtores agrícolas, utiliza o mesmo no plantio de algodão, batata, feijão, melão, etc., entretanto, somente para uso industrial. No entanto, a exposição a este inseticida está relacionado a vários efeitos colaterais adversos, geralmente associados aos sistemas gastrointestinal, neurológico, respiratório e dérmico. Pensando nisso, é necessário detectar e retirar essas substâncias tóxicas do meio ambiente. O presente trabalho tem como objetivo estudar, através de simulações computacionais, as propriedades eletrônicas, estruturais e energéticas do inseticida acefato interagindo com nanotubos de GaN (GaNNT), visto que o mesmo é um composto promissor para diversas aplicações. Um estudo por simulação computacional, desse sistema, é particularmente importante, pois é capaz de prever as propriedades físico-químicas e garantir uma melhor compreensão dos resultados experimentais. Para este fim, utilizamos a Teoria do Funcional da Densidade implementada no programa computacional SIESTA, para verificar a utilização do nanotubo como filtro ou sensor dessa substância tóxica.

In this talk, I will present the existing analogy between the two-dimensional hydrogen atom in the presence of a cosmic string and two-dimensional semiconductors. The two-dimensional hydrogen atom provides a promising alternative to describe the quantum interaction between an electron and a proton in the presence of a cosmic string. We will discuss the calculations for energy levels, probability distribution function, and expected values of the hydrogen atom with a logarithmic potential and under the influence of the topological defect. The aim of this talk is to contribute to a better understanding of the influence of topological defects on the behavior of a charged quantum particle and to emphasize the importance of existing analogies between different branches of physics. To achieve this objective and provide better context to the subject, in the introduction, I will present brief definitions of the studied topological defects and their analogies with systems in condensed matter physics.

In this work, we study the propagation and absorption of cold plasma waves in the context of the Maxwell-Carroll-Field-Jackiw (MCFJ) electrodynamics, in which the timelike and spacelike background play the role of chiral magnetic conductivity and anomalous Hall conductivity, respectively. A first study of cold plasmas considering the purely timelike CFJ background was recently developed [see PRD 107, 096018 (2023)]. In this talk, we revise the basic framework of this first work, starting from the Maxwell equations written for a cold/collisionless fluid plasma, finding the refractive indices and the propagating modes and revising the associated optical effects.  In the sequel, we examine the wave propagation for the cold plasma under the spacelike MCFJ electrodynamics. Such an analysis is performed for the propagation parallel to the external magnetic field, which yields distinct refractive indices associated with RCP and LCP waves. For each index, the propagation and absorption zones are well determined for some parameter values. The low frequency regime is also discussed, with the attainment of RCP and LCP modified helicons. The optical behavior is investigated by means of the rotatory power (RP) and dichroism coefficient. It is observed RP sign reversal, a feature of rotating plasmas.

We investigate the dispersive propagation and absorption in a Drude-Lorentz dielectric modified by a magnetic current, in connection with the chiral magnetic effect (CME). Using standard electromagnetic methods, the dispersion relations and refractive indices are evaluated and discussed, as well as the group and the energy velocities. We consider three configurations for the magnetic conductivity tensor: isotropic, antisymmetric, and symmetric. In all these cases, we carry out the group velocity and the energy velocity for investigating the properties of signal propagation. We observe that the isotropic magnetic conductivity enhances the signal propagation at low and intermediary frequencies, while the symmetric and antisymmetric conductivity severely constrains the wave propagation in these frequency windows.

As halobenzoquinonas constituem uma classe de subprodutos gerados durante o processo de desinfecção da água por meio da cloração, sendo predominantemente identificadas nos efluentes provenientes de estações de tratamento de água potável. A presença crescente de halobenzoquinonas na água potável tem despertado preocupações devido aos seus efeitos adversos à saúde, destacando-se estudos que indicam uma possível associação entre essas substâncias e o risco de câncer de bexiga. Dentre as halobenzoquinonas, destaca-se a 2,6-dicloro-3-metil-1,4 benzoquinona (DCMBQ), cujas investigações revelam uma capacidade de induzir taxas mais elevadas de citotoxicidade e genotoxicidade em comparação com outras moléculas pertencentes à mesma classe. A detecção e remoção eficaz da molécula DCMBQ da água potável representam desafios significativos. Neste estudo, analisamos a interação da molécula DCMBQ com nanomateriais de carbono, como grafeno, nanotubo de carbono e fulereno C60, em diferentes configurações, por meio de cálculos de primeiros princípios baseados na teoria funcional da densidade, implementada no código computacional Siesta. Para assegurar uma descrição precisa da interação entre a molécula DCMBQ e as nanoestruturas de carbono, empregamos dois funcionais para descrever o termo de troca-correlação: a aproximação de densidade local e a correção de Van der Waals. Os resultados obtidos indicam que a adsorção de DCMBQ altera as propriedades eletrônicas das nanoestruturas de carbono, dependendo do local de adsorção da molécula. Através da análise da energia de ligação, observamos que a interação entre a molécula e a nanoestrutura de carbono ocorre por meio de processos químicos ou físicos, dependendo do sítio de adsorção.

What role does time play in quantum theory? Given an arbitrary physical process, how fast can a quantum system evolve? Quantum mechanics imposes fundamental constraints on the time of evolution of physical processes. Noteworthy, the quantum speed limit (QSL) sets the minimum evolution time for a quantum system evolving under an arbitrary dynamics. The study of QSLs in finite-dimensional quantum systems involves the notion of distinguishability measures for quantum states. In this work, we investigate the interplay between QSLs and entropic information-theoretic quantifiers of quantum states. When the quantum system undergoes a nonunitary dynamics, we find upper bounds that depend on both smallest and largest eigenvalues of the initial state, and the Schatten speed of the evolved state. To illustrate our findings, we address the unitary dynamics of a two-level system with time-independent Hamiltonian. In addition, we consider the nonunitary dynamics of a single-qubit state evolving under the amplitude damping channel. Our results might find applications in quantum thermodynamics, quantum metrology, and also in the study of many-body systems.

Neste trabalho investigamos possíveis efeitos da inclinação da energia de simetria nuclear (L) em estrelas de nêutrons. Para estrelas com valores de massa fixa, estudamos como a inclinação influencia o raio estelar, compacidade, deformabilidade de maré, frequência do modo fundamental e tempo de amortecimento. Demonstramos que estas quantidades são sensitivas à inclinação.

We will present models of how dunes move, analyzing aspects of the movement of sand particles. As well as the importance of these studies for coastal and desert regions where large dune fields are found. In addition, practices adopted with the purpose of stabilizing the movement of sand will be discussed, as well as the removal and ways of diverting moving sand, and we will address studies carried out in order to better understand these physical aeolian processes.