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Delayed fluorescence by triplet−triplet annihilation from columnar liquid crystal films.
(2022) Franca, Larissa Gomes; Santos, Paloma Lays dos; Pander, Piotr; Cabral, Marília Gabriela Belarmino; Cristiano, Rodrigo; Cazati, Thiago; Monkman, Andrew P.; Bock, Harald; Eccher, Juliana
Delayed fluorescence (DF) by triplet−triplet annihila- tion (TTA) is observed in solutions of a benzoperylene-imidoester mesogen that shows a hexagonal columnar mesophase at room temperature in the neat state. A similar benzoperylene-imide with a slightly smaller HOMO−LUMO gap, that also is hexagonal columnar liquid crystalline at room temperature, does not show DF in solution, and mixtures of the two mesogens show no DF in solution either, because of collisional quenching of the excited triplet states on the imidoester by the imide. In contrast, DF by TTA from the imide but not from the imidoester is observed in condensed films of such mixtures, even though neat films of either single material are not displaying DF. In contrast to the DF from the monomeric imidoester in solution, DF of the imide occurs from dimeric aggregates in the blend films, assisted by the imidoester. Thus, the close contact of intimately stacked molecules of the two different species in the columnar mesophase leads to a unique mesophase-assisted aggregate DF. This constitutes the first observation of DF by TTA from the columnar liquid crystalline state. If the imide is dispersed in films of polybromostyrene, which provides an external heavy-atom effect facilitating triplet formation, DF is also observed. Organic light-emitting diodes (OLEDs) devices incorporating these liquid crystal molecules demonstrated high external quantum efficiency (EQE). On the basis of the literature and to the best of our knowledge, the EQE reported is the highest among nondoped solution-processed OLED devices using a columnar liquid crystal molecule as the emitting layer.
Water diffusion in carbon nanotubes for rigid and flexible models.
(2023) Mendonça, Bruno Henrique da Silva e; Moraes, Elizane Efigenia de; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Barbosa, Márcia Cristina Bernardes; Chacham, Helio
We compared the diffusion of water confined in armchair and zigzag carbon nanotubes for rigid and flexible water models. Using one rigid model, TIP4P/2005, and two flexible models, SPC/Fw and SPC/FH, we found that the number of the hydrogen bonds that water forms depends on the structure of the nanotube, directly affecting the diffusion of water. The simulation results reveal that, due to the hydrophobic nature of carbon nanotubes and the degrees of freedom imposed by the water force fields, water molecules tend to avoid the surface of the carbon nanotube. This junction of variables plays a central role in the diffusion of water, mainly in narrow and/or deformed nanotubes, governing the mobility of confined water in a nontrivial way, where the greater the degree of freedom of the water force field, the smaller mobility it will have in confinement as we limit the competition between area and volume and it no longer plays the unique role in changing water diffusivity.
Characterization of magnetic tailings from phosphate-ore processing in Alto Paranaíba.
(2022) Silva, Fernando Brandão Rodrigues da; Araújo, Fernando Gabriel da Silva; Krüger, Fernando Leopoldo von; Silva, Guilherme Jorge Brigolini; Batista, Ronaldo Junio Campos; Manhabosco, Taíse Matte
The characterization studies of tailings from mining are crucial for the development of its reuse processes and the reduction of impacts caused by its conditioning on the earth’s surface. This study characterizes the magnetic tailings from phosphate-rock processing using X-ray diffraction, X-ray fluorescence spectrometry and quantitative electron microscopy techniques. Samples were obtained from the magnetic tailings deposit of a mining company in the Alto Paranaíba region, Minas Gerais. The tailings are mainly composed of hematite/magnetite (74.92%), ilmenite (8.91%), fluorapatite (8.8%), anatase (3.07%), calcite (1.67%), goethite (1.62%), and quartz (1.02%). The particle size of the tailings is smaller than that specified for the production of sinter feed. The hematite/magnetite phase is strongly associated with ilmenite and fluorapatite. New stages of comminution and separation are needed due to the low degree of liberation of these minerals for a possible reuse of the components.
Colorimetric nanosensor for the determination of glyphosate herbicide in aqueous solutions.
(2023) Silva, Cinthia Rocha da; Neri, Lara Chrystina Malta; Carvalho, Thaís Adriany de Souza; Bianchi, Jhonatan Rafael de Oliveira; Bianchi, Rodrigo Fernando; Santos, Igor José Boggione
Detection of pesticides depends on complex, time-consuming, and costly techniques performed only in some regions of Brazil. Thus, this study aimed to develop a sensitive, portable, easy- to-handle, and fast nanosensor to determine the presence of glyphosate in aqueous solutions. The Co(OH)2 nanostructure was synthesized, and the kinetic study of the interaction with pesticide glyphosate-based was performed. The Co(OH)2 nanostructures had a fast and effective interaction, confirmed by UV-Visible spectroscopy. Through experimental planning, the process for obtaining nanostructures has been optimized, and the nanostructures obtained were in a size range of 434.2 nm with a hexagonal nanoplate structure. The lower limit of color-based glyphosate detection was 0.178 g .L -1 . It was possible to identify the herbicide in the water of the tomato and sugar cane rinse by the change of the watercolor into pink. Although the samples showed low absorbance, the color change was noticeable to the naked eye. Therefore, to synthesize a structure that allows identifying glyphosate in a colorimetric way.
Immobilization of anthocyanin in polymeric film to obtain a colorimetric sensor for detection of copper in cachaça.
(2022) Figueiredo, Matheus Torres Duarte; Ferreira, Gabriel Max Dias; Ruiz Lopez, Melany Alejandra; Cardoso, Maria das Graças; Oliveira, Juliano Elvis de; Bianchi, Rodrigo Fernando; Ferreira, Guilherme Max Dias; Mageste, Aparecida Barbosa
Cachaça is a uniquely Brazilian product, being the most popular distilled spirit in Brazil and the fourth most consumed world- wide. Its production using copper stills can result in the leaching of the metal, contaminating the product. Then, techniques that are simple, inexpensive, and fast are required for the quantifcation of copper in cachaça. Here, flms composed of starch, with or without enrichment of amylopectin, and polyvinyl alcohol were produced for use as supports to immobilize anthocya- nin, with the aim of obtaining a sensor for detection of Cu2+ in cachaça. FTIR showed that the incorporation of anthocyanin in the flms was according to a non-covalent mechanism. An increase in the amylopectin content altered the morphology of the material, as shown by MEV. The most homogeneous flm, with low solubilization in cachaça, was applied as a sensor to detect Cu2+. The Cu2+ presence in the flm, after its contact with cachaça samples containing Cu2+ at pH 7.0, was confrmed by XEDS, with the metal being homogeneously distributed over the flm. Detection of Cu2+ in the cachaça was achieved by a change of the sensor color from red to green. The LOD and LOQ of the method were 1.39 and 2.00 mg/L, respectively. The method was accurate to determine Cu2+ in real samples of cachaça, with percentual relative error, in modulus, in the range of 3.02–9.54% in comparison with the standard spectrophotometric method using 2,2′-diquinolyn. At pH 7.00 and 5.0 mg/L Cu2+ (the maximum concentration permitted according to Brazilian legislation), the response time of the sensor was 3.16 h, with the sensor being selective towards Cu2+. The characteristics of the sensor evidenced the commercial applicability of the flm as a colorimetric sensor for the simple, inexpensive, and selective identifcation of copper in cachaça.
A formação continuada de professores em tempos da pandemia do COVID-19 : contribuições da neurociência aplicada à educação.
(2022) Gomes, Larissa Layane; Guimarães, Michele Hidemi Ueno; Cruz, Luciana Hoffert Castro
A necessidade de formação continuada de professores é uma questão emergente, apresenta- da como uma das metas a serem cumpridas pelo Plano Nacional de Educação vigente. O presente artigo apresenta o curso colaborativo denominado Multiplicadores, uma formação continuada de professores, que ocorreu durante o período de distanciamento social imposto pela pandemia do COVID-19. As aulas e discussões abordaram temas sobre Neurociência e Educação, Ensino e Aprendizagem no contexto da pandemia, com propósito de promover uma reflexão sobre a prática docente em regime de ensino remoto. Para coleta de dados, foram utilizados questionários; estes foram analisados segundo o método de Análise de Conteúdo proposto por Laurence Bardin. Os resultados demonstraram que, mesmo diante de todos os desafios da profissão docente, os professores participaram ativamente do curso, analisaram de forma crítica a sua atuação profissional e discutiram sobre a importância da valorização do trabalho.
A importância de laços transferenciais na permanência de alunos da graduação em física.
(2022) Carvalho, Gabriel Luiz de; Guimarães, Michele Hidemi Ueno; Passos, Marinez Meneguello
Apresentamos os resultados de uma investigação que teve por objetivo levantar as diversas condutas de estudantes do curso de Física da Universidade Federal de Ouro Preto, procurando compreender as motivações e os interesses que eles demonstravam durante o curso, bem como os motivos que os levaram à permanência ou evasão. Fizemos uso de alguns conceitos fundamentados na Psicanálise de orientação lacaniana, tentando estabelecer um vínculo com situações de ensino e de aprendizado em Ciências. Por meio de levantamentos de informações e entrevistas com alunos, identificamos fatores de considerável relevância, que contribuíram para o estabelecimento de vínculos com o curso e identificação da permanência ou evasão na Universidade, tal como o processo de “trampolim”. Essa conexão cria no professor uma figura que tem como papel nortear o processo de ensino e de aprendizagem no aluno, criando um sentimento de independência por busca de conhecimento inerente a cada sujeito.
On the microstructures of the bulk of P3HT amorphous films obtained from two protocols : insights from molecular dynamics simulations.
(2022) Savedra, Ranylson Marcello Leal; Morais, Marlene Notélio Borges Luíza de; Savedra, Melissa Fabíola Siqueira
An influential factor for the microstructure of semiconductor polymer films is the solvent chosen for their pro- cessing and subsequent performance as an active layer in electronic and optical devices. In this paper, we address the solvent-polymer interplays by reporting a comparison between the microstructure of the bulk of poly(3- hexylthiophene) (P3HT) films formed from two different simulation methodologies: using the o-dichloroben- zene (ODCB) as an aggregation chain parameter and a solvent-free protocol. In comparison to the length of an ideal planar chain, the solvent caused an average reduction of 12% of oligomer chains. Whereas, in the other film, the reduction was around 30%. Furthermore, the solvent allowed pathways of π-interactions due to the cohesional-like distribution of the chains, indicating that the solvent also induces chain orientation affecting its microstructure.
High-pressure studies of atomically thin van der Waals materials.
(2023) Martins, Luiz Gustavo Pimenta; Comin, Riccardo; Matos, Matheus Josué de Souza; Mazzoni, Mário Sérgio de Carvalho; Neves, Bernardo Ruegger Almeida; Yankowitz, Matthew
Two-dimensional (2D) materials and their moire superlattices represent a new frontier for quantum matter research due to the emergent properties associated with their reduced dimensionality and extreme tunability. The properties of these atomically thin van der Waals (vdW) materials have been extensively studied by tuning a number of external parameters such as temperature, electrostatic doping, magnetic field, and strain. However, so far pressure has been an under-explored tuning parameter in studies of these systems. The relative scarcity of high- pressure studies of atomically thin materials reflects the challenging nature of these experiments, but, concurrently, presents exciting oppor- tunities for discovering a plethora of unexplored new phenomena. Here, we review ongoing efforts to study atomically thin vdW materials and heterostructures using a variety of high-pressure techniques, including diamond anvil cells, piston cylinder cells, and local scanning probes. We further address issues unique to 2D materials such as the influence of the substrate and the pressure medium and overview efforts to theoretically model the application of pressure in atomically thin materials.
Nanostructured system based on hydroxyapatite and curcumin : a promising candidate for osteosarcoma therapy.
(2023) Marinho, Jéssica Pauline Nunes; Neme, Natália Paz; Matos, Matheus Josué de Souza; Batista, Ronaldo Junio Campos; Macedo, Waldemar Augusto de Almeida; Gastelois, Pedro Lana; Gomes, Dawidson Assis; Rodrigues, Michele Angela; Cipreste, Marcelo Fernandes; Sousa, Edésia Martins Barros de
Osteosarcoma is the most common type of bone cancer. Despite therapeutic progress, survival rates for meta- static cases or that do not respond well to chemotherapy remain in the 30% range. In this sense, the use of nanotechnology to develop targeted and more effective therapies is a promising tool in the fight against cancer. Nanostructured hydroxyapatite, due to its biocompatibility and the wide possibility of functionalization, is an interesting material to design nanoplatforms for targeted drug delivery. These platforms have the potential to enable the use of natural substances in the fight against cancer, such as curcumin. Curcumin is a polyphenol with promising properties in treating various types of cancer, including osteosarcoma. In this work, hydroxyapatite (n- HA) nanorods synthesized by the hydrothermal method were investigated as a carrier for curcumin. For this, first-principle calculations based on the Density Functional Theory (DFT) were performed, in which the modi- fication of curcumin (CM) with the coupling agent (3-aminopropyl) triethoxysilane (APTES) was theoretically evaluated. Curcumin was incorporated in n-HA and the drug loading stability was evaluated by leaching test. Samples were characterized by a multi-techniques approach, including Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy (UV–Vis), X-ray diffraction (XRD), X-ray fluorescence spectrometry (FRX), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), zeta potential analysis (ζ), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results show that n-HAs with a 90 nm average size were obtained and successful incorporation of curcumin in the nanostructure was achieved. Cell viability and the number of osteosarcoma cells were decreased by CMAP-HA treatment. Furthermore, the stability test suggests that hydroxyapatite nanoparticles present great potential for the trans- portation of curcumin in the bloodstream, crediting this system for biological performance evaluations aiming at the treatment of osteosarcomas. Keywords: nanostructures, curcumin, hydroxyapatite, osteosarcoma.
High throughput investigation of an emergent and naturally abundant 2D material : clinochlore.
(2022) Gonçalves, Raphaela de Oliveira; Guallichico, Luis Antonio Guallichico; Policarpo, Eduardo; Cadore, Alisson Ronieri; Freitas, Raul de Oliveira; Silva, Francisco Mateus Cirilo da; Teixeira, Veronica de Carvalho; Paniago, Roberto Magalhães; Chacham, Helio; Matos, Matheus Josué de Souza; Souza, Angelo Malachias de; Krambrock, Klaus Wilhelm Heinrich; Barcelos, Ingrid David
Phyllosilicate minerals, which form a class of naturally occurring layered materials (LMs), have been recently considered as a low-cost source of two-dimensional (2D) materials. Clinochlore [Mg5Al(AlSi3)O10(OH)8] is one of the most abundant phyllosilicate minerals in nature, exhibiting the capability to be mechanically exfoliated down to a few layers. An important characteristic of clinochlore is the natural occurrence of defects and impurities which can strongly affect their optoelectronic properties, possibly in technologically interesting ways. In the present work, we carry out a thorough investigation of the clinochlore structure on both bulk and 2D exfoliated forms, discussing its optical features and the influence of the insertion of impurities on its macroscopic prop- erties. Several experimental techniques are employed, followed by theoretical first-principles calculations considering several types of naturally-ocurring transition metal impurities in the mineral lattice and their effect on electronic and optical properties. We demonstrate the existence of requirements concerning surface quality and insulating properties of clinochlore that are mandatory for its suitable application in nanoelectronic devices. The results presented in this work provide important informations for clinochlore potential applications and establish a basis for further works that intend to optimize its properties to relevant 2D technological applications through defect engineering.
Investigation of spatially localized defects in synthetic WS2 monolayers.
(2022) Rosa, Bárbara Luiza Teixeira; Fujisawa, Kazunori; Cruz, Joyce Cristina da; Zhang, Tianyi; Matos, Matheus Josué de Souza; Sousa, Frederico Barros de; Barbosa, Tiago Campolina; Fonseca, Lucas Lafetá Prates da; Ramos, Sérgio L. L. M.; Carvalho, Bruno Ricardo de; Chacham, Helio; Neves, Bernardo Ruegger Almeida; Terrones, Mauricio; Moreira, Leandro Malard
While the spatially nonhomogeneous light emission from synthetic WS2 monolayers is frequently reported in the literature, the nature of this phenomenon still requires thoughtful investigation. Here, we combine several characterization techniques (optical imaging, scanning probe and electron microscopy) along with density func- tional theory to investigate the presence of substitutional doping localized at narrow regions along the S zigzag edge of WS2 monolayers. We verified that photoluminescence quenching along narrow regions is not related to grain boundaries but to substitutional impurities of lighter metals at the W sites, which modify the radiative and nonradiative decay channels. We also found potential candidates for occupying the W site through ADF-STEM analysis and discussed their impact on photoluminescence quenching by performing density functional theory calculations. Our findings shed light on how atomic defects introduced during WS2 monolayer’s synthesis impact the crystalline quality and, therefore, the development of high-performance optoelectronic devices based on semiconducting 2D materials.
B–C–N diamondol-like compounds : stability trends and electronic properties.
(2022) Pinto, Allan Kleyton Muniz; Pontes, João Guilherme de Moraes; Matos, Matheus Josué de Souza; Mazzoni, Mário Sérgio de Carvalho; Azevedo, Sérgio André Fontes
In this work we apply first principles calculations to investigate the stability trends of mixed boron, nitrogen and carbon diamondol-like compounds. Several distinct geometric models are tested by varying the stoichiometry and position of boron and nitrogen dopants. We verify the special stability of a complete boron nitride compound – the bonitrol –, and we show that carbon substitutions in the bonitrol structure may also lead to stable systems. The electronic characterization of the resulting compounds indicates a rich phenomenology, with metallic, semimetallic, half-metallic and semiconducting behaviors.
Mensagens falsas sobre o novo coronavírus : legitimidade e manipulação na luta de classes.
(2021) Lima, Guilherme da Silva; Calazans, Marcos Moraes; Massi, Luciana
Este trabalho tem como objetivo analisar a composição das primeiras mensagens falsas sobre o novo coronavírus e Covid-19 que circularam no Brasil visando problematizar as relações entre forma e conteúdo que creditam legitimidade às mensagens e como elas estão inseridas na luta de classes. Usamos as contribuições de Volóchinov, acerca na natureza da linguagem associadas a aportes do campo do materialismo histórico e dialético, para analisar 11 mensagens, sendo duas analisadas com maior profundidade. Os resultados indicaram que as comunicações analisadas estão inseridas na luta de classe buscando manipular o interlocutor e que as mensagens falsas se apropriaram e mobilizaram elementos das esferas da Ciência e do Jornalismo, para dar o efeito de credibilidade e legitimidade.
Phase diagram of flexible polymers with quenched disordered charged monomers.
(2022) Rodrigues, B. B.; Rocha, Julio Cesar Siqueira; Costa, Bismarck Vaz da
Recent advances in Generalized Ensemble simulations and microcanonical analysis allowed the investigation of structural transitions in polymer models over a broad range of local bending and torsion strengths. It is reasonable to argue that electrostatic interactions play a significant role in stabilizing and mediating structural transitions in polymers. We propose a bead–spring polymer model with randomly distributed charged monomers interacting via a screened Coulomb potential. By combining the Replica Exchange Wang–Landau (REWL) method with energy-dependent monomer updates, we constructed the hyperphase diagram as a function of temperature (T ) and charged monomer concentration (η). The coil–globule and globular–solid transitions are second and first order for the entire concentration range. However, above a concentration threshold of η = 80%, electrostatic repulsion hinders the formation of solid and liquid globules, and the interplay between enthalpic and entropic interactions leads to the formation of liquid pearl-necklace and solid helical structures. The probability distribution, P(E, T ), indicates that at high η, the pearl-necklace liquid phase freezes into a stable solid helix-like structure with a free energy barrier higher than the freezing globule transition at low η.
Constraining the anomalous coupling of gravitational waves with the double pulsar.
(2023) Jesus, Diego Santos de; Velten, Hermano Endlich Schneider; Piazza, Federico
We revisit the decay of the orbital period in binary systems that occurs due to the emission of gravitational waves in the context of modifie- gravity models where the coupling Ggw between matter and on shell gravitons is allowed to differ from the Newton constant GN. Using the most precisely-timed double neutron star binary system, those of the double pulsar, we constrain the ratio Ggw=GN to the level of 10−4, improving by two orders of magnitude the present bound on this quantity.
Nonconservative unimodular gravity : a viable cosmological scenario?
(2022) Fabris, Júlio César; Alvarenga, Henrique de; Daouda, Mahamadou Hamani; Velten, Hermano Endlich Schneider
In this work we review the issue of imposing the conservation of the energy–momentum tensor as a necessary condition to recover the equivalence between the unimod- ular gravity and General Relativity (GR) equipped with a cosmological constant. This procedure is usually interpreted as an ad hoc imposition on the unimodular theory’s struc- ture. Whereas the consequences of avoiding the conserva- tion of the total energy–momentum tensor has been already introduced in the literature, it has been not widely explored so far. We study an expanding universe sourced by a sin- gle effective perfect fluid such that the null divergence of its energy–momentum tensor is not imposed. As we shall show, in this scheme, the unimodular theory has its own conservation equation obtained from the Bianchi identities. We explore the evolution of the homogeneous and isotropic expanding background and show that a viable cosmologi- cal scenario exists. Also, we consider scalar perturbations with particular attention given to the gauge issue. We show that contrary to the traditional unimodular theory where the synchronous and longitudinal (newtonian) gauge for cosmo- logical perturbations are not permitted, if the conservation of the energy–momentum is relaxed the scalar perturbations in the synchronous condition survive and present a growing mode behavior. We study therefore a new cosmological sce- nario in which the dynamics of the universe transits from the radiative phase directly to a accelerated one but allowing thus for structure formation.
Early-time thermalization of cosmic components? : a hint for solving cosmic tensions.
(2021) Velten, Hermano Endlich Schneider; Costa, Ingrid; Wilhelm, Zimdahl Winfried Ernst
We study an expanding two-fluid model of nonrelativistic dark matter and radiation, which are allowed to interact during a certain time span and to establish an approximate thermal equilibrium. Such an interaction, which generates an effective bulk viscous pressure at background level, is expected to be relevant for times around the transition from radiation to matter dominance. We quantify the magnitude of this pressure for dark-matter particle masses within the range 1 eV ≲ mχ ≲ 10 eV around the matter-radiation equality epoch (i.e., redshift zeq ∼ 3400) and demonstrate that the existence of a transient bulk viscosity has consequences which may be relevant for addressing current tensions of the standard cosmological model: (i) the additional (negative) pressure contribution modifies the expansion rate around zeq, yielding a larger H0 value, and (ii) large-scale structure formation is impacted by suppressing the amplitude of matter overdensity growth via a new viscous friction-term contribution to the M ́eszáros effect. As a result, the H0 and S8 tensions of the current standard cosmological model are both significantly alleviated.
A apresentação de conceitos em um livro de divulgação científica infantil : o caso Isaac no mundo das partículas.
(2023) Araújo, João Felipe Viana de; Lima, Guilherme da Silva; Almeida, Sheila Alves de
Este trabalho objetiva analisar as ideias e conceitos científicos presentes na obra de divul- gação científica voltada para o público infantil “Isaac no Mundo das Partículas”, escrita por Elika Takimoto. Partimos das contribuições da psicologia histórico-cultural sobre os conceitos potenciais, espontâneos e científicos, buscando compreender as relações e formas de significação das ideias científicas apresentadas pela obra. Foram selecionados e analisados trechos do livro no qual conceitos científicos ou ideias-chave estavam presentes. A palavra foi considerada a unidade de análise e os resultados indicaram que o livro mobiliza diversas significações e estruturações lógico-abstratas (conceituais) para formalizar elaborações mais complexas e conceitos científicos. A análise dos conceitos: átomo, partícula e vácuo, indi- cou estratégias para a produção de sentido, que contemplaram a: contextualização, curiosi- dade, disputas argumentativas, uso de conceitos espontâneos, uso da história da ciência etc.
Considerações sobre o conteúdo presente no artigo "A tríade conteúdo-forma-destinatário: uma análise das práxis pedagógicas do ensino de ciências orientados pela pedagogia histórico-crítica".
(2022) Lima, Guilherme da Silva

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