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Desenvolvimento e estudo de memristores baseados em redes de nanofios de SnO2
(Universidade Federal de São Carlos, 2024-01-17) Moisés, Lucas Augusto; Chiquito, Adenilson José; https://lattes.cnpq.br/7087360072774314; https://orcid.org/0000-0002-2498-4820; https://lattes.cnpq.br/7856086233961011; https://orcid.org/0000-0001-9018-8075
In this work, memristors were produced based on tin dioxide nanowire networks (𝑆𝑛𝑂2). These nanowires were synthesized by the VLS (Vapor-Liquid-Solid) method. The nanowire structural analysis via X-ray diffraction (XRD) showed a single phase of tin dioxide in the rutile phase with tetragonal symmetry and spatial group P42/mm. Scanning electron microscopy (SEM) images showed varying profiles of sizes and thicknesses (from nano to micrometric) of the obtained wires, a variation arising from the self- assembly process in the synthesis. Three different types of memristors devices have been developed; the first and simplest one is based on a nanowire network obtained directly from synthesis, without any kind of wire manipulation, just adding silver electrodes on the nanostructures. This device showed memristive behavior that strongly depends on the atmosphere in which it was located and data from a detailed study of that dependence indicated the resistive switching was linked to the variation of two types of potentials existing in the network. The first one occurs at the contact region between the nanowires that make up the network, while the second comes from the Schottky-type metal- semiconductor junctions existing at the contact region between the nanowires and electrodes. The variation of these potentials occurs due to charge configuration changes at these contact regions, changes arising from carriers’ flow guided by an applied electric field. A variation of the first device was made by adding a polymeric layer over the nanowire network. This device variation presented a more prominent memristive effect and that improvement was attributed to the molecules trapping on the nanostructure surfaces by the polymer, generating a charge state freezing at surface region. The retention data acquired from this memristor showed behavior congruent with the Ebbinghau forgetting curve, indicating potential of this device in synaptic learning application. Emulations of the learning and forgetting cycles were carried out on this device and that potential was confirmed. The second type of device produced, based on just one wire (microwire), was made in order to study anomalous behaviors observed in some first type devices (specifically those without the polymeric layer). This anomalous behavior was reproduced in this second device, which proved to be a memristor, and was attributed to the protons conduction guided by water molecules adsorbed on surface oxygen vacancies. Unlike the first device, the single-wire device presented constant resistive states, presenting two resistive states retention for more than 18 Ks and an ON/OFF ratio of 4.6 between them. The third type device developed in this work consists of a nanowire network deposited via drop-casting on a substrate. The preferred position of the nanowires in that network obtained was perpendicular to the substrate, unlike the wire network present in the first device memristor, and this position favoured the nanostructures interaction with the environment, thus increasing the water molecules adsorption level. This greater water adsorption led this third type to show an electrical behaviour identical to the single-wire memristor device. Like the single-wire device, the third type device showed constant resistance states over time. Data obtained from retention measurements of two resistive states, with an ON/OFF ratio of 27.8 between them, showed its conservation for more than 1400 s. The retention data from the second and third device types made they candidates for applications in electronic memories.
Proposta de ensino de ciências sobre vírus: integração dos três momentos pedagógicos, abordagem CTS e combate às fake news
(Universidade Federal de São Carlos, 2024-01-17) Godoy, Bianca de Oliveira de; Milaré, Tathiane; https://lattes.cnpq.br/4030661520659155; https://orcid.org/0000-0001-6557-1769; https://lattes.cnpq.br/2133261672915349; https://orcid.org/0009-0002-4717-8095
This paper introduces an innovative approach to science education through a didactic sequence designed for 4th-grade students in Elementary School, focusing on the theme of viruses. The proposed sequence integrates the Three Pedagogical Moments, the Science, Technology, and Society (STS) perspective, and addresses the challenge of combating Fake News. The relevance of the topic lies in the contemporary importance of viruses, emphasizing scientific, technological, and social aspects. The STS approach is incorporated to highlight the interconnectedness of science, technology, and society in the context of viruses. Emphasis is placed on the role of science in understanding and combating viral diseases, as well as the influence of technology in information dissemination. The theme of Fake News is integrated to cultivate students' skills in discerning reliable information, promoting scientific and media literacy. Pedagogical strategies, including source analysis, data verification, and discussions on the spread of misinformation, are implemented. The proposal aims to cultivate students who are more conscientious, critical, and participatory, capable of comprehending and addressing virus-related issues from an integrated perspective. By combining the Three Pedagogical Moments, the STS approach, and the confrontation of Fake News, the goal is to provide a comprehensive and relevant learning experience in the current context. While the proposal presents an innovative approach to science education on viruses, it has not been implemented yet. Given this limitation, future research is suggested for the application of the proposed sequence. Practical application will allow for the assessment of teaching strategy effectiveness, identification of challenges, and pursuit of improvements, contributing to the continuous enhancement of the proposed method.
Nitrosaminas em insumos farmacêuticos ativos
(Universidade Federal de São Carlos, 2024-01-17) Rossoni, Carolina; Carneiro, Renato Lajarim; https://lattes.cnpq.br/8065852319463976; https://orcid.org/0000-0002-6857-2190; https://lattes.cnpq.br/0009229316865375
Since 1972, N-nitrosamines have been the subject of study in medication composition. However, in July 2018, the presence of the N-nitrosamine NDMA was identified in Valsartan, leading to the recall of this medication. Subsequently, in August 2018, there were also recalls of Losartan and Irbesartan. Following this milestone, studies on these organic compounds, characterized by the presence of an amine group linked to a nitroso group, have been constantly advancing, prompting regulatory revisions aimed at consumer safety. To prevent medication shortages, guidelines and resolutions have been developed to assist in assessing and controlling risks, considering acceptable limits for daily intake. Consequently, there was a need to understand the pathways of formation of these impurities during the manufacturing process of both pharmaceutics and medications. In this context, this study aimed to evaluate potential formation routes of these impurities and how we can establish their limits, assessing whether there is proper control over nitrosamines.
Oxidação de glicerol via catalisadores híbridos com absorção de luz visível
(Universidade Federal de São Carlos, 2024-01-17) Cunha, Charles Garcia da; Sitta, Elton; https://lattes.cnpq.br/4326476348284298; https://lattes.cnpq.br/0823518787250677; https://orcid.org/0009-0002-8837-3989
The world's energy demand tends to grow exponentially in the next 30 years, obliging the development of more efficient methods to supply it. One of the alternatives to solve this problem is the use of solar energy through storage in chemical bonds, with emphasis on the H2 molecule obtained from water. However, this process is still a large-scale challenge, especially in relation to the oxidation process. In this context, the oxidation of small organic molecules can circumvent this problem, increasing the production of H2 and still providing products of commercial interest. Thus, this work aims to oxidize glycerol using photoelectrocatalysts with visible light absorption based on BiVO4 and X-C3N4/BiVO4, where "X" represents different carbon nitrides (PCN, X-PHI (Na, K, or Cs), Li-PTI, and BiVO4 was synthesized via Bi electrodeposition in FTO followed by thermal conversion at 500 ºC in the presence of vanadium acetylacetonate. The nitrides were synthesized by the method of thermal condensation of melanin in the presence of chlorides of alkali metals. To make the X-C3N4/BiVO4, the nitride of interest was deposited in the FTO via spin coating and the BiVO4 synthesis procedure was followed. The thermogravimetric analysis showed that the PCN has superior thermal stability than other nitrides in oxidizing atmosphere, the other materials showed degradation of ca 30% of the mass at 500 ºC. Although the nitrides presented different values of bandgap energy, Eg, the X-C3N4/BiVO4 heterojunctions presented values of Eg similar to pure BiVO4. XRD analysis also revealed that the BiVO4 phases were not changed by the presence of nitrides but scanning SEM measurements coupled to EDS revealed regions rich in Bi and V and others rich in C and N, suggesting the formation of heterojunctions. Photoelectrochemical assays showed that BiVO4 is active for both water oxidation and glycerol oxidation (1.0 mol L-1), but with four times increase in the presence of glycerol at 1.23 V vs RHE. Clearly, the type of nitride used to make the heterojunctions influences the activity of the material for glycerol oxidation, with the order of photocurrent at 1.23 V vs RHE being: PCN > BiVO4 > Cs-PHI/BiVO4 > K-PHI/BiVO4 > Na-PHI/BiVO4 > Li-PTI/BiVO4. SEM-EDS analysis after electrochemical tests revealed that the presence of carbon nitrides induces the segregation of vanadium oxides, contributing to a decrease in activity. That way, some heterostructures show promising performance for the oxidation of the glycerol molecule. However, besides the electronic structure able to transport electron from BiVO4, is important to look for CN with thermal stability to avoid their degradation during BiVO4 synthesis.
Reflexões sobre um sonho, uma jornada e uma saudade
(Universidade Federal de São Carlos, 2024-01-17) Araújo, Camila Monteiro Faria; Traslaviña, Guillermo Andrey Ariza; https://lattes.cnpq.br/8329010880453672; https://orcid.org/0000-0003-0839-9864; https://lattes.cnpq.br/1351892614642572; https://orcid.org/0000-0001-5288-6155
The Course Conclusion paper presented to the Department of Medicine of the Federal University of São Carlos is an assessment and reflection on how the 6 years of graduation in Medicine were. The work is divided between pre-entrance exam phase, course, divided into cycles that make up the way the course was formulated and projections for the future. This work aims to complete the course and obtain a bachelor's degree in Medicine.