Navegando por Assunto "Tempo de reação"

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Acesso aberto (Open Access)
Estudo de processo de upgrading catalítico de vapores da pirólise de resíduos plásticos de equipamentos de informática em reator catalítico com carvão ativado impregnado com NaOH
(Universidade Federal do Pará, 2023-04-03) COSTA, Augusto Fernando de Freitas; MACHADO, Nélio Teixeira; http://lattes.cnpq.br/5698208558551065
This study investigated thermal cracking and catalytic upgrading of plastic waste from computer equipment on a semi-batch reactor coupled to a heated catalyst fixed bed (2-stage vapor cracking). The catalyst used was a Si–Al ash obtained from commercial activated carbon pellets treated with concentrated NaOH solution and calcination. The purpose of the study was to characterize the waste stream through its thermogravimetry (TG) analysis and pyrolysis products, study the effect of temperature (350 - 500 °C) and catalyst quantity (0.0 - 7.5 wt%) on yields of reaction products, physical chemical properties, and chemical composition of organic liquid product in order to understand and evaluate production of fuels and chemical feedstock by recycling of plastic waste from computer equipment through catalytic upgrading. Time fractioned samples were taken in determined reaction times (15 min, 30 min, 45 min, and 60 min) to study the evolution of cracking reactions during experiment runs through changes to chemical composition (GC-MS). A comparison with other previous work was also presented to show similarities between different feedstocks using the same thermal unit. The results indicate composition of brominated acrylonitrile-butadiene-styrene (Br-ABS), polycarbonate (PC), and high impact polystyrene (HIPS) for the plastic waste from computer equipment. The temperature of 350 °C produced better results when considering acid value but presented lower liquid phase yields (38 %) and high gas phase yields (42 %). Catalytic upgrading experiments revealed the increased presence of polycyclic aromatic hydrocarbons (PAH) with an increase in kinematic viscosity of organic liquid product, increase in char yield (from 11 % to 24 %), and decrease in gas yields (15 % to 5 %). Chemical composition showed presence of aromatic hydrocarbons such as styrene, methyl-styrene, and diphenyl-propane and nitrogenated compounds such as benzene butane-nitrile, phenolic compounds, polycyclic aromatic hydrocarbons, and brominated compounds. Plastic waste from computer equipment pyrolysis is a challenging subject due to contaminant presence and varying composition, and chemical composition evaluation according to reaction time provides interesting insights into the evolution of semi-batch pyrolysis/catalytic upgrading experiments. Standardization and reproducibility of the tool should be conducted to continue the evaluation of pyrolysis and catalytic upgrading of a wide range of feedstocks.
Acesso aberto (Open Access)
Manual responses to visual stimuli: early and late facilitatory effects due to the offset of a peripheral cue
(2003) PINHEIRO, Walter Machado; GAWRYSZEWSKI, Luiz de Gonzaga; PEREIRA JÚNIOR, Antônio
Manual and saccadic reaction times (MRTs and SRTs) are reduced when a warning signal precedes the onset of a target. The decreasing on SRTs observed after the offset of a fixation point has been called the gap effect. Different theories have been proposed to explain it. According to some authors, the offset also allows the saccadic system to generate a separate population of SRTs, the express saccades. Nevertheless there is no agreement about the influence of the offset of a peripheral stimulus on MRT. In two experiments we tested the effects of a peripheral visual offset used as preparatory signal on MRTs to a target after variable intervals. We found a reduction on MRT at short (200-300 ms) and long (1300-2000 ms) intervals after the peripheral offset. MRT distribution shifted toward short latencies, which sometimes formed a separate population. Since MRTs obtained at long intervals were affected by the introduction of catch trials, while MRTs at short intervals were not, we propose that two different mechanisms are involved in the decreasing of MRTs: warning and temporal expectancy. Our data support the hypothesis that the temporal component involved with the preparatory stages for motor responses can be shared by saccadic movements and key press responses, allowing the reduction on motor latencies after the visual offset in the gap paradigm. Our data corroborate the three components model for the gap effect. In our view, the question of the existence or not of a gap effect for manual responses is essentially conceptual.
Acesso aberto (Open Access)
Postura da mão e imagética motora: um estudo sobre reconhecimento de partes do corpo
(2008-10) LAMEIRA, Allan Pablo do Nascimento; SILVA, Sabrina Guimarães; FERREIRA, Fernanda Maciel; Lima, LV; PEREIRA JÚNIOR, Antônio; GAWRYSZEWSKI, Luiz de Gonzaga
Objective: Recognition of body parts activates specifi c somatosensory representations in a way that is similar to motor imagery. These representations are implicitly activated to compare the body with the stimulus. In the present study, we investigate the infl uence of proprioceptive information relating to body posture on the recognition of body parts (hands). It proposes that this task could be used for rehabilitation of neurological patients. Methods: Ten right-handed volunteers participated in this experiment. The task was to recognize the handedness of drawings of a hand that were presented in different perspectives and several orientations. For drawings of a right hand, the volunteers pressed the right key, and for drawings of a left hand, they pressed the left key. The volunteers underwent two sessions: one with their hands in a prone posture and the other with their hands in a supine posture. Results: The manual reaction time was longer for perspectives and orientations for which the real movement was diffi cult to achieve. This showed that, during the task, motor representations were activated to compare the body with the stimulus. Furthermore, the subject’s posture had an infl uence in relation to specifi c perspectives and orientations. Conclusions: These results showed that motor representations are activated to compare the body with the stimulus, and that the position of the hand infl uences this resonance between the stimulus and the body part.
Acesso aberto (Open Access)
A tomada de decisões no judô: o que se diz e o que se faz? Relação entre tomada de decisões e perfil neurocognitivo
(Universidade Federal do Pará, 2023-03) RIVERA, Luis Felipe Sarmiento; GOUVEIA JUNIOR, Amauri; http://lattes.cnpq.br/1417327467050274; https://orcid.org/0000-0003-1710-9662
There are two ways to think about how the decision process is done. The process can be automatic and having psychomotor characteristics, or mediated by linguistic process -in a deliberated way-. Moreover, martial arts bring an environment with high emotionality, where the anxiety is present. The objective of this study is to understand how the decision-making process, the anxiety and the impulsivity is presented in a combat physical activity, a Judo fight, that demands constant decisions and responses with limited time. To do this, there were to groups of participants (30 judo fighters and 15 non-fighters). One of the groups watch a video and anticipated the fighter’s movement with a questionary, and the other group was recorded in a judo fight. Both groups also performed an impulsivity test and an anxiety test. Each participant had more than 4,5 years of training and was an active competitor. There were found differences in the decisions made by the participants in the fight and the decisions that the participants told they would perform, specifically, when they were going to execute and action. Moreover, there was a significant difference in the anxiety levels of the group of fighters compared to controls, where the fighters had higher anxiety levels than controls. There were none significative differences in impulsivity between the groups. The results of the study shown how is cognition in Judo fighters, indicating where to focus the training and competition programs of the fighters.