REPOSITÓRIO INSTITUCIONAL DA UNIVERSIDADE DO VALE DO PARAÍBA
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Submissões Recentes
Characterization of the chemical evolution of CH4 ices under processing by cosmic ray analogues with the PROCODA code – I. Effective reaction rate coefficients and chemical equilibrium phase
(Royal Astronomical Society) Gerasimenko, Svitlana; Carvalho, Geanderson Araújo; Zanatto, Fernanda; Santana, Fernanda Kelly de; Pilling, Sergio
Methane (CH4), the simplest alkane, is a fundamental component of astrophysical ices, particularly in the outer Solar system and the interstellar medium. Understanding its chemical evolution under energetic particle irradiation is essential for modelling these environments. In this work, we investigate the chemical evolution of pure methane ice subjected to high-energy ion irradiation until chemical equilibrium is reached. We employ the procoda code to simulate the time-dependent evolution of molecular abundances and to determine effective reaction rate coefficients. The simulations are constrained using experimental data from a previous study, in which pure CH4 ice at 16 K was irradiated, providing the necessary input parameters for the model. Our reaction network comprises 1857 chemical reactions involving 36 molecular species, both observed and unobserved by Fourier-transform infrared spectroscopy during the experiment. The best-fitting model satisfies multiple criteria: a low for observed species, a desorption yield consistent with experimental estimates, similar trends in abundance evolution for observed and unobserved species, and overall mass conservation. At chemical equilibrium, the most abundant species predicted by the model are H2 (38.0 per cent), CH4 (20.8 per cent), H (17.0 per cent), and CH3CH2CH3 (16.9 per cent). The total desorption yield is calculated as molecules/ion, and the effective destruction cross-section of CH4 is cm. The reaction rate coefficients and equilibrium abundances derived from this study provide valuable inputs for astrochemical models, enhancing our understanding of CH4 processing in interstellar ices under cosmic ray irradiation.
Characterization of a Gelcast AISI 310 SS Matrix Composite Reinforced by Alumina and GNP Particles
(Universidade Federal de São Carlos) Oliveira, Louise Fernanda Rodrigues; Ortega, Fernando dos Santos; Magnabosco, Rodrigo; Neves, Maurício David Martins das
Gelcasting is a versatile forming technique suitable for preparing composite materials with various powders, including metallic and ceramic particles, at any solids concentration. Despite its potential, the application of gelcasting to produce metal matrix composites reinforced with alumina and graphene remains limited. This study investigates the gelcasting of AISI 310 stainless steel composites reinforced with 1, 3, and 5 vol.% nanosized alumina and 0.5 vol.% graphene nanoplatelets (GNPs). Rheological behavior and particle interactions were analyzed to ensure uniform dispersion. Thermal analysis determined optimal sintering conditions, avoiding densification issues. Compression and microhardness tests revealed yield strengths of up to 285 MPa at room temperature (RT) and 140 MPa at 800 °C, exceeding ASTM A351/A351M-18e1 standards. Microstructural refinement and homogeneous alumina distribution were achieved, with 3 vol.% alumina providing the best performance. The gelcasting process proved effective for producing dense, mechanically robust composites at a low cost.
Characteristics of slant sporadic-E layers observed at low-latitudes
(Elsevier) Muka, Peter Taiwo; Muella, Marcio Tadeu de Assis Honorato; Santos, Fredson Conceição; Resende, Laysa Cristina Araújo; Fagundes, Paulo Roberto; Ogunmola, Olufemi Louis; Fontes Neto, Pedro Alves; Pillat, Valdir Gil; Cesar, Mariah; Jesus, Rodolfo de
This study investigates the occurrence, characteristics, and formation mechanisms of slant sporadic-E layers (Ess). The Ess-type layers observed at the Brazilian low-latitude stations of Jata ́ı (17.9°S, 51.7°W) and Sa ̃o Jose ́ dos Campos (23.2°S, 45.8°W), are analyzed using ionosonde data recorded for four months (April, June, September, and December) of 2016. Parameters such as top frequency (ftEs), blanketing frequency (fbEs), and virtual height (h’Es) were scaled from ionograms to characterize the slant (Ess) traces. The results show that Ess-type layers predominantly occur at night, forming between 95 and 120 km altitudes, with monthly and local variations. Model simulations using meteor radar-derived winds revealed that strong and stable zonal wind shear are associated with increased Ess-type layer activity. In addition, wavelet spectral analyses of ftEs and fbEs showed that tidal periodicities (diurnal, semidiurnal, terdiurnal, and quarterdiurnal) and their interactions with gravity waves seem to play fundamental roles in the formation of Ess-type layers. A com- parison of DF (ftEs-fbEs) during Ess-type events confirmed the presence of strong plasma density gradients, supporting the hypothesis that the slanted traces in ionograms result mostly from oblique reflections in inhomogeneous Es layer structures. However, the appearance of slant Es traces may in some cases be related to an actual tilt of the layer. Other relevant aspects of the observations associated with the possible physical mechanisms behind the formation of Ess-type layers at low latitudes are highlighted and discussed.
Advantages and disadvantages of VTEC, ROTI and airglow images in studying equatorial plasma bubbles
(Elsevier) Souza, Ana Lucia Christovam de; Prol, Fabricio dos Santos; Muella, Marcio Tadeu de Assis Honorato; Picanço, Giorgio Arlan da Silva; Camargo, Paulo de Oliveira; Monico, João Francisco Galera
Equatorial plasma bubbles (EPBs) are large-scale plasma depletion structures, observed near the geomagnetic equator and in low- latitude regions after sunset. Several instruments have been employed to study EPBs, such as ionosondes, in situ satellites, coherent and incoherent scatter radars, airglow imagers, GNSS radio occultation, and GNSS ground-based stations. Among these instruments, Total Electron Content (TEC) and Rate of TEC change Index (ROTI) data derived by GNSS measurements are presenting as outstand- ing data sources to study the climatology of EPBs. In this study, we evaluate the reliability of TEC and ROTI index for mapping iono- spheric plasma bubble structures in comparison to airglow images, demonstrating the performance of each technique and highlighting their respective advantages and disadvantages. The results demonstrate that TEC and ROTI time series are effective to identify plasma bubble occurrence in terms of temporal profiles, horizontal maps, and keograms for EPB velocity estimation. In terms of ionospheric temporal profiles, all techniques presented a good correspondence, TEC data may present direct characteristics of plasma bubbles, i.e., the intensity of the electron density depletions, while ROTI values are more suitable to present the occurrence, or not, of plasma bubbles. TEC maps showed advantages in mapping the horizontal distributions of EPBs, specially at the equatorial regions where ROTI failed to detect disturbances. Velocity estimates based on keograms from airglow data averaged 111 m/s, while TEC and ROTI index averaged 106 m/s and 107 m/s, respectively. Overall, TEC data presented better estimates of velocities due to the geometric and physical information, while ROTI offers statistical insights that often mask the natural propagation of EPBs.
Transcranial photobiomodulation therapy associated with cardiorespiratory rehabilitation in spastic subjects
(Springer Nature Link) Pinto, Ana Paula; Lemos, Sergio Luiz; Fagundes, Alessandra de Almeida; Neves, Marcele Florêncio das; Martins, Rodrigo Álvaro Brandão Lopes; Silva, Fernanda Pupio; Silva, Mário Oliveira
The objective of this study was to evaluate the effects of cardiorespiratory rehabilitation (CR) and transcranial photobiomodu- lation (tPBM) on exercise tolerance (ET), heart rate variability (HRV), and peripheral muscle activity in individuals with spasticity. Fifteen participants with spasticity were randomly assigned to two groups: the tPBM group (tPBMG) consisted of eight volunteers who underwent tPBM (on mode) and CR, while the control group (CG) consisted of seven volunteers who underwent simulated tPBM (off mode) and CR. The CR program included 12 weeks of treatment, twice a week for one hour, involving aerobic exercises and lower limb strengthening. For tPBM, a cluster with three lasers (λ = 680 nm, 808 nm), with a power of 100 mW/laser and energy of 36 J, applied to the F7, F8, and Fpz points. The following parameters were evalu- ated after 8 and 12 weeks: ET, HRV, and surface electromyography (EMG) of the rectus femoris muscle during orthostasis (ORT), isometric squatting (ISOM), and isotonic squatting (ISOT). Both groups showed a 40% increase in ET for the CG and a 30% increase for the tPBMG. The CG had more pronounced parasympathetic modulation alterations during post-exercise effort and recovery compared to the tPBMG. The EMG results showed that the tPBMG exhibited progressive improvement in muscle activity during ISOM and ISOT, as well as a decrease in the interlimb difference. In conclusion, both CR and tPBMG demonstrated improvements in ET. However, tPBMG specifically showed promising effects on HRV modulation and peripheral muscle electrical activity, providing additional benefits compared to CR alone.