Navegando por Autor "Silveira, Carolina Hahn da"
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Item Bioabsorbable Poly(vinyl alcohol)–Citric Acid Dressings: Wound Healing Studies in an Experimental In Vivo Model(MDPI) Pereira, Jonalba Mendes; Arisawa, Emilia Angela Lo Schiavo; Maia Filho, Antônio Luiz Martins; Silva, José Figueredo; Alves, Nicoly; Silveira, Carolina Hahn da; Vieira, LuciaBackground: The wound healing process presents notable challenges for nurs- ing teams, requiring extensive knowledge of wound care materials. A nanoparticle-free, bioabsorbable pol-yvinyl alcohol (PVA) with citric acid (CA) dressing produced by simple electrospin-ning was evaluated to treat acute wound healing in rats. This PVA-CA combi- nation promotes crosslinking, increases the dressing capacity of absorption and confers heal-ing properties due to the citric acid antioxidant action. Methods: The dressing was tested in a quantitative experiment on 1.9 cm acute dermatological lesions in rats (n = 12), com-paring the PVA-CA-treated group with the untreated control group (CG). Samples were collected at 3, 7 and 14 days after lesion induction to evaluate the inflammatory process and tissue healing. Results: The macroscopic and histological data on the third day showed similar characteristics in both groups; however, after fourteen days, the PVA- CA group exhibited complete healing, accompanied by recomposition of the skin layers, whereas the wounds in the CG did not close completely. Conclusions: The results highlight that electrospun PVA-AC dressings improve healing outcomes and constitute a prom-ising and affordable solution, providing a suitable environment for tissue repair, re-ducing in- flammatory cell infiltration, blood vessel formation, and restoration of epi-thelial tissue, reducing the time of the healing process of acute wounds.Item Chemical evolution of electron-bombarded crystalline water ices at different temperatures using the procoda code(Royal Astronomical Society) Pilling, Sergio; Silveira, Carolina Hahn da; Ojeda González, ArianWater ices are a common component of cold space environments, including molecular and protostellar clouds, and the frozen surfaces of moons, planets, and comets. When exposed to ionizing and/or thermal processing, they become a nursery for new molecular species and are also responsible for their desorption to the gas-phase. Crystalline water ice, produced by the deposition of gaseous water at warm (80–150 K) surfaces or by the heating of cold amorphous water ice (up to ∼150 K), is also regularly detected by astronomical observations. Here, we employed the procoda code to map the chemical evolution of 5 keV electron-bombarded crystalline water-ices at different temperatures (12, 40, 60 and 90 K). The chemical network considered a total of 61 coupled reactions involving nine different chemical species within the ice. Among the results, we observe that the average calculated effective rate constants for radiation-induced dissociation decrease as the ice´s temperature increases. The abundance of molecular species in the ice at chemical equilibrium and its desorption to gas-phase depend on both the temperature of the ice. H2O molecules are the dominant desorbed species, with a desorption yield of about 1 molecule per 100 electrons, which seems to be enhanced for warmer crystalline ices. The obtained results can be employed in astrochemical models to simulate the chemical evolution of interstellar and planetary environments. These findings have implications for astrochemistry and astrobiology, providing insight into crucial chemical processes and helping us understand the chemistry in cold regions in space.Item Enhancing UV Radiation Resilience of DLC-Coated Stainless Steel with TiO2: A Dual-Layer Approach(MDPI) Macário, Paulo Fabrício; Silveira, Carolina Hahn da; Vieira, Angela Aparecida Moraes; Marcondes, André Ricardo; Marques, Francisco das Chagas; Fechine, Guilhermino José Macêdo; Vieira, LuciaThis study presents an innovative dual-layer coating approach integrating titanium dioxide (TiO2) onto diamond-like carbon (DLC)-coated 316L stainless steel. The combination of PECVD- deposited DLC and ALD-deposited TiO2 aims to preserve the inherent tribological properties of DLC while mitigating UV-induced degradation. By leveraging the ability of TiO2 to absorb, reflect, and scatter UV light, this dual-layer strategy significantly enhances the durability of DLC coatings in radiation-prone environments. The effects of accelerated aging through UV exposure on DLC and DLC/TiO2 films were evaluated using an Accelerated Weathering Tester. Comprehensive analyses were conducted to assess the structural and mechanical properties before and after UV exposure, including Raman spectroscopy, profilometry, SEM, EDS, nanoindentation, and tribometry. The results demonstrate that the TiO2 layer effectively mitigates UV-induced damage, preserving the DLC film’s integrity and tribological performance even after 408 h of UV aging. Specifically, the DLC/TiO2 coatings maintained lower roughness, higher hardness, and better adhesion than DLC- only coatings under identical conditions. This research significantly advances protective coating technology by enhancing the durability and performance of DLC films, particularly in aerospace and other demanding industries where exposure to UV radiation is a critical concern.Item Modeling the chemical evolution and kinetics of pure H2O Ices under various types of radiation employing the PROCODA code(Elsevier) Silveira, Carolina Hahn da; Pilling, SergioWater is one of the most abundant molecules in space, especially in cold environments, where it is the main constituting of astrophysical ices. The space ionizing radiation affects these ices and induces chemical changes, including desorption to gas-phase, which increase the complexity of the interstellar medium. In this work, we employed the PROCODA code to investigate the behavior of several pure water ices under different type of ionizing radiation such as UV, X-rays, electrons and cosmic rays analogues. Here, we employ molecular column densities from laboratory and solved a set of coupled chemical reactions to calculated effective reaction rates (ERCs) and characterize the chemical equilibrium of water ices under high radiation fluences. Briefly, we monitored the evolution of nine species (including the observed ones H2O, H2O2, and O3, and the predicted ones H, O, H2, OH, O2, and HO2). A discussion on the branching ratio for the considered reactions with the type of ionizing radiation is provided. Among the results, we observed that approximately 63% of the modeled molecules quantified at chemical equilibrium were non-observed species in the X-rays experiment, highlighting the importance of this work in providing insights into the processes that occur on the surface of icy interstellar grains exposed to cosmic radiation, including the formation and destruction of water ice. Accurate modeling of these processes can lead to a better understanding of the chemical evolution of interstellar and circumstellar environments, as well as offer insight into the formation and composition of celestial objects such as comets.Item Study of (12Co–4Cr WC) and (Cr3C2–25NiCr) coatings sprayed by the HVOF process and subsequently laser remelted(UFSCar) Oliveira, Ana Claudia Costa; Carvalho, Edinelson; Dyer, Paulo; Silva, Maria Margareth da; Vieira, Lucia; Silveira, Carolina Hahn da; Vasconcelos, Getúlio deThe laser remelting technique on tungsten carbide (12Co–4Cr WC) and chromium carbide (Cr3 C2 –25NiCr) coatings deposited by HVOF provides improvements in surface properties, such as increased hardness and resistance to abrasive wear. This process uses a laser beam to selectively melt the coating, promoting a uniform and adherent layer. In the present work, tungsten carbide and chromium carbide alloy coatings were deposited on properly prepared SAE 1020 substrates using the high-speed oxy-fuel (HVOF) technique. After deposition, the coatings were remelted with a laser beam, varying the scanning speed and the laser beam power of the ytterbium fiber to obtain a pore- and crack-free coating and better metallurgical anchorage to the substrate. The samples were characterized by scanning electron microscopy (SEM), X-ray diffractogram, ASTM G132 Standard Test Method for Pin Abrasion Testing wear and microhardness. The results show that it was possible to obtain coatings with greater hardness after the laser remelting process, reducing pores or imperfections and metallurgically bonding to the substrate.Item Understanding the Molecular Kinetics and Chemical Equilibrium Phase of Frozen CO during Bombardment by Cosmic Rays by Employing the PROCODA Code(IOP science) Pilling, Sergio; Carvalho, Geanderson Araújo; Abreu, Heitor Avelino de; Galvão, Breno Rodrigues Lamaghere; Silveira, Carolina Hahn da; Mateus, Marcelo SilvaWithin the cold regions of space, ices that are enriched with carbon monoxide (CO) molecules are exposed to ionizing radiation, which triggers new reactions and desorption processes. Laboratory studies on astrochemical ices employing different projectiles have revealed the appearance of several new species. In this study, we employed the upgraded PROCODA code, which involves a calculation phase utilizing thermochemistry data, to map the chemical evolution of pure CO ice irradiated by cosmic-ray analogs. In the model, we have considered 18 different chemical species (six observed: CO, CO2, C3, O3, C2O, and C5O3; 12 unobserved: C, O, C2, O2, CO3, C3O, C4O, C5O, C2O2, C2O3, C3O2, and C4O2) coupled at 156 reaction routes. Our best-fit model provides effective reaction rates (effective rate constants, (ERCs)), branching ratios for reactions within reaction groups, several desorption parameters, and the characterization of molecular abundances at the chemical equilibrium (CE) phase. The most abundant species within the ice at the CE phase were atomic oxygen (68.2%) and atomic carbon (18.2%), followed by CO (11.8%) and CO2 (1.6%). The averaged modeled desorption yield and rate were 1.3e5 molecules ion−1 and 7.4e13 molecules s−1, respectively, while the average value of ERCs in the radiation-induced dissociation reactions was 2.4e-1 s−1 and for the bimolecular reactions it was 4.4e-24 cm3 molecule−1 s−1. We believe that the current kinetics study can be used in future astrochemical models to better understand the chemical evolution of embedded species within astrophysical ices under the presence of an ionizing radiation field.Item Wear Rate, Tribo-Corrosion, and Plastic Deformation Values of Co-Cr-Mo Alloy in Ringer Lactate Solution(MDPI) Silva, Raimundo Nonato Alves; Neto, Rui; Vieira, Angela Aparecida; Leite, Priscila Maria Sarmeiro Corrêa Marciano; Radi, Polyana Alves; Silveira, Carolina Hahn da; Santos, Marcos Dantas dos; Viana, Filomena; Vieira, LúciaThis study investigates the tribocorrosion performance of a cast Co-Cr-Mo alloy prepared using casting and electromagnetic stirring (EMS) at specific frequencies. The tribocorrosion behaviour of the alloy was evaluated when exposed to Ringer’s lactate solution to optimize the EMS parameters and improve its properties. The research focuses on biomedical implant applications and explores how EMS affects alloy wear and corrosion resistance. As did the friction coefficient and wear volume, the wear rate of samples produced with EMS frequencies of 75 Hz and 150 Hz decreased. These improvements are attributed to the ability of EMS to refine grain size and homogenize the microstructure, thereby increasing the resistance to tribocorrosion. Techniques such as scanning electron microscopy (SEM) and profilometry were used for surface and wear analysis, while mechanical properties were evaluated through instrumented indentation tests. The findings confirm that EMS improves the alloy’s durability and tribocorrosion resistance, making it highly suitable for demanding biomedical applications such as joint replacements. This highlights the importance of advanced manufacturing techniques in optimizing biomedical alloys for simulated body conditions.