130 research outputs found
Use of seawater to improve the static strength and fatigue life of bonded coated steel joints
La industria de la construcción naval exige soluciones adhesivas para unir componentes a sustratos pintados, ya que las tecnologías de soldadura tradicionales requieren operaciones de procesamiento costosas y que requieren mucho tiempo. Sin embargo, este tema rara vez se considera en la literatura. El objetivo del presente estudio es investigar la influencia de la exposición en disoluciones de cloruro de sodio en la resistencia estática y el rendimiento a la fatiga de juntas de acero pintadas unidas con adhesivo. Para ello, se utilizó un adhesivo epoxídico frágil de dos componentes para fabricar uniones a solape de aceros pintados unidos con adhesivo. Se realizaron ensayos estáticos y de fatiga tras envejecer las uniones mediante inmersión en soluciones cloradas durante diferentes periodos de tiempo. Las pruebas adicionales realizadas incluyeron pruebas FTIR, análisis de la temperatura de transición vítrea y pruebas de tracción de muestras de adhesivo envejecidas y sin envejecer, estudios experimentales y de simulación FEM de la absorción de agua, y análisis de la superficie de fractura de las juntas.
Los resultados muestran, sorprendentemente, que tanto las propiedades mecánicas estáticas como las de fatiga de las juntas aumentan significativamente con el envejecimiento durante el primer mes de exposición. La difusión de agua que tuvo lugar durante el primer mes en las juntas a solape mejoró más del 30% tanto la resistencia estática como la resistencia a la fatiga de las juntas fabricadas con este adhesivo relativamente rígido. La tasa de absorción de agua del adhesivo también se calculó utilizando las relaciones de la ley de Fick. Los resultados se utilizaron para simular numéricamente el nivel de humedad absorbida por la capa de adhesivo de las uniones.
La presente investigación demuestra que el fenómeno de absorción de humedad no conduce a resultados negativos para todas las uniones adhesivas. Para uniones adhesivas frágiles, como la analizada aquí, el contenido de agua reduce la concentración de tensiones en los extremos de unión, proporcionando una distribución de tensiones más uniforme a lo largo de la línea de unión. Este fenómeno permite que la unión sostenga niveles de carga más altos. Este comportamiento mecánico mejorado relacionado con la diferente distribución del contenido de agua puede considerarse una estrategia novedosa en el diseño de juntas, ya que puede reducir los costos del servicio y también puede reducir el peso total de la estructura adherida.
Para aplicaciones navales, este estudio sugiere que la junta adhesiva considerada se puede utilizar en un entorno no sumergido. En este caso, la absorción de agua se desarrollará a un ritmo menor respecto a los resultados obtenidos, manteniendo su rendimiento durante un periodo mayor. Sin embargo, se deberían realizar más investigaciones para analizar este comportamiento.
Esta contribución constituye la publicación más relevante de la Tesis Doctoral Industrial con mención internacional de Dª M. Ortega-Iguña, tesis dirigida por el solicitante (J.M Sánchez-Amaya), y defendida en 2023
Impact of percentage and particle size of sugarcane biochar on the sorption behavior of clomazone in Red Latosol
Biochar is a carbonaceous material that has excellent potential as a fertilizer and soil conditioner. However, there is a lack of information concerning the effects of the amount and particle size of this pyrogenic material on the soil sorption capacity. In this work, evaluation was made of changes in clomazone (CMZ)
sorption in a Red Latosol following soil conditioning using different percentages (0.25, 0.5, and 1% w/w) of sugarcane biochar in three particle sizes (<106, 106-508, and 508-610 μm). The conditioned soils presented apparent sorption coefficients (Kd) up to 1300 times higher than that of pure soil, besides changes in the behavior of CMZ sorption. The biochar particle size and percentage influenced sorption of the herbicide as well as its retention in the amended soil during desorption processes. Both sorption and desorption Freundlich constants were linearly correlated with the external surface area of the biochar present in the soil
Vestibular and oculomotor influences on visual dependency
The degree to which a person relies on visual stimuli for spatial orientation is termed visual dependency (VD). VD is considered a perceptual trait or cognitive style influenced by psychological factors and mediated by central re-weighting of the sensory inputs involved in spatial orientation. VD is often measured using the rod-and-disk test, wherein participants align a central rod to the subjective visual vertical (SVV) in the presence of a background that is either stationary or rotating around the line of sight - dynamic SVV. Although this task has been employed to assess VD in health and vestibular disease, it is unknown what effect torsional nystagmic eye movements may have on individual performance. Using caloric ear irrigation, 3D video-oculography and the rod-and-disk test, we show that caloric torsional nystagmus modulates measures of visual dependency and demonstrate that increases in tilt after irrigation are positively correlated with changes in ocular torsional eye movements. When the direction of the slow phase of the torsional eye movement induced by the caloric is congruent with that induced by the rotating visual stimulus, there is a significant increase in tilt. When these two torsional components are in opposition there is a decrease. These findings show that measures of visual dependence can be influenced by oculomotor responses induced by caloric stimulation. The findings are of significance for clinical studies as they indicate that VD, which often increases in vestibular disorders, is not only modulated by changes in cognitive style but also by eye movements, in particular nystagmus
Well-posedness of minimal time problems with constant dynamics in Banach spaces
This paper concerns the study of a general minimal time problem with a
convex constant dynamics and a closed target set in Banach spaces. We pay the main
attention to deriving sufficient conditions for the major well-posedness properties that include the existence and uniqueness of optimal solutions as well as certain regularity of the optimal value function with respect to state variables. Most of the results obtained are new even in finite-dimensional spaces. Our approach is based on advanced tools of variational analysis and generalized differentiation
Enhancing Humoral Responses Against HIV Envelope Trimers via Nanoparticle Delivery with Stabilized Synthetic Liposomes
An HIV vaccine capable of eliciting durable neutralizing antibody responses continues to be an important unmet need. Multivalent nanoparticles displaying a high density of envelope trimers may be promising immunogen forms to elicit strong and durable humoral responses to HIV, but critical particle design criteria remain to be fully defined. To this end, we developed strategies to covalently anchor a stabilized gp140 trimer, BG505 MD39, on the surfaces of synthetic liposomes to study the effects of trimer density and vesicle stability on vaccine-elicited humoral responses in mice. CryoEM imaging revealed homogeneously distributed and oriented MD39 on the surface of liposomes irrespective of particle size, lipid composition, and conjugation strategy. Immunization with covalent MD39-coupled liposomes led to increased germinal center and antigen-specific T follicular helper cell responses and significantly higher avidity serum MD39-specific IgG responses compared to immunization with soluble MD39 trimers. A priming immunization with liposomal-MD39 was important for elicitation of high avidity antibody responses, regardless of whether booster immunizations were administered with either soluble or particulate trimers. The stability of trimer anchoring to liposomes was critical for these effects, as germinal center and output antibody responses were further increased by liposome compositions incorporating sphingomyelin that exhibited high in vitro stability in the presence of serum. Together these data highlight key liposome design features for optimizing humoral immunity to lipid nanoparticle immunogens.National Institute of Allergy and Infectious Diseases (U.S.) (Award UM1AI100663)National Institutes of Health (U.S.) (Award P01-AI104715)National Institutes of Health (U.S.) (Award P01-AI048240)National Cancer Institute (U.S.) (Grant P30-CA14051
Dectin-1 Activation Exacerbates Obesity and Insulin Resistance in the Absence of MyD88
This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, grant numbers 11/15682-4, 12/02270-2, 15/18121-4), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Regenera INCT Process Grant 465656/2014-5). JL is funded by the NIH/NIDDK R01DK106210. GDB is funded by the Wellcome Trust and the MRC Centre for Medical Mycology. Open access journalPeer reviewedPublisher PD
Effect of ω-conotoxin MVIIA and Phα1β on paclitaxel-induced acute and chronic pain
AbstractThe treatment with the chemotherapeutic agent paclitaxel produces a painful peripheral neuropathy, and is associated with an acute pain syndrome in a clinically significant number of patients. However, no standard therapy has been established to manage the acute pain or the chronic neuropathic pain related to paclitaxel. In the present study, we evaluated the analgesic potential of two N-type voltage-gated calcium channel (VGCC) blockers, ω-conotoxin MVIIA and Phα1β, on acute and chronic pain induced by paclitaxel. Adult male rats were treated with four intraperitoneal injections of paclitaxel (1+1+1+1mg/kg, in alternate days) and the development of mechanical hyperalgesia was evaluated 24h (acute painful stage) or 15days (chronic painful stage) after the first paclitaxel injection. Not all animals showed mechanical hyperalgesia 24h after the first paclitaxel injection, but those that showed developed a more intense mechanical hyperalgesia at the chronic painful stage. Intrathecal administration (i.t.) of ω-conotoxin MVIIA (3–300pmol/site) or Phα1β (10–300pmol/site) reduced the mechanical hyperalgesia either at the acute or at the chronic painful stage induced by paclitaxel. When administered at the acute painful stage, ω-conotoxin MVIIA (300pmol/site, i.t.) and Phα1β (300pmol/site, i.t.) prevented the worsening of chronic mechanical hyperalgesia. Furthermore, Phα1β (30-300pmol/site, i.t.) elicited less adverse effects than ω-conotoxin MVIIA (10-300 pmol/site, i.t.). Taken together, our data evidence the involvement of N-type VGCC in pain sensitization induced by paclitaxel and point out the potential of Phα1β as a safer alternative than ω-conotoxin MVIIA to treat the pain related to paclitaxel
DETERMINAÇÃO DO POTENCIAL ANTIOXIDANTE DA POLPA IN NATURA DE MANGABA (Hancornia speciosa Gomes)
Introdução e objetivos: A mangabeira pertence à família Apocynaceae, gênero Hancornia e à espécie Hancornia speciosa. Seu fruto apresenta ótimo aroma e sabor, destacando-se pelos elevados teores de compostos com propriedades antioxidantes. Antioxidantes podem ser definidos como substâncias que em baixas concentrações, quando comparados a um substrato oxidável, atrasam ou inibem a oxidação desse substrato de maneira eficaz (2). Assim, objetivou-se realizar a determinação da atividade antioxidante in vitro da polpa in natura de mangaba. Metodologia: A atividade antioxidante in vitro foi determinada utilizando-se o radical DPPH (2,2-difenil-1- picril-hidrazil), seguindo a metodologia proposta por (1) modificado por (5) sendo a leitura da absorbância realizada a 515nm, após incubação por 30 minutos. Resultados e discussões: A análise da atividade antioxidante in vitro da polpa in natura de mangaba revelou um teor de EC50 de 2067,38 g/g de DPPH ± 73,28, demonstrando alta atividade antioxidante, o que segundo Lima3, pode ser influenciado pela ação sinérgica entre os constituintes de diferentes frações, sendo os compostos fenólicos e a vitamina C, os componentes mais importantes. Ainda segundo (4), avaliando a atividade antioxidante de sete frutos, incluindo a mangaba, pelo método do DPPH, observou que a mangaba ocupou o terceiro lugar com valores superior ao encontrado neste trabalho, apresentando menor atividade somente do que o caju-amarelo e a acerola, essas diferenças podem ser decorrentes das condições edafoclimáticas dos frutos. Conclusões: O potencial antioxidante in vitro da polpa in natura de mangaba demonstrou-se elevado, confirmando a importância do consumo de frutas frescas, não somente pelas características sensoriais agradáveis, mas também, por serem fontes de compostos bioativos importantes à dieta
ANÁLISE DE ANTOCIANINAS TOTAIS EM CASCAS DE LICHIA (Litchi chinensis)
Introdução e objetivos: A Litchi chinensis é um fruto subtropical de alto potencial devido ao seu sabor, valor nutritivo e atrativa cor da casca. As antocianinas, compostos que fornecem a cor avermelhada da casca, são compostos flavonoides que possuem capacidade antioxidante e podem ser utilizadas como corantes naturais na indústria de alimentos. Desta forma, objetivou-se analisar o teor de antocianinas totais em cascas de lichia. Metodologia: Foram utilizadas cascas de lichia, descartadas durante o processamento de polpas de frutas de uma agroindústria produtora de sorvetes, localizada em Goiânia, GO. As amostras foram congeladas e armazenadas em freezer a -18°C, até o momento de realização das análises. O conteúdo total de antocianinas foi estimado de acordo método descrito por Lees e Francis (1972)¹ e adaptado por Barcia, et al. (2012)². A leitura foi realizada em espectrofotômetro (BiospectroSP-220), no comprimento de onda de 535nm, sendo os resultados expressos em miligramas de cianidina-3-glicosídio por 100g de casca. Resultados e discussões: Obteve-se valor médio de 1,252 ± 0,12 mg de cianidina-3-glicosídeo 100g-1, e o coeficiente de variação foi de 9,6%. Sendo estes valores inferiores aos encontrados por Lima et al. (2010)3, os quais variaram de 86,7 a 94,1 mg de cianidina-3-glicosídeo 100g-1 em casca de lichia fresca. Esta diferença pode ser justificada pelo fato das cascas deste trabalho terem sido obtidas de um resíduo agroindustrial, pois segundo Zhang et al. (2004)4. O índice de escurecimento da lichia aumenta durante o armazenamento à temperatura ambiente, assim como a concentração de antocianina diminui marcadamente. Conclusão: Pode-se concluir que o tipo de tratamento que as cascas de lichia receberam na indústria, antes da realização das análises, tem grande influência no teor de antocianinas das cascas
Iron Deficiency Generates Oxidative Stress and Activation of the SOS Response in Caulobacter crescentus
In C. crescentus, iron metabolism is mainly controlled by the transcription factor Fur (ferric uptake regulator). Iron-bound Fur represses genes related to iron uptake and can directly activate the expression of genes for iron-containing proteins. In this work, we used total RNA sequencing (RNA-seq) of wild type C. crescentus growing in minimal medium under iron limitation and a fur mutant strain to expand the known Fur regulon, and to identify novel iron-regulated genes. The RNA-seq of cultures treated with the iron chelator 2-2-dypiridyl (DP) allowed identifying 256 upregulated genes and 236 downregulated genes, being 176 and 204 newly identified, respectively. Sixteen transcription factors and seven sRNAs were upregulated in iron limitation, suggesting that the response to low iron triggers a complex regulatory network. Notably, lexA along with most of its target genes were upregulated, suggesting that DP treatment caused DNA damage, and the SOS DNA repair response was activated in a RecA-dependent manner, as confirmed by RT-qPCR. Fluorescence microscopy assays using an oxidation-sensitive dye showed that wild type cells in iron limitation and the fur mutant were under endogenous oxidative stress, and a direct measurement of cellular H2O2 showed that cells in iron-limited media present a higher amount of endogenous H2O2. A mutagenesis assay using the rpoB gene as a reporter showed that iron limitation led to an increase in the mutagenesis rate. These results showed that iron deficiency causes C. crescentus cells to suffer oxidative stress and to activate the SOS response, indicating an increase in DNA damage
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