Percorrer por autor "Ferreira, Ricardo"
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- Bioprosthetic Aortic Valve degeneration: a review from a basic science perspectivePublication . Velho, Tiago R.; Pereira, Rafael Maniés; Fernandes, Frederico; Guerra, Nuno Carvalho; Ferreira, Ricardo; Nobre, ÂngeloIntroduction: The increase in the prevalence of aortic stenosis due to an aging population has led to an increasing number of surgical aortic valve replacements. Over the past 20 years, there has been a major shift in preference from mechanical to bioprosthetic valves. However, despite efforts, there is still no "ideal" bioprosthesis. It is crucial to understand the structure, biology, and function of native heart valves to design more intelligent, strong, durable, and physiological heart valve tissues. Methods: A comprehensive review of the literature was performed to identify articles reporting the basic mechanisms of bioprosthetic valve dysfunction and the biology of native valve cells. Searches were run in PubMed,MEDLINE (R) (the Medical Literature Analysis and Retrieval System Online), and Google Scholar. Terms for subject heading and keywords search included "biological heart valve dysfunction", "bioprosthesis dysfunction", "bioprosthesis degeneration", and "tissue heart valves". Results: All the relevant findings are summarized in the appropriate subsections. Structural dysfunction is a logical and expected consequence of the chemical, mechanical, and immunological processes that occur during fixation, manufacture, and implantation. Conclusion: Biological prosthesis valve dysfunction is a clinically significant process. It has become a major issue considering the growing rate of bioprosthesis implantation and improved long-term patient survival. Understanding bioprosthetic aortic valve degeneration from a basic science perspective is a key point to improve technologic advances and specifications that lead to a new generation of bioprostheses.
- Impacto do sismo de 28 de fevereiro de 1969: Comportamento do posto de polícia de viação e trânsito em LagosPublication . Estêvão, João M. C.; Oliveira, C.S.; Ferreira, RicardoCom o intuito de melhor conhecer a forma como a ação sísmica se fez sentir no território nacional durante o sismo de 1969 e poder estimar futuras ações, procedeu-se ao levantamento de um largo conjunto de edifícios que apresentaram algum tipo de dano por todo o país especialmente a sul da Cidade de Lisboa. Embora este conjunto de informação seja de um enorme valor, a melhor forma de quantificar a ação sísmica na época, para além do registo acelerométrico obtido no maciço de ancoragem dos cabos da Ponte sobre o Tejo em Lisboa, consiste em analisar estruturas simples de Betão Armado (BA), essencialmente se estas se assimilarem a um sistema de um grau de liberdade. É o caso do Abrigo do Posto de Polícia de Viação e Trânsito (PVT) em Lagos que sofreu danos ligeiros no pilar central que dá apoio a uma cobertura circular. Esta estrutura foi analisada por Marecos e Castanheta logo após uma visita efetuada ao local durante uma missão de reconhecimento dos efeitos do sismo (Relatório LNEC, maio de 1969). Importa agora proceder ao estudo do comportamento da mesma estrutura, 50 anos depois dos trabalhos de Marecos e Castanheta, recorrendo às técnicas que hoje em dia são utilizadas para a obtenção de curvas de momento-curvatura de pilares. Socorrendo aos elementos de projeto constantes do Relatório LNEC, amavelmente cedidos por M. Pipa, e para diversos tipos de solo, calculou-se um coeficiente sísmico de referência mínimo de 0.04 g (com betão B180), que provoca os danos descritos. O valor a que agora se chegou é idêntico ao apontado no Relatório e constitui um limite inferior da ação sísmica para o local. A variação do coeficiente sísmico introduzida pelas incertezas provenientes do desconhecimento de algumas das características da estrutura, leva agora a uma estimativa máxima de 0.104 g.
- New TiO2-Ag/BEA composites with dual Ag-functionalization for specific adsorption and catalytic sites. Synergism between phases in the ethylene removal for climateric fruit conservationPublication . Ferreira, Ricardo; Regadera-Macías, Ana; Morales-Torres, Sergio; Pastrana-Martínez, Luisa M.; Lourenço, João P.; Silva, João M.; João, Isabel M.A new series of TiO2-Ag/BEA composites was specifically designed for use in filter/photo-reactors intercalated in air recirculation circuits in storage facilities for climacteric fruits. The sol-gel procedure for TiO2 deposition was combined with ionic exchange (IE) or incipient wet impregnation (IWI) techniques for Ag doping, with the proportions of both fractions also varying. The prepared materials were thoroughly characterized in terms of their porous texture, chemical composition, crystalline structure, and Ag dispersion, among other properties. Dynamic ethylene adsorption was recorded in the dark. After saturation, ethylene photooxidation was analyzed under UV or UVA-visible light, with varying contact times, flow rates, and concentrations, and with or without humidity present. The maximum ethylene adsorption capacity (361 μmol g− 1 ) corresponds to the sample with the highest Ag content (5 wt%), added by IE, while the best photocatalytic performance is obtained for samples doped by IWI. The performance of the samples was found to be correlated with their physicochemical properties and was specifically determined by the nature and dispersion of the silver species in the composites. Total ethylene photooxidation is achieved even under UV–Vis radiation; the reaction develops selectively to CO2 in all cases, despite the strong negative effect of humidity on the formation of more active HO• radicals. The high adsorption capacity and effective photooxidation of ethylene enable control of this maturation hormone below the established limits.
- On the characterization and performance of highly dispersed TiO2 nanoparticles onto BEA zeolite in the continuous gas-phase photooxidation of ethylene.Publication . Ferreira, Ricardo; Morales-Torres, Sergio; Pastrana-Martínez, Luisa María; Maldonado Hodar, Francisco Jose; Lourenço, João P.; João, Isabel M.; Silva, João Miguel; Ribeiro, M. Filipa; Fernandes, AugusteTwo series of TiO2-based zeolite composites (BEA structures) were prepared by employing a sol–gel method using two different synthesis approaches, i.e., acidic and basic media. Different photocatalytic composites obtained with increasing amounts of TiO2 (10–50 wt%) were thoroughly characterized and subsequently tested in the photooxidation of ethylene in a continuous gas-phase system. Results showed that sol–gel experimental conditions had a significant effect on the final properties of the samples, as photocatalytic composites obtained under basic conditions showed better TiO2 dispersion and interaction with the BEA support than their counterparts prepared in an acidic medium. The same photocatalysts showed high performance in ethylene photooxidation, demonstrating complete mineralization and results comparable to or even better than those of the bulk TiO2 material.
- Otimização de formulações de extrusão de zeólitos recorrendo a planeamento fatorialPublication . Valle, Lívia ; Ferreira, Ricardo; Fernandes, Auguste; Lourenço, João P.; Silva, João M.; João, Isabel M.; Ribeiro, FilipaUm planeamento de experiencias fatorial completo foi utilizado, abrangendo três variáveis independentes em dois níveis, para avaliar os principais parâmetros que influenciam o processo de extrusão. O estudo teve como objetivo otimizar as propriedades do extraído em relação ‡ microporosa ade e ‡ resistência mecânica. As variáveis investigadas incluíram o teor de zeólito (% mássica), a razão ácido/aglomerante (m/m) e a razão base/ácido (m/m). Os resultados para a otimização foram identificados com um valor de dureza Shore D de 33 e um volume microporoso de 0,117 g/cm³.