47,868 research outputs found

    Comportamiento de puentes prefabricados de viga artesa : influencia del ambiente y del proceso constructivo

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    Los puentes prefabricados continuos a√ļnan las ventajas de la prefabricaci√≥n y de los m√©todos constructivos ‚Äúin situ‚ÄĚ, siendo Espa√Īa pionera en el desarrollo de esta tipolog√≠a de puentes. Entre las ventajas de esta tipolog√≠a de puentes destaca que cumplen con los requerimientos de dise√Īo establecidos en las normativas actuales en cuanto a resistencia, servicio y durabilidad; son estructuras de rapidez de construcci√≥n generando m√≠nimo impacto en el tr√°fico o en el entorno y son est√©ticos. Sin embargo, el comportamiento de estas estructuras es de enorme complejidad, dado que en la fase de dise√Īo es necesario conocer la redistribuci√≥n a lo largo del tiempo de las tensiones entre los materiales de la secci√≥n y la evoluci√≥n de los esfuerzos hiperest√°ticos en el caso de estructuras continuas, estructuralmente evolutivas y compuestas seccionalmente, debidos a los fen√≥menos de fluencia y retracci√≥n de ambos hormigones y a la relajaci√≥n del acero de pretensado. Aunque existen programas generales de c√°lculo estructural que se pueden utilizar para puentes prefabricados continuos con secciones evolutivas, basados en m√©todos num√©ricos, su aplicaci√≥n en la pr√°ctica diaria es complicada. Dichos programas dif√≠cilmente permiten un control real del proceso y de las consecuencias que tiene la variaci√≥n de los datos de partida en la distribuci√≥n final de tensiones, de ah√≠ la importancia de definir un m√©todo simplificado aplicable a esta tipolog√≠a de puentes. El presente trabajo presenta un M√©todo Simplificado Mejorado del M√©todo de la Secci√≥n Homogeneizada con un M√≥dulo Efectivo Ajustado a la Edad para secciones compuestas constituidas por vigas prefabricadas pretensadas y una losa superior de hormig√≥n. El m√©todo surge como respuesta a las limitaciones de la aplicaci√≥n del modelo tradicional del coeficiente de envejecimiento, al estudio de secciones compuestas de hormig√≥n prefabricado - hormig√≥n ‚Äúin situ‚ÄĚ. El m√©todo que se pretende mejorar es el propuesto por Ghali, Favre y Eldbadry (12) que utiliza para el estudio diferido la secci√≥n homogeneizada usando para cada hormig√≥n el modelo del coeficiente de envejecimiento de Trost y BaŇĺant. El M√©todo propuesto est√° basado en la definici√≥n del coeficiente de envejecimiento refinado ajustado a la edad (que tiene en cuenta la retracci√≥n y el nivel de coacci√≥n) y a la partici√≥n del proceso una vez hormigonada la losa en dos procesos - gracias al principio de superposici√≥n - en los que se cumple en cada uno de ellos la cuasi proporcionalidad de los incrementos de tensiones a la de los procesos utilizados para la obtenci√≥n del coeficiente de envejecimiento ajustado correspondiente: proceso 1 que considera la retracci√≥n de la losa y el proceso 2 que considera el efecto de la fluencia del peso propio de la losa. El m√©todo propuesto se verifica con el m√©todo paso a paso. Los resultados son precisos no solo en tensiones sino en curvaturas diferidas, lo que permite su aplicaci√≥n, a todo tipo de puentes continuos con proceso constructivo evolutivo. Adem√°s, el m√©todo se aplica al c√°lculo de un viaducto continuo hiperest√°tico, cuyo proceso constructivo es complejo, presentando varias fases intermedias, desarroll√°ndose la metodolog√≠a para este caso y siendo extensible a cualquier tipolog√≠a de puentes prefabricados continuos independientemente del proceso constructivo. Se comparan los resultados obtenidos con los m√©todos utilizados en la pr√°ctica, as√≠ como los criterios avalados por la experiencia, obteni√©ndose resultados satisfactorios. Asimismo, esta Tesis propone un m√©todo para la comprobaci√≥n del ELS de fisuraci√≥n en secciones compuestas, constituidas por una viga prefabricada pretensada y una losa superior ‚Äúin situ‚ÄĚ que se encuentran traccionadas bajo la combinaci√≥n frecuente de acciones. El m√©todo propuesto est√° basado en el descrito por Luis Albajar en la publicaci√≥n coordinada por Luisa Mar√≠a Gil (13) para secciones pretensadas- no compuestas- que consiste en la neutralizaci√≥n de las tensiones del hormig√≥n en la situaci√≥n de cargas permanentes a tiempo infinito. El m√©todo simplificado de neutralizar exclusivamente el pretensado, muy extendido en el caso de secciones pretensadas monol√≠ticas, no es aplicable a secciones compuestas. Finalmente se analiza la influencia de la humedad y de las distintas edades de continuidad de las vigas, en la redistribuci√≥n de esfuerzos en el tiempo y en el comportamiento tensional de un puente hiperest√°tico de tres vanos formado por una viga prefabricada tipo caj√≥n y una losa superior hormigonada ‚Äúin situ‚ÄĚ, la cual se encuentra armada. Se incluye un estudio de la influencia de la fisuraci√≥n de la losa sobre apoyos intermedios en la redistribuci√≥n de esfuerzos en el tiempo. El estudio ha surgido durante el desarrollo de la Tesis al comprobar que la losa superior, la cual se encuentra armada, para esta tipolog√≠a de puentes, se encuentra fisurada. Se ha realizado una nueva propuesta para incluir el comportamiento de la secci√≥n compuesta con la losa superior fisurada bajo cargas permanentes. La incidencia de la fisuraci√≥n de la losa se ha resuelto variando la rigidez de la cabeza fisurada con datos experimentales de tirantes fisurados (7) e introduciendo este comportamiento en el M√©todo Simplificado Mejorado definido en esta Tesis Doctoral. ----------ABSTRACT---------- Continuous precast concrete bridges have the advantages of both prefabrication and on-site construction methods, and Spain has been a pioneer in the development of such types of bridges. Among the advantages of this type of structures, it stands out that they fulfil the design requirements established by the codes, (strength, serviceability performance, durability, and aesthetics), with high speed of construction and minimum effects on the traffic or environment. However, the behavior of such structures is of enormous complexity, being necessary the analysis of time-dependent stresses and deformations in the design phase. The sequential or staged construction process generates changes in the structural shape, and delayed phenomena occur due to shrinkage and creep of the different concretes within the cross-section and the relaxation of the prestressing steel. Even though structural analysis programs to deal with continuous precast bridges with evolutive cross sections, based on numerical models, exist today, their applicability in every day‚Äôs design practice is not suitable. These programs hardly allow for a real control of the process with a full awareness of what consequences have the variation of the inputs in the final stress, hence the importance of defining a simplified method applicable to this type of bridges. The present paper presents a simplified method as an improvement of the transformed section method with age-adjusted effective modulus for composite sections consisting of precast prestressed beams and a top concrete slab. The method is presented to overcome the drawbacks of the application of the traditional model of the aging coefficient, to the study of composite sections made up of precast concrete and "in situ" concrete, built at a different time. The method to be improved is the one proposed by Ghali, Favre and Eldbadry (12), which uses the age-adjusted effective modulus for composite sections using the Trost and BaŇĺant aging coefficient. The Improved Simplified Method is based on the definition of the refined age-adjusted aging coefficient (which considers shrinkage and the level of constraint) and splitting the whole process once the slab is cast into two stages which separately fulfill the condition of quasi-proportionality of stresses: process 1 that considers the effect of shrinkage of the slab and process 2 that considers the effect of creep due to the self- weight of the slab. Decomposition is consistently justified, and the application of the superposition principle is correct. The proposed method is verified by comparison with the comprehensive step-by-step method. The results are accurate not only in terms of stresses but also delayed curvatures, which allows its application, to all types of continuous bridges with staged construction process. In addition, the Improved Simplified Method is also applied to the calculation of a real bridge whose construction process is complex, presenting several intermediate phases, developing the methodology for this case and being extensible to any type of continuous precast bridges regardless of the construction process. The results obtained are compared with the methods used in practice, as well as the criteria endorsed by experience, obtaining satisfactory results. Furthermore, this Thesis proposes a method for verifying the SLS of cracking in composite sections, made up of a precast prestressed beam and an upper "in situ" slab that are under tension under the frequent combination of actions. The proposed method is based on the method developed by Luis Albajar in a publication coordinated by Maria Luisa Gil (13) for prestressed sections - not composite - which consists of the neutralization of the concrete stresses in the situation of permanent loads at end time. The simplified method of exclusively neutralizing the prestress, widely used in the case of monolithic prestressed sections, is not applicable to composite sections. Finally, the influence of humidity and the different ages of continuity of the beams, in the analysis of time-dependent stresses and deformations of a continuous precast bridge is analyzed. The studied viaduct has three spans and consists of a precast ‚ÄúU‚ÄĚ beam and an upper reinforced slab. A study of the influence of slab cracking on intermediate supports in stress redistribution over time is included. The study has arisen during the development of the Thesis when verifying that the upper slab, made up of reinforced concrete, for this type of bridges, is cracked under permanent loads. A new proposal has been made to include the behavior of the composite section with the upper cracked slab under permanent loads. The incidence of slab cracking has been solved by varying the stiffness of the slab with experimental data of cracked ties (7) and introducing this behavior in the Improved Simplified Method developed in this Thesis

    Nanopartículas para o tratamento avançado de doenças artríticas

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    Tese de doutoramento em Engenharia de Tecidos, Medicina Regenerativa e C√©lulas EstaminaisArthritic diseases affect more than 350 million people worldwide. Their incidence, prevalence and global burden are increasing, mainly due to the aging of the population. The most common forms of arthritis, osteoarthritis (OA) and rheumatoid arthritis (RA), are chronic inflammatory diseases, which are characterized by synovial inflammation and cartilage and bone destruction. Despite the advances in the pharmaceutical field, there is currently no cure for arthritis. Moreover, current treatments are associated with low efficiency and severe side effects. Recently, nanoparticles (NPs) have emerged as a powerful platform to overcome the present treatment limitations. The goal of this PhD work was to develop novel NPs to treat arthritic conditions. Taking into consideration their main drawbacks, we aimed to design NPs able to enhance the therapeutic index of relevant drugs. Therefore, biological agents were immobilized at the surface of biodegradable polymeric NPs and liposomes to protect, extend and enhance their therapeutic efficacy in OA and RA, respectively. While polymeric NPs were biofunctionalized with anti-IL-6 antibodies to selectively capture and neutralize this key pro-inflammatory cytokine, liposomes were biofunctionalized with anti-IL-23 antibodies in order to inhibit the differentiation of naive CD4+ T cells into Th17 cells, by IL-23 neutralization. Furthermore, enzymatic- and redox-responsive polymeric micelles were developed for targeted and controlled drug delivery in arthritis. After accumulation in the inflammatory site, the dexamethasone encapsulated into the polymeric micelles undergo quick release triggered by both redox and glutathione reductase activity. For all NPs formulations, the size distribution, zeta potential and drug immobilization/encapsulation was assessed. Biological tests demonstrated their cytocompatibility in contact with human chondrocytes, macrophages and endothelial cells. Moreover, under inflammatory conditions the NPs were able to demonstrate their enhanced efficacy in comparison with the free drugs. A deeper characterization on the degree of NPs internalization and pathways was performed in a normal and inflammatory scenario by different cells affected by arthritic diseases. The results highlight the importance of considering the targeted cell type when designing functional NPs for specific diseases. Finally, in vivo studies demonstrated the safety and enhanced therapeutic efficacy of the biofunctionalized polymeric NPs immobilizing anti-TNF-őĪ and anti-IL-6 antibodies. In conclusion, as these novel advanced NPs might overcome abovementioned drawbacks, they are promising strategies for radically improving the efficacy of arthritis treatments and severely limiting their side effects.As doen√ßas artr√≠ticas afetam mais de 350 milh√Ķes de pessoas em todo o mundo. A sua incid√™ncia, preval√™ncia e encargos globais est√£o a aumentar sobretudo devido ao envelhecimento da popula√ß√£o. A osteoartrite (OA) e a artrite reumatoide (AR) s√£o as formas mais comuns destas doen√ßas cr√≥nicas inflamat√≥rias, que s√£o caracterizadas pela inflama√ß√£o sinovial e pela destrui√ß√£o da cartilagem e do osso. Apesar dos avan√ßos na √°rea farmac√™utica, atualmente n√£o existe cura para estas doen√ßas. Al√©m disso, os tratamentos dispon√≠veis est√£o associados a uma baixa efic√°cia e a efeitos adversos graves. Recentemente, as nanopart√≠culas (NPs) emergiram como uma plataforma poderosa capaz de superar as limita√ß√Ķes dos tratamentos atuais. Assim, o objetivo desta tese de doutoramento foi o desenvolvimento de novas NPs para o tratamento da artrite. Considerando as atuais limita√ß√Ķes, diferentes NPs foram desenhadas de forma a aumentar o √≠ndice terap√™utico de f√°rmacos. Agentes biol√≥gicos foram imobilizados na superf√≠cie das NPs e lipossomas de forma a proteger, prolongar e aumentar as suas efic√°cias terap√™uticas no tratamento da OA e AR, respetivamente. Enquanto as NPs foram biofuncionalizadas com anticorpos anti-IL-6 de forma a capturar e neutralizar seletivamente esta citoquina central, os lipossomas foram biofuncionalizados com anticorpos anti-IL-23 de forma a inibir a diferencia√ß√£o das c√©lulas T CD4+ em c√©lulas Th17. Al√©m disso, micelas sens√≠veis √† enzima glutationa redutase e a um ambiente redutor foram desenvolvidas para promover a liberta√ß√£o local e controlada do f√°rmaco. De facto, depois de as NPs se acumularem na articula√ß√£o inflamada, a dexametasona encapsulada dentro das micelas ser√° facilmente libertada atrav√©s daqueles mecanismos. Todas as formula√ß√Ķes foram avaliadas em rela√ß√£o √† homogeneidade do tamanho, ao potencial zeta e √† quantidade dos f√°rmacos imobilizada/encapsulada nas NPs. Os testes biol√≥gicos demonstraram a sua citocompatibilidade em contacto com condr√≥citos, macr√≥fagos e c√©lulas endoteliais humanas. Al√©m disso, sob condi√ß√Ķes inflamat√≥rias, as NPs revelaram uma maior efic√°cia em compara√ß√£o com o f√°rmaco livre. A percentagem e via de internaliza√ß√£o das NPs foram avaliadas em condi√ß√Ķes normais e inflamat√≥rias em diferentes tipos de c√©lulas. Os resultados refor√ßam a import√Ęncia de se considerar o tipo de c√©lula alvo aquando do desenvolvimento das NPs. Finalmente, estudos in vivo demonstraram a seguran√ßa e o aumento da efic√°cia terap√™utica das NPs biofuncionalizadas com anticorpos anti-TNF-őĪ e anti-IL-6. Em conclus√£o, as novas NPs desenvolvidas s√£o estrat√©gias promissoras que podem mudar radicalmente a efic√°cia dos tratamentos e limitar significativamente os seus efeitos adversos.Foundation for Science and Technology (FCT) - PhD scholarship PD/BD/11384/201

    Amino-acid-based chiral ionic liquids characterization and application in aqueous biphasic systems

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    By using amino acids as anions, ten chiral ionic liquids (CILs) composed of tetrabutylammonium or cholinium as cations were synthesized by neutralization reactions and further characterized by assessing their optical rotation, thermophysical properties (melting and decomposition temperatures, density, viscosity and refractive index) and ecotoxicity against the marine bacterium Aliivibrio fischeri. The CILs are shown to display, in general, high thermal stability (> 439 K) and low to moderate toxicities (86-217 mg¬∑L‚ąí1). It was found that the cation plays an important role in the density and viscosity of the CILs. Additionally, the effect of CILs optical configuration on these properties was evaluated by comparing the tetrabutylammonium D/L-phenylalaninate ([N4444][D/L-Phe]) and cholinium D/L-phenylalaninate ([N1112(OH)][D/L-Phe]) pairs. Finally, the CILs potential to form aqueous biphasic systems with sodium sulfate, citrate buffer and phosphate buffer was assessed and the ternary phase diagrams were determined. These allowed to infer the impact of the CILs‚Äô cation, anion, and salt on the aqueous biphasic system formation. It was shown that the cation has a more pronounced impact on the aqueous biphasic system formation than the anion. Cholinium-based CILs failed to form aqueous biphasic systems with sodium sulfate under the tested conditions, contrary to the more hydrophobic tetrabutylammonium-based CILs. The ability of the tested salt and buffers to induce liquid-liquid demixing shows that citrate buffer and sodium sulfate represent the weakest and the strongest salting-out agents, respectively.publishe

    An incremental input-to-state stability condition for a generic class of recurrent neural networks

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    This paper proposes a novel sufficient condition for the incremental input-to-state stability of a generic class of recurrent neural networks (RNNs). The established condition is compared with others available in the literature, showing to be less conservative. Moreover, it can be applied for the design of incremental input-to-state stable RNN-based control systems, resulting in a linear matrix inequality constraint for some specific RNN architectures. The formulation of nonlinear observers for the considered system class, as well as the design of control schemes with explicit integral action, are also investigated. The theoretical results are validated through simulation on a referenced nonlinear system

    A Compact Band-Notched UWB MIMO Antenna with Enhanced Isolation Using Comb Shaped Decoupling Element

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    A compact 37mm √ó 26 mm two element multiple-input-multiple-output (MIMO) antenna is presented for ultra wide band (UWB) system application with band notched characteristics. The proposed antenna comprises two semi trapezoidal shaped monopole radiating elements. The band rejection feature around 3.5 GHz has been achieved by incorporating the open ended quarter wavelength spiral shaped slot resonator on the patched surface. In order to realize the enhanced isolation, comb shaped symmetrical stub arrangement are embedded at the U shaped etched periphery to the stepped ground plane between the monopole radiators. This novel design approach leads towards isolation enhancement better than 20 dB throughout the UWB spectral range (3.1 -10.6 GHz) with peak isolation near about 46 dB. The Envelope Correlation Coefficient is significantly lower than 0.005 in entire operating range except the WiMAX rejection band

    Una investigación confirma y concreta las consecuencias y beneficios de lograr una inmunidad híbrida en COVID-19

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    Noticia publicada en la web del ISCIII el 29/03/2023.Un equipo del Instituto de Salud Carlos III (ISCIII) ha publicado un art√≠culo en la revista Journal of Medical Virology que revela los resultados de una investigaci√≥n sobre los efectos de la infecci√≥n por SARS-CoV-2 en el desarrollo de la inmunidad humoral, es decir, la generada por anticuerpos. El estudio analiza la respuesta inmunitaria frente a diferentes variantes del coronavirus, incluyendo √ďmicron, en personas vacunadas contra la COVID-19. Sus conclusiones sugieren que un mecanismo de maduraci√≥n de los anticuerpos neutralizantes -una de las defensas del sistema inmunitario- puede causar el efecto positivo de separar durante cierto tiempo la vacunaci√≥n tras una infecci√≥n natural.N

    Genomic Analysis of Non-B Nucleic Acids Structures in SARS-CoV-2: Potential Key Roles for These Structures in Mutability, Translation, and Replication?

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    Non-B nucleic acids structures have arisen as key contributors to genetic variation in SARS-CoV-2. Herein, we investigated the presence of defining spike protein mutations falling within inverted repeats (IRs) for 18 SARS-CoV-2 variants, discussed the potential roles of G-quadruplexes (G4s) in SARS-CoV-2 biology, and identified potential pseudoknots within the SARS-CoV-2 genome. Surprisingly, there was a large variation in the number of defining spike protein mutations arising within IRs between variants and these were more likely to occur in the stem region of the predicted hairpin stem-loop secondary structure. Notably, mutations implicated in ACE2 binding and propagation (e.g., őĒH69/V70, N501Y, and D614G) were likely to occur within IRs, whilst mutations involved in antibody neutralization and reduced vaccine efficacy (e.g., T19R, őĒE156, őĒF157, R158G, and G446S) were rarely found within IRs. We also predicted that RNA pseudoknots could predominantly be found within, or next to, 29 mutations found in the SARS-CoV-2 spike protein. Finally, the Omicron variants BA.2, BA.4, BA.5, BA.2.12.1, and BA.2.75 appear to have lost two of the predicted G4-forming sequences found in other variants. These were found in nsp2 and the sequence complementary to the conserved stem-loop II-like motif (S2M) in the 3‚Ä≤ untranslated region (UTR). Taken together, non-B nucleic acids structures likely play an integral role in SARS-CoV-2 evolution and genetic diversity

    Investigating the Impacts of Urban Built Environment on Travel Energy Consumption: A Case Study of Ningbo, China

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    The built environment of cities has increasingly affected the travel mode of residents and led to changes in energy consumption, which is crucial to maintaining urban sustainability. Ningbo is a typical representative of urbanization on the east coast of China, and its energy consumption is in a period of rapid growth. Therefore, using the survey data of 22,112 traffic trip samples from nine streets in Ningbo, this paper establishes a regression analysis model, systematically analyzes the relationship between the built environment and domestic energy consumption from multiple dimensions, and reveals the impact mechanism of the built environment on domestic energy consumption. We find that (1) social and economic conditions are the main factors affecting traffic energy consumption. (2) The population density has a significant negative correlation effect on the energy consumption of transportation trips. When the population density increases by 1%, the energy consumption of total transportation trips, commuting trips, high-energy-consumption trips, and low-energy-consumption trips decreases by 0.094%, 0.115%, 0.273%, and 0.124%, respectively. (3) When the degree of mixed use of land increases by one percentage point, the energy consumption of total transportation trips, commuting trips, high-energy-consumption trips, and low-energy-consumption trips decreases by 0.415%, 0.421%, 2.574%, and 1.197%, respectively. (4) The density of road intersections has a significant negative correlation effect on the energy consumption of traffic trips. (5) The impact of the built environment on the energy consumption of transportation trips is greater than that of residential buildings

    Targeted proteomics links virulence factor expression with clinical severity in staphylococcal pneumonia

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    IntroductionThe bacterial pathogen Staphylococcus aureus harbors numerous virulence factors that impact infection severity. Beyond virulence gene presence or absence, the expression level of virulence proteins is known to vary across S. aureus lineages and isolates. However, the impact of expression level on severity is poorly understood due to the lack of high-throughput quantification methods of virulence proteins.MethodsWe present a targeted proteomic approach able to monitor 42 staphylococcal proteins in a single experiment. Using this approach, we compared the quantitative virulomes of 136 S. aureus isolates from a nationwide cohort of French patients with severe community-acquired staphylococcal pneumonia, all requiring intensive care. We used multivariable regression models adjusted for patient baseline health (Charlson comorbidity score) to identify the virulence factors whose in vitro expression level predicted pneumonia severity markers, namely leukopenia and hemoptysis, as well as patient survival.ResultsWe found that leukopenia was predicted by higher expression of HlgB, Nuc, and Tsst-1 and lower expression of BlaI and HlgC, while hemoptysis was predicted by higher expression of BlaZ and HlgB and lower expression of HlgC. Strikingly, mortality was independently predicted in a dose-dependent fashion by a single phage-encoded virulence factor, the Panton-Valentine leucocidin (PVL), both in logistic (OR 1.28; 95%CI[1.02;1.60]) and survival (HR 1.15; 95%CI[1.02;1.30]) regression models.DiscussionThese findings demonstrate that the in vitro expression level of virulence factors can be correlated with infection severity using targeted proteomics, a method that may be adapted to other bacterial pathogens
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