Modelo numérico de elastómeros multi-fase y su aplicación al análisis de estructuras con aislamiento sísmico

Teniendo en cuenta las ventajas del aislamiento sísmico de base en comparación con el diseño convencional de estructuras sismorresistentes y considerando la escasa cantidad de modelos numéricos que permitan una simulación por ordenador de estructuras junto con sus dispositivos de aislamiento, el principal objetivo de este trabajo es desarrollar un modelo numérico aplicando el método de los elementos finitos para analizar edificios con aislamiento sísmico de base, discretizando el conjunto estructura-dispositivo de aislamiento. Se pretende, de esta manera, estimar con mayor precisión la respuesta de tales sistemas y, con ello, facilitar la tarea de diseño y verificación de las mismas.Postprint (published version

Numerical modelling of behaviour of carbon nanotube-reinforced composites

Since their discovery by Lijima in 1991[1], carbon nanotubes (CNTs), are considered a new generation of reinforcement [2]. Their "nano" size structure makes them potentially free of defects, which provides them with excellent physical properties [3,4]. There are two main nanotube types: single wall nanotubes (SWNT) and multi wall nanotubes (MWNT). These last ones consist in several concentric walls, one inside the other. In a composite, one the most important factors that condition their mechanical performance is the interfacial tension between matrix and reinforcement. In general, the loads in a composite structure are introduced to the matrix and then are transferred to the reinforcement through the interface [5]. Therefore, the interface can be defined as the region, surrounding the reinforcement, where this stress transfer takes place. The properties of the composite depend on the properties of this region and its ability to transfer the load efficiently. This work proposes a new formulation to predict the mechanical properties and mechanical behaviour of nanotube-reinforced composites. The formulation is based on the mixing theory [6]. It obtains the behaviour of the composite from the mechanical performance of its constitutive materials: matrix, carbon-nanotube and the interface that bonds both of them.Postprint (published version

Higher transactivation activity associated with LTR and Tat elements from HIV-1 BF intersubtype recombinant variants

BACKGROUND: HIV-1 is characterized by its rapid genetic evolution and high diversity as a consequence of its error-prone reverse transcriptase and genetic recombination. This latter mechanism is responsible for the creation of circulating recombinant forms (CRFs) found in nature. Previous studies from our lab group have shown that the epidemic in Argentina is characterized by one highly prevalent circulating recombinant form, CRF12_BF, and many related BF recombinant forms. Since transcriptional transactivation of the HIV-1 long terminal repeat (LTR) promoter element requires the essential viral Tat protein, since these genetic structures underwent recombination in variants widely spread in South America, the aim of this work was to study transcriptional activity associated with the recombinant LTR and Tat elements. RESULTS: Differential transcriptional activity was measured for the BF recombinant LTR/Tat complex that is present in widely spread viral variants was demonstrated. This analysis demonstrated a higher activity for the BF complex when compared to its B subtype counterpart. CONCLUSION: This study indicates structural and functional consequences of recombination events within the LTR promoter and Tat transactivator protein of a naturally occurring HIV-1 recombinant form

Modelling viscoelastic behaviour of carbón nanotube-reinforced thermo-plastics

Carbon nanotubes (CNTs), since their discovery by Lijima (S. Lijima, Nature, 354:56-58 (1991)), are considered a new generation of reinforcement. Their "nano" size structure makes them potentially free of defects, which provides them with excellent physical properties. There are two main nanotube types: single wall nanotubes (SWCNTs), which are made of a single wall tube; and multiwall nanotubes (MWCNTs), which consist in several concentric walls, one inside the other. A key factor for the reinforcement efficiency in a composite it is the interface bonding between the CNTs and the matrix. This work presents a new constitutive model to predict the mechanical performance of composites made of a thermo-plastic matrix reinforced with CNTs. The model takes into account explicitly the mechanical contribution of the interface between the matrix and the CNTs (F. Otero et. al., Comp Structures, 94:2920-2930 (2012)). The constitutive model is based in the mixing theory, which obtains the composite performance from the response of each constituent component, each one simulated with its own constitutive law. The model has been implemented into an in-house FEM code: PLCd. As an application example, this code is used to predict the mechanical properties of a straight beam with different material configurations. In this case, a viscoelastic constitutive model is proposed for the polymeric matrix. The viscous response within the elastic range of the materials is studied. This response shows a high capacity of energy dissipation in composites reinforced with MWCNTs.Peer ReviewedPostprint (published version

In vitro dynamics of HIV-1 BF intersubtype recombinants genomic regions involved in the regulation of gene expression

HIV-1 intersubtype recombination is a very common phenomenon that has been shown to frequently affect different viral genomic regions. Vpr and Tat are viral proteins known to interact with viral promoter (LTR) during the replication cycle. This interaction is mainly involved in the regulation of viral gene expression, so, any structural changes in the LTR and/or these regulatory proteins may have an important impact on viral replication and spread. It has been reported that these genetic structures underwent recombination in BF variants widely spread in South America. To gain more insight of the consequences of the BF intersubtype recombination phenomenon on these different but functionally related genomic regions we designed and performed and in vitro study that allowed the detection and recovery of intersubtype recombinants sequences and its subsequent analysis. Our results indicate that recombination affects differentially these regions, showing evidence of a time-space relationship between the changes observed in the viral promoter and the ones observed in the Vpr/Tat coding region. This supports the idea of intersubtype recombination as a mechanism that promotes biological adaptation and compensates fitness variations

Numerical homogenization for composite materials analysis: comparison with other micro mechanical formulations

This work presents a two-scale homogenization procedure to analyze three dimension composite structures by FEM. The theory implemented is compared with other micro-structural formulations: micro models and serial parallel mixing theory, in terms of result accuracy and computational cost. The comparison shows that for linear analysis, the homogenization is an excellent alternative to the other formulations. Its computational cost is substantially lower than the one required by the micro-model and it is able to capture several micro-structural phenomena that it is not automatically recorded by the serial parallel methodology. It will also be shown that the extension of the proposed theory to the non-linear range stills represents a challenge. The major limitation is its computational cost because it requires to solve the sub scale at each gauss point and load step. However, the comparison shows that this cost is in terms of CPU time but not in terms of memory. Based on the results obtained, it can be concluded that the homogenization is an excellent alternative for simulation of materials with complex micro structures. The method is also very promising for non linear simulations, when coupled with a threshold criteria to decide whether it is necessary to analyze the RVE or not. (C) 2014 Elsevier Ltd. All rights reserved.Peer ReviewedPostprint (author’s final draft

Non-linear mechanical damage modelling for long fibre-reinforced laminates

A computational methodology is presented for modelling the material non-linear mechanical behaviour of composite structures made of FRP (Fibre-Reinforced Plastic) laminates. The model is based on the appropriate combination of the constitutive models of component materials, considered to behave as isolated continua, together with additional ‘closure equations’ that characterize the micromechanics of the composite from a morphological point of view. To this end, any appropriate constitutive model may be selected for each phase. Each component is modelled separately and the global response is obtained by assembling all contributions taking into account the interactions between components in a general phenomenological way. To model the behaviour of a single unidirectional (UD) composite lamina, a Serial-Parallel continuum approach has been developed assuming that components behave as parallel materials in the fibres alignment direction and as serial materials in orthogonal directions. Taking into account the internal morphology of the composite material, it is devised a strategy for decoupling and coupling component phases. This methodology [1], named “compounding of behaviours”, allows to take into consideration local degradation phenomena (in the constituents materials), like plasticity, damage, fatigue [2], etc. in a coupled manner. It is based on the proper management of homogenous constitutive models, already available for each component. In this way, it is used all developments achieved in constitutive modelling of plain materials, what makes possible the transference of this technology to composites. A lamination theory complemented with the proposed UD model is employed to describe the mechanical behaviour of multidirectional laminates. A specific solution strategy for the general non linear case is proposed. It provides quick local and global convergences, what makes the model suitable for large scale structures. The model brings answers on the non-linear behaviour of composites, where classical micro-mechanics formulas are restricted to their linear elastic part. The methodology is validated through several numerical analyses and contrasted against experimental data and benchmark tests.Postprint (published version

Viral replication is enhanced by an HIV-1 intersubtype recombination-derived Vpu protein

Background: Multiple HIV-1 intersubtype recombinants have been identified in human populations. Previous studies from our lab group have shown that the epidemic in Argentina is characterized by the high prevalence of a circulating recombinant form, CRF12_BF, and many related BF recombinant forms. In these genomic structures a recombination breakpoint frequently involved the vpu coding region. Due to the scarce knowledge of Vpu participation in the virion release process and its impact on pathogenesis and of the functional capacities of intersubtype recombinant Vpu proteins, the aim of this work was to perform a comparative analysis on virion release capacity and relative replication capacity among viral variants harboring either a BF recombinant Vpu or a subtype B Vpu. Results: Our results showed that BF recombinant Vpu was associated to an increased viral particles production when compared to WT B variant in tetherin-expressing cell lines. This observation was tested in the context of a competition assay between the above mentioned variants. The results showed that the replication of the BF Vpu-harboring variant was more efficient in cell cultures than subtype B, reaching a higher frequency in the viral population in a short period of time. Conclusion: This study showed that as a result of intersubtype recombination, a structurally re-organized HIV-1 Vpu has an improved in vitro capacity of enhancing viral replication, and provides evidence of the changes occurring in this protein function that could play an important role in the successful spread of intersubtype recombinant variants.Fil: de Candia, Cristian Ariel. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología. Centro Nacional de Referencia Para El Sida; ArgentinaFil: Espada, Constanza Eleonora. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología. Centro Nacional de Referencia Para El Sida; ArgentinaFil: Duette, Gabriel. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología. Centro Nacional de Referencia para el Sida; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ghiglione, Yanina Alexandra. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología. Centro Nacional de Referencia para el Sida; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Turk, Gabriela Julia Ana. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología. Centro Nacional de Referencia para el Sida; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Salomon, Horacio Eduardo. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología. Centro Nacional de Referencia para el Sida; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Carobene, Mauricio. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Microbiología. Centro Nacional de Referencia para el Sida; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Differential fruit choice in two simpatric monkey species and frugivorous bats in southern Mexico

In order to identify the role played by plant species as a food source in the fruit election of dispersing agents (Alouatta pigra Lawrence 1933, Ateles geoffroyi Kuhl 1820 and frugivorous bats), we developed a study in dry tropical forests in Yucatan, Mexico. We recorded the fruits consumed by frugivorous bats using collectors and, for monkeys, we implemented the focal animal method. The number of fruits consumed by primates (A. pigra and A. geoffroyi) and bats were recorded, 342 and 386, respectively. It was determined that bats deposited fruits with some percentage of pulp, while monkeys contributed more with a fruits without pulp (pairwise LSD contrast p 0.05). Among the variety of fruit species in the diet of primates, we detected that A. pigra chose mostly not an abundant species such as Enterolobium cyclocarpum Jacq. Griseb. (1860) instead of those more abundant (Manilkara zapota (L.) P. Royen (1953) and Brosimum alicastrum Sw. subsp. alicastrum C.C. Berg (1972)). The type of fruit and seed handling caused by primates would be more beneficial to seed germination than those applied by bats. Moreover, this election and fruit handling could depend on the characteristics of fruits and space-temporal availability of plant species as a food source.Con el objetivo de examinar el papel que juegan las especies vegetales como fuentes alimenticias en la selección de frutos de agentes dispersores (Alouatta pigra, Ateles geoffroyi y murciélagos frugívoros), se realizó un estudio en selvas secas en el sureste de Yucatán, México. Se registraron los frutos consumidos por murciélagos usando colectores y, en el caso de los monos, se implementó el método de animal focal. El número de frutos consumidos registrados para ambas especies de primates y murciélagos fueron 342 y 386, respectivamente. Se determinó que los murciélagos depositaron frutos con pequeñas cantidades de pulpa, mientras que los monos contribuyeron mayormente con frutos totalmente despulpados (contrastes por pares LSD p 0.05). Entre la variedad de especies de frutos en la dieta de los primates se detectó que A. pigra eligió frutos de las especies menos abundantes como Enterolobium cyclocarpum Jacq. Griseb. (1860) en vez de aquellas más abundantes (Manilkara zapota (L.) P. Royen (1953) y Brosimum alicastrum Sw. subsp. alicastrum C.C. Berg (1972)). El tipo de manejo de frutos y semillas causado por los primates sería más beneficioso para la germinación de las semillas que los aplicados por los murciélagos. Además, esta elección y manejo del fruto podría depender de sus características y la disponibilidad espacio-temporal de las especies de plantas como fuente de alimento

Interaction Between Macrophage Migration Inhibitory Factor and CD74 in Human Immunodeficiency Virus Type I Infected Primary Monocyte-Derived Macrophages Triggers the Production of Proinflammatory Mediators and Enhances Infection of Unactivated CD4+ T Cells

Understanding the mechanisms of human immunodeficiency virus type I (HIV-1) pathogenesis would facilitate the identification of new therapeutic targets to control the infection in face of current antiretroviral therapy limitations. CD74 membrane expression is upregulated in HIV-1-infected cells and the magnitude of its modulation correlates with immune hyperactivation in HIV-infected individuals. In addition, plasma level of the CD74 activating ligand macrophage migration inhibitory factor (MIF) is increased in infected subjects. However, the role played by MIF/CD74 interaction in HIV pathogenesis remains unexplored. Here, we studied the effect of MIF/CD74 interaction on primary HIV-infected monocyte-derived macrophages (MDMs) and its implications for HIV immunopathogenesis. Confocal immunofluorescence analysis of CD74 and CD44 (the MIF signal transduction co-receptor) expression indicated that both molecules colocalized at the plasma membrane specifically in wild-type HIV-infected MDMs. Treatment of infected MDMs with MIF resulted in an MIF-dependent increase in TLR4 expression. Similarly, there was a dose-dependent increase in the production of IL-6, IL-8, TNFα, IL-1β, and sICAM compared to the no-MIF condition, specifically from infected MDMs. Importantly, the effect observed on IL-6, IL-8, TNFα, and IL-1β was abrogated by impeding MIF interaction with CD74. Moreover, the use of a neutralizing αMIF antibody or an MIF antagonist reverted these effects, supporting the specificity of the results. Treatment of unactivated CD4+ T-cells with MIF-treated HIV-infected MDM-derived culture supernatants led to enhanced permissiveness to HIV-1 infection. This effect was lost when CD4+ T-cells were treated with supernatants derived from infected MDMs in which CD74/MIF interaction had been blocked. Moreover, the enhanced permissiveness of unactivated CD4+ T-cells was recapitulated by exogenous addition of IL-6, IL-8, IL-1β, and TNFα, or abrogated by neutralizing its biological activity using specific antibodies. Results obtained with BAL and NL4-3 HIV laboratory strains were reproduced using transmitted/founder primary isolates. This evidence indicated that MIF/CD74 interaction resulted in a higher production of proinflammatory cytokines from HIV-infected MDMs. This caused the generation of an inflammatory microenvironment which predisposed unactivated CD4+ T-cells to HIV-1 infection, which might contribute to viral spreading and reservoir seeding. Overall, these results support a novel role of the MIF/CD74 axis in HIV pathogenesis that deserves further investigation