Improving the 14c dating of marine shells from the Canary Islands for constructing more reliable and accurate chronologies

Radiocarbon dating of closely associated marine mollusk shells and terrestrial material (charred wood or bone) collected from archaeological contexts on Tenerife and Fuerteventura islands allowed us to quantify the marine C-14 reservoir effect (Delta R) around the Canary Archipelago. Coastal Fuerteventura has a positive weighted mean Delta R value of +185 +/- 30 C-14 yr, while for Tenerife a range of negative and positive values was obtained, resulting in a Delta R weighted mean value of 0 +/- 35 C-14 yr. These values are in accordance with the hydrodynamic system present off the Canary Islands characterized by a coastal upwelling regime that affects the eastern islands (Fuerteventura and Lanzarote) but not the other islands of the archipelago, namely Tenerife. Because of this oceanographic pattern, we recommend the extrapolation of these results to the remaining islands of the archipelago, i.e. the first value must be used for the eastern islands, while for the central and western islands the acceptable Delta R value is 0 +/- 35 C-14 yr

A role for SUMO modification in transcriptional repression and activation

Since the discovery of the SUMO (small ubiquitin-like modifier) family of proteins just over a decade ago, a plethora of substrates have been uncovered including many regulators of transcription. Conjugation of SUMO to target proteins has generally been considered as a repressive modification. However, there are now a growing number of examples where sumoylation has been shown to activate transcription. Here we discuss whether there is something intrinsically repressive about sumoylation, or if the outcome of this modification in the context of transcription will prove to be largely substrate-dependent. We highlight some of the technical challenges that will be faced by attempting to answer this question

Stick-slip instabilities in the shear flow of magnetorheological suspensions

International audienceThis work is devoted to the stick-slip instabilities that appear in the shear flow of highly concentrated suspensions of magnetic microparticles. The effect of the applied magnetic field strength was analyzed in details. With this aim, homogeneous suspensions of iron microparticles with concentration near the limit of maximum-packing fraction were prepared, and shear-flow measurements were performed in a controlled-rate mode using a rheometer provided with a rough parallel-plate geometry. For each given value of the shear rate, the time evolution of the shear stress was monitored for at least 20 min. Saw-tooth-like stress oscillations, typical of stick-slip instabilities, were obtained at low enough shear rate values. The measurements were restricted to small enough oscillations, at which the rheometer was still able to maintain the shear rate constant. From the microscopic viewpoint, these stick-slip instabilities principally appear due to the periodic failure and healing of the field-induced particle structures, as inferred from experimental observations. This hypothesis is corroborated by a theoretical model developed on the basis of the balance of the magnetic and hydrodynamic torques over the particle structures, allows us to predict the correct order of magnitude of the main parameters of the stick-slip instabilities, including the amplitude and period of the stress oscillations

Yield stress in magnetorheological suspensions near the limit of maximum-packing fraction

International audienceThis work deals with the magnetic field-induced static yield stress of magnetorheological (MR) suspensions with concentration near the limit of maximum-packing fraction. With this aim, homogeneous suspensions of iron microparticles with 50 vol.% concentration were prepared, and their yield stress measured as a function of the applied magnetic field. In view of the failure of existing models to predict, on the basis of realistic hypotheses, the values of the yield stress of highly concentrated MR suspensions, we developed a new model. Our model considers that field application induces body-centered tetragonal (BCT) structures. Upon shearing, these structures deform in such a way that interparticle gaps appear between neighboring particles of the same chain, whereas the approach of particles of parallel chains ensures the mechanical stability of the whole multi-chain structure. Based on this hypothesis, and using finite element method simulations of interparticle magnetic interactions, our model is able to quantitatively predict the yield stress of highly concentrated MR suspensions. Furthermore, estimations show that the main contribution to the field-dependent part of the yield stress comes from the change in the permeability of the structures as interparticle gaps are enlarged by the shear

Effect of functionalized PHEMA micro- and nano-particles on the viscoelastic properties of fibrin-agarose biomaterials

Two types of PHEMA-based particles, exhibiting either carboxyl or tertiary ammine functional groups, were incorporated to fibrin-agarose (FA) hydrogels, and the effect of the addition of these synthetic particles on the viscoelastic and microstructural properties of the biomaterials was evaluated. Experimental results indicated that the incorporation of both types of polymeric particles to FA scaffolds was able to improve the biomechanical properties of the biomaterials under steady state and oscillatory shear stresses, resulting in scaffolds characterized by higher values of the storage, loss, and shear moduli. In addition, the microstructural evaluation of the scaffolds showed that the nanoparticles exhibiting carboxyl functional groups were homogeneously distributed across the fibrous network of the hydrogels. The addition of both types of artificial polymeric particles was able to enhance the viscoelastic properties of the FA hydrogels, allowing the biomaterials to reach levels of mechanical consistency under shear stresses in the same range of some human native soft tissues, which could allow these biomaterials to be used as scaffolds for new tissue engineering applications.Peer ReviewedPostprint (author's final draft

Hybrid SDN Evolution: A Comprehensive Survey of the State-of-the-Art

Software-Defined Networking (SDN) is an evolutionary networking paradigm which has been adopted by large network and cloud providers, among which are Tech Giants. However, embracing a new and futuristic paradigm as an alternative to well-established and mature legacy networking paradigm requires a lot of time along with considerable financial resources and technical expertise. Consequently, many enterprises can not afford it. A compromise solution then is a hybrid networking environment (a.k.a. Hybrid SDN (hSDN)) in which SDN functionalities are leveraged while existing traditional network infrastructures are acknowledged. Recently, hSDN has been seen as a viable networking solution for a diverse range of businesses and organizations. Accordingly, the body of literature on hSDN research has improved remarkably. On this account, we present this paper as a comprehensive state-of-the-art survey which expands upon hSDN from many different perspectives

Gestión de recursos electrónicos en el Consorcio de Bibliotecas Universitarias Andaluzas. Una experiencia de cooperación bibliotecaria en entornos digitales

En la actualidad es difícil encontrar bibliotecas digitales nacidas bajo este concepto. La denominación representa más bien la evolución de las bibliotecas tradicionales, sobre todo universitarias, hacia un entorno en que la proliferación de recursos electrónicos en lo últimos años ha cambiado no sólo el concepto de biblioteca sino el mismo concepto de investigación, de estudio y por tanto de trabajo. Bajo esta premisa, en que señalamos recursos electrónicos como origen de bibliotecas digitales, son los consorcios bibliotecarios los que han contribuido de forma extraordinaria y definitiva a su desarrollo. La vieja idea de cooperación se ha materializado en ellos no sólo en la disposición de recursos propios sino que ha encontrado su máxima expresión en el entorno consorciado en que la adquisición y gestión compartidas han sido necesarias para dar respuesta a las necesidades que impone la proliferación de recursos electrónicos en las nuevas bibliotecas digitales. Claro ejemplo de esta afirmación, de estas nuevas formas de organización lo constituye el recientemente creado Grupo de Trabajo de Recursos Electrónicos del Consorcio de Bibliotecas Universitarias Andaluzas (CBUA), cuyo proyecto de cooperación y gestión contribuye a facilitar el acceso a la colección digital en el ámbito universitario andaluz. Se presenta el trabajo realizado hasta la fecha por el Grupo, así como las perspectivas de futuro. Se exponen la metodología de trabajo empleada, las líneas de actuación, las acciones realizadas, las herramientas utilizadas para optimizar la calidad en el acceso y difusión de los recursos de los que disponemos. Palabras clave: bibliotecas universitarias, bibliotecas digitales, gestión de recursos electrónicos, consorcios de bibliotecas, cooperación bibliotecaria

Combinatorial entropy behaviour leads to range selective binding in ligand-receptor interactions

From viruses to nanoparticles, constructs functionalized with multiple ligands display peculiar binding properties that only arise from multivalent effects. Using statistical mechanical modelling, we describe here how multivalency can be exploited to achieve what we dub range selectivity, that is, binding only to targets bearing a number of receptors within a specified range. We use our model to characterise the region in parameter space where one can expect range selective targeting to occur, and provide experimental support for this phenomenon. Overall, range selectivity represents a potential path to increase the targeting selectivity of multivalent constructs

Combinatorial entropy behaviour leads to range selective binding in ligand-receptor interactions

From viruses to nanoparticles, constructs functionalized with multiple ligands display peculiar binding properties that only arise from multivalent effects. Using statistical mechanical modelling, we describe here how multivalency can be exploited to achieve what we dub range selectivity, that is, binding only to targets bearing a number of receptors within a specified range. We use our model to characterise the region in parameter space where one can expect range selective targeting to occur, and provide experimental support for this phenomenon. Overall, range selectivity represents a potential path to increase the targeting selectivity of multivalent constructs