A residual based a posteriori error estimator for an augmented mixed finite element method in linear elasticity

In this paper we develop a residual based a posteriori error analysis for an augmented mixed finite element method applied to the problem of linear elasticity in the plane. More precisely, we derive a reliable and efficient a posteriori error estimator for the case of pure Dirichlet boundary conditions. In addition, several numerical experiments confirming the theoretical properties of the estimator, and illustrating the capability of the corresponding adaptive algorithm to localize the singularities and the large stress regions of the solution, are also reporte

Numerical analysis of a transmission problem with Signorini contact using mixed-FEM and BEM

© EDP Sciences, SMAI 2011This paper is concerned with the dual formulation of the interface problem consisting of a linear partial differential equation with variable coefficients in some bounded Lipschitz domain Ω in Rn (n ≥ 2) and the Laplace equation with some radiation condition in the unbounded exterior domain Ωc := Rn\￣Ω. The two problems are coupled by transmission and Signorini contact conditions on the interface Γ = ∂Ω. The exterior part of the interface problem is rewritten using a Neumann to Dirichlet mapping (NtD) given in terms of boundary integral operators. The resulting variational formulation becomes a variational inequality with a linear operator. Then we treat the corresponding numerical scheme and discuss an approximation of the NtD mapping with an appropriate discretization of the inverse Poincar´e-Steklov operator. In particular, assuming some abstract approximation properties and a discrete inf-sup condition, we show unique solvability of the discrete scheme and obtain the corresponding a-priori error estimate. Next, we prove that these assumptions are satisfied with Raviart- Thomas elements and piecewise constants in Ω, and continuous piecewise linear functions on Γ. We suggest a solver based on a modified Uzawa algorithm and show convergence. Finally we present some numerical results illustrating our theory

Comparación de la cinética de la infección de ovas de trucha arcoíris (Oncorhynchus mykiss) con dos cepas de Piscirickettsia salmonis detectada mediante dot-blot#

En un estudio previo, se comprobó mediante microscopía de barrido, que la cepa LF-89 se adhiere a la pared de la ovamediante prolongaciones de su membrana externa, estructuras que han sido denominadas "Complejo de AdhesiónPiscirickettsial" o CAP, lo que facilitaría la posterior penetración de la bacteria al interior de la ova. Sin embargo,existen otras cepas aisladas, como la SLGO-95, que es más virulenta y resistente a antibióticos que la LF-89 y que no seha estudiado la posibilidad de unión a ovas. Por lo anterior, en el presente trabajo se comparó la cinética de infección deovas de trucha arcoíris, entre ambas cepas, utilizando como metodología la técnica de dot-blot. El método de "dot-blot"se realizó mediante la retención de proteínas en una membrana de polivinildifluoruro (PVDF), incubación conanticuerpos oligoclonales anti-P. salmonis y posteriormente con un segundo anticuerpo anti inmunoglobulina G deratón conjugado con peroxidasa. La reacción antígeno-anticuerpo se evidenció mediante un sustratoquimioluminiscente, utilizando una película autorradiográfica. La evaluación de la reacción se realizó mediantedensitometría utilizando un "software" computacional. Para estandarizar el método se realizaron diluciones seriadas dela suspensión de P. salmonis, desde 0,02 a 56 μg de proteína total. Para aumentar la sensibilidad se centrifugaron lasmuestras a 11.000 x g por 60 min. Además, se probaron diferentes concentraciones de anticuerpo primario, 1:1000,1:5000 y 1:10.000 y muestras de ovas y bacteria fueron sometidas a desnaturalización por ebullición. Se utilizaron ovasde reproductores libres de infecciones virales, Renibacterium salmoninarum y P. salmonis. Las ovas fueron incubadas(en duplicado) con 500 μL de una suspensión de P. salmonis, ya sea con la cepa LF-89 o SLGO-95 por 1,3, 10 y 60min. Luego, cada ova fue congelada a -70°C hasta ser procesada para la técnica de "dot blot". La muestra nocentrifugada de P. salmonis fue detectada como positiva sólo hasta 0,4 μg de proteína total. Cuando fue centrifugada a11.000 g por 1 h, la bacteria fue detectada hasta la última dilución estudiada (0,02 μg). Por otra parte, no hubo grandesdiferencias en la positividad obtenida mediante las tres diluciones de anticuerpos primarios. De acuerdo, al"background" obtenido y nitidez, se consideró como una mejor dilución de trabajo 1:5000. Cuando se realizó la cinéticade infección con la cepa LF-89, los resultados indicaron la aparición de señal positiva desde 1 min de exposición de lasovas a la bacteria. La reacción positiva se mantuvo hasta los 60 min. Con respecto a la cepa SLGO-95, los resultadosfueron similares, sin embargo, la cepa SLGO-95 demostró un mayor número de píxeles, lo que indica que esta cepa seune a la ova en mayor cantidad. Los resultados apoyan los estudios anteriores que indican que P. salmonis es capaz deinfectar verticalmente las ovas y que esta podría ser una de las formas de transmisión del agente en condiciones decultivo. Además, se comprueba que el grado de infección depende del tipo de cepa actuante.  

Simple Model of Capillary Condensation in porous media

We employ a simple model to describe the phase behavior of 4He and Ar in a hypothetical porous material consisting of a regular array of infinitely long, solid, parallel cylinders. We find that high porosity geometries exhibit two transitions: from vapor to film and from film to capillary condensed liquid. At low porosity, the film is replaced by a ``necking'' configuration, and for a range of intermediate porosity there are three transitions: from vapor to film, from film to necking and from necking to a capillary condensed phase.Comment: 14 pages, 7 figure

Narrativas del simulacro: videocultura, tecnología y literatura en Argentina y Uruguay. [RESEÑA]

Montoya Juárez, Jesús Narrativas del simulacro: videocultura, tecnología y literatura en Argentina y Uruguay. Murcia: Universidad de Murcia, 2013. 374 pp. (ISBN: 978-84-16038-01-5

Influence of Silver Nitrate on Somatic Embryogenesis Induction in Arabica Coffee (Coffea arabica L.).

Plant somatic embryogenesis (SE) has been defined as the formation of embryos from a single or group of haploid or somatic cells [1, 2]. Low frequency (LFSE) and high frequency somatic embryogenesis (HFSE) have been described. In the first type, somatic embryos are induced directly from pro-embryogenic cells of explants, while in the second, they originate from embryogenic callus [1]. It has been suggested that in LFSE the origin of somatic embryos is unicellular, whereas in HFSE has been described as unicellular or multicellular [3]. SE is a powerful biotechnological tool used to propagate elite plants or to conserve important genotypes [4]. Moreover, SE offers an efficient in vitro regeneration approach as a fundamental step in plant genetic improvement for studying basic aspects of ontogenesis of somatic embryos [5]. In Coffea spp., the first studies of SE have been reported at the beginning of 1970 [6]. Since then, a large quantity of LFSE and HFSE protocols have been optimized demonstrating that coffee is not a recalcitrant species for SE [4]. In the LFSE the somatic embryos are obtained faster (approximately 70 days) using only one medium meanwhile in HFSE several media are used and somatic embryo formation takes 9-10 months [4]. Although, in LFSE small number of somatic embryos are obtained (around 10 per explant) compared to hundreds of somatic embryos obtained per gram of embryogenic calli [4], the unicellular origin of somatic embryos in LFSE represents an advantage for the chemical and physical mutagenesis, genetic transformation and genetic editing, since prevents or reduces the appearance of chimeras [7]. In C. arabica and C. canephora many factors (such as genotype, explant type, the physiological state, age and growth conditions of the donor plants, the season of collection, nutrient composition of the medium, the volume of dissolved CO2 or O2 in the culture flask, and plant growth regulators) that affect LFSE induction have been studied [3, 8, 9, 10, 11, 12, 13]. However, few studies reported the effect of silver nitrate on LFSE using leaf explants of C. arabica L. and to the best of our knowledge it has not been analyzed using Caturra and Catuaí, which are two economic important producer cultivars in Costa Rica. Since SE is genotype dependent, the culture medium need to be modified for the different genotypes [7].Therefore, the objective of this study was to determine the influence of the benzyladenine (BAP), indole-3-acetic acid (IAA), and silver nitrate (AgNO3) on low frequency somatic embryogenesis using leaf explants of Coffea arabica L. cultivars Caturra and Catuaí

Diversity and neocolonialism in Big Data research: Avoiding extractivism while struggling with paternalism

The extractive logic of Big Data-driven technology and knowledge production has raised serious concerns. While most criticism initially focused on the impacts on Western societies, attention is now increasingly turning to the consequences for communities in the Global South. To date, debates have focused on private-sector activities. In this article, we start from the conviction that publicly funded knowledge and technology production must also be scrutinized for their potential neocolonial entanglements. To this end, we analyze the dynamics of collaboration in an European Union-funded research project that collects data for developing a social platform focused on diversity. The project includes pilot sites in China, Denmark, the United Kingdom, India, Italy, Mexico, Mongolia, and Paraguay. We present the experience at four field sites and reflect on the project’s initial conception, our collaboration, challenges, progress, and results. We then analyze the different experiences in comparison. We conclude that while we have succeeded in finding viable strategies to avoid contributing to the dynamics of unilateral data extraction as one side of the neocolonial circle, it has been infinitely more difficult to break through the much more subtle but no less powerful mechanisms of paternalism that we find to be prevalent in data-driven North–South relations. These mechanisms, however, can be identified as the other side of the neocolonial circle.</p

The Biomechanical Role of Scaffolds in Augmented Rotator Cuff Tendon Repairs

Background Scaffolds continue to be developed and used for rotator cuff repair augmentation; however, the appropriate scaffold material properties and/or surgical application techniques for achieving optimal biomechanical performance remains unknown. The objectives of the study were to simulate a previously validated spring-network model for clinically relevant scenarios to predict: (1) the manner in which changes to components of the repair influence the biomechanical performance of the repair and (2) the percent load carried by the scaffold augmentation component. Materials and methods The models were parametrically varied to simulate clinically relevant scenarios, namely, changes in tendon quality, altered surgical technique(s), and different scaffold designs. The biomechanical performance of the repair constructs and the percent load carried by the scaffold component were evaluated for each of the simulated scenarios. Results The model predicts that the biomechanical performance of a rotator cuff repair can be modestly increased by augmenting the repair with a scaffold that has tendon-like properties. However, engineering a scaffold with supraphysiologic stiffness may not translate into yet stiffer or stronger repairs. Importantly, the mechanical properties of a repair construct appear to be most influenced by the properties of the tendon-to-bone repair. The model suggests that in the clinical setting of a weak tendon-to-bone repair, scaffold augmentation may significantly off-load the repair and largely mitigate the poor construct properties. Conclusions The model suggests that future efforts in the field of rotator cuff repair augmentation may be directed toward strategies that strengthen the tendon-to-bone repair and/or toward engineering scaffolds with tendon-like mechanical properties

Lattice model of gas condensation within nanopores

We explore the thermodynamic behavior of gases adsorbed within a nanopore. The theoretical description employs a simple lattice gas model, with two species of site, expected to describe various regimes of adsorption and condensation behavior. The model includes four hypothetical phases: a cylindrical shell phase (S), in which the sites close to the cylindrical wall are occupied, an axial phase (A), in which sites along the cylinder's axis are occupied, a full phase (F), in which all sites are occupied, and an empty phase (E). We obtain exact results at T=0 for the phase behavior, which is a function of the interactions present in any specific problem. We obtain the corresponding results at finite T from mean field theory. Finally, we examine the model's predicted phase behavior of some real gases adsorbed in nanopores

Capillary condensation in cylindrical nanopores

Using grand canonical Monte Carlo simulations, we have explored the phenomenon of capillary condensation (CC) of Ar at the triple temperature inside infinitely long, cylindrical pores. Pores of radius R= 1 nm, 1.7 nm and 2.5 nm have been investigated, using a gas-surface interaction potential parameterized by the well-depth D of the gas on a planar surface made of the same material as that comprising the porous host. For strongly attractive situations, i.e., large D, one or more (depending on R) Ar layers adsorb successively before liquid fills the pore. For very small values of D, in contrast, negligible adsorption occurs at any pressure P below saturated vapor pressure P0; above saturation, there eventually occurs a threshold value of P at which the coverage jumps from empty to full, nearly discontinuously. Hysteresis is found to occur in the simulation data whenever abrupt CC occurs, i.e. for R>= 1.7 nm, and for small D when R=1nm. Then, the pore-emptying branch of the adsorption isotherm exhibits larger N than the pore-filling branch, as is known from many experiments and simulation studies. The relation between CC and wetting on planar surfaces is discussed in terms of a threshold value of D, which is about one-half of the value found for the wetting threshold on a planar surface. This finding is consistent with a simple thermodynamic model of the wetting transition developed previously.Comment: 13 pages, 7 figure