Difference schemes for time-dependent heat conduction models with delay

Different non-Fourier models of heat conduction, that incorporate time lags in the heat flux and/or the temperature gradient, have been increasingly considered in the last years to model microscale heat transfer problems in engineering. Numerical schemes to obtain approximate solutions of constant coefficients lagging models of heat conduction have already been proposed. In this work, an explicit finite difference scheme for a model with coefficients variable in time is developed, and their properties of convergence and stability are studied. Numerical computations showing examples of applications of the scheme are presented.

A compact difference scheme for numerical solutions of second order dual-phase-lagging models of microscale heat transfer

Dual-phase-lagging (DPL) models constitute a family of non-Fourier models of heat conduction that allow for the presence of time lags in the heat flux and the temperature gradient. These lags may need to be considered when modeling microscale heat transfer, and thus DPL models have found application in the last years in a wide range of theoretical and technical heat transfer problems. Consequently, analytical solutions and methods for computing numerical approximations have been proposed for particular DPL models in different settings. In this work, a compact difference scheme for second order DPL models is developed, providing higher order precision than a previously proposed method. The scheme is shown to be unconditionally stable and convergent, and its accuracy is illustrated with numerical examples.

Moisture Distribution in Partially Saturated Concrete Studied by Impedance Spectroscopy

The moisture content and its spatial distribution has a great influence on the durability properties of concrete structures. Several non-destructive techniques have been used for the determination of the total water content, but moisture distribution is difficult to determine. In this paper impedance spectroscopy is used to study the water distribution in concrete samples with controlled and homogeneously distributed moisture contents. The technique is suitable for the determination of water distribution inside the sample, using the appropriate equivalent circuits. It is shown that using the selected drying procedures there is no change in the solid phase of the samples, although the technique can only be used for the qualitative study of variations in the solid phase when samples are too thick. The results of this work show that for a wide range of concrete percentages of saturation, from full to 18 % saturation, practically all the pores keep at least a thin layer of electrolyte covering their walls, since the capacitance measurement results are practically independent of the saturation degree.

La figura del gaucho en la historieta argentina. De las versiones del Martín Fierro a Inodoro Pereyra

Entre los múltiples personajes propios de la literatura latinoamericana, posiblemente el gaucho argentino ha sido el que ha despertado un mayor interés por la creación literaria, con el Martín Fierro de José Hernández como buque insignia de una amplia tradición. Esta se ve recogida muy pronto por la narración gráfica, ya sea a través de las ilustraciones de las ediciones clásicas, o en las adaptaciones de las grandes obras en revistas de historietas. Todas ellas van configurando una iconografía que completa el imaginario de los guachos, fundamental para la identidad argentina. En el siguiente trabajo haremos una panorámica de las historietas de gauchos desde las revistas tradicionales, las adaptaciones de obras literarias, como las del Martín Fierro, hasta personajes propios como Lindor Covas o Inodoro Pereyra.

La humanització del monstre: Albert Sánchez Piñol vs. H. P. Lovecraft

Aquest article pretén bastir una comparativa entre la figura teratològica mostrada a l’obra A les muntanyes de la follia de Howard Phillips Lovecraft i La pell freda d’Albert Sánchez Piñol. Una comparativa que té per finalitat mostrar com Howard Phillips Lovecraft inicia una evolució en el gènere de por (basada en la introducció de la versemblança en les narracions d’aquest gènere a través d’un racionalisme que connecta amb exactitud tots els elements de la narració, tot introduint una realitat que contrasta amb allò sobrenatural i crea la por als ulls del lector) que és assumida per Sánchez Piñol en alguns aspectes i transgredida en altres. Així, aquest darrer autor traspassa la frontera infranquejable entre humans i monstres que planteja Lovecraft en humanitzar el monstre, tot atribuint-li qualitats físiques i psicològiques humanes. Una acció que ocasiona un sentiment d’empatia dels personatges humans envers els monstres que derivarà, en última instància, en un intent d’aproximació d’aquests al monstre. O, dit d’una altra manera, en una aproximació de l’ésser humà a l’obscuritat, espai que, lluny de ser perniciós per aquest, l’ajudarà a assolir un coneixement aprofundit de si mateix. Una característica del text de Sánchez Piñol que atorga a La pell freda (i a la major part de l’obra de l’autor) un important valor antropològic i sociològic que pot salvaguardar la narrativa de por de la tendència a desaparèixer que experimenta en una societat cada cop més marcada per l’escepticisme.

Optimization of test and maintenance of ageing components consisting of multiple items and addressing effectiveness

There are many models in the literature that have been proposed in the last decades aimed at assessing the reliability, availability and maintainability (RAM) of safety equipment, many of them with a focus on their use to assess the risk level of a technological system or to search for appropriate design and/or surveillance and maintenance policies in order to assure that an optimum level of RAM of safety systems is kept during all the plant operational life. This paper proposes a new approach for RAM modelling that accounts for equipment ageing and maintenance and testing effectiveness of equipment consisting of multiple items in an integrated manner. This model is then used to perform the simultaneous optimization of testing and maintenance for ageing equipment consisting of multiple items. An example of application is provided, which considers a simplified High Pressure Injection System (HPIS) of a typical Power Water Reactor (PWR). Basically, this system consists of motor driven pumps (MDP) and motor operated valves (MOV), where both types of components consists of two items each. These components present different failure and cause modes and behaviours, and they also undertake complex test and maintenance activities depending on the item involved. The results of the example of application demonstrate that the optimization algorithm provide the best solutions when the optimization problem is formulated and solved considering full flexibility in the implementation of testing and maintenance activities taking part of such an integrated RAM model.