El análisis del discurso como metodología para reconstruir el conocimiento didáctico del contenido

Las investigaciones sobre el CDC se han basado en cuestionarios escritos, entrevistas, técnicas inferenciales, mapas conceptuales, y representaciones pictóricas. Nuestras indagaciones mostraron que esta metodología es especialmente útil para la detección del conocimiento declarativo de los profesores que se manifiesta como ideas explícitas. No obstante, hemos encontrado que los profesores de nivel universitario con menor formación pedagógica que sus pares del secundario, presentan dificultades para expresar y describir lo que hacen durante sus clases y el cómo o el por qué lo hacen. Esto nos llevó a buscar nuevas metodologías para indagar sus concepciones implícitas y sus teorías en uso. En este sentido, el análisis del discurso ha resultado una potente alternativa para aproximarnos al estudio de las prácticas de enseñanza y en particular, para el estudio del CDC

El análisis del discurso como metodología para reconstruir el conocimiento didáctico del contenido

Las investigaciones sobre el CDC se han basado en cuestionarios escritos, entrevistas, técnicas inferenciales, mapas conceptuales, y representaciones pictóricas. Nuestras indagaciones mostraron que esta metodología es especialmente útil para la detección del conocimiento declarativo de los profesores que se manifiesta como ideas explícitas. No obstante, hemos encontrado que los profesores de nivel universitario con menor formación pedagógica que sus pares del secundario, presentan dificultades para expresar y describir lo que hacen durante sus clases y el cómo o el por qué lo hacen. Esto nos llevó a buscar nuevas metodologías para indagar sus concepciones implícitas y sus teorías en uso. En este sentido, el análisis del discurso ha resultado una potente alternativa para aproximarnos al estudio de las prácticas de enseñanza y en particular, para el estudio del CDC

Diversidad de poderes en África y resolución de conflictos

El conjunto de textos recogidos en este volumen son el resultado del seminario internacional “La Paz y la Palabra. Procesos de reconciliación posbélica en el África Subsahariana” celebrado los días 27 y 28 de noviembre de 2008 en Barcelona, coordinado científicamente por el Centro de Estudos Africanos del ISCTE de Lisboa y la red de estudios africanos ARDA/RIDA, con sede en Barcelona, y organizado por la Fundación CIDOB. Este encuentro significaba la segunda edición de un proyecto internacional iniciado en Lisboa en marzo de 2007 con un primer seminario que llevaba por título “Autoridades tradicionais: um universo em mudança”, y que fue coordinado por las mismas entidades

Shape matters: relevance of carapace for brachyuran crab invaders

The increasing trend of biological invasions is one of the most concerning threats for ecosystems functioning. The identification of optimal characters determining the invasive potential of nonnative species has always been a challenge in conservation studies. Morphological features can be used as a good proxy to address the invasive success in fish species, assuming that anatomical differences in comparison to native species can provide to newcomers ecological opportunities increasing their probability to become successful. Considering this, the present study constitutes the first applicative attempt of a model based on geometric morphometrics to demonstrate the importance of the carapace shape in the invasive ability in marine decapod crustaceans. The study was performed on the native brachyuran community of Alfacs Bay, in the Ebro Delta, the largest estuarine zone along the north-western Mediterranean, in which two recently established non-native crab species coexist: Dyspanopeus sayi and Callinectes sapidus. Results suggested that invaders with extreme carapace traits located peripherally in the community morphospace, such as C. sapidus, usually possess ecological advantages contributing to understand their success. Conversely, intermediate morphologies within the morphospace, such as D. sayi, imply ecological overlapping with native species reducing their community relevance. Besides, we also assessed the effect on the community morphospace of a hypothetical future invasive event from another crab species (Portunus segnis) with high probabilities to also colonize the community. Our outcomes confirm that the morphometric approach could be an alternative tool for assessing the potential ability of invasive crab species. However, further studies at different spatial and temporal scales, including additional traits and quantitative data from invasions, would be necessary to confirm the efficacy and usefulness of the methodology.Postprint2,89

Simulating the effects of extreme dry and wet years on the water use of flooding-irrigated maize in a mediterranean landplane

The final editorial version is available at: http://www.sciencedirect.com/science/journal/03783774The effects of years of extreme rainfall events on maize water-use under traditional flooding irrigation in a Mediterranean landplane were estimated through a simulation assessment; combining a weather generator with an agrohydrological simulation model. Two options: “Fully Irrigation” and “Deficit Irrigation” were considered in the simulations as the extreme water-management situations. Besides, a 2-m depth shallow water table and Free Drainage were considered as the typical extreme situations that can be found at the bottom of the simulated soil layer. Thirty “Dry” (DY) and “Wet” (WY) years were randomly selected from the weather generator output. The model SWAP was used to simulate the Relative Transpiration (RT), i.e. ratio between actual and maximum maize transpiration, Actual Maize Evapotranspiration (ETC), Percolated Water and Capillary Rising during wet and dry years and for each of the irrigation and bottom condition options. According to the modelling results, average mean RT is about 80% and 90% in dry and wet years, respectively. RT and ETC variability are very high under dry conditions although such variability is notably reduced if a suitable irrigation option is considered. Capillary rising can play a very important role during dry years in those places where irrigation is not enough, but water table is relatively shallower. On the other hand, a shallower water table can carry out RT reductions during wet years, due to water excess, although these negative effects are comparatively lower than those produced by rain scarcity. Besides, percolated water during wet years is very high, particularly in well irrigated farms.Peer reviewe

Ideal hierarchical secret sharing schemes

Hierarchical secret sharing is among the most natural generalizations of threshold secret sharing, and it has attracted a lot of attention from the invention of secret sharing until nowadays. Several constructions of ideal hierarchical secret sharing schemes have been proposed, but it was not known what access structures admit such a scheme. We solve this problem by providing a natural definition for the family of the hierarchical access structures and, more importantly, by presenting a complete characterization of the ideal hierarchical access structures, that is, the ones admitting an ideal secret sharing scheme. Our characterization deals with the properties of the hierarchically minimal sets of the access structure, which are the minimal qualified sets whose participants are in the lowest possible levels in the hierarchy. By using our characterization, it can be efficiently checked whether any given hierarchical access structure that is defined by its hierarchically minimal sets is ideal. We use the well known connection between ideal secret sharing and matroids and, in particular, the fact that every ideal access structure is a matroid port. In addition, we use recent results on ideal multipartite access structures and the connection between multipartite matroids and integer polymatroids. We prove that every ideal hierarchical access structure is the port of a representable matroid and, more specifically, we prove that every ideal structure in this family admits ideal linear secret sharing schemes over fields of all characteristics. In addition, methods to construct such ideal schemes can be derived from the results in this paper and the aforementioned ones on ideal multipartite secret sharing. Finally, we use our results to find a new proof for the characterization of the ideal weighted threshold access structures that is simpler than the existing one.Peer ReviewedPostprint (author's final draft

Optimal non-perfect uniform secret sharing schemes

A secret sharing scheme is non-perfect if some subsets of participants that cannot recover the secret value have partial information about it. The information ratio of a secret sharing scheme is the ratio between the maximum length of the shares and the length of the secret. This work is dedicated to the search of bounds on the information ratio of non-perfect secret sharing schemes. To this end, we extend the known connections between polymatroids and perfect secret sharing schemes to the non-perfect case. In order to study non-perfect secret sharing schemes in all generality, we describe their structure through their access function, a real function that measures the amount of information that every subset of participants obtains about the secret value. We prove that there exists a secret sharing scheme for every access function. Uniform access functions, that is, the ones whose values depend only on the number of participants, generalize the threshold access structures. Our main result is to determine the optimal information ratio of the uniform access functions. Moreover, we present a construction of linear secret sharing schemes with optimal information ratio for the rational uniform access functions.Peer ReviewedPostprint (author's final draft

El CDC de profesores universitarios de química orgánica : el caso del benceno

En este trabajo analizamos el discurso del profesor para reconstruir el CDC, como una metodología que complementa a las tradicionales, y sirve además para indagar las teorías en uso al enseñar determinado tema. Diseñamos y aplicamos un nuevo instrumento al discurso de cinco profesoras universitarias de química orgánica. Su construcción se basó en la teoría fundamentada, y en trabajos sobre el CDC que implican cuestionarios de respuestas abiertas. A partir de las categorías de análisis propuestas pudimos reconstruir el CDC de las ideas centrales del tema Compuestos Aromáticos enseñadas en las distintas clases. Los resultados muestran marcadas diferencias entre los discursos a pesar de la semejanza del contexto. Consecuentemente, considerando la estrecha conexión entre lenguaje y pensamiento, pueden ser atribuidos a las diferencias en el CDC de las profesoras

Developmental responses of bread wheat to changes in ambient temperature following deletion of a locus that includes FLOWERING LOCUS T1

FLOWERING LOCUS T (FT) is a central integrator of environmental signals that regulates the timing of vegetative to reproductive transition in flowering plants. In model plants, these environmental signals have been shown to include photoperiod, vernalization, and ambient temperature pathways, and in crop species, the integration of the ambient temperature pathway remains less well understood. In hexaploid wheat, at least 5 FT‐like genes have been identified, each with a copy on the A, B, and D genomes. Here, we report the characterization of FT‐B1 through analysis of FT‐B1 null and overexpression genotypes under different ambient temperature conditions. This analysis has identified that the FT‐B1 alleles perform differently under diverse environmental conditions; most notably, the FT‐B1 null produces an increase in spikelet and tiller number when grown at lower temperature conditions. Additionally, absence of FT‐B1 facilitates more rapid germination under both light and dark conditions. These results provide an opportunity to understand the FT‐dependent pathways that underpin key responses of wheat development to changes in ambient temperature. This is particularly important for wheat, for which development and grain productivity are sensitive to changes in temperature

Time-resolved broadband analysis of slow-light propagation and superluminal transmission of electromagnetic waves in three-dimensional photonic crystals

A time-resolved analysis of the amplitude and phase of THz pulses propagating through three-dimensional photonic crystals is presented. Single-cycle pulses of THz radiation allow measurements over a wide frequency range, spanning more than an octave below, at and above the bandgap of strongly dispersive photonic crystals. Transmission data provide evidence for slow group velocities at the photonic band edges and for superluminal transmission at frequencies in the gap. Our experimental results are in good agreement with finite-difference-time-domain simulations.Comment: 7 pages, 11 figure