9,209 research outputs found
Effect of crowding on the electron transfer process from plastocyanin and cytochrome c6 to photosystem I: a comparative study from cyanobacteria to green algae
Plastocyanin and cytochrome c 6, the alternate donor proteins to photosystem I, can be acidic, neutral or basic; the role of electrostatics in their interaction with photosystem I vary accordingly for cyanobacteria, algae and plants. The effect of different crowding agents on the kinetics of the reaction between plastocyanin or cytochrome c 6 and photosystem I from three different cyanobacteria, Synechocystis PCC 6803, Nostoc PCC 7119 and Arthrospira maxima, and a green alga, Monoraphidium braunii, has been investigated by laser flash photolysis, in order to elucidate how molecular crowding affects the interaction between the two donor proteins and photosystem I. The negative effect of viscosity on the interaction of the two donors with photosystem I for the three cyanobacterial systems is very similar, as studied by increasing sucrose concentration. Bovine serum albumin seems to alter the different systems in a specific way, probably by means of electrostatic interactions with the donor proteins. Ficoll and dextran behave in a parallel manner, favouring the interaction by an average factor of 2, although this effect is somewhat less pronounced in Nostoc. With regards to the eukaryotic system, a strong negative effect of viscosity is able to overcome the favourable effect of any crowding agent, maybe due to stronger donor/photosystem I electrostatic interactions or the structural nature of the eukaryotic photosystem I-enriched membrane particles.Spanish Ministry of Innovation and Science BFU2006-01361Andalusian Government PAI BIO-02
Return to Tourist Destination. Is it Reputation, After All?
In this paper we study the hypothesis that the repeated purchases in the tourism markets could be considered as a consequence of asymmetrical information problems. We analyze this hypothesis with the case study of the Island of Tenerife by the estimation of a count data model. We obtain that the length of the stay and the information obtained from previous visits and/or relatives and friends might increase the return to a destination suggesting the presence of a reputation mechanism as proposed by Shapiro (1983). We also estimate the determinants of the willingness to return confirming the main results.reputation, tourism, count data, logit
Independent AND-parallel implementation of narrowing
We present a parallel graph narrowing machine, which is
used to implement a functional logic language on a shared memory multiprocessor. It is an extensión of an abstract machine for a purely functional language. The result is a programmed graph reduction machine which integrates the mechanisms of unification, backtracking, and independent
and-parallelism. In the machine, the subexpressions of an expression can run in parallel. In the case of backtracking, the structure of an expression is used to avoid the reevaluation of subexpressions as far as possible. Deterministic computations are detected. Their results are maintained and need not be reevaluated after backtracking
Un modelo taxonómico de las actividades de enseñanza de la ciencia como instrumento de formalización del metalenguaje del diseño didáctico
Este escrito propone una formalización del lenguaje empleado para referir a las actividades de enseñanza de la ciencia. Consiste en un modelo taxonómico que pretende diferenciar e integrar el conjunto de las actividades de esta Ãndole y posibilitar la categorización, de forma unÃvoca, de cualquier propuesta concreta. A modo de valoración e ilustración el modelo es aplicado a diversos diseños curriculares. De confirmarse la funcionalidad del modelo para representar el conjunto de las actividades de enseñanza de la ciencia, se habrá facilitado la comunicación entre especialistas asà como el desarrollo de una teorÃa didáctica. Se incluye un glosario para comodidad del lector.In this paper it is proposed a formalization of the lexicon used in the description of science teaching activities. It consists of a taxonomic model that intends to differentiate and integrate coherently the set of all of these activities and enable the categorisation of any specific proposal. For the purposes of evaluation and illustration the model is applied to a number of designs. If the model's functionality to represent the set of all science teaching activities is con! rmed it should facilitate communication between specialists as well as the development of a didactics theory. For convenience, a glossary is included
Enseñanza y aprendizaje de astronomÃa diurna en primaria mediante «secuencias problematizadas» basadas en «mapas evolutivos»
Existe la imperiosa necesidad de mejorar la enseñanza de la ciencia en todas las etapas educativas, siendo el desarrollo de material curricular probado experimentalmente una de las estrategias ineludibles. Este escrito pretende mostrar, mediante el caso concreto de la astronomÃa diurna, cómo la metodologÃa de «secuencias problematizadas» de carácter descriptivo y basadas en los «mapas evolutivos» del tema constituye una herramienta eficaz para acercar los niños a su entorno, desarrollar formas de pensar cientÃficas, mejorar su actitud hacia la ciencia y sentar las estructuras cognitivas de carácter descriptivo necesarias para el aprendizaje de teorÃas explicativas en etapas posteriores.There is an urgent need to improve Science teaching at all educational levels, and the development of curricular material that has been tested experimentally is undoubtedly one of the necessary strategies. This paper intends to show, through the specific case of daytime astronomy, how descriptive «problematized sequences» based on «evolutionary maps» are an effective tool for bringing children closer to their environment, developing scientific ways of thinking, improving their attitude toward science and establish the descriptive cognitive structures needed for learning explanatory theories in later stages
El mapa evolutivo de las estaciones del año
Els mapes evolutius són estructures que representen la xarxa d'itineraris que poden seguir els nens en la conceptualització de temes especÃfics (en l'à mbit del pensament concret). Estan constituïts pel conjunt d'integracions possibilitades per la successió de diferenciacions que realitza el subjecte d'un aspecte de la seva realitat observacional (a partir de la percepció). En aquest escrit presentem la seva aplicació a un nou tema (el cicle anual del moviment del Sol en el cel), inclosa la contrastació experimental, la qual cosa ha revelat una panoplia de concepcions infantils, reforçat la validesa i versatilitat de la metodologia, suggerit un mecanisme cognitiu de rellevà ncia didà ctica (els models observacionals deduïts) i proporcionat suport addicional a la necessitat de cimentar l'aprenentatge infantil en la realitat empÃrica. A més, com tot mapa evolutiu, possibilita el disseny d'objectius i criteris d'avaluació seqüencials coherents amb el desenvolupament cognitiu, aixà com la identificació de l'arquitectura precisa del canvi conceptual necessari en cada aprenent.Evolutionary maps (emaps) are structures that represent the network of itineraries that children may follow in the conceptualization of specific topics (within concrete thought). They consist of the set of integrations that are made possible by the succession of differentiations that subjects make from perceptual reality. In this paper, we present its application to a new topic (the annual cycle of the motion of the Sun in the sky), including the experimental test, which has revealed a panoply of children’s conceptions, strengthened the validity and versatility of the methodology, suggested a cognitive mechanism of didactical relevance (deduced observational models) and provided additional support to the need for cementing children’s learning in empirical reality. In addition, as all emaps, it enables the design of sequential objectives and evaluation criteria consistent with cognitive development, as well as the identification of the precise architecture of the conceptual change necessary in each student.Los mapas evolutivos son estructuras que representan la red de itinerarios que pueden seguir los niños en la conceptualización de temas especÃficos (en el ámbito del pensamiento concreto). Están constituidos por el conjunto de integraciones posibilitadas por la sucesión de diferenciaciones que realiza el sujeto de un aspecto de su realidad observacional (a partir de la percepción). En este escrito presentamos su aplicación a un nuevo tema (el ciclo anual del movimiento del Sol en el cielo), incluida la contrastación experimental, lo que ha revelado una panoplia de concepciones infantiles, reforzado la validez y versatilidad de la metodologÃa, sugerido un mecanismo cognitivo de relevancia didáctica (los modelos observacionales deducidos) y proporcionado apoyo adicional a la necesidad de cimentar el aprendizaje infantil en la realidad empÃrica. Además, como todo mapa evolutivo, posibilita el diseño de objetivos y criterios de evaluación secuenciales coherentes con el desarrollo cognitivo, asà como la identificación de la arquitectura precisa del cambio conceptual necesario en cada aprendiz
The evolutionary map of the seasons
Los mapas evolutivos son estructuras que representan la red de itinerarios que pueden seguir los niños en la conceptualización de temas especÃficos (en el ámbito del pensamiento concreto). Están constituidos por el conjunto de integraciones posibilitadas por la sucesión de diferenciaciones que realiza el sujeto de un aspecto de su realidad observacional (a partir de la percepción). En este escrito presentamos su aplicación a un nuevo tema (el ciclo anual del movimiento del Sol en el cielo), incluida la contrastación experimental, lo que ha revelado una panoplia de concepciones infantiles, reforzado la validez y versatilidad de la metodologÃa, sugerido un mecanismo cognitivo de relevancia didáctica (los modelos observacionales deducidos) y proporcionado apoyo adicional a la necesidad de cimentar el aprendizaje infantil en la realidad empÃrica. Además, como todo mapa evolutivo, posibilita el diseño de objetivos y criterios de evaluación secuenciales coherentes con el desarrollo cognitivo, asà como la identificación de la arquitectura precisa del cambio conceptual necesario en cada aprendiz.Evolutionary maps (emaps) are structures that represent the network of itineraries that children may follow in the conceptualization of specific topics (within concrete thought). They consist of the set of integrations that are made possible by the succession of differentiations that subjects make from perceptual reality. In this paper, we present its application to a new topic (the annual cycle of the motion of the Sun in the sky), including the experimental test, which has revealed a panoply of children’s conceptions, strengthened the validity and versatility of the methodology, suggested a cognitive mechanism of pedagogical relevance (deduced observational models) and provided additional support to the need for basing children’s learning in empirical reality. In addition, as all emaps, it enables the design of sequential objectives and evaluation criteria consistent with cognitive development, as well as the identification of the precise architecture of the conceptual change necessary in each student
Ideas para una mayor formalización de la didáctica de las ciencias
La enseñanza por investigación es el método recomendado por la mayorÃa de especialistas en Didáctica de las Ciencias desde los albores de la disciplina. Sin embargo es fácilmente argúible que no existe un discurso coherente entre los distintos investigadores y que aún quedan muchas preguntas básicas por resolver. En este escrito proponemos un conjunto de ideas que pretenden contribuir a una mayor formalización de la Didáctica de las Ciencias, con especial atención a la enseñanza por investigación, y facilitar la respuesta a algunas de esas preguntas
Pulsed light inactivation of mushroom polyphenol oxidase: a fluorometric and spectrophotometric study
Polyphenol oxidase (PPO) is one of the most important food enzymes, it is responsible for the browning of many foods. Pulsed light (PL) is a non-thermal method of food preservation that is able to inactivate PPO. The aim of this work was to gain insight into the mechanism of PPO inactivation by PL. To this, the kinetics of PPO inactivation by PL was measured, together with associated changes in tryptophan fluorescence, KI fluorescence quenching and turbidity; and results were analysed by parameter A and phase diagram methods. Enzyme inactivation followed the Weibull model. Tryptophan fluorescence decreased during PL treatment, as well as the parameter A, while Stern-Volmer constants increased and turbidity was constant. The phase diagram showed only two populated states. There was a high correlation between the loss of activity and parameter A. Results indicate that under the experimental conditions, the inactivation of PPO by PL is an all-or-none process where the enzyme progressively unfolds with no evidence of aggregation.Fundación Universitaria San Antonio de CartagenaCiencias de la Alimentació
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