Una estrategia de cambio conceptual en la enseñanza de la física : la resolución de problemas como actividad de investigación

We present in this paper the main results of a research aimed at the study of a learninglteaching process directed to familiarise the students with a researching methodology of open problem solving centered in the Physics field. We have studied how this process favours in the students a conceptual change, incardinated in the learning constructivist theory and whether this change lasts with time and is joined by a positive attitude towards the scientific learning

Liquid phase epitaxy and optical investigation of KYb(WO4)2 thin layers

In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm [1], which provides high efficiency and reduced heat generation. Of high practical interest is the thin-disk laser concept [2], which possesses a tremendous advantage over rod lasers because of its axial-cooling approach and consequent weak thermal lensing and good beam quality.\ud A promising material for Yb3+ thin-disk lasers is KYb(WO4)2 (KYbW) [3]. It can be grown from high-temperature solutions [4]. Nevertheless, the growth of high-quality, single-crystalline layers with thickness in the range of the absorption length of ~13 µm at 981 nm has as yet not been reported. A suitable substrate material is KY(WO4)2 (KYW), but the relatively large differences in the thermal expansion coefficients between KYW and KYbW along the [100], [001], and especially [010] directions [5] favor low temperatures for the hetero-epitaxial growth.\ud For the first time, we demonstrate liquid phase epitaxy (LPE) of KYbW layers. The layers were grown at start temperatures as low as 520°C, which is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. KY1-xYbx(WO4)2 layers with varying x = 0.03-1.00 were grown by LPE. The chloride solvent consisted of the eutectic composition [6] 24.4 mol.% KCl, 30.4 mol.% NaCl, and 42.2 mol.% CsCl. The growth temperature spanned the range from 580 to 500°C and the cooling rate was 0.67-1.00 Kh-1. Crack-free, transparent KYbW layers were grown on (010) substrates.\ud Spectroscopic investigations have shown that the lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [4]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud \ud [1] T.Y. Fan, IEEE J. Quantum Electron. 29, 1457 (1993).\ud [2] A. Giesen, H. Hügel, A. Voss, K. Wittig, U. Brauch, H. Opower, Appl. Phys. B 58, 365 (1994).\ud [3] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 74, 185 (2002).\ud [4] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 65, 165121 (2002).\ud [5] M.C. Pujol, X. Mateos, R. Solé, J. Massons, J. Gavaldà, F. Díaz, M. Aguiló, Mater. Sci. Forum 378-381, 710 (2001).\ud [6] D. Ehrentraut, M. Pollnau, S. Kück, Appl. Phys. B 75, 59 (2002)

Liquid phase epitaxy and spectroscopic investigation of optically active KYb(WO4)2 thin layers

In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm, which provides high efficiency and reduced heat generation. A promising material for Yb3+ lasers is KYb(WO4)2 (KYbW) [1]. It can be grown from high-temperature solutions [2]. A suitable substrate material for the growth of single-crystalline layers with thicknesses in the range of the absorption length of ~13 µm at 981 nm is KY(WO4)2 (KYW).\ud We demonstrate the liquid phase epitaxy (LPE) of KYbW layers at start temperatures as low as 520°C from the chloride solvent KCl-NaCl-CsCl. This temperature is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented KYW substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. Our spectroscopic investigations show that the fluorescence lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [2]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud \ud [1] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 2002, 74, 185\ud [2] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 2002, 65, 16512

Identificación y chequeo de parentesco en la especie canina mediante análisis de ADN

Este trabajo presenta los primeros resultados en España de un estudio de identificación y chequeo de parentesco en la especie canina mediante microsatélites (polimorfismos del ADN). Para este trabajo se han utilizado 79 animales, 48 de los cuales no están emparentados y 31 que pertenecen a 3 familias, en los que Se han analizado 11 microsatélites. Los resultados indican la posibilidad de utilizar estos marcadores en test de paternidad con resultados altamente fiables (99%), si se utilizan más de 7 microsatélites.This work presents the first results in Spain of an study concerning identity and parentage test in dogs by microsatellites (ONA polymorphisms). 79 animals have been used for this work, (48 unrelated dogs and 31 dogs from 3 families). Our main conclusion is the necessity of using more than 7 microsatellites in arder to obtain results with 99% of garanty

Un estudio comparativo sobre el pensamiento profesional y la "acción docente" de los profesores de ciencias de Educación Secundaria. Parte II

Este artículo es la segunda parte de una investigación más amplia sobre el pensamiento del profesor (Martínez et al., 2001). En este caso el estudio gira en torno al análisis de las diferencias y similitudes entre dos muestras de profesores de ciencias de educación secundaria que difieren en sus años de docencia y en su trayectoria profesional, definida por la realización de cursos de formación permanente de alta cualificación científica y didáctica. En un primer apartado se analizan facetas relacionadas con la motivación y la satisfacción en la realización de su tarea, la manera de entender la formación del profesor y sus percepciones sobre diferentes factores profesionales. A continuación se aborda lo que «dicen hacer» en relación a aspectos curriculares referidos a contenidos, metodología y evaluación. A partir del análisis de las respuestas a los cuestionarios elaborados se plantean una serie de reflexiones que buscarían mejorar el «desarrollo profesional» de este colectivo de profesores.This article is a part of a wider research on secondary science teachers' beliefs. Through the use of a questionnaire data were obtained from 103 secondary science teachers in service with different degrees of experience. Analysis of data are discussed in terms of their implication in teacher training in service

Estudio de la capacidad estabilizadora del peroné en fracturas de tibia de conejo

El objetivo de este trabajo es estudiar la capacidad estabilizadora del peroné en fracturas de tibia. Si dicha capacidad es suficiente, sería posible evitar el uso de sistemas de fijación en los experimentos de laboratorio con este tipo de fracturas. Para comprobarlo se ha realizado una simulación computacional por elementos finitos de la tibia y el peroné de un conejo, con una fractura en el tercio medio superior de la diáfisis sin ningún elemento estabilizador. El conjunto ha sido sometido a las cargas más desfavorables del proceso de salto comprobándose que en este caso el peroné fracturaría en su parte inferior del mismo modo que sucede en la experimentación en laboratorio

¿Qué pensamiento profesional y curricular tienen los futuros profesores de ciencias de Secundaria?

This article is a part of a wider research on secondary science teachers' beliefs. Through the use of a questionnaire data were obtained from 211 secondary science teacher candidates. Analyses of data are discussed in terms of their implication in science teacher education

Evidence-based selection on the appropriate FIT cut-off point in CRC screening programs in the COVID pandemic

Background: The COVID pandemic has forced the closure of many colorectal cancer (CRC) screening programs. Resuming these programs is a priority, but fewer colonoscopies may be available. We developed an evidence-based tool for decision-making in CRC screening programs, based on a fecal hemoglobin immunological test (FIT), to optimize the strategy for screening a population for CRC. Methods: We retrospectively analyzed data collected at a regional CRC screening program between February/2014 and November/2018. We investigated two different scenarios: not modifying vs. modifying the FIT cut-off value. We estimated program outcomes in the two scenarios by evaluating the numbers of cancers and adenomas missed or not diagnosed in due time (delayed). Results: The current FIT cut-off (20-mu g hemoglobin/g feces) led to 6, 606 colonoscopies per 100, 000 people invited annually. Without modifying this FIT cut-off value, when the optimal number of individuals invited for colonoscopies was reduced by 10-40%, a high number of CRCs and high-risk adenomas (34-135 and 73-288/100.000-people invited, respectively) will be undetected every year. When the FIT cut-off value was increased to where the colonoscopy demand matched the colonoscopy availability, the number of missed lesions per year was remarkably reduced (9-36 and 29-145/100.000 people, respectively). Moreover, the unmodified FIT scenario outcome was improved by prioritizing the selection process based on sex (males) and age, rather than randomly reducing the number invited. Conclusions: Assuming a mismatch between the availability and demand for annual colonoscopies, increasing the FIT cut-off point was more effective than randomly reducing the number of people invited. Using specific risk factors to prioritize access to colonoscopies should be also considered

Compounds from multilayer plastic bags cause reproductive failures in artificial insemination

High levels of reproductive failure were detected in some Spanish sow farms in the Spring of 2010. Regular returns to estrus and variable reductions in litter size were observed. The problem started suddenly and did not appear to be related to the quality of the ejaculates, disease, alterations of body condition or any other apparent reasons. Subsequent studies determined that the problem was the origin of the plastic bags used for semen storage. Chemical analysis of the suspicious bags identified unexpected compounds such as BADGE, a cyclic lactone and an unknown phthalate that leached into the semen at concentrations of 0.2 to 2.5 mg/L. Spermatozoa preserved in these bags passed all of the routine quality control tests, and no differences were observed between storage in the control and suspicious bags (p . 0.05). In vitro fecundation tests and endocrine profiler panel analysis (EPP) did not show any alterations, whereas the in vivo tests confirmed the described failure. This is the first described relationship between reproductive failure and toxic compounds released from plastic bags