Risk, ambiguity, and diversification

Attitudes toward risk influence the decision to diversify among uncertain options. Yet, because in most situations the options are ambiguous, attitudes toward ambiguity may also play an important role. I conduct a laboratory experiment to investigate the effect of ambiguity on the decision to diversify. I find that diversification is more prevalent and more persistent under ambiguity than under risk. Moreover, excess diversification under ambiguity is driven by participants who stick with a status quo gamble when diversification among gambles is not feasible. This behavioral pattern cannot be accommodated by major theories of choice under ambiguity.

Syllable structures is modulating the optimal viewing position in visual word recognition. 'La estructura silábica modula la posición óptima de visualización en el reconocimiento visual de palabras'.

Resumen en español. Resumen basado en el de la publicación

Autoconcepto y motivación en el aprendizaje.

Hipótesis: entre los componentes de la motivación en el aprendizaje no aparece el autoconcepto, tal como ambos son medidos por el cuestionario de Ballif. No existe relación positiva entre rendimiento académico y autoconcepto. No existe diferencia significativa en las puntuaciones en autoconcepto entre un grupo experimental y dos control, después de la segunda medición. 760 alumnos de sexto, séptimo y octavo de EGB, pertenecientes a dos centros públicos, dos Centros privados y una Ikastola. 75 alumnos de sexto de EGB, divididos en tres grupos: experimental o de tareas, control I o de juegos y control II. En esta investigación se pretende comprobar la presencia del autoconcepto entre los componentes de la motivación en el aprendizaje tal y como es descrita por Ballif -cuyo modelo se ha aplicado-; las relaciones del autoconcepto con el rendimiento académico y la posibilidad de mejorar el autoconcepto mediante un conjunto de tareas diseñadas con este fin, y comprobar que su mejora se refleja en la motivación en el aprendizaje. Especial atención se ha prestado a las relaciones entre autoconcepto y motivación tal como las abordan Markus y Nurius desde una perspectiva cognitiva. El autoconcepto se ha enfocado desde aquellos trabajos realizados durante la última década que sugieren implícita o explícitamente su conexión con la motivación. Variables: autoconcepto, motivación -actividad instrumental, atractivo escolar-, rendimiento académico. Cuestionario de Ballif -adaptación de la forma 'B' del Mocos -Motivation Components for Learning in School-. Test de lectura de J. Pérez González. Pruebas de comprensión y velocidad lectora -cursos sexto, séptimo y octavo-. Calificaciones de dos evaluaciones -inmediatamente anterior y la posterior a la experiencia-. Análisis factorial de componentes principales, rotación Varimax y especificación de tres factores. Coeficiente de correlación 'R' de Pearson. Análisis de varianza simple. Contraste 'T' de Wilcoxon. Coeficiente Alpha de Cronbach. Se confirma la presencia del autoconcepto académico entre los componentes de la motivación en el aprendizaje en los alumnos del Ciclo Superior de EGB. Aparecen también 'la actvidad instrumental' y 'el atractivo escolar' como componentes de la motivación en el aprendizaje. La correlación entre autoconcepto académico y rendimiento es positiva y altamente significativa. Además se comprueba la mejora del autoconcepto por medio de tareas diseñadas con este fin. Dicha mejora supone un incremento de la motivación en el aprendizaje. Los resultados de este estudio indican que un estudiante puede mejorar su autoconcepto si participa en actividades escolares diseñadas con este fin, que la motivación en el aprendizaje puede 'enseñarse en el aula', y que la mejora del autoconcepto se refleja en la motivación e influye significativamente en el rendimiento. Se abre un campo de trabajo en el autoconcepto a través de actividades escolares convenientemente diseñadas.

Pensar y actuar con espíritu empresarial : una tarea de formación para Europa.

El artículo pertenece a una sección de la revista dedicada a artículos de opinión. - Notas a pie de página. - A modo de anexo se incluye análisis de la bibliografía sobre cualificaciones empresariales. - Resumen tomado parcialmente de la revista.

The impact of global warming on the tropical Pacific Ocean and El Niño

The El Niño–Southern Oscillation (ENSO) is a naturally occurring fluctuation that originates in the tropical Pacific region and affects ecosystems, agriculture, freshwater supplies, hurricanes and other severe weather events worldwide. Under the influence of global warming, the mean climate of the Pacific region will probably undergo significant changes. The tropical easterly trade winds are expected to weaken; surface ocean temperatures are expected to warm fastest near the equator and more slowly farther away; the equatorial thermocline that marks the transition between the wind-mixed upper ocean and deeper layers is expected to shoal; and the temperature gradients across the thermocline are expected to become steeper. Year-to-year ENSO variability is controlled by a delicate balance of amplifying and damping feedbacks, and one or more of the physical processes that are responsible for determining the characteristics of ENSO will probably be modified by climate change. Therefore, despite considerable progress in our understanding of the impact of climate change on many of the processes that contribute to El Niño variability, it is not yet possible to say whether ENSO activity will be enhanced or damped, or if the frequency of events will change.

Nonspherical assemblies generated from polystyrene-b-poly(L-lysine) polyelectrolyte block copolymers

This report describes the aqueous solution self-assembly of a series of polystyrene(m)-b-poly(L-lysine)n block copolymers (m = 8-10; n = 10-70). The polymers are prepared by ring-opening polymerization of epsilon-benzyloxycarbonyl-L-lysine N-carboxyanhydride using amine terminated polystyrene macroinitiators, followed by removal of the benzyloxycarbonyl side chain protecting groups. The critical micelle concentration of the block copolymers determined using the pyrene probe technique shows a parabolic dependence on peptide block length exhibiting a maximum at n = approximately 20 (m = 8) or n = approximately 60 (m = 10). The shape and size of the aggregates has been studied by dynamic and static light scattering, small-angle neutron scattering (SANS), and analytical ultracentrifugation (AUC). Surprisingly, Holtzer and Kratky analysis of the static light scattering results indicates the presence of nonspherical, presumably cylindrical objects independent of the poly(L-lysine)n block length. This is supported by SANS data, which can be fitted well by assuming cylindrical scattering objects. AUC analysis allows the molecular weight of the aggregates to be estimated as several million g/mol, corresponding to aggregation numbers of several 10s to 100s. These aggregation numbers agree with those that can be estimated from the length and diameter of the cylinders obtained from the scattering results.

Ferric and ferrous iron in nitroso-myoglobin: computer simulations of stable and metastable states and their infrared spectra

The binding of NO to iron is involved in the biological function of many heme proteins. Contrary to ligands like CO and O-2, which only bind to ferrous (Fe-II) iron, NO binds to both ferrous and ferric (Fe-II) iron. In a particular protein, the natural oxidation state can therefore be expected to be tailored to the required function. Herein, we present an ob initio potential-energy surface for ferric iron interacting with NO. This potential-energy surface exhibits three minima corresponding to eta'-NO coordination (the global minimum), eta(1)-ON coordination and eta(2) coordination. This contrasts with the potential-energy surface for Fe-II-NO, which ex- hibits only two minima (the eta(2) coordination mode for Fe-II is a transition state, not a minimum). In addition, the binding energies of NO are substantially larger for Fe-III than for Fe-II. We have performed molecular dynamics simulations for NO bound to ferric myoglobin (Mb(III)) and compare these with results obtained for Mb(II). Over the duration of our simulations (1.5 ns), all three binding modes are found to be stable at 200 K and transiently stable at 300 K, with eventual transformation to the eta(1)-NO global-minimum conformation. We discuss the implication of these results related to studies of rebinding processes in myoglobin.

Potential energy surface and moleculardynamics of MbNO: existence of an unsuspected FeON minimum

Ligands such as CO, O2, or NO are involved in the biological function of myoglobin. Here we investigate the energetics and dynamics of NO interacting with the Fe(II) heme group in native myoglobin using ab initio and molecular dynamics simulations. At the global minimum of the ab initio potential energy surface (PES), the binding energy of 23.4 kcal/mol and the Fe-NO structure compare well with the experimental results. Interestingly, the PES is found to exhibit two minima: There exists a metastable, linear Fe-O-N minimum in addition to the known, bent Fe-N-O global minimum conformation. Moreover, the T-shaped configuration is found to be a saddle point, in contrast to the corresponding minimum for NO interacting with Fe(III). To use the ab initio results for finite temperature molecular dynamics simulations, an analytical function was fitted to represent the Fe-NO interaction. The simulations show that the secondary minimum is dynamically stable up to 250 K and has a lifetime of several hundred picoseconds at 300 K. The difference in the topology of the heme-NO PES from that assumed previously (one deep, single Fe-NO minimum) suggests that it is important to use the full PES for a quantitative understanding of this system. Why the metastable state has not been observed in the many spectroscopic studies of myoglobin interacting with NO is discussed, and possible approaches to finding it are outlined.

Diastereoselective formation of 2-aryl-3-arenesulfonyl 4-ethyl-1,3-oxazolidines: an X-ray crystallographic and 1H NMR study

N-Arylsulfonamides of (R)- and (S)-2-amino-1-butanol, on condensation with aromatic aldehydes produced diastereomerically pure 2-aryl-3-arenesulfonyl 4-ethyl-1,3-oxazolidines. The absolute configurations of one enantiomeric pair have been determined from two fully refined X-ray structures, supplemented by nmr data.