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The present study tests the effect of ability pairing in two instructional methods in L2 collaborative revision. Two continuous indices determine a pair: individual proficiency level, distance in proficiency between pair members (heterogeneity), and the interaction between both indices. Instructional methods tested are modelling and practising. Results show that the effect of pair composition depends on instructional strategies. In the Practising condition less proficient learners profit most from a heterogeneous ability pair, whereas more proficient learners are best paired homogeneously. In the Modelling

Insights from scientific reading research only partially resonate in Dutch teaching materials for reading comprehension, and hence in the classroom. As an attempt to bridge the gap between science and educational practice, a design-based research was conducted in which four primary school teachers translated four researcher-provided design principles into practice. In two successive design cycles, the teachers designed and implemented lessons on informational text structures, under supervision of two researchers. The aim of the study was to gain insight into the viability of the design principles and into the level of support teachers need in order to become effective co-designers. Based on data from lesson artefacts, teacher logbooks, panel interviews and lesson observations, we found that the teachers experienced several implementation difficulties. These difficulties were partially due to the fact that there was a tension between two design principles, and that one design principle needed refinement. However, in most cases, the implementation difficulties could be explained by teachers’ limited pedagogical content knowledge. As a result, the teachers needed a high level of support, especially in text selection and revision. Teacher beliefs and habits also interfered with the implementation of the design principles, especially when it came to the importance of working with authentic texts, and teachers’ views on effective modeling.Our study raises questions about the feasibility of equal participation of researchers and teachers at the start of a DBR project, but also shows how DBR can successfully contribute to teacher professionalization if researchers provide adequate support throughout the design process.

Magnetohydrodynamic propulsion systems for submarines offer several significant advantages over conventional propeller propulsion systems. These advantages include the potential for greater stealth characteristics, increased maneuverability, enhanced survivability, elimination of cavitation limits, greater payload capability, and the addition of a significant emergency propulsion system. These advantages can be obtained with a magnetohydrodynamic propulsion system that is neutrally buoyant and can operate with the existing submarine propulsion system power plant. A thorough investigation of magnetohydrodynamic propulsion systems for submarine applications has been completed. During the investigation, a number of geometric configurations were examined. Each of these configurations and mounting concepts was optimized for maximum performance for a generic attack class submarine. The optimization considered each thruster individually by determining the optimum operating characteristics for each one and accepting only those thrusters that result in a neutrally buoyant propulsion system. The results of this detailed optimization study show that the segmented, annular thruster is the concept with the highest performance levels and greatest efficiency and offers the greatest potential for a practical magnetohydrodynamic propulsion system for attack class submarines. The optimization study results were used to develop a specific point design for a segmented, annular magnetohydrodynamic thruster for an attack class submarine. The design point case has shown that this thruster may be able to provide the necessary thrust to propel an attack class submarine at the required velocity with the potential for a substantial acoustic signature reduction within the constraints of the existing submarine power plant and the maintenance of neutral buoyancy. This innovative magnetohydrodynamic propulsion system offers an approach for submarine propulsion that can be an important contribution to the development of the submarine force of the next century.

Inflectional morphology causes persistent difficulties for second language (L2) learners (Montrul, Silvina & Kim Potowski. 2007. Command of gender agreement in school-age Spanish-English bilingual children. International Journal of Bilingualism 11(3). 301–328; Montrul, Silvina, Israel de la Fuente, Justin Davidson & Rebecca Foote. 2013. The role of experience in the acquisition and production of diminutives and gender in Spanish: Evidence from L2 learners and heritage speakers. Second Language Research 29(1). 87–118). Learners operate with a default gender value, and overgeneralize the masculine forms of determiners and modifiers (White, Lydia, Elena Valenzuela, Martyna Kozlowska-Macgregor & Ingrid Leung. 2004. Gender and number agreement in nonnative Spanish. Applied Psycholinguistics 25(1). 105–133; Schlig 2003). 111 essays written were collected containing 799 correct uses and 281 errors from Dutch students whose written ability in Spanish is A2 (Common European Framework). The results show that singular masculine nominal agreement marking at the determiner is significantly better produced by Dutch L2 learners of Spanish than when the marking of nominal agreement is plural, feminine or at the adjective. This study corroborates the previous results where learners operate with a default gender value and overgeneralize the masculine forms of determiners. Also these results show that L2 learners of Spanish are significantly less accurate in gender agreement with adjectives than with determiners.