Inconsistent Conceptions of Acceleration Contributing to Formative Assessment Limitations

Science, technology, engineering, and mathematics (STEM) education has become a national priority in light of measures indicating marginal student interest and success in the United States. Just as evidence is integral to policy decisions, so too do teachers depend on evidence to inform instructional choices. Classroom assessment remains a touchstone means of gathering such evidence as indicators of students’ progress, and increasingly, teachers are designing, implementing, and interpreting assessments in collaboration with one another. In rural Maine, the work of the Maine Physical Sciences Partnership (MainePSP) has enabled science educators to come together as a supportive professional community. We focused on a team of MainePSP teachers as they developed common assessments for a unit on force and motion concepts. During group discussions individual members vetted their own ideas about acceleration comprising the following perspectives: a) terminology used to describe acceleration, b) the sign of acceleration as an indicator of speeding up or slowing down, and c) the sign of acceleration as an indicator of direction, dependent on the change in both the magnitude and direction of velocity. The latter two ideas could be in agreement (when motion is in the positive direction) or conflict (when motion is in the negative direction). With objectives to accomplish and limited time, the team opted to only include an item about motion in the positive direction, leaving the inconsistencies of their ideas unresolved. As a result, the assessment lacked the ability to provide sufficient evidence of which idea students might hold. We examined the group’s interactions as captured by video recording and employed basic qualitative methods to analyze the event as a case study. Our findings suggest that an incomplete understanding of acceleration limited the teachers’ ability to resolve their initial conflict. Further, the item’s susceptibility for students to provide correct answers for the wrong reasons was not recognized at the time. We consider the item’s implications on teachers interpreting student assessment responses, masking a potential need for adjusted instruction by teachers and conceptual refinement by students. Finally, we discuss the pedagogical implications and limitations of this study

Discovery of very high energy gamma-rays from the flat spectrum radio quasar 3C 279 with the MAGIC telescope

3C 279 is one of the best studied flat spectrum radio quasars located at a comparatively large redshift of z = 0.536. Observations in the very high energy band of such distant sources were impossible until recently due to the expected steep energy spectrum and the strong gamma-ray attenuation by the extragalactic background light photon field, which conspire to make the source visible only with a low energy threshold. Here the detection of a significant gamma-ray signal from 3C 279 at very high energies (E > 75 GeV) during a flare in early 2006 is reported. Implications of its energy spectrum on the current understanding of the extragalactic background light and very high energy gamma-ray emission mechanism models are discussed.Comment: 4 pages, 6 figures, submitted to proceedings of "4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy 2008

On the Core of Dynamic Cooperative Games

We consider dynamic cooperative games, where the worth of coalitions varies over time according to the history of allocations. When defining the core of a dynamic game, we allow the possibility for coalitions to deviate at any time and thereby to give rise to a new environment. A coalition that considers a deviation needs to take the consequences into account because from the deviation point on, the game is no longer played with the original set of players. The deviating coalition becomes the new grand coalition which, in turn, induces a new dynamic game. The stage games of the new dynamical game depend on all previous allocation including those that have materialized from the deviating time on. We define three types of core solutions: fair core, stable core and credible core. We characterize the first two in case where the instantaneous game depends on the last allocation (rather than on the whole history of allocations) and the third in the general case. The analysis and the results resembles to a great extent the theory of non-cooperative dynamic games.Comment: 25 page