2,060 research outputs found
Two-Photon Total Annihilation of Molecular Positronium
The rate for complete two-photon annihilation of molecular positronium
Ps is reported. This decay channel involves a four-body collision among
the fermions forming Ps, and two photons of 1.022 MeV, each, as the final
state. The quantum electrodynamics result for the rate of this process is found
to be = 9.0
s. This decay channel completes the most comprehensive decay chart for
Ps up to date.Comment: 4 pages, 2figures and 1 tabl
Cooperation and competition in the wave of British student protests 2009-2011
This study analyses the impact that the dynamics of cooperation and competition of collective action had over the political trajectory of the wave of student protests in the UK between 2009 and 2011. Using an exploratory qualitative case study design, the research describes the political trajectory of the student conflict, analysing the relationships of alliance and competition between the main social movement organisations during the conflict. The study suggests that the presence of multiple factionalisms and a predominant competitive relationship between the leading organisations produced a fragmented social movement, which reduced the political impacts of the wave and extension of the protests
Using think-aloud interviews to characterize model-based reasoning in electronics for a laboratory course assessment
Models of physical systems are used to explain and predict experimental
results and observations. The Modeling Framework for Experimental Physics
describes the process by which physicists revise their models to account for
the newly acquired observations, or change their apparatus to better represent
their models when they encounter discrepancies between actual and expected
behavior of a system. While modeling is a nationally recognized learning
outcome for undergraduate physics lab courses, no assessments of students'
model-based reasoning exist for upper-division labs. As part of a larger effort
to create two assessments of students' modeling abilities, we used the Modeling
Framework to develop and code think-aloud problem-solving activities centered
on investigating an inverting amplifier circuit. This study is the second phase
of a multiphase assessment instrument development process. Here, we focus on
characterizing the range of modeling pathways students employ while
interpreting the output signal of a circuit functioning far outside its
recommended operation range. We end by discussing four outcomes of this work:
(1) Students engaged in all modeling subtasks, and they spent the most time
making measurements, making comparisons, and enacting revisions; (2) Each
subtask occurred in close temporal proximity to all over subtasks; (3)
Sometimes, students propose causes that do not follow logically from observed
discrepancies; (4) Similarly, students often rely on their experiential
knowledge and enact revisions that do not follow logically from articulated
proposed causes.Comment: 18 pages, 5 figure
Characterizing lab instructors' self-reported learning goals to inform development of an experimental modeling skills assessment
The ability to develop, use, and refine models of experimental systems is a
nationally recognized learning outcome for undergraduate physics lab courses.
However, no assessments of students' model-based reasoning exist for
upper-division labs. This study is the first step toward development of
modeling assessments for optics and electronics labs. In order to identify test
objectives that are likely relevant across many institutional contexts, we
interviewed 35 lab instructors about the ways they incorporate modeling in
their course learning goals and activities. The study design was informed by
the Modeling Framework for Experimental Physics. This framework conceptualizes
modeling as consisting of multiple subtasks: making measurements, constructing
system models, comparing data to predictions, proposing causes for
discrepancies, and enacting revisions to models or apparatus. We found that
each modeling subtask was identified by multiple instructors as an important
learning outcome for their course. Based on these results, we argue that test
objectives should include probing students' competence with most modeling
subtasks, and test items should be designed to elicit students' justifications
for choosing particular modeling pathways. In addition to discussing these and
other implications for assessment, we also identify future areas of research
related to the role of modeling in optics and electronics labs.Comment: 24 pages, 2 figures, 5 tables; submitted to Phys. Rev. PE
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