We report some of the common, prevalent conceptual resources that students used to reason about energy, based on our analysis of written responses to questions given to 807 introductory physics students. These resources include, for example, associating forms of energy with indicators, relating forces and energy, and representing energy quantitatively. This research responds to a need for large-scale, resourcesoriented research on students' conceptual understanding and has the potential to support the development of an underexplored dimension of pedagogical content knowledge-knowledge of student resources for understanding energy. Our aim is to promote instructor take-up of the resources theory of knowledge, and we suggest a number of ways in which instructors might capitalize on the resources we report.

Much of the literature contributing to physics instructors' knowledge of student ideas (KSI) reports common patterns of reasoning that are framed as discontinuous with canonical concepts. Our work contributes new KSI about mechanical wave propagation from a resources perspective, framing student thinking in terms of context-sensitive pieces of knowledge that are continuous with canonical physics concepts. The intent of this work is to inform instruction on mechanical waves by identifying and illustrating some of the conceptual resources that instructors might expect their students to use. To support instructor predictions about student thinking, we identify resources that are common across multiple samples and questions. Our data include written responses to three versions of a conceptual question about mechanical pulse propagation. We use an emergent coding scheme to characterize a total of 851 written responses from 6 universities in the United States. Our analysis reveals three common conceptual resources: (i) properties of the medium either impede or facilitate the motion of the pulse, (ii) the speed or duration of transverse motion affects pulse speed, and (iii) the speed of the pulse is affected by its kinetic energy. We show how each of these resources can be viewed as continuous with formal understandings of pulse propagation.

In this paper, we begin to explore the role of content knowledge in responsive teaching (RT), using in situ data to draw out and speak to a latent disagreement within the literature. We claim that one role that content knowledge plays in RT is to support teachers in eliciting, seeing, and then pursuing disciplinary connections within their students' thinking. We suggest an approach to teacher education that draws on the historical wisdom of the physics education research community, in which teachers develop content knowledge and then practice using that knowledge to listen and respond to student thinking.

"Content knowledge for teaching" is the specialized content knowledge that teachers use in practicethe content knowledge that serves them for tasks of teaching such as revoicing students' ideas, choosing an instructional activity to address a student misunderstanding, and evaluating student statements. We describe a methodology for selecting and analyzing classroom episodes showing content knowledge for teaching about energy (CKT-E), and illustrate this methodology with examples from high school physics instruction. Our work has implications for research on teacher knowledge and for professional development that enhances teacher CKT-E.

A general method for aligning bent-core smectic liquid crystal materials is described. Alternating electric fields between interdigitated electrodes patterned on one cell surface create torques on the liquid crystal that result in uniform "bookshelf" orientation of the smectic layers. The aligned cell can then be driven in the conventional way by applying an electric field between all of the stripe electrodes connected together and a monolithic electrode on the other cell surface. Fast, analog, optical phase-only modulation is demonstrated in a device containing a polar, bent-core SmAP F material aligned using this technique. V C 2015 AIP Publishing LLC.