Creating spaces for pedagogy : research as learning

As teacher-educators, the authors designed and implemented a small study that mapped teacher-education students\u27 understandings of their own identities and how they made sense of ethnicity and class differences among their secondary students while on teaching rounds. While the authors did not set out to \u27teach\u27 their research participants, it was during the analysis of data from the research project, that they began to realise the potential of research to create opportunities for learning. In this paper the authors speculate on the \u27conditions\u27 of knowledge production and suggest that the dialogic nature of interviews and focus group discussions can offer pedagogical spaces for learning. Research designs that incorporate opportunities for participants to re-tell narratives over periods of time, may position participants as experts in knowledge production and may reposition them and researchers in more equitable power relations. The authors present an example of one participant\u27s narrative together with their interpretations to explore how research potentially offers \u27evidence\u27 of learning. While this is tentative only, the authors suggest there is a need to create spaces for pedagogy in the design and execution of educational research.<br /

A simple and robust method to study after-pulses in Silicon Photomultipliers

The after-pulsing probability in Silicon Photomulti- pliers and its time constant are obtained measuring the mean number of photo-electrons in a variable time window following a light pulse. The method, experimentally simple and statistically robust due to the use of the Central Limit Theorem, has been applied to an HAMAMATSU MPPC S10362-11-100C

Troubling identities : teacher education students\u27 constructions of class and ethnicity

This paper reports on a research project that explored how student teachers understand ethnic and classed difference as it relates to themselves and their students. Discourses of schooling can shape students ethnic and classed identities, frequently positioning non-mainstream students as \u27other\u27 and marginalizing them. Significant numbers of our teacher education students have limited experience of diverse educational settings, having mainly attended white middle-class schools as students and as student teachers. Working with diverse student populations productively depends on teachers recognising and valuing difference. The ways in which they engage with students whose ethnic and classed identities are different from their own is important in creating learning environments that build on and engage with diversity.In a preliminary stage of the research we asked eight third-year teacher education students to explore their own ethnic and classed identities. The complexities of identity are foregrounded in both the assumptions we made in selecting particular students for the project and in the ways they did (not) think about themselves as having ethnic or classed identities.In this paper we draw on these findings to interrogate how categories of identity are fluid, shifting and ongoing processes of negotiation: troubling and complex. We also consider the implications for teacher education.<br /

Making sense of difference? Teaching identities in postmodern contexts

How do teachers make sense of ethnic and classed differences? Frequently students from non-mainstream cultures and of lower socio-economic status are constructed in the literature and through practice as &lsquo;deficit&rsquo; and consequently become marginalised. A range of short-term, &lsquo;quick fix&rsquo; policy and curriculum approaches have aimed to address the &lsquo;problems&rsquo; of those &lsquo;othered&rsquo; from the mainstream due to their perceived difference. These have had little effect on improving educational results for students of specific ethnic and/or class backgrounds whose outcomes remain below the national average.Poststructural theories offer opportunities to think about how teachers are positioned within discourses of identity. Our research (and others&rsquo;) suggests the need for teachers to interrogate their assumptions about class and culture and how these are played out in their pedagogical relationships with students.In this paper we report on a small research project that investigates the professional practices and personal beliefs of teachers. Empirical data from this study will build knowledge about how difference is constructed and diversity is &lsquo;taken up&rsquo; by teachers as they engage with secondary students who have Language Backgrounds Other Than English and who are economically disadvantaged.<br /

AFM Dissipation Topography of Soliton Superstructures in Adsorbed Overlayers

In the atomic force microscope, the nanoscale force topography of even complex surface superstructures is extracted by the changing vibration frequency of a scanning tip. An alternative dissipation topography with similar or even better contrast has been demonstrated recently by mapping the (x,y)-dependent tip damping but the detailed damping mechanism is still unknown. Here we identify two different tip dissipation mechanisms: local mechanical softness and hysteresis. Motivated by recent data, we describe both of them in a onedimensional model of Moire' superstructures of incommensurate overlayers. Local softness at "soliton" defects yields a dissipation contrast that can be much larger than the corresponding density or corrugation contrast. At realistically low vibration frequencies, however, a much stronger and more effective dissipation is caused by the tip-induced nonlinear jumping of the soliton, naturally developing bistability and hysteresis. Signatures of this mechanism are proposed for experimental identification.Comment: 5 pages, 5 figures, Phys Rev B 81, 045417 (2010

Solitons and exact velocity quantization of incommensurate sliders

We analyze in some detail the recently discovered velocity quantization phenomena in the classical motion of an idealized one-dimensional solid lubricant, consisting of a harmonic chain interposed between two periodic sliders. The ratio w = v_cm/v_ext of the chain center-of-mass velocity to the externally imposed relative velocity of the sliders is pinned to exact ``plateau'' values for wide ranges of parameters, such as sliders corrugation amplitudes, external velocity, chain stiffness and dissipation, and is strictly determined by the commensurability ratios alone. The phenomenon is caused by one slider rigidly dragging the density solitons (kinks/antikinks) that the chain forms with the other slider. Possible consequences of these results for some real systems are discussed.Comment: 12 pages 6 figures. Small fixup after Referee's comments. In print in J. Phys.: Condens. Matte

Hysteresis from dynamically pinned sliding states

We report a surprising hysteretic behavior in the dynamics of a simple one-dimensional nonlinear model inspired by the tribological problem of two sliding surfaces with a thin solid lubricant layer in between. In particular, we consider the frictional dynamics of a harmonic chain confined between two rigid incommensurate substrates which slide with a fixed relative velocity. This system was previously found, by explicit solution of the equations of motion, to possess plateaus in parameter space exhibiting a remarkable quantization of the chain center-of-mass velocity (dynamic pinning) solely determined by the interface incommensurability. Starting now from this quantized sliding state, in the underdamped regime of motion and in analogy to what ordinarily happens for static friction, the dynamics exhibits a large hysteresis under the action of an additional external driving force F_ext. A critical threshold value F_c of the adiabatically applied force F_ext is required in order to alter the robust dynamics of the plateau attractor. When the applied force is decreased and removed, the system can jump to intermediate sliding regimes (a sort of ``dynamic'' stick-slip motion) and eventually returns to the quantized sliding state at a much lower value of F_ext. On the contrary no hysteretic behavior is observed as a function of the external driving velocity.Comment: 12 pages, 5 figures, ECOSS 200

Sliding Over a Phase Transition

The effects of a displacive structural phase transition on sliding friction are in principle accessible to nanoscale tools such as the Atomic Force Microscopy, yet they are still surprisingly unexplored. We present model simulations demonstrating and clarifying the mechanism and potential impact of these effects. A structural order parameter inside the material will yield a contribution to stick-slip friction that is nonmonotonic as temperature crosses the phase transition, peaking at the critical Tc where critical fluctuations are strongest, and the sliding-induced order parameter local flips from one value to another more numerous. Accordingly, the friction below Tc is larger when the order parameter orientation is such that flips are more effectively triggered by the slider. The observability of these effects and their use for friction control are discussed, for future application to sliding on the surface of and ferro- or antiferro-distortive materials.Comment: Accepted on PR

An exact approach to the dynamics of locally-resonant beams

Abstract This paper presents an exact analytical approach to calculate the dynamic response of elastic beams with periodically-attached resonators, generally referred to as locally-resonant beams. Showing that a typical resonator is equivalent to an external constraint, whose reaction force on the beam depends on the deflection of the application point through a pertinent frequency-dependent stiffness, the beam-resonators coupled system is handled using only the beam motion equation, with Dirac's deltas modelling the shear-force discontinuities associated with the reaction forces of the resonators. This is the basis to tackle the dynamics of infinite as well as finite beams, the first by a transfer matrix method to calculate frequency band gaps, the second by a generalized function approach. The dynamics of the finite beam is studied in frequency and time domains deriving the exact frequency response and the exact modal response, including modal frequency and impulse response functions. The proposed approach is formulated for arbitrary number of resonators and loads, and applies for both non-proportional and proportional damping