University of Exeter

About: University of Exeter is a education organization based out in Exeter, United Kingdom. It is known for research contribution in the topics: Population & Climate change. The organization has 15820 authors who have published 50650 publications receiving 1793046 citations. The organization is also known as: Exeter University & University of the South West of England.

Iterative learning control using optimal feedback and feedforward actions

Abstract: An algorithm for iterative learning control is developed on the basis of an optimization principle which has been used previously to derive gradient-type algorithms. The new algorithm has numerous benefits which include realization in terms of Riccati feedback and feedforward components. This realization also has the advantage of implicitly ensuring automatic step size selection and hence guaranteeing convergence without the need for empirical choice of parameters. The algorithm is expressed as a very general norm optimization problem in a Hilbert space setting and hence, in principle, can be used for both continuous and discrete time systems. A basic relationship with almost singular optimal control is outlined. The theoretical results are illustrated by simulation studies which highlight the dependence of the speed of convergence on parameters chosen to represent the norm of the signals appearing in the optimization problem.

Long-range surface modes supported by thin films

Abstract: A detailed analysis of the surface modes of a thin slab of material of dielectric constant ${\mathrm{\ensuremath{\epsilon}}}_{2}$ (=${\mathrm{\ensuremath{\epsilon}}}_{\mathit{r}2}$-i${\mathrm{\ensuremath{\epsilon}}}_{\mathit{i}2}$) surrounded symmetrically by dielectric media is presented. Results show that in the thin-film limit, as well as the well-known long-range surface plasmon for a thin metal layer and the TM guided mode for a thin dielectric, a long-range surface mode exists for almost any value of ${\mathrm{\ensuremath{\epsilon}}}_{2}$. This is even true if the imaginary part of ${\mathrm{\ensuremath{\epsilon}}}_{2}$, ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{i}2}$, is much larger than the real part ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{r}2}$. We also find that a long-range surface mode may arise from the coupling between two surfaces which individually cannot support a surface mode. These are a pair of special coupled-surface modes which may exist below a certain critical film thickness and which have two separate propagation vectors each with the same field symmetry. It is also found that the inverse situation may pertain, that is for certain relative values of dielectric constants even though ordinary surface modes may exist, below a critical thickness the resulting coupled long-range mode no longer exists. The analysis has also been extended to practical situations with weakly absorbing surrounding media and to circumstances where the dielectric constants of the surrounding media are slightly different. Both of these effects modify the dispersion relations obtained for the simple case and introduce further limit thicknesses into the problem. Analytic formulas in the thin-film limit are presented for all the above situations and field distributions and energy flow (Poynting vector) profiles presented to illustrate as necessary the nature of the modes supported by these systems. Finally experimental results are presented which illustrate the rather sweeping conclusion that a long-range surface mode may exist on a thin film for almost all values of ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{r}2}$ and ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{i}2}$. This result paves the way for a range of optics experiments on absorbing structures.

Preverbal Infants’ Sensitivity to Synaesthetic Cross-Modality Correspondences

Abstract: Stimulation of one sensory modality can induce perceptual experiences in another modality that reflect synaesthetic correspondences among different dimensions of sensory experience. In visual-hearing synaesthesia, for example, higher pitched sounds induce visual images that are brighter, smaller, higher in space, and sharper than those induced by lower pitched sounds. Claims that neonatal perception is synaesthetic imply that such correspondences are an unlearned aspect of perception. To date, the youngest children in whom such correspondences have been confirmed with any certainty were 2- to 3-year-olds. We examined preferential looking to assess 3- to 4-month-old preverbal infants' sensitivity to the correspondences linking auditory pitch to visuospatial height and visual sharpness. The infants looked longer at a changing visual display when this was accompanied by a sound whose changing pitch was congruent, rather than incongruent, with these correspondences. This is the strongest indication to date that synaesthetic cross-modality correspondences are an unlearned aspect of perception.

ENSO Atmospheric Teleconnections and Their Response to Greenhouse Gas Forcing

Abstract: S. W. Y. is supported by the KoreaMeteorological Administration Researchand Development Program under grant KMIPA2015-2112. Wenju Cai is supported by Earth System and Climate Change Hub of the Australia National Environmental Science Programme, and Centre for Southern Hemisphere Oceans Research, an international collaboration between CSIRO and Qingdao National Laboratory for Marine Sciences and Technology. B. Dewitte acknowledges supports from FONDECYT(1151185) and from LEFE-GMMC. Dietmar Dommenget is supported by ARC Centre of Excellence for Climate System Science (CE110001028).

Distributed leadership in higher education: rhetoric and reality

Abstract: In this article we present findings from research in 12 UK universities that sought to capture a range of perspectives on `distributed leadership' and reveal common and competing experiences within and between institutions. From analysis of findings we identified two principle approaches to the distribution of leadership: `devolved', associated with top-down influence, and `emergent', associated with bottom-up and horizontal influence. We argue that while literature on distributed leadership largely promotes the latter, the former is equally (if not more) significant in terms of how leadership is actually enacted and perceived within universities. We conclude, therefore, that as a description of leadership practice, the concept of `distributed leadership' offers little more clarity than `leadership' alone. As an analytic framework it is a more promising concept drawing attention to the broader contextual, temporal and social dimensions of leadership. Fundamentally, though, we argue that distributed leader...