Dissipative surface solitons in periodic structures

We report dissipative surface solitons forming at the interface between a semi-infinite lattice and a homogeneous Kerr medium. The solitons exist due to balance between amplification in the near-surface lattice channel and two-photon absorption. The stable dissipative surface solitons exist in both focusing and defocusing media, when propagation constants of corresponding states fall into a total semi-infinite and or into one of total finite gaps of the spectrum (i.e. in a domain where propagation of linear waves is inhibited for the both media). In a general situation, the surface solitons form when amplification coefficient exceeds threshold value. When a soliton is formed in a total finite gap there exists also the upper limit for the linear gain.Comment: 5 pages, 3 figures, to appear in Europhysics Letter

Rigidity and volume preserving deformation on degenerate simplices

Given a degenerate $(n+1)$-simplex in a $d$-dimensional space $M^d$ (Euclidean, spherical or hyperbolic space, and $d\geq n$), for each $k$, $1\leq k\leq n$, Radon's theorem induces a partition of the set of $k$-faces into two subsets. We prove that if the vertices of the simplex vary smoothly in $M^d$ for $d=n$, and the volumes of $k$-faces in one subset are constrained only to decrease while in the other subset only to increase, then any sufficiently small motion must preserve the volumes of all $k$-faces; and this property still holds in $M^d$ for $d\geq n+1$ if an invariant $c_{k-1}(\alpha^{k-1})$ of the degenerate simplex has the desired sign. This answers a question posed by the author, and the proof relies on an invariant $c_k(\omega)$ we discovered for any $k$-stress $\omega$ on a cell complex in $M^d$. We introduce a characteristic polynomial of the degenerate simplex by defining $f(x)=\sum_{i=0}^{n+1}(-1)^{i}c_i(\alpha^i)x^{n+1-i}$, and prove that the roots of $f(x)$ are real for the Euclidean case. Some evidence suggests the same conjecture for the hyperbolic case.Comment: 27 pages, 2 figures. To appear in Discrete & Computational Geometr

Narrative in young children’s digital art-making

Digital technologies have material and social properties that have the potential to create new opportunities for children’s expressive arts practices. The presence and development of oral narratives in young children’s visual art-making on paper has been noted in previous research, but little is known about the narratives children create when they engage in digital art-making. How do young children construct narratives during digital art-making? How do the features of these narratives relate to the social and material properties of the digital resources they are using? How can looking at these narratives inform and enrich our understanding of children’s art-making in general? Drawing on a social semiotic perspective, these questions are explored through an in-depth analysis of narrative in three examples of 4-5 year olds’ digital art-making. On the basis of the analysis, features of oral narrative in young children’s digital art-making are suggested and these are linked to potentially influential properties of the digital resources. Being aware of these features and properties offers a starting point for thinking about what digital resources can offer in the context of young children’s art-making. The findings also prompt us to be aware of the diverse potentials that exist in children’s art-making practices regardless of the resources being used

"Evil cats" and "jelly floods": young children’s collective constructions of digital art-making in the early years classroom

Digital technologies have the potential to offer new opportunities for children’s expressive arts practices. While adult expectations surround and shape children’s visual art-making on paper in the early years classroom, such expectations are not so established in relation to digital art-making. So how do children make sense of digital art-making when it is newly introduced into the classroom and adult input is minimal? Drawing on a social semiotic ethnographic perspective, this paper explores this question by examining instances of 4-5 year olds’ spoken dialogue around the computer during a week in which digital art-making was first introduced into the classroom. Analysis focused on interactions where children proposed, reinforced or challenged conceptions of digital art-making. These interactions demonstrated that children’s digital art-making was negotiated and constructed through particular processes. Three such processes are presented here: the use of collective motifs and metaphors; attributing ‘expert’ status; and polarizing conflicts. Understanding these processes offers a starting point for thinking about how a new activity like digital art-making can be integrated into the early years classroom and supported by practitioners

Imitative or Iconoclastic? How young children use ready-made images in digital art

Digital art-making tends to foreground the inclusion of ready-made images in children’s art. While some lament children’s use of such images, suggesting that they constrain creativity and expression (McLennan, 2007; Szyba, 1999), others have argued that ready-made digital materials offer children the opportunity to create innovative and potentially iconoclastic artefacts through processes of ‘remix’ (Lankshear & Knobel, 2006) and ‘mash-up’ (Lamb, 2007). In order to further this debate, observations are needed to explore the different ways that children use ready-made images in their digital art and the various purposes that these images can serve. Adopting a social semiotic perspective, this paper offers an in-depth examination of five episodes of 4-5 year olds’ digital art-making that collectively demonstrate the diversity of approaches that young children take towards the inclusion of ready-made images in their digital art-making. The paper discusses these findings in relation to suggestions for what adults can do to support children to adopt a playful and critically aware approach to the use of ready-made images in digital art-making

Dyslexia and writing: Poor spelling can interfere with good quality composition

This article reports on issues facing students with dyslexia in higher education, and reveals how tutors can offer support. It builds upon research conducted by the authors in order to raise the profile of diversity and disabilities issues. The article provides accessible advice, and calls for more research into supporting students with dyslexia

An infinitesimally nonrigid polyhedron with nonstationary volume in the Lobachevsky 3-space

We give an example of an infinitesimally nonrigid polyhedron in the Lobachevsky 3-space and construct an infinitesimal flex of that polyhedron such that the volume of the polyhedron isn't stationary under the flex.Comment: 10 pages, 2 Postscript figure

Behavioural coping patterns in Parkinson's patients with visual hallucinations

Visual Hallucinations are considered to affect about 20%-40% of patients with Parkinson's disease. They are generally seen as a side effect of this long-term illness and can severely affect the daily quality of life of patients. The aim of this study was to determine the coping patterns or strategies used by patients and establish whether the phenomenology and behaviours used by patients enabled control of the phenomenon. Demographic and clinical variables were recorded, including motor measures, cognitive status, and depressive symptoms. Patient with hallucinations were at a more advance stage of the disease and displayed more depressive symptoms than their non-hallucinating counterparts. Most patients used more than one constructive coping strategy, the most common were simple behavioural strategies based around motor action or cognitive approaches resulting in visual modification. In addition, humour was a common technique used by the patients to deal with the phenomenon. Emotional responses varied between patients, but it was found that the actual content of the hallucination was not directly associated with whether it caused trouble to the patient, but perceived stress was strongly correlated with the subjective disturbing nature of visual hallucinations (VHs). This study gives insight into the role of cognitive-behavioural approaches when dealing with VHs and opens up avenues for future studies in helping patient to deal with hallucinations

Dynamic analysis of a lithium-boiling potassium refractory metal Rankine cycle power system for the Jet Propulsion Laboratory

Lithium-boiling potassium refractory metal Rankine cycle power system heat transfer model

The orbit rigidity matrix of a symmetric framework

A number of recent papers have studied when symmetry causes frameworks on a graph to become infinitesimally flexible, or stressed, and when it has no impact. A number of other recent papers have studied special classes of frameworks on generically rigid graphs which are finite mechanisms. Here we introduce a new tool, the orbit matrix, which connects these two areas and provides a matrix representation for fully symmetric infinitesimal flexes, and fully symmetric stresses of symmetric frameworks. The orbit matrix is a true analog of the standard rigidity matrix for general frameworks, and its analysis gives important insights into questions about the flexibility and rigidity of classes of symmetric frameworks, in all dimensions. With this narrower focus on fully symmetric infinitesimal motions, comes the power to predict symmetry-preserving finite mechanisms - giving a simplified analysis which covers a wide range of the known mechanisms, and generalizes the classes of known mechanisms. This initial exploration of the properties of the orbit matrix also opens up a number of new questions and possible extensions of the previous results, including transfer of symmetry based results from Euclidean space to spherical, hyperbolic, and some other metrics with shared symmetry groups and underlying projective geometry.Comment: 41 pages, 12 figure