Broadcasting Automata and Patterns on Z^2

The Broadcasting Automata model draws inspiration from a variety of sources such as Ad-Hoc radio networks, cellular automata, neighbourhood se- quences and nature, employing many of the same pattern forming methods that can be seen in the superposition of waves and resonance. Algorithms for broad- casting automata model are in the same vain as those encountered in distributed algorithms using a simple notion of waves, messages passed from automata to au- tomata throughout the topology, to construct computations. The waves generated by activating processes in a digital environment can be used for designing a vari- ety of wave algorithms. In this chapter we aim to study the geometrical shapes of informational waves on integer grid generated in broadcasting automata model as well as their potential use for metric approximation in a discrete space. An explo- ration of the ability to vary the broadcasting radius of each node leads to results of categorisations of digital discs, their form, composition, encodings and gener- ation. Results pertaining to the nodal patterns generated by arbitrary transmission radii on the plane are explored with a connection to broadcasting sequences and ap- proximation of discrete metrics of which results are given for the approximation of astroids, a previously unachievable concave metric, through a novel application of the aggregation of waves via a number of explored functions

In search for a perfect shape of polyhedra: Buffon transformation

For an arbitrary polygon consider a new one by joining the centres of consecutive edges. Iteration of this procedure leads to a shape which is affine equivalent to a regular polygon. This regularisation effect is usually ascribed to Count Buffon (1707-1788). We discuss a natural analogue of this procedure for 3-dimensional polyhedra, which leads to a new notion of affine $B$-regular polyhedra. The main result is the proof of existence of star-shaped affine $B$-regular polyhedra with prescribed combinatorial structure, under partial symmetry and simpliciality assumptions. The proof is based on deep results from spectral graph theory due to Colin de Verdiere and Lovasz.Comment: Slightly revised version with added example of pentakis dodecahedro

Null twisted geometries

We define and investigate a quantisation of null hypersurfaces in the context of loop quantum gravity on a fixed graph. The main tool we use is the parametrisation of the theory in terms of twistors, which has already proved useful in discussing the interpretation of spin networks as the quantization of twisted geometries. The classical formalism can be extended in a natural way to null hypersurfaces, with the Euclidean polyhedra replaced by null polyhedra with space-like faces, and SU(2) by the little group ISO(2). The main difference is that the simplicity constraints present in the formalims are all first class, and the symplectic reduction selects only the helicity subgroup of the little group. As a consequence, information on the shapes of the polyhedra is lost, and the result is a much simpler, abelian geometric picture. It can be described by an Euclidean singular structure on the 2-dimensional space-like surface defined by a foliation of space-time by null hypersurfaces. This geometric structure is naturally decomposed into a conformal metric and scale factors, forming locally conjugate pairs. Proper action-angle variables on the gauge-invariant phase space are described by the eigenvectors of the Laplacian of the dual graph. We also identify the variables of the phase space amenable to characterize the extrinsic geometry of the foliation. Finally, we quantise the phase space and its algebra using Dirac's algorithm, obtaining a notion of spin networks for null hypersurfaces. Such spin networks are labelled by SO(2) quantum numbers, and are embedded non-trivially in the unitary, infinite-dimensional irreducible representations of the Lorentz group.Comment: 22 pages, 3 figures. v2: minor corrections, improved presentation in section 4, references update

Introductory lectures to loop quantum gravity

We give a standard introduction to loop quantum gravity, from the ADM variables to spin network states. We include a discussion on quantum geometry on a fixed graph and its relation to a discrete approximation of general relativity.Comment: Based on lectures given at the 3eme Ecole de Physique Theorique de Jijel, Algeria, 26 Sep -- 3 Oct, 2009. 52 pages, many figures. v2 minor corrections. To be published in the proceeding

On the Nature of Students\u27 Digital Mathematical Performances

In this study I investigate the nature of digital mathematical performances (DMPs) produced by elementary school students (Grades 4-6). A DMP is a multimodal text/narrative (e.g., a video) in which one uses the performance arts to communicate mathematical ideas. I analyze twenty-two DMPs available at the Math + Science Performance Festival in 2008. Assuming a sociocultural/postmodern perspective with emphasis on multimodality, my focus is on the role of the arts and technology in shaping students’ mathematical communication and thinking. Methodologically, I employ qualitative case studies, along with video analysis. I conduct a descriptive analysis of each DMP using Boorstin’s (1990) categories of what makes good films, focusing on surprises, sense-making, emotions, and visceral sensations. I also conduct a cross-case analysis using Boorstin’s categories and the mathematical processes and strands of the Ontario Curriculum. The multimodal nature of DMP is one of its most significant pedagogic attributes. Mathematics is traditionally communicated through print-based texts, but the production of DMPs is an alternative that engages students in conceiving multimodal narratives. The playfulness offers scenarios for students’ collaboration, creativity, and imagination. By making DMPs available online, students share their ideas in a public and social environment, beyond the classrooms. Most of the DMPs only explore Geometry and offer opportunities to experience some surprises, sense-making, emotions, and visceral sensations. The lack of focus on other strands (e.g., Algebra) may be seen as a reflection on what (and how) students are (or not) learning in their classes. The production of conceptual DMPs is a rare event, although I acknowledge that I analyzed only DMPs of the first year of the Festival, that is, students did not have examples or references to produce their DMPs. Some DMPs potentially explore conceptual mathematical surprises, but they appear to have gaps in terms of sense-making. The use of the arts and technologies does not guarantee the mathematical conceptuality of DMPs. This study contributes to mathematics education with an exploratory discussion about how mathematical ideas can be (a) communicated and represented as multimodal texts at the elementary school level and (b) seen through a performance arts lens. The study also points out directions about the pedagogic components for conceiving conceptual DMPs in terms of the performance arts and the components of the Ontario Curriculum