What is the Value of Geometric Models to Understand Matter?

This article analyzes the value of geometric models to understand matter with the examples of the Platonic model for the primary four elements (fire, air, water, and earth) and the models of carbon atomic structures in the new science of crystallography. How the geometry of these models is built in order to discover the properties of matter is explained: movement and stability for the primary elements, and hardness, softness and elasticity for the carbon atoms. These geometric models appear to have a double quality: firstly, they exhibit visually the scientific properties of matter, and secondly they give us the possibility to visualize its whole nature. Geometrical models appear to be the expression of the mind in the understanding of physical matter

Common Visual Representations as a Source for Misconceptions of Preservice Teachers in a Geometry Connection Course

In this paper, we demonstrate how atypical visual representations of a triangle, square or a parallelogram may hinder students’ understanding of a median and altitude. We analyze responses and reasoning given by 16 preservice middle school teachers in a Geometry Connection class. Particularly, the data were garnered from three specific questions posed on a cumulative final exam, which focused on computing and comparing areas of parallelograms, and triangles represented by atypical images. We use the notions of concept image and concept definition as our theoretical framework for an analysis of the students’ responses. Our findings have implication on how typical images can impact students’ cognitive process and their concept image. We provide a number of suggestions that can foster conceptualization of the notions of median and altitude in a triangle that can be realized in an enacted lesson

Formal study of plane Delaunay triangulation

This article presents the formal proof of correctness for a plane Delaunay triangulation algorithm. It consists in repeating a sequence of edge flippings from an initial triangulation until the Delaunay property is achieved. To describe triangulations, we rely on a combinatorial hypermap specification framework we have been developing for years. We embed hypermaps in the plane by attaching coordinates to elements in a consistent way. We then describe what are legal and illegal Delaunay edges and a flipping operation which we show preserves hypermap, triangulation, and embedding invariants. To prove the termination of the algorithm, we use a generic approach expressing that any non-cyclic relation is well-founded when working on a finite set

Geometry learning: The role of tasks, working models, and dynamic geometry software

We present several learning experiences that illustrate how three aspects of the geometric competence, constructing and analyzing properties of figures, identifying patterns and investigating and geometric problem solving, were developed by pupils that participated in the implementation of an innovative geometry teaching unit in grade 8. The topics addressed were dealing with properties of two dimensional figures, Pythagoras theorem, loci, translations and similarity of triangles. The development of the geometric competence was clearly supported by the dynamic geometry environment but unfolded in different ways, depending on the way how pupils reacted to the different types of tasks.Apresentamos várias experiências de aprendizagem que ilustram como três aspectos da competência geométrica, construir e analisar propriedades de figuras, identificar regularidades e investigar e resolver foram desenvolvidos por alunos que participaram de uma experiência de ensino inovadora no campo da Geometria no 8.º ano de escolaridade. Os temas tratados incluem o trabalho com figuras bidimensionais, teorema de Pitágoras, lugares geométricos, translações e semelhança de triângulos. O desenvolvimento da competência geométrica foi claramente apoiado pelo ambiente de geometria dinâmica mas processou-se de formas diferentes, em resultado do modo como os alunos reagiram aos diferentes tipos de tarefa

Searching for Hyperbolicity

This is an expository paper, based on by a talk given at the AWM Research Symposium 2017. It is intended as a gentle introduction to geometric group theory with a focus on the notion of hyperbolicity, a theme that has inspired the field from its inception to current-day research