Two-parameter nonsmooth grazing bifurcations of limit cycles: classification and open problems

This paper proposes a strategy for the classification of codimension-two grazing bifurcations of limit cycles in piecewise smooth systems of ordinary differential equations. Such nonsmooth transitions (C-bifurcations) occur when the cycle interacts with a discontinuity boundary of phase space in a non-generic way. Several such codimension-one events have recently been identified, causing for example period-adding or sudden onset of chaos. Here, the focus is on codimension-two grazings that are local in the sense that the dynamics can be fully described by an appropriate Poincaré map from a neighbourhood of the grazing point (or points) of the critical cycle to itself. It is proposed that codimension-two grazing bifurcations can be divided into three distinct types: either the grazing point is degenerate, or the the grazing cycle is itself degenerate (e.g. non-hyperbolic) or we have the simultaneous occurrence of two grazing events. A careful distinction is drawn between their occurrence in systems with discontinuous states, discontinuous vector fields, or that have discontinuity in some derivative of the vector field. Examples of each kind of bifurcation are presented, mostly derived from mechanical applications. For each example, where possible, principal bifurcation curves characteristic to the codimension-two scenario are presented and general features of the dynamics discussed. Many avenues for future research are opened.

DNA Repair: a spatially rooted analysis of the development of a scientific community

International audienceOur aim is to track the emergence of the DNA Repair field (1964-1975) using both bibliometric data and historical sources (interviews, archives, historical accounts). We intend to focus on the geographical diffusion of the research specialty: how did the scientific interest for DNA Repair mechanisms spread at the worldwide level? What role the first scientists specialized in the field play in the diffusion process? In order to localize specialized teams, we follow the use of the keyword “DNA Repair” in scientific publications indexed in bibliometric databases. At first, in analyzing a bibliometric corpus derived from Scopus we draw a general overview of the DNA Repair field geography during the emergence stage (1965-1975). For each territory, we localize the different teams involved in the scientific specialty from the beginning. In a second time, we focus on pioneers’ trajectories. In following individual trajectories with the help of both bibliometric materials and qualitative sources, we shed light on networks of places critical for the field’s diffusion

The Translocal Event and the Polyrhythmic Diagram

This thesis identifies and analyses the key creative protocols in translocal performance practice, and ends with suggestions for new forms of transversal live and mediated performance practice, informed by theory. It argues that ontologies of emergence in dynamic systems nourish contemporary practice in the digital arts. Feedback in self-organised, recursive systems and organisms elicit change, and change transforms. The arguments trace concepts from chaos and complexity theory to virtual multiplicity, relationality, intuition and individuation (in the work of Bergson, Deleuze, Guattari, Simondon, Massumi, and other process theorists). It then examines the intersection of methodologies in philosophy, science and art and the radical contingencies implicit in the technicity of real-time, collaborative composition. Simultaneous forces or tendencies such as perception/memory, content/ expression and instinct/intellect produce composites (experience, meaning, and intuition- respectively) that affect the sensation of interplay. The translocal event is itself a diagram - an interstice between the forces of the local and the global, between the tendencies of the individual and the collective. The translocal is a point of reference for exploring the distribution of affect, parameters of control and emergent aesthetics. Translocal interplay, enabled by digital technologies and network protocols, is ontogenetic and autopoietic; diagrammatic and synaesthetic; intuitive and transductive. KeyWorx is a software application developed for realtime, distributed, multimodal media processing. As a technological tool created by artists, KeyWorx supports this intuitive type of creative experience: a real-time, translocal “jamming” that transduces the lived experience of a “biogram,” a synaesthetic hinge-dimension. The emerging aesthetics are processual – intuitive, diagrammatic and transversal

Vessel tractography using an intensity based tensor model with branch detection

In this paper, we present a tubular structure seg- mentation method that utilizes a second order tensor constructed from directional intensity measurements, which is inspired from diffusion tensor image (DTI) modeling. The constructed anisotropic tensor which is fit inside a vessel drives the segmen- tation analogously to a tractography approach in DTI. Our model is initialized at a single seed point and is capable of capturing whole vessel trees by an automatic branch detection algorithm developed in the same framework. The centerline of the vessel as well as its thickness is extracted. Performance results within the Rotterdam Coronary Artery Algorithm Evaluation framework are provided for comparison with existing techniques. 96.4% average overlap with ground truth delineated by experts is obtained in addition to other measures reported in the paper. Moreover, we demonstrate further quantitative results over synthetic vascular datasets, and we provide quantitative experiments for branch detection on patient Computed Tomography Angiography (CTA) volumes, as well as qualitative evaluations on the same CTA datasets, from visual scores by a cardiologist expert

Education Reform at the "Edge of Chaos": Constructing ETCH (An Education Theory Complexity Hybrid) for an Optimal Learning Education Environment

EDUCATION REFORM AT THE "EDGE OF CHAOS":CONSTRUCTING ETCH (AN EDUCATION THEORY COMPLEXITY HYBRID) FOR AN OPTIMAL LEARNING EDUCATION ENVIRONMENT AbstractCurrently, the theoretical foundation that inspires educational theory, which in turn shapes the systemic structure of institutions of learning, is based on three key interconnected, interacting underpinnings -mechanism, reductionism, and linearity. My dissertation explores this current theoretical underpinning including its fallacies and inconsistencies, and then frames an alternative educational theoretical base - a hybrid complex adaptive systems theory model for education - that more effectively meets the demands to prepare students for the 21st century. My Education Theory Complexity Hybrid (ETCH) differs by focusing on the systemic, autopoietic nature of schools, the open, fluid processes of school systems as a dissipative structure, and nonlinearity or impossibility of completely predicting the results of any specific intervention within a school system.. In addition, I show how ETCH principles, when applied by educational system leaders, permit them to facilitate an optimal learning environment for a student-centered complex adaptive system.ETCH is derived from Complexity Theory and is a coherent, valid, and verifiable systems' framework that accurately aligns the education system with its goal as a student-centered complex adaptive system. In contrast to most dissertations in the School Leadership Program, which are empirical studies, mine explores this new theoretical orientation and illustrates the power of that orientation through a series of examples taken from my experiences in founding and operating the Lancaster Institute for Learning, a private state-licensed alternative high school in eastern Pennsylvania

Mitigation factors

The debate over the costs of GHG emission reduction has become more com-plex recently as disagreements over the existence of economic and environ-mental double dividents have been added to discussions over the existence of a negative cost potential. We argue that basic assumptions about economic effi-ciency, the (sub-)optimality of the baseline and the rate of technical change are more important than model structure, and we underline the importance of the timing of decisions for determining the costs. Moreover the use of a single baseline ‘no policy' scenario and several policy intervention scenarios may be fundamentally misleading in the longer term simply because the very idea of a business as usual scenario is deeply problematic. Ultimately the debate turns on political judgments about the desirability of alternative development paths. Copright© 1996 Elsevier Science Ltd.Greenhouse gas emissions;Costs of GHG reduction; Mitigation options

Retinal Fundus Image Registration via Vascular Structure Graph Matching

Motivated by the observation that a retinal fundus image may contain some unique geometric structures within its vascular trees which can be utilized for feature matching, in this paper, we proposed a graph-based registration framework called GM-ICP to align pairwise retinal images. First, the retinal vessels are automatically detected and represented as vascular structure graphs. A graph matching is then performed to find global correspondences between vascular bifurcations. Finally, a revised ICP algorithm incorporating with quadratic transformation model is used at fine level to register vessel shape models. In order to eliminate the incorrect matches from global correspondence set obtained via graph matching, we proposed a structure-based sample consensus (STRUCT-SAC) algorithm. The advantages of our approach are threefold: (1) global optimum solution can be achieved with graph matching; (2) our method is invariant to linear geometric transformations; and (3) heavy local feature descriptors are not required. The effectiveness of our method is demonstrated by the experiments with 48 pairs retinal images collected from clinical patients