1,241 research outputs found
Restricted density classification in one dimension
The density classification task is to determine which of the symbols
appearing in an array has the majority. A cellular automaton solving this task
is required to converge to a uniform configuration with the majority symbol at
each site. It is not known whether a one-dimensional cellular automaton with
binary alphabet can classify all Bernoulli random configurations almost surely
according to their densities. We show that any cellular automaton that washes
out finite islands in linear time classifies all Bernoulli random
configurations with parameters close to 0 or 1 almost surely correctly. The
proof is a direct application of a "percolation" argument which goes back to
Gacs (1986).Comment: 13 pages, 5 figure
Stability analysis of coupled map lattices at locally unstable fixed points
Numerical simulations of coupled map lattices (CMLs) and other complex model
systems show an enormous phenomenological variety that is difficult to classify
and understand. It is therefore desirable to establish analytical tools for
exploring fundamental features of CMLs, such as their stability properties.
Since CMLs can be considered as graphs, we apply methods of spectral graph
theory to analyze their stability at locally unstable fixed points for
different updating rules, different coupling scenarios, and different types of
neighborhoods. Numerical studies are found to be in excellent agreement with
our theoretical results.Comment: 22 pages, 6 figures, accepted for publication in European Physical
Journal
Magnetism in reduced dimensions
We propose a short overview of a few selected issues of magnetism in reduced
dimensions, which are the most relevant to set the background for more
specialized contributions to the present Special Issue. Magnetic anisotropy in
reduced dimensions is discussed, on a theoretical basis, then with experimental
reports and views from surface to single-atom anisotropy. Then conventional
magnetization states are reviewed, including macrospins, single domains,
multidomains, and domain walls in stripes. Dipolar coupling is examined for
lateral interactions in arrays, and for interlayer interactions in films and
dots. Finally thermally-assisted magnetization reversal and superparamagnetism
are presented. For each topic we sought a balance between well established
knowledge and recent developments.Comment: 13 pages. Part of a Special Issue of the C. R. Physique devoted to
spinelectronics (2005
Stochastic Simulation of Mudcrack Damage Formation in an Environmental Barrier Coating
The FEAMAC/CARES program, which integrates finite element analysis (FEA) with the MAC/GMC (Micromechanics Analysis Code with Generalized Method of Cells) and the CARES/Life (Ceramics Analysis and Reliability Evaluation of Structures / Life Prediction) programs, was used to simulate the formation of mudcracks during the cooling of a multilayered environmental barrier coating (EBC) deposited on a silicon carbide substrate. FEAMAC/CARES combines the MAC/GMC multiscale micromechanics analysis capability (primarily developed for composite materials) with the CARES/Life probabilistic multiaxial failure criteria (developed for brittle ceramic materials) and Abaqus (Dassault Systmes) FEA. In this report, elastic modulus reduction of randomly damaged finite elements was used to represent discrete cracking events. The use of many small-sized low-aspect-ratio elements enabled the formation of crack boundaries, leading to development of mudcrack-patterned damage. Finite element models of a disk-shaped three-dimensional specimen and a twodimensional model of a through-the-thickness cross section subjected to progressive cooling from 1,300 C to an ambient temperature of 23 C were made. Mudcrack damage in the coating resulted from the buildup of residual tensile stresses between the individual material constituents because of thermal expansion mismatches between coating layers and the substrate. A two-parameter Weibull distribution characterized the coating layer stochastic strength response and allowed the effect of the Weibull modulus on the formation of damage and crack segmentation lengths to be studied. The spontaneous initiation of cracking and crack coalescence resulted in progressively smaller mudcrack cells as cooling progressed, consistent with a fractal-behaved fracture pattern. Other failure modes such as delamination, and possibly spallation, could also be reproduced. The physical basis assumed and the heuristic approach employed, which involves a simple stochastic cellular automaton methodology to approximate the crack growth process, are described. The results ultimately show that a selforganizing mudcrack formation can derive from a Weibull distribution that is used to describe the stochastic strength response of the bulk brittle ceramic material layers of an EBC
Self-Evaluation Applied Mathematics 2003-2008 University of Twente
This report contains the self-study for the research assessment of the Department of Applied Mathematics (AM) of the Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS) at the University of Twente (UT). The report provides the information for the Research Assessment Committee for Applied Mathematics, dealing with mathematical sciences at the three universities of technology in the Netherlands. It describes the state of affairs pertaining to the period 1 January 2003 to 31 December 2008
Cybernetic automata: An approach for the realization of economical cognition for multi-robot systems
The multi-agent robotics paradigm has attracted much attention due to the
variety of pertinent applications that are well-served by the use of a multiplicity of
agents (including space robotics, search and rescue, and mobile sensor networks). The
use of this paradigm for most applications, however, demands economical, lightweight
agent designs for reasons of longer operational life, lower economic cost, faster and
easily-verified designs, etc.
An important contributing factor to an agent’s cost is its control architecture.
Due to the emergence of novel implementation technologies carrying the promise of
economical implementation, we consider the development of a technology-independent
specification for computational machinery. To that end, the use of cybernetics toolsets
(control and dynamical systems theory) is appropriate, enabling a principled specifi-
cation of robotic control architectures in mathematical terms that could be mapped
directly to diverse implementation substrates.
This dissertation, hence, addresses the problem of developing a technologyindependent
specification for lightweight control architectures to enable robotic agents
to serve in a multi-agent scheme. We present the principled design of static and dynamical
regulators that elicit useful behaviors, and integrate these within an overall
architecture for both single and multi-agent control. Since the use of control theory
can be limited in unstructured environments, a major focus of the work is on the engineering of emergent behavior.
The proposed scheme is highly decentralized, requiring only local sensing and
no inter-agent communication. Beyond several simulation-based studies, we provide
experimental results for a two-agent system, based on a custom implementation employing
field-programmable gate arrays
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