We consider sets of rectangles and squares recognized by deterministic and non-deterministic two-dimensional finite-state automata. We show that NFAs are strictly more powerful than DFAs, even for pictures over a one-symbol alphabet. In the process, we show that the pitcure languages recognized...

In many applications it is necessary to use a simple and therefore highly misspecified econometric model as the basis for decision-making. We propose an approach to developing a possibly misspecified econometric model that will be used as the beliefs of an objective expected utility maximiser. A...

We apply tiling groups and height functions to tilings of regions in the plane by Wang tiles, which are squares with colored boundaries where the colors of shared edges must match. We define a set of tiles as unambiguous if it contains all tiles equivalent to the identity in its tiling group....

Using data from computer databases of scientific papers in physics, biomedical research, and computer science, we have constructed networks of collaboration between scientists in each of these disciplines. In these networks two scientists are considered connected if they have coauthored one or...

We report on the continuing research program at the Santa Fe Institute that applies complex systems methodology to computational molecular biology. Two aspects are stressed here: (1) the use of coevolving adaptive neural networks for determining predictable protein structure classifications, and...

The repton model is a simple model of the ``reptation'' motion by which DNA diffuses through a gel during electrophoresis. In this paper we show that the model can be mapped onto a system consisting of two types of particles with hard-sphere interactions diffusing on a one-dimensional lattice....

In previous work, the speef of locally coupled quantum computers with infinite size clocks has been investigated in detail. One of the results is that the Feynman quantum computer and the Margolus cellular automaton compute at a constant rate. We show that this is no longer true for computers...

Using a new mathematical model to analyze a detailed set of viral load data collected from five infected patients after the administration of a potent inhibitor of HIV-1 protease, it was estimated that productively infected cells have, on average, a lifespan of 2.2 days (t[sub 1/2]=1.6 days) and...

A long history of dynamical analyses of food-web networks has led to important insights into the effects of complexity, omnivory and interaction strength on food-web stability. Some recent insights are based on nonlinear bioenergetic consumer-resource models that display chaotic behavior in...

Secondary structures of polynucleotides can be view as a certain class of planar vertex-labeled graphs. We construct recursion formulae enumerating various sub-classes of these graphs as well as certain structural elements (sub-graphs). First order asymptotics are derived and their dependence on...