Showing papers by "Santa Fe Institute published in 1990"
TL;DR: In this article, the authors examine the effect of agglomeration in the context of regional economics and show that the presence of increasing returns implies that one product or one technology, out of several possible must come to dominate a market.
424 citations
TL;DR: In this article, the authors define a connectionist model as a dynamical system with two properties: (1) the interactions between the variables at any given time are explicitly constrained to a finite list of connections; and (2) the connections are fluid, in that their strength and/or pattern of connectivity can change with time.
111 citations
TL;DR: In this paper, the requirements for evolvability in complex systems, using random Boolean networks as a canonical example, are discussed, and conditions for crystallization of orderly behavior in such networks are specified.
103 citations
01 Jan 1990
TL;DR: This model can account for some of the puzzling features of AIDS: the long latent period, the almost complete absence of free virus particles, the low frequency of infected T4 cells and the slow T cell depletion seen during the course of the disease.
Abstract: The interactions between the human immune system and HIV are potentially complex. In this paper I review some of these interactions and sketch the beginnings of a general model that can potentially account for many of the immunological consequences of HIV infection. This model involves a large number of ordinary differential equations and many parameters. To make progress, I simplify the general model and develop a four-equation model that involves free HIV and uninfected, latently infected and actively infected CD4+ T cells. Using reasonable guesses for parameter values, I show that this model can account for some of the puzzling features of AIDS: the long latent period, the almost complete absence of free virus particles, the low frequency of infected T4 cells and the slow T cell depletion seen during the course of the disease. Further, the model suggests why the latent period may be significantly shorter in children than in adults.
103 citations
TL;DR: In this article, the statistical properties of random quantum states are examined for four different kinds of random states: a pure state chosen at random with respect to the uniform measure on the unit sphere in a finite-dimensional Hilbert space, a random pure state in a real space, and a mixed state with fixed eigenvalues.
Abstract: This paper examines the statistical properties of random quantum states, for four different kinds of random state:(1) a pure state chosen at random with respect to the uniform measure on the unit sphere in a finite-dimensional Hilbert space;(2) a random pure state in a real space;(3) a pure state chosen at random except that a certain expectation value is fixed;(4) a random mixed state with fixed eigenvalues. For the first two of these, we give examples of simple states of a model system, the kicked top, which have the statistical properties of random states. Interestingly, examples of both kinds of randomness can be found in the same system. In studying the last two kinds of random state, we obtain new results concerning the application of information theory to quantum systems.
102 citations
TL;DR: It is demonstrated that, for a considerable range of parameters, both models account for the existence of localized memory-states in which only the Ab1 and the Ab2 clones are activated and the clones of the Ab3 level remain virgin.
86 citations
TL;DR: The study suggests that the crucial organizing principle in early Drosophila embryogenesis is based on global field mechanisms, not on particular local interactions, which makes it robust to parameter changes, and it has good potential for adapting to size and shape changes.
55 citations
TL;DR: Strong evidence is found that mean field theory, the main tool, gives surprisingly good predictions of the statistical properties of the class of automata the authors consider, and an alternative parameter in terms of which it is likely that the transition will become fairly sharp even if one does not increase the number of symbols.
44 citations
TL;DR: A general model is proposed of a hierarchically-nested set of quasi-autonomous dynamic systems involving gene activities that can generate the progressively finer spatial order that emerges during embryogenesis, which has implications for the general stability properties of evolving epigenetic systems.
34 citations
TL;DR: It is proposed that position is measured simultaneously on at least four colour wheels, which cycle different numbers of times along the anterior-posterior axis, which yield progressively finer grained positional information.
15 citations
TL;DR: In this paper, it was shown that all scalar field theories with symmetric monomial self-interactions of the form ( φ 2 ) p in four dimensions admit spontaneous symmetry breaking, and have a nonperturbative structure in the coupling constant λ.