Ground states for NLS on graphs: a subtle interplay of metric and topology

We review some recent results on the minimization of the energy associated to the nonlinear Schr\"odinger Equation on non-compact graphs. Starting from seminal results given by the author together with C. Cacciapuoti, D. Finco, and D. Noja for the star graphs, we illustrate the achiements attained for general graphs and the related methods, developed in collaboration with E. Serra and P. Tilli. We emphasize ideas and examples rather than computations or proofs.Comment: 18 pages, 17 figures. A review paper for a special number of Mathematical Modellind of Natural Phenomen

Russia's secret services at war

This repository item contains a single issue of Behind the Breaking News, a briefing published from 1999 to 2009 by the Boston University Institute for the Study of Conflict, Ideology, and Policy

On Modelling Life

We present a theoretical as well as experimental investigation of a population of self-replicating segments of code subject to random mutation and survival of the fittest. Under the assumption that such a system constitutes a minimal system with characteristics of life, we obtain a number of statements on the evolution of complexity and the trade-off between entropy and information.Comment: 6 p., postscript with figures (unpack with uufiles), to appear in the Proc. of ``Artificial Life IV'', MIT Pres

Ab Initio Modeling of Ecosystems with Artificial Life

Artificial Life provides the opportunity to study the emergence and evolution of simple ecosystems in real time. We give an overview of the advantages and limitations of such an approach, as well as its relation to individual-based modeling techniques. The Digital Life system Avida is introduced and prospects for experiments with ab initio evolution (evolution "from scratch"), maintenance, as well as stability of ecosystems are discussed.Comment: 13 pages, 2 figure

Self-organized Criticality in Living Systems

We suggest that ensembles of self-replicating entities such as biological systems naturally evolve into a self-organized critical state in which fluctuations, as well as waiting-times between phase transitions are distributed according to a 1/f power law. We demonstrate these concepts by analyzing a population of self-replicating strings (segments of computer-code) subject to mutation and survival of the fittest.Comment: 8 p., tar-compressed uuencoded postscript incl. figures, submitted to Phys. Rev. Let