Decay of DNLS breathers through inelastic multiphonon scattering

We consider the long-time evolution of weakly perturbed discrete nonlinear Schroedinger breathers. While breather growth can occur through nonlinear interaction with one single initial linear mode, breather decay is found to require excitation of at least two independent modes. All growth and decay processes of lowest order are found to disappear for breathers larger than a threshold value.Comment: 4 pages, 1 figure, to be published in Physical Review

Discreteness-induced oscillatory instabilities of dark solitons

We reveal that even weak inherent discreteness of a nonlinear model can lead to instabilities of the localized modes it supports. We present the first example of an oscillatory instability of dark solitons, and analyze how it may occur for dark solitons of the discrete nonlinear Schrödinger and generalized Ablowitz-Ladik equations. [S0031-9007(98)08088-0

Competencies and Institutions Fostering High-growth Firms

High-growth firms (HGFs) are critical for net job creation and economic growth. We analyze HGFs using the theory of competence blocs, linking firm growth to property rights and the interaction of complementary expertise. Specifically, we discuss how the institutional framework affects the prevalence and performance of HGFs. Firm growth is viewed as resulting from the perpetual discovery and use of productive knowledge. A key element in this process is the competence bloc, a nexus of economic actors with complementary competencies that are vital in order to generate and commercialize novel ideas. The institutional framework determines the incentives for these individuals to acquire and utilize knowledge. We identify a number of institutions that foster the emergence of competence blocs and the creation of HGFs. In particular, our analysis points to the pivotal roles played by tax structures, labor market regulation, and the contestability of currently closed service markets. Finally, we characterize institutions beneficial for sclerotic or dynamic capitalism, respectively, depending on whether they provide a favorable environment for the emergence of competence blocs and the creation of HGFs.Competence Bloc; Dynamic Capitalism; Entrepreneurship; Flyers; Gazelles; High-growth Firms; Industrial Policy; Innovation; Institutions; Labor Security; Product Market Regulations; Property Rights; Sclerotic Capitalism; Self-employment; Tax Policy

Gazelles as Job Creators – A Survey and Interpretation of the Evidence

It is often claimed that small and young firms account for a disproportionately large share of net employment growth. We conduct a meta analysis of the empirical evidence regarding whether net employment growth rather is generated by a few rapidly growing firms – so-called Gazelles – that are not necessarily small and young. Gazelles are found to be outstanding job creators. They create all or a large share of new net jobs. On average, Gazelles are younger and smaller than other firms, but it is young age more than small size that is associated with rapid growth. Gazelles seem to be overrepresented in services.Firm growth; Flyers; Gazelles; High-growth firms; Rapidly growing firms

The Discrete Nonlinear Schr\"odinger equation - 20 Years on

We review work on the Discrete Nonlinear Schr\"odinger (DNLS) equation over the last two decades.Comment: 24 pages, 1 figure, Proceedings of the conference on "Localization and Energy Transfer in Nonlinear Systems", June 17-21, 2002, San Lorenzo de El Escorial, Madrid, Spain; to be published by World Scientifi

Gap and out-gap breathers in a binary modulated discrete nonlinear Schr\"odinger model

We consider a modulated discrete nonlinear Schr\"odinger (DNLS) model with alternating on-site potential, having a linear spectrum with two branches separated by a 'forbidden' gap. Nonlinear localized time-periodic solutions with frequencies in the gap and near the gap -- discrete gap and out-gap breathers (DGBs and DOGBs) -- are investigated. Their linear stability is studied varying the system parameters from the continuous to the anti-continuous limit, and different types of oscillatory and real instabilities are revealed. It is shown, that generally DGBs in infinite modulated DNLS chains with hard (soft) nonlinearity do not possess any oscillatory instabilities for breather frequencies in the lower (upper) half of the gap. Regimes of 'exchange of stability' between symmetric and antisymmetric DGBs are observed, where an increased breather mobility is expected. The transformation from DGBs to DOGBs when the breather frequency enters the linear spectrum is studied, and the general bifurcation picture for DOGBs with tails of different wave numbers is described. Close to the anti-continuous limit, the localized linear eigenmodes and their corresponding eigenfrequencies are calculated analytically for several gap/out-gap breather configurations, yielding explicit proof of their linear stability or instability close to this limit.Comment: 17 pages, 12 figures, submitted to Eur. Phys. J.

Parrondo Strategies for Artificial Traders

On markets with receding prices, artificial noise traders may consider alternatives to buy-and-hold. By simulating variations of the Parrondo strategy, using real data from the Swedish stock market, we produce first indications of a buy-low-sell-random Parrondo variation outperforming buy-and-hold. Subject to our assumptions, buy-low-sell-random also outperforms the traditional value and trend investor strategies. We measure the success of the Parrondo variations not only through their performance compared to other kinds of strategies, but also relative to varying levels of perfect information, received through messages within a multi-agent system of artificial traders.Comment: 10 pages, 4 figure

Modeling Epidemic Spread in Synthetic Populations - Virtual Plagues in Massively Multiplayer Online Games

A virtual plague is a process in which a behavior-affecting property spreads among characters in a Massively Multiplayer Online Game (MMOG). The MMOG individuals constitute a synthetic population, and the game can be seen as a form of interactive executable model for studying disease spread, albeit of a very special kind. To a game developer maintaining an MMOG, recognizing, monitoring, and ultimately controlling a virtual plague is important, regardless of how it was initiated. The prospect of using tools, methods and theory from the field of epidemiology to do this seems natural and appealing. We will address the feasibility of such a prospect, first by considering some basic measures used in epidemiology, then by pointing out the differences between real world epidemics and virtual plagues. We also suggest directions for MMOG developer control through epidemiological modeling. Our aim is understanding the properties of virtual plagues, rather than trying to eliminate them or mitigate their effects, as would be in the case of real infectious disease.Comment: Accepted for presentation at Digital Games Research Association (DiGRA) conference in Tokyo in September 2007. All comments to the authors (mail addresses are in the paper) are welcom

Breather mobility and the PN potential: Brief review and recent progress

The question whether a nonlinear localized mode (discrete soliton/breather) can be mobile in a lattice has a standard interpretation in terms of the Peierls-Nabarro (PN) potential barrier. For the most commonly studied cases, the PN barrier for strongly localized solutions becomes large, rendering these essentially immobile. Several ways to improve the mobility by reducing the PN-barrier have been proposed during the last decade, and the first part gives a brief review of such scenarios in 1D and 2D. We then proceed to discuss two recently discovered novel mobility scenarios. The first example is the 2D Kagome lattice, where the existence of a highly degenerate, flat linear band allows for a very small PN-barrier and mobility of highly localized modes in a small-power regime. The second example is a 1D waveguide array in an active medium with intrinsic (saturable) gain and damping, where exponentially localized, travelling discrete dissipative solitons may exist as stable attractors. Finally, using the framework of an extended Bose-Hubbard model, we show that while quantum fluctuations destroy the mobility of slowly moving, strongly localized classical modes, coherent mobility of rapidly moving states survives even in a strongly quantum regime.Comment: 31 pages, 11 figures. In: J.F.R. Archilla, et al. (eds.) Quodons in mica: nonlinear localized travelling excitations in crystals. Springer (2015). To appea

Taxation, Labor Market Policy and High-Impact Entrepreneurship

Public policy affects the prevalence and performance of both productive and high-impact entrepreneurship. High-impact entrepreneurship prospers when knowledge is successfully generated and exploited in the economy. This process depends on complementary key actors who use their competencies in what we denote a competence bloc. Although variations in economic contexts make prescribing a general panacea impossible, a number of relevant policy areas that affect key actors can be identified. In this paper this is done in the areas of tax policy and labor market policy. It is shown that high and/or distortive taxes and heavy labor market regulations impinge on the creation and functioning of competence blocs, thereby reducing high-impact entrepreneurship.Entrepreneurship; Gazelles; High-growth firms; High-impact entrepreneurship Innovation; Institutions; Labor market policy; Tax policy