Scale-free networks in complex systems

In the past few years, several studies have explored the topology of interactions in different complex systems. Areas of investigation span from biology to engineering, physics and the social sciences. Although having different microscopic dynamics, the results demonstrate that most systems under consideration tend to self-organize into structures that share common features. In particular, the networks of interaction are characterized by a power law distribution, $P(k)\sim k^{-\alpha}$, in the number of connections per node, $k$, over several orders of magnitude. Networks that fulfill this propriety of scale-invariance are referred to as ``scale-free''. In the present work we explore the implication of scale-free topologies in the antiferromagnetic (AF) Ising model and in a stochastic model of opinion formation. In the first case we show that the implicit disorder and frustration lead to a spin-glass phase transition not observed for the AF Ising model on standard lattices. We further illustrate that the opinion formation model produces a coherent, turbulent-like dynamics for a certain range of parameters. The influence, of random or targeted exclusion of nodes is studied.Comment: 9 pages, 4 figures. Proceeding to "SPIE International Symposium Microelectronics, MEMS, and Nanotechnology", 11-15 December 2005, Brisbane, Australi

Twenty-four hour behaviour patterns and budgets of free-ranging reindeer in winter

Activities of free-ranging reindeer (Rangifer tarandus) on the Seward Peninsula, Alaska were studied to determine 24-hour behaviour patterns and budgets in winter. Use of daytime active-rest data to predict nighttime behaviour resulted in as much as 37% underestimate of nighttime resting and 37% overestimate of nighttime activity. Three active-rest cycles occurred daily, synchronous with photoperiod.Tjuefiretimers adferdsmønster- og budsjett hos fritt beitende reinsdyr om vinteren.Abstract in Norwegian / Sammendrag: Aktiviteter hos fritt beitende reinsdyr {Rangifer tarandus) på Seward Peninsula, Alaska ble undersøkt for bestemmelse av 24 timers adferdsmønster og -budsjett om vinteren. Bruk av dagtids data for aktivitets-hvile til å forutsi nattlig adferd resulterte i 37% underestimering av natt-hvile og 37% overes-timering av natt-aktivitet. Tre aktivitet-hvile cykler inntraff daglig, synkront med fotoperiode.Vapaana laiduntavan poron vuorokautinen kayttaytyminen ja budjetti talvella.Abstract in Finnish / Yhteenveto: Vapaana laiduntavan poron (Rangifer tarandus) aktiivisuutta tutkittiin Sewardin niemimaalla Alaskassa mààrittàmàllà 24 tunnin kayttaytymismallit ja budjetit talvella. Kàyttàmàllâ pàivàajan aktiivisu-us - lepo -tietoja yôajan kåyttåytymisen ennustamiseen ne alittivat jopa 30%:lla yollisen lepoajan ja ylitti-våt 40%:lla yôajan aktiivisuuden. Påivittain esiintyi kolme aktiivisuus - lepo -sykliå samanaikaisesti valo-jaksojen kanssa

Phase transition from quark-meson coupling hyperonic matter to deconfined quark matter

We investigate the possibility and consequences of phase transitions from an equation of state (EOS) describing nucleons and hyperons interacting via mean fields of sigma, omega, and rho mesons in the recently improved quark-meson coupling (QMC) model to an EOS describing a Fermi gas of quarks in an MIT bag. The transition to a mixed phase of baryons and deconfined quarks, and subsequently to a pure deconfined quark phase, is described using the method of Glendenning. The overall EOS for the three phases is calculated for various scenarios and used to calculate stellar solutions using the Tolman-Oppenheimer-Volkoff equations. The results are compared with recent experimental data, and the validity of each case is discussed with consequences for determining the species content of the interior of neutron stars.Comment: 12 pages, 14 figures; minor typos correcte

Numerical solution of flow fields surrounding Saturn type vehicles

Numerical solution of flow fields surrounding Saturn type vehicle

Precise determination of the strangeness magnetic moment of the nucleon

By combining the constraints of charge symmetry with new chiral extrapolation techniques and recent low mass lattice QCD simulations of the individual quark contributions to the magnetic moments of the nucleon octet, we obtain a precise determination of the strange magnetic moment of the proton. The result, namely G_M^s = -0.046 +/- 0.019 mu_N, is consistent with the latest experimental measurements but an order of magnitude more precise. This poses a tremendous challenge for future experiments.Comment: 4 pages, 7 figures. Submitted to Phys. Rev. Lett. Clairification of manuscript and improved correlation function analysi

Neutron stars and strange stars in the chiral SU(3) quark mean field model

We investigate the equations of state for pure neutron matter and strange hadronic matter in $\beta$-equilibrium, including $\Lambda$, $\Sigma$ and $\Xi$ hyperons. The masses and radii of pure neutron stars and strange hadronic stars are obtained. For a pure neutron star, the maximum mass is about $1.8 M_{\mathrm{sun}}$, while for a strange hadronic star, the maximum mass is around $1.45 M_{\mathrm{sun}}$. The typical radii of pure neutron stars and strange hadronic stars are about 11.0-12.3 km and 10.7-11.7 km, respectively.Comment: 18 pages, 7 figure

Complex Dynamics and Synchronization of Delayed-Feedback Nonlinear Oscillators

We describe a flexible and modular delayed-feedback nonlinear oscillator that is capable of generating a wide range of dynamical behaviours, from periodic oscillations to high-dimensional chaos. The oscillator uses electrooptic modulation and fibre-optic transmission, with feedback and filtering implemented through real-time digital-signal processing. We consider two such oscillators that are coupled to one another, and we identify the conditions under which they will synchronize. By examining the rates of divergence or convergence between two coupled oscillators, we quantify the maximum Lyapunov exponents or transverse Lyapunov exponents of the system, and we present an experimental method to determine these rates that does not require a mathematical model of the system. Finally, we demonstrate a new adaptive control method that keeps two oscillators synchronized even when the coupling between them is changing unpredictably.Comment: 24 pages, 13 figures. To appear in Phil. Trans. R. Soc. A (special theme issue to accompany 2009 International Workshop on Delayed Complex Systems

Liquid-gas phase transition in nuclear matter including strangeness

We apply the chiral SU(3) quark mean field model to study the properties of strange hadronic matter at finite temperature. The liquid-gas phase transition is studied as a function of the strangeness fraction. The pressure of the system cannot remain constant during the phase transition, since there are two independent conserved charges (baryon and strangeness number). In a range of temperatures around 15 MeV (precise values depending on the model used) the equation of state exhibits multiple bifurcates. The difference in the strangeness fraction $f_s$ between the liquid and gas phases is small when they coexist. The critical temperature of strange matter turns out to be a non-trivial function of the strangeness fraction.Comment: 15 pages, 7 figure