A Tale of Two Animats: What does it take to have goals?

What does it take for a system, biological or not, to have goals? Here, this question is approached in the context of in silico artificial evolution. By examining the informational and causal properties of artificial organisms ('animats') controlled by small, adaptive neural networks (Markov Brains), this essay discusses necessary requirements for intrinsic information, autonomy, and meaning. The focus lies on comparing two types of Markov Brains that evolved in the same simple environment: one with purely feedforward connections between its elements, the other with an integrated set of elements that causally constrain each other. While both types of brains 'process' information about their environment and are equally fit, only the integrated one forms a causally autonomous entity above a background of external influences. This suggests that to assess whether goals are meaningful for a system itself, it is important to understand what the system is, rather than what it does.Comment: This article is a contribution to the FQXi 2016-2017 essay contest "Wandering Towards a Goal

Dynamics of damped oscillations: physical pendulum

The frictional force of the physical damped pendulum with the medium is usually assumed proportional to the pendulum velocity. In this work, we investigate how the pendulum motion will be affected when the drag force is modeled using power-laws bigger than the usual 1 or 2, and we will show that such assumption leads to contradictions with the experimental observation. For that, a more general model of a damped pendulum is introduced, assuming a power-law with integer exponents in the damping term of the equation of motion, and also in the nonharmonic regime. A Runge-Kutta solver is implemented to compute the numerical solutions for the first five powers, showing that the linear drag has the fastest decay to rest and that bigger exponents have long-time fluctuation around the equilibrium position, which have not correlation (as is expected) with experimental results.http://unidadinvestigacion.usta.edu.c

Kullback-Leibler and Renormalized Entropy: Applications to EEGs of Epilepsy Patients

Recently, renormalized entropy was proposed as a novel measure of relative entropy (P. Saparin et al., Chaos, Solitons & Fractals 4, 1907 (1994)) and applied to several physiological time sequences, including EEGs of patients with epilepsy. We show here that this measure is just a modified Kullback-Leibler (K-L) relative entropy, and it gives similar numerical results to the standard K-L entropy. The latter better distinguishes frequency contents of e.g. seizure and background EEGs than renormalized entropy. We thus propose that renormalized entropy might not be as useful as claimed by its proponents. In passing we also make some critical remarks about the implementation of these methods.Comment: 15 pages, 4 Postscript figures. Submitted to Phys. Rev. E, 199

Seismic signatures of partial steam saturation in fractured geothermal reservoirs: Insights from poroelasticity

Detecting the presence of gaseous formation fluids, estimatingthe respective volumes, and characterizing their spatial distributionare important for a wide range of applications, notably forgeothermal energy production. The ability to obtain such informationfrom remote geophysical measurements constitutes afundamental challenge, which needs to be overcome to addressa wide range of problems, such as the estimation of the reservoirtemperature and pressure conditions. With these motivations, wecompute the body wave velocities of a fractured granitic geothermalreservoir formation with varying quantities of steam toanalyze the seismic signatures in a partial saturation context.We use a poroelastic upscaling approach that accounts for mesoscalefluid pressure diffusion (FPD) effects induced by the seismicstrain field, and, thus, describes the governing physicalprocessesmore accurately than standard representations. Changesin seismic velocities due to steam saturation are compared with changes associated with fracture density variations, as both areplausible results of pressure changes in geothermal reservoirs.We find that steam saturation has a significant impact on P-wavevelocities while affecting S-wave velocities to a significantlylesser extent. This contrasting behavior allows us to discriminatebetween fracture density and steam saturation changes by meansof P- and S-wave velocity ratio analyses. To evaluate the potentialof seismic methods to provide this information, a canonical geothermalreservoir model is used to compute the Rayleigh wavevelocity dispersion and seismic reflection amplitude variationwith angle (AVA) curves. These studies reveal that AVA analysesallow differentiating changes in fracture density from changesin steam saturation. We also note that the Rayleigh-wave-basedtechniques are much less sensitive to steam content changes thanto fracture density changes. Comparisons with elastic approachesindicate that including FPD effects through the use of a poroelasticmodel is crucial for the reliable detection and characterizationof steam in fractured geothermal reservoirs.Fil: Quiroga, Gabriel E.. Universite de Lausanne; SuizaFil: Rubino, Jorge German. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Solazzi, Santiago Gabriel. Universite de Lausanne; Suiza. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Barbosa, Nicolás D.. Universite de Lausanne; SuizaFil: Favino, Marco. Universite de Lausanne; SuizaFil: Holliger, Klaus. Universite de Lausanne; Suiz

Controlling pulse propagation in optical fibers through nonlinearity and dispersion management

In case of the nonlinear Schr\"odinger equation with designed group velocity dispersion, variable nonlinearity and gain/loss; we analytically demonstrate the phenomenon of chirp reversal crucial for pulse reproduction. Two different scenarios are exhibited, where the pulses experience identical dispersion profiles, but show entirely different propagation behavior. Exact expressions for dynamical quasi-solitons and soliton bound-states relevant for fiber communication are also exhibited.Comment: 4 pages, 5 eps figure

Spin and Center of Mass in Axially Symmetric Einstein-Maxwell Spacetimes

We give a definition and derive the equations of motion for the center of mass and angular momentum of an axially symmetric, isolated system that emits gravitational and electromagnetic radiation. A central feature of this formulation is the use of Newman-Unti cuts at null infinity that are generated by worldlines of the spacetime. We analyze some consequences of the results and comment on the generalization of this work to general asymptotically flat spacetimes.Comment: 20 page