Cooperation in the iterated prisoner's dilemma is learned by operant conditioning mechanisms

The prisoner's dilemma (PD) is the leading metaphor for the evolution of cooperative behavior in populations of selfish agents. Although cooperation in the iterated prisoner's dilemma (IPD) has been studied for over twenty years, most of this research has been focused on strategies that involve nonlearned behavior. Another approach is to suppose that players' selection of the preferred reply might he enforced in the same way as feeding animals track the best way to feed in changing nonstationary environments. Learning mechanisms such as operant conditioning enable animals to acquire relevant characteristics of their environment in order to get reinforcements and to avoid punishments. In this study, the role of operant conditioning in the learning of cooperation was evaluated in the PD. We found that operant mechanisms allow the learning of IPD play against other strategies. When random moves are allowed in the game, the operant learning model showed low sensitivity. On the basis of this evidence, it is suggested that operant learning might be involved in reciprocal altruism.Fil: Gutnisky, D. A.. Universidad de Buenos Aires. Facultad de Ingenieria. Instituto de Ingeniería Biomédica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; ArgentinaFil: Zanutto, Bonifacio Silvano. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Instituto de Ingeniería Biomédica; Argentin

Learning obstacle avoidance with an operant behavioral model

Artificial intelligence researchers have been attracted by the idea of having robots learn how to accomplish a task, rather than being told explicitly. Reinforcement learning has been proposed as an appealing framework to be used in controlling mobile agents. Robot learning research, as well as research in biological systems, face many similar problems in order to display high flexibility in performing a variety of tasks. In this work, the controlling of a vehicle in an avoidance task by a previously developed operant learning model (a form of animal learning) is studied. An environment in which a mobile robot with proximity sensors has to minimize the punishment for colliding against obstacles is simulated. The results were compared with the Q-Learning algorithm, and the proposed model had better performance. In this way a new artificial intelligence agent inspired by neurobiology, psychology, and ethology research is proposed.Fil: Gutnisky, D. A.. Universidad de Buenos Aires. Facultad de Ingeniería.Instituto de Ingeniería Biomédica; ArgentinaFil: Zanutto, Bonifacio Silvano. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería.Instituto de Ingeniería Biomédica; Argentin

Non dissipative decoherence of Rabi oscillations

We present a simple theoretical description of two recent experiments where damping of Rabi oscillations, which cannot be attributed to dissipative decoherence, has been observed. This is obtained considering the evolution time or the Hamiltonian as random variables and then averaging the usual unitary evolution on a properly defined, model-independent, probability distribution.Comment: 4 pages, RevTe

A model independent approach to non dissipative decoherence

We consider the case when decoherence is due to the fluctuations of some classical variable or parameter of a system and not to its entanglement with the environment. Under few and quite general assumptions, we derive a model-independent formalism for this non-dissipative decoherence, and we apply it to explain the decoherence observed in some recent experiments in cavity QED and on trapped ions.Comment: 12 pages, 3 figure

The Semiclassical and Quantum Regimes of Superradiant Light Scattering from a Bose-Einstein Condensate

We show that many features of the recent experiments of Schneble et al. [D. Schneble, Y. Torii, M. Boyd, E.W. Streed, D.E. Pritchard and W. Ketterle, Science vol. 300, p. 475 (2003)], which demonstrate two different regimes of light scattering by a Bose-Einstein condensate, can be described using a one-dimensional mean-field quantum CARL model, where optical amplification occurs simultaneously with the production of a periodic density modulation in the atomic medium. The two regimes of light scattering observed in these experiments, originally described as ``Kapiza-Dirac scattering'' and ``Superradiant Rayleigh scattering'', can be interpreted as the semiclassical and quantum limits respectively of CARL lasing.Comment: 10 pages, 5 figures - to appear in Journal of Optics

Atomic interaction effects in the superradiant light scattering from a Bose-Einstein condensate

We investigate the effects of the atomic interaction in the Superradiant Rayleigh scattering from a Bose-Einstein condensate driven by a far-detuned laser beam. We show that for a homogeneous atomic sample the atomic interaction has only a dispersive effect, whereas in the inhomogeneous case it may increase the decay of the matter-wave grating.Comment: 12 pages, 4 figures, presented to the XII International Laser Physics Workshop, August 24-29, Hamburg, to be published in Laser Physic

Beryllium in turnoff stars of NGC6397: early Galaxy spallation, cosmochronology and cluster formation

We present the first detection of beryllium in two turnoff stars of the old, metal-poor globular cluster NGC 6397. The beryllium lines are clearly detected and we determine a mean beryllium abundance of log(Be/H)=-12.35 +/- 0.2. The beryllium abundance is very similar to that of field stars of similar Fe content. We interpret the beryllium abundance observed as the result of primary spallation of cosmic rays acting on a Galactic scale, showing that beryllium can be used as a powerful cosmochronometer for the first stellar generations. With this method, we estimate that the cluster formed 0.2-0.3 Gyr after the onset of star formation in the Galaxy, in excellent agreement with the age derived from main sequence fitting. From the same spectra we also find low O (noticeably different for the two stars) and high N abundances, suggesting that the original gas was enriched in CNO processed material. Our beryllium results, together with the N, O, and Li abundances, provide insights on the formation of this globular cluster, showing that any CNO processing of the gas must have occurred in the protocluster cloud before the formation of the stars we observe now. We encounter, however, difficulties in giving a fully consistent picture of the cluster formation, able to explain the complex overall abundance pattern.Comment: to appear in A&

Abundance ratios of red giants in low mass ultra faint dwarf spheroidal galaxies

Low mass dwarf spheroidal galaxies are key objects for our understanding of the chemical evolution of the pristine Universe and the Local Group of galaxies. Abundance ratios in stars of these objects can be used to better understand their star formation and chemical evolution. We report on the analysis of a sample of 11 stars belonging to 5 different ultra faint dwarf spheroidal galaxies (UfDSph) based on X-Shooter spectra obtained at the VLT. Medium resolution spectra have been used to determine the detailed chemical composition of their atmosphere. We performed a standard 1D LTE analysis to compute the abundances. Considering all the stars as representative of the same population of low mass galaxies, we found that the [alpha/Fe] ratios vs [Fe/H] decreases as the metallicity of the star increases in a way similar to what is found for the population of stars belonging to dwarf spheroidal galaxies. The main difference is that the solar [alpha/Fe] is reached at a much lower metallicity for the UfDSph than the dwarf spheroidal galaxies. We report for the first time the abundance of strontium in CVnI. The star we analyzed in this galaxy has a very high [Sr/Fe] and a very low upper limit of barium which makes it a star with an exceptionally high [Sr/Ba] ratio. Our results seem to indicate that the galaxies which have produced the bulk of their stars before the reionization (fossil galaxies) have lower [X/Fe] ratios at a given metallicity than the galaxies that have experienced a discontinuity in their star formation rate (quenching).Comment: 22 pages, 12 figures, submitted to A&

Hydrodynamic Luminescence in a Model Diesel Injector Return Valve

A sample of unadditized diesel fuel was passed through an optically accessible model diesel injector return valve, which consisted of two successive nozzles connected to an intermediate fuel gallery. The first nozzle was cylindrical, while the second nozzle was stepped. The fuel was observed to produce a multi-phase, cavitating flow and a luminous blue-violet emission at the entrance to the second nozzle hole. The flow in the upstream intermediate fuel gallery and the first nozzle hole remained single-phase. Spectral analysis of the luminous emission revealed a spectrum with thermal features containing broad spectral lines and peaks at 358 nm, 389 nm, 405 nm, 412 nm, 430 nm and 475 nm, suggesting that the emission was dominated by π* → π transitions in the alkylated mono-, di-, and tri-aromatics, with additional spectral contributions from CH, C2, C3 and hydrogen (H)