Scarcity may promote cooperation in populations of simple agents

In the study of the evolution of cooperation, resource limitations are usually assumed just to provide a finite population size. Recently, however, it has been pointed out that resource limitation may also generate dynamical payoffs able to modify the original structure of the games. Here we study analytically a phase transition from a homogeneous population of defectors when resources are abundant to the survival of unconditional cooperators when resources reduce below a threshold. To this end, we introduce a model of simple agents, with no memory or ability of recognition, interacting in well-mixed populations. The result might shed light on the role played by resource constraints on the origin of multicellularity.Comment: 5 pages, 2 figure

Wear of a chute in a rice sorting machine

In a rice sorting machine, rice grains drop onto and slide down an anodised aluminium chute. The purpose of the chute is to separate the grains and provide a controlled distribution. At the bottom of the chute the grains are examined optically and contaminants or defective grains are removed from the stream by jets of air. The machine has the ability to sort low quality rice which contains a large element of contaminants such as husk. The husk is extremely abrasive and this, along with other factors, can lead to a reduction in the life of the chute by wear of the surface. In this work a failure analysis process was undertaken to establish the nature and causes of the chute surface wear and the mechanisms of material removal. Wear occurs initially at the location where the grains first strike the chute and at subsequent regions down the chute where bounce occurs. An experimental and analytical examination of the rice motion on impacting the chute was also carried out along with some friction testing of potential replacement chute materials. The evidence gathered during the failure analysis along with the experimental analysis was used to propose possible material/design improvements

Small-Scale Structure of Spacetime: Bounds and Conjectures

This review consists of two parts. The first part establishes certain astrophysical bounds on the smoothness of classical spacetime. Some of the best bounds to date are based on the absence of vacuum Cherenkov radiation in ultrahigh-energy cosmic rays. The second part discusses possible implications of these bounds for the quantum structure of spacetime. One conjecture is that the fundamental length scale of quantum spacetime may be different from the Planck length.Comment: 20 pages; invited talk at the Third Mexican Meeting on Mathematical and Experimental Physics, September 10-14, 2007, El Colegio Nacional, Mexico City; v3: final versio

Implementation of min–max MPC using hinging hyperplanes. Application to a heat exchanger

Min–max model predictive control (MMMPC) is one of the few control techniques able to cope with modelling errors or uncertainties in an explicit manner. The implementation of MMMPC suffers a large computational burden due to the numerical min–max problem that has to be solved at every sampling time. This fact severely limits the range of processes to which this control structure can be applied. An implementation scheme based on hinging hyperplanes that overcome these problems is presented here. Experimental results obtained when applying the controller to the heat exchanger of a pilot plant are given.Ministerio de Ciencia y Tecnología DPI2001-2380-C02-01Ministerio de Ciencia y Tecnología DPI2002-04375-C03-0

Performance of the jet Global Sequential Calibration (GSC) in ATLAS

International audienceJet are experimental signatures of quarks and gluons, which are produced in high energy processes such as the hard scattering of partons in pp collisions. Jets are objects reconstructed from the energy signal deposited in the calorimeters by the particles coming from the hadronization of quarks and gluons. Its production cross section is really large, it means they are many channels with jets in the fi nal state. Usually the energy deposited does not correspond to the initial energy carried by the particles, i.e. the response of the calorimeter is di fferent from one. This is due to calorimeter e ffects as dead material, non compensation and crack regions and to jet reconstruction eff ects such as out of cone energy. As a consequence the determination of the jet energy scale and the achievement of the optimal jet energy resolution have become of crucial importance

Calibration Globale Séquentielle (GS) dans l'expérience ATLAS

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