The Shared Reward Dilemma

One of the most direct human mechanisms of promoting cooperation is rewarding it. We study the effect of sharing a reward among cooperators in the most stringent form of social dilemma, namely the Prisoner's Dilemma. Specifically, for a group of players that collect payoffs by playing a pairwise Prisoner's Dilemma game with their partners, we consider an external entity that distributes a fixed reward equally among all cooperators. Thus, individuals confront a new dilemma: on the one hand, they may be inclined to choose the shared reward despite the possibility of being exploited by defectors; on the other hand, if too many players do that, cooperators will obtain a poor reward and defectors will outperform them. By appropriately tuning the amount to be shared a vast variety of scenarios arises, including traditional ones in the study of cooperation as well as more complex situations where unexpected behavior can occur. We provide a complete classification of the equilibria of the $n$-player game as well as of its evolutionary dynamics.Comment: Major rewriting, new appendix, new figure

Shear banding in nematogenic fluids with oscillating orientational dynamics

We investigate the occurrence of shear banding in nematogenic fluids under planar Couette flow, based on mesoscopic dynamical equations for the orientational order parameter and the shear stress. We focus on parameter values where the sheared homogeneous system exhibits regular oscillatory orientational dynamics, whereas the equilibrium system is either isotropic (albeit close to the isotropic--nematic transition) or deep in its nematic phase. The numerical calculations are restricted to spatial variations in shear gradient direction. We find several new types of shear banded states characterized by regions with regular oscillatory orientational dynamics. In all cases shear banding is accompanied by a non--monotonicity of the flow curve of the homogeneous system; however, only in the case of the initially isotropic system this curve has the typical $S$--like shape. We also analyze the influence of different orientational boundary conditions and of the spatial correlation length.Comment: 12 pages, 10 figure

Rewarding cooperation in social dilemmas

One of the most direct human mechanisms of promoting cooperation is rewarding it. We study the effect of sharing a reward among cooperators in the most stringent form of social dilemma. Thus, individuals confront a new dilemma: on the one hand, they may be inclined to choose the shared reward despite the possibility of being exploited by defectors; on the other hand, if too many players do that, cooperators will obtain a poor reward and defectors will outperform them. By appropriately tuning the amount to be shared we can cast a vast variety of scenarios, including traditional ones in the study of cooperation as well as more complex situations where unexpected behavior can occur. We provide a complete classification of the equilibria of the nplayer game as well as of the evolutionary dynamics. Beyond, we extend our analysis to a general class of public good games where competition among individuals with the same strategy exists.

A public good model with lotteries in large groups

We analyze the effect of a large group on a public goods model with lotteries. We show that as populations get large, and with preferences in which people only care about their private consumptions and the total supply of the public good, the level of contributions converges to the one given by voluntary contributions. With altruistic preferences of the warm-glow type, the contributions converge to a level strictly higher than those given by voluntary contributions, but in general they do not yield first-best levels. Our results are important to clarify why in general governments do not rely on lotteries for a large part of the revenue creation for public good provision. They are also useful to understand why lottery proceeds are earmarked to worthy causes, where warm glow is likely to be larger

Effect of social behaviors in the opinion dynamics qq-voter model

Order-disorder phase transition is one of the interesting features in the opinion dynamics model of sociophysics. This phenomenon is caused by noise parameters, which can be treated as social responses such as anticonformity and independence in a social context. This paper explores the effect of anticonformity and independence in the occurrence of the order-disorder phase transition in the model. A probability $p$ represents anticonformity and independence, and the model is defined on the complete graph and two-dimensional (2D) square lattice. We also introduce a skepticism parameter represented by $s =\{0,1\}$, which describes a voter's propensity to behave independently and anticonformist. Our results analytically and numerically show that the model undergoes a continuous and discontinuous phase for all values of non-zero $s$ and at specific $q$-sized agent. No phase transition is observed in the model with independent voters on the 2D square lattice, and the model with anticonformist voters undergoes a continuous phase transition. We also analyze the effect of the probability $p$ and skepticism level $s$ on the outcome of the system's opinion.Comment: 15 pages and 16 figure

On supersymmetric D6D6-Dˉ6\bar D 6 systems with magnetic fields

We study systems of $D6$ and $\bar D 6$ branes with non zero world-volume magnetic fields in the weak coupling limit. We find two configurations for which the conditions for absence of tachyons in the spectra coincide exactly with those found in the low energy effective theory approach, for the systems to preserve 1/8 of the supersymmetries of the Type $IIA$ string theory vacuum. These conditions give rise to a four-parameter family of solutions in each case. We present further evidence of the stability of these systems by computing the lowest order interaction amplitude, verifying the no force condition as well as the supersymmetric character of the spectrum.Comment: Latex file, no figures, 11 pages, references added, to be published in Physics Letters

Trajectory Reconstruction and Uncertainty Analysis Using Mars Science Laboratory Pre-Flight Scale Model Aeroballistic Testing

As part of the Mars Science Laboratory (MSL) trajectory reconstruction effort at NASA Langley Research Center, free-flight aeroballistic experiments of instrumented MSL scale models was conducted at Aberdeen Proving Ground in Maryland. The models carried an inertial measurement unit (IMU) and a flush air data system (FADS) similar to the MSL Entry Atmospheric Data System (MEADS) that provided data types similar to those from the MSL entry. Multiple sources of redundant data were available, including tracking radar and on-board magnetometers. These experimental data enabled the testing and validation of the various tools and methodologies that will be used for MSL trajectory reconstruction. The aerodynamic parameters Mach number, angle of attack, and sideslip angle were estimated using minimum variance with a priori to combine the pressure data and pre-flight computational fluid dynamics (CFD) data. Both linear and non-linear pressure model terms were also estimated for each pressure transducer as a measure of the errors introduced by CFD and transducer calibration. Parameter uncertainties were estimated using a "consider parameters" approach

Estudio descriptivo del programa de rehabilitación cardiaca de la Clínica Las Américas

Estudio descriptivo de antes y después que demuestra la eficacia y seguridad del Programa de Rehabilitación Cardiaca de la Clínica Las Américas, con base en un seguimiento a 77 pacientes, en el que se evidenció mejoría de la capacidad funcional así como disminución del perímetro abdominal y de las cifras basales de presión arterial sistólica y diastólica sin complicaciones severas, en todos los tipos de paciente, independientemente de la fracción de eyección o las variables demográficas. De igual forma, se describen las características epidemiológicas de la población y de los factores de riesgo cardio-cerebro-vascular.A before and after descriptive study that shows the efficacy and safety of the Cardiac Rehabilitation Program of the Clínica Las Americas, based on the follow-up of 77 patients in which we evidenced improvement in functional capacity as well as a decrease of abdominal girth and baseline values of systolic and diastolic blood pressure without severe complications in all type of patients, regardless of ejection fraction or demographic variables. Likewise, we describe the epidemiological characteristics of the population and the cardio-cerebro-vascular risk factors