The Signalling Power of Sanctions in Collective Action Problems

We present a model of collective action in a heterogenous population of egoists and conditional cooperators. Each player is uncertain about the cooperative inclinations of the other player. A government or principal who has information about the distribution of types may introduce sanctions for defection. We study the impact of such sanctions through the e¤ect on the beliefs of the players about the distribution of types they are facing. It is shown that in equilibrium sanctions can crowd out trust between agents by sending a signal that there are many egoists around. This can lead the government to set low sanctions to induce trust and 'crowd in' cooperation. In cases where conditional cooperation is an important factor in collective action, as is the case in tax compliance, the model provides a rationale for the low observed sanctions in the real world.Collective action, trust, incentives, crowding out, conditional cooperation

The birth process of periodic orbits in non-twist maps

We study the birth process of periodic orbits in non-twist systems, by means of a model map which contains all the typical features of such a system. The most common form of the birth process, or standard scenario, is described in detail. This scenario involves several steps: first one “dimerized” chain of saddle-center pairs is born, then a second, and eventually these two chains are reconnected into two Poincaré-Birkhoff chains.\ud \ud We also discuss several variations on this standard scenario. These variations can give rise to arbitrarily many chains, intertwined in a complex fashion, and the reconnection of these chains can be highly non-trivial.\ud Finally we study the effect of dissipation on the birth process. For sufficiently small dissipation one can still recognize the birth and reconnection processes, but with several new features. In the first place, the chains do not consist anymore of conservative saddles and centers, but rather of dissipative saddles and nodes. Furthermore, the dissipation destrtoys the symmetry between the inner and outer chains, and as a result the reconnection does not take place in one single step anymore, but in three

Granular fountains: Convection cascade in a compartmentalized granular gas

This paper extends the two-compartment granular fountain [D. van der Meer, P. Reimann, K. van der Weele, and D. Lohse, Phys. Rev. Lett. 92, 184301 (2004)] to an arbitrary number of compartments: The tendency of a granular gas to form clusters is exploited to generate spontaneous convective currents, with particles going down in the well-filled compartments and going up in the diluted ones. We focus upon the bifurcation diagram of the general K-compartment system, which is constructed using a dynamical flux model and which proves to agree quantitatively with results from molecular dynamics simulations

Status-Seeking in Criminal Subcultures and the Double Dividend of Zero-Tolerance

This paper offers a new argument for why a more aggressive enforcement of minor offenses ('zero-tolerance') may yield a double dividend in that it reduces both minor offenses and more severe crime. We develop a model of criminal subcultures in which people gain social status among their peers for being 'tough' by committing criminal acts. As zero-tolerance keeps relatively 'gutless' people from committing a minor offense, the signaling value of that action increases, which makes it attractive for some people who would otherwise commit more severe crime. If social status is sufficiently important in criminal subcultures, zero-tolerance reduces crime across the board.status concerns, street crime, subcultures, penalties, zero-tolerance, broken windows policing

On the rise and fall of a ball with linear or quadratic drag

We review the problem of a vertically thrown ball, with a drag force which is either linear or quadratic in the speed. It is stressed from the outset that these two types of drag correspond to specific ranges of the Reynolds number (Re<1 and 103<Re<2×105, respectively) and do not hold outside these intervals. We also include the buoyant force in our treatment of the problem. The equations of motion are solved analytically and several true-to-life examples are discussed. The calculations are somewhat harder than for the well-known case without drag force, but no highbrow mathematics is required and the extra effort is amply compensated by the gain in realism and surprise value. © 1999 American Association of Physics Teachers

Efficient interval scoring rules

Scoring rules that elicit an entire belief distribution through the elicitation of point beliefs are time-consuming and demand considerable cognitive e¤ort. Moreover, the results are valid only when agents are risk-neutral or when one uses probabilistic rules. We investigate a class of rules in which the agent has to choose an interval and is rewarded (deterministically) on the basis of the chosen interval and the realization of the random variable. We formulate an e¢ ciency criterion for such rules and present a speci.c interval scoring rule. For single- peaked beliefs, our rule gives information about both the location and the dispersion of the belief distribution. These results hold for all concave utility functions.Belief elicitation, scoring rules, subjective probabilities

Heroes of Agricultural Innovation

New technology has a prominent place in the theory and practice of innovation, but the association between high tech and innovation is not inevitable. In this paper, we discuss six metaphorical heroes of agricultural innovation, starting with the dominant hero of frontier science and technology. At first sight, our six heroes can be divided in those who are pro- and those who are anti-technology. Yet in the end technology, and more specifically GM technology, does not emerge as the main issue. Empowering the poor, finding solutions for urgent climate problems, and enhancing the quality of our daily relations to food and the environment – these are the issues the heroes are fighting for. Relations between innovation and (frontier) technology are better seen as a matter of pragmatic consideration, we will argue

Mode competition in a system of two parametrically driven pendulums: the role of symmetry

This paper is the final part in a series of four on the dynamics of two coupled, parametrically driven pendulums. In the previous three parts (Banning and van der Weele, Mode competition in a system of two parametrically driven pendulums; the Hamiltonian case, Physica A 220 (1995) 485¿533; Banning et al., Mode competition in a system of two parametrically driven pendulums; the dissipative case, Physica A 245 (1997) 11¿48; Banning et al., Mode competition in a system of two parametrically driven pendulums with nonlinear coupling, Physica A 245 (1997) 49¿98) we have given a detailed survey of the different oscillations in the system, with particular emphasis on mode interaction. In the present paper we use group theory to highlight the role of symmetry. It is shown how certain symmetries can obstruct period doubling and Hopf bifurcations; the associated routes to chaos cannot proceed until these symmetries have been broken. The symmetry approach also reveals the general mechanism of mode interaction and enables a useful comparison with other systems

Transient granular shock waves and upstream motion on a staircase

A granular cluster, placed on a staircase setup, is brought into motion by vertical shaking. Molecular dynamics simulations show that the system goes through three phases. After a rapid initial breakdown of the cluster, the particle stream organizes itself in the form of a shock wave moving down the steps of the staircase. As this wave becomes diluted, it transforms into a more symmetric flow, in which the particles move not only downwards but also toward the top of the staircase. This series of events is accurately reproduced by a dynamical model in which the particle flow from step to step is modeled by a flux function. To explain the observed scaling behavior during the three stages, we study the continuum version of this model (a nonlinear partial differential equation) in three successive limiting cases. (i) The first limit gives the correct t−1/3 decay law during the rapid initial phase, (ii) the second limit reveals that the transient shock wave is of the Burgers type, with the density of the wave front decreasing as t−1/2, and (iii) the third limit shows that the eventual symmetric flow is a slow diffusive process for which the density falls off as t−1/3 again. For any finite number of compartments, the system finally reaches an equilibrium distribution with a bias toward the lower compartments. For an unbounded staircase, however, the t−1/3 decay goes on forever and the distribution becomes increasingly more symmetric as the dilution progresses

Interplay of air and sand: Faraday heaping unravelled

We report on numerical simulations of a vibrated granular bed including the effect of the ambient air, generating the famous Faraday heaps known from experiment. A detailed analysis of the forces shows that the heaps are formed and stabilized by the airflow through the bed while the gap between bed and vibrating bottom is growing, confirming the pressure gradient mechanism found experimentally by Thomas and Squires [Phys. Rev. Lett. 81, 574 (1998)], with the addition that the airflow is partly generated by isobars running parallel to the surface of the granular bed. Importantly, the simulations also explain the heaping instability of the initially flat surface and the experimentally observed coarsening of a number of small heaps into a larger one