Sharing or gambling? On risk attitudes in social contexts

This paper investigates experimentally whether risk attitudes are stable across social contexts. In particular, it focuses on situations where some resource (for instance, a position, decision power, a bonus) has to be allocated between two parties: the decision maker can either opt for sharing the resource or for using a random device that allocates the entire prize to one of the two parties. By varying the relative situation of the decision maker with respect to the other party, we show that risk attitude is strongly affected by social contexts: participants in the experiment seem to be relatively risk seeking when they possess a relatively weaker position than the other party and risk averse when the opposite is true. Our main average results seem to be driven by the behavior of around a quarter of subjects whose choices appear to be fully determined by social comparisons. Various interpretations of the behavior are provided linking our results to preferences under risk with a social reference point and on status-seeking preferences

Decision making in uncertain times: what can cognitive and decision sciences say about or learn from economic crises?

B.M. was supported by a Visiting Scholar Award from the British Academy and Grant ME 3717/2 from the Deutsche Forschungsgemeinschaft (DFG) as part of the priority program ‘New Frameworks of Rationality’ (SPP 1516)

Long-lived Giant Number Fluctuations in a Swarming Granular Nematic

Coherently moving flocks of birds, beasts or bacteria are examples of living matter with spontaneous orientational order. How do these systems differ from thermal equilibrium systems with such liquid-crystalline order? Working with a fluidized monolayer of macroscopic rods in the nematic liquid crystalline phase, we find giant number fluctuations consistent with a standard deviation growing linearly with the mean, in contrast to any situation where the Central Limit Theorem applies. These fluctuations are long-lived, decaying only as a logarithmic function of time. This shows that flocking, coherent motion and large-scale inhomogeneity can appear in a system in which particles do not communicate except by contact.Comment: This is the author's version of the work. It is posted here by permission of the AAAS. The definitive version is to appear in SCIENC

Punishment fosters efficiency in the minimum effort coordination game

Using a laboratory experiment, we examine whether informal monetary sanctions can lead to better coordination in a repeated minimum effort coordination game. While most groups first experience inefficient coordination, the efficiency increases substantially after introducing an ex post sanctioning possibility. Namely, subjects can assign punishment points to other group members upon observing their efforts, which is costly for the punisher but twice as costly for the punished member. By contrast, introducing instead an ex post costless communication possibility fails to permanently increase efficiency. This suggests that decentralized monetary sanctions can play a major role as a coordination device in Pareto-ranked coordination settings, such as teamwork in firms and other organizational contexts

A Markov model for inferring flows in directed contact networks

Directed contact networks (DCNs) are a particularly flexible and convenient class of temporal networks, useful for modeling and analyzing the transfer of discrete quantities in communications, transportation, epidemiology, etc. Transfers modeled by contacts typically underlie flows that associate multiple contacts based on their spatiotemporal relationships. To infer these flows, we introduce a simple inhomogeneous Markov model associated to a DCN and show how it can be effectively used for data reduction and anomaly detection through an example of kernel-level information transfers within a computer.Comment: 12 page

Syntectonic granite emplacement at different structural levels: The Closepet granite, South India

The Closepet granite, in South India, is a large (400 km long but only 30 km wide), elongate, Late Archaean granitic body. Structural levels from deep crust to upper levels crop out, as evidenced by a shallowing of paleo-depths from north to south all along the Closepet granite. This allows the study of the emplacement of the same granitic body at various crustal levels. Four zones have been identified: a root zone, where magmas are collected in active shear zones; a transfer zone, featuring large-scale magma ascent and crystal-liquid partitioning in the granitic 'mush'; a 'gap', where the mush was filtered, allowing only the liquids to rise; shallow intrusions, filled with this liquid. The Closepet granite was emplaced syntectonically. Field work and anisotropy of magnetic susceptibility allowed documentation of steep foliations with subhorizontal lineations, both in the root and transfer zones and in the shallow intrusions. Remote sensing evidenced a network of shear zones bounding the Closepet granite. In the porphyritic root and transfer zones, magmas cooled slowly, thus developing strong fabrics during large-scale dextral shearing. Ascent of residual liquids amidst the crystallizing solid framework was not recorded in the fabrics. However, these liquids were channelised through the gap and infilled the homogeneous shallow intrusions, where rapid cooling only permitted the development of feint, although wholly consistent, fabrics. © 2002 Elsevier Science Ltd. All rights reserved

Probing empirical contact networks by simulation of spreading dynamics

Disease, opinions, ideas, gossip, etc. all spread on social networks. How these networks are connected (the network structure) influences the dynamics of the spreading processes. By investigating these relationships one gains understanding both of the spreading itself and the structure and function of the contact network. In this chapter, we will summarize the recent literature using simulation of spreading processes on top of empirical contact data. We will mostly focus on disease simulations on temporal proximity networks -- networks recording who is close to whom, at what time -- but also cover other types of networks and spreading processes. We analyze 29 empirical networks to illustrate the methods

Active contractility in actomyosin networks

Contractile forces are essential for many developmental processes involving cell shape change and tissue deformation. Recent experiments on reconstituted actomyosin networks, the major component of the contractile machinery, have shown that active contractility occurs above a threshold motor concentration and within a window of crosslink concentration. We present a microscopic dynamic model that incorporates two essential aspects of actomyosin self-organization: the asymmetric load response of individual actin filaments and the correlated motor-driven events mimicking myosin-induced filament sliding. Using computer simulations we examine how the concentration and susceptibility of motors contribute to their collective behavior and interplay with the network connectivity to regulate macroscopic contractility. Our model is shown to capture the formation and dynamics of contractile structures and agree with the observed dependence of active contractility on microscopic parameters including the contractility onset. Cooperative action of load-resisting motors in a force-percolating structure integrates local contraction/buckling events into a global contractile state via an active coarsening process, in contrast to the flow transition driven by uncorrelated kicks of susceptible motors.Comment: 15 pages, 4 main figures, 4 supplementary figure

Elastic properties of grafted microtubules

We use single-particle tracking to study the elastic properties of single microtubules grafted to a substrate. Thermal fluctuations of the free microtubule's end are recorded, in order to measure position distribution functions from which we calculate the persistence length of microtubules with contour lengths between 2.6 and 48 micrometers. We find the persistence length to vary by more than a factor of 20 over the total range of contour lengths. Our results support the hypothesis that shearing between protofilaments contributes significantly to the mechanics of microtubules.Comment: 9 pages, 3 figure

From sparse to dense and from assortative to disassortative in online social networks

Inspired by the analysis of several empirical online social networks, we propose a simple reaction-diffusion-like coevolving model, in which individuals are activated to create links based on their states, influenced by local dynamics and their own intention. It is shown that the model can reproduce the remarkable properties observed in empirical online social networks; in particular, the assortative coefficients are neutral or negative, and the power law exponents are smaller than 2. Moreover, we demonstrate that, under appropriate conditions, the model network naturally makes transition(s) from assortative to disassortative, and from sparse to dense in their characteristics. The model is useful in understanding the formation and evolution of online social networks.Comment: 10 pages, 7 figures and 2 table