From Foraging to Agriculture

We consider a world in which the mode of food production, foraging or agriculture, is endogenous, and in which technology grows exogenously. Using a recent model of coalition formation, we allow individuals to rationally form cooperative communities (bands) of foragers or farmers. At the lowest levels of technology, equilibrium entails the grand coalition of foragers, a cooperative structure which avoids over-exploitation of the environment. But at a critical state of technology, the cooperative structure breaks down through an individually rational splintering of the band. At this stage there can be an increase in work and, through the over-exploitation of the environment, a food crisis. In the end, technological growth leads to a one-way transition from foraging to agriculture.

Stochastic approximations of present value functions.

The aim of the paper is to apply the method proposed by Denuit, Genest and Marceau (1999) for deriving stochastic upper and lower bounds on the present value of a sequence of cash flows, where the discounting is performed under a given stochastic return process. The convex approximation provided by Goovaerts, Dhaene and De Schepper (1999) and Goovaerts and Dhaene (1999) is then compared to these stochastic bounds. On the basis of several numerical examples, it will be seen that the convex approximation seems reasonable.Value; Functions;

Swarm behavior of self-propelled rods and swimming flagella

Systems of self-propelled particles are known for their tendency to aggregate and to display swarm behavior. We investigate two model systems, self-propelled rods interacting via volume exclusion, and sinusoidally-beating flagella embedded in a fluid with hydrodynamic interactions. In the flagella system, beating frequencies are Gaussian distributed with a non-zero average. These systems are studied by Brownian-dynamics simulations and by mesoscale hydrodynamics simulations, respectively. The clustering behavior is analyzed as the particle density and the environmental or internal noise are varied. By distinguishing three types of cluster-size probability density functions, we obtain a phase diagram of different swarm behaviors. The properties of clusters, such as their configuration, lifetime and average size are analyzed. We find that the swarm behavior of the two systems, characterized by several effective power laws, is very similar. However, a more careful analysis reveals several differences. Clusters of self-propelled rods form due to partially blocked forward motion, and are therefore typically wedge-shaped. At higher rod density and low noise, a giant mobile cluster appears, in which most rods are mostly oriented towards the center. In contrast, flagella become hydrodynamically synchronized and attract each other; their clusters are therefore more elongated. Furthermore, the lifetime of flagella clusters decays more quickly with cluster size than of rod clusters

Analysis of deciduous tree species dynamics after a severe ice storm using SORTIE model simulations

Ice storms are frequent natural disturbance events in hardwood forests of eastern Canada and the United States, but their effects on forest dynamics are not well understood. Our objectives were to characterize short- and long-term tree species dynamics after a severe ice storm, and to assess the influence of spatial distribution of trees on these dynamics. SORTIE, a spatially explicit individual tree-based forest model, was used to simulate the effects of a severe ice storm on 300 years old stands. Crown radius was reduced and tree mortality was increased for a 5-year period following the ice storm disturbance. To investigate the influence of the spatial distribution of trees, we repeated the same experiment in a uniformly distributed stand where we systematically assigned coordinates of all trees, saplings and seedlings before the ice storm was modeled. Our results showed that six types of dynamics can be adopted by a species following an ice storm and that spatial distribution of trees influenced the species responses. In summary, we found that a combination of factors, namely, species density and spatial distribution, shade tolerance, growth rate, extent of canopy openness and canopy loss resulting from the ice storm, determine how tree species respond to ice storm disturbance

Propagation dynamics on networks featuring complex topologies

Analytical description of propagation phenomena on random networks has flourished in recent years, yet more complex systems have mainly been studied through numerical means. In this paper, a mean-field description is used to coherently couple the dynamics of the network elements (nodes, vertices, individuals...) on the one hand and their recurrent topological patterns (subgraphs, groups...) on the other hand. In a SIS model of epidemic spread on social networks with community structure, this approach yields a set of ODEs for the time evolution of the system, as well as analytical solutions for the epidemic threshold and equilibria. The results obtained are in good agreement with numerical simulations and reproduce random networks behavior in the appropriate limits which highlights the influence of topology on the processes. Finally, it is demonstrated that our model predicts higher epidemic thresholds for clustered structures than for equivalent random topologies in the case of networks with zero degree correlation.Comment: 10 pages, 5 figures, 1 Appendix. Published in Phys. Rev. E (mistakes in the PRE version are corrected here

Simulation of the thermal profile of a mushy metallic sample during tensile tests

Strain measurement is a major challenge in tensile tests performed in a mushy state. While non-contact technique devices like the laser speckle extensometer remain the most reliable facility for this type of measurement, these devices are often not readily available. So the strain measurement is usually performed by determining the length of the ‘‘hot zone’’ of the sample. This is possible with the help of the thermal profile associated with the sample under heating. The purpose of our work is to develop a numerical model to predict the thermal profile of a A356 aluminum alloy sample at high temperature, taking into account the device geometry and characteristics. We simulate the joule heating effect using the FE software Abaqus. Our model takes into account the grips of a Gleeble machine, the thermal contact conductance and electrical contact resistance at the grip-sample interfaces, as well as the convection heat transfer on the free surfaces of the system. These thermo-physical properties have been determined by fitting the experimental thermal profile obtained at 545°C. The model was then used to simulate the temperature profile on the sample at higher temperatures (when the sample is in the mushy state). The thermal profile predicted by our model is in excellent agreement with the profile obtained experimentally

Describing ancient horizontal gene transfers at the nucleotide and gene levels by comparative pathogenicity island genometrics

Motivation: Lateral gene transfer is a major mechanism contributing to bacterial genome dynamics and pathovar emergence via pathogenicity island (PAI) spreading. However, since few of these genomic exchanges are experimentally reproducible, it is difficult to establish evolutionary scenarios for the successive PAI transmissions between bacterial genera. Methods initially developed at the gene and/or nucleotide level for genomics, i.e. comparisons of concatenated sequences, ortholog frequency, gene order or dinucleotide usage, were combined and applied here to homologous PAIs: we call this approach comparative PAI genometrics. Results: YAPI, a Yersinia PAI, and related islands were compared with measure evolutionary relationships between related modules. Through use of our genometric approach designed for tracking codon usage adaptation and gene phylogeny, an ancient inter-genus PAI transfer was oriented for the first time by characterizing the genomic environment in which the ancestral island emerged and its subsequent transfers to other bacterial genera. Contact: [email protected] Supplementary informatio

Research collaboration in the social sciences: What factors are associated with disciplinary and interdisciplinary collaboration?

[EN] Attention is increasingly directed toward better understanding the factors driving collaborations among researchers, particularly between researchers from different disciplinary backgrounds. This study investigates factors associated with disciplinary and interdisciplinary research collaboration in the social sciences. We utilize data from a survey of Australian-based social scientists. Interdisciplinary collaboration constitutes a considerable proportion of social scientists’ collaboration activity. Factors linked to the duration and diversity of research careers are positively associated with participation in collaborations. Job experience in Australian and foreign universities also boosts total collaboration, while holding an international citizenship increases interdisciplinary collaboration. Interdisciplinary collaborations are also associated with researcher orientation toward applied research activity. Investment in social science research is important for maintaining existing interdisciplinary and applied collaborations, although better information on these collaborations is desirable. Measures to expand such collaborations should take career stage into account. Broad-based population policies may also be an important underlying factor supporting international collaboration.Woolley, RD.; Sánchez-Barrioluengo, M.; Turpin, T.; Marceau, J. (2015). Research collaboration in the social sciences: What factors are associated with disciplinary and interdisciplinary collaboration?. Science and Public Policy. 42(4):567-582. doi:10.1093/scipol/scu074S56758242

MS 2053.7-0449: Confirmation of a bimodal mass distribution from strong gravitational lensing

We present the first strong lensing study of the mass distribution in the cluster MS 2053-04 based on HST archive data. This massive, X-ray luminous cluster has a redshift z=0.583, and it is composed of two structures that are gravitationally bound to each other. The cluster has one multiply imaged system constituted by a double gravitational arc. We have performed a parametric strong lensing mass reconstruction using NFW density profiles to model the cluster potential. We also included perturbations from 23 galaxies, modeled like elliptical singular isothermal sphere, that are approximately within 1'x1' around the cluster center. These galaxies were constrained in both the geometric and dynamical parameters with observational data. Our analysis predicts a third image which is slightly demagnified. We found a candidate for this counter-image near the expected position and with the same F702W-F814W colors as the gravitational arcs in the cluster. The results from the strong lensing model shows the complex structure in this cluster, the asymmetry and the elongation in the mass distribution, and are consistent with previous spectrophotometric results that indicate that the cluster has a bimodal mass distribution. Finally, the derived mass profile was used to estimate the mass within the arcs and for comparison with X-ray estimates.Comment: To be published in ApJ (accepted