Slightly generalized Generalized Contagion: Unifying simple models of biological and social spreading

We motivate and explore the basic features of generalized contagion, a model mechanism that unifies fundamental models of biological and social contagion. Generalized contagion builds on the elementary observation that spreading and contagion of all kinds involve some form of system memory. We discuss the three main classes of systems that generalized contagion affords, resembling: simple biological contagion; critical mass contagion of social phenomena; and an intermediate, and explosive, vanishing critical mass contagion. We also present a simple explanation of the global spreading condition in the context of a small seed of infected individuals.Comment: 8 pages, 5 figures; chapter to appear in "Spreading Dynamics in Social Systems"; Eds. Sune Lehmann and Yong-Yeol Ahn, Springer Natur

Efficient Generation of Model Bulk Heterojunction Morphologies for Organic Photovoltaic Device Modeling

Kinetic Monte Carlo (KMC) simulations have been previously used to model and understand a wide range of behaviors in bulk heterojunction (BHJ) organic photovoltaic devices, from fundamental mechanisms to full device performance. One particularly unique and valuable aspect of this type of modeling technique is the ability to explicitly implement models for the bicontinuous nanostructured morphology present in these devices. For this purpose, an Ising-based method for creating model BHJ morphologies has become prevalent. However, this technique can be computationally expensive, and a detailed characterization of this method has not yet been published. Here, we perform a thorough characterization of this method and describe how to efficiently generate controlled model BHJ morphologies. We show how the interaction energy affects the tortuosity of the interconnected domains and the resulting charge transport behavior in KMC simulations. We also demonstrate how to dramatically reduce calculation time by several orders of magnitude without detrimentally affecting the resulting morphologies. In the end, we propose standard conditions for generating model morphologies and introduce a new open-source software tool. These developments to the Ising method provide a strong foundation for future simulation and modeling of BHJ organic photovoltaic devices that will lead to a more detailed understanding of the important link between morphological features and device performance.Comment: Main article: 9 pages, 6 figures, Supplementary Information: 6 pages, 6 figure

Higher-order conservative interpolation between control-volume meshes: Application to advection and multiphase flow problems with dynamic mesh adaptivity

© 2016 .A general, higher-order, conservative and bounded interpolation for the dynamic and adaptive meshing of control-volume fields dual to continuous and discontinuous finite element representations is presented. Existing techniques such as node-wise interpolation are not conservative and do not readily generalise to discontinuous fields, whilst conservative methods such as Grandy interpolation are often too diffusive. The new method uses control-volume Galerkin projection to interpolate between control-volume fields. Bounded solutions are ensured by using a post-interpolation diffusive correction. Example applications of the method to interface capturing during advection and also to the modelling of multiphase porous media flow are presented to demonstrate the generality and robustness of the approach

Is An Oversupply of College Graduates Coming?

[Excerpt] Demand for college graduates workers was strong during the 1980s (Blackburn, Bloom and Freeman 1989; Katz and Murphy 1990; Kosters 1989; Freeman 1991). The relative wage of college graduate workers rose and college attendance rose in response. Have the demand and technology shocks that produced this result run their course? Is the supply response large enough to stop and/or reverse the 1980s escalation of the relative wages of college graduates? Read superficially, Bureau of Labor Statistics projections appear to suggest that the answers to these questions are YES. In the latest BLS report, the growing supply of college graduates was projected to outstrip growth of demand by 300,000 annually (Shelley 1996). Even larger gaps between supply and demand were projected in 1992 and 1994 (Shelley 1992, 1994). Looking at these projections, some in the press have reported that the college graduate labor market is about to go bust. New York Times reporter, Louis Uchitelle, for example, led off an article titled Surplus of College Graduates Dims Job Outlook for Others with the following

The accumulation and trapping of grains at planet gaps: effects of grain growth and fragmentation

We model the dust evolution in protoplanetary disks with full 3D, Smoothed Particle Hydrodynamics (SPH), two-phase (gas+dust) hydrodynamical simulations. The gas+dust dynamics, where aerodynamic drag leads to the vertical settling and radial migration of grains, is consistently treated. In a previous work, we characterized the spatial distribution of non-growing dust grains of different sizes in a disk containing a gap-opening planet and investigated the gap's detectability with the Atacama Large Millimeter/submillimeter Array (ALMA). Here we take into account the effects of grain growth and fragmentation and study their impact on the distribution of solids in the disk. We show that rapid grain growth in the two accumulation zones around planet gaps is strongly affected by fragmentation. We discuss the consequences for ALMA observations.Comment: Accepted for publication in Planetary and Space Science. 13 pages, 4 figure

Child development and success or failure in the youth labor market

Book description: The economic status of young people has declined significantly over the past two decades, despite a variety of programs designed to aid new workers in the transition from the classroom to the job market. This ongoing problem has proved difficult to explain. Drawing on comparative data from Canada, Germany, France, Sweden, and the United Kingdom, these papers go beyond examining only employment and wages and explore the effects of family background, education and training, social expectations, and crime on youth employment. This volume brings together key studies, providing detailed analyses of the difficult economic situation plaguing young workers. Why have demographic changes and additional schooling failed to resolve youth unemployment? How effective have those economic policies been which aimed to improve the labor skills and marketability of young people? And how have youths themselves responded to the deteriorating job market confronting them? These questions form the empirical and organizational bases upon which these studies are founded