Linear response to leadership, effective temperature and decision making in flocks

Large collections of autonomously moving agents, such as animals or micro-organisms, are able to 'flock' coherently in space even in the absence of a central control mechanism. While the direction of the flock resulting from this critical behavior is random, this can be controlled by a small subset of informed individuals acting as leaders of the group. In this article we use the Vicsek model to investigate how flocks respond to leadership and make decisions. Using a combination of numerical simulations and continuous modeling we demonstrate that flocks display a linear response to leadership that can be cast in the framework of the fluctuation-dissipation theorem, identifying an 'effective temperature' reflecting how promptly the flock reacts to the initiative of the leaders. The linear response to leadership also holds in the presence of two groups of informed individuals with competing interests, indicating that the flock's behavioral decision is determined by both the number of leaders and their degree of influence.Comment: 8 pages (incl. supplementary information), 8 figures, Supplementary movies can be found at http://wwwhome.lorentz.leidenuniv.nl/~giomi/sup_mat/20151108

Surface Free Energies, Interfacial Tensions and Correlation Lengths of the ABF Models

The surface free energies, interfacial tensions and correlation lengths of the Andrews-Baxter-Forrester models in regimes III and IV are calculated with fixed boundary conditions. The interfacial tensions are calculated between arbitrary phases and are shown to be additive. The associated critical exponents are given by $2-\alpha_s=\mu=\nu$ with $\nu=(L+1)/4$ in regime III and $4-2\alpha_s=\mu=\nu$ with $\nu=(L+1)/2$ in regime IV. Our results are obtained using general commuting transfer matrix and inversion relation methods that may be applied to other solvable lattice models.Comment: 21 pages, LaTeX 2e, requires the amsmath packag

PECHCV, PECHFV, PEFHCV and PEFHFV: A set of atmospheric, primitive equation forecast models for the Northern Hemisphere, volume 3

As part of the SEASAT program of NASA, a set of four hemispheric, atmospheric prediction models were developed. The models, which use a polar stereographic grid in the horizontal and a sigma coordinate in the vertical, are: (1) PECHCV - five sigma layers and a 63 x 63 horizontal grid, (2) PECHFV - ten sigma layers and a 63 x 63 horizontal grid, (3) PEFHCV - five sigma layers and a 187 x 187 horizontal grid, and (4) PEFHFV - ten sigma layers and a 187 x 187 horizontal grid. The models and associated computer programs are described

Interaction-Round-a-Face Models with Fixed Boundary Conditions: The ABF Fusion Hierarchy

We use boundary weights and reflection equations to obtain families of commuting double-row transfer matrices for interaction-round-a-face models with fixed boundary conditions. In particular, we consider the fusion hierarchy of the Andrews-Baxter-Forrester models, for which we find that the double-row transfer matrices satisfy functional equations with an su(2) structure.Comment: 48 pages, LaTeX, requires about 79000 words of TeX memory. Submitted to J. Stat. Phy

Are We Free to Break the Laws of Providence?

Can I be free to perform an action if God has decided to ensure that I do not choose that action? I show that Molinists and simple foreknowl- edge theorists are committed to answering in the affirmative. This is problematic for their status as theological incompatibilists. I suggest that strategies for preserving their theological incompatibilism in light of this result should be based on sourcehood. However, the path is not easy here either, since Leibniz has shown how theological determinists can o er an extremely robust form of sourcehood. Proponents of these views must identify a valuable form of sourcehood their theories allow that Leibniz\u27s theory doesn\u27t