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Information Aggregation Under Ambiguity: Theory and Experimental Evidence
We study information aggregation in a dynamic trading model with partially informed and ambiguity averse traders. We show theoretically that separable securities, introduced by Ostrovsky (2012) in the context of Subjective Expected Utility, no longer
aggregate information if some traders have imprecise beliefs and are ambiguity averse. Moreover, these securities are prone to manipulation, as the degree of information aggregation can be influenced by the initial price, set by the uninformed market maker. These observations are also confirmed in our experiment, using prediction markets. We define a new class of strongly separable securities which are robust to the above considerations, and show that they characterize information aggregation in both strategic and non-strategic environments. We derive several theoretical predictions, which we are able to confirm in the lab
Statistical state dynamics of weak jets in barotropic beta-plane turbulence
Zonal jets in a barotropic setup emerge out of homogeneous turbulence through
a flow-forming instability of the homogeneous turbulent state (`zonostrophic
instability') which occurs as the turbulence intensity increases. This has been
demonstrated using the statistical state dynamics (SSD) framework with a
closure at second order. Furthermore, it was shown that for small
supercriticality the flow-forming instability follows Ginzburg-Landau (G-L)
dynamics. Here, the SSD framework is used to study the equilibration of this
flow-forming instability for small supercriticality. First, we compare the
predictions of the weakly nonlinear G-L dynamics to the fully nonlinear SSD
dynamics closed at second order for a wide ranges of parameters. A new branch
of jet equilibria is revealed that is not contiguously connected with the G-L
branch. This new branch at weak supercriticalities involves jets with larger
amplitude compared to the ones of the G-L branch. Furthermore, this new branch
continues even for subcritical values with respect to the linear flow-forming
instability. Thus, a new nonlinear flow-forming instability out of homogeneous
turbulence is revealed. Second, we investigate how both the linear flow-forming
instability and the novel nonlinear flow-forming instability are equilibrated.
We identify the physical processes underlying the jet equilibration as well as
the types of eddies that contribute in each process. Third, we propose a
modification of the diffusion coefficient of the G-L dynamics that is able to
capture the asymmetric evolution for weak jets at scales other than the
marginal scale (side-band instabilities) for the linear flow-forming
instability.Comment: 27 pages, 17 figure
Swarm intelligence in fish? The difficulty in demonstrating distributed and self-organised collective intelligence in (some) animal groups
AbstractLarger groups often have a greater ability to solve cognitive tasks compared to smaller ones or lone individuals. This is well established in social insects, navigating flocks of birds, and in groups of prey collectively vigilant for predators. Research in social insects has convincingly shown that improved cognitive performance can arise from self-organised local interactions between individuals that integrates their contributions, often referred to as swarm intelligence. This emergent collective intelligence has gained in popularity and been directly applied to groups of other animals, including fish. Despite being a likely mechanism at least partially explaining group performance in vertebrates, I argue here that other possible explanations are rarely ruled out in empirical studies. Hence, evidence for self-organised collective (or ‘swarm’) intelligence in fish is not as strong as it would first appear. These other explanations, the ‘pool-of-competence’ and the greater cognitive ability of individuals when in larger groups, are also reviewed. Also discussed is why improved group performance in general may be less often observed in animals such as shoaling fish compared to social insects. This review intends to highlight the difficulties in exploring collective intelligence in animal groups, ideally leading to further empirical work to illuminate these issues
Kinetic energy functional for Fermi vapors in spherical harmonic confinement
Two equations are constructed which reflect, for fermions moving
independently in a spherical harmonic potential, a differential virial theorem
and a relation between the turning points of kinetic energy and particle
densities. These equations are used to derive a differential equation for the
particle density and a non-local kinetic energy functional.Comment: 8 pages, 2 figure
Metastable states of a ferromagnet on random thin graphs
We calculate the mean number of metastable states of an Ising ferromagnet on
random thin graphs of fixed connectivity c. We find, as for mean field spin
glasses that this mean increases exponentially with the number of sites, and is
the same as that calculated for the +/- J spin glass on the same graphs. An
annealed calculation of the number <N_{MS}(E)> of metastable states of energy E
is carried out. For small c, an analytic result is obtained. The result is
compared with the one obtained for spin glasses in order to discuss the role
played by loops on thin graphs and hence the effect of real frustration on the
distribution of metastable states.Comment: 15 pages, 3 figure
Does Uranus’ asymmetric magnetic field produce a relatively weak proton radiation belt?
Since the Voyager 2 flyby in 1986 the radiation belts of Uranus have presented a problem for physicists. The observations indicate the electron radiation belt is far more intense than the proton radiation belt, and while the electron intensities are close to the upper theoretical limit, proton intensities are well below. Here we propose the relatively weak proton radiation belt could be due to Uranus' asymmetric magnetic field. We model test particle motion through the field to show that perturbations arising from asymmetry are greater the larger the particle gyroradius, predominantly affecting urn:x-wiley:00948276:media:grl65197:grl65197-math-0001100-keV protons. For these particles, more rapid changes in maximum distance from the planet during a bounce motion promote trajectory evolution into regions where they could be lost through impact with the rings, impact with the atmosphere, or to the distant magnetosphere and solar wind. We suggest this could explain a relatively weak proton radiation belt at Uranus
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