768,943 research outputs found

    Multidimensional communication mechanisms: cooperative and conflicting designs

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    This paper investigates optimal communication mechanisms with a two-dimensional policy space and no monetary transfers. Contrary to the one-dimensional setting, when a single principal controls two activities undertaken by his agent (cooperative design), the optimal communication mechanism never exhibits any pooling and the agent's ideal policies are never chosen. However, when the conflicts of interests between the agent and the principal on each dimension of the agent's activity are close to each other, simpler mechanisms that generalize those optimal in the one-dimensional case perform quite well. These simple mechanisms exhibit much pooling. When each activity of the agent is controlled by a different principal (non-cooperative design) and enters separately into the agent's utility function, optimal mechanisms under private communication take again the form of simple delegation sets, exactly as in the one-dimensional case. When instead the agent finds some benefits in coordinating actions, a one-sided contractual externality arises between principals under private communication. Under public communication instead, there does not exist any pure strategy Nash equilibrium with continuous and piecewise differentiable communication mechanisms. Relaxing the commitment ability of the principals restores equilibrium existence under public communication and yields partitional equilibria. Compared with private communication, public communication generates discipline or subversion effects among principals depending on the profile of their respective biases with respect to the agent's ideal policies.communication ; delegation ; mechanism design ; multi-dimensional decision ; common agency

    Heterogeneity and the Voluntary Provision of Public Goods

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    We investigate the effects of heterogeneity, incomplete information and communication on aggregate contributions to a public good using the voluntary contribution mechanism in a nonlinear laboratory environment. One-dimensional heterogeneity (heterogeneity in income or preferences) and two-dimensional heterogeneity (heterogeneity in income and preferences) both increase voluntary contributions. The effect is greatest when information is incomplete in the sense that subjects do not know each other’s payoffs. Incomplete information also reduces contributions in the homogeneous case. Communication reverses the relative importance of oneand two-dimensional heterogeneity in promoting cooperation.

    Breakdown of scale invariance in a quasi-two-dimensional Bose gas due to the presence of the third dimension

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    In this Rapid Communication, we describe how the presence of the third dimension may break the scale invariance in a two-dimensional Bose gas in a pancake-shaped trap. From the two-dimensional perspective, the possibility of a weak spilling of the atomic density beyond the ground-state of the confinement alters the two-dimensional chemical potential; in turn, this correction no longer supports scale invariance. We compare experimental data with numerical and analytic perturbative results and find a good agreement.Comment: 4 pages, 1 figure, published in PRA Rapid Com

    Fault-tolerant meshes and hypercubes with minimal numbers of spares

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    Many parallel computers consist of processors connected in the form of a d-dimensional mesh or hypercube. Two- and three-dimensional meshes have been shown to be efficient in manipulating images and dense matrices, whereas hypercubes have been shown to be well suited to divide-and-conquer algorithms requiring global communication. However, even a single faulty processor or communication link can seriously affect the performance of these machines. This paper presents several techniques for tolerating faults in d-dimensional mesh and hypercube architectures. Our approach consists of adding spare processors and communication links so that the resulting architecture will contain a fault-free mesh or hypercube in the presence of faults. We optimize the cost of the fault-tolerant architecture by adding exactly k spare processors (while tolerating up to k processor and/or link faults) and minimizing the maximum number of links per processor. For example, when the desired architecture is a d-dimensional mesh and k = 1, we present a fault-tolerant architecture that has the same maximum degree as the desired architecture (namely, 2d) and has only one spare processor. We also present efficient layouts for fault-tolerant two- and three-dimensional meshes, and show how multiplexers and buses can be used to reduce the degree of fault-tolerant architectures. Finally, we give constructions for fault-tolerant tori, eight-connected meshes, and hexagonal meshes

    Stability of quasi-two-dimensional Bose-Einstein condensates with dominant dipole-dipole interactions

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    We consider quasi-two-dimensional atomic/molecular Bose-Einstein condensates with both contact and dipole-dipole interactions. It is shown that, as a consequence of the dimensional reduction, and within mean-field theory, the condensates do not develop unstable excitation spectra, even when the dipole-dipole interaction completely dominates the contact interaction.Comment: 4 pages of RevTex4, 3 figures; Rapid Communication in Physical Review A (to be published

    Critical dynamics of a spin-5/2 2D isotropic antiferromagnet

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    We report a neutron scattering study of the dynamic spin correlations in Rb2_2MnF4_4, a two-dimensional spin-5/2 antiferromagnet. By tuning an external magnetic field to the value for the spin-flop line, we reduce the effective spin anisotropy to essentially zero, thereby obtaining a nearly ideal two-dimensional isotropic antiferromagnet. From the shape of the quasielastic peak as a function of temperature, we demonstrate dynamic scaling for this system and find a value for the dynamical exponent zz. We compare these results to theoretical predictions for the dynamic behavior of the two-dimensional Heisenberg model, in which deviations from z=1z=1 provide a measure of the corrections to scaling.Comment: 5 pages, 4 figures. Submitted to Physical Review B, Rapid Communication
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