32,763 research outputs found
Supermodular mechanism design
This paper introduces a mechanism design approach that allows dealing with the multiple equilibrium problem, using mechanisms that are robust to bounded rationality. This approach is a tool for constructing supermodular mechanisms, i.e. mechanisms that induce games with strategic complementarities. In quasilinear environments, I prove that if a social choice function can be implemented by a mechanism that generates bounded strategic substitutes - as opposed to strategic complementarities - then this mechanism can be converted into a supermodular mechanism that implements the social choice function. If the social choice function also satisfies some efficiency criterion, then it admits a supermodular mechanism that balances the budget. Building on these results, I address the multiple equilibrium problem. I provide sufficient conditions for a social choice function to be implementable with a supermodular mechanism whose equilibria are contained in the smallest interval among all supermodular mechanisms. This is followed by conditions for supermodular implementability in unique equilibrium. Finally, I provide a revelation principle for supermodular implementation in environments with general preferences.Implementation, mechanisms, learning, strategic complementarities, supermodular games
Improved duality estimates and applications to reaction-diffusion equations
We present a refined duality estimate for parabolic equations. This estimate
entails new results for systems of reaction-diffusion equations, including
smoothness and exponential convergence towards equilibrium for equations with
quadratic right-hand sides in two dimensions. For general systems in any space
dimension, we obtain smooth solutions of reaction-diffusion systems coming out
of reversible chemistry under an assumption that the diffusion coefficients are
sufficiently close one to another
Surfaces of constant curvature in R^3 with isolated singularities
We prove that finite area isolated singularities of surfaces with constant
positive curvature in R^3 are removable singularities, branch points or
immersed conical singularities. We describe the space of immersed conical
singularities of such surfaces in terms of the class of real analytic closed
locally convex curves in the 2-sphere with admissible cusp singularities,
characterizing when the singularity is actually embedded. In the global
setting, we describe the space of peaked spheres in R^3, i.e. compact convex
surfaces of constant positive curvature with a finite number of singularities,
and give applications to harmonic maps and constant mean curvature surfaces.Comment: 28 page
The IBIS view of the galactic centre: INTEGRAL's imager observations simulations
The Imager on Board Integral Satellite (IBIS) is the imaging instrument of
the INTEGRAL satellite, the hard-X/soft-gamma ray ESA mission to be launched in
2001. It provides diagnostic capabilities of fine imaging (12' FWHM), source
identification and spectral sensitivity to both continuum and broad lines over
a broad (15 keV--10 MeV) energy range. It has a continuum sensitivity of
2~10^{-7} ph cm^{-2} s^{-1} at 1 MeV for a 10^6 seconds observation and a
spectral resolution better than 7 % at 100 keV and of 6 % at 1 MeV. The imaging
capabilities of the IBIS are characterized by the coupling of the above quoted
source discrimination capability with a very wide field of view (FOV), namely 9
x 9 degrees fully coded, 29 x 29 degrees partially coded FOV. We present
simulations of IBIS observations of the Galactic Center based on the results of
the SIGMA Galactic Center survey. They show the capabilities of this instrument
in discriminating between different sources while at the same time monitoring a
huge FOV. It will be possible to simultaneously take spectra of all of these
sources over the FOV even if the sensitivity decreases out of the fully coded
area. It is envisaged that a proper exploitation of both the FOV dimension and
the source localization capability of the IBIS will be a key factor in
maximizing its scientific output.Comment: 5 pages, LaTeX, to be published in the 4th Compton Symposium
Conference Proceedings, uses aipproc.cls, aipproc.sty (included
Liquid bridging of cylindrical colloids in near-critical solvents
Within mean field theory, we investigate the bridging transition between a
pair of parallel cylindrical colloids immersed in a binary liquid mixture as a
solvent which is close to its critical consolute point . We determine the
universal scaling functions of the effective potential and of the force between
the colloids. For a solvent which is at the critical concentration and close to
, we find that the critical Casimir force is the dominant interaction at
close separations. This agrees very well with the corresponding Derjaguin
approximation for the effective interaction between the two cylinders, while
capillary forces originating from the extension of the liquid bridge turn out
to be more important at large separations. In addition, we are able to infer
from the wetting characteristics of the individual colloids the first-order
transition of the liquid bridge connecting two colloidal particles to the
ruptured state. While specific to cylindrical colloids, the results presented
here provide also an outline for identifying critical Casimir forces acting on
bridged colloidal particles as such, and for analyzing the bridging transition
between them.Comment: 23 pages, 12 figure
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