5 research outputs found
Testing Core Membership in Public Goods Economies
This paper develops a recent line of economic theory seeking to understand
public goods economies using methods of topological analysis. Our first main
result is a very clean characterization of the economy's core (the standard
solution concept in public goods). Specifically, we prove that a point is in
the core iff it is Pareto efficient, individually rational, and the set of
points it dominates is path connected.
While this structural theorem has a few interesting implications in economic
theory, the main focus of the second part of this paper is on a particular
algorithmic application that demonstrates its utility. Since the 1960s,
economists have looked for an efficient computational process that decides
whether or not a given point is in the core. All known algorithms so far run in
exponential time (except in some artificially restricted settings). By heavily
exploiting our new structure, we propose a new algorithm for testing core
membership whose computational bottleneck is the solution of convex
optimization problems on the utility function governing the economy. It is
fairly natural to assume that convex optimization should be feasible, as it is
needed even for very basic economic computational tasks such as testing Pareto
efficiency. Nevertheless, even without this assumption, our work implies for
the first time that core membership can be efficiently tested on (e.g.) utility
functions that admit "nice" analytic expressions, or that appropriately defined
-approximate versions of the problem are tractable (by using
modern black-box -approximate convex optimization algorithms).Comment: To appear in ICALP 201
Doryphoribius chetumalensis sp. nov. (Eutardigrada: Isohypsibiidae) a new tardigrade species discovered in an unusual habitat of urban areas of Mexico
A new species, Doryphoribius chetumalensis, is described from specimens collected in the city of Chetumal (Quintana
Roo state, Mexico). The species was found in a new and unusual habitat for urban tardigrades, i.e. the soil sediment accumulated
on the border of streets. This discovery shows that tardigrades can live in this habitat, demonstrating once again
the wide capacity of this taxon to tolerate adverse habitats, and to survive in environments with high anthropogenic impact.
Doryphoribius chetumalensis sp. nov. differs from all the other species of the genus in having enlarged and wide bulbous
base of the claws. Within Doryphoribius, it belongs to the zappalai group, and differs from the species in this group, not
only in the claw shape, but also by the orange body colour, the smooth cuticle, the absence of a tooth in the wall of the
buccal ring, and the absence of lunules under the claws. This is the first record of tardigrades, identified to species level,
in Quintana Roo state. A taxonomic key of the Doryphoribius genus is also presented
TardĂgrados asociados a una plantaciĂłn de cĂtricos de traspatio en la comunidad de El Palmar en Quintana Roo, MĂ©xico
This study provides records of tardigrades in
lichen in a backyard plantation of citrics of a rural
community in Quintana Roo, Mexico. A diagnosis
is given of Ramazzottius, Mesobiotus and Milnesium genera are given. The richness of species and
abundance of tardigrades in Quintana Roo are
discussed. A comparative table of the most relevant
characteristics of the three genera is proposed.El presente estudio provee el registro de tardĂgrados
de lĂquenes en una plantaciĂłn de cĂtricos de traspatio
de la comunidad de El Palmar en el estado de
Quintana Roo, MĂ©xico. Se proporciona la diagnosis
de los géneros Ramazzottius, Mesobiotus y Milnesium. Se discute sobre la riqueza y abundancias de
tardĂgrados en el estado. Se proporciona un cuadro
comparativo de los caracteres más relevantes de
los tres géneros