59 research outputs found
Sequential Deliberation for Social Choice
In large scale collective decision making, social choice is a normative study
of how one ought to design a protocol for reaching consensus. However, in
instances where the underlying decision space is too large or complex for
ordinal voting, standard voting methods of social choice may be impractical.
How then can we design a mechanism - preferably decentralized, simple,
scalable, and not requiring any special knowledge of the decision space - to
reach consensus? We propose sequential deliberation as a natural solution to
this problem. In this iterative method, successive pairs of agents bargain over
the decision space using the previous decision as a disagreement alternative.
We describe the general method and analyze the quality of its outcome when the
space of preferences define a median graph. We show that sequential
deliberation finds a 1.208- approximation to the optimal social cost on such
graphs, coming very close to this value with only a small constant number of
agents sampled from the population. We also show lower bounds on simpler
classes of mechanisms to justify our design choices. We further show that
sequential deliberation is ex-post Pareto efficient and has truthful reporting
as an equilibrium of the induced extensive form game. We finally show that for
general metric spaces, the second moment of of the distribution of social cost
of the outcomes produced by sequential deliberation is also bounded
Identification of glucose transporters in Aspergillus nidulans
o characterize the mechanisms involved in glucose transport, in the filamentous fungus Aspergillus nidulans, we have identified four glucose transporter encoding genes hxtB-E. We evaluated the ability of hxtB-E to functionally complement the Saccharomyces cerevisiae EBY.VW4000 strain that is unable to grow on glucose, fructose, mannose or galactose as single carbon source. In S. cerevisiae HxtB-E were targeted to the plasma membrane. The expression of HxtB, HxtC and HxtE was able to restore growth on glucose, fructose, mannose or galactose, indicating that these transporters accept multiple sugars as a substrate through an energy dependent process. A tenfold excess of unlabeled maltose, galactose, fructose, and mannose were able to inhibit glucose uptake to different levels (50 to 80 %) in these s. cerevisiae complemented strains. Moreover, experiments with cyanide-m-chlorophenylhydrazone (CCCP), strongly suggest that hxtB, -C, and âE mediate glucose transport via active proton symport. The A. nidulans ÎhxtB, ÎhxtC or ÎhxtE null mutants showed ~2.5-fold reduction in the affinity for glucose, while ÎhxtB and -C also showed a 2-fold reduction in the capacity for glucose uptake. The ÎhxtD mutant had a 7.8-fold reduction in affinity, but a 3-fold increase in the capacity for glucose uptake. However, only the ÎhxtB mutant strain showed a detectable decreased rate of glucose consumption at low concentrations and an increased resistance to 2-deoxyglucose.The authors would like to thank the Fundacao de Amparo a Pesquisa do Estado de Sao Paulo and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Brazil for financial support. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Global patterns of nitrate isotope composition in rivers and adjacent aquifers reveal reactive nitrogen cascading
Remediation of nitrate pollution of Earthâs rivers and aquifers is hampered by cumulative biogeochemical processes and nitrogen sources. Isotopes (ÎŽ15N, ÎŽ18O) help unravel spatiotemporal nitrogen(N)-cycling of aquatic nitrate (NO3â). We synthesized nitrate isotope data (nâ=â~5200) for global rivers and shallow aquifers for common patterns and processes. Rivers had lower median NO3â (0.3â±â0.2âmgâLâ1, nâ=â2902) compared to aquifers (5.5â±â5.1âmgâLâ1, nâ=â2291) and slightly lower ÎŽ15N values (+7.1â±â3.8â°, nâ=â2902 vs +7.7â±â4.5â°, nâ=â2291), but were indistinguishable in ÎŽ18O (+2.3â±â6.2â°, nâ=â2790 vs +2.3â±â5.4â°, nâ=â2235). The isotope composition of NO3â was correlated with water temperature revealing enhanced N-cascading in warmer climates. Seasonal analyses revealed higher ÎŽ15N and ÎŽ18O values in wintertime, suggesting waste-related N-source signals are better preserved in the cold seasons. Isotopic assays of nitrate biogeochemical transformations are key to understanding nitrate pollution and to inform beneficial agricultural and land management strategies
Sensitivity Analysis in Minisum Facility Location-problems
This paper considers tradeoffs between cost and perturbations of the weights in a single facility, minisum location problem over a finite set of feasible points. Specifically, the paper characterizes a tradeoff curve of variability in the weights versus the degree of optimality of a solution. The general theoretical framework includes problems of location on a tree network and location using block norms; special results are given for these cases
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