1,523 research outputs found
On the Complexity of Dynamic Mechanism Design
We introduce a dynamic mechanism design problem in which the designer wants
to offer for sale an item to an agent, and another item to the same agent at
some point in the future. The agent's joint distribution of valuations for the
two items is known, and the agent knows the valuation for the current item (but
not for the one in the future). The designer seeks to maximize expected
revenue, and the auction must be deterministic, truthful, and ex post
individually rational. The optimum mechanism involves a protocol whereby the
seller elicits the buyer's current valuation, and based on the bid makes two
take-it-or-leave-it offers, one for now and one for the future. We show that
finding the optimum deterministic mechanism in this situation - arguably the
simplest meaningful dynamic mechanism design problem imaginable - is NP-hard.
We also prove several positive results, among them a polynomial linear
programming-based algorithm for the optimum randomized auction (even for many
bidders and periods), and we show strong separations in revenue between
non-adaptive, adaptive, and randomized auctions, even when the valuations in
the two periods are uncorrelated. Finally, for the same problem in an
environment in which contracts cannot be enforced, and thus perfection of
equilibrium is necessary, we show that the optimum randomized mechanism
requires multiple rounds of cheap talk-like interactions
Pedestrian Risk Taking While Road Crossing: A Comparison of Observed and Declared Behaviour
AbstractThe objective of this research is the comparative analysis of observed and declared behaviour of pedestrians as regards road crossing in urban areas. A field survey was carried out, in which a panel of 75 young and middle-aged pedestrians (out of which 40 males) were asked to take 8 short walking trips (each one corresponding to a different walking and crossing scenario and involving one road crossing) in the Athens city centre in Greece. This allowed to record their crossing behaviour in different road and traffic conditions, including residential roads, main urban roads and major urban arterials. The same individuals were asked to fill in a questionnaire on their crossing behaviour and preferences at different road and traffic environments, as well as other related questions concerning their travel motivations, their mobility characteristics, their risk perceptions and preferences etc. A comparative analysis of their declared and observed crossing behaviour was carried out. More specifically, for each pedestrian, the rate of mid-block crossing and diagonal crossing during the walking tasks was calculated for the different road and traffic conditions. These were compared to their questionnaire responses on their crossing behaviour in different road and traffic conditions. The results suggest that, overall, pedestrians observed behaviour is in accordance with their declared behaviour. However, there is a non-negligible share of pedestrians, whose observed and declared behaviour were discordant, either at specific road and traffic conditions or overall. For instance, there were pedestrians who declared that they never cross at mid-block on major urban road but did so during the survey. Moreover, there were pedestrians who declared high frequency of mid-block crossing, but did not implement these crossing practices during the survey. The degree of discordance between pedestrian observed and declared behaviour was further analysed in relation to pedestrian demographics. A weak tendency was identified for female pedestrians to have more discordance between observed and declared crossing behaviour on residential roads, and the same was the case for young pedestrians in all road and traffic conditions. Overall, the results suggest that, while most pedestrians appear to have consistent declared and observed behaviour, there may all deviate from their general “profile” under specific conditions
A novel detrimental homozygous mutation in the WFS1 gene in two sisters from nonconsanguineous parents with untreated diabetes insipidus
Given the limited lifespan and with the recent progress in experimental treatments for WS, timely diagnosis and multidisciplinary treatment for DI/DM, hydronephrosis, and visual/psychiatric status-maintaining quality of life-are of crucial importance
Anomalous Supersymmetry
We show that supersymmetry is anomalous in superconformal
quantum field theories (SCFTs) with an anomalous R-symmetry. This anomaly was
originally found in holographic SCFTs at strong coupling. Here we show that
this anomaly is present in general and demonstrate it for the massless
superconformal Wess-Zumino model via a one loop computation. The anomaly
appears first in four-point functions of two supercurrents with either two
R-currents or with an R-current and an energy momentum tensor. In fact, the
Wess-Zumino consistency conditions together with the standard R-symmetry
anomaly imply the existence of the anomaly. We outline the implications of this
anomaly.Comment: 5 pages; v2 - contextual discussion and references added; v3 - final
PRL version, with comments adde
Probabilistic satisfiability
AbstractWe study the following computational problem proposed by Nils Nilsson: Several clauses (disjunctions of literals) are given, and for each clause the probability that the clause is true is specified. We are asked whether these probabilities are consistent. They are if there is a probability distribution on the truth assignments such that the probability of each clause is the measure of its satisfying set of assignments. Since this problem is a generalization of the satisfiability problem for propositional calculus it is immediately NP-hard. We show that it is NP-complete even when there are at most two literals per clause (a case which is polynomial-time solvable in the non-probabilistic case). We use arguments from linear programming and graph theory to derive polynomial-time algorithms for some interesting special cases
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