278,632 research outputs found
Size versus fairness in the assignment problem
When not all objects are acceptable to all agents, maximizing the number of objects
actually assigned is an important design concern. We compute the guaranteed size ratio
of the Probabilistic Serial mechanism, i.e., the worst ratio of the actual expected size to
the maximal feasible size. It converges decreasingly to 1 â 1 e 63.2% as the maximal size
increases. It is the best ratio of any Envy-Free assignment mechanism
Beam Loss in Linacs
Beam loss is a critical issue in high-intensity accelerators, and much effort
is expended during both the design and operation phases to minimize the loss
and to keep it to manageable levels. As new accelerators become ever more
powerful, beam loss becomes even more critical. Linacs for H- ion beams, such
as the one at the Oak Ridge Spallation Neutron Source, have many more loss
mechanisms compared to H+ (proton) linacs, such as the one being designed for
the European Spallation Neutron Source. Interesting H- beam loss mechanisms
include residual gas stripping, H+ capture and acceleration, field stripping,
black-body radiation and the recently discovered intra-beam stripping
mechanism. Beam halo formation, and ion source or RF turn on/off transients,
are examples of beam loss mechanisms that are common for both H+ and H-
accelerators. Machine protection systems play an important role in limiting the
beam loss.Comment: 24 pages, contribution to the 2014 Joint International Accelerator
School: Beam Loss and Accelerator Protection, Newport Beach, CA, USA , 5-14
Nov 201
Mechanism Design for Team Formation
Team formation is a core problem in AI. Remarkably, little prior work has
addressed the problem of mechanism design for team formation, accounting for
the need to elicit agents' preferences over potential teammates. Coalition
formation in the related hedonic games has received much attention, but only
from the perspective of coalition stability, with little emphasis on the
mechanism design objectives of true preference elicitation, social welfare, and
equity. We present the first formal mechanism design framework for team
formation, building on recent combinatorial matching market design literature.
We exhibit four mechanisms for this problem, two novel, two simple extensions
of known mechanisms from other domains. Two of these (one new, one known) have
desirable theoretical properties. However, we use extensive experiments to show
our second novel mechanism, despite having no theoretical guarantees,
empirically achieves good incentive compatibility, welfare, and fairness.Comment: 12 page
Combining Outcome-Based and Preference-Based Matching: A Constrained Priority Mechanism
We introduce a constrained priority mechanism that combines outcome-based
matching from machine-learning with preference-based allocation schemes common
in market design. Using real-world data, we illustrate how our mechanism could
be applied to the assignment of refugee families to host country locations, and
kindergarteners to schools. Our mechanism allows a planner to first specify a
threshold for the minimum acceptable average outcome score that should
be achieved by the assignment. In the refugee matching context, this score
corresponds to the predicted probability of employment, while in the student
assignment context it corresponds to standardized test scores. The mechanism is
a priority mechanism that considers both outcomes and preferences by assigning
agents (refugee families, students) based on their preferences, but subject to
meeting the planner's specified threshold. The mechanism is both strategy-proof
and constrained efficient in that it always generates a matching that is not
Pareto dominated by any other matching that respects the planner's threshold.Comment: This manuscript has been accepted for publication by Political
Analysis and will appear in a revised form subject to peer review and/or
input from the journal's editor. End-users of this manuscript may only make
use of it for private research and study and may not distribute it furthe
Envy Freedom and Prior-free Mechanism Design
We consider the provision of an abstract service to single-dimensional
agents. Our model includes position auctions, single-minded combinatorial
auctions, and constrained matching markets. When the agents' values are drawn
from a distribution, the Bayesian optimal mechanism is given by Myerson (1981)
as a virtual-surplus optimizer. We develop a framework for prior-free mechanism
design and analysis. A good mechanism in our framework approximates the optimal
mechanism for the distribution if there is a distribution; moreover, when there
is no distribution this mechanism still performs well.
We define and characterize optimal envy-free outcomes in symmetric
single-dimensional environments. Our characterization mirrors Myerson's theory.
Furthermore, unlike in mechanism design where there is no point-wise optimal
mechanism, there is always a point-wise optimal envy-free outcome.
Envy-free outcomes and incentive-compatible mechanisms are similar in
structure and performance. We therefore use the optimal envy-free revenue as a
benchmark for measuring the performance of a prior-free mechanism. A good
mechanism is one that approximates the envy free benchmark on any profile of
agent values. We show that good mechanisms exist, and in particular, a natural
generalization of the random sampling auction of Goldberg et al. (2001) is a
constant approximation
Contract Development In A Matching Market: The Case of Kidney Exchange
We analyze a new transplant innovation â Advanced Donation, referred to by some as a kidney âgift certificate,â âlayaway plan,â or âvoucher â as a case study offering insights on both market and contract development. Advanced Donation provides an unusual window into the evolution of the exchange of a single good â a kidney for transplantation â from gift, to simple barter, to exchange with a temporal separation of obligations that relies solely on trust and reputational constraints for enforcement, to a complex matching market in which the parties rely, at least in part, on formal contract to define and clarify their obligations to each other.
The transplant community, however, has historically viewed formal contracts in the transplant setting with discomfort, and that traditional discomfort remains evident in current Advanced Donation practice. We conclude that the use of formal contracts in Advanced Donation is likely inadvertent, and the contracts, in a number of ways, are inadequate to tackle the complex, nonsimultaneous exchange of kidneys in which patients donate a kidney before their intended recipients have been matched with a potential donor
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Selection of earthquake ground motions for multiple objectives using genetic algorithms
Existing earthquake ground motion (GM) selection methods for the seismic assessment of structural systems focus on spectral compatibility in terms of either only central values or both central values and variability. In this way, important selection criteria related to the seismology of the region, local soil conditions, strong GM intensity and duration as well as the magnitude of scale factors are considered only indirectly by setting them as constraints in the pre-processing phase in the form of permissible ranges. In this study, a novel framework for the optimum selection of earthquake GMs is presented, where the aforementioned criteria are treated explicitly as selection objectives. The framework is based on the principles of multi-objective optimization that is addressed with the aid of the Weighted Sum Method, which supports decision making both in the pre-processing and post-processing phase of the GM selection procedure. The solution of the derived equivalent single-objective optimization problem is performed by the application of a mixed-integer Genetic Algorithm and the effects of its parameters on the efficiency of the selection procedure are investigated. Application of the proposed framework shows that it is able to track GM sets that not only provide excellent spectral matching but they are also able to simultaneously consider more explicitly a set of additional criteria
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