14,070 research outputs found
Rethinking the Effective Sample Size
The effective sample size (ESS) is widely used in sample-based simulation
methods for assessing the quality of a Monte Carlo approximation of a given
distribution and of related integrals. In this paper, we revisit and complete
the approximation of the ESS in the specific context of importance sampling
(IS). The derivation of this approximation, that we will denote as
, is only partially available in Kong [1992]. This
approximation has been widely used in the last 25 years due to its simplicity
as a practical rule of thumb in a wide variety of importance sampling methods.
However, we show that the multiple assumptions and approximations in the
derivation of , makes it difficult to be considered even
as a reasonable approximation of the ESS. We extend the discussion of the ESS
in the multiple importance sampling (MIS) setting, and we display numerical
examples. This paper does not cover the use of ESS for MCMC algorithms
The solution space of metabolic networks: producibility, robustness and fluctuations
Flux analysis is a class of constraint-based approaches to the study of
biochemical reaction networks: they are based on determining the reaction flux
configurations compatible with given stoichiometric and thermodynamic
constraints. One of its main areas of application is the study of cellular
metabolic networks. We briefly and selectively review the main approaches to
this problem and then, building on recent work, we provide a characterization
of the productive capabilities of the metabolic network of the bacterium E.coli
in a specified growth medium in terms of the producible biochemical species.
While a robust and physiologically meaningful production profile clearly
emerges (including biomass components, biomass products, waste etc.), the
underlying constraints still allow for significant fluctuations even in key
metabolites like ATP and, as a consequence, apparently lay the ground for very
different growth scenarios.Comment: 10 pages, prepared for the Proceedings of the International Workshop
on Statistical-Mechanical Informatics, March 7-10, 2010, Kyoto, Japa
Neural Mechanisms Underlying Paradoxical Performance for Monetary Incentives Are Driven by Loss Aversion
Employers often make payment contingent on
performance in order to motivate workers. We used
fMRI with a novel incentivized skill task to examine
the neural processes underlying behavioral responses
to performance-based pay. We found that
individuals’ performance increased with increasing
incentives; however, very high incentive levels led
to the paradoxical consequence of worse performance.
Between initial incentive presentation and
task execution, striatal activity rapidly switched
between activation and deactivation in response
to increasing incentives. Critically, decrements in
performance and striatal deactivations were directly
predicted by an independent measure of behavioral
loss aversion. These results suggest that incentives
associated with successful task performance are
initially encoded as a potential gain; however, when
actually performing a task, individuals encode the
potential loss that would arise from failure
A cross impact methodology for the assessment of US telecommunications system with application to fiber optics development: Executive summary
A cross impact model of the U.S. telecommunications system was developed. For this model, it was necessary to prepare forecasts of the major segments of the telecommunications system, such as satellites, telephone, TV, CATV, radio broadcasting, etc. In addition, forecasts were prepared of the traffic generated by a variety of new or expanded services, such as electronic check clearing and point of sale electronic funds transfer. Finally, the interactions among the forecasts were estimated (the cross impacts). Both the forecasts and the cross impacts were used as inputs to the cross impact model, which could then be used to stimulate the future growth of the entire U.S. telecommunications system. By varying the inputs, technology changes or policy decisions with regard to any segment of the system could be evaluated in the context of the remainder of the system. To illustrate the operation of the model, a specific study was made of the deployment of fiber optics, throughout the telecommunications system
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