Coasian Dynamics in Repeated English Auctions

We extend the Coase conjecture to the case of a seller with a single object, who faces n potential buyers and holds a sequence of English auctions until the object is sold. In an independent-private-values environment in which buyers and sellers share the same discount factor, we show that the (perfect Bayesian) equilibrium path of reserve prices obeys a Coasian logic. Moreover, the equilibrium reserve path lies below that for the model of repeated sealed-bid, second-price auctions studied by McAfee and Vincent (1997). Nevertheless, the open (English) and sealed-bid formats are shown to be revenue equivalent.

Varying Alpha Monopoles

We study static magnetic monopoles in the context of varying alpha theories and show that there is a group of models for which the t'Hooft-Polyakov solution is still valid. Nevertheless, in general static magnetic monopole solutions in varying alpha theories depart from the classical t'Hooft-Polyakov solution with the electromagnetic energy concentrated inside the core seeding spatial variations of the fine structure constant. We show that Equivalence Principle constraints impose tight limits on the allowed variations of alpha induced by magnetic monopoles which confirms the difficulty to generate significant large-scale spatial variation of the fine structure constant found in previous works. This is true even in the most favorable case where magnetic monopoles are the source for these variations.Comment: 8 pages, 10 figures; Version to be published in Phys. Rev.

Spatial patterns and biodiversity in rock-paper-scissors models with regional unevenness

Climate changes may affect ecosystems destabilising relationships among species. We investigate the spatial rock-paper-scissors models with a regional unevenness that reduces the selection capacity of organisms of one species. Our results show that the regionally weak species predominates in the local ecosystem, while spiral patterns appear far from the region, where individuals of every species play the rock-paper-scissors game with the same strength. Because the weak species controls all local territory, it is attractive for the other species to enter the local ecosystem to conquer the territory. However, our stochastic simulations show that the transitory waves formed when organisms of the strong species reach the region are quickly destroyed because of local strength unbalance in the selection game rules. Computing the effect of the topology on population dynamics, we find that the prevalence of the weak species becomes more significant if the transition of the selection capacity to the area of uneven rock-paper-scissors rules is smooth. Finally, our findings show that the biodiversity loss due to the arising of regional unevenness is minimised if the transition to the region where the cyclic game is unbalanced is abrupt. Our results may be helpful to biologists in comprehending the consequences of changes in the environmental conditions on species coexistence and spatial patterns in complex systems.Comment: 17 pages, 7 figure

Evolution of the fine-structure constant in the non-linear regime

We study the evolution of the fine-structure constant, $\alpha$, induced by non-linear density perturbations in the context of the simplest class of quintessence models with a non-minimal coupling to the electromagnetic field, in which the two available free functions (potential and gauge kinetic function) are Taylor-expanded up to linear order. We show that the results obtained using the spherical infall model for an infinite wavelength inhomogeneity are inconsistent with the results of a local linearized gravity study and we argue in favour of the second approach. We also discuss recent claims that the value of $\alpha$ inside virialised regions could be significantly different from the background one on the basis of these findings.Comment: 5 pages, 3 figure

The importance of the mixed phase in hybrid stars built with the Nambu-Jona-Lasinio model

We investigate the structure of hybrid stars based on two different constructions: one is based on the Gibbs condition for phase coexistence and considers the existence of a mixed phase (MP), and the other is based on the Maxwell construction and no mixed phase is obtained. The hadron phase is described by the non-linear Walecka model (NLW) and the quark phase by the Nambu-Jona-Lasinio model (NJL). We conclude that the masses and radii obtained are model dependent but not significantly different for both constructions.Comment: 8 pages, 7 figures, 3 table

Coasian Dynamics in Repeated English Auctions

We extend the Coase conjecture to the case of a seller with a single object, who faces n potential buyers and holds a sequence of English auctions until the object is sold. In an independent-private-values environment in which buyers and sellers share the same discount factor, we show that the (perfect Bayesian) equilibrium path of reserve prices obeys a Coasian logic. Moreover, the equilibrium reserve path lies below that for the model of repeated sealed-bid, second-price auctions studied by McAfee and Vincent (1997). Nevertheless, the open (English) and sealed-bid formats are shown to be revenue equivalent

Structural combination of neural network models

Forecasts combinations normally use point forecasts that were obtained from different models or sources ([1], [2], [3]). This paper explores the incorporation of internal structure parameters of feed-forward neural network (NN) models as an approach to combine their forecasts via ensembles. First, the generated NN models that could be part of the ensembles are subject to a clustering algorithm that uses the structure parameters and, from each of the clusters obtained, a small set of models is selected and their forecasts are combined in a two-stage procedure. Secondly, in an alternative and simpler implementation, a subset of the generated NN models is selected by using several reference points in the model structure parameter space. The choice of the reference points is optimised through a genetic algorithm and the models selected are averaged. Hourly electricity demand time series is used to assess multi-step ahead forecasting performance for up to a 12 hours horizon. Results are compared against several statistical benchmarks, the average of the individual forecasts and the best models in the ensembles. Results show that the clusterbased (CB) structural combinations do better than the genetic algorithm (GA) structural combinations in outperforming the average forecast, which is the traditional point forecast from an ensemble