Benchmark Priors for Bayesian Model Averaging

In contrast to a posterior analysis given a particular sampling model, posterior model probabilities in the context of model uncertainty are typically rather sensitive to the specification of the prior. In particular, "diffuse'' priors on model-specific parameters can lead to quite unexpected consequences. Here we focus on the practically relevant situation where we need to entertain a (large) number of sampling models and we have (or wish to use) little or no subjective prior information. We aim at providing an ``automatic'' or ``benchmark'' prior structure that can be used in such cases. We focus on the Normal linear regression model with uncertainty in the choice of regressors. We propose a partly noninformative prior structure related to a Natural Conjugate $g$-prior specification, where the amount of subjective information requested from the user is limited to the choice of a single scalar hyperparameter $g_{0j}$. The consequences of different choices for $g_{0j}$ are examined. We investigate theoretical properties, such as consistency of the implied Bayesian procedure. Links with classical information criteria are provided. More importantly, we examine the finite sample implications of several choices of $g_{0j}$ in a simulation study. The use of the MC$^3$ algorithm of Madigan and York (1995), combined with efficient coding in Fortran, makes it feasible to conduct large simulations. In addition to posterior criteria, we shall also compare the predictive performance of different priors. A classic example concerning the economics of crime will also be provided and contrasted with results in the literature. The main findings of the paper will lead us to propose a "benchmark'' prior specification in a linear regression context with model uncertainty.Bayes Factors, Markov chain Monte Carlo, Posterior odds, Prior elicitation

The emergence and evolution of optimistic expectations in school-children

Al aproximarnos al estudio del optimismo en niños, encontramos la aparición de un sesgo que les lleva a elaborar predicciones optimistas. Con esta investigación pretendemos conocer los cambios que se producen en la etapa de educación primaria (6-12 años), tanto en la aparición del sesgo optimista como en la explicaciones que los niños hacen de sus predicciones. Han participado un total de 77 alumnos a los que de manera individual y mediante un formato de entrevista piagetiana se les ha pedido realizar predicciones sobre diferentes situaciones hipotéticas. Tras un primer análisis para establecer si la predicción del niño implicaba un cambio en sentido optimista o pesimista, se han categorizado las respuestas ofrecidas por los niños al argumentar su predicción. Los resultados muestran que los participantes en esta investigación consideran más probable el cambio positivo para eventos psicológicos o híbridos que para los biológicos, y que estos cambios son más probables entre los niños de menor edad. En cuanto a las explicaciones de estos cambios, los niños consideran que la propia naturaleza o el paso del tiempo pueden ser responsables de los mismos sin mediar otro tipo de intervenciones. Igualmente, razones parecidas suelen dar los niños mayores para explicar el mantenimiento de las situaciones. When we study optimism in children, we note the temporary emergence of a bias that leads them to make optimistic predictions. In this study we intend to learn more about changes that can be observed in the optimistic bias of 6-to 12-year old schoolchildren when they predict future events, and in the way they justify those predictions. A total of 77 pupils participated in this study; we evaluated each one of them individually with a Piagetian interview, asking them to formulate predictions about a series of hypothetical situations. After analyzing whether a child’s prediction implied that the situation would maintain itself or would change for better or for worse, we classified the justifications they provided for their predictions. Results show that these subjects regarded positive change as more likely in the case of psychological or hybrid events than for purely biological ones, and that younger children tended to display a greater bias in favor of the likelihood of positive change. These younger children justified their predictions stating that nature or the passing of time could be responsible for the changes, without needing further intervention on the part of other agents. Older children, on the other hand, tended to provide similar kinds of explanations to justify their expectation of stasis

The ratio of viscosity to entropy density in a pion gas satisfies the KSS holographic bound

We evaluate the ratio of shear viscosity to entropy density in a pion gas employing the Uehling-Uehlenbeck equation and experimental phase-shifts parameterized by means of the SU(2) Inverse Amplitude Method. We find that the ratio for this monocomponent gas stays well above the KSS 1/(4 pi) bound. We find similar results with other sets of phase shifts and conclude the bound is nowhere violated.Comment: 2 page text, three figures. V2: short comment and graph added to assert that a minimum of eta/s is not discarded from the hadron, low T side in a heavy-ion collisio

Horner's Syndrome due to a Spontaneous Internal Carotid Artery Dissection after Deep Sea Scuba Diving

Internal carotid artery dissection (ICAD) is a rare entity that either results from traumatic injury or can be spontaneously preceded or not by a minor trauma such as sporting activities. It represents a major cause of stroke in young patients. The diagnosis should be suspected with the combination of Horner''s syndrome, headache or neck pain, and retinal or cerebral ischaemia. The confirmation is frequently made with a magnetic resonance angiography (MRA). Although anticoagulation with heparin followed by vitamin-K-antagonists is the most common treatment, there is no difference in efficacy of antiplatelet and anticoagulant drugs at preventing stroke and death in patients with symptomatic carotid dissection. We describe a patient with ICAD following deep sea scuba diving, who presented with Horner''s syndrome and neck pain and was successfully treated with anticoagulants

Poisson-Hopf algebra deformations of Lie-Hamilton systems

Hopf algebra deformations are merged with a class of Lie systems of Hamiltonian type, the so-called Lie-Hamilton systems, to devise a novel formalism: the Poisson-Hopf algebra deformations of Lie-Hamilton systems. This approach applies to any Hopf algebra deformation of any Lie-Hamilton system. Remarkably, a Hopf algebra deformation transforms a Lie-Hamilton system, whose dynamic is governed by a finite-dimensional Lie algebra of functions, into a non-Lie-Hamilton system associated with a Poisson-Hopf algebra of functions that allows for the explicit description of its t-independent constants of the motion from deformed Casimir functions. We illustrate our approach by considering the Poisson-Hopf algebra analogue of the non-standard quantum deformation of sl(2) and its applications to deform well-known Lie-Hamilton systems describing oscillator systems, Milne-Pinney equations, and several types of Riccati equations. In particular, we obtain a new position-dependent mass oscillator system with a time-dependent frequency

Allergenicity assessment of novel food proteins: what should be improved?

Allergenicity prediction is one of the most challenging aspects in the safety assessment of foods derived from either biotechnology or novel food proteins. Here we present a bottom-up strategy that defines a priori the specific risk assessment (RA) needs based on a database appropriately built for such purposes

Sweet-and-salty biocatalysis : fructooligosaccharides production using Cladosporium cladosporioides in seawater

Production of fructooligosaccharides (FOS) from sucrose was obtained using a bioprocess entirely performed in seawater. The halophilic fungus Cladosporium cladosporioides MUT 5506 was grown in a seawater-based medium and mycelium displayed an optimal activity in seawater at 50\u201360 \ub0C, being stable up to 60 \ub0C. Under optimized conditions in seawater (50 \ub0C, sucrose 600 g/L, lyophilized mycelium 40 g/L), C. cladosporioides gave a maximum FOS yield of 344 g/L after 72 h with a preponderance of 1F-FOS derivatives (1-kestose 184 g/L, 1-nystose 98 g/L and 1-fructofuranosylnystose 22 g/L), and the noteworthy presence of the non-conventional disaccharide blastose (30 g/L after 144 h). Lyophilized mycelium exhibited good stability in seawater (76% of the initial activity was retained after 15 cycles of reutilization). This proof-of-concept application reports for the first time the production of FOS in a non-conventional medium such as seawater