Characterization of count data distributions involving additivity and binomial subsampling

In this paper we characterize all the $r$-parameter families of count distributions (satisfying mild conditions) that are closed under addition and under binomial subsampling. Surprisingly, few families satisfy both properties and the resulting models consist of the $r$th-order univariate Hermite distributions. Among these, we find the Poisson ($r=1$) and the ordinary Hermite distributions ($r=2$).Comment: Published at http://dx.doi.org/10.3150/07-BEJ6021 in the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

On the lattice of subgroups of a free group: complements and rank

A $\vee$-complement of a subgroup $H \leqslant \mathbb{F}_n$ is a subgroup $K \leqslant \mathbb{F}_n$ such that $H \vee K = \mathbb{F}_n$. If we also ask $K$ to have trivial intersection with $H$, then we say that $K$ is a $\oplus$-complement of $H$. The minimum possible rank of a $\vee$-complement (resp. $\oplus$-complement) of $H$ is called the $\vee$-corank (resp. $\oplus$-corank) of $H$. We use Stallings automata to study these notions and the relations between them. In particular, we characterize when complements exist, compute the $\vee$-corank, and provide language-theoretical descriptions of the sets of cyclic complements. Finally, we prove that the two notions of corank coincide on subgroups that admit cyclic complements of both kinds.Comment: 27 pages, 5 figure

Thread partitioning and value prediction for exploiting speculative thread-level parallelism

Speculative thread-level parallelism has been recently proposed as a source of parallelism to improve the performance in applications where parallel threads are hard to find. However, the efficiency of this execution model strongly depends on the performance of the control and data speculation techniques. Several hardware-based schemes for partitioning the program into speculative threads are analyzed and evaluated. In general, we find that spawning threads associated to loop iterations is the most effective technique. We also show that value prediction is critical for the performance of all of the spawning policies. Thus, a new value predictor, the increment predictor, is proposed. This predictor is specially oriented for this kind of architecture and clearly outperforms the adapted versions of conventional value predictors such as the last value, the stride, and the context-based, especially for small-sized history tables.Peer ReviewedPostprint (published version

Are dictatorships more unequal? : economic growth and wage inequality during Portugal's estado novo, 1944-1974.

This paper relates the changes in the structure of the Portuguese economy to changes in wage inequality, during 1944-1974, when Portugal had its golden age of growth under a dictatorial regime. We present a new wage data set based on surveys conducted by the Portuguese Statistics Office (INE). Our data set covers the whole economy, including 16 sectors, and data on skilled and unskilled labor for manufacturing, and on male and female labor force for agriculture. To measure the evolution of wage inequality we estimate a Theil index. The results reveal an inverted-U curve with a peak in 1959. We proceed by estimating econometrically the relationship between wage inequality and per capita income growth, controlling for the influence of additional variables that capture the effects of industrialization, investment in human and physical capital, emigration, foreign trade and the size of the government. We find a significant relationship between wage inequality, real GDP per capita, human capital and the share of government spending.Wage inequality; Structural change; Portugal;

A Nonparametric Conjugate Prior Distribution for the Maximizing Argument of a Noisy Function

We propose a novel Bayesian approach to solve stochastic optimization problems that involve finding extrema of noisy, nonlinear functions. Previous work has focused on representing possible functions explicitly, which leads to a two-step procedure of first, doing inference over the function space and second, finding the extrema of these functions. Here we skip the representation step and directly model the distribution over extrema. To this end, we devise a non-parametric conjugate prior based on a kernel regressor. The resulting posterior distribution directly captures the uncertainty over the maximum of the unknown function. We illustrate the effectiveness of our model by optimizing a noisy, high-dimensional, non-convex objective function.Comment: 9 pages, 5 figure

Response to Comment on ‘‘Asymmetric Coevolutionary Networks Facilitate Biodiversity Maintenance’’

Mutualistic networks are characterized by weak and asymmetric interactions, which a simple model predicts will facilitate species coexistence. Holland et al. propose a more complex model and argue that coexistence is independent of mutualism strength. However, we show that mutualism strength still plays an important role in their model and that it significantly decreases with species richness as predicted.Peer reviewe

Coevolution and the architecture of mutualistic networks

Although coevolution is widely recognized as an important evolutionary process for pairs of reciprocally specialized species, its importance within species-rich communities of generalized species has been questioned. Here we develop and analyze mathematical models of mutualistic communities, such as those between plants and pollinators or plants and seed-dispersers to evaluate the importance of coevolutionary selection within complex communities. Our analyses reveal that coevolutionary selection can drive significant changes in trait distributions with important consequences for the network structure of mutualistic communities. One such consequence is greater connectance caused by an almost invariable increase in the rate of mutualistic interaction within the community. Another important consequence is altered patterns of nestedness. Specifically, interactions mediated by a mechanism of phenotype matching tend to be antinested when coevolutionary selection is weak and even more strongly antinested as increasing coevolutionary selection favors the emergence of reciprocal specialization. In contrast, interactions mediated by a mechanism of phenotype differences tend to be nested when coevolutionary selection is weak, but less nested as increasing coevolutionary selection favors greater levels of generalization in both plants and animals. Taken together, our results show that coevolutionary selection can be an important force within mutualistic communities, driving changes in trait distributions, interaction rates, and even network structure. © 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.Peer Reviewe

Incremento de los riesgos geomorfológicos en el espacio urbano de Sarajevo como consecuencia del proceso de suburbanización y las políticas de neoliberalización

El pasado mes de mayo de 2014, las precipitaciones asociadas al profundo sistema de bajas presiones Tamara provocaron severas inundaciones y numerosos deslizamientos de tierra que afectaron a vastas áreas de la región balcánica occidental y central, alcanzando también la ciudad de Sarajevo (Bosnia y Herzegovina). En este episodio quedaron evidenciados los riesgos hidrológicos y geomorfológicos que afectan actualmente a un número significativo de áreas urbanas y suburbanas construidas en la capital bosnia desde el fin de la guerra. A partir de un trabajo observacional y etnográfico realizado entre los años 2010 y 2013, y con apoyo operacional de los Sistemas de Información Geográfica, este artículo tiene como objetivo analizar la creciente insostenibilidad urbana de la ciudad de Sarajevo, producida tanto por una densificación del fondo de valle en áreas inundables así como el proceso de suburbanización que ha venido produciéndose principalmente en las laderas de los macizos que abrigan la ciudad. Estos procesos son, respectivamente, resultado de la implementación de las polí- ticas de liberalización económica y de la necesidad por parte de las personas refugiadas en Sarajevo de estabilizar su situación en la ciudad tras el conflicto bélico

Paleopathology of soft tissues : what mummies can reveal

Paleopathology is a science located in a crossroad between history, archaeology, anthropology, and medicine an can offer unique historical knowledge by using techniques of traditional pathology as well as other branches of Medicine, which is especially fruitful when applied to ancient subjects in which soft tissues are preserved: mummies