Robust Covariance Adaptation in Adaptive Importance Sampling

Importance sampling (IS) is a Monte Carlo methodology that allows for approximation of a target distribution using weighted samples generated from another proposal distribution. Adaptive importance sampling (AIS) implements an iterative version of IS which adapts the parameters of the proposal distribution in order to improve estimation of the target. While the adaptation of the location (mean) of the proposals has been largely studied, an important challenge of AIS relates to the difficulty of adapting the scale parameter (covariance matrix). In the case of weight degeneracy, adapting the covariance matrix using the empirical covariance results in a singular matrix, which leads to poor performance in subsequent iterations of the algorithm. In this paper, we propose a novel scheme which exploits recent advances in the IS literature to prevent the so-called weight degeneracy. The method efficiently adapts the covariance matrix of a population of proposal distributions and achieves a significant performance improvement in high-dimensional scenarios. We validate the new method through computer simulations

Diverse Aging and Health Inequality by Race and Ethnicity

Although gerontologists have long embraced the concept of heterogeneity in theories and models of aging, recent research reveals the importance of racial and ethnic diversity on life course processes leading to health inequality. This article examines research on health inequality by race and ethnicity and identifies theoretical and methodological innovations that are transforming the study of health disparities. Drawing from cumulative inequality theory, we propose greater use of life course analysis, more attention to variability within racial and ethnic groups, and better integration of environmental context into the study of accumulation processes leading to health disparities

Evolutionary Physiology: The extent of C4 and CAM photosynthesis in the Genera Anacampseros and Grahamia of the Portulacaceae

The Portulacaceae is one of the few terrestrial plant families known to have both C(4) and Crassulacean acid metabolism (CAM) species. There may be multiple origins of the evolution of CAM within the Portulacaceae but the only clear evidence of C(4) photosynthesis is found in members of the genus Portulaca. In the Portulaca, CAM succulent tissue is overlaid with the C(4) tissue in a unique fashion where both pathways are operating simultaneously. Earlier reports have shown that the clade containing the genera Anacampseros and Grahamia may also contain C(4) photosynthetic species similar to the Portulaca, which would indicate multiple origins of C(4) photosynthesis within the family. The aim of the present study was to ascertain the true photosynthetic nature of these genera. An initial survey of the carbon isotope composition of the Anacampseros ranged from -12.6 per thousand to -24.0 per thousand, indicating very little CAM activity in some species, with other values close to the C(4) range. Anacampseros (=Grahamia) australiana which had been previously identified as a C(4) species had a carbon isotope composition value of -24.0 per thousand, which is more indicative of a C(3) species with a slight contribution of CAM activity. Other Anacampseros species with C(4)-like values have been shown to be CAM plants. The initial isotope analysis of the Grahamia species gave values in the range of -27.1 per thousand to -23.6 per thousand, placing the Grahamia species well towards the C(3) photosynthetic range. Further physiological studies indicated increased night-time CO(2) uptake with imposition of water stress, associated with a large diurnal acid fluctuation and a marked increased phosphoenolpyruvate carboxylase activity. This showed that the Grahamia species are actually facultative CAM plants despite their C(3)-like carbon isotope values. The results indicate that the Grahamia and Anacampseros species do not utilize the C(4) photosynthetic pathway. This is the first to identify that the Grahamia species are facultative CAM plants where CAM can be induced by water stress. This work supports earlier physiological work that indicates that this clade containing Anacampseros and Grahamia species comprises predominantly facultative CAM plants. This report suggests there may be only one clade which contains C(4) photosynthetic members with CAM-like characteristics

Is Social Assistance Contributing to Higher Informality in Turkey?

Although still low for European standards, investments in Social Assistance (SA) transfers in Turkey have been increasing in recent years. The government is expanding access to subsidized health for individuals in the informal sector through a rapid expansion of the Green Card program. Generous non-contributory programs, such as the Green Card, may create perverse incentives for individuals to join or remain in the informal sector as they can access free services without paying taxes and/or contributions, thus potentially being able to get higher “net” labor earnings than in the formal sector. Despite the fact that the Green Card is a large and generous program offered to individuals in the informal sector, empirical analysis in this report does not find an actual impact of the program (or of its rapid expansion) on informality. The reason behind this finding is the existence of a very large differential in wages between formal and informal workers explained by differences worker’s productivity. Low-wage workers facing the possibility to move from the informal sector to the formal sector would have strong incentives to do so even if this would imply losing all SA benefits. As such, the expected monetary and job security gains of having a formal job dominate those of having an informal job even after accounting for SA transfers.Informality, Social Assistance, Green Card, Turkey

The emotional contagion in children with autism spectrum disorder

Studies of the last decade have demonstrated that children with Autism Spectrum Disorder (ASD) showed difficulties in language, social and relational areas, but they had also impairment in the mechanisms of embodied simulation, namely the imitative behaviors that allow the body to give an experiential meaning to own and other’s emotions. The identification of this specific emotional response in ASD children, also defined as emotional contagion, allows to move the therapeutic focus from reducing the behavioral symptomatic expressions of the child to promoting the expression of his ability of emotional regulation. The aim of this study was to investigate the presence of emotional contagion in 53 ASD children aged between 22 and 66 months, through the Test of emotional contagion and verify the presence of compromised emotional contagion areas. Our findings have shown that the severity of the disorder is closely related to the inability of the child to respond to the emotional stimuli, regardless from cognitive abilities, and that emotion to which children responded most frequently was happiness, while the one who responded less was anger