Ensemble Averaging and the Curse of Dimensionality

When comparing climate models to observations, it is often observed that the mean over many models has smaller errors than most or all of the individual models. This paper will show that a general consequence of the nonintuitive geometric properties of high-dimensional spaces is that the ensemble mean often outperforms the individual ensemble members. This also explains why the ensemble mean often has an error that is 30% smaller than the median error of the individual ensemble members. The only assumption that needs to be made is that the observations and the models are independently drawn from the same distribution. An important and relevant property of high-dimensional spaces is that independent random vectors are almost always orthogonal. Furthermore, while the lengths of random vectors are large and almost equal, the ensemble mean is special, as it is located near the otherwise vacant center. The theory is first explained by an analysis of Gaussian- and uniformly distributed vectors in high-dimensional spaces. A subset of 17 models from the CMIP5 multimodel ensemble is then used to demonstrate the validity and robustness of the theory in realistic settings.

Taxi drivers: ethnic segmentation, precarious work, and informal economic strategies in the Swedish taxi industry

This article invesitgates the processes of ethnic segmentation, precarious labour, and informalization in the Swedish taxi industry during a period of rapid deregulation during the 1990s. It does so by focussing on the life story of a single individual―Adem, a taxi driver in the Swedish city of Malmö. Despite his education, long working experience, and all efforts to make use of these advantages, all doors to an appropriate career in Sweden have remained closed to him. As a result, he has been pushed into working in the taxi sector, which is increasingly characterized by ethnic segmentation, hard working conditins, and harsh competition, forcing people to deploy informal economic strategies in order to survive. Adem’s fate becomes strongly determined by these socio-economical processes. At the same time, the article shows that these processes are not separate, but are closely interrelated and reinforce each other. On the broader level these processes are a general consequence of the neoliberal reconstruction of Western economies, and structural economic, political and social changes related to it.

Stili organizzativi del volontariato italiano

The Author initially examines the organizational phenomenon of voluntarism within the broader context of the institutional restructuring processes of modern welfare, and proceeds to analyze the main structural characteristics of voluntary organizations in Italy and the different - and sometimes conflicting - organizational dynamics that can currently be found. These are, in general, consequence of the «tension» that has matured within the associations between the original mission and the professionalization of the services, between tradition and innovation. The aim is to analyze organizations' attitudes towards strategic management of change and towards the development of project management autonomy, essential to preserve social identity in the process of professionalizing services.

Overshooting dynamics in a model adaptive radiation

The history of life is punctuated by repeated periods of unusually rapid evolutionary diversification called adaptive radiation. The dynamics of diversity during a radiation reflect an overshooting pattern with an initial phase of exponential-like increase followed by a slower decline. Much attention has been paid to the factors that drive the increase phase, but far less is known about the causes of the decline phase. Decreases in diversity are rarely associated with climatic changes or catastrophic events, suggesting that they may be an intrinsic consequence of diversification. We experimentally identify the factors responsible for losses in diversity during the later stages of the model adaptive radiation of the bacterium Pseudomonas fluorescens . Proximately, diversity declines because of the loss of biofilm-forming niche specialist morphotypes. We show that this loss occurs despite the presence of strong divergent selection late in the radiation and is associated with continued adaptation of resident niche specialists to both the biotic and abiotic environments. These results suggest that losses of diversity in the latter stages of an adaptive radiation may be a general consequence of diversification through competition and lends support to the idea that the conditions favouring the emergence of diversity are different from those that ensure its long-term maintenance.

When does optional participation allow the evolution of cooperation?

Altruistic punishment has been shown to invade when rare if individuals are allowed to opt out of cooperative ventures. Individuals that opt out do not contribute to the common enterprise or derive benefits from it. This result is potentially significant because it offers an explanation for the origin of large-scale cooperation in one-shot interactions among unrelated individuals. Here, we show that this result is not a general consequence of optional participation in cooperative activities, but depends on special assumptions about cooperative pay-offs. We extend the pay-off structure of optional participation models to consider the effects of economies and diseconomies of scale in public-goods production, rival and non-rival consumption of goods, and different orderings of the pay-offs of freeriding and opting out. This more general model highlights the kinds of pay-offs for which optional participation favours cooperation, and those in which it does not.

Sustainable breeding objectives in developing countries

In the developed world, the last fifty years has seen a great convergence of breeding objectives and strategies in all farmed species. This is part of the effects of globalisation, which has led to ever increasing specialisation of livestock producers. A general consequence is that breeding goals and structures of dairy, beef, pig and poultry production are now very similar throughout the developed world.After some decades of successful concentration on narrow breeding goals (yield of milk solids in the dairy sector, growth, feed conversion and lean yield in meat animals) objectives have now broadened to take in product quality, reproduction and disease traits.

The structure of heterochromatic DNA is altered in polyploid cells of Drosophila melanogaster.

DNA sequences within heterochromatin are often selectively underrepresented during development of polyploid chromosomes, and DNA molecules of altered structure are predicted to form as a consequence of the underrepresentation process. We have identified heterochromatic DNAs of altered structure within sequences that are underrepresented in polyploid cells of Drosophila melanogaster. Specifically, restriction fragments that extend into centric heterochromatin of the minichromosome Dp(1;f)1187 are shortened in polyploid cells of both the ovary and salivary gland but not in the predominantly diploid cells of the embryo or larval imaginal discs and brains. Shortened DNA molecules were also identified within heterochromatic sequences of chromosome III. These results suggest that the structure of heterochromatic DNA is altered as a general consequence of polyploid chromosome formation and that the shortened molecules identified form as a consequence of heterochromatic underrepresentation. Finally, alteration of heterochromatic DNA structure on Dp(1;f)1187 was not correlated with changes in the variegated expression of the yellow gene located on the minichromosome.

5 Comparisons, Contrasts, and Conclusions

Before noting traits shared by the Arnipik and Tyara assemblages, a few words of caution and explanation may prove useful. I hope they will remain alive in the reader's mind as he examines the three closely related conclusions presented in this chapter. The three conclusions are, in order, a preliminary conclusion of restricted application, an intermediate conclusion of wider import, and a final conclusion of general consequence to this study. These conclusions' ranges of consequence increase as the discussion expands to encompass broader reaches of evidence and thinking pertinent to the question of Dorset culture origins. First, I have assumed, for previously presented or self-evident reasons, that the Tyara and Arnapik assemblages are pure assemblages, that is, that neither contains artifacts made by peoples of other cultures. Second, since the Arnapik material comprises only stone artifacts, comparison between that site and the bone, antler, and ivory artifacts from Tyara is precluded.