13,657 research outputs found

    Summary and general conclusions: Childbearing Trends and Policies in Europe

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    European fertility early in the 21st century was at its lowest level since the Second World War. This study explores contemporary childbearing trends and policies in Europe, and gives detailed attention to the past two or three decades. We felt motivated to undertake this project because in many European countries, as well as for the European Union as a whole, the overall fertility level and its consequences are of grave concern and draw attention on the political stage. Our account focuses somewhat more on the previously state socialist countries of Central and Eastern Europe, where available knowledge about the impact on childbearing of the momentous political and economic transition that started in 1989 remains relatively scarce. As family formation and childbearing behaviour are inherent components of societal life, they were influenced and modified by the various political, economic, and social changes that took place in Europe during the past 60 years. There were also profound changes in norms, values, beliefs, and attitudes regarding family and childbearing, and these exerted additional effects on fertility and family trends. To identify such effects, this study pays much attention to the influence of social and family policies on fertility, to the influence of political and economic changes on fertility and family trends, and to the diverse ways changes in values, norms, and attitudes relate to the transformation in family-related behaviour in Europe. In the present chapter, we outline main issues discussed in the subsequent overview chapters, and summarise the main findings of the entire study.childbearing, Europe

    Destroyed quantum Hall effect in graphene with [0001] tilt grain boundaries

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    The reason why the half-integer quantum Hall effect (QHE) is suppressed in graphene grown by chemical vapor deposition (CVD) is unclear. We propose that it might be connected to extended defects in the material and present results for the quantum Hall effect in graphene with [0001] tilt grain boundaries connecting opposite sides of Hall bar devices. Such grain boundaries contain 5-7 ring complexes that host defect states that hybridize to form bands with varying degree of metallicity depending on grain boundary defect density. In a magnetic field, edge states on opposite sides of the Hall bar can be connected by the defect states along the grain boundary. This destroys Hall resistance quantization and leads to non-zero longitudinal resistance. Anderson disorder can partly recover quantization, where current instead flows along returning paths along the grain boundary depending on defect density in the grain boundary and on disorder strength. Since grain sizes in graphene made by chemical vapor deposition are usually small, this may help explain why the quantum Hall effect is usually poorly developed in devices made of this material.Comment: 5 pages, 4 figure

    Correlated connectivity and the distribution of firing rates in the neocortex

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    Two recent experimental observations pose a challenge to many cortical models. First, the activity in the auditory cortex is sparse, and firing rates can be described by a lognormal distribution. Second, the distribution of non-zero synaptic strengths between nearby cortical neurons can also be described by a lognormal distribution. Here we use a simple model of cortical activity to reconcile these observations. The model makes the experimentally testable prediction that synaptic efficacies onto a given cortical neuron are statistically correlated, i.e. it predicts that some neurons receive many more strong connections than other neurons. We propose a simple Hebb-like learning rule which gives rise to both lognormal firing rates and synaptic efficacies. Our results represent a first step toward reconciling sparse activity and sparse connectivity in cortical networks
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