A composition theorem for the Fourier Entropy-Influence conjecture

The Fourier Entropy-Influence (FEI) conjecture of Friedgut and Kalai [FK96] seeks to relate two fundamental measures of Boolean function complexity: it states that $H[f] \leq C Inf[f]$ holds for every Boolean function $f$, where $H[f]$ denotes the spectral entropy of $f$, $Inf[f]$ is its total influence, and $C > 0$ is a universal constant. Despite significant interest in the conjecture it has only been shown to hold for a few classes of Boolean functions. Our main result is a composition theorem for the FEI conjecture. We show that if $g_1,...,g_k$ are functions over disjoint sets of variables satisfying the conjecture, and if the Fourier transform of $F$ taken with respect to the product distribution with biases $E[g_1],...,E[g_k]$ satisfies the conjecture, then their composition $F(g_1(x^1),...,g_k(x^k))$ satisfies the conjecture. As an application we show that the FEI conjecture holds for read-once formulas over arbitrary gates of bounded arity, extending a recent result [OWZ11] which proved it for read-once decision trees. Our techniques also yield an explicit function with the largest known ratio of $C \geq 6.278$ between $H[f]$ and $Inf[f]$, improving on the previous lower bound of 4.615

Autocratic Breakdown and Regime Transitions: A New Data Set

When the leader of an autocratic regime loses power, one of three things happens. The incumbent leadership group is replaced by democratically elected leaders. Someone from the incumbent leadership group replaces him, and the regime persists. Or the incumbent leadership group loses control to a different group that replaces it with a new autocracy. Much scholarship exists on the first kind of transition, but little on transitions from one autocracy to another, though they make up about half of all regime changes. We introduce a new data set that facilitates the investigation of all three kinds of transition. It provides transition information for the 280 autocratic regimes in existence from 1946 to 2010. The data identify how regimes exit power, how much violence occurs during transitions, and whether the regimes that precede and succeed them are autocratic. We explain the data set and show how it differs from currently available data. The new data identify autocratic regime breakdowns regardless of whether the country democratizes, which makes possible the investigation of why the ouster of dictators sometimes leads to democracy but often does not, and many other questions. We present a number of examples to highlight how the new data can be used to explore questions about why dictators start wars and why autocratic breakdown sometimes results in the establishment of a new autocratic regime rather than democratization. We discuss the implications of these findings for the Arab Spring

Role of vitamin A/retinoic acid in regulation of embryonic and adult hematopoiesis

Vitamin A is an essential micronutrient throughout life. Its physiologically active metabolite retinoic acid (RA), acting through nuclear retinoic acid receptors (RARs), is a potent regulator of patterning during embryonic development, as well as being necessary for adult tissue homeostasis. Vitamin A deficiency during pregnancy increases risk of maternal night blindness and anemia and may be a cause of congenital malformations. Childhood Vitamin A deficiency can cause xerophthalmia, lower resistance to infection and increased risk of mortality. RA signaling appears to be essential for expression of genes involved in developmental hematopoiesis, regulating the endothelial/blood cells balance in the yolk sac, promoting the hemogenic program in the aorta-gonad-mesonephros area and stimulating eryrthropoiesis in fetal liver by activating the expression of erythropoietin. In adults, RA signaling regulates differentiation of granulocytes and enhances erythropoiesis. Vitamin A may facilitate iron absorption and metabolism to prevent anemia and plays a key role in mucosal immune responses, modulating the function of regulatory T cells. Furthermore, defective RA/RARα signaling is involved in the pathogenesis of acute promyelocytic leukemia due to a failure in differentiation of promyelocytes. This review focuses on the different roles played by vitamin A/RA signaling in physiological and pathological mouse hematopoiesis duddurring both, embryonic and adult life, and the consequences of vitamin A deficiency for the blood system

Developing the role concept for computer-supported collaborative learning

The role concept has attracted a lot of attention as a construct for facilitating and analysing interactions in the context of Computer-Supported Collaborative Learning (CSCL). So far much of this research has been carried out in isolation and the focus on roles lacks cohesion. In this article we present a conceptual framework to synthesise the contemporary conceptualisation of roles, by discerning three levels of the role concept: micro (role as task), meso (role as pattern) and macro (role as stance). As a first step to further conceptualise ‘role as a stance’, we present a framework of eight participative stances defined along three dimensions: group size, orientation and effort. The participative stances – Captain, Over-rider, Free-rider, Ghost, Pillar, Generator, Hanger-on and Lurker – were scrutinised on two data sets using qualitative analysis. The stances aim to facilitate meaningful description of student behaviour, stimulate both teacher and student awareness of roles at the macro-level in terms of participative stances, and evaluate or possibly change the participation to collaborative learning on all levels

Emerging and scripted roles in computer-supported collaborative learning

Emerging and scripted roles pose an intriguing approach to analysing and facilitating CSCL. The concept of emerging roles provides a perspective on how learners structure and self-regulate their CSCL processes. Emerging roles appear to be dynamic over longer periods of time in relation to learners’ advancing knowledge, but are often unequally distributed in ad hoc CSCL settings, e.g. a learner being the ‘typist’ and another being the ‘thinker’. Empirical findings show that learners benefit from structuring or scripting CSCL. Scripts can specify roles and facilitate role rotation for learners to equally engage in relevant learning roles and activities. Scripted roles can, however, collide with emerging roles and therefore need to be carefully attuned to the advancing capabilities of the learners

Cultura em movimento: Natalie Davis entre a antropologia e a história social

This paper analyzes the work of the historian Natalie Zemon Davis on the basis of its relationship with anthropology. Taking as axis the concept of culture, the goal is to reflect on the explicit and hidden dialogues that the author establishes with the anthropological literature, showing their changes over time. The paper divides Natalie Davis’ career in three stages: the 1970s, when she published her first book (Society and Culture in Early Modern France) and presented her first approach to anthropology; the 1980s, the time of the publication of The Return of Martin Guerre and Fiction in the Archives, which are clearly influenced by the debates of interpretative anthropology; and finally, the books written from the 1990s on, in which the author formulates a more dynamic analysis of cultural processes.Keywords: Natalie Davis, culture, ethnography.O artigo analisa a obra da historiadora Natalie Zemon Davis a partir de sua relação com a antropologia. Tomando como eixo o conceito de cultura, especialmente caro à disciplina vizinha, o objetivo é refletir sobre os diálogos explícitos e ocultos da autora com a literatura antropológica e mostrar suas transformações ao longo do tempo. Para tal, dividimos a trajetória acadêmica de Natalie Davis em três momentos: a década de 1970, quando publica seu primeiro livro (Culturas do povo), e que marca sua primeira aproximação com a antropologia; a década de 1980, período da publicação de O retorno de Martin Guerre e de Fiction in the Archives, marcadamente influenciados pelos debates da antropologia interpretativa; e, finalmente, os trabalhos escritos a partir da década de 1990, nos quais a autora formula uma análise mais dinâmica dos processos culturais.Palavras-chave: Natalie Davis, cultura, etnografia

Cultura em movimento: Natalie Davis entre a antropologia e a história social

This paper analyzes the work of the historian Natalie Zemon Davis on the basis of its relationship with anthropology. Taking as axis the concept of culture, the goal is to reflect on the explicit and hidden dialogues that the author establishes with the anthropological literature, showing their changes over time. The paper divides Natalie Davis’ career in three stages: the 1970s, when she published her first book (Society and Culture in Early Modern France) and presented her first approach to anthropology; the 1980s, the time of the publication of The Return of Martin Guerre and Fiction in the Archives, which are clearly influenced by the debates of interpretative anthropology; and finally, the books written from the 1990s on, in which the author formulates a more dynamic analysis of cultural processes.Keywords: Natalie Davis, culture, ethnography.O artigo analisa a obra da historiadora Natalie Zemon Davis a partir de sua relação com a antropologia. Tomando como eixo o conceito de cultura, especialmente caro à disciplina vizinha, o objetivo é refletir sobre os diálogos explícitos e ocultos da autora com a literatura antropológica e mostrar suas transformações ao longo do tempo. Para tal, dividimos a trajetória acadêmica de Natalie Davis em três momentos: a década de 1970, quando publica seu primeiro livro (Culturas do povo), e que marca sua primeira aproximação com a antropologia; a década de 1980, período da publicação de O retorno de Martin Guerre e de Fiction in the Archives, marcadamente influenciados pelos debates da antropologia interpretativa; e, finalmente, os trabalhos escritos a partir da década de 1990, nos quais a autora formula uma análise mais dinâmica dos processos culturais.Palavras-chave: Natalie Davis, cultura, etnografia

Finsler geometry on higher order tensor fields and applications to high angular resolution diffusion imaging.

We study 3D-multidirectional images, using Finsler geometry. The application considered here is in medical image analysis, specifically in High Angular Resolution Diffusion Imaging (HARDI) (Tuch et al. in Magn. Reson. Med. 48(6):1358–1372, 2004) of the brain. The goal is to reveal the architecture of the neural fibers in brain white matter. To the variety of existing techniques, we wish to add novel approaches that exploit differential geometry and tensor calculus. In Diffusion Tensor Imaging (DTI), the diffusion of water is modeled by a symmetric positive definite second order tensor, leading naturally to a Riemannian geometric framework. A limitation is that it is based on the assumption that there exists a single dominant direction of fibers restricting the thermal motion of water molecules. Using HARDI data and higher order tensor models, we can extract multiple relevant directions, and Finsler geometry provides the natural geometric generalization appropriate for multi-fiber analysis. In this paper we provide an exact criterion to determine whether a spherical function satisfies the strong convexity criterion essential for a Finsler norm. We also show a novel fiber tracking method in Finsler setting. Our model incorporates a scale parameter, which can be beneficial in view of the noisy nature of the data. We demonstrate our methods on analytic as well as simulated and real HARDI data

The effect of functional roles on perceived group efficiency during computer-supported collaborative learning

In this article, the effect of functional roles on group performance and collaboration during computer-supported collaborative learning (CSCL) is investigated. Especially the need for triangulating multiple methods is emphasised: Likert-scale evaluation questions, quantitative content analysis of e-mail communication and qualitative analysis of open-ended questions were used. A comparison of fourty-one questionnaire observations, distributed over thirteen groups in two research conditions – groups with prescribed functional roles (n = 7, N = 18) and nonrole groups (n = 6, N = 23) – revealed no main effect for performance (grade). Principal axis factoring of the Likert-scales revealed a latent variable that was interpreted as perceived group efficiency (PGE). Multilevel modelling (MLM) yielded a positive marginal effect of PGE. Most groups in the role condition report a higher degree of PGE than nonrole groups. Content analysis of e-mail communication of all groups in both conditions (role n = 7, N = 25; nonrole n = 6, N = 26) revealed that students in role groups contribute more ‘coordination’ focussed statements. Finally, results from cross case matrices of student responses to open-ended questions support the observed marginal effect that most role groups report a higher degree of perceived group efficiency than nonrole groups