1,721,220 research outputs found
The influence of magnetic fields, turbulence, and UV radiation on the formation of supermassive black holes
Get PDF<p>Context. The seeds of the supermassive black holes with masses of similar to 10(9) M-circle dot observed already at z similar to 6 may have formed through the direct collapse of primordial gas in T-vir greater than or similar to 10(4) K halos, whereby the gas must stay hot (similar to 10(4) K) in order to avoid fragmentation.</p><p>Aims. The interplay between magnetic fields, turbulence, and a UV radiation background during the gravitational collapse of primordial gas in a halo is explored; in particular, the possibilities for avoiding fragmentation are examined.</p><p>Methods. Using an analytical one-zone model, the evolution of a cloud of primordial gas is followed from its initial cosmic expansion through turnaround, virialization, and collapse up to a density of 10(7) cm(-3).</p><p>Results. It was found that in halos with no significant turbulence, the critical UV background intensity (J(21)(crit)) for keeping the gas hot is lower by a factor similar to 10 for an initial comoving magnetic field B-0 similar to 2 nG than for the zero-field case, and even lower for stronger fields. In turbulent halos, J(21)(crit) is found to be a factor similar to 10 lower than for the zero-field-zero-turbulence case, and the stronger the turbulence (more massive halo and/or stronger turbulent heating), the lower J(21)(crit).</p><p>Conclusions. The reduction in J(21)(crit) is particularly important, since it exponentially increases the number of halos exposed to a super-critical radiation background.</p>
The Netherlands: experiments with non-financial compensation instruments in planning practice
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Building up resilience in cities worldwide – Rotterdam as participant in the 100 Resilient Cities Programme
No full textCities worldwide are challenged by a high complexity of acute and chronic problems, including challenges related to economic development, social polarisation and segregation as well as climate change and ecological degradation. While all of these problems are complex in themselves, they are also interrelated. Addressing them in a meaningful way requires governance systems with systemic capacities to deal with complexity. In order to create resilience in urban systems, cities need to be able to learn, adapt and transform across sectors and levels. One definition of urban resilience is the capacity of individuals, communities, institutions, businesses, and systems within a city to survive, adapt, and grow regardless of the kinds of chronic stress and acute shocks they experience. This is the definition the Rockefeller Foundation adopts in its mission to promote the well-being of humanity throughout the world by facilitating the building of resilience in cities worldwide through its 100 Resilient Cities Programme, launched in 2013. Rotterdam is one of the first cities to participate in this programme. The city has been a front-runner in preparing for climate change and striving for urban sustainability. This paper assesses the concept of urban resilience, introduces the Rockefeller Foundation's effort in building city resilience worldwide and illustrates this with the Rotterdam case.Accepted Author ManuscriptOLD Urban and Regional Developmen
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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