University of Amsterdam

About: University of Amsterdam is a education organization based out in Amsterdam, Noord-Holland, Netherlands. It is known for research contribution in the topics: Population & Context (language use). The organization has 59309 authors who have published 140894 publications receiving 5984137 citations. The organization is also known as: UvA & Universiteit van Amsterdam.

Formation of massive black holes through runaway collisions in dense young star clusters.

Abstract: A luminous X-ray source is associated with MGG 11—a cluster of young stars ∼200 pc from the centre of the starburst galaxy M 82 (refs 1, 2). The properties of this source are best explained3,4 by invoking a black hole with a mass of at least 350 solar masses (350 M⊙), which is intermediate between stellar-mass and supermassive black holes. A nearby but somewhat more massive cluster (MGG 9) shows no evidence of such an intermediate-mass black hole1,3, raising the issue of just what physical characteristics of the clusters can account for this difference. Here we report numerical simulations of the evolution and motion of stars within the clusters, where stars are allowed to merge with each other. We find that for MGG 11 dynamical friction leads to the massive stars sinking rapidly to the centre of the cluster, where they participate in a runaway collision. This produces a star of 800–3,000 M⊙, which ultimately collapses to a black hole of intermediate mass. No such runaway occurs in the cluster MGG 9, because the larger cluster radius leads to a mass segregation timescale a factor of five longer than for MGG 11.

An agenda for purely confirmatory research

Abstract: The veracity of substantive research claims hinges on the way experimental data are collected and analyzed. In this article, we discuss an uncomfortable fact that threatens the core of psychology’s academic enterprise: almost without exception, psychologists do not commit themselves to a method of data analysis before they see the actual data. It then becomes tempting to fine tune the analysis to the data in order to obtain a desired result—a procedure that invalidates the interpretation of the common statistical tests. The extent of the fine tuning varies widely across experiments and experimenters but is almost impossible for reviewers and readers to gauge. To remedy the situation, we propose that researchers preregister their studies and indicate in advance the analyses they intend to conduct. Only these analyses deserve the label “confirmatory,” and only for these analyses are the common statistical tests valid. Other analyses can be carried out but these should be labeled “exploratory.” We illustrate our proposal with a confirmatory replication attempt of a study on extrasensory perception.

Mixed Embeddedness: (In)formal Economic Activities and Immigrant Businesses in the Netherlands

Abstract: Immigrants from non-industrialized countries have become part and parcel of the social fabric of many advanced urban economies, including those in the Netherlands. A significant number of these migrants opt for setting up shop themselves. Lacking access to large financial resources and mostly lacking in educational qualifications, they are funnelled towards the lower end of the opportunity structure of these urban economies. To survive in these cut-throat markets, many migrant entrepreneurs revert to informal economic activities that are strongly dependent on specific social networks – mostly consisting of co-ethnics – to sustain these activities on a more permanent basis. To understand the social position of these migrant entrepreneurs and their chances of upward social mobility, one has to look beyond these co-ethnic networks and focus on their insertion in the wider society in terms of customers, suppliers and various kinds of business organizations. To deal with this latter type of insertion, we propose the use of a more comprehensive concept of mixed embeddedness that aims at incorporating both the co-ethnic social networks as well as the linkages (or lack of linkages) between migrant entrepreneurs and the economic and institutional context of the host society. We illustrate this concept by presenting a case study of Islamic butchers in the Netherlands. — Les immigrants des pays pas industrialises sont devenus une part integrale du tissu social de nombreuses economies urbaines developpees, y compris celles des Pays-Bas. Un nombre significatif de migrants choisissent de s’etablir a leur compte. N’ayant pas acces a des ressources financieres importantes et ayant peu de qualifications academiques, ils sont entraines vers le bas des structures de debouches de ces economies. Pour survivre dans ces economies tres dures, beaucoup d’entrepreneurs immigrants retournent aux activites economiques informelles qui dependent fortement des reseaux sociaux specifiques – principalement co-ethniques – pour soutenir ces activites de facon plus permanente. Afin de comprendre la position sociale de ces migrants entrepreneurs et leurs possibilites de mobilite sociale vers le haut, il faut regarder plus loin que ces reseaux co-ethniques et explorer leur insertion dans la societe en general par rapport aux clients, fournisseurs et divers types d’organisation commerciales. Pour traiter de ce type d’insertion, nous proposons d’utiliser un concept d’incorporation melangee plus comprehensif qui a pour but d’integrer a la fois les reseaux sociaux co-ethniques et les liens (ou manque de liens) entre les migrants entrepreneurs et le contexte economique et institutionnel de la societe d’acceuil. Nous illustrons ce concept par un cas d’etude de bouchers islamiques aux Pays-Bas.

A general introduction to the biochemistry of mitochondrial fatty acid β-oxidation

Abstract: Over the years, the mitochondrial fatty acid β-oxidation (FAO) pathway has been characterised at the biochemical level as well as the molecular biological level. FAO plays a pivotal role in energy homoeostasis, but it competes with glucose as the primary oxidative substrate. The mechanisms behind this so-called glucose–fatty acid cycle operate at the hormonal, transcriptional and biochemical levels. Inherited defects for most of the FAO enzymes have been identified and characterised and are currently included in neonatal screening programmes. Symptoms range from hypoketotic hypoglycaemia to skeletal and cardiac myopathies. The pathophysiology of these diseases is still not completely understood, hampering optimal treatment. Studies of patients and mouse models will contribute to our understanding of the pathogenesis and will ultimately lead to better treatment.

Proposal for a revised definition of dilated cardiomyopathy, hypokinetic non-dilated cardiomyopathy, and its implications for clinical practice : a position statement of the ESC working group on myocardial and pericardial diseases

Abstract: In this paper the Working Group on Myocardial and Pericardial Disease proposes a revised definition of dilated cardiomyopathy (DCM) in an attempt to bridge the gap between our recent understanding of the disease spectrum and its clinical presentation in relatives, which is key for early diagnosis and the institution of potential preventative measures. We also provide practical hints to identify subsets of the DCM syndrome where aetiology directed management has great clinical relevance.