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Search Results: 1 - 10 of 319 matches for " Sacha Epskamp "
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The Small World of Psychopathology
Denny Borsboom, Angélique O. J. Cramer, Verena D. Schmittmann, Sacha Epskamp, Lourens J. Waldorp
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0027407
Abstract: Background Mental disorders are highly comorbid: people having one disorder are likely to have another as well. We explain empirical comorbidity patterns based on a network model of psychiatric symptoms, derived from an analysis of symptom overlap in the Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV). Principal Findings We show that a) half of the symptoms in the DSM-IV network are connected, b) the architecture of these connections conforms to a small world structure, featuring a high degree of clustering but a short average path length, and c) distances between disorders in this structure predict empirical comorbidity rates. Network simulations of Major Depressive Episode and Generalized Anxiety Disorder show that the model faithfully reproduces empirical population statistics for these disorders. Conclusions In the network model, mental disorders are inherently complex. This explains the limited successes of genetic, neuroscientific, and etiological approaches to unravel their causes. We outline a psychosystems approach to investigate the structure and dynamics of mental disorders.
qgraph: Network Visualizations of Relationships in Psychometric Data
Sacha Epskamp,Angelique O. J. Cramer,Lourens J. Waldorp,Verena D. Schmittmann
Journal of Statistical Software , 2012,
Abstract: We present the qgraph package for R, which provides an interface to visualize data through network modeling techniques. For instance, a correlation matrix can be represented as a network in which each variable is a node and each correlation an edge; by varying the width of the edges according to the magnitude of the correlation, the structure of the correlation matrix can be visualized. A wide variety of matrices that are used in statistics can be represented in this fashion, for example matrices that contain (implied) covariances, factor loadings, regression parameters and p values. qgraph can also be used as a psychometric tool, as it performs exploratory and confirmatory factor analysis, using sem and lavaan; the output of these packages is automatically visualized in qgraph, which may aid the interpretation of results. In this article, we introduce qgraph by applying the package functions to data from the NEO-PI-R, a widely used personality questionnaire.
The struggle to detect circulating DNA
Sacha Zeerleder
Critical Care , 2006, DOI: 10.1186/cc4932
Abstract: In the previous issue of Critical Care, Rhodes and colleagues [1] report on significantly increased levels of circulating DNA in patients admitted to the intensive care unit (ICU) in comparison with healthy controls. They show plasma DNA levels to be an independent predictor of mortality and the development of sepsis in these patients. In sepsis and trauma, circulating nucleosomal DNA is positively correlated with disease severity and adverse outcome [2,3]. In cancer, changes in circulating DNA levels have a prognostic value [4]. Interestingly, in systemic lupus erythematosus, an autoimmune disease in which nucleosomal DNA functions as autoantigenic target, no correlation of circulating nucleosomal DNA with disease severity can be found; instead there is a correlation with anti-nucleosomal DNA antibodies [5]. It is very likely that these antibodies take care of enhanced clearance of nucleosomes.DNA in plasma most probably circulates bound to proteins in the form of mononucleosomes and/or oligonucleosomes and is released after the cleavage of easily accessible linkage sites of cellular DNA by endonucleases after cell death [6]. A mononucleosome consists of a core particle composed of an octamer of two copies each of histones H2A, H2B, H3 and H4, around which a stretch of helical DNA 146 base pairs in length is wrapped. Oligonucleosomes are composed of variable amounts of mononucleosomes connected by intact linker DNA with a variable length of 15 to 100 base pairs containing a 'linker' histone H1. Once released into the circulation, nucleosomes seem to be protected by their structure from further degradation by endonucleases [7].In healthy individuals, the concentration of circulating DNA is low, because dead cells are removed efficiently from circulation by phagocytes. Circulating DNA has a short half-life (10 to 15 minutes) and is removed mainly by the liver [8,9]. Accumulation of DNA in the circulation can result from an excessive release of DNA caused by massive c
Flavoured Leptogenesis
Davidson, Sacha
High Energy Physics - Phenomenology , 2007,
Abstract: Thermal leptogenesis, in the seesaw model, is a popular mechanism for generating the Baryon Asymmetry of the Universe. It was noticed recently, that including lepton flavour can modify significantly the results. These proceedings aim to discuss why and when flavour matters, in the thermal leptogenesis scenario for hierarchical right-handed neutrinos. No Boltzmann Equations are introduced.
About a Definition of Nano: How to Articulate Nano and Technology?
Sacha Loeve
Hyle : International Journal for Philosophy of Chemistry , 2010,
Abstract: It is often assumed that 'nano' is merely a communication and marketing token. Our inquiry in a number of French laboratories in the field of artificial molecular machines resulted in a quite different picture: a number of researchers are concerned with the definition of nanotechnology. This paper starts from the attempts made by one of the leading figure in the field of molecular machines, Christian Joachim, to draw a clear demarcation between what is 'really nano' and what is not. Probing the epistemological basis of his strategy, we also underline its limits. As this definition is only focused on the prefix 'nano', it would benefit from being completed and enlarged by a definition of 'technology'. We argue that molecular machines belong to the realm of technology in Gilbert Simondon's meaning of this term: a genesis of individualized objects coordinating natural processes and human projects. Finally, this emphasis on the technological dimension of nanotechnology leads to ethical reflections based on the practices of nanotechnology rather than on their potential applications.
To Eat or Not to Eat: Why Dining on Drug Company Lunches may be Unhealthy for Physicians and Their Patients
Sacha Agrawal
University of Toronto Medical Journal , 2004, DOI: 10.5015/utmj.v81i3.651
History of Medicine: A Scandalously Short Introduction
Sacha Agrawal
University of Toronto Medical Journal , 2000, DOI: 10.5015/utmj.v77i2.1123
Bernard E. Harcourt, The Illusion of Free Markets: Punishment and the Myth of Natural Order.
Sacha Raoult
Champ Pénal , 2012, DOI: 10.4000/champpenal.8349
Abstract: Bernard Harcourt fait figure de chercheur un peu à part dans la sociologie pénale contemporaine. Tour à tour nominaliste et économiste, engagé et sceptique, deux de ses ouvrages ont astucieusement démonté d’importants mythes de la politique criminelle américaine en s’attaquant à des techniques qui avaient un peu rapidement été célébrées comme le nec plus ultra des moyens de lutte contre la délinquance : la tolérance zéro et le profilage. Ces ouvrages avaient re u un succès mérité, et constitu...
Ingredients and Equations for Making a Magnetic Field in the Early Universe
Sacha Davidson
Physics , 1996, DOI: 10.1016/0370-2693(96)00501-1
Abstract: The ingredients required to create a magnetic field in the early Universe are identified, and compared with Sakharov's conditions for baryogenesis. It is also shown that a long range coherent magnetic field is not generated by the classical rolling Higgs vacuum expectation value during the electroweak phase transition.
Cosmological Constraints on B-L Violation
Sacha Davidson
Physics , 1998,
Abstract: This is a review of the cosmological bounds on $B-L$ violating interactions, and the loopholes in the argument that gives these constraints. If one assumes that the baryon asymmetry we observe today was present above the electroweak phase transition in equilibrium with the non-perturbative $B+L$ violating processes, then interactions that violate all three of ${B/3 - L_i}$ cannot simultaneously be in equilibrium. Otherwise the baryon asymmetry would be washed out. Therefore violation of at least one of the $B/3 - L_i$ must be small. This argument can be evaded by not having the observed baryon asymmetry present in the thermal bath (for instance, make it at the electroweak phase transition), by using a non-standard cosmological model, or possibly by some mass effects in models where the difference between lepton flavour asymmetries is conserved.
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