Some remarks concerning rank 2 bundles and Chow groups

[No abstract available

The dynamical distance and intrinsic structure of the globular cluster omega Centauri

We determine the dynamical distance D, inclination i, mass-to-light ratio M/L and the intrinsic orbital structure of the globular cluster omega Cen, by fitting axisymmetric dynamical models to the ground-based proper motions of van Leeuwen et al. and line-of-sight velocities from four independent data-sets. We correct the observed velocities for perspective rotation caused by the space motion of the cluster, and show that the residual solid-body rotation component in the proper motions can be taken out without any modelling other than assuming axisymmetry. This also provides a tight constraint on D tan i. Application of our axisymmetric implementation of Schwarzschild's orbit superposition method to omega Cen reveals no dynamical evidence for a significant radial dependence of M/L. The best-fit dynamical model has a stellar V-band mass-to-light ratio M/L_V = 2.5 +/- 0.1 M_sun/L_sun and an inclination i = 50 +/- 4 degrees, which corresponds to an average intrinsic axial ratio of 0.78 +/- 0.03. The best-fit dynamical distance D = 4.8 +/- 0.3 kpc (distance modulus 13.75 +/- 0.13 mag) is significantly larger than obtained by means of simple spherical or constant-anisotropy axisymmetric dynamical models, and is consistent with the canonical value 5.0 +/- 0.2 kpc obtained by photometric methods. The total mass of the cluster is (2.5 +/- 0.3) x 10^6 M_sun. The best-fit model is close to isotropic inside a radius of about 10 arcmin and becomes increasingly tangentially anisotropic in the outer region, which displays significant mean rotation. This phase-space structure may well be caused by the effects of the tidal field of the Milky Way. The cluster contains a separate disk-like component in the radial range between 1 and 3 arcmin, contributing about 4% to the total mass.Comment: 37 pages (23 figures), accepted for publication in A&A, abstract abridged, for PS and PDF file with full resolution figures, see http://www.strw.leidenuniv.nl/~vdven/oc

The impact of midlife educational, work, health and family experiences on men's early retirement

Objectives. In empirical studies on predictors of retirement, midlife experiences have often remained implicit or been neglected. This study aims to improve our understanding of retirement by examining the impact of midlife educational, work, health, and family experiences on early retirement intentions and behavior. We distinguish theoretically and empirically between financial and nonfinancial preretirement factors through which midlife experiences could affect retirement. Methods. Using panel data of 1,229 Dutch male older workers, we estimated linear regression models to explain retirement intentions and logistic regression models to explain retirement behavior. Results. Midlife experiences in all studied life spheres are related to retirement intentions. Educational investments, job changes, late transitions into parenthood, and late divorces are associated with weaker intentions to retire early. Midlife health problems are related to stronger early retirement intentions. For midlife work and family experiences, the relationships are (partly) mediated by the preretirement financial opportunity structure. In the educational, work, and health spheres, the preretirement nonfinancial situation has a mediating effect. Only some of the predictors of retirement intentions also predicted retirement behavior. Discussion. Given the destandardization of life courses, information on distal life experiences might become even more important toward understanding retirement in the future. keywords: children; divorce; education; life course; retirement; work history

The modes of administration of anabolic-androgenic steroid users (AAS): Are non-injecting people who use steroids overlooked?

Introduction: There is increasing public health concern about the use of anabolic-androgenic steroids (AAS). Understanding of drug use patterns and practices is important if we are to develop appropriate risk-reduction interventions. Yet, much remains unclear about the modes of administration adopted by AAS users. Methods: We used data from a sub-sample of participants from the Global Drug Survey 2015; males who reported using injectable or oral AAS in their lifetime (n=1008). Results: Amongst our sample, approximately one third (35.62%) reported using only injectable AAS during their lifetime while 35.84% reported using only oral, with less than one third (28.54%) using both. Conclusion: These findings suggest there may be a sub-population of individuals who only use AAS orally. Needle and syringe programs (NSPs) are currently the primary point of health service engagement; forming the main healthcare environment for medical and harm reduction advice on steroids. Yet, NSP-based resources are unlikely to reach or be appropriate to those who do not inject AAS. While there is a general need for health services to be more accessible when it comes to AAS use, non-injectors are an overlooked group that require attention

Commentary: Steroid Madness- has the dark side of anabolic-androgenic steroids (AAS) been over-stated?

Recently the journal Performance Enhancement & Health put out a call to produce a special issue on the dark side of human enhancement, including the use of legal and illegal substances, leading us to ponder whether the “dark side” of anabolic-androgenic steroids (from here on, “steroids”) has been overstated. In this commentary, we will briefly engage with this question by unpacking what we describe here as the “narrative of harm”, which tends to dominate discourses on steroid use in wider society. We then consider an alternative perspective on steroid use which focuses on the users’ experience and understanding, with particular attention to the role of pleasure. Finally, we conclude by exploring some of the negative policy consequences arising from the dominance of the “narrative of harm” and advance a regulatory approach grounded in rational research and informed discussions around both the pleasures and pains of steroid use. A more developed version of this argument can be found in the forthcoming collection Human Enhancement Drugs, published by Routledge in 2019 (Mulrooney, van de Ven, McVeigh, & Collins, forthcoming)

General solution of the Jeans equations for triaxial galaxies with separable potentials

The Jeans equations relate the second-order velocity moments to the density and potential of a stellar system. For general three-dimensional stellar systems, there are three equations and six independent moments. By assuming that the potential is triaxial and of separable Staeckel form, the mixed moments vanish in confocal ellipsoidal coordinates. Consequently, the three Jeans equations and three remaining non-vanishing moments form a closed system of three highly-symmetric coupled first-order partial differential equations in three variables. These equations were first derived by Lynden-Bell, over 40 years ago, but have resisted solution by standard methods. We present the general solution here. We consider the two-dimensional limiting cases first. We solve their Jeans equations by a new method which superposes singular solutions. The singular solutions, which are new, are standard Riemann-Green functions. The two-dimensional solutions are applied to non-axisymmetric discs, oblate and prolate spheroids, and also to the scale-free triaxial limit. We then extend the method of singular solutions to the triaxial case, and obtain a full solution. The general solution can be expressed in terms of complete (hyper)elliptic integrals which can be evaluated in a straightforward way, and provides the full set of second moments which can support a triaxial density distribution in a separable triaxial potential. (abridged)Comment: 28 pages (7 figures), LaTeX MN2e, accepted for publication in MNRA

The Internet and lifestyle drugs: an analysis of demographic characteristics, methods, and motives of online purchasers of illicit lifestyle drugs in the Netherlands

Aims: The Internet has marked a revolution in the supply of illegal drugs, while at the same time, new types of illegal and semilegal drugs increasingly are becoming available. In order to deepen our understanding of the demand and supply of these new drugs on the Internet, this study focuses on the demographic characteristics, methods and preferences of people who purchase ‘lifestyle drugs’ through the surface web.Methods: Data were obtained through the following two surveys: a prevalence study of 50,848 Dutch respondents and an in-depth study of 153 people who have purchased lifestyle drugs online.Findings: At least 10.2% of the Dutch adult population has bought medicines online; the majority being lifestyle drugs (5.2%). In addition, an estimated 1.6% of the Dutch population has purchased medicines illicitly, with the majority of products concerning lifestyle drugs (0.9%). Illicit lifestyle drugs are primarily purchased through e-commerce sites and online pharmacies, and users report high satisfaction rates.Conclusion: Purchasing lifestyle drugs is characterised by specific online dynamics, as the drugs are often openly accessible and the boundaries between legal and illegal sale blurred. As new types of drugs become available, it is important to further monitor customers’ preferences and experiences.FdR – Publicaties niet-programma gebonde

One teacher's identity, emotions and commitment to change: a case study into the cognitive-affective processes of a secondary school teacher in the context of reforms

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