Distribution of proper motions in spherical star clusters

Along with data on radial velocities, more and more data on proper motions of individual stars in globular clusters are becoming available. Their usage was until now rather limited. It was mostly restricted to determining cluster membership of individual stars and to determining the spatial velocity of the cluster. We study the two dimensional distribution of the proper motions, in order to clarify the relation between the projection of the velocities and the dynamical structure. Obviously some assumptions on the dynamics of the system have to be made. In this study we chose a Plummer model. This complements an earlier study about line profiles. The three velocity dispersions in the main directions are determined and compared with the three spherical velocity dispersions. Two parameters analogous to Binney's anisotropy parameter $\beta$ are defined. Moreover, since the proper motion components are distance dependent and the line of sight velocity dispersion is distance independent, we show explicitly how to determine distances.Comment: 10 pages, uuencoded compressed postscript. Figures included. Appendices available on request

Comprehensive embryo testing. Experts opinions regarding future directions: an expert panel study on comprehensive embryo testing

What do scientists in the field of preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) consider to be the future direction of comprehensive embryo testing? Although there are many biological and technical limitations, as well as uncertainties regarding the meaning of genetic variation, comprehensive embryo testing will impact the IVF/PGD practice and a timely ethical reflection is needed. Comprehensive testing using microarrays is currently being introduced in the context of PGD and PGS, and it is to be expected that whole-genome sequencing will also follow. Current ethical and empirical sociological research on embryo testing focuses on PGD as it is practiced now. However, empirical research and systematic reflection regarding the impact of comprehensive techniques for embryo testing is missing. In order to understand the potential of this technology and to be able to adequately foresee its implications, we held an expert panel with seven pioneers in PGD. We conducted an expert panel in October 2011 with seven PGD pioneers from Belgium, The Netherlands, Germany and the UK. Participants expected the use of comprehensive techniques in the context of PGD. However, the introduction of these techniques in embryo testing requires timely ethical reflection as it involves a shift from choosing an embryo without a particular genetic disease (i.e. PGD) or most likely to result in a successful pregnancy (i.e. PGS) to choosing the best embryo based on a much wider set of criteria. Such ethical reflection should take account of current technical and biological limitations and also of current uncertainties with regard to the meaning of genetic variance. However, ethicists should also not be afraid to look into the future. There was a general agreement that embryo testing will be increasingly preceded by comprehensive preconception screening, thus enabling smart combinations of genetic testing. The group was composed of seven participants from four Western Europe countries. As willingness to participate in this study may be connected with expectations regarding the pace and direction of future developments, selection bias cannot be excluded. The introduction of comprehensive screening techniques in embryo testing calls for further ethical reflection that is grounded in empirical work. Specifically, there is a need for studies querying the opinions of infertile couples undergoing IVF/PGS regarding the desirability of embryo screening beyond aneuploidy. This research was supported by the CSG, Centre for Society and Life Sciences (project number: 70.1.074). The authors declare no conflict of interest. N/A

Academic Research Values: Conceptualization and Initial Steps of Measure Development

In this paper we draw on value theory in social psychology to conceptualize the range of motives that may influence research-related attitudes, decisions, and actions of researchers. To conceptualize academic research values, we integrate theoretical insights from the personal, work, and scientific work values literature, as well as the responses of 6 interviewees and 255 survey participants about values relevant to academic research. Finally, we propose a total of 246 academic research value items spread over 11 dimensions and 36 sub-themes. We relate our conceptualization and item proposals to existing work and provide recommendations for future measurement development. Gaining a better understanding of the different values researchers have, is useful to improve scientific careers, make science attractive to a more diverse group of individuals, and elucidate some of the mechanisms leading to exemplary and questionable science

Learning Bayes-optimal dendritic opinion pooling

In functional network models, neurons are commonly conceptualized as linearly summing presynaptic inputs before applying a non-linear gain function to produce output activity. In contrast, synaptic coupling between neurons in the central nervous system is regulated by dynamic permeabilities of ion channels. So far, the computational role of these membrane conductances remains unclear and is often considered an artifact of the biological substrate. Here we demonstrate that conductance-based synaptic coupling allow neurons to represent, process and learn uncertainties. We suggest that membrane potentials and conductances on dendritic branches code opinions with associated reliabilities. The biophysics of the membrane combines these opinions by taking account their reliabilities, and the soma thus acts as a decision maker. We derive a gradient-based plasticity rule, allowing neurons to learn desired target distributions and weight synaptic inputs by their relative reliabilities. Our theory explains various experimental findings on the system and single-cell level related to multi-sensory integration, and makes testable predictions on dendritic integration and synaptic plasticity.Comment: 36 pages, 10 figures; Mihai A. Petrovici and Walter Senn share senior authorshi

Conductance-based dendrites perform Bayes-optimal cue integration.

A fundamental function of cortical circuits is the integration of information from different sources to form a reliable basis for behavior. While animals behave as if they optimally integrate information according to Bayesian probability theory, the implementation of the required computations in the biological substrate remains unclear. We propose a novel, Bayesian view on the dynamics of conductance-based neurons and synapses which suggests that they are naturally equipped to optimally perform information integration. In our approach apical dendrites represent prior expectations over somatic potentials, while basal dendrites represent likelihoods of somatic potentials. These are parametrized by local quantities, the effective reversal potentials and membrane conductances. We formally demonstrate that under these assumptions the somatic compartment naturally computes the corresponding posterior. We derive a gradient-based plasticity rule, allowing neurons to learn desired target distributions and weight synaptic inputs by their relative reliabilities. Our theory explains various experimental findings on the system and single-cell level related to multi-sensory integration, which we illustrate with simulations. Furthermore, we make experimentally testable predictions on Bayesian dendritic integration and synaptic plasticity

Risk Assessment for Huntington's Disease for (Future) Offspring Requires Offering Preconceptional CAG Analysis to Both Partners

Amongst the main reasons people at risk for Huntington's disease (HD) have for undergoing predictive genetic testing are planning a family and prevention of passing on an expanded CAG-repeat to future offspring. After having received an unfavourable test result, a couple may consider prenatal testing in the foetus or preimplantation genetic diagnostic testing (PGD) in embryos. Testing of the foetus or embryos is possible by means of direct testing of the expanded repeat. Optimal reliability in testing the foetus or embryos requires the establishment of the origin of the repeats of both parents in the foetus. For PGD the analysis is combined with or sometimes solely based on identification of the at-risk haplotype in the embryo. This policy implies that in the context of direct testing, the healthy partner's CAG repeat lengths in the HD gene are also tested, but with the expectation that the repeat lengths of the partner are within the normal range, with the proviso that the partner's pedigree is free of clinically confirmed HD. However, recent studies have shown that the expanded repeat has been observed more often in the general population than previously estimated. Moreover, we have unexpectedly observed an expanded repeat in the non-HD partner in four cases which had far-reaching consequences. Hence, we propose that in the context of reproductive genetic counselling, prior to a planned pregnancy, and irrespective of the outcome of the predictive test in the HD-partner, the non-HD partner should also be given the option of being tested on the expanded allele. International recommendations for predictive testing for HD should be adjusted.Genetics of disease, diagnosis and treatmen