Forming short-period Wolf-Rayet X-ray binaries and double black holes through stable mass transfer

We show that black-hole High-Mass X-ray Binaries (HMXBs) with O- or B-type donor stars and relatively short orbital periods, of order one week to several months may survive spiral in, to then form Wolf-Rayet (WR) X-ray binaries with orbital periods of order a day to a few days; while in systems where the compact star is a neutron star, HMXBs with these orbital periods never survive spiral-in. We therefore predict that WR X-ray binaries can only harbor black holes. The reason why black-hole HMXBs with these orbital periods may survive spiral in is: the combination of a radiative envelope of the donor star, and a high mass of the compact star. In this case, when the donor begins to overflow its Roche lobe, the systems are able to spiral in slowly with stable Roche-lobe overflow, as is shown by the system SS433. In this case the transferred mass is ejected from the vicinity of the compact star (so-called "isotropic re-emission" mass loss mode, or "SS433-like mass loss"), leading to gradual spiral-in. If the mass ratio of donor and black hole is $>3.5$, these systems will go into CE evolution and are less likely to survive. If they survive, they produce WR X-ray binaries with orbital periods of a few hours to one day. Several of the well-known WR+O binaries in our Galaxy and the Magellanic Clouds, with orbital periods in the range between a week and several months, are expected to evolve into close WR-Black-Hole binaries,which may later produce close double black holes. The galactic formation rate of double black holes resulting from such systems is still uncertain, as it depends on several poorly known factors in this evolutionary picture. It might possibly be as high as $\sim 10^{-5}$ per year.Comment: MNRAS in pres

Expected Coalescence Rate of Double Neutron Stars for Ground Based Interferometers

In this paper we present new estimates of the coalescence rate of neutron star binaries in the local universe and we discuss its consequences for the first generations of ground based interferometers. Our approach based on both evolutionary and statistical methods gives a galactic merging rate of 1.7 10$^{-5}$ yr$^{-1}$, in the range of previous estimates 10$^{-6}$ - 10$^{-4}$ yr$^{-1}$. The local rate which includes the contribution of elliptical galaxies is two times higher, in the order of 3.4 10$^{-5}$ yr$^{-1}$. We predict one detection every 148 and 125 years with initial VIRGO and LIGO, and up to 6 events per year with their advanced configuration. Our recent detection rate estimates from investigations on VIRGO future improvements are quoted.Comment: talk given at the GWDAW9 (Annecy, 2004) to be published in CQ

Mutation supply and the repeatability of selection for antibiotic resistance

Whether evolution can be predicted is a key question in evolutionary biology. Here we set out to better understand the repeatability of evolution. We explored experimentally the effect of mutation supply and the strength of selective pressure on the repeatability of selection from standing genetic variation. Different sizes of mutant libraries of an antibiotic resistance gene, TEM-1 $\beta$-lactamase in Escherichia coli, were subjected to different antibiotic concentrations. We determined whether populations went extinct or survived, and sequenced the TEM gene of the surviving populations. The distribution of mutations per allele in our mutant libraries- generated by error-prone PCR- followed a Poisson distribution. Extinction patterns could be explained by a simple stochastic model that assumed the sampling of beneficial mutations was key for survival. In most surviving populations, alleles containing at least one known large-effect beneficial mutation were present. These genotype data also support a model which only invokes sampling effects to describe the occurrence of alleles containing large-effect driver mutations. Hence, evolution is largely predictable given cursory knowledge of mutational fitness effects, the mutation rate and population size. There were no clear trends in the repeatability of selected mutants when we considered all mutations present. However, when only known large-effect mutations were considered, the outcome of selection is less repeatable for large libraries, in contrast to expectations. Furthermore, we show experimentally that alleles carrying multiple mutations selected from large libraries confer higher resistance levels relative to alleles with only a known large-effect mutation, suggesting that the scarcity of high-resistance alleles carrying multiple mutations may contribute to the decrease in repeatability at large library sizes.Comment: 31pages, 9 figure

The Evolution of Globular Clusters in the Galaxy

We investigate the evolution of globular clusters using N-body calculations and anisotropic Fokker-Planck (FP) calculations. The models include a mass spectrum, mass loss due to stellar evolution, and the tidal field of the parent galaxy. Recent N-body calculations have revealed a serious discrepancy between the results of N-body calculations and isotropic FP calculations. The main reason for the discrepancy is an oversimplified treatment of the tidal field employed in the isotropic FP models. In this paper we perform a series of calculations with anisotropic FP models with a better treatment of the tidal boundary and compare these with N-body calculations. The new tidal boundary condition in our FP model includes one free parameter. We find that a single value of this parameter gives satisfactory agreement between the N-body and FP models over a wide range of initial conditions. Using the improved FP model, we carry out an extensive survey of the evolution of globular clusters over a wide range of initial conditions varying the slope of the mass function, the central concentration, and the relaxation time. The evolution of clusters is followed up to the moment of core collapse or the disruption of the clusters in the tidal field of the parent galaxy. In general, our model clusters, calculated with the anisotropic FP model with the improved treatment for the tidal boundary, live longer than isotropic models. The difference in the lifetime between the isotropic and anisotropic models is particularly large when the effect of mass loss via stellar evolution is rather significant. On the other hand the difference is small for relaxation- dominated clusters which initially have steep mass functions and high central concentrations.Comment: 36 pages, 11 figures, LaTeX; added figures and tables; accepted by Ap

Simple Stellar Population Models as probed by the Large Magellanic Cloud Star Cluster ESO 121-SC03

The presence of blue straggler stars (BSs) in star clusters has proven a challenge to conventional simple stellar population (SSP) models. Conventional SSP models are based on the evolution theory of single stars. Meanwhile, the typical locations of BSs in the colour-magnitude diagram of a cluster are brighter and bluer than the main sequence turn-off point. Such loci cannot be predicted by single-star evolution theory. However, stars with such properties contribute significantly to the integrated light of the cluster. In this paper, we reconstruct the integrated properties of the Large Magellanic Cloud cluster ESO 121-SC03, based on a detailed exploration of the individual cluster stars, and with particular emphasis on the cluster's BSs. We find that the integrated light properties of ESO 121-SC03 are dramatically modified by its BS component. The integrated spectral energy distribution (ISED) flux level is significantly enhanced toward shorter wavelengths, and all broad-band colours become bluer. When fitting the fully integrated ISED of this cluster based on conventional SSP models, the best-fitting values of age and metallicity are significantly underestimated compared to the true cluster parameters. The age underestimate is $\sim40$ per cent if we only include the BSs within the cluster's half-light radius and $\sim60$ per cent if all BSs are included. The corresponding underestimates of the cluster's metallicity are $\sim30$ and $\sim60$ per cent, respectively. The populous star clusters in the Magellanic Clouds are ideal objects to explore the potential importance of BSs for the integrated light properties of more distant unresolved star clusters in a statistically robust manner, since they cover a large range in age and metallicity.Comment: 11 pages, 7 figures, 2 tables, accepted for publication in MNRA

Een Nieuwe Koekelt : kloppend groen hart van Ede

De tuinders van VAT-Ede (Vereniging Amateurtuinders) wilden een verkenning uitvoeren naar de mogelijkheden om het bestaande volkstuincomplex De Koekelt om te vormen tot een multifunctioneel tuinenpark. Het volkstuinencomplex De Koekelt biedt door haar ligging en grootte ongekende mogelijkheden om een multifunctioneel tuinenpark te realiseren. Het volkstuinenterrein kan door herstructurering veranderen in een groene zone waar ecologie en milieu de ruimte krijgen, waar meerdere vormen van recreatie mogelijk zijn en waar meer aansluiting ontstaat met de omgevingEen multifunctioneel tuinenpark zou wel eens de groene motor kunnen zijn voor de herstructurering van het hele Peppelensteeggebied

Budget Impact Analysis of Metformin Sustained Release for the Treatment of Type 2 Diabetes in The Netherlands

BACKGROUND: Adverse drug reactions and medication nonadherence are well-known causes of sub-optimal disease control and worsened disease outcomes in patients who are treated for type 2 diabetes. Metformin sustained release (SR) might reduce these adverse events and improve medication adherence via a simplified treatment regimen for metformin immediate release (IR)-intolerant patients. OBJECTIVES: The aim of this study is to estimate the budget impact of metformin SR for the treatment of type 2 diabetes in the Netherlands, compared to the current standard of care (SoC) with metformin IR. METHODS: A budget impact model was built to represent the course of the disease and treatment pathway of type 2 diabetes patients eligible for metformin SR from a healthcare payer's perspective. Patients were considered eligible if they used less than 2000 mg metformin IR per day, but suffered from adverse events that might lead to therapy discontinuation, and if they were newly diagnosed with type 2 diabetes. The costs of type 2 diabetes treatment and related complications over a time horizon of 3 years were calculated. Univariate sensitivity analyses were conducted to show which parameters have the biggest influence on the budget impact. RESULTS: The budget impact analysis showed cost-savings of - €1,962,335 over a period of 3 years through implementation of metformin SR as an alternative to SoC with metformin IR. Savings were mostly driven by the delay of other, more expensive type 2 diabetes treatments, such as insulin. In sensitivity analyses, medication adherence and persistence appeared to have the biggest influence on the budget impact. CONCLUSION: Metformin SR could potentially be a cost-saving alternative to metformin IR for the treatment of type 2 diabetes in the Netherlands, especially in patients experiencing adverse events with metformin IR. However, more research is needed to better predict the effect of using once-daily metformin, compared to multiple dosages, on medication adherence and persistence and to evaluate whether metformin SR really decreases the amount of adverse events