On the Column Density of AGN Outflows: the Case of NGC 5548

We re-analyze the HST high resolution spectroscopic data of the intrinsic absorber in NGC 5548 and find that the C IV absorption column density is at least four times larger than previously determined. This increase arises from accounting for the kinematical nature of the absorber and from our conclusion that the outflow does not cover the narrow emission line region in this object. The improved column density determination begins to bridge the gap between the high column densities measured in the X-ray and the low ones previously inferred from the UV lines. Combined with our findings for outflows in high luminosity quasars these results suggest that traditional techniques for measuring column densities: equivalent width, curve-of-growth and Gaussian modeling, are of limited value when applied to absorption associated with AGN outflows.Comment: Published ApJ version (566, 699), including a new figure with FUSE data and a useful algebraic expression for the optical depth solutio

Contrasting the UV and X-ray O VI Column Density Inferred for the Outflow in NGC 5548

We compare X-ray and UV spectroscopic observations of NGC 5548. Both data sets show O VI absorption troughs associated with the AGN outflow from this galaxy. We find that the robust lower limit on the column density of the O VI X-ray trough is seven times larger than the column density found in a study of the O VI UV troughs. This discrepancy suggests that column densities inferred for UV troughs of Seyfert outflows are often severely underestimated. We identify the physical limitations of the UV Gaussian modeling as the probable explanation of the O VI column density discrepancy. Specifically, Gaussian modeling cannot account for a velocity dependent covering fraction, and it is a poor representation for absorption associated with a dynamical outflow. Analysis techniques that use a single covering fraction value for each absorption component suffer from similar limitations. We conclude by suggesting ways to improve the UV analysis.Comment: 16 pages, 1 figure, accepted for publication in Ap

Estimating nonresponse bias and mode effects in a mixed mode survey

In mixed-mode surveys, it is difficult to separate sample selection differences from mode-effects that can occur when respondents respond in different interview settings. This paper provides a framework for separating mode-effects from selection effects by matching very similar respondents from different survey modes using propensity score matching. The answer patterns of the matched respondents are subsequently compared. We show that matching can explain differences in nonresponse and coverage in two Internet-samples. When we repeat this procedure for a telephone and Internet-sample however, differences persist between the samples after matching. This indicates the occurrence of mode-effects in telephone and Internet surveys. Mode-effects can be problematic; hence we conclude with a discussion of designs that can be used to explicitly study mode-effects

Jet Acceleration by Tangled Magnetic Fields

We explore the possibility that extragalactic radio jets might be accelerated by highly disorganized magnetic fields that are strong enough to dominate the dynamics until the terminal Lorentz factor is reached. Following the twin-exhaust model by Blandford & Rees (1974), the collimation under this scenario is provided by the stratified thermal pressure from an external medium. The acceleration efficiency then depends on the pressure gradient of that medium. In order for this mechanism to work there must be continuous tangling of the magnetic field, changing the magnetic equation of state away from pure flux freezing (otherwise conversion of Poynting flux to kinetic energy flux is suppressed). This is a complementary approach to models in which the plasma is accelerated by large scale ordered fields. We include a simple prescription for magnetic dissipation, which leads to tradeoffs among conversion of magnetic energy into bulk kinetic energy, random particle energy, and radiation. We present analytic dynamical solutions of such jets, assess the effects of radiation drag, and comment on observational issues, such as the predicted polarization and synchrotron brightness. Finally, we try to make the connection to observed radio galaxies and gamma-ray bursts.Comment: 15 pages, 10 figures, accepted for publication in Ap

Finding White Dwarfs with Transit Searches

We make predictions for the rate of discovery of eclipsing white dwarf-main sequence (WD-MS) binaries in terrestrial-planet transit searches, taking the planned Kepler and Eddington missions as examples. We use a population synthesis model to characterize the Galactic WD-MS population, and we find that, despite increased noise due to stellar variability compared with the typical planetary case, discovery of >100 non-accreting, eclipsing WD-MS systems is likely using Kepler and Eddington, with periods of 2-20 days and transit amplitudes of |delta m|~0.0003-0.00003 magnitudes. Follow-up observations of these systems could accurately test the theoretical white dwarf mass-radius relation or theories of binary star evolution.Comment: 5 pages, 3 figures, one table, accepted for publication in ApJ. Minor changes to Galactic model and to discusion section; conclusions unchange

Dose-effect relations in time-limited combined psycho-pharmacological treatment for depression

BACKGROUND: A limited number of psychotherapy sessions in combination with medication is preferable to pharmacotherapy only in the treatment of ambulatory patients with major depression. Whether there is a relation between the number of sessions and the efficacy of the treatment is uncertain. METHOD: Randomized clinical trial comparing two treatment conditions in outpatients with major depression. All patients studied had a baseline score of at least 14 points on the 17-item Hamilton Depression Rating Scale. The two conditions consist of 8-session or 16-session Short Psychodynamic Supportive Psychotherapy, both in combination with pharmacotherapy. Efficacy was assessed using the 17-item HDRS, the CGI of Severity and of Improvement, the depression subscale of the SCL-90 and the Quality of Life Depression Scale. RESULTS: The rate of change would seem to indicate that eight sessions are preferable for both moderately and severely depressed patients, although the results converged again at the end. Furthermore, in terms of satisfaction with the number of sessions and drop-out percentages during treatment, no differences were found between the conditions. CONCLUSION: In the light of the outcome analysis (faster remission after fewer sessions), a short version of the psychotherapy treatment in a combined course of treatment seems to be justifie

What Determines the Depth of BALs? Keck HIRES Observations of BALQSO 1603+300

We find that the depth and shape of the broad absorption lines (BALs) in BALQSO 1603+3002 are determined largely by the fraction of the emitting source which is covered by the BAL flow. In addition, the observed depth of the BALs is poorly correlated with their real optical depth. The implication of this result is that abundance studies based on direct extraction of column densities from the depth of the absorption troughs are unreliable. Our conclusion is based on analysis of unblended absorption features of two lines from the same ion (in this case the Si IV doublet), which allows unambiguous separation of covering factor and optical depth effects. The complex morphology of the covering factor as a function of velocity suggests that the BALs are produced by several physically separated outflows. The covering factor is ion dependent in both depth and velocity width. We also find evidence that in BALQSO 1603+3002 the flow does not cover the broad emission line region.Comment: 13 pages, 2 figures, accepted for publication in Ap

Milieueffecten van Nederlandse consumptie van eiwitrijke producten : gevolgen van vervanging van dierlijke eiwitten anno 2008

In 2008 heeft Blonk Milieu Advies in samenwerking met de vegetariërsbond en het LEI een onderzoek uitgevoerd naar de milieueffecten van een verschuiving van consumptie van dierlijke naar plantaardige eiwitten in de Nederlandse voeding. Daarbij is vooral de focus gelegd op het broeikaseffect en het ruimtebeslag en de mogelijke biodiversiteitseffecten daarvan. Daarnaast is er meer kwalitatief aandacht besteed aan andere effecten zoals dierenwelzijn en de effecten van een consumptiestop van dierlijke producten op de productiekolom van dierlijke producten in Nederlan

Effectgerichte aanpak verwijdering P uit bodem- en slootwater duinzandgrond

Op bloembollenpercelen bij Egmond a/d Hoef worden twee zuiveringsmethoden getest om fosfaat te verwijderen uit bodem en slootwater. Het doel is het water te zuiveren van fosfaat om daarmee te voldoen aan de Europese Regelgeving voor de kwaliteit van oppervlaktewater