LOFAR: A new radio telescope for low frequency radio observations: Science and project status

LOFAR, the Low Frequency Array, is a large radio telescope consisting about 100 soccer field sized antenna stations spread over a region of 400 km in diameter. It will operate in the frequency range from ~10 to 240 MHz, with a resolution at 240 MHz of better than an arcsecond. Its superb sensitivity will allow for a broad range of astrophysical studies. In this contribution we first discuss four major areas of astrophysical research in which LOFAR will undoubtedly make important contributions: reionisation, distant galaxies and AGNs, transient radio sources and cosmic rays. Subsequently, we will discuss the technical concept of the instrument and the status of the LOFAR projectComment: 8 pages, 2 figures, to appear in the proceedings of the XXI Texas Symposium on Relativistic Astrophysics held on December 9--13 2002, in Florence, Ital

Morphological variability in unrepaired bilateral clefts with and without cleft palate evaluated with geometric morphometrics

In subjects with orofacial clefts, there is an unresolved controversy on the effect of congenital maxillary growth deficiency vs. the effect of surgical intervention on the outcome of treatment. Intrinsic growth impairment in subjects with orofacial clefts can be studied by comparing facial morphology of subjects with untreated cleft and unaffected individuals of the same ethnic background. Bilateral cleft lip and palate is the most severe and least prevalent form of the orofacial cleft. The aim of this study was to compare facial morphology in subjects with unrepaired complete bilateral clefts and unaffected controls using geometric morphometrics. Lateral cephalograms of 39 Indonesian subjects with unrepaired bilateral complete cleft lip and alveolus (mean age: 24 years), or unrepaired bilateral complete cleft lip, alveolus, and palate (mean age: 20.6 years) and 50 age and ethnically matched controls without a cleft (25 males, 25 females, mean age: 21.2 years) were digitized and traced and shape variability was explored using principal component analysis, while differences between groups and genders were evaluated with canonical variate analysis. Individuals with clefts had a more pronounced premaxilla than controls. Principal component analysis showed that facial variation in subjects with clefts occurred in the anteroposterior direction, whereas in controls it was mostly in the vertical direction. Regression analysis with group, sex, and age as covariates and principal components from 1 to 6 as dependent variables demonstrated a very limited effect of the covariates on the facial shape variability (only 11.6% of the variability was explained by the model). Differences between cleft and non-cleft subjects in the direction of facial variability suggest that individuals with bilateral clefts can have an intrinsic growth impairment affecting facial morphology later in life.</p

SPH Simulations of Direct Impact Accretion in the Ultracompact AM CVn Binaries

The ultracompact binary systems V407 Vul (RX J1914.4+2456) and HM Cnc (RX J0806.3+1527) - a two-member subclass of the AM CVn stars - continue to pique interest because they defy unambiguous classification. Three proposed models remain viable at this time, but none of the three is significantly more compelling than the remaining two, and all three can satisfy the observational constraints if parameters in the models are tuned. One of the three proposed models is the direct impact model of Marsh & Steeghs (2002), in which the accretion stream impacts the surface of a rapidly-rotating primary white dwarf directly but at a near-glancing angle. One requirement of this model is that the accretion stream have a high enough density to advect its specific kinetic energy below the photosphere for progressively more-thermalized emission downstream, a constraint that requires an accretion spot size of roughly 1.2x10^5 km^2 or smaller. Having at hand a smoothed particle hydrodynamics code optimized for cataclysmic variable accretion disk simulations, it was relatively straightforward for us to adapt it to calculate the footprint of the accretion stream at the nominal radius of the primary white dwarf, and thus to test this constraint of the direct impact model. We find that the mass flux at the impact spot can be approximated by a bivariate Gaussian with standard deviation \sigma_{\phi} = 164 km in the orbital plane and \sigma_{\theta} = 23 km in the perpendicular direction. The area of the the 2\sigma ellipse into which 86% of the mass flux occurs is roughly 47,400 km^2, or roughly half the size estimated by Marsh & Steeghs (2002). We discuss the necessary parameters of a simple model of the luminosity distribution in the post-impact emission region.Comment: 24 pages, 5 figures, Accepted for publication in Ap

Why do some intermediate polars show soft X-ray emission? A survey of XMM-Newton spectra

We make a systematic analysis of the XMM-Newton X-ray spectra of intermediate polars (IPs) and find that, contrary to the traditional picture, most show a soft blackbody component. We compare the results with those from AM Her stars and deduce that the blackbody emission arises from reprocessing of hard X-rays, rather than from the blobby accretion sometimes seen in AM Hers. Whether an IP shows a blackbody component appears to depend primarily on geometric factors: a blackbody is not seen in those that have accretion footprints that are always obscured by accretion curtains or are only visible when foreshortened on the white-dwarf limb. Thus we argue against previous suggestions that the blackbody emission characterises a separate sub-group of IPs which are more akin to AM Hers, and develop a unified picture of the blackbody emission in these stars.Comment: 9 pages, 6 figures. Accepted for publication in Ap

Actively coping with violation:Exploring upward dissent patterns in functional, dysfunctional, and deserted psychological contract end states

Recently, scholars have emphasized the importance of examining how employees cope with psychological contract violation and how the coping process contributes to psychological contract violation resolution and post-violation psychological contracts. Recent work points to the important role of problem-focused coping. Yet, to date, problem-focused coping strategies have not been conceptualized on a continuum from constructive to destructive strategies. Consequently, potential differences in the use of specific types of problem-focused coping strategies and the role these different strategies play in the violation resolution process has not been explored. In this study, we stress the importance of focusing on different types of problem-focused coping strategies. We explore how employee upward dissent strategies, conceptualized as different forms of problem-focused coping, contribute to violation resolution and post-violation psychological contracts. Two sources of data were used. In-depth interviews with supervisors of a Dutch car lease company provided 23 case descriptions of employee-supervisor interactions after a psychological contract violation. Moreover, a database with descriptions of Dutch court sentences provided eight case descriptions of employee-organization interactions following a perceived violation. Based on these data sources, we explored the pattern of upward dissent strategies employees used over time following a perceived violation. We distinguished between functional (thriving and reactivation), dysfunctional (impairment and dissolution) and deserted psychological contract end states and explored whether different dissent patterns over time differentially contributed to the dissent outcome (i.e., psychological contract end state). The results of our study showed that the use of problem-focused coping is not as straightforward as suggested by the post-violation model. While the post-violation model suggests that problem-focused coping will most likely contribute positively to violation resolution, we found that this also depends on the type of problem-focused coping strategy used. That is, more threatening forms of problem-focused coping (i.e., threatening resignation as a way to trigger one's manager/organization to resolve the violation) mainly contributed to dysfunctional and deserted PC end states. Yet, in some instances the use of these types of active coping strategies also contributed to functional violation resolution. These findings have important implications for the literature on upward dissent strategies and psychological contract violation repair

On the Search for Coherent Radiation from Radio Pulsars

We have examined data from pulsars B0950+08 and B0329+54 for evidence of temporally coherent radiation using the modified coherence function (MCF) technique of Jenet et al. (2001). We consider the influence of both instrumental bandpass and interstellar propagation effects. Even after removal of the effects due to the instrumental bandpass, we detect a signature in the MCF of our PSR B0329+54 data which is consistent with the definition of a coherent signal. However, we model the effects due to interstellar scintillation for this pulsar and show that it reproduces the observed signature. In particular, the temporal coherence time is close to the reciprocal of the decorrelation bandwidth due to diffractive scintillation. Furthermore, comparison of the coherence times of three pulsars reported by Jenet et al. (2001) with their expected diffractive decorrelation bandwidths suggests that the detection of coherence in these pulsars is also likely a result of interstellar scintillation, and is not intrinsic to the pulsars.Comment: 8 pages, 8 figures. Accepted for publication in Astronomy & Astrophysics (A&A

Subarctic Front migration at the Reykjanes Ridge during the mid- to late Holocene:Evidence from planktic foraminifera

Expansion of fresh and sea-ice loaded surface waters from the Arctic Ocean into the sub-polar North Atlantic is suggested to modulate the northward heat transport within the North Atlantic Current (NAC). The Reykjanes Ridge south of Iceland is a suitable area to reconstruct changes in the mid- to late Holocene fresh and sea-ice loaded surface water expansion, which is marked by the Subarctic Front (SAF). Here, shifts in the location of the SAF result from the interaction of freshwater expansion and inflow of warmer and saline (NAC) waters to the Ridge. Using planktic foraminiferal assemblage and concentration data from a marine sediment core on the eastern Reykjanes Ridge elucidates SAF location changes and thus, changes in the water-mass composition (upper ˜200 m) during the last c. 5.8 ka BP. Our foraminifer data highlight a late Holocene shift (at c. 3.0 ka BP) in water-mass composition at the Reykjanes Ridge, which reflects the occurrence of cooler and fresher surface waters when compared to the mid-Holocene. We document two phases of SAF presence at the study site: from (i) c. 5.5 to 5.0 ka BP and (ii) c. 2.7 to 1.5 ka BP. Both phases are characterized by marked increases in the planktic foraminiferal concentration, which coincides with freshwater expansions and warm subsurface water conditions within the sub-polar North Atlantic. We link the SAF changes, from c. 2.7 to 1.5 ka BP, to a strengthening of the East Greenland Current and a warming in the NAC, as identified by various studies underlying these two currents. From c. 1.5 ka BP onwards, we record a prominent subsurface cooling and continued occurrence of fresh and sea-ice loaded surface waters at the study site. This implies that the SAF migrated to the southeast of our core site during the last millennium