The effects of supernovae on the dynamical evolution of binary stars and star clusters

In this chapter I review the effects of supernovae explosions on the dynamical evolution of (1) binary stars and (2) star clusters. (1) Supernovae in binaries can drastically alter the orbit of the system, sometimes disrupting it entirely, and are thought to be partially responsible for `runaway' massive stars - stars in the Galaxy with large peculiar velocities. The ejection of the lower-mass secondary component of a binary occurs often in the event of the more massive primary star exploding as a supernova. The orbital properties of binaries that contain massive stars mean that the observed velocities of runaway stars (10s - 100s km s$^{-1}$) are consistent with this scenario. (2) Star formation is an inherently inefficient process, and much of the potential in young star clusters remains in the form of gas. Supernovae can in principle expel this gas, which would drastically alter the dynamics of the cluster by unbinding the stars from the potential. However, recent numerical simulations, and observational evidence that gas-free clusters are observed to be bound, suggest that the effects of supernova explosions on the dynamics of star clusters are likely to be minimal.Comment: 16 pages, to appear in the 'Handbook of Supernovae', eds. Paul Murdin and Athem Alsabti. This version replaces an earlier version that contained several typo

Can discrete time make continuous space look discrete?

Van Bendegem has recently offered an argument to the effect that, if time is discrete, then there should exist a correspondence between the motions of massive bodies and a discrete geometry. On this basis, he concludes that, even if space is continuous, it should nonetheless appear discrete. This paper examines the two possible ways of making sense of that correspondence, and shows that in neither case van Bendegem's conclusion logically follows

Formation of Supermassive Black Holes

Evidence shows that massive black holes reside in most local galaxies. Studies have also established a number of relations between the MBH mass and properties of the host galaxy such as bulge mass and velocity dispersion. These results suggest that central MBHs, while much less massive than the host (~ 0.1%), are linked to the evolution of galactic structure. In hierarchical cosmologies, a single big galaxy today can be traced back to the stage when it was split up in hundreds of smaller components. Did MBH seeds form with the same efficiency in small proto-galaxies, or did their formation had to await the buildup of substantial galaxies with deeper potential wells? I briefly review here some of the physical processes that are conducive to the evolution of the massive black hole population. I will discuss black hole formation processes for `seed' black holes that are likely to place at early cosmic epochs, and possible observational tests of these scenarios.Comment: To appear in The Astronomy and Astrophysics Review. The final publication is available at http://www.springerlink.co

Determinants of participation in a web-based health risk assessment and consequences for health promotion programs

Background: The health risk assessment (HRA) is a type of health promotion program frequently offered at the workplace. Insight into the underlying determinants of participation is needed to evaluate and implement these interventions. Objective: To analyze whether individual characteristics including demographics, health behavior, self-rated health, and work-related factors are associated with participation and nonparticipation in a Web-based HRA. Methods: Determinants of participation and nonparticipation were investigated in a cross-sectional study among individuals employed at five Dutch organizations. Multivariate logistic regression was performed to identify determinants of participation and nonparticipation in the HRA after controlling for organization and all other variables. Results: Of the 8431 employees who were invited, 31.9% (2686/8431) enrolled in the HRA. The online questionnaire was completed by 27.2% (1564/5745) of the nonparticipants. Determinants of participation were some periods of stress at home or work in the preceding year (OR 1.62, 95% CI 1.08-2.42), a decreasing number of weekdays on which at least 30 minutes were spent on moderate to vigorous physical activity (ORdayPA0.84, 95% CI 0.79-0.90), and increasing alcohol consumption. Determinants of nonparticipation were less-than-positive self-rated health (poor/very poor vs very good, OR 0.25, 95% CI 0.08-0.81) and tobacco use (at least weekly vs none, OR 0.65, 95% CI 0.46-0.90). Conclusions: This study showed that with regard to isolated health behaviors (insufficient physical activity, excess alcohol consumption, and stress), those who could benefit most from the HRA were more likely to participate. However, tobacco users and those who rate

Patient safety culture measurement in general practice. Clinimetric properties of 'SCOPE'

<p>Abstract</p> <p>Background</p> <p>A supportive patient safety culture is considered to be an essential condition for improving patient safety. Assessing the current safety culture in general practice may be a first step to target improvements. To that end, we studied internal consistency and construct validity of a safety culture questionnaire for general practice (SCOPE) which was derived from a comparable questionnaire for hospitals (Dutch-HSOPS).</p> <p>Methods</p> <p>The survey was conducted among caregivers of Dutch general practice as part of an ongoing quality accreditation process using a 46 item questionnaire. We conducted factor analyses and studied validity by calculating correlations between the subscales and testing the hypothesis that respondents' <it>patient safety grade </it>of their practices correlated with their scores on the questionnaire.</p> <p>Results</p> <p>Of 72 practices 294 respondents completed the questionnaire. Eight factors were identified concerning <it>handover and teamwork, support and fellowship, communication openness, feedback and learning from error, intention to report events, adequate procedures and staffing, overall perceptions of patient safety </it>and <it>expectations and actions of managers</it>. Cronbach's alpha of the factors rated between 0.64 and 0.85. The subscales intercorrelated moderately, except for the factor about intention to report events. Respondents who graded patient safety highly scored significantly higher on the questionnaire than those who did not.</p> <p>Conclusions</p> <p>The SCOPE questionnaire seems an appropriate instrument to assess patient safety culture in general practice. The clinimetric properties of the SCOPE are promising, but future research should confirm the factor structure and construct of the SCOPE and delineate its responsiveness to changes in safety culture over time.</p

Effectiveness of manual therapy compared to usual care by the general practitioner for chronic tension-type headache: design of a randomised clinical trial

<p>Abstract</p> <p>Background</p> <p>Patients with Chronic Tension Type Headache (CTTH) report functional and emotional impairments (loss of workdays, sleep disturbances, emotional well-being) and are at risk for overuse of medication. Manual therapy may improve symptoms through mobilisation of the spine, correction of posture, and training of cervical muscles.</p> <p>We present the design of a randomised clinical trial (RCT) evaluating the effectiveness of manual therapy (MT) compared to usual care by the general practitioner (GP) in patients with CTTH.</p> <p>Methods and design</p> <p>Patients are eligible for participation if they present in general practice with CTTH according to the classification of the International Headache Society (IHS).</p> <p>Participants are randomised to either usual GP care according to the national Dutch general practice guidelines for headache, or manual therapy, consisting of mobilisations (high- and low velocity techniques), exercise therapy for the cervical and thoracic spine and postural correction. The primary outcome measures are the number of headache days and use of medication. Secondary outcome measures are severity of headache, functional status, sickness absence, use of other healthcare resources, active cervical range of motion, algometry, endurance of the neckflexor muscles and head posture. Follow-up assessments are conducted after 8 and 26 weeks.</p> <p>Discussion</p> <p>This is a pragmatic trial in which interventions are offered as they are carried out in everyday practice. This increases generalisability of results, but blinding of patients, GPs and therapists is not possible.</p> <p>The results of this trial will contribute to clinical decision making of the GP regarding referral to manual therapy in patients with chronic tension headache.</p

The Evolution of Compact Binary Star Systems

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure

The Formation and Evolution of the First Massive Black Holes

The first massive astrophysical black holes likely formed at high redshifts (z>10) at the centers of low mass (~10^6 Msun) dark matter concentrations. These black holes grow by mergers and gas accretion, evolve into the population of bright quasars observed at lower redshifts, and eventually leave the supermassive black hole remnants that are ubiquitous at the centers of galaxies in the nearby universe. The astrophysical processes responsible for the formation of the earliest seed black holes are poorly understood. The purpose of this review is threefold: (1) to describe theoretical expectations for the formation and growth of the earliest black holes within the general paradigm of hierarchical cold dark matter cosmologies, (2) to summarize several relevant recent observations that have implications for the formation of the earliest black holes, and (3) to look into the future and assess the power of forthcoming observations to probe the physics of the first active galactic nuclei.Comment: 39 pages, review for "Supermassive Black Holes in the Distant Universe", Ed. A. J. Barger, Kluwer Academic Publisher

Ankyrin-mediated self-protection during cell invasion by the bacterial predator Bdellovibrio bacteriovorus

Predatory Bdellovibrio bacteriovorus are natural antimicrobial organisms, killing other bacteria by whole-cell invasion. Self-protection against prey-metabolizing enzymes is important for the evolution of predation. Initial prey entry involves the predator’s peptidoglycan DD-endopeptidases, which decrosslink cell walls and prevent wasteful entry by a second predator. Here we identify and characterize a self-protection protein from B. bacteriovorus, Bd3460, which displays an ankyrin-based fold common to intracellular pathogens of eukaryotes. Co-crystal structures reveal Bd3460 complexation of dual targets, binding a conserved epitope of each of the Bd3459 and Bd0816 endopeptidases. Complexation inhibits endopeptidase activity and cell wall decrosslinking in vitro. Self-protection is vital — DBd3460 Bdellovibrio deleteriously decrosslink self-peptidoglycan upon invasion, adopt a round morpholog, and lose predatory capacity and cellular integrity. Our analysis provides the first mechanistic examination of self-protection in Bdellovibrio, documents protection-multiplicity for products of two different genomic loci, and reveals an important evolutionary adaptation to an invasive predatory bacterial lifestyle