Determination of the Night Sky Background around the Crab pulsar using its optical pulsation

The poor angular resolution of imaging gamma-ray telescopes is offset by the large reflector areas of next generation telescopes such as MAGIC (17~m diameter), which makes the study of optical emission associated with some gamma-ray sources feasible. Furthermore, the extremely fast time response of photomultipliers (PMs) makes them ideal detectors for fast (subsecond) optical transients and periodic sources like pulsars. The optical pulse of the Crab pulsar was detected with the HEGRA CT1 central pixel using a modified PM, similar to the future MAGIC camera PMs. The purpose of these periodic observations was to determine the light of the night sky (LONS) for the galactic anticenter Crab region.Our results are between 2.5 and 3 times larger than the previously measured LONS (outside the galactic plane), as expected since the Crab pulsar is in the galactic plane, which implies a slightly higher energy threshold for Crab observations, if the higher value of CT1 measured LONS rate for galactic sources is used.Comment: 19 pages, 6 figures, accepted by Astroparticle Physic

The yellow hypergiants HR 8752 and rho Cassiopeiae near the evolutionary border of instability

High-resolution near-ultraviolet spectra of the yellow hypergiants HR 8752 and rho Cassiopeiae indicate high effective temperatures placing both stars near the T_eff border of the ``yellow evolutionary void''. At present, the temperature of HR 8752 is higher than ever. For this star we found Teff=7900+-200 K, whereas rho Cassiopeiae has Teff=7300+-200 K. Both, HR 8752 and rho Cassiopeiae have developed strong stellar winds with Vinf ~ 120 km/s and Vinf ~ 100 km/s, respectively. For HR 8752 we estimate an upper limit for the spherically symmetric mass-loss of 6.7X10^{-6}M_solar/yr. Over the past decades two yellow hypergiants appear to have approached an evolutionary phase, which has never been observed before. We present the first spectroscopic evidence of the blueward motion of a cool super/hypergiant on the HR diagram.Comment: 13 pages including 3 figures. Accepted for publication in ApJ Letter

Crossing the `Yellow Void' -- Spatially Resolved Spectroscopy of the Post- Red Supergiant IRC+10420 and Its Circumstellar Ejecta

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the HR diagram. During their post--RSG evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semi--forbidden region, that de Jager and his collaborators have called the `yellow void'. We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double--peaked Halpha emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and mass loss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently the observed variations in apparent spectral type and inferred temperature are changes in the wind and do not necessarily mean that the underlying stellar radius and interior structure are evolving on such a short timescale. To explain the evidence for simultaneous outflow and infall of material near the star, we propose a `rain' model in which blobs of gas condense in regions of lowered opacity outside the dense wind. With the apparent warming of its wind, the recent appearance of strong emission, and a decline in the mass loss rate, IRC +10420 may be about to shed its opaque wind, cross the `yellow void', and emerge as a hotter star.Comment: To appear in the Astronomical Journal, August 200

An exploration of learning styles used by social work students: a systematic review

Social work educators are faced with the challenge of ensuring that students from diverse backgrounds are fully equipped with the necessary knowledge and skills. However, to be effective social work educators, the educator is required to understand the learning style of the student. The aim of this systematic review was to explore the learning styles of social work students for the purpose of understanding how to adapt and refine teaching strategies in social work. To this end, a search for descriptive studies in databases, which included Ebscohost (Academic Premier, CINAHL, SOcIndex, Psycharticles, Medline), DOAJ and Pubmed, was conducted. Eight articles met the criteria for inclusion in this systematic review. The target population included both undergraduate and postgraduate students. The studies were mainly conducted in developed countries. The results suggest that the most common approach for social workers is the diverging learning style, which entails having an interest in people, being aware of emotion, and a tendency to be imaginative. This review recommends that if there is an improved understanding of students’ learning needs then educators could adapt their teaching strategies to accommodate and support students from diverse backgrounds, with diverse learning needs.DHE

Pulsational instability of yellow hypergiants

Instability of population I (X=0.7, Y=0.02) massive stars against radial oscillations during the post-main sequence gravitational contraction of the helium core is investigated. Initial stellar masses are in the range from 65M_\odot to 90M_\odot. In hydrodynamic computations of self-exciting stellar oscillations we assumed that energy transfer in the envelope of the pulsating star is due to radiative heat conduction and convection. The convective heat transfer was treated in the framework of the theory of time-dependent turbulent convection. During evolutionary expansion of outer layers after hydrogen exhaustion in the stellar core the star is shown to be unstable against radial oscillations while its effective temperature is Teff > 6700K for Mzams=65M_\odot and Teff > 7200K for mzams=90M_\odot. Pulsational instability is due to the \kappa-mechanism in helium ionization zones and at lower effective temperature oscillations decay because of significantly increasing convection. The upper limit of the period of radial pulsations on this stage of evolution does not exceed 200 day. Radial oscillations of the hypergiant resume during evolutionary contraction of outer layers when the effective temperature is Teff > 7300K for Mzams=65M_\odot and Teff > 7600K for Mzams=90M_\odot. Initially radial oscillations are due to instability of the first overtone and transition to fundamental mode pulsations takes place at higher effective temperatures (Teff > 7700K for Mzams=65M_\odot and Teff > 8200K for Mzams=90M_\odot). The upper limit of the period of radial oscillations of evolving blueward yellow hypergiants does not exceed 130 day. Thus, yellow hypergiants are stable against radial stellar pulsations during the major part of their evolutionary stage.Comment: 20 pages, 7 gigures. Accepted for publication in Astronomy Letter

Side-effects of oral misoprostol in the third stage of labour – a randomised placebo controlled trial

Background. Misoprostol, an irlexpensive, stable, orally active prostaglandirl analogue, has been suggested for use in the prevention of postpartum haemorrhage. Potential side-effects, however, need to be quantified.Objective. To compare the rate of postpartum shivering and pyrexia following oral misoprostol 600 pg and placebo.Design. A double-blind placebo-controlled trial. Women irl labour were randomly allocated to receive either misoprostol 600 pg orally or placebo after delivery. Conventional oxytocics were given immediately if blood loss was thought to be more than usual. Side-effects were recorded. Postpartum blood loss in the first hour was measured by collection in a special flat plastic bedpan.Setting. The labour ward of an academic hospital irl Johannesburg, with 7 000 deliveries per annum.Main outcome measures. Shivering and pyrexia.Results. The groups were well matched. Misoprostol use was associated with more shivering (44% versus 11%, relative risk (RR) 4.03, 95% confidence irlterval (Cl) 2.85 - 5.70), pyrexia ~ 37.8°C (38% v. 6%, RR 6.23, Cl 3.89 - 9.97), I-hour systolic blood pressure ~ 140 mmHg (33% v. 25%, RR 1.32, Cl 1.031.70), and diastolic blood pressure ~ 90 mmHg (10.5% v. 3.0%, RR 3.44, Cl 1.67 -7.11). There were no other significant differences. The study was not designed to be large enough to assess a difference irl blood loss ~ 1 000 ml (9% v. 9.7%, RR 0.93, Cl 0.56 - 1.53). Possible effects on blood loss may have been obscured by the lesser use of additional oxytocics irl the misoprostol group (14% v. 18%, RR 0.78, Cl 0.54 - 1.13). Conclusions. This study has shown the association of postpartum oral misoprostol 600 Jlg with shivering, pyrexia and hypertension. The increased blood pressure, as for the trend towards increased abdominal pain, may be secondary to the uterotonic effect of misoprostol. Large randomised trials are needed to assess the effectiveness of misoprostol in the prevention of postpartum haemorrhage, against which the disadvantages demonstrated here can be weighed

Limb reduction anomaly after failed misoprostol abortion

No Abstract

The onset of classical QCD dynamics in relativistic heavy ion collisions

The experimental results on hadron production obtained recently at RHIC offer a new prospective on the energy dependence of the nuclear collision dynamics. In particular, it is possible that parton saturation -- the phenomenon likely providing initial conditions for the multi--particle production at RHIC energies -- may have started to set in central heavy ion collisions already around the highest SPS energy. We examine this scenario, and make predictions based on high density QCD for the forthcoming 22 GeV run at RHIC.Comment: 4 pages, 2 figures, revte

Pulsar Magnetospheric Emission Mapping: Images and Implications of Polar-Cap Weather

The beautiful sequences of ``drifting'' subpulses observed in some radio pulsars have been regarded as among the most salient and potentially instructive characteristics of their emission, not least because they have appeared to represent a system of subbeams in motion within the emission zone of the star. Numerous studies of these ``drift'' sequences have been published, and a model of their generation and motion articulated long ago by Ruderman & Sutherland (1975); but efforts thus far have failed to establish an illuminating connection between the drift phemomenon and the actual sites of radio emission. Through a detailed analysis of a nearly coherent sequence of ``drifting'' pulses from pulsar B0943+10, we have in fact identified a system of subbeams circulating around the magnetic axis of the star. A mapping technique, involving a ``cartographic'' transform and its inverse, permits us to study the character of the polar-cap emission ``map'' and then to confirm that it, in turn, represents the observed pulse sequence. On this basis, we have been able to trace the physical origin of the ``drifting-subpulse'' emission to a stably rotating and remarkably organized configuration of emission columns, in turn traceable possibly to the magnetic polar-cap ``gap'' region envisioned by some theories.Comment: latex with five eps figure

Effective Lagrangian approach to nuclear mu-e conversion and the role of vector mesons

We study nuclear mu-e conversion in the general framework of an effective Lagrangian approach without referring to any specific realization of the physics beyond the standard model (SM) responsible for lepton flavor violation (LFV). We examine the impact of a specific hadronization prescription on the analysis of new physics in nuclear mu-e conversion and stress the importance of vector meson exchange between lepton and nucleon currents. A new issue of this mechanism is the presence of the strange quark vector current contribution induced by the phi meson. This allows us to extract new limits on the LFV lepton-quark effective couplings from the existing experimental data.Comment: 19 pages, 3 figures, to be published in Phys Rev