3,917 research outputs found
Charged Dilaton Black Holes with a Cosmological Constant
The properties of static spherically symmetric black holes, which are either
electrically or magnetically charged, and which are coupled to the dilaton in
the presence of a cosmological constant, are considered. It is shown that such
solutions do not exist if the cosmological constant is positive (in arbitrary
spacetime dimension >= 4). However, asymptotically anti-de Sitter black hole
solutions with a single horizon do exist if the cosmological constant is
negative. These solutions are studied numerically in four dimensions and the
thermodynamic properties of the solutions are derived. The extreme solutions
are found to have zero entropy and infinite temperature for all non-zero values
of the dilaton coupling constant.Comment: 12 pages, epsf, phyzzx, 4 in-text figures incl. (minor typos fixed, 1
reference added
Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei
We present an investigation of H-alpha emission line variations observed in
the massive Algol binary, RY Per. We give new radial velocity data for the
secondary based upon our optical spectra and for the primary based upon high
dispersion UV spectra. We present revised orbital elements and an estimate of
the primary's projected rotational velocity (which indicates that the primary
is rotating 7 times faster than synchronous). We use a Doppler tomography
algorithm to reconstruct the individual primary and secondary spectra in the
region of H-alpha, and we subtract the latter from each of our observations to
obtain profiles of the primary and its disk alone. Our H-alpha observations of
RY Per show that the mass gaining primary is surrounded by a persistent but
time variable accretion disk. The profile that is observed outside-of-eclipse
has weak, double-peaked emission flanking a deep central absorption, and we
find that these properties can be reproduced by a disk model that includes the
absorption of photospheric light by the band of the disk seen in projection
against the face of the star. We developed a new method to reconstruct the disk
surface density distribution from the ensemble of H-alpha profiles observed
around the orbit, and this method accounts for the effects of disk occultation
by the stellar components, the obscuration of the primary by the disk, and flux
contributions from optically thick disk elements. The resulting surface density
distribution is elongated along the axis joining the stars, in the same way as
seen in hydrodynamical simulations of gas flows that strike the mass gainer
near trailing edge of the star. This type of gas stream configuration is
optimal for the transfer of angular momentum, and we show that rapid rotation
is found in other Algols that have passed through a similar stage.Comment: 39 pages, 12 figures, ApJ in press, 2004 June 20 issu
Self‐reported sleep quality is more closely associated with mental and physical health than chronotype and sleep duration in young adults: A multi‐instrument analysis
Sleep and circadian rhythms are considered to be important determinants of mental and physical health. Epidemiological studies have established the contribution of self‐reported sleep duration, sleep quality and chronotype to health outcomes. Mental health and sleep problems are more common in women and men are more likely to be evening types. Few studies have compared the relative strength of these contributions and few studies have assessed these contributions separately in men and women. Furthermore, sleep and circadian characteristics are typically assessed with a limited number of instruments and a narrow range of variables is considered, leaving the understanding of the relative contribution of different predictors somewhat fractionary. We compared sleep quality, sleep duration and chronotype as predictors for self‐reported mental and physical health and psychological characteristics in 410 men and 261 women aged 18 to 30. To ascertain that results were not dependent on the use of specific instruments we used a multitude of validated instruments including the Morningness‐Eveningness‐Questionnaire, Munich‐ChronoType‐Questionnaire, Pittsburgh‐Sleep‐Quality‐Index, British‐Sleep‐Survey, Karolinska‐Sleep‐Diary, Insomnia‐Severity‐Index, SF‐36‐Health Survey, General‐Health‐Questionnaire, Dutch‐Eating‐Behaviour‐Questionnaire, Big‐Five‐Inventory, Behaviour‐Inhibition‐System‐Behaviour‐Activation‐System, and the Positive‐Affect‐Negative‐Affect‐Schedule. Relative contributions of predictors were quantified as local effect sizes derived from multiple regression models. Across all questionnaires, sleep quality was the strongest independent predictor of health and in particular mental health and more so in women than in men. The effect of sleep duration and social jetlag was inconspicuous. A greater insight into the independent contributions of sleep quality and chronotype may aid the understanding of sleep‐health interactions in women and men
Gravitational lensing due to dark matter modelled by vector field
The specified constant 4-vector field reproducing the spherically symmetric
stationary metric of cold dark matter halo in the region of flat rotation
curves results in a constant angle of light deflection at small impact
distances. The effective deflecting mass is factor greater than the
dark matter mass. The perturbation of deflection picture due to the halo edge
is evaluated.Comment: 17 pages, LaTeX iopart class, 10 eps figures; explanaitions and
discussion are extended and improved, reference added; version to appear in
Classical and Quantum Gravit
Dynamics of Line-Driven Winds from Disks in Cataclysmic Variables. I. Solution Topology and Wind Geometry
We analyze the dynamics of 2-D stationary, line-driven winds from accretion
disks in cataclysmic variable stars. The driving force is that of line
radiation pressure, in the formalism developed by Castor, Abbott & Klein for O
stars. Our main assumption is that wind helical streamlines lie on straight
cones. We find that the Euler equation for the disk wind has two eigenvalues,
the mass loss rate and the flow tilt angle with the disk. Both are calculated
self-consistently. The wind is characterized by two distinct regions, an outer
wind launched beyond four white dwarf radii from the rotation axis, and an
inner wind launched within this radius. The inner wind is very steep, up to 80
degrees with the disk plane, while the outer wind has a typical tilt of 60
degrees. In both cases the ray dispersion is small. We, therefore, confirm the
bi-conical geometry of disk winds as suggested by observations and kinematical
modeling. The wind collimation angle appears to be robust and depends only on
the disk temperature stratification. The flow critical points lie high above
the disk for the inner wind, but close to the disk photosphere for the outer
wind. Comparison with existing kinematical and dynamical models is provided.
Mass loss rates from the disk as well as wind velocity laws are discussed in a
subsequent paper.Comment: 21 pages, 10 Postscript figures; available also from
http://www.pa.uky.edu/~shlosman/publ.html. Astrophysical Journal, submitte
For the benefit of all? Developing a critical perspective in mega-event leverage
The purpose of this article is to bring to light the need for developing a critical leveraging perspective on mega-events and propose a research agenda that extends the focus of the leverage concept towards this direction. Current research on leverage focuses on the attainment and magnification of mega-event outcomes. A critical lens of inquiry however is needed to move forward and take into account the influence of power structures and social-ordering processes on developing and implementing strategic leveraging programs. Such a perspective can help examine if and how the benefits of mega-events are fairly delivered to host communities, equally distributed among stakeholders and then sustained, while negative impacts are minimised. Ten research themes are brought forward to help build a robust ground for a critical mega-event leveraging perspective
Age-related Differences in Prestimulus Subsequent Memory Effects Assessed with Event-related Potentials
Prestimulus subsequent memory effects (preSMEs)—differences in neural activity elicited by a task cue at encoding that are predictive of later memory performance—are thought to reflect differential engagement of preparatory processes that benefit episodic memory encoding. We investigated age differences in preSMEs indexed by differences in ERP amplitude just before the onset of a study item. Young and older adults incidentally encoded words for a subsequent memory test. Each study word was preceded by a task cue that signaled a judgment to perform on the word. Words were presented for either a short (300 msec) or long (1000 msec) duration with the aim of placing differential benefits on engaging preparatory processes initiated by the task cue. ERPs associated with subsequent successful and unsuccessful recollection, operationalized here by source memory accuracy, were estimated time-locked to the onset of the task cue. In a late time window (1000–2000 msec after onset of the cue), young adults demonstrated frontally distributed preSMEs for both the short and long study durations, albeit with opposite polarities in the two conditions. This finding suggests that preSMEs in young adults are sensitive to perceived task demands. Although older adults showed no evidence of preSMEs in the same late time window, significant preSMEs were observed in an earlier time window (500–1000 msec) that was invariant with study duration. These results are broadly consistent with the proposal that older adults differ from their younger counterparts in how they engage preparatory processes during memory encoding
SuperWASP: Wide Angle Search for Planets
SuperWASP is a fully robotic, ultra-wide angle survey for planetary transits.
Currently under construction, it will consist of 5 cameras, each monitoring a
9.5 x 9.5 deg field of view. The Torus mount and enclosure will be fully
automated and linked to a built-in weather station. We aim to begin
observations at the beginning of 2003.Comment: 4 pages, 1 figure, to be published in proceedings of "Scientific
Frontiers in Research on Extrasolar Planets
Nonlocality without inequalities has not been proved for maximally entangled states
Two approaches to extend Hardy's proof of nonlocality without inequalities to
maximally entangled states of bipartite two-level systems are shown to fail. On
one hand, it is shown that Wu and co-workers' proof [Phys. Rev. A 53, R1927
(1996)] uses an effective state which is not maximally entangled. On the other
hand, it is demonstrated that Hardy's proof cannot be generalized by the
replacement of one of the four von Neumann measurements involved in the
original proof by a generalized measurement to unambiguously discriminate
between non-orthogonal states.Comment: 7 pages, 2 figures. To appear in Phys. Rev.
The impact of a supplementary medication review and counselling service within the oncology outpatient setting
The impact on the care of breast cancer patients, of a pharmacy technician-led medication review and counselling clinic, provided in an outpatient setting, was investigated using a controlled randomised study. Compared to the controls, clinic patients showed a significantly improved level of understanding of their chemotherapy support medication (95% CI for difference in mean knowledge rating scores=2.165–2.826, P<0.001) and a significant reduction in the median number of support items required (two compared to five in the control, P<0.001). This resulted in a significant reduction in mean medication expenditure per patient (£26.70 vs £10.20, 95% CI for the mean difference in cost £6.72–£26.26, P<0.001). The clinic was also associated with significant reductions in chemotherapy delays (P<0.001) and dose reductions due to side effects (P=0.003). Other benefits from the clinic were a reduction in pharmacy dispensing time and a highly significant reduction in pharmacy time spent resolving post-clinic prescription queries (P<0.001). Taking into account the initial technician training cost, the scheme represented an annual saving to the Trust of over £15 000. The clinic serves as a model for those wishing to improve outpatient services to breast cancer patients
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