5,550 research outputs found
Line width distributions as evidence for axisymmetry in the broad line regions of active galaxies
The nuclei of a wide class of active galaxies emit broad emission lines with
widths at half maximum (FWHM) in the range km s. This
spread of widths is not solely a consequence of the range of the luminosities
of these sources since a plot of width versus luminosity shows a large scatter.
We propose that the broad line emission region (BLR) is axially symmetric and
that this scatter in line width arises from an additional dependence on the
angle of the line of sight to the axis of the emission region. Such a relation
is natural in unified models of active nuclei which link a variety of observed
properties to viewing angle. Adopting a simple form for the line width as a
function of luminosity and angle, and convolving this with the observed
luminosity function, allows us to predict a line width distribution consistent
with the available data. Furthermore, we use the relation between the
equivalent width of a line and the luminosity in the continuum (the `Baldwin
Effect') to predict an observed correlation between line width and equivalent
width. The scatter on this correlation is again provided by angular dependence.
The results have applications as diagnostics of models of the broad line
emission region and in cosmology.Comment: 8 pages including 4 figures. Accepted for publication in MNRAS
Letter
The luminosity dependence of opening angle in unified models of active galaxies
In unified models of active galaxies the direct line of sight to the nucleus
is unobscured only within a certain cone of directions. An opening angle for
this cone is usually estimated by methods such as the overall ratio of Seyfert
1s to Seyfert2s, the latter assumed to be obscured versions of the former. Here
we shall show, as has often been suspected, that the opening angle of the cone
depends on the luminosity of the central source, with higher luminosities
corresponding to larger opening angles. This conclusion depends only on the
assumption that the width of the broad emission lines at a given luminosity is
a measure of inclination angle, an assumption that is supported by observation
in radio-loud systems. On the other hand we show that the scatter in X-ray
spectral index is not primarily an effect of viewing angle, in contrast to what
might be expected if the scatter on the spectral index versus luminosity
relation were a consequence of absorption in the obscuring material. The
observed correlation between linewidth and spectral index appears to be a
further consequence of the dependence of opening angle on luminosity.Comment: 8 pages, 7 figures, uses mn.sty. Accepted for publication in MNRA
Determining the cosmological parameters from the linewidths of active galaxies
We have previously shown that the linewidth distribution in AGN can be
accounted for by an axisymmetric broad emission line region. In this paper we
show that the linewidth distribution changes with redshift and that these
changes are dependent on H_0 and q_0. We show that relatively small samples of
AGN at high redshift with measured linewidth at half maximum can be used to
distinguish between values of H_0 and q_0. Furthermore larger low redshift
samples can be used to distinguish between luminosity functions and hence
different models of quasar evolution.Comment: Accepted for publication in MNRAS. 8 pages LaTeX, uses mn.st
Moving Detectors in Cavities
We consider two-level detectors, coupled to a quantum scalar field, moving
inside cavities. We highlight some pathological resonant effects due to abrupt
boundaries, and decide to describe the cavity by switching smoothly the
interaction by a time-dependent gate-like function. Considering uniformly
accelerated trajectories, we show that some specific choices of non-adiabatic
switching have led to hazardous interpretations about the enhancement of the
Unruh effect in cavities. More specifically, we show that the
emission/absorption ratio takes arbitrary high values according to the emitted
quanta properties and to the transients undergone at the entrance and the exit
of the cavity, {\it independently of the acceleration}. An explicit example is
provided where we show that inertial and uniformly accelerated world-lines can
even lead to the same ``pseudo-temperature''.Comment: 13 pages, 6 figures, version accepted in Phys.Rev.
Einstein-Podolsky-Rosen correlations between two uniformly accelerated oscillators
We consider the quantum correlations, i.e. the entanglement, between two
systems uniformly accelerated with identical acceleration a in opposite Rindler
quadrants which have reached thermal equilibrium with the Unruh heat bath. To
this end we study an exactly soluble model consisting of two oscillators
coupled to a massless scalar field in 1+1 dimensions. We find that for some
values of the parameters the oscillators get entangled shortly after the moment
of closest approach. Because of boost invariance there are an infinite set of
pairs of positions where the oscillators are entangled. The maximal
entanglement between the oscillators is found to be approximately 1.4
entanglement bits.Comment: 11 page
Predictors of incident herpes simplex virus type 2 infections in young women at risk for unintended pregnancy in San Francisco.
BackgroundYoung women receiving family planning services are at risk for both unintended pregnancy and herpes simplex virus type 2 (HSV-2) infection.MethodsWe performed a secondary analysis using data from a previously published randomized controlled trial evaluating access to emergency contraception on reproductive health outcomes. Women aged 15 to 24 years were recruited from two Planned Parenthood clinics and two community health clinics in San Francisco. Demographic information and sexual history were obtained by interview. HSV-2 seropositivity was determined by fingerstick blood test. New pregnancies were measured by self-report, urine testing and medical chart review. Subjects were evaluated for incident HSV-2 infection and pregnancy at a 6-month follow-up appointment. Women who were pregnant or intending to become pregnant at enrolment were excluded.ResultsAt enrolment 2,104 women were screened for HSV-2 and 170 (8.1%) were seropositive. Eighty-seven percent of initially seronegative women completed the study (n = 1,672) and 73 (4.4%) became HSV-2 seropositive. HSV-2 seroincidence was 7.8 cases per 100 person-years. One hundred and seventeen women (7%) became pregnant and 7 (6%) of these had a seroincident HSV-2 infection during the study. After adjustment for confounders, predictors of incident HSV-2 infection were African American race and having multiple partners in the last six months. Condom use at last sexual encounter was protective.ConclusionHSV-2 seroincidence and the unintended pregnancy rate in young women were high. Providers who counsel women on contraceptive services and sexually transmitted infection prevention could play an expanded role in counselling women about HSV-2 prevention given the potential sequelae in pregnancy. The potential benefit of targeted screening and future vaccination against HSV-2 needs to be assessed in this population
Stirling-cycle heat-pumps and refrigerators – a realistic alternative?
Concerns about the environmental impact of refrigerants used in vapour-compression heatpumps and refrigerators, have prompted the Stirling-Cycle Research Group at the University of Canterbury to investigate the feasibility of low-cost Stirling-cycle machines that use air as the refrigerant. Such machines theoretically have the highest efficiency possible for any practical thermodynamic system, and thus provide a tempting alternative to traditional vapourcompression technology. This paper outlines the working principles of Stirling-cycle heat-pumps and refrigerators, and describes some of the work performed at Canterbury University. Some of the heat-pump development programme results are also presented, and briefly discussed
Developing the use of diagrammatic representations in primary mathematics through professional development
Background: The research on diagrammatic representations highlights their importance for the teaching and learning of mathematics. However, the empirical evidence to support their use in the classroom is mixed and somewhat lacking. Purpose: The aim of this study was to develop the use of diagrammatic representations of mathematical concepts in primary classrooms, through introducing primary teachers to the research literature in this area, and researching the subsequent impact on children and teachers. A professional development programme was designed, involving three one-day training sessions for mathematics co-ordinators. They were asked to implement the ideas from the training back in their schools. Sample: Mathematics co-ordinators from eight primary schools attended the professional development programme. The study focussed on Year 3 pupils (aged seven–eight) and Year 5 pupils (aged nine–10). Design and methods: In this paper, we report the qualitative findings from the larger project looking at the overall impact of the professional development programme. The paper focuses on semi-structured interviews carried out with the mathematics co-ordinators attending the professional development sessions, and the Year 3 and Year 5 class teachers who subsequently worked with the co-ordinators on their use of diagrammatic representations in their teaching of mathematics. Lesson observations involving the class teachers were also carried out in order to explore further the possible impact of the project on classroom practice. Results: The qualitative results identified the impact of the project on mathematics co-ordinators and class teachers’ knowledge and practice. However, the nature of this impact was complex, with a variety of facilitating and hindering factors identified for the transfer of the professional development ideas on the use of diagrammatic representations. In addition, different levels of sophistication of class teachers’ use of diagrammatic representations were identified. Conclusions: Implications for the development of professional development programmes to facilitate the transfer of research into practice were identified. Recommendations for the use of diagrammatic representations are also put forward
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