T Tauri variability in the context of the beat-frequency model

We examine the implications of a beat frequency modulated model of T Tauri accretion. In particular we show that measurements of the variability of accretion generated lines can be used in conjunction with existing photometry to obtain a measurement of the underlying photospheric and disc flux. This provides an independent way of checking spectral energy distribution modelling. In addition, we show how spectroscopy of T Tauri stars can reveal the inclination angle between the magnetic axis and the plane of the disc.Comment: uuencoded compressed postscript. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm

To what extent does severity of loneliness vary among different mental health diagnostic groups: A cross-sectional study.

Loneliness is a common and debilitating problem in individuals with mental health disorders. However, our knowledge on severity of loneliness in different mental health diagnostic groups and factors associated with loneliness is poor, thus limiting the ability to target and improve loneliness interventions. The current study investigated the association between diagnoses and loneliness and explored whether psychological and social factors were related to loneliness. This study employed a cross-sectional design using data from a completed study which developed a measure of social inclusion. It included 192 participants from secondary, specialist mental health services with a primary diagnosis of psychotic disorders (n = 106), common mental disorders (n = 49), or personality disorders (n = 37). The study explored differences in loneliness between these broad diagnostic groups, and the relationship to loneliness of: affective symptoms, social isolation, perceived discrimination, and internalized stigma. The study adhered to the STROBE checklist for observational research. People with common mental disorders (MD = 3.94, CI = 2.15 to 5.72, P < 0.001) and people with personality disorders (MD = 4.96, CI = 2.88 to 7.05, P < 0.001) reported higher levels of loneliness compared to people with psychosis. These differences remained significant after adjustment for all psychological and social variables. Perceived discrimination and internalized stigma were also independently associated with loneliness and substantially contributed to a final explanatory model. The severity of loneliness varies between different mental health diagnostic groups. Both people with common mental disorders and personality disorders reported higher levels of loneliness than people with psychosis. Addressing perceived mental health discrimination and stigma may help to reduce loneliness

Oscillator strengths and line widths of dipole-allowed transitions in ¹⁴N₂ between 89.7 and 93.5 nm

Line oscillator strengths in the 20 electric dipole-allowed bands of ¹⁴N₂ in the 89.7–93.5nm (111480–106950cm⁻¹) region are reported from photoabsorptionmeasurements at an instrumental resolution of ∼6mÅ (0.7cm⁻¹) full width at half maximum. The absorptionspectrum comprises transitions to vibrational levels of the 3pσᵤc′₄¹Σᵤ⁺, 3pπᵤc³Πᵤ, and 3sσgo₃¹ΠᵤRydberg states and of the b′¹Σᵤ⁺ and b¹Πᵤ valence states. The J dependences of band f values derived from the experimental line f values are reported as polynomials in J′(J′+1) and are extrapolated to J′=0 in order to facilitate comparisons with results of coupled Schrödinger-equation calculations. Most bands in this study are characterized by a strong J dependence of the band f values and display anomalous P-, Q-, and R-branch intensity patterns. Predissociation line widths, which are reported for 11 bands, also exhibit strong J dependences. The f value and line width patterns can inform current efforts to develop comprehensive spectroscopic models that incorporate rotational effects and predissociation mechanisms, and they are critical for the construction of realistic atmospheric radiative-transfer models.This work was supported in part by NASA Grant No. NNG05GA03G to Wellesley College and Australian Research Council Discovery Program Grant No. DP0558962

Fluctuations and correlations in population models with age structure

We study the population profile in a simple discrete time model of population dynamics. Our model, which is closely related to certain ``bit-string'' models of evolution, incorporates competition for resources via a population dependent death probability, as well as a variable reproduction probability for each individual as a function of age. We first solve for the steady-state of the model in mean field theory, before developing analytic techniques to compute Gaussian fluctuation corrections around the mean field fixed point. Our computations are found to be in good agreement with Monte-Carlo simulations. Finally we discuss how similar methods may be applied to fluctuations in continuous time population models.Comment: 4 page

Quasar Microlensing at High Magnification and the Role of Dark Matter: Enhanced Fluctuations and Suppressed Saddlepoints

Contrary to naive expectation, diluting the stellar component of the lensing galaxy in a highly magnified system with smoothly distributed ``dark'' matter increases rather than decreases the microlensing fluctuations caused by the remaining stars. For a bright pair of images straddling a critical curve, the saddlepoint (of the arrival time surface) is much more strongly affected than the associated minimum. With a mass ratio of smooth matter to microlensing matter of 4:1, a saddlepoint with a macro-magnification of mu = 9.5 will spend half of its time more than a magnitude fainter than predicted. The anomalous flux ratio observed for the close pair of images in MG0414+0534 is a factor of five more likely than computed by Witt, Mao and Schechter if the smooth matter fraction is as high as 93%. The magnification probability histograms for macro-images exhibit distinctly different structure that varies with the smooth matter content, providing a handle on the smooth matter fraction. Enhanced fluctuations can manifest themselves either in the temporal variations of a lightcurve or as flux ratio anomalies in a single epoch snapshot of a multiply imaged system. While the millilensing simulations of Metcalf and Madau also give larger anomalies for saddlepoints than for minima, the effect appears to be less dramatic for extended subhalos than for point masses. Morever, microlensing is distinguishable from millilensing because it will produce noticeable changes in the magnification on a time scale of a decade or less.Comment: As accepted for publication in ApJ. 17 pages. Substantial revisions include a discussion of constant M/L models and the calculation of a "photometric" dark matter fraction for MG0414+053

Using an ontology for interoperability and browsing of museum, library and archive information

Ontologies play an important part in the development of the future ‘semantic web’; the CIDOC conceptual reference model (CRM) is an ontology aimed at the cultural heritage domain. This paper describes a Concept Browser, developed for the EU/IST-funded SCULPTEUR project (semantic and content-based multimedia exploitation for European benefit environment (programme IST-2001-no. 35372); May 2002 to May 2005), which is able to access different museum information systems through a common ontology, the CRM. The development of this Concept Browser has required mappings from the legacy museum database systems to the CRM. The crucial process of creating the mappings is described, using the C2RMF catalogue (EROS) and library databases as a case study

Microlensing of Broad Absorption Line Quasars: Polarization Variability

Roughly 10% of all quasars exhibit Broad Absorption Line (BAL) features which appear to arise in material outflowing at high velocity from the active galactic nucleus (AGN). The details of this outflow are, however, very poorly constrained and the particular nature of the BAL material is essentially unknown. Recently, new clues have become available through polarimetric studies which have found that BAL troughs are more polarized than the quasar continuum radiation. To explain these observations, models where the BAL material outflows equatorially across the surface of the dusty torus have been developed. In these models, however, several sources of the BAL polarization are possible. Here, we demonstrate how polarimetric monitoring of gravitationally lensed quasars, such as H 1413+117, during microlensing events can not only distinguish between two currently popular models, but can also provide further insight into the structure at the cores of BAL quasars.Comment: 17 pages, 3 figures, accepted to PAS

An Investigation of Gravitational Lensing in the Southern BL Lac PKS 0537-441

The BL-Lac family of active galaxies possess almost featureless spectra and exhibit rapid variability over their entire spectral range. A number of models have been developed to explain these extreme properties, several of which have invoked the action of microlensing by sub-stellar mass objects in a foreground galaxy; this not only introduces variability, but also amplifies an otherwise normal quasar source. Here we present recent spectroscopy and photometry of the southern BL Lac PKS 0537-441; with an inferred redshift of z~0.9 it represents one of the most distant and most luminous members of the BL Lac family. The goal of the observations was not only to confirm the redshift of PKS~0537-441, but also to determine the redshift of a putative galaxy along the line of sight to the BL-Lac; it has been proposed that this galaxy is the host of microlensing stars that account for PKS 0537-441's extreme properties. While several observations have failed to detect any extended emission in PKS 0537-441, the HST imaging data presented here indicate the presence of a galactic component, although we fail to identify any absorption features that reveal the redshift of the emission. It is also noted that PKS 0537-441 is accompanied by several small, but extended companions, located a few arcseconds from the point-like BL-Lac source. Two possibilities present themselves; either they represent true companions of PKS 0537-441, or are themselves gravitationally lensed images of more distant sources.Comment: 13 Pages with 4 Figures; Accepted for Publication by the Astrophysical Journa