Megamaser Disks in Active Galactic Nuclei

Recent spectroscopic and VLBI-imaging observations of bright extragalactic water maser sources have revealed that the megamaser emission often originates in thin circumnuclear disks near the centers of active galactic nuclei (AGNs). Using general radiative and kinematic considerations and taking account of the observed flux variability, we argue that the maser emission regions are clumpy, a conclusion that is independent of the detailed mechanism (X-ray heating, shocks, etc.) driving the collisionally pumped masers. We examine scenarios in which the clumps represent discrete gas condensations (i.e., clouds) and do not merely correspond to velocity irregularities in the disk. We show that even two clouds that overlap within the velocity coherence length along the line of sight could account (through self-amplification) for the entire maser flux of a high-velocity ``satellite'' feature in sources like NGC 4258 and NGC 1068, and we suggest that cloud self-amplification likely contributes also to the flux of the background-amplifying ``systemic'' features in these objects. Analogous interpretations have previously been proposed for water maser sources in Galactic star-forming regions. We argue that this picture provides a natural explanation of the time-variability characteristics of extragalactic megamaser sources and of their apparent association with Seyfert 2-like galaxies. We also show that the requisite cloud space densities and internal densities are consistent with the typical values of nuclear (broad emission-line region-type) clouds.Comment: 55 pages, 7 figures, AASTeX4.0, to appear in The Astrophysical Journal (1999 March 1 issue

The alignment of disk and black hole spins in active galactic nuclei

The inner parts of an accretion disk around a spinning black hole are forced to align with the spin of the hole by the Bardeen-Petterson effect. Assuming that any jet produced by such a system is aligned with the angular momentum of either the hole or the inner disk, this can, in principle provide a mechanism for producing steady jets in AGN whose direction is independent of the angular momentum of the accreted material. However, the torque which aligns the inner disk with the hole, also, by Newton's third law, tends to align the spin of the hole with the outer accretion disk. In this letter, we calculate this alignment timescale for a black hole powering an AGN, and show that it is relatively short. This timescale is typically much less than the derived ages for jets in radio loud AGN, and implies that the jet directions are not in general controlled by the spin of the black hole. We speculate that the jet directions are most likely controlled either by the angular momentum of the accreted material or by the gravitational potential of the host galaxy.Comment: 4 pages, LateX file, accepted for publication in ApJ Letter

Constraining uncertainty in aerosol direct forcing

The uncertainty in present-day anthropogenic forcing is dominated by uncertainty in the strength of the contribution from aerosol. Much of the uncertainty in the direct aerosol forcing can be attributed to uncertainty in the anthropogenic fraction of aerosol in the present-day atmosphere, due to a lack of historical observations. Here we present a robust relationship between total present-day aerosol optical depth and the anthropogenic contribution across three multi-model ensembles and a large single-model perturbed parameter ensemble. Using observations of aerosol optical depth, we determine a reduced likely range of the anthropogenic component and hence a reduced uncertainty in the direct forcing of aerosol

The lived experience of weight loss maintenance in young people

Introduction There continues to be an imbalance of research into weight loss and weight loss maintenance (WLM), with a particular lack of research into WLM in young people under 18 years. Failure to coherently understand WLM in young people may be a potential contributor to the underdeveloped guidance surrounding long-term support. Furthermore, no research has investigated young people's preferences around WLM support following the attendance of a residential intensive weight loss intervention from a qualitative perspective. This study explored the influences of WLM in young people following a residential intensive weight loss intervention, considered how interventions could be improved and sought to develop recommendations for stakeholders responsible for designing WLM interventions. Methods The context in which this research is framed was taken from a residential Intensive Weight Loss Intervention for young people aged 8–17 years in England. Six semi-structured interviews were carried out to understand the lived experience of WLM, including barriers and enablers influencing WLM, adopting an interpretative phenomenological analysis design. Findings Three superordinate themes were developed to explain the barriers and enablers to WLM; (1) Behavioural control and the psychosocial skills to self-regulate WLM; (2) Delivering effective social support; and (3) Conflicting priorities and environmental triggers. Conclusion The findings of this research mirror that of other studies of WLM in young people, with the majority of young people struggling to maintain weight loss. However, by exploring the experience of WLM in young people through qualitative means, it was possible to understand the specific motivators and barriers influencing WLM behaviours in this context, providing recommendations to support WLM. Patient or Public Contribution The interview guide was developed in consultation with a young person from the intervention, and through discussions with the intervention stakeholders (delivery staff and management staff). The interview guide included topics such as knowledge and skills; experience of weight loss; reflections on weight maintenance, and experiences of daily life postintervention. We piloted the interview schedule with one young person who had consented to take part in the research. This first interview was used to check for understanding of questions and to assess the flow of the interview

The zebrafish xenograft platform-A novel tool for modeling KSHV-associated diseases

Kaposi\u27s sarcoma associated-herpesvirus (KSHV, also known as human herpesvirus-8) is a gammaherpesvirus that establishes life-long infection in human B lymphocytes. KSHV infection is typically asymptomatic, but immunosuppression can predispose KSHV-infected individuals to primary effusion lymphoma (PEL); a malignancy driven by aberrant proliferation of latently infected B lymphocytes, and supported by pro-inflammatory cytokines and angiogenic factors produced by cells that succumb to lytic viral replication. Here, we report the development of the firs

The lived experience of weight loss maintenance in young people

Introduction There continues to be an imbalance of research into weight loss and weight loss maintenance (WLM), with a particular lack of research into WLM in young people under 18 years. Failure to coherently understand WLM in young people may be a potential contributor to the underdeveloped guidance surrounding long‐term support. Furthermore, no research has investigated young people's preferences around WLM support following the attendance of a residential intensive weight loss intervention from a qualitative perspective. This study explored the influences of WLM in young people following a residential intensive weight loss intervention, considered how interventions could be improved and sought to develop recommendations for stakeholders responsible for designing WLM interventions. Methods The context in which this research is framed was taken from a residential Intensive Weight Loss Intervention for young people aged 8–17 years in England. Six semi‐structured interviews were carried out to understand the lived experience of WLM, including barriers and enablers influencing WLM, adopting an interpretative phenomenological analysis design. Findings Three superordinate themes were developed to explain the barriers and enablers to WLM; (1) Behavioural control and the psychosocial skills to self‐regulate WLM; (2) Delivering effective social support; and (3) Conflicting priorities and environmental triggers. Conclusion The findings of this research mirror that of other studies of WLM in young people, with the majority of young people struggling to maintain weight loss. However, by exploring the experience of WLM in young people through qualitative means, it was possible to understand the specific motivators and barriers influencing WLM behaviours in this context, providing recommendations to support WLM. Patient or Public Contribution The interview guide was developed in consultation with a young person from the intervention, and through discussions with the intervention stakeholders (delivery staff and management staff). The interview guide included topics such as knowledge and skills; experience of weight loss; reflections on weight maintenance, and experiences of daily life postintervention. We piloted the interview schedule with one young person who had consented to take part in the research. This first interview was used to check for understanding of questions and to assess the flow of the interview

The Chromospheric Activity and Ages of M Dwarf Stars in Wide Binary Systems

We investigate the relationship between age and chromospheric activity for 139 M dwarf stars in wide binary systems with white dwarf companions. The age of each system is determined from the cooling age of its white dwarf component. The current limit for activity-age relations found for M dwarfs in open clusters is 4 Gyr. Our unique approach to finding ages for M stars allows for the exploration of this relationship at ages older than 4 Gyr. The general trend of stars remaining active for a longer time at later spectral type is confirmed. However, our larger sample and greater age range reveals additional complexity in assigning age based on activity alone. We find that M dwarfs in wide binaries older than 4 Gyr depart from the log-linear relation for clusters and are found to have activity at magnitudes, colors and masses which are brighter, bluer and more massive than predicted by the cluster relation. In addition to our activity-age results, we present the measured radial velocities and complete space motions for 161 white dwarf stars in wide binaries.Comment: 22 pages including 9 figures and 5 tables. Accepted for publication in The Astronomical Journa

Associations between daily sitting time and the combinations of lifestyle risk factors in men

Background: Understanding the reciprocal role that multiple problematic behaviours play in men's health is important for intervention delivery and for reducing the healthcare burden. Data regarding the concurrence of problematic health behaviours is currently limited but offers insights into risk profiles, and should now include total time spent sitting/day. Methods: Self-reported data on lifestyle health behaviours was collected from 232 men aged ≥18 years who engaged in a men's health promotion programme delivered by 16 English Premier League Clubs. Results: Men at risk due to high sitting display multiple concurrent lifestyle risk factors, 88.6% displayed at least two ancillary risk factors and were three times more likely to report ≥2 lifestyle risk factors (OR. =3.13, 95% confidence interval (CI). =1.52-6.42) than those with low sitting risk. Significant differences in the mean number of risk factors reported between those participants in the higher risk (2.43. ±. 0.90) and lower risk (2.13. ±. 0.96) sitting categories were also found (P=0.015). Conclusions: Hard-to-reach men displayed multiple problematic concurrent behaviours, strongly linked to total sitting time. © 2012 WPMH GmbH

A Deep Look at the Emission-Line Nebula in Abell 2597

The close correlation between cooling flows and emission-line nebulae in clusters of galaxies has been recognized for over a decade and a half, but the physical reason for this connection remains unclear. Here we present deep optical spectra of the nebula in Abell 2597, one of the nearest strong cooling-flow clusters. These spectra reveal the density, temperature, and metal abundances of the line-emitting gas. The abundances are roughly half-solar, and dust produces an extinction of at least a magnitude in V. The absence of [O III] 4363 emission rules out shocks as a major ionizing mechanism, and the weakness of He II 4686 rules out a hard ionizing source, such as an active galactic nucleus or cooling intracluster gas. Hot stars are therefore the best candidate for producing the ionization. However, even the hottest O stars cannot power a nebula as hot as the one we see. Some other nonionizing source of heat appears to contribute a comparable amount of power. We show that the energy flux from a confining medium can become important when the ionization level of a nebula drops to the low levels seen in cooling-flow nebulae. We suggest that this kind of phenomenon, in which energy fluxes from the surrounding medium augment photoelectric heating, might be the common feature underlying the diverse group of objects classified as LINERS.Comment: 33 Latex pages, including 16 Postscript figures, to appear in 1997 September 1 Astrophysical Journa