1,734 research outputs found
The Impact of Accretion Disk Winds on the Optical Spectra of Cataclysmic Variables
Many high-state non-magnetic cataclysmic variables (CVs) exhibit blue-shifted
absorption or P-Cygni profiles associated with ultraviolet (UV) resonance
lines. These features imply the existence of powerful accretion disk winds in
CVs. Here, we use our Monte Carlo ionization and radiative transfer code to
investigate whether disk wind models that produce realistic UV line profiles
are also likely to generate observationally significant recombination line and
continuum emission in the optical waveband. We also test whether outflows may
be responsible for the single-peaked emission line profiles often seen in
high-state CVs and for the weakness of the Balmer absorption edge (relative to
simple models of optically thick accretion disks). We find that a standard disk
wind model that is successful in reproducing the UV spectra of CVs also leaves
a noticeable imprint on the optical spectrum, particularly for systems viewed
at high inclination. The strongest optical wind-formed recombination lines are
H and He II . We demonstrate that a higher-density outflow
model produces all the expected H and He lines and produces a recombination
continuum that can fill in the Balmer jump at high inclinations. This model
displays reasonable verisimilitude with the optical spectrum of RW Trianguli.
No single-peaked emission is seen, although we observe a narrowing of the
double-peaked emission lines from the base of the wind. Finally, we show that
even denser models can produce a single-peaked H line. On the basis of
our results, we suggest that winds can modify, and perhaps even dominate, the
line and continuum emission from CVs.Comment: 15 pages, 13 figures. Accepted to MNRA
Line-driven Disk Winds in Active Galactic Nuclei: The Critical Importance of Ionization and Radiative Transfer
Accretion disk winds are thought to produce many of the characteristic
features seen in the spectra of active galactic nuclei (AGN) and quasi-stellar
objects (QSOs). These outflows also represent a natural form of feedback
between the central supermassive black hole and its host galaxy. The mechanism
for driving this mass loss remains unknown, although radiation pressure
mediated by spectral lines is a leading candidate. Here, we calculate the
ionization state of, and emergent spectra for, the hydrodynamic simulation of a
line-driven disk wind previously presented by Proga & Kallman (2004). To
achieve this, we carry out a comprehensive Monte Carlo simulation of the
radiative transfer through, and energy exchange within, the predicted outflow.
We find that the wind is much more ionized than originally estimated. This is
in part because it is much more difficult to shield any wind regions
effectively when the outflow itself is allowed to reprocess and redirect
ionizing photons. As a result, the calculated spectrum that would be observed
from this particular outflow solution would not contain the ultraviolet
spectral lines that are observed in many AGN/QSOs. Furthermore, the wind is so
highly ionized that line-driving would not actually be efficient. This does not
necessarily mean that line-driven winds are not viable. However, our work does
illustrate that in order to arrive at a self-consistent model of line-driven
disk winds in AGN/QSO, it will be critical to include a more detailed treatment
of radiative transfer and ionization in the next generation of hydrodynamic
simulations.Comment: 13 pages, 10 figures - Accepted for publication in Ap
Protein-mediated DNA Loop Formation and Breakdown in a Fluctuating Environment
Living cells provide a fluctuating, out-of-equilibrium environment in which
genes must coordinate cellular function. DNA looping, which is a common means
of regulating transcription, is very much a stochastic process; the loops arise
from the thermal motion of the DNA and other fluctuations of the cellular
environment. We present single-molecule measurements of DNA loop formation and
breakdown when an artificial fluctuating force, applied to mimic a fluctuating
cellular environment, is imposed on the DNA. We show that loop formation is
greatly enhanced in the presence of noise of only a fraction of , yet
find that hypothetical regulatory schemes that employ mechanical tension in the
DNA--as a sensitive switch to control transcription--can be surprisingly robust
due to a fortuitous cancellation of noise effects
A numerical tidal model and its application to Cook Inlet, Alaska
A numerical scheme for predicting tides and tidal currents has been designed for rapid application to new situations with a minimum of effort. The model is two-dimensional and includes Coriolis and fric tional terms. An application to Cook Inlet, Alaska, is described for a tide having a period of 12.42 hours and an amplitude of one half the mean tidal range...
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The 10kTrees Website: A New Online Resource for Primate Phylogeny
The comparative method plays a central role in efforts to uncover the adaptive basis for primate behaviors, morphological traits, and cognitive abilities.[1-4] The comparative method has been used, for example, to infer that living in a larger group selects for a larger neocortex,[5][6] that primate territoriality favors a longer day range relative to home range size,[7] and that sperm competition can account for the evolution of primate testes size.[8][9] Comparison is fundamental for reconstructing behavioral traits in the fossil record, for example, in studies of locomotion and diet.[10-13] Recent advances in comparative methods require phylogenetic information,[2][14-16] but our knowledge of phylogenetic information is imperfect. In the face of uncertainty about evolutionary relationships, which phylogeny should one use? Here we provide a new resource for comparative studies of primates that enables users to run comparative analyses on multiple primate phylogenies Importantly, the 10,000 trees that we provide are not random, but instead use recent systematic methods to create a plausible set of topologies that reflect our certainty about some nodes on the tree and uncertainty about other nodes, given the dataset. The trees also reflect uncertainty about branch lengths.Human Evolutionary Biolog
Resolved Imaging of the HR 8799 Debris Disk with Herschel
We present Herschel far-infrared and submillimeter maps of the debris disk
associated with the HR 8799 planetary system. We resolve the outer disk
emission at 70, 100, 160 and 250 um and detect the disk at 350 and 500 um. A
smooth model explains the observed disk emission well. We observe no obvious
clumps or asymmetries associated with the trapping of planetesimals that is a
potential consequence of planetary migration in the system. We estimate that
the disk eccentricity must be <0.1. As in previous work by Su et al. (2009), we
find a disk with three components: a warm inner component and two outer
components, a planetesimal belt extending from 100 - 310 AU, with some
flexibility (+/- 10 AU) on the inner edge, and the external halo which extends
to ~2000 AU. We measure the disk inclination to be 26 +/- 3 deg from face-on at
a position angle of 64 deg E of N, establishing that the disk is coplanar with
the star and planets. The SED of the disk is well fit by blackbody grains whose
semi-major axes lie within the planetesimal belt, suggesting an absence of
small grains. The wavelength at which the spectrum steepens from blackbody, 47
+/- 30 um, however, is short compared to other A star debris disks, suggesting
that there are atypically small grains likely populating the halo. The PACS
longer wavelength data yield a lower disk color temperature than do MIPS data
(24 and 70 um), implying two distinct halo dust grain populations.Comment: 13 pages, 8 figures (6 color), accepted for publication in the
Astrophysical Journa
Health literacy in schools: prioritising health and well-being issues through the curriculum
Health literacy (HL) is a relatively new concept in health promotion and is concerned with empowering people through enhancing their knowledge of health issues and improving their ability to make choices about their health and well-being. Schools are seen increasingly as key settings for the dissemination of health messages through curricula and other on-site provision. However, such opportunities are amongst many demands being placed on educational providers and finding space in the school day to support the health agenda is a challenge. This practice-based, qualitative study examines the current practices in three schools in the UK. In total 34 pupils (n=16 from Year 9 and n = 18 from Year 11) were interviewed in six focus groups (3 in each school), with up to 6 pupils in each focus group. School staff (n = 8) were also interviewed individually. Findings suggest that pupils and staff have an understanding of health and a capacity for HL, though health education (via taught subjects) is not statutory across the four Key Stages of the National Curriculum. In order to engender health literate young people, with a view to reducing health inequalities, it is recommended that key health messages are delivered through an agenda that integrates current provision for health via the curriculum and other school-based practices, such as the Healthy Schools Programme
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