903 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
Dynamics of Vortex Core Switching in Ferromagnetic Nanodisks
Dynamics of magnetic vortex core switching in nanometer-scale permalloy disk,
having a single vortex ground state, was investigated by micromagnetic
modeling. When an in-plane magnetic field pulse with an appropriate strength
and duration is applied to the vortex structure, additional two vortices, i.e.,
a circular- and an anti-vortex, are created near the original vortex core.
Sequentially, the vortex-antivortex pair annihilates. A spin wave is created at
the annihilation point and propagated through the entire element; the relaxed
state for the system is the single vortex state with a switched vortex core.Comment: to appear in Appl. Phys. Let
Genome-wide association study of behavioural and psychiatric features in human prion disease.
Prion diseases are rare neurodegenerative conditions causing highly variable clinical syndromes, which often include prominent neuropsychiatric symptoms. We have recently carried out a clinical study of behavioural and psychiatric symptoms in a large prospective cohort of patients with prion disease in the United Kingdom, allowing us to operationalise specific behavioural/psychiatric phenotypes as traits in human prion disease. Here, we report exploratory genome-wide association analysis on 170 of these patients and 5200 UK controls, looking for single-nucleotide polymorphisms (SNPs) associated with three behavioural/psychiatric phenotypes in the context of prion disease. We also specifically examined a selection of candidate SNPs that have shown genome-wide association with psychiatric conditions in previously published studies, and the codon 129 polymorphism of the prion protein gene, which is known to modify various aspects of the phenotype of prion disease. No SNPs reached genome-wide significance, and there was no evidence of altered burden of known psychiatric risk alleles in relevant prion cases. SNPs showing suggestive evidence of association (P<10(-5)) included several lying near genes previously implicated in association studies of other psychiatric and neurodegenerative diseases. These include ANK3, SORL1 and a region of chromosome 6p containing several genes implicated in schizophrenia and bipolar disorder. We would encourage others to acquire phenotype data in independent cohorts of patients with prion disease as well as other neurodegenerative and neuropsychiatric conditions, to allow meta-analysis that may shed clearer light on the biological basis of these complex disease manifestations, and the diseases themselves
Volumetric Absorptive Microsampling (VAMS) for Targeted LC-MS/MS Determination of Tryptophan-Related Biomarkers
L-Tryptophan (TRP) metabolites and related biomarkers play crucial roles in physiological functions, and their imbalances are implicated in central nervous system pathologies and neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease, Parkinson's disease, schizophrenia and depression. The measurement of TRP metabolites and related biomarkers possesses great potential to elucidate the disease mechanisms, aid preclinical drug development, highlight potential therapeutic targets and evaluate the outcomes of therapeutic interventions. An effective, straightforward, sensitive and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous determination of 24 TRP-related compounds in miniaturised murine whole blood samples. Sampling and sample pretreatment miniaturisation were achieved thanks to the development of a volumetric dried blood microsampling approach. Volumetric absorptive microsampling (VAMS) allows the accurate sampling of microvolumes of blood with advantages including, but not limited to, minimal sampling invasiveness, logistical improvements, method sustainability in terms of solvents and energy consumption, and improvement of animal studies in the framework of the 3Rs (Replacement, Reduction and Refinement) principles on animal welfare. The VAMS-LC-MS/MS method exhibited good selectivity, and correlation coefficient values for the calibration curves of each analyte were >0.9987. The limits of quantitation ranged from 0.1 to 25 ng/mL. The intra- and inter-day precisions in terms of RSD were <9.6%. All analytes were stable in whole blood VAMS samples stored at room temperature for at least 30 days with analyte losses < 14%. The developed method was successfully applied to the analysis of biological samples from mice, leading to the unambiguous determination of all the considered target analytes. This method can therefore be applied to analyse TRP metabolites and related biomarkers levels to monitor disease states, perform mechanistic studies and investigate the outcomes of therapeutic interventions
Operation of Faddeev-Kernel in Configuration Space
We present a practical method to solve Faddeev three-body equations at
energies above three-body breakup threshold as integral equations in coordinate
space. This is an extension of previously used method for bound states and
scattering states below three-body breakup threshold energy. We show that
breakup components in three-body reactions produce long-range effects on
Faddeev integral kernels in coordinate space, and propose numerical procedures
to treat these effects. Using these techniques, we solve Faddeev equations for
neutron-deuteron scattering to compare with benchmark solutions.Comment: 20 pages, 8 figures, to be published in Few-Body System
A Pair Polarimeter for Linearly Polarized High Energy Photons
A high quality beam of linearly polarized photons of several GeV will become
available with the coherent bremsstrahlung technique at JLab. We have developed
a polarimeter which requires about two meters of the beam line, has an
analyzing power of 20% and an efficiency of 0.02%. The layout and first results
of a polarimeter test on the laser back-scattering photon beam at SPring-8/LEPS
are presented
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