4,808 research outputs found
Core Collapse via Coarse Dynamic Renormalization
In the context of the recently developed "equation-free" approach to
computer-assisted analysis of complex systems, we extract the self-similar
solution describing core collapse of a stellar system from numerical
experiments. The technique allows us to side-step the core "bounce" that occurs
in direct N-body simulations due to the small-N correlations that develop in
the late stages of collapse, and hence to follow the evolution well into the
self-similar regime.Comment: 5 pages, 3 figure
Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
We present improved black hole masses for 35 active galactic nuclei (AGNs)
based on a complete and consistent reanalysis of broad emission-line
reverberation-mapping data. From objects with multiple line measurements, we
find that the highest precision measure of the virial product is obtained by
using the cross-correlation function centroid (as opposed to the
cross-correlation function peak) for the time delay and the line dispersion (as
opposed to full width half maximum) for the line width and by measuring the
line width in the variable part of the spectrum. Accurate line-width
measurement depends critically on avoiding contaminating features, in
particular the narrow components of the emission lines. We find that the
precision (or random component of the error) of reverberation-based black hole
mass measurements is typically around 30%, comparable to the precision attained
in measurement of black hole masses in quiescent galaxies by gas or stellar
dynamical methods. Based on results presented in a companion paper by Onken et
al., we provide a zero-point calibration for the reverberation-based black hole
mass scale by using the relationship between black hole mass and host-galaxy
bulge velocity dispersion. The scatter around this relationship implies that
the typical systematic uncertainties in reverberation-based black hole masses
are smaller than a factor of three. We present a preliminary version of a
mass-luminosity relationship that is much better defined than any previous
attempt. Scatter about the mass-luminosity relationship for these AGNs appears
to be real and could be correlated with either Eddington ratio or object
inclination.Comment: 61 pages, including 8 Tables and 16 Figures. Accepted for publication
in The Astrophysical Journa
Evolution of Supermassive Black Hole Binary and Acceleration of Jet Precession in Galactic Nuclei
Supermassive black hole binary (SMBHB) is expected with the hierarchical
galaxy formation model. Currently, physics processes dominating the evolution
of a SMBHB are unclear. An interesting question is whether we could
observationally determine the evolution of SMBHB and give constraints on the
physical processes. Jet precession have been observed in many AGNs and
generally attributed to disk precession. In this paper we calculate the time
variation of jet precession and conclude that jet precession is accelerated in
SMBHB systems but decelerated in others. The acceleration of jet precession
is related to jet precession timescale and
SMBHB evolution timescale , . Our calculations based on the models
for jet precession and SMBHB evolution show that can be as
high as about with a typical value -0.2 and can be easily detected. We
discussed the differential jet precession for NGC1275 observed in the
literature. If the observed rapid acceleration of jet precession is true, the
jet precession is due to the orbital motion of an unbound SMBHB with mass ratio
. When jets precessed from the ancient bubbles to the currently
active jets, the separation of SMBHB decrease from about to
with an averaged decreasing velocity and evolution timescale . However, if we assume a steady jet precession for many cycles,
the observations implies a hard SMBHB with mass ratio and
separation .Comment: 29 pages, no figure, Accepted for publication in Ap
New Constraints from PAMELA anti-proton data on Annihilating and Decaying Dark Matter
Recently the PAMELA experiment has released its updated anti-proton flux and
anti-proton to proton flux ratio data up to energies of ~200GeV. With no clear
excess of cosmic ray anti-protons at high energies, one can extend constraints
on the production of anti-protons from dark matter. In this letter, we consider
both the cases of dark matter annihilating and decaying into standard model
particles that produce significant numbers of anti-protons. We provide two sets
of constraints on the annihilation cross-sections/decay lifetimes. In the one
set of constraints we ignore any source of anti-protons other than dark matter,
which give the highest allowed cross-sections/inverse lifetimes. In the other
set we include also anti-protons produced in collisions of cosmic rays with
interstellar medium nuclei, getting tighter but more realistic constraints on
the annihilation cross-sections/decay lifetimes.Comment: 7 pages, 3 figures, 3 table
Galactic cannibalism in the galaxy cluster C0337-2522 at z=0.59
According to the galactic cannibalism model, cD galaxies are formed in the
center of galaxy clusters by merging of massive galaxies and accretion of
smaller stellar systems: however, observational examples of the initial phases
of this process are lacking. We have identified a strong candidate for this
early stage of cD galaxy formation: a group of five elliptical galaxies in the
core of the X-ray cluster C0337-2522 at redshift z=0.59. With the aid of
numerical simulations, in which the galaxies are represented by N-body systems,
we study their dynamical evolution up to z=0; the cluster dark matter
distribution is also described as a N-body system. We find that a multiple
merging event in the considered group of galaxies will take place before z=0
and that the merger remnant preserves the Fundamental Plane and the
Faber-Jackson relations, while its behavior with respect to the Mbh-sigma
relation is quite sensitive to the details of black hole merging [abridged].Comment: 30 pages, 7 figures, MNRAS (accepted
Cost-effectiveness analysis of a placebo-controlled randomized trial evaluating the effectiveness of arthroscopic subacromial decompression in patients with subacromial shoulder pain
Aims
The aims of this study were to compare the use of resources, costs, and quality of life outcomes associated with subacromial decompression, arthroscopy only (placebo surgery), and no treatment for subacromial pain in the United Kingdom National Health Service (NHS), and to estimate their cost-effectiveness.
Patients and Methods
The use of resources, costs, and quality-adjusted life-years (QALYs) were assessed in the trial at six months and one year. Results were extrapolated to two years after randomization. Differences between treatment arms, based on the intention-to-treat principle, were adjusted for covariates and missing data were handled using multiple imputation. Incremental cost-effectiveness ratios were calculated, with uncertainty around the values estimated using bootstrapping.
Results
Cumulative mean QALYs/mean costs of health care service use and surgery per patient from baseline to 12 months were estimated as 0.640 (standard error (se) 0.024)/£3147 (se 166) in the decompression arm, 0.656 (se 0.020)/£2830 (se 183) in the arthroscopy only arm and 0.522 (se 0.029)/£1451 (se 151) in the no treatment arm. Statistically significant differences in cumulative QALYs and costs were found at six and 12 months for the decompression versus no treatment comparison only. The probabilities of decompression being cost-effective compared with no treatment at a willingness-to-pay threshold of £20 000 per QALY were close to 0% at six months and approximately 50% at one year, with this probability potentially increasing for the extrapolation to two years.
Discussion
The evidence for cost-effectiveness at 12 months was inconclusive. Decompression could be cost-effective in the longer-term, but results of this analysis are sensitive to the assumptions made about how costs and QALYs are extrapolated beyond the follow-up of the trial
Chaos and the continuum limit in the gravitational N-body problem II. Nonintegrable potentials
This paper continues a numerical investigation of orbits evolved in `frozen,'
time-independent N-body realisations of smooth time-independent density
distributions corresponding to both integrable and nonintegrable potentials,
allowing for N as large as 300,000. The principal focus is on distinguishing
between, and quantifying, the effects of graininess on initial conditions
corresponding, in the continuum limit, to regular and chaotic orbits. Ordinary
Lyapunov exponents X do not provide a useful diagnostic for distinguishing
between regular and chaotic behaviour. Frozen-N orbits corresponding in the
continuum limit to both regular and chaotic characteristics have large positive
X even though, for large N, the `regular' frozen-N orbits closely resemble
regular characteristics in the smooth potential. Viewed macroscopically both
`regular' and `chaotic' frozen-N orbits diverge as a power law in time from
smooth orbits with the same initial condition. There is, however, an important
difference between `regular' and `chaotic' frozen-N orbits: For regular orbits,
the time scale associated with this divergence t_G ~ N^{1/2}t_D, with t_D a
characteristic dynamical time; for chaotic orbits t_G ~ (ln N) t_D. At least
for N>1000 or so, clear distinctions exist between phase mixing of initially
localised orbit ensembles which, in the continuum limit, exhibit regular versus
chaotic behaviour. For both regular and chaotic ensembles, finite-N effects are
well mimicked, both qualitatively and quantitatively, by energy-conserving
white noise with amplitude ~ 1/N. This suggests strongly that earlier
investigations of the effects of low amplitude noise on phase space transport
in smooth potentials are directly relevant to real physical systems.Comment: 20 pages, including 21 FIGURES, uses RevTeX macro
Plasma neurofilament light chain protein is not increased in treatment-resistant schizophrenia and first-degree relatives
Objective:
Schizophrenia, a complex psychiatric disorder, is often associated with cognitive, neurological and neuroimaging abnormalities. The processes underlying these abnormalities, and whether a subset of people with schizophrenia have a neuroprogressive or neurodegenerative component to schizophrenia, remain largely unknown. Examining fluid biomarkers of diverse types of neuronal damage could increase our understanding of these processes, as well as potentially provide clinically useful biomarkers, for example with assisting with differentiation from progressive neurodegenerative disorders such as Alzheimer and frontotemporal dementias.
Methods:
This study measured plasma neurofilament light chain protein (NfL) using ultrasensitive Simoa technology, to investigate the degree of neuronal injury in a well-characterised cohort of people with treatment-resistant schizophrenia on clozapine (n = 82), compared to first-degree relatives (an at-risk group, n = 37), people with schizophrenia not treated with clozapine (n = 13), and age- and sex-matched controls (n = 59).
Results:
We found no differences in NfL levels between treatment-resistant schizophrenia (mean NfL, M = 6.3 pg/mL, 95% confidence interval: [5.5, 7.2]), first-degree relatives (siblings, M = 6.7 pg/mL, 95% confidence interval: [5.2, 8.2]; parents, M after adjusting for age = 6.7 pg/mL, 95% confidence interval: [4.7, 8.8]), controls (M = 5.8 pg/mL, 95% confidence interval: [5.3, 6.3]) and not treated with clozapine (M = 4.9 pg/mL, 95% confidence interval: [4.0, 5.8]). Exploratory, hypothesis-generating analyses found weak correlations in treatment-resistant schizophrenia, between NfL and clozapine levels (Spearman’s r = 0.258, 95% confidence interval: [0.034, 0.457]), dyslipidaemia (r = 0.280, 95% confidence interval: [0.064, 0.470]) and a negative correlation with weight (r = −0.305, 95% confidence interval: [−0.504, −0.076]).
Conclusion:
Treatment-resistant schizophrenia does not appear to be associated with neuronal, particularly axonal degeneration. Further studies are warranted to investigate the utility of NfL to differentiate treatment-resistant schizophrenia from neurodegenerative disorders such as behavioural variant frontotemporal dementia, and to explore NfL in other stages of schizophrenia such as the prodome and first episode
A Radio Study of the Seyfert galaxy Markarian 6: Implications for Seyfert life-cycles
We have carried out an extensive radio study with the Very Large Array on the
Seyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structure in the
source. The radio emission occurs on three different spatial scales, from ~7.5
kpc bubbles to ~1.5 kpc bubbles lying nearly orthogonal to them and a ~1 kpc
radio jet lying orthogonal to the kpc-scale bubble. To explain the complex
morphology, we first consider a scenario in which the radio structures are the
result of superwinds ejected by a nuclear starburst. However, recent Spitzer
observations of Mrk 6 provide an upper limit to the star formation rate (SFR)
of ~5.5 M_sun/yr, an estimate much lower than the SFR of ~33 M_sun/yr derived
assuming that the bubbles are a result of starburst winds energized by
supernovae explosions. Thus, a starburst alone cannot meet the energy
requirements for the creation of the bubbles in Mrk 6. We show that a single
plasmon model is energetically infeasible, and we argue that a jet-driven
bubble model while energetically feasible does not produce the complex radio
morphologies. Finally, we consider a model in which the complex radio structure
is a result of an episodically-powered precessing jet that changes its
orientation. This model is the most attractive as it can naturally explain the
complex radio morphology, and is consistent with the energetics, the spectral
index and the polarization structure. Radio emission in this scenario is a
short-lived phenomenon in the lifetime of a Seyfert galaxy which results due to
an accretion event.Comment: Accepted for publication in Ap
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