22,604 research outputs found
Spitzer IRS observations of k plus a galaxies: a link between polycyclic aromatic hydrocarbon emission properties and active galactic nucleus feedback?
We have performed Spitzer InfraRed Spectrograph (IRS) low-resolution 5-12 mu m spectroscopy on a sample of galaxies selected to be at three distinct poststarburst evolutionary stages based on their optical spectral indices. The resulting IRS spectra show distinctive polycyclic aromatic hydrocarbon (PAH) emission line structures at 6.2, 7.7, 8.6, and 11.3 mu m and little silicate absorption, indicative of ongoing star formation. However, the PAH interline ratios, in particular the 11.3/6.2 mu m and 7.7/6.2 mu m ratio, show large variations. These variations are found to correlate with both time since the most recent starburst and active galactic nucleus (AGN) activity. We speculate that the evolution observed in these PAH ratios is related to an increase in AGN activity with time since starburst
Systematic review and meta-analysis of optimal P2Y₁₂ blockade in dual antiplatelet therapy for patients with diabetes with acute coronary syndrome
Background: Patients with diabetes are at increased risk of acute coronary syndromes (ACS) and their mortality and morbidity outcomes are significantly worse following ACS events, independent of other comorbidities. This systematic review sought to establish the optimum management strategy with focus on P2Y₁₂ blockade in patients with diabetes with ACS. Methods: MEDLINE (1946 to present) and EMBASE (1974 to present) databases, abstracts from major cardiology conferences and previously published systematic reviews were searched to June 2014. Relevant randomised control trials with clinical outcomes for P2Y₁₂ inhibitors in adult patients with diabetes with ACS were scrutinised independently by 2 authors with applicable data was extracted for primary composite end point of cardiovascular death, myocardial infarction (MI) and stroke; enabling calculation of relative risks with 95% CI with subsequent direct and indirect comparison. Results: Four studies studied clopidogrel in patients with diabetes, with two (3122 patients) having primary outcome data showing superiority of clopidogrel against placebo with RR0.84 (95% CI 0.72–0.99). Irrespective of management strategy, the newer agents prasugrel (2 studies) and ticagrelor (1 study) had a lower primary event rate compared with clopidogrel; RR 0.80 (95% CI 0.66 to 0.97) and RR 0.89 (95% CI 0.77 to 1.02), respectively. When ticagrelor was indirectly compared with prasugrel, there was a trend to an improved primary outcome with prasugrel (RR 1.11 (95% CI 0.94 to 1.31)) particularly in those managed with percutaneous coronary intervention (PCI) (RR 1.23 (95% CI 0.95 to 1.59)). Prasugrel demonstrated a statistical superiority with prevention of further MI with RR 1.48 (95% CI 1.11 to 1.97). This was not at the expense of increased major thrombolysis in MI (TIMI) bleeding rates RR 0.94 (95% CI 0.59 to 1.51). Conclusions: This meta-analysis shows the addition of a P2Y₁₂ inhibitor is superior to placebo, with a trend favouring the use of prasugrel in patients with diabetes with ACS, particularly those undergoing PCI
Orbital Evolution of Moons in Weakly Accreting Circumplanetary Disks
We investigate the formation of hot and massive circumplanetary disks (CPDs)
and the orbital evolution of satellites formed in these disks. Because of the
comparatively small size-scale of the sub-disk, quick magnetic diffusion
prevents the magnetorotational instability (MRI) from being well-developed at
ionization levels that would allow MRI in the parent protoplanetary disk. In
the absence of significant angular momentum transport, continuous mass supply
from the parental protoplanetary disk leads to the formation of a massive CPD.
We have developed an evolutionary model for this scenario and have estimated
the orbital evolution of satellites within the disk. We find, in a certain
temperature range, that inward migration of a satellite can be stopped by a
change in the structure due to the opacity transitions. Moreover, by capturing
second and third migrating satellites in mean motion resonances, a compact
system in Laplace resonance can be formed in our disk models.Comment: 10 pages, 9 figure
Lie point symmetries and the geodesic approximation for the Schr\"odinger-Newton equations
We consider two problems arising in the study of the Schr\"odinger-Newton
equations. The first is to find their Lie point symmetries. The second, as an
application of the first, is to investigate an approximate solution
corresponding to widely separated lumps of probability. The lumps are found to
move like point particles under a mutual inverse-square law of attraction
Three-Dimensional Propagation of Magnetohydrodynamic Waves in Solar Coronal Arcades
We numerically investigate the excitation and temporal evolution of
oscillations in a two-dimensional coronal arcade by including the
three-dimensional propagation of perturbations. The time evolution of
impulsively generated perturbations is studied by solving the linear, ideal
magnetohydrodynamic (MHD) equations in the zero-beta approximation. As we
neglect gas pressure the slow mode is absent and therefore only coupled MHD
fast and Alfven modes remain. Two types of numerical experiments are performed.
First, the resonant wave energy transfer between a fast normal mode of the
system and local Alfven waves is analyzed. It is seen how, because of resonant
coupling, the fast wave with global character transfers its energy to Alfvenic
oscillations localized around a particular magnetic surface within the arcade,
thus producing the damping of the initial fast MHD mode. Second, the time
evolution of a localized impulsive excitation, trying to mimic a nearby coronal
disturbance, is considered. In this case, the generated fast wavefront leaves
its energy on several magnetic surfaces within the arcade. The system is
therefore able to trap energy in the form of Alfvenic oscillations, even in the
absence of a density enhancement such as that of a coronal loop. These local
oscillations are subsequently phase-mixed to smaller spatial scales. The amount
of wave energy trapped by the system via wave energy conversion strongly
depends on the wavelength of perturbations in the perpendicular direction, but
is almost independent from the ratio of the magnetic to density scale heights.Comment: 27 pages, 11 figure
Cosmic bulk viscosity through backreaction
We consider an effective viscous pressure as the result of a backreaction of
inhomogeneities within Buchert's formalism. The use of an effective metric with
a time-dependent curvature radius allows us to calculate the luminosity
distance of the backreaction model. This quantity is different from its
counterpart for a "conventional" spatially flat bulk viscous fluid universe.
Both expressions are tested against the SNIa data of the Union2.1 sample with
only marginally different results for the distance-redshift relation and in
accordance with the CDM model. Future observations are expected to be
able to discriminate among these models on the basis of indirect measurements
of the curvature evolution.Comment: 18 pages, 6 figures, comments and references added, accepted for
publication in GR
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