964 research outputs found
Models of OH Maser Variations in U Her
Arecibo spectra of the mainline OH maser emission from U Her over more than a
decade show variations of the OH emission over these time scales. These
observations are combined with high spatial resolution VLBA maps to investigate
the causes of the variations in the velocities of the maser components. Global
properties of the dust shell, such as accelerations, variations in the pump and
shell-wide magnetic field changes are examined as possibilities, and
eliminated. A possible solution to the problem involving plasma turbulence and
the local magnetic field is introduced, and the relevant time scales of the
turbulence are calculated. The turbulent velocity field yields time scales of
the turbulence are calculated. The turbulent velocity field yields time scales
that are too long (of order centuries), while the turbulent magnetic field
produces variations on appropriate time scales of a few years. A line-of-sight
model of the turbulence is developed and investigated. The complete exploration
of this solution requires extensive theoretical and observational work.
Possible avenues of investigation of the plasma turbulence model are presented.Comment: 23 pages, 17 figures, ApJ: accepted Sept, 199
Legal determinants of external finance revisited : the inverse relationship between investor protection and societal well-being
This paper investigates relationships between corporate governance traditions and quality of life as measured by a number of widely reported indicators. It provides an empirical analysis of indicators of societal health in developed economies using a classification based on legal traditions. Arguably the most widely cited work in the corporate governance literature has been the collection of papers by La Porta et al. which has shown, inter alia, statistically significant relationships between legal traditions and various proxies for investor protection. We show statistically significant relationships between legal traditions and various proxies for societal health. Our comparative evidence suggests that the interests of investors may not be congruent with the interests of wider society, and that the criteria for judging the effectiveness of approaches to corporate governance should not be restricted to financial metrics
Discrete Source Survey of 6 GHz OH emission from PNe & pPNe and first 6 GHz images of K 3-35
The aim of this study is to investigate the physical properties of molecular
envelopes of planetary nebulae in their earliest stages of evolution. Using the
100m telescope at Effelsberg, we have undertaken a high sensitivity discrete
source survey for the first excited state of OH maser emission (J=5/2, 2PI3/2
at 6GHz) in the direction of planetary and proto-planetary nebulae exhibiting
18cm OH emission (main and/or satellite lines), and we further validate our
detections using the Nan\c{c}ay radio telescope at 1.6-1.7GHz and MERLIN
interferometer at 1.6-1.7 and 6GHz. Two sources have been detected at 6035MHz
(5cm), both of them are young (or very young) planetary nebulae. The first one
is a confirmation of the detection of a weak 6035MHz line in Vy 2-2. The second
one is a new detection, in K 3-35, which was already known to be an exceptional
late type star because it exhibits 1720MHz OH emission. The detection of
6035MHz OH maser emission is confirmed by subsequent observations made with the
MERLIN interferometer. These lines are very rarely found in evolved stars. The
1612MHz masers surround but are offset from the 1720 and 6035MHz masers which
in turn lie close to a compact 22GHz continuum source embedded in the optical
nebula.Comment: 9 pages, 7 figures, published in A&
The Nature of Composite LINER/HII Galaxies, As Revealed from High-Resolution VLA Observations
A sample of 37 nearby galaxies displaying composite LINER/HII and pure HII
spectra was observed with the VLA in an investigation of the nature of their
weak radio emission. The resulting radio contour maps overlaid on optical
galaxy images are presented here, together with an extensive literature list
and discussion of the individual galaxies. Radio morphological data permit
assessment of the ``classical AGN'' contribution to the global activity
observed in these ``transition'' LINER galaxies. One in five of the latter
objects display clear AGN characteristics: these occur exclusively in
bulge-dominated hosts.Comment: 31 pages, 27 figures, accepted by ApJ
Modelling Conformational Flexibility in a Spectrally Addressable Molecular Multi-Qubit Model System
Dipolar coupled multi-spin systems have the potential to be used as molecular qubits. Herein we report the synthesis of a molecular multi-qubit model system with three individually addressable, weakly interacting, spin (Formula presented.) centres of differing g-values. We use pulsed Electron Paramagnetic Resonance (EPR) techniques to characterise and separately address the individual electron spin qubits; CuII, Cr7Ni ring and a nitroxide, to determine the strength of the inter-qubit dipolar interaction. Orientation selective Relaxation-Induced Dipolar Modulation Enhancement (os-RIDME) detecting across the CuII spectrum revealed a strongly correlated CuII-Cr7Ni ring relationship; detecting on the nitroxide resonance measured both the nitroxide and CuII or nitroxide and Cr7Ni ring correlations, with switchability of the interaction based on differing relaxation dynamics, indicating a handle for implementing EPR-based quantum information processing (QIP) algorithms
The 2D Continuum Radiative Transfer Problem: Benchmark Results for Disk Configurations
We present benchmark problems and solutions for the continuum radiative
transfer (RT) in a 2D disk configuration. The reliability of three Monte-Carlo
and two grid-based codes is tested by comparing their results for a set of
well-defined cases which differ for optical depth and viewing angle. For all
the configurations, the overall shape of the resulting temperature and spectral
energy distribution is well reproduced. The solutions we provide can be used
for the verification of other RT codes.We also point out the advantages and
disadvantages of the various numerical techniques applied to solve the RT
problem.Comment: 13 pages, 10 figures, To appear in Astronomy and Astrophysic
Percutaneous coronary intervention versus medical therapy in patients with angina and grey-zone fractional flow reserve values: a randomised clinical trial
Introduction: There is conflicting evidence regarding the benefits of percutaneous coronary intervention (PCI) in patients with grey zone fractional flow reserve (GZFFR artery) values (0.75â0.80). The prevalence of ischaemia is unknown. We wished to define the prevalence of ischaemia in GZFFR artery and assess whether PCI is superior to optimal medical therapy (OMT) for angina control.
Methods: We enrolled 104 patients with angina with 1:1 randomisation to PCI or OMT. The artery was interrogated with a Doppler flow/pressure wire. Patients underwent Magnetic Resonance Imaging (MRI) with follow-up at 3 and 12 months. The primary outcome was angina status at 3 months using the Seattle Angina Questionnaire (SAQ).
Results: 104 patients (age 60±9 years), 79 (76%) males and 79 (76%) Left Anterior Descending (LAD) stenoses were randomised. Coronary physiology and SAQ were similar. Of 98 patients with stress perfusion MRI data, 17 (17%) had abnormal perfusion (â„2 segments with â„25% ischaemia or â„1 segment with â„50% ischaemia) in the target GZFFR artery. Of 89 patients with invasive physiology data, 26 (28%) had coronary flow velocity reserve <2.0 in the target GZFFR artery. After 3 months of follow-up, compared with patients treated with OMT only, patients treated by PCI and OMT had greater improvements in SAQ angina frequency (21 (28) vs 10 (23); p=0.026) and quality of life (24 (26) vs 11 (24); p=0.008) though these differences were no longer significant at 12 months.
Conclusions: Non-invasive evidence of major ischaemia is uncommon in patients with GZFFR artery. Compared with OMT alone, patients randomised to undergo PCI reported improved symptoms after 3 months but these differences were no longer significant after 12 months
The effects of remote ischaemic preconditioning on coronary artery function in patients with stable coronary artery disease
Background: Remote ischaemic preconditioning (RIPC) is a cardioprotective intervention invoking intermittent
periods of ischaemia in a tissue or organ remote from the heart. The mechanisms of this effect are incompletely
understood. We hypothesised that RIPC might enhance coronary vasodilatation by an endothelium-dependent
mechanism.
Methods: We performed a prospective, randomised, sham-controlled, blinded clinical trial. Patients with stable
coronary artery disease (CAD) undergoing elective invasive management were prospectively enrolled,
and randomised to RIPC or sham (1:1) prior to angiography. Endothelial-dependent vasodilator function
was assessed in a non-target coronary artery with intracoronary infusion of incremental acetylcholine doses
(10â6
, 10â5
, 10â4 mol/l). Venous blood was sampled pre- and post-RIPC or sham, and analysed for circulating
markers of endothelial function. Coronary luminal diameter was assessed by quantitative coronary angiography.
The primary outcome was the between-group difference in the mean percentage change in coronary luminal diameter
following the maximal acetylcholine dose (Clinicaltrials.gov identifier: NCT02666235).
Results: 75 patients were enrolled. Following angiography, 60 patients (mean ± SD age 57.5 ± 8.5 years; 80%
male) were eligible and completed the protocol (n = 30 RIPC, n = 30 sham). The mean percentage change in
coronary luminal diameter was â13.3 ± 22.3% and â2.0 ± 17.2% in the sham and RIPC groups respectively
(difference 11.32%, 95%CI: 1.2â 21.4, p = 0.032). This remained significant when age and sex were included as
covariates (difference 11.01%, 95%CI: 1.01â 21.0, p = 0.035). There were no between-group differences in
endothelial-independent vasodilation, ECG parameters or circulating markers of endothelial function.
Conclusions: RIPC attenuates the extent of vasoconstriction induced by intracoronary acetylcholine infusion. This
endothelium-dependent mechanism may contribute to the cardioprotective effects of RIP
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